A general purpose reporter for cations: absorption, fluorescence and electrochemical sensing of zinc(II)

A fluorescent sensor has been synthesized that comprises a pyrene moiety tethered to a [2,2':6',2"]-terpyridyl ligand via a diethynylated thiophene linker. This multicomponent supermolecule is highly emissive in solution but addition of Zn2+ cations results in a drastic decrease in the fluorescence yield. Complexation between Zn2+ cations and the vacant terpyridyl ligand has been confirmed by NMR spectroscopy and by electrospray mass spectrometry. The ES-MS results provide strong support for the formation of both 1 : 1 and 1 : 2 (metal : ligand) complexes in solution. Complexation is further evidenced by a pronounced shift in the absorption spectrum, by the appearance of a long-wavelength band in the fluorescence spectrum and by cyclic voltammetry. On the basis of UV-visible spectrophotometric titrations, overall binding constants of log beta(1) approximate to 5.1 and log beta(2) approximate to 9.9 were derived for the 1 : 1 and 1 : 2 complexes, respectively, in acetonitrile solution. The possible application of this system as a generic chemical sensor for cationic species, is mentioned.