This short review surveys the development of red fluorescent materials for the application of organic light-emitting diodes (OLEDs) that generate red electroluminescence (EL). The merit and problems of current dopant-based, either fluorescent or phosphorescent, red OLEDs will be addressed first. Materials that offer unique EL characteristics, such as narrow and saturated red EL as well as current density or voltage-independent EL efficiency, are discussed. In addition to dopant-based and assist dopant-based red OLEDs for comparison purposes, the survey emphasizes nondoped red OLEDs that are fabricated with the newly emerging red fluorophores as the host-emitter. The advantage of host-emitting nondoped OLEDs compared with traditional dopant-based red OLEDs is described in view of the chemical and device structures of these materials.

Molecules with weak ground-state absorption that form strongly absorbing excited states can be used in optical limiters, which can protect sensors or human eyes from optical damage. Phthalocyanine complexes bearing heavy atoms or paramagnetic groups or in solvents containing heavy atoms show optical limiting enhanced by excited triplet-state absorption. A nonhomogeneous distribution of indium tetra( tert -butyl)phthalocyanine chloride along the beam path substantially enhances the excited-state absorption, yielding an optical limiter with a linear transmittance of 0.70 that can attenuate 8-nanosecond, 532-nanometer laser pulses by factors of up to 540.

The Extradenticle (Exd) protein in Drosophila acts as a cofactor to homeotic proteins. Its nuclear localization is regulated. We report the cloning of the Drosophila homothorax (hth) gene, a homolog of the mouse Meis1 proto-oncogene that has a homeobox related to that of exd. Comparison with Meis1 finds two regions of high homology: a novel MH domain and the homeodomain. In imaginal discs, hth expression coincides with nuclear Exd. hth and exd also have virtually identical, mutant clonal phenotypes in adults. These results suggest that hth and exd function in the same pathway. We show that hth acts upstream of exd and is required and sufficient for Exd protein nuclear localization. We also show that hth and exd are both negative regulators of eye development; their mutant clones caused ectopic eye formation. Targeted expression of hth, but not of exd, in the eye disc abolished eye development completely. We suggest that hth acts with exd to delimit the eye field and prevent inappropriate eye development.

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...

No abstract

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.

No abstract

Rare red‐fluorescent fluorene derivatives have been designed and synthesized. The long‐wavelength red fluorescence is achieved by incorporating a di(4‐tolyl)amino or diphenylamino electron donor and a dicyanovinyl electron acceptor. The single‐crystal X‐ray structures of the di(4‐tolyl)amino (pTSPDCV) and diphenylamino (PhSPDCV) compounds indicate only weak non‐π van der Waals contacts in addition to long‐distance dipole–dipole interactions of the red‐emitting fluorene molecules in the solid state. The aggregation of the dipolar fluorene is largely suppressed by introducing bulky 9,9‐substituents (spiro‐fused bifluorene) as well as a non‐planar di(4‐tolyl)amino or diphenylamino group. In the solid state, these fluorene derivatives all show red fluorescence that is much brighter than with the red dopants Nile Red and DCM (4‐(dicyanomethylene)‐2‐methyl‐6‐[4‐(dimethylaminostyryl)‐4H‐pyran]). The unique photophysical properties of red‐emitting fluorene derivatives differ from other known red dopants and facilitate the fabrication of non‐doped red organic light‐emitting diodes (OLEDs). Authentic red (CIE, x = 0.65, y = 0.35) electroluminescence with a brightness of more than 12 000 cd m–2 (greater than 600 cd m–2 at 20 mA cm–2) and a remarkable external quantum efficiency as high as 3.6 % have been observed for the red‐emitting OLEDs with pTSPDCV or PhSPDCV as the sole emitting host.