Current developments and future perspectives on the formation of luminescent lanthanide supramolecular self-assembly architectures with a focus on nitrogen-based donor ligands

Abstract

Research on luminescent lanthanide (Ln) self-assembly structures has emerged into a discrete field with clear evolution from monometallic to polymetallic systems over the last few decades. The interest in these assemblies stems, on the one hand, from their structural diversity and fascinating complexity, while on the other hand, from the unique luminescence properties of the lanthanide ions, allowing for the expansion of their applications from materials science to mimicking biological systems. This review begins with a description of the recent advances in the design and properties of monometallic Ln³⁺ self-assemblies, with a particular focus on tridentate motifs, such as dpa, pybox, and btp, and other non-tridentate nitrogen donor ligands. Later, polymetallic systems, including helicates and metallocages, are described with their structures, followed by an elaboration on how a careful ligand design allows for the modification of the overall assembly (i.e. helical, tetrahedral, cubic and other polyhedra). The influences of counter-anions, concentrations, metal:ligand ratios and solvents are also discussed. The fascinating new developments within mechanically interlocked molecules containing lanthanide ions are highlighted with a focus on their structural complexity and reversible binding properties. Furthermore, this review will focus on the functional properties of lanthanide assemblies including their temperature-dependent luminescence, host–guest interaction and aggregation-induced emission. The use of such ligands in metallo-supramolecular polymers is briefly discussed, including their application in the generation of luminescent hydrogels, supramolecular polymers and other conventional polymers. We conclude this review with the perspective of exploring the biological properties and toxicity of lanthanide complexes, their application in imaging, and the recovery of lanthanides for sustainable use as well as their promising applications in smart materials, sensing and diagnostics.