Rodlike macromolecules through spatial overlapping of thiophene dendrons

Article abstract of DOI:10.1002/chem.201003627

Two novel dendritic macromonomers 7 and 8 functionalized with electroactive conjugated thiophene oligomers were synthesized by stepwise cross-coupling reactions and the introduction of a vinyl group at the focal point. Both macromonomers were polymerized

Full text of DOI:10.1002/chem.201003627

FULL PAPER
DOI: 10.1002/chem.201003627
Rodlike Macromolecules through Spatial Overlapping of Thiophene
Dendrons
Mutsumi Kimura,*[a, b] Akiko Kitao,[a] Tadashi Fukawa,[a] and Hirofusa Shirai[b]
Abstract: Two novel dendritic macro-
monomers 7 and 8 functionalized with
electroactive conjugated thiophene
oligomers were synthesized by stepwise
cross-coupling reactions and the intro-
duction of a vinyl group at the focal
point. Both macromonomers were
polymerized into dendronized poly-
mers 9 and 10 by using a radical poly-
merization method. The photophysical
and redox behaviors of dendronized
polymers 9 and 10 are significantly dif-
ferent from those of the corresponding
macromonomers. This difference may
result from the spatial overlapping of
thiophene dendrons through p–p inter-
actions when the dendrons are con-
nected to a polymer backbone. The
dendronized polymers can organize
into large-area two-dimensional sheets
with a thickness of 4.8 nm. Polymer 9,
which has all-dendritic thiophene side
chains, exhibited enhanced conductivity
by partial doping with iodine or nitro-
sonium tetrafluoroborate (NOBF4).
The novel amphiphilic dendronized
polymer 15 was synthesized by the
atom-transfer radical polymerization of
macromonomer 7 from a poly(ethylene
glycol) (PEG) macroinitiator and was
found to have a self-organized struc-
ture in water.
Keywords: amphiphiles · dendrons ·
oligothiophenes
·
organic
electronics · polymerization
Introduction
blies.[6] The fabrication of highly efficient optoelectronic de-
vices requires strict control over the spatial organization of
oligomers and polymers.[7]
Since the discovery of electrical conductivity in p-conjugat-
ed polymers in the late 1970s,[1] conjugated oligomers and
polymers have been the subject of intense study owing to
their potential applications in fields such as organic light-
emitting diodes, photovoltaic cells, field-effect transistors,
and chemical sensors.[2] Oligo- and polythiophenes are the
most prominent organic semiconductors applied in organic
electronics.[3] For example, linear and discrete oligothio-
phene derivatives have been investigated as semiconductors
in field-effect transistors and the structural modification af-
fects the charge-transport characteristics of the bulk solid.[4]
A combination of regioregular poly(3-hexylthiophene) and
[6,6]-phenyl-C61-butyric acid methyl ester shows excellent
performance as an active layer of bulk heterojunction solar
cells.[5] The self-assembling processes of oligo- and polythio-
phenes are crucial to the overall charge mobility in these de-
vices and charge can be transported along the p–p stacking
direction within two- or three-dimensional molecular assem-
New topological architectures of oligothiophenes with
cyclic, star, and spherical shapes have recently been synthe-
sized to control spatial organization as well as improve solu-
bility and processability.[8] Dendrimers are well-defined,
spherical, and nanoscopic macromolecules constructed from
an interior core with a regular array of branching units.[9]
Conjugated dendrimers based on polyphenylene, poly-
phenylacetylene, and polythiophene moieties have been syn-
thesized by step-wise cross-coupling reactions and the rigid
linkages in conjugated dendrimers can control the mobility
of the dendron units.[10] The shape and size of the conjugat-
ed dendrimers persist in all physical environments. All-thio-
phene dendrons and dendrimers were first synthesized by
Advincula and co-workers.[11a] They also reported the assem-
bly of thiophene dendrimers on solid substrates. Bꢀuerle
and co-workers synthesized very large functionalized thio-
phene dendrimers composed of 90 thiophene rings for appli-
cation in solar-energy conversion, photon harvesting, and
optoelectronics.[12] Hexa-peri-hexabenzocorones functional-
ized with a series of thiophene dendrons that exhibited high
power-conversion efficiency in bulk heterojunction solar
cells were reported by Wong et al.[13] The design of a thio-
phene array in the dendrimers allows the creation of molec-
ular-based components with well-defined properties.[14]
Dendronized polymers have been synthesized by attach-
ing branched dendrons with a central polymer backbone as
side chains.[15] At high degrees of dendron attachment,
dendronized linear polymers gain stiffness and adopt a rod-
like morphology by the organization of dendron units
[a] Prof. M. Kimura, A. Kitao, T. Fukawa
Department of Functional Polymer Science
Faculty of Textile Science and Technology
Shinshu University, Ueda 386-8567 (Japan)
Fax : (+81)268-21-5499
E-mail: mkimura@shinshu-u.ac.jp
[b] Prof. M. Kimura, Prof. H. Shirai
Collaborative Innovation Center of Nanotech Fiber (nanoFIC)
Shinshu University, Ueda 386-8567 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201003627.
Chem. Eur. J. 2011, 17, 6821 – 6829
ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
6821

m, ArH), 2.47 ppm (12H, s, CH3); 13C NMR (CDCl3, 100.61 MHz): d=
147.6, 147.4, 146.2, 146.1, 135.0, 134.8, 134.5, 132.9, 132.6, 132.2, 131.9,
131.7, 131.4, 131.1, 130.5, 129.7, 127.9, 127.8, 126.7, 126.5, 125.4, 125.3,
124.9, 122.6, 15.3 ppm; MALDI-TOF-MS: m/z (%): 633 (100) [M+H]+.
around the polymer backbone. Although numerous reports
have focused on the attachment of flexible dendrons with
polymer backbones,[15] the organization of conjugated den-
dron units in dendronized polymers has rarely been ad-
dressed. Schlꢂter and co-workers synthesized thiophene-
based dendronized polymers by the polymerization of mac-
romonomers with different-sized thiophene dendrons.[16]
Herein, a series of dendronized polymers with all-thiophene
dendrons were synthesized and characterized. Moreover,
the electronic conductivities of dendronized polymers with
different conjugated dendritic side chains were investigated.
It is concluded that the organization of thiophene dendrons
within the dendronized polymer may enable a long-range
charge transport in the solid films.
2,3-(4’-Methylphenyl)thiophene (2): 2,3-Dibromothiophene (2.0 g,
8.27 mmol) and 4-methylphenylboronic acid (28 g, 20.7 mmol) were dis-
solved in the mixed solvent of toluene (10 mL), THF (12 mL), and
Na2CO3 aqueous solution (2.0m, 8 mL). After degassing with nitrogen
gas, [PdACHTNUGTRNEGNU(PPh3)4] (0.19 g, 0.17 mmol) was added to the mixed solution. The
reaction mixture was stirred at 708C for 48 h in a nitrogen atmosphere,
after which the reaction mixture was diluted with diethyl ether (50 mL)
and washed with water. The organic layer was dried over magnesium sul-
fate and concentrated under vacuum. The residue was purified by
column chromatography on silica gel with petroleum ether as the eluent
(2.0 g, 91%). Rf =0.6 (petroleum ether); 1H NMR (CDCl3, 400.13 MHz):
d=7.27 (1H, d, J=5.2 Hz, ArH), 7.25 (1H, d, J=7.6 Hz, ArH), 7.20
(2H, d, J=7.8 Hz, ArH), 7.18 (2H, d, J=8.1 Hz, ArH), 7.09 (2H, d, J=
7.8 Hz, ArH), 7.07 (2H, d, J=8.1 Hz, ArH), 2.33 ppm (6H, s, CH3);
13C NMR (CDCl3, 100.61 MHz): d=158.1, 138.4, 133.5, 131.2, 129.2,
129.1, 128.9, 128.8, 126.9, 21.2 ppm.
Phenyl-terminated dendron 4: Compound 4 was synthesized from 2,3-di-
bromothiophene and a stannyl derivative of 2 by the same procedure
used to prepare 3 (78%). 1H NMR (CDCl3, 400.13 MHz): d=7.23–7.27
(2H, m, ArH), 7.22 (1H, s, ArH), 7.21 (1H, s, ArH), 7.18 (4H, d, J=
7.8 Hz, ArH), 7.15 (4H, d, J=7.8 Hz, ArH), 7.09 (4H, d, J=8.0 Hz,
ArH), 7.06 (4H, d, J=8.0 Hz, ArH), 2.34 ppm (6H, s, CH3); 13C NMR
(CDCl3, 100.61 MHz): d=159.1, 140.3, 139.1, 138.3, 137.7, 133.3, 130.2,
129.5, 129.4, 129.3, 1280, 127.3, 1212, 21.6 ppm; MALDI-TOF-MS: m/z
(%): 608 (100) [M+H]+.
Experimental Section
General: 1H NMR spectra were measured on a Bruker Avance 400 FT-
NMR spectrometer. Mass-spectrometric data were obtained on a PerSep-
tive Biosystems Voyager DE-Pro spectrometer with dithranol as the
matrix. FTIR spectra were obtained on a Shimazu FTIR-8400 spectrome-
ter. UV/Vis and fluorescence spectra were measured on a Shimazu Multi-
Spec-1500 spectrophotometer and a JASCO FP-750 machine, respective-
ly. Differential scanning calorimetry (DSC) thermograms were recorded
on a SII Exstar 6000 DSC 6200 machine. Atomic force microscopy
5: The stannyl compound was synthesized by the conversion of the a-po-
sition in 3 with tributyltin chloride. BuLi (1.6m in hexane; 0.54 mL,
0.85 mmol) was added to solution of 3 (0.45 g, 0.71 mmol) in THF (5 mL)
at À788C. After lithiation, tributyltin chloride (0.29 mL, 1.1 mmol) was
added to the reaction mixture and stirred for 30 min at À788C in a nitro-
gen atmosphere. After 30 min, the reaction mixture was allowed to warm
to room temperature for 6 h. The reaction mixture was diluted with n-
hexane (50 mL) and the formed precipitate was removed by filtration.
The filtered solution was evaporated, and the product was used without
further purification (0.66 g). A solution of the stannyl derivative of 3
(0.66 g, 0.71 mmol), 5-bromo-2,2-bithiophene-5’-carboxylic acid methyl
images were acquired in noncontact mode by
a JEOL JSPM-5400
system. Fluorescence quantum efficiencies were determined by Hama-
matsu Photonics absolute PL Quantum Yield Measurement system
C9920–02. Gel-permeation chromatography (GPC) analyses were carried
out with a JASCO HPLC system (pump 1580, UV detector 1575, refrac-
tive index detector 930) and a Showa Denko GPC KF-804L column
(8.0ꢃ300 mm, polystyrene standards, Mw =900–400000 gmolÀ1
THF as the eluent at 358C (1.0 mLminÀ1).
) with
Cyclic voltammetric measurements were recorded on an ALS 700 poten-
tiostat using a three-cell electrode system with a Pt working electrode, a
Pt counterelectrode, and an Ag/AgCl reference electrode. Tetrabutylam-
monium perchlorate (TBAP) was used as the electrolyte.
ester (0.26 g, 0.85 mmol), and [PdACHTNUGRTNEUNG(PPh3)4] (0.05 g, 0.174 mmol) in dry
DMF (7 mL) was stirred at 1008C for 48 h under nitrogen. After cooling
to room temperature, the reaction mixture was poured into water, ex-
tracted with CH2Cl2, and washed with an aqueous solution of KF to
remove the tributyltin chloride. The organic layer was dried over magne-
sium sulfate and the solvent was evaporated. The residue was purified by
column chromatography on silica gel with CH2Cl2 as the eluent and recy-
cling preparative HPLC to give 5 as a dark-red solid (0.27 g, 45%). FTIR
(ATR): n˜ =1708 cmÀ1 (-COOCH3); 1H NMR (CDCl3, 400.13 MHz): d=
7.70 (1H, d, J=4.0 Hz, ArH), 7.18–7.22 (4H, m, ArH), 7.15 (2H, d, J=
3.6 Hz, ArH), 6.94 (2H, d, J=5.3 Hz, ArH), 6.85–6.90 (4H, m, ArH),
6.60–6.65 (2H, m, ArH), 3.88 (3H, s, -COOCH3), 2.47 ppm (12H, s,
CH3); MALDI-TOF-MS: m/z (%): 855 (100) [M+H]+.
Materials: All the chemicals were purchased from commercial suppliers
and used without purification. All the solvents were distilled before each
procedure. The purification of the product was carried out by the combi-
nation of adsorption column chromatography on silica gel (Wakogel C-
200) and recycling preparative HPLC (Japan Analytical Industry, Model
LC-908). Analytical TLC was performed on commercial plates coated
with silica gel (Merck 60 F254). 5,5’’-Dimethyl-[2,2’;3’,2’’]terthiophene (1)
and tributyl(5,5’’-dimethyl-[2,2’;3’,2’’]terthiophen-5’-yl)stannane were syn-
thesized according to the method reported by Advincula and co-work-
ers.[11] The PEG macroinitiator was synthesized from poly(ethylene
glycol) methyl ether with a mass of Mw =2000 gmolÀ1 and 2-boromo-2-
methylpropionyl chloride according to the method reported by Iyoda and
co-workers.[17]
6: Compound 6 was synthesized from 4 and methyl 4-(5’-bromothiophe-
ne)benzoate by the same procedure used to prepare 5 (34%). FTIR
(ATR): n˜ =1707 cmÀ1 (-COOCH3); 1H NMR (CDCl3, 400.13 MHz): d=
8.04 (2H, d, J=8.4 Hz, ArH), 7.65 (2H, d, J=8.2 Hz, ArH), 7.18–7.28
(5H, m, ArH), 7.18–7.20 (8H, m, ArH), 7.06–7.10 (8H, m, ArH), 3.91
(3H, s, -COOCH3), 2.32 ppm (12H, s, CH3); 13C NMR (CDCl3,
100.61 MHz): d=159.2, 140.2, 139.7, 139.0, 138.7, 138.4, 138.1, 137.2,
136.7, 136.6, 133.4, 130.3, 130.1, 129.2, 129.0, 126.9, 121.4, 52.1, 24.5 ppm;
MALDI-TOF-MS: m/z (%): 825 (100) [M+H]+.
Thiophene dendron 3: A solution of tributyl(5,5’’-dimethyl-[2, 2’;3’,2’’]ter-
thiophen-5’-yl)stannane (3.6 g, 7.23 mmol), 2,3-dibromothiophene (0.5 g,
2.07 mmol), and [PdACHTUNGTRENNUNG(PPh3)4] (0.2 g, 0.174 mmol) in dry DMF (17 mL)
was stirred at 1008C for 48 h under nitrogen. After cooling to room tem-
perature, the reaction mixture was poured into water, extracted with
CH2Cl2, and washed with an aqueous solution of KF to remove tributyl-
tin chloride. The organic layer was dried over magnesium sulfate and the
solvent was removed by evaporation. The residue was purified by column
chromatography on silica gel with petroleum ether/CH2Cl2 (7:3) as the
Hydrolysis of the ester group in 5: KOH aqueous solution (10 mL, 1.0m)
was added to a solution of 5 (0.2 g, 0.234 mmol) in THF (20 mL). The re-
sulting mixture was stirred at 808C for 6 h. The reaction mixture was
poured into water, extracted with CH2Cl2, and washed with HCl aqueous
solution (0.1m) for neutralization. The organic layer was dried over mag-
nesium sulfate and the solvent was evaporated to give the target mole-
eluent to give
3
as orange solid (2.9 g, 63%). 1H NMR (CDCl3,
400.13 MHz): d=7.27 (1H, d, J=5.3 Hz, ArH), 7.20 (1H, s, ArH), 7.18
(1H, s, ArH), 7.17 (1H, d, J=5.3 Hz), 6.93 (2H, d, J=3.4 Hz, ArH), 6.85
(1H, d, J=3.5 Hz, ArH), 6.84 (1H, d, J=3.5 Hz, ArH), 6.49–6.52 (4H,
6822
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ꢁ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 6821 – 6829

Redox-Active Polymers with Dendritic Thiophene Side Chains
FULL PAPER
cule as
a
dark-red solid (1.8 g, 94%). FTIR (ATR): n˜ =1697 cmÀ1
br, ArH), 7.37 (2H, br, ArH), 7.02 (5H, br, ArH), 7.00 (8H, br, ArH),
6.88 (8H, br, ArH), 4.30–4.41 (6H, br, -CH2-), 2.16 (12H, br, CH3),
1.80 ppm (3H, br, CH3). 13C NMR (CDCl3, 100.61 MHz): d=167.2, 165.9,
160.1, 142.0, 139.7, 138.7, 138.4, 137.9, 137.4, 136.7, 136.0, 133.4, 130.6,
129.2, 129.1, 128.9, 127.3, 126.6, 125.2, 125.1, 120.9, 62.9, 62.4, 21.2,
18.3 ppm.
(-COOH); 1H NMR (CDCl3, 400.13 MHz): d=7.70 (1H, d, J=4.0 Hz,
ArH), 7.17–7.22 (4H, m, ArH), 7.15 (2H, d, J=3.6 Hz, ArH), 6.93 (2H,
d, J=5.3 Hz, ArH), 6.84–6.89 (4H, m, ArH), 6.60–6.64 (2H, m, ArH),
3.66 (1H, br, -COOH), 2.47 ppm (12H, s, CH3); 13C NMR (CDCl3,
100.61 MHz): d=160.5, 147.2, 144.6, 140.7, 139.3, 139.0, 137.5, 136.2,
135.6, 133.9, 133.7, 127.7, 15.8 ppm; MALDI-TOF-MS: m/z (%): 841
(100) [M+H]+.
Copolymerization of MMA and 7 (11–14): Two solutions of methyl meth-
acrylate (0.2m; MMA) and 7 in toluene (0.2m) were prepared, and the
two solutions were mixed in a Schlenk tube in different ratios (5:95,
20:80, 50:50, 80:20 v/v). AIBN (0.25 mol%) was added to each solution
and the mixed solutions were degassed by three freeze/pump/thaw cycles.
The homogeneous solutions were placed into an oil bath heated to 608C.
After stirring overnight, the solution was evaporated and dissolved in the
minimum amount of CH2Cl2. The addition of acetone caused a precipi-
tate to form, which was collected by filtration. Finally, the polymer was
purified by GPC (Biorad Biobeads SX-1; THF).
11: Yield=5 mg; Mw =4.3ꢃ103 gmolÀ1; PDI=2.3 (determined by GPC
analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.7 (br, ArH), 7.3–6.9 (br,
ArH), 6.6 (br, ArH), 5.0 (br, -COOCH3), 4.5–4.7 (br, -CH2-), 2.27 (s,
-CH3), 1.40–1.45 ppm (m, -CH3).
12: Yield=10 mg; Mw =4.5ꢃ103 gmolÀ1; PDI=2.1 (determined by GPC
analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.7 (br, ArH), 7.3–6.9 (br,
ArH), 6.6 (br, ArH), 5.0 (br, -COOCH3), 4.5–4.8 (br, -CH2-), 2.27 (s,
-CH3), 1.40–1.46 ppm (m, -CH3).
13: Yield=10 mg; Mw =2.3ꢃ104 gmolÀ1; PDI=2.5 (determined by GPC
analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.7 (br, ArH), 7.3–6.9 (br,
ArH), 6.6 (br, ArH), 4.9 (br, -COOCH3), 4.4–4.7 (br, -CH2-), 2.27 (s,
-CH3), 1.40–1.45 ppm (m, -CH3).
Compound 6 was hydrolyzed by using the same procedure (95%). FTIR
(ATR): n˜ =1698 cmÀ1 (-COOH); H NMR (CDCl3, 400.13 MHz): d=8.12
1
(2H, d, J=8.4 Hz, ArH), 7.70 (2H, d, J=8.4 Hz, ArH), 7.39(1H, d, J=
4.0 Hz, ArH), 7.28 (1H, d, J=3.6 Hz, ArH), 7.22–7.24 (3H, m, ArH),
7.17–7.21 (8H, m, ArH), 7.07–7.10 (8H, m, ArH), 3.65 (1H, br,
-COOH), 2.32 ppm (12H, s, CH3); 13C NMR (CDCl3, 100.61 MHz): d=
169.6, 160.1, 140.8, 140.7, 139.4, 138.9, 138.1, 137.7, 136.4, 133.6, 130.3,
129.2, 127.8, 126.5, 121.5, 23.2 ppm. MALDI-TOF-MS: m/z (%): 810
(100) [M+H]+.
Macromonomer 7: A mixture of the hydrolysis product of 5 (0.1 g,
0.124 mmol) and 2-hydroxyethyl methacrylate (HEMA; 19 mL,
0.157 mmol) were dissolved in dry dichloromethane in a nitrogen atmos-
phere. 4-Dimethylaminopyridium toluene-para-sulfonate (DPTS; 10 mg,
36.3 mmol) and 1,3-dicyclohexylcarbodiimide (DCC; 75 mg, 0.36 mmol)
were added to this solution. The reaction mixture was stirred for two
days at room temperature. The reaction mixture was filtered and the fil-
trate was concentrated to dryness by using a vacuum evaporator. The res-
idue was purified by column chromatography on silica gel and recycling
preparative HPLC with CHCl3 as the eluant to give the desired product
(33%). FTIR (ATR): n˜ =1708 cmÀ1 (-COOCH3); 1H NMR (CDCl3,
400.13 MHz): d=7.72 (1H, s, ArH), 7.24 (1H, s, ArH), 7.22 (2H, d, J=
8.1 Hz, ArH), 7.15 (2H, d, J=8.0 Hz, ArH), 6.94 (2H, d, J=3.6 Hz,
ArH), 6.87 (2H, d, J=3.6 Hz, ArH), 6.62–6.65 (4H, m, ArH), 6.16 (1H,
s, -C=CH2), 5.60 (1H, s, -C=CH2), 4.55 (2H, t, J=5.2 Hz, -CH2-), 4.47
(2H, t, J=5.6 Hz, -CH2-), 2.48 (12H, s, CH3), 1.96 ppm (3H, s, -CH3);
13C NMR (CDCl3, 100.61 MHz): d=168.1, 160.1, 145.5, 141.5, 139.3,
138.8, 137.6, 136.8, 136.0, 134.7, 129.4, 128.3, 127.6, 126.6, 126.2, 125.3,
122.7, 62.9, 62.4, 17.2, 15.4 ppm; MALDI-TOF-MS: m/z (%): 953 (100)
[M+H]+; elemental analysis (%) calcd for C47H36O4S9: C 59.21, H 3.81,
O 6.71; found: C 59.1, H 3.9, O 6.7.
14: Yield=49 mg; Mw =5.8ꢃ104 gmolÀ1; PDI=2.7 (determined by GPC
analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.7 (br, ArH), 7.3–6.8 (br,
ArH), 6.6 (br, ArH), 5.0 (br, -COOCH3), 4.4–4.6 (br, -CH2-), 2.23 (s,
-CH3), 1.40–1.45 ppm (m, -CH3).
Atom-transfer radical polymerizartion of 7 from the PEG macroinitiator:
CuCl (3.0 mg, 0.31 mmol), PEG macroinitiator (8.1 mg, 4.26 mmol), and 7
(0.3 g, 0.31 mmol) were mixed in a Schlenk tube. A solution of 4,4’-di-
nonyl-2,2’-bipyridine (12.9 mg, 0.35 mmol) in anisole (60 mL) was added
though a syringe and the mixed solutions were degassed by three freeze/
pump/thaw cycles. The homogeneous solutions were placed into an oil
bath heated to 608C and stirred at 608C for 24 h. The solution was
passed through a neutral Al2O3 column with THF as the eluent to
remove the catalyst. Polymer 15 was purified by GPC (Biorad Biobeads
Macromonomer 8 was synthesized by the same procedure used to pre-
pare
7
(56%). FTIR (ATR): n˜ =1707 cmÀ1 (-COOCH3); 1H NMR
(CDCl3, 400.13 MHz): d=8.04 (2H, d, J=8.4 Hz, ArH), 7.64 (2H, d, J=
8.0 Hz, ArH), 7.26 (1H, s, ArH), 7.24 (1H, s, ArH), 7.22 (1H, s, ArH),
7.08–7.20 (16H, m, ArH), 6.15 (1H, s, -C=CH2), 5.59 (1H, s, -C=CH2),
4.56 (2H, t, J=5.1 Hz, -CH2-), 4.50 (2H, t, J=5.5 Hz, -CH2-), 2.32 (12H,
s, CH3), 1.96 ppm (3H, s, -CH3); 13C NMR (CDCl3, 100.61 MHz): d=
167.2, 165.9, 160.1, 142.0, 139.7, 138.7, 138.4, 137.9, 137.4, 136.7, 136.0,
133.4, 130.6, 129.2, 129.1, 128.9, 127.3, 126.6, 125.2, 125.1, 120.9, 62.9,
62.4, 21.2, 18.3 ppm; MALDI-TOF-MS: m/z (%): 923 (100) [M+H]+; el-
emental analysis calcd for C57H46O4S4: C 74.15, H 5.02, O 6.93; found: C
74.1, H 5.0, O 7.0.
SX-1; THF). Yield=234 mg; Mw =1.1ꢃ104 gmolÀ1
; PDI=1.1 (deter-
mined by GPC analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.5 (br,
ArH), 7.3–6.9 (br, ArH), 6.8 (br, ArH), 6.6 (br, ArH), 5.0 (br,
-COOCH3), 4.5–4.7 (br, -CH2-), 3.4–4.0 (m, -CH2-), 2.4 (s, -CH3), 1.2 ppm
(m, -CH3); 13C NMR (CDCl3, 100.61 MHz): d=173.3, 167.8, 159.7, 144.5,
140.5, 139.0, 138.0, 135.9, 135.1, 133.9, 129.4, 128.6, 126.8, 121.6, 71.9,
65.5, 63.6, 61.9, 58.7, 44.4, 38.5, 30.6, 28.4, 16.6, 15.3, 11.3 ppm.
Dendronized polymer 9: Toluene (1.05 mL) was added to 7 (50 mg,
52.5 mmol) and 2,2’-azoisobutyronitrile (AIBN; 20 mg, 0.25 mol%) in a
Schlenk tube, and the reaction mixture was degassed by three freeze/
pump/thaw cycles. The homogeneous solution was placed into an oil bath
heated to 608C. After stirring overnight, the solution was evaporated and
dissolved in the minimum amount of CH2Cl2. The addition of acetone
caused a precipitate to form, which was collected by filtration. Finally,
the polymer was purified by gel permeation chromatography (GPC;
Results and Discussion
Syntheses of macromonomers: Dendritic macromonomers 7
and 8 were synthesized from 2,3-dibromothiophene by using
metal-catalyzed cross-coupling reactions (Scheme 1). Ter-
thiophene 1 was synthesized by the nickel-catalyzed cross-
coupling reaction of the Grignard regent of 2-bromo-5-
methylthiophene and 2,3-dibromothiophene according to
the method reported by Advincula and co-wokers.[11] The
two a-positions in 1 were protected with methyl groups and
one free a-position was used as the reaction point for build-
ing higher generational dendrons. The other component,
that is, 2, was synthesized by using the Suzuki–Miyaura cou-
pling reaction between 2,3-dibromothiophene and 4-methyl-
Biorad Biobeads SX-1, THF; 66% conversion). Mw =2.1ꢃ105 gmolÀ1
;
1
PDI=2.7 (determined by GPC analysis); H NMR (CDCl3, 400.13 MHz):
d=7.70 (1H, br, ArH), 7.24–6.85 (10H, br, ArH), 6.62–6.65 (4H, br,
ArH), 4.50–4.75 (6H, br, -CH2-), 2.48 (12H, s, -CH3), 1.96 ppm (3H, s,
-CH3); 13C NMR (CDCl3, 100.61 MHz): d=173.1, 160.3, 145.0, 140.3,
140.2, 139.2, 139.2, 138.7, 138.4, 136.5, 135.8, 134.6, 134.0, 129.1, 128.6,
127.6, 127.2, 125.2, 121.2, 63.9, 63.1, 42.0, 26.1, 16.5, 15.3, 11.3 ppm.
Dendronized polymer 10 was synthesized by the same procedure used to
prepares 9 (87% conversion). Mw =1.0ꢃ105 gmolÀ1,; PDI=1.4 (deter-
mined by GPC analysis); 1H NMR (CDCl3, 400.13 MHz): d=7.79 (2H,
Chem. Eur. J. 2011, 17, 6821 – 6829
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6823

M. Kimura et al.
owing to the attachment of
bulky branches. The optimized
geometries and the calculated
torsion angles between aromat-
ic rings for 7 and 8 are shown
in Figure S1 in the Supporting
Information. Although the tor-
sion angle between the focal
thiophene plain and the con-
necting thiophene plain in 7 is
around 158, the angle between
the focal benzene plain and the
first connecting thiophene plain
is 268. The all-thiophene macro-
moner 7 has a more planar con-
formation relative to the
phenyl-terminated macromono-
mer 8. The enhancement of
conjugation in 7 may lead to
one broad absorption peak. The
steady-state fluorescence spec-
tra of 7 and 8 in degassed
CH2Cl2 are shown in Figure 1b.
Macromonomers 7 and 8 emit-
Scheme 1. Synthesis of dendritic macromonomers 7 and 8. a) BuLi, Bu3SnCl; b) 2,3-dibromothiophene, [Pd-
(PPh3)4], DMF; c) 5-bromo-2,2-bithiophene-5’-carboxylic acid methyl ester, [Pd(PPh3)4], DMF; d) methyl 4-
(5’-bromothiophene)benzoate, [Pd(PPh3)4], DMF; e) 1m KOH aq. THF; f) HEMA, DCC, DPTS, CH2Cl2.
G
ACHTUNGTRENNUNG
ted fluorescence peaks at lmax
=
AHCTUNGTRENNUNG
550 and 520 nm by the excita-
phenylboronic acid in the presence of a palladium catalyst.
These compounds were converted into the corresponding
stannyl compounds by treatment with n-buthyllithium and
tributyltin chloride. The Stille coupling reaction of the stan-
nyl compounds with 2,3-dibromothiophene gave second-gen-
eration dendron units 3 and 4 in a yield of 70%. The synthe-
sized dendrons 3 and 4 were treated with 5-bromo-2,2-bi-
thiophene-5’-carboxylic acid methyl ester or methyl 4-(5’-
bromothiophene)benzoate to give 5 and 6. After hydrolysis
of the ester group, 5 and 6 were subsequently converted into
macromonomers 7 and 8 by a reaction with HEMA in the
presence of DCC and DPTS. The synthesized macromono-
Figure 1. a) Absorption and b) fluorescence spectra of macromonomers 7
(solid line) and 8 (dashed line) in CH2Cl2.
1
mers 7 and 8 were fully characterized by H, 13C NMR, and
FTIR spectroscopy, as well as MALDI-TOF mass spectrom-
etry. Both macromonomers are highly soluble in common
solvents, such as CH2Cl2, THF, toluene, DMF, and dimethyl
sulfoxide (DMSO), at room temperature.
tion at the absorption maxima. The fluorescence band has
become somewhat broadened and structureless in contrast
to those of linear oligomers.[18,19] The fluorescence quantum
yields of 7 and 8 (FF =8 and 9%, respectively) are signifi-
cantly lower than those of linear oligomers, thus suggesting
a short length of the p-conjugated system in the dendritic
macromonomers. The fluorescence of the dendrtic oligothio-
phene macromonomers comes from the longest chromo-
phoric a-conjugated unit in a branched structure and the
substitution of the thiophene rings at the b-positions induces
the twisted conformation of the a-conjugated unit.
Although the synthesized macromonomers contain linear
sexithiophene and thiophene-phenylene co-oligomer, the ab-
sorption and fluorescence spectra of 7 and 8 are different
from those of linear oligomers (Figure 1). The absorption
spectra of 7 and 8 exhibited broad bands at lmax =398 and
402 nm, respectively. Although 7 has only one broad absorp-
tion peak, the spectrum of 8 exhibits two peaks at lmax =355
and 402 nm. The observed absorption maxima of 7 and 8
were blueshifted relative to the reported maxima of linear
sexithiophene (lmax =432 nm)[18] and phenyl-terminated qua-
terthiophene[18] (lmax =426 nm),[18] thus suggesting a sterical-
ly driven increase in the twisted angle within the oligomers
Polymerization of macromonomers: Dendritic macromono-
mers 7 and 8 were polymerized in dry toluene by using
0.25 mol% AIBN as a radical initiator at 608C for 24 hours
6824
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Redox-Active Polymers with Dendritic Thiophene Side Chains
FULL PAPER
Figure 2. a) Absorption and b) fluorescence spectra of dendronized poly-
mers 9 (solid line) and 10 (dashed line) in CH2Cl2. c) Fluorescence spec-
tral shift with increasing molar ratio of 7 with copolymers 11, 12, and 14
in CH2Cl2.
this peak disappeared in 9 and a glass-transition tempera-
ture was determined to be Tg =51.08C (see Figure S2 in the
Supporting Information). The decomposition temperatures
for 5% weight loss are 356 and 3608C for 9 and 10, respec-
tively. These results indicate that both polymers exhibited
excellent thermal stability.
Figure 2 shows the absorption and fluorescence spectra of
dendronized polymers 9 and 10 in CH2Cl2. Low concentra-
tions were used to avoid aggregation among polymers. The
absorption band of 9 is slightly broadened and the position
of the absorption maximum in 9 is blueshifted with respect
to 7. The absorption spectrum of the spin-coated film of 9
on quartz plates also shows a broadening relative to that of
7 (see Figure S3 in the Supporting Information). Schlꢂter
and co-workers reported no difference between the absorp-
tion spectra of the thiophene-based macromonomers and
the dendronized polymer.[16] The observed broadening in the
absorption spectrum of 9 may result in the overlapping of
planer dithiophene segments in 7 through the polymeri-
zation. The fluorescence maxima is redshifted by Dl=
21 nm relative to their respective macromonomers. Further-
more, the fluorescence quantum yield of 9 (FF =2%) is de-
crease by the polymerization. On the other hand, the ab-
sorption spectrum of 10 is similar to that of 8. Furthermore,
the shift of the fluorescence maximum and the decrease in
the fluorescence quantum yield (i.e., FF =6%) for 10 are
small relative to those for monomer 8 (Table 1). The fluores-
cence changes are presumably
Scheme 2. Synthesis of the dendronized polymers.
after three freeze/pump/thaw cycles (Scheme 2).[20] Gel-per-
meation chromatography (GPC) of 9 and 10 with THF as
the eluent revealed a monomodal distribution with weight-
average molecular weight of Mw =2.1ꢃ105 and 1.0ꢃ
105 gmolÀ1 (with a polydispersity index (PDI) of 2.7 and
1.4), respectively, relative to polystyrene standards (Table 1).
The resulted dendronized polymers exhibit good solubility
in toluene, THF, and chlorinated organic solvents (above
30 mgmLÀ1) without any flexible and long terminal substitu-
ents. The thermal properties of polymers 9 and 10 were
evaluated by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA) in a nitrogen atmos-
phere. Whereas the DSC profile of 7 shows a sharp transi-
tion peak at 1168C, which corresponds to a melting point,
the result of p–p interactions
between the thiophene den-
Table 1. Photophysical[a] and electrochemical data for the macromonomers and dendronized polymers.[b]
drons by the linkage of focal
points through the polymeri-
zation. The difference between
9 and 10 can be attributed to
the degree of interaction be-
tween the dendrons in the
dendronized polymers. To in-
vestigate the influence of dis-
tance between the thiophene
dendrons within the polymer
chain on the fluorescence spec-
tra, copolymers were synthe-
Macromonomers
lmax [nm]
lem
FF
HOMO
LUMO
[eV]
2.8 (2.8)[c] 2.5
2.7 (2.9)[c] 2.6
Eg
[eV]
E1/2
ACHTUNGTRENN[UNG V vs SEC]
A
U
[%] [eV]
7
8
398 (4.6)
402 (4.5)
550
522
8
9
5.3 (5.3)[c]
+0.70, +0.91, +1.33
+0.82, +1.05, +1.10
5.3 (5.4)[c]
Dendronized Mw
PDI Tg
lmax
lem
FF
HOMO
LUMO
[eV]
Eg
[eV]
E1/2
[V vs SEC]
[d]
polymers
N
]
[o C] [nm] [nm] [%] [eV]
ACHTUNGTRENNUNG
9
10
2.1ꢃ105
1.0ꢃ105
2.7
1.4
51
41
389
423
571
531
2
6
5.4 (5.8)[c] 3.0 (3.4)[c] 2.4
5.4 (5.8)[c] 2.9 (3.2)[c] 2.5
+1.2
+1.1
[a] lmax =maximum of absorption measured in CH2Cl2; e=extinction coefficient at lmax; lem =maximum of
fluorescence measured in degassed CH2Cl2; FF =quantum yield. [b] Measured in CH2Cl2 containing 0.1m
Bu4NPF6 at 295 K, scan rate=100 mVsÀ1. [c] HOMO and LUMO energies estimated from electrochemical
measurements. [d] Weight-average molecular weight relative to polyACTHNUTRGNE(NUG styrene) standards.
Chem. Eur. J. 2011, 17, 6821 – 6829
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6825

M. Kimura et al.
sized by the radical polymerization of 7 and MMA in vari-
ous molar ratios. Four copolymers 11–14 containing 7 at 5,
20, 50, and 80 mol% were prepared by copolymerization be-
tween 7 and MMA. The fluorescence spectra of 11--14 are
shown in Figure 2c. The composition ratios of the copoly-
(AFM) to investigate their individual molecular dimensions
and morphologies. The interaction between the dendrons in
the dendronized polymers can lead to highly ordered mate-
rials in the solid state. The two-dimensional arrays of rodlike
dendronized polymers on the substrates were visualized by
AFM.[22] Thin layers of dendronized polymers were pre-
pared by spin-coating from a dilute solution of 9 in THF
(1.0 mgmLÀ1) on mica. The AFM image of a thin film of 9
shows terraces with height differences of 4.8 nm between ad-
jacent terraces (Figure 3). The molecular dimension of the
1
mers were confirmed by H NMR spectroscopic analysis and
are almost the same as the initial molar ratios. Copolymer
11 containing 5 mol% of 7 shows a fluorescence maximum
at lmax =551 nm, which is close to that of 7. The fluorescence
maximum is gradually redshifted with an increasing molar
ratio of 7 in the copolymers and reaches lmax =570 nm for
14. Moreover, the fluorescence quantum yield decreases
from 8 to 2% by increasing the molar ratio (FF =8, 7, 4,
and 2% for 11–14, respectively). This result confirms the
spatial overlapping of the thiophene dendrons through p–p
interactions when they are connected to the polymer back-
bone.
The optical band gaps (Eg) for the dendritic macromono-
mers and dendronized polymers were determined from the
cross point of the normalized absorbance and fluorescence
spectra of thin films on quartz substrates. The HOMO and
LUMO energies were estimated from the optical band gaps
and the work functions measured by photoelectron spectros-
copy in air. The band gaps and HOMO and LUMO energies
of 7–10 are listed in Table 1. The band gaps of 7 and 8 are
slightly decreased by the polymerization.
Electrochemistry: The electrochemical properties of the oli-
gothiophenes provide important information on their elec-
tronic structures and the charge-transportation mechanism
employed. In this context, many oligothiophenes and den-
dritic thiophenes have been investigated.[11,12,18–20] The elec-
trochemical properties of the macromonomers and dendron-
ized polymers were investigated by using cyclic voltammetry
(CV) experiments, which were performed in degassed
CH2Cl2 containing Bu4NClO4 as a supporting electrolyte at
100 mVsÀ1 at room temperature (Table 1). All the potentials
were calibrated against a ferrocene/ferrocenium couple,
which was used as an internal standard. The CV curve of 7
showed three quasireversible oxidation processes with half-
wave potentials at +0.70, +0.91, and +1.33 V versus SCE
(see Figure S4 in the Supporting Information). Furthermore,
the phenyl-terminated macromonomer 8 also exhibited
three oxidation potentials at +0.82, +1.05, and +1.10 V
versus SCE. The presence of three oxidation peaks indicates
a mixture of different conjugated lengths within the dendrit-
ic oligomers.[21] In contrast, the voltammograms of dendron-
ized polymers 9 and 10 show one irreversible and ill-defined
oxidation peak at +1.20 and +1.08 V, respectively. The oxi-
dation processes of the polymers occurred at higher poten-
tials than those of the corresponding macromonomers. This
outcome indicates that the overlapping of dendrons within
the polymers induces an increased chemical stability of the
oxidized species.
Figure 3. a) AFM image of the spin-coated film of 9 on a mica substrate
and b) cross-sectional profile along the line. The inset shows the schemat-
ic model of the dendronized polymer 9.
dendritc monomonomer 7 was estimated to have a length of
2.6 nm according to computer-generated modeling. The ob-
served terrace height was almost double of the length of 7.
The polymer backbone was encapsulated in a cylindrical
shell of tightly packed thiophene dendrons with a thickness
of approximately 4.9 nm. The estimated diameter of the
dendronized polymer almost agrees with the terrace height
observed in the AFM image. The other dendronized poly-
mer 10 showed a similar AFM image with a terrace height
of 4.7 nm. It is concluded from these results that dendron-
ized polymers 9 and 10 can assemble into two-dimensional
packing arrangements on the solid.
Electronic conductivity: The electric conductivities of the
thin films were measured by a conventional two-point probe
by using interdigitated microcircuit electrodes (IMEs) with
spacing of approximately 5 mm with 65 finger pairs per
device. A thin film of 9 was prepared by spin-coating, and
the finger electrode array in the IMEs was fully covered
with a thin film of 9. The coverage area was confirmed by
Assembly of dendronized polymers: The dendronized poly-
mers were visualized by atomic force scanning microscopy
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Redox-Active Polymers with Dendritic Thiophene Side Chains
FULL PAPER
Figure 4. Current/voltage (I/V) curves of thin films of 9 on IMEs before
and after doping with I2 and NOBF4 at room temperature: (*) 9 without
doping, (*) 9 doped with I2, (~) 9 doped with 10 mol% NOBF4, and
(~) 9 doped with 30 mol% NOBF4.
Scheme 3. Synthesis of the amphiphilic dendronized polymer. dNbpy=
4,4’-d(5-nonyl-2,2’-bipyridine).
using optical microscopy and the film thickness was deter-
mined by the surface profiler (thickness of tested films:
100Æ30 nm). Figure 4 shows the current/voltage curves of
the thin film of dendronized polymer 9 at room tempera-
ture. The film of 9 exhibits low conductivity in the range
10À10–10À9 ScmÀ1. After exposure of the films to I2 vapor,
the conductivity of the film increased to 10À7–10À6 ScmÀ1
owing to the partial oxidation of the thiophene dendrons in
the dendronized polymers.[23] Polymer 9 was oxidized by ni-
trosonium tetrafluoroborate (NOBF4) in toluene.[24] The ab-
sorption band in the l=400–500 nm region decreased and a
broad absorption band in the l=600–800 nm region ap-
peared by adding NOBF4 to a solution of 9 in toluene. This
spectral change indicates that the dendritic thiophene is oxi-
dized by NOBF4. The electronic conductivities of 9 in-
creased with an increasing concentration of NOBF4 and
reached 10À7–10À6 ScmÀ1 above a NOBF4 concentration of
30 mol%. On the other hand, the film of 10 showed low
conductivity (i.e., 10À10–10À9 ScmÀ1) after exposure to I2.
The absorption spectrum of 10 in toluene remained unal-
tered by the addition of NOBF4, thus suggesting a decreased
stability relative to the all-thiophene dendron in 9.
tor (Scheme 3). ATRP, developed by Matyjaszewski and co-
workers, is a versatile method for preparing well-defined
polymers with a narrow molecular-weight distribution.[27]
GPC analysis of 15 revealed a monomodal distribution of
Mw =1.1ꢃ104 gmolÀ1. Block copolymer 15 exhibited
a
narrow PDI of 1.1, thus implying successful polymerization
of the dendritic macromonomers from the PEG macroinitia-
tor by ATRP. Broadening of the absorption band and the
redshift of the fluorescence peak in 15 relative to monomer
7 were also observed, thus indicating the overlapping of
dendrons in the block copolymers. Block copolymer 15 can
disperse readily in water and the dispersed aqueous solution
is stable over a period of several months. The morphologies
of the aggregate in water were examined by TEM. The
sample used for TEM analysis was prepared by drop-casting
the dispersed solution onto a carbon-coated grid. Amphi-
philic diblock copolymer 15 produced a good contrast in the
TEM image without staining, and spherical hollow objects
were observed with a diameter of approximately 20 nm
(Figure 5). The dark image is ascribed to an accumulation of
p-conjugated thiophene dendrons. The amphiphilic block
copolymer is composed of a hydrophobic dendronized poly-
mer and hydrophilic coil organized in aqueous media to pro-
duce capsules by the segregation of the hydrophobic and hy-
drophilic segments.
Self-organization of amphiphilic dendronized polymers:
Amphiphilic block copolymers composed of hydrophilic and
hydrophobic segments can organize into well-defined large-
scaled objects.[25] Iyoda and co-workers reported an organi-
zation of amphiphilic diblock copolymers synthesized by
using atom-transfer radical polymerization (ATRP) of liquid
crystalline monomers from a hydrophilic PEG chain.[26] This
diblock polymer was organized into a two-dimensional
phase-separated structure in which PEG cylinders are ori-
ented vertically with respect to the plane of the films coated
onto the substrates. Incorporating the dendrons into the am-
phiphilic block copolymers could lead to unique organized
structures.
Conclusion
Dendronized polymers containing thiophene dendrons as a
pendant group were synthesized. Absorption, fluorescence,
and electrochemical changes in solution revealed that the
linkage of dendrons with a polymer backbone leads to spa-
tial overlapping of the thiophene dendrons. Furthermore,
the polymerization of the macromonomers from the PEG
macroinitiator produced an amphiphilic diblock copolymer,
and the synthesized copolymer organized into spheres.
These redox-active objects will provide a new way of design-
An amphiphilic block copolymer 15 was synthesized by
the copper-mediated ATRP of 7 from the PEG macroinitia-
Chem. Eur. J. 2011, 17, 6821 – 6829
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M. Kimura et al.
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Received: December 16, 2010
Revised: February 17, 2011
Published online: May 5, 2011
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