OLED Materials Research Articles

Synthesis and Characterization of Phenanthroimidazole Derivatives as Light-Emitting and Ambipolar Materials

Novel phenanthroimidazole derivatives were designed and synthesized for in electroluminescent devices. They were characterized by means of 1H, 13C NMR, FTIR. The optical, electrochemical and thermal properties were also investigated. The relationship between the chemical structure and the properties of these materials was evaluated. Due to the conversion of the substituents onto the 2-imidazole position to the phenanthroimidazole ring, these compounds exhibite efficient emission from blue to yellow-green, red shifs in absorption and photoluminescence spectra. With respect to thermal properties and the oxidation potentials, it can be turned by varying the conjugation length of compounds and the length of alkyl chains. Mostly, all four compounds have suited HOMO and LUMO values, which can be used not only hole-transporting but also electon-tansporting materials in OLEDs.

1,3,4-Oxadiazoles as luminescent materials for organic light emitting diodes via cross-coupling reactions

A literature survey of the cross-coupling reactions in the preparation of 1,3,4-oxadiazole compounds as useful materials for OLEDs is described.

芳基取代蒽衍生物的合成及发光性能研究

芳基取代蒽衍生物的合成及发光性能研究

Electrophilic Borylation Leads to Efficient OLED Materials

Electrophilic Borylation Leads to Efficient OLED Materials

Synthesis and Electroluminescence Property of New Hexaphenyl Benzene Derivatives Including Emitting Materials for OLED

Three new emitting compounds of 5P-VCB, 5P-VAn and 5P-VPy for OLED based on hexaphenylbenzene moiety were synthesized. Physical properties by the change of the substitution groups of the synthesized materials were systematically examined. Photoluminescence spectrum of the synthesized materials showed maximum emitting wavelengths of about 420∼487 nm in solution state and 452∼488 nm in film state, indicating blue emission color. OLED devices were fabricated by the synthesized compounds using vacuum deposition process as an emitting layer. Current efficiencies and CIE values of 5P-VCB, 5P-VAn and 5P-VPy were 1.76, 0.38 and 7.91 cd/A and (0.15, 0.07), (0.20, 0.31) and (0.20, 0.36), respectively.

Synthesis, aggregation-induced emission and electroluminescence properties of a novel compound containing tetraphenylethene, carbazole and dimesitylboron moieties

A novel compound based on tetraphenylethene, carbazole and dimesitylboron moieties with aggregation induced emission properties was synthesized and utilized as a highly efficient blue light-emitting material in OLEDs.

Comparative study of using different alkali metal alkylcarboxylates as electron injection materials in OLEDs

A comparative study of using alkali metal alkylcarboxylates as electron injection materials for different electron transfer layers in OLEDs is carried out.

Journal Growth and Maturation

Journal Growth and Maturation

Electro-active oligomers containing pendent 3-phenylcarbazol-6-yl or 2-phenylfluoren-7-yl fragments as materials for OLEDs

Vinyl oligomers containing 3-phenyl-9-ethylcarbazol-6-yl or 2-phenyl-9,9-diethylfluoren-7-yl fragments were synthesized and characterized by NMR spectroscopy, elemental analysis and gel permeation chromatography. The derivatives represent materials of high thermal stability with initial thermal destruction temperatures of 348°C and 332°C. The glass transition temperatures of the amorphous materials were 150°C and 139°C, respectively. The electron photoemission spectra of layers of the synthesized oligomers showed ionization potentials in a range 5.6–5.9eV. Hole-transporting properties of the materials were tested in the structures of organic light emitting diodes with Alq3 as the green emitter. The device containing hole transporting layers of oligomer with phenyl-9,9-diethylfluoren-7-yl fragments exhibited the best overall performance with a maximal photometric efficiency of about 1.9cd/A and maximum brightness of about 2150cd/m2. The efficiency was about 40% higher than that of a device containing hole transporting layers of poly(9-vinylcarbazole) (PVK).

Guest Editorial: OLED Materials and Devices

Guest Editorial: OLED Materials and Devices

New asymmetrical limb structured blue emitting material for OLED [Invited

New asymmetric limb-structured blue light emitting material, composed of anthracene main core, naphthalene units at 9,10-position of anthracene and m-(di(trifluoromethylphenyl)) units at 2,3-positon of anthracene was designed and developed. And non-doped organic light-emitting diodes have been realized. The maximum efficiency of 1.72 cd/A and the quantum efficiency was around 0.67%.

3,6-Diaryl substituted 9-alkylcarbazoles as hole transporting materials for various organic light emitting devices

Phenyl, naphthyl or biphenyl disubstituted 9-alkylcarbazoles were synthesized by a multi-step synthetic rout. The materials were examined by various techniques including thermogravimetry, differential scanning calorimetry, and electron photoemission spectroscopy. These derivatives were tested as hole transporting materials in OLEDs with Alq3 as the emitter. Some of the devices exhibited promising overall performance with a turn-on voltage of 2.5 V, a maximal current efficiency of 3.25 cd/A and maximum brightness of 8300 cd/m2. The compounds were also applied as hole transporting layers in phosphorescent OLEDs with green phosphorescent emitter of tris(2-phenylpyridine)iridium(III) dispersed in N,N′-dicarbazolyl-4,4′-biphenyl host. An efficient device using 3,6-diphenyl-9-ethylcarbazole as hole transporting layer demonstrated a turn-on voltage of ca. 5 V, a maximum brightness of 9800 cd/m2, and maximum current efficiency of 22.5 cd/A.

Some Metal Complexes of 9-Hydroxyphenalenone as Novel Electron Transporting Materials for OLEDs

Aluminum, zinc, beryllium and lithium complexes with 9-hydroxyhyphenalenone are synthesized, and their spectral properties for powders and films are measured. These complexes may be appropriate of applying them for OLEDs. An example of electroluminescent device based on the beryllium complex is presented.

Copper(I) Complexes Based on Five-Membered P∧N Heterocycles: Structural Diversity Linked to Exciting Luminescence Properties

Bridging P(^)N ligands bearing five-membered heterocyclic moieties such as tetrazoles, 1,2,4-triazoles, oxadiazoles, thiadiazoles, and oxazoles have been investigated regarding their complexation behavior with copper(I) iodide as metal salts. Different complex structures were found, depending either on the ligand itself or on the ligand-to-metal ratios used in the complexation reaction. Two different kinds of luminescent dinuclear complex structures and a kind of tetranuclear complex structure were revealed by X-ray single-crystal analyses and were further investigated for their photophysical properties. The emission maxima of these complexes are in the blue to yellow region of the visible spectrum for the dinuclear complexes and in the yellow to orange region for the tetranuclear complexes. Further investigations using density functional theory (DFT) show that the highest occupied molecular orbital (HOMO) is located mainly on the metal halide cores, while the lowest unoccupied molecular orbital (LUMO) resides mostly in the ligand sphere of the complexes. The emission properties were further examined in different environments such as neat powders, neat films, PMMA matrices, or dichloromethane solutions, revealing the high potential of these complexes for their application in organic light-emitting diodes. Especially complexes with 1,2,4-triazole moieties feature emission maxima in the blue region of the visible spectrum and quantum yields up to 95% together with short decay times of about 1-4 μs and are therefore promising candidates for blue-emitting materials in OLEDs.

Structure and luminescence properties of trichloridothallium(III) complexes with phenanthroline derivatives

Two thallium(III) complexes, [Tl(5-mphen)Cl3(DMSO)] (1) and [Tl(5,6-dmphen)Cl3(DMSO)]·DMSO (2) were prepared from the reaction of TlCl3·4H2O with 5-methyl-1,10-phenanthroline (5-mphen) and 5,6-dimethyl-1,10-phenanthroline (5,6-dmphen) ligands in DMSO solvent through methanol diffusion. Their crystal structures were determined by the X-ray diffraction method. These complexes have a bidentate nitrogenous ligand and a DMSO molecule with three chloride anions attached to a Tl(III) metal in a distorted octahedral environment, where both complexes were crystallized in the same space group (\(P\overline{1}\)) and crystal system (triclinic). The 1H NMR data confirms the stability of the compounds in the DMSO moiety. The luminescence study revealed that their luminescence behaviour is varied in comparison with corresponding ligands, although the thallium complexes exhibit the same structure and the only difference is the number of the methyl group on the phenanthroline ligand. Interestingly, complex 1 demanded a considerable enhancement (nine times), in comparison with the related phenanthroline ligand, a well-known material for OLEDs.

Stable amorphous bis(diarylamino)biphenyl derivatives as hole-transporting materials in OLEDs

Stable bis(diarylamino)biphenyl derivatives N4,N4′-di(biphenyl-4-yl)-N4,N4′-bis(2- methylbiphenyl-4-yl)biphenyl-4,4′-diamine (TPD-Ph) and N4,N4′-bis(2′,4′-difluoro- 2-methylbiphenyl-4-yl)-N4,N4′-bis(2′,4′-difluorobiphenyl-4-yl)biphenyl-4,4′-diamine (TPD-(2,4)-F) were synthesized and characterized. High thermal stability (Td ≥ 480°C and Tg ≥ 108°C) in combination with reversible oxidation process render the both promising candidates as hole-transporting materials for organic light-emitting devices. The device with structure of ITO/TPD-Ph/Alq3/LiF/Al presented the highest current efficiency of 4.2 cd A−1 and good operational stability even under the high current density of 350 mA cm−2, which outperformed TPD or NPB-based devices.

Theoretical Studies on the Electronic Structures and Spectral Properties of Two Iridium(III) Complexes with Tetraphenylimidodiphosphinate Ligand

The geometrical structures, electronic structures, and spectral properties of two Ir(III) complexes with tetraphenylimidodiphosphinate ligand were investigated theoretically. The ground and the lowest lying triplet excited states were fully optimized at the B3LYP/LANL2DZ. TDDFT/PCM calculations have been employed to predict the absorption and emission spectra starting from the ground and excited state geometries, respectively. The lowest lying absorptions were calculated to be at 436 and 405 nm for the two Ir(III) complexes, respectively, and they have the transition configuration of HOMO → LUMO. The lowest lying transitions can be assigned as metal/ligand-to-ligand charge transfer (MLCT/LLCT) character for the two Ir(III) complexes. Ionization potentials (IP) and electron affinities (EA) were calculated to evaluate the injection abilities of holes and electrons. The theoretical results can be expected to provide valuable information to design new OLED materials.

Highly photo- and electroluminescent 1,3-diketonate Eu(iii) complexes with spiro-fluorene-xantphos dioxide ligands: synthesis and properties

Spiro-fluorene-xanthene-bis(diphenylphosphine) dioxide turned out to be a particularly effective co-sensitizer for Eu(hfa)3, Eu(tta)3 and Eu(nta)3 photoluminescent complexes. These ternary complexes proved to be particularly good materials for pure red color OLED devices. Two complexes, Eu(tta)3 and Eu(nta)3, were selected for OLED device testing. Surprisingly, these complexes displayed excellent performance within known Eu(III) complexes, as OLED materials. The electroluminescence (EL) spectra of Eu(tta)3SFXPO and Eu(nta)3SFXPO OLEDs show only Eu emission with a peak at 612 nm. The CIE coordinates are (0.65,0.32) for Eu(tta)3SFXPO OLEDs and (0.66,0.33) for Eu(nta)3SFXPO OLEDs, which means that the emission from these Eu-based OLEDs is pure red. At a brightness of 100 Cd m−2, Eu(tta)3SFXPO OLEDs have an external quantum efficiency of 2.4%, a power efficiency of 0.6 lm W−1 and a current efficiency of 3.2 Cd A−1. To our knowledge, this external quantum efficiency value is more than the best that has been previously reported for solution-processed Eu-based OLEDs at a brightness of 100 Cd m−2. More excitingly, Eu(nta)3SFXPO OLEDs shows an even better performance. At a brightness of 100 Cd m−2, Eu(nta)3SFXPO OLED possesses an external quantum efficiency of 3.7%, a power efficiency of 1.0 lm W−1 and a current efficiency of 5.1 Cd A−1. These OLED devices for testing were manufactured by a solution-processing method.

Synthesis of Cyclotriveratrylene–Phenylacetylene Derivatives and a Photophysical Investigation of Rigid Conjugated Cyclotriveratrylene Dendrimers

AbstractVarious functionalized host molecules and building blocks can be derived from the cone‐shaped cyclotriveratrylene (CTV). In this article, we report on the synthesis of CTV‐I3 derivatives 3a and 3b and their Sonogashira cross‐coupling with various terminal aryl‐alkynes, to synthesize CTV‐phenylacetylene derivatives in moderate to good yields. In this way, three star‐like conjugated dendrimers with rigid macrocyclic cores 4k–m, which showed good photophysical properties, were also synthesized. The band gaps of 4k–m are 3.49, 3.49 and 3.45 eV, and the fluorescence quantum yields are 0.64, 0.78, 0.48 (2‐aminopyridine as a standard and excited at 310 nm), respectively. Electrochemical studies revealed their HOMO and LUMO energy levels. Our research disclosed that these CTV dendrimers could potentially be used as host materials in OLEDs.

Synthesis and Characterization of Un-doped Deep-Blue Organic Light-Emitting Materials Containing Spirofluorene and Biphenyl or Substituted Biphenyl

A series of novel blue light-emitting materials, spirofluorene derivatives, DBSF, 3DBSF, and 5DBSF, based on 2′,7′-dibromospiro- [benzo[c]fluorene-7,9′-fluorene] (DBrSPFF) were successfully synthesized and identified by IR, 1H-NMR, and13C-NMR, MS. Optical properties were examined by UV-Vis absorption spectra and photoluminescence (PL) emission spectra. They performed great blue light characteristics. PL quantum yield was calculated by using quinine sulphate in 0.1M H2SO4 as standard. Electro-chemical behavior was examined through cyclic voltammeter measurement. They may be potential promising blue light-emitting materials for OLED.