Heteroditopic ligands based on ferrocenyl benzimidazoles fused to an additional diaza heterocyclic ring system

The synthesis of ferrocene-based heteroditopic receptors in which the ferrocene moiety is attached to an imidazo[4,5-e]benzothiadiazole or imidazo[4,5-f]quinoxaline is reported. These nitrogen-rich ferrocene derivatives show remarkable ion-sensing properties because of the presence of the redox active ferrocene unit and the polyazaheteroaromatic ring systems which act as a dual binding site for anions and metal cations. They display an anodic shift of the oxidation wave (Delta E-1/2 = 67-200 mV) upon complexation with metal cations and a strong cathodic shift (Delta E-1/2 = -82 to -100 mV) in the presence of F- and HP2O73- anions. For the Zn2+, Cd2+, Hg2+ and Pb2+ metal cations tested, the change in the absorption spectra is accompanied by a dramatic colour change which allows the potential for naked eye detection.