Computational Study on Second-Order Nonlinear Response of a Series of Two-Dimensional Carbazole-Cored Chromophores

The static second-order nonlinear optical (NLO) properties on a series of two-dimensional A−π−D−π−A carbazole-cored chromophores were investigated by density functional theory (DFT). The carbazole heterocycles can be viewed as auxiliary donors in these compounds. It is found that the first hyperpolarizabilities of these two-dimensional NLO molecules are sensitive to the changing of heterocycles on the donor. Moreover, the orientation of the thiophene ring in the chromophore significantly affects the second-order NLO properties. According to the time-dependent DFT calculations, the low transition energy and strong charge transfer are the key factors to determine the first hyperpolarizability, and an auxiliary donor provides an intrinsic enhancement of the NLO response in set III.