Photocontrolled Molecular Assembler Based on Cucurbit[8]uril: [2+2]-Autophotocycloaddition of Styryl Dyes in the Solid State and in Waterстатья
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Аннотация:Three styryl dyes of the 4-pyridine series that form syn-head-dimeric pairs in polycrystalline films were synthesised NMR and UV/Vis spectroscopic studies showed that this promotes stereospecific [2+2]-autophotocycloaddition (PCA) in the dimeric pairs to give rcit-isomers of cyclobutane derivatives For the dye with an N-ammoniopropyl substituent, this transformation was accomplished according to the single-crystal-to-single-crystal pattern In aqueous solutions, the dyes and cucurbit[n]urils (CB[n], n = 7, 8) form complexes with a pseudorotaxane structure CB[7] tends to form 1 1. complexes, and CB[8] forms 1 1 and 2 1 complexes The structure of the termolecular complex formed by the betaine of the N-sulfonatopropyl styryl dye and CB[8] was determined by X-ray diffraction The stability of the complexes was measured by (1)H NMR titration in a D(2)O/[D(3)]MeCN (10 1) mixture (log K(1) (1) >= 3 2, log K(2) (1) >= 2 6) Free dyes and their complexes with CB[7] in water undergo only (E)/(Z) photoisomerisation Termolecular complexes of all dyes with CB[8] were found to undergo effective stereospecific PCA reactions to give rcit isomers of cyclobutane derivatives The 1:1 complexes of the obtained cyclobutanes with CB[8] (log K(cb) = 3 2-4 8) are less stable than those of the starting dyes with the same stoichiometry Thus, CB[8] can play the role of a photocontrolled molecular assembler, i e., even in the presence of 5 mol-% of CB[8], complete conversion of styryl dyes into the corresponding cyclobutane derivatives takes place upon irradiation in solution