Primary photoprocesses in quinones and dyes II. Kinetic studies

Kinetic studies of the semiquinone radical, the radical ion and the triplet state of duroquinone in solution are reported. A scheme of reaction is given which is consistent with all the kinetic data and is in excellent agreement with the assignments of part I. Values are obtained for the rate constants of the reactions 2QH. → Q + QH2, 2Q-. → Q + Q2-, QH. → Q-. + H+ and of the constant for the equilibrium (Q-)(H+)/(QH.). It is shown that, in liquid paraffin, the primary reaction with solvent occurs mainly via the excited singlet and not the triplet state. In ethanol, the dissociation of QH. to Q-. and H+ is observed directly and leads to the conclusion that the primary process is one of hydrogen, rather than electron, abstraction.