Picosecond to millisecond tracking of a photocatalytic decarboxylation reaction provides direct mechanistic insights

Aditi Bhattacherjee*, Mahima Sneha, Luke Lewis-Borrell, Omri Tau, Ian P. Clark, Andrew J. Orr-Ewing

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)

2 Citations (Scopus)
123 Downloads (Pure)

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.
Original languageEnglish
Article number5152 (2019)
Number of pages7
JournalNature Communications
Volume10
DOIs
Publication statusPublished - 13 Nov 2019

Structured keywords

  • BCS and TECS CDTs

Keywords

  • Catalytic mechanisms
  • Reaction kinetics and dynamics
  • Photocatalysis

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