Solvent Effects in Molecular Hyperpolarizability Calculations

Molecular geometries, dipole moments, polarizabilities and first-order hyperpolarizabilities for five classic donor−aromatic π system−acceptor NLO chromophores were calculated, using semiempirical methods (PM3), in both vacuum and solvent environments. Solvent effects on the computed molecular geometries were found to be minimal. Dipole moments calculated for the molecules in vacuo showed good agreement with experimental data obtained in nonpolar solvents, but a substantial solvent dependence was observed for molecules modeled in a polar solvent. This dependence was very pronounced in the calculated first-order hyperpolarizabilities, β, where an increase of a factor as great as 6 was observed upon changing from a vacuum to solvent environment. Hyperpolarizabilities calculated for molecules in solvent were found to be in better agreement with experimental EFISH data than those calculated for molecules in vacuo.