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  2. Koichi Iwata

Koichi Iwata

  (岩田 耕一)

Profile Information

Affiliation
Professor, Faculty of Science, Department of Chemistry, Faculty of Science Department of Chemistry, Gakushuin University
Degree
(BLANK)(The University of Tokyo)
J-GLOBAL ID
200901030161773730
researchmap Member ID
1000255661
External link

Research Interests

 10

Research Areas

 1

Research History

 1

Awards

 3

Papers

 20
  • Shunnosuke Okino, Tomohisa Takaya, Koichi Iwata
    CHEMISTRY LETTERS, 44(8) 1059-1061, Aug, 2015  Peer-reviewed
    The energies of low-lying singlet excited states of oligothiophenes, xT's (x = 3 to 8), and polythiophene are determined using femtosecond time-resolved near-infrared spectroscopy. The energies are linearly correlated with the reciprocal number of the thiophene rings for the oligomers 3T to 7T. The linear relation is not observed for 8T, indicating that the effective conjugation is formed over no more than seven rings in the excited states. Transient absorption spectra of polythiophene show that its thiophene chains are composed of planar segments with five or six thiophene rings.
  • Ashok Zachariah Samuel, Sohshi Yabumoto, Kenichi Kawamura, Koichi Iwata
    ANALYST, 140(6) 1847-1851, 2015  Peer-reviewed
    Raman imaging is one of the very informative methods for the characterization of chemically and structurally heterogeneous materials without employing specific molecular labels. Multifocus Raman imaging is one of the fast-imaging alternatives to the conventional single point mapping technique. Since multiple focal points probe the sample simultaneously, this imaging methodology is faster compared to single point mapping. We have further demonstrated the efficiency of this methodology by investigating the morphological features of a porous PMMA film. A Raman image of a 50 x 50 mu m(2) area was obtained in less than 4 minutes (with a 10 x 10 multifocus configuration). Importantly, a 100 x 100 mu m(2) area could now be analyzed in minutes while a similar Raman image by single point mapping would take hours to days. Optical sectioning using multifocus Raman imaging reveals unique hierarchical features of the porous polymer thin film. Larger pores are limited to the surface and the inner bulk exhibits characteristic small-pores and an interconnected highly porous morphology. The fast multifocal Raman imaging would be advantageous to the diverse field of scientific disciplines where the speed of image acquisition remains a challenge despite the unparalleled specificity and sensitivity of Raman spectroscopy.
  • Yuki Nojima, Koichi Iwata
    JOURNAL OF PHYSICAL CHEMISTRY B, 118(29) 8631-8641, Jul, 2014  Peer-reviewed
    A number of biochemical reactions proceed inside biomembranes. Because the rate of a chemical reaction is influenced by chemical properties of the reaction field, it is important to examine the chemical properties inside the biomembranes, or lipid bilayer membranes, for understanding biochemical reactions. In this study, we estimate viscosity inside the lipid bilayers of liposomes with picosecond time-resolved fluorescence spectroscopy. trans-Stilbene is solubilized in the lipid bilayers formed by phosphatidylcholines, DSPC, DOPC, DPPC, DMPC, and DLPC, with 18, 18, 16, 14, and 12 carbon atoms in their alkyl chains, respectively, and egg-PC. Viscosity inside the lipid bilayer is estimated from the photoisomerization rate constant and from the rotational relaxation time of the first excited singlet state of trans-stilbene. The effect of the hydrocarbon chain length and temperature on viscosity is examined. The presence of two solvation environments within the lipid bilayer is indicated from the two independent estimations. One environment is 30 to 290 times more viscous than the other. Even single-component lipid bilayers are likely to have heterogeneous structures.
  • Tomohisa Takaya, Koichi Iwata
    JOURNAL OF PHYSICAL CHEMISTRY A, 118(23) 4071-4078, Jun, 2014  Peer-reviewed
    Carotenoids have two major low-lying excited states, the second lowest (S-2 (1B(u)(+))) and the lowest (S-1 (2A(g)(-))) excited singlet states, both of which are suggested to be involved in the energy transfer processes in light-harvesting complexes. Studying vibrational dynamics of S-2 carotenoids requires ultrafast time-resolved near-IR Raman spectroscopy, although it has much less sensitivity than visible Raman spectroscopy. In this study, the relaxation mechanism of beta-carotene from the S-2 state to the S-1 state is investigated by femtosecond time-resolved multiplex near-IR absorption and stimulated Raman spectroscopy. The energy gap between the S-2 and S-1 states is estimated to be 6780 cm(-1) from near-IR transient absorption spectra. The near-IR stimulated Raman spectrum of S-2 beta-carotene show three bands at 1580, 1240, and 1050 cm(-1). When excess energy of 4000 cm-' is added, the S-1 C=C stretch band shows a large upshift with a time constant of 0.2 ps. The fast upshift is explained by a model that excess energy generated by internal conversion from the S-2 state to the 5, state is selectively accepted by one of the vibronic levels of the S-1 state and is redistributed among all the vibrational modes.
  • Koichi Iwata
    JOURNAL OF RAMAN SPECTROSCOPY, 39(11) 1512-1517, Nov, 2008  Peer-reviewed
    Ultrafast bimolecular radical reaction proceeds between photoexcited p-terphenyl and carbon tetrachloride. The lifetime of the first excited singlet (Si) state of p-terphenyl in carbon tetrachloride measured with picosecond time-resolved fluorescence spectroscopy is 5.6 ps, shorter than the typical lifetime in ordinary solvents, 0.95-2.8 ns, by a factor of 170 or more. Time-resolved infrared spectroscopy reveals the generation of the trichloromethyl (CCl(3)) radical as a reaction intermediate. The decay kinetics of the CCl(3) radical indicates that the CCl(3) radical and the p-terphenyl-Cl radical adduct, both of which are produced simultaneously by a radical reaction between S(1) p-terphenyl and carbon tetrachloride, recombine to form the product. The picosecond time-resolved Raman spectrum of the reactant S(1) p-terphenyl shows that the dephasing process for the four vibrational modes at 1640, 1497, 1180, and 1017 cm(-1) is selectively accelerated in carbon tetrachloride. The four vibrational modes probably have a large contribution from the motion of a specific atom or atoms where the intermolecular interaction that induces the bimolecular reaction is present. Copyright (C) 2008 John Wiley & Sons, Ltd.
  • Koichi Iwata
    JOURNAL OF THE OPTICAL SOCIETY OF AMERICA A-OPTICS IMAGE SCIENCE AND VISION, 25(9) 2244-2250, Sep, 2008  Peer-reviewed
    This paper describes generalized grating imaging with equations based on geometrical optics and wave optics. It shows that the equation derived by wave optics agrees well with the description by geometrical optics. The derived equation based on wave optics can be used to deduce and calculate the intensity distribution of the grating image. (C) 2008 Optical Society of America.
  • Koichi Iwata, Hajime Okajima, Satyen Saha, Hiro-O Hamaguchi
    ACCOUNTS OF CHEMICAL RESEARCH, 40(11) 1174-1181, Nov, 2007  Peer-reviewed
    We show several pieces of Raman spectroscopic evidence that are indicative of local structure formation in imidazolium-based ionic liquids. Low-frequency Raman spectra of C(n)mimX, where C(n)mim stands for 1-alkyl(CnH2n+1)-3-methylimidazolium cation and X represents the anion, exhibit broad bands assignable to collective modes of local structures. Spatial distributions of coherent anti-Stokes Raman scattering (CARS) signals from C(n)mim[PF(6)l are consistent with local structures whose size increases with increasing n. Picosecond Raman spectra of S, trans-stilbene as a "picosecond Raman thermometer" show microscopic thermal inhomogeneity ascribable to local structure formation in C(2)mimTf(2)N and C(4)mimTf(2)N. We also describe two novel phenomena that we believe are relevant to extraordinary nanoenvironments generated by local structures in a magnetic ionic liquid C(4)mim[FeCl4].
  • Iwata Koichi, Kakita Minoru, Hamaguchi Hiro-o
    JOURNAL OF PHYSICAL CHEMISTRY B, 111(18) 4914-4919, May 10, 2007  Peer-reviewed
  • Motohiro Banno, Koichi Iwata, Hiro-o Hamaguchi
    JOURNAL OF CHEMICAL PHYSICS, 126(20) 204501, May, 2007  Peer-reviewed
    Vibrational energy relaxation of degenerate CO stretches of four tungsten carbonyl complexes, W(CO)(6), W(CO)(5)(CS), W(CO)(5)(CH3CN), and W(CO)(5)(CD3CN), is observed in nine alkane solutions by subpicosecond time-resolved infrared (IR) pump-probe spectroscopy. Between 0 and 10 ps after the vibrational excitation, the bleaching signal of the ground-state IR absorption band shows anisotropy. Decay of the anisotropic component corresponds either to the rotational diffusion of the molecule or to the intramolecular vibrational energy transfer among the degenerate CO stretch modes. The time constant of the anisotropy decay, tau(aniso), shows distinct solvent dependence. By comparing the results for the T-1u CO stretch of W(CO)(6) and the A(1) CO stretch of W(CO)(5)(CS), the time constant of the rotational diffusion, tau(r), and the time constant of the intramolecular energy transfer among the three degenerate vibrational modes, tau(e), are determined as 12 and 8 ps, respectively. The tau(aniso) value increases as the number of carbon atoms in the alkane solvent increases. After 10 ps, the recovery of the bleaching becomes isotropic. The isotropic decay represents the vibrational population relaxation, from v=1 to v=0. In heptane, the time constant for the isotropic decay, tau(1), for W(CO)(5)(CS) and W(CO)(6) was 140 ps. The tau(1) for the two acetonitrile-substituted complexes, however, shows a smaller value of 80 ps. The vibrational energy relaxation of W(CO)(5)(CH3CN) and W(CO)(5)(CD3CN) is accelerated by the intramolecular energy redistribution from the CO ligand to the acetonitrile ligand. In the nine alkane solutions, the tau(1) value of W(CO)(6) ranges between 124 and 158 ps, showing the apparent V-shaped solvent dependence with its minimum in decane, while the tau(1) value shows little solvent dependence for W(CO)(5)(CH3CN) and W(CO)(5)(CD3CN). (C) 2007 American Institute of Physics.
  • Koichi Iwata, Kyousuke Yoshida, Yuta Takada, Hiro-o Hamaguchi
    CHEMISTRY LETTERS, 36(4) 504-505, Apr, 2007  Peer-reviewed
    Vibrational cooling rates in room temperature ionic liquids were measured with picosecond time-resolved Raman spectroscopy. The 1570-cm(-1) Raman band of the first excited singlet (S-1) state of trans-stilbene was used as a "Raman thermometer." The recorded vibrational cooling rates in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (emimTf(2)N) and 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (bmimTf(2)N) were close to those in ordinary molecular solvents despite a large difference in thermal diffusivity. The result is consistent with the assumption that local structures are formed in the ionic liquids.
  • T Takaya, S Saha, H Hamaguchi, M Sarkar, A Samanta, K Iwata
    JOURNAL OF PHYSICAL CHEMISTRY A, 110(13) 4291-4295, Apr, 2006  
    We study the effects of symmetry breaking oil the photogenerated intramolecular charge transfer (CT) state of 9,9'-bianthryl (BA) with femtosecond time-resolved near-IR spectroscopy. The tirne-resolved near-IR spectra are measured in acetonitrile for a symmetric substituted derivative of 10,10'-dicyano-9,9'-bianthryl (DCBA) and asymmetric substituted derivatives of 10-cyano-9,9'-bianthryl (CBA) and 9-(N-carbazolyl)anthracene (CM), as well as nonsubstituted BA. The transient near-IR absorption spectrum of each compound at 0 ps has a locally excited (LE) absorption band, which agrees with the transient absorption band of the corresponding monomer unit. At 3 ps after the photoexcitation, the symmetric compounds show a broad charge transfer (CT) absorption band, whereas no absorption peak appears in the spectra of the asymmetric compounds. The broad CT absorption at 1250 nm only observed for the symmetric compounds can be attributed to the charge resonance transition associated with two equivalent charge separated states.
  • M Banno, S Sato, K Iwata, H Hamaguchi
    CHEMICAL PHYSICS LETTERS, 412(4-6) 464-469, Sep, 2005  
    Solvent-dependent intra- and intermolecular vibrational energy transfer from the triply degenerate CO stretch mode Of W(CO)(6) is observed in nine alkanes (CnH2n+2, n = 5-13) with single-color sub-picosecond time-resolved infrared spectroscopy. In all the solvents, the vibrational relaxation process is well characterized by three time constants: tau(1) (< 1 PS), tau(2) (3-13 ps) and tau(3) (124-160 ps). The solvent dependence of tau(2) and tau(3) cannot be explained by the macroscopic properties of the solvent. In particular, the longest time constant tau(3) shows the minimum value of 124 ps in decane among the nine alkanes. The rate of the vibrational energy relaxation is a sensitive measure of the microscopic environments. (c) 2005 Elsevier B.V. All rights reserved.
  • IWATA Koichi
    Bunko Kenkyu, 54(3),153(3) 153-162, 2005  
  • K Iwata, T Takaya, H Hamaguchi, A Yamakata, TA Ishibashi, H Onishi, H Kuroda
    JOURNAL OF PHYSICAL CHEMISTRY B, 108(52) 20233-20239, Dec, 2004  
    Femtosecond time-resolved near-infrared spectra of TiO2 and Pt/TiO2 powders are measured at the wavelength region of 0.9-1.5 mum with the direct absorption method. Broad absorption bands of charge carriers, mainly free and trapped electrons, are observed for TiO2 and Pt/TiO2. The absorption band shape changes with a time constant of 160 A after the photoirradiation, which most probably reflects the trapping of the generated free electrons. Population decay curves of the carriers after 1 ps, obtained for three different pump light powers, are well-explained by the second-order decay kinetics with a common second-order rate constant, indicating nongeminate recombination of the electron-hole pairs. When Pt is loaded to TiO2, an additional decaying process of 2.3 ps is observed. This decay component represents the transfer of generated electrons from TiO2 to Pt, which is consistent with the known increase of overall catalytic activities by the Pt cocatalyst.
  • T Takaya, H Hamaguchi, H Kuroda, K Iwata
    CHEMICAL PHYSICS LETTERS, 399(1-3) 210-214, Nov, 2004  
    Photoinduced intramolecular electron transfer reaction in 9,9'-bianthryl has been studied with femtosecond time-resolved nearinfrared absorption spectroscopy. In acetonitrile, a strong locally excited (LE) band at 1020 nm and a broad charge transfer (CT) band at 1250 nm are observed simultaneously. The decay of the LE band and the rise of the CT band have time constants of (0.38 +/- 0.01) and (0.3 +/- 0.1) ps, respectively. There is no intermediate with a sub-picosecond lifetime observed between the LE and CT states. In heptane, the LE band shape changes with a time constant of 1.4 ps, which probably reflects a conformational change around the central C-C bond. (C) 2004 Elsevier B.V. All rights reserved.
  • IWATA KOICHI
    Chemical Physics Letters, 347, 331, 2001  
  • J. Phys. Chem. A, 101(4), 632, 1997  
  • IWATA Koichi, HAMAGUCHI Hiro-o
    Bunko Kenkyu, 44(2), 61(2) 61-73, 1995  
  • KATO Chihiro, IWATA Koichi, HAMAGUCHI Hiro-o
    Bunko Kenkyu, 40(5), 255(5) 255-274, 1991  
  • Appl. Spectrosc., 44(9), 1431, 1990  

Misc.

 25
  • Wenjuan Xiong, Lili Du, Kin Cheung Lo, Haiting Shi, Tomohisa Takaya, Koichi Iwata, Wai Kin Chan, David Lee Phillips
    JOURNAL OF PHYSICAL CHEMISTRY LETTERS, 9(14) 3819-3824, Jul, 2018  
    Conjugated polymers incorporated with cycloplatinated complexes (P1-Pt and P2-Pt) were used as dispersants for single-walled carbon nanotubes (SWCNTs). Significant changes in the UV-vis absorption spectra were observed after the formation of the polymer/SWCNT hybrids. Molecular dynamics (MD) simulations revealed the presence of a strong interaction between the cycloplatinated complex moieties and the SWCNT surface. The photoinduced electron transfer processes in these hybrids were strongly dependent on the type of the comonomer unit. Upon photoexcitation, the excited P1-Pt donates electrons to the SWCNT, while P2-Pt accepts electrons from the photoexcited SWCNT. These observations were supported by results from Raman and femtosecond time-resolved transient absorption spectroscopy experiments. The strong electronic interaction between the Pt complexes and the SWCNT gives rise to a new hybrid system that has a controllable photoinduced electron transfer flow, which are important in regulating the charge transport processes in SWCNT-based optoelectronic devices.
  • Tomohisa Takaya, Tatsuya Oda, Yuki Shibazaki, Yumiko Hayashi, Hiroaki Shimomoto, Eiji Ihara, Yukihide Ishibashi, Tsuyoshi Asahi, Koichi Iwata
    MACROMOLECULES, 51(14) 5430-5439, Jul, 2018  
    The excited-state dynamics of pyrene incorporated into poly(substituted methylene)s is investigated by picosecond time-resolved fluorescence spectroscopy and femtosecond time-resolved near-IR absorption spectroscopy in the 900-1400 nm region. The pyrene rings in poly (substituted methylene)s are photoexcited to the monomer excited state immediately after UV irradiation, followed by prompt excimer formation with time constants of a few picoseconds to a few hundred picoseconds. The excimer formation in poly(substituted methylene)s proceeds with much shorter time constants than that in pyrene-incorporated polyacrylates, vinyl polymer counterparts with the same side-chain structures, indicating the presence of stronger electronic interaction between the pyrene rings in poly(substituted methylene)s. The effects of every methylene substitution hold when each pyrene ring is connected to the polymer backbone with a monomethylene linker, while the effects are observed only weakly when a tetramethylene linker is employed. The results demonstrate the effectiveness of every methylene substitution in the prompt excimer formation of pyrene connected to the polymer backbone either directly or with the monomethylene linker.
  • B. Narayan, K. Nagura, T. Takaya, K. Iwata, A. Shinohara, H. Shinmori, H. Wang, Q. Li, X. Sun, H. Li, S. Ishihara, T. Nakanishi
    Physical Chemistry Chemical Physics, 20(5) 2970-2975, Feb 7, 2018  
    Novel regioisomeric alkylated-naphthalene liquids were designed and synthesized. In the solvent-free liquid state, 1-alkyloxy regioisomers showed excimeric luminescence, whereas 2-alkyloxy analogues exhibited monomer-rich luminescence features. Correlations among the molecular structures and the photophysical, calorimetric, and rheological properties are presented, demonstrating the impact of regioisomerism on the alkylated-chromophore liquid systems.
  • Koichi Iwata, Masahide Terazima, Hiroshi Masuhara
    Biochimica et Biophysica Acta - General Subjects, 1862(2) 335-357, Feb 1, 2018  
    Novel methodologies utilizing pulsed or intense CW irradiation obtained from lasers have a major impact on biological sciences. In this article, recent development in biophysical researches fully utilizing the laser irradiation is described for three topics, time-resolved fluorescence spectroscopy, time-resolved thermodynamics, and manipulation of the biological assemblies by intense laser irradiation. First, experimental techniques for time-resolved fluorescence spectroscopy are concisely explained in Section 2. As an example of the recent application of time-resolved fluorescence spectroscopy to biological systems, evaluation of the viscosity of lipid bilayer membranes is described. The results of the spectroscopic experiments strongly suggest the presence of heterogeneous membrane structure with two different viscosity values in liposomes formed by a single phospholipid. Section 3 covers the time-resolved thermodynamics. Thermodynamical properties are important to characterize biomolecules. However, measurement of these quantities for short-lived intermediate species has been impossible by traditional thermodynamical techniques. Recently, development of a spectroscopic method based on the transient grating method enables us to measure these quantities and also to elucidate reaction kinetics which cannot be detected by other spectroscopic methods. The principle of the measurements and applications to some protein reactions are reviewed. Manipulation and fabrication of supramolecues, amino acids, proteins, and living cells by intense laser irradiation are described in Section 4. Unconventional assembly, crystallization and growth, amyloid fibril formation, and living cell manipulation are achieved by CW laser trapping and femtosecond laser-induced cavitation bubbling. Their spatio-temporal controllability is opening a new avenue in the relevant molecular and bioscience research fields. This article is part of a Special Issue entitled “Biophysical Exploration of Dynamical Ordering of Biomolecular Systems” edited by Dr. Koichi Kato.
  • Tomohisa Takaya, Masato Anan, Koichi Iwata
    PHYSICAL CHEMISTRY CHEMICAL PHYSICS, 20(5) 3320-3327, Feb, 2018  
    The electronic and vibrational relaxation of carotenoids is one of the key processes in the protection of living cells as well as in the functions of proteins involved in photosynthesis. In this study, the electronic and vibrational relaxation dynamics of b-carotene and its derivatives with substituents on the terminal rings is investigated using femtosecond time-resolved absorption and stimulated Raman spectroscopy in the near-IR region. The carbonyl substituent induces low-frequency shifts of the steady-state and transient absorption bands, decreases of the excited-state lifetimes and the acceleration of vibrational relaxation of the conjugated main chain, whereas the hydroxyl substituent only slightly affects them. The effects of the carbonyl group in the electronic relaxation dynamics are explained well by the lengthening of effective conjugation by the carbonyl group through a partial conjugation between the main chain and the terminal ring. Time-resolved near-IR stimulated Raman spectroscopy demonstrates the significance of the peripheral substitution with the carbonyl group for the vibrational energy relaxation of b-carotene derivatives in the lowest excited singlet state.
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