Saturated Red Emission Research Articles

Highly efficient saturated red electrophosphorescence from isoquinoline-based iridium complex containing triphenylamino units in polymer light-emitting devices

To obtain highly efficient saturated red-emitting polymer light-emitting devices, the opto-physical and electrophosphorescent properties of a novel isoquinoline-based iridium complex containing triphenylamino units were investigated. The devices using this iridium complex as a dopant and a blend of poly(9,9-dioctylfluorene) and 2- tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole as a host matrix displayed bright saturated red emission at 637 nm with Commission Internationale de I’Eclairage coordinate of (0.64, 0.31). The maximum external quantum efficiency of 10.8% photos/electron and current efficiency of 4.6 cd/A at 1.7 mA/cm 2, and the peak brightness of 5453 cd/m 2 at 228 mA/cm 2 were obtained in the device at 2% dopant concentration.

Phosphorescent chelating polyelectrolytes and their neutral precursors: Synthesis, characterizations, photoluminescence and electroluminescence

Novel chelating polyfluorene polyelectrolytes and their corresponding neutral precursors with Ir complex incorporated into polymer backbone were synthesized by Suzuki polycondensation reaction. The aminoalkyl or quaternized ammonium group provides good solubility of these phosphorescent polymers in alcohols which has a great advantage in fabrication of multi-layer polymer phosphorescent PLEDs. The photophysical and electroluminescent properties of the phosphorescent polyelectrolytes and their neutral precursors were investigated. The phosphorescent emission bands from both polyelectrolytes and neutral polymers which lie at around 640 nm displayed a saturated red emission. Devices fabricated from these phosphorescent polymers with air-stable high work function metals, such as Al, as cathode showed comparable device performance with low work function metals, such as Ba.

Highly efficient and stable red phosphorescent organic light-emitting device using bis[2-(2-benzothiazoyl)phenolato]zinc(II) as host material

The red-emitting phosphorescent organic light-emitting device employing Bis[2-(2-benzothiazoyl)phenolato]zinc(II) (Zn(BTP)2) as a host material has been demonstrated. The device generates saturated red emission with Commission Internationale de l’Eclairage coordinates of (0.67, 0.33), characterized by a low driving voltage of 3.2V and high external quantum efficiency of 10.3% at 10mA∕cm2. Moreover, the efficiency and lifetime are improved by using 30% NPB-doped Zn(BTP)2 host in the emitting layer, where NPB is 4,4′-bis(N-phenyl-1-naphthyl-amino)biphenyl. The maximum external quantum efficiency of the device reaches 12.6% at 1.7mA∕cm2. The device has exhibited excellent stability. The half-luminance lifetime is 240h at 80mA∕cm2 (initial luminance of 6070cd∕m2). The relationship between the employed host material and device performance is discussed.

Non-Doped Organic Light-Emitting Diodes with Saturated Red Emission

Non-doped organic light-emitting diodes with saturated red emission were fabricated using 4(2-(3,3-dicyanomethylene-5,5-dimethyl-1-cyclohexylidene)vinyl)phenyldi(1-naphthyl)amine (DNP2CN) or 4-(2-(3,3-dicyanomethylene-5,5-dimethyl-1-cyclohexylidene)vinyl)phenyl(1-naphthyl)phenylamine (DPN-2CN) as the emitting layer. Dierent electron-transporting materials, tris(8hydroxylquinoline) aluminum (Alq3), 2,2’,2”-(1,3,5-phenylene)tris[1-phenyl-1H-benzimidazole] (TPBI) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD), were introduced into the devices for examining their energy level compatibility of DNP-2CN or DPN-2CN. The device with a structure of ITO/ NPB/ DNP-2CN/ BCP/ Alq3/ LiF/ Al showed red emission with max at 670 nm (CIE coordinates: x = 0.66, y = 0.33) and a high luminance of 438 cd m 2 at a driving voltage of 12 V. The device with a structure of ITO/ NPB/ DPN-2CN/ BCP/ Alq3/ LiF/ Al showed a high brightness of 225 cd m 2 at a driving voltage of 12 V with max at 674 nm (CIE coordinates: x = 0.65, y = 0.33).

Performance improvement of polymer light-emitting diodes based on fluorene copolymer with cesium fluoride/aluminum cathode

Polymer light-emitting diodes with saturated red emission were fabricated using the copolymer, poly ［2,7-(9,9-dioctyl)fluorene-co-5,5′-(4,7-diselenophenyl)-2,2′-yl-2,1,3-benzothiadiazole］ (PFO-SeBT). Special attention was paid to polymer/electrode interface modification. The highest electroluminescence external quantum efficiency of 1.79%, which was more than twice that of devices with low work function metal cathode Ba/Al, was achieved by incorporation of CsF/Al cathode with carefully optimized thickness of CsF, and insertion of PVK layer in the PFO-SeBT1/anode interface. Efficient improvement of electron injection of CsF/Al cathode and blocking effect of PVK to electrons were proposed to be responsible for the improved performances of the device.

Photophysical properties and electroluminescent applications of donor–acceptor–donor functionalized red electroactive fluorescent materials

Four electroactive molecular materials with donor-π-acceptor-π-donor structures have been synthesized for investigation of structure–properties relationships, and used as dopant for electroluminescent applications. The optical and electrical properties of these materials are electronically manipulated by attaching different donors. The twisted intramolecular charge transfer (TICT) model is proposed by photophysical behaviors observed with increasing solvent polarity. Red electroluminescence devices were fabricated by spin coating the blend of polymer host and fluorescent guest. Highly efficient energy transfer leads to a saturated red emission with emission peak at 623 nm, narrow bandwidth of 75 nm and an external quantum efficiency of 0.38%.

Orange and Red Organic Light‐Emitting Devices Employing Neutral Ru(II) Emitters: Rational Design and Prospects for Color Tuning

AbstractA new series of charge‐neutral Ru(II) pyridyl and isoquinoline pyrazolate complexes, [Ru(bppz)2(PPh2Me)2] (bbpz: 3‐tert‐butyl‐5‐pyridyl pyrazolate) (1), [Ru(fppz)2(PPh2Me)2] (fppz: 3‐trifluoromethyl‐5‐pyridyl pyrazolate) (2), [Ru(ibpz)2(PPhMe2)2] (ibpz: 3‐tert‐butyl‐5‐(1‐isoquinolyl) pyrazolate) (3), [Ru(ibpz)2(PPh2Me)2] (4), [Ru(ifpz)2(PPh2Me)2] (ifpz: 3‐trifluoromethyl‐5‐(1‐isoquinolyl) pyrazolate) (5), [Ru(ibpz)2(dpp)] (dpp represents cis‐1,2‐bis‐(diphenylphosphino)ethene) (6), and [Ru(ifpz)2(dpp)] (7), have been synthesized, and their structural, electrochemical, and photophysical properties have been characterized. A comprehensive time‐dependant density functional theory (TDDFT) approach has been used to assign the observed electronic transitions to specific frontier orbital configurations. A multilayer organic light‐emitting device (OLED) using 24 wt % of 5 as the dopant emitter in a 4,4′‐N,N′‐dicarbazolyl‐1,1′‐biphenyl (CBP) host with 4,4′‐bis[N‐(1‐naphthyl)‐N‐phenylamino]biphenyl (NPB) as the hole‐transport layer exhibits saturated red emission with an external quantum efficiency (EQE) of 5.10 %, luminous efficiency of 5.74 cd A–1, and power efficiency of 2.62 lm W–1. The incorporation of a thin layer of poly(styrene sulfonate)‐doped poly(3,4‐ethylenedioxythiophene) (PEDOT) between indium tin oxide (ITO) and NPB gave anoptimized device with an EQE of 7.03 %, luminous efficiency of 8.02 cd A–1, and power efficiency of 2.74 lm W–1 at 20 mA cm–2. These values represent a breakthrough in the field of OLEDs using less expensive Ru(II) metal complexes. The nonionic nature of the complexes as well as their high emission quantum efficiencies and short radiative lifetimes are believed to be the key factors enabling this unprecedented achievement. The prospects for color tuning based on Ru(II) complexes are also discussed in light of some theoretical calculations.

High-performance organic red-light-emitting devices based on a greenish-yellow-light-emitting host and long-wavelength emitting dopant

We demonstrated an organic red-light-emitting device (ORLED) using a host, 5,6-bis-[4-(naphthalene-1-yl-phenyl-amino)-phenyl]-pyrazine-2,3-dicarbonitrile (BNPPDC), and a dopant, 2,3-bis[[[(2-hydroxy-4-diethylamino)phenyl] (methylene)] amino]-2-butanedinitrile (BDPMB). The device achieved a brightness of 9730cd∕m2 at a 11V, a power efficiency of 2.35lm∕W, a current efficiency of 3.36cd∕A at 4.5V, and a low turn-on voltage of 3.0V, with nearly saturated red emission. The device is superior or equal to the best fluorescent ORLEDs reported. BNPPDC generally induced a significant blueshift in dopant emission, thus it may serve as a host for dopants emitting at long wavelengths in ORLEDs with improved performance.

Tuning the saturated red emission: synthesis, electrochemistry and photophysics of 2-arylquinoline based iridium(iii) complexes and their application in OLEDs

A series of novel iridium(III) complexes with two 2-arylquinoline derivatives as cyclometalated ligands and one monoanionic ligand, such as acetylacetonate (acac), N,N′-diethyldithiocarbamate (Et2dtc) and O,O′-diethyldithiophosphate (Et2dtp), as ancillary ligands have been synthesized and structurally characterized by 1H NMR, MS and elemental analysis (EA). The cyclic voltammetry, absorption, emission and electroluminescence properties of these complexes were systematically investigated. Through extending π-conjugation, introducing electron-donating groups in the ligand frame, or changing the ancillary ligands, the HOMO energy levels of the iridium(III) complexes can be tuned, while their LUMO levels remain little affected; in consequence, the emission wavelengths of the iridium(III) complexes can be tuned in the range 606–653 nm. The highly efficient organic light-emitting diodes (OLEDs) with saturated red emission have been demonstrated. A maximum current efficiency of 10.79 cd A−1, at a current density of 0.74 mA cm−2, with an emission wavelength of 616 nm and Commisioon Internationale de L'Eclairage (CIE) coordinates of (0.65, 0.35), which are very close to the National Television System Comittee (NSTC) standard red emission, have been achieved when using complex (DPQ)2Ir(acac) as a phosphor dopant.

Substituted tetrapyrazolylporphyrins: application in organic light-emitting diodes

Six substituted tetrapyrazolylporphyrins ( TAPyPH 2), meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin ( TPPyPH 2), meso-tetrakis[1-(p-tolyl)pyrazol-4-yl] porphyrin ((p- CH 3) TPPyPH 2), meso-tetrakis[1-(p-methoxyphenyl)pyrazol-4-yl]porphyrin ((p- CH 3 O ) TPPyPH 2), meso-tetrakis[1-(p-chlorophenyl) pyrazol-4-yl]porphyrin ((p- Cl ) TPPyPH 2), meso-tetrakis[1-(p-bromophenyl)pyrazol-4-yl]porphyrin ((p- Br ) TPPyPH 2) and meso-tetrakis[1-(m-tolyl)pyrazol-4-yl]porphyrin ((m- CH 3) TPPyPH 2), were synthesized by the condensation of pyrrole with the corresponding substituted formylpyrazole and used as the doping materials in the Organic Light-Emitting Diodes (OLEDs) with hole-transport materials of N , N '-diphenyl- N , N '-bis (4-methylphenyl)-[1,1'-biphenyl]-4,4'-diamine (TPD) within a tris(8-hydroxyquinoline) aluminum ( Alq 3) host layer. Both the electroluminescence properties of these OLEDs and effects of the peripheral substituents of the tetrapyrazolylporphyrins on EL properties of the OLEDs were studied. The tests found that the OLEDs using substituted tetrapyrazolylporphyrins ( TAPyPH 2) as the dopants had the saturated red emission at a concentration of 1.5 wt.%. The electron-donating groups of tetrapyrazolylporphyrins (for example, p- CH 3 and p- CH 3 O ) increased the luminance of OLEDs, while the electron-drawing groups (for example, p- Cl and p- Br ) decreased the luminance. The OLEDs using meso-tetrakis(1-phenylpyrazol-4-yl)porphyrin ( TPPyPH 2) as a dopant showed saturated red emission at 680 nm (CIE coordinates of x = 0.65, y = 0.31) with a luminance of 305 cd/m2 at a driving voltage of 25 V at concentration of 1.5 wt.%. Compared with OLEDs doped by the free-base tetraphenylporphyrin (TPPH2), the OLEDs doped by the tetrapyrazolylporphyrins had better luminance and higher emission efficiency. An explanation for these results was given based on the molecular structure and spectral properties of the porphyrin compounds.

Pure red electrophosphorescent organic light-emitting diodes based on a new iridium complex

A new iridium complex was synthesized and demonstrated a saturated red light emission in organic light-emitting diodes (OLEDs). The maximum brightness of 2800 cd/m 2 and the external quantum efficiency of 5.5% were achieved in multilayer OLEDs. The peak wavelength of the emission was found to be at 677 nm with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.71, 0.27).

Synthesis and Electroluminescent Properties of Copolymers Derived from Fluorene and Metal-Free and Pt (II) Tetraphenylporphyrin

A series of novel soluble conjugated copolymers derived from 9,9-dioctylfluorene (DOF) with metal-free and Pt (II) tetraphenylporphyrin (TPP) were synthesized via palladium-catalyzed Suzuki coupling reaction, with TPP content in the copolymers of 0.5%, 1%, 5%, 20% and 50% respectively. Platinum (II) (Pt) were incorporated into the copolymers by reaction of the copolymers with PtCl 2. Emission from DOF segment was completely quenched at very low metal-free TPP content (1%). The copolymers of DOF-co-TPP emit saturated red emission that is red-shifted slightly with increasing the TPP contents. After Introducing Pt, the emission peak of the copolymers is blue-shifted. Electroluminescent (EL) quantum efficiency of the devices based on the copolymers was 0.12% for copolymer with 5% TPP content and EL efficiency PFO-PtTPP was 0.15% for metal complex with 1% PtTPP content.

Organic light-emitting diodes based on charge-neutral Os(ii) emitters: generation of saturated red emission with very high external quantum efficiency

The OLED device using 6% of Os(fptz)2(PPh2Me)2 as the dopant emitter in a CBP host and BPAPF as hole transporting material shows an external quantum efficiency of 15.3% and luminous efficiency of 21.3 cd A−1, power efficiency of 6.3 lm W−1 at 20 mA cm−2. An even higher external quantum efficiency of ∼20% was achieved at a low current density of ∼1 mA cm−2.

Soluble, saturated‐red‐light‐emitting poly(p‐phenylenevinylene) containing triphenylamine units and cyano groups

AbstractA conjugated poly(p‐CN‐phenylenevinylene) (PCNPV) containing both electron‐donating triphenylamine units and electron‐withdrawing cyano groups was prepared via Knoevenagel condensation in a good yield. Gel permeation chromatography suggested that the soluble polymer had a very high weight‐average molecular weight of 309,000. A bright and saturated red emission was observed under UV excitation in solution and film. Cyclic voltammetry showed that the polymer presented quasi‐reversible oxidation with a relatively low potential because of the triphenylamine unit. A single‐layer indium tin oxide/PCNPV/Mg–Ag device emitted a bright red light (633 nm). © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3947–3953, 2004

High-Efficiency Saturated Red Emitting Polymers Derived from Fluorene and Naphthoselenadiazole

A variety of novel light-emitting copolymers derived from 9,9-dioctylfluorene (DOF) and 2,1,3-naphthozoselenadiazole (NSeD) were prepared by the palladium-catalyzed Suzuki coupling reaction. The feed ratios of DOF to NSeD were 99.9:0.1, 99.5:0.5, 99:1, 98:2, 95:5, and 85:15. All of the polymers are soluble in common organic solvents and highly fluorescent in solid state. Devices based on the copolymers emit saturated red light, and the emission slightly red-shifted gradually with increasing NSeD's contents. The maximal external quantum efficiency of the polymer light-emitting devices (PLED) reaches 3.1%, and luminous efficiency is greater than 1.0 cd/A with emission maximum at 657 nm and Commission Internationale de L'Eclairage (CIE) coordinates of (0.64, 0.33). This is the highest efficiency with saturated red emission for a single-layer device with nonblend type emitter reported so far in the scientific literature. This indicates that the new EL polymers based on fluorene and naphthoselenadiazole are promising as a red emitter in polymer light-emitting displays.

Red electroluminescence and photoluminescence properties of new porphyrin compounds

Three new porphyrin compounds with saturated red emission were synthesized and their photoluminescence and electroluminescence were studied. The emission of the new dopants peaked at about 635–655 nm and the half-width of the emission peaks was very narrow (below 30 nm). Of the three porphyrin compounds, the one (TBDPP) with the smallest conjugation system had the highest fluorescent quantum yield of 21% in solution. Organic light-emitting diodes using TBDPP as a dopant showed saturated red emission (CIE coordinates of x=0.69, y=0.29) with a luminance of 150 cd/m 2 at a driving voltage of 22 V.

Synthesis and electroluminescent properties of fluorene-based copolymers

A series of novel soluble conjugated copolymers derived from 9,9-dioctylfluorene (DOF) with 4,7-dithien-2-yl-2,1, 3-benzothiadiazole (DBT)) were synthesized by palladium-catalyzed Suzuki coupling reaction. The copolymers of DOF-co-DBT emit saturated red emission which is red-shifted with the increasing DBT contents. Highest external electroluminescence (EL) quantum efficiency of the devices based on the copolymers exceeds 1.4% for copolymer with 15% DBT content. The results indicate that the DOF-co-DBI copolymers are promising candidate for full-colour polymer flat panel display.

High-efficiency polymer light-emitting diodes with stable saturated red emission based on blends of dioctylfluorene-benzothiadiazole-dithienylbenzothiadiazole terpolymers and poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene

High-efficiency light-emitting diodes with stable saturated red emission are realized based on blends of poly[2-methoxy,5-(2-ethylhexoxy)-1,4-phenylene vinylene] (MEHPPV) and terpolymers of dioctylfluorene, benzothiadiazole, and dithienylbenzothiadiazole (DBT). External quantum efficiency of more than 3.2 emitted photons per hundred electrons injected (ph/el %) is realized for a device with the Commission Internationale de I’Eclairage coordinates x=0.65, y=0.35. Such high device performance results from effective hole injection induced by the addition of MEHPPV, efficient energy transfer from the [0-0] ground-state emission of MEHPPV to the DBT segments together with the direct contribution of the [0-1] phonon coupling emission of MEHPPV.

Novel red-emitting fluorene-based copolymers

A series of novel soluble conjugated copolymers derived from 9,9-dioctylfluorene (DOF) and 4,7-di-2-thienyl-2,1,3-benzothiadiazole (DBT) were synthesized by a palladium-catalyzed Suzuki coupling reaction with different feed ratios of DOF to DBT. Owing to exciton confinement on the DBT site, exciton emission is centred on the DBT chromophore and gives rise to saturated red emission. Polyfluorene fluorescence is quenched completely at DBT concentrations as low as 1% in the solid film. Devices based on these copolymers emit a saturated red light. Chromaticity coordinates are around x = 0.70, y = 0.30 for the copolymers. The emission peaks are shifted from 628 nm to 674 nm when DBT content increases from 1 to 35%. The highest quantum efficiency achieved with device configuration of ITO/PEDT/PFO-DBT/Ba/Al was 1.4% for the copolymer with 15% DBT content.

Organic light-emitting devices with saturated red emission using 6,13-diphenylpentacene

Organic electroluminescent devices with saturated red emission were developed using 6,13-diphenylpentacene (DPP) doped into tris(8-hydroxyquinolinato) aluminum III (Alq3). DPP exhibits a narrow emission spectrum giving rise to a saturated red peak, centered around 625 nm, with excellent chromaticity coordinates (x=0.63 and y=0.34) in accordance with the Commission Internationale de l’Eclairage. An absolute photoluminescence (PL) quantum yield (φPL) of ∼30% was measured for a composite film of 0.55 mol % of DPP doped into Alq3. An electroluminescence (EL) quantum efficiency of 1.3% at 100 A/m2, close to the estimated theoretical limit (1.5%), was measured for an unoptimized device structure that consists of an active emissive layer sandwiched between hole- and electron-transport layers. In addition, the EL quantum efficiency is constant or stable over a wide range of current densities (1–1000 A/m2) or luminance values (1–1000 cd/m2).