Tetrafluoro(aryl)sulfanylated Bicyclopentane Crystals That Self-Destruct upon Cooling

Whereas single crystals of organic compounds that respond to heat or light have been reported and studied in detail, studies on crystalline organic compounds that elicit an extreme mechanical response upon cooling to very low temperatures are relatively rare in the chemical literature. A tetrafluoro(aryl)sulfanylated bicyclopentane synthesized in our laboratory was discovered to exhibit such behavior; i.e., the crystals jumped and forcefully disintegrated upon cooling below ∼193 K. Accordingly, the origin of this low-temperature thermosalient effect was investigated through NMR, SC-XRD, PXRD, microscopy, DSC, Raman, and Brillouin experiments. To our surprise, NMR, SC-XRD, PXRD, and DSC experiments suggest the phenomenon can neither be attributed solely to a chemical transformation nor a phase transition of the entire material. Rather, XRD, Raman, and Brillouin experiments provide evidence that built-up strain released from the crystal upon self-destruction may be associated with crystal microstructure or a phase transition that occurs in another material (i.e., an impurity) in the crystal. This study demonstrates that molecular structural changes in organic material microstructure or impurity phases (which may not necessarily be visible by X-ray diffraction) can have a significant impact on the behavior of the bulk crystalline material. Thus, the role of microstructure may be considered more heavily in future mechanistic studies on mechanically responsive crystals.