Synthesis and properties of N-carbazole end-capped conjugated molecules

Article abstract of DOI:10.1016/j.tet.2006.12.011

A series of novel N-carbazole end-capped π-conjugated molecules were synthesized by a divergent approach with the use of bromination, Suzuki cross-coupling, and Ullmann reactions and their physical properties were investigated. In dilute solution, UV-vis

Full text of DOI:10.1016/j.tet.2006.12.011

Tetrahedron 63 (2007) 1602–1609
Synthesis and properties of N-carbazole end-capped
conjugated molecules
b
Vinich Promaraka, and Somsak Ruchirawat
*
aAdvanced Organic Materials and Devices Laboratory, Department of Chemistry, Faculty of Science, Ubon Ratchathani University,
Warinchumrap, Ubon Ratchathani 31490, Thailand
bChulabhorn Research Institute, Vipavadee Rangsit Highway, Bangkok 10210, Thailand
Received 4 September 2006; revised 20 November 2006; accepted 7 December 2006
Abstract—A series of novel N-carbazole end-capped p-conjugated molecules were synthesized by a divergent approach with the use of bro-
mination, Suzuki cross-coupling, and Ullmann reactions and their physical properties were investigated. In dilute solution, UV–vis absorption
spectra displayed bathochromic shift with respect to their conjugated backbones, and photoluminescence spectra showed emission maxima in
the blue region. Thermal analysis revealed that they are thermally stable semi-crystalline and amorphous materials. All molecules exhibited
good electrochemical stability with high-lying HOMO energy levels and have potential applications as hole-transporting and light-emitting
layers in organic light-emitting diodes or as host materials for electrophosphorescent applications.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
report on N-carbazole end-capped bisthiophenyl derivatives,
the synthesis and physical properties of which still remain to
be explored.
p-Conjugated small molecules have attracted much atten-
tion in the area of organic chemistry and material science.
They have some very interesting electronic and optical prop-
erties and have been investigated as advanced molecular
electronicmaterials.1–3p-Conjugatedthiophene-basedoligo-
mers have earlier been used as model compounds for poly-
mers4 and have recently attracted interest as the sole active
components in devices.5,6 The advantages of oligomers are
that their physical properties can be easily tuned to the de-
sired properties by changing the structure e.g. solubilizing
chains, end-capping groups, insertion of certain groups,
and different oligomer lengths. Much synthetic effort has
been focused on improving physical characteristics of the
oligothiophene-based compounds.7,8 Due to its unique
photo, electrical, and chemical properties, carbazole has
been widely used as a functional building block or substituent
in the construction of organic photoconductors,9 non-linear
optic (NLO) materials,10 hole-transport, and light-emissive
materials for OLED devices11 and as host materials for phos-
phorescence applications.12 Moreover, thermal stability and
glassy state durability of organic molecules were found to
be significantly improved upon incorporation of a carbazole
moiety in the structure.13 To our best knowledge, there is no
In this paper, we accomplished the synthesis of novel N-car-
bazole end-capped p-conjugated bisthiophenyl derivatives,
aiming at investigating how their optical, thermal, and elec-
trochemical properties were affected by the molecular struc-
ture of the conjugated backbones.
2. Results and discussion
2.1. Synthesis and characterization
Scheme 1 shows a synthetic route to the carbazole end-
capped p-conjugated molecules CTB, CTC, CTF, and
CT using a divergent approach in which the desired mole-
cules were constructed in an outward direction stepwise
from the cores, end-capping with the carbazole units in the
final step. Different cores of dialkoxybenzene 1, alkylcarb-
azole 6, and dialkylfluorene 11, were used and synthesized
as described in the literature. The alkyl substituents would
provide good solubility to the desired products in common
organic solvents. They were first treated with either Br2
solution or N-bromosuccinimide (NBS) as brominating
reagents to give their corresponding dibromo compounds
2, 7, and 11 in high yields. Attachment of thiophene units
to both ends of each molecule was accomplished by coupling
of the resultant dibromo compounds 2, 7, and 11 with
Keywords: Carbazole end-cap; p-Conjugated molecules; Ullmann cou-
pling; Hole-transport; Organic light-emitting diodes.
* Corresponding author. Tel.: +66 15 930005; fax: +66 45 288379; e-mail:
pvinich@sci.ubu.ac.th
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.12.011

V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
1603
OH
OC8H17
S
OC8H17
OC8H17
Br
B
S
S
Br2, AcOH
90%
OH
Br
Pd(PPh3)4, K2CO3,
2M Na2CO3, THF
reflux, 58%
C8H17
O
C8H17
O
C8H17
O
3
1
2
NBS, THF, 97%
OC8H17
S
Cu, K2CO3
Ph-NO2, reflux, 68%
OC8H17
S
Br
S
Br
N
N
S
N
C8H17
O
6
4
C8H17
O
C8H17
CTB
N
H
5
NBS, THF, 100%
Br
Br
Br
OH
B
Br
S
S
S
S
S
OH
NBS, THF
87%
Pd(PPh3)4, K2CO3,
2M Na2CO3, THF
reflux, 63%
N
N
N
9
7
C8H17
C8H17
8
C8H17
Cu, K2CO3
Ph-NO2, reflux, 58%
5
Br2, FeCl3
N
N
Br
Br
11
CHCl3, 90%
S
S
C6H13 C6H13
C6H13 C6H13
10
N
OH
Pd(PPh3)4, K2CO3,
2M Na2CO3, THF, reflux, 58%
CTC
B
S
C8H17
OH
S
S
S
S
NBS, THF
71%
Br
Br
5, Cu, K2CO3
Ph-NO2, reflux
55%
C6H13 C6H13
C6H13 C6H13
12
13
5, Cu, K2CO3
Ph-NO2, reflux
S
S
N
S
S
Br
N
N
Br
N
S
S
81%
14
Scheme 1. Synthetic route to the target p-conjugated molecules.
C6H13 C6H13
CTF
CT
2-thiopheneboronic acid under Suzuki cross-coupling condi-
tions. The reaction was performed using Pd(PPh3)4 as a cat-
alyst and an aqueous solution of Na2CO3 as base in THF. The
corresponding thiophene capped products 3, 8, and 12 were
isolated in reasonable yields (58–63%). Individually, they
were subsequently chemoselectively brominated with NBS
in THF, in which only the most nucleophilic 5-positions of
both terminal thiophene rings reacted to give the correspond-
ing dibromo compounds 4, 9, and 13 in good yields. Then,
coupling of the resulting dibromine compounds 4, 9, and
13 with an excess carbazole (5) under Ullmann amination
reaction conditions in the presence of Cu-bronze as catalyst
and K2CO3 as base, in a refluxing nitrobenzene afforded the
target N-carbazole-capped products, CTB, CTC, and CTF,
in 68, 58, and 55% yields, respectively. For comparison
purposes, compound CT was also prepared using similar
Ullmann coupling reaction and was isolated in 71% yield.
All target molecules CTB, CTC, CTF, and CT are soluble
in all common organic solvents and their structures were
confirmed by IR, 1H NMR, 13C NMR, and HRMS spectro-
metric methods.
2.2. Optical properties
The optical properties of all p-conjugated molecules were
investigated by UV–vis and photoluminescence spectro-
scopies in a dilute CH2Cl2 solution as shown in Figure 1
and summarized in Table 1. Normalized absorption spectra
of CTB, CTC, CTF, and CT exhibit two major absorption
bands, an absorption band at 292 nm assigned to the p–p*

1604
V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
whole molecule. The longest conjugation segments for
CT
compounds CTB and CTF are bisthiophenylbenzene and
bisthiophenylfluorene, respectively. In fact, the absorption
spectrum of CTB is around 10 nm red shifted with respect
to that of CTF. This bathochromic shift is a consequence
of the degree of free rotation about 1,4-positions of benzene
rings in CTB, which is greater than that about 2,7-positions
of fluorene unit in CTF. As a result, p-electrons can be
easily delocalized along the bisthiophenylbenzene backbone
of CTB leading to a decrease in the energy gap (Table 1)
or a red shift of the absorption spectrum.
CTF
CTC
CTB
Photoluminescence spectra of p-conjugated molecules
CTB, CTC, CTF, and CT are located in blue region with
their emission maxima at 440, 403, 428, and 430 nm, respec-
tively (Fig. 1 and Table 1). In fact, the introduction of the
carbazole moieties at terminal of the conjugated backbone
would result in a less planar molecule by means of the plane
of the carbazole unit being nearly perpendicular to that of the
backbone. However, in view of the absorption and photo-
luminescence spectra, the absorption bands and maxima of
CTF were red shifted (w35 nm) relative to those of its cor-
responding bisthiophenylfluorene 12 (Fig. 3). There is a sub-
stantial red shift of the absorption and the emission maxima
of bisthiophenylfluorene core upon incorporation of strong
electron donating carbazole groups at both ends. This sug-
gests that there is p-electron conjugation through the lone
electron pair at the nitrogen atom of the carbazole end-
caps and that p-electrons are delocalized over the entire
conjugated backbone, which is attributed to the asymmetric
destabilization of the HOMO and LUMO energy levels lead-
ing to the decrease of the energy gap. Moreover, upon excita-
tion either at 292 nm attributed to the absorption of carbazole
moiety or at 350 nm corresponding to the absorption of
the conjugated backbone, the emission spectra obtained are
identical, indicating that energy or electrons can efficiently
transfer from the peripheral carbazole to the inner backbone.
300
400
500
Wavelength (nm)
Figure 1. Optical properties of p-conjugated molecules measured in
CH2Cl2 solution (w10ꢀ5 M).
electron transition of the end-capped carbazole units and
a broader absorption band at longer wavelength correspond-
ing to the p–p* transition of the entire p-conjugated back-
bone. Compound CT bearing a dithiophene unit as a core
shows absorption bands at 292 and 336 nm, while com-
pounds CTF and CTB having aromatic fluorene and phenyl-
ene units in between these two thiophene rings show a red
shift of the latter band to 371 and 381 nm, respectively.
This indicates that the additional fluorenyl and phenyl moi-
eties have increased the degree of p-conjugation of the sys-
tem by lowering the HOMO and LUMO energy levels of the
backbones. On the other hand, it is blue shifted to 323 nm
when the carbazole unit is introduced into the system in
compound CTC. An explanation for the different electronic
absorption behaviors of these compounds would be that in
the case of compound CTC, it can be recognized as two thio-
phene rings being linked by a m-biphenyl unit, therefore
there is no long-range conjugation. The conjugation segment
can probably be best described as 5-(4-aminophenyl)thio-
phen-2-amine structure as illustrated in Figure 2. On the con-
trary, in compounds CTB and CTF the two thiophene rings
are linked by p-phenyl and p-biphenyl units, respectively,
therefore delocalization of p-electrons can extend over the
2.3. Electrochemical properties
In order to investigate the redox properties of these p-conju-
gated molecules and their HOMO and LUMO energy levels,
cyclic voltammetry (CV) analysis was performed. The mea-
surements were carried out in CH2Cl2 solution containing
0.1 M n-Bu4NPF6 as supporting electrolyte using three-
electrode systems under an argon atmosphere. The reference
electrode was Ag/Ag+. The results are shown in Figure 4 and
Table 1. Summary of physical measurements of p-conjugated molecules
a
b
a
lonset (nm)/Eg
(eV)
c
d
Compd
labs
(nm)
llum
(nm)
Tg/Tc/Tm/Td
(ꢁC)
E
(V)
1/2/DEe
HOMOf
(eV)
LUMOg
(eV)
CTB
CTF
CTC
292, 381
292, 371
293, 323
440
428
403
428/2.90
416/2.98
390/3.18
NA/116/197/430
85/NA/NA/425
98/NA/NA/427
0.95/0.335, 1.24/0.337
1.07/0.153, 1.63/0.130
0.95/0.244, 1.27/0.276,
1.45/0.249, 1.70/0.232
0.98/0.398, 1.24/0.337
5.23
5.43
5.30
2.33
2.45
2.12
CT
291, 336
430
402/3.08
78/141/209/379
5.24
2.16
Measured in a dilute CH2Cl2 solution (w10ꢀ5 M).
Excited at the absorption maxima.
a
b
c
d
e
Estimated from the onset of absorption (Eg¼1240/lonset).
Obtained from DSC and TGA measurements with a heating rate of 10 ꢁC/min under N2.
Measured using a glassy carbon electrode as a working electrode, a platinum rod as a counter electrode, and Ag/Ag+ as a reference electrode in CH2Cl2
containing 0.1 M n-Bu4NPF6 as a supporting electrolyte at a scan rate of 50 mV/s under an argon atmosphere.
Calculated using the empirical equation: HOMO¼(4.44+Eonset).
f
g
Calculated from LUMO¼HOMOꢀEg.

V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
1605
OC8H17
S
N
N
N
S
N
S
S
C8H17
O
N
CTC
CTB
C8H17
S
S
N
N
C6H13 C6H13
CTF
Figure 2. Chemical structures of compounds CTB, CTF, and CTC. The longest p-conjugation is enclosed in a dashed ellipsoid.
summarized in Table 1. In the case of compound CTC pos-
sessing the least conjugation length, the cyclic voltammo-
gram showed four chemically quasi-reversible oxidation
processes, while the CV curves of compounds CTB, CTF,
and CTC exhibit two chemically quasi-reversible oxidation
processes. During the successive oxidation cycles of all
compounds a slight shift of the CV curves was observed in-
dicating a weak oxidative coupling at 3,6-positions of the pe-
ripheral carbazole moieties (Fig. 5). This is usually detected
in most carbazole derivatives with open 3,6-positions.
However, no additional peak at lower potential on the re-
reduction process (Epc) due to the electropolymerization
of these carbazole end-capped molecules was detected as
in the case of bis{2-[4-(N-carbazolyl)phenyl]-1,3,4-oxadi-
azol-5-yl}-9,9-dihexylfluorene.14 In all samples, no distinct
reduction process was observed. The first oxidation pro-
cesses can be attributed to the removal of electrons from the
peripheral carbazole units and the other reversible processes
corresponding to removal of electrons from the interior
moieties. Their first oxidation values are slightly affected
by the length and structure of the conjugated backbones,
with compound CTF having the highest first oxidation
potential of 1.07 V. However, these first potential values
are slightly smaller than that of carbazole (E1/2¼1.09 V),
suggesting that the incorporation of carbazole ring makes
the resulting molecules more susceptible for electrochemical
oxidation. The HOMO energy levels were calculated from
the onset of oxidation potential (Eonset) according to an em-
pirical formula, HOMO¼(4.44+Eonset) (eV).15 The LUMO
energy levels were calculated by subtracting the HOMO
energy levels with the energy band gaps estimated from
the onset of UV–vis absorption. The results are tabulated
in Table 1. The HOMO energy levels of these p-conjugated
molecules are in the range of 5.23–5.43 eV and this greatly
reduce the energy barrier for the hole injection from ITO
(f¼4.80 eV) to the emissive Alq3 (f¼5.80 eV). As a result,
all compounds CTB, CTC, CTF, and CT showing chemi-
cally reversible oxidation processes and high-lying HOMO
80
60
40
20
0
12
CTF
-20
-40
CTF
CTC
CFB
-60
0.6
0.8
1.0
1.2
1.4
1.6
1.8
Potential vs Ag/Ag+ (V)
250
300
350
400
450
500
550
Wavelength (nm)
Figure 4. Cyclic voltammetry curves of compounds CTC and CTB in
CH2Cl2 containing n-Bu4NPF6 electrolyte at a scan rate of 50 mV/s under
an argon atmosphere.
Figure 3. Absorption and photoluminescence spectra of CTF and 12 mea-
sured in CH2Cl2.

1606
V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
60
40
20
0
CTC
CTF
CTC
-20
-40
1st cycle
2nd cycle
3rd cycle
0.6
0.8
1.0
1.2
1.4
1.6
1.8
50
100
150
200
250
300
Potential vs Ag/Ag+ (V)
Temperature (°C)
Figure 5. The successive cyclic voltammetry curves of CTC measured in
CH2Cl2 at a scan rate of 50 mV/s.
CTB
energy levels can be good and stable hole-transport and in-
jection materials for double-layer OLED. This may be a ben-
efit arising from incorporation of the carbazole end-caps.
2.4. Thermal properties
CT
Thermal properties of the p-conjugated molecules are shown
in Figure 6 and summarized in Table 1. The results reveal that
all p-conjugated molecules exhibit high thermal stability
with the onset of decomposition temperatures in the range
of 379–430 ꢁC under a nitrogen atmosphere. DSC measure-
ments show that both CTB and CT are semi-crystalline.
During the first heating cycle of CTB and CT, sharp endo-
thermic melting peaks at 197 and 209 ꢁC, respectively,
were observed. When the samples were cooled down from
the melt at a cooling rate of 50 ꢁC/min, the samples spontane-
ously formed a glassy state. When the amorphous glassy
samples were heated again, an endothermic phenomenon at
78 ꢁC, at which point the glassy state changed into the super-
cooled liquid state (Tg), was observed for compound CT.
Then broad exothermic peaks due to the crystallization were
observed in both samples around 116 and 141 ꢁC, respec-
tively, to give the same crystals as observed by crystallization
from solution, which melted at 197 and 209 ꢁC, respectively.
Moreover, when the crystalline sample of CTF prepared by
crystallization from a mixture of dichloromethane and meth-
anol was heated, the endothermic peak due to melting was
observed at 149 ꢁC. This was no longer detected during the
second heating scan and only an endothermic baseline shift
due to glass transition was observed at 81 ꢁC, and on further
heating no peaks due to the crystallization and melting ap-
peared. However, compound CTC behaves in a totally differ-
ent manner. Only the glass transition at about 98 ꢁC can be
seen in repeated DSC heating cycles with no crystallization
and melting peaks observed. This unique thermal behavior
of CTC may arise from its V-shape structure. The thermal
and morphological stabilities of all compounds may benefit
from the presence of carbazole moieties at both ends. The
50
100
150
200
250
300
Temperature (°C)
Figure 6. DCS traces of p-conjugated molecules measured under nitrogen
atmosphere at heating rate of 10 ꢁC/min: first heating (dotted lines) and
second heating (solid lines).
ability of CTC and CTF to form a molecular glass and the
possibility to prepare thin films from CTC and CTF both
by evaporation and by solution casting are highly desirable
for applications in OLEDs and OFETs.
3. Conclusions
The properties of novel N-carbazole end-capped p-conju-
gated molecules prepared by a divergent approach using a
combination of bromination, Suzuki cross-coupling, and
Ullmann coupling reactions were investigated. Their optical,
thermal, and electrochemical properties are strongly influ-
enced by molecular structure of the inner conjugated
backbone. All molecules exhibit good electrochemical

V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
1607
reversibility and have the potential to be good hole-transport-
ing and light-emitting layers in organic light-emitting diodes
or as host materials for electrophosphorescent applications.
Attachment of carbazole via its N-position might be an effec-
tive way to make amorphous materials with low oxidation
potential for optoelectronic applications by forming dicarb-
azole end-capped or carbazole dendritic structures with other
fluorescent or non-fluorescent backbones.
were added. The organic phase was separated, washed with
water (100 ml), brine solution (100 ml), dried overanhydrous
Na2SO4, filtered, and the solvents removed to dryness. Puri-
fication by column chromatography using silica gel eluting
with hexane gave yellow-green solids. Yield was 2.91 g,
(58%); IR (KBr) 2956, 1494, 1436, 1213, 1037, 826, and
1
689 cmꢀ1; H NMR (300 MHz, CDCl3) d 0.95–1.00 (12H,
m), 1.34–1.65 (16H, m), 1.82–1.88 (2H, m), 3.99 (4H, d,
J¼5.4 Hz), 7.12 (2H, dd, J¼5.2 Hz, J¼3.6 Hz), 7.28 (2H,
s), 7.36 (2H, d, J¼5.2 Hz), and 7.54 (2H, d, J¼3.6 Hz); 13C
NMR (75 MHz, CDCl3) d 11.19, 14.08, 23.05, 24.06,
29.14, 30.66, 39.66, 71.89, 112.79, 122.95, 125.26, 125.56,
126.67, 139.38, and 149.40; HRMS-ESI m/z: [MH+] calcd
for C30H43O2S2, 499.2699; found, 499.2703.
4. Experimental
4.1. General procedures
Tetrahydrofuran (THF) was refluxed with sodium and benz-
ophenone, and distilled. Nitrobenzene and CHCl3 were dis-
tilled from CaH2 prior to use. CH2Cl2 for cyclic voltammetry
analysis was washed with concd H2SO4 and distilled twice
from CaH2. All reagents and solvents were purchased from
Aldrich, Acros, Fluka or Thai Suppliers and used as received
4.2.2. Synthesis of 1,4-bis(5-bromothiophen-2-yl)-2,5-
bis(2-ethylhexyloxy)benzene (4). N-Bromosuccinimide
(0.93 g, 5.25 mmol) was added in small portions to a solution
of 3 (1.20 g, 2.60 mmol) in THF (50 ml). The mixture was
stirred at room temperature under N2 atmosphere for 1 h.
Water (100 ml) and CH2Cl2 (100 ml) were added. The
organic phase was separated, washed with water (100 ml),
brine solution (100 ml), dried over anhydrous Na2SO4, fil-
tered and the solvents removed to dryness. Purification by
column chromatography using silica gel eluting with hexane
gave yellow solids. Yield was 1.63 g (97%); IR (KBr) 2956,
1
unless otherwise stated. H and 13C NMR spectra were re-
€
corded on a Bruker AVANCE 300 MHz spectrometer with
TMS as an internal reference using CDCl3 as solvent in all
cases. IR spectra were measured on a Perkin–Elmer FT-IR
spectroscopy spectrum RXI spectrometer as KBr disc.
UV–vis spectra were recorded as a dilute solution in spectro-
scopic grade CH2Cl2 on a Perkin–Elmer UV Lambda 25
spectrometer. Photoluminescence spectra were recorded
with a Perkin–Elmer LS 50B Luminescence Spectrometer
as a dilute solution in spectroscopic grade CH2Cl2. Differen-
tial scanning calorimetry (DSC) analysis was performed on
a METTLER DSC823e thermal analyzer under N2 atmo-
sphere. Samples were scanned from 25 to 430 ꢁC at a heating
rate of 10 ꢁC/min then rapidly cooled to 25 ꢁC and heated at
the same heating rate to 430 ꢁC. Thermogravimetric analysis
(TGA) was carried out on a Seiko EXSTAR 6000 TG/DTA
6300 thermal analyzer at heating rate of 10 ꢁC/min under N2
atmosphere. Cyclic voltammetry (CV) measurements were
carried out under an inert argon atmosphere with an Autolab
potentiostat PGSTAT 12 using a three-electrode system fitted
with a platinum rod counter electrode, a glassy carbon work-
ing electrode and a Ag/Ag+ reference electrode. The solvent
was CH2Cl2 with n-Bu4NPF6 (0.1 M) as a supporting elec-
trolyte. The concentration of the samples was 0.9–1.0 mM
and the scan rate was 50 mV/s. High resolution mass
spectrometry (HRMS) analysis was performed by Mass
Spectrometry Unit, Chulabhorn Research Institute (CRI)
1494, 1436, 1213, 1037, 826 and 689 cmꢀ1 1H NMR
;
(300 MHz, CDCl3) d 0.91–1.00 (14H, m), 1.30–1.63 (16H,
m), 1.84–1.90 (2H, m), 3.97 (4H, d, J¼5.7 Hz), 7.05 (2H,
d, J¼4.0 Hz), 7.18 (2H, s), and 7.26 (2H, d, J¼4.0 Hz); 13C
NMR (75 MHz, CDCl3) d 11.17, 14.08, 23.04, 24.04,
29.15, 30.68, 39.58, 72.12, 111.46, 113.01, 122.47, 124.78,
129.30, 140.43, and 149.17; HRMS-ESI m/z: [MH+] calcd
for C30H41O2S2Br2, 655.0909; found, 655.0904.
4.2.3. Synthesis of 1,4-bis[5-(carbazol-9-yl)thiophene-
2-yl]-2,5-bis(2-ethylhexyloxy)benzene (CTB). A mixture
of 4 (1.36 g, 2.07 mmol), carbazole (1.04 g, 6.21 mmol),
K2CO3 (1.16 g, 8.41 mmol), and Cu-bronze (0.13 g,
2.07 mmol) in nitrobenzene (20 ml) was stirred at reflux
under N2 atmosphere for 18 h. After removal of the solvent
in vacuo, ammonia solution (50 ml) was added and the mix-
ture was left to stand for 2 h. CH2Cl2 (150 ml) and water
(100 ml) were added. The organic phase was separated,
washed with water (100 mlꢂ2), brine solution (100 ml),
dried over anhydrous Na2SO4, filtered, and the solvent re-
moved to dryness. Purification by column chromatography
using silica gel eluting with a mixture of CH2Cl2 and hexane
followed by recrystallization with hexane afforded white
solids. Yield was 1.17 g (68%); IR (KBr) 2915, 1553,
€
of Thailand using a Micro TOF Bruker. The synthesis
of compounds 1,4-bis(2-ethylhexyloxy)benzene (1), 1,4-
dibromo-2,5-bis(2-ethylhexyloxy)benzene (2),16 9-(2-ethyl-
hexylcarbazole) (6), 3,6-dibromo-9-(2-ethylhexyl)carbazole
(7),17 9,9-bis-n-hexylfluorene (10), and 2,7-dibromo-9,9-
bis-n-hexylfluorene (11)18 was performed according to or
slightly modified literature procedures.
1509, 1443, 1207, 1026, 750, and 639 cmꢀ1 1H NMR
;
(300 MHz, CDCl3) d 0.78 (6H, t, J¼6.9 Hz), 0.96 (6H, t,
J¼7.5 Hz), 1.26–1.65 (20 H, m), 1.86–1.90 (2H, m), 4.07
(4H, d, J¼5.7 Hz), 7.24 (2H, d, J¼3.9 Hz), 7.32–7.37 (6H,
m), 7.46–7.52 (4H, m), 7.61 (6H, d, J¼8.1 Hz), and 8.14
(4H, d, J¼7.8 Hz); 13C NMR (75 MHz, CDCl3) d 11.21,
14.02, 23.03, 24.07, 29.10, 30.71, 39.63, 72.09, 110.36,
112.02, 120.18, 120.54, 123.56, 123.96, 124.28, 126.23,
137.25, 141.92, and 149.54; HRMS-ESI m/z: [MH+] calcd
for C54H57N2O2S2, 829.3856; found, 829.3839.
4.2. Synthetic procedures
4.2.1. Synthesis of 1,4-bis(thiophen-2-yl)-2,5-bis(2-ethyl-
hexyloxy)benzene (3). A mixture of 2 (4.95 g, 10.05 mmol),
2-thiopheneboronic acid (2.83 g, 22.10 mmol), Pd(PPh3)4
(0.2 g, 0.17 mmol), and 2 M Na2CO3 aqueous solution
(23 ml, 46 mmol) in THF (35 ml) was stirred at reflux under
N2 atmosphere for 24 h. CH2Cl2 (150 ml) and water (150 ml)
4.2.4. Synthesis of 3,6-bis(thiophen-2-yl)-9-(2-ethyl-
hexyl)carbazole (8). A mixture of 7 (5.20 g, 11.89 mmol),

1608
V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
2-thiopheneboronic acid (3.35 g, 26.17 mmol), Pd(PPh3)4
(0.2 g, 0.17 mmol), and 2 M Na2CO3 aqueous solution
(23 ml, 46 mmol) in THF (35 ml) was stirred at reflux under
N2 atmosphere for 24 h. Water (150 ml) and CH2Cl2
(150 ml) were added. The organic phase was separated,
washed with water (150 ml), brine solution (100 ml), dried
over anhydrous Na2SO4, filtered, and the solvents removed
to dryness. Purification by column chromatography using
silica gel eluting with hexane gave light green solids. Yield
was 3.32 g (63%); IR (KBr) 2955, 1601, 1484, 1291, 1221,
J¼8.5 Hz, J¼1.7 Hz), 8.14 (4H, d, J¼7.4 Hz), and 8.44
(2H, d, J¼1.6 Hz); 13C NMR (75 MHz, CDCl3) d 10.94,
14.03, 23.04, 24.46, 28.84, 31.06, 39.51, 47.74, 109.75,
110.37, 117.89, 120.20, 120.57, 120.75, 123.27, 123.53,
124.48, 125.67, 126.00, 126.27, 136.64, 141.20, 142.03,
and 144.00; HRMS-ESI m/z: [MH+] calcd for C52H44N3S2,
774.2971; found, 774.2966.
4.2.7. Synthesis of 2,7-bis(thiophen-2-yl)-9,9-bis-n-hexyl-
fluorene (12). A mixture of 11 (5.0 g, 10.16 mmol), 2-thio-
pheneboronic acid (2.58 g, 20.23 mmol), Pd(PPh3)4 (0.01 g,
0.01 mmol), and 2 M Na2CO3 aqueous solution (33 ml,
46 mmol) in THF (50 ml) was stirred at reflux under N2
atmosphere for 24 h. CH2Cl2 (200 ml) and water (150 ml)
were added. The organic phase was separated, washed with
water (100 ml), brine solution (100 ml), dried over anhydrous
Na2CO3, filtered, and the solvents removed to dryness. Purifi-
cation by column chromatography using silica gel eluting
with hexane gave yellow-green solids. Yield was 2.94 g
(58%); IR (KBr) 2927, 1467, 1214, 1053, 809, and
1
850, and 681 cmꢀ1; H NMR (300 MHz, CDCl3) d 0.88–
0.98 (6H, m), 1.27–1.47 (8H, m), 2.07–2.11 (1H, m), 4.16
(2H, dd, J¼7.8 Hz, J¼1.8 Hz), 7.14 (2H, dd, J¼5.1 Hz,
J¼3.6 Hz), 7.29 (2H, dd, J¼5.1 Hz, J¼1.2 Hz), 7.38–7.40
(4H, m), 7.75 (2H, dd, J¼8.4 Hz, J¼1.8 Hz), and 8.36
(2H, d, J¼1.8 Hz); 13C NMR (75 MHz, CDCl3) d 10.91,
14.03, 23.04, 24.43, 28.84, 31.04, 39.47, 47.63, 109.46,
117.94, 122.12, 123.20, 123.71, 124.59, 125.92, 128.00,
140.91, and 145.67; HRMS-ESI m/z: [MH+] calcd for
C28H30NS2, 444.1814; found, 444.1817.
1
691 cmꢀ1; H NMR (300 MHz, CDCl3) d 0.68–0.79 (10H,
4.2.5. Synthesis of 3,6-bis(5-bromothiophen-2-yl)-9-
(2-ethylhexyl)carbazole (9). N-Bromosuccinimide (2.96 g,
16.67 mmol) was added in small portions to a solution of 8
(3.7 g, 8.33 mmol) in THF (70 ml). The mixture was stirred
at room temperature under N2 for 1 h. Water (100 ml) and
CH2Cl2 (150 ml) were added. The organic phase was sepa-
rated, washed with water (100 ml), brine solution (100 ml),
dried over anhydrous Na2SO4, filtered, and the solvents re-
moved to dryness. Purification by column chromatography
using silica gel eluting with hexane gave gray solids. Yield
was 4.36 g (87%); IR (KBr) 2955, 1601, 1484, 1291,
m), 1.07–1.16 (12H, m), 2.01ꢀ2.07 (4H, m), 7.13 (2H, dd,
J¼4.8 Hz, J¼3.6 Hz), 7.31 (2H, dd, J¼5.1 Hz, J¼0.9 Hz),
7.40 (2H, dd, J¼4.2 Hz, J¼0.9 Hz), 7.58 (2H, s), 7.64 (2H,
dd, J¼7.8 Hz, J¼1.5 Hz), and 7.69 (2H, d, J¼7.8 Hz); 13C
NMR (75 MHz, CDCl3) 13.98, 22.56, 23.72, 29.66, 31.45,
40.43, 55.28, 120.07, 120.16, 122.89, 124.53, 124.98,
128.06, 133.26, 140.21, 145.17, and 151.70; HRMS-ESI
m/z: [MH+] calcd for C33H39S2, 499.2488; found, 499.2487.
4.2.8. Synthesis of 2,7-bis(5-bromothiophen-2-yl)-9,9-
di-n-hexylfluorene (13). N-Bromosuccinimide (0.712 g,
4.00 mmol) was added in small portions to a solution of 12
(1.0 g, 2.00 mmol) in THF (50 ml). The mixture was stirred
at room temperature under N2 for 1 h. Water (100 ml) and
CH2Cl2 (100 ml) were added. The organic phase was sepa-
rated, washed with water (100 ml), brine solution (100 ml),
dried over anhydrous Na2SO4, filtered, and the solvents re-
moved to dryness. Purification by column chromatography
using silica gel eluting with hexane gave yellow-green solids.
Yield was 0.93 g (71%); 1H NMR (300 MHz, CDCl3) d 0.65–
0.70 (4H, m), 0.75–0.80 (6H, m), 1.08–1.28 (14H, m), 1.98–
2.04 (4H, m), 7.08 (2H, d, J¼3.9 Hz), 7.15 (2H, d, J¼3.9 Hz),
7.47 (2H, d, J¼1.2 Hz), 7.50 (2H, dd, J¼6.6 Hz, J¼1.5 Hz),
and 7.68 (2H, d, J¼7.8 Hz); 13C NMR (75 MHz, CDCl3)
d 13.95, 22.53, 23.72, 29.61, 31.41, 40.34, 55.33, 119.84,
120.84, 123.05, 124.70, 130.87, 132.65, 140.41, 146.55,
and 151.85; HRMS-ESI m/z: [MH+] calcd for C33H37Br2S2,
657.0639; found, 657.0643.
1221, 850, and 681 cmꢀ1 1H NMR (300 MHz, CDCl3)
;
d 0.88–0.96 (6H, m), 1.26–1.45 (8H, m), 2.03–2.06 (1H,
m), 4.09 (2H, dd, J¼7.8 Hz, J¼2.1 Hz), 7.08 (4H, AA0BB0,
J¼5.7 Hz, J¼3.9 Hz), 7.32 (2H, d, J¼8.4 Hz), 7.61 (2H, dd,
J¼8.4 Hz, J¼1.5 Hz), and 8.18 (2H, d, J¼1.5 Hz); 13C
NMR (75 MHz, CDCl3) d 10.89, 14.03, 23.04, 24.41,
28.82, 31.02, 39.46, 47.61, 109.61, 109.97, 117.60,
122.18, 123.07, 124.24, 125.22, 130.83, 141.01, and
147.08; HRMS-ESI m/z: [MH+] calcd for C28H28Br2NS2,
600.0024; found, 600.0025.
4.2.6. Synthesis of 3,6-bis[5-(carbazol-9-yl)thiophen-
2-yl]-9-(2-ethylhexyl)carbazole (CTC). A mixture of 9
(2.00 g, 3.33 mmol), carbazole (1.67 g, 9.99 mmol), K2CO3
(1.87 g, 13.52 mmol), and Cu-bronze (0.21 g, 3.33 mmol)
in nitrobenzene (20 ml) was stirred at reflux under N2 for
18 h. After removal of the solvent invacuo, ammonia solution
(50 ml) was added and the mixture was allowed to stand for
2 h. CH2Cl2 (150 ml) and water (100 ml) were added. The or-
ganic phase was separated, washed with water (100 mlꢂ2),
brine solution (100 ml), dried over anhydrous Na2SO4,
filtered, and the solvent removed to dryness. Purification by
column chromatography using silica gel eluting with a mix-
ture of CH2Cl2 and hexane followed by recrystallization
with a mixture of CH2Cl2 and MeOH afforded light yellow
solids. Yield was 1.80 g (58%); IR (KBr) 2925, 1555, 1503,
4.2.9. Synthesis of 2,7-bis[5-(carbazol-9-yl)thiophen-
2-yl]-9,9-di-n-hexylfluorene (CTF). A mixture of 13
(1.48 g, 2.24 mmol), carbazole (1.12 g, 6.71 mmol), K2CO3
(1.25 g, 9.08 mmol), and Cu-bronze (0.14 g, 2.24 mmol) in
nitrobenzene (20 ml) was stirred at reflux under N2 atmo-
sphere for 20 h. After removal of the solvent invacuo, ammo-
nia solution (30 ml) was added and the mixture was left to
stand for 2 h. CH2Cl2 (150 ml) and water (200 ml) were
added. The organic phase was separated, washed with water
(100 mlꢂ2), brine solution (100 ml), dried over anhydrous
Na2SO4, filtered, and the solvents removed to dryness. Puri-
fication by column chromatography using silica gel eluting
with a mixture of CH2Cl2 and hexane followed by
1444, 1226, 795, and 747 cmꢀ1 1H NMR (300 MHz,
;
CDCl3) d 0.91 (3H, t, J¼7.2 Hz), 0.98 (3H, t, J¼7.5 Hz),
1.29–1.48 (8H, m), 2.12–2.15 (1H, m), 4.23 (2H, d,
J¼7.2 Hz), 7.23 (2H, d, J¼3.9 Hz), 7.35 (4H, t, J¼7.4 Hz),
7.44–7.52 (8H, m), 7.61 (4H, d, J¼8.5 Hz), 7.80 (2H, dd,

V. Promarak, S. Ruchirawat / Tetrahedron 63 (2007) 1602–1609
1609
recrystallization with a mixture of CH2Cl2 and MeOH
afforded light yellow solids. Yield was 1.02 g (55%); IR
(KBr) 2925, 1555, 1492, 1444, 1226, 797, and 746 cmꢀ1
References and notes
;
€
1. Brunner, K.; Van Dijken, A.; Borner, H.; Bastiaansen,
J. J. A. M.; Kiggen, N. M. M.; Langeveld, B. M. W. J. Am.
Chem. Soc. 2004, 126, 6035–6042.
1H NMR (300 MHz, CDCl3) d 0.79–0.84 (10H, m), 1.13–
1.19 (12H, m), 2.08–2.13 (4H, m), 7.25 (2H, d, J¼3.9 Hz),
7.37 (4H, t, J¼7.5 Hz), 7.49–7.54 (6H, m), 7.62 (2H, s),
7.64 (4H, d, J¼4.8 Hz), 7.68 (2H, d, J¼8.0 Hz), 7.77 (2H,
d, J¼7.9 Hz), and 8.16 (4H, d, J¼7.5 Hz); 13C NMR
(75 MHz, CDCl3) d 14.02, 22.61, 23.82, 29.70, 31.51,
40.47, 55.47, 110.33, 119.93, 120.27, 120.38, 120.71,
121.66, 123.63, 124.88, 125.95, 126.33, 133.07, 137.07,
140.58, 141.96, 143.37, and 151.96; HRMS-ESI m/z:
[MH+] calcd for C57H53N2S2, 829.3645; found, 829.3631.
2. Schon, J. H.; Kloc, C.; Bucher, E.; Batlogg, B. Nature 2000,
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4.2.10. Synthesis of 5,50-bis(carbazol-9-yl)(bithiophen-
2,20-yl) (CT). A mixtureof 14(1.00 g, 3.08 mmol), carbazole
(0.94 g, 5.62 mmol), copper-bronze (0.14 g, 2.30 mmol), and
K2CO3 (1.49 g, 10.57 mmol) in nitrobenzene (30 cm3) was
stirred at reflux under N2 for 24 h. After removal of the sol-
vent in vacuo, ammonia solution (30 ml) was added and the
mixture was left to stand for 2 h. CH2Cl2 (100 ml) and water
(100 ml) were added. The organic phase was separated,
washed with water (100 mlꢂ2), brine solution (100 ml),
dried over anhydrous Na2SO4, filtered, and the solvents re-
moved to dryness. Purification by column chromatography
using silica gel eluting with a mixture of CH2Cl2 and hexane
followed by recrystallization with a mixture of CH2Cl2 and
MeOH afforded yellow solids. Yield was 1.24 g (81%); IR
(KBr) 1579, 1537, 1451, 1221, 1164, 799, and 744 cmꢀ1
;
1H NMR (300 MHz, CDCl3) d 7.18 (2H, d, J¼3.9 Hz), 7.30
(2H, d, J¼3.9 Hz), 7.36 (4H, dt, J¼7.8 Hz, J¼1.0 Hz), 7.50
(4H, dt, J¼8.0 Hz, J¼1.1 Hz), 7.58 (4H, d, J¼8.0 Hz), and
8.13 (4H, d, J¼7.8 Hz); 13C NMR (75 MHz, CDCl3)
d 110.24, 120.29, 120.85, 122.68, 123.67, 125.67, 126.39,
135.43, 137.84, and 141.81; HRMS-ESI m/z: [MH+] calcd
for C32H21N2S2, 497.1141; found, 497.1149.
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Acknowledgements
This work was supported financially by Thailand Research
Fund (TRF) (Grant Code: MRG4780080).