Viologen-cucurbit[n]uril supramolecular interactions: a comprehensive overview

Viologens, a class of redox-active bipyridinium derivatives, have evolved from their initial discovery in Michaelis' laboratory and later turned into key building blocks in supramolecular chemistry and advanced materials. A breakthrough period in their development came with the introduction of cucurbit[n]urils (CB[n]s) by Kim and co-workers in 2000, which has attracted increased attention in exploring the meticulous host-guest interactions between viologens and CB[n]s. These versatile complexes have led to advancements in molecular self-assembly, charge-transfer systems, and functional materials. This review provides a relevant analysis of viologen/CB[n] interactions, with a particular focus on their complexation with CB[7], CB[8], and CB[10], as well as their role in supramolecular polyrotaxanes. Key factors such as the alkyl chain length, functional substitutions, pH variations, and competing guest species are considered and analysed to understand their impact on complex stability and structural adaptability. Furthermore, this review points out the growth of viologen-based polyrotaxanated covalent organic networks and their potential applications in energy storage, catalysis, and responsive materials. By combining fundamental supramolecular principles with modern innovations, this review offers an insightful view for optimizing viologen/CB[n] chemistry to synthesize multifunctional materials and dynamic molecular structures.