Ionic Iridium Complexes Research Articles

Ionic-pair effect on the phosphorescence of ionic iridium(III) complexes

The synthesis and characterization of two water soluble ionic iridium(III) complexes containing hydrophilic acetate counterions is presented. The complexes exhibit one of the highest phosphorescence quantum yields reported up to now in water solution. The influence of the counterion position on the photophysical properties was highlighted through investigations in several polar solvents and in the crystalline solid state.

Light Emitting Electrochemical Cells Based on Ionic Iridium Complexes and Ionic Conductor Blend as the Active Layer

Recently, light emitting electrochemical cells (LECs) have received considerable attention for their application in display and lighting applications. In this manuscript we put forward a study of cationic iridium complex and ionic conductor blend as the active layer of light emitting electrochemical cells. Tetrabutylammonium triflate functions as an ionic conductor. We have synthesized iridium metal complex using phenanthroline based ancillary ligands and studied light emitting properties of the devices in pristine as well as ionic conductor blends. Current density, luminescence plots were well studied against applied bias and on comparison, the devices with ionic liquids showed better performance.

Electroluminescent Properties of LECs Based on Ionic Transition Metal Complexes Using Tetrazole-Based Ancillary Ligand

Light-emitting electrochemical cells (LECs) are a promising type of electroluminescent device for display and lighting applications. In this study, LECs based on ionic iridium complexes utilizing a tetrazole based ancillary ligand were fabricated and their electrical properties were investigated. Two new iridium(III) complexes with tetrazole based ancillary ligands, namely, [Ir(ppy)2(tetrazole)]PF6 (complex 1) and [Ir(dfppy)2(tetrazole)]PF6 (complex 2) (where ppy is 2-phenylpyridine, dfppy is 2-(2,4-difluorophenyl)pyridine, tetrazole is 5-bromo-2-(2-methyl-2H-tetrazol-5-yl)-pyridine and PF6 is hexafluorophosphate), have been synthesized and characterized. These synthesized complexes were used for the fabrication of LEC devices. LECs based on complex 1 result in orange light emission (576 nm) with the Commission Internationale de l’Eclairage (CIE) coordinates of (0.45, 0.49), while complex 2 emits green (518 nm) electroluminescence with the CIE coordinates of (0.33, 0.49). Our work suggests that the light emission of cationic iridium complexes can easily be tuned by the substituents on the cyclometalated ligands.

Ionic iridium complexes with conjugated phenyl substituent: Synthesis and DFT calculation on the electrochemical and electrochemiluminescent properties

Two ionic iridium complexes, (bpq)2Ir(bpy)+PF6− (1) and (bpq-OCH3)2Ir(bpy)+PF6− (2), where bpq is 6-methyl-2,4-diphenyl quinolone anion, bpy is 2,2′-bipyridine, were synthesized and structurally characterized. Their photophysical, electrochemical and electrochemiluminescence properties were investigated. With the conjugated phenyl substitution, the π–π ligand center transitions in the emission process were enhanced, resulting in a broad and strong photoluminescence emission. The photoluminescence quantum yields were measured to be 0.214, 0.209, respectively for complex 1 and 2. The complex 1 also exhibited greater electrochemiluminescence efficiency than the complex 2. To further elucidate the influence of different structures on the electrochemical and electrochemiluminescence properties, the density functional theory calculations were performed on the complexes 1, 2 along with other four well documented bis-cyclometalated iridium complexes. The calculation revealed that about 90% electronic density in the lowest unoccupied molecular orbital were distributed in N∧N auxiliary ligand for ionic complexes, whereas most electronic density were distributed in C∧N main ligand for neutral complexes.

Smart responsive phosphorescent materials for data recording and security protection

Smart luminescent materials that are responsive to external stimuli have received considerable interest. Here we report ionic iridium (III) complexes simultaneously exhibiting mechanochromic, vapochromic and electrochromic phosphorescence. These complexes share the same phosphorescent iridium (III) cation with a N-H moiety in the N^N ligand and contain different anions, including hexafluorophosphate, tetrafluoroborate, iodide, bromide and chloride. The anionic counterions cause a variation in the emission colours of the complexes from yellow to green by forming hydrogen bonds with the N-H proton. The electronic effect of the N-H moiety is sensitive towards mechanical grinding, solvent vapour and electric field, resulting in mechanochromic, vapochromic and electrochromic phosphorescence. On the basis of these findings, we construct a data-recording device and demonstrate data encryption and decryption via fluorescence lifetime imaging and time-gated luminescence imaging techniques. Our results suggest that rationally designed phosphorescent complexes may be promising candidates for advanced data recording and security protection.

Green and blue–green light-emitting electrochemical cells based on cationic iridium complexes with 2-(4-ethyl-2-pyridyl)-1H-imidazole ancillary ligand

The ionic iridium complexes, [Ir(ppy)2(EP-Imid)]PF6 (Complex 1) and [Ir(dfppy)2(EP-Imid)]PF6 (Complex 2) are used as the light-emitting material for the fabrication of light-emitting electrochemical cells (LECs). These complexes have been synthesized, employing 2-(4-ethyl-2-pyridyl)-1H-imidazole (EP-Imid) as the ancillary ligand, 2-phenylpyridine (ppy) and 2-(2,4-difluorophenyl)pyridine (dfppy) as the cyclometalated ligands, which were characterized by various spectroscopic, photophysical and electrochemical methods. The photoluminescence (PL) emission spectra in acetonitrile solution show blue–green and blue light emission for Complexes 1 and 2 respectively. However, LECs incorporating these complexes resulted in green (522nm) light emission for Complex 1 with the Commission Internationale de L’Eclairage (CIE) coordinates of (0.33, 0.56) and blue–green (500nm) light emission for Complex 2 with the CIE coordinates of (0.24, 0.44). Using Complex 1, a maximum luminance of 1191cdm−2 and current efficiency of 1.0cd A−1 are obtained while that of Complex 2 are 741cdm−2 and 0.88cd A−1 respectively.

Orotate containing anionic luminescent iridium(iii) complexes and their use in soft salts

Two anionic iridium complexes [(R-ppy)2Ir(O^N)]TBA with R-ppy = 2-phenylpyridine or 4,5'-dimethyl-2-phenylpyridine, O^N = dianionic form of orotic acid and TBA = tetrabutylammonium have been synthesised and fully characterised by UV-Vis, emission, IR, NMR and cyclic voltammetric studies. These cyclometallated luminescent complexes containing a dianionic bidentate ancillary ligand show bright emission (60-70% PLQY) with maxima in the green region of the visible spectrum. Coupled with the ionic iridium complexes [(ppy)2Ir(N^N)]X, where N^N = 2-picolylamine or 2,2'-bipyridyl, and X = Cl(-) or CH3CO2(-), a series of new soft salts of general formula [(ppy)2Ir(N^N)][(R-ppy)2Ir (O^N)] have been obtained and fully characterized, with enhanced luminescent properties up to ca. 80% of phosphorescence quantum yields.

The potential of the F127-water soft system towards selective solubilisation of iridium(III) octahedral complexes.

In order to obtain new functional soft systems for use as templating agents for the construction of functional mesostructured materials, the dynamic ordered soft systems formed by a hydrophilic ionic iridium(III) complex (IrPa) embedded into two different concentration F127-water mixtures have been investigated. To this aim, combined spectral and time-resolved photophysical techniques and rheological methods have been employed. The position of the chromophore inside the micellar, cubic and hexagonal phases of the F127 polymeric neutral surfactant in water was effectively determined. The hydrophilic character of the iridium(III) complex chosen allowed preferential functionalization of the F127 corona in the micellar and cubic phases.

A multifunctional ionic iridium complex for field-effect and light-emitting devices

We synthesized a multifunctional ionic iridium complex used for field-effect and light-emitting devices.

Ionic iridium complex coordinated with tetrathiafulvalene-fused phenanthroline ligand: Synthesis, photophysical, electrochemical and electrochemiluminescence properties

A new cationic iridium(III) complex salt, [Ir(ppy)2(L)]PF6 (ppy = 2-phenylpyridine) (1), was synthesized by using tetrathiafulvalene fused 4′,5′-dimethyldithiotetrathiafulvenyl[4,5-f][1,10]phenanthroline (L) as NˆN ancillary ligand. The photophysical, electrochemical and electrochemiluminescence (ECL) behavior of the complex are investigated. Complex 1 is found to be emissive at room temperature with the λmax value at 607 nm. It is expected that this new luminescent complex 1 would be further explored for promising applications in functional emitting material.

Efficient Green‐Light‐Emitting Electrochemical Cells Based on Ionic Iridium Complexes with Sulfone‐Containing Cyclometalating Ligands

A new approach to obtain green-emitting iridium(III) complexes is described. The synthetic approach consists of introducing a methylsulfone electron-withdrawing substituent into a 4-phenylpyrazole cyclometalating ligand in order to stabilize the highest-occupied molecular orbital (HOMO). Six new complexes have been synthesized incorporating the conjugate base of 1-(4-(methylsulfonyl)phenyl)-1H-pyrazole as the cyclometalating ligand. The complexes show green emission and very high photoluminescence quantum yields in both diluted and concentrated films. When used as the main active component in light-emitting electrochemical cells (LECs), green electroluminance is observed. High efficiencies and luminances are obtained at low driving voltages. This approach for green emitters is an alternative to the widely used fluorine-based substituents in the cyclometalating ligands and opens new design possibilities for the synthesis of green emitters for LECs.

Efficient Light‐Emitting Electrochemical Cells (LECs) Based on Ionic Iridium(III) Complexes with 1,3,4‐Oxadiazole Ligands

AbstractEight new iridium(III) complexes 1‐8, with 1,3,4‐oxadiazole (OXD) derivatives as the cyclometalated C^N ligand and/or the ancillary N^N ligands are synthesized and their electrochemical, photophysical, and solid‐state light‐emitting electrochemical cell (LEC) properties are investigated. Complexes 1, 2, 7 and 8 are additionally characterized by single crystal X‐ray diffraction. LECs based on complexes 1‐8 are fabricated with a structure indium tin oxide (ITO)/poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/cationic iridium complex:ionic liquid/Al. LECs of complexes 1–6 with OXD derivatives as the cyclometalated ligands and as the ancillary ligand show yellow luminescence (λmax = 552–564 nm). LECs of complexes 7 and 8 with cyclometalated C^N phenylpyridine ligands and an ancillary N^N OXD ligand show red emission (λmax 616–624 nm). Using complex 7 external quantum efficiency (EQE) values of >10% are obtained for devices (210 nm emission layer) at 3.5 V. For thinner devices (70 nm) high brightness is achieved: red emission for 7 (8528 cd m−2 at 10 V) and yellow emission for 1 (3125 cd m−2 at 14 V).

Do the Intramolecular π Interactions Improve the Stability of Ionic, Pyridine-Carbene-Based Iridium(III) Complexes?

Throughout the last years one of the most intensive research topics in light-emitting electrochemical cells (LECs) focused on the design of blue-emitting, ionic iridium(III) complexes. To this end, the most recent strategy is the use of carbene-based ancillary ligands. Although blue LECs have been successfully fabricated, the stability has been noted as the main drawback. To overcome this problem, Zhang et al. have recently explored the use of π interactions to enhance the strength of pyridine-carbene-based complexes. The authors suggested that the use of intramolecular π–π stacking interactions by means of pendant phenyl rings to improve the stability of LECs is not as effective as in devices with diimine-based complexes. To interpret this phenomenon clearly, the features of a family of pyridine-carbene-based iridium(III) complexes, in which phenyl groups are sequentially attached to the carbene and the pyridine rings of the ancillary ligand, have been thoroughly studied by using a theoretical approach. ...

ChemInform Abstract: Solid‐State Light‐Emitting Electrochemical Cells Based on Ionic Iridium(III) Complexes

AbstractReview: 87 refs.

Simple, Fast, Bright, and Stable Light Sources

In this work we show that solution-processed light-emitting electrochemical cells (LECs) based on only an ionic iridium complex and a small amount of ionic liquid exhibit exceptionally good performances when applying a pulsed current: sub-second turn-on times and almost constant high luminances (>600 cd m(-2) ) and power efficiencies over the first 600 h. This demonstrates the potential of LECs for applications in solid-state signage and lighting.

Solid-state light-emitting electrochemical cells based on ionic iridium(iii) complexes

Solid-state light-emitting electrochemical cells (LECs) have aroused great interest in recent years as novel organic light-emitting devices and a promising lighting solution. LECs have many advantages over multilayered organic lighting-emitting diodes (OLEDs), such as single layer, solution process and air-stable cathodes. In recent years, ionic iridium complexes are widely used in LECs for their high efficiencies and tunable emission colours. In this feature article, we will review the proposed operation mechanisms of LECs, the development of ionic iridium complexes and the progress in improving colour, efficiency, stability and response time of the LECs. Finally, the prospects and remaining problems will be discussed.

Iridium (III) complexes as promising emitters for solid-state Light-Emitting Electrochemical Cells (LECs)

Light–emitting Electrochemical Cells (LECs) constitute one of the most recent generations of Organic Light–Emitting Diodes (OLEDs). The main difference between LECs and OLEDs is that LECs include mobile ions in the active layer. Ionic transition–metal complexes and especially ionic iridium (III) complexes have recently attracted widespread attention as potential electroluminescent materials for LECs. Herein, we present an overview of LECs incorporating ionic iridium (III) complexes as phosphorescent emitters. Synthetic strategies developed to introduce iridium (III) complexes in the active layer are also reviewed. Despite the numerous intrinsic drawbacks still remaining, recent advances make iridium–based LECs promising devices for future commercial and scientific applications.

Optoelectronic properties of OLEC devices based on phenylquinoline and phenylpyridine ionic iridium complexes

Ionic transition metal complexes (iTMCs) have already been demonstrated to be a promising type of material to fabricate low-cost light sources, which are much more competitive in terms of realization costs with respect to standard organic light emitting diodes. The device performance, optical and morphological properties of thin films of two different complexes [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)] and [Ir(phenylquinoline)(2)(5-Me-1,10-phen)][PF(6)] have been measured and compared. The use of an ionic liquid as part of the processing procedure shows advantages in terms of low operation voltage, which is as low as 3.5 Volts. However, it leads to drawbacks in terms of device lifetime, limited to t(1/2) = 2 min, and maximum achievable brightness (1425 cd m(-2) vs. 3040 cd m(-2) without ionic liquid, for the complex [Ir(phenylpyridine)(2)(5-Me-1,10-phen)][PF(6)]).

Stable and Efficient Solid‐State Light‐Emitting Electrochemical Cells Based on a Series of Hydrophobic Iridium Complexes

AbstractLight‐emitting electrochemical cells (LECs) based on ionic transition‐metal complexes (iTMCs) exhibiting high efficiency, short turn‐on time, and long stability have recently been presented. Furthermore, LECs emitting in the full range of the visible spectrum including white light have been reported. However, all these achievements were obtained individually, not simultaneously, using in each case a different iTMC. In this work, device stability is maintained by employing intrinsically stable ionic iridium complexes, while increasing the complex and the device quantum yields for exciton‐to‐photon conversion. This is done by sequentially modifying the archetype ionic iridium complex [Ir(ppy)2(bpy)][PF6], where Hppy is 2‐phenylpyridine and bpy is 2,2'‐bipyridine, with methyl and phenyl groups on the bpy ligand. A full photophysical and theoretical description of a series of four complexes, including the archetype as a reference, is presented and their performance in LECs is characterized. Upon selecting suitable substituents, a twofold increase is obtained in the photoluminescence quantum yield in a solid film. This is reflected in a significant increase in the efficiency over time curve for LECs using this complex.

Efficient white polymeric light-emitting diodes by doping ionic iridium complex

A series of white polymer light-emitting diodes (WPLEDs) each with a single emitting layer using ionic iridium complex is fabricated. The white light is obtained via two complementary colors of orange light emitter ionic iridium complexe PF6 (Hnpy: 2-(naphthalen-1-yl)pyridine, c-phen: 1-ethyl-2-(9-(2-ethylhexyl)-9H-carbazol-3-yl)-1H-imidazo phenanthroline) and sky-blue light emitter Firpic (iridium bis(2-(4,6-difluorophenyl)-pyridinato-N,C(2)) picolinate. The emtting layer consists of poly(N-vinylcarbzole) (PVK) as host polymer, 1,3-bis -phenylene (OXD-7) as electron-transporting materials, Firpic and PF6. The structure of the WPLED is indium-tin-oxide/poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonate)(40 nm)/emtting layer (80 nm)/CsF(1.5 nm)/Al(120 nm). When the mass ratio of PVK, OXD-7, Firpic, PF6 is 67 ∶23 ∶10 ∶0.25, the most efficient white light is obtained with a color coordinate of (0.31,0.40), a maximal luminance efficiency of 13.3 cd/A and a maximal luminance of 6032 cd/m2. Meanwhile, the color coordinate is unchanged with current density. The mechanism of the WPLED is discussed.