On-surface synthesis of thiophene-containing large-sized organometallic macrocycles on the Ag(111) surface

On-surface synthesis is exhibited as a promising “bottom-up” approach for fabricating numerous macromolecular nanostructures. Compared to noncyclic architectures, macrocycles are of significant interest due to their specific “endless” cyclic topology and hence tunable topology-dependent properties. The synthesis of macrocycles with well-defined composition and geometry remains a great challenge, especially for large-sized cyclic rings. Here, we report a successful synthesis of large-sized organometallic macrocycles on the Ag(111) surface via utilizing thiophene-containing molecules, such as 1,3-dibromo-5-hexyl-4H-thieno[3,4-c]pyrrole-4,6(5H)-dione (TPD), as a precursor. The structures of the macrocycles are investigated by scanning tunneling microscopy and density functional theory calculations. The organometallic trans-configured chains and cis-configured (TPD-Ag)_n (n = 12, 14, 16, 18, and 20) rings are the main products of an on-surface reaction. By controlling the on-surface reaction pathway, the 18-membered macrocycle can be made as the dominant product of all cyclic configurations. The (TPD-Ag)_n macrocycles are realized by the cyclization of organometallic units and occurred on the stage of an intermediate phase. The effects of surface diffusion barriers are further demonstrated by our attempts on Ag(110) and Ag(100) surfaces. The feasibility of such a synthetic method for macrocycles is further proven by the on-surface reaction with Me-TPD precursors.