Mechanical Grinding\nEffect: Facile Sublimation and\nIts Application in Molecular Cocrystal Synthesis by Physical Vapor\nTransport

Mechanical grinding of molecules, a straightforward yet\nefficient\nchemical reaction technique, now has established the field of mechanochemistry.\nWhile many physicochemical behaviors upon mechanical grinding have\nbeen revealed, its application on vapor-phase cocrystallization has\nnot been demonstrated. In this work, we show that mechanical grinding\ncan encourage sublimation, which is highly demanded for the successful\nsynthesis of molecular cocrystals by a physical vapor transport (PVT)\nprocess. When a mixture of fluoranthene (FA) and tetracyanoquinodimethane\n(TCNQ) powders is ground together and used as a precursor, PVT at\n170 °C results in large, thin belt-shaped FA-TCNQ cocrystals\nwith high selectivity and yield. In contrast, a simple mixture of\nFA and TCNQ powders results in mostly irregular FA crystals with a\nnegligible yield of FA-TCNQ cocrystals due to the dominance of FA\nvapors at 170 °C. Thermogravimetric analysis results show reduced\nsublimation temperatures of both FA and TCNQ after mechanical grinding,\nwhich is responsible for the efficient formation of FA-TCNQ cocrystals.\nWe believe that this study opens a new chapter in the synthesis of\nmolecular cocrystals and provides a new understanding of the effect\nof mechanical grinding.