Organic triplet-state light-emitting materials (organic phosphorophores) have been one of the most important recent developments in the field of organic light-emitting diodes (OLEDs).[1±4] Organic electrophosphorescent materials provided one of the major breakthroughs in electroluminescence efficiency, which is usually limited to an external quantum efficiency (EQE) of around 5 % for devices based on singletstate fluorescent materials. Owing to its thin-film, lightweight, fast-response, wide-viewing-angle, high-contrast, and low-power attributes, OLEDs promise to be one of the major flat- [16±20]However, the development of highly efficient blue-light-emitting phosphorescent emitters in OLEDs, indispensable for the realization of RGB full-color displays and WOLEDs, is still in its infancy, and blue-light-emitting phosphorescent EL performance lags far behind that of the green-or red-light emitters.One of the best known triplet-state blue-light emitters is iridium(III) bis(4,6-difluorophenylpyridinato)picolate (FIrpic, Scheme 1).[21±23] Although a reasonably good EQE of about 10 % (or 10 lm W ±1 ) has been reported, its blue-light emission was far from saturated, with 1931 Commission Internationale de L'Eclairage x,y coordinates (CIE x,y ) of (0.17, 0.34) [23] thatwere best characterized as cyan in color. The most recent, and probably only the second phosphorescent blue emitter of practical use, was iridium(III) bis(4¢,6¢-difluorophenylpyridinato)tetrakis(1-pyrazolyl) borate) (FIr6), [24] whose blue OLED showed EQEs of 9±10 % (or 11±14 lm W ±1 ), and whose bluecolor chromaticity had been considerably improved to CIE x,y = 0.16, 0.26. There are a couple of limitations in the usage of phosphorescence-based materials for OLEDs. Compared with the short emission lifetime (scale of nanoseconds) of fluorescent materials, the relatively long phosphorescence lifetimes (microseconds scale) of the iridium complexes may lead to dominant triplet±triplet (T 1 ±T 1 ) annihilation at high currents. Long emission lifetimes also cause a long range of exciton diffusion (> 100 nm) that could get quenched in the adjacent layers of materials in the OLED. Consequently, organic phosphorescent materials are often adopted as dopants dispersed in a suitable host material, usually of high bandgap energies and good carrier transport properties. Arylamino-containing organic substances are usually the host materials of choice to alleviate this situation. This has worked reasonably well for phosphorescent green-or red-light-emitting materials. However, it has been demonstrated that the energy differences in the triplet energies of host and guest materials are very important for the confinement of electro-generated triplet excitons on the dopant molecules.[22±28] In cases of triplet-state bluelight emitters, common arylamino-containing substances, such as 4,4¢-bis(9-carbazolyl)-2,2¢-biphenyl (CBP) simply do not have sufficient triplet-state energy for effective T 1 ±T 1 energy transfer; later, a structurally modified host molecule, 1,3-bis(9-carba...

Bright (maximum 10034 cd m(-2), 455 cd m(-2) at 20 mA cm(-2)) and efficient (maximum 2.4% at 4 mA cm(-2)) red (lambda(max)el 634-636 nm) organic light-emitting diodes employ arylamino-substituted fumaronitrile as the novel host emitter, which is readily prepared and easily purified.

We report a systematic comparison study of 3,5‐di(N‐carbazolyl)tetraphenylsilane (SimCP) and N,N′‐dicarbazolyl‐3,5‐benzene (mCP), which are used as the host materials for phosphorescent blue dopants in organic light‐emitting diodes (OLEDs). On the basis of photoexcitation emission spectroscopy, thermal stability analysis, photoelectron analysis, charge transport measurements, and molecular dynamics (MD) simulations, we conclude that the non‐π‐conjugated meta‐substituted triphenylsilyl moiety of SimCP exerts a unique hindering effect on the molecular packing characteristics in the condensed phase. The chemical origin of the superior performance of SimCP over mCP is revealed, and is expected to be helpful for the molecular design of effective host materials for enhancing the performance of blue phosphorescent OLEDs.

A series of group III metal chelates have been synthesized and characterized for the versatile application of organic light-emitting diodes (OLEDs). These metal chelates are based on 4-hydroxy-1,5-naphthyridine derivates as chelating ligands, and they are the blue version analogues of well-known green fluorophore Alq(3) (tris(8-hydroxyquinolinato)aluminum). These chelating ligands and their metal chelates were easily prepared with an improved synthetic method, and they were facially purified by a sublimation process, which enables the materials to be readily available in bulk quantity and facilitates their usage in OLEDs. Unlike most currently known blue analogues of Alq(3) or other deep blue materials, metal chelates of 4-hydroxy-1,5-naphthyridine exhibit very deep blue fluorescence, wide band gap energy, high charge carrier mobility, and superior thermal stability. Using a vacuum-thermal-deposition process in the fabrication of OLEDs, we have successfully demonstrated that the application of these unusual hydroxynaphthyridine metal chelates can be very versatile and effective. First, we have solved or alleviated the problem of exciplex formation that took place between the hole-transporting layer and hydroxynaphthyridine metal chelates, of which OLED application has been prohibited to date. Second, these deep blue materials can play various roles in OLED application. They can be a highly efficient nondopant deep blue emitter: maximum external quantum efficiency eta(ext) of 4.2%; Commision Internationale de L'Eclairage x, y coordinates, CIE(x,y) = 0.15, 0.07. Compared with Alq(3), Bebq(2) (beryllium bis(benzoquinolin-10-olate)), or TPBI (2,2',2''-(1,3,5-phenylene)tris(1-phenyl-1H-benzimidazole), they are a good electron-transporting material: low HOMO energy level of 6.4-6.5 eV and not so high LUMO energy level of 3.0-3.3 eV. They can be ambipolar and possess a high electron mobility of 10(-4) cm(2)/V s at an electric field of 6.4 x 10(5) V/cm. They are a qualified wide band gap host material for efficient blue perylene (CIE(x,y) = 0.14, 0.17 and maximum eta(ext) 3.8%) or deep blue 9,10-diphenylanthracene (CIE(x,y) = 0.15, 0.06 and maximum eta(ext) 2.8%). For solid state lighting application, they are desirable as a host material for yellow dopant (rubrene) in achieving high efficiency (eta(ext) 4.3% and eta(P) 8.7 lm/W at an electroluminance of 100 cd/m(2) or eta(ext) 3.9% and eta(P) 5.1 lm/W at an electroluminance of 1000 cd/m(2)) white electroluminescence (CIE(x,y) = 0.30, 0.35).