title: Open-Shell Singlet Nature and σ-/π-Conjugation Effects on the Third-Order Nonlinear Optical Properties of Si Chains: Polysilane and Poly(disilene-1,2-diyl).
abstract: We theoretically investigate the open-shell singlet nature and σ-/π-conjugation effects on the longitudinal second hyperpolarizabilities (γ) of one-dimensional chains involving silicon-silicon bonds, that is, polysilane and poly(disilene-1,2-diyl), by comparison with their carbon analogues, polyethylene and polyacetylene, respectively. It is found that poly(disilene-1,2-diyl) has less bond length alternation than polyacetylene and that σ-conjugation of polysilane is less effective on the enhancement of γ than π-conjugation of polyacetylene, whereas π-conjugation of poly(disilene-1,2-diyl) indicates a more than 20 times greater enhancement of the γ than that of polyacetylene, which is known to be a typical nonlinear optical molecule with large γ, for one-dimensional chains involving 3-5 double bonds. Further theoretical analyses of poly(disilene-1,2-diyl) reveal the σ- and π-electrons contribute negatively and positively to the γ, respectively. The latter contribution is significantly larger than the former and thus causes the remarkable enhancement of γ amplitudes due to the emerging open-shell singlet nature in the long π-conjugation length.
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Matsui
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Kotaro
authors.initials: K
authors.lastname: Fukuda
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Soichi
authors.initials: S
authors.lastname: Ito
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Nagami
authors.affiliation: Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University , Toyonaka, Osaka 560-8531, Japan.
authors.forename: Masayoshi
authors.initials: M
authors.lastname: Nakano