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

我们能把化学自组装推进到什么程度？这是《科学》杂志为纪念其125周年而提出的25个当前“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之间的相互作用来构建日益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部位观察到的)一直是推动小构件自发组织成大型、复杂、有时甚至是功能结构的最常用的力量。在垂直方向上，目标是建立更大的层级结构。在横向上，其意图是扩展自组装范例，以利用其他交互作用。环状“圆周率堆积”(凝聚碳纳米管的“胶”)和“范德华力”(蜡在环境条件下是固体的原因)的使用现在已经得到了很好的证明。其他分子间力之所以没有被使用，主要是因为到目前为止，人们对它们知之甚少，就像重的p-块元素(位于元素周期表右下方的元素)所形成的原子间接触一样。对这一现象的连续命名与我们理解的演变平行：最初的“非键合接触”变成了“弱键合相互作用”，现在术语“二次键合相互作用”(缩写为SBI)越来越多地被接受。这项申请为一个研究项目寻求资金，该项目致力于在超分子化学和分子自组装中使用重p-嵌段元素的SBI。SBI具有独特的特征，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SBI增强了导电性。此外，SBIs还可以稳定成分不寻常的化合物。一个相关的研究领域涉及重主族元素化合物的高级光学性质，它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.