Multifunctionalized luminescent lanthanide complexes from nonadentate phosphonylated bis-pyrazolyl-pyridine ligands

A series of lanthanide complexes has been prepared from ligands constructed from a bis-pyrazolyl-pyridine core bearing various chelating arms with anionic mixed carboxylate/phosphonate or phosphonate substituents. These ligands form particularly stable complexes with Eu(III) and Tb(III) which display outstanding spectroscopic properties, with excited state lifetimes ranging from 2.6 to 3.2 ms and quantum yields in the 16 to 48% range in water or phosphate buffer. The complexes are significantly more stable than those of analogous ligands bearing only carboxylate groups. Some of the new ligands have a central and flexible pendent link suitable for bio-labelling.