SENSORS AND SWITCHES FROM SUPRAMOLECULAR CHEMISTRY

Efficient sensors for metal ions can be made by assembling an appropri ate receptor with a fluorescent fragment. The occurrence of the recept or/cation interaction is signalled through a sharp change of the fluor escence emission. The situation is especially favourable in the case o f transition metal ions, which are typically redox active and provide an electron release to the excited fluorophore (or uptake therefrom), causing fluorescence quenching. Thus, the supramolecular design of flu orescent sensors should consider a ligating subunit able to promote th e redox activity of the envisaged metal ion. An identical approach can be used for the synthesis of moleculer redox switches, i.e. systems i n which the distinctive property of a given subunit (e.g. fluorescence ) is controlled by an adjacent control subunit, sensitive to the varia tion of the redox potential. Couples involving metal centres can be co nveniently used to switch on/off the fluorescence of the proximate flu orophore through the variation of the redox potential.