Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.)

The variable and versatile co-ordination behaviour of lanthanide metal ions, Ln^III, limits their selective introduction into organised molecular or supramolecular architectures. The design of lanthanide-based devices is thus a special challenge since their specific electronic, magnetic or spectroscopic properties result from a precise control of the co-ordination sphere around the metal ions. The lock-and-key principle associated with the preorganisation of rigid macropolycylic multidentate ligands tailored for one particular Ln^III only partially fulfils these structural requirements. The development of less constrained macrocyclic ligands or macrocycles bearing pendant arms allows a smooth transition toward flexible (predisposed) receptors leading to the application of the induced fit principle in lanthanide co-ordination chemistry. According to this concept, programmed secondary non-covalent interstrand interactions (π-stacking, hydrogen bonds, electrostatic repulsion) assist the complexation process leading to an ultra-fine tuning of the metallic co-ordination sites. These two complementary approaches are discussed and evaluated for the design of organised mono-, di- and polymetallic lanthanide complexes together with the consideration of new semi-rigid multidentate podands which combine both aspects.