First-order hyperpolarizabilities of multipolar molecules: experimental and theoretical analysis

By Hyper-Rayleigh Light Scattering (HLS) experiments, we obtained the first-order hyperpolarizabilities (beta) for a series of 1D polyeno-dipolar and C 3h polyenoctupolar molecules. Theoretically, we applied the additive model to analyze (beta) for multipolar nonlinear optical (NLO) molecules. The hyperpolarizability is dissected into an additive term and an interaction term, and the equations for evaluating the additive (beta) A and interaction (beta) I terms were derived for multipolar molecules. The structure and substituent effects were analyzed for various planar C 3h and C 2v multipolar molecules, based on the calculation results of the (beta) ijk from a CNDO/S program. The relations of experimental (parallel)(beta) (parallel) with conjugation lengths were given, which agree well with out theoretical results.