Insights into solvent polarity associated geometries and ESIPT behaviours for Prz3HC: a theoretical study

Abstract

Given the potential significance of 3-hydroxychromone derivatives, our focus in this study is to investigate the solvent-polarity-associated photo-induced behaviours for 3-hydroxy-2-(1-ethyl-1H-pyrazol-3-yl)-4H-chromen-4-one (Prz3HC). We firstly examine the coexistence of three conformations (i.e. Prz3HC-I, Prz3HC-II and Prz3HC-III) and present a mechanism for their coexistence between Prz3HC-I and Prz3HC-III. Notably, non-polar solvents contain mainly Prz3HC-I while polar solvents contain mainly Prz3HC-III. Analysing infrared vibrational spectra and geometrical variations between S0 and S1 states, we demonstrate a hydrogen bonding strengthening phenomenon that facilitates excited-state intramolecular proton transfer (ESIPT) behaviour for both Prz3HC-I and Prz3HC-III. To qualitatively investigate photo-induced behaviours, by frontier molecular orbitals (MOs), we have discovered that charge redistribution significantly enhances the propensity for ESIPT. By comparing the barriers of potential energy curves (PECs) for twisting dihedral angles and ESIPT paths, we have unequivocally ruled out any mutual transformations in the S1 state. We also propose a solvent-polarity-regulated ESIPT behaviour for Prz3HC-I and Prz3HC-III. Furthermore, through an exploration of transition states (TS), we have further scrutinised the intricate mechanism underlying ESIPT. We sincerely hope this study can elucidate the solvent-polarity-regulated excited-state behaviours of Prz3HC while simultaneously paving the way for future explorations and applications of other 3-hydroxychromone derivatives.