Solvent-controlled excited-state intramolecular proton transfer in 4-methoxy tetramic acid derivative

Excited-state intramolecular proton transfer (ESIPT) has garnered significant attention in fluorescent sensors due to its unique photobiological and photochemical properties. In this work, the ESIPT behavior of a newly developed ESIPT-based fluorescent sensor (PYDP) under solvent polarity modulation has been systematically investigated. Bond parameters, infrared vibrational frequency analysis, nuclear valence branching index (CVB), and bond critical point (BCP) parameters indicate enhanced hydrogen bonding in the first excited state with solvent dependence. By investigating reaction energy barriers, it was elucidated that a reduction in solvent polarity favors the occurrence of the ESIPT reaction in PYDP molecules. Our findings hold significant implications for understanding solvent-polarity-regulated ESIPT characteristics, providing theoretical guidance for designing novel luminescent materials.