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Coherent Chemistry: Ultrabroadband Two-dimensional Electronic Spectroscopy

相干化学：超宽带二维电子光谱

基本信息

批准号：
EP/V00817X/1
负责人：
Stephen Meech
金额：
$ 112.16万
依托单位：
University of East Anglia
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2021
资助国家：
英国
起止时间：
2021 至无数据
项目状态：
未结题

来源：
https://gtr.ukri.org/projects?ref=EP%2FV00817X%2F1
关键词：
Coherent Chemistry Ultrabroadband Two dimensional

项目摘要

Light driven reactions in molecular systems are central to the existence of life on earth and to its successful continuation. Photosynthesis ultimately supports all life on the planet through the conversion of solar to chemical energy, while artificial solar energy conversion, photovoltaic devices and photocatalysis are fundamental technologies in replacing fossil fuel dependent power generation, and thus ameliorating the effects of global warming. This has led to intense research activity in understanding and ultimately controlling excited state reactions. In this work we address the long standing dream of tuning chemical reactivity using the unique properties of laser light, specifically coherence. The tools that we develop will, independently of this overarching objective, yield the clearest and most detailed insight yet into the nature of excited state chemistry.The workhorse for all investigations of photochemical mechanism and dynamics is the technique of 'flash photolysis'. Now called transient absorption (TA) the method is, when combined with modern laser technology, capable of sub 10 fs time resolution, and can be used to measure transient spectra from the UV to the mid IR, and beyond. There are now many variants of TA, but the first truly novel extension came about in the early years of this century with the development of two-dimensional electronic spectroscopy (2DES). The essential feature of 2DES is that it allows a correlation of the input (excitation) energy with the output (emission, product absorption, stimulated emission) signal. Thus an excitation at wavenumber x leading to an output at wavenumber y will have a x:y cross peak. Further the temporal evolution yields information on the nature of the coupling between the initial and final state as a function of time. In our case the cross peak may reveal coherent coupling, which in-turn suggests the possibility of control. Such 2D spectra are very familiar from magnetic resonance studies, revealing spin-spin coupling. However, while these studies reveal exquisitely detailed structural information, the excitation energies are too low to affect chemical transformations. The aim of chemistry is not only to interpret molecular behaviour, but also to change it. The energy implicit in electronic excitation is sufficient to initiate chemical reactions, and by applying 2DES to light driven reactions we will provide unique, new and detailed insights into the nature of excited state reactive dynamics.The advantages of 2DES have already been demonstrated for the important case of electronic energy transfer, where it has provided detailed insight into the pathway and mechanism of the exceptionally fast energy transfer underlying - for example - light harvesting in photosynthesis. The challenge in extending 2DES to the case of chemical change is that the excitation and product signals are energetically far apart, requiring an exceptionally large coherent bandwidth (several hundred THz) to simultaneously excite and probe the reactive system. This necessitates new laser sources, new measurement methodologies and new theory. In this project each aspect is addressed, with the overall objective being to provide the most detailed insight yet into the photochemical dynamics of some of the most important model reactions, such as the electron and proton transfer reactions central to the chemistry of the cell. These measurements will provide unambiguous answers as to whether or not coherence plays an observable role in photochemistry, and can therefore be exploited to modify rates and mechanisms. Even if coherence turns out not to be a key player in these reactions, we will have obtained unprecedented insights into reactivity, with time resolution of only a few fs, the timescale of the fastest nuclear motions.

分子系统中的光驱动反应是地球上生命存在及其成功延续的核心。光合作用最终通过将太阳能转化为化学能来支持地球上的所有生命，而人工太阳能转换，光伏设备和太阳能电池是取代依赖化石燃料发电的基本技术，从而改善全球变暖的影响。这导致了在理解和最终控制激发态反应方面的激烈研究活动。在这项工作中，我们解决了长期以来的梦想调谐化学反应使用激光的独特性质，特别是相干性。我们开发的工具将独立于这一总体目标，产生最清晰和最详细的洞察激发态化学的性质。所有光化学机制和动力学研究的主力是“闪光光解”技术。现在称为瞬态吸收（TA）的方法，当与现代激光技术相结合时，能够达到低于10 fs的时间分辨率，并可用于测量从紫外到中红外以及更远的瞬态光谱。TA现在有许多变体，但第一个真正新颖的扩展是在本世纪早期随着二维电子光谱学（2DES）的发展而出现的。2DES的基本特征是它允许输入（激发）能量与输出（发射、产物吸收、受激发射）信号的相关性。因此，导致波数y处的输出的波数x处的激发将具有x：y交叉峰。此外，时间演化产生关于作为时间的函数的初始状态和最终状态之间的耦合的性质的信息。在我们的例子中，交叉峰可能揭示了相干耦合，这反过来又表明了控制的可能性。这种2D光谱在磁共振研究中非常熟悉，揭示了自旋-自旋耦合。然而，虽然这些研究揭示了精细详细的结构信息，但激发能太低，无法影响化学转化。化学的目的不仅是解释分子行为，而且是改变它。电子激发中隐含的能量足以引发化学反应，通过将2DES应用于光驱动反应，我们将提供独特的，新的和详细的见解激发态反应动力学的本质。2DES的优势已经在电子能量转移的重要情况下得到了证明，在那里，它提供了对异常快速的能量转移的途径和机制的详细见解，例如光合作用中的光捕获。将2DES扩展到化学变化的情况下的挑战是，激发和产物信号在能量上相距很远，需要非常大的相干带宽（几百太赫兹）来同时激发和探测反应系统。这需要新的激光源、新的测量方法和新的理论。在该项目中，每个方面都得到了解决，总体目标是提供迄今为止对一些最重要的模型反应的光化学动力学的最详细的见解，例如对细胞化学至关重要的电子和质子转移反应。这些测量将提供明确的答案，无论是相干性在光化学中发挥可观察到的作用，因此可以利用修改率和机制。即使相干性不是这些反应的关键因素，我们也将获得对反应性的前所未有的了解，时间分辨率只有几fs，这是最快的核运动的时间尺度。