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Last Updated :2024/07/25

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Master

Affiliation (Master)

  • Faculty of Science　Chemistry　Physical Chemistry

Affiliation (Master)

  • Faculty of Science　Chemistry　Physical Chemistry

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Profile and Settings

Profile and Settings

  • Name (Japanese)

    Saita

  • Name (Kana)

    Kenichiro

  • Name

    201501078312775128

Alternate Names

Achievement

Research Areas

  • Nanotechnology/Materials / Basic physical chemistry

Research Experience

  • 2015/05 - Today Hokkaido University Department of Chemistry, Faculty of Science Research Assistant Professor
  • 2014/07 - 2015/05 University of Edinburgh School of Chemistry Postdoctoral Research Associate
  • 2011/06 - 2014/07 University of Leeds School of Chemistry Postdoctoral Research Fellow
  • 2010/04 - 2011/03 Sophia University Department of Materials and Life Sciences, Faculty of Science and Technology Postdoctoral Research Fellow of Japan Society for the Promotion of Science (JSPS)

Education

  • 2007/04 - 2010/03  Kyushu University  Graduate School of Sciences  School of Molecular Sciences
  • 2005/04 - 2007/03  Kyushu University  Graduate School of Sciences  School of Molecular Sciences
  • 2001/04 - 2005/03  Kyushu University  School of Sciences  Department of Chemistry

Awards

  • 2021/06 Royal Society of Chemistry (RSC) 2021 Faraday Division Horizon Prize
     Recording molecular motion with ultrafast X-rays 
    受賞者: Darren Bellshaw;Sébastien Boutet;James Budarz;Sergio Carbajo;Andrés Moreno Carrascosa;Yu Chang;Wenpeng Du;Yiping Feng;James M. Glownia;Nathan Goff;Jerome B. Hastings;Adam Kirrander;Jason E. Koglin;Michael Kozina;Thomas J. Lane;Henrik T. Lemke;Mengning Liang;Lingyu Ma;Michael P. Minitti;Silke Nelson;Thomas Northey;Daniel Ratner;Joseph S. Robinson;Jennifer M. Ruddock;Kenichiro Saita;Marcin Sikorski;Mats Simmermacher;Brian Stankus;Peter M. Weber;Xuan Xu;Haiwang Yong;Diling Zhu;Nikola ZotevThe international team of scientists from the University of Edinburgh, Brown University and the SLAC National Accelerator Laboratory have demonstrated that ultrafast x-ray scattering using X-ray Free-Electron Lasers (XFELs) is a powerful and versatile technique to explore the transformation of matter during chemical reactions.

Published Papers

  • Koki Ogawara, Osamu Inanami, Hideo Takakura, Kenichiro Saita, Kohei Nakajima, Sonu Kumar, Naoya Ieda, Masato Kobayashi, Tetsuya Taketsugu, Mikako Ogawa
    Advanced Science Wiley 11 (12) 2306586  2198-3844 2024/01/15 [Refereed][Not invited]
     
    Caged compounds are frequently used in life science research. However, the light used to activate them is commonly absorbed and scattered by biological materials, limiting their use to basic research in cells or small animals. In contrast, hard X‐rays exhibit high bio‐permeability due to the difficulty of interacting with biological molecules. With the main goal of developing X‐ray activatable caged compounds, azo compounds are designed and synthesized with a positive charge and long π‐conjugated system to increase the reaction efficiency with hydrated electrons. The azo bonds in the designed compounds are selectively cleaved by X‐ray, and the fluorescent substance Diethyl Rhodamine is released. Based on the results of experiments and quantum chemical calculations, azo bond cleavage is assumed to occur via a two‐step process: a two‐electron reduction of the azo bond followed by N─N bond cleavage. Cellular experiments also demonstrate that the azo bonds can be cleaved intracellularly. Thus, caged compounds that can be activated by an azo bond cleavage reaction promoted by X‐ray are successfully generated.
  • Hikaru Kuramochi, Takuro Tsutsumi, Kenichiro Saita, Zhengrong Wei, Masahisa Osawa, Pardeep Kumar, Li Liu, Satoshi Takeuchi, Tetsuya Taketsugu, Tahei Tahara
    Nature Chemistry Springer Science and Business Media LLC 16 (1) 22 - 27 1755-4330 2024/01/05 [Refereed][Not invited]
     
    Trans–cis photoisomerization is generally described by a model in which the reaction proceeds via a common intermediate having a perpendicular conformation around the rotating bond, irrespective of from which isomer the reaction starts. Nevertheless, such an intermediate has yet to be identified unambiguously, and it is often called the ‘phantom’ state. Here we present the structural identification of the common, perpendicular intermediate of stilbene photoisomerization using ultrafast Raman spectroscopy. Our results reveal ultrafast birth and decay of an identical, short-lived transient that exhibits a vibrational signature characteristic of the perpendicular state upon photoexcitation of the trans and cis forms. In combination with ab initio molecular dynamics simulations, it is shown that the photoexcited trans and cis forms are funnelled off to the ground state through the same, perpendicular intermediate.
  • Satoi Wada, Takuro Tsutsumi, Kenichiro Saita, Tetsuya Taketsugu
    Journal of Computational Chemistry Wiley 45 (9) 552 - 562 0192-8651 2023/11/27 [Refereed][Not invited]
     
    Recently, surface‐hopping ab initio molecular dynamics (SH‐AIMD) simulations have come to be used to discuss the mechanisms and dynamics of excited‐state chemical reactions, including internal conversion and intersystem crossing. In dynamics simulations involving intersystem crossing, there are two potential energy surfaces (PESs) governing the motion of nuclei: PES in a spin‐pure state and PES in a spin‐mixed state. The former gives wrong results for molecular systems with large spin‐orbit coupling (SOC), while the latter requires a potential gradient that includes a change in SOC at each point, making the computational cost very high. In this study, we systematically investigate the extent to which the magnitude of SOC affects the results of the spin‐pure state‐based dynamics simulations for the hydride MH2 (M = Si, Ge, Sn, Pb) by performing SH‐AIMD simulations based on spin‐pure and spin‐mixed states. It is clearly shown that spin‐mixed state PESs are indispensable for the dynamics simulation of intersystem crossing in systems containing elements Sn and Pb from the fifth period onward. Furthermore, in addition to the widely used Tully's fewest switches (TFS) algorithm, the Zhu‐Nakamura (ZN) global switching algorithm, which is computationally less expensive, is applied to SH for comparison. The results from TFS‐ and ZN‐SH‐AIMD methods are in qualitative agreement, suggesting that the less expensive ZN‐SH‐AIMD can be successfully utilized to investigate the dynamics of photochemical reactions based on quantum chemical calculations.
  • Akihiro Mutsuji, Kenichiro Saita, Satoshi Maeda
    RSC Advances 13 (46) 32097 - 32103 2023/11/01 [Refereed][Not invited]
     
    A simple approach to the analysis of electron transfer (ET) reactions based on energy decomposition and extrapolation schemes is proposed. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme for the efficient estimation of ET rate constants is also proposed. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. In addition, its energy decomposition and extrapolation schemes provide all the energy values required for activation-strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants as a function of the transition metal complexes. These results suggest that EDEEL is useful for efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes.
  • Shunsaku Yasumura, Kenichiro Saita, Takumi Miyakage, Ken Nagai, Kenichi Kon, Takashi Toyao, Zen Maeno, Tetsuya Taketsugu, Ken-ichi Shimizu
    Nature Communications Springer Science and Business Media LLC 14 (1) 3926  2023/07/03 [Refereed][Not invited]
     
    The catalytic combustion of methane at a low temperature is becoming increasingly key to controlling unburned CH4 emissions from natural gas vehicles and power plants, although the low activity of benchmark platinum-group-metal catalysts hinders its broad application. Based on automated reaction route mapping, we explore main-group elements catalysts containing Si and Al for low-temperature CH4 combustion with ozone. Computational screening of the active site predicts that strong Brønsted acid sites are promising for methane combustion. We experimentally demonstrate that catalysts containing strong Bronsted acid sites exhibit improved CH4 conversion at 250 °C, correlating with the theoretical predictions. The main-group catalyst (proton-type beta zeolite) delivered a reaction rate that is 442 times higher than that of a benchmark catalyst (5 wt% Pd-loaded Al2O3) at 190 °C and exhibits higher tolerance to steam and SO2. Our strategy demonstrates the rational design of earth-abundant catalysts based on automated reaction route mapping.
  • X線によるアゾ結合の開裂により活性化されるケージド化合物の開発
    小河原 浩輝, 高倉 栄男, 中島 孝平, 斉田 謙一郎, Kumar Sonu, 小林 正人, 武次 徹也, 稲波 修, 小川 美香子
    JSMI Report 日本分子イメージング学会 16 (2) 64 - 64 1882-6490 2023/05
  • Taro Sekikawa, Nariyuki Saito, Yutaro Kurimoto, Nobuhisa Ishii, Tomoya Mizuno, Teruto Kanai, Jiro Itatani, Kenichiro Saita, Tetsuya Taketsugu
    Physical Chemistry Chemical Physics Royal Society of Chemistry (RSC) 25 (12) 8497 - 8506 1463-9076 2023/03/28 [Refereed][Not invited]
     
    The stereochemistry of pericyclic reactions is explained by orbital symmetry conservation, referred to as the Woodward–Hoffmann (WH) rule. Although this rule has been verified using the structures of reactants and products, the temporal evolution of the orbital symmetry during the reaction has not been clarified. Herein, we used femtosecond soft X-ray transient absorption spectroscopy to elucidate the thermal pericyclic reaction of 1,3-cyclohexadiene (CHD) molecules, i.e., their isomerization to 1,3,5-hexatriene. In the present experimental scheme, the ring-opening reaction is driven by the thermal vibrational energy induced by photoexcitation to the Rydberg states at 6.2 eV and subsequent femtosecond relaxation to the ground state of CHD molecules. The direction of the ring opening, which can be conrotatory or disrotatory, was the primary focus, and the WH rule predicts the disrotatory pathway in the thermal process. We observed the shifts in K-edge absorption of the carbon atom from the 1s orbital to vacant molecular orbitals around 285 eV at a delay between 340 and 600 fs. Furthermore, a theoretical investigation predicts that the shifts depend on the molecular structures along the reaction pathways and the observed shifts in induced absorption are attributed to the structural change in the disrotatory pathway. This confirms that the orbital symmetry is dynamically conserved in the ring-opening reaction of CHD molecules as predicted using the WH rule.
  • Hideo Takakura, Shino Matsuhiro, Osamu Inanami, Masato Kobayashi, Kenichiro Saita, Masaki Yamashita, Kohei Nakajima, Motofumi Suzuki, Naoki Miyamoto, Tetsuya Taketsugu, Mikako Ogawa
    Organic & Biomolecular Chemistry Royal Society of Chemistry (RSC) 20 (36) 7270 - 7277 2022/08/16 [Refereed][Not invited]
     
    Ligand release from silicon phthalocyanine (SiPc) dyes triggered by near-infrared (NIR) light is a key photochemical reaction involving caged compounds based on SiPc. Although NIR light is relatively permeable compared with visible light, this light can be attenuated by tissue absorption and scattering; therefore, using light to induce photochemical reactions deep inside the body is difficult. Herein, because X-rays are highly permeable and can produce radicals through the radiolysis of water, we investigated whether the axial ligands of SiPcs can be cleaved using X-ray irradiation. SiPcs with different axial ligands (alkoxy, siloxy, oxycarbonyl, and phenoxy groups) were irradiated with X-rays under hypoxic conditions. We found that the axial ligands were cleaved via reactions with hydrated electrons (e−aq), not OH radicals, generated from water in response to X-ray irradiation, and SiPc with alkoxy groups exhibited the highest cleavage efficiency. A quantitative investigation revealed that X-ray-induced axial ligand cleavage proceeds via a radical chain reaction. The reaction is expected to be applicable to the molecular design of X-ray-activatable functional molecules in the future.
  • Taro Sekikawa, Nariyuki Saito, Yutaro Kurimoto, Nobuhisa Ishii, Tomoya Mizuno, Teruto Kanai, Jiro Itatani, Kenichiro Saita, Tetsuya Taketsugu
    The International Conference on Ultrafast Phenomena (UP) 2022 2022/01 [Refereed][Not invited]
     
    The chemical shifts of the carbon K-edge during the ring-opening dynamics of 1,3-cyclohexadiene observed by femtosecond transient soft X-ray absorption confirm that the stereochemistry of the ring-opening reaction follows the Woodward-Hoffmann rule.
  • Kanami Sugiyama, Kenichiro Saita, Satoshi Maeda
    Journal of Computational Chemistry Wiley 42 (30) 2163 - 2169 0192-8651 2021/11/15 [Refereed]
     
    A reaction route network for the decomposition reaction of methanol on a Pt(111) surface was constructed by using the artificial force-induced reaction (AFIR) method, which can search for reaction paths automatically and systematically. Then, the network was kinetically analyzed by applying the rate constant matrix contraction (RCMC) method. Specifically, the time hierarchy of the network, the time evolution of the population initially given to CH3OH to the other species on the network, and the most favorable route from CH3OH to major and minor products were investigated by the RCMC method. Consistently to previous studies, the major product on the network was CO+4H, and the most favorable route proceeded through the following steps: CH3OH → CH2OH+H → HCOH+2H → HCO+3H → CO+4H. Furthermore, paths to byproducts found on the network and their kinetic importance were discussed. The present procedure combining AFIR and RCMC was thus successful in explaining the title reaction without using any information on its product or the reaction mechanism.
  • Yutaro Kurimoto, Nariyuki Saito, Nobuhisa Ishii, Teruto Kanai, Jiro Itatani, Kenichiro Saita, Tetsuya Taketsugu, Taro Sekikawa
    2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) IEEE 2021 21161362  2021/06/21 [Refereed]
     
    Photo-stimulated ring-opening reaction of 1,3-cyclohexadiene (CHD) to 1,3,5-hexatriene (HT) is a pericyclic reaction and its dynamics has been investigated by various spectroscopic techniques and by theoretical approaches. Upon excitation to the 1B state, the molecular structure is distorted, and the electronic state is changed into the 2A state, of which potential energy surface has a conical intersection with that of the 1A ground state of CHD. At the conical intersection, the electronic state bifurcates toward CHD and the ring-opened HT. HT is formed on the order of a few hundred femtoseconds.
  • Yuki Nitta, Oliver Schalk, Hironori Igarashi, Satoi Wada, Takuro Tsutsumi, Kenichiro Saita, Tetsuya Taketsugu, Taro Sekikawa
    2021 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) IEEE 2021 9542767  2021/06/21 [Refereed][Not invited]
  • Yuki Nitta, Oliver Schalk, Hironori Igarashi, Satoi Wada, Takuro Tsutsumi, Kenichiro Saita, Tetsuya Taketsugu, Taro Sekikawa
    Conference on Lasers and Electro-Optics (CLEO): QELS_Fundamental Science Optica Publishing Group (Formerly OSA) 2021 FTu4J.3  2021/05 [Refereed][Not invited]
     
    Photolysis of o-nitrophenol, contained in brown carbon in the atmosphere, was investigated by time-resolved photoelectron spectroscopy with EUV light and by theoretical calculations to disentangle all reaction steps from the excitation to the dissociation.
  • Yuki Nitta, Oliver Schalk, Hironori Igarashi, Satoi Wada, Takuro Tsutsumi, Kenichiro Saita, Tetsuya Taketsugu, Taro Sekikawa
    The Journal of Physical Chemistry Letters American Chemical Society (ACS) 12 (1) 674 - 679 1948-7185 2021/01/14 [Refereed][Not invited]
     
    Photolysis of o-nitrophenol, contained in brown carbon, is considered to be a major process for the generation of nitrous acid (HONO) in the atmosphere. In this Letter, we used time-resolved photoelectron spectroscopy with 29.5 eV probe pulses and ab initio calculations to disentangle all reaction steps from the excitation to the dissociation of HONO. After excitation, intersystem crossing to the triplet manifold follows ultrafast excited-state intramolecular hydrogen transfer, where the molecules deplanarizes and finally splits off HONO after 0.5–1 ps.
  • Yuichi Kitagawa, Satoshi Wada, M. D. Jahidul Islam, Kenichiro Saita, Masayuki Gon, Koji Fushimi, Kazuo Tanaka, Satoshi Maeda, Yasuchika Hasegawa
    Communications Chemistry Springer Science and Business Media LLC 3 (1) 119  2020/08/25 [Refereed][Not invited]
     
    Artificial light plays an essential role in information technologies such as optical telecommunications, data storage, security features, and the display of information. Here, we show a chiral lanthanide lumino-glass with extra-large circularly polarized luminescence (CPL) for advanced photonic security device applications. The chiral lanthanide glass is composed of a europium complex with the chiral (+)-3-(trifluoroacetyl)camphor ligand and the achiral glass promoter tris(2,6-dimethoxyphenyl)phosphine oxide ligand. The glass phase transition behavior of the Eu(III) complex is characterized using differential scanning calorimetry. The transparent amorphous glass shows CPL with extra-large dissymmetry factor of gCPL = 1.2. The brightness of the lumino-glass is one thousand times larger than that of Eu(III) luminophores embedded in polymer films of the same thickness at a Eu(III) concentration of 1 mM. The application of the chiral lanthanide lumino-glass in an advanced security paint is demonstrated.
  • Hitoshi Nabata, Makito Takagi, Kenichiro Saita, Satoshi Maeda
    RSC Advances Royal Society of Chemistry (RSC) 10 (37) 22156 - 22163 2020/07/09 [Refereed][Not invited]
     
    In this study, we focused on the effect of pressure on the crystal structures of dioxides of group 14 elements, i.e. SiO2, GeO2, and CO2. Systematic searches for their crystal structures using the artificial force induced reaction method generated 219 and 147, 102 and 63, and 148 and 76 structures for SiO2, GeO2, and CO2, respectively, at 1 and 106 atm. At 1 atm, cristobalite-like, quartz, anatase-like, and stishovite were stable structures for SiO2 and GeO2. At 106 atm, structures of stishovite and CaCl2 type were relatively stable for SiO2 and GeO2. At 1 atm of CO2, molecular crystals were the most stable, whereas, quartz-like and cristobalite-like structures were obtained as stable structures at 106 atm. We discuss these pressure dependent structural variations systematically using the obtained structural dataset.
  • Kanami Sugiyama, Yosuke Sumiya, Makito Takagi, Kenichiro Saita, Satoshi Maeda
    Physical Chemistry Chemical Physics Royal Society of Chemistry (RSC) 21 (26) 14366 - 14375 1463-9076 2019/01/28 [Refereed][Not invited]
     
    Analysis of a reaction on a solid surface is an important task for understanding the catalytic reaction mechanism. In this study, we studied CO oxidation on the Pt(111) surface by using the artificial force induced reaction (AFIR) method. A systematic reaction path search was done, and the reaction route network was created. This network included not only bond rearrangement paths but also migration paths of adsorbed species. Then, the obtained network was analyzed using a kinetics method called rate constant matrix contraction (RCMC). It is found that the bottleneck of the overall reaction is the CO2 generation step from an adsorbed CO molecule and an O atom. This result is consistent with the Langmuir–Hinshelwood (LH) mechanism with O2 dissociation discussed in previous studies. The present procedure, i.e., construction of the reaction route network by the AFIR method followed by application of the RCMC kinetics method to the resultant reaction route network, was fully systematic and uncovered two aspects: the impact of the existence of multiple paths in each bond rearrangement step and an entropic contribution arising from short-range migration of adsorbed species.
  • Maeda, Satoshi, Harabuchi, Yu, Saita, Kenichiro
    MOLECULAR TECHNOLOGY, VOL 3: MATERIALS INNOVATION 2019
  • Kenichiro Saita, Makito Takagi, Harabuchi Yu, Haruki Okada, Satoshi Maeda
    The Journal of Chemical Physics American Institute of Physics (AIP) 149 (7) 072329  0021-9606 2018/08/21 [Refereed][Not invited]
     
    The intersystem crossing (ISC) pathways of triplet benzene molecules in a benzene crystal were investigated theoretically. A combination of the gradient projection (GP) method, which is a standard method for optimizing the crossing seam of two potential energy surfaces, and the single-component artificial-force-induced reaction (SC-AFIR) method (GP/SC-AFIR) was used. This is the first reported use of a GP/SC-AFIR calculation using a density functional theory calculation with periodic boundary conditions. A systematic search for the minimum-energy structures in the seams of crossing of the singlet (S0) and triplet (T1) potential energy surfaces (S0/T1-MESX structures) found 39 independent S0/T1-MESX structures. Energy barriers between the S0/T1-MESX and the stationary structure of the triplet state (T1-MIN) were computed, and then two competing ISC pathways were extracted; the calculated overall energy barrier to the intermolecular C–C-bonded type (SX3) and the out-of-plane bent C–H type (SX15) S0/T1-MESX structures from T1-MIN were 0.26 and 0.27 eV, respectively. The rate constants for SX3 and SX15 formation were estimated to be 5.07 × 108 and 2.17 × 108 s−1 (at 273 K), respectively, or 9.73 × 10−5 and 4.78 × 10−6 s−1 (at 77 K), respectively. At 273 K, which is close to the melting point of the benzene crystal (278.5 K), SX3 and SX15 are easily accessible from T1-MIN, and ISC could occur through the S0/T1-MESX points. By contrast, at 77 K, T1-MIN survives long enough for phosphorescence to compete with ISC.
  • Shunsuke Sato, Kenichiro Saita, Keita Sekizawa, Satoshi Maeda, Takeshi Morikawa
    ACS Catalysis American Chemical Society 8 (5) 4452 - 4458 2155-5435 2018/05/04 [Refereed][Not invited]
     
    Electrocatalytic CO2 reduction over a Mn-complex catalyst in an aqueous solution was achieved at very low energy with a combination of multiwalled carbon nanotubes (MWCNTs) and K+ cations. Although the bare Mn-complex did not function as a catalyst in an aqueous solution, the combined Mn-complex/MWCNT cathode promoted electrocatalytic CO2 reduction at an overpotential of 100 mV where neither the bare MWCNTs nor bare Mn-complex were catalytically active. The Mn-complex/MWCNT produced CO at a constant rate for 48 h with a current density of greater than 2.0 mA cm-2 at -0.39 V (vs RHE). The MWCNTs with electron accumulation properties, together with surface adsorbed K+ ions, provided an environment to stabilize CO2 adjacent to the Mn-complex and significantly lowered the overpotential for CO2 reduction in an aqueous solution, and these results were consistent with density functional theory (DFT) calculations. Experiments clarified that the synergetic effect of the MWCNTs and K+ ions was also applicable to Co and Re complexes that were almost inert with regard to CO2 reduction in an aqueous solution.
  • Satoshi Maeda, Yu Harabuchi, Makito Takagi, Kenichiro Saita, Kimichi Suzuki, Tomoya Ichino, Yosuke Sumiya, Kanami Sugiyama, Yuriko Ono
    Journal of Computational Chemistry WILEY 39 (4) 233 - 250 0192-8651 2018/02/05 [Refereed][Not invited]
     
    This article reports implementation and performance of the artificial force induced reaction (AFIR) method in the upcoming 2017 version of GRRM program (GRRM17). The AFIR method, which is one of automated reaction path search methods, induces geometrical deformations in a system by pushing or pulling fragments defined in the system by an artificial force. In GRRM17, three different algorithms, that is, multicomponent algorithm (MC-AFIR), single-component algorithm (SC-AFIR), and double-sphere algorithm (DS-AFIR), are available, where the MC-AFIR was the only algorithm which has been available in the previous 2014 version. The MC-AFIR does automated sampling of reaction pathways between two or more reactant molecules. The SC-AFIR performs automated generation of global or semiglobal reaction path network. The DS-AFIR finds a single path between given two structures. Exploration of minimum energy structures within the hypersurface in which two different electronic states degenerate, and an interface with the quantum mechanics/molecular mechanics method, are also described. A code termed SAFIRE will also be available, as a visualization software for complicated reaction path networks.
  • Satoshi Maeda, Kanami Sugiyama, Yosuke Sumiya, Makito Takagi, Kenichiro Saita
    Chemistry Letters Chemical Society of Japan 47 (4) 396 - 399 1348-0715 2018/01/16 [Refereed][Not invited]
     
    In this study, artificial force induced reaction (AFIR) method, which has been utilized extensively in molecular systems, was applied to surface adsorbed species. A systematic strategy for obtaining path networks for surface adsorbed species is described for future applications to various surface reactions. As a case study, global reaction route mapping on the potential energy surface (PES) of H2O adsorbed on Cu(111) surface was performed.
  • Yu Harabuchi, Kenichiro Saita, Satoshi Maeda
    Photochemical & Photobiological Sciences Royal Society of Chemistry 17 (3) 315 - 322 1474-9092 2018/01/10 [Refereed][Not invited]
     
    Radiative and nonradiative decay paths from the first excited singlet electronic state (S1) in four heteroaromatics, indole, isoindole, quinoline, and isoquinoline, were systematically explored. Three decay processes, i.e., internal conversion (IC), intersystem crossing (ISC), and fluorescence emission (FE), were compared. Minimum energy conical intersection structures between the electronic ground and first excited states were investigated to determine the most preferred IC path. The minimum energy seam of crossing (MESX) geometries between S1 and the lowest-lying triplet states and the spin-orbit couplings at these MESX structures were computed to identify the most feasible ISC path. The oscillator strength was calculated at each S1 local minimum to reveal the contribution of the FE process. The calculations clearly showed that indole had the highest fluorescent quantum yield, consistent with the experimental data. The present calculations also explained other experimental properties of the heteroaromatics such as ISC quantum yields.
  • Minas Stefanou, Kenichiro Saita, Dmitrii V. Shalashilin, Adam Kirrander
    Chemical Physics Letters ELSEVIER SCIENCE BV 683 300 - 305 0009-2614 2017/09 [Refereed][Not invited]
     
    We compare ultrafast electron and X-ray diffraction using quantum molecular dynamics simulations in photoexcited ethylene. The simulations of ethylene are done using the ab-initio multiconfigurational Ehrenfest (AI-MCE) approach, with electronic structure calculations at the SA3-CASSCF(2,2)/cc-ppVDZ level. The diffraction signal is calculated using the independent atom model. We find that the electron diffraction is more sensitive to the nuclear wavepacket, and the dynamics of the hydrogen atoms in particular.
  • Kenichiro Saita, Yu Harabuchi, Tetsuya Taketsugu, Osamu Ishitani, Satoshi Maeda
    Physical Chemistry Chemical Physics The Royal Society of Chemistry (RSC) 18 (26) 17557 - 17564 1463-9076 2016/07 [Refereed][Not invited]
     
    The mechanism of the CO ligand dissociation of fac-[ReI(bpy)(CO)3(PR3)]+ has theoretically been investigated, as the dominant process of the photochemical ligand substitution (PLS) reactions of fac-[ReI(bpy)(CO)3(PR3)]+, by using the (TD-)DFT method. The PLS reactivity can be determined by the topology of the T1 potential energy surface because the photoexcited complex is able to decay into the T1 state by internal conversions (through conical intersections) and intersystem crossings (via crossing seams) with sufficiently low energy barriers. The T1 state has a character of the metal-to-ligand charge-transfer (3MLCT) around the Franck-Condon region, and it changes to the metal-centered (3MC) state as the Re-CO bond is elongated and bent. The equatorial CO ligand has a much higher energy barrier to leave than that of the axial CO, so that the axial CO ligand selectively dissociates in the PLS reaction. The single-component artificial force induced reaction (SC-AFIR) search reveals the CO dissociation pathway in photostable fac-[ReI(bpy)(CO)3Cl]; however, the dissociation barrier on the T1 state is substantially higher than that in fac-[ReI(bpy)(CO)3(PR3)]+ and the minimum-energy seams of crossings (MESXs) are located before and below the barrier. The MESXs have also been searched in fac-[ReI(bpy)(CO)3(PR3)]+ and no MESXs were found before and below the barrier.
  • Adam Kirrander, Kenichiro Saita, Dmitrii V. Shalashilin
    Journal of Chemical Theory and Computation American Chemical Society 12 (3) 957 - 967 1549-9618 2016/03 [Refereed][Not invited]
     
    We present a theoretical framework for the analysis of ultrafast X-ray scattering experiments using non adiabatic quantum molecular dynamics simulations of photochemical dynamics. A detailed simulation of a pump probe experiment in ethylene is used to examine the sensitivity of the scattering signal to simulation parameters. The results are robust with respect to the number of wavepackets included in the total expansion of the molecular wave function. Overall, the calculated scattering signals correlate closely with the dynamics of the molecule.
  • Christine C. Pemberton, Yao Zhang, Kenichiro Saita, Adam Kirrander, Peter M. Weber
    The Journal of Physical Chemistry A American Chemical Society 119 (33) 8832 - 8845 1089-5639 2015/08 [Refereed][Not invited]
     
    All stages of the electrocyclic ring-opening of 1,3-cyclohexadiene (CHD) were observed by time-resolved photoionization-photoelectron spectroscopy. Spectra of the 1B state, previously unobserved using time-resolved methods, were obtained upon optical excitation using ultrashort laser pulses at 4.60 or 4.65 eV, followed by ionization with pulses at 3.81, 3.85, and 4.10 eV, revealing a 1B lifetime of 30 fs. In an experiment using 3.07 eV probe photons and a 4.69 eV pump, we observed a time-sequenced progression of Rydberg states that includes s, p, and d states of the series n = 3 to 6. The sequentiality of the Rydberg signals points to an ionization mechanism that captures the molecule on different points along the reaction path in 2A. A dynamic fit of the Rydberg signals, coupled with MS-CASPT2 calculations, reveals that as the wavepacket moves down the potential energy surface it acquires kinetic energy at a rate of 28 eV/ps before reaching the conical intersection to the 1A ground state. During the reaction, the terminal carbon atoms separate at a speed of 16 angstrom/ps. A deconvolution of the Rydberg signals from a broad feature assigned to structurally disperse 1,3,5-hexatriene (HT) shows the formation of the open-chain hexatriene structure with an onset 142 fs after the initial absorption of a pump photon. The experimental observations are discussed in the context of recent ultrafast X-ray scattering experiments and theoretical quantum dynamics simulations.
  • Michael P. Minitti, James M. Budarz, Adam Kirrander, Joseph S. Robinson, Daniel Ratner, Thomas J. Lane, Diling Zhu, James M. Glownia, Michael Kozina, Henrik T. Lemke, Marcin Sikorski, Yiping Feng, Silke Nelson, Kenichiro Saita, Brian Stankus, Thomas Northey, Jerome B. Hastings, Peter M. Weber
    Physical Review Letters American Physical Society (APS) 114 (25-26) 255501  0031-9007 2015/06 [Refereed][Not invited]
     
    Structural rearrangements within single molecules occur on ultrafast time scales. Many aspects of molecular dynamics, such as the energy flow through excited states, have been studied using spectroscopic techniques, yet the goal to watch molecules evolve their geometrical structure in real time remains challenging. By mapping nuclear motions using femtosecond x-ray pulses, we have created real-space representations of the evolving dynamics during a well-known chemical reaction and show a series of time-sorted structural snapshots produced by ultrafast time-resolved hard x-ray scattering. A computational analysis optimally matches the series of scattering patterns produced by the x rays to a multitude of potential reaction paths. In so doing, we have made a critical step toward the goal of viewing chemical reactions on femtosecond time scales, opening a new direction in studies of ultrafast chemical reactions in the gas phase.
  • Dmitry V. Makhov, Kenichiro Saita, Todd J. Martinez, Dmitrii V. Shalashilin
    Physical Chemistry Chemical Physics The Royal Society of Chemistry (RSC) 17 (5) 3316 - 3325 1463-9076 2015/02 [Refereed][Not invited]
     
    We report a detailed computational simulation of the photodissociation of pyrrole using the ab initio Multiple Cloning (AIMC) method implemented within MOLPRO. The efficiency of the AIMC implementation, employing train basis sets, linear approximation for matrix elements, and Ehrenfest configuration cloning, allows us to accumulate significant statistics. We calculate and analyze the total kinetic energy release (TKER) spectrum and Velocity Map Imaging (VMI) of pyrrole and compare the results directly with experimental measurements. Both the TKER spectrum and the structure of the velocity map image (VMI) are well reproduced. Previously, it has been assumed that the isotropic component of the VMI arises from long time statistical dissociation. Instead, our simulations suggest that ultrafast dynamics contributes significantly to both low and high energy portions of the TKER spectrum.
  • Michael P. Minitti, James M. Budarz, Adam Kirrander, Joseph Robinson, Thomas J. Lane, Daniel Ratner, Kenichiro Saita, Thomas Northey, Brian Stankus, Vale Cofer-Shabica, Jerome Hastings, Peter M. Weber
    Faraday Discussions The Royal Society of Chemistry (RSC) 171 (1) 81 - 91 1359-6640 2014/12 [Refereed][Not invited]
     
    We aim to observe a chemical reaction in real time using gas-phase X-ray diffraction. In our initial experiment at the Linac Coherent Light Source (LCLS), we investigated the model system 1,3-cyclohexadiene (CHD) at very low vapor pressures. This reaction serves as a benchmark for numerous transformations in organic synthesis and natural product biology. Excitation of CHD by an ultraviolet optical pulse initiates an electrocyclic reaction that transforms the closed ring system into the open-chain structure of 1,3,5-hexatriene. We describe technical points of the experimental method and present first results. We also outline an approach to analyze the data involving nonlinear least-square optimization routines that match the experimental observations with predicted diffraction patterns calculated from trajectories for nonadiabatic vibronic wave packets.
  • Kenichiro Saita, Michael G. D. Nix, Dmitrii V. Shalashilin
    Physical Chemistry Chemical Physics The Royal Society of Chemistry (RSC) 15 (38) 16227 - 16235 2013/10 [Refereed][Not invited]
     
    We report the first results of ab initio multiconfigurational Ehrenfest simulations of pyrrole photodynamics. We note that, in addition to the two intersections of 11A2 and 11B1 states with the ground state 11A1, which are known to be responsible for N–H bond fission, another intersection between the 12A2 and 12B1 states of the resulting molecular radical becomes important after the departure of the H atom. This intersection, which is effectively between the two lowest electronic states of the pyrrolyl radical, may play a significant role in explaining the branching ratio between the two states observed experimentally. The exchange of population between the two states of pyrrolyl occurs on a longer scale than that of N–H bond fission.
  • Kenichiro Saita, Dmitrii V. Shalashilin
    The Journal of Chemical Physics The American Institute of Physics (AIP) 137 (22) 22A506  0021-9606 2012/12 [Refereed][Not invited]
     
    In this article we report the formalism and first implementation of the ab initio multiconfigurational Ehrenfest (AI-MCE) method for simulation of ultrafast nonadiabatic dynamics, which uses the MOLPRO electronic structure program to calculate the potential energy surfaces on the fly. The approach is tested on the benchmark of the excited pi-pi* state dynamics of ethylene producing the dynamics which agree with previous simulations by ab initio multiple spawning technique. The AI-MCE seems to be robust, stable and efficient.
  • Manabu Nakazono, Kenichiro Saita, Yuji Oshikawa, Kazushi Tani, Shinkoh Nanbu, Kiyoshi Zaitsu
    SPECTROCHIMICA ACTA PART A-MOLECULAR AND BIOMOLECULAR SPECTROSCOPY PERGAMON-ELSEVIER SCIENCE LTD 78 (2) 905 - 908 1386-1425 2011/02 [Refereed][Not invited]
     
    The fluorescence properties of 2-phenylindole, 2-naphthylindole and 2-anthracenylindole were investigated. 2-Anthracenylindole was newly synthesized by Suzuki-Miyaura's coupling. The fluorescence quantum yield of 2-phenylindole was the highest and the fluorescence emission maximum wavelength of 2-anthracenylindole was the longest. The ab initio quantum chemical calculation of the 2-anthracenylindole showed that the HOMO and LUMO of 2-anthracenylindole were localized in the anthracene moiety.
  • Yuko Nagai, Kenichiro Saita, Kenji Sakota, Shinkoh Nanbu, Masahiko Sekine, Munetaka Nakata, Hiroshi Sekiya
    The Journal of Physical Chemistry A American Chemical Society 114 (15) 5041 - 5048 1089-5639 2010/04 [Refereed][Not invited]
     
    Photoreactions of 7-hydroxyquinoline (7-HQ) in low-temperature (77-100 K) 2-methyltetrahydrofuran glass matrices are investigated using electronic spectroscopy. We have observed fluorescence excitation and fluorescence spectra of two long-lived species generated by irradiation of UV light (230-400 nm). The dominant species responsible for the fluorescence spectrum between 470 and 600 nm was assigned to the S1 -> S0 (pi-pi*) transition of the keto form of cyclic 7-HQ dimer [(7-HQ)2] produced by excited-state double-proton transfer, the corresponding S1-S0 fluorescence excitation spectrum of which was detected between 360 and 510 nm. Temperature dependence of the fluorescence excitation spectra showed the occurrence of keto -> enol isomerization in the So state of (7-HQ)2 due to a back double-proton transfer. A very slow rate for the keto -> enol isomerization implies that the potential barrier height for the back double-proton transfer reacion is substantially high. Theoretical calculations at the MP2/aug-cc-pVDZ level of theory indicate that the enol and keto forms of cyclic (7-HQ)2 are nonplanar, therefore a large change in the geometry is necessary for the back double-proton transfer. A second long-lived species that emits between 410 and 600 nm has been tentatively assigned to the D3(2A′′) -> D0(1A′′) transition of the 7-quinolinoxyl radical on the basis of calculated electronic transition energies for possible candidates obtained by MS-CASPT2/aug-cc-pVDZ level calculations as well as IR study of 7-HQ in argon matrices [Sekine, M.; Nagai, Y.; Sekiya, H.; Nakata, M. Phys. Chem. A 2009, 113, 8286]. Photoreaction processes leading to the two long-lived species have been discussed.
  • Manabu Nakazono, Ai Jinguji, Shinkoh Nanbu, Ryoichi Kuwano, Zilong Zheng, Kenichiro Saita, Yuji Oshikawa, Yuta Mikuni, Tatsuhiro Murakami, Yi Zhao, Shigeki Sasaki, Kiyoshi Zaitsu
    Physical Chemistry Chemical Physics The Royal Society of Chemistry (RSC) 12 (33) 9783 - 9793 1463-9076 2010 [Refereed][Not invited]
     
    Various indolylmaleimides (IMs) were synthesized, and their fluorescence (FL) and chemiluminescence (CL) were measured. The substitution at the 2-position of the indole ring and the 3- or 4-position of the maleimide moiety caused an obvious change in the FL and CL of the IMs. An almost on-off switching of the FL of the IMs was observed. The intramolecular charge transfer from the indole moiety to the maleimide moiety occurred in 3-(1H-3-indolyl)-2,5-dihydro-1H-2,5-pyrroledione. In the FL of the IMs, CASPT2 calculations showed deprotonation of the NH group of the indole ring and the maleimide moiety at the excited state. The C=C bond in the maleimide moiety was needed for strong CL in the IMs without substitution at the 2-position of the indole ring. The relationships between the FL or CL properties and the structures of the IMs were clarified. These results provide significant information on the rational design of IMs as FL and CL probes.
  • Manabu Nakazono, Kenichiro Saita, Chika Kurihara, Shinkoh Nanbu, Kiyoshi Zaitsu
    Journal of Photochemistry and Photobiology A: Chemistry ELSEVIER SCIENCE SA 208 (1) 21 - 26 1010-6030 2009/11 [Refereed][Not invited]
     
    The synthesis and fluorescence property of 3-amino-N-(7′-methoxy-4′-methylcoumaryl)phthalimide (AMMP) are described. The fluorescence of AMMP originated during the intramolecular energy transfer from the coumarin moiety to the phthalimide moiety in various solvents. The ab initio quantum chemical calculation of the AMMP revealed that the HOMO and LUMO of AMMP were localized in the coumarin and phthalimide moieties, respectively.
  • Kenichiro Saita, Manabu Nakazono, Kiyoshi Zaitsu, Shinkoh Nanbu, Hiroshi Sekiya
    The Journal of Physical Chemistry A American Chemical Society 113 (29) 8213 - 8220 1089-5639 2009/07 [Refereed][Not invited]
     
    The photophysical properties of two bisindolylmaleimide derivatives, 3,4-bis(3-indolyl)-1-H-pyrrole-2,5-dione (arcyriarubin A) and indolo[2,3-a]pyrrolo[3,4-c] carbazole-5,7-(6 H)-dione (arcyriaflavin A), are investigated by using ab initio molecular orbital (MO) and multireference perturbation theory. These compounds are suggested to exist as monovalent anions deprotonated from an indole NH group in aprotic polar solvents. The analysis of MOs shows that the electronic structures of the S1 and S2 states are described by the single- or double-electron excitation between the naturally localized MOs on all indole moiety and on the maleimide part. This indicates that the intramolecular charge transfer (ICT) transfer may occur by photoexcitation. The minimum-energy structure of the arcyriarubin A anion is twisted; the dihedral angles between the indole and maleimide rings are 83.4 degrees and 20.2 degrees for the S1 and S0 states, respectively. The analysis of the minimum energy path along the coordinate of the twist angle is performed to explore the emission process from the S1 state. It has been shown that the magnitude of the Stokes shift increases with increasing the twist angle, but the oscillator strength decreases. It has been suggested that the experimentally observed fluorescence arises on the way toward the energy minimum of the S1 state. The Stokes-shifted emission of arcyriaflavin A is contributed by the S1-S0 electronic relaxation after the excitation in the S2 state.
  • Kenichiro Saita, Seiya Kobatake, Tuyoshi Fukaminato, Shinkoh Nanbu, Masahiro Irie, Hiroshi Sekiya
    Chemical Physics Letters ELSEVIER SCIENCE BV 454 (1-3) 42 - 48 0009-2614 2008/03 [Refereed][Not invited]
     
    Two isomers of the closed-ring forms of 1,2-bis( 2,5-dimethyl-3-thienyl) perfluorocyclopentene (DMTF) having different S....S distances and dihedral angles between the two thiophene rings, are simultaneously observed in the FT-Raman spectrum by irradiation of UV light on microcrystals of the open-ring forms. Quantum chemistry calculations at the MP2/6-31G(d,p) level for several model clusters predict that an isomer having larger S....S distance is preferentially stabilized in crystal due to the electrostatic interaction between the two stacked thiophene rings of the closed-ring form and the open-ring form.

MISC

  • 中澤伸太, 斉田謙一郎, 堤拓朗, 堤拓朗, 渡辺昭敬, 武次徹也, 武次徹也  化学系学協会北海道支部冬季研究発表会(Web)  2023-  2023
  • 小河原浩輝, 高倉栄男, 中島孝平, 斉田謙一郎, KUMAR Sonu, 小林正人, 武次徹也, 稲浪修, 小川美香子  日本癌学会学術総会抄録集(Web)  82nd-  2023
  • Shunsaku Yasumura, Kenichiro Saita, Takumi Miyakage, Kenichi Kon, Takashi Toyao, Zen Maeno, Tetsuya Taketsugu, Ken-ichi Shimizu  ChemRxiv  2022/08/23  
    The catalytic combustion of methane (CH4) at a low temperature is becoming increasingly key to controlling unburned CH4 emissions from natural gas vehicles and power plants, although the low activity of benchmark platinum-group-metal (PGM) catalysts hinders its application. Based on the automated reaction route mapping, we designed the main-group catalyst for low-temperature CH4 combustion with ozone (O3). The computational screening of the active site predicted the strong Brønsted acid sites (BASs) as promising ones. We experimentally demonstrated that the catalyst comprising strong BASs exhibited improved CH4 conversion at 200 °C, correlating with the theoretically predicted design concept. The main-group catalyst (proton-type beta zeolite) delivered a reaction rate, which was 442 times higher than that of a benchmark catalyst (5wt% Pd-loaded Al2O3), at 190 °C and exhibited higher tolerance to steam and SO2. Our strategy demonstrated the rational design of earth-abundant catalysts based on automated reaction route mapping.
  • Akihiro Mutsuji, Kenichiro Saita, Satoshi Maeda  ChemRxiv  2022/06/30  [Not invited]
     
    A simple approach for analyzing electron transfer (ET) reactions is proposed based on energy decomposition and extrapolation schemes. The present energy decomposition and extrapolation-based electron localization (EDEEL) method represents the diabatic energies for the initial and final states using the adiabatic energies of the donor and acceptor species and their complex. A scheme to estimate ET rate constants efficiently is also proposed by combining it with the Marcus theory. EDEEL is semi-quantitative by directly evaluating the seam-of-crossing region of two diabatic potentials. In a numerical test, EDEEL successfully provided ET rate constants for electron self-exchange reactions of thirteen transition metal complexes with reasonable accuracy. Furthermore, its energy decomposition and extrapolation schemes give all the energy values required in the activation strain model (ASM) analysis. The ASM analysis using EDEEL provided rational interpretations of the variation of the ET rate constants depending on the transition metal complexes. Its extension combining two computational levels was discussed to further reduce its computational costs. These results suggest that EDEEL is useful in efficiently evaluating ET rate constants and obtaining a rational understanding of their magnitudes.
  • 中澤伸太, 斉田謙一郎, 渡辺昭敬, 武次徹也, 武次徹也  分子科学討論会講演プログラム&要旨(Web)  16th-  2022
  • Satoshi Maeda, Yu Harabuchi, Kenichiro Saita  Catalysts & Catalysis  59-  (4)  201  -206  2017/08  [Refereed][Invited]
     
    Artificial force induced reaction method which automatically searches for stable structures, transition state structures, and reaction paths, is introduced. This method induces structural deformation systematically by applying artificial force between fragments defined in the reaction system, to search for different structures. As examples, application to organic reaction, cluster catalysis, and photoreaction are shown.
  • 杉山佳奈美, 高木牧人, 斉田謙一郎, 前田理, 武次徹也  日本化学会春季年会講演予稿集(CD-ROM)  97th-  ROMBUNNO.4A8‐06  2017/03/03  [Not refereed][Not invited]
  • 斉田謙一郎  分子シミュレーション学会会誌「アンサンブル」  18-  (4)  228  -231  2016/10  [Not refereed][Invited]
     
    多配置エーレンフェスト（MCE）法は，従来のエーレンフェスト動力学法の欠点を克服する一つの方法である．本稿では，特に多原子分子の電子励起状態動力学シミュレーションへの適用を目指して筆者らが開発を行ってきたon-the-fly シミュレーション法であるAI-MCE 法を概説し，その応用例について述べる．
  • Manabu Nakazono, Ai Jinguji, Kenichiro Saita, Shinkoh Nanbu, Ryoichi Kuwano, Kiyoshi Zaitsu  ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY  237-  2009/03  [Not refereed][Not invited]

Books etc

  • The Chemical Society of Japan (ContributorChapter 16: Quantum Chemical Calculations of Photochemical Reactions)
    Kagaku-Dojin Publishing Company, inc., Japan 2022/03 (ISBN: 9784759814033) v, 209p, 図版 [4] p 154-161 
    計算手法の発展と計算機性能の向上により，量子化学計算（quantum chemical calculation）の光反応への適用性は劇的に向上した．それに伴い，比較的大きな有機分子であっても，その電子励起状態のポテンシャルエネルギー曲面（potential energy surface: PES）が容易に計算できるようになった．ピコ秒程度以内の超高速過程は，PESの勾配を用いた分子動力学（molecular dynamics: MD）シミュレーションによって解析できる．反応経路自動探索（automated reaction path search）法を用いることで，蛍光やりん光と競合するナノ秒より長い時間スケールの現象についても解析が可能である．本章では，光反応を取り扱うための電子状態理論，励起状態MDシミュレーション（excited state molecular dynamics simulation），および電子励起状態に対する反応経路自動探索法について，いくつかの応用例とともに紹介する．
  • Satoshi Maeda, Yu Harabuchi, Kenichiro Saita (ContributorChapter 8 - Global Reaction Route Mapping Strategy: A Tool for Finding New Chemistry in Computers)
    Wiley-VCH 2019/05 (ISBN: 9783527341610) xvii, 351 p. 173-199

Presentations

Association Memberships

  • THE ROYAL SOCIETY OF CHEMISTRY   JAPAN SOCIETY FOR MOLECULAR SCIENCE   THE SPECTROSCOPICAL SOCIETY OF JAPAN   THE CHEMICAL SOCIETY OF JAPAN   

Research Projects

  • 日本学術振興会：科学研究費助成事業
    Date (from‐to) : 2009/04 -2011/03 
    Author : 斉田 謙一郎
     
    本研究は、分子間相互作用が光吸収・発光に及ぼす影響を微視的立場より考察するための理論的ダイナミクス研究を目的としている(平成21-22年度)。これまで開発を行ってきた半古典動力学計算プログラムは、非断熱遷移を考慮しなければスペクトルの再現ができない硫化水素分子で実施したベンチマーク計算で量子動力学法と遜色ない結果を得ることができ、かつ、計算コストを量子動力学法に比べ大幅に抑えられることを示した。そこで今年度は、当該半古典理論の実際の大自由度分子系への適用を中心に研究を実施した。大自由度分子系として、水分子ネットワークを介した励起状態多重プロトン移動が生じるため多大な興味が持たれている7-アザインドール・水1:2クラスター[7AI(H_2O)_2]を対象に励起状態動力学計算を実施した。63自由度という大自由度系に対して、量子効果を考慮した動力学計算はこれまで報告されていない。また、高精度電子状態計算(CASPT2)を組み合わせた点も本分野で最先端である。光励起直後～50フェムト秒の動力学計算を行い得られた自己相関関数から理論吸収スペクトルを算出したところ、実験的に観測されている7AIの吸収スペクトル[J. Catalan, J. Chem. Phys. 106, 6738(2002)]に酷似していた。これまで多くの実験研究グループの報告で示唆されているように光励起は7AI分子の局所励起(π-π*状態)によるものであり、その吸収スペクトルを理論的に再現できたことは大きな進展である。一方、昨年度に引き続き分子間相互作用が光物理化学過程に顕著に影響を与える系についての研究(電子状態理論)も実施し、実験分野の研究者と共著で論文発表した。本研究から分子間相互作用により非断熱遷移を引き起こすことが光物理的性質制御の鍵であることが明らかとなった。非断熱遷移を考慮した新しい半古典理論を開発した結果、63自由度という大自由度分子系の吸収スペクトルを再現した。今後より「リアルな」分子系への発展が期待される。

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