We have identified a simple experimental protocol to assemble electroactive films with attractive electron transport properties on gold electrodes. Their basic building block is a bipyridinium bisthiol, which adsorbs spontaneously on the electrode surface forming multiple electroactive layers. The resulting interfacial assemblies mediate the transfer of electrons from the electrode to redox probes in the electrolyte solution but prevent electron transfer in the opposite direction. After the insertion of electroactive anionic dopants in the polycationic bipyridinium matrix, the transfer of electrons from the redox probes to the electrode becomes possible. Under these conditions, the probe reduction accompanies that of the surface-confined bipyridinium dications, while the probe reoxidation follows the oxidation of the anionic dopants. This intriguing behavior imposes a large potential difference between the voltammetric reduction and oxidation peaks of the probe, which parallels the difference between the bipyridinium reduction and the dopant oxidation potentials. Thus, the careful selection of the electroactive dopant can be exploited to tune the electronic properties of the composite film. This chemical approach to interfacial assemblies with controlled dimensions and engineered properties can lead to electrode/organic film/electrode junctions with predefined current/voltage signatures.