High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with fluorene core and blue fluorescence chromospheres

Article abstract of DOI:10.1016/j.tet.2017.12.018

Two novel dendrimer-like blue-emitting dinuclear cyclometalated iridium (III) complexes, namely (DNaTPA)₂DBF(FIrpic)₂ and (DPyTPA)₂DBF(FIrpic)₂, have been successfully synthesized and characterized. In which FIrpic is an iridium (III) bis[(4,6-difluorophenyl)pyridinato-N,C2′]picolate blue-emitting phosphorescent chromophore core, DBF is a 2,7-diphenyl-9H-fluorene bridging core, DNaTPA and DPyTPA are deep blue-emitting fluorescent chromophores composed by rigid high-triplet-energy dendrons of triphenylamine-functionalized naphthalene or pyrene units, and the peripheral dendrons are connected with the ancillary ligand of the emitting core through nonconjugated ether linkage. Their photophysical, thermal, electrochemical, as well as electrophosphorescent properties were primarily studied. Both iridium (III) complexes exhibit high efficient blue emission in solution (38.5% and 19.2%) and a typical FIrpic emission in 1,3-bis(N-carbzolyl)benzene (mCP) matrix (27.0% and 24.1%). Simple bilayer phosphorescent organic light-emitting diodes (PHOLEDs) with a configuration of ITO/PEDOT:PSS/mCP:dopants/TmPyPB/Liq/Al achieved high efficiencies of 12.96 cd/A for current efficiency (CE), 6162 cd/m² for brightness, 6.22% for external quantum efficiency (EQE), and 3.13 lm/W for power efficiency (PE) with Commission International de L'Eclairage (CIE) coordinates of (0.19 ± 0.01, 0.35 ± 0.02) at only 2 wt% blend of (DNaTPA)₂DBF(FIrpic)₂. (DPyTPA)₂DBF(FIrpic)₂-doped devices also reach efficiencies of (9.14 cd/A, 7167 cd/m², 4.41%, 2.61 lm/W) at the same doping concentration. The results demonstrate that the introduction of dendritic blue-emitting fluorescent chromophore grafted into the blue phosphorescent chromosphere core through nonconjugated linkage is an efficient way to achieve high-efficiency sky-blue emission.

Full text of DOI:10.1016/j.tet.2017.12.018

Tetrahedron xxx (2017) 1e8
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
High-efficiency blue OLEDs based on dendritic dinuclear iridium (III)
complexes grafted with fluorene core and blue fluorescence
chromospheres
,
b
,
,
Yu Liu a *, Zhaoran Hao b, Haigang Jiang b, Yajun Liu b, Yafei Wang a b, Hua Tan b,
Guohua Xie c
,
**
a Jiangsu Key Laboratory of Environmentally Friendly Polymeric Materials, School of Materials Science & Engineering, Changzhou University, Changzhou
213164, China
b College of Chemistry, Xiangtan University, Key Lab of Environment-Friendly Chemistry and Application in Ministry of Education, Xiangtan 411105, China
c College of Chemistry and Molecular Sciences, Wuhan University, Wuhan 430072, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel dendrimer-like blue-emitting dinuclear cyclometalated iridium (III) complexes, namely
(DNaTPA)2DBF(FIrpic)2 and (DPyTPA)2DBF(FIrpic)2, have been successfully synthesized and character-
ized. In which FIrpic is an iridium (III) bis[(4,6-difluorophenyl)pyridinato-N,C20]picolate blue-emitting
phosphorescent chromophore core, DBF is a 2,7-diphenyl-9H-fluorene bridging core, DNaTPA and
DPyTPA are deep blue-emitting fluorescent chromophores composed by rigid high-triplet-energy den-
drons of triphenylamine-functionalized naphthalene or pyrene units, and the peripheral dendrons are
connected with the ancillary ligand of the emitting core through nonconjugated ether linkage. Their
photophysical, thermal, electrochemical, as well as electrophosphorescent properties were primarily
studied. Both iridium (III) complexes exhibit high efficient blue emission in solution (38.5% and 19.2%)
and a typical FIrpic emission in 1,3-bis(N-carbzolyl)benzene (mCP) matrix (27.0% and 24.1%). Simple
bilayer phosphorescent organic light-emitting diodes (PHOLEDs) with a configuration of ITO/PEDOT:PSS/
mCP:dopants/TmPyPB/Liq/Al achieved high efficiencies of 12.96 cd/A for current efficiency (CE), 6162 cd/
m2 for brightness, 6.22% for external quantum efficiency (EQE), and 3.13 lm/W for power efficiency (PE)
with Commission International de L'Eclairage (CIE) coordinates of (0.19 0.01, 0.35 0.02) at only 2 wt%
blend of (DNaTPA)2DBF(FIrpic)2. (DPyTPA)2DBF(FIrpic)2-doped devices also reach efficiencies of (9.14 cd/
A, 7167 cd/m2, 4.41%, 2.61 lm/W) at the same doping concentration. The results demonstrate that the
introduction of dendritic blue-emitting fluorescent chromophore grafted into the blue phosphorescent
chromosphere core through nonconjugated linkage is an efficient way to achieve high-efficiency sky-
blue emission.
Received 19 October 2017
Received in revised form
5 December 2017
Accepted 8 December 2017
Available online xxx
Keywords:
Electrophosphorescence
Dinuclear iridium (III) complexes
Blue-emitting fluorescent chromophore
Sky blue-emitting phosphorescent
chromophore
OLEDs
© 2017 Published by Elsevier Ltd.
1. Introduction
performance OLEDs in both flat-panel displays and solid-state
lightings. Over the past two decades, various methods have been
High-efficiency blue organic light emitting diodes (OLEDs) act as
a power consumption reducer have been desired to realize high
tried to demonstrate efficient blue OLEDs with both high external
quantum efficiency (EQE) and power efficiency (PE). For example,
in a host/guest doping system, by modifying high triplet energy and
narrow
DEST (energy between singlet and triplet) host materials
(especially some bipolar host,1e10 exciplex co-host systems,11e16
etc.), excitons could strictly confined in the emitting layer (EML),
the electrical balance in the emitting layer can be well tuned, and
the operating voltage of the devices will be also reduced, thus a
series of theoretical limit- breaking blue phosphorescent OLEDs
(PHOLEDs) with a maximum EQE over 30% have been reported.4,16
* Corresponding author. Jiangsu Key Laboratory of Environmentally Friendly
Polymeric Materials, School of Materials Science & Engineering, Changzhou Uni-
versity, Changzhou 213164, China. College of Chemistry, Xiangtan University, Key
Lab of Environment-Friendly Chemistry and Application in Ministry of Education,
Xiangtan 411105, China.
** Corresponding author. College of Chemistry and Molecular Sciences, Wuhan
University, Wuhan 430072, China.
E-mail addresses: liuyu03b@126.com (Y. Liu), guohua.xie@whu.edu.cn (G. Xie).
https://doi.org/10.1016/j.tet.2017.12.018
0040-4020/© 2017 Published by Elsevier Ltd.
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
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2
Y. Liu et al. / Tetrahedron xxx (2017) 1e8
In addition to design host materials, blue-emitting materials act as
the core components in OLEDs which determine device's efficiency
and color purity are crucial important. To fully utilize both singlet
and triplet excitons, and break the 25% internal quantum efficiency
(IQE) limitation in fluorescent OLEDs, some newly-emerging up-
conversion materials with kinds of triplet harvesting processes
such as triplet-triplet annihilation (TTA),17e22 thermally active
delayed fluorescence (TADF),15,23e27 hybrid local and charge
transfer (HLCT),28e31 and triplet-polaron interaction (TPI)32,33 have
also been used in high-efficiency blue OLEDs. And very recently, a
spiroacridine-triazine hybrid sky-blue TADF emitter achieved a
recorded EQE of nearly 37% in conventional planar OLED
structures.23
nonconjugated ether link, namely (DNaTPA)2DBF- (FIrpic)2 and
(DPyTPA)2DBF(FIrpic)2, were successfully synthesized and charac-
terized (Scheme 1), in which DBF is 2,7-diphenyl-9H-fluorene blue
fluorescent bridged core, FIrpic is blue phosphorescent core, and
DNaTPA and DPyTPA are naphthalene- and pyrene-functionalized
triphenylamine dendrimers, respectively. As expected, this kind
of molecular structure not only enable complex retain most lumi-
nescence features of FIrpic, but also the bulky structure of fluo-
rescent groups can suppress molecular aggregation at high currents
in device. The influence of dendritic naphthalene and pyrene
groups on the photophysical and electrochemical properties
were systematically investigated, respectively. As results, a single-
emissive-layered (SEL) device with
a
structure of ITO/
By now, the most widely used and efficiently blue OLEDs are
always phosphorescent OLEDs. A typical used phosphorescent
iridium (III) bis(4,6- (difluorophenyl)-pyridinato-N,C20)picolinate
(FIrPic) has been widely applied as the dopant in blue PHOLEDs, by
using various host and exciton blocking materials, quite high EQE of
around 20e30% have already reported in sky blue PHOLEDs,3e12
and even at 1000 cd/m2, some excellent performances still
remain EQE beyond 23.0%.4,6,11,12 However, the optimum doping
concentration of FIrPic-doped blue PHOLEDs was generally 10%e
20%, which means a costly device manufacturing, and the quantum
efficiency of such materials always dropped sharply at high lumi-
nance, except for some well-designed complicated device struc-
tures. So, it is urgently required to develop some other high efficient
blue PHOLEDs. One successful approach to control efficiency roll-
off is to develop phosphorescent dendrimer materials, for the
purpose of preventing self-aggregation or providing charge trans-
porting properties through peripheral moieties.34e39 Wang et al.
reported an efficient self-host blue-emitting iridium (III) den-
drimer, which have the second-generation oligocarbazole as the
dendrons and through a non-conjugated chain bridged with
Ir(dfppy)3 core, the non-doped device based on this iridium (III)
complex exhibited a EQE of 15.3% along with CIE coordinates of
(0.16, 0.29), which is even superior to the corresponding doped
devices.34 Samuel et al. obtained a kinds of blue phosphorescent
dendrimer where twisted biphenyl-based dendrons are attached to
the saturated blue emissive phenyl triazole-based iridium (III) core,
quite high solution photoluminescence (PL) quantum yield of 94%
was achieved. Unfortunately, for the relative lower triplet energies
for ETL materials, excitons will be formed near the EML/ETL inter-
face and easily quenched, hence the maximum EQE was only
reached to 3.9% in bilayer devices.35 Samuel et al. reported a den-
drimer contains ethylhexyloxy surface group, biphenyl-based
dendrimers with a FIrpic core, the bilayer devices have maximum
EQE of 10.4% and maximum power efficiencies (PE) of 11.0 lm/W,
the efficiencies are even higher than those more complicated
evaporated device structures that contain FIrpic blended with
mCP.36 Huang et al. reported a series of nonconjugated dendritic
iridium (III) complex based on tunable pyridine based ligands,
interestingly, the introduction of the nonconjugated dendrons
improved the solid-state luminescence quantum efficiencies of the
iridium complexes in the case of no significantly alter the emissive
wavelengths of the iridium core, and a highest EQE of 12.8% was
achieved in its doped green PLEDs.38 Although such materials
provided an efficient way to overcome device' efficiency roll-off at
high currents, however, most of the phosphorescent dendrimer are
also performed at high doping concentration or even non-doped
devices, there is still much room to improve device's properties
to achieve a much simpler, high efficiency, and low optimum
doping concentration blue PHOLEDs.
PEDOT:PSSS/mCP:(DA)2DNaTPBF(FIrpic)2/TmPyPB/Liq/Al shows a
maximum CE of 12.96 cd/A, a brightness of 7356 cd/m2, a EQE of
6.22% and a PE of 3.13 lm Wꢀ1 along with CIE coordinates of
(0.19
0.01, 0.35
0.02) at the dopant concentration of 2 wt%.
Meanwhile, at the same doping concentration, the pyrene-
substituted analogues (DPyTPA)2DBF(FIrpic)2 exhibited device
performances of 9.14 cd/A, 7167 cd/m2, 4.41% and 2.61 lm/W with
CIE coordinates of 0.19 0.01, 0.33 0.02. Besides, both devices
show no obvious efficiencies roll-off at high currents. The results
indicate that grafting dendrons blue-emitting fluorescent chro-
mophore into the dinuclear iridium (III) complexes through
nonconjugated ether link is an efficient way to achieve high-
efficiency sky-blue emission in PHOLEDs.
2. Result and discussion
2.1. Thermal properties
The thermogravimetric analyses (TGA) curves of (DNaT-
PA)2DBF(FIrpic)2 and (DPyTPA)2DBF(FIrpic)2 under nitrogen atmo-
sphere are depicted in Fig. 1, and the corresponding data are listed
in Table 1. The decomposition temperature (Td) of 341.0 ꢁC for
(DNaTPA)2DBF(FIrpic)2 and 322.0 ꢁC for (DPyTPA)2DBF(FIrpic)2 are
observed at 5% weight loss, respectively, which means such the
non-conjugated configurations dendron iridium (III) complexes
exhibit good thermal stability and can be applied for using in
OLEDs.
2.2. Optical properties
The photophysical properties of (DNaTPA)2DBF(FIrpic)2 and
(DPyTPA)2DBF- (FIrpic)2 were detected by using ultravioletevisible
(UVevis) and photoluminescence (PL) spectrometers. Fig. 2 depicts
the UVevis absorption and PL spectra of the complexes in dilute
DCM solution and in mCP matrix at RT, the corresponding values
are summarized in Table 1. As shown in Fig. 2, (DNaTPA)2DBF(-
FIrpic)2 shows a wide absorption band peaks at 331 nm which
could be ascribed to the
p-p* electron transitions of molecular
backbone, and some intramolecular charge transfer character to a
certain extent. The weak absorption bands in the region of
380e450 nm is originated from the spin-allowed singlet as well as
spin-forbidden triplet metal-to-ligand charge transfer (1MLCT and
3MLCT) of the FIrpic portion.43 Meanwhile, (DPyTPA)2DBF(FIrpic)2
exhibits a similar absorption profile peaks at 341 nm, and a higher-
energy absorption band peaks at 278 nm could be ascribed to the
spin-allowed
p-p
* electron transition of the pyrene unit,40 an
enhanced absorption band at lower-energy could be ascribed to the
FIrpic emission as well as the charge transfer of the more delo-
calized DPyTPA chromophore.42 The additional absorption band
from the DPyTPA is available to improve energy-transfer from the
host matrix to (DPyTPA)2DBF(FIrpic)2 in OLEDs.44 Furthermore, the
In this article, two sky-blue phosphorescent dinuclear iridium
(III) complexes grafted with naphthalene- or pyrene-functionalized
triphenylamine blue-emitting fluorophore dendrimer through a
optical energy gap (Egopt
)
of (DNaTPA)2DBF(FIrpic)2 and
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Y. Liu et al. / Tetrahedron xxx (2017) 1e8
3
Scheme 1. Synthetic routes of the iridium (III) complexes.
(DPyTPA)2DBF(FIrpic)2 were evaluated from the onset of their ab-
sorption spectra, and estimated to be 3.18 and 2.82 eV, respectively.
Under opto-excitation at 298 K, the PL peaks at 440 and 483 nm
with a full width at half-maximum (FWHM) of 76 and 47 nm, and
luminescence quantum yield (Fp) of 38.5% and 19.2% were obtained
for (DNaTPA)2DBF(FIrpic)2 and (DPyTPA)2DBF(FIrpic)2 in dilute
DCM solution, respectively. When doped in mCP matrix, both
iridium (III) complexes show typical FIrpic emission peaks at
470 nm with a low vibronic shoulder,45 and the Fp values remain
still as high as 27.0% and 24.1%, respectively. Compared to that in
dilute DCM solution, (DNaTPA)2DBF(FIrpic)2-doped film shows a
more than 30 nm red-shift, which may be caused by a motional
relaxation of the excited-state geometry and largely be affected by
the rigidity of the matrix.43,46 Furthermore, the accompanying
decreased Fp of (DNaTPA)2DBF(FIrpic)2 in solid film should be
attributed an energy lose that towards to a longer emission wave
(energy gap law). Also, the increased Fp value of (DPyTPA)2DBF(-
FIrpic)2 than that of (DNaTPA)2DBF(FIrpic)2-doped in mCP matrix
illustrates there exists stronger intermolecular interactions of the
chromophore core in (DNaTPA)2DBF(FIrpic)2 than that in the larger
bulk structure of DPyTPA substitutes.35 Meantime, in the long
wavelength region, both iridium (III) complexes display a shorter
tails in comparison to the FIrpic,48 which is mainly due to the
molecular accumulation decreases, and then can effectively inhibit
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
fluorene core and blue fluorescence chromospheres, Tetrahedron (2017), https://doi.org/10.1016/j.tet.2017.12.018

4
Y. Liu et al. / Tetrahedron xxx (2017) 1e8
Fig. 2. UVevis absorption and PL spectra of (DNaTPA)2DBF(FIrpic)2 (a) and (DPyT-
PA)2DBF(FIrpic)2 (b) in CH2Cl2 solution (1.0 ꢂ 10ꢀ5 M) and mCP host at 298 K.
Fig. 1. TGA curves of the iridium (III) complexes under a stream of nitrogen with a
scanning rate of 20 ꢁC/min.
the intermolecular interactions. This implies that incorporating
large steric aromatic units into the binuclear iridium (III) complexes
can suppress the aggregation and are suitable emitting candidates
in blue electroluminescent devices.
2.3. Electrochemical properties
Electrochemical behaviors of the iridium (III) complexes were
investigated by cyclic voltammetry measurements, and the
resulting electrochemical data are summarized in Table 1. As shown
in Fig. S2, both complexes shows bimetallic oxidation possess, and
the oxidation potential of (DPyTPA)2DBF(FIrpic)2 is much lower
than that of (DNaTPA)2DBF(FIrpic)2, which was caused by the
stronger electron donating ability of pyrene. The HOMO levels were
estimated from the onset oxidation potentials, and measured to
be ꢀ5.58 and ꢀ5.41 eV for (DNaTPA)2DBF(FIrpic)2 and (DPyT-
PA)2DBF(FIrpic)2, respectively. No reduction peaks were observed
in CV measurements during negative scan. The LUMO energy levels
were calculated by using the formula of ELUMO ¼ EHOMO þ Eogpt
estimated to be ꢀ2.40 eV and ꢀ2.59 eV, respectively. The smaller
optical band gap of (DPyTPA)2DBF(FIrpic)2 was caused by a larger
electronic delocalization with a large conjugated pyrene group.
Also, an observed large current intensity increase of (DPyT-
PA)2DBF(FIrpic)2 in comparison with that of (DNaTPA)2DBF
(FIrpic)2 at the oxidation possess illustrate the larger steric aromatic
units can efficiently support the transport of electronic charges.47
Compared to the FIrpic,48 introducing conjugated fluorophore
units through unconjugated ether linkage grafting with iridium (III)
complexes can somewhat lower EHOMO and ELUMO energy levels.
Fig. 3. Device structure and energy level diagram of the PHOLEDs.
2.4. Electroluminescence properties
To evaluate the electroluminescent (EL) performance of the both
iridium (III) complexes, single emitting layered OLEDs were fabri-
cated with a configuration of ITO/PEDOT:PSS (40 nm)/iridium (III)
complex (x wt%): mCP (40 nm)/TmPyPB (40 nm)/Liq (1 nm)/Al
(100 nm). Fig. 3 shows the device structure and energy diagrams, in
which ITO and Al were used as anode and cathode, PEDOT:PSS and
Liq serve as the hole-injection and electro-injection layer, respec-
tively. TmPyPB was used as the hole/exciton-blocking layer, and
mCP doped with x wt% of the iridium (III) complexes was spin-
Table 1
Physical, electrochemical and thermal properties of (DNaTPA)2DBF(FIrpic)2 (a) and (DPyTPA)2DBF(FIrpic)2 (b).
Material
alUV [nm]
alPL [nm]
aFp [%]
blPL [nm]
bFp [%]
cEox (V)
dEogpt (eV)
eHOMO (eV)
fLUMO (eV)
Td (ꢁC)
a
b
331
278, 341
440
483
38.5
19.2
474,499
471,498
27.0
24.1
0.78
0.61
3.18
2.82
ꢀ5.58
ꢀ5.41
ꢀ2.40
ꢀ2.59
341
322
a
Measured in DCM solution.
Measured in mCP matrix.
b
c
d
e
f
Oxidation Potential values are obtained by cyclic voltammetry versus Fc/Fcþ
.
Optical energy band gaps were estimated from the absorption edge by using the equation: Eogpt ¼ 1240/lonset
.
Estimated from the Oxidation Potentials, EHOMO ¼ ꢀ4.8ꢀEox
ELUMO ¼ EHOMO þ Eg.
.
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Y. Liu et al. / Tetrahedron xxx (2017) 1e8
5
coated to form a blue-emitting layer, where the dopant concen-
trations of the iridium (III) complexes varied from 2 to 20 wt%.
The EL spectra of (DNaTPA)2DBF(FIrpic)2- and (DPyTPA)2DBF(-
FIrpic)2- doped devices with different concentrations from 2 to
20 wt% are shown in Fig. 4, respectively, and their corresponding
values are summarized in Table 2. Compared to their PL spectra,
these EL emission performs mainly the intrinsic emissions of FIrpic
chromophore, and the naphthalene or pyrene functionalized tri-
phenylamine dendron seem do not alter the emissive wavelengths
of the FIrpic core. With increasing of dopant concentrations, an
emission shoulder at 497 nm increased, which lead to the color
coordinates vary from sky-blue to greenish. Since the mCP host
exhibit hole transport property where the charge recombination
will occur near the EML/ETL interface,48,49 and the increased
emission shoulder is mainly caused by the intermolecular in-
teractions of dopant materials as well as charge recombination
zone shifts to HTL side as the more component of dopant domi-
nated in EML.1,50 Meanwhile, the EL spectra were very stable at
various voltages from 12 to 18 V as shown in Figs. S3 and S4, and
their EL spectra are almost identical to their PL in films, implying
that the EL emissions derived from the emissive layers, and excimer
or exciplex species were inhibited effectively.
characteristics of these devices are shown in Fig. 6. The optimized
doping concentration of complexes is 2 wt%, and at high doping
concentration of 20 wt%, efficiencies are largely reduced by con-
centration quenching.51 As shown in Fig. 6a, when at 2 wt% dopant
concentration, (DNaTPA)2DBF(FIrpic)2-based devices show the
highest efficiencies with maximum EQE of 6.22%, CE of 12.96 cd Aꢀ1
,
and PE of 3.13 lm Wꢀ1. Meanwhile, the (DPyTPA)2DBF(FIrpic)2-
based device performances were presented in Fig. 6b, and show
maximum efficiencies of 9.14 cd/A for LE, 2.61 lm/W for PE, and
6.22% for EQE at 2 wt% doping concentration. The higher effi-
ciencies of (DNaTPA)2DBF(FIrpic)2-based device correspond well
with the higher quantum yields. The lower efficiency roll-off of the
(DPyTPA)2DBF(FIrpic)2-based device can be observed, remains as
high as 6.38 cd Aꢀ1 at a current density of 100 mA cmꢀ2, which is
due to the larger bulk structure of DPyTPA unit that effectively
suppress molecular aggregation at high currents. These results
demonstrate that by grafting suitable blue fluorophore into blue
phosphorescent materials through nonconjugated ether linkage is
an efficient way to acquire excellent blue-OLEDs.
3. Conclusions
The current densityevoltageeluminance (J-V-L) characteristics
of the (DNaTPA)2DBF(FIrpic)2- and (DPyTPA)2DBF(FIrpic)2-doped
devices at various dopant concentrations from 2 to 20 wt% are
shown in Fig. 5. With increasing dopant concentrations from 2 to
6 wt%, all devices exhibit an increased brightness and turn-on
voltage, but reduce with increasing concentrations from 6 to
20 wt%. The highest brightness of 7356 and 8077 cd/m2 were
achieved from the (DNaTPA)2DBF(FIrpic)2- and (DPyTPA)2DBF(-
FIrpic)2-doped devices at 6 wt% doping concentration, respectively.
Furthermore, the (DPyTPA)2-DBF(FIrpic)2-based devices exhibit
much lower driving voltages at various dopant concentrations than
that of the devices based on (DNaTPA)2DBF(FIrpic)2, however, a
larger LUMO gap between mCP and (DPyTPA)2DBF(FIrpic)2 would
render the electrons injection more difficult. So, there must exist
another charge transfer channel here to alter this trend. From the J-
In summary, two novel efficient sky-blue emissive iridium (III)
complexes are obtained by simultaneous incorporation of iridium
(III) complexes and dendritic blue fluorophore units wired by
nonconjugated ether linkage. Both complexes show excellent
thermal stability, solubility and typical FIrpic emission in mcp
matrix. On the basis of such a guest molecule of (DNaTPA)2DBF(-
FIrpic)2, high efficient and stable sky-blue PHOLEDs were fabricated
and exhibit maximum efficiencies of 12.96 cd/A for CE, 3.13 lm/W
for PE, and 6.22% for EQE with CIE coordinates of (0.19, 0.34) at a
2 wt% doping concentration. While (DPyTPA)2DBF(FIrpic)2-doped
devices also reach efficiencies of (9.14 cd/A, 7167 cd/m2, 4.41%,
2.61 lm/W) at the same doping concentration. This work demon-
strates an efficient approach to achieve high-efficiency sky blue
PHOLEDs by choosing proper dendritic blue-emitting fluorophore
chromosphere grafted with iridium (III) complexes.
€
V character, we can find there also exist Forster or Dexter energy
transfer channel from the host exciton to the guest, and both the
triplet states of FIrpic portion and DPyTPA portion may make
contributions to various energy transfer channels that reduce the
turn-on voltage.
For comparison, the device performances are summarized in
Table 2 and the efficiency-current density (EQE, PE, and CE-J)
4. Experimental section
4.1. General information
1H and 13C NMR spectra were measured with a Bruker Dex-400
NMR instrument using CDCl3 as a solvent. Purification and a spin
coating process were carried out under ambient conditions. Mass
spectra (MS) were recorded on a Bruker Autoflex MALDI-TOF in-
strument using dithranol as a matrix. Elemental analysis was per-
formed on
a Harrios elemental analysis instrument. The
thermogravimetric analysis (TGA) was undertaken using
a
NETZSCH STA449 measurement under nitrogen atmosphere at a
heating rate of 20 ꢁC minꢀ1. The ultravioletevisible (UVevis) ab-
sorption and photoluminescence (PL) spectra of the compound
were recorded on a Varian Cray 50 and Perkin-Elmer LS50B lumi-
nescence spectrometer, respectively. Absolute quantum yields
(PLQY) were recorded on a Horiba Fluoromax 4P provided with the
Quanta-4 integration sphere. The optical band gap (Eg) energy level
was estimated from the onset of the absorption edge. Cyclic vol-
tammetry (CV) measurements were performed on a CHI600E
electrochemical workstation with platinum as the working elec-
trode, platinum wire as the counter electrode, and KCl saturated Ag/
AgCl as the reference electrode at a 100 mV sꢀ1 scanning rate.
Tetrabutylammonium hexafluorophosphate (BU4NPF6, 0.10 M) was
used as the supporting electrolyte in acetonitrile solvent. Standard
ferrocenium/ferrocene (Fcþ/Fc) system was used to calibrate the
experiment data.
Fig. 4. EL spectra of (DNaTPA)2DBF(FIrpic)2 (a) and (DPyTPA)2DBF(FIrpic)2 (b)-doped
devices with different dopant concentrations from 2 wt% to 20 wt%.
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
fluorene core and blue fluorescence chromospheres, Tetrahedron (2017), https://doi.org/10.1016/j.tet.2017.12.018

6
Y. Liu et al. / Tetrahedron xxx (2017) 1e8
Table 2
EL parameters of (DNaTPA)2DBF(FIrpic)2 (a) and (DPyTPA)2DBF(FIrpic)2 (b)-doped PLEDs.
Dopant
a
(wt%)
Lmax [cd/m2]
LE [cd/A]
PE [lm/W]
EQE [%]
CIE [x, y]
Device performance at 100 cd mꢀ2
Voltage [V]
LE [cd Aꢀ1
]
PE [lm Wꢀ1
]
EQE [%]
2
6
12
20
2
6
12
20
6162
7356
5391
3309
7167
8077
6738
5240
12.96
8.38
5.53
4.70
9.14
8.13
5.76
4.23
3.13
1.75
1.15
1.23
2.61
2.00
1.40
1.33
6.22
3.78
2.44
2.01
4.41
3.77
2.58
1.86
(0.19, 0.34)
(0.19, 0.36)
(0.19, 0.37)
(0.20, 0.39)
(0.19, 0.33)
(0.18, 0.34)
(0.19, 0.36)
(0.19, 0.37)
12.7
14.3
12.7
11.8
11.2
12.2
11.0
9.6
4.74
5.88
4.36
2.74
4.91
6.38
4.67
3.42
0.81
0.96
0.70
0.46
0.92
1.08
0.87
0.68
2.24
2.63
1.88
1.14
2.35
2.94
2.11
1.46
b
13
4.2. Device fabrication and characterization
NMR, C NMR, MALDI-TOF mass spectra and elemental analysis
(Fig. S1, see ESI).
The OLED were fabricated on indium tin oxide (ITO)-coated
glass substrates with a sheet resistance of 10 /square. The ITO
U
4.3.1. Synthesis of 4
surface was pre-cleaned in an ultrasonic solvent bath, and dried in
an oven at 120 ꢁC for more than 3 h, then treated with UV ozone for
15 min. After that, the substrates were transferred to the spin-
coating process, and then different functional layers (PEDOT: PSS
layer and emissive layer) were sequentially spin-coated onto the
substrates and were dried in vacuum. Then the samples were
transferred to the deposition system, and TmPyPB and Liq/Al layers
were sequentially deposited onto the substrate by thermal depo-
sition in the vacuum of 10ꢀ6 Torr. The devices were fabricated with
a configuration of ITO/PEDOT:PSSS/mCP:dopants/TmPyPB/Liq/Al.
The electroluminescent (EL) spectra were measured by a PR650
spectrometer. The current density-voltage-brightness (J-V-R) fea-
tures of the OLEDs were measured with a Keithey 2400 Source
meter and Konica Minolta chroma meter CS-200 with a calibrated
silicon photodiode. The EQEs values were calculated from the cur-
rent densities, current efficiencies, and the corresponding EL
spectra. All measurements were carried out at room temperature
(RT) under ambient conditions.
Synthetic method as the synthesis of the compound 5, and
obtain a white solid (71.1%). 1H NMR (400 MHz, CDCl3, TMS),
d
(ppm): 8.04 (d, J ¼ 7.9 Hz, 2H), 7.91 (d, J ¼ 7.5 Hz, 2H), 7.85 (d,
J ¼ 8.0 Hz, 2H), 7.55e7.42 (m, 12H), 7.34e7.28 (m, 8H), 4.50 (s, 2H),
3.54 (t, J ¼ 6.4 Hz, 2H), 3.41 (t, J ¼ 6.8 Hz, 2H), 1.90e1.85 (m, 2H),
1.69e1.64 (m, 2H), 1.47e1.44 (m, 4H).
4.3. Materials and synthesis
Unless otherwise stated, all solvents were carefully dried and
distilled prior to use, commercially available reagents were direct
used without any further purification. The synthesis route is shown
in Scheme 1, and compound of 1, 2, 3 and 5 was prepared according
to the literature procedures.40e42 The new compounds and target
1
complexes in this contribution were fully characterized with
H
Fig. 6. The Current density-Efficiencies (J-CE, PE, and EQE) curves of (DNaTPA)2DBF(-
FIrpic)2 (a) and (DPyTPA)2DBF(FIrpic)2 (b)-doped devices at different dopant
concentrations.
Fig. 5. Current density-voltage-luminescence (J-V-L) curves of (DNaTPA)2DBF(FIrpic)2
(a) and (DPyTPA)2DBF(FIrpic)2 (b)-doped devices at different concentrations.
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
fluorene core and blue fluorescence chromospheres, Tetrahedron (2017), https://doi.org/10.1016/j.tet.2017.12.018

Y. Liu et al. / Tetrahedron xxx (2017) 1e8
7
4.3.2. Synthesis of 6b
J ¼ 8.0 Hz, 4H), 7.90 (d, J ¼ 7.5 Hz, 4H), 7.84 (d, J ¼ 7.9 Hz, 4H), 7.67
(d, J ¼ 8.1 Hz, 2H), 7.58e7.45 (m, 24H), 7.40 (d, J ¼ 8.3 Hz, 8H), 7.35
(d, J ¼ 4.3 Hz, 2H), 7.28 (t, J ¼ 8.4 Hz, 12H), 7.23 (d, J ¼ 2.4 Hz, 6H),
6.97 (d, J ¼ 8.4 Hz, 4H), 4.38 (s, 2H), 4.05e3.96 (m, 14H), 3.37 (t,
J ¼ 6.5 Hz, 4H), 2.05e2.01 (m, 4H), 1.86e1.82 (m, 8H), 1.57e1.50 (m,
8H), 1.45e1.42 (m, 4H), 1.16e1.10 (m, 8H), 0.73 (s, 4H).$13C NMR
A mixture of 5 (2.07 g, 3.0 mmol), 2,7-dibromo-9H-fluorene
(0.49 g, 1.5 mmol), a catalytic amount of tetrabutylammonium
bromide, 8 mL of 50% KOH aqueous solution and 30 mL toluene was
refluxed for 24 h under nitrogen atmosphere. The reaction mixture
was poured into water and extracted with dichloromethane (DCM),
the organic layer was dried over anhydrous magnesium sulfate
(MgSO4) and filtered. The solvent was removed off by rotary
evaporation and the residue was purified by silica gel column
chromatography using DCM/petroleum ether (PE) (1/2; v/v) as
eluent to obtain a white solid (1.65 g, 71.1%).
(100 MHz, CDCl3, TMS),
d (ppm): 165.30, 158.64, 155.02, 151.46,
147.02, 146.97, 140.94, 139.96, 139.64, 135.01, 134.18, 133.98, 133.69,
131.75, 130.96, 128.99, 128.35, 128.18, 127.46, 126.93, 126.88, 126.13,
125.99, 125.78, 125.65, 125.47, 124.81, 123.62, 121.04, 119.91, 114.90,
72.57, 70.61, 69.05, 67.95, 52.48, 40.56, 29.94, 29.92, 29.67, 29.25,
28.94, 25.87, 25.81, 25.69, 23.88. MALDI-TOF MS (m/z) for
1H NMR (400 MHz, CDCl3, TMS),
7.91 (d, J ¼ 7.4 Hz, 4H), 7.85 (d, J ¼ 8.0 Hz, 4H), 7.55e7.40 (m, 30H),
7.29e7.24 (m, 16H), 4.42 (s, 4H), 3.40 (t, J ¼ 6.5 Hz, 4H), 1.94e1.90
(m, 4H), 1.47e1.42 (m, 4H), 1.16e1.09 (m, 8H), 0.59 (s, 4H). MALDI-
d
(ppm): 8.04 (d, J ¼ 8.0 Hz, 4H),
C
141H130N4O10, Calcd: 2038.979, Found, 2062.260 [MþNa]þ.
4.3.7. Synthesis of 8a
TOF MS (m/z) for
1542.858.
C
103H86Br2N2O2, Calcd: 1542.504, Found,
Synthetic method as the synthesis of 8b, and obtain a yellow
solid (61.6%). 1H NMR (400 MHz, CDCl3, TMS),
d (ppm): 8.32 (d,
J ¼ 9.2 Hz, 4H), 8.28e8.13 (m, 14H), 8.09e7.99 (m, 20H), 7.70 (d,
J ¼ 8.2 Hz, 2H), 7.57e7.49 (m, 16H), 7.37 (d, J ¼ 8.3 Hz, 8H), 7.29 (d,
J ¼ 6.4 Hz, 10H), 7.19 (d, J ¼ 8.3 Hz, 2H), 6.94 (d, J ¼ 8.4 Hz, 4H), 4.40
(s, 4H), 3.93 (d, J ¼ 9.5 Hz, 14H), 3.37 (t, J ¼ 6.4 Hz, 4H), 2.03 (d,
J ¼ 6.3 Hz, 4H), 1.76 (s, 8H), 1.47e1.44 (m, 12H), 1.16e1.10 (m, 8H),
4.3.3. Synthesis of 6a
Synthetic method as the synthesis of 6b, and obtain a yellow
solid (62.6%). 1H NMR (400 MHz, CDCl3, TMS),
d
(ppm): 8.32 (d,
J ¼ 9.2 Hz, 4H), 8.23e8.16 (m, 12H), 8.08e7.99 (m, 20H), 7.57 (d,
J ¼ 8.1 Hz, 8H), 7.47e7.32 (m, 22H), 4.43 (s, 4H), 3.40 (t, J ¼ 6.3 Hz,
4H),1.94e1.90 (m, 4H),1.54e1.44 (m, 4H),1.16e1.08 (m, 8H), 0.60 (s,
4H). MALDI-TOF MS (m/z) for C127H94Br2N2O2, Calcd: 1838.566,
Found, 1838.742.
0.74 (s, 4H). 13C NMR (100 MHz, CDCl3, TMS),
d (ppm): 165.25,
158.62, 155.03, 151.47, 146.99, 140.85, 139.63, 139.08, 137.47, 135.40,
134.13, 133.83, 131.58, 131.54, 131.08, 130.47, 129.10, 128.52, 128.19,
127.70, 127.49, 127.44, 127.36, 126.92, 126.05, 125.66, 125.45, 125.13,
125.10, 125.04, 124.99, 124.82, 124.79, 123.74, 121.02, 120.93, 119.95,
114.86, 72.58, 70.60, 68.90, 67.89, 52.53, 40.58, 30.39, 29.93, 29.67,
29.21, 28.87, 25.88, 25.78, 25.65, 23.89. MALDI-TOF MS (m/z) for
4.3.4. Synthesis of 7b
A mixture of compound 6b (1.20 g, 0.78 mmol), 4-(4,4,5,5-
tetramethyl-1,3,2-dioxaborolan-2-yl)phenol (0.34 g, 1.56 mmol),
Pd(PPh3)4 (48 mg, 0.042 mmol) and potassium carbonate (2 M,
10 mL) in 40 mL tetrahydrofuran (THF) was refluxed for 24 h under
nitrogen atmosphere. After cooled to room RT, the reaction mixture
was poured into water and extracted with DCM. The organic layer
was dried over anhydrous MgSO4 and filtered. The solvent was
removed off by rotary evaporation and the residue was purified by
silica gel column chromatography using DCM/THF (40/1; v/v) as
eluent to obtain a white solid (0.78 g, 63.9%). 1H NMR (400 MHz,
C
165H138N4O10, Calcd: 2335.041, Found, 2335.152 [M]þ, 2358.113
[MþNa]þ.
4.3.8. Synthesis of 9b
A mixture of 8b (0.31 g, 0.15 mmol), NaOH (a.q. 5%, 5 mL),
anhydrous methanol (10 mL) and THF (10 mL) was refluxed for 4 h
under nitrogen atmosphere. After cooled to room temperature, the
mixture was poured into water and acidized to pH ¼ 2 with dilute
hydrochloric, and then extracted with DCM. The organic layer was
dried over anhydrous MgSO4 and filtered. The filtrate was evapo-
rated to remove the solvent, and gain a yellow solid (0.29 g, 97.8%).
It was applied directly to the next step without further purified.
CDCl3, TMS),
d
(ppm): 8.03 (d, J ¼ 8.0 Hz, 4H), 7.90 (d, J ¼ 7.7 Hz, 4H),
7.84 (d, J ¼ 8.0 Hz, 4H), 7.68 (d, J ¼ 8.2 Hz, 2H), 7.54e7.45 (m, 24H),
7.40 (d, J ¼ 8.2 Hz, 8H), 7.27e7.23 (m, 16H), 6.85 (d, J ¼ 8.2 Hz, 4H),
4.82 (s, 2H), 4.38 (s, 4H), 3.36 (t, J ¼ 6.4 Hz, 4H), 2.03e1.99 (m, 4H),
1.45e1.42 (m, 4H), 1.11e1.08 (m, 8H), 0.71 (s, 4H). MALDI-TOF MS
(m/z) for C115H96N2O4, Calcd: 1568.737, Found, 1568.929.
4.3.9. Synthesis of 9a
Synthetic method as the synthesis of 9b, and obtain a grey white
solid (98.7%).
4.3.5. Synthesis of 7a
Synthetic method as the synthesis of 7b, and obtain a yellow
4.3.10. Synthesis of (DNaTPA)2DBF(FIrpic)2
solid (46.6%). 1H NMR (400 MHz, DMSO, TMS),
d
(ppm):9.50 (s, 2H),
A mixture of 9b (115 mg, 0.11 mmol), Ir(dfppy)2(m-Cl)2 (267 mg,
8.29 (t, J ¼ 7.6 Hz, 8H), 8.24e8.18 (m, 16H), 8.11e7.98 (m, 12H), 7.71
(d, J ¼ 7.8 Hz, 2H), 7.57e7.44 (m, 16H), 7.27e7.17 (m, 16H), 6.82 (d,
J ¼ 8.3 Hz, 4H), 4.25 (s, 4H), 3.17 (t, J ¼ 5.8 Hz, 4H), 1.99 (s, 4H),
1.21e1.16 (m, 4H), 0.93e0.87 (m, 4H), 0.53 (s, 4H). MALDI-TOF MS
(m/z) for C139H104N2O4, Calcd: 1864.800, Found, 1864.841.
0.22 mmol) and sodium carbonate (93 mg, 0.88 mmol) were stirred
in 2-ethoxyethanol (15 mL) and DMF (5 mL) under N2 atmosphere
at 90 ꢁC for 24 h. After cooled to RT, the mixture was poured into
water and extracted with DCM. The organic layer was dried over
anhydrous MgSO4 and filtered. The solvent was removed off by
rotary evaporation and the residue was purified by silica gel column
chromatography using DCM/THF (10/1; V/V) as eluent to obtain
(DNaTPA)2DBF(FIrpic)2 as an orange solid (88 mg, 48.9%). 1H NMR
4.3.6. Synthesis of 8b
A mixture of 7b (0.50 g, 0.32 mmol), methyl 3-(6-bromo- hex-
yloxy)picolinate (0.40 g, 1.28 mmol), cesium carbonate (0.82 g,
2.5 mmol) in THF (15 mL) and acetone(15 mL) was refluxed for 24 h
under nitrogen atmosphere. After cooled to room temperature, the
reaction mixture was poured into water and extracted with DCM.
The organic layer was dried over anhydrous MgSO4 and filtered.
The solvent was removed off by rotary evaporation and the residue
was purified by silica gel column chromatography using DCM/THF
(20/1; v/v) as eluent to obtain a white solid (0.52 g, 79.8%). 1H NMR
(400 MHz, CDCl3, TMS),
d
(ppm):8.80 (d, J ¼ 4.9 Hz, 2H), 8.27e8.20
(m, 4H), 8.03 (d, J ¼ 7.7 Hz, 4H), 7.91e7.83 (m, 8H), 7.75e7.68 (m,
6H), 7.52e7.39 (m, 36H), 7.30e7.15 (m, 22H), 6.95 (d, J ¼ 6.8 Hz, 6H),
6.47e6.35 (m, 4H), 5.80 (d, J ¼ 8.2 Hz, 2H), 5.53 (d, J ¼ 8.4 Hz, 2H),
4.37 (s, 4H), 4.09 (t, J ¼ 6.0 Hz, 4H), 3.97 (t, J ¼ 6.4 Hz, 4H), 3.35 (t,
J ¼ 5.5 Hz, 4H), 2.12e1.89 (m, 8H), 1.81 (s, 4H), 1.58e1.49 (m, 8H),
1.44 (s, 4H), 1.12 (s, 8H), 0.72 (s, 4H). 13C NMR (100 MHz, CDCl3,
TMS),
d (ppm):171.12, 165.82, 165.75, 164.47, 164.40, 162.71, 162.58,
(400 MHz, CDCl3, TMS),
d
(ppm): 8.25 (d, J ¼ 3.7 Hz, 2H), 8.04 (d,
161.96, 161.83, 159.36, 158.66, 153.21, 153.14, 153.03, 152.97, 151.45,
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
fluorene core and blue fluorescence chromospheres, Tetrahedron (2017), https://doi.org/10.1016/j.tet.2017.12.018

8
Y. Liu et al. / Tetrahedron xxx (2017) 1e8
148.94,148.02, 147.00, 146.98, 140.43, 140.08, 139.96, 139.67, 139.63,
138.03, 135.01, 134.15, 133.98, 133.73, 131.76, 130.94, 128.97, 128.80,
128.34, 128.15, 127.45, 126.92, 126.11, 125.98, 125.77, 125.64, 125.46,
124.81,123.62,123.26,123.08,122.72,122.53,122.40,122.22,121.02,
119.88, 114.93, 114.69, 114.66, 114.52, 114.49, 114.43, 114.40, 114.26,
114.23, 98.20, 97.94, 97.78, 97.67, 97.51, 97.25, 72.54, 70.60, 69.97,
67.98, 40.53, 29.91, 29.72, 29.64, 29.17, 28.85, 25.90, 25.84, 25.61,
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23.87. MALDI-TOF MS (m/z) for
C183H148F8Ir2N8O10, Calcd:
3155.045, Found, 3155.099. Anal. Calcd for C183H148F8Ir2N8O10: C
69.65, H 4.73, N 3.55. Found: C 69.50, H 4.53, N 3.63%.
4.3.11. Synthesis of (DPyTPA)2DBF(FIrpic)2
Synthetic method as the synthesis of (DNaTPA)2DBF(FIrpic)2,
and obtain a yellow solid (76.9%). 1H NMR (400 MHz, CDCl3, TMS),
d
(ppm): 8.79 (d, J ¼ 5.1 Hz, 2H), 8.32 (d, J ¼ 9.2 Hz, 4H), 8.23e8.15
(m, 16H), 8.08e7.98 (m, 20H), 7.71e7.68 (m, 6H), 7.56 (d, J ¼ 8.0 Hz,
12H), 7.49 (d, J ¼ 7.7 Hz, 4H), 7.43 (d, J ¼ 5.2 Hz, 2H), 7.38e7.33 (m,
6.5 Hz, 10H), 7.29e7.26 (m, 10H), 7.16e7.11 (m, 4H), 6.93 (d,
J ¼ 8.3 Hz, 6H), 6.47e6.34 (m, 4H), 5.79 (d, J ¼ 8.4 Hz, 2H), 5.52 (d,
J ¼ 8.5 Hz, 2H), 4.39 (s, 4H), 4.00e3.90 (m, 8H), 3.37 (t, J ¼ 6.1 Hz,
4H), 2.04 (m, 4H),1.89 (m, 4H),1.75 (m, 4H),1.49e1.44 (m,12H),1.13
ꢀ
(m, 8H), 0.73 (m, 4H). 13C NMR (100 MHz, CDCl3, TMS),
d (ppm):
171.18, 165.77, 165.70, 164.89, 164.77, 164.45, 164.38, 162.72, 162.59,
162.34, 162.21, 161.97, 161.84, 160.14, 160.03, 159.91, 159.32, 158.67,
153.24, 153.17, 153.11, 153.05, 151.50, 148.91, 148.02, 147.03, 146.97,
140.37, 139.93, 139.70, 139.65, 138.05, 138.02, 137.50, 135.43, 134.13,
133.96, 131.60, 131.54, 131.11, 130.50, 129.07, 128.80, 128.55, 128.17,
127.71, 127.50, 127.44, 127.35, 126.05, 125.67, 125.45, 125.16, 125.10,
125.06, 125.00, 124.82, 124.79, 123.75, 123.26, 123.15, 123.06,
122.72, 122.53, 122.41, 122.24, 121.05, 119.94, 114.94, 114.70, 114.68,
114.54, 114.51, 114.46, 114.43, 114.28, 114.26, 98.22, 97.95, 97.80,
97.68, 97.54, 97.27, 72.55, 70.61, 69.84, 67.96, 40.55, 29.91, 29.74,
29.66, 29.16, 28.82, 25.86, 25.83, 25.59, 23.91. MALDI-TOF MS (m/z)
for C207H156F8Ir2N8O10, Calcd: 3451.112, Found, 3451.205. Anal.
Calcd for C207H156F8Ir2N8O10: C 72.02, H 4.56, N 3.25. Found: C
71.88, H 4.37, N 3.49%.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (51273168, 51573154), the Hunan Natural
Science Foundation (2015JJ2139), and the key project of Hunan
Provincial Education Department (13A102).
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Appendix A. Supplementary data
Supplementary data related to this article can be found at
https://doi.org/10.1016/j.tet.2017.12.018.
Please cite this article in press as: Liu Y, et al., High-efficiency blue OLEDs based on dendritic dinuclear iridium (III) complexes grafted with
fluorene core and blue fluorescence chromospheres, Tetrahedron (2017), https://doi.org/10.1016/j.tet.2017.12.018