Hideki Hashimoto

Osaka City University, Ōsaka, Ōsaka, Japan

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Publications (180)475.89 Total impact

  • [Show abstract] [Hide abstract]
    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;
  • 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; · 3.04 Impact Factor
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    ABSTRACT: 10'-Phenyl-10'H-10,3':7',10''-terphenothiazine (phenothiazine trimer, PTZ3-PTZ2-PTZ1) radical cation has unique geometric and electronic structures that are considerably different from the neutral structures; the radical cation is localized mainly on the central phenothiazine ring (PTZ2) and conjugated with the nitrogen atoms of the outer folded phenothiazine rings (PTZ3 and PTZ1), showing a unique intramolecular charge-transfer band at ~950 nm. We used picosecond and nanosecond-transient absorption and time-resolved ESR spectroscopy for examining the photoinduced intramolecular electron transfer of the PTZ3-PTZ2-PTZ1-bicyclo[2.2.2]octane (B)-anthraquinone (AQ) dyad system (PTZ3-PTZ2-PTZ1-B-AQ). Immediately after excitation (~20 ps) of the AQ moiety in THF, a new absorption appeared at ~620 nm without appreciable decay in the 20500 ps period. The observed absorption was assigned to an overlapped absorption of PTZ1+ and AQ- in the radical ion pair (RIP) state PTZ3-PTZ2-PTZ1+-B-AQ-. During 500 ps - 6 ns, a new absorption appeared at 950 nm with decrease in intensity and blue-shift of the 620 nm absorption. The 950 nm absorption was assigned to the hole-shifted PTZ3-PTZ2+-PTZ1. The time constant of the hole-shift process was determined to be 6.0 ns. The RIP state PTZ3-PTZ2+-PTZ1-B-AQ- exhibited spin-polarized signals characterized as a spin-correlated radical pair (SCRP) by means of time-resolved ESR. The lifetime of PTZ3-PTZ2+-PTZ1-B-AQ- was determined to be 250 ns. These results were compared with those for the phenothiazine monomer analog PTZ-B-AQ, which produced the triplet RIP state as an all emission signal pattern (time-resolved ESR) that is characteristic for a radical ion pair generated via the triplet mechanism of PTZ-B-3AQ* -> 3[PTZ+-B-AQ-]. The lifetime of 3[PTZ+-B-AQ-] was determined to be 1.9 microsecond. The origin of the lifetime difference between the monomer and trimer 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 (triplet state for PTZ+-B-AQ- and SCRP state for PTZ3-PTZ2+-PTZ1-B-AQ-). Of these, the spin state difference effect provided the most reasonable explanation.
    The Journal of Physical Chemistry A 10/2014; 118(47):11262. · 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; · 4.83 Impact Factor
  • Organic Electronics 09/2014; 15(9):1958–1964. · 3.68 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). · 3.19 Impact Factor
  • Angewandte Chemie 05/2014;
  • Chemical Physics Letters 05/2014; 602:75–79. · 1.99 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 04/2014;
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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 04/2014; · 11.34 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; · 3.19 Impact Factor
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    ABSTRACT: Fucoxanthin is an essential pigment for the highly efficient light-harvesting function of marine algal photosynthesis. It exhibits excited state properties attributed to intramolecular charge transfer (ICT) in polar environments due to the presence of the carbonyl group in its polyene backbone. This report describes the excited state properties of fucoxanthin homologues with four to eight conjugated double bonds in various solvents using the femtosecond pump–probe technique. The results clarified that fucoxanthin homologues with longer polyene chains did not possess pronounced ICT spectroscopic signatures, while the shorter fucoxanthin homologues had a strong ICT character, even in a nonpolar solvent. On the basis of the observations, we quantitatively correlated the ICT character in the excited state to the conjugated polyene chain lengths of fucoxanthin molecules.
    Journal of Physical Chemistry Letters 02/2014; 5(5):792–797. · 6.69 Impact Factor
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    ABSTRACT: Newly synthesized heterometallic trinuclear M2Pt complexes (M = Rh, Ir) containing a platinum moiety having a chelated bis-N-heterocyclic carbene (bisNHC) ligand with a variety of alkylene chain lengths of the bridging part showed two reversible reduction waves in cyclic voltammetry. Only the second reduction potentials were affected by the alkyl chain lengths, which afforded different dihedral angles between the imidazolylidene rings and the platinum coordination plane resulting in the variation of π-back-donation from the platinum center to the carbene carbon atoms.
    Inorganic Chemistry 01/2014; · 4.79 Impact Factor
  • Biochimica et Biophysica Acta (BBA) - Bioenergetics. 01/2014;
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    ABSTRACT: Fucoxanthin is an essential pigment for the light-harvesting of aquatic algae. It exhibits high energy transfer efficiencies to Chl a (>80%) as well as peridinin (>95%). In order to verify the generality and specificity of the noticeable observation on the ICT excited energy state character, which was found in the study of peridinin, we achieved the straightforward synthesis of a series of fucoxanthin short-chain derivatives via the modified-Julia olefination with the aldehyde half segment possessing a β,γ-epoxyketone function. The established method was successfully applied to the synthesis of the epoxy olefin derivative as an allene modified fucoxanthin analogue.
    Tetrahedron Letters 01/2014; 55(2):407–410. · 2.39 Impact Factor
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    ABSTRACT: Ultrafast excited-state dynamics of the photosynthetic pigment (Mg-)bacteriochlorophyll a and its Zn-substituted form were investigated by steady-state absorption∕fluorescence and femtosecond pump-probe spectroscopic measurements. The obtained steady-state absorption and fluorescence spectra of bacteriochlorophyll a in solution showed that the central metal compound significantly affects the energy of the Qx state, but has almost no effect on the Qy state. Photo-induced absorption spectra were recorded upon excitation of Mg- and Zn-bacteriochlorophyll a into either their Qx or Qy state. By comparing the kinetic traces of transient absorption, ground-state beaching, and stimulated emission after excitation to the Qx or Qy state, we showed that the Qx state was substantially incorporated in the ultrafast excited-state dynamics of bacteriochlorophyll a. Based on these observations, the lifetime of the Qx state was determined to be 50 and 70 fs for Mg- and Zn-bacteriochlorophyll a, respectively, indicating that the lifetime was influenced by the central metal atom due to the change of the energy gap between the Qx and Qy states.
    The Journal of Chemical Physics 07/2013; 139(3):034311. · 3.12 Impact Factor
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    ABSTRACT: LH1-α and -β polypeptides, which make up the light harvesting 1 (LH1) complex of purple photosynthetic bacteria along with bacteriochlorophylls, have unique binding properties even for various porphyrin analogs. Herein, we used the porphyrin analogs, Zn-Chlorin and Zn-Chlorin dimer, and examined their binding behaviors to the LH1-α variant, which has His-tag at the C-terminus (MBP-rubα-YH). Zn-Chlorin and Zn-Chlorin dimer could bind to MBP-rubα-YH and form a subunit-type assembly, similar to that from the native LH1 complex. These complexes could be immobilized onto Ni-nitrilotriacetic acid-modified Au electrodes and the cathodic photocurrent was successfully observed by photoirradiation. Since Zn-Chlorins in this complex are too far for direct electron transfer from the electrode, a contribution of polypeptide backbone for efficient electron transfer was implied. These findings not only show interesting properties of LH1-α polypeptides but also suggest a clue to construct artificial photosynthesis systems using these peptide materials.
    Langmuir 04/2013; 29:5104−5109. · 4.38 Impact Factor
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    ABSTRACT: The recently reported efficient charge-separated system based on bipyridine-diacetylide platinum(ii) complexes was applied to photoelectric conversion systems herein, based on the design and synthesis of two triads: MTA-Pt-NDISAc (, MTA: dimethoxytriphenylamine, Pt: platinum(ii) complex, NDISAc: thioacetate derivative linked to naphthalenediimide) and MTA-Pt-MNICOOH (, MNICOOH: naphthaleneimide-4-carboxylic acid). The charge-separated (CS) states of triads and (MOM-protected ) were effectively generated by photo-induced electron transfer in both THF and toluene, although the rate of formation of the CS state from was relatively slow in toluene. The lifetimes of these CS states were determined to be 730 ns in toluene and 61 ns (70%) and 170 ns (30%) as a double exponential decay in THF for , and 600 ns in toluene and 170 ns in THF for . The acetylthio group of triad was exploited in the preparation of a self-assembled monolayer (SAM) on a gold surface. Photocurrent was detected upon irradiation of an electrochemical cell comprising Au//Na ascorbate/Pt, which was ascribed to the platinum(ii) complex based on the action spectrum. The carboxylic acid group of triad facilitated adsorption on the TiO2 surface, and a dye-sensitized solar cell constructed based on FTO/TiO2//electrolyte (LiI-I2)/Pt exhibited a poor energy conversion efficiency (η = 0.20%) based on the incident photon-to-current conversion efficiency spectrum and the I-V curve. This poor efficiency may be derived from the bent molecular shape of , or may be due to a possible high energy barrier in the electron injection process through the adsorption site.
    Physical Chemistry Chemical Physics 03/2013; · 4.20 Impact Factor
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    ABSTRACT: Predicting the complete electronic structure of carotenoid molecules remains an extremely complex problem, particularly in anisotropic media such as proteins. In this paper, we address the electronic properties of nine relatively simple carotenoids by the combined use of electronic absorption and resonance Raman spectroscopies. Linear carotenoids exhibit an excellent correlation between (i) the inverse of their conjugation chain length N, (ii) the energy of their S(0)→S(2) electronic transition, and (iii) the position of their ν1 Raman band (corresponding to the stretching mode of their conjugated C=C bonds). For cyclic carotenoids such as β-carotene, this correlation is also observed between the latter two parameters (S(0)→S(2) energy and ν1 frequency), whereas their "nominal" conjugation length N does not follow the same relationship. We conclude that β-carotene and cyclic carotenoids in general exhibit a shorter effective conjugation length than that expected from their chemical structure. In addition, the effect of solvent polarizability on these molecular parameters was investigated for four of the carotenoids used in this study. We demonstrate that resonance Raman spectroscopy can discriminate between the different effects underlying shifts in the S(0)→S(2) transition of carotenoid molecules.
    The Journal of Physical Chemistry B 01/2013; · 3.38 Impact Factor
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    ABSTRACT: The effect of charge injection in solar cells is usually difficult to examine although it is expected to highly affect the solar cell operation. The effect of charge injection on the operation of bulk-heterojunction (BHJ) solar cells made from blend films of poly(3-hexylthiophene) (P3HT) and methanofullerene (PCBM) is studied using a spectroscopic technique combined with modulation of applied bias, termed a device modulation (DM) spectroscopic technique. The DM measurements enable selective detection of spectroscopic signals from injected P3HT polarons. The voltage dependent-DM measurements in the dark condition reveal the starting point bias of charge injection (∼0 V) and the voltage-dependence of the polaron density, directly from the spectroscopic signals. The frequency dependence of DM signals in the dark condition demonstrates that a bimolecular recombination process dominates the loss mechanism for the injected polarons (© 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
    physica status solidi (c) 12/2012; 9(12):2395-2398.

Publication Stats

1k Citations
475.89 Total Impact Points

Institutions

  • 2002–2014
    • Osaka City University
      • • Graduate School of Science
      • • Department of Physics
      Ōsaka, Ōsaka, Japan
  • 2008–2012
    • Nagoya Institute of Technology
      • • Department of Frontier Materials
      • • Graduate School of Engineering
      • • Department of Life and Materials Engineering
      Nagoya-shi, Aichi-ken, Japan
    • RIKEN
      Вако, Saitama, Japan
    • University of Connecticut
      • Department of Chemistry
      Storrs, CT, United States
  • 2005–2012
    • Tohoku University
      • Department of Physics
      Sendai-shi, Miyagi-ken, Japan
  • 1988–2012
    • Kwansei Gakuin University
      • • Department of Chemistry
      • • School of Science and Technology
      Nishinomiya, Hyōgo, Japan
  • 1993–2011
    • University of Glasgow
      Glasgow, Scotland, United Kingdom
  • 2009
    • Chiba University
      Tiba, Chiba, Japan
  • 2007
    • Bowdoin College
      • Department of Chemistry
      Brunswick, ME, United States
  • 2006
    • Politecnico di Milano
      • Department of Physics
      Milano, Lombardy, Italy
    • Osaka University
      • Department of Physics
      Ibaraki, Osaka-fu, Japan
  • 2004
    • Japan Science and Technology Agency (JST)
      Edo, Tōkyō, Japan
  • 1998–2003
    • Shizuoka University
      • Faculty of Engineering
      Sizuoka, Shizuoka, Japan
  • 1989
    • The University of Tokyo
      • Department of Physics
      Tokyo, Tokyo-to, Japan