Fluorescence investigations of the supramolecular host-guest inclusion complexes of cucurbit[7]uril and sulfonic calixarenes

Fluorescence spectroscopy was used to study the supramolecular host properties of cucurbit[7]uril (CB[7]) and water soluble sulfonic calixarenes and to identify the useful properties of these compounds as potential supramolecular hosts.

The significant enhancement of the fluorescence of 2,6-ANS by CB[7], by a factor of 25, was observed in both potassium phosphate buffer and 0.2 M Na2SO4 solutions. Results suggest that a much stronger complex is formed between 2,6-ANS and CB[7] as compared with CB[6]. CB[7] is seen to have significantly improved host properties over the original cucurbituril, CB[6], as a result of its more spacious internal cavity.

The results obtained by studying the complexation of 1,8-ANS with CB[7] are very different from those with 2,6-ANS.

The time-resolved fluorescence studies showed that the fluorescence decay curve of the inclusion complexes of 2,6-ANS molecule is best described by a two-exponential fit decay, indicating that at least two different types of 1:1 complexes exist, and illustrating that these host-guest inclusion systems are heterogeneous. (Abstract shortened by UMI.).