Ferrocene-thiophene dyads with azadiene spacers: electrochemical, electronic and cation sensing properties

The synthesis, electrochemical, electronic and cation sensing properties of ferrocene-thiophene ligands, linked by 2-aza-1,3-butadiene bridges, whose characteristics have been systematically varied by introducing the ferrocene moiety at the 1- or 4-position of the aza bridge, are presented. Spectroelectrochemical studies revealed the presence of low-energy bands in the partially oxidized forms, which indicate the existence of intramolecular electron-transfer between the iron center and the organic bridges. Some of the reported ligands have also shown to be efficient chemosensors for metal ions. Compounds 5a and 5b function as highly selective chemosensors for Mg2+ ions, while not showing any response to Ca2+ or alkali metal ions, whereas ligand 3b shows a selective sensing response to the soft Cd2+ metal ions over Hg2+ cations.