Decimeter-length elastic organic crystals capable of mechanical post-processing and optical waveguide modulation at 77 K.

The development of decimeter-length organic crystals that remain elastic, functional, and machinable at extremely low temperatures, such as in liquid nitrogen (LN) environments, is a great challenge. Here, we report two novel elastic organic crystals, 1 and 2, derived from mono-benzene compounds. Crystals 1 are elastically bendable with decimeter-scale length (>10 cm) and exhibit better elastic bending ability at LN temperature compared to room temperature. In contrast, centimeter-length crystals 2 show reduced elasticity at LN temperature. Notably, crystals 1 can be cut and stripped at LN temperature. To the best of our knowledge, this is the first report on the cryogenic machinability of organic crystals. By crystallographic analyses of 1 and 2, intermolecular interactions are shown to be responsible for their distinct crystal habits and cryogenic machinability. In addition, after stripping, crystals 1 exhibit programmable optical waveguide properties that vary in proportion to the crystal width and thus have the potential for applications as tunable wavelength modulators, capable of real-time two-dimensional motion detection in cryogenic environments. This material not only advances the field of flexible organic crystals but also opens up new possibilities for the development of smart materials that can be used under extreme conditions.