Construction of Supercryptand Structures and Specific Molecular Recognition

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A new route for rotaxane synthesis via covatent bond formation was developed from macrocyclic compounds (crownophanes) prepared by tandem Claisen rearrangement. The construction of [2]rotaxanes by this method and their functions such as sensing based on the energy transfer phenomenon between molecules were investigated. It was found that these rotaxanes can exhibit the selective complexation with lithium ion, where the roter and axle molecules work cooperatively to catch the ion, and the specific increase of fluorescent intensity was observed only in the presence of lithium ion accompanying with energy transfer phenomenon.In addition, [1]and [3]rotaxanes were successfully synthesized by our method, while their synthesi has not been reported by a synthetic method via covalent bond formation so far. [1]Rotaxanes prepared were confirmed to make complex with lithium ion specifically among alkali metal ions in the NMR and Mass spectra and observed the energy transfer phenomenon. It is concluded that the macrocyclic part and axle part form three dimensional structure (supercryptand structure) to result in the incorporation of lithium ion with high selectivity into the cavity. By our method, [3]rotaxanes were also prepared, and one of them forms 1:1 complex with cesium ion in the manner of sandwich-like structure.Thus, in this project, a novel synthetic method for rotaxanes has been developed and and the functions have been elucidated. That is, our synthetic method can be applied to the synthesis not only of [2]rotaxanes but also of [1]and [3]rotaxanes, and the specific energy transfer behaviors toward cations were observed in the fluorescence spectrum.