二到七环多苯稠合物的三阶非线性光学效应的理论研究

Theoretical Studies of Third-order Nonlinear Optical Responses for Fused Benzenoid Polycyclic Hydrocarbons Having from Two to Seven Rings

利用含组态相互作用的INDO-SDCI和态求和(SOS)方法,计算了二到七环的稠合多苯化合物的三种不同物理过程的频率相关的三阶非线性光学系数.讨论了不同光物理过程的色散行为及π电子离域程度对非线性光学效应的影响,同时给出计算简并四波混合(DFWM)的非线性光学系数的具体表达式.计算结果表明,三阶非线性光学系数随着环沿一维方向扩展而急剧增加,π-π*电荷转移对多苯稠合物的三阶非线性极化率起主要贡献.

The frequency - dependent third - order nonlinear optical polarizabilities with different optical processes have been calculated for fused benzenoid polycyclic hydrocarbons having from two to seven rings, in terms of the INDO - SDCI quantum chemical method combining with the sum - over - states method. The calculated dispersions of the third - harmonic generation (THG), electric - field - induced second - harmonic generation (EFISHG) and degeneration four- wave mixing (DFWM) have been discussed, and influences of the pi - electron delocalizations upon the third - order NLO responses have been described for these hydrocarbons. Additionally, the explicit expression of the calculating DFWM polarizability has been presented in this work. It is found from the obtained results that the third - order NLO polarizability gets larger as the numbers of benzene rings increase in a linear arrangement, and pi - pi* electronic charge transfers make significant contributions to the third - order polarizability in these hydrocarbons.