Photoluminescence and electroluminescence of an iridium(iii) complex with 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine and 2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol ligands

Article abstract of DOI:10.1039/c7nj00163k

Using electron transport units containing 2′,6′-bis(trifluoromethyl)-2,4′-bipyridine as the main ligand and 2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol as the ancillary ligand, an iridium(iii) complex (Ir(BTBP)₂TDZ) was synthesized, characterized and investigated in detail. The greenish yellow photoluminescence spectrum peaks at 551 nm with a quantum yield of 44%. Organic light-emitting diodes (OLEDs) using Ir(BTBP)₂TDZ as the emitter with a single light emitting layer (DS) and double light emitting layers (DD) were fabricated; the DS device exhibited better performances with a maximum current efficiency, power efficiency and external quantum efficiency of up to 54.5 cd A^-1, 31.1 lm W^-1 and 16.1%, respectively. The results suggest that the iridium complex with the 1,3,4-thiadiazole derivative has potential application in efficient OLEDs.

Full text of DOI:10.1039/c7nj00163k

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Photoluminescence and electroluminescence of an iridium(III)
complex with 2',6'-bis(trifluoromethyl)-2,4'-bipyridine and
2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol ligands
Cite this: DOI: 10.1039/x0xx00000x
YiꢀMing Jing a, YouꢀXuan Zheng a,b
*
Using electron transport units containing 2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine as the main ligand
and 2ꢀ(5ꢀphenylꢀ1,3,4ꢀthiadiazolꢀ2ꢀyl)phenol as the ancillary ligand, an iridium(III) complex
Ir(BTBP)2TDZ was synthesized, characterized and investigated in detail. The greenish yellow
photoluminescence spectrum peaks at 551 nm with quantum yield of 44%. Organic lightꢀemitting
diodes (OLEDs) using Ir(BTBP)2TDZ as the emitter with single light emitting layer (DS) and double
light emitting layers (DD) were fabricated, the DS device exhibited better performances with
maximum current efficiency, power efficiency and external quantum efficiency up to 54.5 cd Aꢀ1, 31.1
lm Wꢀ1 and 16.1%, respectively. The results suggest that the iridium complex with 1,3,4ꢀthiadiazol
Received 00th January 2017,
Accepted 00th January 2017
DOI: 10.1039/x0xx00000x
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derivative has potential application for efficient OLED.
of ligand C^N such as bipyridine. Moreover, trifluoromethyl unit
could enhance the electron mobility leading to a better balance of
charge injection and transfer. The lower vibrational frequency of
Introduction
Organic lightꢀemitting diodes (OLEDs) have attracted significant
interest in recent years because of their potential usage in
flexibleꢀpanel display technologies and solidꢀstate lighting due to
advantages over traditional light sources such as color tunability
and low power consumption.1 Remarkably, phosphorescent
iridium(III) complexes are the most widely investigated emitting
materials for highly efficient OLEDs owing to the promising
properties including thermal stability, flexible color tunability and
high quantum yields.2
Whereas, for many OLEDs with high efficiency using long
excited lifetime Ir(III) complexes as the dopants, the device
efficiency rollꢀoff ratios are large, which is mainly due to the
deterioration of chargeꢀcarrier balance and increase in
nonradiative quenching processes including triplet–triplet
annihilation (TTA), triplet–polaron annihilation (TPA), and
electricꢀfieldꢀinduced dissociation of excitons at high current
density.3 Furthermore, since the electron mobility of electron
transport materials is roughly 2ꢀ3 orders of magnitude lower than
the hole mobility of most hole transport materials, the efficiency
rollꢀoff of devices depends on the capability of electron transport.
Thus, highly efficient phosphorescent OLEDs (PhOLEDs) with
low efficiency rollꢀoff could be fulfilled by using ambipolar host
the CꢀF bond would reduce the rate of radiationless deactivation.
Furthermore, the bulky CF3 substituents could influence the
molecular packing, and the steric protection around the metal
would suppress the selfꢀquenching behaviour.5 Furthermore,
1,3,4ꢀoxadiazole and 1,3,4ꢀthiadiazole derivatives are also widely
used units for electron transport materials. In addition, the
introduction of 1,3,4ꢀthiadiazole derivatives by replacing the O
atom of the 1,3,4ꢀoxadiazole derivatives with the S atom could
affect the photophysical properties, the electron mobility and the
electroluminescence (EL) performances of Ir(III) complexes,
which was proved and discussed in our recent work as well.4(b),6
In this work, an Ir(III) complex (Ir(BTBP)2TDZ) with
2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine (BTBP) as the
main ligand and 2ꢀ(5ꢀphenylꢀ1,3,4ꢀthiadiazolꢀ2ꢀyl)phenol
(HTDZ) as the ancillary ligand were synthesized (Scheme
1). The synthesis, structural characterization, thermal
stability, photophysical and electrochemical property were
investigated in detail. Furthermore, the OLED based on this
emitter also show high performances.
Results and discussion
materials or synthesizing Ir(III) complexes with high electron Preparation and X-ray crystallography
mobility.
Scheme 1 shows the synthesis routes and chemical structure of
the Ir(BTBP)2TDZ complex. The cyclometallated ligand
(2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine, BTBP),
cyclometallated Ir(III) chloroꢀbridged dimer ([(BTBP)2Ir(ꢁꢀCl)]2)
and the ancillary ligand (HTDZ) were synthesized according to
our previous report.4,6 The Ir(III) complex was obtained in two
Previously, our group developed high efficient PhOLEDs using
Ir(III) complexes with 2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine
(BTBP) as the main ligand.4 The electron affinity could be
increased by the nitrogen heterocycle, while the electron mobility
of the complex may be improved by a more negative framework
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steps with popular methods via Ir(III) chloroꢀbridged dimer. complex can be vacuum evaporated easily without
Purification of the mixture by silica gel chromatography provided decomposition, which indicates that the complex is
crude products, which were further purified by vacuum potential emitting material for the fabrication of stable
sublimation. The new complex was fully characterized by 1H OLEDs.
NMR and the high resolution electrospray ionization mass spectra
(HR ESIꢀMS). The crystal structure obtained from vacuum
sublimation further confirmed the identity of Ir(BTBP)2TDZ.
CF3
N
F3C
F3C
N
Br
CF3 F3C
IrCl3•3H2O
CF3
Ir
CF3
F3C
CF3
N
N
N
N
Cl
Cl
LDA
B(OPr-i)3
Ir
F3C
Pd(PPh3)4
N
N
B
N
OH
HO
2
2
O
O
O
Cl
O
O
O
NH
NH2
+
HN NH
P2S5
O
OH
S
OK
BBr3
S
KOH
S
Fig. 1. Oak Ridge Thermal Ellipsoidal plot (ORTEP) diagrams of
Ir(BTBP)2TDZ with the atomꢀnumbering schemes. Hydrogen
atoms are omitted for clarity. Ellipsoids are drawn at 30%
probability level. Crystal data: CCDC No. 1524694,
N
N
N
N
N
N
CF3
N
F3C
CF3
N
F3C
CF3
N
F3C
Cl
Ir
Ir
N
N
S
Cl
Ir(BTBP)2TDZ
N
N
C38H19F12IrN6OS, MW
10.5833(4) Å, = 24.6297(8) Å,
= 102.3490(10) °,
= 3963.6(2) Å3,
=
1027.85, Monoclinic,
P
=
21/n,
a
=
β
2
2
Ir
b
c
= 15.5661(5) Å,
α
γ
= 90°,
N
O
2
V
Z
= 4,
F
(000) = 1992, GOF =
Scheme 1. Synthetic routes of ligands and the complex.
1.057, R1 = 0.0358, wR2 = 0.0707.
100
The Oak Ridge Thermal Ellipsoidal plot (ORTEP)
diagram of Ir(BTBP)2TDZ is shown in Fig. 1. The
corresponding crystallographic data are summarized in
Table S1. Selected bond lengths and angles are listed in
Table S2. The central iridium atom is chelated by two
anionic C^N main ligands and one monoanionic bidentate
N^O ancillary ligand. The coordination sphere presents a
distorted octahedral geometry, with the cisꢀC,C and
transꢀN,N in chelating disposition. Concerning the designed
ancillary ligand with three rings, the phenol ring and the
1,3,4ꢀthiadiazol ring chelate with the iridium center via the
O atom and an N atom, respectively, forming a relatively
TG
DSC
1
80
60
40
20
0
0
-1
150
300
450
600
750
Temperature (°C)
rigid hexatomic coordination ring. The IrꢀC and IrꢀN bonds Fig. 2. TG and DSC thermograms of Ir(BTBP)2TDZ
.
between iridium center and C^N main ligands are around
Photophysical property
2.0 Å and the IrꢀN(1) bond (2.1 Å) is the longest among all
The UVꢀvis absorption and emission spectra of Ir(BTBP)2TDZ
in degassed CH2Cl2 at 5 × 10ꢀ5 mol·Lꢀ1 are shown in Fig. 3. The
intense bands at high energy (230ꢀ350 nm) in the absorption
the coordination bonds. Furthermore, the C–C and C–N
bond lengths and angles are in agreement with the
corresponding parameters described in other similarly
constituted complexes.
1
spectrum are assigned to the spinꢀallowed ligandꢀcentered LC
(πꢀπ*) transition of the cyclometalated primary ligand (BTBP)
and the ancillary ligand. The relatively weak absorption bands at
lower energies extending into the spectral region (350ꢀ500 nm)
are attributed to the mixing of the spinꢀallowed singlet
Thermal stability
The thermal stability of the emitter is important for the
stability of OLEDs during application. The thermal
properties of Ir(BTBP)2TDZ were characterized by
thermogravimetric (TG) and different scanning calorimetry
(DSC) measurements under a nitrogen steam. From the
DSC curve in Fig. 2 it can be observed that the melting
point of Ir(BTBP)2TDZ is as high as 349 °C. The TG
curve gives the decomposition temperature (5% loss of
weight) of 369 °C for Ir(BTBP)2TDZ. Furthermore, the
metalꢀtoꢀligand
chargeꢀtransfer
(1MLCT)
and
triplet
metalꢀtoꢀligand chargeꢀtransfer (3MLCT) states, or LLCT
(ligandꢀtoꢀligand chargeꢀtransfer) transition through strong spin–
orbit coupling of iridium atoms.5,7
Under the excitation of 440 nm, Ir(BTBP)2TDZ emits
greenish yellow phosphorescence in CH2Cl2 solution at
room temperature with the peak maxima at 551 nm and a
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shoulder peak at 495 nm. Moreover, the quantum yield of The redox properties and HOMO (highest occupied molecular
the complex in CH2Cl2 solution is 44%. Compared with the orbital)/LUMO (lowest unoccupied molecular orbital) energy
Ir(III) complex with the same main ligand (BTBP) and levels of the dopants are relative to the charge transport ability
1,3,4ꢀoxadiazol derivative as the ancillary ligand,4(c) the PL and the OLED structure. In order to calculate the HOMO and
spectrum is redꢀshifted and the quantum yield is lower, LUMO energy levels of the complex, the electrochemical
which is mainly attributed to the introduction of the properties of Ir(BTBP)2TDZ were measured by cyclic
1,3,4ꢀthiadiazol derivative by replacing the O atom of the voltammetry in deaerated solution (CH2Cl2: CH3CN = 1: 1) (Fig.
1,3,4ꢀoxadiazol with S atom, leading to a lower excited 4 (left)). The HOMO level was calculated from the oxidation
state energy. Therefore, thee lower excited state energy is peak potential (Eox) and the band gap (Eg) was calculated from
always easier to be quenched by solvent resulting in the the UVꢀvis absorption edges.9 Then the LUMO level was
reduced quantum yield. Furthermore, the phosphorescence determined according to the equation LUMO = HOMO + Eg. The
lifetime (
τ
) is the crucial factor that determines the rate of electrochemical data are collected in Table S3. The cyclic
values voltammograms of the complex in the positive range show strong
tripletꢀtriplet annihilation in OLEDs. Longer
τ
usually cause greater tripletꢀtriplet annihilation.8 The oxidation peaks, while the reduction peaks are not obvious,
lifetime of Ir(BTBP)2TDZ is in the range of microseconds demonstrating that the redox process of the complex is not
(2.25 ꢁs in CH2Cl2 solution) at room temperature and is reversible completely, which is also observed in related Ir(III)
indicative of the phosphorescent origin for the excited complexes containing thiadiazol units.10 In the negative potential
states.
scan rang the complex exhibits quasiꢀreversible oxidation and
reduction process due to the 1,3,4ꢀthiadiazol substituent
suggesting the electronꢀtransporting and electron trapping
characteristics. From Fig. 4 and Table S3, it can be observed that
the HOMO and LUMO levels of Ir(BTBP)2TDZ are ꢀ5.58 and
ꢀ3.04 eV, respectively.
UV-vis
PL
For providing further study of the electronic structures of the
complex, the theoretical calculation was performed on optimized
geometries in CH2Cl2. The calculations on the ground electronic
states of the complex were carried out using density functional
theory (DFT) and timeꢀdependent DFT (TDꢀDFT) at the B3LYP
level.11 The basis set used for C, H, N, O, F and S atoms was
6ꢀ31G(d, p) while the LanL2DZ basis set was used for Ir atoms.12
The solvent effect of CH2Cl2 was taken into consideration using
conductorꢀlike polarizable continuum model (CꢀPCM).13 All
these calculations were performed with Gaussian 09.14 QMForge
program was used to give accurate percentage data of the frontier
molecular orbitals (FMOs).15 Contour plots of FMOs are shown
in Fig. 4 (right). The energies and percentage composition of
ligand and metal orbitals are shown in Table S4. The results are
helpful for the assignment of the electron transition
characteristics and the discussion on the photophysical variations.
According to Fig. 4 (right) and Table S4, it is obviously that the
HOMO corresponds to a mixture of the d orbitals of Ir (14.73%)
and the π orbitals of the phenyl ring of the ancillary ligand
(79.96%) with minor contribution from the BTBP ligand (5.31%).
The oxidation processes occurred with metal centered orbitals
and a contribution from the phenyl ring of ancillary ligands.16
The composition of LUMO in the main ligand is 41.77% while
the ratio of the ancillary ligand reaches 56.84%. Compared with
the iridium(III) complex with 1,3,4ꢀoxadiazol derivative as the
ancillary ligand,4(c) the composition of HOMO and LUMO on the
ancillary ligand is increased, leading to the lower LUMO level
and energy gap, which contributes to the redꢀshift of the PL
spectrum and the reduction of PL quantum yield. The calculation
results indicate that the frontier orbitals of the complexes can be
300
400
500
600
700
Wavelength (nm)
Fig. 3. Normalized UVꢀvis absorption and emission spectra of
Ir(BTBP)2TDZ in degassed CH2Cl2 solutions (5 × 10ꢀ5 mol·Lꢀ1) at
room temperature.
Electrochemical property and theoretical calculation
-2.19
LUMO
-3.04
-5.49
HOMO
-5.58
-2
-1
0
1
2
Voltage (V)
Fig. 4. Cyclic voltammogram curve (left) and contour plots of
HOMO/LUMO with theoretical (black) and experimental (red) energy
levels (right) of Ir(BTBP)2TDZ.
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manipulated by introducing 1,3,4ꢀthiadiazole derivatives, which was introduced as the host material, which has a similar transport
has effect on the photopysical and electrochemical properties of capability of holes and electrons (ꢁh = 9 × 10ꢀ6 cm2 Vꢀ1 sꢀ1 and ꢁe
the emitters.
= 3.0 × 10ꢀ6 cm2 Vꢀ1 sꢀ1).3 mCP was added as another hole
transport layer to lower the HOMO energy barrier between TAPC
and PPO21,19 which was also used as the host material in the
double EML devices.
OLEDs performance
To evaluate the EL performances of Ir(BTBP)2TDZ, single
emitting layer device (DS) with the structure of ITO (indiumꢀtinꢀ
oxide)/ MoO3 (molybdenum oxide,
(diꢀ[4ꢀ(N,Nꢀditolylꢀamino)ꢀphenyl]cyclohexane, 30 nm)/ mCP
(1,3ꢀbis(9Hꢀcarbazolꢀ9ꢀyl)benzene, nm)/ PPO21
(3ꢀ(diphenylphosphoryl)ꢀ9ꢀ(4ꢀ(diphenylphosphoryl)phenyl)ꢀ9Hꢀ
carbazole) Ir(BTBP)2TDZ (8 wt%, 10 nm)/ TmPyPB
5
nm)/ TAPC
5
:
(1,3,5ꢀtri(mꢀpyridꢀ3ꢀylꢀphenyl)benzene, 40 nm)/ LiF (1 nm)/ Al
(100 nm) was first fabricated by optimizing the thickness of all
layers and doped concentration. The device structure and energy
level diagrams are depicted in Fig. 5. MoO3 film was deposited
upon ITO layer as anode modification layer to improve the
injection of holes. TAPC, which possesses high hole mobility (ꢁh
= 1 × 10ꢀ2 cm2 Vꢀ1 sꢀ1), was used as hole transport layer (HTL).17
TmPyPB, which has lowꢀlying HOMO level (ꢀ6.70 eV) and high
electron mobility (ꢁe =1 × 10ꢀ3 cm2 Vꢀ1 sꢀ1), was used as hole
block/electron transport layer (HBL/ETL).18 Ambipolar PPO21
Fig. 5. Energy level diagrams of HOMO and LUMO levels (relative to
vacuum level) for materials investigated in this study and their molecular
structures.
104
(b)
(a)
DS
250
DS
DD
DD
200
103
150
102
100
101
50
100
0
300
100
400
500
700
Wavelength (n6m00)
0
18
6 Voltage (V)12
100
(c)
(d)
10
10
DS
DD
DS
DD
1
1
0.1
0.1
102
103
104
102
103
104
Luminance (cd m-2)
Luminance ( )
cd m-2
Fig. 6. Characteristics of singleꢀEML device DS and doubleꢀEMLs device DD: (a) normalized EL spectra at 8V; (b) current densityꢀluminanceꢀvoltage
(JꢀLꢀV) curves; (c) current efficiencyꢀluminance (ηcꢀL) curves and (d) power efficiencyꢀluminance (ηpꢀL) curves
.
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In our previous report, graded distribution of the HOMO levels excellent. One reason is that the carrier mobility of the host
of TAPC (ꢀ5.50 eV), mCP (ꢀ5.90 eV), PPO21 (ꢀ6.21 eV) and the material PPO21 is low. Furthermore, the insertion of mCP would
LUMO levels of TmPyPB (ꢀ2.70 eV), PPO21 (ꢀ2.68 eV), mCP also cause energy loss during the current flow. These two factors
(ꢀ2.30 eV) is beneficial for the injection and transport of holes may lead to the high turnꢀon voltages of the devices. Moreover,
and electrons, respectively.4,20 Thus, balanced distribution of the efficiency rollꢀoff is somehow apparent, the current efficiency
carriers and wide recombination zone could be expected in the and EQE decreased to 29.4 cd Aꢀ1 and 8.7% as the luminance
device structure. Furthermore, the HOMO/LUMO levels of increased to 1000 cd mꢀ2, because of the two reasons.
Ir(BTBP)2TDZ (ꢀ5.58/ꢀ3.04 eV) are within those of mCP and
Subsequently, the double EMLs device DD with the structure
PPO21, carrier trapping is conceived to be the dominant EL of ITO/MoO3 (5 nm)/TAPC (30 nm)/mCP: Ir(BTBP)2TDZ (8
mechanism of these devices.21 The EL spectra, current wt%, 10 nm)/PPO21 : Ir(BTBP)2TDZ (8 wt%, 10 nm)/TmPyPB
densityꢀluminanceꢀvoltage, current efficiencyꢀluminance and (40 nm)/LiF (1 nm)/Al (100 nm) was also fabricated. In most
power efficiencyꢀluminance characteristics of both devices are cases, the double EMLs devices will broaden the exciton
shown in Fig. 6. The key EL data are summarized in Table 1.
formation zone, in result of high efficiency and low efficiency
From Fig. 6 (a) it can be seen that the similarity of the EL and rollꢀoff. But compared with DS, double EML device DD obtained
PL (Fig. 3) spectra indicates that the EL is caused by emission a lower turnꢀon voltage (3.6 V) and lower maximum current
from the triplet excited states of the iridium complex efficiency, power efficiency and EQE of 40.2 cd Aꢀ1, 30.8 lm Wꢀ1
Ir(BTBP)2TDZ. On the other hand, there is no distinction and 11.9%, respectively, and the efficiencies declined obviously
between the EL spectra, the absence of residual emission from as the luminance increased. The usage of double EML led to the
PPO21 suggests a complete energy transfer from the host to the lower charge injection barrier and broadening recombination zone,
dopant in both devices under the electric excitation. The resulting in the lower turnꢀon voltage than the single EML device.
maximum current efficiency, power efficiency and external However, the reduced efficiencies and the high efficiency rollꢀoff
quantum efficiency (EQE) of singleꢀEML device DS up to 54.5 were probably due to the poor electron mobility of hosts and low
cd Aꢀ1, 31.1 lm Wꢀ1 and 16.1 %, respectively. It can also be HOMO level of PPO21. Furthermore, since mCP is a hole
observed that the turn on voltages of these devices are high transporting material, more holes would be aggregated, causing
(around 4.2 V) though the dopants have good electron mobility, the imbalanced injection, transport and recombination of carriers,
and the charge transport ability of TAPC/TmPyPB is also leading to the lower efficiencies and the high efficiency rollꢀoff.
Table 1. EL performances of singleꢀEML device DS and doubleꢀEMLs device DD.
(c)
(e)
ηc,max
ηc,L1000
CIE(i) (x,y)
(b)
(g)
Lmax
[cd mꢀ2 (V)]
ηp,max
λmax(h) (nm)
Device
Vturnꢀon(a) (V)
(cd Aꢀ1)
(cd Aꢀ1)
(lm Wꢀ1
)
(d)
(f)
(EQEmax
)
(EQEL1000 )
DS
4.2
3.6
11932 (15.7) 54.5 (16.1 %)
10635 (12.6) 40.2 (11.9 %)
29.4 (8.7%)
25.0 (7.4%)
31.1
30.8
499, 547
495, 546
0.37, 0.56
0.37, 0.56
DD
(a)
(b)
(c)
(d)
turnꢀon voltage recorded at a luminance of 1 cd mꢀ2,
maximum luminance,
maximum current efficiency,
maximum external quantum
efficiency; current efficiency at 1000 cd mꢀ2; EQE at 1000 cd mꢀ2; maximum power efficiency, values were collected at 8V, Commission
(e)
(f)
(g)
(h)
(i)
Internationale de l'Eclairage coordinates (CIE) at 8V.
derivative has effect on the physical properties and OLED
performances, which indicates that the substitution of the
Conclusion
In conclusion, an iridium(III) complex Ir(BTBP)2TDZ with
2',6'ꢀbis(trifluoromethyl)ꢀ2,4'ꢀbipyridine (BTBP) as the main
ligand and 2ꢀ(5ꢀphenylꢀ1,3,4ꢀthiadiazolꢀ2ꢀyl)phenol (HTDZ) as
the ancillary ligand was synthesized and characterized.
Ir(BTBP)2TDZ emits greenish yellow phosphorescence in
CH2Cl2 at room temperature peaks at 551 nm and a shoulder peak
at 495 nm with photoluminescence quantum efficiency of 44%.
OLEDs using Ir(BTBP)2TDZ as the emitter with singleꢀ (DS)
and doubleꢀ(DD) emitting layers were fabricated. The DS device
exhibits better performances with maximum current efficiency,
power efficiency and EQE up to 54.5 cd Aꢀ1, 31.1 lm Wꢀ1 and
16.1 %, respectively. This work suggests that the 1,3,4ꢀthiadiazol
ancillary ligand would help to find novel materials and adjust the
emission color.
Experimental section
Materials and measurements
All the organic materials used in this study were obtained
commercially and used as received without further purification
except for Ir(BTBP)2TDZ, which was synthesized and purified
1
in our laboratory. H NMR spectra were measured on a Bruker
AM 500 spectrometer. Electrospray ionization mass spectra
(ESIꢀMS) were obtained with ESIꢀMS (LCQ Fleet, Thermo
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DOI: 10.1039/C7NJ00163K
Fisher Scientific). The high resolution electrospray ionization The cyclometallated ligand (BTBP), cyclometallated Ir(III)
mass spectra (HR ESIꢀMS) were recorded on an Agilent 6540 chloroꢀbridged dimer ([(BTBP)2Ir(ꢁꢀCl)]2) and the ancillary
UHD AccurateꢀMass QꢀTOF LC/MS. Elemental analyses for C, ligand (HTDZ) were synthesized according to our previous
H and N were performed on an Elementar Vario MICRO analyzer. report.4,6
TGꢀDSC measurements were carried out on a DSC 823e analyzer
The chloroꢀbridged dimer ([(BTBP)2Ir(ꢁꢀCl)]2, 0.20 mmol) and
(METTLER). UVꢀvis absorption and photoluminescence (PL) the ancillary potassium salt (KTDZ, 0.44 mmol) in
spectra were measured on a Shimadzu UVꢀ3100 and a Hitachi 2ꢀethoxyethanol (20 mL) were refluxed for 24 h. After the
Fꢀ4600 spectrophotometer at room temperature, respectively. The mixture was cooled, the solvent was evaporated at low pressure.
luminescence quantum efficiency was calculated by a comparison The crude product was washed by water, and the column
of a standard sample facꢀIr(ppy)3 in deaerated CH2Cl2 solutions chromatography using CH2Cl2 as the eluent gave the complex
of 5 × 10ꢀ5 mol Lꢀ1.22 Cyclic voltammetry measurements were which was further purified again by sublimation in vacuum.
conducted on a MPIꢀA multifunctional electrochemical and
Ir(BTBP)2TDZ (yield: 49%): 1H NMR (300 MHz, CDCl3) δ
8.77 (d, J = 5.7 Hz, 1H), 8.14 (s, 1H), 8.10 (d, J = 5.5 Hz, 2H),
chemiluminescent system at room temperature using Fc+/Fc as
the internal standard, the scan rate was 0.05 V sꢀ1.
8.05 (t, J = 4.6 Hz, 2H), 7.88 – 7.80 (m, 3H), 7.48 (dd, J = 10.7,
X-ray crystallography
3.9 Hz, 2H), 7.44 – 7.31 (m, 4H), 7.20 (t, J = 6.3 Hz, 2H), 7.14
(dd, J = 11.1, 4.6 Hz, 2H), 6.96 (t, J = 7.2 Hz, 1H), 6.60 (d, J =
8.3 Hz, 1H), 6.46 (t, J = 7.4 Hz, 1H). HR EIꢀMS m/z calcd for
C38H19F12IrN6OS: 1028.0779, found: 1029.0854 [M+H]+. Anal.
Calcd. For C38H19F12IrN6OS: C, 44.40; H, 1.86; N, 8.18. Found:
C, 44.36; H, 1.90; N, 8.21.
Xꢀray crystallographic measurements of the single crystal were
carried out on a Bruker SMART CCD diffractometer (Bruker
Daltonic Inc.) using monochromated Mo Kα radiation (λ =
0.71073 Å) at room temperature. Cell parameters were retrieved
23
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°
Acknowledgements
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).
in ω and an exposure time of 5 s per frame. Absorption
24
corrections were applied using SADABS
supplied by Bruker.
The structures were solved by Patterson methods and refined by
25
fullꢀmatrix leastꢀsquares on F2 using the program Olex2ꢀ1.2
with SHELXLꢀ2014/7 26. 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
Notes and references
a
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, eꢀmail:
yxzheng@nju.edu.cn
atoms with a uniform value of Uiso
.
b
MaAnShan HighꢀTech Research Institute of Nanjing University,
OLEDs fabrication and measurement
MaAnShan, 238200, P. R. China
All OLEDs were fabricated on the preꢀpatterned ITOꢀcoated glass
substrate with a sheet resistance of 15 ꢂ sqꢀ1. The deposition rate
for organic compounds is 1ꢀ2 Å sꢀ1. The phosphor and host were
coꢀevaporated from two separate sources. The cathode consisting
of LiF/Al was deposited by evaporation of LiF with a deposition
rate of 0.1 Å sꢀ1 and then by evaporation of Al metal with a rate
of 3 Å sꢀ1. The effective area of the emitting diode is 0.1 cm2. The
characteristics of the devices were 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.
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6 | New J. Chem., 2017, 00, 1-7
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DOI: 10.1039/C7PNAJ0P0E1R63K
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DOI: 10.1039/C7NJ00163K
100
10
1
DS
DD
0.1
102
103
104
Luminance (cd m-2)
Efficient greenish yellow OLEDs based on an iridium(III) complex containing
electron transport ligands of 2',6'-bis(trifluoromethyl)-2,4'-bipyridine and
2-(5-phenyl-1,3,4-thiadiazol-2-yl)phenol show a maximum current efficiency of 54.5
cd A-1, a maximum external quantum efficiency of 16.1%.