Preparation of supramolecular polymers from a cyclodextrin dimer and ditopic guest molecules: Control of structure by linker flexibility

Cyclodextrin based supramolecular polymers have been prepared using a beta-cyclodextrin dimer and ditopic guest dimers having adamantyl groups. The ditopic guest dimers with various flexibility and adamantyl moieties were prepared to investigate the conformation of supramolecular polymers. The ditopic adamantane guest dimer CO has a stiff spacer having a 4,4'-bipyridinium group between adamantyl groups. The ditopic adamantane guest dimers, C2 and C3, have flexible methylene spacers. The ROESY spectra of the beta-cyclodextrin dimer with the ditopic adamantane guest dimers showed NOE between the protons of adamantyl substituents and the inner protons of cyclodextrin. The ditopic adamantane guest dimers, C2 and C3 formed cyclic supramolecular oligomers in aqueous solutions. The cyclic structure was observed by atomic force microscopy (AFM). On the contrary, the ditopic adamantane guest dimer CO formed the high molecular weight supramolecular polymers.