Solution processable red iridium dendrimers containing oligocarbazole dendrons for efficient nondoped and doped phosphorescent OLEDs

Article abstract of DOI:10.1039/c7tc03374e

Solution processable red Ir dendrimers named R-D1, R-D2 and R-D3, which contain a quinoline-based homoleptic complex as the core and oligocarbazole as the dendron, have been facilely and successfully designed and synthesized via a post-dendronization procedure. With the increasing dendron generation from R-D1 to R-D3, the intermolecular interactions and luminescence quenching in solid states are found to be effectively prevented because of encapsulation from the outer dendrons. As a result, the third-generation dendrimer R-D3 achieves the best nondoped device performance, revealing a promising EQE of 10.5% (9.2 cd A^-1, 7.0 lm W^-1) with CIE coordinates of (0.67, 0.33). Furthermore, the doped devices of R-D3 show a wide doping concentration window in the range of 5-30 wt%, and a maximum EQE as high as 18.3% (25.7 cd A^-1, 33.0 lm W^-1) is realized at about a 10 wt% doping content. The results can compete well with vacuum-deposited small molecular red phosphors, representing important progress on solution processable phosphorescent dendrimers with red emission.

Full text of DOI:10.1039/c7tc03374e

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Nguyên T. K. Thanh, Xiaodi Su et al.
Fine-tuning of gold nanorod dimensions and plasmonic properties using
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DOI: 10.1039/C7TC03374E
Solution Processible Red Iridium Dendrimers Containing
Oligocarbazole Dendrons for Efficient nondoped and doped
Phosphorescent OLEDs
Lei Zhao, Shumeng Wang, Jianhong Lü, Junqiao Ding,* Lixiang Wang*
State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of
Applied Chemistry, Chinese Academy of Sciences, Changchun, 130022, P. R. China

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Abstract:
Solution processible red Ir dendrimers named RꢀD1, RꢀD2 and RꢀD3, which
contain quinolineꢀbased homoleptic complex as the core and oligocarbazole as the
dendron, have been facilely and successfully designed and synthesized via a
postꢀdendronization procedure. With the increasing dendron generation from RꢀD1 to
RꢀD3, the intermolecular interactions and luminescence quenching in solid states are
found to be effectively prevented because of the encapsulation from the outer
dendrons. As a result, the thirdꢀgeneration dendrimer RꢀD3 achieves the best
nondoped device performance, revealing a promising EQE of 10.5% (9.2 cd/A, 7.0
lm/W) with CIE coordinates of (0.67, 0.33). Furthermore, the doped devices of RꢀD3
show a wide doping concentration window in the range of 5ꢀ30 wt.%, and a maximum
EQE as high as 18.3% (25.7 cd/A, 33.0 lm/W) is realized at an about 10 wt.% doping
content. The results can compete well with vacuumꢀdeposited small molecular red
phosphors, representing an important progress on solution processible phosphorescent
dendrimers with red emissions.

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1. Introduction
The development of printing OLED displays requires highly efficient lightꢀemitting
materials suitable for some costꢀeffective wet methods, such as blade coating1, 2 and
inkjet printing.3, 4 According to their topology structures, these solution processible
emitters can be divided into three classes: small molecules,5, 6 dendrimers7ꢀ9 and
polymers.10ꢀ13 Compared with the other two, dendrimers have much greater potential
since they possess not only the wellꢀdefined molecular structures of small molecules
to favor the reproducibility of material synthesis and device fabrication, but also the
good solution processibility of polymers to ensure the formation of high quality films
via solution processing.
Up to now, a series of phosphorescent dendrimers have been successfully explored
for redꢀ,14, 15 greenꢀ16, 17 and blueꢀemitting18, 19 phosphorescent OLEDs (PhOLEDs), in
which the transitionꢀmetal complex acts as the emissive core to harvest both the
generated singlet and triplet excitons in order to realize a theoretical 100% internal
quantum efficiency. For example, when using a heteroleptic iridium (Ir) complex
bis(2,4ꢀdiphenylquinolyl)iridium(acetylacetonate) [(PPQ)2Ir(acac)] as the central core,
we designed and synthesized red Ir dendrimers by only decorating its C^N ligand with
different carbazole dendrons.14 The thirdꢀgeneration dendrimer redꢀG3 achieved a
maximum external quantum efficiency (EQE) of 6.3% for the corresponding
nondoped PhOLEDs, which was further improved to 11.9% in the presence of host.
Considering the still existed intermolecular interactions in redꢀG3 to some degree,
subsequently, a fully oligocarbazoleꢀencapsulated red Ir complex Dꢀ(PPQ)2Ir(acac)

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was newly reported.15 In this case, both the C^N and O^O ligands of (PPQ)2Ir(acac)
were tethered with oligocarbazole, thus leading to a recordꢀhigh nondoped device
EQE of 11.1% (8.7 cd/A, 6.0 lm/W) accompanied by Commission International De
L’Eclairge (CIE) coordinates of (0.67, 0.33). However, the obtained performance
seems to be inferior to that of vacuumꢀdeposited red phosphors,20ꢀ24 and
simultaneously their synthesis remains a big challenge since the preꢀdendronized
ligands often show poor solubility in the polar solvents (e.g. 2ꢀethoxyethanol) during
complexation.19 These problems leave us much room to optimize the molecular
design and synthesis of red phosphorescent dendrimers for highꢀefficiency
solutionꢀprocessed PhOLEDs.
In this paper, we demonstrate novel solution processible red Ir dendrimers, where
oligocarbazole up to the third generation can be facilely incorporated into the
periphery
of
tris(2ꢀthienylꢀ4ꢀphenyl)iridium
[Ir(ThꢀPQ)3]
through
a
postꢀdendronization route (Scheme 1). Instead of the heteroleptic one, a homoleptic
red Ir complex Ir(ThꢀPQ)3 is selected as the core based on several concerns as
followed: i) Without affecting the photophysical property of Ir core, the reactive
bromo groups are easily to be introduced into the C^N ligand other than the O^O one.
So the homoleptic structure is expected to be favorable for the postꢀdendronization
that allows the ease preparation and independent tuning of each component. ii)
Different from the partlyꢀadopted nonꢀconjugated linkage between core and dendron
in the previouslyꢀreported heteroleptic red Ir dendrimers, the conjugated linkage here
could endow these newlyꢀdeveloped homoleptic dendrimers not only with enough

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rigidity to keep the highly emissive nature of the core, but also with effective
encapsulation to prevent the unwanted luminescent quenching in solid states. As for
the resultant red Ir dendrimers RꢀD1, RꢀD2 and RꢀD3, the nondoped device efficiency
is gradually enhanced from 5.1% (4.2 cd/A, 3.3 lm/W) to 10.5% (9.2 cd/A, 7.0 lm/W)
with the increasing generation number. Moreover, a wide doping concentration
window in the range of 5ꢀ30 wt.% is realized for the doped devices of the
thirdꢀgeneration dendrimer RꢀD3, revealing a stateꢀofꢀart EQE of 18.3% (25.7 cd/A,
33.0 lm/W) and CIE coordinates of (0.65, 0.34). To the best of our knowledge, this is
the first report on solution processible red Ir dendrimers with comparable efficiency to
vacuumꢀdeposited small molecular phosphors.
2. Results and Discussion
2.1 Synthesis and characterization
A postꢀdendronization procedure is adopted for the synthesis of red Ir dendrimers
RꢀD1 ~ RꢀD3 as depicted in Scheme 1. Starting from 2ꢀaminoꢀ4'ꢀbromobenzophenone,
an acidꢀcatalyzed Friedländer reaction was performed to afford the quinolineꢀbased
C^N ligand ThꢀPQꢀBr. Then ThꢀPQꢀBr was complexed with IrCl3·3H2O to produce
the Ir core RꢀBr bearing three reactive bromo groups. On the other hand, a selective
CꢀN coupling was carried out between 1,4ꢀdibromobenzene and different
oligocarbazoles to give the bromoꢀcontaining carbazole dendrons D1ꢀBr, D2ꢀBr and
D3ꢀBr, which were converted into the corresponding boronic esters D1ꢀB, D2ꢀB and
D3ꢀB, respectively. Finally, via Suzuki crossꢀcoupling between RꢀBr and D1ꢀBr,

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D2ꢀBr or D3ꢀBr, the desired red Ir dendrimers RꢀD1, RꢀD2 and RꢀD3 were easily and
successfully prepared in an acceptable moderate yield of 54ꢀ78%. Their molecular
1
structures were fully characterized and confirmed by H and 13C NMR spectra,
MALDIꢀTOF mass spectroscopy and elemental analysis. Meanwhile, these
dendrimers are readily soluble in common organic solvents, such as chloroform,
tetrahydrofuran, toluene and chlorobenzene, ensuring their capability to form high
quality films via spinꢀcoating. This is confirmed by their atomic force microscopy
(AFM) topographic images (Figure S1 in ESI), where the films of RꢀD1 ~ RꢀD3
display a pinholeꢀfree and smooth surface with a rootꢀmean square (RMS) roughness
of 0.77–0.81 nm. In addition, the decomposition temperature corresponding to a 5%
weight loss is considerably up from 470 oC of RꢀD1 to 530 oC of RꢀD3 (Table 1). And
no glass transition is detected for RꢀD3, which is different from RꢀD1 with a distinct
o
glass transition temperature of about 199 C. These observations imply that RꢀD3 is
more thermally stable than RꢀD1, favorable for the longꢀterm stability of PhOLEDs.
2.2 Photophysical properties
The UVꢀVis and photoluminescence (PL) spectra in solutions for the red Ir
dendrimers RꢀD1 ~ RꢀD3 are shown in Figure 1a. As one can see, all these
dendrimers display two major absorption bands. Consistent with the literature,5 the
intense absorption below 420 nm can be attributed to the spinꢀallowed ligandꢀcentered
(LC) transitions. And the absorption peaked at around 240 nm, characteristic of
oligocarbazole, is increased with the increasing number of carbazole subunits.

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Meanwhile, the weak bands in 450ꢀ590 nm are also found to be discernible, which are
assigned to the metalꢀtoꢀligand chargeꢀtransfer (MLCT) transitions. The solution PL
spectra of RꢀD1 ~ RꢀD3 are nearly independent on the dendron generation since they
all have the same spectral profiles with similar emission peaks at 606ꢀ609 nm and PL
quantum yields (PLQYs) of 0.40ꢀ0.42. This suggests that the emission is mainly from
the central Ir core, and the extension of oligocarbazole does not affect its optical
property in dilute solutions.
On going from solutions to films, a red shift of about 15ꢀ33 nm is observed for all
the dendrimers, indicative of aggregation to some degree. Despite such a
bathochromic trend, the emission maximum is obviously blueꢀshifted from 639 nm of
RꢀD1 to 624 nm of RꢀD3 (Figure 1b). In fact, when the outer dendron becomes larger
and larger, the emissive inner cores can be isolated more and more effectively because
of the encapsulation from dendrons. Therefore, the intermolecular interactions
between the emissive cores are expected to be reduced to prevent the luminescence
quenching in solid states. To further confirm this point, their film transient PL spectra
were measured (Figure 2), and the average lifetime was estimated based on a
biexponential fit of the corresponding emission decay curve. Attributable to the
reduced intermolecular interactions, it is found that RꢀD3 decays slowly with a
lifetime of 0.92 ꢁs longer than those of RꢀD1 and RꢀD2 (0.54ꢀ0.59 ꢁs).
2.3 Electrochemical properties
Cyclic voltammetry (CV) was used to explore the dendrimers’s electrochemical

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properties. During the anodic scanning in dichloromethane, multiple quasiꢀreversible
oxidation waves is observed for the red Ir dendrimers RꢀD1 ~ RꢀD3 (Figure 3). The
first oxidation is reasonably from the inner Ir core, while the others are from the outer
carbazole dendrons. During the cathodic scanning in N,Nꢀdimethyl formamide, they
all display three quasiꢀreversible reduction waves that originate from the
quinolineꢀbased C^N ligand. According to the onset values of the first oxidation and
reduction potentials, the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) energy levels of RꢀD1 ~ RꢀD3 are determined
to be ꢀ5.12 — ꢀ5.13 eV and ꢀ2.79 — ꢀ2.83 eV, respectively. Obviously, their
HOMO/LUMO levels are almost independent on the carbazole generation, in well
agreement with the similar PL spectra in solutions.
2.4 Electroluminescence properties
To evaluate the electroluminescence (EL) properties of the red Ir dendrimers RꢀD1
~ RꢀD3, their nondoped devices with a configuration of ITO/PEDOT:PSS (40
nm)/dendrimers (45 nm)/TmPyPB (60 nm)/LiF (0.5 nm)/Al were firstly fabricated
(Figure 4a). Here TmPyPB represents 1,3,5ꢀtri[(3ꢀpyridyl)ꢀphenꢀ3ꢀyl]benzene, and is
utilized as the electronꢀtransporting and holeꢀblocking material. As can be clearly seen
in Figure 4b, all the dendrimers emit strong and pure red lights with CIE coordinates
of (0.67, 0.33). The values keep nearly unchanged under the varying voltages in the
range of 4ꢀ10 V, and match well with the National Television System Committee
(NTSC) standard for red subpixels (0.67, 0.33). Different from the film PL

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counterparts showing an obvious hypsochromic shift from RꢀD1 to RꢀD3, the
observed similar EL spectra are probably ascribed to a different excitation
environment in devices. Despite of this, the maximum brightness is gradually elevated
from 10290 cd/m2 of RꢀD1 to 14810 cd/m2 of RꢀD3 (Figure 4c). Correspondingly, the
EQE is improved from 5.1% (4.2 cd/A, 3.3 lm/W) of RꢀD1 to 10.5% (9.2 cd/A, 7.0
lm/W) of RꢀD3 (Figure 4d). As discussed above, with the growing dendron generation,
the intermolecular interactions and luminescence quenching can be effectively
inhibited, which is responsible for the efficiency improvement.
Taking into account there exists aggregation even in RꢀD3, its doped devices were
then
assembled
by
doping
RꢀD3
into
The
4,4',4''ꢀtris(Nꢀ3ꢀmethylphenylꢀNꢀphenylamino)triphenylamine(mꢀMTDATA).
device structure, EL spectra, current densityꢀvoltageꢀluminance curves and current
efficiencyꢀluminanceꢀEQE curves are given in Figure 5, and the related data are
tabulated in Table 2. We note that the turnꢀon voltage at 1 cd/m2 is considerably
lowered from 3.2 V of nondoped device to 2.4 V of doped ones. Consistent with our
previous report,25 the formation of the interfacial exciplex between mꢀMTDATA and
TmPyPB contributes to the decreased voltage, whose energy could be completely
transferred to the dopant RꢀD3. This is verified by the EL spectra (Figure 5b), in
which only the red emission from RꢀD3 is observed without any emissions from
mꢀMTDATA, TmPyPB or mꢀMTDATA/TmPyPB exciplex. More interestingly, unlike
small molecular phosphors, RꢀD3 realizes a very wide doping concentration window
for doped devices. For example, when the doping concentration is up from 5 wt.% to

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30 wt.%, the peak current efficiency varies in a shallow range of 22.7ꢀ25.7 cd/A. An
only 11.7% variation is very beneficial for the reliability and reproducibility of
commercial devices. On one hand, according to the literature,14, 18 the dendritic
phosphor could perform well at high doping concentration because of the reduced
intermolecular interactions after dendron encapsulation. On the other hand, the
formed mꢀMTDATA/TmPyPB interfacial exciplex is a similar low exchange energy
system to the thermally activated delayed fluorescence (TADF) host.26 In this case,
the promoted upconversion from triplet to singlet excitons may facilitate the
longꢀrange Förster energy transfer from host to dopant and spare the shortꢀrange
Dexter to lower the dopant content. Therefore, the achievement of high efficiency
even at low doping concentration is also reasonable and understandable. In addition,
the best doped device performance is obtained at an about 10 wt.% doping
concentration, revealing a maximum brightness of 25270 cd/m2, a maximum current
efficiency of 25.7 cd/A, a maximum power efficiency of 33.0 lm/W, a maximum EQE
of 18.3% and CIE coordinates of (0.65, 0.34). Even at a luminance of 1000 cd/m2, the
EQE still remains to be as high as 17.0% (23.9 cd/A, 23.4 lm/W), indicative of gentle
efficiency rollꢀoff. To our knowledge, the reported performance here is among the
highest for solution processible red dendrimers, and competes well with
vacuumꢀdeposited small molecular phosphors.
3. Conclusions
In summary, we report the synthesis, characterization and application of solution

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processible red Ir dendrimers RꢀD1 ~ RꢀD3 by using a quinolineꢀbased homoleptic
complex as the emissive core and oligocarbazole as the dendron. Owing to the
effective encapsulation from the outer dendrons and high emissive nature of the core,
the thirdꢀgeneration dendrimer RꢀD3 shows a stateꢀofꢀart EQE of 10.5% (9.2 cd/A,
7.0 lm/W) and 18.3% (25.7 cd/A, 33.0 lm/W) for its corresponding nondoped and
doped devices, respectively. Given the comparable efficiency to vacuumꢀdeposited
smallꢀmolecular red phosphors, we believe that this work will promote the
development of efficient red phosphorescent dendrimers for solutionꢀprocessed
PhOLEDs.
4. Experimental section
General information:
1H and 13C NMR spectra were recorded with a Bruker Avance 400 NMR
spectrometer. MALDI/TOF mass spectra were obtained on an AXIMA CFR MS
apparatus (COMPACT). Elemental analyses of carbon, hydrogen, and nitrogen were
performed on a BioꢀRad elemental analysis system. AFM characterization was
performed on SPA300HV with a SPI3800N controller (Seiko Instruments Inc., Japan)
in a tapping mode. Thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC) were performed on Perkin ElmerꢀTGA 7 and Perkin ElmerꢀDSC 7
o
system under nitrogen at a heating rate of 10 C minꢀ1. The UVꢀVis absorption and
PL spectra were measured by a PerkinꢀElmer Lambda 35 UV/vis spectrometer and a
PerkinꢀElmer LS 50B spectrofluorometer, respectively. The PLQYs were measured in

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N2ꢀsaturated toluene solutions by a relative method using facꢀIr(ppy)3 (Фp = 0.97 in
toluene) as the reference. The transient PL spectra were measured in N2 atmosphere
by exciting the samples with 355 nm light pulses with ca. 3 ns pulse width from a
QuantyꢀRay DCRꢀ2 pulsed ND:YAG laser. And the average lifetimes were calculated
2
2
according to the equation: τav= (A1τ1 +A2τ2 )/( A1τ1+A2τ2). Cyclic voltammetry (CV)
measurements were obtained in anhydrous dichloromethane and degassed
N,Nꢀdimethyl formamide with nꢀBu4NClO4 (0.1 mol L−1) as the electrolyte on a
CHI660a electrochemical analyzer under a scan rate of 100 mV s−1. A glass carbon
electrode, a Ag/AgCl electrode and a Pt wire were used as the working electrode, the
reference electrode and the counter electrode, respectively.
Device fabrication and measurement:
Patterned glass substrates coated with indium tin oxide (ITO) were cleaned with
acetone, detergent and distilled water, and then in an ultrasonic solvent bath. After
baking in a heating chamber at 120 °C for 8 h, the ITOꢀglass substrates were treated
with
O2
plasma
for
30
min.
Subsequently,
poly(3,4ꢀethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS, Batronꢀ
P4083, Bayer AG) was spinꢀcoated on top of the ITO at a speed of 5000 rpm for 60 s
and then baked at 120 °C for 45 min. Then, solutions of the red Ir dendrimers without
or with mꢀMTDATA in oꢀdichlorobenzene were filtered through a filter (0.45 ꢁm) and
spinꢀcoated on PEDOT:PSS as the emissive layer (EML) at a speed of 1500 rpm for
60 s. Successively, the substrate was annealed at 100 °C for 30 min inside a

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nitrogenꢀfilled glovebox and then transferred to a vacuum thermal evaporator. On top
of the EML, a 60 nm thick film of TmPyPB was thermally deposited at a pressure of
4.0 × 10−4 Pa. Finally, 0.5 nm LiF and 100 nm Al were deposited as the cathode
through a shadow mask with an array of 14 mm2 openings. The EL spectra and CIE
coordinates were measured using a PR650 spectra colorimeter. The current−voltage
and brightness−voltage curves of devices were measured using a Keithley 2400/2000
source meter and a calibrated silicon photodiode. The EQE was calculated from the
luminance, current density and EL spectra assuming a Lambertian distribution. All the
measurements were carried out at room temperature under ambient conditions.
Synthesis:
All solvents for chemical synthesis were refined according to the standard
procedures. Carbazoleꢀbased dendrons including D1, D2, and D3 were synthesized
according to the literature.14
Th-PQ-Br:
A
mixture of 3ꢀacetylthiophene (2.0 g, 15.8 mmol),
2ꢀaminoꢀ4'ꢀbromobenzophenone (4.4 g, 15.8 mmol), diphenylphosphate (4.0 g, 15.8
mmol), and mꢀcresol (20 mL) was flushed with N2 while stirring at room temperature
for 30 min and then refluxed for 12 h at 140 °C. The reaction mixture was distilled to
remove mꢀcresol, diluted with dichloromethane and washed with 10% sodium
hydroxide solution. The resultant organic layer was dried over anhydrous NaSO4 and
evaporated to remove the solvent. The residue was then purified by column
chromatography on silica gel with hexane/ethylacetate (9:1) as eluent to furnish a

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1
white powder ThꢀPQꢀBr (4.0 g, 70.0%). H NMR (400 MHz, CDCl3) δ 8.16 (d, J =
8.0 Hz, 1H), 7.75 (dd, J = 14.0, 7.8 Hz, 3H), 7.71 – 7.63 (m, 4H), 7.47 (dd, J = 8.7,
4.3 Hz, 1H), 7.42 (d, J = 8.3 Hz, 3H), 7.16 (t, J = 4.2 Hz, 1H).
.
R-Br: IrCl3 3H2O (0.7 g, 2.0 mmol) and ThꢀPQꢀBr (1.8 g, 5.0 mmol) were added to a
40 mL mixture of 2ꢀethoxyethanol (30 mL) and water (10 mL). The mixture was
refluxed for 24 h and then poured into water. The solid was collected by filtration and
dried in a vacuum to give the crude chloroꢀbridged dimer. Without further purification,
the dimer was added to a mixture of silver trifluoroacetate (0.6 g, 2.2 mmol),
ThꢀPQꢀBr (0.7 g, 2.0 mmol), K2CO3 (0.4 g, 3.0 mmol) and mesitylene (20 mL). After
reflux for 24 h, the mixture was poured into water, and extracted with
dichloromethane. The organic layer was carefully washed with water and dried with
Na2SO4. The crude product was purified by chromatography on silica gel with
hexane/dichloromethane (3:1) as eluent to furnish a red powder RꢀBr (1.8 g, 68.2%).
1H NMR (400 MHz, C6D6) δ 8.44 (d, J = 8.8 Hz, 3H), 7.88 (s, 3H), 7.74 (d, J = 8.3
Hz, 3H), 7.70 (d, J = 7.8 Hz, 6H), 7.40 (s, 3H), 7.30 (d, J = 5.7 Hz, 6H), 7.26 – 7.18
(m, 3H), 6.96 (t, J = 7.7 Hz, 3H), 6.57 (d, J = 4.5 Hz, 3H).
D1-Br: A mixture of D1 (12.0 g, 42.9 mmol), 1,4ꢀdibromobenzene (10.1 g, 42.9
mmol), CuI (0.4 g, 2.1 mmol) and K2CO3 (13.7 g,64.4 mmol) in DMI (30 mL) was
heated at 160 oC for 24 h under argon. After cooling to room temperature, the mixture
was poured into water, and extracted with dichloromethane. The organic layer was

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carefully washed with water and dried with Na2SO4. The crude product was purified
by chromatography on silica gel with hexane/dichloromethane (4:1) as eluent to
furnish a white powder D1ꢀBr (13.0 g, 70.0%). 1H NMR (400 MHz, CDCl3): δ 8.13 (d,
J = 1.5 Hz, 2H),7.70 (d, J = 8.6 Hz, 2H), 7.46 (dd, J = 8.3, 1.9 Hz, 2H), 7.43 (d, J =
6.1 Hz, 2H), 7.31 (d, J = 8.6 Hz, 2H), 1.46 (s, 18H).
D2-Br: This compound was prepared according to the procedure for the synthesis of
1
D1ꢀBr by using D2 instead of D1 in a yield of 72.0%. H NMR (400 MHz, CDCl3) δ
8.23 (d, J = 1.8 Hz,2H), 8.15 (d, J = 1.7 Hz, 4H), 8.02 (d, J = 8.3 Hz, 2H), 7.65 (d, J =
8.7 Hz, 2H), 7.59 (dd, J = 8.7, 2.0 Hz, 2H), 7.43 (dd, J = 8.7, 1.9 Hz, 4H), 7.34 (d, J =
8.6Hz, 4H) , 1.46 (s, 36H).
D3-Br: This compound was prepared according to the procedure for the synthesis of
1
D1ꢀBr by using D3 instead of D1 in a yield of 63.2%. H NMR (400 MHz, CDCl3) δ
8.56 (s, 2H), 8.31 (d, J = 8.5 Hz, 2H), 8.27 (d, J = 1.5 Hz, 4H), 8.15 (d, J = 1.7 Hz,
8H), 7.92 (d, J = 8.4 Hz, 2H), 7.74 (s, 4H), 7.63 – 7.56 (m, 8H), 7.43 (dd, J = 8.7, 1.9
Hz, 8H), 7.34 (d, J = 8.6 Hz, 8H), 1.46 (s, 72H).
D1-B: D1ꢀBr (5.4 g, 12.4 mmol), bis(pinacolato)diboron (7.8 g, 31.1 mmol),
Pd(dppf)Cl2 (0.2 g, 0.3 mmol), and KOAc (3.7 g, 37.3 mmol) were added to a clean
dry threeꢀneck flask filled with argon. 30 mL N,Nꢀdimethylformamide was added into
o
the mixture. Then the solution was stirred at 100 C for 12 h. After cooling to room

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temperature, 100 mL water was slowly added to the solution. The mixture was filtered
and the residue was washed with water and dried in a vacuum and then purified by
column chromatography on silica gel with hexane/ethyl acetate (20:1) as eluent to
furnish a white powder D1ꢀB (5.7 g, 96.0%). 1H NMR (400 MHz, CDCl3) δ 8.13 (d, J
= 1.5, 2H), 8.02 (d, J = 8.2, 2H), 7.58 (d, J = 8.2, 2H), 7.46 (dd, J = 8.7, 1.8, 2H), 7.39
(d, J= 8.7, 2H), 1.46 (s, 18H), 1.40 (s, 12H).
D2-B: This compound was prepared according to the procedure for the synthesis of
1
D1ꢀB by using D2ꢀBr instead of D1ꢀBr in a yield of 87.5%. H NMR (400 MHz,
CDCl3) δ 8.23 (d, J = 1.8 Hz ,2H), 8.15 (d, J = 1.7 Hz, 4H), 7.75 (d, J = 8.3 Hz, 2H),
7.66 (d, J = 8.7 Hz, 2H), 7.59 (dd, J = 8.7, 2.0 Hz, 2H), 7.45 (dd, J = 8.7, 1.9 Hz, 4H),
7.33 (d, J = 8.6Hz, 4H) , 1.46 (s, 36H), 1.42 (s, 12H).
D3-B: This compound was prepared according to the procedure for the synthesis of
1
D1ꢀB by using D3ꢀBr instead of D1ꢀBr in a yield of 82.9%. H NMR (400 MHz,
CDCl3) δ 8.56 (s, 2H), 8.31 (d, J = 8.5 Hz, 2H), 8.27 (d, J = 1.5 Hz, 4H), 8.15 (d, J =
1.7 Hz, 8H), 8.04 (d, J = 8.4 Hz, 2H), 7.87 (s, 4H), 7.68 – 7.57 (m, 8H), 7.45 (dd, J =
8.7, 1.9 Hz, 8H), 7.34 (d, J = 8.6 Hz, 8H), 1.45 (s, 72H), 1.42 (s, 12H).
R-D1: Compound RꢀBr (0.3 g, 0.2 mmol), D1ꢀBr (0.5 g, 1.1 mmol), Pd2(dba)3 (16 mg,
0.018 mmol) and sꢀPhos (59 mg, 0.14 mmol) were dissolved in 30 mL mesitylene, an
aqueous solution of 2M K2CO3 (1 mL, 2 mmol) and one drop of Aliquat 336 was

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added to the solution and then the mixture was heated to 100 oC for 12 h under argon.
After cooled to room temperature, 50 mL dichloromethane was added to the solution.
The organic phase was washed with water and dried with anhydrous Na2SO4.
Solvents were removed under vacuum and the residue was purified by column
chromatography over silica gel with hexane/dichloromethane (2:1) as the eluent to
give the product as a red solid (0.3g, 74.2%). 1H NMR (400 MHz, CDCl3) δ 8.17 (d, J
= 1.4 Hz, 9H), 7.89 (t, J = 8.4 Hz, 15H), 7.74 (d, J = 3.5 Hz, 6H), 7.73 – 7.66 (m, 9H),
7.50 (dd, J = 8.7, 1.8 Hz, 6H), 7.45 (d, J = 8.6 Hz, 6H), 7.21 (d, J = 4.7 Hz, 6H), 6.90
13
– 6.81 (m, 3H), 6.16 (d, J = 4.8 Hz, 3H), 1.49 (s, 54H). C NMR (400 MHz, CDCl3)
δ 161.86, 158.87, 149.45, 149.23, 143.04, 140.62, 139.21, 138.90, 138.22, 137.85,
137.03, 134.76, 130.41, 129.74, 128.71, 128.45, 127.52, 127.25, 127.05, 126.29,
125.02, 124.73, 123.70, 123.53, 118.26, 116.32, 109.31, 34.79, 32.06. MS
(MALDIꢀTOF) m/z: 2110.81 [M+] . Anal.Calcd. for C135H117IrN6S3: C, 76.78; H, 5.58;
N, 3.98. Found: C, 76.18; H, 5.94; N, 3.37.
R-D2: This compound was prepared according to the procedure for the synthesis of
RꢀD1 by using D2ꢀB instead of D1ꢀB in a yield of 65.1%. 1H NMR (400 MHz, CDCl3)
δ 8.27 (t, J = 4.0 Hz, 6H), 8.18 (t, J = 5.5 Hz, 15H), 8.01 (d, J = 8.5 Hz, 6H), 7.90 (dt,
J = 18.1, 9.1 Hz, 15H), 7.81 – 7.70 (m, 15H), 7.64 (dd, J = 8.7, 1.9 Hz, 6H), 7.52 –
7.42 (m, 12H), 7.39 – 7.31 (m, 12H), 7.24 – 7.17 (m, 6H), 6.93 – 6.81 (m, 3H), 6.16
(dd, J = 10.3, 3.1 Hz, 3H), 1.47 (m, 108H). 13C NMR (400 MHz, CDCl3) δ 161.85,
158.89, 149.44, 149.13, 142.59, 140.35, 140.14, 138.19, 137.31, 136.81, 134.74,

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131.02, 130.48, 129.75, 128.86, 128.76, 127.55, 127.35, 126.25, 126.03, 124.86,
124.57, 124.10, 123.58, 123.15, 119.35, 118.27, 116.23, 111.21, 109.09, 34.73, 32.05.
MS (MALDIꢀTOF) m/z: 3437.54 [M+]. Anal.Calcd. for C231H207IrN12S3: C, 80.66; H,
6.07; N, 4.89. Found: C, 81.12; H, 5.94; N, 4.37.
R-D3: This compound was prepared according to the procedure for the synthesis of
RꢀD1 by using D3ꢀB instead of D1ꢀB in a yield of 54.1%. 1H NMR (400 MHz, CDCl3)
δ 8.58 (s, 6H), 8.28 (s, 12H), 8.23 – 8.13 (m, 30H), 8.10 (d, J = 8.1 Hz, 6H), 7.96 (t, J
= 7.8 Hz, 12H), 7.89 (q, J = 8.8 Hz, 15H), 7.85 – 7.75 (m, 12H), 7.64 (dd, J = 18.9,
8.6 Hz, 24H), 7.45 (d, J = 8.6 Hz, 24H), 7.35 (d, J = 8.6 Hz, 14H), 7.23(s,10H), 6.98
– 6.80 (m, 3H), 6.18 (d, J = 4.6 Hz, 3H), 1.46 (s, 216H). 13C NMR (400 MHz, CDCl3)
δ 161.92, 158.97, 149.50, 149.13, 142.59, 141.41, 141.17, 140.68, 140.25, 138.24,
137.54, 136.54, 130.83, 130.62, 130.20, 129.11, 127.77, 127.46, 126.53, 126.08,
124.91, 124.31, 123.85, 123.60, 123.16, 120.08, 119.47, 116.26, 111.88, 111.72,
109.15, 34.77, 32.09. MS (MALDIꢀTOF) m/z: 6091.98 [M+]. Anal.Calcd. for
C423H387IrN24S3: C, 83.35; H, 6.40; N, 5.52. Found: C, 83.21; H, 6.49; N, 5.37.
Author Information:
*Corresponding authors: junqiaod@ciac.ac.cn; lixiang@ciac.ac.cn
Acknowledgements
The authors acknowledge the financial support from the National Key Research and

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Development Program (2016YFB0401301), the 973 Project (2015CB655001) and the
Natural Science Foundation of China (Nos. 51573183, 21604083 and 91333205).
References：
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Scheme 1. Synthetic route (a) and molecular structures (b) of the red Ir dendrimers
.
Reagents and conditions: (i) 3ꢀacetylthiophene, DPP, mꢀcresol; (ii) iridium(III)
chloride trihydrate, water, 2ꢀethoxyethanol, reflux; (iii) silver trifluoroacetate,
ThꢀPQꢀBr, K2CO3, mesitylene, reflux; (iv) 1,4ꢀdibromobenzene, CuI, K2CO3, DMI,
o
o
160 C; (v) bis(pinacolato)diboron, Pd(dppf)Cl2, KOAc, DMF, 80 C; (vi) Pd2(dba)3,
SꢀPhos, 2M K2CO3, mesitylene, 100 oC.

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Figure 1. Photophysical properties of the red Ir dendrimers RꢀD1 ~ RꢀD3: (a) UVꢀVis
absorption spectra in dichloromethane and PL spectra in toluene at a concentration of
10ꢀ5 M; (b) PL spectra in solid films.

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Figure 2. Transient PL spectra of the red Ir dendrimers RꢀD1 ~ RꢀD3 in solid films.

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Figure 3. CV curves of the red Ir dendrimers RꢀD1 ~ RꢀD3.

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Figure 4. Nondoped device performance for the red Ir dendrimers RꢀD1 ~ RꢀD3 : (a)
device configuration; (b) EL spectra at 6 V; (c) current density–voltage–luminance
characteristics; (d) luminance dependence on the current efficiency and EQE.

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Figure 5. Doped device performance for the thirdꢀgeneration dendrimer RꢀD3: (a)
device structure; (b) EL spectra at 6 V; (c) current density–voltage–luminance
characteristics; (d) luminance dependence on the current efficiency and EQE.

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Table 1. Photophysical, electrochemical and thermal properties of the red Ir
dendrimers.
b
c
λabs (log ԑ) a
(nm)
λem
λem
τ e
HOMO f LUMO f
Td
Tg
d
Dendrimer
ФPL
(nm)
(nm)
(ꢁs)
(eV)
(eV)
(oC) (oC)
240 (5.3), 297 (5.1), 349 (5.0), 418
(4.5), 462 (4.4), 586 (3.4)
RꢀD1
RꢀD2
606
639
0.42
0.42
0.40
0.54
0.59
0.92
ꢀ5.12
ꢀ2.79
470
526
530
199
n.d.
n.d.
242 (5.7), 267 (5.5), 298 (5.4), 349
(5.1), 420 (4.5), 461 (4.3), 585 (3.4)
242 (6.0), 269 (5.8), 297 (5.8), 348
(5.3), 419 (4.5), 463 (4.3), 585 (3.3)
607
609
630
624
ꢀ5.13
ꢀ5.13
ꢀ2.80
ꢀ2.81
RꢀD3
a
b
Measured in dichloromethane at a concentration of 10ꢀ6 M;
Measured in toluene at a
c
d
concentration of 10ꢀ5 M; Measured in solid films; Measured in degassed toluene with
e
f
facꢀIr(ppy)3 (ФPL = 0.97) as the reference; Measured in solid films degassed by N2; HOMO =
ꢀe(Eox + 4.8 V), LUMO = ꢀe(Ered + 4.8 V), where Eox.and Ered are the onset values from the first
oxidation and reduction waves, respectively.

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Table 2. Device performance for the red Ir dendrimers.
a
b
Von
Lmax
LE c
PE d
EQE e
(%)
Device
CIE (x, y)
(V)
3.0
3.2
3.2
2.4
2.4
2.4
2.4
2.4
(cd mꢀ2)
10290
11470
14810
18990
25270
25730
25080
26690
(cd Aꢀ1)
(lm Wꢀ1)
RꢀD1
4.2/3.2/4.2
4.8/3.6/4.8
3.3/3.0/3.2
3.3/3.0/3.3
5.1/3.9/5.1
5.7/4.3/5.6
(0.67,0.33)
(0.67,0.33)
(0.67,0.33)
(0.65,0.34)
(0.65,0.34)
(0.65,0.34)
(0.65,0.34)
(0.66,0.34)
RꢀD2
RꢀD3
9.2/8.5/9.1
7.0/7.0/6.9
10.5/9.7/10.1
18.1/18.1/16.4
18.3/18.2/17.0
17.9/17.9/16.3
17.0/17.0/15.3
RꢀD3 (5 wt.%)
RꢀD3 (10 wt.%)
RꢀD3 (15 wt.%)
RꢀD3 (20 wt.%)
RꢀD3 (30 wt.%)
25.6/25.5/23.2
25.7/25.6/23.9
25.0/25.0/22.7
23.7/23.7/21.3
33.2/29.6/22.7
33.0/29.9/23.4
30.0/28.0/20.9
28.6/26.6/19.7
29.4/24.5/17.8
22.7/22.6/20.4
16.9/16.8/15.2
b
c
a Turnꢀon voltage at a brightness of 1 cd mꢀ2; The maximum brightness; The current efficiency
e
at maximum, 100 and 1000 cd mꢀ2; d The power efficiency at maximum, 100 and 1000 cd mꢀ2;.
The external quantum efficiency at maximum, 100 and 1000 cd mꢀ2
.