Towards a Complete Description of a Polymorphic Crystal: The Example of Perylene

Abstract Crystal structures of the two polymorphs of perylene have been determined at low temperatures (150 and 200 K), and the molecular geometry was compared with earlier crystallographic and NMR measurements. Cell dimensions have been measured for both polymorphs over the ranges 150–320 K for (EI‐ β ) and 150–420 K for (EII‐ α ). Combination of thermodynamic and crystallographic measurements has permitted inference of pressuretemperature phase diagrams for perylene and pyrene that are compatible with available measurements up to ca. 50 kbar. Perylene and pyrene are both enantiotropic systems, while phenazine appears to be monotropic.