Photochemical proton-coupled C-H activation: an example using aliphatic fluorination.

Selective functionalization of unactivated C-H bonds is an ongoing chemical challenge. C-H activation requires the transfer of H+ and e-, so called proton-coupled electron transfer (PCET) reactions. Recent efforts in photochemical PCET involving C-H bonds show great promise for the synthesis of new compounds. One such example is photochemical C-H fluorination reactions. In many cases, the discrete PCET mechanisms are yet to be defined in a systematic way. Here, we investigated electron transfer (ET) and PCET reactions of electronically excited 1,2,4,5-tetracyanobenzene and anthraquinone with the components of typical fluorination reactions. Analysis using kinetic and thermodynamic models, and steady-state and time-resolved fluorescence data, suggest that C-H activation proceeds efficiently where electronically excited sensitizers accept H˙.