Hydrogelation Landscape Engineering and a Novel Strategy To Design Radically Induced Healable and Stimuli-Responsive Hydrogels

Herein, we report the versatile ways to prepare both low-molecular weight hydrogels and polymeric hydrogels based on various types of supramolecular interactions, starting from a simple amphiphilic terpyridine-based molecule TPYA. Notably, we report that stable terpyridine-based radicals can be generated by light or heat irradiation in polymeric hydrogels based on hydrogen bonding interactions between −COOH of PAA and the terpyridine motif of TPYA for the first time. The generation of radicals is confirmed by EPR and UV–vis experiments, and the process is accompanied by significant color changes from white to dark purple. The stable radical hydrogels prepared by the supramolecular strategy are self-healing, stretchable, and self-supporting and can be molded into different geometrical shapes. It is deduced that the generation of terpyridine-based radicals enhances the intermolecular hydrogen bonding and π–π interaction of molecules in a hydrogel matrix, which is responsible for the self-healing ability. Finally, we also show that the radical gels can selectively respond to ammonia and stretch with reversible color changes based on the reversible hydrogen-bonding interaction.