Photoredox-catalyzed dehalogenation of aryl halides in an aerated supramolecular hydrogel enabled by triplet-triplet annihilation upconversion.

Abstract

Triplet-triplet annihilation upconversion (TTA-UC) is a powerful strategy to access high-energy excited states under low-energy irradiation, yet its practical implementation simultaneously in aqueous and aerobic environments remains severely limited by dye insolubility and oxygen quenching. By integrating a sensitizer-emitter pair within a surfactant-assisted hydrogel matrix, TTA-UC emission is sustained in an EtOH/H₂O (1 : 1 v/v) medium under ambient air, consistent with our previous photophysical characterization of this hydrogel platform. This work expands the applicability of intragel TTA-UC systems to the photoreduction of aryl and heteroaryl halides in aqueous media under aerobic conditions. Systematic optimization of key parameters, including base identity, surfactant concentration, gelator content, and irradiation protocol, affords reaction yields approaching 50% in aerated EtOH/H₂O mixtures without prior deoxygenation. The results are consistent with the previously reported oxygen-tolerant behaviour of this hydrogel platform and further demonstrate that the system can be used as a reaction medium for aerobic photodehalogenation. Overall, this work establishes supramolecular hydrogels as soft photochemical reactors for oxygen-tolerant photocatalysis and expands the scope of TTA-UC-assisted photochemistry in predominantly aqueous media under aerobic conditions.