Birch-Type-Reduced Carbazole Anions Enable Redox-Adaptive Super-Reducing Photocatalysis

Photocatalytic activation of inert chemical bonds is constrained by the redox potential of the catalyst. Here, we report a redox-adaptive photocatalytic strategy in which an electron-rich carbazole photocatalyst, CBZ6, functions as a molecular redox transformer through the formation of Birch-type carbazole anions. Under visible light, CBZ6 switches between a neutral state for conventional photoredox reactions and an anionic state for super-reducing catalysis. Excitation of the anionic state generates a super-reducing species with an excited-state oxidation potential of approximately -3.6 V versus SCE, substantially beyond that of the neutral excited state (-2.2 V). This adaptive redox switching enables activation of otherwise inaccessible C-F bonds in aryl fluorides, polyfluoroalkyl compounds, and fluoropolymers. The complementary reactivities of the two states further enable diverse photoredox transformations, establishing redox adaptation as a strategy for expanding the accessible reactivity of organic photocatalysts.