Supramolecular Chemistry with Heavy Main-Group Elements

超分子化学寻求对分子间作用力的理解和应用。超分子系统的终极例子是一个生命体，在这个生命体中，大量的分子被组织成精巧的自组装结构，并演奏出令人惊叹的化学和物理过程的交响乐。化学家在实验室中研究的较为温和的系统主要基于少数超分子相互作用，即氢键、金属离子的配位和由碳原子构成的平面结构的堆叠。然而，其他分子间相互作用的详细研究才刚刚开始。我在麦克马斯特大学的研究小组在加拿大率先系统地研究了“ChB键合”（ChB），这是富电子原子与渴望负电荷的硫原子（元素周期表中氧族的重成员）之间的相互作用。典型的ChB原子间距离比“规则的共价键”长得多，并且可以在相互作用分子结构变化最小的情况下可逆地形成和断裂。这种现象类似于氢键，但由于重原子的性质而更加复杂。值得注意的是，ChB相互作用具有独特的特征，有助于调整与技术应用相关的材料的结构和物理性质。本课课组之前的研究表明，ChB相互作用导致宏观光学性质，如显色性，并可以诱导具有非线性光学性质的晶体的生长。与其他分子间相互作用相比，ChB实现了分子间电子迁移，这一特性可以实现半导体特性，并可用于构建自组装分子线。这种导电的单分子厚结构对构建集成电路很有吸引力，因为与全硅元件相比，它们不太容易发生电流泄漏。在这里，自组装分子有一个特别的优势：热力学使错误能够自我纠正，这解决了在合成低硫噻吩和其他大型有机分子时不可避免的偶尔缺陷的问题，这些有机分子通常用于纳米技术的分子电子学部分。我们的首要目标是确定在功能超分子结构中利用ChBs的方法。在下一个资助期内，我们将会扩充屋宇署的积木及自组装构筑物。虽然我们的研究追求基本的理解，但从这项工作中获得的知识与精细化学合成、光学信息技术和电子等多种行业的应用高度相关。因为这个研究项目结合了现代化学的多种实验和计算方法，它构成了为加拿大工业、国家实验室和学术界培养高素质人才的优秀工具。

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.