Tetsuya Taketsugu

Hokkaido University, Sapporo, Hokkaidō, Japan

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Publications (134)396.09 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Femtosecond relaxation and picosecond photodissociation dynamics of 1,3-butadiene were investigated by time-resolved photoelectron spectroscopy with high harmonics pulses, probing the deeper molecular orbitals which are sensitive to the molecular structure.
    CLEO: QELS_Fundamental Science; 06/2014
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    ABSTRACT: In trans-1,3-butadiene, the ultrafast relaxation from the doubly excited state 21Ag and the corresponding recovery of the ground state 11Ag were observed simultaneously for the first time by time-resolved photoelectron spectroscopy (TRPES) using 29.5 eV high harmonic pulses. The fast recovery of 11Ag shows that the following dissociation upon photoexcitation takes place after returning to the ground state. At 427 fs after photoexcitation, only the ionization energy from the C═C σ bond was found to remain shifted. Accompanying theoretical calculations with an assumption of Koopmans’ theorem show that the ionization energy of the C═C σ bond is modulated by vibrational excitation of the antisymmetric C═C stretching mode. TRPES by high harmonics can probe the changes in the molecular structure sensitively.
    Journal of Physical Chemistry Letters 05/2014; 5(10):1760–1765. · 6.59 Impact Factor
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    ABSTRACT: Boron nitride (BN), which is an insulator with a wide band gap, supported on Au is theoretically suggested and experimentally proved to act as an electrocatalyst for oxygen reduction reaction (ORR). Density-functional theory calculations show that the band gap of a free h-BN monolayer is 4.6 eV but a slight protrusion of the unoccupied BN states toward the Fermi level is observed if BN is supported on Au(111) due to the BN-Au interaction. A theoretically predicted metastable configuration of O2 on h-BN/Au(111), which can serve as precursors for ORR, and free energy diagrams for ORR on h-BN/Au(111) via two- and four-electron pathways show that ORR to H2O2 is possible at this electrode. It is experimentally proved that overpotential for ORR at the gold electrode is significantly reduced by depositing BN nanosheets. No such effect is observed at the glassy carbon electrode, demonstrating the importance of BN-substrate interaction for h-BN to act as the ORR electrocatalyst. A possible role of the edge of the BN islands for ORR is also discussed.
    Journal of the American Chemical Society 04/2014; · 10.68 Impact Factor
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    ABSTRACT: Main-group-element catalysts are a desirable alternative to transition-metal catalysts because of natural abundance and cost. However, the examples are very limited. Catalytic cycles involving a redox process and E-ligand cooperation (E=main-group element), which are often found in catalytic cycles of transition-metal catalysts, have not been reported. Herein theoretical investigations of a catalytic hydrogenation of azobenzene with ammonia-borane using a trivalent phosphorus compound, which was experimentally proposed to occur through P(III) /P(V) redox processes via an unusual pentavalent dihydridophosphorane, were performed. DFT and ONIOM(CCSD(T):MP2) calculations disclosed that this catalytic reaction occurs through a P-O cooperation mechanism, which resembles the metal-ligand cooperation mechanism of transition-metal catalysts.
    Angewandte Chemie International Edition 03/2014; · 11.34 Impact Factor
  • Min Gao, Andrey Lyalin, Satoshi Maeda, Tetsuya Taketsugu
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    ABSTRACT: A new theoretical approach to find metal-cluster-catalyzed single bond activation pathways is introduced. The proposed approach combines two automated reaction path search techniques: the anharmonic downward distortion following (ADDF) and the artificial force induced reaction (AFIR) methods, developed in our previous works [Maeda, S.; Ohno, K.; Morokuma, K. Phys. Chem. Chem. Phys. 2013, 15, 3683−3701]. A simple model reaction of the H−H bond activation catalyzed by Aun (n = 7, 8) clusters is considered as an example. We have automatically found 33 and 20 transition-state (TS) structures for H2 dissociation on Au7 and Au8 clusters, respectively, and successfully identified the best dissociation pathways with the lowest barrier. Systematic analysis of the structure-dependent reactivity of small gold clusters is performed. It is demonstrated that the most stable structures of the gold clusters are not always highly reactive and several isomeric structures must be taken into account for adequate description of the reaction rates at finite temperatures. The proposed approach can serve as a promising tool for investigation of the chemical reactions catalyzed by small metal clusters.
    Journal of Chemical Theory and Computation 03/2014; 10:1623-1630. · 5.39 Impact Factor
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    ABSTRACT: Photophysical behavior of three lowest-energy tautomers of uric acid and seven most stable isomers of uric acid monohydrate is comprehensively studied by ab initio calculations. Ground-state energies are calculated with the CCSD(T) method, while excitation and ionization energies as well as excited-state potential-energy profiles of photoinduced processes are calculated with the CC2 method. For the (1)ππ* state, it is found that excitation energy of the monohydrate cluster is significantly lower than that of isolated uric acid when the water molecule is hydrogen-bonded at a specific carbonyl group. The calculated excited-state potential-energy profiles suggest that some monohydrate isomers can undergo a migration of the water molecule from one site to another site in the (1)ππ* state with a small energy barrier. It is also found for both uric acid and its monohydrate that nonradiative decay via the NH bond dissociation in the (1)πσ* state is likely to occur at higher excitation energies. Based on the computational results, possible mechanisms for the absence of specific isomers of uric acid monohydrate from the resonant two-photon ionization spectrum are discussed.
    The Journal of Physical Chemistry A 01/2014; · 2.77 Impact Factor
  • Keisuke Niimi, Akira Nakayama, Yuriko Ono, Tetsuya Taketsugu
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    ABSTRACT: The hybrid quantum-classical simulations are performed to investigate the unusual vibrational spectral shifts of a noble-gas hydride HXeCl in matrix environments (in Ne, Ar, Kr, and Xe matrices). The high-level ab initio calculations employing the CCSD(T) method are performed to construct interaction potential energy surfaces between HXeCl and noble-gas atoms (Ne, Ar, Kr, and Xe). The configurations of noble-gas atoms are sampled by the Monte Carlo simulations and the vibrational levels of HXeCl in the presence of the surrounding noble-gas atoms are solved by the DVR approach. It is found that the H-Xe stretching frequencies are blue-shifted from the isolated gas-phase value in all matrix environments and that the relative blue shifts are in good agreement with the experimental results (Ne < Xe < Kr), demonstrating that the explicit treatment of matrix environments around HXeCl is essential to reproduce the observed unusual vibrational shifts.
    The Journal of Physical Chemistry A 12/2013; · 2.77 Impact Factor
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    ABSTRACT: On-the-fly excited-state quantum mechanics∕molecular mechanics molecular dynamics (QM∕MM-MD) simulations of thymine in aqueous solution are performed to investigate the role of solvent water molecules on the nonradiative deactivation process. The complete active space second-order perturbation theory (CASPT2) method is employed for a thymine molecule as the QM part in order to provide a reliable description of the excited-state potential energies. It is found that, in addition to the previously reported deactivation pathway involving the twisting of the C-C double bond in the pyrimidine ring, another efficient deactivation pathway leading to conical intersections that accompanies the out-of-plane displacement of the carbonyl group is observed in aqueous solution. Decay through this pathway is not observed in the gas phase simulations, and our analysis indicates that the hydrogen bonds with solvent water molecules play a key role in stabilizing the potential energies of thymine in this additional decay pathway.
    The Journal of Chemical Physics 12/2013; 139(21):214304. · 3.12 Impact Factor
  • Satoshi Maeda, Tetsuya Taketsugu, Keiji Morokuma
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    ABSTRACT: Finding all required transition state (TS) structures is an important but hard task in theoretical study of complex reaction mechanisms. In the present article, an efficient automated TS search method, artificial force induced reaction (AFIR), was extended to intramolecular reactions. The AFIR method has been developed for intermolecular associative pathways between two or more reactants. Although it has also been applied to intramolecular reactions by dividing molecules manually into fragments, the fragmentation scheme was not automated. In this work, we propose an automated fragmentation scheme. Using this fragmentation scheme and the AFIR method, a fully automated search algorithm for intramolecular pathways is introduced. This version for intramolecular reactions is called single-component AFIR (SC-AFIR), to distinguish it from multicomponent AFIR for intermolecular reactions. SC-AFIR was tested with two reactions, the Claisen rearrangement and the first step of cobalt-catalyzed hydroformylation, and successfully located all important pathways reported in the literature. © 2013 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 11/2013; · 3.84 Impact Factor
  • Ryohei Uematsu, Satoshi Maeda, Tetsuya Taketsugu
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    ABSTRACT: A systematic search for reaction pathways for the vinylogous Mannich-type reaction was performed by the artificial force induced reaction method. This reaction affords δ-amino-γ-butenolide in one pot by mixing 2-trimethylsiloxyfuran, imine, and water under solvent-free conditions. Surprisingly, the search identified as many as five working pathways. Among them, two concertedly produce anti and syn isomers of the product. Another two give an intermediate, which is a regioisomer of the main product. This intermediate can undergo a retro-Mannich reaction to give a pair of intermediates: an imine and 2-furanol. The remaining pathway directly generates this intermediate pair. The imine and 2-furanol easily react with each other to afford the product. Thus, all of these stepwise pathways finally converge to give the main product. The rate-determining step of all five (two concerted and three stepwise) pathways have a common mechanism: concerted SiO bond formation through the nucleophilic attack of a water molecule on the silicon atom followed by proton transfer from the water molecule to the imine. Therefore, these five pathways have comparable barriers and compete with each other.
    Chemistry - An Asian Journal 10/2013; · 4.57 Impact Factor
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    ABSTRACT: The catalytic activity for the oxygen reduction reaction (ORR) of a hexagonal boron nitride (h-BN) monolayer supported on a Ni(111) surface has been studied theoretically using density-functional theory. It is shown that the Ni(111) support can critically change the chemical and physical properties of defect-free monolayer h-BN, considerably promoting the adsorption of O2, OOH, OH, and O species, and therefore, it is demonstrated that inert defect-free monolayer h-BN can be functionalized by the metal support and become catalytically active for the ORR. Although simple potential-dependent modeling of the energetics of the ORR on h-BN/Ni(111) indicates the limitation of the ORR process due to the large overpotential, our calculations demonstrate the ability to functionalize inert materials for the ORR and open new ways to design effective Pt-free catalysts for fuel-cell technology.
    The Journal of Physical Chemistry C 09/2013; 117:21359-21370. · 4.84 Impact Factor
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    ABSTRACT: Automated search for minimum energy conical intersection geometries between the lowest two singlet states (S0/S1-MECIs) was performed by combining the anharmonic downward distortion following (ADDF) method, the seam model function (SMF) approach, and the spin-flip (SF) TDDFT method. SMF/ADDF has been employed previously in automated searches for MECIs on potential energy surfaces (PESs) with expensive multireference methods. In this work, we adopt the SF-TDDFT method that enables efficient optimization of S0/S1-MECIs in the framework of TDDFT. To evaluate the performance of the present approach, it was applied to ethylene and 1,3-butadiene. The present method automatically gave unknown S0/S1-MECIs as well as all previously reported ones. Therefore, the present hybrid method of SMF/ADDF and SF-TDDFT is shown to be a promising approach to locate S0/S1-MECIs of large systems automatically with modest computational costs.
    Journal of Chemical Theory and Computation 08/2013; 9(9):4116–4123. · 5.39 Impact Factor
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    ABSTRACT: A comprehensive picture of the ultrafast nonradiative decay mechanisms of three cytosine tautomers (amino-keto, imino-keto, and amino-enol forms) is revealed by high-level ab initio potential energy calculations using the multistate (MS) CASPT2 method and also by on-the-fly excited-state molecular dynamics simulations employing the CASSCF method. To obtain a reliable potential energy profile along the deactivation pathways, the MS-CASPT2 method is employed even for the optimization of minimum energy structures in the excited state and conical intersection (CI) structures between the ground and excited states. In the imino (imino-keto) form, we locate a new CI structure involving the twisting of the imino group, and the decay pathway leading to this CI is found to be barrierless, suggesting a remarkably efficient deactivation of imino cytosine. In the keto (amino-keto) form, the MS-CASPT2 calculations exhibit an efficient decay path to the ethylene-like CI involving the twisting of the C-C double bond in the six-membered ring, with a barrier of ∼0.08 eV from the minimum of the (1)ππ* state. In the enol (amino-enol) form, three types of CIs are identified for the first time. Among them, the ethylene-like CI with a similar molecular structure to the keto form provides the most preferred deactivation pathway in enol cytosine. This pathway exhibits a higher barrier of ∼0.22 eV and a higher energy of CI than those of keto cytosine. Nonadiabatic molecular dynamics simulations provide a time-dependent picture of the deactivation processes, including the excited-state lifetime of each tautomer. In particular, the decay time of the imino tautomer is predicted to be only ∼100 fs. Our computational results are in remarkably good agreement with the experimental findings of recent femtosecond pump-probe photoionization spectroscopy [J. Am. Chem. Soc., 2009, 131, 16939; J. Phys. Chem. A, 2011, 115, 8406], supporting the coexistence of more than one tautomer in the photophysics of isolated cytosine and that each tautomer exhibits a different excited-state lifetime.
    Physical Chemistry Chemical Physics 06/2013; · 3.83 Impact Factor
  • Min Gao, Andrey Lyalin, Tetsuya Taketsugu
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    ABSTRACT: The mechanism of CO oxidation by O2 on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. Two possible routes for catalytic oxidation are considered. The first route consists in a preliminary dissociation of the adsorbed O2 followed by consequential oxidation of a reactant molecule by atomic oxygen. Although the presence of h-BN surface can change the O2 dissociation barrier, it remains relatively high. The second route is a direct oxidation reaction between the activated molecular oxygen and the reactant. We have found two different pathways for CO oxidation: a two-step pathway where two CO2 molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak.
    Journal of Physics Conference Series 06/2013; 438(1):2003-.
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    ABSTRACT: The combination of o-phenylenediamine (opda), which possesses two proton- and electron-pooling capability, with Fe(II) leads to the photochemical hydrogen-evolution reaction (HER) in THF at room temperature without addition of photosensitizers. From the THF solution, the tris(o-phenylenediamine) iron(II) complex, [FeII(opda)3](ClO4)2 (1), was isolated as a photoactive species, while the deprotonated oxidized species was characterized by X-ray crystallographic analysis, electrospray ionization-mass spectrometry, and UV-vis-NIR spectra. Furthermore, the HER is photocatalyzed by hydroquinone, which serves as a H+/e- donor. The present work demonstrates that the use of a metal-bound aromatic amine as a H+/e- pooler opens an alternative strategy for designing nonprecious-metal-based molecular photochemical H2 production/storage materials.
    Journal of the American Chemical Society 04/2013; · 10.68 Impact Factor
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    ABSTRACT: A multireference second-order perturbation theory is applied to calculate equilibrium structures and vibrational frequencies of trans-azobenzene in the ground and nπ(∗) excited states, as well as the reaction pathways for rotation and inversion mechanism in the nπ(∗) excited state. It is found that the NN stretching frequency exhibits a slight increase at the minimum energy structure in the nπ(∗) state, which is explained by the mixing of the NN stretching mode with the CN symmetric stretching mode. We also calculate the NN stretching frequency at several selected structures along the rotation and inversion pathways in the nπ(∗) state, and show that the frequency decreases gradually along the rotation pathway while it increases by ca. 300 cm(-1) along the inversion pathway. The frequencies and energy variations along the respective pathways indicate that the rotation pathway is more consistent with the experimental observation of the NN stretching frequency in nπ(∗) excitation.
    The Journal of Chemical Physics 02/2013; 138(6):064305. · 3.12 Impact Factor
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    ABSTRACT: The catalytic activity for the oxygen reduction reaction (ORR) of both the pristine and defect-possessing hexagonal boron nitride (h-BN) monolayer and H-terminated nanoribbon have been studied theoretically using density functional theory. It is demonstrated that an inert h-BN monolayer can be functionalized and become catalytically active by nitrogen doping. It is shown that the energetics of adsorption of O(2), O, OH, OOH, and H(2)O on N atom impurities in the h-BN monolayer (N(B)@h-BN) is quite similar to that known for a Pt(111) surface. The specific mechanism of destructive and cooperative adsorption of ORR intermediates on the surface point defects is discussed. It is demonstrated that accounting for entropy and zero-point energy (ZPE) corrections results in destabilization of the ORR intermediates adsorbed on N(B)@h-BN, while solvent effects lead to their stabilization. Therefore, entropy, ZPE and solvent effects partly cancel each other and have to be taken into account simultaneously. Analysis of the free energy changes along the ORR pathway allows us to suggest that a N-doped h-BN monolayer can demonstrate catalytic properties for the ORR under the condition that electron transport to the catalytically active center is provided.
    Physical Chemistry Chemical Physics 01/2013; · 3.83 Impact Factor
  • Min Gao, Andrey Lyalin, Tetsuya Taketsugu
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    ABSTRACT: The mechanism of CO oxidation by O(2) on Au atoms supported on the pristine and defected hexagonal boron nitride (h-BN) surface has been studied theoretically using density functional theory. It is found that O(2) binds stronger than CO on an Au atom supported on the defect free h-BN surface and h-BN surface with nitrogen vacancy (V(N)@h-BN), but weaker than CO on a free Au atom or Au trapped by a boron vacancy (V(B)@h-BN). The excess of the positive or negative charge on Au can considerably change its catalytic properties and enhance activation of the adsorbed O(2). Coadsorption of CO and O(2) on Au, Au/V(N)@h-BN, and Au/V(B)@h-BN results in additional charge transfer to O(2). Various pathways of the CO oxidation reaction by molecular oxygen are studied. We found two different pathways for CO oxidation: a two-step pathway where two CO(2) molecules are formed independently, and a self-promotion pathway where oxidation of the first CO molecule is promoted by the second CO molecule. Interaction of Au with the defect-free and defected h-BN surface considerably affects the CO oxidation reaction pathways and barriers. Therefore, Au supported on the h-BN surface (pristine or defected) cannot be considered as pseudo-free atom and support effects have to be taken into account, even when the interaction of Au with the support is weak.
    The Journal of Chemical Physics 01/2013; 138(3):034701. · 3.12 Impact Factor
  • Min Gao, Andrey Lyalin, Tetsuya Taketsugu
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    ABSTRACT: Molecular and dissociative adsorption of O2 on Au atoms supported on the regular and defected hexagonal boron nitride (h‐BN) surface has been studied theoretically using density functional theory. It is shown that even weak interaction of Au with the defect‐free h‐BN support has an unusually strong influence on the binding and catalytic activation of the molecular oxygen. The strong interaction of Au with vacancy point defects on the h‐BN surface is accompanied by the large charge transfer to/from the adsorbate which can considerably affect the catalytic activity of the supported Au. It is demonstrated that activation of the molecular O2 and barriers for O2 dissociation on the supported Au atom can be affected by the interaction of Au with the pristine or defected h‐BN support. Therefore, the h‐BN surface cannot be considered as an absolutely inert support for Au. © 2012 Wiley Periodicals, Inc.
    International Journal of Quantum Chemistry 01/2013; 113(4). · 1.17 Impact Factor
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    ABSTRACT: Axially-ligated iron phthalocyanines have been found to be good molecular conductors with giant negative magnetoresistance (GNMR) which originates from a strong intramolecular -d interaction between the metal and phthalocyanine. Ab initio theoretical calculations showed that substitution of ruthenium into the phthalocyanine complex would result in a significant increase in the -d interaction of the system, potentially intensifying GNMR. This paper presents the crystal preparation and X-ray structural characterization of bis(triphenylphosphine)iminium dichloro(phthalocyaninato(2-))ruthenium(III), PNP [(Pc2−)Cl2]. It is observed that [(Pc2−)Cl2] system has a symmetric planar RuPc unit with perpendicular axial ligands which results in a unidirectional and uniform solid-state arrangement, suitable for -d interaction-based molecular conductors with potentially exceptional GNMR.
    Journal of Chemistry. 10/2012; 2013.

Publication Stats

734 Citations
396.09 Total Impact Points

Institutions

  • 2005–2014
    • Hokkaido University
      • • Division of Chemistry
      • • Graduate School of Science
      • • Department of Chemistry
      Sapporo, Hokkaidō, Japan
  • 2008–2012
    • RIKEN
      • Nuclear Spectroscopy Laboratory
      Wako, Saitama-ken, Japan
  • 2011
    • Gunma University
      • Department of Chemistry and Chemical Biology
      Maebashi-shi, Gunma-ken, Japan
    • Minoufiya University
      • Department of Chemistry
      Shibīn al Kawm, Muhafazat al Minufiyah, Egypt
  • 1999–2008
    • Ochanomizu University
      • Department of Chemistry
      Tōkyō, Japan
  • 2004
    • Tokyo Institute of Technology
      • Research Laboratory for Nuclear Reactors
      Tokyo, Tokyo-to, Japan
    • Institute for Molecular Science
      Okazaki, Aichi, Japan
  • 1993–2004
    • The University of Tokyo
      • • Faculty & Graduate School of Engineering
      • • Department of Applied Chemistry
      Tokyo, Tokyo-to, Japan
  • 2001–2002
    • University of Cambridge
      • Department of Chemistry
      Cambridge, England, United Kingdom