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

The prediction, control, understanding and elucidation of phase transition from gel to crystal is in high demand for the de-velopment of various functional materials with macroscopic properties. Here, we show a detailed and systematic description of the self-assembly process of 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.