Heavy main-group elements in supramolecular chemistry and nonlinear optical materials

我们能把化学自组装推进多远？这是《科学》杂志为纪念其125周年而重点提出的25个“大问题”之一（第309卷，第5731期，2005年7月1日，第95页）。在过去的30年里，科学家们在利用分子间的相互作用构建越来越复杂的超分子结构方面取得了惊人的进展。这种方法通常受到自然界的启发：氢键（存在于液态水和DNA中）和金属离子的配位（如在血红蛋白的活性位点中观察到的）是最常用的力量，用于驱动小构件自发组织成大的，复杂的，有时是功能性结构。在垂直方向上，目标是建立更大的分层结构。在横向上，目的是扩展自组装范式，以利用其他相互作用。环的“π堆积”（使碳纳米管聚集的“胶水”）和“货车德瓦尔斯力”（蜡在环境条件下是固体的原因）的使用现在已经有了很好的文献记载。其他的分子间力没有被使用，主要是因为到目前为止，人们对它们的理解还很有限，比如重p区元素（位于元素周期表右下方的元素）的原子间接触。对这种现象的连续命名与我们理解的演变相平行：最初的“非键合接触”变成了“弱键合相互作用”，现在术语“次级键合相互作用”（缩写为SBI）正在获得越来越多的接受。该申请旨在为一项研究计划提供资金，该研究计划追求在超分子化学和分子自组装中使用重p-区元素的SBI。SBIs具有独特的功能，可以用来控制自组装材料的性能。例如，虽然氢键是电子迁移率的障碍，但SBIs增强了导电性。此外，SBIs可以稳定具有不寻常组成的化合物。一个相关的研究方向是重主族元素化合物的先进光学特性，这种特性将允许以光脉冲的形式传输和处理大量信息。

How far can we push chemical self-assembly? This is one of the 25 current "Big Questions" highlighted by the journal Science to mark its 125th anniversary (vol. 309, No. 5731, 1 July 2005, p. 95). During the last 30 years scientists have made astonishing progress in using the interactions between molecules to construct supramolecular structures with increasing complexity. This approach is often inspired by nature: hydrogen bonds (present in liquid water and DNA) and the coordination of metal ions (as observed in the active site of haemoglobin) have been the most-commonly used forces to drive the spontaneous organisation of small building blocks into large, complex, and sometimes functional structures. In a vertical direction, the goal is to build bigger and hierarchical structures. In the horizontal, the intention is to expand the self-assembly paradigm to take advantage of other interactions. The use of "pi-stacking" of rings (the "glue" that agglomerates carbon nanotubes) and "van der Waals forces" (the reason wax is solid under ambient conditions) is now well documented. Other intermolecular forces have not been used mostly because they have been poorly understood until now, as is the case for the inter-atomic contacts made by the heavy p-block elements (those on the lower right hand side of the periodic table). The succession of names given to this phenomenon parallels the evolution of our understanding: the initial "non-bonded contact", became "weakly bonding interaction" and now the term "secondary bonding interaction" (abbreviated SBI) is gaining increasing acceptance. This application seeks funding for a research program that pursues the use of SBIs of heavy p-block elements in supramolecular chemistry and molecular self-assembly. SBIs have distinctive features that can be exploited to control the properties of self-assembled materials. For example, while hydrogen bonds are barriers to electron mobility, SBIs enhance conductivity. In addition, SBIs can stabilise compounds with unusual compositions. A related line of research is concerned with advanced optical properties of compounds of heavy main-group elements that will permit transmission and processing of large amounts of information as light pulses.