Plastic Deformation in a Molecular Crystal Enables a Piezoresistive Response

Organic materials are promising candidates for the development of efficient sensors for many medicinal and materials science applications. Single crystals of a small molecule, 4-trifluoromethyl phenyl isothiocyanate (4CFNCS), exhibit plastic deformation when bent, twisted, or coiled. Synchrotron micro-focus X-ray diffraction mapping of the bent region of the crystal confirms the mechanism of deformation. The crystals are incorporated into a flexible piezoresistive sensor using a composite constituting PEDOT: PSS/4CFNCS, which shows an impressive performance at high-pressure ranges (sensitivity 0.08 kPa^-1 above 44 kPa).

Temperature-Reliant Dynamic Properties and Elasto-Plastic to Plastic Crystal (Rotator) Phase Transition in a Metal Oxyacid Salt

Although, dynamic crystals are attractive for use in many technologies, molecular level mechanisms of various solid-state dynamic processes and their interdependence, remain poorly understood. Here, we report a rare example of a dynamic crystal (1), involving a heavy transition metal, rhenium, with an initial two-face elasticity (within ≈1 % strain), followed by elasto-plastic deformation, at room temperature. Further, these crystals transform to a rotator (plastic) crystal phase at ≈105 °C, displaying exceptional malleability. Qualitative and quantitative mechanical tests, X-ray diffraction, μ-Raman and polarized light microscopy experiments reveal that the elasto-plastic deformation involves both partial molecular rotations and slip, while malleability in the rotator phase is facilitated by reorientational motions and increased symmetry (slip planes). Our work, connecting the plastically bendable (1D or 2D) crystals with the rotator phases (3D), is important for designing multi-functional dynamic crystals.

Self-Waveguide Single-Benzene Organic Crystal with Ultralow-Temperature Elasticity as a Potential Flexible Material

With the increasing popularity and burgeoning progress of space technology, the development of ultralow-temperature flexible functional materials is a great challenge. Herein, we report a highly emissive organic crystal combining ultralow-temperature elasticity and self-waveguide properties (when a crystal is excited, it emits light from itself, which travels through the crystal to the other end) based on a simple single-benzene emitter. This crystal displayed excellent elastic bending ability in liquid nitrogen (LN). Preliminary experiments on optical waveguiding in the bent crystal demonstrated that the light generated by the crystal itself could be confined and propagated within the crystal body between 170 and -196 °C. These results not only suggest a guideline for designing functional organic crystals with ultralow-temperature elasticity but also expand the application region of flexible materials to extreme environments, such as space technology.

Mechanical-Bending-Induced Fluorescence Enhancement in Plastically Flexible Crystals of a GFP Chromophore Analogue

Single crystals of optoelectronic materials that respond to external stimuli, such as mechanical, light, or heat, are immensely attractive for next generation smart materials. Here we report single crystals of a green fluorescent protein (GFP) chromophore analogue with irreversible mechanical bending and associated unusual enhancement of the fluorescence, which is attributed to the strained molecular packing in the perturbed region. Soft crystalline materials with such fluorescence intensity modulations occurring in response to mechanical stimuli under ambient pressure conditions will have potential implications for the design of technologically relevant tunable fluorescent materials.