Mechanical Grinding Effect: Facile Sublimation and Its Application in Molecular Cocrystal Synthesis by Physical Vapor Transport

Mechanical grinding of molecules, a straightforward yet efficient chemical reaction technique, now has established the field of mechanochemistry. While many physicochemical behaviors upon mechanical grinding have been revealed, its application on vapor-phase cocrystallization has not been demonstrated. In this work, we show that mechanical grinding can encourage sublimation, which is highly demanded for the successful synthesis of molecular cocrystals by a physical vapor transport (PVT) process. When a mixture of fluoranthene (FA) and tetracyanoquinodimethane (TCNQ) powders is ground together and used as a precursor, PVT at 170 °C results in large, thin belt-shaped FA-TCNQ cocrystals with high selectivity and yield. In contrast, a simple mixture of FA and TCNQ powders results in mostly irregular FA crystals with a negligible yield of FA-TCNQ cocrystals due to the dominance of FA vapors at 170 °C. Thermogravimetric analysis results show reduced sublimation temperatures of both FA and TCNQ after mechanical grinding, which is responsible for the efficient formation of FA-TCNQ cocrystals. We believe that this study opens a new chapter in the synthesis of molecular cocrystals and provides a new understanding of the effect of mechanical grinding.