Quenching of alkyl ketone fluorescence by 1,3-dienes

Excited Singlet State Radiative and Nonradiative Transition Probabilities for Acetone, Acetone-d6, and Hexafluoroacetone in the Gas Phase, in Solution, and in the Neat Liquid

“…A value of 2.0 nsec was also reported by Wettack et al 32 for AH6 in hexane. No mention was made in their report of decay curve deconvolution.…”

Molecular photochemistry. L. Molecular photochemistry of alkanones in solution. .alpha.-Cleavage, hydrogen abstraction, cycloaddition, and sensitization reactions

“…MeOH the efficiency of formation of 18 and 19 from the Si state is the same as in benzene, but the efficiency of formation of 18 and 19 from Ti is increased by a factor of 10. As expected,35 the more polar solvent inhibits hydrogen back-transfer in the biradical produced from Ti only, and allows cyclization to compete more effectively with regeneration of starting ketone.…”

“…Results for methyl ¿erf-butyl ketone16b and for cyclohexanone90 (1) reveal that, while the plot for cyclohexanone does indeed follow Stern-Volmer kinetics, the plot for methyl ¿erf-butyl ketone is distinctly nonlinear, decreasing in slope at higher concentrations of 1,3-diene. This latter behavior is prima facie evidence for reaction from two different alkanone excited states.14 In addition, the quenching which occurs at high diene concentration is paralleled by quenching of ketone fluorescence.18• 19 We can conclude that quenching of Si is occurring at high concentrations of diene, while at low concentrations of diene predominantly Tj is being quenched. The data allow us to estimate the reactivity of both Si and Ti of 2 toward a cleavage, while for 1 we can only estimate the reactivity for Ti because no reaction from Si could be detected by diene quenching.…”

Evidence for comparable reactivity of alkanone excited singlet and triplet states toward hydrogen donors

“…Clearly there is a major discrepancy between the conclusions of our work and the earlier report that the Si state of acetone is at least two to three orders of magnitude less reactive than the Ti state toward intermolecular hydrogen abstraction from TBTH.6 The latter conclusion was derived from the absence of photoreduction from Si22 as demonstrated by the complete quenching of both 2-propanol formation and acetone disappearance in the presence of 5 M piperylene, which was assumed to be quenching only acetone Ti states. 23 Although it is now known24 that piperylene quenches , * Si as well as Ti states, singlet diene quenching is usually a relatively inefficient process. Even at the high concentrations of dienes used only partial, not complete, quenching of the Si state would be expected.…”