Visible light-mediated C (sp3)–H bond functionalization inside an all-organic nanocavity

Abstract

Ultrafast C–H bond activation and functionalization in confinement using visible light will enable engineering chemical reactions with extraordinary speed and selectivity. To provide a transition metal-free route, here we demonstrate C–H bond activation reactions on poly-aromatic hydrocarbons (PAH) in all-organic cationic nanocage ExBox⁴⁺ for the first time. Visible light excitation in the host–guest charge transfer (CT) state allows the formation of oxidized photoproducts with high selectivity. Mechanistic understanding of this CT-mediated photoreaction using femtosecond broadband transient absorption revealed a few ∼100 ps timescale for C–H bond breaking on the attached –CH₃ group via sequential electron transfer and proton transfer steps. We envision that our photosensitizer-free method will open up new avenues to pursue organic reactions using cavities that could serve both as photoredox catalysts and hosts for reactive reaction intermediates.