In the last decade, photochemical and photocatalytic applications have developed into one of the dominant research fields in chemistry. However, mechanistic investigations to sustain this enormous progress are still relatively sparse and in high demand by the photochemistry community. UV/Vis spectroscopy and EPR spectroscopy have been the main spectroscopic tools to study the mechanisms of photoreactions due to their higher time resolution and sensitivity. On the other hand, application of NMR in photosystems has been mainly restricted to photo-CIDNP, since the initial photoexcitation was thought to be the single key to understand photoinduced reactions. In 2015 the Gschwind group showcased the possibility that different reaction pathways could occur from the same photoexcited state depending on the reaction conditions by using in situ LED illumination NMR. This was the starting point to push the active participation of NMR in photosystems to its full potential, including reaction profiling, structure determination of intermediates, downstream mechanistic studies, dark pathways, intermediate sequencing with CEST etc. Following this, multiple studies using in situ illumination NMR have been reported focusing on mechanistic investigations in photocatalysis, photoswitches, and polymerizations. The recent increased popularity of this technique can be attributed to the simplicity of the experimental setup and the availability of low cost, high power LEDs. Here, we review the development of experimental design, applications and new concepts of illuminated NMR. In the first part, we describe the development of different designs of NMR illumination apparatus, illuminating from the bottom/side/top/inside, and discuss their pros and cons for specific applications. Furthermore, we address LASERs and LEDs as different light sources as well as special cases such as UVNMR(-illumination), FlowNMR, NMR on a Chip etc. To complete the discussion on experimental apparatus, the advantages and disadvantages of in situ LED illumination NMR versus ex situ illumination NMR are described. The second part of this review discusses different facets of applications of inside illumination experiments. It highlights newly revealed mechanistic and structural information and ideas in the fields of photocatalyis, photoswitches and photopolymerization. Finally, we present new concepts and methods based on the combination of NMR and illumination such as sensitivity enhancement, chemical pump probes, experimental access to transition state combinations and NMR actinometry. Overall this review presents NMR spectroscopy as a complementary tool to UV/Vis spectroscopy in mechanistic and structural investigations of photochemical processes. The review is presented in a way that is intended to assist the photochemistry and photocatalysis community in adopting and understanding this astonishingly powerful in situ LED illumination NMR method for their investigations on a daily basis.

中文翻译：

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照明和高分辨率 NMR 光谱的结合：主要特征和实际方面、光化学应用和新概念

在过去的十年中，光化学和光催化应用已发展成为化学领域的主要研究领域之一。然而，维持这一巨大进步的机械研究仍然相对稀少，光化学界的需求量很大。由于紫外/可见光谱和 EPR 光谱具有较高的时间分辨率和灵敏度，它们已成为研究光反应机制的主要光谱工具。另一方面，核磁共振在光系统中的应用主要限于光 CIDNP，因为最初的光激发被认为是理解光诱导反应的唯一关键。2015 年，Gschwind 小组通过使用原位 LED 照明 NMR 展示了根据反应条件从相同的光激发态可能发生不同反应途径的可能性。这是推动 NMR 积极参与光系统发挥其全部潜力的起点，包括反应分析、中间体的结构测定、下游机制研究、暗通路、CEST 中间体测序等。 此后，使用原位照明的多项研究据报道，核磁共振专注于光催化、光开关和聚合的机理研究。这种技术最近越来越流行可归因于实验设置的简单性和低成本、高功率 LED 的可用性。这里，我们回顾了照明核磁共振的实验设计、应用和新概念的发展。在第一部分，我们描述了不同设计的核磁共振照明装置的发展，从底部/侧面/顶部/内部照明，并讨论它们在特定应用中的优缺点。此外，我们将 LASER 和 LED 作为不同的光源，以及 UVNMR(-illumination)、FlowNMR、NMR on a Chip 等特殊情况进行处理。 完成对实验设备的讨论，原位 LED 照明 NMR 的优缺点与非原位照明核磁共振进行了描述。本综述的第二部分讨论了内部照明实验应用的不同方面。它突出了光催化领域新揭示的机械和结构信息和想法，光开关和光聚合。最后，我们提出了基于 NMR 和照明组合的新概念和方法，例如灵敏度增强、化学泵探针、过渡态组合的实验访问和 NMR 光度测定法。总的来说，这篇综述将核磁共振光谱作为紫外/可见光谱在光化学过程的机械和结构研究中的一种补充工具。该评论旨在帮助光化学和光催化界采用和理解这种强大的原位 LED 照明 NMR 方法进行日常研究。过渡态组合和核磁共振光度测定的实验访问。总的来说，这篇综述将核磁共振光谱作为紫外/可见光谱在光化学过程的机械和结构研究中的一种补充工具。该评论旨在帮助光化学和光催化界采用和理解这种强大的原位 LED 照明 NMR 方法进行日常研究。过渡态组合和核磁共振光度测定的实验访问。总的来说，这篇综述将核磁共振光谱作为紫外/可见光谱在光化学过程的机械和结构研究中的一种补充工具。该评论旨在帮助光化学和光催化界采用和理解这种强大的原位 LED 照明 NMR 方法进行日常研究。