Resonant and nonresonant hyper–Rayleigh scattering of charge-transfer chromophores

Abstract

The first molecular hyperpolarizabilities (β) of a series of charge-transfer nonlinear optical (NLO) chromophores are measured with the hyper-Rayleigh scattering (HRS) technique using two excitation wavelengths at 1064 and 1907 nm. The 1907 nm wavelength is the longest excitation wavelength used for the HRS experiment. For some of these chromophores, β values in excess of 1000×10−30 esu at 1907 nm are obtained, and due to two-photon enhancement, even greater β values are found with the 1064 nm excitation. Chromophores with such large hyperpolarizability are expected to have potential applications in practical electro-optical devices. The dispersion of β is analyzed using a two-vibronic-state model developed previously in our laboratory. The study shows that it is necessary to consider the vibronic structure of the chromophore in the excited state in order to account for the behavior of the first molecular hyperpolarizability of the charge-transfer NLO chromophores.