Luminescence cation sensing by ruthenium(II) complexes containing an iminodiacetic acid-appended ligand

A series of ruthenium(II) polypyridine complexes with iminodiacetic acid-containing ligand have been synthesized and characterized. The photophysical properties of the complexes at different pH were studied. Distinct emission occurred from both the protonated and deprotonated species. The pKa values both in the ground state and excited state for the deprotonation–protonation associated with the iminodiacetic acid groups on the ligands were determined. The cation-binding properties of these complexes for lanthanide ions have been studied by electronic absorption spectroscopy, emission and cyclic voltammetry. The binding constants Ks for europium(III) and lanthanum(III) ions have been determined.