Competitive Singlet-Singlet Energy Transfer and Electron Transfer Activation of Aryl Azides: Application to Photo-Cross-Linking Experiments

Article abstract of DOI:10.1021/jo00250a017

Direct irradiation of 4-<(dimethylamino)carbonyl>phenyl azide (DAA) in an inert solvent with UV light causes ring expansion to an inermediate dehydroazepine and eventual isolation of 4,4'-azobis<<(dimethylamino)carbonyl>benzene> (AZB).The dehydroazepine can be trapped with nucleophilic reagents to give substituted 3H-azepines.The photochemistry of DAA takes a different course when it is sensitized by pyrene, 1-acetamidopyrene (5), or 9-acetamidoacridine (2).Under these conditions, single-electron transfer occurs in competition with energy transfer as evidenced by detection of radical ions in laser transient absorption spectroscopy and by formation of 4-<(dimethylamino)carbonyl>aniline (DAH) as a major product.Energy transfer and electron transfer compete also when the sensitizer and the aryl azide are linked together by a flexible chain of methylene groups.These results have particular significance for the application of such compounds to phtolabeling experiments.