Synthesis of graphene nanoribbons with defined mixed edge-site sequence by surface assisted polymerization of (1,6)-dibromopyrene on Ag(110)

It is now well established that the polymerization process at the base of the bottom-up production of graphene nanostructures on noble metals occurs in two steps. The former is the de-halogenation process, which often involves the formation of an organometallic intermediate with metal atoms extracted from the surface, followed by a surface catalysed C-C bond formation (Ullman coupling reaction). The latter consists of a thermally induced dehydrogenation of these surface species with the formation of further C–C covalent bonds. In the last years, a number of experimental and theoretical works have characterized both the graphene-based nanostructures and the chemical path leading from the molecular precursors to the final products. Both organometallic intermediates and final products are strongly dependent on the nature of the initial halogenated precursor as well as on chemical nature and atomic structure of the substrate. 

The surface-catalysed polymerization reaction of 1,6-dibromopyrene (DBP) on Ag(110) has been investigated by complementary experimental and theoretical methods: X-ray spectroscopic (XPS) techniques, scanning tunneling microscopy (STM) and density functional theory calculations. The brominated pyrene derivative was chosen as a prototypical planar polycyclic hydrocarbon molecule with a shape suppressing the almost fixed adsorption geometry typical, for example, of the rod-shaped dibromotetracene. We show the self-assembled structures generated upon annealing the DBP multilayer to 150 °C and discuss their subsequent, thermally induced dehydrogenation. As final product, we observe the formation of C–conjugated polymers with alternated zig-zag and armchair edge sites, the length and order of which can be tuned by acting both on the annealing process and on the initial DBP coverage.  These GNRs are monodispersed in width and significantly narrower than those obtained from the much more common DBBA precursor. 

This work was supported by the Italian MIUR through progetto premiale ABNANOTECH, FIRB RBAP11ETKA and  the national grant Futuro in ricerca 2012 RBFR128BEC ‘‘Beyond graphene: tailored C-layers for novel catalytic materials and green chemistry’’

Synthesis of graphene nanoribbons with defined mixed edge-site sequence by surface assisted polymerization of (1,6)-dibromopyrene on Ag(110)
Marco Smerieri, Igor Píš, Lara Ferrighi, Silvia Nappini, Angelique Lusuan, Cristiana Di Valentin, Luca Vaghi, Antonio Papagni, Mattia Cattelan, Stefano Agnoli, Elena Magnano, Federica Bondino and Letizia Savio

Nanoscale (2016).