Measurements of the first hyperpolarizabilities of thiophene-based charge-transfer chromophores with hyper-Rayleigh scattering at 1064 and 1907 nm

Abstract

The first hyperpolarizability β is determined for 10 new thiophene-based charge-transfer (CT) chromophores using the hyper-Rayleigh scattering (HRS) technique at the wavelengths of 1064 and 1907 nm. Exceptionally high hyperpolarizabilities for several chromophores are obtained, exceeding 1700×10 −30 esu at the long wavelength of 1907 nm. The “intrinsic hyperpolarizability” β 0 is calculated using the Oudar–Chemla equation from the β values obtained at these two excitation wavelengths. For some chromophores β 0 calculated from 1064 nm HRS data differ from the 1907 nm results. Using the two-state model, we show that self-consistent intrinsic hyperpolarizability β 0 and CT transition frequency ω 0 can be obtained for data from these two-excitation wavelengths, provided that one does not identify ω 0 with the maximum of the linear absorption spectrum. The discrepancy is attributed to the effect of two-photon resonance associated with the 1064 nm radiation employed in the HRS experiment. We show that the β 0 discrepancy and difference in ω 0 can be removed if both damping (or dephasing) and vibrational detuning mechanism are incorporated in the two-state model. The structure–function relationship for the various chromophores investigated is also elucidated.