Self-assembly of cucurbiturils and cyclodextrins to supramolecular millstones with naphthalene derivatives capable of translocations in the host cavities

Abstract

Quaternary 4-(2-naphthyl)pyridinium salts with various N-substituents were synthesized. The structure of these salts was determined by X-ray crystallography. The self-assembly of the salts with cavitand molecules – β- and γ-cyclodextrins and cucurbit[7,8]urils – in aqueous solutions was studied by electronic spectroscopy and ¹H NMR spectroscopy, including spectrophotometric, fluorescence, and ¹H NMR titrations. The formation of inclusion complexes of different stoichiometry and stability, was observed, depending on the structure of N-substituent in the quaternary salt and the cavitand nature and cavity size. The complex formation with cucurbiturils results in considerable changes in the absorption and fluorescence spectra of naphthylpyridine derivatives. Motion of the guest molecules in the cavitand cavities was detected. The X-ray diffraction study was carried out for two polymorphs of 2 : 1 complexes formed by betaine type naphthylpyridine and cucurbit[8]uril, in which the cavitand was located either above the naphthalene residues of a dimeric pair of guest molecules or above the centers of their conjugated moieties.