Photochemical reactions of several halogen-substituted benzophenones were investigated using femtosecond transient absorption (fs-TA) and nanosecond time-resolved resonance Raman (ns-TR3) spectroscopy combined with density functional theory (DFT) simulations. The behaviors of halogen-substituted benzophenones were similarly to their parent compound benzophenone (BP), regarding the ability of hydrogen abstraction under triplet excited state in isopropyl alcohol solvents. In acidic aqueous solutions, an efficient aromatic photosubstitution reaction of meta-fluorinated derivatives and a competitive photohydration reaction were detected simultaneously. Excited at 266 nm in acidic aquoues solution, the halogen-substituted benzophenone formed the corresponding m-hydroxy derivative with the release of a fluoride leaving group from the meta position. In contrast, only the photohydration reaction was observed for other halogen-substituted benzophenones under the same conditions. These transient species were characterized with TR3 spectra. Experimental observations were rationalized by DFT computations. This meta effect of the halogen substitution might provide insight to several possible applications, which are also briefly discussed.

Time-resolved resonance Raman study of an efficient photosubstitution reaction in aqueous solution

247th National Meeting (2014)

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