Interconnective host-guest complexation of β-cyclodextrin-calix[4]arene couples

The two beta-cyclodextrin-calix[4] arene couples 1 and 2 were prepared as sensing 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 fibers, which change into vesicles upon guest addition. This behavior is accompanied by a reduction in fluorescence intensity. The aggregates were visualized by transmission electron microscopy using both the freeze fracture technique and the uranyl staining method. Langmuir monolayer experiments show 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 slower decay process of low amplitude is observed for both compounds, indicating free rotational motion of single molecules of 1 but the absence of rotational motion of individual molecules within the aggregates of 2. This difference indicates the intermolecular complexation of the fluorophores in the aggregates of 2. The fluorescence lifetimes of aqueous solutions of 2 reveal 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 presence of vesicular bilayers of independent amphiphiles for 1, and for 2 the formation of assemblies of molecular threads which are composed by interconnective, linear host-guest complexation.