Cross-linked supramolecular polymer networks can be useful as adaptive materials. The interaction between bridged hosts and guests is one of the most efficient ways to construct cross-liked supramolecular polymers. However, most of these structures are connected covalently. Developing new oligomers connected by dynamic bonds is still challenging.

Weitao Gong, Dalian University of Technology, China, and colleagues have developed a strategy to construct a cross-linked supramolecular polymer gel via hierarchical charge-transfer and host–guest interactions. Two types of pillar[5]arene dimers, NDI-P (naphthalene-diimide-bridged pillar[5]arene dimer) and NAP-P (naphthalene-bridged pillar[5]arene dimer), were designed and synthesized (simplified structures pictured above). These two dimers can assemble to a dynamic X-type pillar[5]arene tetramer via charge-transfer interactions (pictured below, bottom left).

The introduction of a neutral guest (NG) with two the 5‐(1H‐1,2,3‐triazol‐1‐yl) pentanenitrile binding sites into this pillar[5]arene tetramer causes the formation of a cross-linked supramolecular polymeric gel (pictured below, bottom right). The interaction of NDI-P or NAP-P separately with a neutral guest gives linear supramolecular polymers (pictured below, top right). According to the researchers, this strategy may provide a new path toward the fabrication of soft and smart supramolecular materials.

• Construction of Pillar[5]arene Tetramer-Based Cross-Linked Supramolecular Polymers through Hierarchical Charge-Transfer and Host-Guest Interactions,
  Wajahat Ali, Guiling Ning, Mehdi Hassan, Weitao Gong,
  Asian J. Org. Chem. 2019, 8, 74–78.
  https://doi.org/10.1002/ajoc.201800581