Phosphorescent Ir Research Articles

Phosphorescent iridium (III) complex with covalent organic frameworks as scaffolds for highly selective and sensitive detection of homocysteine.

Introduction: Developing a convenient and cost-effective platform for detecting homocysteine (Hcy) is of great interest as Hcy has been found to be a biomarker for Alzheimer's disease, gastric cancer, and other diseases. Methods: In this study, we synthesized five phosphorescent Ir(C∧N)2(N∧N)+ compounds (Irn, n = 1-5) with various substituents (-CHO or -CHO/-NH2), which were then doped into a covalent organic framework (COF) host via covalent bonding. Results and Discussion: The resulting optimal composites (denoted as Ir4/5@EBCOF) with -CHO/-NH2 substituents not only overcame the self-quenching issue of the bare Ir4/5 complexes but also showed rapid, highly selective, and sensitive detection of Hcy, with a limit of detection (LOD) of 0.23μM and reaction time of 88s. The sensing mechanism was revealed as the unique cyclization reaction between Ir(III) and Hcy that forms a six-membered ring. During the process, the color changes in the composites can be observed visually. It is expected that these phosphorescent Iridium (III) complexes with COFs will have the potential to serve as promising platforms for detecting thiols.

A Steric Interlocked Phosphorescent Iridium(III) Complex Toward Ultrapure Green Electroluminescence

AbstractThe development of phosphorescent materials with ultrapure emission is of great significance for wide‐color‐gamut organic light‐emitting diodes (OLEDs). Herein, a ligand steric interlocking strategy is introduced to achieve the narrowband emission of phosphorescent Ir(III) complexes. The steric interlocking effect contributed by the short distance between ligands leads to enhanced rigidity, and suppresses the high‐frequency vibrations of oICz‐Ir. In this context, oICz‐Ir exhibits an ultrapure green phosphorescence with a small full width at half maximum (FWHM) of 23 nm peaking at 521 nm in solution. Furthermore, the oICz‐Ir‐based OLED achieves a maximum external quantum efficiency (EQEmax) of 18.9%, an excellent color purity with Commission Internationale de L'Eclairage coordinate y (CIEy) of 0.69, making it the purest green bottom‐emitting phosphorescent OLEDs. Meanwhile, with oICz‐Ir as the sensitizer, a phosphorescence sensitized fluorescent OLED shows an excellent EQEmax of 31.1% with the CIEy of 0.7.

Influential effect of C^N ligands containing O, S, and Se heteroatoms in the color tuning of four phosphorescent Ir(III) complexes

AbstractA group of new iridium(III) complexes were rationally designed and synthesized with 2‐phenylbenzo[d]oxazole (bo), 2‐phenylbenzo[d]thiazole (bt), 2‐(thiophen‐2‐yl)benzo[d]thiazole (thbt), and 2‐(selenophen‐2‐yl)benzo[d]thiazole (sebt) as C^N ligands and bis(diphenylthiophosphoryl)amide (S‐tpip) as ancillary ligand. They are phosphorescent in a wide region of green to red with short lifetimes around 0.31–0.98 μs and quantum yields up to 64.7%. The detailed photophysical properties were investigated by experiment and further supported by density functional theory (DFT) calculation. These research results show that the spectroscopic properties are tuned by the replacement between oxygen, sulfur, and selenium or the change in aromatic ring. It has been demonstrated that the lowest energy‐level absorption and emission are dominated apparently by C^N ligands, and are ascribed to metal‐to‐ligand charge transfer (MLCT) and intra‐ligand charge transfer (ILCT) characters.

Theoretical study on a series of iridium(III) complexes with low-efficiency roll-off properties for application in OLEDs

To find a series of suitable materials for phosphorescent organic light-emitting diodes (OLEDs), in this paper, we design six phosphorescent Ir(III) complexes that have low-efficiency roll-off properties. Density functional theory (DFT) and time-dependent density functional theory (TD-DFT) were used to study the properties of (1-methyl-3-phenyl-2H-1λ^4,3λ^4-benzodiazole [dfbmb])2Ir(acetylacetonate [acac]), (dfbmb)2Ir(picolinate [pic]), (dfbmb)2Ir((Z)-5-tert-butyl-N'-(trifluoroethanimidoyl)pyridine-2-carboximidamide [tptz]), (1-(4-fluorophenyl)-3-methyl-2H-1λ^4,3λ^4-benzodiazole [F-dfbmb])2Ir(acac), (F-dfbmb)2Ir(pic), and (F-dfbmb)2Ir(tptz). Here, the main ligands are dfbmb and F-dfbmb, while the auxiliary ligands are acac, pic, and tptz. The advantages of these complexes were analyzed in terms of electronic structure, frontier molecular orbital (FMO) properties, spectral properties, electron affinities, ionization potentials, and OLED display effect. We hope that our research will contribute to the development of the OLED industry.

Unsymmetric Phosphorescent Ir(III) Complexes with Ambipolar Features and Investigation for Both Aggregation-Induced Phosphorescent Emission and Electroluminescent Properties

Unsymmetric Phosphorescent Ir(III) Complexes with Ambipolar Features and Investigation for Both Aggregation-Induced Phosphorescent Emission and Electroluminescent Properties

Theoretical study of blue‐green iridium(III) complexes with low‐efficiency roll‐off properties for application in phosphorescent organic light‐emitting diodes

To find an array of suitable materials for phosphorescent organic light‐emitting diodes (OLEDs), in this paper, we design six blue‐green phosphorescent Ir (III) complexes that have low‐efficiency roll‐off properties. Density functional theory and time‐dependent density functional theory were used to study the properties of (2‐[4‐phenoxyphenyl]pyridine [oppy])2Ir(acetylacetonate [acac]), (oppy)2Ir(picolinate [pic]), (oppy)2Ir(tetraphenylimido‐diphosphinate [tpip]), (5‐fluoro‐2‐(4‐phenoxyphenyl)pyridine [F‐oppy])2Ir(acac), (F‐oppy)2Ir(pic), and (F‐oppy)2Ir(tpip). Here, the main ligands are oppy and F‐oppy, while the auxiliary ligands are acac, pic, and tpip. The advantages of these complexes were analyzed in terms of electronic structure, frontier molecular orbital properties, spectral properties, and OLED display effect. We hope that our research will contribute to the development of the OLED industry.

Narrowband Pure Near-Infrared (NIR) Ir(III) Complexes for Solution-Processed Organic Light-Emitting Diode (OLED) with External Quantum Efficiency Over 16 .

Highly efficient near-infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light-emitting diode (OLED) fabricated by the solution-processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution-processed NIR-OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR-emitters.

Narrowband Pure Near‐Infrared (NIR) Ir(III) Complexes for Solution‐Processed Organic Light‐Emitting Diode (OLED) with External Quantum Efficiency Over 16 %

AbstractHighly efficient near‐infrared (NIR) emitters have significant applications in medical and optoelectronic fields, but the development stays a great challenge due to the energy gap law. Here, we report two NIR phosphorescent Ir(III) complexes which display emission peaks around 730 nm with a narrow full width at half maximum of only 43 nm. Therefore, pure NIR luminescence can be obtained without having a very long emission wavelength, thus alleviating the restriction of the energy gap law, and obtaining impressively high photoluminescence quantum yield up to 0.70. More importantly, the pure NIR organic light‐emitting diode (OLED) fabricated by the solution‐processed mothed shows outstanding device performance with the highest external quantum efficiency of 16.43 %, which sets a new record for solution‐processed NIR‐OLEDs based on different emitters. This work sheds light on the development of Ir(III) complexes with narrowband emissions as highly efficient pure NIR‐emitters.

Turning the energy channel of side-chain TADF polymers by monomer optimization for high-efficiency solution-processed white OLEDs

Suppressing non-radiative channel in luminescent polymer is the key factor for high device efficiency of organic light-emitting diodes (OLEDs). In this paper, we synthesized three side-chain TADF polymers, PTRZ-TRZ, PTRZ-TPA and PTRZ-Cz, to deeply investigate the relationship between energy transfer and molecular structure. The photophysical measurements show that the copolymerized monomer has significant effect on the exciton deexcitation process of TADF fragment. The rigid carbazole unit can efficiently separate the TADF units to inhibit the aggregation-caused quenching (ACQ) of polymer, while electron-donating triphenylamine unit will induce the severe charge transfer state to form low energy exciplex, which lead to severe energy leakage of the excited TADF. Moreover, according to the single-charge devices test, the ideal separation unit also can improve the capability of charge injection and carrier balance. As a result, the solution-processed OLEDs host with PTRZ-Cz achieved the external quantum efficiency (EQEmax) of 14.2%, which was much higher than that of PTRZ-TPA and PTRZ-TRZ. By doping red phosphorescent emitter Ir(MDQ)2(acac), the hybrid white OLED devices (T-P WOLEDs) based on PTRZ-Cz achieved the maximum current efficiency (CEmax), power efficiency (PEmax) and EQEmax of 46.8 cd/A, 32.6 lm/W and 20.7%, respectively, with a high CRI of 80.6. The outcomes obtained in this study can provide useful insights into the structure−property relationship for further development of efficient TADF polymer hosts for solution-processable OLEDs.

73‐4: The Value and Benefit of Multiscale Material Simulation for OLED R&D: Prediction and Validation of Triplet Emitter Orientation Yielding > 90% In‐plane Transition Dipole Orientation for Ir(ppy)3 Derivatives

In order to fulfill the demand for ever‐improving OLED panel properties, material design has to adapt quickly. We propose multiscale material simulations as a tool to elucidate structure‐property relations guiding us towards materials with desired properties. As an example, we present benchmarking and application of a simulation workflow for triplet emitter optical orientation validated by experiment. Using this we were able to improve the isotropic optical orientation of the phosphorescent triplet emitter Ir(ppy)3 to unprecedented orientation parameters o<0.1. This means that >90% of the emitter transition dipoles can be in the substrate plane, allowing for better outcoupling and thus higher external quantum efficiency. Such a high degree of orientation realized by help of material simulation is a remarkable result for octahedral (non‐planar) complexes based on Ir(ppy)3.

Bifunctional Bicarbazole-Benzophenone-Based Twisted Donor-Acceptor-Donor Derivatives for Deep-Blue and Green OLEDs.

Organic light-emitting diodes (OLEDs) have played a vital role in showing tremendous technological advancements for a better lifestyle, due to their display and lighting technologies in smartphones, tablets, television, and automotive industries. Undoubtedly, OLED is a mainstream technology and, inspired by its advancements, we have designed and synthesized the bicarbazole-benzophenone-based twisted donor-acceptor-donor (D-A-D) derivatives, namely DB13, DB24, DB34, and DB43, as bi-functional materials. These materials possess high decomposition temperatures (>360 °C) and glass transition temperatures (~125 °C), a high photoluminescence quantum yield (>60%), wide bandgap (>3.2 eV), and short decay time. Owing to their properties, the materials were utilized as blue emitters as well as host materials for deep-blue and green OLEDs, respectively. In terms of the blue OLEDs, the emitter DB13-based device outperformed others by showing a maximum EQE of 4.0%, which is close to the theoretical limit of fluorescent materials for a deep-blue emission (CIEy = 0.09). The same material also displayed a maximum power efficacy of 45 lm/W as a host material doped with a phosphorescent emitter Ir(ppy)3. Furthermore, the materials were also utilized as hosts with a TADF green emitter (4CzIPN) and the device based on DB34 displayed a maximum EQE of 11%, which may be attributed to the high quantum yield (69%) of the host DB34. Therefore, the bi-functional materials that are easily synthesized, economical, and possess excellent characteristics are expected to be useful in various cost-effective and high-performance OLED applications, especially in displays.

Finely-tuned heteroleptic phosphorescent Ir(III) complexes for CIEy < 0.2-based pure blue organic light-emitting diodes with external quantum efficiencies > 30%

Three pure blue phosphorescent Ir (III) complexes F5OFpt, F5MFpt and F5SiFpt with the amazing CIEy coordinate value<0.2 have been obtained by introducing different electron-donating groups (-OMe, -Me and -TMS) into the corresponding C^N ligands. Based on a well matched mixed host combination of mCBP and TSPO1, all the emitting systems achieve quite high maximum EQE > 30% with low efficiency roll-off and ideal blue color with the CIEy < 0.2.

Extending Anisotropy Dynamics of Light‐Emitting Dipoles as Necessary Condition Toward Developing Highly‐Efficient OLEDs

AbstractDesigning in‐plane‐oriented light‐emitting dipoles is known as a critical method to develop high‐efficiency organic light‐emitting diodes (OLEDs) by enhancing light extraction. However, in‐plane‐oriented light‐emitting dipoles must demonstrate sufficient polarization memory extended into light emission lifetime window, generating extended anisotropy dynamics shown as the necessary condition to increase light extraction toward developing high‐efficiency OLEDs. This paper reports experimental studies on anisotropy dynamics of light‐emitting dipoles in both time and energy domains by using time‐resolved and steady‐state photoluminescence anisotropy measurements based on the in‐plane oriented exciplex‐heterostructured [BCzPh:CN‐T2T] host dispersed with phosphorescent molecules. It is found that, when host–guest Coulomb scattering is suppressed by parallel placing of the in‐plane‐configured phosphorescent Ir(ppy)2(acac) molecules into the in‐plane‐oriented exciplex‐heterostructured [BCzPh:CN‐T2T] host, the anisotropy dynamics of light‐emitting dipoles can be extended into microseconds time window comparable with its phosphorescence lifetime, satisfying the necessary condition in time domain to increase light out‐coupling efficiency toward developing high external quantum efficiencies (EQEs) in Ir(ppy)2(acac):exciplex system. More importantly, by suppressing host–guest Coulomb scattering, the high‐energy transition dipoles can still maintain extended anisotropy dynamics in the energy domain in Ir(ppy)2(acac):exciplex system while hot electrons are relaxing toward lowest unoccupied molecular orbital (LUMO). Consequently, the extended anisotropy dynamics of light‐emitting dipoles demonstrate a high EQE of 34.01% in the Ir(ppy)2(acac):exciplex OLED.

In Vivo Imaging of Lipid Droplets and Oxygen Status in Hepatic Tissues of Nonalcoholic Fatty Liver Model Mice Using a Lipophilic Ir(III) Complex

Nonalcoholic fatty liver disease (NAFLD) is becoming common worldwide. In pathophysiological studies of NAFLD, an in vivo optical probe that enables visualization of lipid droplets (LDs) and imaging of oxygen status in hepatic tissues simultaneously would be very useful. Here, we present the phosphorescent Ir(III) complex BTP ((btp)2Ir(acac) (btp = benzothienylpyridine, acac = acetylacetone)) as the first probe that meets this requirement. BTP was efficiently taken up into cultured 3T3-L1 adipocytes and selectively accumulated into LDs. Quantifying oxygen levels in LDs based on the phosphorescence lifetime of BTP allowed us to track changes in cellular oxygen tension after treatment with metabolic stimulants. Phosphorescence lifetime imaging microscopy combined with intravenously administered BTP in mice enabled specific visualization of LDs in hepatic lobules and simultaneous imaging of the oxygen gradient that decreased from the portal vein (PV) to the central vein (CV). NAFL model mice were created by feeding a high-fat diet (HFD) to mice for 3 or 7 days. The mice fed an HFD showed a marked increase in the amount and size of LDs in hepatocytes compared with those fed a normal diet, leading to abnormal microvascular structures. In addition, HFD-fed mice also exhibited reduced oxygen tension in areas other than the CV. Multicolor imaging with the LD-accumulated oxygen probe BTP and vasculature-staining FITC-lectin suggested that structural distortions of the sinusoidal microvasculature caused by enlarged LDs were associated with partial hypoxia in NAFL.

2-Phenylpyridine-based phosphorescent Ir(III) complexes for highly efficient greenish-blue organic light-emitting diodes with EQEs up to 33.5%

A group of heteroleptic cyclometalated iridium complexes Ir1–Ir4 were designed with 2-phenylpyridine (ppy) derivatives as cyclometalating ligands and 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridine (fppz) or 2-(5-(4-(trifluoromethyl)phenyl)-2H-1,2,4-triazol-3-yl)pyridine (Htaz) as ancillary ligands. The incorporation of electro-donating group into ppy ligands to elevate ligands-centered 3π-π* energy level and utilization of fppz or Htaz ancillary ligands combined to tune the intrinsic electronic properties. These complexes showed greenish-blue or green phosphorescence and are characterized by high photoluminescence quantum yields of up to 70% and short lifetimes below 1 μs. The organic light-emitting diodes (OLEDs) with Ir1–Ir4 as doped emitters all exhibited high efficiencies with low efficiency roll-off. Particularly, the Ir3 device exhibited distinguished performances with the maximum current efficiency of 86.9 cd A−1 and an external quantum efficiency (EQE) of 33.5%. Even at high brightness of 1000 cd m−2, the EQE still remained at 24.6%. Evidently the EQE of 33.5% of Ir3 device is one of the highest efficiencies ever reported for greenish-blue phosphorescence OLEDs.

Theoretical study on a series of Blue-Green Ir(III) complexes used in OLED

Here six phosphorescent heteroleptic cyclometalated Ir (III) complexes were theoretically designed to identify some suitable OLED materials. (fppzb)2Ir(acac), (fppzb)2Ir(tpip), (dfbdp)2Ir(fppzb), (F-fppzb)2Ir(acac), (F-fppzb)2Ir(tpip), and (dfbdp)2Ir(F-fppzb) were studied via density functional theory (DFT) and time-dependent density functional theory (TD-DFT) methods. Here, acac denotes acetylacetonate, tpip denotes tetraphenylimido-diphosphinate, fppzb denotes 4-tert-butyl-2-(5-(trifluoromethyl)-4H-pyrazol-3-yl) pyridine and F-fppzb denotes 4-tert-butyl-2-(5-fluoro-4H-pyrazol-3-yl) pyridine. Further, we discuss the value of these materials from the electronic structure, spectral properties, ionisation potentials, electron affinities, and application prospects of the complexes. We hope that these light-emitting materials contribute to the OLED sector. This theoretical study included the energy transfer mechanism of the complexes with acac and tpip substituents as auxiliary ligands: We analyzed the possibilities and inevitability of the results in the experiments as well as evaluated the underlying mechanism for these materials’ low-efficiency roll-off.

A theoretical study on blue‐green phosphorescent iridium (III) complexes with low‐efficiency roll‐off properties

AbstractHere, eight phosphorescent heteroleptic cyclometalated Ir (III) complexes were theoretically designed to identify some suitable organic light‐emitting diode materials. (F2‐PYBPY)2Ir (acac) (marked 1), (F2‐PYBPY)2Ir (tpip) (marked 2), (PYBPY)2Ir (acac) (marked 3), (PYBPY)2Ir (tpip) (marked 4), (F2‐PYPY)2Ir (acac) (marked 5), (F2‐PYPY)2Ir (tpip) (marked 6), (PYPY)2Ir (acac) (marked 7), and (PYPY)2Ir (tpip) (marked 8) were studied via density functional theory (DFT) and time‐dependent density functional theory (TD‐DFT) methods. Here, acac denotes acetylacetonate, tpip denotes tetraphenylimido‐diphosphinate, F2‐PYBPY denotes 3‐(4‐tert‐butylpyridin‐2‐yl)‐2,6‐difluoropyridine, PYBPY denotes 4‐tert‐butyl‐2‐(pyridin‐3‐yl) pyridine, F2‐PYPY denotes 2,6‐difluoro‐3‐(pyridin‐2‐yl) pyridine, and PYPY denotes 2‐(pyridin‐3‐yl) pyridine. Further, we discuss the value of these materials from the electronic structure, spectral properties, ionization potentials, electron affinities, and application prospects of the complexes. We hope that these light‐emitting materials contribute to the organic light‐emitting diode sector. This theoretical study included the energy transfer mechanism of the complexes with acac and tpip substituents as auxiliary ligands: We analyzed the possibilities and inevitability of the results in the experiments as well as evaluated the underlying mechanism for these materials' low‐efficiency roll‐off.

Comprehensive investigation of triplet states of red phosphorescent cationic Ir(III) complexes from cryogenic temperature

Comprehensive investigation of triplet states of red phosphorescent cationic Ir(III) complexes from cryogenic temperature

9-Phenyl-9-phosphafluorene oxide based organic ligands synthesized via successive SNAr reactions and their symmetric phosphorescent Ir(III) complexes for highly efficient solution-processed OLEDs

Three organic ligands with 9-phenyl-9-phosphafluorene oxide (PhFlPO) group have been synthesized via successive nucleophilic aromatic substitution (SNAr) reactions between dibenzothiophene dioxides and PhPH2-KOH under mild reaction conditions at room temperature. In this way, the novel PhFlPO-type organic ligands can be easily obtained without either highly sensitive Grignard or organolithium reagents of noble metal catalysts. Using these PhFlPO-type organic ligands, cyclometalated Ir(III) phosphorescent complexes with PhFlPO groups have been developed through well-accepted two-step strategy. To the best of our knowledge, these complexes represent the unprecedented examples of symmetric cyclometalated Ir(III) phosphorescent complexes bearing PhFlPO group. It has been found that electron-density on the coordinated carbon atom in the PhFlPO unit can exert a significant influence on the metal-to-ligand charge transfer transition (MLCT) processes and phosphorescent emission behavior of these cyclometalated Ir(III) phosphorescent complexes. In addition, the electroluminescent potential of these new cyclometalated Ir(III) phosphorescent complexes with PhFlPO groups has been characterized in solution-processed organic light-emitting diodes (OLEDs). They can show very impressively high external quantum efficiency (ηext), current efficiency (ηL) and power efficiency (ηP) of 20.0%, 71.7 cd A−1 and 56.1 lm W−1, respectively. These encouraging research results can furnish critical information for developing new PhFlPO-based Ir(III) phosphorescent emitters.

Robust sky-blue aggregation-induced delayed fluorescence materials for high-performance top-emitting OLEDs and single emissive layer white OLEDs

The development of blue luminescent materials plays a crucial role in the industry of organic light-emitting diodes (OLEDs). Herein, two sky-blue luminescent materials (mCP-BP-DMAC and DCB-BP-DMAC) comprised of electron donors of 9-(3-(9H-carbazol-9-yl)phenyl, 9-(4-(9H-carbazol-9-yl)phenyl and 9,9-dimethyl-9,10-dihydroacridine and electron acceptor of benzoyl are synthesized and characterized. They exhibit excellent thermal and electrochemical stabilities, strong aggregation-induced delayed fluorescence and bipolar carrier transport ability, and behavior efficiently in nondoped and doped bottom-emitting OLEDs with high external quantum efficiencies (ηexts) of up to 26.6% and small efficiency roll-offs. Efficient top-emitting OLEDs employing mCP-BP-DMAC and DCB-BP-DMAC as emitters are also achieved, providing sky-blue lights with high color purity and impressive ηexts over 30%. In addition, hybrid white OLEDs with stable emission color and high color rendering index are fabricated based on a single emissive layer consisting of orange-red phosphorescent Ir(MDQ)2acac dopant and sky-blue mCP-BP-DMAC and DCB-BP-DMAC hosts, furnishing excellent ηexts of up to 24.1% and small efficiency roll-offs. These results demonstrate mCP-BP-DMAC and DCB-BP-DMAC are outstanding luminescent and host materials with great application potentials in display and lighting devices.