Electronic structures of linear polysilane radical anions for ground and low-lying excited states: a theoretical study

MM2-molecular dynamics and semi-empirical PM3-MO calculations were performed on linear polysilane oligomer radical anions. The electronic structures for the ground and low-lying excited states have been determined by means of the semi-empirical PM3-CI method. The permethyloligosilane radical anion [Sin(Me)2n+2]− (n=6–20) was chosen as a model compound of the polysilane radical anion. The molecular dynamics calculation and the geometry optimization suggested that the regular all-trans chain was most stable for the polysilane radical anions. In all cases, an unpaired electron is occupied in an in-plane π*(Si–Si) orbital and widely delocalized along the main Si–Si chain. The first excitation energy is gradually red-shifted as a function of number of chain Si atoms and the oscillator strength is increased. The band structure for polysilane radical anions is discussed on the basis of theoretical results.