Inclusion complex formation of ionic liquids with cucurbit[7]uril studied by competitive binding of methylene blue fluorescent probe.

Methylene blue (MB) was used as a fluorescent probe to study the encapsulation of three kinds of 1-butyl-3-methylimidazolium ionic liquids in cucurbit[7]uril (CB7) at pH 3. Addition of ionic liquids to the aqueous solution of MB-CB7 inclusion complexes brought about considerable fluorescence intensity quenching, and it was because that MB was extruded from the cavity of CB7 into the aqueous phase by the ionic liquid. NMR and AM1 semi-empirical calculations indicated that the 1-butyl-imidazolium moiety of ionic liquid was responsible for the complexation with CB7.