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 \npolyenes containing 3-8 π-bonds are studied using the semiempirical AMl parametrization \nand finite-field (hyper)polarizability computations as a function molecular polarization and \nresulting changes in bond-length alternation. Plots of α, β, and γ versus bond length \nalternation had similar shapes (although different magnitudes) for each chain length. The \nchanges in α, β, and γ with molecular length were fit to exponential functions (N^m) for various \nbond-length alternations. These values varied over a significant range depending upon the \nvalue of bond-length alternation chosen.