Synthesis and characterization of novel conjugated bisindenocarbazoles

Article abstract of DOI:10.1016/j.tet.2006.06.015

We present the synthesis of five new bisindenocarbazoles with different alkyl substituents. The synthesis starts from 2,7-dibromocarbazole and leads to the bisindenocarbazoles 6-10 in five steps with an overall yield of about 50%. By substitution of the c

Full text of DOI:10.1016/j.tet.2006.06.015

Tetrahedron 62 (2006) 8103–8108
Synthesis and characterization of novel conjugated
bisindenocarbazoles
*
Martin Sonntag and Peter Strohriegl
Lehrstuhl Makromolekulare Chemie I, Universita€t Bayreuth, 95440 Bayreuth, Germany
Received 9 March 2006; revised 1 June 2006; accepted 2 June 2006
Available online 21 June 2006
Abstract—We present the synthesis of five new bisindenocarbazoles with different alkyl substituents. The synthesis starts from 2,7-dibromo-
carbazole and leads to the bisindenocarbazoles 6–10 in five steps with an overall yield of about 50%. By substitution of the core with different
alkyl chains in the last step of the synthesis, the morphology of the bisindenocarbazoles can be varied from crystalline materials to molecular
glasses. The bisindenocarbazoles are electrochemically stable and exhibit a strong, saturated blue emission with a quantum yield of 63% in
solution.
Ó 2006 Elsevier Ltd. All rights reserved.
1. Introduction
2. Results and discussion
Fused aromatics like pentacene and rubrene are attractive
materials for organic electronics. Both pentacene single
crystals1 and thin, polycrystalline pentacene films exhibit
carrier mobilities above 1 cm2/Vs in organic field effect tran-
sistors (OFETs).2 Single crystalline rubrene shows carrier
mobilities up to 15 cm2/Vs in OFETs.3 In addition, rubrene
has been used as efficient yellow dopant in organic light
emitting diodes (OLEDs).4
2.1. Preparation of the bisindenocarbazoles
Scheme 1 shows the synthetic route to the new bisindenocar-
bazoles. The preparation of 2,7-dibromocarbazole (1) and
the N-alkylated carbazole monomers (2a–c) has been re-
ported elsewhere.9–13
For phenylation (B) of the N-alkyl carbazoles 2a–c in posi-
tions 2 and 7, the Suzuki cross coupling reaction was chosen,
as it is an excellent tool for unsymmetrical aryl–aryl cou-
plings.14 The reactions were carried out in a two-phase sys-
tem of toluene and aqueous potassium carbonate, with
trimethylbenzylammonium chloride as phase-transfer cata-
lyst (PTC). For Suzuki coupling of 2-acetylphenylboronic
acid and N-alkylated 2,7-dibromocarbazoles 2a–c, a mixture
of Pd(OAc)2 and P(o-tol)3 was used as catalyst. Excellent
yields of up to 91% of 3a–c were achieved. In the next
step, the keto groups were reduced to the corresponding
secondary alcohols 4a–c by reaction with lithium triethyl
borohydride (super-hydride) in abs THF. In the case of bis-
indenocarbazoles, the reduction with super-hydride solution
works fast and quantitatively.
Besides pure hydrocarbons like pentacene, materials con-
taining fused heterocycles have attracted increasing interest
as materials for organic electronics during the last years. For
example, indolo- and bisindolocarbazoles have been synthe-
sized and successfully tested in OFETs.5–8
In this paper, we present the synthesis of five new bisindeno-
carbazoles, a class of fused heterocycles that has not yet been
described in the literature. We have developed a new and
versatile strategy for the preparation of these materials,
which makes it possible to introduce different alkyl substit-
uents to the core in the very last step of the synthesis. This
allows us to tailor the properties of this new class of mate-
rials. For example, 6 with four small methyl substituents in
the 1- and 10-positions is highly crystalline, whereas 7 with
two butyl and two methyl groups is an amorphous molecular
glass.
The ring closure reaction of 4a–c to the bisindenocarbazoles
5a–c was carried out with boron trifluoride etherate as
Lewis-acid catalyst in dichloromethane at room tempera-
ture. Ring closure occurs exclusively in the 3- and 6-posi-
tions of the carbazole, which are highly activated.
Keywords: Bisindenocarbazole; Carbazole; Suzuki cross coupling.
* Corresponding author. Tel.: +49 921 55 3296; fax: +49 921 55 3206;
e-mail: peter.strohriegl@uni-bayreuth.de
Finally, different alkyl side chains can be introduced to
the planar bisindenocarbazole core with n-BuLi and the
0040–4020/$ - see front matter Ó 2006 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2006.06.015

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M. Sonntag, P. Strohriegl / Tetrahedron 62 (2006) 8103–8108
4
5
O
O
6
3
2
7
A
B
Br
Br
Br
Br
9
N
H
8
1
N
R
N
R
O
1
1
1
OH
OH
2 a-c
3 a-c
B
2
C
R
R
2
OH
2
HO
1'
2'
1
2
3'
E
D
b
h
3
9
N
R
N
R
N
1
1
R
1
6 - 10
5 a-c
4 a-c
2a,b: A = alkyl bromide, acetone, KOH, PTC, 70 °C, 5 h
2c: A = Me2SO4, acetone, 10N KOH, 50 °C, 30 min
C = lithium triethylborohydride, THF, 0 °C, 1 h
D = BF3*O(C2H5)2, CH2Cl2, RT, 30 min
E = 1.6 M n-BuLi, alkyl bromide, THF, -78 °C, 1 h
B = P(otol)3, Pd(OAc)2, 2N KOH, toluene, PTC, 90 °C, 2 h
compd
R1
R2
---
---
2-5a
2-5b
2-5c
6
sec-butyl
2-ethylhexyl
methyl
---
sec-butyl
sec-butyl
sec-butyl
2-ethylhexyl
methyl
methyl
n-butyl
ethyl
ethyl
ethyl
7
8
9
10
Scheme 1. Synthesis of bisindenocarbazoles with different alkyl substituents.
corresponding alkyl halide. The alkylation of bisindenocar-
bazoles in thevery last step is a big advantage ofthis synthetic
approach. As we will show in the next paragraphs, the mor-
phology and the thermal properties of the target molecules
can be tailored by adding alkyl groups of different lengths
without changing the optical and electrical properties.
melts at 273 ꢀC. In contrast, it was not possible to separate
the bisindenocarbazoles 7–9, which are a mixture of four
diastereomers. Therefore, the NMR and thermal data refer
to the isomeric mixtures.
All bisindenocarbazoles show good solubility in common
organic solvents (e.g., THF, toluene, chloroform). The struc-
1
The bisindenocarbazoles 6–10 are mixtures of stereoiso-
mers. Compound 6 is a mixture of two enantiomers, 7–9
have three stereocenters and hence eight enantiomers and
four diastereomers. Compound 10 with two stereocenters
in the 1- and 10-positions is a mixture of two enantiomers
and two diastereomers. Only in the case of 10 we were
able to separate the two diastereomers by medium pressure
liquid chromatography (MPLC). The first fraction is the
meso form with (R,S)-configuration. The second fraction
consists of the (R,R)- and (S,S)-enantiomers (Scheme 2).
The (R,R/S,S)- and (R,S)-isomers are formed in a ratio of
2:1. The melting points of the two isomers differ by 19 ꢀC.
The (R,S)-isomer melts at 292 ꢀC and the (R,R/S,S) racemate
tures of the bisindenocarbazoles were confirmed by IR, H
and 13C NMR, mass spectrometry, and elemental analysis.
The synthetic procedures and the analytical data of all com-
pounds are given in Section 4.
2.2. Thermal properties
The thermal properties of the bisindenocarbazoles were
determined by thermogravimetric analysis (TGA) and dif-
ferential scanning calorimetry (DSC) and are summarized
in Table 1. TGA experiments in nitrogen showed that the
bisindenocarbazoles 6–10 start to sublime at temperatures
above 260 ꢀC. Between 300 and 350 ꢀC, quantitative weight
N
N
N
(R,S)-isomer of 10
(S,S)-isomer of 10
(R,R)-isomer of 10
Scheme 2. Different isomers and configurations of 10.

M. Sonntag, P. Strohriegl / Tetrahedron 62 (2006) 8103–8108
Table 1. Thermal properties of the bisindenocarbazoles 6–9
8105
1,2x105
1,0x105
8,0x104
6,0x104
4,0x104
Compd
Tg [ꢀC]a
Tm [ꢀC]a
Tsubl [ꢀC]b
6
7
8
9
—
265
—
310
320
305
330
260
260
N
106c
103c
74c
—
250c,d
164c
292
273
10 (R,S)
10 (R,R/S,S)
—
a
Determined by DSC, scan rate 10 K/min, second run, N2 atmosphere.
Onset of sublimation determined by TGA, heating rate 10 K/min, N2
atmosphere.
Tg and Tm refer to mixtures of four diastereomers.
Melting point only detected in the first heating cycle.
b
2,0x104
c
d
0,0
250
300
350
400
450
500
loss was detected in all cases. The fact that the molecules can
be sublimed quantitatively at z320 ꢀC at normal pressure
allows to prepare high quality films of the materials by vapor
deposition.
Wavelength [nm]
Figure 1. Absorption and fluorescence spectra of the bisindenocarbazole 6.
The absorption spectra were taken from 10ꢁ5 M cyclohexane solutions and
the fluorescence spectra from 10ꢁ6 M cyclohexane solutions with an excita-
tion wavelength of 350 nm.
DSC measurements clearly show how the morphology of the
molecules can be tailored by changing the alkyl side groups.
Compound 6 with four methyl substituents in the 1- and
10-positions is crystalline (Tm¼265 ꢀC), whereas 7 with two
butyl and two methyl side chains is amorphous and exhibits
only a glass transition at 106 ꢀC. In contrast to 6, which
recrystallizes upon cooling, the ethyl/methyl-substituted
molecule 8 can be transferred into a glassy state upon cool-
ing in the DSC experiment. Melting point of 8 is only ob-
served in the first heating cycle at 250 ꢀC. In the second
and third run only the glass transition at 103 ꢀC is detected.
In the bisindenocarbazole 9, the N-sec-butyl substituent of
the central carbazole unit is replaced by a longer 2-ethyl-
hexyl chain. This leads to a low glass transition temperature
of 74 ꢀC and melting point at 164 ꢀC.
to two discrete carbazole skeleton vibrations in the IR-
spectrum.
In order to estimate the fluorescence quantum yield (Ff) of
the bisindenocarbazoles, the fluorescence of 6 was com-
pared with the well known blue laser dye Exalite 428
[7,700-bis(4-tert-amylphenyl)-9,9,90,90,900,900-hexapropyl-2,20:
70,200-terfluorene]. Exalite 428 has a quantum efficiency of
90% in cyclohexane solution.16 Solutions (10ꢁ5 M) of 6
and Exalite 428 in cyclohexane were prepared and diluted
to an optical density of z0.1 in order to minimize self-
absorption.17 From these solutions, fluorescence spectra
were taken and by integration, a fluorescence quantum yield
of 63% was calculated for 6.
In the case of 10, we were able to separate the two diastereo-
mers. Both the (R,R/S,S)- and (R,S)-isomers of 10 are crys-
talline and melt at 273 and 292 ꢀC, respectively. Upon
cooling, both compounds show recrystallization in the
DSC experiment. The mixture of the two diastereomers is
also crystalline. In contrast to the two pure isomers, the mix-
ture does not recrystallize upon cooling but forms a glass,
which recrystallizes during the subsequent heating cycle.
This shows that the mixture has a higher tendency to form
a molecular glass than the pure diastereomers.
2.4. Electrochemical properties
The electrochemical stability of the bisindenocarbazoles
was examined by cyclic voltammetry (CV). All measure-
ments were carried out at 25 ꢀC in CH2Cl2 solution con-
taining 0.1 M tetrabutylammonium hexafluorophosphate
(TBAPF6) as supporting electrolyte with a glassy carbon
working electrode. The oxidation potentials were measured
versus Ag/AgCl as the reference electrode.18 The CV curve
of 6 (Fig. 2) shows one oxidation peak at 0.60 V, which is
fully reversible. Repeated oxidation and reduction cycles
had no influence on the CV curve. The same results are
obtained for other bisindenocarbazoles 7–10. This is a proof
for the electrochemical stability of the new bisindenocarba-
zoles. It has been reported that the electrochemical oxidation
of compounds based on 2,7-linked carbazoles is not fully
reversible and that such materials undergo dimerization re-
actions in the activated 3- and 6-positions of the carbazole
rings.6,10 The high electrochemical stability of the bisinde-
nocarbazoles 6–10, in which these positions are blocked
by ring closure, strongly supports this argument and shows
that the activated 3- and 6-positions in 2,7-linked carbazole
compounds have to be blocked in order to obtain electro-
chemically stable materials.
2.3. Optical properties
As expected, identical UV–vis spectra are obtained from the
bisindenocarbazoles. The change of the alkyl side chains has
no influence on the absorption of the bisindenocarbazole
chromophore. The absorption and fluorescence spectra of 6
(Fig. 1) are representative for the bisindenocarbazoles 6–10.
The absorption maximum is at 380 nm. The bisindenocarba-
zoles exhibit a strong, saturated blue fluorescence with an
emission maximum at 410 nm. The small Stokes shift of
6 nm is typical for the rigid structure of the bisindenocarba-
zoles.15
The fluorescence spectrum of 6 shows characteristic vi-
bronic structures. The separation between the peaks at 388
and 410 nm is 1382 cmꢁ1, and between 410 and the
shoulder at 435 nm is 1461 cmꢁ1. These values correspond
The HOMO levels of the bisindenocarbazoles 6–10 can be
estimated from the CV measurement. For this purpose, the
CV was calibrated with the standard ferrocene/ferrocenium

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M. Sonntag, P. Strohriegl / Tetrahedron 62 (2006) 8103–8108
40
30
20
10
0
Emission spectra were obtained from a Shimadzu spectro-
0.60
fluorophotometer RF-5301PC. Conventional mass spectra
(MS) were recorded with a Finnigan MAT 8500 (70 eV)
with a MAT 112S Varian. Thermogravimetric analysis
(TGA) was performed on a Perkin–Elmer TAS-409 at a heat-
ing rate of 10 K/min under N2. For differential scanning
calorimetry measurements (DSC), Perkin–Elmer DSC-7
apparatus was used (heating/cooling rate: 10 K/min). Cyclic
voltammetry measurements (CV) were performed with
a glassy carbon working electrode (0.2 mm) in a three-elec-
trode potentiostat configuration from EG&G Princeton
Applied Research.
-10
-20
All chemicals and reagents were used as received from
Aldrich. Tetrahydrofuran (THF) was distilled over potas-
sium before use. The synthesis of 2,7-dibromocarbazole
(1) and N-alkylated 2,7-dibromocarbazoles (2a–c) has
been reported elsewhere.9–13
0.53
0,0
0,2
0,4
0,6
0,8
E vs. Ag/Ag+ [V]
Figure 2. CV measurement of 6, measured at 25 ꢀC at a scan rate of 50 mV/s
versus Ag/Ag+ in acetonitrile with TBAPF6 as supporting electrolyte.
4.2. 2,7-Bis-(2-acetylphenyl)-9-sec-butyl-carbazole (3a)
redox system. Taking ꢁ4.8 eVas HOMO level for the ferro-
cene redox system,19 HOMO values of ꢁ5.3 eV were ob-
tained. With an optical band gap of 3.2 eV, calculated from
the absorption edge at 391 nm, LUMO values of ꢁ2.1 eV
are calculated for compounds 6–10.
2,7-Dibromo-9-sec-butyl-carbazole (2a) (1.3 g, 3.5 mmol)
and 2-acetylphenylboronic acid (1.3 g, 7.7 mmol) were dis-
solved in 45 ml of toluene. A 2 M solution of K2CO3 (25 ml)
and 0.2 g of trimethylbenzylammonium chloride was added.
The reaction mixture was degassed by three freeze/thaw cy-
cles before 31.3 mg (0.14 mmol) Pd(OAc)2 and 127.0 mg
(0.42 mmol) tri-o-tolylphosphine (P(o-tol)3) were added un-
der argon. The mixture was stirred for 15 h at 90 ꢀC before it
was poured into ice water and extracted with diethyl ether.
After evaporation of the solvent, the product was purified
by column chromatography on silica gel with hexane/THF
(6:1) as eluent yielding 1.42 g (89%) of 3a as a colorless
3. Conclusions
In conclusion, we have developed a new versatile synthetic
route to conjugated bisindenocarbazoles. The title com-
pounds 6–10 are obtained in five steps from 2,7-dibromocar-
bazole 1 with an overall yield of 50%. By substitution with
a variety of alkyl substituents in the very last step of the syn-
thesis, their morphology can be varied from highly crystal-
line materials (6) to amorphous molecular glasses (7). The
compounds sublime quantitatively at temperatures around
320 ꢀC and excellent films can be prepared by evaporation.
In CV experiments, the bisindenocarbazoles showed a high
electrochemical stability. This is in contrast to the 2,7-carba-
zole trimers, which have been reported before.10 These tri-
mers show irreversible electrochemical oxidation due to
dimerization reactions in the highly activated 3- and 6-posi-
tions of the carbazole ring. In the bisindenocarbazoles 6–10,
the reactive 3- and 6-positions in the central carbazole unit
are blocked by the ring closure. From CV measurements
and optical band gap, HOMO levels of ꢁ5.3 eV and LUMO
values of ꢁ2.1 eV were calculated. All bisindenocarbazoles
6–10 exhibit a strong, saturated blue emission with a quan-
tum yield of 63% in solution and will be tested as blue dop-
ants in organic light emitting diodes in the near future.
1
solid. H NMR (250 MHz, CDCl3): d (ppm) 0.71(t, 3H),
1.58 (d, 3H), 1.86 (s, 6H), 1.95 (m, 1H), 2.21 (m, 1H),
4.53–4.67 (m, 1H), 7.20 (m, 2H), 7.37 (m, 4H), 7.52 (m,
6H), 8.13 (d, 2H). MS (70 eV): m/z¼459 (M+).
4.3. 2,7-Bis-(2-acetylphenyl)-9-(2-ethylhexyl)-carbazole
(3b)
Compound 3b was prepared according to the procedure de-
scribed above (yield: 91%). H NMR (250 MHz, CDCl3):
1
d (ppm) 0.78–0.87 (m, 6H), 1.12–1.40 (m, 8H), 1.48 (s,
6H), 2.07 (m, 1H), 4.16 (m, 2H), 7.17 (d, 2H), 7.34 (m,
6H), 7.36 (m, 2H), 7.70 (d, 2H), 8.14 (d, 2H). MS (70 eV):
m/z¼515 (M+).
4.4. 2,7-Bis-(2-acetylphenyl)-9-methyl-carbazole (3c)
Compound 3c was prepared according to the procedure de-
scribed above (yield: 83%). H NMR (250 MHz, CDCl3):
1
d (ppm) 1.99 (s, 6H), 3.88 (s, 3H), 7.24 (d, 1H), 7.27 (d,
1H), 7.40 (m, 2H), 7.39–7.48 (m, 2H), 7.54–7.58 (m, 6H),
8.16 (d, 2H). MS (70 eV): m/z¼417 (M+).
4. Experimental
4.1. General
4.5. 2,7-Bis-[2-(2-hydroxyethylphenyl)-9-sec-butyl]-
carbazole (4a)
1H NMR spectra were recorded with a Bruker AC 250
(250 MHz) apparatus. All data are given as chemical shifts
d [ppm] downfield from Si(CH3)4. The IR spectra were re-
corded using a Bio-Rad Digilab FTS-40. The UV–vis spec-
tra were recorded with a Hitachi U-3000 spectrophotometer.
Compound 3a (0.37 g, 0.80 mmol) was dissolved in 25 ml
abs THF. The solution was flushed with argon and cooled
to 0 ꢀC before 2.3 ml (2.40 mmol) of 1 M lithium triethyl
borohydride solution in THF (super-hydride) was added

M. Sonntag, P. Strohriegl / Tetrahedron 62 (2006) 8103–8108
8107
slowly. The reaction mixture was stirred at 0 ꢀC for 1 h and
15 ml of an aqueous NH4Cl solution was added. Thereafter,
the reaction batch was poured into 150 ml water and ex-
tracted with diethyl ether. The organic layer was washed
with water and the solvent was removed. The product was
purified by column chromatography on silica gel with hex-
ane/ethyl acetate (1.5:1) as eluent yielding 0.35 g (95%) of
4a as a colorless solid. 1H NMR (250 MHz, DMSO):
d (ppm) 0.74 (t, 3H), 1.29–1.33 (m, 6H), 1.67 (m, 3H),
2.01 (m, 1H), 2.24 (m, 1H), 4.93 (m, 3H), 5.14 (m, 2H),
7.20 (d, 2H), 7.35–7.51 (m, 6H), 7.68 (d, 2H), 7.73 (d,
2H), 8.29 (d, 2H). MS (70 eV): m/z¼463 (M+).
4.13 (q, 2H), 4.51 (s, 3H), 7.32–7.40 (m, 4H), 7.55 (d,
2H), 7.72 (s, 2H), 7.86 (d, 2H), 8.20 (s, 2H). MS (70 eV):
m/z¼385 (M+).
4.11.1,10-Di-n-butyl-1,10-dimethyl-bisindeno[3,2-b:2030-h]-
9-sec-butyl-carbazole (7)
Compound 5a (60 mg, 0.14 mmol) was dissolved in 15 ml
THF (abs) under argon. The solution was cooled to
ꢁ78 ꢀC before 0.19 ml (0.3 mmol) n-BuLi (1.6 M solution
in hexane) was added slowly. After 15 min stirring, 0.2 ml
(0.4 mmol) 1-bromobutane was added. The solution was al-
lowed to warm to room temperature and stirred for another
hour before it was poured into 50 ml ice water. The reaction
batch was extracted with diethyl ether, the organic phase was
washed with water, and the solvent was evaporated. Purifica-
tion was carried out by column chromatography on silica gel
with hexane/THF (10:1) as eluent. In addition, 7 was purified
by MPLC with hexane/THF (15:1) at a pressure of 18 bar.
4.6. 2,7-Bis-[2-(2-hydroxyethylphenyl)-9-
(2-ethylhexyl)]-carbazole (4b)
Compound 4b was prepared according to the procedure de-
scribed above (yield: 96%). H NMR (250 MHz, CDCl3):
1
d (ppm) 0.71–0.88 (m, 6H), 1.14–1.46 (m, 11H), 1.49 (d,
3H), 2.07 (m, 1H), 4.16 (d, 2H), 5.09 (m, 2H), 7.17 (d,
2H), 7.36–7.49 (m, 8H), 7.71 (d, 2H), 8.12 (d, 2H). MS
(70 eV): m/z¼519 (M+).
1
The reaction yielded 51 mg (75%) of 7 as white solid. H
NMR (250 MHz, CDCl3): d (ppm) 0.62 (m, 9H), 0.87 (t,
4H), 1.01–1.10 (m, 4H), 1.51 (m, 6H), 1.74 (d, 3H), 1.96–
2.17 (m, 5H), 2.28–2.47 (m, 1H), 4.76 (m, 1H), 7.27–7.37
(m, 6H), 7.69 (s, 2H), 7.76 (d, 2H), 8.01 (s, 2H). 13C NMR
(62.5 MHz, CDCl3): d (ppm) 12.2, 14.3, 19.6, 23.5, 26.9,
28.1, 28.6, 41.8, 50.4, 53.6, 114.1, 119.9, 123.2, 123.3,
123.6, 127.1, 127.3, 128.5, 141.2, 143.7, 153.4. IR (Si-
wafer): ~n (cmꢁ1) 3011, 2958, 2972, 1488, 1452, 1378,
1342, 1240, 740. MS (70 eV): m/z¼539 (M+). Anal. Calcd
for C40H45N (539.8): C, 89.00; H, 8.40; N, 2.59. Found: C,
89.09; H, 8.31; N, 2.58.
4.7. 2,7-Bis-[2-(2-hydroxyethylphenyl)-9-methyl]-
carbazole (4c)
Compound 4c was prepared according to the procedure de-
scribed above (yield: 98%). H NMR (250 MHz, CDCl3):
1
d (ppm) 1.45 (d, 6H), 3.90 (s, 3H), 5.10 (q, 2H), 7.18 (d,
1H), 7.35–7.40 (m, 6H), 7.43–7.51 (m, 3H), 7.73 (d, 2H),
8.15 (d, 2H). MS (70 eV): m/z¼421 (M+).
4.8. 1,10-Dimethyl-bisindeno[3,2-b:2030-h]-9-sec-butyl-
carbazole (5a)
4.12. 1,1-Dimethyl-10,10-dimethyl-bisindeno[3,2-b:2030-h]-
9-sec-butyl-carbazole (6)
To a solution of 0.1 g (0.22 mmol) 4a in 10 ml dichloro-
methane, 0.1 ml (0.65 mmol) boron trifluoride etherate was
added. The mixture was stirred for 30 min at room tempera-
ture before 15 ml ethanol and 20 ml water were added. The
reaction batch was extracted with dichloromethane, washed
with water, and dried with Na2SO4 before the solvent was
evaporated. Purification by column chromatography on
silica gel with hexane/THF (3:1) as eluent yielded 83 mg
(92%) of 5a as colorless solid. 1H NMR (250 MHz,
DMSO): d (ppm) 0.81 (t, 3H), 1.64 (d, 6H), 1.80 (d, 3H),
2.12 (m, 1H), 2.49 (m, 1H), 4.10 (q, 2H), 5.05 (m, 1H),
7.35–7.46 (m, 4H), 7.64 (d, 2H), 8.12 (d, 2H), 8.21 (s,
2H), 8.39 (d, 2H). MS (70 eV): m/z¼427 (M+).
Compound 6 was prepared according to the procedure de-
scribed for 7. For alkylation, iodomethane was used (yield:
70%). Compound 6 was purified by MPLC with hexane/
1
THF (10:1) at a pressure of 18 bar. H NMR (250 MHz,
CDCl3): d (ppm) 0.90 (t, 3H), 1.61 (m, 12H), 1.78 (d, 3H),
2.05–2.21 (m, 1H), 2.35–2.53 (m, 1H), 4.81 (m, 1H),
7.28–7.49 (m, 6H), 7.82 (s, 2H), 7.89 (d, 2H), 8.15 (s, 2H).
13C NMR (62.5 MHz, CDCl3): d (ppm) 12.2, 19.6, 26.8,
28.5, 46.5, 53.6, 101.4, 114.0, 120.8, 123.1, 123.7, 127.4,
132.1, 137.6, 140.3, 145.3, 154.9. IR (Si-wafer): ~n (cmꢁ1
)
3014, 2961, 2926, 1489, 1452, 1377, 1342, 1241, 740. MS
(70 eV): m/z¼455 (M+). Anal. Calcd for C34H33N (455.7):
C, 89.63; H, 7.30; N, 3.07. Found: C, 89.56; H, 7.33; N, 3.12.
4.9. 1,10-Dimethyl-bisindeno[3,2-b:2030-h]-9-(2-ethyl-
hexyl)-carbazole (5b)
4.13. 1,10-Diethyl-1,10-dimethyl-bisindeno[3,2-b:2030-h]-
9-sec-butyl-carbazole (8)
Compound 5b was prepared as described above (yield: 90%).
1H NMR (250 MHz, CDCl3): d (ppm) 0.84 (m, 6H), 1.51–
1.46 (m, 8H), 1.49 (d, 6H), 2.05 (m, 1H), 3.96 (q, 2H),
4.86 (m, 2H), 7.33–7.44 (m, 4H), 7.60 (d, 2H), 8.10 (d,
2H), 8.19 (s, 2H), 8.35 (d, 2H). MS (70 eV): m/z¼483 (M+).
4.10. 1,10-Dimethyl-bisindeno[3,2-b:2030-h]-9-methyl-
carbazole (5c)
Compound 8 was prepared according to the procedure de-
scribed for 7. For alkylation, bromoethane was used. Com-
pound 8 was purified by MPLC with hexane/THF (15:1) at
a pressure of 18 bar (yield: 80%). 1H NMR (250 MHz,
CDCl3): d (ppm) 0.41 (m, 6H), 0.90 (m, 3H), 1.58 (s, 6H),
1.78 (d, 3H), 2.05–2.22 (m, 5H), 2.34–2.41 (m, 1H), 4.78
(m, 1H), 7.26–7.41 (m, 6H), 7.78 (s, 2H), 7.82 (d, 2H),
8.05 (s, 2H). 13C NMR (62.5 MHz, CDCl3): d (ppm) 9.0,
11.8, 19.2, 27.3, 28.2, 34.1, 50.4, 53.2, 113.7, 115.0,
119.4, 122.9, 124.1, 126.4, 138.3, 141.0, 142.9, 152.6. IR
(Si-wafer): ~n (cmꢁ1) 3049, 2963, 2929, 1488, 1452, 1378,
Compound 5c was prepared as described above (yield:
88%). H NMR (250 MHz, CDCl3): d (ppm) 1.56 (d, 6H),
1

8108
M. Sonntag, P. Strohriegl / Tetrahedron 62 (2006) 8103–8108
1342, 1240, 741. MS (70 eV): m/z¼483 (M+). Anal. Calcd
for C36H37N (483.7): C, 89.39; H, 7.71; N, 2.90. Found: C,
89.54; H, 7.69; N, 2.85.
1349, 1307, 1264, 739. MS (70 eV): m/z¼441 (M+). Anal.
Calcd for C33H31N (441.6): C, 89.75; H, 7.08; N, 3.17.
Found: C, 89.73; H, 7.09; N, 3.09.
4.14. 1,10-Diethyl-1,10-dimethyl-bisindeno[3,2-b:2030-h]-
9-(2-ethylhexyl)-carbazole (9)
Acknowledgements
The authors would like to thank Professor K. Seifert for
helpful discussions and Professor M. Thelakkat for the intro-
duction to the CV measurements and the BMBF (POLITAG
program) and the EU (EUROFET Network) for financial
support.
Compound 9 was prepared according to the procedure de-
scribed for 7. For alkylation, 5b was treated with bromo-
ethane. Compound 9 was purified by MPLC with hexane/
1
THF (20:1) at a pressure of 18 bar (yield: 76%). H NMR
(250 MHz, CDCl3): d (ppm) 0.33 (m, 6H), 0.80–0.96 (m,
6H), 1.18–1.48 (m, 8H), 1.52 (s, 6H), 1.98–2.16 (m, 5H),
4.20 (m, 2H), 7.21–7.39 (m, 6H), 7.58 (s, 2H), 7.75 (d,
2H), 7.98 (s, 2H). 13C NMR (62.5 MHz, CDCl3): d (ppm)
7.8, 9.8, 12.9, 21.8, 23.4, 26.0, 27.6, 29.8, 32.9, 38.2, 46.5,
49.2, 98.6, 112.5, 118.2, 121.6, 125.6, 125.7, 137.3, 139.7,
141.8, 151.4. IR (Si-wafer): ~n (cmꢁ1) 3046, 2960, 2928,
1491, 1460, 1354, 1330, 1265, 739. MS (70 eV): m/z¼539
(M+). Anal. Calcd for C40H45N (539.8): C, 89.00; H, 8.40;
N, 2.59. Found: C, 89.03; H, 8.46; N, 2.59.
References and notes
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9-methyl-carbazole (10)
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Compound 10 was prepared according to the procedure de-
scribed for 7. For alkylation, 5c was treated with bromo-
ethane. Compound 10 was purified by MPLC with hexane/
THF (25:1) at a pressure of 18 bar (yield: 76%). In case of
10, it was possible to separate the two isomers by this tech-
nique. The (R,S)-isomer (200 mg) and (S,S/R,R)-isomer
(400 mg) were obtained after vacuum freeze drying.
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1
(R,S)-isomer: H NMR (250 MHz, CDCl3): d (ppm) 0.28–
0.45 (m, 6H), 1.59 (s, 3H), 1.88 (s, 3H), 2.15 (q, 2H),
2.29–2.45 (m, 1H), 2.51–2.68 (m, 1H), 4.32 (s, 3H), 7.28–
7.44 (m, 6H), 7.71–7.76 (m, 2H), 7.78 (d, 1H), 7.86 (d,
1H), 8.05 (s, 1H), 8.17 (d, 1H). 13C NMR (62.5 MHz,
CDCl3): d (ppm) 9.41, 27.74, 27.83, 28.04, 34.19, 34.48,
50.96, 52.91, 100.29, 112.33, 113.82, 119.56, 119.80,
119.94, 122.35, 123.30, 123.994, 124.64, 127.21, 127.30,
127.35, 127.39, 132.41, 139.34, 139.64, 140.47, 141.22,
141.29, 142.38, 144.25, 152.96. IR (Si-wafer): ~n (cmꢁ1
)
3049, 2962, 2923, 1495, 1457, 1378, 1307, 1225, 743. MS
(70 eV): m/z¼441 (M+). Anal. Calcd for C33H31N (441.6):
C, 89.75; H, 7.08; N, 3.17. Found: C, 89.54; H, 6.95; N, 3.20.
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17. Crosby, G. A.; Demas, J. N. J. Phys. Chem. 1971, 75,
991–1024.
1
(S,S/R,R)-isomer: H NMR (250 MHz, CDCl3): d (ppm)
0.37–0.40 (m, 6H), 1.63 (s, 6H), 2.08–2.16 (m, 4H), 4.00
(s, 3H), 7.30–7.45 (m, 6H), 7.69 (s, 2H), 7.85 (d, 2H), 8.06
(s, 2H). 13C NMR (62.5 MHz, CDCl3): d (ppm) 9.42,
27.79, 29.82, 34.56, 50.50, 99.81, 114.22, 119.94, 123.20,
123.26, 127.34, 139.08, 141.36, 142.07, 143.59, 152.96.
IR (Si-wafer): ~n (cmꢁ1) 3050, 2961, 2920, 1494, 1458,
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Bassler, H.; Porsch, M.; Daub, J. Adv. Mater. 1995, 7,
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