Investigation on the Second-Order Nonlinear Optical Responses in the Keto−Enol Equilibrium of Anil Derivatives

This paper addresses the linear and second-order nonlinear optical properties of two anil derivatives and in particular their variations upon switching between the enol-imine and keto-amine forms. Quantum chemical evaluations of the first hyperpolarizabilities, accounting for both solvent and electron correlation effects, are compared with hyper-Rayleigh scattering and electric field-induced second harmonic generation measurements. For both compounds, the E/K first hyperpolarizability ratios are larger than 2, demonstrating that the enol forms present the largest responses but also that the switching is associated with a substantial β contrast.