Three differently coloured polymorphs of 3,6‐bis(4‐chlorophenyl)‐2,5‐dipropyl‐2,5‐dihydropyrrolo[3,4‐c]pyrrole‐1,4‐dione

• Published in: Acta crystallographica Section B, Structural science, crystal engineering and materials Structural science, crystal engineering and materials, 2019-06, Vol.75 (3), p.414-422
• Main Authors: So, Hee-Soo, Matsumoto, Shinya
• Format: Article
• Language: English
• Subjects: conformational polymorph; diketopyrrolopyrrole; halogen‐bonding interaction; propyl substituent
• ISSN: 2052-5206; 2052-5206
• DOI: 10.1107/S2052520619004773

In this paper, the conformational polymorphism of a chlorinated diketopyrrolopyrrole (DPP) dye having flexible substituents in a non‐hydrogen‐bonding system is reported. The propyl‐substituted DPP derivative (PR3C) has three polymorphic forms, each showing a different colour (red, orange and yellow). All polymorphs could be obtained concomitantly under various crystallization conditions. The results of the crystal structure analysis indicate that PR3C adopts different conformations in each polymorph. The packing effect caused by the difference in the arrangement of neighbouring molecules was found to play an important role in the occurrence of the observed polymorphism. The thermodynamic stability relationship between the three polymorphs was identified by thermal analysis and indicates that the yellow polymorph is the thermally stable form. The results indicate that the yellow form and orange form are enantiotropically related, and the other polymorph is monotropically related to the others. A very rare example of a diketopyrrolopyrrole derivative showing polymorphism with completely different molecular conformations and a different arrangement of neighbouring molecules is reported. The thermodynamic stability relationships between the three polymorphic forms are also interpreted.