FLUOROMETRIC STUDY OF THE MOLECULAR-STATES OF 2,5-DIPHENYLOXAZOLE IN-GROUND MIXTURES WITH GAMMA-CYCLODEXTRIN

Molecular states of 2,5-diphenyloxazole (PPO) were investigated in gro und mixtures with gamma-cyclodextrin (gamma-CD). Crystalline PPO gradu ally became amorphous upon grinding in the presence of gamma-CD. Solid -state fluorescence spectra of the ground mixtures showed that the flu orescence emission peak due to PPO crystals was reduced in intensity w ith an increasing duration of grinding. A new fluorescence peak attrib uted to PPO excimer appeared at a longer wavelength. Results of the ti me-reserved fluorescence study indicated that the cogrinding caused an increase in the portion of PPO excimer in the gamma-CD ground mixture . On the other hand, only a small portion of excimer was formed in gro und mixtures with beta-CD, which has a smaller cavity than gamma-CD. T hese results suggest that cogrinding of PPO with gamma-CD caused two P PO molecules to be included in the gamma-CD cavity, contributing to ex cimer formation.