Chlorinated diketopyrrolopyrrole dye exhibits a three-step polymorphic transition with thermosalient effects†
A tetramorphic system was discovered in a diketopyrrolopyrrole dye (3,6-bis(4-chlorophenyl)-2-propyl-2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione), with thermosalient effects during thermal phase transitions. Two polymorphs, the red and orange forms, were obtained using liquid–liquid and liquid–gas diffusion. The other two polymorphs, the vermilion and deep red forms, were obtained by a thermal phase transition from the red and orange forms, respectively. The orange form was also prepared by a thermal phase transition from the vermilion form. Crystallinity was maintained during these thermal phase transitions. The thermosalient effect was also observed during each phase transition, with crystal deformation as the major observed effect. The molecular and crystal structures of the red, orange, and vermilion forms were analysed in terms of structural similarity and the intermolecular interactions.