Nonclassical Crystal Growth of Supramolecular Polymers in Aqueous Medium

A mechanistic understanding of the principles governing the hierarchical organization of supramolecular polymers offers a paradigm for tailoring synthetic molecular architectures at the nano to micrometric scales. Herein, the unconventional crystal growth mechanism of a supramolecular polymer of superbenzene(coronene)-diphenylalanine conjugate (Cr-FFOEt) is demonstrated. 3D electron diffraction (3D ED), a technique underexplored in supramolecular chemistry, is effectively utilized to gain a molecular-level understanding of the gradual growth of the initially formed poorly crystalline hairy, fibril-like supramolecular polymers into the ribbon-like crystallites. The further evolution of these nanosized flat ribbons into microcrystals by oriented attachment and lateral fusion is probed by time-resolved microscopy and electron diffraction. The gradual morphological and structural changes reveal the nonclassical crystal growth pathway, where the balance of strong and weak intermolecular interactions led to a structure beyond the nanoscale. The role of distinct & pi;-stacking and H-bonding interactions that drive the nonclassical crystallization process of Cr-FFOEt supramolecular polymers is analyzed in comparison to analogous molecules, Py-FFOEt and Cr-FF forming helical and twisted fibers, respectively. Furthermore, the Cr-FFOEt crystals formed through nonclassical crystallization are found to improve the functional properties. The concept of nonclassical crystal growth is applied to the fibril-to-crystal conversion of a supramolecular polymer. Gradual optimization of the intermolecular interactions and the favorable surface topology of the intermediates are found to be critical in the facile creation of a complex form of hierarchy.image

Automated summary

This study demonstrates the unconventional crystal growth mechanism of a supramolecular polymer, Cr-FFOEt, using 3D electron diffraction and time-resolved microscopy. The balance of strong and weak intermolecular interactions in the nonclassical crystal growth leads to the formation of structures beyond the nanoscale, improving the functional properties of the Cr-FFOEt crystals.