EFFECT OF MOLECULAR-POLARIZATION ON BOND-LENGTH ALTERNATION, LINEAR POLARIZABILITY, FIRST AND SECOND HYPERPOLARIZABILITY IN DONOR-ACCEPTOR POLYENES AS A FUNCTION OF CHAIN-LENGTH

The linear (alpha) and nonlinear (beta, gamma) molecular polarizabilities of a series of donor-acceptor polyenes containing 3-8 pi-bonds are studied using the semiempirical AM1 parametrization and finite-field (hyper)polarizability computations as a function molecular polarization and resulting changes in bond-length alternation. Plots of alpha, beta, and gamma versus bond length alternation had similar shapes (although different magnitudes) for each chain length. The changes in alpha, beta, and gamma with molecular length were fit to exponential functions (N-m) for various bond-length alternations. These values varied over a significant range depending upon the value of bond-length alternation chosen.