On-Surface Synthesis of a π‑Extended Diaza[8]circulene

Heterocyclic [8]­circulenes are an
important class of polycyclic
aromatic hydrocarbon molecules because of their unique structural
properties and promising applications. However, the synthesis of heterocyclic
[8]­circulenes is still limited and thus is an important synthetic
challenge. Here we describe the first example of a π-extended
diaza[8]­circulene surrounded by and fused with six hexagons and two
pentagons, which was successfully synthesized only by a combined in-solution
and on-surface synthetic strategy. State-of-the-art scanning tunneling
microscopy with a CO-functionalized tip and density functional theory
calculations revealed its planar conformation and unique electronic
structure.