Interactions between a surface-active cationic 3H-indole molecular probe and β-cyclodextrin. Design of a novel type of rotaxane

We report herein the interactions of a cationic surface-active molecular probe having long aliphatic chains, i.e., iodo-methyldioctadecyl 2-(p-hexylaminophenyl)-3,3-dimethyl-5-carboethoxy-3H-indole ammonium, with β-CD investigated by spectral and photophysical characterizations. It is found through lifetime measurements that only two species exist within the whole range of β-CD concentrations. Both the steady-state and the time-resolved fluorescence results further show that the stoichiometry of the inclusion complex is 1:3. It is also suggested that an interaction of the aliphatic chains of the cationic 3H-indole with β-CD takes place. Finally it is shown that a new rotaxane forms spontaneously in solution.