On-surface synthesis has emerged as a powerful strategy to fabricate unprecedented forms of atomically precise graphene nanoribbons(GNRs).However,the on-surface synthesis of zigzag GNRs(ZGNR)has met with only limited ...On-surface synthesis has emerged as a powerful strategy to fabricate unprecedented forms of atomically precise graphene nanoribbons(GNRs).However,the on-surface synthesis of zigzag GNRs(ZGNR)has met with only limited success.Herein,we report the synthesis and on-surface reactions of 2,7-dibromo-9,9′-bianthryl as the precursor towardπ-extended ZGNRs.Characterization by scanning tunneling microscopy and high-resolution noncontact atomic force microscopy clearly demonstrated the formation of anthracene-fused ZGNRs.Unique skeletal rearrangements were also observed,which could be explained by intramolecular Diels-Alder cycloaddition.Theoretical calculations of the electronic properties of the anthracene-fused ZGNRs revealed spin-polarized edge-states and a narrow bandgap of 0.20 eV.展开更多
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 modifica...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 °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. 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.展开更多
On-surface synthesis is a rapidly developing field involving chemical reactions on well-defined solid surfaces toaccess synthesis of low-dimensional organic nanostructures which cannot be achieved via traditional solu...On-surface synthesis is a rapidly developing field involving chemical reactions on well-defined solid surfaces toaccess synthesis of low-dimensional organic nanostructures which cannot be achieved via traditional solutionchemistry. On-surface reactions critically depend on a high degree of chemoselectivity in order to achieve anoptimum balance between target structure and possible side products. Here, we demonstrate synthesis of graphenenanoribbons with a large unit cell based on steric hindrance-induced complete chemoselectivity as revealed byscanning probe microscopy measurements and density functional theory calculations. Our results disclose thatcombined molecule-substrate van der Waals interactions and intermolecular steric hindrance promote a selectivearyl-aryl coupling, giving rise to high-quality uniform graphene nanostructures. The established coupling strategyhas been used to synthesize two types of graphene nanoribbons with different edge topologies inducing apronounced variation of the electronic energy gaps. The demonstrated chemoselectivity is representative forn-anthryl precursor molecules and may be further exploited to synthesize graphene nanoribbons with novelelectronic, topological and magnetic properties with implications for electronic and spintronic applications.展开更多
基金This work was supported by the Swiss National Science Foundation(Grant No.200020_212875)the NCCR MAR-VEL funded by the Swiss National Science Foundation(Grant No.205602)the Werner Siemens Foundation,the Max Planck Society,and the Okinawa Institute of Science and Technology Graduate University.K.M.acknowledges a fellowship from Gutenberg Research College,Johannes Gutenberg University Mainz.Computational support from the Swiss Supercomputing Center(CSCS)under project ID s1141 is gratefully acknowl-edged.We acknowledge PRACE for awarding access to the Fenix Infrastructure resources at CSCS,which are partially funded by the European Union’s Horizon 2020 research and innovation program through the ICEI project under grant agreement No.800858.Technical support from Lukas Rotach is gratefully acknowledged.
文摘On-surface synthesis has emerged as a powerful strategy to fabricate unprecedented forms of atomically precise graphene nanoribbons(GNRs).However,the on-surface synthesis of zigzag GNRs(ZGNR)has met with only limited success.Herein,we report the synthesis and on-surface reactions of 2,7-dibromo-9,9′-bianthryl as the precursor towardπ-extended ZGNRs.Characterization by scanning tunneling microscopy and high-resolution noncontact atomic force microscopy clearly demonstrated the formation of anthracene-fused ZGNRs.Unique skeletal rearrangements were also observed,which could be explained by intramolecular Diels-Alder cycloaddition.Theoretical calculations of the electronic properties of the anthracene-fused ZGNRs revealed spin-polarized edge-states and a narrow bandgap of 0.20 eV.
基金We are grateful for the financial support by the Max Planck Society,the Swiss National Science Foundation under Grant No.200020_182015the NCCR MARVEL funded by the Swiss National Science Foundation(No.51NF40-182892)+3 种基金the European Union’s Horizon 2020 research and innovation programme under grant agreement number 785219(Graphene Flagship Core 2)the Office of Naval Research(No.N00014-18-1-2708)the Okinawa Institute of Science and Technology Graduate University(OIST)The Swiss National Supercomputing Centre(CSCS)under project ID s904 is acknowledged for computational resources.
文摘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 °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. 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.
基金support from the Swiss National Science Foundation under Grant No.200020_182015support by the Max Planck Society.CAP acknowledges the NCCR MARVEL funded by the Swiss National Science Foundation(grant no.51NF40-205602)The Swiss Supercomputing Center(CSCS)is acknowledged for computational resources(project ID s1141).
文摘On-surface synthesis is a rapidly developing field involving chemical reactions on well-defined solid surfaces toaccess synthesis of low-dimensional organic nanostructures which cannot be achieved via traditional solutionchemistry. On-surface reactions critically depend on a high degree of chemoselectivity in order to achieve anoptimum balance between target structure and possible side products. Here, we demonstrate synthesis of graphenenanoribbons with a large unit cell based on steric hindrance-induced complete chemoselectivity as revealed byscanning probe microscopy measurements and density functional theory calculations. Our results disclose thatcombined molecule-substrate van der Waals interactions and intermolecular steric hindrance promote a selectivearyl-aryl coupling, giving rise to high-quality uniform graphene nanostructures. The established coupling strategyhas been used to synthesize two types of graphene nanoribbons with different edge topologies inducing apronounced variation of the electronic energy gaps. The demonstrated chemoselectivity is representative forn-anthryl precursor molecules and may be further exploited to synthesize graphene nanoribbons with novelelectronic, topological and magnetic properties with implications for electronic and spintronic applications.
