Effect of Charge-Assisted Hydrogen Bonds on Single-Molecule Electron Transport

The effect of the in-backbone presence of charge-assisted hydrogen bonds (CAHBs) in the conductance of single-molecule junctions has been studied by the scanning tunneling microscope break junction technique. In particular, two amidinium–carboxylate supramolecular complexes of different lengths have been tested. We observed that the ionic character that gives extra stability to the CAHB is a hindrance toward the electron transport through the complexes. Theoretical calculations using the DFT + Σ method indicate that both the highest occupied molecular orbital and lowest unoccupied molecular orbital of the complexes are fully localized in only one of the moieties of the complex explaining the low single-molecular conductance of the compounds.