A novel iridium complex, [bis-(2-phenylpyridine)(2-carboxy-4-dimethylaminopyridine)iridium(III)] (N984), was synthesized and characterized using spectroscopic and electrochemical methods; a solution processable OLED device incorporating the N984 complex displays electroluminescence spectra with a narrow bandwidth of 70 nm at half of its intensity, with colour coordinates of x = 0.322; y = 0.529 that are very close to those suggested by the PAL standard for a green emitter.Organic light emitting diodes (OLEDs) are becoming increasingly successful as a new display technology. 1,2 Although OLED displays have reached commercialization, there is still a need for improvement of the efficiency, colour purity and stability. This is true for multilayered OLEDs prepared via vacuum evaporation and even more so for OLED architectures obtained via solution processing. The latter technique offers a more economic production route and hence is of great interest for the more widespread application of the OLED technology. The introduction of iridium(III) containing complexes led to very efficient multilayered OLEDs, reaching internal conversion efficiency of almost 100%. 3 These high efficiencies originate from the strong spin orbit coupling present in these heavy metal complexes which makes it possible for both singlet and triplet excitons generated to decay radiatively. 4,5 A large number of iridium complexes have been utilized for this purpose, which are mostly based on the cyclometalating ligand 2-phenylpyridine (ppy) with an auxiliary ligand such as acetylacetonate (acac) or picolinate (pic). [6][7][8][9][10] Several groups have demonstrated tuning of the phosphorescence wavelength from blue to red by functionalization of the ligands with electron withdrawing and electron donating substituents. [11][12][13] Nevertheless, no attempts were made to tune the colour purity by decreasing the emission bandwidth, which of course is attractive for both fundamental research and practical applications. Therefore, in this communication we report a novel approach for tuning bandwidth by modulating the LUMO levels of the ancillary ligand.The N984 complex was synthesized in one step by reacting the dimeric iridium(III) complex [Ir(ppy) 2 (Cl)] 2 with methyl-dimethylamino-picolinate and sodium carbonate in 2-ethoxy-ethanol affording the N984 compound as a yellow powder.{ The 1 H NMR spectrum of the N984 complex shows 19 resonance signals (two doublets (d), five doublet of doublets (dd), six doublet of doublet of doublets (ddd) and six doublet of triplets (dt); see Fig. S1) in the aromatic region. The pyridine 6-H protons of the 2-phenylpyridine ligands are assigned to ddd at d 7.64 and d 8.82 on the basis of the distinctive pattern of the coupling constants expected for these substituted pyridines (J 3,6 0.8, J 4,6 1.6 and J 5,6 5.8). The different magnetic environments of these protons are a result of the trans geometry of the pyridine rings which directs one 6-H proton towards the 4-dimethylaminopyridine ring and the other towards the car...

A novel solution processable phosphorescent dendrimer based on cyclic phosphazene (CP) cores has been prepared and used as emissive layers in simple OLED architectures, providing efficiencies of 24.0 cd A 21 and 16.7 lm W 21 .Organic and polymeric light emitting diode (OLED) technology has progressed immensely since the initial reports by Tang 1 and Friend 2 in 1987 and 1990 respectively. From these earliest discoveries through the late 1990's, almost all OLED reports were based on fluorescent emissive materials. As a result, champion OLED efficiencies were limited to around 10 lm W 21 which made their application in display technology promising but no chance for solid-state lighting that requires efficiencies of .30 lm W 21 . With the discovery of platinum and iridium based phosphorescent complexes, 3,4 OLED efficiencies .30 lm W 21 have been achieved and thus application in both display and lighting applications have become even more promising. 5 For these active materials, both small molecules and polymers are currently the preferred candidates. Small-molecules are advantageous as they can be highly purified and vacuum deposited in multi-layer stacks, both important for device lifetime and efficiency. However, vacuum deposition techniques generally require expensive equipment, a limitation to display size, and complicated full color display production processes at high volume using masking technologies. 6 Polymers are generally of lower purity than small molecules but can access larger display sizes at much lower costs using solution-based deposition techniques such as spray coating, ink jet and screen printing. 7,8 Having a set of materials with properties intermediate between small molecules and polymers would be very advantageous. One such family of materials are dendrimers that have molecular weights in the favorable range between 1000-10 000 g mol 21 . Favorable because dendrimers can be purified to a high degree using chromatographic techniques, are soluble in common solvents, and allow synthetic versatility for tuning charge transport 9-12 and emissive [13][14][15][16] properties. Finally dendrimers of different emission colors can be physically blended together without phase separation for possible application in white lighting.Cyclic phosphazenes (CP), with a planar non-delocalized cyclic ring consisting of alternating N and P atoms, are an interesting class of materials that offers access to dendrimeric materials. The inorganic phosphazenes have been well studied in both the cyclic and linear forms by several groups due to their diverse properties including excellent hydrolytic stability, thermal stability, flame retardant properties, and liquid crystalline behaviour to name a few. [17][18][19][20] The CP core provides many advantageous properties towards useful materials for solution processable OLEDs. First, the chemistry to prepare functionalized CP cores is very straightforward. Second, the functionalized CP cores are very stable and do not breakdown even under very aggressive chemical condition...

The synthesis and characterisation of 2,5-bis(5′-hexyl-[2,2′-bithiophen]-5-yl)pyridine (Th4PY) and its use as a blue emitter in organic light emitting diodes (OLEDs) is reported. Th4PY was synthesised in high yield using a straightforward Suzuki coupling route with commercially available starting materials. As Th4PY is both soluble and has low molecular weight, blue OLEDs were fabricated using both spin-coating and vacuum deposition thin film processing techniques to study the effect of processing on device performance. OLED devices using a spin-coated layer consisting of 4′,4′′-tris(N-carbazolyl)triphenylamine (TCTA) and 2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix together with Th4PY as emitter exhibited highly efficient sky-blue emission with a low turn-on voltage of 3 V, a maximum brightness close to 15000 cd m–2 at 8 V, and a maximum luminous efficiency of 7.4 cd A–1 (6.3 lm W–1) with CIE coordinates of x = 0.212, y = 0.320. The device performance characteristics are compared using various matrices and processing techniques. The promising sky-blue OLED performance, solution processability, and ambient stability make Th4PY a promising blue emitter for application in OLEDs.

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