Photochemistry of ketones in solution LXXVIII: kinetics of fluorescence quenching of 9,10-dicyanoanthracene and 9,10-dimethoxyanthracene by acyclic and cyclic unsaturated ketones and the behavior of the resulting radical ions pairs

Abstract

The rates of quenching of the fluorescence of 9,10-dicyanoanthracene (DCA) and 9,10-dimethoxyanthracene by a series of cyclic conjugated ketones, acyclic homoconjugated ketones, 3,5-cycloheptadienones and 3,5-cycloheptadienols have been determined in several solvents. In general, these rates are consistent with the ability of the quenchers to act as either electron donors or acceptors toward the electronically excited anthracenes. The cycloheptadienones are unique in showing both donor and acceptor reactivity. For some of these systems, no reactions are seen under these photosensitization conditions, while in other cases typical triplet state products are observed, which can be attributed to the generation of substrate triplets from the initial radical ion pair produced in the reaction. Novel products formed on DCA-sensitized photo-oxygenation of 2,2,7,7-tetramethyl-3,5-cycloheptadienone and the corresponding alcohol in acetonitrile appear to be formed via intermediate radical cations in processes which do not involve singlet oxygen. © 1987.