Coordination Mode-Regulated Lanthanide Supramolecular Hydrogels with Tunable Luminescence and Stimuli-Responsive Properties

Hydrogels with tunable luminescence and stimuli responsiveness have attracted wide interest, owing to the desire to design soft machines and/or wearable electronic devices. Yet, it is challenging to obtain those that possess multicolorimetric change properties when exposed to complex mechanical stimuli and are strong, elastic, and capable of self-healing. Strong polymers with adjustable and switchable mechanical and fluorescence properties were designed using fluorescent lanthanide (Eu/Tb) as a cross-linker. The resulting compounds contained dynamic coordination and hydrogen bonds forming the physical cross-linking network; sodium 4-(allyloxy)­pyridine-2,6-dicarboxylate (SPD) and H2O ligands coordinated with Eu/Tb­(III) centers through different coordination modes and interactions. Three SPDs coordinated with Tb­(III), and two SPDs and three weaker H2O coordinated with Eu­(III). As a result, Eu/Tb–ligand bonds with different degrees of cleavages showed changes in the fluorescence color when exposed to complex mechanical stimuli. Also, for the reversible formation and dissociation of the Eu/Tb–SPD complexes, the designed hydrogel showed potential application in human fingerprint sensing.具有可调谐发光性能与刺激响应特性的水凝胶，因软质智能机器及可穿戴电子设备的研发需求而受到广泛关注。然而，制备同时具备复杂机械刺激下多比色变化特性，且兼具高强度、高弹性与自修复能力的此类水凝胶仍颇具挑战。本研究以荧光镧系元素（lanthanide，Eu/Tb）为交联剂，设计制备出兼具可调谐与可切换机械及荧光性能的高强度聚合物。所制备的聚合物体系包含动态配位键与氢键，可形成物理交联网络；4-烯丙氧基吡啶-2,6-二羧酸钠（sodium 4-(allyloxy)pyridine-2,6-dicarboxylate，SPD）与水分子（H₂O）配体通过不同配位模式与相互作用，与Eu/Tb(III)中心配位结合。其中，3个SPD配体与Tb(III)中心配位，2个SPD配体与3个结合力较弱的H₂O配体共同与Eu(III)中心配位。据此，当受到复杂机械刺激时，不同解离程度的Eu/Tb-配体键会表现出荧光颜色的变化。此外，由于Eu/Tb-SPD配合物可可逆形成与解离，所设计的水凝胶在人体指纹传感领域展现出潜在应用价值。