A Modified Cyclodextrin with a Fully Encapsulated Dansyl Group: Self-Inclusion in the Solid State and in Solution

A monofunctionalized β-cyclodextrin contg. a dansyl moiety, 6-deoxy-6-N-[N'-(5-dimethylamino-1-naphthalenesulfonyl)diaminoethane]-β-cyclodextrin (I), was synthesized and its crystal structure was detd. It was shown that the dansyl group is fully encapsulated within the cyclodextrin cavity, with the dimethylamino and sulfonyl groups emerging from opposite sides. The conformation of the diaminoethane linker was found to be detd. by the inclusion of the dansyl group and by a hydrogen bond between the sulfonamide NH and one of the O(6)-H groups on the cyclodextrin rim. Fluorescence spectra showed that the inclusion of the dansyl group in the cyclodextrin cavity considerably increases the quantum yield; time-resolved fluorescence expts. showed the presence of a long-lifetime component (16.1 ns), which was attributed to the included fluorophore. The ability of I to act as a fluorescence sensor was evaluated by the addn. of several guests of different shape: fluorescence intensity was lowered, esp. upon addn. of adamantane-carboxylic acid. Copper(II) was shown to enhance the difference in the fluorescence of I in the presence of guests by addnl. static quenching.