Light-promoted synthesis of highly-conjugated crystalline covalent organic framework

Low electrical conductivity caused by low degree of π -conjugation and structural disorders induces critical limitations in electronic applications of covalent organic frameworks (COFs). Here we focus on improving the electrical properties of COFs by synthesis of highly conjugated and crystalline COF (hcc-COF). Addition of a small amount of water and acetic acid induces the efficient reversible dynamic imine condensation reaction that is required to obtain uniform and crystalline products. Also, simulated sunlight irradiation facilitates the reversible imine condensation reaction, and achieves formation of hcc-COF with high-yield within short reaction time. The obtained hcc-COF has an extended π -conjugated structure along the lateral direction and an inclined stacking structure. The intrinsic electron transport properties along the in-plane direction are evaluated using a hcc-COF film grown on a water surface from a polarity-controlled precursor solution. To the best of our knowledge, our hcc-COF film shows the highest reported electrical conductivity for highly conjugated organic porous polymers. The electrical conductivity of covalent organic frameworks may be limited by a low degree of π-conjugation or structural disorder. Here the authors produce uniform and highly conjugated COFs via a reversible dynamic imine condensation and demonstrate enhanced electrical conductivity in their product.