The Triplet State of Ketones in Solution: Quenching of Triplet Acetone by Amines

Abstract

Rate constants for quenching of triplet excited acetone by primary and tertiary amines in solution have been measured directly by flash and pulsed laser techniques. The rate constants were found to be independent of solvent dielectric constant over the range ε 1.9 to ε 80, but were influenced by amine ionization potential. The results are interpreted as supporting a charge-transfer model for the quenching of triplet ketones by tertiary amines. The intervention of free ions in the quenching process is discussed. Free energy calculations indicate that electron transfer from N,N-dimethylaniline to triplet ketones is exothermic but is slightly more favorable for triplet aromatic ketones than for triplet acetone. Evidence for direct hydrogen atom transfer was obtained for quenching of triplet acetone by n-hexylamine.