M. Encinas, J. Scaiano
Apr 11, 1979
Citations
0
Influential Citations
29
Citations
Journal
Journal of the American Chemical Society
Abstract
The photochemistry of ..beta..-(dimethylamino)propiophenone has been examined in aqueous solvents using laser flash photolysis technique. The triplet state decays via charge-transfer interactions which lead to intramolecular electron transfer and a product which is best described as a biradical zwitterion; the yield of biradical generation is 0.18 in aqueous methanol (1:4). The triplet decay is strongly pH dependent and is suggested to be preceded by deprotonation at pH values below pK/sub a/. The lifetime of the nonprotonated triplet is short enough to prevent the complete establishment of the acid-base equilibria in the excited state. The triplet lifetimes are concentration dependent as a result of self-quenching. The biradical zwitterions produced in the triplet decay process can be trapped by a variety of electron acceptors, including 1,1'-dimethyl-4,4'-bipyridylium dications. From a study of the pH dependence of the trapping reaction we have determined the pK/sub a/ value of the biradical as 10.0. The biradical lifetimes are in the neighborhood of 1 to 2 ..mu..s, considerably longer than those derived from simple phenyl alkyl ketones. 6 figures, 4 tables.