How important is the quenching influence of the transition metal ions in the design of fluorescent PET sensors?

The fluorescence response of a nitrobenzoxadiazole fluorophore, attached to an amine receptor through a spacer unit, in the presence of a strongly quenching metal ion Cr3+ is reported. It is shown that the supramolecular system exhibits considerable enhancement of fluorescence in the presence of the metal ion, despite the quenching nature of the metal ion. This observation is rationalised in terms of the excited state lifetime of the fluorophore and the possible implication of this result in the design of fluorosensors for the quenching transition metal ions is discussed