Side Chain Vibration\nTriggers the Thermosalient Effect\nin an Organic Crystal of Asymmetric Fluorenone Derivatives

Materials\nwith dynamic effects are invaluable for the\nadvancement\nof microscale actuators and soft robotics. However, the directional\nconstruction and mechanistic research of dynamic molecular crystals\nremains challenging. Here, we introduce a flexible methoxy group into\na rigid fluorenone system to modulate intermolecular interactions,\nthereby inducing thermosalient effects. During the single-crystal-to-single-crystal\nphase transition, the α-phase of 2-MeP-7-PFO crystal exhibits\nvarious dynamic behaviors such as hopping, flipping, and breaking.\nIn contrast, the β-phase crystal is primarily characterized\nby jumping, promising its potential for application in microdrive\ndevices. A comprehensive analysis using in-situ snapshots, single-crystal\nX-ray diffraction, Raman spectroscopy, and theoretical calculations\nreveals that incorporating the methoxy group introduces significant\nstructural disorder, which contributes to the dynamic response of\nthe system. The construction of these thermosalient crystals provides\nvaluable insights and guidance for the advancement of dynamic crystalline\nmaterials.