Electrochemically controlled hydrogen bonding for supramolecular assembly: Challenges and opportunities

The electrostatic nature of the hydrogen bond makes it straightforward, in principle, to electrochemically perturb the strength of hydrogen bonds by using oxidation to create stronger H-donors or reduction to create stronger H-acceptors. However, oxidation or reduction can also lead to proton transfer and subsequent electron transfer, which can nullify the effect of the initial electron transfer. Illustrative examples of these complications based on a series of investigations of electroactive, urea-containing 2 H-bond dimers are described. It is also shown that proton transfer accompanying electron transfer can be used to advantage with two examples of oxidative dissociation of 4 H-bond dimers that are of interest for the construction of supramolecular polymers and gels. In both cases proton transfer is key to achieving the desired outcome. Moving forward, it is argued that proton transfer should always be considered as a possible useful component in the design of electrochemically controllable H-bonding systems.