Synthesis Pathway Oriented Heterogeneous Stacking Mode of Homogeneous Two-Dimensional Hydrazone-Linked COFs

The study of isomerism phenomena in covalent organic frameworks (COFs), such as dimensional isomerism, interpenetration isomerism, and stacking isomerism, along with their influence on the properties of COFs, has become an intriguing research avenue in recent years. Nevertheless, the current techniques for synthesizing COF isomers predominantly rely on extensive trial and error, lacking efficient, target-driven synthetic methodologies. The development of synthetic protocols capable of selectively enhancing the crystallization of one COF isomer over another continues to pose a significant challenge, remaining an empirical process at present. In this work, through subtly designing with the same structure and different stacking modes, we elucidate how altering the sequence of hydroxyl site modifications on the monomer impacts dissolution, polymerization, and assembly processes during COF synthesis, thereby influencing the stacking modes of two kinds of hydrazine-linked COFs with reversed AA stacking and AA stacking structures. The quasi-in-situ PXRD analysis during methanol volatilization and the N 2 adsorption experiments revealed that the crystallinity and stability of the COFs prepared by the pre- and post-modified method are significantly different. These structural differences are further reflected in applications such as photocatalytic reduction of uranium and iodine adsorption. This work sheds light on the crucial role of non-covalent interactions in influencing and regulating the stability-crystallinity-functionality of COFs, offering valuable insights for future investigations.