Study of complexation of styrylheterocycles with cavitands by spectroscopic methods

The complexation of crown-containing or dimethoxy-substituted styrylheterocycles (guest molecules) with β-cyclodextrin (β-CD), mono-6-amino-6-deoxy-β-cyclodextrin hydrochloride (β-CD-NH3Cl), and cucurbit[7]uril (CB[7]) (host molecules, cavitands) in water and water–acetonitrile solvent mixtures was studied by electronic and 1H NMR spectroscopy. Spectrophotometric, fluorescence, and 1H NMR titration, as well as 2D NMR experiments, were used to infer spectral properties, 1: 1 stoichiometry, a pseudorotaxane structure, and stability of the inclusion complexes formed. The solvent composition, the size and the charge of the heterocyclic moiety, and the size of the crown ether fragment of the guest were found to exert influence on the stability of the complexes. A synergistic effect upon complexation of 18-crown-6-containing styrylpyridines with β-CD-NH3Cl was found to be in place due to a cooperative contribution of encapsulation of the conjugated part of the guest by the cavitand cavity and hydrogen bonding between the crown ether fragment and the ammonium group. A photoinduced protonation of neutral styrylpyridines in water was demonstrated.