title: High on-off conductance switching ratio in optically-driven self-assembled conjugated molecular systems.
abstract: A new azobenzene-thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7 x 10(3) (with an average value of 1.5 x 10(3)) is reported. The "on" conductance state is clearly identified to the cis isomer of the azobenzene moiety. The high on/off ratio is explained in terms of photoinduced, configuration-related changes in the electrode-molecule interface energetics (changes in the energy position of the molecular orbitals with respect to the Fermi energy of electrodes) in addition to changes in the tunnel barrier length (length of the molecules). First principles density functional calculations demonstrate a better delocalization of the frontier orbitals as well as a stronger electronic coupling between the azobenzene moiety and the electrode for the cis configuration over the trans one. Measured photoionization cross sections for the molecules in the SAM are close to the known values for azobenzene derivatives in solution.
authors.affiliation: Molecular Nanostructures & Devices Group, Institute for Electronics Microelectronics and Nanotechnology, CNRS & University of Lille, B.P. 60069, 59652 Villeneuve d'Ascq, France.
authors.forename: Kacem
authors.initials: K
authors.lastname: Smaali
authors.forename: Stéphane
authors.initials: S
authors.lastname: Lenfant
authors.forename: Sandrine
authors.initials: S
authors.lastname: Karpe
authors.forename: Maïténa
authors.initials: M
authors.lastname: Oçafrain
authors.forename: Philippe
authors.initials: P
authors.lastname: Blanchard
authors.forename: Dominique
authors.initials: D
authors.lastname: Deresmes
authors.forename: Sylvie
authors.initials: S
authors.lastname: Godey
authors.forename: Alain
authors.initials: A
authors.lastname: Rochefort
authors.forename: Jean
authors.initials: J
authors.lastname: Roncali
authors.forename: Dominique
authors.initials: D
authors.lastname: Vuillaume