Dialkoxybithiazole: A new building block for head-to-head polymer semiconductors

Article abstract of DOI:10.1021/ja3120532

Polymer semiconductors have received great attention for organic electronics due to the low fabrication cost offered by solution-based printing techniques. To enable the desired solubility/processability and carrier mobility, polymers are functionalized with hydrocarbon chains by strategically manipulating the alkylation patterns. Note that head-to-head (HH) linkages have traditionally been avoided because the induced backbone torsion leads to poor π-π overlap and amorphous film microstructures, and hence to low carrier mobilities. We report here the synthesis of a new building block for HH linkages, 4,4′-dialkoxy-5,5′-bithiazole (BTzOR), and its incorporation into polymers for high performance organic thin-film transistors. The small oxygen van der Waals radius and intramolecular S(thiazolyl) ?O(alkoxy) attraction promote HH macromolecular architectures with extensive π-conjugation, low bandgaps (1.40-1.63 eV), and high crystallinity. In comparison to previously reported 3,3′-dialkoxy-2,2′-bithiophene (BTOR), BTzOR is a promising building block in view of thiazole geometric and electronic properties: (a) replacing (thiophene)C-H with (thiazole)N reduces steric encumbrance in -BTzOR-Ar.06-0.25 cm²/(V s)) in organic thin-film transistors, as well as enhanced I_on:I_off ratios and greater ambient stability than the BTOR analogues. These geometric and electronic properties make BTzOR a promising building block for new classes of polymer semiconductors, and the synthetic route to BTzOR reported here should be adaptable to many other bithiazole-based building blocks.

Full text of DOI:10.1021/ja3120532

Article
pubs.acs.org/JACS
Dialkoxybithiazole: A New Building Block for Head-to-Head Polymer
Semiconductors
Xugang Guo,†,‡ Jordan Quinn,§ Zhihua Chen,§ Hakan Usta,§ Yan Zheng,§ Yu Xia,§ Jonathan W. Hennek,†
Rocío Ponce Ortiz,†,∥ Tobin J. Marks,*,† and Antonio Facchetti*,†,§
†Department of Chemistry and the Materials Research Center, Northwestern University, 2145 Sheridan Road, Evanston, Illinois
60208, United States
‡Department of Chemistry, South University of Science and Technology of China, No. 1088, Xueyuan Boulevard, Shenzhen,
Guangdong 518055, China
§Polyera Corporation, 8045 Lamon Avenue, Skokie, Illinois 60077, United States
∥Department of Physical Chemistry, University of Mal
́ ́
aga, Campus de Teatinos s/n, Malaga 29071, Spain
S
* Supporting Information
ABSTRACT: Polymer semiconductors have received great
attention for organic electronics due to the low fabrication
cost offered by solution-based printing techniques. To enable
the desired solubility/processability and carrier mobility,
polymers are functionalized with hydrocarbon chains by
strategically manipulating the alkylation patterns. Note that
head-to-head (HH) linkages have traditionally been avoided
because the induced backbone torsion leads to poor π−π
overlap and amorphous film microstructures, and hence to low
carrier mobilities. We report here the synthesis of a new building
block for HH linkages, 4,4′-dialkoxy-5,5′-bithiazole (BTzOR),
and its incorporation into polymers for high performance
organic thin-film transistors. The small oxygen van der Waals
radius and intramolecular S(thiazolyl)···O(alkoxy) attraction promote HH macromolecular architectures with extensive π-
conjugation, low bandgaps (1.40−1.63 eV), and high crystallinity. In comparison to previously reported 3,3′-dialkoxy-2,2′-
bithiophene (BTOR), BTzOR is a promising building block in view of thiazole geometric and electronic properties: (a) replacing
(thiophene)C−H with (thiazole)N reduces steric encumbrance in −BTzOR−Ar− dyads by eliminating repulsive C−H···H−C
interactions with neighboring arene units, thereby enhancing π−π overlap and film crystallinity; and (b) thiazole electron-
deficiency compensates alkoxy electron-donating characteristics, thereby lowering the BTzOR polymer HOMO versus that of
the BTOR analogues. Thus, the new BTzOR polymers show substantial hole mobilities (0.06−0.25 cm2/(V s)) in organic thin-
film transistors, as well as enhanced Ion:Ioff ratios and greater ambient stability than the BTOR analogues. These geometric and
electronic properties make BTzOR a promising building block for new classes of polymer semiconductors, and the synthetic
route to BTzOR reported here should be adaptable to many other bithiazole-based building blocks.
structure and solid-state packing, hence device performance.
For example, the substituent steric repulsions engendered in
head-to-head (HH) π-monomer linkages typically induce
backbone twisting and greatly reduced π-conjugation as in
regioirregular poly(3-alkylthiophene)s (Figure 1b).6
Several strategies have been employed to access highly
conjugated, high-performance semiconducting polymers. First,
efficient synthetic routes have been developed to achieve self-
oriented head-to-tail poly(3-alkylthiophene)s having regiore-
gular alkyl chain placement (Figures 1c and 2a);19,20 the
resulting highly regioregular poly(3-hexylthiophene) (rr-
P3HT) is highly conjugated and with a mobility >0.1 cm2/(V
INTRODUCTION
■
Polymeric semiconductors are important materials classes both
for fundamental soft matter charge transport studies and for
flexible opto-electronics technologies.1−8 In both areas,
optimum materials should possess good solubility/process-
ability, tunable bandgaps, tailorable frontier molecular orbital
(FMO) energies, and optimally ordered film microstructure
and morphology9−16 to achieve high carrier mobility in organic
thin-film transistors (OTFTs),1,3 and sizable power conversion
efficiencies in organic photovoltaic cells (OPVs),4 combined
with acceptable environmental stability.5 To increase polymer
processability, a common strategy is to functionalize the
backbone with solubilizing groups (Figure 1a),17,18 commonly
alkyl chains (R). However, depending on the substitution
regiochemistry, this tactic can negatively affect core electronic
Received: December 10, 2012
Published: January 17, 2013
© 2013 American Chemical Society
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Figure 1. Chemical structures of (a) 3-alkylthiophene, in which the 2-position is designated head (H) and the 5-position is designated tail (T); (b)
regioirregular poly(3-alkylthiophene), which contains head-to-head (HH), tail-to-tail (TT), and head-to-tail (HT) linkages; and (c) regioregular
poly(3-alkylthiophene), which contains exclusively head-to-tail (HT) linkages.
Figure 2. Design strategies for polymer semiconductors to achieve enhanced planarity, conjugation, and mobility by introducing: (a) Substituent
regioregularity. (b) Spacer groups (X): 2T = bithiophene; TT = thienothiophene; DTT = dithienothiophene or other thiophene/thiazole-terminated
groups. (c) Linker atoms (X) for conformational locking. (d) Head-to-head linkages via intramolecular S···O conformational locking; S···O =
S(thienyl)···O(alkoxy) and S(thienyl)···O(carbonyl).
s) (a record at the time for a polymer TFT).21 Nevertheless,
the limited chemical structure variability leads to limited
diversity and opto-electronic properties for poly(3-
alkylthiophene)s. Subsequently, Ong and McCulloch reported
polythiophenes, PQT22 and PBTTT,23 respectively, with
thiophene-arene spacers to yield p-type polymers with 3-D
lamellar structures and substantial hole mobility (0.1−0.6 cm2/
(V s)).3,24 This pioneering strategy of using thiophene-arene
spacers (Figure 2b) has been now widely adopted for materials
design. The principal limitations of this approach are polymer
solubility25,26 because the spacers are typically nonalkylated
arenes, such as bithiophene (2T),22 thienothiophene (TT),23,27
and dithienothiophene(DTT),28 and the requirement that the
spacer be thiophene/thiazole-terminated arenes, such as
naphthodithiophene (NDT)26 and thiazolothiazole (TzTz),29
and benzobisthiazole (BBTz).30 Bulkier arene-terminated
spacers, such as indenofluorene31 and benzothienobenzothio-
phene,26 likely induce high degrees of polymer backbone
torsion and destroy π−π stacking; therefore, the OTFTs
fabricated from such polymers exhibit low TFT mobilities31 or
are TFT inactive.32 Another successful approach uses linker
atoms such as C, Si, Ge, and N to lock the polymer backbone
conformation (Figure 2c). Thus, cyclopentadithiophene,33,34
dithienosilole/germole,35−37 and dithienopyrrole38 incorpora-
tion promote main-chain coplanarity along with improved
processability. The limitation here is that the out-of-plane
disposition of the linker substituents may interfere with π−π
stacking36,39 and/or reduce solubility due to the extended fused
architecture.38 Although the linker atom strategy yields
polymers having extended conjugation and small bandgaps, it
generally leads to moderate mobility <10−2 cm2/(V s)35,40 due
to enlarged π−π stacking34 and/or limited side chain
interdigitation. This linker atom strategy has been highly
successful for designing low-bandgap polymer OPV materials,
for which mobilities of 10−3−10−2 cm2/(V s) are usually
sufficient. Also note that ultrahigh hole TFT mobilities up to 3
cm2/(V s) have been achieved in benzothiadiazole-cyclo-
pentadithiophene copolymers; however, slow film deposition
techniques such as drop-casting34,41 or dip-coating42 are usually
required to achieve long-range microstructural order.43
In contrast to the above strategies, if HH linkage-based
polymers could be constructed with coplanar backbone
conformations, two intriguing characteristics should be
possible: (a) alkyl substituents along with rotational freedom
within the HH monomers should promote good solubility/
processability; (b) the HH building block should be suitable for
polymerization reactions with many arene classes, not only
thiophene/thiazole-terminated derivatives, but also phenyl-
terminated arenes due to HH substituent orientations, which
should reduce steric congestion with neighboring arenes.
Nevertheless, HH linkages have traditionally been avoided in
polymer semiconductor design for alkyl substituents6 because
the van der Waals radius of the alkyl substituent methylene
groups (2.0 Å)44 typically imposes unacceptable steric
hindrance, resulting in backbone torsion (Figure 1b). However,
if the substituents have smaller van de Waals radii and/or
engage in intramolecular noncovalent planarizing interactions
(e.g., Figure 2d), the macromolecular conformation may
approach coplanarity, even in the presence of HH linkages.
In comparison to methylene groups, the oxygen van der Waals
radius (1.4 Å) is far smaller, so that inserting an oxygen atom
between the thienyl and methylene groups, combined with
attractive S(thienyl)···O(alkoxy) interactions,45,46 yields 3,3′-
dialkoxy-2,2′-bithiophene (BTOR, Figures 3c), with a high
degree of backbone coplanarity.47 Furthermore, BTOR-based
polymers yield excellent p-type (0.2 cm2/(V s))48 or ambipolar
transport.49,50 Unfortunately, the very electron-rich character of
BTOR strongly destabilizes the HOMO energies of the
resulting polymers, limiting OTFT Ion:Ioff ratios and likely
long-term environmental stability. Also note that a significant
S···O interaction exists in the S(thienyl)···O(carbonyl)
derivatives (Figure 2d),51 in which the carbonyl group is
electron-withdrawing. The S···O-induced backbone coplanarity,
TPD electron-deficiency, and high alkyl chain density afford
superior performance in both OTFTs52 and OPVs.53−55 This
TPD versatility56 highlights the importance of realizing new
building blocks, which can simultaneously achieve significant
backbone planarity, high solubilizing group densities, and
desirable electronic properties.
In this regard, thiazole is an electron-deficient hetero-
cycle,57−59 and thiazole-based polymers exhibit, versus their
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counits.63−65 However, thiazole-based small molecules and
polymers typically exhibit lower hole mobilities than the
corresponding thiophene analogues due to nonoptimal HOMO
energetics as well as synthetic barriers to accessing high
molecular weights.62,66 We hypothesized that combining
electron-poor thiazoles with the electron-donating alkoxy
substituents would balance the electronic structure such that
hole mobility would be enhanced while retaining low-HOMO
characteristics such as air stability and large current on−off
ratios. Comparative geometries and DFT-derived frontier MO
energies are shown in Figure 3 for 2,2′-bithiophene (2T), 3,3′-
dimethyl-2,2′-bithiophene (BTMe), 3,3′-dimethoxy-2,2′-bithio-
phene (BTOMe), and 4,4′-dimethoxy-5,5′-bithiazole
(BTzOMe). Methoxy group incorporation leads to coplanar
geometries for both BTOMe and BTzOMe (dihedral angle
∼0°) versus twisted 2T (∼22°) and BTMe (∼68°).
Importantly, the BTzOMe HOMO (−5.07 eV) lies between
that of BTMe (−5.84 eV) and that of BTOMe (−4.67 eV),
with the BTzOMe LUMO being the lowest in the series,
suggesting a promising candidate for soluble, environmentally
stable, semiconducting π-conjugated polymers.
Figure 3. Chemical structures, optimized geometries, LUMO energies,
and HOMO energies for (a) bithiophene (2T), (b) 3,3′-dimethyl-2,2′-
bithiophene (BTMe), (c) 3,3′-dimethoxy-2,2′-bithiophene (BTOMe),
and (d) 4,4′-dimethoxy-5,5′-bithiazole (BTzOMe). Calculations were
carried out at the DFT//B3LYP/6-31G** level.
thiophene analogues, lower-lying HOMOs and greater TFT air
stability.60−62 In the present context, thiazole should reduce
steric congestion-induced backbone twisting by eliminating
repulsive C−H···H−C interactions when linked to arene
a
Scheme 1. Synthetic Route to BTzOR Monomers and BTzOR/BTOR-Based Polymers
a
R = n-dodecyl. Reagents/conditions: (i) POCl3, C6H5N, reflux; (ii) Zn, HOAc, reflux; (iii) NaOMe, CuI, MeOH, reflux; (iv) PTSA, C12H25OH,
toluene, 130 °C; (v) n-BuLi, THF, −78 °C, then room temperature; TIPSCl, −78 °C, then room temperature; (vi) n-BuLi, THF, −78 °C, then
room temperature; Fe(acac)3, 0 °C, then 80 °C; (vii) TBAF, THF, 0 °C, then room temperature; (viii) NBS, CHCl3, 60 °C; (ix) n-BuLi, THF, −78
°C, then room temperature; Me3SnCl, −78 °C, then 60 °C; (x) Pd2(dba)3, P(o-tolyl)3, toluene.
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Figure 4. (a) Optical absorption spectra of BTzOR-based polymers in CHCl3 solutions (dashed line, 1 × 10−5 M) and as thin films (solid line) cast
from chloroform solution (5 mg/mL). (b) Optical absorption spectra of BTzOR-based polymer P1a and BTOR-based polymer analogue P4a in
chloroform solution (dashed line, 1 × 10−5 M) and as pristine films (solid line) cast from chloroform solution (5 mg/mL).
Table 1. Physicochemical and Thin-Film Transistor Properties of Polymers P1−P5
a
b
b
polymer
Mn (kDa)
PDI
λmax film (nm)
Egopt (eV)
HOMO (eV)
Tannealing (°C)
μh (cm2/(V s))
Ion/Ioff
P1a
P1b
P2
5.2
34.6
11.7
8.8
3.2
3.7
2.0
5.2
3.6
2.8
4.2
647
668
637
727
614
618
644
1.62
1.58
1.63
1.40
1.66
1.66
1.64
−5.18
−5.16
−4.94
−4.80
−5.07
−5.09
−4.55
210
150
0.06
0.13
105
105
c
c
120
0.15 (0.25)
103 (102)
102 (102)
d
c
d
c
P3
120
0.07 (0.15)
P4a
P4b
P5
6.3
150
0.07
0.04
104
103
44.3
9.0
room temp
90
d
d
0.02
<5
a
b
c
Annealing temperature, which yields optimal device performance. BGTC OTFT performance measured in air. TGBC OTFT performance
measured in air. Device measured in vacuum.
d
thiophene. Despite the interesting chemistry and different solid-
state properties, bithiazole-based copolymers are very rare due
to the synthetic challenges.61,70,71,75−77
RESULTS AND DISCUSSION
■
In this Article, we report the synthesis of a novel
dialkoxybithiazole (BTzOR) building block and its incorpo-
ration into polymer backbones for OTFT applications. The
new series of BTzOR-based polymer semiconductors shows
extensive conjugation, low optical bandgaps, and significant
crystallinity; their implementation in OTFTs yields substantial
hole mobilities (0.06−0.25 cm2/(V s)), as well as significantly
enhanced Ion:Ioff ratios and ambient stability versus BTOR-
based analogues. The solubilizing ability, as well as geometric
and electronic properties, makes BTzOR a promising prototype
building block for new classes of polymeric semiconductors.
Synthesis of BTzOR-Based Monomers and Polymers.
The chemistry of thiazole differs significantly from that of
thiophene,67,68 making the synthesis of bithiazole-based
building blocks far more challenging and less developed.69−71
For example, 4,4′-dialkyl-2,2′-bithiazole, a tail-to-tail bithiazole
unit, was prepared from halomethyl ketones and dithioox-
amide,70 which is greatly different from the synthesis of 4,4′-
dialkyl-2,2′-bithiophene achieved via dimerization of alkylth-
iophenes.72 Furthermore, when 2,5-dibromothiazole is reacted
with 2,5-distannylated thiophenes, highly regioregular polymers
with an estimated head-to-tail content >90% are achieved,
which is not the case for polymerizations of 3-subsituted-2,5-
dibromothiophenes.73 Furthermore, as reported in the
Introduction, thiazole-based organic semiconductors also
show electrical properties and film microstructures distinctively
different from those of the thiophene analogues. Head-to-head
linkage in polythiophene strongly twists the polymer backbone
resulting in amorphous or poorly crystalline films.6 On the
other hand, Curtis70 and Yamamoto74 found that the head-to-
head bithiazole homopolymers achieve a high degree of
polymer backbone coplanarity and extensive π-stacking in the
solid state due to the reduced steric hindrance of thiazole versus
The synthetic routes to the key intermediate BTzOC12 (7)
and the corresponding polymers P1−P3 are depicted in
Scheme 1. First, 4-chlorothiazole (2)78 is converted to 4-
methoxythiazole (3) via a nucleophilic aromatic substitution.47
Transetherification of 3 produces compound 4,47 which
exhibits reactivity very different from that of the thiophene
analogue, 3-dodecoxythiophene. The thiazole 2-position is the
most reactive site,79 rendering the synthetic strategy used for
BTOR47 not viable for BTzOR. Therefore, after protecting the
2-position of 4 with a triisopropylsilyl (TIPS) group, the 5-
position is lithiated and subsequent Fe-mediated coupling80
affords BTzOC12 (7) in high yield (96%), which is then
converted to the monomers 8 and 9. BTzOR-based polymers
P1−P3, as well as the corresponding BTOR-based polymer
analogues P4 and P5 (vide infra), were synthesized using Stille
coupling. The identity and purity of all polymers are supported
1
by elemental analysis (EA) and high-temperature H NMR
spectra in 1,1,2,2-tetrachloroethane-d2. As compared to
previously reported BTOR-phthalimide copolymer P4a (Mn
≈ 200 kDa),48 P1a is obtained with significantly lower Mn for
the soluble fraction (5.2 kDa), probably due to the reduced
polymer solubility. The lower solubility of P1a is an indication
of strong intra- and/or intermolecular interactions. Thus, to
compare the performance of thiazole-based P1a to the
thiophene analogue, polymer P4a with Mn ≈ 6 kDa was
synthesized by lowering the polymerization temperature.
Interestingly, P1b having branched N-2-ethylhexyl imide
substituents achieves good solubility and high Mn (∼35 kDa),
comparable to P4b synthesized under the same conditions
(∼44 kDa). The Mn’s of P2 and P3 are 11.7 and 8.8 kDa with
polydispersities of 2.0 and 5.2, respectively.
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Figure 5. Optimized geometries for the polymer repeat units of (a) P1 dialkoxybithiazole-phthalimide repeat unit, and (b) P4 dialkoxybithiophene-
phthalimide repeat unit. Calculations were carried out at the DFT//B3LYP/6-31G** level; dihedral angles between the planes of the donor and
acceptor blocks and the regions of steric repulsion engendering torsion are indicated by blue circles. Alkyl substituents are replaced here by methyl
groups to simplify the calculations.
Optical and Electrochemical Properties. Optical
absorption spectra of the bithiazole polymers P1−P3 in
chloroform solutions and as thin films are shown in Figure
4a, and relevant data are collected in Table 1. All absorption
degree of backbone coplanarity versus P4, which also accounts
for the structured absorption profiles and decreased solubility
of P1a.
Next, DFT computation was carried out to clarify the
electronic structures and optical properties of the BTzOR- and
BTOR-based polymers. The energy-minimized dihedral angle
(Figure 5) is ∼23° between the phthalimide and alkoxythio-
phene planes,83 while it is computed to be 0° between the
phthalimide and alkoxythiazole planes. The greater coplanarity
in the latter case is due to the elimination of repulsive C−
H···H−C interactions63,65 and the presence of S(thiazolyl)···O
(carbonyl) interaction,55 and therefore affords the smaller
bandgaps and also structured absorption profiles. DFT
calculation of the P4 repeat unit yields a S(thiazolyl)···O
(carbonyl) distance of 2.78 Å, which is significantly shorter than
the sum of S and O van der Waals radius of 3.32 Å. The greater
degrees of conformational coplanarity can be also expected in
other BTzOR-based polymer semiconductors, making BTzOR
units promising building blocks for developing highly
conjugated heterocyclic polymer semiconductors.
profiles of the BTzOR-based polymers show a maximum (λmax
)
in addition to an absorption shoulder, which is somewhat
indicative of ordering.24 The BTzOR-based polymers P1−P3
exhibit extensive aggregation in solution as evidenced by the
negligible blue-shift of the λmax and the absorption shoulder on
going from film to solution (<10 nm shift). These polymers
exhibit large oscillator strengths in the visible, and the optical
bandgaps (Egopt’s) estimated from the absorption edges of 1.62,
1.58, 1.63, and 1.40 eV for P1a, P1b, P2, and P3, respectively.
Bulkier imide N-2-ethylhexyl groups usually result in slightly
enlarged polymer bandgaps over linear imide substituents due
to the increased intermolecular π−π stacking distance and
attendant decreased π-orbital overlap.55,81 Therefore, the
smaller Egopt of P1b (1.58 eV) versus that of P1a (1.62 eV)
is reasonably attributed to extended conjugation due to the
higher P1b Mn, which also indicates that the P1a Mn is
insufficient to reach saturation of the conjugation length. The
narrow Egopt’s of the BTzOR-based polymers indicate extended
polymer backbone conjugation, enabled by significant back-
bone coplanarity in P2 and P3, as well as the electron-rich
character of BTzOR in P1, albeit less than in BTOR. Figure 4b
shows the optical spectra of phthalimide-BTzOR copolymer
P1a and phthalimide-BTOR copolymer P4a; it is evident that
replacing BTOR with BTzOR leads to smaller Egopt’s in the
resulting polymers: 1.62 eV (P1a) vs 1.66 eV (P4a, Figure 4b),
1.58 eV (P1b) vs 1.66 eV (P4b, Figure S2), and 1.40 eV (P3)
vs 1.64 eV (P5, Figure S3). The smaller Egopt of P3 than that of
P5 is in good agreement with the calculated optical gaps of
their repeating units (Figure 3c and d), which can be attributed
to enhanced push−pull interactions in the alkoxythiazole unit
of P3. Such push−pull interactions have been shown to be
effective for lowering the optical gaps in small molecule
chromophores.82 Thus, as the polymer backbone expands, a
very low bandgap (1.40 eV) is achieved in P3. Also, the
replacement of BTOR with BTzOR results in structured
absorption profiles for P1 in solution as well as in the thin film
state versus P4.48 Because BTzOR is less electron-rich than
BTOR, the smaller bandgap of P1 must reflect the higher
The ionization potentials (IPs) of these polymers were next
estimated using cyclic voltammetry (Figure 6), and the derived
HOMO energies are compiled in Table 1. P2 and P3 have
HOMOs at −4.94 and −4.80 eV, respectively, which are higher
Figure 6. (a) Cyclic voltammograms of BTzOR-based polymers. (b)
Comparison of cyclic voltammograms of BTzOR- and BTOR-based
polymers. The measurements were carried out in 0.1 M (n-
−
Bu)4N+PF6 CH3CN solution, and the Fc/Fc+ redox couple was
used as an external standard having an oxidation potential of +0.36 V
vs SCE.
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than that of P3HT measured under identical conditions (−5.05
eV). The high HOMOs can lead to high off-currents and
eroded device stability (vide infra).6,38 By copolymerization
with electron-deficient phthalimides,84 polymers P1a and P1b
achieve lower HOMOs of −5.16 eV to −5.18 eV. Importantly,
replacement of BTOR with BTzOR lowers the HOMOs of P1
and P3 by ∼0.1 and ∼0.25 eV versus those of P4 and P5,
respectively (Table 1, Figure 6b), which indicates the less
electron-rich characteristics of BTzOR versus BTOR. Note that
replacing BTOR with BTzOR does not significantly lower the
P1 HOMO, which may reflect the higher degree of coplanarity
in P1. While backbone torsion can lower the polymer
HOMOs,10,85 the eliminated C−H···H−C repulsive interac-
tions in P1 compress the bandgap, and the net result is that the
HOMO is not significantly lower than in P4.
Figure 7. (a) Comparison of P1−P5-based OTFT transfer character-
istics. (b) Comparison of transfer characteristics of BTzOR-based
polymer P1a and BTOR-based P4a BGTC OTFTs stored and
characterized in air.
Thin-Film Transistor Response and Polymer Film
Morphology. The charge transport properties of the new
BTzOR-based polymers were investigated by fabricating
bottom-gate/top-contact (BGTC) and top-gate/bottom-con-
tact (TGBC) TFTs. For the BGTC devices, the polymers were
dissolved in chloroform (10 mg/mL) at 50−60 °C on a hot
plate, and then deposited by spin-coating the polymer solution
under ambient conditions onto octadecyltrichlorosilane
(OTS)-treated or hexamethyldisilazane (HMDS)-treated, p-
doped Si (001) wafers having a 300 nm thermal SiO2 dielectric
layer. The spin-coating should be carried out within 5 min of
polymer dissolution, because longer storage at room temper-
ature leads to gelation of P1a and P3. After spin-coating, the
polymer films were thermally annealed under vacuum over a
range of temperatures (see the Supporting Information for
details). Device characterization was performed under ambient
or vacuum as specified. All of the present polymers exhibit
distinct p-type response, and the optimal average performance
data (at least five devices measured for each sample) are
collected in Table 1. The average hole mobilities for P1a, P1b,
P2, and P3-based BGTC OTFTs are 0.06, 0.13, 0.15, and 0.07
cm2/(V s) with current modulations (Ion/Ioff) of 105, 105, 103,
and 102 after thermally annealing at 210, 150, 120, and 120 °C,
respectively. As for other organic TFTs, TGBC devices (see the
Supporting Information for fabrication details) perform
better,86,87 for example, with average μh ≈ 0.25 cm2/(V s) for
P2 TFT. The analysis of the TFT performance is instructive in
understanding the difference between the BTzOR- and BTOR-
based polymers. The progressive Ion/Ioff fall from P1 to P3
nicely tracks the rise in the corresponding HOMO energies.
Note that μh of P4a here (Mn = 6.3 kDa, μh = 0.07 cm2/(V s))
is somewhat lower than that of high Mn P4a (Mn ≈ 200 kDa, μh
= 0.17 cm2/(V s)),48 indicating that a substantial Mn is essential
for optimum performance.41,88,89 However, when a consistent
comparison is carried out between thiazole polymers P1b/P3
and thiophene analogues P4b/P5, the hole mobility of the
thiazole family is up to ∼3× greater. For example, the average
μh of P1b (Mn = 34.6 kDa) is 0.13 cm2/(V s), while the average
μh of P4b (Mn = 44.3 kDa) is 0.04 cm2/(V s). The greater μh of
the BTzOR-based polymer agrees with the higher degree of
backbone coplanarity by eliminating C−H···H−C interactions
(Figure 5) and/or greater film crystallinity (vide infra).
Furthermore, the BTzOR-based OTFTs exhibit greater Ion/
significantly for P4a OTFTs. These results are consistent
with the more electron-deficient character of the thiazole core
versus the thiophene core.
To understand the charge transport properties of the new
BTzOR head-to-head polymers, the film microstructures and
morphologies were investigated by differential scanning
calorimetry (DSC), specular X-ray diffraction (XRD), and
atomic force microscopy (AFM). The DSC scan reveals no
significant thermal transitions for the BTzOC12-based
polymers in the range of 25−320 °C (Figure S1), similar to
the BTOR-based analogues.48 Figure 8 shows Θ−2Θ XRD
Figure 8. XRD scattering patterns and AFM data (inset: 5 × 5 μm
topographic images) of BTzOR-based polymer P1 and BTOR-based
polymer P4 films fabricated under conditions that yield the best-
performing thin-film transistors.
scans and AFM topographic images of P1 films, with those of
P4 films included for comparison. A single family of Bragg
reflections assigned to the lamellar packing (lateral chain
backbone to backbone distance) is observed for P1a and P1b
films, with progressions up to the third order, indicating highly
ordered film microstructures.90 However, the P4a and P4b
films show lower degrees of order and less intense lamellar
diffraction features,48 consistent with their featureless optical
absorption spectra. The higher degree of ordering of P1 (Figure
8) can be attributed to the higher degree of backbone
coplanarity induced by deleting C−H···H−C repulsions
Ioff values (>10−100×) and far greater I−V stability in ambient
than the BTOR-based analogues (Figure 7). After 6 weeks in
air, the mobility and Ion/Ioff ratio of P1a OTFTs basically
remain unchanged while the Ion/Ioff ratio of P4a OTFTs falls by
more than 100×, and the threshold voltage also drifts
1991
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between the phthalimide and thiazole units (Figure 5),
ultimately enhancing carrier mobility. Interestingly, the
BTzOR-based polymer films do not exhibit any significant
reflections from the polymer π-stacking in comparison to the
weak π-stacking reflection (∼24°) observed for the BTOR-
based polymer P448 (note that the reflection at ∼22° is due to
the Si substrate). The absence of perpendicular π-stacking in
BTzOR-based polymers and thus having a unique edge-on
polymer backbone orientation90 may also facilitate charge
transport in BTzOR polymer OTFTs.91 The thermal
annealing-induced device performance enhancement corre-
sponds well with the film microstructure evolution. For
example, μh increases from 3.7 × 10−2 to 0.13 cm2/(V s) for
a P1b TFT after thermally annealing at 150 °C. The XRD scans
of the P1b films exhibit the strongest diffraction features after
annealing at 150 °C versus those of films annealed at other
temperatures. Note also that the AFM images show
distinctively different P1 and P4 morphologies. P4 has more
textured and fibrillar-like domains and more distinct intergrain
boundaries, which should act as charge carrier traps, while P1
exhibits more extensive domain interconnectivity, which should
enhance bulk charge transport.38 The greater hole mobility of
P1b versus P1a can be ascribed to the higher degree of film
crystallinity as revealed by the XRD data (Figure 8a and b).
The P1b films show more intense diffraction than the P1a
films; hence, the greater crystallinity may be due to the higher
Mn of P1b.41,87
here should be adaptable to other bithiazole-based building
blocks.
EXPERIMENTAL SECTION
■
Details of monomer and polymer characterization and raw materials
suppliers can be found in the Supporting Information.
Monomer Synthesis. 2,4-Dichlorothiazole 1.78 A mixture of 2,4-
thiazolidinedione (50.0 g, 0.427 mol), phosphorus oxychloride (460 g,
3.0 mol), and pyridine (74 g, 0.93 mol) was refluxed for 3 h. The
reaction mixture was then reduced in volume by 1/2 by distilling the
volatiles through a short column. The resulting dark slurry was poured
into ice (500 g). The mixture was then extracted with diethyl ether (3
× 500 mL), and the combined organic layer was washed successively
with 5% aqueous NaOH (500 mL) and brine (500 mL). The
separated organic layer was dried over MgSO4, filtered, and
concentrated in vacuo to a brown oil, which was purified by vacuum
distillation through an air condenser. The solid distillate was
recrystallized from 100 mL of cold hexanes to give 2,4-dichlorothiazole
1 as colorless needles (34 g, 52% yield). mp 42−43 °C (lit. 42−43
1
°C). H NMR (500 MHz, CDCl3, ppm): δ 7.04 (s, 1H).
4-Dichlorothiazole 2.78 A mixture of 2,4-dichlorothiazole 1 (29 g,
188 mmol), zinc dust (43.5 g, 665 mmol), and acetic acid (400 mL)
was refluxed for 6 h. After TLC indicated complete consumption of 1,
the mixture was cooled to room temperature and filtered. The filter
cake was washed with acetic acid (3 × 30 mL). The filtrate was then
poured into ice (1000 g) and was treated with about 50% (w/v)
aqueous NaOH (0.65 L) until a slightly alkaline mixture resulted (pH
= 9). The mixture was extracted with diethyl ether (3 × 300 mL), and
the combined ethereal extracts were washed successively with
saturated aqueous NaHCO3 (300 mL) and brine (300 mL). The
separated organic layer was dried over K2CO3, filtered, and
concentrated in vacuo to give 4-chlorothiazole as a colorless liquid
(16.5 g, 73% yield), which was pure enough for the next step without
CONCLUSIONS
■
We report an efficient synthetic route to the novel head-to-head
polymer semiconductor building block, 4,4′-dialkoxy-5,5′-
bithiazole (BTzOR), and the properties of the resulting π-
electron macromolecules. This design strategy differs greatly
from two other widely employed ones that introduce backbone
spacers or linker atoms, and therefore offers a new motif for
polymer semiconductors intended for organic electronics.
BTzOR-containing head-to-head polymers exhibit promising
properties, such as high degrees of subunit coplanarity induced
by attractive (thiazolyl)S···O(alkoxy) contacts and the absence
of repulsive (thiophene)C−H···H−C(arene) interactions, low
bandgaps, highly crystalline film microstructures, and, with the
proper imide N-substituents, good solubilities. More impor-
tantly, the electron-deficient thiazole core can offset the
electron-donating tendencies of alkoxy substituents, and
therefore BTzOR is more electron neutral than the previously
reported thiophene-based BTOR, and thus BTzOR-based
polymers have more balanced HOMO energetics. Furthermore,
because BTzOR units impose less steric hindrance with respect
to neighboring monomers by eliminating nonbonding C−
H···H−C interactions, BTzOR can tolerate neighboring
counits having greater steric hindrance while maintaining
significant backbone coplanarity and conjugation, as illustrated
here by a phthalimide unit. All of the present BTzOR-based
polymers show substantial hole mobilities of 0.06−0.25 cm2/(V
s), reflecting the backbone coplanarity and crystallinity. By
polymerizing with an electron-deficient comonomer, the
BTzOR-phthalimide copolymer exhibits an average TFT hole
mobility of 0.13 cm2/(V s), high current on−off ratios (105),
and enhanced device ambient stability versus BTOR-
phthalimide copolymer TFTs. The high degrees of conjugation,
low bandgaps, high crystallinities, and efficient transport
properties render BTzOR-based polymers promising for
organic electronics. Furthermore, the synthetic route reported
1
further purification. H NMR (500 MHz, CDCl3, ppm): δ 8.77 (d,
1H), 7.19 (d, 1H).
4-Methoxythiazole 3. A mixture of sodium methoxide, prepared by
treating methanol (450 mL) with sodium metal (21 g, 913 mmol), and
4-chlorothiazole 2 (29.3 g, 245 mmol) was refluxed for 24 h. The
mixture was next cooled to room temperature and was reduced in
volume by about 1/2 by concentrating on a rotovap. The mixture was
then dissolved in water (500 mL) and extracted with diethyl ether (3
× 300 mL). The combined ethereal extracts were washed with brine
(500 mL), dried over MgSO4, filtered, and concentrated in vacuo. The
resulting red oil was purified by column chromatography using
chloroform as the eluent, and then by vacuum distillation to give the
1
title compound 3 as a colorless liquid (17.5 g, 62%). H NMR (500
MHz, CDCl3, ppm): δ 8.54 (d, 1H), 6.13 (d, 1H), 3.92 (s, 3H). 13C
NMR (125 MHz, CDCl3, ppm): δ 166.25, 150.63, 88.85, 57.49.
4-Dodecoxythiazole 4. A mixture of 4-methoxythiazole 3 (4.0 g,
34.7 mmol), n-dodecanol (12.8 g, 68.7 mmol), p-toluenesulfonic acid
monohydrate (0.7 g, 3.7 mmol), and toluene (75 mL) was heated at
130 °C for 24 h. The mixture was cooled to room temperature and
purified by column chromatography using dichloromethane as the
eluent. The resulting oily solid was recrystallized from cold pentane
1
(20 mL) to give the product 4 as a colorless solid (5.15 g, 55%). H
NMR (500 MHz, CDCl3, ppm): δ 8.52 (d, 1H), 6.09 (d, 1H), 4.09 (t,
2H), 1.79 (m, 2H), 1.45 (m, 2H), 1.25 (m, 16H), 0.87 (t, 3H). 13C
NMR (125 MHz, CDCl3, ppm): δ 165.63, 150.28, 89.07, 70.47, 32.07,
29.81, 29.79, 29.74, 29.71, 29.51, 29.35, 26.10, 22.84, 14.33 (note:
some peaks in the 13C NMR spectrum overlap).
2-Triisopropylsilyl-4-dodecoxythiazole 5. A solution of 4-dodecox-
ythiazole 4 (4.38 g, 16.3 mmol) in THF (150 mL) was cooled to −78
°C. The resulting suspension was treated dropwise with n-BuLi (2.5 M
in hexane, 6.50 mL, 16.3 mmol). The mixture was stirred for 2 h, and
then the dry ice bath was removed for several minutes and a yellow
solution resulted. The mixture was then cooled to −78 °C and treated
with triisopropylchlorosilane (3.76 g, 19.5 mmol). The dry ice bath
was removed, and the mixture was stirred at ambient temperature for
90 min. The mixture was next concentrated in vacuo and purified by
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column chromatography using chloroform as the eluent to give the
title compound as a pale yellow oil (6.24 g, 90% yield). 1H NMR (500
MHz, CDCl3, ppm): δ 6.24 (s, 1H), 4.12 (t, 2H), 1.83 (m, 2H), 1.45
(m, 5H), 1.23 (d, 16H), 1.32 (d, 18H), 0.89 (t, 3H). 13C NMR (125
MHz, CDCl3, ppm): δ 167.74, 167.37, 91.82, 70.65, 32.14, 29.88,
29.82, 29.79, 29.64, 29.57, 29.49, 26.25, 22.91, 18.70, 17.89, 14.34,
11.71 (note: some peaks in the 13C NMR spectrum overlap).
Calcd for C36H68N2O2S2Sn2: C, 50.13; H, 7.95; N, 3.25. Found: C,
50.46; H, 7.72; N, 3.43.
5,5′-Dibromo-3,3′-bis(dodecoxy)-2,2′-bithiophene 10. To a sol-
ution of 3,3′-bis(dodecoxy)-2,2′-bithiophene48 (0.32 g, 0.60 mmol) in
chloroform (10 mL) was added N-bromosuccinimide (0.21 g, 1.20
mmol) in small portions over 2 min at −30 °C. After addition, the
reaction was stirred at −30 °C for 2 h. The reaction then was warmed
to 25 °C, and to the reaction was added 50 mL saturated aqueous
Na2SO3 solution. The reaction was extracted three times with
dichloromethane and the combined organic layer was washed with
brine three times. After drying over MgSO4 and filtration, the solvent
was removed using rotovap, and a green residue was obtained as the
crude product, which was purified by column chromatography using
dichloromethane:hexane (1:1) as the eluent. The product was
obtained as a yellow-green solid (0.38 g, 92%). 1H NMR (500
MHz, CDCl3, ppm): 6.82 (s, 2H), 4.04 (t, 4H), 1.83 (m, 4H), 1.48
(m, 4H), 1.31 (m, 32H), 0.89 (t, 6H). 13C NMR (125 MHz, CDCl3,
ppm): δ 150.54, 119.25, 115.33, 110.05, 72.59, 32.15, 29.89, 29.86,
29.80, 29.76, 29.72, 29.59, 29.49, 26.14, 22.92, 14.35. Anal. Calcd for
C32H52Br2O2S2: C, 55.49; H, 7.57; N, 0.00. Found: C, 55.44; H, 7.38;
N, not found.
5,5′-Bis(trimethylstannyl)-3,3′-bis(dodecoxy)-2,2′-bithiophene
11. A solution of 3,3′-bis(dodecoxy)-2,2′-bithiophene48 (1.27 g, 2.37
mmol) in THF (60 mL) was cooled to −78 °C. The resulting
suspension was treated dropwise with n-BuLi (2.5 M in hexanes; 2.10
mL, 5.22 mmol) and stirred for 30 min. The dry ice bath was removed,
and the mixture was stirred at ambient temperature for 30 min. The
mixture was treated with trimethyltin chloride (1 M in hexane; 5.93
mL, 5.93 mmol) as one portion. The reaction then was warmed to
room temperature and stirred at 25 °C for 2 h. The reaction mixture
was then carefully quenched with H2O and diluted with H2O (100
mL). The reaction mixture was extracted with EtOAc (3 × 50 mL),
and the combined organic layer was washed with H2O (100 mL),
brine (100 mL), and dried over MgSO4. After filtration and removal of
solvent in vacuo, the title compound was obtained as an off-white
solid, which was further purified by recrystallization from methanol to
provide pale yellow needle-like crystals as the product (1.55 g, 76%).
1H NMR (500 MHz, CDCl3, ppm): 6.89 (s, 2H), 4.12 (t, 4H), 1.86
2,2′-Bis(triisopropylsilyl)-4,4′-bis(dodecoxy)-5,5′-bithiazole 6. A
solution of 2-triisopropylsilyl-4-dodecoxythiazole 5 (6.24 g, 14.7
mmol) in THF (150 mL) was cooled to −78 °C and treated
dropwise with n-BuLi (2.5 M in hexanes; 6.45 mL, 16.1 mmol). After
the mixture was stirred for 45 min, the dry ice bath was removed, and
the mixture was stirred at ambient temperature for 1 h. The mixture
was then cooled to 0 °C and treated with Fe(acac)3 (5.69 g, 16.1
mmol). The reaction mixture was heated in an 80 °C oil bath for 2 h,
cooled to room temperature, and filtered. The filter cake was washed
with THF (3 × 25 mL). The filtrate was concentrated in vacuo and
purified by column chromatography using dichloromethane/hexane
(1:2) as eluent to give the title compound as a yellow solid (6.0 g, 96%
1
yield). H NMR (500 MHz, CDCl3, ppm): δ 4.52 (t, 4H), 1.85 (m,
4H), 1.57 (m, 4H), 1.43 (m, 10H), 1.28 (m, 28H), 1.17 (d, 36H), 0.90
(t, 6H). 13C NMR (125 MHz, CDCl3, ppm): δ 162.18, 161.86, 105.94,
70.82, 32.17, 29.98, 29.96, 29.93, 29.90, 29.79, 29.63, 26.55, 22.94,
18.77, 14.35, 11.84 (note: some peaks in the 13C NMR spectrum
overlap).
4,4′-Bis(dodecoxy)-5,5′-bithiazole 7. To a solution of 2,2′-
bis(triisopropylsilyl)-4,4′-bis(dodecoxy)-2,2′-bithiazole 6 (6.00 g,
7.06 mmol) in THF (150 mL) at 0 °C was added tetrabutylammo-
nium fluoride (1.0 M in THF; 21.2 mL, 21.2 mmol) dropwise over 5
min. The mixture was next stirred for 30 min at 0 °C, and then the ice
bath was removed and the mixture was stirred at 25 °C for 90 min.
The mixture was treated with water (2 mL), concentrated in vacuo,
and purified by column chromatography using dichloromethane/
hexane (1:1) as the eluent. The product was further purified by
recrystallization from hexane to give a yellow solid as the title
1
compound (2.98 g, 79%). H NMR (500 MHz, CDCl3, ppm): δ 8.40
(s, 2H), 4.45 (t, 4H), 1.85 (m, 4H), 1.50 (m, 4H), 1.26 (m, 32H), 0.88
(t, 6H). 13C NMR (125 MHz, CDCl3, ppm): δ 159.52, 146.98, 102.93,
71.16, 32.14, 29.88, 29.82, 29.80, 29.78, 29.58, 29.54, 26.22, 22.91,
14.34 (note: some peaks in the 13C NMR spectrum overlap).
(m, 4H), 1.55 (m, 4H), 1.27 (m, 32H), 0.89 (t, 6H), 0.37 (s, 18H).
13C NMR (125 MHz, CDCl3, ppm): δ 154.03, 133.54, 123.78, 120.33,
2,2′-Dibromo-4,4′-bis(dodecoxy)-5,5′-bithiazole 8. A mixture of 7
(0.30 g, 0.56 mmol), N-bromosuccinimide (0.24 g, 1.35 mmol), and
chloroform (40 mL) was heated in an oil bath at 60 °C for 1.5 h. The
mixture was then concentrated in vacuo, and the resulting solid was
purified by column chromatography using dichloromethane/hexane
(1:1) as the eluent to afford colorless crystals as the product (0.286 g,
72.16, 45.20, 32.15, 30.06, 29.93, 29.87, 29.74, 29.59, 26.45, 22.91,
14.34, −8.10 (note: some peaks in the 13C NMR spectrum overlap).
Anal. Calcd for C38H70O2S2Sn2: C, 53.04; H, 8.20; N, 0.00. Found: C,
52.71; H, 7.91; N, not found.
Polymer Synthesis. General Procedure for Stille Coupling
Polymerizations in the Synthesis of P1−P5. An air-free flask was
charged with the two monomers (0.20 mmol each), tris-
(dibenzylideneacetone)dipalladium(0) (Pd2(dba)3) and tris(o-tolyl)-
phosphine (P(o-tolyl)3) (1:8, Pd2(dba)3:P(o-tolyl)3 molar ratio; Pd
loading 0.03−0.05 equiv). The flask and its contents were next
subjected to three pump/purge cycles with argon, followed by addition
of anhydrous toluene (8 mL) via syringe. The sealed reaction flask was
then stirred at various temperatures for differing durations based on
the solubility of the polymers. Next, 0.1 mL of 2-(tributylstanny)-
thiophene was added, and the reaction mixture was stirred for another
12 h. Finally, 0.20 mL of 2-bromothiophene was added, and the
reaction mixture was stirred for another 12 h. After cooling to room
temperature, the deep-colored reaction mixture was slowly dripped
into 100 mL of methanol (containing 5 mL of 12 N hydrochloric acid)
with vigorous stirring. After stirring for 4 h, the solid precipitate was
transferred to a Soxhlet thimble. After drying, the crude product was
subjected to sequential Soxhlet extractions, with the choice of solvents
and sequence depending on the solubility of the particular polymer.
After final extraction with CHCl3, the polymer solution was
concentrated to approximately 20 mL, and then dripped into 100
mL of methanol with vigorous stirring. The polymer was collected by
filtration and dried under reduced pressure to afford a deep colored
solid as the product.
1
74%). mp 65 °C. H NMR (500 MHz, CDCl3, ppm): 4.38 (t, 4H),
1.80 (m, 4H), 1.47 (m, 4H), 1.34 (m, 32H), 0.89 (t, 6H). 13C NMR
(125 MHz, CDCl3, ppm): δ 156.65, 131.45, 105.79, 71.82, 32.14,
29.89, 29.87, 29.80, 29.75, 29.59, 29.58, 29.45, 26.07, 22.92, 14.34.
Anal. Calcd for C30H50Br2N2O2S2: C, 51.87; H, 7.25; N, 4.03. Found:
C, 51.93; H, 7.44; N, 4.09.
2,2′-Bis(trimethylstannyl)-4,4′-bis(dodecoxy)-5,5′-bithiazole 9. A
solution of 7 (0.373 g, 0.694 mmol) in THF (50 mL) was cooled to
−78 °C. The resulting suspension was treated dropwise with n-BuLi
(2.5 M in hexanes; 0.69 mL, 1.74 mmol) and stirred for 30 min. The
dry ice bath was removed, and the mixture was stirred at ambient
temperature for 30 min. The mixture was treated with 0.167 g (0.84
mmol) of trimethyltin chloride (1 M in hexane; 2.08 mL, 2.08 mmol)
as one portion and heated in an oil bath at 60 °C for 1 h. The reaction
mixture was then carefully quenched with H2O and diluted with H2O
(100 mL). The reaction mixture was extracted with EtOAc (3 × 50
mL). The combined organic layer was washed with H2O (100 mL),
brine (100 mL), and dried over MgSO4. After filtration and removal of
solvent, the title compound was obtained as an off-white solid (587
mg, 98%). 1H NMR (500 MHz, CDCl3, ppm): 4.48 (t, 4H), 1.84 (m,
4H), 1.52 (m, 4H), 1.27 (m, 32H), 0.89 (t, 6H), 0.45 (s, 18H). 13C
NMR (125 MHz, CDCl3, ppm): δ 167.35, 162.20, 106.54, 71.08,
32.15, 29.97, 29.94, 29.89, 29.88, 29.68, 29.60, 26.38, 22.92, 14.34,
−7.90 (note: some peaks in the 13C NMR spectrum overlap). Anal.
P1a. This polymer was synthesized from N-dodecyl-3,6-dibromoph-
thalimide48 and 9. The polymerization was carried out at 60 °C for 2 h.
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The solvent sequence for Soxhlet extraction was methanol, acetone,
hexane, dichloromethane, and chloroform. This product was obtained
as a blue solid (156 mg, 92% yield). Mn = 5.2 kDa, PDI = 3.2. H
material is available free of charge via the Internet at http://
pubs.acs.org.
1
NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ 8.15 (br, 2H), 4.71 (br,
4H), 3.86 (br, 2H), 2.09 (br, 4H), 1.46 (m, 56H), 0.95 (br, 9H). Anal.
Calcd for C50H77N3O4S2: C, 70.79; H, 9.15; N, 4.95. Found: C, 71.23;
H, 9.42; N, 4.77.
AUTHOR INFORMATION
Corresponding Author
t-marks@northwestern.edu; a-facchetti@northwestern.edu
■
P1b. This polymer was synthesized from N-(2-ethylhexyl)-3,6-
dibromophthalimide48 and 9. The polymerization was carried out at
110 °C for 48 h. The solvent sequence for Soxhlet extraction was
methanol, acetone, hexane, dichloromethane, and chloroform. This
product was obtained as a blue solid (135 mg, 85% yield). Mn = 34.6
kDa, PDI = 3.7. 1H NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ 8.17
(br, 2H), 4.71 (br, 4H), 3.79 (br, 2H), 2.07 (br, 4H), 1.99 (m, 1H),
1.49 (m, 44H), 0.97 (br, 12H). Anal. Calcd for C46H69N3O4S2: C,
69.74; H, 8.78; N, 5.30. Found: C, 70.19; H, 8.47; N, 5.21.
P2. This polymer was synthesized from 4,4′-bis(n-dodecyl)-5,5′-
bis(trimethylstannyl)-2,2′-bithiophene87 and 8. The polymerization
was carried out at 110 °C for 72 h. The solvent sequence for Soxhlet
extraction was methanol, acetone, hexane, and chloroform. This
product was obtained as a blue solid (135 mg, 65% yield). Mn = 11.7
kDa, PDI = 2.0. 1H NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ 7.15
(s, 2H), 4.61 (br, 4H), 3.05 (br, 4H), 1.99 (br, 4H), 1.86 (br, 4H),
1.66 (br, 4H), 1.41 (m, 68H), 0.96 (b, 12H). Anal. Calcd for
C62H102N2O2S4: C, 71.90; H, 9.93; N, 2.70. Found: C, 72.18; H, 9.62;
N, 3.01.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the ONR for financial support through the Multi-
University Research Initiative (MURI Award N00014-11-1-
0690) and AFOSR (FA9550-08-1-0331) for support of this
research, and the NSF-MRSEC program through the North-
western University Materials Research Science and Engineering
Center for characterization facilities (DMR-1121262). R.P.O.
acknowledges funding from the European Community’s
Seventh Framework Programme through a Marie Curie
International Fellowship (Grant Agreement 234808).
REFERENCES
■
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Soxhlet extraction was methanol, acetone, hexane, and chloroform.
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1
8.8 kDa, PDI = 5.2. H NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ
4.65 (br, 4H), 1.99 (br, 4H), 1.47 (m, 36H), 0.96 (br, 6H). Anal.
Calcd for C30H50N2O2S2: C, 67.37; H, 9.42; N, 5.24. Found: C, 67.71;
H, 9.69; N, 5.18.
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1214.
P4a.48 This polymer was synthesized from N-dodecyl-3,6-
dibromophthalimide48 and 11. The polymerization was carried out
at 50 °C for 2 h. The solvent sequence for Soxhlet extraction was
methanol, acetone, hexane, and chloroform. This product was
obtained as a blue solid (153 mg, 90% yield). Mn = 6.3 kDa, PDI =
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732.
1
3.6. H NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ 7.99 (brs, 2H),
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Koganezawa, T.; Takimiya, K. J. Am. Chem. Soc. 2012, 134, 3498−
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7.91 (brs, 2H), 4.37 (brs, 4H), 3.79 (brs, 2H), 2.07 (brs, 4H), 1.77
(brs, 2H), 1.65 (brs, 4H), 1.42 (m, 50H), 0.91 (m, 9H). Anal. Calcd
for C52H79NO4S2: C, 73.80; H, 9.41; N, 1.66. Found: C, 73.28; H,
9.23; N, 1.76.
P4b.48 This polymer was synthesized from N-(2-ethylhexyl)-3,6-
dibromophthalimide48 and 11. The polymerization was carried out at
110 °C for 48 h. The solvent sequence for Soxhlet extraction was
methanol, acetone, hexane, dichloromethane, and chloroform. This
product was obtained as a blue solid (137 mg, 87% yield). Mn = 44.3
kDa, PDI = 2.8. 1H NMR (400 MHz, C2D2Cl4, 130 °C, ppm): δ 7.89
(brs, 2H), 7.84 (brs, 2H), 4.32 (brs, 4H), 3.68 (brs, 2H), 2.00 (brs,
4H), 1.96 (m, 1H), 1.67 (brs, 4H), 1.34 (m, 40H), 0.95 (m, 12H).
Anal. Calcd for C48H71NO4S2: C, 72.96; H, 9.06; N, 1.77. Found: C,
72.76; H, 9.11; N, 1.84.
́
as, J. L.; Salleo, A.; Bao,
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P5. This polymer was synthesized from 10 and 11. The
polymerization was carried out at 110 °C for 24 h. The solvent
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chloroform. This product was obtained as a blue solid (75 mg, 35%
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1
yield). Mn = 9.0 kDa, PDI = 4.2. H NMR (400 MHz, C2D2Cl4, 130
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°C, ppm): δ 6.80 (brs, 2H), 4.12 (brs, 4H), 1.98 (m, 4H), 1.70 (m,
4H), 1.41 (brs, 32H), 0.96 (t, 6H). Anal. Calcd for C32H52O2S2: C,
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ASSOCIATED CONTENT
■
S
* Supporting Information
Details of the monomer and polymer characterization and raw
materials suppliers; procedure for TFT fabrication and
characterization (XRD, AFM); and UV and DSC plots. This
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dx.doi.org/10.1021/ja3120532 | J. Am. Chem. Soc. 2013, 135, 1986−1996

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