Efficient deep red electroluminescence of iridium(III) complexes with 2,3-diphenylquinoxaline derivatives and tetraphenylimidodiphosphinate

Article abstract of DOI:10.1039/c7tc00348j

Four novel iridium(iii) complexes (Ir1-Ir4) containing 2,3-diphenylquinoxaline derivatives with or without fluoro-substituents at different positions (L1: 2,3-diphenylquinoxaline; L2: 6,7-difluoro-2,3-diphenylquinoxaline; L3: 2,3-bis(4-fluorophenyl)quinoxaline; L4: 6,7-difluoro-2,3-bis(4-fluorophenyl)quinoxaline) as the main ligands and tetraphenylimidodiphosphinate as an ancillary ligand were synthesized and thoroughly investigated. All the complexes emit deep red photoluminescence (PL) with high quantum yields (Ir1: λ_max: 662 nm, :_PL: 68.2%; Ir2: λ_max: 669 nm, :_PL: 60.4%; Ir3: λ_max: 639 nm, :_PL: 78.6%; Ir4: λ_max: 642 nm, :_PL: 98.3%). Organic light-emitting diodes (OLEDs) with single- or double-emitting layers (EMLs) were fabricated using these new emitters. The double-EML device using Ir4 with a structure of ITO (indium-tin-oxide)/MoO₃ (molybdenum oxide, 5 nm)/TAPC (di-[4-(N,N-ditolyl-amino)-phenyl]cyclohexane, 30 nm)/TcTa (4,4′,4′′-tris(carbazol-9-yl)triphenylamine): Ir4 (2 wt%, 10 nm)/26DCzPPy (2,6-bis(3-(carbazol-9-yl)phenyl)pyridine): Ir4 (2 wt%, 10 nm)/TmPyPB (1,3,5-tri(m-pyrid-3-yl-phenyl)benzene, 40 nm)/LiF (1 nm)/Al (100 nm) displays good electroluminescence (EL) performance with a maximum luminance, current efficiency, power efficiency and external quantum efficiency of up to 25926 cd m^-2, 16.6 cd A^-1, 13.7 lm W^-1 and 19.9%, respectively, and the efficiency roll-off ratio is mild. The results demonstrated that the number and position of fluoro-substituents can affect both the PL and EL properties of the Ir(iii) complexes, which are potential deep red phosphorescent materials for specific applications in OLEDs.

Full text of DOI:10.1039/c7tc00348j

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PAPER
Cite this: DOI:
Efficient deep red electroluminescence of iridium(III)
complexes with 2,3-diphenylquinoxaline derivatives and
tetraphenylimidodiphosphinate
10.1039/x0xx00000x
a
a
a,b
a
YiꢀMing Jing, FangꢀZhou Wang, YouꢀXuan Zheng, * JingꢀLin Zuo
Four novel iridium(III) complexes (Ir1ꢀIr4) containing 2,3ꢀdiphenylquinoxaline derivatives
with or without fluroꢀsubstituted on different positions (L1: 2,3ꢀdiphenylquinoxaline; L2:
Received 00th January 2017,
Accepted 00th January 2017
6
6
,7ꢀdifluoroꢀ2,3ꢀdiphenylquinoxaline; L3: 2,3ꢀbis(4ꢀfluorophenyl)quinoxaline); L4:
,7ꢀdifluoroꢀ2,3ꢀbis(4ꢀfluorophenyl)quinoxaline) as main ligands and
DOI: 10.1039/x0xx00000x
tetraphenylimidodiphosphinate as ancillary ligand were synthesized and thoroughly
investigated. All the complexes emit deep red photoluminescence (PL) with high quantum
www.rsc.org/MaterialsC
yields (Ir1:
8.6%; Ir4:
singleꢀ or doubleꢀemitting layers (EML) were fabricated using these new emitters. The
doubleꢀEML device using Ir4 with the structure of ITO (indiumꢀtinꢀoxide)/MoO
molybdenum oxide, 5 nm)/TAPC (diꢀ[4ꢀ(N,Nꢀditolylꢀ amino)ꢀphenyl]cyclohexane, 30
nm)/TcTa (4,4’,4”ꢀtris(carbazolꢀ9ꢀyl)triphenylamine): Ir4 (2 wt%, 10 nm)/ 26DCzPPy
λmax: 662 nm,
η
PL: 68.2%; Ir2:
PL
λmax: 669 nm, ηPL: 60.4%; Ir3: λmax: 639 nm, η :
7
λ
max: 642 nm,
η
PL: 98.3%). The organic lightꢀemitting diodes (OLEDs) with
3
(
(
(
2,6ꢀbis(3ꢀ(carbazolꢀ9ꢀyl)phenyl)pyridine):
1,3,5ꢀtri(mꢀpyridꢀ3ꢀylꢀphenyl)benzene, 40 nm)/ LiF (1 nm)/Al (100 nm) displays good
Ir4
(2
wt%,
10
nm)/
TmPyPB
electroluminescence (EL) performances with the maximum luminance, current efficiency,
ꢀ
2
ꢀ1
power efficiency and external quantum efficiency up to 25926 cd m , 16.6 cd A , 13.7 lm
ꢀ1
W
and 19.9%, respectively, and the efficiency rollꢀoff ratio is mild. The results
demonstrated that the number and position of fluroꢀsubstitution can affect both PL and EL
properties of the Ir(III) complexes, which are potential deep red phosphorescent materials for
specific applications of OLEDs.
yields tend to be lower due to the smaller energy gap, implying
5
Introduction
that the emitters could be prone to poor efficiencies. Ir(III)
dopants with 2,3ꢀdiphenylquinoxaline (DPQ) derivatives as the
Organic lightꢀemitting diodes (OLEDs) have attracted enormous
interest in last decades for application in largeꢀsize,
flexibleꢀpanel display technologies and solidꢀstate lighting due to
their advantages over conventional light sources, such as color
main ligands were reported to exhibit saturated red or deep red
phosphorescence. But the deep red devices with high
performances are still rare reported.
6
In this work, we synthesized a series of deep red Ir(III)
complexes using DPQ derivatives as the main ligands with
fluorine (F) substituted on different positions of the phenyl or
quinoxaline rings. The energies of excited states, i.e. the energy
gap between the ground and the lowest excited states, can be
effectively reduced by substituting the carbon atom with a more
electronegative nitrogen atom and extending the πꢀconjunction of
1
tunability and low power consumption. Notably, iridium(III)
complexes are the most widely investigated phosphorescent
emitting materials for highly efficient OLEDs owing to their
encouraging properties including thermal stability, flexible color
2
tunability, short excited lifetime and high quantum yields.
Efficient red and deep red Ir(III) dopants, which not only act as a
primary color for high color quality redꢀgreenꢀblue (RGB)
displays but also determine the efficiency and color purity of
white OLEDs (WOLEDs), are indispensable in various kinds of
7
the aromatic ligand, giving emitters with the deep red color.
Furthermore, fluorination can enhance the electron mobility of
the complexes resulting in a better balance of charge injection
and transfer, and the lower vibrational frequency of CꢀF bond
can reduce the rate of nonradiative deactivation. Besides, the
position of fluoroꢀsubstitution will affect the photoluminescence
3
OLEDs such as RGB fullꢀcolor displays and WOLEDs. In
addition, deep red emitters and devices are as well as important
for the applications in the fields of optical signal processing,
4
luminescent sensing, bioimaging and photodynamic therapy.
(
PL) and electroluminescence (EL) properties of the complexes
by changing the levels of highest occupied molecular orbital
HOMO) and lowest unoccupied molecular orbital (LUMO). On
Therefore, tuning the emission wavelength of heavyꢀmetal
phosphorescent emitters to the red and deep red range has
emerged as a significant ongoing research task. However,
compared with the wellꢀdeveloped green phosphorescent
emitters, the design and synthesis of the red or deep red materials
is intrinsically more difficult because their luminescent quantum
(
the other hand, Htpip (tetraphenylimidodiphosphinate acid)
derivatives reported by our group previously were introduced as
2
ancillary ligands, which have two diphenyl phosphoryl (Ph P=O)
8
groups. Thus, not only the charge transport ability of the
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complexes be improved, the four bulky phenyl groups also lead
to a larger spatial separation of the neighboring molecules of the
complexes to suppress triplet–triplet annihilation (TTA) and
was purchased, while the ligands L2, L3 and L4 were
synthesized via condensation reaction from benzil and
a
1,2ꢀdiaminobenzene. The tetraphenylimidodiphosphinate acid
(Htpip) and potassium salt (Ktpip) were prepared according to
9
tripletꢀpolaron annihilation (TPA) effects , resulting in high
8
device efficiency and low efficiency rollꢀoff. Herein, as shown in
Scheme 1, four novel Ir(III) complexes (Ir1ꢀIr4) using DPQ
with fluoroꢀsubstitution as the main ligands and tpip as the
ancillary ligand were prepared and investigated in details.
our previous publications. The Ir(III) complexes were obtained
in two steps with popular methods via Ir(III) chloroꢀbridged
dimer. Purification of the mixture by silica gel chromatography
provided crude products (Ir1ꢀIr4), which were further purified
by vacuum sublimation. All the new compounds were fully
R
2
R
2
1
19
characterized by H NMR, F NMR, the electrospray ionization
mass spectra (ESIꢀMS), the high resolution electrospray
ionization mass spectra (HR ESIꢀMS) and elemental analyses.
The crystal structures of Ir2ꢀIr4 further confirmed the identity of
the complexes.
Fig. 1 shows the Oak Ridge Thermal Ellipsoidal plot (ORTEP)
diagrams of Ir2, Ir3 and Ir4 single crystals, the corresponding
crystallographic data are summarized in Table S1, and the
selected bond lengths and angles are listed in Table S2. The
O
O
L1: R
1 2
= R = H;
R
2
NH
2
N
N
L2: R1 = H, R2 = F;
L3: R
L4: R
i
1
1
= F, R
2
= H;
R
2
NH
2
= R = F.
2
R
1
R
1
R
1
R
1
IrCl
3
ii
R
2
R
2
O
P
R
2
R
2
NK Ktpip
R
2
R
2
O
P
N
N
O
O
P
N
N
Ir
N
N
Cl
N
Ir
2
Ir
P
Cl
iii
R
1
2
R
1
R
1
R
1
2
R
1
R1
OH:H O=2:1, reflux, 24 h;
iridium centre adopts a distorted octahedral coordination
Ir1: R
Ir3: R
1
1
= R
2
= H; Ir2: R
1
= H, R
= R
2
= F;
= F.
^
^
i: EtOH, reflux, 24 h; ii: EtOCH
iii: EtOCH CH OH, reflux, 24 h.
2
CH
2
2
= F, R
2
= H; Ir4: R
1
2
geometry with two C N cyclometalated ligands and one O O
ancillary ligand. Obviously, the phenyl rings of the main ligands
which do not coordinate to the iridium atom are not coplanar
with the cyclometalated ligands to reduce the steric hindrance.
For the three complexes, the IrꢀC bond lengths are in the range of
2
2
Scheme 1. Synthetic routes of ligands and the complexes.
Results and discussion
1.955(4) Åꢀ1.998(8) Å, the IrꢀN bond lengths range from 2.045(7)
Åꢀ2.077(3) Å, and the IrꢀO bond lengths range from 2.191(3)
Åꢀ2.277(5) Å. Furthermore, the C–C and CꢀN bond lengths and
angles are in agreement with the corresponding parameters
Preparation and X-ray crystallography
Scheme 1 shows the chemical structures and synthetic routes of
ligands and Ir(III) complexes. The cyclometallated ligand L1
6
,8
described in other similarly constituted complexes.
Fig. 1. Oak Ridge Thermal Ellipsoidal plot (ORTEP) diagrams of the complexes (a) Ir2 (CCDC No. 1527197); (b) Ir3 (CCDC No. 1527198); (c) Ir4
CCDC No. 1527194). Hydrogen atoms are omitted for clarity. Ellipsoids are drawn at 30% probability level.
(
The thermal stability of emitters is very important for efficient
OLEDs. Complexes that are suitable for application in OLEDs
should have as high melting points and decomposition
temperatures as to guarantee that they could be deposited onto
the solid face and long period application without any
decomposition. The thermal properties of the complexes were
characterized by different scanning calorimetry (DSC) and
thermogravimetric (TG) measurements under a nitrogen steam.
From the DSC curves in Fig. 2(a) it can be seen that the melting
Thermal stability
1
00
80
60
(a)
Ir1
Ir2
Ir3
Ir4
(b)
Ir1
Ir2
Ir3
Ir4
4
2
0
0
0
100
200
300
400
500
200
400
600
Temperature (°C)
Temperature (°C)
points (T )of Ir1, Ir2, Ir3 and Ir4 are as high as 387 °C, 374 °C,
m
Fig. 2. DSC (a) and TG (b) thermograms of the complexes.
344 °C and 371 °C, respectively. The TG curves in Fig. 2(b) give
the decomposition temperature (T , 5% loss of weight) of 413 °C
d
2
2
| J. Mater. Chem. C, 2017, 00, 1-9
017
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DOI: 10.1039/C7TC00348J
for Ir1, 406 °C for Ir2, 373 °C for Ir3 and 404 °C for Ir4,
respectively. Furthermore, all complexes can be vacuum
evaporated easily without decomposition, which indicates that
the complexes are potential emitting materials for the fabrication
of stable OLEDs.
deaerated CH
2
Cl
2
solutions at room temperature (Fig. 3(b) and
Table 1). Under the excitation of different wavelengths (380 nm
for Ir1 and Ir3, 385 nm for Ir2 and Ir4, respectively), the
complexes emitted deep red phosphorescence in the range from
639 nm to 669 nm. From Fig.3(b) and Table 1, it is obvious that
the PL spectra of Ir3 and Ir4 have hypsochromic shift compared
with Ir1, which suggests that the fluorine substituted on the
phenyl rings of the main ligand (DPQ) can affect the emission
spectra significantly. On the other hand, the PL spectrum of Ir2
is redꢀshifted mildly indicating that the fluroꢀsubstitution on the
quinoxaline moiety has slight influence on the emission band of
the Ir(III) complexes, which can be discovered from the
comparison between the spectra of Ir3 and Ir4 as well. From Fig.
S2 (Supporting Information) and Table 1 it can be seen that the
PL spectra of Ir1 and Ir3 at 77 K become structured compared
with those at room temperature, while the PL spectra of Ir2 and
Ir4 remain almost the same. In general, the emission bands from
the MLCT states are broad and featureless, whereas a highly
structured emission band mainly originates from the πꢀπ* state.
Accordingly, the complexes Ir1 and Ir3 emit from a mixture of
MLCT states and the ligandꢀbased πꢀπ* state, the emission of
Ir2 and Ir4 is mainly generated from MLCT states. This
indicates that the MLCT characters involved in the emitting T
states of different complexes are various but significant, since a
dominant MLCT character in usually leads to large
inhomogeneity and lowꢀenergy lying metalꢀligand vibrational
satellites, smearing out the spectrum below the electronic
original emission. In addition, the position of F substitution can
Photophysical property
(a)
(b)
Ir1
Ir2
Ir3
Ir4
Ir1
Ir2
Ir3
Ir4
500
600
700
800
200
300
400
500
600
700
Wavelength (nm)
Wavelength (nm)
Fig. 3. Normalized (a) UVꢀvis absorption and (b) emission spectra of Ir1,
ꢀ5
ꢀ1
2 2
Ir2, Ir3 and Ir4 in degassed CH Cl solutions (5 × 10 mol·L ) at room
temperature.
3
The UVꢀvis absorption spectra of the complexes in degassed
ꢀ5
ꢀ1
CH
2
Cl
2
at 5 × 10 mol·L are shown in Fig. 3(a) and the
3
photophysical data are listed in Table 1. The intense bands at
high energy (250ꢀ350 nm) are assigned to the spinꢀallowed
1
1
ligandꢀcentered LC (πꢀπ*) transition of the cyclometallated and
ancillary ligands. The relatively weak absorption bands at lower
energies extending into the spectral region (350ꢀ500 nm) are
attributed to the mixing of the spinꢀallowed singlet
T
1
1
metalꢀtoꢀligand
chargeꢀtransfer
( MLCT)
and
triplet
3
metalꢀtoꢀligand chargeꢀtransfer ( MLCT) states, or LLCT
ligandꢀtoꢀligand chargeꢀtransfer) transition through strong spin–
3
affect the proportion of MLCT states and the πꢀπ* state in the
(
emission of complexes. In the comparison of Ir1 and Ir2, the
fluorine on the quinoxaline ring increases the proportion of
MLCT states, which can also be figured out from the comparison
of Ir3 and Ir4. On the other hand, the proportion of the πꢀπ*
state is raised by the fluorination on the phenyl ring of the main
10
orbit coupling of iridium atoms. From Fig. 3(a) and Table 1 it
can be observed that there is no apparent distinction among the
absorption spectra of the four complexes, which indicates that
the position of fluoroꢀsubstitution has negligible effect on the
absorption spectra.
3
ligands, concluded from the difference between Ir1 and Ir3.
Photoluminescence measurements were conducted in
Table 1. Physical properties of Ir1, Ir2, Ir3 and Ir4.
c)
a)
b)
λ
em (nm)
d)
e)
f)
g)
g)
Tm/Td
°C)
λabs
Φ
τ
(
HOMO/LUMO
(eV)
kr
k
nr
5
Complex
5
ꢀ1
ꢀ1
(
(nm)
(%)
ꢀs)
(10 s )
(10 s )
2
98 K
77 K
646, 660
671
Ir1
Ir2
Ir3
Ir4
387/413
374/406
344/373
371/404
230/277/380
232/276/385
230/275/381
231/274/385
662
669
639
642
68.2
60.4
78.6
98.3
2.44
2.30
2.69
2.83
ꢀ5.37/ꢀ3.56
ꢀ5.48/ꢀ3.68
ꢀ5.54/ꢀ3.65
ꢀ5.64/ꢀ3.75
2.80
2.63
2.92
1.30
1.72
629, 680
641
0.796
3.47
0.0601
a)
b)
ꢀ5
ꢀ1
T
m
: melting temperature, T
d
: decomposition temperature; Measured in degassed CH
2
Cl
2
solution at a concentration of 5 × 10 mol·L at room
c)
ꢀ5
ꢀ1
d)
temperature; Measured in degassed CH
2
Cl
2
solution at a concentration of 5 × 10 mol·L at 298 K and 77 K, respectively; Measured in degassed
e)
CH
2
Cl
2
solution at room temperature using facꢀIr(piq)
3
as the standard sample (Φ = 0.26). Measured in degassed CH
Cl
2 2
solution at a concentration of
ꢀ5
ꢀ1
f)
5
× 10 mol·L at room temperature; From the onset of oxidation potentials of the cyclovoltammetry (CV) diagram using ferrocene as the internal
g)
standard and the optical band gap from the absorption spectra in degassed solution (CH
2
Cl
2
:CH
3
CN = 1:1); Radiative (k
r
) and nonꢀradiative (knr
)
constants are calculated according to the equations: k = Φ/τ and knr = 1/τ ꢀ k
r
r
.
Moreover, the PL quantum yields (PLQYs) of Ir1, Ir2, Ir3
and Ir4 are as high as 68.2%, 60.4%, 78.6% and 98.3%,
respectively. These results suggest that the position of
fluroꢀsubstitution can affect not only the PL spectra of Ir(III)
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1
2
complexes but also PLQYs, and the complex Ir4 with the
fluorine substituted on both the phenyl rings and the quinoxaline
moiety of the main ligand achieves the highest PLQY among
gap (E
Then the LUMO levels were determined according to the
equation LUMO = HOMO + E . The electrochemical data are
g
) was calculated from the UVꢀvis absorption edges.
g
3
,6
these complexes. In most cases,
the fluorination would
collected in Table S3. It is can be observed that the F atoms in
the main ligands decrease the HOMO/LUMO levels of the
enhance the PLQYs of iridium(III) complexes, the steric
hindrance of bulky F atoms leads to a larger spatial separation of
the neighboring molecules of the complexes, suppressing the
tripletꢀtriplet annihilation (TTA), in addition, the lower
vibrational frequency of CꢀF bond can reduce the rate of
nonradiative deactivation. Both will contribute to higher PLQYs.
Therefore, the complex Ir4 with the fluorine substituted on both
the phenyl rings and the quinoxaline moiety of the main ligands
achieves the highest PLQY among these complexes. On the other
hand, the fluorine substituted on the quinoxaline ring reduces the
excited state energy of the complex Ir2, resulting in the redꢀshift
of its PL spectrum. The reduced excited state energy may be
quenched more easily, for example, by the solvent molecules in
the solution, the lower PLQY is expected. In all, by introducing F
atoms into the 2,3ꢀdipenylquinoxaline moieties, complexes with
high PLQYs were realized, and the OLEDs utilizing them as the
dopants have good performances with high efficiency and low
efficiency rollꢀoff. Furthermore, the phosphorescence lifetime (τ)
is the crucial factor that determines the rate of tripletꢀtriplet
annihilation in OLEDs. Longer τ values usually cause greater
complexes leading to different E
contributes to the variations of the PL spectra. The complexes
Ir3 and Ir4 have the largest E (1.89 eV for both) among all the
complexes which emits the phosphorescence with similar
maximum peaks at 639 and 642 nm, respectively. Whereas, the
g
of the complexes which
g
g
complex Ir2 with the smallest E (1.80 eV) exhibits the deepest
red emission peaking at 669 nm. This phenomena demonstrate
that fluorination on the quinoxaline ring of the main ligand will
reduce the energy gap of Ir(III) complexes resulting in the
bathochromic shift of the emission spectra.
(
a)
Ir1
Ir2
Ir3
Ir4
-2.45
-2.50
-2.58
-3.68
Ir2
-2.62
LUMO
HOMO
-3.56
-3.65
Ir3
-3.75
Ir4
Ir1
-
-
5.36
5.37
-5.44
-5.48
-
5.52
-5.60
0
.0
0.5
1.0
1.5
-5.54
-5.64 (b)
Potential (V)
11
tripletꢀtriplet annihilation. The lifetimes of the four complexes
are in the range of microseconds (2.44, 2.30, 2.69 and 2.83 ꢁs in
2 2
CH Cl solution respectively) at room temperature (Table 1) and
are indicative of the phosphorescent origin for the excited states
in each case. To better understand the emission properties of the
four complexes, the radiative (k
r
) and nonꢀradiative (knr)
constants are calculated and summarized in Table 1. The k
values are in the range of 10 s and do not show enormous
r
5
ꢀ1
change as the maximum PL peaks shift, the complex Ir4 with the
5
ꢀ1
highest PLQY has the highest k
r
value (3.47 × 10 s ). The knr
values increase as the maximum peak shifts to the deep red
3
ꢀ1
region, knr of Ir4 is as extremely low as 6.01 × 10 s , while
5
ꢀ1
the deep red emitter Ir2 has the highest knr as 1.72 × 10 s .
The high PLQYs of the complex Ir3 and Ir4 are partly ascribed
to the large k and small knr value.
r
Fig. 4. (a) Cyclic voltammogram curves, (b) theoretical (black) and
experimental (red) energy levels and (c) contour plots of HOMO/LUMO
of Ir1ꢀIr4.
3
(a)(b)(d)
Electrochemical properties and theoretical calculation
To provide further study of the electronic structures of the
complexes, the theoretical calculations were performed on
optimized geometries in CH Cl . The calculations on the ground
2 2
The redox properties and HOMO/LUMO energy levels of the
dopants are relative to the charge transport ability and the OLED
structure. To investigate these properties and calculate the
HOMO/LUMO levels of the complexes, the electrochemical
properties of Ir1ꢀIr4 were measured by cyclic voltammetry in
electronic states of the complexes were carried out using density
functional theory (DFT) and timeꢀdependent DFT (TDꢀDFT) at
13
the B3LYP level. The basis set used for C, H, N, O, F and P
atoms was 6ꢀ31G(d, p) while the LanL2DZ basis set was used
2 2 3
deaerated solution (CH Cl : CH CN = 1: 1) using ferrocene as
14
the internal standard (Fig. 4 (a)). During the anodic scan, all the
complexes exhibit an obvious oxide peaks with oxidation
potentials in the region of 0.706ꢀ0.977 V, which is attributed to
the metalꢀcentered Ir(III)/Ir(IV) oxide couple, in accordance with
for Ir atoms. The solvent effect of CH
Cl was taken into
2 2
consideration using conductorꢀlike polarizable continuum model
1
5
(CꢀPCM). All these calculations were performed with Gaussian
16
09. QMForge program was used to give accurate percentage
6,8
17
the reported cyclometallated Ir(III) complexes. Noteworthily,
the complexes Ir2, Ir3 and Ir4 show higher oxidation potentials
than that of Ir1, which is ascribed to the electronegative effect of
data of the frontier molecular orbitals (FMOs). Contour plots of
FMOs are shown in Fig. 4(b). The energies and percentage
composition of ligands and metal orbitals are shown in Table S4.
the fluorine making the complexes more difficult to lose electron, The results are helpful for the assignment of the electron
leading to lower HOMO levels. The HOMO levels were
calculated from the oxidation peak potential (Eox) and the band
transition characteristics and the discussion on the photophysical
variations. For these complexes, the HOMOs correspond to a
4
2
| J. Mater. Chem. C, 2017, 00, 1-9
017
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Journal of Materials Chemistry C
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mixture of DPQ group (46.66ꢀ51.65%) and the d orbitals of Ir
All the singleꢀEML devices DS1-DS4 exhibit typical emission
with the peak maxima at 656, 631, 660 and 631 nm, respectively,
in accordance with the PL spectra of Ir1ꢀIr4 in solution (Fig.
3(b)). The CIE (Commission Internationale de l'Eclairage)
coordinates operated at 8 V are corresponded to the deep red
region. Apart from the characteristic emission of Ir complexes
(peaked at 631ꢀ660 nm), these devices displayed weak emission
range from 350 nm to 500 nm, which originate from the host
26DCzPPy attributed to the accumulation of holes and electrons
within the EML and few holes/electrons would recombine on
(
(
44.29ꢀ49.15%) with minor contribution from the tpip ligand
4.06ꢀ4.18%), while the LUMOs are mainly localized on the
main ligands (94.41ꢀ94.67%) with minor contribution from Ir d
orbitals (3.74ꢀ4.00%) and tpip ligand (1.57ꢀ1.62%). Compared
with the complex Ir1, the orbital distributions of HOMO/LUMO
for Ir2, Ir3 and Ir4 have more contributions from the main
ligands and less from Ir d orbitals. The calculation results
indicates that the fluorination affects the orbital distributions and
the HOMO/LUMO levels of the Ir(III) complexes.
26DCzPPy molecules. From Fig. 6 and Table 2, it can be found
OLEDs performance
that the singleꢀEML device DS4 using Ir4 as the emitter shows
the best EL performances among these devices with the
maximum luminance (Lmax), current efficiency (ηc,max), power
efficiency (ηp,max) and external quantum efficiency (EQEmax) up
ꢀ
2
ꢀ1
ꢀ1
to 22089 cd m , 15.4 cd A , 12.4 lm W and 17.7%,
respectively. This is due to the high PLQY of Ir4 (98.3%) as well
as the lowꢀlying LUMO level which is beneficial for the electron
trapping in the EML. These results indicate that fluorine on both
the phenyl rings and the quinoxaline ring of the main ligand will
enhance the EL performances of the Ir(III) complexes. On the
other hand, the singleꢀEML device DS2 with the Ir2 dopant
displays relatively poor EL performances with the maximum
ꢀ1
current efficiency, power efficiency and EQE up to 3.7 cd A ,
Fig. 5. Energy level diagrams of HOMO and LUMO levels (relative to
vacuum level) for materials investigated in this study and their molecular
structures.
ꢀ1
2.4 lm W and 12.5%, respectively, caused by the low PLQY
(60.4%) of Ir2 and the deepest red emission expanding into
nearꢀinfrared region which is hard to be detected by our
measurement equipment. This is also can explain the higher
external efficiency values than that of current efficiency. In
addition, the efficiency rollꢀoff of all the devices is apparent as
the luminance increases. For example, the current efficiency and
To evaluate the EL performances of these complexes, single
emitting layer (EML) devices DS1, DS2, DS3 and DS4 using Ir1,
Ir2, Ir3 and Ir4 as the emitters, respectively, were fabricated
with the structure of ITO (indiumꢀtinꢀoxide)/ MoO3
(
molybdenum oxide, 5 nm)/ TAPC (diꢀ[4ꢀ(N,Nꢀditolylꢀamino)ꢀ
phenyl]cyclohexane, 30 nm)/ 26DCzPPy (2,6ꢀbis(3ꢀ(carbazolꢀ
ꢀyl)phenyl)pyridine) : Ir complexes (2 wt%, 10 nm)/ TmPyPB
1,3,5ꢀtri(mꢀpyridꢀ3ꢀylꢀphenyl)benzene, 40 nm)/ LiF (1 nm)/Al
100 nm). MoO and LiF served as holeꢀ and electronꢀinjecting
ꢀ1
EQE of the device DS4 decrease to 10.4 cd A and 11.9%,
ꢀ2
respectively, at the luminance of 1000 cd m . The holeꢀelectron
9
recombination and excition accumulation is expected near the
interface of the EML (26DCzPPy: Ir complexes) and ETL
(TmPyPB) leading to serious TTA/TPA and consequently high
efficiency rollꢀoff as the current density rises. Thus, more devices
with double EMLs were prepared and investigated subsequently
which would broadens the recombination zone of holes and
electrons leading to more balanced holeꢀelectron recombination
and better energy transport from the host to the dopant.
(
(
3
interface modified materials, respectively. TAPC owning high
ꢀ2
2
ꢀ1 ꢀ1
hole mobility (1 × 10 cm V s ) and highꢀlying LUMO level
(
(
1
ꢀ2.0 eV) was used as hole transport/electron block layer
1
8
HTL/EBL), while TmPyPB with high electron mobility (1 ×
ꢀ
3
2
ꢀ1 ꢀ1
0 cm V s ) and lowꢀlying HOMO level (ꢀ6.7 eV) was used
19
as electron transport/hole block layer (ETL/HBL).
To further improve the EL performances of the complexes,
doubleꢀEML devices with the configuration of ITO/MoO3 (5
nm)/ TAPC (30 nm)/ TcTa (4,4’,4”ꢀtris(carbazolꢀ9ꢀyl)
triphenylamine): Ir complexes (2 wt%, 10 nm)/ 26DCzPPy: Ir
complexes (2 wt%, 10 nm)/ TmPyPB (40 nm)/ LiF (1 nm)/ Al
Ambipolar material 26DCzPPy was chosen as the host
because its' nearly equal electron mobility (ꢀ ) and hole mobility
e
ꢀ
5
2
ꢀ1 ꢀ1
(
×
ꢀ ) values (1ꢀ8 × 10 cm V
s
at an electric field between 6.0
10 and 1.0 × 10 V cm ), which benefits the electronꢀhole
h
5
6
ꢀ1
2
0
balance in the EML. The chemical structures of the materials
mentioned above as well as the device structure and energy level
diagrams are depicted in Fig. 5. Apparently, the HOMO/LUMO
levels of the Ir complexes are within those of 26DCzPPy, thus,
carriers are expected to transport easily between layers and
excellent carrier trapping would be the main mechanism in the
(100 nm) were also fabricated. The doubleꢀEML devices using
Ir1ꢀIr4 as the emitters were named as DD1ꢀDD4, respectively.
The widely used pꢀtype material TcTa were added as another host
material which would also lower the HOMO energy barrier
between TAPC and 26DCzPPy due to its matched HOMO level
22
2
1
(
ꢀ5.70 eV, Fig. 5). The EL characteristics of these devices are
devices.
Notably, carriers would be well confined and
depicted in Fig. 7 and the key EL data are also collected in Table
recombined within the EML. The EL spectra, current
densityꢀluminanceꢀvoltage, current efficiencyꢀluminance and
power efficiencyꢀluminance characteristics of all the devices are
shown in Fig. 6. The key EL data are summarized in Table 2.
2
as well.
From the EL spectra in Fig. 7(a), it can be observed that all the
devices exhibit deep red emission with the maximum peaks in
the range of 632ꢀ662 nm, proved by the CIE coordinates
This journal is © The Royal Society of Chemistry 2017
J. Mater. Chem. C, 2017, 00, 1-9 | 5

Journal of Materials Chemistry C
Page 6 of 11
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DOI: 10.1039/C7TC00348J
additionally. And there is no obvious distinction compared with
the EL spectra (Fig. 6(a)) of the singleꢀEML devices and the PL
spectra of the complexes in solution (Fig. 3(b)). Weak emission
in the range of 350ꢀ500 nm was observed in the EL spectra of
doubleꢀEML devices caused by the emission of TcTa peaked at
is that the usage of double EMLs lowers the carrier transporting
barrier and broadens the recombination zone of holes and
electrons leading to more balanced holeꢀelectron recombination
and better energy transport from the host to the dopant. However,
TcTa is wellꢀknown as a kind of hole transport material, within
the layer the imbalanced distribution of holes and electrons will
cause the recombination of excitons on the TcTa molecules.
3
85 nm, the intensity of which is much lower than that in the EL
spectra of singleꢀEML devices caused by 26DCzPPy. On reason
1
000
(
a)
(b)
4
3
2
1
0
DS1
DS2
DS3
DS4
10
DS1
DS2
DS3
DS4
0
.05
1
1
1
1
0
0
0
0
0
.00
3
00
400
500
Wavelength (nm)
0
2
00
400
600
800
0
4
8
12
Wavelength (nm)
Voltage (V)
1
0
1
10
(c)
(d)
DS1
DS2
DS3
DS4
DS1
DS2
DS3
DS4
1
0
.1
0.1
10
100
1000
10000
1
10
100
1000
10000
-
2
-2
Luminance (cd m )
Fig. 6. Characteristics of singleꢀEML devices DS1ꢀDS4: (a) normalized EL spectra at 8 V; (b) current densityꢀluminanceꢀvoltage (JꢀLꢀV) curves; (c)
current efficiencyꢀluminance (η ꢀL) curves and (d) external quantum efficiencyꢀluminance (η ꢀL) curves.
Luminance (cd m )
c
p
Compared with the singleꢀEML devices, all the doubleꢀEML
devices display better EL performances and lower efficiency
rollꢀoff. Among these devices, the device DD4 with the Ir4
the
main
ligands
and
the
introduction
of
tetraphenylimidodiphosphinate as the ancillary ligand, which can
benefit the charge transport ability of iridium complexes and
suppress TTA and TPA effects, resulting in the significant
OLED performances.
dopant has the best performances with the Lmax, η
, ηp,max and
c,max
ꢀ1
ꢀ
2
ꢀ1
EQEmax of 25926 cd m , 16.6 cd A , 13.7 lm W and 19.9%,
respectively. Furthermore, the η and EQE is still up to 13.4 cd
c
ꢀ
1
To determine whether the device architecture has been fully
optimized, the theoretical maximum EQE (EQEtheo) is calculated
according to the equation: EQEtheo = ФPL × Ф , Ф represents
A
and 16.1%, respectively, as the luminance increases to 1000
ꢀ
2
cd m . Compared with singleꢀEML devices, doubleꢀEML
devices possess improved hole injection ability from HTL into
EMLs because the HOMO level of TcTa situates between those
of TAPC and 26DCzPPy, thus causing the low hole injection
barrier. Consequently, doubleꢀEMLs devices obtained better
balance of carriers within EMLs, wider recombination zone and
lower densities of excitons within EMLs, thus realizing higher
luminance and efficiency as well as lower efficiency rollꢀoff.
Compared with previously reported iridium(III) complexes with
oc
PL
the PL quantum yield of the dopant, Фoc represents the
outꢀcoupling efficiency of the devices and is assumed as 20ꢀ25%,
23
the data are summarized in Table 2. It can be summed that the
EQE of singleꢀEML devices DS1ꢀDS4 is below or around the
prescribed minimum of EQEtheo
, whereas the EQE of
doubleꢀEML devices DD1ꢀDD4 is in the range of or close to the
ceiling of EQEtheo. The results demonstrate that the utilization of
doubleꢀEML can optimize the OLED performances of these
complexes and enhance the EQE close to the theoretical maxima.
Additionally, the efficiency rollꢀoff of doubleꢀEML devices is
milder, which is an important indicator for the commercial
application of OLEDs.
2
,3ꢀdiphenylquinoxaline derivatives, the OLED performances of
these complexes are improved greatly , especially the complex
Ir4 in the doubleꢀEML device shows high efficiency and low
efficiency rollꢀoff. These results indicate fluorine substitutes in
6
2
| J. Mater. Chem. C, 2017, 00, 1-9
017
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC00348J
1
000
(
a)
(b)
4
3
2
1
0
DD1
DD2
DD3
DD4
10
DD1
DD2
DD3
DD4
0
.05
10
10
10
10
0
.00
300
400
500
Wavelength (nm)
0
200
400
600
800
0
4
8
12
Wavelength (nm)
Voltage (V)
10
10
(
d)
(c)
DD1
DD2
DD3
DD4
1
DD1
DD2
DD3
DD4
1
0.1
0.1
1
10
100
1000
10000
10
100
1000
10000
-2
-
2
Luminance (cd m )
Luminance (cd m )
Fig. 7. Characteristics of doubleꢀEML devices DD1ꢀDD4: (a) normalized EL spectra at 8 V; (b) current densityꢀluminanceꢀvoltage (JꢀLꢀV) curves; (c)
current efficiencyꢀluminance (η ꢀL) curves and (d) external quantum efficiencyꢀluminance (η ꢀL) curves.
c
p
Table 2. EL performances of singleꢀEML devices DS1ꢀDS4 and doubleꢀEMLs devices DD1ꢀDD4.
ηc,max c)
e)
ηc,L1000
a)
b)
g)
i)
j)
Vturnꢀon
V)
Lmax
ηp,max
λmax
CIE
ꢀ
1
ꢀ1
h)
Device
Emitter
(cd A )
(cd A )
EQEtheo
ꢀ
2
ꢀ1
(
[cd m (V)]
(lm W )
(nm)
(x,y)
d)
f)
(
EQEmax
)
(EQEL1000 )
DS1
DS2
DS3
DS4
DD1
DD2
DD3
Ir1
Ir2
Ir3
Ir4
Ir1
Ir2
Ir3
Ir4
3.6
3.7
3.6
3.5
3.7
3.7
3.6
3.6
6801 (12.3)
6879 (13.1)
18370 (13.3)
22089 (13.2)
8864 (12.7)
8745 (12.5)
19597 (12.9)
25926 (12.8)
4.1 (11.8%)
3.7 (12.5%)
13.8 (15.8%)
15.4 (17.7%)
4.6 (16.6%)
3.8 (14.6%)
14.9 (18.6%)
16.6 (19.9%)
2.6 (7.4%)
2.2 (7.6%)
3.0
2.4
13.6ꢀ17.0%
12.1ꢀ15.1%
15.6ꢀ19.6%
19.7ꢀ24.6%
13.6ꢀ17.0%
12.1ꢀ15.1%
15.6ꢀ19.6%
656
660
631
631
660
662
632
632
0.704, 0.295
0.707, 0.293
0.686, 0.314
0.685, 0.315
0.714, 0.285
0.715, 0.285
0.687, 0.311
0.687, 0.313
10.0 (11.4%)
10.4 (11.9%)
2.6 (9.4%)
10.5
12.4
3.6
2.9 (11.1%)
11.0 (13.7%)
2.8
12.0
13.7
DD4
13.4 (16.1%)
19.7ꢀ24.6%
a)
ꢀ2 b)
c)
d)
turnꢀon voltage recorded at a luminance of 1 cd m , maximum luminance, maximum current efficiency, maximum external quantum efficiency
e)
ꢀ2 f)
ꢀ2 g)
h)
(
EQE); current efficiency at 1000 cd m ; EQE at 1000 cd m ; maximum power efficiency, theoretical maximum EQE, calculated according to
i)
the equation: EQEtheo = ФPL × Фoc, ФPL for the PL quantum yield of the dopant, Фoc for the outꢀcoupling efficiency of the devices assumed as 20ꢀ25%;
j)
values were collected at 8 V, Commission Internationale de l'Eclairage coordinates (CIE) at 8 V.
tetraphenylimidodiphosphinate as the ancillary ligand were
thoroughly characterized. All the complexes emit deep red
phosphorescence with high quantum efficiency. Compared with
Conclusions
In conclusion, four novel Ir(III) complexes containing
,3ꢀdiphenylquinoxaline derivatives with or without
fluroꢀsubstituted on different positions as the main ligands and
the singleꢀEML devices, all the doubleꢀEML devices display
better EL performances and lower efficiency rollꢀoff. The
doubleꢀEML device DD4 using the Ir4 dopant with four F atoms
2
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ꢀ
1
in the main ligands exhibits the best performances with the
maximum luminance, current efficiency, power efficiency and
deposition rate for organic compounds is 1ꢀ2 Å s . The phosphor
and host were coꢀevaporated from two separate sources. The
cathode consisting of LiF/Al was deposited by evaporation of
ꢀ
2
ꢀ1
external quantum efficiency of 25926 cd m , 16.6 cd A , 13.7
ꢀ
1
ꢀ1
lm W and 19.9 %, respectively. Furthermore, the η
c
and EQE of
LiF with a deposition rate of 0.1 Å s and then by evaporation of
Al metal with a rate of 3 Å s . The effective area of the emitting
diode is 0.1 cm . The characteristics of the devices were
ꢀ1
ꢀ1
the device DD4 can still be retained as high as 13.4 cd A and
6.1%, respectively, at the practical luminance of 1000 cd m .
ꢀ
2
2
1
The results suggest that the positions of fluroꢀsubstitution can
affect not only the photophysical properties but also the EL
performances of the iridium complexes. These Ir(III) complexes
are potential deep red phosphorescent materials for specific
applications of OLEDs.
measured with a computer controlled KEITHLEY 2400 source
meter with a calibrated silicon diode in air without device
encapsulation. On the basis of the uncorrected PL and EL spectra,
the CIE coordinates were calculated using a test program of the
spectra scan PR650 spectrophotometer.
Syntheses
Experimental section
Solvents were carefully dried and distilled from appropriate
drying agents prior to use. All reactions were performed under
nitrogen. The ligand 2,3ꢀdiphenylquinoxaline (L1) was
purchased and used without further purification. The
General information
1
19
H and F NMR spectra were measured on a Bruker AM 500
spectrometer. Electrospray ionization mass spectra (ESIꢀMS)
were obtained with ESIꢀMS (LCQ Fleet, Thermo Fisher
Scientific). The high resolution electrospray ionization mass
spectra (HR ESIꢀMS) were recorded on an Agilent 6540 UHD
AccurateꢀMass QꢀTOF LC/MS. Elemental analyses for C, H and
N were performed on an Elementar Vario MICRO analyzer.
TGꢀDSC measurements were carried out on a DSC 823e
tetraphenylimidodiphosphinate acid (Htpip) and potassium salt
8
(
Ktpip) were prepared according to our previous publications.
General syntheses of ligands. Benzil (5.00 mmol) or
4
1
,4’ꢀdifluorobenzil (5.00 mmol) was dissolved with
,2ꢀdiaminoꢀ4,5ꢀdifluoro benzene (5.00 mmol) or
oꢀphenylenediamine (5.00 mmol) in 50 mL ethanol, and the
solution was refluxed for 24 h. Silica column chromatography
purification (petroleum ether : ethyl acetate = 40 : 1) gave white
powder for 6,7ꢀdifluoroꢀ2,3ꢀdiphenylquinoxaline (L2), 2,3ꢀbis(4ꢀ
fluorophenyl)quinoxaline (L3) or 6,7ꢀdifluoroꢀ2,3ꢀbis(4ꢀ
analyzer
(METTLER).
UVꢀvis
absorption
and
photoluminescence spectra were measured on a Shimadzu
UVꢀ3100 and a Hitachi Fꢀ4600 spectrophotometer at room
temperature, respectively. The luminescence quantum efficiency
fluorophenyl)quinoxaline (L4).
was calculated by a comparison of a standard sample facꢀIr(piq)
3
1
ꢀ5
ꢀ1 3(a)
6
,7-Difluoro-2,3-diphenylquinoxaline (L2). 85% yield.
H
in deaerated CH Cl2 solutions of 5 × 10 mol L .
voltammetry measurements were conducted on
Cyclic
MPIꢀA
2
NMR (400 MHz, CDCl ) δ 7.91 (t, J = 9.3 Hz, 2H), 7.51ꢀ7.48 (m,
a
3
19
4H), 7.37 (t, J = 1.7 Hz, 2H), 7.36 (s, 4H). F NMR (376 MHz,
multifunctional electrochemical and chemiluminescent system at
+
CDCl ) δ ꢀ129.98 (2F). MS(ESI) m/z calcd for C H F N :
room temperature using Fc /Fc as the internal standard and scan
3
20 12
2
2
+
+
ꢀ1
318.10 [M] , found: 319.15 [M+H] . Anal. Calcd. For
rate of 0.05 V s .
C H F N : C, 75.46; H, 3.80; N, 8.80. Found: C, 75.50; H, 3.79;
20
12
2
2
X-ray crystallography
N, 8.75.
,3-Bis(4-fluorophenyl)quinoxaline (L3). 87% yield.
NMR (400 MHz, CDCl ) δ 8.16 (dd, J = 6.4, 3.4 Hz, 2H), 7.79
1
2
H
Xꢀray crystallographic measurements of the single crystals were
carried out on a Bruker SMART CCD diffractometer (Bruker
Daltonic Inc.) using monochromated Mo Kα radiation (λ =
3
(
(
dd, J = 6.4 Hz, 3.4 Hz, 2H), 7.51 (dd, J = 8.9, 5.4 Hz, 4H), 7.06
1
9
t, J = 8.7 Hz, 4H). F NMR (376 MHz, CDCl ) δ ꢀ111.94 (2F).
3
0
.71073 Å) at room temperature. Cell parameters were retrieved
+
MS(ESI) m/z calcd for C H F N : 318.10 [M] , found: 319.23
[
2
4
20 12
2
2
using SMART software and refined using SAINT program in
order to reduce the highly redundant data sets. Data were
collected using a narrowꢀframe method with scan width of 0.30°
in ω and an exposure time of 5 s per frame. Absorption
corrections were applied using SADABS supplied by Bruker.
The structures were solved by Patterson methods and refined by
+
M+H] . Anal. Calcd. For C H F N : C, 75.46; H, 3.80; N, 8.80.
20 12 2 2
Found: C, 75.45; H, 3.82; N, 8.81.
,7-Difluoro-2,3-bis(4-fluorophenyl)quinoxaline (L4). 90%
6
1
yield. H NMR (400 MHz, CDCl ) δ 7.89 (t, J = 9.3 Hz, 2H),
2
5
3
19
7.54ꢀ7.44 (m, 4H), 7.11ꢀ7.02 (m, 4H). F NMR (376 MHz,
CDCl ) δ ꢀ111.31 (2F), ꢀ129.30 (2F). MS(ESI) m/z calcd for
2
3
fullꢀmatrix leastꢀsquares on
F
using the program
+
+
C H F N : 354.08 [M] , found: 355.16 [M+H] . Anal. Calcd.
20 10
26
4
2
SHELXSꢁ2014. The positions of metal atoms and their first
coordination spheres were located from directꢀmethods Eꢀmaps,
other nonꢀhydrogen atoms were found in alternating difference
Fourier syntheses and leastꢀsquares refinement cycles and during
the final cycles refined anisotropically. Hydrogen atoms were
placed in calculated position and refined as riding atoms with a
For C H F N : C, 67.80; H, 2.84; N, 7.91. Found: C, 67.78; H,
20
10
4
2
2
.86; N, 7.89.
General syntheses of iridium complexes. A mixture of IrCl3
1.00 mmol) and L1ꢀL4 (2.05 mmol) in 2ꢀethoxyethanol and
(
water (20 mL, 2:1 v/v) was refluxed for 24h. After cooling to
room temperature, the mixture was filtered, and the precipitate
uniform value of Uiso
.
was washed with H O and petroleum ether to give the crude
2
OLEDs fabrication and measurement
cyclometalated Ir(III) chloroꢀbridged dimer. The slurry of crude
chloroꢀbridged dimer (0.50 mmol) and Ktpip (1.10 mmol) in
All OLEDs were fabricated on the preꢀpatterned ITOꢀcoated
glass substrate with a sheet resistance of 15 ꢂ sq . The
2ꢀethoxyethanol (40 mL) was refluxed for 24 h. The crude
ꢀ1
8
2
| J. Mater. Chem. C, 2017, 00, 1-9
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Journal of Materials Chemistry C
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product was purified by silica column chromatography
petroleum ether : ethyl acetate = 4 : 1), which were further
†Electronic Supplementary Information (ESI) available. Parameters
associated with the single crystal diffraction data, selected bond
(
purified by sublimation in vacuum.
Ir1. 50% yield. H NMR (400 MHz, CDCl
lengths and angles of Ir2, Ir3 and Ir4. Electrochemical data,
1
3
) δ 9.41 (dd, J =
percentage distributions of HOMO/LUMO, the lifetime curves in
degassed solution at room temperature and the PL spectra in degassed
8
2
.7, 1.2 Hz, 2H), 8.02ꢀ7.82 (m, 8H), 7.76 (dd, J = 8.3, 1.4 Hz,
H), 7.59 (q, J = 12.1, 7.1 Hz, 6H), 7.44ꢀ7.33 (m, 8H), 7.02ꢀ6.89
solution at 77 K of Ir1ꢀIr4. Power efficiencyꢀluminance curves of
(
m, 8H), 6.85 (ddd, J = 8.9, 6.7, 1.5 Hz, 2H), 6.54 (td, J = 7.6,
DS1 DS4 and DD1 DD4 devices.
ꢀ
ꢀ
3
1
.1 Hz, 4H), 6.48 (ddd, J = 8.2, 7.0, 1.3 Hz, 2H), 6.35 (td, J = 7.5,
.4 Hz, 2H), 6.07 (dd, J = 7.8, 1.2 Hz, 2H). HR EIꢀMS m/z calcd
1
(a) C. W. Tang, S. A. VanSlyke and C. H. Chen, J. Appl. Phys., 1989, 65,
3610; (b) M. A. Baldo, D. F. O’Brien, Y. You, A. Shoustikov, S. Sibley, M.
E. Thompson and S. R. Forrest, Nature, 1998, 395, 151; (c) C. Adachi, M.
A. Baldo, M. E. Thompson and S. R. Forrest, J. Appl. Phys., 2001, 90,
5048; (d) X. L. Yang, G. J. Zhou and W. Y. Wong, Chem. Soc. Rev., 2015,
+
+
for C64
Anal. Calcd. For C64
Found: C, 65.66; H, 4.00; N, 5.92.
H46IrN
5
O
2
P
2
: 1171.2756 [M] , found: 1172.3854 [M+H] .
: C, 65.63; H, 3.96; N, 5.98.
5 2 2
H46IrN O P
1
3
Ir2. 48% yield. H NMR (400 MHz, CDCl ) δ 9.52 (dd, J =
4
4, 8484; (e) H. A. Al Attar and A. P. Monkman, Adv. Mater., 2016, 28,
014; (f) H. W. Mo, Y. Tsuchiya, Y. Geng, T. Sagawa, C. Kikuchi, H.
1
7
2.4, 8.4 Hz, 2H), 7.99ꢀ7.89 (m, 8H), 7.74ꢀ7.56 (m, 6H),
.52ꢀ7.38 (m, 8H), 7.05 (ddd, J = 12.7, 8.0, 1.4 Hz, 4H), 6.98 (dd,
8
Nakanotani, F. Ito and C. Adachi, Adv. Funct. Mater., 2016, 26, 6703; (g)
R. GómezꢀBombarelli, J. AguileraꢀIparraguirre, T. D. Hirzel, D.
Duvenaud, D. Maclaurin, M. A. BloodꢀForsythe, H. S. Chae, M.
Einzinger, D. G. Ha, T. Wu, G. Markopoloulos, S. Jeon, H. Kang, H.
Miyazaki, M. Numata, S. Kim, W. Huang, S. I. Hong, M. Baldo, R. P.
Adams and A. AspuruꢀGuzik, Nat. Mater., 2016, 15, 1120; (h) D. Yin, J.
Feng, N. R. Jiang, R. Ma, Y. F. Liu and H. B. Sun, ACS Apl. Mater.
Interfaces, 2016, 8, 31166; (i) G. P. Tan, S. M. Chen, C. H. Siu, A.
Langlois, Y. F. Qiu, H. B. Fan, C. L. Ho, P. D. Harvey, Y. H. Lo, L. Liu
and W. Y. Wong, J. Mater. Chem. C, 2016, 4, 6016.
J = 8.2, 1.3 Hz, 2H), 6.87 (tq, J = 7.5, 1.4 Hz, 2H), 6.57 (td, J =
7
.7, 3.1 Hz, 4H), 6.51 (ddd, J = 8.3, 7.1, 1.3 Hz, 2H), 6.38 (ddd,
1
9
J = 8.4, 7.1, 1.4 Hz, 2H), 5.93 (dd, J = 7.8, 1.2 Hz, 2H).
F
NMR (376 MHz, CDCl
3
) δ ꢀ128.27 (1F), ꢀ128.33 (1F), ꢀ132.43
1F), ꢀ132.49 (1F). HR EIꢀMS m/z calcd for C64 IrN
243.2379 [M] , found: 1244.3211 [M+H] . Anal. Calcd. For
(
H
42
F
4
5 2 2
O P :
+
+
1
C
64
H
42
F
4
IrN
5
2
O P
2
: C, 61.83; H, 3.41; N, 5.63. Found: C, 61.80;
H, 3.40; N, 5.66.
Ir3. 57% yield. H NMR (400 MHz, CDCl
1
3
) δ 9.34 (dd, J =
8
2
6
2
.8, 1.2 Hz, 2H), 8.14ꢀ7.79 (m, 8H), 7.74 (dd, J = 8.3, 1.4 Hz,
H), 7.50ꢀ7.39 (m, 8H), 7.38ꢀ7.27 (m, 4H), 7.01ꢀ6.93 (m, 4H),
.92ꢀ6.83 (m, 6H), 6.53 (td, J = 7.8, 3.1 Hz, 4H), 6.28 (td, J = 8.8,
2
(a) S. Lamansky, P. Djurovich, D. Murphy, F. AbdelꢀRazzaq, H. E. Lee, C.
Adachi, P. E. Burrows, S. R. Forrest and M. E. Thompson, J. Am. Chem.
Soc., 2001, 123, 4304; (b) W. Y. Wong and C. L. Ho, J. Mater. Chem.,
19
.7 Hz, 2H), 5.70 (dd, J = 9.7, 2.7 Hz, 2H). F NMR (376 MHz,
) δ ꢀ109.90 (2F), ꢀ110.86 (2F). HR EIꢀMS m/z calcd for
2
009, 19, 4457; (c) W. Y. Wong and C. L. Ho, Coord. Chem. Rev., 2009,
CDCl
3
+
+
253, 1709; (d) G. Zhou, W. Y. Wong and S. Suo, J. Photochem. Photobio.
C: Photochem. Rev., 2010, 11, 133; (e) G. Zhou, W. Y. Wong and X. Yang,
Chem. Asian J., 2011, 6, 1706; (f) C. L. Ho and W. Y. Wong, New J.
Chem., 2013, 37, 1665; (g) H. Sun, S. Liu, W. Lin, K. Y. Zhang, W. Lv, X.
Huang, F. Huo, H. Yang, G. Jenkins, Q. Zhao and W. Huang, Nat.
Commun., 2014, 5, 3601; (h) L. Ying, C. L. Ho, H. Wu, Y. Cao and W. Y.
Wong, Adv. Mater., 2014, 26, 2459; (i) X. Yang, G. Zhou and W. Y. Wong,
J. Mater. Chem. C, 2014, 2, 1760; (j) X. Xu, X. Yang, J. Zhao, G. Zhou
and W. Y Wong, Asian J. Org. Chem., 2015, 4, 394; (k) J. Zhao, Y. Yu, X.
L. Yang, X. G. Yan, H. M. Zhang, X. B. Xu, G. J. Zhou, Z. X. Wu, Y. X.
Ren and W. Y. Wong, ACS Appl. Mater. Interfaces, 2015, 7, 24703; (l) K.
Y. Zhang, X. Chen, G. Sun, T. Zhang, S. Liu, Q. Zhao and W. Huang, Adv.
Mater., 2016, 28, 7137; (m) Y. H. Zhou, Q. L. Xu, H. B. Han, Y. Zhao, Y.
X. Zheng, L. Zhou, J. L. Zuo and H. J. Zhang, Adv. Opt. Mater., 2016, 4,
1726.
C
64
H
42
F
4
IrN
Anal. Calcd. For C64
Found: C, 61.86; H, 3.44; N, 5.57.
5
2
O P
2
: 1243.2379 [M] , found: 1244.2869 [M+H] .
H
42
F
4
IrN : C, 61.83; H, 3.41; N, 5.63.
5 2 2
O P
1
3
Ir4. 62% yield. H NMR (400 MHz, CDCl ) δ 9.44 (dd, J =
1
7
2
5
2.2, 8.3 Hz, 2H), 8.06ꢀ7.87 (m, 8H), 7.55ꢀ7.36 (m 10H),
.35ꢀ7.27 (m, 2H), 7.04ꢀ6.95 (m, 6H), 6.88 (tq, J = 7.4, 1.4 Hz,
H), 6.55 (td, J = 7.7, 3.1 Hz, 4H), 6.31 (td, J = 8.8, 2.6 Hz, 2H),
1
9
3
.56 (dd, J = 9.5, 2.6 Hz, 2H). F NMR (376 MHz, CDCl ) δ
ꢀ
(
1
C
108.60 (2F), ꢀ109.89 (2F), ꢀ127.36 (1F), ꢀ127.42 (1F), ꢀ131.71
1F), ꢀ131.77 (1F). HR EIꢀMS m/z calcd for C64 IrN
315.2002 [M] , found: 1316.2160 [M+H] . Anal. Calcd. For
IrN : C, 58.45; H, 2.91; N, 5.33. Found: C, 58.50;
H, 2.98; N, 5.29.
H
38
F
8
5 2 2
O P :
+
+
64
H
38
F
8
5 2 2
O P
Acknowledgements
3
(a) A. Tsuboyama, H. Iwawaki, M. Furugori, T. Mukaide, J. Kamatani, S.
Igawa, T. Moriyama, S. Miura, T. Takiguchi, S. Okada, M. Hoshino and
K. Ueno, J. Am. Chem. Soc., 2003, 125, 12971; (b) S. Okada, K. Okinaka,
H. Iwawaki, M. Furugori, M. Hashimoto, T. Mukaide, J. Kamatani, S.
Igawa, A. Tsuboyama, T. Takiguchi and K. Ueno, Dalton Trans., 2005, 9,
This work was supported by the National Natural Science
Foundation of China (21371093, 91433113), the Major State
Basic Research Development Program (2013CB922101) and the
Natural Science Foundation of Jiangsu Province (BK20130054).
1
583; (c) G. Zhou, C. L. Ho, W. Y. Wong, Q. Wang, D. Ma, L. Wang, Z.
Notes and references
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State Key Laboratory of Coordination Chemistry, Jiangsu Key
Laboratory of Advanced Organic Materials, Collaborative Innovation
Center of Advanced Microstructures, School of Chemistry and Chemical
Engineering, Nanjing University, Nanjing 210093, P. R. China, *eꢁmail:
yxzheng@nju.edu.cn
b
MaAnShan HighꢁTech Research Institute of Nanjing University,
MaAnShan, 238200, P. R. China
This journal is © The Royal Society of Chemistry 2017
J. Mater. Chem. C, 2017, 00, 1-12 | 9

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DOI: 10.1039/C7TC00348J
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1
0 | J. Mater. Chem. C, 2017, 00, 1-9
This journal is © The Royal Society of Chemistry
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Journal of Materials Chemistry C
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DOI: 10.1039/C7TC00348J
Graphical abstract
DD1
DD3
DD2
DD4
10
R
2
R
2
Ir1
Ir2
Ir3
Ir4
N
1
N
O
O
P
Ir
N
P
R
1
2
R
1
Ir1: R
Ir3: R
1
1
= R
2
= H; Ir2: R
1
= H, R
= R
2
= F;
= F.
= F, R
2
= H; Ir4: R
1
2
500
600
700
800
Wavelength (nm)
0.1
1
10
100
1000
10000
-2
Luminance (cd m )
Efficient deep red OLEDs based on iridium(III) complex show a
maximum current efficiency and external quantum efficiency up to 16.6
-
1
cd A and 19.9%, respectively, with mild efficiency roll-off.