Activation of Aryl Halides by Triplet–Triplet Annihilation Upconversion Enabling Coupling Processes Under an Open‐to‐Air Environment

Herein, several CC and C–heteroatom coupling reactions were successfully achieved by combining triplet–triplet annihilation upconversion (TTA‐UC) photochemistry with supramolecular viscoelastic gels as confined media under green‐light LED irradiation. Unlike conventional TTA‐UC, which typically requires strict anaerobic conditions due to efficient oxygen quenching of triplet states, the present methodology operates under open‐to‐air conditions. The gel matrix, made of low‐molecular‐weight gelators, provides a nanostructured microenvironment that restricts oxygen diffusion and minimizes triplet‐oxygen collisional quenching, thereby preserving the efficiency of the upconversion process without additional additives. Using the well‐established PtOEP/DPA sensitizer–annihilator pair embedded within the gel network, aryl halides were activated through a photoinduced single‐electron transfer pathway enabled by the upconverted excited state. The method proved effective for a range of substrates affording the corresponding coupling products in moderate to good yields under mild conditions (ambient temperature, atmospheric pressure, visible light). Rheological and microscopic studies confirmed that the fibrillar gel architecture remains largely intact after irradiation, highlighting the mechanical robustness and recyclability of the confined medium for photoredox transformations.