Tailoring the first hyperpolarizability of acetamide-chalcone derivatives

Abstract

We employed the femtosecond laser-induced Hyper-Rayleigh Scattering technique to measure the dispersion of the first-order molecular hyperpolarizability (β) of five acetamide-chalcone derivatives containing different electron-donating groups. Our results show that β strongly depends on the excitation wavelength, exhibiting an approximately sevenfold increase at 750 nm compared to the static value, β∘. We demonstrated that this effect is the result of two-photon resonance enhancement. We also observed that the β dispersion increases with the electron-donating strength of the substituents, reflecting the intensification of intramolecular charge transfer (ICT) along the π-conjugated system. Both β and the two-photon absorption (2 PA) cross-section show a linear increase with the Hammett constant, reinforcing the central role of ICT in the nonlinear optical response. Furthermore, we employed a phenomenological n-level model (nLM) to fit the experimental β dispersion and compared it with the well-known Sum-Over-States model for 2 PA. Both models showed good agreement, resulting in similar photophysical parameters, demonstrating the consistency of the adopted treatment. Thus, this work elucidates an efficient mechanism for optimizing β in acetamide-chalcone derivatives, combining appropriate molecular functionalization with the selection of the excitation spectral region.