Ethynyl Substituents as Rheostatic Triggers in Single‐Molecule Junctions

ABSTRACT Miniaturised mechanoresistive devices, where charge transport efficiency is modulated by mechanical displacement, are an important class of electromechanical systems that promise unique sensing accuracy and sensitivity. Single‐molecule junctions have emerged recently as the ultimately scaled down system, operating in the quantum realm. Several strategies have been developed to impart mechanoresistivity to a molecular junction, but all these require structural modifications to the conducting backbone, to introduce either short‐circuiting anchoring points to the electrode or conformationally flexible moieties. Here, we show a synthetically accessible way to impart mechanoresistivity, by adding silyl‐protected ethynyl functional groups that extend the π‐system orthogonally to the transport axis. Junctions fabricated with ethynyl‐extended acenes demonstrate strong and reproducible mechanoresistivity, with log‐linear dependence of conductance on displacement and large amplitude (> 10 2 per nanometer). Analytical and density functional modeling demonstrate that the compressed junctions are better coupled to the electrodes, due to overlap between the extended π‐system and the density of states of the Au electrodes. As ethynyl moieties are trivial to attach to a variety of substrates, we expect this strategy to be widely applicable as a synthetically advantageous way to impart mechanoresistivity to a wide variety of molecular wires.