A comparative study of the spectral-luminescent and spectral-kinetic properties of 3,3'-diethyl-9-methylthiacarbocyanine (MTCC) and 3,3'-diethylthiacarbocyanine (TCC) and their complexes with cucurbit[8]uril in aqueous solution was carried out. Dimeric complexes of TCC with cucurbit[8]uril consist of trans-isomers and exhibit only delayed fluorescence while dimeric complexes of MTCC consist of cis-isomers and exhibit both delayed fluorescence and phosphorescence in water. The dimeric complexes of MTCC and TCC with cucurbit[8]uril participate in the electron phototransfer reaction where the dimeric complex of MTCC exhibits a greater ability to enter into photooxidation reactions. Keywords: polymethine dyes, trans-cis isomerization, cucurbiturils, absorption, fluorescence, triplet-triplet absorption, electron phototransfer.

The photooxidation of 3,3′-diethyl-9-methylthiacarbocyanine and 3,3′-diethylthiacarbocyanine by viologens (methyl viologen, p-chlorophenyl viologen, p-cyanophenyl viologen) in acetonitrile and their dimeric complexes with cucurbit[8]uril by monomeric complexes of viologens with cucurbit[8]uril in water has been studied. The photooxidation products of dye monomers in acetonitrile are radical dications of the dyes and radical cations of viologens. The photooxidation of dimeric complexes produces radical trications of the dimeric complexes and radical cations of the monomeric complexes of viologens. The photooxidation reaction of the dyes occurs most efficiently in acetonitrile.

The effect of cucurbit[7,8]urils on the absorption and luminescent properties of bis-thiacarbocyanine (bis-TCC) based on 3,3'-dimethylthiacarbocyanine (TCC) perchlorate in water was studied. The existence of two forms of bis-TCC that absorb in the long-wavelength and short-wavelength ranges was established. The properties of the form absorbing in the long-wavelength region are similar to those of the TCC monomer (monomer form), whereas the form absorbing in the short-wavelength region exhibits the properties of the non-fluorescent TCC dimer (dimer form). The effect of cucurbit[7,8]urils was manifested as shifts of the absorption and fluorescence maxima, increase in the fluorescence intensity of both the monomer and the dimer forms, and the presence of thermally activated delayed fluorescence of the dimer form in deoxygenated solutions at room temperature. The results derived from spectral and luminescent measurements indicate the ability of bis-TCC to form complexes with cucurbit[7,8]urils.

The effect of cucurbit[7,8]urils on absorption and luminescent properties of bis-thiacarbocyanine (bis-TCC) based on 3,3'-dimethylthiacarbocyanine perchlorate (TCC) has been studied in water. The existence of two forms of bis-TCC which absorb in the long-wavelength and short-wavelength regions of the spectrum has been established. The properties of the form absorbing in the long-wavelength region are similar to that of the monomer of TCC (monomeric form), whereas the form which absorbs in the short-wavelength region exhibits the properties of a non-fluorescent dimer of TCC (dimeric form). The influence of cucurbit[7,8]urils manifests itself in shifts of the band maxima in the absorption and fluorescence spectra as well as in increase in the fluorescence intensity of the monomeric and dimeric forms, and also in the presence of thermally activated delayed fluorescence of the dimeric form in deoxygenated solutions at room temperature. Results obtained from the spectral and luminescent properties indicate the ability of bis-TCC to form complexes with cucurbit[7,8]urils.

Spectral, spectral–kinetic, and photochemical properties of bisthiacarbocyanine (bis-TCC) dyes, based on 3,3′-dimethylthiacarbocyanine perchlorate, in water have been studied. The existence of two bis-TCC forms absorbing in the long-wavelength (monomeric form) and short-wavelength (dimeric form) spectral regions has been revealed. The monomeric form of bis-TCC is capable of fluorescence, photoisomerization, and transition to the triplet state. The dimeric form is characterized by effective intersystem crossing, the almost complete absence of fluorescence, and photoisomerization. Both the monomeric and dimeric forms of bis-TCC undergo complexation with cucurbit[7,8]urils. Complex formation leads to an increase in the fluorescence intensity of the monomeric and dimeric forms and increases the yield of delayed fluorescence and the lifetime of the dimeric form in the triplet state and those of the photoisomer of the monomeric form. The dimeric form of bis-TCC in the triplet state is capable of entering into the photooxidation reaction with p-nitroacetophenone both in the absence and in the presence of cucurbit[7,8]urils.

A comparative study of the spectral-luminescent and spectral-kinetic properties of 3,3'-diethyl-9-methylthiacarbocyanine (MTCC) and 3,3'-diethylthiacarbocyanine (TCC) and their complexes with cucurbit[8]uril in aqueous solution was carried out. Dimeric complexes of TCC with cucurbit[8]uril consist of trans-isomers and exhibit only delayed fluorescence while dimeric complexes of MTCC consist of cis-isomers and exhibit both delayed fluorescence and phosphorescence in water. The dimeric complexes of MTCC and TCC with cucurbit[8]uril participate in the electron phototransfer reaction where the dimeric complex of MTCC exhibits a greater ability to enter into photooxidation reactions.

Spectroscopic, luminescent, and spectral kinetic properties of cycloalkanone-based dienones and their dieth-ylamino, methylthio, methoxy, and dimethoxy derivatives were studied. The presence of electron-donating substituents results in a red shift of the absorption and fluorescence spectral maxima. A laser pulse causes dienones to undergo intersystem crossing to the underlying triplet state with a lifetime of 0.2-40 mu s as well as results in the formation of stable photoproducts capable of photoinduced conversion to the initial dienones. It also gives rise to intermediate products resulting from redox photoreactions of 2,4-bis(4-diethylaminobenzyli-dene)cyclobutanone in methanol in the presence of electron donor (ascorbic acid) and acceptor (para-nitro-acetophenone) compounds.

The review is devoted to the structure and photoprocesses in dimers of polymethine dyes and their complexes as objects of supramolecular photochemistry. The results of studies on the structure of dimers and dimeric complexes with cucurbiturils obtained from quantum chemical calculations are presented. The spectral-luminescent properties of dimers and approaches to their origin are considered. Data on the triplet states of dimers and dimeric complexes are presented. The results of studies on triplet-triplet energy transfer, electron phototransfer in redox reactions of dimers, and photosensitized oxidation reaction are analyzed.

Formation of intermediates (triplet states, radical anions, and radical cations) has been revealed by pulse laser photolysis in the photoinduced redox reaction of 2,4-bis(4-diethylaminpbenzyliden)cyclobutanone in methanol in the presence of an electron donor (ascorbic acid) and electron acceptors (methylviologen and p-nitroacetophenone). The reactions of photoinduced reduction by ascorbic acid and oxidation by methylviologen and p-nitroacetophenone occur via the triplet state with the formation of the dye radical anion and radical cation, respectively. The formation of the radical products of the photoinduced redox reaction is characterized by short-lived changes in the absorption spectra at λmax = 460 nm and a lifetime of 3 × 10−4 s for the radical anion and at λmax = 395 and 620 nm and a lifetime of 5 × 10−5 s for the radical cation.

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.

Spectral, luminescent, and time-resolved properties of 2,4-dibenzylidenecyclobutanone and its diethylamino, methylthio, methoxy, and dimethoxy derivatives have been studied. The electron-donating substituents shift bathochromically the absorption band maximum by 45–140 nm relative to unsubstituted dienones and the fluorescence maximum by 50–125 nm relative to the methoxy derivative. Upon the laser pulse, dienones convert to the triplet state with a lifetime of 0.15–3.5 μs and a stable photoproduct is formed.

The results of investigations of the properties of cyanine dye dimers in the triplet state are presented. The formation of dimers is demonstrated as two absorption bands of differing intensities, which are due to splitting of the S*-level of monomers as a result of their resonance interaction. The cyanine dye dimers are characterized by a relatively high quantum yield of the intersystem crossing. In the triplet-triplet absorption spectra two bands appear, where the long-wavelength band is assigned to a charge transfer state. The cyanine dye dimers in the triplet state are involved in the energy and electron transfer and can act as the photosensitizes of redox reactions.

Spectral, luminescent, and time-resolved properties of 2-bezylidene-5-(pyridin-3-ylmethylene)cyclopentanone and its derivatives with electron-donating substituents (diethylamino, methoxy, methylthio, and dimethoxy) on the benzene cycle have been studied in acetonitrile at room temperature. The presence of substituents causes a long-wavelength shift of the absorption band maximum by 26–114 nm in comparison with the unsubstituted dienone and a long-wavelength shift of the fluorescence maximum by 43–125 nm in comparison with the methoxy derivative. Under laser irradiation of oxygen-free dienone solutions, intersystem crossing to the triplet state occurs with a half-life of 0.7–1.5 μs. A stable photoproduct is formed for the methoxy, methylthio, and dimethoxy derivatives of dienone.

The effect of cucrbit[7]uril (CB7) on the redox reactions of thionine (ThH + ) in the triplet state are considered in the absence and the presence of electron donor (FeSO 4 ) and acceptor ( p -nitroacetophenone). The formation of the 1 : 1 host–guest complex between thionine and CB7 increases the lifetime of the thionine triplet state. In the absence of exogenous electron donor and acceptor, the thionine triplet molecules in the host-guest complex enter into reactions of disproportionation and concentration quenching to give semioxidized and semireduced forms of thionine. The yield and lifetime of semioxidized and semireduced thionine forms exceed the yield and lifetime of these forms for free thionine. The complexation of thionine with CB7 decreases the efficiency of the thionine photoreduction and that of the reduction of the semioxidized form by the Fe 2+ ions by factors of 5 and 2.5, respectively.