Elastic Bending Flexibility of a Fluorescent Organic Single Crystal: New Aspects of the Commonly Used Building Block 4,7-Dibromo-2,1,3-benzothiadiazole

Commercially available 4,7-dibromo-2,1,3-benzothiadiazole can be used as a building block for the organic synthesis of high performance optoelectronics devices. Herein, we report that a single crystal of 4,7-dibromo-2,1,3-benzothiadiazole displays elastic bending flexibility and crystalline-state fluorescence. A large needle-shaped single crystal (over 1 cm long) exhibited a fibril lamella type structure based on slip-stacked (J-aggregated) molecular wires. The crystal was capable of bending under applied stress and quickly reverts to its original shape upon relaxation. The crystal shows a reversible fluorescence change via mechanical bending–relaxation that can be performed many times.