On-surface synthesis is of importance to fabricate low dimensional carbon-based nanomaterials with atomic precision. Here, we synthesize nitrogen-doped nanographene with an [18]annulene pore and its dimer through sequential reactions of debromination, aryl–aryl coupling, cyclodehydrogenation and C–N coupling on Ag(111) from 3,12-dibromo-7,8-diaza[5]helicene. The inner structures of the products were characterized with scanning tunneling microscopy with a CO terminated tip at low temperature. Furthermore, the first four unoccupied electronic states of the nanographene were investigated with a combination of scanning tunneling spectroscopy and theoretical calculations. Except for the LUMO + 2 state observed at +1.3 V, the electronic states at 500 mV, 750 mV and 1.9 V were attributed to the superatom molecular orbitals at the [18]annulene pore, which were significantly shifted towards the Fermi level due to the hybridization with the confined surface state.

表面合成对于制造具有原子精度的低维碳基纳米材料非常重要。在这里，我们通过3,12-二溴-7,8的Ag(111)上的脱溴、芳基-芳基偶联、环脱氢和C-N偶联的连续反应合成了具有[18]轮烯孔的氮掺杂纳米石墨烯及其二聚体-diaza[5]螺旋烯。在低温下使用带有 CO 端接尖端的扫描隧道显微镜对产品的内部结构进行了表征。此外，结合扫描隧道光谱和理论计算研究了纳米石墨烯的前​​四个未占据电子态。除了在+1.3 V处观察到的LUMO + 2态外，500 mV、750 mV和1.9 V处的电子态归因于[18]轮烯孔处的超原子分子轨道，由于与受限表面态的杂化。