中文摘要：

采用密度泛函理论（DFT）UB3LYP方法,在6-31g（d）水平上对2,2＇-（1,2-乙炔基-4,1-亚苯基）双[4,4＇,5,5＇-四氢]咪唑氧自由基分子及其异构体的自旋耦合性质进行分析,并结合有限场（FF）方法计算它们的非线性光学（NLO）系数,以探讨咪唑氧环在共轭链不同位置时体系的自旋耦合规律和NLO系数.结果表明,所有体系基态自旋符合自旋极化规则,它们的极化率随自旋多重度的增加而减小;一阶超极化率因受分子对称性影响,对称性不同其一阶超极化率的变化也不同;二阶超极化率呈现随着自旋多重度的增加而增加的趋势.从理论上探讨这些自由基分子自旋耦合规律与NLO活性的关系,为有机自由基NLO材料的分子设计与实验研究提供一定的理论依据。

英文摘要：

Spin-coupling properties of 2,2＇-（1,2-acetylene-4,1-phenyl）bis[4,4＇,5,5＇-tetrahydro]imidazole- oxide radical and their isomers were investigated by using the DFT UB3LYP method at the level of 6-31G（d）. Nonlinear optical （NLO） coefficients were studied at the same level combined with finite field approach. We discussed the relationship bewteen spin-coupling and nonlinear optical properties of imidazole-oxide radicals. The calculated results show that ground state spin accords with spin coupling rules. The polarizability decreased with increasing spin multiplicity. Due to molecular symmetry effects, the first hyperpolarizability changed when molecular symmetry changed. The second hyperpolarizability increased with increasing spin multiplicity. We probe into relationship between spin coupling rules and NLO activity, which provides theoretical guide for molecular design and experimental synthesis of organic radical NLO materials.