Engineering Solid-State Morphologies in Carbazole-Ethynylene Macrocycles

We present a crystallographic study that systematically investigates the effects of the n-alkyl side-chain length on the crystal packing in shape-persistent macrocycles. The solid-state packing of carbazole-ethynylene-containing macrocycles is sensitive to the alkyl-chain length. In macrocycles containing n-alkyl side chains up to nine carbons in length, face-on aromatic. pi interactions predominate, while the addition of one carbon leads to a completely different packing arrangement. Macrocycles with C-10 or C-11 chains exhibit a novel packing motif wherein the alkyl chains intercalate between macrocycles, leading in one case to continuous solvent-filled channels. When crystals of the C-10 macrocycle are bathed in solvent, the included molecules exchange with the external solvent, and the alkyl chain disorder changes in response to changes in the guest volume in order to retain crystallinity. Powder X-ray diffraction data indicate that alkyl-macrocycle interactions in the longer chains "emulate" the distances typical of face-to-face pi interactions, leading to deceptive indicators of pi stacking.