The bottom-up approach through on-surface synthesis of porous graphene nanoribbons (GNRs) presents a controllable manner for implanting periodic nanostructures to tune the electronic properties of GNRs in addition to bandgap engineering by width and edge configurations. However, owing to the existing steric hindrance in small pores like divacancies, it is still difficult to embed periodic divacancies with a nonplanar configuration into GNRs. Here, we demonstrate the on-surface synthesis of atomically precise eight-carbon-wide armchair GNRs embedded with periodic divacancies (DV8-aGNRs) by utilizing the monatomic step edges on the Au(111) surface. From a single molecular precursor correspondingly following a trans- and cis-coupling, the DV8-aGNR and another porous nanographene are respectively formed at step edges and on terraces at 720 and 570 K. Combining scanning tunneling microscopy/spectroscopy, atomic force microscopy, and first-principles calculations, we determine the out-of-plane conformation, wide bandgap (∼3.36 eV), and wiggly shaped frontier orbitals of the DV8-aGNR. Nudged elastic band calculations further quantitatively reveal that the additional steric hindrance effect in the cyclodehydrogenative reactions has a higher barrier of 1.3 eV than that in the planar porous nanographene, which also unveils the important role played by the monatomic Au step and adatoms in reducing the energy barriers and enhancing the thermodynamic preference of the oxidative cyclodehydrogenation. Our results provide the first case of GNRs containing periodic pores as small as divacancies with a nonplanar configuration and demonstrate the strategy by utilizing the chemical heterogeneity of a substrate to promote the formation of novel carbon nanomaterials.

中文翻译：

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嵌入周期性空位的石墨烯纳米带的分步辅助表面合成

除了通过宽度和边缘配置进行带隙工程之外，通过表面合成多孔石墨烯纳米带 (GNR) 的自下而上方法提供了一种植入周期性纳米结构以调节 GNR 电子特性的可控方式。然而，由于像双空位这样的小孔中存在空间位阻，仍然难以将具有非平面配置的周期性双空位嵌入到 GNR 中。在这里，我们通过利用 Au(111) 表面上的单原子阶梯边缘，展示了嵌入周期性双空位 (DV8-aGNR) 的原子精确的八碳宽扶手椅 GNR 的表面合成。从单个分子前体相应地遵循反式和顺式-耦合，DV8-aGNR和另一种多孔纳米石墨烯分别在720和570 K的台阶边缘和平台上形成。结合扫描隧道显微镜/光谱、原子力显微镜和第一性原理计算，我们确定了- DV8-aGNR 的平面构象、宽带隙（~3.36 eV）和弯曲形状的前沿轨道。轻推弹性带计算进一步定量地揭示了环脱氢反应中的额外空间位阻效应比平面多孔纳米石墨烯具有更高的 1.3 eV 势垒，这也揭示了单原子 Au 台阶和吸附原子在降低能量中所起的重要作用障碍和增强氧化环化脱氢的热力学偏好。