Phase Transformation, Thermal Expansion, Librations and Translations in Di-indenoperylene

The thermal expansion of the low temperature alpha-phase and the phase transformation to the enantiotropic polymorphic β- phase at 403 K in diindenoperylene (DIP) has been studied in the temperature range from 110 K to 430 K, using single crystal X-ray diffraction. Both - and β-phases have a herringbone-type structure, but the -phase is 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 transition to the -phase involves bending and torsion of the DIP molecules. Differential scanning calorimetry reveals values of 1.0±0.2 kJ/mol for the enthalpy and 2.4±0.5 J/(mol K) for the entropy, which are in good agreement with calculations by density functional theory.