Design, Synthesis and Supramolecular Assembly of Furan-Based Macrocycles: Understanding Intra- and Intermolecular Conjugation

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With the support of the Macromolecular, Supramolecular and Nanochemistry Program in the NSF Division of Chemistry, Drs. Kevin Noonan and Tomasz Kowalewski of Carnegie Mellon University aim to develop and explore a new class of cyclic (or ring-like) organic molecules comprised of smaller rings (“rings of rings”). Generally, the path to making cyclic molecules involves bending linear molecules to join the ends together. As the size of the ring increases, it can be difficult to make the “ends meet” resulting in lower yield of the desired structure. Noonan and Kowalewski recently discovered that short linear chains of small furan rings can be modified in such a way that they spontaneously bend into macrocyclic ring-like shapes. They will be exploring the extension of this method to different variants of small rings to tune the properties for different potential applications. In these cyclic structures, a portion of the electrons reside in so-called pi-bonds, which under certain conditions enables them to flow freely such that the material behaves as a metal or semiconductor rather than an insulator. As such, they belong to the family of “green” organic electronic materials that can be derived from biomass, with high promise for sustainable energy applications such as solar cells, displays, and catalysts for generation of fuels and chemicals. The interdisciplinary character of this work will lead to training of chemists with a unique skill set encompassing chemical synthesis, novel methods, and advanced computational tools facilitating precise, efficient, and environmentally friendly chemical synthesis. The PIs will also use social media and podcasts to raise public awareness on key scientific concepts of essential societal importance such as energy, sustainability, and health.Drs. Noonan and Kowalewski and their research teams will use a combination of synthesis, computation, and characterization to build a library of furan macrocycles and map the interplay between their structure and properties. The key synthetic strategy will involve using structure-directing ester side groups to promote efficient cyclization and extend it to achieve precise control of supramolecular assembly of these molecules. Computation will play a particularly important role in the studies of self-assembly by allowing exploration of a wide range of candidate structures and scenarios. It will help in determining the nature of intra- and intermolecular organization of the resulting nanostructures. Mapping the molecular and supramolecular properties of these materials will be paralleled, and correlated, with the investigation of their behavior in redox, charge transport and ion-binding processes. In addition, work on conjugated macrocycles will advance fundamental understanding of aromaticity by addressing key questions about the impact of molecular structure and conjugation on aromatic stabilization energy.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.