Substitution Pattern Controlled Quantum Interference in [2.2]Paracyclophane-Based Single-Molecule Junctions

Abstract

Quantum interference (QI) of electron waves passing through a single-molecule junction provides a powerful means to influence its electrical properties. Here, we investigate the correlation between substitution pattern, conductance, and mechanosensitivity in [2.2]paracyclophane (PCP)-based molecular wires in a mechanically controlled break junction experiment. The effect of the <i>meta</i> versus <i>para</i> connectivity in both the central PCP core and the phenyl ring connecting the terminal anchoring group is studied. We find that the <i>meta</i>-phenyl-anchored PCP yields such low conductance levels that molecular features cannot be resolved; in the case of <i>para</i>-phenyl-coupled anchoring, however, large variations in conductance values for modulations of the electrode separation occur for the pseudo-<i>para</i>-coupled PCP core, while this mechanosensitivity is absent for the pseudo-<i>meta</i>-PCP core. The experimental findings are interpreted in terms of QI effects between molecular frontier orbitals by theoretical calculations based on density functional theory and the Landauer formalism.