Twisted growth of organic crystal in a polymer matrix: Sigmoidal and helical morphologies of pyrene

The crystal morphology of pyrene formed in a solution changes from polyhedral shapes surrounded with flat planes into characteristic curving forms, such as sigmoidal and helical architectures, in the presence of polyvinyl pyrrolidone. Dendritic patterns and linear alignments of lozenge units are produced under the intermediate conditions. The formation of hierarchical structures with increasing the polymer concentration is based on a pile of pyrene units. The curving forms are inferred to be constructed through a twisted assembly of asymmetric units under diffusion-limited conditions. Because similar morphological variation was observed in other systems, such as chrysazin-polyvinyl pyrrolidone and pyrene-polystyrene, the controlled growth of organic crystals using the polymer matrix would provide a novel type of functional materials having various curving morphologies.