Single-molecule contact switching via electro-inductive effects†

The non-faradaic application of electric fields generated at the surface of charged electrodes to polarize bound molecules, also termed as electro-inductive effects, have recently attracted increasing attention in modifying the chemical reactivity of molecules in electrosynthesis. Herein, we applied this electro-inductive effect to control the Lewis adduct formation and dissociation between BF₃ and pyridine N of heterocycles to realize single-molecule contact switching. In situ single-molecule conductance measurements, in situ Raman analysis and theoretical calculations clearly show that the outward electric field along the positively-charged electrode surface polarizes adsorbed molecules to withdraw electron density from the terminal pyridine N, which weakens the N–BF₃ Lewis bond for dissociation upon applied positive potentials. The released unbounded pyridine N can connect the molecule into a molecular circuit for electron transfer (considered as the “ON” state). Meanwhile, the inward electric field along the negatively charged electrode surface promotes the formation of an N–BF₃ Lewis bond, leading to breaking of the molecular circuit (considered as the “OFF” state). Combined with the optimization of BF₃ concentration from the equilibrium BF₄⁻ ⇌ BF₃ + F⁻, the electro-inductive effect can reversibly switch single-molecule conductance in conductance measurements and tunnelling currents in I–V measurements.