Polyindolo[3,2-b]carbazoles: A new class of p-Channel semiconductor polymers for organic thin-film transistors

Article abstract of DOI:10.1021/ma0612069

The synthesis and field-effect transistor (FET) properties of a novel class of indolocarbazole-based conjugated polymers, poly(indolo[3,2-b]carbazole)s, are described. Dehalogenative coupling polymerization of dichloroindolo[3,2-b] carbazoles with Zn/NiCl

Full text of DOI:10.1021/ma0612069

Macromolecules 2006, 39, 6521-6527
6521
Polyindolo[3,2-b]carbazoles: A New Class of p-Channel
Semiconductor Polymers for Organic Thin-Film Transistors
Yuning Li, Yiliang Wu, and Beng S. Ong*
Materials Design and Integration Laboratory, Xerox Research Centre of Canada,
Mississauga, Ontario, Canada L5K 2L1
ReceiVed May 30, 2006; ReVised Manuscript ReceiVed July 25, 2006
ABSTRACT: The synthesis and field-effect transistor (FET) properties of a novel class of indolocarbazole-
based conjugated polymers, poly(indolo[3,2-b]carbazole)s, are described. Dehalogenative coupling polymerization
of dichloroindolo[3,2-b]carbazoles with Zn/NiCl2/PPh3/2.2′-dipyridil gave the corresponding poly(indolo[3,2-b]-
carbazole)s, while oxidative coupling polymerization of indolo[3,2-b]carbazoles with FeCl3 proceeded regio-
selectively, affording poly(indolo[3,2-b]carbazole-2,8-diyl)s. Crystallization and optical properties of these polymers
were different, depending on the regiochemistry of backbone linkages and peripheral substitutions. Thin film
transistor devices using these polymer semiconductors exhibited p-channel FET behavior, dictated predominantly
by nature of substitution and backbone linkages (2,8- or 3,9-linkage). Solution-processed polyindolo[3,2-b]carbazole
thin-film semiconductors obtained from FeCl3 polymerization generally provided better FET performance.
Introduction
The phenomenal explosion in research activities in organic
thin-film transistors (OTFTs) in recent years is driven by the
expectation that these are potentially very low-cost alternatives
to silicon-based technologies for use in large-area, flexible, and
ultra low-cost electronic applications.1,2 OTFTs may be fabri-
cated by common solution deposition/patterning techniques (e.g.,
coating, stamping, offset printing, inkjet printing, etc.) and on
plastic substrates to enable flexible electronics. However, many
organic semiconductors (e.g., pentacene,3 regioregular poly(3-
hexylthiophene)4) are sensitive to photoinduced oxidative inter-
actions with atmospheric oxygen, leading to adversely degraded
semiconductor properties. To overcome the photooxidative sen-
sitivity, we recently developed a new class of indolo[3,2-b]-
carbazole-based semiconductors, which exhibited significantly
enhanced photostability by virtue of their relatively low-lying
HOMOs and larger optical band gaps.5,6 OTFTs using vacuum-
evaporated indolo[3,2-b]carbazole thin-film semiconductors
afforded field-effect transistor (FET) mobility up to ∼0.14 cm2/
(V s), manifesting efficient charge carrier injection and transport.
As with most small-molecule organic semiconductors such as
sexithiophenes, however, solution-processed indolo[3,2-b]-
carbazole thin-film semiconductors yielded much lower mobilitys
a consequence attributable to difficulties in controlling thin-
film quality of solution-processed small molecules as well as
inefficiency of small molecules to establish optimum molecular
ordering in thin films from solution. From this perspective, we
envisioned that a polymeric system based on an indolo[3,2-b]-
carbazole building block would be an ideal approach and offer
a scalable process to stable, solution-processed semiconductors
for OTFTs.
Figure 1. General structures of poly(indolo[3,2-b]carbazole-3,9-diyl),
I, and poly(indolo[3,2-b]carbazole-2,8-diyl), II.
polymer II has a greatly restricted π-conjugation not along its
backbone and resembles those of polyarylamines. In view of
their different geometric and electronic structures, these poly-
mers7 are expected to exhibit different molecular organization
behaviors and display distinctly different optoelectronic and
electrical properties.
Polymers I and II were synthesized via a dehalogenative
coupling polymerization of dihaloindolo[3,2-b]carbazole mono-
mers, as described in Scheme 1. 3,9-Dichloroindolo[3,2-b]-
carbazole (1) and 2,8-dichloroindolo[3,2-b]carbazole (2) were
prepared respectively from condensation of 3- and 4-chloro-
phenylhydrazine with 1,4-cyclohexanedione, followed by double
Fischer indolization. Subsequent alkylation or arylation with
1-bromododecane or 1-dodecyl-4-iodobenzene gave the corre-
sponding 5,11-disubstituted monomers 3 and 4. Dehalogenative
coupling polymerization of 3 and 4 using Zn/NiCl2/PPh3/2,2′-
dipyridyl in dimethylacetamide (DMAc)/toluene gave the
respective poly(indolo[3,2-b]carbazole)s I and II. Gel permea-
tion chromatography (GPC) analysis showed that these polymers
had number-average molecular weights ranging from 3300 to
9200 against polystyrene standards (Table 1). The observed
relatively low molecular weights of isolated polymer products
were primarily due to their poor solubility characteristics in the
polymerization medium (gelation or precipitation occurred in
the late stage of polymerization). In THF solutions (Figure 2A
and Table 1), polymers Ia and Ib showed strong UV-vis
absorptions with λmax at 421 and 410 nm, respectively, while
polymers IIa and IIb exhibited absorptions at significantly
shorter wavelengths with λmax at 357 and 355 nm, respectively,
and only very weak absorptions beyond 400 nm. These differ-
Results and Discussion
The indolo[3,2-b]carbazole units can be coupled at C-3/C-9
or C-2/C-8 positions to give poly(indolo[3,2-b]carbazole-3,9-
diyl) (I) or poly(indolo[3,2-b]carbazole-2,8-diyl) (II), respec-
tively (Figure 1). Polymer I has an extended π-conjugation along
its backbone, which resembles those of poly(p-arylene)s, while
* Corresponding author. E-mail: Beng.Ong@xrcc.xeroxlabs.com.
10.1021/ma0612069 CCC: $33.50 © 2006 American Chemical Society
Published on Web 08/24/2006

6522 Li et al.
Macromolecules, Vol. 39, No. 19, 2006
Scheme 1. Synthesis of Polyindolo[3,2-b]carabzoles via Dehalogenative Coupling Polymerizationa
a (i) EtOH/50 °C, 1 h; (ii) H2SO4/AcOH/65 °C; (iii) C12H15Br/NaOH/DMSO/50 °C (3a and 4a) or C12H25C6H4I, K2CO3, 1,2-dichlorobenzene/
reflux (3b and 4b); (iv) Zn/NiCl2/2,2′-dipyridyl/DMAc.
Table 1. Properties of Polyindolo[3,2-b]carbazoles
absorption λmax, nm
polyindolo[3,2-b]carbazole
polymerization methods
yield, %
80.9
Mn
Mw/Mn
THF solution
421, 400 (s)
film
Ia
Zn-mediated
9200
1.25
477 (s), 438, 396 (s)
dehalogenative coupling
polymerization
Ib
56.0
37.1
89.9
53.9
5700
3300
5700
1.15
1.44
1.16
2.63
410, 392 (s)
444 (s), 415
IIa
IIb
IIa
428, 408, 357
418, 401, 355
428, 409, 360
435 (s), 414, 359
423 (s), 403, 358
425, 365
FeCl3-mediated oxidative
coupling polymerization
11200
IIb
IIc
38.8
81.2
7000
4930
2.08
3.34
418, 400, 354
427, 407, 358
422, 403, 356
425, 362
ences in spectral properties reflected the extensive π-conjugation
along the polymer backbone of I and the restricted π-conjugation
systems of II. In fact, the spectral features of II are essentially
similar to those of the corresponding monomeric indolo[3,2-b]-
carbazoles.5,6 In addition, I also exhibited 20-30 nm batho-
chromic shifts from solution to thin-film spectra (Figure 2B),
indicative of the establishment of higher structural orders in
the solid state through intermolecular π-π interactions. In sharp
contrast, the thin-film spectrum of II showed little bathochromic
shifts over its solution spectral properties, revealing its inability
to achieve higher molecular orders in the solid state.
An alternate synthesis of II could be realized by a regio-
selective oxidative coupling of indolo[3,2-b]carbazole since its
C-2/C-8 positions are highly activated toward oxidative reaction
owing to their para relationship to the amino functions. Accord-
ingly, when 5,11-disubstituted indolo[3,2-b]carbazole 5 was
treated with excess FeCl3 in chlorobenzene at 50 °C for 24 h,
oxidative coupling polymerization leading to the formation of
II occurred in good yields (Scheme 2). The polymer products
obtained from this polymerization process possessed higher
molecular weight than those by dehalogenative polymerization
(Table 1), primarily because of higher solubility characteristics
1
of II in chlorobenzene reaction medium. H NMR spectral
analysis showed that these polymers were structurally similar
to those obtained by dehalogenative coupling method (e.g., IIa;
Figure 3), indicating that the present oxidative coupling reactions
were highly regioselective. This was further supported by
similarities in their other spectral properties (UV-vis and IR
spectra).
The structural orderings of polyindolo[3,2-b]carbazoles in thin
films were studied by X-ray diffraction (XRD). Thin films of
these polymers were prepared on a silicon wafer by drop-casting
from their hot 1 wt % solutions in chlorobenzene and then
annealed at 80 °C for 2 h in vacuo before their XRD patterns
were recorded (Figure 4). Poly(indolo[3,2-b]carbazole)s Ia, Ib,
and IIa prepared by dehalogenative polymerization exhibited
highly crystalline patterns with distinct primary diffraction peaks,
while IIb showed broad and weak diffraction peaks, revealing

Macromolecules, Vol. 39, No. 19, 2006
Polyindolo[3,2-b]carbazoles 6523
Figure 2. UV-vis absorption properties of polyindolocarbazoles I and II: A (THF solutions) and B (thin films) from polymers prepared by
dehalogenative polymerization; C (THF solutions) and D (thin films) from polymers prepared via FeCl3 polymerization.
Scheme 2. Synthesis of Polyindolocarabzoles via Oxidative Coupling Polymerizationa
a (i) RBr/NaOH/DMSO/50 °C (5a and 5c) or C12H25C6H4I, K2CO3, 1,2-dichlorobenzene/reflux (5b); (ii) FeCl3/chlorobenzene/50 °C.
its poor crystallinity. IIa and IIc prepared by FeCl3 polymer-
ization also displayed high crystallinity, with strong primary
diffraction peaks at 2θ ) 7.24° and 5.22°, corresponding to d
spacing of 12.2 and 16.9 Å, respectively. However, the d spacing
of the primary diffraction peak (16.9 Å) for IIa from FeCl3
polymerization was significantly shorter than that from dehalo-
genative polymerization (d ) 22.3 Å), which was likely due to
markedly different molecular weights and thus different molec-
ular orderings. IIb from FeCl3 polymerization showed similar
poor crystallinity as that from dehalogenative polymerization.
The FET characteristics of poly(indolo[3,2-b]carbazole) semi-
conductors were studied using a bottom-gate, top-contact TFT
configuration. The fabrication and characterization of TFT
devices were carried out under ambient conditions without tak-
ing any precautions to insulate the materials and devices from
exposure to air, moisture, and light. The test TFT devices were
built on an n-doped silicon wafer with the wafer itself serving
as the gate electrode and its 110 nm surface thermal SiO2 layer
as the gate dielectric. The dielectric surface was modified with
various modification agents [octyltrichlorosilane (OTS-8),
phenyltrichlorosilane (PTS), and polystyrene] to improve device
performance. For silane modification, the wafer SiO2 surface
was first cleaned with argon plasma and then washed with
distilled water and 2-propanol. Subsequently, the wafer was
immersed in 0.1 M solution of silane modification agent in
toluene at 60 °C for 20 min, rinsed with toluene and 2-propanol,
and then dried with an air stream. For polystyrene modification,
a 0.5 wt % solution of polystyrene in o-xylene was spin-coated
on the cleaned wafer surface at 3000 rpm for 30 s and dried to
provide a thin polystyrene film, which was cross-linked by
exposure to a 250 nm UV lamp at an intensity of 0.16 W/cm2
Figure 3. 1H NMR spectra of polyinodolocarbazole IIa (a) from
dehalogenative polymerization and (b) from FeCl3 polymerization.

6524 Li et al.
Macromolecules, Vol. 39, No. 19, 2006
Figure 4. X-ray diffractions of drop-cast thin films of polyindolocarbazoles: A, B, C, and D were respectively from Ia, Ib, IIa, and IIb prepared
by dehalogenative polymerization; E and F were respectively from IIa and IIc prepared by FeCl3 polymerization.
for 12 s. The irradiated film was immersed in toluene at 60 °C
for 20 min to remove the non-cross-linked fractions, followed
by drying before use. The poly(indolo[3,2-b]carbazole) semi-
conductor was deposited on the nonmodified and modified wafer
by spin-coating a 0.3-1 wt % solution of the polymer in 1,2-
dichlorobenzene at 1000 rpm for 120 s and vacuum-dried to
give a 20-50 nm thick semiconductor layer. Subsequently, the
gold source/drain electrodes were deposited by vacuum evapo-
ration through a shadow mask, thus creating a series of TFTs
with various channel length (L) and width (W) dimensions.
The test TFT devices with channel length of 90 or 190 µm
and channel width of 1 or 5 mm were used for I-V measure-
ments. The mobility in the saturated regime was extracted from
the following equation:
the saturated regime and VG of the device by extrapolating the
measured data to ID ) 0.
The FET performance of poly(indolo[3,2-b]carbazole) semi-
conductor in the TFT test devices depended on its backbone
linkage positions (i.e., C-2/C-8 or C-3/C-9), nature of side
chains, and polymerization methods. Poly(indolo[3,2-b]carba-
zole)s prepared by Zn-mediated dehalogenative coupling polym-
erization showed little or no FET properties. On the other hand,
poly(indolo[3,2-b]carbazole)s obtained from FeCl3-mediated
oxidative coupling polymerization exhibited significant FET
behaviors, with extracted mobility in the saturation regime up
to 0.02 cm2/(V s). Figure 5 depicts the I-V characteristics of a
typical OTFT with poly(indolo[3,2-b]carbazole) IIc, which
conformed to the conventional transistor models in both the
linear and saturated regimes. The output curves showed good
saturation behaviors with no observable contact resistance while
the transfer curve in the saturated regime exhibited a near-
quadratic increase in current as a function of gate bias; slight
deviations at high voltages, which were likely due to bias stress
effects, were however noted. The extracted mobility in the linear
saturated regime (VD > VG): ID ) Ciµ(W/2L)(VG - VT)2
where ID is the drain current, Ci is the capacitance per unit area
of the gate dielectric layer, and VG and VT are respectively the
gate voltage and threshold voltage. VT of the device was deter-
mined from the relationship between the square root of ID at

Macromolecules, Vol. 39, No. 19, 2006
Polyindolo[3,2-b]carbazoles 6525
optimum surface chemistry for poly(indolo[3,2-b]carbazole IIc
likely because of its phenyl groups which provided better
interaction with the fused-ring aromatic poly(indolo[3,2-b]-
carbazole) semiconductor. This was partly supported by the
finding that when OTS-8 was replaced with PTS (which as a
phenyl group) as the modification agent for the SiO2 dielectric
in the TFT devices, a higher mobility was also observed.
The TFT devices using solution-processed thin-film semi-
conductors of poly(indolo[3,2-b]carbazole) II were stable under
ambient conditions even when exposed to visible light. The
HOMO levels of polymers IIa-c, as determined by cyclic
voltammetry, are 5.1-5.2 eV from vacuum, almost identical
to their small molecule counterparts. Their low-lying HOMOs
and larger optical band gaps may explain for the resistance of
these polymer semiconductors to photoinduced oxidative doping
and degradation.
Figure 5. FET characteristics of an exemplary OTFT with IIc on
polystyrene-modified substrate (channel length ) 90 µm, channel width
) 5000 µm): (a) output curves at different gate voltages and (b) transfer
curve in saturated regime at constant source-drain voltage of -60 V
and square root of the absolute value of current as a function of gate
voltage.
In conclusion, we have synthesized a new class of poly-
(indolo[3,2-b]carbazole)s with backbone linkages at C-2/C-8 and
C-3/C-9 using a Zn-mediated dehalogenative coupling polym-
erization of dichloroindolo[3,2-b]carbazole. Poly(indolo[3,2-b]-
carbazole)s with backbone linkages at C-2/C-8 were also
synthesized by an FeCl3-mediated oxidative coupling polym-
erization of indolo[3,2-b]carbazole. TFTs using solution-
processed poly(indolo[3,2-b]carbazole) thin-film semiconductors
with C-2/C-8 backbone linkages provided better FET perfor-
mance, which may be attributed to the capability of the polymer
to provide sufficient resonance stabilization to the ammonium
radical cations formed in the charge carrier transport process.6
In addition, poly(indolo[3,2-b]carbazole)s obtained from FeCl3
polymerization were found to be better thin-film semiconductors,
affording FET mobility to 0.02 cm2 V-1 s-1. The low-lying
HOMOs and relatively large optical band gaps of poly(indolo-
[3,2-b]carbazole)s also rendered these semiconductors unusually
stable under ambient conditions even in the presence of visible
light. These poly(indolo[3,2-b]carbazole)s therefore represent
a useful class of solution-processable semiconductors for fabri-
cation of stable OTFT circuits for printed electronics.
regime was slightly lower than that in the saturated regime, and
this was quite similar to OTFTs with most organic semiconduc-
tors. Table 2 summarizes the maximum saturation mobility
values, threshold voltages, and current on/off ratios of OTFTs
with solution-processed poly(indolo[3,2-b]carbazole) semicon-
ductors on various dielectric surfaces. Both poly(indolo[3,2-b]-
carbazole)s Ia and Ib prepared from dehalogenative polymer-
ization at C-3/C-9 formed poor-quality thin films on hydrophobic
surfaces (e.g., silane- and polystyrene-modified SiO2 surface).
Although they did form excellent films on nonmodified SiO2
surface, no significant FET activity was detected. Similarly,
while poly(indolo[3,2-b]carbazole)s IIa and IIb from dehalo-
genative polymerization also formed uniform semiconductor thin
films on OTS-8-modified SiO2 surface, their TFTs provided low
mobility. This was not however the case with poly(indolo[3,2-
b]carbazole)s prepared by FeCl3 polymerization. Specifically,
IIa and IIc exhibited better FET characteristics on polystyrene-
modified SiO2 surface, providing mobility as high as 0.02 cm2
V-1 s-1. On the other hand, poly(indolo[3,2-b]carbazole) IIb
afforded much lower mobility due to the amorphous nature of
its semiconductor film. The above results clearly showed that
the FET performance of poly(indolo[3,2-b]carbazole)s depended
not only on the regiochemistry and substutuents of the polymers
but also on the processes by which they were synthesized.
In addition, the surface chemistry of gate dielectric also played
a critical role on FET performance. As can be noted, with poly-
(indolo[3,2-b]carbazole) IIc as the semiconductor, OTS-8 modi-
fication of SiO2 dielectric surface provided a conducive surface
chemistry for semiconductor molecules to achieve optimum
molecular ordering for charge carrier transport. The extracted
mobility in this case was as much as 5 times higher than those
of TFTs built on nonmodified SiO2 surface. A further mobility
improvement by a factor of 5 was achieved when polystyrene
was used as surface modification layer. Polystyrene offered an
Experimental Section
1. Measurements. 1H NMR spectra were recorded in CDCl3 on
a 300 MHz Bruker Spectrospin 300 spectrometer with tetramethyl-
silane as an internal standard. IR spectra were obtained on a Nicolet
Magna-IR 500 Series II spectrophotometer. UV-vis absorption
spectra were carried out on a Varian Cary 5 UV-vis NIR spectro-
photometer. Thermal analysis was performed on TA Instruments
DSC 2910 differential scanning calorimeter (DSC) at a heating rate
of 5 °C/min under a nitrogen atmosphere. X-ray diffraction was
recorded at room temperature on a Rigaku MiniFlex diffractometer
using Cu KR radiation (λ 1.54 18 Å) with a θ-2θ scans config-
uration. OTFTs were characterized using Keithley SCS-4200
characterization system in ambient conditions.
Table 2. Summary of FET Properties of Poly(indolo[3,2-b]carbazole)s
poly(indolo[3,2-b]-
surface
modification agent
mobility
threshold
voltage (V)
on/off
ratio
carbazole)s
polymerization method
(cm2 V-1 s-1
)
Ia
Zn-mediated dehalogenative
coupling polymerization
none
N.A.
N.A.
N.A.
Ib
none
OTS-8
OTS-8
polystyrene
N.A.
N.A.
-12
-10
-8
N.A.
102
IIa
IIb
IIa
1.5 × 10-5
8.0 × 10-4
9.6 × 10-3
103
FeCl3-mediated oxidative
coupling polymerization
105
IIb
IIc
polystyrene
none
OTS-8
PTS
polystyrene
1.8 × 10-3
7.0 × 10-4
3.8 × 10-3
5.3 × 10-3
2.0 × 10-2
-10
-20
-14
-8
103
103
104
105
105
-4

6526 Li et al.
Macromolecules, Vol. 39, No. 19, 2006
Cyclic voltammetric measurements were performed on a BAS
100 voltammetric system with a three-electrode cell in a solution
of tetrabutylammonium perchlorate (Bu4NClO4) (0.10 M) in aceto-
nitrile at a scanning rate of 40 mV s-1. An Ag/AgCl electrode, a
platinum wire, and a sealed platinum rod were used as the reference
electrode, counter electrode, and working electrode, respectively.
The working platinum electrode was coated with a 0.5 wt % solution
of poly(indolo[3,2-b]carbazole) in chlorobenzene and heated in a
vacuum oven at 150 °C for 10 min to give a thin poly(indolo[3,2-
b]carbazole) film on the electrode. The HOMO energy levels were
estimated using the equations EHOMO ) Ep′ + 4.38 eV, where Ep′
is the onset potential for oxidation relative to the Ag/AgCl reference
electrode.8
(CDCl3): δ 8.07 (dd, J1 ) 1.8 Hz, J2 ) 0.9 Hz, 2H), 7.97 (s, 2H),
7.49 (m, 8H), 7.32 (d, J ) 1.8 Hz, 2H), 7.31 (d, J ) 0.9 Hz, 2H),
2.78 (t, J ) 7.8 Hz, 4H), 1.77 (pent, J ) 7.4 Hz, 4H), 1.25-1.60
(m, 36H), 0.89 (t, J ) 6.6 Hz, 6H). IR (NaCl): 2922, 2851, 1605,
1518, 1465, 1456, 1375, 1319, 1261, 1235, 1179, 1074, 835, 797
cm-1. MS (TOF): m/z 812.4578 (812.4603 calcd for C54H66N2-
Cl2).
5,11-Bis(4-dodecylphenyl)indolo[3,2-b]carbazole (5b). This
compound was prepared from indolo[3,2-b]carbazole and 1-
dodecyl-4-iodobenzene using a similar synthetic procedure for 3b;
1
yield 48.3%, mp 126.5 °C. H NMR (CDCl3): δ 8.12 (d, J ) 7.7
Hz, 2H), 8.05 (s, 2H), 7.58 (d, J ) 8.3 Hz, 4H), 7.47 (d, J ) 8.3
Hz, 4H), 7.40 (m, 4H), 7.22 (m, 2H), 2.78 (t, J ) 7.7 Hz, 4H),
1.77 (m, 4H), 1.25-1.60 (m, 36H), 0.89 (t, J ) 6.5 Hz, 6H). IR
(NaCl): 3047, 2955, 2920, 2851, 1607, 1517, 1476, 1451, 1324,
1236, 839, 731 cm-1. MS (TOF): m/z 744.5340 (744.5383 calcd
for C54H68N2).
2. Materials Synthesis. All reagents were used as received from
Sigma-Aldrich. 5,11-Indolo[3,2-b]carbazole,9 3,9-dichloroindolo-
[3,2-b]carbazole (1),6 2,8-dichloroindolo[3,2-b]carbazole (2),6 3,9-
dichloro-5,11-didodecylinodolo[3,2-b]carbazole (3a),6 2,8-dichloro-
5,11-didodecylindolo[3,2-b]carbazole (4a),6 5,11-dioctylinodolo[3,2-
b]carbazole (5a),5 and 5,11-didodecylinodolo[3,2-b]carbazole (5b)5
were synthesized according to the procedures in the literature.
Poly(5,11-didodecylindolo[3,2-b]carbazole-3,9-diyl) (Ia). To a
25 mL flask were added 3a (0.662 g, 1 mmol), zinc powder (0.262
g, 4 mmol), triphenylphosphine (0.131 g, 0.5 mmol), 2,2′-dipyridil
10.9 mg, 0.07 mmol), anhydrous nickel(II) chloride (9.1 mg, 0.07
mmol), and DMAc (2 mL). The flask containing the mixture was
degassed and then filled with argon, and the procedure was repeated
two more times. The reaction mixture was heated to 80 °C and
maintained at this temperature for 10 min. Toluene (1 mL) was
added, and the heating was continued for 40 min until the mixture
became viscous and some insoluble materials formed. At this time,
additional toluene (2 mL) was added, and the mixture was stirred
for 40 min until the mixture became viscous again. Then toluene
(3 mL) was added and stirred for another 24 h. The reaction mixture
was cooled to room temperature and poured into methanol (200
mL) containing 2 N aqueous HCl solution (20 mL). After stirring
for 30 min, 2 N aqueous ammonia solution (30 mL) was added.
The precipitated solid was filtered, washed with water and methanol,
and dried. The solid was extracted with heptane in a Soxhlet
apparatus for 24 h to remove oligomer materials. The resulting solid
was dissolved in chlorobenzene and precipitated from methanol
(200 mL); yield 0.478 g (80.9%). GPC: Mn ) 9200, Mw/Mn )
3,9-Dichloro-5,11-bis(4-dodecylphenyl)indolo[3,2-b]carba-
zole (3b). 1-Dodecyl-4-iodobenzene which was used in the
condensation reaction was prepared as follows. A mixture of
1-phenyldodecane (26.33 g, 106.84 mmol), iodine (10.85 g, 42.75
mmol), H5IO6 (4.87 g, 21.37 mmol), acetic acid (54 mL), deionized
water (9.6 mL), and 98% sulfuric acid (3.53 g) in a 250 mL flask
was heated at 80 °C for ∼3 h until the purple iodine color
disappeared. The resulting mixture was extracted with dichloro-
methane, neutralized with saturated aqueous NaHCO3 solution, and
washed three times with water. The organic layer was separated,
dried over MgSO4, and filtered, and the solvent was removed using
a rotary evaporator. After column chromatography on silica gel
using hexane as an eluent, 38.80 g of a colorless viscous liquid
was obtained. 1H NMR indicated that the crude product was a mix-
ture of 1-dodecyl-4-iodobenzene (69%), 1-dodecyl-2-iodobenzene
(24%), and unreacted 1-phenyldodecane (7%). This crude product
was used in subsequent preparation of 5,11-bis(4-dodecylphenyl)-
indolo[3,2-b]carbazole, 3b, without purification. 1H NMR data for
1-iodo-4-dodecylbenzene (CDCl3): δ 7.58 (d, J ) 8.3 Hz, 2H),
6.92 (d, J ) 8.3 Hz, 2H), 2.53 (t, J ) 7.8 Hz, 2H), 1.57 (m, 2H),
1.20-1.40 (m, 18H), 0.88 (t, J ) 6.5 Hz, 3H).
1
1.25. H NMR (CDCl3): δ 8.32 (2H), 8.09 (2H), 7.76 (2H), 7.65
(2H), 4.53 (4H), 2.05 (4H), 1.25-1.60 (m, 36H), 0.86 (6H). IR
(NaCl): 2921, 2851, 1619, 1510, 1468, 1445, 1375, 1340, 1247,
1120, 832, 798 cm-1
.
A mixture of 3,9-dichloroindolo[3,2-b]carbazole, 1 (0.69 g, 2.12
mmol), 18-crown-6 (0.11 g, 0.42 mmol), K2CO3 (2.34 g, 17.0
mmol), 1-iodo-4-octylbenzene (3.43 g, 6.37 mmol, 69% of purity)
as prepared above, copper (0.54 g, 8.5 mmol), and 1,2-dichloro-
benzene (8.5 mL) was charged into an argon-filled 50 mL flask
fitted with a condenser. The mixture was heated under reflux in an
argon atmosphere for 24 h. Subsequently, the reaction mixture was
cooled to room temperature, diluted with tetrahydrofuran, and
filtered. A viscous liquid, which was obtained after removal of sol-
vent using a rotary evaporator, was added to 100 mL of methanol
with vigorous stirring. The precipitated yellow solid was filtered,
washed several times with water and methanol, then dissolved in
100 mL of hexane by heating, and filtered to remove the insoluble
materials. The filtrate was concentrated to about 50 mL, allowed
to cool to room temperature, and then chilled at 0 °C overnight.
The crystallized yellow product was filtered, washed with a small
amount of hexane, and dried to yield 1.23 g (71.4%) of 5,11-bis-
(4-dodecylphenyl)indolo[3,2-b]carbazole, 3b; mp 151.7 °C. 1H
NMR (CDCl3): δ 7.99 (d, J ) 8.3 Hz, 2H), 7.95 (s, 2H), 7.50 (m,
8H), 7.35 (d, J ) 1.8 Hz, 2H), 7.18 (dd, J1 ) 8.3 Hz, J2 ) 1.8 Hz,
2H), 2.78 (t, J ) 7.7 Hz, 4H), 1.77 (pent, J ) 7.5 Hz, 4H), 1.25-
1.60 (m, 36H), 0.89 (t, J ) 6.6 Hz, 6H). IR (NaCl): 2923, 2852,
1614, 1517, 1502, 1463, 1438, 1375, 1337, 1304, 1235, 1068, 960,
799 cm-1. MS (TOF): m/z 812.4595 (812.4603 calcd for C54H66N2-
Cl2).
Poly(5,11-bis(4-dodecylphenyl)indolo[3,2-b]carbazole-3,9-
diyl) (Ib). This polymer was prepared in accordance with the
synthetic procedure for Ia using 3b as the monomer; yield 56.0%.
GPC: Mn ) 5700, Mw/Mn ) 1.15. 1H NMR (CDCl3): δ 8.14, 8.05,
7.64, 7.50, 2.80 (4H), 1.80 (4H), 1.29-1.52 (m, 36H), 0.88 (6H).
IR (NaCl): 3033, 2923, 2852, 1610, 1518, 1459, 1340, 1230, 1190,
840, 794 cm-1
.
Poly(5,11-didodecylindolo[3,2-b]carbazole-2,8-diyl) (IIa). This
polymer was prepared in accordance with the synthetic procedure
for Ia using 4a as the monomer; yield 37.1%. GPC: Mn ) 3300,
1
Mw/Mn ) 1.44. H NMR (CDCl3): δ 8.59 (2H), 8.19 (2H), 7.92
(2H), 7.55 (2H), 4.50 (4H), 2.04 (4H), 1.23-1.60 (m, 36H), 0.84
(6H). IR (NaCl): 2923, 2851, 1616, 1509, 1468, 1314, 1232, 834,
794 cm-1
.
Poly(5,11-bis(4-dodecylphenyl)indolo[3,2-b]carbazole-2,8-
diyl) (IIb). This polymer in accordance with the synthetic procedure
for Ia using 4b as the monomer; yield 89.9%. GPC: Mn ) 5700,
1
Mw/Mn ) 1.16. H NMR (CDCl3): δ 8.43 (2H), 8.18 (2H), 7.74
(2H), 7.64 (4H), 7.51 (6H), 2.81 (4H), 1.80 (4H), 1.26-1.55 (m,
36H), 0.87 (6H). IR (NaCl): 3033, 2923, 2852, 1608, 1516, 1453,
1320, 1232, 840, 801 cm-1
.
Poly(5,11-dioctylindolo[3,2-b]carbazole-2,8-diyl)-FeCl3 (IIc).
5a (0.481 g, 1 mmol) in chlorobenzene (10 mL) was added to a
mixture of FeCl3 (0.681 g, 4.2 mmol) and chlorobenzene (20 mL)
in a 50 mL flask under an argon atmosphere. The reaction mixture
was heated to 50 °C and stirred for 24 h. After cooling to room
temperature, the reaction mixture was poured into methanol (200
mL). The precipitated solid was washed with water and methanol
2,8-Dichloro-5,11-bis(4-dodecylphenyl)indolo[3,2-b]carba-
zole (4b). This compound was prepared from 2,8-dichloroindolo-
[3,2-b]carbazole (1b) and 1-dodecyl-4-iodobenzene using a similar
1
synthetic procedure for 3b; yield 68.5%, mp 165.8 °C. H NMR

Macromolecules, Vol. 39, No. 19, 2006
Polyindolo[3,2-b]carbazoles 6527
for many times. The solid was then suspended in 2 N aqueous
ammonia solution (100 mL) for 1 h, filtered, and subjected to
Soxhlet extraction with methanol for 24 h and then heptane for
24 h. The residue in the Soxhlet apparatus was dissolved with
chlorobenzene and precipitated from methanol; yield 0.40 g
(81.2%). GPC (THF-soluble fraction): Mn ) 4930, Mw/Mn ) 3.34.
1H NMR (CDCl3): δ 8.61 (2H), 8.19 (2H), 7.93 (2H), 7.55 (2H),
4.51 (4H), 2.06 (4H), 1.23-1.60 (m, 20H), 0.88 (6H). IR (NaCl):
References and Notes
(1) (a) Sirringhaus, H. AdV. Mater. 2005, 17, 2411-2425. (b) Ling, M.
M.; Bao, Z. Chem. Mater. 2004, 16, 4824-4840. (c) Katz, H. E. Chem.
Mater. 2004, 16, 4748-4756. (d) Dimitrakopoulos, C. D.; Malenfant,
P. R. L. Adv. Mater. 2002, 14, 99-117. (e) Katz, H. E.; Bao, Z. N.;
Gilat, S. L. Acc. Chem. Res. 2001, 34, 359-369.
(2) (a) Bao, Z.; Dodabalapur, A.; Lovinger, A. J. Appl. Phys. Lett. 1996,
69, 4108-4110. (b) Arias, A. C.; Ready, S. E.; Lujan, R.; Wong, W.
S.; Paul, K. E.; Salleo, A.; Chabinyc, M. L.; Apte, R.; Street, R. A.;
Wu, Y.; Liu, P.; Ong, B. Appl. Phys. Lett. 2004, 85, 3304-3306.
(3) (a) Dimitrakopoulos, C. D.; Brown, A. R.; Pomp, A. J. Appl. Phys.
1996, 80, 2501-2508. (b) Lin, Y. Y.; Gundlach, D. J.; Nelson, S.;
Jackson, T. N. IEEE Trans. Electron DeVices 1997, 44, 1325-1331.
(c) Kelly, T. W.; Boardman, L. D.; Dunbar, T. D.; Muyres, D. V.;
Pellerite, M. J.; Smith, T. P. J. Phys. Chem. B 2003, 107, 5877-
5881.
3045, 2923, 2852, 1618, 1507, 1467, 1313, 1227, 833, 788 cm-1
.
Poly(5,11-didodecylindolo[3,2-b]carbazole-2,8-diyl)-FeCl3 (IIa).
This polymer was in accordance with the synthetic procedure for
IIc using 5b as the monomer; yield 53.9%. GPC: Mn ) 11 200,
1
Mw/Mn ) 2.63. H NMR (CDCl3): δ 8.61 (2H), 8.19 (2H), 7.92
(2H), 7.55 (2H), 4.52 (4H), 2.06 (4H), 1.23-1.60 (m, 36H), 0.85
(6H). IR (NaCl): 3036, 2922, 2852, 1619, 1507, 1467, 1314, 1228,
(4) (a) Sirringhaus, H.; Friend, R. H. Science 1998, 280, 1741-1744. (b)
Sirringhaus, H.; Brown, P. J.; Friend, R. H.; Nielsen, M. M.;
Bechgaard, K.; Langeveld-Voss, B. M. W.; Spiering, A. J. H.; Janssen,
R. A. J.; Meijer, E. W.; Herwig, P.; de Leeuw, D. M. Nature (London)
1999, 401, 685-688.
834, 789 cm-1
.
Poly(5,11-bis(4-dodecylphenyl)indolo[3,2-b]carbazole-2,8-diyl)-
FeCl3 (IIb). This polymer was prepared in accordance with the
synthetic procedure for IIc using 5c as a monomer; yield 38.8%.
GPC: Mn ) 7000, Mw/Mn ) 2.08. 1H NMR (CDCl3): δ 8.43 (2H),
8.18 (2H), 7.75 (2H), 7.65 (2H), 7.50 (4H), 7.42 (2H), 2.80 (4H),
1.79 (4H), 1.26-1.55 (m, 36H), 0.87 (6H). IR (NaCl): 3033, 2924,
(5) Wu, Y.; Li, Y.; Gardner, S.; Ong, B. S. J. Am. Chem. Soc. 2005, 127,
614-618.
(6) Li, Y.; Wu, Y.; Gardner, S.; Ong, B. S. AdV. Mater. 2005, 17, 849-
853.
(7) Similar polymers were recently reported: (a) Blouin, N.; Michaud,
A.; Wakim, S.; Boudreault, P. T.; Leclerc, M.; Vercelli, B.; Zecchin,
S.; Zotti, G. Macromol. Chem. Phys. 2006, 207, 166-174. (b) Blouin,
N.; Leclerc, M.; Zecchin, S.; Vercelli, B.; Zotti, G. Macromol. Chem.
Phys. 2006, 207, 175-182.
(8) (a) Li, Y.; Ding, J.; Day, M.; Tao, Y.; Lu, J.; D’iorio, M. Chem. Mater.
2004, 16, 2165-2173. (b) de Leeuw, D. M.; Simenon, M. M. J.;
Brown, A. R.; Einerhand, R. E. F. Synth. Met. 1997, 87, 53-59. (c)
Cui, Y.; Zhang, X.; Jenekhe, S. A. Macromolecules 1999, 32, 3824-
3826.
2852, 1608, 1516, 1452, 1320, 1233, 841, 802 cm-1
.
Acknowledgment. Partial financial support is provided by
the National Institute of Standards and Technology through an
Advanced Technology Program Grant (70NANB0H3033).
Note Added after ASAP Publication. This article was
published ASAP on August 24, 2006. A new reference 7 was
added to the paper. The correct version was published on
August 28, 2006.
(9) Robinson, B. J. Chem. Soc. 1963, 3097-3099.
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