Calculation of quadratic hyperpolarizabilities for organic π electron chromophores: Molecular geometry sensitivity of second‐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 π‐electron molecular chromophores is calculated for four different types of input geometries using the ZINDO‐SOS formalism. The calculated nonlinear optical susceptibilites are found to be surprisingly sensitive to certain key alternations in molecular structure; this is understandable in terms of modifications in the conjugation strength through the π system. We also describe an efficient, a priori prescription for constructing chromophore input geometries that yield accurate quadratic hyper‐polarizabilities 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.