Theoretical Exploration Related to Excited State Behaviors for Bis‐2,5‐(2‐Benzoxazolyl)‐Naphthalenediol Fluorophore in Surrounding Solvents With Different Polarities

ABSTRACT In this work, we investigate the excited‐state intramolecular proton transfer (ESIPT) of the bis‐2,5‐(2‐benzoxazolyl)‐naphthalenediol (BYND) system theoretically based on density functional theory (DFT) and time‐dependent density functional theory (TDDFT). We verify the hydrogen bond strengthening mechanism in the excited state by comparing the parameters of the two hydrogen bonds in S 0 and S 1 states. Through comparisons of the ∆ ρ ( S 1 − S 0 ) and ∆ E ( S 1 − S 0 ) values for the two hydrogen bonds across different solvents, we put forward the notion that the distinct responsiveness of the dual hydrogen bond motif to solvent polarity stems from the asymmetric molecular structure. Finally, we have elucidated that the excited‐state double proton transfer (ESDPT) mechanism of the BYND system proceeds in a stepwise pathway (I → III → IV) based on an analysis of the potential energy surfaces (PESs) and energy barriers in various reaction pathways.