Dinuclear Iridium Research Articles

Pyrimidine-Based Mononuclear and Dinuclear Iridium(III) Complexes for High Performance Organic Light-Emitting Diodes.

Containing two nitrogen atoms, the electron-deficient pyrimidine ring has excellent coordinating capability with transition metal ions. However, compared with the widely used pyridine ring, applications of the pyrimidine ring in phosphorescent Ir(III) complexes are rare. In this research, two highly emissive pyrimidine-based mononuclear Ir(III) complexes and their corresponding dinuclear Ir(III) complexes were prepared with a simple one-pot reaction. The incorporation of the second Ir(III) center can lead to dramatic differences of both photophysical and electrochemical properties between the mono- and dinuclear complexes. Besides, these properties can also be fine-tuned with different substituents. Theoretical calculations have also been performed to understand their photophysical behaviors. The electroluminescent investigations demonstrate that the pyrimidine-based mono- and dinuclear Ir(III) complexes could show impressive device performance. The vacuum-deposited organic light-emitting diode (OLED) based on the mononuclear Ir(III) complex exhibited an external quantum efficiency (EQE) of 16.1% with almost no efficiency roll-off even at 10 000 cd m-2. More encouragingly, the solution-processed OLED based on the dinuclear Ir(III) complex achieved the outstanding EQE, current efficiency (CE), and power efficiency (PE) of 17.9%, 52.5 cd A-1, and 51.2 lm W-1, respectively, representing the highest efficiencies ever achieved by OLEDs based on dinuclear Ir(III) complexes.

Synthesis and optoelectronic properties of dinuclear iridium (III) complexes containing deep blue fluorescence chromophore in the single-emissive-layer WPLEDs

To explore the influence of molecular structure on formation excimer and obtain high efficiency white polymer light-emitting devices (WPLEDs), two novel blue-emitting dinuclear cyclometalated iridium (III) complexes, namely C8DBCzC6-DF2Ir(pic) and DPy(TPA)-C6DBCzC6-DF2Ir(pic), have been successfully synthesized and characterized, in which DBCz is 3,6-diphenyl-carbazole bridged core, DPy(TPA) is 4,4′-di(pyren-1-yl)triphenylamine deep blue-emitting fluorescent chromophore, DF2Ir(pic) is dinuclear iridium (III) bis[(4,6-difluorophenyl)-pyridinato-N,C2′](picolinate) blue-emitting phosphorescent chromophore, and C6 is an nonconjugated dioxyhexyloxy linkage, respectively, and each parts of molecular skeleton are wired through nonconjugated ether linkage. Their thermal, electrochemical and optophysical properties were primarily investigated. Near white light emission were obtained in the C8DBCzC6-DF2Ir(pic)-doped devices using a blend of polyvinylcarbazole (PVK) and 2-(4-biphenyl)-5-(4-tert-butylphenyl)-1,3,4-oxadiazole (PBD) as a host matrix at dopant concentrations of 1 wt%. However, after triphenylamine functionalized pyrene DPy(TPA) replaced the alkyl chain C6 unit, at first unexpected, substitution effect occurs, more stable white light emissions with the CIE coordinates of (0.297 ± 0.009, 0.345 ± 0.007) and a maximum brightness of 961 cd/m2 were observed in the same device at the doping concentrations of 8 wt% under different applied voltages from 8 to 13 V. The results indicate that aggregation/excimer emissions of iridium (III) complexes can be effectively tuned by inserting a deep blue fluorescent chromophore into the dual picolinic acid derivative, and it aslo be an efficient way to get white-emitting WPLEDs.

ChemInform Abstract: Asymmetric Hydrogenation of 3‐Amido‐2‐arylpyridinium Salts by Triply Chloride‐Bridged Dinuclear Iridium Complexes Bearing Enantiopure Diphosphine Ligands: Synthesis of Neurokinin‐1 Receptor Antagonist Derivatives.

We describe a most straightforward synthetic method for preparing neurokinin-1 (NK1) receptor antagonist derivatives by asymmetric hydrogenation of 3-amido-2-arylpyridinium salts using dinuclear iridium complexes with enantiopure diphosphine ligands, affording the corresponding chiral piperidines in high cis-diastereoselectivity (>95:5) and moderately high enantioselectivity (up to 86%). Deprotection treatments afforded the NK-1 receptor antagonist (+)-CP-99,994 (83% ee). In addition, we observed unique additive effects of 10-camphorsulfonic acid in the asymmetric hydrogenation of 3-amido-2-arylpyridinium salts.

Dinuclear cyclometalated iridium (III) complex containing functionalized triphenylamine core: synthesis, photophysics and application in the single-emissive-layer WOLEDs

To obtain highly efficient white-emitting devices, a novel functionalized dinuclear iridium (III) complex of C8TPA(FIrpic)2 was successfully synthesized and characterized. In this phosphor, FIrpic is a blue-emitting phosphorescent chromophore of iridium(III) bis[(4,6-difluorophenyl)pyridinato-N,C2′] picolate and C8TPA is a blue-emitting fluorescent chromophore of triphenylamine as bridging donor. Its optophysical and electro-phosphorescent properties were primarily investigated. White emission with an increasing current efficiency of 1.31 cd/A at 15.3 mA/cm2 and brightness of 1770 cd/m2 at 656.3 mA/cm2 was obtained in its single-emissive-layer OLEDs with a configuration of ITO/PEDOT:PSS/C8TPA(FIrpic)2 (10 wt %):TCTA/TPBi/LiF/Al. The results indicate that an introduction of triphenylamine group into dinuclear iridium (III) complexes as bridged donor can improve the performance of its iridium (III) complexes-doped OLEDs.

Triply Halide-Bridged Dinuclear Iridium(III) Complexes with Chiral Diphosphine Ligands as New Easy-to-Handle Iridium Catalysts for Asymmetric Hydrogenation of Imines and N-Heteroaromatics.

Iridium(III) complexes bearing chiral ligands have proved to be active species in asymmetric hydrogenation of C=N bonds, though there are only a few iridium(III) precursors. We prepared triply halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands by simple treatment of the iridium(I) precursor, chiral diphosphine, and aqueous hydrogen halide. The strong advantage of these dinuclear iridium complexes is that they are air and moisture stable, leading to easy handling in asymmetric synthesis. The dinuclear iridium complexes exhibited high catalytic activity toward asymmetric hydrogenation of imines and N-heteroaromatics. Moreover, we demonstrated the application of triply halide-bridged dinuclear ruthenium(II) and rhodium(III) catalyst precursors for the asymmetric hydrogenation of ketonic substrates and simple olefins, respectively.

E-Selective Semi-hydrogenation of Alkynes with Dinuclear Iridium Complexes under Atmospheric Pressure of Hydrogen

Semi-hydrogenation of alkynes was catalyzed by halide-bridged dinuclear iridium complexes, yielding (E)-alkenes with high selectivity. Mechanistic studies conducted with monohydride dinuclear species, dihydride mononuclear species, and trihydride dinuclear species led us to propose a mechanism involving dual cycles.

Time-resolved luminescence imaging of intracellular oxygen levels based on long-lived phosphorescent iridium(III) complex.

Time-resolved luminescence imaging of intracellular oxygen levels has been demonstrated based on long-lived phosphorescent signal. A phosphorescent dinuclear iridium(III) complex Ir1 has been designed and synthesized, which exhibits excellent optical properties, such as high quantum yields, large Stokes shift, high photostability and long emission lifetime. The phosphorescent intensity and lifetime of complex are very sensitive to oxygen levels. Thus, the application of Ir1 for monitoring intracellular oxygen levels has been realized successfully. Especially, utilizing the advantageous long emission lifetime of Ir1, the background fluorescence interference could be eliminated effectively by using the photoluminescence lifetime imaging and time-gated luminescence imaging techniques, improving the signal-to-noise ratios in bioimaging.

Asymmetric Hydrogenation of 3‐Amido‐2‐arylpyridinium Salts by Triply Chloride‐Bridged Dinuclear Iridium Complexes Bearing Enantiopure Diphosphine Ligands: Synthesis of Neurokinin‐1 Receptor Antagonist Derivatives

AbstractWe describe a most straightforward synthetic method for preparing neurokinin‐1 (NK1) receptor antagonist derivatives by asymmetric hydrogenation of 3‐amido‐2‐arylpyridinium salts using dinuclear iridium complexes with enantiopure diphosphine ligands, affording the corresponding chiral piperidines in high cis‐diastereoselectivity (>95:5) and moderately high enantioselectivity (up to 86%). Deprotection treatments afforded the NK‐1 receptor antagonist (+)‐CP‐99,994 (83% ee). In addition, we observed unique additive effects of 10‐camphorsulfonic acid in the asymmetric hydrogenation of 3‐amido‐2‐arylpyridinium salts.magnified image

A novel dinuclear iridium(III) complex as a G-quadruplex-selective probe for the luminescent switch-on detection of transcription factor HIF-1α.

A novel dinuclear Ir(III) complex 5 was discovered to be specific to G-quadruplex DNA, and was utilized in a label-free G-quadruplex-based detection platform for transcription factor activity. The principle of this assay was demonstrated by using HIF-1α as a model protein. Moreover, this HIF-1α detection assay exhibited potential use for biological sample analysis.

From Mononuclear to Dinuclear Iridium(III) Complex: Effective Tuning of the Optoelectronic Characteristics for Organic Light-Emitting Diodes.

Phosphorescent dinuclear iridium(III) complexes that can show high luminescent efficiencies and good electroluminescent abilities are very rare. In this paper, highly phosphorescent 2-phenylpyrimidine-based dinuclear iridium(III) complexes have been synthesized and fully characterized. Significant differences of the photophysical and electrochemical properties between the mono- and dinuclear complexes are observed. The theoretical calculation results show that the dinuclear complexes adopt a unique molecular orbital spatial distribution pattern, which plays the key role of determining their photophysical and electrochemical properties. More importantly, the solution-processed organic light-emitting diode (OLED) based on the new dinuclear iridium(III) complex achieves a peak external quantum efficiency (η(ext)) of 14.4%, which is the highest η(ext) for OLEDs using dinuclear iridium(III) complexes as emitters. Besides, the efficiencies of the OLED based on the dinuclear iridium(III) complex are much higher that those of the OLED based on the corresponding mononuclear iridium(III) complex.

When two are better than one: bright phosphorescence from non-stereogenic dinuclear iridium(III) complexes.

A new family of eight dinuclear iridium(iii) complexes has been prepared, featuring 4,6-diarylpyrimidines L(y) as bis-N^C-coordinating bridging ligands. The metal ions are also coordinated by a terminal N^C^N-cyclometallating ligand L(X) based on 1,3-di(2-pyridyl)benzene, and by a monodentate chloride or cyanide. The general formula of the compounds is {IrL(X)Z}2L(y) (Z = Cl or CN). The family comprises examples with three different L(X) ligands and five different diarylpyrimidines L(y), of which four are diphenylpyrimidines and one is a dithienylpyrimidine. The requisite proligands have been synthesised via standard cross-coupling methodology. The synthesis of the complexes involves a two-step procedure, in which L(X)H is reacted with IrCl3·3H2O to form dinuclear complexes of the form [IrL(X)Cl(μ-Cl)]2, followed by treatment with the diarylpyrimidine L(y)H2. Crucially, each complex is formed as a single compound only: the strong trans influence of the metallated rings dictates the relative disposition of the ligands, whilst the use of symmetrically substituted tridentate ligands eliminates the possibility of Λ and Δ enantiomers that are obtained when bis-bidentate units are linked through bridging ligands. The crystal structure of one member of the family has been obtained using a synchrotron X-ray source. All of the complexes are very brightly luminescent, with emission maxima in solution varying over the range 517-572 nm, according to the identity of the ligands. The highest-energy emitter is the cyanide derivative whilst the lowest is the complex with the dithienylpyrimidine. The trends in both the absorption and emission energies as a function of ligand substituent have been rationalised accurately with the aid of TD-DFT calculations. The lowest-excited singlet and triplet levels correlate with the trend in the HOMO-LUMO gap. All the complexes have quantum yields that are close to unity and phosphorescence lifetimes - of the order of 500 ns - that are unusually short for complexes of such brightness. These impressive properties stem from an unusually high rate of radiative decay, possibly due to spin-orbit coupling pathways being facilitated by the second metal ion, and to low non-radiative decay rates that may be related to the rigidity of the dinuclear scaffold.

Differential Anticancer Activities of the Geometric Isomers of Dinuclear Iridium(III) Complexes

AbstractThe anticancer activities of dinuclear iridium(III) complexes [{Ir(tpy)Cl}2{μ‐bbn}]4+ {Cl‐Irbbn; tpy = 2,2′:6′,2″‐terpyridine, bbn = bis[4(4′‐methyl‐2,2′‐bipyridyl)]‐1,n‐alkane (n = 7, 12 and 16)} against MCF‐7 and MDA‐MB‐231 breast cancer cell lines have been determined. The activities of the Cl‐Irbbn complexes increased with increasing chain length, the Cl‐Irbb16 complex showing the best anticancer properties. However, while Cl‐Irbb16 was active against the metastatic MDA‐MB‐231 cells (3 μM), it was relatively inactive against the nonmetastatic MCF‐7 line (29 μM). The three geometric isomers of Cl‐Irbb16 were isolated and characterised by NMR spectroscopy and mass spectrometry, and their anticancer activities, lipophilicities (log P) and DNA‐binding abilities were examined. The trans,trans (t,t) isomer (IC50 = 2 μM against MDA‐MB‐231) showed considerably greater anticancer activity than the cis,trans (c,t) and cis,cis (c,c) isomers (8 and 31 μM, respectively). From log P measurements, the t,t isomer of Cl‐Irbb16 (log P = –0.62) was found to be slightly more lipophilic than the other geometric isomers (–0.95 and –0.98 for the c,c and c,t isomers, respectively). Calf‐thymus (CT) DNA‐binding experiments demonstrated that the t,t isomer did induce a different alteration to the helix conformation compared to the other isomers. The results of this study also highlight the significance of the differences in three‐dimensional shape that can be obtained through geometric isomerism for octahedral coordination complexes.

ChemInform Abstract: Asymmetric Hydrogenation of Quinazolinium Salts Catalyzed by Halide‐Bridged Dinuclear Iridium Complexes Bearing Chiral Diphosphine Ligands.

ChemInform Abstract: Asymmetric Hydrogenation of Quinazolinium Salts Catalyzed by Halide‐Bridged Dinuclear Iridium Complexes Bearing Chiral Diphosphine Ligands.

Dinuclear iridium(iii) complexes as phosphorescent trackers to monitor mitochondrial dynamics

Mitochondrial dynamic processes are essential for mammalian development and are engaged in several diseases. However, commercial mitochondrial probes are currently too limited to satisfactorily track these dynamics. In this present work, seven dinuclear iridium(iii) complexes [(ppy)2Ir(L1-7)Ir(ppy)2]2+ (Ir1-Ir7, ppy = 2-phenylpyridine, L = 1,3-bis(1-substituted-imidazo[4,5-f][1,10]phenanthroline-2-yl)benzene) were synthesized. Possessing a high specificity for mitochondria, low cytotoxicity and high resistance to the loss of the mitochondrial membrane potential, Ir2-Ir7 can serve as mitochondrial imaging dyes. Ir3 and Ir6 are further developed for tracking mitochondrial morphological changes during the early stages of apoptosis. In addition, the relationship of the electron donating/withdrawing groups in these systems with the photophysical properties and photostability is also discussed.

Dinuclear iridium and rhodium complexes with bridging arylimidazolide-N(3),C(2) ligands: synthetic, structural, reactivity, electrochemical and spectroscopic studies.

Deprotonation of 1-arylimidazoles (aryl = mesityl (Mes), 2,6-diisopropylphenyl (Dipp)), with n-butyl lithium afforded the corresponding derivatives (1-aryl-1H-imidazol-2-yl)lithium (1a, Ar = Mes; 1b, Ar = Dipp) in good yield. Reaction of 1a with 0.5 equiv. of [Ir(cod)(μ-Cl)]2 yielded two geometrical isomers of a doubly C2,N3-bridged dinuclear complex [Ir(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (3), 3H-H, a head-to-head (H-H) isomer of CS symmetry, and 3H-T, the thermodynamically preferred head-to-tail (H-T) isomer of C2 symmetry. The metallated carbon of the 4 electron donor anionic bridging ligands has some carbene character, reminiscent of the situation in N-metallated protic NHC complexes. Displacement of cod ligands from 3H-H and 3H-T afforded the tetracarbonyl complexes [Ir(CO)2{μ-C3H2N2(Mes)-κC2,κN3}]24H-H and 4H-T, respectively. The reaction with PMe3, which gave only one complex, [Ir(CO)(PMe3){μ-C3H2N2(Mes)-κC2,κN3}]2 (5), demonstrates that the isomerization of the central core Ir[μ-C3H2N2(Mes)-κC2,κN3]2Ir from H-H to H-T on going from 4H-H to 5 is readily triggered by phosphine substitution under mild conditions. Oxidative-addition of MeI to 5 afforded the formally metal-metal bonded d(7)-d(7) complex [Ir2(CO)2(PMe3)2(Me)I{μ-C3H2N2(Mes)-κC2,κN3}2] (6). The blue [Ir(C2H4)2{μ-C3H2N2(Mes)-κC2,κN3}]2 (7) and purple [Rh(C2H4)2{μ-C3H2N2(Dipp)-κC2,κN3}]2 (9) tetraethylene complexes were also obtained with only a H-T arrangement of the bridging ligands. Although only modestly efficient in alkane dehydrogenation, complex 7 was found to be a more active pre-catalyst than 3H-T, 4H-T and 5, probably because of the favorable lability of the ethylene ligands. From cyclic voltammetry, exhaustive coulometry and spectroelectrochemistry studies, it was concluded that 3H-T undergoes a metal-based one electron oxidation to generate the mixed-valent Ir(i)/Ir(ii) system. The energy of the intervalence band for the orange dirhodium complex [Rh(cod){μ-C3H2N2(Mes)-κC2,κN3}]2 (8) is shifted toward lower energies in comparison with 3H-T, reflecting the decrease of the energy with the intermetallic distance. It was concluded from the EPR study that the Ir and Rh centres contribute substantially to the experimental magnetic anisotropy and thus to the singly occupied molecular orbital (SOMO) in the mixed-valent Ir(i)/Ir(ii) and Rh(i)/Rh(ii) systems. The molecular structures of 3H-H, 3H-T, 8 and 9 have been determined by X-ray diffraction.

Asymmetric hydrogenation of quinazolinium salts catalysed by halide-bridged dinuclear iridium complexes bearing chiral diphosphine ligands.

Asymmetric hydrogenation of quinazolinium salts was catalysed by halogen-bridged dinuclear iridium complexes bearing chiral diphosphine ligands, yielding tetrahydroquinazoline and 3,4-dihydroquinazoline with high enantioselectivity. A derivative of chiral dihydroquinazoline was used as a chiral NHC ligand.

Enhancing effects of salt formation on catalytic activity and enantioselectivity for asymmetric hydrogenation of isoquinolinium salts by dinuclear halide-bridged iridium complexes bearing chiral diphosphine ligands.

Asymmetric hydrogenation of 1- and 3-substituted and 1,3-disubstituted isoquinolinium chlorides using triply halide-bridged dinuclear iridium complexes [{Ir(H)(diphosphine)}2 (μ-Cl)3 ]Cl has been achieved by the strategy of HCl salt formation of isoquinolines to afford the corresponding chiral 1,2,3,4-tetrahydroisoquinolines (THIQs) in high yields and with excellent enantioselectivities after simple basic work-up. The effects of salt formation have been investigated by time-course experiments, which revealed that the generation of isoquinolinium chlorides clearly prevented formation of the catalytically inactive dinuclear trihydride complex, which was readily generated in the catalytic reduction of salt-free isoquinoline substrates. Based on mechanistic investigations, including by (1) H and (31) P{(1) H} NMR studies and the isolation and characterization of several intermediates, the function of the chloride anion of the isoquinolinium chlorides has been elucidated, allowing us to propose a new outer-sphere mechanism involving coordination of the chloride anion of the substrates to an iridium dihydride species along with a hydrogen bond between the chloride ligand and the N-H proton of the substrate salt.

Bimetallic cyclometalated iridium(III) diastereomers with non-innocent bridging ligands for high-efficiency phosphorescent OLEDs.

Two phosphorescent dinuclear iridium(III) diastereomers (ΛΔ/ΔΛ) and (ΛΛ/ΔΔ) are readily separated by making use of their different solubilities in hot hexane. The bridging diarylhydrazide ligand plays an important role in the electrochemistry and photophysics of the complexes. Organic light-emitting devices (OLEDs) that use these complexes as the green-emissive dopants in solution-processable single-active-layer architectures feature electroluminescence efficiencies that are remarkably high for dinuclear metal complexes, achieving maximum values of 37 cd A(-1), 14 lm W(-1), and 11% external quantum efficiency.

Bimetallic Cyclometalated Iridium(III) Diastereomers with Non‐Innocent Bridging Ligands for High‐Efficiency Phosphorescent OLEDs

AbstractTwo phosphorescent dinuclear iridium(III) diastereomers (ΛΔ/ΔΛ) and (ΛΛ/ΔΔ) are readily separated by making use of their different solubilities in hot hexane. The bridging diarylhydrazide ligand plays an important role in the electrochemistry and photophysics of the complexes. Organic light‐emitting devices (OLEDs) that use these complexes as the green‐emissive dopants in solution‐processable single‐active‐layer architectures feature electroluminescence efficiencies that are remarkably high for dinuclear metal complexes, achieving maximum values of 37 cd A−1, 14 lm W−1, and 11 % external quantum efficiency.

Synthesis and optoelectronic properties of novel fluorene-bridged dinuclear cyclometalated iridium (III) complex with A–D–A framework in the single-emissive-layer WOLEDs

To explore the influence of push–pull chromophores on properties of emitter in organic light-emitting devices (OLEDs), an acceptor–donor–acceptor (A–D–A)-based dinuclear iridium (III) complex of (dfppy)4Ir2(dipic-FL) was synthesized via Suzuki coupling reaction, in which dfppy is 2-(2,4-difluorophenyl)pyridine and dipic-FL is 2,7-di(5-pyridyl-2-carboxyl)-9,9-dioctyl-9H-fluorene. An intense emission peak at about 480nm resulting from the (dfppy)2Ir(pic) chromophore and a weak long-wavelength emission band at 580–660nm attributed to intramolecular charge transfer transition were exhibited for (dfppy)4Ir2(dipic-FL) in dichloromethane solution. But a remarkably hypsochromic photoluminescence profile with an intense characteristical emission peak at 422nm was observed, which is attributed to the intraligand (IL) π–π∗ excited states in its thin film. White emission with a maximum luminance of 1040cd/m2 and current efficiency of 1.2cd/A was obtained in its single-emissive-layer (SEL) OLEDs with a configuration of ITO/PEDOT:PSS/(dfppy)4Ir2(dipic-FL) (10 wt%):TCTA/TPBi/LiF/Al. To our knowledge, this is one of the best examples in term of dinuclear iridium complex as single dopant in the high-performance white-emitting SEL-OLEDs.