Singlet Oxygen Generation Via Irradiation of 4-Benzylamino-7-Nitrobenz-2-Oxa-1, 3-Diazole

Abstract

This study was undertaken to determine whether 4-benzylamino-7-nitrobenz-2-oxa-l,3-diazole (BBD) generates the first excited singlet state of molecular oxygen in liquid solution. The problem was first approached using the sensitized photooxidation method of singlet oxygen detection with 1, 3-cyclohexadiene (CHD) as acceptor. A reaction between BBD and the acceptor rendered this method of singlet oxygen detection useless. In a second approach, the rate of light-induced oxygen consumption for solutions having various components was measured. The results showed that for a given monoolefin acceptor the solutions with BBD as sensitizer consumed oxygen about 25 times slower than solutions containing the known singlet oxygen sensitizer rose bengal. This suggests that either BBD does not generate singlet oxygen or that it does so about 25 times less efficiently than rose bengal. Both possibilities are discussed. Further insight into the photochemical reaction of BBD and CHD was obtained by carrying out a quantity preparation of this reaction. Two major products were isolated by tlc. Evidence for a (4s + 4s) photochemically allowed cycloaddition reaction was obtained leading to hypothesized structures for the two products.