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 i n the photoionization process. Excitation of triplet diphenylamine at 532 nm lends to irreversible triplet bleaching in all solvents, althou gh the yields decrease by approximately an order of magnitude in compa ring 1:1 aqueous acetonitrile to neat methanol or 2-propanol. Photoion ization to yield the diphenylamine radical cation accounts for a subst antial fraction of the triplet bleaching in all cases, demonstrating t hat biphotonic photoionization via an upper triplet is a viable mechan ism. Triplet bleaching does not lend to either N-H bond cleavage or re verse intersystem crossing in aqueous acetonitrile. Plots of the radic al cation yield as a function of laser power for one-laser (308 nm) ex citation of diphenylamine are linear, consistent with monophotonic ion ization under these conditions.