Photochemistry of trans-10,11-Dibromodibenzosuberone: A Near-UV Photoacid Generator

Article abstract of DOI:10.1021/jo00056a025

Pulsed laser irradiation of trans-10,11-dibromodibenzosuberone, I, in room-temperature benzene and acetonitrile solutions resulted in efficient debromination to yield dibenzosuberone, II.In benzene, the transient absorption due to the bromine atom (Br^.)-benzene ?-complex was observed, while in acetonitrile with added Br^- the transient absorption due to Br2^.- was detected.In both cases, transient production was instantaneous, indicating that Br^. is a primary photoproduct.Transient actinometric experiments using the benzophenone triplet state as a standard and Br2^.- as the Br^. probe allowed the determination of the quantum yield for Br^. production, Φ = 2.4 +/- 0.6.In acetonitrile, in the presence of the H-atom donor, 2-propanol, Br^.-Br^. recombination to give Br2 competes with H-atom abstraction to yield the acid HBr.Under high-intensity laser irradiation, recombination and H-atom abstraction are competitive, while under low flux laser or UV lamp irradiation, H-atom abstraction is very efficient.In the presence of 1-3 M 2-propanol, acid formation was found to be nearly quantitative.