Steady-state fluorescence, anisotropy, and UV-visible absorption measurements have been used to investigate the structure and spectroscopic characteristics of the complexes formed by trans , trans 1,4-diphenyl-1,3-butadiene (DPB) with alpha -, beta -, and gamma -cyclodextrins (CDs). The behavior of alpha -CD with DPB is very different from that of DPB with respect to beta -CD or gamma -CD. In the presence of alpha -CD, clear solutions with high absorption and fluorescence emission, relatively high anisotropy, a rapid equilibrium reaction, and BenesiHildebrand plots lead us to conclude that normal 2:1 inclusion compounds are formed. In the presence of gamma -CD, turbid solutions, with absorption and fluorescence emission intensities lower than those in alpha -CD, higher values of anisotropy, slow equilibrium reaction, and spectral shifts to the red in the absorption, excitation, and emission wavelengths are evidence of the formation of extended linear aggregates. In the presence of beta -CD, both mechanisms of inclusion appear to be present.
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