Photoinduced excited state intramolecular proton transfer of 2-(2′-hydroxyphenyl)phenanthro[9,10-d]oxazole: A comprehensive theoretical study

• The geometrical and spectral properties of HPO are investigated.
• Both excited- and ground-state PESs are explored for elucidation of ESIPT.
• The overall scenario for ESIPT and possible mechanism for DF are discussed.

To gain an in-depth knowledge on the enol–keto photoisomerization of an oxazole derivative, namely, 2-(2′-hydroxyphenyl)phenanthro[9,10-d]oxazole (HPO), a thorough theoretical investigation was performed on the geometrical and electronic spectroscopic properties. The present results suggest that the bond length exclusively dominates in the photoinduced process with all involved critical points keeping planar geometries. The predicted absorptions centered at 3.82 and 3.07 eV account for experimental bands at 3.61 and 3.42 eV corresponding to enol and keto forms, respectively. Orbital analysis shows that both absorption and emission bands in the title molecule essentially stem from HOMO to LUMO with typical ππ* transition character. Furthermore, both the ground- and excited-state energy profiles after photo-excitation were explored for exhaustive elucidation of the excited state intramolecular proton transfer (ESIPT). In addition, the delayed fluorescence (DF) behavior at low temperature of 77 K in experiment was tentatively attributed to triplet–triplet annihilation (TTA).

Scheme of the photoinduced decay mechanism suggested by the present quantum-chemical calculations.Figure optionsDownload as PowerPoint slide