title: Cooperative Switching in Nanofibers of Azobenzene Oligomers.
abstract: Next-generation molecular devices and machines demand the integration of molecular switches into hierarchical assemblies to amplify the response of the system from the molecular level to the meso- or macro-scale. Here, we demonstrate that multi-azobenzene oligomers can assemble to form robust supramolecular nanofibers in which they can be switched repeatedly between the E- and Z-configuration. While in isolated oligomers the azobenzene units undergo reversible photoisomerization independently, in the nanofibers they are coupled via intermolecular interactions and switch cooperatively as evidenced by unusual thermal and kinetic behavior. We find that the photoisomerization rate from the Z-isomer to the E-isomer depends on the fraction of Z-azobenzene in the nanofibers, and is increased by more than a factor of 4 in Z-rich fibers when compared to E-rich fibers. This demonstrates the great potential of coupling individual photochromic units for increasing their quantum efficiency in the solid state with potential relevance for actuation and sensing.
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Christopher
authors.initials: C
authors.lastname: Weber
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Liebig
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Manuel
authors.initials: M
authors.lastname: Gensler
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Anton
authors.initials: A
authors.lastname: Zykov
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Linus
authors.initials: L
authors.lastname: Pithan
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.|IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Jürgen P
authors.initials: JP
authors.lastname: Rabe
authors.affiliation: IRIS Adlershof, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.|Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Hecht
authors.affiliation: Department of Chemistry, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Bléger
authors.affiliation: Department of Physics, Humboldt-Universität zu Berlin, 12489 Berlin, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Kowarik