A. I. Tolmachev

Effect of meso-alkyl substituents in the polymethine chain of thiacarbocyanines on the morphology of dye aggregates

Using the example of meso-alkylsubstituted thiacarbocyanine dyes, it has been demonstrated that an ethyl substituent, as a rule, promotes the formation of long-wave J-aggreagtes in aqueous solutions and a methyl substituent favors the formation of short-wave H*-aggregates. The formation of dye aggregates proceeds through dimers by the block mechanism. The formation of three bands in the absorption region of dimers, which plausibly relate to three different forms of dimers and can be attributed to dimers consisting of the cis-, cis-/trans-, and trans-conformations of the dyes, has been recorded for the first time in meso-CH3-substituted thiacarbocyanines. The formation of three different types of H*-aggregates from the three appropriate dimeric forms has also been shown for the first time. It has been established that introducing a multicharged Eu+3 cation into aqueous solutions of dyes shifts the equilibrium, nD-aggregate, towards aggregates; meso-CH3-substituted dyes in this case shift towards H*-aggregates and meso-C2H5-substituted dyes shift towards J-aggregates. Hence it has been shown that an alkyl group in the meso-position to the polymethine chain of thiacarbocyanines plays the role of a regulating agent in the aggregation process due to stereochemical effects and, by this means, predetermines the morphology and spectral properties of the formed aggregate.

Formation of mixed J-aggregates of cyanine dyes stimulated by Eu+3 cations

The block mechanism of the formation of J-aggregates from the dimers of various dyes in an aqueous solution under the action of the multiply charged Eu+3 cation was considered for the first time. It was shown that the structure and the position of the absorption maximum of the mixed J-aggregates are determined by the length of the dye chromophore moiety. It was concluded that the mixed J-aggregates are of interest as nanosized optical elements with varying optical and electronic properties depending on the structure of cyanines used.

Infrared Electroluminescence in Polymer Composites Based on Organic Nanocrystals

Electroluminescence in polymer nanocomposite structures with electron–hole transport, called J-aggregates, which are based on aromatic polyimides and nanosized crystals of cyanine dyes, is studied. In the near-IR range, the electroluminescence with a narrow emission spectrum (with a maximum at 815 nm) is observed for the first time. It is shown that not only are the organic nanosized crystals of the J-aggregates effective acceptors of the exciton state energy, but they play the role of active electron–hole transport centers in these novel polyfunctional polymer materials.

J-aggregates of thiadicarbocyanine dyes with fixed polymethine chain incorporated in Langmuir-Blodgett films

Abstract Langmuir-Blodgett films, incorporating N-sulphopropyl substituted thiadcarbocyanine dyes with a fixed polymethine chain adsorbed on octadecylpyridinium monolayer, have been prepared. Dye mocules in Langmuir monolayers form J-aggregates, which structures depend on monolayer preparation conditions. The dyes also form mixed J-aggregates. The film structure has been studied by using X-ray small-angle diffraction and spectroscopy. It was shown, that optical anisotropy of J-aggregated dye films is related to the conditions of monolayer transfer onto solid supports.

Interaction between gold nanoparticle plasmons and aggregates of polymethine dyes: “Invisible” nanoparticles

Composite nanoparticles consisting of rodlike gold particles coated by an organic layer and polymethine (cyanine) dyes of J-aggregates of different structures absorbing light in red and infrared spectrum ranges have been synthesized. It has been demonstrated that, for dyes with J-band absorption maxima in the gold plasmon-band range, one observes an absorption dip as a result of the interference of the photoexcited states of nanoparticles and J-aggregates. The latter results in the decoloration of the gold colloid solution. The effect of the emergence of new intensive absorption bands of dye aggregates, which is assumed to be related to the perturbance of dye aggregate electron levels by gold plasmons and, consequently, lifting the ban on electron transitions to perturbed levels of aggregates, has been found.

Effect of organic polyelectrolytes on H*-aggregation of meso -methyl-substituted thiacarbocyanine dyes

H*-Aggregation of anionic meso-methyl-substituted thiacarbocyanines of different structures has been studied in dilute aqueous solutions and in the presence of cationic organic polyelectrolytes. The thermodynamic parameters of the H*-aggregation from the trans-dimers have been determined. The thermodynamic equilibrium between two forms of the H*-aggregates in the presence of poly-N,N-dimethyl-N,N-diallylammonium chloride has been observed for the first time, and these forms have been assigned to H*cis and H*trans forms.

Mixed J Aggregates of Oxacarbocyanine Dyes and Their Photographic Properties

Formation of mixed J aggregates from two oxacarbocyanine dyes of different structures was established. Mixed J aggregates were shown to be photographically active states of spectral sensitizers. The fundamental conclusion was made that the photosensitization maximum and the photographic activity of mixed J aggregates can be varied over a wide range by changing the concentration of the dyes incorporated into the aggregates.

J-aggregates of the thiatricarbocyanine dyes incorporated into LB films

Abstract The N-sulphopropyl-substituted thiatricarbocyanine dyes can be incorporated into composite monolayers with hexadecylamine (HDA) at the air-water interface. The composite monolayers including the dyes can be transferred onto a solid substrate. The spectroscopic properties of Langmuir-Blodgett (LB) films were investigated by optical spectroscopy. The J-aggregate formation was first observed for three tricar-bocyanine dyes. The J-aggregate structure depends on the dye concentration in the mixture with HDA as well as on the constant pressure value at which the transfer onto quartz slides is performed. LB films with a molar ratio of dye to HDA of 1:10, transferred at 30 mN m−1, show the greatest shift of the J-band from the monomeric one.

Pyrylocyanines. 29. tert-Butyl-substituted benzopyrylocyanines

Abstract2-tert-Butyl-4-methyl- and 2-methyl-4-tert-butylbenzopyrylium salts, as well as the sulfitr analog of the latter, were synthesized. Polymethine dyes with symmetrical and unsymmetrical structures were obtained from these salts. The factors that affect the color are analyzed.

Pyrilocyanines. 24. Symmetrical tetra-tert-butyl substituted pyrilo-2-cyanines

Abstract2,4-di-tert-butyl-6-methylpyrilium and -thiopyrilium salts were synthesized. From them were obtained symmetrical tetra-tert-butyl substituted α-pyrilocarbo- and dicarbocyanines and their sulfur analogs. The α-pyrilocyanines were converted to symmetrical α-pyridocyanines. The effects of heteroresidue structure, length of polymethine chain, and solvent on the location and shape of the absorption bands of these dyes were studied. Their experimental spectral properties were compared with the results of quantum chemical calculations of average band locations, second-power changes of bond order upon excitation, and theoretical electron donor capabilities.