Ionic Liquid Gating Enol–Keto Tautomerism

Keto-enol tautomerism plays an important role in functional organic synthesis, pharmaceutical chemistry, biological activity, and molecular-scale charge transport. It is, therefore, critical to find a reliable approach to manipulate keto-enol tautomerism at the single-molecular level. In this study, we demonstrated that the β-diketone derivative, which existed dominantly in the enol form, can be reversibly switched between keto and enol forms with remarkable conductance discrepancy by modulating the electrochemical potential of the gate electrode in an ionic liquid, paving the way for the fabrication of single-molecule circuit switches. It has been recognized for a long time that the enol-keto tautomerism is governed by an excited intramolecular proton transfer process, and we provide evidence that the enol-keto tautomerism in the biased electro-circuit is governed by the proton-coupled electron transfer (PCET) rather than the intramolecular proton transfer (IPT) upon the electrochemical-gated ionic interfacial redistribution, clarifying the mechanism of keto-enol tautomerism in circuits and benefiting the application of tautomerism in different research areas.