Electrostatic interactions dominate thermal conductivity and anisotropy in three-dimensional hydrogen-bonded organic frameworks

Abstract

Hydrogen-bonded organic frameworks (HOFs), an emerging class of porous molecular materials assembled through hydrogen bonds (H-bonds), have shown intriguing latent for multifunctional materials or devices. Understanding thermal transport in HOFs is crucial to guiding the functional material design with desired thermal properties. Here, we report thermal transport properties in HOFs and reveal the significance of electrostatic interactions (H-bonds and π-π interactions) to heat conduction with molecular dynamics simulations. It is found that despite relatively weak H-bonds, tetracarboxylic-based frameworks (TCFs), a three-dimensional (3D) HOF, show relatively high thermal conductivity compared with known 3D porous covalent organic frameworks and metal-organic frameworks. Electrostatic interactions in TCFs dominate thermal conductivity and anisotropy but central atoms in the monomers show negligible impact. The structural analysis and x-ray diffraction patterns highlight the importance of electrostatic interactions in maintaining the high crystallinity of TCFs. The vibrational density of states and spectral thermal conductivity further demonstrate that phonon modes with frequencies below 25 THz contribute about 90 % of total thermal conductivity in TCFs, and electrostatic interactions sustain phonon modes with frequencies of 5–25 THz to carry heat. These findings provide a fundamental understanding of structure-thermal conductivity relation in HOFs and advance their applications for multifunctional materials and devices.