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 Cr(3+) in aqueous solution was assembled by a low-selectivity luminogenic receptor with Cu(2+) 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 Cu(2+) efficiently quenches the emission. The further addition of Cr(3+) into the Cu(2+)-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.