Confirming the relationship between first hyperpolarizability and the bond length alternation coordinate for merocyanine dyes.

We investigated the first electronic hyperpolarizability of a typical merocyanine dye in several solvents in a wide range of dielectric constants. The equilibrium geometry of the molecule was obtained in each solvent by employing an optimization technique allied to atomistic simulations. The results confirm, for the first time with a realistic model of the molecular environment, the relationship between the first electronic hyperpolarizability (β) and the bond length alternation (BLA) coordinate, with a maximum value of β for intermediate positive BLA and a vanishing β when the BLA goes to zero.