Layer Stacking Order Tunes Thermal and Mechanical Properties in the 2D Covalent Organic Framework TAPB-DMPDA

Two-dimensional covalent organic frameworks (2D COFs) are layered, porous macromolecular sheets with remarkable structural tunability. Their layered nature allows them to adopt a variety of stacking arrangements, much like traditional 2D materials. Recent studies have revealed that such stacking motifs may naturally occur in COFs, yet their influence on physical properties remains largely unexplored. In this work, we use atomistic simulations to investigate stacking-dependent thermal conductivity (k) and mechanical behavior in TAPB-DMPDA, a prototypical imine-linked 2D COF. Six representative stacking motifs were modeled to establish structure–property relationships. In-plane conductivity (k_∥) is maximized in ABC (1.3 W/m-K) and staggered (1.2 W/m-K) geometries due to reduced spacing and enhanced π- π overlap, while the serrated yields the highest cross-plane (k_⊥) value (0.21 W/m-K). Anisotropy ratio (k_∥ / k_⊥) spans from 4.4 to 19.1, underscoring the sensitivity of directional transport to stacking. These k trends correlate strongly with elastic moduli and structural descriptors, clarifying how stiffness and geometry govern phonon transport. Temperature-dependent simulations reveal that stackings with higher conductivity undergo weaker elastic softening, maintaining transport efficiency at high temperatures. Moreover, we also show that a subtle linker modification leaves k_∥ largely unchanged but nearly doubles k_⊥ across all stackings, highlighting the potential of side-group chemistry and supramolecular interactions to enhance interlayer coupling. Our work demonstrates how stacking geometry emerges as a powerful design strategy for tailoring thermal and mechanical performance in 2D COFs.