Reactive polythiophenes with zincke salt structure: Synthesis, polymer reactions, and chemical properties

Article abstract of DOI:10.1002/pola.26120

Polythiophenes with reactive Zincke salt structure, such as PThThPy ⁺DNP(Cl^-)Th, were synthesized by the oxidation polymerization of 3'-(4-N-(2,4-dinitrophenyl)pyridinium chloride)-2,2':5', 2″-terthiophene (ThThPy⁺DNP(Cl^-)Th) with iron(III) chloride or copper(II) trifluoromethanesulfonate. The reaction of PThThPy ⁺DNP(Cl^-)Th with R-NH₂ (R = n-hexyl (Hex) and phenyl (Ph)) substituted the 2,4-dinitrophenyl group into the R group with the elimination of 2,4-dinitroaniline to yield PThThPy⁺R(Cl ^-)Th. Similarly, model compounds, ThThPy⁺R(Cl ^-)Th (R = Hex and Ph), were also synthesized. In contrast to the photoluminescent ThThPyTh and PThThPyTh, the compounds PThThPy ⁺DNP(Cl^-)Th, PThThPy⁺R(Cl^-)Th, and ThThPy⁺R(Cl^-)Th showed no photoluminescence because their internal pyridinium rings acted as quenchers. Cyclic voltammetry measurements suggested that PThThPy⁺DNP(Cl^-)Th received an electrochemical reduction of the pyridinium and 2,4-dinitrophenyl groups and oxidation of the polymer backbone. PThThPy⁺DNP(Cl^-)Th was electrically conductive (ρ = 2.0 × 10^-6 S cm^-1) in the non-doped state.

Full text of DOI:10.1002/pola.26120

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Reactive Polythiophenes with Zincke Salt Structure: Synthesis, Polymer
Reactions, and Chemical Properties
Isao Yamaguchi, Takuya Nakahara
Department of Material Science, Faculty of Science and Engineering, Shimane University, 1060 Nishikawatsu,
Matsue 690-8504, Japan
Correspondence to: I. Yamaguchi (E-mail: iyamaguchi@riko.shimane-u.ac.jp)
Received 16 March 2012; accepted 19 April 2012; published online
DOI: 10.1002/pola.26120
ABSTRACT: Polythiophenes with reactive Zincke salt structure,
such as PThThPyþDNP(Clꢀ)Th, were synthesized by the oxida-
tion polymerization of 30-(4-N-(2,4-dinitrophenyl)pyridinium
ThThPyþR(Clꢀ)Th showed no photoluminescence because their
internal pyridinium rings acted as quenchers. Cyclic voltamme-
try measurements suggested that PThThPyþDNP(Clꢀ)Th
received an electrochemical reduction of the pyridinium and
2,4-dinitrophenyl groups and oxidation of the polymer back-
bone. PThThPyþDNP(Clꢀ)Th was electrically conductive (q ¼
chloride)-2,20:50,200-terthiophene
iron(III) chloride or copper(II) trifluoromethanesulfonate. The
reaction of PThThPyþDNP(Clꢀ)Th with R-NH2 (R
n-hexyl
(ThThPyþDNP(Clꢀ)Th)
with
¼
2.0 ꢁ 10ꢀ6 S cmꢀ1) in the non-doped state. 2012 Wiley Peri-
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(Hex) and phenyl (Ph)) substituted the 2,4-dinitrophenyl group
into the R group with the elimination of 2,4-dinitroaniline to
yield PThThPyþR(Clꢀ)Th. Similarly, model compounds,
ThThPyþR(Clꢀ)Th (R ¼ Hex and Ph), were also synthesized. In
contrast to the photoluminescent ThThPyTh and PThThPyTh,
the compounds PThThPyþDNP(Clꢀ)Th, PThThPyþR(Clꢀ)Th, and
KEYWORDS: conjugated polymers; electrochemistry; reactive
polythiophene; Zincke salt
INTRODUCTION Poly(thiophene-2,5-diyl)s (PThs) have been
extensively studied because of their interesting chemical
properties and practical applications.1–4 PRThs with substitu-
ents (R) on the thiophene ring have attracted considerable
attention because they exhibit high solubility in organic sol-
vents and have unique solid-state structures.5–35 For exam-
ple, regioregular PRThs (where R is a long alkyl chain) cause
p-stacking between the polymer chains to form ordered
structures in the solid state or in films, which results in high
electric conductivity and carrier ion mobility.32,33 These
properties allow the use of PRThs for the development of
electroluminescence, field-effect transistors, and solar cell
devices. Furthermore, PRThs (R ¼ (CH2)mSO3H) with an
alkylsulfonic acid group exhibit a self-doping nature.36–40
These characteristic properties of PRThs depend on the
structure of the side chain groups. In other words, the chem-
ical properties of PRThs can be easily modulated by chang-
ing the side chain group. To obtain PRThs, the corresponding
RTh monomers should be synthesized and polymerized. Usu-
ally, such reactions require transition-metal complex cata-
lysts. The use of transition-metal complexes is a disadvant-
age in terms of cost, safety, and environmental concerns. In
this study, we designed reactive PRThs that can be converted
into various PR0Ths derivatives through simple polymer reac-
tions without the use of transition-metal complexes.
It is well known that N-(2,4-dinitrophenyl)pyridinium chlor-
ides, the so-called Zincke salts, react with primary amines to
yield N-substituted pyridinium compounds.41–49 Recently, we
reported the synthesis of various Zincke salts, and some of
them were used as starting materials for the synthesis of
functional aromatic compounds and p-conjugated poly-
mers.50–58 Based on these reports, PRThs (R ¼ PyþDNP(Clꢀ),
where Pyþ ¼ pyridinium, and DNP ¼ 2,4-dinitrophenyl)
with a reactive N-(2,4-dinitrophenyl)pyridinium chloride unit
bonded to the Th ring are promising materials as reactive
PRThs. In this study, 30-(4-N-(2,4-dinitrophenyl)pyridinium
chloride)-2,20:50,200-terthiophene (ThThPyþDNP(Clꢀ)Th) was
synthesized as a monomer and polymerized with iron (III)
chloride or copper(II) trifluoromethanesulfonate. The result-
ing PThThPyþDNP(Clꢀ)Th reacted with both aromatic and
aliphatic amines (RANH2) to yield PThThPyþR(Clꢀ)Th. This
reactivity promises to offer high synthetic flexibility for the
generation of a large number of PTh derivatives.
Herein, we report the synthesis of ThThPyþDNP(Clꢀ)Th,
PThThPyþDNP(Clꢀ)Th, and PThThPyþR(Clꢀ)Th (R ¼ n-
hexyl (Hex) and phenyl (Ph)) through the polymer reactions
and their optical, electrochemical, and electric properties. In
addition, the model compounds ThThPyþR(Clꢀ)Th (R ¼
Hex and Ph) and a polymer without a Zincke structure,
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PThThPyTh, were synthesized for comparison with the cor-
responding PThThPyþR(Clꢀ)Th. This is the first report on
the synthesis, chemical properties, and polymer reactions of
PThs with a reactive Zincke salt structure.
was washed with acetone, collected by filtration, and dried
under vacuum to give ThThPyþDNP(Clꢀ)Th as a reddish or-
ange powder (0.17 g). The solvent of the filtrate was
removed by evaporation. The resulting solid was washed
with acetone, collected by filtration, and dried under vacuum
to give ThThPyþDNP(Clꢀ)Th (0.11 g). After the filtration
was further refluxed for 12 h, the solvent was removed by
evaporation. The resulting solid was recrystallized from chlo-
roform, collected by filtration, and dried under vacuum to
give ThThPyþDNP(Clꢀ)Th (0.14 g). The total yield of
ThThPyþDNP(Clꢀ)Th was 85%. 1H NMR (400 MHz, DMSO-
d6, d, ppm): 9.29 (d, J ¼ 6.8 Hz, 2H), 9.13 (d, J ¼ 2.4 Hz,
1H), 8.98 (dd, J ¼ 2.4 and 8.8 Hz, 1H), 8.43 (d, J ¼ 8.8 Hz,
1H), 8.39 (d, J ¼ 6.8 Hz, 2H), 7.81 (s, 1H), 7.82 (d, J ¼ 4.8
Hz, 1H), 7.67 (d, J ¼ 4.8 Hz, 1H), 7.52 (d, J ¼ 2.4 Hz, 1H),
7.33 (d, J ¼ 2.4 Hz, 1H), 7.18-7.22 (m, 2H). 13C NMR (100
MHz, DMSO-d6, d, ppm): 153.0, 149.1, 145.7, 143.2, 138.5,
137.5, 136.6, 134.4, 133.0, 132.0, 131.9, 130.2, 129.9, 129.4,
128.9, 128.7, 127.3, 126.5, 126.0, 125.8, 121.5. Calcd for
EXPERIMENTAL
General
Solvents were dried, distilled, and stored under nitrogen.
2,5-Di(2-thienyl)-3-bromothiophene and 4-(3-thienyl)pyri-
dine were synthesized according to the reported manner.59
Other reagents were purchased and used without further pu-
rification. Reactions were carried out with standard Schlenk
techniques under nitrogen.
IR and NMR spectra were recorded on a JASCO FT/IR-660
PLUS spectrophotometer with a KBr pellet and JEOL AL-400
and ECX-500 spectrometers, respectively. Elemental analysis
was conducted on a Yanagimoto MT-5 CHN corder. Gel per-
meation chromatography (GPC) analyses were carried out by
a Toso HLC 8020 with polystyrene gel columns (TSKgel
G2000HHR and TSKgel GMHHR-M) using a N,N-dimethylfor-
mamide (DMF) solution of LiBr (0.006 M) as an eluent with
RI and UV detectors. UV–vis and photoluminescence (PL)
spectra were obtained by a JASCO V-560 spectrometer and a
JASCO FP-6200, respectively. Quantum yields were calculated
by using a diluted ethanol solution of 7-dimethylamino-4-
methylcoumarin as the standard. Cyclic voltammetry was
performed in a dimethyl sulfoxide (DMSO) solution contain-
ing 0.10 M [Et4N]BF4 with a Hokuto Denko HSV-110. Electric
conductivity measurements were conducted on the molded
pellets of the polymers by an Advantest R8340A ultra high
resistance meter with a two-probe method.
C
23H14ClN3O4S3 ꢂ 1.2H2O: C, 50.26; H, 3.01; N, 7.65. Found:
C, 50.14; H, 3.11; N, 7.34.
Synthesis of ThPy1DNP(Cl2)
ThPyþDNP(Clꢀ) was synthesized by the reaction of ThPy
with 1-chloro-2,4-dinitrophenylbenzene in a similar manner.
Data of ThPyþDNP(Clꢀ)
1
Yield ¼ 57%. H NMR (400 MHz, DMSO-d6, d, ppm): 9.32 (d,
J ¼ 6.4 Hz, 2H), 9.14 (d, J ¼ 2.4 Hz, 1H), 9.01 (d, J ¼ 2.0 Hz,
1H), 8.98 (dd, J ¼ 2.8 and 8.8 Hz, 1H), 8.75 (d, J ¼ 6.8 Hz,
1H), 8.42 (d, J ¼ 8.4 Hz, 1H), 8.09 (dd, J ¼ 1.4 and 5.2 Hz,
1H), 7.95 (dd, J ¼ 2.8 and 5.2 Hz, 1H). 13C NMR (125 MHz,
DMSO-d6, d, ppm): 151.4, 149.0, 145.8, 143.2, 138.5, 135.7,
133.4, 132.1, 130.2, 129.8, 126.7, 123.0, 121.4. Calcd for
Synthesis of ThThPyTh
C
15H10ClN3O4S ꢂ H2O: C, 47.19; H, 3.17; N, 11.01. Found: C,
2,5-Di(2-thienyl)-3-bromothiophene (1.33 g, 4.1 mmol) and
4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)pyridine (0.83
g, 4.1 mmol) were dissolved in 15 mL of dry THF under N2.
K2CO3(aq) (2.0 M, 6 mL; N2 bubbled before use) and
Pd(PPh3)4 (0.47 g, 0.41 mmol) were added to the solution.
After the mixture was refluxed for 60 h, the precipitate from
the reaction solution was removed by filtration and the sol-
vent of the filtrate was removed under vacuum. The result-
ing solid was purified by silica gel column chromatography
(eluent ¼ CHCl3). The solvent was removed by evaporation,
a resulting solid was recrystallized from chloroform, and
dried in vacuo to give ThThPyTh as a yellow crystal (0.50 g,
47.50; H, 3.21; N, 11.36.
Synthesis of PThThPy1DNP(Cl2)Th-a
ThThPyþDNP(Clꢀ)Th (0.24 g, 0.50 mmol) and FeCl3
(0.32 g, 2.0 mmol) were dissolved in dry acetonitrile (25
mL). After the reaction solution was stirred in an ice bath
for 62 h, the solvent was removed by evaporation.
The resulting solid was extracted with acetone and the sol-
vent was removed by evaporation. The resulting solid was
washed with water, diethyl ether, and chloroform until the
filtrate became colorless and dried under vacuum to give
PThThPyþDNP(Clꢀ)Th-a as a black powder (0.11 g, 43%).
1H NMR (500 MHz, DMSO-d6, d, ppm): 9.32–9.49 (2H), 9.13
(1H), 9.00 (1H), 8.32–8.52 (3H), 7.98 (0.55H), 7.86 (0.11H),
7.84 (0.45H), 7.65 (0.11H), 7.57 (1H), 7.49 (1H), 7.35 (1H),
7.22 (1H). Calcd for C23H12ClN3O4S3 ꢂ 1.5H2O: C, 49.95; H,
2.73; N, 7.60. Found: C, 50.21; H, 3.03; N, 7.99.
1
38%). H NMR (400 MHz, DMSO-d6, d, ppm): 8.46 (d, J ¼ 6.0
Hz, 2H), 7.37–7.39 (m, 2H), 7.25–7.27 (m, 4H), 7.00 (dd, J ¼
3.6 and 5.0 Hz, 1H), 6.98 (d, J ¼ 7.2 Hz, 1H), 6.94 (dd, J ¼
3.6 and 5.4 Hz, 1H). 13C NMR (125 MHz, DMSO-d6, d, ppm):
150.0, 143.6, 136.8, 136.5, 136.2, 134.4, 131.8, 128.0, 127.6,
127.4, 126.7, 125.7, 125.1, 124.3, 123.8. Calcd for C17H11NS3:
C, 62.73; H, 3.41; N, 4.30. Found: C, 62.32; H, 3.67; N, 4.31.
Synthesisþof PThThPy1DNP(Cl2)Th-b
ꢀ
ꢃ
PThThPy DNP(Cl )Th-b was synthesized at 20 C in a sim-
Synthesis of ThThPy1DNP(Cl2)Th
ilar manner.
ThThPyTh (0.53 g, 1.5 mmol) and 1-chloro-2,4-dinitrophe-
nylbenzene (0.30 g, 1.5 mmol) were dissolved in dry ethanol
(50 mL). After the reaction solution was refluxed for 39 h,
the solvent was removed by evaporation. The resulting solid
Data of PThThPyþDNP(Clꢀ)Th-b
Yield ¼ 64%. 1H NMR (500 MHz, DMSO-d6, d, ppm): 9.33–
9.50 (2H), 9.14 (1H), 9.00 (1H), 8.33–8.54 (3H), 8.00
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SCHEME 1 Synthesis of monomers.
(0.55H), 7.90 (0.26H), 7.84 (0.45H), 7.68 (0.26H), 7.57 (1H),
7.50 (1H), 7.36 (1H), 7.22 (1H). Calcd for C23H12ClN3O4S3
1.5H2O: C, 49.95; H, 2.73; N, 7.60. Found: C, 49.53; H, 2.65;
N, 7.51.
Data of PThThPyþHex(Clꢀ)Th
ꢂ
Yield ¼ 85%. 1H NMR (500 MHz, DMSO-d6, d, ppm): 9.23
(0.3H), 9.08 (1.7H), 8.24–8.32 (2H), 7.11–7.82 (5H), 4.67
(0.55H), 4.58 (1.45H), 1.93 (2H), 1.29 (6H), 0.85 (3H). Calcd
for C23H22ClNS3 ꢂ H2O: C, 59.78; H, 5.24; N, 3.03. Found: C,
59.65; H, 4.90; N, 2.88.
Synthesis of PThThPy1DNP(Cl2)Th-c
ThThPyþDNP(Clꢀ)Th (0.30 g, 0.57 mmol) and Cu(CF3SO3)2
(0.82 g, 2.3 mmol) were dissolved in dry acetonitrile (25
mL). After the reaction solution was stirred in an ice bath
for 60 h, the resulting precipitate was filtered off. The sol-
vent of the filtrate was removed by evaporation and result-
ing solid was washed with acetonitrile until the filtrate
became colorless. The acetonitrile insoluble part was col-
lected by filtration and dried under vacuum to give
PThThPyþDNP(Clꢀ)Th-c as a black powder (0.23 g, 79%).
1H NMR (500 MHz, DMSO-d6, d, ppm): 9.49 (0.35H), 9.35
(1.65H), 9.14 (1H), 9.01 (d, J ¼ 8.5 Hz, 1H), 8.45–8.57 (3H),
7.17–8.21 (5H). Calcd for C23H12ClN3O4S3 ꢂ H2O: C, 50.78; H,
2.59; N, 7.72. Found: C, 50.53; H, 2.18; N, 8.15.
Synthesis of ThThPy1Ph(Cl2)Th
After an ethanol (20 mL) solution of ThThPyþPh(Clꢀ)Th
(0.10 g, 0.19 mmol) and aniline (25 mg, 0.28 mmol) was
refluxed for 12 h, the solvent was removed by evaporation.
The resulting solid was washed with water and chloroform,
collected by filtration, and dried under vacuum to give
ThThPyþPh(Clꢀ)Th as an orange powder (19 mg, 56%). H
1
NMR (400 MHz, DMSO-d6, d, ppm): 9.30 (d, J ¼ 7.2 Hz, 2H),
8.27 (d, J ¼ 6.8 Hz, 2H), 7.88–7.90 (m, 2H), 7.86 (s, 1H),
7.81 (d, J ¼ 4.8 Hz, 1H), 7.74–7.76 (m, 3H), 7.68 (d, J ¼ 5.2
Hz, 1H), 7.51 (d, J ¼ 3.6 Hz, 1H), 7.34 (d, J ¼ 2.8 Hz, 1H),
7.18–7.21 (m, 2H). 13C NMR (125 MHz, DMSO-d6, d, ppm):
151.1, 144.6, 142.3, 137.3, 135.8, 134.5, 133.0, 131.9, 131.2,
130.2, 129.7, 129.4, 128.9, 128.7, 127.2, 126.6, 126.1, 125.7,
124.6. Calcd for C23H16ClNS3 ꢂ 0.3H2O: C, 62.30; H, 3.77; N,
3.16. Found: C, 62.50; H, 3.79; N, 2.81.
Synthesisþof PThThPy1DNP(Cl2)Th-d
ꢀ
ꢃ
PThThPy DNP(Cl )Th-d was synthesized at 20 C in a sim-
ilar manner.
Data of PThThPyþDNP(Clꢀ)Th-d
Yield ¼ 58%. 1H NMR (500 MHz, DMSO-d6, d, ppm): 9.51
(1H), 9.36 (1H), 9.15 (1H), 9.02 (1H), 8.46–8.57 (3H), 7.24–
7.97 (5H). Calcd for C23H12ClN3O4S3 ꢂ H2O: C, 50.78; H, 2.59;
N, 7.72. Found: C, 50.33; H, 2.20; N, 7.29.
Synthesis of ThThPy1Hex(Cl2)Th
After an EtOH (3 mL) solution of ThThPyþPh(Clꢀ)Th
(0.10 g, 0.19 mmol) and n-hexylamine (29 mg, 0.28 mmol)
was refluxed for 12 h, the solvent was removed by evapora-
tion. The resulting paste was washed with cold ether,
collected by filtration, and dried under vacuum to give
ThThPyþHex(Clꢀ)Th as a yellow powder (55 mg, 65%). 1H
NMR (400 MHz, DMSO-d6, d, ppm): 9.03 (d, J ¼ 6.4 Hz, 2H),
8.13 (d, J ¼ 6.8 Hz, 2H), 7.74–7.76 (m, 2H), 7.65 (d, J ¼ 5.2
Hz, 1H), 7.47 (d, J ¼ 3.2 Hz, 1H), 7.26 (d, J ¼ 3.2 Hz, 1H),
7.15–7.18 (m, 2H), 4.54 (t, J ¼ 7.6 Hz, 2H), 1.91 (m, 2H),
1.28 (s, 6H), 0.87 (t, J ¼ 7.2 Hz, 3H). 13C NMR (125 MHz,
DMSO-d6, d, ppm): 150.2, 144.5, 137.0, 134.7, 134.4, 133.3,
131.9, 129.3, 129.0, 128.6, 128.5, 127.0, 126.9, 125.9, 125.5,
60.0, 30.4, 24.9, 21.7, 13.7. Calcd for C23H24ClNS3 ꢂ 0.2H2O:
C, 61.43; H, 5.47; N, 3.11. Found: C, 61.34; H, 5.31; N, 2.89.
Synthesis of PThThPy1Ph(Cl2)Th
After a DMSO (2 mL) solution of PThThPyþPh(Clꢀ)Th (40
mg, 0.076 mmol) and aniline (0.011 g, 0.11 mmol) was
stirred at 90 ꢃC for 12 h, the solvent was removed under
vacuum. The resulting solid was washed with acetone, col-
lected by filtration, and dried under vacuum to give
PThThPyþPh(Clꢀ)Th as a black powder (0.019 g, 56%). 1H
NMR (500 MHz, DMSO-d6, d, ppm): 9.50 (0.6H), 9.36 (1.4H),
8.38–8.44 (2H), 8.00 (1H), 7.90 (2H), 7.76 (3H), 7.20–7.56
(4H). Calcd for C23H14ClNS3 ꢂ 1.2H2O: C, 60.36; H, 3.61; N,
3.06. Found: C, 60.45; H, 3.39; N, 2.87.
Synthesis of PThThPy1Hex(Cl2)Th
PThThPyþHex(Clꢀ)Th was synthesized in a similar manner.
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SCHEME 2 Synthesis of PThThPyþDNP(Clꢀ)Th and PThThPyTh.
RESULTS AND DISCUSSION
RANH2 (Scheme 4). The synthesis results are summarized in
Table 1.
Synthesis
PThThPyþDNP(Clꢀ)Th-a, PThThPyþDNP(Clꢀ)Th-b, PThThPyþ-
DNP(Clꢀ)Th-c, PThThPyþDNP(Clꢀ)Th-d, and PThThPyþR(Clꢀ)-
Th (R ¼ Ph and Hex) were soluble in polar organic solvents
such as DMF and DMSO, but were insoluble in non-polar or-
ganic solvents such as chloroform and toluene. These solu-
bilities are in contrast to those of PRThs (R ¼ alkyl chain)
that are soluble in non-polar organic solvents such as chlo-
roform and toluene but insoluble in polar organic solvents.
The difference in solubility is attributed to the presence
of the polar PyþDNP pendant group in PThThPyþ-
DNP(Clꢀ)Th. On the other hand, PThThPyTh was partly
soluble in DMF and DMSO probably due to its structural ri-
gidity. However, UV–vis and PL measurements of the DMSO
solution component of PThThPyTh were possible (vide
infra). The monomers and model compounds were soluble
in water and organic solvents such as chloroform, DMF, and
DMSO.
The monomers, 3-(4-N-(2,4-dinitrophenyl)pyridinium chlori-
de)thiophene (ThPyþDNP(Clꢀ)) and ThThDNP(Clꢀ)Th, were
synthesized through the reaction of 4-(3-thienyl)pyridine
(ThPy) and 40-(4-pyridyl)-2,20:50,200-terthiophene (ThThPyTh),
which were synthesized by Pd-catalyzed coupling reactions,
with 1-chloro-2,4-dinitrobenzene (Scheme 1).
PThPyþDNP(Clꢀ) could not be obtained from either oxida-
tive polymerizations by treating ThPyþDNP(Clꢀ) with FeCl3
or by applying positive potential. This result can be possibly
attributed to the presence of an electron-withdrawing
PyþDNP group bonded to the thiophene ring. On treating
ThThPyþDNP(Clꢀ)Th with FeCl3 at 0 ꢃC and 20 ꢃC yielded
PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP(Clꢀ)Th-b in
43% and 64% yields, respectively [Scheme 2(a)]. The lower
yield of PThThPyþDNP(Clꢀ)Th-a is similar to that reported
for PHexTh obtained from the oxidation polymerization of
3-hexylthiophene with FeCl3 at 0 ꢃC that is lower than
that at room temperature.58 PThThPyþDNP(Clꢀ)Th-c and
PThThPyþDNP(Clꢀ)Th-d were obtained by treating
ThThPyþDNP(Clꢀ)Th with copper(II) trifluoromethanesulfo-
The Mn and Mw values of the obtained polymers were
determined by GPC measurements and are summarized
in Table 1. The Mn values of the DMF solutions of
PThThPyþDNP(Clꢀ)Th-a, PThThPyþDNP(Clꢀ)Th-b, PTh-
ThPyþDNP(Clꢀ)Th-c, and PThThPyþDNP(Clꢀ)Th-d were
5,690, 3,190, 5,820, and 2,660, respectively. The higher
Mn values of PThThPyþDNP(Clꢀ)Th-a and PThThPyþ-
DNP(Clꢀ)Th-c as compared with PThThPyþDNP(Clꢀ)Th-b
and PThThPyþDNP(Clꢀ)Th-d correspond to a previous
report that the Mn value of PHexTh obtained from the oxida-
tion polymerization of 3-hexylthiophene at 0 ꢃC is higher
than that obtained at room temperature.60
ꢃ
ꢃ
nate at 0 C and 20 C in 79% and 58% yields, respectively
[Scheme 2(a)]. PThThPyTh was synthesized using the same
procedure with FeCl3 to compare the chemical properties
with PThThPyþDNP(Clꢀ)Th [Scheme 2(b)].
PThThPyþDNP(Clꢀ)Th-c was converted to PThThPyþ-
R(Clꢀ)Th (R ¼ Ph and Hex) by reaction with RANH2 in
refluxing ethanol (Scheme 3). Model compounds
ThThPyþR(Clꢀ)Th (R ¼ Ph and Hex) were synthesized by
the analogous reactions of ThThPyþDNP(Clꢀ)Th with
SCHEME 3 Polymer reactions of PThThPyþDNP(Clꢀ)Th with
amines.
SCHEME 4 Synthesis of model compounds.
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spectrum of PThThPyþDNP(Clꢀ)Th-a was attributed to po-
lymerization at the thiophene rings. Absorption correspond-
ing to the symmetric and asymmetric stretching vibrations
of the NO2 groups disappeared in the IR spectra of
PThThPyþPh(Clꢀ)Th and PThThPyþHex(Clꢀ)Th. Further-
more, instead of the stretching vibrations corresponding to
the NO2 group, new absorption peaks corresponding to the
stretching vibration of the CAH bonds of the hexyl group
appears at 2862 cmꢀ1, 2931 cmꢀ1, and 2954 cmꢀ1 in the IR
spectrum of PThThPyþHex(Clꢀ)Th. The presence of peaks
corresponding to m(OAH) around 3400 cmꢀ1 in the IR spec-
tra of the polymers suggests that they contain hydrated
water molecule(s). This view is supported by the elemental
analysis.
Figure
2
shows the 1H NMR spectra of ThThPyþ-
DNP(Clꢀ)Th, PThThPyþDNP(Clꢀ)Th-a, PThThPyþDNP-
(Clꢀ)Th-b, and PThThPyþDNP(Clꢀ)Th-c in DMSO-d6. The
peak assignments are indicated in the figure. The peaks cor-
responding to the DNP protons (H8–H10) of the polymers are
observed at almost the same positions as those of the mono-
mer. However, the two peaks corresponding to the protoꢀn
3
þ
0
(H ) of the thiophene ring bonded to the Py (DNP)Cl
group are observed at d 7.85 and 8.00 in the 1H NMR spec-
tra of PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP-
(Clꢀ)Th-b. This observation is attributed to the presence of
the head-to-tail (HT) and head-to-head (HH) linkages in the
main chain (Chart 1).
It has been reported that poly(3-alkylthiophene-2,5-diyl)s
obtained from the oxidation polymerization with FeCl3 ex-
hibit several peaks corresponding to the thiophene proton in
the HT and HH linkages.13,60 The amount of HT and HH link-
ages in PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP-
(Clꢀ)Th-b were estimated to be 0.45:0.55 and 0.55:0.45,
respectively, from the integral ratio of the peaks at d 7.85
FIGURE 1 IR spectra of (a) ThThPyþDNP(Clꢀ)Th, (b) PThThPyþ-
DNP(Clꢀ)Th-a, (c) PThThPyþPh(Clꢀ)Th, and (d) PThThPyþ-
Hex(Clꢀ)Th.
The reduced viscosities (gsp/c) of PThThPyþDNP(Clꢀ)Th-a
and PThThPyþDNP(Clꢀ)Th-b in DMSO were 0.13 and 0.10
gꢀ1 dL (c ¼ 0.10 g dLꢀ1), respectively. The gsp/c values of
the polymers in DMSO increased when their concentration c
was reduced. The gsp/c value of PThThPyþDNP(Clꢀ)Th-a
changes from 0.13 gꢀ1 dL (c ¼ 0.10 g dLꢀ1) to 0.57 gꢀ1 dL
(c ¼ 0.056 g dLꢀ1) through to a value of 0.32 gꢀ1 dL (c ¼
0.070 g dLꢀ1). These results suggest that the polymers
behave as polymeric electrolytes in dilute solutions.61
and 8.00. The peaks corresponding to the terminal protons
00
(H5 and H5 ) decreased in the 1H NMR spectra of
PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP(Clꢀ)Th-b.
The peaks at d 7.68 and 7.90 in the 1H NMR spectra of
PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP(Clꢀ)Th-b are
assigned to the terminal protons of the polymers. The peak
integral ratio between the protons corresponding to
the polymer main chain and the terminal protons suggests
that the degree of polymerization (DP) values of
PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP(Clꢀ)Th-b are
1
IR and H NMR Spectra
9
and 4, respectively. The molecular weights of
Figure 1 shows the IR spectra of ThThPyþDNP(Clꢀ)Th,
PThThPyþDNP(Clꢀ)Th-a, PThThPyþPh(Clꢀ)Th, and PTh-
ThPyþHex(Clꢀ)Th.
PThThPyþDNP(Clꢀ)Th-a and PThThPyþDNP(Clꢀ)Th-b
calculated from the DP values are 4,590 and 2,040, res-
pectively. These values are largely consistent with the Mn
values determined by GPC. The 1H NMR spectra of
PThThPyþDNP(Clꢀ)Th-c and PThThPyþDNP(Clꢀ)Th-d
exhibited complex signals corresponding to the thiophene
protons. The DP values of PThThPyþDNP(Clꢀ)Th-c and
PThThPyþDNP(Clꢀ)Th-d could not be determined from
their 1H NMR spectra because the peaks corresponding
to the terminal thiophene protons were ambiguous. How-
ever, the content of the HT and HH linkages in
PThThPyþDNP(Clꢀ)Th-c could be estimated from the 1H
The absorption peaks corresponding to the symmetric and
asymmetric stretching vibrations of the NO2 groups were
observed at 1342 cmꢀ1 and 1543 cmꢀ1 in the IR spectra
of ThThPyþDNP(Clꢀ)Th and PThThPyþDNP(Clꢀ)Th-a,
respectively. The IR spectrum of ThThPyþDNP(Clꢀ)Th
showed an absorption peak corresponding to the out-of-
plane bending vibrations of the thiophene rings at 835 cmꢀ1
.
The decrease in absorption corresponding to the out-of-
plane bending vibrations of the thiophene rings in the IR
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CHART 1 HT and HT linkages in the PRTh main chain.
PThThPyþDNP(Clꢀ)Th with aniline or n-hexylamine pro-
ceeded to completion. The observation that the peak corre-
sponding to the b-protons of the pyridinium ring of
ThThPyþPh(Clꢀ)Th and ThThPyþHex(Clꢀ)Th shifted to
the upper magnetic field positions by 0.13 ppm and 0.49
ppm,
respectively,
as
compared with
those
of
ThThPyþDNP(Clꢀ)Th is attributed to the displacement of
the DNP group in ThThPyþPh(Clꢀ)Th and ThThPyþ-
Hex(Clꢀ)Th with phenyl and hexyl groups, respectively. The
FIGURE 2 1H NMR spectra of (a) ThThPyþDNP(Clꢀ)Th, (b)
PThThPyþDNP(Clꢀ)Th-a, (c) PThThPyþDNP(Clꢀ)Th-b, and (d)
PThThPyþDNP(Clꢀ)Th-c in DMSO-d6. The peaks with an aster-
isk in (b) and (c) correspond to the terminal protons.
NMR spectra of PThThPyþR(Clꢀ)Th (R ¼ Ph and Hex) as
described below.
Figure 3 shows the 1H NMR spectra with peak assignments
of
ThThPyþPh(Clꢀ)Th,
ThThPyþHex(Clꢀ)Th,
PTh-
ThPyþPh(Clꢀ)Th, and PThThPyþHex(Clꢀ)Th in DMSO-d6.
The peaks corresponding to the DNP protons are not present
in the 1H NMR spectra of ThThPyþPh(Clꢀ)Th, ThThPyþ-
FIGURE 3 1H NMR spectra of ThThPyþPh(Clꢀ)Th, ThThPyþ-
Hex(Clꢀ)Th, PThThPyþPh(Clꢀ)Th, and PThThPyþHex(Clꢀ)Th in
DMSO-d6.
Hex(Clꢀ)Th,
PThThPyþPh(Clꢀ)Th,
and
PThThPyþ-
Hex(Clꢀ)Th. This suggests that the polymer reaction of
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c (kmax ¼ 440 nm) were observed at a longer wavelength
than that of ThThPyþDNP(Clꢀ)Th (kmax ¼ 324 nm), suggest-
ing that the p-conjugation system was expanded along the
polymer chain. The kmax values of PThThPyþDNP(Clꢀ)Ths
are comparable to those of poly(3-alkylthiophene)s (kmax
¼
430–450 nm) synthesized by oxidative polymerization with
FeCl3.8,60 The resulting kmax value of PThThPyþDNP(Clꢀ)Th-a
was larger than that of PThThPyþDNP(Clꢀ)Th-b and corre-
sponds to the fact that the DP value of PThThPyþ-
DNP(Clꢀ)Th-a was larger than that of PThThPyþDNP-
(Clꢀ)Th-b. The larger kmax value of PThThPyþPh(Clꢀ)Th-c
(kmax
¼
442 nm) as compared with those of PTh-
ThPyþPh(Clꢀ)Th (kmax ¼ 433 nm) suggests that the p-conju-
gation system was expanded to the nitro groups in PTh-
ThPyþDNP(Clꢀ)Th-c.
FIGURE 4 UV–vis spectra of ThThPyþDNP(Clꢀ)Th, PThThPyþ-
DNP(Clꢀ)Th-a, PThThPyþDNP(Clꢀ)Th-b, and PThThPyþDNP-
(Clꢀ)Th-c in DMSO.
ThThPyTh and PThThPyTh were photoluminescent in solu-
tion. The emission peak position of PThThPyTh (kem ¼ 570
nm) was higher than that of ThThPyTh (kem ¼ 481 nm).
These observations are consistent with the results that the
kmax value of PThThPyTh was larger than that of
ThThPyTh. The PL peak of the polymer appears at the onset
position of its absorption band, which is typical of photolu-
minescent aromatic compounds. The quantum yields (U val-
ues) of the PL of ThThPyTh and PThThPyTh were 0.10
and 0.09, respectively. On the other hand, ThThPyþ-
DNP(Clꢀ)Th, PThThPyþDNP(Clꢀ)Th-a, PThThPyþDNP-
(Clꢀ)Th-b, PThThPyþDNP(Clꢀ)Th-c, PThThPyþDNP(Clꢀ)-
Th-d, and PThThPyþR(Clꢀ)Th (R ¼ Ph and Hex) did not
show PL because of the presence of the pyridinium rings. It
has been reported that pyridinium salts quench the PL of
photoluminescent p-conjugated polymers.62
larger shift of ThThPyþHex(Clꢀ)Th as compared with
ThThPyþPh(Clꢀ)Th is because of the presence of the elec-
tron-donating hexyl group in ThThPyþHex(Clꢀ)Th. The new
peaks corresponding to the phenyl group of PThThPyþ-
Ph(Clꢀ)Th were observed at d 7.76 and 7.90, whereas those
of the hexyl group of PThThPyþHex(Clꢀ)Th were observed
at d 4.67, 4.58, 1.93, 1.29, and 0.85. These peak positions are
comparable to those of the corresponding model compounds.
The peak integral ratios between the phenyl or hexyl protons
and the main chain protons suggest reaction completion of
the polymer reactions. The observation that PThThPyþ-
Ph(Clꢀ)Th and PThThPyþHex(Clꢀ)Th exhibited the two
peaks corresponding to the protons at the 2-position of the
pyridinium ring and the a-position of the hexyl group sug-
gests that the polymers contain HT and HH linkages in the
main chain. It has been reported that poly(3-alkylthiophene-
2,5-diyl)s synthesized by the oxidative polymerization with
Cyclic Voltammograms
Figure 5 shows the cyclic voltammograms of PThThPyþ-
DNP(Clꢀ)Th-a and ThThPyþDNP(Clꢀ)Th in a DMSO solu-
tion containing [Et4N]BF4 (0.10 M). PThThPyþDNP(Clꢀ)Th-
a and ThThPyþDNP(Clꢀ)Th exhibited a peak at 0.72 V (vs.
Agþ/Ag) and 0.83 V (vs. Agþ/Ag) corresponding to the elec-
trochemical oxidation of the thiophene rings, respectively.
The observation that the oxidation potential of PThThPyþ-
DNP(Clꢀ)Th-c is more negative than that of ThThPyþDNP-
(Clꢀ)Th is attributed to the expanded p-conjugation system
of PThThPyþDNP(Clꢀ)Th-a. PThThPyþPh(Clꢀ)Th and
PThThPyþHex(Clꢀ)Th exhibited electrochemical oxidation
peaks of the thiophene rings at more negative potentials (Ea
1
FeCl3 contain HT and HH linkages in the main chain. The H
NMR peak corresponding to the a-methylene protons in the
HH linkage is 0.24 ppm upfield of the HT linkage.60 The con-
tent of the HT and HH linkages of PThThPyþDNP(Clꢀ)Th-c
1
could not be determined because of the unresolved H NMR
spectrum. However, the content of the HT and HH linkages
in PThThPyþHex(Clꢀ)Th are estimated at 1:2.3 from the
peak integral ratio of the a-methylene protons at d 4.67 and
4.58 in the 1H NMR spectrum of PThThPyþHex(Clꢀ)Th.
This value is consistent with the content of the HT and HH
linkages in PThThPyþPh(Clꢀ)Th (HT/HH ¼ 1:2.3) esti-
¼
0.63 V and 0.63 V vs. Agþ/Ag, respectively) than
PThThPyþPh(Clꢀ)Th-c. These observations can be
explained by the absence of an electron-withdrawing nitro
group in PThThPyþPh(Clꢀ)Th and the presence of an elec-
tron-donating hexyl group in PThThPyþHex(Clꢀ)Th.
ThThPyþDNP(Clꢀ)Th exhibited peaks corresponding to the
electrochemical reduction of the nitro groups and the ben-
zene and pyridinium rings at –0.84 V (vs. Agþ/Ag), –2.14 V
1
mated from the integral ratio of the H NMR peaks at d 9.50
and 9.36.
UV–Vis and Photoluminescence Spectra
Optical data are summarized in Table 1. Figure 4 shows the
UV–vis spectra of the DMSO solutions of ThThPyþ-
DNP(Clꢀ)Th, PThThPyþDNP(Clꢀ)Th-a, PThThPyþDNP-
(Clꢀ)Th-b, and PThThPyþDNP(Clꢀ)Th-c.
(vs. Agþ/Ag), and –2.38
V
(vs. Agþ/Ag), respectively.
PThThPyþDNP(Clꢀ)Th-a exhibited peaks corresponding to
the electrochemical reduction of the nitro groups as well as
benzene and pyridinium rings at –0.81 V (vs. Agþ/Ag), –1.98
V (vs. Agþ/Ag), and –2.24 V (vs. Agþ/Ag), respectively. The
The absorption peaks corresponding to the p–p* transition of
PThThPyþDNP(Clꢀ)Th-a (kmax
¼
436 nm), PThThPyþ-
DNP(Clꢀ)Th-b (kmax ¼ 426 nm), and PThThPyþDNP(Clꢀ)Th-
8
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CONCLUSIONS
Polythiophenes with a reactive Zincke salt (PyþDNP(Clꢀ))
structure, such as PThThPyþDNP(Clꢀ)Th, were obtained
from oxidation polymerizations. The reaction of PThThPyþ-
DNP(Clꢀ)Th with aromatic and aliphatic amines (RANH2; R
¼ phenyl and n-hexyl) resulted in the substitution of the
2,4-dinitrophenyl (DNP) group into the R group to yield
PThThPyþR(Clꢀ)Th. The UV–vis measurements suggested
that PThThPyþDNP(Clꢀ)Th had an expanded p-conjugation
system along the polymer main chain. The pyridinium group
of PThThPyþDNP(Clꢀ)Th acted as a quencher for photolu-
minescence.
PThThPyþDNP(Clꢀ)Th
and
PThThPyþ-
R(Clꢀ)Th received both electrochemical oxidation and reduc-
tion reactions. PThThPyþDNP(Clꢀ)Th exhibited semi-con-
ductive electrical properties in a non-doped state. The
results suggest that the methodology developed in this study
has a lot of potential as a fucntionalization tool for a large
number of PTh derivatives.
ACKNOWLEDGMENTS
The authors wish to thank H. Fukumoto (Tokyo Institute of
Technology) for help with GPC measurements.
FIGURE 5 Cyclic voltammograms of PThThPyþDNP(Clꢀ)Th-a
and ThThPyþDNP(Clꢀ)Th in
[Et4N]BF4 (0.10 M). Scan rate was 50 mV sꢀ1
a DMSO solution containing
.
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