Sensitised luminescence from lanthanide complexes offers many potential advantages in imaging and assay, particularly when coupled with time-gating protocols that can be used to gate out background signal. In this perspective, we discuss the routes by which lanthanide arrays and polymetallic d-f hybrids can be prepared by conventional synthesis and self-assembly, and discuss and evaluate the possibilities for exploiting and evaluating the intermediates in the sensitisation process, with particular emphasis on the mechanisms of energy transfer.

Alkyne appended lanthanide complexes derived from DO3A undergo copper catalysed cycloaddition reactions with azides to form triazole appended complexes: coordination of one of the triazole nitrogen atoms to the metal centre changes the local coordination environment and the spectroscopic properties of the complex.

A series of bimetallic complexes has been prepared in which an octadentate DOTA-monoamide pocket containing a bound lanthanide ion is linked covalently to a Re(I) or Ru(II) bipyridyl unit via an alkyl spacer group. The transition metal chromophores incorporated in this way act as effective sensitisers for lanthanide-centred luminescence. The rate and efficiency of energy transfer are dependent upon the nature of the spacer group, and upon the nature of the lanthanide acceptor. For the RuNd diad, there is a long rise-time associated with the energy-transfer step, such that energy transfer is rate determining in H(2)O, but not in D(2)O. The results also lead us to suggest that energy transfer may precede formation of the (3)M((Ru/Re))L((bpy))CT state and may be a competitive deactivation pathway for the precursor state ((1)M((Ru/Re))L((bpy))CT).

Homodinuclear lanthanide complexes derived from a ligand featuring two DO3A chelating sites linked by a 4,4'-dimethyl-2,2'-bipyridyl spacer were prepared and characterized. The bipyridyl coordination site of 1 was used to introduce Ru(Bpy)(2) and Re(CO)(3)Cl moieties, leading to the formation of heterometallic d-f(2) complexes with general formulae [Ln(2)·1·Ru(Bpy)(2)](2+) (Ln = Nd, Eu, Tb, Yb and Lu) and [Ln(2)·1·Re(CO)(3)Cl] (Ln = Nd, Yb and Lu). The luminescence properties of the complexes were investigated by means of absorption spectroscopy and steady-state and time-resolved luminescence spectroscopy covering the visible and NIR regions. Both Ru and Re chromophores were shown to act as efficient sensitizers of the NIR emission of Yb and Nd in aqueous solutions. We also consider the unsaturated coordination spheres of the Ln cations in the Ln(2)·1 complexes, which form ternary complexes with bidentate anions without showing particular synergistic effects for polyanionic species.