Local cation-tuned reversible single-molecule switch in electric double layer

The nature of molecule-electrode interface is critical for the integration of atomically precise molecules as functional components into circuits. Herein, we demonstrate that the electric field localized metal cations in outer Helmholtz plane can modulate interfacial Au-carboxyl contacts, realizing a reversible single-molecule switch. STM break junction and I-V measurements show the electrochemical gating of aliphatic and aromatic carboxylic acids have a conductance ON/OFF behavior in electrolyte solution containing metal cations (i.e., Na+, K+, Mg2+ and Ca2+), compared to almost no change in conductance without metal cations. In situ Raman spectra reveal strong molecular carboxyl-metal cation coordination at the negatively charged electrode surface, hindering the formation of molecular junctions for electron tunnelling. This work validates the critical role of localized cations in the electric double layer to regulate electron transport at the single-molecule level. A common approach to design single-molecule switch is to use molecular backbones in response to external stimulus, but often requires complex organic synthesis. Here, Tong et al. show how to in situ control of the molecule-electrode contact using electrochemical gating to realize a reversible switch.

Automated summary

This study demonstrates that the electric field localized metal cations in outer Helmholtz plane can regulate interfacial Au-carboxyl contacts, achieving a reversible single-molecule switch. STM break junction and I-V measurements show that the conductance of aliphatic and aromatic carboxylic acids can be toggled on/off through electrochemical gating in the presence of metal cations (e.g. Na+, K+, Mg2+, and Ca2+). In situ Raman spectra reveal strong carboxyl-metal cation coordination at the negatively charged electrode surface, which hinders the formation of molecular junctions for electron tunnelling. This work highlights the crucial role of localized cations in the electric double layer in regulating single-molecule electron transport.