Enhancement of non-resonant non-linear refractive index with reduction of absorption in push–pull molecules by reduction of their donor group strength

Abstract

We show that reducing the strength of the amine donor group in push-pull molecules increases their non-resonant non-linear refractive index in the infrared although the blue-shift of their visible absorption peak, associated with the donor strength reduction, can decrease their linear and non-linear absorption at the excitation wavelength. This effect is explained phenomenologically using a two-level model, and we present experimental results in good agreement with semi-empirical calculations.