Polymer networks cross-linked by the metal–organic polyhedra have attracted dramatic attention in recent years due to the high degrees of freedom in tuning their structures and functions. Particularly, the 4f electrons from lanthanide ions have offered the lanthanide organic complex with unique magnetic and optical properties. Herein, for the first time, we proposed a facile scheme to construct polymer hydrogels with superior stretchability, strong luminescence, and magnetic resonance relaxation properties via the incorporation of a minute amount of lanthanide organic polyhedra as the cross-links. A bipyridyl bis-tetrazole ligand, bearing an alkene group, was synthesized for coordination with Ln³⁺ (Eu³⁺ and/or Gd³⁺) ions in water to form lanthanide organic polyhedra complexes (K₂₄Ln₈L₁₂), which were subsequently used as cross-linkers (0.0083–0.033 mol % of the monomer) for the free radical polymerization with acrylamide monomers to obtain Ln-polyhedra hydrogels. Thanks to the large functionalities and the dynamic feature in lanthanide metal coordination complexes as the network junctions, a tiny amount of cross-linker has rendered these hydrogels superior stretchability exceeding 4200% and tensile stress at break beyond 400 kPa at a stretching rate of 100 mm/min. In addition, Eu³⁺ and Gd³⁺ polyhedra can offer hydrogels with a high luminescence quantum yield and efficient magnetic resonance relaxation properties, respectively. In particular, Eu³⁺ and Gd³⁺ ions can coassemble with the ligand to form K₂₄Eu_xGd_8–xL₁₂ polyhedra, simultaneously rendering the cross-linked hydrogels superior stretchability, strong luminescence, and fast spin–lattice relaxation rate, and thus a great potential for applications in both luminescent and magnetic resonance imaging.

中文翻译：

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由微量水溶性镧系元素有机多面体交联的高可拉伸和发光聚合物水凝胶


近年来，由金属-有机多面体交联的聚合物网络因其在调整其结构和功能方面的高度自由度而引起了极大的关注。特别是，来自镧系元素离子的 4f 电子为镧系元素有机络合物提供了具有独特磁性和光学特性的有机络合物。在此，我们首次提出了一种简单的方案，通过掺入微量的镧系元素有机多面体作为交联，构建具有优异可拉伸性、强发光和磁共振弛豫性能的聚合物水凝胶。合成了带有烯烃基团的双吡啶基双四唑配体，用于与水中的 Ln³⁺（Eu³⁺ 和/或 Gd³⁺）离子配位，形成镧系有机多面体络合物 （K₂₄Ln₈L₁₂），随后用作交联剂（单体的 0.0083-0.033 mol %）与丙烯酰胺单体进行自由基聚合，得到 Ln-多面体水凝胶。由于镧系金属配位配合物作为网络连接物中的强大官能团和动态特性，少量交联剂使这些水凝胶在 100 mm/min 的拉伸速率下具有超过 4200% 的优异拉伸性和超过 400 kPa 的断裂拉伸应力。此外，Eu³⁺ 和 Gd³⁺ 多面体可以分别提供具有高发光量子产率和高效磁共振弛豫特性的水凝胶。 特别是，Eu³⁺ 和 Gd³⁺ 离子可以与配体共组装形成 K₂₄Eu_xGd_8–xL₁₂ 多面体，同时使交联水凝胶具有优异的可拉伸性、强发光和快速的自旋晶格弛豫速率，因此在发光和磁共振成像中具有很大的应用潜力。