Highly Selective On-Surface Synthesis of sp²/sp-Hybridized Heterochiral Triangular Nanorings

A central challenge in on-surface synthesis of topologically unique carbon nanostructures lies in the precise and selective construction of triangular nanorings. Achieving the resulting chirality and the sp²/sp-hybridized state simultaneously from prochiral precursors is critical, yet immensely difficult. Here, we design an asymmetric α‑cyanostilbene derivative with aggregation‑induced emission properties as a prochiral building block to achieve deterministic pathway selection through controlling the substrate- and thermal-directed strategy, allowing for the targeted formation of heterochiral nanorings with defined sp²- and sp-hybridization on Ag(111). Direct thermal deposition onto a hot Ag(111) surface at 443 K drives a highly selective cyclotrimerization, yielding discrete sp²-hybridized heterochiral triangular nanorings. Subsequent annealing induces an elimination reaction, converting these rings into their sp-hybridized analogues while preserving chirality. In contrast, room-temperature deposition and postannealing predominantly produces linear chains. The structural evolution and selective reaction mechanisms are unequivocally characterized by scanning tunneling microscopy (STM), bond-resolution STM, synchrotron radiation photoemission spectroscopy (SRPES), and density functional theory (DFT) calculations. This work establishes a novel strategy for the precise synthesis of chiral triangular nanorings, revealing the critical role of surface-mediated conformational control and dynamic covalent bonding in determining product topology and chirality.