Supramolecular Chemistry with Heavy Main-Group Elements

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Supramolecular chemistry seeks understanding and application of the forces between molecules. The ultimate example of a supramolecular system is a living entity, in which a multitude of molecules are organized into exquisitely self-assembled structures and perform an astonishing symphony of chemical and physical processes. The more modest systems studied by chemists in the laboratory have been primarily based on a handful of supramolecular interactions, namely hydrogen bonding, coordination of metal ions, and stacking of flat structures made from carbon atoms. However, other intermolecular interactions are just beginning to be investigated in detail. My research group at McMaster has pioneered in Canada the systematic investigation of "Chalcogen Bonding" (ChB), which is the interaction between electron-rich atoms and atoms of the chalcogens (the heavy members of the oxygen family of the periodic table) that are avid for negative electric charge. Typical ChB interatomic distances are much longer than "regular covalent" bonds and can be reversibly formed and broken with minimal structural changes of the interacting molecules. This phenomenon is analogous to hydrogen bonding, but more complex due to the nature of heavy atoms. Notably, ChB interactions have unique features that help tune the structure and physical properties of materials relevant to technological applications. Previous work by our group showed that ChB interactions lead to macroscopic optical properties such as chromotropism and can induce the growth of crystals with nonlinear optical properties. In contrast to other intermolecular interactions, ChB enables intermolecular electron mobility, a feature that can enable semiconductor properties and could be applied to build self-assembled molecular wires. Such conducting one-molecule thick structures are appealing to construct integrated circuits because, compared to all-silicon components, they should be less prone to current leaks. Here self-assembling molecules have a particular advantage: thermodynamics enables error self-correction, which solves the problem of occasional defects that are inevitable in the synthesis of oligothiophenes and other large organic molecules commonly used in the part of nanotechnology known as molecular electronics. Our overarching goal is to define methods to utilize ChBs in functional supramolecular structures. During the next grant period, we will expand the repertoire of ChB building blocks and self-assembled structures. While our investigations pursue a fundamental understanding, knowledge derived from this work is highly relevant to applications in industries as diverse as fine-chemical synthesis, optical information technologies, and electronics. Because this research program combines a wide variety of experimental and computational methods of modern chemistry, it constitutes an excellent vehicle to train highly qualified personnel for Canadian industry, national laboratories, and academia.