Bis-cyclometalated Iridium Research Articles

Synthesis, characterization, luminescence properties, and DFT calculation of a cationic cyclometalated iridium(III) complex with fluorine-containing phenylquinolinyl and 2,2′-bipyridine ligands

A cationic bis-cyclometalated iridium(III) complex, [Ir(hfppq)2(bipy)][PF6]·0.5H2O (hfppq=1,1,1,3,3,3-hexafluoro-2(2-phenylquinolin-4-yl)propan-2-ol, bipy=2,2′-bipyridine, 1), was obtained from the reaction of the μ-chloro-bridged dimeric complex [Ir(hfppq)2(μ-Cl)]2 and bipy in the presence of KPF6. Complex 1 shows a strong emission both in the solid state (ca. 595nm) and in CH2Cl2 solution (ca. 585nm) at room temperature with the phosphorescence quantum yield of ca. 0.698 and emission lifetime of 0.96μs. Density functional theory (DFT) calculation was performed on the ground and excited states of complex 1 to provide insight into the structural, electronic, and optical properties of the cationic cyclometalated iridium(III) complex.

Phosphorescence of iridium(III) complexes with 2-(2-pyridyl)-1,3,4-oxadiazoles

Cationic bis-cyclometalated iridium(III) complexes [(C^N)2Ir(N^N)](PF6) with 2-(2′-pyridyl)-5-R-1,3,4-oxadiazoles (N^N; R=1-adamantyl, mesityl, N-diphenylamino) have a redox gap of 2.58–2.68V and exhibit orange–red phosphorescence in argon-saturated dichloromethane solution with a maximum, quantum yield, and excited-state lifetime of 613–644nm, 2–6%, and 90–280ns.

Photoluminescence color tuning of phosphorescent bis-cyclometalated iridium(III) complexes by ancillary ligand replacement

A series of bis-cyclometalated iridium(III) complexes bearing various types of 1,3-diketonate ancillary ligands were prepared, and their photoluminescent (PL) properties were investigated, especially focusing on the emission color tuning. When the dipivaloylmethanate ancillary ligand ( O ^ O -1a ) was replaced by conjugated 1,3-diketonates such as 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate ( O ^ O -1b ) and 1,3-bis(4-(dibenzo[ b , d ]furan-4-yl)phenyl)propane-1,3-dionate ( O ^ O -1c ), the blue-emitting bis[2-(3,5-bis(trifluoromethyl)phenyl)pyridinato- N,C 2 ′ ]iridium(III) ( Ir-1 ) and bluish green-emitting bis[2-phenylpyridinato- N,C 2′ ]iridium(III) ( Ir-2 ) complexes exhibited significantly red-shifted phosphorescence in solution ( λ PL ; 474–604 nm and 521–661 nm for Ir-1a – c and Ir-2a – c , respectively: the subscripts a , b , and c corresponding to O ^ O -1a – c ). On the other hand, the ancillary ligand replacement was less effective on tuning the emission color of the green-emitting bis[2-(2,4-bis(trifluoromethyl)phenyl)pyridinato- N,C 2 ′ ]iridium(III) complex ( λ PL ; 541–566 nm for Ir-3a – c ), and no PL color change was observed for the red-emitting bis[1-(dibenzo[ b,d ]furan-4-yl)isoquinolinato- N,C 3 ′ ]iridium(III) complex ( Ir-4 ). The X-ray crystallographic analysis for Ir-1a – c revealed that these complexes adopt cis - C , C and trans - N , N configuration, indicating that the coordination geometry around the iridium center is not a main factor for the emission spectral differences caused by the O^O ancillary ligands. Furthermore, the ancillary ligand effect on the PL properties of the present iridium(III) complexes is independent on solvent polarity and concentrations. Taking these results into consideration, the ancillary ligand effect should be attributed to the electronic structures of the complexes, and the inter-ligand energy transfer from the triplet metal-to-ligand charge transfer level at the cyclometalated ligand ( 3 MLCT C ^ N ) to the ancillary ligand-related triplet level ( 3 LC O ^ O or 3 MLCT O^O ) should play a significant role in the triplet exciton formation. The PL properties of Ir-1 – Ir-4 in PMMA films were also investigated, and the remarkable blue shifts of λ PL s due to rigidochromism were observed for Ir-1b , c and Ir-2b , c that have the aromatic O ^ O ancillary ligands. It was found that some of the complexes developed here exhibited larger Φ PL s in PMMA films than in toluene solutions. ► Ir(III) complexes with various 1,3-diketonate ancillary ligands were prepared. ► The aromatic 1,3-diketonate ancillary ligands give rise to red-shifted PL. ► For the red-emitting complexes, the PL color is independent on the ancillary ligand. ► The ancillary ligand effect on PL is attributed to the inter-ligand energy transfer.

Impact of Ligand Modification on Hydrogen Photogeneration and Light-Harvesting Applications Using Cyclometalated Iridium Complexes

To explore structure-activity relationships with respect to light-harvesting behavior, a family of bis-cyclometalated iridium complexes [Ir(C^N)(2)(Hbpdc)] 2-5 (where C^N = 2-phenylbenzothiazole and its functionalized derivatives, and H(2)bpdc =2,2'-bipyridine-4,4'-dicarboxylate) was synthesized using a facile method. The photophysical and electrochemical properties of these complexes were investigated and compared to those of analogue 1 (C^N = (4-trifluoromethyl)-2-phenylbenzothiazole); they were also investigated theoretically using density functional theory. The molecular structures of complexes 2-4 were determined by X-ray crystallography, which revealed typical octahedral coordination geometry. The structural modifications involved in the complexes were accomplished through the attributes of electron-withdrawing CF(3) and electron-donating NMe(2) substituents. The UV-vis spectra of these species, except for that of 5, displayed a broad absorption in the low-energy region, which originated from metal-to-ligand charge-transfer transitions. These complexes were found to exhibit visible-light-induced hydrogen production and light-to-electricity conversion in photoelectrochemical cells. The yield of hydrogen production from water using these complexes was compared, which revealed substantial dependences on their structures, particularly on the substituent of the cyclometalated ligand. Among the systems, the highest turnover number of 1501 was achieved with complex 2, in which the electron-withdrawing CF(3) substituent was connected to a phenyl ring of the cyclometalated ligand. The carboxylate anchoring groups made the complexes highly suitable for grafting onto TiO(2) (P25) surfaces for efficient electron transfer and thus resulted in an enhancement of hydrogen evolution compared to the unattached homogeneous systems. In addition, the combined incorporation of the electron-donating NMe(2) group and the electron-withdrawing CF(3) substituent on the cyclometalated ligand caused complex 5 to not work well for hydrogen production. Their incorporation, however, enhanced the performance of 5 in the light-harvesting application in nanocrystalline TiO(2) dye-sensitized solar cells, which was attributed to the intense absorption in the visible region.

Bright Blue Phosphorescence from Cationic Bis-Cyclometalated Iridium(III) Isocyanide Complexes

We report new bis-cyclometalated cationic iridium(III) complexes [(C(^)N)(2)Ir(CN-tert-Bu)(2)](CF(3)SO(3)) that have tert-butyl isocyanides as neutral auxiliary ligands and 2-phenylpyridine or 2-(4'-fluorophenyl)-R-pyridines (where R is 4-methoxy, 4-tert-butyl, or5-trifluoromethyl) as C(^)N ligands. The complexes are white or pale yellow solids that show irreversible reduction and oxidation processes and have a large electrochemical gap of 3.58-3.83 V. They emit blue or blue-green phosphorescence in liquid/solid solutions from a cyclometalating-ligand-centered excited state. Their emission spectra show vibronic structure with the highest-energy luminescence peak at 440-459 nm. The corresponding quantum yields and observed excited-state lifetimes are up to 76% and 46 μs, respectively, and the calculated radiative lifetimes are in the range of 46-82 μs. In solution, the photophysical properties of the complexes are solvent-independent, and their emission color is tuned by variation of the substituents in the cyclometalating ligand. For most of the complexes, an emission color red shift occurs in going from solution to neat solids. However, the shift is minimal for the complexes with bulky tert-butyl or trifluoromethyl groups on the cyclometalating ligands that prevent aggregation. We report the first example of an iridium(III) isocyanide complex that emits blue phosphorescence not only in solution but also as a neat solid.

Dipyridylketone as a versatile ligand precursor for new cationic heteroleptic cyclometalated iridium complexes

Three new bis-cyclometalated iridium(III) complexes, of general formula [Ir(2-phenylpyridine)(2)(L)](+), are reported. The compounds contain a dipyridine-type ligand (L) derived from di-2-pyridylketone (dipyridin-2-ylmethanol, 2,2'-(hydrazonomethylene)dipyridine and 3-hydroxy-3,3-di(pyridine-2-yl)propanenitrile) and were synthesized through two different reaction pathways. The alternative synthetic pathway herein proposed, namely the direct reactions on the complex [Ir(2-phenylpyridine)(2)(2,2'-dipyridylketone)](+), overcame the inconveniences encountered with the standard reaction between the dimeric precursor [Ir(2-phenylpyridine)(2)(μ-Cl)](2) and the ancillary ligands (L). The photophysical characterization of the iridium complexes reveals that modifications on the ancillary ligand introduce large changes in the photophysical behaviour of the complexes. High emission quantum yield is associated with the presence of a saturated carbon between the two pyridyl moieties: [Ir(2-phenylpyridine)(2)(2,2'-dipyridylketone)](+) and [Ir(2-phenylpyridine)(2)(2,2'-(hydrazonomethylene)dipyridine)](+) are extremely low emissive, while [Ir(2-phenylpyridine)(2)(dipyridin-2-ylmethanol)](+) and [Ir(2-phenylpyridine)(2)(3-hydroxy-3,3-di(pyridine-2-yl)propanenitrile)](+) are good photoemitters. DFT and TD-DFT calculations confirmed the mixed LC/MLCT character of the excited states involved in the absorption and emission processes and highlighted the role of the π-conjugation between the two subunits of the ancillary ligand in determining the nature of the LUMO.

1,12-Diazaperylene and 2,11-dialkylated-1,12-diazaperylene iridium(iii) complexes [Ir(C^N)2(N^N)]PF6: new supramolecular assemblies

A series of new monocationic iridium(III) complexes [Ir(C^N)(2)(N^N)]PF(6) with "large-surface"α,α'-diimin ligands N^N (dap = 1,12-diazaperylene, dmedap = 2,11-dimethyl-1,12-diazaperylene, dipdap = 2,11-diisopropyl-1,12-diazaperylene) and different cyclometalating ligands C^N (piq = 1-phenylisoquinoline, bzq = benzo[h]quinoline, ppz = 1-phenylpyrazole, thpy = 2-(2-thienyl)pyridine, ppy = 2-phenylpyridine, meppy = 2-(4-methylphenyl)pyridine, dfppy = 2-(2,4-difluorophenyl)pyridine) were synthesized. The solid structures of the complexes [Ir(piq)(2)(dap)]PF(6), [Ir(bzq)(2)(dap)]PF(6), [Ir(ppy)(2)(dipdap)]PF(6), [Ir(piq)(2)(dmedap)]PF(6), [Ir(ppy)(2)(dap)]PF(6) and [Ir(ppz)(2)(dap)]PF(6) are reported. In [Ir(piq)(2)(dap)]PF(6), the dap ligand and one of the piq ligands of each cationic complex are involved in π-π stacking interactions forming supramolecular channels running along the crystallographic c axis. In the crystalline [Ir(bzq)(2)(dap)]PF(6)π-π stacking interactions between the metal complexes lead to the formation of a 2D layer structure. In addition, CH-π interactions were found in all compounds, which are what stabilizes the solid structure. In particular, a significant number of them were found in [Ir(piq)(2)(dap)]PF(6) and [Ir(bzq)(2)(dap)]PF(6). The crystal structures of [Ir(ppy)(2)(dipdap)]PF(6) and [Ir(ppy)(2)(dmedap)]PF(6) are also presented, being the first examples of bis-cyclometalated iridium(iii) complexes with phenanthroline-type α,α'-diimin ligands bearing bulky alkyl groups in the neighbourhood of the N-donor atoms. These ligands implicate a distorted octahedral coordination geometry that in turn destabilized the Ir-N(N^N) bonds. The new iridium(iii) complexes are not luminescent. All compounds show an electrochemically irreversible anodic peak between 1.15 and 1.58 V, which is influenced by the different cyclometalated ligands. All of the new complexes show two reversible successive one-electron "large-surface" ligand-centred reductions around -0.70 V and -1.30 V. Electrospray ionisation mass spectrometry (ESI-MS) and collision induced decomposition (CID) measurements were used to investigate the stability of the new complexes. Thereby, the stability agreed well with the order of the Ir-N(N^N) bond lengths.

Shedding light on unusual photophysical properties of bis-cyclometalated iridium(iii) complexes containing 2,5-diaryl-1,3,4-oxadiazole-based and acetylacetonate ligands

A DFT/TDDFT investigation was conducted on a series of cyclometalated iridium(iii) complexes with 2,5-diaryl-1,3,4-oxadiazole (oxd(n)) derivatives to shed light on the effects of the stereoisomeric and steric factors on the photophysical properties. On the basis of the results reported herein, we attempt to explain the experimental observations according to which complexes N,N-trans [Ir(oxd(0))(2)(acac)] (1a) and N,N-trans [Ir(oxd(1))(2)(acac)] (2a) [with oxd(0) = 2,5-diphenyl-1,3,4-oxadiazole, oxd(1) = 2,5-bis(4-fluorophenyl)-1,3,4-oxadiazole and acac = acetylacetonate] show high quantum phosphorescence efficiencies (Φ(PL)) of 35 and 44%, while an extremely low Φ(PL) (<1%) was observed for a number of oxd(n) based complexes including N,N-cis [Ir(oxd(3))(2)(acac)] (4b) [with oxd(3) = 2-(4-fluorophenyl)-5-(2,4,6-triisopropylphenyl)-1,3,4-oxadiazole]. While new insights were gained on structural and electronic properties, the unusual photophysical properties recently reported for 4b were found to be not inherent to spin-orbit coupling (SOC) effects, but determined by both the S(1)-T(1) splitting energy (ΔE(S1-T1)) and the transition dipole moment (μ(S1)) upon the S(0)→ S(1) transition. Drastically large ΔE(S1-T1) and small μ(S1) for 4b (0.70 eV and 0.23 D, respectively) comparative to those for 2a (0.38 eV and 2.76 D, respectively) and 1a (0.58 eV and 2.44 D, respectively) were found to be tightly linked to the twisting degree of the oxd(n) ligand and to the trans-cis structural isomerism. On the basis of these parameters, the unusual physical properties of 4b were interpreted with respect to 1a and 2a, and the higher Φ(PL) of 2a with respect to that for 1a was explained.

Synthesis and Photoelectric Property of Bis-Cyclometalated Iridium Complexes with 3-Acetyl Camphor as the Ancillary Ligand

Synthesis and Photoelectric Property of Bis-Cyclometalated Iridium Complexes with 3-Acetyl Camphor as the Ancillary Ligand

Near-UV to red-emitting charged bis-cyclometallated iridium(iii) complexes for light-emitting electrochemical cells

Herein we report a series of charged iridium complexes emitting from near-UV to red using carbene-based N^C: ancillary ligands. Synthesis, photophysical and electrochemical properties of this series are described in detail together with X-ray crystal structures. Density Functional Theory calculations show that the emission originates from the cyclometallated main ligand, in contrast to commonly designed charged complexes using bidentate N^N ancillary ligands, where the emission originates from the ancillary N^N ligand. The radiative process of this series of compounds is characterized by relatively low photoluminescence quantum yields in solution that is ascribed to non-radiative deactivation of the excited state by thermally accessible metal-centered states. Despite the poor photophysical properties of this series of complexes in solution, electroluminescent emission from the bluish-green to orange region of the visible spectrum is obtained when they are used as active compounds in light-emitting electrochemical cells.

Bis-Cyclometalated Iridium(III) Complexes Bearing Ancillary Guanidinate Ligands. Synthesis, Structure, and Highly Efficient Electroluminescence

We report the synthesis, structure, and photophysical and electroluminescent (EL) properties of a series of heteroleptic bis(pyridylphenyl)iridium(III) complexes with various ancillary guanidinate ligands. The reaction of the bis(pyridylphenyl)iridium(III) chloride [(ppy)(2)Ir(μ-Cl)](2) with the lithium salt of various guanidine ligands Li{(N(i)Pr)(2)C(NR(1)R(2))} at 80 °C gave in 60-80% yield the corresponding heteroleptic bis(pyridylphenyl)/guanidinate iridium(III) complexes having a general formula of [(ppy)(2)Ir{(N(i)Pr)(2)C(NR(1)R(2))}], where NR(1)R(2) = NPh(2) (1), N(C(6)H(4)(t)Bu-4)(2) (2), carbazolyl (3), 3,6-bis(tert-butyl)carbazolyl (4), N(C(6)H(4))(2)S (5), N(C(6)H(4))(2)O (6), indolyl (7), NEt(2) (8), N(i)Pr(2) (9), N(i)Bu(2) (10), and N(SiMe(3))(2) (11). These heteroleptic cyclometalated (C^N) iridium(III) complexes showed intense absorption bands in the UV region assignable to π-π* transitions and weaker metal-to-ligand charge-transfer transitions extending to the visible region. These complexes also showed intense emissions at room temperature. Their photoluminescence spectra were influenced to some extent by the ancillary guanidinate ligands, giving λ(max) values in the range of 528-560 nm with quantum yields (Φ) of 0.16-0.37 and lifetimes of 0.61-1.43 μs. Organic light-emitting diodes were fabricated by the use of these complexes as dopants in various concentrations (5-100%) in a N,N'-dicarbazolylbiphenyl host. High current efficiency (η(c); up to 137.4 cd/A) and power efficiency (η(p); up to 45.7 lm/W) were observed under appropriate conditions. Their high EL efficiency may result from efficient trapping and radiative relaxation of the excitons formed in the EL process. Because of the steric hindrance of the guanidinate ligands, no significant intermolecular interaction was observed in these complexes, thus leading to the reduction of self-quenching and triplet-triplet annihilation at high currents. The EL emission color could be changed in the range of green to yellow by choosing appropriate guanidinate ligands.

Influence of Halogen Atoms on a Homologous Series of Bis-Cyclometalated Iridium(III) Complexes

A series of homologous bis-cyclometalated iridium(III) complexes Ir(2,4-di-X-phenyl-pyridine)(2)(picolinate) (X = H, F, Cl, Br) HIrPic, FIrPic, ClIrPic, and BrIrPic has been synthesized and characterized by NMR, X-ray crystallography, UV-vis absorption and emission spectroscopy, and electrochemical methods. The addition of halogen substituents results in the emission being localized on the main cyclometalated ligand. In addition, halogen substitution induces a blue shift of the emission maxima, especially in the case of the fluoro-based analogue but less pronounced for chlorine and bromine substituents. Supported by ground and excited state theoretical calculations, we rationalized this effect in a simple manner by taking into account the σp and σm Hammett constants on both the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) energy levels. Furthermore, in comparison with FIrPic and ClIrPic, the impact of the large bromine atom remarkably decreases the photoluminescence quantum yield of BrIrPic and switches the corresponding lifetime from mono to biexponential decay. We performed theoretical calculations based on linear-response time-dependent density functional theory (LR-TDDFT) including spin-orbit coupling (SOC), and unrestricted DFT (U-DFT) to obtain information about the absorption and emission processes and to gain insight into the reasons behind this remarkable change in photophysical properties along the homologous series of complexes. According to theoretical geometries for the lowest triplet state, the large halogen substituents contribute to sizable distortions of specific phenylpyridine ligands for ClIrPic and BrIrPic, which are likely to play a role in the emissive and nonradiative properties when coupled with the heavy-atom effect.

Highly Efficient Green and Blue‐Green Phosphorescent OLEDs Based on Iridium Complexes with the Tetraphenylimidodiphosphinate Ligand

Two novel bis-cyclometalated iridium complexes are successfully applied in organic light-emitting diodes (OLEDs). Because of their better carrier transport ability and shorter excited stated lifetimes, good electroluminescence performances of the complexes are observed.

Multifunctional red phosphorescent bis-cyclometallated iridium complexes based on 2-phenyl-1,2,3-benzotriazole ligand and carbazolyl moieties

Multifunctional phosphorescent bis-cyclometallated iridium(III) complexes based on the 2-phenyl-1,2,3-benzotriazole moiety and bearing branched hole-transporting carbazole fragments were synthesized. The isolated compounds were found to be amorphous and expressed very good solubility. Introduction of flexible aliphatic chains of various lengths into the iridium complexes enabled manipulation of their glass transition temperature. The iridium complexes exhibited red phosphorescence emission at 650 nm with the lifetime of 5.7 μs and phosphorescence quantum yields of 0.22 and 0.17 in solution and solid state, respectively, at room temperature. The shielding effect of the carbazolyl moieties on the concentration quenching of phosphorescence of the iridium centers was found to result in the increased excited state lifetime and quantum yield due to the suppressed exciton migration. Non-optimized OLED devices, based on the phosphorescent bis-cyclometallated iridium(III) complex without host material were fabricated and their electroluminescence properties were evaluated.

Room-temperature combinatorial screening of cyclometallated iridium(iii) complexes for a step towards molecular control of colour purity

A library of emission spectra of 90 bis-cyclometallated iridium complexes has been obtained using a simple combinatorial approach performed at room temperature. Trends in emission maxima are rationalized using Hammett parameters and invoking inter ligand energy transfer (ILET) processes. The screening approach allowed us to observe trends in the broadness of emission spectra opening the way for a rational approach to the engineering of the emission colour purity at a molecular level. Finally limitations to the screening strategy are discussed using a case study that involves two different monodentate ligands.

Cyclometalated Iridium(III) Complexes Based on Phenyl-Imidazole Ligand

Phenyl-imidazole-based ligands with various substitution patterns have been used as the main ligand for heteroleptic bis-cyclometalated iridium complexes. Two series of complexes have been prepared and their photophysical and electrochemical properties were studied. The phosphorescence emission maxima range from about 490 to 590 nm, that is, from greenish-blue to orange. The first series is of the form Ir(L)2(acac) (L: a phenyl-imidazole based ligand; acac: acetylacetonate). In the first complex, 1a, L is 1,4,5-trimethyl-2-phenyl-1H-imidazole. Then, methyl groups are replaced with phenyl groups and chlorines are grafted on the cyclometalated phenyl ring. The second series is of the form Ir(4,5-dimethyl-1,2-diphenyl-1H-imidazole)2(La) (La: ancillary ligand being acetylacetonate, acac, N,N-dimethylamino-picolinate, NPic, picolinate, Pic, or 2-(diphenylphosphino)acetic acid, P). These series show that modifying the substitution pattern on the ligands can alter the photophysical and electrochemical properties of the complexes. Overall, we show that compared to complexes containing phenyl-pyridine ligands, highest occupied molecular orbitals (HOMOs) and lowest unoccupied molecular orbitals (LUMOs) are more delocalized over the entire main ligand in complexes containing phenyl-imidazole. Contrary to expectations, when chlorine atoms are used as strong acceptor substituents on the orthometalated phenyl, a red shift of the emission is observed. This behavior has been rationalized using theoretical calculations on the excited state of the chloro-substituted complex 3a compared to the model 1a.

Efficient Dipyrrin-Centered Phosphorescence at Room Temperature from Bis-Cyclometalated Iridium(III) Dipyrrinato Complexes

A series of seven dipyrrin-based bis-cyclometalated Ir(III) complexes have been synthesized and characterized. All complexes display a single, irreversible oxidation wave and at least one reversible reduction wave. The electrochemical properties were found to be dominated by dipyrrin centered processes. The complexes were found to display room temperature luminescence with emission maxima ranging from 658 to 685 nm. Through systematic variation of the cyclometalating ligand and the meso substituent of the dipyrrin moiety, it was found that the observed room temperature emission was due to phosphorescence from a dipyrrin-centered triplet state with quantum efficiencies up to 11.5%. Bis-cyclometalated Ir(III) dipyrrin based organic light emitting diodes (OLEDs) display emission at 682 nm with maximum external quantum efficiencies up to 1.0%.

Pure red electrophosphorescence from polymer light-emitting diodes doped with highly emissive bis-cyclometalated iridium(III) complexes

In order to develop highly emissive red phosphorescent materials for OLED application, novel bis-cyclometalated iridium(III) complexes were developed using the 1-(dibenzo[ b, d]furan-4-yl)isoquinolinato- N, C 3′ ( dbfiq) cyclometalating ligand. When 1,3-bis(3,4-dibutoxyphenyl)propane-1,3-dionate ( bdbp) is employed as an ancillary ligand, Ir( dbfiq) 2( bdbp) 1 exhibits red photoluminescence (PL) at 640 nm with a quantum yield ( Φ PL) of 0.61 (in toluene, 298 K). Replacement of bdbp to dipivaloylmethanate ( dpm) and acetylacetonate ( acac) (Ir( dbfiq) 2( dpm) 2 and Ir( dbfiq) 2( acac) 3, respectively) does not affect the PL spectrum, but reduces Φ PL to 0.55 and 0.49 for 2 and 3, respectively. Similar tendency is also found in the doped poly(methyl methacrylate) (PMMA) film, and 1 is more emissive ( Φ PL = 0.17) than 2 and 3 ( Φ PL = 0.08 and 0.06, respectively). Using 1 as a phosphorescent dopant, polymer light-emitting diodes (PLEDs) were fabricated, of which structure was ITO/PEDOT:PSS (40 nm)/PVCz: 1:PBD (100 nm)/CsF (1 nm)/Al (250 nm). Pure red electroluminescence (EL) is obtained from the fabricated PLEDs, affording a CIE chromaticity coordinate of (0.68, 0.31). When 0.51 mol% of 1 is incorporated in the PVCz-based emitting layer, the PLED shows maximum luminance of 7270 cd m −2 at 16.5 V, power efficiency of 1.4 lm W −1 at 7.5 V, and external quantum efficiency of 6.4% at 9.0 V. PLEDs with the same structure and components were also fabricated using 2 and 3, and their device characteristics were investigated. In proportion to the PL quantum yields, 1 affords better device performance than 2 and 3. Owing to four butoxy groups introduced to the bdbp ligand, 1 exhibits high solubility in organic solvents such as chloroform and toluene, and thus, is an excellent red phosphorescent dopant for solution-processed OLEDs.

Unexpected metal-mediated oxidation of hydroxymethyl groups to coordinated carboxylate groups by bis-cyclometalated iridium(iii) centers

Two different procedures of the ‘click’ reaction were applied to synthesize a library of 1-aryl- and 4-aryl-functionalized 1H-[1,2,3]triazoles as new ligands for phosphorescent iridium(III) complexes. For three examples, single crystal X-ray analysis was carried out and the structural properties were discussed. The reactive μ-dihydroxy-bridged iridium(III) precursor complex [(ppy)2Ir-μ-(OH)]2 (ppy = 2-phenylpyridinato) was prepared for the complexation of the herein described ligands. During these complexation studies, an unexpected metal-assisted oxidation pathway was observed for the hydroxymethyl-substituted 1-aryl-1H-[1,2,3]triazoles 2d–f leading selectively to a [carboxylate-N3,O]-coordination of the ligands to the iridium(III) centers.

Highly luminescent bis-cyclometalated iridium(iii) ethylenediamine complex: synthesis and correlation between the solid state polymorphism and the photophysical properties

The solvent induced polymorphism observed in a cyclometalated iridium(iii) ethylenediamine ionic complex is a new tool to modulate and enhance emission in the solid crystalline state.