Characterization of Helicene Molecules for Molecular Electronics

Helical molecules have been proposed as candidates for producing spin-polarized currents, even at room conditions, due to their chiral asymmetry. However, describing their transport mechanism in single molecular junctions is not straightforward. In this work, we study the electronic transport in break junctions of a series of three helical molecules: dithia[n]helicenes, with n = 7, 9, and 11 molecular units [1,2,3] . The different molecules are deposited on top of Au(111) surfaces and visualized using a Scanning Tunneling Microscope under ambient conditions. The electronic transport of the single molecules is characterized by the Mechanically Controlled Break Junction Technique and through the STM-BJ Technique.

Our experimental measurements and clustering-based analysis demonstrate low conductance values that remain similar across different applied voltages and molecules. Additionally, we assess the length dependence of the conductance for each helicene, revealing an exponential decay characteristic of off-resonant transport. This behavior is primarily attributed to the misalignment between the energy levels of the molecule−electrodes system. The length dependence trend described above is supported by ab initio calculations, further confirming an off-resonant transport mechanism.

References

[1] T. de Ara et al. J. Phys. Chem. Lett. 2024, 15, 8343

[2] B.C. Baciu et al. J. Mater. Chem. C, 2022, 10, 14306

[3] B.C. Baciu et al. Nanoscale Adv., 2020, 2, 1921