Fluorescence Polarization Studies of Inclusion Complexes between β-Cyclodextrin and 1-Chloronaphthalene in Aqueous and Aqueous d-Glucose Solutions

Abstract

In aqueous and aqueous d-glucose solutions, 1-chloronaphthalene (1CN) has been found to form a 2:2 inclusion complex with β-cyclodextrin (β-CD), which is generated by the self-association of 1:1 β-CD−1CN inclusion complexes. The 2:2 inclusion complex is responsible for the excimer fluorescence of 1CN. Equilibrium constants for the formation of the 1:1 and 2:2 inclusion complexes in aqueous solutions have been evaluated from a simulation of the 1CN excimer fluorescence intensity which is a function of β-CD concentration. When a wavelength of 315 nm has been selected as an excitation light, the degree of polarization has been maximized at the wavelengths of the 1CN monomer fluorescence band, and is decreased at the 1CN excimer fluorescence band. The decrease in the degree of polarization is due to the long lifetime of the excimer fluorescence. The results of the fluorescence polarization are consistent with the theory that the transition moment of the 1CN excimer fluorescence is parallel to that of the monomer fluorescence. On the basis of a Perrin plot, the molecular volume of the 1CN excimer has been estimated to be 0.20 nm3, which corresponds to the molecular volume of the sandwich-type excimer of 1CN; the 1CN excimer does not rotate as the 2:2 inclusion complex but rotates as the guest within the β-CD cavities.