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用密度泛函理论(DFT)和含时密度泛函理论(TD-DFT)对线型(N-杂环化)硅烷低聚体系与简单聚硅烷的电子结构和吸收光谱性质进行了比较研究。对各体系的基态分子结构在B3LYP/6-31G**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,应用含时密度泛函理论计算了电子吸收光谱的性质。计算结果显示,当主链硅原子被氮杂环环化后,由于空间位阻作用使相邻硅硅键明显伸长,使主链结构变得松散。但同时改善了分子主链的电子离域范围,增强了分子结构的可塑性。随着氮杂环数目的增加,低聚硅烷的电子吸收光谱发生明显的红移。氮杂环的引入对聚硅烷的最大吸收光谱带影响非常大。
The electronic structures and absorption spectra of linear (N-hetercyclic) silane oligomers and simple polysilanes were compared using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) The ground state molecular structure of each system was fully optimized at B3LYP / 6-31G ** level, and the charge distribution and frontier molecular orbital properties were discussed. Based on the stable configuration of ground state, the properties of electron absorption spectra were calculated by using time-dependent density functional theory. The calculated results show that when the main ring silicon atom is cyclized by the nitrogen heterocycle, the steric hindrance causes the adjacent silicon-silicon bonds to be obviously elongated, which makes the main chain structure loose. At the same time, however, the delocalization of the molecular backbone has been improved and the plasticity of the molecular structure has been enhanced. With the increase of the number of nitrogen heterocycles, the red shift of the electron absorption spectra of the oligomeric silane occurred. The introduction of nitrogen heterocycles has a great influence on the maximum absorption band of polysilane.