Abstract text (incl. figure legends and references)

Organic crystal nucleation and growth are complex processes that often do not fit into the scope of the existing crystallization theories. We investigated a crystal growth mechanism of an organic dye, perylene diimide, using high-resolution cryogenic transmission electron microscopy and optical spectroscopy. We were able to demonstrate that the evolution of order in our system had a high level of complexity and involved both classical and nonclassical steps. The crystallization mechanism included a series of supramolecular transformations, where each step defined the next one. The crystal growth started from a molecular self-assembly into π-stacks that eventually underwent intermolecular ordering that optimized interactions within the stacks. The latter transformed at the larger scale, by stack interactions, which formed crystalline domains. Finally, the formed faceted crystals gradually grew through oriented attachment of other crystal, and attachment of residual monomeric molecules from solution (Figure 1).

Fig.1 An illusration of order evolution during the crystallization of perylene diimide.

Our findings present a detailed insight into organic crystal growth and reveal that both classical and nonclassical mechanisms can operate within a crystallization process. However, classical/nonclassical dichotomy provides only a partial insight into the crystallization mechanism, which may be described as a sequence of supramolecular events, traversing a vast size scale from the optimization of intermolecular interactions to the oriented attachment of crystals. In summary, our work revealed the inherent nature of supramolecular transformations occurring in organic crystallization, thus advancing conceptually our understanding of order evolution in organic matter.¹

1. Biran, I.; Rosenne, S.; Weissman, H.; Tsarfati, Y.; Houben, L.; Rybtchinski, B. Cryst. Growth Des. 2022, 22 (11), 6647–6655.