Synthesis of thermally stable and hole-transporting amorphous molecule having four carbazole moieties

A novel thermally stable and hole-transporting amorphous molecule, 9,9-bis(4-[bis-(4′-carbazol-9-yl-biphenyl-4-yl)-amino]-phenyl)fluorene (T-Caz) has been synthesized in two-step reactions from carbazole. T-Caz showed UV–Vis absorption bands at 290 and 340 nm in chloroform solution, and the photoluminescence spectrum showed a maximum peak at 420 nm in a purplish blue region. Differential scanning calorimetry (DSC) showed a high glass transition temperature at 250 °C. The organic light-emitting device prepared by spin-coating T-Caz solution onto the indium-tin oxide (ITO)-coated glass substrate in conjunction with tris(8-quinolinolato)aluminum (Alq) and LiF/Al, as an electron transporting light-emissive layer and a metal cathode, respectively, showed a maximum luminescence of 10,300 cd/m² at 11 V.     

Effect of electron- and hole-transporting materials on the performance of FIrpic-doped PVK phosphorescent devices

PVK-based phosphorescent FIrpic-doped devices have been fabricated and the effect of carrier transporting materials on the device performance has been investigated. We have fabricated the single-layer and double-layer devices to investigate the role of electron- and hole-transporting materials both when they are mixed in the single- and separated from the emissive layer. We have studied NPB as a hole-transporting material, OXD-7 and PBD as electron-transporting materials. Even though PBD had been well known to be unsuitable as an electron-transporting material for FIrpic-doped PVK devices, it was found in this study that the separate utilization of PBD from PVK:FIrpic layer instead of mixing it with the emissive layer could enhance the device performance significantly. Nevertheless, the OXD-7 was found not only superior to PBD as the electron-transporting material for FIrpic-doped PVK devices but also suitable as an electron-transporting material for the single-layer devices.     

Synthesis and electro-optical properties of carbazole derivatives for organic device applications

Two materials, DNCz and TCzPB, which contain carbazole moieties and exhibit high band gap energies, were synthesized via CN coupling and Suzuki coupling reactions, respectively. The ionization potential and electron affinity of the synthesized TCzPB were measured at 5.89 and 2.39 eV, respectively, implying that it is suitable for a host material. A doped multilayer device, ITO/DNTPD/NPD/TCzPB + Ir(ppy)₃/BCP/Alq₃/LiF/Al, exhibited a bright green emission with a maximum luminance of 27,200 cd/m² (17.6 cd/A at 18.0 V) when the synthesized TCzPB was used as the host material for a phosphorescent green dopant. The compound DNCz exhibited similar electronic energy levels to those of NPD, and was applied as a hole-transporting material. Bright green light originated from the Alq₃ layer was observed in the double layer device, ITO/DNCz/Alq₃/LiF/Al. The high hole-transporting property of DNCz was also demonstrated.     

Luminance materials containing carbazole and triphenylamine exhibiting high hole-transporting properties

Two novel 2-substitutd-8-hydroxyquinoline derivatives were designed and synthesized. Their luminance properties and carrier transporting abilities were studied when integrated in four different organic light-emitting device structures. The four devices are structured as following—device A: indium tin oxide glass substrate (ITO)/2-TNATA/NPB/(2-[2-(9-ethyl-9H-carbazol-2-yl)-vinyl]-quinolato zinc (1) and 2-[2-(4-diphenylamino-phenyl)-vinyl]-quinolato zinc (2))/Alq₃/LiF/aluminum (Al); device B: ITO/2-TNATA/NPB/1 or 2/LiF/Al; device C: ITO/2-TNATA/1 or 2/Alq₃/LiF/Al; device D: ITO/2-TNATA/1 or 2/Alq₃/LiF/Al. In the device A, the maximum brightness of compound 1 is 5857 cd m⁻² at 11 V with the luminance efficiency 1.84 cd A⁻¹. For 2 it is 6047 cd m⁻² at 10 V with an efficiency of 2.22 cd A⁻¹. In the device B, the maximum brightness of 1 is 745 cd m⁻² at 11 V and efficiency is 0.32 cd A⁻¹. These values are 1748 cd m⁻² at 10 V and 0.42 cd A⁻¹ for 2, respectively. In the device C, the maximum brightness of 1 and 2 are 8729 and 5838 cd m⁻² at 10 V, respectively, with an efficiency of 1.99 and 1.71 cd A⁻¹. In the device D, the maximum brightness and efficiency of 1 are 8512 cd m⁻² at 13 V and 3.10 cd A⁻¹, and they are 9818 cd m⁻² at 13 V and 0.42 cd A⁻¹, for 2. Our results also show that both 1 and 2 are good bipolar and bifunctional molecules with high hole-transporting and luminance properties.     

Synthesis,photophysics and electroluminescence of dendronized styryl-substituted fluorene with triphenylamine units

Compound 2, a dendronized styryl-substituted fluorene with bulky hole-transporting triphenylamine units, was synthesized by a simple two-step procedure. At the first step of synthesis two triphenylamine units were attached to the C-9 of fluorene while at the second step styryl segments were introduced both on fluorene and triphenylamine by Heck coupling. Compound 2 dissolved in common organic solvents like THF, chloroform, dichloromethane and toluene. This compound was stable up to ～320 °C and showed high glass transition temperature (T_g) of 175 °C. Compound 2 absorbed around 370 nm with optical band gap of 2.89 eV. It behaved as blue-green light emitter with photoluminescence (PL) emission maximum at 444–465 nm and PL quantum yield of 0.36 in THF solution. The HOMO and LUMO levels of compound 2, estimated from cyclic voltammograms, were ?5.20 and ?2.40 eV, respectively. The electroluminescence (EL) emission maxima (530–570 nm) were very different from PL maximum (465 nm), which could be explained by the direct cross recombination transition between electrons and holes trapped on triphenylamine subunits. The maximal brightness (current efficiency) of the EL devices (ITO/PEDOT:PSS/2/Ca/Al) was 1348 cd/m² (0.12 cd/A) and the color showed obvious blue-shift with an increase in operating voltage.     

Synthesis of new hole-transporting molecular glass with pendant carbazolyl moieties

The synthesis and properties of amorphous hole-transporting 4,4′-bis[11-carbazol-9-yl)-6,8,10-tri(carbazol-9-methyl)-3-hydroxy-5,7,9-trioxa-1-thia]thiobisbenzene with two end and six pendant carbazolyl moieties, separated from the main chain by CH₂ spacers, is reported. It was prepared by a multistep synthesis route from 1,6-di(carbazol-9-yl)-5-(carbazol-9-methyl)-4-oxa-2-hexanol glycidyl ether. Glass transition temperatures of intermediate and final products established by differential scanning calorimetry are reported. The hole drift mobility, measured by the time of flight technique, in this well defined molecular glass depends little on the strength of the electric field and exceeds 10⁻⁵ cm² V⁻¹ s⁻¹. The ionization potentials measured by electron photoemission method, light absorption and fluorescence spectra are closed to those reported for the other organic photoconductors containing electronically isolated carbazole moieties.     

Synthesis and electrochemical characterization of a new polymer constituted of alternating carbazole and oxadiazole moieties

We report herein the synthesis and electrochemical characterization of a novel copolymer containing an electron rich carbazole moiety and an electron deficient oxadiazole unit—poly[N-(2′-ethylhexyl)-carbazole-3,6-diyl-1″,3″,4″-oxadiazole-2″,5″-diyl] (PCO). PCO can be dissolved in THF, CHCl₃, xylene, and DMSO. The structure of the polymer is confirmed by FT-IR, NMR and elemental analysis. The optical and electronic properties of the polymer are investigated by UV–Vis absorption spectroscopy and photoluminescence spectroscopy as well as cyclic voltammetry. The results show that the polymer films emit greenish-blue light (λ_max 485 nm) upon UV excitation. Both p-doping and n-doping processes are observed in cyclic voltammetric investigation. A comparison between the properties of polycarbazole and polycarbazole–oxadiazole has been presented.     

Synthesis and characterization of light-emitting materials composed of carbazole,pyrene and fluorene

A series of ethynyl-linked π-conjugated light-emitting molecules with good photoluminescence properties were designed and synthesized through Pd/Cu-catalyzed Sonogashira coupling reaction. The main structure comprised of different fluorophors (pyrene, carbazole, and fluorene), which were linked with triple bonds in order to be screened for high emission efficiency. Optical properties of these synthesized compounds (I_a–I_f) were examined in solutions, thin films and solid states, respectively. All of them showed relative high quantum yields both in solutions (Φ_s: 0.70–0.83) and in films (Φ_f: 0.17–0.34). Light-emitting diode using I_e as an emissive layer was fabricated in the ITO/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS)/I_e/2, 2′, 2″-(1, 3, 5)-benzene-triyl)tris[1-phenyl-1H-benzimidazole] (TPBI)/Al configuration. The maximum emission wavelength of the device was 496 nm. The maximum luminance and electroluminescence efficiency was 1000 cd/m² and 0.41%, respectively.     

Synthesis and characterization of red phosphorescent-conjugated polymers containing charged iridium complexes and carbazole unit

A series of homogeneous red-light phosphorescent polymers with charged iridium (Ir) complex in the backbones and carbazole unit on the side were synthesized by Suzuki polycondensation. These polymers are made up of three repeat units: (i) charged iridium (Ir) complex; (ii) 9,9-dihexylfluorene; (iii) 9,9-bis(N-carbazolyl-hexanyl)-fluorene. Their structures have been identified by nuclear magnetic resonance (NMR) and elemental analysis. All chelating polymers displayed good thermal stability, redox reversibility and film formation. Compared with our former study on these charged Ir complex containing polymers, the addition of carbazole unit has a strong influence on their hole injection and charge attraction ability as well as the host–guest energy transfer efficiency.     

Microstructure evolution and thermal stability of an Fe-based amorphous alloy powder and thermally sprayed coatings

High velocity oxy-fuel (HVOF) thermal spraying has been used to produce coatings of an Fe–18.9%Cr–16.1%B–4.0%C–2.8%Si–2.4%Mo–1.9%Mn–1.7%W (in at.%) alloy from a commercially available powder (Nanosteel SHS7170). X-ray diffraction (XRD), differential scanning calorimetry (DSC) and scanning electron microscopy (SEM) were employed to investigate the powder, as-sprayed coatings and annealed coatings which had been heated to temperatures in the range of 550–925 °C for times ranging from 60 to 3900 min. Microhardness changes of the coatings were also measured as a function of annealing time and temperature. The powder was found to comprise amorphous and crystalline particles; the former had a maximum diameter of around 22 μm. The coating was composed of splat like regions, arising from rapid solidification of fully molten powder, and near-spherical regions from partially melted powder which had a largely retained its microstructure. The amorphous fraction of the coating was around 50% compared with 18% for the powder. The enthalpies and activation energies for crystallization of the amorphous phase were determined. Crystallization occurred in a two stage process leading to the formation of α-Fe (bcc), Fe_1.1Cr_0.9B_0.9 and M₂₃C₆ phases. DSC measurements showed that the first stage occurred at 650 °C. Annealing the coating gave a hardening response which depended on temperature and time. The as-sprayed coating had a hardness of 9.2 GPa and peak hardnesses of 12.5 and 11.8 GPa were obtained at 650 and 750 °C, respectively. With longer annealing times hardness decreased rapidly from the peak.     

Efficient and color stable phosphorescent white organic light-emitting devices based on an ultra wide band-gap host

We report high efficiency phosphorescent white organic light-emitting devices (WOLEDs) employing single emissive layer (EML) based on an ultra wide band-gap host. Effective exciton/charge confinement and balanced recombination within EML was achieved by employing adequate interlayer and stepwise hole-transporting layer (step HTL) system. Moreover, this step HTL system lower driving voltage of WOLEDs, therefore power efficiency was enhanced over 40%. These WOLEDs showed external quantum, and power efficiencies of 17.6%, and 37.5 lm/W at 100 cd/m² without outcoupling enhancements. We also found that these WOLEDs exhibited little change of color coordinate from 100 to 10,000 cd/m².     

Electrochemical,optical and electrochromic properties of imine polymers containing thiophene and carbazole units

New imine polymers containing thiophene and carbazole moiety were synthesized by using both chemically oxidative in the presence of FeCl₃ and electrochemically oxidative process. While UV–vis, FT-IR, ¹H- and ¹³C NMR techniques were used for the structural characterization, the number-average molecular weight (M_n), weight-average molecular weight (M_w) and polydispersity index (PDI) values were determined by size exclusion chromatography (SEC). The highest occupied molecular orbital (HOMO), the lowest unoccupied molecular orbital (LUMO) energy levels, electrochemical (E^′g)$({E^{\prime }}_g)$ and optical band gap (E_g) values were calculated by using the results of cyclic voltammetry and UV–vis absorption spectroscopy measurements, respectively. Spectroelectrochemical measurements were carried out against the changes in the optical properties of conducting polymers upon voltage changed. Also the yellow color of film changed to green color with applied potential. Conductivities of these polymers were determined by using four-point probe technique. It was seen that the conductivities were increased by iodine doping.     

Synthesis and light-emitting properties of copolymers composed of fluorene and N-alkoxyphenylphenothiazine

Poly[10-(4′-octyloxyphenyl)-phenothiazine-3,7-diyl] (POPPTZ), poly[9,9-bis(4′-octyloxyphenyl)fluorene-2,7-diyl] (PBOPF), and their random copolymers, poly(BOPF-co-OPPTZ), were synthesized through Ni(0) mediated polymerization. Light-emitting devices were fabricated using these polymers in an ITO (indium-tin oxide)/PEDOT:PSS/polymer/Ca/Al configuration. Each EL device constructed with a poly(BOPF-co-OPPTZ) copolymer exhibited significantly enhanced efficiency and brightness compared to devices constructed from the POPPTZ and PBOPF homopolymers. The EL device constructed with poly(83BOPF-co-17OPPTZ) exhibited the highest power efficiency and brightness (8,610 cd/m² and 2.831 cd/A, respectively). This enhanced efficiency of the copolymer devices results from their improved hole injection and more efficient charge carrier balance, which arise due to the HOMO levels (5.42 eV) of the poly(BOPF-co-OPPTZ) copolymers, which are lower than that of the PBOPF homopolymer (5.79 eV).     

Synthesis and characterization of amorphous Zr-based alloys with Ta and W additions

A reference Zr₅₇Cu₂₀Al₁₀Ni₈Ti₅ bulk metallic glass as well as a number of alloys obtained by addition of refractory elements Ta or W (combined with Sn) to the main Zr–Cu–Al–Ni system were elaborated by mould casting, twin roll casting and planar flow casting. The chemical compositions were chosen according to empirical rules, and as combinations of the binary eutectics for strongly interacting elements, taking into account the corresponding enthalpies of mixing. Optical microscopy, X-ray diffractometry, differential thermal analysis, differential scanning calorimetry, scanning electron microscopy and tensile mechanical testing were used to characterize the fully and partially obtained amorphous materials. Correlation of glass forming ability, thermodynamic parameters, crystallization behaviour and mechanical properties with chemical composition and production technology is discussed.     

Synthesis and characterization of completely soluble and highly thermally stable PANI-DBSA salts

This paper presents synthesis and characterization of soluble polyaniline-dodecylbenzenesulfonic acid (PANI-DBSA) via inverse polymerization. A mixture of chloroform and 2-butanol was used as dispersion medium for the first time. This polymerization pathway leads to the formation of PANI-DBSA salts which are completely soluble in a number of common organic solvents (such as DMSO, DMF, chloroform and in a mixture of toluene) and 2-propanol (so far highest number of solvents for solubility of PANI). The influence of synthesis parameters such as concentration of aniline, benzoyl peroxide and dodecylbenzenesulfonic acid (DBSA) on the yield and other properties of the resulting PANI-DBSA salts was studied. Further characterization of the synthesized materials was done with the help of viscosity measurements, UV–Vis spectroscopy, cyclic voltammetry, XRD and SEM. TGA was used to analyze the thermal properties of synthesized polymer. The synthesized salts were found to be highly stable.     

Synthesis and characterization of thermally cross-linkable hole injection polymer based on poly(10-alkylphenothiazine) for polymer light-emitting diode

A new thermally cross-linkable hole injecting/transporting polymer, poly{[10-hexyl-10H-phenothiazine-3,7-diyl]-alt-[10-(6-hexyloxy-4-(2-methyl-acrylic acid benzyl ester))-10H-phenothiazine-3,7-diyl]} (PTMMA), was synthesized. From the HOMO energy level of thermally cured PTMMA (−4.95 eV), the polymer is a very good hole injection material. From the spectroscopic and electrochemical data, thermally cured PTMMA (c-PTMMA) film is very safe for the successive layer coating by the solution process. Bi-layer structured polymer light-emitting diode with c-PTMMA as a hole injection layer (HIL) and green-emitting copolymer (PF9B) as a emissive layer was fabricated successfully. The maximum efficiency and brightness of the device with c-PTMMA as a HIL (device II) are 0.34 cd/A and 854 cd/m², respectively, which are superior to those of the device without c-PTMMA (device I, 0.039 cd/A and 228 cd/m², respectively). Also, the turn-on electric field of device II (0.89 MV/cm) is much lower compared to that of device I (1.92 MV/cm). From the results, thermally cured PTMMA has not only good hole injection property but also good solvent resistant property for the successive layer coating.     

A microscopic and impedance spectroscopy study of Finemet-Co amorphous alloys

Structural characterization of some Finemet-Co alloys is performed by scanning and transmission electron microscopies. The results show a response independent of the composition and state. In addition to this, electrode impedances were measured in 0.5 N KOH water solution. Three time constants were found for the electrode reaction at open circuit potential. The effect of cobalt addition was analyzed as well as the influence of the thermal treatment (TT). The values of the different parameters indicates that both, the substitution of iron by cobalt and the TT result in the increase of the stability of the oxide layers.     

Electrografting of 3-methyl thiophene and carbazole random copolymer onto carbon fiber: characterization by FTIR-ATR, SEM, EDX

Electrografting of poly(3-methylthiophene-co-carbazole) onto high tenacity (TENAX HTA 5000) carbon fiber was carried out under preparative constant-current electrolysis conditions by electropolymerizing in non-aqueous media. The surface morphology of the electrografted carbon fibers was determined by scanning electron microscopy (SEM). For characterization of the chemical composition of the random copolymer, FTIR reflectance measurements (FTIR-ATR) were performed. The efficiency of the electrocopolymerization on carbon fiber surfaces under preparative constant-current electrolysis conditions as a function of the experimental conditions was evaluated (effect on thickness and morphology).