Ir Complexes Research Articles

Red and Near Infrared Emissive Bis‐Tridentate Ir(III) Phosphors for Organic Light Emitting Diodes

AbstractEfficient saturated red and near‐infrared (NIR) emissive materials are needed in the development of organic light‐emitting diodes (OLEDs), with applications extending beyond flat panel displays and lighting luminaries. Toward this aim, a series of bis‐tridentate Ir(III) complexes (3a ‒ 3c and 4a ‒ 4c) are designed and synthesized, showing emission spanning the region of 601‒694 nm in degassed toluene. Their emission tuning is mainly achieved using monoanionic chromophoric chelates, L1H for red and L2H for deep‐red and NIR, where the extended π‐conjugation and electron deficient N atoms are introduced synergistically. Moreover, three ancillary chelates, X1H2, X2H2, and X3H2, delivered a secondary influence via varied donor strength to the central Ir(III) atom. The resulting red and deep‐red OLED devices exhibit maximum (max.) external quantum efficiencies (EQEs) of 21.4% and 18.1% with peak maximum at 620 and 666 nm, respectively. More impressively, the device based on 4b delivers a NIR emission peak maximum at 702 nm with a maximum EQE of 10.0%.

Antibactericidal Ir(III) and Ru(II) Complexes with Phosphine-Alkaloid Conjugate and Their Interactions with Biomolecules: A Case of N-Methylphenethylamine.

The phosphine ligand (Ph2 PCH2 N(CH3 )(CH2 )2 Ph, PNMPEA) obtained by the reaction of the (hydroxymethyl)diphenylphosphine with naturally occurring alkaloid N-methylphenethylamine, was used to synthesize the half-sandwich iridium(III) (Ir(η5 -Cp*)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, IrPNMPEA) and ruthenium(II) (Ru(η6 -p-cymene)Cl2 Ph2 PCH2 N(CH3 )(CH2 )2 Ph, RuPNMPEA) complexes. They were characterized using a vast array of methods, including 1D and 2D NMR, ESI(+)MS spectrometry, elemental analysis, cyclic voltammetry (CV), electron spectroscopy in the UV-Vis range (absorption, fluorescence) and density functional theory (DFT). The initial antimicrobial activity in vitro toward Gram-positive and Gram-negative bacterial strains was examined, indicating that both complexes are selective towards Gram-positive bacteria, e. g., Staphylococcus aureus, where the IrPNMPEA has been more bactericidal compared to RuPNMPEA. Additionally, the interactions of these compounds with various biomolecules, such as DNA (ctDNA, plasmid DNA, 9-ethylguanine (9-EtG), and 9-methyladenine (9-MeA)), nicotinamide adenine dinucleotide (NADH), glutathione (GSH), and ascorbic acid (Asc) were described. The results showed that both Ir(III) and Ru(II) complexes accelerate the oxidation process of NADH, GSH and Asc that appeared to occur by an electron transfer mechanism. Interestingly, only IrPNMPEA leads to the formation of various biomolecule adducts, which can explain its higher activity. Furthermore, RuPNMPEA and IrPNMPEA have been interacting with the DNA through weak noncovalent interactions.

Iridium complexes of acridine-based PNP-type pincer ligands: Synthesis, structure and reactivity

Acridine-based PNP-type pincer ligands (AcrPNP) have previously been used for the construction of a small number of Ru(II), Mn(I), Rh(III) and Ir(III) complexes, with most attention being given to the catalytically-active ruthenium complexes. In the present work, we significantly expand the scope of known AcrPNP complexes by introducing a series of new Ir(I) and Ir(III) complexes. These were synthesized from two AcrPNP ligands differing in their P-substituents (iPr vs Ph), in conjunction with various Ir(I)-olefin precursors, through different sequences of reactions that include intramolecular CH activations and additions of H2 and NaBEt3H. The new iridium complexes, with their observed structures and reactivities, reflect the unique properties of the acridine-based PNP ligands, i.e., their inherent structural flexibility and ability to support both metal-centered reactivity (CH and HH oxidative addition) and ligand-centered reactivity (hydride- and H2-induced dearomatization).

Cell Death Mechanism of Organometallic Ruthenium(II) and Iridium(III) Arene Complexes on HepG2 and Vero Cells.

Due to side effects and toxicity associated with platinum-derived metal-based drugs, extensive research has been conducted on ruthenium (Ru) complexes. We aim to synthesize a highly oil soluble Ru(II)-p-cymene complex (Ru1) with an aliphatic chain group, a bimetallic Ru(II)-p-cymene complex (Ru2) with N,S,S triple-coordination and a bimetallic Ir(III)-pentamethylcyclopentadienyl complex (Ir1) with S,S double-coordination. Subsequently, we investigate the effects of these complexes on Vero and HepG2 cell lines, focusing on cell death mechanisms. Characterization of the complexes is performed through nuclear magnetic resonance spectroscopy (1H and 13C NMR) and Fourier-transform infrared spectroscopy. The effective doses are determined using the (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide) (MTT) assay, applying different doses of the complexes to the two cell lines for 24 and 48 h, respectively. Immunoreactivities of Bax, Bcl2, caspase-3, RIP3, and RIPK1 are analyzed using the indirect immunoperoxidase technique. Notably, all the complexes (Ru1, Ru2, and Ir1) exhibit distinct cell death mechanisms, showing greater effectiveness than cisplatin. This study reveals the diverse mechanisms of action of Ru and Ir complexes based on different ligands. To the best of our knowledge, this study represents the first investigation of a novel RAED-type complex (Ru1) and unexpected bimetallic complexes (Ru2 and Ir1).

Asymmetric tris-heteroleptic iridium(III) complexes towards blue phosphorescence: Synthesis, photophysics and OLED application

The development of blue phosphorescent iridium(III) complexes has been a formidable challenge in the field of organic light-emitting diodes (OLEDs). Unlike the conventional blue Ir-complex structure of symmetric tri-/bis-cyclometalated coordination geometry, we herein report a new configuration of [Ir(C1^N1)(C2^N2)(LX)]-tris-heteroleptic Ir(III) complex, where C1^N1 and C2^N2 denote two different main ligands, and LX stands for a third ancillary ligand. By the new configuration, two asymmetric blue iridium complexes, namely dfbpy-Ir-dfppy and dfppy-Ir-dfbpy, were designed and synthesized, displaying the highly desirable blue emission peaks at 450 nm and 452 nm, respectively. Based on the two new emitters, the blue OLEDs exhibited good performances with the maximum external quantum efficiency (EQEmax) reaching 8.5% and CIE(x, y) coordinates of (0.21, 0.31). This study provides a new strategy for efficient blue iridium complexes through reasonably engineering the asymmetric tris-heteroleptic Ir-complex configuration.

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.

Synthesis, characterization and in vitro antitumor activities of a biimidazole-chelated Ir(III) complex

Synthesis, characterization and in vitro antitumor activities of a biimidazole-chelated Ir(III) complex

Synthesis and Characterization of Platinum(IV) Complexes Containing 1‐Phenyl‐1H‐pyrazole and α‐Diimine Ligands

AbstractThe paper deals with the synthesis of a series of cationic [Pt(ppz)2(N^N)]2+ complexes containing deprotonated 1‐phenyl‐1H‐pyrazole as cyclometallating (C^N) ligands and α‐diimines (N^N) in the form of water‐soluble salts with OTf− (trifluoromethanesulfonate) counter ions. These complexes were obtained from cis‐[Pt(ppz)2Cl2] through chloride ligands substitution with α‐diimines. The complexes were identified by means of NMR spectroscopy and their molecular structures were confirmed by X‐ray crystallography. The photophysical properties of these complexes were studied in detail. These complexes showed strong luminescence in MeOH/EtOH 1 : 1 glasses at 77 K but were almost non‐emitting in MeCN solutions at room temperature. Their emission properties were compared to analogues IrIII complexes.

Density functional theory investigation of photoelectric conversion in graphene quantum dot/Ir(III) complex nanocomposites: the influence of π-conjugation in cyclometalating ligands.

Using density functional theory (DFT), this study investigates the photoelectric performance of nanocomposites formed by coupling graphene quantum dots (GQDs) with Ir(III) complexes. The goal is to evaluate the influence of different π-conjugation levels in cyclometalating ligands and determine the most efficient ligand for energy conversion in the nanocomposite. The analysis covers seven distinct Ir(III) complexes, each featuring a common bpy ligand but differing diimine ligands. These complexes are linked to GQDs through amide connections. The study comprehensively examines electronic structure, absorption spectra, charge transfer, and chemical reactivity. Our results show that increased ligand π-conjugation causes a redshift in the absorption spectrum due to smaller highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gaps, ultimately enhancing light harvesting. This effect becomes more pronounced when GQDs are incorporated. For less-conjugated ligands, attaching GQDs enhances metal-to-ligand charge transfer, facilitating electron injection into TiO2. Moreover, higher conjugation and GQD coupling reduce chemical hardness while increasing chemical potential and electrophilicity, thus improving electron acceptance. Furthermore, strategic structural variations modify free energy changes for electron injection and ground-state regeneration. Notable is the inclusion of perylene and pyrene moieties in the ligand, which accelerates injection and extends recombination lifetimes, while GQD incorporation accelerates injection across all ligands. Additionally, photocurrent generation primarily influences energy conversion efficiency. Finally, adding GQDs enhances the first-order hyperpolarizability, further boosting light harvesting. This study demonstrates the potential of tuning ligand π-conjugation and GQD interfaces to optimize optoelectronic properties and charge transfer dynamics, thereby enhancing solar energy conversion in GQD/Ir(III) complex systems.

Iridium(III)-Based Infrared Two-Photon Photosensitizers: Systematic Regulation of Their Photodynamic Therapy Efficacy.

Cyclometalated iridium(III) complexes are of significant importance in the field of antitumor photodynamic therapy (PDT), whether they exist as single molecules or are incorporated into nanomaterials. Nevertheless, a comprehensive examination of the relationship between their molecular structure and PDT effectiveness remains awaited. The influencing factors of two-photon excited PDT can be anticipated to be further multiplied, particularly in relation to intricate nonlinear optical properties. At present, a comprehensive body of research on this topic is lacking, and few discernible patterns have been identified. In this study, through systematic structure regulation, the nitro-substituted styryl group and 1-phenylisoquinoline ligand containing YQ2 was found to be the most potent infrared two-photon excitable photosensitizer in a 4 × 3 combination library of cyclometalated Ir(III) complexes. YQ2 could enter cells via an energy-dependent and caveolae-mediated pathway, bind specifically to mitochondria, produce 1O2 in response to 808 nm LPL irradiation, activate caspases, and induce apoptosis. In vitro, YQ2 displayed a remarkable phototherapy index for both malignant melanoma (>885) and non-small-cell lung cancer (>1234) based on these functions and was minimally deleterious to human normal liver and kidney cells. In in vivo antitumor phototherapy, YQ2 inhibited tumor growth by an impressive 85% and could be eliminated from the bodies of mice with a half-life as short as 43 h. This study has the potential to contribute significantly to the development of phototherapeutic drugs that are extremely effective in treating large, profoundly located solid tumors as well as the understanding of the structure-activity relationship of Ir(III)-based PSs in PDT.

Iridium(III) complex induces apoptosis in HeLa cells by regulating mitochondrial and PI3K/AKT signaling pathways: In vitro and in vivo experiments

Cyclometalated iridium complexes with mitochondrial targeting show great potential as substitutes for platinum-based complexes because of their strong anti-cancer properties. Three novel cyclometalated iridium(III) compounds were synthesized and evaluated in five different cell lines as part of the ongoing systematic investigations of these compounds. The complexes were prepared using 4,7-dichloro-1,10-phenanthroline ligands. The cytotoxicity of complexes Ir1-Ir3 towards HeLa cells was shown to be high, with IC50 values of 0.83±0.06, 4.73±0.11, and 4.95±0.62 μM, respectively. Complex Ir1 could be ingested by HeLa cells in 3 h and has shown high selectivity toward mitochondria. Subsequent investigations demonstrated that Ir1 triggered apoptosis in HeLa cells by augmenting the generation of reactive oxygen species (ROS), reducing the mitochondrial membrane potential, and depleting ATP levels. Furthermore, the movement of cells was significantly suppressed and the progression of the cell cycle was arrested in the G0/G1 phase following the administration of Ir1. The Western blot analysis demonstrated that the induction of apoptosis in HeLa cells by Ir1 involves the activation of the mitochondria-dependent channel and the PI3K/AKT signaling pathway. No significant cytotoxicity was observed in zebrafish embryos at concentrations less than or equal to 16 µM, e.g., survival rate and developmental abnormalities. In vivo, antitumor assay demonstrated that Ir1 suppressed tumor growth in mice. Therefore, our work shows that complex Ir1 could be a promising candidate for developing novel antitumor drugs.

P-Stereogenic threonine derived Ir–P,N complexes. Reversible cyclometallation and asymmetric hydrogenation reactions

A threonine-derived phosphine-oxazoline iridium catalyst is reported, showcasing excellent selectivity in the hydrogenation of N-Boc-2,3-diarylallylamines. The reversible cyclometallation process between the square planar Ir(I) complex and the corresponding octahedral Ir(III) species is thoroughly investigated, while considering the influence of substitution at the phenyl group of the oxazoline on this equilibrium. X-Ray analysis reveals that the cyclometallated tridentate ligand adopts a fac coordination mode. Furthermore, the catalytic performance of these complexes in the asymmetric hydrogenation is evaluated and the utilization of Ir(III) pre-catalysts or Ir(I)/Ir(III) mixtures in hydrogenation reactions is proposed based on the observed equilibrium dynamics.

Cyclometalated Ir(III) Complexes as Lysosome-Targeted Photodynamic Anticancer Agents.

We have designed and synthesized two Ir(III) complexes (Ir1 and Ir2) coordinated with an 8-sulfonamidoquinoline derivative ligand as photosensitizers, which exhibit strong red phosphorescence emission and a long phosphorescence lifetime. The Ir(III) complexes exhibit a high population of triplet states, which enable red phosphorescence and efficient singlet oxygen generation. Ir1 and Ir2 rapidly enter the cancer cells and accumulate in lysosomes, producing large amounts of intracellular singlet oxygen when exposed to light irradiation, eventually leading to cancer cell death, and the phototoxic indexes of complexes Ir1 and Ir2 against cancer cells are in the range of 76-228. Overall, our studies indicate that the synthesized Ir(III) complexes with quinoline ligands exhibit photosensitizing properties, effectively inducing cancer cell death when exposed to light. These promising results suggest their potential application in photodynamic therapy.

Cyclometalated iridium(III) complexes induce immunogenic cell death in HepG2 cells via paraptosis

Immunotherapy has been shown to provide superior antitumor efficacy by activating the innate immune system to recognize, attack and eliminate tumor cells without seriously harming normal cells. Herein, we designed and synthesized three new cyclometalated iridium(III) complexes (Ir1, Ir2, Ir3) then evaluated their antitumor activity. When co-incubated with HepG2 cells, the complex Ir1 localized in the lysosome, where it induced paraptosis and endoplasmic reticulum stress (ER stress). Notably, Ir1 also induced immunogenic cell death (ICD), promoted dendritic cell maturation that enhanced effector T cell chemotaxis to tumor tissues, down-regulated proportions of immunosuppressive regulatory T cells within tumor tissues and triggered activation of antitumor immunity throughout the body. To date, Ir1 is the first reported iridium(III) complex-based paraptosis inducer to successfully induce tumor cell ICD. Furthermore, Ir1 induced ICD of HepG2 cells without affecting cell cycle or reactive oxygen species levels.

Unusual formation of Ir(III) complexes with non‐symmetrical NacNac ligands: Synthesis, characterization, and evaluation of catalytic activity in transfer hydrogenation reduction reactions

A new type of trans‐dichloro‐Ir(III) complexes derived from non‐symmetrical NacNac‐type ligands was unexpectedly obtained as the main reaction product from the former ligands and the dimeric species [Ir(COD)Cl2]. One equivalent of LH was reacted with an excess of [Ir(COD)Cl]2 in dichloromethane or toluene as solvent and at room temperature. The general formula of the product is [IrCl2(COD)L] and was isolated as a sole product instead of the expected Ir(I) compound [Ir(COD)L]; all the new Ir(III) were prepared in high yields as microcrystalline solids. They were all stable under laboratory atmosphere, lasting for weeks in solution and for months in solid state. The structure of each compound was examined by 1D and 2D nuclear magnetic resonance (NMR) and high‐resolution mass spectrometry (HRMS). Complex 1k was selected for an X‐ray diffraction study. Finally, an evaluation was made of the catalytic activity of all complexes in the transfer hydrogenation reaction of ketones and imines.

Half-Sandwich Iridium(III), Rhodium(III), and Ruthenium(II) Complexes Chelating Hybrid sp2-N/sp3-N Donor Ligands to Achieve Improved Anticancer Selectivity.

The biological efficacy of half-sandwich platinum group organometallic complexes of the formula [(η5-Cpx)/(η6-arene)M(XY)Cl]0/+ (XY = bidentate ligands; Cpx = functionalized cyclopentadienyl; M = Ir, Rh, Ru, Os) has received considerable attention due to the significance of the metal center, chelating ligand, and Cpx/arene moieties in defining their anticancer potency and selectivity. With a facile access to the BIAN-derived imine-amine ligands using alkylaluminum as the reductant, we herein described the preparation and characterization of 16 half-sandwich Ir(III), Rh(III), and Ru(II) complexes chelating the hybrid sp2-N/sp3-N donor ligand. A nonplanar five-member metallacycle was confirmed by X-ray single-crystal structures of Ir1-Ir3, Ir7, Rh1, Ru1, and Ru4. The attempt to prepare imine-amido complexes using a base as the deprotonating agent led to the mixture of imine-amine complexes, within which the leaving group Cl- was displaced, and 16-electron imine-amido complexes without Cl-. The half-sandwich imine-amine complexes in this system underwent rapid hydrolysis in aqueous solution, exhibited weak photoluminescence, and showed the ability of binding to CT-DNA and BSA. The cytotoxicity of all imine-amine complexes against A549 lung cancer cell lines, HeLa cervical cancer cell lines, and 4T1 mouse breast cancer cells was determined by an MTT assay. The IC50 values of these complexes were in a range of 5.71-67.28 μM. Notably, most of these complexes displayed improved selectivity toward A549 cancer cells versus noncancerous BEAS-2B cells in comparison with the corresponding α-diimine complexes chelating the sp2-N/sp2-N donor ligand, which have been shown no selectivity in our previous report. The anticancer selectivity of these complexes appeared to be related to the redox-based mechanism including the catalytic oxidation of NADH to NAD+, reactive oxygen species (ROS) generation, and depolarization of the mitochondrial membrane. Further, inducing apoptosis of these complexes in A549 cancer cells and BEAS-2B normal cells also correlated with their anticancer selectivity, indicating the apoptosis mode of cell death in this system. In addition, these complexes could enter A549 cells via energy-dependent pathway and were able to impede the in vitro migration of A549 cells.

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.

All-small-molecule organic solar cells based on cyclometalated tris-Ir(III) complexes as donor materials

Cyclometalated tris-Ir(III) complexes with six-coordinated octahedral configuration are beneficial to reduce aggregation for improved film morphology in organic solar cells (OSCs). Herein, two homoleptic tris-Ir complexes of eBz3Ir and eTBz3Ir showing majority absorption from UV to light-blue range are designed as electron donor materials. Owing to the extended π-conjugation by an extra thiophene ring in each ligand, eTBz3Ir exhibits red-shifted and stronger absorption as well as better charge transport property than eBz3Ir. Therefore, when employing the fused-ring non-fullerene acceptor Y6 or L8-BO to fabricate all-small-molecule OSCs (ASMOSCs), eTBz3Ir blended devices demonstrate higher efficiency than eBz3Ir, with maximum power conversion efficiency (PCE) achieving at 9.48/7.55% for Y6 and 10.48/6.46% for L8-BO devices, respectively. To our knowledge, over 10% PCE is among the highest values for binary ASMOSCs based on organometallic Ir complexes as photovoltaic materials. Such uncompetitive solar-light absorption but relatively high PCE indicates homoleptic Ir complexes with octahedral configurations are expected as promising photoactive materials for high-efficiency ASMOSCs.

Automatic Screen‐out of Ir(III) Complex Emitters by Combined Machine Learning and Computational Analysis (Advanced Optical Materials 18/2023)

Automatic Screen‐out of Ir(III) Complex Emitters by Combined Machine Learning and Computational Analysis (Advanced Optical Materials 18/2023)