Interpenetration Control in Three-Dimensional Covalent Organic Frameworks: Architectural Modulation and cis -Imine Configuration

Interpenetration is ubiquitous in three-dimensional covalent organic frameworks (3D COFs), yet it is often regarded as a passive outcome of framework assembly rather than a tunable design parameter. Here we show that interpenetration can be deliberately tuned and, more importantly, directly governs both the architecture and dynamic behavior of 3D COFs. We constructed an isoreticular series of highly crystalline 3D COFs featuring different substituents (-OMe, -OEt, and -OiPr), which exhibit 5-fold, 4-fold, and 2-fold interpenetration while maintaining the pts topology. This systematic variation reveals that reducing interpenetration reshapes pore architecture, leading to enlarged pore apertures and increased accessible surface areas. Strikingly, the minimally interpenetrated framework exhibits an unusual bond-level structural feature, in which a subset of imine linkages adopts an unambiguously determined cis configuration, a motif rarely observed in COFs. These linkages undergo reversible guest-induced cis-to-trans isomerization, imparting pronounced framework flexibility and driving an exceptional ∼220% expansion of the crystal volume. This work provides the systematic experimental demonstration that interpenetration can be harnessed to govern both framework architecture and dynamic behavior, highlighting its key role in designing 3D COFs with tailored functions.