Stilbene like carbazole dimer-based electroluminescent materials

Article abstract of DOI:10.1016/j.tet.2006.06.067

Two carbazole dimers (1 and 10) were synthesized from 9-ethyl-9H-carbazole-3-carbaldehyde and 6-bromo-9-ethyl-9H-carbazole-3-carbaldehyde by McMurry C-C coupling reaction. Palladium(0)-catalyzed C-N coupling reactions of 10 and various diarylamines result in the formation of stable carbazole derivatives in good yields. These compounds are fluorescent in blue to yellow region with moderate to good quantum yields. Also, they are thermally stable and capable of hole-transporting due to the presence of the carbazole moieties. The electroluminescent devices fabricated using 1, 2, and 3 as hole-transporters/emitters with a bilayer structure ITO/Cpd/TPBI or Alq₃/LiF/Al (Cpd=1, 2, and 3) exhibit good performance (e.g., η_ext=1.0-2.1%; η_p=0.9-1.9 lm/W; η_c=2.4-4.8 cd/A at a current density of 100 mA/cm²).

Full text of DOI:10.1016/j.tet.2006.06.067

Tetrahedron 62 (2006) 8564–8570
Stilbene like carbazole dimer-based electroluminescent materials
a,b
Chih-Hsin Chen, Jiann T. Lin and Ming-Chang P. Yeh
a,*
b,*
a
Institute of Chemistry, Academia Sinica, 128 Sec. 2, Academia Rd, Nankang, Taipei 115, Taiwan
Department of Chemistry, National Taiwan Normal University, 88 Sec. 4, Ting-Chow Rd, Taipei 116, Taiwan
b
Received 9 May 2006; revised 13 June 2006; accepted 19 June 2006
Available online 7 July 2006
Abstract—Two carbazole dimers (1 and 10) were synthesized from 9-ethyl-9H-carbazole-3-carbaldehyde and 6-bromo-9-ethyl-9H-carba-
zole-3-carbaldehyde by McMurry C–C coupling reaction. Palladium(0)-catalyzed C–N coupling reactions of 10 and various diarylamines
result in the formation of stable carbazole derivatives in good yields. These compounds are fluorescent in blue to yellow region with moderate
to good quantum yields. Also, they are thermally stable and capable of hole-transporting due to the presence of the carbazole moieties. The
electroluminescent devices fabricated using 1, 2, and 3 as hole-transporters/emitters with a bilayer structure ITO/Cpd/TPBI or Alq /LiF/Al
3
2
(
Cpd¼1, 2, and 3) exhibit good performance (e.g., hext¼1.0–2.1%; h
p
¼0.9–1.9 lm/W; h
c
¼2.4–4.8 cd/A at a current density of 100 mA/cm ).
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
peripheral arylamines. These materials were found to be
green or blue emitting and capable of hole-transporting. In
4
Considerable progress has been made on organic light emit-
ting diodes (OLEDs) since the seminal report by Tang et al.,
on the device with a double-layer structure. Now OLEDs
this report, we further integrated two carbazole moieties by
McMurry C–C coupling reaction. For the sake of tuning
the emission color in visible light region or altering energy
level to adjust the ability of hole injection, the stilbene like
carbazole dimer was followed by encapsulation with aryl-
1
have become visible in consumer electronics such as car
stereos, mobile phones, and digital cameras. Appropriate
choosing of the electron- and hole-transporting materials is
necessary in order to have high performance small mole-
1
1,12
amines. Although, the stilbene-containing materials
and
1
3
oligomericcarbazolylcompounds werereportedforelectro-
luminescent applications, to our knowledge, no stilbene like
carbazole dimer-based electroluminescent materials have
been reported so far. Double-layer EL devices using these
compounds as hole-transporting layer and emitting layer
2
3
cules or polymeric OLEDs. The durability of the devices,
which depends on the thermal and morphological stability of
the organic films, is also a key factor in affecting the device
performances. We have been interested in the development
of new materials for OLED application. We found that
carbazolyl unit is beneficial to raise both glass transition
temperature and thermal stability of luminescent chromo-
1
4
and Alq [tris(8-quinolinolato)aluminum] or TPBI [1,3,5-
3
1
5
tris(N-phenyl-benzimidazol-2-yl)benzene] as electron-
transporting layer were fabricated by vacuum deposition.
4
phores. Further, it is relatively easy to functionalize the
carbazolyl moiety at the 3-, 6-, or 9-positions for tuning its
physical properties. A variety of carbazole derivatives, in-
cluding small molecules, dendrimers, or polymers, which
2
. Results and discussion
4
5
6
7
8
9
served as hosts, dopants, hole-transporters, or emitters
The compounds for electroluminescent study are depicted in
Figure 1. Scheme 1 illustrates the synthesis of these new
compounds. 9-Ethyl-9H-carbazole-3-carbaldehyde (8) was
obtained starting from ethylation of carbazole followed
1
0
with a wide color range, have been reported. Recent devel-
opments in carbazole derivatives and their application as
advanced amorphous materials for photorefractive systems,
organic light emitting diodes as well as other optoelectronic
by treating the resulting 9-ethyl-9H-carbazole with POCl
3
1
1
1
6
devices are investigated. Earlier we synthesized a series of
compounds containing a carbazolyl core encapsulated with
in DMF via Vilsmeier–Haack reaction in 65% yield.
Compound 8 was further treated with NBS (N-bromosucci-
nimide) to give 6-bromo-9-ethyl-9H-carbazole-3-carbalde-
hyde (9), which reacted with titanium(IV) chloride and
zinc powder to afford 10 in good yield (85%). Finally, palla-
dium-catalyzed coupling reactions of 10 with arylamines
using Pd(OAc) /P(t-Bu) as the catalyst and t-BuONa as
the base resulted in efficient C–N bond formation to give
Keywords: Carbazole dimmer; Electroluminescent; McMurry C–C coupling
reaction.
17
*
Corresponding authors. Tel.: +886 2 27898522; fax: +886 2 27831237
J.T.L.); tel.: +886 2 29320204; fax: +886 2 29341742 (M.-C.P.Y.);
e-mail addresses: jtlin@chem.sinica.edu.tw; cheyeh@scc.ntnu.edu.tw
(
2
3
0
040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.067

C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
8565
N
N
N
N
N
N
N
N
N
N
N
N
N
N
1
2
3
4
N
N
N
OMe
N
N
N
N
N
N
MeO
N
N
N
5
6
7
Figure 1. Structure of the compounds.
N
CHO
EtBr, 50% aq. NaOH
POCl3
TiCl , Zn
4
BTEAC, benzene
rt, 2h
DMF
80 °C, 16h
THF
N
H
N
N
reflux, 4h
N
1
8
NBS
DMF
rt, 16h
N
N
Ar2
N
Ar1Ar2NH
Br
CHO
Br
Br
N
Ar2
Ar1
TiCl , Zn
Pd(OAc)2, (t-Bu)3P
Ar1
4
t-BuONa
toluene
reflux, 16h
THF
reflux, 4h
N
N
N
9
10
2-7
Scheme 1.
diaminocarbazole dimers 2–7. It must be mentioned that the
ꢀ
purified by flash column chromatography. Compounds 1–7
1
13
reactions readily occurred at lower temperature (ca. 80 C)
were fully characterized by H and C NMR spectros-
copies, mass spectroscopy, and elementary analyses. The
thermal properties of the compounds were determined by
DSC (differential scanning calorimetry) and TGA (thermo-
gravimetric analysis) measurements (Table 1). All the com-
pounds except 5 and 7 are crystalline. No crystallization and
to form both Z- and E-isomers. However, higher reaction
temperature (reflux in toluene) gave predominantly E-form
in 65 to 80% yields. All the target products were soluble
in common organic solvents such as CH Cl , CHCl , or
2
2
3
THF so that all these diaminocarbazole dimers can be easily
Table 1. Physical properties of the compounds
a
a
b
, %)
c
b
, %)
d
e
,
ꢀ
f
), mV
Compd
l
abs, nm
l
em, nm (F
f
l
em, nm (F
f
l
em, nm
T /T
m d
C
Eox (DE
p
HOMO, eV
LUMO, eV
1
2
3
4
5
6
7
308, 342
294, 344
309, 346
310, 347
306, 344
321, 356
334, 361
411 (40)
416 (45)
434 (18)
441 (20)
507 (9)
407 (44)
412 (49)
422 (10)
421 (8)
454 (8)
503 (33)
516 (35)
447
451
463
468
472
523
545
218/268
335/403
284/349
207/370
na/382
245 (92), 555 (82)
370 (55), 676 (i)
201 (120), 755 (i)
190 (68), 764 (i)
198 (142), 769 (i)
192 (144), 690 (i)
107 (114), 601 (i)
5.05
5.17
5.00
4.99
5.00
4.99
4.91
2.05
2.17
2.05
2.04
2.07
2.33
2.34
549 (16)
560 (20)
295/403
na/468
Oxidation potential reported is adjusted to the potential of ferrocene (E1/2¼245 mV vs Ag/AgNO
cyclic voltammetric measurements: glassy carbon working electrode; Ag/AgNO reference electrode. Scan rate: 100 mV/s. Electrolyte: tetrabutylammonium
hexafluorophosphate; i, irreversible process. HOMO calculated from CV potentials using ferrocene as standard [HOMO¼4.8+(EoxꢁEFc)]. LUMO derived from
the relationship E was obtained from optical spectroscopy; na: not available.
, HOMOꢁLUMO, where E
Recorded in dichloromethane solutions.
3
), which was used as an internal reference. Conditions of
3
g
g
a
b
Quantum yield was measured with reference to Coumarin 1 (99%) in ethyl acetate. Refractive index change due to the use of different solvent correction was
applied in the calculation.
Recorded in toluene solutions.
Film samples.
Decomposition temperature (T
Recorded in dichloromethane solutions.
c
d
e
f
d
) corresponds to the 5% weight loss.

8566
C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
melting were noticed for these compounds after fast cooling
of the melt. However, no glass transition can be detected.
The thermal decomposition temperatures of these com-
pounds range from 268 to 468 C. Introduction of aryl-
amines into the central carbazole dimer greatly enhanced
noncoplanarity between the carbazolyl moiety and central
core. All other compounds, 3–7, have better conjugation
between the periphery arylamines and the central core, and
exhibit longer lem. No solvatochromic effect in the absorp-
tion spectra was observed. However, there is significant di-
polar character in the excited state of the compounds 5–7
in view of the large positive solvatochromic effect in more
polar solvent (l (CH Cl )ꢁlem(toluene)>45 nm).
ꢀ
the decomposition temperature (T ) of the materials. This
d
effect is prominent when the carbazole (2) or pyrenyl amine
0
(
6 and 7) is introduced at 3- and 3 -positions.
em
2
2
The photophysical properties of the carbazole dimer deriva-
tives were examined by UV–vis and fluorescence spectros-
copies in both dichloromethane and toluene solutions. The
absorption and emission spectra of the compounds in di-
chloromethane were shown in Figure 2. In general, each of
these compounds has absorption at w350 nm, which was
assigned to p–p* transition of the carbazole dimer core.
In addition, there exist localized p–p* transition due to
end-capping arylamines such as carbazole, diphenylamine,
N-phenylnaphthalen-1-amine, or N-phenylpyren-1-amine.
Compounds 6 and 7, which have pyrene moieties display
an extra band at the longer wavelength due to pyrenyl amine.
These compounds emit blue to yellow light with emission
maxima ranging from 416 to 560 nm in dichloromethane so-
lution. The emission of 2 is almost identical to the emission
of the central carbazole dimer (compound 1), possibly due to
the weak donating ability of the carbazolyl moiety and the
From cyclic voltammetric measurements and square wave
voltammetric methods, the electrochemical properties of
the compounds were studied and the redox potentials of
the compounds are compiled in Table 1. Compound 1
exhibits two reversible one-electron redox waves, which
indicates that there exist some electronic communications
between the two carbazole moieties and cause them to be
oxidized individually. In addition, compounds 2–7, in
which the carbazole dimer was incorporated with arylamines,
exhibit two reversible one-electron redox waves, which are
barely resolvable and an irreversible two-electron wave
due to the oxidation of the peripheral diarylamines and the
central carbazole dimer (Table 1 and Fig. 3), respectively.
The first oxidation potential decreases (2>3>5>4>6>7) in
accordance with the electron donating ability of the sub-
stituent at the nitrogen atoms of the peripheral amines.
Lack of electronic communication between the two
1
8
(a)
0
0
0
0
0
0
0
0
0
0
0
.20
.18
.16
.14
.12
.10
.08
.06
.04
.02
.00
1
(
a)
1
2
3
4
5
6
7
0
-5
Fc
0
-
10
20
30
40
50
-10
-15
Fc
-
-
-
-
2
00
400
600
Potential, mV vs Ag/AgNO
800
1000
-
20
2
00
400
Potential, mV vs Ag/AgNO3
600
800
1000
2
50
300
350
400
Wavelength, nm
450
500
550
(b)
6
(b)
1.0
0.8
0.6
0.4
0.2
0.0
1
0
2
3
4
5
6
7
-20
0
-10
-20
-30
-
40
60
-40
Fc
-50
-60
-70
-80
2
00
400
600
800 1000 1200
Potential, mV vs Ag/AgNO
-
2
00
400
Potential, mV vs Ag/AgNO3
600
800
1000
350
400
450
500
550
Wavelength, nm
600
650
700
750
Figure 3. Cyclic voltammograms of (a) 1 and (b) 6 recorded in CH
2 2
Cl
Figure 2. (a) Absorption and (b) emission spectra of compounds 1–7 in
CH Cl . The excitation wavelength in emission spectra is 345 nm.
(scan rate 100 mV/s). Inset: different pulse voltammograms in the oxidiza-
tion region.
2
2

C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
8567
peripheral amines in these compounds is in contrast to the
,6-diarylamine substituted carbazoles (carb) we reported
earlier, and can be attributed to the longer distance between
1
.0
3
1/TPBI
1/Alq3
4
the two peripheral amines. In carb compounds, the two
0.8
2/TPBI
peripheral amines are electronically communicated and two
one-electron oxidation waves are observed. The first
oxidation potential of the carb compounds is, therefore,
more cathodic than that of the compounds in this study.
2
/Alq3
/TPBI
/Alq3
0
0
.6
.4
3
3
Double-layer EL devices using compounds 1, 2, and 3 as the
hole-transporting (HTL) as well as emitting layer and TPBI
0.2
0.0
(
or Alq (tris(8-quinolinolato)aluminum) (device II) as elec-
1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene) (device I)
3
tron-transporting layer (ETL) were fabricated with the struc-
ture: ITO/Cpd (40 nm)/TPBI or Alq (40 nm)/LiF (1 nm)/Al
400
450
500
550
600
Wavelength, nm
650
700
750
3
(
200 nm) (Cpd¼1, 2, or 3). Relative energy alignment of the
Figure 5. EL curves for device I and device II containing 1, 2, and 3.
constituents is shown in Figure 4 and the device performance
parameters are collected in Table 2. Device I containing
compounds 1 and 2 emitted blue light characteristic of the
carbazole dimer derivatives while the device containing 3
emitted greenish blue light, which possibly resulted from
the exciplex generated at the interface between the com-
pound and TPBI layer. The electroluminescent (EL) spectra
were shown in Figure 5. Such an outcome may be due to the
higher hole mobility of 3 than 1 or 2, which facilitated the
configuration ITO/3 (60 nm)/TPBI (20 nm)/LiF (1 nm)/Al
(200 nm) was fabricated. The thicker HTL and thinner
ETL led to better balance of electrons and holes in the device
III. Consequently, the EL spectrum of the device III
matched with the film spectrum of 3 at an operating voltage
of 6 V (Fig. 6). As the applied voltage increased, more holes
reached the interface of HTL and ETL and more exciplexes
were generated (Inset of Fig. 6). At a voltage of 12 V, the EL
spectrum was nearly superimposable with that of the device
I operated at 6 V. Such an explanation was further supported
by the similar emission spectrum between device I and
a mixed film of TPBI and 3, where the exciplex of them
should surely generate. Device II containing 1, 2, or 3 emit-
1
9
carrier recombination to occur between the two layers.
In order to verify this argument, device III of the
2
.05
.17
2.05
2.17
2
2
.7
ted green light from Alq . We believe that the HOMO energy
3
gap (DE¼1.03ꢁ1.20 eV) between HTL and ETL in the de-
vice I is sufficiently large to effectively block the injection of
holes from the Cpd layer to the TPBI layer. In contrast, the
smaller HOMO energy gap (DE¼1.00–0.83 eV) between
HTL and ETL allowed easier injection of holes from Cpd
3
.3
1
~3
1~3
Al
Al
ITO
TPBI
ITO
4.3
Alq3 4.3
4
.7
4.7
into the Alq layer in the device II. This result is consistent
3
5.00
5.00
5.17
with our previous studies in arylamine-containing carbazole
derivatives.
5.17
6.0
4
6.2
Device I
Device II
The current–voltage (I–V), luminance–current (L–I), and
current efficiency–current density curves of devices I and
II were shown in Figures 7–9. The relative low turn-on
Figure 4. Energy alignment of the constituents in device I and device II.
a
Table 2. Electroluminescence data for the devices I and II
1
TPBI/Alq
3
2 TPBI/Alq
3
3 TPBI/Alq
3
3
(60 nm)/TPBI (20 nm) at 6V
V
L
l
on, V
max, cd/m
em, nm
3.0/2.5
4.0/3.5
5533/28526
454/520
3.0/2.5
10817/24494
484/526
1.0
3 (60 nm)/TPBI (20 nm) at 12V
3 film
3 (40 nm)/TPBI (40 nm) at 6V
2
8703/36913
454/522
0.17, 0.19/0.30, 0.16, 0.15/0.30, 0.20, 0.31/0.32,
0.56
82/94
2.25/1.47
0
0
0
0
.8
.6
.4
.2
CIE (x, y)
1.0
0.8
0.6
0.4
0.2
0.0
0.54
74/96
0.56
92/98
6V
8
V
12V
fwhm, nm
h
h
h
ext,max, %
2.41/1.56
1.95/3.05
2.93/4.96
2334/4776
1.93/1.51
0.88/1.79
2.35/4.78
1.31/1.03
2.34/1.75
2.77/3.31
2549/3306
1.21/1.02
1.14/1.35
2.56/3.31
p,max, lm/W 1.92/2.91
c,max, cd/A
3.26/4.74
3100/4347
2.14/1.47
2
L, cd/m (*)
h
h
h
ext, % (*)
p
, lm/W (*) 1.31/1.88
, cd/A (*) 3.10/4.74
400
500
600
700
Wavelength (nm)
c
a
The measured values are given in the order of devices I and device II.
L
h
max, maximum luminance; L, luminance; Von, turn-on voltage; V, voltage;
ext,max, maximum external quantum efficiency; hp,max, maximum power
0.0
400
500
600
Wavelength, nm
700
800
efficiency; hc,max, maximum current efficiency; hext, external quantum ef-
ficiency; h , power efficiency; h , current efficiency; fwhm, full width at
half maximum; *, at a current density of 100 mA/cm . Von was obtained
from the x-intercept of log (luminance) versus applied voltage plot.
p
c
2
Figure 6. Comparison of EL and film PL curves for 3. Inset: EL spectra of
the device ITO/3 (60 nm)/TPBI (20 nm)/LiF/Al at 6, 8, and 12 V.

8568
C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
exhibit good performance at operating voltage (e.g.,
2
1
1
200
000
L¼2334–3100 cd/m ; h ¼1.2–2.1%; h ¼0.9–1.3 lm/W;
ext
p
2
1
/TPBI
h ¼2.4–3.1 cd/A at a current density of 100 mA/cm ). For
c
1
/Alq
3
green-emitting device II, the CIE coordinates (x, y) are
almost superimposable ((0.30, 0.56), (0.30, 0.54), and (0.32,
2
/TPBI
/Alq3
2
8
6
4
2
00
00
00
00
0
0.56) for 1, 2 and 3, respectively). The performance without
optimization appear to be approximately equal (e.g., L
3
/TPBI
¼
max
3/Alq3
2
2
3
4494–36913 cd/m ; h
.1 lm/W; hc, max¼3.3–5.0 cd/A) compared with the standard
¼1.0–1.6%; h
¼1.8–
ext, max
p, max
device of the structure ITO/a-NPD (40 nm)/Alq (40 nm)/
3
2
0
LiF (1 nm)/Al (150 nm) referred in previous literature.
3. Conclusions
0
2
4
6 8
Voltage, V
10
12
14
To summarize, we have prepared a series of stilbene like car-
bazolyl derivatives by incorporating diarylamines at the
peripheries of a carbazole dimer unit via McMurry C–C
coupling reaction followed by palladium(0)-catalyzed C–N
bond formation. The arylamine substituents significantly en-
hance the thermal stability of the carbazole dimer core. By
altering the peripheral amines, the emitted color of these ma-
terials can be tuned from blue to yellow with moderate to
good quantum yields. Double-layer devices using 1–3 as
hole-transporting and emitting layer were fabricated. These
devices exhibit very promising performance in blue or green
Figure 7. I–V curves for device I and device II containing compounds 1, 2,
and 3.
4
3
3
2
2
1
1
0000
5000
0000
5000
0000
5000
0000
1
/TPBI
1/Alq3
2
/TPBI
2
/Alq
3
3/TPBI
/Alq
3
region when TPBI and Alq were selected as electron-trans-
3
porting layers.
3
5000
4. Experimental
0
4
.1. General
0
2
4
6 8
Voltage, V
10
12
14
Unless otherwise specified, all the reactions were carried out
under nitrogen atmosphere using standard Schlenk tech-
niques. Solvents were dried by standard procedures. All
column chromatography was performed with the use of
silica gel (230–400 mesh, Macherey-Nagel GmbH & Co.)
Figure 8. L–V curves for device I and device II containing 1, 2, and 3.
6
5
5
4
4
3
3
2
2
1
1
0
0
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
.5
.0
1
/TPBI
1
1/Alq
as stationary phase. The H NMR spectra were recorded
3
on a Bruker AMX400 spectrometer. Electronic absorption
spectra were measured in toluene, dichloromethane, and
acetonitrile using a Cary 50 Probe UV–vis spectrophoto-
meter. Emission spectra were recorded by a Jasco FP-6500
fluorescence spectrometer. Emission quantum yields were
measured in various organic solvents by standard methods
with reference to Coumarin 1 in acetonitrile. Cyclic voltam-
metry experiments were performed with a CHI-621B elec-
trochemical analyzer. All measurements were carried out
at room temperature with a conventional three-electrode
configuration consisting of platinum working and auxiliary
2
/TPBI
2/Alq3
3
/TPBI
3/Alq3
electrodes and a nonaqueous Ag/AgNO reference elec-
3
0
200
400
600
800 1000 1200 1400 1600
2
a
c
trode. The E values were determined as 1/2(E +E ), where
1
/2
p
p
a
c
Current Density, mA/cm
E and E were the anodic and cathodic peak potentials, re-
spectively. The solvent in all experiments was CH Cl and
p
p
2
2
Figure 9. Current efficiency–current density curves for device I and device
II containing 1, 2, and 3.
the supporting electrolyte was 0.1 M tetrabutylammonium
perchlorate. DSC measurements were carried out using
a Perkin–Elmer 7 series thermal analyzer at a heating rate
ꢀ
and operating voltages in all devices I and II makes them
promising for better performances. For blue emitting
of 10 C/min. TGA measurements were performed on a Per-
kin–Elmer TGA7 thermal analyzer. FAB-mass spectra were
collected on a JMS-700 double focusing mass spectrometer
(JEOL, Tokyo, Japan) with a resolution of 8000 (5% valley
definition). For FAB-mass spectra, the source accelerating
ꢀ
device I, the Commission International de l’Eclairage
CIE) coordinates (x, y) of 1, 2, and 3 are located at (0.17,
.19), (0.16, 0.15), and (0.20, 0.31), respectively. They also
(
0

C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
8569
voltage was operated at 10 kV with a Xe gun, using 3-nitro-
benzyl alcohol as the matrix. Elementary analyses were
performed on a Perkin–Elmer 2400 CHN analyzer.
filtration and removal of the solvent, the crude product was
further purified by column chromatography on silica gel us-
ing dichloromethane/hexane¼1/4 as the eluant to yield 2 as
1
a pale yellow solid. Yield: 75%. H NMR (d, CDCl ): 1.52 (t,
3
4
.2. Synthesis
J¼3.6 Hz, 6H), 4.45 (q, J¼7.2 Hz, 4H), 7.25–7.29 (m, 4H),
7
.31 (s, 2H), 7.36–7.38 (m, 8H), 7.45 (d, J¼9.6 Hz, 2H),
6
-Bromo-9-ethyl-9H-carbazole-3-carbaldehyde (9) was
7.58 (dd, J¼9.5, 8.6 Hz, 4H), 7.74 (dd, J¼8.5, 1.6 Hz,
2H), 8.16 (d, J¼7.7 Hz, 4H), 8.21 (s, 2H), 8.25 (s, 2H).
2
1
synthesized by following literature procedures. (E)-1,2-
Bis(9-ethyl-9H-carbazol-3-yl)ethene (1) and (E)-1,2-bis(6-
bromo-9-ethyl-9H-carbazol-3-yl)ethene (10) were synthe-
sized by similar procedure. Only the preparation of 10 will
be described in detail.
1
3
C NMR (CDCl ): 141.9, 140.1, 139.4, 129.6, 129.0,
3
127.1, 125.8, 125.3, 125.0, 123.9, 123.1, 123.0, 120.3,
120.2, 119.7, 119.5, 119.4, 118.5, 110.5, 109.8, 109.5,
109.0, 38.0, 14.0. FABMS (m/z): 744.2 (M ). Anal. Calcd
+
for C H N : C, 87.07; H, 5.41; N, 7.52. Found: C, 86.80;
5
4 40 4
4.2.1. (E)-1,2-Bis(6-bromo-9-ethyl-9H-carbazol-3-yl)-
ethene (10). A mixture of 6-bromo-9-ethyl-9H-carbazole-
H, 5.29; N, 7.47.
0
diphenyl-9H-carbazol-3-amine) (3). Pale yellow solid.
3
6
-carbaldehyde (6.04 g, 20 mmol) and zinc powder (3.92 g,
0 mmol) in a 250 mL two-neck flask was added dry THF.
4.2.4. (E)-6,6 -(Ethene-1,2-diyl)bis(9-ethyl-N,N-
1
Titanium(IV) chloride (3.29 mL, 30 mmol) was added drop-
wise to the flask immersed in an ice bath. The ice bath was
removed after addition was complete, and the reaction mix-
ture was refluxed under nitrogen for 4 h. After being cooled,
the solution was added to ice water and extracted with
dichloromethane. The organic layer was collected, washed
with brine, and dried over anhydrous MgSO . After filtration
4
and removal of the solvent, the crude product was further re-
crystallized from CH Cl /hexane to give 1 as a pale yellow
Yield: 79%. H NMR (d, CDCl ): 1.47 (t, J¼3.6 Hz, 6H),
3
4.35 (q, J¼7.2 Hz, 4H), 6.95 (t, J¼6.8 Hz, 4H), 7.12 (d,
J¼7.9 Hz, 8H), 7.22 (d, J¼7.9 Hz, 8H), 7.25 (s, 2H),
7.29–7.38 (m, 6H), 7.65 (dd, J¼8.5, 1.6 Hz, 2H), 7.91 (s,
1
3
2H), 8.11 (s, 2H). C NMR (CDCl ): 148.7, 139.9, 139.6,
3
137.6, 129.2, 129.0, 126.8, 125.5, 124.6, 123.9, 123.0,
122.7, 121.5, 118.9, 118.3, 109.4, 108.7, 37.8, 14.0. FABMS
(m/z): 748.5 (M ). Anal. Calcd for C H N : C, 86.60; H,
+
5
4 44 4
5.92; N, 7.48. Found: C, 86.20; H, 6.24; N, 7.30.
2
2
1
solid. Yield: 85%. H NMR (d, CDCl ): 1.43 (t, J¼3.6 Hz,
3
0
m-tolyl-9H-carbazol-3-amine) (4). Pale yellow solid.
6
H), 4.34 (q, J¼7.2 Hz, 4H), 7.26 (d, J¼8.6 Hz, 2H), 7.31
4.2.5. (E)-6,6 -(Ethene-1,2-diyl)bis(9-ethyl-N-phenyl-N-
(
2
s, 2H), 7.38 (d, J¼8.5 Hz, 2H), 7.53 (dd, J¼8.6, 1.9 Hz,
1
H), 7.72 (dd, J¼8.5, 1.6 Hz, 2H), 8.18 (d, J¼1.2 Hz, 2H),
Yield: 80%. H NMR (d, CDCl ): 1.45 (t, J¼3.6 Hz, 6H),
3
+
8
.23 (d, J¼1.9 Hz, 2H). FABMS (m/z): 571.9 (M ).
2.23 (s, 6H), 4.33 (q, J¼7.2 Hz, 4H), 6.77 (d, J¼8.6 Hz,
2
H), 6.88–6.93 (m, 6H), 7.07–7.13 (m, 6H), 7.19 (d,
4.2.2. (E)-1,2-Bis(9-ethyl-9H-carbazol-3-yl)ethene (1).
White solids. Yield: 90%. H NMR (d, CDCl ): 1.44 (t,
J¼7.9 Hz, 4H), 7.22 (s, 2H), 7.26–7.36 (m, 6H), 7.63 (dd,
1
13
J¼8.5, 1.6 Hz, 2H), 7.89 (s, 2H), 8.10 (s, 2H). C NMR
3
J¼3.6 Hz, 6H), 4.37 (q, J¼7.2 Hz, 4H), 7.23 (d, J¼8.6 Hz,
(CDCl ): 148.5, 139.1, 137.1, 131.5, 128.9, 128.7, 125.8,
3
2
H), 7.35 (s, 2H), 7.39 (d, J¼8.5 Hz, 4H), 7.44 (t,
123.9, 123.2, 122.5, 122.2, 120.4, 119.8, 119.7, 109.2,
108.5, 37.7, 21.5, 14.0. FABMS (m/z): 776.4 (M ). Anal.
+
J¼7.4 Hz, 2H), 7.71 (dd, J¼8.5, 1.6 Hz, 2H), 8.13 (d,
1
3
J¼7.6 Hz, 2H), 8.26 (d, J¼1.9 Hz, 2H).
C NMR
CDCl ): 140.3, 139.4, 129.2, 127.0, 125.7, 124.3, 123.3,
Calcd for C H N : C, 86.56; H, 6.23; N, 7.21. Found: C,
5
6 48 4
(
86.48; H, 6.31; N, 6.88.
3
1
(
6
23.0, 120.5, 118.9, 118.3, 108.6, 108.5, 37.6, 13.9. FABMS
m/z): 414.1 (M ). Anal. Calcd for C H N : C, 86.92; H,
.32; N, 6.76. Found: C, 86.50; H, 6.28; N, 6.37.
+
0
len-1-yl)-N-phenyl-9H-carbazol-3-amine) (5). Yellow
4.2.6. (E)-6,6 -(Ethene-1,2-diyl)bis(9-ethyl-N-(naphtha-
3
0 26 2
1
solid. Yield: 70%. H NMR (d, CDCl ): 1.52 (t, J¼3.6 Hz,
3
0
E)-6,6 -(ethene-1,2-diyl)bis(9-ethyl-N,N-diphenyl-9H-car-
(
(
E)-1,2-Bis(9-ethyl-3,9 -bi(9H-carbazol)-6-yl)ethene (2),
0
6H), 4.45 (q, J¼7.2 Hz, 4H), 6.84–6.91 (m, 6H), 7.15 (t,
J¼7.9 Hz, 4H), 7.19 (s, 2H), 7.26–7.37 (m, 10H), 7.42–
7.50 (m, 4H), 7.60 (dd, J¼8.5, 1.6 Hz, 2H), 7.73 (d,
J¼8.2 Hz, 2H), 7.88 (d, J¼8.2 Hz, 2H), 7.91 (d, J¼1.9 Hz,
0
bazol-3-amine) (3), (E)-6,6 -(ethene-1,2-diyl)bis(9-ethyl-N-
0
phenyl-N-m-tolyl-9H-carbazol-3-amine) (4), (E)-6,6 -(eth-
ene-1,2-diyl)bis(9-ethyl-N-(naphthalen-1-yl)-N-phenyl-9H-
1
3
2H), 8.04 (d, J¼1.2 Hz, 2H), 8.08 (d, J¼8.6 Hz, 2H).
C
0
N-phenyl-N-(pyren-1-yl)-9H-carbazol-3-amine) (6), and
carbazol-3-amine) (5), (E)-6,6 -(ethene-1,2-diyl)bis(9-ethyl-
NMR (CDCl ): 150.1, 144.5, 140.7, 139.9, 137.1, 135.3,
3
131.1, 129.0, 128.9, 128.3, 126.8, 126.4, 126.2, 126.0,
125.8, 124.6, 124.4, 123.9, 123.6, 123.0, 119.9, 119.6,
118.3, 116.8, 115.2, 109.1, 108.6, 37.7, 14.0. FABMS
0
(
E)-6,6 -(ethene-1,2-diyl)bis(9-ethyl-N-(4-methoxyphenyl)-
N-(pyren-1-yl)-9H-carbazol-3-amine) (7) were synthesized
by a similar procedure as described for 2.
+
(m/z): 848.4 (M ). Anal. Calcd for C H N : C, 87.70; H,
2 48 4
6
5
.70; N, 6.60. Found: C, 88.09; H, 5.95; N, 6.37.
0
4
.2.3. (E)-1,2-Bis(9-ethyl-3,9 -bi(9H-carbazol)-6-yl)-
0
(pyren-1-yl)-9H-carbazol-3-amine) (6). Yellow solid.
ethene (2). The mixture of carbazole (0.37 g, 2.2 mmol),
compound 1 (0.57 g, 1.0 mmol), sodium tert-butoxide
0.29 g, 3.0 mmol), Pd(OAc) (9.0 mg, 0.040 mmol), tri-
2
tert-butyl)phosphine (11 mg, 0.040 mmol), and dry toluene
20 mL) were refluxed under nitrogen for 16 h. After cool-
ing, it was quenched with water and extracted with dichloro-
methane. The combined organic layer was washed with
brine solution and dried over anhydrous MgSO . After
4.2.7. (E)-6,6 -(Ethene-1,2-diyl)bis(9-ethyl-N-phenyl-N-
1
(
(
(
Yield: 77%. H NMR (d, CDCl ): 1.42 (t, J¼3.6 Hz, 6H),
3
4.28 (q, J¼7.2 Hz, 4H), 6.87 (t, J¼7.3 Hz, 2H), 6.95 (d,
J¼7.7 Hz, 4H), 7.14 (s, 2H), 7.17 (d, J¼7.7 Hz, 4H),
7.26–7.29 (m, 4H), 7.34 (dd, J¼8.7, 2.1 Hz, 2H), 7.55 (dd,
J¼8.4, 1.3 Hz, 2H), 7.86 (d, J¼8.2 Hz, 2H), 7.90–7.96
(m, 8H), 8.03 (s, 4H), 8.08 (d, J¼7.5 Hz, 2H), 8.12–8.16
4

8570
C.-H. Chen et al. / Tetrahedron 62 (2006) 8564–8570
1
3
(
m, 4H), 8.26 (d, J¼9.2 Hz, 2H). C NMR (CDCl ): 150.2,
3. Yang, Y.; Pei, Q.; Heeger, A. J. J. Appl. Phys. 1996, 79, 934.
4. Justin Thomas, K. R.; Lin, J. T.; Tao, Y.-T.; Ko, C.-W. J. Am.
Chem. Soc. 2001, 123, 9404.
5. (a) McClenaghan, N. D.; Passalacqua, R.; Loiseau, F.;
Campagna, S.; Verheyde, B.; Hameurlaine, A.; Dehaen, W.
J. Am. Chem. Soc. 2003, 125, 5356; (b) Kimoto, A.; Cho,
J.-S.; Higuchi, M.; Yamamoto, K. Macromolecules 2004, 37,
5531.
6. (a) Qiu, S.; Liu, L. L.; Wang, B. L.; Shen, F. Z.; Zhang, W.; Li,
M.; Ma, Y. G. Macromolecules 2005, 38, 6782; (b) Jiang, J.;
Jiang, C. Y.; Yang, W.; Zhen, H. Y.; Huang, F.; Cao, Y.
Macromolecules 2005, 38, 4072.
7. (a) Brunner, K.; Dijken, A. V.; B €o rner, H.; Bastiaansen,
J. J. A. M.; Kiggen, N. M. M.; Langeveld, B. M. W. J. Am.
Chem. Soc. 2004, 126, 6035; (b) Wong, K.-T.; Chen, Y.-M.;
Lin, Y.-T.; Su, H.-C.; Wu, C.-C. Org. Lett. 2005, 7, 5361.
8. Ko, C.-W.; Tao, Y.-T.; Lin, J. T.; Justin Thomas, K. R. Chem.
Mater. 2002, 14, 357.
3
1
1
1
9
5
41.9, 140.9, 139.9, 137.0, 131.3, 131.1, 129.1, 129.0, 127.6,
27.3, 126.8, 126.1, 126.0, 125.0, 124.9, 123.7, 122.9, 120.1,
19.9, 118.2, 116.9, 109.2, 108.6, 37.7, 13.9. FABMS (m/z):
+
96.3 (M ). Anal. Calcd for C H N : C, 89.13; H, 5.26; N,
7
4 52 4
.62. Found: C, 88.80; H, 5.48; N, 5.52.
0
.2.8. (E)-6,6 -(Ethene-1,2-diyl)bis(9-ethyl-N-(4-meth-
oxy-phenyl)-N-(pyren-1-yl)-9H-carbazol-3-amine) (7).
Yellow solid. Yield: 65%. H NMR (d, CDCl ): 1.38 (t,
3
4
1
J¼3.6 Hz, 6H), 3.75 (s, 6H), 4.26 (q, J¼7.2 Hz, 4H), 6.74
(
7
d, J¼7.7 Hz, 4H), 6.99 (d, J¼7.7 Hz, 4H), 7.12 (s, 2H),
.15–7.26 (m, 6H), 7.54 (dd, J¼8.4, 1.3 Hz, 2H), 7.80 (d,
J¼8.2 Hz, 2H), 7.83–7.96 (m, 8H), 8.03 (s, 4H), 8.05–8.13
1
3
(
m, 6H), 8.26 (d, J¼9.2 Hz, 2H). C NMR (CDCl ):
3
1
1
1
1
36.5, 131.4, 131.2, 128.9, 128.6, 127.3, 126.6, 126.5,
26.1, 125.9, 125.0, 124.8, 124.7, 123.9, 123.2, 123.0,
22.8, 120.5, 118.2, 115.3, 114.5, 109.1, 108.5, 55.5, 37.7,
+
4.0. FABMS (m/z): 1056.2 (M ). Anal. Calcd for
C H N O : C, 86.34; H, 5.34; N, 5.30. Found: C, 85.91;
6 56 4 2
H, 5.65; N, 5.46.
.3. OLEDs fabrication and measurements
9. Li, J.; Liu, D.; Li, Y. Q.; Lee, C.-S.; Kwong, H.-L.; Lee, S.
Chem. Mater. 2005, 17, 1208.
10. (a) Morin, J.-F.; Leclerc, M. Macromolecules 2002, 35, 8413;
7
(b) Justin Thomas, K. R.; Lin, J. T.; Tao, Y.-T.; Chuen, C.-H.
Chem. Mater. 2002, 14, 3852.
4
1
1. Grigalevicius, S. Synth. Met. 2006, 156, 1.
Electron-transporting materials TPBI and Alq were synthe-
3
12. (a) Ko, C.-W.; Tao, Y.-T. Chem. Mater. 2001, 13, 2441; (b)
Huang, L.; Tian, H.; Li, F.-Y.; Gao, D.-Q.; Huang, Y.-Y.;
Huang, C.-H. J. Lumin. 2002, 97, 55; (c) Lee, M.-T.;
Liao, C.-H.; Tsai, C.-H.; Chen, C. H. Adv. Mater. 2005,
17, 2493.
13. Sonntag, M.; Strohriegl, P. Chem. Mater. 2004, 16, 4736.
14. (a) Shi, J.; Tang, C. W.; Chen, C. H. U.S. Patent 5,645,948,
1997; (b) Sonsale, A. Y.; Gopinathan, S.; Gopinathan, C.
Indian J. Chem. 1976, 14, 408.
sized according to literature procedures and were sublimed
twice prior to use. Pre-patterned ITO substrates with an ef-
fective individual device area of 3.14 mm were cleaned as
2
2
2
described in a previous report. Double-layer EL devices
using carbazole derivatives as the hole-transport layer and
TPBI or Alq as the electron-transport layer were fabricated.
3
For comparison, a typical device using NPB (1,4-bis(1-
naphthylphenylamino)biphenyl) as the hole-transporting
layer was also fabricated. All devices were prepared by
vacuum deposition of 40 nm of the hole-transporting layer,
15. Chen, C. H.; Shi, J.; Tang, C. W. Coord. Chem. Rev. 1998, 171,
161.
followed by 40 nm of TPBI or Alq , and then 1 nm of LiF
3
16. Vilsmeier, A.; Haack, A. Chem. Ber. 1927, 60, 119.
17. Hartwig, J. F.; Kawatsura, M.; Hauck, S. I.; Shaughnessy,
K. H.; Alcazar-Roman, L. M. J. Org. Chem. 1999, 64, 5575.
18. Kim, Y. E.; Kwon, Y. S.; Lee, K. S.; Park, J. W. Mol. Cryst. Liq.
Cryst. 2004, 424, 153.
and 200 nm of Al were deposited as the cathode. I–V curve
was measured on a Keithley 2400 source meter in an ambient
environment. Light intensity was measured with a Newport
1
835 optical meter.
1
9. (a) Blazys, G.; Grigalevicius, S.; Grigalevicius, J. V.; Gaidelis,
V.; Jankauskas, V.; Kampars, V. J. Photochem. Photobiol. A:
Chem. 2005, 174, 1; (b) Grigalevicius, S.; Getautis, V.;
Grigalevicius, J. V.; Gaidelis, V.; Jankauskas, V.; Montrimas,
E. Mater. Chem. Phys. 2001, 72, 395.
Acknowledgements
We are thankful to Academia Sinica, National Taiwan Nor-
mal University, and National Science Council for financial
support.
2
2
0. Huang, T.-H.; Whang, W.-T.; Shen, J. Y.; Lin, J. T.; Zheng,
H. G. J. Mater. Chem. 2005, 15, 3233.
1. (a) Moon, H.; Hwang, J.; Kim, N.; Park, S. Y. Macromolecules
2000, 33, 5116; (b) Justin Thomas, K. R.; Velusamy, M.; Lin,
J. T.; Tao, Y.-T.; Chuen, C.-H. Adv. Funct. Mater. 2004,
14, 387.
References and notes
1
2
. Tang, C. W.; VanSlyke, S. A. Appl. Phys. Lett. 1987, 51, 913.
. Lin, X. Q.; Chen, B. J.; Zhang, X. H.; Lee, C. S.; Kwong, H. L.;
Lee, S. T. Chem. Mater. 2001, 13, 456.
22. Wu, I.-Y.; Lin, J. T.; Tao, Y.-T.; Balasubramaniam, E.; Su,
Y.-Z.; Ko, C.-W. Chem. Mater. 2001, 13, 2626.