Abstract
Connecting molecular-level phenomena to larger scales and, ultimately, to sophisticated molecular systems that resemble living systems remains a considerable challenge in supramolecular chemistry. To this end, molecular self-assembly at higher hierarchical levels has to be understood and controlled. Here, we report unusual self-assembled structures formed from a simple porphyrin derivative. Unexpectedly, this formed a one-dimensional (1D) supramolecular polymer that coiled to give an Archimedean spiral. Our analysis of the supramolecular polymerization by using mass-balance models suggested that the Archimedean spiral is formed at high concentrations of the monomer, whereas other aggregation types might form at low concentrations. Gratifyingly, we discovered that our porphyrin-based monomer formed supramolecular concentric toroids at low concentrations. Moreover, a mechanistic insight into the self-assembly process permitted a controlled synthesis of these concentric toroids. This study both illustrates the richness of self-assembled structures at higher levels of hierarchy and demonstrates a topological effect in noncovalent synthesis.
Highlights
Connecting molecular-level phenomena to larger scales and, to sophisticated molecular systems that resemble living systems remains a considerable challenge in supramolecular chemistry
When the solution was spin-coated onto a highly oriented pyrolytic graphite (HOPG) substrate and examined by atomic-force microscopy (AFM), we were surprised to find that the 1D supramolecular polymer coiled to form a series of circular nanosheets (Fig. 2c, d)
The surface visualized by AFM is not satisfactorily explained by the proposed molecular packing geometry of 6FF in the Archimedean spiral. To address this discrepancy between the spacing and the sidechain distance, we examined the Archimedean spiral by scanning transmission electron microscopy (STEM) and by small-angle Xray scattering (SAXS)
Summary
Connecting molecular-level phenomena to larger scales and, to sophisticated molecular systems that resemble living systems remains a considerable challenge in supramolecular chemistry. One of us[6] identified pathway complexity in supramolecular polymerization, the mechanism of which was elucidated experimentally and computationally, thereby permitting the synthesis of an otherwise thermodynamically inaccessible helical supramolecular polymer In such cases, weak interactions and subtle structural constraints accumulate, and kinetic effects often play significant roles, resulting in unexpected outcomes. By unveiling this intricate self-assembly mechanism, we succeeded in obtaining supramolecular nanosheets with controlled areas and a distinct aspect ratio. A mechanistic insight into the self-assembly process of 6FF permitted a controlled synthesis of the concentric toroids
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