Guiding the Design of Multifunctional Covalent Organic Frameworks: High-Throughput Screening of Thermal and Mechanical Properties.

Covalent organic frameworks (COFs) are crystalline, porous polymers with exceptional structural tunability and low density, making them ideal candidates for diverse applications, including gas storage, catalysis, electronics, and thermal management. However, their widespread use is often hindered by limited thermal and mechanical stabilitiesproperties that are not well understood across the vast COF chemical space. In this work, we perform a comprehensive high-throughput screening of over 38,000 2D and 3D COFs, comprising more than 1,000 unique organic linkers, to explore their mechanical stiffness and thermal conductivity through large-scale atomistic simulations. Our results reveal that COFs span an extraordinarily wide property space, with thermal conductivities ranging from ∼0.02 W m-1 K-1 to ∼50 W m-1 K-1 and bulk moduli from less than 0.1 to 100 GPa. Surprisingly, we discover that high thermal conductivity can arise not only in stiff frameworks but also in mechanically flexible COFs through directional alignment and anisotropy. Flexible COFs with carbon-carbon or carbon-nitrogen linkages, moderate-to-high densities, and low or intermediate void fractions exhibit ultrahigh thermal conductivities with phonon mean free paths that can extend up to several hundred nanometers when polymeric chains are well-aligned along the transport direction. These findings overturn conventional assumptions linking stiffness to thermal transport and demonstrate that structure-property relationships in COFs are highly tunable via chemical composition and topology. By establishing predictive design rules for achieving multifunctionality in porous polymers, this study provides a valuable roadmap for developing next-generation COFs with tailored thermal and mechanical performance.