Directly measured high in-plane thermal conductivity of two-dimensional covalent organic frameworks

Two-dimensional covalent organic frameworks are promising low-density porous materials for lightweight thermal management, yet comprehensive thermal conductivity measurements remain scarce. Particularly, direct in-plane thermal conductivity data for large-area, fully suspended covalent organic framework thin films has not been reported previously. This study addresses this gap by measuring in-plane and cross-plane thermal conductivities of two-dimensional covalent organic frameworks with varying pore sizes using laser-based pump-probe techniques. Transient thermal grating spectroscopy revealed a high in-plane thermal conductivity of 1.18 ± 0.21 W/(m⋅K) for a sample with a 1.4 nm pore size, highlighting a notable pore size effect. Cross-plane thermal conductivity measured via frequency-domain thermoreflectance indicated weak thermal anisotropy for samples with larger pores. Grazing-incident wide-angle X-ray scattering provided structural insights and clarified heat conduction mechanisms. These direct in-plane thermal conductivity measurements enhance understanding of thermal transport behaviors in covalent organic frameworks, supporting their development as advanced thermal management materials.