Highly efficient bluish green organic light-emitting diodes of iridium(iii) complexes with low efficiency roll-off

Article abstract of DOI:10.1039/c8dt00952j

Two novel iridium(iii) complexes Ir(BTBP)₂mepzpy and Ir(BTBP)₂phpzpy were successfully synthesized, in which 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine (BTBP) was used as the main ligand, and 2-(3-methyl-1H-pyrazol-5-yl)pyridine (mep

Full text of DOI:10.1039/c8dt00952j

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High efficient bluish green organic light-emitting diodes of
iridium(III) complexes with low efficiency roll-off
1
,2
Ning Su, ZhengꢀGuang Wu, YouꢀXuan Zheng
*
Received 00th January 20xx,
Accepted 00th January 20xx
Two novel iridium(III) complexes Ir(BTBP) mepzpy and Ir(BTBP) phpzpy were successfully synthesized,
2
2
DOI: 10.1039/x0xx00000x
in which 2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine (BTBP) was used as main ligand, 2ꢀ(3ꢀmethylꢀ1Hꢀpyrazolꢀ
ꢀyl)pyridine (mepzpy) and 2ꢀ(3ꢀ2ꢀ(3ꢀphenylꢀ1Hꢀpyrazolꢀ5ꢀyl)pyridine (phpzpy) were introduced as the
5
www.rsc.org/
ancillary ligands, respectively. Both Ir(III) complexes displayed bluish green emission peaked at 486 and 487
nm with high quantum efficiencies of 0.73 and 0.69, respectively. The organic lightꢀemitting diodes (OLEDs)
with the structure of ITO/ HATCN (hexaazatriphenylenehexacabonitrile, 5 nm)/ TAPC (bis[4ꢀ(N,Nꢀ
ditolylamino)ꢀphenyl]cyclohexane, 40 nm)/ Ir(BTBP) mepzpy or Ir(BTBP) phpzpy (10 wt%):
2
2
26DCzPPy(2,6ꢀbis(3ꢀ(9Hꢀcarbazolꢀ9ꢀyl)phenyl)pyridine, 10 nm)/ TmPyPB (1,3,5ꢀtri[(3ꢀpyridyl)ꢀphenꢀ3ꢀ
yl]benzene, 30 nm)/ LiF (1 nm)/ Al (100 nm) exhibited high efficiency with low efficiency rollꢀoff.
Especially, the device based on Ir(BTBP) mepzpy complex achieved the maximum current efficiency of
2
ꢀ
1
5
1
8.17 cd A and the maximum external quantum efficiency of 25.33% with Commission Internationale de
’Eclairage coordinates of (0.19, 0.43). These results indicate that novel cyclometalated Ir(III) complexes for
high efficient OLEDs with low efficiency rollꢀoff simultaneously were obtained by our rational design.
2
',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine (BTBP) was introduced as
Introduction
the main ligand and tetraphenylimidodiphosphinate (tpip) and 2ꢀ(5ꢀ
phenylꢀ1,3,4ꢀoxadiazole/thiadiazolꢀ2ꢀyl)phenol ligands were utilized
Organic lightꢀemitting diodes (OLEDs) using heavyꢀmetal
complexes as dopants have been widely used in the next generation
flatꢀpanel displays and solidꢀstate lighting sources because they can
harvest both singlet and triplet excitons arising from the strong spinꢀ
orbital coupling and therefore its internal quantum efficiency up to
14ꢀ17
as the auxiliary ligands, respectively.
Moreover, four orangeꢀred
Ir(III) complexes with good OLEDs performances and low
efficiency rollꢀoff were also exploited, in which 1ꢀ(2,6ꢀ
bis(trifluoromethyl)pyridinꢀ4ꢀyl)isoquinoline (tfmpiq) and 4ꢀ(2,6ꢀ
bis(trifluoromethyl)pyridinꢀ4ꢀyl)quinazoline (tfmpqz) were applied
as the main ligands and tpip was utilized as ancillary ligands,
1
ꢀ7
1
00%. In recent years, cyclometalated iridium(III) complexes have
received a great deal of attention due to their high luminescent
efficiency, stable chemical stability and tunable emission colour in
the visible region.
1
8, 19
respectively.
Therefore, it is an efficient method for us to
8
ꢀ13
achieve the balance of the carrier injection and transportation of for
high efficient device performances and low efficiency rollꢀoff by the
rational design of the main ligands and the auxiliary ligands of the
Ir(III) complexes.
Therefore, more and more cyclometalated
Ir(III) complexes were used as the emitters in efficient OLEDs.
However, the efficiency rollꢀoff of some devices is serious, which is
attributed to the deterioration of chargeꢀcarrier balance and increase
in nonꢀradioactive quenching processes including tripletꢀtriplet
annihilation (TTA), tripletꢀpolaron annihilation (TPA), and electricꢀ
fieldꢀinduced dissociation of excitons at high current density. It is
crucial to develop novel cyclometalated Ir(III) complexes with high
efficient device performances and low efficiency rollꢀoff
simultaneously.
With this consideration, in this work, we synthesized two novel
Ir(III)
complexes
namely
Ir(BTBP)
2
mepzpy
and
1
4
Ir(BTBP) phpzpy, in which BTBP was used as main ligand, 2ꢀ(3ꢀ
2
methylꢀ1Hꢀpyrazolꢀ5ꢀyl)pyridine (mepzpy) and 2ꢀ(3ꢀ2ꢀ(3ꢀphenylꢀ
1
Hꢀpyrazolꢀ5ꢀyl)pyridine (phpzpy) were introduced as the ancillary
ligands, respectively. Two nitrogen atoms in BTBP ligand would
increase the electron affinity, and the two trifluoromethyl units are
beneficial to increase the steric hindrance of the Ir(III) complex and
thus further suppress the TTA effect. Two pyrazol pyridine
Recently, our teamwork developed some Ir(III) complexes with
good OLEDs performances and low efficiency rollꢀoff, in which
^
derivatives (mepzpy and phpzpy) were applied as (N N)H chelating
ligands, which are easily to extend the highest occupied molecular
orbit (HOMO) and the lowest occupied molecular orbit (LUMO) gap
of the complexes. Therefore, they would have an effect on colour
20ꢀ23
tuning of the Ir(III) complexes.
Furthermore, the nitrogen
heterocycle would enhance the electron affinity and the electron
15, 24, 25
mobility of the Ir(III) complexes.
As a result, the devices
based on both Ir(III) complexes exhibit high efficiency with low
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efficiency rollꢀoff simultaneously. It is worth mentioning that the Single crystal of Ir(BTBP)
device based on Ir(BTBP)
current efficiency (ηc,max) of 58.17 cd A and the maximum external Selected bond lengths of Ir(BTBP)
quantum efficiency (EQEmax of 25.33% with Commission in Tables S1 (ESI). The iridium atom adopts a distorted octahedral
2
phpzpy complex was obtained from
2
mepzpy complex achieved the maximum vacuum sublimation and analysized by Xꢀray diffraction (Fig. 1).
ꢀ1
2
phpzpy complex were collected
)
^
Internationale de 1’Eclairage (CIE) coordinates at (0.19, 0.43).
coordination geometry with two C N cyclometalated ligands and one
^
N N ligand. The bond lengths of Ir1ꢀN5 (2.139(5) Å) and Ir1ꢀN6
Results and discussion
Synthesis and Characterization
(2.081(4) Å) of Ir(BTBP) phpzpy complex are longer than that of
Ir1ꢀN1 (2.063(4) and Ir1ꢀN3 (2.052(4) Å), respectively. This
2
phenomenon confirms the sigma donation of the carbons (transꢀ
27ꢀ30
The synthetic procedures of Ir(III) complexes are shown in Scheme effect) in the Ir(III) complexes.
1
. All the synthesis experiments were carried out under nitrogen, and
The thermal stabilities of Ir(III) complexes are important for the
OLEDs fabrication and application. From the recorded
the solvents were dried prior to use. The main ligand BTBP was
obtained by a twoꢀstep synthetic method. The ꢁꢀchloroꢀbridged
thermogravimetric analysis (TGA) curves in Fig. S1, it can be
dimer [(BTBP)
methods by heating IrCl
2.5 equiv) in 2ꢀethoxyethanol and water (v/v =3/1) at 110 °C. The
ancillary ligands (mepzpy and phpzpy) were obtained by
2
Ir(ꢁꢀCl)]
2
was synthesized according to the reported
o
observed that the decomposition temperatures (T ) of 389 and 409 C
d
3
·3H O (1 equiv) and the main ligand BTBP
2
are observed for Ir(BTBP) mepzpy and Ir(BTBP) phpzpy
2
2
(
complexes with 5% loss of weight, respectively. The good thermal
stabilities of both Ir(III) complexes are beneficial for the OLEDs
a
26
successive condensation and cyclization reactions. Both Ir(III)
complexes were confirmed with H NMR, high resolution mass
spectrometer (HRMS) and Xꢀray crystallography (see ESI).
application. Moreover, Ir(BTBP) phpzpy complex has an obvious
2
1
better thermal stability, which is due to the phenyl group
31
introduction of the ancillary ligand. The relevant data were
summarized in Table 1.
F
3
C
N
CF
3
F
3
C
N
CF
3
Cl
Cl
N
F
3
C
N
CF
3
F3
C
N
CF3
Br
LDA
2-ethoxyethanol
Ir
N
Ir
2
B(OPr-i)
3
H
2
O
2
Photophysical property
Pd(PPh
3
)
4
N
N
B(OH)
2
F
3
C
N
CF
3
1
BTBP
2
O
N
NH
Ir(BTBP) mepzpy
N
N
N
NaH
THF
O
R
N
2
H
4
R= CH
3
, mepzpy
2
O
+
R C O
EtOH
R
R=phenyl, phpzpy
Ir(BTBP) phpzpy
O
2
3
F C
CF
3
N
N
F
3
C
N
CF
3
3 3
CF F C
Cl
N
N
NH
N
2-ethoxyethanol
H2
Ir
Ir
R
O
N
Ir
2
N
N
2
Cl
F
3
C
N
CF
3
N
N
N
R
R= CH
3
, Ir(BTBP)
2
mepzpy
phpzpy
R=phenyl, Ir(BTBP)
2
2 2
Scheme 1. Synthetic route of Ir(BTBP) mepzpy and Ir(BTBP) phpzpy
complexes.
X-ray crystallographic analysis
250
300
350
400
450
500
550
600
650
Wavelength (nm)
Fig. 2 Normalized UV/vis absorption and emission spectra of both Ir(III)
ꢀ5
complexes in dilute DCM (10 M).
As shown in Fig. 2, the UV/vis absorption spectra of
2 2
Ir(BTBP) mepzpy and Ir(BTBP) phpzpy complexes in dilute
ꢀ
5
DCM solution (10 M) at room temperature (RT) are similar in the
range of 260ꢀ500 nm. The relevant data were also collected in Table
1
. The high energy absorption bands below 360 nm are definitely
1
4
ascribed to πꢀπ* transitions of the ligands. However, the lowerꢀ
energy absorption bands (360ꢀ500 nm) can be assigned to the mixed
1
3
MLCT and MLCT (metalꢀtoꢀligand chargeꢀtransfer) states or
LLCT (ligandꢀtoꢀligand charge transfer) transition through strong
spinꢀorbit coupling of iridium atom. The photoluminescence (PL)
ꢀ5
spectra of both Ir(III) complexes in DCM (10 M) at RT were also
displayed in Fig. 2. Both Ir(III) complexes showed similar emissions
peaked at 486 and 487 nm with a shoulder at 512 and 514 nm at RT,
respectively. While at 77 K, the two major emission peaks become
shaper, and the third ones are also appear (Fig. S2, ESI), which is
2
Fig. 1 ORTEP diagram of Ir(BTBP) phpzpy complex (CCDC No. 1819959)
with the atomꢀnumbering schemes. Hydrogen atoms are omitted for clarity.
Ellipsoids are drawn at the 50% probability level.
2
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3
3
25
attributed to the hybrid states such as major MLCT and minor
ILCT characters.
Table 1. Photophysical data of both Ir(III) complexes
a
b
d
T
d
UVꢀvis
(nm)
PL(nm)
τ
E
HOMO
e
E
LUMO
f
c
Complexes
ΦPL
o
(
C)
RT
77 K
(ꢁs)
(eV)
(eV)
Ir(BTBP)
2
mepzpy
phpzpy
398
409
269,329
486,514
483,512,549
0.73
0.69
3.87
2.60
ꢀ5.75
ꢀ5.91
ꢀ3.17
ꢀ3.33
Ir(BTBP)
2
269,323,374
487,512
483,517,556
a
ꢀ5
b
ꢀ5
c
ꢀ5
Measured in dilute DCM (10 M) at RT. Measured in dilute DCM (10 M) at RT or 77K. Measured in dilute DCM (10 M) in N
2
atmosphere
atmosphere.
2
2
r
d
ꢀ5
according to the equation of Φ
s
=Φ
r s
(ɳ
r
A I
s
/ɳ
s
A I
r
) using facꢀIr(ppy)
3
as a reference (Φ
P
= 0.40). Measured in dilute DCM (10 M) in N
2
e
f
opt
Calculated from empirical equation: EHOMO = ꢀ (Eox+ 4.8) eV. Calculated from ELUMO = E
g
+ EHOMO.
It is well known that the phosphorescence excited state lifetime (τ) good agreement with our design intention. In general, both Ir(III)
of Ir(III) complex is a crucial factor that determines the rate of TTA complexes display the similar LUMO energy distributions but a
both in the solution and OLEDs. The longer τ of the emitter would different HOMO energy proportion owing to the distinct substituents
3
2
causes more serious TTA effect. In this cases, the lifetimes of attached in the ancillary ligands.
Ir(BTBP) mepzpy and Ir(BTBP) phpzpy complexes measured in
2
2
degassed DCM at RT are 3.87 and 2.60 ꢁs (Table 1), respectively,
which can illustrate the phosphorescent origin of the excited states.
Experimental
Theoretical
Furthermore, Ir(BTBP) mepzpy and Ir(BTBP) phpzpy complexes
2
2
display high phosphorescence quantum efficiency yields of 0.73 and
.69, respectively. These results indicated that both Ir(III) complexes
are potential emitters in the OLEDs.
-
2.17
-2.19
3.33
Ir(BTBP) phpzpy
0
LUMO
HOMO
-3.17
-
Ir(BTBP) mepzpy
2
Electrochemical property and theoretical calculation
2
-
-
5.79
5.75
-5.55
-5.91
The HOMO and LUMO energy levels of the Ir(III) complexes are
important for the design of the device structure. Cyclic voltammetry
measurements were carried out using ferrocene as the internal
standard to calculate the HOMO and LUMO energy levels of both
Ir(III) complexes (Fig. S3). The HOMO energy levels (EHOMO) can
be calculated according to the equation of EHOMO = ꢀ (Eox + 4.8)
1
5
eV. Moreover, based on the corresponding optical energy gaps
Fig. 3 Theoretical (black) and experimental (red, determined by cyclic
voltammetry) HOMO/LUMO energy levels of complexes Ir(BTBP) mepzpy
and Ir(BTBP) phpzpy.
opt
15
(
Eg ) and EHOMO levels,
the LUMO energy levels (ELUMO) are
2
estimated. The corresponding data were collected in Table 1, Fig. 3
2
and Table S2. Moreover, compared with Ir(BTBP) mepzpy,
2
Ir(BTBP) phpzpy complex owns a lower HOMO energy indicating Electroluminescent property
2
that the phenyl group in the ancillary ligand has an obvious influence
on electrochemical property.
In order to further investigate the electroluminescence (EL)
performances of both Ir(III) complexes, the OLEDs with the
Furthermore, the density functional theory (DFT) calculation
employing Gaussian09 software with the B3LYP functional was
carried out to investigate the electronic states and orbital
distributions of both Ir(III) complexes. The optimized
HOMO/LUMO structures of two Ir(III) complexes were also clearly
shown in Fig. 3. And the corresponding HOMO and LUMO electron
cloud density distributions of each fragment of Ir(III) complexes
were shown in Table S3. Obviously, the LUMO energy distributions
of both Ir(III) complexes are mainly located in main ligand (BTBP)
with a large proportion (as high as 94.28% and 94.11%) (Table S3),
while the HOMO energy distributions of both Ir(III) complexes are
mainly distributed in metal iridium atom and the ancillary ligands.
Moreover, the ancillary ligands of both Ir(III) complexes (mepzpy
and phpzpy) own the HOMO energy proportion of 70.44% and
structure
Ir(BTBP)
of (5
ITO/HATCN
nm)/TAPC
(40
nm)/
2
mepzpy or Ir(BTBP) phpzpy (10 wt%): 26DCzPPy (10
2
nm)/ TmPyPB (30 nm)/ LiF (1 nm)/Al (100 nm) were fabricated
Scheme 2). For convenience, the devices using Ir(BTBP) mepzpy
and Ir(BTBP) phpzpy emitters as dopants are named as G1 and G2,
(
2
2
respectively. HATCN was used as holeꢀinjection layer, TAPC was
applied as holeꢀtransporting layer, and 26DCzPPy was used as host
material. While TmPyPB and LiF were utilized as electronꢀ
transporting and electronꢀinjection layer, respectively. Fig.
displays the EL spectra, luminance (L) versus voltage (V), current
efficiency (η ) versus luminance, and power efficiency (η ) versus
luminance characteristics of the devices. In addition, Table 2 collects
the key EL data of devices G1 and G2. From Fig. 4a, it can be
observed that almost identified EL spectra are observed for devices
G1 and G2 peaked at 483 nm with a shoulder at 511 nm at the
dopant concentrations of 10 wt%, and they are similar to the
4
c
p
83.67% (Table S3), respectively, indicating that this kind of ancillary
ligands have a great impact on the HOMO energy levels, which is in
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phosphorescence emissions in DCM at RT, which indicates that the yield (ΦPL) played a decisive role in determining the OLEDs
EL emissions derive from the triplet excited states of the Ir(III) performances. Respectively, G1 device exhibited the higher
ꢀ
1
complexes. It is shown that G1 and G2 devices display bluish green maximum current efficiency (ηc,max) of 58.17 cd A , the maximum
OLEDs with the CIE coordinates at (0.19, 0.43) and (0.18, 0.43), external quantum efficiency (EQEmax of 25.33% and power
)
ꢀ
1
respectively.
efficiency (ηp,max) of 31.84 lm W . Moreover, the device also shows
low efficiency rollꢀoff. Even at the practical brightness of 1000 cd m
ꢀ
2
ꢀ1
ꢀ1
,
these values still keep at 54.97 cd A , 24.06% and 30.96 lm W ,
respectively. Because Ir(BTBP) phpzpy complex has a lower ΦPL
0.69) than that of Ir(BTBP) mepzpy, the G2 device exhibited
relative lower performances with the maximum current efficiency of
2
(
2
ꢀ1
5
4.89 cd A , the maximum external quantum efficiency of 24.31%
ꢀ1
and the maximum power efficiency of 31.92 lm W , respectively.
However, this device even shows lower efficiency rollꢀoff. For
example, at the brightness of 1000 cd m , these values still as high
ꢀ
2
ꢀ
1
ꢀ1
as 52.66 cd A , 23.29% and 29.01 lm W , respectively. In general,
the devices using both Ir(III) complexes as dopants exhibited high
efficiencies with low efficiency rollꢀoff, which is mainly due to the
special advantages of the BTBP main ligand and the unique
properties of the auxiliary ligands of pyrazol pyridine derivatives.
Moreover, G2 device also exhibited higher maximum luminance
(Lmax) of 38200 cd m than that of device G1 (19700 cd m ). These
results suggest that both Ir(III) complexes are potential materials for
efficient OLEDs.
Scheme 2. The OLEDs device structure and their molecular structures used
in this work.
Both devices exhibited high efficiencies with low efficiency rollꢀ
off. From Fig. 4bꢀ4d, it is clearly seen that G1 device with
Ir(BTBP) mepzpy (ΦPL=0.73) as dopant exhibited the better
2
performances. Because both Ir(III) complexes have similar
photophysical and electrochemical properties due to the same main
ligand and similar ancillary ligands, the phosphorescence quantum
ꢀ2
ꢀ2
(b)
(a)
G1
G2
G1
G2
4
3
2
1
1
1
0
0
0
200
300
400
500
600
700
800
4
5
6
7
8
9
10
11
12
Wavelength (nm)
Voltage (V)
1
00
10
1
1
00
G1
G2
(c)
(d)
G1
G2
1
0
1
0.1
0.1
0
2000
4000
6000
8000
10000
0
2000
4000
6000 -2
cd m )
8000
10000
-2
Luminance
(
cd m
)
Luminance
(
Fig. 4 Characteristics of devices with configuration ITO/ HATCN (5 nm)/ TAPC (40 nm)/ Ir(BTBP)
2
mepzpy or Ir(BTBP)
2
phpzpy: 26DCZppy (10 nm, 10
wt%)/ TmPyPB (30 nm)/ LiF (1 nm)/ Al (100 nm): (a) EL spectra; (b) LꢀV curves; (c) η ꢀL curves; (d) η
c
p
ꢀL curves for G1 and G2.
4
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Table 2. Key EL data of devices G1 and G2.
ꢀ1
c
ꢀ1
d
e
Devices
V
on
L
max
η
c
(cd A )
η
p
(lm W )
EQE(%)
CIE
a
ꢀ2
b
ꢀ2
ꢀ2
ꢀ2
(
10 wt%)
(V)
(cd m )
Max
58.17
54.89
at 1000 cd m
54.97
Max
at 1000 cd m
Max
25.33
24.31
at 1000 cd m
(x,y)
G1
G2
4.6
4.5
19700
38200
31.84
31.92
c
30.96
29.01
d
24.06
(0.19,0.43)
(0.18,0.43)
52.66
23.29
a
ꢀ2
b
e
Turnꢀon voltage, the driving voltage at 1 cd m ; Maximum luminance; Current efficiency; Power efficiency; External quantum efficiency
calculated within visible spectrum region.
From the references and our previous publications, we conclude refluxed for 24 h. Then the solution was concentrated and the residue
that the deterioration of chargeꢀcarrier balance and increase in nonꢀ was dissolved in EA. After washing with brine, dried over Na
radioactive quenching processes including tripletꢀtriplet annihilation and concentrated, the crude product was purified through a flash
TTA), tripletꢀpolaron annihilation (TPA) and electricꢀfieldꢀinduced silica gel column to give a white solid.
2 4
SO ,
(
1
dissociation of excitons at high current density would cause the
mepzpy (yield: 60%) H NMR (400 MHz, DMSO) δ 12.72 (s,
To balance the holeꢀelectron injection 1H), 8.55 (d, = 4.8 Hz, 1H), 8.02 ꢀ 7.66 (m, 2H), 7.38 ꢀ 7.12 (m,
and transportation, the use of ambipolar host materials is one choice 1H), 6.58 (s, 1H), 2.27 (s, 3H). MS (ESI): m/z 159 [M ].
1
ꢀ25
serious efficiency rollꢀoff.
J
+
1
to gain phosphorescent OLEDs with low efficiency rollꢀoff.
Furthermore, the synthesis of dopants with excellent electron 8.63 (d,
mobility is also very important since the majority of holeꢀ (d, = 7.6 Hz, 2H), 7.46 (t,
transporting materials’ hole mobility is much higher than the MS (ESI): m/z 299 [M ].
electronꢀtransporting materials’ electron mobility, the OLEDs
phpzpy (yield: 62%) H NMR (400 MHz, DMSO) δ 13.55 (s, 1H),
= 4.5 Hz, 1H), 7.94 (s, 1H), 7.90 (d, = 6.9 Hz, 1H), 7.86
= 7.4 Hz, 2H), 7.36 (d, = 6.5 Hz, 3H).
J
J
J
J
J
+
General Synthesis of Ir(III) complexes
3
3
performances depend on electron transport’s capability. In most
2
cases, the nitrogen heterocycle (such as bipyridine), P=O (such as Under the protection of N atmosphere, BTBP (0.79 g, 2.70 mmol)
3 2
tpip) or oxadiazole (such as 1,3,4ꢀoxadiazole) moieties etc. in the and IrCl .H O (0.32 g, 1.08 mmol) were added to a mixture of 2ꢀ
main and ancillary ligands would increase the electron mobility of ethoxyethanol (15 mL) and water (5 mL). The suspension was
Ir(III) complexes, which can broaden the carrier formation zone of heated at 110 °C for 24 h. After cooling, the mixture was poured into
the emissive layer and suppress the TPA effective. To avoid the TTA distilled water (50 mL) and the precipitate was collected and washed
effect, a larger spatial separation of the neighboring molecules of the with water (2
Ir(III) complexes such as the bulky aromatic groups and ꢀCF for 2 h to give chloroꢀbridged dimmer as yellow solid (0.86 g). Then
substituents can affect the molecular packing and the steric reaction with the ancillary ligands (2.07 mmol) and potassium
protection around the metal and also suppress the selfꢀquenching carbonate (K CO ) (0.95 g, 6.9 mmol) in 2ꢀethoxyethanol (15 mL) to
× 10 mL). The crude precipitate was dried in vacuum
3
2
3
behaviour. Moreover, due to the lower vibrational frequency of the reflux for 24 h. After cooling, the mixture was poured into 50 mL
CꢀF bond can reduce the rate of radiationless deactivation, distilled water. It was extracted with dichloromethane (2 × 50 mL)
fluorination in the ligands can also increase the efficiency of the and the combined organic layer was dried over Na SO . The solvent
2 4
complexes and devices.
was removed off by rotary evaporation and the residue was passed
through a flash silica gel column with petroleum ether (PE)/ EA (V/V
= 1/3) as the eluent to give light yellow solid. The target Ir(III)
complexes were further purified by vacuum sublimation to give light
Experiments
yellow crystal.
General Synthesis of the auxiliary ligands
1
Ir(BTBP)
2
mepzpy (yield: 38%) H NMR (400 MHz, CDCl
3
) δ
1
2
ꢀ(Pyridinꢀ2ꢀyl)ethanone (1.26 g, 10.4 mmol) and esters (20.8 mmol, 8.10 ꢀ 7.98 (m, 4H), 7.78 ꢀ 7.73 (m, 2H), 7.72 ꢀ 7.66 (m, 1H), 7.56
.0 equiv) were slowly added to a stirred suspension of sodium (d,
= 7.8 Hz, 1H), 7.44 (d, = 5.5 Hz, 1H), 7.36 (t, = 4.7 Hz, 2H),
J
J
J
hydride (0.50 g, 20.8 mmol) in dry tetrahydrofuran (THF) (50 mL) at 7.04 ꢀ 6.98 (m, 1H), 6.97 ꢀ 6.86 (m, 2H), 6.34 (s, 1H), 2.20 (s, 3H).
o
+
0
2
(
C. After the mixture was refluxed for 12 h, it was quenched with HRMS (m/z): calcd for C H F IrN [M+H] 934.1140, found
33
18 12
7
N HCl until pH 5ꢀ6 and extracted three times with ethyl acetate 934.1134.
EA). The organic phase was washed with brine, dried over sodium
1
Ir(BTBP) phpzpy (yield: 36%) H NMR (400 MHz, CDCl ) δ
2
3
sulphate (Na SO ), and concentrated under vacuum to yield the 8.08 (s, 1H), 8.04 (dd,
2
4
J
= 9.2, 5.5 Hz, 3H), 7.78 ꢀ 7.70 (m, 3H), 7.68
crude 1, 3ꢀdione. Then hydrazine monohydrate (104 mmol, 10 ꢀ 7.63 (m, 3H), 7.52 ꢀ 7.41 (m, 3H), 7.29 (d,
J = 7.4 Hz, 2H), 7.17 (t,
equiv) was added to the crude 1, 3ꢀdione in 50 ml of ethanol and
J
= 7.4 Hz, 1H), 6.98 (dd,
J
= 5.9, 3.9 Hz, 1H), 6.97 ꢀ 6.93 (m, 1H),
This journal is © The Royal Society of Chemistry 20xx
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ARTICLE
Journal Name
6
C
.93 ꢀ 6.90 (m, 1H), 6.86 (s, 1H). HRMS (m/z): calcd for
Wang, S.ꢀT. Lee and J.ꢀX. Tang, Adv. Funct. Mater., 2014, 24,
7249ꢀ7256.
+
38
H
20
7
F12IrN [M + H] 996.1296, found 996.1297.
1
1
1
1
1
1
3. C.ꢀH. Yang, M. Mauro, F. Polo, S. Watanabe, I. Muenster, R.
Fröhlich and L. De Cola, Chem. Mater., 2012, 24, 3684ꢀ3695.
Conclusions
4. Y.ꢀM. Jing, Y.ꢀX. Zheng and J.ꢀL. Zuo, RSC Adv., 2017,
620.
5. Q.ꢀL. Xu, X. Liang, S. Zhang, Y.ꢀM. Jing, X. Liu, G.ꢀZ. Lu, Y.ꢀ
X. Zheng and J.ꢀL. Zuo, J. Mater. Chem. C, 2015, , 3694ꢀ3701.
6. Y. M. Jing, Y. Zhao and Y. X. Zheng, Dalton Trans., 2017, 46
45ꢀ853.
7. Y.ꢀM. Jing and Y.ꢀX. Zheng, New J. Chem., 2017, 41, 3029ꢀ
035.
8. H.ꢀB. Han, R.ꢀZ. Cui, Y.ꢀM. Jing, G.ꢀZ. Lu,Y.ꢀX. Zheng, L.
Zhou, J.ꢀL. Zuo and H. Zhang, J. Mater. Chem. C, 2017, , 8150ꢀ
159.
7, 2615ꢀ
2
In summary, two efficient bluish green Ir(III) complexes
Ir(BTBP) mepzpy and Ir(BTBP) phpzpy peaked at around 486 nm
2 2
with quantum yields of 0.73 and 0.69, respectively, were obtained
and characterized. Using both Ir(III) complexes as dopants, the
OLEDs exhibited high efficiency with low efficiency rollꢀoff.
Especially, the device based on Ir(BTBP)
exhibited the better performances with the maximum current
efficiency of 58.17 cd A and the maximum EQE value of 25.33%,
respectively, with CIE coordinates at (0.19, 0.43). Even at the
3
,
8
2
mepzpy complex
3
ꢀ1
5
ꢀ
2
8
practical brightness of 1000 cd m , these efficiency values still keep
ꢀ1
1
2
9. H.ꢀB. Han, R.ꢀZ. Cui, G.ꢀZ. Lu, Z.ꢀG. Wu, Y.ꢀX. Zheng, L. Zhou
and H. Zhang, Dalton Trans., 2017, 46, 14916ꢀ14925.
0. C. H. Yang, S. W. Li, Y. Chi, Y. M. Cheng, Y. S. Yeh, P. T. Chou,
at 54.97 cd A and 24.06%, respectively. This work provides an
efficient strategy to obtain high efficiency phosphorescence Ir(III)
complexes for OLEDs with low efficiency rollꢀoff.
G. H. Lee, C. H. Wang and C. F. Shu, Inorg. Chem., 2005, 44
,
Acknowledgments
7770ꢀ7780.
2
1. S. Y. Chang, J. Kavitha, S. W. Li, C. S. Hsu, Y. Chi, Y. S. Yeh, P.
T. Chou, G. H. Lee, A. J. Carty, Y. T. Tao and C. H. Chien, Inorg.
Chem., 2006, 45, 137ꢀ146.
This work was supported by the National Natural Science
Foundation of China (51773088) and the Natural Science
Foundation of Jiangsu Province (BY2016075ꢀ02).
2
2. S. Y. Chang, J. Kavitha, J. Y. Hung, Y. Chi, Y. M. Cheng, E. Y.
Li, P. T. Chou, G. H. Lee and A. J. Carty, Inorg. Chem., 2007, 46
064ꢀ7074.
23. K. Tuong Ly, R.ꢀW. ChenꢀCheng, H.ꢀW. Lin, Y.ꢀJ. Shiau, S.ꢀH.
Liu, P.ꢀT. Chou, C.ꢀS. Tsao, Y.ꢀC. Huang and Y. Chi, Nat. Photon.
016, 11, 63ꢀ68.
,
7
Conflicts of interest
,
There are no conflicts to declare.
2
2
4. Y.ꢀM. Jin, C.ꢀC. Wang, L.ꢀS. Xue, T.ꢀY. Li, S. Zhang, X. Liu, X.
Liang, Y.ꢀX. Zheng and J.ꢀL. Zuo, J. Organomet. Chem., 2014,
Notes and references
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| J. Name., 2012, 00, 1-3
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DOI: 10.1039/C8DT00952J
Graphical abstract
100
F C
3
CF3
N
N
G1
G2
CF3 F3C
10
N
Ir
N
N
N
N
1
R
R= CH , Ir(BTBP) mepzpy G1
3
2
R=phenyl, Ir(BTBP) phpzpy G2
2
0.1
0
2000
4000
6000
8000
10000
-
2
Luminance (cd m )
Two efficient bluish green iridium(III) complexes were applied as
emitters in the organic light-emitting diodes, which showing high current
-1
efficiency of 58.17 cd A and external quantum efficiency of 25.33%
with low efficiency roll-off.