CALCULATION OF QUADRATIC HYPERPOLARIZABILITIES FOR ORGANIC PI-ELECTRON CHROMOPHORES - MOLECULAR-GEOMETRY SENSITIVITY OF 2ND-ORDER NONLINEAR OPTICAL-RESPONSE

This contribution explores the sensitivity of computed quadratic hyperpolarizabilities to the choice of chromophore molecular geometry. The nonlinear optical response of 25 organic pi-electron molecular chromophores is calculated for four different types of input geometries using the ZINDO-SOS formalism. The calculated nonlinear optical susceptibilities are found to be surprisingly sensitive to certain key alterations in molecular structure; this is understandable in terms of modifications in the conjugation strength through the pi-system. We also describe an efficient, a priori prescription for constructing chromophore input geometries that yield accurate quadratic hyperpolarizabilities within the ZINDO-SOS formalism. The first optical absorption maxima, the dipole moments, and the second-order nonlinear optical responses computed from these idealized geometries are essentially identical to those derived from MOPAC-optimized structures and correspond well with available experimental data.