Photoluminescent and Shape Memory Hydrogels Cross-linked by Hydrophobic Interactions of Isolated Bromine-Substituted Benzene Rings

Photoluminescent hydrogels have developed rapidly in recent years. However, most reported photoluminescent hydrogels rely on the photoluminescence of the incorporated photoluminescent materials rather than the hydrogel networks. Here, we prepare a poly(2,4,6-tribromophenyl acrylate-co-acrylamide) [poly(PABr3-co-AAm)] hydrogel with excellent mechanical properties and intrinsic fluorescence and room-temperature phosphorescence (RTP). The aggregation of hydrophobic tribromophenyl groups and the clustering of the separated benzene rings and bromine atoms lead to the formation of strong π–π stacking and halogen–halogen interactions among them, which are effective in enhancing the mechanical properties of the hydrogel and promoting the occurrence of photoluminescence. Moreover, the presence of halogen atoms promotes the origin of the RTP emission of the hydrogel. Therefore, the poly(PABr3-co-AAm) hydrogel exhibits excitation-dependent fluorescence and RTP with a maximum lifetime of 90 ms. In addition, the hydrogel also exhibits an excellent thermoresponsive shape memory property, showing fast shape recovery in only 2.5 s after being immersed in 70 °C hot water. The poly(PABr3-co-AAm) hydrogel is ideal for surgical fixation and 3D information encryption. This work provides a direction for preparing photoluminescent hydrogels with multifunctionalities, which greatly expands the practical applications of nontraditional photoluminescent materials.