Tailoring the first hyperpolarizability of acetamide-chalcone derivatives

We employed the femtosecond laser-induced Hyper-Rayleigh Scattering technique to measure the dispersion of the first-order molecular hyperpolarizability ( ) of five acetamide-chalcone derivatives containing different electron-donating groups. Our results show that strongly depends on the excitation wavelength, exhibiting an approximately sevenfold increase at 750 nm compared to the static value, . We demonstrated that this effect is the result of two-photon resonance enhancement. We also observed that the dispersion increases with the electron-donating strength of the substituents, reflecting the intensification of intramolecular charge transfer (ICT) along the π-conjugated system. Both and the two-photon absorption (2PA) 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 ( n LM) to fit the experimental dispersion and compared it with the well-known Sum-Over-States model for 2PA. 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 in acetamide-chalcone derivatives, combining appropriate molecular functionalization with the selection of the excitation spectral region. • Hyper Rayleight scattering spectra of a class of organic materials • Tunable femtosecond laser-induced Hyper-Rayleigh Scattering technique • The Hyper-Rayleigh Scattering increases systematically with the electron-donating strength of the substituent groups • Hyper-Rayleigh Scattering increases by a resonant enhancement effect due to a two-photon absorption