Luminescent metalloreceptors with pendant macrocyclic ionophores with NS2O3 donor sites: Synthesis, characterization and ion-binding property

Abstract Three new luminescent metalloreceptors have been synthesized, incorporating the Ru(II)-bipyridine moiety as a fluorogenic unit and a six membered macrocyclic moiety containing NS 2 O 3 donor atoms as ionophores. The sulfur donor atoms have been incorporated to enhance the complexing ability of the ionophore towards heavy metal ions, although for comparison, an ionophore having NO 5 donor sites has also been used. The ion-binding property of these fluoroionophores has been investigated with a large number of cations and anions, and the recognition event is monitored by fluorescence and NMR spectroscopy. The luminescence intensity is strongly quenched in the presence of Cu 2+ and Fe 3+ for 1 ; Cu 2+ , Fe 3+ , Hg 2+ and Pb 2+ for 2 and with Cu 2+ for 3 , indicating strong complexation of these metal ions with the ionophore. The fluoroionophore 2 also exhibited strong interactions with the anions F − , H 2 PO 4 − and I − . A 1 H NMR study was carried out to get information about the binding site of the ions with the ionophores. Binding constants ( K s ) and the composition of the complexes formed for all the three fluoroionophores with strongly interacting ions have been determined from emission titration data. The K s values for the metal ions are in the range 3.19 × 10 2 –8.86 × 10 3  M −1 and for anions they are in the range 8.89 × 10 2 –5.33 × 10 3  M −1 . The ion-selectivity and energy transfer involved in quenching process have been discussed.