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

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 2was also characterized by means of X-ray crystallography. Both 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 consisting of 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 on the basis of their structural diversity. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this work, two fluorescent 2-pyrazoline derivatives with remarkable (fluoro) solvatochromic behavior were successfully synthesized and fully characterized. The effects of solvent polarity on the absorption and fluorescence spectra of the derivatives were quantified and rationalized using LSERs. Differences in the solvatochromic behavior among the derivatives were revealed based on their structural diversity.