Linkage-sparing Assembly of Single-crystalline Phenylene-linked Covalent Organic Frameworks

Crystallising two-dimensional (2D) covalent organic frameworks (COFs) from irreversible bonds is hindered by the absence of error correction and out-of-plane disorder. Here, we establish linkage-sparing assembly (LSA) as a novel strategy for overcoming this limitation: preformed oligomeric motifs encode part of the target lattice, reducing the number of new irreversible C–C bonds required for framework growth. Combined with kinetic control through temperature and water content, LSA yields micrometre-scale single crystals of a phenylene-linked COF (HPPCOF) formed by ketone cyclotrimerisation. Electron diffraction resolves its honeycomb (hcb) structure and reveals local disorder and unreacted defects, providing insight into the real structure of an irreversibly formed 2D network. The heteroatom-free polyphenylene COF photocatalyses oxygen reduction to H2O2 via the oxygen reduction reaction, with activity comparable to heteroatom-containing COFs and without sacrificial electron donors. These results identify preassembly and kinetic control as complementary tools for crystallising robust COFs and broaden design opportunities for irreversible linkages.