两端具有推拉电子基团的偶氮化合物中的N=N双键提供了优异的电子通道,有利于产生非线性光学效应,并且推拉电子基团对偶氮化合物的非线性光学特性有较大的影响。采用紫外可见吸收和二次谐波产生(SHG)技术研究了两种“推-拉”型偶氮苯分子Langmuir-Blodgett(LB)膜的光谱和二阶非线性光学特性。4-硝基-4′-氨基偶氮苯(NAA)和4-羧基-4′-氨基偶氮苯(CAA)分子在亚相表面可以形成稳定的单分子膜,并且能较好地转移到固体基板上形成LB多层膜;由于－NO2比－COOH具有更强的吸电子能力,电子在NAA分子内更容易转移,并形成较大分子偶极矩,分子具有更大的一阶超极化率。实验测得NAA和CAA的二阶非线性系数d33分别为40.8 pm/V和24.2 pm/V,一阶超极化率β分别为1.97×10-29 esu和1.17×10-29 esu,NAA分子的一阶超极化率约为CAA的1.7倍,实验与理论计算结果符合较好。

The N=N bridge in azobenzenes molecules with push-pull structures at the two ends provides excellent channels for electrons. This is an advantage for generation of nonlinear optics effect. And the nonlinear optical properties of the azobenzene compounds are greatly affected by the push-pull electronic groups. The spectra and nonlinear optical properties of Langmuir-Blodgett (LB) films of two kinds of push-pull azobenzene compounds were investigated by using ultraviolet (UV)-visible absorption spectra and second harmonic generation (SHG) technique. The steady mono-molecular film could be formed at the interface of air/water and transferred well onto solid substrates, forming high-quality LB multilayer films for the 4-(nitro)-4′-(amido)-azobenzene (NAA) and 4-(carboxylic)-4′-(amidogen)-azobenzene(CAA) molecules. Because the －NO2 has a stronger ability on pulling electron than －COOH, the transfer of the intra-molecular electron is easier and could form bigger molecular dipole for NAA than that for CAA. So it could have a more significant second-order nonlinear hyperpolarizability. The second-order nonlinear optical coefficient d33 of experimental measurement for NAA and CAA in LB films were 40.8 pm/V and 24.2 pm/V, and the hyperpolarizabilities β were 1.97×10-29 esu and 1.17×10-29 esu respectively. The hyperpolarizabilities β of NAA molecule was about 1.7 times bigger than CAA molecule′s. The experimental results agreed well with the theoretical calculation.