ADSORPTION BEHAVIOR OF FUNCTIONALIZED FERROCENYLALKANE THIOLS AND DISULFIDE ONTO AU AND ITO AND ELECTROCHEMICAL PROPERTIES OF MODIFIED ELECTRODES - EFFECTS OF ACYL AND ALKYL-GROUPS ATTACHED TO THE FERROCENE RING

The effects of introduction of the acyl and alkyl groups into the ferrocene ring on the redox potentials and the adsorption behavior were investigated by studying the electrochemical characteristics of Au and ITO electrodes modified with six novel ferrocenylalkane thiol and disulfide derivatives. On introducing an acyl group into the ferrocene ring, the redox potentials of the modified electrodes in 0.1 M HClO4 shifted in the positive direction by ca. 300 mV per acyl group. This shift is due to the electron-withdrawing effect of the carbonyl group. Introduction of a butyl group into the ring shifted the redox potential about 15 mV in the positive direction, possibly because of steric hindrance of counter-ion movement. The surface concentration of these ferrocene derivatives was estimated from the redox charge of the ferrocene moieties. Both the maximum surface concentration Gamma(max) and the adsorption rate constants k(ad) on Au and ITO decreased as the number of the acyl groups increased. The effect of the butyl group on Gamma(max) and k(ad) was smaller. Both Gamma(max) and k(ad) of the disulfide derivative on Au were smaller than those of the corresponding thiol derivative. Although the redox potentials were the same at the modified Au and ITO electrodes, both Gamma(max) and k(ad) on ITO were much smaller than those on Au.