Synthesis, photophysics, electrochemistry, thermal stability and electroluminescent performances of a new europium complex with bis(β-diketone) ligand containing carbazole group

Article abstract of DOI:10.1002/bio.3206

We synthesized a new europium complex [Eu(ecbpd)₃(Phen)] with bis(β-diketone) ligand containing a carbazole group, in which ecbpd and Phen are dehydro-3,3′-(9-ethyl-9H-carbazole-3,6-diyl)bis(1-phenylpropane-1,3-dione) and 1,10-phenanthroline, respectively. Its UV/vis and photoluminescent spectra, quantum yield, luminescence lifetime, electrochemistry, thermal stability and electroluminescent performances were studied. This europium complex showed low efficiency luminescence, which is probably due to the mismatching energy levels of its ligand and Eu^{3 +}, as well as the double Eu^{3 +} core resonance.

Full text of DOI:10.1002/bio.3206

Received: 17 June 2016
DOI 10.1002/bio.3206
Revised: 23 July 2016
Accepted: 29 July 2016
R E S E A R C H A R T I C L E
Synthesis, photophysics, electrochemistry, thermal stability and
electroluminescent performances of a new europium complex
with bis(β‐diketone) ligand containing carbazole group
1*
2
2
|
|
Jian Liu
Quan‐Bin Liang
Hong‐Bin Wu
1
School of New Energy Science and
Abstract
Engineering, Xinyu University, Xinyu, China
2
3
We synthesized a new europium complex [Eu(ecbpd) (Phen)] with bis(β‐diketone) ligand
Institute of Polymer Optoelectronic Materials
and Devices, State Key Laboratory of
Luminescent Materials and Devices, South
China University of Technology, Guangzhou,
China
containing a carbazole group, in which ecbpd and Phen are dehydro‐3,3′‐(9‐ethyl‐9H‐carba-
zole‐3,6‐diyl)bis(1‐phenylpropane‐1,3‐dione) and 1,10‐phenanthroline, respectively. Its UV/vis
and photoluminescent spectra, quantum yield, luminescence lifetime, electrochemistry, thermal
stability and electroluminescent performances were studied. This europium complex showed
low efficiency luminescence, which is probably due to the mismatching energy levels of its ligand
Correspondence
Jian Liu, School of New Energy Science and
Engineering, Xinyu University, Xinyu 338004,
China.
3+
3+
and Eu , as well as the double Eu core resonance.
Email: liujian_18@126.com
KEYWORDS
electroluminescence, europium complex, photoluminescence
1
|
INTRODUCTION
performance, and many europium complexes with triarylamine or
[
3]
carbazole group have been synthesized, and used in OLED.
Of the red, green and blue three‐color display in organic light‐emitting
In addition, bis(β‐diketone) europium complex has previously been
[9]
[
1,2]
diodes (OLEDs),
the red display is the most important. Red light‐
found to display good thermal stability. Europium complexes with
emitting materials generally include precious metal complexes, such
high thermal stability can be purified by thermal sublimation and fabri-
cated into a thermal‐deposit OLED, with the benefit of achieving a
highly efficient luminescent device.
[
3–8]
as iridium and platinum complexes and europium complex.
Although the electroluminescent efficiencies of platinum and iridium
complexes are higher than those of europium complexes, their color
purity is insufficient because of their wide‐scale luminescent spectra.
In addition, platinum and iridium are precious metals and scarce
resources, so they are non‐optimal red‐emission materials. However,
europium complexes, with their strongest emission peak at 613 nm
and a half‐peak width of only 10 nm, are regarded as standard red
materials. Therefore, over the years, europium complexes have been
extensively investigated for use in OLEDs. Regrettably, to date, euro-
pium complexes are unable to act as ideal red‐emitting materials
because of their low light‐emitting efficiencies.
In order to further enhance the light‐emitting efficiency of euro-
pium complex‐based OLEDs, in this work, a new europium complex
with bis(β‐diketone) ligand containing a carbazole moiety was designed
and synthesized. The UV/vis, photoluminescence, luminescent quan-
tum yield, lifetime, electrochemical, stability and electroluminescent
performances of the complex were studied.
2
2
|
EXPERIMENTAL
OLED work is comprised of several procedures as follows: elec-
trons and holes (carriers) are injected from the cathode and anode,
and then transfer on the electron‐ and hole‐transport layer, respec-
tively, before recombining on the light‐emitting layer (EML). To improve
the light‐emitting efficiency, carriers need to transfer smoothly, and
then recombine on the EML, so introducing a carrier‐transfer group to
a europium complex may result in a highly effective red‐emission
device. Triarylamine and carbazole show excellent hole‐transporting
.1
|
Synthesis of Eu(ecbpd) (Phen)
3
3
The synthesis route for Eu(ecbpd) (Phen) is given in Scheme 1.
2.1.1
|
Synthesis of 1,1′‐(9‐ethyl‐9H‐carbazole‐3,6‐diyl)
diethanone
To a 500 ml one‐neck flask were added 40.00 g of anhydrous AlCl
3
(0.30 mol, AR), acetyl chloride (39.25 g, 0.5 mol, AR) and 160 ml of
Luminescence 2016; 1–6
wileyonlinelibrary.com/journal/bio
Copyright © 2016 John Wiley & Sons, Ltd.
1

2
LIU ET AL.
3
SCHEME 1 Synthetic route of Eu(ecbpd) (Phen)
CH Cl
2 2
; the mixture was stirred magnetically until the AlCl
3
had
prepared EuCl
3
was dissolved in 20 ml of ethanol. Then 1.46 g of
dissolved completely and the solution became green–black. A solution
of 9‐ethyl‐9H‐carbazole (19.53 g, 0.1 mol, AR) dissolved in 60 ml of
Hecbpd (3 mmol), 0.4 g of Phen (1,10‐phenanthroline, 2 mmol, AR),
0.49 g of triethylamine and 30 ml of tetrahydrofuran (THF) were added
to a 100 ml one‐neck flask, stirred magnetically under THF reflux for
2 2
CH Cl was added dropwise to the solution over a period of 40 min.
The green–black solution slowly turned green and cloudy. The reaction
3
40 min and then cooled to 50°C. The ethanol solution of EuCl was
lasted for 15 h at ambient temperature. The flask was inserted into a
added dropwise to the flask over a period of 30 min. The reaction
drying tube with anhydrous CaCl
2
. After CH
2
Cl
2
was removed by
lasted for 4 h under THF reflux. The THF was removed by rotation‐
evaporation, the contents of the flask were poured into 345 ml of
hydrochloric acid (1.5 mol/L) and the resulting sediment was filtered
under vacuum. The residue was washed once with hydrochloric acid
at the same concentration, and finally washed with distilled water until
the filtrate became neutral. The raw product was dried in a dry oven
and purified by recrystallization using ethyl acetate as a solvent;
evaporation, and the resulting Eu(ecbpd)
3
(Phen) was washed with
distilled water and ethanol several times, filtered under vacuum and
3
dried in a dry oven; 1.52 g of Eu(ecbpd) (Phen) was obtained as a
1
red powder (yield: 71.67%). H NMR (400 MHz, DMSO) δ 9.27
(d, J = 19.5 Hz, 5H), 9.11 (s, 3H), 8.60–8.33 (m, 8H), 8.23 (s, 12H),
8.09–7.74 (m, 13H), 7.74–7.33 (m, 23H), 5.02(s, 3H), 4.60 (s, 6H),
2
6.04 g of 1,1′‐(9‐ethyl‐9H‐carbazole‐3,6‐diyl)diethanone (Ecdde)
2 7
1.32 (d, J = 66.8 Hz, 9H). HPLC‐ESI/MS of C120H85Eu N O12, found
1
+
was obtained as a brown crystal (yield: 71.74%). H NMR (400 MHz,
(calcd.): 2123.98 (2122.48) [M + H ].
DMSO) δ 9.07 (s, 2H), 8.14 (d, J = 8.7 Hz, 2H), 7.78 (d, J = 8.6 Hz,
2
H), 4.55 (q, J = 6.9 Hz, 2H), 2.71 (s, 6H), 1.35 (t, J = 7.0 Hz, 3H).
2
.2
|
Instrumentation and measurements
1
H NMR spectra were recorded with a Bruker‐400 MHz nuclear mag-
as solvent and
2.1.2
|
Synthesis of 3,3′‐(9‐ethyl‐9H‐carbazole‐3,6‐diyl)bis
netic resonance spectrometer by using DMSO‐d
6
(
1‐phenylpropane‐1,3‐dione)
Tetramethylsilane (TMS) as an internal reference. High‐performance
3
,3′‐(9‐Ethyl‐9H‐carbazole‐3,6‐diyl)bis(1‐phenylpropane‐1,3‐dione)
liquid chromatography electrospray ionization mass spectrometry
[10]
(
Hecbpd) was synthesized as described in the literature. First, 14.00 g
(
HPLC‐ESI/MS) was performed (model: LCQ DECA XP). Absorption
of Ecdde (0.05 mol), 54.46 g of methyl benzoate (0.4 mol, AR), 17.95 g of
spectra were obtained using a Perkin‐Elmer Lambda‐35 UV/vis
spectrometer. Photoluminescent spectra were obtained on a Hitachi
F‐4500 luminescence spectrometer. The absolute quantum yield of
Potassium tert‐butoxide (t‐BuOK) (0.16 mol, AR) and 110 ml of xylene
(
2
AR) were added to a 250 ml two‐neck flask, N was injected into the
flask and the mixture was stirred magnetically under reflux for 8 h. The
xylene and excess methyl benzoate were removed by reduced‐pressure
vaporization, and then the residue in the flask poured into distilled water
and filtered under negative pressure. The raw product was purified by
recrystallization using ethyl acetate as a solvent, giving 18.52 g of Hecbpd
Eu(ecbpd)
equipped with a xenon lamp, calibrated integrating sphere and model
C10027 photomic multichannel analyzer. Powdered Eu(ecbpd) (Phen)
was placed in a quartz cuvette and de‐aerated by passing N over
the sample through a flexible tube. The luminescent lifetime of Eu
ecbpd) (Phen) in the powdered state was tested using an IBH
Fluorocube instrument equipped with a 405 LED excitation source.
The sample was de‐aerated using N . Fitting to the decay curve was
3
(Phen) was measured by using a Hamamatsu C9920 system
3
2
1
as a light‐yellow crystal (yield: 76%). H NMR (400 MHz, DMSO) δ
(
3
9
7
2
.31–9.14 (m, 2H), 8.39 (d, J = 8.7 Hz, 2H), 8.21 (dd, J = 18.2, 7.3 Hz, 4H),
.86 (dd, J = 15.2, 8.6 Hz, 2H), 7.72–7.57 (m, 6H), 7.53 (d, J = 11.6 Hz,
H), 5.02 (s, ~1H), 4.61 (dd, J = 13.8, 6.8 Hz, 2H), 1.39 (q, J = 7.1 Hz, 3H).
2
performed using the Origin (v. 8.0) software package. Cyclic
voltammetry (CV) was performed by using CHI760 electrochemical
2.1.3
|
3
Synthesis of Eu(ecbpd) (Phen)
3
workstation under nitrogen. The Eu(ecbpd) (Phen) was dissolved in
−
4
Prior to synthesis of Eu(ecbpd)
3
(Phen), 0.35 g of Eu
2
O
3
(1 mmol, AR)
freshly distilled dimethylformamide (~ 1 × 10 mol/l). Glassy carbon
was used as the working electrode, a Pt plate as the auxiliary electrode,
was prepared into EuCl according to the universal method. The
3

LIU ET AL.
3
a standard calomel electrode as the reference electrode and (n‐C
4
H
9
)
photometer; the external quantum efficiencies were determined using
a Si photodiode in an integrating sphere (IS080, Labsphere).
4
6
NPF as the supporting electrolyte. Prior to measurement, nitrogen
was passed into the solution for 5 min. The CV was recorded at a scan
rate of 50 mV/s. Thermogravimetric analysis (TGA)–differential ther-
mal gravity (DTG) was carried out in the atmosphere with a Shimadzu
DT‐40 system at a heating rate of 10°C/min from 30°C to 800°C.
3
3
|
RESULTS AND DISCUSSION
.1
|
Photophysical properties, luminescent quantum
yield and lifetime of Eu(ecbpd) (Phen)
3
2
.3
|
Fabrication and test of devices
3
Figure 2 shows the UV/vis spectra of Hecbpd and Eu(ecbpd) (Phen) in
−
6
The configuration of the device and the molecular structures of the
materials are described in Figure 1. The EML was composed of
Polyvinylcarbazole (PVK) : 2‐([1, 1'‐biphenyl]‐4‐yl)‐5‐(4‐(tert‐butyl)phe-
2 2
CH Cl at the same concentration of ~1 × 10 mol/L. The absorption
intensity of Eu(ecbpd) (Phen) is approximately three times that of
3
Hecbpd because Eu(ecbpd) (Phen) contains three Hecbpd. The absorp-
3
*
3
nyl)‐1,3,4‐oxadaizole (PBD) : Eu(ecbpd) (Phen) 100:40:2 or 100:40:4
tion of Hecbpd at 399 and 364 nm is assigned to π–π transitions,
(mass ratio, denoted as 2 wt%‐doping device or 4 wt%‐doping device).
because two different dihedral angles probably exist between the car-
[
11]
PVK and PBD were purchased from Sigma‐Aldrich Co., Ltd. Poly(3,4‐
ethylenedioxythiophene)polystyrene sulfonate (PEDOT 4083) was
obtained commercially from SCM Industrial Chemical Co., Ltd (Shanghai).
All chemicals were of analytical grade. Prior to the manufacture of the
bazole and β‐diketone moieties,
resulting in different degrees of
*
conjugation and two π–π transition absorptions. There is only one
absorption of Eu(ecbpd) (Phen) at 381 nm because the difference in
3
the dihedral angle is eliminated due to the formation of a six‐membered
3
+
devices, the solutions of PVK, PBD and Eu(ecbpd)
in chlorobenzene, then mixed into two solutions with concentrations of
wt% and 4 wt%, depending on the amount of solution taken.
3
(Phen) were dissolved
ring comprising Eu and the β‐diketone moiety. The absorption at
*
381 nm is attributable to the π–π transition of Eu(ecbpd) (Phen).
3
2
Compared with the absorption of Hecbpd at 399 nm, that of Eu
PEDOT4083 was also dissolved in chlorobenzene. The devices were
(ecbpd) (Phen) has a blue shift of 18 nm. No absorption from Phen
3
made on a cleaned indium tin oxide (ITO) glass square with an area of
can be observed in the UV/vis spectrum. In addition, the band gap
2
0
.15 cm and a sheet resistance of 10 Ω/sq. PEDOT4083 as a hole injec-
(Eg) of Eu(ecbpd) (Phen) was obtained based on its UV/vis spectrum
3
[
12]
3
tion layer and the Eu(ecbpd) (Phen)‐doped blend of PVK and PBD as the
according to Kubelka–Munk theory,
and was found to be 2.88 eV.
EML were successively spin‐coated onto the ITO glass square. The EML
was allowed to anneal at 120°C for 10 min. Subsequently, CsF as an elec-
tron injection layer and Al as a cathode were deposited on the EML by
The photoluminescent spectra of Hecbpd and Eu(ecbpd) (Phen) in
3
the solid state and in CH Cl2 are shown in Figure 3. The
2
photoluminescent spectra of Hecbpd in the solid state and in solvent
−4
thermal evaporation under a high‐vacuum pressure of ~3 × 10 Pa.
The deposition speed and thickness were monitored using a thickness/
rate meter (model: STM‐100). All these operations were performed in a
nitrogen‐filled dry glove box with <1 ppm water and oxygen. The current
voltage characteristics were measured using a computerized Keithley
are similar, but the peaks in the solid state and in solvent are located
at 457 and 478 nm, respectively, i.e. the emissive peak of Hecbpd in
the solid state is red‐shifted by 21 nm compared with that of Hecbpd
[
13]
in CH Cl , this is because Hecbpd adopts a J‐aggregation mode.
2
2
The photoluminescent spectra of Eu(ecbpd) (Phen) in the solid state
3
2
63 source measurement unit; the electroluminescence spectra were
and in CH Cl2 display typical europium complex emission, but the
2
collected using a PR 705 photometer (Photo Research). Luminescence
was recorded on a calibrated silicon diode and calibrated by a PR 705
two emissions contain the emission of Hecbpd, and are stronger in
CH Cl than in the solid state. As a result, there is a weaker emission
2
2
FIGURE 1 The structure of device and the
chemical structure of the materials used in
the device

4
LIU ET AL.
3
FIGURE 2 The UV/vis spectra of Hecbpd and Eu(ecbpd) (Phen) in
2 2
CH Cl
FIGURE 4 The luminescent decay curve of Eu(ecbpd)
3
(Phen) in a
powder state. Fitted by an exponential decay function: y = y
−x/τ ) + A *exp (−x/τ ) , τ = 1.5 μs, τ = 14.1 μs, respectively, the
adjust R square of the fitting is 0.98427
0 1
+ A *exp
(
1
2
2
1
2
FIGURE 3 The photoluminescent spectra of Hecbpd and Eu(ecbpd)
Phen) in solid state and in CH Cl
3
(
2
2
[
14]
at 612 nm for this europium complex in CH
2 2
Cl .
The strongest emissive
3+
3
FIGURE 5 The cyclic voltammogram curve of Eu(ecbpd) (Phen) vs.
5
7
0 2
peak at 612 nm is assigned to the D – F transition of Eu ; other emis-
standard calomel electrode (SCE)
5
7
sive peaks, such those at ~592, 651 and 703 nm, correspond to D
0
– F
transitions of Eu , respectively. The absolute quan-
tum yield of Eu(ecbpd) (Phen) in a powdered state is 0.084718. This is
1
,
5
7
5
7
3+
0 3 0 4
D – F and D – F
is seen at 0.81 V, its onset potential is 0.70 V and is determined by
the intersection of the rising oxidative and background current tan-
gents, the highest occupied molecular orbital energy level is −5.10 eV.
According to its optical bandgap (2.88 eV), the lowest unoccupied
molecular orbital energy level is −2.22 eV. In a cathodic sweep, a re‐
reduction peak appears at −0.71 V. The CV curve obviously shows good
reversible oxidation–reduction.
3
lower than the absolute quantum yield of other europium complexes,
and this low‐efficiency luminescence probably is due to two factors: (1)
3
+
the mismatching energy levels of bis(β‐diketone) ligand and Eu ; and (2)
significant quenching of the luminescence takes place, due to the reso-
3+
nance of two adjacent Eu ions in the same europium complex molecule.
Figure 4 shows the luminescence decay cure, which is fitted by an
exponential decay function y = y
0 1 1 2 2
+ A *exp(−x/τ ) + A *exp(−x/τ ),
3
.3
|
Thermal stability of Eu(ecbpd) (Phen)
3
2
τ
1
= 1.5 μs, τ = 14.1 μs, the adjusted R for this fit is 0.98427. Com-
2
Figure 6 shows the TGA–DTG curves. From these, it can be seen that
the initial dissociation occurs at 276°C, involving decomposition of
Phen; whereas dissociation of the bis(β‐diketone) ligand initially
appears at 330°C, as estimated by the decomposed mass of Eu
pared with the luminescence lifetime of other europium complexes,
this is shorter; a short lifetime commonly corresponds to a low light‐
emitting efficiency in the case of europium complex emission.
(
3
ecbpd) (Phen). The fastest and second fastest decompositions occur
3
.2
|
Electrochemical properties of Eu(ecbpd) (Phen)
3
at 333°C and 532°C, respectively. This complex shows moderate ther-
[9]
−4
Figure 5 gives the CV curve of Eu(ecbpd)
3
(Phen) in DMF (~ 1 × 10
mal stability, unlike the reported β‐diketone europium complex
mol/l). For the CV curve, during an anodic sweep, an oxidation peak
which has a high decomposition temperature. So, the thermostability

LIU ET AL.
5
FIGURE 8 The curves of luminous efficiencies and external quantum
efficiencies vs. current density
3
FIGURE 6 The thermal‐stable property of Eu(ecbpd) (Phen)
of the europium complex is related to a specific ligand, rather than to
all bis(β‐diketone) ligands.
0.083% and 0.080%, respectively. The low‐efficiency luminescence
of this europium complex in OLED may be due to several factors. First,
3+
the energy levels of bis(β‐diketone) ligand (ecbpd) and Eu do not
3
.4
|
Performances of OLED
match, i.e. the triplet energy level of ecbpd is probably slightly higher
5
3+
5
Because of the moderate thermal stability of Eu(ecbpd)
mal vacuum technique is not suitable for the fabrication of Eu(ecbpd)
Phen)‐based OLEDs. We therefore used a solution spin‐coated fabrica-
tion technique to manufacture the OLED. The structure of the device is
ITO/PEDOT4083 (40 nm)/Eu(ecbpd) (Phen) (120 nm)/CsF (1.5 nm)/Al
80 nm), this is a simple solution‐process device with a bilayer structure.
3
(Phen), the ther-
0 0
than the D level of Eu , thus, significant energy reversal from D
3
to ecbpd can take place. We know this because the absolute quantum
(
yield of the europium complex is as low as 0.084718. Second, self‐
3
quenching of the luminescence of Eu(ecbpd) (Phen) is probably severe
3+
3
and results from double Eu core resonance in the same Eu(ecbpd)
3
[
16,17]
(
(Phen) molecule.
Third, the structure of the device is not suitable
Figure 7 shows the normalized electroluminescence spectra for
wt% and 4 wt% doping level devices. Intense electroluminescence
for highly effective luminescence because of its solution‐process
bilayer structure. We know this based on the PVK emission in the elec-
troluminescence spectra, which indicates inadequate energy transfer
2
can be observed at ~614 nm and originates from the europium com-
5
7
3+
plex emission due to
for the two spectra can be attributed to the emission of PVK
to inadequate energy transfer from PVK to Eu(ecbpd) (Phen). In the
wt% doping device, PVK emission is stronger, suggesting Föster's
energy transfer.
D
0
– F
2
transition of Eu . The peak at 443 nm
3
from PVK to Eu(ecbpd) (Phen). Fourth, Europium complexes are
[
15]
due
poor‐performance semiconductors. Carrier transfer is difficult on
europium complexes, and so an OLED based on a europium complex
usually shows low‐efficiency luminescence. Finally, the purity of the
europium complex also influences on the performance of the device.
3
2
Figure 8 shows the luminescence efficiency curves and the exter-
nal quantum efficiency vs. current density. The maximum lumines-
cence efficiencies for 2 wt% and 4 wt% doping devices are 0.041
and 0.040 cd/A, and the peak external quantum efficiencies are
3
Purification of Eu(ecbpd) (Phen) was performed by washing several
times with distilled water and ethanol because other purification
methods are unsuitable, and the purity is not high. We would like to
3
think that the low‐efficiency luminescence of Eu(ecbpd) (Phen)‐based
OLED mainly results from the first two factors given above.
FIGURE 7 The electroluminescent (EL) spectra of Eu(ecbpd)
doped blend of PVK and PBD as light‐emitting layer
3
(Phen)‐
FIGURE 9 The characteristics of current density vs. voltage and the
curves of luminance vs. voltage

6
LIU ET AL.
Figure 9 presents curves for the current density (J) or luminescence
OLED
PBD
Organic light‐emitting diode
vs. voltage for the two devices. The maximum luminescence values for
2‐([1, 1'‐biphenyl]‐4‐yl)‐5‐(4‐(tert‐butyl)phenyl)‐
1,3,4‐oxadaizole
2
the 2 wt% and 4 wt% doping devices are 16.0 and 4.4 cd/m , and the
turn‐on voltages are 12.5 and 17.0 V, respectively.
Phen
1,10‐Phenanthroline
PEDOT 4083 Poly(3,4‐ethylenedioxythiophene)polystyrene
sulfonate
4
|
CONCLUSION
PVK
TGA
THF
UV
Polyvinylcarbazole
Thermogravimetric analysis
Tetrahydrofuran
Ultraviolet
In summary, we synthesized
a new europium complex with
bis(β‐diketone) ligand containing a carbazole group, and investigated
its UV/vis, photoluminescent spectra, luminescent quantum yield, life-
time, electrochemistry and thermal stability. This europium complex
shows characteristic emission and low absolute quantum yield in the
solid state. A europium complex‐based OLED was fabricated using a
solution‐processed spin‐coated technique. The performance of the
OLED was less than desirable, probably, mainly because of the lack
of a match between the energy levels of bis(β‐diketone) ligand (ecbpd)
vis
Visible
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2
[
[
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ABBREVIATIONS USED
CV
Cyclic voltammetry
DTG
ecbpd
Differential thermal gravity
Dehydro‐3,3′‐(9‐ethyl‐9H‐carbazole‐3,6‐diyl)bis(1‐
phenylpropane‐1,3‐dione)
6
1, 2455.
Ecdde
EML
1,1′‐(9‐Ethyl‐9H‐carbazole‐3,6‐diyl)diethanone
Light‐emitting layer
How to cite this article: Liu, J., Liang, Q.‐B., and Wu, H.‐B.
(2016), Synthesis, photophysics, electrochemistry, thermal sta-
bility and electroluminescent performances of a new europium
complex with bis(β‐diketone) ligand containing carbazole
group. Luminescence, doi: 10.1002/bio.3206
ESI‐MS
Hecbpd
Electrospray ionization mass spectrometry
3,3′‐(9‐Ethyl‐9H‐carbazole‐3,6‐diyl)bis(1‐
phenylpropane‐1,3‐dione)
HPLC
ITO
High‐performance liquid chromatography
Indium tin oxide