Time-resolved resonance Raman identification and structural characterization of a light absorbing transient intermediate in the photoinduced reaction of benzophenone in 2-propanol

Abstract

(Chemical Equation Presented) A nanosecond time-resolved resonance Raman (ns-TR 3) spectroscopic study of the triplet state benzophenone reaction with the 2-propanol hydrogen-donor solvent and subsequent reactions is presented. The TR 3 spectra show that the benzophenone triplet state (nπ*) hydrogen-abstraction reaction with 2-propanol is very fast (about 10 to 20 ns) and forms a diphenylketyl radical and an associated 2-propanol radical partner. The temporal evolution of the TR 3 spectra also indicates that recombination of these two radical species occurs with a time constant of about 1170 ns to produce a LAT (light absorbing transient) intermediate that is identified as the 2-[4-(hydroxylphenylmethylene)cyclohexa- 2,5-dienyl]propan-2-ol (p-LAT) species. Comparison of the TR 3 spectra with results obtained from density functional theory calculations for the species of interest was used to elucidate the identity, structure, properties, and major spectral features of the intermediates observed in the TR 3 spectra. The structures and properties of the reaction intermediates observed (triplet benzophenone, diphenyl ketyl radical, and p-LAT) are briefly discussed. © 2007 American Chemical Society.