Photo-Fries rearrangement of phenyl salicylate studied by two-dimensional infrared spectroscopy

Photo-Fries rearrangement of phenyl salicylate was examined by real-time infrared (IR) monitoring in conjunction with density functional theory (DFT) calculation. Changes in the spectral features were readily captured during the photo-induced chemical reaction of the phenyl salicylate by means of two-dimensional (2D) correlation spectroscopy. The obvious variations of spectral intensities due to the production of 2,2′-dihydroxybenzophenone and 2,4′-dihydroxybenzophenone are clearly identified to provide in-depth understanding to the photo-Fries rearrangement. Namely, when exposed to UV-irradiation, the majority of the phenyl salicylate undergoes photothermal degradation. Further irradiation to the rest of the phenyl salicylate then results in the production of 2,2′-dihydroxybenzophenone followed by the development 2,4′-dihydroxybenzo-phenome products. Such delay in the production of 2,4′-dihydroxybenzo-phenome implies the presence of some more pathways, which makes its reaction efficiency lower than that of 2,2′-dihydroxybenzophenone.