Reversible Supramolecular Hydrogel for Air-Tolerant Photon Upconversion: Key Development for Photocatalyst Recovery and Product Extraction in Aqueous Medium

The development of upconversion hydrogels that operate in water and under aerobic conditions remains a significant challenge, especially when postreaction separation and component recovery are needed. Here, we present the first supramolecular photocatalytic hydrogel based on a low-molecular-weight gelator (LMWG) that enables green-to-blue triplet-triplet annihilation upconversion (TTA-UC) in aerated water. The hydrogel forms through the coassembly of the LMWG, surfactant, and a sensitizer/emitter pair (PtOEP/DPAS), giving rise to nanostructured compartments that protect long-lived excited triplet states from oxygen quenching. Unlike previous systems based on biopolymers or covalent networks, this supramolecular gelation is fully reversible, allowing the photochemical reaction to be carried out in situ, followed by gel disassembly for the easy extraction of reaction products without the need for heat. Notably, up to 77% of the precious Pt-based sensitizer can be recovered from the gel matrix. This modular, recyclable platform offers an approach to performing photochemical transformations under mild and environmentally friendly conditions, with advantages over previous air-stable UC hydrogels in terms of reusability, extractability, and operational simplicity.