Excited singlet and triplet state electron-transfer reactions of aluminium(III) sulphonated phthalocyanine

Abstract

Conventional and nanosecond flash photolysis has been used to study the excited-state reactions of aluminium(III) sulphonated phthalocyanine (AlSP) with benzohydroquinone (BQH₂), methyl viologen (MV), benzyl viologen (BV) and anthraquinone-2,6-disodium sulphonate (AQDS). The fluorescent state of AlSP was quenched by all of these reagents at rates close to the diffusion-controlled limit; however, no separated electron-transfer products were detected from the reaction with BV, MV or AQDS despite the electrostatic repulsion between the phthalocyanine and semiquinone radical anions. In contrast, quenching by BQH₂ produced a transient (τ≃ 100 ns), which is attributed to a long-lived geminate ion pair, from which separated ions escaped.

The triplet state of AlSP did not react with AQDS, BV or MV, but it was quenched by oxygen and BQH₂. Separated ions were produced three times as efficiently from the triplet reaction of AlSP with BQH₂ than from the excited-singlet-state reaction.