ABINITIO TIME-DEPENDENT COUPLED PERTURBED HARTREE-FOCK STUDIES OF OPTICAL NONLINEARITIES OF ORGANIC-MOLECULES - ALKYL DERIVATIVES OF 4-AMINO-BETA-NITROSTYRENE

The dipole moment, mu, linear polarizability, alpha, first hyperpolarizability, beta, and second hyperpolarizability, gamma, of intramolecular charge transfer (ICT) molecules derived from the alkyl substitution of 4-amino-beta-nitrostyrene (ANST) have been calculated by ab initio self-consistent-field method using a double-zeta valence Gaussian basis set. The calculated results for alpha, beta, and gamma show strong dependence on mu and the energy difference DELTAepsilon between the lowest unoccupied and highest occupied molecular orbitals. For the (dimethylamino)-beta-nitrostyrene and (diethylamino)-beta-nitrostyrene, the calculated results for beta(-2omega;omega,omega) are in qualitative agreement with the experimental values. The changes in the values of gamma for various third-order effects among the various alkyl-substituted ANST are parallel to the corresponding changes in the values of beta. The results indicate that the mechanism which leads to the enhancement of beta is also responsible for the enhancement of gamma values of ICT molecules and that these molecules may provide an alternative to conjugated polymers as a third-order nonlinear optical material.