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 (E_T1), the intrinsic triplet lifetime (τ_T^°) and the quantum yield (Φ_T) of intersystem crossing have been determined. A rather large self-quenching rate constant (k_sq=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.