Shape-persistent ladder molecules exhibit nanogap-independent conductance in single-molecule junctions

Molecular electronic devices require precise control over the flow of current in single molecules. However, the electron transport properties of single molecules critically depend on dynamic molecular conformations in nanoscale junctions. Here, we report a unique strategy for controlling molecular conductance using shape-persistent ladder molecules. Chemically diverse, charged ladder molecules, synthesized via one-pot multicomponent ladderization strategy, show a molecular conductance (dlog(G/G0)/dx ≈ -0.1 nm-1) that is nearly independent of junction displacement x, in stark contrast to the nanogap-dependent conductance (dlog(G/G0)/dx ≈ -7 nm-1) observed for non-ladder analogs. Ladder molecules show an unusually narrow distribution of molecular conductance during dynamic junction displacement which is attributed to the shape-persistent backbone and restricted rotation of terminal anchor groups. Our results further show that molecular conductance remains unaffected by the chemical identity of counterions or substitution groups on the ladder backbone. Overall, our work provides new avenues for controlling molecular conductance using shape-persistent ladder molecules.