Supramolecular assembler based on cucurbituril: Photodimerization of a styryl dye in water
Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbituril (CB) has been studied by optical spectroscopic methods for the molar ratios n = c CB/c 1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes (1)2@CB dominate in the solution at n ≤ 0.5, whereas the complexes 1@CB dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K 1 = 6.2 (L mol−1)) and 2: 1 (log β = 11.9 (L2 mol−2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form cyclobutane derivative 2. The stability constant of the complex 2@CB (log K 3 = 5.9 (L mol−1)) and the quantum yield of cycloaddition (⃜ ≈ 0.07 at n ≈ 0.5) have been determined.
KeywordsPhotolysis Inclusion Complex Stability Constant High Energy Chemistry Styryl
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