Solvent-Induced, Highly Unusual, Triangular-Shaped Organic Polar Crystal

Crystal habit is a key physical attribute that impacts the processing and performance of organic crystalline materials, especially pharmaceuticals and organic electronics. Here, we report that the presence of a solvent creates the highly unusual triangular habit of an organic crystal, biochanin A (BCA), a natural product with multiple pharmacological activities. From the vapor phase, BCA grows as needles with equal rates along the opposite directions of the polar c axis. In contrast, crystal growth from a toluene solution is observed only along the –c direction, leading to a triangular plate. This rare growth morphology is attributed to the polar crystal structure of BCA and differences in solvent–surface interactions. Molecular dynamics simulations show that toluene molecules bind to the hydroxyl exposing face more strongly than the methoxy exposing face, leading to inhibition of growth along the +c axis. This study contributes in-depth understanding regarding the solvent effect on the habit modification of polar crystals.