Programmable Synthesis of Atomically Precise Nanoporous Graphene Materials

The bottom-up synthesis is a powerful approach for fabricating graphene-based nanomaterials (GNMs) with atomic precision. This approach relies on well-defined chemical reactions between specially designed molecular precursors that dictate the structure of the resulting GNMs. Therefore, preparing a new GNM generally requires the design and synthesis of a new molecular precursor, which is often very challenging and laborious. In this work, we demonstrate a family of molecular precursors based on 7,10-dibromo-triphenylenes that can selectively produce different varieties of atomically precise GNMs, porous nanographenes (pNGs), and porous graphene nanoribbons (pGNRs), using different synthetic environments. More specifically, we show that upon Yamamoto polymerization of these molecules in a solution environment, the free rotations of the triphenylene units around the C-C bonds result in forming cyclotrimers at high yields. In contrast, in the case of on-surface polymerization of the same molecules on Au(111), these rotations are impeded, and the coupling proceeds toward forming long polymer chains. These chains can then be converted into pGNRs by annealing. Correspondingly, the solution-synthesized cyclotrimers can also be deposited onto Au(111) and converted into pNGs via a thermal treatment. Thus, both processes start with the same molecular precursor and end with an atomically precise GNM on Au(111), but the product type, pNG or pGNR, depends on the specific coupling approach. We also produced extended nanoporous graphenes (NPGs) through the lateral inter-ribbon cyclodehydrogenation of highly aligned pGNRs at high coverage. All synthesized products were atomically precise, including the NPGs, which were shown to be deterministic in terms of the nanopore shape and size and contain only [18]annulene nanopores if occasional defects are not considered. We demonstrate the generality of this approach by synthesizing two varieties of 7,10-dibromo-triphenylenes that produced six GNM products with different dimensionalities. By constructing different GNMs from the same building blocks, it is possible to tune the band gap in a wide range. The basic 7,10-dibromo-triphenylene is amenable to structural modifications, potentially providing access to many new GNMs. The fact that the synthesized GNMs possess atomically precise nanopores suggests using these materials for fundamental studies of the nanopore effect on the electrical and mechanical properties of graphene and their potential use for electronic, optoelectronic, and molecular sieving applications.<br/><br/>This work was supported by the Office of Naval Research (N00014-19-1-2596)"