Ab initio MO studies on polysilane oligomer radical anions as model molecules of polysilane radical anions

Polysilane oligomer radical anions with up to six Si atoms have been theoretically investigated as model molecules of high polymer polysilane radical anions by ab initio MO, theory. According to the calculated results, the polysilane oligomer radical anions can exist as bound anions having a sigma-type ground state with an impaired electron occupying a Si-Si antibonding sigma* orbital. They are stabilized with an increase in the Si-Si main chain length both in terms of the boundness of an unpaired electron and bonding strength. The pi-type states, on the other hand, exist as excited states for these oligomer radical anions. The calculated results strongly suggest that polysilane radical anions with pi-type ground state are hardly generated regardless of their molecular size and geometry. The Si 3d orbital contributions in the ground and excited states of the polysilane radical anions, such as dpi-dpi conjugations, have also been investigated.