Stereoselective inhibitors based on nonpolar hydrocarbons for polar organic crystals

Nonpolar aliphatic hydrocarbons are usually regarded as solely antisolvents in solution crystallization processes of polar organic crystals, because of their very weak interactions with the surfaces of polar crystals compared to polar solvent interactions. Here we show that such weak interfacial interactions induced by nonpolar aliphatic hydrocarbons can be additionally used for controlling the morphology of polar organic π-conjugated crystals. Various hydrocarbons, such as n-hexane, n-octane, and n-decane, act as stereoselective inhibitors for highly polar 2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile (OH1) crystals having large nonlinear optical and fluorescent activities. In the presence of hydrocarbons, a significant morphologic change of OH1 crystals is observed; OH1 crystals grown in conventional polar solvents exhibit a diamond-shaped plate morphology, while in the presence of nonpolar hydrocarbons, a belt-shaped morphology with an extremely large aspect ratio is obtained. The origin of the unusual stereoselective interfacial interactions on specific surfaces of OH1 crystals inducing the morphological change is investigated with molecular dynamics simulations. The theoretically predicted morphology is well-matched with the experimental morphology