Solution processable alternating oligothiophene-PEO-block-copolymers: Synthesis and evidence for solvent dependent aggregation

Article abstract of DOI:10.1039/b002899l

A new route to oligothiophene-PEO-block-copolymers has been developed, in which well-defined α-oligothiophene blocks (from bithiophene to sexithiophene) alternate with poly(ethylene oxide) blocks. These materials show high solubility in common organic solvents. UV/visible and fluorescence studies in solution indicate that the oligothiophene segments are molecularly dissolved in good solvents like chloroform. Aggregation of the oligothiophenes occurs in dioxane-water mixtures, which is manifest by shifts of the UV/ visible absorption maxima towards the blue and quenching of the fluorescence. An oligothiophene length of three thiophenes (terthiophene) is necessary to observe this aggregation phenomenon.

Full text of DOI:10.1039/b002899l

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J O U R N A L O F
Solution processable alternating oligothiophene-PEO-block-co-
polymers: synthesis and evidence for solvent dependent aggregation
Andreas F. M. Kilbinger and W. James Feast*
IRC in Polymer Science and Technology, University of Durham, Durham, UK DH1 3LE.
E-mail: w.j.feast@durham.ac.uk
C H E M I S T R Y
Received 11th April 2000, Accepted 18th May 2000
Published on the Web 29th June 2000
A new route to oligothiophene±PEO-block-co-polymers has been developed, in which well-de®ned a-
oligothiophene blocks (from bithiophene to sexithiophene) alternate with poly(ethylene oxide) blocks. These
materials show high solubility in common organic solvents. UV/visible and ¯uorescence studies in solution
indicate that the oligothiophene segments are molecularly dissolved in good solvents like chloroform.
Aggregation of the oligothiophenes occurs in dioxane±water mixtures, which is manifest by shifts of the UV/
visible absorption maxima towards the blue and quenching of the ¯uorescence. An oligothiophene length of
three thiophenes (terthiophene) is necessary to observe this aggregation phenomenon.
the aggregation and stacking of a-substituted oligothiophenes
or a-substituted oligothiophene main chain polymers. If a-
substituted oligothiophenes or oligothiophene main chain
polymers are to be of use in electronic devices, such as
FETs, a high degree of order will be necessary in order to
obtain high carrier mobilities.
Here we report the ®rst synthetic route to solution
processable alternating oligothiophene±PEO-block-co-poly-
mers in which the oligothiophene blocks can be varied from
bithiophene to sexithiophene and are exclusively a-substituted.
Also UV/visible spectroscopic evidence for aggregation of the
oligothiophene segments in these polymers in aqueous solution
is presented.
Introduction
There is considerable interest in exploiting the semiconducting
properties of solution processable conjugated organic com-
pounds in electronic device structures with the aim of cost
reduction and ease of fabrication in the area of disposable
electronics.1 The ®rst generation of conjugated polymers had
poor structural de®nition and very limited processability.2,3
Generally such materials had large distributions of conjugation
lengths and structural defects. Progress in the ®eld of
electronics based on organic materials demanded the synthesis
of well-de®ned processable materials and the importance of
well-controlled organic synthesis to this ®eld is now widely
acknowledged. The synthesis and study of truly monodisperse
high purity oligomers has proved a fruitful area. Among the
series of thiophene oligomers, the hexamer, sexithiophene, was
found to be a very promising material for use in organic ®eld
effect transistors (FET).4 The FET has been envisioned as the
key component for the development of displays in portable
computers, pagers, memory elements in transaction cards and
disposable electronics in general.5,6 From the commercial
interest viewpoint, organic conjugated materials that are
processable from solution have an advantage. The higher
oligothiophenes (¢quaterthiophene) have interesting solid
state properties but suffer from low solubilities and cannot
be processed at room temperature. Solubilising substituents
have been attached to the oligothiophene units in both the a-
and the b-positions. Whereas a-substituted sexithiophenes did
not show very high solubilities,7±10 highly soluble derivatives
with b-side chains have been prepared.11±15 Alternating
oligothiophene main chain polymers with oligothiophenes of
various lengths have been reported16±24 but in all cases b-
substituents were employed to ensure solubility. It has been
suggested that substitution anywhere other than at the 4- or 5-
carbons of the terminal rings of the oligothiophene leads to
distortions of conformation and decreased p-overlap.25 The
electronic and optical properties of p-conjugated oligomers and
polymers are highly dependent on the conformation of the
conjugated segment and the interaction between different
polymer chains. It is known that p-conjugated polymers
aggregate in poor solvents or upon cooling solutions in good
solvents.26±29 These aggregates exhibit properties which are
similar to those observed in the solid state. For various b-
substituted polythiophenes these phenomena have been
extensively studied but very little data has been reported on
Experimental
Melting points were obtained using an Electrothermal IA9200
series digital melting point apparatus. Elemental analysis data
were recorded on an Exeter Analytical Elemental Analyser CE-
440. Mass spectra were recorded on either a Micromass
AutoSpec mass spectrometer or using a Hewlett Packard Series
II gas chromatograph with a HP1 GC column, attached to a
Fisons Trio 1000 mass spectrometer. NMR-spectra were
recorded using either a Varian VXR400S (1H at 399.95 MHz
and 13C at 100.58 MHz), a Varian Unity (1H at 299.91 MHz
and 13C at 75.41 MHz) or a Varian Inova (1H at 500 MHz and
13C at 125 MHz). Chemical shifts are reported in parts per
million with respect to the internal reference tetramethylsilane
(TMS). Deuterated solvents were used as supplied (Goss).
Calculated molecular weights are reported in g mol21. GPC
analyses were performed using an ERC 7515A refractive index
detector, three 5 mm Polymer Laboratories gel columns
3
5
Ê
(exclusion limits 100, 10 , 10 A) and chloroform as eluent.
Columns were calibrated using polystyrene standards (Polymer
Labs). n-Butyllithium was purchased from Acros (Fisher
Scienti®c), all other reagents were purchased from Aldrich
Chemicals and used without further puri®cation. UV/visible-
spectra were recorded on a ATI Unicam UV2 spectrometer in
quartz cuvettes. Stock solutions for UV/visible-spectroscopy
were prepared in dioxane (Aldrich, spectrophotometric grade)
and diluted with distilled water to give the following solvent
mixtures: 20% water (v/v) (2 ml dioxane stock solution, 0.5 ml
water), 50% water (v/v) (1.5 ml dioxane stock solution, 1.5 ml
DOI: 10.1039/b002899l
J. Mater. Chem., 2000, 10, 1777±1784
This journal is # The Royal Society of Chemistry 2000
1777

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with a water bath. After complete addition the mixture was
water), 83% water (v/v) (0.5 ml dioxane stock solution, 2.5 ml
water).
stirred for another 5 h at 70 ³C and then at rt overnight. A solid
precipitated. Excess Grignard reagent was quenched with water
and the remaining suspension extracted with diethyl ether. The
combined organic extracts were washed with brine, dried
(MgSO4) and the solvent removed under vacuum. The residual
black oil was distilled under reduced pressure (1 mmHg, 84 ³C)
to give pure 2,2'-bithiophene (56.6 g, 46%) which crystallised in
the receiver ¯ask, mp 32±33 ³C (lit.32 34 ³C). Found C, 57.49;
H, 3.54%; M(MS,EI) 166 (Mz). Calculated for C8H6S2, C,
57.79; H, 3.64%; M 166.27. 1H NMR (300 MHz, CDCl3) d 7.04
(dd, J~4.8 Hz, J~3.6 Hz, 2H), 7.22 (m, 4H); 13C NMR
(100 MHz, CDCl3) d 123.71, 124.30, 127.72, 137.34.
GPC analysis of commercial PEO (Aldrich, average Mn ca.
2000) in chloroform using polystyrene calibration gave values
of Mn~3700, Mw~3900, PDI (polydispersity index, Mw/
Mn)~1.05 whereas MALDI TOF mass spectroscopic analysis
con®rmed the Mn of ca. 2000 as reported by Aldrich. The high
molecular weights of the functionalised PEO derivatives 3 and
8 are probably due to the same effect.
2-Bromothiophene-5-carboxylic acid, 1
Compound 1 was prepared using the reported route30 and
obtained as a white crystalline solid (49%, lit.30 47%), mp
132 ³C (lit.30 135±136 ³C). Found C, 28.31; H, 1.31%;
M(MS,EI) 206 (Mz [79Br]), 208 (Mz [81Br]). Calculated for
C5H3BrO2S, C, 29.01; H, 1.46%; M 207.05. 1H NMR
(300 MHz, CDCl3) d 7.11 (d, J~3.9 Hz, 1H), 7.64 (d,
J~3.9 Hz, 1H), 11.4 (broad, COOH); 13C NMR (75 MHz,
CDCl3) d 122.28, 131.34, 133.81, 135.34, 166.66.
2,2'-Bithiophene-5-carboxylic acid, 5, 5-bromo-2,2'-bithiophene-
5'-carboxylic acid, 6 and 5-bromo-2,2'-bithiophene-5'-carbonyl
chloride, 7
Compounds 5±7were prepared as previously reported.33
2-Bromothiophene-5-carbonyl chloride, 2
a-(5-Bromo-2,2'-bithiophen-5'-ylcarbonyl)-v-(5-bromo-2,2'-
bithiophen-5'-ylcarbonyloxy)poly(oxyethylene), 8
Compound 2 was prepared using the reported route31 and
obtained as colourless needles (92%, lit.31 100%), mp 36±38 ³C
(lit.31 41±42 ³C). 1H NMR (300 MHz, CDCl3) d 7.18 (d,
J~4.2 Hz, 1H), 7.73 (d, J~4.2 Hz, 1H); 13C NMR (75 MHz,
CDCl3) d 126.55, 131.89, 138.00, 139.24, 158.46. Due to the
rapid hydrolysis of the material no satisfying mass spectrum
and elemental analysis data could be recorded for this
compound.
Poly(oxyethylene) (Aldrich, average Mn ca. 2000, 10.8 g, ca.
5.4 mmol) was heated (90 ³C) in a round-bottomed single-
necked ¯ask and the melt stirred under vacuum for 1/2 h.
Toluene (50 ml) and pyridine (1.3 g, 16.3 mmol) were added to
the degassed polymer melt and the mixture stirred until a clear
solution was obtained (ca. 1/2 h). 5-Bromo-2,2'-bithiophene-5'-
carbonyl chloride, 7 (5 g, 16.3 mmol) was added as a solid to
the hot (90 ³C) polymer solution. After complete addition the
mixture was stirred at 90 ³C for 3 h then at rt for 3 d. The
mixture was ®ltered through Celite (Aldrich) and the product
precipitated by addition of the clear solution to hexane. The
crude polymer was recovered by ®ltration, dried under vacuum,
re-dissolved in toluene and precipitated in hexane. The pale
yellow waxy solid was recovered by ®ltration, washed with
hexane and dried under vacuum for 1 d to give a-(5-bromo-
2,2'-bithiophen-5'-ylcarbonyl)-v-(5-bromo-2,2'-bithiophen-5'-
ylcarbonyloxy)poly(oxyethylene) (10 g, 73%). GPC (CHCl3):
a-(5-Bromo-2-thenoyl)-v-(5-bromo-2-thenoyloxy)poly(oxy-
ethylene), 3
Poly(oxyethylene) (Aldrich, average Mn ca. 2000, 50 g, ca.
25 mmol) was melted in a round-bottomed single-necked ¯ask
and stirred in the melt under vacuum (1023 mmHg) for 1/2 h.
Toluene (100 ml) and pyridine (6 g, 75 mmol) were added to the
degassed polymer melt and the mixture stirred until a clear
solution was obtained (ca. 1/2 h). A solution of 2-bromothio-
phene-5-carbonyl chloride, 2 (18.1 g, 75 mmol) in toluene
(50 ml) was added slowly to the polymer solution at rt. After
complete addition the mixture was stirred at rt for 48 h, ®ltered
through Celite (Aldrich) and the product precipitated by
addition of the clear solution to hexane. The crude polymer was
recovered by ®ltration, dried under vacuum, re-dissolved in
toluene and precipitated in hexane. The white waxy solid was
recovered by ®ltration, washed with hexane and dried under
vacuum for 1 d to give a-(5-bromo-2-thenoyl)-v-(5-bromo-2-
thenoyloxy)poly(oxyethylene) (50 g, 84%). GPC (CHCl3):
1
Mn~4380 g mol21; Mw~4660 g mol21; PDI~1.06. H NMR
(300 MHz, CDCl3) d 3.59 (m, 175H), 3.75 (m, 4H), 4.39 (m,
4H), 6.96 (m, 4H), 7.02 (d, J~3.9 Hz, 2H), 7.64 (d, J~3.9 Hz,
2H); 13C NMR (75 MHz, CDCl3) d 64.22, 68.89, 70.36, 70.42,
70.44, 70.52, 112.73, 123.91, 125.16, 130.80, 131.56, 134.17,
137.49, 142.81, 161.56.
2,5-Bis(trimethylstannyl)thiophene, 9
Mn~4300 g mol21
;
Mw~4500 g mol21
;
PDI~1.05. 1H
n-Butyllithium (1.6 M, 19.8 ml, 31.6 mmol) was added drop-
wise to a solution of thiophene (1.33 g, 15.8 mmol) and
N,N,N',N'-tetramethylethylenediamine (TMEDA) (3.67 g,
31.6 mmol) in hexane (8 ml) at rt. The mixture was re¯uxed
for 1/2 h then cooled to 260 ³C and a solution of trimethyltin
chloride (6.29 g, 31.6 mmol) in THF (30 ml) added quickly.
The mixture was stirred at 260 ³C for 10 min before the dry
ice±acetone bath was removed and the reaction mixture
allowed to warm to rt. The clear solution was stirred at rt
for 12 h. The reaction mixture was poured into water and
extracted with diethyl ether (2650 ml). The combined organic
extracts were dried (MgSO4) and the solvent removed under
reduced pressure. The crude solid was recrystallised from
ethanol to give 2,5-bis(trimethylstannyl)thiophene (3.9 g, 60%)
as light brown crystals, mp 99.5 ³C (lit.34 100±101.6 ³C). Found
C, 29.47; H, 4.93%; M(MS,EI) 408, 410, 412 (Mz, three most
intense peaks of the isotope pattern). Calculated for
C10H20SSn2, C, 29.31; H, 4.92%; M 409.75. 1H NMR
(300 MHz, CDCl3) d 0.39 (s, 18H), 7.40 (s, 2H); 13C NMR
(75 MHz, CDCl3) d 28.18, 135.78, 142.99.
NMR (300 MHz, CDCl3) d 3.54 (m, 175H), 3.69 (m, 4H),
4.32 (m, 4H), 6.98 (d, J~3.9 Hz, 2H), 7.46 (d, J~3.9 Hz, 2H);
13C NMR (75 MHz, CDCl3) d 64.16, 68.64, 70.21, 70.28, 70.37,
119.93, 130.62, 133.51, 134.33, 160.56.
2,2'-Bithiophene, 4
Magnesium turnings (22 g, 192 mmol) were heated with a hot
air gun under a dry nitrogen ¯ow and rapid stirring. After
cooling, THF (300 ml) was added to the magnesium and 2-
bromothiophene (120 g, 0.74 mol) was added slowly via a
dropping funnel. After complete addition the mixture was
re¯uxed for 1 h, cooled to rt and transferred into a dropping
funnel by decanting the solution from excess magnesium. 2-
Bromothiophene (100 g, 0.61 mol) was dissolved in THF
(300 ml), the catalyst Ni(dppp)Cl2 (1.5 g, 3.6 mmol) was
suspended in the THF mixture and the Grignard reagent was
added slowly via a dropping funnel. During addition of the
Grignard reagent the reaction mixture had to be cooled (rt)
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2,5-bis(trimethylstannyl)thiophene was determined. To
5,5'-Bis(trimethylstannyl)-2,2'-bithiophene, 10
account for this loss more 2,5-bis(trimethylstannyl)thiophene
(200 mg, 0.5 mmol) and Pd(PPh3)4 (30 mg, 0.03 mmol) were
added after 42 h and the melt stirred at 120 ³C for another 12 h.
See general work up procedure for polymers 14±16.
Compound 10 was prepared using the reported route35 and
obtained as colourless needles (85%, lit.35 85%), mp 99.5 ³C
(lit.35 95.5±96.5 ³C). Found C, 34.48; H, 4.51%; M(MS,EI) 490
(8.96%), 492 (9.05%), 494 (5.74%) (Mz, three most intense
peaks of the isotope pattern). Calculated for C14H22S2Sn2, C,
34.19; H, 4.51%; M 491.88. 1H NMR (300 MHz, CDCl3) d 0.42
(s, 18H), 7.12 (d, J~3.3 Hz, 2H), 7.31 (d, J~3.3 Hz, 2H); 13C
NMR (75 MHz, CDCl3) d 28.22, 124.80, 135.81, 135.97,
142.96.
The oil was dissolved in more chloroform and the product
precipitated by addition of the solution to hexane to give
poly[oxycarbonyl-2,2':5',2@-terthiophen-5,5@-ylenecarbonyl-
block-poly(oxyethylene)] which had a higher average molecular
weight than the crude product (determined by GPC). Analysis
of the higher molecular weight fraction: GPC (CHCl3):
, ,
Mn~14 360 g mol21 Mw~21 780 g mol21 PDI~1.52. 1H
Dilithium 2,2'-bithiophene-5,5'-dicarboxylate, 11
NMR (500 MHz, CDCl3) d 3.62 (m, 150H), 3.78 (m, 4H),
4.42 (m, 4H), 7.13 (d, J~3.5 Hz, 2H), 7.19 (s, 2H), 7.68 (d,
J~3.5 Hz, 2H); 13C NMR (125 MHz, CDCl3) d 63.41, 68.10,
69.62 (broad), 123.31, 125.09, 130.91, 133.46, 135.66, 142.31,
160.79.
n-Butyllithium (1.6 M, 12.5 ml, 20 mmol) was added slowly
dropwise to a stirred solution of 2,2'-bithiophene, 4 (1.52 g,
9.1 mmol) in THF (30 ml). The mixture was heated to 50 ³C for
1/2 h, cooled to rt and CO2 gas introduced for 1/2 h while
stirring vigorously. The solvent was removed under reduced
pressure and the residue stirred in hexane for 1 h. The solid was
recovered by ®ltration and washed with hexane to give
dilithium 2,2'-bithiophene-5,5'-dicarboxylate (0.8 g, 34%)
which was used without further puri®cation in the next
reaction step. No analyses were performed at this stage of
the reaction sequence.
Poly[oxycarbonyl-2,2':5',2@:5@,2'''-quaterthiophen-5,5'''-
ylenecarbonyl-block-poly(oxyethylene)], 15
a-(5-Bromo-2-thenoyl)-v-(5-bromo-2-thenoyloxy)poly(oxy-
ethylene), 3 (10 g, 4.1 mmol) was heated to 100 ³C and the
reaction ¯ask purged with nitrogen for 1/2 h while stirring the
melt. 5,5'-Bis(trimethylstannyl)-2,2'-bithiophene, 10 (2.02 g,
4.1 mmol) and Pd(PPh3)4 (237 mg, 0.2 mmol) were added to
the melt and the mixture heated to 120 ³C for 22 h. See general
work up procedure for polymers 14±16.
2,2'-Bithiophene-5,5'-dicarbonyl dichloride, 12
SOCl2 (40 ml) was added slowly to dilithium 2,2'-bithiophene-
5,5'-dicarboxylate, 11 (2 g, 7.5 mmol) and the resulting
suspension re¯uxed for 1 h. The SOCl2 was removed under
reduced pressure and the residue recrystallised twice from
CHCl3±hexane mixture (v/v~4 : 1) to give pure 2,2'-bithio-
phene-5,5'-dicarbonyl dichloride (700 mg, 32%) in the form of
orange needles, mp 172 ³C. Found C, 41.74; H, 1.50%;
M(MS,EI) 289.6 (Mz). C10H4Cl2O2S2 requires C, 41.25; H,
1.38%; M 289.9. 1H NMR (300 MHz, CDCl3) d~7.39 (broad,
2H), 7.93 (broad, 2H).
The oil was dissolved in more chloroform and the product
precipitated by addition of the solution to hexane to give
poly[oxycarbonyl-2,2':5',2@:5@,2'''-quaterthiophen-5,5'''-ylene-
carbonyl-block-poly(oxyethylene)] which had a higher average
molecular weight than the crude product (determined by GPC).
Analysis of the higher molecular weight fraction: GPC
(CHCl3):
Mn~14 500 g mol21
,
Mw~20 700 g mol21
,
PDI~1.43. 1H NMR (400 MHz, CDCl3) d 3.66 (m, 184H),
3.79 (m, 4H), 4.43 (m, 4H), 7.12 (m, 4H), 7.18 (d, J~4.0 Hz,
2H), 7.69 (d, J~4.0 Hz, 2H); 13C NMR (100 MHz, CDCl3) d
64.28, 69.01, 70.52 (broad), 123.91, 124.90, 125.97, 131.46,
134.38, 135.45, 137.02, 143.53, 161.75.
Poly[oxycarbonyl-2,2'-bithiophen-5,5'-ylenecarbonyl-block-
poly(oxyethylene)], 13
Poly(oxyethylene) (Aldrich, average Mn ca. 2000, 3.67 g, ca.
1.84 mmol) was melted and stirred under vacuum for 1/2 h
before toluene (10 ml) was added to give a clear solution. 2,2'-
Poly[oxycarbonyl-2,2':5',2@:5@,2''':5''',2''''-quinquethiophen-
5,5''''-ylenecarbonyl-block-poly(oxyethylene)], 16
Bithiophene-5,5'-dicarbonyl
dichloride,
12
(535 mg,
a-(5-Bromo-2,2'-bithiophen-5'-ylcarbonyl)-v-(5-bromo-2,2'-
1.84 mmol) and pyridine (0.2 ml) were added and the solution
stirred at rt for 1/2 h. All solvents were removed under reduced
pressure and the melt stirred at 150 ³C under high vacuum for
5 h. The viscous melt was dissolved in toluene, ®ltered through
Celite (Aldrich) and the product precipitated by addition of the
solution to hexane to give poly[oxycarbonyl-2,2'-bithiophen-
5,5'-ylenecarbonyl-block-poly(oxyethylene)] (3.5 g) as a white
bithiophenyl-5'-ylcarbonyloxy)poly(oxyethylene),
8
(10 g,
3.83 mmol) was heated to 100 ³C and the reaction ¯ask
purged with nitrogen for 1/2 h while stirring the melt. 2,5-
Bis(trimethylstannyl)thiophene, 9 (1.57 g, 3.83 mmol) and
Pd(PPh3)4 (221 mg, 0.2 mmol) were added to the melt and
the mixture heated to 120 ³C for 4 d. During the reaction a
fraction of the 2,5-bis(trimethylstannyl)thiophene sublimed
powder.
GPC
(CHCl3):
Mn~13 500 g mol21
,
1
from the reaction vessel. An H NMR spectrum of a sample
Mw~21 100 g mol21
,
PDI~1.56. 1H NMR (400 MHz,
was taken after 4 d from which the amount of lost 2,5-
bis(trimethylstannyl)thiophene was determined. To account for
this loss more 2,5-bis(trimethylstannyl)thiophene (1.2 g,
2.9 mmol) and Pd(PPh3)4 (270 mg, 0.03 mmol) were added
after 4 d and the melt stirred at 120 ³C for another 2 d. See
general work up procedure for polymers 14±16.
The oil was dissolved in more chloroform and the product
precipitated by addition of the solution to hexane to give
poly[oxycarbonyl-2,2':5',2@:5@,2''':5''',2''''-quinquethiophen-
CDCl3) d 3.60 (m, 190H), 3.78 (m, 4H), 4.42 (m, 4H), 7.21
(d, J~4.0 Hz, 2H), 7.69 (d, J~4.0 Hz, 2H); 13C NMR
(75 MHz, CDCl3) d 64.37, 68.93, 70.50 (broad), 125.24,
132.95, 134.25, 142.62, 161.53.
Poly[oxycarbonyl-2,2':5',2@-terthiophen-5,5@-ylenecarbonyl-
block-poly(oxyethylene)], 14
a-(5-Bromo-2-thenoyl)-v-(5-bromo-2-thenoyloxy)poly(oxy-
ethylene), 3 (10 g, 4.1 mmol) was heated to 100 ³C and the
reaction ¯ask purged with nitrogen for 1/2 h while stirring the
melt. 2,5-Bis(trimethylstannyl)thiophene, 9, (1.69 g, 4.1 mmol)
and Pd(PPh3)4 (237 mg, 0.2 mmol) were added to the melt and
the mixture heated to 120 ³C for 42 h. During the reaction a
fraction of the 2,5-bis(trimethylstannyl)thiophene sublimed
5,5''''-ylenecarbonyl-block-poly(oxyethylene)] which had
higher average molecular weight than the crude product
a
(determined by GPC). Analysis of the higher molecular
weight fraction: GPC (CHCl3): Mn~9300 g mol21
,
Mw~16 900 g mol21
,
PDI~1.82. 1H NMR (400 MHz,
CDCl3) d 3.64 (m, 186H), 3.67 (m, 4H), 4.42 (m, 4H), 7.08
(m, 4H), 7.39 (d, J~4.0 Hz, 2H), 7.14 (d, J~3.6 Hz, 2H), 7.63
(d, J~3.6 Hz, 2H); 13C NMR (100 MHz, CDCl3) d 64.24,
1
from the reaction vessel. An H NMR spectrum was recorded
for a sample taken after 42 h from which the amount of lost
J. Mater. Chem., 2000, 10, 1777±1784
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68.98, 70.48 (broad), 123.77, 124.55, 124.82, 125.92, 131.29,
134.35, 135.08, 135.26, 137.26, 143.60, 161.72.
General work-up procedure for polymers 14±16
The melt was cooled to rt, dissolved in toluene and the product
precipitated by addition of the solution to hexane. The yellow
powder was dried under vacuum. The polymer was dissolved in
chloroform (100 ml) and hexane added to the stirred solution
until the onset of precipitation could be observed. After 12 h of
standing without stirring an oil had separated from the
solution. The oil was separated from the rest of the solution
from which a polymeric product was precipitated by addition
to hexane.
Poly[oxycarbonyl-2,2':5',2@:5@,2''':5''',2'''':5'''',2'''''-sexithiophen-
5,5'''''-ylenecarbonyl-block-poly(oxyethylene)], 17
Scheme 1 Synthesis of the bis-bromo-thiophene macromonomer 3. a)
AcOH, Br2; b) SOCl2; c) toluene, pyridine, PEO (Mn~2000).
a-(5-Bromo-2,2'-bithiophen-5'-ylcarbonyl)-v-(5-bromo-2,2'-
bithiophen-5'-ylcarbonyloxy)poly(oxyethylene), 8, (12.65 g,
4.85 mmol) was heated to 100 ³C and the reaction ¯ask
purged with nitrogen for 1/2 h while stirring the melt. 5,5'-
Bis(trimethylstannyl)-2,2'-bithiophene, 10 (2.38 g, 4.85 mmol)
and Pd(PPh3)4 (280 mg, 0.2 mmol) were added to the melt and
the mixture heated to 120 ³C for 3 h. After 3 h the melt had
become too viscous to be stirred any more. Toluene (7 ml) was
added and the solution stirred for another 12 h at 100 ³C. The
solution was cooled to rt, dissolved in more toluene and the
product precipitated by addition of the solution to hexane. The
red powder was dried under vacuum. The polymer was
dissolved in chloroform (100 ml) and hexane added to the
stirred solution until the onset of precipitation could be
observed. After 12 h of standing without stirring an oil had
separated from the solution. The oil was separated from the
rest of the solution from which a polymeric product was
precipitated by addition to hexane. The oil was dissolved in
more chloroform and the product precipitated by addition of
the solution to hexane to give poly[oxycarbonyl-
2,2':5',2@:5@,2''':5''',2'''':5'''',2'''''-sexithiophen-5,5'''''-ylenecarbo-
Scheme 2 Synthesis of bis-bromo-bithiophene macromonomer 8. a)
THF, n-butyllithium, CO2; b) DMF, NBS; c) SOCl2; d) toluene,
pyridine, PEO (Mn~2000).
nyl-block-poly(oxyethylene)] which had
a higher average
molecular weight than the crude product (determined by
GPC). Analysis of the higher molecular weight fraction: GPC
(CHCl3):
Mn~13 300 g mol21
,
Mw~19 000 g mol21
,
PDI~1.43. 1H NMR (400 MHz, CDCl3) d 3.61 (m, 192H),
3.79 (m, 4H), 4.42 (m, 4H), 7.07 (m, 6H), 7.10 (d, J~4.0 Hz,
2H), 7.16 (d, J~4.0 Hz, 2H), 7.68 (d, J~3.6 Hz, 2H); 13C
NMR (100 MHz, CDCl3) d 64.25, 69.00, 70.41 (broad), 123.74,
124.45, 124.51, 124.81, 125.93, 131.24, 134.38, 134.97, 135.53,
136.15, 137.39, 143.67, 161.76.
Results and discussion
Fig. 1 2,5-Bis(trimethylstannyl)thiophene 9 and 5,5'-bis(trimethylstan-
nyl)-2,2'-bithiophene 10 used in a Stille poly-condensation reaction.
Synthesis
boxylic acid (6) obtained was converted into the acid chloride
7 using thionyl chloride. Reaction with PEO gave the
macromonomer 8 (Scheme 2). Bis(trimethyltin) derivatives of
thiophene, 9, and bithiophene, 10 (Fig. 1) were prepared using
standard lithiation/nucleophilic substitution chemistry. Pre-
paration of the bithiophene±PEO block co-polymer (13)
(Scheme 3) was accomplished by di-lithiation of bithiophene
followed by reaction with CO2 to give the bis-carboxylate 11.
Reaction with thionyl chloride yielded the di-acid chloride 12
which was subsequently melt polymerised with PEO to give
polymer 13.
Synthesis of the higher oligothiophene polymers 14±17 was
achieved by cross-coupling of all combinations of the
monomers 3,8 and 9,10 in the melt under Pd(0)-catalysis
(Scheme 4).
All polymers prepared by Stille cross-coupling were
fractionated to remove lower molecular weight material.
Because of their low solubility the oligothiophene blocks of the
co-polymer could not be synthesised and manipulated directly
and so they were constructed in the polymer forming step. Two
types of monomer, each carrying a segment of the ®nal
oligothiophene block were prepared (3 and 8, Schemes 1 and 2)
and cross-coupled with a 2,5-bis(trimethylstannyl)thiophene
(9), or 5,5'-bis(trimethylstannyl)-2,2'-bithiophene (10, Fig. 1) to
give the target polymeric products.
a-Bromination of thiophene-2-carboxylic acid and subse-
quent reaction of the acid 1 with thionyl chloride gave the 2-
bromothiophene-5-carbonyl chloride (2). Reaction of 2 with
commercial PEO gave the di-ester monomer 3 (Scheme 1).
Mono-lithiation of 2,2'-bithiophene (4) was achieved using n-
butyllithium in THF at 278 ³C. Introduction of CO2 gas into a
solution of the anion gave 2,2'-bithiophene-5-carboxylic acid
(5). Bromination in the 5'-position was carried out using NBS
in DMF at 210 ³C. The 5-bromo-2,2'-bithiophene-5'-car-
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Mechanical properties
Pure PEO even of high molecular weight is a brittle semi-
crystalline material and ®lms made from PEO do not show any
signi®cant mechanical strength. Qualitative examination of
melt formed ®lms of the above polymers showed markedly
different properties with the mechanical strength increasing
from the bithiophene polymer 13 to the sexithiophene polymer
17. While the bithiophene polymer 13 exhibits a behaviour
similar to pure PEO, the sexithiophene polymer 17 has
properties reminiscent of a cross-linked rubber. This behaviour
is consistent with noncovalent crosslinking of disordered PEO
caused by aggregation of the oligothiophene blocks within the
polymer. The aggregation strength is likely to be lower for
shorter and higher for longer oligothiophenes leading to
physically cross-linked polymers with a gradation of mechan-
ical properties with the sexithiophene block copolymer 17
displaying the largest effect.
UV/visible-spectroscopic evidence for aggregation
Scheme 3 Synthesis of the bithiophene polymer 13. a) THF, n-
butyllithium, CO2; b) SOCl2; c) PEO (Mn~2000).
Chloroform solutions of polymers 13±17 with chromophore
concentrations of 6.761026 mol l21 were prepared and their
UV/visible spectra recorded (Fig. 2). The absorption spectra
show broad bands with little or no resolved vibronic structure
as expected for molecularly dissolved chromophores. Due to
increasing p-conjugation the absorption maximum shifts
progressively towards the red as the thiophene oligomer
block length increases.
Molecular weights were estimated by GPC in chloroform using
poly(styrene) standards (Table 1).
All polymeric materials showed very good solubility in
various organic solvents like chloroform, dichloromethane,
THF and aromatic solvents. Also, dilute solutions in THF or
dioxane could be further diluted with water without precipita-
tion of the polymers.
The ¯uorescence spectra show more ®ne structure than the
Scheme 4 Synthesis of the terthiophene polymer 14, quaterthiophene polymer 15, quinquethiophene 16 and sexithiophene 17.
J. Mater. Chem., 2000, 10, 1777±1784
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Table 1 Molecular weights of polymers 13±17, determined by GPC (chloroform)
Low molecular weight fraction
High molecular weight fraction
Compound
Mn
Mw
Mn
Mw
13
14
15
16
17
13 500
3710
11 464
8150
12 200
21 100
9740
16 600
10 900
17 400
Ð
14 360
14 500
9300
Ð
21 780
20 700
16 900
19 000
13 300
absorption spectra (Fig. 3). Each emission spectrum shows two
clearly resolved bands and a shoulder which have been
identi®ed as the vibronic replicas of the 0±0 transition.36
UV/visible-spectra of dioxane solutions of the polymers 13±
17 with chromophore concentrations of 6.761026 mol l21
were identical with those recorded for chloroform solutions
(Fig. 4±Fig. 8, 0% water traces). Dilution with water gave
solutions with 20%, 50% and 83% (v/v) water content. UV/
visible spectra of these solutions were recorded and normalised
to chromophore concentrations of 6.761026 mol l21 (Fig. 4±
Fig. 8). The absorption maximum of the bithiophene polymer
13 does not shift with varying the water content of the solution,
remaining at 350 nm for all four solvent mixtures (Fig. 4).
The absorption maximum of the terthiophene polymer 14
displayed a small shift to shorter wavelength (386 nm) when
dissolved in 83% water in dioxane but remained at 396 nm for
all other solvent compositions (Fig. 5).
bithiophene polymer 13. A change of refractive index of the
polymer solutions in dioxane±water mixtures compared to pure
This effect became more pronounced for the quaterthio-
phene polymer 15 for which the absorption maximum shifts
from 422 nm for pure dioxane to 404 nm for 83% water in
dioxane (Fig. 6).
For the quinquethiophene polymer 16 the absorption
maximum shifted from 436 nm (pure dioxane) to 410 nm
(83% water in dioxane, Fig. 7) and for the sexithiophene
polymer 17 from 448 nm (pure dioxane) to 410 nm (83% water
in dioxane, Fig. 8).
This phenomenon is well known for oligothiophenes p-
stacked in a parallel manner and has been observed in thin solid
®lms.36 Recently we reported helical p-stacking of a chiral di-
substituted sexithiophene derivative in solution.33 This com-
pound is structurally very similar to the materials described
here and can be used as a model system for the sexithiophene
polymer 17. The model system showed the same solvent
dependent UV/visible absorption phenomena, independent of
the chromophore concentration, while circular dichroism
spectroscopy gave evidence for aggregation in polar solvents.33
Further evidence for parallel face-to-face stacking is the
observed quenching of the ¯uorescence in 83% water in
dioxane solutions for all the polymers (14±17) except the
Fig. 3 Fluorescence spectra of the polymers 13±17 in chloroform
(chromophore concentration ~6.761026 mol l21). The excitation
wavelengths for the different polymers were: 13: 350 nm, 14: 392 nm,
15: 419 nm, 16: 436 nm, 17: 450 nm.
dioxane or pure chloroform could potentially cause a blue shift
in the UV/visible absorption but this phenomenon should be
seen for all polymers (14±17) and be independent of the size of
Fig. 4 UV/visible-spectra of the bithiophene polymer 13 in various
dioxane±water mixtures (chromophore concentration~6.761026
mol l21).
the oligothiophene. However, we did not observe this effect for
the bithiophene polymer 14 and therefore conclude that the
observed blue shift is not caused by a refractive index change.
The model compound described33 was also used to give mass
spectroscopic evidence for aggregation, dependent on the
polarity of the solution injected into a Fourier Transform Ion
Cyclotron Mass Spectrometer (FTICR).37 The solvent induced
p-stacking might prove useful for the use of these materials in
FET devices where a high degree of order enhances carrier
Fig. 2 UV/visible-spectra of the polymers 13±17 in chloroform
(chromophore concentration~6.761026 mol l21).
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Fig. 5 UV/visible-spectra of the terthiophene polymer 14 in various
dioxane±water mixtures (chromophore concentration~6.761026
mol l21).
Fig. 8 UV/visible-spectra of the sexithiophene polymer 17 in various
dioxane±water mixtures (chromophore concentration~6.761026
mol l21).
gothiophene length. PEO side-chains were shown to have
excellent solubilising effects on otherwise insoluble rigid
oligothiophenes. The new materials show good solubility in
various organic solvents and also mixtures of dioxane±water .
In solutions in 83% water in dioxane (v/v) UV/visible-spectra
suggest that the oligothiophene rods aggregate in a face-to-face
manner.
Acknowledgements
The authors wish to acknowledge the European Commission
TMR Network SELOA (contract number ERBFMRX-
CT960083) for ®nancial support.
References
Fig. 6 UV/visible-spectra of the quaterthiophene polymer 15 in various
dioxane±water mixtures (chromophore concentration~6.761026
mol l21).
1
2
I. D. W. Samuel, Philos. Trans. R. Soc. London, A, 2000, 358, 193.
W. J. Feast, `The Synthesis of Conducting Polymers', in The
Synthesis of Conducting Polymers, ed. T. A. Skotheim, Marcel
Dekker, N.Y., 1986.
3
4
W. J. Feast, Chem. Ind. (London), 1985, 8, 263.
G. Horowitz, F. Garnier, A. Yassar, R. Hajlaoui and F. Kouki,
Adv. Mater., 1996, 8, 52.
5
6
7
H. Stubb, E. Punkka and J. Paloheimo, J. Mater. Sci. Eng., 1993,
10, 85.
C. P. Jarrett, R. H. Friend, A. R. Brown and D. M. de Leeuw,
J. Appl. Phys., 1995, 77, 6289.
F. Garnier, A. Yassar, R. Hajlaoui, G. Horowitz, F. Deloffre,
B. Servet, S. Ries and P. Alnot, J. Am. Chem. Soc., 1993, 115,
8716.
8
9
Y. Wei, Y. Yang and J. M. Yeh, Chem. Mater., 1996, 8, 2659.
H. E. Katz, J. G. Laquindanum and A. J. Lovinger, Chem. Mater.,
1998, 10, 633.
10 H. E. Katz, A. Dodabalapur, L. Torsi and D. Elder, Chem.
Mater., 1995, 7, 2238.
11 G. Barbarella, M. Zambianchi, A. Bongini and L. Antolini, J. Org.
Chem., 1996, 61, 4708.
12 G. Bidan, A. DeNicola, V. Enee and S. Guillerez, Chem. Mater.,
1998, 10, 1052.
13 J. M. Tour and R. L. Wu, Macromolecules, 1992, 25, 1901.
14 F. Goldoni, D. Iarossi, A. Mucci and L. Schenetti, Chem.
Commun., 1997, 2175.
15 D. Delabouglise, M. Hmyene, G. Horowitz, A. Yassar and
F. Garnier, Adv. Mater., 1992, 4, 107.
16 H. Ago, T. Kuga, T. Yamabe, K. Tanaka, A. Kunai and
M. Ishikawa, Chem. Mater., 1997, 9, 1159.
17 J. K. Herrema, P. F. Vanhutten, R. E. Gill, J. Wildeman,
R. H. Wieringa and G. Hadziioannou, Macromolecules, 1995, 28,
8102.
Fig. 7 UV/visible-spectra of the quinquethiophene polymer 16 in
various
dioxane±water
tion~6.761026 mol l21).
mixtures
(chromophore
concentra-
mobilities.38 Together with the greatly enhanced solubility
compared with that of the unsubstituted oligothiophenes this
approach might lead to commercially interesting processable
and highly organised materials.
18 W. C. Chen and S. A. Jenekhe, Macromolecules, 1995, 28, 454.
19 K. Y. Musick, Q. S. Hu and L. Pu, Macromolecules, 1998, 31,
2933.
Conclusions
20 M. Belletete, L. Mazerolle, N. Desrosiers, M. Leclerc and
G. Durocher, Macromolecules, 1995, 28, 8587.
21 M. Sato and M. Hiroi, Chem. Lett., 1996, 495.
We have synthesised a new class of solution processable
oligothiophene±PEO block co-polymers with variable oli-
J. Mater. Chem., 2000, 10, 1777±1784
1783

View Online
32 E. Lescot, N. P. Buu-Hoi and N. D. Xuong, J. Chem. Soc., 1959,
3234.
33 A. F. M. Kilbinger, A. P. H. J. Schenning, F. Goldoni, W. J. Feast
and E. W. Meijer, J. Am. Chem. Soc., 2000, 122, 1820.
34 D. E. Seitz, S. H. Lee, R. N. Hanson and J. C. Bottaro, Synth.
Commun., 1983, 13, 121.
22 Y. L. Hong and L. L. Miller, Chem. Mater., 1995, 7, 1999.
23 A. DonatBouillud, L. Mazerolle and M. Leclerc, Synth. Met.,
1997, 84, 235.
24 Y. Kunugi, L. L. Miller, T. Maki and A. Canavesi, Chem. Mater.,
1997, 9, 1061.
25 H. E. Katz, J. Mater. Chem., 1997, 7, 369.
26 E. Ramos Lermo, B. M. W. Langeveld, R. A. J. Janssen and
E. W. Meijer, Chem. Commun., 1999, 791.
35 S. Kotani, K. Shiina and K. Sonogashira, J. Organomet. Chem.,
1992, 429, 403.
27 B. M. W. Langeveld-Voss, M. P. T. Christiaans, R. A. J. Janssen
and E. W. Meijer, Macromolecules, 1998, 31, 6702.
28 A. F. Drake, P. Udvarhelyi, D. J. Ando, D. Bloor, J. S. Obhi and
S. Mann, Polymer, 1989, 30, 1063.
29 G. Bidan, S. Guillerez and V. Sorokin, Adv. Mater., 1996, 8, 157.
30 G. Karminskizamola, J. Dogan, M. Bajic, J. Blazevic and
M. Malesevic, Heterocycles, 1994, 38, 759.
36 A. Yassar, G. Horowitz, P. Valat, V. Wintgens, M. Hmyene,
F. Deloffre, P. Srivastava, P. Lang and F. Garnier, J. Phys. Chem.,
1995, 99, 9155.
37 A. F. M. Kilbinger, H. J. Cooper, L. A. McDonnell, W. J. Feast,
P. J. Derrick, A. P. H. J. Schenning and E. W. Meijer, Chem.
Commun., 2000, 383.
38 F. Garnier, G. Horowitz, D. Fichou and A. Yassar, Synth. Met.,
1996, 81, 163.
31 P. Buu-Hoi and N. Hoan, Recl. Trav. Chim. Pays-Bas, 1949, 68, 5.
1784
J. Mater. Chem., 2000, 10, 1777±1784