Geometrical effect on the nonlinear optical properties of model rigid-rod polymers. Ab initio time-dependent coupled Hartree-Fock studies

The linear and nonlinear optical (NLO) properties of the cis and trans isomers of diphenylbenzobisoxazole (PBO) and diphenylbenzobisthiazole (PBT) have been calculated by ab initio time-dependent coupled perturbed Hartree-Fock method using a split-valence basis set. The second-order NLO susceptibilities of the trans isomers are calculated to be larger by a factor of 1.5 or more compared to the cis isomers over a wide range of optical frequency. Between the two homologues (PBO and PBT), the linear and the NLO susceptibilities of the thiazole systems are calculated to be slightly higher than the oxazole systems.