Polyanionic Polydentate Europium Complexes as Ultrabright One- or Two-photon Bioprobes

International audienceA family of europium (III) complexes based on a polydentate ligand functionalized by charge‐transfer antennae presents remarkable one‐ and two‐photon photophysical proper‐ties in water or buffer. A detailed analysis of their emission properties suggests that the wrapping of the ligand around the central rare‐earth ion results in an overall Cs symmetry in agreement with the theoretical simulation and that about 65–70 % of the emission intensity is concentrated in the hypersensitive 5D0→7F2 transition at 615 nm. Their brightness is excellent, in the range of the best lanthanide bioprobes making them very attractive for bio‐imaging experiments