Voltage-driven control of single-molecule keto-enol equilibrium in a two-terminal junction system

Keto-enol tautomerism, describing an equilibrium involving two tautomers with distinctive structures, provides a promising platform for modulating nanoscale charge transport. However, such equilibria are generally dominated by the keto form, while a high isomerization barrier limits the transformation to the enol form, suggesting a considerable challenge to control the tautomerism. Here, we achieve single-molecule control of a keto-enol equilibrium at room temperature by using a strategy that combines redox control and electric field modulation. Based on the control of charge injection in the single-molecule junction, we could access charged potential energy surfaces with opposite thermodynamic driving forces, i.e., exhibiting a preference for the conducting enol form, while the isomerization barrier is also significantly reduced. Thus, we could selectively obtain desired and stable tautomers, which leads to significant modulation of the single-molecule conductance. This work highlights the concept of single-molecule control of chemical reactions on more than one potential energy surface. Keto-enol tautomerism offers a promising platform for modulating charge transport at the nanoscale. Here, the authors show that the keto-enol equilibrium can be modulated on the single-molecule scale by controlling charge injection in a two-terminal junction system.

Automated summary

By utilizing a strategy of redox control and electric field modulation, we successfully achieve single-molecule control of a keto-enol equilibrium at room temperature. Through the control of charge injection in the single-molecule junction, we can access charged potential energy surfaces with opposite thermodynamic driving forces, preferentially favoring the conducting enol form and significantly reducing the isomerization barrier. This allows us to selectively obtain desired and stable tautomers, leading to significant modulation of the single-molecule conductance. This work highlights the concept of single-molecule control of chemical reactions on multiple potential energy surfaces. Keto-enol tautomerism offers a promising platform for modulating charge transport at the nanoscale.