Fluorescence visualization of cucurbit[8]uril-triggered dynamic host–guest assemblies

Cucurbit[8]uril (Q[8] or CB[8]), as a synthetic macrocyclic host, plays an important role in constructing various water soluble dynamic supramolecular polymers and materials. Here we report host–guest interactions of Q[8] with π-conjugated bispyridinium guests in aqueous solution that resulted in a series of unprecedented dynamic 2 : 2, 2 : 3, and 1 : 2 assemblies (guest/Q[8]). Most importantly, these subtly different host–guest binding modes could be distinguished by naked-eye observation of the resulting quantitative fluorescence emissions. Further characterization suggested that the Q[8] host-stabilized charge-transfer interactions could be dissociated and controlled by the N-substituted alkyl chains on the cationic guests via the formation of a 2 : 3 quinary complex or a U-shaped conformation, which led to the discovery of new possible binding modes for the Q[8] host.