Controlling Molecular Conductance: Switching Off π Sites through Protonation

Conductance switching through chemical modification of a molecular bridge is a major goal in molecular electronics, with the potential to lead to molecule-based functional devices. In terms of switching speed, mechanisms that rely on only minor rearrangements of molecular structures are particularly promising. We demonstrate, based on density functional theory calculations combined with a coherent tunneling approach, how protonation and deprotonation of amine-substituted or amine-bridged model molecular wires can switch off and on pi-sites and thus: a) remove or introduce interference features in the electron transmission, and b) decrease or increase coupling along a chain. This mechanism may also be relevant for interactions between molecular bridges and metal cations, for example, in sensor applications.