Controlling the Surface Structure of Viologen SAMs through Dilution: CV and XPS Studies

Functionalizing electrodes with self-assembled monolayers (SAMs) is a highly tunable way to alter their function and performance. Mixed SAMs of redox-active and inactive molecules can quickly alter electrode function. However, control of the formation process and modeling of the resultant surface structure is challenging. We report the results of experiments that modified Au electrodes with mixed SAMs of viologen and two redox-inactive diluent molecules. Mixed SAMs were formed with the dual purpose of (1) increasing SAM stability through increased molecular density and (2) separating viologen molecules to minimize intermolecular interactions. These mixed SAMs were characterized by cyclic voltammetry (CV) and X-ray photoelectron spectroscopy (XPS). We observed that the polar diluent molecule formed SAMs with an increasingly heterogeneous distribution of viologen microenvironments. The nonpolar diluent molecule formed SAMs with regions of viologen surrounded by diluent molecules. Our results provide valuable insights into controlling electrode functionalization and surface structure with charged redox species through dilution and diluent molecule properties.