Photoprocesses of alkyl meso-thiacarbocyanine dyes in the presence of cucurbit[7]uril

Abstract The effects of cucurbit[7]uril, CB7, on the photophysical processes of 3,3′-diethyl-9-methylthiacarbocyanine iodide ( 1 ), 3,3′-dihydroxyethyl-9-methylthiacarbocyanine chloride ( 2 ) and 3,3′-diethyl-5,5′-dichloro-9-ethylthiacarbocyanine p -toluene sulfonate ( 3 ) were studied in phosphate buffer (pH 6.86) mostly at room temperature. Dyes 1 – 3 are cationic and present as equilibrated mixtures of monomers and dimers. Without CB7 the monomers demonstrate low yield of fluorescence which is increased 7–15 fold in the presence of CB7 as a result of formation of monomeric inclusion complexes. The dimers practically do not fluoresce. In the presence of CB7 the dimers produce dimeric inclusion complexes which exhibit both prompt and delayed fluorescence. The portion of delayed fluorescence is 0.08–0.1 of the total emission and the lifetimes are 0.07, 0.1, 0.25 ms for 1 , 2 and 3 respectively. The presence of monovalent metal ions or ammonium cation in aqueous solution of the dyes is prerequisite for delayed fluorescence of dimeric inclusion complexes. On the basis of quantum-chemical calculations the proposed structure of dimeric inclusion complex is characterized by near parallel orientation of two π-stacking chromophores retaining planar configuration, whereby each of them is partly inserted into the CB7 inner cavity. The difference in counter ions (chloride and p -toluene sulfonate) is reflected in the structure of dimeric inclusion complexes.