On-surface activation of benzylic C-H bonds for the synthesis of pentagon-fused graphene nanoribbons

In the record we provide the inputs and outputs for the calculations that support our recent results in the synthesis of pentagon-fused graphene nanoribbons (GNRs). GNRs have potential for applications in electronic devices. A key issue, thereby, is the fine-tuning of their electronic characteristics, which can be achieved through subtle structural modifications. These are not limited to the conventional armchair, zigzag, and cove edges, but also possible through incorporation of non-hexagonal rings. On-surface synthesis enables the fabrication and visualization of GNRs with atomically precise chemical structures, but strategies for the incorporation of non-hexagonal rings have been underexplored. In the manuscript, we describe the on-surface synthesis of armchair-edged GNRs with incorporated five-membered rings through the C-H activation and cyclization of benzylic methyl groups. ortho-Tolyl-substituted dibromobianthryl was employed as the precursor monomer, and visualization of the resulting structures after annealing at 300 °C on a gold surface by high-resolution noncontact atomic force microscopy clearly revealed the formation of methylene-bridged pentagons at the GNR edges. These persisted after annealing at 340 °C, along with a few fully conjugated pentagons having singly-hydrogenated apexes. The benzylic methyl groups could also migrate or cleave-off, resulting in defects lacking the five-membered rings. Moreover, unexpected and unique structural rearrangements, including the formation of embedded heptagons, were observed, providing novel insights into the on-surface reactions en route to functional carbon nanomaterials.