The Regioselective Solid-State Photo-Mechanochemical Synthesis of Nanographenes with UV light

Photochemical reactors inherently suffer from the low penetration depth of light and therefore rely on high dilutions to enable chemical reactions. Here we present the first method of UV (ultraviolet) photochemistry in the complete absence of bulk solvents in a ball mill. Triphenylene was synthesized by two routes, the Mallory reaction and the cyclodehydrochlorination (CDHC), resulting in yields of 81 and 92 %, respectively. The reaction was successfully scaled up to the gram scale and the robustness of the method was demonstrated for several different substrates. Finally, the regioselective assembly of nanographenes by mechanochemistry was demonstrated for larger systems. Thus, the mechanochemical approach presented here provides a powerful new tool for the atomically precise construction of nanographenes.

Automated summary

Photochemical reactions in reactors are limited by the penetration depth of light and require high dilutions. This study presents a method of UV photochemistry in a ball mill without bulk solvents. Triphenylene was synthesized with yields of 81% and 92% using the Mallory reaction and cyclodehydrochlorination (CDHC) respectively. The method was successfully scaled up to gram scale and demonstrated robustness for different substrates. Mechanosynthesis was also used to assemble nanographenes, providing a new tool for precise construction.