Uncovering the excited state trends and ESIPT mechanism for 2-(hydroxy-3-dimethyl-phenyl)-benzooxazole-6-carboxylicacid.

• Geometry parameters reveal strengthened intramolecular hydrogen bond of HDPB in S 1. • Photoinduced charge transfer facilitates the ESIPT reaction for HDPB system. • Low potential energy barrier reveals the ultrafast ESIPT process for HDPB molecule. In this work, the ESIPT mechanism of the novel HDPB compound is investigated. Probing into non-hydrogen bonding HDPB-O, we verify the stabilization of hydrogen bond. Based on simulating geometrical changes, we present O H⋯N of HDPB is enhanced by photoexcitation. Exploring MOs, we present charge recombination facilitates attracting proton, which promotes ESIPT tendency. Constructing potential energy curves (PECs) for HDPB, the low potential barrier 2.2107 kcal/mol is found for ESIPT process. Due to the low barrier, ultrafast ESIPT reaction occurs. It explains the non-fluorescent phenomenon of HDPB itself. This work clarifies ESIPT mechanism for HDPB, but also explains experimental phenomenon. [ABSTRACT FROM AUTHOR]