Series Of Ir Research Articles

Purinylidene‐Based Iridium(III) Phosphors for Efficient Purple Phosphorescence and Organic Light‐Emitting Devices

It is very challenging to achieve highly efficient and low roll‐off purple to deep‐blue organic light‐emitting diodes (OLEDs) due to the limited selection of suitable emitters. Herein, a series of Ir(III) phosphors‐bearing purinylidene‐based N‐heterocyclic carbene (NHC) chelates are reported, namely, f‐ct2a–d, which have successfully turned the emission peak maxima to the purple region (427–432 nm) in degassed toluene, together with high quantum yields of 77%–81%. Notably, f‐ct2b is further employed as the phosphorescent dopant in the fabrication of OLEDs to afford deep‐blue emission paking at 448 nm and an EQE of 6.7% at 100 cd m−2. Furthermore, a true‐blue hyperphosphorescent OLED with 21 wt% of f‐ct2a as sensitizer and 1 wt% of ν‐DABNA as terminal emitter is also fabricated, giving excellent performance with max. EQE up to 22.2% and an EQE of 19.2% at a brightness of 100 cd m−2.

Identification of Crucial Photosensitizing Factors to Promote CO2 -to-CO Conversion.

The sensitizing ability of a catalytic system is closely related to the visible-light absorption ability, excited-state lifetime, redox potential, and electron-transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)-based PSs (Ir-1-Ir-6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible-light absorption capacity results in lower CO yields of Ir-1, Ir-2 or Ir-4. Ir-3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir-3 is ≈10 times higher than that of Ir-5, the CO yield of Ir-3 is slightly higher than that of Ir-5 due to the compensation of Ir-5's strong visible-light-absorbing ability. Ir-6 exhibits excellent photocatalytic performance due to the strong visible-light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir-6 can achieve 91.5 μmol, over 54 times higher than Ir-1, and the optimized TONC-1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction.

Identification of Crucial Photosensitizing Factors to Promote CO2‐to‐CO Conversion

AbstractThe sensitizing ability of a catalytic system is closely related to the visible‐light absorption ability, excited‐state lifetime, redox potential, and electron‐transfer rate of photosensitizers (PSs), however it remains a great challenge to concurrently mediate these factors to boost CO2 photoreduction. Herein, a series of Ir(III)‐based PSs (Ir‐1–Ir‐6) were prepared as molecular platforms to understand the interplay of these factors and identify the primary factors for efficient CO2 photoreduction. Among them, less efficient visible‐light absorption capacity results in lower CO yields of Ir‐1, Ir‐2 or Ir‐4. Ir‐3 shows the most efficient photocatalytic activity among these mononuclear PSs due to some comprehensive parameters. Although the Kobs of Ir‐3 is ≈10 times higher than that of Ir‐5, the CO yield of Ir‐3 is slightly higher than that of Ir‐5 due to the compensation of Ir‐5’s strong visible‐light‐absorbing ability. Ir‐6 exhibits excellent photocatalytic performance due to the strong visible‐light absorption ability, comparable thermodynamic driving force, and electron transfer rate among these PSs. Remarkably, the CO2 photoreduction to CO with Ir‐6 can achieve 91.5 μmol, over 54 times higher than Ir‐1, and the optimized TONC‐1 can reach up to 28160. Various photophysical properties of the PSs were concurrently adjusted by fine ligand modification to promote CO2 photoreduction.

Iridium(III) complexes conjugated with naproxen exhibit potent anti-tumor activities by inducing mitochondrial damage, modulating inflammation, and enhancing immunity.

A series of Ir(III)-naproxen (NPX) conjugates with the molecular formula [Ir(C^N)2bpy(4-CH2ONPX-4'-CH2ONPX)](PF6) (Ir-NPX-1-3) were designed and synthesized, including C^N = 2-phenylpyridine (ppy, Ir-NPX-1), 2-(2-thienyl)pyridine (thpy, Ir-NPX-2) and 2-(2,4-difluorophenyl)pyridine (dfppy, Ir-NPX-3). Cytotoxicity tests showed that Ir-NPX-1-3 exhibited excellent antitumor activity, especially in A549R cells. The cellular uptake experiment showed that the complexes were mainly localized in mitochondria, and induced apoptosis in A549R cells by damaging the structure and function of mitochondria. The main manifestations are a decrease in the mitochondrial membrane potential (MMP), an increase in reactive oxygen species (ROS) levels, and cell cycle arrest. Furthermore, Ir-NPX-1-3 could inhibit the migration and colony formation of cancer cells, demonstrating potential anti-metastatic ability. Finally, the anti-inflammatory and immunological applications of Ir-NPX-1-3 were verified. The downregulation of cyclooxygenase-2 (COX-2) and programmed death-ligand 1 (PD-L1) expression levels and the release of immunogenic cell death (ICD) related signaling molecules such as damage-associated molecular patterns (DAMPs) (cell surface calreticulin (CRT), high mobility group box 1 (HMGB1), and adenosine triphosphate (ATP)) indicate that these Ir(III) -NPX conjugates are novel ICD inducers with synergistic effects in multiple anti-tumor pathways.

Blue Electrophosphorescence from Iridium(III) Phosphors Bearing Asymmetric Di-N-aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene Chelates.

Efficient blue phosphors remain a formidable challenge for organic light-emitting diodes (OLEDs). To circumvent this obstacle, a series of Ir(III)-based carbene complexes bearing asymmetric di-N-aryl 6-(trifluoromethyl)-2H-imidazo[4,5-b]pyridin-2-ylidene chelates, namely, f-ct6a‒c, are synthesized, and their structures and photophysical properties are comprehensively investigated. Moreover, these emitters can undergo interconversion in refluxing 1,2,4-trichlorobenzene, catalyzed by a mixture of sodium acetate (NaOAc) and p-toluenesulfonic acid monohydrate (TsOH·H2O) without decomposition. All Ir(III) complexes present good photoluminescence quantum yield (ΦPL = 83-88%) with peak maximum (max.) at 443-452nm and narrowed full width at half maximum (FWHM = 66-73nm). Among all the fabricated OLED devices, f-ct6b delivers a max. external quantum efficiency (EQE) of 23.4% and Commission Internationale de L'Eclairage CIEx , y coordinates of (0.14, 0.12), whereas the hyper-OLED device based on f-ct6a and 5H,9H,11H,15H-[1,4] benzazaborino [2,3,4-kl][1,4]benzazaborino[4',3',2':4,5][1,4]benzazaborino[3,2-b]phenazaborine-7,13-diamine, N7,N7,N13,N13,5,9,11,15-octaphenyl (ν-DABNA) exhibits max. EQE of 26.2% and CIEx , y of (0.12, 0.13). Finally, the corresponding tandem OLED with f-ct6b as dopant gives a max. luminance of over 10000 cd m-2 and max. EQE of 42.1%, confirming their candidacies for making true-blue OLEDs.

2-Arylbenzo[d]xazolyl based iridium(III) complexes as highly efficient photoredox catalysts

The [Ir(C^N)2(N^N)]+ complexes are one of the most employed family of photocatalyst. The substituent effect of C^N ligand, specifically 2-arylbenzo[d]oxazole (pbo) and 2-arylbenzo[d]thiazole (pbt), on complexes was discussed in this work. For this purpose, a series of Ir(III) complexes (A1∼C9) with differently substituted pbo/pbt ligands were designed, synthesized and characterized. Crystal structures show that A2 and A6 have a C2-symmetric trans-configuration while B8 possesses C1-symmetric cis-isomeric structure. These complexes are highly photoluminescent with quantum yield up to 69% in dilute solution. The maximum emission wavelength span from 485 to 615 nm. The substituent electronic effects on the para-position of phenyl have the greatest impact on the fluorescence properties of the complexes. Electron withdrawing nitro group on the 4-site of phenyl make the greatest red shift in the emission spectra while fluorination leads to blue shifts. The electrochemical measurements were combined with fluorescence data to estimate the excited-state potentials (ESP) of these complexes. Both oxidative and reductive ESP are in a good range compared to the widely applied [Ir(dF(CF3)ppy)2dtbbpy]PF6, suggesting that they are high-potential in photoredox catalysis. The complexes A1∼C9 were further applied in the deoxygenation-addition synthesis of N-dimethyl-4-oxo-4-(p-tolyl)butanamide to test the catalytic activity. Excellent yields (up to 91%) were obtained with catalyst A2, A8 and B8. Substitution on substrates was also tolerated in a degree.

Phenanthroimidazole as molecularly engineered switch for efficient and highly long-lived light-emitting electrochemical cell

Light-emitting electrochemical cells (LECs) based on Ir(III) complexes owing to the superior advantages exhibit high potential for display and lighting applications. Herein, a series of Ir(III) complexes based on phenanthroimidazole (PI) as an ancillary ligand were synthesized to achieve efficient and highly stable yellow-to-orange LEC devices with fast response. These complexes exhibit appropriate electrochemical stability and significant suppression of concentration quenching in the thin films compared to the archetype complex. The fabricated LECs showed remarkably long device lifetimes over 1400 and 2100 h and external quantum efficiency of 2 and 3% for yellow and orange-LECs, respectively. The obtained t1/2 for yellow LEC is much higher than archetype [Ir(ppy)2(phen)]+ and their phenanthroline-based analogues reported so far. The incorporation of an ionic tethered functional group on PI, improved the mobility of the emissive layer and reduced the device turn-on time by 75–88%. This study shows a facile functionalization and characterization of the PI ligand as well as its potential application in optoelectronic devices (OLED).

Dynamics of Photoinduced Intramolecular and Intermolecular Electron Transfers in Ligand-Conjugated Ir(III)–Re(I) Photocatalysts

We report the electron transfer (ET) dynamics in a series of Ir(III)-Re(I) photocatalysts where two bipyridyl ligands of Ir and Re moieties are conjugated at the meta (m)- or para (p)-position of each side. Femtosecond transient absorption (TA) measurements identify the intramolecular ET (IET) dynamics from the Ir to Re moiety, followed by the formation of one-electron-reduced species (OERS) via the intermolecular ET with a sacrificial electron donor (SED). The IET rate depends on the bridging ligand (BL) structures (∼25 ps for BLmm/mp vs ∼68 ps for BLpm/pp), while the OERS formation happens on an even slower time scale (∼1.4 ns). Connecting the Re moiety at the meta-position of the bipyridyl of the Ir moiety can restrict the rotation around a covalent bond between two bipyridyl ligands by steric hindrances and facilitate the IET process. This highlights the importance of BL structures on the ET dynamics in photocatalysts.

Pyridine aldoxime ligation to iridium(III) centre: An innocent ancillary ligand in a series of organometallic complexes

A series of Ir(III) complexes (4)-(6) of formula [Ir(C^N)2(pyrald)] were designed and synthesised from the reaction of [(C^N)2Ir(μ-Cl)2Ir(C^N)2] and pyridine-2-aldoxime (pyrald) {C^N=1-phenylpyrazole (phpyr), 2,5-diphenylbenzoxazole (phox) and 2,3-diphenylquinoxaline (phquinox)}. All the complexes were purified on a neutral alumina oxide column and characterised through IR, 1H NMR, UV-Vis, emission spectroscopy, mass analysis and cyclic voltammetric studies. The molecular structure of [Ir(phquinox)2(pyrald)](6) was determined using single crystal X-ray data analysis, which presents an expected bidentate chelation of cyclometallating ligands (phquinox) against our previous report of an ortho CH bond activation in a coordinated cyclometallating ligand (7,8-benzoquinoline) mediated by pyridine-2-aldoxime. The characterisation data of complexes (4) and (5) are also in agreement with the unexceptional coordination behaviour of coordinating ligands. On TD-DFT calculations, all the complexes revealed the dominant ligand centred (LC) transitions and were reasoned for observed weak luminescence.

Investigating the Effect of Iridium Based Water Electrolysis Catalysts on the Performance and Durability of the Catalyst Layer in PEMFCs

Hydrogen-based polymer electrolyte fuel cells (PEMFCs), are becoming very popular, especially for automobile applications, given their high power density, high efficiency and zero emissions characteristics. However, they still face durability issues of the catalyst layer. Catalysts supported on carbon based materials show high electrochemically active surface area and performance [1] but are, at the same time, susceptible to carbon based degradation. To avoid carbon corrosion, it has recently become common strategy to include a water electrolysis catalyst like Ir or IrO2 to preferentially promote water electrolysis reaction since it is electrochemically more favourable than the harmful carbon corrosion reaction, thus improving the durability of the catalyst layer [2,3].In our group, a series of Ir(IrOx)-Pt/Vulcan catalysts (Fig. 1) were developed by varying Ir/Pt atomic ratio, 0.21 to 1.20. It was used on the cathode side, and the durability test simulating the stop/start cycle of FCVs was evaluated. Ir(IrOx)-Pt/Vulcan catalysts showed a slight decrease in the initial performance relative to Pt/Vulcan due to the presence of Ir, but there was a point after which a further increase in Iridium content did not noticeably affect the performance any longer. In contrast to the initial performance, post durability-test performance was expected to be higher for catalysts with higher Ir content, but our results showed the worst performance in the most Ir-rich catalyst after 10000 cycles. This was attributed to water electrolysis products trapped in small pores of the catalyst layer thereby affecting mass transport. We confirmed this by studying the various losses in each catalyst type, and found the highest concentration overvoltage in the Ir-rich catalyst. On repeating durability experiments for Ir-rich catalyst, but this time purging it with N2 gas overnight, results showed much higher performance relative to other samples for the same number of durability test cycles, supporting our hypothesis.We also consider water electrolysis catalysts on the anode side as well, since fuel starvation is commonly encountered in the anode under extreme operating conditions. Specifically, we explore Iridium-based corrosion tolerant anode catalysts and outline several strategies to reduce degradation at high humidity and loads where carbon corrosion becomes more preferable to water electrolysis. Our findings in understanding and addressing these durability issues could greatly aid in better catalyst design.

Development of Dual Phosphorescent Materials Based on Multiple Stimuli-Responsive Ir(III) Acyclic Carbene Complexes

A new series of Ir(III) carbene complexes with luminescent mechanochromism derived from trans–cis isomerization has been developed. Through the introduction of π-conjugating groups into the acyclic...

New design strategy for chemically-stable blue phosphorescent materials: improving the energy gap between the T1 and 3MC states.

A series of Ir- and Pt-based blue phosphorescent materials were theoretically investigated by means of density functional theory (DFT) calculations to improve their chemical stability in the excited state. High energy splitting between the lowest triplet state (T1 state), generally a metal-to-ligand charge transfer state (3MLCT), and the triplet metal-centred state (3MC) can prohibit ligand dissociation and suppress the decomposition reaction from the 3MC state to the dissociated S0. Here, we suggest a new design strategy to improve the chemical stability of blue phosphorescent materials in the excited state. Introducing inter- and intra-ligand interactions in Ir and Pt complexes can dramatically increase the ΔE(3MC-T1) because attractive or repulsive couplings arising from intra- or inter-ligand interactions can effectively prevent the out-of-plane bending vibrational mode in Ir complexes and the ring deformation vibrational mode in Pt complexes. A ΔE(3MC-T1) values of 18.62 kcal mol-1 for an Ir complex and 22.86 kcal mol-1 for a Pt complex from the T1 energy were obtained while the T1 energy was maintained in the blue region. To the best of our knowledge, these are the highest ΔE(3MC-T1) values reported to date. We believe that the present research provides profound insights into the excited state chemical stability of deep blue phosphorescent materials that could be implemented to improve device lifetimes.

New phosphorescent iridium(III) dipyrrinato complexes: synthesis, emission properties and their deep red to near-infrared OLEDs.

A series of heteroleptic Ir(iii) complexes composed of two cyclometalated C^N ligands and one dipyrrinato ligand used as an ancillary ligand are synthesized and characterized. With the introduction of a fluorine atom, phenyl ring or diphenylamino group into both C^N ligands and by keeping the ancillary ligand unchanged, these Ir(iii) dipyrrinato phosphors do not show an obvious shift in their emission bands. They exhibit emissions extending well into the near-infrared region with an intense band located at around 685 nm in both photo- and electroluminescence spectra, and the deep red to near-infrared organic light emitting diodes (OLEDs) based on them afforded a maximum external quantum efficiency of 2.8%. Density functional theory (DFT) calculations show that both the electronic contributions on the lowest unoccupied molecular orbitals (LUMOs) and the highest energy semi-occupied molecular orbitals (HSOMOs) are mainly localized on the dipyrrinato ligand, indicating that the ancillary ligand, which remains unchanged in this series, exhibits a lower triplet state energy in the iridium phosphors than those involving the C^N ligands. Therefore a switch from "(C^N)2Ir" to dipyrrinato ligand-based emission is observed in these iridium(iii) complexes.

New design of two series of Ir(Ⅲ) complexes by changing substitute group at main ligand or ancillary ligand from theoretical viewpoint

Using DFT/TDDFT methods to investigate the electronic structure, absorption and emission spectra, charge injection/transport ability and phosphorescence quantum efficiency of two series of Ir(Ⅲ) complexes. Complexes 1a–1c introduce F atom, acetyl group (–COCH3), 1-fluoro-4-methanesulfonyl-benzene group (–SO2PhF) to substitute methyl on benzene ring of mpmi main ligand (1-(4- tolyl)-3-methyl-imidazole) in complex 1, and complexes 2–4 introduce different ligands to substitute the dmpypz ancillary ligand (3,5-dimethyl-2-(1H-pyrazol-5-yl)pyridine) of complex 1, such as heppy ligand (4-(1-hydroxy-ethyl)-5-methyl-2-phenyl-3,4-dihydro-2H-pyrazol-3-ol), typy ligand (2-thiophen-2-yl-pyridine), quol ligand (quinolin-8-ol). The introduction of F atom, –COCH3 and –SO2PhF has the important effect on the photophysical properties of all studied complexes. Thereinto, introducing –COCH3 and –SO2PhF have great influence on the transition dipole moment from S0 to S1 state (μS1) and can improve electron transport property. Introducing different ancillary ligands can adjust emission wavelength effectively, has great influence on μS1, typy ligand and quol ligand can adjust hole/electron injection ability. Typy ancillary ligand could improve electron balance ability. Complexes 1–1c and 2 have larger HOMO–LUMO energy level, and they are potential blue materials. Complex 1c has better electron injection ability. Complexes 3 and 4 have the larger μS1, so they may have higher quantum efficiency.

Vegetation Area Monitoring Through NDVI Technique: A Case Study of Dengei Pahad Micro Watershed, Khurda District, Odisha

Watershed treatment includes implementation of participatory micro-watershed-based soil and moisture conservation programs and income generation through proper natural resource management areas. This has led to increased productivity and income. Training and holistic management along with aforestation programs has led to reduction of silt flow to the lake. The assessment revealed that land degradation in the drainage basin not only leads to enhanced silt flow into the lagoon but also causes poverty, due to low productivity in the drainage basin. The drainage basin management program is conceived as a long-term participatory process to achieve an environmentally, economically and socially sustainable management of water resources. The present study deals with periodic assessment and monitoring the vegetation cover of the Dengei pahad micro watershed, Khurda District, Odisha, using NDVI techniques. NDVI is the traditional vegetation index used by researchers for extracting vegetation abundance from remotely sensed data. In essence, the algorithm isolates the dramatic increase in reflectance over the visible red to near infrared wavelengths, and normalized it by dividing by the overall brightness of each pixel in those wavelengths. Satellite data of IRS series from 1999 to 2010 and Resources at series from 2011 to 2014 along with other spatial and non-spatial data were used to find out the changes that occurred in vegetation and other land cover categories during the last 16 years. It was analyzed that dense vegetation cover has decreased up to 20.24 Ha in the year 2010 and after the awareness to the local people by CDA, has taken active role to sustain the natural resource and it has shown positive impact after the analysis through Remote Sensing data. Keywords: Micro-watershed, participatory, degradation, sustainable, NDVI, satellite, remote sensing

Theoretical investigation of the electronic structure and photophysical properties of a series of Ir(iii) complexes bearing pentafluorosulfanyl groups

The electronic structure, absorption and emission spectra, charge injection/transport ability and phosphorescence quantum efficiency of a series of cyclometalated iridium(iii) complexes with different ancillary ligands are studied using density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods.

Aqueous-Phase Hydrogenation of Succinic Acid Using Bimetallic Ir–Re/C Catalysts Prepared by Strong Electrostatic Adsorption

Aqueous phase hydrogenation of succinic acid was investigated using a series of Ir–Re/C bimetallic catalysts prepared by strong electrostatic adsorption. Activity measurements show remarkable synergistic effects, forming a volcano-shaped plot over a range of bulk Re mole fractions with a peak at a fraction of 0.4–0.5, which corresponds to a 20-fold enhancement of activity over either monometallic catalyst. This intermediate catalyst composition exhibiting optimum activity strongly suggests a bifunctional effect. Through a consecutive reaction pathway with γ-butyrolactone as an intermediate, the main product is tetrahydrofuran with 60–75% selectivity. Butanol formation is minimized with decreasing Re mole fraction.

Synthesis, structural characterization, opto-electrical properties of Ir(III) complexes with imidazolium-based carbene ligands

A series of Ir(III) complexes with N–heterocyclic carbenes (NHC) ligands (1–3) were synthesized and characterized. The opto-electrical properties of these complexes were investigated spectroscopically, electrochemically and theoretically. All complexes exhibit ligand-based 1π,π* transitions in the UV region, 1MLCT absorption in the UV region, and weak low energy 3π, π* transition in visible region. These complexes all exhibit blue phosphorescence at both room temperature and 77K, which is dominated by 3π,π* character. DFT calculation results indicate their lowest unoccupied molecular orbitals (LUMO) from −0.47 to −0.33eV and the highest occupied molecular orbitals (HOMO) from −4.97 to −5.33eV. The opto-electrical properties can be influenced drastically by NHC ligands, which would be useful for rational design of optical functional materials.

Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of Ir(III) Complexes containing Extended Phenanthrolines.

A series of Ir(III) complexes, based on 1,10-phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross-coupling reactions using a "chemistry-on-the-complex" method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light-harvesting group. Intense UV/Vis absorption was observed for the Ir(III) complexes with two light-harvesting groups at the 3- and 8-positions of the phenanthroline. The asymmetric Ir(III) complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature (77 K) and nanosecond time-resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet-oxygen ((1) O2 ) sensitization and triplet-triplet annihilation (TTA)-based upconversion were explored. Highly efficient TTA upconversion (ΦUC =28.1 %) and (1) O2 sensitization (ΦΔ =97.0 %) were achieved for the asymmetric Ir(III) complex, which showed intense absorption in the visible region (λabs =482 nm, ϵ=50900 m(-1) cm(-1) ) and had a long-lived triplet excited state (53.3 μs at RT).

Stable Blue Phosphorescence Iridium(III) Cyclometalated Complexes Prompted by Intramolecular Hydrogen Bond in Ancillary Ligand.

Improvement of the stability of blue phosphorescent dopant material is one of the key factors for real application of organic light-emitting diodes (OLEDs). In this study, we found that the intramolecular hydrogen bonding in an ancillary ligand from a heteroleptic Ir(III) complex can play an important role in the stability of blue phosphorescence. To rationalize the role of intramolecular hydrogen bonding, a series of Ir(III) complexes is designed and prepared: Ir(dfppy)2(pic-OH) (1a), Ir(dfppy)2(pic-OMe) (1b), Ir(ppy)2(pic-OH) (2a), and Ir(ppy)2(pic-OMe) (2b). The emission lifetime of Ir(dfppy)2(pic-OH) (1a) (τem = 3.19 μs) in dichloromethane solution was found to be significantly longer than that of Ir(dfppy)2(pic-OMe) (1b) (τem = 0.94 μs), because of a substantial difference in the nonradiative decay rate (knr = 0.28 × 10(5) s(-1) for (1a) vs 2.99 × 10(5) s(-1) for (1b)). These results were attributed to the intramolecular OH···O═C hydrogen bond of the 3-hydroxy-picolinato ligand. Finally, device lifetime was significantly improved when 1a was used as the dopant compared to FIrpic, a well-known blue dopant. Device III (1a as dopant) achieved an operational lifetime of 34.3 h for an initial luminance of 400 nits compared to that of device IV (FIrpic as dopant), a value of 20.1 h, indicating that the intramolecular hydrogen bond in ancillary ligand is playing an important role in device stability.