中文摘要：

运用密度泛函理论（DFT）UB3LYP和有限场（FF）方法,探讨了6,6＇-二氧-3,3＇-二四联氮自由基及其衍生物构象变化对非线性光学性质的影响,分析了自由基分子极化率、二阶超极化率对构象、自旋多重度的依赖关系.结果表明,不同构象下各体系有效交换积分值都小于零,自由基间表现为反铁磁性耦合.各体系单三态不同构象时极化率α值的变化很小,且不同构象时单重态的α值都大于三重态.在构象变化过程中,体系（a）和（b）单重态的二阶超极化率均为负值（体系（a）的45°和135°除外）,且绝对值都小于三重态的二阶超极化率值,体系（c）的单三重态二阶超极化率值均为正值,且在分子接近平面构型时,三重态的γ值大于单重态.不同的取代基R,对体系的构型、极化率和二阶超极化率的影响也不同.

英文摘要：

The effects of conformation change on the nonlinear optical properties of 6,6＇-dioxo-3,Y-biver- dazyl radical and its derivatives were investigated by using density functional theory （DFT） UB3LYP. In addition, the dependent relationships of the radical polarizability and the second hyperpolarizability with conformation, spin multiplicity were studied at the same level combined with the finite field （FF） approach. The results show that the effective exchange integral values are less than zero under different conformations, so the radicals display the anti-ferromagnetic coupling. No matter whether it is singlet or triplet, polarizabil- ity change is very small and the value of the singlet is greater than that of the triplet under different conformations. In the conformation change process, the second hyperpolarizability values of system （a） and （b） for singlet are negative （system （a） of 45° and 135° with the exception）, and less than the absolute value of all triplets. The second hyperpolarizability values of system （c） for singlet and triplet states are positive and in molecular close plane configuration time, the value of triplet is greater than that of the singlet. The effects of the different substituent groups R on the system conformation, polarizability and the second hyperpolariza- bility are also different.