Electronic Transitions in Conformationally Controlled Peralkylated Hexasilanes.
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.
SOKENDAI, The Graduate University for Advanced Studies, Nishigonaka, Myodaiji, Okazaki, 444-8585, Japan.|Institute for Molecular Science and Research Center for Computational Science, Nishigonaka, Myodaiji, Okazaki, 444-8585, Japan.
Yuki
Y
Kanazawa
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan. tsujiha@kanagawa-u.ac.jp.|Department of Chemistry, Faculty of Science, Kanagawa University, 2946 Tsuchiya, Hiratsuka, Kanagawa, 259-1293, Japan. tsujiha@kanagawa-u.ac.jp.
Hayato
H
Tsuji
SOKENDAI, The Graduate University for Advanced Studies, Nishigonaka, Myodaiji, Okazaki, 444-8585, Japan. ehara@ims.ac.jp.|Institute for Molecular Science and Research Center for Computational Science, Nishigonaka, Myodaiji, Okazaki, 444-8585, Japan. ehara@ims.ac.jp.|Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto, 615-8520, Japan. ehara@ims.ac.jp.
Masahiro
M
Ehara
Elements Strategy Initiative for Catalysts and Batteries (ESICB), Kyoto University, Kyoto, 615-8520, Japan.
Ryoichi
R
Fukuda
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado, 80309-0215, USA.
Deborah L
DL
Casher
International Research Center for Elements Science (IRCELS), Institute for Chemical Research, Kyoto University, Uji, Kyoto, 611-0011, Japan.|RIKEN, 2-1 Hirosawa, Saitama, 351-0198, Japan.
Kohei
K
Tamao
Quantum Chemistry Research Institute, Goryo Oohara 1-36, Nishikyo-ku, Kyoto, 615-8245, Japan.
Hiroshi
H
Nakatsuji
Department of Chemistry and Biochemistry, University of Colorado at Boulder, Boulder, Colorado, 80309-0215, USA. michl@eefus.colorado.edu.|Institute of Organic Chemistry and Biochemistry, Academy of Sciences of the Czech Republic, Flemingovo nám. 2, 16610, Prague, Czech Republic. michl@eefus.colorado.edu.
Josef
J
Michl
UV/Vis spectroscopy; configuration interaction; density functional calculations; magnetic circular dichroism; oligosilanes