Emitting Iridium Complexes Research Articles

Bulky Iridium NHC Complexes for Bright, Efficient Deep‐Blue OLEDs

AbstractFour new deep‐blue‐emitting iridium(III) NHC complexes containing sterically demanding ligands are synthesized. The four complexes show bright, deep‐blue emission, with emission maxima between 420 and 427 nm in both acetonitrile solution and 30 wt% doped films in TSPO1; the two meridional isomers showing photoluminescence quantum yields, ΦPL, in doped films of 80% and 89%. The two meridional isomers are used to assess the impact of emitters containing bulky, sterically demanding ligands on the performance of organic light‐emitting diodes (OLEDs). OLEDs employing a stepped doping profile with mer‐Ir(tfpi_tmBn)3 as the emitter produce the highest performing devices in this study, with these devices exhibiting deep‐blue [λEL = 429 nm, CIE = (0.16, 0.08)] emission and a maximum external quantum efficiency (EQEmax) of 14.9%, which decreases to 11.7% at 100 cd m−2. The performance of the OLEDs shows very good efficiencies and moderate efficiency roll‐offs in comparison to reported phosphorescent deep‐blue OLEDs with CIEy ≤ 0.08, as required for commercial displays. The promising results suggest that the design strategy of adding steric bulk to blue emitting iridium complexes containing NHC ligands is a useful strategy for reducing intermolecular interactions between emitters in OLEDs.

Three Types of Charged‐Ligand‐Based Blue–Green to Near‐Infrared Emitting Iridium Complexes: Synthesis, Structures, and Organic Light‐Emitting Diode Application

AbstractThe development of a class of simple‐structure‐based small molecule iridium complexes with adjustable color emission from blue to near‐infrared (NIR) remains a major challenge. A novel straightforward strategy toward a series of three types of charged ligand (0, −1, −2)‐based neutral iridium(III) complexes is described, as it can be easily obtained by efficient three‐step synthesis. All the complexes contain an unusual dianionic ligand (−2) biphenyl and show a great color variation from blue–green (465–503 nm) to NIR (688–706 nm) by controlling different neutral (0) and monoanionic (−1) ligands. Notably, all the NIR‐emitting iridium(III) complexes have excellent chemical and thermal stability, which makes them easy to sublimate and purify, and are eventually applied to organic light‐emitting diode device with a good external quantum efficiency of 2.5%, and low efficiency roll‐off and turn‐on voltage (3 V). This study opens an important avenue for the construction of novel phosphorescent iridium(III) complex materials with tunable properties featuring three types of charged ligands (0, −1, −2), thus providing new opportunities for their optoelectronic applications.

An 850 nm pure near-infrared emitting iridium complex for solution-processed organic light-emitting diodes

The first example of an iridium(iii) emitter in pure near-infrared OLEDs with an emission peak at 850 nm and full emission over 700 nm.

Efficient saturated red electrophosphorescence by using solution-processed 1-phenylisoquinoline-based iridium phosphors with peripheral functional encapsulation

A series of saturated-red emitting iridium complexes with bifunctional charge-transporting peripheral groups were designed and synthesized. The relationship between the structures and their photophysical, electrochemical and electrophosphorescent properties was investigated. Through the incorporation of hole-transporting triphenylamine units and/or electron-transporting phosphine oxide groups to the cyclometalating ligand, the new complexes exhibited good thermal stabilities with high glass-transition temperatures up to 284°C, while maintained the saturated-red emission of the center core. Besides, the peripheries sufficiently protect the emissive core from the intermolecular interactions. Solution-processed single-layer phosphorescent organic light-emitting device (PhOLED) based on phosphor R2 showed a maximum external quantum efficiency of 7.6% with Commission Internationale de l’Eclairage coordinates of (0.68, 0.30).

Water-soluble Ir(iii) complexes of deprotonated N-methylbipyridinium ligands: fluorine-free blue emitters.

New blue or blue-green emitting iridium complexes have been synthesised with cyclometalating ligands derived from the 1-methyl-3-(2'-pyridyl)pyridinium cation. Efficient luminescence is observed in MeCN or aqueous solutions, with a large range of lifetimes in the μs region and relatively high quantum yields.

Colour tuning by the ring roundabout: [Ir(C^N)2(N^N)]+ emitters with sulfonyl-substituted cyclometallating ligands

A series of fluorine-free blue and green emitting iridium complexes containing sulfone-substituted cyclometallating and pyrazolyl-pyridine ancillary ligands has been synthesized and their properties investigated.

Highly efficient green organic light emitting diode with a novel solution processable iridium complex emitter

We demonstrate a high-efficiency green organic light-emitting diode (OLED) with a solution-processed emissive layer composed of a novel green light emitting iridium complex, bis [5-methyl-8-trifluoromethyl-5H-benzo(c) (1,5)naphthyridin-6-one]iridium(pyrazinecarboxylate). By coupling with a proper host, the green device shows at 1000 cd m−2 an external quantum efficiency of 23.8%, current efficiency of 95.6 cd A−1, and efficacy of 60.8 lm W−1, the highest among all reported OLEDs with a solution-processed emissive layer. The high efficiency may be attributed to the host possessing a zero electron injection barrier, resulting in a more balanced carrier-injection.

Synthesis and characterization of new blue light emitting iridium complexes containing a trimethylsilyl group

New blue iridium complexes with a trimethylsilyl group as a bulky electron donating group, Ir(F2-p-trimethylsilyl)2(fptp) and Ir(F2-m-trimethylsilyl)2(fptp), were synthesized via μ-chloro-bridged dimer and perfluoropropylated triazole-based ancillary ligands and then characterized using various spectroscopic studies. Both Ir(F2-p-trimethylsilyl)2(fptp) and Ir(F2-m-trimethylsilyl)2(fptp) exhibited high photoluminescence quantum efficiencies of 75 ± 5% and 76 ± 5% in films, respectively. The DFT calculation demonstrated that the new blue iridium complexes have a wide bandgap compared with FIrpic and the Ir(F2-p-trimethylsilyl)2(fptp) with a trimethylsilyl group in the para position has a slightly deeper HOMO level than that of the Ir(F2-p-trimethylsilyl)2(fptp) with a trimethylsilyl group in the meta position. The UV-vis absorption and photoluminescent (PL) spectra of the complexes were blue shifted compared with those of FIrpic. The device using the Ir(F2-p-trimethylsilyl)2(fptp) exhibited a maximum external quantum efficiency of 19.3% (at 0.00152 mA cm−2) and commission Internationale de l'Eclairage (CIE) coordinates of (0.145, 0.247).

The New Iridium Complexes Involving Pyridylpyridine Derivatives for the Saturated Blue Emission

To obtain a saturated blue phosphorescent material with a good color purity, we have synthesized the new blue emitting iridium complexes with 2, 6-difluoro-3-(4-methylpyridin-2-yl)pyridine (4-Me-dfpypy) as a main ligand. We expected that the LUMO energy levels of the complex might increase upon introduction of an electron donating group such as a methyl group to the pyridyl moieties of the ligand, leading to a wide energy gap of the complex to give the saturated blue emission. We have also introduced a variety of the ancillary ligands to the iridium center to compare the effect of the ancillary ligards on the emission of their complexes. The resulting iridium complexes, Ir(4-Me-dfpypy)3, Ir(4-Me-dfpypy)2(acac), Ir(4-Me-dfpypy)2(pic) and Ir(4-Me-dfpypy)2(trzl-CH3) where acac, pic, and trzl-CH3 represent acetylacetonate, picolinate, and 2-(5-methyl-2H-1,2,4-triazol-3-yl) pyridinate, respectively exhibited the blue emission at 451, 447, 440 and 425 nm in CH2Cl2 solution. The organic light emitting device (OLED) employing homoleptic Ir(4-Me-dfpypy), as the blue dopant was prepared and their electroluminescence was investigated. Ir(4-Me-dfpypy)3 exhibited the blue emission of CIE coordinates (0.22, 0.32).

Ladder polysilsesquioxane for wide-band semiconductors: synthesis, optical properties and doped electrophosphorescent device

A ladder polysilsesquioxane with side chain 3-methyl-1,5-diphenylbenzene groups (Tp-LPSQ) is synthesized successfully and confirmed by the MALDI-TOF MS, 29Si-NMR and 1H-NMR. DSC, TGA, AFM and PL spectra reveal its good film-forming property, high thermal and morphological stability and good miscibility to the dopant FIrpic. In addition, it also shows a high triplet energy and a wide bandgap. Thus Tp-LPSQ may act as a host for the blue light emitting iridium complex FIrpic. The electrophosphorescent device based on Tp-LPSQ as the active layer exhibits typical blue emission and the performance of device is superior to other reported polymeric host materials.

Novel solid state emitting iridium complexes with reduced phosphorescence-self-quenching triggered by steric blocking phosphine ligands

In this paper, we report two easily-synthesized Ir(III) complexes equipped with steric blocking phosphine ligands of bis(2-(diphenylphosphanyl)phenyl) (POP) and triphenylphosphane (PPh3), Ir–POP and Ir–PPh3. Their crystal structures, electronic nature, photophysical properties, and phosphorescence self-quenching mechanism are discussed in detail. It is found that the thermally activated intermolecular interaction is responsible for the phosphorescence self-quenching. The introduction of steric blocking ligands into Ir(III) complexes can efficiently suppress the phosphorescence self-quenching in solid state. We successfully realize a solid state emission peaking at 494nm, with a long excited state lifetime of 15μs and a high photoluminescence quantum yield of 0.17.

Phosphorescent Light–Emitting Iridium Complexes Serve as a Hypoxia-Sensing Probe for Tumor Imaging in Living Animals

Iridium complex is a promising organic light-emitting diode material for next generation video displays that emits phosphorescence quenched by oxygen. We used this oxygen-quenching feature for imaging tumor hypoxia. Red light-emitting Ir(btp)(2)(acac) (BTP) presented hypoxia-dependent light emission in culture cell lines, whose intensity was in parallel with hypoxia-inducible factor-1alpha images. BTP was further applied to imaging five nude mouse transplanted with tumors. All tumors presented a bright BTP-emitting image even 5 minutes after injection. The minimal image recognition size was approximately 2 mm in diameter. By morphologic examination and phosphorescence lifetime measurement, BTP appeared to localize to the tumor cells. Because BTP is easily modifiable, we synthesized BTP analogues with a longer excitation/emission wavelength. One of them, BTPHSA, depicted clear imaging from tumors transplanted 6 to 7 mm deep from the skin surface. We suggest that iridium complex materials have a vast potential for imaging hypoxic lesions such as tumor tissues.

The Blue Phosphorescent Iridium Complexes Containing New Triazole Ligands for OLEDs

For the application to organic light-emitting diodes (OLEDs), the blue light emitting iridium complexes containing a new triazole (trzl) ancillary ligand were prepared and their photophysical properties was studied with respect to substituent effect at the 5-position of the triazole in the complexes. As substituents, electron donating groups, CMe3 and CH2OMe were introduced to the triazole ligand of the complex to investigate the electronic effect on their chromacity and efficiency. The absorption patterns of the iridium complexes, Ir(F2-ppy)2(trzl-CMe3) and Ir(F2-ppy)2(trzl-CH2OMe) prepared in this study were very similar. Their PL spectra exhibited the blue emission at 464 and 462 nm with the shoulder at 490 nm, respectively. Previously reported Ir(F2-ppy)2(trzl-Me) showed almost identical emission maxima at 461 nm with a shoulder at 492 nm. Such similar emission patterns of these complexes indicate that the ancillary ligands, derivatives of triazole, did not make significant influence on chromaticity of their iridium complexes.

Theoretical studies of the spectroscopic properties of blue emitting iridium complexes

Electronic structures, absorptions and emissions of a series of (ppy)2Ir(acac) derivatives (ppy = 2- phenylpyridine; acac = acetoylacetonate) with fluoro substituent on ppy ligands were investigated theoretically. The ground and excited states geometries were fully optimized at B3LYP/LANL2DZ and CIS/LANL2DZ level, respectively. The HOMO is composed of d(Ir) and π(C∧N), while the LUMO is localized on C∧N ligand. The absorptions and emissions in CH2Cl2 media were calculated under the TD–DFT level with PCM model. The lowest-lying absorption of these complexes is dominantly attributed to metal-to-ligand and intraligand charge transfer (MLCT/ILCT) transitions and the emission of them originates from 3MLCT/3ILCT excited states. The absorption and emission of these complexes are blue-shifted by increasing the number of fluoro on phenyl, but the spectra are red-shifted by adding fluoro on pyridyl. While a single fluoro of different substituted site on phenyl results in different extent blue-shift to the spectra.

Synthesis and electroluminescent properties of Ir complexes with benzo[c]acridine or 5,6-dihydro-benzo[c]acridine ligands

Two red emitting iridium complexes (DBA) 2Ir(acac) and (BA) 2Ir(acac) (DBA = 5,6-dihydro-benzo[c]acridine, BA = benzo[c]acridine, acac = acetylacetone) were synthesized. Organic light-emitting devices using these complexes as dopant emitters have been fabricated. The results showed that these complexes have strong phosphorescent characters and the devices emit pure red light. The maximum brightness of the device based on (DBA) 2Ir(acac) is 9540 cd/m 2 with an external quantum efficiency of 4.66%.

Blue emitting iridium complexes: synthesis, photophysics and phosphorescent devices

Homoleptic Ir(Fnppy)3 and heteroleptic (Fnppy)2Ir(acac) complexes (n = 3: F3ppy = 2-(3′,4′,6′-trifluorophenyl)pyridine; n = 4: F4ppy = 2-(3′,4′,5′,6′-tetrafluorophenyl)pyridine; acac = acetylacetonate) have been synthesized and their spectroscopic properties investigated. The homoleptic complexes exist as two stereoisomers, facial (fac) and meridional (mer), that have been isolated and fully characterized. Their electrochemical and photophysical properties have been studied both in solution and in the solid state and electroluminescent devices have been fabricated. The emissive layers in devices have been obtained mixing the iridium complexes with a PVK [poly(9-vinylcarbazole)] host matrix, in the presence of the electron carrier Bu-PBD [2-(4-biphenylyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole]. The application of a voltage (5.0–6.5 V) between the electrodes of devices leads to electro-generated blue luminescence which has similar energy to the solution emissions. Interestingly, the stability of the devices made with the homoleptic fluorinated iridium complexes strongly depends on the stereochemistry of these phosphors and high (up to 5.5%) external quantum efficiencies for the fac complexes are measured.