Thermosalient effect of two polymorphs of a diketopyrrolopyrrole dye with different crystal systems and molecular arrangements

Two polymorphs of a N,N'-dipropylated diketopyrrolopyrrole dye, one yellow and the other orange, were obtained. The yellow polymorph showed a mechanical response upon heating. The X-ray analytical results indicated that the yellow polymorph changed into the orange one during the mechanical response, with a significant change in molecular conformation, molecular arrangement, and space group.