Elucidating the role of water-mediated hydrogen bonds in the ESIPT process of a reversible fluorescent probe: A TD-DFT investigation

Abstract

This investigation harnesses DFT and TD-DFT to unravel the pivotal role of water-mediated hydrogen bonding in orchestrating the ESIPT dynamics of the fluorescent probe BT-Se and its oxidized derivative BT-SeO, within PBS solvent. First, excited-state analysis of the monomers shows that intramolecular hydrogen bonds are strengthened upon photoexcitation, catalyzing ESIPT, as evidenced by infrared spectroscopy and reduced density gradient analyses. To further explore the influence of solvent interactions, we constructed water-mediated hydrogen-bonded models to analyze their excited-state properties. Potential energy curves demonstrate that increasing water molecules markedly reduces ESIPT barriers, while frontier molecular orbital analyses indicate negligible charge transfer alterations. BT-Se exhibits greater conformational twisting and charge transfer than BT-SeO, resulting in more pronounced TICT processes. These findings illuminate the synergistic interplay of intra- and intermolecular hydrogen bonds in sculpting ESIPT processes. Our research provides theoretical insights into designing advanced ESIPT-based fluorescent probes for bioimaging and sensing in aqueous environments.