The design of nanoscale electronics is an important technical objective with significant scientific challenges. Single-molecule junctions are considered as potential building blocks of nano-electronic devices (e.g. switches and diodes), whose physical and chemical properties can be modulated in a controllable manner. In particular, the orientation and coordination of the molecule relative to the electrode can dramatically affect the electrical properties of the junction. In this study, we use the unique power of electrochemical scanning tunneling microscopy (EC-STM), in combination with the break junction (BJ) method, to measure charge transport through two fundamentally important molecules, TCNQ and F4TCNQ. Our experimental results recorded on the negatively charged Au(111) electrode show discrete conductance values ranging from 0.24 G0 to 0.02 G0. In conjunction with the experiment, density functional theory (DFT) and non-equilibrium Green’s function (NEGF) calculations were performed to reveal distinct junction configurations allowing for different directions of charge transport relative to the molecular π-system and a varying number of anchoring groups with the electrodes. The calculated transmission functions show that the conductance increases with lower molecule-electrode denticity. This is a result of smaller molecular orbital offset with respect to the Fermi level of the electrode as the denticity is reduced. The findings of this study highlight the importance of orientation, denticity and orbital alignment as controlling factors in the design of efficient nanoscale devices such as in dye-sensitized solar cells, molecular switches, and sensors.

Effect of denticity and orientation control on single molecule charge transport

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.