B. I. Shapiro

Electroluminescence of polymer/J-aggregate composites

Efficient electroluminescence was revealed in single-layer light-emitting diodes based on electron-hole conducting polymers containing the nanocrystalline phase of cyanine dyes (J-aggregates). These species exhibit a very narrow emission band with a maximum in the red to infrared spectrum range. The J-aggregates play an active role in the charge carrier transport of the composites.

Near-infrared electroluminescence in polymer composites based on organic nanocrystals

IR electroluminescence was revealed in single-layer light-emitting diodes based on a type of electroactive polymer nanocomposites-electron-hole conducting aromatic polyimide and organic nanocrystalline particles of cyanine molecules, known as J-aggregates. These materials exhibit a very narrow emission band with a maximum at 815 nm. Dramatic increase of charge-carrier mobility was observed for these layers containing the J-aggregate nanocrystalline phase.

Photoelectric, nonlinear optical and photorefractive properties of polyimide doped with J-aggregates of cyanine dye

Abstract Novel solid-state photorefractive compositions consisting of the aromatic polyimide ( T g is about 230 °C) and the thiacarbocyanine dyes were prepared. These systems have the high net gain coefficient, Γ − α , about 360 cm −1 . The dyes form the nanocrystalline J -aggregates that are responsible for photoelectric sensibility in the region of action of Ar–Kr laser and are known to have also very high third-order macroscopic polarizability. The Kerr electrooptical effect is mainly responsible for the light induced refractive index change. It is established that the charge photogeneration time constant determines the time of the photorefractive grating formation and depending on the dye used may be about 20 ms. So, it became possible to develop the solid-state high-performance photorefractive layers based on the polymer with high T g .

J-AGGREGATE ELECTROLUMINESCENCE IN DYE DOPED POLYMER LAYERS

The electroluminescence (EL) of a dye nanocrystalline phase was revealed in single layer light-emitting diodes based on polymers doped with cyanine dye molecules. Observation of light emission in the visible range depended on the redox potentials of the dyes used. The 9,10-dithioanthracene-containing polyimides exhibiting efficient electron-hole transport appeared to be appropriate media for the generation of J-aggregate EL.

Photorefractive Polyimide Containing J-Aggregates of Thiacarbocyanine Dye

The paper demonstrates photorefractive characteristics of the aromatic polyimide (T_g=230\,^\circ\hbox{C}) containing J-aggregates of the thiacarbocyanine dye. The two wavelengths 647\,\hbox{nm} and 514\,\hbox{nm} of Ar-Kr-laser were used. The J-aggregates of the dye are responsible for optical absorption at 647\,\hbox{nm} . At that wavelength the net gain coefficient increases from \Gamma-\alpha=217\,\hbox{cm}^{-1} to 361\,\hbox{cm}^{-1} with growth of external electric field E_0 from 16 to 123\,\hbox{V}/\rmu\hbox{m} . Only samples containing J-aggregates exhibit the PR effect at wavelength 514\,\hbox{nm} at which the laser excites monomeric form of the dye. The estimated at 514\,\hbox{nm} and E_0=16\,\hbox{V}/\rmu\hbox{m} two-beam gain coefficient is near 480\,\hbox{cm}^{-1} and the net gain \Gamma-\alpha is about 118\,\hbox{cm}^{-1} . The high glass temperature of aromatic polyimide should appreciably limit the orientation...

Reaction of polymethine dyes with hydroperoxides and free radicals

The interaction kinetics of the cationic and anionic polymethine dyes with radicals has been studied. Azoinitiator AAPH, as well as tert-butyl hydroperoxide, and hydrogen peroxide were used as radical initiators in water and buffer solutions at 37 °C. It is shown that the dyes are active scavengers of peroxyl radicals. It is found that reactivity and behavior of dyes in relation to the peroxides are strongly dependent on the structure of lateral substituents in polymethine chains.

J-aggregate electroluminescence in polymer matrices

Cyanine dye electroluminescence was observed in single layer light-emitting diodes based on electron-hole conducting polymers. The appearance of light emission in the visible range depended on the reduction/oxidation potentials of the dyes used. In polymer systems, the electroluminescence of cyanine dye J-aggregate nanocrystalline phase was detected for the first time. J-aggregate/polymer composites exhibiting intense absorption band with a maximum in the red range were developed on the base of polyimides and a copolymer coformed from phenylacetylene and 4-methylcoumarin-4-pentynoate doped with the dye luminophores. Efficient electrolumunescence was revealed in these systems. It was demonstrated that J- aggregates play an active role in charge carrier transport in the composite materials. In particular, anthracene-containing polyimides exhibiting electron-hole transport appeared to be appropriate media for the generation of J-aggregate electroluminescence.

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.

Kinetic characteristics of the reaction of natural thiols with peroxyl radicals and hydrogen peroxide

Kinetic characteristics of the reaction between natural thiols, viz., glutathione, cysteine, and homocysteine, and peroxyl radicals formed upon decomposition of the azo initiator AAPH (2,2´-azobis(2-methylpropionamidine) dihydrochloride) in aqueous solutions at 37 °С were determined by the competing reaction method. The kinetics of radicals formation in the reaction between natural thiols and H2O2 was studied by the inhibitor method. The polymethine dye, pyridinium 3,3´-di-γ-sulfopropyl-9-methylthiacarbocyanine, was used as the radical scavenger. Cysteine was found to exhibit the highest activity in the reactions with peroxyl radicals and in the free radical generation upon the reaction with H2O2. The data obtained can be useful for understanding the physiological role of thiols in oxidative processes.

Kinetic characteristics of the reaction of resveratrol with peroxyl radicals and natural thiols in aqueous medium

The method of competing reactions was used to determine the rate constants of the reaction of resveratrol (RVT) with peroxyl radicals formed on decomposition of the azoinitiator ААРН in aqueous solutions at 37 °С. The polymethine dye A (3,3′-di-γ-sulfopropyl-9-metylthiacarbocyanine-betaine pyridinium salt) was used as a competing acceptor of radicals. It was found that resveratrol can be involved in the reaction with natural thiols, glutathione (GSH) and cysteine (CSH), in aqueous solutions at 37 °С. The reaction of RVT with thiols (thiol—еne reaction) follows a chain mechanism and accelerates in the presence of Н2О2. The results obtained can be useful for understanding the physiological role of thiols in oxidation processes.