Theoretical insight into the substituent effects on linear and nonlinear optical properties of azobenzene-based chromophores

The linear and nonlinear optical properties of 4 kinds of experimental synthesized azobenzene-based chromophores were investigated by different density functional theories (DFTs) upon the electronic structures. The structure-property relationship was studied on each single molecule either in the gas phase or in diethylether and tetrahydrofuran (THF) solutions. The substituent effect on optical properties was revealed by checking the positions of substituent groups, and the influence of dynamic perturbation to the optical nonlinearity was investigated by simulating the experimental excitation. The results revealed that the substituent in the metaposition of the azobenzene group affects the optical properties more significantly than that in the ortho-position, which is in agreement with the experimental finding. The modulation of molecular hyperpolarizability of bridge-substituted azobenzene derived by dynamic perturbation is not recommended because of the reduced dynamic hyperpolarizability relative to the static one. The different functions of the DFT method hardly affect the calculated results, while solvent effects of diethylether and THF solutions are significant on the optical properties, especially for optical nonlinearity. The information derived from the single chromophore may be helpful in the design and preparation of high-performance nonlinear optical materials in further.