Theoretical investigation on the polarizability and second hyperpolarizability of polysilole

The polarizability and second hyperpolarizability of polysilole chains containing 2-9 silole units have been calculated ab initio. The MP2/6-31G∗ longitudinal polarizability per silole unit converges towards 324 au, which is at least of semi-quantitative accuracy because basis set and electron correlation effects compensate each other. On the other hand, the second hyperpolarizability per silole unit does not show any sign of leveling off, demonstrating substantial electron delocalization effects associated with a small bond length alternation. These second hyperpolarizabilities are amongst the largest values reported so far, though they remain a factor of 2-3 smaller than in polybutatriene.

Small bond length alternation along the conjugated backbone confers on polysilole chains substantial second hyperpolarizability per unit cell.