Hideki Hashimoto

Osaka City University, Ōsaka, Ōsaka, Japan

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Publications (212)560.79 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fucoxanthin shows a large bathochromic shift of its absorption band when it is bound to photosynthetic antenna pigment-protein complexes derived in brown algae (fucoxanthin-chlorophyll a/c binding protein; FCP). In order to try to understand the intermolecular interactions of fucoxanthin responsible for this shift, we attempted to create a system that can control intermolecular interactions of carotenoids. In this study, we prepared the fucoxanthin-silica gel (CARiACT Q-6, mesoporous material) conjugates by adsorbing fucoxanthin molecules into the mesopores of CARiACT, and investigated their spectroscopic properties by recording electronic absorption and circular dichroism spectra. Fucoxanthin in the pores of CARiACT showed spectra that suggested the formation of H- or J-aggregates. The form of the aggregate could be controlled by adjusting the ratio of fucoxanthin to CARiACT. The exciton chirality of H-aggregated fucoxanthin was detected by circular dichroism spectroscopy. Based on the point-dipole approximation we were able to determine the molecular arrangement of H-aggregated fucoxanthin in the pores of CARiACT.
    Journal of Photochemistry and Photobiology A Chemistry 05/2015; DOI:10.1016/j.jphotochem.2015.05.009 · 2.29 Impact Factor
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    ABSTRACT: A series of potentially tridentate Schiff base ligands, {HOPhC=N-(CH2)3-XMe: X = S (HLSMe), Se (HLSeMe)}, was prepared by condensation reactions of salicylaldehyde and the corresponding functionalized propylamines. These ligands were used to form the monocationic complexes, [Mo3S4(LXMe)3]+ (X = S (1+), Se (2+)), through treatment of [Mo3S4(H2O)9]4+ with the appropriate Schiff base ligand in methanol. Single-crystal X-ray structural analysis of 1-PF6 revealed that one Schiff base ligand coordinates to each Mo via the O, N, and SMe donor atoms, and then the mono cationic cluster [Mo3S4(LSMe)3]+ has a pseudo C3 symmetry if the chirality around the coordinated sulfur atoms is not taken into account. Because of the arrangements of the asymmetric Schiff base ligand, this monocationic cluster possibly adopts one of two axial chiralities. Furthermore, each sulfur atom of the three coordinated SMe groups in the complex cation is also chiral affording the two enantiomers observed in the unit cell. Dynamic behaviors of complexes 1-PF6 and 2-PF6 in solution were examined using line shape analyses of variable temperature NMR spectra revealing that the rate constant of the chiral inversion at the S atoms in 1-PF6 is greater than that at the Se atoms in 2-PF6 and the difference in the ΔH‡ values of 1-PF6 (47.1 kJ mol−1) and 2-PF6 (56.7 kJ mol−1) and the negative ΔS‡ values (−39.9 and −57.5 J mol−1 K−1 for 1-PF6 and 2-PF6, respectively) suggest that the inversion processes involve bond cleavage between the metal centers and S or Se atoms followed by coordination of solvent molecules. The electrochemical properties of 1-PF6 and 2-PF6 were evaluated using cyclic voltammetry and this revealed that both 1+ and 2+ exhibit two consecutive, reversible one-electron reduction waves that are assigned to formal Mo(IV IV IV)/Mo(III IV IV) and Mo(III IV IV)/Mo(III III IV) couples, respectively. The ability of 1-PF6 and 2-PF6 to catalyze the electroreduction of H+ was also examined using CH3CO2H or CF3CO2H as a proton source. Noteworthy, the redox potentials for the catalytic wave depend on the acidity of the added acids. Thus, the catalytic current around the first reduction wave is observed in the presence of the stronger trifluoroacetic acid as a proton source, while the current around the second reduction wave appears when the weaker acetic acid is used.
    Bulletin of the Chemical Society of Japan 02/2015; 88(2):292-299. DOI:10.1246/bcsj.20140275 · 2.22 Impact Factor
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    ABSTRACT: Since photochemical CO2 reduction using long wavelength regions of sunlight is important, we have reported the first photochemical CO2 reduction with red visible light (>650 nm) by using a synthetic chlorophyll derivative covalently linked with a rhenium bipyridine complex. In the reported system, electron/energy transfer from the photoexcited chlorophyll to the catalytic Re complex was not so effective. To accelerate the process for achieving efficient photochemical reduction of CO2, we controlled the redox potential of Re complex and improved the chlorophyll donor by a simple modification. As a result, we achieved strong quenching of the excited states of a 131-deoxochlorophyll derivative with a rhenium bipyridine complex in a molecule.
    Bulletin of the Chemical Society of Japan 02/2015; 88(2):346-351. DOI:10.1246/bcsj.20140326 · 2.22 Impact Factor
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    ABSTRACT: Absorption and Raman spectra of spheroidene dissolved in various organic solvents and bound to peripheral light-harvesting LH2 complexes from photosynthetic purple bacteria Rhodobacter (Rba.) sphaeroides 2.4.1 were measured. The results showed that the peak energies of absorption and C-C and C=C stretching Raman lines are linearly proportional to the polarizability of solvents, as has already been reported. When comparing these results with those measured on LH2 complexes, it was confirmed that spheroidene is surrounded by a media with high polarizability. However, the change in the spectral width of the Raman lines, which reflect vibrational decay time, cannot be explained simply by a similar dependence of solvent polarizability. The experimental results were analyzed using a potential theoretical model. Consequently, a systematic change in the Raman line widths in the ground state can be satisfactorily explained as a function of the viscosity of the surrounding media. Even when the absorption peaks appear at the same energy, the vibrational decay time of spheroidene in the LH2 complexes is approximately 15-20 % slower than that in organic solvents.
    Photosynthesis Research 02/2015; 124(1). DOI:10.1007/s11120-015-0095-z · 3.19 Impact Factor
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    ABSTRACT: Heterometallic trinuclear M2M' complexes (M = Rh, Ir; M' = Pt, Pd) containing a platinum or palladium moiety with chelated bis-N-heterocyclic carbene ligands, [(MCp*)2{M'(bisNHC-Cn-R)}(μ3-S)2](BPh4)2 (M = Rh, Ir; M' = Pt, Pd; bisNHC-Cn-R = methylene-, ethylene-, or propylene-bridged bis(N-alkyl-imidazolylidene)), were synthesized by reacting bis(hydrosulfido)platinum(II) or palladium(II) complexs with bisNHC-Cn-R and hydroxo-bridged dinuclear complexes [(MCp*)2(μ-OH)3](BPh4), whose dinuclear structures remained intact during the formation of the trinuclear complexes, which was confirmed by using electrospray mass spectrometry and NMR spectroscopy. The heterometallic trinuclear M2M' complexes with a variety of alkylene bridges in bisNHC-Cn-R showed two reversible reduction waves in the cyclic voltammogram, and the second reduction potentials were affected by the alkylene chain lengths, which caused different dihedral angles between the imidazolylidene rings and the coordination plane of the platinum or palladium center. The M2M' complexes, except for those containing the platinum unit with the ethylene-bridged bisNHC ligands, showed dynamic behavior in solution due to the flapping wing motion of the NHC ligand moieties. Although activation parameters obtained from line-shape analyses on variable-temperature NMR spectra of the complexes suggested that the flapping wing motion occurred without bond cleavage, large negative ΔS(‡) values were obtained for the complexes with the palladium unit with the ethylene-bridged ligand, suggesting that the Pd-Ccarbene bond cleavage, accompanied by coordination of solvent molecules, occurred.
    Inorganic Chemistry 01/2015; 54(2). DOI:10.1021/ic502039d · 4.79 Impact Factor
  • Yosuke Imanaka, Hideki Hashimoto, Takanori Nishioka
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    ABSTRACT: Sugar-incorporated C-C-N pincer Pd complexes possessing NHC units with various substituents, namely, methyl, isopropyl, benzyl, or D-glucopyranosyl unit were synthesized. Ratio of the isomers with P- or M-helicity of the ligands, and the catalytic activities of the Pd complexes depend on the substituent. Excellent catalytic activity with high TON (800,000) was achieved for a Suzuki-Miyaura reaction in water.
    Bulletin of the Chemical Society of Japan 01/2015; DOI:10.1246/bcsj.20150083 · 2.22 Impact Factor
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    ABSTRACT: A novel complex with the terminal acetonitrile and bridging trifluoroacetate (tfa) ligands of [Mo3S4(dtp)3(μ-tfa)(NCCH3)] (dtp: diethyl dithiophospate) (1-tfa) was prepared from the substitution reaction of [Mo3S4(dtp)3(μ-dtp)(NCCH3)] (1-dtp) with trifluoroacetate anhydride in acetonitrile. The reaction of 1-dtp with trifluoroacetic acid in dichloromethane also afforded 1-tfa. Complex 1-tfa reacts with pyridine in ethanol resulting in the formation of a complex with the terminal pyridine ligand (py), [Mo3S4(dtp)3(μ-tfa)(py)] (2-tfa). Structures of 1-tfa and 2-tfa were determined by single-crystal X-ray structural analysis showing that one of three Mo-Mo distances depend on a kind of the bridging ligands, dtp, OAc, and tfa, while no trends in the other two Mo-Mo distances in each of the complexes with the different bridging ligands. Each of the cyclic voltammograms of 1-dtp, [Mo3S4(dtp)3(μ-OAc)(NCCH3)] (OAc: acetate) (1-OAc), 1-tfa, [Mo3S4(dtp)3(μ-OAc)(py)] (2-OAc), and 2-tfa showed two consecutive one-electron reduction waves and an oxidation wave, which are formally assigned to the Mo(IV IV IV)/Mo(III IV IV), Mo(III IV IV)/Mo(III III IV), and Mo(V IV IV)/Mo(IV IV IV) couples, respectively. The re-oxidation and re-reduction peaks for the second reduction and the oxidation processes were not observed for all of the complexes. The redox potentials of the first reduction processes were shifted up to ca. 200 mV with the bridging and terminal ligands, for example, the redox potentials appeared at −0.98 and −1.19 V vs. Fc/Fc+ 2-OAc and 1-tfa, respectively, due to the lower electron-donating ability of CH3CN and tfa ligands compared to that of the py and OAc ligands. The re-oxidation peak for the second reduction process of 2-OAc was observed at −80 °C suggesting that this is an EC process and the chemical reaction following the second electrochemical reduction is probably inhibited at low temperature. On the other hand, no re-reduction peak for the oxidation process appeared even at −80 °C implying that the oxidation process is accompanied by a significant structural change. This argument is supported by the results of the DFT calculation. The HOMO component of the complex contains a bonding character between the two acetate-bridged Mo centers and the other acetate-unbridged one, and the spin densities of the 1-electron oxidized complex mostly located at the one of two acetate-bridged Mo centers and the other acetate-unbridged one. Cyclic voltammograms of these complexes in the presence of trifluoroacetic acid as a proton source exhibited catalytic currents around the first reduction wave for each complex. The DFT calculations for 2-OAc and 2-tfa demonstrated that the HOMO components are also distributed over the doubly bridged sulfur ligands in addition to the Mo centers in the Mo3S4 core. These result suggests that a protonation reaction of 2-OAc and 2-tfa probably occurs on the doubly bridged sulfur ligand in the Mo3S4 core.
    Bulletin of the Chemical Society of Japan 01/2015; 88(4). DOI:10.1246/bcsj.20140364 · 2.22 Impact Factor
  • Tomoko Horibe, Pu Qian, C. Neil Hunter, Hideki Hashimoto
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    ABSTRACT: Stark absorption spectroscopy was applied to clarify the structural differences between carotenoids bound to the B800-820 and B800-850 LH2 complexes from a purple photosynthetic bacterium Phaeospirillum (Phs.) molischianum DSM120. The former complex is produced when the bacteria are grown under stressed conditions of low temperature and dim light. These two LH2 complexes bind carotenoids with similar composition, 10% lycopene and 80% rhodopin, each with the same number of conjugated C=C double bonds (n = 11). Quantitative classical and semi-quantum chemical analyses of Stark absorption spectra recorded in the carotenoid absorption region reveal that the absolute values of the difference dipole moments |Δμ| have substantial differences (2 [D/f]) for carotenoids bound to either B800-820 or B800-850 complexes. The origin of this striking difference in the |Δμ| values was analyzed using the X-ray crystal structure of the B800-850 LH2 complex from Phs. molischianum DSM119. Semi-empirical molecular orbital calculations predict structural deformations of the major carotenoid, rhodopin, bound within the B800-820 complex. We propose that simultaneous rotations around neighboring C=C and C-C bonds account for the differences in the 2 [D/f] of the |Δμ| value. The plausible position of the rotation is postulated to be located around C21-C24 bonds of rhodopin. Copyright © 2014. Published by Elsevier Inc.
    Archives of Biochemistry and Biophysics 12/2014; 572. DOI:10.1016/j.abb.2014.12.015 · 3.04 Impact Factor
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    ABSTRACT: Photoinduced intramolecular electron transfer of dyad PTZ3-PTZ2-PTZ1-B-AQ consisting of phenothiazine trimer (PTZ3-PTZ2-PTZ1), bicyclo[2.2.2]octane (B), and anthraquinone (AQ) was investigated. After excitation (similar to 20 ps) of the AQ moiety in THF, a metastable radical ion pair (RIP) PTZ3-PTZ2-PTZ1(+)-B-AQ(-) appeared at similar to 620 nm. From 500 ps to 6 ns the spectrum changed to a new absorption (similar to 950 nm), which was assigned to the hole-shifted stable RIP state PTZ3-PTZ2(+)-PTZ1-B-AQ(-). The time constant of the hole-shift process was determined to be 6.0 ns. The hole-shifted RIP state had a lifetime (t) of 250 ns and was characterized by spin-polarized signals as a spin-correlated radical pair (SCRP) by means of time-resolved ESR. These results were compared with those for the phenothiazine monomer analog PTZ-B-AQ, which also produced the RIP state PTZ(+)-B-AQ( with t = 1.9 mu s. Time-resolved ESR showed an all emission signal pattern showing the triplet mechanism of PTZ-B-(3)AQ* -> (3)[PTZ(+)-B-AQ(-)]. The origin of the difference in the lifetimes between the trimer and the monomer RIP states was discussed from various points of view, including free energy difference in the RIP states, reorganization energy difference in the charge recombination process, and the spin-state difference. Of these, the spin-state difference effect provided the most reasonable explanation.
    The Journal of Physical Chemistry A 10/2014; 118(47):11262. DOI:10.1021/jp509643q · 2.78 Impact Factor
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    ABSTRACT: This review discusses the application of time-resolved vibrational spectroscopies to the studies of carotenoids in photosynthesis. The focus is on the ultrafast time regime and the study of photophysics and photochemistry of carotenoids by femtosecond time-resolved stimulated Raman and four-wave mixing spectroscopies.
    Biochimica et Biophysica Acta (BBA) - Bioenergetics 09/2014; 1847(1). DOI:10.1016/j.bbabio.2014.09.001 · 4.83 Impact Factor
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    ABSTRACT: Charge injection processes in polymer: fullerene composite diodes have been investigated for blend films of poly(3-hexylthiophene) (P3HT) and methanofullerene (PCBM) using spectroscopic techniques combined with bias application, termed a device modulation (DM) spectroscopic technique. The voltage dependence of DM signals under the dark condition demonstrates that injection of mobile carriers into P3HT in the blend diode occurs at much lower voltage than that for a P3HT diode, suggesting that the bulk-hetero junction structure of the blend film induces inhomogeneity in the energy level and partly lowers the barrier for carrier injection. Recombination processes of injected P3HT carriers for the blend device in the dark are analyzed by the frequency dependence of DM signals and found to be dominated by bimolecular recombination processes. The DM measurements under illumination demonstrate that, although charge injection under illumination occurs to the same extent as that in the dark condition, some photo-generated charge-transfer states at the interface of P3HT and PCBM are lost on a slow timescale by recombination with injected carriers.
    Organic Electronics 09/2014; 15(9):1958–1964. DOI:10.1016/j.orgel.2014.05.023 · 3.68 Impact Factor
  • Katsuichi Kanemoto, Shinya Domoto, Hideki Hashimoto
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    ABSTRACT: It has recently been reported that characteristic signals resulting from a Stark effect are included in the spectra of photoinduced absorption (PIA) measurements for dye-sensitized solar cells (DSCs), and the origin of the Stark effect has been discussed in several papers. Here, we explore the origin of the Stark signal observed under continuous photoirradiation from results of continuous wave (cw)-PIA experiments for several control DSCs of ruthenium-based sensitizers (N719). Typical line shape resulting from the Stark effect was observed in the quadrature phase of cw-PIA spectra under short-circuit conditions. The Stark signals are found to arise in relation to stable photocurrent and be independent of the presence of particular electrolyte ions. Time-resolved PIA measurements demonstrate that the Stark signals rise and decay in time scales much slower than the response time of injected electrons in TiO2. We conclude that redox actions of a pair of I-/I-3(-) are responsible for the Stark effect under continuous photoirradiation and conjecture that the observed Stark signals are due to local electric fields acting on neutral dyes given by complexes consisting of dyes and iodine molecules or iodine-based ions. We propose to use Stark signals to monitor electrostatic environments around neutral dyes in working DSCs.
    The Journal of Physical Chemistry C 08/2014; 118(31):17260-17265. DOI:10.1021/jp503085f · 4.84 Impact Factor
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    ABSTRACT: Siphonous green algae, a type of deep-sea green algae, appear olive drab and utilize blue–green light for photosynthesis. A siphonous green alga, Codium (C.) intricatum, was isolated from Okinawa prefecture in Japan, and a clonal algal culture in filamentous form was established. The major light-harvesting antenna was analogous to the trimeric LHCII found in higher plants, but the C. intricatum complex contained an unusual carbonyl carotenoid siphonaxanthin. Culture conditions were optimized to achieve high siphonaxanthin content in intact lyophilized filamentous bodies. Interestingly, the carotenoid composition was different when cultured under high irradiance: all-trans neoxanthin was accumulated in addition to the normal 9′-cis form in whole cell extract. Resonance Raman spectra of intact filamentous bodies, cultured under high- and low-light conditions, confirmed the accumulation of all-trans neoxanthin under high irradiance conditions. A plausible function of the presence of all-trans neoxanthin will be discussed in relation to the regulation against high light stress.
    Photosynthesis Research 07/2014; 121(1). DOI:10.1007/s11120-014-0011-y · 3.19 Impact Factor
  • Angewandte Chemie International Edition 06/2014; 53(26):6827-6827. DOI:10.1002/anie.201401150 · 11.34 Impact Factor
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    ABSTRACT: The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail through transient absorption measurements. The derivatives showed ultrafast formation of triplet excited state(s) in the pentacene moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission. Detailed kinetic analyses for the transient absorption data were conducted to quantify the excited-state characteristics of the derivatives.
    Angewandte Chemie International Edition 06/2014; 53(26). DOI:10.1002/anie.201310291 · 11.34 Impact Factor
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    ABSTRACT: The excited-state dynamics of pentacene derivatives with stable radical substituents were evaluated in detail through transient absorption measurements. The derivatives showed ultrafast formation of triplet excited state(s) in the pentacene moiety from a photoexcited singlet state through the contributions of enhanced intersystem crossing and singlet fission. Detailed kinetic analyses for the transient absorption data were conducted to quantify the excited-state characteristics of the derivatives.
    Angewandte Chemie 06/2014; 126(26). DOI:10.1002/ange.201310291
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    ABSTRACT: A Pd complex With a pincer ligand constituted of two N-heterocyclic carbenes and a triazole moiety containing a sugar unit, which was incorporated using click chemistry, was synthesized. Two diastereomers of the complex, which were in equilibrium, were observed in solution. The complex worked as a catalyst for the Suzuki-Miyaura cross-coupling reaction in aqueous media showing a turnover number of up to 76000.
    Chemistry Letters 05/2014; 43(5):687-689. DOI:10.1246/cl.140017 · 1.30 Impact Factor
  • Angewandte Chemie 05/2014; DOI:10.1002/ange.201401150
  • Chemical Physics Letters 05/2014; 602:75–79. DOI:10.1016/j.cplett.2014.04.022 · 1.99 Impact Factor
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    ABSTRACT: Fucoxanthin, containing a carbonyl group in conjugation with its polyene backbone, is a naturally occurring pigment in marine organisms and is essential to the photosynthetic light-harvesting function in brown alga and diatom. Fucoxanthin exhibits optical characteristics attributed to an intramolecular charge transfer (ICT) state that arises in polar environments due to the presence of the carbonyl group. In this study, we report the spectroscopic properties of fucoxanthin in methanol (polar and protic solvent) observed by femtosecond pump-probe measurements in the near-infrared region, where transient absorption associated with the optically allowed S2 (1(1)B u (+) ) state and stimulated emission from the strongly coupled S1/ICT state were observed following one-photon excitation to the S2 state. The results showed that the amplitude of the stimulated emission of the S1/ICT state increased with decreasing excitation energy, demonstrating that the fucoxanthin form associated with the lower energy of the steady-state absorption exhibits stronger ICT character.
    Photosynthesis Research 03/2014; 121(1). DOI:10.1007/s11120-014-9995-6 · 3.19 Impact Factor

Publication Stats

2k Citations
560.79 Total Impact Points


  • 1998–2015
    • Osaka City University
      • • Graduate School of Science
      • • Department of Physics
      • • Department of Applied Physics
      Ōsaka, Ōsaka, Japan
  • 2004–2013
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 2002–2012
    • Tohoku University
      • Department of Physics
      Sendai-shi, Miyagi-ken, Japan
    • Kobe City University of Foreign Studies
      Kōbe, Hyōgo, Japan
  • 2001–2011
    • University of Glasgow
      • • Institute of Molecular, Cell and Systems Biology
      • • School of Chemistry
      Glasgow, Scotland, United Kingdom
  • 1985–2008
    • Kwansei Gakuin University
      • Department of Chemistry
      Nishinomiya, Hyōgo, Japan
  • 2007
    • Bowdoin College
      • Department of Chemistry
      Brunswick, ME, United States
  • 2006
    • University of Connecticut
      • Department of Chemistry
      Storrs, Connecticut, United States
    • Osaka University
      • Department of Physics
      Ibaraki, Osaka-fu, Japan
  • 1997–2002
    • Shizuoka University
      • • Faculty of Engineering
      • • Department of Electrical and Electronic Engineering
      Sizuoka, Shizuoka, Japan
  • 1989
    • The University of Tokyo
      • Department of Physics
      Tokyo, Tokyo-to, Japan