1D Fully sp² Carbon-Linked Covalent Organic Frameworks for Powerful Photoreduction of CO₂

Precisely arranging organic π-conjugated macrocyclic units to long-range-ordered arrays might not only diversify the geometric and topological structures, but also bring out exceptional semiconducting properties. Herein, upon Knoevenagel condensation of angular ditopic phenanthroline and tetratopic biphenyl or bipyridinyl derivatives, we synthesized new types of 1D fully sp² carbon-linked covalent organic frameworks (COFs). Powder X-ray diffraction patterns and nitrogen adsorption/desorption isotherms revealed the repeated vinylene-linked macrocycles interconnected by carbon-carbon single bonds, which further assembled to long-range ordered alignments along the in-plane and vertical directions. Such unique 1D COF motifs are the congeners of the crystalline assemblies of linear conjugated polymacrocycles, favorable for dispersion and active site exposure. The π-delocalization of these COFs can be efficiently modulated by the macrocycle moieties with the cross- or linear-conjugation mode, then affecting their electron coupling and exciton dynamics. With the phenanthroline nitrogen atoms in the macrocyclic backbones serving as catalytic active sites, they exhibited photocatalytic reduction of CO₂ to CO in a generation rate of 3535.9 µmol.g^-1.h^-1, and up to 19678.3 µmol.g^-1.h^-1 upon loading cobalt (II) cation. Both values are among the highest values of the organic or organic-inorganic hybrid photocatalysts to date.