Supramolecular assembler based on cucurbit[8]uril: Photodimerization of a styryl dye in water

Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = cCB[8]/c1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes (1)2@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1@CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K1 = 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[8] 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[8] (log K3 = 5.9 (L mol−1)) and the quantum yield of cycloaddition (⃜ ≈ 0.07 at n ≈ 0.5) have been determined.