Organic Crystalline Optical Waveguides That Remain Elastic from −196 to ≈200 °C

Organic crystals that are capable to deform (reversibly or irreversibly) similar to polymer materials have been widely reported over the past ten years. However, most of the reported organic crystals can only be elastically bent within a narrow temperature range, and reports on their thermal behavior that would encourage applications of these energy-transducing elements in extreme conditions are not readily available. This work designs a linear and flat π-conjugated molecule with double intramolecular hydrogen bonds that prevent thermally induced conformational distortions. The molecule assembles as a rigid building block into centimeter-sized wide organic crystals that can be elastically bent over a temperature range spanning close to 400 °C, from −196 to ≈200 °C. The emission wavelength of the crystals is also temperature dependent, and can be continually tuned from 547 to 577 nm upon heating from 20 to ≈200 °C. This inspires the design of a lightweight, organic, elastic optical waveguide where the output energy is controlled by the operating temperature. The wide range of crystal flexibility expands the range of conditions for application of organic crystals as optical waveguides.