MF研究者総覧

Researcher Database

Advance
Researchers' Page on researchmap
Last Updated :2024/09/03

Researcher Profile and Settings

Master

Affiliation (Master)

  • Faculty of Science　Chemistry　Inorganic and Analytical Chemistry

Affiliation (Master)

  • Faculty of Science　Chemistry　Inorganic and Analytical Chemistry

researchmap

Profile and Settings

Degree

  • Ph.D.

Profile and Settings

  • Name (Japanese)

    Kobayashi

  • Name (Kana)

    Atsushi

  • Name

    200901074462271060

Alternate Names

Achievement

Research Interests

  • Sensors   Luminescent materials   nanoparticle   photocatalyst   Metal complex   

Research Areas

  • Nanotechnology/Materials / Energy chemistry / Photocatalysis
  • Nanotechnology/Materials / Inorganic and coordination chemistry / Coordination Chemistry

Research Experience

  • 2014/10 - Today Hokkaido University Faculty of Science, Department of Chemistry
  • 2012/10 - 2016/03 科学技術振興機構 戦略的創造研究推進事業 さきがけ研究 「エネルギー高効率利用と相界面」 領域研究員（兼任）
  • 2013/06 - 2014/09 Hokkaido University Faculty of Science, Department of Chemistry
  • 2007/05 - 2013/05 Hokkaido University Faculty of Science, Department of Chemistry
  • 2012/10 - 2012/12 アメリカ・ロチェスター大学化学科 無機化学研究室(R. Eisenberg教授） 訪問研究員
  • 2006/05 - 2007/04 Kyushu University Faculty of Sciences
  • 2006/12 - 2007/03 オーストラリア・シドニー大学化学科 分子材料グループ(C.J.Kepert教授） 客員研究員
  • 2006/04 - 2006/05 Kyushu University Faculty of Sciences
  • 2003/04 - 2006/03 Kyushu University Graduate School of Sciences, Department of Chemistry and Physics of Condensed Matter
  • 2001/04 - 2003/03 筑波大学大学院数理物質科学研究科
  • 1997/04 - 2001/03 University of Tsukuba First Cluster of Colleges,College of Natural Sciences

Awards

  • 2023/08 北海道大学 令和4年度 全学教育科目エクセレントティーチャーズ
     
    受賞者: 小林 厚志
  • 2017/01 Hokkaido University Hokkaido University President's Award
     
    受賞者: KOBAYASHI Atsushi
  • 2016/07 Hokkaido University Excellent Teachers
     
    受賞者: KOBAYASHI Atsushi
  • 2016/01 Chemical Society of Japan, Hokkaido Branch Encouraging prize of the Chemical Society of Japan, Hokkaido Branch
     Development of new environmentally-responsive multichromic complexes 
    受賞者: KOBAYASHI Atsushi
  • 2015/01 Hokkaido University Hokkaido University President's Award
     
    受賞者: KOBAYASHI Atsushi

Published Papers

  • Tomoya Saito, Masaki Yoshida, Kaito Segawa, Daisuke Saito, Junichi Takayama, Satoshi Hiura, Akihiro Murayama, Nishshanka M. Lakshan, W. M. C. Sameera, Atsushi Kobayashi, Masako Kato
    Chemical Science 2041-6520 2024 
    The emissions of isomorphous Pt(ii) and Pd(ii) one-dimensional chains exhibited distinct thermal responses, revealing the limiting factor for extending the excited-state delocalization across multiple molecules through metallophilic interactions.
  • Atsushi Kobayashi
    Catalysis Science & Technology 2044-4753 2024 [Refereed][Not invited]
     
    A photoredox cascade catalyst for concurrent organic synthesis and hydrogen production was developed by combining a dual-dye sensitized Pt-TiO2 photocatalyst and an N-hydroxyphthalimide hydrogen atom transfer catalyst.
  • Takanari Mochizuki, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 1477-9226 2024 
    The selectivity of the porous crystal phase of luminescent platinum(ii) complexes with Pt⋯Pt interactions has been systematically controlled by the ancillary N-heteroaryl carboxylate ligand.
  • Sae Kondo, Nobutaka Yoshimura, Atsushi Kobayashi, K. D. Charith Kuruppu, W. M. C. Sameera, Saki Fujii, Masaki Yoshida, Masako Kato
    Journal of Materials Chemistry C 2050-7526 2023/12 [Refereed][Not invited]
     
    A vapoluminescent thin film including a coordinatively unsaturated Cu(i) complex acts as an efficient light-on sensor for N-heteroaromatic vapours and exhibits intense emission of different colours.
  • Atsushi Kobayashi
    Angewandte Chemie International Edition 1433-7851 2023/09/21 [Refereed][Not invited]
     
    Biomass photoreforming is a promising method to provide both a clean energy resource in the form of hydrogen (H2) and valuable chemicals as the results of water reduction and biomass oxidation. To overcome the poor contact between heterogeneous photocatalysts and biomass substrates, we fabricated a new photoredox cascade catalyst by combining a homogeneous catalyst, 2,2,6,6‐tetramethylpiperidine 1‐oxyl (TEMPO), and a heterogeneous dual‐dye sensitized photocatalyst (DDSP) composed of two Ru(II)‐polypyridine photosensitizers (RuP6 and RuCP6) and Pt‐loaded TiO2 nanoparticles. During blue‐light irradiation (λ = 460 ± 15 nm; 80 mW), the DDSP photocatalytically reduced aqueous protons to form H2 and simultaneously oxidized TEMPO· radicals to generate catalytically active TEMPO+. It oxidized biomass substrates (water‐soluble glycerol and insoluble cellulose) to regenerate TEMPO·. In the presence of N‐methyl imidazole as a proton transfer mediator, the photocatalytic H2 production activities for glycerol and cellulose reforming reached 2670 and 1590 µmol H2 (gTiO2)‐1 h‐1, respectively, which were comparable to those of state‐of‐the‐art heterogeneous photocatalysts.
  • Tamami Morimoto, Masaki Yoshida, Ayana Sato-Tomita, Shunsuke Nozawa, Junichi Takayama, Satoshi Hiura, Akihiro Murayama, Atsushi Kobayashi, Masako Kato
    Chemistry – A European Journal 0947-6539 2023/08/15 
    Controlled self‐assembly of Pt(II) complexes is key to the development of optical and stimuli‐responsive materials, but designing and precisely controlling them is still difficult owing to weak intermolecular interactions. Herein, we report the successful water‐vapor‐induced assembly of an anionic Pt(II) complex [Pt(CN)2(ppy)]– (Hppy = 2‐phenylpyridine) electrostatically loaded on cationically charged layered double hydroxide (LDH) nanoparticles consisting of Mg2+ and Al3+ ions. When the Pt(II) complexes were densely loaded onto the LDH nanoparticles, the assembly was maintained, even in dilute aqueous media. In the case of sparse loading, the Pt(II) complexes were loaded discretely in the dry state; however, when water vapor was adsorbed, the increased mobility of the Pt(II) complexes led to their assembly on the LDH nanoparticles. This resulted in a drastic change in luminescence from green to orange owing to the presence of water vapor.
  • Yusuke Higashida, Shin-ya Takizawa, Masaki Yoshida, Masako Kato, Atsushi Kobayashi
    ACS Applied Materials & Interfaces 1944-8244 2023/05/25 [Refereed][Not invited]
  • Kono Sasaki, Daisuke Saito, Masaki Yoshida, Fuka Tanaka, Atsushi Kobayashi, Kazuki Sada, Masako Kato
    Chemical communications (Cambridge, England) 2023/05/16 
    A series of Pt(II) complexes bearing N-heterocyclic carbenes, [Pt(CN)2(Rim-Mepy)] (Rim-MepyH+ = 3-alkyl-1-(4-methyl-(2-pyridinyl))-1H-imidazolium, R = Me, Et, iPr, or tBu), exhibits triboluminescence in the visible range from blue to red, as well as the corresponding intense photoluminescence. Remarkably, among the complexes, the iPr-substituted one exhibits chromic triboluminescence behaviour during the process of rubbing and also vapour exposure.
  • Nobutaka Yoshimura, Masaki Yoshida, Atsushi Kobayashi
    Journal of the American Chemical Society 145 (11) 6035 - 6038 0002-7863 2023/03/13 [Refereed]
  • Nobutaka Yoshimura, Osamu Tomita, Ryu Abe, Masaki Yoshida, Atsushi Kobayashi
    ChemCatChem 15 (4) 1867-3880 2023/01/26 [Refereed][Not invited]
  • Yusuke Makino, Masaki Yoshida, Shotaro Hayashi, Toshiyuki Sasaki, Satoshi Takamizawa, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 1477-9226 2023 [Refereed][Not invited]
     
    Molecular crystals composed of platinum(ii) complexes exhibited elastic deformation without cracking and bright assembly-induced emission with an extremely high emission quantum yield of 0.94.
  • Taku Shimamura, Nobutaka Yoshimura, Hiroki Otsuka, Masaki Yoshida, Atsushi Kobayashi
    Journal of Photochemistry and Photobiology A: Chemistry 436 114412 - 114412 1010-6030 2022/11 [Refereed][Not invited]
  • Hiroyuki Takeda, Atsushi Kobayashi, Kiyoshi Tsuge
    Coordination Chemistry Reviews 470 214700 - 214700 0010-8545 2022/11 [Refereed][Invited]
  • Atsushi Kobayashi, Shin-ya Takizawa, Masanari Hirahara
    Coordination Chemistry Reviews 467 214624 - 214624 0010-8545 2022/09 [Refereed][Invited]
  • Nobutaka Yoshimura, Masaki Yoshida, Masako Kato, Atsushi Kobayashi
    Inorganic Chemistry 61 (29) 11095 - 11102 0020-1669 2022/07/25 [Refereed][Not invited]
  • Taku Shimamura, Atsushi Kobayashi, Yuya Oaki, Masaki Yoshida, Masako Kato
    Energy & Fuels 0887-0624 2022/06/21 [Refereed]
  • Masako Kato, Masaki Yoshida, Yu Sun, Atsushi Kobayashi
    Journal of Photochemistry and Photobiology C: Photochemistry Reviews 51 100477 - 100477 1389-5567 2022/06 [Refereed]
  • Atsushi Kobayashi, Hiroki Otsuka, Masaki Yoshida, Masako Kato
    Chemistry Letters 51 (7) 697 - 699 0366-7022 2022/05/07
  • Daisuke Saito, Tomasz Galica, Eiji Nishibori, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Chemistry – A European Journal 28 (32) 0947-6539 2022/04/21 [Refereed][Not invited]
  • Masaki Yoshida, Verner Sääsk, Daisuke Saito, Nobutaka Yoshimura, Junichi Takayama, Satoshi Hiura, Akihiro Murayama, Kaija Põhako‐Esko, Atsushi Kobayashi, Masako Kato
    Advanced Optical Materials 10 (7) 2102614 - 2102614 2195-1071 2022/04 [Refereed][Not invited]
  • Nobutaka Yoshimura, Atsushi Kobayashi, Tomoki Kondo, Ryu Abe, Masaki Yoshida, Masako Kato
    ACS Applied Energy Materials 4 (12) 14352 - 14362 2574-0962 2021/12/27 [Refereed]
  • Hiroki Otsuka, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    Dalton Transactions 50 (44) 16233 - 16241 1477-9226 2021/10 [Refereed][Not invited]
     
    We newly synthesised oxygen-evolving molecular Ru(II) catalysts with one or two carbazole moieties on the axial pyridyl ligands, namely [Ru(bda)(cbz-py)(py)] and [Ru(bda)(cbz-py)2] [C1 and C2; bdaH2 = 2, 2’-bipyridyl-6, 6’-dicarboxylic...
  • Atsushi Kobayashi, Shin-ichiro Imada, Yuze Yao, Yuki Nagao, Yuto Kubota, Masaki Yoshida, Masako Kato
    Bulletin of the Chemical Society of Japan 94 (10) 2466 - 2473 0009-2673 2021/09/28 [Refereed][Not invited]
  • Masaki Yoshida, Yusuke Makino, Toshiyuki Sasaki, Shunichi Sakamoto, Satoshi Takamizawa, Atsushi Kobayashi, Masako Kato
    CrystEngComm 23 (34) 5891 - 5898 2021/06 [Refereed]
     

    A series of polyhalogenated platinum(ii)–bipyridine complexes showed solvent-of-crystallisation-dependent elastic flexibility and luminescence.

  • Atsushi Kobayashi, Eiichirou Muramatsu, Masaki Yoshida, Masako Kato
    Energies 14 (9) 2425 - 2425 2021/04/24 [Refereed]
     
    Interfacial electron injection from a photoexcited surface-immobilized dye to a semiconductor substrate is a key reaction for dye-sensitized photocatalysts. We previously reported that the molecular orientation of heteroleptic Ir(III) photosensitizer on the TiO2 nanoparticle surface was important for efficient interfacial electron injection. In this work, to overcome the weak light absorption ability of heteroleptic Ir(III) photosensitizer and to improve the photoinduced charge-separation efficiency at the dye–semiconductor interface, we synthesized two heteroleptic Ir(III) complexes with different coumarin dyes, [Ir(C6)2(H4CPbpy)]Cl and [Ir(C30)2(H4CPbpy)]Cl [Ir-CX; X = 6 or 30; HC6 = 3-(2-enzothiazolyl)-7-(diethylamino)coumarin, HC30 = 3-(2-N-methylbenzimidazolyl)-7-N,N-diethylaminocoumarin, H4CPbpy = 4,4′-bis(methylphosphonic acid)-2,2′-bipyridine], as the cyclometalated ligands and immobilized them on the surface of Pt-cocatalyst-loaded TiO2 nanoparticles. Ultraviolet-visible absorption and emission spectroscopy revealed that the singlet ligand-centered (1LC) absorption and triplet 3LC emission bands of Ir-C30 occurred at shorter wavelengths than those of Ir-C6, while time-dependent density-functional-theory data suggested that the ligand-to-ligand charge transfer (LLCT) excited states of the two complexes were comparable. The photocatalytic H2 evolution activity of the Ir-C6-sensitized Pt-TiO2 nanoparticles (Ir-C6@Pt-TiO2) under visible light irradiation (λ > 420 nm) was higher than that of Ir-C30@Pt-TiO2. In contrast, their activities were comparable under irradiation with monochromatic light (λ = 450 ± 10 nm), which is absorbed comparably by both Ir-CX complexes. These results suggest that the internal conversion from the higher-lying LC state to the LLCT state effectively occurs in both Ir-CX complexes to trigger electron injection to TiO2.
  • Ryota Yano, Masaki Yoshida, Takahiro Tsunenari, Ayana Sato-Tomita, Shunsuke Nozawa, Youhei Iida, Noriaki Matsunaga, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 50 (25) 8696 - 8703 1477-9226 2021/04 [Refereed][Not invited]
     

    The nickel(ii)–chloranilato complex shows reversible vapochromism with changes in dimensionality upon exposure to various vapours and subsequent drying by heating.

  • Nobutaka Yoshimura, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    Chemistry – A European Journal 26 (70) 16939 - 16946 0947-6539 2020/12/15 [Refereed][Not invited]
  • Daisuke Saito, Tomohiro Ogawa, Masaki Yoshida, Junichi Takayama, Satoshi Hiura, Akihiro Murayama, Atsushi Kobayashi, Masako Kato
    Angewandte Chemie International Edition 59 (42) 18723 - 18730 1433-7851 2020/10/12 [Refereed][Not invited]
  • Atsushi Kobayashi, Tomoka Ehara, Masaki Yoshida, Masako Kato
    Inorganic Chemistry 59 (14) 9511 - 9520 0020-1669 2020/07/20 [Refereed][Not invited]
  • Chuei Wakasugi, Masaki Yoshida, W. M. C. Sameera, Yasuhiro Shigeta, Atsushi Kobayashi, Masako Kato
    Chemistry – A European Journal 26 (24) 5449 - 5458 0947-6539 2020/04/24 [Refereed][Not invited]
  • Atsushi Kobayashi, Shin-ichiro Imada, Dongjin Wang, Yuki Nagao, Masaki Yoshida, Masako Kato
    Faraday Discussions 225 184 - 196 1359-6640 2020/04 [Refereed][Not invited]
     

    The cooperative phenomenon between proton conduction and vapochromism of luminescent Pt(ii) complexes, [PtCl(tpypy)]Cl and [PtCl(tpypyH)]Cl2, is reported.

  • Masaki Yoshida, Sae Yanagida, Daisuke Saito, Atsushi Kobayashi, Masako Kato
    Analytical sciences : the international journal of the Japan Society for Analytical Chemistry 36 (1) 67 - 73 2020/01/10 [Refereed][Not invited]
     
    The electrochemical and photophysical properties of a heteroleptic Cu(I) complex bearing an aliphatic α-diimine ligand, [Cu(dab)(xantphos)]+ (Cu-dab; dab = N,N'-diphenyl-2,3-dimethyl-1,4-diazabutadiene, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), were evaluated together with those of complexes [Cu(dmp)(xantphos)]+ (Cu-dmp; dmp = 2,9-dimethyl-1,10-phenanthroline), [Cu(dmbpy)(xantphos)]+ (Cu-dmbpy; dmbpy = 5,5'-dimethyl-2,2'-bipyridine), and [Cu(bq)(xantphos)]+ (Cu-bq; bq = 2,2'-biquinoline), bearing aromatic diimine ligands. Cu-dab exhibited a two-step ligand-centered redox behavior, where the first wave corresponded to an electrochemically reversible one-electron reduction process. Although Cu(I)-aromatic diimine complexes Cu-dmp, Cu-dmbpy, and Cu-bq exhibited obvious luminescence from the metal-to-ligand charge transfer (MLCT) excited state, Cu-dab did not show any luminescence. Computational studies indicated that this non-luminescent property was caused by the large structural relaxation of Cu-dab during photoexcitation.
  • Sae Kondo, Nobutaka Yoshimura, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 49 (46) 16946 - 16953 1477-9226 2020 [Refereed][Not invited]
     

    The spin-coated thin film fabricated with a simple Cu(i) complex exhibits luminescence colour changes in response to N-heteroaromatic vapours reversibly.

  • Mari Kimura, Masaki Yoshida, Sho Fujii, Atsushi Miura, Kosei Ueno, Yasuhiro Shigeta, Atsushi Kobayashi, Masako Kato
    Chemical Communications 56 (85) 12989 - 12992 1359-7345 2020 [Refereed][Not invited]
     

    A Pt(ii)-based luminescent porous molecular crystal was selectively crystallised at the liquid–liquid interface, allowing control of porosity and luminescence.

  • Nobutaka Yoshimura, Atsushi Kobayashi, Wataru Genno, Takashi Okubo, Masaki Yoshida, Masako Kato
    Sustainable Energy & Fuels 4 (7) 3450 - 3457 2398-4902 2020 [Refereed][Not invited]
     

    Photocatalytic H2 evolution activity in iodide aqueous solution was improved by increasing the Ru(ii)–dye layer number on the Pt–TiO2 surface.

  • T. Ogawa, W. M. C. Sameera, M. Yoshida, A. Kobayashi, M. Kato
    Chem. Phys. Lett. 739 137-24  2019/12 [Refereed][Not invited]
  • Vapochromic Luminescent Proton Conductors: Switchable Vapochromism and Proton Conduction of Luminescent Pt(II) Complexes with Proton-exchangeable Sites
    A. Kobayashi, S. Imada, Y. Shigeta, Y. Nagao, M. Yoshida, M. Kato
    J. Mater. Chem. C 7 14923 - 14931 2019/10 [Refereed][Not invited]
  • H. Matsukawa, M. Yoshida, T. Tsunenari, S. Nozawa, A. Sato-Tomita, Y. Maegawa, S. Inagaki, A. Kobayashi, M. Kato
    Sci. Rep. 9 (1) 15151 - 15151 2019/10 [Refereed][Not invited]
     
    A hybrid vapoluminescent system exhibiting fast and repeatable response was constructed using periodic mesoporous organosilica with bipyridine moieties (BPy-PMO) and a Pt(II) complex bearing a potentially luminescent 2-phenylpyridinato (ppy) ligand. An intense red luminescence appeared when the Pt(II)-complex immobilised BPy-PMO was exposed to methanol vapour and disappeared on exposure to pyridine vapour. The ON-OFF vapochromic behaviour occurred repeatedly in a methanol/pyridine/heating cycle. Interestingly, a rapid response was achieved in the second cycle and cycles thereafter. Scanning and transmission electron microscopies (SEM/TEM), absorption and emission, and nuclear magnetic resonance spectroscopies, mass spectrometry, and powder X-ray diffraction indicated that methanol vapour induced Si-C cleavage and thus liberated [Pt(ppy)(bpy)]Cl (bpy = 2,2'-bipyridine) from the BPy-PMO framework. Furthermore, the self-assembling properties of the Pt(II) complex resulted in the formation of highly luminescent micro/nanocrystals that were homogeneously dispersed on the porous support. The unique vapoluminescence triggered by the unprecedented protodesilylation on exposure to protic solvent vapour at room temperature is attributable to BPy-PMO being a giant ligand and an effective vapour condenser. Consequently, this hybrid system presents a new strategy for developing sensors using bulk powdery materials.
  • N. Yoshimura, A. Kobayashi, M. Yoshida, M. Kato
    Bull. Chem. Soc. Jpn. 92 (11) 1793 - 1800 2019/10 [Refereed][Not invited]
  • S. Yanagida, M. Yoshida, W. M. C. Sameera, A. Kobayashi, M. Kato
    Bull. Chem. Soc. Jpn. 92 (10) 1684 - 1693 2019/07 [Refereed][Not invited]
  • M. Dosen, Y. Kawada, S. Shibata, K. Tsuge, Y. Sasaki, A. Kobayashi, M. Kato, S. Ishizaka, N. Kitamura
    Inorg. Chem. 58 8419 - 8431 2019/06 [Refereed][Not invited]
  • Y. Shigeta, A. Kobayashi, M. Yoshida, M. Kato
    Inorg. Chem. 58 7385 - 7392 2019/05 [Refereed][Not invited]
  • M. Yoshida, H. Shitama, W. M. C. Sameera, A. Kobayashi, M. Kato
    Chem. Eur. J. 25 7669 - 7678 2019/03 [Refereed][Not invited]
  • A. Kobayashi, M. Fujii, Y. Shigeta, M. Yoshida, M. Kato
    Inorg. Chem. 58 4456 - 4464 2019/03 [Refereed][Not invited]
  • A. Kobayashi, K. Shimizu, A. Watanabe, Y. Nagao, N. Yoshimura, M. Yoshida, M. Kato
    Inorg. Chem. 58 2413 - 2421 2019/01 [Refereed][Not invited]
  • Y. Shigeta, A. Kobayashi, M. Yoshida, M. Kato
    Eur. J. Inorg. Chem. 1011 - 1017 2019/01 [Refereed][Not invited]
  • T. Ogawa, W. M. C. Sameera, D. Saito, M. Yoshida, A. Kobayashi, M. Kato
    Inorg. Chem. 57 14086 - 14096 2018/10 [Refereed][Not invited]
  • H. Otsuka, A. Kobayashi, M. Yoshida, M. Kato
    J. Photochem. Photobiol. A: Chem. 369 189 - 194 1010-6030 2018/10 [Refereed][Not invited]
  • Anionic platinum(II) complexes bearing N-heterocyclic carbenes in a discrete space: Intense luminescence and colour variation based on regioselective π-extension
    T. Ogawa, W. M. C. Sameera, M. Yoshida, A. Kobayashi, M. Kato
    Inorg. Chem. 57 14086 - 14096 2018/10 [Refereed][Not invited]
  • H. Kitano, A. Kobayashi, M. Yoshida, M. Kato
    Sustainable Energy&Fuels 2 2609 - 2615 2018/08 [Refereed][Not invited]
  • A. Kobayashi, Y. Yoshida, M. Yoshida, M. Kato
    Chem. Eur. J. 24 14750 - 14759 2018/07 [Refereed][Not invited]
  • Yasuhiro Shigeta, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    Crystal Growth and Design 18 (6) 3419 - 3427 1528-7505 2018/06/06 [Refereed][Not invited]
     
    A novel Pt(II) diimine complex, [Pt(CN)2(H2dpcpbpy)] (1, H2dpcpbpy = 4,4′-di(p-carboxyphenyl)-2,2′-bipyridine), was synthesized, and its vapochromic behavior was investigated. The yellow amorphous form of 1, 1-Ya, transformed into the porous orange crystalline form, 1-Oc, upon exposure to ethanol vapor. This behavior is similar to that of the previously reported complex, [Pt(CN)2(H2dcphen)] (2, H2dcphen = 4,7-dicarboxy-1,10-phenanthroline). X-ray diffraction study showed that 1-Oc possessed similar but larger porous channels (14.3 × 8.6 Å) compared to the red crystalline form of 2, 2-Rc (6.4 × 6.8 Å). Although the porous structure of 2-Rc was retained after vapor desorption, that of 1-Oc collapsed to form the orange amorphous solid, 1-Oa. However, the orange color was unchanged in this process. The initial color was recovered by grinding 1-Oa and 2-Rc. These vapor-writing and grinding-erasing functions can be applied to both in situ vapor sensing and vapor-history sensing, i.e., sensors that can memorize the existence of previous vapors. A notable difference was observed for humid air sensitivity the orange emission of 1-Oa was largely unaffected upon exposure to humid air, whereas the red emission of 2-Rc was significantly affected. The lesser sensitivity of 1-Oa toward humidity is important for stable vapor-history sensor applications.
  • Panyi Liang, Atsushi Kobayashi, W. M.C. Sameera, Masaki Yoshida, Masako Kato
    Inorganic Chemistry 57 (10) 5929 - 5938 1520-510X 2018/05/21 [Refereed][Not invited]
     
    Luminescent [Cu2I2(pyrpy)2(PR3)2] complexes (pyrpy = 4-pyrrolidinopyridine PR3 = triphenylphosphine (1), tri-m-tolylphosphine (2), tri-p-tolylphosphine (3)) were prepared by solution reactions and a rarely reported solvent-free thermal method. X-ray structure analyses reveal that complexes composed of dinuclear {Cu2I2} cores surrounded by two PR3 and two pyrpy ligands were formed. Although the melting point of pyrpy is the lowest among the organic units used in this study, the temperature required to form the luminescent dinuclear complex, prepared by the thermal synthesis method, depended strongly on the PR3 moiety. Two of the three complexes (1 and 3) were successfully prepared by the solvent-free thermal method. Complexes 1-3 exhibited blue emissions at around 450 nm with moderately high quantum yields (φ) of 0.24, 0.31, and 0.51, respectively. Emission-lifetime measurements and time-dependent density functional theory (TD-DFT) calculations suggest thermally activated delayed fluorescence (TADF) in each complex. This solvent-free thermal synthesis of TADF materials represents a promising method for the preparation of luminescent layers directly onto substrates of thin-layer electronic devices, such as organic light-emitting diodes.
  • A. Kobayashi, S. Watanabe, M. Yoshida, M. Kato
    ACS Appl. Energy Mater. 1 2882  2018/05 [Refereed][Not invited]
  • Masaki Yoshida, Kento Saito, Hiroki Matsukawa, Sae Yanagida, Masanori Ebina, Yoshifumi Maegawa, Shinji Inagaki, Atsushi Kobayashi, Masako Kato
    Journal of Photochemistry and Photobiology A: Chemistry 358 334 - 344 1010-6030 2018/05/01 [Refereed][Not invited]
     
    Pt(II) complexes have been immobilized on a periodic mesoporous organosilica (PMO) consisting of 2,2′-bipyridine (bpy) units bridged by siloxane bonds (BPy-PMO). Although these Pt(II) complexes are luminescent in their discrete molecular states, the luminescence properties of the immobilized complexes largely depend on the origin of the emission luminescence is quenched when the emission originates from the 3ππ* excited state of bipyridine due to the coupling of the C–H bending vibration of the bpy and the Si-O stretching vibration of the siloxane framework, while luminescence is maintained when the 3ππ* excited state of bipyridine is not the lowest excited state. Although the simple coexistence of Pt(0) nanoparticles and Pt(II) complexes did not catalyze water reduction even in the presence of an electron relay, photocatalytic water reduction is observed when Pt(0)/Pt(II)-co-immobilized BPy-PMOs are used. This result clearly demonstrates the importance of the integration of photosensitizers and catalysts on the PMO for enhancing intermolecular electron-transfer processes.
  • Tomohiro Ogawa, W. M.C. Sameera, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 47 (16) 5589 - 5594 1477-9234 2018 [Refereed][Not invited]
     
    Luminescent ionic liquids, based on anionic Pt(ii) complexes, were developed. Depending on the cyclometalating ligands used, they exhibit thermochromic luminescence with different colours. The chromic properties in the flexible liquid and glass states emerge through the self-assembling character of the square-planar Pt(ii) complexes.
  • Atsushi Kobayashi, Naotaka Yamamoto, Yasuhiro Shigeta, Masaki Yoshida, Masako Kato
    Dalton Transactions 47 (5) 1548 - 1556 1477-9234 2018 [Refereed][Not invited]
     
    A luminescent Pt(ii) complex [Pt(CN)2(H4dpbpy)] (1P H4dpbpy = 2,2′-bipyridine-4,4′-diphosphonic acid) bearing a phosphonic-acid-functionalized bipyridine ligand was successfully synthesized and its unique two-way vapochromic behaviour investigated. X-ray structure analyses of both the anhydrous 1P and penta-hydrated 1P·5H2O phases clearly reveal the activation of intermolecular Pt⋯Pt interactions through the adsorption of water vapour. Emission spectroscopy reveals that the penta-hydrated 1P·5H2O complex exhibits an orange emission at 585 nm that shifts in two directions, to a blue-green emission at 469 nm by drying at 100 °C or to a red emission at 701 nm by drying under vacuum at room temperature. Thermogravimetric analyses and powder X-ray diffraction studies clearly reveal that anhydrous 1P, with negligible intermolecular Pt⋯Pt interactions, is formed by drying at 100 °C whereas the monohydrate 1P·H2O phase, with effective Pt⋯Pt interactions, is formed by drying under vacuum.
  • Panyi Liang, Atsushi Kobayashi, Tatsuya Hasegawa, Masaki Yoshida, Masako Kato
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (44) 5134 - 5142 1434-1948 2017/12 [Refereed][Not invited]
     
    Mononuclear Cu-I iodide complexes, [CuI(PPh3)(2)L] {PPh3 = triphenylphosphine; L = 4-aminoisoquinoline (4-aiq) (2), 5-aminoisoquinoline (5-aiq) (3), and 5-nitroisoquinoline (niq) (4)}, were prepared by three different methods: normally used reactions in the solution state, mechanochemical synthesis, and newly developed solvent-free thermal synthesis. Although no solvent was required for the mechanochemical synthesis of the parent complex [CuI(PPh3)(2)(iq)] (1; iq = isoquinoline), a minimal amount of assisting solvent (PhCN) was required for the mechanochemical syntheses of the three functionalized isoquinoline complexes. The amino-functionalized isoquinoline complexes were successfully synthesized by heating the ground mixture of three types of starting materials at ca. 100 degrees C, where the PPh3 ligand melted to promote complex formation by acting as the ligand and the solvent. The emission properties strongly depend on the L ligand: Complexes 2 and 3 showed vibronic emission spectra originating from the (3)* excited state localized on the L ligand, whereas complex 4 did not show any emission in the visible region.
  • Atsushi Kobayashi, Shuhei Watanabe, Masanori Ebina, Masaki Yoshida, Masako Kato
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 347 9 - 16 1010-6030 2017/10 [Refereed][Not invited]
     
    Two heteroleptic Ir(III) complexes bearing two diethyl phosphonate groups, [Ir(ppy-PE)(2)(bpy)(PF6) and [Ir(ppy)(2)(bpy-dPE)](PF6) (1pPE and 1bPE; Hppy = 2-phenylpyridine, Hppy-PE =4-(diethylphosphonomethyl)-2-phenylpyridine, bpy = 2,2'-bipyridine, bpy-dPE=4,4'-bis(diethylphosphonomethyl)-2,2'bipyridine), were successfully synthesized, and their photophysical properties were investigated by UV-vis absorption and emission spectroscopic and electrochemical measurements. Both IpPE and IbPE complexes exhibited similar IJV-vis absorption and emission spectra and cyclic voltammograms as those of nonmodified complex [Ir(ppy)2(bpy)](PF6) (1), indicating the suitability for photocatalytic H-2 evolution reaction. (MLCT)-M-3 emissions of both IbPE and 1pPE were quenched by electron transfer from triethylamine (TEA) sacrificial electron donor, but the quenching rate of IpPE was lower than that of nonmodified complex 1 and 1bPE. In contrast, the quenching rate of IbPE by an electron-accepting [Co (bpy)(3)](2+) moiety was slightly lower than 1 or IpPE. These results suggest that the two diethylphosphonate ester groups regulate the direction of photoinduced electron-transfer reaction at the (MLCT)-M-3 excited state due to their steric bulkiness. In addition, the photocatalytic activity for H-2 evolution in the presence of K2PtC14 precatalyst clearly showed remarkably extended longevity for both IpPE and 1bPE compared to that of 1, indicating that the two diethyl phosphonate groups attached on IpPE and IbPE also play an important role in the extended longevity of H-2-evolution activity of in-situ generated Pt colloidal catalyst from K2PtC14. The deactivation pathway of IpPE and 1bPE during photo H-2 evolution reaction is mainly due to the substitution of the bpy-type ligand by CH3CN solvent of the one electron reduced Ir(II) species like the non-substituted complex 1. (C) 2017 Elsevier B.V. All rights reserved.
  • Sogo Furugori, Atsushi Kobayashi, Ayako Watanabe, Masaki Yoshida, Masako Kato
    ACS Omega 2 (7) 3901 - 3912 2470-1343 2017/07/31 [Refereed][Not invited]
     
    To improve the efficiency of photoinduced charge separation on the surface of dye-sensitized TiO2 nanoparticles, we synthesized the Ru(II)-photosensitizer-immobilized, Pt-cocatalyst-loaded TiO2 nanoparticles RuCP2@Pt-TiO2, RuCP2-Zr-RuP6@Pt-TiO2, and RuCP2-Zr-RuP4-Zr-RuP6@Pt-TiO2 (RuCP2 = [Ru(bpy)2(mpbpy)]2-, RuP4 = [Ru(bpy)(pbpy)2]6-, RuP6 = [Ru(pbpy)3]10-, H4mpbpy = 2,2′-bipyridine-4,4′-bis(methanephosphonic acid), and H4pbpy = 2,2′-bipyridine-4,4′-bis(phosphonic acid)) using phosphonate linkers with bridging Zr4+ ions. X-ray fluorescence and ultraviolet-visible absorption spectra revealed that a layered molecular structure composed of Ru(II) photosensitizers and Zr4+ ions (i.e., RuCP2-Zr-RuP6 and RuCP2-Zr-RuP4-Zr-RuP6) was successfully formed on the surface of Pt-TiO2 nanoparticles, which increased the surface coverage from 0.113 nmol/cm2 for singly layered RuCP2@Pt-TiO2 to 0.330 nmol/cm2 for triply layered RuCP2-Zr-RuP4-Zr-RuP6@Pt-TiO2. The photocatalytic H2 evolution activity of the doubly layered RuCP2-Zr-RuP6@Pt-TiO2 was three times higher than that of the singly layered RuCP2@Pt-TiO2, whereas the activity of triply layered RuCP2-Zr-RuP4-Zr-RuP6@Pt-TiO2 was less than half of that for RuCP2@Pt-TiO2. The photosensitizing efficiencies of these Ru(II)-photosensitizer-immobilized nanoparticles for the O2 evolution reaction catalyzed by the Co(II)-containing Prussian blue analogue [CoII(H2O)2]1.31[{CoIII(CN)6}0.63{PtII(CN)4}0.37] decreased as the number of Ru(II)-photosensitizing layers increased. Thus, crucial aspects of the energy- and electron-transfer mechanism for the photocatalytic H2 and O2 evolution reactions involve not only the Ru(II)-complex-TiO2 interface but also the multilayered structure of the Ru(II)-photosensitizers on the Pt-TiO2 surface.
  • Masanori Wakizaka, Takeshi Matsumoto, Atsushi Kobayashi, Masako Kato, Ho-Chol Chang
    CHEMISTRY-A EUROPEAN JOURNAL 23 (41) 9919 - 9925 0947-6539 2017/07 [Refereed][Not invited]
     
    The design of redox-active metal-organic frameworks and coordination networks (CNs), which exhibit metaland/or ligand-centered redox activity, has recently received increased attention. In this study, the redox-active metalloligand (RML) [Me4N](3)fac-[CrIII(mp)(3)] (1) (mp= 2-mercaptophenolato) was synthesized and characterized by single-crystal X-ray diffraction analysis, and its reversible ligand-centered one-electron oxidation was examined by cyclic voltammetry and spectroelectrochemical measurements. Since complex 1 contains O/S coordination sites in three directions, complexation with K+ ions led to the formation of the two-dimensional honeycomb sheet-structured [K(3)fac{ Cr-III(mp)(3)}(H2O)(6)] n (2.6H(2)O), which is the first example of a redox-active CN constructed from a RML with o-disubstituted benzene ligands. Herein, we unambiguously demonstrate the ligand-centered redox activity of the RML within the CN 2.6H(2)O in the solid state.
  • Tatsuya Hasegawa, Atsushi Kobayashi, Hiroki Ohara, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 56 (9) 4928 - 4936 0020-1669 2017/05 [Refereed][Not invited]
     
    We have synthesized two luminescent mononuclear Cu(I) complexes, [Cu(PPh(2)Tol)(THF)(4Mepy)(2)](BF4) (1) and [Cu-(PPh(2)Tol) (4Mepy)(3)] (BF4) (2) (PPh(2)Tol = diphenyl(o-tolyl)phosphine, 4Mepy = 4-methylpyridine, THF = tetrahydrofuran), and investigated their crystal structures, luminescence properties, and vapor-induced ligand exchange reactions in the solid state. Both coordination complexes are tetrahedral, but one of the three 4Mepy ligands of complex 2 is replaced by a THF solvent molecule in complex 1. In contrast to the very weak blue emission of the THF-bound complex 1 (wavelength of emission maximum (lambda(em)) = 457 nm, emission quantum yield (Phi(em)) = 0.02) in the solid state at room temperature, a very bright blue-green emission was observed for 2 (lambda(em) = 484 rim, Phi(em) = 0.63), suggesting a contribution of the THF ligand to nonradiative deactivation. Time dependent density functional theory calculations and emission lifetime measurements suggest that the room-temperature emissions of the complexes are due to thermally activated delayed fluorescence from the metal-to-ligand charge transfer excited state. Interestingly, by exposing the solid sample of THF-bound 1 to 4Mepy vapor, the emission intensity drastically increased and the emission color changed from blue to blue-green. Powder X-ray diffraction measurements revealed that the emission change of 1 is due to the vapor-induced ligand exchange of THF for 4Mepy, forming the strongly emissive complex 2. Further emission tuning was achieved by exposing 1 to pyrimidine or pyrazine vapors, forming green (lambda(em) = 510 nm) or orange (lambda(em) = 618 rim) emissive complexes, respectively. These results suggest that the vapor-induced ligand exchange is a promising method to control the emission color of luminescent Cu(I) complexes.
  • Atsushi Kobayashi, Ryuya Arata, Tomohiro Ogawa, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 56 (8) 4280 - 4288 0020-1669 2017/04 [Refereed][Not invited]
     
    Two luminescent pyrazine-bridged dinuclear Cu(I) complexes, namely, [{Cu(PPh3)(2)(H2O)}(mu-MeOpyz){ Cu (PPh3)(2)(CH3CN)}] (BF4)(2) and [{Cu (PPh3)(2)(H2O)} (mu-MeOpyz){Cu(PPh3)(2)(H2O)}] (BF4)(2)(H2O-Cu(2-)AN PPh3 = triphenylphosphine, MeOpyz = 2-methoxypyrazine), were successfully synthesized and characterized by single-crystal X-ray diffraction and luminescence measurements. X-ray analysis revealed that the water molecules are coordinated to both Cu(I) ions to form almost the same P2N1O1 coordination structure in H2O-Cu-2-H2O, whereas one of the two Cu ions in H2O-Cu-2-AN was coordinated by acetonitrile instead of water to form a different P2N2 coordination environment. The asymmetric H2O-Cu-2-AN exhibits very bright yellow-green emission with a high emission quantum yield (lambda(em) = 550 nm, Phi= 0.70) at room temperature in the solid state in spite of the coordination of water molecule, which usually tends to deactivate the emissive state through O H vibration. The intense emission at room temperature is a result of thermally activated delayed fluorescence, and the remarkable temperature dependence of emission lifetimes indicates the existence of unique multiple emission states for the asymmetric dinuclear complex. In contrast, the emission of H2O-Cu-2-H2O was observed at longer wavelengths with remarkably a lower quantum yield (lambda(em) = 580 nm, Phi = 0.05). Time-dependent density functional theory calculations suggested that the emission could result from the metal-to-ligand charge-transfer transition state. However, it could be rapidly deactivated by the structural distortion around the Cu ion with a less-bulky coordination environment in H2O-Cu-2-H2O.
  • Hiroki Ohara, Tomohiro Ogawa, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    DALTON TRANSACTIONS 46 (11) 3755 - 3760 1477-9226 2017/03 [Refereed][Not invited]
     
    [CuCl(PPh3)(2)(4-Mepy)] (PPh3 = triphenylphosphine, 4-Mepy = 4-methylpyridine), a highly blue-luminescent mononuclear copper(I) complex, shows reversible emission colour change ranging from blue-green to red by vapour exposure to N-heteroaromatics, such as pyridine, pyrimidine, and 2-methylpyrazine. The remarkable colour changes occur due the ligand exchange reaction between the solid and gas. Such ligand exchange reactions would be applicable to various vapours with coordination ability and be useful for the sensing of such volatile organic compounds as well as a new convenient methodology for the preparation of luminescent complexes.
  • Ayako Watanabe, Atsushi Kobayashi, Erika Saitoh, Yuki Nagao, Shun Omagari, Takayuki Nakanishi, Yasuchika Hasegawa, W. M. C. Sameera, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 56 (5) 3005 - 3013 0020-1669 2017/03 [Refereed][Not invited]
     
    We synthesized two new porous coordination polymers (PCPs) {Ln(7)(OH)(5)[Ru(dcbpy)(3)](4).4nH(2)O} (Ln(7)-Ru-4; Ln = Ce, Nd) composed of the luminescent ruthenium (II) metalloligand [Ru(4,4'-dcbpy)(3)](4-) ([4Ru]; 4,4'-dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and lanthanide ions Ln(3+) (Ln = Ce, Nd). These two PCPs Ln7-Ru4 are isomorphous with the previously reported PCP La-7-Ru-4, and the lattice constants (a, c, and unit cell volume V) changed systematically according to the lanthanide contraction. All three Ln(7)-Ru-4 compounds have OW anion containing porous structures and a large number of hydrate water molecules within the pores, resulting in moderate ion conductivities (10(-6)-10(-7) S cm(-1)) at 90% relative humidity Wavelength / nm (RH) and 298 K. In contrast, the structural transformation of Ln(7)-Ru-4 associated with water-vapor adsorption/desorption strongly depends on the lanthanide ion; the Ln(7)-Ru-4 compounds with larger Ln(3+) ions recover the original porous structure at lower relative humidities (RH). A similar trend was observed for the ion conduction activation energy, suggesting that the bridging Ln(3+) ion plays an important role in the formation of the ion conductive pathways. La-7-Ru-4 and Ce-7-Ru-4 exhibit vapochromic luminescence associated with water vapor adsorption/desorption, arising from the (MLCT)-M-3 emission of [4Ru]. This vapochromic behavior is also affected by the replacement of the Ln3(+) ion; the vapochromic shift of Ce-7-Ru-4 was observed at RH values (near 100% RH) higher than that of La-7-Ru-4. (MLCT)-M-3 emissions of the [4Ru] metalloligand in Nd-7-Ru-4 were barely observable in the visible region, but sharp emission bands characteristic of 4f-4f transitions of the Nd3+ ion were observed in the near -infrared (NIR) region (arising from the (MLCT)-M-1 transition of [4Ru]), suggesting the transfer of energy from the [4Ru] (MLCT)-M-3 excited state to the 4f-4f transition state of the Nd3+ ions.
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie Wiley 129 (9) 2556  2017/02 [Refereed][Not invited]
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie Wiley 129 (9) 2385  2017/02 [Refereed][Not invited]
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    Angewandte Chemie International Edition Wiley 56 (9) 2514  2017/02 [Refereed][Not invited]
  • Paramita Kar, Masaki Yoshida, Yasuhiro Shigeta, Akane Usui, Atsushi Kobayashi, Takaaki Minamidate, Noriaki Matsunaga, Masako Kato
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 56 (9) 2345 - 2349 1433-7851 2017/02 [Refereed][Not invited]
     
    A highly methanol-selective vapochromic response has been realized in a Ni-II-quinonoid complex, [Ni(HLMe)(2)] (H2LMe=4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate) which exhibits a reversible structural transformation including a coordination geometrical change between the square-planar and octahedral structure by the selective uptake of methanol vapor. This was accompanied by a remarkable color change between purple and orange, as well as temperature-robust spin-state switching in the solid state under ambient conditions. It is remarkable that the properties are derived by the fine structural modification of the quinonoid ligand such as methyl or ethyl analogues. Such a system has high potential for applications in memory devices as well as chemical sensors and smart responsive materials.
  • Kana Sawaguchi-Sato, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 335 182 - 189 1010-6030 2017/02 [Refereed][Not invited]
     
    We have synthesized CdSe (cadmium selenide) quantum dots (QDs) with three different surface-passivating ligands: 3-mercaptopropionic acid (MPA), 4-mercaptobenzoic acid (MBA), and 4-mercaptomethylbenzoic acid (MMBA). Although all the QDs possessed similar diameters and thiol-based ligands, the MPA-passivated QD exhibited the highest photocatalytic H2 evolution activity in the presence of a polyvinylpyrrolidone-protected Pt (Pt-PVP) colloidal catalyst. Moreover, dynamic light scattering and zeta potential measurements clearly indicated a significant difference in their dispersibility in water. Thus, CdSe-MPA, having the sterically smallest thiol ligand, displayed the largest negative zeta potential and the best dispersibility owing to the presence of negatively charged carboxylate groups on the QD surface. This was sufficient for the QD to disperse as single particles. In contrast, the bulkier MMBA ligand covered the surface of the CdSe QD with a smaller number of ligand moieties, resulting in a smaller zeta potential and the formation of large aggregates (similar to 126 nm in diameter). In the presence of a Pt-PVP colloid as the hydrogen evolution catalyst, CdSe-MPA formed large aggregates (similar to 1.6 mu m in diameter) with the Pt-PVP colloid by electrostatic interactions. Conversely, CdSe-MMBA did not form such large aggregates with the Pt-PVP colloid. Since the emission of the CdSe QD was effectively quenched in the presence of the Pt-PVP colloid, we concluded that CdSe-MPA exhibits the highest photocatalytic hydrogen evolution activity with the Pt-PVP colloidal catalyst because the electron transfer efficiency from the photosensitizing CdSe QD to the Pt-PVP colloidal catalyst is enhanced by the formation of aggregates. (C) 2016 Elsevier B.V. All rights reserved.
  • Atsushi Kobayashi, Masako Kato
    CHEMISTRY LETTERS 46 (2) 154 - 162 0366-7022 2017/02 [Refereed][Invited]
     
    Extensive studies of luminescent copper(I) complexes were conducted, revealing that some of them exhibit interesting chromic luminescence in response to external stimuli such as temperature, vapor, light, and mechanical force. In this review, recent progress in the field of luminescent chromic copper(I) complexes is discussed. Tetranuclear copper(I) clusters with a cubane-type {Cu4I4} core are the most prominent group, which shows thermochromic, vapochromic, and mechanochromic luminescence, and their responsiveness to external stimuli greatly depends on coordinating organic ligands. Coordination polymerization of copper(I) cluster cores using organic linkers provides new luminescent thermochromic and vapochromic materials with behavior strongly dependent on the flexibility of the framework. The diversity of the cluster core structure and the lability to the ligand exchange are also useful to derive unique behaviors of photochromic and vapochromic response. In addition to such stimuli-responsive luminescence, the mechanochemical synthesis of highly luminescent copper(I) complexes is introduced, since the phenomenon is closely related to the mechanochromic luminescence and this approach allows the preparation of an emission layer directly on the substrate.
  • Erika Saitoh, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    CRYSTAL GROWTH & DESIGN 16 (12) 7051 - 7057 1528-7483 2016/12 [Refereed][Not invited]
     
    In this study, we examined the reduction in crystal size of the porous coordination polymers (PCPs) {Sr-4(H2O)(9)][4Ru](2)center dot 9H(2)O]} (Sr-2[4Ru]) and [Mg(H2O)(6)]-{[Mg, (H2O)(3)[4Ru]center dot 4H(2)O} (Mg-2[4Ru]) composed of a luminescent metalloligand [Ru(4,4'-dcbpy)](4-) ([4Ru]; 4,4'= 4,4'-dicarboxy-2,2'-bipyridine) using a coordination modulation method. Scanning electron microscopy measurements clearly show that the sizes of crystals of Sr-2[4Ru] and Mg-2[4Ru] were successfully reduced to the mesoscale (about 500 nm width and 10 nm thickness for Sr-2[4Ru] (abbreviated as m-Sr-2[4Ru]) and about 1 mu m width and 30 nm thickness for Mg-2[4Ru] (abbreviated as m-Mg-2[4Ru])) using lauric acid as a coordination modulator. Interestingly, the nanocrystals of m-Sr-2[4Ru] formed flower-like aggregates with diameters of 1 mu m, whereas flower-like aggregates were not formed in m-Mg-2[4Ru]. Water vapor adsorption isotherms of these nanocrystals suggest that the water adsorption behavior of m-Sr-2[4Ru], which has a three-dimensional lattice structure containing small pores, is significantly different from that of the bulk Sr-2[4Ru] crystal, as shown by the vapor adsorption isotherm. In contrast, m-Mg-2[4Ru], which has a two-dimensional sheet structure, had an adsorption isotherm very similar to that of the bulk sample. These contrasting results suggest that the dimensionality of the coordination framework is an important factor for the guest adsorption behavior of nanocrystalline PCPs.
  • Kazuya Otsubo, Tomohiko Suto, Atsushi Kobayashi, Ryuichi Ikeda, Masato Hedo, Yoshiya Uwatoko, Hiroshi Kitagawa
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2016 (27) 4402 - 4407 1434-1948 2016/09 [Refereed][Not invited]
     
    One-dimensional (1D) halogen-bridged mixed-valent binuclear metal compounds, the so-called MMX chains, are well known as highly conductive coordination polymers because of the high electronic flexibility within their metal-dimer unit. Herein, we report on the conducting behavior and electronic state of a highly conductive MMX-chain compound, Pt-2(dta)(4)I (dta: CH3CS2-) under high pressure. Electrical resistivity measurements showed that this compound exhibits semiconducting behavior in a broad pressure region, despite metallic conduction under ambient pressure. Raman spectra provided clear information about the semiconducting state of this compound under pressure, which was also supported by X-ray diffraction (XRD) studies. Moreover, we successfully clarified the pressure temperature phase diagram of this material. By comparing with an analogous material, we found that the difference in the alkyl chain length of the terminal ligand plays an important role for the conducting behavior and the electronic phase under pressure.
  • Kotaro Shimada, Atsushi Kobayashi, Yuriko Ono, Hiroki Ohara, Tatsuya Hasegawa, Tetsuya Taketsugu, Eri Sakuda, Soichiro Akagi, Noboru Kitamura, Masako Kato
    JOURNAL OF PHYSICAL CHEMISTRY C 120 (29) 16002 - 16011 1932-7447 2016/07 [Refereed][Not invited]
     
    Thiolato-bridged dinuclear, tetranuclear, and hexanuclear Cu(I) complexes [Cu-2(P boolean AND S)(2)(PPh3)(2)], [Cu-4(P boolean AND S)(4)(CH3CN)(2)], and [Cu-6(P boolean AND S)(6)] (abbreviated as Cu-2, Cu-4, and Cu-6, respectively, P boolean AND S = 2-(diphenylphosphino)benzenethiolate, PPh3 = triphenylphosphine) were synthesized and characterized by elemental analyses and single-crystal X-ray diffraction measurements. These complexes had {Cu2S2}, {Cu4S4}, and {Cu6S6} cluster cores and exhibited strong luminescence at room temperature in solid states. Different luminescence properties were observed depending on the core structure. Cu-2, Cu-4, and Cu-6 exhibited blue-green (lambda(max) = 482 nm, Phi(em) = 0.52), green (lambda(max) = 526 nm, Phi(em) = 0.19), and yellow (lambda(max) = 553 nm, Phi(em) = 0.49) luminescence, respectively, at 298 K in the solid state; among them, only Cu6 showed luminescence thermochromism. Different radiative rate constants at room temperature and 78 K derived from the emission lifetimes and quantum yields indicate that the luminescence from Cu-2 and Cu-4 at room temperature originated from thermally activated delayed fluorescence (TADF), whereas the luminescence at low temperatures was attributed to the phosphorescence. The temperature dependence of the emission lifetimes was successfully analyzed by the singlettriplet two-state model with an energy difference (Delta ES1-T1) of 547 and 775 cm(-1) for Cu-2 and Cu-4, respectively. Based on the time-dependent density-functional theory calculations, the origin of the luminescence for Cu-2 and Cu-4 was attributed to the charge transfer from the cluster core to the ligand. Moreover, the small values of Delta ES1-T1 for Cu-2 and Cu-4 were supported by the excited state calculations. On the other hand, the emission origin of Cu-6 was attributed to the phosphorescence from the triplet cluster-centered (3CC) excited state in which the electron is located on a bonding in-phase orbital constructed from the 4s/4p orbitals of the Cu atoms because only Cu6 contains trigonal-planar Cu(I) ions in the cluster.
  • Atsushi Kobayashi, Sogo Furugori, Masaki Yoshida, Masako Kato
    CHEMISTRY LETTERS 45 (6) 619 - 621 0366-7022 2016/06 [Refereed][Not invited]
     
    We synthesized a novel tris(bipyridyl)Ru(II) complex with sulfonic acid groups, [Ru(dSbpy)(bpy)(2)] (RuCS2; H(2)dSbpy: 2,2'-bipyridine-4,4'-bis(methanesulfonic acid)). The photosensitizing efficiency of water oxidation in the presence of a Na2S2O8 sacrificial electron acceptor was higher than that of the widely used phosphonic acid analog, [Ru(H(4)dPbpy)(bpy)(2)]Cl-2 (RuCP2; H(4)dPbpy: 2,2'-bipyridine-4,4'-bis(methanephosphonic acid)). The photosensitizing efficiency of RuCP2 for water oxidation was remarkably enhanced by immobilization onto semiconducting TiO2 nanoparticles.
  • Yuka Okano, Hiroki Ohara, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 55 (11) 5227 - 5236 0020-1669 2016/06 [Refereed][Not invited]
     
    We have newly synthesized two solution-stable luminescent dinuclear copper(I) complexes, [Cu-2(mu-I)(2)(dpppy)(2)] (Cu-py) and [Cu-2(mu-I)(2)(dpppyz)(2)] (Cu-pyz), where dpppy = 2,3-bis(diphenylphosphino)pyridine and dpppyz = 2,3-bis(diphenylphosphino)pyrazine, using chelating diphosphine ligands composed of N-heteroaromatic rings. X-ray analysis clearly indicates that the molecular structures of Cu-py and Cu-pyz are almost identical with that of the parent complex, [Cu-2(mu-I)(2)(dppb)(2)] [Cu-bz; dppb = 2,3-bis(diphenylphosphino)benzene]. Complexes Cu-py and Cu-pyz exhibit luminescence [emission quantum yield (Phi(em)) = 0.48 and 0.02, respectively] in the solid state at 298 K. A wide emission color tuning, from 497 to 638 nm (energy = 0.55 eV, with an emission color ranging from green to reddish-orange), was achieved in the solid state by the introduction of pyridinic N atoms into the bridging phenyl group between the two diphenylphosphine groups. Density functional theory calculations suggest that the emission could originate from the effective combination of the metal-to-ligand charge-transfer excited state with the halide-to-ligand charge-transfer excited state. Thus, the emission color change is due to stabilization of the pi* levels of the central aryl group in the diphosphine ligand. Furthermore, these copper(I) complexes exhibit thermally activated delayed fluorescence at 298 K because of the small singlet-triplet energy difference (Delta E = 523 and 564 cm(-1) for Cu-py and Cu-pyz, respectively). The stability of these complexes in chloroform, due to the rigid bonds between the diphosphine ligands and the Cu-I ions, enables the preparation of emissive poly(methyl methacrylate) films by the solution-doping technique.
  • Atsushi Kobayashi, Tatsuya Hasegawa, Masald Yoshida, Masako Kato
    INORGANIC CHEMISTRY 55 (5) 1978 - 1985 0020-1669 2016/03 [Refereed][Not invited]
     
    Luminescent dinuclear Cu(I) complexes, [Cu2X2(dpypp)(2)] [Cu-X; X = Cl, Br, I; dpypp = 2,2'(phenylphosphinediyl)dipyridine], were successfully synthesized by a solvent-assisted mechanochemical method. A trace amount of the assisting solvent plays a key role in the mechanochemical synthesis; only two solvents possessing the nitrile group, CH3CN and PhCN, were effective for promoting the formation of dinuclear Cu-X. X-ray analysis revealed that the dinuclear structure with no Cu center dot center dot center dot Cu interactions, bridged by two dpypp ligands, was commonly formed in all Cu-X species. These complexes exhibited bright green emission in the solid state at room temperature (phi = 0.23, 0.50, and 0.74; lambda(em) = 528, 518, and 530 nm for Cu-Cl, Cu-Br, and Cu-I, respectively). Emission decay measurement and TD-DFT calculation suggested that the luminescence of Cu-X could be assigned to phosphorescence from the triplet metal-to-ligand charge-transfer ((MLCT)-M-3) excited state, effectively mixed with the halide-to-ligand charge-transfer ((XLCT)-X-3) excited state, at 77 K. The source of emission changed to thermally activated delayed fluorescence (TADF) with the same electronic transition nature at room temperature. In addition, the CH3CN-bound analogue, [Cu-2(CH3CN)(2)(dpypp)(2)](BF4)(2), was successfully mechanochemically converted to Cu-X by grinding with solid KX in the presence of a trace amount of assisting water.
  • Yasuhiro Shigeta, Atsushi Kobayashi, Tadashi Ohba, Masaki Yoshida, Takeshi Matsumoto, Ho-Chol Chang, Masako Kato
    CHEMISTRY-A EUROPEAN JOURNAL 22 (8) 2682 - 2690 0947-6539 2016/02 [Refereed][Not invited]
     
    A novel platinum(II)-diimine complex, [Pt(CN)(2)(H(2)dcphen)] (1; H(2)dcphen=4,7-dicarboxy-1,10- phenanthroline), was synthesized and its vapochromic shape-memory behavior was evaluated. The as-synthesized amorphous purple solid, [Pt(CN)(2)(H(2)dcphen)]2H(2)O (1P), exhibited vapochromic behavior in the presence of alcoholic vapors through transformation to a red, crystalline, porous, vapor-adsorbed form, 1Rvapor. The obtained 1Rvapor complex released the adsorbed vapors upon heating without collapse of the porous structure. The vaporfree, porous 1Ropen could detect water or n-hexane vapor, although these vapors could not induce 1P-to-1Rvapor transformation, and 1Ropen could easily be converted to the initial 1P by manual grinding. These results indicate that 1 is a new shape-memory material that functions through formation and collapse of the porous framework with an emission change upon vapor-adsorption and grinding; this enables it to exhibit vapor history and ON-OFF switching sensing functions.
  • Masaki Yoshida, Naoki Yashiro, Hotaka Shitama, Atsushi Kobayashi, Masako Kato
    CHEMISTRY-A EUROPEAN JOURNAL 22 (2) 491 - 495 0947-6539 2016/01 [Refereed][Not invited]
     
    A redox series of cyclometalated platinum complexes based on a dinuclear motif linked by acetamidato (aam) bridging ligands, [Pt-2(mu-aam)(2)(ppy)(2)] (ppy(-) = 2-phenylpyridinate ion), has been synthesized. The complexes in this series are easily oxidized and reduced by both electrochemical and chemical methods, and this is accompanied by multistep changes in their optical properties, that is, multiple color changes and luminescence. Isolation of the complexes and the structural determination of three oxidation states, +2, +2.33, and +3, have been achieved. The mixed-valent complex, with an average oxidation state of +2.33, forms a trimer based on the dinuclear motif. The mixed-valent complex has a characteristic color owing to intervalence transitions in the platinum chain. In contrast, the divalent complex exhibits strong red phosphorescence originating from a triplet metal-metal-toligand charge transfer ((MMLCT)-M-3) state. This study demonstrates the unique chromic behavior of a redox-active and luminescent platinum complex.
  • Paramita Kar, Masaki Yoshida, Atsushi Kobayashi, Lucie Routaboul, Pierre Braunstein, Masako Kato
    DALTON TRANSACTIONS 45 (36) 14080 - 14088 1477-9226 2016 [Refereed][Not invited]
     
    The stepwise reaction of a zwitterionic ligand, 4-methylamino-6-methyliminio-3-oxocyclohexa-1,4-dien-1-olate (QH(2)) with [Pt-2(mu-Cl)(2)(ppy)(2)] (Hppy = 2-phenylpyridine) afforded a mononuclear complex, [Pt(ppy)(QH)] (1), and a dinuclear complex, [{Pt(ppy)}(2)(mu-Q)] (2). Using [ Pd-2(mu-Cl)(2)(ppy)(2)] in the second step resulted in the formation of a heterodinuclear complex, [{Pt(ppy)}(mu-Q){Pd(ppy)}] (3), which is the first heterodinuclear complex bridged by a quinonoid ligand. Single crystal X-ray diffraction analysis revealed that all three complexes adopted double-decker structures in the crystal. For 1, intermolecular N-H center dot center dot center dot O interactions between uncoordinated N-H and O groups in two adjacent square-planar mononuclear units led to the formation of hydrogen-bonded dimers, which stacked to form a herringbone structure with a double-decker tetranuclear motif. For 2 and 3, dinuclear units bridged by Q(2) formed a double-decker motif similar to that of 1, but a tetranuclear chain in the herringbone pattern was characteristic of the dinuclear complexes. Pt. Pt (or Pt. Pd) distances were more than 3.5 angstrom, twice the van der Waals radii of Pt, suggesting weak electronic metal-metal interactions in the crystal structures. Thus, the different colours observed (brown, purple, and dark green for 1, 2, and 3, respectively) mainly originated from the molecular structures. In fact, the three complexes exhibited colourful solutions of yellow, red, and green. UV-vis absorption spectroscopy and time-dependent density-functional theory (TD-DFT) calculations revealed that colour variations occurred depending on the electronic states composed of metal ions and the quinonoid ligand.
  • Atsushi Kobayashi, Shiori Oizumi, Yasuhiro Shigeta, Masaki Yoshida, Masako Kato
    DALTON TRANSACTIONS 45 (43) 17485 - 17494 1477-9226 2016 [Refereed][Not invited]
     
    We synthesized a carboxy-substituted Pt(II)-terpyridine complex, i.e. [PtCl(Hctpy)] Cl ([1H] Cl; Hctpy = 4'-carboxy-2,2': 6',2''-terpyridine), that shows interesting switchable vapochromic behaviour upon protonation/deprotonation of the carboxy group. The as-synthesized dark-blue amorphous-like solid [1H] Cl center dot 3H(2)O was converted to a yellow crystalline solid, [1H] Cl center dot H2O, upon exposure to various polar organic solvent vapours (e.g., acetonitrile, ethanol, 1-propanol, and dichloromethane), which promote the removal of water molecules. The reaction of [1H] Cl center dot 3H(2)O with aqueous ammonia afforded a deprotonated bright-yellow crystalline complex, i.e. [PtCl(ctpy)]center dot H2O (1 center dot H2O), which exhibits red luminescence with an emission maximum at 622nm. Although the colour of 1 center dot H2O was not affected by exposure to various polar organic solvent vapours, interesting vapochromic luminescence with a remarkable red-shift of the emission maximum from 622 to 652 nm was observed upon exposure to saturated water vapour to form orange crystalline 1 center dot 3.5H(2)O X-ray structural analysis revealed that the planar and neutral complex molecule 1 forms a one-dimensional columnar structure with an intermolecular Pt center dot center dot center dot Pt distance of 3.518(2) angstrom in the orange crystall 1 center dot 3.5H(2)O, while the cationic molecule [1H](+) in the protonated form, [1H] Cl center dot H2O, generates a dimeric structure with an intermolecular Pt center dot center dot center dot Pt distance of 3.439(2) angstrom. This difference suggests that the vapochromic behaviours of the protonated and deprotonated forms could be caused by structural changes induced by water-vapour adsorption/desorption, which affect the intermolecular Pt. Pt distance, thereby changing the energy of the metal-metal-to-ligand charge-transfer (MMLCT) transition. These contrasting results for the protonated and deprotonated complexes clearly indicate that the hydrophilicity of complex 1 is significantly affected by protonation/deprotonation of the carboxy group. In addition, quasi-reversible conversion between [1H] Cl center dot 3H(2)O and 1 center dot H2O was achieved by exposure of the protonated and deprotonated forms to triethylamine and humid hydrochloric acid vapours, respectively.
  • Masaki Yoshida, Show Ueno, Yuka Okano, Akane Usui, Atsushi Kobayashi, Masako Kato
    JOURNAL OF PHOTOCHEMISTRY AND PHOTOBIOLOGY A-CHEMISTRY 313 99 - 106 1010-6030 2015/12 [Refereed][Not invited]
     
    A series of 3d transition-metal complexes bearing o-phenylenediamine (opda) ligands [M(opda)(3)](2+) (M = Mn2+, Co2+, Ni2+, and Zn2+) were systematically synthesized as perchlorate salts and their structures were determined. All the opda complexes exhibited hydrogen-evolving activities under photoirradiation conditions as in the case of previously reported [Fe(opda)(3)](2+), whereas replacement of the opda ligands with other aromatic amine ligands caused a dramatic decrease of hydrogen-evolving activities. These results support a ligand-based reaction mechanism for photochemical hydrogen evolution from [M(opda)(3)](2+), which involves (1)pi pi* excitation of the opda ligand followed by homolytic N-H bond cleavage. In contrast to the non-catalytic reactions, an obvious metal-ion dependency was observed for the catalytic systems including hydroquinone as a proton/electron donor. The results of this work demonstrate a strategy for the design of a molecular photochemical hydrogen-production system under ambient temperature and pressure. (C) 2015 Elsevier B.V. All rights reserved.
  • Ayako Watanabe, Atsushi Kobayashi, Erika Saitoh, Yuki Nagao, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 54 (23) 11058 - 11060 0020-1669 2015/12 [Refereed][Not invited]
     
    We synthesized a new porous coordination polymer {La-1.75(OH)(1.25)[RU(dcbpy)(3)]center dot 16H(2)O} (La-7-[4Ru](4); H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) composed of a luminescent ruthenium(II) metalloligand [Ru(4,4'-dcbpy)(3)](4-) and La3+ cations. X-ray analysis for La-7-[4Ru](4) revealed that the La3+ cations and [4Ru] metalloligands are crystallized in a molar ratio of 7:4 with OH- counteranions and a void fraction of similar to 25.5%. Interestingly, La-7-[4Ru](4) shows a reversible structural transition triggered by water ad/desorption, which affects not only the triplet metal-to-ligand charge-transfer ((MLCT)-M-3) emission energy but also the ion conductivity in the solid state. This correlation suggests that La-7-[4Ru](4) is an interesting material that enables visualization of the ion conductivity via the 3MLCT emission energy.
  • Fumi Kitamura, Kana Sawaguchi, Asami Mori, Shoji Takagi, Takayoshi Suzuki, Atsushi Kobayashi, Masako Kato, Kiyohiko Nakajima
    INORGANIC CHEMISTRY 54 (17) 8436 - 8448 0020-1669 2015/09 [Refereed][Not invited]
     
    We prepared hydrazone palladium(II) complexes of [PdCl2(HLn)] and [PdCl(L-n)] (n = 1-3) by the reaction of [PdCl2(cod)] or [PdCl2(PhCN)(2)] and the hydrazone ligands of HLn {N'-(pyridin-2-ylmethylene)picolinohydrazide (HL1), N'-[1-(pyridin-2-yl)ethylidene]picolinohydrazide (HL2), and N'-[(6-methylpyridin-2-yOmethylene]picolinohydrazide (HL3)}. The structures of the complexes were determined by X-ray analysis. The hydrazone ligands had kappa N(pyl), kappa N(imine) and kappa N(amidate) kappa N(py2) bidentate coordination modes in [PdCl2(HLn] (1, n = 1; 2, n = 2) and in [PdCl2(HL3)] (3), respectively. In contrast, tridentate coordination modes of kappa N(pyl)), kappa N(imine), kappa N(py2) and kappa N(py1), kappa N(amidate), kappa N(py2) were observed in [PdCl(L-n)] (4, n = 1; 5, n = 2) and in [PdCl(L-n)] (6, n = 1; 7, n = 2; 8, n = 3). Thermal conversion of complexes 1-3 to complexes 6-8 proceeded in acetonitrile. Complexes 4 and 5 were obtained from complexes 1 and 2, respectively, in a basic acetonitrile solution under dark conditions. Complex 4 reverted immediately to complex 1 in an acidic acetonitrile solution that included hydrochloric acid. However, under room light, in the basic acetonitrile solution that included trimethylamine, complex 4 converted photochemically to complex 6. The thermochromic or vapochromic structure conversion of these complexes also occurred in the solid state. On heating at 180 degrees C, the color of the crystals of complexes 1, 2, and 3 changed from yellow to orange in the solid state. H-1 NMR and/or UV vis absorption spectroscopy confirmed that the orange complexes 6-8 were produced. The reddish-orange crystals of complexes 4 and 5 were exposed to hydrogen chloride vapor to yield the yellow products of complexes 1 and 2, respectively.
  • Masanori Ebina, Atsushi Kobayashi, Tomohiro Ogawa, Masaki Yoshida, Masako Kato
    INORGANIC CHEMISTRY 54 (18) 8878 - 8880 0020-1669 2015/09 [Refereed][Not invited]
     
    A new luminescent cyclometalated platinum(II) complex containing a carboxyl group, trans-[Pt(pcppy)(pic)] [1-COOH; Hpcppy = 2-(p-carboxyphenyl)pyridine and Hpic = picolinic acid] has been synthesized and characterized. The luminescence behavior of 1-COOH in the solid and solution states is completely different despite the similarity of the luminescence in both states for the nonsubstituted complex, [Pt(ppy)(pic)] (1-H; Hppy = 2-phenylpyridine). Interestingly, 1-COOH exhibits concentration-dependent absorption and emission behavior based on its aggregation in a basic aqueous solution despite the absence of amphiphilic character.
  • Takahiro Hayashi, Atsushi Kobayashi, Hiroki Ohara, Masaki Yoshida, Takeshi Matsumoto, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 54 (18) 8905 - 8913 0020-1669 2015/09 [Refereed][Not invited]
     
    Two luminescent porous coordination polymers (PCPs), i.e., [Cu-2(mu(2)-I)(2)ctpyz](n) and [Cu-4(mu(3)-I)(4)ctpyz](n) (Cu2 and Cu4, respectively; ctpyz = cis-1,3,5-cyclohexanetriyl-2,2',2 ''-tripyrazine), were successfully synthesized and characterized by single-crystal X-ray diffraction and luminescence spectroscopic measurements. Cu2 consists of rhombus-type dinuclear {Cu2I2} cores bridged by ctpyz ligands, while Cu4 is constructed of cubane-type tetranuclear {Cu4I4} cores bridged by ctpyz ligands. The void fraction of Cu4 is estimated to be 48.0%, which is significantly larger than that of Cu2 (19.9%). Under UV irradiation, both PCPs exhibit red luminescence at room temperature in the solid state (lambda(em) values of 660 and 614 nm for Cu2 and Cu4, respectively). Although the phosphorescence of Cu2 does not change upon removal and/or adsorption of EtOH solvent molecules in the porous channels, the solid-state emission maximum of Cu4 red-shifts by 36 run (lambda(em) = 650 nm) upon the removal of the adsorbed benzonitrile (PhCN) molecules from the porous channels (and vice versa). This large difference in the vapochromic behavior of Cu2 and Cu4 is closely related to the framework flexibility. The framework of Cu2 is sufficiently rigid to retain the porous structure without solvated EtOH molecules, whereas the porous structure of Cu4 collapses easily after removal of the adsorbed PhCN molecules to form a nonporous amorphous phase. The original vapor-adsorbed porous structure of Cu4 is regenerated by exposure of the amorphous solid to not only PhCN vapor but also tetrahydrofuran, acetone, ethyl acetate, and N,N-dimethylformamide vapors. The Cu4 structures with the various adsorbed solvents showed almost the same emission maxima as the original PhCN-adsorbed Cu4, except for DMF-adsorbed Cu4, which showed no luminescence probably because of weak coordination of the DMF vapor molecules to the Cu(I) centers of the tetranuclear {Cu4I4} core.
  • Tomohiro Ogawa, Masaki Yoshida, Hiroki Ohara, Atsushi Kobayashi, Masako Kato
    Chemical Communications 51 (69) 13377 - 13380 1364-548X 2015/07/14 [Refereed][Not invited]
     
    An ionic liquid fabricated from an anionic cyclometalated platinum(ii) complex and an imidazolium cation exhibits dual emission from the monomeric and aggregated forms of the platinum complex anions, leading to temperature-dependent color changes of luminescence.
  • Hiroki Ohara, Atsushi Kobayashi, Masako Kato
    COMPTES RENDUS CHIMIE 18 (7) 766 - 775 1631-0748 2015/07 [Refereed][Not invited]
     
    A series of mononuclear Cu(I)-halide complexes, [CuX(PPh3)(2)(L)] (X= CI-, Br-, I-; PPh3 = triphenylphosphine; L = pyridine (py), isoquinoline (iq), 1,6-naphthyridine (nap)), were synthesized. The emission color of [CuX(PPh3)2(L)] varies from blue to red by changing the L ligands and the halide ions, and all the complexes exhibit high emission quantum yields (0.16-0.99) in the crystals. The emission studies revealed that the emissive states of [CuX(PPh3)(2)(L)] differ depending on the L ligand. Complexes [CuX(PPh3)(2)(py)] and [CuX(PPh3)2(nap)] mainly emit from the singlet metal-to-ligand charge transfer mixed with the halide-to-ligand charge transfer ((1)(M + X)LCT) state at room temperature. In contrast, emissions from [CuX(PPh3)(2)(iq)] at room temperature originate from both (3)(M + X)LCT and (3)pi pi* states. These results indicate that N-heterodomatic ligands play an important role in the emission properties of mononuclear Cu(I)-halide complexes. (C) 2015 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.
  • Yasuchika Hasegawa, Nao Sato, Yuichi Hirai, Takayuki Nakanishi, Yuichi Kitagawa, Atsushi Kobayashi, Masako Kato, Tomohiro Seki, Hajime Ito, Koji Fushimi
    JOURNAL OF PHYSICAL CHEMISTRY A 119 (20) 4825 - 4833 1089-5639 2015/05 [Refereed][Not invited]
     
    Enhanced luminescence of a lanthanide complex with dynamic polarization of the excited state and molecular motion is introduced. The luminescent lanthanide complex is composed of one Eu(hfa)(3) (hfa, hexafluoroacetylacetonate) and two phosphine oxide ligands with ruthenocenyl units Rc, [Eu(hfa)(3)(RcPO)(2)] (RcPO = diphenylphosphorylruthenocene). The ruthenocenyl units in the phosphine oxide ligands play an important role of switching for dynamic molecular polarization and motion in liquid media. The oxidation states of the ruthenocenyl unit (Rc(1+)/Rc(1+)) are controlled by potentiostatic polarization. Eu(III) complexes attached with bidentate phosphine oxide ligands containing ruthenocenyl units, [Eu(hfa)(3)(RcBPO)] (RcBPO = 1,1'-bis(diphenylphosphoryl)ruthenocene), and with bidentate phosphine oxide ligands, [Eu(hfa)(3)(BIPHEPO)] (BIPHEPO =1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide), were also prepared as references. The coordination structures and electrochemical properties were analyzed using single crystal X-ray analysis, cyclic voltammetry, and absorption spectroscopy measurements. The luminescence properties were estimated using an optoelectrochemical cell. Under potentiostatic polarization, a significant enhancement of luminescence was successfully observed for [Eu(hfa)(3)(RcPO)(2)], while no spectral change was observed for [Eu(hfa)(3)(RcBPO)]. In this study, the remarkable enhanced luminescence phenomena of Eu(III) complex based on the dynamic molecular motion under potentiostatic polarization have been performed.
  • Atsushi Kobayashi, Yui Suzuki, Tadashi Ohba, Tomohiro Ogawa, Takeshi Matsumoto, Shin-ichiro Noro, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 54 (6) 2522 - 2535 0020-1669 2015/03 [Refereed][Not invited]
     
    A series of flexible porous coordination polymers (PCPs) RE-Co, composed of a Co(III)-metalloligand [Co(dcbpy)(3)](3-) (Co; H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and lanthanide cations (RE3+ = La3+, Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, Tb3+, Er3+), was systematically synthesized. X-ray crystallographic analysis revealed that the six carboxylates at the top of each coordination octahedron of Co(III)-metalloligand were commonly bound to RE3+ cations to form a rock-salt-type porous coordination framework. When RE-Co contains a smaller and heavier RE3+ cation than Nd3+, the RE-Co crystallized in the cubic Fm-3m space group, whereas the other three RE-Co with larger RE3+ crystallized in the lower symmetrical orthorhombic Fddd space group, owing to the asymmetric 10-coordinated bicapped square antiprism structure of the larger RE3+ cation. Powder X-ray diffraction and vapor-adsorption isotherm measurements revealed that all synthesized RE-Co PCPs show reversible amorphous-crystalline transitions, triggered by water-vapor-adsorption/desorption. This transition behavior strongly depends on the kind of RE3+; the transition of orthorhombic RE-Co was hardly observed under exposure to CH3OH vapor, but the RE-Co with smaller cations such as Gd3+ showed the transition under exposure to CH3OH vapors. Further tuning of vapor-adsorption property was examined by doping of Ru(II)-metalloligands, [Ru(dcbpy)(3)](4-), [Ru(dcbpy)(2)Cl-2](4-), [Ru(dcbpy)(tpy)Cl](-), and [Ru(dcbpy)(dctpy)](3-) (abbreviated as RuA, RuB, RuC, and RuD, respectively; tpy = 2,2':6',2?-terpyridine, H2dctpy = 4,4"-dicarboxy-2,2':6',2"-terpyridine), into the Co(III)-metalloligand site of Gd-Co to form the Ru(II)-doped PCP RuX@Gd-Co (X = A, B, C, or D). Three Ru(II)-metalloligands, RuA, RuB, and RuD dopants, were found to be uniformly incorporated into the Gd-Co framework by replacing the original Co(III)-metalloligand, whereas the doping of RuC failed probably because of the less number of coordination sites. In addition, we found that the RuA doping into the Gd-Co PCP had a large effect on vapor-adsorption due to the electrostatic interaction originating from the negatively charged RuA sites in the framework and the charge-compensating Li+ cations in the porous channel.
  • Takeshi Matsumoto, Hirokazu Yano, Masanori Wakizaka, Atsushi Kobayashi, Masako Kato, Ho-Chol Chang
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 88 (1) 74 - 83 0009-2673 2015/01 [Refereed][Not invited]
     
    The reactions of [Mo-2(II)(OAc)(4)] (OAc-: acetato) with catecholato derivatives (R-Cat(2-)), possessing electron-donating t-Bu groups (3,6-DTBCat(2-)) or electron-withdrawing Br groups (Br(4)Cat(2-)), results in the formation of a mononuclear complex [Na(THF)(6)][Mo-V(3,6-DTBCat)(3)] (1) and a dinuclear complex either [Na-6(Br(4)SQ)(2)][Mo-2(IV)(mu-O)(2)-(Br(4)Cat)(4)] or [Na-6(Br(4)Cat)(2)][Mo-2(V)(mu-O)(2)(Br(4)Cat)(4)] (3). Complex 3 has a [Mo(mu-O)(2)Mo] core as part of a dimer of [O=Mo-m(Br(4)Cat)(2)](n-) (m = IV or V, n= 2 or 1) moieties assembled in a head-to-tail arrangement, which has been structurally characterized as the a bis-mu-oxo molybdenum dinuclear complex containing catecholato ligands. The bond distance between the Mo atoms (2.4286(17) angstrom) strongly suggests that a Mo-IV=Mo-IV or Mo-V-Mo-V bonding character exists in 3. Differences in the substituent groups on the catecholato ligand affect not only the product formed but also the reactivity of both complexes. Complex 3 shows O-atom abstraction reactivity with dimethyl sulfoxide (DMSO) and forms dimethyl sulfide (DMS). These results support a high oxophilicity of the Mo center in 3.
  • Masanori Wakizaka, Takeshi Matsumoto, Atsushi Kobayashi, Masako Kato, Ho-Chol Chang
    DALTON TRANSACTIONS 44 (32) 14304 - 14314 1477-9226 2015 [Refereed][Not invited]
     
    The redox-active metalloligand (RML) (Et3NH)(3)[Cr-III(F(4)Cat)(3)] (F(4)Cat = perfluorocatecholato) (1) was synthesized and its interactions with guest metal ions Li+, Mn2+, Fe2+, Co2+, Cu2+, and Zn2+ were examined. Cyclic voltammetry measurements and spectroelectrochemical studies revealed that complex 1 shows three-step ligand-centred one-electron oxidation to consecutively generate [Cr-III(F(4)Cat)(2)(F(4)SQ)](2-) (F(4)SQ = perfluorosemiquinonato), [Cr-III(F(4)Cat)(F(4)SQ)(2)](-), and [Cr-III(F(4)SQ)(3)] at -0.12, 0.23, and 0.53 V vs. Ag/Ag+ in dichloromethane, or at -0.21, 0.08, and 0.50 V in acetonitrile (MeCN), respectively. Titration experiments in MeCN revealed that treatment of 1 with Cu2+ leads to the formation of [Cr-III(F(4)Cat)(2)(F(4)SQ)](2-) and Cu+ via a redox reaction. However, when 1 was treated with Li+, Mn2+, Fe2+, Co2+, and Zn2+, further titration experiments revealed that these metal ions coordinated via the lone pairs on the coordinating oxygen atoms of the F(4)Cat(2-) moieties in a one-to-one ratio, and binding constants of 3.7 (+/- 0.3) x 10(4) (Li+), 1.5 (+/- 0.2) x 10(5) (Mn2+), 2.2 (+/- 0.4) x 10(5) (Fe2+), 1.9 (+/- 0.2) x 10(5) (Co2+), and 3.8 (+/- 0.4) x 10(5) M-1 (Zn2+) were established. Moreover, the oxidation potentials of 1 were positively shifted by 0.08-0.33 V upon addition of guest metal ions. Spectroelectrochemical studies of 1 in the presence of guest metal ions suggested that ligand-centred one- and two-electron oxidation of the RML occurred for Li+, Mn2+, Co2+, and Zn2+, respectively, while guest metal-centred one-electron oxidation was observed for Fe2+. Considering all the aforementioned results, this study demonstrated for the first time the ability of [Cr-III(F(4)Cat)(3)](3-) to act as a RML in solution.
  • Hiroki Ohara, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 43 (46) 17317 - 17323 1477-9234 2014/12/14 [Refereed][Not invited]
     
    Simple mononuclear Cu(i)-halide complexes, [CuX(PPh3)2(4-Mepy)] (X = Cl-, Br-, I- PPh3 = triphenylphosphine 4-Mepy = 4-methylpyridine), were prepared. They exhibit blue light emission, with extremely high photoluminescence quantum yields approaching 100% in the crystals. Emission lifetime analyses and density functional theory calculations revealed that the bright blue light emission at room temperature is mainly delayed fluorescence originating from the singlet metal-to-ligand charge transfer (MLCT) state combined with the halide-to-ligand charge transfer (XLCT) state, (1(M + X)LCT), while that at 77 K is phosphorescence from the 3(M + X)LCT transition state, due to the small singlet-triplet energy differences (ΔE = 940-1170 cm-1). The ternary ligand systems consisting of halide, bulky phosphine, and N-heteroaromatic ligands constitute inexpensive pure-blue-light-emitting materials, which can be fabricated by facile procedures such as simple manual grinding. This journal is
  • Yurika Yamashita, Tomoya Tateishi, Kana Sawaguchi, Atsushi Kobayashi, Masako Kato, Kiyohiko Nakajima
    CHEMISTRY LETTERS 43 (12) 1912 - 1914 0366-7022 2014/12 [Refereed][Not invited]
     
    Pt(II) complexes containing tridentate hydrazone ligands were prepared. Reversible protonation and deprotonation of the hydrazone complexes occurred in solution and in the solid state. On grinding and heating the yellow-colored crystals of the protonated complex [PtCl(HL)]Cl, the deprotonated red-colored product, [PtCl(L)], was produced, and HCl vapor was released. The deprotonated complex reverted to the yellow-colored protonated complex on exposure of the red-colored crystals to HCl vapor. Both [PtCl(HL)]Cl and [PtCl(L)] exhibited different luminescence colors in acetonitrile solution.
  • Atsushi Kobayashi, Masako Kato
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2014 (27) 4469 - 4483 1434-1948 2014/09 [Refereed][Invited]
     
    Vapochromic materials that show reversible color change driven by vapor adsorption/desorption have drawn significant attention because of their potential applications in chemical sensors and chemical-switching modules. Among the vapochromic coordination complexes reported so far, a series of square-planar Pt-II complexes has been studied and represents one of the most promising systems for practical chemical sensors. For such systems, the color of the complexes strongly depends not only on the ligand-field splitting, but also on the intermolecular distance between the Pt-II ions. This microreview presents recent results of vapochromic complexes centered on one-dimensionally stacked Pt-II systems from the viewpoint of the origin of their vapochromic behavior. The design of vapochromic materials has been facilitated because several useful chromophores, including metallophilic interaction between Pt-II ions, have been developed. However, it is still challenging to realize a specifically sensitive and selective response to targeted vapors. This review focuses on strategies to achieve assembled Pt-II complexes with selective vapochromic responses.
  • Hirotaka Honda, Takeshi Matsumoto, Ryo Tamura, Katsuhiko Kanaizuka, Atsushi Kobayashi, Masako Kato, Masa-aki Haga, Ho-Chol Chang
    CHEMISTRY LETTERS 43 (8) 1189 - 1191 0366-7022 2014/08 [Refereed][Not invited]
     
    The reaction of tetraethyl [2,3-dihydroxy-1,4-phenylenebis-(methylene)]bisphosphonate (Et4LH2) with [PtCl2(DTBbPY)] (DTBbpy: 4,4'-di-tert-butyl-2,2'-bipyridine) afforded [Pt(Me4L)-(DTBbpY)] (1), [Pt(Bn4L-)(DTBbPY)] (2), Na-2[Pt(Me2L)-(DTBbpy)] (3), and [Pt(H4L)(DTBbpy)] (4) with tetramethyl-, tetrabenzyl-, half-protected, and fully-deprotected groups under different reaction conditions. The introduction of phosphonatomethyl groups at the 3,6-position of a redox-active catecholato unit led to slight shifts in charge-transfer bands and catecholato-centered redox processes in solution. The presence of deprotonated anchors in 3 resulted in the immobilization of the complex onto an indium-doped tin oxide electrode, demonstrating a well-defined redox response from the tethered complex.
  • Hiroki Ohara, Atsushi Kobayashi, Masako Kato
    CHEMISTRY LETTERS 43 (8) 1324 - 1326 0366-7022 2014/08 [Refereed][Not invited]
     
    Highly luminescent mononuclear copper(I) iodide complexes [CuI(PPh3)(2)(L)] have been synthesized by simple manual grinding of copper(I) iodide, PPh3, and N-heteroaromatic ligands (L = isoquinoline, 1,6-naphthyridine, and pyridine). They exhibit different colors of luminescence depending on L affording very high quantum yields (0.63-0.99).
  • Atsushi Kobayashi, Akira Sugiyama, Tadashi Ohba, Yui Suzuki, Ho-Chol Chang, Masako Kato
    CHEMISTRY LETTERS 43 (7) 1070 - 1072 0366-7022 2014/07 [Refereed][Not invited]
     
    A new porous coordination polymer (PCP), formulated as {[La-2(III)(mu(3)-OH)(CH3COO)(2)(H2O)][Cu-I(dmdcbpy)(2)]center dot 9H(2)O} (La2Cu center dot 9H(2)O; H(2)dmdcbpy: 6,6'-dimethyl-5,5'-dicarboxy-2,2'bipyridine), was synthesized and characterized by X-ray diffraction and vapor-adsorption isotherms. The porous framework of La2Cu consists of a 3-D coordination network of the Cu(I)-metalloligand and the tetranuclear La-4 cluster {La-4(mu(3)-OH)(2)(CH3COO)(4)(H2O)(2)}. La2Cu exhibits reversible guest adsorption desorption for various vapors, with reversible structural transformations.
  • Atsushi Kobayashi, Daisuke Yamamoto, Hiroyuki Horiki, Kana Sawaguchi, Takeshi Matsumoto, Kiyohiko Nakajima, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 53 (5) 2573 - 2581 0020-1669 2014/03 [Refereed][Not invited]
     
    Photoreactivities of Ni(II)- and Pt(II)- hydrazone complexes, [NiCI(L)] (Ni1) and [PtCl(L)] (Pt1), respectively [HL = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone], were investigated in detail via UV-vis absorption, H-1 nuclear magnetic resonance (NMR) spectroscopy, and electrospray ionization time-of-flight (ESI-TOF) mass spectrometry; the two photoproducts obtained from the photoreaction of Pt1 were also successfully identified via X-ray analysis. The absorption bands of the Ni1 and Pt1 complexes were very similar, centered around 530 nm, and were assigned as an intraligand charge transfer transition of the hydrazone moiety. The absorption spectrum of Pt1 in a CH3CN solution changed drastically upon photoirradiation (lambda = 530 nm), whereas no change was observed for Ni1. H-1 NMR and ESI-TOF mass spectra under various conditions suggested that the photoexcited Pt1* reacts with dissolved dioxygen to form a reactive intermediate, and the ensuing dark reactions afforded two different products without any decomposition. In contrast to the simple photo-oxidation of HL to form a phosphine oxide HL(P=O), the X-ray crystallographic analyses of the photoproducts clearly indicate the formation of a mononuclear Pt complex with the oxygenated hydrazone ligand (Pt10) and a dinuclear Pt complex with the oxygenated and dimerized hydrazone ligand (Pt2). The photosensitized reaction in the presence of an O-1(2)-generating photosensitizer, methylene blue (MB), also produced Pt1O and Pt2, indicating that the reaction between O-1(2) and ground-state Pt1 is the important step. In a highly viscous dimethyl sulfoxide solution, Pt1 was slowly, but quantitatively, converted to the mononuclear form, Pt1O, without the formation of the dinuclear product, Pt2, upon photoirradiation (and in the reaction photosensitized by MB), suggesting that this photoreaction of Pt1 involves at least one diffusion-controlled reaction. On the other hand, the same complexes Pt1O and Pt2 were also produced in the degassed solution, probably because of the reaction of the photoexcited Pt1* with the biradical character and H2O.
  • Atsushi Kobayashi, Tadashi Ohba, Erika Saitoh, Yui Suzuki, Shin-ichiro Noro, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 53 (6) 2910 - 2921 0020-1669 2014/03 [Refereed][Not invited]
     
    Coordination polymerization reactions between ruthenium(II) metalloligands [Ru(n,n'-dcbpy)](4-) ([nRu]; n = 4, 5; n,n'-dcbpy = n,n'-dicarboxy-2,2'-bipyridine) and several divalent metal salts in basic aqueous solutions afforded porous luminescent complexes formulated as [Mg(H2O)(6)]{[Mg(H2O)(3)][4Ru]center dot 4H(2)O} (Mg-2[4Ru]center dot 13H(2)O), [Mg-2(H2O)(9)][5Ru]center dot 10H(2)O (Mg-2[5Ru]center dot 19H(2)O), {[Sr-4(H2O)(9)][4Ru](2)center dot 9H(2)O} (Sr-2[4Ru]center dot 9H(2)O)(2), {[Sr-2(H2O)(8)][5Ru]center dot 6H(2)O} (Sr-2[5Ru]center dot 14H(2)O), and {[Cd-2(H2O)(2)][5Ru]center dot 10H(2)O} (Cd-2[5Ru]center dot 12H(2)O). Single-crystal X-ray structural analyses revealed that the divalent metal ions were commonly coordinated by the carboxyl groups of the [nRu] metalloligand, forming porous frameworks with a void fraction varying from 11.4% Mg-2[4Ru]center dot 13H(2)O to 43.9% Cd-2[5Ru]center dot 12H(2)O. M-2[4Ru]center dot nH(2)O showed a reversible structural transition accompanied by water and methanol vapor adsorption/desorption, while the porous structures of M-2[5Ru]center dot nH(2)O were irreversibly collapsed by the removal of crystal water. The triplet metal-to-ligand charge-transfer emission energies of M-2[4Ru]center dot nH(2)O were lower than those of [4Ru] in aqueous solution, whereas those of M-2[5Ru]center dot nH(2)O were close to those of [5Ru] in aqueous solution. These results suggested that the position of the coordination site in the metalloligand played an important role not only on the structure of the porous framework but also on the structural flexibility involving the guest adsorption/desorption properties.
  • Asami Mori, Takayoshi Suzuki, Yukinari Sunatsuki, Atsushi Kobayashi, Masako Kato, Masaaki Kojima, Kiyohiko Nakajima
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2014 (1) 186 - 197 1434-1948 2014/01 [Refereed][Not invited]
     
    The reactions of quinoline-2-carbaldehyde (pyridine-2-carbonyl)hydrazone (HL) and [RuCl2(PPh3)(3)] in various solvents at different temperatures gave the three geometrical isomers trans(Cl,Cl)-, cis(Cl,Cl),trans(P,N)-, and trans(P,P)-[RuCl2(PPh3)(2){HL-O(amide),N(imine)}] (1, 2, and 3, respectively) as well as a linkage isomer trans(P,P)-[RuCl2(PPh3)(2){HL-N(imine),N(quin)}] (4). The molecular and crystal structures of 1-4, together with both E and Z configurational isomers (with respect to the C=N double bond) of the free ligand HL, were determined by X-ray analysis. The ligand HL adopted a Z form and acted as a O(amide),N(imine) bidentate ligand in 1-3, whereas it was an E isomer with a N(imine),N(quin) coordination mode in 4. The gradual thermal conversions of 1 to 2 and of 2 to 3 were observed in dichloromethane and ethanol, respectively, but an interconversion between 3 and 4 was not detected. In dichloromethane, all complexes have a reversible Ru-III/II redox couple in the range 110-412 mV (vs. Ag/Ag+), and the redox potential was largely dependent on the coordination mode of HL and on the mutual configuration of the two PPh3 ligands. Such a potential shift can be interpreted as a combination of Cl-/amide O -donor and PPh3/quinoline N -acceptor orbital contributions to the Ru-II d orbitals [highest occupied molecular orbitals (HOMOs)]. Complexes 3 and 4 in acetonitrile showed a gradual spectral change, probably because of the substitution of the Cl- ligand by the acetonitrile solvent. In addition, 2-4 showed solvatochromic behavior even in noncoordinating solvents that resulted from a blueshift of the metal-to-ligand charge-transfer (MLCT) transition band in polar solvents. These electrochemical and spectroscopic properties are also supported by DFT and time-dependent DFT (TD-DFT) calculations.
  • Kazuya Otsubo, Atsushi Kobayashi, Kunihisa Sugimoto, Akihiko Fujiwara, Hiroshi Kitagawa
    INORGANIC CHEMISTRY 53 (2) 1229 - 1240 0020-1669 2014/01 [Refereed][Not invited]
     
    Ladder systems situated in a crossover from one dimensionality to two dimensionalities have been an attractive research target, because the physical properties, which are associated with dimensionality, are strongly dependent on the number of constituent legs. However, control of the intraladder configuration and electronic properties based on the substitution of structural components remain challenging tasks in materials science. On the other hand, structural design using coordination chemistry offers crucial advantages for architectural and electronic variations through substitutions, of metal-organic building blocks. Here, we show the rational design and electronic properties of novel metal complex-based two-legged ladder compounds with several organic rung units: 4,4'-bipyridine, trans-1,4-diaminocyclohexane, and 4,4'-azopyridine. Single-crystal X-ray studies show that these two-legged ladder compounds are composed of halogen-bridged mixed-valence one-dimensional chains (MX chains) as their constituent legs. Depending on the molecular shape of the organic rung units, unique configurations of two-legged ladder lattices with periodic distortion of the legs are achieved. In addition, the electronic absorption spectra show that intervalence charge-transfer (IVCT) band gap of the two-legged ladder system increases with increasing degree of distortion of the leg. We have demonstrated for the first time that a two-legged ladder system shows a unique relationship between IVCT energy and the distortion parameter of the leg, as distinct from a single MX chain system. These systematic investigations, not only of configurations based on the rung variation but also of electronic states in metal-organic ladder system, provide the possibility for wide and rational tunings of physical and electronic properties of metal complex-based functional materials.
  • Tadashi Ohba, Atsushi Kobayashi, Ho-Chol Chang, Takahiko Kouyama, Tatsuhisa Kato, Masako Kato
    DALTON TRANSACTIONS 43 (20) 7514 - 7521 1477-9226 2014 [Refereed][Not invited]
     
    A heterodinuclear complex, syn-[PtCu(mu-pyt)(2)(bpy)(2)](2+) (syn-[PtCu]; Hpyt = pyridine-2-thiol, bpy = 2,2 '-bipyridine), was synthesized by stepwise complexation. Three different crystal structures of the hexafluorophosphate salts with solvent molecules as guests at the axial sites of the Cu(II) ions, i.e. syn-[PtCu-G] (G = acetonitrile, acetone, and methanol), were determined by X-ray analyses. In the solid-state, these complexes adopt dimer-of-dimer motifs characteristic of the syn isomers of dinuclear complexes with two pyt bridging ligands arranged in a head-to-head configuration. These dinuclear complexes have a short Pt. Cu distance (2.75-2.81 angstrom) and slightly different intermolecular Pt...Pt distances (3.43-3.51 angstrom), which affect the colour of the solid complexes. All the syn-[PtCu-G] systems absorbed/desorbed vapour molecules; however, they exhibit different chromic changes because of the unique structural hysteresis of the desorbed form, i. e. syn-[PtCu], according to powder X-ray diffraction measurements. In addition, guest exchange occurred in the syn-[PtM-G] complexes upon exposure to the vapour of different solvents.
  • Tomohiro Ogawa, Misaki Sakamoto, Hirotaka Honda, Takeshi Matsumoto, Atsushi Kobayashi, Masako Kato, Ho-Chol Chang
    Dalton Transactions 42 (45) 15995 - 16005 1477-9226 2013/12/07 [Refereed][Not invited]
     
    The introduction of a Au(iii) ion into a mesogenic core, [M(Bdt)(Cnbpy)]+ (Bdt = 1,2-benzenedithiolato and Cnbpy = 4,4′-di-alkyl-2,2′-bipyridine (n = 13 (4,4′-di-tridecyl-2, 2′-bipyridine (C13bpy)) and 8,10 (4,4′-di-(3-octyltridecyl)-2, 2′-bipyridine (C8,10bpy)))), leads to the formation of ionic molecular assemblies in crystalline and mesophases. Successive syntheses of precursor complexes, [AuCl2(Cnbpy)]PF6 (n = 13 (1) and 8,10 (2)), followed by the target complexes, [Au(Bdt)(Cnbpy)]PF6 (n = 13 (3) and 8,10 (4)), were achieved. The crystallographic analysis of 3 revealed that the central cationic cores form a characteristic one-dimensional columnar structure, which is an essential property for the formation of columnar structures in the liquid crystalline phase. The central cores of the [Au(Bdt)(C13bpy)]+ cations in 3 stack alternatively so as to cancel out their dipole moments and the counteranions lie between the cationic columns. Furthermore, the introduction of the branched alkyl tails in 4 induces the formation of a rectangular columnar liquid crystalline phase (Colr) with C2/m symmetry, and it melts to an isotropic liquid at 69 °C. The Colr phase of 4 is partially similar in its liquid crystalline structure to the neutral [Pt(Bdt)(C8,10bpy)] liquid crystal in a hexagonal columnar phase reported previously, while complex 4 shows a lower clearing point than that of the Pt analogue. Based on these results, the present study demonstrates the designability of the liquid crystalline structures of the [M(Bdt)(C8,10bpy)] skeleton together with their assembled structures and physico-chemical properties. © 2013 The Royal Society of Chemistry.
  • Yasuchika Hasegawa, Tomoki Ohkubo, Takayuki Nakanishi, Atsushi Kobayashi, Masako Kato, Tomohiro Seki, Hajime Ito, Koji Fushimi
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2013 (34) 5911 - 5918 1434-1948 2013/12 [Refereed][Not invited]
     
    The effect of ligand polarization on the formation of strongly luminescent lanthanide complexes with asymmetric structures is described for the first time. The lanthanide complexes are composed of Eu-III ions, three hexafluoroacetylacetonate (hfa) ligands, and two monodentate phosphine oxide ligands, namely, triphenylphosphine oxide (TPPO), p-tolyldiphenylphosphine oxide (TPPO-Me), tri-p-tolylphosphine oxide (TPPO-3Me) or o-phenoxyphenyldiphenylphosphine oxide (TPPO-OPh). The luminescence properties of the Eu-III complexes are characterized by their emission quantum yields, emission lifetimes, and their radiative (k(r)) and nonradiative (k(nr)) rate constants. The Eu-III complex with TPPO-OPh ligands offers a markedly high emission quantum yield (72% in [D-6]acetone, 85% in the solid state) owing to enhancement of the electric dipole transition and suppression of vibrational relaxation, which are directly related to k(r) and k(nr). The coordination geometries of the Eu-III complexes are categorized by shape-measure calculations. The Eu-III complexes exhibit characteristic square-antiprismatic or trigonal-dodecahedral structures, depending on the ligand polarization. Strongly luminescent Eu(hfa)(3)(TPPO-OPh)(2) has an asymmetric dodecahedron structure. The formation of distorted dodecahedral structures with low vibrational frequencies for the enhancement of luminescence is elucidated in terms of the ligand polarization of the monodentate phosphine oxide ligands in the Eu-III complexes.
  • Atsushi Kobayashi, Kahori Komatsu, Hiroki Ohara, Waka Kamada, Yuko Chishina, Kiyoshi Tsuge, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 52 (22) 13188 - 13198 0020-1669 2013/11 [Refereed][Not invited]
     
    Halide-bridged rhombic dicopper(I) complexes, [Cu-2(mu-X)(2)(DMSO)(2)(PPh3)(2)] (X = I-, Br-; DMSO = dimethyl sulfoxide; PPh3 = triphenylphosphine), were synthesized, the iodide complex of which exhibited interesting photochromic luminescence driven by photoirradiation and by exposure to DMSO vapor in the solid state. Single-crystal Xray diffraction measurements revealed that the iodo and bromo complexes (abbreviated Cu2I2-[O,O] and Cu2Br2-[O,O]) were isomorphous, and that the two DMSO ligands were coordinated to the Cu(I) ion via the O atom in both complexes. Both complexes exhibited bright blue phosphorescence at room temperature (lambda(em) = 435 nm, Phi(em) = 0.19 and 0.14 for Cu2I2[O,O] and Cu2Br2-[O,O], respectively) with a relatively long emission lifetime (tau(em) similar to 200 mu s at 77 K) derived from the mixed halide-to-ligand and metal-to-ligand charge transfer ((XLCT)-X-3 and (MLCT)-M-3) excited state. Under UV irradiation, the blue phosphorescence of Cu2Br2-[O,O] disappeared uneventfully and no new emission band appeared, whereas the blue phosphorescence of Cu2I2-[O,O] rapidly disappeared with simultaneous appearance of a new green emission band (lambda(em) = 500 nm). On further irradiation, the green emission of the iodide complex gradually changed to bright yellowish-green (lambda(em) = 540 nm); however, this change could be completely suppressed by lowering the temperature to 263 K or in the presence of saturated DMSO vapor. The initial blue phosphorescence of Cu2I2-[O,O] was recovered by exposure to DMSO vapor at 90 degrees C for a few hours. IR spectroscopy and theoretical calculations suggest that the DMSO ligand underwent linkage isomerization from O-coordination to S-coordination, and both the occurrence of linkage isomerization and the removal of DMSO result in contraction of the rhombic Cu2O4-O-2 core to make the Cu.-Cu interaction more effective. In the contracted core, the triplet cluster-centered ((CC)-C-3) emissive state is easily generated by thermal excitation of the (XLCT)-X-3 and (MLCT)-M-3 mixed transition state, resulting in the green to yellowish-green emission. In contrast, the Cu"Cu distance in Cu2Br2-[O,O] is considerably longer than that of Cu2I2[O,O], which destabilizes the (CC)-C-3 emissive state, resulting in the nonemissive character.
  • Takeshi Matsumoto, Ho-Chol Chang, Masanori Wakizaka, Sho Ueno, Atsushi Kobayashi, Akira Nakayama, Tetsuya Taketsugu, Masako Kato
    Journal of the American Chemical Society 135 (23) 8646 - 8654 0002-7863 2013/06/12 [Refereed][Not invited]
     
    The combination of o-phenylenediamine (opda), which possesses two proton- and electron-pooling capability, with Fe(II) leads to the photochemical hydrogen-evolution reaction (HER) in THF at room temperature without addition of photosensitizers. From the THF solution, the tris(o-phenylenediamine) iron(II) complex, [FeII(opda)3](ClO4)2 (1), was isolated as a photoactive species, while the deprotonated oxidized species was characterized by X-ray crystallographic analysis, electrospray ionization mass spectrometry, and UV-vis NIR spectra. Furthermore, the HER is photocatalyzed by hydroquinone, which serves as a H+/e- donor. The present work demonstrates that the use of a metal-bound aromatic amine as a H+/e- pooler opens an alternative strategy for designing nonprecious-metal-based molecular photochemical H2 production/storage materials. © 2013 American Chemical Society.
  • Hirotaka Honda, Takeshi Matsumoto, Misaki Sakamoto, Atsushi Kobayashi, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 52 (8) 4324 - 4334 0020-1669 2013/04 [Refereed][Not invited]
     
    The presence of lone pairs on the Pt and S atoms of [Pt(Bdt)(DTBbpy)] (1) (Bdt = 1,2-benzenedithiolato and DTBbpy = 4,4'-di-tert-butyl-2,2'-bipyridine) and [Pt (Bdt) (C13bpy)] (2) (C13bpy = 4,4'-ditridecyl-2,2'-bipyridine) led to selective dative bond formation with Cd(II). Complexes 1 and 2 show no binding interaction with Zn(II), while they bind selectively with Cd(II) to give a twisted trinuclear complex, [Cd{Pt(Bdt)(DTBbpy)}(2)(ClO4)(H2O)](ClO4) (3), and a shuttlecock-shaped tetranuclear complex, [Cd{Pt(Bdt)(C13bpy)}(3)(H2O)](ClO4)(2)center dot CH2Cl2 (4), respectively, depending upon the alkyl groups substituted on the 2,2'-bipyridine. The two platinum moieties in 3 are connected to the seven-coordinated Cd atom through Pt -> Cd (2.7331(7) and 2.7936(7) angstrom) and S -> Cd (2.690(3), 2.940(3), and 3.067(3) angstrom) dative bonds, while the three moieties in 4 are connected to the tetrahedral Cd atom only by S -> Cd (2.552(4) angstrom) dative bonds. These structural variations found in 3 and 4 are caused not only by steric hindrance of the t-Bu groups but also by the microsegregation effect derived from the tridecyl chains. The three platinum moieties in 4 align so as to form a parallel orientation of their dipole moments, in contrast to the twisted arrangement found in 3. The dative bonds formed in 3 and 4 are commonly stable in the solid state and in less coordinative solvents such as dichloromethane, while dissociation behavior of platinum moieties with Cd(II) was observed in more coordinative THF. UV-vis and NMR spectroscopy unsealed the characteristic association/dissociation properties depending on the coordination abilities of solvents. Finally, the present study revealed that the formation of dative bonds between the platinum moieties with Cd(II) plays important roles not only in stabilizing the ground states, which leads to blue shifts in both absorption and emission energies, but also in electronic interactions between the moieties, which are revealed by electrochemical studies.
  • Tadashi Ohba, Atsushi Kobayashi, Ho-Chol Chang, Masako Kato
    DALTON TRANSACTIONS 42 (15) 5514 - 5523 1477-9226 2013 [Refereed][Not invited]
     
    Heterodinuclear complexes, syn-[MPt(mu-pyt)(2)(bpy)(2)](n+) (syn-[MPt], M = Pd2+, Au3+, Hpyt = pyridine-2-thiol, bpy = 2,2'-bipyridine), were synthesized as a selective geometrical isomer by stepwise complexation. X-ray analyses of the hexafluorophosphate salts of these complexes proved their dinuclear structures with short M...Pt distances (2.9084(4) angstrom for syn-[PdPt] and 2.9071(4) angstrom for syn-[AuPt]), similar to the homodinuclear complex (2.9292(2) angstrom for syn-[PtPt]). In the syn-[PdPt] crystal, two dinuclear motifs are arranged closely in a head-to-head manner with a short Pt...Pt distance (3.3757(3) angstrom), forming a dimer-of-dimer structure as in the case of syn-[PtPt], whereas the corresponding crystal of syn-[AuPt] has a discrete arrangement of the dinuclear motifs. By the isomerisation of syn-[PdPt], anti-[PdPt] with equivalent environments of the Pd2+ and Pt2+ ions was also obtained successfully. Syn-[PdPt](PF6)(2) exhibits vapochromic behaviour based on the absorption/desorption of CH3CN vapour, similar to that observed for syn-[PtPt](PF6)(2). The reversible structural transformations induced by the uptake and release of CH3CN molecules were investigated by powder and single-crystal X-ray diffraction studies. These revealed that the vapochromic behaviour was based on the interconversion between two phases, the dimer-of-dimer structure with a short Pt. Pt distance and a p-p stacked arrangement with no Pt. Pt intermolecular interaction. The introduction of the heterometal ions enabled control of the colour region: orange. red for syn-[PdPt] vs. light red. dark red for syn-[PtPt], reflecting the weaker metal-metal interaction between Pd2+ and Pt2+ ions in the dinuclear motif. In addition, these complexes were found to exhibit mechanochromic behaviour based on a crystal-to-amorphous transformation upon grinding, and the reconstruction of the crystal structures by vapour sorption.
  • Kohei Miyata, Yuji Konno, Takayuki Nakanishi, Atsushi Kobayashi, Masako Kato, Koji Fushimi, Yasuchika Hasegawa
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 52 (25) 6413 - 6416 1433-7851 2013 [Not refereed][Not invited]
  • Atsushi Kobayashi, Yuki Fukuzawa, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 51 (14) 7508 - 7519 0020-1669 2012/07 [Refereed][Not invited]
     
    We synthesized a novel Pt(II)-diimine complex with a typical ambidentate thiocyanato ligand, [Pt(thiocyanato)(2)(H(2)dcbpy)] (1; H(2)dcbpy =4,4'-dicarboxy-2,2'-bipyridine), and found that the complex 1 exhibits unique linkage isomerizations with drastic color and luminescence changes driven by exposure to volatile organic chemical (VOC) vapors in the solid state. Reaction between [PtCl2(H(2)dcbpy)] and KSCN in aqueous solution at 0 degrees C enabled successful isolation of an isomer with the S-coordinated thiocyanato ligand, [Pt(SCN)(2)(H(2)dcbpy)] (1SS center dot H2O), as a nonluminescent orange solid. Interestingly, 1SS center dot H2O was isomerized completely to one isomer with the N-coordinated isothiocyanato ligand, [Pt(NCS)(2)(H(2)dcbpy)] (1NN center dot 3DMF) by exposure to DMF vapor, and this isomerization was accompanied by significant color and luminescence changes from nonluminescent orange to luminescent red. IR spectroscopy and thermogravimetric analysis revealed that adsorption of the DMF vapor and transformation of the hydrogen-bonded structure both played important roles in this vapor-induced linkage isomerization. Another isomer containing both S- and N-coordinated thiocyanato ligands, [Pt(SCN)(NCS)(H(2)dcbpy)] (1SN), was obtained as a nonluminescent yellow solid simply by exposure of 1SS center dot H2O to acetone vapor at room temperature, and about 80% of 1SS center dot H2O was found to be converted to 1SN. In the solution state, each isomer changed gradually to an isomeric mixture, but pure 1SS was regenerated by UV light irradiation (lambda(irr) = 300 nm) of an MeOH solution of the mixture. In the crystal structure of 1SN, the complex molecules were hydrogen-bonded to each other through the carboxyl groups of the H(2)dcbpy ligand and the N site of the thiocyanato ligand, whereas the 1NN molecules in the 1NN.4DMF crystal were hydrogen-bonded to the solvated DMF molecules. Competition of the hydrogen-bonding ability among the carboxyl groups of the H(2)dcbpy ligand, N and S atoms of the thiocyanato ligand, and the vapor molecule was found to be one of the most important factors controlling linkage isomerization behavior in the solid state. This unique linkage isomerization controlled by vapor can provide an outstanding vapochromic system as well as a new molecular switching function driven by vapor molecules.
  • Kohei Miyata, Tadashi Ohba, Atsushi Kobayashi, Masako Kato, Takayuki Nakanishi, Koji Fushimi, Yasuchika Hasegawa
    CHEMPLUSCHEM 77 (4) 277 - 280 2192-6506 2012/04 [Not refereed][Not invited]
  • Takeshi Matsumoto, Masanori Wakizaka, Hirokazu Yano, Atsushi Kobayashi, Ho-Chol Chang, Masako Kato
    DALTON TRANSACTIONS 41 (27) 8303 - 8315 1477-9226 2012 [Refereed][Not invited]
     
    The redox-active fac-[Mo-V(mp)(3)](-) (mp: o-mercaptophenolato) bearing asymmetric O- and S-cation binding sites can bind with several kinds of metal ions such as Na+, Mn-II, Fe-II, Co-II, Ni-II, and Cu-I. The fac-[Mo-V(mp)(3)](-) metalloligand coordinates to Na+ to form the contact ion pair {Na+(THF)(3)[fac-Mo-V(mp)(3)]} (1), while a separated ion pair, n-Bu4N[fac-Mo-V(mp)(3)] (2), is obtained by exchanging Na+ with n-Bu4N+. In the presence of asymmetric binding-sites, the metalloligand reacts with (MnCl2)-Cl-II center dot 4H(2)O, (FeCl2)-Cl-II center dot 4H(2)O, (CoCl2)-Cl-II center dot 6H(2)O, and (NiCl2)-Cl-II center dot 6H(2)O to afford UV-vis-NIR spectra, indicating binding of these guest metal cations. Especially, for the cases of the MnII and CoII products, trinuclear complexes, {M(H2O)(MeOH)-[ fac-Mo-V(mp)(3)](2)}center dot 1.5CH(2)Cl(2) (3.1.5CH(2)Cl(2) (M = Mn-II), 4.1.5CH(2)Cl(2) (M = Co-II)), are successfully isolated and structurally characterized where the M are selectively bound to the hard O-binding sites of the fac-[Mo-V(mp)(3)](-). On the other hand, a coordination polymer, {Cu-I(CH3CN)[mer-MoV(mp)(3)]}(n) (5), is obtained by the reaction of fac-[Mo-V(mp)(3)]-with [Cu-I(CH3CN)(4)]ClO4. In sharp contrast to the cases of 1, 3.1.5CH(2)Cl(2), and 4.1.5CH(2)Cl(2), the Cu-I in 5 are selectively bound to the soft S-binding sites, where each CuI is shared by two [MoV(mp) 3]-with bidentate or monodentate coordination modes. The second notable feature of 5 is found in the geometric change of the [MoV(mp) 3]-, where the original fac-form of 1 is isomerized to the mer-[Mo-V(mp)(3)](-) in 5, which was structurally and spectroscopically characterized for the first time. Such isomerization demonstrates the structural flexibility of the [Mo-V(mp)(3)](-). Spectroscopic studies strongly indicate that the association/dissociation between the guest metal ions and metalloligand can be modulated by solvent polarity. Furthermore, it was also found that such association/dissociation features are significantly influenced by coexisting anions such as ClO4- or B(C6F5)(4)(-). This suggests that coordination bonds between the guest metal ions and metalloligand are not too static, but are sufficiently moderate to be responsive to external environments. Moreover, electrochemical data of 1 and 3.1.5CH(2)Cl(2) demonstrated that guest metal ion binding led to enhance electron-accepting properties of the metalloligand. Our results illustrate the use of a redox-active chalcogenolato complex with a simple mononuclear structure as a multifunctional metalloligand that is responsive to chemical and electrochemical stimuli.
  • Atsushi Kobayashi, Hirofumi Hara, Tsubasa Yonemura, Ho-Chol Chang, Masako Kato
    DALTON TRANSACTIONS 41 (6) 1878 - 1888 1477-9226 2012 [Refereed][Not invited]
     
    Reactions of a Pt(II)-diimine-based metalloligand Na-2[Pt(CN)(2)(4,4'-dcbpy)] (4,4'-H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) with alkaline-earth metal salts Mg(NO3)(2)center dot 6H(2)O, CaCl2, SrCl2 center dot 6H(2)O, and BaBr2 center dot 2H(2)O in aqueous solution gave luminescent complexes formulated as [Mg(H2O)(5)][ Pt(CN)(2)(4,4'-dcbpy)]center dot 4H(2)O (MgPt-4 center dot 9H(2)O), {[Ca(H2O)(3)][Pt(CN)(2)(4,4'-dcbpy)]center dot 3H(2)O}(infinity) (CaPt-4 center dot 6H(2)O), {[Sr(H2O)(2)][Pt(CN)(2)(4,4'-dcbpy)]center dot H2O}(infinity) (SrPt-4 center dot 3H(2)O), and {[Ba(H2O)(2)][ Pt(CN)(2)(4,4'-dcbpy)]center dot 3H(2)O}(infinity) (BaPt-4 center dot 5H(2)O), respectively. The crystal structures of all MPt-4 complexes were determined by X-ray crystallography. In these structures, the alkaline-earth metal ions are commonly coordinated to the carboxyl groups of the [Pt(CN)(2)(4,4'-dcbpy)](2-) metalloligand. In the case of MgPt-4 center dot 9H(2)O, the Mg(II) ion is bound by five water molecules and one oxygen atom of a carboxyl group to form a neutral complex molecule [Mg(H2O) 5][Pt(CN)(2)(4,4'-dcbpy)]. In contrast, the alkaline-earth metal ion and metalloligand form two-dimensional (CaPt-4 center dot 6H(2)O) and three-dimensional (SrPt-4 center dot 3H(2)O and BaPt-4 center dot 5H(2)O) coordination networks, respectively. All fully hydrated complexes exhibited a strong phosphorescence from the triplet pi-pi* transition state. Luminescence spectroscopy revealed that MgPt-4 center dot 9H(2)O exhibited interesting multichromic (i.e., thermo-, mechano-, and vapochromic) luminescence, whereas CaPt-4 center dot 6H(2)O showed only thermochromic luminescence. The other two complexes did not exhibit any chromic behaviour. Combination analysis of powder X-ray diffraction, thermogravimetry, and IR spectroscopy suggests that the dimensionality of the coordination network contributes considerably to both the structural flexibility and luminescence properties; that is, the low-dimensional flexible coordination network formed in MPt-4 complexes with smaller alkaline-earth metal ions enables a structural rearrangement induced by thermal and mechanical stimuli and vapour adsorption, resulting in the observed multichromic behaviour.
  • Mee Chang, Atsushi Kobayashi, Ho-Chol Chang, Kiyohiko Nakajima, Masako Kato
    CHEMISTRY LETTERS 40 (12) 1335 - 1337 0366-7022 2011/12 [Refereed][Not invited]
     
    A new copper(II)-hydrazone complex, [Cu(paph)Cl(CH3-OH)] (Hpaph: 2-pyridinecarboxaldehyde 2-pyridylhydrazone) (1) has been synthesized and characterized by single-crystal X-ray diffraction and UV-vis spectroscopy. This complex shows distinctive color changes by the protonation/deprotonation and exhibits interesting ON OFF switching of solvatochromic behavior on the basis of the protonation/deprotonation of the hydrazone moiety.
  • Mee Chang, Atsushi Kobayashi, Kiyohiko Nakajima, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 50 (17) 8308 - 8317 0020-1669 2011/09 [Refereed][Not invited]
     
    We describe the novel synthesis of a bis(hydrazone)iron(B) complex in protonated [Fe(Hpbph)(2)]Cl-2 (1) and deprotonated [Fe(pbph)(2)] (2) forms and several hydrogen-bonded proton-transfer (HBPT) assemblies having different dimensionalities of hydrogen-bonded network structures, [Fe(Hpbph)2] (CA)center dot 2CH(3)OH (3), [Fe(Hpbph)(2)](HCA)(2)center dot 2THF (4), and [Fe(Hpbph)(2)](CA)(H(2)CA)(2)center dot 2CH(3)CN (5) (Hpbph = 2-(diphenylphosphino)benzaldehyde-2-pyridylhydrazone), consisting of a deprotonated Fe(II)-hydrazone complex (2) as a proton acceptor (A) and chloranilic acid (H2CA) as a proton donor (D). The deprotonated complex 2 exhibited two-step reversible protonation reactions to form the double-protonated form 1, and the acid-dissociation constants were determined to be 7.6 and 10.3 in methanol solution. Utilizing this proton-accepting ability of 2, we succeeded in synthesizing HBPT assemblies 3, 4, and 5 from the reactions in CH3OH, THF, and CH3CN, respectively, with the same D/A ratio of H(2)CA/[Fe(pbph)(2)] = 10:1. These assemblies were found to have one-dimensional (1-D), two-dimensional (2-D), and three-dimensional (3-D) hydrogen-bonded networks with D/A ratios of 1:1, 2:1, and 3:1 for 3, 4, and 5, respectively. In 3, a 1-D hydrogen-bonded chain composed of the alternate arrangement of [Fe(Hpbph)(2)](2+) and CA(2-), {center dot center dot center dot[Fe(Hpbph)(2)](2+)center dot center dot center dot CA(2-)center dot center dot center dot}(infinity), was surrounded by solvated methanol molecules to form isolated 1-D hydrogen-bonded chains. In the HBPT assembly 4, a 2-D hydrogen-bonded sheet was formed from two types of hydrogen-bonded chains, {center dot center dot center dot[Fe(Hpbph)(2)](2+)center dot center dot center dot HCA(-)center dot center dot center dot HCA(-)center dot center dot center dot}(infinity) and {center dot center dot center dot HCA(-)center dot center dot center dot HCA(-)center dot center dot center dot}(infinity), and solvated THF molecules did not form any hydrogen bonds. In 5, two orthogonal hydrogen-bonded chains constructed from the neutral chloranilic acid molecules, {center dot center dot center dot CA2(-)center dot center dot center dot 2(H(2)CA)center dot center dot center dot}(infinity), were formed in addition to the 1-D hydrogen-bonded chain similar to that in 3, resulting in the formation of a rigid 3-D hydrogen-bonded network structure. By controlling the dimensionality of the hydrogen bond network, we found that the 2-D HBPT assembly 4 is sufficiently flexible to exhibit interesting vapochromic behavior in response to various organic vapors.
  • Ho-Chol Chang, Kazuki Komasaka, Keisuke Kishida, Tomoki Shiozaki, Takeshi Ohmori, Takeshi Matsumoto, Atsushi Kobayashi, Masako Kato, Susumu Kitagawa
    INORGANIC CHEMISTRY 50 (10) 4279 - 4288 0020-1669 2011/05 [Refereed][Not invited]
     
    Liquid crystalline (LC) platinum(II) complexes with 1,2-thiophenolato and 1,2-benzendithiolato have been newly synthesized and investigated by spectroscopy together with the catecholato analogue. The variations in coordinating atoms (O or S or O/S mixed) lead to significant modulation in electrochemical properties in solution and absorption and emission properties of the complexes both in solution media and in the condensed phases. The asymmetric, polar mesogens/chromophores consisting of Pt(II), redox-active ligands, and alkyl-substituted bipyridine commonly play important roles not only in stabilizing the columnar LC phases, but also in fluctuations of the ground state energies. A key finding of the present work is the chromic properties of LC complexes induced by the interplay of self-association of the mesogens/chromophores and their fluctuating properties.
  • Atsushi Kobayashi, Yui Suzuki, Tadashi Ohba, Shin-ichiro Noro, Ho-Chol Chang, Masako Kato
    INORGANIC CHEMISTRY 50 (6) 2061 - 2063 0020-1669 2011/03 [Refereed][Not invited]
     
    We synthesized new porous coordination polymers (PCPs) {Ln(III)[Co(III)(dcbpy)(3)]center dot nH(2)O} (Ln = Nd(3+), Gd(3+); H(2)dcbpy = 4,4'-dicarboxy-2,2'-bipyridine) and characterized them by X-ray diffraction and vapor-adsorption measurements. These three Ln-Co-based PCPs have similar rock-salt types and highly symmetrical porous structure and show a reversible structural collapse regeneration accompanied by water-vapor desorption adsorption. Similar structural regeneration was also observed for the Gd-Co PCP upon exposure to MeOH and CH(3)CN vapors, whereas the remaining two PCPs barely responded to organic vapors.
  • Rie Aoki, Atsushi Kobayashi, Ho-Chol Chang, Masako Kato
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 84 (2) 218 - 225 0009-2673 2011/02 [Refereed][Not invited]
     
    A series of cyclometalated dinuclear platinum(II) complexes bridged by pyridine-2-thiolate (pyt) ions, [Pt-2(L)(2)-(pyt)(2)] (HL = 2-(p-tolyl)pyridine (Hptpy), 2-(2-thienyl)pyridine (Hthpy), or benzo[h]quinoline (Hbzqn)), as well as their two-electron-oxidized dinuclear platinum(III) complexes, [Pt2Cl2(L)(2)(pyt)(2)], have been synthesized and characterized. The structures and luminescence properties have been investigated by comparing them with those of the corresponding 2-phenylpyridinato (ppy) complex. All divalent complexes have similar dinuclear frameworks, with short Pt center dot center dot center dot Pt distances (ca. 2.85 angstrom), and exhibit similar intense luminescence from the triplet metal metal-to-ligand charge-transfer ((MMLCT)-M-3) state in glassy solutions. However, they provide different luminescence features reflecting their dynamic behaviors in fluid solutions and their intermolecular interactions in the solid state. [Pt-2(bzqn)(2)(pyt)(2)] containing fused aromatic rings exhibits the most sensitive features to the environment, i.e., it shows the most red-shifted luminescence spectrum in the solid state due to the intermolecular pi-pi interaction. However, in fluid solution, it provides very weak luminescence based on a rapid nonradiative deactivation mainly caused by the fluctuation of the intramolecular pi-pi repulsion between the ligands. [Pt-2(Ptpy)(2)(pyt)(2)], on the other hand, is the most stable luminophore, which always exhibits intense luminescence with an almost constant emission maximum independent of its temperature and state.
  • Atsushi Kobayashi, Korin Ohbayashi, Rie Aoki, Ho-Chol Chang, Masako Kato
    DALTON TRANSACTIONS 40 (14) 3484 - 3489 1477-9226 2011 [Refereed][Not invited]
     
    We synthesized a thiosemicarbazone-functionalized flavin (Fl-(H) TSC: 2-[2-(3,4-dihydro-7,8-dimethyl-2,4-dioxobenzo[g]pteridin-10(2H)-yl)ethylidene]-hydrazinecarbothioamide) and its Pt(II) complex [Pt(Fl-TSC)(2)], and characterized it using X-ray diffraction, UV-visible absorption and luminescence spectroscopy. X-ray structural analysis for [Pt(Fl-TSC)(2)] revealed that the structure of the isoalloxazine part was almost the same as that in lumiflavin (7,8,10-trimethylisoalloxazine), and the thiosemicarbazone moiety acted as a bidentate ligand to form a PtS2N2 planar conformation. UV-visible absorption and luminescence spectra of these compounds were very similar to those of riboflavin, but the emission intensity and the lifetime decreased considerably. Theoretical calculations suggested that the charge-separated state (Fl(center dot-)-TSC center dot+) contributed to the faster quenching from the (1)pi-pi* emission state.
  • Hirofumi Hara, Atsushi Kobayashi, Shin-ichiro Noro, Ho-Chol Chang, Masako Kato
    DALTON TRANSACTIONS 40 (31) 8012 - 8018 1477-9226 2011 [Refereed][Not invited]
     
    Four new bimetallic coordination polymers (CPs), {M[Pt(CN)(2)(5,5'-dcbpy)]center dot 4H(2)O}(n) (M = Mg(2+), Ca(2+), Sr(2+), Ba(2+); 5,5'-H(2)dcbpy = 5,5'-dicarboxy-2,2'-bipyridine) were synthesized using four alkaline-earth metal ions and a Pt(II)-diimine metalloligand [Pt(CN)(2)(5,5'-H(2)dcbpy)]. All four CPs are isomorphous with the Zn complex, {Zn[Pt(CN)(2)(5,5'-dcbpy)]center dot 4H(2)O}(n), which exhibits effective metallophilic interactions between Pt(II) ions. These CPs exhibited colourful thermochromic behaviour and solid-state solvatochromic-like behaviours when suspended in various solvents. Thermogravimetric analysis and vapour-adsorption measurements revealed that the CPs can reversibly adsorb water and MeOH vapours. The emission energy of the triplet metal-metal-to-ligand charge-transfer ((3)MMLCT) state varied markedly upon guest adsorption/desorption. The chromic and vapour-adsorption properties of these CPs depend strongly on the cross-linking M(2+) ions.
  • KOBAYASHI Atsushi, KATO Masako
    X-RAYS The Crystallographic Society of Japan 53 (6) 402 - 408 0369-4585 2011 [Not refereed][Not invited]
     
    Recently, vapochromic materials have drawn increasing attention because of their promising vapor sensing functions. In this paper, from the viewpoint of structural chemistry, several types of vapochromic metal complexes are described. The first one is vapochromic materials composed of Pt (II)-diimine complexes in which the origin of vapochromic behavior is the modification of the intermolecular metallophilic interactions. Second are the materials utilizing porous frameworks to adsorb/desorb vapor molecules. Third is the vapochromic hydrogen-bonded proton-transfer assembly which can recognize the hydrogen-bonding ability of vapor molecules.
  • Atsushi Kobayashi, Masa-aki Dosen, Mee Chang, Kiyohiko Nakajima, Shin-ichiro Noro, Masako Kato
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 132 (43) 15286 - 15298 0002-7863 2010/11 [Refereed][Not invited]
     
    We synthesized and investigated a new series of metal-hydrazone complexes, including deprotonated [MX(mtbhp)] and protonated forms [MX(Hmtbhp)](ClO(4)) (M = Pd(2+), Pt(2+); X = Cl(-), Br(-); Hmtbhp = 2-(2-(2-(methylthio)benzylidene)hydrazinyl)pyridine) and hydrogen-bonded proton-transfer (HBPT) assemblies containing [PdBr(mtbhp)] and bromanilic acid (H(2)BA). The mtbhp hydrazone ligand acts as a tridentate SNN ligand and provides a high proton affinity. UV-vis spectroscopy revealed that these metal-hydrazone complexes follow a reversible protonation-deprotonation reaction ([MX(mtbhp)] + H(+) -[MX(Hmtbhp)](+)), resulting in a remarkable color change from red to yellow. Reactions between proton acceptor [PdBr(mtbhp)] (A) and proton donor H(2)BA (D) afforded four types of HBPT assemblies with different D/A ratios: for D/A = 1:1, {[PdBr(Hmtbhp)](HBA)center dot Acetone} and {[PdBr(Hmtbhp)](HBA)center dot 2(1,4-dioxane)}; for D/A = 1:2, [PdBr(Hmtbhp)](2)(BA); and for D/A = 3:2, {[PdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)center dot 2Acetonitrile}. The proton donor gave at least one proton to the acceptor to form the hydrogen bonded A center dot center dot center dot D pair of [PdBr(Hmtbhp)]+center dot center dot center dot HBA(-). The strength of the hydrogen bond in the pair depends on the kind of molecule bound to the free monoanionic bromanilate OH group. Low-temperature IR spectra (T < 150 K) showed that the hydrogen bond distance between [PdBr(Hmtbhp)](+) and bromanilate was short enough (ca. 2.58 A) to induce proton migration in the [pdgr(Hrhtbhp)](2)(BA) assembly in the solid state. The hydrogen bonds formed not only between [PdBr(Hmtbhp)](+) and HBA(-) but also between HBA(-) and neutral H(2)BA molecules in the {[pdBr(Hmtbhp)](2)(HBA)(2)(H(2)BA)center dot 2Acetonitrile} assembly. The H(2)BA-based flexible hydrogen bond network and strong acidic host structure result in an interesting vapor adsorption ability and vapochromic behavior in this assembly because the vapor-induced rearrangement of the hydrogen bond network, accompanied by changes in pi-pi stacking interactions, provides a recognition ability of proton donating and accepting properties of the vapor molecule.
  • Mee Chang, Hiroyuki Horiki, Kiyohiko Nakajima, Atsushi Kobayashi, Ho-Chol Chang, Masako Kato
    BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 83 (8) 905 - 910 0009-2673 2010/08 [Refereed][Not invited]
     
    A new series of substituted hydrazone complexes, [Cu(Hpbph)I] (1), [Cu(Hpbph)PPh3]PF6 (2-PF6), [NiCl-(Hpbph)]Cl (3-Cl), [PtCl(Hpbph)]ClO4 (4-ClO4), and [PtCl(pbph)] (4b) (Hpbph = 2-(diphenylphosphino)benzaldehyde 2-pyridylhydrazone) have been synthesized and characterized. X-ray crystallography revealed that the copper(1) complexes adopt pseudo-tetrahedral geometry, while the nickel(II) and platinum(II) complexes provide square-planar forms. All the complexes exhibit distinct color changes on the basis of the deprotonation/protonation on the ligand although their acid/base behaviors are largely different. The acidity constants (pK(a)) in methanol were determined to be 11.4 (1), 12.5 (2), 7.7 (3), and 6.7 (4). The results indicate that the dissociation of the proton on the ligand strongly depends on the ligand deformation controlled by the coordination geometry of the complexes and ancillary ligands also somewhat affect the acidity.
  • Atsushi Kobayashi, Tsubasa Yonemura, Masako Kato
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY 2010 (17) 2465 - 2470 1434-1948 2010/06 [Refereed][Not invited]
     
    A novel luminescent platinum(II)-diimine complex, Na(2)[Pt(CN)(2)(dcbpy)]center dot nH(2)O (H(2)dcbpy = 4,4 '-dicarboxy-2,2'-bipyridine, n = 2 or 5) was synthesized and investigated by using X-ray diffraction measurements and spectroscopy. Complex Na(2)[Pt(CN)(2)(dcbpy)]center dot 2H(2)O was first obtained as a red amorphous solid (IA) that exhibits bright luminescence at 623 nm. After recrystallization, two crystalline forms, the dihydrate form, 1C, and the pentahydrate form, Na(2)[Pt(CN)(2)(dcbpy)]center dot 5H(2)O (2), were obtained and analyzed by the single-crystal X-ray diffraction method. Upon exposure of the amorphous form 1A to hydrophilic vapours such as those of MeOH and acetone, 1A irreversibly changed to a yellow crystalline solid 1C that showed luminescence at 608 nm with a shoulder at 568 nm. This vapour-induced amorphous-crystalline transformation has never been observed either by exposing 1A to hydrophobic vapours nor by increasing the temperature up to 410 K. IR spectroscopy revealed that the amorphous-crystalline transformation did not involve the adsorption of the vapour. This phenomenon of irreversible structural transformation accompanied by change of luminescence is possibly applicable to vapour history sensors.
  • Atsushi Kobayashi, Hirofumi Hara, Shin-ichiro Noro, Masako Kato
    DALTON TRANSACTIONS 39 (14) 3400 - 3406 1477-9226 2010 [Refereed][Not invited]
     
    We synthesized a new Pt/Zn-based coordination polymer, {Zn[Pt(CN)(2)(5,5'-dcbpy)]center dot 4H(2)O}(n), (5,5'-H(2)dcbpy = 5,5'-dicarboxy-2,2'-bipyridine), which exhibits reversible colour changes in response to temperature change or exposure to chemical vapours and liquids. Such chromic behaviour shows promise for sensing not only changes in temperature but also for detecting chemical solvents and vapours. The single crystal X-ray structure indicates that one-dimensional coordination polymeric chains formed by an alternating arrangement of [Zn(H(2)O)(3)](2+) and [Pt(CN)(2)(5,5'-dcbpy)](2-) stacked to produce moderate metallophilic interactions between the Pt(II) ions. Thermogravimetric analysis and water vapour adsorption measurements show that both the crystal water and water coordinated to Zn(II) ions can be removed and re-adsorbed reversibly by heating or under vacuum. Emission spectra at various temperatures and/or in the presence of vapours or liquids reveal that the complex exhibits thermochromic and solvatochromic-like behaviours, with the emission band shifting between 616 and 671 nm. IR spectroscopy and powder X-ray diffraction measurements suggest that this multichromic behaviour is a result of the cooperative phenomena of water adsorption/desorption around the Zn(II) ions and the modi. cation of the metallophilic interaction.
  • Shinya Takaishi, Miyuki Hosoda, Takashi Kajiwara, Hitoshi Miyasaka, Masahiro Yamashita, Yasuyuki Nakanishi, Yasutaka Kitagawa, Kizashi Yamaguchi, Atsushi Kobayashi, Hiroshi Kitagawa
    INORGANIC CHEMISTRY 48 (19) 9048 - 9050 0020-1669 2009/10 [Not refereed][Not invited]
     
    We synthesized a new porous coordination polymer Cu[Cu(pdt)(2)], which shows relatively high electrical conductivity (6 x 10(-4) S cm(-1) at 300 K) by the introduction of electron donors and acceptors as building units. This compound is applicable as a porous electrode with high power density. In addition, this compound forms a triangular spin lattice and shows spin frustration.
  • Atsushi Kobayashi, Yuki Fukuzawa, Shin-ichiro Noro, Takayoshi Nakamura, Masako Kato
    CHEMISTRY LETTERS 38 (10) 998 - 999 0366-7022 2009/10 [Refereed][Not invited]
     
    A simple Pt-II-terpyridine complex [Pt(NCS)(tpy)](SCN) (tpy = 2,2': 6', 2 ''-terpyridine) shows distinct two-step vapochromism from red to yellow through dark red in response to methanol vapor. The adsorption isotherm for methanol vapor reveals that the two-step vapochromic behavior originates from breathing-like structural transformations.
  • Atsushi Kobayashi, Shinji Kitao, Makoto Seto, Ryuichi Ikeda, Hiroshi Kitagawa
    Inorganic Chemistry 48 (16) 8044 - 8049 0020-1669 2009/08/17 [Refereed][Not invited]
     
    One-dimensional iodide-bridged mixed-valence binuclear platinum complexes (the so-called "MMX chains") and their Pt(III) dimer precursors were investigated with 129I Mössbauer spectroscopy. Spectra consisting of two sets of octuplets were observed at low temperatures for a neutral MMX chain complex, Pt2(dtp)4l (dtp = C 2H5CS2-), with various charge-ordering states at the Pt dimers, indicating that the charge-ordering state is in an alternate-charge-polarization phase (ACP: · · ·[Pt2+-Pt3+]-l0.4--[Pt 3+-Pt2+]- · · · -10.3-- · · ·), which is consistent with a previous low-temperature X-ray diffraction study. The estimated valence states of the bridging iodines of [(C2H5)2NH2]4[Pt 2(pop)4l] (pop = H2P2O 52-), with a charge-polarization phase (CP: · · · [Pf-Pt3+]-I0-4-· · · [Pt2+-Pt3+]-I0.4--· · ·), and [H3N(CH2)6NH 3]2[Pt2(pop)4l], with a charge-density-wave phase (CDW: · · · [Pt 2+-Pt2+] · · ·I0.3- -[Pt3+-Pt3+]-I30.3- · · ·), suggest that the covalent bond interaction is dominant in the CDW phase, whereas the Coulomb interaction is dominant in the CP phase. The estimated absolute quadrupole coupling constant (QCC) values for negatively charged MMX chain complexes with pop ligands are larger than those for neutral MMX chain complexes with CH3CS2- (dta) ligands, implying that the Madelung potential formed by the more-negative pop ligands and countercations effectively contributes to the physical properties of the pop system. The three Pt(III) dimer complexes Pt2(dta)4l 2, Pt2(dtp)4l2, and K 4[Pt2(pop)4l2] showed almost the same isomer shifts, indicating that the valence state of the iodide ion (1 0.5-) depends negligibly on the terminal ligand. The QCC value observed for K4[Pt2(pop)4l2] was larger than those for Pt2(dta)4l2 and Pt 2(dtp)4l2, originating from the anisotropic arrangement of the iodide anions, which form layers lying on the ab plane in the crystal. © 2009 American Chemical Society.
  • Kazuya Otsubo, Atsushi Kobayashi, Masato Hedo, Yoshiya Uwatoko, Hiroshi Kitagawa
    CHEMISTRY-AN ASIAN JOURNAL 4 (11) 1673 - 1676 1861-4728 2009 [Refereed][Not invited]
  • Tohru Suemoto, Youtarou Takahashi, Keizo Yasukawa, Daisuke Kawakami, Shinya Takaishi, Masahiro Yamashita, Atsushi Kobayashi, Hiroshi Kitagawa
    Journal of Luminescence 128 (5-6) 1081 - 1083 0022-2313 2008/05 [Not refereed][Not invited]
     
    The properties and the dynamics of the excited states in out-of-phase ladder-type halogen-bridged Pt complexes (Pt-Br-out and Pt-I-out) are studied using femtosecond luminescence spectroscopy. In both materials, Gaussian-shaped broad luminescence bands with large Stokes shifts are found around 0.8 eV and assigned to self-trapped excitons (STE). The wave-packet oscillations with periods of 290 and 306 fs were observed in Pt-Br-out and Pt-I-out, respectively. The higher oscillation frequency in Pt-I-out compared with the one-dimensional (1D)-type Pt-I is ascribed to the smaller lattice relaxation in the ladder system. Although the lifetime of the STE is almost the same as that of the 1D-type Pt-Br, the lifetime in Pt-I-out is one order of magnitude longer than that in the 1D-type Pt-I. This is ascribed to the phase locking of the charge density wave due to the interchain interaction. © 2007 Elsevier B.V. All rights reserved.
  • Atsushi Kobayashi, Aya Tokunaga, Ryuichi Ikeda, Hajime Sagayama, Yusuke Wakabayashi, Hiroshi Sawa, Masato Hedo, Yoshiya Uwatoko, Hiroshi Kitagawa
    EUROPEAN JOURNAL OF INORGANIC CHEMISTRY (18) 3567 - 3570 1434-1948 2006/09 [Refereed][Not invited]
     
    The electrical conductivity and X-ray diffraction measurements were performed for a highlyconductive halogen-bridged binuclear-metal mixed-valence complex (the so-called MMX chain), Pt-2(C2H5CS2)(4)I, under high pressure up to 2.5 GPa. The complex exhibited pressure-induced metal-semiconductor-metal transitions at 0.5 and 2.1 GPa. The Xray diffuse scatterings were observed at k = n+0.5 (n: integer) under ambient pressure, which are derived from the charge-density wave (CDW:center dot center dot center dot Pt-2-Pt2+center dot center dot center dot I-Pt3+-Pt3+-I center dot center dot center dot) fluctuation in the MMX chain. Above 0.5 GPa, where the pressure-induced metal-semiconductor transition occurred, these scatterings disappeared. The electronic phases under high pressure (P) were found to be attributable to the metallic averaged-valence state (AV: -Pt2.5+-Pt2.5+-I-Pt2.5+-Pt2.5+-I-) with CDW fluctuation of P < 0.5 GPa, semiconducting charge-polarization state (CP:center dot center dot center dot Pt2+-Pt3+-I center dot center dot center dot Pt2+-Pt3+-I center dot center dot center dot) of 0.5 < P < 2.1 GPa, and metallic AV state of P > 2.1 GPa. The electronic state Of Pt-2(C2H5CS2)(4)I is very sensitive to pressure, which implies that the phase competition among the CP, CDW, and AV phases is present in the MMX chain.
  • Masahiro Yamashita, Shinya Takaishi, Atsushi Kobayashi, Hiroshi Kitagawa, Hiroyuki Matsuzaki, Hiroshi Okamoto
    COORDINATION CHEMISTRY REVIEWS 250 (17-18) 2335 - 2346 0010-8545 2006/09 [Refereed][Not invited]
     
    This review describes the tuning of electronic structures and variable phase transitions in quasi one-dimensional iodide-bridged dinuclear Pt compounds (MMX chains). These are classified into two types of MMX chain compounds, that is, Pt-2(dta)(4)(I) (dta = dithioacetate derivatives) and R-4[Pt-2(pop)(4)I].nH(2)O (R = alkylammonium, etc.; pop = P2O5H22-). These MMX chains compounds can take four electronic structures such as average valence (AV), charge-density-wave (CDW), charge-polarization (CP) and alternating charge-polarization (ACP) states. The Pt-2(dta)(4)I compounds show a phase transition from metallic AV, CP, to ACP state with decreasing temperature. The phase transition feature depends on the alkyl derivatives of the dta ligands. The R-4[Pt-2(pop)(4)I].nH(2)O exhibits three oxidation states, AV, CDW, and CP states, depending on the kind of cations. Some of these compounds show a phase transition by pressure, photo-irradiation, temperature, and humidity. (c) 2006 Elsevier B.V. All rights reserved.
  • Atsushi Kobayashi, Hiroshi Kitagawa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (37) 12066 - 12067 0002-7863 2006/09 [Refereed][Not invited]
  • Kazuya Otsubo, Atsushi Kobayashi, Hiroshi Kitagawa, Masato Hedo, Yoshiya Uwatoko, Hajime Sagayama, Yusuke Wakabayashi, Hiroshi Sawa
    Journal of the American Chemical Society 128 (25) 8140 - 8141 0002-7863 2006/06/28 [Refereed][Not invited]
     
    The electrical resistivity and X-rayoscillation photograph measurements for an MMX-chain complex, Pt2(dtp)4I (dtp = C2H5CS2-), under high pressure were performed. We observed the most stable metallic phase (TMI = 70 K, under 2.2 GPa) in the 1-D purely d-electronic conductors and pressure-induced metal-insulator transition including the structural phase transition at 3.0 GPa. Copyright © 2006 American Chemical Society.
  • Yusuke Wakabayashi, Atsushi Kobayashi, Hiroshi Sawa, Hiroyuki Ohsumi, Naoshi Ikeda, Hiroshi Kitagawa
    JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 128 (20) 6676 - 6682 0002-7863 2006/05 [Refereed][Not invited]
     
    A powerful method to determine the hidden structural parameters in functional molecules has been developed. Local valence arrangements that dominate the material properties are sometimes not three-dimensionally ordered. This method that comprises diffuse X-ray scattering and resonant X-ray scattering is suitable in such cases. Using this method, we present clear evidence of the low-dimensional valence arrangement in two halogen-bridged one-dimensional metal complexes, so- called MMX chains. This family allows us to control many physical and structural parameters by chemical substitution of bridging halogen, counterions, or metal ions, and one of our samples carries an unusual metallic phase. It is demonstrated with this complex that the present method makes it possible to have microscopic insight to low-dimensionally ordered systems.
  • A Kobayashi, T Kojima, R Ikeda, H Kitagawa
    INORGANIC CHEMISTRY 45 (1) 322 - 327 0020-1669 2006/01 [Refereed][Not invited]
     
    A metal-dimer assembled system, M-2(dtp)(4) (M = Ni, Pd; dtp = dithiopropionate, C2H5CS2-), was synthesized and analyzed by the X-ray single-crystal diffraction method, UV-vis-near-IR spectra of solutions, solid-state diffuse reflectance spectroscopies, and electrical conductivity measurements. The structures exhibit one-dimensional metal-dimer chains of M-2(dtP)(4) with moderate interdimer contact. These complexes are semiconducting or insulating, which is consistent with the fully filled d(Z2) band of M-II(d(8)). Interdimer metal-metal distances were 3.644(2) angstrom in Ni-2(dtp)(4) and 3.428(2) angstrom in Pd-2(dtp)(4), each of which is marginally longer than twice the van der Waals radius of the metal. Interdimer charge-transfer transitions were nevertheless observed in diffuse reflectance spectra. The origin of this transition is considered to be due to an overlap of two adjacent d(a*) orbitals, which spread out more than the d(Z2) orbital because of the antibonding d(sigma*) character of the M(d(Z2))-M(d(Z2)). The Ni-2(dtp)(4) exhibited an interdimer charge-transfer band at a relatively low energy region, which is derived from the Coulomb repulsion of the 3d(sigma*). orbital of Ni.
  • Inagaki Yuji, Kobayashi Atsushi, Asano Takayuki, Sakon Takuo, Kitagawa Hiroshi, Motokawa Mitsuhiro, Ajiro Yoshitami
    J Phys Soc Jpn 一般社団法人日本物理学会 74 (10) 2683 - 2686 0031-9015 2005/10/15 
    The ground-state properties of an $S=1/2$quasi-one-dimensional quantum spin system (CH3)2NH2CuCl3 were investigated by X-ray structure analyses and high-field magnetization measurements. X-ray studies confirmed that the structural phase transition from monoclinic to triclinic phases occurs between 300 and 200 K. The magnetic chain realized at low temperatures involves three types of chlorine-bridged pathways that result in bond alternation with $n=4$, where $n$is the period of the spatial structure. High-field magnetization measurements at the lowest temperature of 0.5 K revealed a unique magnetization process with an initial rapid increase in a low field and a relatively gradual increase in a high field, separated by the magnetization plateau with half of the saturation moment. On the basis of these experimental facts, a novel quantum chain model, which is characterized by the alternation of an $S=1$triplet dimer and an $S=0$singlet dimer is proposed for the ground state of the present system.
  • A Kobayashi, H Kitagawa, R Ikeda, S Kitao, M Seto, M Mitsumi, K Toriumi
    SYNTHETIC METALS 135 (1-3) 405 - 406 0379-6779 2003/04 [Refereed][Not invited]
     
    I-129 Mossbauer spectroscopic measurement was made for the title complex to investigate the insulating phase below a metal-insulator transition (TM-I = 205 K). Two chemically independent sites of iodine were observed, suggesting that the insulating phase is in alternate charge-polarization state of -Pt2+-Pt3+-I-Pt3+-Pt2+-I-Pt2+-Pt3+-I-Pt3+-Pt2+-I-.
  • A Kobayashi, H Kitagawa, R Ikeda
    MOLECULAR CRYSTALS AND LIQUID CRYSTALS 379 315 - 320 1058-725X 2002 [Refereed][Not invited]
     
    A novel binuclear Pt(III) complex, Pt-2(dtp)(4)Br-2 (dtp = CH3CH2CS2-, dithiopropionato), was synthesized by a reaction of Pt-2(dtp)(4) and Br-2 in refluxing toluene, which could be used as starting material for a new MMX-chain system such as a possible mixed-valence Pt-2(dtp)(4)Br. The title complex has been characterized by X-ray single-crystal structure analysis, UV-Visible-NearIR, IR, and polarized Raman spectroscopies. The Pt-2(dtp)(4)Br-2 crystallized in monoclinic P2(1)/a and this structure is almost same as Pt-2(dtp)(4)I-2. Halogen-replacement effect from X = I to Br on Pt-2(dtp)(4)X-2 has been examined. The Pt-Pt distance in X = Br is slightly shorter than that in X = I. Raman peak of the v(Pt-Pt) mode is slightly shifted to higher wavenumber from X = I to Br. These changes are considered to be mainly caused by the difference of electron densities of antibonding d(sigma)* orbitals.

MISC

Association Memberships

  • THE JAPANESE PHOTOCHEMISTRY ASSOCIATION   JAPAN SOCIETY FOR MOLECULAR SCIENCE   JAPAN SOCIETY OF COORDINATION CHEMISTRY   THE CHEMICAL SOCIETY OF JAPAN   複合系の光機能研究会   ナノ学会   

Research Projects

  • 日本学術振興会：科学研究費助成事業 基盤研究(B)
    Date (from‐to) : 2023/04 -2027/03 
    Author : 小林 厚志
  • Development of flexible water splitting photoelectrochemical cells using conductive photocatalytic ink
    Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Challenging Research (Exploratory)
    Date (from‐to) : 2022/06 -2024/03 
    Author : Atsushi Kobayashi
  • 機能性分子の自己集積能に基づくZスキーム水分解光触媒の開発
    岩谷直治記念財団：第48回岩谷科学技術研究助成
    Date (from‐to) : 2022/04 -2023/03
  • 人工光合成を加速する固-固界面制御分子素子の開発
    カシオ科学振興財団：
    Date (from‐to) : 2021/12 -2022/11
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research on Innovative Areas (Research in a proposed research area)
    Date (from‐to) : 2020/04 -2022/03 
    Author : 小林 厚志
     
    【高活性光増感色素多層膜の開発】Ru色素多層膜の内部および表面構造を分子レベルで制御しつつ、Pt担持二酸化チタンまたは層状ニオブ酸ナノ粒子表面へ担持させることで、酸化還元可逆な電子伝達剤との反応性を向上させながら、高活性な水素生成光触媒の創出に成功した。470nmの青色光照射下における見かけの量子収率は1％を超え、色素増感光触媒として非常に高活性であることも確認でき、色素多層膜を用いた本手法が従来の単純な色素増感機構を刷新しうる有望性を持つことが明らかとなった。 【水素生成光カソードの開発】多孔質酸化ニッケル電極に対して、Ru色素複層膜を形成後に有機ポリマー触媒を蒸着することで、水素生成光カソードを創出した。このポリマー触媒と色素複層膜からなる新規光カソードは可視光照射下で水素を生成することが確認され、その効率向上には色素多層膜-ポリマー触媒間のエネルギー・電子移動過程の制御が重要であることがわかった。さらに、Ru色素がNiO電極表面から脱離することをポリマー触媒蒸着により効果的に抑制可能なこともわかり、本手法が水素生成光カソードの活性・耐久性向上に資する有望なものであることが実証できた。 【酸素生成光アノードの開発】多孔質二酸化チタン電極に対し、Ru色素と正孔輸送剤となるプルシアンホワイト類縁体やカルバゾール重合体を修飾し、酸素生成触媒となるプルシアンブルー類縁体やRu錯体触媒を結合させたヘテロ接合型光アノードを新たに創出した。これらの光電極は十分な正電位印加下で酸素生成活性を有することが明らかとなり、正孔輸送剤を導入した電極では光照射下における光電流がさらに増強される特性を有することがわかった。これらの結果は酸素生成光アノード構築において、色素-触媒界面に正孔輸送剤を導入することが、活性向上に有望であることを強く示唆するものと考えられる。
  • 固相合成法を用いた強発光性銅錯体の成膜プロセスにおけるその場合成法の開発
    Japan Society for the Promotion of Science：Challenging Research(Exploratory)
    Date (from‐to) : 2018 -2019 
    Author : KOBAYASHI Atsushi
  • 色素-触媒界面にキャリヤー集約ナノ薄膜を形成させた水分解色素増感光電気化学セルの開発
    ENEOS Hydrogen Trust Fund：-
    Date (from‐to) : 2018 
    Author : KOBAYASHI Atsushi
  • 相対湿度の三次元可視化のための発光性ナノ集積体の構築
    島津科学技術振興財団：
    Date (from‐to) : 2016/04 -2017/03 
    Author : 小林 厚志
  • Visualization of Proton Conductivity by Luminescence Energy of Nano-sized Coordination Polymer
    Inamori Foundation：
    Date (from‐to) : 2016/04 -2017/03 
    Author : KOBAYASHI Atsushi
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Scientific Research (C)
    Date (from‐to) : 2014/04 -2017/03 
    Author : Kobayashi Atsushi
     
    To develop a new methodology to control of photo-excitation energy dynamics in the mesoscopic region, we have investigated the effect of meso-crystallization on the photoluminescence properties of coordination polymers (CPs), and the effect of surface modification of semiconductor nanoparticles on the photosensitization ability. We found that meso-crystallized CP exhibited different luminescence behavior from that of bulk crystals and molecular complexes. In the solar water splitting reaction driven by semiconductor nanoparticles, we found that the ligand covering the surface of the photosensitizing nanoparticle was involved in the formation of the catalyst-photosensitizer complex. In addition, we demonstrate that the efficiency of the interfacial electron transfer reaction on the dye-semiconductor interface was drastically improved by the formation of multilayers of sensitizing dyes. These results indicate the importance of the nanostructure in the photo-generated exciton dynamics.
  • 正孔の迅速拡散に立脚した新しい太陽光水分解セルの開発
    村田学術振興財団：第32回研究助成
    Date (from‐to) : 2016/09 
    Author : 小林 厚志
  • Development of a self-assembled super-nanocrystal photocatalyst
    JST：PRESTO
    Date (from‐to) : 2012/12 -2016/03 
    Author : KOBAYASHI Atsushi
  • 発光性Pt(II)錯体配位子からなる環境マルチセンシングナノ集積体の構築
    松籟科学技術振興財団：
    Date (from‐to) : 2016/03 
    Author : 小林 厚志
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2011/04 -2014/03 
    Author : KATO Masako, KOBAYASHI Atsushi, CHANG Ho-chol
     
    The purpose of this project is to construct novel assembled metal complex systems with dynamical ordering by using various intermolecular interactions such as metal-metal, pai-pai, hydrophobic, and hydrogen bonding interactions. In this concept, we have developed luminescent metal complexes which exhibit unique chromic behaviors in response to the various environmental stimuli such as vapor, light, and heat: 1) Vapochromic coordination polymers and suplamolecular restorable systems based on luminescent platinum(II) or ruthenium(II) complexes; 2) Luminescent dinuclear copper(I) complexes which exhibit luminescence changes induced by light and vapor; 3) Vapor and mechanically induced chromic behavior of platinum(II) complexes with a dimer-of-dimer motif and the effect of hetero metal ions.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2009/07 -2014/03 
    Author : CHANG Ho-Chol, KATO Masako, KOBAYASHI Atsushi, KANAIZUKA Katsuhiko
     
    We have developed the design of redox-active liquid crystals which allow us to switch molecular and assembled states simultaneously by means of electrochemical redox processes. We experimentally demonstrate that [M(L)(C10,8bpy)]n (L = redox-active ligand, n = 0 or +) shows versatility not only for mesogen for LC but also for thermochromism, emission, Lewis-acid binding, and redox-activity at LC phase. These physicochemical functions of the skeleton, in particular, appear at columnar LC phase, where the functional moieties play an essential role for constructing their physical structures. Therefore, the results could be foundational for developing chemical devices with the aid of the Coordination programming. In addition to the above results, we uncover novel features of coordination complexes with redox-active ligand, for example, redox-active metalloligand, photocatalytic hydrogen production, valence tautomerism coupled with macroscopic phase, and multiresponsive chromism.
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2012/04 -2014/03 
    Author : KOBAYASHI Atsushi
     
    The purpose of this project is to create a new photofunctional coordination polymer system composed of luminescent metalloligand in mesoscopic region where several unique properties based on the quantum confinement effect are well known. We successfully synthesized new coordination polymers composed of well-known photosensitizer, Ru(bpy)3 moiety, and found that the photosensitizing ability of the coordination polymer with ca. 100 nm diameter is remarkably higher than that of Ru(bpy)3 in the solution state or the bulk of coordination polymer.
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2009 -2010 
    Author : 加藤 昌子, 小林 厚志
     
    本研究の目的は、光により誘起された配位構造の変化が連鎖的もしくは協奏的に集積構造の変化に波及してクロミズム現象として現れる、新しいタイプのフォトクロミック系の構築である。22年度は光構造変換を誘起するために、チオシアン酸イオン等の両座配位子を含む錯体の光誘起結合異性化や中心金属イオンの光誘起酸化状態変化など、配位化合物特有の性質を利用した以下の3つの系の開発と機構解明を行った。 1.ジメチルスルホキシド銅(I)錯体のフォトクロミック挙動の解明と高性能化.昨年度までに見出した菱形骨格を有する銅(I)複核錯体、[Cu_2(μ-I)_2(dmso)_2(PPh_3)_2]のフォトクロミック発光の機構を解明するために、対応する臭素架橋錯体とともに構造化学的、分光学的検討を行った。また、ヨウ素架橋銅(I)複核錯体は加熱により二量化が起こり、強発光性の四核錯体[Cu_4(μ-I)_4(PPh_3)_4]が生成することが確認された。 2.チオシアナト白金(II)錯体の光誘起結合異性化によるフォトクロミズムの発現.以前に見出している[Pt(SCN)_2(bpy)]の光誘起結合異性化を基盤に、多孔性水素結合ネットワークを形成する[Pt(NCS)_2(H_2dcbpy)]および柔軟集積構造を形成する[Pt(NCS)_2(dCnbpy)]を構築した。これらが熱や蒸気に対して応答性を示すことを見出した。また、溶液中では光により結合異性化が誘起され、これに伴う発光変化を観測した。 3.白金複核錯体の酸化状態の光制御に基づくフォトクロミズムの発現.アミダト架橋シクロメタレート型白金(II)複核錯体がアセトン中可視光照射により紫色⇔無色の可逆的な色変化を示すことを見出した。光励起による酸化状態の変化と混合原子価状態生成に伴う集積構造変化が起こっていると考えられ、フォトクロミック挙動を示す混合原子価白金錯体として明確に示された初めての例である。
  • 新規低次元電子系金属錯体の合成と物性解明
    Japan Society for the Promotion of Science：Grant-in-Aid for Young Scientists (B)
    Date (from‐to) : 2007/04 -2009/03 
    Author : KOBAYASHI Atsushi
  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2008 -2008 
    Author : 加藤 昌子, 小林 厚志
     
    本研究では, 環境感応型発光性金属錯体を基盤にして, 光により誘起された配位構造の変化が連鎖的もしくは協奏的に集積構造の変化に波及してクロミズム現象として現れる, 全く新しいタイプのフォトクロミックシステムの構築をめざしている。今年度は光による構造変換を誘起するために, ジメチルスルホキシド(dmso)、ニトロシル(NO)、チオシアン酸イオン(NCS^-)などの両座配位子を用いて新規系の探索を行った。 1. フォトクロミックな発光変化を示すハロゲン架橋銅(I)複核錯体. 銅(I)多核錯体はしばしば強発光性を示すため、近年、安価で高効率な発光材料として注目を集めている。今回、dmsoが配位した銅(I)複核錯体、[Cu2(μ-1) 2(dmso) 2(PPh3)2]の結晶の単離に成功し、構造を明らかにした。この錯体は強発光性を示すが、350nmの光を照射すると、発光色が青色から緑色に変化し、逆に、照射後の錯体をdmso雰囲気下で加熱すると元の青色に戻ることが見出された。この"光で発光色が変化する"ユニークなフォトクロミック挙動は、光励起によるdmso分子の動きに誘起された構造変化に基づくものと考えられる。 2. 光誘起結合異性化を示す白金(II)錯体の構築とフォトクロミズムの発現. ニトロシル錯体は光に鋭敏に反応して結合異性化が起こることが知られているが, 異性化状態 (M-ON) は一般に低温では安定であるものの室温ではもとの(M-NO)に容易に戻ってしまう。異性化状態も室温でも2つの異性体がともに比較的安定で, 異性化に伴って著しい色変化が起こるニトロシル白金錯体を構築する。今回、 [PtBr (NH3) 4 (NO) ] (PF6) 2を合成し、フォトクロミック挙動を調べた。その結果、対応するCl錯体より光異性化状態が安定になることが見出された。
  • Japan Society for the Promotion of Science：Grants-in-Aid for Scientific Research
    Date (from‐to) : 2007 -2008 
    Author : KOBAYASHI Atsushi
     
    1-2次元の境界領域に位置する新規MX-Ladder 錯体を合成し、その電子状態を詳細に検討した。その結果、一次元系MX-Chain 錯体で観測されていた、電荷密度波相が梯子内だけでなく、梯子間でも秩序化した新たな電子相を発見し、また梯子内の物理パラメータを化学的に制御することで、梯子内の電子状態を逆位相電荷密度波から、同位相電荷密度波へと制御可能なことを見出した。

Copyright © MEDIA FUSION Co.,Ltd. All rights reserved.