On-Surface Synthesis of Large-Scaled Kagome-Like Metal-Coordinated Framework and Polymerized Chains with Phenylacetylene on Cu(111) Surface

Single-layer metal-organic framework (MOF) structures on solid surfaces, known as the surface MOF (SMOF), have attracted extensive interest in the past decade. However, preparing large-scale uniform and well-defined SMOF structures remains challenging. Herein, we used the phenylacetylene (PA) molecule as the building block to synthesize the two-dimensional (2D) Kagome-like SMOF, subsequently the <i>cis</i>-Cu-coordinated linear structure, and finally <i>trans</i>-polymerized chains on the Cu(111) surface. Characterized by cryogenic scanning tunneling microscopy (STM), noncontact atomic force microscopy (nc-AFM), and rationalized by first-principles calculations, the optimized structure and electronic bands of the Kagome-like SMOF, <i>cis</i>-coordinated linear structure, and polymerized chains were investigated. We clarified that the formation of the 2D Kagome-like SMOF is based on Cu-coordination reaction between the terminal acetylene group of PA molecules and the <i>ortho</i>-site of the phenyl ring, followed by self-assembly of PA-Cu-PA units on the Cu(111) surface. By further step-by-step postannealing, PA molecules undergo a series of surface reactions, transitioning to a well-defined Cu-coordinated <i>cis</i>-linear structure and finally developing into a <i>trans</i>-polymerized line structure. Our results demonstrate a stepwise approach for achieving linear polymerization by using surface metal coordination. Hybrid SMOF, linear coordinated chains, and linear polymer could lead to intriguing quantum states, giving rise to a variety of applications in future molecular devices.