Reversible On–Off Luminescence Switching in Self-Healable Hydrogels

We present herein an easy way to prepare novel responsive hydrogels by simply doping lanthanide complexes into a polymer hydrogel, poly­(2-acrylamido-2-methyl-1-propanesulfonicacid) (PAMPSA). The resulting hybrid hydrogels can be readily processed into a range of shapes. Both the on–off luminescence switching and the healable properties are simultaneously achieved in the resulting responsive hybrid hydrogels. They exhibit effectively self-healing performance without any external stimulus and reversible “on–off” luminescence switching triggered by exposure to acid–base vapor. The key to this on–off luminescence switching behavior is that the protonation of the organic ligands compete with full coordination to Ln³⁺ and that incomplete coordination affects the luminescence yield. The high proton strength in the resulting hydrogels makes the doped lanthanide complexes unstable, and ammonia (or triethylamine) vapor can dramatically decrease the proton strength through neutralization, driving the full coordination of the ligand to Ln<sup>3+