Efficient luminescence from fluorene- and spirobifluorene-based lanthanide complexes upon near-visible irradiation

We describe herein the synthesis and photophysical characterization of new lanthanide complexes that consist of a (9,9-dimethylfluoren-2-yl)-2-oxoethyl or a (9,9-spirobifluoren-2-yl)-2-oxoethyl unit as the antenna, covalently linked to a 1,4,7,10-tetraazacyclododecane-1,4,7-triacetic acid (DO3A) unit as the Ln3+ (Gd3+, Eu3+, Sm3+, Tb 3+, Dy3+) coordination site. We were able to translate the spectroscopic properties of the innovative bipartite ligands into the formation of highly luminescent europium complexes that exhibit efficient emission (φse>0.1) upon sensitization in the near-visible region, that is, with an excitation wavelength above 350 nm. The luminescence of the Eu 3+complexes is clearly detectable at concentrations as low as 10 pM. Furthermore, the structural organization of these bipartite ligands makes the complexes highly soluble in aqueous solutions and chemically stable over time. Lighting up: Innovative fluorene- and spirobifluorene-based lanthanide complexes show efficient luminescence upon sensitization in the near-visible region. Lanthanide emission is detectable at concentration as low as 10 pM in aqueous solution (see figure).