Lanthanide bindings of phenanthroimidazole-based clicked cage-ligands; designed by schiff base condensation

Phenanthroimidazole-based cage-ligands 1 and 2 and their Eu(III), La(III) lanthanide complexes were synthesized and characterized. Schiff base condensation is the main step to obtain cage-shaped ligand design. Connection between clicked-phenanthroimidazole dipodal aldehyde and a fluorescent amine resulted great numbers of possible bindings that make the cage-shaped ligands suitable for lanthanide bindings. Lanthanide selectivities of the ligands 1 and 2 were investigated towards Dy(III), Yb(III), Er(III), Tb(III), La(III) and Eu(III) ions by absorption and emission studies in half-aqueous medium. The binding stoichiometries with the most fluorescence quenching ion Eu(III) were determined by Job's plotting as 1:1 ratio between ligand/Eu(III). The binding constants were calculated as 1.074 × 104 M−1 for 1 and 6.67 × 103 M−1 for 2 according to the concentration studies and the limit of detections (LOD) were determined as 5.23 × 10−4 μM for 1 and 4.65 × 10−4 μM for 2 by Benesi-Hildebrand plotting.