Self-assembly is an important phenomenon in chemistry, biology, and materials science. Researchers are looking for tunable and versatile self-assembly systems. Self-assembly systems in water are particularly interesting because they could provide insights into biological processes.

Macrocyclic hosts such as cyclodextrins, calix[n]arenes, cucurbit[n]urils, pillar[n]arenes or PA[n]s, have been used to mediate self‐assembly of guests. By selecting proper host‐guest systems, tunable nanoscale architectures can be obtained.

Da Ma and colleagues, Fudan University, Shanghai, China, have studied tunable self-assembly systems in water. They used water-soluble pillar[n]arene homologues with different sizes (n = 5–7) as host and bipyridinium‐azobenzene guests. Pillar[n]arenes are a type of macrocyclic host molecules which can serve as artificial receptors. The team obtained multi-dimensional microscale or nanoscale self-assembly architectures: 0D micelles, 1D nanofibers, 2D nanosheets, and 3D nanorods and vesicles. They discovered that the host size has an impact toward self‐assembly morphology.

The team also discovered that the developed self-assembly systems undergo morphology conversions under UV irradiation. When irradiated by UV‐light, azobenzene‐moiety had an E‐to‐Z transition, which led to the morphology conversion of self‐assemblies. In addition, UV‐induced cargo release was investigated. This could make the self-assembly systems useful carriers for biological and medicinal applications.

• Water-Soluble Pillar[n]arene Mediated Supramolecular Self-Assembly: Multi-Dimensional Morphology Controlled by Host Size,
  Yamin Liu, Kejia Shi, Da Ma,
  Chem. Asian J. 2018.
  https://doi.org/10.1002/asia.201801705