Self-assembly of β-cyclodextrin-pillar[5]arene molecules into supramolecular nanoassemblies: morphology control by stimulus responsiveness and host–guest interactions

Abstract

Macrocyclic molecules have attracted considerable attention as new functional materials owing to their unique pore size structure and excellent host–guest properties. With the development of macrocyclic compounds, the properties of mono-modified macrocyclic materials can be improved by incorporating pillar[n]arene or cyclodextrin derivatives through bridge bonds. Herein, we report the self-assembly of amphiphilic di-macrocyclic host molecules (H_1–2) based on β-cyclodextrin and pillar[5]arene units linked by azophenyl or biphenyl groups. In a H₂O/DMSO (19 : 1, v/v) mixed polar solvent, an amphiphile H₁ with an azophenyl group self-assembled into unique nanorings and exhibited an obvious photoresponsive colour change. This photochromic behaviour makes H₁ suitable for application in carbon paper materials on which arbitrary patterns can be erased and rewritten. The amphiphile H₂, with a biphenyl unit, self-assembled into spherical micelles. These differences indicate that various linker units lead to changes in the intermolecular and hydrophilic–hydrophobic interactions. In a CHCl₃/DMSO (19 : 1, v/v) mixed low-polarity solvent, the amphiphile H₁ self-assembled into fibrous aggregates, whereas the molecule H₂ assembled into unique nanoring aggregates. In this CHCl₃/DMSO mixed solvent system, small nanosheet aggregates were formed by the addition of a guest molecule (G) composed of tetraphenylethene and hexanenitrile groups. With prolonged aggregation time, the small sheet aggregates further aggregated into cross-linked nanoribbons and eventually formed large nanosheet aggregates. The data reveal that the morphology of H_1–2 can be controlled by tuning the intermolecular interactions of the molecules via the formation of host–guest complexes. Moreover, the polyhydroxy cyclodextrin unit on H_1–2 can be strongly adsorbed on the stationary phase in column chromatography via multiple hydrogen bonds, and the singly modified pillar[5]arenes can be successfully separated by host–guest interactions.