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Artificially Produced UV Light and Challenging Photoreactions Enabled by Upconversion in Water
preprintsubmitted on 28.02.2020, 18:10 and posted on 02.03.2020, 13:11 by Björn Pfund, Debora M. Steffen, Mirjam R. Schreier, Maria-Sophie Bertrams, Chen Ye, Karl Börjesson, Oliver S. Wenger, Christoph Kerzig
Sensitized triplet-triplet annihilation is the most promising mechanism for pooling the energy of two visible photons, but its applications in solution were so far limited to organic solvents, with a current maximum of the excited-singlet state energy of 3.6 eV. By combining tailor-made iridium complexes with naphthalenes, we demonstrate blue-light driven upconversion in water with unprecedented singlet-state energies approaching 4 eV. The annihilators have outstanding excited-state reactivities enabling challenging photoreductions driven by sTTA. Specifically, we found that an aryl-bromide bond activation can be achieved with blue photons, and we obtained full conversion for the very energy-demanding decomposition of a persistent ammonium compound as typical water pollutant, not only with a cw laser but also with an LED light source. These results provide the first proof-of-concept for the usage of low-power light sources for challenging reactions employing blue-to-UV upconversion in water, and pave the way for the further development of sustainable light-harvesting applications.