Intrinsic Room‐Temperature Phosphorescent Hydrogel Driven by Phase Separation and Glass Transition

Abstract Designing room‐temperature phosphorescent (RTP) hydrogels presents a unique challenge in comparison to RTP polymeric films and powders, due to the quenching of phosphorescence by water molecules within the hydrogel and their inherent softness. This study presents the first example of intrinsic RTP hydrogels without doping by luminophores or stiffening agents. The hydrogel is synthesized by copolymerizing acrylamide (Am) with N ‐acryloyl‐aminoundecanoic acid (NAUA). The hydrophobic NAUA induces phase separation in the hydrogel network and the glass transition of the hydrophobic phase can stiffen the structure and constrain the mobility of water molecules and chain segments. Under such condition, the clustering of amide and carboxylic acid groups triggers the emission of RTP with a persistent afterglow exceeding 1.5 s, which is as good as the reported RTP hydrogels with dopants. When the hydrogel is heated above its glass transition temperature, its modulus drops quickly from 20.0 to 0.026 MPa within 2 s and RTP also diminishes. Taking advantage of the temperature‐switchable rigidity and RTP behavior, the hydrogels are endowed with functions such as shape memory, temperature‐sensing, and information concealment.