L. S. Atabekyan

Photoprocesses in aqueous solutions of 9-ethylthiacarbocyanine dyes in the presence of surfactants

The effect of cationic (CTAB), anionic (SDS) and neutral (Triton X-100) surfactants on the spectral and luminescence properties and photoreactions of three sulfopropyl-9-ethylthiacarbocyanine dyes (Dyes 1–3) was studied in aqueous solutions. In the absence of the surfactants, Dyes 1–3 occur in the form of an equilibrium mixture of cis-monomers and dimers. Neither monomers nor dimers are capable of fluorescence and cis-trans photoisomerization, and only the dimers experience intersystem crossing into the triplet state. In the presence of any of the surfactants at a concentration below the critical micelle concentration, the dimers undergo disaggregation; it is only in the presence of CTAB that the formation of a J-aggregate—which dissociates into monomers with an increase in the CTAB concentration—takes place. As the surfactant concentration increases, dye fluorescence appears, which is accompanied by a decrease in the yield of the dimer triplet state, and the amenability of the thiacarbocyanine monomers to cis-trans photoisomerization and transition to the triplet state is observed. The spectral effects observed are related to the conversion of the cis-form of the monomer to the trans-form upon solubilization of the dye molecules.

Trans-cis photoisomerization and photoinduced electron transfer as competitive reactions of 9-etylthiacarbocyanine in binary mixtures

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.

Photonics of azacrown-containing styryl dye and its complexes with metal ions: 1. Triplet states

Photophysical processes in a styryl dye; an azacrown-containing analog; and its complexes with barium, lead, calcium, sodium, and silver cations have been studied by laser kinetic and luminescent spectroscopy. The participation of the triplet state in the degradation of photoexcitation energy has been established. Phosphorescence and delayed fluorescence of dyes and its complexes have been revealed found. It has been concluded that the molecules can exist in the excited TICT state.

Primary photoprocesses of 3,3’-diethylthiacarbocyanine in the presence of cucurbit[7]uril: Laser flash photolysis and quantum chemical calculations

The effect of cucurbit[7]uril on the phototransformation of 3,3′-diethylthiacarbocyanine iodide dye in aqueous solution has been investigated by nanosecond laser flash photolysis. The presence of cucurbit[7]uril results in the formation of its complex with the dye molecule producing a dimer. The dimer formation is evident from the ground and triplet-triplet absorption spectra. The dimers in the triplet state are capable of electron transfer. The structure of the complexes is suggested on the basis of quantum chemical calculations.

Nitrogen-Containing Analog of Dibenzoylmethanate of Boron Difluoride: Luminescence, Structure, Quantum Chemical Modeling, and Delay Fluorescence

AbstractBoron difluoride of 3-amino-1,3-diphenyl-2-propene-1-onate (1) has been synthesized and its crystal structure has been determined. The comparative studies of 1 and its oxygen analog 1,3-diphenyl-1,3-dionate (dibenzoylmethanate) of boron difluoride (2) have been performed using the methods of stationary and time-resolved spectroscopy and quantum chemical modeling. It was established that at the transition from solutions to crystals, a bathochromic shift of the spectra and a significant increase of luminescence intensity of 1 take place. The luminescent properties of solutions of 1 and 2 are similar. The peculiarities of crystal packings of 1 and 2 are responsible for differences in crystals luminescent properties. For crystals of 2, one observes the luminescence of J-aggregates and excimers, while for 1, in which a dimer is an elementary structural fragment, only the excimer luminescence is registered. A delayed excimer fluorescence of the P-type was observed for crystals of 1 and 2 at room temperature. The intensity of the delayed fluorescence of 1 is 300-fold higher than that of 2. Graphical AbstractLuminescence of J-aggregates and the formation of excimers in crystals of 1 and 2

The Kinetics of Photocoloration of Spiropyrans upon Complexation

The kinetics of photocoloration of spiropyrans in the presence of a metal ion in solution was studied using laser kinetic spectroscopy. Mathematical simulation of the photocoloration process, semiempirical quantum-chemical calculation, and comparison of their results with experimental data have provided evidence that several trans-isomers of the merocyanine form of spiropyrans can take part in the complex formation reaction. An experimental procedure for determining the involvement of one, or two, or more trans-isomers of spiropyrans in the complexation reaction in the course of photoinduced opening of the pyran cycle and the formation of a stable trans-isomer was proposed. The scheme of the photoreaction is given.

Spiropyrans complexes with metal ions. Kinetics of complexation, photophysical properties and photochemical behaviour

Abstract The results on spectrophotometric, luminescent, stopped—flow and ns—laser flash—photolysis study of complexation between indoline spiropyrans and metal ions are discussed.

Photochromic Transformations of Spiro Compounds: 2. The Kinetics of Photocoloration under Continuous Irradiation

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.

Laser photolysis study of 1-aryl-3-methyl-5-(benzothiazole-2-yl) formazan phototransformation

Photochromism of 1-aryl-3-methyl-5-(benzothiazole-2-yl)formazans in toluene has been investigated by the laser flash photolysis method. It was established that the photochromic transformations involve the triplet state of the initial chelate form of formazans. The intermediate short-lived products of phototransformation were detected that could be related to one of the conformers or to the tautomers of the formazan molecule.

Photonics of N -ammonioalkyl derivatives of azacrown-containing styryl dyes

Photophysical and photochemical processes in diperchlorates of styryl dyes containing an N-ammonioalkyl substituent have been studied by the absorption, luminescence, and laser kinetic spectroscopy techniques. Participation of the triplet state in photoexcitation energy degradation processes and the ability of the dyes to enter the trans-cis photoisomerization reaction have been revealed. Dimerization and delayed fluorescence of the dyes at 77 K have been detected.