Macrosized single crystals are not always an appropriate media for single-crystal-to-single-crystal (SCSC) reactions because of their mechanical properties (i.e. they crack). A recent study by Nakanishi (J. Am. Chem. Soc., 2002, 124, 10944) has described a method to achieve single-crystal-to-single-crystal (SCSC) chemical reactivity in organic solids by reducing crystal size. We anticipated that an important step toward generalizing co-crystals as media for controlling SCSC [2+2] photoreactivity would be to achieve reaction in co-crystals of nano and submicron dimensions.

In this contribution, we wish to introduce sonocrystallization as a method to prepare organic co-crystals of nanosized dimensions. In particular, we demonstrate that the application of low-intensity ultrasonic radiation to co-crystals of composition 2(resorcinol)∙2(1,2-bis(4-pyridyl)-ethylene) grown during solvent reprecipitation produces nano- and micrometer-sized co-crystals that exhibit SCSC reactivity. We demonstrate that the sonochemical treatment succeeds where sole reprecipitation fails.

We anticipate that the sonochemical method can be applied to other co-crystal systems (e.g. pharmaceutical co-crystals) to affect physical properties of bioactive materials (e.g. solubility).