Mechanochemistry: Fundamentals, applications and future

The regioselective synthesis of nanographenes via photo- mechanochemistry Daniel Baier, Carolina Spula, Dr. Sven Grätz, Prof. Dr. Lars Borchardt Ruhr-Universität Bochum, Germany The use of mechanical force to initiate chemical reactions is as old as mankind itself. [1] Likewise, light-induced reactions have been taking place on earth since time immemorial. [2] Both mechanochemistry and photochemistry allow unique reactivities and the synthesis of otherwise inaccessible compounds. The combination of both is a promising approach for the synthesis of new or elusive compounds; for example, by overcoming solubility limitations in photochemical reactions. So far, there has been little work on the combination of irradiation and milling. [3] The main reasons for this are the lack of suitable equipment and the violent milling environment. In this contribution we present our work in the field of photo-mechanochemistry. [4] We present our custom-made photoreactor for performing solid-state reactions and show how nanographenes, a notorious poorly soluble compound class, can be synthesized using this method. Specifically, we use two examples - the Mallory reaction and the cyclodehydrochlorination (CDHC) - to show how photochemical reactions can be carried out with almost complete solvent avoidance. Building on these results, we show how the CDHC can be used for the regioselective synthesis of nanographenes using two larger polyphenylene compounds. This is the first work on the combination of milling and UV light and the first report on the regioselective assembly of nanographenes using mechanochemistry. References 1. L. Takacs, Chem. Soc. Rev. 2013, 42, 7649. 2. H. D. Roth, Angew. Chem. Int. Ed. Engl. 1989, 28, 1193.

3. T. Friščić, Angew. Chem. Int. Ed. 2020, 59, 1018. 4. D. Baier, Manuscript under preparation, 2022.

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© The Author(s), 2022

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