Easily functionalizable carbazole based building blocks with extended conjugated systems for optoelectronic applications

Article abstract of DOI:10.1016/j.tet.2010.02.086

Carbazole based building blocks, possessing diphenylethenyl fragments, have been synthesized. Condensation of the carbazol-2-ol with diphenylacetaldehyde yields 1,3-substituted derivatives. Change of the synthesis sequence, however, (i.e., substitution at

Full text of DOI:10.1016/j.tet.2010.02.086

Tetrahedron 66 (2010) 3199–3206
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Easily functionalizable carbazole based building blocks with extended
conjugated systems for optoelectronic applications
Giedre Bubniene a, Tadas Malinauskas a, Maryte Daskeviciene a, Vygintas Jankauskas b,
,
Vytautas Getautis a
*
a Department of Organic Chemistry, Kaunas University of Technology, Radvilenu pl. 19, LT-50270 Kaunas, Lithuania
b Department of Solid State Electronics, Vilnius University, Sauletekio 9, LT-10222, Vilnius, Lithuania
a r t i c l e i n f o
a b s t r a c t
Article history:
Carbazole based building blocks, possessing diphenylethenyl fragments, have been synthesized.
Condensation of the carbazol-2-ol with diphenylacetaldehyde yields 1,3-substituted derivatives.
Change of the synthesis sequence, however, (i.e., substitution at the hydroxyl and NH groups, followed
by the condensation reaction) results in the 3,6-substituted products. Thermal, optical, electro-
chemical and photophysical properties of the synthesized derivatives have been investigated. Room
temperature hole-drift mobilities, evaluated using xerographic time-of-flight technique, were found to
exceed 10ꢀ4 cm2 Vꢀ1 sꢀ1 at strong electric fields. The obtained results indicate high charge mobility for
molecularly doped polymers, especially considering the fact that these measurements were carried out
under ambient conditions and not in high vacuum. Commercial availability and relative cheapness of
the starting materials, simple synthetic method, number of sites available for easy functionalization
and covalent linking to other molecules makes these precursors attractive building blocks for the
construction of more complex low-molecular-weight or polymeric materials for optoelectronic
applications.
Received 10 December 2009
Received in revised form 2 February 2010
Accepted 22 February 2010
Available online 25 February 2010
Keywords:
Carbazole
Diphenylacetaldehyde
Charge transport
Ionization energy
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
are of excellent hole transport ability, due to their electron-
donating capabilities.5 Furthermore, carbazole derivatives are of
Electronic and optoelectronic devices using organic materials as
active elements, for example, organic light-emitting diodes (OLEDs),
organic photovoltaic devices (OPVs), organic field-effect transistors
(OFETs), organic photorefractive devices, and so forth, have recently
received a great deal of attention from the standpoint of potential
technological applications as well as fundamental science.1 The
devices using organic materials are attractive because they can take
advantage of organic materials such as light weight, potentially low
cost, thin-film capable, large-area, flexible device fabrication.
Due to their specific optical and electrochemical properties,
carbazole and its derivatives have been widely used as functional
building blocks in the fabrication of various optoelectronic de-
vices.2 In the field of OLED technology, carbazole derivatives are
usually used as promising blue light-emitting materials.3
high triplet energy and capable of functioning as host materials in
highly efficient blue, green, or red electrophosphorescent devices,6
due to the efficient energy transfer from these hosts to doped
triplet emitters.
The carbazole moiety can be easily functionalized or covalently
linked to other molecules. Numerous ways are known for en-
hancement of its conjugated p-electron system. For instance, 3,6- or
2,7-linking of carbazole molecules into dimers, trimers or oligo-
mers,7a,b and addition of enamine,7c hydrazone7d–f or diarylamino2a
fragments.
An efficient carbazole based building block for the synthesis of
more complex, low-molecular-weight or polymeric materials
designed for optoelectronic applications, should be easily functio-
nalizable and possess good charge transport properties. Apart from
the factors mentioned above, other important requirements are:
relatively low cost and commercial availability of starting materials
as well as simple and easy synthesis on a multigram scale.
Preliminary research results on this type of building blocks have
been reported by us recently.8 Herein, we present the detailed
synthesis and photophysical properties of the new carbazole based
Interestingly, white light is also achieved from carbazole dimers
or oligomers serving as a single-emitting-component layer.4
Meanwhile, a great many carbazole homopolymers or oligo-
mers, as well as carbazole-containing polymers or small molecules,
precursors with increased
the mentioned conditions.
p-conjugated systems, who meet all of
* Corresponding author. Tel.: þ370 37 300196; fax: þ370 37 300152.
E-mail address: vgetaut@ktu.lt (V. Getautis).
0040-4020/$ – see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.02.086

3200
G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
2. Results and discussion
+
_
OH
H
OH
OH
δ+
δ−
N
H
H
N
H
N
H
O
2.1. Synthesis
H
OH
Ph
O
Ph
Ph
Ph
Ph
Ph
Condensation of 9H-carbazol-2-ol with diphenylacetaldehyde in
1,4-dioxane (water generated during the course of the reaction was
removed with 4 Å molecular sieves) at a reflux temperature results
in formation of 1,3-bis(2,2-diphenylethenyl)-9H-carbazol-2-ol (1)
(Scheme 1). The presence of the strongly ortho/para-directing hy-
droxyl group activates the 1- and 3-positions of the carbazole ring,
and the reaction is more likely to proceed at those sites.
Most probably, delocalization of the lone pair pushes electrons
from the nitrogen atom into the ring and the heterocycle becomes
electron-rich at the expense of the nitrogen atom. An obvious con-
sequence of this delocalization is the increased acidity of the NH
group as a whole; therefore, protonation does not occur at the ni-
trogen atom when using an acid catalyst. The nucleophilic nature of
the ring means that carbazole is attacked readily by electrophiles,
this is further enhanced by the presence of the electron-donating
hydroxyl group at the 2-position. Because nitrogen is less electro-
negative than oxygen, the lone pair is higher in energy and so more
OH
OH
OH
Ph
N
H
N
H
N
H
OH2
H
Ph
Ph
Ph
Ph
Ph
H
O
Ph
O
HO
Ph
Ph
H
δ+
δ−
Ph
OH
Ph
+
_
H
Ph
OH
Ph
Ph
OH
Ph
N
H
N
H
N
H
Ph
Ph
H
Ph
H2O
Ph
Ph
Ph
Ph
Ph
OH
Ph
Ph
OH
Ph
OH
Ph
N
H
N
H
N
H
1
Ph
Ph
Ph
available to interact with the
Delocalization increases the
p
d
system than the lone pair on oxygen.
ꢀ charge on the carbon atoms at the 1-
Scheme 2. Proposed reaction mechanism.
and 3-positions of the 2-hydroxycarbazole molecule, and these po-
sitions are more susceptible to the electrophilic attack (Scheme 2).
hydroxyl group and subsequent loss of water by elimination fol-
lowed by the loss of a proton leads to the formation of the mono-
substituted compound. Identically, reaction at the 3-position
follows the same route. Theoretical calculations indicate that the
dꢀ charge is slightly larger at the 1-position, therefore reaction is
somewhat more likely to proceed at this position first. However,
synthetic experiments showed that disubstituted derivative 1 is
During the electrophilic substitution, a
tween diphenylacetaldehyde and 2-hydroxycarbazole, the carbonyl
bond polarized leaving an oxyanion (alkoxide) and an iminium
s bond is formed be-
p
cation is created. This is followed by a loss of a proton at the 1-
position of the carbazole ring, and acceptance of a proton by the
formed alkoxide ion to form the hydroxyl group. Protonation of the
O
R
KOH
X
R
N
R
O
N
H
OH
1,4-dioxane,
4Å sieves,
CSA, Δ, 3h
N
H
OH
3a 87%
3b 97%
1 60%
O
Toluene, CSA,
Δ, 3h
KOH
R
X
a: R = CH3, X = I
b: R = C3H7, X = Br
CSA = (+/-)-camphor-10-sulfonic acid
R
R
N
R
O
N
R
O
4a 68%
4b 77%
POCl3,
DMF
O
2a 62%
2b 78%
N
O
5 78%
Scheme 1. Synthesis of 1,3- and 3,6-substituted carbazole based precursors 2a,b and 4a,b.

G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
3201
readily formed even when an excess of 9H-carbazol-2-ol is used;
consequently, reactivity at both positions is quite similar.
The isolated 1,3-disubstituted derivative 1 possesses reactive
hydroxyl and NH groups, as well as an unsubstituted 6-position of
the carbazole, which is activated by the nitrogen atom. In order to
investigate the photophysical properties of the synthesized pre-
cursor and test the reactivity of hydroxyl group, as it is located
between two bulky substituents, simple alkylation reactions were
performed. Reaction of 1 with iodomethane and 1-bromopropane,
in the presence of KOH, yielded alkylated carbazole derivatives
2a,b.
Additionally, Vilsmeier formylation of 2b was also performed to
confirm that the 6-position of the carbazole remained active for
electrophilic substitution reactions. 1,3,6-Trisubstituted 2-hydroxy-
carbazole derivative 5 was successfully obtained.
Changing the synthetic sequence, however, (i.e., substitution at
hydroxyl and NH groups, followed by the condensation reaction)
results in products of a different structure. In this case, condensa-
tion of the alkylated intermediate derivatives 3a,b with diphenyl-
acetaldehyde yields 3,6-disubstituted carbazoles 4a,b.
Apparently, substitution of the strongly ortho/para-directing
hydroxyl group with a moderate alkoxyl one, and the additional
steric hindrance resulting from such a change, prevent the reaction
from proceeding at the 1-position of the carbazole ring. Structural
evidence for compounds 2a,b and 4a,b were obtained by NMR
spectroscopy. Furthermore, suitable single crystals of 2b and 4b
were grown from mixtures of n-hexane/acetone and THF/2-
propanol accordingly, and both structures were proven un-
ambiguously by X-ray crystallography (Fig. 1).
Usually the photoemission experiments are carried out in vacuum,
and high vacuum is one of the main requirements for these mea-
surements. If the vacuum is not high enough, the sample surface
oxidation and gas adsorption are influencing the measurement
results. In our case, however, the organic materials investigated are
stable enough to oxygen and the measurements may be carried out
in air. The measured ionization energies vary in the range from
5.62 eV to 5.50 eV.
To elucidate the energetic conditions for energy and electron
transfer in dilute solutions, the HOMO/LUMO values were also
determined using cyclic voltammetry (CV). These EHOMO values do
not represent any absolute solid-state or gas-phase ionization en-
ergies, but can be used to compare different compounds relative to
one another. The cyclic voltammograms of the synthesized com-
pounds in dichloromethane show one quasi-reversible oxidation
couple and no reduction waves (Fig. 3). The electrochemical data
are summarized in Table 2.
The 1,3-substituted derivative 2b shows an oxidation peak cor-
responding to 0.59 V vs Fc, which results in a EHOMO value of
ꢀ5.32 eV (on the basis of the EHOMO energy level of ferrocene as
4.8 eV). Similarly, compound 4b exhibits an oxidation at 0.52 V vs
Fc. This gives a EHOMO value of ꢀ5.23 eV for the compound 4b.
Results from both CV and photoemission in air methods indicate
that EHOMO energy level of 3,6-substituted carbazole derivatives
4a,b is slightly lower than that of 1,3-substituted ones (2a,b).
Charge transport properties of the molecularly doped polymers
consisting of 1,3-substituted (2a,b) or 3,6-substituted (4a,b) car-
bazole derivatives, and bisphenol Z polycarbonate (PC-Z) as poly-
mer host (50% solid solutions) were studied by the xerographic
time-of-flight (XTOF) technique.10
2.2. Thermal analysis
For the solid solution in PC-Z, electron mobility
culated using the formula:
m
may be cal-
Both 1,3- and 3,6-substituted derivatives of 2-hydroxycarbazole
are soluble in common organic solvents such as THF, toluene and
chloroform. The thermal properties of the alkylated precursors
were determined by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA) measurements (Table 1). TGA
shows that all compounds exhibit high thermal stability. In a ni-
trogen atmosphere, decomposition starts above 360 ꢁC and 410 ꢁC
for 2a,b and 4a,b, respectively. DSC measurements (Supplementary
data Fig. S1, S2) indicate that both 1,3- and 3,6-substituted carba-
zole derivatives are able to form molecular glasses.
In general, glass transition temperatures were higher for the
3,6-substituted derivatives 4a,b, compared with the 1,3-substituted
2a,b. Most likely this is a consequence of tighter packing of the
molecules in the compounds 4a,b. Obviously, introduction of longer
flexible aliphatic chains leads to the decrease of Tg in both cases.
ꢀ
ꢁ
pffiffiffi
m ¼ m0exp
a
E
(1)
where m0 is the zero field mobility,
a
is the Poole–Frenkel parameter
and E is the electric field strength. The values of charge mobility
defining parameters m0 and the mobility at the electric field of
,
a
106 V cmꢀ1 for the compounds 2a,b and 4a,b are given in Table 3.
The examples of the dU/dt transients for the corresponding PC-Z
blends are shown in Figure 4. XTOF measurements reveal that small
charge transport transients are with a well-defined transit time on
linear plots in case of 4b. The XTOF transients for the compounds
2a,b and 4a, on the other hand, were of disperse character, but the
transit time was well seen on lg–lg plots.
Room temperature hole-drift mobilities were found to approach
10ꢀ4 cm2 Vꢀ1 sꢀ1 at strong electric fields (Fig. 5). Presence of longer
flexible aliphatic chains in compounds 2b and 4b ensures better
quality of the obtained layers and consequently noticeably higher
hole-drift mobility.
2.3. The optical, electrochemical and photophysical
properties
In general, the obtained results indicate high charge mobility for
molecularly doped polymers, especially considering the fact that
these measurements were carried out under ambient conditions
and not in high vacuum.
The UV–vis absorption spectra of the carbazole derivatives 2a,b
and 4a,b were recorded at room temperature in THF (Table 1, Fig. 2).
The absorption spectra of both 2b and 4b are bathochromically
shifted (z22 nm) with respect to the spectrum of 9-ethylcarbazole
(
lmax¼294 nm). Specifically, the
p
/
p
* absorption band is in-
3. Conclusion
tensified (hyperchromic shift) and shifted to lower energy, in-
dicating extended conjugation in these compounds.
In conclusion, novel carbazole based derivatives possessing
diphenylethenyl fragments have been synthesized. Commercial
availability and relative cheapness of the starting materials, simple
synthetic method, number of sites available for easy functionali-
zation and covalent linking to other molecules, glass-forming
properties, good charge drift mobility and solubility in common
organic solvents makes these precursors attractive building blocks
for the construction of more complex low-molecular-weight or
polymeric materials for optoelectronic applications.
The fluorescence spectra of the carbazole based precursors 2b
and 4b are also included in Figure 2. The shape and the maxima of
the fluorescence curves are almost identical, fluorescence maxima
are detected at 476 and 474 nm, respectively. The carbazole de-
rivatives exhibit blue fluorescence, which is usual for carbazole-
containing compounds.
The ionization energy (EI) was measured by the electron pho-
toemission in air method,9 and results are presented in Table 2.

3202
G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
Figure 1. ORTEP projection of the crystal structure of 2b (top) and 4b (bottom). Displacement ellipsoids are drawn at 50% probability level.

G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
3203
Table 1
Optical and thermal characteristics of the synthesized derivatives
3
2
2b
4b
ab
Entry
l
/nma
e
/Mꢀ1cmꢀ1
lflmax/nmb
Tg/ꢁCc
Tdec/ꢁCd
Tm/ꢁCe
max
2a
2b
4a
4b
316
316
316
316
2.1ꢂ104
2.8ꢂ104
2.4ꢂ104
3.7ꢂ104
476
476
474
474
87
64
96
72
365
369
415
413
212
144
230
195
a
UV–vis and FL spectra measured in 10ꢀ4 M THF solution.
b
c
lex¼330 nm.
1
Determined by DSC: scan rate, 10 K/min; N2 atmosphere; second run.
d
Onset of decomposition determined by TGA: heating rate, 10 K/min; N2
atmosphere.
e
Melting point was only detected during the first heating; the compound vitrified
on cooling to room temperature with 10 K/min.
0
-1
1,0
0,8
0,6
0,4
0,2
0,0
1,0
0,8
0,6
0,4
0,2
0,0
2 b
4 b
Cz
0,0
0,2
0,4
0,6
E vs Fc/Fc+ (V)
Figure 3. Cyclic voltammograms of 2b (scan rate¼50 mV sꢀ1) and 4b (scan rate¼
20 mV sꢀ1) in argon-purged dichloromethane solutions.
Table 3
Hole mobility data for mixtures of 2a,b and 4a,b with PC-Z
Transport material, d/
host polymer
m
m
m0/cm2
V
ꢀ1 sꢀ1a
m
/cm2
V
ꢀ1 sꢀ1b
a
/cm1/2 Vꢀ1/2
2aþPC-Z, 1:1
2bþPC-Z, 1:1
4aþPC-Z, 1:2
4bþPC-Z, 1:1
7
2ꢂ10ꢀ8
3ꢂ10ꢀ6
3ꢂ10ꢀ8
1ꢂ10ꢀ6
1.1ꢂ10ꢀ5
6.9ꢂ10ꢀ5
2.5ꢂ10ꢀ6
8.1ꢂ10ꢀ5
0.006
12
12
7.5
0.0031
0.0044
0.0044
200 250 300 350 400 450 500 550 600 650
Wavelength / nm
a
Mobility value at zero field strength.
Mobility value at 106 V cmꢀ1 field strength.
b
Figure 2. Absorption and fluorescence spectra of 10ꢀ4 M THF solutions of the carba-
zole derivatives 2b and 4b. The absorption spectrum of 9-ethylcarbazole (Cz) is shown
for comparison.
150 Å, Aldrich) was used for column chromatography. Elemental
analysis was performed with an Exeter Analytical CE-440 Elemen-
tal. IR-spectroscopy was performed on a Perkin Elmer Spectrum BX
II FTIR System, using KBr pellets. X-ray crystallography analysis was
carried out utilizing Bruker-Nonius Kappa CCD single crystal dif-
Table 2
HOMO, LUMO, band gap energies and electrochemical properties of 2a,b and 4a,ba
vs Eopxa vs Eogpt/eVc EI/eVd EHOMO/eVe ELUMO/eVf
ox
Entry E1/2
Eonset vs
E
pc
vs Fc/Vb Fc/V
Fc/V Fc/V
fractometer, using Mo Ka radiation (
l
¼0.71073 Å). Single crystal
data was processed using maXus, SIR 97, ORTEP, SHELXL-97 soft-
ware. Melting points were determined using Electrothermal Mel-
Temp melting point apparatus. MS were recorded on an Aligent
110 (series MS with VL) apparatus. The UV–vis and FL spectra were
recorded as dilute solutions of the synthesized compounds in THF
on Perkin Elmer Lambda 35 and Hitachi MPF-4 spectrophotometers
accordingly. Microcells with an internal width of 1 and 10 mm were
used, respectively. The DSC and TGA measurements were carried
out on a Mettler DSC 30 calorimeter at a scan rate of 10 K/min. CV
measurements were carried out by a three-electrode assembly cell
from Bio-Logic SAS and a micro-AUTOLAB Type III potentiostat–
galvanostat. The measurements were carried out with a glassy
carbon electrode in dichloromethane solutions containing 0.1 M
tetrabutylammonium perchlorate as electrolyte, Ag/AgNO3 as the
reference electrode and a Pt wire counter electrode.
2a
2b
4a
4b
0.53
0.52
0.45
0.43
0.46
0.45
0.38
0.36
0.60 0.46 2.99
0.59 0.45 3.01
0.55 0.35 2.96
0.52 0.34 2.97
5.62 ꢀ5.33
5.60 ꢀ5.32
5.56 ꢀ5.25
5.50 ꢀ5.23
ꢀ2.34
ꢀ2.31
ꢀ2.29
ꢀ2.26
a
The measurements were carried out at a glassy carbon electrode in dichloro-
methane solutions containing 0.1 M tetrabutylammonium perchlorate as electrolyte
and Ag/AgNO3 as the reference electrode. Each measurement was calibrated with
FC
ferrocene (Fc), with the measured E ¼0.105 V vs Ag/AgNO3.
1/2
b
E1/2¼(EpaþEpc)/2; Epa and Epc are peak anodic and peak cathodic potentials,
respectively.
c
The optical band gaps Eogpt estimated from the edges of electronic absorption
spectra.
d
Ionization energy was measured by the photoemission in air method from films.
e
f
FC
EHOMO¼4.8þ(E1/2ꢀE ).
1/2
ELUMO¼EHOMOꢀEgopt
.
4. Experimental section
4.1. General
4.1.1. Ionization energy measurements. The ionization energy EI of
the layers of the synthesized compounds was measured by the
electron photoemission in air method. The samples for the ioniza-
tion energy measurement were prepared by dissolving materials in
All chemicals were purchased from Aldrich and used as received
without further purification. The 1H NMR spectra were recorded on
a Varian Unity Inova (300 MHz) spectrometer at room temperature.
THF and were coated on Al plates pre-coated with w0.5
methylmethacrylate and methacrylic acid copolymer adhesive
layer. The thickness of the transporting material layer was 0.5–1 m.
mm thick
All the data are given as chemical shifts in
d (ppm), (CH3)4Si (TMS,
m
0 ppm) was used as an internal standard. The course of the reactions
products were monitored by TLC on ALUGRAM SIL G/UV254 plates
and developed with I2 or UV light. Silica gel (grade 62, 60–200 mesh,
The samples were illuminated with monochromatic light from
the quartz monochromator with a deuterium lamp. The power of
the incident light beam was (2–5)ꢂ10ꢀ8 W. The negative voltage of

3204
G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
I
0.5 and h
extrapolated to the h
n
near the threshold. The linear part of this dependence was
axis and the EI value was determined as the
n
photon energy at the interception point.
4.1.2. Hole mobility measurements. The samples for mobility mea-
surements were prepared from 1:1 mass proportion composition of
the investigated compound with polycarbonate-Z (Iupilon Z-200
from Mitsubishi Gas Chemical Co.). The sample substrate was
polyester film with conductive Al layer. The layer thickness was in
the range 5–10 mm.
The hole-drift mobility was measured by the xerographic time-
of-flight technique. Electric field was created by positive corona
charging. The charge carriers were generated at the layer surface by
illumination with pulses of nitrogen laser (pulse duration was 2 ns,
wavelength 337 nm). The layer surface potential decrease as a re-
sult of pulse illumination was up to 1–5% of initial potential before
illumination. The capacitance probe that was connected to the wide
frequency band electrometer measured the speed of the surface
potential decrease dU/dt. The transit time tt was determined by the
kink on the curve of the dU/dt transient in double logarithmic scale.
The drift mobility was calculated by the formula
d is the layer thickness, U0dthe surface potential at the moment of
m
¼d2/U0tt, where
illumination.
4.2. Synthesis
4.2.1. 1,3-Bis(2,2-diphenylethenyl)-9H-carbazol-2-ol (1). 9H-Carba-
zol-2-ol (15 g, 0.082 mol) was dissolved in 1,4-dioxane (110 mL),
(þ/ꢀ)-camphor-10-sulfonic acid (19.04 g, 0.082 mol) was added
and the mixture was heated at reflux for 20 min. Diphenylace-
taldehyde (40.17 g, 0.205 mol) was next added and reflux continued
(3 h). Water generated during the course of the reaction was re-
moved with 4 Å molecular sieves. After termination of the reaction
(TLC control, acetone/n-hexane, 7:18), the mixture was treated with
ethyl acetate and washed with distilled water. The organic layer
was dried over anhydrous MgSO4, filtered and solvents were re-
moved. The residue was purified by column chromatography using
acetone/n-hexane (1:24 and 1:4 v/v) as eluent. Recrystallization of
the residue from toluene yielded 1 (26.51 g, 60%) as a pale yellow
powder, mp: 194–195 ꢁC (recrystallized from toluene); [Found: C,
89.16; H, 5.50; N, 2.51. C40H29NO requires C, 89.02; H, 5.42; N,
2.60%]; Rf (acetone/n-hexane, 7:18, v/v) 0.49; nmax(KBr) 3537, 3440,
3077, 3056, 3028, 1625, 1611, 1594, 1490, 1444, 1183, 806, 779, 769,
Figure 4. XTOF transientsforthe2b and 4b. Insetsshow one transient curve in linearplot.
t=25oC
10-4
760, 736, 701, 654 cmꢀ1
; dH (300 MHz, CDCl3) 7.57–7.50 (m, 1H),
10-5
7.47–7.09 (m, 25H), 7.08–6.97 (m, 2H), 5.31 (s, 1H); dC (75 MHz,
CDCl3) 150.5, 145.7, 143.5, 143.1, 142.9, 140.4, 139.68, 139.62, 137.4,
130.7, 129.8, 128.96, 128.74, 128.66, 128.49, 128.37, 128.09, 127.65,
126.18, 124.6, 123.8, 121.6, 120.5, 119.57, 119.36, 117.9, 116.7, 110.3,
107.4; MS(APCIþ, 20 V), m/z: 540 ([MþH]þ).
μ
2b+PC-Z, 1:1
4b+PC-Z, 1:1
10-6
0
200
400
600
1/2 (V/cm)1/2
800
1000
1200
4.2.2. 1,3-Bis(2,2-diphenylethenyl)-9-methyl-2-methoxycarbazol
(2a). Compound 1 (1.98 g, 0.004 mol) was dissolved in iodo-
methane (11.5 mL, 0.183 mol), 85% powdered KOH (1.45 g,
0.022 mol) and anhydrous Na2SO4 (0.78 g, 0.006 mol) were added
and the reaction mixture was heated at reflux for 3 h. After ter-
mination of the reaction (TLC control, acetone/n-hexane, 1:4), the
mixture was treated with ethyl acetate and washed with distilled
water. The organic layer was dried over anhydrous MgSO4, filtered,
solvents were removed. Recrystallization of the residue from ethyl
acetate yielded 2a (1.29 g, 62%) as a pale yellow powder, mp: 210–
212 ꢁC (recrystallized from ethyl acetate); [Found: C, 88.76; H, 5.93;
N, 2.51. C42H33NO requires C, 88.86; H, 5.86; N, 2.47%]; Rf (acetone/
n-hexane, 1:4, v/v) 0.49; nmax(KBr) 3054, 3028, 2997, 2927, 1621,
1589, 1485, 1464, 1443, 1238, 1217, 1052, 1031, 774, 764, 753, 742,
E
Figure 5. Electric field dependencies of the hole-drift mobilities (
port layers of compounds 2b and 4b doped in PC-Z (mass proportion 1:1).
m) in charge trans-
–300 V was supplied to the sample substrate. The counter-electrode
with the 4.5ꢂ15 mm2 slit for illumination was placed at an 8 mm
distance from the sample surface. The counter-electrode was con-
nected to the input of the BK2-16 type electrometer, working in the
open input regime, for the photocurrent measurement. The
10ꢀ15d10ꢀ12 A strong photocurrent was flowing in the circuit under
illumination. The photocurrent I is strongly dependent on the in-
cident light photon energy h
ted. Usually the dependence of the photocurrent on incident light
quanta energy is well described by the linear relationship between
n
. The I0.5¼f(h
n) dependence was plot-
725, 698 cmꢀ1
(m, 6H), 3.90 (s, 3H), 3.79 (s, 3H); dC (75 MHz, CDCl3) 156.2, 146.1,
; dH (300 MHz, CDCl3) 7.49–7.19 (m, 21H), 7.16–7.04

G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
3205
143.88, 143.46, 142.5, 141.24, 141.06, 139.86, 139.19, 130.9, 129.9,
128.71, 128.62, 128.57, 128.30, 127.94, 127.81, 127.45, 127.31, 127.27,
125.1, 124.2, 123.1, 122.9, 121.54, 121.16, 119.53, 119.42, 119.22, 115.1,
108.7, 61.6, 32.1; MS(APCIþ, 20 V), m/z: 568 ([MþH]þ).
continued (3 h) using a Dean–Stark trap. After termination of the
reaction (TLC control, acetone/n-hexane, 1:4), the mixture was
treated with ethyl acetate and washed with distilled water. The
organic layer was dried over anhydrous MgSO4, filtered and sol-
vents were removed. The residue was purified by column chro-
matography using acetone/dichloromethane/n-hexane (0.5:0.5:4
v/v/v) as eluent. Recrystallization of the residue from ethyl acetate
yielded 4a (10.96 g, 68%) as a pale yellow powder, mp: 228–230 ꢁC
(recrystallized from ethyl acetate); [Found: C, 88.80; H, 5.78; N,
2.54. C42H33NO requires C, 88.86; H, 5.86; N, 2.47%]; Rf (acetone/n-
hexane, 1:4, v/v) 0.30; nmax(KBr) 3076, 3055, 3020, 2933, 2832,
1632, 1600, 1591, 1492, 1473, 1443, 1253, 1212, 1208, 1121, 1059, 893,
4.2.3. 1,3-Bis(2,2-diphenylethenyl)-9-propyl-2-propoxycarbazol
(2b). Compound 2b was prepared and isolated according to the
same procedure as 2a, except that 1 (12 g, 0.022 mol), 1-brompro-
pane (100 mL, 1.1 mol), 85% powdered KOH (8.81 g, 0.133 mol) and
anhydrous Na2SO4 (4.74 g, 0.033 mol) of were used. Re-
crystallization of the residue from ethyl acetate yielded 2b (10.82 g,
78%) as a pale yellow powder, mp: 140–141 ꢁC (recrystallized from
ethyl acetate); [Found: C, 88.50; H, 6.54; N, 2.20. C46H41NO requires
C, 88.57; H, 6.62; N, 2.25%]; Rf (acetone/n-hexane, 1:4, v/v) 0.74;
nmax(KBr) 3077, 3055, 3020, 2990, 2958, 2948, 2877, 2866, 1621,
1595, 1579, 1494, 1479, 1467, 1457, 1056, 1005, 893, 774, 767, 749,
803, 778, 761, 741, 731, 697 cmꢀ1
; dH (300 MHz, CDCl3) 7.45–7.17 (m,
23H), 7.07 (s, 1H), 7,02–6,92 (m, 2H), 6,70 (s, 1H), 3,92 (s, 3H), 3,68
(s, 3H); dC (75 MHz, CDCl3) 157.9, 144.22, 144.05, 141.70, 141.22,
141.12, 140.84, 140.02, 130.75, 130.72, 129.38, 128.88, 128.78, 128.67,
128.36, 128.26, 127.98, 127.60, 127.33, 127.25, 127.20, 126.25, 124.1,
123.0, 121.95, 121.01, 119.5, 115.7, 107.7, 90.6, 55.9, 29.2; MS(APCIþ,
20 V), m/z: 568 ([MþH]þ).
726, 715, 696 cmꢀ1
; dH (300 MHz, CDCl3) 7.49–7.15 (m, 21H), 7.12–
7.00 (m, 6H), 4.65–4.46 (m, 1H), 4.28–4.09 (m, 1H), 4.00–3.67 (m,
2H), 1.85–1.63 (m, 4H), 0.91 (t, J¼7.4 Hz, 3H), 0.78 (t, J¼7.4 Hz, 3H);
dC (75 MHz, CDCl3) 155.2, 146.2, 143.85, 143.61, 141.73, 141.16, 140.5,
139.8, 138.6, 130.9, 129.9, 128.76, 128.52, 128.37, 128.28, 127.82,
127.73, 127.37, 127.23, 127.15, 124.96, 124.35, 123.31, 123.13, 121.5,
120.9,119.57, 119.24,119.11, 114.8,108.9, 75.9, 46.1, 23.86, 23.81, 11.5,
10.9; MS(APCIþ, 20 V), m/z: 624 ([MþH]þ).
4.2.7. 3,6-Bis(2,2-diphenylethenyl)-9-propyl-2-propoxycarbazol
(4b). Compound 4b was prepared according to the same procedure
as 4a except that 3b (5 g, 0.019 mol), (þ/ꢀ)-camphor-10-sulfonic
acid (4.41 g, 0.019 mol) and diphenylacetaldehyde (9.17 g,
0.047 mol) were used. After termination of the reaction (TLC con-
trol, acetone/n-hexane, 1:4), the mixture was treated with ethyl
acetate and washed with distilled water. The organic layer was
dried over anhydrous MgSO4, filtered and solvents were removed.
Recrystallization of the residue from ethylmethylketone yielded 4b
(8.98 g, 77%) as a pale yellow powder, mp: 193–194 ꢁC (recrystal-
lized from ethylmethylketone); [Found: C, 88.65; H, 6.57; N, 2.32.
C46H41NO requires C, 88.57; H, 6.62; N, 2.25%]; Rf (acetone/n-hex-
ane, 1:4, v/v) 0.58; nmax(KBr) 3077, 3055, 3020, 2964, 2873, 1630,
1592, 1491, 1485, 1472, 1442, 1260, 1199, 1125, 1069, 798, 776, 758,
4.2.4. 9-Methyl-2-methoxycarbazol (3a). 9H-Carbazol-2-ol (8 g,
0.044 mol) was dissolved in DMF (30 mL), iodomethane (16.3 mL,
0.262 mol), 85% powdered KOH (11.62 g, 0.176 mol) and anhydrous
Na2SO4 (6.25 g, 0.044 mol) were added and reaction mixture stir-
red at room temperature (10 min). After termination of the reaction
(TLC control, acetone/n-hexane, 1:4), water was added and the
precipitate was filtered off, washed with water and ethanol. Re-
crystallization of the residue from acetone yielded 3a (8.05 g, 87%)
as a pale brown powder, mp: 98–99 ꢁC (recrystallized from ace-
tone); [Found: C, 79.66; H, 6.14; N, 6.55. C14H13NO requires C, 79.59;
H, 6.20; N, 6.63%]; Rf (acetone/n-hexane, 1:4, v/v) 0.44; nmax(KBr)
3010, 2965, 2944, 2909, 2836, 1628, 1608, 1569, 1503, 1462, 1443,
737, 724, 702, 694 cmꢀ1
; dH (300 MHz, CDCl3) 7.44–7.17, (m, 23H),
7.05 (s, 1H), 6.99–6.88 (m, 2H), 6.69 (s, 1H), 4.14–3.97 (m, 4H), 1.91–
1.71 (m, 4H), 1.08 (t, J¼7.4 Hz, 3H), 0.92 (t, J¼7.4 Hz, 3H); dC
(75 MHz, CDCl3) 157.4, 144.38, 144.14, 141.35, 141.24, 141.16, 140.24,
139.88, 139.67, 130.79, 130.73, 129.44, 128.89, 128.78, 128.64,
128.36, 128.29, 127.89, 127.62, 127.31, 127.21, 127.05, 126.0, 124.0,
123.2, 121.89,121.15,119.7, 115.8,107.9, 92.0, 70.6, 44.8, 22.90, 22.42,
12.0, 11.0; MS(APCIþ, 20 V), m/z: 624 ([MþH]þ).
1306, 1163, 764, 746, 727 cmꢀ1
; dH (300 MHz, CDCl3) 8.03–7.91 (m,
2H), 7.44–7.29 (m, 2H), 7.26–7.15 (m, 1H), 6.88–6.81 (m, 2H), 3.93 (s,
3H), 3.78 (s, 3H); dC (75 MHz, CDCl3) 159.3, 142.5, 141.2, 124.5, 123.1,
121.2, 119.57, 119.11, 116.8, 108.3, 107.4, 92.9, 55.8, 29.2; MS(APCIþ,
20 V), m/z: 212 ([MþH]þ).
4.2.5. 9-Propyl-2-propoxycarbazol (3b). Compound 3b was pre-
pared and isolated according to the same procedure as 3a, except
that 9H-carbazol-2-ol (25 g, 0.137 mol), 1-brompropane (74.4 mL,
0.819 mol), 85% powdered KOH (54.04 g, 0.819 mol) and of anhy-
drous Na2SO4 (29.09 g, 0.205 mol) were used. Recrystallization of
the residue from methanol yielded 3b (35.31 g, 97%) as a pale
brown powder, mp: 38–39 ꢁC (recrystallized from methanol);
[Found: C, 80.78; H, 7.84; N, 5.30. C18H21NO requires C, 80.86; H,
7.92; N, 5.24%]; Rf (acetone/n-hexane, 1:4, v/v) 0.85; nmax(KBr)
3043, 3024, 2965, 2935, 2875, 1628, 1600, 1573, 1498, 1467, 1459,
4.2.8. 1,3-Bis(2,2-diphenylethenyl)-6-methanoyl-9-propyl-2-propoxy-
carbazol (5). DMF (2.49 mL, 0.032 mol) was cooled in a ice/salt
bath to 0 ꢁC and POCl3 (3 mL, 0.032 mol) was slowly added. During
the addition of POCl3 temperature of mixture was not allowed to
rise above 5 ꢁC. After addition of POCl3 the reaction mixture was
allowed to warm to room temperature and 2b (3.35 g, 0.005 mol),
dissolved in DMF (20 mL), was added. The mixture was heated for
3 h at 90 ꢁC. After termination of the reaction (TLC control, acetone/
n-hexane, 7:18), hot reaction mixture was poured into a beaker
with ice, neutralized by adding sodium acetate (9.58 g; 0.12 mol)
solution in water and allowed to stand at 5 ꢁC for 24 h. Re-
crystallization of the residue from ethanol/ethyl acetate,1:3 yielded
5 (3.42 g, 98%) as pale yellow powder, mp: 194–195 ꢁC (recrystal-
lized from ethanol/ethyl acetate, 1:3); [Found: C, 86.45; H, 6.42; N,
2.24. C47H41NO2 requires C, 86.60; H, 6.34; N, 2.15%]; Rf (acetone/n-
hexane, 7:18, v/v) 0.59; nmax(KBr) 3054, 3024, 2961, 2934, 2874,
2820, 1686, 1621, 1590, 1572, 1489, 1468, 1442, 1340, 1199, 1133,
1194, 1117, 768, 760, 746 cmꢀ1
; dH (300 MHz, CDCl3) 7.97 (d,
J¼7.6 Hz,1H), 7.92 (d, J¼8.3 Hz,1H), 7.41–7.29 (m, 2H), 7.23–7.12 (m,
1H), 6,87–6,79 (m, 2H), 4.17 (t, J¼7.2 Hz, 2H), 4.03 (t, J¼6.6 Hz, 2H),
1.95–1.79 (m, 4H), 1.08 (t, J¼7.4 Hz, 3H), 0.96 (t, J¼7.4 Hz, 3H); dC
(75 MHz, CDCl3) 158.7, 142.1, 140.8, 124.4, 123.2, 121.1, 119.6, 118.9,
116.8, 108.6, 107.6, 94.2, 70.2, 44.7, 22.97, 22.35, 12.0, 10.8;
MS(APCIþ, 20 V), m/z: 268 ([MþH]þ).
1061, 1032, 807, 799, 772, 763, 737, 727, 698 cmꢀ1
; dH (300 MHz,
4.2.6. 3,6-Bis(2,2-diphenylethenyl)-9-methyl-2-methoxycarbazol
(4a). Compound 3a (6 g, 0.028 mol) was dissolved in toluene
(30 mL), (þ/ꢀ)-camphor-10-sulfonic acid (6.5 g, 0.028 mol) was
added and the mixture was heated at reflux for 20 min. Afterwards
diphenylacetaldehyde (13.93 g, 0.071 mol) was added and reflux
CDCl3) 9.95 (s, 1H), 7.95 (d, J¼1.5 Hz, 1H), 7.86 (dd, J1¼8.6 Hz,
J2¼1.5 Hz, 1H), 7.50–6.98 (m, 24H), 4.70–4.50 (m, 1H), 4.31–4.09 (m,
1H), 4.04–3.72 (m, 2H), 1.92–1.56 (m, 4H), 0.92 (t, J¼7.4 Hz, 3H),
0.81 (t, J¼7.4 Hz, 3H); dC (75 MHz, CDCl3) 191.8, 156.0, 146.8, 145.4,
143.58, 143.26, 141.7, 140.8, 139.88, 139.55, 139.10, 130.85, 129.81,

3206
G. Bubniene et al. / Tetrahedron 66 (2010) 3199–3206
2. (a) Shirota, Y.; Kageyama, H. Chem. Rev. 2007, 107, 953; (b) Grazulevicius, J. V.;
Strohriegl, P. Adv. Mater. 2002, 14, 1439; (c) Sonntag, M.; Kreger, K.; Hanft, D.;
Strohriegl, P. Chem. Mater. 2005, 17, 3031.
3. (a) Adhikari, R. M.; Mondal, R.; Shah, B. K.; Neckers, D. C. J. Org. Chem. 2007, 72,
4727; (b) Zhao, Z.; Zhang, P.; Wang, F.; Wang, Z.; Lu, P.; Tian, W. Chem. Phys. Lett.
2006, 423, 293; (c) Shen, J.-Y.; Yang, X.-L.; Huang, T.-H.; Lin, J. T.; Ke, T.-H.; Chen,
L.-Y.; Wu, C.-C.; Yeh, M.-C. P. Adv. Funct. Mater. 2007, 17, 983.
4. (a) Liu, Y.; Nishiura, M.; Wang, Y.; Hou, Z. J. Am. Chem. Soc. 2006, 128, 5592; (b)
Li, J. Y.; Liu, D.; Ma, C. W.; Lengyel, O.; Lee, C.-S.; Tung, C.-H.; Lee, S. T. Adv. Mater.
2004, 16, 1583; (c) Zhao, Z.; Zhao, Y.; Lu, P.; Tian, W. J. Phys. Chem. C 2007, 111,
6883.
5. (a) Liu, B.; Yu, W.; Lai, Y.; Huang, W. Chem. Mater. 2001, 13, 1984; (b) Xia, C.;
Advincula, R. C. Macromolecules 2001, 34, 5854; (c) Stephan, O.; Vial, J.-C. Synth.
Met. 1999, 106, 115; (d) Promarak, V.; Ichikawa, M.; Sudyoadsuk, T.; Saengsu-
wan, S.; Jungsuttiwong, S.; Keawin, T. Synth. Met. 2007, 157, 17; (e) Li, J.; Ma, C.;
Tang, J.; Lee, C.-S.; Lee, S. T. Chem. Mater. 2005, 17, 615; (f) Qian Zhang, Q.; Chen,
J.; Cheng, Y.; Wang, L.; Ma, D.; Jing, X.; Wang, F. J. Mater. Chem. 2004, 14, 895.
6. (a) Chen, Y.-C.; Huang, G.-S.; Hsiao, C.-C.; Chen, S.-A. J. Am. Chem. Soc. 2006, 128,
5592; (b) Tsai, M.-H.; Hong, Y.-H.; Chang, C.-H.; Su, H.-C.; Wu, C.-C.; Mato-
liukstyte, A.; Simokaitiene, J.; Grigalevicius, S.; Grazulevicius, J. V.; Hsu, C.-P.
Adv. Mater. 2007, 19, 862; (c) Shih, P.-I.; Chiang, C.-L.; Dixit, A. K.; Chen, C.-K.;
Yuan, M.-C.; Lee, R.-Y.; Chen, C.-T.; Diau, E. W.-G.; Shu, C.-F. Org. Lett. 2006, 8,
2799.
7. (a) Sonntag, M.; Strohriegl, P. Chem. Mater. 2004, 16, 4736; (b) Morin, J.-F.;
Leclerc, M.; Ade`s, D.; Siove, A. Macromol. Rapid Commun. 2005, 26, 761; (c)
Matoliukstyte, A.; Burbulis, E.; Grazulevicius, J. V.; Gaidelis, V.; Jankauskas, V.
Synth. Met. 2008, 158, 462; (d) Lygaitis, R.; Getautis, V.; Grazulevicius, J. V. Chem.
Soc. Rev. 2008, 37, 770; (e) Bubniene, G.; Malinauskas, T.; Stanisauskaite, A.;
Jankauskas, V.; Getautis, V. Synth. Met. 2009, 159, 1695; (f) Getautis, V.;
Daskeviciene, M.; Malinauskas, T.; Stanisauskaite, A.; Stumbraite, J. Molecules
2006, 11, 64.
128.83, 128.60, 128.34, 128.32, 128.04, 127.81, 127.70, 127.45, 127.42,
126.50, 124.9, 123.95, 123.48, 123.09, 121.3, 120.6, 119.3, 115.8, 109.2,
75.9, 46.3, 23.81, 23.79, 11.5, 10.9; MS(APCIþ, 20 V), m/z: 652
([MþH]þ).
Crystallographic data (excluding structure factors) for the
structures in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication num-
bers CCDC 741268 and 741269. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing
data_request@ccdc.cam.ac.uk, or by contacting The Cambridge
Crystallographic Data Centre, 12, Union Road, Cambridge CB2 1EZ,
UK; fax: þ44 1223 336033.
Acknowledgements
Financial support by the Lithuanian Science and Studies Foun-
dation is gratefully acknowledged. Habil. Dr. V. Gaidelis from the
Department of Solid State electronics, Vilnius University is thanked
for the ionization energy measurements.
Supplementary data
Supplementary data associated with this article can be found in
the online version at doi:10.1016/j.tet.2010.02.086.
8. Bubniene, G.; Stanisauskaite, A.; Getautis, V; Daskeviciene, M.; Jankauskas, V.;
Sidaravicius; J. Abstract Book, International Conference on Organic Synthesis,
Vilnius, Lithuania, June 29–July 2, 2008; Vilnius University: Vilnius, 2008; PO 19.
9. (a) Kirkus, M.; Tsai, M. H.; Grazulevicius, J. V.; Wu, C. C.; Chi, L. C.; Wong, K. T.
Synth. Met. 2009, 159, 729; (b) Miyamoto, E.; Yamaguchi, Y.; Yokoyama, M.
Electrophotography 1989, 28, 364; (c) Cordona, M.; Ley, L. Top. Appl. Phys. 1978,
26, 1.
References and notes
1. (a) Forrest, S. R. Nature 2004, 428, 911; (b) Shirota, Y. J. Mater. Chem. 2005, 15,
75; (c) Organic Light-Emitting Devices, Synthesis, Properties, and Applications;
Mu¨llen, K., Scherf, U., Eds.; Wiley-VCH: Weinheim, 2006; (d) Organic Photo-
voltaics, Mechanisms, Materials and Devices; Sun, S. S., Sariciftci, N. S., Eds.; CRC:
New York, NY, 2005; (e) Mas-Torrent, M.; Rovira, C. J. Mater. Chem. 2006, 16, 433.
10. (a) Vaezi-Nejad, S. M. Int. J. Electron. 1987, 62, 361; (b) Archie, Y.; Chan, C.;
Juhasz, C. Int. J. Electron. 1987, 62, 625.