中文摘要：

采用密度泛函理论（DFT）的UB3LYP（B3LYP）/6-31＋G＊＊方法对双咪唑苯和双三咪唑苯双自由基及其衍生物几何结构进行优化,并结合有限场（FF）方法计算这些体系的非线性光学（NLO）系数.结果表明,引入给、受体取代基都能使体系的极化率α和二阶超极化率γ增大.在双自由基体系中,引入给体NH2的α和γ值大于引入受体NO2的值,与闭壳层体系中结果相反.分析自由基成分和电荷对体系的二阶超极化率γ影响的结果表明,处于中间双自由基成分的分子比相似共轭性的闭壳层分子有更大的二阶超极化率γ; 带电荷的双自由基体系引入给、受体之后,与中性自由基体系相比具有更大的二阶超极化率γ.

英文摘要：

The UB3LYP（B3LYP）/6-31＋G＊＊ method of density functional theory（DFT） was employed to optimize the geometrical structures of bisimidazole and bistriazole benzenes and their derivatives.In addition,the nonlinear optical（NLO） coefficients of these systems were calculated with a finite field（FF） approach.Results show that the polarizability α and second hyperpolarizability γ values of all systems increase by introducing a donor NH2 or an acceptor NO2.For the diradical systems,the α and γ values of these systems with a donor are larger than those with an acceptor,which is opposite to the behavior of closed shell systems.By analyzing the effect of the diradical character and charge on the second hyperpolarizability,we demonstrate that the neutral molecule with intermediate diradical character exhibits a much larger γ value than the neutral closed shell molecule with a similar π conjugation property.The charged diradical systems with a donor and an acceptor exhibited larger γ values compared to the neutral diradical systems.