A theoretical study on excited state proton transfer in 2-(2′-dihydroxyphenyl) benzoxazole

This research investigates the dynamic excited state process for a novel system 2-(2-dihydroxyphenyl) benzoxazole (DHBO) for excited state proton transfer (ESPT) process based on density functional theory (DFT) and time-dependent DFT (TDDFT) methods. Because 2 intramolecular hydrogen bonds (O-1?H2<bold>N</bold>3 and O-4?H5<bold>O</bold>6) in DHBO molecules may trigger proton transfer process in the S-1 state, we focus on these 2 hydrogen bonds. Our results show that only the O-1?H2<bold>N</bold>3 bond has obvious changes in both bond length and bond angle upon photoexcitation. Charge redistribution also confirms that hydrogen bond wire (O-1?H2<bold>N</bold>3) is the best way to achieve the ESPT process in the S-1 state. Considering the ESPT mechanism, our theoretical potential energy curves of DHBO indicate that only the excited state single-proton transfer process occurs via O-1?H2<bold>N</bold>3 rather than O-4?H5<bold>O</bold>6. We believe that our work not only clarifies the excited state dynamical behavior of DHBO but also promotes the investigations about ESPT reactions in intramolecular or intermolecular hydrogen bonded chemical systems.