Incorporation of π-conjugated polymer into silica: Preparation of poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]/silica and poly(3-hexylthiophene)/silica composites

Article abstract of DOI:10.1021/ma0508956

The Wittig reaction of 2-methoxy-5-(2-ethylhexyloxy)-p- xylylenebis(triphenylphosphonium chloride) with 2-methoxy-5-(2-ethylhexyloxy) benzene-1,4-dicarbaldehyde was carried out to obtain poly-[2-methoxy-5-(2- ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) terminated with a phosphonium moiety at the chain end. Poly[3-hexylthiophene-co-3-(6-hydroxyhexyl)thiophene]s were prepared by regioselective coupling reaction of 2-bromo-3-hexylthiophene and 2-bromo-3-(6-(2-tetrahydropyranyloxy)-hexyl)thiophene and subsequent cleavage of a tetrahydropyranyl group. Acid-catalyzed polycondensations of tetraethoxysilane (TEOS) were carried out in the presence of these polymers to give homogeneous composites with silica. The resulting composite materials were characterized by UV-vis and emission spectra.

Full text of DOI:10.1021/ma0508956

7314
Macromolecules 2005, 38, 7314-7320
Incorporation of π-Conjugated Polymer into Silica: Preparation of
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene]/Silica and
Poly(3-hexylthiophene)/Silica Composites
Masataka Kubo,* Chiharu Takimoto, Yuya Minami, Takahiro Uno, and
Takahito Itoh
Department of Chemistry for Materials, Faculty of Engineering, Mie University, Tsu 514-8507, Japan
Masashi Shoyama
Industrial Research Division, Mie Science and Technology Promotion Center, Tsu 514-0819, Japan
Received April 27, 2005; Revised Manuscript Received July 1, 2005
ABSTRACT: The Wittig reaction of 2-methoxy-5-(2-ethylhexyloxy)-p-xylylenebis(triphenylphosphonium
chloride) with 2-methoxy-5-(2-ethylhexyloxy)benzene-1,4-dicarbaldehyde was carried out to obtain poly-
[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) terminated with a phosphonium
moiety at the chain end. Poly[3-hexylthiophene-co-3-(6-hydroxyhexyl)thiophene]s were prepared by
regioselective coupling reaction of 2-bromo-3-hexylthiophene and 2-bromo-3-(6-(2-tetrahydropyranyloxy)-
hexyl)thiophene and subsequent cleavage of a tetrahydropyranyl group. Acid-catalyzed polycondensations
of tetraethoxysilane (TEOS) were carried out in the presence of these polymers to give homogeneous
composites with silica. The resulting composite materials were characterized by UV-vis and emission
spectra.
Scheme 1
Introduction
Organic/inorganic composite materials have rapidly
become a fascinating new field of research in materials
science. The sol-gel method is widely studied for
obtaining an organic/silica composite which combines
the advantages of the organic molecule (flexibility,
prosessability, ductility) and the inorganic material
(rigidity, high thermal stability).1,2 A three-dimensional
silica network can be formed by a stepwise polyconden-
sation reaction of alkoxysilane. Its low-temperature
processing allows organic molecule to be incorporated
into silica without decomposition. We are interested in
the incorporation of π-conjugated polymer into silica
because π-conjugated polymers are a class of materials
that hold promise as a basis for electrooptical applica-
tions. Although π-conjugated polymer/silica composites
have attracted particular interest, its preparation is
severely limited by the incompatibility of the two
components. Several laboratories have reported the
incorporation of π-conjugated polymers into silica. Poly-
(1,4-phenylenevinylene)s/silica composites have been
successfully prepared by the sol-gel method using
water/alcohol-soluble sulfonium salt precursors.3-6 Wei
et al. reported polyaniline/silica composite using the
sol-gel method of poly[methyl methacrylate-co-3-(tri-
methoxysilyl)propyl methacrylate] in the presence of
camphorsulfonic acid-doped polyaniline.7
In this study poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-
phenylenevinylene] (MEH-PPV) and poly(3-hexylth-
iophene) (P3HexTh) have been chosen as representative
soluble π-conjugated polymers (Scheme 1). We intro-
duced phosphonium salt moiety and hydroxy group onto
MEH-PPV and P3HexTh, respectively. Preparations
and optical properties of MEH-PPV/silica and P3HexTh/
silica composites will be reported.
Experimental Section
Materials. Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenyle-
nevinylene] (MEH-PPV) and butyllithium were purchased
from Aldrich and used as received. Tetraethoxysilane (TEOS)
was distilled under reduced pressure. Tetrahydrofuran (THF)
was purified by distillation over sodium under nitrogen using
benzophenone as an indicator for dryness. Diisopropylamine
was distilled from sodium hydroxide under nitrogen. N-Bromo-
succinimide (NBS) was recrystallized from boiling water. All
other reagents were purchased from Tokyo Kasei Kogyo (TCI)
and used without further purification. Merck silica gel (grade
60, 70-230 mesh) was used for column chromatography.
Instrumentation. 1H and 13C NMR spectra were recorded
at room temperature on a JEOL EX-270 nuclear magnetic
resonance at 270 and 67.5 MHz, respectively. Samples were
dissolved in CDCl3, and tetramethylsilane (TMS) was added
as the internal standard. Infrared spectra were recorded on a
Jasco IR-700 infrared spectrophotometer. Gel permeation
chromatography (GPC) was carried out on a Tosoh HLC-8020
chromatograph equipped with polystyrene gel columns (Tosoh
G2500H + G3000H; exclusion limit ) 6 × 104; 300 × 7.5 mm)
This report describes another approach for preparing
π-conjugated polymer/silica composites employing the
sol-gel method. Our idea is to introduce polar functional
groups into π-conjugated polymers in order to improve
the compatibility between the polymer and silica. The
interaction between the functional group of the polymer
and silanol group of silica during sol-gel process is
expected to help a homogeneous composite formation.
* Corresponding author: Tel +81-59-231-9411; Fax +81-59-231-
9471; e-mail kubo@chem.mie-u.ac.jp.
10.1021/ma0508956 CCC: $30.25 © 2005 American Chemical Society
Published on Web 07/30/2005

Macromolecules, Vol. 38, No. 17, 2005
Incorporation of π-Conjugated Polymer into Silica 7315
and refractive/ultraviolet dual mode detectors. Tetrahydrofu-
ran (THF) was used as the eluent at a flow rate of 1.0 mL/
min. The calibration curves for GPC analysis were obtained
using polystyrene standards. UV-vis spectra were recorded
on a Jasco Ubest V-570 spectrophotometer. Photoluminescence
spectra were recorded on a Hitachi F-4500 fluorescence spec-
trophotometer with exciting wavelength of 365 nm. Elemental
analysis was performed on a Yanaco MT-5 CHN CORDER.
Diethyl 2,5-Bis(5-hexenyloxy)terephthalate (2). A mix-
ture of diethyl 2,5-dihydroxyterephthalate8 (1) (32.4 g, 9.5
mmol), 6-bromo-1-hexene (3.4 g, 21 mmol), potassium carbon-
ate (87.3 g, 53 mmol), and 80 mL of N,N-dimethylformamide
(DMF) was stirred at 80 °C for 20 h. The reaction mixture was
poured in water and extracted with ethyl acetate. The organic
layer was washed with water three times, dried over anhy-
drous magnesium sulfate, and placed under reduced pressure
to give 2.8 g (69%) of 2 as a yellow oil. 1H NMR (CDCl3, δ,
ppm): 7.34 (s, 2H), 5.9-5.7 (m, 2H), 5.1-4.9 (m, 4H), 4.37 (q,
J ) 7.3 Hz, 4H), 4.01. 13C NMR (CDCl3, δ, ppm): 166.0, 151.6,
138.4, 124.7, 116.5, 114.7, 69.5, 61.2, 33.3, 28.7, 25.2, 14.2. IR
(NaCl, ν, cm-1): 1731 (CdO). Anal. Calcd for C24H34O6: C,
68.88; H, 8.19. Found: C, 68,57; H, 8.10.
It was dissolved in a small amount of THF, and the resulting
solution was poured into methanol to precipitate the polymer
again. This procedure was repeated twice to give 0.11 g (77%)
of 7 as a red powder: 1H NMR (CDCl3, δ, ppm): 7.7-6.7
(phenyls and vinylene), 5.9-5.7 (-CH)), 5.1-4.8 (CH2)), 4.1-
3.7 (OCH2), 3.6-3. (CH3O), 1.9-0.8 (CH, CH2, and CH3). GPC
(THF eluent, polystyrene standard): Mn ) 17 000 Da.
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevi-
nylene-co-2,5-bis(6-triethoxysilylhexyloxy)-1,4-phenyle-
nevinylene] (8). A mixture of polymer 7 (1.0 g), triethoxysi-
lane (1.7 g, 10 mmol), hydrogen hexachloroplatinate(IV)
hexahydrate (10 mg), and 16 mL of dichloromethane was
heated under reflux for 60 h. The reaction mixture was diluted
with dichloromethane and filtered. The filtrate was placed
under reduced pressure to remove the solvents to give 1.2 g
(quant) of 8 as a red powder: 1H NMR (CDCl3, δ, ppm): 7.7-
6.7 (phenyls and vinylene), 4.1-3.7 (OCH2), 3.6-3. (CH3O),
1.9-0.8 (CH, CH2, and CH3). GPC (THF eluent, polystyrene
standard): Mn ) 17 000 Da.
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevi-
nylene] (10). To a stirred solution of an equimolar amount of
dialdehyde 5 (200 mg, 0.670 mmol) and 2-methoxy-5-(2-
ethylhexyloxy)-p-xylylenebis(triphenylphosphonium chloride)11
(9) (576 mg, 0.670 mmol) in a mixture of 3 mL of ethanol and
2 mL of chloroform was added dropwise a solution of 176 mg
(2.6 mmol) of sodium methoxide dissolved in 3 mL of ethanol
at room temperature under nitrogen. The reaction mixture was
stirred for 24 h and poured into methanol to precipitate the
polymer. It was washed well with methanol to give 150 mg
(44%) of 10 as a red powder. GPC (THF eluent, polystyrene
standard): Mn ) 10 200 Da.
2,5-Bis(5-hexenyloxy)-p-xylylene Alcohol (3). Into a
suspension of lithium aluminum hydride (0.55 g, 15 mmol) in
40 mL of ether was added diester 2 in 40 mL of ether, and the
mixture was heated under reflux for 1 h. The reaction mixture
was cooled to 0 °C, and water was added dropwise to the
solution. The mixture was extracted with ethyl acetate. The
organic layer was dried with magnesium sulfate and placed
under reduced pressure to remove the solvent to give 2.0 g
1
(82%) of 3 as white needles. H NMR (CDCl3, δ, ppm): 6.85
(s, 2H), 5.9-5.7 (m, 2H), 5.1-4.9 (m, 4H), 4.67 (d, J ) 6.6 Hz,
4H), 3.99 (t, J ) 6.3 Hz, 4H), 2.31 (t, J ) 6.6 Hz, 2H), 2.13 (q,
J ) 6.9 Hz, 4H), 1.9-1.7 (m, 4H), 1.7-1.5 (m, 4H). 13C NMR
(CDCl3, δ, ppm): 150.6, 138.4, 129.1, 114.9, 112.3, 8.5, 62.0,
33.3, 28.8, 25.3. IR (KBr, ν, cm-1): 3292 (O-H). Anal. Calcd
for C20H30O4: C, 71.82; H, 9.04. Found: C, 71.99; H, 8.95.
2,5-Bis(5-hexenyloxy)benzene-1,4-dicarbaldehyde (4).
To a stirred suspension of pyridinium chlorochromate (PCC)
(1.9 g, 8.9 mmol) and sodium acetate (0.49 g, 6.0 mmol) in 100
mL of dichloromethane was added a solution of diol 3 (2.0 g,
6.0 mmol) in 20 mL of dichloromethane at room temperature.
After 12 h, the mixture was filtered through Florisil (magne-
sium silicates), and the solvent was evaporated at reduced
pressure. The residue was purified by silica gel column
chromatography (eluent: dichloromethane) to give 0.87 g (44%)
of dialdehyde 4 as a yellow solid: mp 55 °C. 1H NMR (CDCl3,
δ, ppm): 10.50 (s, 2H), 7.43 (s, 2H), 5.9-5.7 (m, 2H), 5.1-4.9
(m, 4H), 4.10 (t, J ) 6.3 Hz, 4H), 2.14 (q, J ) 7.3 Hz, 4H),
1.9-1.8 (m, 4H), 1.7-1.5 (m, 4H). 13C NMR (CDCl3, δ, ppm):
189.2, 138.1, 129.2, 115.0, 111.6, 69.0, 33.3, 28.4, 25.2. IR (KBr,
ν, cm-1): 1713 (CdO). Anal. Calcd for C20H26O4: C, 72.70; H,
7.93. Found: C, 72.40; H, 7.25.
2-Methoxy-5-(2-ethylhexyloxy)-1,4-bis(diethoxyphos-
phinylmethyl)benzene (6). A mixture of 2-methoxy-5-(2-
ethylhexyloxy)-p-xylylene chloride9 (2.8 g, 8.4 mmol) and
triethyl phosphite (2.8 g, 17 mmol) was heated at 160 °C for 3
h. After cooling, the reaction mixture was charged on a silica
gel column using ethyl acetate as the eluent. After the first
band was collected, the eluent was changed to a mixture of
dichloromethane and methanol (8:2 by volume), and the second
band was collected to give 3.8 g (85%) of 6 as an orange oil. 1H
NMR (CDCl3, δ, ppm): 6.91 (s, 2H), 4.1-3.8 (m, 12H), 3.22
(d, J ) 20.5 Hz, 4H), 1.8-1.6 (m, 6H), 1.5-1.2 (m, 46H), 0.88
(t, J ) 6.6 Hz, 6H). 13C NMR (CDCl3, δ, ppm): 150.5, 150.4,
119.2, 119.0, 114.5, 113.6, 70.9, 61.6, 61.5, 55.8, 39.4, 30.3, 28.8,
23.6, 22.7, 16.0, 13.6, 10.8. IR (NaCl, ν, cm-1): 1219 (PdO).
Poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevi-
nylene-co-2,5-bis(5-hexenyloxy)-1,4-phenylenevinyl-
lene] (7). Into a solution of 4 (179 mg, 0.59 mmol), 2-methoxy-
5-(2-ethylhexyloxy)benzene-1,4-dicarbaldehyde10 (5) (618 mg,
2.11 mmol), and 6 (1.451 g, 2.70 mmol) in 15 mL of THF was
added potassium tert-butoxide (0.62 g, 8.1 mmol) at room
temperature. The reaction mixture was heated under reflux
for 20 h and poured into methanol to precipitate the polymer.
3-(6-(2-Tetrahydropyranyloxy)hexyl)thiophene (13). A
solution of 6-chlorohexyl 2-tetrahydropyranyl ether12 (11) (9.6
g, 45 mmol) in 15 mL of THF was added to magnesium ribbons
(1.1 g, 45 mmol). After completion of the addition, the mixture
was heated under reflux for 12 h. To the Grignard solution
was added [1,3-bis(diphenylphosphino)propane]nickel(II) dichlo-
ride (0.23 g, 0.38 mmol) and a solution of 3-bromothiophene
(12) (6.2 g, 38 mmol) in 10 mL of THF at 0 °C. The mixture
was then heated under reflux for 12 h. After cooling, the
reaction mixture was poured into ammonium chloride solution
and extracted with ether. The organic layer was washed with
water, dried over anhydrous magnesium sulfate, and placed
under reduced pressure to remove the solvent. The residue
was distilled under reduced pressure to give 7.3 g (72%) of 13
as a colorless liquid: bp 160-161 °C/2 mmHg. 1H NMR
(CDCl3, δ, ppm): 7.3-7.1 (m, 1H), 7.0-6.8 (m, 2H), 4.6-4.5
(m, 1H), 3.9-3.3 (m, 4H), 2.62 (t, J ) 7.6 Hz, 2H), 1.9-1.3 (m,
14H). 13C NMR (CDCl3, δ, ppm): 143.1, 128.2, 125.0, 119.8,
98.8, 67.6, 62.3, 30.7, 30.5, 30.2, 29.7, 29.1, 26.1, 25.5, 19.7.
Anal. Calcd for C15H24O2S: C, 67.21; H, 9.01. Found: C, 67.40;
H, 8.89.
2-Bromo-3-(6-(2-tetrahydopyranyloxy)hexyl)th-
iophene (14). A mixture of 13 (2.6 g, 9.7 mmol), N-bromo-
succinimide (NBS) (1.8 g, 10 mmol), 6 mL of acetic acid, and
6 mL of chloroform was stirred at 50 °C for 30 min. The
reaction mixture was poured into water and extracted with
chloroform. The organic layer was washed with NaOH solution
until pH ∼6, dried over magnesium sulfate, and placed under
reduced pressure to remove the solvent. The crude product was
purified by silica gel column chromatography (eluent: dichlo-
romethane) to give 1.6 g (48%) of 14 as a yellow liquid. 1H
NMR (CDCl3, δ, ppm): 7.18 (d, J ) 6.4 Hz, 1H), 6.79 (d, J )
6.4 Hz, 1H), 4.6-4.5 (m, 1H), 3.9-3.3 (m, 4H), 2.62 (t, J ) 7.6
Hz, 2H), 1.9-1.3 (m, 14H). 13C NMR (CDCl3, δ, ppm): 141.8,
128.1, 125.1, 108.8, 98.8, 67.5, 62.3, 30.7, 29.6, 29.5, 29.3, 29.0,
26.0, 25.5, 19.6. Anal. Calcd for C15H23BrO2S: C, 51.87; H, 6.67.
Found: C, 51.99; H, 6.83.
Poly[3-hexylthiophene-co-3-(6-(2-tetrahydropyrany-
loxy)hexyl)thiophene] (16). In a typical example, 4.1 mL
of 1.6 M n-butyllithium in hexane (6.5 mmol) was added to a
solution of diisopropylamine (0.66 g, 6.5 mmol) in 30 mL of
THF at -78 °C. The solution was warmed to 0 °C, stirred for
5 min, and cooled back at -78 °C. To this reaction mixture
was added a solution of 2-bromo-3-hexylthiophene12 (1.26 g,

7316 Kubo et al.
Macromolecules, Vol. 38, No. 17, 2005
Table 1. Preparation of MEH-PPV/Silica Composite
run
MEH-PPV (mg)
TEOS (mL)
THF (mL)
acid (mL)
additive (mL)
appearance
1
2
3
4
5
10
5
4
4
4
4
4
6
6
6
6
6
2 M HCl (1)
1 M HCl (1)
1 M HCl (1)
1 M HCl (1)
0.1 M HCl (1)
none
phase separated
phase separated
phase separated
phase separated
phase separated
none
5
DMF (1)
DMF (1)
DMF (2)
1
1
5.1 mmol) and 14 (0.44 g, 1.3 mmol) in 5 mL of THF and the
solution was stirred at -78 °C for 40 min. This mixture was
cooled to -60 °C, magnesium bromide diethyl etherate (1.67
g, 6.5 mmol) was added, and then the reaction mixture was
stirred at -40 °C for 20 min. The reaction mixture was slowly
allowed to warm to 0 °C, and [1,3-bis(diphenylphosphino)-
propane]nickel(II) dichloride (17 mg, 0.03 mmol) was added.
The mixture was stirred at room temperature for 12 h and
poured into methanol to precipitate the polymer. It was further
purified by Soxhlet extraction using methanol for 24 h and
then hexane for 24 h to remove oligomers. Finally, the polymer
was isolated from the remaining residue via Soxhlet extraction
with chloroform. The chloroform solution was evaporated to
give copolymer 16b (0.46 g, 39%) as a dark purple solid. GPC
(THF eluent, polystyrene standard): Mn ) 9200 Da.
Poly[3-hexylthiophene-co-3-(6-hydroxyhexyl)th-
iophene] (17). In a typical example, a mixture of 16b (100
mg), 20 mL of THF, and 1 mL of 10% hydrochloric acid solution
was heated under reflux for 24 h. The reaction mixture was
poured into methanol to precipitate the polymer to give 90 mg
(quant) of 17b as a red powder. GPC (THF eluent, polystyrene
standard): Mn ) 8800 Da.
into silica by sol-gel reaction. As a preliminary experi-
ments, we carried out the sol-gel reaction of TEOS in
the presence of commercial available MEH-PPV (Ald-
rich, average Mn: 40 000-70 000). The results are sum-
marized in Table 1. In all runs the organic polymer pre-
cipitated during the sol-gel process to give heterogene-
ous solid. Obviously, this is due to the lack of any
physical or chemical interactions between organic com-
ponent and inorganic material.
To prevent phase separation during the sol-gel
process, Chujo and co-workers utilized the formation of
the covalent bonds between organic polymers and
inorganic phase. They prepared triethoxysilyl-termi-
nated polyoxazolines and carried out their acid-cata-
lyzed cohydrolysis polymerization with TEOS to produce
homogeneous transparent glassy composite materials.14
The organic polymers are covalently attached to the
silica network. From this background information,
we designed a triethoxysilyl-functionalized MEH-PPV.
2,5-Bis(5-hexenyloxy)benzene-1,4-dicarbaldehyde (4)
was prepared from diethyl 2,5-dihydroxyterephthalate
(1) according to Scheme 2. Then, we carried out the
Horner-Emmons reaction between 2-methoxy-5-(2-eth-
ylhexyloxy)-1,4-bis(diethoxyphosphinylmethyl)-
benzene (6) and 2-methoxy-5-(2-ethylhexyloxy)benzene-
1,4-dicarbaldehyde (5) in the presence of 4 to obtain
precursor polymer 7 (Scheme 2). Its 1H NMR spectrum
gave a CH peak at 5.9 ppm assigned to terminal vinyl
group and a CH3 peak at 3.5 ppm assigned to methoxy
group. The composition of the copolymer was deter-
mined from the ratio of integrals of these peaks to yield
m:n ) 81:19, which is consistent with the feed ratio.
The hydrosilylation reaction of polymer 7 was carried
out in the presence of hydrogen hexachloroplatinate to
obtain triethoxysilyl-functionalized MEH-PPV 8 (Scheme
3). Clear pregel solution was obtained by dissolving
polymer 8 in a mixture of TEOS and THF. However,
Poly(3-hexylthiophene) (P3HexTh). Structurally homo-
geneous head-to-tail P3HexTh was prepared from 2-bromo-3-
hexylthiophene according to the procedure12 reported by
1
McCullough and co-workers. H NMR (CDCl3, δ, ppm): 6.97
(thiophene), 2.9-2.7 (CH2),1.7-1.3 (CH2), 0.9 (CH3). GPC (THF
eluent, polystyrene standard): Mn ) 7500 Da.
Sol-Gel Method. Given amounts of polymer, tetraethox-
ysilane (TEOS), 1,4-dioxane or THF, hydrochloric acid, and
DMF or dimethyl sulfoxide (DMSO) were mixed with stirring
in a polypropylene test tube (15 mm in diameter and 150 mm
in length). The tube was set in an oven and heated at 60 °C
for 48 h. The temperature was gradually increased to 100 °C
and allowed to stand for additional 48 h. Finally, the gel was
dried under vacuum to give a solid of cylindrical shape (ca. 6
mm in diameter and ca. 25 mm in length).
Results and Discussion
Preparation of MEH-PPV/Silica Composite. A
number of different polymers have been incorporated
Scheme 2

Macromolecules, Vol. 38, No. 17, 2005
Incorporation of π-Conjugated Polymer into Silica 7317
Scheme 3
Scheme 5
by considering the possible terminal structures as
shown in Scheme 5.
The acid-catalyzed hydrolysis and polycondensation
of TEOS was carried out in the presence of 10. The
results are summarized in Table 2. In all cases, clear
transparent composites were obtained. The addition of
dimethyl sulfoxide (DMSO) or N,N-dimethylformamide
(DMF) as a drying control additive15 was effective to give
a crack-free composite (runs 2 and 3). Without such a
high boiling point solvent crack formation was observed
during the drying process (run 1).
Scheme 4
Optical Property of MEH-PPV/Silica Composite.
Figure 2 shows UV-vis absorption spectra of pristine
MEH-PPV (10) in dioxane solution and 10/silica com-
posite (obtained from run 2 in Table 2). Both spectra
exhibited similar absorption spectra and absorption
edges, indicating no significant effect on the electronic
structure of MEH-PPV after composite formation. The
photoluminescence spectra of 10 in dioxane solution and
10/silica composite are shown in Figure 3. The emission
of 10/silica composite showed similar spectrum to that
of 10 in dioxane solution. A slight red shift of the
spectrum in silica composite compared with that in
diluted solution may be attributed to aggregation or
precipitation of the polymer occurred after the addition
of hydrochloric acid into the solution to start the
polycondensation reaction. This is probably due to the
chemical cross-linking reaction of polymers by the
intermolecular condensation of triethoxysilyl groups,
indicating that the formation of the organic gel is much
faster than that of silica gel.
Utilizing ionic interaction between organic polymer
and silica is also useful for homogeneous composite
formation. To introduce an ionic functional group onto
MEH-PPV, Wittig reaction between dialdehyde 5 and
diphosphonium salt 9 was carried out to obtain 10
(Scheme 4). Statistically, a MEH-PPV polymer chain
prepared by this method has a polar phosphonium salt
group at the chain end. The polar group at the chain
end is expected to be effective for homogeneous com-
posite formation due to the existence of the electrostatic
interaction between phosphonium salt moiety and SiOH
groups. The 1H NMR spectrum of 10 is shown in Figure
1. The peaks due to the terminal structures are clearly
observed. The peak at 5.5 ppm corresponds to the
methylene protons arising from the terminal triph-
enylphosphoniomethyl group. The existence of two
aldehyde peaks (10.4 and 10.5 ppm) can be explained
Figure 2. UV-vis spectra of 10 in dioxane solution (dashed
line) and 10/silica composite (solid line).
Figure 1. 1H NMR (270 MHz, CDCl3, 25 °C) spectrum of
MEH-PPV (10) prepared by the Wittig method.
Figure 3. Photoluminescence spectra of 10 in dioxane solution
(dashed line) and 10/silica composite (solid line).

7318 Kubo et al.
Macromolecules, Vol. 38, No. 17, 2005
Table 2. Preparation of 10/Silica Composite
run
10 (mg)
TEOS (mL)
THF (mL)
1 M HCl (mL)
additive (mL)
appearance
1
2
3
5
5
5
4
4
4
6
6
6
1
1
1
none
DMSO (1)
DMF (1)
transparent
transparent
transparent
Scheme 6
group. The peaks at 4.6 and 3.8-3.3 ppm are assigned
as CH and OCH2 protons, respectively. The composition
of the resulting copolymers was determined by 1H NMR
through the peak area ratio between the signals coming
from the CH3 protons from 15 (at 0.9 ppm) and the ones
belonging to the OCH2 protons from 14 (at 3.8-3.3
ppm). The results are summarized in Table 3. The
copolymer compositions were in good agreement with
the monomer feed ratios. The molar fractions of THP-
functionalized thiophene in 16a and 16b were deter-
mined to be 0.11 and 0.22, respectively. The THP group
was then removed by acid treatment in THF (Scheme
7). The reaction mixture was poured into methanol to
obtain the desired copolymer 17 in quantitative yield.
interaction of polymer chains. The polymer concentra-
tion in the silica composite calculating from the gel
volume (ca. 3 mg/mL) is much higher than that in
dioxane solution (ca. 0.01 mg/mL). The observed simi-
larities between the spectrum in dioxane solution and
that of silica composite indicate that MEH-PPV was
successfully incorporated in inorganic glass, retaining
its π-conjugated structure. Since Wittig reaction is often
used for preparation of π-conjugated polymers, a num-
ber of π-conjugated polymer/silica composites are ex-
pected to be obtained employing the sol-gel technique.
Preparation of P3HexTh/Silica Composite. Of
the many π-conjugated polymers, poly(3-alkylthiophene)s
have been found to be an unusual class of polymers with
good solubility, processability, environmental stability,
electroactivity, and other interesting properties such as
thermochromism and solvatochromism.16-22 Therefore,
their composites with silica are expected to find a wide
range of potential applications. Since poly(alkylth-
iophene)s are neutral organic polymers which do not
have any functionality that interacts with silica, we
intended to introduce hydroxy functionalitiy on the alkyl
side chain. Our idea is to introduce a polar functional
group on poly(3-hexylthiophene) (P3HexTh). The func-
tionalized monomer 14 was prepared in two steps using
6-chlorohexyl 2-tetrahydropyranyl ether (11) and 3-bro-
mothiophene (12) as starting materials according to
Scheme 6. The hydroxy group was masked as the
2-tetrahydropyranyl ether (THP group). The THP group,
like other acetals and ketals, is inert to nucleophilic
reagent and is unchanged under organometallic reac-
tions. Holdcroft and co-workers reported preparations
and polymerizations of thiophenes containing a 2-tet-
rahydropyranyl group.23-25 Copolymerization of 14 with
2-bromo-3-hexylthiophene (15) was carried out to obtain
copolymer 16 (Scheme 7). To know the effect of hydroxyl
group on the compatibility with silica, copolymers with
two different composition were prepared. Figure 4 shows
1
The H NMR of the product is shown in Figure 5. The
protons due to THP group disappeared, indicating
complete conversion of 16 to 17. The signal at 3.6 ppm
can be assigned to the OCH2 protons of 6-hydroxyhexyl
group. Polymers 17a and 17b were with metallic lustra
and soluble in THF and chloroform to give an orange
solution.
Figure 4. 1H NMR (270 MHz, CDCl3, 25 °C) spectrum of 16b.
The results of the sol-gel reaction of TEOS in the
presence of P3HexTh, 17a, or 17b are summarized in
Table 4. Photographs of the representative composites
are shown in Figure 6. The sample using P3HexTh
without hydroxy functionality showed phase separation
resulting from the aggregation of P3HexTh in the silica
matrix because there is no interaction between organic
polymer and silica (runs 1-3). On the other hand,
1
a H NMR spectrum of the copolymer 16. The protons
in the 4-position of the thiophene ring mainly appeared
at 6.96 ppm, which denotes the head-to-tail structure.
The peak at 0.9 ppm is due to CH3 protons of hexyl
Scheme 7

Macromolecules, Vol. 38, No. 17, 2005
Incorporation of π-Conjugated Polymer into Silica 7319
Table 3. Copolymerizationsaof 14 and 15
monomer feed
b
sample
15 (mmol)
14 (mmol)
14 (mol %)
yield (%)
Mn
copolym compc n:m
16a
16b
5.9
5.1
0.65
1.3
10
20
35
39
6000
9200
89:11
78:22
a Conditions: diisopropylamine, 6.5 mmol; 1.6 N BuLi, 6.5 mmol; MgBr2‚Et2O, 6.5 mmol; Ni(dppp)Cl2, 0.006 mmol; THF, 30 mL; temp,
rt; time, 48 h. b Determined by GPC. c Determined by 1H NMR.
Figure 7. UV-vis spectra of P3HexTh (dashed line), 17a
(solid line), and 17b (dotted line) in THF solution.
Figure 5. 1H NMR (270 MHz, CDCl3, 25 °C) spectrum of 17b.
Figure 8. Photoluminescence spectra of P3HexTh (dashed
line), 17a (solid line), and 17b (dotted line) in THF solution.
increasing the compatibility between P3HexTh and
silica.
Figure 6. Photographs of silica composites obtained from run
2 (left) and obtained from run 5 (right).
Optical Property of P3HexTh/Silica Composite.
Figure 7 shows the solution UV-vis absorption spectra
of P3HexTh, 17a, and 17b. The maximum absorption
wavelengths of 17a (445 nm) and 17b (430 nm) were
slightly blue-shifted compared to that of P3HexTh (460
nm). The reason for the blue shift of 17a and 17b was
probably due to the small change of π-conjugated
structure by the steric interaction between terminal
hydroxy groups. Figure 8 shows solution photolumines-
cence spectra of P3HexTh, 17a, and 17b. No significant
effect of hydroxy group was observed. These spectra
showed the emission maxima at almost the same
wavelength (570 nm). Figure 9 shows the photolumi-
nescence spectra of 17a/silica and 17b/silica composites
together with that of P3HexTh in THF solution. The
emission peak of 17a/silica composite occurred at around
570 nm, which is similar to that of P3HexTh in THF
solution. This means the backbone structure of polymer
17a in the silica matrix is essentially the same to that
of P3HexTh in the solution state. The spectrum of 17a/
Table 4. Preparationsa of P3HexTh/Silica, 17a/Silica, and
17b/Silica Composites
TEOS
(mL)
THF
(mL)
run
polymer (mg)
appearance
1
2
3
4
5
6
7
8
9
P3HexTh (0.01)
P3HexTh (0.05)
P3HexTh (1.0)
17a (0.01)
4
4
4
4
4
4
4
4
4
6
6
6
6
6
6
6
6
6
phase separated
phase separated
phase separated
transparent
17a (0.05)
transparent
17a (0.1)
phase separated
transparent
transparent
phase separated
17b (0.1)
17b (2.0)
17b (5.0)
a 1 M HCl, 1 mL; DMSO, 1 mL.
introduction of the hydroxy group was effective for
homogeneous composite formation (runs 4, 5, 7, 8).
Further, polymer 17b was more compatible with silica
than 17a, indicating that hydrogen bonding between
hydroxy and silanol groups played an important role in

7320 Kubo et al.
Macromolecules, Vol. 38, No. 17, 2005
Scheme 8
introduction of too much hydroxy group on P3HexTh
caused the decrease of conjugation length due to the
stronger interaction between hydroxy group and silica.
These findings will open the way to the preparation of
a wide variety of π-conjugated polymer/silica composites
as light-emitting, nonlinear optical, and conductive
materials.
Figure 9. Photoluminescence spectra of 17a/silica composite
(solid line), 17b/silica composite (dotted line), and P3HexTh
in THF solution.
Acknowledgment. We gratefully acknowledge the
support of this research by the Mie Industry and
Enterprise Support Center.
References and Notes
(1) Novak, B. M. Adv. Mater. 1993, 5, 422.
(2) Wen, J.; Wilkes, G. L. Chem. Mater. 1996, 8, 1667.
(3) Wung, C. J.; Pang, Y.; Prassad, P. N.; Karasz, F. E. Polymer
1991, 32, 605.
(4) Luther-Davies, B.; Samoc, M.; Wooddruff, M. Chem. Mater.
1996, 8, 2586.
(5) Faraggi, E. Z.; Sorek, Y.; Levi, O.; Avny, Y.; Davidov, D.;
Neumann, R.; Reisfeld, R. Adv. Mater. 1996, 8, 833.
(6) Donval, A.; Josse, D.; Kranzelbinder, G.; Hierle, R.; Tous-
saere, E.; Zyss, J.; Perpelitsa, G.; Levi, O.; Davidov, D.; Bar-
Nahum, I.; Neumann, R. Synth. Met. 2001, 124, 59.
(7) Wei, Y.; Yeh, J.-M.; Jin, D.; Jia, X.; Wang, J.; Jang, G.-W.;
Chen, C.; Gumbs, R. W. Chem. Mater. 1995, 7, 969.
(8) Guha, P. C. Chem. Ber. 1939, 72, 1359.
Figure 10. UV-vis spectra of 17b/silica composite (dotted
line) and its pregel solution (solid line).
silica composite is broader than that of 17a in solution
state (Figure 8, solid line), suggesting intermolecular
hydrogen bonding between hydroxy group and silica. On
the other hand, 17b/silica composite showed a drastic
decrease of emission wavelength compared to that of
P3HexTh. The reason for this large blue shift can be
explained by the decrease of π-conjugation length. The
decrease of π-conjugation length was further confirmed
by the change of UV-vis absorption spectrum during
the sol-gel process. Figure 10 shows the UV-vis
absorption spectra of 17b/silica composite and its pregel
solution. The maximum absorption wavelength shifted
from 430 to 296 nm after gelation, indicating the
twisting of the polythiophene segment through the
interaction between hydroxy and silanol groups in the
silica matrix (Scheme 8).
In conclusion, we have shown molecular designs for
π-conjugated polymers that form homogeneous compos-
ites with silica using the sol-gel reaction. Introduction
of phousponium salt moiety at the chain end of MEH-
PPV improved the compatibility with silica. MEH-PPV
was successfully immobilized in silica matrix retaining
its optical properties. In the case of P3HexTh, 10%
introduction of hydroxy functionality onto the side chain
was sufficient for homogeneous composite formation
without destroying its π-conjugated structure. The
(9) Burn, P. L.; Kraft, A.; Baigent, D. R.; Bradley, D. D. C.;
Brown, A. R.; Friend, R. H.; Gymer, R. W.; Holmes, A. B.;
Jackson, R. W. J. Am. Chem. Soc. 1993, 115, 10117.
(10) Park, L. S.; Han, Y. S.; Hwang, J. S.; Kim, S. D. J. Polym.
Sci., Part A: Polym. Chem. 2000, 38, 3173.
(11) Ahn, T.; Jang, M. S.; Shim, H.-K.; Hwang, D.-H.; Zyung, T.
Macromolecules 1999, 32, 3279.
(12) Green, N.; Jacobson, M.; Henneberry, T. J.; Kishaba, A. N.
J. Med. Chem. 1967, 10, 533.
(13) McCullough, R. D.; Lowe, R. D.; Jayaraman, M.; Anderson,
D. L. J. Org. Chem. 1993, 58, 904.
(14) Chujo, Y.; Ihara, E.; Kure, S.; Saegusa, T. Macromolecules
1993, 26, 5681.
(15) Wallace, S.; Hench, L. L. Mater. Res. Symp. Proc. 1984, 32,
47.
(16) Baughman, R. H.; Bre´das, J. L.; Chance, R. R.; Elsenbaumer,
R. L.; Shacklette, L. W. Chem. Rev. 1982, 82, 209.
(17) Bre´das, J. L.; Street, G. B. Acc. Chem. Res. 1985, 18, 309.
(18) Kovacic, P.; Jones, M. B. Chem. Rev. 1987, 87, 357.
(19) Patil, A. O.; Heeger, A. J.; Wudl, F. Chem. Rev. 1988, 88,
183.
(20) Roncali, J. Chem. Rev. 1992, 92, 711.
(21) Yoshino, K.; Nakajima, S.; Park, D. H.; Sugimoto, R. Jpn. J.
Appl. Phys. 1988, 27, L718.
(22) Yoshino, K.; Love, P. Onoda, M.; Sugimoto, R. Jpn. J. Appl.
Phys. 1988, 27, L2388.
(23) Yu, J.; Holdcroft, S. Macromolecules 2000, 33, 5073.
(24) Yu, J.; Holdcroft, S. Chem. Mater. 2002, 14, 3705.
(25) Han, X.; Chen, X.; Vamvounis, G.; Holdcroft, S. Macromol-
ecules 2005, 38, 1114.
MA0508956