采用密度泛函理论(DFT)UB3LYP/6-31G(d,p)方法对不同共轭桥的氮氧双自由基分子4个体系的非线性光学(NLO)系数进行了计算.结果表明:所有体系单重态为稳定的基态,与自旋极化规则一致;4个体系的极化率在单重态时较大,三重态时较小;体系a,b和c在单重态与三重态的二阶超极化率与极化率规律相同,而具有垂直稳定构型的体系d,由于强的反铁磁性耦合体现出三重态时具有较大的二阶超极化率.
Nonlinear optical properties of nitroxide diradicals with different conjugated bridge were investigated by using the DFT UB3LYP/6-31g(d,p) method.The results show that these singlet-state diradicals are stable ground state,according with spin coupling rules.The polar of all diradicals decrease with increasing spin multiplicity.The second hyperpolarizability of system a,b and c decrease with an increase of their spin multiplicity.Stable structure of system d is vertical and its second hyperpolarizability is the biggest in triplet state due to strong anti-ferromagnetic coupling.