中文摘要：

采用密度泛函理论（DFT）B3LYP／6-31G＊优化一系列以芳环为桥联基团，1，3-二硫杂环戊二烯为供电子基团，丙二氰为吸电子基团的D-π-A型分子的几何结构，在此基础上对分子的极化率和第一超极化率进行计算．结果分析表明，桥联苯环数的增加，供电子基团（OCHs）的引入及共轭桥的增长对分子的几何构型影响很小，但能使分子的二阶非线性光学（NLO）系数增加，且分子的最大吸收波长发生红移．甲氧基的引入或共轭桥的增长，分子的前线分子轨道能级差减小，TD—DFT计算表明分子深层占有轨道与空轨道之间的电子跃迂对二阶NLO效应也有较明显贡献．

英文摘要：

Density functional theory （DFT） B3LYP/6-31G＊ has been carried out to optimize a series of D-π-A molecules, in which the aromatic ring acts as the bridging group, the 1,3-dithiol cyclopenta diene acts as the electron-donor group, and the propanedinitrile acts as the electron-accepter group. On the basis of the geometry optimization, the molecular polarizability and first hyperpolarizability have been calculated. The results show, the increase of the number of the bridge biphenyl ring, intro- duction of the electron-donor group （-OCH3） and the elongation of the conjugated bridge have a little influence on the geometry structures, but result in the enhancement of second-order nonlinear optical （NLO） coefficients and the red-shift of the maximum absorption wavelength. Introducing substituent group --OCH3 or increasing conjugated bridge is helpful to decrease the energy difference of the fron- tier molecular orbital. The TDDFT calculations show that the deep electron transition between the occupied and unoccupied orbitals obviously contributes to the molecular second-order NLO responses.