Hydrogen-bonded self-assembly, spectral properties and structure of supramolecular complexes of thiamonomethine cyanines with cucurbit[5,7]urils

Abstract

Abstract The complex formation of thiamonomethine cyanine dyes bearing two N-ammoniohexyl or two N-ethyl substituents with cucurbit[5,7]urils (CB[5,7]) in aqueous solutions was studied by electronic and 1H NMR spectroscopy, including spectrophotometric, fluorescence, and 1H NMR titration methods. It was found that CB[5] forms external complexes with the dyes, while CB[7] forms internal (inclusion) complexes of 1:1 and 1(dye):2(CB[5,7]) composition. The complexation with CB[5,7] changes the absorption spectra of cyanine dyes and induces a considerable fluorescence enhancement. The stability constants of the complexes were determined (logK1:1 varies in the range from 3.53 to more than 6, and logK1:2 varies in the range from 3.5 to 4.32). The dye with ammoniohexyl substituents forms more stable complexes owing to hydrogen bond formation between the NH3+ groups and the carbonyl groups of the CB[5,7] portals. The structure of supramolecular complexes was confirmed by quantum chemical calculations.