On-Surface Synthesis of Giant Conjugated Macrocycles

We have achieved an on-surface synthesis of giant conjugated macrocycles of diameter ~7 nm consisting of up to 30 subunits. The synthesis was initiated from a debrominative coupling of the molecular precursors occurring on a hot Ag(111) surface, leading to the formation of arched oligomeric chains and macrocycles. These products, revealed by scanning tunneling microscopy in combination with density functional theory, were covalent oligomers assisted by C-Ag organometallic bonds between parallel molecular subunits, due to a site-selective debromination and the asymmetric molecular conformation. A consecutive cyclodehydrogenation activated by thermal treatments at higher temperatures steered the final conjugation of the macrocycles. Our finding provides a novel design strategy toward π-conjugated macrocycles, and opens up new opportunities for precise synthesis of organic nanostructures.