Remarkable solvent effects on first hyperpolarizabilities of zwitterionic merocyanine dyes: ab initio TD-DFT/PCM approach

We present a quantum–chemical analysis of the solvent effect on molecular structure and first hyperpolarizabilities of a series of zwitterionic molecules. The molecular geometries are obtained via B3LYP/6-31G** optimization including self-consistent reaction field/polarizable continuum model approach, while the dynamics non-linear optical (NLO) properties are calculated with the time-dependent density functional theory/sum-over-state method including solvent effects. It was found that solvents play a remarkable role on the structure and first hyperpolarizabilities of zwitterionic dyes. Changing the solvent from low to high dielectric causes not only an increase in magnitude of β but also a change in sign, therefore passing through zero at intermediate dielectric. There are clearly important consequences from this, in choice of solvent and molecular environment when evaluating NLO molecules.