Dispersion of the first molecular hyperpolarizability of charge-transfer chromophores studied by hyper-Rayleigh scattering

Stimulated Raman scattering from pressurized CH₄ gas confined in a Raman shifter is employed to obtain an excitation wavelength at 1543 nm for the hyper-Rayleigh scattering (HRS) experiment. The first molecular hyperpolarizabilities (β) of a series of thiophene-based organic chromophores are determined using this excitation wavelength to help shed light on their frequency dependence. By combining the HRS results at 1543 nm with those using the 1907 and 1064 nm excitation previously obtained, we arrive at an unambiguous result about the intrinsic hyperpolarizability calculated from the β values at these two wavelengths. The results are interpreted using an extended two-state model previously put forth by our laboratory. The extended model that includes the vibration and damping in the hyperpolarizability expression is intended for interpreting HRS data obtained using excitation wavelength in the resonance regime. © 2001 Elsevier Science B.V.