NONCOVALENT POLYMERS OF OXADIAZOLE DERIVATIVES INDUCED BY GAMMA-CYCLODEXTRIN IN AQUEOUS-SOLUTIONS - FLUORESCENCE STUDY

The fluorescence properties of inclusion complexes of 2,5-diphenyl-1,3,4-oxadiazole (PPD), 2-phenyl-5-(4-biphenyl)-1,3,4-oxadiazole (PBD) and 2,5-biphenyl-1,3,4-oxadiazole (BBD) in aqueous solutions of cyclodextrins (CDs) were examined and compared. Excimer/dimer fluorescence appeared only in the presence of gamma-CD but not with the other CDs. The results indicate the formation of extended linear beads emitting excimer fluorescence of 2,5-diphenyloxazole (PPO). Brilliant crysel blue (BCB) is a fluorescent terminator molecule which causes shortening of the extended linear beads of PPO and gamma-CD. The excimer fluorescence of BBD is reported here for the first time. The difficulties encountered in the detection and identification of the excimer fluorescence of the other oxadiazoles are well known. The identification of the steady state excimer fluorescence of BBD is almost impossible unless it is compared with the excimer fluorescence spectra of PPD and PBD.