Unraveling the Excited State Proton Transfer Mechanism of Salicylamide: A TD ‐ DFT Study

Excited‐state proton transfer (ESPT) plays a crucial role in photochemical processes, serving as an important mechanism for modulating molecular structures and fluorescence behaviors. In this study, the ESPT mechanism of salicylamide (SAM) was systematically investigated in the gas phase, aqueous solution, and ethanol solution using density functional theory (DFT) and time‐dependent DFT (TD‐DFT) methods. Explicit solvent‐complex models were constructed to evaluate solvent effects. The calculated results indicate that ESPT is both thermodynamically and kinetically feasible for SAM in the gas phase. In contrast, in aqueous and ethanol environments, ESPT occurs through intermolecular proton transfer facilitated by solvent molecules, giving rise to dual fluorescence behavior. The primary fluorescence emission originates from the local excitation.