Photochemical reactions of triplet state of N-hydroxyacridine-9-thione studied by laser-flash photolysis

Abstract

By laser-flash photolysis of N-hydroxyacridine-9-thione (HOAT) in organic solvents, the transient absorption bands observed at 410 and 530 nm, are assigned to the triplet–triplet absorption of 3(HOAT)*. The lowest triplet energy (ET1), the intrinsic triplet lifetime (τT°) and the quantum yield (ΦT) of intersystem crossing have been determined. A rather large self-quenching rate constant (ksq=1.6±0.1×109 mol-1 d s-1 in THF) was observed. In the photoinduced electron-transfer reactions, 3(HOAT)* acts as electron acceptor for tetramethylbenzidine and triphenylamine, while for dinitrobenzene and the methylviologen dication it acts as electron donor in polar solvents. In the addition reactions of 3(HOAT)* with various alkenes, the electrophilic character of 3(HOAT)* has been established. By comparison of the experimental results with MO calculations, the lowest triplet electronic-configuration of 3(HOAT)* is revealed.