SECOND-ORDER HYPERPOLARIZABILITIES OF STILBAZOLIUM CATIONS STUDIED BY SEMIEMPIRICAL CALCULATION

Second-order hyperpolarizabilities (β), electron distribution, dipole moment, and excitation energy together with oscillator strength of stilbazolium cations have been investigated by a semiempirical calculation with PM3 parametrization of the MNDO Hamiltonian. Since stilbazoliums were found to generally have several times larger β value than nitrostilbene derivatives with similar experimental absorption maximum wavelength, such ionic species are concluded to be advantageous to create new second-order nonlinear optical materials having large β and short cutoff. Among the stilbazolium derivatives investigated, the β values increase with increasing electron-donating ability of the substituent at the para position of benzene ring, and exceptionally chlorinated one was found to have comparatively large β value withstanding its short absorption maximum wavelength. The main reason for the large β values of stilbazolium cations is the strong acceptor property of the pyridinium ring resulting in large difference ...