Low-Temperature Dynamics at Nano- and Macroscales: Organic Crystal That Exhibits Low-Temperature Molecular Motion and the Thermosalient Effect

The thermosalient effect is a rarely observed, potentially very useful and at the present, unpredictable mechanical response during a phase transition that is thought to hold the potential for rapid and clean energy conversion devoid of gaseous products. Here, we report the serendipitous discovery of a rare instance of a thermosalient organic solid that exhibits the effect below room temperature. The crystals of this carbazole-based material are dynamic at both molecular and macroscopic scales. Using variable temperature synchrotron X-ray diffraction and variable-temperature solid-state nuclear magnetic resonance (ssNMR), we thoroughly examined the hysteretic structural transition in this material, emphasizing its macroscopic reconfigurability. We discovered unexpected large-amplitude molecular oscillations in the low-temperature phase, which challenge conventional assumptions about salient materials. Notably, we combined ²H ssNMR with computational modeling to reveal this dual-scale dynamism, setting the groundwork for advancements in energy-efficient actuators, sensors, and intelligent materials. This work might open new avenues for developing crystalline materials that can be implemented in innovative devices operating seamlessly across various scales.