Multiplexing, time-resolution, FRET…lanthanide-based biolabels reveal exceptional spectroscopic properties for bioanalytical applications.

Up conversion is an Anti-Stokes luminescent process by which photons of low energy are piled up to generate light at a higher energy. Here we show that the addition of fluoride anions to a D₂O solution of a macrocyclic erbium complex leads to the formation of a supramolecular [(ErL)₂F]⁺ assembly in which fluoride is sandwiched between two complexes, held together by the synergistic interactions of the Er-F-Er bridging bond, four intercomplex hydrogen bonds and two aromatic stacking interactions. Room temperature excitation into the Er absorption bands at 980 nm of a solution of the complex in D₂O results in the observation of up converted emission at 525, 550 and 650 nm attributed to Er centred transitions via a two-step excitation. The up conversion signal is dramatically increased upon formation of the [(ErL)₂F]⁺ dimer in the presence of 0.5 equivalents of fluoride anions.