High-performance and stable warm white OlEds based on orange iridium(III) phosphors modified with simple alkyl groups

Article abstract of DOI:10.1021/acs.organomet.0c00472

Phosphorescent organic light-emitting diodes (OLEDs) with high electroluminescence (EL) efficiency and low efficiency roll-off are urgently required to meet the continuously increasing market need in lighting industry fields. There is an urgent demand for

Full text of DOI:10.1021/acs.organomet.0c00472

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Article
High-Performance and Stable Warm White OLEDs Based on Orange
Iridium(III) Phosphors Modified with Simple Alkyl Groups
Lei Ding, Chun-Xiu Zang, Li−Li Wen, Guo-Gang Shan,* Ying Gao, Hai-Zhu Sun,* Wen-Fa Xie,*
and Zhong-Min Su*
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ABSTRACT: Phosphorescent organic light-emitting diodes (OLEDs) with high
electroluminescence (EL) efficiency and low efficiency roll-off are urgently
required to meet the continuously increasing market need in lighting industry
fields. There is an urgent demand for phosphorescent emitters with excellent
photoluminescence quantum yields (PLQYs) to realize a high EL performance of
OLEDs. In this work, four new orange phosphorescent iridium(III) emitters,
namely Ir-1−Ir-4, were designed and synthesized successfully, in which
functionalized 1,2-diphenylbenzimidazole and conjugated quinoline-benzimida-
zole moieties are employed as the main ligands and ancillary ligands, respectively.
The obtained phosphors show relatively high efficiency and broad full width at
half-maximums (FWHMs) of about 110 nm, which are favorable for constructing
high-quality white OLEDs. The optimized monochromatic orange-emitting
OLED of Ir-1 shows a maximum current efficiency (CE) of 27.2 cd A−1, a power
efficiency of 24.0 lm W−1, and an external quantum efficiency (EQE) of 10.6%. A two-color OLED employing Ir-1 as the orange-
emitting layer shows a maximum brightness of 43980 cd m−2, a CE of 27.7 cd A−1, a PE of 21.8 lm W−1, an EQE of 11.3%, and a low
CE efficiency roll-off ratio of 7.9%. Moreover, this device displays warm white emission with CIE coordinates of (0.39, 0.43) at 7 V
and high color stability with a CIE variation of (0.003, 0.001).
White organic light-emitting diodes (WOLEDs) for lighting
applications have many issues to be addressed so that they can
successfully enter the commercial market.17−22 Usually,
WOLEDs are made up of three colors (red, green, and blue)
or more to cover the whole spectrum and thus have excellent
color rendering indexes (CRI).23−27 However, the short-
comings of complicated multilayer structure, high driving
voltage, and complex synthetic method have severely limited
their applications in the lighting market.24 Consequently,
WOLEDs comprising two colors (orange and blue) exhibit a
greater potential for practical application, owing to the
prominent characteristics of simpler device fabrication, lower
costs, fewer masks, etc.28,29 However, two-color WOLEDs
have higher requirements for the full width at half-maximums
(FWHMs) of the phosphorescent iridium(III) complexes. In
addition, most WOLEDs based on phosphors have suffered
from serious efficiency roll-offs,30 resulting mainly from
triplet−triplet annihilation (TTA),14,31 unbalanced carrier
INTRODUCTION
■
Currently, OLEDs have developed rapidly in the field of large-
area plane display and solid-state lighting owing to their
outstanding features, including flexibility, color tunability, and
low power consumption.1−4 Phosphorescent OLEDs (PHO-
LEDs) based on transition-metal complexes can theoretically
achieve 100% internal quantum efficiency by harvesting singlet
and triplet excitons simultaneously.5−7 Notably, iridium(III)
complexes are the most widely studied phosphorescent
materials for high-performance PHOLEDs because of their
encouraging properties, such as photostability, thermal
stability, flexible color tunability, and short phosphorescence
lifetime.8 Highly efficient red/orange iridium(III) complexes
play an important role in the construction of high-performance
full-color displays and white OLEDs.9 Significant improve-
ments have been achieved in the efficiencies and stability of
green PHOLEDs.10−12 However, the electroluminescence
(EL) performance of red/orange phosphors has still fallen
behind with inferior EL efficiency and efficiency roll-off at high
brightness.13 The photoluminescence quantum yields
(PLQYs) of red/orange phosphorescent emitters tend to be
lower because of their narrow energy gap.14−16 Therefore, it is
desirable to design and synthesize more efficient red/orange
iridium(III) complexes with sufficient luminous efficiency for
high-performance monochromatic OLEDs.
Received: July 12, 2020
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distribution, and field-induced quenching. Furthermore, the EL
spectra for two-color WOLEDs vary markedly under different
driving voltages, leading to a great variation in the Commission
Internationale de l’Eclairage (CIE) coordinates.32 Thus,
efficient two-color WOLEDs with high EL efficiency, low
efficiency roll-off, and good color stability are still highly
desirable but remain a challenge.
RESULTS AND DISCUSSION
■
Syntheses. The iridium(III) complexes were prepared by
the reaction of dichloro-bridged diiridium complex with the
ancillary ligands HBIQ and HBISQ (Scheme 1). All crude
products were purified by silica chromatography. Mass
spectrometry and 1H NMR spectroscopy were used to identify
the structures of iridium(III) emitters (see Figures S1−S4 in
the Supporting Information). In addition, the structures of Ir-
1, Ir-3, and Ir-4 were further confirmed by X-ray
crystallography.
To date, many red/orange iridium(III) emitters have been
used to fabricate excellent performance two-color WOLEDs,
providing many new molecular design concepts.33−35 Recently,
our group reported a new orange iridium(III) complex which
used 2-(1H-benzo[d]imidazol-2-yl)quinoline (HBIQ) with
strong structural rigidity as an ancillary ligand. Using this
complex as an orange dopant, the two-color WOLED achieved
a maximum current efficiency (CE) of up to 22.1 cd A−1 and
maximum power efficiency (PE) of up to 25.5 lm W−1.
However, the two-color WOLED displays serious efficiency
roll-off, which limits its practical application.36 Alkyl
substituents introduced on the main ligand can suppress self-
quenching to some extent, thereby enhancing efficiency and
dropping efficiency roll-off.37 On the basis of the above
discussion, in this work, the four phosphors (mPBI)2Ir(BIQ)
(Ir-1), (tbPBI)2Ir(BIQ) (Ir-2), (mPBI)2Ir(BISQ) (Ir-3), and
(tbPBI)2Ir(BISQ) (Ir-4) using 1-phenyl-2-p-tolyl-1H-benzo-
[d]imidazole (HmPBI) and 2-(4-tert-butylphenyl)-1-phenyl-
1H-benzo[d]-imidazole (HtbPBI) as the main ligands and
rigid 2-(1H-benzo[d]imidazol-2-yl)quinoline (HBIQ) and 1-
(1H-benzo[d]imidazol-2-yl)isoquinoline (HBISQ) as the
ancillary ligand have been designed and characterized (Figure
1). Ir-1 and Ir-2 show high luminous efficiency with PLQYs of
X-ray Crystallographic Analysis. The molecular struc-
tures of Ir-1, Ir-3, and Ir-4 analyzed via X-ray crystallography
of single crystals are illustrated in Figure 2. Single crystals were
grown from a mixed solvent of CH2Cl2 and CH3OH. The
iridium(III) centers of these three complexes are coordinated
with the same two main ligands (HmPBI or HtbPBI) and an
ancillary ligand (HBIQ or HBISQ), resulting in a distorted-
octahedral coordination geometry. In all cases, these molecular
structures contained trans-nitrogen and cis-metalated carbon
dispositions, similarly to the other previously reported
analogous phosphors.38−40 As shown in Table S1 in the
Supporting Information, the Ir1−N1 and Ir1−N3 bond
lengths of all three complexes are slightly shorter than the
Ir1−N5 and Ir1−N6 bond lengths due to the trans disposition
of the main ligands. In addition, the two Ir−C bonds of Ir-3
and Ir-4 have almost the same length, while the Ir1−C21 bond
length is longer than the Ir1−C1 bond length of Ir-1 due to
the influence of the ancillary ligand HBIQ. The bond lengths
of three complexes are given in Table S1 in the Supporting
Information. The detailed crystal data and structure refinement
are summarized in Table S2 in the Supporting Information.
Photophysical Properties. Figure 3 shows the UV−
visible absorption and PL spectra of these four complexes in
dichloromethane solution at room temperature. All complexes
display intense absorption bands between 230 and 350 nm
assigned to π → π* transitions of cyclometalated ligands,26 and
the relatively weak absorption bands above 350 nm are
probably related to the singlet metal to ligand charge transfer
transitions (1MLCT) and spin-forbidden metal to ligand
charge transfer transitions (3MLCT).41,42
At room temperature, the spectra of all phosphors reveal
intense structureless emission bands. The emission maxima of
of Ir-3 and Ir-4 are red-shifted by ∼15 nm in comparison to Ir-
1 and Ir-2, which were observed at 605, 603, 620, and 619 nm,
respectively. Simultaneously, the neat films of four complexes
give featureless and broadened PL spectra centered at 607,
601, 610, and 613 nm, respectively (see Figure S5 in the
Supporting Information). The structureless and broad
emission indicates that the emissive excited states of these
complexes have predominantly 3LLCT and/or 3MLCT
Figure 1. Chemical structures of the four orange emitters studied in
this work.
up to 57.5% and 56.4% in dilute solution, respectively. The
optimized orange-emitting OLED based on Ir-1 exhibits a
maximum CE of 27.2 cd A−1 and an external quantum
efficiency (EQE) of 10.6%. Then, two-color WOLEDs
employing orange emitters were fabricated due to the broad
FWHMs. W1 exhibits warm white emission with CIE
coordinates of (0.39, 0.43) at 7 V and shows a maximum
brightness of 43980 cd m −2, a highest CE of 27.7 cd A−1, a
highest PE of 21.8 lm W−1, and a highest EQE of 11.3%. In
addition, a small efficiency roll-off was achieved in W1.
Interestingly, the device W1 displays excellent color stability
with a CIE variation of (0.003, 0.001) when the driving
voltages were varied from 4 to 6 V.
3
characters rather than LC characters, which often exhibit
vibronically structured emission spectra.43 When Ir-1−Ir-4
were cooled to 77 K, the PL spectra, showing evident blue
shifts relative to their spectra at room temperature, are also
3
structureless, implying that the emissive excited-states LLCT
3
and/or MLCT transitions play a significant role (see Figure
S6 in the Supporting Information).44−46 As shown in Table 1,
the emission lifetimes (τ) for Ir-1−Ir-4 in dichloromethane
solution are 0.73, 1.20, 0.50, and 1.24 μs, respectively.
Emission lifetimes in the microsecond range suggest the origin
of triplet emission. In addition, in degassed dichloromethane,
Ir-1 and Ir-2 exhibit similar PLQYs of 57.5% and 56.4%,
B
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Scheme 1. Synthetic Routes for Designed Iridium(III) Emitters
Figure 2. Single-crystal structures of three complexes with ellipsoids drawn at the 50% probability level: Ir-1 (CCDC no. 1980337), Ir-3 (CCDC
no. 1969397), and Ir-4 (CCDC no. 1980338).
and nonradiative decay rate constants (knr) were determined
and are given in Table 1. kr and knr for Ir-1 are 7.88 × 105 and
5.82 × 105 s−1, for Ir-2 are 4.70 × 105 and 3.63 × 105 s−1, for
Ir-3 are 6.58 × 105 and 13.42 × 105 s−1, and for Ir-4 are 2.58 ×
105 and 5.48 × 105 s−1, respectively.
Theoretical Calculations. To gain insight into the
photophysical properties of all the iridium(III) complexes,
the highest occupied molecular orbital (HOMO) and lowest
unoccupied molecular orbital (LUMO) levels and distributions
of Ir-1−Ir-4 were calculated. As shown in Figure 4, it is found
that all complexes exhibit similar electronic cloud distributions,
indicating that the substituents have a negligible influence on
molecular orbital energy levels and distributions. The LUMOs
of Ir-1−Ir-4 distributed over the ancillary ligand with a slight
extension to the iridium(III) atom, while their HOMOs spread
across the iridium(III) atom, the main ligands, and the
ancillary ligand. The triplet excited states (T1) were calculated
to understand the emission characteristics. As shown in Table
S3, the T1 of Ir-1 and Ir-2 were almost a HOMO → LUMO
transition (90%), and the T1 of Ir-3 and Ir-4 were mainly a
HOMO → LUMO transition (71% for Ir-3, 72% for Ir-4),
Figure 3. UV−vis and PL spectra of Ir-1−Ir-4 in dichloromethane
solution with a concentration of 10−5 M at room temperature.
respectively, and phosphors Ir-3 and Ir-4 show relatively lower
PLQYs of 32.9% and 32.0%. To gain a deeper understanding of
the emission properties of all the complexes, the radiative (kr)
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Table 1. Electrochemical and Photophysical Data for Ir-1−Ir-4
a c
−
a
d
e
f
g
ac
h
h
complex
λPL,max
(nm)
τ
(μs)
Eox(onset) (V)
Eg (eV)
HOMO /LUMO (eV)
Φp (%)
kr (105 s−1
)
knr (105 s−1
)
Ir-1
Ir-2
Ir-3
Ir-4
605, 581, 607
603, 572, 601
620, 602, 610
619, 605, 613
0.73
0.39
0.38
0.37
0.35
2.17
2.18
2.07
2.11
−5.19/−3.02
−5.18/−3.00
−5.17/−3.10
−5.15/−3.04
57.5, 38.4
56.4, 12.0
32.9, 32.4
32.0, 29.5
b
7.88
4.70
6.58
2.58
5.82
3.63
13.42
1.20
0.50
1.24
5.48
a
Ir-1−Ir-4 measurements were performed in dichloromethane solution (10−5 M) at room temperature. Ir-1−Ir-4 measurements were measured
c
d
e
in 10−5 M dichloromethane at 77 K. Measured in the neat film at room temperature. Measured by CV with ferrocene as the standard. Estimated
f
g
from the UV−vis absorption spectra. Obtained from the onset oxidation potentials according to HOMO = −Eox(onset) + 4.8 eV. Obtained
according to LUMO = HOMO + Eg. Calculated from τ and Φ (kr = Φ/τ, knr = (1 − Φ)/τ).
h
Figure 5. CV curves of Ir-1−Ir-4.
−3.02, −3.00, −3.10, and −3.04 eV, respectively, on the basis
of the energy gaps.
Monochromatic OLED Characterization. To evaluate
the EL performances of the designed iridium(III) complexes,
the phosphorescent devices D1−D4 based on Ir-1−Ir-4 were
fabricated with the same device structure of ITO/TAPC (4,4′-
(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline, 35 nm)/
TCTA (tris(4-(9H-carbazol-9-yl)phenyl)amine, 5 nm)/
26DCzPPy (2,6-bis(3-(9H-carbazol-9-yl)phenyl)pyridine):Ir-
1−Ir-4 (5 wt %, 20 nm)/TmPyPB (1,3,5-tris(3-pyridyl-3-
phenyl)benzene, 40 nm)/LiF (0.5 nm)/Ag:Mg (1:15, 120
nm). LiF acts as the electron injection material. In addition,
TAPC was used as the hole-transporting layer (HTL) because
−2
2
−1
of its high hole mobility of ∼10 cm
V
s−1, and TCTA
Figure 4. HOMO and LUMO distributions of Ir-1−Ir-4 (isocontour
served as a electron/exciton blocking layer (EBL). Further-
more, the bipolar material 26DCzPPy, which has equivalent
electron and hole transport capabilities, was chosen as the host
material.47 TmPyPB acts as an electron-transporting layer
(ETL).48 Figure S7 in the Supporting Information shows the
molecular structures of these materials. The corresponding EL
characteristics and key data are shown in Figure 6 and Table 2.
As depicted in Figure 6b, devices D1 and D2 exhibit the
same strong orange EL at 590 nm, with the same CIE
coordinates of (0.53, 0.46). Furthermore, the EL spectra of the
devices are in good agreement with those of the PL
counterparts, indicating that the orange emission mainly
comes from iridium(III) dopants. D3 and D4 show orange
emission peaks at 590 and 625 nm and at 588 and 625 nm,
respectively, with the same CIE coordinates of (0.60, 0.40). In
addition, no significant emission from 26DCzPPy was
observed in any spectra, indicating complete efficient energy
transfer from 26DCzPPy to the iridium(III) dopants during
0.02).
indicating that their T1 emission contains a mixture of 3MLCT
3
and LLCT (see the Supporting Information).
Electrochemical Properties. The electrochemical proper-
ties of the four phosphors have been studied by cyclic
voltammetry (CV), and the corresponding data are shown in
Figure 5 and Table 1. The energy gaps for Ir-1−Ir-4 were
calculated to be 2.17, 2.18, 2.07, and 2.11 eV, respectively, and
so it is reasonable that iridium(III) complexes could show
orange emissions. Using the ferrocene/ferrocenium (Fc/Fc+)
pair as a reference, the Eox(onset) values are 0.39, 0.38, 0.37,
and 0.35 V for Ir-1−Ir-4, respectively. Their HOMO energy
levels were deduced to be −5.19, −5.18, −5.17, and −5.15 eV,
respectively according to the Eox(onset) values. Consequently,
the corresponding LUMO energy levels were calculated to be
D
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Figure 6. (a) Schematic energy-level diagram of monochromatic OLEDs. (b) EL spectra for monochromatic OLEDs. (c) Current density and
luminance characteristics of monochromatic OLEDs. (d) CE, PE, and EQE curves of monochromatic OLEDs.
Table 2. EL Performance of OLEDs Based on Ir-1−Ir-4
a
b
bc
CE (cd A−1
,
b c
PE (lm W−1
,
bc
,
device
Vturn‑on (V)
λEL (nm)
Lmax (cd m−2
)
)
)
EQE
CIE [(x, y), V]
D1
D2
D3
D4
D5
D6
3.8
3.8
3.7
3.5
3.1
3.5
590
590
590, 625
588, 625
581
28440
39420
16930
21260
38799
31274
16.1, 15.7
19.5, 19.2
13.9, 10.5
16.9, 13.2
27.2, 24.3
22.2, 20.4
10.1, 9.3
12.2, 11.9
10.9, 6.5
13.3, 8.5
24.0, 14.8
17.4, 12.0
6.6, 6.3
8.1, 8.0
8.7, 6.8
10.6, 8.2
10.6, 9.4
8.7, 8.0
(0.53, 0.46), 7.0
(0.53, 0.46), 7.0
(0.60, 0.40), 7.0
(0.60, 0.40), 7.0
(0.52, 0.47), 7.0
(0.52, 0.47), 7.0
d
e
581
a
b
c
Driving voltages at 1 cd m−2. Maximum values (luminance, current efficiency, power efficiency, external quantum efficiency). Efficiency values at
d
e
1000 cd m−2. Optimized device based on Ir-1. Optimized device based on Ir-2.
electroluminescence.49−52 Here, the four orange devices also
possess broad FWHMs of 107 nm for device D1, 109 nm for
device D2, and 110 nm for devices D3 and D4, which are very
favorable for the development of outstanding color quality
WOLEDs.26 These orange devices can be driven at low
voltages from 3.5 to 3.8 V. Figure 6c,d exhibits the EL
performance of the four devices. As shown in Table 2, devices
D1 and D2 have better performance with maximum
luminances of 28440 cd m−2 for D1 and 39420 cd m−2 for
D2, maximum CEs of 16.1 cd A−1 for D1 and 19.5 cd A−1 for
D2, maximum PEs of 10.1 lm W−1 for D1 and 12.2 lm W−1 for
D2, peak EQEs of 6.6% for D1 and 8.1% for D2. Although the
maximum PEs and EQEs of D3 and D4 have better results
(10.9 and 13.3 lm W−1, 8.7% and 10.6%) in comparison D1
and D2, D3 and D4 exhibit lower performance in the
maximum luminance and maximum CE (16930 and 21260 cd
m−2, 13.9 and 16.9 cd A−1). In addition, devices D1 and D2
show tiny CE efficiency roll-offs of 2.5% and 1.5%, respectively,
outperforming the CE efficiency roll-offs of D3 and D4 (24.5%
and 21.9%). Encouraged by the better EL performances of Ir-1
and Ir-2, the optimized devices D5 and D6 were prepared.
MoO3, which act as a hole injection material, was introduced,53
and Bphen (4,7-diphenyl-1,10-phenanthroline) replaced
TmPyPB as the new electron-transporting layer during the
optimization process. As shown in Figure S8c in the
Supporting Information, the two orange devices exhibit
maximum luminances of 38799 cd m−2 for D5 and 31274 cd
m−2 for D6. From Figure S4d in the Supporting Information,
the efficiency of D5 attained a peak CE of 27.2 cd A−1, a peak
PE of 24.0 lm W−1, and a peak EQE of 10.6%, respectively.
Relative to D5, D6 shows slightly lower efficiencies for a
maximum CE of 22.2 cd A−1, a maximum PE of 17.4 lm W−1,
and a maximum EQE of 8.7%. In addition, the two devices
both show low CE and EQE efficiency roll-offs. They retained
CE and EQE values of 24.3 cd A−1, 9.4% for D5 and 20.4 cd
A−1 and 8.0% for D6 at a luminance of 1000 cd m−2,
suggesting a well-balanced charge-transport characteristic in
the devices.54 The excellent performances of devices D1, D2,
D5, and D6 indicate that Ir-1 and Ir-2 can act as efficient
orange emitters for efficient white OLEDs.55
WOLED Characterization. Encouraged by the broad
FWHMs and high efficiency of the monochromatic devices,
warm WOLEDs which comprise blue and orange emitters
were prepared with the structure ITO/MoO3 (3 nm)/TAPC
(4,4′-(cyclohexane-1,1-diyl)bis(N,N-di-p-tolylaniline), 35
nm)/TCTA ((tris(4-(9H-carbazol-9-yl)phenyl)amine), 5
nm)/26DCzPPy (2,6-bis(3-(9H-carbazol-9-yl)phenyl)-
pyridine):FIrpic (10%, 5 nm)/26DCzPPy:Ir-1 (W1) and Ir-
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Figure 7. (a) Schematic energy-level diagram of two-color warm WOLEDs. (b) EL spectra for two-color warm WOLEDs. (c) Current density and
luminance characteristics of two-color warm WOLEDs. (d) CE, PE, and EQE curves of two-color warm WOLEDs.
Table 3. EL Performance of White OLEDs Based on Ir-1 and Ir-2
a
b
b c
,
bc
,
bc
,
device
Vturn‑on (V)
Lmax (cd m−2
)
CE (cd A−1
)
PE (lm W−1
)
EQE
CRI
CIE [(x, y), V]
W1
W2
3.3
3.3
43980
39811
27.7, 25.5
26.1, 23.6
21.8, 15.7
20.5, 14.8
11.3, 10.4
10.9, 9.9
69
67
(0.39, 0.43), 7.0
(0.32, 0.41), 7.0
a
b
c
Driving voltages at 1 cd m−2. Maximum values (luminance, current efficiency, power efficiency, external quantum efficiency). Efficiency values at
1000 cd m−2.
2 (W2) (7%, 15 nm)/Bphen (4,7-diphenyl-1,10-phenanthro-
line, 40 nm)/LiF (0.5 nm)/Ag:Mg (1:15, 120 nm). Figure 7a
displays the schematic energy-level diagram. The HOMO and
LUMO energy levels of Ir-1 and Ir-2 were embedded between
the HOMO and LUMO levels of 26DCzPPy, which is
expected to have good carrier-trapping performance. In
addition, significantly different energy levels between the
emitters and the host indicate efficient energy transfer from
26DCzPPy to the dopants. Furthermore, TCTA not only
facilitates hole injection but also acts as an electron-blocking
layer to block the migration of electrons from the host
material, making carriers well confined within the emitting
layers (EML). The EL spectra, current density, luminance
characteristics, and CE, PE, and EQE curves for two-color
warm WOLEDs are illustrated in Figure 7, and related EL data
are given in Table 3.
From Figure 7b, two main emission peaks (470 and 577 nm
for W1, 471 and 569 nm for W2) which can be observed from
the EL spectra of W1 and W2 correspond to emissions of
FIrpic and Ir-1 and Ir-2. In addition, the main emission
intensity is located at the orange band in EL spectra, which
makes the device W1 have a lower correlated color
temperature (CCT) of 4024 K in comparison to W2 (5709
K) at 6 V.56 W1 shows warm white emission with CIE
coordinates of (0.39, 0.43) at 7 V. It is worth mentioning that
W1 also displays excellent color stability. When the voltage
changes from 4 to 6 V, the CIE coordinates change slightly
from (0.392, 0.432) to (0.395, 0.433) (Figure 8). Additionally,
Figure 8. EL spectra of a WOLED (W1) with the designed emitter
Ir-1 at various voltages.
the CIE coordinates of W2 remain almost invariable when the
voltage goes from 4 V (0.321, 0.414) to 6 V (0.326, 0.415)
(see Figure S9 in the Supporting Information). However,
WOLEDs have a lower color rendering index (CRI) of 69 for
W1 and 67 for W2, which probably is due to limited blue-
emitting spectra not covering the whole spectral region well.26
Due to the good matching of the energy levels, W1 and W2
have the same low turn-on voltage of 3.3 V. The devices W1
and W2 reach maximum luminances of 43980 and 39811 cd
m−2, respectively (Figure 7c). As depicted in Figure 7d, a
F
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maximum CE of 27.7 cd A−1, PE of 21.8 lm W−1, and EQE of
11.3% are realized in W1. The performance of W2 has a slight
drop in comparison with W1, which possesses a maximum CE
of 26.1 cd A−1, PE of 20.5 lm W−1, and EQE of 10.9%.
Importantly, both W1 and W2 show negligible CE and EQE
efficiency roll-offs. At a luminance of 1000 cd m−2, CE and
EQE of W1 are still maintained at 25.5 cd A−1 and 10.4%,
respectively, revealing an attenuation of about 7.9% and 8.0%
relative to the maximum value. For W2, CE and EQE declined
to 23.6 cd A−1 and 9.9% when the luminance was 1000 cd m−2.
5H), 7.35−7.31 (m, 3H), 7.27−7.23 (m, 2H), 7.11 (d, J = 8.0 Hz,
2H), 2.34 (s, 3H).
Synthesis of 2-(4-tert-Butylphenyl)-1-phenyl-1H-benzo[d]-
imidazole (HtbPBI). The synthesis of HtbPBI was similar to that of
1
HmPBI with 4-tert-butylbenzoyl chloride as the starting material. H
NMR (500 MHz, CDCl3, δ): 7.88 (d, J = 8.0 Hz, 1H), 7.53−7.48 (m,
5H), 7.35−7.30 (m, 5H), 7.26−7.21 (m, 2H), 1.29 (s, 9H).
Synthesis of Dichloro-Bridged Diiridium Complex [Ir-
(mPBI)2Cl]2. IrCl3·3H2O (1.06 g, 3.00 mmol), HmPBI (2.05 g,
7.20 mmol), 2-ethoxyethanol (60 mL), and water (20 mL) were
mixed together and refluxed under argon for 24 h. The reaction
mixture was then cooled to 25 °C and filtered. After washing and
drying, the product was collected.
CONCLUSIONS
Synthesis of [Ir(tbPBI)2Cl]2. The synthetic method of [Ir-
(tbPBI)2Cl]2 is similar to that of [Ir(mPBI)2Cl]2, in which the
HmPBI is replaced by HtbPBI.
■
In summary, tye four efficient orange iridium complexes Ir-1−
Ir-4 were successfully designed and synthesized, of which Ir-1
and Ir-2 had PLQYs of 57.5% and 56.4%, respectively. The
corresponding OLEDs based on these complexes have broad
FWHMs of about 110 nm. The optimized device D5 based on
Ir-1 achieved the best performance with a maximum CE of
27.2 cd A−1, PE of 24.0 lm W−1, and EQE of 10.6%. The
corresponding two-color warm WOLED comprising Ir-1 as
the orange dopant achieves a maximum brightness of 43980 cd
m−2, a peak CE of 27.7 cd A−1, a peak PE of 21.8 lm W−1, and
a peak EQE of 11.3% accompanied by a small CE roll-off of
7.9%. Importantly, the warm WOLED also displays excellent
color stability with ΔCIE = (0.003, 0.001) when driving
voltages were varied from 4 to 6 V. In view of the achieved
high PLQYs and promising device efficiency associated with
the tiny roll-off at high luminance, we believe that the two
complexes have great prospects in the field of solid-state
lighting and displays.
Synthesis of Ir-1. The ancillary ligand HBIQ (0.15 g, 0.60 mmol),
dichloro-bridged diiridium complex [Ir(mPBI)2Cl]2 (0.38 g, 0.24
mmol), and K2CO3 (0.08 g, 0.60 mmol) were dissolved in
dichloromethane (60 mL) and ethanol (20 mL). Then the mixture
was refluxed for 24 h under the protection of argon in the dark. After
it was cooled to room temperature, the mixture was distilled off the
solvent, and then the crude product was purified through silica gel
column chromatography to afford complex Ir-1 in 68% yield. 1H
NMR (600 MHz, DMSO-d6, δ): 8.65 (s, 2H), 8.12 (d, J = 9.0 Hz,
1H), 8.04 (d, J = 7.8 Hz, 1H), 7.71−7.80 (m, 7H), 7.52−7.56 (m,
4H), 7.30 (s, 1H), 7.03−7.15 (m, 6H), 6.71−6.94 (m, 2H), 6.62 (d, J
= 8.4 Hz, 2H), 6.54 (d, J = 8.4 Hz, 1H), 6.45−6.49 (m, 2H), 6.40 (s,
1H), 6.22 (s, 1H), 5.95 (d, J = 8.4 Hz, 1H), 5.91 (d, J = 7.8 Hz, 1H),
5.43 (d, J = 8.4 Hz, 1H), 2.07 (s, 3H), 2.03 (s, 3H). MS (MALDI-
TOF, m/z): 1004.3 [M + H]+.
Synthesis of Ir-2. The synthetic method of Ir-2 is similar to that
of Ir-1, in which the dichloro-bridged diiridium complex [Ir-
(mPBI)2Cl]2 is replaced by [Ir(tbPBI)2Cl]2.Yield: 67%. 1H NMR
(600 MHz, DMSO-d6, δ): 8.72 (s, 2H), 8.04 (d, J = 7.2 Hz, 1H), 7.98
(d, J = 9.0 Hz, 1H), 7.74−7.80 (m, 7H), 7.66−7.67 (m, 2H), 7.50 (s,
1H), 7.31 (d, J = 5.4 Hz, 1H), 7.26 (d, J = 6.6 Hz, 1H), 7.07−7.14
(m, 3H), 6.98−7.02 (m, 3H), 6.86 (d, J = 8.4 Hz, 1H), 6.77−6.81 (m,
2H), 6.73 (s, 1H), 6.59 (s, 1H), 6.45−6.50 (m, 3H), 6.35 (s, 1H),
6.06 (d, J = 8.4 Hz, 1H), 5.59 (d, J = 7.8 Hz, 1H), 5.46 (s, 1H), 0.93
(s, 9H), 0.87 (s, 9H). MS (MALDI-TOF, m/z): 1088.4 [M + H]+.
Synthesis of Ir-3. The synthetic method of Ir-3 is similar to that
of Ir-1, in which the ancillary ligand HBIQ is replaced by HBISQ.
Yield: 63%. 1H NMR (600 MHz, DMSO-d6, δ): 10.79 (s, 1H), 8.05−
8.07 (m, 2H), 7.71−7.93 (m, 11H), 7.58 (t, J = 3.6 Hz, 2H), 7.45 (d,
J = 6.0 Hz, 1H), 6.95−7.10 (m, 5H), 6.81 (t, J = 7.8 Hz, 1H), 6.73 (s,
1H), 6.69 (t, J = 7.5 Hz, 1H), 6.49−6.58 (m, 4H), 6.37 (d, J = 13.2
Hz, 2H), 6.26 (d, J = 8.4 Hz, 1H), 5.83 (d, J = 8.4 Hz, 1H), 5.64 (d, J
= 4.8 Hz, 1H), 2.03 (d, J = 9.0 Hz, 6H). MS (MALDI-TOF, m/z):
1004.3 [M + H]+.
EXPERIMENTAL SECTION
■
General Information. All reagents and solvents used in the
experiment were commercially available. The molecular weights of Ir-
1−Ir-4 were measured by using a matrix-assisted laser desorption
ionization time-of-flight (MALDI-TOF) mass spectrometer. Photo-
luminescence (PL) emission spectra of emitters were recorded by
using a FL-4600 fluorescent spectrophotometer. UV−vis absorption
spectra of emitters were tested on a Cary 500 UV−vis−NIR
spectrophotometer, and lifetimes were performed with an Edinburgh
FLSP920 spectrofluorimeter at room temperature. The spin-coating
method was used to fabricate the neat films. Cyclic voltammetry (CV)
investigations were conducted on a workstation (BAS 100 W
instrument) using dichloromethane or acetonitrile containing 0.1 M
n-Bu4NPCl6 as a supporting electrolyte under a N2 atmosphere. The
ferrocene/ferrocenium (Fc/Fc+) couple was chosen for calibration.
PLQYs in solution were measured on a C9920-02 system under a N2
atmosphere. PLQYs in neat films were measured in an integrating
sphere.
Synthesis of Ir-4. The synthetic method of Ir-4 is similar to that
of Ir-2, in which the ancillary ligand HBIQ is replaced by HBISQ.
1
Yield: 62%. H NMR (600 MHz, DMSO-d6, δ): 10.86 (s, 1H), 8.05
(d, J = 7.2 Hz, 1H), 7.98 (d, J = 6.0 Hz, 1H), 7.92−7.94 (m, 2H),
7.70−7.85 (m, 10H), 7.27−7.32 (m, 2H), 7.14−7.15 (m, 1H), 7.06−
7.09 (m, 2H), 6.99 (d, J = 8.4 Hz, 2H), 6.91 (t, J = 7.8 Hz, 1H),
6.79−6.81 (m, 1H), 6.75−6.76 (m, 1H), 6.72 (t, J = 7.8 Hz, 1H),
6.58−6.60 (m, 2H), 6.47−6.52 (m, 3H), 5.97−6.00 (m, 2H), 5.75−
5.76 (m, 1H), 0.89 (d, J = 7.2 Hz, 18H). MS (MALDI-TOF, m/z):
1088.4 [M + H]+.
Single-Crystal X-ray Diffraction Analysis. Single crystals of Ir-
1, Ir-3, and Ir-4 were grown from mixed solution of CH2Cl2 and
CH3OH by slowly evaporating the solutions. The single-crystal X-ray
diffraction data for the complexes were confirmed on a Bruker Apex
CCD II area-detector diffractometer.
Computational Details. Theoretical calculations on Ir-1−Ir-4
were performed with the Gaussian 09 software package.58 The
ground-state (S0) and triplet-state (T1) structures of the phosphors
were fully optimized with B3LYP spin-unrestricted open-shell B3LYP,
respectively. The standard 6-31G(d,p) basis set was used for C, H,
Synthesis of 2-(1H-Benzo[d]imidazol-2-yl)quinolone (HBIQ)
and 1-(1H-Benzo[d]imidazol-2-yl)isoquinoline (HBISQ). The
preparations of HBIQ and HBISQ are given in previously reported
literature.57
Synthesis of 1-Phenyl-2-p-tolyl-1H-benzo[d]imidazole
(HmPBI). A 50.00 mmol amount (9.21 g) of N-phenyl-o-phenyl-
enediamine was dissolved in 30 mL of N,N-dimethylacetamide. Under
nitrogen, 20 mL of an N,N-dimethylacetamide solution of 4-
methylbenzoyl chloride (50.00 mmol, 7.73 g) was slowly added
dropwise to the above solution and stirred at room temperature for 2
h. After the reaction, a large amount of water was added to obtain a
solid. After washing and drying, the resulting intermediate was added
to 20 mL of glacial acetic acid and refluxed for 16 h. Water was added
to obtain the product after the mixture was cooled to 25 °C. Then,
1
the product was purified by silica gel column chromatography. H
NMR (500 MHz, CDCl3, δ): 7.89 (d, J = 8.0 Hz, 1H), 7.52−7.45 (m,
G
https://dx.doi.org/10.1021/acs.organomet.0c00472
Organometallics XXXX, XXX, XXX−XXX

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pubs.acs.org/Organometallics
Article
and N atoms, and the LANL2DZ basis set was employed for the
iridium(III) atom in all calculations.
Notes
The authors declare no competing financial interest.
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.organomet.0c00472.
ACKNOWLEDGMENTS
■
■
sı
The authors gratefully acknowledge financial support from the
National Natural Science Foundation of China (21303012,
51902124 and 61474054), the Fundamental Research Funds
for the Central Universities (2412019FZ012 and
2412019QD007), and the China Postdoctoral Science
Foundation funded project (2019M651184).
OLED fabrication and measurements and figures and
calculated energy levels of the lower-lying transitions of
all complexes (PDF)
Accession Codes
REFERENCES
■
CCDC 1969397 and 1980337−1980338 contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge via www.ccdc.cam.ac.uk/data_request/
cif, or by emailing data_request@ccdc.cam.ac.uk, or by
contacting The Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
(1) Gomez-Bombarelli, R.; Aguilera-Iparraguirre, J.; Hirzel, T. D.;
Duvenaud, D.; Maclaurin, D.; Blood-Forsythe, M. A.; Chae, H. S.;
Einzinger, M.; Ha, D. G.; Wu, T.; Markopoulos, G.; Jeon, S.; Kang,
H.; Miyazaki, H.; Numata, M.; Kim, S.; Huang, W.; Hong, S. I.; Baldo,
M.; Adams, R. P.; Aspuru-Guzik, A. Design of efficient molecular
organic light-emitting diodes by a high-throughput virtual screening
and experimental approach. Nat. Mater. 2016, 15, 1120−1127.
(2) Xiao, L.; Chen, Z.; Qu, B.; Luo, J.; Kong, S.; Gong, Q.; Kido, J.
Recent progresses on materials for electrophosphorescent organic
light-emitting devices. Adv. Mater. 2011, 23, 926−952.
AUTHOR INFORMATION
Corresponding Authors
■
Guo-Gang Shan − Institute of Functional Material Chemistry
and National & Local United Engineering Lab for Power
Battery, Faculty of Chemistry, Northeast Normal University,
Changchun 130024, People’s Republic of China; orcid.org/
0000-0002-1050-219X; Phone: +86-431-85099108;
Email: shangg187@nenu.edu.cn; Fax: +86-431-85684009
Hai-Zhu Sun − Institute of Functional Material Chemistry and
National & Local United Engineering Lab for Power Battery,
Faculty of Chemistry, Northeast Normal University, Changchun
130024, People’s Republic of China; orcid.org/0000-0002-
5113-8267; Email: sunhz335@nenu.edu.cn
Wen-Fa Xie − State Key Laboratory on Integrated
Optoelectronics, College of Electronic Science and Engineering,
Jilin University, Changchun, Jilin 130012, People’s Republic of
China; orcid.org/0000-0003-0912-8046; Phone: +86-
13844907598; Email: xiewf@jlu.edu.cn
Zhong-Min Su − Institute of Functional Material Chemistry and
National & Local United Engineering Lab for Power Battery,
Faculty of Chemistry, Northeast Normal University, Changchun
130024, People’s Republic of China; School of Chemistry &
Environmental Engineering, Changchun University of Science
and Technology, Changchun, Jilin 130012, People’s Republic of
China; orcid.org/0000-0002-3342-1966; Email: zmsu@
nenu.edu.cn
(3) Wu, T.-L.; Huang, M.-J.; Lin, C.-C.; Huang, P.-Y.; Chou, T.-Y.;
Chen-Cheng, R.-W.; Lin, H.-W.; Liu, R.-S.; Cheng, C.-H. Diboron
compound-based organic light-emitting diodes with high efficiency
and reduced efficiency roll-off. Nat. Photonics 2018, 12, 235−240.
(4) Yan, Z.-P.; Liao, K.; Han, H.-B.; Su, J.; Zheng, Y.-X.; Zuo, J.-L.
Chiral iridium(iii) complexes with four-membered Ir−S−P−S
chelating rings for high-performance circularly polarized OLEDs.
Chem. Commun. 2019, 55, 8215−8218.
(5) Fleetham, T.; Li, G.; Li, J. Phosphorescent Pt(II) and Pd(II)
Complexes for Efficient, High-Color-Quality, and Stable OLEDs. Adv.
Mater. 2017, 29, 1601861.
(6) Costa, R. D.; Ortí, E.; Bolink, H. J.; Monti, F.; Accorsi, G.;
Armaroli, N. Luminescent Ionic Transition-Metal Complexes for
Light-Emitting Electrochemical Cells. Angew. Chem., Int. Ed. 2012, 51,
8178−8211.
(7) Pashaei, B.; Karimi, S.; Shahroosvand, H.; Abbasi, P.; Pilkington,
M.; Bartolotta, A.; Fresta, E.; Fernandez-Cestau, J.; Costa, R. D.;
Bonaccorso, F. Polypyridyl ligands as a versatile platform for solid-
state light-emitting devices. Chem. Soc. Rev. 2019, 48, 5033−5139.
(8) Lee, J.; Chen, H.-F.; Batagoda, T.; Coburn, C.; Djurovich, P. I.;
Thompson, M. E.; Forrest, S. R. Deep blue phosphorescent organic
light-emitting diodes with very high brightness and efficiency. Nat.
Mater. 2016, 15, 92−98.
(9) Fan, C.; Yang, C. Yellow/orange emissive heavy-metal
complexes as phosphors in monochromatic and white organic light-
emitting devices. Chem. Soc. Rev. 2014, 43, 6439−69.
(10) Zhu, Y.-C.; Zhou, L.; Li, H.-Y.; Xu, Q.-L.; Teng, M.-Y.; Zheng,
Y.-X.; Zuo, J.-L.; Zhang, H.-J.; You, X.-Z. Highly Efficient Green and
Blue-Green Phosphorescent OLEDs Based on Iridium Complexes
with the Tetraphenylimidodiphosphinate Ligand. Adv. Mater. 2011,
23, 4041−4046.
Authors
Lei Ding − Institute of Functional Material Chemistry and
National & Local United Engineering Lab for Power Battery,
Faculty of Chemistry, Northeast Normal University, Changchun
130024, People’s Republic of China
Chun-Xiu Zang − State Key Laboratory on Integrated
Optoelectronics, College of Electronic Science and Engineering,
Jilin University, Changchun, Jilin 130012, People’s Republic of
China
Li−Li Wen − Institute of Functional Material Chemistry and
National & Local United Engineering Lab for Power Battery,
Faculty of Chemistry, Northeast Normal University, Changchun
130024, People’s Republic of China
(11) Fukagawa, H.; Oono, T.; Iwasaki, Y.; Hatakeyama, T.; Shimizu,
T. High-efficiency ultrapure green organic light-emitting diodes.
Mater. Chem. Front. 2018, 2, 704−709.
(12) Sree, V. G.; Maheshwaran, A.; Kim, H.; Park, H.-Y.; Kim, Y.;
Lee, J. C.; Song, M.; Jin, S.-H. Synthesis and Characterization of
Highly Efficient Solution-Processable Green Ir(III) Complexes with
High Current Efficiency and Very Low Efficiency Roll-Off. Adv. Funct.
Mater. 2018, 28, 1804714.
(13) Hao, Z.; Zhang, K.; Wang, P.; Lu, X.; Lu, Z.; Zhu, W.; Liu, Y.
Deep Red Iridium(III) Complexes Based on Pyrene-Substituted
Quinoxaline Ligands for Solution-Processed Phosphorescent Organic
Light-Emitting Diodes. Inorg. Chem. 2020, 59, 332−342.
(14) Xu, T.; Zhang, Y.-X.; Wang, B.; Huang, C.-C.; Murtaza, I.;
Meng, H.; Liao, L.-S. Highly Simplified Reddish Orange Phosphor-
escent Organic Light-Emitting Diodes Incorporating a Novel Carrier-
Ying Gao − Jilin Engineering Normal University, Changchun
130052, People’s Republic of China
Complete contact information is available at:
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and Exciton-Confining Spiro-Exciplex-Forming Host for Reduced
Efficiency Roll-off. ACS Appl. Mater. Interfaces 2017, 9, 2701−2710.
(15) Yan, Z.; Wang, Y.; Ding, J.; Wang, Y.; Wang, L. Highly Efficient
Phosphorescent Furo[3,2-c]pyridine Based Iridium Complexes with
Tunable Emission Colors over the Whole Visible Range. ACS Appl.
Mater. Interfaces 2018, 10, 1888−1896.
(16) Zhou, W.; Wang, Z.; Zhang, J.; Hu, S.; Xie, Q.; Liu, Z.; Liu, L.;
Liang, A. Orange-emitting supramolecular phosphorescent polymer
with different counterions for polymer light-emitting diodes. Dyes
Pigm. 2020, 172, 107790.
(17) Reineke, S.; Lindner, F.; Schwartz, G.; Seidler, N.; Walzer, K.;
Lussem, B.; Leo, K. White organic light-emitting diodes with
fluorescent tube efficiency. Nature 2009, 459, 234−238.
(18) Farinola, G. M.; Ragni, R. Electroluminescent materials for
white organic light emitting diodes. Chem. Soc. Rev. 2011, 40, 3467−
3482.
(19) Kamtekar, K. T.; Monkman, A. P.; Bryce, M. R. Recent
advances in white organic light-emitting materials and devices
(WOLEDs). Adv. Mater. 2010, 22, 572−582.
(20) Schwartz, G.; Reineke, S.; Rosenow, T. C.; Walzer, K.; Leo, K.
Triplet Harvesting in Hybrid White Organic Light-Emitting Diodes.
Adv. Funct. Mater. 2009, 19, 1319−1333.
(21) Dai, X.; Yao, F.; Li, J.; Yu, H.; Cao, J. Color-stable non-doped
white phosphorescent organic light-emitting diodes based on ultrathin
emissive layers. J. Phys. D: Appl. Phys. 2020, 53, 055106.
(22) Chen, Z.; Ho, C. L.; Wang, L.; Wong, W. Y. Single-Molecular
White-Light Emitters and Their Potential WOLED Applications. Adv.
Mater. 2020, 32, 1903269.
(23) Kuei, C. Y.; Tsai, W. L.; Tong, B.; Jiao, M.; Lee, W. K.; Chi, Y.;
Wu, C. C.; Liu, S. H.; Lee, G. H.; Chou, P. T. Bis-Tridentate Ir(III)
Complexes with Nearly Unitary RGB Phosphorescence and Organic
Light-Emitting Diodes with External Quantum Efficiency Exceeding
31%. Adv. Mater. 2016, 28, 2795−2800.
(24) Miao, Y.; Wang, K.; Zhao, B.; Gao, L.; Tao, P.; Liu, X.; Hao, Y.;
Wang, H.; Xu, B.; Zhu, F. High-efficiency/CRI/color stability warm
white organic light-emitting diodes by incorporating ultrathin
phosphorescence layers in a blue fluorescence layer. Nanophotonics
2018, 7, 295−304.
(25) Sasabe, H.; Takamatsu, J.; Motoyama, T.; Watanabe, S.;
Wagenblast, G.; Langer, N.; Molt, O.; Fuchs, E.; Lennartz, C.; Kido, J.
High-efficiency blue and white organic light-emitting devices
incorporating a blue iridium carbene complex. Adv. Mater. 2010,
22, 5003−5007.
(26) Tao, P.; Li, W.-L.; Zhang, J.; Guo, S.; Zhao, Q.; Wang, H.; Wei,
B.; Liu, S.-J.; Zhou, X.-H.; Yu, Q.; Xu, B.-S.; Huang, W. Facile
Synthesis of Highly Efficient Lepidine-Based Phosphorescent Iridium-
(III) Complexes for Yellow and White Organic Light-Emitting
Diodes. Adv. Funct. Mater. 2016, 26, 881−894.
(27) Li, X.; Cui, J.; Ba, Q.; Zhang, Z.; Chen, S.; Yin, G.; Wang, Y.;
Li, B.; Xiang, G.; Kim, K. S.; Xu, H.; Zhang, Z.; Wang, H. L.
Multiphotoluminescence from a Triphenylamine Derivative and Its
Application in White Organic Light-Emitting Diodes Based on a
Single Emissive Layer. Adv. Mater. 2019, 31, 1900613.
(28) Yang, X.; Zhao, Y.; Zhang, X.; Li, R.; Dang, J.; Li, Y.; Zhou, G.;
Wu, Z.; Ma, D.; Wong, W.-Y.; Zhao, X.; Ren, A.; Wang, L.; Hou, X.
Thiazole-based metallophosphors of iridium with balanced carrier
injection/transporting features and their two-colour WOLEDs
fabricated by both vacuum deposition and solution processing-
vacuum deposition hybrid strategy. J. Mater. Chem. 2012, 22, 7136−
7148.
(29) Zhang, G. H.; Xie, F. M.; Wu, K.; Li, Y. Q.; Xie, G.; Zou, S. J.;
Shen, Y.; Zhao, X.; Yang, C.; Tang, J. X. High-Efficiency White
Organic Light-Emitting Diodes Based on All Nondoped Thermally
Activated Delayed Fluorescence Emitters. Adv. Mater. Interfaces 2020,
7, 1901758.
(31) Yan, Z.; Wang, Y.; Wang, J.; Wang, Y.; Ding, J.; Wang, L. A
novel furo[3,2-c]pyridine-based iridium complex for high-perform-
ance organic light-emitting diodes with over 30% external quantum
efficiency. J. Mater. Chem. C 2017, 5, 10122−10125.
(32) Mondal, E.; Hung, W.-Y.; Dai, H.-C.; Wong, K.-T. Fluorene-
Based Asymmetric Bipolar Universal Hosts for White Organic Light
Emitting Devices. Adv. Funct. Mater. 2013, 23, 3096−3105.
(33) Wen, L.-L.; Zang, C.-X.; Gao, Y.; Shan, G.-G.; Sun, H.-Z.;
Wang, T.; Xie, W.-F.; Su, Z.-M. Molecular Engineering of Phenyl-
benzimidazole-Based Orange Ir(III) Phosphors toward High-
Performance White OLEDs. Inorg. Chem. 2018, 57, 6029−6037.
(34) Gong, S.; Chen, Y.; Yang, C.; Zhong, C.; Qin, J.; Ma, D. De
Novo Design of Silicon-Bridged Molecule Towards a Bipolar Host:
All-Phosphor White Organic Light-Emitting Devices Exhibiting High
Efficiency and Low Efficiency Roll-Off. Adv. Mater. 2010, 22, 5370−
5373.
(35) Guo, L. Y.; Zhang, X. L.; Wang, H. S.; Liu, C.; Li, Z. G.; Liao,
Z. J.; Mi, B. X.; Zhou, X. H.; Zheng, C.; Li, Y. H.; Gao, Z. Q. New
homoleptic iridium complexes with C^N = N type ligand for high
efficiency orange and single emissive-layer white OLEDs. J. Mater.
Chem. C 2015, 3, 5412−5418.
(36) Cao, H.; Shan, G.; Wen, X.; Sun, H.; Su, Z.; Zhong, R.; Xie, W.;
Li, P.; Zhu, D. An orange iridium(iii) complex with wide-bandwidth
in electroluminescence for fabrication of high-quality white organic
light-emitting diodes. J. Mater. Chem. C 2013, 1, 7371−7379.
(37) Jiang, B.; Zhao, C.; Ning, X.; Zhong, C.; Ma, D.; Yang, C. Using
Simple Fused-Ring Thieno[2,3-d]pyrimidine to Construct Orange/
Red Ir(III) Complexes: High-Performance Red Organic Light-
Emitting Diodes with EQEs up to Nearly 28%. Adv. Opt. Mater.
2018, 6, 1800108.
(38) Na, H.; Teets, T. S. Highly Luminescent Cyclometalated
Iridium Complexes Generated by Nucleophilic Addition to
Coordinated Isocyanides. J. Am. Chem. Soc. 2018, 140, 6353−6360.
(39) Liang, B.; Yu, Z.; Zhuang, X.; Wang, J.; Wei, J.; Ye, K.; Zhang,
Z.; Liu, Y.; Wang, Y. Achieving High-Performance Pure-Red
Electrophosphorescent Iridium(III) Complexes based on Optimizing
Ancillary Ligand. Chem. - Eur. J. 2020, 26, 4410−4418.
(40) Pal, A. K.; Krotkus, S.; Fontani, M.; Mackenzie, C. F. R.;
Cordes, D. B.; Slawin, A. M. Z.; Samuel, I. D. W.; Zysman-Colman, E.
High-Efficiency Deep-Blue-Emitting Organic Light-Emitting Diodes
Based on Iridium(III) Carbene Complexes. Adv. Mater. 2018, 30,
1804231.
(41) Li, Q.; Shi, C.; Huang, M.; Wei, X.; Yan, H.; Yang, C.; Yuan, A.
B- and N-embedded color-tunable phosphorescent iridium complexes
and B-N Lewis adducts with intriguing structural and optical changes.
Chem. Sci. 2019, 10, 3257−3263.
(42) Liu, X.; Yu, Z.; Yu, M.; Zhang, X.; Xu, Y.; Lv, P.; Chu, S.; Liu,
C.; Lai, W. Y.; Huang, W. Iridium(III)-Complexed Polydendrimers
for Inkjet-Printing OLEDs: The Influence of Solubilizing Steric
Hindrance Groups. ACS Appl. Mater. Interfaces 2019, 11, 26174−
26184.
(43) Yang, X.; Guo, H.; Liu, B.; Zhao, J.; Zhou, G.; Wu, Z.; Wong,
W. Y. Diarylboron-Based Asymmetric Red-Emitting Ir(III) Complex
for Solution-Processed Phosphorescent Organic Light-Emitting Diode
with External Quantum Efficiency above 28%. Adv. Sci. 2018, 5,
1701067.
(44) Ma, D.; Liu, R.; Qiu, Y.; Duan, L. High-performance yellow-
and orange-emitting diodes based on novel sublimable cationic
iridium(iii) complexes by ligand control. J. Mater. Chem. C 2018, 6,
5630−5638.
(45) Niu, Z.-G.; Han, H.-B.; Li, M.; Zhao, Z.; Chen, G.-Y.; Zheng,
Y.-X.; Li, G.-N.; Zuo, J.-L. Tunable Emission Color of Iridium(III)
Complexes with Phenylpyrazole Derivatives as the Main Ligands for
Organic Light-Emitting Diodes. Organometallics 2018, 37, 3154−
3164.
(46) Sun, Y.; Yang, X.; Feng, Z.; Liu, B.; Zhong, D.; Zhang, J.; Zhou,
G.; Wu, Z. Highly Efficient Deep-Red Organic Light-Emitting Devices
Based on Asymmetric Iridium(III) Complexes with the Thianthrene
(30) Tian, Q. S.; Zhang, L.; Hu, Y.; Yuan, S.; Wang, Q.; Liao, L. S.
High-Performance White Organic Light-Emitting Diodes with
Simplified Structure Incorporating Novel Exciplex-Forming Host.
ACS Appl. Mater. Interfaces 2018, 10, 39116−39123.
I
https://dx.doi.org/10.1021/acs.organomet.0c00472
Organometallics XXXX, XXX, XXX−XXX

Organometallics
pubs.acs.org/Organometallics
Article
5,5,10,10-Tetraoxide Moiety. ACS Appl. Mater. Interfaces 2019, 11,
26152−26164.
(47) Chaskar, A.; Chen, H. F.; Wong, K. T. Bipolar host materials: a
chemical approach for highly efficient electrophosphorescent devices.
Adv. Mater. 2011, 23, 3876−3895.
(48) Yu, Z.; Zhang, J.; Liu, S.; Zhang, L.; Zhao, Y.; Zhao, H.; Xie, W.
High-Efficiency Blue Phosphorescent Organic Light-Emitting Devices
with Low Efficiency Roll-Off at Ultrahigh Luminance by the
Reduction of Triplet-Polaron Quenching. ACS Appl. Mater. Interfaces
2019, 11, 6292−6301.
(49) Udagawa, K.; Sasabe, H.; Igarashi, F.; Kido, J. Simultaneous
Realization of High EQE of 30%, Low Drive Voltage, and Low
Efficiency Roll-Off at High Brightness in Blue Phosphorescent
OLEDs. Adv. Opt. Mater. 2016, 4, 86−90.
(50) Liang, X.; Zhang, F.; Yan, Z. P.; Wu, Z. G.; Zheng, Y.; Cheng,
G.; Wang, Y.; Zuo, J. L.; Pan, Y.; Che, C. M. Fast Synthesis of
Iridium(III) Complexes Incorporating a Bis(diphenylphorothioyl)-
amide Ligand for Efficient Pure Green OLEDs. ACS Appl. Mater.
Interfaces 2019, 11, 7184−7191.
(51) Lu, G. Z.; Zhu, Q.; Liu, L.; Wu, Z. G.; Zheng, Y. X.; Zhou, L.;
Zuo, J. L.; Zhang, H. Pure Red Iridium(III) Complexes Possessing
Good Electron Mobility with 1,5-Naphthyridin-4-ol Derivatives for
High-Performance OLEDs with an EQE over 31%. ACS Appl. Mater.
Interfaces 2019, 11, 20192−20199.
(52) You, C.; Liu, D.; Meng, F.; Wang, Y.; Yu, J.; Wang, S.; Su, S.;
Zhu, W. Iridium(iii) phosphors with rigid fused-heterocyclic chelating
architectures for efficient deep-red/near-infrared emissions in polymer
light-emitting diodes. J. Mater. Chem. C 2019, 7, 10961−10971.
(53) Liu, Y.; Nell, B.; Ortstein, K.; Wu, Z.; Karpov, Y.; Beryozkina,
T.; Lenk, S.; Kiriy, A.; Leo, K.; Reineke, S. High Electron Affinity
Molecular Dopant CN6-CP for Efficient Organic Light-Emitting
Diodes. ACS Appl. Mater. Interfaces 2019, 11, 11660−11666.
(54) Jing, Y.-M.; Wang, F.-Z.; Zheng, Y.-X.; Zuo, J.-L. Efficient deep
red electroluminescence of iridium(iii) complexes with 2,3-diphe-
nylquinoxaline derivatives and tetraphenylimidodiphosphinate. J.
Mater. Chem. C 2017, 5, 3714−3724.
(55) Li, G.; Zhu, D.; Peng, T.; Liu, Y.; Wang, Y.; Bryce, M. R. Very
High Efficiency Orange-Red Light-Emitting Devices with Low Roll-
Off at High Luminance Based on an Ideal Host-Guest System
Consisting of Two Novel Phosphorescent Iridium Complexes with
Bipolar Transport. Adv. Funct. Mater. 2014, 24, 7420−7426.
(56) Miao, Y.; Tao, P.; Wang, K.; Li, H.; Zhao, B.; Gao, L.; Wang,
H.; Xu, B.; Zhao, Q. Highly Efficient Red and White Organic Light-
Emitting Diodes with External Quantum Efficiency beyond 20% by
Employing Pyridylimidazole-Based Metallophosphors. ACS Appl.
Mater. Interfaces 2017, 9, 37873−37882.
(57) Chen, T.-R. Synthesis, structure, and field-effect property of 2-
(benzimidazol-2-yl) quinoline. Mater. Lett. 2005, 59, 1050−1052.
(58) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.;
Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.;
Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M.;
Heyd, J. J.; Brothers, E.; Kudin, K. N.; Staroverov, V. N.; Keith, T.;
Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A.; Burant, J.
C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega, N.; Millam, J. M.;
Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo,
J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi,
R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.;
Zakrzewski, V. G.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.;
Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman, J. B.; Ortiz, J. V.;
Cioslowski, J.; Fox, D. J. Gaussian 09, Rev. D.01; Gaussian, Inc.:
Wallingford, CT, 2013.
J
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Organometallics XXXX, XXX, XXX−XXX