Berdonces-Layunta Alejandro, Schulz Fabian, Aguilar-Galindo Fernando, Lawrence James, Mohammed Mohammed S G, Muntwiler Matthias, Lobo-Checa Jorge, Liljeroth Peter, de Oteyza Dimas G
Donostia International Physics Center, 20018 San Sebastián, Spain.
Centro de Física de Materiales, 20018 San Sebastián, Spain.
ACS Nano. 2021 Oct 26;15(10):16552-16561. doi: 10.1021/acsnano.1c06226. Epub 2021 Oct 11.
The advent of on-surface chemistry under vacuum has vastly increased our capabilities to synthesize carbon nanomaterials with atomic precision. Among the types of target structures that have been synthesized by these means, graphene nanoribbons (GNRs) have probably attracted the most attention. In this context, the vast majority of GNRs have been synthesized from the same chemical reaction: Ullmann coupling followed by cyclodehydrogenation. Here, we provide a detailed study of the growth process of five-atom-wide armchair GNRs starting from dibromoperylene. Combining scanning probe microscopy with temperature-dependent XPS measurements and theoretical calculations, we show that the GNR growth departs from the conventional reaction scenario. Instead, precursor molecules couple by means of a concerted mechanism whereby two covalent bonds are formed simultaneously, along with a concomitant dehydrogenation. Indeed, this alternative reaction path is responsible for the straight GNR growth in spite of the initial mixture of reactant isomers with irregular metal-organic intermediates that we find. The provided insight will not only help understanding the reaction mechanisms of other reactants but also serve as a guide for the design of other precursor molecules.
真空环境下表面化学的出现极大地提升了我们以原子精度合成碳纳米材料的能力。在通过这些方法合成的目标结构类型中，石墨烯纳米带（GNRs）可能最受关注。在此背景下，绝大多数GNRs都是通过相同的化学反应合成的：乌尔曼偶联反应，随后进行环脱氢反应。在此，我们对从二溴苝开始的五原子宽扶手椅型GNRs的生长过程进行了详细研究。结合扫描探针显微镜、温度依赖的X射线光电子能谱测量和理论计算，我们表明GNRs的生长与传统反应情况不同。相反，前驱体分子通过协同机制进行偶联，即同时形成两个共价键，并伴随脱氢反应。实际上，尽管我们发现反应物异构体与不规则金属有机中间体最初混合在一起，但这种替代反应路径却是GNRs直线生长的原因。所提供的见解不仅有助于理解其他反应物的反应机制，还可为设计其他前驱体分子提供指导。
