Synthesis, characterization, and OFET and OLED properties of π-extended ladder-type heteroacenes based on indolodibenzothiophene

Article abstract of DOI:10.1246/bcsj.20110255

Ladder-type heteroacenes based on indolodibenzothiophene have been synthesized. The route involved a regioselective twofold intramolecular acid-induced cyclization of the central bis(butylsulfinyl)phenyl unit onto the adjacent carbazole units, followed by

Full text of DOI:10.1246/bcsj.20110255

136
Bull. Chem. Soc. Jpn. Vol. 85, No. 1, 136-143 (2012)
© 2012 The Chemical Society of Japan
Synthesis, Characterization, and OFET and OLED
Properties of ³-Extended Ladder-Type Heteroacenes
Based on Indolodibenzothiophene
Changsheng Wang,1 Jun-ichi Nishida,*2 Martin R. Bryce,*1 and Yoshiro Yamashita2
1Department of Chemistry, Durham University, Durham, DH1 3LE, U.K.
2Department of Electronic Chemistry, Interdisciplinary Graduate School of Science and Engineering,
Tokyo Institute of Technology, Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502
Received August 23, 2011; E-mail: m.r.bryce@durham.ac.uk, jnishida@echem.titech.ac.jp
Ladder-type heteroacenes based on indolodibenzothiophene have been synthesized. The route involved a
regioselective twofold intramolecular acid-induced cyclization of the central bis(butylsulfinyl)phenyl unit onto the
adjacent carbazole units, followed by dealkylation to give diindolobenzobisbenzothiophene (DIBBBT) derivatives.
Importantly, this sequence proceeded efficiently in the presence of the chloro substituents which provided reactive sites
for further ³-extension of the DIBBBT core. The chloro derivative underwent twofold palladium-catalyzed Suzuki-
Miyaura reactions with phenylboronic acid or 4-n-octylphenylboronic acid. Compounds have been characterized by
1H NMR spectroscopy, mass spectrometry, elemental analysis, optical spectroscopy, and solution electrochemical studies.
Organic field-effect transistors (OFETs) have been constructed based on drop-cast thin films and the performances as
p-type semiconductor are presented. The chloro derivative was also copolymerized with 9,9-dioctyl-2,7-fluorenyl-
enediboronic acid bis(1,3-propanediol) ester to give the alternating copolymer which exhibits blue photoluminescence in
solution and blue-green electroluminescence in a solution processed organic light-emitting diode (OLED).
Conjugated oligomers are of particular interest in organic
challenging target molecules. Extended linearly-condensed
systems can offer enhanced ³-³ overlap in the solid state
leading to high mobility.
electronic and optoelectronic applications, for example as
components for organic light-emitting devices (OLEDs),1
solar cells,2 and organic field-effect transistors (OFETs).3 The
planar and rigid frameworks of ladder-conjugated oligomers
facilitate electron delocalization compared to linear and
branched counterparts and ladder systems generally show
enhanced mechanical, thermal, and chemical stability. Classical
systems with high charge carrier mobility are linear acenes
(notably pentacene)4 although their oxidative stability is rather
limited due to their narrow band gaps. Instability remains a
significant issue with higher homologues.5 Pentacene also
suffers from extreme insolubility, so derivatives with pendant
functionality,6 and thiophene units in the backbone7 have been
developed.
We now describe the synthesis and characterization of new
DIBBBT derivatives, in particular the first derivative 8 bearing
functionality which has enabled subsequent transformations.
The terminal chloro substituents of 8 have been utilized in
palladium-catalyzed cross-coupling reactions to afford the
diphenyl derivative 9, the 4-n-octylphenyl derivative 10, and
the alternating copolymer 11. The performances of OFETs
based on drop-cast thin films of 8-10 as p-type semiconductors
are presented, and OLEDs based on spin-coated thin films of
11 are described.
Results and Discussion
New ladder-type heteroacenes with multi-heteroatom
components to enhance stability and alkyl substituents for
improved solubility are current targets. Examples include
fused oligothiophene,8 benzothiophenes,9 benzobisthiazole,10
thiazolothiazole,11 indolocarbazole,12 bisindenocarbazole,13
and thienopyrrole derivatives.14 In this regard, pyrrole, indole,
and carbazole are attractive building blocks due to the ease
of attaching solubilizing chains to the nitrogen atoms. Alkyl
substituents attached to these sp2 hybridized nitrogen atoms
may align within the molecular planes and improve the
intermolecular ³-³ stacking in the solid state. However, only
a limited number of extended heteroacenes (>7 fused rings)
have been synthesized,15 for example, diindolobenzobisbenzo-
thiophene (DIBBBT) with 9 fused rings,9c and they are
Synthesis. The synthetic strategy is outlined in Scheme 1.
The significant new feature in our synthesis, compared to
the previous synthesis of the DIBBBT skeleton,9c is that we
retained the 7-chloro substituent of 1 until the end of the
sequence, where it provides a versatile handle for the attach-
ment of terminal groups and ³-extension by metal-catalyzed
processes. Carbazole derivative 1 was synthesized by treatment
of 4-bromo-4¤-chloro-2-nitrobiphenyl with triethylphosphite at
reflux, as described.16 Attachment of the 2-ethylhexyl sub-
stituent to 1 enhanced the solubility in organic solvents.
Compound 2 was readily obtained and converted into the
boronic ester derivative 3 by reaction with 2-isopropoxy-
4,4,5,5-tetramethyl-1,3,2-dioxaborolane, utilizing the enhanced
reactivity of the bromo substituent in this reaction. A double
Published on the web December 30, 2011; doi:10.1246/bcsj.20110255

C. Wang et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
137
O
ii
i
Br
Cl
Cl
Br
Cl
B
N
R
N
H
1
O
N
R
2
SC4H9
3
Br
Br
iii
C4H9S
4
R
N
O
R
N
SC4H9
iv
SC4H9
Cl
Cl
Cl
N
R
Cl
C4H9S
N
R
C4H9S
O
6
5
v
R
N
R
N
C4H9
S
+
Cl
S
Cl
vi
+
Cl
S
Cl
S
N
R
N
R
C4H9
8
7
vii
R
N
O
O
R1
B
B
viii
S
O
O
C8H17 C8H17
12
S
N
R
R1
9 (R1 = H)
10 (R1 = n-Octyl)
C4H9
C8H17
C8H17
S
R
N
n
N
R
C4H9
S
11 (DIBBBT-Fl)n
R = 2-Ethylhexyl
Scheme 1. Synthesis of DIBBBT derivatives 9 and 10 and polymer (DIBBBT-Fl)n (11). Reagents and conditions: (i) Kt-OBu, THF,
rt, then 2-ethylhexyl bromide, 60 °C (88%); (ii) n-BuLi, ¹78 °C, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-dioxaborolane, ¹78 °C
(69%); (iii) [Pd(PPh3)2Cl2], KOH, PhMe, THF, H2O, reflux (59%); (iv) mcpba, DCM, 0 °C (90%); (v) MeSO3H, rt (product 7 not
purified); (vi) pyridine, reflux (30% from 6); (vii) K3PO4¢2H2O, phenylboronic acid or 4-n-octylphenylboronic acid (excess), THF,
water, Pd(OAc)2, dicyclohexyl-2¤,6¤-dimethoxy-2-biphenylylphosphine (Sphos), 60 °C (87% or 90%); (viii) (a) K3PO4¢2H2O, 12
(1.0 equiv), THF, water, Pd(OAc)2, Sphos, 60 °C, (b) 4-n-butylbromobenzene, 60 °C (c) 4-n-butylphenylboronic acid 60 °C (82%).
reaction of 3 with reagent 4 under standard Suzuki-Miyaura
cross-coupling conditions gave 5 in 59% yield. Oxidation of 5
with m-chloroperoxybenzoic acid gave disulfinyl derivative 6.
step. Dealkylation of 7 was achieved in refluxing pyridine9 to
afford 8 (30% yield from 6). The 1H NMR spectrum of 8
confirmed a highly symmetric structure with the regiochemistry
shown, with no evidence obtained for the formation of isomeric
products. It was gratifying that the chloro substituents were
retained throughout the reaction conditions; this was crucial for
our strategy of retaining reactive terminal sites for further
functionalization. Compound 8 served as an efficient synthon
for compounds with extended conjugation, namely diphenyl
1
The H NMR spectrum of 6 (See Supporting Information) is
consistent with two diastereomers arising from the presence
of two sulfoxide groups in the molecule. Reaction of 6 with
methanesulfonic acid gave a yellow solid product, presumed to
be the intermediate salt 7, based on literature precedents.9 Salt 7
was isolated but not purified; it was used directly in the next

138
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
Ladder-Type Heteroacenes Based on Indolodibenzothiophene
derivatives 9 and 10 and the alternating copolymer 11. Twofold
Suzuki-Miyaura reactions of 8 with phenylboronic acid or
4-n-octylphenylboronic acid using a mixture of palladium
acetate and dicyclohexyl-2¤,6¤-dimethoxy-2-biphenylylphos-
phine (Sphos) as catalyst17 gave products 9 and 10 in 87 and
90% yields, respectively. Compounds 8-10 were isolated as
air-stable yellow solids with limited solubility in common
organic solvents. Using similar conditions, compound 8 was
copolymerised18 with 9,9-dioctyl-2,7-fluorenylenediboronic
acid bis(1,3-propanediol) ester 1219 to afford an alternating
copolymer which was end-capped in situ with 4-n-butylphenyl
groups. This was achieved by sequential reaction with 4-n-
butylbromobenzene and 4-n-butylphenylboronic acid to yield
the (DIBBBT-Fl)n copolymer 11 which was obtained in 82%
yield as a pale yellow solid. Copolymer 11 had Mw 48 kDa,
polydispersity of ca. 1.8 and showed good thermal stability
464 for 8, and 443, 472 nm for 9). Photoluminescence quantum
yields in CHCl3 (Φ: 5.1% for 8 and 7.9% for 9) were
determined by using 9,10-diphenylanthracene (-ex 366 nm,
Φ 0.81 in EtOH) as standard. Octyl-substituted compound 10
afforded similar absorption and emission maxima compared
with 9 (see Experimental section). Copolymer 11 is a blue
emitter: compared to 9, the absorption and photoluminescence
spectra of 11 (Figure S1) are slightly broadened and red shifted
by ca. 15 nm: for 11 -max (em) (CHCl3) 459, 472 (sh) nm.
Photoluminescence quantum yields of 11 were 63 («5)% in
toluene and 21 («5)% in film. For film the data was obtained
by using an integrating sphere.22 These data are typical for
fluorene copolymers.21
The redox potentials of 8 and 9 were investigated by cyclic
voltammetry (CV) and differential pulse voltammetry (DPV) in
acetonitrile. The CVs of 8 and 9 revealed reversible oxidation
waves at E1/2 0.989 V (Eox 1.023; Ered 0.956 V) and 0.956 V (Eox
0.989; Ered 0.922 V) vs. Ag/Ag+, respectively, when the scan
was terminated at +1.1 V (potentials calibrated with ferrocene
as the internal standard) (Figure 2a). Since octyl-substituted
compound 10 did not dissolve in acetonitrile, a CV of 10 was
measured in dichloromethane and revealed a reversible wave
at E1/2 0.954 V (Eox 0.994; Ered 0.914 V) and two additional
quasi-reversible oxidation waves as shown in Figure 2b.
The DPVs of 8 and 9, vs. ferrocene/ferrocenium+ are shown
in Figure 3. Both compounds show three clear oxidation peaks
each of which is shifted to less positive potentials when the
chloro substituents are replaced by phenyl (i.e., 8 ¼ 9). Taking
the HOMO level of ferrocene as ¹4.8 eV,23 the HOMO levels
5%
with Td 380 °C, typical for conjugated polycarbazole20 and
polyfluorene21 derivatives.
UV-vis Absorption, Photoluminescence Spectra, and
Solution Electrochemical Properties.
Absorption and
emission spectra of compounds 8 and 9 were recorded in
chloroform (Figure 1). The strong absorption bands at 367 and
389 (8) and 378, 389, and 398 nm (9) are attributed to ³-³*
transitions of the heteroacene backbone. A small red shift
(ca. 10 nm) in both the absorption and emission spectra is
observed on replacing the terminal chlorine substituents of
8 with phenyl rings (compound 9) consistent with extended
conjugation in 9. Based on the onset of the low energy band
(ca. 440 nm), the optical band gap of 9 can be estimated as
2.82 eV. Both compounds show blue fluorescence (-max 437,
of 8 and 9 can thus be estimated as ¹5.3 eV based on the onset
onset
of the first oxidation wave (Eox
ca. +0.50 and ca. 0.47 V).
This value is lower than that of pentacene (¹4.60 eV)24
indicating enhanced oxidative stability of 8 and 9, and is
similar to that of indolo[3,2-b]carbazole derivatives ¹(5.4-
5.6 eV) reported by Leclerc et al.12e
Organic Field-Effect Transistor Devices. Device proper-
ties have not been reported previously for the DIBBBT system.
To investigate the carrier transporting properties, preliminary
FET devices were tested by using simple DIBBBT derivatives
8-10 with chloro, phenyl, and alkylphenyl groups. The FET
devices were fabricated on thermally oxidized silicon dioxide
with interdigitated Au bottom electrodes. The surface of silicon
dioxide was treated with hexamethyldisilazane (HMDS). Thin
films were deposited by a drop-cast method from the chloro-
form solution followed by annealing at 110-180 °C for 20 min
Figure 1. Absorption and emission spectra of 8 and 9 in
chloroform.
(a)
(b)
Figure 2. Cyclic voltammograms of (a) 8 (dotted line) and 9 (solid line) in acetonitrile solution and (b) 10 in dichloromethane.

C. Wang et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
139
in a high vacuum chamber (ca. 10¹5 Pa). The FET measure-
ments were carried out in situ and in the air. All films of 8-10
exhibited p-type FET characteristics (Table 1). Among them,
compound 9 with terminal phenyl groups afforded the highest
(a)
Fc/Fc+
8
6
4
2
0
¹1
mobility of 1.2 © 10¹2 cm2 V¹1 s on HMDS treated surface
as shown in Figure 4. Film 9 on untreated surface showed
notable air stability as expected from the oxidation potential
(Table 1). On the other hand, compound 10 with octyl groups
did not improve the carrier transportation, although the surfaces
of films were apparently flat and continuous. In this system,
alkyl groups of the molecular long axis may disturb the
formation of large overlap between molecular orbitals. How-
ever, suitable elongation and modification to the DIBBBT core
is expected to increase the carrier transporting properties.
The X-ray diffraction profiles of drop-cast films of 8 and 9
indicate a primary diffraction peak at 2ª = 4.5 (d-spacing
1.97 nm) and 5.2° (d-spacing 1.69 nm), respectively (Figure 5).
Although crystal structures could not be obtained, the XRD
profiles suggest that the molecules are oriented with a specific
regularity on the substrate surface. Compound 8 with terminal
chloro substituents showed a longer d-spacing than compound
9, although the calculated molecular length of 8 (2.26 nm) is
shorter than that of 9 (2.98 nm). On the other hand, the film
of 8 showed lower mobility than that of 9. Compound 8
afforded a discontinuous crystalline film compared with 9, and
the terminal chloro substituents may be unfavorable for the
hole transportation.
0.576
0.800
0.973
0.0
0.5
1.0
1.5
E / V (vs. Fc/Fc+)
(b)
8
6
4
2
0
0.543
0.730
0.940
0.0
0.5
1.0
1.5
E / V (vs. Fc/Fc+)
Polymer Light-Emitting Diode (PLED) Devices of 11.
A
Figure 3. DPVs of compounds (a)
acetonitrile solution, vs. Fc/Fc+.
8 and (b) 9 in
copolymer 11 containing DIBBBT cores was used for
fabrication of polymer LEDs, and two device structures were
Table 1. FET Characteristicsa) of Compounds 8-10
Measurement
Comp. Surface of SiO2
condition
Hole mobility
Threshold
/V
On/off ratio
¹1
/cm2 V¹1 s
¹6
8
9
Untreated
Untreated
Untreated
Untreated
HMDS
In vacuo
In vacuo
In the air, after 12 h
In the air, after 24 h
In vacuo
5.6 © 10
4.0 © 10
6.3 © 10
7.2 © 10
1.2 © 10
4.1 © 10
6.3 © 10
1 © 103
1 © 106
5 © 105
5 © 105
2 © 104
3 © 103
1 © 105
¹15
¹39
¹10
¹5
¹11
¹42
¹25
¹3
¹4
¹4
¹2
¹5
10
Untreated
HMDS
In vacuo
In vacuo
¹4
a) Bottom contact geometry. Interdigitated gold source and drain electrodes.
(a)
(b)
Figure 4. (a) Output and (b) transfer characteristics of FET based on 9 (HMDS treated surface).

140 Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
Ladder-Type Heteroacenes Based on Indolodibenzothiophene
(a)
Cl
S
N
N
S
Cl
1.69 nm
2.26 nm
Figure 6. Electroluminescence spectrum of device B:
(b)
ITO/PEDOT:PSS/11:PBD (30% w/w)/Ba/Al at current
¹2
density of 20 mA cm
.
H
S
(a)
N
N
S
H
1.69 nm
2.98 nm
Figure 5. X-ray diffraction profiles of films based on
(a) 8 and (b) 9. Calculated molecular lengths (MOPAC:
PM5 method).
(b)
tested. Solution processing was used for deposition of the
emissive layer. Devices A were fabricated with the config-
uration ITO/PEDOT:PSS/11/Ba/Al. To achieve more bal-
anced electron injection and transport,25,26 a second set of
devices (devices B) were fabricated with addition of the
electron transporter 2-(4-biphenylyl)-5-(t-butylphenyl)-1,3,4-
oxadiazole (PBD) blended into the emissive layer. Following
previous procedures,26 screening of various concentrations of
PBD (5-50% w/w) showed that 30% w/w incorporation was
optimal. Device B architecture is, therefore: ITO/PEDOT:
PSS/11:PBD (30% w/w)/Ba/Al.
(c)
The characterization of the devices is shown in Figures 6-8.
The electroluminescence spectra of devices A and B were
identical showing that emission is solely from polymer 11,
-
max 484, 510 (shoulder) visible as blue-green light (Figure 6).
Figure 7 shows the external quantum efficiency (EQE), the
device current efficiency, and brightness data for devices A
and B. Device B, with the added electron transport material,
exhibits significantly improved performance. This can be
explained by the predominant hole transport characteristics
of the DIBBBT core of the polymer limiting the efficiency
of devices A. Devices B achieve respectable values for
EQE (0.9%) current efficiency (2.7 cd A¹1) and brightness
(1500 cd m¹2) at a current density of 60 mA cm¹2. Brightness
Figure 7. (a) EQE, (b) efficiency, and (c) brightness data
for the device A (squares) and the device B (circles).
enhanced performance of the blended device B is again evident
in these data. It should be noted that these are simple solution
processed single-active-layer devices. These are unoptimized
devices and performance might be improved by inserting
¹2
increases to ca. 3000 cd m at higher current densities. The
current-voltage (I-V) characteristics are shown in Figure 8.
Turn-on voltages for light emission are low (3.0-3.5 V). The

C. Wang et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
141
10.97. Anal. Calcd for C54H66Cl2N2S2: C, 73.86; H, 7.58; N,
3.19%. Found: C, 73.93; H, 7.58; N, 3.15%. MS (MALDI-
TOF): m/z 876.2 (M+, 100%).
Compound 6. To a solution of 5 (395 mg, 0.45 mmol)
in DCM (50 mL) at 0 °C was added a solution of m-chloro-
peroxybenzoic acid (250 mg, Avocado, 57-86%) in DCM
(15 mL) dropwise through a syringe. The mixture was stirred
with ice-bath cooling for 12 h to yield a colorless clear solution,
which was concentrated and chromatographed on a silica
column (eluent: 3% diethyl ether in DCM) to afford a white
foamy solid (368 mg, 90%) as mixtures of two diastereomers
arising from the presence of two sulfoxide groups, mp 93.0-
1
94.5 °C. H NMR (300 MHz, CDCl3): ¤ 8.18 (s, 2H), 8.14 (d,
J = 8.1 Hz, 2H), 8.03 (d, J = 8.4 Hz, 2H), 7.53 (d, J = 3.0 Hz,
2H, major 65%), 7.50 (br s, 2H, minor 35%), 7.41 (d, J =
1.5 Hz, 2H), 7.36 (br d, J = 8.1 Hz, 2H, major 65%), 7.31 (br d,
J = 8.1 Hz, 2H, minor 35%), 7.22 (dd, J = 1.5, 8.4 Hz, 2H),
4.18 (d, J = 7.5 Hz, 4H), 2.65-2.31 (m, 4H), 2.10 (br m, 2H),
1.68-1.11 (m, 24H), 1.05-0.79 (m, 12H), 0.63 (m, 6H).
13C NMR (101 MHz, CDCl3): ¤ 144.99, 141.98, 141.03,
140.07, 134.36, 132.06, 126.56, 122.55, 121.32, 120.94,
120.74, 120.29, 119.76, 109.49, 109.32, 53.56, 47.62, 39.25,
30.89, 28.73, 28.56, 24.31, 24.09, 22.97, 21.29, 13.95, 13.26,
10.99, 10.81. MS (MALDI-TOF): m/z 909.3 (M+, 100%).
Anal. Calcd for C54H66Cl2N2O2S2: C, 71.26; H, 7.31; N,
3.08%. Found: C, 71.35; H, 7.35; N, 3.03%.
Compound 8. Compound 6 (0.41 g, 0.45 mmol) was mixed
with methanesulfonic acid (5 mL) and the yellow solution was
stirred at r.t. for 12 h to yield a greenish-yellow solution. Ice-
water (50 mL) was added with stirring and the precipitated
yellow solid was collected by suction filtration and washed
with a large volume of water, then dried in air. The solid
(presumed to be 7) was dissolved in pyridine (30 mL) and the
solution was refluxed for 3 h. The pyridine was removed by
vacuum evaporation and the yellow solid residue was boiled in
ethanol (25 mL) for 5 min then suction filtered. The precipitate
was dissolved in chloroform then flash columned on silica
(eluent: chloroform). The first fraction collected was recrystal-
lized from chloroform-ethanol to afford 8 as yellow micro-
crystals (0.103 g, 30%); mp >320 °C. 1H NMR (500 MHz,
373 K, TCE-d2): ¤ 8.54 (s, 2H), 8.46 (s, 2H), 8.05 (d, J =
8.2 Hz, 2H), 7.99 (s, 2H), 7.35 (s, 2H), 7.27 (d, J = 8.1 Hz,
2H), 4.13 (s, 4H), 2.18 (s, 2H), 1.61-1.26 (m, 16H), 1.01
(t, J = 7.3 Hz, 6H), 0.95 (t, J = 7.1 Hz, 6H). MS (MALDI-
TOF): m/z 760.3 (M+, 100%). Anal. Calcd for C46H46Cl2N2S2:
C, 72.51; H, 6.09; N, 3.68%. Found: C, 72.48; H, 6.10; N,
3.67%. UV-vis: -max (CHCl3) (log ¾) 285 (4.99), 367 (5.01),
389 (5.04) nm.
Figure 8. Current-voltage data for the device A (squares)
and the device B (circles).
additional layers to improve charge balance. However, we have
not explored this aspect as our aim is to retain as simple a
device structure as possible.
Conclusion
We have described the efficient synthesis of the extended
ladder-type heteroacene 8 bearing nine linearly-fused rings
and terminal chloro substituents which have been efficiently
converted into phenyl and octylphenyl groups by a palladium-
catalyzed cross-coupling reaction to afford 9 and 10. Com-
pounds 8-10 are blue emitters; a red shift (ca. 10 nm) in
both the absorption and emission spectra is observed for 9
compared to 8. These compounds show multistage oxidation
processes in solution electrochemical studies. Films 8-10
prepared by the drop-casting method exhibited p-type FET
¹6
¹1
characteristics with mobilities of 10 to 10¹2 cm2 V¹1 s
(maximum 1.2 © 10¹2 cm2 V¹1 s¹1) with high on/off ratio.
FET device on 9 showed notable air stability. This work has
demonstrated the potential of DIBBBT derivatives for organic
electronic device applications. Furthermore, it has been
established that 8 is a suitable building block for DIBBBT
copolymers, as exemplified by the synthesis of the blue-
emitting (DIBBBT-Fl)n copolymer 11.
Experimental
Compound 5. To the solution of 3 (0.727 g, 1.65 mmol)
and 4 (0.320 g, 0.78 mmol) in toluene (50 mL) were added
THF (5 mL) and water (5 mL), followed by KOH (0.21 g) and
[Pd(PPh3)2Cl2] (27 mg, 5 mol %). The mixture was refluxed
with stirring for 12 h then evaporated under vacuum to dryness
and the residue was chromatographed on a silica column
(eluent: hexane-DCM 3:1 v/v). The product was recrystallized
from DCM-ethanol to yield 5 as a white solid (0.40 g, 59%);
Compound 9. All procedures were performed under argon.
A mixture of palladium acetate (5.0 mg) and dicyclohexyl-
2¤,6¤-dimethoxy-2-biphenylylphosphine (Sphos) (20.0 mg) in
degassed THF/water (6 mL, 3:1 v/v) was stirred for 10 min
to generate the active catalyst. To a mixture of 8 (30 mg,
0.0394 mmol), K3PO4¢2H2O (100 mg, 0.403 mmol) and phen-
ylboronic acid (45 mg, 0.369 mmol) was added a mixture of
THF/water (12 mL, 3:1 v/v) and the temperature raised to
60 °C, whereupon the freshly-prepared catalyst solution (2 mL)
was added. The mixture was stirred at 60 °C for 20 h, cooled to
r.t., the solvent was removed and the residue was extracted with
1
mp 147.0-148.5 °C. H NMR (400 MHz, CDCl3): ¤ 8.13 (d,
J = 8.0 Hz, 2H), 8.02 (d, J = 8.3 Hz, 2H), 7.56 (d, J = 0.8 Hz,
2H), 7.41-7.38 (m, 4H), 7.36 (dd, J = 1.4, 8.0 Hz, 2H), 7.22
(dd, J = 1.8, 8.3 Hz, 2H), 4.16 (d, J = 7.4 Hz, 4H), 2.81-2.75
(m, 4H), 2.13 (m, 2H), 1.55 (m, 4H), 1.50-1.19 (m, 20H), 0.88
(m, 18H). 13C NMR (101 MHz, CDCl3): ¤ 142.00, 141.96,
140.98, 138.02, 133.02, 131.49, 129.85, 121.72, 121.31,
121.14, 120.90, 119.92, 119.43, 110.43, 109.14, 47.78, 39.32,
33.14, 31.02, 30.76, 28.77, 24.42, 23.07, 21.98, 14.01, 13.60,

142
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
Ladder-Type Heteroacenes Based on Indolodibenzothiophene
DCM. The organic layer was washed with water, then with
brine, dried (MgSO4) and evaporated in vacuo. The residue was
purified by column chromatography on silica (eluent: DCM)
and recystallized from a mixture of DCM-ethanol to yield 9
to precipitate which was washed sequentially with methanol
and hexane and dried in vacuo at room temperature to afford
copolymer 11 as a pale yellow solid (9.0 mg, 82% yield). Size
exclusion chromatography (SEC, vs. polystyrene standard): Mw
1
5%
(29 mg, 87%) as a pale yellow solid; mp >320 °C. H NMR
48 kDa, polydispersity of ca. 1.8; thermal decomposition Td
1
(400 MHz, CDCl3): ¤ 8.55 (s, 2H), 8.25 (d, J = 8.0 Hz, 2H),
8.14 (br s, 2H), 7.67 (dd, J = 7.8, 1.5 Hz, 4H), 7.56 (d, J =
7.7 Hz, 2H), 7.49-7.38 (m, 8H), 7.29 (br s, 2H), 3.43 (br d,
4H), 1.89 (m, 2H), 1.40-1.19 (m, 16H), 0.96-0.82 (m, 12H).
MS (MALDI-TOF): m/z 844.3 (M+, 100%). Anal. Calcd for
C58H56N2S2¢0.5H2O: C, 81.55; H, 6.73; N, 3.28%. Found: C,
81.36; H, 6.62; N, 3.05%. UV-vis: -max (CHCl3) (log ¾) 288
(4.92), 378 (5.03), 389 (5.03), 398 (5.06) nm.
380 °C. H NMR (400 MHz, CDCl3): ¤ 8.50-8.10 (m), 7.64-
7.34 (br), 3.42 (br), 2.13 (br), 1.43-1.20 (br), 0.98-0.80 (br).
UV-vis: -max (abs) (CHCl3) 327, 385, 412 nm; -max (em)
(CHCl3) 459, 472 (sh) nm.
OFET Fabrication.
FET devices were prepared with
bottom contact geometries. Highly doped n+-Si wafers were
used as substrates, and a layer of 300 nm of silicon dioxide
(grown by thermal oxidation) was used as a gate dielectric
layer. Cr (10 nm)/Au (20 nm) were sequentially evaporated and
photolithographically delineated to obtain source and drain
electrodes. The interdigitated structure of the source-drain
contacts determined a channel length of 25 ¯m and a channel
width of 294 mm (6 mm © 49). Substrates were cleaned with
acetone, 2-propanol and ozone for 20 min, and immersed in
hexamethyldisilazane (HMDS) at rt for over 12 h to treat the
surface. Thin films of compounds 8-10 were deposited by a
drop-cast method of chloroform solution onto the channel
region followed by annealing at 110-180 °C for 20 min in a
high vacuum chamber (ca. 10¹5 Pa). The FET measurements
were carried out in situ then in air. Mobilities (®) were
calculated in the saturation regime by the relationship:
Compound 10.
All procedures were performed under
argon. A mixture of palladium acetate (5.0 mg) and dicyclo-
hexyl-2¤,6¤-dimethoxy-2-biphenylylphosphine (Sphos) (20.0
mg) in degassed THF/water (6 mL, 3:1 v/v) was stirred for
10 min to generate the active catalyst. To a mixture of 8 (17 mg,
0.0224 mmol), K3PO4¢nH2O (60 mg) and 4-n-octylphenyl-
boronic acid (54 mg, 0.231 mmol) was added a mixture of
THF/water (12 mL, 3:1 v/v) and the temperature raised to
60 °C, whereupon the freshly-prepared catalyst solution (2 mL)
was added. The mixture was stirred at 60 °C for 21 h, cooled
to r.t., the solvent was removed and the residue was extracted
with DCM. The organic layer was washed with water, then
with brine, dried (Na2SO4) and the organic layer evaporated
in vacuo. The residue was purified by column chromatography
on silica (eluent: DCM) and recystallized from a mixture
of DCM-ethanol to yield 10 (21 mg, 90%) as a yellow solid;
mp 309.5-315.5 °C (a sharp peak of DSC). 1H NMR (300
MHz, CDCl3): ¤ 8.51 (s, 2H), 8.21 (d, J = 8.4 Hz, 2H), 8.16
(s, 2H), 7.59 (d, J = 8.4 Hz, 4H), 7.53 (dd, J = 6.6, 1.5 Hz,
2H), 7.44 (s, 2H), 7.31 (br s, 2H), 7.24 (d, J = 8.4 Hz, 4H),
3.49 (br d, J = 6.6 Hz, 4H), 2.70 (t, J = 7.8 Hz, 4H), 1.95-1.85
(m, 2H), 1.80-1.60 (m, 4H), 1.50-1.10 (m, 36H), 0.95-0.80
(m, 18H). MS (FAB): m/z 1069 (M+). Anal. Calcd for
C74H88N2S2: C, 83.09; H, 8.29; N, 2.62%. Found: C, 82.74;
H, 8.41; N, 2.56%. UV-vis: -max (abs) (CHCl3) (log ¾) 287
(5.03), 387 (5.04), 400 (5.05) nm. -max (em) (CHCl3) 444,
471 nm.
®
sat = (2IDSL)/[WCox(VG ¹ Vth)2] where IDS is the source-
drain saturation current: Cox is the oxide capacitance. VG is the
gate voltage and Vth is the threshold voltage. The latter can be
estimated as the intercept of the linear section of the plot of
1/2
(IDS
)
vs. VG.
OLED Fabrication. OLEDs were fabricated on indium tin
oxide (ITO)-coated glass substrates of thickness 125 nm and
possessing a sheet resistance of 20 ³/square. Poly(3,4-ethyl-
enedioxythiophene) doped with poly(styrenesulfonic acid)
(PEDOT:PSS), obtained commercially from Bayer A.G.
Germany, was spin coated at 2500 rpm for 60 s to produce a
ca. 45 nm thick hole-transporting layer (HTL). These HTL-
coated substrates were then annealed at 200 °C for 5 min to
remove any residual water. A chlorobenzene solution of
¹1
(DIBBBT-Fl)n 11. A mixture of DIBBBT-Cl2 8 (7.6 mg,
0.010 mmol) and 9,9-dioctyl-2,7-fluorenylenediboronic acid
bis(1,3-propanediol) ester 12 (5.8 mg, 0.010 mmol), K3PO4¢
2H2O (10 mg, 0.040 mmol) was prepared in THF/water (12
mL, 3:1 v/v) and the temperature raised to 60 °C. Freshly-
prepared catalyst solution (as described for compound 9)
(2 mL) was added and the mixture was stirred at 60 °C for
20 h. 4-n-Butylbromobenzene (0.05 mL) was added and stirring
continued at 60 °C for 1 h before 4-butylbenzeneboronic acid
(10 mg) was added and stirring continued at 60 °C for 1 h. After
cooling to r.t., the mixture was added slowly to stirring
methanol (30 mL) to precipitate the crude polymer as a yellow
solid. The solid was washed with methanol, water, and hexane.
The resulting yellow solid was placed in a thimble and
extracted in a Soxhlet apparatus with acetone for 20 h. After
removal of the acetone from the thimble under vacuum, the
residue was extracted into chloroform. The chloroform solution
was concentrated under reduced pressure to ca. 5 mL and
poured dropwise into methanol (10 mL) with vigorous stirring
5 mg mL of polymer 11 was prepared (Devices A). For
Devices B 30% w/w of 2-(4-biphenylyl)-5-(t-butylphenyl)-
1,3,4-oxadiazole (PBD) was added to the solution. The
mixtures were filtered with a 0.45 ¯m pore filter and spin
coated at 2500 rpm on the top of the HTL and baked for 10 min
at 120 °C to produce film thicknesses of 50 « 5 nm. The
samples were then introduced into a nitrogen glove box, where
barium cathodes (thickness ca. 4 nm) were evaporated onto the
device at a rate of ca. 1 ¡ s¹1 under vacuum at a pressure of ca.
1 © 10¹6 mmHg. Subsequently a layer of aluminium (100 «
5 nm) was deposited under the same conditions. All samples
were encapsulated inside a glove box. The devices were tested
on the same day as their preparation to minimize any
degradation of the cathode.
The current-voltage (I-V) and the emission characteristics
of the OLEDs were measured using a calibrated integrating
sphere. The electroluminescence (EL) spectra were measured
using an Ocean Optics USB 4000 CCD spectrometer supplied
with 400 ¯m UV-vis fiber optics.

C. Wang et al.
Bull. Chem. Soc. Jpn. Vol. 85, No. 1 (2012)
143
Commun. 2008, 1548. c) P. Gao, X. Feng, X. Yang, V. Enkelmann,
M. Baumgarten, K. Müllen, J. Org. Chem. 2008, 73, 9207.
10 a) H. Pang, F. Vilela, P. J. Skabara, J. J. W. McDouall, D. J.
Crouch, T. D. Anthopoulos, D. D. C. Bradley, D. M. de Leeuw,
P. N. Horton, M. B. Hursthouse, Adv. Mater. 2007, 19, 4438. b) M.
Mamada, J.-i. Nishida, S. Tokito, Y. Yamashita, Chem. Lett. 2008,
37, 766.
J. Nishida thanks the Japan Society for the Promotion
of Science (JSPS) for the International Training Program
(Japan-Europe-U.S. International Training Program for Young
Generation in Molecular Materials Science for Development
of Molecular Devices). We thank EPSRC for funding the work
in Durham. We thank A. P. Monkman for use of equipment
for OLED characterization.
11 M. Mamada, J.-i. Nishida, D. Kumaki, S. Tokito, Y.
Yamashita, Chem. Mater. 2007, 19, 5404.
Supporting Information
12 a) J. Bouchard, S. Wakim, M. Leclerc, J. Org. Chem. 2004,
69, 5705. b) S. Wakim, J. Bouchard, M. Simard, N. Drolet, Y. Tao,
M. Leclerc, Chem. Mater. 2004, 16, 4386. c) S. Wakim, J.
Bouchard, N. Blouin, A. Michaud, M. Leclerc, Org. Lett. 2004, 6,
3413. d) Y. Wu, Y. Li, S. Gardner, B. S. Ong, J. Am. Chem. Soc.
2005, 127, 614. e) P.-L. T. Boudreault, S. Wakim, N. Blouin, M.
Simard, C. Tessier, Y. Tao, M. Leclerc, J. Am. Chem. Soc. 2007,
129, 9125. f) K. Kawaguchi, K. Nakano, K. Nozaki, J. Org. Chem.
2007, 72, 5119.
Detailed experimental procedures; absorption and emission
spectra of (DIBBBT-Fl)n 11; additional OFET data for 8-10;
copies of 1H, 13C NMR, and mass spectra. This material is
available free of charge on the Web at: http://www.csj.jp/
journals/bcsj/.
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