Turning Rattling Motions from Phonon Scatterers to Thermal Conductivity Enhancers in Hydrogen-Bonded Organic Frameworks.

Conventional rattling motions of guest species in porous materials suppress the thermal conductivity by scattering phonons. Here, we demonstrate a paradigm shift: rattling can be engineered into a thermal conductivity enhancer. Using molecular dynamics and phonon analysis of a hydrogen-bonded organic framework (TCF-1) loaded with xenon, we show that strengthening the host-guest interaction drives a transition from long-range diffusive (off-center) to localized (on-center) rattling. Reducing the guest mass in the on-center regime further intensifies localization. Both strategies boost thermal conductivity along the pore direction, with mass reduction achieving up to an 86% increase. The underlying mechanism is the emergence of a solid-like vibrational mode in confined gas, which reduces phonon scattering, blue shifts the rattling-induced flat band, and enhances heat transfer. Our work establishes rattling dynamics as a tuning knob for thermal transport, opening a new route to design porous crystals with tailored heat conduction for applications in gas management.