Facile Synthesis of Highly Efficient Lepidine-Based Phosphorescent Iridium(III) Complexes for Yellow and White Organic Light-Emitting Diodes

Article abstract of DOI:10.1002/adfm.201503826

Highly efficient lepidine-based phosphorescent iridium(III) complexes with pentane-2,4-dione or triazolpyridine as ancillary ligands have been designed and prepared by a newly developed facile synthetic route. Fluorine atoms and trifluoromethyl groups have been introduced into the different positions of ligand, and their influence on the photophysical properties of complexes has been investigated in detail. All the triazolpyridine-based complexes display the blueshifted dual-peak emission compared to the pentane-2,4-dione-based ones with a broad single-peak emission. The complexes show emission with broad full width at half maximum (FWHM) over 100 nm, and the emissions are ranges from greenish-yellow to orange region with the absolute quantum efficiency (Φ_PL) of 0.21-0.92 in solution, i.e., Φ_PL = 0.92 (18), which is the highest value among the reported neutral yellow iridium(III) complexes. Furthermore, high-performance yellow and complementary-color-based white organic light-emitting diodes (OLEDs) have been fabricated. The FWHMs of the yellow, greenish-yellow OLEDs are in the range of 94-102 nm, which are among the highest values of the reported yellow or greenish-yellow-emitting devices without excimer emission. The maximum external quantum efficiency of monochrome OLEDs can reach 24.1%, which is also the highest value among the reported yellow or greenish-yellow devices. The color rendering indexes of blue and complementary yellow-based white OLED is as high as 78.

Full text of DOI:10.1002/adfm.201503826

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Facile Synthesis of Highly Efficient Lepidine-Based
Phosphorescent Iridium(III) Complexes for Yellow
and White Organic Light-Emitting Diodes
Peng Tao, Wei-Ling Li, Jing Zhang, Song Guo, Qiang Zhao,* Hua Wang,* Bin Wei,
Shu-Juan Liu, Xin-Hui Zhou, Qi Yu, Bing-She Xu, and Wei Huang*
for organic light-emitting diodes (OLEDs)
that are regarded as potential replacements
Highly efficient lepidine-based phosphorescent iridium(III) complexes with
pentane-2,4-dione or triazolpyridine as ancillary ligands have been designed
and prepared by a newly developed facile synthetic route. Fluorine atoms and
trifluoromethyl groups have been introduced into the different positions of
ligand, and their influence on the photophysical properties of complexes has
been investigated in detail. All the triazolpyridine-based complexes display
the blueshifted dual-peak emission compared to the pentane-2,4-dione-based
ones with a broad single-peak emission. The complexes show emission with
broad full width at half maximum (FWHM) over 100 nm, and the emissions
are ranges from greenish–yellow to orange region with the absolute quantum
efficiency (ΦPL) of 0.21–0.92 in solution, i.e., ΦPL = 0.92 (18), which is the
highest value among the reported neutral yellow iridium(III) complexes.
Furthermore, high-performance yellow and complementary-color-based white
organic light-emitting diodes (OLEDs) have been fabricated. The FWHMs of
the yellow, greenish–yellow OLEDs are in the range of 94–102 nm, which are
among the highest values of the reported yellow or greenish–yellow-emitting
devices without excimer emission. The maximum external quantum efficiency
of monochrome OLEDs can reach 24.1%, which is also the highest value
among the reported yellow or greenish–yellow devices. The color rendering
indexes of blue and complementary yellow-based white OLED is as high as 78.
in future display and solid-state lighting
techniques.[1–15]
The phosphorescent
transition-metal complexes harness both
singlet and triplet excitons to improve
device efficiency greatly compared with
electrofluorescent emitters.[16–20] To meet
the target of full-color flat-panel displays
and low-cost lighting sources, recent
efforts have been devoted to the color
tuning of these complexes.[21–27] Among
all kinds of transition-metal complexes,
the cyclometalated iridium(III) complexes
are considered as the most attractive can-
didates for electroluminescent devices
owing to their stable chemical structure,
high luminescent efficiency, and tun-
able emission wavelength over the whole
visible region.[28–32]
The greenish–yellow or yellow emis-
sion is one crucial chromaticity compo-
nent to high-performance white OLEDs
(WOLEDs).[33–35] Usually, the WOLEDs
are made up of three primary colors
(RGB),[16,19,36–39] so there is a great gap
(up to 100 nm) in the white-light spec-
trum because the wavelengths of typical green and red emitters
are 520 and 620 nm, respectively, leading to the uncontinuity
of the spectrum of WOLEDs. In other words, the emission in
the range from 520 to 620 nm is missing, which greatly affects
1. Introduction
Considerable progress has been made in the design and syn-
thesis of phosphorescent transition-metal complexes suitable
P. Tao, Prof. H. Wang, Prof. B.-S. Xu
W.-L. Li, J. Zhang, Prof. B. Wei
MOE Key Laboratory of Advanced
Display and System Applications
Shanghai University
Research Center of Advanced Materials Science
and Technology and MOE Key Laboratory of Interface
Science and Engineering in Advanced Materials
Taiyuan University of Technology
Shanghai 200072, P. R. China
Taiyuan 030024, P. R. China
E-mail: wanghua001@tyut.edu.cn
Prof. W. Huang
Key Laboratory of Flexible Electronics
(KLOFE) and Institute of Advanced Materials (IAM)
Jiangsu National Synergetic Innovation
Center for Advanced Materials (SICAM)
Nanjing Tech University (NanjingTech)
Nanjing 211816, P. R. China
P. Tao, S. Guo, Prof. Q. Zhao, Prof. S.-J. Liu, Prof. X.-H. Zhou, Q. Yu
Key Laboratory for Organic Electronics and Information Displays and
Institute of Advanced Materials (IAM)
Jiangsu National Synergetic Innovation Center for
Advanced Materials (SICAM)
Nanjing University of Posts and Telecommunications (NUPT)
Nanjing 210023, P. R. China
E-mail: wei-huang@njtech.edu.cn
E-mail: iamqzhao@njupt.edu.cn
DOI: 10.1002/adfm.201503826
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the color rendering indexes (CRI) of WOLEDs. To solve this
problem, one way is to incorporate yellow emitter into RGB-
based WOLEDs,[33,34] and the other is to directly replace the
green emitter or replace both green and red emitters by a
greenish–yellow emitter with broad full width at half maximum
(FWHM).[40–42] For the first approach, much more compli-
cated device structures are needed, although the incorporation
of yellow emitter into RGB-based WOLEDs can be effective
to increase the CRI of WOLEDs. In contrast, combination of
blue and complementary yellow emissions is more attractive.
So the phosphors exhibiting greenish–yellow and yellow emis-
sion, especially, with broad FWHM become very significant
for high-quality device fabrication. Recently, some efforts have
been devoted to broaden the FWHM of yellow or greenish–
yellow-emitting OLEDs. Lee et al.[35] reported yellow-emitting
OLEDs incorporating 2-(2-naphthyl)pyridine-based iridium(III)
complex with much broader FWHM up to 87 nm. Li et al.[43]
and Laskar et al.[44] have demonstrated yellow phosphorescent
OLEDs with FWHMs over 100 nm by utilizing excimer emis-
sion induced by platinum(II) complexes with low efficien-
cies of 6.6 and 2.4 lm W−1. However, the electroluminescence
(EL) spectra and the corresponding 1931 Commission Inter-
nationale de L’Eclairage (CIE) coordinates based on excimer
emission are greatly influenced by the dopant concentration.
Li et al.[45] reported 2-aryl-benzothiazole-based iridium(III)
complexes exhibiting yellow emission with the solution
quantum efficiency (ΦPL) of 0.34–0.42, and the device with
external quantum efficiency (EQE) of 23.0% based on yellow
emitter was achieved. Hou et al.[46] reported bis(pyridylphenyl)
iridium(III) complexes bearing ancillary guanidinate ligands
with emission wavelength (λmax) of 528–560 nm and ΦPL of
0.16–0.37. Jou et al.[47] reported 5-methyl-7-fluoro-5H-benzo[c]
[1,5]naphthyridin-6-one-based iridium(III) complex emitting
at 545 nm with ΦPL up to 0.71, and the EQE of yellow device
with FWHM of 80 nm is up to 22.6%. Dumur et al.[48] reported
an iridium(III) complex containing 7,8-benzoquinoline as the
cyclometalated ligand emitting at 551 nm, and the FWHM
of the device is 75 nm. Chang et al.[33] reported a greenish–
yellow emitter [bis(2-methyldibenzo[f,h]quinoxaline) tetrakis(1-
pyrazolyl)-borate iridium(III)] with ΦPL up to 0.74. Using this
greenish–yellow emitter, the device with EQE of 21.5% can
be obtained. However, the relatively narrow FWHM (63 nm)
of the device is achieved. Cao et al.[49] reported the blue- and
red-based WOLEDs with low CRI of 52 due to the bad match
of blue and red emission. They also fabricated a blue-orange
codoped WOLED.[50] The resulting moderate color quality with
a CRI falling in the narrow range of 52–55 was not impressive,
which can be attributed to the very narrow FWHM (50 nm)
of orange emitter used. Recently, Xie et al.[18] reported a blue-
orange complementary-color-based phosphorescent WOLED
exhibiting the relatively low CRI of 65, which is caused by the
narrow FWHM (63 nm) of orange emitter used. Very recently,
Ye et al.[51] reported the binary blue and complementary orange
color WOLEDs with a high CRI of 71.
solid-state lighting industry.[33,34,40–48] 2-Phenylquinoline (HPQ)
is an excellent cyclometalated ligand, and red or deep red-emit-
ting phosphors derived from HPQ have been reported.[52–55]
However, the greenish–yellow or yellow emitters based on
HPQ derivatives are quite rare.[56] From the perspective of
molecular design, the photophysical properties of the phospho-
rescent complexes can be tuned by choosing different types of
cyclometalated or ancillary ligands, or introducing special func-
tional groups to the ligands.[57] For instance, using fluorine (F)
atom or trifluoromethyl (CF3) group to replace hydrogen in the
cyclometalated ligand could alter the energy levels of emitters,
i.e., the highest occupied molecular orbital (HOMO) and the
lowest unoccupied molecular orbital (LUMO), which may in
turn allow the tuning of emission colors.[58] Fluorination can
also be used to markedly reduce concentration quenching of
luminescence and meanwhile increase volatility to favor vapor
deposition.[59] In most cases, fluorination can enhance electron
mobility, resulting in a more balanced carrier injection and
hence a higher device efficiency.[60] In previous studies, tria-
zolpyridine,[61,62] which is a well-known ancillary ligand for its
remarkable blueshifting capability than that of β-diketonates by
reducing the HOMO level of the iridium(III) complex, is usu-
ally introduced into iridium(III) complexes to achieve deep blue
emission. Thus, the triazolpyridine ligand could have a poten-
tial application in design of yellow-emitting iridium(III) com-
plex. For the commonly used synthetic route of β-diketonate-
based and triazolpyridine-based neutral iridium(III) complexes,
there are two steps: (i) the cyclometalated iridium(III)-chloro-
bridged dimers of a general formula (C^N)2Ir(µ-Cl)2Ir(C^N)2
were synthesized according to the Nonoyama route by refluxing
IrCl3·3H2O with 2.0–2.5 equiv. of cyclometalated ligand in a
3:1 (V:V) mixture of 2-ethoxyethanol and water;[63] (ii) the chlo-
robridged dimers together with 2.5 equiv. of ancillary ligands
and 10 equiv. of anhydrous Na2CO3 were refluxed at 110 °C
under an inert atmosphere in 2-ethoxyethanol for 24 h. Thus,
the high boiling 2-ethoxyethanol and harsh reaction condition
are required, especially in the second step. What’s more, inter-
mediate complexes have a potential risk of oxidation process
or thermal decomposition, especially for complex containing
sensitive functional groups at such a high-temperature reac-
tion, leading to hard purification and low yields. Hence, the
convenient synthetic methods are needed for the preparation of
phosphorescent complexes.
Herein, we developed a more facile method to prepare
both β-diketonate-based and triazolpyridine-based neutral
iridium(III) complexes. That is, the corresponding chloro-
bridged dimers together with 2.2 equiv of β-diketonate or tria-
zolpyridine were stirred under very mild condition with dichlo-
romethane as solvent and anhydrous potassium carbonate as
deacid reagent at room temperature (≈25 °C). The complexes
obtained by this method are easy to be purified with high
yields. By modifying the phenyl ring of HPQ ligand with one or
more F atoms and (or) CF3 group or choosing suitable ancillary
ligands (β-diketonate or triazolpyridine), as shown in Scheme 2,
we realized the effective color tuning of iridium(III) phosphors
in the range of greenish–yellow, yellow, and orange-yellow emis-
sion (emission wavelength from 545 to 597 nm) with markedly
improved phosphorescent quantum efficiency (up to 0.92, the
highest value among the reported neutral yellow iridium(III)
Considering that the performance of greenish–yellow or
yellow emitters is significantly behind those emitting in the
three primary colors, it is urgent to design and synthesize
these phosphorescent emitters with high quantum efficiency
and broad width at half maximum, which are driven by the
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complexes) and the broad emission bands (FWHM up to
103 nm). In addition, we also introduced a methyl group into
4-position of quinoline ring to increase solubility in organic sol-
vents and to suppress triplet-triplet annihilation of iridium(III)
complexes.[64] Based on the newly synthesized complexes,
highly efficient monochrome yellow, greenish–yellow and com-
plementary-color-based white OLED have been fabricated. The
FWHMs of the fabricated OLEDs are in the range of 94–102 nm,
which are among the highest values of the reported yellow or
greenish–yellow-emitting devices without excimer emission.
The maximum EQE of monochrome devices based on complex
9, 13, 15, 17, and 18 are in the range of 20.8%–24.1%, respec-
tively. Especially, the maximum EQE of device based on 9 is up
to 24.1%, which is the highest value among the reported yellow
or greenish–yellow OLEDs. And the CRI of blue and comple-
mentary yellow-based WOLED is as high as 78.
Supporting Information). The F atom(s) and (or) CF3 group were
successfully introduced into the HC^N ligands. The new cyclo-
metalated HC^N ligands were fully characterized by nuclear mag-
netic resonance (1H NMR, 13C{1H} NMR and 19F{1H} NMR).
The chemical structures of the Ir(C^N)2(acac) and
Ir(C^N)2(4FPZ) complexes are shown in Scheme 2. The newly
synthesized iridium(III) complexes can be divided into two
classes according to the different ancillary ligands of pentane-
2,4-dione (Hacac) or 2-(3-(4-fluorophenyl)-1H-1,2,4-triazol-5-yl)-
pyridine (H4FPZ). The change of ancillary ligands is intended
to further tune the phosphorescent energy. What’s more, the
F atom(s) and (or) CF3 group bonded to C^N ligands of the
iridium(III) complexes could not only finely tune the energy
gap but also greatly affect the quantum efficiency of complexes.
The synthetic procedures of iridium(III) complexes are
shown in Scheme S2 (Supporting Information). Cyclometa-
lated iridium(III) µ-chlorobridged dimers of a general formula
(C^N)2Ir(µ-Cl)2Ir(C^N)2 were synthesized according to the
reported Nonoyama route.[63] Notably, different from commonly
used synthetic method of neutral iridium(III) complexes,[64,65]
a more facile way to prepare both β-diketonate-based and tri-
azolpyridine-based iridium(III) complexes was presented here
for the first time, that is, the corresponding chlorobridged
dimers together with 2.2 equiv. of Hacac or H4FPZ were stirred
under very mild condition with dichloromethane as solvent
and anhydrous potassium carbonate as deacid reagent at room
temperature (≈25 °C), This mild condition leads to the easy
treatment and purification of the target iridium(III) complexes
in high yields of ≈75%–92%, which is very important for the
future large-scale preparation of phosphorescent complexes.
2. Results and Discussion
2.1. Synthesis and Characterization
The cyclometalated HC^N ligands (abbreviated HMePQ,
HMePQ-4F, HMePQ-24F, HMePQ-234F, HMePQ-35F, HMePQ-
345F, HMePQ-2345F, HMePQ-3CF3, and HMePQ-3CF3-4F), as
shown in Scheme 1, were synthesized by highly efficient Suzuki
coupling reaction between the corresponding fluorine-containing
arylboronic acid and 2-chloro-4-methylquinoline. The key inter-
mediate compound 2-chloro-4-methylquinoline was synthesized
by three-step reactions in overall yields of 74%. The isolated yields
of the new cyclometalated ligands are ≈81%−93% (Scheme S1,
Scheme 1. Illustration of the modification of 2-phenylquinoline by fluorine atoms and (or) a trifluoromethyl (CF3) group.
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Scheme 2. The chemical structures of the complexes a) Ir(C^N)2(acac), b) Ir(C^N)2(4FPZ), c) and the abbreviations of selected protons, labels of
position in iridium(III) complexes.
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Using commonly synthetic method under the condition
of 2-ethoxyethanol and anhydrous sodium carbonate at
100 °C, unexpectedly, gave low yields of products. Especially
for Ir(MePQ-234F)2(4FPZ) (13), no products could be obtained
from its chlorobridged dimer and H4FPZ ligand under that
condition, and the unexpected complex 19 with one F atom
replaced by 2-ethoxyethanol in each cyclometalated ligand was
isolated and identified (Scheme S3 and Figure S1, Supporting
Information), which is probably the result of easily occurring
substitution process of the fluorine by 2-ethoxyethanol under
that condition. So the commonly used synthetic method is not
suitable for the preparation of multifluorine-containing neutral
iridium(III) complexes. All iridium(III) complexes have been
fully characterized by 1H NMR, 13C{1H} NMR and 19F{1H}
NMR (13C{1H} NMR was not recorded for all Ir(C^N)2(4FPZ)
because of their poor solubility) and matrix-assisted laser des-
orption ionization time-of-flight mass spectrometry (MALDI-
TOF-MS). The structures of complexes 1, 2, 4, 6, 7, 9, and 15
were further confirmed by single-crystal X-ray diffraction.
The NMR spectra (shown in the Supporting Information)
of all iridium(III) complexes show the clearly well-resolved
resonance signals, indicating that the complexes have a high
purity suitable for device fabrication. The two cyclometalated
ligands in the acac-based complexes, i.e., MePQ-4F, are equiva-
lent to each other owing to the symmetry of ancillary ligand
in OLEDs. Moreover, the decomposition temperature of 13 is
higher than that of 9, which is probably owing to higher molec-
ular weight.
2.2. X-ray Structure Determination
The single crystals of acac-based irdium(III) complexes 1, 2, 4,
6, 7, and 9 suitable for X-ray diffraction analysis were grown
from dichloromethane solutions, while the single crystal of
4FPZ-based complex 15 was obtained from dimethyl sulfoxide
solutions. The crystallographic refinement parameters of com-
plexes 1, 2, 4, 6, 7, 9, and 15 are summarized in Tables S3–S5
(Supporting Information), respectively. ORTEP plots of these
complexes are displayed in Figure 1. The iridium center adopts
a distorted octahedral coordination geometry with cis-metalated
carbons and trans-phenylquinoline nitrogen atoms, the same as
previously observed in other analogous complexes.[48] From the
ORTEP plots of the isomers 4 and 6, it is shown clearly that
the three F substituents located in the 2,3,4-positions of phenyl
ring in complex 4, whereas in the 3,4,5-positions in complex 6,
which causes different electronic effects and then different photo-
physical properties. The four F atoms in the phenyl ring of each
cyclometalated HC^N ligand of complex 7 are undoubtedly
confirmed by its single-crystal structure, indicating that the
four F atoms of cyclometalated HC^N ligand can be maintained
in the synthesis of the corresponding µ-chlorobridged dimers.
In the crystal of 9, the two bulky CF3 substituents are in the
para position of iridium atom rather than in the ortho posi-
tion, which is the result of van der Waals repulsion between the
bulky CF3 group and the π plane of another ligand. For 4FPZ-
based complex 15, the center Ir atom bonds to nitrogen atom
in the 1-position of 1,2,4-triazol ring due to the steric hindrance
effect of the bulky 4-fluorophenyl moiety, which is also revealed
by its ORTEP plot. The F atoms and (or) CF3 group also have
great effects on the crystal packing of the complex. There are
three kinds of π–π interactions observed in these complexes
(Figures S4–S10, Supporting Information), that is, π–π interac-
tions between lepidine ring and lepidine ring, lepidine ring and
(F and (or) CF3 modified) phenyl ring, (F and (or) CF3 modi-
fied) phenyl ring and (F and (or) CF3 modified) phenyl ring.
In the fluorine-free complex 1, there exist two kinds of weak
intermolecular π–π interaction. One is between the lepdine
units (the distance is 3.70 Å), and the other is between the lep-
dine unit and phenyl ring (the distance is 3.60 Å) from two dif-
ferent molecules. Note that the two CH3 groups located in the
4-position of quinoline ring of these complexes are far away
from each other, which effectively increase the distance among
iridium(III) complexes and thus suppress triplet–triplet annihi-
lation of iridium(III) complexes.
1
acac as evidenced by 11 resonances in the H NMR spectrum
(Figure S2a, Supporting Information) and 19 resonances (not
considering the extra splitting of 13C affected by 19F nucleus)
in the 13C{1H} NMR spectrum (Figure S2b, Supporting Infor-
mation) of Ir(MePQ-4F)2(acac), supporting that the acac-based
complexes possess a configuration with C2 symmetry. In con-
trast, this symmetry is lost in complex Ir(C^N)2(4FPZ). This
molecular symmetry of complexes is also consistent with 19F
resonance signals in 19F{1H} NMR spectrum. Protons adja-
cent to the C Ir bonds (Hc protons in Ir(C^N)2(acac) and
Ir(C^N)2(4FPZ) in Scheme 2c) are susceptible to shielding
because of ring current perturbation from an adjacent ligand,[66]
thereby suggesting high-field assignments of these protons
(5.97–6.51 ppm for Ir(C^N)2(acac) (Table S1, Supporting Infor-
mation) and 5.92–6.75 ppm for Ir(C^N)2(4FPZ) (Table S2, Sup-
porting Information)). Moreover, the acetylacetonate CHa pro-
tons in Ir(C^N)2(acac) appear in the region of 4.53–4.69 ppm
as a sharp singlet (Table S1, Supporting Information). For
the control complex Ir(acac)3, this signal appears at 5.49 ppm
(Table S1, Supporting Information). The acetylacetonate CHa
protons in Ir(C^N)2(acac) are more shielded due to the ring
current perturbation from two cyclometalated ligands.[55] The
above-mentioned shielding effect is also manifested on the
chemical shift of the acetylacetonate CHb3 protons. In Ir(acac)3
complex they are observed at 2.01 ppm (Table S1, Supporting
Information), while in the present acac-based complexes
they resonate from 1.46 to 1.53 ppm (Table S1, Supporting
Information).
2.3. Photophysical Properties
In addition, we evaluated the chemical stability of the com-
plex 13 and 9 (as examples) by thermogravimetric analysis, as
shown in Figure S3 (Supporting Information). From the ther-
mogravimetric curves, the decomposition temperatures of 5%
weight loss of both complexes exceed 300 °C, indicating that the
two complexes exhibit sufficient thermal stability for application
The absorption and emission spectra of all complexes were
measured at room temperature in dichloromethane (Figure 2).
All acac-based fluorine-containing complexes feature the intense
absorption bands in the region of 250–360 nm, assigned to
1π→π* transition of ligand (1LC), and show ≈5 nm blueshift
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Figure 1. ORTEP diagrams of the complexes 1, 2, 4, 6, 7, 9, and 15 with thermal ellipsoids drawn at the 30% probability level and H atoms, solvent
molecules removed for clarity.
Figure 2. a) UV–vis absorption and b) photoluminescence spectra of 1–9 in CH2Cl2; c) UV–vis absorption and d) photoluminescence spectra of 10–18
in CH2Cl2. Inset: Luminescence photographs of 1–18 in CH2Cl2.
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related to the fluorine-free complex Ir(MePQ)2(acac) (1) due to
the electron-withdrawing nature of F atoms and (or) CF3 group
in the phenyl ring of cyclometalated ligands. The weak bands in
the range of 360–550 nm are likely assigned to the singlet and
triplet metal-to-ligand charge-transfer transitions (1MLCT and
3MLCT) (Figure 2a). The similar absorption properties were
observed for all 4FPZ-based complexes (Figure 2c). It is notable
that MLCT bands of 4FPZ-based complex exhibit the obvious
blueshift related to those of the corresponding acac-based com-
plex. This indicates that the ancillary ligand H4FPZ exhibits the
strong ability to induce the blueshift of spectral properties of
phenyl quinoline-based iridium(III) complexes.
The introduction of F atoms and (or) CF3 group into
Ir(C^N)2(acac) or Ir(C^N)2(4FPZ) has great effect on the emis-
sion spectra. First, both the acac-based and 4FPZ-based
complexes show obvious blueshift emission related to the
corresponding fluorine-free complexes, indicating the elec-
tron-withdrawing nature of F atoms and (or) CF3 group in
the phenyl ring of cyclometalated ligands. Correspondingly,
the emission color is changed from red for the fluorine-free
complex 1 to orange–yellow and yellow for Ir(C^N)2(acac), and
from yellow for the fluorine-free complex 10 to greenish–yellow
for Ir(C^N)2(4FPZ). The acac-based complexes exhibit broad
and featureless emission peaks in the range of 560–597 nm
with the absolute quantum yields of 0.21–0.80 in CH2Cl2 and
the emission lifetime (τ) of 0.33–7.45 µs (Figure 2b and Table 1).
In contrast, the 4FPZ-based complexes show dual emission
peaks, and the emissions are in the range of 545–567 nm
with the absolute quantum yields of 0.36–0.92 and the life-
time of 1.03–6.77 µs in CH2Cl2 (Figure 2d and Table 1). More
notably, both Ir(C^N)2(acac) and Ir(C^N)2(4FPZ) exhibit very
broad FWHMs in the range of 87–103 nm (Table 1), which is of
great importance in enhancing the CRI of white devices, espe-
cially for the blue and complementary yellow-based WOLEDs
with the simple device structure. Moreover, F atoms and (or)
CF3-substitution remarkably improve phosphorescence effi-
ciency owing to the rigidity of carbon–fluorine bond than that
of carbon–hydrogen bond, for example, ΦPL = 0.92 (18) versus
0.35 (control complex 10), the highest value among the reported
neutral yellow iridium(III) complexes.[47] These results suggest
that the fluorine substituents on the cyclometalated ligands
play a significant role in controlling the excited-state properties.
Compared to the pentane-2,4-dione ligand of acac-based com-
plex, the auxiliary ligand triazolpyridine of 4FPZ-based complex
has less electron-donating ability to the Ir center due to the
more delocalization effect of π electrons within the conjugated
π system. This relatively weak electron-donating ability to the
Ir center effectively stabilized the HOMO orbital of the 4FPZ-
based complex, thus, the HOMO energy level was decreased
and then the energy gap of lepidine-based iridium(III) com-
plex was enlarged. Hence the blueshift of emission spectra was
observed. This is well consistent with the fact that the more
positive oxidations for 4FPZ-based complexes are observed
than those for acac-based complexes, which will be further dis-
cussed in the following section of electrochemical properties.
The low-temperature phosphorescence spectra of the
complexes were measured in a glass 2-methyltetrahydro-
furan (2-MeTHF) matrix at 77 K (Figure S11, Supporting
Table 1. Absorption, luminescence, and electrochemical data for iridium(III) complexes.
Emissionb)
FWHM [nm]
Eonsetoxc) [eV] Egd) [eV]
HOMO/LUMOd) [eV]
Absorptiona)
λabs [nm] (lg ε)
Complex
λ
em [nm]
597
574
577
584
579
564
564
578
560
567
552
559
559
560
550
554
554
545
τ [µs]
0.33
0.46
0.77
0.88
0.81
0.71
7.45
0.69
1.58
1.03
1.05
1.73
1.88
1.57
1.62
6.77
1.44
1.69
ΦPL
0.21
0.24
0.52
0.60
0.62
0.75
0.64
0.70
0.80
0.35
0.51
0.63
0.91
0.89
0.87
0.83
0.88
0.92
1
265(4.83), 341(4.26), 463(3.59), 510(3.36), 549(2.94)
263(4.89), 334(4.37), 444(3.76), 497(3.33), 531(2.96)
269(4.86), 330(4.45), 407(3.85), 443(3.89), 537(2.63)
269(4.64), 330(4.24), 446(3.71), 509(3.15), 549(2.53)
272(4.51), 329(4.14), 454(3.54), 502(3.12), 548(2.83)
271(4.56), 328(4.22), 442(3.68), 494(3.07), 539(2.70)
272(4.75),325(4.30), 403(3.73), 438(3.73), 523(2.68)
265(4.85), 336(4.31), 450(3.78), 499(3.30), 533(2.56)
268(4.71), 324(4.27), 435(3.76), 495(3.07), 534(2.70)
269(4.90), 336(4.53), 398(3.92), 443(3.81), 504(3.33)
267(4.91), 324(4.53), 424(3.88), 462(3.43), 498(2.92)
265(4.82), 324(4.43), 424(3.79), 445(3.39), 490(1.97)
267(4.72), 328(4.32), 384(3.75), 432(3.62), 493(1.59)
271(4.82), 330(4.42), 393(3.80), 434(3.67), 504(1.59)
272(4.68), 324(4.28), 392(3.69), 422(3.62), 485(2.54)
271(4.74),340(4.31), 396(3.71), 420(3.70), 457(2.60)
267(4.81), 330(4.33), 386(3.83), 435(3.68), 483(3.18)
266(4.75), 324(4.28), 388(3.74), 422(3.62), 468(2.55)
93
98
0.53
0.65
0.79
0.80
0.69
0.81
0.98
0.77
0.89
0.69
0.84
0.97
1.00
0.89
1.01
1.16
0.96
1.05
2.08
2.16
2.15
2.12
2.14
2.20
2.20
2.16
2.21
2.19
2.25
2.22
2.22
2.21
2.25
2.24
2.28
2.28
−5.33/−3.25
−5.45/−3.29
−5.59/−3.44
−5.60/−3.48
−5.49/−3.35
−5.61/−3.41
−5.78/−3.58
−5.57/−3.41
−5.69/−3.48
−5.49/−3.30
−5.64/−3.39
−5.77/−3.55
−5.80/−3.58
−5.69/−3.48
−5.81/−3.56
−5.96/−3.72
−5.76/−3.48
−5.85/−3.57
2
3
100
101
90
4
5
6
95
7
103
98
8
9
103
88
10
11
12
13
14
15
16
17
18
96
101
92
87
98
103
96
100
a)At a concentration of 1.0 × 10−5 mol L−1 in CH2Cl2; b)At a concentration of 1.0 × 10−5 mol L−1 in degassed CH2Cl2, λex = 365 nm; c)In CH2Cl2; d)HOMO
(eV) = −e(Eonsetox + 4.8), Eg = 1240/λ, LUMO (eV) = Eg + HOMO.
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Information). All of the complexes show obvious blueshift of
the emission maxima with fine structures of vibronic bands
(Table S6, Supporting Information), which is different from
the broad and featureless emission spectra at room tempera-
ture discussed above. And the triplet energy (T1) levels were
estimated from the highest-energy vibronic subband of the
phosphorescence spectra. The T1 are summarized in Table S6
(Supporting Information). The Ir(C^N)2(4FPZ) exhibit higher
T1 than the corresponding acac-based complexes, for example,
T1 = 2.27 eV (13) versus 2.21 eV (4), which is consistent with
the fact that the triazolpyridine-based complexes display the
blueshifted emission compared to the pentane-2,4-dione-based
ones at room temperature.
(1 nm)/Al (150 nm). As shown in Figure S13a (Supporting
Information), the ITO acts as anode, HAT-CN acts as hole injec-
tion layer (HIL), TAPC acts as hole-transporting layer (HTL),
both mCP and TPBi layers doped with iridium(III) complexes
act as emissive layer for the purpose of balanced carrier trans-
portation in this layer, 1,3,5-tri(m-pyrid-3-yl-phenyl)benzene
(TmPyPb) acts as electron-transporting layer (ETL), a 1 nm
8-hydroxyquinolinolato lithium (Liq) layer and a 150 nm alu-
minium act as cathode layer. The energy diagram of the mono-
chrome devices and the molecular structures of the materials
used are shown in Figure S14 and Scheme S4 (Supporting
Information), respectively. To optimize the device efficiency,
concentration dependence experiments were carried out for
iridium(III) complex 13. The optimized iridium(III) complexes
with 8 wt% doping concentration in mCP and 15 wt% doping
concentration in TPBi were used as the emitting layers (Table
S7, Supporting Information). It can be seen in energy level
diagram of OLEDs (Figure S14, Supporting Information) that
the HOMO/LUMO levels of the iridium(III) complexes are all
within those of the host materials mCP and TPBi. So, good car-
rier trapping is expected in these devices, which is the domi-
nant EL mechanism. Furthermore, holes and electrons will be
well confined within the doped light-emitting layer owing to the
large energy gap (0.5 eV) between the HOMO of TPBi and the
HOMO of TmPyPb.
The electroluminescence spectrum, current efficiency (ηc)
versus luminance (L), power efficiency (ηp) versus luminance
(L), and external quantum efficiency versus current density (J)
characteristics of devices are shown in Figure 3. The L–V–J
curves could be found in Figure S15a (Supporting Informa-
tion). All OLEDs emit yellow or greenish–yellow light with
the EL emission peaks at 564, 559, 550, 555, and 545 nm for
iridium(III) complexes 9, 13, 15, 17, and 18, respectively. As
shown in Figure 3d, the EL spectra of all OLEDs exhibit domi-
nant emission bands corresponding to the iridium(III) complex
without any other residual emission band originating from host
and/or adjacent layers, suggesting that excitons generated in
emissive layer mainly deactivate by phosphorescence emission
of iridium(III) complex. As shown in Figure S15b (Supporting
Information) and Table 2, the CIE color coordinates of all
OLEDs are in yellow or greenish–yellow region of the CIE chro-
maticity diagram. In addition, the close resemblance between
the PL and EL spectra (Figure S16, Supporting Information)
suggests that the EL emission of all monochrome OLEDs origi-
nates from the unimolecular triplet excited states of the phos-
phors instead of excimer emission. It is highlighted that all
yellow or greenish–yellow-emitting OLEDs exhibit very broad
emission band with FWHMs in the range of 94–102 nm, and,
more importantly, these high values in FWHMs do not rely on
the presence of excimer emission. As previously discussed, the
use of excimer emission can effectively broaden the EL spec-
trum of yellow-emitting OLEDs, however, the EL spectra and
the corresponding CIE are greatly influenced by the dopant
concentration. To the best of our knowledge, the FWHMs of
our novel iridium(III) complex-based OLEDs are among the
highest values of yellow or greenish-yellow-emitting OLEDs
without excimer emission reported in the literature, as sum-
marized in Table S8 (Supporting Information). Especially, the
FWHM of OLED based on complex 9 is up to 102 nm, which
2.4. Electrochemical Properties
The electrochemical properties of all complexes were examined
by cyclic voltammetry in CH2Cl2 solution (Figure S12, Sup-
porting Information). Both acac-based and 4FPZ-based com-
plexes have reversible oxidation waves with potentials in the
range of 0.53–1.16 V (Table 1). We attribute this positive oxida-
tion potential to the Ir centered oxidation. The oxidation poten-
tials of acac-based complexes containing fluorine atoms show
a positive shift of ≈0.45 V in comparison to the corresponding
Ir(MePQ)2(acac) (1), demonstrating that more electron-with-
drawing nature of the ligands may result in the variation in
the electronic properties at the metal center. The values of oxi-
dation potentials of acac-based complexes follow the order of
9 > 8 > 6 > 4 > 3 > 7 > 5 > 2 > 1, and those of 4FPZ-based complexes
follow the order of 18 = 17 > 15 > 13 > 12 > 16 > 14 > 11 > 10,
indicating that the electron-withdrawing ability of the fluorine
was not only affected by the number of the fluorines or trifluo-
romethyl group but also by the position to which the fluorines
or trifluoromethyl group bonded. The results reveal that fluo-
rines or trifluoromethyl group can increase oxidation potentials
and reduce the energy level of HOMO, as observed in previous
report. In addition, the 4FPZ-based complex shows more posi-
tive oxidation potential than the corresponding acac-based com-
plex (i.e., Eonset = 1.01 V for 15 and Eonset = 0.81 V for 6), clearly
indicating that the triazolpyridine has the stronger ability to
reduce the energy level of HOMO than acac.
2.5. Electroluminescence Performance
2.5.1. Monochrome OLEDs
Considering that these iridium(III) phosphors possessing highly
efficient emission from greenish–yellow to yellow and very broad
emission (FWHM up to 103 nm), the complexes have been used
for fabrication of OLEDs. To evaluate the EL performances, the
monochrome OLEDs using iridium(III) complexes 9, 13, 15,
17, and 18 as the emitters were fabricated with the structures
of indium tin oxide (ITO)/1,4,5,8,9,11-hexaazatriphenylene-
hexacarbonitrile (HAT-CN) (2 nm)/di-[4-(N,N-ditolylamino)-
phenyl]cyclohexane (TAPC) (35 nm)/1,3-di(9H-carbazol-9-yl)
benzene (mCP): x% Ir (10 nm)/1,3,5-tris(1-phenyl-1H-benzo[d]
imidazol-2-yl)benzene (TPBi): y% Ir (10 nm)/TmPyPb (30 nm)/Liq
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Figure 3. a) The ηc–L curves, b) ηp–L curves, c) EQE–J curves, and d) EL spectra of the yellow and greenish–yellow emitting devices based on
iridium(III) complexes 9, 13, 15, 17, and 18. Inset: EL photograph of device based on complex 13.
is competitive with the reported yellow OLEDs by utilizing
excimer emission.[43]
range of 28 204–39 872 cd m−2. The maximum ηc, ηp, and EQE
of OLEDs based on iridium(III) complexes 9, 13, 15, 17, and
18 are in the range of 58.3–67.5 cd A−1, 53.3–57.2 lm W−1, and
20.8%–24.1%, respectively. Especially, the maximum EQE of
OLED based on iridium(III) complex 9 is up to 24.1%, which
is the highest value among the reported yellow or greenish–
yellow OLEDs.[47]
The monochrome OLEDs based on iridium(III) complexes
9, 13, 15, 17, and 18 also exhibit encouraging EL performances,
as summarized in Table 2. All devices exhibit low turn-on
voltages (Vturn-on) around 3.0 V (defined as bias at a luminance
of 1 cd m−2). The maximum luminance of the OLEDs is in the
Table 2. Electroluminescence data for the devices.
Complex
CIEa) (x, y)
(0.52, 0.47)
(0.51, 0.47)
(0.50, 0.49)
(0.51, 0.48)
(0.47, 0.50)
VONb) [V]
3.0
EQEmax [%]
24.1
FWHM [nm]
λ
EL [nm]
564
L
max [cd m−2
]
η
cmax [cd A−1
]
η
pmax [lm W−1
]
9
40 011
63.8
57.2
102
94
13
15
17
18
559
3.0
39 872
60.7
54.5
22.2
550
3.0
31 613
61.4
53.3
21.4
99
555
3.0
28 204
58.3
53.9
20.8
96
545
3.1
33 571
67.5
55.8
22.7
100
a)Current density is 100 mA cm−2 b)Luminance is 1 cd m−2
; .
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It has been reported that the exciplex can be formed in
donor–acceptor cohost doping system (e.g., mCP:TPBi),
which enables efficient singlet and triplet energy transfer
from the host exciplex to the phosphorescent dopant.[35,42,67–
2.5.2. White OLEDs
Considering that these iridium(III) complexes exhibit very
broad emission band covering the greenish–yellow to red
region in EL spectra, which is very significant for high-quality
complementary-color WOLEDs (such as CRI), the WOLED
containing the blue emission layer and the yellow emission
layer was designed and fabricated in this work. We chose
iridium(III) complex 18 as the yellow phosphorescent emitter
and BmPAC (chemical structure shown in Scheme S4, Sup-
porting Information) as blue fluorescent emitter previously
reported by us.[70] So, the fluorescent-phosphorescent hybrid
WOLED with symmetrical cascade emissive layer struc-
ture (Figure S13b, Supporting Information) of ITO/HAT-CN
(2.5 nm)/N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)benzidine
(NPB) (20 nm)/TCTA (10 nm)/mCP: 15% Ir18 (5 nm)/mCP
(3 nm)/9,10-di(naphthalen-2-yl)anthracene (ADN): 3% BmPAC
(4 nm)/mCP (3 nm)/mCP: 15% Ir18 (5 nm)/TPBi (30 nm)/Liq
(1 nm)/Al (150 nm) were fabricated. In the WOLED, the HAT-
CN, NPB and tris(4-(9H-carbazol-9-yl)phenyl)amine (TCTA),
TPBi and Liq/Al act as HIL, HTL, ETL and cathode, respec-
tively. Herein, we used mCP as the host material for the highly
efficient energy transfer from mCP to complex 18 owing to its
higher triplet energy level (2.90 eV) than that of complex 18
69]
So, the generation of exciplex in mCP:TPBi is beneficial
for increasing EQE of yellow OLEDs. However, different from
exciplex in mCP:TPBi cohost doping system (≈20 nm),[67–69]
the mCP and TPBi in our yellow OLEDs were double sepa-
rated layers, in which the exciplex could be only formed in
the mCP:TPBi interface area (about several nm). The con-
tribution of exciplex in mCP:TPBi interface to high EQE is
not significant, and the carrier trapping effect of lepidine-
based iridium(III) complexes mainly contributes to high
EQE of yellow OLEDs. In addition, the overlap between the
PL spectrum of the exciplex and the UV–vis absorption spec-
trum of iridium(III) complexes is the basic requirement for
the energy transfer from the exciplex to iridium(III) com-
plexes.[68,69] For acquiring high energy-transfer efficiency,
the spectra overlap should be large. However, the overlap
between the PL spectrum of the exciplex of mCP:TPBi[67] and
the absorption of the lepidine-based iridium(III) complexes
(as shown in Figure 2a,c) is not large enough for high energy-
transfer efficiency, further indicating small contribution of
exciplex to high EQE in our OLEDs.
Figure 4. a) The J–V–L curves, b) ηc–L–ηp curves, c) EQE–J curves, d) and 1931 CIE coordinates of the white device. Inset: EL spectrum and corre-
sponding photograph of white device.
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(2.34 eV) and used ADN as the host for fluorescent blue emitter
BmPAC. The energy diagram of the WOLED is shown in
Figure S17 (Supporting Information). The ηc, ηp versus L and
EQE versus J of the WOLED can be found in Figure 4, and the
inset shows its EL spectrum and photograph at 2000 cd m−2.
As shown in Figure 4c, it can be seen that the EL spectrum
of WOLED exhibits double emission peaks located at 467 and
545 nm, respectively, covering nearly all visible light region
with the CRI as high as 78, which is very close to the critical
value (80) required for the practical solid-state lighting applica-
tions. It is believed that the CRI of this WOLED can be further
improved (over 80) by using a deep-blue emitter. As far as we
known, there are few reports of such a high CRI, especially for
the devices with wide spectra covering the white region based
on two colors without excimer emission, which usually exhibit
the CRI in the range of 50–65, as summarized in Table S9
(Supporting Information). Such a high CRI of the two com-
plementary colors-based WOLED was attributed to the well-
matched emission spectra, especially the very broad FWHM
(up to 100 nm) of the greenish–yellow emitter 18. As shown
in Figure 4d and Table S10 (Supporting Information), the CIE
color coordinates of WOLED is (0.37, 0.38) at 2000 cdm−2, cor-
responding to the white-light region in CIE chromaticity dia-
gram. Moreover, the WOLED display low turn-on voltages of
3.5 V, high luminance of 22 019 cd m−2, the maximum cur-
rent efficiency of 32.2 cd A−1, the maximum power efficiency
of 19.5 lm W−1, and the maximum external quantum efficiency
of 10.7%, respectively. We believe that the efficiencies of the
WOLED fabricated could be further improved by optimizing
the doping ratio of iridium(III) complexes, choosing more suit-
able host materials or using a blue phosphorescent emitter
without compromising the CRI of the WOLEDs.
among the highest values of the reported yellow or greenish–
yellow OLEDs without excimer emission. The maximum EQE
of monochrome OLEDs based on iridium(III) complexes 9, 13,
15, 17, and 18 are in the range of 20.8%–24.1%, respectively.
Especially, the maximum EQE of OLEDs based on iridium(III)
complex 9 is up to 24.1%, which is the highest value among
the reported yellow or greenish–yellow devices. The CRI of blue
and complementary yellow-based WOLED is as high as 78.
These preliminary results obtained indicated that this family of
highly emissive greenish–yellow and yellow neutral iridium(III)
complexes based on fluorine modified cyclometalated lepidine-
based ligands are the promising candidates for the WOLEDs,
which is of great significance for the development of solid-state
lighting techniques.
4. Experimental Section
General Experimental Information: All operations were performed
under an inert nitrogen atmosphere using standard Schlenk unless
otherwise stated. All solvents were used after distillation and stored
over activated molecular sieves (5 Å). All reagents and chemicals
were purchased from commercial sources and used without further
purification. Aniline, ethyl 3-oxobutanoate, concentrated sulfuric acid,
phosphorus oxychloride, tetrakis(triphenylphosphine)palladium(0),
iridium(III) trichloride hydrate, pentane-2,4-dione (Hacac), and
iridium(III) tris(acetylacetonate) (Ir(acac)3) were obtained from Acros.
Deuterated solvents from Cambridge Isotope Laboratories were used.
The NMR spectra were recorded with a Bruker spectrometer at 600 or
1
400 MHz (600 or 400 MHz for H, 150 or 100 MHz for 13C) at ambient
temperature. Chemical shifts are given in ppm and are referenced
against external Me4Si (1H, 13C). Mass spectra were obtained on
SHIMADZU matrix-assisted laser desorption/ionization time-of-flight
mass pectrometer (MALDI-TOF-MASS). Elemental analyses were carried
out with a VarioEL III O-Element Analyzer system. The UV–vis spectra
were recorded on a Shimadzu UV-2550 spectrometer. Steady-state
emission experiments at room temperature or 77 K were measured on
an Edinburgh LFS-920 spectrometer. Excited-state lifetime studies were
performed with an Edinburgh LFS-920 spectrometer with a hydrogen-
filled excitation source. The data were analyzed by iterative convolution
of the luminescence decay profile with the instrument response function
using a software package provided by Edinburgh Instruments. The
absolute quantum yields of the complexes were determined through
an absolute method by employing an integrating sphere. The solution
was degassed by three freeze–pump–thaw cycles. Cyclic voltammetry
measurements were carried out in acetonitrile (5 × 10−4 M) with a three-
electrode cell configuration consisting of platinum working and counter
electrodes and an Ag/AgNO3 (0.01 M in CH3CN) reference electrode
at room temperature. Tetra-n-butylammonium hexafluorophosphate
(0.1 M in CH2Cl2) was used as the supporting electrolyte. The redox
potentials were recorded at a scan rate of 100 mV s−1 and are reported
with reference to the ferrocene/ferrocenium (Fc/Fc+) redox couple.
The ancillary HN^N ligand 2-(3-(4-fluorophenyl)-1H-1,2,4-triazol-
5-yl)pyridine (H4FPZ) was synthesized according to the literature
procedures.[71]
3. Conclusion
In summary, we developed a facile synthetic route, that is,
using dichloromethane as solvent and anhydrous potassium
carbonate as deacid reagent at room temperature to prepare
both β-diketonates-based and triazolpyridine-based neutral
iridium(III) complexes in excellent yields, which is a promising
method for the future large-scale preparation of phosphores-
cent materials. Based on the facile synthetic method, two series
of new fluorine atoms and (or) trifluoromethyl group modi-
fied lepidine-based phosphorescent iridium(III) complexes
have been prepared with pentane-2,4-dione or triazolpyridine
as ancillary ligands, respectively. And the effects of fluorine
atoms and (or) trifluoromethyl group on tuning optical proper-
ties of two series of complexes have been examined in detail.
All triazolpyridine-based complexes display blueshifted dual-
peak emission compared to pentane-2,4-dione-based complexes
with a broad single-peak emission. The complexes show emis-
sion with FWHM up to 103 nm, and their emission colors vary
from greenish–yellow, yellow, orange-yellow to orange. Among
them, the iridium(III) complex 18 exhibits the quantum yields
up to 0.92, which is the highest one among the reported neutral
yellow iridium(III) complexes. Highly efficient monochrome
OLEDs and WOLEDs have been fabricated. The FWHMs of
the monochrome OLEDs in the range of 94–102 nm, which are
Synthesis of the Cyclometalated HC^N Ligands: The synthetic routes
(Scheme S1, Supporting Information) of the cyclometalated HC^N
ligands (HMePQ, HMePQ-4F, HMePQ-24F, HMePQ-234F, HMePQ-35F,
HMePQ-345F, HMePQ-2345F, HMePQ-3CF3, and HMePQ-3CF3-4F)
were synthesized by highly efficient Suzuki coupling reactions. 2-chloro-
4-methylquinoline was synthesized by three-step reactions in overall
yield of 74% and can be found in the Supporting Information. Herein, a
detailed description was provided only for HMePQ-234F.
4-Methyl-2-(2,3,4-trifluorophenyl)quinoline (HMePQ-234F): Pd(PPh3)4
(320mg, 0.28mmol)wasaddedtoamixtureof2-chloro-4-methylquinoline
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(c) (1.50 g, 8.45 mmol), 2,3,4-trifluorophenylboronic acid (1.03 g,
8.45 mmol), toluene (40 mL), methanol (10 mL), and 2.0 M potassium
carbonate aqueous solution (20 mL) under vigorous stirring. The
mixture was stirred at 80 °C for 24 h under N2 atmosphere. After being
cooled to room temperature, and extracted with dichloromethane, then
washed with water, and dried over anhydrous Na2CO3, The solvent was
removed under reduced pressure. The crude product was purified by
column chromatography using a 80:1 mixture of petroleum ether and
ethyl acetate as the eluent to give white crystalline powder (84% Yiled).
1H NMR (600 MHz, CDCl3, δ): 8.15 (d, J = 8.4 Hz, 1H), 8.01 (d, J =
8.4 Hz, 1H), 7.88–7.83 (m, 1H), 7.74 (ddd, J = 1.2 Hz, J = 6.6 Hz, J =
7.8 Hz, 1H), 7.66 (d, J = 2.4 Hz, 1H), 7.59 (ddd, J = 1.2 Hz, J = 7.2 Hz,
J = 8.4 Hz, 1H), 7.14–7.1 (m, 1H), 2.76 (s, 3H); 13C{1H} NMR (100 MHz,
CDCl3, δ): 151.9 (ddd, J = 2.9 Hz, J = 2.3 Hz, J = 1.3 Hz), 151.7 (ddd, J =
250.7 Hz, J = 10.1 Hz, J = 3 Hz), 150.1 (ddd, J = 252.1 Hz, J = 10.8 Hz,
J = 3.2 Hz), 148.2, 145.1, 140.3 (ddd, J = 249.1 Hz, J = 16 Hz, J = 15.3 Hz),
130.4, 129.7, 127.5, 126.9, 125.8 (ddd, J = 9.5 Hz, J = 3.8 Hz, J = 1.2 Hz),
125.1 (ddd, J = 7.8 Hz, J = 4.2 Hz, J = 3.5 Hz), 123.8, 122.6 (d, J = 7.8 Hz),
112.6 (dd, J = 17.3 Hz, J = 3.9 Hz), 19.1; 19F{1H} NMR (376 MHz, CDCl3,
δ): −133.2 (dd, J = 8.7 Hz, J = 20.7 Hz), −138.2 (dd, J = 8.7 Hz, J = 21.1 Hz),
−160.3 (t, J = 20.7 Hz); Anal. calcd for C16H10F3N: C 70.33, H 3.69,
N 5.13; found: C 70.40, H 3.72, N 5.10.
under reduced pressure. The crude product was purified by column
chromatography using CH2Cl2 as the eluent to give target complexes.
Ir(MePQ-3CF3-4F)2(4FPZ) (18): Yellow powder (85% yield). H NMR
1
(600 MHz, DMSO-d6, δ): 8.67 (d, J = 7.2 Hz, 1H), 8.66 (s, 1H), 8.62 (s,
1H), 8.56 (d, J = 7.8 Hz, 1H), 7.98 (t, J = 8.4 Hz, 2H), 7.93 (d, J = 5.4 Hz,
1H), 7.88 (dt, J = 1.2 Hz, J = 7.8 Hz, 1H), 7.84–7.81 (m, 3H), 7.72 (d,
J = 7.8 Hz, 1H), 7.46 (t, J = 7.2 Hz, 1H), 7.43 (t, J = 7.8 Hz, 1H), 7.40
(ddd, J = 1.2 Hz, J = 6 Hz, J = 7.2 Hz, 1H), 7.34 (d, J = 9 Hz, 1H),
7.18–7.14 (m, 2H), 7.07 (ddd, J = 1.2 Hz, J = 7.8 Hz, J = 9 Hz, 1H), 7.04
(ddd, J = 1.2 Hz, J = 7.2 Hz, J = 8.4 Hz, 1H), 6.43 (d, J = 11.4 Hz, 1H),
6.22 (d, J = 11.4 Hz, 1H), 2.9 (s, 3H), 2.85 (s, 3H); 19F{1H} NMR (376
MHz, DMSO-d6, δ): −58.8 (d, J = 12 Hz), −59.0 (d, J = 12 Hz), −114.3
(s), −115.0 (q, J = 12 Hz), −115.8 (q, J = 12 Hz); MALDI-TOF-MS (m/z):
calcd for C47H28F9IrN6, 1040.19; found, 1040.45.
Characterization data for complex 10, 11, 12, 13, 14, 15, 16, and 17
can be found in the Supporting Information.
EL Device Fabrication: The devices were fabricated on the prepatterned
ITO glass substrate with sheet resistance of 10 Ω sq−1 by vacuum
deposition. ITO substrates as the anode were scrubbed and sonicated
consecutively with detergent water, deionized water, and acetone,
dried in drying cabinet, and then exposed to a UV-ozone environment
for 10 min. After these processes, the substrates were transferred into
a vacuum chamber for sequential deposition of all organic functional
layers by thermal evaporation below a vacuum of 5 × 10−4 Pa. The
deposition rates for organic materials, 8-hydroxyquinolinolato lithium
(Liq), and aluminium, were ≈1, 0.1, and 3 Å s−1, respectively. The
thickness of the films was controlled by a quartz thickness monitor.
The active layer of devices is 3 × 3 mm2. The current–voltage–forward
luminance characteristics, color rendering indexes, CIE coordinates
were measured with a PR655 Spectrascan spectrometer and a Keithley
2400 programmable voltage current source. All the samples were
measured directly after fabrication without encapsulation in ambient
atmosphere at room temperature.
X-Ray Crystallography Analysis: The X-ray diffraction data were
collected on a Bruker Smart CCD Apex DUO diffractometer with
graphite monochromated Mo Kα radiation (λ = 0.71073 Å) using the
ω–2θ scan mode. The data were corrected for Lorenz and polarization
effects. The structure was solved by direct methods and refined on
F2 by full-matrix least-squares methods using SHELXTL-2000. All
calculations and molecular graphics were carried out on a computer
using the SHELX-2000 program package and Mercury. Crystallographic
data for the structural analyses have been deposited with the Cambridge
Crystallographic Data Center (CCDC). CCDC reference numbers for 1, 2,
4, 6, 7, 9, and 15 are 1 421 363, 1 421 364, 1 421 366, 1 421 368, 1 421
369, 1 421 365, and 1 421 367, respectively. Copies of this information
can be obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge, CB2 1EZ, UK (Fax: +441223336033; E-mail: deposit@ccdc.
cam.ac.uk, or www: http://www.ccdc.cam.ac.uk).
Characterization data for HMePQ, HMePQ-4F, HMePQ-24F,
HMePQ-35F, HMePQ-345F, HMePQ-2345F, HMePQ-3CF3, and
HMePQ-3CF3-4F can be found in the Supporting Information.
Synthesis of Iridium(III) Complexes: The general procedures for each
class of iridium(III) complexes are provided below.
General Procedure for the Synthesis of Ir(C^N)2(acac) 1–9
(Scheme S2, Supporting Information): Cyclometalated iridium(III)
µ-chlorobridged dimers of a general formula (C^N)2Ir(µ-Cl)2Ir(C^N)2
were synthesized according to the Nonoyama route,[63] by refluxing
IrCl3·3H2O with 2.2 equiv of corresponding cyclometalated HC^N
ligand in a 3:1 mixture of 2-ethoxyethanol and water. To the mixture
of chlorobridged dimer (0.2 mmol) and anhydrous potassium
carbonate(K2CO3) powder (2 mmol) were added dichloromethane
(30 mL) and pentane-2,4-dione (0.5 mmol), and then the slurry was
stirred at room temperature (≈25 °C) for 24 h without any inert gas
protection. After the reaction was finished, the dichloromethane solution
containing Ir(C^N)2(acac) was filtered to remove insoluble salts. The
solvent was removed under reduced pressure. The crude products were
purified by column chromatography using a 10:1 mixture of petroleum
ether and CH2Cl2 as the eluent to give the target complexes, finally the
complexes were recrystallized from CH2Cl2/hexane to remove trace
soluble impurities.
Ir(MePQ-345F)2(acac) (6): Orange powder (90% yield). 1H NMR
(600 MHz, CDCl3, δ): 8.23 (d, J = 8.4 Hz, 2H), 7.93 (dd, J = 1.2 Hz, J = 8.4 Hz,
2H), 7.75 (s, 2H), 7.58 (ddd, J = 0.6 Hz, J = 6.6 Hz, J = 10.8 Hz, 2H),
7.51 (ddd, J = 1.2 Hz, J = 6.6 Hz, J = 7.8 Hz, 2H), 7.44 (ddd, J = 1.2 Hz,
J = 6.6 Hz, J = 8.4 Hz, 2H), 4.55 (s, 1H), 2.91 (s, 6H), 1.47 (s, 6H);
13C{1H} NMR (150 MHz, CDCl3, δ): 185.2, 167.5 (d, J = 2.3 Hz), 157.8
(ddd, J = 2.4 Hz, J = 7.7 Hz, J = 237.9 Hz), 149.4, 147.8 (ddd, J = 3.3 Hz,
J=12Hz, J=238.8Hz), 146.7, 144.1(ddd, J=4.1Hz, J=7.2Hz, J=16.1Hz),
139.8 (ddd, J = 15.3 Hz, J = 20.1 Hz, J = 255.2 Hz), 130.2, 126.8,
126.7, 126.3, 126.1 (d, J = 32.6 Hz), 124.0, 117.8, 110.0 (dd, J = 3 Hz,
J = 17.7 Hz), 100.1, 28.1, 19.4; 19F{1H} NMR (376 MHz, CDCl3, δ):
−128.4 (dd, J = 4.1 Hz, J = 24.1 Hz), −144.8 (dd, J = 4.1 Hz, J = 19.9 Hz),
−159.6 (dd, J = 19.6 Hz, J = 24.1 Hz); MALDI-TOF-MS (m/z): calcd for
C37H25F6IrN2O2, 836.14; found, 836.02.
Supporting Information
Supporting Information is available from the Wiley Online Library or
from the author.
Acknowledgements
Characterization data for complex 1, 2, 3, 4, 5, 7, 8, and 9 can be
found in the Supporting Information.
The authors thank Program for New Century Excellent Talents in
University of Ministry of Education of China (NCET-13-0927), National
Natural Scientific Foundation of China (Grant Nos. 61205179, 61274018
and 21471111), Natural Science Foundation of Jiangsu Province of China
(Grant Nos. BK20130038, BM2012010 and BM2012010), Scientific and
Technological Innovation Teams of Colleges and Universities in Jiangsu
Province (TJ215006), Jiangsu National Synergetic Innovation Center for
Advanced Materials (SICAM), Shanxi Provincial Key Innovative Research
Team in Science and Technology (Grant No. 2012041011), Synergetic
General Procedure for the Synthesis of Ir(C^N)2(4FPZ) 10–18
(Scheme S2, Supporting Information): To the mixture of chlorobridged
dimer (C^N)2Ir(µ-Cl)2Ir(C^N)2 (0.2 mmol) and anhydrous potassium
carbonate (K2CO3) powder (2 mmol) were added dichloromethane
(30 mL) and H4FPZ (0.5 mmol), and then the slurry was stirred at room
temperature (≈25 °C) for 24 h without any inert gas protection. After the
reaction was finished, the dichloromethane solution containing Ir(C^N)2
(4FPZ) was filtered to remove insoluble salts. The solvent was removed
©
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2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Funct. Mater. 2016, 26, 881–894

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Innovation Center for Organic Electronics and Information Displays,
Specialized Research Fund for the Doctoral Program of Higher Education
(20113223110005), and Priority Academic Program Development of
Jiangsu Higher Education Institutions (Grant No. YX03001) for financial
support.
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Adv. Funct. Mater. 2016, 26, 881–894