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Electronic Transitions in Conformationally Controlled Tetrasilanes with a Wide Range of SiSiSiSi Dihedral Angles
Author(s) -
Tsuji Hayato,
Fogarty Heather A.,
Ehara Masahiro,
Fukuda Ryoichi,
Casher Deborah L.,
Tamao Kohei,
Nakatsuji Hiroshi,
Michl Josef
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201403495
Subject(s) - dihedral angle , range (aeronautics) , crystallography , materials science , physics , chemistry , quantum mechanics , composite material , hydrogen bond , molecule
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 ‐Si 4 Me 10 ( 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 .