Cucurbit[8]uril/cucurbit[7]uril controlled off/on fluorescence of the acridizinium and 9-aminoacridizinium cations in aqueous solution

The blue fluorescence of acridizinium bromide (ADZ(+)) and the green fluorescence of 9-aminoacridizinium bromide (AADZ(+)) in aqueous solutions can be almost entirely switched off upon the double inclusion of these guests in the. cavity of cucurbit[8]uril (CB[8]) owing to the formation of a nonfluorescent, non-covalent dimer complex, and then fluorescence can be effectively restored by adding cucurbit[7]uril (CB[7]) to the complex because it competitively extracts the fluorophores out of the CB[8] cavity.