Halogen-bonded Liquid Crystals

卤键液晶

• 批准号: EP/C011295/1
• 负责人: Duncan Bruce
• 金额: $ 26.52万
• 依托单位: University of York
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2006
• 资助国家: 英国
• 起止时间: 2006 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FC011295%2F1
• 关键词: Halogen; bonded; Liquid; Crystals

When a solid is heated, at some temperature it will melt to form a liquid (eg the melting of ice to form water). However some compounds exist in a state that is intermediate between the solid and liquid states and has some properties of both. This state is known as a 'liquid crystal phase' and the compounds that form it are called liquid crystals (LCs). LCs are familiar to all as liquid crystal displays found in mobile phones, calculators, laptop computers etc. LCs are important in other ways, too and, it is known that they are important in the workings of the cells of living organisms and are the reason soaps and washing-up liquids clean so well.The molecules which make up liquid crystals have a special shape, being either long and thin (like a pencil), or thin and flat (like a pizza), and chemists knows how to make molecules with these shapes. Occasionally it is possible to make these molecules by using two parts instead of one. Thus, if we want to make a rod-shaped molecule, then while neither of the two parts would be long enough to show a LC phase, joining them together would give a 'supermolecule' that did show a liquid crystal phase. Normally, very strong bonds hold the atoms in these molecules together, but here the two parts are held together by a very specific but rather weak interaction.One of these weak interactions, the 'hydrogen bond', has been known for many years, but there is a very similar interaction that is weaker and much less well known called the 'halogen bond'. Recently the Exeter team showed that it could make LCs by using a halogen bond to hold together a supermolecule. We now want to make more examples where we vary the two parts carefully so that we learn more about these supermolecules. Because halogen bonding is used in other parts of chemistry, what we learn will be important for others, too.As the name suggests, halogen bonds involve the elements we call the halogens, and one of the two parts (the acceptor) will contain at least one halogen; in this work the halogen will be iodine. In the acceptor the iodine carries some positive charge because the acceptor design means negative charge is pulled away from it. It is then be happy to find another part to join with that carries some negative charge. This other part is called a donor and ours contain a nitrogen atom. In the donor, negative charge is pushed towards nitrogen allowing it to be attracted to the positive iodine. The two are attracted and a supermolecule is formed.We will first investigate how positive the iodine must be for the supermolecule to form by making several related acceptors. Then, if we put two iodines in our acceptor, we can bind two donors - a different type of supermolecule. We can also change the shape of the donor so that these 2-to-1 supermolecules look more like a pizza than a pencil. Next we can vary the donor, for if we add an oxygen atom to the nitrogen, it is then the oxygen that is attracted to the iodine of the acceptor; the oxygen is attracted more strongly than the nitrogen so the properties of the supermolecule will change.After we make these new systems, we need to look at the donor-acceptor interaction and the LC behaviour; this needs special experiments. We can see how strongly the donor and acceptor are attracted to each other in the solid state of the supermolecule using X-rays which 'see' the distance between the iodine and the nitrogen. We use light to help us understand the LC behaviour (the liquid crystal causes pretty patterns to be seen), and we can use light in a different way to estimate the separation of the iodine and nitrogen in the liquid crystal phase (the light absorbed by the donor changes depending how far the iodine is from the nitrogen).This work will give a precise picture of the behaviour of the halogen bond in general and, in particular, in liquid crystals, and show how it might usefully be used in the future.NB This was tried on my 14 year-old daughter!

固体受热时，在一定温度下会融化成液体（如冰融化成水）。然而，一些化合物以介于固态和液态之间的中间状态存在，并且具有两者的一些性质。这种状态被称为“液晶相”，形成它的化合物被称为液晶（LC）。液晶显示器是大家都熟悉的液晶显示器在移动的电话，计算器，笔记本电脑等。液晶显示器在其他方面也很重要，众所周知，他们是重要的工作细胞的生物体和原因肥皂和洗涤液清洁这么好。分子组成的液晶有一个特殊的形状，或长或薄（像铅笔），或者薄而平（像比萨饼），化学家知道如何制造这些形状的分子。有时候，用两个部分而不是一个部分来制造这些分子是可能的。因此，如果我们想制造一个棒状分子，那么虽然这两个部分都不足以显示液晶相，但将它们连接在一起将产生一个显示液晶相的“超分子”。通常情况下，分子中的原子是通过很强的键结合在一起的，但在这里，这两部分是通过一种非常特殊但相当弱的相互作用结合在一起的。其中一种弱相互作用是“氢键”，人们已经知道很多年了，但还有一种非常类似的相互作用，它更弱，也更不为人所知，称为“卤素键”。最近，埃克塞特研究小组证明，它可以通过使用卤素键将超分子连接在一起来制造LC。我们现在想做更多的例子，仔细改变这两个部分，以便我们更多地了解这些超分子。因为卤素键在化学的其他部分也有应用，所以我们所学到的知识对其他部分也很重要，顾名思义，卤素键涉及我们称之为卤素的元素，两个部分中的一个（受体）将包含至少一个卤素;在这项工作中，卤素将是碘。在受体中，碘带有一些正电荷，因为受体的设计意味着负电荷被拉离它，然后它很高兴找到另一个带负电荷的部分加入。另一部分叫做施主，我们的部分含有一个氮原子。在供体中，负电荷被推向氮，使其被吸引到正碘。这两个分子相互吸引，形成一个超分子。我们将首先通过制造几个相关的受体来研究碘的正性有多大才能形成超分子。然后，如果我们在受体中加入两个碘，我们就可以结合两个供体-一种不同类型的超分子。我们还可以改变供体的形状，使这些2比1的超分子看起来更像披萨而不是铅笔。接下来，我们可以改变给体，因为如果我们在氮原子上添加一个氧原子，那么就是氧原子被吸引到受体的碘原子上;氧原子比氮原子被更强地吸引，所以超分子的性质会发生变化。在我们制造了这些新系统之后，我们需要观察给体-受体相互作用和LC行为;这需要特殊的实验。我们可以看到供体和受体在超分子的固态中相互吸引的强度，使用X射线“看到”碘和氮之间的距离。我们利用光来帮助我们理解LC行为（液晶可以产生漂亮的图案），我们可以用不同的方式来估计液晶相中碘和氮的分离（被供体吸收的光根据碘离氮的距离而变化）。这项工作将给出卤键一般行为的精确图像，特别是在液晶中，并展示它在未来如何有用。注意：这是在我14岁的女儿身上试过的！

项目成果

Halogen-Bonded Liquid Crystals

卤键液晶

• DOI: 10.1002/hlca.202300008
• 发表时间: 2023
• 期刊: Helvetica Chimica Acta
• 影响因子: 1.8
• 作者: Präsang C