Ryoichi Fukuda

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Photophysical Properties and Photochemistry ofEE-,EZ-, andZZ-1,4-Dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] Benzene in Solution: Theory and Experiment

The Journal of Physical Chemistry A (2011)

Songwut Suramitr Suphawarat Phalinyot Peter Wolschann Ryoichi Fukuda Masahiro Ehara

Photophysical properties and photoisomerization of 1,4-dimethoxy-2,5-bis[2-(thien-2-yl)ethenyl] benzene (DMTB) have been investigated for the EE-, EZ-, and ZZ- stereoisomers. The EE-DMTB was prepared, and the absorption/fluorescence spectra of EE- isomer as well as transient spectra in photoisomerization among three isomers were observed. Absorption and fluorescence spectra of three isomers were analyzed by the symmetry-adapted cluster-configuration interaction (SAC-CI) and time-dependent density functional theory (TDDFT) methods. The characteristics of the absorption spectra of three isomers were satisfactorily reproduced by the direct SAC-CI and TDDFT methods in both peak position and intensity. The relative stability of three isomers and the photoisomerization among these isomers were also examined theoretically. The ground (S(0)) and first excited state (S(1)) geometries were calculated by the DFT/TDDFT method with the M06HF functional, and the calculated S(0) structures of EE- and ZZ- isomers agreed well with those of the X-ray structures. The geometry relaxation in the S(1) state was interpreted with regard to the excitation character. The solvent effect in the absorption and fluorescence spectra was examined by the polarizable continuum model (PCM) and was found to be 0.05-0.20 eV, reflecting the charge polarization. The results show that the photophysical properties of DMTB can be controlled with the conformation constraint and also indicate the possibility of a photofunctional molecular device such as a switching function.

Polarizable continuum model

10.1021/jp206463k

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Citations (5)

Photomechanical behaviour of monolayers of azobenzene derivatives

Thin Solid Films (1996)

Takahiro Seki Kunihiro Ichimura Ryoichi Fukuda Takashi Tamaki

Azobenzene

10.1016/s0040-6090(95)08343-x

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Citations (9)

Electronic excited states and electronic spectra of biphenyl: a study using many-body wavefunction methods and density functional theories

Physical Chemistry Chemical Physics (2013)

Ryoichi Fukuda Masahiro Ehara

The low-lying electronic excited states of biphenyl were studied using the symmetry-adapted cluster-configuration interaction (SAC-CI), complete active space self-consistent field (CASSCF), complete active space perturbation theory of the second-order (CASPT2), and the time-dependent density functional theory (TDDFT). The molecular geometries in the ground and excited states were optimized using the SAC-CI and TDDFT for singlet and triplet states. The energies of vertical excitations, emissions, and adiabatic transitions were calculated. The TDDFT calculations significantly underestimated the excitation energy of the 1(1)B1 state, while the SAC-CI and CASPT2 provided essentially similar results. The present SAC-CI and CASPT2 calculations concluded that the lowest singlet state of isolated biphenyl is the 1(1)B3 state that takes a planar geometry and the second lowest state is the 1(1)B2 state with a twisted geometry. The present results were consistent with the previous experimental findings. The 1(1)B1 state that has a charge-separated biracial character in the vertical excitation relaxed into a planar quinoid structure in which bond alternations were emphasized. The other states took a benzenoid structure. The ultraviolet (UV) absorption and circular dichroism (CD) spectra below 7 eV were calculated with the SAC-CI method. The valence-Rydberg mixings were found to be significant in the second and higher series of excited states.

Excited electronic state

Biphenyl

10.1039/c3cp52636d

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Citations (24)

An efficient computational scheme for electronic excitation spectra of molecules in solution using the symmetry-adapted cluster–configuration interaction method: The accuracy of excitation energies and intuitive charge-transfer indices

The Journal of Chemical Physics (2014)

Ryoichi Fukuda Masahiro Ehara

Solvent effects on electronic excitation spectra are considerable in many situations; therefore, we propose an efficient and reliable computational scheme that is based on the symmetry-adapted cluster-configuration interaction (SAC-CI) method and the polarizable continuum model (PCM) for describing electronic excitations in solution. The new scheme combines the recently proposed first-order PCM SAC-CI method with the PTE (perturbation theory at the energy level) PCM SAC scheme. This is essentially equivalent to the usual SAC and SAC-CI computations with using the PCM Hartree-Fock orbital and integrals, except for the additional correction terms that represent solute-solvent interactions. The test calculations demonstrate that the present method is a very good approximation of the more costly iterative PCM SAC-CI method for excitation energies of closed-shell molecules in their equilibrium geometry. This method provides very accurate values of electric dipole moments but is insufficient for describing the charge-transfer (CT) indices in polar solvent. The present method accurately reproduces the absorption spectra and their solvatochromism of push-pull type 2,2'-bithiophene molecules. Significant solvent and substituent effects on these molecules are intuitively visualized using the CT indices. The present method is the simplest and theoretically consistent extension of SAC-CI method for including PCM environment, and therefore, it is useful for theoretical and computational spectroscopy.

Coupled cluster

10.1063/1.4897561

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Citations (11)

Quasirelativistic theory for the magnetic shielding constant. I. Formulation of Douglas–Kroll–Hess transformation for the magnetic field and its application to atomic systems

The Journal of Chemical Physics (2003)

Ryoichi Fukuda Masahiko Hada Hiroshi Nakatsuji

A two-component quasirelativistic theory based on the Douglas–Kroll–Hess (DKH) transformation has been developed to study magnetic properties of molecules. The proposed Hamiltonian includes the relativistic magnetic vector potential in the framework of the DKH theory, and is applicable to the calculations of magnetic properties without further expansion in powers of c−1. By combining with the finite-perturbation theory and the generalized-UHF method, new pictures of the magnetic shielding constant are derived. We apply the theory to calculations of the magnetic shielding constants of He isoelectronic systems, Ne isoelectronic systems, and noble gas atoms. The results of the present theory compare well with those of the four-component Dirac–Hartree–Fock calculations; the differences were within 3%. We note that the quasirelativistic theory that handles the magnetic vector potential at a nonrelativistic level greatly underestimates the relativistic effect. The so-called “picture change” effect is quite important for the magnetic shielding constant of heavy elements. The change in the orbital picture plays a significant role in the valence-orbital magnetic response as well as the core-orbital one. The effect of the finite nucleus is also studied using Gaussian nucleus model. The present theory reproduces the correct behavior of the finite-nucleus effect that has been reported with the Dirac theory. In contrast, the nonrelativistic theory and the quasirelativistic theory with the nonrelativistic vector potential underestimate the finite-nucleus effect.

Hamiltonian (control theory)

10.1063/1.1528933

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Citations (106)

Separation of the resonance and background and the possibility for a Pomeranchuk term

Lettere al nuovo cimento della societa italiana di fisica/Lettere al nuovo cimento (1971)

Ryoichi Fukuda

Separation (statistics)

10.1007/bf02780416

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Citations (0)

Electronic Structure and Stability of Binary Metal Cluster with Core-Shell Structure: Theoretical Approach

Journal of Computer Chemistry Japan (2019)

Nozomi Takagi Ryoichi Fukuda Masahiro Ehara Shigeyoshi Sakaki

複数の金属元素からなる複合金属クラスターや微粒子は,貴金属減量触媒や卑金属触媒の候補として興味がもたれ,自動車排気ガス浄化触媒,燃料電池電極触媒などの実験分野で活発に研究がおこなわれている.新規な触媒の効率的な設計のためには,電子状態理論計算による複合金属クラスターの電子状態と安定構造, 分子吸着特性, 反応性の相関に対する知見が不可欠である.最近,銅とVIII族からXI族までの金属の複合クラスター(Cu32M6; M = Ru, Rh, Pd, Ag, Os, Ir, Pt, Au) ,および白金とVIII,IX族金属との複合クラスター(Pt42M13; M = Ru, Rh, Os, Ir)に関して統一的な電子状態理論研究がおこなわれ,シェルからコアへの電荷移動がコアシェル型構造の安定性を決める一つの重要な因子であることが報告された.本総説では,それらのコアシェル型構造の安定性と電子状態,安定性を支配する因子に関する議論をまとめて紹介する.

10.2477/jccj.2018-0043

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Citations (1)

Dynamical Theory of the Yang-Mills Field. I: --Instability of the Vacuum and Singlet Pair Condensation--

Progress of Theoretical Physics (1978)

Ryoichi Fukuda Taichiro Kugo

The normal vacuum of Yang-Mills field theory is argued to be unstable. A group singlet pair of transverse Yang-Mills gauge bosons forms a bound state with a negative energy eigenvalue (Cooper pair). Stable vacuum is realized after the condensation of these pairs. Global group symmetry remains unbroken and the excitation spectrum has a gap: Gauge bosons acquire a common mass. This massive phase is realized for whatever small coupling constant: The critical coupling constant is zero. These are explicitly shown by solving the approximate gap equation in detail.

Mass gap

Yang–Mills theory

Coupling constant

Gauge group

10.1143/ptp.60.565

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Citations (39)

Aerobic oxidation of methanol to formic acid on Au20−: a theoretical study on the reaction mechanism

Physical Chemistry Chemical Physics (2012)

Karan Bobuatong Sangita Karanjit Ryoichi Fukuda Masahiro Ehara Hidehiro Sakurai

The aerobic oxidation of methanol to formic acid catalyzed by Au20− has been investigated quantum chemically using density functional theory with the M06 functional. Possible reaction pathways are examined taking account of full structure relaxation of the Au20−cluster. The proposed reaction mechanism consists of three elementary steps: (1) formation of formaldehyde from methoxy species activated by a superoxo-like anion on the gold cluster; (2) nucleophilic addition by the hydroxyl group of a hydroperoxyl-like complex to formaldehyde resulting in a hemiacetal intermediate; and (3) formation of formic acid by hydrogen transfer from the hemiacetal intermediate to atomic oxygen attached to the gold cluster. A comparison of the computed energetics of various elementary steps indicates that C–H bond dissociation of the methoxy species leading to formation of formaldehyde is the rate-determining step. A possible reaction pathway involving single-step hydrogen abstraction, a concerted mechanism, is also discussed. The stabilities of reactants, intermediates and transition state structures are governed by the coordination number of the gold atoms, charge distribution, cooperative effect and structural distortion, which are the key parameters for understanding the relationship between the structure of the gold cluster and catalytic activity in the aerobic oxidation of alcohols.

Elementary reaction

Hydrogen atom abstraction

10.1039/c2cp23446g

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Citations (40)

Modeling Molecular Systems at Extreme Pressure by an Extension of the Polarizable Continuum Model (PCM) Based on the Symmetry-Adapted Cluster-Configuration Interaction (SAC–CI) Method: Confined Electronic Excited States of Furan as a Test Case

Journal of Chemical Theory and Computation (2015)

Ryoichi Fukuda Masahiro Ehara Roberto Cammi

Novel molecular photochemistry can be developed by combining high pressure and laser irradiation. For studying such high-pressure effects on the confined electronic ground and excited states, we extend the PCM (polarizable continuum model) SAC (symmetry-adapted cluster) and SAC-CI (SAC-configuration interaction) methods to the PCM-XP (extreme pressure) framework. By using the PCM-XP SAC/SAC-CI method, molecular systems in various electronic states can be confined by polarizable media in a smooth and flexible way. The PCM-XP SAC/SAC-CI method is applied to a furan (C4H4O) molecule in cyclohexane at high pressure (1-60 GPa). The relationship between the calculated free-energy and cavity volume can be approximately represented with the Murnaghan equation of state. The excitation energies of furan in cyclohexane show blueshifts with increasing pressure, and the extents of the blueshifts significantly depend on the character of the excitations. Particularly large confinement effects are found in the Rydberg states. The energy ordering of the lowest Rydberg and valence states alters under high-pressure. The pressure effects on the electronic structure may be classified into two contributions: a confinement of the molecular orbital and a suppression of the mixing between the valence and Rydberg configurations. The valence or Rydberg character in an excited state is, therefore, enhanced under high pressure.

10.1021/ct5011517

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Citations (43)