Self-Assembled Lanthanide-Cored Dendrimer Complexes:  Enhancement of the Luminescence Properties of Lanthanide Ions through Site-Isolation and Antenna Effects

The site isolation of lanthanide cations (Er 3+, Tb 3+, and Eu 3+ ) has been achieved through the self-assembly of three convergent polyether dendrons, each with a carboxylate anion focal point, around the central trivalent cation. Evidence for the self-assembly of the dendritic complexes can be obtained by a variety of spectroscopic and other analytical means both in solution and in the solid state. The luminescence properties of these new dendrimers measured both in solution and in the bulk show a dependence of luminescence activity on the size of the dendritic shell. The observed enhancement in luminescence properties can be attributed both to a large antenna effect, involving the nonconjugated phenyl benzyl ether dendrimer framework, and to a shell effect that results from the effective site isolation of each lanthanide cation within a dendritic sphere, preventing their mutual interaction and decreasing their rate of self-quenching. The site isolation afforded by self-assembly and the antenna effect provided by the polyether dendrimer may be of general applicability in the design of energy-harvesting devices and amplifiers for fiber optics.