Synthesis and properties of methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole

Article abstract of DOI:10.1021/jo202677j

The synthesis and full characterization of new derivatives of indolo[3,2-b]carbazole with differently substituted phenyl groups at nitrogen atoms is reported. Comparative study on their thermal, optical electrochemical, and photoelectrical properties is presented. The synthesized compounds are electrochemically stable. Their highest occupied molecular orbital energy values range from -5.14 to -5.07 eV. The electron photoemission spectra of the films of synthesized materials revealed the ionization potentials of 5.31-5.47 eV. Hole drift mobility of the amorphous film of 5,11-bis(3-methoxyphenyl)-6-pentyl- 5,11-dihydroindolo[3,2-b]carbazole exceed 10^-3 cm²/ V?s at high electric fields, as it was established by xerographic time-of-flight technique. In contrast to diphenylamino substituted derivatives of carbazole, no effect of the position of methoxy groups on the photoelectrical properties was observed for the synthesized methoxyphenyl-substituted derivatives of indolo[3,2-b]carbazole. The indolo[3,2-b]carbazole core has a larger resonance structure that includes 3 phenyl rings, and thus the energy gap of the HOMO and LUMO π orbitals is lower as compared to that of carbazoles. With a larger energy difference between the phenyl substituents and the core moiety, the indolo[3,2-b]carbazole derivatives studied all have a weaker coupling between the phenyl group and a much weaker dependence of the molecular properties on the position of substituents on the phenyl groups as compared to those observed in substituted carbazoles.

Full text of DOI:10.1021/jo202677j

Article
pubs.acs.org/joc
Synthesis and Properties of Methoxyphenyl-Substituted Derivatives
of Indolo[3,2-b]carbazole
Jurate Simokaitiene,† Egle Stanislovaityte,† Juozas V. Grazulevicius,*,† Vygintas Jankauskas,‡ Rong Gu,§
Wim Dehaen,§ Yi-Chen Hung,∥ and Chao-Ping Hsu∥
†Department of Organic Technology, Kaunas University of Technology, Radvilenu pl. 19, LT-50254, Kaunas, Lithuania
‡Department of Solid State Electronics, Vilnius University, Sauletekio al. 9, LT-2040, Vilnius, Lithuania
§Department of Chemistry, University of Leuven, Celestijnenlaan 200F, B-3001 Leuven, Belgium
∥Institute of Chemistry, Academia Sinica, 128 Sec. 2 Academia Road, Taipei 115, Taiwan
S
* Supporting Information
ABSTRACT: The synthesis and full characterization of new
derivatives of indolo[3,2-b]carbazole with differently substi-
tuted phenyl groups at nitrogen atoms is reported.
Comparative study on their thermal, optical electrochemical,
and photoelectrical properties is presented. The synthesized
compounds are electrochemically stable. Their highest
occupied molecular orbital energy values range from −5.14
to −5.07 eV. The electron photoemission spectra of the films
of synthesized materials revealed the ionization potentials of
5.31−5.47 eV. Hole drift mobility of the amorphous film of
5,11-bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-
b]carbazole exceed 10−3 cm2/V·s at high electric fields, as it
was established by xerographic time-of-flight technique. In contrast to diphenylamino substituted derivatives of carbazole, no
effect of the position of methoxy groups on the photoelectrical properties was observed for the synthesized methoxyphenyl-
substituted derivatives of indolo[3,2-b]carbazole. The indolo[3,2-b]carbazole core has a larger resonance structure that includes 3
phenyl rings, and thus the energy gap of the HOMO and LUMO π orbitals is lower as compared to that of carbazoles. With a
larger energy difference between the phenyl substituents and the core moiety, the indolo[3,2-b]carbazole derivatives studied all
have a weaker coupling between the phenyl group and a much weaker dependence of the molecular properties on the position of
substituents on the phenyl groups as compared to those observed in substituted carbazoles.
diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) as compared to
the nonsubstituted TPD,9 which has been partly explained by
the change in dipole moment upon substitution. Among
organic charge-transporting materials, derivatives of carbazole
are also widely synthesized and studied.10−13 Most of
carbazolyl-containing materials are capable of transporting
positive charges, i.e., holes; however, recently ambipolar
derivatives of carbazole, which are capable of transporting
effectively both positive and negative charges, were re-
ported.14,15 It was recently established that introduction of
methoxy-substuted diphenylamino moieties into the structures
of carbazole derivatives leads to the decrease of ionization
potentials and to the increase of hole drift mobilities.16 The
extent of decrease of ionization potential depends on the
position of the methoxy groups. The lowest ionization
potentials and the best charge transport properties were
observed for the compounds containing one methoxy group
in para- and ortho- positions of phenyl rings of diphenylamino
INTRODUCTION
■
Organic charge-transporting materials are currently widely
studied and used as the components of modern electronic and
optoelectronic devices such as organic thin film transistors, dye-
sensitized and bulk heterojunction solar cells, organic light
emitting diodes, electrophotographic photoreceptors.1−6
Among charge-transporting materials, hole-transporting ones
are most widely studied and used. In certain fields of
application, e.g., in solid-state dye sensitized solar cells, hole
transporting materials with low ionization potentials are
required. With the aim of designing organic p-type semi-
conductors with required set of properties, the structure−
properties relationship of aromatic amines was studied. It was
established that introduction of methoxy groups into the
structures of the derivatives of triphenylamine (TPA) leads to
the decrease of their ionization potentials,7 with stronger
influence found in the case of para-methoxy substituted TPA
compounds as compared to the meta-substituted ones.8 As for
the influence of these substitutions on the hole mobilities,
lower mobility was observed, for instance, in the case of p-
methoxy and p-butoxy substituted N,N′-bis(m-tolyl)-N,N′-
Received: January 13, 2012
Published: April 26, 2012
© 2012 American Chemical Society
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Scheme 1
moiety. Indolocarbazoles represent a class of very promising
but until now much less studied of organic semiconductors.
Substituted indolo[3,2-b]carbazoles were successfully used for
the preparation of high-mobility organic thin film transis-
tors.17−21 The best performance was observed for vapor
deposited thin films of 3,9-diphenyl-5,11-dioctylindolo[3,2-
b]carbazole1 9 and 3,9-di(p-octylbenzene)-5,11-
dihydroxyindolo[3,2-b]carbazole20 with the maximum field-
effect mobility of 0.22 cm2 V−1 s−1. Derivatives of indolo[3,2-
b]carbazole are also regarded as promising materials for
efficient electroluminescence.22 In addition, indolo[3,2-b]-
carbazole copolymers were reported as potential photovoltaic
materials.23,24 They can also be applied in anion complexation
and sensing.25 To our knowledge, the influence of methoxy
groups on the properties of the derivatives of indolo[3,2-
b]carbazole has not yet been studied.
In this article, we report on the synthesis and properties of
new derivatives of indolo[3,2-b]carbazole containing differently
substituted phenyl groups at 5 and 11 positions. The aims of
this work were to extend the choice of charge-transporting
derivatives of indolo[3,2-b]carbazole and to study the influence
of phenyl moieties having methoxy groups in the different
positions on the properties of the materials.
chromatography. They were identified by elemental analysis,
1
IR, H NMR, 13C NMR, and mass spectrometries.
The behavior on heating of compounds 1−6 was studied by
DSC and TGA under a nitrogen atmosphere. The values of
glass transition temperatures (Tg), melting points (Tm),
crystallization temperatures (Tcr), and the temperatures of the
onsets of thermal degradation (TID) are summarized in Table 1.
Table 1. Thermal Characteristics of Compounds 1−6
compound
Tm, °C
Tcr, °C
Tg, °C
TID, °C
1
2
3
4
5
6
185
230
157
199
371
364
55
65
57
76
422
441
432
426
453
469
176
271
309
The synthesized compounds demonstrate high thermal
stability. The values of TID well exceed 400 °C, as confirmed
by TGA with a heating rate of 20 °C/min. The derivatives of
6,12-di(3,5-di-tert-butylphenyl)-5,11-dihydroindolo[3,2-b]-
carbazole (5, 6) having extended aromatic system show
superior thermal stability relative to that of the derivatives of
6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (1−4).
Compounds 1−6 were isolated after the synthesis as
crystalline materials. In the first DSC heating scans, they
showed endothermal melting signals with the maxima in the
range of 157−364 °C. Compounds 1−4 can exist in the solid
amorphous phase; i.e., they form molecular glasses. Their glass
transition temperatures (Tg) range from 46 to 76 °C. The
morphological stability of the molecular glass of 2 seems to be
somewhat lower than that of 1, 3, and 4. In the second DSC
heating scan, it shows not only glass transition at 65 °C but also
crystallization at 176 °C with the following melting at 230 °C
(Figure 1b). Compounds 1, 3, and 4 showed the comparable
behavior in the DSC experiments. As an example, DSC curves
RESULTS AND DISCUSSION
■
Methoxyphenyl-substuted derivatives of 5,11-dihydroindolo-
[3,2-b]carbazole (2−6) were synthesized as described in
Scheme 1 from 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole
(M1) or 6,12-di(3,5-di-tert-butylphenyl)-5,11-dihydroindolo-
[3,2-b]carbazole (M2) and the corresponding iodoanisoles by
Ullmann coupling.26 6-Pentyl-5,11-dihydroindolo[3,2-b]-
carbazole (M1)27,28 and 6,12-di(3,5-di-tert-butylphenyl)-5,11-
dihydroindolo[3,2-b]carbazole (M2)29 were prepared by the
earlier reported procedures. 5,11-Bisphenyl-6-pentyl-5,11-
dihydroindolo[3,2-b]carbazole (1) was prepared for the
comparison of the properties by the similar synthetic route.29
All the compounds (1−6) were purified by column
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Figure 1. DSC termograms of compounds 1 (a) and 2 (b) (scan rate 10 °C/min, N2 atmosphere).
Figure 2. UV and fluorescence spectra of dilute THF solutions (10−5 mol/L) of compounds 1−6.
Figure 3. Cyclic voltammograms of compounds 1−6 in dichloromethane at 25 °C at sweep rate of 0.1 V/s.
of compound 1 are shown in Figure 1a. In the first heating scan,
compound 1 showed melting at 185 °C. Upon cooling, it did
not crystallize and showed glass transition at 55 °C in the
second heating scan. Comparison of Tg of compound 1 with
those of compounds 2−4 shows that introduction of methoxy
groups leads to the increase of Tg. The highest Tg is observed
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for compound 4, having methoxy groups in ortho positions.
Apparently, methoxy groups situated close to the nitrogen
atoms hinder rotation of phenyl rings around C−N bonds.
Compounds 5 and 6 could not be transformed into the glassy
state by cooling from the melt.
Figure 2 shows UV and fluorescence spectra of dilute
solutions of compounds 1−6. UV and fluorescence spectra of
compounds 1−6 are similar to those of indolo[3,2-b]-
carbazole.30 Absorption edges and low-energy absorption
maxima of 4-methoxyphenyl-substituted compounds 2 and 5
exhibit small bathochromic shifts with respect to those of 2- or
3-methoxyphenyl-substituted compounds (3, 4, 6). Fluores-
cence spectrometry data correlate with the UV spectrometry
results. Fluorescence spectra are similar to those of alkyl-
substituted indolo[3,2-b]carbazole.31 The fluorescence intensity
maxima of 2 and 5 are slightly red-shifted with respect of those
of 3, 4, and 6.
of HOMO and Ip energy levels obtained by electron
photoemission spectrometry and by electrochemical studies
can be explained by the differencies in molecular interactions
and molecular arrangements in thin solid layers and in dilute
solutions.
In order to obtain insights on the electronic properties of the
molecules studied, quantum chemical calculations were
performed. The core model indolo[3,2-b]carbazole molecules,
M1 and M2, were also included in the computational study.
Two different theoretical estimates for the vertical ionization
potential (Ip) energies are listed in Table 3, with first being the
Table 3. Ip, Excitation Energies, Population Analysis Data,
and Dihedral Angles (°) for Molecules 1−6 and the Core
Models M1 and M2
excitation
energies, eV
a
b
Ip, eV
To elucidate the energetic conditions for energy and electron
transfer in dilute solutions, the HOMO/LUMO energy values
were estimated by cyclic voltammetry (CV). The cyclic
voltammograms of the synthesized compounds in dichloro-
methane show a quasi-reversible oxidation couple (Figure 3).
The electrochemical data are summarized in Table 2. The
HF-
KT
substituent
dihedral
d
c
molecule
ΔDFT TDDFT CIS
charge
angles
1
6.91
6.83
6.84
6.66
6.71
6.69
6.82
6.71
6.00
5.83
5.87
5.79
5.73
5.72
6.23
5.95
3.33
3.30
3.33
3.35
3.36
3.36
3.36
3.36
4.72
4.71
4.72
4.71
4.69
4.70
4.71
4.70
0.226
0.242
0.229
0.216
0.174
0.171
56; 59
64; 64
60; 60
64; 65
90; 80
93; 93
2
3
4
5
Table 2. HOMO, LUMO, Band Gap Energies, Ionization
6
a
Potentials, and Electrochemical Characteristics of
M1
M2
Compounds 1−6
b
c
d
e
a
compound E1/2 vs Fc/V Eogpt/eV
Ip/eV
EHOMO/eV
ELUMO/eV
Vertical ionization potential reported. Both are calculated with 6-
b
31G* basis set. The B3LYP functional is employed in ΔDFT. Vertical
excitation energies reported for the S1 state. The B3LYP functional is
employed in TDDFT, and the 6-31G* basis set is used for both data
sets. The amount of additional positive charge on the two
methoxyphenyl groups upon ionization. The dihedral angles between
the phenyl groups and the indolo[3,2-b]carbazole core, in degrees. For
molecules 1−4, the first numbers refer to the one without steric
interaction with the pentyl substituent.
1
2
3
4
5
6
0.33
0.30
0.34
0.30
0.27
0.30
2.99
2.95
2.98
2.99
2.95
2.94
5.39
5.31
5.41
5.35
5.47
5.47
−5.13
−5.10
−5.14
−5.10
−5.07
−5.10
−2.14
−2.15
−2.16
−2.11
−2.12
−2.16
c
d
a
The measurements were carried out at a glassy carbon electrode in
dichloromethane solutions containing 0.1 M tetrabutylammonium
perchlorate as electrolyte and Ag/AgNO3 as the reference electrode.
negative energy of the HOMO from a HF calculation following
the Koopmans theorem (HF-KT), and the second is the
difference of the DFT total energies of the neutral or cationic
molecules (ΔDFT). All calculations were performed with a
developmental version of Q-Chem.32
b
Each measurement was calibrated with Fc. The optical band gaps Egopt
c
estimated from the edges of electronic absorption spectra. Ionization
energy EIp was measured by the photoemission in air method from
d
e
films. EHOMO = 4.8 + E1/2 vs Fc. ELUMO = EHOMO − Egopt
From Table 3, it is seen that all Ip values obtained are very
similar across all molecules studied, for both Ip data sets. The Ip
values and the excitation energies of the core model molecules
(M1 and M2) are similar to those of the substituted molecules.
For the similar Ip values, we analyzed the electron population in
ionization. As shown in Figure 4, all the HOMO are
concentrated in the core region, with a small population in
the amine and the methoxyphenyl-substituents. On the other
hand, the excitation is also pretty much localized to the core
region, as seen in the natural transition orbital (NTO) plots
included in Figure 4. The NTOs are a set of 1-electron orbitals
that best describe the electron hole in a transition. They are
equivalent to the HOMO and LUMO if the S1 state were a
pure transition from HOMO to LUMO, and NTOs are more
general, as they can include the effects of other MOs if they are
also involved.33 It is seen that both ionization and the excitation
are mainly in the indolo[3,2-b]carbazole core.
oxidation potentials for reversible oxidation were taken as the
average of the anodic and cathodic peak potentials. The EHOMO
values were determined from the first oxidation potential values
with respect to ferrocene (Fc). The EHOMO values of the
synthesized compounds are very close and range from −5.14 to
−5.07 eV. The ELUMO levels were determined from optical
energy band gaps and EHOMO values. They are also close and
range from −2.16 to −2.11 eV.
The ionization potentials (Ip) of amorphous layers of
compounds 1−6 established by electron photoemission
method in air range from 5.31 to 5.47 eV (Table 2). The
ionization potentials recorded for the derivatives of 6-pentyl-
5,11-dihydroindolo[3,2-b]carbazole (1−4) are a little lower
than those observed for the derivatives of 6,12-di(3,5-di-tert-
butylphenyl)-5,11-dihydroindolo[3,2-b]carbazole (5, 6). The
lowest ionization potential is observed for 4-methoxyphenyl-
substituted compound 2. Nevertheless, in contrast to our earlier
observation,21 the influence of the position of methoxy groups
on the values of ionization potential is not very obvious for
these series of materials. The differencies observed in the values
We have also performed the population analysis on the
difference charge of the cationic and the neutral states, to gain a
quantitative picture on the distribution of the charge. The data
given in Table 3 show that ca. 17−24% of the positive charge is
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of their indolo[3,2-b]carbazole cores, and the methoxyphenyl
substituents have rather small effect on the Ip and the excitation
energy values.
In an earlier work,16 the methoxyphenyl substituents were
attached to an amino group, which was attached to the carbon
at the third position of a carbazole ring, and the dihedral angles
between the carbazole and the methoxy phenylene were
between 35 and 58 degrees for DFT structures. The HOMO
for those molecules were shown to be delocalized to the
methoxyphenyl-substituents, and the position of methoxy
substituent in the phenyl group had a more significant effect
than for our current set of molecules. The phenyl amine group
in the substituents contributed to the delocalization of HOMO,
and the HOMO energy would be higher. On the other hand,
the indolo[3,2-b]carbazole core has a larger resonance structure
that includes 3 phenyl rings, and thus the energy gap between
the HOMO and LUMO is smaller as compared to that of
carbazoles. We have calculated the HOMO and LUMO
energies for the fragment models, benzene, methoxybenzene,
carbazole, and indolo[3,2-b]carbazole. As seen in Table 4,
Table 4. HOMO and LUMO Energies and the
Corresponding Energy Gap, in the Units of eV
a
molecule
HOMO
LUMO
gap
benzene
−6.70
−6.44
−4.92
−4.88
−5.44
−5.33
0.10
0.01
6.80
6.45
3.92
3.87
4.80
4.68
methoxybenzene
indolo[3,2-b]carbazole
N-phenyl indolo[3,2-b]carbazole
carbazole
−1.00
−1.01
−0.64
−0.65
N-phenyl carbazole
a
Obtained with the B3LYP functional and 6-31G* basis set. While
DFT may not offer the right energies for the HOMO and LUMO, and
the energy gaps prediction is rather limited, we note that these results
are mainly used for discussion on the origin of localized HOMO and
LUMO distribution within a set of calculation.
indolo[3,2-b]carbazole has a larger energy difference with the
phenyl substituents (benzene or methoxybenzene) in both
HOMO and LUMO, as compared to that of carbazole. For
indolo[3,2-b]carbazole, the larger energy differences in HOMO
(LUMO) between the phenyl group and the core group leads
to a smaller perturbative interaction, and thus a smaller
contribution from the phenyl group in the HOMO (LUMO)
indolo[3,2-b]carbazole. As a result, the HOMO (LUMO)
energies for the N-phenyl carbazole and N-phenyl indolo[3,2-
b]carbazole are very similar to those of the core carbazoles. The
smaller contribution can also explain the much weaker
dependence of the molecular properties on the position of
substituents on the phenyl groups as compared to those in
substituted carbazoles.
The Ip values of the core molecules (M1 and M2) are in
general higher than those of the substituted molecules. The
addition of di-tert-butylphenyl groups to the indolo[3,2-
b]carbazole core slightly reduces the Ip. The position of the
methoxy groups in molecules 2−4 slightly affects the Ip energy.
Molecules 2 and 4 have slightly lower Ip, which should have to
do with their ortho and para substitution that allows a
resonance in the electrons. However, this effect is very small
because of the low coupling between the methoxyphenyl group
and the indolo[3,2-b]carbazole core, and this effect is barely
observable in experimental data (Table 2). On the other hand,
the dihedral angles for molecules 5 and 6 are even larger than
Figure 4. (A) HOMOs and (B) NTOs of molecules 1−6. The
HOMOs are models for the ionized electrons, while the NTOs are the
electron and hole orbitals involved in an excitation. In all cases, the
population of the NTOs shown constitutes more than 94% of the
excited states. Contour surfaces at the isovalue of 0.02 au are shown.
distributed to the two methoxyphenyl groups. The dihedral
angles between the phenyl substituents and the core indolo-
[3,2-b]carbazole, derived from DFT computational structures,
are also listed in Table 3. It is seen that they are quite large,
ranging from 56 to 93 degrees, which limits the electronic
interaction between those moieties. For molecules 1−4, the
two dihedral angles are similar, and the nearby pentyl groups do
not affect the angle much. We note that the pentyl group is
likely offering an attractive CH−π interaction, instead of a
bulky, repulsive interaction (Figure S1 in the Supporting
Information). From these results, we conclude that the
electronic structure of molecules 1−6 is very similar to those
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Figure 5. XTOF transients of the neat film of compound 3 (a) and of the layer of compound 3 doped in PC-Z (50%) (b).
for other molecules, likely because of the presence of bulky di-
tert-butyl phenyl substituents. Molecules 5 and 6 are very
similar in their physical properties, and the values of Ip and
excitation energies are very close to that of the core model M2.
Time of flight measurements were used to characterize
charge-transporting properties of the synthesized compounds.
The representative dU/dt transients for the neat film of
compound 3 and for the solid solution of 3 in PC-Z are shown
in Figure 5. Distinct inflection points indicating transit times
with the sign of nondispersive hole transport were observed in
air both for the neat film of 3 and for its molecular mixture with
PC-Z. Nondispersive hole transport was also observed for the
glassy layer of compound 4. The layers of compound 1 and of
molecular mixtures of compounds 1, 2, 4−6 with PC-Z
exhibited dispersive charge transport. These differencies in
charge transport can apparently be explained by the differencies
in molecular packing.
Table 5. Hole Mobility Data for the Amorphous Layers of
Net Compound 1, 3, 4 and Compounds 1−6 Doped in PC-Z
(50%)
a
b
charge-transporting material
μ0 , cm2/V·s
μ , [cm2/V·s]
1
2.1 × 10−4
7 × 10−6
2.8 × 10−3
5 × 10−4
3
4
1.3 × 10−5
1.2 × 10−6
3 × 10−7
2.3 × 10−4
2.4 × 10−5
3 × 10−5
1+(PC-Z), 1:1
2+(PC-Z), 1:1
3+(PC-Z), 1:1
4+(PC-Z), 1:1
5+(PC-Z), 1:1
6+(PC-Z), 1:1
8 × 10−7
4 × 10−5
4 × 10−7
1.9 × 10−6
4.4 × 10−8
2.1 × 10−5
c
1.8 × 10−5
3 × 10−6
a
b
The zero field hole drift mobility. The hole drift mobility at electric
c
field of 6.4 × 105 V/cm. The hole drift mobility at electric field of 1.6
× 105 V/cm.
Figure 6 shows electric field dependencies of hole drift
mobilities (μ) for the amorphous layers of compounds 1, 3, 4
Among the layers of the net materials, the best charge-
transporting properties were observed for compound 1 having
no methoxy groups. Hole drift mobilities in the layers of 1 well
exceed of 10−3 cm2/V·s at high electric fields. No clear effect of
the position of methoxy groups on charge-transporting
properties can be identified for this series of materials.
Among methoxy-substituted derivatives of 6-pentyl-5,11-
dihydroindolo[3,2-b]carbazole (2−4), the best charge transport
properties were observed for compound 3 having methoxy
groups in meta positions. The glassy layer of compounds 3
showed hole drift mobility of 5 × 10−4 cm2/V·s at an electric
field of 6.4 × 105 V/cm at room temperature. Compound 3 also
showed the best performance in the molecular mixture with
bisphenol Z poycarbonate The 50% solid solution of 3 in PC-Z
demonstrated hole drift mobility of 4 × 10−5 cm2/V·s at the
electric field of 6.4 × 105 V/cm. Among the derivatives of 6,12-
di(3,5-di-tert-butylphenyl)-5,11-dihydroindolo[3,2-b]carbazole
(5, 6), the superior charge-transporting properties were shown
by compound 5 having methoxy groups in para positions. The
molecular mixture of 5 with PC-Z showed hole mobilities of 1.8
× 10−5 cm2/V·s at the electric field of 1.6 × 105 V/cm.
Figure 6. Electric field dependencies of hole drift mobility in charge
transport layers of compounds 1, 3, 4 and compounds 1−6 doped in
PC-Z (50%).
CONCLUSIONS
■
and for the bisphenol Z polycarbonate molecularly doped with
compounds 1−6. At room temperature, μ showed linear
dependencies on the square root of the electric field for all the
samples studied. The hole-drift mobility values are summarized
in Table 5.
In conclusion, we have synthesized new derivatives of
indolo[3,2-b]carbazole with phenyl groups having methoxy
groups in different positions. The synthesized compounds
exhibit high thermal stability with the temperatures of the onset
of thermal degradation ranging from 426 to 469 °C. The
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3.88 (s, 3H), 6.99 (d, 1H, J = 8 Hz), 7.03−7.60 (m, 13H), 7.95 (s,
1H), 8.07 (d, 1H, J = 8 Hz), 8.14 (d, 1H, J = 8 Hz).
13C NMR (75.4 MHz, CDCl3, δ, ppm): 14.5, 22.8, 28.7, 29.4, 32.7,
55.7, 55.8, 97.8, 109.7, 110.4, 113.6, 114.7, 115.0, 119.5, 119.7, 120.2,
120.3, 121.8, 122.1, 123.0, 123.5, 123.9, 124.7, 125.5, 126.3, 130.5,
131.0, 135.8, 137.7, 139.6, 142.5, 142.6, 145.0, 160.9, 161.2.
IR, νmax (KBr), 3047 (CHAr), 2957, 2917 (CHaliph.), 2854 (CH3−
O−), 1599, 1491, 1467, 1455 (CCAr), 1316 (C−N); γ cm−1: 748
(CHAr).
derivatives of 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole
form glasses with glass transition temperatures of 46−76 °C.
The HOMO values of the synthesized compounds range from
−5.14 to −5.07 eV. The electron photoemission spectra of the
films of the materials revealed ionization potentials of 5.31−
5.47 eV. The lowest ionization potential was observed for 4-
methoxyphenyl-substituted compound, i.e., for 5,11-bis(4-
methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-b]carbazole.
Time-of-flight hole drift mobilities of the amorphous films of
5,11-bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo[3,2-
b]carbazole exceed 10−3 cm2/V·s at high electric fields. The
indolo[3,2-b]carbazole core has a larger resonance structure
that includes 3 phenyl rings, and thus the energy difference of
the HOMO and LUMO π orbitals is lower as compared to that
of carbazoles. The energy difference between the phenyl
substituents and the core moiety becomes larger. The lower
energy in the core moiety of indolo[3,2-b]carbazoles leads to a
larger energy gap between the phenyl substituents and the core
moiety, and therefore, the indolo[3,2-b]carbazole derivatives
studied all have a weaker coupling between the phenyl group
and a much weaker dependence of the molecular properties on
the position of substituents on the phenyl groups as compared
to those observed in substituted carbazoles.
MS calcd for C37H34N2O2 538.70, (APCI+, 20 V), m/z: 539 ([M +
H]+).
5,11-Bis(2-methoxyphenyl)-6-pentyl-5,11-dihydroindolo-
[3,2-b]carbazole (4). Prepared according to the general procedure
from 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (M1) and 2-iodoa-
nisole. The resulting solid product was purified by column
chromotography using a mixture of chloroform and hexane in a
volume ratio of 1:4 as the eluent. Yellowish crystals were obtained with
a yield of 0.74 g (45%); mp = 195−196 °C.
1H NMR (300 MHz, CDCl3, δ, ppm): 0.85 (t, 3H, J = 7 Hz), 1.00−
1.28 (m, 4H), 1.48−1.74 (m, 2H), 2.90−3.22 (m, 2H), 3.65 (s, 3H),
3.70 (d, 3H, J = 3 Hz), 6.84 (d, 1H, J = 8 Hz), 7.08−7.38 (m, 9H),
7.45−7.57 (m, 4H), 7.66 (s, 1H), 8.03 (d, 1H, J = 7 Hz), 8.12 (d, 1H, J
= 7 Hz).
13C NMR (75.4 MHz, CDCl3, δ, ppm): 14.5, 22.9, 28.5, 29.5, 32.8,
55.8, 56.1, 97.9, 109.9, 112.3, 113.2, 113.2, 118.9, 119.1, 120.0, 121.2,
121.4, 121.6, 121.9, 122.7, 123.5, 123.8, 124.5, 125.1, 125.9, 126.7,
129.6 129.7, 130.2, 131.8, 135.4, 137.8, 142.7, 144.4, 156.7, 157.7.
IR, νmax (KBr), 3049 (CHAr), 2957, 2929 (CHaliph.), 2871, 2837
(CH3−O-), 1596, 1500, 1464 (CCAr), 1321 (C−N); γ cm−1: 741
(CHAr).
EXPERIMENTAL SECTION
■
General Procedure. Compounds 2−6 were prepared by the
method of Ullmann and Bielecki.22 The reaction mixtures consisting of
6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (M1) (1.00 g, 3.06
mmol) or 6,12-di(3,5-di-tert-butylphenyl)-5,11-dihydroindolo[3,2-b]-
carbazole (M2) (1.94 g, 3.06 mmol), potassium carbonate (2.88 g,
20.81 mmol), iodoanisole (2.86 g, 12.24 mmol), copper (0.78 g, 12.24
mmol), 18-crown-6 (0.16 g, 0.61 mmol), and 1,2-dichlorobenzene (ca.
8 mL) were stirred at reflux temperature for 24 h. The reaction
mixtures were cooled down and filtrated, the solvent was distilled in a
vacuum, and the crude product was subjected to silica gel column
chromatography.
MS calcd for C37H34N2O2 538.70, (APCI+, 20 V), m/z: 539 ([M +
H]+).
5,11-Bis(4-methoxyphenyl)-6,12-di(3,5-di-tert-butylphenyl)-
5,11-dihydroindolo[3,2-b]carbazole (5). Prepared according to
the general procedure from 6,12-di(3,5-di-tert-butylphenyl)-5,11-
dihydroindolo[3,2-b]carbazole (M2) and 4-iodoanisole. The resulting
solid product was purified by column chromotography using an eluent
mixture of chloroform and hexane in a volume ratio of 1:2. Yellowish
crystals were obtained with a yield of 0.9 g (67%); mp = 350−352 °C.
1H NMR (300 MHz, CDCl3, δ, ppm): 1.29 (s, 36H), 3.74 (s, 6H),
6.51 (s, 1H), 6.53 (s, 1H), 6.58 (d, 4H, J = 8 Hz), 6.74−6.81 (m, 4H),
6.90 (d, 4H, J = 8 Hz), 7.02 (d, 4H, J = 2 Hz), 7.13−7.23 (m, 2H),
7.29 (t, 2H, J = 2 Hz).
5,11-Bis(4-methoxyphenyl)-6-pentyl-5,11-dihydroindolo-
[3,2-b]carbazole (2). Prepared according to the general procedure
from 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (M1) and 4-iodoa-
nisole. The resulting solid product was purified by column
chromotography using an eluent mixture of chloroform and hexane
in a volume ratio of 1:4. Yellowish crystals were obtained with a yield
of 1.1 g (67%); mp = 226−228 °C.
13C NMR (75.4 MHz, CDCl3, δ, ppm): 31.7, 35.1, 55.4, 109.8,
114.0, 118.7, 120.1, 121.0, 122.7, 123.2, 123.4, 125.1, 125.4, 130.9,
132.1, 134.5, 136.6, 145.0, 150.4, 158.1.
IR, νmax (KBr), 3048 (CHAr), 2963 (CHaliph.), 2865 (CH3−O-),
1595, 1510, 1456 (CCAr), 1389, 1362 (tert-butyl), 1314 (C−N); γ
cm−1: 745 (CHAr).
1H NMR (300 MHz, CDCl3, δ, ppm): 0.86 (t, 3H, J = 7 Hz), 1.05−
1.30 (m, 4H), 1.48−1.72 (m, 2H), 3.00−3.13 (m, 2H), 3.92 (s, 3H),
3.93 (s, 3H), 6.92 (d, 1H, J = 8 Hz), 7.07 (d, 2H, J = 9 Hz), 7.11−7.37
(m, 7H), 7.43 (d, 2H, J = 9 Hz), 7.52 (d, 2H, J = 9 Hz), 7.81 (s, 1H),
8.04 (d, 1H, J = 8 Hz), 8.13 (d, 1H, J = 8 Hz).
MS calcd for C60H64N2O2 845.19, (APCI+, 20 V), m/z: 845 ([M +
H]+).
5,11-Bis(3-methoxyphenyl)-6,12-di(3,5-di-tert-butylphenyl)-
5,11-dihydroindolo[3,2-b]carbazole (6). Prepared according to
the general procedure from 6,12-di(3,5-di-tert-butylphenyl)-5,11-
dihydroindolo[3,2-b]carbazole (M2) and 3-iodoanisole. The resulting
solid product was purified by column chromotography using a mixture
of chloroform and hexane in a volume ratio of 1:2 as an eluent.
Yellowish crystals were obtained with a yield of 0.9 g (67%); mp =
362−363 °C.
13C NMR (75.4 MHz, CDCl3, δ, ppm): 14.5, 22.8, 28.6, 29.4, 32.7,
55.9, 55.9, 97.5, 109.5, 110.2, 115.0, 115.5, 119.2, 119.3, 120.1, 121.6,
121.8, 122.9, 123.3, 123.7, 124.5, 125.4, 126.1, 129.5, 130.9, 131.1,
134.0, 135.8, 138.2, 143.0, 145.4, 159.2, 159.8.
IR, νmax (KBr), 3050 (CHAr), 2952, 2910 (CHaliph.), 2861, 2836
(CH3−O-), 1610, 1515, 1462, 1452 (CCAr), 1319 (C−N); γ cm−1:
742 (CHAr).
1H NMR (300 MHz, CDCl3, δ, ppm): 1.26 (s, 18H), 1.29 (s, 18H),
3.67 (s, 6H), 6.55 (s, 1H), 6.57 (s, 1H), 6.60−6.65 (m, 2H), 6.68−
6.82 (m, 6H), 6.97 (t, 4H, J = 8 Hz), 7.12−7.24 (m, 6H), 7.28 (t, 2H, J
= 2 Hz).
MS calcd for C37H34N2O2 538.70, (APCI+, 20 V), m/z: 539 ([M +
H]+).
5,11-Bis(3-methoxyphenyl)-6-pentyl-5,11-dihydroindolo-
[3,2-b]carbazole (3). Prepared according to the general procedure
from 6-pentyl-5,11-dihydroindolo[3,2-b]carbazole (M1) and 3-iodoa-
nisole. The resulting solid product was purified by column
chromotography using an eluent mixture of chloroform and hexane
in a volume ratio of 1:4. White crystals were obtained with a yield of
1.2 g (73%); mp = 154−156 °C.
13C NMR (75.4 MHz, CDCl3, δ, ppm): 31.8, 31.7, 35.0, 35.1, 55.3,
109.9, 112.8, 115.5, 118.9, 120.3, 121.1, 122.6, 122.8, 123.4, 123.5,
124.8, 125.1, 125.5, 129.4, 134.5, 136.4, 140.5, 144.7, 150.3, 150.6,
159.6.
IR, νmax (KBr), 3049 (CHAr), 2961 (CHaliph.), 2867 (CH3−O-),
1591, 1491, 1459 (CCAr), 1386, 1362 (tert-butyl), 1317 (C−N); γ
cm−1: 743 (CHAr).
1H NMR (300 MHz, CDCl3, δ, ppm): 0.85 (t, 3H, J = 7 Hz), 1.05−
1.30 (m, 4H), 1.48−1.78 (m, 2H), 3.00−3.15 (m, 2H), 3.82 (s, 3H),
4930
dx.doi.org/10.1021/jo202677j | J. Org. Chem. 2012, 77, 4924−4931

The Journal of Organic Chemistry
Article
MS calcd for C60H64N2O2 845.19, (APCI+, 20 V), m/z: 845 ([M +
(21) Boudreault, P. L.; Virkar, A. A.; Bao, Z.; Leclerc, M. Org.
Electron. 2010, 11, 1649−1659.
H]+).
(22) Zhao, H. P.; Wang, F. Z.; Yuan, C. X.; Tao, X. T.; Sun, J. L.;
Zou, D. C.; Jiang, M. H. Org. Electron. 2009, 10, 925−931.
(23) Wakim, S.; Aich, B. R.; Tao, Y.; Leclerc, M. Polym. Rev. 2008,
48, 432−462.
ASSOCIATED CONTENT
■
S
* Supporting Information
General experimental conditions, 1H and 13C NMR spectra for
all new compounds, and the details of quantum chemical
calculations. This material is available free of charge via the
Internet at http://pubs.acs.org.
(24) Zhou, E.; Yamakawa, S.; Zhang, Y.; Tajima, K.; Yang, C.;
Hasimoto, K. J. Mater. Chem. 2009, 19, 7730−7737.
(25) Gale, P. A. Chem. Commun. 2008, 4525−4540.
(26) Ullmann, F.; Bielecki, J. Chem. Ber. 1901, 34, 2174−2178.
(27) Gu, R.; Hameurlaine, A.; Dehaen, W. Synlett 2006, 10, 1535−
1538.
AUTHOR INFORMATION
Corresponding Author
*E-mail: juozas.grazulevicius@ktu.lt.
Notes
■
(28) Tang, C.; Liu, F.; Xia, Y. J.; Xie, L. H.; Wei, A.; Li, S. B.; Fan, Q.
L.; Huang, W. J. Mater. Chem. 2006, 16, 4074−4080.
(29) Gu, R.; Van Snick, S.; Robeyns, K.; Van Meervelt, L.; Dehaen,
W. Org. Biomol. Chem. 2009, 7, 380−385.
(30) Kirkus, M.; Grazulevicius, J. V.; Grigalevicius, S.; Gu, R.;
Dehaen, W.; Jankauskas, V. Eur. Polym. J. 2009, 45, 410−417.
(31) Belletete, M.; Blouin, N.; Boudreault, P. L. T.; Leclerc, M.;
Durocher, G. J. Phys. Chem. A 2006, 110, 13696−13704.
(32) Shao, Y.; Molnar, L. F.; Jung, Y.; Kussmann, J.; Ochsenfeld, C.;
Brown, S. T.; Gilbert, A. T. B.; Slipchenko, L. V.; Levchenko, S. V.;
O’Neill, D. P., Jr.; Distasio, R. A.; Lochan, R. C.; Wang, T.; Beran, G. J.
O.; Besley, N. A.; Herbert, J. M.; Lin, C. Y.; Van Voorhis, T.; Chien, S.
H.; Sodt, A.; Steele, R. P.; Rassolov, V. A.; Maslen, P. E.; Korambath,
P. P.; Adamson, R. D.; Austin, B.; Baker, J.; Bird, E. F. C.; Dachsel, H.;
Doerksen, R. J.; Drew, A.; Dunietz, B. D.; Dutoi, A. D.; Furlani, T. R.;
Gwaltney, S. R.; Heyden, A.; Hirata, S.; Hsu, C. P.; Kedziora, G.;
Khalliulin, R. Z.; Klunziger, P.; Lee, A. M.; Lee, M. S.; Liang, W. Z.;
Lotan, I.; Nair, N.; Peters, B.; Proynov, E. I.; Pieniazek, P. A.; Rhee, Y.
M.; Ritchie, J.; Rosta, E.; Sherrill, C. D.; Simmonett, A. C.; Subotnik, J.
E.; Woodcock, H. L., III.; Zhang, W.; Bell, A. T.; Chakraborty, A. K.;
Chipman, D. M.; Keil, F. J.; Warshel, A.; Herhe, W. J.; Schaefer, H. F.,
III.; Kong, J.; Krylov, A. I.; Gill, P. M. W.; Head-Gordon, M. Phys.
Chem. Chem. Phys. 2006, 8, 3172−3191.
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This research was funded by a grant (No. MIP-059/2011) from
the Research Council of Lithuania. W.D. thanks the F. W. O.-
Vlaanderen, the Ministerie voor Wetenschapsbeleid, and the
University of Leuven for continuing financial support.
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