Synthesis, Crystal Structure and Photoluminescence of a Cyclometalated Iridium(III) Coumarin Complex

In this paper a new cyclometalated iridium(III) coumarin complex, Ir(III)bis(3-(2-benzothiazolyl)coumarinato N,C⁴)(acetylacetonate) (Ir(L)₂(acac)), was synthesized and characterized. X-ray crystallography demonstrated that the iridium(III) ion is hexacoordinated by two C atoms and two N atoms from 3-(2-benzothiazolyl)coumarinato ligands and two O atoms from acac ligand, displaying distorted octahedral coordination geometry. The Ir(L)₂(acac) complex has good thermal stability with less than 2 % weight-reduction occurring at 300 °C, and exhibits strong reddish orange emission. The results shown that Ir(L)₂(acac) is useful for fabrication organic light-emitting diodes.     

Density functional theory and time-dependent density functional study a series of iridium complexes with low-efficiency roll-off properties

ABSTRACT

A series of blue phosphorescent heteroleptic cyclometalated Ir(III) complexes with mesitylphenyl-imidazole ligands for organic light-emitting devices have been theoretically studied. We want to find their electronic structures, spectroscopic properties, and application value for organic light-emitting devices. (fppz)₂Ir(acac), (fppz)₂Ir(tpip), (dfbdp)₂Ir(fppz), (F-fppz)₂Ir(acac), (F-fppz)₂Ir(tpip), and (dfbdp)₂Ir(F-fppz) are investigated with DFT and TD-DFT approaches, where, for (fppz)₂Ir(acac), (fppz denotes 2-(5-(trifluoromethyl)-4H-pyrazol-3-yl)pyridine, and acac denotes acetylacetonate); for (fppz)₂Ir(tpip), tpip denotes tetraphenylimido-diphosphinate; and, for (F-fppz)₂Ir(acac) and (F-fppz)₂Ir(tpip), F-fppz denotes 2-(5-fluoro-4H-pyrazol-3-yl)pyridine.     

New red electrophosphor based on Ir(III) complex of 2,3,4-triphenylquinoline

2,3,4-Triphenylquinoline (tpq) ligand and its Ir(III) complex Ir(tpq)₂(acac) were prepared and their photonic properties were investigated as red electrophosphorescent material. The photoluminescence (PL) spectra of tpq and Ir(tpq)₂(acac) in dichloromethane showed a peak at 450 nm and 607 nm, respectively, at room temperature. The small Stokes shift between the ³MLCT absorption and emission bands shows that Ir(tpq)₂(acac) emits from a predominantly ³MLCT excited state. The theoretical calculation of the Ir(III) complex was performed by an ab initio method, and the result calculated by time dependent density functional theory (TD-DFT) showed that the Ir(III) complex underwent a strong ³MLCT transition because of the strong coupling between the 5d-orbital of Ir atom and the highest occupied molecular orbital (HOMO) of tpq ligand. Thus, it is concluded that this complex is a good candidate for a highly efficient electrophosphorescent material.     

Iridium(III) Complexes with Orthometalated Phenylimidazole Ligands Subtle Turning of Emission to the Saturated Green Colour

A series of novel six iridium complexes (1–6) bearing two substituted phenylimidazole and an additional acetylacetone as the third co-auxilary ligand are reported. The lowest absorption band for all iridium complexes consist of a mixture of heavy atom Ir(III) enhanced ³MLCT and ³ π-π* transitions and the phosphorescent peak wavelength can be fine-tuned to cover the spectral range 455–518 nm with high quantum efficiencies. The peak wavelength of the dopants can be finely tuned depending upon the electronic properties of the substituents. On the basis of onset potentials of the oxidation and reduction, the HOMO-LUMO energies were calculated and the reported iridium complexes emit green light with exceeding higher efficiency.     

Organic light‐emitting materials based on iridium(III) complexes bearing phenanthroimidazole ligands

We present the elegant synthesis and the photophysical and electroluminescent properties of a series of cyclometalated iridium(III) complexes [Ir(PPI)₂(pic), PPI: 1,2‐diphenyl‐1H‐phenanthro[9,10‐d]imidazole; pic: picolinic acid]. The Ir(PPI)₂(pic) complexes showed characteristic phosphorescence with an emission range of 556–579 nm and a high quantum efficiency with microsecond lifetimes. The strongly allowed phosphorescence in these complexes is the result of significant spin–orbit coupling of the Ir center. All bis(PPI) derivatives exhibit intense triplet metal‐to‐ligand charge transfer (MLCT) photoluminescence in the fluid solutions at room temperature. The impact of different solvents, substituents on the phenanthroimidazole ligands and complex concentrations upon their emissive behavior have been examined and demonstrate that their emission energies can be systematically modified. Weak bands located at longer wavelength have been assigned to the ¹MLCT ← S₀ and ³MLCT ← S₀ transitions of iridium complexes. Application of the ³MLCT excited state of the [Ir(PPI)₂(pic)] materials in organic light‐emitting devices are described. Copyright © 2014 John Wiley & Sons, Ltd.     

Photophysical and Analyte Sensing Properties of Cyclometalated Ir(III) Complexes

The synthesis of some heteroleptic, cyclometalated iridium(III) complexes is described. The utility of these [Ir(ppy)₂(N-N)]Cl (ppy = 2-phenylpyridine and N-N = substituted bipyridine, biquinoline, or phenanthroline) complexes as luminescence-based sensors is assessed. The emission intensity of an Ir(III) complex featuring the 3,3′-H_ndcbpy ligand (H_ndcbpy = dicarboxylic acid-2,2′-bipyridine; n = 0,1,2 to indicate deprotonated, mono- and diprotonated species, respectively) is seen to increase in the presence of Pb(II). Insight into the structure and analyte-sensing capability is achieved by X-ray crystallography in conjunction with computational modeling. Complexes incorporating carboxylic acid-functionalized bipyridine and biquinoline as the polypyridyl ligand show pH sensitivity while similar phenanthroline complexes do not.     

铱金属配合物磷光材料掺杂聚合物体系的电致发光特性

通过对一种新型贵金属铱的配合物磷光材料(pbi)₂Ir(acac)与咔唑共聚物进行物理掺杂, 制备了结构为indium-tin oxide(ITO)/poly(N-vinylcarbazole)(PVK): (pbi)₂Ir(acac)(x)/2,9-dimethyl-4,7-diphenyl-1,10-phenan throline(BCP)(20nm)/8-Hydroxyquinoline aluminum(Alq₃)(10nm)/Mg:Ag的聚合物电致磷光器件,研究了磷光聚合物掺杂体系在低掺杂浓度时(0.1%和0.5%(质量百分数,全文同))的光致发光(PL)和电致发光(EL)特性. 结果表明, 该掺杂体系的PL光谱和EL光谱中均同时存在主体材料PVK与磷光客体(pbi)₂Ir(acac)的发光光谱, 但主客体的发射强度不同,推测该掺杂体系在电致发光条件下, 同时存在主体材料到客体的不完全的能量传递和载流子直接俘获过程. 磷光掺杂浓度为0.1%的器件在19V电压下实现了白光发射, 色坐标为(0.32, 0.38), 掺杂浓度为0.5%的器件在20.6V电压下的最大发光亮度为11827 cd·m^-2, 而在13.4V电压下的最大流明效率为4.13 cd·A^-1. 关键词： 有机电致发光器件 铱配合物磷光 聚合物掺杂     

Optical and electrochemical characteristics of ethylenediamine complexes of Pt(II) and Ir(III) with metalated 2-phenyl- and 2-naphthylbenzothiazole

The cyclometalated complexes [Pt(С^N)En]PF₆ and [Ir(C^N)₂En]PF₆ ((C^N)^– are deprotonated forms of 2-phenylbenzothiazole or 2-naphthylbenzothiazole and En is ethylenediamine) are studied by ¹Н NMR, IR, electronic absorption, and emission spectroscopy, as well as by voltammetry. Metalation of heterocyclic ligands leads to the formation of five-membered {M(C^N)} cycles in the composition of squareplanar Pt(II) complexes and octahedral Ir(III) complexes of the cis-С,С structure. A bathochromic shift of the metal-to-cyclometalated ligand charge transfer bands and a decrease in the potential difference between the single-electron waves of metal-centered oxidation and ligand-centered reduction of complexes upon substitution of 2-phenylbenzothiazole by 2-naphthylbenzothiazole and of Pt(II) by Ir(II) are shown. The phosphorescence of complexes in the visible region is assigned to the radiative transition from the metal-modified intraligand electronic excited state.     

On the photophysics of four heteroleptic iridium(III) phenylpyridyl complexes investigated by relativistic multi-configuration methods

ABSTRACT

In this work, we present a detailed analysis of the photophysical properties of four phosphorescent iridium(III) complexes, i.e. trans-N,N- and cis-N,N-(ppy)₂Ir^III(acac) as well as their fluorinated derivatives trans-N,N- and cis-N,N-(F₂ppy)₂Ir^III(acac). These properties include absorption and emission characteristics, intersystem crossing rates from the lowest singlet excited state, phosphorescence lifetimes of the individual triplet sublevels as well as the orientations of the transition dipole vectors. To this end, we have carried out combined density functional theory and multi-reference configuration interaction studies including spin–orbit coupling by perturbational as well as variational procedures. For the experimentally known complexes, we observe excellent agreement between our computed data and literature data. Also the blueshifts of the emission maxima occurring upon fluorination of the (ppy)₂Ir(acac) compounds are well reproduced. To our surprise, we find the experimentally not yet investigated cis-N,N-(F₂ppy)₂Ir(acac) isomer to be thermodynamically more stable than the well-known blue phosphorescent emitter trans-N,N-(F₂ppy)₂Ir(acac).     

Luminescence of carbazolyl-containing polymers doped with iridium chelates

White light emission is shown to be obtainable at room temperature through the mixing of poly-N-vinylcarbazole (PVC) host fluorescence with fac-tris(2-phenylpyridyl)Ir(III) [Ir(ppy)₃] and bis[2-(2′-benzothienyl)pyridinato-N,C^3′](acetylacetonate)iridium (III) [Btp₂Ir(acac)] dopant phosphorescence whereas at very low temperature through the superposition of poly-N-epoxypropyl-3,6-dibromocarbazole (3,6-DBrPEPC) host and Btp₂Ir(acac) dopant phosphorescence emissions. The balance between basic colors is adjusted by the variation of triplet-emitter dopant concentrations. Spin-allowed singlet-singlet energy transfer from the host to iridium chelate dopants by the Forster mechanism is the dominant process in PVC. Spin-forbidden triplet-singlet transfer by the Forster mechanism from the host to the dopant occurs at low temperatures in 3,6-DBrPEPC due to strong spin-orbit coupling induced by the heavy bromine atoms. Spin-allowed transfer from the same host’s triplet excited state to the iridium chelate occurs via electron exchange at high temperatures. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 3, pp. 324–330, May–June, 2008.     

Manipulating charge‐transfer character and tuning emission color with electron‐withdrawing main‐group moieties in iridium‐based electrophosphors: a theoretical investigation

A new way has been investigated for tuning the optical and electronic performance of cyclometalated iridium(III) phosphors by simple tailoring of the phenyl ring of ppy (Hppy = 2‐phenylpyridine) with various main group moieties in [Ir(ppy‐X)₂(acac)] (X = POPh₂, SO₂Ph, GePh₃, OPh, OPh(CF₃)₃, SOPh). The geometric and electronic structures of the complexes in the ground state are studied with time‐dependent density functional theory (TD‐DFT) and Hartree–Fock method, whereas the lowest singlet and triplet excited states are optimized by the configuration interaction singles method. At the TD‐DFT level, absorptions and phosphorescence properties of the studied molecules were calculated on the basis of the optimized ground‐ and excited‐state geometries, respectively. The various main group moieties produce a remarkable influence on their optoelectronic properties. The calculated data reveal that the studied molecules have improved charge transfer rate and balance and can be used as hole and electron transport materials in organic light‐emitting devices. In particular, the work can provide valuable insight toward future design of new and relatively rare luminescent materials with enhanced electron‐injection and electron‐transporting features. Copyright © 2012 John Wiley & Sons, Ltd.     

Synthesis and photophysics of a new deep red soluble phosphorescent iridium(III) complex based on chlorine-methyl-substituted 2,4 diphenyl quinoline

A new iridium complex with a chlorine-methyl-substituted 2,4 diphenyl quinoline, (Cl-MDPQ) ligand has been synthesized. The synthesized iridium metal complex, Ir(Cl-MDPQ)₂(acac) where Cl-MDPQ=chlorine-methyl substituted, 2,4 diphenyl quinoline, acac=acetyl acetone is characterized by employing different techniques such as mass spectrometry, ¹H NMR, DTA/TGA, XRD, and FTIR. The molecular structures of Cl-MDPQ and Ir(Cl-MDPQ)₂(acac) complexes are confirmed by the FTIR spectra. Strong singlet metal-to-ligand charge-transfer (¹MLCT) and triplet metal-to-ligand charge-transfer (³MLCT) absorption peaks at 353 and 437 nm in tetrahydrofuran (THF) are reported in the synthesized complex, respectively. A deep red emitting Ir(Cl-MDPQ)₂(acac) complex at 662 nm is promising for flexible organic devices.     

Phosphorescent iridium(III) complexes with hetero (C ˆN) ligands

In order to improve luminescence efficiency, it is necessary to design a phosphorescent material which is capable of transferring the excited energy without triplet–triplet (T–T) annihilation. For this purpose, new types of metal complexes were designed with different species of (C ˆN) ligands. Herein, Ir(ppy)₂(piq), Ir(ppy)₂(piq-F) and Ir(ppy)₂(piq-CF₃) were designed and prepared, where ppy, piq, piq-F and piq-CF₃ represent 2-phenylpyridine, 1-(phenyl)isoquinoline, 1-(4′-fluorophenyl)isoquinoline and 1-(4′-trifluoromethylphenyl)isoquinoline, respectively. These Ir(III) complexes having two different ligands (hetero-Ir complexes) are expected to have a high luminescence efficiency by intramolecular energy transfer from the energy absorbing ligand to the luminescent ligand leading to a decrease in quenching or energy deactivation. To compare luminescent characteristics of these hetero-Ir complexes, homo-Ir complexes Ir(ppy)₃, Ir(piq)₃, Ir(piq-F)₃ and Ir(piq-CF₃)₃ were prepared and investigated photophysically.     

Synthesis and Luminescent Properties of Lanthanide Complexes with Structurally Related Novel Multipodal Ligands

To explore the relationship between the structure of the ligands and the luminescent properties of the lanthanide complexes, a series of lanthanide nitrate complexes with two novel structurally related multipodal ligands, 1,3-bis{[(2’-(2-picolylaminoformyl))phenoxyl]methyl}benzene (L ^I ) and 1,2-bis{[(2’-(2-picolylaminoformyl))phenoxyl]methyl}benzene (L ^II ), have been synthesized and characterized by elemental analysis, infrared spectra and molar conductivity measurements. At the same time, the luminescent properties of the Eu(III) and Tb(III) nitrate complexes in solid state and the Tb(III) nitrate complexes in solvents were investigated at room temperature. Under the excitation of UV light, these complexes exhibited characteristic emissions of central metal ions. The lowest triplet state energy levels T₁ of these ligands both match better to the lowest resonance energy level of Tb(III) than to Eu(III) ion. The influence of the structure of the ligands on the luminescent intensity of the complexes was also discussed.     

Optical and electrochemical properties of cyclometalated Rh(III) complexes based on 4,6-diphenylpyrimidine with ethylenediamine, 2,2′-bipyridyl,and 1,10-phenanthroline

The [Rh(Hdp)₂(N∧N)]ClO₄ complexes (Hdp⁻ is the monodeprotonated form of 4,6-diphenylpyrimidine and (N∧N) is ethylenediamine, 2,2′-bipyridyl, and 1,10-phenanthroline) are synthesized and characterized by ¹H and ¹³C NMR, IR, electronic absorption, and emission spectroscopy, as well as by cyclic voltammetry. The magnetic equivalence of two cyclometalated 4,6-diphenylpyrimidine ligands in the composition of complexes points to the cis position of metalated phenyl rings in the inner sphere. Quasi-reversible one-electron reduction waves are attributed to the ligand-centered electron transfer to the π* antibonding orbital of heterocyclic ligands, while irreversible oxidation waves are associated with electron detachment from the Rh-C σ bonding orbital of the {Rh(Hdp)₂} metal-complex fragment. The characteristic long-wave-length absorption bands and the vibrationally structured phosphorescence bands of complexes are assigned to the spin-allowed and spin-forbidden charge-transfer optical transitions between the σ_Rh-C and π_Hdp* orbitals localized on the {Rh(Hdp)₂} fragment of the complex.     

A novel blue-emitting Ir(III) complex with short excited state lifetime: Synthesis,structure, photophysical property,and electrophosphorescence performance

In this paper, we synthesize a triphenylamine-derived cyclometalating ligand of (4-benzothiazol-2-yl-phenyl)-diphenyl-amine (referred as BPDA) and its corresponding Ir(III) complex of (BPDA)₂Ir(acac) (acac=acetylacetone). The photophysical property, molecular structure, thermal property and electroluminescence performance of (BPDA)₂Ir(acac) are investigated in detail. It is found that (BPDA)₂Ir(acac) is an efficient emitter with high thermal stability and short excited state lifetime. The emission of (BPDA)₂Ir(acac) changes from deep blue (417 nm) to bluish green (500 nm) upon addition of different solvents. We also investigate its electrophosphorescence performance. A maximum electroluminance of 8820 cd/m² peaking at 494 nm is achieved, with the highest device efficiency of 1.72 cd/A.     

Theoretical study on the influence of different NˆN ligands on the electronic structures and optoelectronic properties of heteroleptic Iridium(III) complexes

DFT/TDDFT calculations were carried out to investigate the electronic structures, absorption and phosphorescence properties of a series of heteroleptic Ir(III) complexes consisting of two N-heterocyclic carbene ligands and a conjugated bicyclic N,N′-heteroaromatic (N?N) ligand. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complex (mpmi)₂Ir(pybi) (1) [Hmpmi = 1-(4-tolyl)-3-methyl-imidazole; Hpybi = 2-(pyridin-2-yl)-1H-benzo[d]imidazole] emits green light with an extremely high-quantum phosphorescence efficiency (Φ _PL ) of 79.3%, while a relatively lower Φ _PL (only 11%) was measured for (fpmi)₂Ir(tfpypz) (2) [fpmi = 1-(4-fluorophenyl)-3-methylimdazolin-2-ylidene-C, C^2′; tfpypz = 2-(3-(trifluoromethyl)-1H-pyrazol-5-yl)pyridinato] emitting blue light by tuning the N?N ligands. Besides, we also designed (fpmi)₂Ir(pyN3) (3) [pyN3H = 2-(5-(trifluoromethyl)-2H-1,2,4-triazol-3-yl)pyridine] and (fpmi)₂Ir(pyN4) (4) [pyN4H = 2-(1H-tetrazol-5-yl)pyridine] to explore the influence of electron-withdrawing substituents on N?N ligands on the electronic and optical properties of these Ir(III) complexes. The results revealed that electron-withdrawing substituents can stabilise both HOMOs and LUMOs and induce HOMO–LUMO energy gap change. Moreover, the emission properties can be significantly tuned by introducing different N?N ligands. While new insights were gained on structural and electronic properties, the extremely high Φ _PL of 1 was found to be not inherent to spin-orbital coupling effects, but determined by its large transition dipole moment (μ_{S 1}) upon S ₀–S ₁ transition compared with that of 2. On the basis of these results, the designed complexes 3 and 4 are considered to be the promising candidates for blue-emitting phosphorescence materials with higher Φ _PL than the complex 2.     

Theoretical study of Ir(III) complexes with cyclometalated alkenylquinoline ligands

Recently, it was reported that cyclometalated iridium(III) complexes of 2-((E)-2-phenyl-1-ethenyl)quinoline (PEQ) and 1-((E)-2-phenyl-1-ethenyl)isoquinoline (PEIQ) emitted saturated red light with high quantum efficiency and brightness. However, the energy difference between specific wavelengths due to the metal-to-ligand charge transfer (³MLCT) absorption and emission spectra showed rather large Stokes shifts, which originated at the predominant ³(π–π¹) ligand-based emission. In this paper, it is shown that these complexes are consistent with predominant ³(π–π¹) ligand-based emission. To develop the predominant ³MLCT emission of Ir complexes for a highly efficient phosphorescent complex suitable for red OLED devices, proper ligands having a highest occupied molecular orbital (HOMO) energy level similar to that of 2-phenylpyridine (ppy) ligand were designed to lead to strong mixing between π-orbitals of ligands and the 5d orbital of the centric iridium atom. In order to decrease the HOMO energy level and the lowest an occupied molecular orbital (LUMO) level simultaneously to maintain the same HOMO–LUMO energy gap, an electron accepting group such as F or CF₃ was introduced. By such manipulation of ligands in Ir complexes, it was theoretically possible to change the origin of emission in Ir complex from the predominant ligand-centered ³(π–π¹) excited state to the predominant ³MLCT excited state.     

Spectral and luminescent properties of ammonia cyclopalladated complexes

The synthesis of ammonia cyclometalated palladium(II) complexes [Pd(NH₃)₂C^N]ClO₄ (C^N is the deprotonated form of 2-phenylpyridine, 2-(para-tolyl)pyridine, 7,8-benzo(h)quinoline, 2,6-diphenylpyridine, and 4-phenylpyrimidine) is developed. The IR and electronic absorption and emission spectra of these complexes are studied. It is found that the ammine and analogous ethylenediamine cyclometalated Pd(II) complexes have similar spectral and luminescent properties and the same nature of the electronically excited ³(π-π*)-type state responsible for the long-lived luminescence, the π and π* orbitals being localized on the corresponding cyclometalating ligand. The efficient temperature quenching of the luminescence of Pd(II) complexes at room temperature is assigned to the thermally activated population of metal-centered electronically excited states with subsequent nonradiative deactivation.     

The Effects of Different Solvents and Excitation Wavelength on the Photophysical Properties of Two Novel Ir(III) Complexes Based on Phenylcinnoline Ligand

Two novel cyclometalated iridium(III) complexes, Ir(pcl)₂(pic) and Ir(pcl)₂(fpic) (pcl: 3-phenylcinnoline, pic: picolinic acid, fpic: 5-fluoro-2-picolinic acid) were synthesized and characterized by FTIR, ¹H NMR spectroscopy, UV-vis, PL, and MALDI-TOF. These two Ir-complexes geometry were predicted using the Sparkle/PM6 model and suggested to a chemical environment of very low symmetry around the Ir ions (C ₁). The PL spectrum of Ir(pcl)₂(pic) and Ir(pcl)₂(fpic) indicated that these complex belonged to red light emission, and maximum emission wavelength located at 647 and 641 nm, respectively. Most importantly, the effects of different solvents on their photoluminescent properties were detailed investigated. The results indicated that the polarity of solvent played an important role for their emission spectra. With introducing fluoro group to the pyridyl ring, the maximum emission wavelength of Ir(pcl)₂(fpic) was blue shifted about 6 nm, and the quantum yield was slightly higher than that of Ir(pcl)₂(pic). In addition, the thermal properties of these two Ir-complexes were measured by TGA, and results indicated that they had relative good thermal properties.