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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.

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.

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.

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.

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.

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