Conformation and Solvent Dependence of the First Molecular Hyperpolarizability of Pyridinium- N -Phenoxide Betaine Dyes. Quantum Chemical Calculations

The static and frequency-dependent first hyperpolarizabilities (β) of Reichardt's betaine dye and two simplest pyridinium- N -phenoxide betaines were computed in the gas phase and in aqueous solution. The sum-over-state formalism was used to calculate individual components of the β-tensors. The solvent effect was included via the Langevin dipoles/Monte Carlo approach. The influence of the molecular geometry on the β values of the betaine dyes was investigated as well. The calculations demonstrate that the β values strongly depend on the interplanar angle between the pyridinium and the phenoxide ring. Moreover, we observed dramatically decreased values of β (for all investigated betaines) in aqueous solution as compared to the gas phase.