An important class of supramolecular systems are those capable of forming dimers held together by multiple linear H-bonds. Of these, the 4 H-bond arrays based on the ureidopyrimidone or UPy unit have found particularly use, having the right combination of ease-of-synthesis and appropriate binding strengths to be useful for the formation of supramolecular polymers and gels. The selling points for these materials are there self-healing properties. By application of heat or mechanical stress the polymer chains will break reversibly at the H-bonds making the material more fluid and allowing a defect to fill in. Upon cooling or relief of the mechanical stress, the H-bonds re-form locking the repair in place. For many applications the use of heat or mechanical stress as the external signal to alter structure is perfect, however, for other applications, a more selective stimulus such as electron transfer would be advantageous. To do this, a reversible redox couple needs to be attached to the UPy in such a way that oxidation or reduction perturbs the H-bond strength. Over the last several years, we have synthesized and investigated the electrochemistry of several such systems, shown below. With UPyH, there is a phenylenediamine redox couple attached to the urea allowing perturbation of the H-donating ability of the urea NH. In the other examples, the redox couple, either a pyridinium [UPy(MeP⁺)] or a ferrocene [UPy(Fc)], is attached to the pyrimidone ring, allowing perturbation of the H-accepting ability of the pyrimidine N and O. In addition to their potential use in redox-responsive supramolecular materials, these compounds also provide good platforms for fundamental investigations on the role of H-bonding in proton-coupled electron transfer. Indeed, our studies show that with both UPyH and UPy(MeP⁺) electron transfer leads to proton transfer, resulting in interesting, albeit rather complicated electrochemistry. In both these cases, electron transfer would be expected to increase H-bond strength. In contrast, with UPy(Fc), oxidation should decrease H-bond strength. The result is no proton transfer and greatly simplified electrochemistry, which is more amenable to future supramolecular applications. A thorough analysis of the voltammetry indicates a 10⁷ decrease in K_dim upon oxidation. This result coupled with the high stability of the oxidized form suggests UPy(Fc) is highly amenable to supramolecular applications. Currently we are working on the synthesis of linked UPy(Fc)’s suitable for the formation of supramolecular polymers. Progress on this work will be reported.