Proceedings PaperAb initio molecular design of third-order nonlinear optical susceptibilities of polysilanes
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Third-order nonlinear optical susceptibilities (chi) (3) of polysilanes were estimated both at molecular and crystalline levels, in order to establish a molecular design strategy of (chi) (3) of polysilanes, by using an ab initio coupled perturbed Hartree-Fock (CPHF) method and the oriented-gas approximation. Molecular calculation results showed the main chain conformation of polysilanes directly affects second hyperpolarizabilities (gamma) of polysilane oligomers, and the trans planar oligomers have larger (gamma) than the 7/3 helical or alternating trans gauche (TGTG') oligomers, due to a stronger (sigma) -electron delocalization in their trans planar main chain. On the other hand, it was found that crystalline (chi) (3) of polysilanes are influenced not only by the main chain confirmation, but also by the molecular weight of polysilane repeating unit MSi. Based on those molecular and crystalline results, a strategy of molecular design of polysilane (chi) (3) was proposed which predicts trans planar poly[dimetylsilane] may have the largest (chi) (3) among polysilanes investigated so far, owing to its trans planar main chain and smallest MSi.