Dissipative crystallization of ion-pair receptors

Temporally controlled assemblies exhibit behaviors associated with living systems. Thus far, these transient assemblies have been studied primarily in soft materials, such as gels, vesicles, and colloidal assemblies. Here, we describe transient single crystals of supramolecular assemblies based on calix[4]pyrrole as an ion-pair receptor. The crystals form transiently upon the addition of a chemical stimulus, terephthalic acid, and disassemble when the chemical stimulus is consumed by alkylation using bromoethane. Single crystals observable by optical microscopy were grown and allowed to degrade repetitively by adding the chemical stimulus multiple times to a solution of the monomers. Partially degraded crystals were rescued and healed by adding more chemical stimulus to the solution before they dissolved completely. These results demonstrate that host-guest chemistry can be leveraged to create high-quality yet dynamic crystals that exhibit dissipative behavior. The modular nature of calix[4]pyrrole ion-pair recognition shows promise for obtaining diverse molecular materials capable of transient assembly.