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 (α) and nonlinear (β, γ) molecular polarizabilities of a series of donor-acceptor polyenes containing 3-8 π-bonds are studied using the semiempirical AMl parametrization and finite-field (hyper)polarizability computations as a function molecular polarization and resulting changes in bond-length alternation. Plots of α, β, and γ versus bond length alternation had similar shapes (although different magnitudes) for each chain length. The changes in α, β, and γ 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.