High conductivity and a tunability of the band gap make quasi-one-dimensional
graphene nanoribbons (GNRs) highly interesting materials for the use in field
effect transistors. Especially bottom-up fabricated GNRs possess well-defined
edges which is important for the electronic structure and accordingly the band
gap. In this study we investigate the formation of a sub-nanometer wide
armchair GNR generated on a Au(111) surface. The on-surface synthesis is
thermally activated and involves an intermediate non-aromatic polymer in which
the molecular precursor forms polyanthrylene chains. Employing angle-resolved
two-photon photoemission in combination with density functional theory
calculations we find that the polymer exhibits two dispersing states which we
attribute to the valence and the conduction band, respectively. While the band
gap of the non-aromatic polymer obtained in this way is relatively large,
namely 5.25 ± 0.06 eV, the gap of the corresponding aromatic GNR is strongly
reduced which we attribute to the different degree of electron delocalization
in the two systems