Ultra-high Yield On-surface Synthesis and Assembly of Circumcoronene into Chiral Electronic Kagome-honeycomb Lattice

On-surface synthesis has revealed remarkable potential in the fabrication of a plethora of elusive nanographenes with tailored structural, electronic and magnetic properties unattainable by conventional wet-chemistry synthesis. Unfortunately, surface-assisted synthesis often involves multiple-step cascade reactions with competing pathways, leading to the formation of a diversity of products with limited yield, which reduces its feasibility towards the large-scale production for future technological applications. Here, we devise a new on-surface synthetic strategy for the ultra-high yield synthesis of a hexagonal nanographene with six zigzag edges, namely circumcoronene on Cu(111) via surfaceassisted intramolecular dehydrogenation of the rationally-designed precursor molecule, followed by methyl radical-radical coupling and aromatization. An elegant electrostatic interaction between circumcoronene and Cu(111) drives their self-organization into an extended superlattice, as revealed by bond-resolved low-temperature scanning probe microscopy and spectroscopy 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 (2D) electron gas in Cu(111) surface into 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 novel 2D superlattices with possible nontrivial electronic properties towards their future technological applications.