Kanna Fujishiro, Yuta Morinaka, Yohei Ono, Tsuyoshi Tanaka, Lawrence T. Scott, Hideto Ito,* and Kenichiro Itami*
Submitted to ChemRxiv. DOI: 10.26434/chemrxiv-2023-k4z34
J. Am. Chem. Soc. 2023, 145, 8163–8175. DOI: 10.1021/jacs.3c01185

For more details, please see [Nagoya University Press Release]

Nanographenes, one of polycyclic aromatic hydrocarbons consisting of multiple fused benzene rings in a planar fashion, is expected to be applied to functional materials such as organic electronic materials. Nanographene is so familiar and abundant in nature that it is found in soot after combustion, crude petroleum, the rings of Saturn, and interstellar medium in space. For fundamental researches and material applications, it is necessary to synthesize nanographenes by organic synthesis with precisely controlling structures at the atomic level.

In this research, we have developed a new method for cyclodehydrogenation (graphitization), which is always necessary in the final step of nanographene synthesis, with over coming the drawbacks and problems of conventional methods. The drawback of the conventional method is that it uses potassium, which is highly pyrophoric, and requires a long reaction time of more than 10 hours in a heated organic solvent under an argon atmosphere. The new method uses lithium, which is relatively safe and easy to handle in air, and requires almost no organic solvents (less than 1/250 of the conventional method). The new method is achieved by mechanically mixing and stirring solid reactants without dissolving them in organic solvents (mechanochemical reaction) using a stainless steel jar and a ball mill machine. This method not only makes it possible to use metallic lithium pieces cut from commercially available lithium wire with scissors without special treatment, but also is an epoch-making method that is superior to the conventional method in organic solvents in terms of cost, reaction time, safety, and possibility of mass synthesis. In addition, the new method enables the rapid and highly efficient synthesis of more than 20 types of nanographene, including quintellilene, which had previously been impossible to synthesize.