Cucurbit[n]uril Host‐Guest Complexes of Acids, Photoacids, and Super Photoacids

The supramolecular chemistry of host-guest complexes of cucurbit[n]urils (CB[n]) with acidic guests in the ground (HG+) and excited states (HG+*) are reviewed. The effects of CB[n] complexation on the guests’ pKa and/or pKa* values are related to relative binding constants and host-guest structures of the acid form of the guest and its conjugate base. Included are carbon acids, guests of biological and medicinal interest, dyes and related polyaromatic guests, and other organic and organometallic guests. The applications of the pKa shifts to the solubility, stability, and bioavailabilty of drug molecules, the stability and enhanced spectral properties of dyes, and in pH-induced self-sorting, micelle formation, host-guest shuttling, and controlled guest release, are discussed.