A density functional theory‐time‐dependent density functional theory investigation of photo‐induced hydrogen bond and proton transfer for 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid

Abstract

AbstractGiven the paramount importance of excited‐state relaxation in the photochemical process, excited‐state hydrogen bonding interactions and excited‐state intramolecular proton transfer (ESIPT) are always hot topics. In this work, we theoretically explore the excited‐state dynamical behaviors for a novel 2‐(3,5‐dichloro‐2,6‐dihydroxy‐phenyl)‐benzoxazole‐6‐carboxylicacid (DDPBC) system. As two intramolecular hydrogen bonds (O1H2⋯N3 and O4H5⋯O6) exist in the DDPBC structure, we first check if the double proton transfer form cannot be formed in the S1 state. Then, we explore the changes of geometrical parameters involved in hydrogen bonds, based on which we confirm that the dual intramolecular hydrogen bonds are strengthened on photo‐excitation. The O1H2⋯N3 hydrogen bond particularly plays a more important role in excited state. When it comes to the photo‐induced excitation, we find charge transfer and electronic density redistribution around O1H2 and N3 atom moieties. We verify the ESIPT tendency arising from the O1H2⋯N3 hydrogen bond. In the analysis of the potential energy curves, along with O1H2⋯N3 and O4H5⋯O6, we demonstrate that the ESIPT reaction should occur along with O1H2⋯N3 rather than O4H5⋯O6. This work not only clarifies the specific ESIPT mechanism for DDPBC system but also paves the way for further novel applications based on DDPBC structure in the future.