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The noncovalent interaction between various polymethine dyes (45 compounds in total) and a spike protein (S), one of the main structural component of the SARS-CoV-2 coronavirus, is studied in silico (molecular docking) to develop effective probes to detect the virus. The interaction energies and the spatial configurations of the complexes of the dye molecules with S are found. We showed that cationic polymethine dyes and neutral squarylium dyes do not form stable complexes with S. Some anionic dyes having negative total energies Etot may be recommended for practical research.

Primary photochemical processes (photoisomerization, triplet state formation) involving meso-substituted anionic cyanine dyes 3,3'-di(γ-sulfopropyl)-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine betaine, 3,3'-di(γ-sulfopropyl)-4,5,4',5'-dibenzo-9-methylthiacarbocyanine betaine, 3,3'-di(γ-sulfopropyl)-5,5'-dimethoxy-9-ethylthiacarbocyanine betaine, and 3,3'-di(γ-sulfopropyl)-5,6,5',6'-di(methylenedioxy)-9-ethylthiacarbocyanine betaine in noncovalent complexes with human and bovine serum albumins are studied by flash photolysis. For comparison, the photochemistry of these dyes in solutions (in water and dioxane) is also studied. It is found that upon the flash photolysis of dye solutions in water, photoisomerization and triplet state formation are not observed; however, unstable photoisomers are formed in a nonpolar solvent—dioxane. In this solvent, the formation of the triplet states of the dyes is not observed in the absence of oxygen. At the same time, upon flash photolysis of the dyes in an aqueous solution in the presence of serum albumins, photoisomerization is not observed, but (in the absence of oxygen) the formation (with subsequent decay) of the triplet states of the dyes occur. The quenching rate constants of the triplet states of the dyes by molecular oxygen are determined, which are found to be much lower than the diffusion-controlled quenching rate constant. This is possibly explained by the hindered access of oxygen to the dye molecule in the complex with albumin.

The spectral and luminescent properties of compounds A3–SA, A4–o–SA, and A4–o–K have been studied, whose structures include moieties of triphenylimidazole A3, tetraphenylimidazole A4, and hydroxyazomethines salicylideneaniline SA and coumarin-substituted azomethine K. Due to electronic conjugation of moieties, the compound A3–SA exhibits switchable luminescence only in alcohol solutions, whereas independent behavior of the moieties is observed in the case of linking of these luminophores by an oxygen bridge and luminescence switching by changing the excitation wavelength is possible both in solutions and polymeric media.

Studies of the photonics of dyes in structurally organized systems are of great fundamental and applied importance. In this regard, the search for simple and convenient methods for analyzing the composition and studying structurally organized systems based on biomolecules (proteins, nucleic acids, etc.) using dye probes is highly relevant. meso-substituted polymethine (carbocyanine) dyes can serve as such probes, as such dyes have a unique set of spectral-fluorescent and photochemical properties that are sensitive to the molecular environment. In structurally organized systems, the photonics of these dyes changes drastically, which allows them to be used in studies of such systems. One peculiarity of these dyes is the mobile equilibrium between the trans- and cis-isomers, which differently interact with biomolecules. The interaction of the dyes with components of structurally organized systems leads to an increase in fluorescence and intersystem crossing to the triplet state. We have developed and put into practice spectral-fluorescent and photochemical probes based on meso-substituted carbocyanines. In particular, we widely used one of the anionic carbocyanines as a probe in biological systems containing serum albumin and collagens. This review is devoted to the works of the authors on the interaction of meso-substituted carbocyanine dyes with biomolecules and the photonics of meso-substituted carbocyanines in complexes with biomolecules. The works on the use of these dyes as probes in biological systems are also considered.

Spectral-fluorescent properties of polymethine dye probes anionic 3,3'-di(sulfopropyl)-4,5,4',5'-dibenzo-9-ethylthiacarbocyanine-betaine (DEC) and cationic 3,3',9-trimethylthiacarbocyanine iodide (Cyan 2) in the presence of biological surfactants, bile salts sodium cholate (NaC), sodium deoxycholate (NaDC) and sodium taurocholate (NaTC), as well as sodium dodecyl sulfate (SDS), have been studied in a wide range of surfactant concentrations. When a surfactant is introduced into a solution of DEC, changes of the spectral-fluorescent properties are observed due to decomposition of dye dimers into cis-monomers and cis-trans conversion of the resulting monomers. In the presence of SDS, both processes occur in parallel, caused by noncovalent interaction of dye monomers with micelles, and mainly occur near the critical micelle concentration (CMC). In contrast, upon the introduction of increasing concentrations of bile salts, decomposition of dye dimers into the monomers begins at lower concentrations than cis-trans conversion. The former process is almost completed at concentrations close to CMC of secondary micelles (CMC2), while the latter process occurs even at concentrations of bile salts much higher than CMC2. Hence, DEC can serve as a probe that permits estimating the value of CMC2 and is indicative of reorganization of secondary micelles upon an increase in bile salt concentration. Aggregation of DEC and Cyan 2 on bile salts is also observed. Since it is observed at relatively low concentrations of bile salts (CMC2), the aggregation probably occurs on monomeric molecules of bile salts and their small associates and primary micelles. Decomposition of the aggregates formed begins at concentrations of bile salts above CMC2 (that is, upon the interaction with secondary micelles).

The absorption and fluorescence spectral properties of three meso-substituted hydrophilic thiacarbocyanine dyes were studied in solutions and in noncovalent complexes with human and bovine serum albumins (HSA and BSA, respectively). The presence of alkyl substituents at the meso-position of the polymethine chain of the dyes determines the occurrence of a cis–trans equilibrium. Dyes form aggregates in aqueous media; the effect of electrolyte (NaCl) on aggregation has been studied. The interaction of the dyes with albumins leads to the decomposition of the aggregates and is accompanied by a shift in the isomeric equilibrium. Complexation with HSA leads to accumulation of dye monomers in the trans-form. However, in the case of BSA the cis-to-trans isomeric shift is incomplete. Using the fluorescence data, the effective binding constants of the trans-isomers with albumins (Ka) and the detection limits of albumin molecules (LD and LQ) were determined. The data obtained are indicative of high selectivity of some dyes to HSA compared to BSA. The results of molecular docking experiments correspond to the data obtained from the spectra. The influence of the dyes on intrinsic fluorescence of HSA and BSA was also studied, and fluorescence quenching, static in nature, was detected.

The photochromic properties of new di- and tetranitrobisspiropyrans have been studied. Dinitrobisspiropyran solutions are characterized by direct photochromism, whereas reverse photochromism—coloration of the solution in the dark and its discoloration under the action of visible or UV light—is observed in solutions of tetranitrobisspiropyran in polar and weakly polar solvents and in polymer matrices of poly(methyl methacrylate) (PMMA) and polyvinyl butyral (PVB). The features of reverse photochromism are discussed, and a comparison with the photochromism of model nitrosubstituted monospiropyrans and dinitrobisspiropyran is carried out.

Primary photochemical processes in polymethine dye probes 3,3′-di(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine (DEC) and 3,3′,9-trimethylthiacarbocyanine iodide (Cyan 2) in micellar systems of bile-acid salts (BASs) sodium cholate, deoxycholate, and taurocholate and sodium dodecyl sulfate (SDS) as a reference are studied by flash photolysis. Signals due to photoisomerization of dye trans-isomers and dark reverse isomerization of the resulting cis-photoisomers are observed during pulse photolysis of air-saturated aqueous dye solutions in the presence of BAS and SDS micelles. The lifetimes of the photoisomers are 60–190 μs. Pulse photolysis of Cyan 2 and DEC solutions without oxygen and with BAS and SDS micelles induced photoisomerization and transition of the dyes into an excited triplet state followed by the reverse transition (intersystem crossing) into the initial singlet state. Triplet–triplet absorption spectra of these dyes isomers in polar (EtOH, i-PrOH) and nonpolar (dioxane) solvents were obtained for comparison using triplet–triplet energy transfer from anthracene. The conclusion was drawn that the photochemical behavior of the dyes in BAS and SDS micellar systems were similar.

The bilirubin content in the vitreous body of the eye of human fetuses of gestation week 17-31 was measured. During gestation weeks 17-19, the mean bilirubin concentration was 8.67 μmol/liter; then, decreased to 1.37 μmol/liter (gestation weeks 20 to 31). Bilirubin, being an endogenous antioxidant, is probably involved in protection of the retina and lens from LPO processes that intensively develop in retinal neurons and lens fibers.

The noncovalent interaction of meso-aryl-substituted thiacarbocyanine dyes I and II with dsDNA and ssDNA in aqueous solutions has been studied by spectral-fluorescent methods. Complexation with DNA is accompanied by both aggregation of the dyes and the formation of monomeric strongly fluorescent complexes. Experiments on molecular docking of dyes I and II with dsDNA confirm the previous assumption about the possibility of the formation of complexes of different types: intercalation between base pairs and in the grooves of the double helix of the biopolymer. The possibility of intercalation of the dyes in the complex is confirmed by experiments on thermal dissociation of dsDNA in the presence of dyes I and II, as well as experiments on the interaction of the dyes with ssDNA. An increase in the melting temperatures T

The literature on the spectral properties of ketocyanine dyes are reviewed from the viewpoint of chromophore interaction theory. It is shown that this theory can be used to describe the properties of a number of bichromophoric polyene donor–acceptor compounds and to predict their molecular configurations and spectral features.

The effect of OMe and NO2 substituents in the phenol ring of hydroxytetraphenylimidazole (HTPI) derivatives on their luminescence in solutions and in the solid phase has been studied. The presence of the nitro group leads to multiple luminescence. In addition to the band of the photoproduct of intramolecular proton transfer, which is single for unsubstituted HTPI, nitrosubstituted imidazoles additionally have emission bands at shorter and longer wavelengths. The ratio between the bands depends on the solvent, concentration, and excitation wavelength. In solutions and polymer media, it is possible to switch luminescence by changing the excitation wavelength, and under certain conditions, white light emission is observed.

The presence of alpha-fetoprotein (AFP) was shown in the retina and lens of the human fetal eye at different stages of prenatal development. PCR analysis revealed AFP mRNA neither in the retina nor in the lens, whereas in the fetal liver (control) AFP mRNA was found to be expressed. The data obtained indicate that AFP is not synthesized in retinal and lens cells of the human fetal eye but is imported from elsewhere to be taken up by these cells. The presence of AFP in the retina and lens implies its involvement in early morphogenesis and differentiation of these ocular tissues during prenatal human development.

Spectral-fluorescent and photochemical properties (photoisomerization and generation of the triplet state) of meso-substituted cationic carbocyanine dyes, 3,3′-di-(β-hydroxyethyl)-5,5′-dimethoxy-9-ethylthiacarbocyanine iodide (K1) and 3,3′-di-(β-hydroxyethyl)-9-methylthiacarbocyanine iodide (K2), have been studied in solutions and in the presence of DNA. In solutions, on passing from acetonitrile to dioxane, a growth of fluorescence of the dyes is observed due to a shift of the equilibrium of cis/trans isomers toward the fluorescent trans-isomer. Upon flash photolysis of dye solutions in dioxane, the formation and subsequent decay of the cis-photoisomers of the dyes are observed. In aqueous solutions, the interaction with DNA leads to the formation of noncovalent complexes of K1 and K2 with DNA, which is accompanied by a significant increase in the fluorescence intensity. The results of the molecular docking experiments showed the possibility of several types of binding, which was confirmed by the data obtained from other experiments. The effects of temperature and additions of NaCl on the stability of the dye–DNA complexes were studied. The spectral-fluorescent data were used to estimate the binding constants of the dyes with DNA and other characteristics of the dyes that are important for their use as probes. Upon flash photolysis of the dyes in complexes with DNA, photoisomerization is not observed, but the quantum yield of intersystem crossing to the triplet state increases. The decay of the triplet states occurs by a two-exponential law. The rate constants for quenching of the triplet states of the dyes complexed with DNA by oxygen were found to be lower than the expected values for diffusion-controlled quenching (taking into account the spin statistical factor 1/9), which is explained by the steric factor of complexation.

The presence of carotenoids in the vitreous body, retina, lens, retinal pigment epithelium together with choroid (hereinafter RPE), and ciliary body and iris together with choroidal stroma (hereinafter CBI) was studied throughout the second trimester of prenatal development of the human eye. It has been found that the vitreous body, retina, and RPE contain lutein and its oxidized forms. Zeaxanthin was not found in the tissues studied. The presence of lutein in the vitreous body is transient and no longer detected after 28 weeks of gestation. Lutein was not detected in the lens and CBI, but its oxidized forms were found. The presence of carotenoids in different tissues of the eye in the course of normal eye development and the antioxidant role of carotenoids are discussed.

J-aggregation of the anionic oxacarbocyanine dye 3,3′-di-(γ-sulfopropyl)-5,5′-diphenyl-9-ethyloxacarbocyanine betaine was studied in aqueous solutions in the presence of proteins (collagens, immunoglobulin G, serum albumins) and polyelectrolytes (polyethyleneimine, polyvinylpyrrolidone). It was found that denaturation of human serum albumin by urea stimulated J-aggregation of the dye. The dye formed two types of J-aggregates in the presence of denatured albumin and polyethyleneimine. J-aggregates formed in the presence of polyethyleneimine rearranged over time.

The noncovalent interaction of a number of cationic and anionic meso-substituted polymethine (carbocyanine) dyes with sodium deoxycholate (NaDC) as a biologically important surfactant was studied by spectral-fluorescent methods. The following dyes were studied: 3,3′-di(β-hydroxyethyl)-9-methylthiacarbocyanine-iodide (K1), 3,3′-di(β-hydroxyethyl)-5,5′-dimethoxy-9-ethylthiacarbocyanine iodide (K2), 3,3′,9-trimethylthiacarbocyanine iodide (K3, Cyan 2), 3,3′-di(γ-sulfopropyl)-9-methylthiacarbocyanine-betaine (A1), and 3,3′-di(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine-betaine (A2, DEC). Upon addition of increasing concentrations of NaDC, the absorption spectra of dyes K1–K3 in aqueous solutions exhibit changes due to the formation of dye aggregates and their subsequent decomposition into monomers. The formation of aggregates of K1–K3 leads to broadening of the absorption spectra and an appearance of additional bands. Upon binding to the surfactant, the cis-monomers of the dyes undergo partial cis–trans conversion, which is accompanied by an increase in the fluorescence intensity. The binding constants of the dyes to NaDC were estimated on the basis of Scatchard and Hill models from the dependences of the absorption and fluorescence spectra on the concentration of NaDC.

The influence of the formation of noncovalent intermolecular complexes with bovine serum albumin (BSA) on the spectral and fluorescent properties of the anionic oxacarbocyanine dye 3,3′-di-(γ-sulfopropyl)-5,5′-diphenyl-9-ethyloxacarbocyanine betaine (OCC) was studied. Binding of OCC to BSA increased significantly the dye fluorescence. Changes in the absorption and fluorescence spectra of OCC upon interaction with BSA argued in favor of a shift of the dye cis–trans equilibrium in the complex. The effects of adding albumin-denaturing compounds (urea, sodium dodecyl sulfate) on the spectral and fluorescent properties of the dye in the OCC–BSA complex were studied. It was concluded that OCC can act as a probe for albumins and can be used to study protein denaturing.

Absorption spectra of meso-substituted anionic polymethine dyes – oxonols were studied in solvents of different polarity. Two bands observed in the absorption spectra were shown to belong to two isomers of the dyes: trans-isomer (with a shorter-wavelength absorption band) and cis-isomer (with a longer-wavelength shoulder or band), being in equilibrium. A decrease in the solvent polarity shifts the trans-cis equilibrium toward trans-isomer for the fluoro-substituted oxonol and cis-isomer for the methyl-substituted oxonol, which can be explained by different structure of oxonol ion pairs formed in low-polarity medium. Spectral measurements at different temperatures permitted estimation of the energetic difference between the isomers.

Spectral and luminescent properties of novel derivatives of 2,4,5-triphenylimidazole synthesized in this study have been investigated in different solvents. For solutions of azomethine-substituted hydroxytriphenylimidazole (I) and two structural isomers, hydroxy-meta-bisimidazoles III and IV differing in the position of the OH group, two luminescence bands due to the presence of two ground-state conformers are observed. The equilibrium between the two conformers depends on the structure of the molecule and the solvent. For solutions of III and IV in polar and nonpolar solvents and for I in nonpolar solvents, long-wave-length luminescence dominates from the conformer with possibility of intramolecular proton transfer in the excited state. For I in protic and highly polar solvents, short-wavelength luminescence is the main one; depending on the excitation wavelength, it is possible to detect weak long-wavelength (green) or more intense short-wavelength (blue) luminescence.

Using the method of microsecond flash photolysis with UV and visible light, the spectral and kinetic characteristics of intermediate products of photolysis in toluene and methanol solutions of a new biphotochromic compound have been studied, in which two photochromic moieties, spironaphthoxazine and azomethine, are linked to each other in such a way that there is conjugation between π-electronic systems of the moieties in the ground state of the molecule. Two intermediate products have detected, whose relative efficiency of formation substantially depends on the solvent and the wavelength of excitation light.

A novel biphotochromic compound (BPC) with two photochromic fragments, namely spironaphthopyran and hydroxyazomethine, was synthesized and studied by nanosecond laser flash photolysis using the excitation wavelengths of 337, 430, 470 and 500 nm in methanol and toluene. The photoexcitation of BPC results in the formation of at least two colored transients. The first one is the merocyanine form B (the maximum in the absorption spectrum is near 600 nm and the lifetime is 0.1 and 0.05 s in methanol and toluene, respectively) due to the spiro-bond break followed by isomerization. The second one is the trans-keto form A(Kt) (the maximum in the absorption spectra is near 480 nm and the lifetime is 0.1 and 5 ms in methanol and toluene, respectively) as a result of cis-enol or cis-keto tautomer transformations. The relative yields of B and A(Kt) depends essentially on the wavelength of excitation. The form A(Kt) is the key transient formed under excitation with the visible light, whereas its yield under excitation with UV light is comparable with that of B. The specific solvation by methanol molecules favors the spirocycle opening even under visible light excitation. The results obtained for novel BPC were compared with those for other BPC where the same fragments are combined in such a way that the form B is the major one under excitation with UV light whereas it virtually is not observed under visible light excitation. The difference in both BPC is discussed in terms of conjugation (π-coupling) between photochromic fragments.

Spectral-fluorescent properties of the meso-substituted anionic cyanine dye 3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-methylthiacarbocyanine betaine (DMC) were studied in solutions and in the presence of human serum albumin (HSA). The properties of DMC were compared with those of the previously studied meso-substituted anionic dyes 3,3′-di(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine (DEC), 3,3′-di-(γ-sulfopropyl)-9-methylthiacarbocyanine betaine (MTC) and 3,3′-di-(γ-sulfopropyl)-5,5′-diphenyl-9-ethyloxacarbocyanine betaine (OCC), which were studied here in more detail. In aqueous solutions, DMC, like DEC, is prone to dimerization; it also forms H– and J-aggregates. The noncovalent interaction of DMC with HSA leads to decomposition of the dimers with a shift in the cis–trans isomeric equilibrium toward the trans-monomer complexed with HSA, which is accompanied by a significant increase in fluorescence. The spectral-fluorescent data were used to estimate the binding constants of the dyes with HSA and other characteristics of the dyes, which are important when used as probes for HSA. The effect of structural rearrangements of HSA upon denaturation by urea on the spectral-fluorescent properties of the dyes was studied. Molecular docking of the dye–HSA systems was performed. A comparative assessment of the prospects for the use of the dyes as spectral-fluorescent probes for HSA in vitro was carried out.

Magnetically guided liposomes (158±32 nm diameter) loaded with cytostatic drug rubomycin were produced using optimized procedure of hydration of thin phospholipid film. Magnetite nanoparticles (7.3±1.2 nm diameter) serving as the magnetic phase of the liposomes were produced using the polyol method. The liposomes were stable, with a shelf life of several weeks.

The spectral and fluorescent properties of cross-conjugated bichromophoric ω,ω′-aminopolyenes containing the pyran or dihydropyridine cycle with acceptor groups of different structures have been studied. According to the two-dimensional 1H NMR spectroscopy (NOESY and ROESY) data obtained earlier, chromophores are arranged at an acute or obtuse angle in compounds with the pyran or the dihydropyridine moiety, respectively, thereby leading to significant differences in the absorption spectra of these compounds. The absorption spectra have been considered on the basis of the theory of interaction of chromophores. Since the long-wavelength bands of the absorption spectra of the compounds with the dihydropyridine cycle are broad and poorly resolved, we used decomposition of the absorption spectra of these compounds into Gaussian components. The angles between the chromophores, estimated from the ratio of the intensities of the absorption bands, were found to comply with the NMR data. Fluorescence quantum yields of the compounds studied have been also determined. In the case of the dyes with carbonyl, dinitrile, or indandione acceptors, the fluorescence quantum yields were found to be significantly higher for the compounds with the pyran rather than the dihydropyridine cycle.

The spectral fluorescence properties of the anionic oxacarbocyanine dye 3,3'-di-(γ-sulfopropyl)-5,5'-diphenyl-9-ethyloxacarbocyanine betaine (OCC) were studied in solutions and in complexes with human serum albumin (HSA). Interaction with HSA leads to a significant increase in the fluorescence of the dye. We studied quenching of the fluorescence of OCC in a complex with HSA by ibuprofen and warfarin. Data on quenching of fluorescence by ibuprofen indicate binding of the dye to binding site II of subdomain IIIA in the HSA molecule. Synchronous fluorescence spectra of human serum albumin in the presence of OCC showed that complexation with OCC does not lead to appreciable rearrangement of the protein molecule at the binding site.

Photochromic and luminescent properties of a novel spiropyran modified by attachment of the nitroazomethine moiety in the 5′-position have been studied by laser photolysis and spectral and luminescent methods. Intermediate products have been detected and their decay rate constants have been determined during laser photolysis in toluene and a poly(methyl methacrylate) film. In alcohol solutions reverse photochromism is observed: coloration of the solution in the dark and its discoloration under exposure to light. The reasons for the appearance of reverse photochromism and the peculiarities of luminescence in alcohol solutions are discussed in comparison with the model nitrospiropyran.

Magnetite nanoparticles have been obtained with stable coatings formed from bovine and human serum albumins. The coatings are fixed by free-radical cross-linking of the proteins with the use of their ability to form interchain covalent bonds under the action of free radicals, which are generated with participation of transition metals present on nanoparticle surface. The method of spectral and fluorescent probes has been employed for the first time to describe the properties of coatings with the use of various dyes. It has been shown that, when studying the adsorption and free-radical cross-linking of proteins on nanoparticles, it is reasonable to use polymethine and squarylium dyes for estimating the functional properties of the proteins forming the coatings. It has been found that as many as 50% of molecules forming an albumin coating crosslinked via the free-radical mechanism retain their capability of bonding to a fluorescent dye. It has been concluded that the proteins occurring in the structure of the coatings retain their functional properties.

An anionic polymethine dye (a fluoro-oxonol abbreviated FDID), which forms monomers and oligomers according to the surrounding medium, is used in this work to probe the stability and dynamics of bicationic colloidal nanostructures, namely micelles and vesicles. Using pure water as the reference solvent (medium 1 ), five aqueous colloidal media of the lipid–detergent system DDAB–DTAC (didodecyldimethylammonium bromide–dodecyltrimethylammonium chloride) were analyzed: pre-micelle DTAC media ( 2 ); pure DTAC micelles ( 3 ); DDAB–DTAC micelles ( 4 ); DDAB–DTAC vesicles ( 5 ); and pure DDAB vesicles ( 6 ). In systems 4–6 , containing the double-chained DDAB, FDID showed a slow-dynamics disaggregation, H-aggregates → monomers. The kinetics of this transition was followed by running UV–vis absorption spectra along time. The transition lifetimes τ increased in the order τ medium 3 ≪ τ media 4,5 τ medium 6 , reflecting the much faster mobility of the single-chained DTA + long ion, as compared to that of the more hydrophobic, double-chained, DDA + . This paper showed that FDID can probe the exchanging dynamics of the DDA + /DTA + long cations between the water phase and the colloidal nanostructures.

A comparative study of the noncovalent interaction of the cyanine dye probe 3,3′-di-(γ-sulfopropyl)-4,5,4′,5′-dibenzo-9-ethylthiacarbocyanine betaine with serum albumins of different vertebrates: rat, rabbit, bovine, and human serum albumins (RSA, TSA, BSA, and HSA, respectively) has been performed by spectral and fluorescent methods. It has been shown that, the dye forms only one product, the trans-monomer bound to HSA, by interacting with HSA, whereas other binding products are also formed with other albumins. This is probably explained by a higher interaction energy of the dye with HSA than with other serum albumins.

Photoisomerization, thermal back isomerization, and spectral and kinetic properties of the triplet state of the oxacarbocyanine dyes 3,3′-diethyloxacarbocyanine iodide (OC1), 3,3′-dimethyl-9-ethyloxacarbocyanine iodide (OC2), and 3,3′,9-triethyl-5,5′-dimethyloxacarbocyanine iodide (OC3) have been studied by the flash photolysis method in solutions and in complexes with DNA. Upon flash photoexcitation, photoisomerization processes were observed for OC1–OC3, and difference absorption spectra of the photoisomers were obtained. The formation of complexes of OC1–OC3 with DNA impedes photoisomerization and leads to an increase in the quantum yield of the triplet state of the dyes. Deactivation of the triplet state follows the two-exponential law, which indicates the possibility to form complexes of two different types. The processes of quenching of OC3 triplet state by oxygen have been studied in solutions and in complexes with DNA.

Spectral, luminescent, and photochemical properties of the novel bifunctional compounds BF1 and BF2 based on indoline spiropyrans and o-hydroxyazomethines have been studied in solid media. In PMMA films and frozen solutions, redistribution of photoexcitation relaxation channels in favor of photochemical processes leading to photochromic products in the azomethine moiety and luminescence is observed as compared with liquid solutions.

New cross-conjugated ω,ω′-dimethylaminopolyenes containing the central pyrane or N-methyldihydropyridine fragment were synthesized. In new compounds, the interaction of the aminopolyene chromophores occurs through the dicyanomethylidene, 1-cyano-1-(4-nitrophenyl)methylidene, or 1,3-dioxoindan-2-ylidene groups in position 4 of the heterocycle. The conformation of the synthesized compounds was determined by 2D 1H NMR spectroscopy (NOESY and ROESY): the chromophores are arranged at an acute or obtuse angle in the structures with the pyrane or dihydropyridine fragment, respectively. The conformational differences in polyenes result in a drastic change in their spectral properties: for the dyes with an acute angles between the chromophores, the long-wavelength absorption band is less intense, as a rule, than the shorter-wavelength band, while the situation is opposite for the compounds with an obtuse angle. The absorption spectra of the synthesized compounds with dinitrile and other acceptor groups lie in a longer-wavelength region than the absorption spectra of the corresponding compounds with carbonyl acceptor groups. The central bridging substituent NMe decreases the energy of interaction of the chromophores.

Four hybrid compounds (HCs), which molecules contain two or three photochromic fragments of different nature, have been examined by the nanosecond laser flash photolysis techniques using excitation wavelengths of 337 and 430 nm in methanol solutions. In HC molecules the photochromic spironaphthoxazine fragment, which is able to generate a colored merocyanine form B upon UV excitation, is linked to the substituted salicylideneaniline (SA) fragment, where reversible photochemical transformations from cis -enol to trans -keto form having distinguishably different absorption spectra can occur. An azobenzene group prones to trans–cis photoisomerization is the substituent in SA fragment in the fourth compound. Four intermediates of different nature were found. A decrease in the relative efficiency of the ESIPT process with respect to that of spiro-bond cleavage was found to be the result of the influence of the electronegative substituents in SA fragments. The excitation light wavelength was shown to be the main factor determining the relative yields of the intermediates of different nature for the hybrid compound with the azobenzene group. The mechanism of different intermediates formation is discussed.

Photochemical processes (photoisomerization and generation of the triplet state) of the thiacarbocyanine dyes 3,3′,9-trimethylthiacarbocyanine iodide (Cyan 2), 3,3′-diethyl-9-methylthiacarbocyanine iodide (DMTC), and 3,3′,9-triethylthiacarbocyanine iodide (TETC) in complexes with biomacromolecules—DNA and chondroitin-4-sulfate—were studied by flash photolysis. It has been shown that, along with generation of the triplet state, enhancement of the photoisomer formation is observed for Cyan 2 and DMTC complexed with the biomolecules. This effect can be explained by the influence of the biopolymer matrix on the potential energy curves of the photoisomerization process.

Spectral and kinetic characteristics of intermediate products of photolysis of a novel phototrifunctional compound (PTC), whose molecule combines spironaphthoxazine, hydroxyazomethine, and azobenzene fragments, have been studied by microsecond flash photolysis with UV and visible light in toluene and methanol solutions. Three products of PTC photolysis have been detected. It has been found that the efficiency of the photoprocesses substantially depends on the solvent and the wavelength of excitation light.

Cis-trans equilibrium for a number of meso-substituted oxacarbocyanine dyes, 3,3′-diethyloxacarbocyanine iodide (K1), 3,3′-diethyl-9-methyloxacarbocyanine iodide (K2), 3,3′-dimethyl-9-ethyloxacarbocyanine iodide (K3), 3,3′,9-triethyl-6,6′-dimethoxyoxacarbocyanine iodide (K4), and 3,3′,9-triethyl-5,5′-dimethyloxacarbocyanine iodide (K5), has been studied in solutions and in a complex with DNA by spectral and fluorescent methods. A shift of the cis-trans isomer equilibrium toward the formation of the trans-isomer was observed in the presence of DNA, which determined in many respects the spectral effects observed upon the complexation of the oxacarbocyanine dyes. A steep rise of fluorescence (due to binding of the trans-isomer) in a complex with DNA is favorable for using oxacarbocyanine dyes to determine DNA.

The spectral, fluorescent, and photochemical properties of new merocyanines containing nitrile groups as acceptors have been studied. Positive solvatochromism is observed for most of these compounds; however, for the dye containing three nitrile groups as acceptors—polyenic aminotrinitrile—negative solvatochromism is observed: the absorption spectrum is shifted to shorter wavelengths with increasing the solvent polarity. In all solvents used, the fluorescence and fluorescence excitation spectra of the merocyanines almost do not depend on the excitation and fluorescence registration wavelengths, respectively. Using the flash photolysis method, the formation of photoisomers of the merocyanines has been detected and the kinetics of their decay in solvents of different polarity has been studied. Backward (dark) isomerization of the photoisomers has been shown to take place more slowly in nonpolar solvents.