Search

Photoprocesses in 3,3'-diethyl-5,5'-dichlorothiacarbocyanine have been studied in the cases of direct and sensitized photoexcitation in methanol and water in the absence and in the presence of cucurbit[7]uril. Under laser pulse excitation, trans–cis isomerization occurring via the excited singlet state of the dye (S*) takes place preferentially. The population of the dye triplet T state increases in the sensitized excitation as a result of triplet–triplet energy transfer from a triplet energy donor (anthracene and anthracenecarboxylic acid) to the dye (acceptor). Deactivation of the molecules in the T state occurs via electron transfer and back Т→S* intersystem crossing. The S* state formed in the Т→S* process decays via both conventional and delayed fluorescence. The presence of cucurbit[7]uril in the dye aqueous solution does not affect the mechanism of the photoprocesses in the dye, but it facilitates dimerization and increase in the yield into the T state, mainly of the dimers, and increases the lifetime of the dye cis-isomers.

The aim of this work was to develop chemosensors by analogy with bioreceptors based on lipid membranes stabilized on silica gel nanoparticles. Dansylglycine (DG) and a host–guest complex of DG with cucurbituril CB[8] were used as receptor fluorophores, and naphthalene and trimethylamine (TMA) in a gas phase were used as analytes. Stabilized lipid bilayers (SLBs) were obtained by the sorption of bilayer liposomes on nanoparticles under conditions that ensure the rupture of liposomes and the formation of a flat bilayer. The binding of CB[8] to SLB was performed for the first time and detected by measuring the fluorescence of the thiazole orange complex with CB[8] in a supernatant. The formation of the DG@CB[8] complex in water and a membrane manifested itself in FDG quenching and a shift of the FDG maximum toward short or long waves in water and in the membrane, respectively. On naphthalene excitation at 290 nm, the FDG response was due to energy transfer from naphthalene to DG. The FDG sharply decreased in the presence of TMA–H2O vapors, but it increased above the initial value upon the removal of H2O vapor. It was found that, unlike dyes embedded in a lipid matrix or sorbed on nanoparticles, the FDG response for host–guest complexes was proportional to analyte concentration, and the FDG wavelength did not change with analyte concentration.

The effect of cucurbit[7,8]urils (CB7, CB8) on photoprocesses in indocarbocyanine dyes has been studied. Complexation with CB7 and CB8 reveals bathochromic shifts of the maxima in the absorption and fluorescence spectra. Fluorescence enhancement and decreasing have been observed for the complexes with CB7 and CB8, respectively. The dyes and their complexes are capable of trans–cis photoisomerization and hardly undergo intersystem crossing to the triplet state. The rate of the thermal cis–trans isomerization reaction is decreased due to complexation.