From Capsule to Helix: Guest-Induced Superstructures of Chiral Macrocycle Crystals

Predicting, controlling, understanding, and elucidating the phase transition from gel to crystal are highly important for the development of various functional materials with macroscopic properties. Here, we show a detailed and systematic description of the self-assembly process of an enantiopure trianglimine macrocyclic host from gel to single crystals. This proceeds via an unprecedented formation of capsule-like or right-handed helix superstructures as metastable products, depending on the nature of the guest molecule. Mesitylene promotes the formation of capsule-like superstructures, whereas toluene results in the formation of helices as intermediates during the course of crystallization. Single-crystal results demonstrate that the crystals obtained via the direct self-assembly from the gel phase are different from the crystals obtained from the stepwise assembly of the intermediate superstructures. Hence, investigating the phase-transition superstructures that self-assemble through the process of crystallization can unravel new molecular ordering with unexplored host-guest interactions. Such understanding will provide further tools to control hierarchical assemblies at the molecular level and consequently design or dictate the properties of evolved materials.