Time-resolved luminescence in aqueous solution -: New europium labels derived from macro(bi)cyclic ligands with aminocarboxylic units

A new family of macro(bi)cyclic ligands has been designed and synthesized, with the goal of developing lanthanide labels suitable for time-resolved luminescence-based biological applications. They are constructed from diamide (3) or tetralactam (4) complexing moieties associated with an intracyclic 2,2'-bipyridine chromophore and two exocyclic carboxylic groups. The luminescence properties of their Eu3+ complexes were studied in aqueous solution. In this medium, noticeable enhancements in the lifetime and quantum yield were observed, in comparison with those of other bipyridine-based ligands considered interesting as luminescent labels. The effects of coordinated water molecules, LMCT states, and ligand triplet state energy on the nonradiative deactivation processes to the ground state were examined. According to these results and in view of the stability of these complexes in aqueous solutions, the (Eu(3)](+) complex may be considered as a promising luminescent bioprobe.