Ultrafast spectroscopy studies of photoredox catalysed reaction mechanismsUltrafast spectroscopy studies of photoredox catalysed reaction mechanisms

许多化学应用利用催化来提高关键反应步骤的速度和效率，但改进催化剂设计和开发新的催化方法需要对它们的反应机理有深刻的了解。催化循环由一系列步骤组成，这些步骤可以在从飞秒到毫秒或更长的时间尺度上发生，跨越超过10个数量级的时间。这些单独的步骤涉及活性中间体，这些中间体可能很难分离，但必须进行识别，才能完全了解反应机理。这项研究项目将使用先进的超快光谱技术来观察溶液中光引发催化循环的步骤序列，从亚皮秒时间尺度上的催化剂活化到反应的完成。红外和紫外可见吸收光谱的瞬时特征将识别中间物种，测量它们产生和损失的时间尺度，在分子水平上表征影响催化剂性能的溶剂-溶质相互作用，并构建完整的催化途径的综合图景。该研究将集中在光氧化还原催化，这将改变化学合成。光氧化还原催化剂利用可见光和近紫外光在温和的条件下引发化学转化。瞬时吸收光谱测量将试图观察从紫外光激发光氧化还原催化剂到由电子转移引发的双分子自由基反应，最后到催化剂回收的整个步骤循环。这些结果将确定控制其性能的分子光催化剂的性质，并将指导有机光催化剂的优化设计，以用于可持续的未来应用，包括合成具有多种医药和技术应用的分子和材料。

Many applications of chemistry use catalysis to enhance the rates and efficiencies of critical reaction steps, but refinement of catalyst design and development of new catalytic methods require a deep understanding of their mechanisms of reaction. Catalytic cycles are made up of a sequence of steps that can occur on timescales from femtosecond through to millisecond or longer, spanning more than 10 orders of magnitude of time. These individual steps involve reactive intermediates which can be difficult to isolate, but which must be identified for a complete understanding of the reaction mechanism. This research project will use advanced ultrafast spectroscopy techniques to observe the sequence of steps in photo-initiated catalytic cycles in solution, from catalyst activation on sub-picosecond timescales to completion of reactions. Transient features in infra-red and ultraviolet/visible absorption spectra will identify the intermediate species, measure the timescales for their production and loss, characterize solvent-solute interactions which influence catalyst performance at the molecular level, and build a comprehensive picture of complete catalytic pathways.The research will focus on photoredox catalysis, which is transforming chemical synthesis. Photoredox catalysts use visible and near-UV light to initiate chemical transformations under mild conditions. Transient absorption spectroscopy measurements will seek to observe the complete cycle of steps from UV excitation of the photoredox catalyst to bimolecular radical reactions initiated by electron transfer, and ultimately to recovery of the catalyst. The outcomes will identify the properties of the molecular photocatalysts which control their performance, and will direct the optimized design of organic photocatalysts for sustainable future applications including the synthesis of molecules and materials with numerous medicinal and technological applications