Electroactive Self-Assembled Monolayers: Putting Surface-Confined Redox Reactions to Work

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The proposed research is aimed at harnessing redox-terminated monomolecular films to electrochemically activate, drive, and modulate physicochemical processes at solid-liquid interfaces in ways that can potentially facilitate the development of macro- to nano-scale electrochemical technologies. Self-assembled monolayers (SAMs) of organothiolates, functionalized with ferrocene, biferrocenylene, electron donor or electron acceptor moieties, chemisorbed to gold surfaces are used as electroactive molecular interfaces. Charge-transfer-induced changes in these redox-active SAMs will be exploited for micromechanical actuation and the formation of two-dimensional ensembles, including solid-supported lipid membranes, films of lyotropic liquid crystal nanomaterials, and nanoparticle arrays. The objective of the former research thrust is to establish how small (angstrom-scale) conformational changes can be electrochemically triggered and harnessed to perform much larger-scale mechanical work, while that of the latter is to demonstrate how the interfacial ion pairs or charge transfer complexes generated by a redox stimulus can be used to create surface-adsorbed assemblies. We specifically seek to establish the roles played by the steric crowding of the redox moieties, number of repeat units in the monolayer backbone, (supra-)molecular organization in the monolayer, intermolecular van der Waals interactions, and the strength of the ion pair or charge transfer interactions on the processes investigated. Charge storage in binary SAMs comprising two ferrocene derivatives with nonoverlapping redox potentials, as well as biferrocenylene-terminated SAMs, whose redox stability is far superior to that of the usual ferrocene-terminated counterparts, will be investigated for the development of electrochemically robust multistate molecular switches. Finally, the effect of localized surface plasmon excitation on the Faradaic electrochemistry and chemical lability of surface-tethered molecules will be explored with the aim of facilitating surface-confined electrochemical reactions and enabling the regiospecific chemical functionalization of nanostructures. The expected outcomes are the development of redox- and light-mediated processes for manipulating molecular events at solid-liquid interfaces and that can be used to engineer functional redox-responsive systems such as electromechanical actuators, electronic memories or electrooptical devices.**