Building Pentagons into Graphenic Structures by On-Surface Polymerization and Aromatic Cyclodehydrogenation of Phenyl-Substituted Polycyclic Aromatic Hydrocarbons

Five-membered carbon rings play a crucial role in determining the geometric structures and electronic properties of carbon-based materials. However, incorporating five-membered rings into low-dimensional carbon nanomaterials with atomic precision is still a challenge. Here, we report on the on-surface synthesis of a one-dimensional conjugated polymer comprising fluoranthene subunits obtained by the surface-assisted aromatic cyclodehydrogenation of 1-phenylnaphthalene moieties within the precursor monomers. By using scanning tunneling microscopy (STM), we investigate the formation of the polymer by thermally induced dehalogenative aryl–aryl coupling and subsequent aromatic cyclodehydrogenation on a Au(111) substrate. The formed five-membered carbon rings are directly observed with atomic resolution by noncontact atomic force microscopy (nc-AFM). Our results show that carefully designed phenyl-substituted polycyclic aromatic hydrocarbons can be used for the rational fabrication of five-membered rings in the bottom-up synthesis of carbon-based nanomaterials and thus add a further tool to the emerging field of on-surface synthesis.