Binding affinity of aniline-substituted dodecaborates to cyclodextrins

A new set of hybrid guest molecules bearing organic and inorganic residues have been studied for their recognition by cyclodextrins in aqueous solution. The guest molecules consist of nitroanilines linked through their amino group to the dodecahydrido-closo-dodecaborate cluster B₁₂H₁₂^2-, which serves as an anchor group. They show sizable affinity to cyclodextrins, and unexpected photophysical properties, with a very strong and low-energy charge-transfer band. The dodecaborate cluster increases the pK_a of the anilines by 5.0 to 5.7 pH units, and the deprotonated forms of the o- and p-nitroaniline derivatives show strong charge transfer absorption bands in the visible part of the spectrum.