Graphene nanoribbons (GNRs), nanometer-wide strips of graphene, are promising candidates as materials for the next generation of nanoelectronics. Armchair GNRs (AGNRs) can be classified into three subfamilies, N=3p, N=3p+1, and N=3p+2, where p is an integer and N denotes the rows of carbon atoms across the ribbon width. AGNRs that fall into the N=3p+2 subfamily are projected to exhibit outstanding electrical properties, such as high charge-carrier mobilities. However, the synthesis of this particular subgroup of AGNRs with N > 5 in solution is challenging.

Xuelin Yao, Max Planck Institute for Polymer Research, Mainz, Germany, and University of Oxford, UK, Hai I. Wang, Max Planck Institute for Polymer Research and Utrecht University, The Netherlands, Klaus Müllen, Max Planck Institute for Polymer Research, Akimitsu Narita, Max Planck Institute for Polymer Research and Okinawa Institute of Science and Technology Graduate University, Japan, and colleagues have successfully synthesized N=8 AGNRs in solution utilizing a custom arylated polynaphthalene precursor (pictured below). The researchers designed an arylated naphthalene monomer with bromo substituents and boronic ester groups, which underwent a palladium-catalyzed Suzuki polymerization to give the arylated polynaphthalene precursor. A Scholl reaction of the precursor then led to the desired 8-AGNRs.

 

 

The synthesized 8-AGNRs exhibited a near-infrared (NIR) absorption extending up to about 2400 nm, corresponding to an optical band gap as low as 0.52 eV. The nanoribbons also showed a record high dc charge-carrier mobility up to ca. 270 cm² V⁻¹ s⁻¹. According to the researchers, this development highlights the potential of 8-AGNRs for use in electronic devices. In addition, they state that the synthesis method could be extended to the synthesis of wider AGNRs within the N=3p+2 subgroup by changing the aryl substituent.

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• N=8 Armchair Graphene Nanoribbons: Solution Synthesis and High Charge Carrier Mobility,
  Xuelin Yao, Heng Zhang, Fanmiao Kong, Antoine Hinaut, Rémy Pawlak, Masanari Okuno, Robert Graf, Peter N. Horton, Simon J. Coles, Ernst Meyer, Lapo Bogani, Mischa Bonn, Hai I. Wang, Klaus Müllen, Akimitsu Narita,
  Angew. Chem. Int. Ed. 2023.
  https://doi.org/10.1002/anie.202312610