Structural aspects of marked difference in intramolecular exciplex emissions from self-complexes of β-cyclodextrins modified with ( R) or ( S)-1-(1-aminoethyl)naphthalene

Abstract

Novel β-cyclodextrin (β-CyD) derivatives having an ( R) or ( S)-1-(1-aminoethyl)-naphthyl group exhibited red-shifted and structureless fluorescence and the normal fluorescence of the naphthyl group in alkaline aqueous solutions. The red-shifted fluorescence is attributed to the intramolecular exciplex. The intensity of the exciplex fluorescence is dependent on the chirality of the naphthyl group; the ( S)-isomer emitted a stronger exciplex fluorescence than the ( R)-isomer. From the NMR and circular dichroism spectral studies, the conformation of the intramolecular complexes of the ( R)- and ( S)-isomers is suggested; the naphthyl group of the ( S)-isomer exists outside the β-CyD cavity, while the ( R)-isomer is in the cavity. This conformational difference provides in the difference in the intramolecular exciplex formation.