Novel copolyfluorenes (CPFs) containing 2.5 or 10 mol% of carbazole-2,7-diyl (2,7-Cz) or carbazole-3,6-diyl (3,6-Cz) derivatives in the backbone have been synthesized by means of palladium-catalyzed Suzuki polymerization under microwave irradiation. The structure of the CPF polymers was also modified by insertion of additional 2-ethylhexyl or carbazole, diaryloxadiazole, or triphenylamine units via 3,6-Cz or 2,7-Cz comonomer units in the side chains of polymers. The self-organization of molecules in chloroform solutions was investigated using light scattering and within a wide concentration interval. Analysis of the behavior of the CPFs showed that the synthesized copolymers have an increased equilibrium rigidity of molecules with a Kuhn segment length A = (10-15) nm. The A value decreases with the introduction of Cz-units into the macromolecule in the meta-position. It is shown that chemical structure of the CPFs and thermal treatment in the temperature range 60-150 degrees C have a dominant effect on the optoelectronic properties as well as on microstructures of their films. Published by Elsevier Ltd.

Estimation of the influence of molecular substituents on electroluminescence and electron–hole mobility in copolyfluorenes with the use of a CELIV technique has revealed that minor changes in the number of benzothiadiazole fragments in copolyfluorenes has a dramatic effect on the optoelectronic properties of these polymers to improve the electroluminescence and electron mobility by factors of 20 and 10, respectively.

New copolyfluorenes containing 4,7-di-2-thienyl-2,1,3-benzothiadiazole and 2,1,3-benzothiadiazole or derivatives of naphthalimide as luminophores were synthesized under microwave heating. Charge-transporting carbazole, triphenylamine, or diphenyloxadiazole groups were introduced into the side chains of polymers through 9,9-bis-(4-phenoxy)-2,7-fluorene units. Copolyfluorenes were also modified via insertion of 10 mol% of 2,7-[9,9-bis-(6'-diethoxyphosphorylhexyl)]fluorene or dibenzothiophene-S,S-dioxide comonomer units into the polymer backbone. This study demonstrates the influence of chemical compositions, molecular masses of the polymers under investigation, and thermal treatment on microstructures of their films. Photo- and electroluminescent characteristics of the synthesized copolyfluorenes were determined. The best samples of devices manifested the luminance of 5110 cd m(-2), the current efficiency of 1.33 cd A(-1), and the CIE 1931 xy chromaticity coordinates of (0.339 0.364), or 7930 cd m(-2), 2.18 cd A(-1), and of (0.300 0.369) respectively. The effect of active layer thickness on the white emission color of polymer light-emitting diodes was revealed.

In the paper we present synthesis and characterization of new donor–acceptor thiophene derivatives (TDs) containing vinylbenzo[d]thiazole, vinylpyridine and 1H-imidazo[4,5-f][1,10]phenanthroline residues. Using CELIV method, electron and hole mobility have been studied in the polymer layers based on poly [9,9-bis(6-diethoxyl-phosphorylhexyl)fluorine] (PF-EP) doped with the TDs. Polymer light-emitting diodes (PLEDs) containing newly synthesized polyfluorene (PF) as emitting layers and PF-EP/TD composites as electron transporting layers show higher brightness at 15V as compared with TD free PF-EP.

The synthesis of copolyfluorenes by the Suzuki method under microwave heating carried out under conditions that were previously used for convection heating in an open system is studied. Using size-exclusion liquid chromatography, the stages of polycondensation, namely, oligomer formation, chain growth, and end group termination, are examined. The influence of temperature, solvent, and catalyst type Pd(PPh 3 ) 4 , PdCl 2 (dppf), polymer-bound Pd(PPh 3 ) 4 , and SiliaCatDPP-Pd on the molecular-mass characteristics of the polymers is analyzed. The optical properties of new copolyfluorenes obtained by different methods are compared.

Using Suzuki and Yamamoto coupling reactions, copoly-(9,9-dioctylfluorenes) (CPF) were synthesized and compared regarding their photophysical properties using the spectroscopic and ab initio DFT approaches. The CPFs were functionalized by benzo [2,3,5] thiadiazole (BT) or carbazole-3,6-diyl (3,6-Cz). The latter was used to introduce different luminophore fragments, including Nile red and 4-pyrrolidinyl-1,8-naphthalimide derivatives. The effect of the two synthesis techniques on the polymer microstructure, the influence of embedding of 3,6-Cz moieties in the polymer backbone on polymer structuring, and the impact of the end groups like novel quinoxaline-containing compounds on the luminescent properties of CPFs were investigated. By comparing electron density distribution using the ab initio DFT approach with photoluminescence, it was shown that Suzuki reaction provides a chain microstructure with individual BT fragments separated by 9,9-dioctylfluorene monomeric units, while Yamamoto reaction leads to the blocks of BT units. This effect leads to different CPF photophysical properties (absorption and emission spectra).

Seven polyfluorenes containing new carbazole derivatives of Nile Red dye and 1,8-naphthalimide in the chain (obtained by the Suzuki and Yamamoto coupling) are characterized by the Nile Red emission band being less intense in their electroluminescence spectra than in photoluminescence spectra. In the optimal composition, 0.15 mol% fraction of Nile Red and 0.5 mol% fraction of N-[6-(2,7-dibromocarbazol-9-yl)hexyl]-4-diethylamino-1,8-naphthalimide provide a nearly white light electroluminescence (CIE coordinates x = 0.28; y = 0.36) with the brightness of 3278 cd m–2 and the current efficiency of 1.86 cd A–1.

Polyfluorene copolymers containing 33 mol% of 2,5-difluoro-1,4-phenylene units and other comonomers comprising chargetransporting triphenylamine, carbazole, and 1,8-naphthalimide groups were synthesized by the Suzuki polycondensation under microwave irradiation. On heating the obtained copolymers to 180 °C, their photoluminescence spectra remain stable. The best sample herein obtained provided the OLED brightness of 2830 cd m–2, current efficiency of 0.5 cd A–1 and CIE coordinates of x = 0.168 and y = 0.228.

The evolution of the structure and mechanical behavior upon deformation has been studied experimentally in situ by room-temperature high-pressure torsion (HPT) of the initially crystalline Ti2NiCu alloy. An abrupt increase in the shear stress upon HPT has been revealed. It was found that the observed effect is due to the deformation-induced “crystalline⇒amorphous state” phase transformation and the corresponding change in the mechanism of severe plastic deformation. It is shown that the amorphization of the material begins at the boundaries of grains and fragments of the crystalline phase as a result of grain boundary sliding processes. It was established that the amorphous boundaries form a “grain-boundary framework”, which upon deformation is expanded and transformed into bulk amorphous phase.

The fcc → fct martensitic transformation in Mn–Cu alloys, which contain two isomorphous fcc phases with different manganese contents, is considered. The influence of the ratio of contents of these phases, the phase dispersity, and the state of interphase boundaries on the development of the martensitic transformation in the volume of the alloys is described. As a result of these factors, the martensitic transformation can cover the entire volume of an alloy, including particles with the manganese content that is lower than the critical content required for the martensitic transformation to occur in single-phase solid solutions, and can take place only in manganese-rich particles. In the first case, a general tetragonal structure modulated with respect to lattice parameter c forms in the volume of a two-phase alloy.

Organic light-emitting diodes (OLEDs) are attracting great interest of the scientific community and industry because they can be grown on flexible substrates using relatively simple and inexpensive technologies (solution processes). However, a problem in the fabrication of white OLEDs is that it is difficult to achieve a balance between the intensities of individual emission components in the blue, green, and red spectral regions. In this work, we try to solve this problem by creating a two-component light-emitting diode based on modified polyfluorene (PF-BT), which efficiently emits in the blue–green region, and CdSe/ZnS/CdS/ZnS semiconductor quantum dots emitting in the orange–red region with a fluorescence quantum yield exceeding 90%. By changing the mass ratio of components in the active light-emitting composite within 40–50%, it is possible to transform the diode emission spectrum from cold to warm white light without loss of the diode efficiency. It is very likely that optimization of the morphology of multilayer light-emitting diodes will lead to further improvement of their characteristics.

Spectral, luminescent and electro-optical properties of poly(9,9-dioctylfluorene), containing small quantity (1–2mol%) of 2,1,3-benzothiadiazole comonomer units, obtained by means of either Suzuki or Yamamoto polycondensation reactions were studied and compared. The difference of luminescent properties of the two copolymers with nearly identical chemical compositions was explained by different molecular structure of their macromolecules. The films of Yamamoto type copolymer, containing, obviously, microblock sequences of 2,1,3-benzothiadiazole units, exhibit a nearly white electroluminescence (CIE x=0.276, y=0.274) with a high brightness (3747cd/m2 at 10V), while the films of Suzuki type copolymer with randomly distributed isolated 2,1,3-benzothiadiazole fragments – green electroluminescence.

The study of conformational properties and tendency to association for chromophore-containing comb-like copolymer of β-(3,4-dicyanophenylazobenzenethyazole) methacrylate (A) and amylmethacrylate (B) (1:1) has been carried out. The copolymer AB is of particular interest because of non-linear optical properties of its films. Dielectric permittivity and dipole moment temperature dependences in dilute cyclohexanone solutions in the temperature range from 20 to 70 °С, in the electric field E ≤ 104 V/cm were investigated by means of static dielectric polarization. It was shown that temperature and concentration dependences of dielectric permittivity for the solvent, copolymer AB, monomer A and polymer B were linear indicating low molecular interactions at temperatures and fields used. The invariable stoichiometry of components in solution for concentration lower than 10–3 mol/mol was proved. The values of dielectric permittivity were extrapolated to infinite dilution and increments α=(Δɛ12/Δx2)x2=0 were calculated. The solvent dipole moments were calculated in terms of the Onsager theory whereas dipole moments of AB, A and B were calculated in terms of the Backingham statistical theory of dielectric polarization. Intramacromolecular conformational transition was found to be at ∼40 °C. Dipole moment of A was shown to increase with both temperature and electric field strength. Copolymer side chains trans-location takes place due to intramacromolecular association resulting in the compensation of dipole moments and Kirkwood factor g ≈ 0.6. The association of A units increases in the electric field reducing the dipole moment per monomer unit significantly and g values approximately twice.

Features of structural phase transitions under the high-pressure torsion of layered amorphouscrystalline Ti 50 Ni 25 Cu 25 composite with 3 : 1 ratios of the layer thicknesses of the amorphous and crystalline phases, respectively, are analyzed by means of X-ray diffraction and transmission electron microscopy. The applied pressure is varied from 2 to 8 GPa. It is found that the structure of the layered Ti 50 Ni 25 Cu 25 composite evolves in different ways in different parts of the material.

When a polarized ray is obliquely incident on a film, rotating the film around an axis perpendicular to its surface results in birefringence (BR), which has been studied in a previous paper. Surface BR in triphenylamine-containing polyheteroarylene films has been investigated as a function of the angle of incidence of the light and the film thickness. The results made it possible to estimate the orientational-order parameter of fragments of the macromolecules in the near-surface layers, as well as to estimate the statistical segment length of the polyheteroarylene chains.

This review concerns the specific features of photo- and electroexcited processes of excitation energy deactivation in one of the most widely studied classes of organic semiconducting polymers, copolyfluorenes. Spectral-luminescent, electroluminescent, and light-generating properties of a number of copolyfluorenes are discussed, and ways to create organic electronics devices on their basis are revealed.