Researcher Database

Masaki Yoshida
Faculty of Science Chemistry Inorganic and Analytical Chemistry
Assistant Professor

Researcher Profile and Settings


  • Faculty of Science Chemistry Inorganic and Analytical Chemistry

Job Title

  • Assistant Professor


Research funding number

  • 20712293


J-Global ID

Research Interests

  • 触媒・化学プロセス   電子状態   錯体化学   

Research Areas

  • Nanotechnology/Materials / Inorganic and coordination chemistry

Academic & Professional Experience

  • 2014/01 - Today Hokkaido University Department of Chemistry, Faculty of Science Assistant Professor
  • 2013/04 - 2013/12 Institute for Molecular Science Department of Life and Coordination-Complex Molecular Science Postdoctoral Fellow
  • 2010/04 - 2013/03 JSPS Research Fellow (DC1)


  •        - 2013/03  Kyushu University  Faculty of Science  Department of Chemistry
  •        - 2008/03  Kyushu University  School of Sciences  Department of Chemistry

Research Activities

Published Papers

  • Atsushi Kobayashi, Shin-ichiro Imada, Yuze Yao, Yuki Nagao, Yuto Kubota, Masaki Yoshida, Masako Kato
    Bulletin of the Chemical Society of Japan 0009-2673 2021/09/28 [Refereed]
  • 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.
  • Hiroki Otsuka, Atsushi Kobayashi, Masaki Yoshida, Masako Kato
    Dalton Transactions 1477-9226 2021 [Refereed]
    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...
  • Masaki Yoshida, Yusuke Makino, Toshiyuki Sasaki, Shunichi Sakamoto, Satoshi Takamizawa, Atsushi Kobayashi, Masako Kato
    CrystEngComm 23 (34) 5891 - 5898 2021 [Refereed]
    A series of polyhalogenated platinum(ii)–bipyridine complexes showed solvent-of-crystallisation-dependent elastic flexibility and luminescence.
  • 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 [Refereed]

    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 0947-6539 2020/10/16 [Refereed][Not invited]
  • Sae Kondo, Nobutaka Yoshimura, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Dalton Transactions 49 (46) 16946 - 16953 1477-9226 2020/10 [Refereed]

    A homogeneous thin film of a simple and highly luminescent Cu(I) complex, [CuI(PPh3)2(py)] (PPh3 = triphenylphosphine, py = pyridine) (Cu-py), was fabricated via spin coating using polyvinylpyrrolidone (PVP) and pyridine...

  • Mari Kimura, Masaki Yoshida, Sho Fujii, Atsushi Miura, Kosei Ueno, Yasuhiro Shigeta, Atsushi Kobayashi, Masako Kato
    Chemical Communications 56 (85) 12989 - 12992 1359-7345 2020/09 [Refereed]

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

  • 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 2020/07/14 [Refereed][Not invited]
  • Atsushi Kobayashi, Tomoka Ehara, Masaki Yoshida, Masako Kato
    Inorganic Chemistry 59 (14) 9511 - 9520 0020-1669 2020/07/02 [Refereed][Not invited]
  • Masaki Yoshida, Masako Kato
    Coordination Chemistry Reviews 408 213194  0010-8545 2020/04 [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 2020/02/22 [Refereed][Not invited]
    Transition-metal complexes bearing biaryl-2,2'-diyl ligands are expected to show intense luminescence. However, difficulties in synthesis have prevented their further functionalization and practical applications. Herein, a series of platinum(II) complexes bearing biaryl-2,2'-diyl ligands, which have never been prepared in air up to now, were synthesized via transmetalation and successive cyclometallation of biarylboronic acids. This approach does not require any air/moisture-sensitive reagents and features a simple synthesis even in air. The resulting (Et4N)2[Pt(m,n-F2bph)(CN)2] (m,n-F2bph = m,n -difluorobiphenyl-2,2'-diyl) complexes exhibited intense green emissions with high quantum efficiencies of up to 0.80 at 298 K. The emission spectral fitting and variable-temperature emission lifetime measurements indicated that the high quantum efficiency was achieved owing to the tight packing structure and strong σ-donating ability of bph.
  • Masaki Yoshida, Sae Yanagida, Daisuke Saito, Atsushi Kobayashi, Masako Kato
    Analytical Sciences 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.
  • Nobutaka Yoshimura, Atsushi Kobayashi, Wataru Genno, Takashi Okubo, Masaki Yoshida, Masako Kato
    Sustainable Energy & Fuels 4 (7) 3450 - 3457 2020 

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

  • Junichi Yanagisawa, Tomoaki Hiraoka, Fumiya Kobayashi, Daisuke Saito, Masaki Yoshida, Masako Kato, Fumitaka Takeiri, Genki Kobayashi, Masaaki Ohba, Leonard F. Lindoy, Ryo Ohtani, Shinya Hayami
    Chemical Communications 56 (57) 7957 - 7960 1359-7345 2020 

    Luminescent ionic liquids are formed by the melting of tetranuclear rhenium(v) clusters.

  • Atsushi Kobayashi, Shin-ichiro Imada, Dongjin Wang, Yuki Nagao, Masaki Yoshida, Masako Kato
    Faraday Discussions 225 184 - 196 1359-6640 2020 [Refereed][Not invited]

    The luminescent and proton conductive Pt(II) complex [PtCl(tpy-o-py)]Cl and its HCl adduct [PtCl(tpy-o-pyH)]Cl2 (o-Pt and o-Pt·HCl, respectively; tpy-o-py = 2,2′: 6′,2′′-terpyridine-6′,2′′′-pyridine) were synthesised and their crystal structures, vapochromic behaviour, and...

  • Tomohiro Ogawa, W. M. C. Sameera, Masaki Yoshida, Atsushi Kobayashi, Masako Kato
    Chemical Physics Letters 739 137024  0009-2614 2020/01 [Refereed][Not invited]
  • Atsushi Kobayashi, Shin-ichiro Imada, Yasuhiro Shigeta, Yuki Nagao, Masaki Yoshida, Masako Kato
    Journal of Materials Chemistry C 7 14923 - 14931 2050-7534 2019/12 [Refereed][Not invited]

    New switchable vapochromic luminescent and highly-proton-conducting Pt(ii) complexes [PtCl(tpypy)]Cl and [PtCl(tpypyH)]Cl2 are reported.

  • Fumiya Kobayashi, Ryo Ohtani, Saki Teraoka, Masaki Yoshida, Masako Kato, Yingjie Zhang, Leonard F. Lindoy, Shinya Hayami, Masaaki Nakamura
    Chemistry – A European Journal 25 (23) 5875 - 5879 0947-6539 2019/04/23 [Refereed][Not invited]
  • Matsukawa H, Yoshida M, Tsunenari T, Nozawa S, Sato-Tomita A, Maegawa Y, Inagaki S, Kobayashi A, Kato M
    Scientific Reports 9 (1) 15151 - 15151 2019 [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.
  • Yoshimura N, Kobayashi A, Yoshida M, Kato M
    Bulletin of the Chemical Society of Japan 92 1793 - 1800 2019 [Refereed][Not invited]
  • Yanagida S, Yoshida M, Sameera WMC, Kobayashi A, Kato M
    Bulletin of the Chemical Society of Japan 92 1684 - 1693 2019 [Refereed][Not invited]
  • Sun Y, Amsler M, Goedecker S, Caravella A, Yoshida M, Kato M
    CrystEngComm 21 3948 - 3953 2019 [Refereed][Not invited]
  • Ishigaki Y, Sugawara K, Yoshida M, Kato M, Suzuki T
    Bulletin of the Chemical Society of Japan 92 (7) 1211 - 1217 2019 [Refereed][Not invited]
  • Shigeta Y, Kobayashi A, Yoshida M, Kato M
    Inorganic Chemistry 58 (11) 7385 - 7392 0020-1669 2019 [Refereed][Not invited]
  • Kobayashi A, Shimizu K, Watanabe A, Nagao Y, Yoshimura N, Yoshida M, Kato M
    Inorganic Chemistry 58 (4) 2413 - 2421 0020-1669 2019 [Refereed][Not invited]
  • Kobayashi A, Fujii M, Shigeta Y, Yoshida M, Kato M
    Inorganic Chemistry 58 (7) 4456 - 4464 0020-1669 2019 [Refereed][Not invited]
  • Yoshida M, Shitama H, Sameera WMC, Kobayashi A, Kato M
    Chemistry - A European Journal 25 7669 - 7678 0947-6539 2019 [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.
  • 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.
  • Masaki Yoshida, Masako Kato
    Coordination Chemistry Reviews 355 101 - 115 0010-8545 2018/01/15 [Refereed][Not invited]
    Double-decker platinum complexes with N-heteroaromatic ligands have attracted increasing interest due to their outstanding luminescent properties and rich redox behavior. In this review, the design principles and recent observations on luminescent and redox-active double-decker platinum complexes are discussed. Because these properties are precisely controlled by intra- and intermolecular Pt⋯Pt electronic interactions, double-decker platinum complexes have been also used to obtain phenomena driven by stimulus–responsive color and luminescence change, such as vapochromism, mechanochromism, thermochromism, and electrochromism. This review also summarizes chromic materials based on double-decker platinum complexes influenced by changes in the Pt⋯Pt electronic interactions.
  • Kitano H, Kobayashi A, Yoshida M, Kato M
    Sustainable Energy & Fuels Royal Society of Chemistry ({RSC}) 2398-4902 2018 [Refereed][Not invited]
  • Kobayashi A, Yoshida Y, Yoshida M, Kato M
    Chemistry - A European Journal Wiley 24 14750 - 14759 0947-6539 2018 [Refereed][Not invited]
  • Kobayashi A, Watanabe S, Yoshida M, Kato M
    ACS Applied Energy Materials 1 2882 - 2890 2018 [Refereed][Not invited]
  • 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.
  • Ogawa T, Sameera WMC, Saito D, Yoshida M, Kobayashi A, Kato M
    Inorganic chemistry 57 (22) 14086 - 14096 0020-1669 2018 [Refereed][Not invited]
  • 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.
  • Masaki Yoshida, Mio Kondo, Masaya Okamura, Mari Kanaike, Setsiri Haesuwannakij, Hidehiro Sakurai, Shigeyuki Masaoka
    FARADAY DISCUSSIONS 198 181 - 196 1359-6640 2017/06 [Refereed][Not invited]
    A series of group 8 metal complexes with the same molecular framework, [M(PY5Me(2))L](n+) (M = Fe, Ru, and Os; PY5Me(2) = 2,6-bis[1,1-bis(2-pyridyl)ethyl]pyridine; L = monodentate ligand), were successfully synthesized and structurally characterized. The spectroscopic and electrochemical properties as well as the catalytic activity for water oxidation of these complexes were investigated.
  • 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-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.
  • 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.
  • 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, 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.
  • Atsushi Kobayashi, Tatsuya Hasegawa, Masaki 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.
  • Masaya Okamura, Mio Kondo, Reiko Kuga, Yuki Kurashige, Takeshi Yanai, Shinya Hayami, Vijayendran K. K. Praneeth, Masaki Yoshida, Ko Yoneda, Satoshi Kawata, Shigeyuki Masaoka
    NATURE 530 (7591) 465 - 468 0028-0836 2016/02 [Refereed][Not invited]
    Although the oxidation of water is efficiently catalysed by the oxygen-evolving complex in photosystem II (refs 1 and 2), it remains one of the main bottlenecks when aiming for synthetic chemical fuel production powered by sunlight or electricity. Consequently, the development of active and stable water oxidation catalysts is crucial, with heterogeneous systems(3,4) considered more suitable for practical use and their homogeneous counterparts more suitable for targeted, molecular-level design guided by mechanistic understanding(5-19). Research into the mechanism of water oxidation has resulted in a range of synthetic molecular catalysts, yet there remains much interest in systems that use abundant, inexpensive and environmentally benign metals such as iron (the most abundant transition metal in the Earth's crust and found in natural(20,21) and synthetic(22) oxidation catalysts). Water oxidation catalysts based on mononuclear iron complexes have been explored(9,12,16,18), but they often deactivate rapidly and exhibit relatively low activities. Here we report a pentanuclear iron complex that efficiently and robustly catalyses water oxidation with a turnover frequency of 1,900 per second, which is about three orders of magnitude larger than that of other iron-based catalysts. Electrochemical analysis confirms the redox flexibility of the system, characterized by six different oxidation states between Fe-5(II) and Fe-5(III); the Fe-5(III) state is active for oxidizing water. Quantum chemistry calculations indicate that the presence of adjacent active sites facilitates O-O bond formation with a reaction barrier of less than ten kilocalories per mole. Although the need for a high overpotential and the inability to operate in water-rich solutions limit the practicality of the present system, our findings clearly indicate that efficient water oxidation catalysts based on iron complexes can be created by ensuring that the system has redox flexibility and contains adjacent water-activation sites.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • 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.
  • Masaki Yoshida, Mio Kondo, Sena Torii, Ken Sakai, Shigeyuki Masaoka
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 54 (27) 7981 - 7984 1433-7851 2015/06 [Refereed][Not invited]
    Rational molecular design of catalytic systems capable of smooth OO bond formation is critical to the development of efficient catalysts for water oxidation. A new ruthenium complex was developed, which bears pendant SO3- groups in the secondary coordination sphere: [Ru(terpy)(bpyms)(OH2)] (terpy=2,2:6,2-terpyridine, bpyms=2,2-bipyridine-5,5-bis(methanesulfonate)). Water oxidation driven by a Ce4+ oxidant is distinctly accelerated upon introduction of the pendant SO3- groups in comparisons to the parent catalyst, [Ru(terpy)(bpy)(OH2)](2+) (bpy=2,2-bipyridine). Spectroscopic, electrochemical, and crystallographic investigations concluded that the pendant SO3- groups promote the formation of an OO bond via the secondary coordination sphere on the catalyst, whereas the influence of the pendant SO3- groups on the electronic structure of the [Ru(terpy)(bpy)(OH2)](2+) core is negligible. The results of this work indicate that modification of the secondary coordination sphere is a valuable strategy for the design of water oxidation catalysts.
  • Nakamura T., Yoshida M., Kondo M., Masaoka S.
    Meeting Abstracts of the Physical Society of Japan 一般社団法人日本物理学会 70 1867 - 1867 2189-079X 2015
  • Tomohiro Ogawa, Masaki Yoshida, Hiroki Ohara, Atsushi Kobayashia, Masako Kato
    CHEMICAL COMMUNICATIONS 51 (69) 13377 - 13380 1359-7345 2015 [Refereed][Not invited]
    An ionic liquid fabricated froman 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.
  • Tomomi Koshiyama, Nao Kanda, Koki Iwata, Masayuki Honjo, Sana Asada, Tatsuru Hatae, Yasuhiro Tsuji, Masaki Yoshida, Masaya Okamura, Reiko Kuga, Shigeyuki Masaoka, Masaaki Ohba
    DALTON TRANSACTIONS 44 (34) 15126 - 15129 1477-9226 2015 [Refereed][Not invited]
    A composite containing a liposome and a lipophilic ruthenium complex was synthesized to regulate an O-2 evolution reaction using cerium(IV) ammonium nitrate as an oxidizing reagent. We found that the surrounding environment of the reaction centre is an important factor for controlling the O-2 evolution catalytic reaction. We successfully regulated the reaction activity using the linker length of the lipophilic ligand and using the head groups of the phospholipid component.
  • Masaki Yoshida, Shigeyuki Masaoka
    RESEARCH ON CHEMICAL INTERMEDIATES 40 (9) 3169 - 3182 0922-6168 2014/11 [Refereed][Not invited]
    This paper reviews results from study of mononuclear ruthenium complexes capable of catalyzing the oxidation of water to molecular oxygen. These catalysts may be classified into three groups, with different rate laws associated with O-2 evolution. In one class, O-2 evolution proceeds via radical coupling of the oxygen atom of an Ru-V=O species with a hydroxocerium(IV) ion. O-2 evolution catalyzed by the second class occurs via acid-base reaction of the oxygen atom of an Ru-V=O species with a water molecule. In the third group, the dominant mechanism is oxo-oxo radical coupling between two Ru-V=O species. Several significant properties of the oxidant Ce(IV) are also discussed, including the singlet biradical character of the hydroxocerium(IV) ion.
  • Masaki Yoshida, Mio Kondo, Toshikazu Nakamura, Ken Sakai, Shigeyuki Masaoka
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 53 (43) 11519 - 11523 1433-7851 2014/10 [Refereed][Not invited]
    A series of [{(terpy)(bpy)Ru}(-O){Ru(bpy)(terpy)}](n+) ([RuORu](n+), terpy=2,2;6,2-terpyridine, bpy=2,2-bipyridine) was systematically synthesized and characterized in three distinct redox states (n=3, 4, and 5 for Ru-2(II,III), Ru-2(III,III), and Ru-2(III,IV), respectively). The crystal structures of [RuORu](n+) (n=3, 4, 5) in all three redox states were successfully determined. X-ray crystallography showed that the RuO distances and the Ru-O-Ru angles are mainly regulated by the oxidation states of the ruthenium centers. X-ray crystallography and ESR spectra clearly revealed the detailed electronic structures of two mixed-valence complexes, [(RuORuIV)-O-III](5+) and [(RuORuIII)-O-II](3+), in which each unpaired electron is completely delocalized across the oxo-bridged dinuclear core. These findings allow us to understand the systematic changes in structure and electronic state that accompany the changes in the redox state.
  • Go Nakamura, Masaya Okamura, Masaki Yoshida, Takayoshi Suzuki, Hideo D. Takagi, Mio Kondo, Shigeyuki Masaoka
    INORGANIC CHEMISTRY 53 (14) 7214 - 7226 0020-1669 2014/07 [Refereed][Not invited]
    A series of phosphine-substituted ruthenium poly-pyridine complexes, cis(P,Cl)-[Ru(trpy)(Pqn)Cl]PF6 (cis-Cl), trans(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)](PF6)(2) (trans-PN), cis(P,MeCN)-[Ru(trpy)(Pqn)(MeCN)] (PF6)(2) (cis-PN), and [Ru(trpy)(dppbz)(MeCN)] (PF6)(2) (PP), were synthesized and crystallographically characterized (trpy = 2,2':6',2 ''-terpyridine, Pqn = 8-(diphenylphosphanyl)quinoline, and dppbz = 1,2-bis(diphenylphosphanyl)benzene). In electrochemical measurements for cis-PN and PP, the reduction of cis-PN resulted in the formation of trans-PN via cis trans isomerization and that of PP proceeded via a two-electron-transfer reaction. The mechanism of the electrochemical behaviors is discussed through consideration of five-coordinated species, [Ru(trpy)(Pqn)](n+) or [Ru(trpy)(dppbz)](n+) (n = 0-2), formed by liberation of a monodentate labile ligand.
  • Arisa Fukatsu, Mio Kondo, Masaya Okamura, Masaki Yoshida, Shigeyuki Masaoka
    SCIENTIFIC REPORTS 4 5327  2045-2322 2014/06 [Refereed][Not invited]
    The electrochemical detection of metal complexes in the photoexcited state is important for understanding photoinduced electron transfer (PET) processes, which play a central role in photo-energy conversion systems. In general, however, the redox potentials of excited states have been indirectly estimated by a combination of spectroscopic properties and ground-state redox potentials. To establish a simple method for directly determining the redox potentials of the photoexcited states of metal complexes, electrochemical measurements under several conditions were performed. The electrochemical response was largely influenced not only by the generation of photoexcited molecules but also by the convection induced by photoirradiation, even when the global temperature of the sample solution was unchanged. The suppression of these unfavourable electrochemical responses was successfully achieved by adopting well-established electrochemical techniques. Furthermore, as an initial demonstration, the photoexcited state of a Ru-based metal complex was directly detected, and its redox potential was determined using a thin layer electrochemical method.
  • 吉田 将己, 正岡 重行
    化学 化学同人 67 (6) 12 - 16 0451-1964 2012/06 [Not refereed][Not invited]
  • Ayano Kimoto, Kosei Yamauchi, Masaki Yoshida, Shigeyuki Masaoka, Ken Sakai
    CHEMICAL COMMUNICATIONS 48 (2) 239 - 241 1359-7345 2012 [Refereed][Not invited]
    The Ru-V=O species and other intermediates in O-2 evolution from water catalyzed by [Ru(terpy)(bpy)(OH2)](2+) were spectrophotometrically characterized, and the spectral components observed were identified based on the TD-DFT calculations. Moreover, important insights into the rapid paths after the RDS were given by the DFT studies.
  • Keita Kuroiwa, Masaki Yoshida, Shigeyuki Masaoka, Kenji Kaneko, Ken Sakai, Nobuo Kimizuka
    ANGEWANDTE CHEMIE-INTERNATIONAL EDITION 51 (3) 656 - 659 1433-7851 2012 [Refereed][Not invited]
  • Masaya Okamura, Masaki Yoshida, Reiko Kuga, Ken Sakai, Mio Kondo, Shigeyuki Masaoka
    DALTON TRANSACTIONS 41 (42) 13081 - 13089 1477-9226 2012 [Refereed][Not invited]
    Two new ruthenium(II) complexes bearing dissociable protons, [Ru(trpy)(H(2)bim)Cl]PF6 (1) and [Ru(trpy)(H(2)bim)(OH2)](PF6)(2) (2) (H(2)bim = 2,2'-biimidazole and trpy = 2,2':6',2 ''-terpyridine), were synthesized and characterized, where the H(2)bim and M-OH2 moieties are expected to serve as proton-dissociation sites. Single crystal X-ray diffraction analyses revealed that the H(2)bim and M-OH2 moieties act as proton donors in intermolecular hydrogen bonds. Two pK(a) values of 2 (pK(a1) = 9.0 and pK(a2) = 11.3) were spectrophotometrically determined, where the first proton dissociation is assigned to that from H(2)bim and the second is from M-OH2. This assignment was supported by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations for two sets of conjugated bases, [Ru(trpy)(Hbim)(OH2)](+) and [Ru(trpy)(H(2)bim)(OH)](+) for the first proton dissociation, and [Ru(trpy)(Hbim)(OH)](+) and [Ru(trpy)(bim)(OH2)](+) for the second dissociation. Electrochemical studies in aqueous solutions under various pH conditions afforded the Pourbaix diagram (potential versus pH diagram) of 2, where the pK(a) values found from the diagram agree well with those determined spectrophotometrically. It was also found that 2 demonstrates four-step proton-coupled electron transfer (PCET) reactions to give the four-electron oxidized species, [Ru-IV(trpy)(bim)(O)](2+), without electrostatic charge buildup during the reactions. The multiple PCET ability of 2 would be applicable to various multi-electron oxidation reactions. Catalysis of electrochemical water oxidation was indeed evaluated in the initial attempt to demonstrate multi-electron oxidation reactions, revealing that the water oxidation potential for 2 is lower than that for other ruthenium catalysts, [Ru(trpy)(bpy)(OH2)](2+), [Ru(trpy)(bpm)(OH2)](2+) and [Ru(tmtacn)(bpy)(OH2)](2+) (bpy = 2,2'-bipyridine, bpm = 2,2'-bipyrimidine, and tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane), which are known to be active catalysts for water oxidation.
  • YOSHIDA Masaki, MASAOKA Shigeyuki, SAKAI Ken
    J. Synth. Org. Chem. Jpn. The Society of Synthetic Organic Chemistry, Japan 69 (4) 370 - 378 0037-9980 2011/04/01 [Not refereed][Not invited]
    [Ru(terpy)(bpy)(OH2)]2+ and its analogues were found to be highly active as catalysts toward water oxidation in the presence of Ce4+ as an oxidizing reagent in acidic aqueous media. These findings were considered as a significant breakthrough in this field because there had been a long belief that the four-electron process (i.e., 2H2O→O2+4H++4e−) is much more effectively accelerated by dinuclear or tetranuclear metal complexes. The kinetics of O2 evolution is investigated as a function of either the catalyst concentration or the oxidant concentration, revealing that these catalysts can be classified into two groups exhibiting different rate laws for O2 evolution. Moreover, the singlet biradical character of the hydroxocerium(IV) ion is realized, indicating that the radical coupling of the oxygen atoms of a RuV=O species and a hydroxocerium(IV) ion is the key step for the catalysis. Several important insights into the mechanism of oxygen evolution from water catalyzed by the mononuclear aquaruthenium complexes will also be discussed.
  • Josaku Kiyota, Junpei Yokoyama, Masaki Yoshida, Shigeyuki Masaoka, Ken Sakai
    CHEMISTRY LETTERS 39 (11) 1146 - 1148 0366-7022 2010/11 [Refereed][Not invited]
    An ITO (indium tin oxide) electrode modified with [Ru(terpy)-{4,4'-(CH2PO3H2)(2)-2,2'-bpy}(OH2)](2+) was prepared to gain insight into the mechanism of O-2 evolution from water catalyzed by a series of mononuclear aquaruthenium complexes, such as [Ru-(terpy)(bpy)(OH2)](2+) The modified ITO electrode showed a clear decrease in overpotential for O-2 evolution (1 35 V in an aqueous 0 1 M Na2SO4/H2SO4 solution, pH 4 0), indicating that the O-2 evolution proceeds in a ummolecular fashion without having any intermolecular associations
  • Masaki Yoshida, Shigeyuki Masaoka, Jiro Abe, Ken Sakai
    CHEMISTRY-AN ASIAN JOURNAL 5 (11) 2369 - 2378 1861-4728 2010 [Refereed][Not invited]
    The mechanism of O-2 evolution from water catalyzed by a series of mononuclear aquaruthenium complexes, [Ru(terpy)(bpy)(OH2)(2+), [Ru-(tmtacn)(R(2)bpy)(OH2)(2+) (R = H, Me, and OMe; R(2)bpy = 4,4'-disubstituted-2,2'-bipyridines), and [Ru(tpzm)-(R(2)bpy)(OH2)(2+) (R = H, Me, and OMe), is investigated, where terpy = 2,2':6',2 ''-terpyridine, bpy = 2,2'-bipyridine, tmtacn = 1.,4,7-trimethyl-1,4,7-triazacyclononane, and tpzm = tris(1-pyrazolyl)methane. The kinetics of O-2 evolution is investigated as a function of either the catalyst concentration or the oxidant concentration by employing Ce(NH4)(2)(NO3)(6) as an oxidant; these catalysts can be classified into two groups that have different rate laws for O-2 evolution. In one class, the rate of O-2 evolution is linear to both the catalyst and Ce4+ concentrations, as briefly reported for [Ru(terpy)(bpy)(OH2)](2+) (S. Masaoka, K. Sakai, Chem. Lett. 2009, 38, 182). For the other class, [Ru-(tmtacn)(R(2)bpy)(OH2)](2+), the rate of O-2 evolution is quadratic to the catalyst concentration and independent of the Ce4+ concentration. Moreover, the singlet biradical character of the hydroxocerium(IV) ion was realized by experimental and DFT investigations. These results indicate that the radical coupling between the oxygen atoms of a Ru-v=O species and a hydroxocerium(IV) ion is the key step for the catalysis of [Ru(terpy)(bpy)(OH2)](2+) and [Ru(tpzm)(R(2)bpy)(OH2)](2+), while the well-known oxo-oxo radical coupling among two Ru-v=O species proceeds in the catalysis of [Ru(tmtacn)(R(2)bpy)-(OH2)](2+). This is the first report demonstrating that the radical character provided by the hydroxocerium(IV) ion plays a crucial role in the catalysis of such ruthenium complexes in the evolution of O-2 from water.
  • Masaki Yoshida, Shigeyuki Masaoka, Ken Sakai
    CHEMISTRY LETTERS 38 (7) 702 - 703 0366-7022 2009/07 [Refereed][Not invited]
    [Ru(tmtacn)(R(2)bpy)(OH2)](2+) (tmtacn = 1,4,7-trimethyl-1,4,7-triazacyclononane; R(2)bpy = 4,4'-disubstituted-2,2'-bipyridines, R = H, Me, and OMe) with tmtacn ligated in a facial fashion is found to be active as O-2-evolving catalysts. It is also found that the stronger electron-donating character of R(2)bpy gives rise to the higher O-2-evolving activity.

Awards & Honors

  • 2021/03 日本化学会第101春季年会 若い世代の特別講演
    受賞者: 吉田将己
  • 2019/04 CSJ Presentation Award 2019 in the 99th Annual Meeting of the Chemical Society of Japan
    受賞者: 吉田将己
  • 2018/01 Young Chemist Award of the Hokkaido Branch of the Japan Society for Analytical Chemistry for 2017
    受賞者: 吉田将己
  • 2012/11 Poster award in the 2nd CSJ Chemistry Festa
    受賞者: Masaki Yoshida

Educational Activities

Teaching Experience

  • Freshman Seminar
    開講年度 : 2020
    課程区分 : 学士課程
    開講学部 : 全学教育
    キーワード : 【2020年度限定: 新型 コロナ ウィルス 感染症 】化学 機能性物質 化学産業 ものづくり 高分子科学 生物物理学 科学倫理

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