Linear and Nonlinear Polarizabilities of Fragmental Molecules for the Phenylacetylene Dendrimers

Abstract

Abstract Linear and nonlinear polarizabilities of small fragmental molecules for the phenylacetylene dendrimers have been calculated with the frequency-dependent moment schemes based on the sum-over-states expressions of the polarizabilities, including all of the singly-excited configurations in the semiempirical CNDO/S approximation. The smallest system, consisting of two benzene rings connected by an acetylene chain, corresponds to a molecular unit that is usually adopted in the exciton model for a theoretical analysis of the phenylacetylene dendrimers. The dependences of the polarizabilities upon the molecular size were examined. It has been shown that the linear polarizability in the static-field condition increases linearly with the number of acetylene chains (N). MO calculations of the nonlinear polarizabilities of these molecules have been carried out for the first time. The third-order polarizability in the static-field condition is shown to depend quadratically upon N, which suggests that two chromophores at a time participate in the optical process of the third-order polarization.