Self-assembly mechanism in nucleation processes of molecular crystalline materials

Abstract

Molecular crystals consist of an array of periodically arranged molecules in a three-dimensional space. Although nowadays we can routinely obtain crystal structures at the atomic level, the picture of how individual molecules gather together in an orderly manner and grow into crystals of visible size is still unresolved. Over the last decade, we focused on the mechanism of crystal nucleation, which is the initial step of crystallization®it plays a critical role in determining the crystal structure. We investigated the self-assembly mechanism of crystal nuclei of organic crystals and metalorganic frameworks using single-molecule-level electron microscopic imaging and bulk analysis. Statistical information on the size and structure of the individual prenucleation clusters, which cannot be investigated by conventional analytical methods, allowed us to study how the nucleating crystals acquire order and dimensionality in the nucleation process. We expanded understandings of the nucleation process to prepare submicrometer-sized amorphous particles of organic compounds from supersaturated solution by suppressing transition to crystalline nuclei, by external environment control. Further elucidation of the nucleation mechanism for various molecules will realize the controlled formation of crystals with desired structure and morphology, thus improving the efficiency of industrial processes, e.g., the production of pharmaceuticals and organic electronic devices.