Hyper-Rayleigh scattering of azulenic donor–acceptor molecules at 1064 and 1907 nm

Abstract

Hyper-Rayleigh scattering (HRS) has been carried out for new azulenic donor–acceptor chromophores using near-infrared laser excitation at wavelengths of 1064 and 1907 nm. Hyperpolarizabilities obtained with the 1064 nm incident excitation are large compared with those obtained using the 1907 nm excitation, due to the effects of two-photon resonance enhancements in the former case. The HRS experiment using the 1907 nm excitation, while challenging to carry it out, gives the hyperpolarizability value closer to the intrinsic molecular hyperpolarizability. The popular two-level model that is used to predict the first hyperpolarizability of donor–acceptor charge transfer chromophores is employed to compare the measurements made on the same chromophores with 1064 and 1907 nm excitations. The model is found not to be able to correlate the results obtained at the two wavelengths. The first hyperpolarizability data obtained by using the 1907 nm excitation are consistent with electric field induced second harmonic generation data obtained by using the same wavelength.