Vibrational Excitations & Conformational Switching in Single-Molecule Junctions

Johannes V. Barth^a, Hai Bi^a, Carlos-Andres Palma^a, Yuxian Gong^a, Peter Hasch^a, Mark Elbing^b, Marcel Mayor^b^,^c, Joachim Reichert^a

^aTechnical University of Munich, Physics Department, D-85748 Garching, Germany

^bInstitute of Nanotechnology, Karlsruhe Institute of Technology, D-76021 Karlsruhe, Germany

^cDepartment of Chemistry, University of Basel, Spitalstrasse, 51, Basel, Switzerland

Materials for Sustainable Development Conference (MATSUS)
Proceedings of nanoGe Fall Meeting 2018 (NFM18)

S5 Charge Carrier Dynamics at the Nanoscale

Torremolinos, Spain, 2018 October 22nd - 26th

Organizers: David Egger, Arjan Houtepen and Freddy Rabouw

Invited Speaker, Johannes V. Barth, presentation 179
DOI: https://doi.org/10.29363/nanoge.nfm.2018.179
Publication date: 6th July 2018

The development of robust, chemically-sensitive techniques is crucial for the advancement of single-molecule electronics. Studies in single-molecule junctions largely rely on indirect electrical characterization to statistically evaluate the chemistry and quality of the established circuits. One fundamental challenge is the direct, quantitative determination of charge-vibrational coupling for well-defined single-molecule junctions. The ability to record molecular charge-vibrational coupling for individual species grants access to the determination of maximal charge transport efficiencies for specific molecular configurations and currents. Here we explore the charge-vibrational coupling for current-carrying tethered molecules by combined vibrational and metal-molecule-metal junction current-voltage spectroscopy. By inspecting the steady-state vibrational distribution during charge transport in a bis-phenyl-ethynyl-anthracene derivative by Raman scattering, we deduce a coupling constant of ≈0.35 vibrational excitations per charge carrier. Furthermore we follow the conformational response of a two-state molecular switch. Specifically, we remove the ground state polarizability and symmetry of a known p-terphenyl-4,4´´-dithiol (TPD) molecule by employing the 2,2´,5´,2´´-tetramethylated (TM-TPD) derivate. Whereas the highly sterically hindered, non-planar TM-TPD, lacking π-conjugation, in its pristine conformation does not exhibit a Raman signature, a marked on/off modulation of the single-molecule Raman signal exceeding a factor of 100 is achieved via redox state control by means of the applied voltage.

Support by the Deutsche Forschungsgemeinschaft (DFG) via SPP 1234 (Grant RE2592) & Munich Centre for Advanced Photonics (MAP), the European Research Council via Advanced Grant MolArt (n° 247299) and Chinese Scholarhip Council (H.B., Y.G.) is gratefully acknowledged.

Key refs.: JACS 140 (2018) 4835 | Nature Comm. 7 (2016) 10700 | Nature Nanotechn. 7 (2012), 673

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