The impact of UV light on synthetic photochemistry and photocatalysis

During the past 15 years, an increasing number of research groups have embraced visible-light-mediated synthetic transformations as a powerful strategy for the construction and functionalization of organic molecules. This trend has followed the advent and development of photocatalysis, which often operates under mild visible-light irradiation. Nowadays, the general perception of UV-light photochemistry is often as an out-of-fashion approach that is difficult to perform and leads to unselective reaction pathways. Here we wish to propose an alternative and more realistic point of view to the scientific community. First, we will provide an overview of the use of UV light in modern photochemistry, highlighting the pivotal role it still plays in the development of new, efficient synthetic methods. We will then show how the high levels of mechanistic understanding reached for UV-light-driven processes have been key in the implementation of the related visible-light-driven transformations. Although generally perceived as an old-fashioned and unselective tool to build molecules, the photochemistry community is now re-discovering the power of UV light and is using key mechanistic information to develop new catalytic processes driven by visible light. This Perspective discusses the progress and impact of UV light in organic synthesis.