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 (DeltaE(1/2) = 67-200 mV) upon complexation with metal cations and a strong cathodic shift (DeltaE(1/2) = -82 to -100 mV) in the presence of F(-) and HP(2)O(7)(3-) anions. For the Zn(2+), Cd(2+), Hg(2+) and Pb(2+) metal cations tested, the change in the absorption spectra is accompanied by a dramatic colour change which allows the potential for "naked eye" detection.