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.