Fabrication and Transport Properties of Single-Molecule-Thick Electrochemical Junctions

A V-shaped compound incorporating two bipyridinium units, which emanate from a central hydrophilic core and bear hydrophobic tetraarylmethane-based stoppers at each end, was designed and synthesized. In a thermodynamically controlled self-assembly process in solution, either one or two 1,4-dioxybenzene-based macrocyclic polyethers can be slipped over the bulky stoppers of the V-shaped compound, affording either a [2]rotaxane or a [3]rotaxane, respectively. The parent V-shaped compound and the two rotaxanes incorporate two redox-active bipyridinium units that can be reduced reversibly and two redox-active phenoxy groups in the stoppers that can be oxidized irreversibly. Furthermore, these three compounds have amphiphilic character and, as a result, form stable monolayers at the air/water interface. Langmuir−Blodgett monolayers of these compounds were sandwiched between two electrodes to afford molecule-based solid-state switches. In forward bias mode, the I−V characteristics of the junction are reversible,...