Synthesis and (fluoro)solvatochromism of two 3-styryl-2-pyrazoline derivatives bearing benzoic acid moiety: A spectral, crystallographic and computational study

Abstract In this work we report the synthesis of two fluorescent 2-pyrazoline derivatives exhibiting remarkable (fluoro)solvatochromic behavior. The pyrazolines were synthesized in one step from the corresponding monocarbonyl curcuminoids and 4-hydrazinobenzoic acid in high yield and purity and were fully characterized by means of NMR and FT-IR spectroscopy and HRMS spectrometry. The structure of the novel derivative 2 was also characterized by means of X-ray crystallography. All compounds were studied computationally in the gas phase. Additionally, the effects of solvent polarity on the absorption and fluorescence spectra of these derivatives were investigated in a solvent group involving various neat molecular solvents exhibiting hydrogen bond donating (HBD), hydrogen bond accepting (HBA), and/or dipolar behavior. The solvent effects observed were quantified and rationalized by employing suitable multiparametric Linear Solvation Energy Relationships (LSERs) involving dipolarity, HBD-acidity and HBA-basicity terms. The contribution of each of these parameters provided insights on the predominant solute-solvent interactions occurring in solution. Importantly, some differences in the (fluoro)solvatochromic aptitude/behavior were revealed among the derivatives and they were rationalized, based on their structural diversity.