Ordered Adlayers of a Combined Lateral Switch and Rotor

Abstract

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.

Rotation of Ethoxy and Ethyl Moieties on a Molecular Platform on Au(111)

“…Rotor molecules deposited on surfaces may be investigated at a submolecular scale using scanning tunneling microscopy (STM). , The compounds thus studied fall into two classes. Either molecular adsorbates serve as a rotor and the substrate is used as a stator − or the stator and the rotor are subunits of the same molecule. − Besides rotors there are also rotary switches that alternate between two rotation angles − and consequently do not enable studies on the directionality of the motion, which is essential for using a rotor in a motor. , …”

Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling

“…Furthermore, the TOTA platform and the related compound triazatriangulenium are very versatile and the methyl moiety may be exchanged for other moieties of interest. This has been demonstrated for small moieties such as hydrogen, ethyl, ethynyl, and propynyl as well as porphyrins, diazocine, norbornadiene, imine, and azobenzene derivatives …”

“…Furthermore, honeycomb superstructures may turn out useful to control the density of functional molecules on surfaces. In the context of platform molecules, where a functional unit is attached to a molecular base, the pattern of the platforms is imposed on the functional units.…”

Coverage‐Controlled Superstructures of C3‐Symmetric Molecules: Honeycomb versus Hexagonal Tiling

“…This has been demonstrated for small moieties such as hydrogen, ethyl, ethynyl, and propynyl [43][44][45] as well as porphyrins,diazocine,norbornadiene,imine,and azobenzene derivatives. [32,35,40,41,[46][47][48] Using low-temperature scanning tunneling microscopy (STM) along with density functional theory (DFT) calcula-Abstract: The competition between honeycomb and hexagonal tiling of molecular units can lead to large honeycomb superstructures on surfaces.Suchsuperstructures exhibit pores that may be used as 2D templates for functional guest molecules.H oneycomb superstructures of molecules that comprise aC 3 symmetric platform on Au(111) and Ag(111) surfaces are presented. The superstructures cover nearly mesoscopic areas with unit cells containing up to 3000 molecules,m ore than an order of magnitude larger than previously reported.…”

“…[26] Although this control via coverage should, in principle,e nable superstructures of any size,t he largest unit cells reported so far were comprised of some two hundred molecules per unit cell. Furthermore,h oneycomb superstructures may turn out useful to control the density of functional molecules on surfaces.I nt he context of platform molecules, [32][33][34] where af unctional unit is attached to am olecular base, [35][36][37][38][39][40][41][42] the pattern of the platforms is imposed on the functional units.…”