Host‒guest supramolecular polymers based on cucurbit[5]uril (Q[5]), cucurbit[6]uril (Q[6]), and cucurbit[7]uril (Q[7]) have been rarely investigated due to the limited size of their cavities, which cannot simultaneously accommodate two aromatic groups. The development and fabrication of Q[7]-based host‒guest supramolecular polymers remain challenging.

Jing-Xin Liu, Guo-Zheng Huang, Anhui University of Technology, Maanshan, China, and colleagues designed and synthesized three thiophene-pyridinium guests and investigated their binding interactions with Q[7]. NMR, Electrospray Ionization Mass Spectrometry (ESI-MS), and DFT calculations revealed that Q[7] can encapsulate one or two thiophene groups of the guests to form supramolecular complexes, including discrete inclusion complexes and supramolecular polymers. Importantly, all supramolecular complexes demonstrated reversible photochromism in the solid state, which is attributed to viologen radical generation, as confirmed by UV-vis-NIR, Electron Spin Resonance (ESR), and DFT studies.

Due to the aggregation-caused quenching (ACQ) effect induced by the intermolecular π···π stacking interaction of thiophene groups within the Q[7] cavity, the Q[7]-based supramolecular polymers remained fluorescence-silent, whereas the discrete inclusion complexes showed enhanced fluorescence compared to the thiophene-pyridinium guests. The dual photochromic and fluorescence properties of the Q[7]-based supramolecular complexes make them suitable for applications in erasable inkless printing, multi-level anti-counterfeiting, and advanced information encryption.

This study provides a strategy for constructing dual-functional supramolecular polymers using Q[7]-based host‒guest interactions.

• Cucurbit[7]uril-Based Supramolecular Polymers with Dual Photochromism and Fluorescence: From Host‒Guest Design to Smart Applications
  Long-Jing Wu, Anqi Deng, Jing-Xin Liu, Rui-Lian Lin, Ming-Fu Ye, Guo-Zheng Huang
  Aggregate 2025
  https://doi.org/10.1002/agt2.70145