Two green iridium(iii) complexes containing the electron-transporting group of 4-phenyl-4H-1,2,4-triazole for highly efficient OLEDs

Article abstract of DOI:10.1039/C8TC06010J

Two new iridium(iii) cyclometalated complexes (Ir-TN₃T and Ir-TN₄T) with 2′,6′-bis(trifluoromethyl)-2,3′-bipyridine (TN₃T) and 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (TN₄T) as the cyclometalated ligands and

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Fine-tuning of gold nanorod dimensions and plasmonic properties using
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Two green iridium(III) complexes containing the electron-transporting
Cite this: DOI:
10.1039/x0xx00000x
group of 4-phenyl-4H-1,2,4-triazole for highly efficient OLEDs
Guang-Zhao Lu1,2,3, Liang Liu2, Zhen-Long Tu2, Yong-Hui Zhou1*, You-Xuan Zheng2*
Two new iridium(III) cyclometalated complexes (Ir-TN3T and Ir-TN4T) with 2',6'-
bis(trifluoromethyl)-2,3'-bipyridine (TN3T) and 2',6'-bis(trifluoromethyl)-2,4'-bipyridine (TN4T) as
the cyclometalated ligands and 2-(4,5-diphenyl-4H-1,2,4-triazol-3-yl)phenol (dptp) as the ancillary
ligand were developed. Both complexes are green phosphors with high photoluminescence quantum
efficiency yields (λmax = 540 nm,  = 71.2% for Ir-TN3T and λmax = 513 nm,  = 91.0% for Ir-TN4T,
respectively) in CH2Cl2 solutions at room temperature. The organic light emitting diodes (OLEDs)
with the single-emitting-layer and double-emitting-layer structures show good performances.
Particularly, device D2 with double-emitting-layer structure based on complex Ir-TN4T with 8 wt%
doped concentration shows superior performances with a peak current efficiency of 94.29 cd A-1 and
a peak external quantum efficiency (EQEmax) of 31.43%, and the efficiency roll-off is mild. When the
luminance reaches to 10000 cd m-2, the EQE value can still be kept at 30.26%. This study
demonstrates that the Ir(III) complexes containing ancillary ligand attached with the electron-
transporting group 4-phenyl-4H-1,2,4-triazole group could facilitate charge trapping across the bulk
of the device and have promising application in OLEDs.
Received 00th January 2012,
Accepted 00th January 2012
DOI: 10.1039/x0xx00000x
www.rsc.org/
complexes and benefit their OLEDs performances.7
Introduction
Triazole derivatives have received considerable attention in
Interest in cyclometalated iridium(III)1 and platinum(II)2
complexes has soared over the past decade following the
demonstration of their potential application in the manufacture of
highly efficient light-emitting devices (OLEDs). The spin-orbit
coupling exerted by the heavy metal effect allows the harvest of
both singlet and triplet electro-generated excitons in devices,
leading to a theoretically achievable 100% internal quantum
efficiency.3 In the past years, extensive studies of the effect of
modifications of the phenylpyridine ligands on the photophysical
properties have been carried out.4 By introducing electron-
withdrawing group CF3 or more nitrogen atoms into the phenyl
rings of ppy, the photophysical and electrochemical properties of
Ir(III) or Pt(II) complexes can be tuned. Furthermore, the good
electron transport property of these emitters is also important for
efficient OLEDs in view of the better hole transport ability of
hole transport materials than the electron transport ability of
electron transport materials.5 Many research groups reported
efficient devices based on complexes containing cyclometalated
and ancillary ligands with nitrogen, oxygen, phosphorus, sulphur
and boron-heterocyclic derivatives for better electron mobility.6
For example, some high-performance phosphorescent OLEDs
were reported by our group employing Ir(III) emitters with the
tetraphenylimidodiphosphinate, oxadiazole and thiadiazole
derivatives containing electron-transporting groups as ancillary
ligands, which may improve the electron mobility of the Ir(III)
electro/opto-active materials due to their high electron affinity,
high photoluminescence quantum yield and good thermal and
chemical stability, which make them good candidates for electron
injection and transportation materials.8 In the last several years,
the highly efficient electron-type and bipolar host materials
containing the 4-phenyl-4H-1,2,4-triazole group as the electron
transporting unit have been widely studied.9 Additionally, several
groups like Huang et. al., Kim et. al. and Chi et. al. have also
reported efficient Ir(III) complexes using triazole derivatives as
cyclometalated ligands to increase their electron transporting
ability and consequently facilitate charge trapping across the bulk
for high performance OLEDs.10 However, few heteroleptic Ir(III)
complexes containing the group 4-phenyl-4H-1,2,4-triazole as
ancillary ligands have been reported, which have more nitrogen
heterocycles compared to oxadiazole and thiadiazole, which is
beneficial for their device performances. In addition, the two
bulky -CF3 substituents on the phenyl rings of ppy and the three
benzene rings spatially distributed on triazole can affect the
molecular packing and the steric protection around the metal can
suppress the self-quenching behavior.11 From our former study,
the Ir(III) complexes with 2',6'-bis(trifluoromethyl)-2,3'-
bipyridine (TN3T) and 2',6'-bis(trifluoromethyl)-2,4'-bipyridine
(TN4T) as the cyclometalated ligands show good electron
mobility and high photoluminescence quantum yield (PLQY). On
this basis, as is shown in Fig. 1, we designed and synthesized two
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new heteroleptic Ir(III) complexes containing TN3T and TN4T as As shown in Fig. 1, the cyclometalated ligands TN3T and TN4T
the cyclometalated ligands and 2-(4,5-diphenyl-4H-1,2,4-triazol- and the ancillary ligand dpdt were synthesized according to the
3-yl)phenol (dptp) as the ancillary ligand.12 Both complexes (Ir- reported publications.12 The Ir(III) complexes were prepared by
TN3T and Ir-TN4T) show green emission with PLQY up to the reaction of corresponding chloride-bridged dimmers
91.0%. Using them as emitters, the OLEDs also show good [(C^N)2Ir(µ-Cl)]2 with Kdpdt to give the products Ir-TN3T and
performances with a peak current efficiency of 94.29 cd A-1 and a Ir-TN4T.
Purification
of
the
mixture
by
peak external quantum efficiency of 31.43% with mild efficiency silica gel chromatography provided crude products, which were
roll-off.
further purified by vacuum sublimation. All the new compounds
were fully characterized by 1H NMR spectrometry, high-resolved
mass (HR-MS) spectrometry and elemental analysis, and the
crystal structures further confirmed the identity of the complexes.
Results and discussion
Preparation and characterization of compounds
Fig. 1 The synthetic routes of Ir-TN4T and Ir-TN3T.
The thermal stability of the emitters is important for the stable
OLEDs. In this cases, the thermal properties of the two Ir(III)
complexes were characterized by thermogravimetric (TG)
measurements under a nitrogen steam. From the TG curves in Fig.
S1, it can be observed the decomposition temperatures (5% loss
of weight) of TN3T and Ir-TN4T complexes are as high as 350
oC and 394 oC, respectively. And the good stability of the
complexes suggested they are suitable for application in OLEDs.
Electrochemical properties and theoretical calculation
Fig. 2 Oka Ridge Thermal Ellipsoidal plot (ORTEP) diagrams of Ir-
TN3T (left, CCDC No. 1832350) and Ir-TN4T (right, CCDC No.
1832348) complexes with the atom-numbering schemes. Hydrogen atoms
are omitted for clarity. Ellipsoids are drawn at 50% probability level.
Single crystals of Ir-TN3T and Ir-TN4T were obtained by
vacuum sublimation. Fig. 2 shows the Oak Ridge thermal
ellipsoidal plot (ORETP) diagrams of the complexes given by X-
ray analysis. Selected parameters of the molecular structures and
tables of atomic coordinates were collected in the Table S1 and
Table S2. As shown in Fig. 2, both complexes have distorted
octahedral coordination geometry around iridium center by three
chelating ligands with cis-C-C and trans-N-N dispositions, in
which the N-Ir-N angles are all almost around 175.0° and 172.0°,
respectively. The Ir-C bond lengths are 1.957-2.032 Å and the Ir-
N bonds lengths are 2.017-2.058 Å, respectively, and these values
are similar to those reported in other mononuclear Ir(III)
complexes.13
Fig. 3 Molecular orbital diagram for the HOMOs/LUMOs and their
energy levels of Ir-TN3T and Ir-TN4T calculated in CH2Cl2.
2 | J. Name., 2012, 00, 1-3
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The highest occupied molecular orbital (HOMO) and lowest electronic absorption data are listed in Table 1. The absorption
unoccupied molecular orbital (LUMO) energy levels of the spectra of both complexes shows intense bands with extinction
dopants are important for the design of the OLED structure. In below 350 nm, which are assigned to the spin-allowed intraligand
order to determine the HOMO/LUMO values of the Ir-TN3T and (π→π*) transition of cyclometalated ppy derivatives and ancillary
Ir-TN4T, their electrochemical properties were investigated by ligand. The lower-energy absorption bands in the range 350-500
3
cyclic voltammetry in deaerated CH2Cl2, relative to an internal nm can be assigned to the mixing of 1MLCT and MLCT (metal-
ferrocenium/ferrocene reference (Fc+/Fc) (Figure S2). The cyclic to-ligand charge-transfer) transitions, or LLCT (ligand-to-ligand
voltammograms of the complexes in the positive range show charge-transfer) transition through strong spin-orbit coupling of
strong oxidation peaks, while the reduction peaks are not iridium atom.14 Compared with complex Ir-TN3T in CH2Cl2 with
obvious, demonstrating that the redox process of the complexes is a emission band at 540 nm at RT, complex Ir-TN4T shows blue-
not reversible completely. It is observed that the difference of the shifted emission at 513 nm with much stronger intensity (Fig.
HOMO/LUMO values of the iridium complexes is not obvious 4(b)), which fits well the energy gap calculated by the theoretical
from the Table 1, in which the LUMOs levels all stay at -2.91 eV calculation and electrochemical analysis. Additionally, the PL
and their HOMO levels (-5.34 eV and -5.40 eV) remain almost quantum yields for Ir-TN3T and Ir-TN4T are 71.2% and 91.0%,
the same. These values are much higher than those Ir(III) respectively. These results suggest that the change of the nitrogen
complexes with TNT cyclometalated ligands,12 suggesting the atom position on the phenyl ring affect the emitting properties of
dptp can increase the HOMO and LUMO energy levels.
Ir(III) complexes greatly. Furthermore, the lifetimes are in the
To determine the HOMO/LUMO distributions of the Ir(III) range of microseconds for both complexes (1.47 μs for Ir-TN3T
molecules and further investigate their electronic structures, the and 1.54 μs for Ir-TN4T, respectively) (Fig. S3). The short
density functional theory (DFT) calculations were performed and lifetimes would improve the spin-state mixing and suppress the
the detailed results of the theoretical calculations are included in excitons annihilation.
the SI. As shown in Fig. 3, the HOMO orbitals of two Ir(III)
(a)
(b)
Ir-TN3T
Ir-TN4T
Ir-TN3T
Ir-TN4T
1.0
0.8
0.6
0.4
0.2
0.0
1.0
0.8
0.6
0.4
0.2
0.0
complexes mostly located on the ancillary ligands (77.83% and
77.54%) with a small portion of the cyclometalated ligands
(8.20% and 6.94%) and d- orbitals of iridium atom (13.97% and
15.52%). The LUMO is mostly distributed over the π* orbitals of
the cyclometalated ligands (94.66% and 94.18%) and to a small
extent on Ir d orbitals (3.45% and 3.02%) and ancillary ligands
(1.89% and 2.80%). And the calculated HOMO levels (-5.357 eV
and -5.400 eV) fit well with the electrochemical results (-5.340
eV and -5.400 eV) (Table 1).
300
400
500
600
500
600
Wavelength (nm)
700
Wavelength (nm)
Fig. 4 The UV-vis absorption (a) and emission (b) spectra of complexes
Ir-TN3T and Ir-TN4T in degassed dichloromethane (5  10-5 M) at room
temperature.
Photophysical property
The UV-vis absorption spectra of the complexes Ir-TN3T and Ir-
TN4T in CH2Cl2 at 5 × 10-5 M are shown in Fig. 4(a), and the
Table 1. Photophyscial date of two iridium complexes.
a)
b)
b)
Td
λabs
λem
Φ c)
(%)
 b)
(s)
HOMO/LUMOd)
(eV)
Energy Gap
(eV)
Complex
Ir-TN3T
Ir-TN4T
(°C)
350
394
(nm)
(nm)
540
513
2.43
244/358
237/369
71.2
91.0
1.47
1.54
-5.34/-2.91
-5.40/-2.91
2.49
a)
b)
c)
Decomposition temperature; measured in degassed CH2Cl2; Φ: emission quantum yields were calculated with fac-Ir(ppy)3 standard in degassed
CH2Cl2 solution (P = 0.4); d) HOMO (eV) = -(Eox-E1/2,Fc)-4.8, LUMO (eV) = HOMO+Ebandgap
.
OLEDs performance
Ir-TN3T and Ir-TN4T (x wt%) : 2,6DCzPPy (2,6-bis(3-
(carbazol-9-yl)phenyl)pyridine, 16 nm) / TmPyPB (1,3,5-tri[(3-
pyridyl)-phen-3-yl]benzene, 50 nm) / LiF (1 nm) / Al (100 nm)
are named as S1 and S2, respectively. As shown in Fig. 5, the
materials of HAT-CN and LiF served as hole- and electron-
injecting interface modified materials, respectively. The bipolar
2,6DCzPPy was chosen as host material. The TAPC with high
HOMO level (-5.5 eV) acts as electron-donating and hole-
To illustrate the electroluminescent properties of both
complexes, typical OLEDs using two complexes as dopants
were fabricated. Firstly, the device configuration consists of
single emissive layer with ITO / HAT-CN (dipyrazino[2,3-
f:2',3'-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile,
TAPC (di-[4-(N,N-ditolylamino)phenyl]cyclohexane, 50 nm) /
5 nm) /
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transport media, while TmPyPB with low LUMO level (-2.7 eV)
used as electron-accepting and electron-transport material. The
HOMO and LUMO levels of Ir(III) complexes were all
embedded between those of 2,6DCzPPy (HOMO = 6.10 eV,
LUMO = 2.60 eV). Thus, efficient energy transfer from the host
to Ir(III) complexes occurred in the emitting layer (EML). All
the devices were optimized and the details of optimizing the
doping concentration of Ir(III) emitters are included in the SI.
The electroluminescence (EL) spectra, current density (J)-
voltage (V)-luminance (L), current efficiency (ηc) and power
efficiency (ηp) versus luminance, and EQE as a function of
luminance characteristics of the devices are displayed in Fig. 6,
and the parameters of these devices are summarized in Table 2.
cd A-1 and the peak power efficiency (ηp,max) of 49.76 lm W-1
and a maximum external quantum efficiency (EQEmax) of
24.25%. Relatively, the device S2 (P of Ir-TN4T is 91.0%) at
the 8 wt% concentration displays better performances with the
Lmax, ηc,max and EQEmax of 32085 cd m-2, 88.12 cd A-1 and
29.41%, respectively.
In order to further improve the EL performances of these
complexes,
a
hole transport material TCTA (4,4',4''-
tris(carbazol-9-yl)triphenylamine) was introduced as another
host due to its suitable HOMO level (-5.70 eV) between TAPC
and 2,6DCzPPy and the holes and electrons will be distributed
in more balanced emissive layers and the exciton recombination
zone is expected to be broadened in the double-emitting layer
devices. The OLEDs with double emissive layers with the
configuration of ITO / HAT-CN (5 nm) / TAPC (50 nm) / Ir(III)
complexes (x wt%) : TCTA (8 nm) / Ir complexes (x wt%) :
2,6DCzPPy (8 nm) / TmPyPB (50 nm) / LiF (1 nm) / Al (100
nm) using the dopants of Ir-TN3T and Ir-TN4T are named as
D1 and D2, respectively. The corresponding EL characteristics
of the devices are shown in Fig. 6, and the detailed results are
also summarized in Table 2. Compared to the single-emitting-
layer devices, the double-emitting-layer devices exhibit lower
turn-on voltages due to the stepwise changed HOMO energy
levels of TAPC (-5.5 eV), TCTA (-5.7 eV) and 2,6DCzPPy (-
6.1 eV) and the gradual changed LUMO energy levels of
TmPyPB (-2.7 eV), 2,6DCzPPy (-2.6 eV) and TCTA (-2.4 eV),
which are beneficial for the hole/electron injection and transport.
For complex Ir-TN3T, the double-emitting layer device D1
exhibit slightly inferior performances compared to the single-
emitting layer device S1 with the ηc,max and EQEmax of 72.77 cd
A-1 and 20.90%, respectively owing to the imbalance of electron
and hole transporting properties of the hole-type host TCTA.
However, for complex Ir-TN4T with very high PL efficiency,
the double-layer emitting layer device D2 exhibit better
performances than the single-emitting-layer device S2 with the
ηc,max and EQEmax of 94.29 cd A-1 and 31.43%, respectively,
which is among the best results of those devices based on Ir(III)
complexes.15 Furthermore, both devices show low efficiency
roll-off. When the luminance reached to 10000 cd m-2, the
EQEmax data of D1 and D2 can still be kept at 20.74% and
30.26%, respectively.
Fig. 5 Energy level diagram of HOMO and LUMO levels (relative to
vacuum level) for materials investigated in this work and their
molecular structures.
Fig. 6(a) shows the normalized EL spectra of the devices
measured at the voltage of 4.0 V with peaks at about 518 nm
and 500 nm for devices S1 and S2, which are close to the PL
spectra of the Ir(III) complexes in CH2Cl2 solutions, indicating
that the EL emissions of the devices originate from the triplet
excited states of the phosphors in which the CIE coordinates fall
in the green region. Due to the same ancillary ligand and similar
molecular structures, the device performances of both materials
mainly depend on their PL efficiencies and electrochemical
properties.
Respectively, the device S1 (P of Ir-TN3T is 71.2%) at the
6 wt% concentration shows the maximum luminance (Lmax
)
above 40588 cd m-2, the peak current efficiency (ηc,max) of 83.93
Table 2. EL performances of the devices S1-S2 and D1-D2.
a)
b)
Vturn-on
(V)
Lmax
(cd m-2)
ηc,max
(cd A-1)
ηext,max
(%)
ηp,max
(lm W-1)
ηcb)
(cd A-1)
ηext
CIE
(x, y)
Device
(%)
49.76
S1 (6%)
S2 (8%)
3.9
3.7
40588
32085
83.93
88.12
24.25
29.41
82.91
83.69
23.94
27.92
(0.286, 0.613)
(0.203, 0.592)
49.37
44.82
57.14
D1 (6%)
D2 (8%)
3.6
3.5
39888
39638
72.77
94.29
20.90
31.43
72.38
90.87
20.74
30.26
(0.285, 0.612)
(0.213, 0.588)
a) Applied voltage recorded at a luminance of 1 cd m-2; b) Recorded at 10000 cd m-2.
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104
103
102
101
100
90
100
90
80
70
60
50
40
30
20
10
30
25
20
15
10
5
(c)
(d)
(a)
(b)
120
1.0
0.8
0.6
0.4
0.2
0.0
S1
S2
80
100
S1
S2
S1
S2
80
70
60
60
40
S1
S2
20
0
50
40
S1
S2
S1
S2
0
10000
20000
400
500
600
700
0
10000
20000
3
4
5
6
7
8
9
10 11 12
Wavelength (nm)
Voltage (V)
Luminance (cd m-2
)
Luminance (cd m-2
)
104
103
102
101
100
100
80
60
40
20
0
100
35
30
25
20
15
10
5
(h)
(g)
(f)
120
100
80
60
40
20
0
(e)
1.0
0.8
0.6
0.4
0.2
0.0
D1
D2
90
80
70
60
50
40
30
D1
D2
D1
D2
D1
D2
D1
D2
D1
D2
20
20000
0
0
10000
0
10000
20000
400
500
600
700
3
4
5
6
7
8
9
10 11
Wavelength (nm)
Voltage (V)
Luminance (cd m-2
)
Luminance (cd m-2
)
Fig. 6 Characteristics of single-emitting-layer: (a) EL spectra, (b) J-V-L, (c) c-L-p, (d) EQE-L and characteristics of double-emitting-
layer devices: (e) EL spectra, (f) J-V-L, (g) c-L-p, (h) EQE-L.
The good device performances of the complexes may be
due to their possible good electron mobility for the reason that
the hole mobility of the TAPC is higher than the electron
mobility of the TmPyPB in OLEDs,5 the excitons
accumulation is expected in hole blocking layer (TmPyPB)
near the interface of emitting layer (Ir(III) complexes (x wt%)
: 2,6DCzPPy) / TmPyPB.16 The accumulation of excitons is
expected to cause the serious triplet-triplet annihilation (TTA)
and triplet-polaron annihilation (TPA) of the iridium
complexes, and high efficiency roll-off consequently. From
our former study we knew both the TN3T and TN4T ligands
are beneficial for the electron mobility of the Ir(III) complexes,
and due to the nitrogen heterocycle structure, the application
of dptp as the ancillary ligand also has the same effect.
measurement were listed in the SI. The synthesis of the
ligands and complexes were performed under nitrogen
atmosphere. All reagents and chemicals were purchased from
commercial sources and used without further purification.
2-Phenyl-1,3,4-oxadiazole. Benzhydrazide (21.66 g, 159.0
mmol) and triethyl orthoformate (90 mL) were placed in a 500
mL, two-neck round-bottom flask, and the mixture was
vigorously stirred at 160 °C for 24 h. After cooling to room
temperature, the solvent was evaporated under reduced
pressure. The product was used for the next step without
further purification.
3,4-Diphenyl-4H-1,2,4-triazole. 2-Phenyl-1,3,4-oxadiazle
(9.0 g, 62 mmol), phenylamine (5.7g, 61.5 mmol), and o-
dichlorobenzene (30 mL) were combined into a 100 mL
round-bottom flask equipped with a stir bar, condenser and N2
bubbler. Trifluoroacetic acid (4.7 mL, 61.4 mmol) was added,
and the reaction mixture was refluxed at 182 °C for 16 h.
After cooling to room temperature, it was poured into 10%
aqueous sodium carbonate (200 mL). The mixture was
adjusted to pH~10 and then transferred to a separatory funnel.
The product was extracted with dichloromethane two times.
The organic layers were combined and washed with brine,
dried over MgSO4, and concentrated under reduced pressure.
o-Dichlorobenzene was vacuum distilled at 90 °C to give a
white solid (8.1 g, 60%).
Conclusions
In conclusion, two cyclometalated Ir(III) complexes Ir-TN3T
and Ir-TN4T with 2',6'-bis(trifluoromethyl)-2,3'-bipyridine
and
2',6'-bis(trifluoromethyl)-2,4'-bipyridine
as
the
cyclometalated ligands and 2-(4,5-diphenyl-4H-1,2,4-triazol-
3-yl)phenol as the ancillary ligand were successfully
investigated and applied in the OLEDs. The OLEDs based on
complexes Ir-TN3T and Ir-TN4T with single and double
emissive layers showed high EQEmax as 24.25% and 31.43%,
respectively and also showed slow roll-off. When the
luminance reaches to 10000 cd m-2, the EQE values can still
be kept at 23.94% and 30.26%, respectively. This study
suggested that the nitrogen heterocycle cyclometalated ligands
and ancillary ligands could be employed well in Ir(III)
complexes, which would have potential applications in
OLEDs.
3-Bromo-4,5-diphenyl-4H-1,2,4-triazole.
A
500 ml
round-bottom flask was charged with 3,4-diphenyl-4H-1,2,4-
triazole (7.1 g, 32 mmol), N-bromosuccinimide (7.2 g, 40. 0
mmol), carbon tetrachloride (60 mL), and acetic acid (60 mL).
The flask was heated at 120°C. The reaction was monitored
by TLC (3:2 CH2Cl2: EtOAc) after 4 h to show a product
forming. After 4.5 h, more N-bromosuccinimide (1.5 g) was
added to the reaction. After 6.5 h, TLC showed a faint spot
corresponding to the starting triazole. The flask was lifted out
after 7.75 h. Aqueous Na2CO3 (10%) was added to the
Experimental Section
The general information for the sample and device
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reaction mixture until the pH was ~ 8. The product was
extracted with CH2Cl2 three times, and the combined organic
solution was washed with brine, dried over MgSO4, filtered,
concentrated under reduced pressure to give the faint yellow
solid (7.6 g, 80%).
[M+H]+. Anal. Calcd for C44H24N7F12OIr: C, 48.62; H, 2.23;
N, 9.02. Found: C, 48.67; H, 2.32; N, 9.24%.
Ir-TN4T: Yield: 75.0%.1H NMR (400 MHz, CDCl3) δ 8.99
(d, J = 5.62 Hz, 1H), 8.22 (d, J = 5.65 Hz, 1H), 8.04-7.99 (m,
4H), 7.76 (t, J = 7.81 Hz, 1H), 7.62 (t, J = 8.52 Hz, 1H), 7.46
(dt, J = 7.21, 24.73 Hz, 4H), 7.31 (t, J = 7.50 Hz, 1H), 7.17
(dd, J = 6.54, 14.08 Hz, 4H), 6.90-6.88 (m, 2H), 6.75-6.68 (m,
2H), 6.27 (ddd, J = 1.20, 3.55, 8.38 Hz, 2H), 6.04 (t, J = 7.55
Hz, 1H). HR-MS, m/z: calcd for C44H24N7F12OIr, 1087.1480
[M]; found 1088.1565 [M+H]+. Anal. Calcd for
C44H24N7F12OIr: C, 48.62; H, 2.23; N, 9.02. Found: C, 48.74;
H, 2.47; N, 9.32%.
3-(2-Methoxyphenyl)-4,5-diphenyl-4H-1,2,4-triazole.
A
500 ml, 2-neck round-bottom flask was charged with 3-
bromo-4,5-diphenyl-4H-1,2,4-triazole (9.0 g, 23 mmol), 2-
methoxy benzyl boronic acid (7.1 g, 46.8 mmol), toluene (200
mL), and K3PO4 monohydrate (16.2 g, 70.3 mmol). In the
glovebox, Pd2dba3 (0.43 g, 0.47 mmol), S-Phos (0.77 g, 1.9
mmol), and toluene (30 mL) were combined in a sealed
round-bottom flask and stirred at room temperature for 20
minutes. The catalyst solution was quickly transferred to the
reaction outside of the glovebox. The reaction was heated for
10 h and concentrated. The resulting residue was purified by
silica gel column chromatography (eluent EtOAc: Hexanes =
1:1), which gave dark brown power (2.3 g, 30%).
Acknowledgements
This work was supported by the National Natural Science
Foundation of China (51773088).
Notes and references
1Jiangsu Key Laboratory of Atmospheric Environment Monitoring
and Pollution Control, Collaborative Innovation Center for
Atmospheric environment and equipment technology, College of
Environmental Science and Engineering, Nanjing University of
Information Science & Technology, Nanjing 210044, P. R. China *E-
mail: 002083@nuist.edu.cn
2-(4,5-Diphenyl-4H-1,2,4-triazol-3-yl)phenol.
To
a
mixture of 3-(2-methoxyphenyl)-4,5-diphenyl-4H-1,2,4-
o
triazole (1.5 g) in 20 mL CH2Cl2 at -78 C was added BBr3
(1.25 g, 50 mmol in 20 mL CH2Cl2 ) dropwise. The mixture
was stirred for 24 h at -78 oC and the resulting solution was
poured into water, extracted with CH2Cl2 (50 mL × 3 times)
and the solvent was removed under and recrystallization of
the residue from ethanol gave dark brown solid (dptp). Then,
to a suspension of tpdp (1.3g) in methanol (30 mL) was
added the equivalent KOH in methanol (5 mL) and stirred for
2State Key Laboratory of Coordination Chemistry, Collaborative
Innovation Center of Advanced Microstructures, School of Chemistry
and Chemical Engineering, Nanjing University, Nanjing 210093, P. R.
China, *E-mail: yxzheng@nju.edu.cn
3Shenzhen Key Laboratory of Polymer Science and Technology,
College of Materials Science and Engineering, Shenzhen University,
Shenzhen 518060, P.R. China, *E-mail: gzhlu@szu.edu.cn
†Electronic Supplementary Information (ESI) available: Details of
materials and measurements. Synthesis details of the cyclometalated
ligand. Details of X-ray Crystallography, electrochemical tests and
theoretical calculation. Procedures of OLEDs fabrication and
measurements. The crystallographic data of iridium complexes. The
electronic cloud density distribution, TG curves, cyclic
voltammograms and selected lifetime curves of complexes. Current
efficiency versus luminance of device with different doped
concentrations.
2
hr at room temperature. Concentration in vacuum
precipitated a dark brown solid (Kdptp). 1H NMR (400 MHz,
CDCl3) δ 10.33 (s, 1H), 7.45-7.40 (m, 3H), 7.34-7.31 (m, 2H),
7.27-7.24 (m, 2H), 7.22-7.17 (m, 3H), 6.90 (t, J = 7.5 Hz, 2H),
6.75 (d, J = 7.5 Hz, 2H). ESI-MS, m/z: calcd for C20H15N3O,
313.12 [M]; found 312.08 [M-H]-.
General synthesis of Ir(III) complexes. The IrCl3 (0.64 g,
2.14 mmol) and 2.4 equivalent of cyclometalated ligand (5.14
mmol) were added in a 2-ethoxyethanol and water mixture.
o
Then, the solution was heated for 16 h at 110 C. After the
addition of water, the precipitated yellow powder was filtered
and reacted with Kdptp without further purification for
another 16 h at 110 oC. After cooling, the solution was
concentrated and the resulting residue was purified by silica
gel column chromatography (CH2Cl2/petroleum ether 1:2
(v/v)) and vacuum sublimation gave yellow-green crystals.
Ir-TN3T: Yield: 72.0%.1H NMR (400 MHz, CDCl3) δ 9.19
(dd, J = 1.12, 5.70 Hz, 1H), 8.49-8.47 (m, 2H), 8.34 (d, J =
8.41 Hz, 1H), 7.93 (t, J = 8.01 Hz, 1H), 7.77 (t, J = 8.00 Hz,
1H), 7.54-7.46 (m, 3H), 7.33 (dd, J = 5.17, 12.43 Hz, 3H),
7.19 (dd, J = 9.93, 18.02 Hz, 4H), 6.96 (dd, J = 6.91, 19.31
Hz, 3H), 6.89 (s, 1H), 6.82 (t, J = 8.65 Hz, 1H), 6.55 (s, 1H),
6.38-6.35 (m, 2H), 6.11(t, J = 7.52 Hz, 1H). HR-MS, m/z:
calcd for C44H24N7F12OIr, 1087.1480 [M]; found 1088.1560
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Two novel iridium(III) complexes containing the electron-transporting group of 4-
phenyl-4H-1,2,4-triazole showed good photoluminescence and electroluminescence
performances with EQE of 31.43% and mild efficiency roll-off.