Structure and Electrochemical Characterization of 4-Methyl-4‘-(<i>n</i>-mercaptoalkyl)biphenyls on Au(111)-(1 × 1)

Abstract

4-Methyl-4‘-(n-mercaptoalkyl)biphenyl (CH3−C6H4−C6H4−(CH2)n−SH, n = 1−6, BPn) monolayers self-assembled on Au(111)-(1 × 1) electrode surfaces were studied by scanning tunneling microscopy, cyclic voltammetry, and chronoamperometry. Distinct odd−even effects were found for the adlayer structures, the interfacial adlayer capacitances, as well as for the potentials and charges of reductive and oxidative desorption. The potential of zero charge, Epzc, of BPn- modified gold electrodes was estimated by a controlled immersion technique in hanging meniscus configuration to Epzc = −(0.30 ± 0.05) V, rather independent of the length of the alkyl spacer. The reductive desorption of BP3 and BP4 adlayers were quantitatively described by models based on hole nucleation and growth mechanisms, such as the exponential law of one-step hole nucleation (BP3), or hole nucleation according to a power law (BP3, BP4) in combination with a linear law of growth. No odd−even characteristics were found for the kinetic currents of the Fe(CN)64-/Fe(CN)63- redox reaction in the presence of BPn's. For the dependence on alkyl chain length, a structure sensitive attenuation parameter β = (11.5 ± 1.0) nm-1 was derived, which is interpreted according to a “through-bond” tunneling mechanism.