Design of novel σ *-π * conjugated polysilanes

Abstract

Electronic structures of two novel σ *-π * conjugated polysilanes, poly(1,1-silole) and poly(1,1-benzo[ c] silole), have been studied theoretically using the one-dimensional tight-binding self-consistent field-crystal orbital (SCF-CO) method at the modified neglect of diatomic overlap, Austin Model 1 (MNDO-AM1) level of approximation. It is found that the bandgaps corresponding to the σ-σ * transition of the polymers are smaller than that of the conventional polysilanes. The σ-σ * bandgaps of these two polymers are essentially determined by the lower-lying conduction band derived from the mixing of the delocalized σ *-band of the silicon skeleton and the localized π *-band of the side chains. Results suggest that the σ *-π * conjugation may be more effective for the reduction of the bandgap than the σ-π conjugation in a polysilane with aryl side chains.