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Coordination-Assembled Water-Soluble Anionic Lanthanide Organic Polyhedra for Luminescent Labeling and Magnetic Resonance Imaging.

Lanthanide-containing functional complexes have found a variety of applications in materials science and biomedicine because of their unique electroptical and magnetic properties. However, the poor stability and solubility in water of multi-component lanthanide organic assemblies significantly limit their practical applications. We report here a series of water-stable anionic Ln2nL3n-type (n = 2, 3, 4, and 5) lanthanide organic polyhedra (LOPs) constructed by deprotonation self-assembly of three fully-conjugated ligands (H4L1 and H4L2a/b) featuring a 2,6-pyridine bitetrazolate chelating moiety. The outcomes of the LOPs were found to be very sensitive toward the reaction conditions including base, metal source, solvents and concentrations as characterized by a combination of NMR, high-resolution ESI-MS and X-ray crystallography. Ligands H4L2a/b manifested an excellent sensitization toward lanthanide ions (Ln = EuIII and TbIII), with high luminescent quantum yields for Tb8L2a12 (Φ = 11.17% in water) and Eu8L2b12 (Φ = 76.75% in DMSO) measured in polar solvents. Furthermore, due to the giant molecular weight and rigidity of the polyhedral skeleton, Gd8L2b12 showed a very high longitudinal relaxivity (r1) of 400.53 mM-1S-1. The performance of Gd8L2b12 as potential magnetic resonance imaging contrast agents (CAs) in vivo was evaluated with much longer retention time in the tumor sites compared with the commercial GdIII-based CAs. Dual-modal imaging potential has also been demonstrated with the mixed Eu/Gd LOPs. Our results not only provide a new design route toward water-stable multi-nuclear lanthanide organic assemblies but also offer potential candidates of supramolecular-edifices for bioimaging and drug delivery.