Polymorphic transition is important for the functionality of crystalline materials. However, the
underlying mechanism remains unclear, especially when the crystal structure contains disordered
fragments. We report that C−H⋯π interactions play an important role in polymorphic transitions in
a molecular crystal with disordered fragments. The crystal has three phases, namely the a (< -80°C),
β (-80-40°C), and γ (< 40°C) phases, which are reversible through single-crystal-to-single-crystal
transformation in association with temperature change. Disorder of bulky tert-butyl substituents
appears at high-temperature in the β and γ phases. Intermolecular interaction analysis based on
Hirshfeld surfaces and related fingerprint plots revealed that the proportion of π⋯π interactions
decreased, while that of C−H⋯π interactions increased, at the transition from a to β phase. The
proportion of C−H⋯π interactions also increased at the transition from β to γ phase, but continuously
decreased in the β phase due to elevated temperature. Intermolecular interaction energies clarified the
contribution of C−H⋯π interactions to the stability of high-temperature crystal β and γ phases via polymorphic transitions. Our results potentially lead to design molecular crystals with polymorphic
transitions.
Contribution of C−H⋯π Interactions to Polymorphic Transitions of a Molecular Crystal with Disordered Fragments
