Enantiotropic Polymorphism in Di-indenoperylene

The enantiotropic polymorphic phase transformation of di-indenoperylene (DIP) at 403 K has been structurally characterized, using single-crystal X-ray diffraction. Both the low temperature α- and the high-temperature β-phase have a herringbone-type structure, with the α-phase being triclinic with doubled unit cell volume compared to the monoclinic β-phase. In the latter, the molecules have a more upright orientation in the herringbone plane. The epitactic transformation from β- to α-phase involves strong shearing displacements as well as bending and torsional deformations of the DIP molecules.