title: Influence of conformation on conductance of biphenyl-dithiol single-molecule contacts.
abstract: 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 phi between two phenyl rings; twisting the biphenyl system from flat (phi = 0 degrees ) to perpendicular (phi = 90 degrees ) 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 cos(2) phi correlation between the junction conductance G and the torsion angle phi. The TLM describes the pair of hybridizing highest occupied molecular orbital (HOMO) states on the phenyl rings and illustrates that the pi-pi coupling dominates the transport under "off-resonance" conditions where the HOMO levels are well separated from the Femi energy.
authors.affiliation: Department of Chemistry and Biochemistry, University of Bern, Bern, Switzerland.
authors.forename: Artem
authors.initials: A
authors.lastname: Mishchenko
authors.forename: David
authors.initials: D
authors.lastname: Vonlanthen
authors.forename: Velimir
authors.initials: V
authors.lastname: Meded
authors.forename: Marius
authors.initials: M
authors.lastname: Bürkle
authors.forename: Chen
authors.initials: C
authors.lastname: Li
authors.forename: Ilya V
authors.initials: IV
authors.lastname: Pobelov
authors.forename: Alexei
authors.initials: A
authors.lastname: Bagrets
authors.forename: Janne K
authors.initials: JK
authors.lastname: Viljas
authors.forename: Fabian
authors.initials: F
authors.lastname: Pauly
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Evers
authors.forename: Marcel
authors.initials: M
authors.lastname: Mayor
authors.forename: Thomas
authors.initials: T
authors.lastname: Wandlowski
mesh_terms: D001713:Biphenyl Compounds / Q000737:chemistry*; D002625:Chemistry, Organic / Q000379:methods; D003460:Crystallization; D004553:Electric Conductivity; D004563:Electrochemistry / Q000379:methods; D008670:Metals / Q000737:chemistry; D016252:Microscopy, Scanning Tunneling / Q000379:methods; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D049329:Nanostructures; D036103:Nanotechnology / Q000379:methods; D011789:Quantum Theory; D014050:Toluene / Q000031:analogs & derivatives* / Q000737:chemistry
chemical_list: D001713:Biphenyl Compounds; D008670:Metals; D014050:Toluene; C010574:biphenyl; C004848:dithiol