Methoxyl modification in furo[3,2-: C] pyridine-based iridium complexes towards highly efficient green- and orange-emitting electrophosphorescent devices

Article abstract of DOI:10.1039/c7tc04269h

Two new furo[3,2-c]pyridine-based Ir complexes, namely (4-MeOpfupy)₂Ir(acac) and (3-MeOpfupy)₂Ir(acac), were designed and synthesized by introducing a methoxyl group into the 4- and 3-positions of the phenyl ring on the C^N ligand. It was found that the position of the methoxyl group has an important influence on the electrochemical and photophysical properties, as well as electrophosphorescent device performance. Compared with the reference complex (pfupy)₂Ir(acac) without any methoxyl group (538 nm), (4-MeOpfupy)₂Ir(acac) with a methoxyl group at the 4-position shows a blue-shifted emission peak at 523 nm originating from the methoxyl-induced enhancement of the LUMO level, whereas (3-MeOpfupy)₂Ir(acac) with a methoxyl group at the 3-position shows a red-shifted emission peak at 602 nm originating from the methoxyl-induced enhancement of the HOMO level. The corresponding PhOLEDs based on (4-MeOpfupy)₂Ir(acac) and (3-MeOpfupy)₂Ir(acac) realize highly efficient green and orange electroluminescence with CIE coordinates of (0.37, 0.60) and (0.60, 0.40), revealing a state-of-the-art EQE as high as 29.5% (100.7 cd A^-1) and 16.7% (43.9 cd A^-1), respectively. These impressive results indicate that methoxyl modification is a valid way to tune the molecular energy levels and emissive color for Ir complexes while not obviously sacrificing the final device performance.

Full text of DOI:10.1039/c7tc04269h

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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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Methoxyl modification in furo[3,2-c]pyridine based iridium
complexes towards highly efficient green- and orange-emitting
electrophosphorescent devices
Received 00th January 20xx,
Accepted 00th January 20xx
Zhimin Yan,a,b Yanping Wang,c Junqiao Ding,*,b Yue Wang,*,a Lixiang Wang*,b
DOI: 10.1039/x0xx00000x
Two new furo[3,2-c]pyridine based Ir complexes, namely (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac), have been
designed and synthesized by introducing methoxyl into the 4- and 3-position of phenyl ring on the C^N ligand. It is found
that the position of methoxyl plays an important role on the electrochemical and photophysical properties as well as
electrophosphorescent device performance. Compared to the reference complex (pfupy)2Ir(acac) without any methoxyl
(538 nm), (4-MeOpfupy)2Ir(acac) with 4-position methoxyl shows a blue-shifted emission peaked at 523 nm originating
from the methoxyl-induced enhancement of the LUMO level, whereas (3-MeOpfupy)2Ir(acac) with 3-position methoxyl
shows a red-shifted emission peaked at 602 nm originating from the methoxyl-induced enhancement of the HOMO level.
The corresponding PhOLEDs based on (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac) realize highly efficient green and
orange electroluminescence with CIE coordinates of (0.37, 0.60) and (0.60, 0.40), revealing a state-of-art EQE as high as
29.5% (100.7 cd/A) and 16.7% (43.9 cd/A), respectively. The impressive results indicate that methoxyl modification is a
valid way to tune the molecular energy levels and emissive color for Ir complexes while not obviously sacrificing the final
device performance.
www.rsc.org/
quinoxaline based polymers PTTQx, the meta-alkoxyl-phenyl was
found to reduce the highest occupied molecular orbital (HOMO)
level and lowest unoccupied molecular orbital (LUMO) level with
Introduction
Alkoxyl is one of the basic substituents in organic chemistry owing
to its facile synthesis through a Williamson route.1-4 Unlike the
other groups (e.g. alkyl, amine, halogen, cyano and nitro), it displays
two opposite electronic effect: 1) a resonance electron-donating
effect due to the lone pair electrons of oxygen; 2) an inductive
electron-withdrawing effect due to the stronger electronegativity of
respect to the para-alkoxyl-phenyl.10 Further replacing alkylthienyl
with meta-alkoxyl-phenyl in benzo[1,2-b;4,5-b]dithiophene (BDT)
based two-dimensional conjugated polymers led to the significant
enhancement of the open-circuit voltage from 0.60 V to 0.78 V and
consequently improved power conversion efficiency from 5.56% to
7.50% for the corresponding polymer solar cells (PSCs).11 On the
other hand, the emission color regulation of iridium (Ir) complexes,
which is related to their energy levels, is also a research hotpot in
phosphorescent organic light-emitting diodes (PhOLEDs).12-29
Although alkoxyl was incorporated into Ir complexes, few
systematic investigations have been reported about the effect of
alkoxyl on their photophysical properties and final device
performance.30-33
oxygen than carbon.5, Since the resonance electron-donating
6
effect is dominant over the inductive electron-withdrawing one,
alkoxyl is often seen as an electron-donating group.7 Therefore, it
could be purposely used to modulate the molecular energy level at
the same time when introduced to the conjugated main chain to
increase the solubility of conjugated polymers.8-9 For instance, in
In previous work, we designed and synthesized a novel furo[3,2-
c]pyridine based Ir complex (pfupy)2Ir(acac)34 by replacing sulfur
with oxygen in the C^N ligand. Compared with the typical
thiophene-containing yellow phosphor (pthpy)2Ir(acac),
a
hypsochromic shift was observed for the furan-containing
(pfupy)2Ir(acac), which exhibits a yellowish-green emission with
Commission International De L’Eclairge (CIE) coordinates of (0.44,
0.55) and an unexpected external quantum efficiency (EQE) over 30%
without any out-coupling technology. Considering the deviated
emission of (pfupy)2Ir(acac) from the green region, there will be
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plenty of room for improvements in color purity while not
sacrificing device efficiency.
Synthesis
All chemicals and reagents were used as received from
With this idea in mind, we further demonstrate the methoxyl
modification in (pfupy)2Ir(acac) towards highly efficient green- and
orange-emitting PhOLEDs. When the methoxyl locates at the 4- commercial sources without further purification. Solvents for
position of phenyl in the C^N ligand, the resultant complex chemical synthesis were purified according to the standard
(denoted as (4-MeOpfupy)2Ir(acac)) achieves a more greenish procedures.
emission than (pfupy)2Ir(acac), revealing CIE coordinates of (0.37,
0.60) and a peak EQE of 29.5% (100.7 cd/A). Meanwhile, the 3-
General procedure for the synthesis of C^N ligands
position substitution of methoxyl on phenyl can endow the
To
a
mixture of 4-chlorofuro[3,2-c]pyridine (1 equiv.),
resultant complex (denoted as (3-MeOpfupy)2Ir(acac)) with a red-
shifted orange emission accompanied by CIE coordinates of (0.60,
0.40) and a peak EQE of 16.7% (43.9 cd/A). The impressive results
manifest that methoxyl modification is a valid way not only to tune
the emissive wavelength of Ir complexes but also to keep the high
device efficiency.
methoxylphenyl boronic acid (1.5 equiv.) and Pd(PPh3)4 (0.03
equiv.), the refined tetrahydrofuran (THF) and degassed 2M Na2CO3
a.q (3 equiv.) were added in an argon atmosphere. After heating to
reflux for 8 h, the organic layer was extracted by DCM and dried by
Na2SO4. The crude product was purified by chromatography on
silica gel using petroleum ether and ethyl acetate as the eluent.
Experimental
4-MeOpfupy: 75% yield. 1H NMR (400 MHz, CDCl3) δ 8.66 (dd, J =
9.2, 6.0 Hz, 1H), 8.01 (dd, J = 11.4, 5.5 Hz, 2H), 7.83 (d, J = 12.0 Hz,
1H), 7.53 (dd, J = 8.6, 5.1 Hz, 1H), 7.20 – 7.14 (m, 1H), 7.14 (s, 2H),
3.91 (d, J = 1.3 Hz, 3H).
Measurements and Characterization
1H NMR spectra were recorded by Bruker Avance NMR
spectrometer. The elemental analysis was performed using a Bio-
Rad elemental analysis system. MALDI/TOF (Matrix assisted laser
desorption ionization/Time-of-flight) mass spectra were performed
on an AXIMA CFR MS apparatus (COMPACT) with 2-[(2E)-3-(4-tert-
butylphenyl)-2-methylprop-2-enylidene] malononitrile (DCTB) as
the matrix. Thermal gravimetric analysis (TGA) and differential
1
3-MeOpfupy: 78% yield. H NMR (400 MHz, CDCl3) δ 8.68 (d, J = 6.0
Hz, 1H), 7.81 (d, J = 2.3 Hz, 1H), 7.63 – 7.60 (m, 1H), 7.59 – 7.52 (m,
2H), 7.47 (t, J = 7.9 Hz, 1H), 7.17 (dd, J = 2.2, 0.9 Hz, 1H), 7.08 (ddd, J
= 8.2, 2.6, 0.9 Hz, 1H), 3.95 (s, 3H).
scanning calorimetry (DSC) were performed under
nitrogen using a Perkin-Elmer-TGA 7 and Perkin-Elmer-DSC 7
system, respectively. The UV-Vis absorption and
a flow of
General procedure for the synthesis of Ir complexes
IrCl3•3H2O (1 equiv.), C^N ligand (2.1 equiv.), 2-ethoxyethanol
and H2O were added to a round bottom flask. The mixture was
stirred at 110 oC in argon atmosphere for 48 h. After cooling, the
mixture was directly filtered and washed with water and ethanol.
The yellow solid (dimer) was dried in vacuum at 65 oC without
further purification. Subsequently, a round bottom flask was
charged with dimer (1 equiv.), 2,4-pentanedione (5 equiv.) and
Na2CO3 (5 equiv.). After heated to 80 oC in argon atmosphere for 12
h, the mixture was cooled, and the resulting solid was collected by
filtration and washed with water. Further purification was operated
by column chromatography using DCM and petroleum ether as the
eluent.
photoluminescence (PL) spectra were measured by a Perkin–Elmer
Lambda 35 UV/Vis spectrometer and a Perkin–Elmer LS 50B
spectrofluorometer, respectively. The PL quantum yields (PLQYs)
were measured in N2-saturated toluene solutions with a typical
green phosphor Ir(ppy)3 (ΦPL = 0.97) as the reference.35 The
transient PL spectra in toluene solutions were measured under N2
atmosphere and excited at a 355 nm pulse with ca. 3 ns width from
a Quanty-Ray DCR-2 pulsed Nd:YAG laser. Cyclic voltammetry (CV)
experiments were performed on
a CHI660a electrochemical
analyzer under a scan rate of 100 mV s−1. The measurements were
carried out in dichloromethane (DCM) for anodic sweeping and in
N,N-dimethylformamide (DMF) for cathodic sweeping with
conventional three-electrode system consisting of platinum
working electrode, a platinum counter electrode and an Ag/AgCl
reference electrode. The supporting electrolyte was 0.1
a
a
(4-MeOpfupy)2Ir(acac): 61% yield. 1H NMR (400 MHz, DMSO) δ 8.34
(d, J = 2.3 Hz, 2H), 8.26 (d, J = 6.6 Hz, 2H), 8.01 (d, J = 8.7 Hz, 2H),
7.88 (d, J = 1.7 Hz, 2H), 7.67 (dd, J = 6.6, 0.7 Hz, 2H), 6.46 (dd, J =
8.7, 2.6 Hz, 2H), 5.48 (d, J = 2.6 Hz, 2H), 5.26 (s, 1H), 3.44 (s, 6H),
1.70 (s, 6H). MALDI-TOF MS: 740.1 [M+]. Anal. calcd for
M
tetrabutylammonium perchlorate (n-Bu4NClO4). All potentials were
calibrated against the ferrocene/ferrocenium couple (Fc/Fc+). The
HOMO and LUMO energy levels were determined by the equations
HOMO = -e(Eox, onset + 4.8 V) and LUMO = -e(Ered, onset + 4.8 V), where
Eox, onset and Ered, onset were the potential onset obtained from the
first oxidation and reduction waves, respectively. The theoretical
calculations were performed on Gauss 09 program. And the ground
state structures of Ir complexes were optimized by the DFT using
the B3LYP hybrid functional. The “double-ξ” basis set LANL2DZ was
employed for Ir atom and 6-31G(d) basis sets for H, C, N, and O
atoms.
C
33H27IrN2O6: C, 53.58; H, 3.68; N, 3.79. Found: C, 53.30; H, 3.65; N,
3.70.
(3-MeOpfupy)2Ir(acac): 35% yield. 1H NMR (400 MHz, DMSO) δ 8.37
(d, J = 2.3 Hz, 2H), 8.33 (d, J = 6.5 Hz, 2H), 7.87 (d, J = 1.7 Hz, 2H),
7.75 (d, J = 6.5 Hz, 2H), 7.53 (d, J = 2.6 Hz, 2H), 6.36 (dd, J = 8.4, 2.6
Hz, 2H), 5.91 (d, J = 8.4 Hz, 2H), 5.25 (s, 1H), 3.71 (s, 6H), 1.69 (s,
2 | J. Name., 2012, 00, 1-3
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6H). MALDI-TOF MS: 740.1 [M+]. Anal. calcd for C33H27IrN2O6: C,
53.58; H, 3.68; N, 3.79. Found: C, 52.99; H, 3.63; N, 3.67.
Device fabrication and testing
All the devices were fabricated on glass substrates pre-coated
with 180 nm indium tin oxide (ITO) with a sheet resistance of 10
Ω/sq. The ITO substrates were degreased in ultrasonic solvent bath
and then dried at 120 oC for 30 min. Before loaded into the vacuum
deposition chamber, the ITO surface was treated with UV-ozone for
15 min. In successive, 10 nm of MoO3 was deposited on the top of
ITO, followed by 60 nm TAPC (4,4'-(cyclohexane-1,1-diyl)bis(N,N-di-
p-tolylaniline)), 5 nm TCTA (tris(4-(9H-carbazol-9-yl)phenyl)amine),
20 nm emissive layer, and 35 nm BmPyPB (3,3'',5,5''-tetra(pyridin-3-
yl)-1,1':3',1''-terphenyl). Finally, 1 nm thickness of LiF and 120 nm
thickness of Al were deposited to form the cathode. All the layers
were grown by thermal evaporation in a high-vacuum system with a
pressure of less than 5×10-4 Pa without breaking vacuum. The
organic materials were evaporated at the rate in a range of 1-2 Å/s
while the evaporation rate of LiF layer is 0.1 Å/s, and the metal Al
was evaporated at a rate of 8-10 Å/s. The overlap between ITO and
Al electrodes was 4 mm × 4 mm, which is the active emissive area
of PhOLEDs. The current-voltage-brightness characteristics were
measured by using a set of Keithley source measurement units
Scheme 1. Synthetic route for the methoxyl-modified Ir complexes (4-
MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac).
refined using full matrix least squares. All non-hydrogen atoms
were assigned with anisotropic displacement parameters, whereas
hydrogen atoms were placed at calculated positions theoretically
and included in the final cycles of refinement in a riding model
along with the attached carbons.
Results and discussion
Molecular design, synthesis and characterization
Starting from (pfupy)2Ir(acac), methoxyl is introduced to the 4-
and 3-positions of phenyl to design the corresponding Ir complexes
(4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac), respectively. As
depicted in Figure 1, the LUMO is mainly localized on furo[3,2-
c]pyridine and phenyl, while the HOMO is concentrated on Ir centre
and phenyl in (pfupy)2Ir(acac). And varying the methoxyl positions
on (pfupy)2Ir(acac) can lead to the different LUMO and HOMO
(Keithley 2400 and Keithley 2000) with
a calibrated silicon
photodiode. The electroluminescence (EL) spectra were measured
by a Spectrascan PR650 spectrophotometer. All the measurements
were carried out in ambient atmosphere at room temperature.
X-ray Crystallography Analysis
The single crystal X-ray diffraction experiments were carried out
using a Bruker Smart APEX diffractometer with CCD detector and
graphite monochromator, Mo Kα radiation (λ =0.71073 Å). The
intensity data were recorded with ω scan mode (187 K). Lorentz,
polarization factors were made for the intensity data and
absorption corrections were performed using SADABS program. The
crystal structure was determined using the SHELXTL program and
Figure 2. ORTEP diagram of (4-MeOpfupy)2Ir(acac) with thermal
ellipsoids drawn at 50% probability level and
removed for clarity.
H atoms, solvent
Figure 1. Molecular structures of the Ir complexes (top) together with
the LUMO and HOMO distribution obtained from DFT calculations
(bottom).
Figure 3. CV curves of (4-MeOpfupy)2Ir(acac) and (3-
MeOpfupy)2Ir(acac) compared with (pfupy)2Ir(acac).
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distribution. For example, in (4-MeOpfupy)2Ir(acac) where the
methoxyl group is meta to Ir centre but para to furo[3,2-c]pyridine,
its contribution to furo[3,2-c]pyridine by the resonance electron-
donating effect is stronger than that to Ir centre. Accordingly, the
LUMO distribution of (4-MeOpfupy)2Ir(acac) is extended to
methoxyl without obviously affecting the HOMO one. Benefiting
from the elevated LUMO and similar HOMO energy levels, a wide
bandgap could be anticipated for (4-MeOpfupy)2Ir(acac) relative to
(pfupy)2Ir(acac). By contrast, in (3-MeOpfupy)2Ir(acac), the
methoxyl group does contribute to the HOMO distribution rather
than the LUMO one because of the para arrangement between
methoxyl and Ir centre. From (pfupy)2Ir(acac) to (3-
MeOpfupy)2Ir(acac), therefore, the HOMO energy level is increased
and the LUMO remains nearly unchanged, resulting in a shallow
bandgap. The DFT calculations clearly indicate the effectiveness of
methoxyl to modulate the molecular energy levels of furo[3,2-
c]pyridine based Ir complexes.
The synthetic procedure for (4-MeOpfupy)2Ir(acac) and (3-
MeOpfupy)2Ir(acac) is shown in Scheme 1. The furo[3,2-c]pyridine
based C^N ligands were firstly prepared by a Suzuki coupling
reaction between 4-chlorofuro[3,2-c]pyridine and corresponding
methoxyl-functionalized boric acids. Then a traditional two step
route was performed to afford the terminal Ir complexes as
reported by M. E. Thompson.36 Their molecular structures were
fully characterized by 1H NMR spectroscopy, MALDI-TOF mass
spectrometry and elemental analysis (Figure S1-S2). In addition, the
single crystal of (4-MeOpfupy)2Ir(acac) for X-ray diffraction analysis
was successfully grown from the mixed solution of DCM and
methanol, but the attempt to the single crystal of (3-
MeOpfupy)2Ir(acac) failed. As one can see in Figure 2, (4-
MeOpfupy)2Ir(acac) assumes a similar distorted quasi-octahedral
geometric structure to (pfupy)2Ir(acac).34 Nevertheless, different
from (pfupy)2Ir(acac) showing a π-π interaction between furo[3,2-
c]pyridine and phenyl ring, an interaction between two furo[3,2-
c]pyridine moieties with a π-π stacking distance of 3.267-3.287 Å is
actually observed for (4-MeOpfupy)2Ir(acac) (Figure S3). The
difference may be tentatively attributed to the steric hindrance
from methoxyl substituted on phenyl.
Figure 4. UV-Vis absorption spectra in DCM (a) and PL spectra in
toluene for (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac)
compared with (pfupy)2Ir(acac) (b). Inset: the enlarged absorption part
ranging from 400 nm to 600 nm.
(pfupy)2Ir(acac). For all the Ir complexes, a reversible oxidation and
an irreversible reduction are detected during the anodic scan in
DCM and cathodic scan in DMF, respectively (Figure 3). With
respect to Fc/Fc+ (4.8 eV under vacuum), their corresponding
HOMO and LUMO levels can be determined, and the data are
tabulated in Table 1. Compared with (pfupy)2Ir(acac) (HOMO: -5.15
eV; LUMO: -2.40 eV), (4-MeOpfupy)2Ir(acac) displays an invariable
HOMO of -5.15 eV and an elevated LUMO of -2.29 eV, whereas (3-
MeOpfupy)2Ir(acac) exhibits an enhanced HOMO of -4.94 eV and a
close LUMO of -2.45 eV. The experimental trend is in well line with
the DFT calculations at the beginning of the molecular design.
Electrochemical properties
CV was used to study the electrochemical properties of (4-
MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac) relative to
Table 1. Photophysical, electrochemical and thermal properties of (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac) relative to (pfupy)2Ir(acac).
a
b
f
g
g
c
λabs
[nm]
λem
τ d
[μs]
HOMO e
[eV]
LUMO e
[eV]
Td
kr
knr
[s-1]
Φ
Complex
[oC]
354
350
323
[s-1]
PL
[nm]
538
523
602
(pfupy)2Ir(acac)
279, 355, 426, 479
296, 314, 422, 444
280, 386, 439, 507
0.80
0.88
0.32
1.04
1.07
1.33
-5.15 (-4.75)
-5.15 (-4.68)
-4.94 (-4.42)
-2.40 (-1.39)
-2.29 (-1.19)
-2.45 (-1.42)
7.7×105
8.2×105
2.4×105
1.9×105
1.1×105
5.1×105
(4-MeOpfupy)2Ir(acac)
(3-MeOpfupy)2Ir(acac)
a Measured in 10-5 M DCM solution; b Measured in 10-5 M toluene solution; c Measured in N2-saturated toluene solution with Ir(ppy)3 (ΦPL = 0.97) as the
reference; d Estimated from the transient PL spectrum measured in N2-saturated toluene solution excited by a 355 nm pulse; e HOMO = - e(Eox, onset + 4.8
V), LUMO = - e(Ered, onset + 4.8 V), where Eox, onset and Ered, onset are the onset values of the first oxidation and reduction waves, respectively. The
corresponding data from DFT calculations were also shown in brackets; f Decomposition temperature corresponding to a 5% weight loss; g Calculated
according to the equations: τ = 1/(kr + knr) and Φ = kr/(kr + knr).
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Figure 5. Device performance for (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac): device configuration and chemical structures of
used materials (a); EL spectra at 6 V (b); current density-voltage-luminance characteristic (c); luminance dependence on the EQE and
current efficiency (d).
of 1.07 μs and 1.33 μs are determined for (4-MeOpfupy)2Ir(acac)
Photophysical properties
and (3-MeOpfupy)2Ir(acac), respectively (Figure S4). Despite this,
the PLQY of (4-MeOpfupy)2Ir(acac) (0.88) seems to be a bit higher
than that of (pfupy)2Ir(acac) (0.80) because of the slightly faster
radiative rate constant (kr) and slower non-radiative rate constant
(knr). On the contrary, (3-MeOpfupy)2Ir(acac) shows a significantly
descent PLQY of 0.32 with a tardy kr and rapid knr owing to the
energy gap law.37
Figure 4 portrays the UV-Vis absorption and PL spectra in diluted
solutions. Similar to (pfupy)2Ir(acac), both (4-MeOpfupy)2Ir(acac)
and (3-MeOpfupy)2Ir(acac) possess two absorption bands including
the intense ligand-centered (LC) π-π* absorption below 400 nm and
the weak metal-to-ligand charge transfer (MLCT) absorption in the
range of 400-575 nm (Figure 4a).13 Moreover, the lowest-energy-
level absorption shows an obvious bathochromic shift following a
sequence of (4-MeOpfupy)2Ir(acac), (pfupy)2Ir(acac) and (3-
MeOpfupy)2Ir(acac). Correspondingly, the emission maxima move
from 523 nm to 538 nm and 602 nm (Figure 4b). The methoxyl
EL properties
To evaluate whether these Ir complexes are suitable for the
dependence on the optical properties is consistent with the evaporation deposition method, TGA was performed to detect their
electrochemical properties as well as the DFT simulations. As decomposition temperatures (Td) corresponding to a 5% weight
discussed above, the blue-shifted absorption and PL of (4- loss. It is found that the introduction of methoxyl has little influence
MeOpfupy)2Ir(acac) could be ascribed to the wider bandgap than on the thermal stability. For example, (4-MeOpfupy)2Ir(acac) shows
(pfupy)2Ir(acac), originating from the 4-position methoxyl an almost equal Td of 354 oC to (pfupy)2Ir(acac), and (3-
contribution mainly to the increased LUMO level. And for (3- MeOpfupy)2Ir(acac) exhibits a slightly lower Td of 323 oC (Figure S5
MeOpfupy)2Ir(acac), the rise of the HOMO level caused by the 3- and Table 1). Such a relative high Td above 300 oC can ensure the
position methoxyl is responsible for the shallower bandgap, and further thermal-deposited device test for (4-MeOpfupy)2Ir(acac)
thus red-shifted absorption and PL with regard to (pfupy)2Ir(acac).
and (3-MeOpfupy)2Ir(acac). Moreover, no obvious glass transition
In comparison to (pfupy)2Ir(acac) (1.04 μs), close decay lifetimes behaviours are observed for (4-MeOpfupy)2Ir(acac) and (3-
Table 2. Device performance for (4-MeOpfupy)2Ir(acac) and (3-MeOpfupy)2Ir(acac).
a
b
b
Von
Lmax
[cd/m2]
ηc
ηp
EQE b
[%]
CIE c
[V]
4.2
[cd/A]
[lm/W]
[x, y]
48790
28885
100.7/86.3/76.7
75.3/38.7/25.6
29.5/25.2/22.8
16.7/11.9/9.2
0.37, 0.60
0.60, 0.40
(4-MeOpfupy)2Ir(acac)
(3-MeOpfupy)2Ir(acac)
3.2
43.9/30.7/24.4
42.5/11.5/6.5
a Turn-on voltage at a brightness of 1 cd/m2; b maximum data, data at 1000 cd/m2 and 5000 cd/m2 for current efficiency (ηc), power efficiency (ηp) and
EQE, respectively; c CIE at 1000 cd/m2.
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MeOpfupy)2Ir(acac) in their DSC curves (Inset in Figure S5), meaning
the formation of amorphous films during thermal deposition.
This work was supported by the National Key Research and
Development Program of China (No. 2016YFB0400701) and
the National Natural Science Foundation of China (No.
Then we utilized them as the triplet dopants to fabricate 51573183, 91333205 and 21174144).
PhOLEDs with a structure of ITO/MoO3 (10 nm)/TAPC (60 nm)/ TCTA
(5 nm)/TCTA: Ir complex (20 nm)/BmPyPB (35 nm)/LiF (1 nm)/Al Conflicts of interest
(100 nm). Here MoO3 and LiF were used as the hole- and electron-
There are no conflicts of interest to declare.
injecting layers, respectively; TAPC and BmPyPB were employed as
the hole- and electron-transporting layers, respectively; and TCTA
was adopted as the electron-blocking layer and the host at the
Notes and references
same time (Figure 5a). The best doping concentration was
1. A. Williamson, Philos. Mag., 1850, 37, 350-356.
2. Y. Wang, S. Wang, N. Zhao, B. Gao, S. Shao, J. Ding, L. Wang, X.
optimized to be 6 wt.% and 4 wt.% for (4-MeOpfupy)2Ir(acac) and
(3-MeOpfupy)2Ir(acac), respectively. As can be clearly seen in Figure
5b, (4-MeOpfupy)2Ir(acac) emits a bright green EL peaked at 524 nm.
Compared to the yellowish-green (pfupy)2Ir(acac) (CIE: (0.44, 0.55)),
the CIE coordinates of (4-MeOpfupy)2Ir(acac) are blue-shifted to
(0.37, 0.60) and are more close to the standard viz. (0.30, 0.60) for
green light, indicative of the better green color purity. Meanwhile,
an orange EL peaked at 597 nm is observed for (3-
MeOpfupy)2Ir(acac), giving CIE coordinates of (0.60, 0.40).
Jing and F. Wang, Polym. Chem., 2015,
3. Y. Wang, Y. M. Lu, B. X. Gao, S. M. Wang, J. Q. Ding, L. X. Wang,
6, 1180-1191.
X. B. Jing and F. S. Wang, ACS Appl. Mater. Interfaces, 2016, 8,
29600-29607.
4. Y. F. Gong, X. K. Fu, S. P. Zhang and Q. L. Jiang, Chin. J. Polym.
Sci., 2008, 26, 91-97.
5. L. P. Hammett, J. Am. Chem. Soc., 1937, 59, 96-103.
6. F. Wu, J. L. Liu, G. Wang, Q. L. Song and L. N. Zhu, Chem. Eur. J.
2016, 22, 16636-16641.
,
Figure 5c and 5d plot the current density-voltage-luminance
characteristics and the luminance dependence on the EQE and
current efficiency, respectively. We note that the turn-on voltage at
1 cd/m2 of (4-MeOpfupy)2Ir(acac) is 4.2 V, higher than that of (3-
MeOpfupy)2Ir(acac) (3.2 V). The observation is understandable
when considering the large charge injection barrier induced by the
wider bandgap of (4-MeOpfupy)2Ir(acac) relative to (3-
MeOpfupy)2Ir(acac), which is further confirmed by the lower
current density at a driving voltage below 6 V. In spite of this, high
device performance is achieved for the green-emitting (4-
MeOpfupy)2Ir(acac), revealing a maximum luminance of 48790
cd/m2, a peak current efficiency of 100.7 cd/A and a peak EQE of
29.5%. And the orange-emitting (3-MeOpfupy)2Ir(acac) gives a
maximum luminance of 28885 cd/m2, a peak current efficiency of
43.9 cd/A and a peak EQE of 16.7%. To our knowledge, the obtained
performance is among the best for green38-40 and orange41-43
PhOLEDs.
7. X. C. Wang, L. Zhao, S. Y. Shao, J. Q. Ding, L. X. Wang, X. B. Jing
and F. S. Wang, Polym. Chem., 2014, , 6444-6451.
5
8. M. Sang, S. Z. Cao, W. Y. Lai and W. Huang, Acta Chim. Sinica
2015, 73, 770-782.
,
9. S. K. Lee, W. H. Lee, J. M. Cho, S. J. Park, J. U. Park, W. S. Shin, J.
C. Lee, I. N. Kang and S. J. Moon, Macromolecules, 2011, 44
,
5994-6001.
10. Y. Huang, M. Q. Zhang, L. Ye, X. Guo, C. C. Han, Y. F. Li and J. H.
Hou, J. Mater. Chem., 2012, 22, 5700-5705.
11. M. J. Zhang, X. Guo, W. Ma, S. Q, Zhang, L. J. Huo, H. Ade and J.
H. Hou, Adv. Mater., 2014, 26, 2089-2095.
12. M. A. Baldo, D. F. O'Brien, Y. You, A. Shoustikov, S. Sibley, M. E.
Thompson and S. R. Forrest, Nature, 1998, 395, 151-154.
13. S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, H. E.
Lee, C. Adachi, P. E. Burrows, S. R. Forrest and M. E. Thompson,
J. Am. Chem. Soc., 2001, 123, 4304-4312.
14. Y. You and S. Y. Park, J. Am. Chem. Soc., 2005, 127, 12438-
12439.
15. J. Li, P. I. Djurovich, B. D. Alleyne, M. Yousufuddin, N. N. Ho, J. C.
Thomas, J. C. Peters, R. Bau and M. E. Thompson, Inorg. Chem.
,
2005, 44, 1713-1727.
16. Y. Chi and P. T. Chou, Chem. Soc. Rev., 2010, 39, 638-655.
Conclusions
In summary, we report two new methoxyl-functionalized Ir
complexes bearing furo[3,2-c]pyridine based C^N ligand. By
simply modifying the methoxyl position on the ligand, highly
efficient green- and orange-emitting PhOLEDs can be realized
17. X. L. Yang, X. B. Xu and G. J. Zhou, J. Mater. Chem. C, 2015,
3
,
913-944.
18. S. M. Wang, B. H. Zhang, X. D. Wang, J. Q. Ding, Z. Y. Xie and L.
X. Wang, Adv. Opt. Mater., 2015, , 1349-1354.
3
at the same time. Compared to (pfupy)2Ir(acac) without any 19. Y. Wang, S. M. Wang, J. Q. Ding, L. X. Wang, X. B. Jing and F. S.
Wang, Chem. Commun., 2016, 53, 180-183.
methoxyl, (4-MeOpfupy)2Ir(acac) with 4-position methoxyl
shows a blue-shifted green emission of 523 nm accompanied
by CIE coordinates of (0.37, 0.60) and a peak EQE of 29.5%,
while (3-MeOpfupy)2Ir(acac) with 3-position methoxyl shows a
red-shifted orange emission of 602 nm accompanied by CIE
coordinates of (0.60, 0.40) and a peak EQE of 16.7%. We
believe that this work will shed light on the great potential of
furo[3,2-c]pyridine based Ir complexes in high-performance
PhOLEDs.
20. J. Q. Ding, J. H. Lu, Y. X. Cheng, Z. Y. Xie, L. X. Wang, X. B. Jing
and F. S. Wang, J. Organomet. Chem., 2009, 694, 2700-2704.
21. C. Y. Kuei, W. L. Tsai, B. H. Tong, M. Jiao, W. K. Lee, Y. Chi, C. C.
Wu, S. H. Liu, G. H. Lee and P. T. Chou, Adv. Mater., 2016, 28
2795-2800.
22. P. Tao, W. L. Li, J. Zhang, S. Guo, Q. Zhao, H. Wang, B. Wei, S. J.
Liu, X. H. Zhou, Q. Yu, B. S. Xu and W. Huang, Adv. Funct. Mater.
2016, 26, 881-894.
23. G. Sarada, W. Cho, A. Maheshwaran, V. G. Sree, H. Y. Park, Y. S.
,
,
Gal, M. Song and S. H. Jin, Adv. Funct. Mater., 2017, 27
,
1701002.
Acknowledgements
6 | J. Name., 2012, 00, 1-3
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24. X. Yang, G. Zhou and W.-Y. Wong, Chem. Soc. Rev., 2015, 44
,
8484-8575.
25. B. Liu, F. Dang, Z. Feng, Z. Tian, J. Zhao, Y. Wu, X. Yang, G. Zhou,
Z. Wu and W.-Y. Wong, J. Mater. Chem. C, 2017, , 7871-7883.
26. X. Yang, Z. Feng, J. Zhao, J.-S. Dang, B. Liu, K. Zhang and G. Zhou,
ACS Appl. Mater. Interfaces, 2016, , 33874-33887.
5
8
27. W.-Y. Wong and C.-L. Ho, J. Mater. Chem., 2009, 19, 4457-4482.
28. W.-Y. Wong and C.-L. Ho, Coord. Chem. Rev., 2009, 253, 1709-
1758.
29. G. Tan, S. Chen, C.-H. Siu, A. Langlois, Y. Qiu, H. Fan, C.-L. Ho, P.
D. Harvey, Y. H. Lo, L. Liu and W.-Y. Wong, J. Mater. Chem. C
2016, , 6016-6026.
,
4
30. S. Okada, K. Okinaka, H. Iwawaki, M. Furugori, M. Hashimoto, T.
Mukaide, J. Kamatani, S. Igawa, A. Tsuboyama, T. Takiguchi and
K. Ueno, Dalton Trans., 2005,
31. J. H. Seo, S. C. Lee, Y.K. Kim, Y. S. Kim J. Nanosci. Nanotechnol.
2009, , 7048–7051.
0, 1583-1590.
,
9
32. Y. Hisamatsu and S. Aoki, Eur. J. Inorg. Chem., 2011, 2011, 5360-
5369.
33. Y. Jiao, M. Li, N. Wang, T. Lu, L. Zhou, Y. Huang, Z. Y. Lu, D. B.
Luo and X. M. Pu, J. Mater. Chem. C, 2016, 4, 4269-4277.
34. Z. M. Yan, Y. P. Wang, J. X. Wang, Y. Wang, J. Q. Ding, L. X.
Wang, J Mater. Chem. C, 2017, 5, 10122-10125.
35. T. Sajoto, P. I. Djurovich, A. B. Tamayo, J. Oxgaard, W. A.
Goddard and M. E. Thompson, J. Am. Chem. Soc., 2009, 131
,
9813-9822.
36. S. Lamansky, P. Djurovich, D. Murphy, F. Abdel-Razzaq, R.
Kwong, I. Tsyba, M. Bortz, B. Mui, R. Bau and M. E. Thompson,
Inorg. Chem., 2001, 40, 1704-1711.
37. H. Yersin, A. F. Rausch, R. Czerwieniec, T. Hofbeck and T.
Fischer, Coord. Chem. Rev., 2011, 255, 2622-2652.
38. H. Sasabe, H. Nakanishi, Y. Watanabe, S. Yano, M. Hirasawa, Y. J.
Pu and J. Kido, Adv. Funct. Mater., 2013, 23, 5550-5555.
39. G. P. Tan, S. M. Chen, N. Sun, Y. H. Li, D. Fortin, W.Y. Wong, H. S.
Kwok, D. G. Ma, H. B. Wu, L. X. Wang and P. D. Harvey, J. Mater.
Chem. C, 2013, 1, 808-821.
40. K. H. Kim, C. K. Moon, J. H. Lee, S. Y. Kim and J. J. Kim, Adv.
Mater., 2014, 26, 3844-3847.
41. S. Lee, H. Shin and J. J. Kim, Adv. Mater., 2014, 26, 5864-5868.
42. H. U. Kim, J. H. Jang, W. Song, B. J. Jung, J. Y. Lee and D.-H.
Hwang, J. Mater. Chem. C, 2015,
43. B. Liu, J. W. Zhao, C. Y Luo, F. Lu, S. Tao and Q. X. Tong, J. Mater.
Chem. C, 2016, , 2003-2010.
3, 12107-12115.
4
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Graphic Abstract
Highly efficient green- and orange-emitting PhOLEDs have been successfully
realized via a simple methoxyl modification in furo[3,2-c]pyridine based Ir
complexes.