Researcher Database

Nobuyuki Tamaoki
Research Institute for Electronic Science Material and Molecular Sciences

Researcher Profile and Settings


  • Research Institute for Electronic Science Material and Molecular Sciences

Job Title

  • Professor

J-Global ID

Research Interests

  • molecular switch   molecular machine   chirality   azobenzene   liquid crystal   photochromism   分子組織体   フルカラー表示   液晶   分子機械   フォトクロミック反応   

Research Areas

  • Nanotechnology/Materials / Functional solid-state chemistry

Association Memberships

  • 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 Activities

Published Papers

  • Yuna Kim, Ken’ichi Aoki, Masaya Fujioka, Junji Nishii, Nobuyuki Tamaoki
    ACS Applied Materials & Interfaces 10 (42) 36407 - 36414 2018/10 [Refereed][Not invited]
  • 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 1520-5126 2018/02/07 [Refereed][Not invited]
    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.
  • Kimizuka N, Mase K, Sasaki Y, Tamaoki N, Weder C, Yanai N, Sagara Y
    Angewandte Chemie (International ed. in English) 1433-7851 2018/01 [Refereed][Not invited]
  • Yoshimitsu Sagara, Atsushi Seki, Yuna Kim, Nobuyuki Tamaoki
    Journal of Materials Chemistry C 6 (31) 8453 - 8459 2050-7534 2018 [Refereed][Not invited]
    © 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.
  • Ammathnadu S. Amrutha, K. R. Sunil Kumar, Takashi Kikukawa, Nobuyuki Tamaoki
    ACS Nano 11 (12) 12292 - 12301 1936-086X 2017/12/26 [Refereed][Not invited]
    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.
  • Halley M. Menezes, Md. Jahirul Islam, Masayuki Takahashi, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY 15 (42) 8894 - 8903 1477-0520 2017/11 [Refereed][Not invited]
    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.
  • Yoshimitsu Sagara, Christoph Weder, Nobuyuki Tamaoki
    CHEMISTRY OF MATERIALS 29 (14) 6145 - 6152 0897-4756 2017/07 [Refereed][Not invited]
    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.
  • Minsu Han, Mithrabinda K. Poduval, Haijin Shin, Nobuyuki Tamaoki, Taiho Park, Yuna Kim, Eunkyoung Kim
    OPTICAL MATERIALS EXPRESS 7 (6) 2117 - 2125 2159-3930 2017/06 [Refereed][Not invited]
    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
  • Yoshimitsu Sagara, Kazuya Kubo, Takayoshi Nakamura, Nobuyuki Tamaoki, Christoph Weder
    CHEMISTRY OF MATERIALS 29 (3) 1273 - 1278 0897-4756 2017/02 [Refereed][Not invited]
    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.
  • Yoshimitsu Sagara, Nobuyuki Tamaoki
    RSC ADVANCES 7 (74) 47056 - 47062 2046-2069 2017 [Refereed][Not invited]
    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.
  • Yuna Kim, Michel Frigoli, Nicolas Vanthuyne, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS 53 (1) 200 - 203 1359-7345 2017/01 [Refereed][Not invited]
    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.
  • Reji Thomas, Nobuyuki Tamaoki
    BEILSTEIN JOURNAL OF ORGANIC CHEMISTRY 12 1860-5397 2016/10 [Refereed][Not invited]
    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.
  • Yuna Kim, Nobuyuki Tamaoki
    ACS APPLIED MATERIALS & INTERFACES 8 (7) 4918 - 4926 1944-8244 2016/02 [Refereed][Not invited]
    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.
  • Yoshimitsu Sagara, Yoan C. Simon, Nobuyuki Tamaoki, Christoph Weder
    CHEMICAL COMMUNICATIONS 52 (33) 5694 - 5697 1359-7345 2016 [Refereed][Not invited]
    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.
  • Yoshimitsu Sagara, Christoph Weder, Nobuyuki Tamaoki
    RSC ADVANCES 6 (84) 80408 - 80414 2046-2069 2016 [Refereed][Not invited]
    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.
  • Ammathnadu S. Amrutha, K. R. Sunil Kumar, Kazuya Matsuo, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY 14 (30) 7202 - 7210 1477-0520 2016 [Refereed][Not invited]
    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.
  • K. R. Sunil Kumar, Ammathnadu S. Amrutha, Nobuyuki Tamaoki
    LAB ON A CHIP 16 (24) 4702 - 4709 1473-0197 2016 [Refereed][Not invited]
    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.
  • Rika Ochi, Nishad Perur, Kazutoshi Yoshida, Nobuyuki Tamaoki
    TETRAHEDRON 71 (21) 3500 - 3506 0040-4020 2015/05 [Refereed][Not invited]
    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.
  • K. Rijeesh, P. K. Hashim, Shin-ichiro Noro, Nobuyuki Tamaoki
    CHEMICAL SCIENCE 6 (2) 973 - 980 2041-6520 2015 [Refereed][Not invited]
    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.
  • Yuna Kim, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C 2 (43) 9258 - 9264 2050-7526 2014/11 [Refereed][Not invited]
    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.
  • K. R. Sunil Kumar, Takashi Kamei, Tuyoshi Fukaminato, Nobuyuki Tamaoki
    ACS NANO 8 (5) 4157 - 4165 1936-0851 2014/05 [Refereed][Not invited]
    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.
  • Ei-Ichiro Sunamura, Takashi Kamei, Hiroki Konno, Nobuyuki Tamaoki, Toru Hisabori
    BIOCHEMICAL AND BIOPHYSICAL RESEARCH COMMUNICATIONS 446 (1) 358 - 363 0006-291X 2014/03 [Refereed][Not invited]
    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.
  • Yuna Kim, Momoyo Wada, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY C 2 (10) 1921 - 1926 2050-7526 2014 [Refereed][Not invited]
    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.
  • Yuna Kim, Masahiro Funahashi, Nobuyuki Tamaoki
    RSC ADVANCES 4 (105) 60511 - 60518 2046-2069 2014 [Refereed][Not invited]
    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.
  • Nishad Perur, Masao Yahara, Takashi Kamei, Nobuyuki Tamaoki
    Chemical Communications 49 (85) 9935 - 9937 1359-7345 2013/11/04 [Refereed][Not invited]
    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.
  • Mahdi Roohnikan, Morteza Ebrahimi, Seyed Reza Ghaffarian, Nobuyuki Tamaoki
    LIQUID CRYSTALS 40 (3) 314 - 320 0267-8292 2013/03 [Refereed][Not invited]
    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.
  • P. K. Hashim, Meethale C. Basheer, Nobuyuki Tamaoki
    Tetrahedron Letters 54 (2) 176 - 178 0040-4039 2013/01/09 [Refereed][Not invited]
    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.
  • Reji Thomas, Yohei Yoshida, Takehito Akasaka, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL 18 (39) 12337 - 12348 0947-6539 2012/09 [Refereed][Not invited]
    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.
  • Tuyoshi Fukaminato, Emi Tateyama, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS 48 (88) 10874 - 10876 1359-7345 2012 [Refereed][Not invited]
    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.
  • Takashi Kamei, Tuyoshi Fukaminato, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS 48 (61) 7625 - 7627 1359-7345 2012 [Refereed][Not invited]
    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.
  • M. K. Abdul Rahim, Takashi Kamei, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY 10 (16) 3321 - 3331 1477-0520 2012 [Refereed][Not invited]
    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.
  • 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 1948-7185 2011/11 [Refereed][Not invited]
    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.
  • Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki
    IEICE TRANSACTIONS ON ELECTRONICS E94C (11) 1720 - 1726 0916-8524 2011/11 [Refereed][Not invited]
    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.
  • M. K. Abdul Rahim, Tuyoshi Fukaminato, Takashi Kamei, Nobuyuki Tamaoki
    LANGMUIR 27 (17) 10347 - 10350 0743-7463 2011/09 [Refereed][Not invited]
    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.
  • P. K. Hashim, Reji Thomas, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL 17 (26) 7304 - 7312 0947-6539 2011/06 [Refereed][Not invited]
    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.
  • Tuyoshi Fukaminato, Takao Doi, Nobuyuki Tamaoki, Katsuki Okuno, Yukihide Ishibashi, Hiroshi Miyasaka, Masahiro Irie
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 133 (13) 4984 - 4990 0002-7863 2011/04 [Refereed][Not invited]
    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.
  • Jun'ichi Nagasawa, Masaru Yoshida, Nobuyuki Tamaoki
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (12) 2247 - 2255 1434-193X 2011/04 [Refereed][Not invited]
    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.
  • P. K. Hashim, Nobuyuki Tamaoki
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 50 (49) 11729 - 11730 1433-7851 2011 [Refereed][Not invited]
  • Juin-Meng Yu, Takeshi Sakamoto, Kento Watanabe, Seiichi Furumi, Nobuyuki Tamaoki, Yun Chen, Tamaki Nakano
    CHEMICAL COMMUNICATIONS 47 (13) 3799 - 3801 1359-7345 2011 [Refereed][Not invited]
    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.
  • Reji Thomas, Nobuyuki Tamaoki
    ORGANIC & BIOMOLECULAR CHEMISTRY 9 (15) 5389 - 5393 1477-0520 2011 [Refereed][Not invited]
    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.
  • Nagatoshi Koumura, Hajime Matsumoto, Hajime Kawanami, Nobuyuki Tamaoki, Masaru Yoshida
    POLYMER JOURNAL 42 (9) 759 - 765 0032-3896 2010/09 [Refereed][Not invited]
    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
  • Nobuyuki Tamaoki, Takashi Kamei
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY C-PHOTOCHEMISTRY REVIEWS 11 (2-3) 47 - 61 1389-5567 2010/09 [Refereed][Not invited]
    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.
  • Yoshimi Oka, Nobuyuki Tamaoki
    INORGANIC CHEMISTRY 49 (11) 4765 - 4767 0020-1669 2010/06 [Refereed][Not invited]
    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.
  • Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    ORGANIC ELECTRONICS 11 (3) 363 - 368 1566-1199 2010/03 [Refereed][Not invited]
    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.
  • Yoko Matsuzawa, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY B 114 (4) 1586 - 1590 1520-6106 2010/02 [Refereed][Not invited]
    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.
  • Seiichi Furumi, Nobuyuki Tamaoki
    ADVANCED MATERIALS 22 (8) 886 - + 0935-9648 2010/02 [Refereed][Not invited]
    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).
  • 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 1474-905X 2010 [Refereed][Not invited]
    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.
  • Meethale C. Basheer, Yoshimi Oka, Manoj Mathews, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL 16 (11) 3489 - 3496 0947-6539 2010 [Refereed][Not invited]
    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 1883-2490 2010 [Refereed][Not invited]
    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 %.
  • 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 1010-6030 2009/09 [Refereed][Not invited]
    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.
  • Yasuo Norikane, Riju Davis, Yoshinobu Nishimura, Tatsuo Arai, Nobuyuki Tamaoki
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 205 (2-3) 116 - 121 1010-6030 2009/06 [Refereed][Not invited]
    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.
  • Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Haruhisa Akiyama, Nobuyuki Tamaoki
    JOURNAL OF FLUORINE CHEMISTRY 130 (2) 151 - 161 0022-1139 2009/02 [Refereed][Not invited]
    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.
  • Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    ORGANIC ELECTRONICS 10 (1) 73 - 84 1566-1199 2009/02 [Refereed][Not invited]
    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.
  • Takashi Kamei, Haruhisa Akiyama, Hisayuki Morii, Nobuyuki Tamaoki, Taro Q. P. Uyeda
    NUCLEOSIDES NUCLEOTIDES & NUCLEIC ACIDS 28 (1) 12 - 28 1525-7770 2009 [Refereed][Not invited]
    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.
  • Yasuo Norikane, Riju Davis, Nobuyuki Tamaoki
    NEW JOURNAL OF CHEMISTRY 33 (6) 1327 - 1331 1144-0546 2009 [Refereed][Not invited]
    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.
  • Manoj Mathews, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS (24) 3609 - 3611 1359-7345 2009 [Refereed][Not invited]
    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.
  • Haruhisa Akiyama, Asuka Tanaka, Hideo Hiramatsu, Jun'ichi Nagasawa, Nobuyuki Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY 19 (33) 5956 - 5963 0959-9428 2009 [Refereed][Not invited]
    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.
  • Yoshihiro Misawa, Nagatoshi Koumura, Hajime Matsumoto, Nobuyuki Tamaoki, Masaru Yoshida
    MACROMOLECULES 41 (22) 8841 - 8846 0024-9297 2008/11 [Refereed][Not invited]
    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.
  • Ratheesh K. Vijayaraghavan, Shibu Abraham, Haruhisa Akiyama, Seiichi Furumi, Nobuyuki Tamaoki, Suresh Das
    ADVANCED FUNCTIONAL MATERIALS 18 (17) 2510 - 2517 1616-301X 2008/09 [Refereed][Not invited]
    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.
  • Manoj Mathews, Nobuyuki Tamaoki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 130 (34) 11409 - 11416 0002-7863 2008/08 [Refereed][Not invited]
    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.
  • Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki, Jun-ichi Hanna
    CHEMPHYSCHEM 9 (10) 1465 - 1473 1439-4235 2008/07 [Refereed][Not invited]
    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.
  • Hideyuki Kihara, Nobuyuki Tamaoki
    MACROMOLECULAR CHEMISTRY AND PHYSICS 209 (14) 1424 - 1431 1022-1352 2008/07 [Refereed][Not invited]
    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.
  • Yasuo Norikane, Ryuzi Katoh, Nobuyuki Tamaoki
    CHEMICAL COMMUNICATIONS (16) 1898 - 1900 1359-7345 2008/04 [Refereed][Not invited]
    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.
  • 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 1932-7447 2008/02 [Refereed][Not invited]
    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.
  • Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY A 111 (51) 13441 - 13451 1089-5639 2007/12 [Refereed][Not invited]
    \(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.
  • V. Ajay Mallia, Masahiro Funahashi, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL ORGANIC CHEMISTRY 20 (11) 878 - 883 0894-3230 2007/11 [Refereed][Not invited]
    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.
  • 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 - + 0002-7863 2007/09 [Refereed][Not invited]
    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).
  • Fapei Zhang, Masahiro Funahashi, Nobuyuki Tamaoki
    APPLIED PHYSICS LETTERS 91 (6) 0003-6951 2007/08 [Refereed][Not invited]
    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.
  • Haruhisa Akiyama, Nobuyuki Tamaoki
    MACROMOLECULES 40 (14) 5129 - 5132 0024-9297 2007/07 [Refereed][Not invited]
    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.
  • 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 1434-193X 2007/06 [Refereed][Not invited]
  • Yoko Matsuzawa, Katsuyuki Ueki, Masaru Yoshida, Nobuyuki Tamaoki, Tohru Nakamura, Hideki Sakai, Masahiko Abe
    ADVANCED FUNCTIONAL MATERIALS 17 (9) 1507 - 1514 1616-301X 2007/06 [Refereed][Not invited]
    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.
  • 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 1434-193X 2007/04 [Refereed][Not invited]
    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).
  • Masahiro Funahashi, Fapei Zhang, Nobuyuki Tamaoki
    ADVANCED MATERIALS 19 (3) 353 - + 0935-9648 2007/02 [Refereed][Not invited]
    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).
  • Masahiro Funahashi, Nobuyuki Tamaoki
    CHEMISTRY OF MATERIALS 19 (3) 608 - 617 0897-4756 2007/02 [Refereed][Not invited]
    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.
  • Rijn Davis, Nobuyuki Tamaoki
    CHEMISTRY-A EUROPEAN JOURNAL 13 (2) 626 - 631 0947-6539 2007 [Refereed][Not invited]
    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.
  • Hideyuki Kihara, Nobuyuki Tamaoki
    LIQUID CRYSTALS 34 (11) 1337 - 1347 0267-8292 2007 [Refereed][Not invited]
    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 - + 2007 [Refereed][Not invited]
    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).
  • Hideyuki Kihara, Nobuyuki Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 470 31 - 37 1542-1406 2007 [Refereed][Not invited]
    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.
  • Masahiro Funahashi, Nobuyuki Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 475 123 - + 1542-1406 2007 [Refereed][Not invited]
    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.
  • Yoriko Sonoda, Midori Goto, Seiji Tsuzuki, Nobuyuki Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY A 110 (50) 13379 - 13387 1089-5639 2006/12 [Refereed][Not invited]
    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.
  • Masabumi Takahashi, Kentaro Masui, Hiroki Sekiguchi, Nobuhiko Kobayashi, Atsunori Mori, Masahiro Funahashi, Nobuyuki Tamaoki
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (33) 10930 - 10933 0002-7863 2006/08 [Refereed][Not invited]
    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.
  • Shibu Abraham, V. Ajay Mallia, K. Vijayaraghavan Ratheesh, Nobuyuki Tamaoki, Suresh Das
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (23) 7692 - 7698 0002-7863 2006/06 [Refereed][Not invited]
    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.
  • M Funahashi, N Tamaoki
    CHEMPHYSCHEM 7 (6) 1193 - 1197 1439-4235 2006/06 [Refereed][Not invited]
  • H Kihara, N Tamaoki
    MACROMOLECULAR RAPID COMMUNICATIONS 27 (11) 829 - 834 1022-1336 2006/06 [Refereed][Not invited]
    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.
  • Nobuyuki Tamaoki, Momoyo Wada
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (19) 6284 - 6285 0002-7863 2006/05 [Refereed][Not invited]
  • H Akiyama, VA Mallia, N Tamaoki
    ADVANCED FUNCTIONAL MATERIALS 16 (4) 477 - 484 1616-301X 2006/03 [Refereed][Not invited]
    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.
  • Y Norikane, N Tamaoki
    EUROPEAN JOURNAL OF ORGANIC CHEMISTRY (5) 1296 - 1302 1434-193X 2006/02 [Refereed][Not invited]
    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).
  • 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 2006 [Refereed][Not invited]
    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.
  • VA Mallia, N Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 454 81 - 90 1542-1406 2006 [Refereed][Not invited]
    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.
  • S Kumaresan, VA Mallia, Y Kida, N Tamaoki
    JOURNAL OF MATERIALS RESEARCH 20 (12) 3431 - 3438 0884-2914 2005/12 [Refereed][Not invited]
    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.
  • SA Nagamani, Y Norikane, N Tamaoki
    JOURNAL OF ORGANIC CHEMISTRY 70 (23) 9304 - 9313 0022-3263 2005/11 [Refereed][Not invited]
    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.
  • R Davis, N Tamaoki
    ORGANIC LETTERS 7 (8) 1461 - 1464 1523-7060 2005/04 [Refereed][Not invited]
    [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.
  • N Tamaoki
    JOURNAL OF SYNTHETIC ORGANIC CHEMISTRY JAPAN 63 (4) 370 - 376 0037-9980 2005/04 [Refereed][Not invited]
    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.
  • K Kishimoto, Y Sagara, T Kato, T Mukai, H Ohno, N Tamaoki
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 435 777 - 785 1542-1406 2005 [Refereed][Not invited]
    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.
  • N Koumura, M Kudo, N Tamaoki
    LANGMUIR 20 (23) 9897 - 9900 0743-7463 2004/11 [Refereed][Not invited]
    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.
  • H Akiyama, N Tamaoki
    JOURNAL OF POLYMER SCIENCE PART A-POLYMER CHEMISTRY 42 (20) 5200 - 5214 0887-624X 2004/10 [Refereed][Not invited]
    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.
  • K Aoki, M Kudo, N Tamaoki
    ORGANIC LETTERS 6 (22) 4009 - 4012 1523-7060 2004/10 [Refereed][Not invited]
    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.
  • J Nagasawa, M Kudo, S Hayashi, N Tamaoki
    LANGMUIR 20 (19) 7907 - 7916 0743-7463 2004/09 [Refereed][Not invited]
    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.
  • R Davis, VA Mallia, S Das, N Tamaoki
    ADVANCED FUNCTIONAL MATERIALS 14 (8) 743 - 748 1616-301X 2004/08 [Refereed][Not invited]
    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.
  • Y Norikane, N Tamaoki
    ORGANIC LETTERS 6 (15) 2595 - 2598 1523-7060 2004/07 [Refereed][Not invited]
    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).
  • M Matsumoto, T Nakazawa, VA Mallia, N Tamaoki, R Azumi, H Sakai, M Abe
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 126 (4) 1006 - 1007 0002-7863 2004/02 [Refereed][Not invited]
  • VA Mallia, N Tamaoki
    CHEMICAL SOCIETY REVIEWS 33 (2) 76 - 84 0306-0012 2004/02 [Refereed][Not invited]
    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.
  • VA Mallia, N Tamaoki
    CHEMICAL COMMUNICATIONS (22) 2538 - 2539 1359-7345 2004 [Refereed][Not invited]
    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.
  • M Kidowaki, M Moriyama, M Wada, N Tamaoki
    JOURNAL OF PHYSICAL CHEMISTRY B 107 (44) 12054 - 12061 1520-6106 2003/11 [Refereed][Not invited]
    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.
  • Yasuo Norikane, Naofumi Nakayama, Nobuyuki Tamaoki, Tatsuo Arai, Umpei Nagashima
    Journal of Physical Chemistry A 107 (41) 8659 - 8664 1089-5639 2003/10/16 [Refereed][Not invited]
    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.
  • Y Norikane, K Kitamoto, N Tamaoki
    JOURNAL OF ORGANIC CHEMISTRY 68 (22) 8291 - 8304 0022-3263 2003/10 [Refereed][Not invited]
    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.
  • VA Mallia, N Tamaoki
    CHEMISTRY OF MATERIALS 15 (17) 3237 - 3239 0897-4756 2003/08 [Refereed][Not invited]
  • A Belaissaoui, S Shimada, A Ohishi, N Tamaoki
    TETRAHEDRON LETTERS 44 (11) 2307 - 2310 0040-4039 2003/03 [Refereed][Not invited]
    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.
  • N Tamaoki, Y Aoki, M Moriyama, M Kidowaki
    CHEMISTRY OF MATERIALS 15 (3) 719 - 726 0897-4756 2003/02 [Refereed][Not invited]
    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.
  • A Takahashi, VA Mallia, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY 13 (7) 1582 - 1587 0959-9428 2003 [Refereed][Not invited]
    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.
  • H Akiyama, N Tamaoki
    KOBUNSHI RONBUNSHU 60 (10) 575 - 580 0386-2186 2003 [Refereed][Not invited]
    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.
  • VA Mallia, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY 13 (2) 219 - 224 0959-9428 2003 [Refereed][Not invited]
    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.
  • Y Norikane, K Kitamoto, N Tamaoki
    ORGANIC LETTERS 4 (22) 3907 - 3910 1523-7060 2002/10 [Refereed][Not invited]
    [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.
  • 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 0065-7727 2002/04 [Refereed][Not invited]
  • 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 0272-9172 2002 [Refereed][Not invited]
    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.
  • N Tamaoki, Y Aoki, M Moriyama, M Kidowaki
    LIQUID CRYSTALS VI 4799 103 - 112 0277-786X 2002 [Refereed][Not invited]
    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.
  • N Tamaoki, H Matsuda
    LIQUID CRYSTALS 28 (12) 1823 - 1829 0267-8292 2001/12 [Refereed][Not invited]
    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.
  • M Moriyama, N Tamaoki
    CHEMISTRY LETTERS (11) 1142 - 1143 0366-7022 2001/11 [Refereed][Not invited]
    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.
  • N Tamaoki
    ADVANCED MATERIALS 13 (15) 1135 - + 0935-9648 2001/08 [Refereed][Not invited]
    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.
  • M Moriyama, S Song, H Matsuda, N Tamaoki
    JOURNAL OF MATERIALS CHEMISTRY 11 (4) 1003 - 1010 0959-9428 2001 [Refereed][Not invited]
    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 1058-725X 2001 [Refereed][Not invited]
    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.
  • N Tamaoki, S Shimada, Y Okada, A Belaissaoui, G Kruk, K Yase, H Matsuda
    LANGMUIR 16 (19) 7545 - 7547 0743-7463 2000/09 [Refereed][Not invited]
  • A Parfenov, N Tamaoki, S Ohnishi
    JOURNAL OF APPLIED PHYSICS 87 (4) 2043 - 2045 0021-8979 2000/02 [Refereed][Not invited]
    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].
  • N Tamaoki, M Moriyama, H Matsuda
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 39 (3) 509 - + 1433-7851 2000 [Refereed][Not invited]
  • N Tamaoki, S Song, M Moriyama, H Matsuda
    ADVANCED MATERIALS 12 (2) 94 - 97 0935-9648 2000/01 [Refereed][Not invited]
  • G Kruk, N Tamaoki, H Matsuda, Y Kida
    LIQUID CRYSTALS 26 (11) 1687 - 1693 0267-8292 1999/11 [Refereed][Not invited]
    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.
  • N Tamaoki, G Kruk, H Matsuda
    JOURNAL OF MATERIALS CHEMISTRY 9 (10) 2381 - 2384 0959-9428 1999/10 [Refereed][Not invited]
    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.
  • N Tamaoki, T Terai, H Matsuda
    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.
  • S Shimada, K Ishikawa, N Tamaoki
    ACTA CHEMICA SCANDINAVICA 52 (3) 374 - 376 0904-213X 1998/03 [Refereed][Not invited]
  • K Harada, M Itoh, IN Kompanets, H Matsuda, AV Parfenov, N Tamaoki, T Yatagai
    OPTICAL REVIEW 5 (2) 89 - 92 1340-6000 1998/03 [Refereed][Not invited]
    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.
  • M Itoh, K Harada, H Matsuda, S Ohnishi, A Parfenov, N Tamaoki, T Yatagai
    JOURNAL OF PHYSICS D-APPLIED PHYSICS 31 (5) 463 - 471 0022-3727 1998/03 [Refereed][Not invited]
    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
    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.
  • N Tamaoki, AV Parfenov, A Masaki, H Matsuda
    ADVANCED MATERIALS 9 (14) 1102 - 1104 0935-9648 1997/11 [Refereed][Not invited]
  • N Tamaoki, S Shimada
    ACTA CHEMICA SCANDINAVICA 51 (11) 1138 - 1140 0904-213X 1997/11 [Refereed][Not invited]
  • N Tamaoki, E VanKeuren, H Matsuda, K Hasegawa, T Yamaoka
    APPLIED PHYSICS LETTERS 69 (9) 1188 - 1190 0003-6951 1996/08 [Refereed][Not invited]
    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.
  • Nobuyuki Tamaoki, Yasushi Takahashi, Tsuguo Yamaoka
    Journal of the Chemical Society, Chemical Communications (15) 1749 - 1750 0022-4936 1994 [Not refereed][Not invited]
    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.
  • Yasushi Takahashi, Nobuyuki Tamaoki, Yuichi Komiya, Yoshihiro Hieda, Kenichi Koseki, Tsuguo Yamaoka
    Journal of Applied Physics 74 (6) 4158 - 4162 0021-8979 1993 [Not refereed][Not invited]
    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.
  • Nobuyuki Tamaoki, Kenichi Koseki, Tsuguo Yamaoka
    Journal of the Chemical Society, Perkin Transactions 2 1107 - 1110 1472-779X 1992/12/01 [Not refereed][Not invited]
    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.
    THIN SOLID FILMS 221 (1-2) 132 - 139 0040-6090 1992/12 [Not refereed][Not invited]
    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.
  • Nobuyuki Tamaoki, Tsuguo Yamaoka
    Journal of the Chemical Society, Perkin Transactions 2 873 - 878 1472-779X 1991/12/01 [Not refereed][Not invited]
    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.
  • Nobuyuki Tamaoki, Kenichi Koseki, Tsuguo Yamaoka
    Tetrahedron Letters 31 3309 - 3312 0040-4039 1990/01/01 [Not refereed][Not invited]
    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.
    TETRAHEDRON 46 (17) 5931 - 5942 0040-4020 1990 [Not refereed][Not invited]
    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.
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION IN ENGLISH 29 (1) 105 - 106 0570-0833 1990/01 [Not refereed][Not invited]
    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

Books etc

  • 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


Awards & Honors

  • 2001 化学バイオつくば賞

Research Grants & Projects

  • フォトクロミズムの攻究とメカニカル機能の創出
    Date (from‐to) : 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)
  • Synthesis and characterization of light-driven molecular machine

Educational Activities

Teaching Experience

  • Biomaterials Science
    開講年度 : 2018
    課程区分 : 修士課程
    開講学部 : 生命科学院
    キーワード : 自己組織化、超分子化学、ナノテクノロジー、分子機械、液晶、DNA、スマート分子
  • Thermodynamics for Life Science
    開講年度 : 2018
    課程区分 : 学士課程
    開講学部 : 理学部
    キーワード : 熱力学、エンタルピー、エントロピー、自由エネルギー、化学ポテンシャル

Campus Position History

  • 2017年10月1日 

Position History

  • 2017年10月1日 

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