β-Cyclodextrin forms the 1:1 inclusion complex with Crystal Violet, Methylene Blue, Methyl Orange, or Congo Red in water. On the other hand, γ-cyclodextrin forms the 1:2 complex with Crystal Violet, Methylene Blue, or Methyl Orange, while the 1:1 complex is given with Congo Red. The one host-two guest complexations are shown on the bases of the changes of the electronic spectra, dependence of induced circular dichroisms on the concentrations of dyes, and the continuous variation methods with induced circular dichroism. The dissociation constants for the 1:2 complexes are determined with the improved Benesi-Hildebrand equation. Alternation between the 1:1 and 1:2 complexation is discussed in terms of the cavity size of cyclodextrin and the aggregation character of dye.

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