【摘 要】
：
Graphene nanoribbons (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 convent
【机 构】
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Max Planck Institute for Polymer Research,55128 Mainz,Germany;Organic and Carbon Nanomaterials Unit,
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Graphene nanoribbons (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.Herein,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 ℃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 ℃,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.Despite the coexistence of different reaction pathways that hamper selective synthesis of a uniform structure,our results provide novel insights into on-surface reactions en route to functional,non-benzenoid carbon nanomaterials.
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