Tamaoki Nobuyuki

Research Institute for Electronic Science Material and Molecular SciencesProfessor
Last Updated :2024/12/06

■Researcher basic information

Researchmap personal page

Research Keyword

  • photopharmacology
  • photoswitch
  • molecular switch
  • molecular machine
  • azobenzene
  • photochromism
  • chirality
  • liquid crystal
  • モータータンパク質
  • 分子スイッチ
  • アゾベンゼン
  • フォトクロミック反応
  • 分子機械
  • 細胞操作
  • 液晶

Research Field

  • Nanotechnology/Materials, Functional solid-state chemistry

■Career

Position History

  • 電子科学研究所附属グリーンナノテクノロジー研究センター長, 2017年10月1日 - 2019年9月30日

■Research activity information

Awards

  • 2001, 化学バイオつくば賞               
    Japan

Papers

  • Photochemical Control of Cell Division Using a Photoswitchable CENP-E Inhibitor.
    Akira Matsura, Shota Hiruma, Nobuyuki Tamaoki, Ryota Uehara
    Methods in molecular biology (Clifton, N.J.), 2872, 101, 113, 2025, [International Magazine]
    English, Scientific journal, Photoswitchable compounds are potent tools for elucidating molecular functions in dynamic cellular processes. Photoswitchable inhibitors targeting various mitotic spindle factors have been developed. In this chapter, we describe experimental methods for photo-controlling mitotic chromosome dynamics using a recently developed photoswitchable inhibitor of mitotic kinesin, CENP-E. This inhibitor undergoes reversible photoisomerization to a more inhibitory trans or less inhibitory cis state by visible or UV light irradiation, respectively, enabling photoswitching of CENP-E function both in vitro and in vivo. First, we explain the procedures used to optimize the experimental condition for efficient photoswitching of CENP-E functionality in cultured cells. We then describe how to conduct de novo photo-control of mitotic chromosome motion using the inhibitor under a microscope.
  • Photoswitchable Auxin-Inducible Degron System for Conditional Protein Degradation with Spatiotemporal Resolution.
    Saugata Sahu, Koya Yoshizawa, Takahiro Yamamoto, Ryota Uehara, Nobuyuki Tamaoki
    Journal of the American Chemical Society, 146, 31, 21203, 21207, 07 Aug. 2024, [International Magazine]
    English, Scientific journal, The auxin-inducible degron (AID) system degrades target proteins rapidly in a controllable manner. Although this is a highly versatile technique for studying protein functionality, protein degradation with spatiotemporal resolution is not currently possible. Herein we describe a photoswitchable AID using a light-active auxin derivative for reversible and site-specific protein degradation with temporal resolution.
  • Caging Bioactive Triarylimidazoles: An Approach to Create Visible Light-Activatable Drugs
    Jiajun Qi, Ammathnadu S. Amrutha, Sumire Ishida-Ishihara, Hisham M. Dokainish, P. K. Hashim, Ryu Miyazaki, Masumi Tsuda, Shinya Tanaka, Nobuyuki Tamaoki
    Journal of the American Chemical Society, American Chemical Society (ACS), 21 Jun. 2024
    Scientific journal
  • Spatiotemporal regulation of CENP-E-guided chromosomes using a fast-relaxing arylazopyrazole photoswitch.
    Kazuya Matsuo, Ryota Uehara, Takashi Kikukawa, Tomonori Waku, Akio Kobori, Nobuyuki Tamaoki
    Chemical communications (Cambridge, England), 07 Jun. 2024, [International Magazine]
    English, Scientific journal, We developed a centromere-associated protein E (CENP-E) inhibitor employing trans to cis photoisomerization with 405 nm visible light illumination and fast thermal relaxation. This photoswitching characteristic of the inhibitor enabled selective blockage or release of the motion of particular chromosomes within a single mitotic cell. Using this technique, we successfully demonstrated targeted chromosome gain and loss in daughter cells by introducing asymmetric chromosome segregation.
  • Geometry‐Induced Oligomerization of Fluorine‐Substituted Phenylazothiazole Photoswitches
    P. K. Hashim, Saugata Sahu, Kiyonori Takahashi, Shakkeeb Thazhathethil, Takayoshi Nakamura, Nobuyuki Tamaoki
    Chemistry – A European Journal, 30, 19, Wiley, 09 Feb. 2024
    Scientific journal, Abstract

    Photoswitches are molecules that can absorb light of specific wavelengths and undergo a reversible transformation between their trans and cis isomeric forms. In phenylazo photoswitches, it is common for the less stable cis (Z) isomer to convert back to the more stable trans (E) isomer either through photochemical or thermal means. In this research, we designed new derivatives of phenylazothiazole (PAT) photoswitches, PAT‐Fn, which feature fluorine substituents on their phenyl component. These derivatives can reversibly isomerize under visible light exposure with the enrichment of E and Z isomers at photostationary state (PSS). Surprisingly, we observed an unconventional phenomenon when these PAT‐Fn (n≧2) photoswitches were in their cis isomeric state in the absence of light. Instead of the anticipated transformation from cis to trans isomer, these compounds converted to an oligomeric compound. Our detailed experimental investigation and theoretical calculations, indicated the crucial role of fluorine substituents and the distinctive geometric arrangement of the cis isomer in driving the unexpected oligomerization process originating from the cis isomeric state.
  • A photoswitchable CENP-E inhibitor with single blue-green light to control chromosome positioning in mitotic cells
    Kazuya Matsuo, Takashi Kikukawa, Tomonori Waku, Akio Kobori, Nobuyuki Tamaoki
    RSC Medicinal Chemistry, Royal Society of Chemistry (RSC), 2024
    Scientific journal, A photoswitchable centromere-associated protein E (CENP-E) inhibitor based on the 4-methylaminoazobenzene photoswitch is reported, which is characterized with cis–trans photoisomerization with blue-green light and fast thermal relaxation.
  • Phenylazothiazoles as Visible-Light Photoswitches
    Runze Lin, P. K. Hashim, Saugata Sahu, Ammathnadu S. Amrutha, Nusaiba Madappuram Cheruthu, Shakkeeb Thazhathethil, Kiyonori Takahashi, Takayoshi Nakamura, Takashi Kikukawa, Nobuyuki Tamaoki
    Journal of the American Chemical Society, American Chemical Society (ACS), 12 Apr. 2023
    Scientific journal
  • Tetraploidy-linked sensitization to CENP-E inhibition in human cells.
    Koya Yoshizawa, Akira Matsura, Masaya Shimada, Sumire Ishida-Ishihara, Fuyu Sato, Takahiro Yamamoto, Kan Yaguchi, Eiji Kawamoto, Taruho Kuroda, Kazuya Matsuo, Nobuyuki Tamaoki, Ryuichi Sakai, Yasuhito Shimada, Mithilesh Mishra, Ryota Uehara
    Molecular oncology, 17, 6, 1148, 1166, 23 Jan. 2023, [International Magazine]
    English, Scientific journal, Tetraploidy is a hallmark of cancer cells, and tetraploidy-selective cell growth suppression is a potential strategy for targeted cancer therapy. However, how tetraploid cells differ from normal diploids in their sensitivity to anti-proliferative treatments remains largely unknown. In this study, we found that tetraploid cells are significantly more susceptible to inhibitors of a mitotic kinesin (CENP-E) than diploids. Treatment with a CENP-E inhibitor preferentially diminished the tetraploid cell population in a diploid-tetraploid co-culture at optimum conditions. Live imaging revealed that a tetraploidy-linked increase in unsolvable chromosome misalignment caused substantially longer mitotic delay in tetraploids than in diploids upon moderate CENP-E inhibition. This time gap of mitotic arrest resulted in cohesion fatigue and subsequent cell death, specifically in tetraploids, leading to tetraploidy-selective cell growth suppression. In contrast, the microtubule-stabilizing compound paclitaxel caused tetraploidy-selective suppression through the aggravation of spindle multipolarization. We also found that treatment with a CENP-E inhibitor had superior generality to paclitaxel in its tetraploidy selectivity across a broader spectrum of cell lines. Our results highlight the unique properties of CENP-E inhibitors in tetraploidy-selective suppression and their potential use in the development of tetraploidy-targeting interventions in cancer.
  • Chaperonin GroEL hydrolyses ortho-nitrophenyl β-galactoside
    P. K. Hashim, Hisham M. Dokainish, Nobuyuki Tamaoki
    Organic & Biomolecular Chemistry, 21, 30, 6120, 6123, Royal Society of Chemistry (RSC), 2023
    Scientific journal, A serendipitous finding that the chaperonin GroEL hydrolyses ortho-nitrophenyl β-galactoside (ONPG), a well-known substrate of the enzyme β-galactosidase.
  • Excited State Charge-Transfer Complexes Enable Fluorescence Color Changes in a Supramolecular Cyclophane Mechanophore
    Shakkeeb Thazhathethil, Tatsuya Muramatsu, Nobuyuki Tamaoki, Christoph Weder, Yoshimitsu Sagara
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 61, 42, WILEY-V C H VERLAG GMBH, Oct. 2022
    English, Scientific journal, Mechanochromic mechanophores are reporter molecules that indicate mechanical events through changes of their photophysical properties. Supramolecular mechanophores in which the activation is based on the rearrangement of luminophores and/or quenchers without any covalent bond scission, remain less well investigated. Here, we report a cyclophane-based supramolecular mechanophore that contains a 1,6-bis(phenylethynyl)pyrene luminophore and a pyromellitic diimide quencher. In solution, the blue monomer emission of the luminophore is largely quenched and a faint reddish-orange emission originating from a charge-transfer (CT) complex is observed. A polyurethane elastomer containing the mechanophore displays orange emission in the absence of force, which is dominated by the CT-emission. Mechanical deformation causes a decrease of the CT-emission and an increase of blue monomer emission, due to the spatial separation between the luminophore and quencher. The ratio of the two emission intensities correlates with the applied stress.
  • Dynamic Control of Microbial Movement by Photoswitchable ATP Antagonists
    Sampreeth Thayyil, Yukinori Nishigami, Md. Jahirul Islam, P. K. Hashim, Ken'ya Furuta, Kazuhiro Oiwa, Jian Yu, Min Yao, Toshiyuki Nakagaki, Nobuyuki Tamaoki
    Chemistry – A European Journal, 28, 30, Wiley, 25 May 2022
    Scientific journal
  • Synthesis and Properties of Aromatic-Terminated Diacetylene Organogelators and Their Application to Photopatterning of Polydiacetylenes
    Ken’ichi Aoki, Nobuyuki Tamaoki, Atsushi Seki, Kenta Narazaki, Daiki Takahashi, Kousuke Horitsugu
    Langmuir, 37, 44, 13160, 13169, American Chemical Society (ACS), 09 Nov. 2021
    Scientific journal
  • Pressure-tunable thermal conductivity observed for bisamide functionalized diacetylene crystals
    Jiajun Qi, Yuzhang Wu, Hai Jun Cho, Yuna Kim, Hiromichi Ohta, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS SCIENCE, 56, 27, 15481, 15490, SPRINGER, Sep. 2021, [Peer-reviewed]
    English, Scientific journal, The polymerization of monomeric diacetylene (DA) crystals exhibits a strong dependence on the intermolecular distance relative to the van der Waals distance, which can be tuned with macroscopic mechanical stimuli. In this study, we report the effect of external pressure on the heat transport characteristics of bisamide functionalized DA (BA-DA) crystals. The thermal conductivity (kappa) of BA-DA crystals in the monomeric state could be enhanced with pressure from 0.42 +/- 0.13 W m(-1) K-1(<= 30 MPa) to 1.10 +/- 0.50 W m(-1) K-1(>= 50 MPa) but was not significantly affected by the structural change after photopolymerization. Raman and Fourier-transform infrared spectroscopy revealed that the kappa of the BA-DA crystals is correlated with the IR-active vibrational modes of N-H and C=O bonds correlated with the intermolecular hydrogen bonding. The UV polymerization significantly affected the Raman-active vibrational modes of monomers (-C C-C C-), but their effect on the kappa was negligible, which is likely attributed to the anharmonic interatomic potential. These results can potentially be utilized in polymer-based material design for thermal management technologies, such as printing heat circuits in an economically viable way or realizing a thermal barrier coating based on DA monomers.
  • Rational design and development of a lit-active photoswitchable inhibitor targeting CENP-E.
    Kazuya Matsuo, Nobuyuki Tamaoki
    Organic & biomolecular chemistry, 19, 32, 6979, 6984, 28 Aug. 2021, [International Magazine]
    English, Scientific journal, In the emerging field of photopharmacology, synthetic photoswitches based on reversible photochemical reactions are fused to bioactive molecules. Azobenzene derivatives, which can undergo trans-cis photoisomerization, are typical photoswitches. Most azobenzene-based photochemical tools are active in the thermodynamically stable trans, but not cis, form. cis-Active photochemical tools would be ideal because they can be "initially inactive and active after light illumination" in a reversible mode only by light illumination. However, only a few rational strategies for constructing such "lit-active" photopharmacological tools has been developed. Herein, we report a rationally designed lit-active photoswitchable inhibitor targeting centromere-associated protein E (CENP-E). Using the lit-active inhibitor, we were able to photoregulate CENP-E-dependent mitotic chromosome location in cells. This study provides a framework to facilitate further progress in the development of photopharmacological tools.
  • Rotaxane-Based Dual Function Mechanophores Exhibiting Reversible and Irreversible Responses
    Tatsuya Muramatsu, Yuji Okado, Hanna Traeger, Stephen Schrettl, Nobuyuki Tamaoki, Christoph Weder, Yoshimitsu Sagara
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 143, 26, 9884, 9892, AMER CHEMICAL SOC, Jul. 2021
    English, Scientific journal, Mechanochromic mechanophores permit the design of polymers that indicate mechanical events through optical signals. Here we report rotaxane-based supramolecular mechanophores that display both reversible and irreversible fluorescence changes. These responses are triggered by different forces and are achieved by exploiting the molecular shuttling function and force-induced dethreading of rotaxanes. The new rotaxane mechanophores are composed of a ring featuring a luminophore, which is threaded onto an axle with a matching quencher and two stoppers. In the stress-free state, the luminophore is preferentially located in the proximity of the quencher, and the emission is quenched. The luminophore slides away from the quencher when a force is applied and the fluorescence is switched on. This effect is reversible, unless the force is so high that the luminophore-carrying ring slips past the stopper and dethreading occurs. We show that the combination of judiciously selected ring and stopper moieties is crucial to attain interlocked structures that display such a dual response. PU elastomers that contain such doubly responsive rotaxanes exhibit reversible fluorescence changes over multiple loading-unloading cycles due to the shuttling function, whereas permanent changes are observed upon repeated deformations to high strains due to breakage of the mechanical bond upon dethreading of the ring from the axle. This response allows one, at least conceptually, to monitor the actual deformation of polymer materials and examine mechanical damage that was inflicted in the past on the basis of an optical signal.
  • Mechanically Responsive Luminescent Polymers Based on Supramolecular Cyclophane Mechanophores
    Yoshimitsu Sagara, Hanna Traeger, Jie Li, Yuji Okado, Stephen Schrettl, Nobuyuki Tamaoki, Christoph Weder
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 143, 14, 5519, 5525, AMER CHEMICAL SOC, Apr. 2021, [Peer-reviewed]
    English, Scientific journal, A new approach to cyclophane-based supramolecular mechanophores is presented. We report a mechanically responsive cyclic motif that contains two fluorescent 1,6-bis(phenylethynyl)pyrene moieties that are capable of forming intramolecular excimers. The emission spectra of dilute solutions of this cyclophane and a polyurethane elastomer into which a small amount of the mechanophore (0.08 wt %) had been covalently integrated are dominated by excimer emission. Films of the cyclophane-containing polyurethane also display a considerable portion of excimer emission, but upon deformation, the fluorescence becomes monomerdominated and a perceptible change from cyan to blue is observed. The response is instant, reversible, and consistent with a mechanically induced change of the molecular conformation of the mechanophore so that the excimer-promoting interactions between the luminophores are suppressed. In-depth investigations show a correlation between the applied strain and the emission color, which can conveniently be expressed by the ratio of monomer to excimer emission intensity. The current study suggests that cyclophanes can be utilized to develop various supramolecular mechanophores that detect and visualize weak forces occurring in polymeric materials or generated by living tissues.
  • A Series of Bisamide-Substituted Diacetylenes Exhibiting a Terminal Alkyl Odd/Even Parity Effect on Mechanoactivated Photopolymerization
    Jiajun Qi, Yuna Kim, Kiyonori Takahashi, Ken'ichi Aoki, Ichiro Hisaki, Takayoshi Nakamura, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL, 27, 11, 3832, 3841, WILEY-V C H VERLAG GMBH, Feb. 2021, [Peer-reviewed], [Last author, Corresponding author]
    English, Scientific journal, Diacetylene derivatives exhibit solid-state polymerization to polydiacetylene initiated by UV light or gamma-ray irradiation. The activation of the photopolymerization relies on the monomer diynes arrangement. Recently, it has been demonstrated that the first mechanoresponsive bisamide substituted diacetylenes (DAs) show dramatic switching from light-inert to light-reactive states at a given pressure. The origin of this unique phenomenon was apparently related to the pressure-sensitive crystalline transition in DAs, but the molecular mechanism remains elusive. To obtain more insight, herein a series of DAs with varying terminal alkyl spacer length is presented, and their molecular structural effect on the intermolecular hydrogen bonding and steric repulsion is examined. In pristine states, even-parity DAs were inactive upon UV irradiation (lambda=254 nm) unless external pressure was applied. By contrast, odd-parity DAs were easily polymerized upon UV irradiation without pressure application. However, the pressure-induced crystalline phase transition exhibiting photopolymerization was valid for all DAs regardless of their alkyl spacer length. A systematic investigation revealed that the terminal alkyl spacer length, especially its odd/even parity plays a key role in determining the intrinsic intermolecular hydrogen-bonding nature of DA crystals and the resultant molecular packing. In addition, the relevant thermochromic behavior was also observed from photopolymerized polydiacetylenes.
  • Two-step mechanoresponsive luminescence and mechanical stimuli-induced release of small molecules exhibited by a luminescent cyclophane
    Yoshimitsu Sagara, Kiyonori Takahashi, Atsushi Seki, Tatsuya Muramatsu, Takayoshi Nakamura, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C, 9, 5, 1671, 1677, ROYAL SOC CHEMISTRY, Feb. 2021, [Peer-reviewed]
    English, Scientific journal, Achieving multiple mechanoresponsive luminescence-related functions from a single molecule remains challenging. Here, we demonstrate that both two-step mechanoresponsive luminescence and the release of small guest molecules are achieved by a 9,10-bis(phenylethynyl)anthracene-based cyclophane. When gently crushed, the yellow-emissive crystal of the cyclophane exhibits a hypsochromic shift of the emission band, because of alterations in molecular packing at the surface. Subsequent grinding results in a bathochromic shift of the emission band due to excimer formation accompanying the transition from the crystalline state to an amorphous state. Another pseudopolymorph of the cyclophane exhibits the release of chloroform from its crystal structure in response to mechanical stimuli, accompanied by a photoluminescent color change from yellow-green to yellow. These results reveal that luminescent cyclophanes are promising candidates for creating sophisticated mechanoresponsive luminescent materials.
  • A visible light-controllable Rho kinase inhibitor based on a photochromic phenylazothiazole
    Kazuya Matsuo, Sampreeth Thayyil, Mitsuyasu Kawaguchi, Hidehiko Nakagawa, Nobuyuki Tamaoki
    Chemical Communications, 57, 93, 12500, 12503, Royal Society of Chemistry (RSC), 2021
    Scientific journal, Rho-associated coiled-coil-containing protein kinase (ROCK) is a serine–threonine kinase whose inhibitors are useful for the regulation of the actomyosin system.
  • Glycomacrocycle-Based Azobenzene Derivatives as Chiral Dopants for Photoresponsive Cholesteric Liquid Crystals.
    Yuna Kim, Noushaba Nusrat Mafy, Stéphane Maisonneuve, Chaoqi Lin, Nobuyuki Tamaoki, Juan Xie
    ACS applied materials & interfaces, 12, 46, 52146, 52155, 18 Nov. 2020, [International Magazine]
    English, Scientific journal, We demonstrate photoresponsive cholesteric liquid crystals (CLCs) doped with glycomacrocyclic azobenzene derivatives, which exhibit large conformational changes, providing dynamic control of helical superstructures in response to a light stimulus. An unprecedented shortening of the helical pitch length and the empowerment of helical twisting power up to 500% are observed upon trans (E) to cis (Z) photoisomerization. Light-driven dynamic helix twisting and untwisting behavior affords the first example of glycomacrocyclic azobenzene-based CLCs, which can drive the mechanical movement of micro-objects. Two modes of rotation-two-directional or one-directional rotational motion (crankshaft mode)-are realized. In particular, the latter mode based on the reversible cholesteric texture transition between homogeneous stripes and focal conics leads to the accumulation of the rotation angles achieving the amplified mechanical movements.
  • Electrofluorochromic Device Based on a Redox-Active Europium(III) Complex
    Yuna Kim, Hitomi Ohmagari, Akira Saso, Nobuyuki Tamaoki, Miki Hasegawa
    ACS Applied Materials & Interfaces, 12, 41, 46390, 46396, American Chemical Society (ACS), 14 Oct. 2020
    Scientific journal
  • Photoisomerization of azobenzene units drives the photochemical reaction cycles of proteorhodopsin and bacteriorhodopsin analogues.
    Shariful Haque, Takashi Kikukawa, Nobuyuki Tamaoki
    Organic & biomolecular chemistry, 18, 32, 6312, 6327, 19 Aug. 2020, [International Magazine]
    English, Scientific journal, In this study we substituted the retinal units in proteorhodopsin (PR) and bacteriorhodopsin (BR) with azo chromophores to investigate the mechanism of photoinduced proton pumping in rhodopsins and potentially develop new artificial molecular pumps. We used an indium tin oxide electrode to investigate the photoinduced proton transfer of the azo analogues of PR and BR. We also employed flash photolysis to determine the characteristic photocycles, comprising multiple transient intermediates, of the azo chromophore-bound PR and BR. Moreover, our studies of the photoinduced proton pumping functions of azo-proteoopsin and azo-bacterioopsin complexes revealed that they did not pump protons upon illumination, even though they underwent photoinduced proton transfer and the characteristic photocycle. Mutational analysis suggested that the proton pumping malfunction of the azo analogues of PR and BR resulted from the absence of proton transfer reactions through cytoplasmic channels, even though these reactions were evoked in extracellular channels. Based on our experimental findings, we propose herein a putative model of the proton transfer reaction mechanism for the azo analogues of PR and BR.
  • Mechanical and thermal stimuli-induced release of toluene included in luminescent crystals as one-dimensional solvent channels
    Yoshimitsu Sagara, Kiyonori Takahashi, Takayoshi Nakamura, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C, 8, 29, 10039, 10046, ROYAL SOC CHEMISTRY, Aug. 2020, [Peer-reviewed]
    English, Scientific journal, Luminescent materials that change their photophysical properties and molecular arrangement in response to external stimuli have attracted attention because of the potential application in sensors, memory, security inks, and informational displays. The combination of external stimuli-responsive luminescence with the release of volatile molecules would give more sophisticated photofunctional materials. Herein we discuss a 9,10-bis(phenylethynyl)anthracene derivative that formed green-emissive crystals containing one-dimensional toluene channels. Amide groups of the compounds formed linear hydrogen-bonds in the crystals. Thermal treatment resulted in a phase transition to another crystalline state with the release of the guest toluene molecules. However, little alteration in the photoluminescent properties occurred during the transition. Mechanical stimuli led to the release of volatile molecules along with an emission colour change with a transition from the crystalline to an amorphous phase. Infrared spectroscopy showed that linear hydrogen bonds remained after a thermal treatment-induced phase transition, whereas mechanical stimuli disturbed them.
  • Mechanochromic Luminescence from Crystals Consisting of Intermolecular Hydrogen-Bonded Sheets
    Yoshimitsu Sagara, Kiyonori Takahashi, Takayoshi Nakamura, Nobuyuki Tamaoki
    CHEMISTRY-AN ASIAN JOURNAL, 15, 4, 478, 482, WILEY-V C H VERLAG GMBH, Feb. 2020, [Peer-reviewed]
    English, Scientific journal, Introduction of functional groups that can form intermolecular hydrogen bonds into highly-emissive luminophores is a promising way to induce mechanochromic luminescence. Herein, we report that a 9,10-bis(phenylethynyl)anthracene derivative featuring two amide groups forms green-emissive crystals based on two-dimensional hydrogen-bonded molecular sheets. Mechanical grinding changed the emission from green to yellow, owing to a transition from a crystalline to an amorphous phase. Infrared spectroscopy revealed that mechanical stimuli disrupted the linear hydrogen-bonding formation. A thermal treatment recovered the original green photoluminescence.
  • Photoswitchable CENP-E Inhibitor Enabling the Dynamic Control of Chromosome Movement and Mitotic Progression.
    Noushaba Nusrat Mafy, Kazuya Matsuo, Shota Hiruma, Ryota Uehara, Nobuyuki Tamaoki
    Journal of the American Chemical Society, 142, 4, 1763, 1767, 29 Jan. 2020, [Peer-reviewed], [Last author, Corresponding author], [International Magazine]
    English, Interfering with mitosis is a potential cancer therapy strategy. However, the lack of controllability of antimitotic drugs in cell growth suppression causes severe side effects and limits their clinical utility. Herein, we developed an azobenzene-based photoswitchable inhibitor of CENP-E, a mitotic kinesin required for chromosome transportation. The new inhibitor enabled reversible photoswitching of CENP-E activity with ∼10-fold change in IC50 between cis and trans photoisomerization states both in vitro and in living cells. It also enabled repeatable photoswitching of CENP-E-dependent chromosome congression and hence mitotic progression with UV/vis light illumination cycles. Using this technique, we could specify the exact process of mitotic progression in which CENP-E plays an indispensable role. Our data demonstrate the power of a photochemical approach for highly controllable mitotic interference as well as for discovery of precise molecular functions in dynamic cellular processes.
  • Crystal structure and thermoresponsive luminescence of a 9,10-bis(phenylethynyl)anthracene-based cyclophane
    Yoshimitsu Sagara, Kiyonori Takahashi, Takayoshi Nakamura, Nobuyuki Tamaoki
    MOLECULAR SYSTEMS DESIGN & ENGINEERING, 5, 1, 205, 211, ROYAL SOC CHEMISTRY, Jan. 2020, [Peer-reviewed]
    English, Scientific journal, Introducing a cyclic structure to luminophores is a promising approach for achieving external stimuli-responsive luminescence. This is because luminescent cyclophanes containing flexible linkers tend to form several molecular assembled states. However, previously reported cyclophanes exhibiting thermoresponsive and/or mechanoresponsive luminescence have not given crystals suitable for single crystal X-ray structure analysis because of the flexible cyclic molecular structures. Such analysis is important because solved crystal structures can show unambiguous correlation between the arrangement of luminophores and photophysical properties. Here, we report the crystal structure of a cyclophane featuring a 9,10-bis(phenylethynyl)anthracene group and the thermoresponsive luminescence. The cyclophane was designed with shorter flexible oligo(ethyleneglycol) chains used as linkers bridging the luminophore and another aromatic group. The two different pi-conjugated groups were orthogonally arranged in the individual molecule, and the luminophores partially overlapped between adjacent molecules. The cyclophane showed a supercooled nematic phase at room temperature upon cooling. Thermal treatment for the kinetically trapped state led to a transition to another crystalline state and, consequently, a change in photoluminescence colour. Emission spectroscopic studies and emission lifetime measurements revealed that the luminophores formed excimers in the supercooled nematic phase, whereas no excimer formation was observed for the crystalline phases.
  • Mechanoresponsive Behavior of a Polymer-Embedded Red-Light Emitting Rotaxane Mechanophore
    Muramatsu Tatsuya, Sagara Yoshimitsu, Traeger Hanna, Tamaoki Nobuyuki, Weder Christoph
    ACS APPLIED MATERIALS & INTERFACES, 11, 27, 24571, 24576, 10 Jul. 2019, [Peer-reviewed]
  • Azobenzene‐Based Photoswitches Facilitating Reversible Regulation of Kinesin and Myosin Motor Systems for Nanotechnological Applications
    Ammathnadu S. Amrutha, K. R. Sunil Kumar, Nobuyuki Tamaoki
    ChemPhotoChem, 3, 6, 337, 346, Wiley, Jun. 2019
    Scientific journal
  • Rotaxane-Based Mechanophores Enable Polymers with Mechanically Switchable White Photoluminescence
    Sagara Yoshimitsu, Karman Marc, Seki Atsushi, Pannipara Mehboobali, Tamaoki Nobuyuki, Weder Christoph
    ACS CENTRAL SCIENCE, 5, 5, 874, 881, AMER CHEMICAL SOC, 22 May 2019, [Peer-reviewed]
    English, Scientific journal, Three mechanoresponsive polyurethane elastomers whose blue, green, and orange photoluminescence can be reversibly turned on by mechanical force were prepared and combined to create a blend that exhibits deformation-induced white photoluminescence. The three polyurethanes contain rotaxane-based supramolecular mechanoluminophores based on pi-extended pyrene, anthracene, or 4-(dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran (DCM) lumino-phores, respectively, and 1,4,5,8-naphthalenetetracarboxylic diimide as an electronically matched quencher. Each polymer shows instantly reversible, strain-dependent switching of its photoluminescence intensity when stretched and relaxed, as deformation leads to a spatial separation of the luminophore and quencher. The present study shows that the photoluminescence color can easily be tailored by variation of the luminophore and also by combining several mechanophores in one material and demonstrates that adaptability is a key advantage of supramolecular approaches to create mechanoresponsive polymers.
  • Mechano- and Photoresponsive Behavior of a Bis(cyanostyryl)benzene Fluorophore
    Kaneko Ryohei, Sagara Yoshimitsu, Katao Shouhei, Tamaoki Nobuyuki, Weder Christoph, Nakano Hideyuki
    CHEMISTRY-A EUROPEAN JOURNAL, 25, 24, 6162, 6169, 26 Apr. 2019, [Peer-reviewed]
  • Molecular Crankshaft Effect Converting Piston-like Molecular Motion to Continuous Rotation of Macro Objects.
    Noushaba Nusrat Mafy, Yuna Kim, Reji Thomas, Takehito Akasaka, Nobuyuki Tamaoki
    ACS applied materials & interfaces, 11, 16, 15097, 15102, 24 Apr. 2019, [International Magazine]
    English, Scientific journal, A molecular system inducing an accumulative unidirectional rotation motion of glass flakes with about 100 μm in size is introduced. The molecular system is a chiral nematic liquid crystal containing a chiral azobenzene derivative which shows a reversible E- Z photoisomerization accompanying a large helical twisting power change. A film of the molecular system shows different texture change paths upon UV and visible light irradiations inducing " E to Z" and " Z to E" photoisomerizations, respectively, of the chiral azobenzene dopant. Namely, a polygonal fingerprint texture inducing the rotation of glass flakes on the film surface was maintained during UV irradiation, while a focal conic texture inducing no rotation of glass flakes emerged during visible light irradiation. As a result, cycles of the alternative irradiation of UV and visible lights afforded many rotations toward a single direction of the glass flakes which can be considered as a continuous conversion of light energy to mechanical work. We may compare the effect of this molecular system converting "back and forth" structural change between E and Z isomers of the chiral azobenzene to a continuous rotational motion of glass flakes with the crankshaft effect converting a piston-like motion to a rotational motion seen in engines in the real world.
  • A 1,6-Diphenylpyrene-Based, Photoluminescent Cyclophane Showing a Nematic Liquid-Crystalline Phase at Room Temperature
    Sagara Yoshimitsu, Muramatsu Tatsuya, Tamaoki Nobuyuki
    CRYSTALS, 9, 2, MDPI, Feb. 2019, [Peer-reviewed]
    English, Scientific journal, Photoluminescent nematic liquid crystals have been an attractive research target for decades, because of their potential applications in optoelectrical devices. Integration of luminescent motifs into cyclic structures is a promising approach to induce low-ordered liquid-crystalline phases, even though relatively large and rigid luminophores are used as emitters. Here, we demonstrate a 1,6-diphenylpyrene-based, unsymmetric cyclophane showing a stable nematic phase at room temperature and exhibiting strong photoluminescence from the condensed state. The observed sky-blue photoluminescence was dominated by the emission species ascribed to assembled luminophores rather than monomers.
  • Substrate selectivity and its mechanistic insight of the photo-responsive non-nucleoside triphosphate for myosin and kinesin.
    Islam MJ, Matsuo K, Menezes HM, Takahashi M, Nakagawa H, Kakugo A, Sada K, Tamaoki N
    Organic & biomolecular chemistry, 17, 1, 53, 65, ROYAL SOC CHEMISTRY, Dec. 2018, [Peer-reviewed], [Last author, Corresponding author]
    English, Scientific journal, Linear motor proteins including kinesin and myosin are promising biomaterials for developing nano-devices. Photoswitchable substrates of these biomotors can be used to optically regulate the motility of their associated cytoskeletal filaments in in vitro systems. Here, we describe the discovery of the myosin selective azobenzene-tethered triphosphate. It enables the specific photocontrol over myosin in a reversible mode with the composite motility assay composed of both kinesin and myosin. The mechanistic insight into this myosin selectivity is also explained with the docking simulation study.
  • Photochemical chirality induction and inversion in soft materials
    Yuna Kim, Noushaba N. Mafy, Nobuyuki Tamaoki
    Photoactive Functional Soft Materials: Preparation, Properties, and Applications, 125, 166, wiley, 12 Nov. 2018
    English, In book, This chapter focuses on the recent progress harnessing chirality induction in achiral molecules by utilizing light as a chiral stimulus to achieve chiral assemblies based on photochromic switches in soft materials such as liquid crystals and polymeric organizations. It discusses the modulation of their induced supramolecular chirality such as helix inversion between opposite handedness and helical twisting power (HTP) control through photochemical reactions. Circularly polarized light (CPL) or circularly polarized ultraviolet light (CPUL) irradiation is introduced as a light stimulus for the induction and modulation of the chiral helical structures from achiral polymers bearing photochromophores. At the low molecular weight (LMW) supramolecular level, helical organization usually occurs in chiral smectic and chiral nematic liquid crystals. When a photoresponsive chiral dopant is dissolved in an achiral nematic liquid crystal (NLC), its molecular chirality can be transferred to the NLC medium, resulting in the photoresponsive chiral nematic liquid crystal phase.
  • Cyclophane-Based Fluorescence Tuning Induced by Hydrostatic Pressure Changes
    Sagara Yoshimitsu, Tamaoki Nobuyuki, Fukuhara Gaku
    CHEMPHOTOCHEM, 2, 11, 959, 963, WILEY-V C H VERLAG GMBH, Nov. 2018, [Peer-reviewed]
    English, Scientific journal, In contrast to a standard steady fluorescence intensity increase of a chloroform solution of a linear chromophore unit under high pressure, a fluorescent cyclophane solution shows significant fluorescence quenching under elevated pressure. A pressure-induced enhancement of the formation of an intramolecular pi-stacked conformation is proposed to be responsible.
  • Pressure-Induced Transition of Bisamide Substituted Diacetylene Crystals from Non-Photopolymerizable to Photopolymerizable State
    Yuna Kim, Ken’ichi Aoki, Masaya Fujioka, Junji Nishii, Nobuyuki Tamaoki
    ACS Applied Materials & Interfaces, 10, 42, 36407, 36414, Oct. 2018, [Peer-reviewed], [International Magazine]
    English, Scientific journal, Mechanoresponsive diacetylenes (DAs) exhibiting a transition of crystalline orientation from light-inert to light-active state upon applied force are reported. Amide units are introduced to DAs where hydrogen bonding is utilized to control intermolecular interactions. Application of external pressure (2-150 MPa) to DAs results in an emergence of new crystal phases with changing the d-spacing which possibly reduces the reaction barrier. Accordingly, the dramatic crystalline transition from "perfectly off" to "on" state to undergo the light-induced topochemical polymerization of bulk DA crystals is obtained. Subsequent UV irradiation at a wavelength of 254 nm enables the polymerization of the pressed region, changing its color from white to blue which suggests the selective formation of polydiacetylene (PDA) polymorphs. In addition, by utilizing the mechanoresponsive crystallinity with low-enough activation pressure, a new strategy for PDA patterning is demonstrated based on the selective transfer of information by means of force to a DA film. This phenomenon can be applicable to a new nanoimprinting technique where no mechanical deformation of resist materials but phase transition is induced by the mold.
  • Stimuli-Responsive Dual-Color Photon Upconversion: A Singlet-to-Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane
    Kazuma Mase, Yoichi Sasaki, Yoshimitsu Sagara, Nobuyuki Tamaoki, Christoph Weder, Nobuhiro Yanai, Nobuo Kimizuka
    Angewandte Chemie - International Edition, 57, 11, 2806, 2810, Wiley-VCH Verlag, 05 Mar. 2018, [Peer-reviewed]
    English, Scientific journal, Reversible emission color switching of triplet–triplet annihilation-based photon upconversion (TTA-UC) is achieved by employing an Os complex sensitizer with singlet-to-triplet (S-T) absorption and an asymmetric luminescent cyclophane with switchable emission characteristics. The cyclophane contains the 9,10-bis(phenylethynyl)anthracene unit as an emitter and can assemble into two different structures, a stable crystalline phase and a metastable supercooled nematic phase. The two structures exhibit green and yellow fluorescence, respectively, and can be accessed by distinct heating/cooling sequences. The hybridization of the cyclophane with the Os complex allows near-infrared-to-visible TTA-UC. The large anti-Stokes shift is possible by the direct S-T excitation, which dispenses with the use of a conventional sequence of singlet–singlet absorption and intersystem crossing. The TTA-UC emission color is successfully switched between green and yellow by thermal stimulation.
  • Stimuli-Responsive Dual-Color Photon Upconversion: A Singlet-to-Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane
    Kazuma Mase, Yoichi Sasaki, Yoshimitsu Sagara, Nobuyuki Tamaoki, Christoph Weder, Nobuhiro Yanai, Nobuo Kimizuka
    Angewandte Chemie, 130, 11, 2856, 2860, Wiley-Blackwell, Mar. 2018, [Peer-reviewed]
    Scientific journal
  • Inside Cover: Stimuli-Responsive Dual-Color Photon Upconversion: A Singlet-to-Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane (Angew. Chem. Int. Ed. 11/2018)
    Kazuma Mase, Yoichi Sasaki, Yoshimitsu Sagara, Nobuyuki Tamaoki, Christoph Weder, Nobuhiro Yanai, Nobuo Kimizuka
    Angewandte Chemie International Edition, 57, 11, 2730, Wiley-Blackwell, Mar. 2018, [Peer-reviewed]
  • Innentitelbild: Stimuli-Responsive Dual-Color Photon Upconversion: A Singlet-to-Triplet Absorption Sensitizer in a Soft Luminescent Cyclophane (Angew. Chem. 11/2018)
    Kazuma Mase, Yoichi Sasaki, Yoshimitsu Sagara, Nobuyuki Tamaoki, Christoph Weder, Nobuhiro Yanai, Nobuo Kimizuka
    Angewandte Chemie, 130, 11, 2778, Wiley-Blackwell, Mar. 2018, [Peer-reviewed]
  • Rotaxanes as mechanochromic fluorescent force transducers in polymers
    Yoshimitsu Sagara, Marc Karman, Ester Verde-Sesto, Kazuya Matsuo, Yuna Kim, Nobuyuki Tamaoki, Christoph Weder
    Journal of the American Chemical Society, 140, 5, 1584, 1587, American Chemical Society, 07 Feb. 2018, [Peer-reviewed]
    English, Scientific journal, The integration of mechanophores, motifs that transduce mechanical forces into chemical reactions, allows creating materials with stress-dependent properties. Typical mechanophores are activated by cleaving weak covalent bonds, but these reactions can also be triggered by other stimuli, and this renders the behavior unspecific. Here we show that this problem can be overcome by extending the molecular-shuttle function of rotaxanes to mechanical activation. A mechanically interlocked mechanophore composed of a fluorophore-carrying macrocycle and a dumbbell-shaped molecule containing a matching quencher was integrated into a polyurethane elastomer. Deformation of this polymer causes a fluorescence turn-on, due to the spatial separation of fluorophore and quencher. This process is specific, efficient, instantly reversible, and elicits an easily detectable optical signal that correlates with the applied force.
  • Linearly polarized photoluminescence from an asymmetric cyclophane showing thermo- and mechanoresponsive luminescence
    Yoshimitsu Sagara, Atsushi Seki, Yuna Kim, Nobuyuki Tamaoki
    Journal of Materials Chemistry C, 6, 31, 8453, 8459, 2018, [Peer-reviewed]
    English, Scientific journal, © The Royal Society of Chemistry. The first cyclophane to exhibit linearly polarized photoluminescence in the liquid-crystalline and crystalline states is described. An asymmetric cyclophane featuring a 4,7-bis(phenylethynyl)-2,1,3-benzothiadiazole group forms a thermodynamically metastable nematic liquid-crystalline phase at room temperature. The compound sandwiched between two glass substrates coated with rubbed polyimide thin layers exhibits homogeneous alignment after shearing. The transition dipole moments of the luminophores align along the rubbing direction. As a result, linearly polarized photoluminescence is achieved at room temperature without any other host materials. Furthermore, the polarized emission is retained after the transition to the crystalline phase, which is induced by annealing at 60 °C for 1 h. The cyclophane also shows a thermal and mechanical stimuli-induced change in the photoluminescence colors.
  • Targeted Activation of Molecular Transportation by Visible Light
    Ammathnadu S. Amrutha, K. R. Sunil Kumar, Takashi Kikukawa, Nobuyuki Tamaoki
    ACS Nano, 11, 12, 12292, 12301, American Chemical Society, 26 Dec. 2017, [Peer-reviewed]
    English, Scientific journal, Regulated transportation of nanoscale objects with a high degree of spatiotemporal precision is a prerequisite for the development of targeted molecular delivery. In vitro integration of the kinesin-microtubule motor system with synthetic molecules offers opportunities to develop controllable molecular shuttles for lab-on-a-chip applications. We attempted a combination of the kinesin-microtubule motor system with push-pull type azobenzene tethered inhibitory peptides (azo-peptides) through which reversible, spatiotemporal control over the kinesin motor activity was achieved locally by a single, visible wavelength. The fast thermal relaxation of the cis-isomers of azo-peptides offered us quick and complete resetting of the trans-state in the dark, circumventing the requirement of two distinct wavelengths for two-way switching of kinesin-driven microtubule motility. Herein, we report the manipulation of selected, single microtubule movement while keeping other microtubules at complete rest. The photoresponsive inhibitors discussed herein would help in realizing complex bionanodevices.
  • Driving and photo-regulation of myosin-actin motors at molecular and macroscopic levels by photo-responsive high energy molecules
    Halley M. Menezes, Md. Jahirul Islam, Masayuki Takahashi, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY, 15, 42, 8894, 8903, ROYAL SOC CHEMISTRY, Nov. 2017, [Peer-reviewed]
    English, Scientific journal, We employed an azobenzene based non-nucleoside triphosphate, AzoTP, in a myosin-actin motile system and demonstrated its efficiency as an energy molecule to drive and photo-regulate the myosin-actin motile function at the macroscopic level along with an in vitro motility assay. The AzoTP in its trans state induced shortening of a glycerinated muscle fibre whilst a cis isomer had no significant effect. Direct photoirradiation of a cis-AzoTP infused muscle fibre induced shortening triggered by a locally photo-generated trans-AzoTP in the muscle fibre. Furthermore, we designed and synthesized three new derivatives of AzoTPs that served as substrates for myosin by driving and photo-regulating the myosin-actin motile function at the molecular as well as the macroscopic level with varied efficiencies.
  • Asymmetric Cyclophanes Permit Access to Supercooled Nematic Liquid Crystals with Stimulus-Responsive Luminescence
    Yoshimitsu Sagara, Christoph Weder, Nobuyuki Tamaoki
    CHEMISTRY OF MATERIALS, 29, 14, 6145, 6152, AMER CHEMICAL SOC, Jul. 2017, [Peer-reviewed]
    English, Scientific journal, A novel material with stimulus-responsive luminescence was created by integrating a chromophore with assembly-dependent emission properties into a liquid crystalline compound that can be kinetically trapped in a supercooled liquid crystalline state. This was achieved by synthesizing an asymmetric cyclophane containing one 1,6-bis(phenylethynyl)pyrene group. The new compound displays a broad nematic phase above similar to 110 degrees C upon being heated. Quenching to room temperature allows one to avoid crystallization, and the supercooled nematic phase is stable for at least 1 h. When the compound is heated, a phase transition from the kinetically trapped state to a crystalline state occurs, concomitant with a pronounced change in photoluminescence. The crystalline phase thus accessed shows mechanoresponsive luminescence behavior.
  • Programmable dual electrochromism in azine linked conjugated polymer
    Minsu Han, Mithrabinda K. Poduval, Haijin Shin, Nobuyuki Tamaoki, Taiho Park, Yuna Kim, Eunkyoung Kim
    OPTICAL MATERIALS EXPRESS, 7, 6, 2117, 2125, OPTICAL SOC AMER, Jun. 2017, [Peer-reviewed]
    English, Scientific journal, A conjugated polymer consisting of tri-EDOT and azine groups was synthesized and explored for a programmable dual electrochromic device. Electrochemical doping (oxidation) and de-doping (reduction) resulted in the two distinct redox pairs, depending on the applied potential range. In situ spectroelectrochemical analyses revealed that the stepwise redox process of two units was associated with dual electrochromic responses: tri-EDOT unit for purple electrochromism followed by azine unit for blue electrochromism. Dual electrochromism of purple and blue was attainable at below 1.0 V which could induce the color transition upon the potential application of around +/- 1 V. Maximum coloration efficiency of 393 cm(2)/C with a response time of 1 s was obtained. (C) 2017 Optical Society of America
  • Temperature-Dependent Mechanochromic Behavior of Mechanoresponsive Luminescent Compounds
    Yoshimitsu Sagara, Kazuya Kubo, Takayoshi Nakamura, Nobuyuki Tamaoki, Christoph Weder
    CHEMISTRY OF MATERIALS, 29, 3, 1273, 1278, AMER CHEMICAL SOC, Feb. 2017, [Peer-reviewed]
    English, Scientific journal, Mechanoresponsive luminescent (MRL) compounds change their emission color upon mechanical treatment. Hundreds of MRL compounds have been studied, but their mechanically triggered response at elevated temperature has remained virtually unexplored. Here, we demonstrate that the temperature can have a significant influence on the mechanically induced response of MRL compounds. The photoluminescence of a new cyano-substituted oligo(p-phenylenevinylene) derivative was shown to exhibit a significant red-shift when ground at ambient temperature, whereas the same treatment at 100 degrees C leads to a hypsochromic shift. The behavior at ambient is caused by a mechanically induced phase transition from a crystalline to an amorphous solid in which the dye molecules form excimers, whereas at elevated temperature the hypsochromic shift is ascribed to a crystalline-crystalline phase transition. Such temperature-dependent MRL behavior was not previously observed, but it appears to be a general effect that is useful for sophisticated mechano-sensing materials and devices.
  • Unexpected Responses of Luminescent Molecular Materials Upon Simultaneous Exposure to Mechanical Force and Heat
    Y. Sagara, K. Kubo, T. Nakamura, N. Tamaoki, C. Weder
    Chemistry of Materials, 29, 1273, 1278, Jan. 2017, [Peer-reviewed]
    English, Scientific journal
  • Mechanoresponsive luminescence and liquid-crystalline behaviour of a cyclophane featuring two 1,6-bis(phenylethynyl)pyrene groups
    Yoshimitsu Sagara, Nobuyuki Tamaoki
    RSC ADVANCES, 7, 74, 47056, 47062, ROYAL SOC CHEMISTRY, 2017, [Peer-reviewed]
    English, Scientific journal, Cyclophanes have been attractive targets over recent decades because of their fascinating molecular structures and inherent ability to act as supramolecular hosts. However, cyclophanes that exhibit stimuli-responsive luminescence in their condensed states are still very rare, although luminescent cyclophanes could be suitable platforms for sophisticated photofunctional molecular assembled materials. We here report that a pyrenophane featuring two p-extended pyrene groups exhibits mechanoresponsive luminescence in the solid states and shows a nematic liquid-crystalline phase at elevated temperature. Two 1,6-bis(phenylethynyl)pyrene moieties form intramolecular excimers in a diluted chloroform solution, whereas no clear intra-and/or intermolecular excimer formation was observed for the solid state accessed through slow cooling from the nematic phase. Photoluminescence spectroscopic measurements, emission lifetime measurements, and X-ray diffraction patterns confirmed that mechanical stimuli result in conversion to much less ordered molecular assembled states in which some luminophores form excimers, leading to changes in photoluminescence colours.
  • A helical naphthopyran dopant for photoresponsive cholesteric liquid crystals
    Yuna Kim, Michel Frigoli, Nicolas Vanthuyne, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS, 53, 1, 200, 203, ROYAL SOC CHEMISTRY, Jan. 2017, [Peer-reviewed]
    English, Scientific journal, The first photoresponsive cholesteric liquid crystal comprising a photoisomerizable helical naphthopyran derivative dopant and a nematic liquid crystal is reported. An unprecedented helical twisting power switching ratio of over 90% allowed us to demonstrate multicycle rotational motion of micro-objects by UV light irradiation.
  • Determination of the absolute stereostructure of a cyclic azobenzene from the crystal structure of the precursor containing a heavy element
    Reji Thomas, Nobuyuki Tamaoki
    BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY, 12, BEILSTEIN-INSTITUT, Oct. 2016, [Peer-reviewed]
    English, Scientific journal, Single crystal X-ray diffraction has been used as one of the common methods for the unambiguous determination of the absolute stereostructure of chiral molecules. However, this method is limited to molecules containing heavy atoms or to molecules with the possibility of functionalization with heavy elements or chiral internal references. Herein, we report the determination of the absolute stereostructure of the enantiomers of molecule (E)-2, which lacks the possibility of functionalization, using a reverse method, i.e., defunctionalization of its precursor of known stereostructure with bromine substitution (S-(-)-(E)-1). A reductive debromination of S-(-)-(E)-1 results in formation of one of the enantiomers of (E)-2. Using a combination of HPLC and CD spectroscopy we could safely assign the stereostructure of one of the enantiomers of (E)-2, the reduced product R-(-)-(E)-1.
  • Asymmetric Dimers of Chiral Azobenzene Dopants Exhibiting Unusual Helical Twisting Power upon Photoswitching in Cholesteric Liquid Crystals
    Yuna Kim, Nobuyuki Tamaoki
    ACS APPLIED MATERIALS & INTERFACES, 8, 7, 4918, 4926, AMER CHEMICAL SOC, Feb. 2016, [Peer-reviewed]
    English, Scientific journal, In this study, we synthesized asymmetric dimeric chiral molecules as photon-mode chiral switches for reversible tuning of self-assembled helical superstructures. The chiral switches bearing two mesogen units cholesterol and azobenzene moieties connected through flexible alkylenedioxy bridges were doped into nematic liquid crystals, resulting in a chiral nematic (cholesteric) phase. Under irradiation with UV light, photoisomerization of the azobenzene units led to unprecedented switching of the cholesteric pitch and helical twisting power (HTP, beta), with a higher HTP found in the cis-rich state (bent-form) than in the trans-state (rod-form). We attribute this behavior to the elongated cybotactic smectic clusters disrupting the helical orientation of the molecules in the cholesteric liquid crystals; their reversible decay and reassembly was evidenced upon sequential irradiation with UV and visible light, respectively. In addition to the photoisomerization of the azobenzene units, the odd/even parity of the alkylenedioxy linkers of the dimeric dopants also had a dramatic effect on the transitions of the cybotactic smectic domains. On the basis of the large rotational reorganization of the cholesteric helix and HTP switching (Delta beta/beta(ini) of up to 50%), we could control the macroscopic rotational motion of microsized glass rods upon irradiating the surface of a cholesteric liquid crystal film featuring a polygonal fingerprint texture using UV and visible light.
  • A mechano- and thermoresponsive luminescent cyclophane
    Yoshimitsu Sagara, Yoan C. Simon, Nobuyuki Tamaoki, Christoph Weder
    CHEMICAL COMMUNICATIONS, 52, 33, 5694, 5697, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
    English, Scientific journal, The first fluorescent cyclophane with mechano- and thermoresponsive solid-state fluorescence characteristics is reported. The new cyclophane comprises two 9,10-bis(phenylethynyl)anthracene moieties that are bridged by tetraethylene glycol spacers. The stimuli-responsiveness is based on molecular assembly changes.
  • Tuning the thermo- and mechanoresponsive behavior of luminescent cyclophanes
    Yoshimitsu Sagara, Christoph Weder, Nobuyuki Tamaoki
    RSC ADVANCES, 6, 84, 80408, 80414, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
    English, Scientific journal, Many cyclophanes have been investigated in dilute solution, where their internal cavities are accessible for supramolecular interactions. However, their photophysical properties in the solid state remain largely unexplored. We here report a new mechano- and thermoresponsive luminescent cyclophane that is comprised of two 9,10-bis(phenylethynyl) anthracene moieties and features two hexaethylene glycol bridges. The compound was found to exhibit a nematic liquid-crystalline phase at elevated temperature. X-ray diffraction patterns confirm that thermal and mechanical treatments induce changes in the molecular assembly, which are the basis for the observed photoluminescent color variations. The stimuli-responsive behavior of the new compound is quite different from that of a previously reported cyclophane with similar structure but shorter bridges. Thus, merely changing the ring size is an effective tool to tailor the stimuli-responsiveness and the phase behaviour of luminescent cyclophanes.
  • Structure-property relationships of photoresponsive inhibitors of the kinesin motor
    Ammathnadu S. Amrutha, K. R. Sunil Kumar, Kazuya Matsuo, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY, 14, 30, 7202, 7210, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
    English, Scientific journal, Recently we demonstrated the photoregulation of the activity of kinesin-1 using an azobenzene-tethered peptide (azo-peptide: Azo-Ile-Pro-Lys-Ala-Ile-Gln-Ala-Ser-His-Gly-Arg-OH). To understand the mechanism behind this photoswitchable inhibition, here we studied the structure-property relationships of a range of azo-peptides through systematic variations in the structures of the peptide and azobenzene units. The vital peptide sequence for kinesin inhibition-mediated through electrostatic, hydrophobic and C-H center dot center dot center dot pi interactions-was the same as that for the self-inhibition of kinesin. We also identified substituents on the azobenzene capable of enhancing the photoswitchability of inhibition. As a result, we developed a new inhibitor featuring a relatively short peptide unit (-Arg-Ile-Pro-Lys-Ala-Ile-Arg-OH) and an azobenzene unit bearing a para-OMe group. In the trans form of its azobenzene unit, this finely tuned inhibitor stopped the kinesin-driven gliding motility of microtubules completely at a relatively low concentration, yet allowed gliding motility with a relatively high velocity in the cis form obtained after UV irradiation.
  • Spatiotemporal control of kinesin motor protein by photoswitches enabling selective single microtubule regulations
    K. R. Sunil Kumar, Ammathnadu S. Amrutha, Nobuyuki Tamaoki
    LAB ON A CHIP, 16, 24, 4702, 4709, ROYAL SOC CHEMISTRY, 2016, [Peer-reviewed]
    English, Scientific journal, Artificial control of bio-nanomachines should have a major impact on the development of controllable transport systems for specific cargo transport on chips. Precise spatiotemporal control and local regulation of the bio-motor activity will, however, be necessary if we are to accomplish such a goal. In this study, we exploited the photoswitching properties of azobenzene-based high-energy molecules and inhibitors to control a single kinesin-driven microtubule that has potential to work as a nanocarrier for molecular cargos. In particular, we could influence the local concentration and dispersion of the microtubules at any desired position and time by irradiating a local area of the motility system at one wavelength, while irradiating the entire area at another wavelength, to enrich either cis or trans isomers of photoswitches in the selected region. Furthermore, various regulations (e.g., transporting, bending, breaking) of single microtubules were possible while almost arresting ambient microtubules-all without the need for any surface patterning.
  • Fast thermal cis-trans isomerization depending on pH and metal ions of water-soluble azobenzene derivatives containing a phosphate group
    Rika Ochi, Nishad Perur, Kazutoshi Yoshida, Nobuyuki Tamaoki
    TETRAHEDRON, 71, 21, 3500, 3506, PERGAMON-ELSEVIER SCIENCE LTD, May 2015, [Peer-reviewed]
    English, Scientific journal, We observed unique thermal cis-trans isomerization properties of water-soluble azobenzene derivatives in which a phosphate group was substituted at ortho position of an azobenzene via an amide linkage. Here, we report the effect of the structure of the phosphate groups (the length and the position), pH, and metal ions on thermal cis-trans isomerization. We revealed that the water-soluble azobenzene derivatives, in which di- or tri-phosphate group was substituted at ortho position of the azobenzene via the amide linkage, showed the fast thermal isomerization in low pH condition. In addition, we showed that the effects of the metal ions on the thermal isomerization rate. (C) 2015 Elsevier Ltd. All rights reserved.
  • Dynamic induction of enantiomeric excess from a prochiral azobenzene dimer under circularly polarized light
    K. Rijeesh, P. K. Hashim, Shin-ichiro Noro, Nobuyuki Tamaoki
    CHEMICAL SCIENCE, 6, 2, 973, 980, ROYAL SOC CHEMISTRY, 2015, [Peer-reviewed]
    English, Scientific journal, The ability to photoinduce enantiomeric excess from the chirality of circularly polarized light (CPL) is pertinent to the study of the origin of homochirality in biomolecules. Such CPL-induced reactions, including both chirality generation and formation of partial enantiomeric imbalance, from nonchiral starting compounds have been known, however, only for the conversion of diarylolefins into chiral helicenes. In this study we synthesized three different prochiral molecules, each featuring a pair of photoisomerizable phenylazo moieties arranged symmetrically upon the phenyl rings of an sp(3)-hybridized carbon atom (1), the phenyl rings of [2.2]paracyclophane (2), and the ortho positions of a phenyl ring bearing a naphthyl unit (3), and then investigated the possibility of photoinducing enantiomeric excess under CPL. Irradiation of 1-3 with light induced E <-> Z photoisomerizations of their azobenzene moieties, giving mixtures of their EE, EZ, and ZZ isomers in the photostationary state (PSS). Among these regioisomers, the EZ forms are chiral and existed as racemic mixtures of R and S stereoisomers. Upon CPL irradiation of 3, circular dichroism (CD) revealed enantiomeric enrichment of one of the EZ stereoisomers; furthermore, irradiation with r- or l-CPL gave CD signals opposite in sign, but with equal intensity, in the PSS. In contrast, 1 and 2 did not give any detectable induced CD upon CPL irradiation. These experimental results can be explained by considering the different Kuhn anisotropy factors (g) of the (R)-EZ and (S)-EZ stereoisomers of 1-3, assuming that the origin of the enantiomeric excess is the enantio-differentiating photoisomerization from EZ stereoisomers to nonchiral EE or ZZ regioisomers by r- or l-CPL. In short, we demonstrate the simultaneous induction of chirality and enantiomeric excess from a prochiral azobenzene dimer via a chiral regioisomer formed in situ upon CPL irradiation.
  • A photoresponsive planar chiral azobenzene dopant with high helical twisting power
    Yuna Kim, Nobuyuki Tamaoki
    Journal of Materials Chemistry C, 2, 9258, 9264, 21 Nov. 2014
    © 2014 the Partner Organisations. A planar chiral molecule as a photon-mode chiral switch was synthesized for the reversible control of self-assembled superstructures based on doped chiral nematic liquid crystals. The chiral switch is composed of bis-hexyl substituted diphenylnaphthalene and a photoisomerizing azobenzene unit connected by ethylene spacers in a cyclic manner. Bis-hexyl substitution to the mesogenic unit promoted the chirality transfer to the host LC medium resulting in a high initial helical twisting power (HTP) and a large change in HTP by photo-isomerization of the chiral dopant. At very low doping concentrations, both reversible tuning of RGB reflection colors and rotation motion control of micro glass rods on the cholesteric liquid crystal surface were achieved.
  • A photoresponsive planar chiral azobenzene dopant with high helical twisting power
    Yuna Kim, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C, 2, 43, 9258, 9264, ROYAL SOC CHEMISTRY, Nov. 2014, [Peer-reviewed]
    English, Scientific journal, A planar chiral molecule as a photon-mode chiral switch was synthesized for the reversible control of self-assembled superstructures based on doped chiral nematic liquid crystals. The chiral switch is composed of bis-hexyl substituted diphenylnaphthalene and a photoisomerizing azobenzene unit connected by ethylene spacers in a cyclic manner. Bis-hexyl substitution to the mesogenic unit promoted the chirality transfer to the host LC medium resulting in a high initial helical twisting power (HTP) and a large change in HTP by photo-isomerization of the chiral dopant. At very low doping concentrations, both reversible tuning of RGB reflection colors and rotation motion control of micro glass rods on the cholesteric liquid crystal surface were achieved.
  • Complete ON/OFF Photoswitching of the Motility of a Nanobiomolecular Machine
    K. R. Sunil Kumar, Takashi Kamei, Tuyoshi Fukaminato, Nobuyuki Tamaoki
    ACS NANO, 8, 5, 4157, 4165, AMER CHEMICAL SOC, May 2014, [Peer-reviewed]
    English, Scientific journal, To apply motor proteins as natural nanomolecular machines to transporting systems in nanotechnology, complete temporal control over ON/OFF switching of the motility is necessary. We have studied the photoresponsive inhibition properties of azobenzene-tethered peptides for regulation of kinesin-microtubule motility. Although a compound containing a peptide having an amino acid sequence derived from the kinesin's C-terminus (a known inhibitor of kinesin's motor domain) and also featuring a terminal azobenzene unit exhibited an inhibition effect, the phototunability of this behavior upon irradiation with UV or visible light was only moderate. Unexpectedly, newly synthesized peptides featuring the reverse sequence of amino acids of the C-terminus of kinesin exhibited excellent photoresponsive inhibition. In particular, azobenzene-CONH-IPKAIQASHGR completely stopped and started the motility of kinesin-microtubules in Its trans- and cis-rich states, respectively, obtained after irradiation with visible and UV light, respectively. A gliding motility system containing this photoresponsive Inhibitor allowed in situ control of the motion of microtubules on a kinesin-coated glass substrate. It is expected that the present results on the photoresponsive nanomotor system open up new opportunities to design nanotransportation systems.
  • Reversible control of F-1-ATPase rotational motion using a photochromic Cross Mark ATP analog at the single molecule level
    Ei-Ichiro Sunamura, Takashi Kamei, Hiroki Konno, Nobuyuki Tamaoki, Toru Hisabori
    BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS, 446, 1, 358, 363, ACADEMIC PRESS INC ELSEVIER SCIENCE, Mar. 2014, [Peer-reviewed]
    English, Scientific journal, Motor enzymes such as F-1-ATPase and kinesin utilize energy from ATP for their motion. Molecular motions of these enzymes are critical to their catalytic mechanisms and were analyzed thoroughly using a single molecule observation technique. As a tool to analyze and control the ATP-driven motor enzyme motion, we recently synthesized a photoresponsive ATP analog with a p-tert-butylazobenzene tethered to the 2' position of the ribose ring. Using cis/trans isomerization of the azobenzene moiety, we achieved a successful reversible photochromic control over a kinesin-microtubule system in an in vitro motility assay. Here we succeeded to control the hydrolytic activity and rotation of the rotary motor enzyme, F1-ATPase, using this photosensitive ATP analog. Subsequent single molecule observations indicated a unique pause occurring at the ATP binding angle position in the presence of cis form of the analog. (c) 2014 Elsevier Inc. All rights reserved.
  • Dicholesteryl icosanedioate as a glass-forming cholesteric liquid crystal: properties, additive effects and application in color recording
    Yuna Kim, Momoyo Wada, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C, 2, 10, 1921, 1926, ROYAL SOC CHEMISTRY, 2014, [Peer-reviewed]
    English, Scientific journal, A cholesteric ester dimer - dicholesteryl icosanedioate - was examined for color imaging. Cholesterol was introduced as one of the dopants which performed an important role reducing phase transition temperatures. The other dopants, 4,4'-dialkoxyazobenzene and 4,4'-dialkoxybiphenyl promoted formation of smectic domains in cholesteric phases which resulted in the expansion of the reflective band shift over the whole visible region. In particular, the photo-responsive dopant 4,4'-dialkoxyazobenzene allowed us to realize reversible RGB color tuning of the cholesteric film by both photon and thermal modes. The trans-cis photoisomerization led to a cholesteric pitch change which resulted in reflective color change, and recorded optical images that have been stable for more than 8 months in a glassy solid film state.
  • Thieno[3,2-b]thiophene derivatives exhibiting semiconducting liquid-crystalline phases at lower temperatures
    Yuna Kim, Masahiro Funahashi, Nobuyuki Tamaoki
    RSC ADVANCES, 4, 105, 60511, 60518, ROYAL SOC CHEMISTRY, 2014, [Peer-reviewed]
    English, Scientific journal, We synthesized novel liquid crystalline semiconductors bearing an extended pi-conjugated mesogen based on thieno[3,2-b]thiophene, which exhibit high solubility and low phase transition temperature. In particular, lateral methyl substitution to the mesogenic unit led to the formation of efficiently self-organized LC domains at lower temperature than that of reported liquid crystalline thieno[3,2-b]thiophene derivatives. Smectic A and smectic E phases were observed by a polarizing optical microscope over a wide temperature range between 75 and 125 degrees C. Hole mobility was determined by the time-of-flight (TOF) method, and calculated up to 2 x 10(-3) cm(2) V-1 s(-1). Herein we report the synthesis, thermophysical and carrier transport properties of novel thieno[3,2-b]thiophene based liquid-crystalline semiconductors.
  • A non-nucleoside triphosphate for powering kinesin-microtubule motility with photo-tunable velocity
    Nishad Perur, Masao Yahara, Takashi Kamei, Nobuyuki Tamaoki
    Chemical Communications, 49, 85, 9935, 9937, 04 Nov. 2013, [Peer-reviewed]
    English, Scientific journal, Three non-nucleoside triphosphates, one containing an azobenzene moiety, power a kinesin-microtubule system with high motile activity, with an observed maximum velocity of almost half of that obtained with ATP. The cis-trans photoisomerization of the azobenzene unit allows reversible and repeated control over the motile properties of kinesin. © 2013 The Royal Society of Chemistry.
  • Supramolecular self-assembly of a novel hydrogen-bonded cholesteric liquid crystal exhibiting macromolecular behaviour
    Mahdi Roohnikan, Morteza Ebrahimi, Seyed Reza Ghaffarian, Nobuyuki Tamaoki
    LIQUID CRYSTALS, 40, 3, 314, 320, TAYLOR & FRANCIS LTD, Mar. 2013, [Peer-reviewed]
    English, Scientific journal, The mesomorphic, thermoptic and glass-forming properties of 4-[6-((cholesteryloxy) carbonyl)oxy hexyloxy] benzoic acid (Ch-BA) have been investigated as a novel supramolecular hydrogen-bonded cholesteric mesogen. Fourier transform infrared and H-1 nuclear magnetic resonance studies have confirmed the chemical structure and the hydrogen-bond formation between the mesogens. According to polarising optical microscope observations, the compound exhibited smectic and chiral nematic phases. Differential scanning calorimetry indicated an unexpected glass transition (T-g) around 32 degrees C and a liquid crystalline region between 32 and 122 degrees C, in which the cholesteric phase appeared at 80 degrees C. As a result of the glass formation, samples of Ch-BA which were rapidly cooled below the T-g were found to preserve the long-range ordering of the liquid crystalline state and retained the iridescent colours of the cholesteric phase. These results led to the conclusion that the formation of identical dimers by intermolecular hydrogen-bonding of the terminal carboxylic acids accompanying the lateral packing of the rigid cores, built a trimeric arrangement and this was responsible for the macromolecular behaviour of Ch-BA, despite its relatively simple structure and low molecular weight.
  • Chirality induction by E-Z photoisomerization in [2,2]paracyclophane- bridged azobenzene dimer
    P. K. Hashim, Meethale C. Basheer, Nobuyuki Tamaoki
    Tetrahedron Letters, 54, 2, 176, 178, 09 Jan. 2013, [Peer-reviewed]
    English, Scientific journal, We designed and synthesized a new prochiral molecule in which two azobenzene moieties were embedded in [2,2]paracyclophane and showed the chirality induction by E-Z photoisomerization. We also demonstrated the on/off switching of asymmetry by irradiation and reflux respectively. © 2012 Elsevier Ltd. All rights reserved.
  • Influence of a Change in Helical Twisting Power of Photoresponsive Chiral Dopants on Rotational Manipulation of Micro-Objects on the Surface of Chiral Nematic Liquid Crystalline Films
    Reji Thomas, Yohei Yoshida, Takehito Akasaka, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL, 18, 39, 12337, 12348, WILEY-V C H VERLAG GMBH, Sep. 2012, [Peer-reviewed]
    English, Scientific journal, Herein we report a group of five planar chiral molecules as photon-mode chiral switches for the reversible control of the self-assembled superstructures of doped chiral nematic liquid crystals. The chiral switches are composed of an asymmetrically substituted aromatic moiety and a photoisomerizing azobenzene unit connected in a cyclic manner through methylene spacers of varying lengths. All the molecules show conformational restriction in the rotation of the asymmetrically substituted aromatic moiety in both the E and Z states of the azobenzene units resulting in planar chirality with separable enantiomers. Our newly synthesized compounds in pure enantiomeric form show high helical twisting power (HTP) in addition to an improved change in HTP between the E and Z states. The molecule with a diphenylnaphthalene unit shows the highest ever known initial helical twisting power among chiral dopants with planar chirality. In addition to the reversible tuning of reflection colors, we employed the enantiomers of these five compounds in combination with four nematic liquid crystalline hosts to study their properties as molecular machines; the change in HTP of the chiral dopant upon photoisomerization induces rotation of the texture of the liquid crystal surfaces. Importantly, this study has revealed a linear dependence of the ratio of the difference between HTPs before and after irradiation against the absolute value of the initial HTP, not the absolute value of the change in helical twisting power between two states, on the angle of rotation of micro-objects on chiral nematic liquid crystalline films. This study has also revealed that a change in irradiation intensity does not affect the maximum angle of rotation, but it does affect the speed of rotational reorganization of the cholesteric helix.
  • 3PT102 Driving and Reversible Photo-control of Motility of a Kinesin/Microtubule System by a Novel Photochromic ATP Analogue(The 50th Annual Meeting of the Biophysical Society of Japan)
    Kamei Takashi, Fukaminato Tuyoshi, Tamaoki Nobuyuki
    Seibutsu Butsuri, 52, S157, The Biophysical Society of Japan General Incorporated Association, 2012
    English
  • Fluorescence photoswitching based on a photochromic pK(a) change in an aqueous solution
    Tuyoshi Fukaminato, Emi Tateyama, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS, 48, 88, 10874, 10876, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
    English, Scientific journal, Reversible fluorescence photoswitching of RSA-AZO dyad 1 was clearly demonstrated in an acidic aqueous solution. The fluorescence photoswitching mechanism is based on the reversible ring opening/closing reactions of the RSA unit induced by a photochromic pK(a) change along with the photoisomerization of the AZO unit.
  • A photochromic ATP analogue driving a motor protein with reversible light-controlled motility: controlling velocity and binding manner of a kinesin-microtubule system in an in vitro motility assay
    Takashi Kamei, Tuyoshi Fukaminato, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS, 48, 61, 7625, 7627, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
    English, Scientific journal, We synthesized two photochromic ATP analogues (ATP-Azos) featuring azobenzene derivatives tethered at the 2' position of the ribose ring. In the presence of the ATP-Azo tethering p-tert-butylazobenzene, we observed reversible photo-control of the motility, velocity and binding manner, of a kinesin-microtubule system in an in vitro motility assay.
  • Dynamic photo-control of kinesin on a photoisomerizable monolayer - hydrolysis rate of ATP and motility of microtubules depending on the terminal group
    M. K. Abdul Rahim, Takashi Kamei, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY, 10, 16, 3321, 3331, ROYAL SOC CHEMISTRY, 2012, [Peer-reviewed]
    English, Scientific journal, The reversibly and repeatedly altered gliding motility of microtubules driven by kinesin on the photoresponsive monolayer surface is studied. It was confirmed that an azobenzene monolayer surface needs to have free amino terminal groups for the successful dynamic control of the motility of microtubule. The surface of the azobenzene monolayer with terminal amino groups can dynamically control the ATP hydrolysis activity of kinesin which resulted in the change in motility of the microtubules.
  • Reversible Photogeneration of a Stable Chiral Radical-Pair from a Fast Photochromic Molecule
    Sayaka Hatano, Kana Fujita, Nobuyuki Tamaoki, Takashi Kaneko, Takuya Nakashima, Masanobu Naito, Tsuyoshi Kawai, Jiro Abe
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 2, 21, 2680, 2682, AMER CHEMICAL SOC, Nov. 2011, [Peer-reviewed]
    English, Scientific journal, The photochromic naphthalene-bridged imidazole dimer containing a naphthyl moiety that tethers two triarylimidazole units shows instantaneous coloration upon exposure to UV light and rapid fading in the dark. In this work, we demonstrate the formation of a stable chiral radical-pair that exhibits no photoracemization even by repeated photochromic cycles. The photogenerated radical-pair from the imidazole dimer exhibits the Cotton effect in the visible light region, indicating the retention of the enantiomeric conformation of the radical-pair. This result suggests that the chirality resulting from the binaphthyl moiety induces exciton coupling between the two radical chromophores by through-space interaction.
  • Temperature-Independent Hole Mobility in Field-Effect Transistors Based on Liquid-Crystalline Semiconductors
    Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki
    IEICE TRANSACTIONS ON ELECTRONICS, E94C, 11, 1720, 1726, IEICE-INST ELECTRONICS INFORMATION COMMUNICATIONS ENG, Nov. 2011, [Peer-reviewed]
    English, Scientific journal, Thin-film transistors based on Liquid-crystalline phenylterthiophenes, 3-TTPPh-5 and 3-TTPPhF4-6 are fabricated with a spin-coating method. The devices exhibit p-type operation with the mobility on the order of 10(-2) cm(2)V(-1)s(-1). The field-effect mobilities of the transistors using 3-TTPPh-5 and 3-TTPPhF4-6 are almost independent of the temperature above room temperature. In particular, the temperature range in which the mobility is constant is between 230 and 350 K for 3-TTPPh-5.
  • Dynamic Photocontrol of the Gliding Motility of a Microtubule Driven by Kinesin on a Photoisomerizable Mono layer Surface
    M. K. Abdul Rahim, Tuyoshi Fukaminato, Takashi Kamei, Nobuyuki Tamaoki
    LANGMUIR, 27, 17, 10347, 10350, AMER CHEMICAL SOC, Sep. 2011, [Peer-reviewed]
    English, Scientific journal, The gliding motility of microtubules driven by kinesin on the surface of an azobenzene monolayer presenting lysine terminal groups is reversibly and repeatedly altered upon photoisomerization of the monolayer.
  • Induction of Molecular Chirality by Circularly Polarized Light in Cyclic Azobenzene with a Photoswitchable Benzene Rotor
    P. K. Hashim, Reji Thomas, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL, 17, 26, 7304, 7312, WILEY-BLACKWELL, Jun. 2011, [Peer-reviewed]
    English, Scientific journal, New phototriggered molecular machines based on cyclic azobenzene were synthesized in which a 2,5-dimethoxy, 2,5-dimethyl, 2,5-difluorine or unsubstituted-1,4-dioxybenzene rotating unit and a photoisomerizable 3,3'-dioxyazobenzene moiety are bridged together by fixed bismethylene spacers. Depending upon substitution on the benzene moiety and on the E/Z conformation of the azobenzene unit, these molecules suffer various degrees of restriction on the free rotation of the benzene rotor. The rotation of the substituted benzene rotor within the cyclic azobenzene cavity imparts planar chirality to the molecules. Cyclic azobenzene 1, with methoxy groups at both the 2- and 5-positions of the benzene rotor, was so conformationally restricted that free rotation of the rotor was prevented in both the E and Z isomers and the respective planar chiral enantiomers were resolved. In contrast, compound 2, with 2,5-dimethylbenzene as the rotor, demonstrated the property of a light-controlled molecular brake, whereby rotation of the 2,5-dimethylbenzene moiety is completely stopped in the E isomer (brake ON, rotation OFF), while the rotation is allowed in the Z isomer (brake OFF, rotation ON). The cyclic azobenzene 3, with fluorine substitution on the benzene rotor, was in the brake OFF state regardless of E/Z photoisomerization of the azobenzene moiety. More interestingly, for the first time, we demonstrated the induction of molecular chirality in a simple monocyclic azobenzene by circular-polarized light. The key characteristics of cyclic azobenzene 2, that is, stability of the chiral structure in the E isomer, fast racemization in the Z isomer, and the circular dichroism of enantiomers of both E and Z isomers, resulted in a simple reversible enantio-differentiating photoisomerization directly between the E enantiomers. Upon exposure to r- or l-circularly polarized light at 488 nm, partial enrichment of the (S)- or (R)-enantiomers of 2 was observed.
  • Single-Molecule Fluorescence Photoswitching of a Diarylethene-Perylenebisimide Dyad: Non-destructive Fluorescence Readout
    Tuyoshi Fukaminato, Takao Doi, Nobuyuki Tamaoki, Katsuki Okuno, Yukihide Ishibashi, Hiroshi Miyasaka, Masahiro Irie
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 133, 13, 4984, 4990, AMER CHEMICAL SOC, Apr. 2011, [Peer-reviewed]
    English, Scientific journal, Single-molecule fluorescence photoswitching plays an essential role in ultrahigh-density (Tbits/inch(2)) optical memories and super-high-resolution fluorescence imaging. Although several fluorescent photochromic molecules and fluorescent proteins have been applied, so far, to optical memories and super-high-resolution imaging, their performance is unsatisfactory because of the absence of "non-destructive fluorescence readout capability". Here we report on a new molecular design principle of a molecule having non-destructive readout capability. The molecule is composed of acceptor photochromic diarylethene and donor fluorescent perylenebisimide units. The fluorescence is reversibly quenched when the diarylethene unit converts between the open- and the closed-ring isomers upon irradiation with visible and UV light. The fluorescence quenching is based on an electron transfer from the donor to the acceptor units. The fluorescence photoswitching and non-destructive readout capability were demonstrated in solution (an ensemble state) and at the single-molecule level. Femtosecond time-resolved transient and fluorescent lifetime measurements confirmed that the fluorescence quenching is attributed to the intramolecular electron transfer.
  • Synthesis, Gelation Properties and Photopolymerization of Macrocyclic Diacetylenedicarboxamides Derived from L-Glutamic Acid and trans-1,4-Cyclohexanediol
    Jun'ichi Nagasawa, Masaru Yoshida, Nobuyuki Tamaoki
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 2011, 12, 2247, 2255, WILEY-V C H VERLAG GMBH, Apr. 2011, [Peer-reviewed]
    English, Scientific journal, Novel macrocyclic diacetylene compounds derived from L-glutamic acid and trans-1,4-cyclohexanediol have been synthesized and their gelation ability, photopolymerizability and aggregation state have been studied. Most of the compounds with decyl groups gelatinize hexane, cyclohexane, cyclohexene and carbon tetrachloride. Some of the compounds also gelatinize toluene and 2-propanol. An FTIR spectroscopy study indicated hydrogen-bonding in the gel state. An X-ray crystallographic analysis of one of the macrocyclic compounds with methyl groups demonstrated a tubular assembly based on the face-to-face packing of the macrocyclic rings as a result of intermolecular hydrogen-bonding. Upon photoirradiation, most of the gels changed their hue from colourless to red or orange, which suggests photopolymerization of the diacetylene moieties.
  • Induction of Point Chirality by E/Z Photoisomerization
    P. K. Hashim, Nobuyuki Tamaoki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 50, 49, 11729, 11730, WILEY-V C H VERLAG GMBH, 2011, [Peer-reviewed]
    English, Scientific journal
  • Synthesis and efficient circularly polarized light emission of an optically active hyperbranched poly(fluorenevinylene) derivative
    Juin-Meng Yu, Takeshi Sakamoto, Kento Watanabe, Seiichi Furumi, Nobuyuki Tamaoki, Yun Chen, Tamaki Nakano
    CHEMICAL COMMUNICATIONS, 47, 13, 3799, 3801, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
    English, Scientific journal, An optically active, hyperbranched poly(fluorenevinylene) derivative was synthesized by polymerization of (-)-2,4,7-tris(bromomethyl)-9-neomenthyl-9-pentylfluorene. A spin-coated film sample of the polymer exhibited efficient circularly polarized light (CPL) emission in the visible range of 400-700 nm on photo excitation even without annealing processes leading to chain ordering.
  • Chirality transfer from chiral solvents and its memory in an azobenzene derivative exhibiting photo-switchable racemization
    Reji Thomas, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY, 9, 15, 5389, 5393, ROYAL SOC CHEMISTRY, 2011, [Peer-reviewed]
    English, Scientific journal, The transfer and dynamic fixation of chirality in cyclic azobenzenes using R-(+)-1-phenylethylalcohol (R-PEA) and S-(-)-1-phenylethylalcohol (S-PEA) as solvents or additives are investigated. The cyclic azobenzenes used in this study carry a 1,5-dioxynaphthalene moiety as rotating unit, connected to the photoisomerizing (E-Z) azobenzene unit with spacers of varying lengths. With suitable lengths of the spacers the molecules exhibit stable enantiomers originated from the element of planar chirality in the E form due to the stopped rotation of the rotor, while in the Z form the allowed rotation results in racemization. The CD spectra of racemic compounds in the E form in chiral solvents were inert or almost negligible before irradiation, while 366 nm irradiation causing E-Z photoisomerization resulted in induction of clear CD bands. The thermal or photochemical reverse Z E isomerization causes a change in the CD spectra to new ones which are reasonably matching with the spectra of the pure enantiomers recorded in non-chiral solvents. The obtained new CD spectra are maintained even in a racemic solvent system attained by the dilution with an equal amount of chiral solvent of opposite stereostructure. These results indicate that the chirality is transferred from the chiral solvents or additives to the racemizing Z form of cyclic azobenzene and it is fixed in the non-racemizing E form. The molecule without racemization in both E and Z forms did not show any significant induced CD bands irrespective of E-Z isomerizations. The molecule showing racemization in E and Z forms just shows the non-fixed induced CD. The property of photo-switchable racemization is necessary for the effective transfer and temporal fixation of the chirality in this type of chirality sensors.
  • Tuning of solubility and gelation ability of oligomeric electrolyte by anion exchange
    Nagatoshi Koumura, Hajime Matsumoto, Hajime Kawanami, Nobuyuki Tamaoki, Masaru Yoshida
    POLYMER JOURNAL, 42, 9, 759, 765, NATURE PUBLISHING GROUP, Sep. 2010, [Peer-reviewed]
    English, Scientific journal, To tune the miscibility of the gel-forming oligomeric electrolyte, we examined anion exchange reactions using appropriate ammonium or alkali-metal salts. Nine oligomeric electrolytes with different anions were obtained in high yields by the reactions. The solubility of these oligomeric electrolytes in organic solvents was carefully tested. Although the starting material with chloride as a counter anion was not soluble in any organic solvents, excellent miscibility and gelation ability of the oligomeric electrolytes with different anions were consequently observed with dipolar protophilic and aprotic solvents such as N,N-dimethylformamide, dimethylsulfoxide and N, N-dimethylacetamide. Furthermore, ionogels based on aliphatic ionic liquids were readily formed using the oligomer with bis(trifluoromethanesulfonyl) amide anion at a 40 g l(-1) concentration. It is remarkable that the ionic conductivity of the above-mentioned ionogels is almost identical to that of neat ionic liquids, despite the significant increase in the apparent viscosity. This study shows a novel and convenient approach to gelators for multiple solvents. Polymer Journal (2010) 42, 759-765; doi:10.1038/pj.2010.65; published online 4 August 2010
  • Reversible photo-regulation of the properties of liquid crystals doped with photochromic compounds
    Nobuyuki Tamaoki, Takashi Kamei
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS, 11, 2-3, 47, 61, ELSEVIER SCIENCE BV, Sep. 2010, [Peer-reviewed]
    English, Photochromic reactions in liquid crystals induce re-alignments of the host molecules, accompanied by changes in the optical properties and various other properties of the materials. Since the first report by Sackmann in 1971, various combinations of photochromic compounds and liquid crystals have been studied to elicit the reversible photo-regulated changes of various properties. In this report we review the advances of this field during the past 5 years, which include the creation of mechanical functions, the regulation of novel optical properties, cholesteric liquid crystals doped with azobenzene compounds in high concentrations, the regulation of ferroelectric liquid crystals, the induction of chirality by circularly polarized light, photoresponsive chiral dopants, and the photo-regulation of the oscillation wavelength of mirrorless lasers. (C) 2010 Elsevier B.V. All rights reserved.
  • Structure of Silver(I) Complex Prepared from Azobenzenonaphthalenophane, Photochemical Coordination Change of Silver(I) and Silver(I)-Induced Acceleration of Z-E Thermal Isomerization of Azobenzene Unit
    Yoshimi Oka, Nobuyuki Tamaoki
    INORGANIC CHEMISTRY, 49, 11, 4765, 4767, AMER CHEMICAL SOC, Jun. 2010, [Peer-reviewed]
    English, Scientific journal, A Ag(I) complex was prepared from azobenzenonaphthalenophane as a photoreactive multidentate ligand. The coordination of Ag(I) was reversibly controlled by photoisomerization of the azobenzene unit, and at the same time, Ag(I) accelerated the Z-E thermal isomerization of the azobenzene unit.
  • Flexible field-effect transistors from a liquid crystalline semiconductor by solution processes
    Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    ORGANIC ELECTRONICS, 11, 3, 363, 368, ELSEVIER SCIENCE BV, Mar. 2010, [Peer-reviewed]
    English, Scientific journal, We have fabricated the flexible field-effect transistors based on the liquid crystalline phenylterthiophene derivative via a solution process. A dielectric layer of polyvinyl alcohol (PVA) are deposited on a polyimide sheet substrate by a spin-coating method and then the thin film of 5-propyl-5 ''-(4-pentylphenyl)-2,2': 5',2 ''-terthiophene is fabricated from its chlorobenzene solution on the dielectric layer by spin-coating or solution sheared deposition method. The fabricated devices exhibit good electrical performance with a hole mobility of up to 0.05 cm(2) V-1 s(-1) as well as excellent mechanical flexibility. The performance does not degrade at the external strain reached 3%. Our results demonstrate that liquid crystalline semiconductors are promising materials for low-cost flexible electronic devices. (C) 2009 Elsevier B.V. All rights reserved.
  • Photoisomerization of Azobenzene Units Controls the Reversible Dispersion and Reorganization of Fibrous Self-Assembled Systems
    Yoko Matsuzawa, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY B, 114, 4, 1586, 1590, AMER CHEMICAL SOC, Feb. 2010, [Peer-reviewed]
    English, Scientific journal, N-(L-valyl-L-valyl-L,-valyl)azobenzene-4-carboxamide [AZO(LVal)(3)] is a low molecular weight gelator that forms a photo functional Fibrous assembled system; this assembly undergoes dispersion/reorganization upon trans-to-cis photoisomerization, which, as a result of the breaking and reforming of hydrogen bonds, induces reversible sol-gel transitions. In this paper, we describe the mechanism by which azobenzene isomerization induces the breaking and reorganization of these assembled systems. We applied Fourier transform infrared spectroscopy to investigate the effect of the irradiation time on the change in absorption intensity in the amide I region. The lifetime of the cis isomer influences the photoinduced breaking and reforming of hydrogen bonds between trivalyl units. Because the cis isomer of AZO(LVal)(3) had a long lifetime, its assemblies underwent reversible phototriggered dispersion and organization. In contrast. the lifetime of the cis isomer of 4'-dimeethylamino-N-(L-valyl-L-valyl-L-valyl)azobenzene-4-carboxmide [PMR(Lval)(3)] was too short to disrupt the hydrogen bonds in its fibrous self-assembled system.
  • Glass-Forming Cholesteric Liquid Crystal Oligomers for New Tunable Solid-State Laser
    Seiichi Furumi, Nobuyuki Tamaoki
    ADVANCED MATERIALS, 22, 8, 886, +, WILEY-V C H VERLAG GMBH, Feb. 2010, [Peer-reviewed]
    English, Scientific journal, A new potential utility of glass-forming cholesteric liquid crystal (G-CLC) oligomers for application in tunable solid-state laser is presented. The G-CLC is capable of tuning the photonic band gaps (PBGs) by way of the annealing temperature and preserving the tuned PBGs by a subsequent supercooling treatment. This G-CLC film enables the facile fabrication of a continuously gradated PGB structure and, thus, the continuous tuning of a single laser-emission peak (see figure).
  • Fluorescence photoswitching of a diarylethene-perylenebisimide dyad based on intramolecular electron transfer
    Tuyoshi Fukaminato, Masaaki Tanaka, Takao Doi, Nobuyuki Tamaoki, Tetsuro Katayama, Arabinda Mallick, Yukihide Ishibashi, Hiroshi Miyasaka, Masahiro Irie
    PHOTOCHEMICAL & PHOTOBIOLOGICAL SCIENCES, 9, 2, 181, 187, ROYAL SOC CHEMISTRY, 2010, [Peer-reviewed]
    English, Scientific journal, A fluorescent photochromic molecule, which is composed of a photochromic diarylethene (DE) and a fluorescent perylenebisimide (PBI), was synthesized and its fluorescence photoswitching was studied. The fluorescence quantum yield of the open-ring isomer is constant irrespective of solvent polarity, while that of the closed-ring isomer decreases with an increase in the dielectric constant of solvents. Femtosecond time-resolved transient and fluorescence lifetime measurements revealed that the fluorescence quenching of the closed-ring isomer is attributed to the intramolecular electron transfer from the PBI chromophore to the DE unit.
  • A Light-Controlled Molecular Brake with Complete ON-OFF Rotation
    Meethale C. Basheer, Yoshimi Oka, Manoj Mathews, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL, 16, 11, 3489, 3496, WILEY-V C H VERLAG GMBH, 2010, [Peer-reviewed]
    English, Scientific journal, A light-controlled molecular machine based on cyclic azobenzenophanes consisting of a dioxynaphthalene rotating unit and a photoisomerizable dioxyazobenzene unit bridged by methylene spacers is reported. In compounds 1 and 2, 1,5- and 2,6-dioxynaphthalene moieties, respectively, are linked to p-dioxyazobenzene by different methylene spacers (n=2 in la and 2; n=3 in 1b), whereas a 1,5-dioxynaphthalene moiety is bonded to m-dioxyazobenzene by bismethylene spacers in 3. In 1b and 2, the naphthalene ring can rotate freely in both the trans and cis states at room temperature. The rotation speed can be controlled either by photoinduced reversible trans cis (E-Z) isomerization of the azobenzene or by keeping the system at low temperature, as is evident from its NMR spectra. Furthermore, for the first time, we demonstrate a light-controlled molecular brake, wherein the rotation of the naphthalene moiety through the cyclophane is completely OFF in the trans isomer of compound 3 due to its smaller cavity size. Such restricted rotation imparts planar chirality to the molecule, and the corresponding enantiomers could be resolved by chiral HPLC. However, the rotation of the naphthalene moiety is rendered ON in the cis isomer due to its increased cavity size, and it is manifested experimentally by the racemization of the separated enantiomers by photoinduced E-Z isomerization.
  • Flexible Field-Effect Transistors Based on a Liquid-Crystalline Semiconductor Fabricated by the Solution Shared-Deposition Method
    Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki
    IDW'10: PROCEEDINGS OF THE 17TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3, 1705, 1708, INST IMAGE INFORMATION & TELEVISION ENGINEERS, 2010, [Peer-reviewed]
    English, International conference proceedings, Thin-film transistors based on Liquid-crystalline phenylterthiophene, 3-TTP-Ph-5 were fabricated with a solution-shared deposition method. The transistors on Si/SiO2 substrates exhibit the field-effect mobility of the hole reached 8x10-2 cm(2)V(-1)s(-1) with the on/off ratio of 10(7). The carrier mobility and the on/off ratio of the field-effect transistors fabricated on a polyimide films improved to be 5x10(-2) cm(2)V(-1)s(1) and 10(5), respectively. Their carrier mobilities are retained when the strain reaches 3 %.
  • Indane-1,3-dione and cholesterol containing butadione derivatives: Photoresponsive liquid crystalline glasses for imaging applications
    N. S. Saleesh Kumar, Shibu Abraham, K. Vijayaraghavan Ratheesh, Nobuyuki Tamaoki, Seiichi Furumi, Suresh Das
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 207, 1, 73, 78, ELSEVIER SCIENCE SA, Sep. 2009, [Peer-reviewed]
    English, Scientific journal, Synthesis, thermo-optical and glass forming properties of a series of photoresponsive luminescent mesogenic materials containing a butadiene moiety linked to a cholesterol group (CBIN, CBIN8 and CBIN12) as well as colour imaging devices based on them are described. These molecules exhibited relatively high fluorescence quantum efficiency in the solid and liquid crystalline states. The cholesteric phase was observed to be the major phase in these molecules and the pitch of cholesteric helix was sensitive to external stimuli such as temperature and light, making it possible to tune their iridescent colour in the visible region. The colour reflected by the cholesteric films could be stabilized by converting them to the glassy state by sudden cooling from their cholesteric phase to similar to 0 degrees C. Selective exposure of the material in its liquid crystalline phase to light resulted in trans-cis photoisomerization of the butadiene chromophore. Consequently the pitch of the irradiated portion changed depending upon the intensity of the illuminating light. The coloured images thus formed could be stored for long periods by converting the films to glasses by sudden cooling. The images stored in the glassy state were stable over long periods of time (>one year). (C) 2008 Elsevier BY. All rights reserved.
  • Drastic solvent effect on thermal back reaction of spiroperimidine photochromic compounds
    Yasuo Norikane, Riju Davis, Yoshinobu Nishimura, Tatsuo Arai, Nobuyuki Tamaoki
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY, 205, 2-3, 116, 121, ELSEVIER SCIENCE SA, Jun. 2009, [Peer-reviewed]
    English, Scientific journal, The photochromic behavior of two spiroperimidine compounds, 2,3-dihydro-2-spiro-7'-(8'-imino-7',8'-dihydronaphthalen-1'-amine)perimidine, PNI and 2,3-dihydro-2-spiro-4'-[8'-aminonaphthalen-1'(4H)-one]perimidine, PNO-p has been studied by absorption and transient absorption spectroscopies. Both PNI and PNO-p exhibit extremely large solvent effect on the thermal back reaction from the colored (open) to the initial (close) state. The lifetime of the colored state ranges from 600 mu s (methanol) to 22 days (acetonitrile) at room temperature. The relative energies of isomers have been estimated by the DFT calculations. (C) 2009 Elsevier B.V. All rights reserved.
  • 螺旋構造を持つ液晶性半導体               
    舟橋 正浩, 玉置信之
    光技術コンタクト 2009年2月号p84-89, 2009, 2, 84-89, Feb. 2009, [Peer-reviewed]
  • [2+2] Photodimerization and photopolymerization of diphenylhexatriene crystals utilizing perfluorophenyl-phenyl stacking interactions
    Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Haruhisa Akiyama, Nobuyuki Tamaoki
    JOURNAL OF FLUORINE CHEMISTRY, 130, 2, 151, 161, ELSEVIER SCIENCE SA, Feb. 2009, [Peer-reviewed]
    English, Scientific journal, Irradiation of the crystal of 1-perfluorophenyl-6-phenyl-1,3,5-hexatriene (1), the 1:1 cocrystal of 1,6diphenyl-1,3,5-hexatriene (2) and 1,6-bis(perfluorophenyl)-1,3,5-hexatriene (3) (2/3), and crystal 3 gave a mixture of dimer, trimer and higher oligomers that was soluble in common organic solvents. The highest molecular weight was 5000-8000 (the degree of polymerization = 15-20). The order of reactivity was 1 > 2/3 >> 3. The reaction of I was relatively efficient compared to typical organic crystals. The conversion reached 100% after 3 h irradiation. In each case, the regio- and stereoselectivity in the photodimerization was high, whereas in the formation of trimer and higher oligomers, the selectivity was much lower. The main dimer was spectroscopically identified to be the face-to-face dimer formed by the [2 + 2] cycloaddition at the 1,2-position of the triene double bonds. The photoproducts from 1 and 2/3 were amorphous, as evidenced by powder X-ray diffraction and polarizing optical microscopy. This is probably due to the nonplanar and bulky structures of the cyclobutane products. The photodimerization and polymerization are considered to be non-topochemical reactions. (C) 2008 Elsevier B.V. All rights reserved.
  • Thin-film transistors based on liquid-crystalline tetrafluorophenylter thiophene derivatives: thin-film structure and carrier transport
    Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    ORGANIC ELECTRONICS, 10, 1, 73, 84, ELSEVIER SCIENCE BV, Feb. 2009, [Peer-reviewed]
    English, Scientific journal, The authors fabricated thin films by solution processes using liquid-crystalline (LC) semiconductors, 5-alkyl-5 ''-(4-hexyltetrafluorophenyl)-2,2':5',2 ''-terthiophene (2-5). Films of 5-propy 1-5 ''-(4-hexyl tetrafluorophenyl)-2,2': 5',2 ''-terthiophene (2) show similar molecular packing as their non-fluorinated counterparts. However, the degree of molecular packing ordering from X-ray diffraction measurement is higher, and the films exhibit a more crystal-like structure. Moreover, fluorination has a remarkable effect on their mesomorphic behaviors. Films of 2 consist of large size LC domains (in the range of 100 pm) at room temperature. Thin-film transistors (TFTs) of 2 show p-type operation with good hole mobility up to 0.027 cm(2)/Vs as well as improved operation stability under ambient conditions and high on/off ratio. Tetrafluorophenyl substitution leads to lowering of HOMO energy by 0.15 eV for 2 and 0.35 eV for 5, resulting in operation stability. Variable-temperature current-voltage measurements indicate intrinsic carrier transport in films of 2. (C) 2008 Elsevier B.V. All rights reserved.
  • Visible-Light Photocontrol of (E)/(Z) Isomerization of the 4-(Dimethylamino)azobenzene Pseudo-Nucleotide Unit Incorporated into an Oligonucleotide and DNA Hybridization in Aqueous Media
    Takashi Kamei, Haruhisa Akiyama, Hisayuki Morii, Nobuyuki Tamaoki, Taro Q. P. Uyeda
    NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS, 28, 1, 12, 28, TAYLOR & FRANCIS INC, 2009, [Peer-reviewed]
    English, Scientific journal, We demonstrate significant photoresponsivity in aqueous media to visible light of pseudo-oligonucleotides possessing 4-(dimethylamino)azobenzene (4-DMAzo) side chains. The spectrum of the 4-DMAzo moiety during 436 nm light irradiation at pH 9 was clearly different from that of the all (E)-form, indicating the presence of the (Z)-form. Thermal (Z)-to-(E) recovery isomerization was faster at pH 9 (kZ-E = 101 s-1) than at pH 11; however, addition of 50% ethanol significantly slowed the thermal recovery isomerization at pH 9 (kZ-E = 2 s-1) and increased the magnitude of the spectral changes. Significant photoregulation of DNA hybridization by visible light was demonstrated under this condition.
  • Photochromism of a spiroperimidine compound in polymer matrices
    Yasuo Norikane, Riju Davis, Nobuyuki Tamaoki
    NEW JOURNAL OF CHEMISTRY, 33, 6, 1327, 1331, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
    English, Scientific journal, The photochromic behavior of a spiroperimidine compound, 2,3-dihydro-2-spiro-7'-(8'-imino-7',8'-dihydronaphthalen-1'-amine)-perimidine (PNI), doped in various polymers has been studied. Upon irradiation with 405 nm light, PNI exhibits photochromism, and a color change (light yellow to brown) is observed. The initial (closed) and colored (open) forms exhibit absorption maxima (lambda(max)) around 400 and 500 nm, respectively. The open form possesses a wide absorption band, extending to similar to 750 nm. Little effect of the polymer matrix on the lambda(max) of either the closed or open forms was observed, and these values were also similar to those in solution. The lifetime of the open form depends mainly on the glass transition temperature (T(g)) of the polymer, and ranges from, for example, 11 min to 5.4 d. This indicates that the lifetime of the open form can be readily tuned by simply choosing a suitable polymer matrix. Photochromism in different polymer substrates are demonstrated herein.
  • Reversibly tunable helicity induction and inversion in liquid crystal self-assembly by a planar chiroptic trigger molecule
    Manoj Mathews, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS, 24, 3609, 3611, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
    English, Scientific journal, Reversible control of the helical pitch length and inversion of helical handedness in an induced cholesteric liquid crystal phase were accomplished via a combination of photochemical and thermal isomerizations of a planar chiral azobenzenophane molecule.
  • Reflection colour changes in cholesteric liquid crystals after the addition and photochemical isomerization of mesogenic azobenzenes tethered to sugar alcohols
    Haruhisa Akiyama, Asuka Tanaka, Hideo Hiramatsu, Jun'ichi Nagasawa, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY, 19, 33, 5956, 5963, ROYAL SOC CHEMISTRY, 2009, [Peer-reviewed]
    English, Scientific journal, We controlled reflection colour of the glass-forming cholesteric liquid crystals over the whole visible region using the smectic liquid crystalline photochromic dopants on the basis of the different mechanism from the conventional helical twisting power change, which gave rise to full-colour recording and display materials at a lower additive concentration than that reported previously. We simply tethered multiple mesogenic azobenzene units to sugar alcohols to obtain effective dopants in which the intramolecular mesogenic moieties could adopt smectic-like alignments. The new dopants that featured linear sugar alcohol backbones exhibited increasingly stable smectic phases upon increasing the number of mesogenic groups in the molecule; a corresponding cyclic sugar alcohol derivative exhibited no such smectic phase. Addition of these smectic liquid crystalline dopants to the glass-forming cholesteric liquid crystalline material induced increasingly larger pitch shifts upon increasing the number of intramolecular mesogenic groups in the dopant. Dopants prepared from stereoisomeric sugar alcohol backbones provided similar liquid crystalline phases and induced similar pitch shifts after their addition to the cholesteric liquid crystals. The colour images recorded on the thin layer of the cholesteric liquid crystalline mixture were stabilized by fixing the cholesteric alignment into glassy states, which withstood heating at 70 degrees C.
  • Flexible field-effect transistors fabricated on polymer films using liquid crystalline semiconductors with solution process
    Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    IDW '08 - Proceedings of the 15th International Display Workshops, 2, 1495, 1498, 01 Dec. 2008
    Thin-film transistors based on Liquid crystalline oligothiophene derivatives were fabricated. The transistors with the high performance were produced by the simple solution process. When the surface of the gate dielectrics were treated with octatrichlorosilane, the field-effect mobility of the hole reached 0.04 cm 2/Vs with the on/off ratio of 10 7 Furthermore flexible thin-film transistors could be fabricated on polymer thin films. They maintained the performance when the strain reached 3%.
  • Hydrogels Based on Surfactant-Free Ionene Polymers with N,N '-(p-Phenylene)dibenzamide Linkages
    Yoshihiro Misawa, Nagatoshi Koumura, Hajime Matsumoto, Nobuyuki Tamaoki, Masaru Yoshida
    MACROMOLECULES, 41, 22, 8841, 8846, AMER CHEMICAL SOC, Nov. 2008, [Peer-reviewed]
    English, Scientific journal, Ionene Polymers with N,N'-(p-phenylene)dibenzamide linkages were synthesized in high yields by the copolymerization of 1,4-bis[4-(chloromethyl)benzamide] benzene and alpha, omega-ditertiary amines in N,N-dimethylformamide. The ionene polymers provided physical hydrogels under ca. 1-5 wt % of the concentrations after heating and cooling at room temperature without any other additives. The gelation ability was dependent on the diamine spacers and/or the molecular weights, and the ionene polymer with the longest hexylene linker connecting ammonium cations was the most effective gelation capability in water among these ionene polymers. In the theological measurement, the hydrogel showed a unique thixotropic nature that was a fast self-recovering property after the continuous oscillatory shear stress. Furthermore, the ionene polymer has an additional function as a dispersant for single-walled carbon nanotubes (SWNT) in water.
  • Photoresponsive glass-forming butadiene-based chiral liquid crystals with circularly polarized photoluminescence
    Ratheesh K. Vijayaraghavan, Shibu Abraham, Haruhisa Akiyama, Seiichi Furumi, Nobuyuki Tamaoki, Suresh Das
    ADVANCED FUNCTIONAL MATERIALS, 18, 17, 2510, 2517, WILEY-V C H VERLAG GMBH, Sep. 2008, [Peer-reviewed]
    English, Scientific journal, The synthesis and study of the photo and thermoresponsive behavior of a series of novel trimesogenes consisting of a diphenylbutadiene core linked to cholesterol moietes on either side via flexible alkyl chains are reported. These molecules possess the combined glass forming properties of bischolesterols and photochromic and luminescent properties of the butadiene moity. The pitch of the cholesteric phase of these materials could be continuosly varied thermally and photochemically, making it possible to tune the color of the film over the entire visible region. The color images thus generated could be stabilized by coverting them to N glasses. These materials were also highly photoluminescent, exhibiting circularly polarized characteriztics in the glassy liquid-crystalline state even by linearly polarized excitation.
  • Planar chiral azobenzenophanes as chiroptic switches for photon mode reversible reflection color control in induced chiral nematic liquid crystals
    Manoj Mathews, Nobuyuki Tamaoki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 130, 34, 11409, 11416, AMER CHEMICAL SOC, Aug. 2008, [Peer-reviewed]
    English, Scientific journal, In this report, for the first time, a planar chiral photoresponsive compound has been employed in commercially available nematic liquid crystals to achieve phototunable reflection colors.. We designed an azobenzenophane compound having conformational restriction on the free rotation of naphthalene moiety to impose an element of planar chirality and the corresponding enantiomers were resolved by HPLC on chiral column. We have determined the absolute configuration by comparison of density functional theory (DFT) calculations of its electronic circular dichroism (ECD) spectrum and specific rotation [alpha](D) to experimental ECD and [alpha](D) data. Enantiomers exhibit photochemically reversible isomerization in solution without undergoing thermal or photoinduced racemization. As chiroptic switches in different host nematic liquid crystals, they exhibit good solubility, moderately high helical twisting power, as well as a large change in helical twisting power due to photoisomerization. A unique feature of these chiral photochromic compounds is that no other auxiliary chiral agents is required to achieve a fast photon mode reversible full-range color control in induced cholesterics, that is, both the hypsochromic and bathochromic shift can be obtained from a single LC formulation by reversible photoisomerization of the single chiral compound.
  • Ambipolar transport in the smectic E phase of 2-propyl-5 ''-hexynylterthiophene derivative over a wide temperature range
    Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki, Jun-ichi Hanna
    CHEMPHYSCHEM, 9, 10, 1465, 1473, WILEY-BLACKWELL, Jul. 2008, [Peer-reviewed]
    English, Scientific journal, 5-Hexyl-5 ''-hexynyl-2,2':5',2 ''-terthiophene exhibits the smectic E phase below 200 degrees C and does not crystallize when it is cooled to -100 degrees C Between 200 and -100 degrees C, non-dispersive transport is observed for holes and electrons with time-of-flight spectroscopy. Over the entire temperature range, the electron mobility is approximately twice as high as that of the hole. The hole and electron transport characteristics in the smectic phase below 0 degrees C are explained by the Gaussian disorder model, which was proposed for amorphous organic semiconductors. The disorder parameters, sigma and Sigma, are almost the some for holes and electrons. However, the pre-exponential parameter mu(0) for the electron is twice as large as that for the hole, which can be attributed to the difference in the extension of the LUMO of the molecules. The energetic disorder a is primarily determined by the disorder in the orientation of the permanent dipoles of liquid crystal molecules.
  • An H-bonded main-chain liquid-crystalline polymer obtained by in situ photochemical conversion from an H-bonded LC dimer
    Hideyuki Kihara, Nobuyuki Tamaoki
    MACROMOLECULAR CHEMISTRY AND PHYSICS, 209, 14, 1424, 1431, WILEY-V C H VERLAG GMBH, Jul. 2008, [Peer-reviewed]
    English, Scientific journal, An H-bonded main-chain liquid-crystalline (LC) polymer was obtained by in situ photochemical conversion from an H-bonded LC dimer. A bifunctional compound, 1, having a cinnamoyl group at one end and a carboxylic acid group at the other, was synthesized as the H-bonded LC dimer. UV irradiation of 1 in the LC phase in the presence of a sensitizer resulted in its conversion to a photodimer, with a carboxylic acid at both ends, through photocycloaddition of the cinnamoyl moiety. The LC phase was maintained during irradiation, because that of the photodimer was more thermally stable than that of 1. FT-IR analysis revealed that the carboxylic acids of the photodimer dominantly formed hydrogen bonds in the LC phase, which suggests that the photodimers assembled into an H-bonded main-chain LC polymer.
  • Unconventional thermodynamically stable cis isomer and trans to cis thermal isomerization in reversibly photoresponsive [0.0](3,3 ')-azobenzenophane
    Yasuo Norikane, Ryuzi Katoh, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS, 16, 1898, 1900, ROYAL SOC CHEMISTRY, Apr. 2008, [Peer-reviewed]
    English, Scientific journal, Sterically hindered [ 0.0]( 3,3')-azobenzenophane exhibits thermal trans-to-cis isomerization to the thermodynamically stable cis-cis isomer, and reversible photochemical isomerization with good fatigue resistance.
  • Molecular packing and solid-state fluorescence of alkoxy-cyano substituted diphenylbutadienes: Structure of the luminescent aggregates
    Riju Davis, N. S. Saleesh Kumar, Shibu Abraham, C. H. Suresh, Nigam P. Rath, Nobuyuki Tamaoki, Suresh Das
    JOURNAL OF PHYSICAL CHEMISTRY C, 112, 6, 2137, 2146, AMER CHEMICAL SOC, Feb. 2008, [Peer-reviewed]
    English, A detailed study on the photophysical properties of a series of alkoxy substituted diphenylbutadienes in solution and in the solid state providing a molecular level understanding of the factors controlling their solid-state luminescence behavior is reported. Our studies provide clear evidence for exciton splitting in the solid state resulting in red-shifted emission for this class of materials. The role of the number of alkoxy substituents and the alkyl chain length in controlling the nature of the molecular packing and consequently their fluorescence properties has been elucidated. Whereas in the di- and tri-alkoxy substituted derivatives, the solid-state fluorescence was independent of the length of the alkyl chains, in the monoalkoxy substituted derivatives, increasing the length of the alkyl chain resulted in a visual change in fluorescence from green to blue. On the basis of the analysis of the molecular packing in the single crystals, this difference could be attributed to fluorescence arising from aggregates with an edge-to-face alignment in the molecules possessing short alkyl chains (methyl and butyl) to monomer fluorescence in the long alkyl chain containing derivatives.
  • Fluorinated diphenylpolyenes: Crystal structures and emission properties
    Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY A, 111, 51, 13441, 13451, AMER CHEMICAL SOC, Dec. 2007, [Peer-reviewed]
    English, Scientific journal, \(E,E,E)-1,6-Diaryl(Ar)-1,3,5-hexatrienes (2, Ar = 4-fluorophenyl; 3, Ar = 2,4-difluorophenyl; 4, Ar = 2,4,6-trifluorophenyl; 5, Ar = perfluorophenyl) and (E,E,E)-1-perfluorophenyl-6-phenyl-1,3,5-hexatriene (6) were prepared. The absorption and fluorescence spectra in methylcyclohexane solution showed only a small dependence on the fluorine ring substituent, and were similar to those of the unsubstituted parent compound (1, Ar = phenyl). The solid-state absorption and fluorescence spectra shifted to red relative to those in solution and strongly depended on the substituent. The emission from crystals 1-5 originated mainly from monomeric species with the maximum wavelength (lambda(f(max))) of 440-465 nm, which overlapped the emission from molecular aggregates (1-4) or excimeric species (5) in the red region. Crystal 6 exhibited red-shifted (lambda(f(max))) = 530 nm) and structureless emission due to excimers. The cocrystal of 1 and 5 (1/5) showed red-shifted (lambda(f(max))) = 558 nm) and distinctly structured emission, not from exciplexes but from the excited states of molecular aggregates in which molecules 1 and 5 strongly interact already in the ground state. These assignments were confirmed by the results of fluorescence lifetime and quantum yield measurements in the solid state. Singlecrystal X-ray structure analyses showed that the molecules were basically planar in each crystal, whereas the crystal packing was strongly substituent-dependent. Weak pi-pi interactions in the herringbone (1 and 2) and in the pi-stacked but largely offset structures (3 and 4) account for their predominantly monomeric origin of emission. The observation of excimer fluorescence from 5 was rather unexpected, since the molecules in this crystal were arranged in an offset stacking fashion due to perfluorophenyl-perfluorophenyl (C(6)F(5)center dot center dot center dot C(6)F(5)) interaction. The structures of 6 and 1/5 considerably resembled each other, in which molecules were 7-stacked with more face-to-face geometries than those in 5, as a result of strongly attractive perfluorophenyl-phenyl (C(6)F(5)center dot center dot center dot C(6)F(5)) interaction. Nevertheless, the fluorescence origin was clearly different for 6 and 1/5. This can be ascribed to the difference in the strength of orbital-orbital interaction between molecular pi-planes in the ground and excited states in crystals.
  • Study of unsymmetrical dimesogens containing 4-heptylazobenzene
    V. Ajay Mallia, Masahiro Funahashi, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, 20, 11, 878, 883, JOHN WILEY & SONS LTD, Nov. 2007, [Peer-reviewed]
    English, Scientific journal, 4-Heptylazobenzene (HAB) has been covalently attached to cholesterol (Ch) by varying the methylene spacers and to cyanobiphenyl (CB) moiety with an octyl methylene linkage. Enhancement of short-range translational correlations in the chiral nematic (N*) phase has been observed by the introduction of HAB moiety. HAB-Ch dimesogens exhibit chiral smectic C (SmC*), chiral smectic A (SmA*) and N* phases depending on the methylene spacer length. The dimesogen containing HAB-CB shows a SmA and an N phase. The HAB-Ch dimesogen with octyl methylene spacer shows co-existence of multiple periodicities in its SmA* as well as in SmC* phases. A dramatic increase of > 150 nm in the N* reflected wavelength shift (Delta lambda) with change in temperature has been observed for the HAB-Ch dimesogen containing an octyl spacer compared to the similar dimesogen that does not have a heptyl side chain. Ferroelectric switching has been studied for a representative dimesogen containing HAB-Ch having hexyl spacer in its SmC* phase, the spontaneous polarization value was determined to be 150 nC cm(-2) (at 125 degrees C) by applying a triangular wave field. A reversible photochemical switching between SmA and N phases also has been reported for the dimesogen containing HAB-CB. Copyright (c) 2007 John Wiley & Sons, Ltd.
  • Oligomeric electrolyte as a multifunctional gelator
    Masaru Yoshida, Nagatoshi Kouimura, Yoshihiro Misawa, Nobuyuki Tamaoki, Hajime Matsumoto, Hajime Kawanami, Said Kazaoui, Nobutsugui Minami
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 129, 36, 11039, +, AMER CHEMICAL SOC, Sep. 2007, [Peer-reviewed]
    English, Scientific journal, We prepared a novel oligomeric electrolyte that acts as a multifunctional gelator. The gelator has the following notable characteristics: (1) facile preparation in one pot involving condensation and subsequent intermolecular quaternization reaction; (2) tunable solubility to apply to various solvents (e.g., organic, aqueous) and ionic liquids by a simple anion-exchange reaction; (3) resistant to acids; (4) fast recovery of the mechanical strength after stress; (5) synergistic use as dispersant for single-wailed carbon nanotubes (SWNT).
  • High-performance thin film transistors from semiconducting liquid crystalline phases by solution processes
    Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    APPLIED PHYSICS LETTERS, 91, 6, AMER INST PHYSICS, Aug. 2007, [Peer-reviewed]
    English, Scientific journal, The authors have prepared liquid crystalline (LC) semiconducting thin films with smectic phases at room temperature from 5-propyl-5(')-(4-pentylphenyl)-2,2('):5('),2(')-terthiophene (3-TTPPh-5) by spin-coating process. The films consist of large-size (approximately several tens of micrometers) LC domains with a lamellar structure. The ordering of molecular packing within the smectic layer is enhanced after annealing. The performance of thin film transistors (TFTs) based on 3-TTPPh-5 is influenced largely by silane agent modification of the dielectric. The octyltrichlorosilane (OTS) treatment enhances performance and leads to a high hole mobility of more than 4 x 10(-2) cm(2)/V s in ambient air. It is attributed to the formation of highly ordered domains with the size comparable to channel length of the TFT as well as the favorable interaction between OTS and LC molecules. (c) 2007 American Institute of Physics.
  • Synthesis and photoinduced phase transitions of poly(N-isopropylacrylamide) derivative functionalized with terminal azobenzene units
    Haruhisa Akiyama, Nobuyuki Tamaoki
    MACROMOLECULES, 40, 14, 5129, 5132, AMER CHEMICAL SOC, Jul. 2007, [Peer-reviewed]
    English, Scientific journal, We have used an azobenzene derivative substituted with a 2-chloropropionyl group as an initiator for the atom transfer radical polymerization of N-isopropylacrylamide. The resulting polymers, which possessed azobenzene moieties at one of their termini, had molecular weights of 1.7-12.0 kDa. Aqueous solutions of these polymers displayed low critical solution temperatures that alternated reversibly in response to E-to-Z photoisomerization cycles of the terminal azobenzene moieties. The difference between the transition temperatures after exposure to UV and visible irradiation increased linearly up to a value of over 10 degrees C upon decreasing the molecular weight of the polymer.
  • Characterization of poly(N-isopropylacrylamide)-grafted interfaces with sum-frequency generation spectroscopy
    Miyamae Takayuki, Akiyama Haruhisa, Yoshida Masaru, Tamaoki Nobuyuki
    Macromolecules, 40, 13, 4601, 4606, 26 Jun. 2007, [Peer-reviewed]
  • Visible-light photoresponsivity of a 4-(dimethylamino)azobenzene unit incorporated into single-stranded DNA: Demonstration of a large spectral change accompanying isomerization in DMSO and detection of rapid (Z)-to-(E) isomerization in aqueous solution (April, pg 1846, 2007)
    Takashi Kamei, Masabumi Kudo, Haruhisa Akiyama, Momoyo Wada, Jun'ichi Nagasawa, Masahiro Funahashi, Nobuyuki Tamaoki, Taro Q. P. Uyeda
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 18, 3053, 3053, WILEY-V C H VERLAG GMBH, Jun. 2007, [Peer-reviewed]
    English
  • Assembly and photoinduced organization of mono- and oligopeptide molecules containing an azobenzene moiety
    Yoko Matsuzawa, Katsuyuki Ueki, Masaru Yoshida, Nobuyuki Tamaoki, Tohru Nakamura, Hideki Sakai, Masahiko Abe
    ADVANCED FUNCTIONAL MATERIALS, 17, 9, 1507, 1514, WILEY-V C H VERLAG GMBH, Jun. 2007, [Peer-reviewed]
    English, Scientific journal, Assembled systems consisting of an azobenzene moiety as the photofunctional component and valyl units as the network backbone are investigated. The molecular ordering of these assemblies is examined by spectroscopy and theoretical calculations. The number of valyl units greatly influences the molecular order in the organized systems. Only N-(L-valyl-L-valyl-L-valyl)azobenzene-4-carboxamide (3) forms a complete beta-sheet structure in this artificial assembly. Upon photoirradiation, the azobenzene moieties isomerize completely, revealing the reversibility in the structural organization through the flexibility of the beta-sheet network in this system.
  • Visible-light photoresponsivity of a 4-(dimethylamino)azobenzene unit incorporated into single-stranded DNA: Demonstration of a large spectral change accompanying isomerization in DMSO and detection of rapid (Z)-to-(E) isomerization in aqueous solution
    Takashi Kamei, Masabumi Kudo, Haruhisa Akiyama, Momoyo Wada, Jun'ichi Nagasawa, Masahiro Funahashi, Nobuyuki Tamaoki, Taro Q. P. Uyeda
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 11, 1846, 1853, WILEY-V C H VERLAG GMBH, Apr. 2007, [Peer-reviewed]
    English, Scientific journal, We demonstrate significant visible-light photoresponsivity in a synthesized oligonucleotide containing a built-in pseudonucleotide possessing a 4-(dimethylamino)azobenzene (4-DMAzo) side chain. In dry DMSC) as solvent, two clearly distinguishable spectra corresponding to the (E) and (Z) forms of the 4-DMAzo moiety tethered to the oligonucleotide were recorded with a conventional spectrophotometer before and after irradiation with 420 nm wavelength light, which induced (E)-to-(Z) isomerization. In addition, (Z)-to-(E) isomerization was accelerated by irradiation with either visible (lambda = 550 nm) or UV (lambda = 350 nm) light, demonstrating reversible photoresponsivity of the pseudo-oligonucleotide. In aqueous solutions the (Z)-to-(E) thermal isomerization of the photoresponsive pseudo-oligonucleotide was very rapid and was only detectable by laser flash photolysis. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007).
  • Four (E,Z,E)-1-(4-alkoxyphenyl)-6-(4-nitrophenyl)hexa-1,3,5-trienes
    Yoriko Sonoda, Seiji Tsuzuki, Nobuyuki Tamaoki, Midori Goto
    ACTA CRYSTALLOGRAPHICA SECTION C-CRYSTAL STRUCTURE COMMUNICATIONS, 63, O196, O200, BLACKWELL PUBLISHING, Mar. 2007, [Peer-reviewed]
    English, Scientific journal, The crystal structures of the four E, Z, E isomers of 1-(4-alkoxyphenyl)-6-(4-nitrophenyl)hexa-1,3,5-triene, namely (E,Z,E)-1-(4-methoxyphenyl)-6-(4-nitrophenyl) hexa-1,3,5-triene, C19H17NO3, (E,Z,E)-1-(4-ethoxyphenyl)-6-(4-nitrophenyl)hexa-1,3,5-triene, C20H19NO3, (E,Z,E)-1-(4-nitrophenyl)6-(4-n-propoxyphenyl)hexa-1,3,5-triene, C21H21NO3, and (E,Z,E)-1-(4-n-butoxyphenyl)-6-(4-nitrophenyl)hexa-1,3,5-triene, C22H23NO3, have been determined. Intermolecular N center dot center dot center dot O dipole interactions between the nitro groups are observed for the methoxy derivative, while for the ethoxy derivative, two adjacent molecules are linked at both ends through N center dot center dot center dot O dipole-dipole interactions between the N atom of the nitro group and the O atom of the ethoxy group to form a supramolecular ring-like structure. In the crystal structures of the n-propoxy and n-butoxy derivatives, the shortest intermolecular distances are those between the two O atoms of the alkoxy groups. Thus, the nearest two molecules form an S-shaped supramolecular dimer in these crystal structures.
  • High ambipolar mobility in a highly ordered smectic phase of a dialkylphenylterthiophene derivative that can be applied to solution-processed organic field-effect transistors
    Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki
    ADVANCED MATERIALS, 19, 3, 353, +, WILEY-V C H VERLAG GMBH, Feb. 2007, [Peer-reviewed]
    English, Scientific journal, A phenylterthiophene derivative that exhibits a highly ordered smectic phase around room temperature is synthesized. In the bulk of the smectic phase, ambipolar carrier transport is observed and electron mobility exceeds 0.2 cm(2) V-1 S-1. Thin-film transistors (see the AFM image in the figure) are fabricated by a spin-coating method and exhibit p-type operation, a field-effect mobility of 0.02 cm(2) v(-1) s(-1), and an on/off ratio of 10(6).
  • Effect of pretransitional organization in chiral nematic of oligothiophene derivatives on their carrier transport characteristics
    Masahiro Funahashi, Nobuyuki Tamaoki
    CHEMISTRY OF MATERIALS, 19, 3, 608, 617, AMER CHEMICAL SOC, Feb. 2007, [Peer-reviewed]
    English, Scientific journal, We have synthesized three phenylquaterthiophene derivatives (liquid-crystalline semiconductors that exhibit a chiral nematic phase) and investigated their carrier transport characteristics in the chiral nematic phases with the time-of-flight technique. In contrast to the ionic nature of negative carrier transport, positive carrier transport in the chiral nematic phases of these compounds should be attributed to electronic charge carrier transport. The temperature dependence of the positive carriers in the chiral nematic phases of these compounds were strongly affected by a pretransitional smectic order formation.
  • Modulation of unconventional fluorescence of novel photochromic perimidine spirodimers
    Rijn Davis, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL, 13, 2, 626, 631, WILEY-V C H VERLAG GMBH, 2007, [Peer-reviewed]
    English, Scientific journal, Fluorescence modulation by a class of photochromic perimidine spirodimers, which exhibit a characteristic fluorescence associated with their photochromic reactions, has been described. Upon irradiation using 365 nm light, these non-fluorescent spiro molecules undergo a thermally-reversible ring opening at their spiro junction resulting in the generation of strong fluorescence. The fluorescing species is distinctly different from both the stable ring-closed and the ring-opened compounds, though it appears to have been formed from and remains in equilibrium with the photochemically generated ring-opened form. While the fluorescing species possesses a narrow absorption band with its maximum centered at 500 nm, the ring-opened form exhibits a broad absorption across the visible region with two maxima centered at 410 and 650 nm, respectively. After initiating the photochromic reactions in these molecules using 365 nm light, purely photochemically-controlled fluorescence modulation can be carried out using two wavelengths in the visible region, that is, 500 and 700 nm, while the equilibrium concentration of the ring-opened form and the fluorescing species is controlled. Fluorescence modulation is attained also by controlling the ratio of the ring-closed and ring-opened forms by photochemical ring-opening and thermal ring-closing reactions. The study on the effect of substitution of these molecules suggests that by extending the conjugation of the perimidine core in the ring-opened form the molecule is rendered nonfluorescent and hence it can be assumed that the perimidine core forms the fluorescing entity of the molecule.
  • In situ photochemical conversion from cinnamoyl-functionalized liquid-crystalline monomers to liquid-crystalline dimers
    Hideyuki Kihara, Nobuyuki Tamaoki
    LIQUID CRYSTALS, 34, 11, 1337, 1347, TAYLOR & FRANCIS LTD, 2007, [Peer-reviewed]
    English, Scientific journal, Liquid-crystalline ( LC) monomers, which were functionalized with a cinnamoyl group on their extremity, were synthesized and irradiated with UV light in their LC phases. In the presence of a triplet sensitizer, most LC monomers were converted into the corresponding dimers, which were produced by the cycloaddition reaction of the cinnamoyl group. The photodimerization reaction could proceed while the LC phases were maintained, because the dimers showed LC phases whose temperature ranges were wider than those of the corresponding monomers. A H-1 NMR study of the LC dimers indicated that the cyclobutane unit dominantly had an anti-head-to-head configuration, that is, delta-truxinate. As the LC monomers, which had a phenyl biphenyl-4-carboxylate moiety as a mesogen, showed smectic A phases and the corresponding dimers also exhibited smectic A phases, we estimated the smectic layer distances by X-ray diffraction analysis and found that the dimers adopted the structure in which the two mesogens aligned laterally and existed in the same smectic layer in the LC phases.
  • Field-effect transistors based on liquid crystalline oligothiophene semiconductors with solution process
    M. Funahashi, F. Zhang, N. Tamaoki
    IDW '07: PROCEEDINGS OF THE 14TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3, 459, +, INST IMAGE INFORMATION & TELEVISION ENGINEERS, 2007, [Peer-reviewed]
    English, International conference proceedings, 2-Alkyl-5 ''-(p-alkylphenyl)terthiophene derivatives were synthesized and around room temperature, they exhibited highly ordered smectic phases in which fast electronic carrier transport is possible. This compound was applied to thin film transistors fabricated with solution process. Thin films have molecular packing structure and their surface morphology is remarkably developed by thermal annealing at low temperature and in short time. The carrier mobility of the FET was 0.042 cm(2)/Vs with the on/off ratio exceeding 10(6).
  • Photochemical synthesis of a main-chain LC oligomer from an alpha,omega-dicinnamoyl-functionalized LC monomer: Photoirradiation in the crystalline state
    Hideyuki Kihara, Nobuyuki Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 470, 31, 37, TAYLOR & FRANCIS LTD, 2007, [Peer-reviewed]
    English, Scientific journal, An LC compound 1,4-bis[4-(6-cinnamoyloxyhexyloxy)benzoyloxy]benzene, 1, was Synthesized, having cinnamoyl groups at the each end of the molecule, and was found to show polymorphism in the crystalline state. A rapid cooling from the isotropic melt of 1 to room temperature gave a K1 crystal, while annealing the mesophase of 1 at 95 degrees C afforded a K2 crystal. LW irradiation (>300nm) of both the K1 and K2 crystals at room temperature resulted in the formation of linear LC oligomers with cyclobutane rings in the main chain. H-1 NMR spectroscopy revealed that the cyclobutane units of the oligomer obtained from K1 assumed anti and syn head-to-head configurations, whereas those from K2 predominantly formed an anti head-to-tail structure.
  • Organic semiconductors with helical structure based on oligothiophene derivatives exhibiting chiral nematic phase
    Masahiro Funahashi, Nobuyuki Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 475, 123, +, TAYLOR & FRANCIS LTD, 2007, [Peer-reviewed]
    English, Scientific journal, We have synthesized 2-[5-(4-[ (S)-2-methylbutoxy]phenyl)-3-methyl]-2'''-propyl-2: 5'-2'-5 ''-2 ''-5"'-quaterthiophene (10), a liquid crystalline semiconductor that exhibits a chiral nematic phase, and used the time-of-flight technique to determine its carrier mobility behavior. In the chiral nematic phase, the positive carrier mobility was 2 x 10(-4)cm(2)/Vs at 120 degrees C and the negative carrier mobility was 1 x 10-4 cm(2)/Vs, both of which we attribute to electronic processes. For the negative carrier, in addition to the fast electronic process, we also observed a slow carrier transport, having mobility on the order of 10(-5)cm(2)/Vs, which we attribute to ionic conduction. Chiral dimers containing binaphthyl group exhibited stable glassy cholesteric phase and cholesteric thin films with selective reflection band in visible light area could be fabricated. They emitted circularly polarized light with dichroic parameter of 1.3 when UV light was illuminated.
  • Fluorescence spectroscopic properties and crystal structure of a series of donor - Acceptor diphenylpolyenes
    Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY A, 110, 50, 13379, 13387, AMER CHEMICAL SOC, Dec. 2006, [Peer-reviewed]
    English, Scientific journal, A series of p-nitro-p'-alkoxy(OR)-substituted (E,E,E)-1,6-diphenyl-1,3,5-hexatrienes (1a,R)Me;1b,R= Et;1c, R = n-Pr; 1d, R = n- Bu) were prepared. The absorption and fluorescence spectra in solution were almost independent of the alkoxy chain length. The absorption maximum showed only a small dependence on the solvent polarity, whereas the fluorescence maximum red-shifted largely as the polarity increased. The solid-state absorption and fluorescence spectra were red-shifted relative to those in low polar solvents and were clearly dependent on the alkoxy chain length. The fluorescence maxima for the crystals of 1b and 1d were observed at 635-650 nm, which were red-shifted by 40-50 nm relative to those for 1a and 1c. The Stokes shifts were all relatively small (3000-3500 cm(-1)). For all four compounds, the fluorescence decay curves in the solid state were able to be analyzed by single-exponential fitting to give the lifetimes of 1.1-1.3 ns. This indicates that the emission of 1a-d is not originated from an excimer or molecular aggregates, but from only one emitting monomeric species. The fluorescence quantum yields of 1a-d were considerably high compared with the values for organic solids, which is consistent with their monomeric origin of emission. Single-crystal X-ray structure analyses of 1a, 1c, and 1d showed that the crystal packing was dependent on the alkoxy chain length. The crystals of 1a and 1c had herringbone structure, whereas that of 1d had pi-stacked structure. Strong pi-pi interaction in the crystal of 1d would be the cause of the spectral red shifts relative to those for 1a and 1c. No observation of excimer fluorescence from crystal 1d can be attributed to the limited overlap between the pi-planes of the molecules due to its "slipped-parallel" structure.
  • Palladium-catalyzed C-H homocoupling of bromothiophene derivatives and synthetic application to well-defined oligothiophenes
    Masabumi Takahashi, Kentaro Masui, Hiroki Sekiguchi, Nobuhiko Kobayashi, Atsunori Mori, Masahiro Funahashi, Nobuyuki Tamaoki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 33, 10930, 10933, AMER CHEMICAL SOC, Aug. 2006, [Peer-reviewed]
    English, Scientific journal, Synthesis of oligothiophenes of well-defined structures that possess 2-8 thiophene units is performed with a new synthetic strategy involving C-H homocoupling of bromothiophenes and cross-coupling with organostannanes. Tolerance of the carbon-bromine bond to the palladium-catalyzed C-H homocoupling results in oligothiophenes bearing C-Br bonds at the terminal thiophene rings, which allow further transformation by the catalysis of a transition-metal complex.
  • Reversible thermal and photochemical switching of liquid crystalline phases and luminescence in diphenylbutadiene-based mesogenic dimers
    Shibu Abraham, V. Ajay Mallia, K. Vijayaraghavan Ratheesh, Nobuyuki Tamaoki, Suresh Das
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 23, 7692, 7698, AMER CHEMICAL SOC, Jun. 2006, [Peer-reviewed]
    English, Scientific journal, The synthesis and study of the photo- and thermoresponsive behavior of a series of novel asymmetric mesogenic dimers, consisting of a cholesterol moiety linked to a diphenylbutadiene chromophore via flexible alkyl chains are reported. These mesogenic dimers possess the combined glass forming properties of the cholesterol moiety and the photochromic and luminescent properties of the butadiene moiety. Photoinduced cis/trans isomerization of the butadiene chromophore in these materials could be utilized to bring about an isothermal phase transition from the smectic to the cholesteric state. By photochemically controlling the cis/trans isomer ratio, the pitch of the cholesteric could be continuously varied making it possible to tune the color of the film over the entire visible region, and the color images thus generated could be stabilized by converting them to N* glasses. These materials were also polymorphic, exhibiting two crystalline forms possessing distinctly different fluorescence properties. The ability to thermally switch these materials from one crystalline form to the other in a reversible manner also makes them useful for recording fluorescent images.
  • Electronic conduction in the chiral nematic phase of an oligothiophene derivative
    M Funahashi, N Tamaoki
    CHEMPHYSCHEM, 7, 6, 1193, 1197, WILEY-V C H VERLAG GMBH, Jun. 2006, [Peer-reviewed]
    English, Scientific journal
  • A main-chain liquid-crystalline oligomer prepared by in situ photopolymerization of an LC monomer having cinnamate moieties
    H Kihara, N Tamaoki
    MACROMOLECULAR RAPID COMMUNICATIONS, 27, 11, 829, 834, WILEY-V C H VERLAG GMBH, Jun. 2006, [Peer-reviewed]
    English, Scientific journal, A liquid-crystalline (LC) compound, having a cinnamate moiety on each end of the molecule, was synthesized and irradiated with UV light in its LC phase in the presence of a triplet sensitizer. Various measurements of the irradiated sample revealed that the linearly structured LC oligomer were formed by [2+2] cycloaddition of the cinnamate moieties, and that the resultant cyclobutane units dominantly assumed an anti head-to-head configuration.
  • Dynamic control of racemization rate through E-Z photoisomerization of azobenzene and subsequent partial photoresolution under circular polarized light
    Nobuyuki Tamaoki, Momoyo Wada
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 128, 19, 6284, 6285, AMER CHEMICAL SOC, May 2006, [Peer-reviewed]
    English, Scientific journal
  • Synthesis, liquid-crystalline properties, and photo-optical studies of photoresponsive oligomeric mesogens as dopants in a chiral glassy liquid crystal
    H Akiyama, VA Mallia, N Tamaoki
    ADVANCED FUNCTIONAL MATERIALS, 16, 4, 477, 484, WILEY-V C H VERLAG GMBH, Mar. 2006, [Peer-reviewed]
    English, Scientific journal, We have prepared photoresponsive oligomers that have Molecular weights of ca. 4500, 8000, and 1.6 000 g mol(-1) via the free-radical polymerization of 4-[4-alkylplienylazo]phenoxyalkyl acrylates. All of the oligomers possess bilayer smectic A (SmA) and smectic B (SmB) phases. Increasing, the concentration of these oligomeric dopants in a glass-forming cholesteric liquid crystal causes a dramatic red-shift in the reflection wavelength. The pitch shifts are very dependent on the alkyl chain lengths and molecular weights of the dopants. The oligomer that contains octyl chains and an octyl spacer, and that has a molecular weight of 4500 g mol(-1) exhibits the largest shift in the reflection wavelength. UV exposure has been used to control the cholesteric reflection pitch of the oligomer-cholesteric glassy liquid-crystal mixture over the entire visible region of the electromagnetic spectrum and vitrifies the samples by rapid cooling from their cholesteric temperatures to 0 degrees C. Extremely stable, even at 70 degrees C, erasable, full-color images have been created using this host-guest mixture.
  • Photochemical and thermal cis/trans isomerization of cyclic and noncyclic azobenzene dimers: Effect of a cyclic structure on isomerization
    Y Norikane, N Tamaoki
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, 5, 1296, 1302, WILEY-BLACKWELL, Feb. 2006, [Peer-reviewed]
    English, Scientific journal, The effect of ring strain on the photochemical and thermal isomerization of azobenzene dimers was investigated by comparison of macrocyclic (1) and noncyclic (2) azobenzene dimers. The macrocycle 1 comprises two azobenzene moieties connected at their meta positions through two methylene linkers, whereas the noncyclic dimer 2 has only one methylene linker bridging two azobenzenes at the meta positions. Upon irradiation of 1 or 2 with UV light, each (E/E) (transl/ trans) isomer exhibited a stepwise photoisomerization to give the corresponding (E/Z) (trans/cis) isomer, followed by isomerization to yield the (Z/Z) (cis/cis) isomer. Quantum yields for the isomerization indicated that the photochemical isomerizations of 1 were altered by its cyclic structure. The effect on the photochemical isomerization process can be explained in terms of the ring strain, causing shifts in the absorption spectra of the azobenzene chromophore and perturbations in molecular motion in the excited state. Thermal (Z) -> (E) isomerization was observed in each I and 2, taking place in stepwise manner as (Z/Z) -> (E/Z) -> (E/E). The cyclic structure gave higher activation barriers (E(a) and Delta H(double dagger)) and activation entropies (Delta S(double dagger)). HF/6-31G** calculations were carried out for 1 and 2 in their ground electronic states in order to estimate the ring strain of each isomer of 1. ((c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006).
  • Photochemical conversion from H-bonded LC dimer to H-bonded main-chain LC polymer               
    Hideyuki Kihara, Nobuyuki Tamaoki
    Polymer Preprints, Japan, 55, 2, 2878, 2006
    Japanese, International conference proceedings, We synthesized a novel compound, which had a biphenylcarboxylic acid and a cinnamoyl group on the each end. The compound showed stable LC phases due to the dimerization via hydrogen bonds of the carboxylic acid group. UV irradiation of the compound in the presence of a triplet sensitizer during the LC phase caused photocycloaddition reaction of the cinnamoyl group, which resulted in the formation of the linear H-bonding chain. It was found that the obtained H-bonded main-chain polymer exhibited an LC phase, which was more thermally stable than that of unirradiated sample.
  • Synthesis and photoinduced phase transition of poly(N-isopropylacrylamide) functionalized with an azobenzene at the terminal or central position               
    Haruhisa Akiyama, Nobuyuki Tamaoki
    Polymer Preprints, Japan, 55, 2, 3889, 3890, 2006
    Japanese, International conference proceedings, An azobenzene derivative with one or two 2-chloropropionyl moieties was applied to an initiator for atom transfer radical polymerization (ATRP) of N-isopropylacrylamide. The resulting polymer has an azobenzene moiety at the end or center of the polymer chain with several thousands of molecular weight. The water solution of the polymers showed lower critical solution temperature which was affected by the molecular weight of the polymers. The phase transition temperature was reversibly alternated with trans-cis photoisomerization cycle of an azobenzene moiety.
  • Surface characterization of poly(NIPAAm) by using sum-frequency generation spectroscopy               
    Takayuki Miyamae, Haruhisa Akiyama, Masaru Yoshida, Nobuyuki Tamaoki
    Polymer Preprints, Japan, 55, 1, 1223, 2006
    Japanese, International conference proceedings, Surface-immobilized poly(N-isopropyl acrylamide) (poly(NIPAAm)) surfaces and water/poly(NIPAAm) interfaces have been investigated by using sum-frequency generation (SFG) spectroscopy. The change of the surface wettability vs. temperature is attributed to different conformations taken by the side chain of the polymer.
  • Carrier transport properties in liquid crystalline oligothiopehene semiconductors and their device applications
    M. Funahashi, F. Zhang, N. Tamaoki
    IDW '06: PROCEEDINGS OF THE 13TH INTERNATIONAL DISPLAY WORKSHOPS, VOLS 1-3, 19, 22, INST IMAGE INFORMATION & TELEVISION ENGINEERS, 2006, [Peer-reviewed]
    English, International conference proceedings, asymmetrically substituted oligothiophene derivatives were synthesized and around room temperature, they exhibited highly ordered smectic phases in which fast electronic carrier transport. In particular high electron mobility exceeding over 0.2 cm(2)/Vs was observed in propyl(4-pentylphenyl)terthiophene. This compound was applied to thin film transistors fabricated with solution process. In addition to smectic phases, electronic charge carrier transport was also observed in the cholesteric phase of phenylquarterthiophene derivatives with extended p-conjugated system which emitted circularly polarized light by UV light excitation.
  • Study of chiral dimesogens: Liquid crystalline properties, effect of smectic cybotactic domains in controlling the chiral reflections and glassy liquid crystal forming properties
    VA Mallia, N Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 454, 81, 90, TAYLOR & FRANCIS LTD, 2006, [Peer-reviewed]
    English, Scientific journal, Liquid crystalline properties, temperature dependent reflection studies and glassy liquid crystal forming properties of azobenzene/alkylazobenzene containing cholesterol dimesogens with varying methylene spacers have been described. All these compounds exhibit chiral nematic phases, and both chiral nematic and smecticA phases have been observed for the dimesogens containing 4-alkylazobenzene moieties. X-ray diffraction studies in the smecticA phases of these dimesogens show that both monolayer and intercalated arrangements co-exist in the meso phase. Selective reflection observed in the chiral nematics was found to be red shifted upon lowering the temperature due to fluctuations in smectic order. By rapid cooling of the 4-alkylazobenzene compounds from the cholesteric phase transition temperature to 0 degrees C, solid films maintaining a helical molecular order were obtained.
  • Thermal and photo optical properties of azoxybenzene/alkyloxy-ambenzene-cholesterol dimesogens with alkyl diacetylene linker
    S Kumaresan, VA Mallia, Y Kida, N Tamaoki
    JOURNAL OF MATERIALS RESEARCH, 20, 12, 3431, 3438, MATERIALS RESEARCH SOCIETY, Dec. 2005, [Peer-reviewed]
    English, Scientific journal, Thermal and photo-optical properties of azoxybenzene/alkyloxy-azobenzene containing chiral dimesogens are presented. Alkyloxyazobenzene containing dimesogenic materials exhibited two kinds of smectic A phases. Photoirradiation at temperatures exhibiting, smectic phases of pure materials in azobenzene linked dimesogens resulted in formation of the isotropic phase, and this was systematically studied at different liquid crystalline temperatures. The efficacy of these compounds as a dopant in the glassy liquid crystalline material was also explored. Increasing concentration to 4 wt%/5 wt% in azobenzene/azoxy-benzene derivatives caused a dramatic red-shift in the wavelength of reflected light by the host cholesteric glassy liquid crystal. Photo-isomerization of these dopants led to a blue-shift of the reflected light, and this effect could be used to tune the light reflectivity of these mixtures over the visible region.
  • Photoinduced hinge-like molecular motion: Studies on xanthene-based cyclic azobenzene dimers
    SA Nagamani, Y Norikane, N Tamaoki
    JOURNAL OF ORGANIC CHEMISTRY, 70, 23, 9304, 9313, AMER CHEMICAL SOC, Nov. 2005, [Peer-reviewed]
    English, Scientific journal, Molecular devices incorporating azobenzene units represent active components of smart systems, as they are capable of exhibiting photoregulated cooperative molecular motion. Herein, we describe the synthesis, X-ray crystal analysis, and photochemical and thermal studies of a xanthene based cyclic azobenzene dimer and its precursor. The trans-trans isomer of the azobenzene dimer upon photoirradiation transforms to the cis-cis isomer through an intermediate trans-cis isomer. The X-ray crystal structures of the trans-trans isomer (open) and the cis-cis isomer (closed) provide unambiguous proof for the hinge-like molecular motion in this class of molecules. The inferences drawn from photochemical and thermal studies shed light on the effect of varied substitution and cyclic structures on the different transitions. The lifetime of the cis-cis isomer is estimated to be 6.43 years, whereas the trans-cis isomer is short-lived (2.73 min) at 303 K. A rational explanation for the relative stability of the different isomers is derived from the isokinetic plot and theoretical calculations.
  • Novel photochromic spiroheterocyclic molecules via oxidation of 1,8-diaminonaphthalene
    R Davis, N Tamaoki
    ORGANIC LETTERS, 7, 8, 1461, 1464, AMER CHEMICAL SOC, Apr. 2005, [Peer-reviewed]
    English, Scientific journal, [GRAPHICS]
    Novel spiroheterocyclic molecules, namely, 2,3-dihydro-2-spiro-7'-[8'-imino-7',8'-dihydronaphthalen-1'-amine]perimidine, PNI, and 2,3-dihydro2-spiro-4'-[8'-aminonaphthalen-1'(4H)-one]perimidine, PNO-p, were obtained by oxidation of 1,8-diaminonaphthalene using manganese dioxide. These molecules exhibit thermally reversible photochromism with good photofatigue resistance, and their photogenerated forms possess broad absorption in the visible region.
  • Synthesis, isomerization and functions of cyclophanes containing azobenzene units in the main frame
    N Tamaoki
    JOURNAL OF SYNTHETIC ORGANIC CHEMISTRY JAPAN, 63, 4, 370, 376, SOC SYNTHETIC ORGANIC CHEM JPN, Apr. 2005, [Peer-reviewed]
    Japanese, The photochromic reaction of azobenzenes has been applied to many soft materials whose functions can be controlled by the action of light. In order to accomplish a selective photochromic reaction, a new strategy utilizing a macrocyclic structure in which photochromic units are inserted into the main frame of the ring is proposed. The isomerization rate of azobenzene units from a cis form to a trans form is affected by the ring strain, the extent of which depends on the length of the spacers and the positions connecting azobenzene chromophores. This effect was applied to realize the bistability and light-intensity dependence in the photochromic systems. The concept shown here can be used for the photoresponsive molecular machines or the molecular memory.
  • Facile preparation of novel "ionic gelator" and the application as the efficient dispersant for SWNTs in water               
    Masaru Yoshida, Said Kazaoui, Nagatoshi Koumura, Nobuyuki Tamaoki, Nobutsugu Minami
    Polymer Preprints, Japan, 54, 2, 4741, 4742, 2005
    Japanese, International conference proceedings, Gels, both natural and synthetic, have been a new class of soft organic materials with very attractive properties of great interest to basic and applied science. Herein, we report a novel "ionic gelator" belonging to the class of physical hydrogelator. This gelator was easily prepared by a simple one-pot condensation reaction of 4-(amino)pyridine and 4-(chloromethyl)benzoyl chloride. We observed that the hydrogel was formed from ca. 1 wt % of an aqueous solution not only in a neutral water but also in an acidic one (pH=1). In addition, the gelator was found to act as the efficient dispersant for single-walled carbon nanotubes (SWNTs) in water.
  • Two dimensionally ion-conductive liquid crystals of cholesterol/tetra(ethylene oxide) block molecules
    K Kishimoto, Y Sagara, T Kato, T Mukai, H Ohno, N Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 435, 777, 785, TAYLOR & FRANCIS LTD, 2005, [Peer-reviewed]
    English, Scientific journal, Two-dimensionally ion-conductive liquid crystals have been simply obtained by self-assembly of a cholesterol/tetra(ethylene oxide) block molecule and lithium triflate. Nanophase-segregation between cholesterol and tetra(ethylene oxide) blocks leads to the formation of a smectic A liquid crystalline phase in a wide range of temperature. A homeotropically aligned lithium salt complex in the smectic A phase shows two-dimensional ionic conductivity. The ionic conductivities parallel to the smectic layers are higher than those perpendicular to the layers. The maximum value of the anisotropy in the ionic conductivity is about 2.4 x 10(3) at 30 degrees C.
  • Photocontrolled gel-to-sol-to-gel phase transitioning of meta-substituted azobenzene bisurethanes through the breaking and reforming of hydrogen bonds
    N Koumura, M Kudo, N Tamaoki
    LANGMUIR, 20, 23, 9897, 9900, AMER CHEMICAL SOC, Nov. 2004, [Peer-reviewed]
    English, Scientific journal, An azobenzene derivative substituted at its meta positions with two urethane moieties linked to two cholesteryl ester units forms a gel that exhibits sol-gel phase transitions upon photoirradiation as a result of trans-cis isomerization of the azobenzene unit. During the sol-gel phase transitions, hydrogen bonds, which are partly responsible for stabilizing the gels, are broken or reformed. Using circular dichroism spectroscopy, we detected asymmetrical fibrous networks in the aggregates of these gelators.
  • Polymers derived from N-isopropylacrylamide and azobenzene-containing acrylamides: Photoresponsive affinity to water
    H Akiyama, N Tamaoki
    JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY, 42, 20, 5200, 5214, JOHN WILEY & SONS INC, Oct. 2004, [Peer-reviewed]
    English, Scientific journal, N-Isopropylacryamide was copolymerized by free-radical polymerization with N-[2-(4-phenylazophenoxy)ethyllacrylamide derivatives that were substituted at their 4'-position with ethoxy, methoxyethoxy, or isopropyl units, or with N-{2-[4(pyridin-2-ylazo)phenoxyl ethyl) acrylamide. The polymers were soluble in cold water and possessed lower critical solution temperatures (LCSTs). The value of the LCST rose a few degrees after UV irradiation and dropped after irradiation with visible light, reversibly, in processes that corresponded to the isomerization of the azobenzene units. The polymers became increasingly hydrophobic after increasing their azobenzene content. The difference of hydrophobicity correlates with the absorption band height at about 400 nm. The structure of the substituent on the azobenzene unit affected both the transition temperature and the hydrophobicity. A change in photoinduced wettability for water was observed to occur on a prepared film at a temperature different from the LCST determined in water. (C) 2004 Wiley Periodicals, Inc.
  • Novel odd/even effect of alkylene chain length on the photopolymerizability of organogelators
    K Aoki, M Kudo, N Tamaoki
    ORGANIC LETTERS, 6, 22, 4009, 4012, AMER CHEMICAL SOC, Oct. 2004, [Peer-reviewed]
    English, Scientific journal, Starting from diactylene diacarboxylic acids, we have synthesized a series of photopolymerizable organogelators that possess simple amide structures, different alkylene chain lengths, and either optically active or racemic 3,7-dimethyl-1-octylamine units. The alkylene chain length of these compounds exhibits a prominent odd/even effect with respect to the photopolymerization in the gel state and is accompanied by a stereostructural effect on the gelation ability.
  • Organogelation of diacetylene cholesteryl esters having two urethane linkages and their photopolymerization in the gel state
    J Nagasawa, M Kudo, S Hayashi, N Tamaoki
    LANGMUIR, 20, 19, 7907, 7916, AMER CHEMICAL SOC, Sep. 2004, [Peer-reviewed]
    English, Scientific journal, Various diacetylene cholesteryl esters having two urethane linkages were synthesized to study the relationship between their gelation properties and chemical structures. Most of these compounds form organogels in cyclohexane, and some compounds gelatinized hexane, diethyl ether, N,N-dimethylformamide, and ethanol. The cholesteryl moieties play an important role in gel formation, but IR spectroscopic measurements show that the main driving force for gelation is hydrogen bonding of the urethane groups. Upon UV irradiation, most of the gels polymerized to give polydiacetylenes, with concomitant changes from colorless to a variety of hues, such as dark blue, orange, and pink. The polymerization proceeds efficiently in cases where the gels change color to dark blue. The polymerization reached 52% chemical yield, with the quantum yield estimated to be at least 54. Solid-state NMR spectroscopy confirmed that polymerization in the gel state proceeds via 1,4-addition.
  • Butadienes as novel photochromes for color tuning of cholesteric glasses: Influence of microscopic molecular reorganization within the helical superstructure
    R Davis, VA Mallia, S Das, N Tamaoki
    ADVANCED FUNCTIONAL MATERIALS, 14, 8, 743, 748, WILEY-BLACKWELL, Aug. 2004, [Peer-reviewed]
    English, Scientific journal, 1-(Alkoxyphenyl)-4-(cyanophenyl)buta-1E,3E-dienes have been used as novel photoresponsive dopants for investigating light-induced changes in the pitch of a glass-forming cholesteric liquid crystal (CLC), dicholesteryl-10,12-docosadiynedioate. X-ray diffraction studies have helped to establish the role of microscopic changes of smectic domains within the helical superstructure, induced by the dopant molecules and their photoisomers, which result in changes in their macroscopic light-reflecting properties. Increasing concentration (1-12 wt.-%) of these dopants causes a dramatic red-shift in the wavelength of reflected light by the host CLC, extending it into the near-infrared region. The extent of red-shift depends strongly on the molecular length of the dopants and those possessing lengths between 25-28 Angstrom, namely 1-(octyloxyphenyl)-4-(cyanophenyl)buta-1E,3E-diene and 1-(decyloxyphenyl)-4-(cyanophenyl)buta-1E,3E-diene, exhibit the maximum shift (Deltalambda(max)=435 nm). Photoisomerization of these dopants leads to a blue-shift of the reflected light and this effect could be used to tune the light reflectivity of these mixtures over a large part of the visible region. The cholesteric pitch and hence the reflected light by these materials could be fixed in a glassy state by rapidly cooling them from their cholesteric temperatures to 0 degreesC. The efficacy of these materials for full-color photoimaging has also been demonstrated.
  • Light-driven molecular hinge: A new molecular machine showing a light-intensity-dependent photoresponse that utilizes the trans-cis isomerization of azobenzene
    Y Norikane, N Tamaoki
    ORGANIC LETTERS, 6, 15, 2595, 2598, AMER CHEMICAL SOC, Jul. 2004, [Peer-reviewed]
    English, Scientific journal, A new class of molecular machine exhibits a hingelike motion upon photo irradiation. The motion (close and open) can be operated by alternate irradiation with UV and visible light. The trans/trans and cis/cis isomers are thermally stable at 40degreesC, and the photochemical closure reaction (from trans/trans to cis/cis isomer) is dependent on the intensity of the light used because of the short-lived intermediate (trans/cis isomer).
  • Thermal hysteresis in the photoresponsivity of a Langmuir film of amphiphilic spiropyran
    M Matsumoto, T Nakazawa, VA Mallia, N Tamaoki, R Azumi, H Sakai, M Abe
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY, 126, 4, 1006, 1007, AMER CHEMICAL SOC, Feb. 2004, [Peer-reviewed]
    English, Scientific journal
  • Design of chiral dimesogens containing cholesteryl groups; formation of new molecular organizations and their application to molecular photonics
    VA Mallia, N Tamaoki
    CHEMICAL SOCIETY REVIEWS, 33, 2, 76, 84, ROYAL SOC CHEMISTRY, Feb. 2004, [Peer-reviewed]
    English, Photoresponsive liquid crystals and organogels are finding increasing application in information technology and photonics. In this tutorial review, the authors describe how weak intermolecular interactions facilitate molecular organization of cholesterol-containing dimesogens to form such materials. Design considerations and photoresponsive properties of both organogels and glassy liquid crystals are discussed and their applications to molecular photonics highlighted. The review will be of value to readers interested in the development of new materials which respond to the different properties of light.
  • Photoactive dimesogen having different pathways of light driven phase transitions at different temperatures
    VA Mallia, N Tamaoki
    CHEMICAL COMMUNICATIONS, 22, 2538, 2539, ROYAL SOC CHEMISTRY, 2004, [Peer-reviewed]
    English, Scientific journal, We hereby describe a novel example of light driven phase transitions in a photoresponsive dimesogen, which goes through different pathways at different temperatures. The isomer ratios required to obtain the phase transition in each case have also been determined.
  • Molecular mechanism of anomalous increase in the helical pitch of cholesteric liquid crystals induced by achiral dopants
    M Kidowaki, M Moriyama, M Wada, N Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY B, 107, 44, 12054, 12061, AMER CHEMICAL SOC, Nov. 2003, [Peer-reviewed]
    English, Scientific journal, A dopant-induced anomalous increase in the helical pitch of dicholesteryl 10,12-docosadiynedioate 1 is explained by generation of smectic clusters in the cholesteric phase where the dopants act as promoters of smectic domains. The dopants, having a mesogenic core and the proper length of alkyl chains on both their molecular sides, such as 4,4'-dialkylazobenzenes, 4,4'-dialkylazoxybenzenes and 4,4'-dialkylbiphenyls, considerably increase the pitch. However, dopants having benzene or a binaphthyl structure in the molecular center, an alkyl chain at one side of the molecules and Z-isomers of azobenzene and azoxybenzene derivatives, slightly decrease the pitch by acting as impurities that decrease the transition temperature of the host. An X-ray diffraction study of the cholesterics revealed that the pitch increases with an increase in size and amount of the smectic domains induced by the appropriate dopants.
  • Quantum chemical studies on photoinduced Cis-Trans isomerization and intramolecular hydrogen atom transfer of 2′-hydroxychalcone
    Yasuo Norikane, Naofumi Nakayama, Nobuyuki Tamaoki, Tatsuo Arai, Umpei Nagashima
    Journal of Physical Chemistry A, 107, 41, 8659, 8664, 16 Oct. 2003, [Peer-reviewed]
    Scientific journal, The reaction mechanism of the one-way isomerization of 2′-hydroxychalcone (2HC) was studied by calculating the potential energy surfaces of the twist of the C=C double bond and the intramolecular hydrogen atom transfer in the excited triplet state by the UB3LYP/6-31G** level. The calculations reveal the following. The potential energy curve of the triplet state between the keto forms (trans-2HC and cis-2HC) is similar to that of stilbene, which exhibits mutual isomerization. On the other hand, the potential energy curve between the enol forms (trans-2HC′ and cis-2HC′) is similar to that of styrylanthracene, which exhibits one-way isomerization from the cis to trans isomer. Although the hydrogen atom transfer has an energy barrier (<2 kcal mol-1), the relative energy of the transition state with zero-point correction is lower than that of trans-2HC. Electronic spins localize around the C=C double bond in the intermediate states (p-2HC and p-2HC′) of isomerization. During the hydrogen atom transfer, electronic spins shift from the phenyl group to the 2-hydroxyphenyl moiety. The electronic charge on hydrogen-bonded proton does not change significantly during the hydrogen atom transfer process.
  • Novel crystal structure, Cis-Trans isomerization, and host property of meta-substituted macrocyclic azobenzenes with the shortest linkers
    Y Norikane, K Kitamoto, N Tamaoki
    JOURNAL OF ORGANIC CHEMISTRY, 68, 22, 8291, 8304, AMER CHEMICAL SOC, Oct. 2003, [Peer-reviewed]
    English, Scientific journal, Azobenzenophanes, in which two (2), three (3), and four (4) azobenzene units are connected cyclically by methylene linkers at the meta positions, were synthesized. The effect of ring strain on the structure and the photochemical and the thermal isomerization of azobenzene were investigated. Complex formation with guest species such as alkali metal cations and solvent molecules was observed. X-ray crystal analyses revealed the crystal structure of all three isomers of 2. Compound 2(t,c) was distorted due to the ring strain and 2(c,c) was not deformed. Both 3 and 4 formed supramolecular channel structures in which an azobenzenophane molecule holds a solvent molecule in the molecular cavity. Upon exposure to light, 2, 3, and 4 exhibited stepwise trans-cis photoisomerization in solutions. The quantum yields for all isomerization steps of 2 were determined, and these values suggested that interactions between chromophores such as energy transfer and/ or steric distortion affect the isomerization process. The lifetime of 2(c,c) (19.7 days) was longer than that of 2(t,c) (6.1 days) at room temperature. The relative stability of these isomers was explained by the isokinetic (or compensation) relationship between DeltaH(double dagger) and DeltaS(double dagger) values and by the effect of the ring strain. The relative energies of three isomers of 2 were estimated by HF/6-31G** calculations, and these values indicated that 2(t,c) has the largest ring strain. Complexes (1:1 and 2:1) between macrocycles and alkali metal cations (Li+, Na+, K+, Rb+, Cs+) were observed by ESIMS. The cation selectivity was shifted upon photoirradiation especially in 4.
  • Photochemically driven smectic-cholesteric phase transition in an inherently photoactive dimesogen
    VA Mallia, N Tamaoki
    CHEMISTRY OF MATERIALS, 15, 17, 3237, 3239, AMER CHEMICAL SOC, Aug. 2003, [Peer-reviewed]
    English, Scientific journal
  • Synthesis of a mechanically linked oligo[2]rotaxane
    A Belaissaoui, S Shimada, A Ohishi, N Tamaoki
    TETRAHEDRON LETTERS, 44, 11, 2307, 2310, PERGAMON-ELSEVIER SCIENCE LTD, Mar. 2003, [Peer-reviewed]
    English, Scientific journal, A bifunctional [2]rotaxane, bearing two free functional groups each in the ring and axial parts, was synthesized, followed by its polycondensation with methylene diphenyl diisocyanate leading to a mechanically linked oligo[2]rotaxane. (C) 2003 Elsevier Science Ltd. All rights reserved.
  • Photochemical phase transition and molecular realignment of glass-forming liquid crystals containing cholesterol/azobenzene dimesogenic compounds
    N Tamaoki, Y Aoki, M Moriyama, M Kidowaki
    CHEMISTRY OF MATERIALS, 15, 3, 719, 726, AMER CHEMICAL SOC, Feb. 2003, [Peer-reviewed]
    English, Scientific journal, We synthesized dimesogenic liquid crystals with both cholesterol and azobenzene groups by esterification of 10,12-docosadiynedioic acid or docosanedioic acid with 4-alkyl-4'-hydroxyazobenzene (or 4-hydroxyazobenzene) and cholesterol and studied the thermal, optical, and glass-forming properties. Especially, we focused on the effect of the length of the alkyl chain substituted on the azobenzene unit and the photochemical isomerization of the azobenzene unit on the properties of the mesophases of the compounds or a host cholesteric liquid crystal forming stable glass when using them as a dopant. Two compounds without an alkyl chain on the azobenzene unit show a cholesteric phase, while five compounds with an alkyl chain from butyl to hexadecyl show only a smectic phase. The cholesteric reflection bands of the compounds without an alkyl chain on the azobenzene unit shifted toward shorter wavelengths upon photoisomerization of the azobenzene unit from the trans to cis form. Further photoirradiation induced an isotropic phase in the compounds. The compounds with an alkyl chain showing a smectic phase directly changed to an isotropic phase after the photochemical formation of a certain amount of the cis form. All compounds attained a glassy state by maintaining a molecular order if the compounds between the substrates were rapidly cooled from their liquid-crystalline temperature to 0 degreesC. When the compounds were doped with 2-10 wt % of a dicholesteryl ester forming a stable cholesteric glass, the cholesteric band of the mixtures shifted toward shorter wavelengths following the photoisomerization from trans to cis of the azobenzene unit on the dopant. The extent of the shift depends on the irradiation energy, temperature, and length of the alkyl chain on the azobenzene unit. The mixture went into the glassy state, keeping the shifted cholesteric reflection band after rapid cooling from the liquid-crystalline temperature to 0 degreesC. The cholesteric glassy state was stable up to 80 degreesC. Since the molecular arrangement of the liquid-crystalline compounds and the conformation of the azobenzene unit completely returned to the initial state upon reheating to its isotropic temperature, the photoresponsibility and glass-forming property of the compounds or mixtures are applicable to rewritable recording materials.
  • Unique crystal structures of donor-acceptor complexes: crossed arrangement of two charge-transfer columns
    M Kidowaki, N Tamaoki
    CHEMICAL COMMUNICATIONS, 2, 290, 291, ROYAL SOC CHEMISTRY, 2003, [Peer-reviewed]
    English, Scientific journal, Unique crystal structures containing two kinds of crossed charge-transfer (CT) columns are demonstrated by cocrystals consisting of ion pairs of acceptors of methyl viologen and anthraquinone disulfonate derivatives and a donor, hydroquinone, mediated by electrostatic and donor-acceptor (DA) interactions.
  • Novel supramolecular hydrogen-bonded cholesteric mesogens: liquid crystalline, thermoptical and glass-forming properties
    A Takahashi, VA Mallia, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY, 13, 7, 1582, 1587, ROYAL SOC CHEMISTRY, 2003, [Peer-reviewed]
    English, Scientific journal, Liquid crystalline, thermoptical and glass-forming properties of a series of novel supramolecular hydrogen bonded cholesteric mesogens have been described. These assemblies were built via intermolecular hydrogen bonding between cholesteric esters containing pyridine groups and cholesterol containing carboxylic acid moieties. All hydrogen-bonded complexes exhibit well defined cholesteric phases over a range of temperatures depending upon the number of carbon atoms present in their alkyl chains. The formation of pure LC materials on 1 : 1 complexation could be confirmed from the phase diagrams of the binary mixtures and infrared absorption spectra. By rapid cooling of the hydrogen bonded assemblies from their cholesteric temperature to 0 degreesC glassy liquid crystalline films maintaining helical molecular order were obtained. Different reflection colors of the cholesteric phase were selectively and repeatedly fixed by changing the starting temperature of rapid cooling.
  • Effects of polymerized photoresponsive additives on cholesteric pitch of medium molecular weight liquid crystals
    H Akiyama, N Tamaoki
    KOBUNSHI RONBUNSHU, 60, 10, 575, 580, SOC POLYMER SCIENCE JAPAN, 2003, [Peer-reviewed]
    Japanese, Scientific journal, Effects of polymeric additives on the cholesteric pitch of medium molecular weight liquid crystals were investigated. Copolymers of an azobenzene acrylate with long alkyl chains and a cholesteryl acrylate prepared by free radical polymerization in solution showed a low compatibility with the cholesteric liquid crystal. Photopolymerization of these monomers in the liquid crystalline phase brought about a dispersible polymer. The liquid crystal cell containing the photopolymerized materials shows shifts of the cholesteric pitch in response to irradiation.
  • Photoresponsive vitrifiable chiral dimesogens: photo-thermal modulation of microscopic disordering in helical superstructure and glass-forming properties
    VA Mallia, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY, 13, 2, 219, 224, ROYAL SOC CHEMISTRY, 2003, [Peer-reviewed]
    English, Scientific journal, Thermal, photooptical as well as glass-forming properties of a series of photoresponsive chiral dimesogenic compounds containing cholesterol-azobenzene moieties linked to varying alkyl chain lengths (6-14) are described. All compounds except the dimesogen containing 7 methylene spacers show a cholesteric phase. Selective reflections observed in the cholesteric liquid crystals were found to be blue shifted upon increasing the temperature due to variations in smectic fluctuations. X-Ray diffraction studies of these compounds in the cholesteric phase show a low intensity reflection at small angles, the half widths of which decrease on decreasing the temperature, confirming the presence of smectic cybotactic groups. These materials also exhibit a strong odd-even effect in their reflection wavelength as a function of spacer length. Compounds with even numbers of methylene units show a drastic change in their reflection wavelength (102-225 nm) on temperature change compared to those with odd numbers of methylene units (9-14 nm). UV photolysis, using light of 366 nm wavelength, in the cholesteric super-cooled state exhibits a hypsochromic shift in the reflection wavelength. This can be explained by the formation of the cis isomer destroying the smectic clusters in the helical superstructure due to its bent geometry, which in turn causes a decrease in the reflected wavelength. A maximum wavelength shift of 215 nm (703-488 nm) has been observed on photolysis at 80 degreesC (cooling cycle) for the dimesogen having 12-methylene spacers. By rapid cooling of the compounds from the cholesteric temperature to 0 degreesC glassy liquid crystalline films maintaining helical molecular order were obtained. The optical properties of these dimesogens, such as cholesteric reflections, controlled by light and temperature combined with their glass forming properties, can be utilized for the construction of information storage materials.
  • [1.1](3,3 ')-azobenzenophane: Novel crystal structure and cis-trans isomerization of distorted azobenzene
    Y Norikane, K Kitamoto, N Tamaoki
    ORGANIC LETTERS, 4, 22, 3907, 3910, AMER CHEMICAL SOC, Oct. 2002, [Peer-reviewed]
    English, Scientific journal, [GRAPHICS]
    [1.1](3,3')-Azobenzenophane, in which two azobenzenes are cyclically connected by -CH2- chains at the meta positions, has been synthesized, The crystal structures of all isomers have been revealed. This is the first report on the crystal structure of the cis isomer of macrocyclic azobenzenes. The trans,trans isomer was slightly distorted, the trans,cis isomer highly deformed, and the cis,cis isomer unstrained. The thermal stability of cis isomers in solutions are deducible from the crystal structures.
  • DFT study on triplet ground state silylenes revisited: The quest for the triplet silylene must go on
    Masaru Yoshida, Nobuyuki Tamaoki
    Organometallics, 21, 13, 2587, 2589, 24 Jun. 2002, [Peer-reviewed]
    English, Scientific journal, The density functional theory on triplet ground state silyenes was presented. Precise calculation methods without an effective core potential approximation was used. The overestimation of the stability of the triplet state of bis(silyl)silylenes was confirmed. The results showed that the quest for the triplet ground state silylene must go until the direct electron spin resonance observation of the unequivocally predicted triplet silylene was accomplished.
  • Photochemical control of reflection colors of glass-forming non-polymeric cholesterics with azobenzene chromophore.
    N Tamaoki, M Moriyama
    ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY, 223, D47, D47, AMER CHEMICAL SOC, Apr. 2002, [Peer-reviewed]
    English
  • Substituent effects on a photo-induced alternation of the lower critical solution temperatures of Poly(N-isopropylacrylamide) with azobenzene units
    H Akiyama, N Tamaoki
    POLYMER INTERFACES AND THIN FILMS, 710, 67, 72, MATERIALS RESEARCH SOCIETY, 2002, [Peer-reviewed]
    English, International conference proceedings, We synthesized copolymers of N-isopropylacrylamide (NIPAM) and azobenzene-containing acrylates or acrylamides by free radical polymerization, and investigated the water solubility of these polymers upon irradiation with ultra-violet and visible light. The solubility depended on concentration and structure of photoreactive azobenzene unit in the polymers. The soluble polymers showed the lower critical solution temperature, which was varied along with light irradiation. Photo-induced large wettability alteration was observed in the film.
  • Photochemical control of helical pitch of glass-forming dimeric cholesteric liquid crystals by isomerization of embedded di-mesogenic compounds with both cholesterol and azobenzene groups
    N Tamaoki, Y Aoki, M Moriyama, M Kidowaki
    LIQUID CRYSTALS VI, 4799, 103, 112, SPIE-INT SOC OPTICAL ENGINEERING, 2002, [Peer-reviewed]
    English, International conference proceedings, We synthesized di-mesogenic liquid crystals with both cholesterol and azobenzene groups by esterification of 10,12-docosadiynedioic acid or docosanedioic acid with 4-alkyl-4'-hydroxyazobenzene (or 4-hydroxyazobenzene) and cholesterol. Two compounds without an alkyl chain on the azobenzene unit show cholesteric and smectic phases, while five compounds with an alkyl chain from butyl to hexadecyl show only a smectic phase. When the compounds were doped in 2-10 w% to a dicholesteryl ester forming stable cholesteric glass, the mixture became photo-responsive. Upon irradiation at 366 nm, the cholesteric band of the mixtures shifted toward shorter wavelength caused by the photo-isomerization from trans to cis of the azobenzene unit on the dopant. The extent of the shift depends on irradiation energy, temperature and the length of the alkyl chain on the azobenzene unit. When a thin film of the dicholesteryl compounds containing 5 w% of the dopant having a heptyl substituent on the azobenzene unit was irradiated at 90 degreesC, the reflection band shifted from 730 nm (infrared) to 490 nm (blue). The mixture went into the glassy state keeping the shifted cholesteric reflection band after rapid cooling from the liquid crystalline temperature to 0 degreesC. The cholesteric glassy state was stable up to 80 degreesC. Since the molecular arrangement of the dicholesteryl compound and the conformation of the doped azobenzene derivatives completely returned to the initial state upon reheating to isotropic temperature, the photo-responsibility and glass-forming property of the mixture is applicable to full-color rewritable recording materials.
  • Thermal and optical properties of newly synthesized dicholesteryl esters with a phenylene oxide link in the normal and solidified cholesteric phases
    N Tamaoki, H Matsuda
    LIQUID CRYSTALS, 28, 12, 1823, 1829, TAYLOR & FRANCIS LTD, Dec. 2001, [Peer-reviewed]
    English, Scientific journal, A series of liquid crystalline compounds with a central phenylene oxide group to which two cholesteryl groups are attached via two alkanoate spacers has been synthesized and investigated. All the compounds except the one with ethanoate spacers showed a cholesteric phase as a single mesophase. The phase transition temperatures, the corresponding enthalpy changes and the wavelengths of selective reflection associated with the cholesteric phases showed a strong odd-even effect as a function of the spacer length. By rapid cooling of the compounds from the cholesteric phase to 0 degreesC, solid films maintaining a cholesteric molecular order were obtained. At room temperature, the solid film showed stable cholesteric colours controlled by changing the temperature at which the rapid cooling was begun. Heating the cholesteric solid film of the compound with hexanoate spacers gave two forms of crystals above 80 degreesC, whose ratio changed depending on the colour of the starting solid films. This result suggests the existence of two conformational isomers in the liquid crystalline state. Since it is possible repeatedly to fix stable red, green and blue colours by thermal treatment of this compound, we may apply it to a rewritable full colour recording in the thermal mode.
  • Photo-controllable and fixative optical properties of non-polymeric liquid crystals with azobenzene chromophore
    M Moriyama, N Tamaoki
    CHEMISTRY LETTERS, 11, 1142, 1143, CHEMICAL SOC JAPAN, Nov. 2001, [Peer-reviewed]
    English, Scientific journal, A new series of non-polymer photochromic liquid crystalline compounds which form glassy solids maintaining the liquid crystalline molecular alignment has been synthesized; their optical properties such as cholesteric reflections, controlled by the intramolecular photoreaction and temperature, can be utilized for the construction of information-storing materials.
  • Cholesteric liquid crystals for color information technology
    N Tamaoki
    ADVANCED MATERIALS, 13, 15, 1135, +, WILEY-V C H VERLAG GMBH, Aug. 2001, [Peer-reviewed]
    English, Fixation of the molecular ordering of cholesteric liquid crystals is essential for use of these materials in color information technology.. Methods to achieve this as well as thermal and photochemical control of the cholesteric pitch of the liquid crystals are addressed and applications in rewritable color recording are highlighted. The Figure shows a sample recorded using a laser.
  • Effects of doped dialkylazobenzenes on helical pitch of cholesteric liquid crystal with medium molecular weight: utilisation for full-colour image recording
    M Moriyama, S Song, H Matsuda, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY, 11, 4, 1003, 1010, ROYAL SOC CHEMISTRY, 2001, [Peer-reviewed]
    English, Scientific journal, The effects of small amounts of achiral photochromic dopants, 4,4'-di-n-alkylazobenzenes, with various lengths of substituted alkyl chain (CnH2n+1:n = 4, 7, 11, 12, 13, 14, 15, 16) on the helical pitch of a cholesteric liquid crystal (CLC) with ca. 1000 molecular weight were investigated in order to utilise the cholesteric reflected colour of these combinations for a rewritable colour image recording. The (E)-azobenzenes (similar to2 wt%) in the host CLC induced pitch changes dependent on temperature, the concentration of the azobenzenes and the length of substituted alkyl chain on the azobenzenes. In the low region of the cholesteric temperature (below 100 degreesC), some (E)-azobenzenes remarkably lengthened the pitch. Contrary to this, upon irradiation, E-Z photoisomerization of all the azobenzenes in the CLC phase induced consecutive pitch shortenings in response to the formation of the Z isomers. The changed pitch (reflected colour) could be fixed in cholesteric glassy solids. In the glassy solid state, the photo and thermal isomerization of the azobenzenes could not influence the cholesteric pitch any longer, therefore, the colour was stably stored. However, since the molecular arrangement of the CLC and the conformation of the doped azobenzenes completely returned to the initial state upon re-heating to isotropic temperatures, the stored colour could be easily erased. Based on these fundamental investigations, it is suggested that the mixed systems of the medium-molecular-weight CLCs and the 4,4'-dialkylazobenzenes will be effective materials for a rewritable full-colour image recording in a photon mode.
  • Photoinduced alignment of nematic liquid crystal on the polymer surface microrelief
    A Parfenov, N Tamaoki, S Ohni-Shi
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS, 359, 487, 495, GORDON BREACH PUBLISHING, TAYLOR & FRANCIS GROUP, 2001, [Peer-reviewed]
    English, Scientific journal, Polymer film surface modified in the holographic process under the laser illumination was used for nematic liquid crystal (LC) alignment. Azobenzene - containing polyurethanes were taken fur a material of the film. A relief grating inscribed by laser illumination onto the surface of these polymers induced a reorientation of LC director from initial homeotropic alignment. Possible applications of described processes include command-surface creation for liquid crystal displays, reversible and adaptable in real-time liquid crystal structures for laser beam targeting and aiming, etc.
  • Polymerization of a diacetylene dicholesteryl ester having two urethanes in organic gel states
    N Tamaoki, S Shimada, Y Okada, A Belaissaoui, G Kruk, K Yase, H Matsuda
    LANGMUIR, 16, 19, 7545, 7547, AMER CHEMICAL SOC, Sep. 2000, [Peer-reviewed]
    English, Scientific journal
  • Photoinduced alignment of nematic liquid crystal on the polymer surface microrelief
    A Parfenov, N Tamaoki, S Ohnishi
    JOURNAL OF APPLIED PHYSICS, 87, 4, 2043, 2045, AMER INST PHYSICS, Feb. 2000, [Peer-reviewed]
    English, Scientific journal, A polymer film surface modified by laser illumination was used as a command surface for nematic liquid crystal (LC). Azobenzene-containing polyurethanes were taken for the material of the film. A relief grating inscribed by laser illumination onto the surface of these polymers induced a reorientation of the LC director from the initial homeotropic alignment. Possible applications of the described processes include command-surface creation for liquid-crystal displays, reversible and adaptable liquid-crystal structures for laser-beam targeting and aiming, etc. (C) 2000 American Institute of Physics. [S0021-8979(00)07604-0].
  • Cholesteric solid films formed by spin-coating solutions of dicholesteryl esters
    N Tamaoki, M Moriyama, H Matsuda
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION, 39, 3, 509, +, WILEY-V C H VERLAG GMBH, 2000, [Peer-reviewed]
    English, Scientific journal
  • Rewritable full-color recording in a photon mode
    N Tamaoki, S Song, M Moriyama, H Matsuda
    ADVANCED MATERIALS, 12, 2, 94, 97, WILEY-V C H VERLAG GMBH, Jan. 2000, [Peer-reviewed]
    English, Scientific journal
  • Optical and liquid crystalline properties of dicholesteryl derivatives having different configurations of the hydrocarbon linkages
    G Kruk, N Tamaoki, H Matsuda, Y Kida
    LIQUID CRYSTALS, 26, 11, 1687, 1693, TAYLOR & FRANCIS LTD, Nov. 1999, [Peer-reviewed]
    English, Scientific journal, The liquid crystalline and optical properties of four dicholesteryl derivatives having various linkage configurations, but with the same number of connecting carbons (18), have been investigated, using differential scanning calorimetry, polarizing optical microscopy, Fourier transform infrared (FTIR) spectroscopy and UV-Vis spectroscopy. Quite different phase behaviours and optical properties have been found for these compounds, while all of them exhibited the behaviour specific for a cholesteric phase. By rapid cooling from the cholesteric phase to 0 degrees C, the iridescent colours of some of the dicholesteryl esters were fixed in the cholesteric glassy state. It was difficult but possible to fix various stable colours in the cholesteric glassy state of one compound with a polymethylene (CH2)(18) linking chain. It was much easier to fix less stable colours for samples with the linking groups (CH2)(6) and C=C double bonds between them. Very unstable colours could also be fixed for the compound with the (CH2)(7) chains and a diyne group. The fourth compound with a branched linking chain gave a cholesteric phase which showed colours at room temperature. FTIR spectroscopy measurements provided interesting results concerning the average change in molecular configuration between the blue cholesteric glass and the crystal for the compound with the (CH2)(7) polymethylene chains which crystallized within a few hours; also frequency changes associated with some bands were found and reported.
  • Optical and thermal properties of cholesteric solid from dicholesteryl esters of diacetylenedicarboxylic acid
    N Tamaoki, G Kruk, H Matsuda
    JOURNAL OF MATERIALS CHEMISTRY, 9, 10, 2381, 2384, ROYAL SOC CHEMISTRY, Oct. 1999, [Peer-reviewed]
    English, Scientific journal, Dicholesteryl esters of diacetylenedicarboxylic acid with different lengths of methylene linkages were synthesised. Compounds with (CH2)(n)(n=2, 4, 5, 6, 7, 8, 10) showed a cholesteric phase. Phase transition temperatures from the isotropic phase to the anisotropic phase showed an odd-even effect of the number of (CH2) units. By rapid cooling from the cholesteric phase to 0 degrees C, the compounds were solidified retaining the cholesteric colours (cholesteric solid), some of which were stable at room temperature. Changing the temperature at which rapid cooling started changed the colours of the cholesteric solid. The thermal stability of the cholesteric solid also showed an odd-even effect of the number of (CH2) units. The effect can be explained by the difference in the stable structures of the molecules and the strength of the weak intermolecular interactions via carbonyl groups between the compounds with odd and even (CH2), which was observed in the FT-IR spectra.
  • Laser recording on a solid cholesteric glass of a medium-molecular-weight compound
    N Tamaoki, T Terai, H Matsuda
    JAPANESE JOURNAL OF APPLIED PHYSICS PART 1-REGULAR PAPERS BRIEF COMMUNICATIONS & REVIEW PAPERS, 37, 11, 6113, 6114, JAPAN SOC APPLIED PHYSICS, Nov. 1998, [Peer-reviewed]
    English, Scientific journal, The possibility of laser-addressing a new full color recording material, that is, a solid film of a medium-molecular weight cholesteric compound, was investigated. A red image was clearly recorded on the blue background by laser-heating using CO2 laser followed by natural cooling. By increasing the laser power, the fixed color is changed from red to yellow and then to blue. A resolution of about 500 mu m, that should depend on the profile of the laser beam, was obtained after 1 s of recording time.
  • Synthesis and switchable condensation reaction of bifunctional [2]catenane
    S Shimada, K Ishikawa, N Tamaoki
    ACTA CHEMICA SCANDINAVICA, 52, 3, 374, 376, BLACKWELL MUNKSGAARD, Mar. 1998, [Peer-reviewed]
    English, Scientific journal
  • Diffraction-based spatial light modulation: Transverse linear electrooptic effect in polymers
    K Harada, M Itoh, IN Kompanets, H Matsuda, AV Parfenov, N Tamaoki, T Yatagai
    OPTICAL REVIEW, 5, 2, 89, 92, OPTICAL SOC JAPAN, Mar. 1998, [Peer-reviewed]
    English, Scientific journal, We propose a new type of spatial light modulator using nonlinear organic polymer film as a phase modulation element. Using polymer poly-Disperse Red-19 Toluendiiso-cyanate, a more than 150:1 contrast ratio has been realized for electrical addressing in transverse geometry.
  • Photomodification of polymer films: azobenzene-containing polyurethanes
    M Itoh, K Harada, H Matsuda, S Ohnishi, A Parfenov, N Tamaoki, T Yatagai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS, 31, 5, 463, 471, IOP PUBLISHING LTD, Mar. 1998, [Peer-reviewed]
    English, Scientific journal, New results are presented on optical recording to the films of polymers substituted with azo dyes. Holographic gratings are formed in the polyurethane films by exposure to Ar(+) laser light without any post-treatment as in previous works using polyacrylates, epoxy-based polymers and polyesters substituted with azo dyes. It is shown for the first time that the principal mechanism of optical recording could be the mass transfer of polymers during the cis-trans isomerization of azo dye units on the polymers from illuminated areas to non-illuminated areas. Besides this transport, some irreversible photochemical reactions involving atmospheric oxygen are suggested as another possible origin for the holographic recording.
  • Thermally stable iridescent colors of a new low-molecular-weight cholesteric compound in the solid state and the application to full-color recording
    N Tamaoki, AV Parfenov, A Masaki, H Matsuda
    ELECTRICAL, OPTICAL, AND MAGNETIC PROPERTIES OF ORGANIC SOLID-STATE MATERIALS IV, 488, 915, 919, MATERIALS RESEARCH SOCIETY, 1998, [Peer-reviewed]
    English, International conference proceedings, We synthesized a series of new di-cholesteryl esters of several diacids. One of the compounds containing both of a diyne unit and long alkylene units, in the form of a thin solid film, showed stable iridescent colours in the visible region after rapid cooling process from the temperature of the cholesteric liquid crystalline phase. Measurement of selective reflectance of visible light, X-ray diffraction, optical rotation dispersion of the solid films proved that the films remained the cholesteric ordering of the molecules. The cholesteric structure in the solid films were completely stable at room temperature. The colour of the solid film was totally, partially or in imagewise manner changed into selected colours by adjusting the temperature of the surface just before the rapid cooling process. The property of this compound can be applicable to memory media with high density using the spectrum of light, or to thermosensitive full-colour recording materials.
  • Rewritable full-color recording on a thin solid film of a cholesteric low-molecular-weight compound
    N Tamaoki, AV Parfenov, A Masaki, H Matsuda
    ADVANCED MATERIALS, 9, 14, 1102, 1104, WILEY-V C H VERLAG GMBH, Nov. 1997, [Peer-reviewed]
    English, Scientific journal
  • Synthesis of rotaxanes with functional groups
    N Tamaoki, S Shimada
    ACTA CHEMICA SCANDINAVICA, 51, 11, 1138, 1140, MUNKSGAARD INT PUBL LTD, Nov. 1997, [Peer-reviewed]
    English
  • Photoreversible optical nonlinearities of polymeric films containing spiropyran with long alkyl chains
    N Tamaoki, E VanKeuren, H Matsuda, K Hasegawa, T Yamaoka
    APPLIED PHYSICS LETTERS, 69, 9, 1188, 1190, AMER INST PHYSICS, Aug. 1996, [Peer-reviewed]
    English, Scientific journal, It was demonstrated that the third-order optical nonlinearity of polymer films could be reversibly controlled by the photochromic conversion and following J-aggregate formation of spiropyr;tn embedded in an inert polymer matrix. Patterns consisting of areas with high and low third-order nonlinear optical activities were prepared by imagewise exposure of the photochromic films followed by thermal treatment to form thermally stable J aggregates of photoinduced merocyanine in the exposed area. This system could be useful in developing new unconventional optical devices based on optical nonlinearities, including new types of spatial light modulators. (C) 1996 American Institute of Physics.
  • Photochemistry of benzenediazonium anthracenesulfonates: Photolysis of benzenediazonium salts by excitation of the anion
    Nobuyuki Tamaoki, Yasushi Takahashi, Tsuguo Yamaoka
    Journal of the Chemical Society, Chemical Communications, 15, 1749, 1750, 1994
    English, Scientific journal, 4-Substituted benzenediazonium 1,8-dimethoxyanthracene-3-sulfonates photodecompose under visible light, which is absorbed only by the anionic part, via intra-ion pair electron transfer from the excited anionic part to the benzene diazonium.
  • Thermo-optic effects of 4-alkoxy-3-chlorobenzoic acids in polymeric matrices
    Yasushi Takahashi, Nobuyuki Tamaoki, Yuichi Komiya, Yoshihiro Hieda, Kenichi Koseki, Tsuguo Yamaoka
    Journal of Applied Physics, 74, 6, 4158, 4162, 1993
    English, Scientific journal, Polymer films containing 4-alkoxy-3-chlorobenzoic acid heated to 140°C showed two optically different states at room temperature depending on the cooling rate. If after heating the film cooled rapidly, it froze in the transparent state. In contrast, it reverted to the light scattering state when cooled slowly. Cycles between the two optical states were reproducible, therefore these films may offer potential as a rewritable recording material. The reversibility in the optical transmittance may be caused by a reversible change in the crystal size of the acid in the polymer matrix.
  • Photo- and thermal cis-trans isomerization of [23](4,4′) azobenzenophane
    Nobuyuki Tamaoki, Kenichi Koseki, Tsuguo Yamaoka
    Journal of the Chemical Society, Perkin Transactions 2, 1107, 1110, 01 Dec. 1992
    Four isomers, EEE, EEZ, EZZ and ZZZ, exist for [2 3 ] (4,4′)azobenzenophane depending on the degree of the isomerization of three azobenzene units. These isomers are stable enough to be separated by reversed-phase liquid chromatography. The compound in methanol exists as the EEE form in the dark. Upon irradiation at 366 nm the EEE form isomerizes via the EEZ form and the EZZ form to the ZZZ form. At the photostationary state at 366 nm, 85% of the compound exists as the ZZZ form. From the photostationary state the compound thermally isomerizes gradually to the EEE form. The thermal reaction from the ZZZ form to the EEE form also proceeds in a stepwise fashion. The relative values of the quantum yields for the photoisomerization and the absolute value of the rate for the thermal isomerization have been determined for each step. Both the photo- and thermal processes in the Z → E direction show the different efficiencies (or rates) depending on the processes. These experimental results can be explained by supposing that the different degree of ring strain works for ground and (or) excited states of each isomer. In this compound, a certain isomer can be enriched by the combination of external stimuli, such as light or heat. This raises the possibility of synthesizing molecules with more than two functional states.
  • A PHOTOCHROMIC MEMORY WITH A NONDESTRUCTIVE READ-OUT PROPERTY
    N TAMAOKI, S YOSHIMURA, T YAMAOKA
    THIN SOLID FILMS, 221, 1-2, 132, 139, ELSEVIER SCIENCE SA, Dec. 1992
    English, Scientific journal, Isomerizations of [2.2](4,4')-azobenzenophane (1) in polycarbonate films were investigated spectrophotometrically, and the light-intensity dependent efficiency of the photoisomerization of macrocyclic azobenzene dimers, including 1, was analyzed theoretically. It is demonstrated that the efficiency of photoisomerization of 1 is dependent on the light intensity, even in a polymer film. A correlation between the lifetimes of the trans-cis isomers of macrocyclic azobenzene dimers and light intensities, where the efficiency of photoisomerization becomes dependent on light intensity, is also described. A photochromic memory composed of 1 and polycarbonate shows a non-destructive read-out property.
  • Light-intensity dependence in the photochromism of dibenzo[2.2](4,4′) -azobenzenophane
    Nobuyuki Tamaoki, Tsuguo Yamaoka
    Journal of the Chemical Society, Perkin Transactions 2, 873, 878, 01 Dec. 1991
    Reduction of 4′,4″-dinitro-o-terphenyl under conditions of high dilution, produces a mixture of macrocyclic poly(azobenzene) compounds. From the mixture, three kinds of macrocycle, namely, dimer 2 {dibenzo[2.2](4, 4′)azobenzenophane}, trimer 3 and tetramer 4 have been isolated pure. In toluene, absorption peaks due to the π → π* transition for the macrocycles undergo dramatic hypsochromic shifts as the ring size of the macrocycles decreases from the trimer 3 to the dimer 2; this is an indication that benzene rings at both ends of the dimer 2 are fixed perpendicularly to two azobenzene planes in the macrocycle. The photostationary state of the dimer 2 in toluene at λ = 366 nm contained the EZ isomer which undergoes thermal isomerization to the more stable EE isomer at the first-order rate of 0.768 s -1 . The reaction of 2 is much faster than that of the dimer 5, which was described in our last paper. Due to the fast thermal EZ to EE isomerization, the efficiency of the photoisomerization from the EE isomer to the ZZ isomer is light-intensity dependent. This dependence is observed at higher light intensities for the dimer 2 than for the dimer 5.
  • LIGHT-INTENSITY DEPENDENCE IN THE PHOTOCHROMISM OF DIBENZO[2.2](4.4')-AZOBENZENOPHANE
    N TAMAOKI, T YAMAOKA
    JOURNAL OF THE CHEMICAL SOCIETY-PERKIN TRANSACTIONS 2, 6, 873, 878, ROYAL SOC CHEMISTRY, Jun. 1991, [Peer-reviewed]
    English, Scientific journal, Reduction of 4',4"-dinitro-o-terphenyl under conditions of high dilution produces a mixture of macrocyclic poly(azobenzene) compounds. From the mixture, three kinds of macrocycle, namely, dimer 2 {dibenzo[2.2](4,4')azobenzenophane}, trimer 3 and tetramer 4 have been isolated pure. In toluene, absorption peaks due to the pi --> pi* transition for the macrocycles undergo dramatic hypsochromic shifts as the ring size of the macrocycles decreases from the trimer 3 to the dimer 2; this is an indication that benzene rings at both ends of the dimer 2 are fixed perpendicularly to two azobenzene planes in the macrocycle. The photostationary state of the dimer 2 in toluene at lambda = 366 nm contained the EZ isomer which undergoes thermal isomerization to the more stable EE isomer at the first-order rate of 0.768 s-1. The reaction of 2 is much faster than that of the dimer 5, which was described in our last paper. Due to the fast thermal EZ to EE isomerization, the efficiency of the photoisomerization from the EE isomer to the ZZ isomer is light-intensity dependent. This dependence is observed at higher light intensities for the dimer 2 than for the dimer 5.
  • THE PHOTOISOMERIZATION AND THERMAL CIS-TRANS ISOMERIZATION OF [23](4,4')AZOBENZENOPHANE
    N TAMAOKI, K KOSEKI, T YAMAOKA
    TETRAHEDRON LETTERS, 31, 23, 3309, 3312, PERGAMON-ELSEVIER SCIENCE LTD, 1990
    English, Scientific journal, The cis-trans isomerization of the title compound in methanol has been investigated kinetically by HPLC, confirming the existence of relatively stable four isomers and giving the thermodynamic parameters of the isomerization among the isomers. © 1990.
  • [2.2](4,4')AZOBENZENOPHANE - SYNTHESIS, STRUCTURE, AND CIS-TRANS ISOMERIZATION
    N TAMAOKI, K OGATA, K KOSEKI, T YAMAOKA
    TETRAHEDRON, 46, 17, 5931, 5942, PERGAMON-ELSEVIER SCIENCE LTD, 1990
    English, Scientific journal, The title compound 2 was synthesized by the reduction of 1,2-bis(4'-nitrophenyl) ethane. Spectral data and results of X-ray crystal structure analyses suggest that facing two azobenzene units in 2 are deformed from the planes both in solution and crystal. The cis-cis form of2 (cc-2), which was generated photochemically, isomerized thermally via the transcis form (tc-2), whose life time was only 22 second at 25°C, to the trans-trans form (tt-2). Due to a short life time of tc-2, the efficiency of photo-isomerization of 2 from tt-2 to cc-2 became light intensity dependent. © 1990.
  • [2.2](4,4')AZOBENZENOPHANE
    N TAMAOKI, K KOSEKI, T YAMAOKA
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH, 29, 1, 105, 106, VCH PUBLISHERS INC, Jan. 1990
    English, The long sought after [2,2]azobenzenophane 1 has been prepared quite simply by reduction of l,2‐bis(4‐nitrophenyl)ethane. According to 1 H‐NMR and UV/VIS spectra the CNNC moiety in 1 is noticeably bent. Photochemically generated cis,cis‐1 isomerizes 10000 times more slowly to the trans,trans‐form than does the cis,trans‐isomer. (Figure Presented.) Copyright © 1990 by VCH Verlagsgesellschaft mbH, Germany
  • HISTOCHEMISTRY OF BUNGAROTOXIN BINDING-SITES AT ELECTRON-MICROSCOPIC LEVEL
    N TAMAOKI, S YOSHIMURA, A AKATSUKA
    ACTA HISTOCHEMICA ET CYTOCHEMICA, 15, 4, 592, 599, JAPAN SOC HISTOCHEMISTRY & CYTOCHEMISTRY, 1982, [Peer-reviewed]
    English, Scientific journal

Other Activities and Achievements

Books and other publications

  • Molecular photoswitches : chemistry, properties, and applications
    Tamaoki, Nobuyuki, Pianowski, Zbigniew L. etc
    Wiley-VCH, 2022, 9783527351046, xx p., p. 477-1112, English
  • 光機能性有機・高分子材料の新局面(分著)               
    シーエムシー出版, 2002
  • 光を制御する次世代高分子・超分子(分著)               
    高分子学会編, 2000

Affiliated academic society

  • 液晶学会               
  • 高分子学会               
  • 日本化学会               
  • The Chemical Society of Japan               
  • The Society of Polymer Science, Japan               

Research Themes

  • 新世代分子スイッチによるATPシステムの完全制御
    科学研究費助成事業 基盤研究(B)
    01 Apr. 2022 - 31 Mar. 2025
    玉置 信之, 津田 真寿美
    日本学術振興会, 基盤研究(B), 北海道大学, 22H02153
  • Diriving motor proteins by photoisomerization reactions
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (B)
    01 Apr. 2018 - 31 Mar. 2021
    TAMAOKI NOBUYUKI
    We clarified the structure-activity relationship of photoresponsive high-energy compounds that drive motor proteins, and discovered compounds that distinguish and drive kinesin and myosin. We have synthesized a photoresponsive inhibitor to a motor protein that arranges chromosomes in the process of the cell cycle, and succeeded in photoswitching the arrangement of chromosomes in the cell. We synthesized a photoresponsive inhibitor that acts on dynein and succeeded in photocontrolling the movement of Chlamydomonas using flagella. Furthermore, we succeeded in replacing the retinal of the proton pump with an azobenzene derivative, and confirmed the photocycle and photoinduced proton transfer. We also succeeded in creating a completely artificial molecular system that converts light energy into continuous work in contrast to proteins.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (B), Hokkaido University, 18H02042
  • Development of a molecular function enabling one to take mechanical works from the piston-like molecular motion.
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    01 Apr. 2012 - 31 Mar. 2015
    TAMAOKI NOBUYUKI
    We aimed the development of a molecular function of a crank-shaft with which we can take the mechanical work out from the photochromic reaction (piston motion). We found out some photoresponsive chiral dopants for liquid crystals showing the change in a large helical twisting power upon photoirradiation. When some of them are doped, the motion of liquid crystal texture showed a hysteresis between forward and backward photoisomerization of the dopant by UV and visible irradiation, respectively. As the result we could attain a molecular crank-shaft function. We also developed some achiral compounds transformable to chiral form by the action of light. If we use a circular polarized light we obtained the chiral molecule with an enantio excess from the achiral compound. On the mechanism of the crank-shaft effect we explained the phenomenon with the contribution of a more disordered molecular alignment of the dopant upon backward photoisomerization.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research (C), Hokkaido University, 24550142
  • Reversible photoregulaton of microtubule dynamics and development of artificial bio-molecular machines
    Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    2011 - 2012
    FUKAMINATO Tsuyoshi, KAMEI Takashi, TAMAOKI Nobuyuki
    In this study, we tried to synthesize novel azobenzene derivatives, which can reversibly regulate the microtubule depolymerization-polymerization dynamics with external light stimuli, and attempted to develop artificial bio-molecular machines. For such purpose, we prepared several azobenzene derivatives having different kinds of substituent with different positions and rigorously investigated the effect on the microtubule polymerization dynamics. From detailed investigations, it was revealed that the amphiphilic structure of azobenzene was essential to achieve the reversible photoregulation of microtubule polymerization dynamics.
    Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, Hokkaido University, 23655111
  • Glass-forming chiral liquid crystals with white light emission and their tunable laser applications
    Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Exploratory Research
    2010 - 2011
    FURUMI Seiichi, TAMAOKI Nobuyuki
    This research project aims at the molecular design and synthesis of glass-forming chiral liquid crystals(G-CLCs) with white light emission, leading to tunable laser action on the basis of the photonic band effect of G-CLCs. Such G-CLCs are prepared by utilizing energy transfer, and the gradation structure of Bragg reflection is fabricated into the highly aligned G-CLC films by super-cooling process. We will demonstrate the tunable lasing in a fully visible wavelength range through our original optical measurement system.
    Japan Society for the Promotion of Science, Grant-in-Aid for Challenging Exploratory Research, National Institute for Materials Science, 22655047
  • フォトクロミズムの攻究とメカニカル機能の創出               
    科学研究費補助金
    2007 - 2011
    光駆動の分子機械を創成するための基盤研究
    (計画研究代表者)
    Competitive research funding
  • Basic study for the synthesis of photo-driven molecular machines
    Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Priority Areas
    2007 - 2010
    TAMAOKI Nobuyuki, AKIYAMA Haruhisa
    We investigated the possibility of photo-control of the action or the speed in synthetic or biological molecular machines. In the synthetic molecular machines we synthesized compounds cyclically connected a photoisomerizable azobenzene and an aromatic ring as a rotor unit via spacers. By tuning the spacer lengths and the bulkiness of the rotor unit, it is for the first time accomplished to demonstrate the complete ON-OFF switching of the intra-molecular rotation of the rotor by the action of lights. In the kinesin/microtubuline system as one of motor proteins, it was demonstrated that reversible photo-regulations of the motility velocity were possible by the introduction of azobenzene moiety on surface of the substrate, in an inhibitor, or in the ATP structure.
    Japan Society for the Promotion of Science, Grant-in-Aid for Scientific Research on Priority Areas, 19050013
  • 水素結合による分子組織体を経由するナノワイヤー形成の動的制御
    科学研究費助成事業 特定領域研究
    2002 - 2003
    玉置 信之, 長沢 順一
    二つのコレステロール部と一つのジアセチレン部が二つづつのアルキレン鎖とウレタン結合でつながった構造の重合性有機ゲル化剤について分子構造とゲル化のおよび光重合性の関係について調べた。ゲル化を起こし光重合するために少なくともコレステリル基が1つあること、ウレタン部位が2つあることが必要条件であることが判明した。また、スペーサー部位の構造を変化させることでエタノールのような極性溶媒中でゲル化を起こす化合物が得られた。ゲルの構造については赤外スペクトル、透過型電子顕微鏡により、光重合性については核磁気共鳴スペクトル、重合度測定により解析を進めた。その結果、ゲル中ではウレタン結合は完全に水素結合していること、ゲルは10〜100nm程度の幅を有する細長いファイバー状分子集合体からなっていること、光重合はジアセチレン部が1,4位で付加して起こっていること、平均重合度は50程度であることが判明した。また、10〜15テスラの磁場下でゲル化し、その後重合することで配向した共役ポリマーのゲルが生成することが初めて明らかになった。
    日本学術振興会, 特定領域研究, 独立行政法人産業技術総合研究所, 14045270
  • Synthesis and characterization of light-driven molecular machine               
    Competitive research funding

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