Quenching of the triplet states of aromatic hydrocarbons by tertiary amines

Abstract

Rate constants for the quenching of the triplet states of 4-chlorobiphenyl, 1-chloronaphthalene, 9-chloroanthracene and anthracene have been determined. Whilst the quenching efficiency of the more energetic triplet states (ca. 60 kcal mol^–1) by amines appears to be related to the ionisation potential of the latter, no clear trend was seen for the anthracenes. The degree of charge transfer appears, therefore, to decrease as the triplet energy of the hydrocarbon is reduced. By use of α, ω-diaminoalkanes it was found that the triplet states do not participate in complex formation involving simultaneous interaction of the two amino groups and the aromatic hydrocarbon. The quenching efficiency of the diamines increases as the chain linking the amino group is lengthened, suggesting that these compounds undergo multicollisional quenching. The fluorescence of 3,3′-bipyrenyl is quenched by N,N′-dimethylaniline (K_SV= 75 ± 1 dm³ mol^–1 in acetonitrile and 2.8 ± 0.1 dm³ mol^–1 in cyclohexane), but in acetonitrile no evidence for triplet formation could be found. It is suggested that conformational linking in the bipyrene aids radiationless decay to the ground state.