Yellow Phosphorescent Iridium Research Articles

Oxygen‐Bridged Triphenylamine Units Tuning the Photophysical Properties of Classical Phosphorescent Iridium(III) Complex

AbstractA new yellow phosphorescent iridium(III) complex Ir(ppybop)2acac with two oxygen‐bridged triphenylamine units were prepared and investigated. The cyclometalating ligand ppybop was synthesized by the efficient Suzuki‐Miyaura cross‐coupling reaction of oxygen‐bridged triarylamine unit based boron reagent 1‐a and 2‐(4‐Bromophenyl)pyridine, and the acetylacetone (acac) was used as an auxiliary ligand. Notably, the complex Ir(ppybop)2acac measured with a fluorescence spectrophotometer can show a larger redshift emission (λem=568 nm), a narrower full width at half maximum (FWHM=59 nm), a longer emission lifetime (τ[b]=3127 ns) and a better solubility in comparison with the classical green complex Ir(ppy)2acac (λem=520 nm, FWHM=70 nm, τ[b]=1206 ns). In addition, the DFT calculation results indicate that the strong electron‐donating ability of the unit can lead to the unusual ligand‐to‐metal charge transfer (3LMCT) excited state characteristics of Ir(ppybop)2acac, which is completely different from the metal‐to‐ligand charge transfer (3MLCT) in Ir(ppy)2acac. This result can provide a new strategy for the design of new phosphorescent iridium(III) complexes.

Novel yellow phosphorescent iridium(Ⅲ) complex with broad emission: Synthesis, photophysical properties and efficient electroluminescence

Novel yellow phosphorescent iridium(Ⅲ) complex with broad emission: Synthesis, photophysical properties and efficient electroluminescence

Novel yellow phosphorescent iridium complexes with cycolmetalated (pyridin-2-yl)dibenzothiophene-S,S-dioxide ligands for singly doped emissive layer hybrid white organic light-emitting diodes

Two novel dibenzothiophene-S,S-dioxide-based iridium complexes with yellow emission were fully synthesized and characterized. The photophysical, electrochemical and thermal properties, as well as electroluminescent properties of the resulting iridium complexes were discussed. Both the iridium complexes possess good thermal stability and high photoluminescence quantum yields. Also, we have successfully fabricated singly doped emissive layer (SDEL) hybrid white organic light-emitting devices (WOLEDs) using (3-PyFSO)2IrPic or (2-PyFSO)2IrPic as yellow-emitting phosphors and 4,4′,4″-tris(N-carbazolyl)triphenylamine (TCTA) as host and blue-emitting fluorophor. The WOLEDs with (3-PyFSO)2IrPic show a maximal power efficiency (PE) of 4.28 lm/W at a brightness of 3.7 cd/m2 and a Commission Internationale de L'Eclairage (CIE) coordinates of (0.227, 0.260). Compared to (3-PyFSO)2IrPic, the WOLEDs based on (2-PyFSO)2IrPic exhibit a little better device's performances with a maximum PE of 4.70 lm/W at a brightness of 2.6 cd/m2 and a CIE coordinates of (0.244, 0.243).

Green and yellow pyridazine-based phosphorescent Iridium(III) complexes for high-efficiency and low-cost organic light-emitting diodes

Despite efficient electroluminescence performance, the high fabrication cost due to the utilization of noble metals impedes the commercialization of phosphorescent organic light-emitting diodes (PHOLEDs) based on iridium(III) complexes. In this paper, we designed and synthesized a series of green and yellow phosphorescent iridium(III) complexes with 3-(2,4-difluorophenyl)-6-methylpyridazine as the cyclometalating ligand to fabricate high-performance and low-cost PHOLEDs. By the introduction of a pyridazine moiety to enhance the coordination bond between iridium(III) ion and cyclometalating ligands, these iridium(III) complexes were obtained in high yields and exhibit good thermal stabilities and volatilities, which are beneficial to reduce the device manufacturing cost. Besides, high photoluminescence quantum yields (PLQYs) and short phosphorescent lifetimes of these pyridazine-based iridium(III) complexes endow their PHOLEDs with excellent device performance, which can be promising for practical applications. Particularly, the green emitter (fpdz)2Irpic exhibited a high PLQY of 0.89 in solid doped thin-film; PHOLED based on (fpdz)2Irpic achieved an outstanding maximum external quantum efficiency (EQEmax) of 28.7% with ultralow efficiency roll-off of 2% at the high luminance of 1000 cd m−2, which was superior to the commercial green phosphor bis(phenylpyridineyl)iridium(acetylacetonate) [(ppy)2Ir(acac), EQEmax = 24.2%].

Novel yellow phosphorescent iridium complexes with dibenzothiophene-S,S-dioxide-based cyclometalated ligand for white polymer light-emitting diodes

We have designed and synthesized two novel yellow phosphorescent iridium complexes using dibenzothiophene-S,S-dioxide-based cyclometalated ligand for the first time, which are capable of producing highly efficient yellow and white polymer light-emitting devices (PLEDs). The resulted iridium complexes display good thermal stability and high photoluminescence quantum yields. Both yellow and white PLEDs are fabricated with an identical single-emission-layer configuration of ITO/PEDOT:PSS/emission layer (EML)/CsF/Al. For the yellow phosphorescent PLEDs based on (p-CzFSOPy)2IrPic, the best device performances with a peak luminous efficiency (LE) of 13.3 cd/A and a peak external quantum efficiency (EQE) of 5.3% are achieved. More importantly, the two-element WPLEDs containing iridium (III)bis (2-(4,6-difluorophenyl)-pyridinato-N,C2′) picolinate (FIrpic) as blue and (p-CzFSOPy)2IrPic as yellow phosphors doped into a PVK:OXD-7 matrix at an appropriate ratio exhibited a maximum LE of 19.2 cd/A, a maximum EQE of 9.6%, an extremely high luminance of 18717 cd/m2 and Commission Internationale de L'Eclairage (CIE) coordinate of (0.317, 0.448). Moreover, at a luminance for practical application of 1000 cd/m2, the LE still remains as high as 19.0 cd/A, with a very slight decrease.

Orange–Yellow Phosphorescent Iridium(III) Complex for Solution‐processed Organic Light‐Emitting Diodes: Structural, Optical and Electroluminescent Properties of Bis(2‐phenylbenzothiazole)[2‐(2‐hydroxyphenyl)benzothiazole]iridium(III)

New orange–yellow phosphorescent cyclometalated iridium(III) complex, (bt)2Ir(btz), where btH = 2‐phenylbenzothiazole and btzH = 2‐(2‐hydroxyphenyl)benzothiazole, was synthesized, and its structural, photophysical and electroluminescence properties were investigated to apply for organic light‐emitting diodes (OLEDs) applications. The coordination geometry around iridium metal ion was distorted octahedral, exhibiting cis‐C, C′ and trans‐N, N′ chelate dispositions with narrow ligand bite angles ranging from 79.7° (2) to 84.5° (1). The optical properties revealed that the π‐conjugated nature of bt ligand caused a bathochromic shift in emission and btz ligand played a role in fine color tuning. The synthesized (bt)2Ir(btz) was soluble in common organic solvents and the emitting layer was readily spin‐coated in chlorobenzene solution onto substrate. The OLED fabricated with the configuration of ITO/PEDOT:PSS/PVK:TCTA:OXD‐7: (bt)2Ir(btz) (32:32:28:8)/Bphen/LiF/Al exhibited a maximum external quantum efficiency (EQE) of 4.67% and a maximum luminance efficient (LE) of 8.61 cd/A with CIE (x, y) coordinates of (0.54,0.45).

Novel iridium complexes as yellow phosphorescent emitters for single-layer yellow and white polymer light-emitting diodes

Both yellow and white polymer light-emitting devices are achieved using novel yellow phosphorescent iridium complexes with triphenylamine- and fluorene-functionalized cyclometalating ligands as dopants.

Novel yellow phosphorescent iridium complexes containing a carbazole–oxadiazole unit used in polymeric light-emitting diodes

Yellow iridium complexes Ir(PPOHC) 3 and (PPOHC) 2Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9 H-carbazole) were synthesized and characterized. The Ir(PPOHC) 3 complex has good thermal stability with 5% weight-reduction occurring at 370 °C and a glass-transition temperature of 201 °C. A polymeric light-emitting diode using the Ir(PPOHC) 3 complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC) 3 which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazole–oxadiazole unit are promising candidates in high-efficiency electroluminescent devices.

Efficient white organic light-emitting devices based on phosphorescent iridium complexes

Mixing yellow and blue emissions is a commonly used approach for achieving white emission in organic light-emitting devices (OLEDs). However, as there are relatively few efficient yellow phosphors, their performance is often the bottleneck for the efficiency of phosphorescent white OLEDs (WOLEDs) based on “yellow plus blue” approach. Here, a yellow phosphorescent iridium complex, bis[2-(2-naphthyl)pyridine] (acetylacetonate) iridium(III), has been designed, synthesized and applied in WOLEDs by combining blue emission from iridium-bis-(4,6,-difluorophenyl-pyridinato-N,C 2)-picolinate. Without using optical out-coupling or p–i–n confinement structure, the optimized WOLEDs demonstrate a maximum forward viewing power efficiency of 29.2 lm/W (37.2 cd/A and 12.6%) with CIE coordinates of (0.32, 0.45).