Solvent-dependent photophysics of a hydroxychalcone: UV–Vis/fluorescence solvatochromism, hydrogen bonding, and computed hyper-Rayleigh first hyperpolarizability

Abstract

The present work investigates the solvent-dependent optical response of the previously reported hydroxychalcone (2E)-3-(4-hydroxyphenyl)-1-(4-methylphenyl)prop-2-en-1-one (HXC). UV–Vis absorption and fluorescence spectra were recorded in five solvents of different polarity and hydrogen-bonding ability, and the solvent effects were analyzed using the Kamlet–Taft multiparameter approach. HXC shows a bathochromic shift of the main absorption band with increasing solvent polarity, while the fluorescence data reveal a reproducible broad long-wavelength emissive component in MeOH. Global deconvolution and slit-width comparison indicate that this red-shifted feature is a reproducible spectral contribution rather than a trivial instrumental artifact. Excited-state calculations further show substantial relaxation of the low-lying excited state in methanol, although the optimized S1 geometry does not support a fully developed classical TICT structure. The results therefore support the interpretation of a more strongly relaxed charge-transfer-like, TICT-like emissive state in protic methanol, while the overall solvent dependence of HXC is dominated by polarity/polarizability effects with secondary hydrogen-bonding contributions. The frequency-dependent Hyper-Rayleigh first hyperpolarizability was also computed, predicting βHRS(−2ω;ω,ω) =33.7 ×10−30⁢𝑒𝑠𝑢 at 1064 nm and a pronounced resonance enhancement around 638 nm. These results show that HXC behaves as a stable donor–π–acceptor chromophore with a significant second-order NLO response, especially in the near-IR.