Probing the electrochemical reductive stability of decanethiol/triazole-ferrocene mixed self-assembled monolayers on Au

Abstract

Understanding the crit. factors that affect the electrochem. stability of functionalized mixed self-assembled monolayers (SAMs) is a cornerstone to improving the reductive stability of electroactive monolayers on transition metal electrodes. It is well-known that van der Waals forces play a large role in contributing to the electrochem. stability of SAMs, but less is known about how bulky terminal groups affect SAM packing in mixed-monolayers. In this presentation, we propose the reductive stability of mixed-SAMs on Au composed of ferrocene-terminated C11-thiol (Fc-C11-SH) and a C10-thiol (C10-SH) diluent as a model system for evaluating the electrochem. stability of electroactive mixed-monolayers with bulky terminal groups. Fc-C11-SH coverage is modulated by controlling the ratio of azide-terminated C11-thiols to the C10-SH diluent in the deposition soln. followed by "Click" chem. with ethynyl-ferrocene to form 1,2,3-triazole-ferrocene terminated SAMs. Reductive stability is probed by applying const. potentials followed by measuring the change in Fc-C11-SH coverage. Isotherms constructed from const. potential desorption were compared to desorption peaks from linear sweep voltammetry which is traditionally used to measure SAM electrochem. stability. The desorption potential was measured as a function of the fractional coverage of the Fc-C11-SH in the mixed monolayer. The SAM reductive stability was also measured under hydrodynamic flow using rotating disk electrodes to help reduce SAM re-adsorption, and the resulting desorption isotherms under hydrodynamic flow are compared to those measured in quiescent soln. Insights gained from this system will be applied to measuring the stability of SAMs on other transition metals (Cu, Ni) where traditional cyclic voltammetry fails to produce clear desorption peaks due to interference from the hydrogen evolution reaction.