Violet/deep-blue fluorescent organic light-emitting diode based on high-efficiency novel carbazole derivative with large torsion angle

A novel and highly efficient violet/deep-blue fluorescent carbazole and naphthalene-based compound (1) is designed and synthesized. The compound shows intensive violet/deep-blue fluorescence, high photoluminescence efficiency (0.72 in CH₂Cl₂, 0.65 in film) and narrow full width at half maximum (48 nm). The large torsion angles between carbazole and naphthalene guarantee the weak intermolecular interactions and suppress the π-π interactions in solid state, resulting in the highly efficient violet/deep-blue fluorescence. The maximum emission peak, luminance and external quantum efficiency for violet/deep-blue electroluminescence are 410 nm, 1326 cd/m² and ～2%, respectively.     

Color tuning of iridium complexes for organic light-emitting diodes: The electronegative effect and π-conjugation effect

Novel red phosphorescent emitter bis(4-phenylquinazolinato-N,C^2′) iridium(acetylacetonate) [(pqz)₂Ir(acac)], bis(1-(1′-naphthyl)-5-methylisoquinolinato-N,C^2′)iridium(acetylacetonate) [(1-mniq)₂Ir(acac)] and bis(1-(2′-naphthyl)-5-methylisoquinolinato-N,C^2′)iridium(acetylacetonate) [(2-mniq)₂Ir(acac)] have been synthesized and fully characterized. The electronegative effect of (pqz)₂Ir(acac) ligand shows almost the same influence as the extended π-conjugation effect of (2-mniq)₂Ir(acac). Density functional theory (DFT) was applied to calculate the Kohn-Sham orbitals of HOMOs and LUMOs in the iridium complexes to illustrate the N(1) electronegative atom effect. Finally, lowest triplet state (T₁) energies calculated by time-dependent DFT (TDDFT) were compared with the experimental electroluminescent data. The calculated data for the iridium complexes agreed fairly well with experimental data. Electroluminescent devices with a configuration of ITO/NPB/CBP:dopant/BCP/AlQ₃/LiF/Al were fabricated. The device using (pqz)₂Ir(acac) as a dopant showed deep-red emission with 1931 CIE (Commission International de L’Eclairage) chromaticity coordinates x = 0.70, y = 0.30.     

Synthesis and characterization of deep blue emitters from starburst carbazole/fluorene compounds

A series of well-defined, highly fluorescent starburst compounds with a carbazole core and oligo(2,7-fluorene ethynylene) arms have been synthesized by Sonogashira coupling reaction and fully characterized. These conjugated compounds exhibit good solubility, high thermal stability, and excellent fluorescence quantum yields (up to 0.99). The incorporation of carbazole core interrupted the main-chain conjugation and resulted in blue-shifted absorption and emission. Moreover, deep blue light has been approached from organic light-emitting diodes (OLEDs) adopting these compounds as emitting layer.     

Synthesis and characterization of fluorene and carbazole dithienosilole derivatives for potential applications in organic light-emitting diodes

Several fluorene or carbazole-based dithienosiloles (DTSs) have been synthesized and their thermal, photophysical, and electrochemical properties have been systematically investigated. These compounds show high thermal stability with glass transition temperature above 110 °C as well as decomposition temperatures at ∼400 °C. Intense green emission is observed in the spectral region of 500-510 nm for all compounds (Φ_PL=0.31-0.80), that is, attributed to both the 5,5′-substituents of the DTS ring and DTS-based π-π^∗ transition. Based on the emission spectra at 77 K, the triplet energy for these compounds was calculated to be within 2.1-2.2 eV, indicating that they may be used as host materials for red emitters in organic light-emitting diodes (OLEDs). All compounds exhibit reversible oxidation and possess low-lying LUMO energies, owing to the conjugated fluorene/carbazole substituents on the DTS. This along with the high thermal/electrochemical stabilities and high fluorescent quantum efficiencies makes the new DTSs compounds promising candidates for use in OLEDs as emitters, host and electron-transporting materials.     

Efficient deep-red organic light-emitting diodes based on blending MEH-PPV with a small molecule compound

Efficient deep-red organic light-emitting diodes(OLEDs) were investigated based on the blend of poly[2- methoxy-5-(2’-ethyl-hexyloxy)-l,4-phenylene vinylene](MEH-PPV) with 4,7-bis(5-(7-(9H-carbazol-9-yl)-9,9-dioctyl-9H-fluoren -2-yl)thiophen-2-yl)benzo[c][1,2,5]thiadiazole(compound 1).By optimizing the blend ratio,the turn-on voltage of the devices was significantly reduced from 4.9 V to 2.4 V.A highest external quantum efficiency of 2.56%was achieved at a blend ratio of 95:5(wt) for compound 1:MEH-PPV.The CIE coordinate was measured to be(0.70,0.30),with the luminescence peak at around 680 nm.Based on experimental observations the improvement mechanism is described.     

Synthesis,characterization, and electrogenerated chemiluminescence of deep blue emitting eumelanin‐inspired poly(indoylenearylene)s for polymer light emitting diodes

Deep blue emitting copolymers were synthesized by uniting the Eumelanin‐inspired indole core with fluorene and carbazole units via Suzuki polymerization. The resulting polymers, PIF and PIC, showed deep blue emission in the range of 416–418 nm and quantum yields of 0.39–0.60. Both polymers exhibited an intense and stable electrogenerated chemiluminescence. Interestingly, deep HOMO levels of −5.71 and −5.61 eV were observed for PIF and PIC, respectively. Solution processed polymer light emitting diodes (PLEDs) were fabricated using the PIF as a guest. PLEDs emitted deep blue light at 418 nm, with the luminous efficiency peaking at 1 Cd/A, given that the photopic response at that wavelength is 0.0151. The electroluminescence of PIF displayed a Commission Internationale de l'Eclairage coordinates of (0.16, 0.07) with a maximum external quantum efficiency of 1.1%. Hence, these materials prove to be promising candidates for the fabrication of deep blue PLEDs. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 125–131     

Novel iridium complexes as high-efficiency yellow and red phosphorescent light emitters for organic light-emitting diodes

A series of novel biscyclometallated iridium complexes based on spirobifluorene ligands and acetyl acetonate (acac) ancillary ligands have been synthesized and characterized. Their electrochemical properties were investigated by cyclic voltammetry (CV). HOMO, LUMO, and energy band gaps of all the complexes were calculated by the combination of UV-vis absorption spectra and CV results. TGA and DSC results indicated their excellent thermal stability and amorphous structure. All the iridium complexes were fabricated into organic light-emitting devices with the device configuration of ITO/PEDOT:PSS (50 nm)/PVK (50 wt %):PBD (40 wt %):Ir complex (10 wt %) (45 nm)/TPBI (40 nm)/LiF (0.5 nm)/Ca (20 nm)/Ag (150 nm). Yellow to red light emission has been achieved from the iridium complexes guest materials. Complex C1 (yellow light emission) achieved an efficiency of 36.4 cd/A (10.1%) at 198 cd/m² and complex C4 (red light emission) reached external quantum efficiency of 4.6%. The slight decrease of external quantum efficiency at high current density revealed that the triplet-triplet (T₁-T₁) annihilation was effectively suppressed by the new developed complexes.     

Novel linear and tri-branched copolymers based on triphenylamine for non-doping emitting materials

Novel linear and tri-branched copolymers with triphenylamine and cyano groups in the main chain were synthesized by a concise route and an environment-friendly procedure without metal catalyst. They show strong fluorescence in solid state and can be used as non-doping emitter to fabricate emitting diodes. The single-layer electroluminescence devices with PVK or PEDOT buffer layer have been made with these copolymers as non-doping red-orange emitter, electron-transporting as well as hole-transporting material. The single-layer devices show preliminary results with maximum efficiency of 0.052% and EL wavelengths around 614 nm.     

Surface treatment and characterization of ITO thin films using atmospheric pressure plasma for organic light emitting diodes

Ar atmospheric pressure plasma (APP) was used to treat indium-tin-oxide (ITO). The plasma conditions were varied to treat the ITO surface, e.g., plasma treatment time, RF power, flow rate, and the plasma outlet-to-sample distance. The plasma effectiveness was measured by the contact angle. The change in the surface energy calculated with the Owens-Wendt method mainly arises from the polar component. The dynamic contact angle measurements show that APP-treated surface showed considerably lower hysteresis in the water and ethylene glycol but there was no change in hysteresis in methylene iodide compared with the untreated ITO. Atomic force microscopy showed that the Ar APP-treated surface sharply decreased the surface roughness and showed a similar morphology as the untreated ITO. X-ray photoelectron spectroscopy showed that the Ar APP treatment not only effectively removed carbon contamination from the surface but also introduced oxygen. Therefore, it is believed that the APP treatment modifies the physico-chemical properties of ITO, which can in turn improve the performance of the organic light-emitting diodes.     

Soluble polynorbornenes with pendant carbazole derivatives as host materials for highly efficient blue phosphorescent organic light‐emitting diodes

We report novel host polymers for a high‐efficiency polymer‐based solution‐processed phosphorescent organic light‐emitting diode with typical blue‐emitting dopant bis(4,6‐difluorophenylpyridinato‐N,C²)iridium(III) picolinate (FIrpic). The host polymers, soluble polynorbornenes with pendant carbazole derivatives, N‐phenyl‐9H‐carbazole ( P1 ), N‐biphenyl‐9H‐carbazole ( P2 ), and 9,9′‐(1,3‐phenylene)bis‐9H‐carbazole (mCP) ( P3 ) are efficiently synthesized by vinyl addition polymerization of norbornene monomers using Pd(II) catalyst in combination with 1‐octene chain transfer agent. The polymers exhibit high thermal stability with high decomposition (T_d5 > 410 °C) and glass transition temperatures (T_g ≈ 268 °C). The HOMO (ca. ?5.5 to ?5.7 eV) and LUMO (ca. ?2.0 to ?2.1 eV) levels with the high triplet energy of about 2.7–3.0 eV suggest that the polymers are suitable for a host material for blue emitters. Among the solution‐processed devices that were fabricated based on the emissive layers containing the P1 ? P3 host doped with various concentrations of FIrpic (7–13 wt %), the best device with P3 host exhibits power efficiency of 3.0 lm W^?1 and external quantum efficiency of 4.0% at a luminance of 1000 cd m^?2 that is outstanding among the polymeric rivals. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Pyrene‐functionalized oligofluorenes as non‐doped deep blue emitters for solution‐processed organic light‐emitting diodes

Two pyrene‐functionalized oligofluorenes (TPA‐PyF₃ and CBP‐PyF₃) are prepared using the condensation reaction by the Friedel–Crafts procedure. In the produced oligomers, the triphenylamine or N,N′‐dicarbazolyl‐4,4′‐biphenyl core serves as a spacer bearing spiro‐linked fluorene moieties to form a multi‐H shaped structure. This specific structure efficiently retards the crystallization tendency of the pyrene groups, and gives the materials completely amorphous morphological structure and film forming ability. Solution‐processed OLEDs with the structure of ITO/PEDOT:PSS (25 nm)/TPA‐PyF₃ or CBP‐PyF₃ (40 nm)/TPBI (35 nm)/Ca (10 nm)/Ag (100 nm) show low turn‐on voltages of 3.6 V, and the maximum external quantum efficiencies reach 1.78% and 2.07% for TPA‐PyF₃ and CBP‐PyF_3, respectively. Moreover, both devices exhibit stable deep‐blue light emission with Commission International de I'Eclairage (CIE) coordinates of around (0.16, 0.09) at the brightness of 100–1000 cd m^?2. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 795–801     

Synthesis and properties of a star-shaped organic material with triphenylamine and N-vinyl carbazole units

A starburst triphenylamine cored N-vinyl carbazole (V-Cz) branched compound was designed and synthesized via optimized Heck reaction in a yield of 40-60%.Moderate yield came from decomposition of V-Cz and self-coupling of triiodo-triphenylamine. TCz-TPA adopts a highly twisted propeller conformation by molecular mechanical optimization.It is readily soluble for its highly twisted conformation.Transparent and pinhole free films could be easily fabricated by spin-coating for its starburst structure.It emits blue-greenish light in CH_2Cl_2 peaked at 460 nm with a narrow full-width at half-maximum (FWHM) of 65 nm.As compared, the absorption peaks of the spin-coated film blue shifted and emission peak red shifted to 510 nm with a FWHM of 96 nm.     

Synthesis, characterization, photophysics and electrophosphorescent applications of phosphorescent platinum cyclometalated complexes with 9-arylcarbazole moieties

A series of cyclometalating platinum(II) complexes with substituted 9-arylcarbazolyl chromophores have been synthesized and characterized. These complexes are thermally stable and most of them have been characterized by X-ray crystallography. The phosphorescence emissions of the complexes are dominated by ³MLCT excited states. The excited state properties of these complexes can be modulated by varying the electronic characteristics of the cyclometalating ligands via substituent effects, thus allowing the emission to be tuned from bright green to yellow, orange and red light. The correlation between the functional properties of these metallophosphors and the results of density functional theory calculations was made. Because of the propensity of the electron-rich carbazolyl group to facilitate hole injection/transport, the presence of such moiety can increase the highest occupied molecular orbital levels and improve the charge balance in the resulting complexes relative to the parent platinum(II) phosphor with 2-phenylpyridine ligand. The solution-processed electrophosphorescent organic light-emitting diodes doped with these platinum-based phosphors have been fabricated which showed a maximum external quantum efficiency of 2.77% for the best device, corresponding to a power efficiency of 3.48 lm/W and a luminance efficiency of 8.49 cd/A. The present work enables the rational design of platinum-carbazolyl electrophosphors by synthetically tailoring the structure of carbazolylpyridine ring that can permit good color-tuning versatility suitable for multi-color display technology.     

Solution processable high band gap hosts based on carbazole functionalized cyclic phosphazene cores for application in organic light‐emitting diodes

A new class of solution processable dendrimers based on cyclic phosphazene (CP) cores have been prepared and used as host materials for blue and green organic light emitting diodes (OLEDs). The dendrimers are prepared in high yield from minimal step reactions, are soluble in common solvents for solution processing, are amorphous, and have excellent thermal properties necessary for application in OLEDs. OLED efficiencies of 10.3 cd/A (4.2 lm/W) and 35.3 cd/A (33.5 lm/W) were achieved using commercially available FIrpic and Ir(mppy)₃ as blue and green phosphorescent emitters, respectively. These efficiencies were 2× higher than control devices prepared using poly(N‐vinylcarbazole), the most commonly used host material in solution processed phosphorescent OLEDs. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2011     

Synthesis and properties of nitrogen‐linked poly(2,7‐carbazole)s as hole‐transport material for organic light emitting diodes

A novel class of carbazole polymers, nitrogen‐linked poly(2,7‐carbazole)s, was synthesized by polycondensation between two bifunctional monomers using the palladium‐catalyzed amination reaction. The polymers were characterized by ¹H NMR, Infrared, Gel permeation chromatography, and MALDI‐TOF MS and it was revealed that the combination of the monomer structures is important for producing high molecular weight polymers. Thermal analysis indicated a good thermal stability with high glass transition temperatures, e.g., 138 °C for the higher molecular weight polymer P2 . To pursue the application possibilities of these polymers, their optical properties and energy levels were investigated by UV‐Vis absorption and fluorescence spectra as well as their electrochemical characteristics. Although the blue light emission was indeed observed for all polymers in solution, the quantum yields were very low and the solid films were not fluorescent. On the other hand, the HOMO levels of the polymers estimated from the onset potentials for the first oxidation in the solid thin films were relatively high in the range of ?5.12 to ?5.20 eV. Therefore, light emitting diodes employing these polymers as a hole‐transport layer and iridium(III) complex as a triplet emitter were fabricated. The device of the nitrogen‐linked poly(2,7‐carbazole) P3 with p,p′‐biphenyl spacer, which has a higher HOMO level and a higher molecular weight, showed a much better performance than the device of P2 with m‐phenylene spacer. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3880–3891, 2009     

Synthesis and application of a novel 9,9-diethyl-1,2-diaryl-1,9-dihydrofluoreno[2,3-d]imidazole for blue organic light emitting diode

Two novel 2-(4-(9,9-disubstitued-9 H-fluoren-2-yl)phenyl)-9,9-diethyl-l-phenyl-1,9-dihydrofluoreno-[2,3-d]imidazole derivatives 2 a and 2 b were synthesized and characterized.Their photophysical and electrochemical properties,thermal stability property,and electroluminescence(EL)performance of 2 b were investigated.The fabricated device based on 2 b doping into 4,4’-N,N’-dicarbazole-biphenyl(5%)as an emitter present a maximum brightness of 1272 cd/m^2 at 4 V with the CIE coordinate of(0.1590,0.0465).     

Synthesis and characterization of 9,10‐diphenylanthracene‐based blue light emitting materials

A new series of conjugated polymers having diphenylanthracene vinylene biphenylene and diphenylanthracene vinylene terphenylene in the main chain and fluorene pendant group, were synthesized by nickel catalized Yamamoto coupling and palladium catalized Suzuki coupling. The obtained polymers showed good solubility in the common organic solvent and number average molecular weights of 14,000–9500 with a polydispersity indexes ranging from 1.7 to 2.1. Both polymers possess excellent thermal stability with glass transition temperatures of 123–127 °C and the onset decomposition temperatures of 420–400 °C. The obtained polymers showed blue emission (λ_max = 461 for PFPA and λ_max = 455 nm for PFPAME) in PL spectra, specially, PFPAME containing diphenylanthracene vinylene terphenylenevinylene showed the consistent emission in the solution and film. The double‐layered device with an ITO/PEDOT/PFPAME/LiF/Al structure has a turn‐on voltage of about 5.8 V, maximum brightness of 152 cd/m² and an electroluminescent efficiency of 0.143 lm/W, and stable blue EL emission that is not altered by increased voltage. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5908–5916, 2009     

Efficient and stable non-doped deep-blue organic light emitting diode based on an anthracene derivative

A new anthracene derivative 9,10-bis[3,5-di(4-tert-butylphenyl)phenyl]anthracene (BPPA) was synthesized via Suzuki coupling reaction and characterized by 1H NMR spectrum,mass spectrum,and elemental analysis.BPPA exhibits deep-blue emission both in solution and in solid thin film.This compound has a non-planar structure that results in high thermal stability and the phenomenon of polymorphism.The non-doped device based on this material shows stable deep-blue emission with the 1931 Commission international de...     

Sky-blue phosphorescent organic light-emitting diode with superior performance based on novel chlorine functionalized iridium(III) complex

A novel and highly efficient chlorine functionalized iridium(III) complex is designed and synthesized. The complex shows intensive sky-blue phosphorescence (with a peak of 492?nm and a shoulder at 524?nm), high photoluminescence efficiency (0.78) and moderate full width at half maximum (62?nm). The aromatic chlorine introduced into the complex provides the robust chemical stability and effective sky-blue phosphorescence for organic light-emitting diodes (OLEDs). The maximum power efficiency, current efficiency and external quantum efficiency for the complex based OLED are up to 48.46?lm/W, 55.04?cd/A and 18.47%, respectively.