Highly efficient blue organic light-emitting diodes (OLEDs) are necessary for high-resolution full-color displays and solid-state lighting applications.[1] The dopant-host system is often adopted to improve OLED performance. However, electroluminescence (EL) properties, including color purity, are extremely sensitive to the dopant concentration, [2] which is usually less than 2 wt % with a AE0.5 wt % variation. Precise control of the dopant concentration using co-evaporation methods is not an easy task. The development of highperformance blue-light-emitting materials suitable for nondoped OLEDs is one method of circumventing such fabrication problems. With many literature examples, nondoped-type

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A stable glassy structureenhances the lifespan and performance of molecular blue‐light‐emitting devices: The authors present an easily synthesized tetraphenylsilane framework derivatized with one or more triphenylamino‐oxadiazole groups (see Figure), for which DSC showed no measurable crystallization tendency. Trilayer OLED devices containing this chromophore exhibit bright blue electroluminescence exceeding 20000 cd/m2.

Molecular glass material (4-(5-(4-(diphenylamino)phenyl)-2-oxadiazolyl)phenyl)triphenylsilane (Ph(3)Si(PhTPAOXD)) was used as the blue light-emitting material in the fabrication of high-performance organic light-emitting diodes (OLEDs). In the optimization of performance, five types of OLEDs were constructed from Ph(3)Si(PhTPAOXD): device I, ITO/NPB/Ph(3)Si(PhTPAOXD)/Alq(3)/Mg:Ag, where NPB and Alq(3) are 1,4-bis(1-naphylphenylamino)biphenyl and tris(8-hydroxyquinoline)aluminum, respectively; device II, ITO/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where TPBI is 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene; device III, ITO/Ph(2)Si(Ph(NPA)(2))(2)/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag, where Ph(2)Si(Ph(NPA)(2))(2) is bis(3,5-bis(1-naphylphenylamino)phenyl)-diphenylsilane, a newly synthesized tetraphenylsilane-containing triarylamine as hole-transporting material; device IV, ITO/Ph(2)Si(Ph(NPA)(2))(2)/NPB/Ph(3)Si(PhTPAOXD)/TPBI/Mg:Ag; device V, ITO/CuPc/NPB /Ph(3)Si(PhTPAOXD)/Alq(3)/LiF/Al, where CuPc is Cu(II) phthalocyanine. Device performances, including blue color purity, electroluminescence (EL) intensity, current density, and efficiency, vary drastically by changing the device thickness (100-600 A of the light-emitting layer) and materials for hole-transporting layer (NPB and/or Ph(2)Si(Ph(NPA)(2))(2)) or electron-transporting material (Alq(3) or TPBI). One of the superior OLEDs is device IV, showing maximum EL near 19 000 cd/m(2) with relatively low current density of 674 mA/cm(2) (or near 3000 cd/m(2) at 100 mA/cm(2)) and high external quantum efficiency of 2.4% (1.1 lm/W or 3.1 cd/A). The device possesses good blue color purity with EL emission maximum (lambda(max)(EL)) at 460 nm, corresponding to (0.16, 0.18) of blue color chromaticity on CIE coordinates. In addition, the device is reasonably stable and sustains heating over 100 degrees C with no loss of luminance on the basis of the annealing data for device V. Formation of the exciplex at the interface of NPB and Ph(3)Si(PhTPAOXD) layers is verified by EL and photoluminescence (PL) spectra studies on the devices with a combination of different charge transporting materials. The EL due to the exciplex (lambda(max)(EL) at 490-510 nm) can be properly avoided by using a 200 A layer of Ph(3)Si(PhTPAOXD) in device I, which limits the charge-recombination zone away from the interface area.

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A series of newly designed 3,4-diphenylmaleimide-based π-conjugated copolymers that exhibit red fluorescence in both solution and solid state were synthesized and characterized. Bright and efficient red fluorescence in the solid state was achieved by varying the structural combination of thiophene and/or fluorene with 3,4-diphenylmaleimide fluorophore. The range of thiophene- and fluorene-derived 3,4-diphenylmaleimide model compounds revealed that thiophene moieties were effective in extending the emission wavelength to the red region, and fluorene moieties significantly enhanced fluorescence intensity. Polymer light-emitting diodes (PLEDs) fabricated from 3,4-diphenylmaleimide−terthiophene copolymer (PTTML) exhibited saturated red electroluminescence (EL) with emission of 676 nm, although the diode was inefficient and dim. TPBI (2,2‘,2‘ ‘-(1,3,5-phenylene)-tris(1-phenyl-1H-benzimidazole)) as the electron-transporting layer in PLEDs was found to improve the performance of 3,4-diphenylmaleimide−bithiophene copolymer (PBTML). PBTML PLED yielded reddish EL (emission of 620 nm) with peak efficiencies of 0.61% (0.89 cd/A) and a maximum electroluminance of 1290 cd/m2. A rare fluorene copolymer of a 3,4-diphenylmaleimide−thiophene−fluorene triad (PFTML) emitted orange-red photoluminescence (PL) at a of 598 nm in solution and of 601 nm in a solid thin film, with relatively high fluorescence quantum yields of 37 and 22%, respectively. Its PLEDs yielded bright orange-red EL (emission of 614 nm) with a high intensity of over 2000 cd/m2 and an enhanced peak luminous efficiency of 1.25 cd/A or an external quantum efficiency of 0.74%.

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