LASER FLASH-PHOTOLYSIS AND PRODUCT STUDIES OF THE PHOTOIONIZATION OF N-METHYLACRIDAN IN AQUEOUS-SOLUTION

Photolysis of N-methylacridan (1) in deaerated aqueous CH3CN solution results in photoionization, to give the N-methylacridan radical cation (1.+) as the first-formed intermediate. Subsequent deprotonation from 1.+ gives N-methylacridyl (1.), which dimerizes to give 9,9'-bis(N-methylacridyl) (2) as the only isolable product. Quantum yields for loss of 1 are 0.085 and 0.022 in 1:1 H2O-CH3CN and 100% CH3CN, respectively. In the presence of oxygen, 1. is believed to be oxidized further (electron transfer to O2), to give N-methylacridinium ion (4), which was detected by its characteristic UV absorption and fluorescence emission spectra. Laser flash photolysis studies provide direct evidence for photoionization of 1 to give the radical cation 1. which subsequently deprotonates to form 1+. The combined transient and product studies indicate a monophotonic mechanism from the first excited state. The results demonstrate that photoexcited 1 is an excellent electron donor to bulk solvent. The process does not require externally added electron acceptors for photoredox chemistry.