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)
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- 作者：Hiroshi Matsui ; Kotaro Fukuda ; Soichi Ito ; Takanori Nagami ; Masayoshi Nakano
- 刊名：Journal of Physical Chemistry A
- 出版年：2016
- 出版时间：February 18, 2016
- 年：2016
- 卷：120
- 期：6
- 页码：948-955
- 全文大小：458K
- ISSN：1520-5215
文摘
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.