Induced circular-dichroism spectra of complexes of cyclomalto-oligosaccharides and azo dyes containing naphthalene nuclei

Abstract

In the circular-dichroism spectra of inclusion complexes of 7 types of cyclodextrin (CDs) with 6 kinds of azo dyes containing the naphthalene nucleus, the direction of inclusion and the stacking mode may be elucidated from patterns in the u.v. and the first π→π * regions. The patterns in the former region indicate that the naphthalene fragment in almost all of complexes is incorporated equatorially into the cavity. Those azo dyes that have a tight fit in the CD cavity exhibit exciton interaction between two molecules of the chromophoric dye included in the complexes. The spectral pattern changes in sign according to the inclusion mode of the guest molecules and the angle between the chromophores. For example, the spectral pattern of the Orange II-cyclomaltoheptaose (β CD) complex indicates that the naphthalene nucleus is included axially, and that the angle between two molecules of the azo dye is >90°. On the other hand, the spectral pattern of the Croceine Orange-DM-β CD complex indicates equatorial inclusion and a stacking angle of <90°. The most important driving force for the host-guest interaction is van der Waals attraction; hydrogen bonding is not significant.