Synthesis and photo- and electro-luminescent properties of Ir(III) complexes attached to polyhedral oligomeric silsesquioxane materials

Article abstract of DOI:10.1039/c5ra16201g

This paper describes synthesis, photophysical, electrochemical characterizations of two new polyhedral oligomeric silsesquioxane (POSS)-based green-light phosphorescent materials, consisting of an emissive Ir(iii) complex and carbazole moieties covalently attached to a polyhedral oligomeric silsesquioxane (POSS) core. 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 state indicate a reduction in the degrees of interactions among Ir(iii) complex units and concentration quenching due to the bulky POSS core. Solution processed light-emitting devices with a configuration of ITO/PEDOT:PSS (45 nm)/CBP:POSS materials (50 nm)/TPBi (50 nm)/Liq (2 nm)/Al (150 nm) were fabricated. The devices based on these POSS materials exhibit a maximum external quantum efficiency (EQE) of 7.82% and a maximum luminance of 21:285 cd m^-2.

Full text of DOI:10.1039/c5ra16201g

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Graphical Abstract:
Two new inorganic-organic hybrid materials based on polyhedral oligomeric
silsesquioxane (POSS) capped with an emissive Ir(III) complex and carbazole units
were successfully synthesized and characterized. The photophysical and
electrochemical characterization, and thermal stabilities of two inorganic/organic
hybrid materials were investigated detailedly. Solution processed light-emitting
devices based on the POSS materials exhibited ultrahigh brightness and higher
external quantum efficiency.
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DOI: 10.1039/C5RA16201G
Synthesis and Photoꢀ and Electroꢀluminescent Properties of Ir(III)
Complexes Attached Polyhedral Oligomeric Silsesquioxane Materials
Tianzhi Yu1,*, Xin Wang1, Wenming Su2,*, Chengcheng Zhang1, Yuling Zhao3, Hui Zhang1,
Zixuan Xu1
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: This paper describes synthesis, photophysical, electrochemical characterizations of two
new polyhedral oligomeric silsesquioxane (POSS)ꢀbasded greenꢀlight phosphorescent materials,
consisting of an emissive Ir(III) complex and carbazole moieties covalently attached to a polyhedral
oligomeric silsesquioxane (POSS) core. 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 to the bulky POSS core. Solution processed
lightꢀemitting devices with a configuration of ITO/PEDOT:PSS (45 nm)/CBP: POSS materials (50
* Corresponding Author. Tel. +86ꢀ931ꢀ4956935; Fax: +86ꢀ931ꢀ4938756; eꢀmail: yutianzhi@hotmail.com (T.Z. Yu);
wmsu2008@sinano.ac.cn (W.M. Su).
1

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nm)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm) were fabricated. The devices based on these POSS
materials exhibit maximum external quantum efficiency (EQE) of 7.82% and a maximum luminance
of 21285 cd/m2.
Keywords: Iridium complex; POSS; Photoluminescence; Electroluminescence
1. Introduction
Phosphorescent heavyꢀmetal complexes as emitters in organic lightꢀemitting diodes (OLEDs)
have attracted tremendous attention because they can fully utilize both singlet and triplet excitons
through the strong spinꢀorbital coupling of heavyꢀmetal ions [1ꢀ4]. Among those phosphorescent
materials, iridium complexes are the most valuable emitting materials due to their high quantum
efficiency, brightness, color diversity, short excitedꢀstate lifetime and good thermal stability, which
make them an attractive alternative for optoelectronic applications including OLEDs, lightꢀemitting
electrochemical cells, chemosensors and biological labeling [5ꢀ10]. Over the past several years,
considerable efforts have been devoted to the exploitation of novel Ir(III) complexes for highly
efficient OLEDs. Upon to now, blue, green, yellow, orange and red emitting Ir(III) complexes have
been developed by the design and synthesis of cyclometalating ligands or by modulating the
ancillary ligands [3,4,6,11,12]. However, the Ir(III) complexes used as EL materials are suffering from
selfꢀquenching in solid state due to interaction and aggregation with its neighboring complexes.
Introducing steric hindrance or bulky side groups into Ir(III) complexes is an effective strategy to
suppress the emission quenching and enhance the device performance [7,12ꢀ14]
.
Polyhedral oligomeric silsesquioxane (POSS) unit is a cubeꢀshaped nanoparticle in which the
rigid silicaꢀlike inorganic core can be attached with eight organic functional groups at its silicon
2

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vertices [15,16]. POSS has attracted considerable interest in materials science due to its wellꢀdefined
nanoꢀscale organicꢀinorganic structure, which makes it an ideal building block for constructing
nanoꢀstructured hybrid materials and nanocomposites [17ꢀ19]. POSS macromolecules can be easily
synthesized to be monofunctional or multifunctional materials for commercial applications by
grafting with organic functional groups. Moreover, POSS macromolecules 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
[20,21]. The incorporation of POSS into organic light emitting materials has led to significant
improvements in the performance of organic light emitting devises (OLEDs). 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. The
Heeger group pioneered the use of POSSꢀbased light emitting polymers in which POSS cores as
endꢀcappers
were
attached
at
the
chain
ends
of
poly[2ꢀmethoxyꢀ5ꢀ(2ꢀethylhexyloxy)ꢀ1,4ꢀphenylenevinylene]
(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 coated glass substrate.
Thereafter, some research groups reported the photoluminescence and electroluminescence
properties of POSSꢀfunctionalized polyfluorene materials in which POSS units were appended to the
3

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polyfluorene backbone using an alkoxy spacer [24,25]. These POSSꢀfunctionalized polyfluorene
materials showed higher fluorescence quantum yields and better thermal stability than the
corresponding pristine polymers because the inorganic POSS units strongly suppressed
intermolecular aggregation and/or thermal oxidation and crosslinking. Recently, research on
phosphorescent emitters and efficient lightꢀemitting devices based on POSS materials have also
[21]
attracted tremendous interest [21,26,27]. Yang et al.
reported efficient monochromatic and
whiteꢀemitting OLEDs utilizing Ir(III) complexꢀfunctionalized POSS materials, in which the
monochromatic OLEDs exhibited maximum external quantum efficiencies in the range of 5–9% and
maximum brightness of 1000 cd/m2, and the whiteꢀemitting OLEDs shown EQEs of 8.0%, power
efficiencies of 8.1 lm/W, and CIE coordinates of (0.36, 0.39) at 1000 cd/m2. Singh et al. [27] reported
the inkjet printing OLEDs based on Ir(III) complexꢀfunctionalized POSS meterials, the devices
exhibited peak luminances of ~ 10000 cd/m2 with peak quantum efficiencies of ~ 2.5%.
The cyclometalated Ir(III) coumarin complexes have been investigated detailedly in our
laboratory, which exhibited good photoꢀ and electroꢀluminescence properties [28]. In this paper, we
first used 3ꢀallylpentaneꢀ2,4ꢀdione (acacꢀallyl) as the ancillary ligand to synthesize a new iridium(III)
coumarin complex, Ir(L)2(acacꢀallyl), which was as an emissive iridium complex. Then two new
Ir(III) complexꢀfunctionalized POSS meterials, 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS,
consisting of one or two emissive iridium(III) complexes and carbazole moieties covalently attached
to a polyhedral oligomeric silsesquioxane (POSS) core were successfully synthesized and
characterized. The photophysical properties and thermal stability of these POSS materials were
investigated. Furthermore, solution processed lightꢀemitting devices based on these POSS materials
were fabricated to investigate the electroluminescence properties of the POSS materials.
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The synthetic routes of 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS were shown in
Scheme 1.
2. Experimental
2.1 Materials and methods
Carbazole and allyl bromide were bought from Alfa Aesar. Acetylacetone was purchased from
Shanghai
Jingchun
Reagent
Co.
Ltd.
(China).
Platinum
complex
(platinumꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane, Ptꢀdvs, 2 wt% Pt in xylene) was purchased
H
from Aldrich, USA. Octakis(dimethylsiloxy)silsesquioxane (Q8M8 ) containing eight hydroꢀsilane
groups was purchased from the Hybrid Plastics Co., USA. 8ꢀHydroxyquinolinolatoꢀlithium (Liq),
4,4ʹꢀBis(9ꢀcarbazolyl)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 [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
(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. Melting points were measured by using an Xꢀ4 microscopic melting
5

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point apparatus made in Beijing Taike Instrument Limited Company, and the thermometer was
uncorrected.
2.2 Synthesis and characterization of Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS
3ꢀallylpentaneꢀ2,4ꢀdione (acacꢀallyl): Under N2, a suspension of fresh sodium (3.160 g, 0.137
mol) in anhydrous toluene (60 mL) was placed in a threeꢀnecked flask. The mixture was heated up
to 120 °C and stirred vigorously till the sodium was molten and scattered, then acetylacetone
o
(13.750 g, 0.137 mol) was added into the mixture. The mature was stirred at 120 C for 1 h, the
white sodium salt of βꢀdiketone was precipitated. Allyl bromide (20 g, 0.165 mol) was added
dropwise. The reaction mixture was stirred at and refluxed overnight, then cooled and filtered to
remove excess NaBr. Toluene and the excess allyl bromide were removed by distillation, collecting
o
14.50 g (75.2% yield) of yellow oil at 195ꢀ196 C. 1H NMR (CDCl3, 400 MHz, δ, ppm): 5.89ꢀ5.80
(m, 0.5 H), 5.75ꢀ5.66 (m, 0.5 H), 5.15ꢀ4.99 (m, 2H), 3.01ꢀ2.98 (m, 1H), 2.59 (dt, J = 7.6 Hz, J = 7.2
Hz, 2H), 2.19 (s, 3H), 2.11 (s, 3H).
9ꢀallylꢀ9Hꢀcarbazole (Czꢀallyl): A mixture of carbazole (10.0 g, 0.06 mol), potassium
hydroxide (8.98 g, 0.16 mol) and acetone (100 mL) was stirred vigorously for 2 h at room
temperature. Allyl bromide (6.6 mL, 0.072 mol) was added dropwise. After stirring for 20 h at room
temperature, the reaction mixture was poured into cold water (300 mL). The mixture was extracted
with CH2Cl2 (3 × 200 mL), and the combined organic phase was dried over anhydrous Na2SO4.
After filtering, the filtrate was evaporated to dryness under reduced pressure. The crude was purified
by chromatography on silica gel using petroleum ether as the eluent to give Czꢀallyl as a white solid
o
(9.1 g, 73.4%). m.p.: 51ꢀ53 C. 1H NMR (400 MHz, CDCl3, δ, ppm): 8.11 (d, J = 8.0 Hz, 2H), 7.46
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(t, J = 8.8 Hz, 2H), 7.37 (d, J = 8.0 Hz, 2H), 7.25 (t, J = 8.0 Hz, 2H), 6.03 ꢀ 5.94 (m, 1H), 5.15 (d, J
= 10.6 Hz, 1H), 5.05 (d, J = 18.3 Hz, 1H), 4.91 (d, J = 4.8 Hz, 2H). Anal. Calcd for C15H13N: C,
86.92; H, 6.32; N, 6.76; Found: C, 87.02; H, 6.29; N, 6.71.
Ir(L)2(acacꢀallyl): The cyclometalated Ir(III) ꢁꢀchlorobridged dimmer ((L)2Ir(ꢁꢀCl)2Ir(L)2) (1
g, 0.74 mmol), acacꢀallyl (0.53 g, 3.78 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 dichloromethane/petroleum ether/ acetone (10:10:1, v/v/v) as the eluent to give
yellow powdery Ir(L)2(acacꢀallyl) in 81.5% yield (0.47 g). 1H NMR(CDCl3, δ, ppm): 9.14 (d, 2H, J
= 8.8 Hz, ArylꢀH), 8.05 (d, 2H, J = 8.0 Hz, ArylꢀH), 7.92 (t, 2H, J = 8.4 Hz, ArylꢀH), 7.27 (t, 2H, J =
8.4 Hz, ArylꢀH), 7.19 (d, 2H, J = 8.4 Hz, ArylꢀH), 7.06 (t, 2H, J = 8.0 Hz, ArylꢀH), 6.63 (t, 2H, J =
8.0 Hz, ArylꢀH), 6.11 (d, 2H, J = 8.0 Hz, ArylꢀH), 5.79ꢀ5.68 (m, 1H, ꢀCH=CH2), 4.90 (d, 1H, J = 8.0
Hz, ꢀCH=CH2), 4.63 (d, 1H, J = 17.2 Hz, ꢀCH=CH2), 2.86 (d, 2H, J = 2.0 Hz, ꢀCH2ꢀ), 1.80 (s, 6H,
ꢀCH3). IR (KBr pellet, cmꢀ1): 3077, 2977, 2925, 2865, 1694, 1599, 1564, 1464, 1358, 1264, 1169,
987, 804, 768, 657. Anal. Calc. for C36H27IrN2O6 (%): C, 55.73; H, 3.51; N, 3.61. Found: C, 55.81;
H, 3.57; N, 3.65. MS: Calcd for C36H27IrN2O6, 776.15; Found, 777.15.
7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS: A round bottom flask (100 mL) was
charged with octakis(dimethylsiloxy)silsesquioxane (1.0 g, 0.98 mmol), Ir(L)2(acacꢀallyl) (0.76 g,
0.98 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
7

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in xylene) were added, and the reaction mixture was stirred at room temperature under positive
argon pressure for 4 h. Then Czꢀallyl (2.03 g, 9.80 mmol) was introduced, and the resulting reaction
o
mixture was allowed to stir at 50 C overnight. The toluene was evaporated in vacuo and the crude
product was isolated by chromatography on silica gel using dichloromethane/ethyl acetate/petroleum
ether (1:1:8, v/v/v) as the eluent to yield pure fractions of 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS, which were isolated separately in 23% and 12.5% yields.
1
7CzꢀIr(L)2(acac)ꢀPOSS: H NMR (400 MHz, CDCl3, δ, ppm): 9.21 (d, 2H, J = 8.0 Hz,
ArylꢀH), 8.42 (d, 2H, J = 5.2 Hz, ArylꢀH), 8.06ꢀ8.02 (m, 16H, ArylꢀH), 7.91 (t, 2H, J = 8.4 Hz,
ArylꢀH), 7.41ꢀ7.35 (m, 14H, ArylꢀH), 7.31ꢀ7.25 (m, 16H, ArylꢀH), 7.20ꢀ7.15 (m, 16H, ArylꢀH), 6.64
(t, 2H, J = 8.0 Hz, ArylꢀH), 5.99 (d, 2H, J = 8.4 Hz, ArylꢀH), 4.16ꢀ4.06 (m, 14H,ꢀNꢀCH2ꢀ), 2.52 (t,
2H, J = 7.2 Hz, ꢀCH2ꢀ), 1.80ꢀ1.76 (m, 16H, ꢀCH2ꢀ), 1.57 (s, 6H, ꢀCH3), 0.90ꢀ0.83 (m, 2H, ꢀCH2ꢀSi),
0.60ꢀ0.51 (m, 14H, ꢀCH2ꢀSi), 0.07ꢀ(ꢀ0.05) (m, 48H). 13C NMR (CDCl3, δ, ppm): 186.1, 184.2, 166.0,
157.2, 150.4, 148.0, 140.3, 139.3, 138.3, 131.6, 129.0, 125.6, 124.0, 123.6, 122.7, 120.3, 118.7,
116.1, 108.6, 77.3, 77.2, 77.0, 76.7, 45.5, 29.8, 27.1, 22.3, 14.8, 1.0, ꢀ0.4. IR (KBr pellet, cmꢀ1):
3082, 2962, 2915, 2864, 1696, 1598, 1564, 1466, 1356, 1260, 1168, 1098, 980, 802, 762, 555. MS:
Calcd for C157H174IrN9O26Si16, 3244.69; Found, 3245.72.
1
6Czꢀ2Ir(L)2(acac)ꢀPOSS: H NMR (400 MHz, CDCl3, δ, ppm): 9.21 (d, 2H, J = 8.4 Hz,
ArylꢀH), 9.10 (d, 2H, J = 8.0 Hz, ArylꢀH), 8.43 (d, 4H, J = 5.6 Hz, ArylꢀH), 8.07ꢀ8.02 (m, 16H,
ArylꢀH), 7.97 (t, 2H, J = 8.4 Hz, ArylꢀH), 7.79 (t, 2H, J = 7.2 Hz, ArylꢀH), 7.41ꢀ7.33 (m, 12H,
ArylꢀH), 7.31ꢀ7.23 (m, 16H, ArylꢀH), 7.20ꢀ7.13 (m, 16H, ArylꢀH), 6.66ꢀ6.57 (m, 4H, ArylꢀH), 6.02
(dd, 4H, J = 8.0 Hz, ArylꢀH), 4.16ꢀ4.06 (m, 12H,ꢀNꢀCH2ꢀ), 2.59ꢀ2.49 (m, 4H, ꢀCH2ꢀ), 1.83ꢀ1.76 (m,
16H, ꢀCH2ꢀ), 1.72ꢀ1.62 (m, 12H, ꢀCH3), 0.90ꢀ0.83 (m, 4H, ꢀCH2ꢀSi), 0.60ꢀ0.51 (m, 12H, ꢀCH2ꢀSi),
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13
0.07ꢀ(ꢀ0.04) (m, 48H). C NMR (CDCl3, δ, ppm): 186.0, 184.6, 166.0, 157.0, 150.7, 149.2, 147.9,
140.2, 139.3, 138.3, 131.7, 131.0, 130.5, 129.1, 125.6, 124.1, 123.5, 122.7, 120.3, 118.7, 116.3,
116.1, 108.5, 77.3, 77.0, 76.7, 45.6, 29.7, 27.2, 22.4, 14.8, 1.0, ꢀ0.4. IR (KBr pellet, cmꢀ1): 3053,
2963, 2924, 2872, 1694, 1609, 1564, 1480, 1467, 1350, 1331, 1260, 1234, 1163, 1098, 981, 839,
800, 755, 729, 554. MS: Calcd for C178H188Ir2N10O32Si16, 3813.25; Found, 3814.61.
2.3 OLEDs fabrication and characterization
The multilayer OLEDs with a device architecture of ITO/PEDOT:PSS (45 nm)/CBP: POSS
materials (50 nm)/TPBi
(50
nm)/Liq
(2
nm)/Al(150 nm) were fabricated.
Poly(3,4ꢀethylenedioxythiophene) doped with poly(styrenesulfonate) (PEDOT:PSS) was
spinꢀcoated onto precleaned and O2ꢀplasmaꢀtreated indium tin oxide (ITO) substrates, yielding
o
layers ca. 45 nm thick. 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 of the PEDOT:PSS layers, yielding films ca. 50 nm thick. The samples were
o
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 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.
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3. Results and discussion
3.1 Synthesis and characterization of the POSS materials
The synthesis of the phosphorescent Ir(III) complex [Ir(L)2(acacꢀallyl)] from Scheme 1 began
first with preparing the ancillary ligand, 3ꢀallylpentaneꢀ2,4ꢀdione (acacꢀallyl), which has a allyl
group at 3ꢀposition of pentaneꢀ2,4ꢀdione for later attachment to POSS core. The ancillary ligand
acacꢀallyl was successfully synthesized by reacting acetylacetone with allyl bromide in the presence
of metal sodium as a base. This method leads to higher yield of the target product (75.2%). The
ancillary ligand was then reacted with the chlorobridged dimer complex based on the cyclometalated
coumarin ligand (3ꢀ(pyridineꢀ2ꢀyl)coumarin) and anhydrous K2CO3 in refluxing dichloroethane
under nitrogen atmosphere to obtain the allylꢀfunctionalized Ir(III) complex. Furthermore, the
carbazole moiety is chosen because it has good holeꢀtransporting properties, which was also
modified with a terminal allyl for attachment to POSS core.
The holeꢀtransporting and Ir(III) complex unit functionalized POSS materials
(7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS) were obtained via hydrosilylation reaction in
the presence of platinum(0)ꢀ1,3ꢀdivinylꢀ1,1,3,3ꢀtetramethyldisiloxane (Ptꢀdvs) as the catalyst. The
POSS materials were synthesized in a stepwise mode by sequentially reacting the Ir(III) complex
H
Ir(L)2(acacꢀallyl) with octakis(dimethylsiloxy)silsesquioxane (Q8M8 ) in a 1:1 ratio, and followed
by reaction with excess Czꢀallyl. 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS can then be
isolated from the reaction mixture chromatographically. These POSS materials 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
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easily by spinꢀcoating onto the quartz glasses and indium tin oxide (ITO) substrates.
1
7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS were characterized using H NMR, 13C
NMR, MS, FTꢀIR and Xꢀray diffraction (XRD) analysis. The resonance of SiꢀH protons in Q8M8H 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 allyl group of Ir(L)2(acacꢀallyl)
are observed at ca. 5.74, 4.90 and 4.63 ppm with a relative molar ratio of 1:1:1, corresponding to
1
isoꢀ, transꢀ and substituted vinyl protons. In H NMR spectra of 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS, the peaks for the vinyl groups of Czꢀallyl (5.03, 5.15 and 5.99 ppm) and
Ir(L)2(acacꢀallyl) (4.63, 4.90 and ca. 5.74 ppm) and SiꢀH protons (4.7 ppm) disappeared, supporting
the complete hydrosilylation reaction and the vinyl groups of Czꢀallyl and Ir(L)2(acacꢀallyl)
H
underwent hydrosilylation of the SiꢀH bonds of Q8M8 .
H
The FTꢀIR spectra of Q8M8 , Ir(L)2(acacꢀallyl) and 7CzꢀIr(L)2(acac)ꢀPOSS are shown in Fig. 1.
The strong absorption peak around 1098 cmꢀ1 for Q8M8H and 7CzꢀIr(L)2(acac)ꢀPOSS represented the
vibrations of the siloxane SiꢀOꢀSi groups, and it is a general feature of POSS derivatives. The
H
characteristic stretching vibration of the SiꢀH groups of Q8M8 appears as a signal at 2147 cmꢀ1. In
7CzꢀIr(L)2(acac)ꢀPOSS, the peak for the SiꢀH groups 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 6Czꢀ2Ir(L)2(acac)ꢀPOSS
was similar to that of 7CzꢀIr(L)2(acac)ꢀPOSS.
Fig. 2 presents the Xꢀray diffraction (XRD) patterns of Czꢀallyl, Ir(L)2(acacꢀallyl),
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7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS. Czꢀallyl and Ir(L)2(acacꢀallyl) exhibit several
sharp XRD peaks because of their crystallinity, suggesting that Czꢀallyl and Ir(L)2(acacꢀallyl) show
the crystal morphology. Interestingly, the attachment of Czꢀallyl and Ir(L)2(acacꢀallyl) to the POSS
core led to the disappearance of these sharp peaks except for a sharp peak at 5.9o, which were
replaced by a broad amorphous halo appearing at ca. 21o, indicating that the crystalline Czꢀallyl and
Ir(L)2(acacꢀallyl) became amorphous state after their attachments to the POSS cage.
The thermogravimetric analyses (TGA) were performed in flowing drying nitrogen atmosphere
o
at the heating rate of 10 C/min. In a comparison of the thermal stabilities, we used the complex
Ir(L)2(acacꢀallyl) as the contrastive sample. The result of TGA measurements of Ir(L)2(acacꢀallyl)
and the POSS materials are shown in Fig. 3. An increase in the decomposition temperature of the
o
POSS materials compared with Ir(L)2(acacꢀallyl) was observed. At about 352 and 379 C, there are
two sharp weight losses in the TGA cueve of Ir(L)2(acacꢀallyl), it shows that the complex
Ir(L)2(acacꢀallyl) undergoes two largeꢀstage decomposition processes. For the POSS materials, at
o
373 C the materials began to decompose, and corresponding to a sharp weight loss in their TGA
curves. Compared with Ir(L)2(acacꢀallyl), the inorganic silsesquioxane (POSS) provided additional
heat capacity, thereby stabilizing the materials against thermal decomposition.
3.2 Electrochemical, optical and electroluminescence properties of the POSS materials
The UVꢀvis absorption and photoluminescence spectra of Ir(L)2(acacꢀallyl),
7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS were measured in diluted dichloromethane
solutions, as shown in Fig. 4. The absorption spectrum of the complex Ir(L)2(acacꢀallyl) exhibits two
intense absorption bands at about 227 and 274 nm, and three weak absorption bands at 345, 384 and
438 nm, respectively, in which the absorption bands below 360 nm could be ascribed to
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spinꢀallowed πꢀπ* transitions of the ligands, the band around 384 nm can be assigned to the
spinꢀallowed metalꢀtoꢀligand charge transfer 1MLCT (metalꢀligandꢀchargeꢀtransfer), and the band at
the longer wavelength (438 nm) can be assigned to both spinꢀorbit coupling enhanced 3(π → π*)and
spinꢀforbidden 3MLCT transitions [30ꢀ32].
The absorption spectra of 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS approximately
resemble each other, which can be described as two components: an intense absorption region in
high energy region ranging from 220 to 360 nm and a weak absorption region in low energy region
ranging from 360 to 480 nm. In intense absorption region, there are five visible absorption peaks at
236 (246), 262, 295, 335 and 346 nm, which can be attributed to the π → π* transitions of the ligands.
In weak absorption region, there are two absorption peaks at 384 and 440 nm, the former can be
1
assigned to the spinꢀallowed metalꢀtoꢀligand charge transfer MLCT, the latter can be assigned to
both spinꢀorbit coupling enhanced 3(π → π*) and spinꢀforbidden 3MLCT transitions.
The photoluminescence spectra of Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS strongly resemble each other, they all exhibit a strong green emission with
a maximum main peak at 530 nm and a shoulder peak at 567 nm.
The quantum yields of Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS
at room temperature were measured to be 9.15%, 9.43% and 9.39% from the THF solutions (ca. 10ꢀ6
mol/L) by an absolute method using the Edinburgh Instruments (FLS920) integrating sphere excited
at 380 nm with the Xe lamp. The lifetime decays of Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS were measured to be (τ1 = 0.79 ꢁs, τ2 = 9.22 ꢁs), (τ1 = 0.89 ꢁs, τ2 = 9.27 ꢁs)
and (τ1 = 1.41 ꢁs, τ2 = 9.85 ꢁs) by a timeꢀcorrelated single photon counting spectrometer using
Edinburgh Instruments (FLS920) with a microsecond flashlamp as the excitation source (repetition
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rate 90 Hz) at room temperature (Supplementary Fig. S1ꢀS3).
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 absorption spectra. 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. 5, the potentials for oxidation of the POSS materials
were observed to be 0.88 and 0.89 V, respectively. At the same condition, the oxidation peak and the
reductive peak of ferrocene were observed at 0.56 and 0.32 V, respectively, then the E1/2 (Fc/Fc+) is
0.44 V. Thus the HOMO energy levels of 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS were
determined to be ꢀ5.24 and ꢀ5.25 eV regarding the energy level of ferrocene/ferrocenium as ꢀ4.80 eV
[33]. The optical band edge of the POSS materials was estimated to be 468 nm, which corresponds to
2.65 eV. Then the LUMO energy levels of the POSS materials are calculated to be ꢀ2.59 and ꢀ2.60
eV, respectively. The cyclic voltammetry curve of Ir(L)2(acacꢀallyl) was also shown in Fig. 5. From
its oxidation potential (1.11 V) and optical band edge (471 nm), the HOMO and LUMO energy
levels of Ir(L)2(acacꢀallyl) are calculated to be ꢀ5.47 and ꢀ2.84 eV, which are lower in contrast with
the HOMO and LUMO energy levels of the POSS materials.
Table 1 summarizes the photophysical, thermal and electrochemical properties of the POSS
materials. While attachment of Ir(III) complex on the POSS core has no significant effects on the
photophysical properties of the materials, it does significantly increase the thermal stability
compared with the parent Ir(III) complex.
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To investigate the electroluminescence (EL) properties of the POSS materials, the
lightꢀemitting devices with the architecture of ITO/PEDOT:PSS (45 nm)/CBP: POSS materials (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 20
mg/mL. The mixture solutions with different volume ratios between CBP and the POSS materials
were used to fabricate the emitting layers (spin speed: 1000 rpm/min).
The electroluminescence (EL) spectra of the devices based on 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS with different dopant concentrations and at different voltages are shown in
Fig. 6 and 7. Exclusive emissions from the Ir(III) complex were found in the EL spectra of the
devices, which were independent of the different dopant concentrations and at different driving
voltages. The doped devices of the POSS materials exhibit green emissions with a maximum main
peak at 530 nm and a shoulder peak at 567 nm, it was indicated that the EL spectra of the POSS
materials resemble closely their PL spectra in dichloromethane solutions. The Commission
Internationale de LʹEclairage (CIE) coordinates of the devices based on 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS are (0.39, 0.61) and (0.41, 0.60), respectively.
The luminance vs. the driving voltage and the current efficiency vs. the driving voltage
characteristics of the devices fabricated with different 7CzꢀIr(L)2(acac)ꢀPOSS doping concentrations
are shown in Fig. 8 and 9. Table 2 summarized the performances of the devices based on the POSS
materials. As shown in Fig. 8, at doped concentration ratios between CBP and
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7CzꢀIr(L)2(acac)ꢀPOSS were 1:2, 1:1, 2:1, 3:1, 4:1, 6:1 and 8:1, the turnꢀon voltages (Von) of the
devices (to achieve the luminance of 1 cd/m2) are between 6.3 V and 6.7 V. The difference of the
turnꢀon voltages is not large, but at the same luminance (for example, 5000 cd/m2) the luminance vs.
the driving voltage characteristics of the devices shift to higher drive voltages, where the driving
voltages are 11.19, 11.11, 12.50, 13.70, 15.52, 15.72 and 15.37 V. At a driving voltage of 15.6 V,
brightness of 18360, 19530, 14019, 11735, 5185, 4236 and 6392 cd/cm2 were observed in the
devices with 1:2, 1:1, 2:1, 3:1, 4:1, 6:1 and 8:1 between CBP and 7CzꢀIr(L)2(acac)ꢀPOSS,
respectively. The devices based on 7CzꢀIr(L)2(acac)ꢀPOSS with 3:1 doping concentration showed a
maximum luminance of 21285 cd/m2 at 19.3 V. Fig. 9 shows the relationship between luminous
efficiency and the driving voltage in the devices fabricated with different 7CzꢀIr(L)2(acac)ꢀPOSS
doping concentrations. It was found that the luminous efficiency showed a downward trend with
decreasing the weight ratio of 7CzꢀIr(L)2(acac)ꢀPOSS. When the doping concentration is 1:1
between CBP and 7CzꢀIr(L)2(acac)ꢀPOSS, a maximum luminous efficiency of 28.22 cd/A at 8.9 V
and a maximum external quantum efficiency (EQE) of 7.82% were achieved in the devices based on
7CzꢀIr(L)2(acac)ꢀPOSS. By comparison of the performances of different doping concentrations, we
can see that the doped devices exhibited higher luminous efficiency at lower CBP concentrations, it
can be attributed to improved balance of carrier injection and transport.
Fig. 10 and 11 display the luminance vs. the driving voltage and the current efficiency vs. the
driving voltage characteristics of the devices based on 6Czꢀ2Ir(L)2(acac)ꢀPOSS at different doping
concentrations 1:2, 1:1, 2:1 and 3:1 between CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS. The performances
of the devices with various 6Czꢀ2Ir(L)2(acac)ꢀPOSS doping concentrations in CBP host are
summarized in Table 2. The device with 2:1 doping concentration exhibited the best EL performance.
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The device had a maximum brightness of 18300 cd/m2 at 15.6 V and a maximum current efficiency
of 25.12 cd/A at 8.9 V and a maximum external quantum efficiency (EQE) of 6.96%.
As can be observed from the Table 2, the electroluminescent performance of the devices based
on 7CzꢀIr(L)2(acac)ꢀPOSS is substantially higher than that of the devices based on
6Czꢀ2Ir(L)2(acac)ꢀPOSS, 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 and brightness increase 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. Similar phenomenon was reported by Yang and coꢀworkers [34]
As shown in Table 2, the turnꢀon voltages for the OLEDs are relatively high. Probably, it caused by
mismatching the energy levels of the different layers.
.
4. Conclusions
We have reported on the synthesis, photophysical and electrochemical characterization, and
thermal stabilities of two inorganic/organic hybrid materials, 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS, consisting of an emissive Ir(III) complex and carbazole moieties
covalently attached to a polyhedral oligomeric silsesquioxane (POSS) core. Compared with the
emissive Ir(III) complex (Ir(L)2(acacꢀallyl)), the inorganic/organic hybrid materials have good
thermal stability due to the inorganic POSS core. Attachment of Ir(III) complex on the POSS core
has no significant effects on the photophysical properties of the POSS materials. Solution processed
lightꢀemitting devices based on the POSS materials exhibited ultrahigh brightness and higher
external quantum efficiency. At the doping concentration of 3:1 between CBP and
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7CzꢀIr(L)2(acac)ꢀPOSS, the devices based on 7CzꢀIr(L)2(acac)ꢀPOSS exhibited green emission with
a maximum luminance of 21285 cd/m2 at 19.3 V. When the doping concentration is 1:1 between
CBP and 7CzꢀIr(L)2(acac)ꢀPOSS, a maximum luminous efficiency of 28.22 cd/A at 8.9 V and a
maximum external quantum efficiency (EQE) of 7.82% were achieved in the devices based on
7CzꢀIr(L)2(acac)ꢀPOSS. For 6Czꢀ2Ir(L)2(acac)ꢀPOSS, at the doping concentration of 2:1 between
CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS, the device had a maximum brightness of 18300 cd/m2 at 15.6 V
and a maximum current efficiency of 25.12 cd/A at 8.9 V and a maximum external quantum
efficiency (EQE) of 6.96%. Furthermore, the device efficiency and brightness increase 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.
Supplementary material:
Fig. S1ꢀS3 are given as supplementary information.
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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efficiency of polyfluorene derivatives: Organic–inorganic hybrid polymer lightꢀemitting diodes,
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Efficient lightꢀemitting devices based on platinumꢀcomplexesꢀanchored polyhedral oligomeric
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Legend:
Scheme 1. The synthetic routes of 7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS.
H
Fig. 1. The FTꢀIR spectra of Q8M8 , Ir(L)2(acacꢀallyl) and 7CzꢀIr(L)2(acac)ꢀPOSS.
Fig. 2. The Xꢀray diffraction (XRD) patterns of Czꢀallyl, Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS
and 6Czꢀ2Ir(L)2(acac)ꢀPOSS.
Fig. 3. Thermogravimetric analyses (TGA) of Ir(L)2(acacꢀallyl), 7CzꢀIr(L)2(acac)ꢀPOSS and
6Czꢀ2Ir(L)2(acac)ꢀPOSS.
Fig. 4. UVꢀvis absorption and photoluminescence spectra of Ir(L)2(acacꢀallyl),
7CzꢀIr(L)2(acac)ꢀPOSS and 6Czꢀ2Ir(L)2(acac)ꢀPOSS in diluted dichloromethane solutions. (C = 1.0
× 10ꢀ5 mol/L)
Fig. 5. Cyclic voltammograms of ferrocene and the POSS materials. (scan rate: 10 mV/s, solvent:
dichloromethane)
Fig. 6. EL spectra of 7CzꢀIr(L)2(acac)ꢀPOSS at different doped concentrations (a) and different
voltages (b). Device configuration: ITO/PEDOT:PSS (45 nm)/CBP: 7CzꢀIr(L)2(acac)ꢀPOSS (50 nm,
v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
Fig. 7. EL spectra of 6Czꢀ2Ir(L)2(acac)ꢀPOSS at different doped concentrations (a) and different
voltages (b). Device configuration: ITO/PEDOT:PSS (45 nm)/CBP: 6Czꢀ2Ir(L)2(acac)ꢀPOSS (50
nm, v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
Fig. 8. Luminance vs. voltage characteristics of the devices with different volume ratios between
CBP and 7CzꢀIr(L)2(acac)ꢀPOSS. Device configuration: ITO/PEDOT:PSS (45 nm)/CBP:
7CzꢀIr(L)2(acac)ꢀPOSS (50 nm, v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
(Concentrations of CBP and 7CzꢀIr(L)2(acac)ꢀPOSS: 20 mg/mL)
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Fig. 9. Current efficiency vs. voltage characteristics of the devices with different volume ratios
between CBP and 7CzꢀIr(L)2(acac)ꢀPOSS. Device configuration: ITO/PEDOT:PSS (45 nm)/CBP:
7CzꢀIr(L)2(acac)ꢀPOSS (50 nm, v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
(Concentrations of CBP and 7CzꢀIr(L)2(acac)ꢀPOSS: 20 mg/mL)
Fig. 10. Luminance vs. voltage characteristics of the devices with different volume ratios between
CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS. Device configuration: ITO/PEDOT:PSS (45 nm)/CBP:
6Czꢀ2Ir(L)2(acac)ꢀPOSS (50 nm, v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
(Concentrations of CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS: 20 mg/mL)
Fig. 11. Current efficiency vs. voltage characteristics of the devices with different volume ratios
between CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS. Device configuration: ITO/PEDOT:PSS (45 nm)/CBP:
6Czꢀ2Ir(L)2(acac)ꢀPOSS (50 nm, v/v)/TPBi (50 nm)/Liq (2 nm)/Al(150 nm).
(Concentrations of CBP and 6Czꢀ2Ir(L)2(acac)ꢀPOSS: 20 mg/mL)
Table 1. Photophysical, thermal and electrochemical properties of the POSS materials.
Table 2. EL performances of the POSS materials.
25

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DOI: 10.1039/C5RA16201G
O
O
O
O
O
O
O
Cl
Cl
Ir
O
Ir
Ir
O
O
N
N
Na2CO3
N
2
ClCH2CH2Cl, 85 oC, 12 h
2
2
Ir(L)2(acacꢀallyl)
H
H
Si
N
Si
O
O
O
O
O
Si
Si
O
H
O
Si
O
Si
O
Ir
O
Ptꢀcatalyst
O
Si
Si
H
Si
O
O
+
POSS materials
O
O
O
O
Si
O
Si
O
Toluene
O
O
Si
N
O
H
Si
2
O
O
Si
Si
Si
H
H
H
POSS materials:
R
O
O
R
R
Si
O
Si
Si
Si
R
Si
O
O
O
O
O
O
Si
Si
O
O
O
O
Si
Si
O
O
O
Si
N
O
Si
O
Si
O
O
R
O
Si
Si
Ir
O
O
O
O
Si
Si
R
R
O
Si
Si
O
O
O
O
N
O
Si
Si
O
O
O
O
O
2
Si
O
Si
O
O
O
R
Si
Si
O
O
O
O
Si
Si
O
Si
R
Si
O
O
Si
O
Si
Si
Si
R
R
O
R
O
O
R
r
I
O
6Czꢀ2Ir(L)2(acac)ꢀPOSS
N
2
7CzꢀIr(L)2(acac)ꢀPOSS
R =
N
Scheme 1.
26

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Fig. 1
27

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RSC Advances
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DOI: 10.1039/C5RA16201G
Ir(L)2(acacꢀallyl)
Czꢀallyl
7CzꢀIr(L)2(acac)ꢀPOSS
6Czꢀ2Ir(L)2(acac)ꢀPOSS
40 50
0
10
20
30
2? (degrees)
2θ (degrees)
Fig. 2
28