Interconnective host-guest complexation of beta-cyclodextrin-calix[4]arenecouples

The two beta-cyclodextrin-calix[4] arene couples 1 and 2 were prepared as s ensing molecules for the detection of organic analytes in water. Compounds 1 and 2 are amphiphilic in nature and form aggregates in aqueous solution. Compound 1 forms vesicles both in the absence and in the presence of guest species, and its fluorescence intensity does not change. Compound 2 forms f ibers, which change into vesicles upon guest addition. This behavior is acc ompanied by a reduction in fluorescence intensity. The aggregates were visu alized by transmission electron microscopy using both the freeze fracture t echnique and the uranyl staining method. Langmuir monolayer experiments sho w that intermolecular interactions lead to a preorganization of 2, whereas molecules of 1 behave independently analogous to conventional amphiphiles. Fluorescence anisotropy decay measurements give evidence for rapid internal dye motion in the aggregates of both compounds 1 and 2. In addition, a slo wer decay process of low amplitude is observed for both compounds, indicati ng free rotational motion of single molecules of 1 but the absence of rotat ional motion of individual molecules within the aggregates of 2. This diffe rence indicates the intermolecular complexation of the fluorophores in the aggregates of 2. The fluorescence lifetimes of aqueous solutions of 2 revea l that the reduction in fluorescence intensity is based on static quenching by the amino group present in the spacer of 2. Our results show the presen ce of vesicular bilayers of independent amphiphiles for 1, and for 2 the fo rmation of assemblies of molecular threads which are composed by interconne ctive, linear host-guest complexation.