Prismatic and Antiprismatic Conformations of a Six-Connected Node Direct Topological Isomerism in Three-Dimensional Covalent Organic Frameworks

Three-dimensional covalent organic frameworks (3D COFs) constructed from high-connectivity polyhedral nodes have attracted increasing attention due to their structural complexity and functional diversity, yet the influence of node conformation on framework topology and related properties in 3D COFs has not been previously reported. Here, using a rationally designed phenothiazine-based six-connected building block capable of adopting distinct conformations, we selectively synthesized two topological isomers of 3D COFs from identical precursors. Structural analysis revealed that the two COFs adopt 6-fold Class IIIa interpenetrated acs and 6-fold Class IIa interpenetrated pcu topologies, with the six-connected nodes exhibiting triangular prismatic and antiprismatic conformations, respectively. In addition, these two COFs show different fluorescent sensing responses toward 2,4,6-trinitrophenol in water. This work demonstrates the potential of conformational adaptation in high-connectivity nodes to modulate framework topology and related properties, providing new insights into expanding the structural and functional diversity of high-connectivity 3D COFs.