Electrical molecular switch addressed by chemical stimuli

Abstract

We demonstrate that the conductance switching of benzo-bis(imidazole) molecules upon protonation depends on the lateral functional groups. The protonated H-substituted molecule shows a higher conductance than the neutral one (G_pro > G_neu), while the opposite (G_neu > G_pro) is observed for a molecule laterally functionalized by amino-phenyl groups. These results are demonstrated at various scale lengths: self-assembled monolayers, tiny nanodot-molecule junctions and single molecules. From ab initio theoretical calculations, we conclude that for the H-substituted molecule, the result G_pro > G_neu is correctly explained by a reduction of the LUMO–HOMO gap, while for the amino-phenyl functionnalized molecule, the result G_neu > G_pro is consistent with a shift of the HOMO, which reduces the density of states at the Fermi energy.