Synthesis and characterization of carbazole dendrimers as solution-processed high Tg amorphous hole-transporting materials for electroluminescent devices

Article abstract of DOI:10.1002/ejoc.201300757

We report on an efficient and facile synthesis of up to 4^th generation carbazole dendrons by using a mild Ullmann coupling reaction. The dendrimers, namely GnC (n = 1-4), are thermally stable amorphous materials with high glass transition tempe

Full text of DOI:10.1002/ejoc.201300757

Job/Unit: O30757
/KAP1
Date: 22-08-13 16:33:46
Pages: 11
FULL PAPER
DOI: 10.1002/ejoc.201300757
Synthesis and Characterization of Carbazole Dendrimers as Solution-Processed
High T Amorphous Hole-Transporting Materials for Electroluminescent
g
Devices
[
a]
[a]
[b]
[a]
Narid Prachumrak, Sukrawee Pansay, Supawadee Namuangruk, Tinnagon Kaewin,
[a]
[a]
[c]
Siriporn Jungsuttiwong, Taweesak Sudyoadsuk, and Vinich Promarak*
Keywords: Dendrimers / Thin films / Glasses / Solid-state structures / Organic light-emitting diodes
We report on an efficient and facile synthesis of up to 4th
generation carbazole dendrons by using a mild Ullmann cou-
pling reaction. The dendrimers, namely GnC (n = 1–4), are
thermally stable amorphous materials with high glass transi-
ITO/PEDOT: PSS/GnC(spin-coating)(40 nm)/Alq3(50 nm)/
LiF(0.5 nm):Al(150 nm) emit a bright green color (λem
=
514 nm) from the Alq3 layer, with maximum luminance,
maximum current efficiency, and turn-on voltage of
–
2
–1
tion temperatures (T
g
) up to 347 °C and exhibit chemically
29,262 cdm , 5.11 cdA , and 3.0 V, respectively. The abili-
ties of GnC to act as hole-transporting materials in terms of
thermal property and device performance are superior to
common hole-transporters, N,NЈ-diphenyl-N,NЈ-bis(1-naph-
thyl)-(1,1Ј-biphenyl)-4,4Ј-diamine (NPB) and N,NЈ-bis(3-
methylphenyl)-N,NЈ-bis(phenyl)benzidine (TPD).
stable redox properties. The compounds show great potential
to work as solution-processed hole-transporting materials for
electroluminescent devices. Double-layer Alq3-based or-
ganic light-emitting diodes employing these dendrimers as
the hole-transporting layers with the device configuration of
Introduction
properties such as high charge carrier mobility and ease of
sublimation. However, their low T (65 °C for TPD and
g
Organic light-emitting diodes (OLEDs) have received
enormous attention from the scientific community due to
their potential use in flat-panel displays and lighting appli-
100 °C for NPB), ease of crystallization, and low morpho-
logical stability usually lead to degradation and short life-
[4]
time of the devices. Recently, many arylamine- and carb-
[
1]
cations. In the past decade, great progress has been made
in both device fabrication techniques and materials devel-
azole-based AHTMs with high T such as carbazole end-
g
[5]
capped
molecules,
9,9-bis{4-[bis(4-carbazol-N-yl-bi-
phenyl-4-yl)amino]phenyl}fluorenes, binaphthalene deriv-
[
2]
opment. One of the key developments is the use of hole-
transporting layers (HTLs) for hole injection from the an-
ode into the emitting layer, providing significant improve-
ment in the performance of the device.[3] In general, high
[6]
[7]
[8]
atives, triarylamine-based starburst molecules, and carb-
[9]
azole dendronised triphenylamines have been reported.
It is known that suppression of crystallization and im-
provements in the morphological stability of the molecule
glass transition temperature (T ) amorphous hole-trans-
g
porting materials (AHTMs) are needed for highly efficient
and long lifetime OLED devices. The most commonly used
HTMs, N,NЈ-diphenyl-N,NЈ-bis(1-naphthyl)-(1,1Ј-biphen-
yl)-4,4Ј-diamine (NPB) and N,NЈ-bis(3-methylphenyl)-
N,NЈ-bis(phenyl)benzidine (TPD), provide many attractive
can be achieved by forming a bulky structure, in particular
[5,10]
the structure of a dendrimer.
Dendrimers have several
unique characteristics that arise from their spherical shape,
giving them properties that are very different from both
polymers and small molecules. Because of their precise
structure, they can be characterized like any small mo-
lecules. Unlike polymers, they have distribution size that
can lead to slight variations their properties. However, as
macromolecules, they can form amorphous films, and have
high melting temperature (T ) and high T , and are there-
[
a] Department of Chemistry and Center of Excellence for
Innovation in Chemistry, Faculty of Science, Ubon Ratchathani
University,
Ubon Ratchathani, 34190 Thailand
[
[
b] National Nanotechnology Center (NANOTEC),
m
g
1
30 Thailand Science Park, Klong Luang, Pathumthani 12120
fore much less likely to crystallize. Recent progress in or-
Thailand
c] School of Chemistry and Center of Excellence for Innovation ganic synthesis has enabled dendritic molecules to be con-
in Chemistry, Institute of Science, Suranaree University of
structed with well-designed building blocks in the core,
Technology,
[
10b,11]
Nakhon Ratchasima, 30000 Thailand
E-mail: pvinich@sut.ac.th
Homepage: none
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejoc.201300757.
branching points, and on the surface.
Many kinds of
dendrons and dendrimers have been synthesized and con-
sidered for several applications including electroactive mate-
rials for OLEDs such as stilbene and phenylacetylene den-
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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V. Promarak et al.
FULL PAPER
drimers as emitting materials,[12] and arylamine and oxa- thin films that could be deposited by straightforward solu-
diazole dendrimers as hole- and electron-transporting lay- tion processes. In terms of device fabrication, solution-pro-
ers.[
13]
cessed OLEDs fabricated by using small molecules have
Owing to its excellent hole-transporting ability, high great advantages, because the materials used are easy to
charge carrier mobility, high thermal, morphological and synthesize and to purify, and the fabricating method is con-
photochemical stability, and the ease of functionality at the venient, low cost and can be adapted to large-scale synthe-
[
15]
3
-, 6-, or N-positions, carbazole has been used as a building sis with less material waste. Herein, we report a detailed
[5,14]
block to form many HTMs.
Certainly, it is very attract- synthesis of carbazole dendrimers up to 4th generation. An
ive to explore and develop high generation carbazole den- investigation of their physical and photophysical properties,
drons and their dendrimers, which meet the requirements and green OLED fabrication and characterization are also
as AHTMs for OLEDs and can be synthesized by using reported.
simple and low-cost methods. To this end, we wanted to
incorporate all the required aspects for efficient AHTMs in
Results and Discussion
the chosen dendrimers (GnC; Scheme 1). Use of carbazole
as both the branching unit and the core offers perfect hole-
transporting ability with high charge carrier mobility and
Synthesis and Characterization
high T . The strongly twisted carbazole unit in the dendron
The synthetic route to carbazole dendrimers (GnC) is
g
th
and the presence of tert-butyl groups at the surface leads to outlined in Scheme 1. Dendrimers up to the 4 generation
bulky dendrimers with high solubility,[ and thereby de- were synthesized by using a combination of convergent and
livers electrochemically and thermally stable amorphous divergent approaches. In the former method, the dendrimer
5]
Scheme 1. Synthetic route to the carbazole dendrimers (GnC).
2
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Carbazole Dendrimers for Electroluminescent Devices
is assembled from the outside or the surface groups and branching units got exponentially larger, while the volume
then built inwards through the branching groups towards available increased as the cube of the generation number.
the core, whereas in the latter method, the dendrimer grows The dendrimers therefore become increasingly sterically
outwards from the core, diverging into space. tert-Butyl hindered structures, which are pushed into a sphere with
substituents on the 3- and 6-positions of the peripheral car- the core at the center and the outer face covered by the
bazole ring were chosen as the surface groups to provide surface groups. Apart from the differences in the size, the
solubility and add to the electrochemical stability of the conformations of all dendrimers are very similar. In the
dendrimer. The key reaction in the synthesis was the HOMO, π-electrons are able to delocalize over the bis(car-
Ullmann coupling reaction involving a coupling of carba- bazol-NЈ-yl)carbazole moieties, while in the LUMO, the ex-
zole with aryl halides under a mild catalytic system of CuI cited electrons localize on the N-dodecylcarbazole core.
as catalyst, (Ϯ)-trans-1,2-diaminocyclohexane as co-cata-
lyst, and K PO as base in toluene at reflux. From available
3
4
16]
3
,6-dibromo-N-dodecylcabazole (2),[ the tetrabromo in-
termediate, 3,6-bis(3Ј,6Ј-dibromocarbazol-NЈ-yl)-N-dode-
cylcarbazole (7) was prepared. Ullmann coupling of 2 with
carbazole (1) followed by bromination of the resultant com-
pound
5 with N-bromosuccinimide (NBS) in tetra-
hydrofuran (THF) gave tetrabromo compound 6 in a total
yield of 80%.
The 3,6-bis(3Ј,6Ј-di-tert-butylcarbazol-NЈ-yl)carbazole
(
8) intermediate was prepared from available 3,6-di-tert-bu-
[
17]
tylcarbazole (4). First, tosyl-protected amine, 3,6-diiodo-
N-tosylcabazole (3), was synthesized from carbazole (1) by
iodination with KI/KIO in AcOH followed by N-tosyl-
3
ation with TsCl in the presence of KOH in acetone. Cou-
pling of 3 with 4 under the Ullmann coupling conditions
followed by detosylation of the resultant compound 7 with
KOH in a mixture of THF/dimethyl sulfoxide (DMSO)/
st
H O afforded 8 in 75% yield over two steps. The 1 genera-
2
tion carbazole dendrimer G1C was formed by alkylation
of 4 with dodecylbromide in the presence of NaH in N,N-
dimethylformamide (DMF) and obtained as a colorless oil
nd
rd
in 96% yield. To form the 2 and 3 generation dendri-
mers G2C and G3C, respectively, intermediate 2 was cou-
pled with either carbazoles 4 or 8 under the Ullmann cou-
pling conditions to give G2C and G3C as white solids in
good yields of 77 and 71%, respectively. The Ullmann cou-
pling of intermediate 6 with 8 under the same conditions
th
afforded the 4 generation dendrimer G4C as a white solid
Figure 1. The HOMO and LUMO orbitals of G4C calculated by
in 69% yield. The structures of GnC were characterized un- using the TDDFT/B3LYP/6-31G (d,p) method in CH Cl .
ambiguously by FTIR, H NMR, and C NMR spec-
2
2
1
13
troscopy as well as by MALDI-TOF mass spectrometry,
The optical properties of GnC were investigated by UV/
which confirmed that all dendrimers were monodisperse, Vis and photoluminescence (PL) spectroscopy in both di-
with their molecular weights being identical to the calcu- lute CH Cl2 solution and thin-film spin-coated from
2
lated masses. These dendrimers showed good solubility in CHCl /toluene (1:1) solution on quart substrates. The re-
3
most organic solvents, allowing thin films of GnC to be sults are shown in Figure 2 and summarized in Table 1. The
fabricated by a solution casting process, thus overcoming solution absorption spectra of these dendrimers showed
the high cost of the vacuum deposition process.
similar absorption features, which were characterized by
strong absorption bands at around 289 nm assigned to the
π-π* local electron transition of each carbazole unit, and
less intense absorption bands at longer wavelength (ca.
Theoretical Calculations and Optical Properties
300 nm) related to the π-π* electron transition of the conju-
The geometrical structures of the dendrimers GnC opti- gated bis(carbazol-NЈ-yl)carbazole segments. The absorp-
[
18]
mized by using the TDDFT/B3LYP/6-31G (d,p) method
tion edge of G1C slightly red-shifted (ca. 5 nm) relative to
are shown in Figure 1 (see also the Supporting Infor- those of G2–4C, suggesting that the generation number of
mation). The results showed that each new generation of the dendrons has little effect on electronic properties of the
the dendrimers introduced further bulk to the structure. As dendrimers. The energy band gaps (E ) of G2–4C, estimated
g
the generation number increased, the number of repeating from the absorption edge, were nearly identical (3.69–
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Electrochemical Properties
To analyze the redox properties of these dendrimers, cy-
clic voltammetry (CV) was carried out by using a three-
electrode cell setup with 0.1 m nBu NPF as a supporting
4
6
electrolyte in CH Cl under an argon atmosphere; the re-
2
2
sults are shown in Figure 3 and tabulated in Table 1. G1C
displayed one quasireversible oxidation process at 1.09 V,
whereas G2–4C exhibited well-separated multiple quasire-
versible oxidation processes. The first oxidation waves of
G2–4C occurred at nearly the same potentials (0.99–1.02 V)
and were lower than that of G1C indicating that there is π-
electron delocalization between the carbazoles. Their mul-
tiple CV scans revealed identical CV curves with no ad-
ditional peak at lower potential on the cathodic scan (Epc)
being observed, indicating no oxidative coupling at the 3-
or 6-positions of the peripheral carbazole leading to electro-
polymerization. The present of 3,6-di-tert-butyl groups
could prevent this type of electrochemical coupling reac-
tion, which is usually detected in carbazole derivatives with
Figure 2. UV/Vis absorption and PL spectra of dendrimers mea- unsubstituted 3,6-positions.[19] The results suggested that
sured in CH
2
Cl
2
and as thin-film spin-coated on quartz substrates. these dendrimers were electrochemically stable molecules.
Moreover, under these measurement conditions, no distinct
reduction process was detected in any of the samples. The
HOMO energy levels of the dendrimers were calculated
3
.60 eV), indicating similar π-conjugation length despite
from the onset of the oxidation. The HOMO level of G1C
–5.47 eV) was somewhat lower than those of G2–4C (–5.35
their large differences in molecular size. This can be ex-
plained by an out-of-plane twisting of each carbazole unit
in the dendron, which limits π-interaction between the car-
bazoles. However, the lone electron pair of the nitrogen of
the carbazole allows π-electron delocalization between the
carbazoles in the bis(carbazol-NЈ-yl)carbazole moiety as
observed in the calculated HOMO orbitals of G2–4C (Fig-
ure 1). The solution photoluminescence (PL) spectra of
GnC showed emission bands in the purple–blue region
(
to 5.38 eV). The LUMO energy levels of these materials
were calculated by subtracting the energy band gaps (Eg)
from HOMO levels and were foud to lie between –1.98 and
–2.05 eV (Table 1). With their HOMO energy levels match-
(363–402 nm). PL spectra of G2–4C were featureless, nearly
the same, and redshifted (39 nm) compared with that of
G1C. Fluorescence quantum yields (Φ ) of GnC, deter-
F
mined in CH Cl using quinine sulfate as a standard, grad-
2
2
ually decreased from 0.42 to 0.11 as the generation number
of the dendrimer increased. The thin-film PL spectra of
G2–4C also showed featureless emission bands and exhib-
ited slight shifts of emission maxima relative to their solu-
tion spectra, suggesting that the intermolecular π-π interac-
tions of these dendrimers in the solid state were highly hin-
dered by their bulky molecular structures.
2 2
Figure 3. CV curves of the dendrimers measured in CH Cl /
nBu NPF at a scan rate of 50 mVs .
4 6
–
1
Table 1. Optical, thermal, electrochemical and electronic properties of the dendrimers.
[
a]
[a]
em
[b]
[c]
Stokes shift[d]
[nm]
/T5d[e]
1/2 vs. Ag/Ag+[f] Eoxonset[f]
[g]
HOMO[h] LUMO[h]
Compd.
λ
[
abs (logε)
λ
λ
e
Φ
F
T
[°C]
g
E
[V]
E
g
nm (m–1 cm )]
–1
[nm]
[nm]
[V]
[eV]
[eV]
[eV]
G1C
G2C
G3C
G4C
353 (4.17)
349 (4.09)
349 (1.05)
349 (3.92)
363, 378 366sh, 376 0.42 25
–/250
1.09
0.99, 1.17
1.00, 1.17, 1.45
1.02, 1.18, 1.49
1.03
0.91
0.93
0.94
3.41
3.69
3.60
3.60
–5.47
–5.35
–5.37
–5.38
–2.05
–1.98
–2.01
–2.02
402
402
402
397, 412sh 0.30 53
114/369
257/370
347/420
401
403
0.25 53
0.11 53
[
[
a] Measured in CH
d] Calculated from the difference of λabs
2
Cl
2
. [b] Measured in thin-film on quartz substrate. [c] Measured in CH
2
Cl
and λem . [e] Measured by DSC/TGA at a heating rate of 10 °C min . [f] Obtained from
= 1240/λonset. [h] Calculated by HOMO = –(4.44 +
2
with quinine sulfate as a standard.
max
max
–1
–1
CV at a scan rate of 50 mVs . [g] Estimated from the optical absorption edge, E
E
g
ox
ox
onset); LUMO = HOMO – E
g
, where E onset is the onset potential of the oxidation.
4
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Carbazole Dendrimers for Electroluminescent Devices
ing well with the work functions of indium tin oxide (ITO)
electrode and their stable electrochemical properties, these
dendrimers have great potential for hole-injection and
transport in OLEDs.[
20]
Thermal and Morphological Properties
For OLED applications, the thermal stability of organic
materials is crucial for device stability and lifetime. Thermal
instability or low T of the amorphous organic layer may
g
result in the degradation of organic devices due to morpho-
logical changes. The thermal properties of G2–4C were in-
vestigated by thermogravimetric analysis (TGA) and
differential scanning calorimetry (DSC), and the results are
shown in Figure 4 and summarized in Table 1. The results
suggested that all the dendrimers tested were thermally
stable materials with decomposition temperature at 5%
weight loss (T ) over 369 °C in TGA measurements. The
5
d
phase transition properties of these dendrimers analyzed by
st
nd
DSC revealed amorphous phases. In both 1 and 2 heat-
ing scans of G2–4C, the DSC curves displayed an endother-
mic baseline shift owing to glass transition (T ), with no
g
crystallization or melting being detected at higher tempera-
tures in either scans. These results indicated that the tested Figure 5. (a) Tapping mode AFM image of a spin-coated film of
dendrimers were stable amorphous materials with T values G4C. (b) Powder XRD patterns of the dendrimers on silicon wafer
g
substrate.
higher than those of commonly used HTMs such as NPB
(
T = 100 °C) and TPD (T = 63 °C), and many reported
g
g
[4–8]
can reduce the degree of crystallization and improve the
amorphous stability of the materials, which, in turn, could
enhance the morphological stability of the thin film and
carbazole and triphenylamine derivatives.
that as the size of the dendrimers increased, the T values
of these materials increased from 114 °C for G2C, 257 °C
for G3C and 347 °C for G4C, because of the rigid and
highly twisted structure of the carbazole branching unit.
The results indicate that the dendritic carbazole backbone
It was noticed
g
[
21]
improve the lifetime of the device.
Moreover, the ability
of GnC to form a molecular glass and dissolve well in or-
ganic solvents offer the possibility of preparing good thin
films by solution casting processes, which are highly desir-
able for applications in electroluminescent devices. The
amorphous characteristics of GnC were further charac-
terized by powder X-ray diffraction (XRD) using silicon
wafer as a substrate. The GnC bulk powders were scattered
on top of the substrate. The XRD patterns are shown in
Figure 5 (b). For G2C, a series of peaks were recorded at 2
theta of 15, 17 and 19° (the corresponding d-spacing values
being 5.93, 5.21 and 4.67 Å), which were attributed to π-π
stacking of carbazole segments. In higher generation den-
drimers G3–4C, these peaks became broad amorphous
peaks at the same positions. The morphologies of the den-
drimers were also analyzed by atomic force microscope
(AFM) by using the standard tapping mode. The thin films
were spin-coated from CHCl /toluene solution on a glass
3
substrate and then heated at 60 °C for 30 min to remove the
solvents. As depicted in Figure 5 (a) (see also the Support-
ing Information), the films of GnC showed a relatively
smooth surface, indicating their good film-formation abili-
ties.
OLED Studies
According to the excellent properties of the dendrimers
discussed above, the abilities of GnC as a hole-transporting
Figure 4. (a) DSC and (b) TGA thermograms of the dendrimers
measured at a heating rate of 10 °C min–1 under N
.
2
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Figure 6. (a) Schematic structure and (b) EL spectra of the OLEDs.
layer (HTL) in OLEDs were investigated. Alq3-based green
OLEDs with the structure ITO/PEDOT:PSS/GnC (spin- Figure 7. (a) J-V-L characteristics and (b) variation in luminance
efficiency with current density of the OLEDs.
coating) (40 nm)/Alq3 (50 nm)/LiF (0.5 nm):Al (200 nm)
were fabricated, in which Alq3 is the green light-emitting
and electron-transporting layer (EML) (Figure 6, a). The vice as a hole injection layer not only increased the maxi-
–
2
GnC layers as HTL were spin-coated from CHCl /toluene mum luminance (Lmax) from 9043 cdm [luminance effi-
3
–1
–2
(
1:1) solution with a controlled thickness. To evaluate the ciency (η) of 1.03 cdA ] in device I to 24548 cdm (η of
effect of the interfacial layer and to compare hole-trans- 4.11 cdA ) in device II, but also significantly decreased the
–1
porting abilities of the synthesized dendrimers GnC with turn-on voltages (V ) from 6.1 to 3.2 V. Moreover, their
on
commercial HTM, reference devices I, V–VII of the same EL spectra were almost identical. It has been pointed out
structure with and without commercial HTMs, N,NЈ-di- that the lower operating voltage of PEDOT:PSS-based de-
phenyl-N,NЈ-bis(1-naphthyl)-(1,1Ј-biphenyl)-4,4Ј-diamine vices can be attributed to the rough and porous surface of
(NPB) and N,NЈ-bis(3-methylphenyl)-N,NЈ-bis(phenyl)- the spin-coated PEDOT:PSS polymer layer, which increases
benzidine (TPD) as HTL were made. Because the devices the contact area to enhance hole injection and lowers the
were fabricated in an identical manner, any changes be- barrier at the organic-organic interface by relocating the
[
23]
tween them should indicate differences due to the new ma- barrier to the more conductive PEDOT:PSS layer. To en-
terial or device structure. The optical and electrical charac- able high-performance devices, therefore, PEDOT:PSS as
teristics of all fabricated OLED devices are illustrated in hole injection layer was integrated into the devices. Under
Figure 6 (b), Figure 7 (see also the Supporting Information) applied voltage, all GnC-based devices II–IV exhibited a
and all parameters are summarized in Table 2. From our bright-green emission with peaks centered at 514 nm and
study and other reports,[ it was found that incorporation CIE coordinates of (0.27, 0.51) (Figure 6, b). The electrolu-
of the conductive polymer poly(3,4-ethylenedioxythi- minescence (EL) spectra of these diodes were identical, and
ophene):poly(4-styrenesulfonate) (PEDOT:PSS) in the de- matched with the PL spectrum of Alq3, the EL of the refer-
22]
Table 2. Device characteristics of the fabricated OLEDs.
EL [nm][c]
V
on/V100 [V][d]
L
max [V] (cdm / V)
–2
[e]
J
max (mAcm–2)[f] η (cdA )
–1 [g]
EQE (%)[h]
CIE (x, y)[i]
Device HTL
λ
I[
a]
G2C
G2C
G3C
G4C
NPB
TPD
–
515
514
514
514
519
519
518
6.1/7.0
3.2/4.5
3.0/4.4
3.0/5.6
2.5/3.6
2.5/3.7
4.2/5.4
9043 (12.0)
24548 (10.8)
29262 (11.6)
28450 (12.8)
31857 (9.4)
22539 (8.8)
4961 (10.0)
1036
1196
1114
944
1599
1296
693
1.03
4.11
5.11
5.01
4.45
4.05
0.91
0.09
0.20
0.25
0.24
0.22
0.20
0.07
0.28, 0.51
0.27, 0.50
0.26, 0.51
0.27, 0.51
0.30, 0.53
0.29, 0.53
0.30, 0.54
[
b]
II
[
b]
III
[
b]
IV
[
b]
V
[
b]
VI
[
b]
VII
[
a] ITO/HTL(spin-coating)/Alq3/LiF:Al. [b] ITO/PEDOT:PSS/HTL(spin-coating)/Alq3/LiF:Al. [c] Emission maximum. [d] Turn-on volt-
–2
ages at 1 and 100 cdm . [e] Maximum luminance at applied voltage. [f] Current density at maximum luminance. [g] Luminance efficiency.
h] External quantum efficiency. [i] CIE coordinates.
[
6
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Carbazole Dendrimers for Electroluminescent Devices
ence devices V–VII, and also other reported EL spectra of layer with a maximum luminance, maximum efficiency, and
Alq3-based devices.[
5,24]
No emission at the longer wave- low turn-on voltage of 29262 cdm , 5.11 cdA , and 3.0 V,
–2
–1
length owing to exciplex species formed at the interface of respectively. The suitability of these dendrimers to act as
HTL and ETL materials, which often occurs in devices fab- solution-processed HTLs for green OLEDs in terms of de-
ricated from HTL with planar molecular structure, was de- vice performance and thermal properties were better than
[
25]
tected.
In our case, the formation of exciplex species commonly used hole-transporters NPB and TPD. These
could be prevented by the bulky nature of the dendritic dendrimers may also be promising materials for long-life-
carbazole backbone. From these results, and in view of the time device applications, especially for high-temperature ap-
fact that a barrier for electron-migration at the Alq3/HTL plications in OLEDs or other organic optoelectronic de-
interface (ca. 1.00 eV) is about twice as high as those for vices. The use of these carbazole dendrons to form dendritic
hole-migration at the HTL/Alq3 interface (ca. 0.44 eV), the structures with other fluorescent or nonfluorescent core
present device configuration of ITO/PEDOT:PSS/GnC/ units might be an effective way to prepare high T amorph-
g
Alq3/LiF:Al, GnC would act only as HTM, and Alq3 ous materials for various applications.
would act preferably as an electron blocker more than as a
hole blocker and charge recombination would thus be con-
fined to the Alq3 layer. More importantly, a stable emission Experimental Section
was obtained from all diodes II–IV and the EL spectra and
Materials and Instruments: All reagents were purchased from Ald-
CIE coordinates did not change over the entire applied volt-
rich, Acros or Fluka, and used without further purification. All
solvents were supplied by Thai companies and used without further
distillation. THF was heated to reflux with sodium and benzophe-
age range (see the Supporting Information).
The light turn-on voltages for all devices II–IV were in
the range of 3.2–3.0 V and the operating voltages at
none, and distilled prior to use. CH
2 2
Cl for electrochemical mea-
–
2
1
00 cdm (V100) were in the range of 4.5–5.6 V, indicating surements was washed with concentrated H SO and distilled twice
2
4
good performance is achieved for all devices. By compari- from calcium hydride. Chromatographic separations were carried
1
13
son with the reference device VII, it was found that the out on Merck silica gel 60 (0.0630–0.200 mm). H and C NMR
spectra were recorded with a Bruker Avance 300 MHz spectrometer
incorporation of GnC in the device as HTL not only in-
–
2
with TMS as the internal reference by using CDCl as solvent in
creased Lmax from 4961 to 24548–29262 cdm , but also
significantly decreased the Von from 4.2 to 3.0 V. Further-
more, their EL spectra were nearly identical. Moreover, the
device characteristics in terms of maximum luminous effi-
ciency clearly demonstrated that the hole-transporting abili-
ties of G3–4C were greater than those of the most com-
3
all cases. Infrared (IR) spectra were measured as KBr discs with a
Perkin–Elmer FTIR RXI spectrometer. UV/Vis spectra were re-
corded as dilute solutions in CH
Lambda 25 spectrometer. Photoluminescence spectra were re-
corded as dilute solutions in CH Cl and thin films spin-coated
from CHCl /toluene (1:1) solution with a Perkin–Elmer LS 50B
2 2
Cl with a Perkin–Elmer UV
2
2
3
monly used HTMs, NPB (device V) and TPD (device VI). Luminescence Spectrometer. DSC and TGA were performed with
Device III, having dendrimer G3C as HTL, exhibited the a Mettler DSC823e thermal analyzer and a Rigaku TG-DTA 8120
best performance with a high Lmax of 29262 cdm–2 for thermal analyzer, respectively, under nitrogen with heating rates of
–
1
1
0 °C min . CV was carried out with an Autolab potentiostat
green OLED at 11.6 V, a low V of 3.0 V, a maximum η of
on
–
1
PGSTAT 12 with a three-electrode system (platinum counter elec-
trode, glassy carbon working electrode and Ag/Ag reference elec-
trode) at a scan rate of 50 mVs in the presence of nBu
a supporting electrolyte in CH Cl under argon. Melting points
were measured with an Electrothermal IA 9100 series digital melt-
ing point instrument and are uncorrected. MALDI-TOF mass
spectra were recorded with a Bruker Daltonics (Bremen, Germany)
5
0
.11 cdA , and a maximum external quantum efficiency of
.25%. Comparable device performance was observed from
+
–
1
4 6
NPF as
device IV (with G4C as HTL) (Table 2), however, the device
using G2C as HTL showed lower device performance. Al-
though, many HTMs have been reported, in terms of the
2
2
amorphous morphology, significantly high T , solution pro-
g
cessability, and device efficiency, these dendrimers G3–4C Autoflex II Matrix-Assisted Laser Desoprtion/Ionization-Time of
are among the best HTMs reported. They are therefore Flight Mass Spectrometer (BIFEX) using α-cyano-4-hydroxycin-
highly promising as an alternative hole-transport material namic acid as matrix. Atomic force microscopy (AFM) analysis
was performed with a SPA 4000 STM/AFM system using standard
to NPB and TPD.
tipping mode with resonance of 222.223 kHz, force constant of
–
1
6
.1 N m (Ϯ20%), cantilever length of (87Ϯ5) μm, cantilever
width of (32Ϯ5) μm), scan area of 3–5 μm and scan speed of 1 Hz.
Powder X-ray diffraction (XRD) was analyzed with a PHILIPS
Conclusions
XЈPert-MDP X-ray diffractometer using Cu-K
.5418 Å) at 1,400 W, 40 kV and 35 mA in the scanning angle (2
theta) of 10–40° with resolution of 0.04° at a counting step of
α
radiation (λ =
We have presented a facile and efficient synthesis of rigid
carbazole dendrimers up to the 4th generation by using sim-
1
ple Ullmann coupling and detosylation reactions. These 1 s/step. The samples in powder form were placed on silicon wafer
dendrimers showed chemically stable redox and thermally substrate.
stable amorphous properties with high glass transition tem-
Quantum Chemical Calculations: Ground-state geometries were
fully optimized by using a DFT level with the B3LYP hybrid func-
tional. All optimizations were calculated without any symmetry
peratures (T ) up to 347 °C. Alq3-based green OLEDs
g
using these materials as the hole-transporting layer (HTL)
with the device configuration of ITO/PEDOT:PSS/HTL/ constraints using the 6-31G(d,p) basis set on the Gaussian09 soft-
Alq3/LiF:Al emit brightly (λem = 514 nm) from the Alq3 ware package.[
18]
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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7

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Pages: 11
V. Promarak et al.
136.54, 137.81, 145.48 ppm. MALDI-TOF: m/z calcd. for
FULL PAPER
Fabrication and Characterization of OLEDs: Alq3-based green
OLED devices using GnC, TPD and NPB as HTL with con-
+
C
19
H
13
I
2
NO
,6-Bis(carbazol-NЈ-yl)-N-dodecylcarbazole (5): A mixture of 2
2.00 g, 4.04 mmol), 1 (1.49 g, 8.89 mmol), CuI (0.38 g, 2.02 mmol),
PO (2.14 g, 10.10 mmol), and (Ϯ)-trans-1,2-diaminocyclohex-
ane (0.23 g, 2.10 mmol) in toluene (50 mL) was stirred and heated
to reflux under N for 24 h. After cooling to room temperature,
water (30 mL) was added and the mixture was extracted with
CH Cl (2ϫ 40 mL). The combined organic phases were washed
with water (2ϫ 30 mL), brine (50 mL), dried with anhydrous
Na SO , filtered, and the solvents were removed to dryness. Purifi-
cation by column chromatography over silica gel (CH Cl /hexane,
:4) followed by recrystallization (CH Cl /methanol) afforded the
product (2.18 g, 81%) as a colorless solid (m.p. 232 °C). H NMR
300 MHz, CDCl ): δ = 8.26 (s, 2 H), 8.21 (d, J = 7.80 Hz, 4 H),
.68 (s, 4 H), 7.47–7.41 (m, 8 H), 7.36–7.28 (m, 4 H), 4.49 (t, J =
.20 Hz, 2 H), 2.06 (t, J = 6.90 Hz, 2 H), 1.56–1.33 (m, 18 H), 0.93
2
S [M ] 572.875; found 572.280.
figuration
of
ITO/PEDOT:PSS/HTL(40 nm)/Alq3(50 nm)/
3
(
LiF(0.5 nm):Al(150 nm) were fabricated and characterized as fol-
lowed. Patterned indium tin oxide (ITO) glass substrate with a
sheet resistance 14 ohm sq–1 (purchased from Kintec Company)
was thoroughly cleaned by successive ultrasonic treatment in deter-
gent, deionized water, 2-propanol, and acetone, and then dried at
K
3
4
2
60 °C in a vacuum oven. A 50 nm thick PEDOT:PSS hole injection
2
2
layer was spin-coated on top of ITO from a 0.75 wt.-% dispersion
in water at a spin speed of 3000 rpm for 20 s and dried at 200 °C
for 15 min under vacuum. Thin films of GnC layers as THL were
2
4
2
2
3
cast on top of the PEDOT:PSS layer by spin-coating a CHCl /
1
2
2
toluene solution of GnC (1.5% w/v) at a spin speed of 3000 rpm
for 30 second to obtain a 40 nm thick layer. The film thickness was
measured by using a Tencor α-Step 500 surface profiler. Alq3 was
then deposited onto the surface of the HTL film as light-emitting
1
(
3
7
7
(EML) and electron-transporting layer (ETL) with a thickness of
1
3
(
t, J = 6.30 Hz, 3 H) ppm. C NMR (300 MHz, CDCl
3
): δ =
41.91, 129.35, 125.98, 125.87, 123.15, 120.29, 119.86, 110.13,
09.77, 43.15, 31.94, 29.67, 29.61, 29.51, 29.38, 29.21, 27.46, 22.86,
50 nm by evaporation from resistively heated alumina crucibles at
1
1
1
–
1
an evaporation rate of 0.5–1.0 nm s by vacuum evaporator depo-
sition (ES280, ANS Technology) under a base pressure of ca.
+
47 3
4.29 ppm. MALDI-TOF: m/z calcd. for C48H N [M ] 665.377;
–5
1
0 mbar. The film thickness was monitored and recorded with a
found 665.412.
quartz oscillator thickness meter (TM-350, MAXTEK). The cham-
ber was vented with dry air to load the cathode materials and
pumped back; a 0.5 nm thick LiF and a 150 nm thick aluminum
layer were subsequently deposited through a shadow mask on the
top of EML film without braking vacuum, to from active diode
3,6-Bis(3Ј,6Ј-dibromocarbazol-NЈ-yl)-N-dodecylcarbazole (6): To a
stirred solution of 5 (1.00 g, 1.50 mmol) in THF (60 mL) in the
dark, was added NBS (1.10 g, 6.16 mmol) in small portions. The
mixture was stirred at room temperature for 5 h, then water
2
areas of 4 mm . The measurement of device efficiency was per-
(15 mL) was added and the mixture was extracted with CH
(2ϫ 30 mL). The combined organic phases were dried with anhy-
drous Na SO , filtered, and the solvent was removed in vacuo to
dryness. Purification by column chromatography over silica gel
(CH Cl /hexane, 1:3) followed by recrystallization (CH Cl /meth-
anol) gave the product (1.45 g, 99%) as a white solid (m.p. 150 °C).
2 2
Cl
formed according to M. E. Thomson’s protocol and the external
quantum efficiencies of the device was calculated by using a pre-
2
4
viously reported procedure.[
26]
Current density-voltage-lumines-
cence (J-V-L) characteristics were measured simultaneous by the
use of a Keithley 2400 source meter and a Newport 1835C power
meter equipped with a Newport 818-UV/CM calibrated silicon
photodiode. The EL spectra were acquired by an Ocean Optics
USB4000 multichannel spectrometer. All the measurements were
performed under ambient atmosphere at room temperature.
2
2
2
2
1
3
H NMR (300 MHz, CDCl ): δ = 8.21 (s, 4 H), 8.16 (s, 2 H), 7.68
(d, J = 8.70 Hz, 2 H), 7.57 (d, J = 8.70 Hz, 2 H), 7.48 (d, J =
8.55 Hz, 4 H), 7.22 (d, J = 8.70 Hz, 4 H), 4.49 (t, J = 7.20 Hz, 2
H), 2.04 (t, J = 6.90 Hz, 2 H), 1.57–1.27 (m, 18 H), 0.87 (t, J =
1
3
6
3
.30 Hz, 3 H) ppm. C NMR (300 MHz, CDCl ): δ = 140.82,
3
5
5
,6-Diiodo-N-tosylcarbazole (3):
9.80 mmol), KI (25.80 g, 77.75 mmol), and KIO
A
mixture of
1
(20.0 g,
(25.58 g,
140.45, 129.33, 128.46, 126. 61, 125.78, 123.32, 123.21, 119.72,
112.85, 111.48, 110.45, 43.78, 31.92, 29.64, 29.58, 29.46, 29.35,
29.17, 27.41, 22.69, 14.12 ppm. MALDI-TOF: m/z calcd. for
3
9.81 mmol) in acetic acid (334 mL) was stirred and heated to re-
for 30 min. After cooling to room temperature, the
reaction mixture was poured into water and extracted with CH Cl
3ϫ 150 mL). The combined organic phases were washed with
water (2ϫ 150 mL), brine (100 mL), dried with anhydrous Na SO
filtered, and the solvent was remove in vacuo to dryness. The resi-
due was purified by recrystallization with a mixture of CH Cl and
+
flux under N
2
C H Br N [M ] 977.019; found 977.107.
4
8
43
4
3
2
2
3,6-Bis(3Ј,6Ј-di-tert-butylcarbazol-NЈ-yl)-N-tosylcarbazole
(7):
(
Compound 7 (4.77 g, 78%) was synthesized from 3 and 4 in a man-
ner similar to that for 5 and obtained as a white solid (m.p. 222–
2
4
,
2
1
8
24 °C). FTIR (KBr): ν˜ = 2949, 1614, 1453, 1374 (S=O), 1362,
2
2
325, 1295, 1261, 1235, 1179, 1169 (S=O), 1132, 1092, 1033, 973,
hexane to give 3,6-diiodocarbazole (23.04 g, 92%) as a white pow-
der. To a solution of 3,6-diiodocarbazole (10.0 g, 23.87 mmol) and
KOH (6.11 g, 109.15 mmol) in acetone (150 mL) under an N
–
1 1
3
75, 807, 740 cm . H NMR (300 MHz, CDCl ): δ = 1.48 (s, 36
H), 2.42 (s, 3 H), 7.28–7.37 (m, 6 H), 7.47 (dd, J = 9.0, 1.5 Hz, 4
H), 7.76 (dd, J = 9.0, 1.8 Hz, 2 H), 7.94 (d, J = 8.1 Hz, 2 H), 8.07
2
at-
mosphere was added slowly p-toluenesulfonylchloride (20.07 g,
(
(
3
1
1
8
d, J = 1.8 Hz, 2 H), 8.16 (s, 2 H), 8.17 (s, 2 H), 8.58 (s, 1 H), 8.61
1
1
09.15 mmol). The reaction mixture was then heated at reflux for
5 min, then the reaction solution was poured into water (100 mL)
1
3
s, 1 H) ppm. C NMR (300 MHz, CDCl
3
): δ = 21.70, 32.04,
2.08, 34.77, 109.01, 109.14, 116.20, 116.34, 118.53, 123.43, 123.57,
23.73, 126.79, 127.13, 130.10, 134.58, 135.06, 137.41, 139.55,
and extracted with CH
phases were washed with water (2ϫ 100 mL), brine (100 mL), dried
with anhydrous Na SO , filtered, and the solvent was remove in
vacuo to dryness. Purification by recrystallization (CH Cl /hexane)
2 2
Cl (3ϫ 100 mL). The combined organic
+
61 3 2
45.51 ppm. MALDI-TOF: m/z calcd. for C59H N O S [M ]
2
4
75.448; found 874.919.
2
2
gave the product (12.31 g, 90%) as a yellow solid (m.p. Ͼ 250 °C).
FTIR (KBr): ν˜ = 2958, 1594, 1465, 1423, 1362 (S=O), 1207, 1188,
3,6-Bis(3Ј,6Ј-di-tert-butylcarbazol-NЈ-yl)carbazole (8): A mixture of
7 (1.0 g, 1.14 mmol), KOH (0.13 g, 2.32 mmol), DMSO (6 mL),
–1
1
1
169 (S=O), 1130, 1090, 1020, 967, 819, 711 cm . H NMR THF (12 mL) and water (2 mL) was stirred and heated at reflux
300 MHz, CDCl ): δ = 2.30 (s, 3 H), 7.15 (d, J = 8.4 Hz, 2 H), under an N atmosphere for 25 min. After cooling to room tem-
.66 (d, J = 8.4 Hz, 2 H), 7.79 (dd, J = 9, 1.5 Hz, 2 H), 8.09 (d, J
9 Hz, 2 H), 8.17 (s, 2 H) ppm. 13C NMR (300 MHz, CDCl
): δ =
(
3
2
7
perature, 10% HCl (20 mL) was added followed by water (10 mL)
and methanol (5 mL). The precipitate was collected by filtration
=
3
21.55, 32.02, 87.96, 116.97, 126.46, 127.17, 129.15, 129.90, 134.45, and washed with water several times followed by recrystallization
8
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Job/Unit: O30757
/KAP1
Date: 22-08-13 16:33:46
Pages: 11
Carbazole Dendrimers for Electroluminescent Devices
(
CH
2
Cl
2
/methanol) to give the product (0.78 g, 95%) as a white
123.91, 123.77, 123.53, 123.10, 120.08, 119.41, 116.18, 111.69,
111.05, 109.09, 34.70, 32.03, 31.92, 30.92, 29.66, 29.55, 29.36,
solid (m.p. 246–248 °C). FTIR (KBr): ν˜ = 3450 (NH), 2958, 1627,
–
1 1
1
363, 1325, 1292, 1262, 1236, 1168, 1033, 875, 809, 741 cm . H
NMR (300 MHz, CDCl ): δ = 1.48 (s, 36 H), 7.33 (d, J = 8.4 Hz,
H), 7.47 (d, J = 8.4 Hz, 4 H), 7.59 (d, J = 6.9 Hz, 4 H), 8.18 (s,
H), 8.45 (s, 1 H) ppm. 13C NMR (300 MHz, CDCl
): δ = 30.93,
27.53, 22.39, 14.12 ppm. MALDI-TOF: m/z calcd. for C256
[MH ] 3544.081; found 3544.091.
H
260
N
15
+
3
4
6
3
1
Supporting Information (see footnote on the first page of this arti-
3
cle): Quantum chemical calculation results, AFM images, OLED
2.06, 34.74, 109.14, 111.89, 116.19, 119.40, 123.09, 123.56, 124.09,
25.93, 130.44, 139.04, 140.22, 142.53 ppm. MALDI-TOF: m/z
1
13
device data, and H and C NMR spectra.
+
calcd. for C52
H
55
N
3
[M ] 721.439; found 720.876.
Acknowledgments
3
,6-Di-tert-butyl-N-dodecylcarbazole (G1C): To a stirred ice-cooled
solution of 4 (0.50 g, 1.79 mmol) in N,N-dimethylformamide
15 mL) was added sodium hydride (0.10 g, 4.47 mmol) followed by
-bromododecane (0.62 g, 2.51 mmol). The reaction mixture was
stirred at 70 °C for 24 h. After cooling to room temperature, water
This work was supported by the Thailand Research Fund (grant
number DBG5580001). The authors acknowledge scholarship sup-
port from the Center of Excellence for Innovation in Chemistry
(
1
(
PERCH-CIC), Thailand and the Science Achievement Scholarship
(30 mL) was added and the mixture was extracted with CH
2 2
Cl
of Thailand (SAST).
(2ϫ 30 mL). The combined organic phases were washed with dilute
HCl (2ϫ 30 mL), water (30 mL), and brine (30 mL), dried with
anhydrous Na SO , filtered, and the solvents were removed to dry-
2
4
[
1] a) B. W. D’Andrade, S. R. Forrest, Adv. Mater. 2004, 16, 1585–
ness. Purification by column chromatography over silica gel (hex-
11595; b) M. C. Gather, A. Köhnen, A. Falcou, H. Becker, K.
1
ane) gave the product (0.80 g, 92%) as a pale-yellow oil. H NMR
Meerholz, Adv. Funct. Mater. 2007, 17, 191–200; c) C.-C. Wu,
C.-W. Chen, C.-L. Lin, C.-J. Yang, J. Disp. Technol. 2005, 1,
248–266; d) F. So, J. Kido, P. Burrows, MRS Bull. 2008, 33,
(
300 MHz, CDCl
3
): δ = 8.39 (s, 2 H), 7.74 (d, J = 8.70 Hz, 2 H),
.51 (d, J = 8.20 Hz, 2 H), 4.41 (t, J = 7.20 Hz, 2 H), 2.06 (t, J =
.90 Hz, 2 H), 1.28–1.51 (m, 18 H), 0.91 (t, J = 6.90 Hz, 3 H) ppm.
7
6
663–669.
1
3
[2] a) T. W. Kelley, P. F. Baude, C. Gerlach, D. E. Ender, D. Mu-
3
C NMR (300 MHz, CDCl ): δ = 141.55, 139.25, 123.40, 122.97,
yres, M. A. Haase, D. E. Vogel, S. D. Theiss, Chem. Mater.
1
2
16.44, 108.25, 43.31, 34.31, 34.86, 32.35, 32.20, 29.88, 29.76,
2
004, 16, 4413–4422; b) A. Thangthong, D. Meunmart, N. Pra-
9.70, 29.62, 29.36, 27.57, 22.97, 14.40 ppm. MALDI-TOF: m/z
chumrak, S. Jungsuttiwong, T. Keawin, T. Sudyoadsuk, V. Pro-
marak, Chem. Commun. 2011, 47, 7122–7124.
+
calcd. for C32
H
50N [MH ] 448.394; found 448.391.
[
[
[
3] C. W. Tang, S. A. VanSlyke, Appl. Phys. Lett. 1987, 51, 913–
3
(
,6-Bis(3Ј,6Ј-di-tert-butylcarbazol-NЈ-yl)-N-dodecylcarbazole
G2C): Synthesized from 2 and 4 in a manner similar to that for 5
and obtained as a white solid, yield 0.30 g (77%); m.p. 166–167 °C.
915.
4] H. Aziz, Z. D. Popovic, N.-X. Hu, A.-M. Hor, G. Xu, Science
1999, 283, 1900–1902.
1
H NMR (300 MHz, CDCl
3
): δ = 8.20 (s, 2 H), 8.18 (s, 2 H), 7.65
5] a) V. Promarak, M. Ichikawa, T. Sudyoadsuk, S. Saengsuwan,
(s, 4 H), 7.46 (d, J = 8.40 Hz, 4 H), 7.33 (d, J = 8.70 Hz, 4 H),
S. Jungsuttiwong, T. Keawin, Thin Solid Films 2008, 516, 2881–
4
1
.48 (t, J = 7.20 Hz, 2 H), 2.06 (t, J = 6.90 Hz, 2 H), 1.29–1.56 (m,
8 H), 0.89 (t, J = 6.90 Hz, 3 H) ppm. 1 C NMR (300 MHz,
;
b) A. Thaengthong, S. Saengsuwan, S. Jungsuttiwong, T. Kea-
3
win, T. Sudyoadsuk, V. Promarak, Tetrahedron Lett. 2011, 52,
4749–; c) V. Promarak, M. Ichikawa, T. Sudyoadsuk, S. Saeng-
suwan, S. Jungsuttiwong, T. Keawin, Synth. Met. 2007, 157,
CDCl
3
): δ = 142.46, 140.29, 139.98, 129.83, 125.69, 123.51, 123.40,
23.07, 119.45, 116.17, 109.93, 109.14, 43.71, 34.73, 32.06, 31.93,
9.67, 29.65, 29.59, 29.48, 29.37, 29.21, 27.45, 22.70, 14.12 ppm.
1
2
1
7–22; d) J. Lu, P. F. Xia, P. K. Lo, Y. Tao, M. S. Wong, Chem.
+
Mater. 2006, 18, 6194–6203.
MALDI-TOF: m/z calcd. for C64
80 3
H N [MH ] 890.635; found
[
6] M. Nomura, Y. Shibasaki, M. Ueda, K. Tugita, M. Ichikawa,
890.646.
Y. Taniguchi, Synth. Met. 2005, 148, 155–160.
3
,6-Bis[3Ј,6Ј-bis(3ЈЈ,6ЈЈ-di-tert-butylcarbazol-NЈЈ-yl)carbazol-NЈ-
[7] B. Wei, J.-Z. Liu, Y. Zhang, J.-H. Zhang, H.-N. Peng, H.-L.
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yl]-N-dodecylcarbazole (G3C): Synthesized from 2 and 8 in a man-
2458.
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1
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71%); m.p. Ͼ 250 °C. H NMR (300 MHz, CDCl
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H), 8.28 (s, 2 H), 8.16 (s, 8 H), 7.85 (q, 4 H), 7.61 (s, 8 H), 7.56 (d,
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6
1
1
3
1
1
H), 2.14 (t, J = 6.90 Hz, 2 H), 1.28–1.57 (m, 18 H), 0.87 (t, J =
.90 Hz, 3 H) ppm. 13C NMR (300 MHz, CDCl
): δ = 142.51,
3
41.46, 140.22, 130.67, 128.98, 125.97, 123.72, 123.61, 123.53,
23.10, 120.08, 119.37, 116.18, 111.10, 110.54, 109.11, 43.90, 34.71,
2.04, 31.90, 30.89, 29.64, 29.60, 29.50, 29.34, 29.25, 27.48, 22.67,
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140
N
7
[MH ]
775.117; found 1775.182.
2012, 48, 3382–3384.
3
,6-Bis{3Ј,6Ј-bis[3ЈЈ,6ЈЈ-bis(3ЈЈЈ,6ЈЈЈ-di-tert-butylcarbazol-NЈЈЈ-yl)- [10] a) T. Qin, W. Wiedemair, S. Nau, R. Trattnig, S. Sax, S. Wink-
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300 MHz, CDCl
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.15 (s, 16 H), 7.69 (d, J = 2.40 Hz, 8 H), 7.81 (q, 8 H), 7.62 (q,
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Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
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/KAP1
Date: 22-08-13 16:33:46
Pages: 11
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Received: May 23, 2013
Published Online: ᭿
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Eur. J. Org. Chem. 0000, 0–0

Job/Unit: O30757
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Date: 22-08-13 16:33:46
Pages: 11
Carbazole Dendrimers for Electroluminescent Devices
Dendrimers
N. Prachumrak, S. Pansay,
S. Namuangruk, T. Kaewin,
S. Jungsuttiwong, T. Sudyoadsuk,
V. Promarak* .................................. 1–11
Synthesis and Characterization of Carb-
azole Dendrimers as Solution-Processed
g
High T Amorphous Hole-Transporting
Materials for Electroluminescent Devices
Keywords: Dendrimers
/ Thin films /
Glasses / Solid-state structures / Organic
light-emitting diodes
Carbazole dendrimers have high glass tran-
sition temperatures and have amorphous
and stable electrochemical properties. Their
abilities to act as solution-processed hole-
transporting layers in Alq3-based green
OLEDs are superior to common hole-
transporters such as NBP and TPD.
Eur. J. Org. Chem. 0000, 0–0
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjoc.org
11