Side Chain Vibration Triggers the Thermosalient Effect in an Organic Crystal of Asymmetric Fluorenone Derivatives

Materials with dynamic effects are invaluable for the advancement of microscale actuators and soft robotics. However, the directional construction and mechanistic research of dynamic molecular crystals remains challenging. Here, we introduce a flexible methoxy group into a rigid fluorenone system to modulate intermolecular interactions, thereby inducing thermosalient effects. During the single-crystal-to-single-crystal phase transition, the α-phase of 2-MeP-7-PFO crystal exhibits various dynamic behaviors such as hopping, flipping, and breaking. In contrast, the β-phase crystal is primarily characterized by jumping, promising its potential for application in microdrive devices. A comprehensive analysis using in-situ snapshots, single-crystal X-ray diffraction, Raman spectroscopy, and theoretical calculations reveals that incorporating the methoxy group introduces significant structural disorder, which contributes to the dynamic response of the system. The construction of these thermosalient crystals provides valuable insights and guidance for the advancement of dynamic crystalline materials.