Tetsuya Taketsugu

Hokkaido University, Sapporo, Hokkaidō, Japan

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Publications (140)428.03 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: To expand the originally developed fluorescent 1,3a,6a-triazapentalenes as fluorescent labeling reagents, the fluorescence wavelength of 1,3a,6a-triazapentalene was extended to the red color region. Based on the noteworthy correlation of the fluorescence wavelength with the inductive effect of the 2-substituent, further electron-deficient 2-(2-cyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene and 2-(2,6-dicyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene were synthesized. The former exhibited yellow and the latter exhibited red fluorescence, and both compounds exhibited large Stokes shifts, and the 1,3a,6a-triazapentalene system enabled the same fluorescent chromophore to cover the entire region of visible wavelengths. The potential applications of the 1,3a,6a-triazapentalenes as fluorescent probes in the fields of the life sciences were investigated, and the 1,3a,6a-triazapentalene system was clearly proven to be useful as a fluorescent reagent for live cell imaging. Quantum chemical calculations were performed to investigate the optical properties of 1,3a,6a-triazapentalenes. These calculations revealed that the excitation involves a significant charge-transfer from the 1,3a,6a-triazapentalene skeleton to the 2-substituent. The calculated absorption and fluorescence wavelengths showed a good correlation with the experimental ones, and thus the system would enable the theoretical design of substituents with the desired optical properties.
    Chemical Science 10/2014; · 8.31 Impact Factor
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    ABSTRACT: Locating accessible conical intersections (CIs), especially minimum energy CI (MECI) structures, near the Franck-Condon (FC) region is one of the most important tasks in theoretical analyses of photoreactions. Many MECIs may exist around a FC point in molecules with many vibrational degrees of freedom. Usually, MECIs are optimized one by one starting from arbitrary chosen initial structures. In order to eliminate the arbitrariness, we have developed automated MECI search methods. In this paper, a new approach is described. It combines the seam model function approach with the recently proposed single-component artificial force induced reaction method. Starting from a FC point, the present method finds MECIs systematically. It requires neither a Hessian nor a derivative coupling vector. In an example of the automated search, the spin-flip TDDFT was employed as an efficient electronic structure calculation method, which, together with an automated algorithm to recognize proper electronic states, allowed for evaluation of energy and gradient in a black-box fashion. The present approach was tested with trans- and cis-1,3-butadiene, thymine, and coumarin molecules. The usefulness of the present approach was demonstrated by comparing obtained MECIs with those in the literature. It is hoped that the present technique will be useful in exploration of unknown photoreaction pathways.
    The journal of physical chemistry. A. 09/2014;
  • Akira Nakayama, Shohei Yamazaki, Tetsuya Taketsugu
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    ABSTRACT: The nonradiative deactivation pathways of cytosine derivatives (cytosine, 5-fluorocytosine, 5-methylcytosine, and 1-methycytosine) and their tautomers are investigated by quantum chemical calculations, and the substituent effects on the deactivation process are examined. The MS-CASPT2 method is employed in the excited-state geometry optimization and also in the search for conical intersection points, and the potential energy profiles connecting the Franck-Condon point, excited-state minimum energy structures, and the conical intersection points are investigated. Our calculated vertical and adiabatic excitation energies are in quite good agreement with experimental results, and the relative barrier heights leading to the conical intersections are correlated with the experimentally observed excite-state lifetimes, where the calculated barrier heights are in the order of cytosine < 5-methylcytosine < 5-fluorocytosine.
    The journal of physical chemistry. A. 09/2014;
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    ABSTRACT: On-the-fly dynamics simulations were carried out using spin-flip time dependent density functional theory (SF-TDDFT) to examine the photoisomerization and photocyclization mechanisms of cis-stilbene following excitation to the ππ* state. A state tracking method was devised to follow the target state among nearly degenerate electronic states during the dynamics simulations. The steepest descent path from the Franck-Condon structure of cis-stilbene in the ππ* state is shown to reach the S1-minimum of 4,4-dihydrophenanthrene (DHP) via a cis-stilbene-like structure (referred to as (S1)cis-min) on a very flat region of the S1-potential energy surface. From the dynamics simulations, the branching ratio of the photoisomerization is calculated as trans: DHP = 35: 13, in very good agreement with the experimental data, trans: DHP = 35: 10. The discrepancy between the steepest descent pathway and the significant trans-stilbene presence in the branching ratio observed experimentally and herein computationally is clarified from an analysis of geometrical features along the reaction pathway, as well as the low barrier of 0.1 eV for the pathway from (S1)cis-min to the twisted pyramidal structure on the S1-potential energy surface. It is concluded that ππ*-excited cis-stilbene propagates primarily toward the twisted structural region due to dynamic effects, with partial branching to the DHP structural region via the flat-surface region around (S1)cis-min.
    The journal of physical chemistry. A. 09/2014;
  • Source
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    ABSTRACT: The intrinsic reaction coordinate (IRC) approach has been used extensively in quantum chemical analysis and prediction of the mechanism of chemical reactions. The IRC gives a unique connection from a given transition structure to local minima of the reactant and product sides. This allows for easy understanding of complicated multistep mechanisms as a set of simple elementary reaction steps. In this article, three topics concerning the IRC approach are discussed. In the first topic, the first ab initio study of the IRC and a recent development of an IRC calculation algorithm for enzyme reactions are introduced. In the second topic, cases are presented in which dynamical trajectories bifurcate and corresponding IRC connections can be inaccurate. In the third topic, a recent development of an automated reaction path search method and its application to systematic construction of IRC networks are described. Finally, combining these three topics, future perspectives are discussed. © 2014 Wiley Periodicals, Inc.
    International Journal of Quantum Chemistry 09/2014; · 1.17 Impact Factor
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    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
  • Source
    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; · 4.20 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

Publication Stats

827 Citations
428.03 Total Impact Points


  • 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