Cobalt-Assisted On-Surface Synthesis of Circumcoronene on Au(111)

Circumcoronene is the largest fully benzenoid, hexagonal-shaped and zigzag-edged polycyclic aromatic hydrocarbon. However, it's synthesis is not attainable by conventional in-solution synthetic approaches. In this work, we demonstrate successful fabrication of circumcoronene using surface-assisted synthetic strategy. Specifically, we utilize methyl radical-radical coupling and aromatization of judiciously designed precursor molecule on the Cobalt (Co)-decorated Au(111) surface. In stark contrast, this reaction is not feasible on the pristine Au(111) surface. We employ chemical bond-resolved scanning tunneling microscopy and spectroscopy measurements to elucidate remarkably distinct precursor transformation pathways on the Co-free and Co-decorated Au(111) surfaces. Our results underpin the Co adatoms as effective catalytic centers to trigger methyl radical–radical coupling on Au(111), thereby enriching toolbox of a model on-surface reactions.