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

Two-dimensional pi-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 (H(2)TAPP) were prepared through simultaneous adsorption in a mixed solution as well as partial replacement of FeTAPP by H(2)TAPP in an as-prepared metal-porphyrin framework. In the mixed framework, the relative distribution of FeTAPP to H(2)TAPP was not random and revealed a preference for homo-connection rather than hetero-connection. The construction of substrate-supported, pi-conjugated covalent frameworks from multiple building blocks, including metal centers, will be of significant utility in the design of functional molecular nanoarchitectures.