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Ordered Adlayers of a Combined Lateral Switch and Rotor

Rusch, Talina R., Schlimm, Alexander, Krekiehn, Nicolai R., Flöser, Benedikt M., Röhricht, Fynn, Hammerich, Melanie, Lautenschläger, Irene, Strunskus, Thomas, Herges, Rainer, Tuczek, Felix, Magnussen, Olaf M.
Journal of physical chemistry 2019 v.123 no.22 pp. 13720-13730
ambient temperature, gold, irradiation, moieties, nanotechnology, photochemistry, rotors, spectral analysis, ultraviolet radiation
Rotors and switches are elementary building blocks of molecular machines. To achieve more advanced functions, these units have to be integrated into solid-state devices, which triggered interest in mounting these functional units in well-defined geometries onto surfaces. While vertically oriented switches and rotors have been obtained by various strategies, the design of surface-parallel switches and of altitudinal rotors with an in-plane oriented rotation axis has proven to be more difficult. We here demonstrate a molecular adlayer system with highly defined geometry and laterally oriented functional groups that combines facile photoswitching and rotation. We employ a custom-designed molecule with two platforms and pillars that span an azobenzene unit between them. The molecules form well-ordered monolayers on Au(111) with the azobenzene units parallel to and above the surface. Spectroscopic data and density functional calculations suggest that in the trans configuration, at room temperature, the azo unit is freely rotating. Upon irradiation with UV light, the azo unit switches to the bent cis configuration and rotation stops. Irradiation with 430 nm restores the rotating trans state. Notably, the photochemistry is not quenched by the metal surface. This approach offers a promising strategy to operate molecular machines on metal surfaces with light, which is still a major problem in molecular nanotechnology.