Triplet state mechanism for diphenylamine photoionization

The photoionization of diphenylamine has been studied using both one- and two-laser flash photolysis in acetonitrile, alcohols, and aqueous solvent mixtures with the aim of elucidating the role of the triplet in the photoionization process. Excitation of triplet diphenylamine at 532 nm leads to irreversible triplet bleaching in all solvents, although the yields decrease by approximately an order of magnitude in comparing 1:1 aqueous acetonitrile to neat methanol or 2-propanol. Photoionization to yield the diphenylamine radical cation accounts for a substantial fraction of the triplet bleaching in all cases, demonstrating that biphotonic photoionization via an upper triplet is a viable mechanism. Triplet bleaching does not lead to either N-H bond cleavage or reverse intersystem crossing in aqueous acetonitrile. Plots of the radical cation yield as a function of laser power for one-laser (308 nm) excitation of diphenylamine are linear, consistent with monophotonic ionization under these conditions.Peer reviewed: YesNRC publication: Ye