Photophysical properties of aqueous solutions of a styryl dye in the presence of cucurbit[n]uril (n = 5, 6, 8)
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Photophysical properties of aqueous solutions of the styryl dye 4-[(E)-2-(3,4-dimethoxyphenyl)-1-ethylpyridinium] perchlorate (1) in the presence of cucurbit[n]urils (CB[n]; n = 5, 6, 8) have been studied by fluorescent spectroscopy methods. The fluorescence intensity of a 10–6 mol L–1 solution of 1 increases by a factor of 12.6 upon the formation of 1 : 1 inclusion complexes with CB or 1.3 in complexes with CB. Upon the formation of inclusion complexes, the average lifetime of the electronically excited state of 1 increases to about 1 ns for both CB and CB. On the basis of fluorescence anisotropy measurements, the rotational relaxation times were estimated to be 408, 314, and 183 ps for the complexes with CB, CB, and for unbound 1, respectively. Using the fluorescence titration method developed for the case of poorly soluble cavitands, the binding constant of 1 with CB was determined to be 1.1 × 105 L mol–1. The addition of CB does not lead to changes in the photophysical properties of a solution of 1, indicating the absence of complexes between CB and 1. It has been found on the basis of the experimental data that the fluorescence rate constant of 1 decreases about twice in the complex with CB, but doubles in the complex with CB.
KeywordsInclusion Complex Fluorescence Quantum Yield Photophysical Property High Energy Chemistry Styryl
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