Lamellar Twinning Explains the Nearly Racemic Composition of Chiral, Single Crystals of Hexahelicene

Solvent etching of single crystals of hexahelicene grown from a racemic solution reveals an unusual layer-like pattern in which pure (+)- and pure (-)-layers alternate through the crystal; this arrangement results in a nearly racemic composition although the crystal is ostensibly chiral, space group P2(1)2(1)2(1). Etched crystals of enantiomerically pure hexahelicene display no such pattern. The two kinds of crystal are indistinguishable by x-ray diffraction.