Mixed-ligand Iridium Research Articles

Mixed-Ligand Iridium(III) Nitro Complexes with Phenantroline

Interaction of iridium(III) nitro-aqua complexes with 1,10-phenanthroline is studied. Complex anions [Ir(phen)(NO2)4]− and [Ir(phen)(OH)(NO2)3]− are isolated in the solid phase. The complex Na[Ir(phen)(NO2)4](phen)(H2O) is structurally characterized for the first time. Crystallographic data: \(a = 8.0752(5)\acute{\overset{\circ}{\mathrm{A}}}\), \(b = 11.690(7)\acute{\overset{\circ}{\mathrm{A}}}\), \(c = 14.012(7)\acute{\overset{\circ}{\mathrm{A}}}\), α = 105.55(2)°, β = 91,99(2)°, γ = 103,71(2)° space group P-1, Z = 2, ρcalc = 1,936 g/cm3. The coordination sphere of the iridium atom has a distorted octahedral geometry. The obtained structure contains an island motif consisting of the pairs of complex anions [Ir(phen)(NO2)4]− linked to each other by sodium cations.

Structure and thermal properties of (1,1,1-trifluoro-4-methyliminopentanoato-2) (cyclooctadiene-1,5)iridium(I)

A mixed-ligand iridium(I) complex with the imino-derivative of asymmetric β-diketone [Ir(cod)(Meitfac)] (cod = C8H12, cyclooctadiene-1,5; Mei-tfac = CF3C(O)CHC(NMe)CH3, 1,1,1-trifluoro-4-methyliminopentanoato-2) is synthesized for the first time. The compound is obtained by the interaction of [Ir(cod)Cl]2 with sodium β-iminoketonate in diethyl ether in the inert atmosphere and is characterized by elemental analysis, IR and NMR spectroscopy. According to the single crystal X-ray diffraction analysis, the compound is a monomeric molecular complex. The coordination environment of iridium is a distorted square; the Ir–O and Ir–N bond lengths are 2.031(1) A and 2.086(2) A respectively; the average distance Ir–C′ = 1.994(8) A (C′ is the center of the С=С bond of the cod ligand); the NIrO chelate angle is 91.30(6)°, and the C′IrC′ angle is 87.63°. The crystal packing contains dimers formed by weak F…H–C hydrogen interactions. The thermal properties of the complex are studied by thermogravimetry. The compound passes into the gas phase in the temperature range 150-260 °C (mass loss 93.5%) and is characterized by a lower volatility as compared with its β-diketonate analog [Ir(cod)(tfac)] (tfac = CF3C(O)CHC(O)CH3, 1,1,1-trifluoropentadionato-2,4).

Mixed-ligand iridium(iii) complexes as photodynamic anticancer agents.

Many phosphorescent iridium complexes are potent candidates as photodynamic therapeutic agents. In this work, a series of mixed-ligand phosphorescent iridium complexes (Ir1: [Ir(L1)(bpy)Cl](PF6)2; Ir2: [Ir(L1)(ppy)Cl](PF6); Ir3: [Ir(L2)(bpy)Cl](PF6)2; Ir4: [Ir(L2)(ppy)Cl](PF6). L1 = 2,6-bis(2-benzimidazolyl)pyridine; bpy = 2,2'-bipyridine; L2 = 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine; ppy = 2-phenylpyridine) have been synthesized and characterized. These complexes display high luminescence quantum yields and long phosphorescence lifetimes. All the complexes are resistant to hydrolysis in aqueous solutions, and can produce singlet oxygen (1O2) effectively upon irradiation. Ir1 and Ir2 show pH-sensitive emission properties. Interestingly, higher cellular uptake efficiency is observed for Ir2 and Ir4 with the cyclometalated ppy ligand in human lung adenocarcinoma A549 cells. Ir2 with pH-sensitive emission properties can selectively image lysosomes, and Ir4 can specifically target mitochondria. Both Ir2 and Ir4 exhibit potent photodynamic therapy (PDT) effects, with Ir2 displaying a higher phototoxicity index (PI) especially in A549 cells (PI > 54). Mechanism studies indicate that Ir2 and Ir4 can induce apoptosis through reactive oxygen species (ROS) generation and caspase activation upon visible light (425 nm) irradiation. As expected, Ir2 can damage lysosomes more effectively with a pH-sensitive singlet oxygen (1O2) yield, while Ir4 tends to impair mitochondrial function. Nevertheless, the practical application of Ir2 and Ir4 for PDT may be limited to superficial tumors due to the short excitation wavelength (425 nm). Our study gives insights into the design and anticancer mechanisms of new metal-based PDT anticancer agents.

Volatile iridium(I) complexes with β-diketones and cyclooctadiene: syntheses, structures and thermal properties

A series of volatile mixed-ligand iridium(I) complexes [Ir(cod)(L)] (cod = cyclooctadiene-1,5, L = R1C(O)CHC(O)R2, R1 = CF3, R2 = CF3 – hfac 1, Me – tfac 2; tBu – ptac 3, Ph – btfac 4, R1 = R2 = Me – acac 5; tBu – thd 6) was synthesized and investigated in terms of usage in metal-organic chemical vapor deposition processes. Compounds 3 and 4 were obtained for the first time. All compounds were investigated by elemental analysis, NMR spectroscopy, thermogravimetry, and mass spectrometry. Crystal structures of 2–4 and 6 were determined by single-crystal XRD. The influence of β-diketonate ligand on the thermal properties of complexes in condensed and gas phase was revealed. The following volatility order was arranged: L = hfac 1 > tfac 2 ≈ ptac 3 > acac 5 > thd 6 > btfac 4. Complexes 1 and 6 vapors demonstrated the lowest and the highest thermostability, respectively.

Carboxy derivatised Ir(III) complexes: synthesis, electrochemistry, photophysical properties and photocatalytic hydrogen generation.

In this contribution the synthesis and characterisation of a series of novel mixed ligand iridium(iii) complexes, functionalised with a carboxy ester or phosphonate groups are reported. These groupings are introduced on the 4-position of either the phenyl pyridine or the 2,2'-bipyridyl ligands. A low temperature high yield synthesis for the precursor [Ir(ppy-COOEt)2(μ-Cl)]2 was developed. The photophysical and electrochemical properties of these compounds are also described, together with their behaviour as photosensitisers for the generation of hydrogen from water.

Four emission bands from a mixed-ligand iridium complex IrQ(ppy)2 at room temperature

Four photoluminescence bands are observed from iridium complex in UV, violet, green, and red spectral regions at room temperature. Such a multiple emission is found from a mixed-ligand iridium(III) complex, (8-quinolinolato) bis(2-phenylpyridyl) iridium IrQ(ppy)2, which consists of IrQ and Ir(ppy)2 components (Q: 8-quinolinolato, ppy: phenylpyridyl). Of the four emission bands, the UV emission band with maximum at about 330nm and the red emission band are attributed to the ligand-centered (1LC) 1nπ* and metal-to-ligand charge transfer (3MLCT) 3(ππ*) states from IrQ, respectively, while the violet emission band with maximum at about 400nm and the green emission band at about 513nm are attributed to the 1LC 1(nπ*) and 3MLCT 3ππ* states from Ir(ppy). It is suggested that (1) IrQ and Ir(ppy) generate their own emissions by the inefficient Förster energy transfer between IrQ and Ir(ppy) due to the orientation factor of nearly zero, and (2) each of IrQ and Ir(ppy) gives rise to two emissions from the singlet and triplet states by the inefficient intersystem crossing.

Theoretical Studies of Blue Phosphorescent Iridium(III) Complexes with Phenylpyrazole and Phosphines

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dppz)(PPhMe2)2(H)(C1) and Ir(dppz)(PPhMe2)2(H)(CN), [dppz = 3,5-Diphenylpyrazole] were studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission and increase the emission efficiency, the following must occur: (1) substitution of phenyl group on the 3-position of the pyrazole ring that lower the triplet energy enough that the quenching channel is not thermally accessible, (2) changing ancillary ligands coordinated to iridium atom to phosphine and cyano groups known as very strong field ligands. Using the density functional theory (DFT) and time-dependent DFT method calculations on the ground and excited states of the complexes, we have studied how the ancillary ligand influences the emission peak as well as MLCT transition efficiency. It is showed that the strong-field ancillary ligand such as CN, PPhMe2 alters the energy gap mainly by changing the highest occupied molecular orbitals (HOMO) energy level. Their inclusion in the coordination sphere can increase the energy gap to achieve the hypsochromic shift in emission color and also lower the triplet energy level to avoid the thermal quenching.

Synthesis and Photophysical Studies of Blue Phosphorescent Ir(III) Complexes with Dimethylphenylphospine

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir{(CF3)2Meppy}(PPhMe3)2(H)(L) [L = CI, NCMe, CN] [(CF3)2Meppy = 2-(3', 5'-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission, the trifluoromethyl group substituted on the phenyl ring and the methyl group substituted on the pyridyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discuss how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The maximum emission spectra of Ir{(CF3)2Meppy}(PPhMe3)2(H)(Cl), [Ir{(CF3),Meppy)(PPhMe3),(H)(NCMe)]+ and Ir{(CF3)2Meppy}(PPhMe3)2(H)(CN) were in the ranges of 441, 435, 434 nm, respectively.

Theoretical Studies of Mono-Cyclometalated Ir(III) Complexes with Phenylpyrazole Based Ligands and Phosphines

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dppzc)(PPhMe2)2(H)(L) (L = Cl, CN) [dppzc = 1,3-Diphenyl-1H-pyrazole-4-carboxaldehyde] were studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discussed how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The calculated energies of triplets are 3.09 and 3.16 eV, respectively, which are all higher than that of Ir(dfppy)2(acac) and FIrpic known as blue phosphorescence materials with 2.69 and 2.73 eV.

Synthesis and Photophysical Properties of Blue Mono-Cyclometalated Ir(III) Complexes with Phenylpyidine Based Ligands and Phosphines

New blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other such as Ir(dFOMeppy)(PPh3)2(H)(Cl), [Ir(dFOMeppy)(PPh3)2(H)(NCMe)]+ and Ir(dFOMeppy)(PPh3)2(H)(CN), [dFOMeppy = 2-(2′,4′-difluorophenyl)-4-methoxypyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. To achieve deep blue emission, the difluoro group substituted on the phenyl ring and the methoxy group substituted on the pyridyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift. To gain insight into the factors responsible for the emission color change and the different luminescence efficiency, we investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the complexes. From these results, we discuss how the ancillary ligand influences the emission peak as well as the metal to ligand charge transfer (MLCT) transition efficiency. The maximum emission spectra of Ir(dFOMeppy)(PPh3)2(H)(Cl), [Ir(dFOMeppy)(PPh3)2(H)(NCMe)]+ and Ir(dFOMeppy)(PPh3)2(H)(CN) were in the ranges of 438, 433, 432 nm, respectively.

ChemInform Abstract: Chemoselective Asymmetric Hydrogenation of α,β-Unsaturated Carbonyl Compounds to Allylic Alcohols Catalysed by (Ir(binap)(cod)) BF4-Aminophosphine.

Asymmetric hydrogenation of (E)-4-phenyl-3-buten-2-one by use of [Ir(binap)(cod)]BF4 and o-di-methylaminophenyldiphenylphosphine afforded (E)-4-phenyl-3-buten-2-ol in 97% chemoselectivity and in 65% enantiomeric excess. A mixed ligand iridium dihydride complex containing both BINAP and the aminophosphine ligand has been shown to be the catalytically active species.

Strong Ligand Field Effects of Blue Phosphorescent Iridium(III) Complexes

In this study, new deep blue emitting mixed ligand iridium(III) complexes such as Ir(dFppy)(PPhMe2)2(H)(Cl), [Ir(dFppy)(PPhMe2)2(H)(NCMe)]+ and Ir(dFppy)(PPhMe2)2(H)(CN), [dFppy = 2-(2′,4′-difluoro-phenyl)pyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. These iridium complexes comprise one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands. We investigate the electron-withdrawing capabilities of ancillary ligands using the DFT and TD-DFT calculations on the ground and excited states of the three complexes to gain insight into the factors responsible for the emission color change and the different luminescence efficiency. Reducing the molecular weight of phosphine ligand with PPhMe2 leads to a strategy of the efficient deep blue organic light-emitting devices (OLED) by thermal processing instead of the solution processing. The electron-withdrawing difluoro group substituted on the phenyl ring and the cyano strong field ancillary ligand in the trans-position to the carbon atom of phenyl ring increased HOMO-LUMO gap and achieved the hypsochromic shift in emission color. As a result, the maximum emission spectra of Ir(dFppy)(PPhMe2)2(H)(Cl), [Ir(dFppy) (PPhMe2)2(H)(NCMe)]+ and Ir(dFppy)(PPhMe2)2(H)(CN) were in the ranges of 452, 443, 442 nm, respectively.

Mixed-ligand iridium(IV) complexes with amino acids, adenine and hypoxanthine

The complexation in iridium(IV)-purine base (adenine, hypoxanthine)-amino acid (α-alanine, aspartic acid, lysine) systems was studied by pH titration. The stability constants of 1: 1: 1 complexes were determined. The stability of 1: 1: 1 mixed-ligand complexes with hypoxanthine and adenine increases in the series Ala < Lys < Asp. Reactions between aqueous solutions gave the following coordination compounds: [Ir(C5H4N4O)(C3H6NO2)Cl]Cl2, [Ir(C5H4N4O)(C4H5NO4)]Cl2, [Ir(C5H4N4O)(C6H13N2O2)]Cl3, [Ir(C5H5N5)(C3H6NO2)]Cl3, [Ir(C5H5N5)(C4H5NO4)]Cl2, and [Ir(C5H5N5)(C6H13N2O2)]Cl3. The individual character of the complexes was established by chemical and thermogravimetric analyses and powder X-ray diffraction. The complexes were characterized by NMR, IR, and X-ray photoelectron spectroscopy. Alanine and lysine in mixed-ligand iridium(IV) complexes are bidentate (α-NH2 and COO− groups), aspartic acid is tridentate, and purine bases function as polydentate ligands through heterocycle N atoms and functional groups (NH2 in adenine and C=O in hypoxanthine).

The Role of Ancillary Ligands in Iridium(III) Complexes for Blue OLEDs

In this study, new deep blue emitting mixed ligand iridium(III) complexes comprising one cyclometalating, two phosphines trans to each other and two cis-ancillary ligands, such as Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy} (PPh3)2(H)(CN), [(CF3)2Meppy = 2-(3′,5′-bis-trifluoromethylphenyl)-4-methylpyridine] were synthesized and studied to tune the phosphorescence wavelength to the deep blue region and to enhance the luminescence efficiencies. We investigate the strong field capabilities of ancillary ligands to gain insight into the factors responsible for the emission color change and the different luminescence efficiencies. This work represents a strategy for the design of deep blue phosphorescent iridium complexes. The electron-withdrawing trifluoromethyl group substituted on the phenyl ring, the electron-donating methyl group on the pyridyl ring and the cyano strong field ancillary ligand increase HOMO-LUMO gap to achieve the hypsochromic shift in emission color. As a result, the maximum emission spectrum of Ir{(CF3)2Meppy}(PPh3)2(H)(Cl), [Ir{(CF3)2Meppy}(PPh3)2(H)(NCMe)]+ and Ir{(CF3)2Meppy}(PPh3)2(H)(CN) were in the ranges of 436, 434 and 434 nm, respectively.

Optical characteristics of organic light emitting diode with IrQ(ppy) 2–5Cl and its emitter

The synthesis and photophysical study of a cyclometalated mixed-ligand iridium(III) complex are reported. The iridium complex (called IrQ(ppy) 2–5Cl) has two cyclometalated 2-phenylpyridine (ppy) ligands and one 8-hydroxyquinoline (Q) ligand, where one of the H atom is substituted by Cl atom. Absorption and photoluminescence spectra are studied for the neat film and films of IrQ(ppy) 2–5Cl doped in 4,4′-N,N′-dicarbazole-biphenyl and polystyrene, together with the electroluminescence spectra using multi-layer light emitting devices. The electronic states are studied using density functional theory calculations. Emission bands are observed at 502 and 666 nm, which arise from ppy and Q ligands, respectively.

Photochemical production of hydrogen and carbon dioxide from formate using mixed-ligand iridium complexes as catalysts

Photochemical production of hydrogen and carbon dioxide from formate using mixed-ligand iridium complexes as catalysts

Chemoselective asymmetric hydrogenation of α,β-unsaturated carbonyl compounds to allylic alcohols catalysed by [Ir(binap)(cod)]BF 4-aminophosphine

Asymmetric hydrogenation of ( E)-4-phenyl-3-buten-2-one by use of [Ir(binap)(cod)]BF 4 and o-di-methylaminophenyldiphenylphosphine afforded ( E)-4-phenyl-3-buten-2-ol in 97% chemoselectivity and in 65% enantiomeric excess. A mixed ligand iridium dihydride complex containing both BINAP and the aminophosphine ligand has been shown to be the catalytically active species.

Spectroscopic behavior of a new family of mixed-ligand iridium(III) complexes

We report the results concerning the absorption spectra, luminescence spectra and luminescence lifetimes of the complexes [(η 5-Me 5C 5)Ir(bpy)Cl]Cl ( 1), [(η 5-Me 5C 5)Ir(phen)Cl]Cl ( 2), [(η 5-Me 5C 5)Ir(bpy)H]BPh 4 ( 3) and [(η 5-Me 5C 5)Ir(phen)H]BPh 4 ( 4) (bpy = 2,2′-bipyridine, phen = 1,10-phenanthroline and η 5-Me 5C 5 = pentamethylcyclopentadienyl = Cp*). For all complexes examined the low energy absorption band is assigned to metal-to-ligand charge-transfer transitions involving the diimine ligands. For the hydrido complexes 2 and 4 the luminescence observed both at 77 K and at room temperature is assigned to metal-to-ligand charge-transfer transitions involving the diimine ligands. The chloride complexes 1 and 3 were not found to emit.