Figure 2. Proposed mechanism for the direct trifluoromethylation of aryl C–H bonds via photoredox catalysis.

The photoredox catalytic cycle is initiated via excitation of photocatalyst 1 to excited state 2 with a household light bulb. Subsequent reduction of triflyl chloride by reductant 2 (via single electron transfer, that is, SET) provides oxidant 3 along with the radical anion of triflyl chloride. This high energy species spontaneously collapses to form CF₃ radical (top left), which selectively combines with aromatic systems enabling direct CF₃ substitution. Catalyst 3-promoted oxidation of the ensuing radical 4 completes the catalytic cycle and provides cyclohexadienyl cation 5, whose facile deprotonation provides the desired CF₃ arene. This mechanism is consistent with measured redox values (shown below respective compounds, in maroon).