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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.

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.

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.

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.

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.

Effect of cucurbit[8]uril on the efficiency of triplet–triplet energy transfer between the donor dimer and the acceptor monomer or dimer has been studied. The efficiency depends on the rate constant of quenching of donor delayed fluorescence by the triplet energy acceptor, on the lifetime of the donor triplet state in the absence of a quencher, and on the acceptor concentration. Triplet–triplet energy transfer between the 3,3'-diethylthiacarbocyanine dimer (donor) and indodicarbocyanine (acceptor) occurs with a rate constant of 1.5 × 108 L mol–1 s–1 . Replacing the indodicarbocyanine monomer by the thiadicarbocyanine dimer decreases the energy transfer rate constant by a factor of 4.5. In the case of the 3,3'-dimethylthiacarbocyanine dimer as a donor, the quantum yield of energy transfer to the indodicarbocyanine monomer decreases fourfold.

Quenching of the eosin triplet state by europium(III) in water has been studied in the absence and in the presence of cucurbit[6–8]uril by means of phosphorescence and triplet–triplet absorption in a deoxygenated aqueous solution at room temperature. The quenching is due to photoinduced electron transfer from eosin to europium and to its complexes with cucurbit[6–8]urils. The value of the quenching rate constant of eosin phosphorescence by europium in the absence of cavitands is 1.9 × 106 L mol–1 s–1, whereas in the presence of CB6, CB7, and CB8, the values of the rate constant increase to 2.1, 2.2, and 2.6 × 106 L mol–1 s–1, respectively. Simultaneously with the decrease in the lifetime of the eosin molecule in the triplet state, an increase in the yield of the eosin semioxidized form was observed as a product of photoinduced electron transfer. It has been also shown that with an increase in the concentration of CB7 and CB8, the quenching rate constant increases two times. The difference in the values of the quenching rate constants may be due to the fact that europium, being as a quencher, is present in the form of complexes of different compositions with cucurbit[6–8]urils.

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 (FeSO4) 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 Fe2+ ions by factors of 5 and 2.5, respectively.

Types of dimers of aluminum and cobalt complexes of tetraanthraquinoneporphyrazines were identified. Thermodynamic characteristics of dissociation of the dimers in aqueous media were obtained. The kinetics of the deactivation of the triplet state of the aluminum complexes of sulfonated phthalocyanine and tetraanthraquinoneporphyrazine was studied.

Quenching of the triplet state of eosin by thionine in water in the absence and in presence of cucurbit[7,8]urils has been studied by measuring phosphorescence, delayed fluorescence, and triplet–triplet absorption. The quenching is due to triplet–triplet (T–T) energy transfer between eosin (energy donor) and thionine, as well as its monomeric (with cucurbit[7]uril, CB7) and dimeric (with cucurbit[8]uril, CB8) complexes (energy acceptors) in deoxygenated aqueous solution at room temperature. The value of the quenching rate constant of phosphorescence, delayed fluorescence, and the triplet state of eosin by free (unbound) thionine is 3.8 × 109 L mol–1 s–1. Triplet–triplet energy transfer between eosin and the monomeric complex of thionine with CB7 occurs with a rate constant of 3.7 × 109 L mol–1 s–1. The triplet–triplet transfer between eosin and dimeric complexes of thionine with CB8, measured by quenching of delayed fluorescence and phosphorescence, occurs with a rate constant of 8.3 × 109 L mol–1 s–1. The energy transfer according to the triplet–triplet absorption data occurs with a rate constant of 8.7 × 109 L mol–1 s–1. The different effect of cucurbit[7]uril and cucurbit[8]uril on the quenching efficiency is due to the structural features of the monomeric and dimeric complexes of thionine, as well as to the value of the Coulomb interaction between the eosin anion and the cation of monomeric and dication of dimeric complexes. The observed differences in the values of quenching rate constants can be due to the different shape and extension of the molecular orbitals of the monomeric and dimeric complexes of thionine, which leads to different overlapping of the energy donor and acceptor wave functions.

Spectral, luminescent, and kinetic properties of 2,5-bis(4-diethylaminobenzylidene)cyclopentanone (ketocyanine, A) in air-saturated and oxygen-free acetonitrile have been studied. The ns-Laser and continuous photoexcitation of A results in a product B undergoing in the oxygen-free solution the intersystem crossing into the triplet state with the lifetime of 1 µs. The photoinduced conversion of A into B occurs within a time shorter than 1 µs and is manifested in a decrease in both the fluorescence intensity of A and absorbance at 457 nm and in the appearance of a new absorption at λ > 535 nm. The product B undergoes photoinduced conversion to the parent A via both the excited singlet and triplet states of B.

Thionine (ThH+) molecules form monomeric ThH+@CB7 (1: 1) and dimeric 2ThH+@CB8 (2: 1) complexes with cucurbit[7,8]urils (CB7) and (CB8) in water. Unlike the case free ThH+ molecules, the absorption spectrum of the complexes is characterized by a hypsochromic shift of the maximum by 6 and 41 nm for ThH+@CB7 and 2ThH+@CB8, respectively. The ThH+@CB7 complexes exhibit fluorescence, unlike the nonfluorescing 2ThH+@CB8 complexes. The monomeric complexes undergo intersystem crossing to the triplet state with a lifetime of 14 μs. The dimeric complexes have a very low quantum yield of the triplet state. The triplet state of the dimeric complexes was populated by photosensitized excitation by triplet–triplet energy transfer. The lifetime of the triplet state is ≈50 μs.

Thiacarbo- and thiadicarbocyanine indolenine and thiazoline polymethine dyes form host‒guest complexes with cucurbit[7,8]urils in water. Cucurbit[7]uril forms preferentially 1: 1 and 1: 2 monomeric complexes and cucurbit[8]uril forms 2: 1 and 2: 2 dimeric complexes. On the basis of quantum-chemical calculations, the structure of monomeric and dimeric complexes has been suggested. The complexation manifested itself in absorption, prompt and thermally activated delayed fluorescence spectra, as well as in the triplet‒triplet absorption spectra. Dimeric complexes in the triplet state are involved in one-electron oxidation and participate in triplet‒triplet energy transfer.

In the presence of cucurbit[8]uril, polymethine dyes 3,3’-dimethylthiacarbocyanine (DMCy) and 3,3’-diethylthiacarbocyanine (DECy) in aqueous solution can form both nonfluorescing D@CB8 and fluorescing D@2CB8 dimer complexes. The D@2CB8 complexes with DMCy have a symmetrical narrow absorption band. The substitution of the СН3 group in DMCy for the С2Н5 group in the DECy molecule results in a difference in the absorption spectra of the dimeric dye complexes. Quantum chemical calculations show a difference in structure between the dimeric complexes for DMCy and DECy. The enthalpies of dimerization of DMCy and DECy in water and of the formation of complexes D@CB8 and D@2CB8 are close.

Spectral, luminescent and time-resolved characteristics of 2,5-dibenzylidenecyclopentanone and its symmetrical derivatives (bis(N,N-diethylamino-), dimethoxy-, tetramethoxy-, dimethylthio-, and bis-18- crown-6 derivative) have been studied in media of different polarity (cyclohexane, toluene, acetonitrile, DMSO, and methanol) at room temperature. The absorption maximum of dibenzylidenecyclopentanone shifts bathochromically by 15 nm with an increase in polarity of the medium (cyclohexane–methanol). The introduction of electron-donating substituents in the aromatic rings of dibenzylidenecyclopentanone also results in a bathochromic shift of the absorption maximum by 100–130 nm in the media of different polarity and shifts the fluorescence maximum by 130 nm relative to the maximum of the dimethoxy derivative. Upon laser irradiation of oxygen-free solutions of dibenzylidenecyclopentanone and its tetramethoxy- and bis-18-crown-6 derivatives in acetonitrile, the triplet state with a half-life time of 0.3–1 μs is generated. For dimethoxy-, dimethylthio-, tetramethoxy-, and bis-18-crown-6 derivatives of dibenzylidenecyclopentanone, the isomers with a lifetime of ~50 ms are formed.

Photoinduced processes in bis(diethylaminobenzylidene)cyclohexanone (CH1) and its bis(aza-18-crown-6) derivative (CH2) in acetonitrile at ambient temperature and 77 K have been studied. The absorption, fluorescence, and phosphorescence spectra of CH1 and CH2 are similar. The probability of the formation of the triplet state is higher for CH2 molecules (λT-Tmax = 660 nm, lifetime τT ~ 20 μs). The lifetime of the CH1 molecule in the triplet state is estimated at τT ~ 2–3 μs. Photoisomers of CH1 and CH2 are formed along with the triplet state. According to DFT calculation results, the formation of trans–cis photoisomers of CH1 and CH2 is the most energetically favorable.

The paper presents the results of analysis of the effect of a high-affinity peptide (HAP) homologous to a fragment of the nicotinic acetylcholine receptor (nAChR) on the absorption and fluorescence spectra of thiazole orange and thioflavin T complexes with cucurbit[8]uril in aqueous solution. In the presence of HAP, a change in the absorption spectra of the dye complexes and a drop in the fluorescence intensity occur; for thiazole orange, the fluorescence intensity is restored to the initial level in the presence of α-bungarotoxin capable of high-affinity binding to nAChR. The proposed method make it possible to detect the presence of α-bungarotoxin.

Photoprocesses in bis(diethylaminobenzylidene)cyclopentanone (D1) and its bis(aza-18-crown-6) derivative (D2) have been studied in acetonitrile. The absorption, fluorescence, and phosphorescence spectra of D1 are similar to those of D2. Laser excitation of oxygen-free solutions of D1 and D2 leads to generation of a triplet state with a lifetime of ∼1 μs and two intermediate species with lifetimes of ∼100 μs and longer than 1 s.

Spectral, luminescent, and time-resolved properties of 2,6-dibenzylidene cyclohexanone and its symmetric derivatives in the para-position of benzene ring (dimethoxy, dimethylthio, and bis-N,N-diethylamino groups) have been studied in media of different polarity (cyclohexane, acetonitrile, dimethylsulfoxide, and methanol). Introduction of electro-donating substituents to dibenzylidene cyclohexanone results in the red shift of the absorption maximum by 81–138 nm upon passing from the nonpolar to polar medium. Bis(N,N-diethylamino)dibenzylidene cyclohexanone fluoresces in polar solvents, acetonitrile, dimethylsulfoxide and methanol. The bathofluoric shift on passing from acetonitrile to methanol is 39 nm. The relative quantum yield of fluorescence in acetonitrile is seven times that in methanol. An intermediate species absorbing in the range of 400–560 nm with a maximum at 430–460 nm has been observed under the action of the laser pulse on dibenzylidene cyclohexanone solutions in acetonitrile. The intermediate species has a lifetime of 40, 20, and 7 μs for dibenzylidene cyclohexanone and its dimethylthio and dimethoxy derivatives, respectively.

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.

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.

Cationic dye 3,3-diethylthiacarbocyanine (TCC) in a phosphate buffer solution (pH 6.86) in the presence of cucurbit[7]uril (CB7) occurs in the form of monomeric TCC@CB7 and dimeric (TCC@CB7)2 complexes. The TCC@CB7 and (TCC@CB7)2 complexes display fast (conventional) and delayed (thermally activated, of type E) fluorescence, as well as free TCC. The relative yield of fast fluorescence of TCC@CB7 is six times that of free TCC. The delayed fluorescence lifetimes τdfl of TCC@CB7 and (TCC@CB7)2 are 0.5 and 1.6 ms, respectively. In the presence of p-nitroacetophenone (electron acceptor), the delayed fluorescence of (TCC@CB7)2 is quenched dynamically with the rate constant of 7 × 108 L mol—1s—1.

Molecules of 3,3′-diethyl-5,5′-dichloro-9-ethylthiacarbocyanine form dimers in aqueous solutions, which are capable of fluorescence and intersystem crossing to the triplet state. In the presence of cucurbit[7]uril and alkali metals or ammonium cations, dye dimer complexes are formed, which exhibit phosphorescence and thermally activated delayed (E-type) fluorescence in air-saturated solutions at room temperature. With the use of quantum-chemical calculations, the structure of dimeric dye complexes with cucurbit[7]uril is suggested.

The photophysical properties as well as photoisomerization of a series of malononitrile based merocyanines with various electron donating groups and polymethine chain length were studied by ns-laser photolysis. The absorption spectra and the kinetics of cis–trans backward conversion of the photoisomers were investigated in air-saturated solutions upon direct photoexcitation. The T–T absorption of merocyanines was recorded upon sensitized excitation with benzophenone or anthracene as the triplet energy donor and kinetics of the triplet state decay was measured. The obtained results together with the data of DFT/B3LYP quantum-chemical calculation allowed revealing the influence of the merocyanines electronic structure on the spectral properties and the lifetimes of the photoisomers. The long-wavelength absorption bands of photoisomers of the dyes with 3H-indole and benzimidazole electron donating groups were shifted bathochromically whereas the bands of the benzo[cd]indole derivatives were shifted hypsochromically with respect to the corresponding bands of the initial all-trans isomers. The interpretation of the results obtained is given.

The UV photostability of boron difluoride dibenzoylmethanate (DBMBF2) in the aprotic solvents acetonitrile, dimethylsulfoxide, acetone, methyl cyclohexane, dioxane, and tetrahydrofuran has been studied. The DBMBF2 half-life largely depends on the solvent and varies from 3 min in tetrahydrofuran to 9 h 40 min in acetonitrile. It has been found that the photodegradation of DBMBF2 involves the detachment of the BF2 molecule to yield dibenzoylmethane occurring in the ketone (absorption at 220–240 nm) and enol (absorption at 340–345 nm) forms. It has been shown that DBMBF2 can be stabilized by sterically hindered piperidines, thereby suggesting the participation of singlet oxygen in the photodegradation of DBMBF2.

Primary processes in the reduction of p-nitroacetophenone (p-NAP) by ascorbic acid (AA) in water photosensitized by thiacyanine dimers M22− have been considered. For M22−, the quantum yields of fluorescence and intersystem crossing to the triplet state (M22−)T increases in comparison to the monomers M−. The dimers (M22−)T enter into the reactions of both one-electron photoreduction by ascorbic acid to give AA+· and M23∸ and one-electron photooxidation by p-nitroacetophenone to give p-NAP−· and the dimeric radical anion M2∸ which dissociates to M− and M· within 25–30 μs. The primary oxidative or reductive photosensitization in the ternary systems containing (M22−)T, p-NAP, and AA affords p-NAP−· and AA+·.

The primary steps of the redox reaction of dimers of the thiadicarbocyanine dye and its 5,5′-dichloro derivative in aqueous solutions were studied in the presence of 4-nitroacetophenone, ascorbic acid, or hydroquinone. In water the dye molecules (anion, M−) mainly exist as dimers M2 2−. The laser pulse irradiation (10 ns, 532 nm) results in the population of the lowest triplet level M2 2−, whose depletion occurs due to both intersystem crossing to the ground state and photoinduced transition to the highest triplet state of the dimer followed by photoionization. Photoionization at low intensities of a laser pulse proceeds via the one-quantum mechanism going to the two-quantum mechanism with an increase in the laser pulse intensity. The photooxidation of the dimer in the lowest triplet state with 4-nitroacetophenone results in the formation of unstable radical anion M2 −· that spontaneously dissociates to monomer M− and radical M· of the dye. In the presence of electron donors (ascorbic acid, hydroquinone), the dimers in the triplet state are not photoreduced, but the electron donors reduce M2 −· and M· to the dye dimer and monomer, respectively.

Pathways of electron transfer reaction between p-nitroacetophenone (p-NAP) and ascorbic acid (AA) photosensitized by dimers of 3,3'-disulfopropyl-5,5'-dichlorothiacyanine triethylammonium (TC) and 3,3'-disulfopropyl-5,5'-dichloro-9,11-[ββ-dimethyltrimethylene]thiadicarbocyanine triethylammonium (TDC) are considered. In aqueous solution the dyes are present as an equilibrated mixture of monomers (M(-)) and dimers (M(2)(2-)). In contrast to monomers, the dimers of TC are characterized by a noticeable yield of intersystem crossing, whereas for TDC the triplet-triplet absorption of both monomers and dimers is easily observed upon ns-laser pulse. In the presence of p-NAP and AA the triplet state of the dimers of both dyes is mostly quenched by p-NAP yielding the radical pair [M(2)(-)˙p-NAP(-)˙] with subsequent dissociation of M(2)(-)˙ into M(-) and M˙ followed by one-electron reduction of M˙ by AA. These steps constitute a pathway of photosensitization by the dimers. For TDC an additional pathway of photosensitization was found to occur. The primary step consists of electron transfer in the excited singlet state of the dimer resulting in the formation of the radicals M˙ and M(2-)˙. The next steps involve one-electron reduction of M˙ by AA and one-electron oxidation of M(2-)˙ by p-NAP which results in the formation of M(-) followed by dimerization.

The presence of organic solvents (acetonitrile, acetone, and dioxan) as additives (up to 5 vol %) in an aqueous solution of alkylmesothia- and oxacarbocyanine dyes containing KCl and/or Mg(NO3)2 results in a variation of the rate of both J-aggregation and deaggregation. The rate of J-aggregation is increased as well as decreased in the presence of organic solvents as additives. For thiacarbocyanine dye, increase of the additive concentration up to 3–5 vol % results in a decrease of the rate of J-aggregation, as well as an increase of the rate of deaggregation. For oxacarbocyanine, the presence of additives up to a critical concentration results in an increase of J-aggregation. At a higher than critical concentration, the rate of J-aggregation is decreased so that no J-aggregates are formed.

The spectral-kinetic study of deactivation processes of the excited singlet and triplet states of indocarbocyanine dyes (Dye1, Dye2, and Dye3) and chlorin e6 (Chl), which constitute dyads I–III (Dye-Chl), was performed. In dyad Dye1-Chl, deactivation of the excited singlet state of the dye occurs mainly due to inductive-resonance energy transfer to Chl with the efficiency of 97%. The consequence of the energy transfer is population of the triplet level of Chl due to singlet-triplet intersystem crossing. In dyads Dye2-Chl and Dye3-Chl, deactivation of the excited singlet state of Chl occurs mainly due to inductive-resonance energy transfer to the dye molecule. The transfer efficiency is 96% for dyad Dye2-Chl and 85% for dyad Dye3-Chl with the shorter length of the -(CH2)-spacer, which binds the Dye3 and Chl molecules. In solutions of Chl and Dye2 (Dye3) mixtures in acetonitrile, exchange-resonance energy transfer occurs from the triplet level of Chl to the Dye2 (Dye3) molecule and electron transfer takes place involving triplet molecules of Dye2 (Dye3).

The photostability of J aggregates of the pseudoisocyanine dye in polyvinylpyrrolidone (PVP) and poly(vinyl alcohol) (PVA) polymer films under continuous irradiation with visible light was investigated. The decay of J aggregates in PVP is predominantly due to the reaction of photooxidation with singlet oxygen generated by triplet-state pseudoisocyanine dimers. Unlike the case of PVP, J aggregates in PVA demonstrate significantly higher photostability because of a lower PVP permeability for oxygen. A significant improvement in the photostability of J aggregates is achieved by the introduction of scavengers of singlet oxygen into the polymer films.

Data on syphilis and sexually transmitted diseases (STD) in Tomsk starting from the late 19th century are presented. The state of medical inspection of prostitution and organization of hospitals for STD patients are reviewed in the historic aspect. Statistical data on the current situation with STD and results of questionnaire survey of sex workers in Tomsk are presented.

The effect of the composition of the dioxane-water mixture on the ability of 9-ethylthiacarbocyanine to participate in competitive reactions of trans-cis photoisomerization and photoinduced electron transfer was studied. An increase in the dioxane content in the range 0–50 vol % leads to a shift of the equilibrium between the dye dimers and monomers toward the monomers (cis-monomers), which is accompanied by a drop in the yield of the triplet dimer molecules, which appear under the action of a laser flash, and electron-transfer products that are formed via the triplet state of dimers in the presence of methylviologen. With growing the dioxane content in the range 50–80 vol %, a shift of the equilibrium between the cis-and trans-monomers toward the trans-monomers occurs, which is accompanied by an increase in the fluorescence intensity. At the dioxane content above 80 vol %, a further shift of the equilibrium toward the trans-monomers occurs, which is accompanied by a substantial increase in the fluorescence intensity and an appearance under the action of a laser flash of the band of the triplet-triplet absorption of the trans-monomer and the absorption band of the cis-monomer as a result of trans-cis photoisomerization. The trans-monomers in the triplet state participate in the electron-transfer reaction with methylviologen. The intersystem crossing process competes with fluorescence and the trans-cis isomerization reaction, which occurs via the excited singlet state of the trans-monomers.

The relative stability of the trans-and cis-isomers of 3,3′-diethylthiacarbocyanine (Dye1) and 3,3′-diethyl-9-methylthiacarbocyanine (Dye2)1, as well as sections of the potential energy surfaces along the internal coordinate of the isomerization reaction, were studied using the density functional theory. Calculation of the minimum energy pathway for the isomerization reaction showed that the barrier for rotation about the C8–C9 bond is higher for Dye1 than for Dye2. Local minimums were found for the singlet excited state of the 8,9-cis-and trans-isomers of the dyes. In the case of the trans-isomers, substantial changes in the dye structure do not occur and the local minimum of the excited state corresponds to the geometry of the starting trans-isomers, which favors efficient fluorescence. A search for the nearest local minimum of the singlet excited state of the 8,9-cis-isomers leads to structures, which differ significantly from the starting structures, and the intensity of the S1 → S0 transition in those structures appears to be practically zero. The results are in agreement with experimental data on the absorption, fluorescence, and fluorescence excitation spectra of the dyes.

Spectral and kinetic study on deactivation processes of electronically excited states of molecules of cationic (Dye1, Dye2 and anionic (Dye3–Dye5) thiacarbocyanine dyes adsorbed on cellulose was performed. Adsorption of the dyes leads to an increase in the concentration of dimers. The dimers of adsorbates of Dye3–Dye5 exhibit only phosphorescence, whereas the monomers of the adsorbates are capable of both phosphorescence and delayed fluorescence. Adsorbates of Dye3–Dye5 prepared from water and methanol exhibit phosphorescence of cis-monomers. Adsorbates of Dye1 from water and ethanol as well as adsorbates of Dye2–Dye5 from chloroform exhibit delayed fluorescence of trans-monomers. Phosphorescence and delayed fluorescence are observed at room temperature in the presence of air oxygen.

The kinetics and the mechanism of the reaction of donor (ascorbic acid) oxidation by electron acceptors (methylviologen and p-nitroacetophenone) photosensitized by dimers of sulfoalkyl-9-ethylthiacarbocyanine dyes (Dye1, Dye2, and Dye3) were studied in aqueous solutions. Dimers of the dyes (dianions) are capable of transition to the triplet state that is mainly quenched by acceptors to form radical anions of dimers, which are unstable and dissociate within 10–12 μs into the monomer (anion) and its radical (the limiting reaction stage). The presence of a donor in the dye-acceptor mixture leads to one-electron reduction of the monomer radical to its anion followed by the dimerization reaction. The results of the analysis of the experimental data obtained by the laser photolysis technique are in good agreement with the calculated kinetic curves for the formation and the decay of the dimer radical anions.

The J-aggregation capability of meso-ethylsubstituted thiacarbocyanine (Dye 1 and Dye 2) and oxacarbocyanine (Dye 3) dyes was studied in poly(vinyl alcohol) (PVA) and poly(vinylpyrrolidone) (PVP) films and aqueous solutions, as well as in water. In water, Dye 1 and Dye 3 form J aggregates and dimers, whereas Dye 2 occurs mainly in the dimer form. The addition of PVA to an aqueous solution leads to deaggregation of J aggregates of Dye 1 and Dye 3 and dimers of Dye 1, Dye 2, and Dye 3. Unlike PVA, PVP stimulates the J aggregation of Dye 1 in aqueous solution, with the J aggregate yield depending on the ratio between the PVP monomer unit and dye concentrations. The J aggregation of Dye 1 and Dye 3 takes place in PVA films, whereas the J aggregates of only Dye 1 are formed in PVP films. The photostability of Dye 1 J aggregates in aqueous solutions strongly depends on the spectral region of irradiation and the presence of atmospheric oxygen. The photostability is appreciably lower in aerated solutions and substantially increases in PVA films.

The kinetics of photocoloration of spiro compounds under continuous UV irradiation were analyzed. Using spirooxazine as an example, it was shown that the shape of the kinetic curve of spirooxazine absorbance in the course of photocoloration is the most sensitive to the photocoloration quantum yield and the molar decadic absorption coefficient of the colored form in the visible spectral region. The photocoloration rate was found to increase with increasing temperature as a result of the temperature dependence of the photocoloration quantum yield. The activation energies for photocoloration E‡col and for thermal bleaching E‡bleach were determined for a series of spiropyrans, and it was found that E‡col < E‡bleach.

The photophysical properties and the monomer–dimer equilibrium of four thiamonomethinecyanine dyes (1–4) were studied by time-resolved and steady-state spectroscopic methods. In ethanol and aqueous solution at room temperature the behaviour is mainly due to a monomer and dimer, respectively. The dimerization constant for 2, the triethylammonium salt of 3,3′-di-(γ-sulfopropyl)-4,5-benzo-5′-chlorothiamonomethinecyaninebetaine, in aqueous solution is KD = 7 × 105 M−1 and lower in the presence of ethanol. Fluorescence occurs from both monomer and dimer; the quantum yield is Φf⩽0.006 for 1–4 in ethanol and 10–20 times higher in aqueous solution. The triplet state of the dimers was characterized; the lifetime is 0.1–0.9 ms and the yield ⩽0.2. With increasing temperature the amount of dimer is reduced, resulting in a correspondingly smaller value for T–T absorption. In microheterogeneous media, e.g. cetyltrimethylammonium bromide (CTAB), sodium dodecyl sulfate (SDS) or Triton X-100, the equilibrium is shifted at 25°C towards the solubilized monomer above the critical micellization concentration (c.m.c). The CTAB concentrations for dimer deaggregation of 1, 3 and 4 are much lower (10–30 μM) than the c.m.c. The amount of T–T absorption decreases with the CTAB concentration and resembles that of the dimer ground state. For 2 the dimers are converted into J-aggregates at [CTAB] in the 10–20 μM range and split into monomers around the c.m.c.

A new approach to determining a photocoloration quantum yield for photochromic compounds was considered. This approach is based on comparison between the calculated and experimental values of maximum absorbance ABmaxof a photocolored form upon monochromatic irradiation. Using spirooxazines as an example, the quantum yield of photocoloration was determined, and ABmaxwas examined as a function of a number of parameters that characterize the photocolored form (the quantum yields of photocoloring and photobleaching and the lifetime of the colored form). It was found that ABmaxnonlinearly increased with decreasing rate constant (

The cyanine dyes thiamonomethinecyanine (I), thiacarbocyanine (II), and thiadicarbocyanine (III) in an aqueous poly(methacrylic acid) (PMA) solution form different molecular species: monomers anchored to PMA, dimers, and H aggregates, in proportions determined by the [dye]/[PMA] concentration ratio. Each molecular species is characterized by its own probabilities of radiative and nonradiative transitions: the absence of photoisomerization for I–IIIdimers and H aggregates, the absence of fluorescence for H aggregates of IIand III, the capability of transition to a triplet state for PMA-anchored monomers I–III, and considerable enhancement of intersystem crossing to the triplet state for the dimers of II.

The properties of monomeric and dimeric thiacarbocyanine (1) and three derivatives with methyl (2) and ethyl (3 and 4) meso-substituents were studied in aqueous solution by time-resolved and steady-state spectroscopic methods. Dimerization is characterized by a blue-shifted band at 512–536 nm, a high association constant, e.g. KD=3.8×104 and 2.8×105 d mol-1 for 1 and 3, respectively and a negative enthalpy and enthropy, e.g. ΔHD=-72 kJ mol-1 and ΔSD=-142 J mol-1 K-1 for 3. Dimers are composed from the all-trans isomers for 1 and from mono-cis isomers for 2–4 with face-to-face alignment. They are non-fluorescent and the observed weak fluorescence originates essentially from the all-trans monomers. The triplet state of the monomer/dimer composition was observed upon naphthalene-sensitized and direct excitation. The triplet yield is largest for 3 and is due only to the dimer, whereas for 2 both monomer and dimer contribute to the overall T-T absorption spectrum. The amounts of T-T absorption and bleaching as a function of temperature resemble that of the ratio of monomer to dimer concentrations. Reasons for the lack of trans→cis photoisomerization in the cases of 2–4 are discussed.