Amide-bridged terphenyl and dithienylbenzene units for semiconducting polymers

Article abstract of DOI:10.1039/c5ra28140g

We here describe the synthesis, characterization, and structures of new semiconducting polymers (PIQP2T and PTPQ2T) based on amide-bridged terphenyl (IQP) and dithienylbenzene (TPQ), and their performances in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The polymers are found to have relatively wide band gaps of >2.0 eV and deep HOMO energy levels of -5.4 eV. Interestingly both the HOMO and LUMO energy levels similarly shift upward and downward, respectively, by the π-extension from the monomer unit to the polymer, which can be ascribed to the delocalized HOMO and LUMO along the molecular frameworks. This suggests that IQP and TPQ can be viewed as electron-neutral building units. Both polymers had similar ordering structures in the thin film despite the fact that the IQP is more sterically hindered at the end of the moiety than TPQ. This is probably due to the strong intermolecular interactions originating in the amide group. The polymers exhibited similar hole mobilities of 0.03-0.04 cm² V^-1 s^-1 in the OFET devices. Although the PCEs were modest, the OPV devices based on these polymers showed a quite high V_OC of 0.94 V.

Full text of DOI:10.1039/c5ra28140g

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PAPER
Amide-bridged terphenyl and dithienylbenzene
units for semiconducting polymers†
Cite this: RSC Adv., 2016, 6, 16437
a
b
b
Masahiro Akita,‡ Masahiko Saito,‡ Itaru Osaka, Tomoyuki Koganezawac
*
and Kazuo Takimiyaab
We here describe the synthesis, characterization, and structures of new semiconducting polymers (PIQP2T
and PTPQ2T) based on amide-bridged terphenyl (IQP) and dithienylbenzene (TPQ), and their performances
in organic field-effect transistors (OFETs) and organic photovoltaics (OPVs). The polymers are found to have
relatively wide band gaps of >2.0 eV and deep HOMO energy levels of ꢀ5.4 eV. Interestingly both the
HOMO and LUMO energy levels similarly shift upward and downward, respectively, by the p-extension
from the monomer unit to the polymer, which can be ascribed to the delocalized HOMO and LUMO
along the molecular frameworks. This suggests that IQP and TPQ can be viewed as electron-neutral
building units. Both polymers had similar ordering structures in the thin film despite the fact that the IQP
is more sterically hindered at the end of the moiety than TPQ. This is probably due to the strong
intermolecular interactions originating in the amide group. The polymers exhibited similar hole mobilities
of 0.03–0.04 cm2 Vꢀ1 sꢀ1 in the OFET devices. Although the PCEs were modest, the OPV devices based
on these polymers showed a quite high VOC of 0.94 V.
Received 31st December 2015
Accepted 27th January 2016
DOI: 10.1039/c5ra28140g
www.rsc.org/advances
the distortion of the aryl–aryl linkage, which would offer rigidity
and coplanarity and thus strong interemolecular interaction, in
turn leading to good ordering in thin lms.20 The use of amide or
Introduction
Semiconducting polymers are an important class of materials
that can be used as the active layers for organic optoelectronic
devices such as transistors (OFETs), and photovoltaics (OPVs).1,2
In the development of semiconducting polymers, synthetic
chemists must carefully design the backbone structure to have
strong intermolecular interactions and thus good ordering
structures as well as suitable electronic structures.3–5 Since the
p-building unit is the most important component of the poly-
mer that determines the ordering and electronic structures, the
exploration of new p-building units is crucial for the materials
development.
Bridged oligo-arylenes/heteroarylenes consisting of phenylene
and thiophene are widely studied p-building units so far. Ter-
phenyl or dithienylbenzene bridged with substituted C,6–10 Si,11
Ge,11,12 N,13–17 and olen18,19 (Fig. 1) offer good optical and elec-
trical properties when incorporated in donor–acceptor (D–A)
semiconducting polymers, where they act as donor units.
Bridging of terphenyl or dithienylbenzene moieties can suppress
imide containing building unit, such as diketopyrrolopyrrole
(DPP),21,22 isoindigo (IID),23,24 thienopyrroledione (TPD),25,26
bithiopheneimide (BTI),27,28 and naphthalenedicarboximide
(NDI)29–31 (Fig. 2) in semiconducting polymers is also a promising
strategy to offer strong intermolecular interaction and thus good
ordering structure in thin lms. Such good ordering structure in
those polymers is believed to originate in the local dipole of
amide and/or imide substructures,32 as well as in the donor–
acceptor backbone, where they act as the acceptor units.
Recently, Kim and co-workers reported on amide-bridged
dithienylbenzene, 5,11-dihydrothieno[20,30:4,5]pyrido[2,3-g]thieno-
[3,2-c]quinoline-4,10-dione (TPQ, Fig. 3) and its copolymers.33 On
the other hand, Ding and co-workers reported on an isomeric
structure of TPQ, namely, thieno[20,30:5,6]pyrido[3,4-g]thieno[3,2-c]
aDepartment of Applied Chemistry, Graduate School of Engineering, Hiroshima
University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan
bEmergent Molecular Function Research Group, RIKEN Center for Emergent Matter
Science, Wako, Saitama 351-0198, Japan. E-mail: itaru.osaka@riken.jp
cJapan Synchrotron Radiation Research Institute (JASRI), 1-1-1 Kouto, Sayo-cho, Sayo-
gun, Hyogo 679-5198, Japan
† Electronic supplementary information (ESI) available. See DOI:
10.1039/c5ra28140g
Fig. 1 Chemical structures of bridged terthiophene (left) and dithie-
‡ These authors contributed equally.
nylbenzene (right).
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Fig. 2 Chemical structures of amide and imide-based p-building units.
5,10-dione.36 Therefore, we alternatively attempted to prepare
a N,N0-dialkyl-IQP derivative via the route B, where the alkyl
groups were introduced before the formation of the IQP moiety.
1,4-Dibromo-2,5-phenylenediboronate (4) was synthesized from
1,4-dibromobenzene. In the meantime, 5-bromo-2-iodobenzoyl
chloride was treated with 2-decyltetradecan-1-amine to give an
N-alkylbenzamide 5. 4 and 5 were then cross-coupled to afford
the precursor 6, which was then cyclized via the Ullmann-type
reaction, yielding the desired dibrominated monomer (7). 7
was copolymerized with distannylated bithiophene via the Stille
coupling reaction to afford PIQP2T.
Fig. 3 Chemical structures of 5,11-dihydrothieno[20,30:4,5]pyrido[2,3-
g]thieno[3,2-c]quinoline-4,10-dione (TPQ), thieno[20,30:5,6]pyrido
[3,4-g]thieno[3,2-c]isoquinoline-5,11-dione (TPTI), and 6,13-dihy-
droisoquinolino[3,4-b]phenanthridine-5,12-dione (IQP).
Scheme 2 depicts the synthesis of the TPQ monomer and the
corresponding copolymer (PTPQ2T), in which the similar
synthetic protocol to PIQP2T was used. 3-Thiophenecarboxylic
acid was brominated at the 5-position, giving 8, which was
subsequently iodinated at the 2-position (9). 9 was converted
into acid chloride and then treated with 2-decyltetradecan-1-
amine to afford N-alkylthiophenecarboxamide 10. 10 was
cross-coupled with 4 to give 11, which was then cyclized to yield
the TPQ monomer (12). 12 was copolymerized with dis-
tannylated bithiophene to afford PTPQ2T.
isoquinoline-5,11-dione (TPTI, Fig. 3) and its copolymers.34 Inde-
pendently, we have also been investigating a series of amide-
bridged oligoarylenes such as TPQ and 6,13-dihydroisoquinolino
[3,4-b]phenanthridine-5,12-dione (IQP, Fig. 3) where terphenyl is
the platform. Herein, we describe the synthesis of IQP and TPQ
and the corresponding polymers, their properties, thin lm
structures, and OFET and OPV performance. It is interesting to
note that, in contrast to the fact that the most of amide or imide
bridged building units has strong electron decient nature, IQP
and TPQ are found to be “electron-neutral” building units35 when
incorporated in the p-conjugated polymer backbone. Although
TPQ-based polymers were reported to show low eld-effect
Both polymers were soluble in hot chlorinated benzenes.
The number average (Mn) and weight average molecular weight
(Mw), which were determined using the gel permeation chro-
mobilities of around 10ꢀ5 cm2 Vꢀ1 sꢀ1
,
33 the TPQ-based polymer
ꢁ
matography at 140 C, were as follows: Mn ¼ 21.6 kDa, Mw
¼
synthesized in this work exhibited mobilities as high as 0.03 cm2
Vꢀ1 sꢀ1, which was comparable to those for the IQP-based poly-
mer. Furthermore, the both TPQ- and IQP-based polymers were
found to provide high open-circuit voltages (VOCs) of 0.94 V in the
OPV devices.
105.0 kDa for PIQP2T and Mn ¼ 28.0 kDa, Mw ¼ 98.1 kDa for
PTPQ2T (Table 1). The relatively large polydispersity index for
both the polymers is likely due to the relatively low solubility
originating in the strong aggregation, which oen seen in D–A
semiconducting polymers.37,38
Results and discussion
Electronic structures
UV-vis absorption spectra of 7, 12, PIQP2T, and PTPQ2T in the
solution are shown in Fig. 4a. While 7 afforded absorption
Synthesis
Scheme 1 shows the synthetic route to the IQP monomer and the maxima (lmax) at 387 nm and 407 nm, 12 afforded at 407 nm
corresponding polymer (PIQP2T), where bithiophene was used as and 430 nm. This red-shi in 12 can be attributed to the
the co-unit. First, we have attempted to synthesize the IQP enhanced coplanarity as compared to 7, which arise from the
monomer via preparation of IQP (route A). 1 was reacted with 2- difference of the geometry between benzene and thiophene.
iodobenzoic acid methyl ester via the Suzuki–Miyaura cross- The optical band gap (Eg) calculated with the absorption edge
coupling reaction, in which the cross-coupling and cyclization (ledge), was 2.95 eV and 2.81 eV for 7 and 12, respectively. In the
were underwent sequentially in one-pot, yielding IQP. However, polymer solution, PIQP2T provided a spectrum with lmax at 490
alkylation reaction did not afford N,N0-dialkyl-IQP (2), and nm and 517 nm. As similar to the monomer system, PTPQ2T
instead it afforded the lactim tautomer (3) in a moderate yield. provided a red shied spectrum as compared to PIQP2T, with
Similar reaction has been observed for a tetracyclic lactam the lmax at 530 nm and 565 nm. In the polymer thin lm, both
compound, 4,9-dihydro-dithieno[3,2-c:30,20-h][1,5]naphthyridine- polymers provided lmax similar to that in solution. ledge was
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Scheme 1 Synthetic routes to the IQP moieties and the polymer.
estimated to be 550 nm and 613 nm for PIQP2T and PTPQ2T, of PIQP2T and PTPQ2T were 1.02 V and 1.07 V, with which
which corresponds to Eg of 2.25 eV and 2.02 eV, respectively EHOMOs were determined to be ꢀ5.38 eV and ꢀ5.43 eV,
(Table 1).
respectively. ELUMOs of PIQP2T and PTPQ2T were estimated to
Cyclic voltammetry (CV) was used to evaluate the highest be ꢀ3.13 eV and ꢀ3.41 eV, respectively. As a result, in these
occupied molecular orbital (HOMO) energy level (EHOMO) of systems, EHOMO and ELUMO shied upward and downward,
the materials (Fig. 4b). While the measurement of 7 and 12 respectively, by the polymerization (extension of p-conjuga-
was carried out in the solution, the measurement of PIQP2T tion along the backbone), which is similar to the case in TPD
and PTPQ2T was carried out in the thin lm. The onset and thiazolothiazole polymer systems.39 With such variation
oxidation potentials of 7 and 12 against Ag/AgCl were 1.34 V of the EHOMO and ELUMO between the monomers and poly-
and 1.38 V, which correspond to EHOMOs of ꢀ5.70 eV and mers and the fact that the EHOMO and ELUMO were not so
ꢀ5.74 eV, respectively. The lowest unoccupied molecular shallow and deep, respectively, the IQP and TPQ units can be
orbital (LUMO) energy level (ELUMO), estimated by the addi- regarded as “electron-neutral” building units.35 Such pertur-
tion of Eg to EHOMO, were ꢀ2.75 eV and ꢀ2.93 eV for 7 and 12, bation of EHOMO and ELUMO probably due to the fact that both
respectively. This means that TPQ has relatively higher elec- HOMOs and LUMOs are well-delocalized along the backbone
tron affinity than IQP, and the difference in Eg mostly arise (Fig. 4c).
from the difference in ELUMO. The onset oxidation potentials
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Scheme 2 Synthesis of the TPQ-based polymer.
Table 1 Chemical, physicochemical, and optical properties of the polymers
PDIa
lmaxb (nm)
Eg (eV)
EHOMOd (eV)
ELUMO (eV)
c
e
Polymer
Mna (kDa)
Mwa (kDa)
PIQP2T
PTPQ2T
21.6
28.0
105.0
98.1
4.9
3.5
490, 517
530, 565
2.25
2.02
ꢀ5.38
ꢀ5.43
ꢀ3.13
ꢀ3.41
a
b
c
Determined by GPC using polystyrene standard and DCB as the eluent at 140 ꢁC. Absorption maxima in the thin lm. Optical bandgaps
d
e
determined from the absorption onset. HOMO energy levels evaluated by cyclic voltammetry. LUMO energy levels determined by adding the
optical bandgap to the HOMO energy level.
spectra and current density–voltage curves of the devices. The
photovoltaic parameters are summarized in Table 2. Both the
PIQP2T and PTPQ2T-based cells showed the photoresponse up
to slightly longer wavelength region than ledge of the polymer
absorption spectra. Whereas ledge for PIQP2T and PTPQ2T was
550 nm and 613 nm, respectively, as described above, the
photoresponse reaches over 700 nm for both the cells (Fig. 6a).
The photoresponse at longer wavelength region such as 550–
700 nm likely comes from PC61BM. The EQE was around 40–
45% at the region of lmax for both the cells, which reect the
modest short-circuit currents (JSCs) (Fig. 6b, Table 2). Again,
similar power conversion efficiencies (PCEs) such as 2.3%
(PIQP2T) and 2.7% (PTPQ2T) were obtained for these polymer
cells. It should be noted that although the overall PCEs were not
so high, fairly high VOCs of 0.94 V was obtained for both cells.
This is consistent with the relatively deep EHOMO of the poly-
mers. The relatively wide band gap and the very high VOC could
be advantageous for the use as the front cell in tandem
architecture.40,41
OFET properties
OFET devices with PIQP2T and PTPQ2T were fabricated and
evaluated by using a bottom gate top contact architecture.
1H,1H,2H,2H-Peruorodecyltriethoxysilane (FDTS) was used as
the self-assembled monolayer (SAM) on top of the SiO2/Si
substrate, on which the polymer solution in o-dichlorobenzene
(DCB) was spun and then the resulting thin lms were annealed
at 150 ꢁC for 30 minutes. Both polymers demonstrated p-
channel behavior. Fig. 5 shows the typical transfer and output
curves of the OFETs, in which the transfer characteristics were
obtained with the drain voltage (VD) of ꢀ60 V. Although the
output curves showed a slight non-linear behavior at the low VD
region, they gave fairly good saturation behavior at the higher
VD region. The hole mobilities extracted from the saturation
region were similar for both polymers. The highest hole
mobility was 0.037 and 0.027 cm2 Vꢀ1 sꢀ1 for PIQP2T and
PTPQ2T, respectively, and the current on/off ratios were as high
as 106 (Table 2).
OPV properties
Thin lm structure and morphology
OPV cells were fabricated using an inverted architecture with
ZnO as the electron transport layer and MoO3 as the hole The ordering structure of the polymers and polymer/PC71BM
transport layer. The polymer/[6,6]-phenyl-C71-butyric acid blend lms were investigated by the grazing incidence X-ray
methyl ester (PC71BM) solution in DCB with 3 volume% of 1,8- diffraction (GIXD) measurements. Fig. 7a and c displays the
diodooctane (DIO) was spin-coated to form bulk heterojunction two-dimensional (2D) GIXD patterns of the polymer neat lm
thin lms. Fig. 6 displays the external quantum efficiency for PIQP2T and PTPQ2T, respectively. Both the polymers gave
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Fig. 4 (a) UV-vis absorption spectra in the solution (solid lines) and in the film (dot lines). (b) Cyclic voltammograms. 7 and 12 were measured in
benzonitril solution, and PIQP2T and PTPQ2T were measured in thin film. (c) HOMO and LUMO geometries calculated by the DFT method at the
B3LYP/6-31 g (d) level.
˚
diffractions corresponding to the lamellar structure and the p– of ca. 3.7 A. In general, thiophene–thiophene linkage (TPQ–
p stacking structure along the qz and qxy axes, respectively, thiophene) provide smaller dihedral angle than benzene-
indicating the edge-on orientation (Fig. 7a and c). Fig. 7e and f thiophene linkage (IQP–thiophene), and thus is expected to
shows the cross sectional proles of the patterns along the qz give better ordering structure. However, it was found that the
and qxy axes, respectively. It is interesting to note that the p–p ordering structures of PIQP2T and PTPQ2T were fairly similar.
stacking peaks of both PIQP2T and PTPQ2T appeared at qxy
¼
This is probably as a result of strong intermolecular interaction
1.71 Aꢀ1 (indicated by arrows), which corresponds to a distance originating in the amide moiety having a local dipole, which
˚
Fig. 5 Transfer (a) and output (b, c) curves of the OFETs. (b) PIQP2T, (c) PTPQ2T. Transfer curves were obtained with the drain voltage (VD)
of ꢀ60 V.
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Table 2 OFET and OPV properties of the polymer-based devices
OFET
OPV
ma (cm2 Vꢀ1 sꢀ1
)
VTb (V)
Ion/Ioff
JSC (mA cmꢀ2
)
VOC (V)
FF
PCE (%)
c
Polymer
PIQP2T
PTPQ2T
0.037
0.027
ꢀ19.6
ꢀ23.0
106
106
4.7
5.6
0.94
0.94
0.50
0.51
2.3
2.7
Hole mobilities evaluated at the saturation region. b Threshold voltages. c Current on and off ratios.
a
Fig. 6 EQE spectra (a) and J–V curves (b) of the OPV cells using PIQP2T and PTPQ2T combined with PC71BM.
reduces the difference of the steric effect. These results agree due to the strong intermolecular interactions originating in the
well with the charge transport property observed in OFETs. In amide group. With these aspects, IQP and TPQ can be useful p-
the blend lm (Fig. 7b and d), both PIQP2T and PTPQ2T gave building units for semiconducting polymers.
similar patterns to the neat lm, i.e., the backbone orientation
was preserved. The p–p stacking distance was also almost the
same as in the neat lm. The unfavorable orientation for OPV
Experimental section
devices seen in the blend lm could be one of the limiting
factors for the OPV performance. Nevertheless, further modi-
cation of the molecular structure can realize the favorable face-
on orientation, which possibly enhances the OPV performance.
Synthesis
All chemicals and solvents are of reagent grade unless otherwise
indicated. THF, toluene, cyclohexane, and DMF were puried by
a Glass Contour Solvent System (Nikko Hansen & Co., Ltd.) prior
to use. 1 was synthesized according to the literature proce-
dure.42 Polymerization was carried out with a microwave reactor
Conclusion
We have synthesized new semiconducting polymers (PIQP2T (Biotage Initiator). Nuclear magnetic resonance (NMR) spectra
and PTPQ2T) based on amide-bridged terphenyl (IQP) and were obtained in deuterated chloroform and DCB with TMS as
dithienylbenzene (TPQ) building units. These polymers had internal reference by using a JNM-ECS400 (JEOL RESONANCE).
relatively wide band gap of >2.0 eV with deep EHOMOs of ꢀ5.4 eV. Molecular weights were determined by gel permeation
EHOMO and ELUMO similarly shied upward and downward, chromatography (GPC) by calibrating with polystyrene
respectively, by the p-extension from the monomer unit to the standards using a TOSOH HLC-8121GPC/HT at 140 ꢁC with
polymer, which can be ascribed to the delocalized HOMO and DCB as the solvent.
LUMO along the frameworks. These results imply that IQP and
Isoquinolino[3,4-b]phenanthridine-5,12(6H,13H)-dione (IQP).
TPQ can be viewed as electron-neutral building units.35 The 2 (100 mg, 1.8 mmol), methyl 2-bromobenzoate (92.1 mg, 4.46
polymers presented here exhibited similar hole mobilities of mmol), Pd(PPh3)4 (1.4 mg, 0.0012 mol), 1.0 mL of 1 M K2CO3 aq, 1
0.03–0.04 cm2 Vꢀ1 sꢀ1 in the OFET devices. Although the PCEs drop of aliquat 336, and 5 mL of toluene were added to a vial. The
were modest, the OPV devices based on these polymers showed vial was then purged with argon and sealed. The sealed vial was
quite high VOC of 0.94 V, which reects deep EHOMOs of ꢀ5.4 eV. heated at 130 ꢁC for 5 hour in a microwave reactor. Aer cooling
Interestingly, both polymers had similar ordering structures in to room temperature, the reaction mixture was ltered and the
the thin lm despite that the IQP is likely to be more sterically residue was washed with aceton to give the desired compound as
hindered at the end of the moiety than TPQ. This is probably yellow solid (34.0 mg, 62%). HRMS: calcd for C20H13O2N2: [M +
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Fig. 7 2D GIXD patterns (a–d) and cross sectional profiles along the qz (e) and qxy (f) axes. (a) PIQP2T neat film, (b) PIQP2T/PC71BM blend film
(1 : 2), (c) PTPQ2T neat film, (d) PTPQ2T/PC71BM blend film (1 : 2). The arrows in Fig. 6f show the p–p stacking peaks.
H]+: 313.09715. Found: 313.09732. NMR not available due to the 140.2, 134.3, 128.0, 124.5, 123.5, 122.3, 122.1, 120.5, 69.6, 37.8,
insolubility.
5,12-Bis((2-decyltetradecyl)oxy)isoquinolino[3,4-b]phenan-
32.0, 31.9, 30.2, 29.9, 29.5, 27.1, 22.8, 14.3.
2,20-(2,5-Dibromo-1,4-phenylene)bis(4,4,5,5-tetramethyl-1,3,2-
thridine (3). IQP (50.0 mg, 0.16 mmol), 1-bromo-2- dioxaborolane) (4). A mixture of (1,5-cyclooctadiene) (methoxy)
decyltetradecane (267 mg, 0.64 mmol), and K2CO3 (88.0 g, iridium(I) (116 mg, 0.17 mmol), 4,40-di-tert-butyl-2,20-dipyridyl
0.64 mmol) were added in 5 mL of DMF. The mixture was stirred (110 mg, 0.40 mmol) in 150 mL of cyclohexane was reuxed for 30
at 100 ꢁC for 12 hours. The reaction mixture was then cooled to minutes, aer which bis(pinacolato)diboron (11.8 g, 46.6 mmol)
room temperature, and then ltered through Celite. Aer the was added and the mixture was reuxed for 30 minutes. 1,4-
solvent was removed, the residue was puried by column Dibromobenzene (5.00 g, 21.2 mmol) was then added and the
chromatography on silica gel eluted with chloroform/hexane mixture was reuxed for 12 hours. Aer cooling to room
(1 : 2), giving 3 (not 2) as colorless oil (30.0 mg, 19%). HRMS temperature, water was added and the aqueous layer was
calcd for C68H109N2O2 [M + H]+: 985.84890. Found: 985.84887. extracted with chloroform. The organic layer was washed with
1H NMR (400 MHz, CDCl3): d 8.81 (s, 2H), 8.54 (d, 2H, J ¼ 8.4 water and brine, and then dried over anhydrous MgSO4. The
Hz), 8.49 (d, 2H, J ¼ 8.4 Hz), 7.95 (dd, 2H, J ¼ 7.3 Hz), 7.93 (dd, solvent was removed, and the residue was washed with cold
2H, J ¼ 7.5 Hz), 4.60 (d, 4H, J ¼ 5.4 Hz), 3.72 (m, 2H), 1.63–1.24 methanol to give the desired compound as white solid (6.88 g,
(m, 48H), 0.88 (t, 6H, J ¼ 7.2 Hz). 13C NMR (100 MHz, CDCl3): 67%). HRMS: calcd for C18H27O4B2Br2 [M + H]+: 487.04567.
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Found: 487.04532. 1H NMR (400 MHz, CDCl3): d 7.74 (s, 2H), 1.37 136.0, 132.9, 132.6, 131.7, 127.8, 123.5, 123.5, 120.6, 109.8, 46.7,
(s, 24H). 13C NMR (100 MHz, CDCl3): d 140.3, 126.5, 85.0, 25.1.
5-Bromo-N-(2-decyltetradecyl)-2-iodobenzene (5). To a solu-
37.1, 32.3, 32.2, 30.4, 30.1, 30.0, 30.0, 29.7, 27.6, 23.0, 14.5.
5-Bromothiophene-3-carboxylic acid (8). To a solution of
tion of 2-decyltetradecylamine (7.00 g, 19.8 mmol) in 30 mL of thiophene-3-carboxylic acid (2.00 g, mmol) in 20 mL of acetic
pyridine was added 5-bromo-2-iodobenzoyl chloride (5.80 g, acid was added bromine (2.49 g, 15.6 mmol). The mixture was
16.8 mmol) in 20 mL ofꢁdichloromethane at 0 ꢁC. Aer the stirred at room temperature for 30 minutes, and then water was
solution was stirred at 0 C for 30 minutes and then at room added. The precipitate was ltered and recrystallized with hot
temperature for 2 hours, 150 mL of 2 M HCl aq and 100 mL of water to give the desired compound as white solid (1.42 g, 44%).
dichloromethane were added. The organic layer was washed HRMS calcd for C5H2O2BrNa2S [M ꢀ H + 2Na]+: 250.87488.
1
twice with 100 mL of brine and dried over MgSO4. Aer the Found: 250.87491. H NMR (400 MHz, CDCl3): d 8.11 (s, 1H),
solvent was removed, the residue was puried by column 7.51 (s, 1H). 13C NMR (100 MHz, CDCl3): d 167.3, 136.2, 133.4,
chromatography on silica gel with chloroform to give the 130.7, 113.7.
desired compound as white solid (3.54 g, 70%). HRMS calcd for
C
5-Bromo-2-iodothiophene-3-carboxylic acid (9). 8 (1.00 g,
1
31H54ONBrI [M + H]+: 662.24280. Found: 662.24274. H NMR 4.83 mmol), periodic acid (0.33 g, 1.45 mmol), and iodine (0.98
(400 MHz, CDCl3): d 7.69 (d, 1H, J ¼ 6.8 Hz), 7.50 (d, 1H, J ¼ 1.6 g, 3.86 mmol) was added to 30 mL of acetic acid and 15 mL of
Hz), 7.23 (dd, 1H, J ¼ 6.8 Hz, J ¼ 1.5 Hz), 5.70 (s, 1H), 3.39 (dd, water. The mixture was stirred at 80 ꢁC for 9 hours. Aer cooling
2H, J ¼ 4.7 Hz), 1.40–1.20 (m, 40H), 0.88 (t, 6H, J ¼ 5.3 Hz). 13
C
to room temperature, Na2S2O3 aq was added and the resulting
NMR (100 MHz, CDCl3): d 168.3, 144.7, 141.5, 134.4, 1331.6, precipitate was ltered. The residue was washed with water and
123.0, 90.7, 43.7, 38.2, 32.3, 30.3, 30.0, 27.0, 23.1, 14.5.
dried in vacuo to give the desired compound as white solid (1.38
20,4,400,50-Tetrabromo-N,N00-bis(2-decyltetradecyl)-(1,10:40,100- g, 86%). HRMS calcd for C5HO2BrINa2S [M ꢀ H + 2Na]+:
terphenyl)-2,200-dicarboxamide (6). 4 (0.90 g, 1.84 mmol), 5 (2.50 376.77152. Found: 376.77164. 1H NMR (400 MHz, CDCl3): d 7.36
g, 3.77 mmol), and 15 mL of 2 M K2CO3 aq were added in 30 mL (s, 1H). 13C NMR (100 MHz, CDCl3): d 162.2, 142.5, 132.0, 116.9,
of toluene, which was purged with N2 for 30 minutes. Pd(PPh3)4 74.3.
(0.11 mg, 0.09 mmol) and 1 drop of Aliquat 336 was then added,
5-Bromo-N-(2-decyltetradecyl)-2-iodothiophene-3-carboxamide
and the reaction mixture was reuxed for 15 hours. Aer cool- (10). To a solution of 9 (2.17 g, 10.5 mmol) in 20 mL of
ing to room temperature, water was added and the aqueous dichloromethane was added 20 mL of thionyl chloride, and the
layer was extracted with dichloromethane. The organic layer solution was reuxed for 3 hours. The solution was then added to
was washed with water and brine, and then dried over anhy- a solution of 2-decyltetradecyl (4.45 g, 12.6 mmol) in 30 mL of
ꢁ
ꢁ
drous MgSO4. The solvent was removed and the residue was pyridine at 0 C. The reaction solution was stirred at 0 C for 30
purication by column chromatography on silica gel with minutes and then at room temperature for 3 hours. 100 mL of 2 M
chloroform, and was further puried with preparative GPC HCl aq and 100 mL of dichloromethane were added and the
using chloroform as the eluent to give the desired compound as extracted organic layer was washed twice with 100 mL of brine and
white solid (1.28 g, 53%). HRMS calcd for C68H109O2N2Br4 [M + dried over MgSO4. Aer the solvent was removed, the residue was
H]+: 1301.52171. Found: 1301.52368. 1H NMR (400 MHz, puried by column chromatography on silica gel with chloroform
CDCl3): d 7.83 (d, 2H, J ¼ 1.8 Hz), 7.64 (dd, 2H, J ¼ 8.0 Hz), 7.57 to give the desired compound as white solid (4.75 g, 68%). HRMS
(s, 2H), 7.11 (dd, 2H, J ¼ 8.2 Hz), 5.50 (s, 2H), 3.22 (m, 4H), 1.50– calcd for C29H51ONBrINaS [M
+
Na]+: 690.18116. Found:
1.20 (m, 80H), 0.90–0.84 (m, 12H). 13C NMR (100 MHz, CDCl3): 690.18085. 1H NMR (400 MHz, CDCl3): d 7.73 (s, 2H), 7.37 (s, 2H),
d 167.2, 142.2, 138.3, 136.0, 134.8, 133.3, 132.5, 131.6, 123.3, 5.4 (s, 2H), 3.24 (m, 4H), 1.41 (m, 2H), 1.30–1.00 (m, 80H), 0.90–
122.3, 42.9, 38.1, 32.3, 32.1, 30.3, 30.0, 30.0, 29.7, 29.7, 27.0, 0.86 (m, 12H). 13C NMR (100 MHz, CDCl3): d 162.2, 142.5, 132.0,
23.1, 14.5.
3,10-Dibromo-6,13-bis(2-decyltetradecyl)-6,13-dihydroiso-
117.0, 74.3, 43.4, 38.1, 32.3, 30.3, 30.0, 30.0, 30.0, 29.7, 27.0, 23.1.
2,20-(2,5-Dibromo-1,4-phenylene)bis(5-bromo-N-(2-decyl-
quinolino[3,4-b]phenanthridine-5,12-dione (7). 6 (1.00 g, 0.77 tetradecyl)thiophene-3-carboxamide) (11).
5 (0.51 g, 1.03
mmol) CuI(I) (0.073 mg, 0.38 mmol), and K2CO3 (0.26 mg, 1.91 mmol), 11 (1.53 g, 2.27 mmol), and 5 mL of 2 M K2CO3aq were
mmol) were added in 30 mL of DMF. The mixture was stirred at added in 16 mL of toluene, which was purged with N2 for 30
ꢁ
120 C for 12 hours. Aer cooling to room temperature, water minutes. Pd(PPh3)4 (60.0 mg, 0.05 mmol) and 1 drop of Aliquat
was added and the aqueous layer was extracted with chloro- 336 were added, and the mixture was reuxed for 15 hours. Aer
form. The organic layer was washed with water and brine, and cooling to room temperature, water was added and the aqueous
then dried over anhydrous MgSO4. The solvent was removed layer was extracted with dichloromethane. The organic layer
and the residue was puried by column chromatography on was washed with water and brine, and then dried over anhy-
silica gel with hexane/chloroform (1 : 1), and then was recrys- drous MgSO4. The solvent was removed and the residue was
tallized with ethyl acetate/acetone to give the desired compound puried by column chromatography on silica gel with hexane/
as yellow solid (0.87 g, 99%). HRMS calcd for C68H107O2N2Br2 chloroform (1 : 1), and was further puried with preparative
1
[M + H]+: 1141.66938. Found: 1141.67078. H NMR (400 MHz, GPC using chloroform as the eluent to give the desired
CDCl3): d 8.75 (dd, 2H), 8.17 (s, 2H), 8.09 (dd, 2H, J ¼ 8.6 Hz), compound as white solid (0.163 g, 12%). HRMS calcd for C64-
7.88 (dd, 2H, J ¼ 8.6 Hz), 4.50 (s, 4H), 2.07 (s, 2H), 1.50–1.20 (m,
H
105Br4N2O2S2 [M + H]+: 1313.43455. Found: 1313.43652. 1H
80H), 0.90–0.86 (m, 12H). 13C NMR (100 MHz, CDCl3): d 160.5, NMR (400 MHz, CDCl3): d 7.73 (d, 2H), 7.37 (d, 2H), 5.40 (s, 2H),
3.24 (d, 2H), 1.41–0.95 (m, 82H), 0.90–0.86 (m, 12H). 13C NMR
16444 | RSC Adv., 2016, 6, 16437–16447
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(100 MHz, CDCl3): d 162.2, 140.9, 136.9, 136.5, 136.3, 130.8, of a platinum disc working electrode (4 ¼ 3 mm), a platinum
124.1, 113.9, 42.7, 37.7, 32.3, 32.2, 30.4, 30.1, 30.0, 30.0, 29.7, wire counter electrode, and an Ag/AgCl reference electrode
27.0, 23.1, 14.5.
in a acetonitrile containing tetrabutylammonium hexa-
2,8-Dibromo-5,11-bis(2-decyltetradecyl)thieno[20,30:4,5]pyr- uorophosphate (0.1 M) at a scan rate of 100 mV sꢀ1. Polymer
ido[2,3-g]thieno[3,2-c]quinoline-4,10-dione (12). 11 (100 mg, thin lms were cast from DCB solutions on the working elec-
0.076 mmol), CuI(I) (8.0 mg, 0.038 mmol), and K2CO3 (21.0 mg, trode. All the potentials were calibrated with the half-wave
0.15 mmol) wꢁere added to 10 mL of DMF. The mixture was potential of the ferrocene/ferrocenium redox couple measured
stirred at 120 C for 12 hours. Aer cooling to room tempera- under identical condition. UV-vis absorption spectra were
ture, water was added and the aqueous layer was extracted with recorded on a Shimadzu UV-3600 spectrometer. Differential
chloroform. The organic layer was washed with water and brine, scanning calorimetry (DSC) analysis was carried out with an
and then dried over anhydrous MgSO4. The solvent was EXSTAR DSC7020 (SII Nanotechnology, Inc.) at a cooling and
removed and the residue was puried by column chromatog- heating rate of 10 ꢁC minꢀ1. 2D GIXD experiments were con-
raphy on silica gel with hexane/chloroform (1 : 1) and by ducted at SPring-8 on beamline BL19B2. The samples were
˚
preparative GPC using chloroform as the eluent, and then irradiated with an X-ray energy of 12.39 keV (l ¼ 1 A) at a xed
recrystallized with ethyl acetate/chloroform to give the desired incident angle of 0.12ꢁ through a Huber diffractometer, and the
compound as yellow solid (0.062 mg, 82%). HRMS calcd for GIXD patterns were recorded on a 2D image detector (Pilatus
C
64H103Br2N2O2S2 [M + H]+: 1153.58222. Found: 1153.58350. 1H 300K). The polymer thin lms for the GIXD measurement were
NMR (400 MHz, CDCl3): d 7.73 (s, 2H), 7.59 (s, 2H), 4.36 (m, 4H), prepared under the same condition used for the OFET and OPV
1.98 (m, 2H), 2.00 (m, 4H), 1.50–1.20 (m, 80H), 0.90–0.86 (m, fabrication as described below. AFM images were obtained with
12H). 13C NMR (100 MHz, CDCl3): d 157.6, 145.5, 132.6, 132.5, Nanocute scanning probe microscope system (SII Nanotech-
130.2, 118.9, 114.5, 110.3, 46.5, 37.1, 32.3, 30.5, 30.0, 29.7, 27.5, nology, Inc.).
23.1, 14.5.
PIQP2T. 8 (57.2 mg, 0.05 mmol), 5,50-bis(trimethylstannyl)- Fabrication and characterization of OFET devices
2,20-bithiophene (24.6 mg, 0.05 mmol), Pd(PPh3)4 (2.31 mg, 2.0
OFET devices were fabricated in a bottom-gate-top-contact
mmol), and 2 mL of toluene were added to a vial. The vial was then
conguration on a heavily doped n+-Si(100) wafer with 200
purged with Ar and sealed. The sealed vial was heated 180 ꢁC for
nm-thickness thermally grown SiO2 (Ci ¼ 17.3 nF cmꢀ2). The Si/
40 min using a microwave reactor. Aer cooling to room
SiO2 substrates were ultrasonicated with water for three min
temperature, the reaction mixture was precipitated into 100 mL
thrice, and acetone and isopropanol for 5 min, respectively, and
of methanol containing 5 mL of concentrated HCl, and stirred at
rinsed in boiled isopropanol for 10 min, and then were sub-
room temperature for 6 hours. The precipitate was ltered and
jected to UV-ozone treatment for 30 min. The cleaned substrates
were then treated by FDTS as follows. The substrates were le in
subjected to soxhlet extraction with methanol and hexane to
remove low molecular weight fraction. The residue was washed
a Teon container with several drops of FDTS and then the
out with chloroform, which was concentrated and precipitated
into methanol. The precipitate was ltered to give the polymer as
dark orange solid (60.0 mg, 98%). Anal. calcd for C68H107O2N2: C,
74.43; H, 9.37; N, 2.41. Found: C, 74.20; H, 9.21; N, 2.36. GPC
(DCB, 140 ꢁC): Mn ¼ 21.6 kDa, Mw ¼ 105.0 kDa, PDI ¼ 4.9.
PTPQ2T. 13 (57.8 mg, 0.05 mmol), 5,50-bis(trimethylstannyl)-
2,20-bithiophene (24.6 mg, 0.05 mmol), Pd(PPh3)4 (2.31 mg, 2.0
mmol), and 2 mL of toluene were added to a vial. The vial was
then purged with Ar and sealed. The sealed vial was heated 180
ꢁC for 40 min using a microwave reactor. Aer cooling to room
temperature, the reaction mixture was precipitated into 100 mL
of methanol containing 5 mL of concentrated HCl, and stirred
at room temperature for 6 hours. The precipitate was ltered
and subjected to soxhlet extraction with methanol, hexane, and
chloroform to remove low molecular weight fraction. The
residue was washed out with chlorobenzene, which was
concentrated and precipitated into methanol. The precipitate
was ltered to give the polymer as dark red solid (34.0 mg, 59%).
Anal. calcd for C82H113N6S2: C, 79.39; H, 9.82; N, 2.44. Found:
ꢁ
container was heated to 120 C for 2 h in the desiccator. The
FDTS-treated substrates were ultrasonicated with acetone and
isopropanol for 5 min, respectively, and rinsed in boiled iso-
propanol for 10 min. Polymer thin lms were spin-coated from
hot DCB solutions (3 g Lꢀ1) at 1000 rpm for 10 s and then 2500
rpm for 35 s. The polymer lms were annealed at 150 ꢁC for 30
min under nitrogen. On top of the polymer thin lms, gold
drain and source contact electrodes (thickness: 80 nm) with the
channel length and width of 40 mm and 1500 mm, respectively,
were deposited using a vacuum evaporator. Current–voltage
characteristics of the OFET devices were measured at room
temperature under ambient conditions (relative humidity: 30–
40%) with a Keithley 4200-SCS semiconductor parameter
analyzer. Threshold voltages of the devices were estimated from
the transfer plots by extrapolating the square root of the drain
current to the horizontal axis. The eld-effect mobilities were
extracted from the square root of the drain current in the
saturation regime (VD (source–drain current) ¼ ꢀ60 V) by using
the following equation,
ꢁ
GPC (DCB, 140 C): Mn ¼ 28.0 kDa, Mw ¼ 98.1 kDa, PDI ¼ 3.5.
ID ¼(WCi/2L)m(VG ꢀ VT)2
Instrumentation
where L and W are channel length and width, respectively, Ci is
Cyclic voltammograms were recorded on a ALS Electrochemical the capacitance of the SiO2 gate dielectric, ID is the source–drain
Analyzer Model 612D with the three electrode system consisting current, and VG, and VT are the gate, and threshold voltages,
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respectively. The mobilities and threshold voltages were ob-
tained over more than 10 devices.
7 W. Zhang, J. Smith, R. Hamilton, M. Heeney, J. Kirkpatrick,
K. Song, S. E. Watkins, T. Anthopoulos and I. McCulloch, J.
Am. Chem. Soc., 2009, 131, 10814–10815.
8 Q. Zheng, B. J. Jung, J. Sun and H. E. Katz, J. Am. Chem. Soc.,
2010, 132, 5394–5404.
Fabrication and characterization of OPV devices
ITO substrates were pre-cleaned sequentially by sonicating in
a detergent bath, de-ionized water, acetone, and isopropanol at
rt, and in a boiled isopropanol bath, each for 10 min. Then, the
substrates were subjected to UV/ozone treatment at rt for 20
min. The ITO substrates masked at the electrical contacts were
coated with ZnO precursor by spin coating (3000 rpm for 30 s)
a precursor solution prepared by dissolving zinc acetate dehy-
drate (0.5 g) and ethanolamine (0.14 mL) in 5 mL of 2-
9 W. Zhang, J. Smith, S. E. Watkins, R. Gysel, M. McGehee,
A. Salleo, J. Kirkpatrick, S. Ashraf, T. Anthopoulos and
M. Heeney, J. Am. Chem. Soc., 2010, 132, 11437–11439.
10 Y.-C. Chen, C.-Y. Yu, Y.-L. Fan, L.-I. Hung, C.-P. Chen and
C. Ting, Chem. Commun., 2010, 46, 6503–6505.
11 R. S. Ashraf, B. C. Schroeder, H. A. Bronstein, Z. Huang,
S. Thomas, R. J. Kline, C. J. Brabec, P. Rannou,
T. D. Anthopoulos, J. R. Durrant and I. McCulloch, Adv.
Mater., 2013, 25, 2029–2034.
12 Z. Fei, R. S. Ashraf, Z. Huang, J. Smith, R. J. Kline,
P. D'Angelo, T. D. Anthopoulos, J. R. Durrant, I. McCulloch
and M. Heeney, Chem. Commun., 2012, 48, 2955–2957.
13 Y. Li, Y. Wu and B. S. Ong, Macromolecules, 2006, 39, 6521–
6527.
14 J. Lu, F. Liang, N. Drolet, J. Ding, Y. Tao and R. Movileanu,
Chem. Commun., 2008, 5315–5317.
15 J.-H. Tsai, C.-C. Chueh, M.-H. Lai, C.-F. Wang, W.-C. Chen,
B.-T. Ko and C. Ting, Macromolecules, 2009, 42, 1897–
1905.
16 J. E. Donaghey, R. S. Ashraf, Y. Kim, Z. G. Huang,
C. B. Nielsen, W. Zhang, B. Schroeder, C. R. G. Grenier,
C. T. Brown, P. D'Angelo, J. Smith, S. Watkins, K. Song,
T. D. Anthopoulos, J. R. Durrant, C. K. Williams and
I. McCulloch, J. Mater. Chem., 2011, 21, 18744–18752.
17 C.-A. Tseng, J.-S. Wu, T.-Y. Lin, W.-S. Kao, C.-E. Wu,
S.-L. Hsu, Y.-Y. Liao, C.-S. Hsu, H.-Y. Huang, Y.-Z. Hsieh
and Y.-J. Cheng, Chem.–Asian J., 2012, 7, 2102–2110.
18 J.-S. Wu, C.-T. Lin, C.-L. Wang, Y.-J. Cheng and C.-S. Hsu,
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ꢁ
methoxyethanol. They were then baked in air at 200 C for 30
min, then rinsed with acetone and isopropanol, and dried in
a glove box. The active layer was deposited in a glove box by spin
ꢁ
coating hot (100 C) DCB solution containing the polymer and
PC71BM with the weight ratio of 1 : 2 at 600 rpm for 20 s. MoOx
(7.5 nm) and Ag (100 nm) were deposited sequentially by
thermal evaporation under ꢂ10ꢀ5 Pa, where the active area of
the cells was 0.16 cm2. J–V characteristics of the devices were
measured with a Keithley 2400 source measure unit in nitrogen
atmosphere under 1 Sun (AM1.5G) conditions using a solar
simulator (SAN-EI Electric, XES-40S1, 1000 W mꢀ2). The light
intensity for the J–V measurements was calibrated with a refer-
ence PV cell (Konica Minolta AK-100 certied by the National
Institute of Advanced Industrial Science and Technology,
Japan). More than 10 devices were analysed. EQE spectra were
measured with a Spectral Response Measuring System (Soma
Optics, Ltd., S-9241).
Acknowledgements
This work was nancially supported by Grants-in-Aid for
Scientic Research (No. 24685030) from MEXT, Japan. High-
resolution mass spectrometry and elemental analysis was
carried out at the Materials Characterization Support Unit in
RIKEN, Advanced Technology Support Division. GIXD experi-
ments were performed at the BL19B2 of SPring-8 with the
approval of the Japan Synchrotron Radiation Research Institute
(JASRI) (Proposal No. 2013B1719).
19 L. Biniek, B. C. Schroeder, J. E. Donaghey, N. Yaacobi-Gross,
R. S. Ashraf, Y. W. Soon, C. B. Nielsen, J. R. Durrant,
T. D. Anthopoulos and I. McCulloch, Macromolecules, 2013,
46, 727–735.
20 I. McCulloch, R. S. Ashraf, L. Biniek, H. Bronstein,
C. Combe, J. E. Donaghey, D. I. James, C. B. Nielsen,
B. C. Schroeder and W. Zhang, Acc. Chem. Res., 2012, 45,
714–722.
21 M. M. Wienk, M. Turbiez, J. Gilot and R. A. J. Janssen, Adv.
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