Highly efficient phosphorescent materials based on Ir(III) complexes-grafted on a polyhedral oligomeric silsesquioxane core

Article abstract of DOI:10.1039/c6dt02383e

A new iridium(iii) complex containing a coumarin derivative as the cyclometalated ligand (L) and a carbazole-functionalized β-diketonate (Cz-acac-allyl) as the ancillary ligand, namely, Ir(iii) bis(3-(pyridin-2-yl)coumarinato-N,C⁴)(1-(9-butyl-9H-carbazol-3-yl)hept-6-ene-1,3-dionato-O,O) [Ir(L)₂(Cz-acac-allyl)], was firstly synthesized as the emissive iridium(iii) complex. Then three new phosphorescent polyhedral oligomeric silsesquioxane (POSS) materials, consisting of the emissive Ir(iii) complex and carbazole moieties covalently attached to a polyhedral oligomeric silsesquioxane (POSS) core were successfully synthesized by hydrosilylation reaction in the presence of platinum(0)-1,3-divinyl-1,1,3,3-tetramethyldisiloxane (Pt-dvs) as the catalyst. These phosphorescent POSS materials offer many advantages including amorphous properties, good thermal stabilities, and good solubility in common solvents, and high purity via column chromatography. The photoluminescence spectra of the POSS materials in solution and in the solid state indicate a reduction in the degrees of interactions among the Ir(iii) complex units and concentration quenching due to the bulky POSS core. Solution processed light-emitting devices based on these phosphorescent POSS materials exhibit a maximum external quantum efficiency (EQE) of 9.77%.

Full text of DOI:10.1039/c6dt02383e

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DOI: 10.1039/C6DT02383E
Highly efficient phosphorescent materials based on Ir(III) complexesꢀ
grafted on polyhedral oligomeric silsesquioxane core
Tianzhi Yu1,*, Zixuan Xu1, Wenming Su2,*, Yuling Zhao3, Hui Zhang1, Yanjun Bao1
1Key Laboratory of OptoꢀElectronic Technology and Intelligent Control (Ministry of Education),
Lanzhou Jiaotong University, Lanzhou 730070, China
2Printable electronics research center, Suzhou Institute of NanoꢀTech and NanoꢀBionics, Chinese
Academy of Sciences, Suzhou 215123, China
3School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070,
China
Abstract: A new iridium(III) complex containing coumarin derivative as the cyclometalated ligand
(L) and a carbazoleꢀfunctionalized βꢀdiketonate (Czꢀacacꢀallyl) as the ancillary ligand, namely, Ir(III)
bis(3ꢀ(pyridinꢀ2ꢀyl)coumarinatoꢀN,C4)(1ꢀ(9ꢀbutylꢀ9Hꢀcarbazolꢀ3ꢀyl)heptꢀ6ꢀeneꢀ1,3ꢀdionatoꢀO,O)
[Ir(L)2(Czꢀacacꢀallyl)], was firstly synthesized as the emissive iridium(III) complex. Then three new
phosphorescent polyhedral oligomeric silsesquioxane (POSS) materials, consisting of the emissive
Ir(III) complex and carbazole moieties covalently attached to a polyhedral oligomeric silsesquioxane
(POSS) core were successfully synthesized by hydrosilylation reaction in the presence of
platinum(0)ꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane (Ptꢀdvs) as the catalyst. These phosphorescent
POSS materials offer many advantages including amorphous properties, good thermal stabilities, and
good solubility in common solvents, and high purity via column chromatography. The
photoluminescence spectra of the POSS materials in solutions and in the solid states indicate a
reduction in the degrees of interactions among Ir(III) complex units and concentration quenching due
*Corresponding Author. Tel. +86ꢀ931ꢀ4956935; Fax: +86ꢀ931ꢀ4938756; eꢀmail: yutzh@mail.lzjtu.cn (T.Z. Yu);
wmsu2008@sinano.ac.cn (W.M. Su).
1

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to the bulky POSS core. Solution processed lightꢀemitting devices based on these phosphorescent
POSS materials exhibit maximum external quantum efficiency (EQE) of 9.77%.
Keywords:
Iridium
complex;
POSS;
Carbazole;
βꢀdiketone;
Photoluminescence;
Electroluminescence
1. Introduction
Phosphorescent heavyꢀmetal complexes are widely used in organic lightꢀemitting diodes
(OLEDs) [1ꢀ4], lightꢀemitting electrochemical cells [5ꢀ7], chemosensors [8ꢀ10], biological labeling and
bioimaging [11ꢀ13], which successfully overcome low luminescent efficiency of traditional fluorescent
materials because they can fully utilize both singlet and triplet excitons through the strong spinꢀ
orbital coupling of heavyꢀmetal ions and the internal quantum efficiency of phosphorescent emitters
can theoretically approach 100%. Among phosphorescent heavyꢀmetal complexes, cyclometalated
iridium complexes are the most promising emitting materials due to their high quantum efficiency,
brightness, color diversity and short excitedꢀstate lifetime. In the past decades, considerable efforts
have been devoted to the exploitation of novel Ir(III) complexes for highly efficient OLEDs.
However, the Ir(III) complexes used as electroluminescent (EL) materials are suffering from selfꢀ
quenching in solid state due to interaction and aggregation with its neighboring complexes. Thus, as
the EL materials they are always doped in the host materials at appropriate concentration to fabricate
OLEDs with reasonable, luminant efficiency. Unfortunately, this method usually leads to the phase
separation during the device manufacturing process by the vacuum deposition. Alternative feasible
approach is to introduce the steric hindrance or bulky side groups into Ir(III) complexes to suppress
the emission quenching and enhance the device performance [14ꢀ16]
.
Recently, polyhedral oligomeric silsesquioxanes (POSS) derivatives have attracted a great deal
of attention in the materials field because of their unique nanoscale cageꢀshaped structures and good
solubility in organic solvents. POSS derivatives are threeꢀdimensional, structurelly wellꢀdifined cage
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molecules which can provide huge stretching space for chromophoric groups, which are regarded as
organicꢀinorganic hybrid materials at a molecular level and used for the development of high
performance materials in medical, aerospace, microelectronics and so on [17ꢀ21]. Polyhedral
oligomeric silsesquioxane has eight hydrogen atoms linked with silicon atoms at the corner of the
Si8O12 core, the introduction of chromophoric groups onto the corner of POSS greatly improved the
quantum efficiency by suppressing πꢀπ aggregation of chromophoric groups and effectively
inhibiting the aggregationꢀcaused quenching (ACQ) effect. Furthermore, the incorporation of POSS
core into luminescent materials produces nanocomposites with improved properties such as increases
in glass transition temperature, thermal stability, mechanical strength, oxidation resistance and ease
of processing. On the other hand, POSS materials attaching the carrierꢀtransporting moieties and/or
chromophores can provide the advantages of both small molecule and polymer lightꢀemitting
materials including high purity and solution processability. Since the first use of POSS as central
cores for solution processed hybrid hole transport materials in OLEDs that enhanced brightness and
efficiencies as compared to the devices that used traditional hole transport materials [22], the POSS
functionalized light emitting materials were widely used in OLEDs [20, 23ꢀ26]. In previous research, the
Heeger group pioneered the use of POSSꢀbased light emitting polymers in which POSS cores as endꢀ
cappers were attached at the chain ends of poly[2ꢀmethoxyꢀ5ꢀ(2ꢀethylhexyloxy)ꢀ1,4ꢀ
phenylenevinylene] (MEHꢀPPV) and poly(9,9ʹꢀdioctylfluorene) [23]. The electroluminescent device
made from the POSSꢀcapped MEHꢀPPV polymer was found to exhibit higher brightness (1320
cd/m2 at 3.5V) and external quantum efficiency (EQE) (ηext = 2.2%) than the POSSꢀfree MEHꢀPPV
(230 cd/m2 at 3.5 V and ηext = 1.5%). The enhanced device properties may be attributed to reduced
aggregation caused by the bulky POSS end groups and improved adhesion of the polymer to the ITO
[24]
[25]
coated glass substrate. Jabbour et al.
and Shim et al.
synthesized POSS materials containing
eight chromophore groups and reported that they enhanced the EL properties and quantum
[26,27]
efficiencies of the host through energy transfer. Besides, Jabbour et al.
reported a group of Irꢀ
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complexes anchored POSS macromolecules and platinumꢀcomplexesꢀanchored polyhedral
oligomeric silsesquioxane materials. The devices based on holeꢀtransporting and Irꢀcomplex moieties
dualfunctionalized POSS materials and platinumꢀcomplexesꢀanchored POSS materials exhibited
encouraging efficiency, which was significantly higher than that of the analogous devices with a
physical blend of the platinumꢀcomplexes and a polymer matrix, indicating that POSS core was
necessary to improve the efficiencies of the devices. Recently, we have succeeded in the synthesis
and electroluminescence of two new POSSꢀbased organicꢀinorganic hybrid materials, the devices
based on these POSS materials exhibit maximum external quantum efficiency (EQE) of 7.82% and a
maximum luminance of 21285 cd/m2 [28]. These previous researches indicated that the lightꢀemitting
devices fabricated with the POSSꢀfunctionalized materials showed much improved brightness and
quantum efficiency in comparison with devices fabricated with the corresponding parent materials.
Developing new organicꢀinorganic hybrid materials based on POSS is of interest both for scientific
knowledge and applications.
Previously, we have reported the phosphorescent OLEDs (PhOLEDs) based on the
cyclometalated Ir(III) coumarin complexes [29ꢀ31], in which 3ꢀ(pyridinꢀ2ꢀyl)coumarin was used as the
cyclometalated ligand and the βꢀdiketone derivatives were used as the ancillary monoanionic ligand,
respectively. The research results indicated that the device performance can be improved by
modifying the ancillary ligand. Especially, a carbazoleꢀfunctionalized βꢀdiketonate as the ancillary
ligand, the PhOLEDs possess better performance as compared with those fabricated by similar
complexes containing acac or TTA as the ancillary ligand [29]. Encouraged by the advantages of the
carbazoleꢀfunctionalized βꢀdiketonate ligands and POSSꢀbased lightꢀemitting materials, in this paper,
we used a carbazoleꢀfunctionalized βꢀdiketonate (Czꢀacacꢀallyl) as the ancillary ligand to synthesize
a new iridium(III) coumarin complex, Ir(L)2(Czꢀacacꢀallyl), which was as an emissive iridium
complex. Then three new Ir(III) complexꢀfunctionalized POSS meterials, 7CzꢀIr(L)2(Czꢀacac)ꢀPOSS
(POSSꢀ1), 6Czꢀ2Ir(L)2(Czꢀacac)ꢀPOSS (POSSꢀ2) and 5Czꢀ3Ir(L)2(Czꢀacac)ꢀPOSS (POSSꢀ3) (Fig. 1),
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were successfully synthesized and characterized. The photophysical and electrochemical properties
and thermal stabilities of these POSS materials were investigated. Furthermore, solution processed
lightꢀemitting devices based on POSSꢀ1 and POSSꢀ2 materials were fabricated to investigate the
electroluminescence properties of the POSS materials.
The synthetic routes of the Ir(III) complexꢀfunctionalized POSS meterials were shown in
Scheme 1.
2. Experimental
2.1 Materials and methods
Carbazole, potassium tertꢀbutoxide and allyl bromide were bought from Alfa Aesar. 4ꢀ
Pentenoic acid was obtained from Energy Chemical (China). Platinum complex (platinumꢀ1,3ꢀ
divinylꢀ1,1,3,3ꢀtetramethyldisiloxane, Ptꢀdvs, 2 wt% Pt in xylene) was purchased from Aldrich, USA.
H
Octakis(dimethylsiloxy)silsesquioxane (Q8M8 ) containing eight hydroꢀsilane groups was purchased
from the Hybrid Plastics Co., USA. 8ꢀHydroxyquinolinolatoꢀlithium (Liq), 4,4ʹꢀBis(9ꢀ
carbazolyl)biphenyl (CBP) and 1,3,5ꢀTri(Nꢀphenylbenzimidazolꢀ2ꢀyl)benzene (TPBi) were
purchased from ElectroꢀLight Technology Corp., Beijing. Toluene was dried by distillation before
use in the hydrosilylation reaction. All other chemicals were analytical grade reagent.
The cyclometalated coumarin ligand (3ꢀ(pyridineꢀ2ꢀyl)coumarin, L) and the cyclometalated
Ir(III) ꢁꢀchlorobridged dimmer ((L)2Ir(ꢁꢀCl)2Ir(L)2) were prepared as previously described [32]. 9ꢀ
allylꢀ9Hꢀcarbazole (Czꢀallyl) and 3ꢀAcetylꢀ9ꢀbutylꢀcarbazole were synthesized as previously
described [28,29]
.
1H NMR spectra were obtained on Unity Varianꢀ500MHz. IR spectra (400 – 4000 cmꢀ1) were
measured on a Shimadzu IRPrestigeꢀ21 FTꢀIR spectrophotometer. C, H, and N analyses were
obtained using an Elemental VarioꢀEL automatic elemental analysis instrument. Mass spectrum was
obtained from a Thermo Scientific Orbitrap Elite mass spectrometer. Thermogravimetric analysis
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(TGA) was performed on a PerkinꢀElmer Pyris system. UVꢀvis absorption and photoluminescent
spectra were recorded on a Shimadzu UVꢀ2550 spectrometer and on a PerkinꢀElmer LSꢀ55
spectrometer, respectively.
2.2 Synthesis and characterization of Ir(L)2(Czꢀacacꢀallyl) and the POSS materials
Butyl pentꢀ4ꢀenoate: In a 250 mL flask equipped with a reflux condenser and a water
segregater was placed NaHSO4•H2O (0.2 g, 1.45 mmol), 4ꢀpentenoic acid (10 g, 0.1 mol) and butyl
alcohol (15 g, 0.2 mol) and cyclohexane (20 mL). The reaction mixture was stirred at 110 oC for 5 h.
After cooling, the reaction mixture was poured into water (100 mL), and neutralization with
saturated aqueous sodium bicarbonate to pH 6 followed by extration with ethyl acetate (100 mL × 3)
was performed. The obtained organic layer was dried over anhydrous magnesium sulfate and
concentrated, collecting 13.51 g (86.48% yield) of colorless oil. 1H NMR (CDCl3, 400 MHz, δ, ppm):
5.87ꢀ5.77 (m, 1H), 5.08ꢀ4.98 (m, 2H), 4.08 (t, J = 6.8 Hz, 2H), 2.42ꢀ2.35 (m, 4H), 1.64ꢀ1.57 (m, 2H),
1.43ꢀ1.36 (m, 2H), 0.94 (t, J = 7.6 Hz, 3H).
1ꢀ(9ꢀbutylꢀ9Hꢀcarbazolꢀ3ꢀyl)heptꢀ6ꢀeneꢀ1,3ꢀdione (Czꢀacacꢀallyl): To a solution of butyl
pentꢀ4ꢀenoate (9.185 g, 58.76 mmol) in anhydrous toluene (50 mL) was added tꢀBuOK (13.19 g,
117.55 mmol). The mixture was stirred at room temperature for 1 h. A solution of 3ꢀacetylꢀ9ꢀbutylꢀ
carbazole (5.23 g, 19.71 mmol) in 20 mL of anhydrous toluene was added dropwise over 5 min, and
o
then stirring overnight at 40 C. The mixture was poured into cooled water (150 mL), and then
acidified with dilute hydrochloric acid to pH 5. The mixture was extracted with CH2Cl2 (3 × 100
mL), and the combined organic phase was dried over anhydrous MgSO4. The solvent was removed
under reduced pressure and the residue was purified by column chromatography on silica gel with a
mixture of ethyl acetate/petroleum ether (1:20, v/v) as eluent to obtain Czꢀacacꢀallyl as a yellow solid
(3.72 g, 54.3%). 1H NMR (400 MHz, CDCl3) δ: 15.71 (s, 1H), 8.69 (s, 1H), 8.15 (d, J = 7.2 Hz, 1H),
8.03 (d, J = 8.8 Hz, 1H), 7.51 (d, J = 6.8 Hz, 1H), 7.42 (t, J = 9.2 Hz, 2H), 7.29 (d, J = 6.4 Hz, 1H),
6.32 (s, 1H), 5.95ꢀ5.74 (m, 1H), 5.15ꢀ4.97 (m, 2H), 4.32 (t, J = 6.4 Hz, 2H), 2.55 (t, J = 6.0 Hz, 2H),
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2.49 (t, J = 5.2 Hz, 2H), 1.86ꢀ1.82 (m, 2H), 1.41ꢀ1.38 (m, 2H), 0.95 (t, J = 6.8 Hz, 3H). C NMR
(CDCl3, δ, ppm): 193.0, 185.7, 143.0, 141.0, 137.1, 126.4, 125.8, 125.0, 123.0, 122.9, 120.6, 120.3,
119.8, 115.5, 109.2, 108.5, 95.4, 43.1, 37.9, 31.1, 29.9, 20.5, 13.9. Anal. Calc. for C23H25NO2: C
79.51, H 7.25, N 4.03; Found C 79.62, H 7.21, N 4.07 %.
Ir(L)2(Czꢀacacꢀallyl): The cyclometalated Ir(III) ꢁꢀchlorobridged dimmer ((L)2Ir(ꢁꢀCl)2Ir(L)2)
(1.20 g, 0.89 mmol), Czꢀacacꢀallyl (1.60 g, 4.60 mmol) and anhydrous K2CO3 (1.00 g, 7.24 mmol)
were refluxed in dichloroethane under nitrogen atmosphere for 24 h. After cooling, a small quantity
of water was added. The mixture was extracted with dichloromethane (100 mL × 3). The organic
phase was washed with water (2 × 100 mL) and dried over anhydrous MgSO4. After filtering, the
filtrate was evaporated to dryness under reduced pressure. The crude was purified by
chromatography on silica gel using petroleum ether/acetone (15:1, v/v) as the eluent to give yellow
powdery Ir(L)2(Czꢀacacꢀallyl) in 77.5% yield (1.36 g). 1H NMR(CDCl3, δ, ppm): 9.17 (d, 2H, J = 8.0
Hz, ArylꢀH), 8.38 (s, 1H, ArylꢀH), 8.15ꢀ8.08 (m, 3H, ArylꢀH), 7.91ꢀ7.82 (m, 2H, ArylꢀH), 7.77 (d,
1H, J = 7.2 Hz, ArylꢀH), 7.48 (t, 1H, J = 7.6 Hz, ArylꢀH), 7.39 (d, 1H, J = 8.4 Hz, ArylꢀH), 7.27 (d,
6H, J = 6.8 Hz, ArylꢀH), 6.99 (t, 2H, J = 8.8 Hz, ArylꢀH), 6.67 (d, 2H, J = 6.8 Hz, ArylꢀH), 6.23 (d,
2H, J = 5.2 Hz, ArylꢀH), 5.97 (s, 1H), 5.58ꢀ5.52 (m, 1H, ꢀCH=CH2), 4.85 (t, 2H, J = 17.6 Hz, ꢀ
CH=CH2), 4.28 (t, 2H, J = 6.2 Hz, ꢀNꢀCH2ꢀ), 2.26 (t, 2H, J = 7.2 Hz), 2.11ꢀ2.04 (m, 2H), 1.81 (t, 2H ,
J = 7.2 Hz), 1.38ꢀ1.32 (m, 2H), 0.92 (t, J = 6.8 Hz, 3H). Anal. Calc. for C51H40IrN3O6 (%): C, 62.31;
H, 4.10; N, 4.27. Found: C, 62.56; H, 3.97; N, 4.32. ESIꢀMS: Calcd for [C51H40IrN3O6 + H]+, 984.12;
Found, 984.34.
POSS Materials:
A
round bottom flask (100 mL) was charged with
octakis(dimethylsiloxy)silsesquioxane (0.92 g, 0.90 mmol), Ir(L)2(Czꢀacacꢀallyl) (0.89 g, 0.90 mmol)
and anhydrous toluene (30 mL). The solution was degassed with argon for 5 min and then 5 drops of
a solution of platinumꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane (Ptꢀdvs) (2 wt% Pt in xylene) were
added, and the reaction mixture was stirred at room temperature under positive argon pressure for 4 h.
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Then Czꢀallyl (1.87 g, 9.02 mmol) was introduced, and the reaction mixture was allowed to stir at
room temperature overnight. The toluene was evaporated in vacuo and the crude product was
isolated by chromatography on silica gel using dichloromethane/ethyl acetate/petroleum ether
(1:1:20, v/v/v) as the eluent to yield pure fractions of POSSꢀ1, POSSꢀ2 and POSSꢀ3, which were
isolated separately in 26.2%, 14.7% and 6.4% yields, respectively.
1
POSSꢀ1: H NMR (400 MHz, CDCl3, δ, ppm): 9.12 (t, 2H, J = 7.6 Hz, ArylꢀH), 8.34 (s, 1H,
ArylꢀH), 8.06ꢀ8.00 (m, 16H, ArylꢀH), 7.71 (dd, 3H, J = 7.6 Hz, ArylꢀH), 7.42 (t, 2H, J = 8.0 Hz,
ArylꢀH), 7.37ꢀ7.32 (m, 16H, ArylꢀH), 7.24ꢀ7.22 (m, 17H, ArylꢀH), 7.15ꢀ7.10 (m, 16H, ArylꢀH),
6.81ꢀ6.76 (m, 2H, ArylꢀH), 6.63 (t, 2H, J = 7.8 Hz, ArylꢀH), 6.19 (t, 2H, J = 7.8 Hz, ArylꢀH), 5.88 (s,
1H), 4.18 (t, 2H, J = 7.2 Hz, ꢀNꢀCH2ꢀ), 4.10ꢀ4.02 (m, 14H,ꢀNꢀCH2ꢀ), 2.03 (t, 2H, J = 8.0 Hz, ꢀCH2ꢀ),
1.82ꢀ1.72 (m, 18H, ꢀCH2ꢀ), 1.32ꢀ1.28 (m, 4H, ꢀCH2ꢀ), 1.13ꢀ1.06 (m, 3H, ꢀCH3), 0.57ꢀ0.41 (m, 16H, ꢀ
CH2ꢀSi), 0.06ꢀ(ꢀ0.05) (m, 48H, SiꢀCH3). IR (KBr pellet, cmꢀ1): 3058, 2963, 2924, 2875, 1693, 1603,
1542, 1475, 1352, 1330, 1263, 1230, 1168, 1089, 800, 560, 471. ESIꢀMS: Calcd for
[C172H187IrN10O26Si16 + H]+, 3452.97; Found, 3452.98.
1
POSSꢀ2: H NMR (400 MHz, CDCl3, δ, ppm): 9.13 (t, 4H, J = 7.6 Hz, ArylꢀH), 8.36 (s, 2H,
ArylꢀH), 8.07ꢀ7.99 (m, 18H, ArylꢀH), 7.72ꢀ7.68 (m, 6H, ArylꢀH), 7.43ꢀ7.40 (m, 4H, ArylꢀH), 7.35ꢀ
7.31(m, 14H, ArylꢀH), 7.28ꢀ7.18 (m, 20H, ArylꢀH), 7.16ꢀ7.11 (m, 14H, ArylꢀH), 6.85ꢀ6.76 (m, 4H,
ArylꢀH), 6.64 (t, 4H, J = 7.2 Hz, ArylꢀH), 6.21 (t, 4H, J = 6.8 Hz, ArylꢀH), 5.90 (s, 2H), 4.18 (t, 4H, J
= 7.6 Hz, ꢀNꢀCH2ꢀ), 4.14ꢀ4.01 (m, 12H,ꢀNꢀCH2ꢀ), 2.03 (t, 4H, J = 7.6 Hz, ꢀCH2ꢀ), 1.81ꢀ1.74 (m, 18H,
ꢀCH2ꢀ), 1.32ꢀ1.23 (m, 10H, ꢀCH2ꢀ), 1.14ꢀ1.07 (m, 6H, ꢀCH3), 0.63ꢀ0.42 (m, 16H, ꢀCH2ꢀSi), 0.08ꢀ(ꢀ
0.06) (m, 48H, SiꢀCH3). IR (KBr pellet, cmꢀ1): 3058, 2963, 2924, 2875, 1693, 1597, 1542, 1514,
1469, 1408, 1352, 1330, 1258, 1230, 1157, 1089, 845, 800, 750, 560, 471. ESIꢀMS: Calcd for
[C208H214Ir2N12O32Si16 + H]+, 4228.80; Found, 4229.12.
1
POSSꢀ3: H NMR (400 MHz, CDCl3, δ, ppm): 9.12 (t, 6H, J = 7.6 Hz, ArylꢀH), 8.35 (s, 3H,
ArylꢀH), 8.06ꢀ7.97 (m, 18H, ArylꢀH), 7.71ꢀ7.67 (m, 9H, ArylꢀH), 7.44ꢀ7.39 (m, 3H, ArylꢀH), 7.34ꢀ
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7.30(m, 15H, ArylꢀH), 7.28ꢀ7.17 (m, 22H, ArylꢀH), 7.15ꢀ7.08 (m, 15H, ArylꢀH), 6.82ꢀ6.77 (m, 6H,
ArylꢀH), 6.64 (t, 6H, J = 7.2 Hz, ArylꢀH), 6.19 (t, 6H, J = 6.8 Hz, ArylꢀH), 5.89 (s, 3H), 4.19ꢀ4.15 (m,
6H, ꢀNꢀCH2ꢀ), 4.12ꢀ3.99 (m, 10H,ꢀNꢀCH2ꢀ), 2.06ꢀ1.99 (m, 6H, ꢀCH2ꢀ), 1.81ꢀ1.74 (m, 18H, ꢀCH2ꢀ),
1.31ꢀ1.23 (m, 16H, ꢀCH2ꢀ), 1.13ꢀ1.07 (m, 9H, ꢀCH3), 0.61ꢀ0.39 (m, 16H, ꢀCH2ꢀSi), 0.07ꢀ(ꢀ0.09) (m,
48H, SiꢀCH3). IR (KBr pellet, cmꢀ1): 3047, 2958, 2925, 2875, 1693, 1603, 1547, 1519, 1464, 1402,
1352, 1325, 1263, 1229, 1163, 1089, 845, 800, 744, 722, 549, 471. ESIꢀMS: Calcd for
[C244H241Ir3N14O38Si16 + H]+, 5004.62; Found, 5004.27.
2.3 Crystallography
The diffraction data were collected with a Bruker Smart Apex CCD area detector with graphiteꢀ
monochromatized MoꢀKα radiation (λ = 1.54178 Å) at 293(2) K. The structure was solved by using
the program SHELXL and Fourier difference techniques, and refined by fullꢀmatrix leastꢀsquares
method on F2. All hydrogen atoms were added theoretically.
2.4 OLEDs fabrication and characterization
The multilayer OLEDs with a device architecture of ITO/PEDOT:PSS (30 nm)/CBP: POSS
materials (x wt %, 50 nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm) were fabricated. Poly(3,4ꢀ
ethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) was spinꢀcoated onto
precleaned and O2ꢀplasmaꢀtreated indium tin oxide (ITO) substrates, yielding layers ca. 45 nm thick.
o
PEDOT:PSS layers were heated at 180 C for 10 min to remove residual water. Blends of POSS
materials + 4,4ʹꢀBis(9ꢀcarbazolyl)biphenyl (CBP) in chlorobenzene solution was spinꢀcoated on top
o
of the PEDOT:PSS layers, yielding films ca. 50 nm thick. The samples were then dried at 80 C for
30 min. A TPBi hole/excitonꢀblocking layer was deposited via thermal evaporation at a rate of ~ 2 Ǻ
sꢀ1. A cathode consisting of an ultrathin Liq interfacial layer with a nominal thickness of 2 nm and an
Al layer ca. 150 nm thick was deposited by thermal evaporation. The deposition rates for Liq and Al
were ~ 1 and 10 Ǻ sꢀ1, respectively. The active area of the devices was 12 mm2. The EL spectra and
Commission Internationale de L'Eclairage (CIE) coordinates were measured on a Hitachi MPFꢀ4
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fluorescence spectrometer. The characterization of brightnessꢀcurrentꢀvoltage (B–I–V) were
measured with a 3645 DC power supply combined with a 1980A spot photometer and were recorded
simultaneously. All measurements were done in the air at room temperature without any
encapsulation.
3. Results and discussion
3.1 Synthesis and characterization of the POSS materials
The synthesis of the phosphorescent Ir(III) complex [Ir(L)2(Czꢀacacꢀallyl)] from Scheme 1
began first with preparing the ancillary ligand, 1ꢀ(9ꢀbutylꢀ9Hꢀcarbazolꢀ3ꢀyl)heptꢀ6ꢀeneꢀ1,3ꢀdione
(Czꢀacacꢀallyl), which has a terminal alkene group for later attachment to POSS core. The ancillary
ligand Czꢀacacꢀallyl was successfully synthesized via three steps including Nꢀalkylation reaction of
carbazole, Friedelꢀcrafts acylation of carbazole ring and Claisen condensation reaction. This method
leads to medium yield of the target product (41%). The ancillary ligand was then reacted with the
chlorobridged dimer complex based on the cyclometalated coumarin ligand (3ꢀ(pyridineꢀ2ꢀ
yl)coumarin) and anhydrous K2CO3 in refluxing dichloroethane under nitrogen atmosphere to obtain
Ir(L)2(Czꢀacacꢀallyl) complex. The ancillary ligand and the Ir(III) complex were characterized using
1H NMR, MS, elemental analysis and Xꢀray crystallograpgy.
Yellow columnar crystal of the Ir(III) complex [Ir(L)2(Czꢀacacꢀallyl)] was obtained by the
evaporation of the ethyl acetate solution. The crystallographic data of Ir(L)2(Czꢀacacꢀallyl) are
shown in Table 1. The selected bond lengths and bond angles of Ir(L)2(Czꢀacacꢀallyl) are listed in
Table 2.
The crystal structure of the complex Ir(L)2(Czꢀacacꢀallyl) is given in Fig. 2. The crystal of
Ir(L)2(Czꢀacacꢀallyl) belongs to the monoclinic space group P2(1)/n, a = 10.0465(6) Ǻ, b =
30.8172(15) Ǻ, c = 13.9390(11) Ǻ, α = γ = 90o, β = 98.719(2)o, U = 4265.7(5) Å3, Z = 4, Dc = 1.531
g/cm3, ꢁ = 6.503 mmꢀ1. It is shown that the iridium(III) ion in Ir(L)2(Czꢀacacꢀallyl) is
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hexacoordinated by two C atoms and two N atoms from 3ꢀ(pyridinꢀ2ꢀyl)coumarin ligands and two O
atoms from Czꢀacacꢀallyl ligand, displaying a distorted octahedral coordination geometry. Two C
atoms and two N atoms from the 3ꢀ(pyridinꢀ2ꢀyl)coumarin ligands exhibit cisꢀCꢀC and transꢀN,N
chelate mode, and two O atoms from Czꢀacacꢀallyl ligand locate cisꢀOꢀO chelate disposition. The Irꢀ
C bonds (1.989(10) and 2.006(11) Å) are shorter than the IrꢀN bonds (2.016(9) and 2.030(9) Å). In
the βꢀdiketone chelate ring of the complex, the average distances for the carbon–carbon (C17–C18
and C18–C19) bonds of 1.404 Å and the average distances for the carbon–oxygen (C17–O1 and
C19–O2) bonds of 1.270 Å lie between the singleꢀ and doubleꢀbond distances, indicating that the
delocalized π bond formed when Czꢀacacꢀallyl ligand coordinated to Ir atom. Two IrꢀO bonds are
2.104(6) and 2.126(7) Å, respectively. In addition, the dihedral angle between the plane defined by
the carbazole ring and the plane defined by the βꢀdiketone chelate ring (Ir1/O1/O2/C17/C18/C19) is
19.37o. Compared with the free Czꢀacacꢀallyl ligand, it is twisted slightly due to the steric hindrance.
The holeꢀtransporting and Ir(III) complex unit functionalized POSS materials were obtained via
hydrosilylation reaction in the presence of platinum(0)ꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane (Ptꢀ
dvs) as the catalyst. The POSS materials were synthesized in a stepwise mode by sequentially
H
reacting the Ir(III) complex Ir(L)2(Czꢀacacꢀallyl) with octakis(dimethylsiloxy)silsesquioxane (Q8M8 )
in a 1:1 ratio, and followed by reaction with excess Czꢀallyl. There are several different amount of
new products finding in the reaction system, but only three products (POSSꢀ1, POSSꢀ2 and POSSꢀ3)
were larger and easily isolated from the reaction mixture chromatographically. The other products’
amount was very small, so we did not separate them. The POSS materials (POSSꢀ1, POSSꢀ2 and
POSSꢀ3) were found to be completely soluble in common organic solvents (toluene, chlorobenzene,
THF, chloroform, dichloromethane and acetone), and homogeneous thin films of these POSS
materials were fabricated easily by spinꢀcoating onto the quartz glasses and indium tin oxide (ITO)
substrates.
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1
These POSS materials were characterized using H NMR, MS, FTꢀIR and Xꢀray diffraction
H
(XRD) analysis. The resonance of SiꢀH protons in Q8M8 is located at 4.7 ppm. For Czꢀallyl, two
doublets (with fine coupling) and the quartet resonance proton resonance peaks from the allyl group
are located at 5.03, 5.15 and 5.99 ppm with a relative molar ratio of 1:1:1, corresponding to isoꢀ,
transꢀ and substituted vinyl protons. The resonance of methylene (ꢀCH2ꢀCz) is observed at 4.90 ppm.
The peaks from the terminal alkene group of Ir(L)2(Czꢀacacꢀallyl) are observed at ca. 4.85 and 5.54
1
ppm with a relative molar ratio of 2:1. In H NMR spectra of the POSS materials, the peaks for the
vinyl groups of Czꢀallyl (5.03, 5.15 and 5.99 ppm) and Ir(L)2(Czꢀacacꢀallyl) (4.85 and 5.54 ppm) and
SiꢀH protons (4.7 ppm) disappeared, supporting the complete hydrosilylation reaction and the vinyl
H
groups of Czꢀallyl and Ir(L)2(Czꢀacacꢀallyl) underwent hydrosilylation of the SiꢀH bonds of Q8M8 .
H
The FTꢀIR spectra of Q8M8 , POSSꢀ1 and POSSꢀ2 are shown in Fig. 3. The strong absorption
H
peak around 1098 cmꢀ1 for Q8M8 , POSSꢀ1 and POSSꢀ2 represented the vibrations of the siloxane
SiꢀOꢀSi groups, and it is a general feature of POSS derivatives. In POSSꢀ1 and POSSꢀ2, the
characteristic stretching vibration of the SiꢀH groups (2147 cmꢀ1) disappeared completely, indicating
that the hydrosilylation occurred to completion. The characteristic stretching vibration bands of ꢀCH3
and ꢀCH2ꢀ are clearly observed at 2800 – 2900 cmꢀ1. The FTꢀIR spectrum of POSSꢀ3 was similar to
that of POSSꢀ1 and POSSꢀ2.
The thermogravimetric analyses (TGA) were performed in flowing drying nitrogen atmosphere
at the heating rate of 10 oC/min. The result of TGA measurements of the POSS materials are shown
o
in Fig. 4. The POSS materials display good thermal stability up to 345 C. With increasing
o
temperature, the POSS materials begin to decompose at 347 C accompanied by a sharp weight loss
in their TGA curves, indicating that the POSS materials meet with the thermal stability requirement
of fabrication of OLED luminescence application. For the POSS materials, the final residues should
mainly be iridium oxide (Ir2O3) and silicon oxide (SiO2) in the thermal decomposition processes.
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Because the POSS materials have different quantities of carbazole moieties and Ir(III) complex units,
the results of TGA measurements of them display different weight losses.
Figure 5 presents the Xꢀray diffraction (XRD) patterns of Czꢀallyl, Ir(L)2(Czꢀacacꢀallyl) and the
POSS materials. Czꢀallyl and Ir(L)2(Czꢀacacꢀallyl) exhibit several sharp XRD peaks because of their
crystallinity, suggesting that Czꢀallyl and Ir(L)2(Czꢀacacꢀallyl) show the crystal morphology.
Interestingly, the attachment of Czꢀallyl and Ir(L)2(Czꢀacacꢀallyl) to the POSS core led to the
disappearance of these sharp peaks, which were replaced by two broad amorphous halos appearing at
ca. 8.5o and 20o, indicating that the crystalline Czꢀallyl and Ir(L)2(Czꢀacacꢀallyl) became amorphous
state after their attachments to the POSS cage.
3.2 Electrochemical, optical and electroluminescence properties of the POSS materials
The UVꢀvis absorption and photoluminescence spectra of Ir(L)2(Czꢀacacꢀallyl) and the POSS
materials were measured in diluted dichloromethane solutions, as shown in Fig. 6. The absorption
spectrum of the complex Ir(L)2(Czꢀacacꢀallyl) exhibits two intense absorption bands at about 227
and 271 nm, and three weak absorption bands at 341, 410 and 446 nm, respectively, in which the
absorption bands below 360 nm could be ascribed to spinꢀallowed πꢀπ* transitions of the ligands and
the bands at the longer wavelength (410 and 446 nm) can be assigned to both spinꢀorbit coupling
enhanced 3(π → π*) and spinꢀforbidden 3MLCT transitions [33ꢀ35]
.
The absorption spectra of POSSꢀ1, POSSꢀ2 and POSSꢀ3 approximately resemble each other,
which can be described as two components: an intense absorption region in high energy region
ranging from 230 to 360 nm and a weak absorption region in low energy region ranging from 360 to
480 nm. In intense absorption region, there are six visible absorption peaks at 236 (242), 264, 284,
295, 334 and 347 nm, which can be attributed to the π → π* transitions of the ligands. In weak
absorption region, there are three absorption peaks at 380, 418 and 440 nm, in which the band around
1
380 nm can be assigned to the spinꢀallowed metalꢀtoꢀligand charge transfer MLCT (metalꢀligandꢀ
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chargeꢀtransfer) and the latter bands (418 and 440 nm) can be assigned to both spinꢀorbit coupling
enhanced 3(π → π*) and spinꢀforbidden 3MLCT transitions.
As shown in Fig. 6, the photoluminescence spectra of Ir(L)2(Czꢀacacꢀallyl) and the POSS
materials strongly resemble each other, they all exhibit a strong green emission with a maximum
main peak at 530 nm and a shoulder peak at 570 nm.
The luminescence quantum yields of the POSS materials in the solid states were measured in
order to study their optical characteristics. The quantum yields of POSSꢀ1, POSSꢀ2 and POSSꢀ3 at
room temperature were measured to be 47.49%, 18.98% and 18.41% in the solid states by an
absolute method using the Edinburgh Instruments (FLS920) integrating sphere excited at 380 nm
with the Xe lamp. The result indicates that the luminescence quantum yields of the POSS materials
decrease as the Ir(III) complex unit content on the POSS materials increases, which can be attributed
to the interactions among the Ir(III) complex units and the concentration quenching. The lifetime
decays of POSSꢀ1, POSSꢀ2 and POSSꢀ3 were measured to be 9.27, 9.85 and 9.92 ꢁs, respectively,
by a timeꢀcorrelated single photon counting spectrometer using Edinburgh Instruments (FLS920)
with a microsecond flashlamp as the excitation source (repetition rate 90 Hz) at room temperature.
Cyclic voltammetry (CV) was employed to investigate the electrochemical behavior of the
POSS materials. The highest occupied molecular orbital (HOMO) and the lowest unoccupied
molecular orbital (LUMO) energy levels of the POSS materials were calculated from their cyclic
voltammetry measurements and their extrapolated UVꢀVis absorption edges. The POSS materials
were dissolved in dichloromethane with tetraꢀnꢀbutylammonium tetrafluoroborate (0.1 mol/L) as the
electrolyte. A platinum working electrode and a saturated Ag/AgCl reference electrode were used.
Ferrocene was used for potential calibration. As shown in Fig. 7, the potentials for oxidation of the
POSS materials were observed to be 0.88, 0.86 and 0.87 V, respectively. At the same condition, the
oxidation peak and the reductive peak of ferrocene were observed at 0.55 and 0.34 V, respectively,
then the E1/2 (Fc/Fc+) is 0.445 V. Thus the HOMO energy levels of POSSꢀ1, POSSꢀ2 and POSSꢀ3
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were determined to be ꢀ5.24, ꢀ5.22 and ꢀ5.23 eV regarding the energy level of ferrocene/ferrocenium
as ꢀ4.80 eV [37]. The optical band edge of the POSS materials was estimated to be about 464 nm,
which corresponds to 2.67 eV. Then the LUMO energy levels of POSSꢀ1, POSSꢀ2 and POSSꢀ3 are
calculated to be ꢀ2.57, ꢀ2.55 and ꢀ2.56 eV, respectively. Table 3 summarizes the photophysical,
thermal and electrochemical properties of the POSS materials.
Due to the amount of POSSꢀ3 was too little to investigate its electroluminescence (EL) property,
POSSꢀ1 and POSSꢀ2 were selected as the lightꢀemitting materials in the paper. The lightꢀemitting
devices with the architecture of ITO/PEDOT:PSS (30 nm)/CBP: POSS materials (x wt %, 50
nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm) have been made and fabricated. The emitting layers are
consisted of host materials CBP and dopants of the POSS materials at different concentrations (x
wt%), and prepared by solutionꢀprocessable method. TPBi was used as the electron transport and
hole/excitonꢀblocking material. Liq was used as the electronꢀinjection layer. CBP and the POSS
materials were dissolved in 1,2ꢀdichlorobenzene, and their concentrations were prepared to be 10 and
5 mg/mL, respectively. The mixture solutions with different volume ratios (3:2, 1:1, 2:3 and 1:2)
between CBP and the POSS materials were used to fabricate the emitting layers (spin speed: 1000
rpm/min). The doped concentrations of the POSS materials were about 25 wt%, 33.33 wt%, 42.86 wt%
and 50 wt%, respectively.
The electroluminescence (EL) spectra of the devices based on POSSꢀ1 with different dopant
concentrations and at different voltages are shown in Fig. 8. The doped devices of POSSꢀ1 exhibit
green emissions with a maximum main peak at 530 nm and a shoulder peak at 570 nm, it was found
that the EL spectra of POSSꢀ1 resemble closely its PL spectrum in dichloromethane solution, and the
EL spectra of the devices were independent of the different dopant concentrations and the different
driving voltages. The Commission Internationale de LʹEclairage (CIE) coordinates of the devices
based on POSSꢀ1 is (0.41, 0.57). The EL spectra of the doped devices based on POSSꢀ2 were
identical with that of the devices based of POSSꢀ1.
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The luminance vs. the driving voltage and the current efficiency vs. the driving voltage
characteristics of the devices fabricated with different POSSꢀ1 doping concentrations in CBP host
are shown in Fig. 9. Table 4 summarized the performances of the devices based on the POSS
materials. As shown in Fig. 9, the maximum brightness of 8311, 10940, 10160 and 10725 cd/m2
were observed in the devices with 25 wt%, 33.33 wt%, 42.86 wt% and 50 wt% doping
concentrations, respectively. The maximum luminous efficiencies of 9.56, 35.24, 29.38 and 28.51
cd/A were obtained in the devices with different doping concentrations. By comparing the device
performances of the different doping concentrations, the devices based on POSSꢀ1 with 33.33 wt%
doping concentration showed the best EL performance. The maximum current efficiency of 35.24
cd/A at 6.1 V and maximum brightness of 10940 cd/m2 at 12.2 V have been observed in the device,
and the maximum external quantum efficiency (EQE) was 9.77%.
For POSSꢀ2 material, the EL performances of the devices with the different doping
concentrations varying from 25 wt%, 33.33 wt%, 42.86 wt% and 50 wt% were also investigated.
Figure 10 displays the luminance vs. the driving voltage and the current efficiency vs. the current
density characteristics of the devices with various POSSꢀ2 doping concentrations in CBP host. The
performances of the devices based on POSSꢀ2 are summarized in Table 4. The device with 25 wt%
doping concentration exhibited the best EL performance. The device had a maximum brightness of
12390 cd/m2 at 10.7 V and a maximum current efficiency of 30.52 cd/A at 1.57 mA/cm2 and a
maximum external quantum efficiency (EQE) of 8.46%.
As shown in Table 4, the EL performances of the devices fabricated from POSSꢀ1 are
substantially higher than that of the devices based on POSSꢀ2, indicating that concentration
quenching leads to the reduction in device efficiency with increasing amounts of the Ir(III) complex
units on the POSS core. The device efficiency increases as the Ir(III) complex unit content on the
POSS materials decreases, which can be attributed to reduced interactions among the Ir(III) complex
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units and diminished concentration quenching. Similar phenomenon was found in our previous work
[28]
.
4. Conclusion
We reported the synthesis, photophysics, electrochemical characterization and thermal
stabilities of three inorganic/organic hybrid materials, 7CzꢀIr(L)2(Czꢀacac)ꢀPOSS (POSSꢀ1), 6Czꢀ
2Ir(L)2(Czꢀacac)ꢀPOSS (POSSꢀ2) and 5Czꢀ3Ir(L)2(Czꢀacac)ꢀPOSS (POSSꢀ3), consisting of an
emissive Ir(III) complex and carbazole moieties covalently attached to a polyhedral oligomeric
silsesquioxane (POSS) core. Attachment of Ir(III) complex on the POSS core has no significant
effects on the photophysical properties of the POSS materials, and the POSS materials have high
thermal stability and exhibit strong green emission with a main peak (530 nm) and a shoulder peak
(570 nm). Solution processed lightꢀemitting devices with a configuration of ITO/PEDOT:PSS (30
nm)/CBP: POSS materials (x wt %, 50 nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm) exhibited higher
brightness and higher external quantum efficiency, in which POSSꢀ1 and POSSꢀ2 were used as the
emitting materials. At the doping concentration of 33.33 wt%, the devices fabricated from POSSꢀ1
material exhibited green emission with a maximum luminance of 10940 cd/m2 at 12.2 V and a
maximum current efficiency of 35.24 cd/A at 6.1 V and a maximum external quantum efficiency
(EQE) of 9.77%. When the doping concentration was 25 wt%, the devices based on POSSꢀ2 material
showed a maximum brightness of 12390 cd/m2 at 10.7 V and a maximum current efficiency of 30.52
cd/A at 1.57 mA/cm2 and a maximum external quantum efficiency (EQE) of 8.46%. Compared the
device performances of POSSꢀ1 and POSSꢀ2 materials, it is found that the device efficiency
increases as the Ir(III) complex unit content on the POSS materials decreases, which can be
attributed to reduced interactions among the Ir(III) complex units and diminished concentration
quenching.
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Supplementary material
CCDC 1472276 contains the supplementary crystallographic data for the complex Ir(L)2(Czꢀ
acacꢀallyl) in this paper. The data can be obtained free of charge via
http:www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223ꢀ336ꢀ033; or eꢀmail:
deposit@ccdc.cam.ac.uk.
Acknowledgements
This work was supported by the National Natural Science Foundation of China (Grant
61166003), and also supported by the Program for Changjiang Scholars and Innovative Research
Team in University (IRT0629).
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Legends:
Fig. 1 The molecular structures of the POSS materials used in this study.
Scheme 1. Synthetic routes to the ancillary ligand and the POSS materials.
Fig. 2 Crystal structure of the Ir(III) complex [Ir(L)2(Czꢀacacꢀallyl)].
H
Fig. 3 The FTꢀIR spectra of Q8M8 , POSSꢀ1 and POSSꢀ2.
Fig. 4 Thermogravimetric analyses (TGA) of the POSS materials.
Fig. 5 The Xꢀray diffraction (XRD) patterns of Czꢀallyl, Ir(L)2(Czꢀacacꢀallyl) and the POSS
materials. (a: Ir(L)2(Czꢀacacꢀallyl); b: Czꢀallyl; c: POSSꢀ3; d: POSSꢀ2; e: POSSꢀ1)
Fig. 6 UVꢀvis absorption and photoluminescence spectra of Ir(L)2(Czꢀacacꢀallyl) and the POSS
materials in diluted dichloromethane solutions (C = 1.0 × 10ꢀ5 mol/L, λex = 430 nm).
Fig. 7 Cyclic voltammograms of ferrocene and the POSS materials (scan rate: 10 mV s1, solvent:
dichloromethane).
Fig. 8 EL spectra of POSSꢀ1 at different doped concentrations and different voltages (inset). Device
configuration: ITO/PEDOT:PSS (30 nm)/CBP: POSSꢀ1 (x wt%, 50 nm)/TPBi (50 nm)/Liq (2
nm)/Al(150 nm).
Fig. 9 The luminance vs. voltage (a) and current efficiency vs. voltage (b) curves of the doped
devices with different POSSꢀ1 concentrations. Device configuration: ITO/PEDOT:PSS (30 nm)/CBP:
POSSꢀ1 (x wt%, 50 nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
Fig. 10 The luminance vs. voltage (a) and current efficiency vs. current density (b) curves of the
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doped devices with different POSSꢀ2 concentrations. Device configuration: ITO/PEDOT:PSS (30
nm)/CBP: POSSꢀ2 (x wt%, 50 nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
Table 1. Crystallographic data for Ir(L)2(Czꢀacacꢀallyl).
Table 2. Selected bond lengths and bond angles for Ir(L)2(Czꢀacacꢀallyl).
Table 3. Photophysical, thermal and electrochemical properties of the POSS materials.
Table 4. EL performances of the POSS materials.
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POSS materials:
O
O
O
O
N
R
N
R
Si
Si
O
O
R
O
O
Si
Si
O
R
O
Si
O
Si
O
Si
O
Si
O
O
O
O
O
O
Si R
O
Si
Si
N
Si
O
O
O
Si
O
Si
O
O
O
O
Si R
Si
Si
Si
O
O
O
O
O
Si
R
O
O
Si
Si
O
O
O
O
Si
O
Si
O
N
O
Si
O
Si
R
Si
O
Si
R
O
Si
Si
O
O
R
O
Si
Si
Si
R
R
N
R
POSSꢀ1
O
O
N
R =
N
O
O
POSSꢀ2
O
O
N
R
O
R
O
Si
Si
Si
Si
O
O
O
O
O
Si
N
Si
2
O
Si
O
Si
O
O
N
O
R
Si
O
O
O
O
Si
O
Si
O
O
O
O
Si
Si
O
O
O
O
Si
O
Si
Si
R
N
R
O
O
N
N
O
O
POSSꢀ3
Fig. 1
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O
O
O
C
OC4H9
Br
(CH3CO)O
AlCl3, CH2Cl2
O
NH
N
N
N
NaOH, DMSO
tꢀBuOK, Toluene
Czꢀacacꢀallyl
O
O
N
O
O
O
O
O
O
Ir
Cl
Cl
O
Ir
Ir
K2CO3, ClCH2CH2Cl
O
N
N
N
2
2
2
N
Ir(L)2(Czꢀacacꢀallyl)
N
H
H
H
Si
Si
Si
O
O
O
O
Si
O
O
Si
Si
O
H
O
O
Si
O
Ptꢀcatalyst
Toluene
Si
O
O
O
O
+
POSS materials
Ir
O
O
Si
O
Si
O
O
O
N
Si
O
H
Si
Si
Si
2
O
O
O
Si
Si
H
H
H
N
Scheme 1
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Fig. 2
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Fig. 3
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100
80
60
40
20
0
POSSꢀ3
POSSꢀ2
POSSꢀ1
0
200
400
600
800
o
Temperature ( C)
Fig. 4
29