Synthesis and properties of small band gap thienoisoindigo based conjugated polymers

Article abstract of DOI:10.1039/c2jm34668k

Using Stille and Suzuki polymerization reactions we incorporate thienoisoindigo (TII) as an acceptor co-monomer into a series of alternating π-conjugated copolymers with combinations of benzene, thiophene and carbazole as donor co-monomers. By changing the nature and length of the donor segments, the optical band gap of these soluble TII copolymers can be varied over a large range from 1.52 eV down to 0.87 eV. The semiconducting properties of the TII copolymers were established in bottom-gate bottom-contact field-effect transistors that provide hole mobilities for these materials in the range of 10^-3 to 10^-2 cm² V^-1 s^-1.

Full text of DOI:10.1039/c2jm34668k

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PAPER
Synthesis and properties of small band gap thienoisoindigo based conjugated
polymers
Gijs W. P. Van Pruissen, Fatemeh Gholamrezaie, Martijn M. Wienk and Ren ꢀe A. J. Janssen*
Received 16th July 2012, Accepted 13th August 2012
DOI: 10.1039/c2jm34668k
Using Stille and Suzuki polymerization reactions we incorporate thienoisoindigo (TII) as an acceptor
co-monomer into a series of alternating p-conjugated copolymers with combinations of benzene,
thiophene and carbazole as donor co-monomers. By changing the nature and length of the donor
segments, the optical band gap of these soluble TII copolymers can be varied over a large range from
1
.52 eV down to 0.87 eV. The semiconducting properties of the TII copolymers were established in
bottom-gate bottom-contact field-effect transistors that provide hole mobilities for these materials in
ꢀ
3
the range of 10 to 10 cm V s .
ꢀ2
2
ꢀ1 ꢀ1
Introduction
Semiconducting polymers form the active functional material in
organic field-effect transistors (FETs) and organic photovoltaic
(
OPV) cells. For designing new conjugated polymers for these
applications, several parameters must be considered. The most
relevant electronic parameters are the optical band gap, redox
levels and charge carrier mobility, but material properties such as
solubility, molecular weight and tendency to form ordered
aggregates or semi-crystalline domains are likewise important.
The leading design motif for controlling the optical band gap and
energy levels of conjugated semiconducting polymers is the
alternation of electron rich and electron deficient units along the
Fig. 1 Structures of pyrrolo[3,4-c]pyrrole-1,4-dione (or diketopyrrolo-
0
pyrrole, DPP), benzo[1,2-b:4,5-b ]dipyrrole-2,6(1H,5H)-dione (BDPD),
thieno[3,4-c]pyrrole-4,6-dione (TPD), isoindigo (II) and thienoisoindigo
(
TII).
16,20
17,21–27
and polymers
Isoindigo based small molecules
show
1,2
3
chain as pioneered by Havinga and Tanaka. For the electron
rich unit conjugated oligomers are often used. These commonly
include benzene, thiophene, pyrrole and furan or combinations
thereof as building blocks, sometimes in fused ring configura-
tions. For the electron deficient unit, aromatic heterocycles such
as quinoxaline, benzothiadiazole and thienopyrazine that
contain electron withdrawing nitrogen atoms have been
great potential for OPV, as do isoindigo derived materials for
28
29
FETs and organic memory devices. Replacing the benzene
ring of isoindigo with a thiophene to give a thienoisoindigo (TII)
might further enhance planarity along the backbone resulting in
better packing and higher mobilities for both holes and electrons.
The potential for such materials was recently shown for a TII-
30
benzothiadiazole copolymer.
4–6
effective.
Here we present the synthesis of five new TII-copolymers in
which TII alternates with benzene, thiophene, carbazole or
combinations thereof and we explore this new class of TII-based
materials for their semiconducting properties. The TII copoly-
mers show band gaps in the range of 0.87–1.52 eV and mobilities
In recent years, the incorporation of cyclic amides or diimides
has been established as a very effective way to combine strong
electron accepting properties with a tendency to provide close
intermolecular packing. This favours small optical band gaps
and high charge carrier mobilities and has resulted in excep-
ꢀ3
ꢀ2
2
ꢀ1 ꢀ1
in the range of 10 to 10 cm V
contact FETs.
s in bottom-gate bottom-
7,8
tionally good performance in FETs and OPV cells. Examples
9
–11
of these new acceptor units are diketopyrrolopyrrole,
13–15
benzo-
16–19
1
2
dipyrrolidiones, thienopyrroledione,
shown in Fig. 1.
and isoindigo
as
Results and discussion
Synthesis
The synthesis of the TII monomer starts with an Ullmann
coupling of 3-bromothiophene (1) with 2-hexyldecan-1-amine to
30,31
give 2 (Scheme 1),
Molecular Materials and Nanosystems, Eindhoven University of
Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
E-mail: r.a.j.janssen@tue.nl; Fax: +31-40-451036; Tel: +31-40-2473597
followed by a Friedel–Crafts reaction with
oxalyl chloride to give the thiophene derivative of isatin (3). The
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ꢁ
ꢁ
Scheme 1 (i) CuI, DMAE, 90 C; (ii) Et
ꢁ
3
N, DCM, 0 C; (iii) Lawesson’s
ꢁ
reagent, toluene, 65 C; (iv) NBS, DCM 0 C; (v) Pd
ꢁ
2
3 3 3 4
dba , PPh , K PO ,
ꢁ
Aliquat 336, toluene–H
2
O, 115 C; (vi) NBS, DCM, 0 C.
isatin derivative was dimerised with Lawesson’s reagent to give 4,
following a procedure previously used for various pyrrole-2,3-
32
diones. This procedure is known to give exclusively the E
2
isomer, which is confirmed for 4 by six sp carbon signals in the
1
3
C NMR spectrum indicating a single isomer and a single IR
ꢀ
1
band at 1667 cm of the C]O stretch vibration. For the Z
isomer symmetrical and anti-symmetrical vibrations would be
expected. Bromination of the coupled product 4 with NBS
provided the TII-monomer 5 as a dark purple solid. Using 5 an
extended TII-derivative was made by coupling 3-dodecylth-
iophene via a Suzuki reaction and bromination of the product 6
with NBS to give the dark blue TII-monomer 7.
ꢁ
Scheme 2 (i) and (iv) Pd
and (v) Pd dba , PPh , K
2
dba
PO
3
, PPh , toluene–DMF, 110 C; (ii), (iii)
3
ꢁ
2
3
3
3
4
, Aliquat 336, toluene–H
2
O, 115 C.
PTIITPT, PTIICb and PTII3T, that do not suffer from this
problem have extra side chains attached to the donor units
probably inhibiting the interaction with the column.
Based on monomers 5 and 7 a series of new TII-based poly-
mers was synthesized via Stille and Suzuki couplings using
different co-monomers (Scheme 2). PTIIT and PTII3T were
synthesized by Stille coupling with 2,5-bis(trimethylstannyl)-
thiophene because polymerization reactions with thiophene tend
to give higher molecular weights with Stille reactions compared
Optical and electrochemical properties
33
to Suzuki polymerizations. For the co-polymerisations aimed
at incorporating benzene (PTIIP and PTIITPT) or carbazole
Fig. 2 shows the UV-vis-near IR absorption spectra of the TII-
based copolymers in solution and as thin films on glass. The
absence of a bathochromic shift in these polymers between the
solution and thin film samples shows that they have a strong
tendency to aggregate in solution. The optical band gaps for
these materials, measured as the onset of absorption, range from
0.87 eV for the PTIIT polymer to 1.52 eV for the PTIICb poly-
mer (Table 1). Relevant optical data for thienoisoindigo (PTIIX)
polymers from this work and isoindigo (PIIX) polymers avail-
able from the literature are collected in Table 1 and reveal that
the optical band gaps of PTIIX derivatives are smaller than that
(
PTIICb) the Suzuki coupling generally gives higher molecular
weights. All polymerization reactions used end-capping with
mono-functionalized thiophene stannanes and bromides or
phenyl boronic acid pinacol esters and bromobenzenes depend-
ing on the type of polymerization to remove reactive end
34
groups.
In many optoelectronic applications of conjugated copolymers
the molecular weight is a critical factor because it controls the
morphology and interchain ordering in the material. For
PTIITPT, PTIICb and PTII3T the molecular weight was deter-
of PIIX. The difference is very pronounced for PTIIT (E ¼
g
ꢀ
1
mined with GPC to be respectively M ¼ 32 400 g mol , 33 100
0.87 eV) and PIIT (E ¼ 1.65 eV (ref. 21)). For none of these
n
g
ꢀ
1
ꢀ1
g mol and 13 400 g mol versus polystyrene standards with
PDIs of 2.5, 2.5 and 4.0 as summarized in Table 1. For PTIIT
and PTIIP, GPC measurements of the molecular weight gave
inconclusive results because these polymers showed a strong
interaction with the column material. The three copolymers,
polymers significant fluorescence could be observed.
Cyclic voltammetry (CV) was used to determine the onsets of
+
oxidation and reduction potentials versus the Fc/Fc redox
couple of the co-polymers in solution (Fig. 3). Using the redox
potentials the HOMO and LUMO levels were estimated using
2
0388 | J. Mater. Chem., 2012, 22, 20387–20393
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Table 1 Molecular weight, optical and electrochemical data of the TII-based and II-based copolymers
ꢀ1
sol
max/nm
sol
g
film
g
a
a
cvb
g
c
c
Polymer
M /g mol
n
PDI
l
E
/eV
E
/eV
E
ox /V
E
red /V
E
/eV
E
HOMO /eV
E
LUMO /eV
Ref.
Thienoisoindigo polymers (PTII-X)
PTIIT
PTIIP
PTIICb
PTII3T
PTIITPT
n/a
n/a
33 100
13 400
32 400
n/a
n/a
2.5
4.0
2.5
1006
872
746
768
742
0.92
1.21
1.57
1.36
1.53
0.87
1.18
1.52
1.29
1.45
ꢀ0.41
ꢀ0.24
0.01
ꢀ1.45
ꢀ1.60
ꢀ1.49
ꢀ1.51
ꢀ1.48
1.04
1.36
1.50
1.31
1.28
ꢀ4.82
ꢀ4.99
ꢀ5.24
ꢀ5.03
ꢀ5.03
ꢀ3.78
ꢀ3.63
ꢀ3.74
ꢀ3.72
ꢀ3.75
ꢀ0.20
ꢀ0.20
d
Isoindigo polymers (PII-X)
e
PIIT (PT-ID1)
PIICb (PCzID)
PII3T (P3TI)
17 200
8956
73 000
2.1
1.5
2.9
684
576
645
1.68
1.80
1.63
1.65
1.75
1.50
0.69
0.43
0.48
—
ꢀ1.20
—
1.63
1.66
ꢀ5.92
ꢀ5.66
ꢀ5.71
21
23
19
e
ꢀ4.03
ꢀ4.05
e
ꢀ1.18
a
+
Onsets, potentials vs. Fc/Fc .
b
cv
g
c
d
E
corrections (e.g. for reference potentials) made to allow direct comparison. The acronyms used in the cited references are included between parentheses.
¼ e(Eox ꢀ Ered). E ¼ ꢀ5.23 ꢀ eEredox
.
Values may differ slightly from those stated in the cited papers due to small
e
Values for the isoindigo polymers were measured for thin films in ref. 19, 21 and 23.
Fig. 3 Cyclic voltammetry of TII-based polymers recorded in ODCB
4
6ꢀ
with NBu PF as a supporting electrolyte.
+
Fig. 2 Normalized absorption spectra of TII-based polymers in chlo-
roform solution (a) and as thin films on glass (b).
Electrical characterization
3
5
E ¼ ꢀ5.23 ꢀ eEredox. The results are summarized in Table 1.
The high HOMO levels for PTIIT (ꢀ4.82 eV) and to a lesser
extend for PTIIP (ꢀ4.99 eV), PTII3T (ꢀ5.03 eV) and PTIITPT
We investigated the electrical transport of conjugated polymers
discussed above in field-effect transistors. In the transfer curves
of the polymers PTIIT, PTIIP, PTIITPT, PTII3T and PTIICb
measured immediately after spin-coating, i.e. prior to thermal
annealing, a large hysteresis was observed and the threshold
voltage was not at zero gate bias. After annealing the transistors
(
ꢀ5.03 eV) make these polymers strong electron donors that can
easily be oxidized. PTIICb is the only polymer that has a
somewhat deeper HOMO (ꢀ5.24 eV). Compared to the corre-
21
ꢁ
sponding isoindigo (II) analogues PIIT (PT-ID1, ꢀ5.92 eV),
at 180 C overnight, the performance improved for all polymers
23
19
PIICb (PCzID, ꢀ5.66 eV) and PII3T (P3TI, ꢀ5.71 eV), which
were measured as thin films, a large difference of up to 1.1 eV for
the HOMO level is observed.
except PTIIT. We note that for small band gap polymers often
ambipolar transport is observed and has been reported for a
30
related TII based conjugated polymer. In the FETs of PTII-X
we observed hole transport but no electron transport. Fig. 4
shows the typical transfer characteristics of a ring transistor for
the four other polymers measured at room temperature after
annealing. The curves for PTIIP, PTIITPT, PTII3T and PTIICb
show almost no hysteresis and have threshold voltages at zero
voltage as well as high on–off ratios with a current modulation of
almost five to six decades for all these four copolymers.
The differences between optical and electrochemical properties
of the thienoisoindigo and isoindigo polymers are induced by the
stronger electron donating properties of the thiophene ring
compared to the benzene ring. In addition, co-planarity with the
neighbouring aromatic units is easier whilst steric hindrance is
reduced, especially when a phenyl or carbazole is used as an
aromatic unit adjacent to isoindigo.
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spectrometer in a chloroform solution in a quartz cell or as a thin
film spin coated on a glass substrate. Cyclic voltammetry (CV)
was conducted under an inert atmosphere using an Autolab
PGSTAT30 with a three electrode setup equipped with a plat-
inum disc working electrode, a silver counter electrode and a
silver electrode coated with silver chloride (Ag/AgCl) as a quasi
reference electrode in combination with ferrocene/ferrocenium
+
Fc/Fc ) as an internal standard. A 1 M solution of tetrabuty-
(
6
lammonium hexafluorophosphate (TBAPF ) in ortho-dichloro-
benzene (ODCB) was used as the electrolyte. Matrix-assisted
laser desorption ionization time-of-flight (MALDI-TOF) was
measured on a PerSeptive Biosystems Voyager – DE PRO
spectrometer using either a-cyano-4-hydroxycinnamic acid
(
CHCA) and/or trans-2-[3-(4-tert-butylphenyl)-2-methyl-2-pro-
penylidene]malononitrile (DCTB) as matrices. Molecular
weights of the polymers were determined with two high
temperature GPC setups, a Shimadzu LC-20AD Prominence
Liquid Chromatograph equipped with a SPD-20A UV-Vis
detector and a RID-10A refractive index detector and a Mixed-D
(
200–400 000 Da versus polystyrene standards) column running
ꢁ
on chloroform at 110 C and a PL-GPC 120 High temperature
Chromatograph with a Mixed-C (200–2 000 000 Da versus
ꢁ
polystyrene standards) column using ODCB at 80 C as eluent.
FETs were fabricated on a heavily doped silicon wafer as a
common gate electrode, covered by 200 nm thermally grown
silicon dioxide passivated with HMDS as a gate dielectric and
gold source and drain electrodes were defined using conventional
photolithography and a 10 nm Ti adhesion layer. The polymers
were applied via spin coating at 1000 rpm for 30 s with an
acceleration of 100 rpm per s in chloroform solution and ther-
Fig. 4 Linear (V
D
¼ ꢀ2 V) and saturated (V
D
¼ ꢀ20 V) transfer
characteristics of a spin-coated field-effect transistor. The channel length
is 40 mm and channel width is 1000 mm. To prevent parasitic leakage
currents, ring geometry was used in all cases. (a) PTIIP, (b) PTIITPT, (c)
PTII3T and (d) PTIICb.
ꢁ
mally annealed for 24 h at 180 C in vacuum before measuring.
The electrical transport was measured using a HP 4155C semi-
The linear and saturated mobilities are quite similar and are
ꢀ1 ꢀ1
ꢀ
6
about 5 ꢂ 10ꢀ cm V
3
2
ꢀ1 ꢀ1
s
for PTIIP, 8 ꢂ 10 cm V
ꢀ3
2
s
for
2
conductor parameter analyzer in vacuum of 10 mbar. To
compare the current all measurements were done on a 40 mm
channel length and a channel width of 1000 mm.
ꢀ
3
2
ꢀ1 ꢀ1
ꢀ3
PTIITPT, 2 ꢂ 10 cm V
s
for PTII3T and 5 ꢂ 10 cm
ꢀ
1
ꢀ1
s for PTIICb.
V
Conclusion
A first series of TII based p-conjugated polymers has been
synthesized, extending the class of polymers incorporating an
amide functionality as an acceptor in their backbone. The TII
unit influences the energy levels significantly when compared to
isoindigo polymers by raising the HOMO levels and therewith
lowering the optical band gap to as low as 0.87 eV. The FET
mobilities are in line with other well performing polymers
showing that these amide derived materials can be valuable in
many organic electronic devices.
2-Hexyldecan-1-amine
Triphenylphosphine (36.5 g, 139 mmol) and phthalimide (20.5 g,
ꢁ
1
39 mmol) were suspended in DCM and cooled to 0 C. Then 2-
hexyl-1-decanol (30.6 g, 126.4 mmol) was added and stirred for
0 min before the dropwise addition of diisopropyl azodi-
3
carboxylate (28.1 g, 139 mmol) while maintaining the tempera-
ꢁ
ture under 10 C. Upon the complete addition the mixture was
stirred for another one hour at room temperature before it was
concentrated in vacuo. After redissolving in hexanes and filtra-
tion the resulting oil was subjected to a short silica column and
concentrated. Then hydrazine and THF were added and the
mixture was refluxed overnight. After cooling 2 M KOH was
added and the product was extracted with ethyl acetate, washed
Experimental section
General procedures
All starting materials and reagents were purchased from
1
commercial suppliers unless stated otherwise. All H NMR and
with brine and dried over MgSO before the crude oil was sub-
4
ꢁ
jected to distillation. The product was distilled at 180 C and 2 ꢂ
1
3
ꢀ1
C NMR spectra were recorded on a 400 MHz Varian Mercury
Spectrometer using CDCl3 as solvent with tetramethylsilane
TMS) as an internal standard. The given values are in ppm
relative to TMS (0 ppm). UV-vis-near IR optical absorption
spectra were recorded on Perkin-Elmer Lambda 900
10 mbar to give 17.3 g (57%) 2-hexyldecan-1-amine as a col-
1
ourless oil. H NMR (400 MHz, CDCl , ppm): d 2.60 (d, J ¼ 4.7
3
(
Hz, 2H), 1.36–1.18 (m, 25H), 1.08 (s, 2H), 0.88 (t, J ¼ 6.6 Hz,
1
3
3
6H). C NMR (100 MHz, CDCl , ppm): d 45.25, 40.93, 31.88,
a
31.54, 30.09, 29.76, 29.61, 29.32, 26.78, 26.75, 22.66, 14.08.
2
0390 | J. Mater. Chem., 2012, 22, 20387–20393
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(E)-2,2 -dibromo-4,4 -bis(2-hexyldecyl)-[6,6 -bithieno[3,2-b]
0
0
0
N-(2-hexyldecyl)thiophen-3-amine (2)
0
0
pyrrolylidene]-5,5 (4H,4 H)-dione (5)
A mixture of 3-bromothiophene (1) (11.023 g, 67.6 mmol), 2-
0
0
hexyldecan-1-amine (16.3 g, 67.6 mmol), copper(I) iodide (1.3 g,
To a solution of (E)-4,4 -bis(2-hexyldecyl)-[6,6 -bithieno[3,2-b]
0
0
6
.8 mmol) and grinded potassium phosphate tribasic (43.0 g, 200
ꢁ
pyrrolylidene]-5,5 (4H,4 H)-dione (4) (280 mg, 0.53 mmol) in
dichloromethane was added N-bromosuccimide (189 mg, 1.06
mmol) in dimethylaminoethanol (30 ml) was heated to 90 C for
ꢁ
2
days under an argon atmosphere. The reaction was cooled to
mmol) at 0 C. Upon completion the reaction mixture was
room temperature and filtered. The residue was washed with
ethyl acetate and the filtrate was concentrated and subjected to
silica column chromatography (gradient heptanes–dichloro-
4
washed with water and brine and dried over MgSO before it was
purified over a silica column with a heptanes–chloroform
1
mixture to give 366 mg of the desired monomer (79% yield). H
methane 0–100%) to give 7.7 g (35.5%) of the desired air sensitive
1
NMR (400 MHz, CDCl , ppm): d 6.81 (s, 2H), 3.62 (d, J ¼ 7.4
3
compound. H NMR (400 MHz, CDCl , ppm): d 7.13 (dd, J ¼
Hz, 4H), 1.87–1.78 (m, 2H), 1.38–1.19 (m, 48H), 0.91–0.82 (m,
1
3
3
5
1
1
.1, 2.9 Hz, 1H), 6.61 (dd, J ¼ 5.1, 1.5 Hz, 1H), 5.91 (dd, J ¼ 3.0,
3
12H). C NMR (100 MHz, CDCl , ppm): d 170.20, 150.07,
.5 Hz, 2H), 3.56 (s, 1H), 2.97 (d, J ¼ 6.0 Hz, 2H), 1.70–1.52 (m,
122.97, 119.50, 114.88, 114.62, 46.13, 37.19, 31.86, 31.77, 31.41,
31.38, 29.93, 29.62, 29.50, 29.28, 26.34, 22.66, 22.63, 14.10, 14.07.
+
MALDI-TOF m/z: 880.26 (M , 100%).
1
3
H), 1.45–1.12 (m, 24H), 0.88 (t, J ¼ 6.7 Hz, 6H). C NMR (100
MHz, CDCl
3
, ppm): d 149.10, 124.94, 119.90, 94.76, 49.87, 37.82,
3
2
2.22, 32.21, 31.90, 31.88, 30.07, 29.74, 29.60, 29.33, 26.79, 26.76,
2.69, 22.68, 14.10.
0 0 0
E)-2,2 -bis(4-dodecylthiophen-2-yl)-4,4 -bis(2-hexyldecyl)-[6,6 -
(
0
0
bithieno[3,2-b]pyrrolylidene]-5,5 (4H,4 H)-dione (6)
4
-(2-Hexyldecyl)-4H-thieno[3,2-b]pyrrole-5,6-dione (3)
Under an argon atmosphere toluene (3 ml), water (0.3 ml) and one
0
0
drop of Aliquat 336 were added to (E)-2,2 -dibromo-4,4 -bis(2-
0
To a solution of 20 ml dichloromethane and oxalyl chloride (2.6
ml, 30 mmol) was added dropwise a solution of N-(2-hexyldecyl)
thiophen-3-amine (2) (7.7 g, 24 mmol) in dichloromethane (40
0
0
hexyldecyl)-[6,6 -bithieno[3,2-b]pyrrolylidene]-5,5 (4H,4 H)-dione
5) (100 mg, 114 mmol), 2-(4-dodecylthiophen-2-yl)-4,4,5,5-tet-
(
ramethyl-1,3,2-dioxaborolane (171.7 mg, 454 mmol) and potas-
sium phosphate tribasic (106 mg, 500 mmol). Then argon was
bubbled through for 30 min before adding tris(dibenzylidenea-
ꢁ
ml) while cooling the reaction at 0 C. After 30 min a solution of
triethylamine (6 ml) in dichloromethane (40 ml) was added
dropwise after which the reaction was warmed to room
temperature and stirred overnight. The mixture was concen-
trated and purified by silica column chromatography using a
heptanes–dichloromethane 70 : 30 mixture as eluent to give 5.9 g
cetone)dipalladium(0) (4.6 mg, 5 mmol) and triphenylphosphine
ꢁ
(
3.3 mg, 12.5 mmol). The reaction mixture was heated to 115 C
and stirred overnight. After extraction with chloroform and
water the organic fraction was washed with brine and dried over
of 4-(2-hexyldecyl)-4H-thieno[3,2-b]pyrrole-5,6-dione as an
1
orange oil in 70% yield. H NMR (400 MHz, CDCl
4
MgSO before it was subjected to column chromatography using
3
, ppm): d
a heptanes–chloroform gradient. Product containing fractions
8
.00 (d, J ¼ 5.0 Hz, 1H), 6.76 (d, J ¼ 4.7 Hz, 1H), 3.53 (d, J ¼ 7.4
were combined to give 123 mg of the title compound (88% yield).
1
H NMR (400 MHz, CDCl , ppm): d 7.25 (s, 2H), 6.93 (s, 2H),
3
Hz, 2H), 1.81–1.74 (m, 1H), 1.36–1.18 (m, 24H), 0.87 (td, J ¼ 6.8,
1
3
2
1
3
1
3
.2 Hz, 6H). C NMR (100 MHz, CDCl , ppm): d 172.96,
6
1
0
1
1
3
.80 (s, 2H), 3.63 (d, J ¼ 7.4 Hz, 4H), 2.61 (t, J ¼ 7.8 Hz, 4H),
65.50, 161.72, 143.77, 113.11, 111.01, 46.44, 36.96, 31.83, 31.73,
1.38, 29.88, 29.55, 29.47, 29.24, 26.34, 26.31, 22.63, 22.59, 14.08,
4.04.
.87 (s, 2H), 1.64 (q, J ¼ 7.2 Hz, 4H), 1.47–1.05 (m, 84H), 0.99–
1
3
.67 (m, 18H). C NMR (100 MHz, CDCl , ppm): d 170.59,
3
51.36, 145.04, 144.72, 137.40, 125.61, 120.36, 118.81, 113.27,
07.03, 45.77, 37.15, 31.95, 31.91, 31.84, 31.40, 30.46, 30.44,
0 0
E)-4,4 -bis(2-hexyldecyl)-[6,6 -bithieno[3,2-b]pyrrolylidene]-
0.00, 29.72, 29.68, 29.57, 29.52, 29.40, 29.38, 29.36, 26.34, 26.32,
+
(
0 0
22.70, 22.69, 13.88. MALDI-TOF m/z: 1222.86 (M , 100%).
5
,5 (4H,4 H)-dione (4)
Lawesson’s reagent (1.9 g, 4.72 mmol) was put under argon and a
0 0
E)-2,2 -bis(5-bromo-4-dodecylthiophen-2-yl)-4,4 -bis(2-
(
solution of 4-(2-hexyldecyl)-4H-thieno[3,2-b]pyrrole-5,6-dione
0
0
0
hexyldecyl)-[6,6 -bithieno[3,2-b]pyrrolylidene]-5,5 (4H,4 H)-
dione (7)
(
3) (3.342 g, 9.44 mmol) in dry toluene (20 ml) was added. The
ꢁ
reaction was heated to 65 C and stirred until complete conver-
sion was seen on TLC. After cooling, water was added and the
product was extracted with chloroform, washed with brine and
0
0
A solution of (E)-2,2 -bis(4-dodecylthiophen-2-yl)-4,4 -bis(2-
0
0
0
hexyldecyl)-[6,6 -bithieno[3,2-b]pyrrolylidene]-5,5 (4H,4 H)-
dione (6) (123 mg, 100.7 mmol) in dichloromethane (4 ml) was
4
dried over MgSO . After removal of the solvent the crude
ꢁ
product was subjected to silica column chromatography with
cooled to 0 C and wrapped in aluminium foil. Then N-bromo-
hexanes–dichloromethane as eluent to give 1.238 g of the title
1
compound in 36.3% yield. H NMR (400 MHz, CDCl
succimide (36.23 mg, 201.3 mmol) was added. When complete
conversion was observed by TLC the solvent was removed in
vacuo and the crude product was subjected to silica column
chromatography with heptanes–dichloromethane 75/25 to give
3
, ppm): d
7
.52 (d, J ¼ 5.1 Hz, 2H), 6.78 (d, J ¼ 5.1 Hz, 2H), 3.69 (d, J ¼ 7.4
Hz, 4H), 1.93–1.85 (m, 2H), 1.35–1.21 (m, 48H), 0.92–0.81 (m,
1
2H). C NMR (100 MHz, CDCl , ppm): d 171.28, 151.51,
3
1
1
1
3
1
1
107 mg of the extended monomer (76.8% yield). H NMR (400
3
34.19, 121.04, 114.20, 111.32, 46.12, 37.13, 31.87, 31.85, 31.76,
1.46, 29.93, 29.60, 29.49, 29.25, 26.40, 26.37, 22.68, 22.64, 22.61,
MHz, CDCl , ppm): d 7.03 (s, 2H), 6.62 (s, 2H), 3.61 (dt, J ¼ 7.4,
3
3.9 Hz, 4H), 2.53 (t, J ¼ 7.6 Hz, 4H), 1.80 (p, J ¼ 6.5 Hz, 2H),
1.60 (p, J ¼ 7.2 Hz, 4H), 1.45–1.23 (m, 42H), 0.95–0.80 (m, 18H).
+
4.09, 14.05. MALDI-TOF m/z: 722.43 (M , 100%). FT-IR:
ꢀ
1
+
MALDI-TOF m/z: 1378.66 (M , 100%).
667 cm (C]O).
This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 20387–20393 | 20391

View Article Online
PTIIT
addition of tris(dibenzylideneacetone)dipalladium(0) (3.0 mg, 3.3
mmol) and triphenylphosphine (1.7 mg, 6.6 mmol) after which the
ꢁ
To a mixture of monomer 5 (99 mg, 112.7 mmol) and 2,5-bis-
(
reaction was heated to 115 C for 3 h. Then subsequently 4,4,5,5-
trimethylstannyl)thiophene (46.2 mg, 112.7 mmol) under an
tetramethyl-2-phenyl-1,3,2-dioxaborolane (16.7 mg, 82.0 mmol)
and bromobenzene (17.3 ml, 164 mmol) are added with 30 min
interval to end cap the polymer. After another 30 minutes the
reaction was cooled and quenched by precipitation in acetone.
Filtration through a Soxhlet thimble and subsequent extraction
with acetone, hexanes and chloroform gave most of the polymer
in the chloroform fraction. Reducing the volume and precipita-
tion in methanol followed by filtration over a PTFE filter and
argon atmosphere were added dry toluene (2 ml) and dry dime-
thylformamide (0.2 ml). Argon was bubbled through for 30 min
before addition of tris(dibenzylideneacetone)dipalladium(0) (4.1
mg, 4.5 mmol) and triphenylphosphine (2.4 mg, 9 mmol) and
ꢁ
heating the reaction mixture to 110 C. After 2 h subsequently
tributyl(thiophen-2-yl)stannane (42 mg, 112.7 mmol) and 2-bro-
mothiophene (37 mg, 225.2 mmol) were added with 30 min
interval to end cap the polymer. After another 30 min the reac-
tion mixture was cooled, precipitated in acetone and filtered
through a Soxhlet thimble. The polymer was extracted with
acetone, hexanes, dichloromethane and chloroform. The
dichloromethane fraction was concentrated to a minimal
amount, precipitated in methanol, filtered over a PTFE filter and
ꢁ
drying the polymer in a vacuum oven at 40 C resulted in 88 mg
ꢁ
ꢁ
of the desired polymer. GPC (CHCl , 110 C): M ¼ 33 100 g
3
n
ꢀ1
mol and PDI ¼ 2.5. GPC (ODCB, 80 C): M ¼ 42 700 g
n
ꢀ1
mol and PDI ¼ 2.3. lmax (CHCl
3
) ¼ 746 nm.
ꢁ
dried in a vacuum oven at 40 C to give 85 mg of the title
ꢁ
PTII3T
polymer. GPC (both in chloroform at 110 C and in ODCB at
ꢁ
8
0 C) was inconclusive as the polymer had interaction with the
To monomer 7 (52 mg, 39.2 mmol) and 2,5-bis(trimethyl-stannyl)
thiophene (16.06 mg, 39.2 mmol), under an argon atmosphere,
were added dry toluene (3 ml) and dry dimethylformamide
column. lmax (CHCl ) ¼ 1006 nm.
3
(
0.6 ml). Argon was bubbled through for 30 minutes before
Synthesis of PTIIP
tris(dibenzylideneacetone)dipalladium(0) (1.44 mg, 1.57 mmol)
and triphenylphosphine (1.03 mg, 3.9 mmol) were added. The
To a mixture of 5 (49.5 mg, 56.4 mmol), 1,4-bis(4,4,5,5-tetra-
methyl-1,3,2-dioxaborolan-2-yl)benzene (18.6 mg, 56.4 mmol)
and potassium phosphate tribasic (48 mg, 225.6 mmol) under an
argon atmosphere were added toluene (0.8 ml), 0.1 ml demi water
ꢁ
reaction was heated to 110 C and stirred overnight. Then the
polymer was end capped subsequently with tributyl(thiophen-2-
yl)stannane (14.9 mg, 40 mmol) and 2-bromothiophene (13 mg,
8
(
(
0.1 ml) and a 50 : 50 mixture of toluene and Aliquat 336
0.1 ml). Argon was bubbled through this solution for 30 minutes
0 mmol) in 30 min interval. After another one hour the reaction
was cooled, precipitated in methanol and filtered through a
Soxhlet thimble and washed with acetone. The polymer was
subjected to Soxhlet extraction under an argon atmosphere with
acetone, hexanes and chloroform to give 33 mg of the desired
before addition of tris(dibenzylideneacetone)dipalladium(0)
(
2.75 mg, 3 mmol) and triphenylphosphine (2 mg, 8 mmol). The
ꢁ
reaction was started in a preheated oil bath at 115 C and stirred
at that temperature for 3 h. Then subsequently 4,4,5,5-tetra-
methyl-2-phenyl-1,3,2-dioxaborolane (46 mg, 225.6 mmol) and
bromobenzene (48 mL, 451.2 mmol) were added with 30 min
intervals to end cap the polymer. After another 30 min the
reaction was cooled and quenched by precipitation in methanol
ꢁ
ꢀ1
polymer. GPC (CHCl
3
, 110 C): M
n
¼ 13 400 g mol and PDI ¼
ꢁ
ꢀ1
4
.0. GPC (ODCB, 80 C): M
n
¼ 14 300 g mol and PDI ¼ 2.1.
l
max (CHCl
3
) ¼ 768 nm.
(
100 ml). The polymer was redissolved in chloroform and stirred
PTIITPT
ꢀ
1
overnight with diethylthiocarbamate solution (4 g l , 50 ml).
After extraction the organics were washed with water, concen-
trated to a minimal amount and precipitated in methanol. The
precipitates were filtered through a Soxhlet thimble and extracted
under argon with methanol, heptanes, dichloromethane and
chloroform. The dichloromethane fraction contained most of the
polymer and was precipitated in methanol after which the
precipitates were filtered over a PTFE filter and dried in a
To monomer 7 (45.2 mg, 32.7 mmol), 1,4-bis(4,4,5,5-tetramethyl-
,3,2-dioxaborolan-2-yl)benzene (10.8 mg, 32.7 mmol) and
K PO (27.8 mg, 130.8 mmol) under an argon atmosphere was
1
3
4
added THF : H O 5 : 1 (3.6 ml). Argon was bubbled through this
2
solution for 15 minutes after which Pd dba (1.2 mg, 1.3 mmol)
2
3
t
and Bu PHBF (0.8 mg, 2.6 mmol) were added. The mixture was
3
4
ꢁ
then heated to 80 C and stirred overnight at this temperature.
Then bromobenzene (27.5 ml, 261.6 mmol) was added 1 h after the
addition of 4,4,5,5-tetramethyl-2-phenyl-1,3,2-dioxaborolane
ꢁ
vacuum oven at 40 C to give 36 mg of the dark polymer. GPC
ꢁ ꢁ
(
both in chloroform at 110 C and in ODCB at 80 C) was
(
26.7 mg, 130.8 mmol) to terminate all reactive end groups. After
h the reaction was quenched by precipitating the polymer in
inconclusive as the polymer had interaction with the column.
1
lmax (CHCl ) ¼ 872 nm.
3
methanol including the solids that had already formed in the
reaction mixture. After filtration the residue was subjected to
Soxhlet extraction with acetone, heptanes, dichloromethane,
chloroform, chlorobenzene and ortho-dichlorobenze. Approxi-
mately 20 mg of the polymer remained as solids in the Soxhlet
timble. The chloroform fraction was concentrated to give 2 mg of
PTIICb
To a mixture of monomer 5 (72 mg, 82.0 mmol), 9-(heptadecan-9-
yl)-2,7-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)-9H-carba-
zole (53.9 mg, 82.0 mmol) and potassium phosphate tribasic
ꢁ
ꢀ1
ꢀ1
(
87 mg, 410 mmol) were added, under an argon atmosphere,
toluene (3 ml) and water (0.3 ml) together with one drop of
Aliquat 336. Argon was bubbled through for 30 minutes before
the desired polymer. (CHCl
3
, 110 C): M
ꢁ
n
¼ 29 500 g mol and
PDI ¼ 2.5. GPC (ODCB, 80 C): M
n
¼ 32 400 g mol and
PDI ¼ 2.5. lmax (CHCl
3
) ¼ 737 nm.
2
0392 | J. Mater. Chem., 2012, 22, 20387–20393
This journal is ª The Royal Society of Chemistry 2012

View Article Online
1
1
1
7 R. Stalder, J. Mei and J. R. Reynolds, Macromolecules, 2010, 43,
8
Acknowledgements
348.
8 E. Wang, Z. Ma, Z. Zhang, P. Henriksson, O. Ingan €a s, F. Zhang and
M. R. Andersson, Chem. Commun., 2011, 47, 4908.
We thank Dr J.-C. Flores and Dr M. Turbiez (BASF Switzer-
land) for helpful discussions. The work was supported by the
9 E. G. Wang, Z. Ma, Z. Zhang, K. Vandewal, P. Henriksson,
O. Ingan €a s, F. Zhang and M. R. Andersson, J. Am. Chem. Soc.,
2011, 133, 14244.
‘‘Europees Fonds voor Regionale Ontwikkeling’’ (EFRO) in the
Interreg IV-A project Organext.
2
0 K. R. Graham, J. Mei, R. Stalder, J. W. Shim, H. Cheun, F. Steffy,
F. So, B. Kippelen and J. R. Reynolds, ACS Appl. Mater.
Interfaces, 2011, 3, 1210–1215.
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This journal is ª The Royal Society of Chemistry 2012
J. Mater. Chem., 2012, 22, 20387–20393 | 20393