Structural Differentiation of Homologous Anisodimensional Frameworks Driven by Site-Selective Polymerization.

Theoretically, distinguished from the dimensional isomers in reticular chemistry, structures with different dimensions can also be formed by site-selective polymerization using identical building blocks bearing a high density of reactive sites. Unfortunately, the spatial confinement imposes significant challenges for molecular building blocks to achieve dimensional differentiation via their intrinsic site-selective reactivity. In this work, we first report the dimensional transformation of covalent organic frameworks (COFs) driven by site-selective polymerization of identical molecular building blocks with a high density of reactive sites. This unique phenomenon was demonstrated for the first time to originate from the role of aniline in enhancing the reversibility of the reaction system and modulating the conformational flexibility of the monomers. We systematically elucidated the mechanism underlying this dimensional transformation and successfully demonstrated the generality of the synthetic strategy. Moreover, the residual benzaldehyde in the frameworks generated via the site-selective polymerization of the building blocks can serve as exciton acceptors, significantly enhancing the photocatalytic performance. This work not only offers a novel strategy for regulating the dimensionality of COFs, but also provides a valuable reference for precisely controlling the conformational flexibility of building blocks to enable topological transformations.