THEORETICAL STUDY OF MACROSCOPIC OPTICAL NONLINEARITIES OF "PARALLEL CONNECTION" CHROMOPHORES CONTAINING PNA UNITS

The semi-empirical method ZINDO was employed to study relationship between macroscopic optical nonlinear parameter μβ/MW (where μ is the dipole moment, β is the first hyperpolarizability, and MW is molecular weight) and the number of parallel non-conjugated D-π-A units in a chromophore. The computational results show that macroscopic optical nonlinear parameter μβ/MW value increases remarkably from 1.64 to 2.53 with increasing the number of parallel and non-conjugated p-Nitroaniline (PNA) units in a chromophore from 1 to 3. Then the μβ/MW value decreases rapidly from 2.53 to 0.43 with increasing the number of PNA units in a chromophore from 3 to 5. It suggests that design of chromophores containing two or three parallel non-conjugated D-π-A units would be an effective strategy for increasing the first hyperpolarizability and macroscopic optical nonlinearity of designed NLO materials.