Crystal-to-crystal polymorphic phase transition in a cocrystal accompanied by expansion and surface wettability change

Abstract

In this study, cocrystallization of n-propylparaben and a ditopic bipyridine-based azine derivative in a 2 : 1 stoichiometric ratio was carried out. The resulting single crystals of the cocrystal displayed crystal-to-crystal polymorphic phase transformation on heating. The phase transformation is associated with naked-eye visible expansion and cracking of the single crystals. The two polymorphs are distinct in their surface wettability.