Seven aliphatic thioketones, several of them possessing bicyclo[2.2.1]heptane geometries, have been examined for triplet-state behaviour in benzene using laser excitation into their low-lying 1(n, π*) band systems (485-490 and 532 nm). In the case of di-t-butylthioketone (DTBTK) a transient absorption (280-500 nm) was attributable to its triplet (εT ≈ 1.5 × 103 dm3 mol-1 cm-1 at 280 nm). The thioketone triplets were, however, probed in all cases by energy transfer to all-trans-1,6-diphenyl-1,3,5-hexatriene (DPH). Results are presented for triplet lifetimes (0.1-0.6 μs at 1 × 10-3 mol dm-3 thioketone concentration), intersystem-crossing yields (0.85-1.0), self-quenching kinetics [(0.1-7) × 109 dm3mol-1 s-1] and kinetics of energy transfer to DPH [(6-8) × 109 dm3 mol-1 s-1]. The steric crowding at α positions severely hinders the self-quenching interaction in DTBTK. The efficiency of singlet-oxygen formation as a result of DTBTK triplet quenching by oxygen is close to unity (0.85 ± 0.17 in benzene).
|Original language||English (US)|
|Number of pages||11|
|Journal||Journal of the Chemical Society, Faraday Transactions 2: Molecular and Chemical Physics|
|State||Published - Dec 1 1985|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics
- Physical and Theoretical Chemistry