Direct measurement of ultrafast carbon-carbon cleavage rates via the subpicosecond charge-transfer activation of pinacols

Article abstract of DOI:10.1021/ja980097d

Highly transient (benzpinacol) cation radicals (D₂^+.) and their ultrafast mesolytic fragmentations to the diarylhydroxymethyl radical (D^.) and cation (D⁺) are directly observed on the early picosecond time scale upon the charge-transfer photoactivation of the intermolecular donor-acceptor complexes of pinacol donors with methyl viologen. Ultrashort lifetimes of the cation radicals with τ ~ 10 ps obtain (for the first time) from quantitative kinetics analysis of the time-resolved spectroscopic results. These rapid C-C bond scissions successfully compete with back-electron transfer, which normally predominates on this time scale, and lead to exceptionally high efficiencies for the oxidative fragmentation of pinacols.