C. Hélène
Dec 1, 1972
Citations
0
Influential Citations
24
Citations
Journal
Photochemistry and Photobiology
Abstract
BENZOPHENONE has been used in aqueous solution to photosensitize the formation of cyclobutane dimers of pyrimidine derivatives (Charlier and Helene, 1967; Von Wilucki et af., 1967; Greenstock and Johns, 1968). This photosensitized reaction is assumed to involve energy transfer from the benzophenone triplet state, thus populating the triplet state of the pyrimidine derivative, which then reacts with a ground-state molecule to give a cyclobutane dimer. In order to provide evidence for the energy-transfer step, we studied the transient species produced during flash excitation of benzophenone and their subsequent reactions with pyrimidine and purine derivatives (Charlier and Helene, 1972). Two transient species (triplet-state molecules and ketyl radicals) were identified on the basis of different decay kinetics and different spectra. The benzophenone triplet-' state lifetime in water was determined to be 65 psec from the decay of the triplet-triplet absorption (A,,,= = 525 nm). However, overlap of the triplet-triplet and ketyl radical absorption spectra prevents accurate determination of the triplet-state lifetime in the presence of quenchers, especially in the case of purine derivatives, which do not affect markedly the yield of ketyl radicals (Charlier and Helene, 1972). Since phosphorescence emission from the benzophenone triplet state has already been observed in organic solvents at room temperature (Parker, 1968; Clark et al., 1969; Saltiel et al., 1970), an investigation of benzophenone phosphorescence in water, and of its quenching by pyrimidine and purine derivatives, was undertaken to overcome the abovementioned difficulties.