Relaxation and luminescence studies on hydrated bipyridyl- and terpyridyl-based lanthanide complexes
Abstract
The synthesis of the novel ligand, based on a 2,2’-bipyridine functionalized by a carboxylate function and a methyleneiminodiacetate group is described. Its europium complex has been prepared and characterized.
The spectroscopic properties were studied by means of absorption and luminescence spectroscopy. Although the complex displays a very good sensitization efficiency, the overall luminescence quantum yield is rather poor.
This results from strong non-radiative deactivations due to the presence of three water molecules in the first coordination sphere. The relaxation properties of the Gd3+ complexes obtained with two ligands, the latter containing an additional pyridine ring in the aromatic core, were assessed by means of 17O NMR and 1H NMRD.
The water exchange rates are faster than those of currently used contrast agents. The rotational correlation time appeared to be long, pointing to a hindered rotation due to the larger aromatic frame.