THE INFLUENCE OF CONFORMATION ON THE ELECTRONIC-PROPERTIES OF POLYSILANES

Valence effective Hamiltonian (VEH) nonempirical calculations are performed on the electronic structure of unsubstituted polysilane. The band structure of all-trans polysilane is analyzed in detail and the effects of changes of the backbone conformation on the electronic and optical properties are studied for regular 7/3, 3/1, and 4/1 helical chains. The VEH results predict a decrease of the band gap of approximately 0.6 eV in going from a 7/3 helix to an all-trans conformation. This result supports the conformational description currently used to explain the thermochromism and piezochromism observed for symmetrically substituted polysilanes.