Cationic Ir Research Articles

Rational Design of Efficient Organometallic Ir(III) Complexes for High-Performance, Flexible, Monochromatic, and White Light-Emitting Electrochemical Cells.

Highly efficient light-emitting electrochemical cells (LECs) have attracted tremendous interest because of their simple structures and low-cost fabrication processing, showing great potential for full-color displays and solid-state lighting. In this work, we rationally designed and synthesized two red-emitting cationic Ir(III) complexes, [Ir(tBuPBI)2(biq)]PF6 (R1) and [Ir(tBuPBI)2(qibi)]PF6 (R2), in which a tert-butyl-functionalized 1,2-diphenyl-1H-benzo[d]imidazole (PBI) unit and conjugated 2,2'-biquinoline (biq) and 2-(1-phenyl-1H-benzo[d]imidazol-2-yl)quinolone (qibi) were employed as cyclometalated and ancillary ligands, respectively. The introduced tert-butyl group led to homogeneous and highly emissive thin films by increasing the solubility and suppressing the strong intermolecular interactions due to steric hindrance. Based on the abovementioned high-quality emissive layer, high-efficiency LECs were achieved. An efficient red-emitting LEC fabricated on a glass substrate achieved a current efficiency (ηC) of 7.18 cd/A and an external quantum efficiency (ηext) of 9.32%. By doping both complexes into a blue-green-emitting cationic Ir(III) complex, high-performance white LECs were also successfully fabricated with Commission International de L'Eclairage (CIE) coordinates of (0.39,0.39), a ηC of 17.43 cd/A, and a ηext of 8.92%. In addition, we also fabricated flexible red and white LECs with outstanding efficiencies and mechanical flexibilities. The ηC and ηext values of a flexible white LEC could be as high as 13.50 cd/A and 6.86%, respectively. The efficiency of the flexible device remained at approximately 95% of the initial value after 500 bends with a radius of curvature of 5 mm, demonstrating the great potential of these complexes for full-color displays and flexible optoelectronics.

Retraction: Sublimable cationic Ir(iii) phosphor using chlorine as a counterion for high-performance monochromatic and white OLEDs

Retraction of 'Sublimable cationic Ir(iii) phosphor using chlorine as a counterion for high-performance monochromatic and white OLEDs' by Lei Ding et al., Chem. Commun., 2018, 54, 11761-11764.

Heteroleptic cationic iridium(iii) complexes bearing phenanthroline derivatives with extended π-conjugation as potential broadband reverse saturable absorbers

Fluorenyl substitution at the diimine ligand broadened the excited-state absorption to near-IR, and enhanced reverse saturable absorption at 532 nm for the cationic Ir(iii) complexes.

Near-infrared-emitting AIE multinuclear cationic Ir(III) complex-assembled nanoparticles for photodynamic therapy.

Near-infrared (NIR) emission and impressive singlet oxygen (1O2) generation ability are highly desirable but remain difficult to realize as aggregation-induced emission (AIE) photosensitizers (PSs). Herein, mono- and tri-nuclear NIR AIE cationic Ir(iii) complexes and their corresponding self-assembled nanoparticles (NPs) without any surfactants or adjuvants were designed and synthesized by integrating rigid 1,3,5-triphenyl benzene as an extended π-conjugation bridge. The pure NPs exhibit multiple merits of stronger NIR emission, higher 1O2 production capacity, better water solubility and negligible dark toxicity compared with the Ir(iii) complexes. Notably, the AIE PS3 NPs possess bright NIR emission at 730 nm, suitable spherical sizes below 100 nm, favorable cellular uptake and superior phototoxicity (IC50 = 1.4 × 10-6 M). These are the first pure NIR-emitting multinuclear Ir(iii) complex NPs obtained by self-assembly that exhibit excellent cell imaging and photodynamic therapy (PDT) performance.

A mechanochromic cyclemetalated cationic Ir(iii) complex with AIE activity by strategic modification of ligands.

Two new aggregation-induced emission (AIE)-active cyclemetalated cationic Ir(iii) complexes have been rationally designed and synthesized by introducing O-H substituents into Schiff base ligands. π-Hydrogen bonding is successfully exploited for the first time to realize the mechanochromic luminescence (MCL) property by the synergistic effect of O-H and F substituents in complex 1. An X-ray crystal structure analysis of the two complexes suggests that the intramolecular hydrogen bonding effectively restricted the molecular motions, thus causing typical AIE characteristics. More importantly, a loosely packed structure constructed from intermolecular hydrogen bonding interactions (O-Hπ and C-HF) is obtained, and it is susceptible to mechanical stimulation. Powder X-ray diffraction (PXRD) studies also prove that the MCL behavior of complex 1 is caused by the reversible phase transition from crystalline to amorphous state under grinding and solvent recrystallization, leading to a change in emission colors. A re-writable phosphorescence data recording device was fabricated using complex 1 as the active material. Our molecular design strategies provide a new avenue for achieving efficient phosphorescence materials with AIE and MCL properties.

Real-Time Monitoring of Low Pressure Oxygen Molecules over Wide Temperature Range: Feasibility of Ultrathin Hybrid Films of Iridium(III) Complexes and Clay Nanosheets

Abstract An ultrathin film was prepared by hybridizing a cationic Ir(III) complex with exfoliated nanosheets of clay minerals such as natural montmorillonite (denoted by MON) or synthetic saponite (denoted by SAP). The utilized Ir(III) complex with two long alkyl chains was [Ir(dfppy)2(dc9bpy)]+ (fppyH = 2-(2′,4′-difluorophenyl)pyridine; dc9bpy = 4,4′-dinonyl-2,2′-bipyridine) (denoted by DFPPY). Hybridization was performed at an air-water interface between a floating monolayer of the Ir(III) complex and the nanosheets exfoliated in an aqueous subphase. The hybrid floating film thus formed was transferred onto a hydrophilic quartz plate by a vertical dipping method. The emission from the deposited films exhibited rapid reversible change of intensity in response to the introduction or evacuation of oxygen gas in the pressure range of 0.1–101.3 kPa and the temperature range from 253 K to 313 K. The lifetime of the emission decay was measured as a function of oxygen pressure, confirming the occurrence of dynamic quenching of excited Ir(III) complexes by oxygen molecules.

Cationic Polymerization via Activation of Alkoxyamines Using Photoredox Catalysts

AbstractThe front cover artwork is provided by the group of Prof. Masami Kamigaito at the Department of Molecular and Macromolecular Chemistry, Nagoya University (Japan). The image shows cationic polymerization via the mesolytic cleavage of alkoxyamine triggered by an exited cationic Ir(III) catalyst under blue LED irradiation, in contrast to radical polymerization via the homolytic cleavage under heat. Read the full text of the Article at 10.1002/cptc.201900148.

Efficient Generation of Singlet Oxygen and Photooxidation of Sulfide into Sulfoxide via Tuning the Ancillary of Bicyclometalated Iridium(III) Complexes.

With 2-phenylquinoline (pq) as a cyclometalated ligand, a series of cationic Ir(III) complexes [Ir(pq)2(L1)2](PF6) (L1 is pyridine (1a), 4-methoxypyridine (1b), 4-dimethylaminopyridine (1c), and 4-acetylpyridine (1d)) and [Ir(pq)2(L2)](PF6) (L2 is 2,2'-bipyridine (1e), 2,2'-bipyrimidyl (1f), 4,4'-dimethyl-2,2'-bipyridine (1g), and 4,4'-dimethoxy-2,2'-bipyridine (1h)) were synthesized and characterized. The influence of the metal-based highest occupied molecular orbital on triplet-state lifetime, triplet-state quantum yield, and 1O2 generation quantum yield as well as aerobic photo-oxidation of sulfide into sulfoxide was evaluated via tuning the ancillary ligand of Ir(pq)2 complexes. The results revealed that 1h with chelate ancillary ligand bearing electron-donating group possesses a high 1O2 generation quantum yield (0.90) and photocatalytic activity for sulfide oxidation with high chemoselectivity and a low catalyst loading (0.5 mol %) under mild conditions. Moreover, one-pot two-step procedure for preparation of enantiopure sulfoxides, including aerobic photo-oxidation of sulfide using 1h as a photosensitizer and chiral resolution of sulfoxide via a chiral-at-metal strategy, was also developed.

Photosensitizers based on Ir(III) complexes for highly efficient photocatalytic hydrogen generation

A series of new cationic Ir(III) complexes [Ir(C∧N)2(ppba)][PF6] P1–P5 as photosensitizers (PSs) has been rationally designed and synthesized. According to the study of photocatalytic hydrogen generation from water based on these five Ir(III) PSs, the highest yield of hydrogen generation has been achieved by P5, in which the strong electron-withdrawing substituent, 2,6-difluoropyridine, is adopted to cyclometalated ligands. Moreover, the hydrogen generation yield of P5 is ca.11 times than that of P3, revealing that the hydrogen generation activity of PSs can be effectively improved through the variation of cyclometalated ligands. Based on the discussion of light absorption, charge separation and electron transfer processes, P3 with the broadest absorption and the highest molar absorption coefficient in the visible region displays the best visible light absorption capacity among P1–P5 due to the attribute of electron-donating substituent (benzothiazole). As the introduction of 2,6-difluoropyridine substituent, P5 with the longest excited-state lifetime and the greatest potential difference between E(TEA+/TEA) and E(PS∗/PS−) among P1–P5 possesses the best charge separation and electron transfer capacities. These results illuminate that the introduction of electron-withdrawing substituents into cyclometalated ligands is beneficial for the improvement of hydrogen generation activity in this system. This article reveals that it is important to take into full consideration the relationship between structure and performance for the design of highly efficient PSs.

Cyclometalated iridium(III) complex containing indolinyl-based phenanthroline ligand: Synthesis, structure and photophysical properties

A heteroleptic cationic Ir(III) complex [(X)2Ir(L)]+PF6− was designed and synthesized, where L = 2-(1,3,3-trimethylindolin-2-yl)oxazolo[4,5-f] [1,10]phenanthroline, X = 2-phenylpyridine (ppy). Its structural and photophysical properties have been systematically investigated via a series of spectroscopic methods. This complex exhibits ligand-localized 1π,π* transitions below 350 nm, broad and structureless metal-to-ligand/ligand-to-ligand charge transfer (1MLCT/1LLCT) transitions between 350 and 450 nm, and spin-forbidden 3MLCT/3LLCT/3π,π* transitions above 450 nm. Upon excitation at its absorption maximum, the complex exhibits orange phosphorescence in solution. In addition, this complex exhibits strong excited-state absorption in the visible spectral region, good anti-photobleaching and electrochemical stability. Reverse saturable absorption (RSA) of this complex was demonstrated at 532 nm using 4.1 ns laser pulses, which would be useful for a rational design of nonlinear optical materials.

Inkjet-printed pixelated light-emitting electrochemical cells based on cationic Ir(III) complexes

Abstract Inkjet printing technology is one of the most attractive methods for the realization of full-color patterning for displays. In this work, we successfully introduce this technology into fabricating pixelated light-emitting electrochemical cells (LECs). By carefully controlling the poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate), and cationic Ir(III) complexes ink formulation, as well as their inkjet printing properties, patterned LEC pixels in ultrahigh definition TV format was fabricated, leading to a resolution of 73 pixels per inch. The as-resulted inkjet-printed LEC exhibits a maximum luminance and a current efficiency of 3402 cd/m2, and 7.5 cd/A, respectively, which is close to that of the spin-coated one. This work paves a new way for the fabrication of low-cost material-efficient, pixelated light-emitting electrochemical cells.

Electrochemical C-H bond activation via cationic iridium hydride pincer complexes.

A C-H bond activation strategy based on electrochemical activation of a metal hydride is introduced. Electrochemical oxidation of ( tBu4 PCP)IrH4 ( tBu4 PCP is [1,3-( t Bu2PCH2)-C6H3]-) in the presence of pyridine derivatives generates cationic Ir hydride complexes of the type [( tBu4 PCP)IrH(L)]+ (where L = pyridine, 2,6-lutidine, or 2-phenylpyridine). Facile deprotonation of [( tBu4 PCP)IrH(2,6-lutidine)]+ with the phosphazene base tert-butylimino-tris(pyrrolidino)phosphorane, t BuP1(pyrr), results in selective C-H activation of 1,2-difluorobenzene (1,2-DFB) solvent to generate ( tBu4 PCP)Ir(H)(2,3-C6F2H3). The overall electrochemical C-H activation reaction proceeds at room temperature without need for chemical activation by a sacrificial alkene hydrogen acceptor. This rare example of undirected electrochemical C-H activation holds promise for the development of future catalytic processes.

Two new phosphorescent Ir(III) complexes as efficient selective sensors for the Cu2+ ion

Two new cationic iridium(III) complexes were successfully synthesized as highly sensitive and selective phosphorescent sensors for detection of Cu2+ in MeOH/H2O (1:1) solution and in living cells. These cationic Ir(III) complexes were prepared by reactions of two different Ir(III) chloro-bridged dimers with 2,2′-dipyridine tethered DPA (di(2-picolyl)amine) moiety as the ancillary ligand. These phosphorescent sensors displayed significant reversible phosphorescence quenching upon binding to Cu2+ ions with a 10 ppb detection limit. They had strong binding ability with Cu2+ ions and the binding ratios were approximately 1:1, and also exhibited good cell permeability and good imaging characteristics in detecting Cu2+ ions in living cells. It is worth mentioning that one of the phosphorescent sensors is almost nontoxic to Hela cells, indicating that it greatly increases the possibility of application in biochemistry.

Dynamical Mechanism May Avoid High-Oxidation State Ir(V)-H Intermediate and Coordination Complex in Alkane and Arene C-H Activation by Cationic Ir(III) Phosphine.

Organometallic reaction mechanisms are assumed to be appropriately described by minimum energy pathways mapped out by density functional theory calculations. For the two-step oxidative addition/reductive elimination mechanism for C-H activation of methane and benzene by cationic Cp*(PMe3)IrIII(CH3), we report quasiclassical direct dynamics simulations that demonstrate the IrV-H intermediate is bypassed in a significant amount of productive trajectories initiated from vibrationally averaged velocity distributions of oxidative addition transition states. This organometallic dynamical mechanism is akin to the σ-bond metathesis pathway but occurs on the oxidative addition/reductive elimination energy surface and blurs the line between two- and one-step mechanisms. Quasiclassical trajectories also reveal that the momentum of crossing the reductive elimination structure always induces complete alkane and arene dissociation from the Ir metal center, skipping weak C-H σ and π coordination complexes. This suggests that these weak coordination complexes after reductive elimination are not necessarily on the reaction pathway and likely result from a solvent cage.

A complete evaluation from theoretical aspect on the phosphorescent efficiency improvement through ancillary ligands modifications of a blue Ir(III) complex

Abstract Five blue-emitting cationic Ir(III) materials with the form [ I r ( C ∧ N ) 2 ( N ∧ N ) ] + , where C ∧ N = 2-(2,4-difluorophenyl)pyridine (dfppy) cyclometalating ligands, and N ∧ N = biimidazole-type ancillary ligands, are investigated through a comprehensive theoretical scheme. Experimental researches concentrating on decorations of ancillary ligand, revealed that complex with 1,1′-CH3-2,2′-biimidazole (dMebiim) ancillary ligand is a non-emissive material due to the detrimental twisting of dMebiim resulting from steric hindrance of the methyl groups. When getting rid of methyl substituents that becomes the complex with a 1,1′-H-2,2′-biimidazole ancillary ligand, the quantum efficiency has been lifted to a large extent. Further rigidifying the biimidazole-type ancillary ligands, complex with an ortho-xylyl-tethered biimidzole ancillary ligand (1) was synthesized and has a higher quantum yield. From experimental aspect, the approaches employed in quantum efficiency enhancement is mainly concentrate on geometrical control through chelate effect. However, from theoretical aspect, we are not confined the strategies to rigidify the biimidazole ligand by divers chelates. In this study, our comprehensive theoretical scheme is firstly employed on the synthesized complex 1. Results show that the calculated radiative ( k r )and non-radiative ( k n r ) decay rates are consistence with the experimental findings. And further vibrational analysis clarified its nuclear behaviors during electronic transitions. Based on such vibrational analysis, it is found that substituting on the flanks of biimidzole can also effectively avoid detrimental twist. Therefore, in this study, we provide several new designed Ir(III) materials with substituent groups on the flanks of biimidzole, with the consideration of electron-withdrawing or -donating characters of the substituent groups. And Ir(III) materials with better performance are predicted from theoretical aspect.

Insights into the luminescent properties of anionic cyclometalated iridium(III) complexes with ligands derived from natural products

AbstractIn the search of remarkable anionic electroluminescent semiconductors to be applied in energy conversion devices such as Light Emitting Electrochemical Cells, we report the electronic, photophysical, and charge injection/transfer properties of a series of cyclometalated iridium(III) complexes through a DFT/TD‐DFT procedure. The proposed semiconductors involve bidentated ligands based on natural products (salicylic acid and boldine), and phenylpyridine and phenylpyrazole as the cyclometalating units. The proposed compounds emit in the range of 446 to 571 nm, where the boldine based compounds have red‐shifted emissions compared to their analogs with salicylic acid. Blue phosphors were obtained by the use of phenylpyrazole units; however, the ligand field is weak in these cases compared to the ligand field exerted by the phenylpyridine ligands. The latter allows the accessibility to the radiationless states for emitters below 495 nm as a result of the increased stability of the metal centered excited states; consequently, the luminescent quantum yield could be decreased. Conversely, the semiconductors with phenylpyridine units show a restricted accessibility to radiationless processes, which could result in emitters with a high luminescent quantum yield and low non‐radiative constants. Finally, the proposed anionic semiconductors show a better balance between hole/electron transfer rate compared to related cationic Ir(III) complexes; while, the easier hole‐electron injection is favored for semiconductors with salicylic acid and phenylpyridine units.

Iridium‐Catalyzed Direct Asymmetric Alkylation of Aniline Derivatives using 2‐Norbornene

AbstractAn efficient and highly enantioselective direct alkylation process of acetanilides with 2‐norbornene using a bis(phosphoramidite) cationic Ir catalytic system (up to 99 % ee) has been reported. This methodology allows the facile preparation of enantiomerically enriched exo‐2‐(bicyclo[2.2.1]heptan‐2‐yl)anilines, which can be readily transformed into other functionalities.

Substituent influence in phenanthroline-derived ancillary ligands on the excited state nature of novel cationic Ir(iii) complexes

Influence of ancillary ligands derived from phenanthroline on the nature of the deactivation pathways of novel cationic Ir(iii) cyclometalated complexes.

Phosphorescent cationic iridium(iii) complexes bearing a nonconjugated six-membered chelating ancillary ligand: a strategy for tuning the emission towards the blue.

This study concerns an assessment of the impact of the interruption of the electronic crosstalk between the pyridine rings in the ancillary ligand on the photoluminescence properties of the corresponding iridium(iii) complexes. Two new cationic Ir(iii) complexes, [Ir(dFmesppy)2(pmdp)]PF6, 1, and [Ir(mesppy)2(pmdp)]PF6, 2, [where dFmesppy is 2-(2,4-difluorophenyl)-4-mesitylpyridinato, mesppy is 4-mesityl-2-phenylpyridinato and pmdp is 2,2'-(phenylmethine)dipyridine, L1] possessing sterically congested cyclometalating ligands combined with the nonconjugated diimine ancillary N^N ligand are reported and their solution-state and thin film photophysical properties analyzed by both experimental and theoretical methods. The crystal structure of 1 confirms the formation of a six-membered chelate ring by the N^N ligand and illustrates the pseudo-axial configuration of the phenyl substituents. Upon photoexcitation in acetonitrile, both complexes exhibit a ligand-centered emission profile in the blue-green region of the visible spectrum. A significant blue-shift is observed in solution at room temperature compared to the analogous reference Ir(iii) complexes (R1 and R2) bearing 4,4'-di-tert-butyl-2,2'-bipyridine (dtBubpy) as the N^N ligand. The computational investigation demonstrates that the HOMO is mainly centered on the metal and on both cyclometalating aryl rings of the C^N ligands, whereas the LUMO is principally localized on the pyridyl rings of the C^N ligands. The photoluminescence quantum yield is reduced compared to the reference complexes, a probable consequence of the greater flexibility of the ancillary ligand.

Insight into catalytic reduction of CO2 to methane with silanes using Brookhart's cationic Ir(iii) pincer complex.

Using density functional theory computations, we investigated in detail the underlying reaction mechanism and crucial intermediates present during the reduction of carbon dioxide to methane with silanes, catalyzed by the cationic Ir-pincer complex ((POCOP)Ir(H)(acetone)+, POCOP = 2,6-bis(dibutylphosphinito)phenyl). Our study postulates a plausible catalytic cycle, which involves four stages, by sequentially transferring silane hydrogen to the CO2 molecule to give silylformate, bis(silyl)acetal, methoxysilane and the final product, methane. The first stage of reducing carbon dioxide to silylformate is the rate-determining step in the overall conversion, which occurs via the direct dissociation of the silane Si–H bond to the C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O bond of a weakly coordinated Ir–CO2 moiety, with a free energy barrier of 29.5 kcal mol−1. The ionic SN2 outer-sphere pathway in which the CO2 molecule nucleophilically attacks at the η1-silane iridium complex to cleave the η1-Si–H bond, followed by the hydride transferring from iridium dihydride [(POCOP)IrH2] to the cation [OC–OSiMe3]+, is a slightly less favorable pathway, with a free energy barrier of 33.0 kcal mol−1 in solvent. The subsequent three reducing steps follow similar pathways: the ionic SN2 outer-sphere process with silylformate, bis(silyl)acetal and methoxysilane substrates nucleophilically attacking the η1-silane iridium complex to give the ion pairs [(POCOP)IrH2] [HC(OSiMe3)2]+, [(POCOP)IrH2] [CH2(OSiMe3)2(SiMe3)]+, and [(POCOP)IrH2] [CH3O(SiMe3)2]+, respectively, followed by the hydride transfer process. The rate-limiting steps of the three reducing stages are calculated to possess free energy barriers of 12.2, 16.4 and 22.9 kcal mol−1, respectively. Furthermore, our study indicates that the natural iridium dihydride [(POCOP)IrH2] generated along the ionic SN2 outer-sphere pathway could greatly facilitate the silylation of CO2, with a potential energy barrier calculated at a low value of 16.7 kcal mol−1.