Spectral and Photophysical Studies of the 1:3 (Guest/Host) Rotaxane-like Inclusion Complex Formed by a 3H-Indole and β-Cyclodextrin

In the present paper, we report a new type of rotaxane-like inclusion complex, i.e., the 1:3 (guest/host) type formed by iodotrimethyl 2-( p -hexylaminophenyl)-3,3-dimethyl-5-carboethoxy-3 H -indole ammonium ( 1 ), a fluorescent cationic surfactant, and β-cyclodextrin (β-CD). The time-resolved fluorescence measurement reveals that only two species of 1 exist within the whole range of β-CD concentrations. Both the steady-state and the time-resolved fluorescence results show that the stoichiometry of the inclusion complex is 1:3. The urea effect on the formation of the inclusion complex has been investigated. It was found that the 1:3 inclusion complex is still formed in the presence of 3 M urea, while the association constant is markedly reduced. This suggests the hydrophobic nature of the interaction of 1 with either β-CD or urea.