New, efficient electroluminescent materials based on organometallic Ir complexes

Design and syntheses of four red phosphorescent heteroleptic cationic iridium(III) complexes containing two substituted phenylquinoxaline (pqx) or benzo [b]thiophen-2-yl-pyridin (btp) main ligands and one 2,2'-biimidazole (H2biim) ancillary ligand are reported: (4). Complex 1 showed a distorted octahedral geometry around the iridium(III) metal ion with cis metallated carbons and trans nitrogen atoms. The absorption, emission and electrochemical properties were systematically evaluated. The complexes exhibited red phosphorescence in the spectral range of 580 to 620 nm with high quantum efficiencies of 0.58 -0.78 in both solution and solid-state at room temperature depending on the cyclometalated main ligands. The cyclic voltammetry of the complexes (1-3) showed a metal-centered irreversible oxidation in the range of 1.40 to 1.90 V as well as two quasi reversible reduction waves from -1.15 to -1.45 V attributed to the sequential addition of two electrons to the more electron accepting heterocyclic portion of two distinctive cyclometalated main ligands, whereas complex 4 showed a reversible oxidation potential at 1.24 V and irreversible reduction waves at -1.80 V.

Section: Introductionmentioning

confidence: 99%

Tuning Photophysical and Electrochemical Properties of Heteroleptic Cationic Iridium(III) Complexes Containing Substituted 2-Phenylquinoxaline and Biimidazole

Sengottuvelan¹,

Seo²,

Kang³

et al. 2010

“…2 On the other hand, there are a few red-emitting iridium complexes, which are important for the realization of RGB full-color displays and the creation of white organic light-emitting devices (WOLEDs). 3 Compared to green and blue phosphorescent iridium complexes, red emitting iridium complexes tend to have limited quantum yields 4 due to the energy gap law. Increasing the vibrational overlap between the excited and ground states causes an increase in nonradiative rates (k nr ) and a decrease in the radiative rates (k r ) for longer wavelength emission, resulting in lower quantum efficiency in red emitters.…”

Section: Introductionmentioning

confidence: 99%

“…The cis C-C arrangement is expected from the fact that the trans C-C is higher in energy and more labile due to the electron-rich σ-phenyl ligand, which is referred to as "transphobia". 9 The bond angles in the iridium octahedron vary from 75.7(3) to 103.1 (2) o and from 168.6(3) to 174.5 (3) o as shown in Table 2. The bite angles at iridium are 79.6(3) and 80.0 (3) o because the cyclometalated ligands are distinctly smaller than those of similar complexes.…”

mentioning

confidence: 99%

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Highly Efficient Red Emissive Heteroleptic Cyclometalated Iridium(III) Complexes Bearing Two Substituted 2-Phenylquinoxaline and One 2-Pyrazinecarboxylic Acid

Sengottuvelan¹,

Yun²,

Kim³

et al. 2013

A series of highly efficient red phosphorescent heteroleptic iridium(III) complexes 1-6 containing two cyclometalating 2-(2,4-substitued phenyl)quinoxaline ligands and one chromophoric ancillary ligand were synthesized: (pqx) 2 Ir(mprz) (1), (dmpqx) 2 Ir(mprz) (2), (dfpqx) 2 Ir(mprz) (3), (pqx) 2 Ir(prz) (4), (dmpqx) 2 Ir(prz) (5), (dfpqx) 2 Ir(prz) (6), where pqx = 2-phenylquinoxaline, dfpqx = 2-(2,4-diflourophenyl)quinoxaline, dmpqx = 2-(2,4-dimethoxyphenyl)quinoxaline, prz = 2-pyrazinecarboxylate and mprz = 5-methyl-2-pyrazinecarboxylate. The absorption, emission, electrochemical and thermal properties of the complexes were evaluated for potential applications to organic light-emitting diodes (OLEDs). The structure of complex 2 was also determined by single-crystal X-ray diffraction analysis. Complex 2 exhibited distorted octahedral geometry around the iridium metal ion, for which 2-(2,4-dimethoxyphenyl)quinoxaline N atoms and C atoms of orthometalated phenyl groups are located at the mutual trans and cis-positions, respectively. The emission spectra of the complexes are governed largely by the nature of the cyclometalating ligand, and the phosphorescent peak wavelengths can be tuned from 588 to 630 nm with high quantum efficiencies of 0.64 to 0.86. Cyclic voltammetry revealed irreversible metal-centered oxidation with potentials in the range of 1.16 to 1.89 V as well as two quasi-reversible reduction waves with potentials ranging from −0.94 to −1.54 V due to the sequential addition of two electrons to the more electron-accepting heterocyclic portion of two distinctive cyclometalated C^N ligands.

“…19 These results motivated us to carry out a systematic study to improve the EL performance of the Ir(III) complexes based on the benzoyphenyl pyridine ligand with fluorine substituents. 20 In this study, a series of red-phosphorescent Ir(III) complexes 1-4 based on fluorine-substituted benzoylphenylpyridine ligands were synthesized, and their electrophosphorescent properties were examined. Multilayered organic light-emitting diodes (OLEDs) were fabricated using the complexes as a dopant and their electroluminescent properties were assessed.…”

Section: Introductionmentioning

confidence: 99%

Highly Efficient Red Phosphorescent OLEDs Based on Ir(III) Complexes with Fluorine-substituted Benzoylphenylpyridine Ligand

Kang¹,

Lee²,

Lee³

et al. 2010

Four orange-red phosphorescent Ir(III) complexes were designed and synthesized based on the benzoylphenylpyridine ligand with a fluorine substituent. Multilayered OLEDs with the device structure, ITO/2-TNATA/NPB/CBP : 8% Ir(III) complexes/BCP/Liq/Al, were fabricated using these complexes as dopant materials. All the devices exhibited orange-red electroluminescence and their electroluminescent properties were quite sensitive to the structural features of the dopants in the emitting layers. Among these, the maximum luminance (14700 cd/m 2 at 14.0 V) was observed in the device containing Ir(III) complex 1 as the dopant. In addition, its luminous, power and quantum efficiency were 11.7 cd/A, 3.88 lm/W and 9.58% at 20 mA/cm 2 , respectively. The peak wavelength of electroluminescence was 606 nm with CIE coordinates of (0.61, 0.38) at 12.0 V. The device also showed stable color chromaticity with various voltages.