Single Molecule Conductance of Anthraquinone-Based Molecular Wire: Effect of the Anchoring Group

Functional molecular electronics require molecular design that provides integrity and stability. In this work, we explored two types of single molecule devices differing in anchoring to the conducting leads. Single molecule conductance was measured by STM break junction method and the molecular conductor was composed of the redox active anthraquinone center (switching element) containing either 4-pyridyl or p-phenylene thioacetate anchoring groups. The experimental results were supported by quantum chemical charge transport calculations. Molecular junctions containing 4-pyridyl anchors displayed two stable configurations with conductance values of 4.9 nS and 20 pS, respectively. Molecules anchored via p-phenylene thioacetate groups led to one main junction configuration with conductance of 0.1 nS. Junctions employing 4-pyridyl anchoring groups had higher junction formation probability, which in combination with lower conductance makes them better candidates for switching purposes.