The 1:1 Host-Guest Complexation between Cucurbit[7]uril and Styryl Dye

The photophysical properties of aqueous solution of styryl dye, 4-[(E)-2-(3,4-dimethoxyphenypethenyl]-1-ethylpyridinium perchlorate (dye 1), in the presence of cucurbit[7]util (CB[7]) was studied by means of fluorescence spectroscopy methods. The production of 1:1 host guest complexes in the range of CB [7] concentrations up to 16 mu M with K = 1.0 X 10(6) M-1 has been observed, which corresponds to appearance of the isosbestic point at 396 nm in the absorption spectra and a 5-fold increase in fluorescence intensity. The decay of fluorescence was found to fit to double-exponential functions in all cases; the calculated average fluorescence lifetime increases from 145 to 352 ps upon the addition of CB [7]. Rotational relaxation times of dye 1 solutions 119 +/- 14 ps without CB [7] and 277 +/- 35 ps in the presence of CB [7] have been determined by anisotropy fluorescence method. The comparison of the results of quantum-chemical calculations and experimental data confirms that in the host cavity dye 1 rotates as a whole with CB[7].