Steady state fluorescence studies of the complexes between pyrene and per-6-O-tert-butyldimethylsilyl α-, β- and γ-cyclodextrins

The complexation of pyrene by α-, β- and γ-cyclodextrins (CDs), persubstituted at the 6 position by tert-butyldimethylsilyl groups, has been investigated using steady state fluorescence spectroscopy. The α-CD derivative does not, as would be expected from steric considerations, form complexes. The β- and γ-CD derivatives form 1:1 host-guest complexes which show high association constants in 90:10 H₂O-DMF solution [i.e. β-CD(SiR)₇, 4.85 × 10⁵ M^-1; γ-CD(SiR)₈, 4.91 × 10⁵ M^-1]. Analysis of the polarity of the microenvironment by means of the I/III peak ratios shows a more polar cavity in the case of γ-CD(SiR)₈. The concentration dependence of I/III suggests that a weak supramolecular complex γ-CD(SiR)₈-pyrene-n·DMF, may exist.