饱和、不饱和(N-杂环化)低聚硅烷的结构和光谱性质

Structures and spectrum properties of saturated and unsaturated(N-heterocyclic)oligosilanes

用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对线型(饱和N-杂环化)和(苯并N-杂环化)低聚硅烷的电子结构和吸收光谱性质以及溶剂效应进行了比较研究.对各体系的基态电子结构在B3LYP/6-31G(d,p)水平上进行了全优化,讨论了电荷分布和前线分子轨道性质.在获得基态稳定构型的基础上,用B3LYP/6-311+G(d)方法计算了电子吸收光谱的性质,探讨了主链的线型增长和溶剂对电子吸收光谱的影响.结果表明,随着主链的增长,低聚硅烷的电子结构发生明显扭曲,在(苯并N-杂环化)聚硅烷中形成了邻近苯并N-杂环之间π-π堆积作用,有利于结构的稳定.两类低聚硅烷的吸收光谱都随着主链的增长而发生明显的红移,(苯并N-杂环化)聚硅烷最大吸收光谱红移幅度要比(饱和N-杂环化)聚硅烷大得多.溶剂效应使得光谱略向短波长移动,溶剂的极性改变对吸收波长的影响不明显.

The electronic structures and absorption spectral properties of the linear （saturated N-heter- ocyclic） and （benzo-N-Heterocyclic） oligosilanes were studied using density functional theory （DFT） and time-dependent density functional theory （TD-DFT）. The geometrical structures of eight oligosi- lanes were obtained at the B3LYP/6-31G（d,p） level. The charge distribution and the frontier molecu- lar orbitals were also analyzed. Based on the optimized structures, the electronic absorption spectra have been investigated at the B3LYP/6-311 ＋ G（d） level, and the effects of the number of N-heterocy- cle and the solvent on the electronic spectra have been discussed. The results show that the molecular framework of oligosilanes twisted with the elongation of the molecular chain, and the π-π overlap in- teraction existed between adjacent benzo-N-heterocycles which leading to stable structures. The ab- sorption bands of （saturated N-heterocyclic） oligosilanes and （benzo-N-heterocyclic） oligosilanes suf- fered an evidently bathochromic shift with increasing number of N-heterocycle and benzoN-heteroey- cle. The maximum absorption peak of （benzo-N-heterocyclic） oligosilanes had much more bathochro- mic shift than （saturated N-heterocyclic） ones. The absorption bands of oligosilanes suffer slightly hypsochromic shift in solvent relative to those in the gas phase, but the influence of solvent polarity is very little.