Thermodynamic Self-Assembly of Two-Dimensional π-Conjugated Metal–Porphyrin Covalent Organic Frameworks by “On-Site” Equilibrium Polymerization

Two-dimensional π-conjugated metal–porphyrin covalent organic frameworks were produced in aqueous solution on an iodine-modified Au(111) surface by “on-site” azomethine coupling of Fe^III-5,10,15,20-tetrakis(4-aminophenyl)porphyrin (FeTAPP) with terephthal dicarboxaldehyde and investigated in detail using in-situ scanning tunneling microscopy. Mixed covalent organic porphyrin frameworks consisting of FeTAPP and metal-free TAPP (H₂TAPP) were prepared through simultaneous adsorption in a mixed solution as well as partial replacement of FeTAPP by H₂TAPP in an as-prepared metal-porphyrin framework. In the mixed framework, the relative distribution of FeTAPP to H₂TAPP was not random and revealed a preference for homo-connection rather than heteroconnection. The construction of substrate-supported, π-conjugated covalent frameworks from multiple building blocks, including metal centers, will be of significant utility in the design of functional molecular nanoarchitectures.