Recent advances in photoredox catalysis have made it possible to achieve various challenging synthetic transformations, polymerizations and surface modifications1,2,3. All of these reactions require ultraviolet- or visible-light stimuli; however, the use of visible-light irradiation has intrinsic challenges. For example, the penetration of visible light through most reaction media is very low, leading to problems in large-scale reactions. Moreover, reactants can compete with photocatalysts for the absorption of incident light, limiting the scope of the reactions. These problems can be overcome by the use of near-infrared light, which has a much higher penetration depth through various media, notably biological tissue4. Here we demonstrate various photoredox transformations under infrared radiation by utilizing the photophysical process of triplet fusion upconversion, a mechanism by which two low-energy photons are converted into a higher-energy photon. We show that this is a general strategy applicable to a wide range of photoredox reactions. We tune the upconversion components to adjust the output light, accessing both orange light and blue light from low-energy infrared light, by pairwise manipulation of the sensitizer and annihilator. We further demonstrate that the annihilator itself can be used as a photocatalyst, thus simplifying the reaction. This approach enables catalysis of high-energy transformations through several opaque barriers using low-energy infrared light.
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The data that support the findings of this study are available from the corresponding authors on reasonable request.
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L.M.C. thanks the National Science Foundation (NSF CAREER DMR-1351293) for funding. A.B.P. thanks the NSF Graduate Research Fellowship Program (DGE-16-44869). D.N.C. is supported by the Rowland Fellowship at the Rowland Institute at Harvard. T.R. thanks the National Institute of General Medical Sciences (GM125206).
A provisional patent has been filed on this technology by the institutions on behalf of the authors of this work (US Provisional Application 62/641,739).
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Ravetz, B.D., Pun, A.B., Churchill, E.M. et al. Photoredox catalysis using infrared light via triplet fusion upconversion. Nature 565, 343–346 (2019). https://doi.org/10.1038/s41586-018-0835-2
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