Effect of cucurbit[7]uril on redox photoprocesses of thionine in water

Abstract

The effect of cucrbit[7]uril (CB7) on the redox reactions of thionine (ThH⁺) in the triplet state are considered in the absence and the presence of electron donor (FeSO₄) and acceptor (p-nitroacetophenone). The formation of the 1 : 1 host–guest complex between thionine and CB7 increases the lifetime of the thionine triplet state. In the absence of exogenous electron donor and acceptor, the thionine triplet molecules in the host-guest complex enter into reactions of disproportionation and concentration quenching to give semioxidized and semireduced forms of thionine. The yield and lifetime of semioxidized and semireduced thionine forms exceed the yield and lifetime of these forms for free thionine. The complexation of thionine with CB7 decreases the efficiency of the thionine photoreduction and that of the reduction of the semioxidized form by the Fe²⁺ ions by factors of 5 and 2.5, respectively.