Turn-On Luminescent Sensing of Metal Cations via Quencher Displacement: Rational Design of a Highly Selective Chemosensor for Chromium(III)

A highly selective luminescent chemosensor for Cr3+ in aqueous solution was assembled by a low-selectivity luminogenic receptor with Cu2+ as a metal quencher. Three tetranitrogen chelating sites were integrated into the multichannel receptor with a tris(1,10-phenanthroline)ruthenium(II) luminophore at the core. This receptor (2) exhibits chelating affinity for many transition-metal cations, among which Cu2+ efficiently quenches the emission. The further addition of Cr3+ into the Cu2+-titrated solution of 2 results in a metal-exchange reaction and a sensitive turn-on luminescence response highly selective over other metal cations. The quencher displacement sensing strategy in this design can be a simple but efficient approach for OFF–ON luminescent sensing of metal cations that inherently lack selective ligands.