Theoretical studies on anisotropy of the first hyperpolarizabilities in one- and two-dimensional charge transfer molecules: Role of frequency dispersion

We calculate the frequency-dependent first hyperpolarizabilities and their anisotropy properties of one- and two-dimensional charge transfer (CT) molecules on examples of para-nitroaniline (pNA) and 1,3-diamino-4,6-dinitrobenzene (DADB) using semi-empirical and ab initio methods, respectively. The results show that not only the first hyperpolarizability but also its anisotropy can be significantly influenced by the frequency of incident light. The contribution of off-diagonal terms to the first hyperpolarizability can be enhanced by dispersion effect for two-dimensional CT molecules whereas decreased for one-dimensional CT dipolar systems, comparing to the contribution of diagonal term.