Water soluble molecular switches of fluorescence based on the Nilll/Nill redox change

The water soluble Ni-II complexes of the cyclam derivatives with 1,3-benzodioxole and 1,2,3-trimethoxybenzene display the fluorescent emission typical of the covalently linked fluorophores, which results from a charge transfer excited state. On oxidation to Nil", the fluorescence is completely quenched due to the occurrence of an electron, transfer (eT) process from the excited fluorogenic fragment FI* to the oxidized metal. Thus, fluorescence can be switched off/on at will, for several cycles, by consecutively oxidizing and reducing the metal center, in controlled potential electrolysis experiments both in acetonitrile and in aqueous 0.1 M HClO4. Occurrence of an eT process from FI* to Ni-II ultimately depends upon the easy oxidation of FI to FI+, whereas failure of the occurrence of an eT process from Ni-II to FI* has to be ascribed to the particular resistance of FI fragments to the reduction.