On-surface synthesis has revealed remarkable potential in the fabrication of atomically precise nanographenes. However, surface-assisted synthesis often involves multiple-step cascade reactions with competing pathways, leading to a limited yield of target nanographene products. Here, we devise a strategy for the ultrahigh-yield synthesis of circumcoronene molecules on Cu(111) via surface-assisted intramolecular dehydrogenation of the rationally designed precursor, followed by methyl radical-radical coupling and aromatization. An elegant electrostatic interaction between circumcoronenes and metallic surface drives their self-organization into an extended superlattice, as revealed by bond-resolved scanning probe microscopy measurements. Density functional theory and tight-binding calculations reveal that unique hexagonal zigzag topology of circumcoronenes, along with their periodic electrostatic landscape, confines two-dimensional electron gas in Cu(111) into a chiral electronic Kagome-honeycomb lattice with two emergent electronic flat bands. Our findings open up a new route for the high-yield fabrication of elusive nanographenes with zigzag topologies and their superlattices with possible nontrivial electronic properties.

Centre for Advanced 2D Materials National University of Singapore 6 Science Drive 2 Singapore 117546 Singapore

Department of Chemistry National University of Singapore 3 Science Drive 3 Singapore 117543 Singapore

Department of Petrochemistry and Refining University of Kinshasa Kinshasa Democratic Republic of Congo

Institute of Physics The Czech Academy of Sciences 162 00 Prague Czech Republic

Regional Centre of Advanced Technologies and Materials Palacký University 78371 Olomouc Czech Republic

School of Physics and Astronomy Monash University Clayton Victoria Australia

Universidad Autónoma de Madrid Campus Cantoblanco Madrid Spain

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On-Surface Synthesis of a Radical 2D Supramolecular Organic Framework

Visualizing designer quantum states in stable macrocycle quantum corrals