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 alpha 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. (C) 2004 Elsevier B.V. All rights reserved.