Highly Selective On‐Surface Synthesis of sp ² /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 sp 2 /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 sp 2 ‐ 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 sp 2 ‐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.