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

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 (H1-2) based on beta-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 H-1 with an azophenyl group self-assembled into unique nanorings and exhibited an obvious photoresponsive colour change. This photochromic behaviour makes H-1 suitable for application in carbon paper materials on which arbitrary patterns can be erased and rewritten. The amphiphile H-2, 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 H-1 self-assembled into fibrous aggregates, whereas the molecule H-2 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 H1-2 can be controlled by tuning the intermolecular interactions of the molecules via the formation of host-guest complexes. Moreover, the polyhydroxy cyclodextrin unit on H1-2 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.