An integrated experimental-theoretical approach to understand the electron transfer mechanism of adsorbed ferrocene-terminated alkanethiol monolayers

Abstract

In this work, the electron transfer mechanism of self-assembled monolayers of 6-ferrocenyl-1-hexanethiol (FcC6SH) on Au(111) substrates is addressed from two perspectives. To acquire a complete overview of the involved pathways, cyclic voltammetry and scanning electrochemical microscopy (SECM) were combined using an integrated experimental-theoretical approach. In the first case, the electrochemical behaviour is evaluated in the light of computer simulations of the experimental voltammetric response measured at successive potential scans in different supporting electrolytes. Successive potential scans change the lateral interactions between adsorbed Fc molecules that affect the oxidation of the electroactive monolayer. Furthermore, ion-pair formation between the oxidized ferrocene moieties and the anions of the supporting electrolyte controls the electron transfer process as well as the type of the lateral interactions. In the second case, a thin-layer cell based formalism is used to develop a new model to understand feedback SECM experiments carried out with an additional redox mediator in solution. Since these experiments sense the parallel pathways of the electron transfer mechanism (pinholes and direct electron tunnelling and mediated electron transfer through the monolayer), the results are processed by using the new developed model for the analysis of the multipathway electron transfer mechanism. On that sense, the experimental results are processed by using the new SECM model accounting for the parallel electron transfer via the monolayer and the pinholes simultaneously.