New Chemistry of CTC-based Cavitands and Cryptophanes - Spin-Transition Switches, Near-IR Absorbers and Hosts for Gases

环三藜芦烯(CTV)是一种浅碗形的刚性环状分子，具有与其空腔中的其他分子结合的公认能力。虽然可以容纳溶剂和其他小有机分子客体，但CTV特别值得注意的是它能够与富勒烯(C60)和其他球形或球状化合物结合。因此，CTV是一类被称为空洞的重要超分子宿主的典型例子；也就是具有客人可进入的空洞的分子。这项提议的标题化合物是环三叠氮杂环烯(CTC)，是CTV的略微精简版本，具有相同的刚性碗形状。这项提议涉及将CTV化学扩展到几个新的领域。首先，是通过制备具有氧化禁用功能的CTV的化学修饰的衍生物，以将金属离子结合在分子碗边缘周围的方式布置。先例表明，碗状空穴在这些条件下可能很容易被氧化，产生金属稳定的自由基产物。人们特别感兴趣的将是确定激进的中间派能否在碗里跳来跳去。如果他们能做到这一点，这将使这些化合物强烈吸收红外线辐射。如果是这样的话，下一步将是研究打开和关闭红外吸收的方法。这可以通过电化学来实现，或者在适当设计的材料中，通过加热或冷却来实现。这种可切换的近红外吸收器在光纤通信设备中非常有用。将金属中心绑定到有线电视的外围也将产生显著扩大其腔的效果，使其直径增加一倍以上。我们还将研究这些新扩大的洞穴作为接待小型和大型有机客人的场所。特别令人感兴趣的是腔内客体结合对上一段中提到的光吸收和开关现象的影响。我们还将把两个CTV碗连接在一起，以制造新的胶囊分子。我们将寻求两种方式来实现这一点。如果我们使用金属离子间隔物将碗连接在一起，我们将制造出相对较大的胶囊，它将有可能像以前一样形成可切换的自由基产品。现在，我们制造的自由基中心将有可能在胶囊的两半之间跳跃，以及在两个单独的碗周围迁移，这可能会导致更复杂的光谱和切换行为。我们还将研究另一类新的胶囊，它们具有相当不同的潜在用途。这将是迄今已知的最小的共价胶囊分子，它将具有合适的大小来结合氢气、氧气或二氧化碳等气体分子。气体的超分子络合物是非常不寻常的。除了他们强烈的学术兴趣外，络合作用还能使气体比没有络合的情况下更容易溶解。这涉及到两个特殊的技术问题。首先是废物修复。例如，能够强烈结合二氧化碳的太空舱可以从发电站排放的气体中去除温室气体。其次是在医学领域，可以使用氙气和二氧化碳的特定同位素来增加诊断图像的对比度。一种可以增加体内组织中这些气体浓度的添加剂将带来更清晰的图像。Halcrow博士在基于金属-有机分子化合物的可切换材料研究方面拥有丰富的专业知识，而Hardie博士是CTV及其类似物的合成和主持人：客体化学方面的世界领先者。

Cyclotriveratrylene ('CTV') is a rigid cyclic molecule with a shallow bowl shape, that has a well-established ability to bind other molecules in its cavity. While solvents and other small organic molecule guests can be accommodated, CTV is particularly notable for its ability to bind to fullerene (C60) and other spherical or globular compounds. As such, CTV is a prototypical example of an important class of supramolecular host known as the cavitands; that is, molecules with guest-accessible cavities. Cyclotriguaiacyclene (CTC), the title compound of this proposal, is a slightly cut-down version of CTV with the same rigid bowl shape.This proposal involves an extension of CTV chemistry into several new areas. First, is by preparing chemically modified derivatives of CTV with oxidisable functionalities, disposed in such a way as to bind metal ions around the edge of the molecular bowl. Precedent suggests that the bowl-shaped cavitand might be easily oxidised under these conditions, yielding metal-stabilised free radical products. Of particular interest will be to determine whether the radical centres can hop around the bowl. If they can, that would make the compounds strongly absorb infra-red radiation. If so, the next step would be to investigate ways of switching that IR absorption on and off. That might be done electrochemically or, in appropriately designed materials, by warming it up or cooling it down. Switchable near-IR absorbers like these can be very useful in fibre-optic communications devices.Binding metal centres to the periphery of CTV will also have the effect of substantially extending its cavity, more than doubling its diameter. We will also investigate these new enlarged cavitands as hosts for small and large organic guests. Of particular interest will be the effects of in-cavity guest binding on the light absorption and switching phenomena mentioned in the previous paragraph.We will also link two CTV bowls, on top of each other, to make new capsule molecules. There are two ways we will seek to do this. If we use metal ion spacers to join the bowls together, we will make relatively large capsules that will have potential to form switchable free-radical products as before. Now, the radical centres we make will have potential to jump between the halves of the capsule, as well as migrating around the two individual bowls, which might lead to even more complicated spectroscopic and switching behaviour. We will also study another new class of capsule, which have a rather different potential use. These will be the smallest covalent capsule molecules yet known, which will be of appropriate size to bind gas molecules like hydrogen, oxygen or carbon dioxide (among others). Supramolecular complexes of gases are very unusual. As well as their strong academic interest, complexation has the effect of making the gas more soluble than it would otherwise be. This has implications for two particular technological problems. First is waste remediation. A capsule that can bind CO2 strongly could strip that greenhouse gas from power station emissions for example. Second is in medicine, where particular isotopes of xenon and carbon dioxide can be used to add contrast to diagnostic images. An additive that can increase the concentration of those gases in bodily tissue will lead to clearer pictures.Dr Halcrow has strong expertise in the study of switchable materials based on metal-organic molecular compounds, while Dr Hardie is a world leader in the synthesis and host:guest chemistry of CTV and its analogues.