Electrochemical Identification of Molecular Heterogeneity in Binary Redox Self-Assembled Monolayers on Gold

Abstract

Ferrocenylalkanethiols are excellent probes to study the structure and properties of mixed self-assembled monolayers (SAMs) on gold; in this paper, the molecular heterogeneity in binary redox-active SAMs on gold prepared via postassembly exchange and coadsorption processes is revealed electrochemically. The exchange process of single-component 11-ferrocenyl-1-undecanethiolate SAMs on gold (FcC11S–Au) with 1-undecanethiol (C11SH) is first investigated; it is shown that a single pair of redox peaks can be obtained upon prolonged immersion in C11SH/ethanol solution. For the coadsorption of FcC11SH and C11SH on gold, the splitting of the redox peak diminishes when the molar ratio FcC11SH decreases to <10%. The binary FcC11S-/C11S–Au SAMs with low surface density of ferrocene moieties prepared by these two methods are compared by fitting the cyclic voltammograms (CVs) in considering their intermolecular interactions. The essentially different distributions of the redox centers in these diluted binary SAMs, as indicated by the varied formal potentials and intermolecular repulsion forces, provide further insights in understanding molecular self-assembly processes on the surface.