On-Surface Synthesis of a Nitrogen-Doped Curved Cycloarene: π-Extended Pentaazaquintulene and Its Gold Complex

The interplay between π-electron conjugation and molecular geometry has been a central focus in the development of modern hydrocarbon research. Herein, we report the on-surface synthesis and characterization of the nonplanar, π-extended, nitrogen-doped quintulene C85N5 on a Au(111) surface. The as-synthesized C85N5 adopts a convex geometry, which can be inverted to a concave geometry by single-molecule manipulation. In its convex conformation, C85N5 may coordinate a gold atom within its central pore, forming an Au-C85N5 complex through interactions with the pyridinic nitrogen atoms. The structures and electronic properties of these cycloarenes are elucidated by noncontact atomic force microscopy (nc-AFM), scanning tunneling microscopy and spectroscopy (STM/STS), and density functional theory (DFT) calculations. Our results highlight that on-surface synthesis enables the atomically precise generation of curved (hetero)nanographenes and their metal complexes. Despite the inherent challenges of the nonplanar π-system, both geometric and electronic features can be characterized in detail, and controlled manipulation by scanning probe techniques is feasible.