Quantum Chemistry Research Institute

Kyoto, Japan

Quantum Chemistry Research Institute

Kyoto, Japan
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Poolmee P.,Kasetsart University | Ehara M.,Japan Institute for Molecular Science | Nakatsuji H.,Quantum Chemistry Research Institute | Nakatsuji H.,Chiyoda Corporation
Theoretical Chemistry Accounts | Year: 2011

The π-conjugated ladder-type molecules constitute an attractive field of organic photoactive materials. In this work, the photophysical properties of ladder-type penta-p-phenylene (LPP) and carbazole derivatives (bisindenocarbazole and diindolocarbazole) have been investigated theoretically using the symmetry-adapted cluster-configuration interaction (SAC-CI) method. The equilibrium geometries in the ground (S0) and first excited (S1) states were calculated to be planar, and the excitation is delocalized over the molecules. SAC-CI/DZP calculations have been applied to the absorption and emission spectra of these molecules. The absorption spectra were well reproduced in both peak positions and the shape of the absorption bands. The strong absorption is attributed to the highest occupied molecular orbital to the lowest unoccupied molecular orbital (H-L) transition; however, in carbazoles, the H-1→L transition is located below the H-L transition. The vibrational structure in the S0-S1 absorption band of LPP was analyzed by calculating the Franck-Condon (FC) factors based on the potential energy surfaces (PESs) along the normal coordinates that are relevant to the geometry change. The vibrational structure was well reproduced by the theoretical simulation. The C-C stretching mode dominantly contributes to the vibrational structure, while the breathing motion of the molecular frame does not influence the structure. The emission energies calculated by the SAC-CI method also agree well with the experimental values. The vibrational structure in the fluorescence band was also examined by the FC analysis; the theoretical spectrum is satisfactory for the two carbazoles, while the 0-0 transition is overestimated in LPP. In diindolocarbazole, the S2 state has a large oscillator strength, while the S1 state has a small oscillator strength. © 2011 Springer-Verlag.


Ehara M.,Japan Institute for Molecular Science | Ehara M.,Chiyoda Corporation | Saha B.,Kyoto University | Poolmee P.,Kasetsart University | And 5 more authors.
AIP Conference Proceedings | Year: 2012

Electronic structure and optical properties of some organic conjugated molecules, that is the oligomers for organic-light emitting diodes (OLED), chelating hetero-atomic conjugated ligands, and UVB blocking molecules, have been investigated by the SAC-CI method. The absorption and emission spectra of these molecules were reproduced accurately. For OLED molecules, chain length dependence of the excitation and emission energies was evaluated for poly para-phenylene vinylene and poly para-phenylene. Thermal effect on the electronic spectra of fluorene-thiophene and its derivatives was examined with taking accounts the Boltzmann distribution. The photophysical properties of the chelating hetero-atomic molecules including pyridine-, benxazole-, and benzothiazole derivatives which are useful for electroluminescent metal complex were systematically calculated. The UVB blocking function of the methoxy substituted cinnamates was investigated with regard to the substitution position. The excited-state geometry relaxation of these molecules was interpreted based on the electrostatic force theory. The present work provides a useful basis for the theoretical design predicting the optical properties of the photo-functional molecules. © 2012 American Institute of Physics.


Kanazawa Y.,Graduate University for Advanced Studies | Kanazawa Y.,Japan Institute for Molecular Science | Tsuji H.,Kyoto University | Tsuji H.,Kanagawa University | And 10 more authors.
ChemPhysChem | Year: 2016

The photophysical properties of oligosilanes show unique conformational dependence due to σ-electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n-hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds. The results compare well with those obtained by using the symmetry-adapted-cluster configuration interaction method and almost as well with those obtained by time-dependent density functional theory with the PBE0 functional. The conformational dependence of the transition energies and other properties of free-chain permethylated n-hexasilane, n-Si6Me14, was also examined as a function of dihedral angles, and the striking effects found were attributed to avoided crossings between configurations of σσ* and σπ* character. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim


Tsuji H.,Kyoto University | Tsuji H.,University of Tokyo | Fogarty H.A.,University of Colorado at Boulder | Ehara M.,Kyoto University | And 13 more authors.
Chemistry - A European Journal | Year: 2014

Unlike π-electron chromophores, the peralkylated n-tetrasilane σ-electron chromophore resembles a chameleon in that its electronic spectrum changes dramatically as its silicon backbone is twisted almost effortlessly from the syn to the anti conformation (changing the SiSiSiSi dihedral angle ω from 0 to 180°). A combination of UV absorption, magnetic circular dichroism (MCD), and linear dichroism (LD) spectroscopy on conformationally controlled tetrasilanes 1-9, which cover fairly evenly the full range of angles ω, permitted a construction of an experimental correlation diagram for three to four lowest valence electronic states. The free chain tetrasilane n-Si4Me10 (10), normally present as a mixture of three enantiomeric conformer pairs of widely different angles ω, has also been included in our study. The spectral trends are interpreted in terms of avoided crossings of 1B with 2B and 2A with 3A states, in agreement with SAC-CI calculations on the excited states of 1-7 and conformers of 10. Chemical chameleon: The facile rotation of Si 4Me10 around the central SiSi bond transforms its absorption spectrum dramatically (calculated transition intensities are shown). © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Ehara M.,Japan Institute for Molecular Science | Ehara M.,Research Center for Computational Science | Ehara M.,Graduate University for Advanced Studies | Ehara M.,Chiyoda Corporation | And 13 more authors.
Physical Review A - Atomic, Molecular, and Optical Physics | Year: 2011

In this study, angle-resolved energetic-ion yield spectra were measured in the N 1s excitation region of N2O. A Franck-Condon analysis based on ab initio two-dimensional potential energy surfaces of the core-excited Rydberg states, which were calculated by the symmetry-adapted cluster-configuration interaction method, reproduced observed vibrational excitations specific to the individual Rydberg states well and enabled quantitative assignments. Geometric changes in the terminal nitrogen Nt 1s and the central nitrogen Nc 1s excited states with respect to the 3pπ, 3pσ, and 4sσ transitions were analyzed. The coupling of these valence and Rydbergs states was examined based on the second moment analysis. Irregular Rydberg-state behavior in the Nc 1s-1 4sσ state was observed. © 2011 American Physical Society.


PubMed | Quantum Chemistry Research Institute, Kyoto University, Graduate University for Advanced Studies and University of Colorado at Boulder
Type: Journal Article | Journal: Chemphyschem : a European journal of chemical physics and physical chemistry | Year: 2016

The photophysical properties of oligosilanes show unique conformational dependence due to -electron delocalization. The excited states of the SAS, AAS, and AEA conformations of peralkylated n-hexasilanes, in which the SiSiSiSi dihedral angles are controlled into a syn (S), anti (A), or eclipsed (E) conformation, were investigated by using UV absorption, magnetic circular dichroism (MCD), and linear dichroism spectroscopy. Simultaneous Gaussian fitting of all three spectra identified a minimal set of transitions and the wavenumbers, oscillator strengths, and MCD B terms in all three compounds. The results compare well with those obtained by using the symmetry-adapted-cluster configuration interaction method and almost as well with those obtained by time-dependent density functional theory with the PBE0 functional. The conformational dependence of the transition energies and other properties of free-chain permethylated n-hexasilane, n-Si


Ehara M.,Japan Institute for Molecular Science | Oyagi F.,Kyoto University | Abe Y.,Kyoto University | Fukuda R.,Japan Institute for Molecular Science | And 3 more authors.
Journal of Chemical Physics | Year: 2011

In this series of studies, we systematically apply the analytical energy gradients of the direct symmetry-adapted cluster-configuration interaction singles and doubles nonvariational method to calculate the equilibrium geometries and vibrational frequencies of excited and ionized states of molecules. The harmonic vibrational frequencies were calculated using the second derivatives numerically computed from the analytical first derivatives and the anharmonicity was evaluated from the three-dimensional potential energy surfaces around the local minima. In this paper, the method is applied to the low-lying valence singlet and triplet excited states of HAX-type molecules, HCF, HCCl, HSiF, HSiCl, HNO, HPO, and their deuterium isotopomers. The vibrational level emission spectra of HSiF and DSiF and absorption spectra of HSiCl and DSiCl were also simulated within the Franck-Condon approximation and agree well with the experimental spectra. The results show that the present method is useful and reliable for calculating these quantities and spectra. The change in geometry in the excited states was qualitatively interpreted in the light of the electrostatic force theory. The effect of perturbation selection with the localized molecular orbitals on the geometrical parameters and harmonic vibrational frequencies is also discussed. © 2011 American Institute of Physics.


Ichikawa K.,Kyoto University | Wagatsuma A.,Kyoto University | Kurokawa Y.I.,Quantum Chemistry Research Institute | Sakaki S.,Kyoto University | Tachibana A.,Kyoto University
Theoretical Chemistry Accounts | Year: 2011

We study the electronic structure of two types of transition metal complexes, the inverted-sandwich-type and open-lantern-type, by the electronic stress tensor. In particular, the bond order bε measured by the energy density which is defined from the electronic stress tensor is studied and compared with the conventional MO-based bond order. We also examine the patterns found in the largest eigenvalue of the stress tensor and corresponding eigenvector field, the "spindle structure" and "pseudo-spindle structure". As for the inverted-sandwich-type complex, our bond order bε calculation shows that relative strength of the metal-benzene bond among V, Cr, and Mn complexes is V > Cr > Mn, which is consistent with the MO-based bond order. As for the open-lantern-type complex, we find that our energy density-based bond order can properly describe the relative strength of Cr-Cr and Mo-Mo bonds by the surface integration of the energy density over the "Lagrange surface" which can take into account the spatial extent of the orbitals. © 2011 Springer-Verlag.


Kurokawa Y.I.,Quantum Chemistry Research Institute | Nakashima H.,Quantum Chemistry Research Institute | Nakatsuji H.,Quantum Chemistry Research Institute
Advances in Quantum Chemistry | Year: 2015

We have extended and generalized Kato's cusp condition (CC) and Rassolov and Chipman's CC, which are necessary conditions for the exact solution to the Schrödinger equation. We named them general coalescence conditions (GCCs). The GCCs can be applied not only to Coulombic systems. In this article, we review the GCCs for two- and many-particle systems. Then, we numerically verify that the GCC equations are satisfied by the free complement (FC) wave function of a hydrogen atom in the 1. s and 2. p states, a harmonic oscillator, V = r system, and a helium atom. Based on the GCCs, a new method is proposed to determine parameters in a trial wave function. We named them GCC constrained (GCCC) method. Using the GCCC method combined with the FC wave function, we could obtain the exact wave function that behaves correctly in the coalescence point. © 2015 Elsevier Inc.


Ishikawa A.,Kyoto University | Ishikawa A.,Quantum Chemistry Research Institute | Tanimura Y.,Kyoto University | Nakao Y.,Kyoto University | And 2 more authors.
Organometallics | Year: 2012

C-C σ-bond activation of cyclopropene by RuCl2(PPh 3)2 and IrCl(CO)(PMe3)2 was theoretically investigated. The activation barrier and the reaction energy calculated here indicate that the reaction occurs more easily by the ruthenium complex than by the iridium complex, which is consistent with the experimental results that the Ru-vinylcarbene species is formed but the Ir-vinylcarbene is not. The valence bond analysis of the CASSCF wave function disclosed that the Ir-vinylcarbene bond is significantly weaker than that of the Ru complex because the d6 square pyramidal complex of Ru is more favorable than the d8 complex of Ir for this bonding interaction. In both the Ru and Ir systems, a precursor complex is formed by coordination of the C 1=C2 double bond of cyclopropene with the metal center, where C1 and C2 are sp2 carbons and C 3 is an sp3 carbon. In the transition state, one C-C single bond (named C1-C3) is almost broken, but the M-C1 bond (M = Ru or Ir) and another C-C single bond (named C 2-C3) are becoming stronger. When moving from the transition state to a metal-vinylcarbene product, the C1=C 2 double bond changes to the C1-C2 single bond with the concomitant change of the C2-C3 single bond to the C2=C3 double bond. To induce these bond formation and bond breaking processes, the valence state of the metal center must change in the reaction. The promotion energy to the valence state becomes smaller in the ruthenium reaction system when going from the reactant to the product but becomes considerably larger in the iridium reaction system. This is the reason that the C-C σ-bond cleavage of cyclopropene occurs more easily in the ruthenium complex than in the iridium complex. The difference in promotion energy between the ruthenium and iridium systems is reasonably interpreted in terms of d-d orbital splitting by ligand-field and d electron number. © 2012 American Chemical Society.

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