Novel yellow phosphorescent iridium complexes containing a carbazole–oxadiazole unit used in polymeric light-emitting diodes

Yellow iridium complexes Ir(PPOHC)₃ and (PPOHC)₂Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole) were synthesized and characterized. The Ir(PPOHC)₃ complex has good thermal stability with 5% weight-reduction occurring at 370 °C and a glass-transition temperature of 201 °C. A polymeric light-emitting diode using the Ir(PPOHC)₃ complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC)₃ which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazole–oxadiazole unit are promising candidates in high-efficiency electroluminescent devices.     

Novel yellow phosphorescent iridium complexes containing a carbazole-oxadiazole unit used in polymeric light-emitting diodes

Yellow iridium complexes Ir(PPOHC)₃ and (PPOHC)₂Ir(acac) (PPOHC: 3-(5-(4-(pyridin-2-yl)phenyl)-1,3,4-oxadiazol-2-yl)-9-hexyl-9H-carbazole) were synthesized and characterized. The Ir(PPOHC)₃ complex has good thermal stability with 5% weight-reduction occurring at 370 °C and a glass-transition temperature of 201 °C. A polymeric light-emitting diode using the Ir(PPOHC)₃ complex as a phosphorescent dopant showed a luminance efficiency of 16.4 cd/A and the maximum external quantum efficiency of 6.6% with CIE coordinates of (0.50, 0.49). A white polymeric light-emitting diode was fabricated using Ir(PPOHC)₃ which showed a luminance efficiency of 15.3 cd/A, with CIE coordinates of (0.39, 0.44). These results indicate that the iridium complexes containing a linked carbazole-oxadiazole unit are promising candidates in high-efficiency electroluminescent devices.     

一种铱磷光配合物的合成表征及性能研究

利用2-苯基吡啶(ppy)、三水合氯化铱(IrCl_3·3H_2O)和2-吡啶甲酸(pic)配位,得到铱配位物Ir(ppy)_2pic,合成产率9 0%,该方法适合于Ir(ppy)2pic的批量制备。通过元素分析、核磁共振(~1H-NMR、~(13)C-NMR)和质谱(MS)对产物分子结构进行了表征,此外结合紫外吸收光谱(UV-Vis)和荧光光谱(PL)对其光物理性能进行了研究。结果表明:该配合物在紫外谱图上的250~300 nm处出现了强的配体单重态π-π*自旋跃迁吸收峰,在400~500 nm处出现了铱(Ш)到配体的单重态和三重态(~1MLCT和~3MLCT)电子跃迁吸收峰,在荧光光谱的514 nm处有较强的金属配合物三重态的磷光发射峰,显示为一种高效的绿色磷光材料。     

Selective reduction of NO with CO in the presence of O2 with Ir/WO3 catalysts: Influence of preparation variables on the catalytic performance

Several Ir/WO₃ catalysts were prepared, which were different in the loading of Ir (up to 10 wt.%) and in the pretreatment conditions, and used for the reduction of NO (500 ppm) with CO (3000 ppm) in the presence of excess O₂ (5%), SO₂ (2 ppm), and H₂O (1%). The rate of NO conversion per unit mole of Ir was found to be maximal at a small Ir loading of 0.5–1.0 wt.%. The good catalytic performance was achieved when the Ir precursors (IrO_x) supported on WO₃ were reduced under mild conditions by He at 400 °C or H₂/He at a lower temperature of 130 °C. The catalysts were characterized by XRD, FTIR after CO adsorption, and H₂-TPR. The characterization results show that the active sites are exposed zero-valent Ir species, in accordance with previous works using Ir on WO₃ and other supports, and that the fraction of these active species is larger for a higher degree of Ir dispersion (smaller Ir particles). The preparation conditions for highly active Ir/WO₃ catalysts were confirmed and possible reaction mechanisms were discussed.     

Selective Ring-Opening of Methylcyclopentane Over Titania-Supported Monometallic (Pt, Ir) and Bimetallic (Pt–Ir) Catalysts

An investigation of the selective ring-opening of methylcyclopentane (MCP) was conducted for the first time on Pt/TiO₂, Ir/TiO₂ and Pt?CIr/TiO₂ catalysts with low amounts of noble metals (0.5?wt%) over a temperature range of 180?C400?°C under hydrogen at atmospheric pressure. The catalysts were prepared by impregnation or co-impregnation and characterized by different physico-chemical techniques, including SEM, XRD, H₂-TPR, N₂-sorption, TEM and elemental analysis. The metallic particles were highly dispersed on the TiO₂ support at isodispersion of ~1?nm. The particles exhibited icosahedral Mackay structures limited by (111) planes. The catalytic results show that the activity in the MCP was strongly influenced by the intrinsic nature of the metal and by the temperature. The most active catalyst was Ir/TiO₂. The order of the reactivity as a function of the temperature and total conversion was Ir/TiO₂ 180?°C (???=?2?%)?>?Pt?CIr/TiO₂ 220?°C (???=?27.8?%)?>?Pt/TiO₂ 260?°C (???=?9.9?%). Under these conditions, all of the catalysts exhibited the ability to open the ring of MCP with an atom economy, without unwanted products of cracking and ring-enlargement reactions. The synergy between Pt?CIr bimetallic particles was assessed by the total conversion of MCP, whereas the ring-opening results indicated that the reaction took place on Ir sites. These results suggest that the bimetallic catalyst contained separate entities of two metals. Increased reaction temperatures led to reduced reaction selectivity with respect to ring-opening of MCP versus the cracking side reaction.     

Bipolar Hosts Based on a Rigid 9,10-Dihydroanthracene Scaffold for Full-Color Electrophosphorescent Devices

Two bipolar hosts, CzDPO and CzDOxa , comprising a hole-transporting carbazole and an electron-transporting diphenyl phosphine oxide or oxadiazole with a saturated linker (9,10-dihydroanthracene) have been synthesized and characterized. The saturated linker limited the effective extension of π conjugation, leading to high triplet energies (E_T=2.97–2.98 eV). The diastereomers with a rigid configuration provided an amorphous thin film with high thermal (T_d=415–444 °C) and morphological stability (T_g=188–224 °C). The high triplet energies and bipolar carrier transport characteristics (ambipolariy) of CzDPO and CzDOxa can facilitate exothermic energy transfer to the dopants and balance carrier injection/transport in the emission layers. As a result, they were utilized as universal hosts for various phosphorescent OLEDs (from blue to red), showing average external quantum efficiencies (η_ext=8.2–13.1 %) and low efficiency roll-off. In addition, we also fabricated dual-emitter white organic light-emitting diodes with a co-doped single emissive layer. WOLED hosted by CzDOxa exhibited satisfactory device efficiencies (14.4 %, 25.7 cd A⁻¹, 27 lm W⁻¹) with highly stable chromaticity (CIE_x=0.26–0.28 and CIE_y=0.38) at brightnesses from 560 to 15200 cd m⁻².     

Catalytic hydrogenation of linoleic acid over platinum-group metals supported on alumina

Catalytic activity and selectivity for hydrogenation of linoleic acid (cis-9,cis-12 18:2) were studied on Pt, Pd, Ru, and Ir supported on Al₂O₃. Stearic acid (18:0) and 10 different octadecenoic isomers (18:1) in the products could be separated completely by using a new capillary column coated by isocyanopropyl trisilphenylene siloxane for gas-liquid chromatography. The monoenoic acid isomers and dienoic acid isomers in the products on the various catalysts showed different distributions. The catalysts exhibited nearly equal selectivity for stearic acid formation. The 12-position double bond in linoleic acid has higher reactivity than the 9-position double bond in catalytic hydrogenation on platinum-group metal catalysts. In addition to hydrogenation products of linoleic acid, geometrical and positional dienoic acid isomers (trans-9,trans-12; trans-8,cis-12; cis-9,trans-13; trans-9,cis-13; cis-9,trans-12 18:2), due to isomerization of linoleic acid during hydrogenation, were contained in the reaction products. Ru/Al₂O₃ exhibited the highest activity for isomerization of linoleic acid with the noble metal catalysts. Conjugated octadecadienoic acid isomers have been observed in products of the reaction on Pt/Al₂O₃, Ru/Al₂O₃, and Ir/Al₂O₃. Catalytic activities of noble metals for positional and geometric isomerization of linoleic acid during hydrogenation decreased in the sequence of Ru ≥ Pt > Ir » Pd.     

Cyclometallated iridium(III) complexes with dicyanamide or tricyanomethanide

Reaction of cyclometallated iridium(III) complex Ir(ppy)₂(PPh₃)Cl (2, ppy = 2-phenylpyridine) with dicyanamide or tricyanomethanide gave neutral mononuclear complexes Ir(ppy)₂(PPh₃)N(CN)₂ (3a) or Ir(ppy)₂(PPh₃)C(CN)₃ (3b), and dicyanamide/tricyanomethanide-linked binuclear iridium(III) complexes [{Ir(ppy)₂(PPh₃)}₂N(CN)₂]⁺ (4a) or [{Ir(ppy)₂(PPh₃)}₂C(CN)₃]⁺ (4b). Substitution of coordinated chloride in the precursor 2 with dicyanamide or tricyanomethanide improved significantly the luminescence properties of 3a–4b. Compared with that in the precursor 2 (1.6%), 2.2 to 9.3-fold enhancement of emission quantum yields was detected in 3a–4b.     

Aqueous phase hydrogenation of acetic acid to ethanol over Ir-MoOx/SiO2 catalyst

Mo modified Ir/SiO₂ (Ir-MoO_x/SiO₂) was firstly used for the aqueous-phase hydrogenation of acetic acid to ethanol and exhibited the best performance among the investigated catalysts. The synergy effect between the closely contacted Ir and Mo species is responsible for the excellent performance of Ir-MoO_x/SiO₂. Ir-MoO_x/SiO₂ is also effective for the hydrogenation of other biomass derived carboxylic acids. Especially when levulinic acid was used as the feedstock, high yields of 2-pentanol (39.0%) and 1,4-pentanediol (42.3%) were obtained simultaneously. To our knowledge, this is the first report about the direct hydrogenation of levulinic acid to 2-pentanol and 1,4-pentanediol over heterogeneous catalyst.     

Synthesis and properties of novel poly(tetramethylsilnaphthylenesiloxane) derivatives

Novel poly(tetramethylsilnaphthylenesiloxane) derivatives were synthesized and characterized by differential scanning calorimetry (DSC), thermogravimetry (TG), and X-ray diffraction analyses. Poly(tetramethylsilnaphthylenesiloxane) derivatives were obtained by condensation polymerization of the corresponding disilanol derivatives, i.e. 1,4-, 1,5-, 2,6-, and 2,7-bis(dimethylhydroxysilyl)naphthalenes, which were prepared by the Grignard reaction using chlorodimethylsilane and the corresponding dibromonaphthalene derivatives followed by the hydrolyses, catalyzed by palladium on charcoal. The obtained poly(tetramethyl-1,5-silnaphthylenesiloxane) was insoluble in common organic solvents; however, the other polymers exhibited the good solubility in common organic solvents, such as tetrahydrofuran (THF), chloroform, dichloromethane, and toluene. The introduction of tetramethyl-1,5-silnaphthylenesiloxane units into the resulting polymer was confirmed by ¹H NMR spectrum of the copolymer obtained by condensation copolymerization of 1,5-bis(dimethylhydroxysilyl)naphthalene with 1,4-bis(dimethylhydroxysilyl)naphthalene. It was revealed from the DSC and X-ray diffraction measurements that poly(tetramethyl-1,5-silnaphthylenesiloxane) and poly(tetramethyl-2,6-silnaphthylenesiloxane) exhibited the crystallinity; however, poly(tetramethyl-1,4-silnaphthylenesiloxane) and poly(tetramethyl-2,7-silnaphthylenesiloxane) were amorphous. The glass transition temperature (T_g) and the temperature at 5% weight loss (T_d5) of poly(tetramethylsilnaphthylenesiloxane) derivatives with dimethylsilyl group at 1-position of the naphthylene moiety were higher than those at 2-position of the naphthylene moiety. The T_g and melting point (T_m) of the present polymers were higher than those of poly(tetramethyl-1,4-silphenylenesiloxane).     

Highly active and stable bimetallic Ir/Fe-USY catalysts for direct and NO-assisted N2O decomposition

The current research investigated N₂O decompositions over the catalysts Ir/Fe-USY, Fe-USY and Ir-USY under various conditions, and found that a trace amount of iridium (0.1 wt%) incorporated into Fe-USY significantly enhanced N₂O decomposition activity. The decomposition of N₂O over this catalyst (Ir/Fe-USY-0.1%) was also partly assisted by NO present in the gas mixture, in contrast to the negative effect of NO over noble metal catalysts. Moreover, Ir/Fe-USY-0.1% can decompose more than 90% at 400 °C (i.e. the normal exhaust temperature) under simulated conditions of a typical nitric acid plant, e.g. 5000 ppm N₂O, 5% O₂, 700 ppm NO and 2% H₂O in balance He, and such an activity can be kept for over 110 h under these strict conditions. The excellent properties of bimetallic Ir/Fe-USY-0.1% catalyst are presumably related to the good dispersion of Fe and Ir on the zeolite framework, the formation of framework Al–O–Fe species and the electronic synergy between the Ir and Fe sites. The reaction mechanism for N₂O decomposition has been further discussed on the temperature-programmed desorption profiles of O₂, N₂ and NO₂.     

Hybrid Organic Light-Emitting Diodes with Low Color-Temperature and High Efficiency for Physiologically-Friendly Night Illumination

Low color-temperature (CT) light sources are preferred for physiologically-friendly illumination at night due to their low suppression of melatonin secretion. We fabricated low-CT hybrid organic light-emitting diodes (OLEDs) by constructing a double emissive-layer (EML) structure, with a blue-red fluorescent-phosphorescent hybrid EML and a green phosphorescent EML, separated by a bipolar interlayer. By doping a red phosphor in a blue fluorescent mixed-host with a decent concentration, blue and red emissions from the host and dopant, respectively, were obtained. The CT of the optimized device was tuned to less than 2500 K, with the brightness ranging from 100 to 10,000 cd m⁻². In addition, the low-CT OLED exhibited much higher efficacy than other low-CT light sources, such as incandescent bulbs and candles. The maximum power efficiency and external quantum efficiency of the hybrid OLED reached 54.6 lm W⁻¹ and 24.3 %, respectively, which only rolled off to 44.2 lm W⁻¹ and 23.6 % at 1000 cd m⁻², with a CT of 1910 K. Low-CT OLEDs with high efficacy provide a promising alternative for night lighting that will safeguard human health.     

Activation of porous Ni cathodes towards hydrogen evolution by electrodeposition of Ir nuclei

Porous Ni electrodes were modified by electrodeposition of Ir nuclei from H₂IrCl₆ solutions at 70 °C, with the aim of activating them towards the hydrogen evolution reaction and comparing their performance with those of porous Ni electrodes activated by spontaneous deposition of noble metals (Ir and Ru). The current efficiency of Ir deposition was found to be very low (1% or lower, decreasing upon increasing deposition current density). Ir deposits characterised by SEM-EDX and XRD consisted of nanocrystals decorating the Ni dendrites forming the porous layers. Ir electrodeposition led to a strong activation of the hydrogen evolution reaction from aqueous 1 M NaOH. The electrocatalytic activity of the cathodes was independent of the Ir deposition charge above the minimum explored value of 1  C cm^?2. This charge is estimated to correspond to the deposition of ca. 2.5 10^?8 Ir moles cm^?2. The kinetic parameters for hydrogen evolution were similar for porous Ni electrodes modified by either spontaneous deposition (studied in a previous work) or electrodeposition of Ir.     

Ir promotion of TiO2 supported Au catalysts for selective hydrogenation of cinnamaldehyde

We synthesized Ir-on-Au (Au–Ir) nanoparticles (NPs) using 8–9 nm Au NPs, which had a partial coverage of Ir. Both the studied systems allowed the obtainment of cinnamyl alcohol with high selectivities (> 83%). However, Au–Ir/TiO₂ delivered a hydrogenation rate 5 times higher than that of Au/TiO₂. The deposition of Ir onto the surface of Au and the presence of surface Au–Ir alloy were confirmed by UV–vis and HRTEM respectively. Moreover. Moreover, the strongly shifted XPS binding energy implyed the electron transfer from Ir to Au, which was believed to be responsible for the enhanced H₂ activation capacity of Au.     

Catalytic activity of various supported Ir–Re catalysts for liquid phase methanol reforming with water

The catalytic activity of various supported Ir–Re catalysts was investigated for the liquid phase reforming reaction of methanol. Although Ir/SiO₂ exhibited poor activity for the hydrogen production but the addition of Re enhanced the activity more than one order of magnitude, and reached to the comparable value of Pt–Ru/SiO₂. The TOF of H₂ formation over Ir–Re/SiO₂ catalysts increased with the increase of Re/Ir ratio, accompanied with the increase of the particle sizes of Ir–Re composites. From the investigation of support effect, it was disclosed that CeO₂ and ZrO₂ enhanced catalytic activity of Ir–Re catalysts significantly.     

Fabrication of supported Pd–Ir/Al2O3 bimetallic catalysts for 2‐ethylanthraquinone hydrogenation

A series of χ wt % Pd‐(1‐χ) wt % Ir (χ = 0.75, 0.50, and 0.25) catalysts supported on γ‐Al₂O₃ have been prepared by co‐impregnation and calcination‐reduction, and subsequently employed in the hydrogenation of 2‐ethylanthraquinone—a key step in the manufacture of hydrogen peroxide. Detailed studies showed that the size and structure of the bimetallic Pd–Ir particles vary as a function of Pd/Ir ratio. By virtue of its small metal particle size and the strong interaction between Pd and Ir, the 0.75 wt % Pd–0.25 wt % Ir/Al₂O₃ catalyst afforded the highest yield of H₂O₂, some 25.4% higher than that obtained with the monometallic 1 wt % Pd catalyst. Moreover, the concentration of the undesired byproduct 2‐ethyl‐5,6,7,8‐tetrahydroanthraquinone (H₄eAQ) formed using the Pd–Ir bimetallic catalysts was much lower than that observed with the pure Pd catalyst, which can be assigned to the geometric and electronic effects caused by the introduction of Ir. © 2017 American Institute of Chemical Engineers AIChE J, 63: 3955–3965, 2017     

Selective Hydrogenation of <Emphasis Type="Italic">trans</Emphasis>-Cinnamaldehyde over SiO<Subscript>2</Subscript>-Supported Co–Ir Bimetallic Catalysts

Selective hydrogenation of trans-cinnamaldehyde was studied on SiO₂-supported Co–Ir bimetallic catalysts. Addition of Ir to Co/SiO₂ increased the hydrogenation selectivity and activity of cinnamaldehyde to the corresponding cinnamyl alcohol (UOL). A selectivity as higher as 93% to UOL at ambient temperature under H₂ pressure of 2.0 MPa was obtained over catalyst with loadings of 10 wt% Co and 0.5 wt% Ir (Co_10.0Ir_0.5/SiO₂). The XRD, Raman and TPR results showed that the higher dispersed Co₃O₄ particles were formed on SiO₂ due to the addition of Ir, which increased the reducibility of Co₃O₄ to Co⁰. The reduction of oxidized Co–Ir/SiO₂ samples occurred at the temperatures with about 200 K lower than that of the one without Ir species as evidenced by the observations of TPR and in-situ Raman characterizations. The XPS results indicated that the large parts of Co₃O₄ in the sample of Co–Ir/SiO₂ were reduced to Co⁰, but only small parts of that were reduced to Co⁰ in the sample of Co/SiO₂ under flowing 5%H₂/Ar at 673 K. The CO chemisorptions revealed that the irreversible uptakes of CO on the reduced Co–Ir/SiO₂ sample was much higher than those on the reduced Co/SiO₂ and Ir/SiO₂, and also higher than the combination of that on the reduced Co/SiO₂ and Ir/SiO₂, respectively. The experimental data suggested that the presence of Ir played a key role in the reduction of Co₃O₄ to Co⁰ through a strong interaction between them and that the amount of Co⁰ at the catalyst surfaces was correlated to the activity and more importantly to the UOL selectivity.     

Catalytic CO2 reforming of methane over Ir/Ce0.9Gd0.1O2−x

CO₂ reforming of methane over Ir loaded Ce_0.9Gd_0.1O_2−x (Ir/CGO) has been studied between 600 and 800 °C and for CH₄/CO₂ ratios between 2 and 0.66 in order to evaluate its potential use as an anode material for direct conversion of biogas at moderate temperatures in solid oxide fuel cells. The catalyst exhibited a superior catalytic activity compared to the support alone and other Ir based catalysts. High CH₄/CO₂ ratios and temperatures were required to obtain the maximum H₂/CO ratio, which could never exceed unity. Long-term experiments were carried out, showing the excellent stability of the catalyst with time on stream. Carbon formation was totally inhibited (in most experimental conditions) or very limited in the most severe conditions of the study (800 °C, CH₄/CO₂ = 2). This carbon was found to be highly reactive towards O₂ upon TPO experiments.     

Structure Sensitivity of NO Reduction over Iridium Catalysts in HC–SCR

Ir black with different crystallite sizes and Ir–H–ZSM-5 prepared using two different precursors were investigated for their behavior in selective catalytic reduction using hydrocarbons as reducing agents (HC–SCR). Emphasis was given to the study of the influence of time onstream on N₂ yield, the change in Ir crystallite size, and the change in the ratio of Ir : IrO₂. Under reaction conditions at 450°C Ir–H–ZSM-5 did not reach steady-state catalytic behavior within 32 h. In contrast, unsupported Ir black showed higher initial yields of nitrogen and approached steady-state considerably faster. Ir black with the largest crystallite size (45 nm) required the shortest time for reaching steady-state behavior. The influence of crystallite size on the reaction of Ir with O₂ and NO was addressed and related to the increase in N₂ yields with increasing Ir crystallite size in the reduction of NO using propene as a reducing agent. Comparative pulse thermoanalysis studies of NO and O₂ adsorption on Ir black with different crystallite sizes (5–45 nm) revealed that the relative uptake of NO (m_NO/m_O2) increases strongly with increasing crystallite size. This behavior is due to a strong structure sensitivity of NO adsorption, whereas O₂ adsorption is relatively insensitive to crystallite size. The improved yield of N₂ with increasing crystallite size under HC–SCR conditions is traced to the higher surface concentration of NO relative to O₂ with increasing crystallite size.     

Recent Advances in Multicolor Emission and Color Tuning of Heteroleptic Iridium Complexes

We review recent advances in the spectroscopic properties of heteroleptic Ir(N^C)₂(LX)-type iridium complexes, which are known as color-tuning materials. Most Ir(N^C)₂(LX)-type Ir complexes give single emission, in accordance with Kasha’s rule. Dual emission, however, has been observed from a single Ir(N^C)₂(LX) complex, depending on the choice of the N^C moiety and LX ligands. For example, Ir(dfppy)₂(pq), Ir(ppy)₂(dpq-3F), Ir(ppy)₂(pq), and Ir(pq)₂(tpy) (dfppy=2-(2,4-difluorophenyl)pyridine, pq=2-phenylquinoline, ppy=2-phenylpyridine, dpq-3F=2-(3-fluorophenyl)-4-phenylquinoline, tpy=2-p-tolylpyridine). Recently, triple emission was observed from Ir(ppy)₂(BTZ)-type iridium complexes with two ppy ligands as (N^C)₂ and one 2-(2-hydroxyphenyl)benzothiazole (BTZ) ligand, while quadruple emission from Ir(ppy)₂Q-type iridium complexes with two ppy ligands as (N^C)₂ and one quinolinolato (Q) ligand. These multiple emissions cover a spectral range from blue to red, leading to white emission. Of the four emission bands from Ir(ppy)₂Q, the UV and violet emissions are attributed to the emission from the singlet states of IrQ and Ir(ppy), respectively, while the green and red emissions are attributed to emission from the triplet states of Ir(ppy) and IrQ. The appearance of the emission from each of the Ir(ppy) and IrQ (or Ir(BTZ)) components is understood by reduced Förster energy transfer between IrQ (or Ir(BTZ)) and Ir(ppy) due to an orientation factor of nearly zero, that is, due to orthogonality between the two ligand planes, while the appearance of both the fluorescence and phosphorescence bands from each of the ligands is understood by inefficient intersystem crossing from the upper singlet state to the lower triplet state.