Use of Quadruple Hydrogen Bonding as the Switching Phase in Thermo- and Light-Responsive Shape Memory Hydrogel

2-Ureido-4[1H]-pyrimidinone (UPy) is widely deployed in bulk materials for switching phase or physical cross-linking because of exceptional quadruple H-bond strength and thermal reversibility. However, utilization of UPy dimers as the switching phase to prepare shape memory hydrogels has been rarely explored due to the competition with water molecules. Herein, hydrogels with high UPy contents are synthesized and exhibit excellent shape memory ability, even at high water contents. By introduction of tetraphenylporphyrin into hydrogels, the shape memory behavior can further be controlled by light through a photothermal effect. This finding offers possibilities for applications of UPy in developing shape memory hydrogels.