Theoretical Insights Into Effects of Surrounding Polarity on ESDPT Behaviors for the 2,7‐bis‐(5‐ethyl‐benzooxazol‐2‐yl)‐pyrene‐1,6‐diol Fluorophore

To reveal the regulatory mechanism of solvent polarity on the excited‐state double proton transfer (ESDPT) of 2,7‐bis‐(5‐ethyl‐benzooxazol‐2‐yl)‐pyrene‐1,6‐diol (BEBPD), we systematically investigated its geometric structures, hydrogen bond interactions, electronic structures and potential energy surfaces in vacuum, chloroform, acetone, and DMSO via DFT/TDDFT methods. We unambiguously confirm that the dual intramolecular hydrogen bonds of BEBPD are significantly enhanced in the S 1 excited state relative to the S 0 ground state, and this strengthening effect is further amplified by increasing solvent polarity. Frontier molecular orbital analyses demonstrate that photoexcitation induces obvious charge redistribution from hydroxyl oxygen atoms to benzoxazole nitrogen atoms, providing a strong intrinsic driving force for ESDPT. Potential energy surface calculations explicitly verify that the ESDPT reaction of BEBPD proceeds via a stepwise pathway (normal enol → monoketo intermediate → diketo product) rather than a synchronous double proton transfer. Importantly, elevated solvent polarity effectively stabilizes polar proton‐transfer intermediates and products, consecutively reduces the energy barriers of both proton‐transfer steps, and thus remarkably promotes the ESDPT reactivity. This work clarifies the solvent‐polarity‐dependent ESDPT mechanism of BEBPD at the atomic level, and offers a solid theoretical foundation for designing solvent‐responsive organic luminescent materials.