This paper addresses the linear and second-order nonlinear optical properties of two anil derivatives and inparticular their variations upon switching between the enol-imine and keto-amine forms. Quantum chemicalevaluations of the first hyperpolarizabilities, accounting for both solvent and electron correlation effects, arecompared 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 enolforms present the largest responses but also that the switching is associated with a substantial
contrast.