Purely Armchair or Partially Chiral: Noncontact Atomic Force Microscopy Characterization of Dibromo-Bianthryl-Based Graphene Nanoribbons Grown on Cu(111)

Abstract

We report on the atomic structure of graphene nanoribbons (GNRs) formed via on-surface synthesis from 10,10'-dibromo-9,9'-bianthryl (DBBA) precursors on Cu(111). By means of ultrahigh vacuum noncontact atomic force microscopy with CO-functionalized tips we unveil the chiral nature of the so-formed GNRs, a structure that has been under considerable debate. Furthermore, we prove that-in this particular case-the coupling selectivity usually introduced by halogen substitution is overruled by the structural and catalytic properties of the substrate. Specifically, we show that identical chiral GNRs are obtained from 9,9'-bianthryl, the unsubstituted sister molecule of DBBA.

Dibromobianthryl ordering and polymerization on Ag(100)

“…By inspection, it would appear that the STM images most closely match that shown in Figure 5(b), which would mirror the interaction found on Cu(111) [10].…”

“…In fact, it may be that the Ullmann reaction is not important in this system, as has been shown for DBBA adsorption atop Cu(111) [10]. …”

“…Following polymerization, the temperature is raised further and cyclodehydrogenation occurs, with the result that the DBBA chains flatten into GNRs as C-C bonds form between the angled moieties. This happens as described for Ag(111) and Au(111) substrates, but, following some controversy, it has recently become unambiguously clear that the molecules line up side-by-side on a Cu(111) substrate, following which polymerisation into chiral GNRs occurs [10], meaning that Ullmann dissociation is not crucial for this process. This has been further supported by the successful growth of identical chiral GNRs using bianthryl precursors without terminal Br atoms, reported in the same study.…”

“…There has been some controversy regarding the formation of purely armchair versus partially chiral GNRs from DBBA on Cu(111) [9,10]. This originated in di↵ering interpretations of the relative orientation of DBBA molecules in the rows of molecules that form as precursors to GNRs.…”

“…The progression of DBBA to GNRs has been described at length [5][6][7][8][9][10]. The use of DBBA has apparently been motivated by a wish to use the advantageous Ullmann dissociation reaction to polymerize DBBA in an ordered, Br-end to Br-end, fashion [5].…”