Substituent Effects on Excited‑State Intramolecular Proton Transfer in 3‑Hydroxychromone Derivatives

3-Hydroxychromone (3-HCs) and its derivatives, as typical excited-state intramolecular proton transfer (ESIPT) systems, exhibit outstanding photophysical properties and broad application prospects. Therefore, in this work, we conducted an in-depth investigation towards the excited-state proton transfer behavior of a series of novel 5-substituted 3-HCs derivatives under the regulation of different substituents. Analysis of bond parameters, infrared vibrational frequencies, the nuclear valence branching index (CVB), bond critical point (BCP) parameters, and RDG analysis revealed a significant enhancement of intramolecular hydrogen bonding following photoexcitation. This enhancement effect progressively increased as the electron-withdrawing ability of the substituents diminished. Further investigation of reaction energy barriers demonstrates that 3-HCs-COOH, 3-HCs-COOMe and 3-HCs-CONHCH₂CONH₂ molecules exhibit modulated ESIPT behavior due to differing substituent properties. This work holds significant implications for understanding substituent-effect-modulated excited-state intramolecular proton transfer characteristics, providing theoretical guidance for designing organic light-emitting materials with ESIPT properties.