Triangulene and its homologues are of considerable interest for molecular spintronics due to their high-spin ground states as well as the potential for constructing high spin frameworks. Realizing triangulene-based high-spin system on surface is challenging but of particular importance for understanding π-electron magnetism. Here, we report two approaches to generate triangulene trimers on Au(111) by using surface-assisted dehydration and alkyne trimerization, respectively. We find that the developed dehydration reaction shows much higher chemoselectivity thus resulting in significant promotion of product yield compared to that using alkyne trimerization approach, through cutting the side reaction path. Combined with spin-polarized density functional theory calculations, scanning tunneling spectroscopy measurements identify the septuple (S = 3) high-spin ground state and quantify the collective ferromagnetic interaction among three triangulene units. Our results demonstrate the approaches to fabricate high-quality triangulene-based high spin systems and understand their magnetic interactions, which are essential for realizing carbon-based spintronic devices.

Bottom-up synthesis of carbon nanomaterials embedded with periodic arrays of nanoporous structures is of great interest for potential applications in nanotechnology. In limited examples, lateral fusion of polymer chains or armchair/ chevron graphene nanoribbons with phenyl functional groups upon dehydrogenative coupling has been observed for the generation of porous nanoribbons or nanoporous graphene.Here we report a stepwise on-surface synthesis of porous carbon nanoribbons upon hierarchical Ullmann coupling for promoting highly selective inter-ribbon connections, which results in porous carbon nanoribbon structures with a notched zigzag edge and variable widths. By combining scanning tunneling microscopy and atomic force microscopy, the nanoporous structure and the corresponding electronic structures are fully characterized, which shows that localized electronic states are generated at pore−ribbon interfaces and ribbon zigzag edges. Further first principle calculations unveil the observed electronic states near the Fermi level originating from the two flat bands upon nanoporous structure imprinting. Our results provide a promising strategy for the atomically precise synthesis of porous carbon nanoribbons with engineered electronic structures, which can potentially enrich the synthetic routes to porous nanostructures and also expand the variety of carbon nanomaterials with characteristic electronic properties.