Highly phosphorescent perfect green emitting iridium(iii) complex for application in OLEDs

Abstract

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...

Recent Developments in the Application of Phosphorescent Iridium(III) Complex Systems

“…[38] Acetoacetone-resembling acetoacetates with a large variety of residues are accessible from diketenes or by transesterification and can be coordinated under mild conditions. Complexes with vinyl-, oxetane-, or methacrylate-functionalized acetoacetate ligands have found use in the formation of more complex systems.…”

New oxazoline- and thiazoline-containing heteroleptic iridium(iii) complexes for highly-efficient phosphorescent organic light-emitting devices (PhOLEDs): colour tuning by varying the electroluminescence bandwidth

“…The effective tuning of EL colour through adjusting the emission bandwidth is a strategy that has previously received only limited attention. 5 In addition, due to the wide FWHM of (ppy) 2 Ir(thoz) (2) being a desirable spectral property, further studies will aim at fabricating WOLEDs possessing a high colour rendering index (CRI) based on this yellow emitter.…”

“…However, to date this approach has been limited in extent. 5 In this work, we report the synthesis, structure, electrochemical, photophysical and electroluminescent (EL) properties of two new iridium(III) complexes, namely, bis(2-phenylpyridine)(2-(2´-hydroxyphenyl)-2-oxazoline)iridium(III) (1) and bis-(2-phenylpyridine)(2-(2´-hydroxyphenyl)-2-thiazoline)iridium(III) [(ppy) 2 Ir(thoz)] (2). The ancillary N^O oxazoline (oz) and thiazoline (thoz) ligands were chosen as they are readily available and have not been studied previously in this context.…”

Efficient non-doped blue organic light-emitting diodes: donor–acceptor type host materials

“…1-5 The development of efficient green [6][7][8] and red devices 9 with pure color Commission International de l'Eclairage (CIE) coordination has been well reported. However, there is a lack of blue phosphorescent emission with long lifetime and pure color CIE due to wide band gaps.…”