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Influence of Conformation on Conductance of Biphenyl-Dithiol Single-Molecule Contacts

2009; American Chemical Society; Volume: 10; Issue: 1 Linguagem: Inglês

10.1021/nl903084b

1530-6992

Artem Mishchenko, David Vonlanthen, Velimir Meded, Marius Bürkle, Chen Li, Ilya V. Pobelov, A. Bagrets, J. K. Viljas, Fabian Pauly, Ferdinand Evers, Marcel Mayor, Thomas Wandlowski,

Quantum and electron transport phenomena

The conductance of a family of biphenyl-dithiol derivatives with conformationally fixed torsion angle was measured using the scanning tunneling microscopy (STM)-break-junction method. We found that it depends on the torsion angle φ between two phenyl rings; twisting the biphenyl system from flat (φ = 0°) to perpendicular (φ = 90°) decreased the conductance by a factor of 30. Detailed calculations of transport based on density functional theory and a two level model (TLM) support the experimentally obtained cos2 φ correlation between the junction conductance G and the torsion angle φ. The TLM describes the pair of hybridizing highest occupied molecular orbital (HOMO) states on the phenyl rings and illustrates that the π−π coupling dominates the transport under "off-resonance" conditions where the HOMO levels are well separated from the Femi energy.