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Publication - Professor Andrew Orr-Ewing

    Picosecond to Millisecond Tracking of a Photocatalytic Decarboxylation Reaction Provides Direct Mechanistic Insights

    Citation

    Bhattacherjee, A, Sneha, M, Lewis-Borrell, L, Tau, O, Clark, IP & Orr-Ewing, A, 2019, ‘Picosecond to Millisecond Tracking of a Photocatalytic Decarboxylation Reaction Provides Direct Mechanistic Insights’. Nature Communications, vol 10.

    Abstract

    The photochemical decarboxylation of carboxylic acids is a versatile route to free radical intermediates for chemical synthesis. However, the sequential nature of this multi-step reaction renders the mechanism challenging to probe. Here, we employ a 100 kHz mid-infrared probe in a transient absorption spectroscopy experiment to track the decarboxylation of cyclohexanecarboxylic acid in acetonitrile-d3 over picosecond to millisecond timescales using a photooxidant pair (phenanthrene and 1,4-dicyanobenzene). Selective excitation of phenanthrene at 256 nm enables a diffusion-limited photoinduced electron transfer to 1,4-dicyanobenzene.  A measured time offset in the rise of the CO2 byproduct reports on the lifetime (520 ± 120 ns) of a reactive carboxyl radical in solution, and spectroscopic observation of the carboxyl radical confirms its formation as a reaction intermediate. Precise clocking of the lifetimes of radicals generated in situ by an activated C-C bond fission will pave the way for improving the photocatalytic selectivity and turnover.

    Full details in the University publications repository