Coordination-Assembly of Lanthanide Supramolecular Hydrogels with Luminescent Multi-stimulus Response

Luminescent supramolecular hydrogels have shown extensive potential for a variety of applications due to their unique optical properties and biocompatibility. Coordination self-assembly provides a promising strategy for the preparation of supramolecular hydrogels. In this contribution, a series of luminescent lanthanide (Ln) supramolecular hydrogels HG-Ln₂L₃^1/2 are synthesized by coordination self-assembly of Ln ions and V shaped bis-tetradentate ligands (H₄L¹ and H₄L²) with different bent angles (∠B). Two rigid conjugated ligands H₄L¹ and H₄L² with bent angles (∠B ≈ 150°) featuring a 2,6-pyridine bitetrazolate chelating moiety were designed and synthesized, which generated hydrogels via the deprotonation self-assembly with lanthanide ions. Characteristic Eu³⁺ and Yb³⁺ emissions were realized in the corresponding hydrogels, with intriguing multi-stimulus response behaviors. The luminescence of the HG-Eu₂L₃¹ hydrogel can be enhanced or quenched when stimulated by diverse metal ions, attributed to the replacement of the coordinated lanthanide ions and changes in the intersystem crossing efficiency of the ligand. Furthermore, pH-responsive emission of the HG-Eu₂L₃¹ hydrogel has also been observed. Our work provides potential strategies for the design of next-generation smart responsive hydrogel materials with variable structures.