Characterizing intermolecular interactions in redox-active pyridinium-based molecular junctions

Intermolecular interactions play a key role in the charge transport properties of molecular electronic devices. In this work, we characterize charge transport in redox-active pyridinium-based molecular junctions mediated by host-guest interactions and intermolecular electrostatic effects. Charge transport through single pyridinium molecules generally shows that intramolecular conductance occurs over displacements consistent with the molecular contour length. However, pyridinium-based junctions exhibit charge transport over reduced molecular displacements upon increasing the solution concentration of the charged pyridinium complex, which is attributed to intermolecular electrostatic effects. Interestingly, formation of host-guest complexes via addition of a crown ether resulted in recovery of charge transport over molecular displacements corresponding to single pyridinium junctions at low concentrations, thereby suggesting that host-guest complexes efficiently screen electrostatic repulsions between cationic molecules. Bulk electrochemical characterization shows that pyridinium molecules exhibit stable redox-active properties over a wide array of conditions. Overall, this work opens new avenues for utilizing host-guest interactions that may be useful in informing the design of new redox-active flow batteries or programmable electronic devices.