A matter of doping: Graphene nanoribbons (GNRs) were generated through an on‐surface bottom‐up synthesis and selectively doped at their edges by introducing nitrogen atoms in the precursor monomers. While the size of the band gap of 2.8 eV remains almost unchanged upon N substitution, a linear shift of the band structure is observed and corresponds to n‐type doping (see picture; CB=conduction band and VB=valence band).

Angle-resolved two-photon photoemission and high-resolution electron energy loss spectroscopy are employed to derive the electronic structure of a sub-nanometer atomically precise quasi-onedimensional graphene nanoribbon (GNR) on Au(111). We resolved occupied and unoccupied electronic bands including their dispersion and determined the band gap, which possesses an unexpected large value of 5.1 eV. Supported by density functional theory (DFT) calculations for the idealized infinite polymer and finite size oligomers an unoccupied non-dispersive electronic state with an energetic position in the middle of the band gap of the GNR could be identified. This state resides at both ends of the ribbon (end state) and is only found in the finite sized systems, i.e. the oligomers.

No abstract

Eine Frage der Dotierung: Graphen‐Nanobänder (GNRs) wurden auf einer Oberfläche in einer Bottom‐up‐Synthese hergestellt und selektiv an den Ecken durch Einführen von Stickstoffatomen in den Vorstufen dotiert. Während die Bandlückengröße von 2.8 eV durch die N‐Substitution beinahe unverändert bleibt, wird eine lineare Verschiebung der Bandstruktur beobachtet, die einer n‐Dotierung entspricht (siehe Bild; CB=Leitungsband, VB=Valenzband).

Spiropyrans are prototype molecular switches, which undergo a reversible photoinduced ring-opening/-closure reaction between the closed three-dimensional spiropyran (SP) and the open, planar merocyanine (MC) form. In solution the SP isomer is the thermodynamically stable form. Using high resolution electron energy loss spectroscopy, we resolve a thermally-activated irreversible ring-opening reaction of nitrospiropyran resulting in the MC form for coverages above one monolayer. Thus, the situation found in solution is reversed for the adsorbed molecules, since the MC form is more stable due to the modified energetics by the presence of the substrate. In addition, illumination with blue light (445 nm) induced also the ring-opening, while the photostimulated back-reaction could not be observed. The photoisomerization is driven by a substrate-mediated process, i.e. a charge transfer from the substrate into molecular states. The situation changes completely in the monolayer regime. Neither a thermally-assisted nor a photoinduced ring-opening reaction has been identified. We ascribe the suppression to sterical effects stabilizing the SP form due to the surface structure of Bi(1 1 4), which consists of straight atomic rows separated by rough valleys.