Ionic Liquids in-vacuo; marrying Surface Science with Solution Chemistry.

科学问题：科学、环境和商业压力都在迫使化学家发明更好的催化反应，以最少的浪费产生所需的产品。生物系统利用化学复杂的催化剂，即所谓的酶，非常有效地实现了这一目标。合成化学家越来越有能力设计和制备复杂的分子催化剂；然而，它们在货币价值和环境负担方面都非常昂贵。因此，催化剂的保存和不丢失在产品混合物中是至关重要的。有几种固定催化剂以防止其损失的策略，其中一种更令人兴奋的新方法是离子液体作为选择性溶剂的应用，促进催化物质的吸附。催化剂溶液不溶解在反应混合物中；因此，它可以很容易地在反应结束时从产品中移出，然后再使用。尽管世界各地的研究小组都在研究离子液体，但人们对催化剂在离子液体溶液中的作用以及离子液体作为溶剂的基本性质都缺乏了解。如果要改进催化和优化反应选择性，这些信息是必不可少的。该项目将解决这种不平衡，并产生对设计更好的催化剂至关重要的信息。方法的独创性：离子液体通常是熔点低于室温的有机盐。因为它们完全由离子组成，所以它们的蒸汽压几乎为零；它们即使在真空中也不会蒸发。这意味着离子液体很难点燃，不像大多数传统上用于化学合成的溶剂。我们已经认识到，由于缺乏挥发性，离子液体可以用于需要高真空操作的各种分析仪器中。因此，离子液体可以使溶液和液体首次用于高真空仪器，从而使我们能够应用这些技术来探测离子液体溶液中催化剂的行为。此外，我们可以获得离子液体本身的基本物理化学的理解。我们的初步实验表明，这个想法在实践中是可行的；我们获得了纯液体以及掺杂简单金属盐的液体的高质量x射线光电子能谱（XPS）数据。XPS提供有关化合物中不同元素的电子结构的信息，并且具有足够的灵敏度来区分位于不同化学环境中的同一元素的原子。我们将扩展特高压光谱的应用，允许通过XPS和电化学方法（包括循环伏安法）对氧化还原活性底物进行原位同时表征，从而在金属的电子结构与氧化还原行为之间提供直接联系。研究应用：在我们的初步调查中，我们注意到离子液体的电导率随着基底被冻结形成固体而发生了相当大的变化。我们观察到，当用聚焦离子束（FIB）照射冷却表面时，会在衬底上写入图像。由+ve电荷局部区域组成的图像被发现非常稳定，此外还指出，通过两种简单的方法之一可以很容易地擦除图像，i)通过加热表面以增加动员，促进整个体中电荷的耗散，或ii)通过简单地将冻结的表面暴露于来自电子泛滥枪的低能电子供应。该工艺是可重写的，对基材表面没有不利影响。

The Scientific Problem: Scientific, environmental and commercial pressures are all forcing chemists to invent ever better catalytic reactions that generate the desired products with minimal waste. Biological systems achieve this goal very efficiently using chemically complex catalysts, so-called enzymes. Synthetic chemists are becoming increasingly able to design and prepare complex molecular catalysts; however, they are extremely costly in both monetary worth and environmental burden. Thus it is essential that the catalyst is conserved and not lost in the product mixture. There are several strategies for immobilising catalysts to prevent their loss and one of the more exciting new approaches is the application of ionic liquids as a selective solvent facilitating the entrapment of the catalytic species. The catalyst solution does not dissolve in the reaction mixture; hence it can be easily decanted away from the products at the end of the reaction and then reused. Although research groups throughout the world are studying ionic liquids, there is a lack of understanding about how catalysts function in ionic liquid solutions and indeed about the fundamental nature of ionic liquids as solvents. Such information is essential if catalysis is to be refined and reaction selectivity optimised. This project will address this imbalance and generate information vital to the design of better catalysts. Originality of Approach: Ionic liquids are, in general, organic based salts with melting points below room temperature. Because they are composed entirely of ions, they have an almost zero vapour pressure; they do not evaporate even under vacuum. This means that ionic liquids are difficult to ignite, unlike most of the solvents that are conventionally used for chemical synthesis. We have recognised that this lack of volatility allows ionic liquids to be used in a whole range of analytical instruments that require high vacuum for their operation. Thus ionic liquids could enable solutions and liquids to be used in high vacuum instruments for the first time, thereby allowing us to apply such techniques to probe the behaviour of catalysts in ionic liquid solutions. In addition, we can obtain an understanding of the fundamental physical chemistry of the ionic liquids themselves. Our preliminary experiments have demonstrated that this idea works in practice; we have obtained high quality X-ray photoelectron spectroscopy (XPS) data of the pure liquids as well as the liquids doped with simple metal salts. XPS provides information about the electronic structure of different elements within a compound and has sufficient sensitivity to distinguish between atoms of the same element situated in chemically distinct environments. We will extend the application of UHV spectroscopies to allow the in-situ simultaneous characterisation of REDOX active substrates by both XPS and electrochemical methods including cyclic voltammetry, providing a direct link between the electronic structure of the metal to REDOX behaviour.Application of Research: During our preliminary investigations, we noted that the conductivity of Ionic liquids changes quite dramatically as the substrate is frozen to form a solid. We observed that when the cooled surface was irradiated with a focused beam of ions (FIB) an image was written to the substrate. The image, composed of localised areas of +ve charge was found to be remarkably stable, furthermore it was noted that the image could be easily erased by one of two simple methods, i) by warming the surface to increase mobilisation that facilitated dissipation of the charge throughout the bulk, or ii) by simply exposing the frozen surface to a supply of low energy electrons from an electron flood gun. The process is rewritable and there is no detrimental effect on the substrate surface.