Direct access to terpyridine-containing polyazamacrocycles as photosensitizing ligands for Eu(III) luminescence in aqueous media

The synthesis of new 18-membered hexaazamacrocycles containing a functionalized 2,2':6',2"-terpyridine moiety as part of the cyclic backbone and three acetate pendant arms is described. The reported synthetic procedure is based on the use of an efficient metal template ion effect which controls the macrocyclization step. This procedure is compatible with some functional groups present in the macrocyclic structure. The photophysical properties of the Eu(III) complexes derived from these ligands were examined in aqueous solutions. Their luminescence lifetimes (tau approximate to 1 ms) and quantum yields (13% < Phi < 18%) on one hand, their high kinetic inertness on the other hand, and the presence of additional functionality allowing their covalent conjugation to biomolecules seriously nominate these complexes as very promising candidates for luminescent labeling of biological materials.