Effects of Cyclodextrins on the Fluorescence of Diphenyl Phosphate in Aqueous Solution

Abstract

Abstract The effects of α-, β-, and γ-cyclodextrin (CD) on intramolecular excimer formation between the two phenyl groups of diphenyl phosphate (DP) in aqueous solution were investigated by means of absorption and fluorescence spectra. It was found that DP forms 1 : 1 inclusion compounds with α-, β-, and γ-CDs. In the inclusion compound with α- or β-CD, only one phenyl group of a DP molecule is incorporated in the cavity of a CD molecule. In the case of γ-CD, however, the cavity can accommodate either one or two phenyl groups of a DP molecule. The pH dependence of the equilibrium constant for the formation of the inclusion compound between DP and β-CD has also been examined. Over the pH range from 3.46 to ≈10 the equilibrium constant does not change, whereas for pH values above ≈11 it decreases drastically.