Topology-Driven Node-Linker Coupling Enables Exceptional Thermal and Mechanical Performance in Covalent Organic Frameworks.

Abstract

Materials that combine low density with high thermal and mechanical performance are essential for applications ranging from thermal management to lightweight structural systems, yet such combinations are rarely achieved in porous solids due to intrinsic trade-offs between porosity, stiffness, and heat transport. Here, we demonstrate that covalent organic frameworks (COFs) can overcome this limitation through topology-driven control of node-linker coupling. Using a high-fidelity computational framework that integrates density functional tight binding with machine-learned interatomic potentials, we systematically investigate thermal transport and elastic behavior in three-dimensional COFs with nearly identical chemistry and density but distinct topologies. With our emergent computational framework for modeling phonon transport, we show that framework topology alone can tune thermal conductivity by more than an order of magnitude and elastic modulus by nearly a factor of 10, with optimized COFs exhibiting room-temperature thermal conductivities exceeding 10 W m^-1 K^-1 and Young's moduli approaching ∼160 GPa, which are values uncommon for nanoporous polymers. Spectral and heat-flux decomposition analyses reveal that cooperative node-linker vibrational coupling enables long phonon lifetimes and mean free paths comparable to those of fully dense inorganic crystals, while simultaneously enhancing mechanical rigidity through balanced stress distribution. In contrast, such correlated transport is suppressed in metal-organic frameworks due to mass mismatch and bond heterogeneity. These findings establish node-linker topology as a powerful and general design principle for simultaneously optimizing thermal and mechanical performance in nanoporous materials, providing a framework for the design of lightweight thermomechanical materials.