Signal amplification by a fluorescent indicator of a pH-driven intramolecular translocation of a Copper(II) ion

An auxillary light-emitting fragment (coumarin-343) binds to a CuII ion in the right-hand compartment (B) of the ligand shown and its fluorescence is "switched off". If the pH value is raised from 7 to 11 the metal moves to the left compartment (A), which imposes a square stereochemistry and forces dissociation of the indicator, thus "switching on" the fluorescence. The pH-driven metal translocation is reversible and can be carried out for many cycles.