N-phenylamino ] Biphenyl Research Articles

Efficient Red Electrophosphorescent Devices Based on Iridium Complexes of Fluorinated 1-Phenylisoquinoline

The iridium complexes containing fluorinated 1-phenylisoquinoline ligands were prepared and their luminescent properties were investigated. Density functional theory (DFT) was applied to calculate the energies of highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) in the iridium complexes. Electroluminescent devices were fabricated with a configuration of indium tin oxide (ITO)/4,4',4''-tris[2-naphthylphenylamino]triphenylamine (2-TNATA)/4,4'-bis[N-(naphthyl)-N-phenyl-amino]biphenyl (NPB)/4,4,N,N'-dicarbazolebiphenyl (CBP):dopant/bathocuproine (BCP)/tris-(8-hydroxy-quinoline) aluminum (Alq3)/lithium quinolate (Liq)/Al. The device using bis[1-(5-fluorophenyl)isoquinolinato-C2,N] iridium acetylacetonate [Ir(5-Fpiq)2(acac)] as a dopant showed red emission with 1931 Commission Internationale de I'Eclairage (CIE) chromaticity coordinates (x=0.68, y=0.30). Organic light-emitting device (OLED) based on bis[1-(4,5-difluorophenyl)isoquinolinato-C2,N] iridium(III) acetylacetonate [Ir(4,5-F2piq)2(acac)] yielded luminous efficiency of 9.9 cd/A at a luminance of 11840 cd/m2.

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.

Novel hole-transporting materials based on 1,4-bis(carbazolyl)benzene for organic light-emitting devices

Novel hole-transporting molecules containing 1,4-bis(carbazolyl)benzene as a central unit and different numbers of diphenylamine moieties as the peripheral groups have been synthesized and characterized. These compounds are thermally stable with high glass transition temperatures of 141–157 °C and exhibit chemically reversible redox processes. Their amorphous state stability and hole transport properties can be significantly improved by increasing the number of diphenylamine moieties in the outer part and by controlling the symmetry of the carbazole-based molecules. These compounds can be used as good hole-transporting materials for organic electroluminescent (EL) devices. The device performance based on tri- and tetra-substituted carbazole derivatives is comparable to that of a typical 4,4′-bis[N-(1-naphthyl)-N-phenylamino] biphenyl (NPB)-based device.

Degradation of Organic Layers of Organic Light Emitting Devices by Continuous Operation

Voltage increases of organic mono layered devices under constant-current operation were investigated in order to clarify the origin of the degradation of organic light emitting devices (OLED). The rate of voltage increase for tris(8-hydroxyquinoline)aluminum (Alq3), which is the most popular material for the electron transport layer, was the largest, whereas those for hole transporting materials (4,4′,4′′-tris(3-methylphenyl-phenylamino)-triphenyl-amine (MTDATA), 4,4′-bis[N-(1-naphthyl)-N-phenylamino] biphenyl (NPB), N,N′-diphenyl-N,N′-bis(3-methylphenyl)-1,1′-biphenyl-4,4′-diamine (TPD)) were small. The origin of the recoverable voltage change of the Alq3 layer was attributed to the electronic characteristic change of the Alq3 layer, that is, the ionic impurities or the orientation of Alq3 molecules.

Dipyrazolopyridine derivatives as bright blue electroluminescent materials

Very bright blue organic light emitting diodes were fabricated using highly fluorescent dipyrazolopyridine derivatives, 4-(4-substituted phenyl)-1,7-diphenyl-3,5-dimethyl-1,7dihydrodipyrazolo[3,4-b,4′,3′-e]pyridine (PAP–X, X=CN, Ph, and OMe), as emitter by doping the dye in an electron-transporting host, 2,2′,2″-(1,3,5-benzenetriyl)tris-[1-phenyl-1H-benzimidazole] (TPBI). Two hole-transporting layers, 4,4′-bis[N-(1-naphthyl-1-)-N-phenyl-amino]-biphenyl (NPB) and 4,4′-dicarbazolyl-1,1′-biphenyl (CBP) were used to achieve the emission from PAP–X. The devices with a general configuration of indium tin oxide/NPB/CBP/TPBI:PAP(2%)/Mg:Ag showed a bright blue emission. The PAP–CN-based device is exceptionally good, with a brightness of 11 200 cd/m2 at 14.2 V and the peak external quantum efficiency of 3.2%. The efficiency is the highest for the blue emission.