The regulation mechanism of the excited-state behaviour of 3-Hydroxy-2-(1-ethyl-1H-pyrazol-3-yl)-4H-chromen-4-one fluorophore by solvent polarity: a computational study

Abstract

Given the unique spectral properties of exhibiting dual-band fluorescence, excited-state intramolecular proton transfer (ESIPT) materials have attracted wide attention. In light of a promising, highly efficient fluorescent probe with potential ratiometric emission detection, in this work, 3-Hydroxy-2-(1-ethyl-1H-pyrazol-3-yl)-4H-chromen-4-one (3ePz3HC) has been explored its photo-induced excited-state behaviours. In analyses of structural variations and infrared (IR) vibrational spectra between S0 and S1 states, the enhanced hydrogen-bonding interactions could reveale that promote the ESIPT tendency. Particularly, 3ePz3HC in aprotic nonpolar solvents with stronger hydrogen bonds shows an easier proton-transfer tendency. Paying attention to the changes of primarily related frontier molecular orbitals, we find that the charge transfer process occurs in excited-state molecules, and the reorganisation of charge densities should be conducive to promoting the ESIPT process. Simulated potential energy curves indicate that the ultrafast ESIPT reaction occurs for 3ePz3HC with low barriers, which could be further regulated and controlled by solvent polarity. HIGHLIGHTS Photo-induced, enhanced hydrogen bonding provides the tendency for ESIPT reaction of the 3ePz3HC fluorophore. Increased electronic densities around the O3 moiety of 3ePz3HC play vital roles in facilitating the ESIPT process. Aprotic nonpolar solvents are more favourable for accelerating the ESIPT behaviour for the 3ePz3HC compound.