Chiral transfer amidst one-dimensional linear polymers and two-dimensional network covalent organic frameworks: Striking a fine balance between helicity and crystallinity

The current landscape of chiral covalent organic frameworks (COFs) predominantly centered on constructing asymmetric molecular-scale chirality, often introducing an inherent contradiction to the COF symmetry and limiting diversity. Herein, we overcome these challenges by achieving chiral transfer between one-dimensional (1D) imine linear polymers (LPs) and two-dimensional (2D) network β-ketoenamine COFs composed of achiral monomers. We successfully synthesize several 1D imine LPs with mesoscopic helical chirality, comprising achiral C2-symmetric terephthalaldehyde and diamine linkers in a chiral supramolecular transcription system. Leveraging the irreversible tautomerism mechanism within the linker replacement approach, terephthalaldehyde (TPA) units in these helical 1D LPs are substituted with C3-symmetric 1,3,5-triformylphloroglucinol (TP), yielding the corresponding 2D network β-ketoenamine COFs. Crystallinity and helicity of the resultant β-ketoenamine COFs intimately hinge on reaction conditions, including the aldehyde stoichiometry of Tp and TPA, as well as the quantity and concentration of the catalyst employed. Under optimized conditions, the nucleation and growth were precisely governed, achieving a harmonious equilibrium of crystallinity and helicity within the generated 2D network β-ketoenamine COFs, even with covalent bond rupture, recombination, and topological transition (from [C2 + C2] to [C3 + C2]). Impressively, the ground state chirality inherent to helical 1D LPs seamlessly transfers to helical 2D network β-ketoenamine COFs. This study not only offers new perspectives on the development of chiral functional COFs, but also provides fresh insights into the precise control of COFs' microscopic morphology.