Amplified fluorescence quenching and electroluminescence of a cationic poly(p-phenylene-co-thiophene) polyelectrolyte

Article abstract of DOI:10.1021/ma048360k

A water-soluble conjugated polymer was developed that displays significant fluorescence quenching (25% quenching of polymer's fluorescence at quencher concentrations of 500 nM) and forms well-defined multilayer structures via electrostatic deposition. The

Full text of DOI:10.1021/ma048360k

234
Macromolecules 2005, 38, 234-243
Articles
Amplified Fluorescence Quenching and Electroluminescence of a
Cationic Poly(p-phenylene-co-thiophene) Polyelectrolyte
,
†
‡
‡
§
Michael B. Ramey,* Jeri’Ann Hiller, Michael F. Rubner, Chunyan Tan,
§
§
Kirk S. Schanze, and John R. Reynolds
Department of Chemistry, Appalachian State University, Boone, North Carolina 28608,
Department of Materials Science and Engineering, Massachusetts Institute of Technology,
Cambridge, Massachusetts 02139, and Department of Chemistry, Center for Macromolecular Science
and Engineering, University of Florida, Gainesville, Florida 32611-7200
Received August 9, 2004; Revised Manuscript Received October 28, 2004
ABSTRACT: A water-soluble conjugated polymer was developed that displays significant fluorescence
quenching (25% quenching of polymer’s fluorescence at quencher concentrations of 500 nM) and forms
well-defined multilayer structures via electrostatic deposition. The polymer contains alternating 2,5-
thienyl- and 2,5-bis[2-(N,N-diethylamine)-1-oxapropyl]-substituted 1,4-phenylene units formed by a Stille
reaction protocol. Poly({2,5-bis[2-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylene}-alt-2,5-thienylene) (PPT-
NEt
2
) was synthesized in 80% yield from 2,5-bis(trimethylstannyl)thiophene and the reactive diiodinated
species 2,5-bis(3-[N,N-diethylamino]-1-oxapropyl)-1,4-diiodobenzene. The neutral polymer was soluble
-
1
in THF, chloroform, and 1 M HCl (aq). A number-average molecular weight of 5300 g mol (ca. 40 rings)
was measured by GPC (relative to polystyrene standards). PPT-NEt is easily converted to the water-
soluble polymer, poly{2,5-bis[2-(N,N,N-triethylammonium)-1-oxapropyl]-1,4-phenylene-alt-2,5-thienylene}
2
+
dibromide (PPT-NEt
dependent on quaternization with absorption/emission wavelength maxima (λmax) corresponding to 460/
19 nm for the neutral polymer and 411/495 nm for the quaternized version in the appropriate solvent.
3
), by quaternization with bromoethane. The polymer’s electronic absorption is
5
+
Well-defined, thin multilayer films of PPT-NEt
3
, alternating with poly(acrylic acid)[PAA] or poly(styrene
sulfonic acid)[PSS], were deposited via electrostatic deposition onto indium tin oxide coated glass. Polymer
light-emitting diodes prepared from PPT-NEt /PSS exhibited the best results with a λmax of absorption
3
+
and emission equal to 450 and 558 nm, respectively, external quantum efficiency of 0.017%, and light
output of 110 nW.
Introduction
Wegner and Rehahn et al. reported the synthesis and
characterization of substituted poly(p-phenylene’s) (PPP’s)
that mimic “true” PPP but possess solubility in organic
Conjugated polyelectrolytes (CPE’s) are an interesting
class of polymers that combine the optoelectronic and
redox properties of traditional conjugated polymers with
the aqueous solubility and ionic nature of polyelectro-
lytes with potential uses in electroluminescent and
electrooptic devices.1 With appropriate substitution,
numerous conjugated polymers have been prepared that
are soluble in organic media. Water-soluble polyelec-
trolytes (PE’s) are known for their uses in redox and
6
or aqueous media. Novak et al. investigated water-
soluble PPP’s functionalized with carboxylic acid groups.7
Our group reported the synthesis of sulfonatopropoxy-
8
substituted poly(p-phenylene) (PPP-ORSO ) along with
3
the cationic quaternary ammonium-substituted poly-
[
2,5-bis(2-{N,N,N-triethylammonium}-1-oxapropyl)-1,4-
+
9
phenylene-alt-1,4-phenylene] dibromide (PPP-NEt3 ).
2
PPP-ORSO3 has been used to create self-assembled
electroactive systems, concentration control of ionic
3
multilayer LED devices.10 PPP-NEt + has been used as
reactants in chemical reactions, and photoinduced
3
4
electron-transfer events. Careful incorporation of an-
a buffer layer for hybrid ink-jet printing of pixylated
LED’s using sulfonatopropoxy-substituted poly(phenyl-
enevinylenes)1 and for amplified fluorescence quench-
ing studies with several anionic quenchers, including
ionic or cationic functionality into a CPE yields a
material that possesses the beneficial properties of a
conjugated polymer with the aqueous solubility/process-
ability of a PE. The conducting and luminescent proper-
ties of conjugated polymers, including CPE’s, have been
exploited for use in detection devices for a wide range
1a
Ru(phen′)34 and Fe(CN)6 , in aqueous solution
(phen′ ) 4,7-bis(4-sulfophenyl)-1,10-phenanthroline).1
While PPP-NEt3+ is a strong blue-emitting polymer,
-
4-
1b
5
of chemical and biological agents.
it is desirable to have structurally similar materials
with a range of emission wavelengths. Yu and co-
workers reported on the Stille synthesis of phenylene-
co-thienylene polymers with emission wavelengths in
*
To whom correspondence should be addressed. E-mail:
rameymb@appstate.edu.
†
Appalachian State University.
Massachusetts Institute of Technology.
University of Florida.
‡
§
the green region which were soluble in organic sol-
12a-c
vents,
while Wang et al. reported on the synthesis
1
0.1021/ma048360k CCC: $30.25 © 2005 American Chemical Society
Published on Web 12/30/2004

Macromolecules, Vol. 38, No. 2, 2005
Poly(p-phenylene-co-thiophene) Polyelectrolyte 235
Scheme 1. Synthesis of 2,5-Bis(3-[N,N-diethylamino]-1-oxapropyl)-1,4-diiodobenzene (DINEt
2
)
and electrochromic properties of linear and star branched
ments needed for complete conversion of functional
groups.
poly(3,4-ethylenedioxythiophene-co-didocyloxyben-
1
2d
zene) polymers.
Herein, we utilize a modified Stille
Scheme 1 illustrates the three-step synthesis of 2,5-
1
3
reaction protocol in the synthesis of poly({2,5-bis[2-
N,N-diethylamino)-1-oxapropyl]-1,4-phenylene}-alt-2,5-
bis(3-[N,N-diethylamino]-1-oxapropyl)-1,4-diiodoben-
(
zene (DINEt ). 1,4-Dimethoxybenzene (1) was iodonated
2
thienylene) (PPT-NEt2), which is easily converted to the
CPE quaternary ammonium salt, poly{2,5-bis[2-(N,N,N-
triethylammonium)-1-oxapropyl]-1,4-phenylene-alt-2,5-
under acidic conditions using potassium periodate,
iodine, and a mixed-solvent system consisting of 90:7:3
HOAc/H O/H SO by volume with heating to yield 2,5-
2
2
4
+
17
thienylene} dibromide (PPT-NEt3 ).
dimethoxy-1,4-diiodobenzene (2). Compound 2 was
reacted with boron tribromide in methylene chloride at
-78 °C, producing 2,5-diiodohydroquinone (3).18 The
desired diiodo, dialkoxyamine product, 2,5-bis(3-[N,N-
diethylamino]-1-oxapropyl)-1,4-diiodobenzene (DINEt2),
was synthesized by the Williamson etherification of 3
by refluxing in acetone for 3 days with 2-chloroethyldi-
ethylamine hydrochloride and potassium carbonate. The
+
PPT-NEt3 is highly water soluble and forms uniform
thin-layer structures over a wide pH range upon elec-
trostatic deposition with poly(acrylic acid) [PAA] or poly-
(
styrene sulfonic acid) [PSS]. The layer-by-layer, thin
film processing technique provides a simple means of
creating multilayer films with molecular-level control.14
This technique is based on the spontaneous adsorption
of oppositely charged polymers or molecules from aque-
ous solution. The adsorption cycle can be repeated to
create a highly uniform multilayer film. This technique
has been applied to organic light-emitting device (LED)
overall yield for DINEt based on dimethoxybenzene (1)
2
was 46%.
Polymer Syntheses. To compare the relative reac-
tivity of the new DINEt2 monomer with its dibromo
analogue (DBrNEt2), a Suzuki coupling polymerization
1
0,15,16
technology
and is particularly attractive because
of its ease of use and flexibility as well as the high
control over molecular architecture and the potential
for uniform large-area coverage. Conjugated polyelec-
trolytes provide a means to create highly molecularly
controlled conducting layers in an environmentally
sound setting. We previously demonstrated layer-by-
layer assembled green-emitting LEDs containing poly-
(see Scheme 2) was conducted to synthesize poly({2,5-
bis[2-(N,N-diethylamino)-1-oxapropyl]-1,4-phenylene}-
alt-1,4-phenylene) (PPP-NEt2), described previously by
9
our group. Using identical protocols, reactions were
conducted to couple DINEt2 and DBrNEt2 with bisneo-
pentylglycol-1,4-phenylene diboronate (4) via a Suzuki
protocol. Both reactions were quenched by precipitation
into MeOH after 3 h. GPC results in chloroform (vs
polystyrene [PS] standards) revealed low molecular
1
5
(
p-phenylenevinylene)(PPV) as well as blue-emitting
1
0
LEDs containing poly(p-phenylene) derivatives. The
LED and amplified fluorescence quenching character-
istics of a green-luminescent cationic poly(p-phenylene-
co-thiophene) (PPT-NEt3 ) polyelectrolyte synthesized
via the Stille-coupling reaction will be demonstrated.
-1
weight oligomers ( Mh n < 1500 g mol , multimodal) for
the reaction using the dibromonated species [PPP-NEt2-
+
(
Br-3)], while the polymer prepared using the diiodo-
nated reagent [PPP-NEt2(I-3)] reached a Mh n ) 10 900
-
1
g mol (unimodal). Published results using DBrNEt2
Results and Discussion
-1
in the reaction for 72 h showed Mh n ) 15 900 g mol for
Monomer Synthesis. To effectively synthesize PPT-
the resulting polymer [PPP-NEt2(Br-72)].9 The GPC
results are summarized in Table 1. Longer reaction
times (complete polymerization stopped after 24 h) with
+
NEt3 of high molecular weight via a Stille polymeri-
zation, we selected 2,5-bis(3-[N,N-diethylamino]-1-oxa-
propyl)-1,4-diiodobenzene (DINEt2) and 2,5-bis(trimethyl-
stannyl)thiophene (5) as co-monomers. A diiodobenzene
monomer was chosen over a dibromo reagent due to its
higher reactivity in Pd coupling reactions. The use of a
diiodo monomer was necessitated by the fact that the
aryl tin reagents used in the Stille reaction are some-
what less reactive than the aryl boronic acids used in
the Suzuki coupling reaction. Particular attention was
paid to the stringent monomer purification require-
-
1
DINEt2 [PPP-NEt2 (I-24); Mh n ) 15 900 g mol ] ap-
proached the molecular weight values reported for
PPP-NEt2(Br-72). The use of DINEt2 leads to formation
of a polymer with similar molecular weight properties
to PPP-NEt2(Br-72) in a shorter amount of time. Once
the polymer has reached a certain molecular weight, it
begins to precipitate out of solution, terminating poly-
mer growth and negating the advantages of the more
reactive iodine reagent at longer reaction times.

236 Ramey et al.
Macromolecules, Vol. 38, No. 2, 2005
2
via a Suzuki Coupling Protocol
Scheme 2. Synthesis of PPP-NEt
Table 1. Gel Permeation Chromatography Results
reaction
solvent
reaction
type
reaction
time (h)
Mh n
MP
kg mol
Mh w
(kg mol-1)
-1
(kg mol-1)
Mh w/ Mh n
polymer
a
PPP-NEt2(Br-72)
DMF/H2O
DMF/H2O
DMF/H2O
DMF
Suzuki
72
3
24
48
96
240
96
15.9
10.9
15.3
3.2
24.3
13.3
19.5
4.3
35.0
16.6
27.5
5.2
2.20
1.52
1.80
1.70
1.68
1.71
1.70
PPP-NEt2(I-3)a
Suzuki
a
PPP-NEt2 (I-24)
Suzuki
b
PPT-NEt2(48)
Stille
b
PPT-NEt2(96)
DMF
Stille
4.1
5.8
6.9
b
PPT-NEt2(240)
DMF
DMF
Stille
4.2
5.3
5.4
6.9
7.2
9.0
b
PPT-NEt2(96-drop)
Stille (dropwise)
a
Indicates CHCl3 as solvent for GPC analysis. b Indicates THF as solvent for GPC analysis.
Scheme 3. Stille Coupling Polymerization Used in
Elemental analysis data for the neutral PPP-NEt2-
Br-72) and PPP-NEt2(I-3,24) is provided as Supporting
the Synthesis of Poly({2,5-bis[2-(N,N-diethylamino)-
(
1
-oxapropyl]-1,4-phenylene}-alt-2,5-thienylene)
Information (Table S1) and indicates only a small
percentage of Br or I end groups remained in the final
polymer. Taking into account the different atomic
weights of Br and I with the associated error in
elemental analysis, (0.04%, the percentage of each
element found in PPP-NEt2(Br-72), [Br ) 0.54%] and
PPP-NEt2(I-24), [I ) 0.76%], are indicative of materials
with approximately 0.025 halogen atoms per polymer
repeat unit. Solution UV-vis absorption properties
(PPT-NEt )
2
-
1
-1
(
λmax ) 349 nm; molar absorptivity ≈ 8,000 L mol cm
in THF) for both PPP-NEt2(Br-72) and PPP-NEt2(I-24)
were identical. DINEt2 proved to be a more active
halogenated species for Suzuki coupling reactions, and
these results indicate that DINEt2 should be a more
effective monomer when used in the Stille polymeriza-
tion protocol as compared to DBrNEt2.
The Stille coupling polymerization used in the syn-
thesis of poly({2,5-bis[2-(N,N-diethylamino)-1-oxapro-
pyl]-1,4-phenylene}-alt-2,5-thienylene) (PPT-NEt2) is
depicted in Scheme 3. Compound 5 was easily prepared
in good yield using a literature methodology19 and
purified by vacuum distillation followed by two recrys-
tallizations from pentane. Elemental analyses for the
subsequent polymerization experiments described herein
are presented in the Supporting Information (Table S1).
It should be noted that the carbon analyses are some-
what lower than expected. One possible explanation of
this is that these highly aromatic polymers are difficult
to fully combust and some carbonization may have
occurred during the measurements. A second possible
explanation of the lowered carbon percentages is that
in Stille polymerizations hydrolyzed tin byproducts can
remain trapped in the resulting polymer. In the PPP’s
prepared via Suzuki polymerization, where tin contami-
nation was not possible, carbon analysis was similarly
low, and if tin-contaminated PPT samples were present
in this study, one would expect a deviation for all
elemental percentages analyzed. The iodine elemental
analyses provide a rough method for approximating the
degrees of polymerization. Using PPT-NEt2(96-drop) as
an example, elemental analysis showed 0.97% iodine in
the polymeric sample, resulting in a theoretical repeat
unit formula of C22H32N2O2SI0.030. If the polymer sample
consisted solely of chains terminated with one iodophen-
ylene group, a degree of polymerization of approximately
33 (∼66 rings) would be necessary to result in an iodine
elemental percentage of 0.97%. If the polymer sample
consisted solely of chains terminated with two iodophen-
ylene groups, a degree of polymerization of approxi-
mately 66 (∼132 rings) would result. More likely, the
individual polymer molecules are a mixture of chains
terminated with one and two iodophenylene groups or
with two thienyl groups. Chains with double thienyl
termination would show no iodine in their elemental

Macromolecules, Vol. 38, No. 2, 2005
Poly(p-phenylene-co-thiophene) Polyelectrolyte 237
analysis, even if they were of very small molecular
weight. Taking the double thienyl termination into
account, the perceived degree of polymerization (33-
6
6 repeat units) based on elemental iodine analysis
alone would be higher than the actual value. Gel
permeation chromatography (GPC) analysis revealed
-
1
Mh n ) 5300 g mol
for sample PPT-NEt2(96-drop),
corresponding to a degree of polymerization of ap-
proximately 15 repeat units (30 rings) [see Table 1]. A
general trend observed among the different PPT-NEt2
samples was that as the percent of iodine decreased in
a polymer sample, the degree of polymerization of the
sample, as determined by GPC, was proportionately
higher as well, thus allowing iodine analysis to provide
a relative indication of the degree of polymerization
between samples.
PPT-NEt2 molecular weight optimization was carried
out by varying polymerization conditions. Initial polym-
erization reactions consisted of adding the stannylated
compound, DINEt2, and DMF to an appropriately sized
flask under argon with heating to 70 °C. A catalytic
amount of PdCl2(PPh3)2 was added in one portion to the
reaction flask. PPT-NEt2(48) and PPT-NEt2(96) were
synthesized with 48 and 96 h reaction times followed
by precipitation into MeOH. The precipitated material
was extracted with MeOH and acetone for 24 h, sepa-
rately, via Soxhlet extraction to remove low molecular
weight species. The remaining polymeric solid was
extracted with chloroform. The chloroform-soluble frac-
tion of polymer was used for all subsequent character-
izations and analyses. PPT-NEt2(48) was collected in
-
1
7
5% yield with Mh n ) 3200 g mol , while PPT-NEt2(96)
-
1
was collected in 80% yield with Mh n ) 4100 g mol (see
Table 1). Polydispersities of 1.7 were found for both.
Doubling the reaction time led to modest improvements
in both yield and Mh n, while increasing the reaction time
to 10 days in PPT-NEt2(240) led to no appreciable
-
1
molecular weight enhancement ( Mh n ) 4200 g mol ).
Figure 1. (a) H NMR and (b) 13C NMR for PPT-NEt
1
in
Structural Characterization. 1H and 13C NMR
analysis of the recovered PPT-NEt2 polymers gave
expected shift values with the proton peaks appearing
as broad multiplets (see Figure 1 and Experimental
2
3
CDCl .
(
trimethylstannyl)thiophene (5) was degrading when
exposed to the elevated reaction temperatures for
extended periods of time. PPT-NEt2(96-drop) was syn-
thesized by slow dropwise addition of 5 (dissolved in
DMF) to a solution of catalyst, DINEt2, and DMF over
the course of 24 h. The reaction was allowed to remain
at 70 °C for an additional 72 h. The polymer was isolated
as described previously for PPT-NEt2(96) and exhibited
1
Section). Expansion of the aromatic region of the H
NMR (ppm >7.0) spectrum did not reveal the presence
of terminal thienyl protons, although the peaks may be
hidden under the broadened aromatic peaks from the
1
backbone protons (Ha and Hb). H peaks were not
present for the methylene protons of trimethylstannyl
groups (∼0.38 ppm) or tolylene protons (∼2.35 ppm),
which would have resulted from an unreacted trimeth-
ylstannyl group or the transfer of a methyl group from
the 2,5-bis(trimethylstannyl)thiophene to an iodophen-
ylene ring during the catalytic cycle. If signals from any
of the above-mentioned end-group protons were readily
visible, a low molecular weight polymer would have been
-1
a Mh n of 5300 g mol (GPC versus PS standards). This
methodology produced a polymer with the lowest per-
cent of halogentated end groups (wt % I ) 0.98) and
highest molecular weight by GPC of all trials. Slow
addition of the more reactive tin compound allows for
immediate coupling of the thiophene to DINEt2, thereby
limiting exposure of the stannylated thiophene com-
pound to elevated temperatures, which would promote
destannylation of the thiophene and result in a loss of
stoichiometric balance between the halogen and tri-
methylstannyl functional groups.
1
3
indicated. The C NMR spectrum shows a small peak
slightly upfield from the peak #3, 126.49 ppm, which
most likely corresponds to the carbon atom beta to the
sulfur atom on terminal thienyl groups. No other 13
C
peaks were evident for perceived chain-terminating
The dropwise addition of bis(trimethylstannyl)thio-
phene (5) led to the highest degree of polymerization
for the PPT-NEt2 polymers prepared. These molecular
weights are lower than those reported by Yu and co-
workers for poly(p-phenylene-co-thiophene)’s ( Mh n of
1
3
carbons. Due to the relatively low-intensity C peak at
126 ppm, as compared to the signals from the major
∼
backbone aromatic carbons, a polymer sample consisting
of low molecular weight oligomers can be excluded.
On the basis of the 13C NMR results which indicated
that thienyl end groups were present in the final
polymeric materials, it was hypothesized that 2,5-bis-
14 000 g mol ), which had longer alkoxy groups as side
-1
chains, thereby increasing the polymer solubility in
DMF.1 Onset of polymer precipitation from the reac-
2b

238 Ramey et al.
Macromolecules, Vol. 38, No. 2, 2005
Scheme 4. Quaternization of Neutral PPT-NEt
Polymers with Bromoethane
2
in the TGA (see Supporting Information, Figure S1)
with loss of triethylamine fragments occurring at 200
+
and 250 °C for PPT-NEt3 and PPT-NEt2, respectively.
Both polymers have a final degradation occurring over
4
00 °C, attributed to the breakdown of the conjugated
backbone with little residual mass remaining at a
temperature of 650 °C.
Absorption, Emission, and PL Quenching. Figure
2
shows the UV-vis absorption and photoluminescence
+
spectra for PPT-NEt2 in THF and PPT-NEt3 in H2O
normalized for convenience). It is interesting to note
(
the shift in absorption maxima between the neutral and
charged polymers. PPT-NEt2 exhibits a λmax at 460 nm
with a corresponding molar absorptivity of about 18 000
-
1
-1
+
L mol cm , while PPT-NEt3 ’s λmax is blue shifted
9 nm to 411 nm with a corresponding molar absorp-
4
-
1
-1
tivity of about 16 000 L mol cm . The blue shift of
the π to π* transition for these polymers may be due to
a solvatochromic effect as seen in substituted poly-
thiophenes20 and poly(diacetylene). Fine tuning of λmax
could be achieved by controlling the extent of quater-
nization as incomplete quaternization leads to a lower
extent of hypsochromic shift.
tion media was observed after approximately 40 h for
all PPT-NEt2 reactions and appears to be the predomi-
nant mechanism of molecular weight limitation for our
systems.
21
Cationic, water-soluble polymers are easily formed
from the neutral PPT-NEt2 by quaternization with
bromoethane in THF as shown in Scheme 4. The
Solution photoluminescence experiments revealed
peak emission wavelengths of 519 and 494 nm for PPT-
+
quaternized polymer, PPT-NEt3 , was precipitated into
+
acetone, collected, and dried at 50 °C under vacuum.
NEt2 in THF and PPT-NEt3 in H2O, respectively, when
+
+
The elemental analysis results for PPT-NEt3 (96) and
excited at the λmax of absorption. PPT-NEt3 exhibited
+
PPT-NEt3 (96-drop), which are the quaternized forms
a fluorescence quantum efficiency of 10% in water. The
spectra display the typical characteristics of conjugated
polymers in solution with a Stoke’s-shifted emission
maximum tailing broadly to higher wavelengths. Table
S2 (Supporting Information) summarizes the optical
properties for both the neutral and water-soluble PPP-
NEt and PPT-NEt polymers.
of PPT-NEt2(96) and PPT-NEt2(96-drop), respectively,
are provided as Supporting Information (Table S1).
Bromine elemental analysis provides one method of
determining the quaternization efficiency of the reaction
between the neutral polymers and bromoethane. PPT-
+
NEt3 (96-drop) would reflect a theoretical 26.24% Br by
weight for complete alkylation compared to the 23.62%
In a previous study, the fluorescence quenching of the
+
+
Br found, and PPT-NEt3 (96) would reflect a theoretical
poly(p-phenylene)-type polyelectrolyte, PPP-NEt3 , by
2
6.20% Br by weight for complete alkylation compared
oppositely charged metal complexes Ru[(4,7-bis(4-
4
-
4-
to the 24.18% Br found. Elemental analysis indicates
quaternization of approximately 90% of the available
sulfophenyl)-1,10-phenanthroline]34 (Ru(phen)3 ) and
-
potassium ferrocyanide (Fe(CN)6 ) via an energy-
1
11b
amine sites. This is in good agreement with H NMR
transfer mechanism was investigated. Quenching by
integration determination of quaternization efficiency
which was on the order of 80-90% per sample. The
quaternized polymers are soluble in acidic and neutral
aqueous solutions.
photoinduced electron transfer was also observed when
the anionic electron acceptors, sodium anthraquinone-
2,6-disulfonate (AQS) and sodium 1,4,5,8-naphthalene-
diimide-N,N′-bis(methylsulfonate) (NDS), electrostati-
cally bind to the polymer chain.
Thermogravimetric analysis was used to probe the
+
thermal stability of both the PPT-NEt2 and PPT-NEt3
In the present investigation three anionic quenchers,
Fe(CN)64 , AQS, and NDS, were used to study the
-
polymers. Thermal dealkylation of the amine sites is the
initial degradation event of the polymers as evidenced
+
solution quenching behavior of PPT-NEt3 . The results
2
Figure 2. Normalized UV-vis absorption and PL emission spectra for the PPT derivatives. (A) PPT-NEt absorption (s) and
+
emission (0) in THF. (B) PPT-NEt
3
2
absorption (O) and emission (4) in H O.

Macromolecules, Vol. 38, No. 2, 2005
Poly(p-phenylene-co-thiophene) Polyelectrolyte 239
+
Figure 3. UV-vis absorption spectra of 10 µM PPT-NEt
3
4
-
with addition of Fe(CN)
6
. Each curve corresponds to an
4-
Fe(CN)
6
concentration increment of 0.2 µM. Arrows indicate
4-
direction of change in absorbance with addition of Fe(CN)
6
.
4
-
[
Fe(CN)
6
concentration range 0-2 µM].
show that the quenching efficiency is strongly depend-
ent on ion-pair association of the cationic polymer and
anionic quenchers. However, electrostatic interaction
may not be the only contribution for the ground-state
complexation, as hydrophobic and charge-transfer in-
teractions between the polymer chain and quencher may
also contribute to the binding. Because of the different
charges and different hydrophobic character of these
three quenchers, their ability to bind to the polymer is
different. From the UV-vis absorption spectra of the
Figure 4. (a) UV-vis absorption spectra of pure AQS at
+
7
µM (-‚‚‚-), pure PPT-NEt
3
at 10 µM (s), and two PPT/
+
AQS mixtures at the same PPT-NEt
3
concentration of 10 µM
and two different AQS concentrations of 3.6 µM (‚‚‚) and 5.4
µM (- - -), respectively. (b) UV-vis absorption spectra of pure
+
4-
titrations of PPT-NEt3 with Fe(CN)6 (Figure 3), it is
evident that there is a decrease in intensity of the 415
nm absorption band along with formation of a red-
shifted band with a maximum absorbance at 452 nm.
The clear isosbestic point at 430 nm suggests that
complexation induces a change between two distinct
NDS at 20 µM (-‚‚‚-), pure PPT-NEt
+
at 10 µM (s), and two
3
+
PPT/NDS mixtures at the same PPT-NEt
0 µM and two different NDS concentrations of 3.6 µM (‚‚‚)
and 5.4 µM (- - -), respectively.
3
concentration of
1
electron acceptors. Thus, it is reasonable to argue that
+
+
these molecules interact with PPT-NEt3 in a donor-
chromophoric states of the PPT-NEt3 polymer chain.
acceptor manner and contribute a charge-transfer com-
ponent to the red-shifted absorption band.
A possible cause for the change in absorption could be
that the polyvalent ion induces aggregation of the PPT-
+
+
NEt3 chains. Interactions could result in a planariza-
The binding constant for AQS and PPT-NEt3 is
5
-1
tion of the backbone, increasing the effective conjugation
length. Similar red shifts in absorption are observed
when polyvalent ions are added to solutions of poly-
approximately 1.0 × 10 M . The difference in binding
4- +
constants between Fe(CN)6 /PPT-NEt3 and AQS/PPT-
+
NEt3 is mostly likely due to the different charge of the
5
h
(
phenyleneethynylene)-conjugated polyelectrolytes.
A
anionic quenchers as the more negatively charged
5
-1
4-
binding constant of 3 × 10 M was determined for the
complex using a Scatchard plot (See Supporting Infor-
mation, Figure S2) with the assumption that the
absorption band at 415 nm is from the free polymer
chain and the red-shifted band at 452 nm is from the
Fe(CN)6 displays a stronger binding with the polymer.
+
The complexation of NDS and PPT-NEt3 results in
partial precipitation in solution at concentrations higher
than 5 µM, thereby precluding determination of a
binding constant.
+
4-
+
PPT-NEt3 /Fe(CN)6 complex.
The fluorescence quenching of PPT-NEt3 by Fe-
(CN)64 , AQS, and NDS was investigated, and the
Stern-Volmer (SV) quenching plots are shown in Figure
5. At very low quencher concentrations (<600 nM) the
SV plots are linear and the Ksv values for all three
-
Similar phenomena, including the decrease of the
polymer absorption band at 415 nm and the formation
of a red-shifted band, can be seen in the UV-vis
+
absorption spectra of mixtures of PPT-NEt3 with AQS
6
-1
or NDS (Figure 4). For the AQS system an isosbestic
point is observed at 460 nm and the red-shifted band
appears at a λmax ) 490 nm, whereas for the NDS
system an isosbestic point at 480 nm and a red-shifted
band with λmax ) 500 nm is seen. The λmax of the red
shift that occurs on addition of NDS and AQS is greater
quenchers are similar (Ksv )1.2 × 10 M , Ksv )0.6 ×
6 -1 6 -1 4-
10 M , and Ksv ) 0.5 × 10 M for Fe(CN)6 , AQS,
and NDS, respectively). Note that quenching is very
efficient in all three cases with 25% of the polymer’s
fluorescence being quenched with quencher concentra-
tions of 500 nM. This corresponds to a polymer repeat
unit to quencher ratio of 20:1. The efficient quenching
arises because the quenchers are associated with the
polymer chains and because the fluorescent exciton is
strongly delocalized and able to diffuse along the chain
4
-
+
than that in the Fe(CN)6 /PPT-NEt3 complex. There
are reasons why the absorption shift is larger for AQS
and NDS addition. First, these quenchers feature large
hydrophobic planar π-electron systems resulting in a
face-to-face association with the polymer. This associa-
tion leads to a conformational change in the polymer
structure. Second, both AQS and NDS are strong
22
to the quencher unit rapidly. At higher quencher
concentration the SV plots for Fe(CN)64 and AQS
display upward curvature, whereas the plot for NDS
-

240 Ramey et al.
Macromolecules, Vol. 38, No. 2, 2005
Figure 7. Normalized absorbance and electroluminescence
+
spectra of a typical PPT-NEt
3
/SPS multilayer PLED.
+
Figure 5. Stern-Volmer plots of 10 uM PPT-NEt
3
quench-
4
-
PAA pH at a fixed PPT-NEt3+ solution pH of 5.0.
Similar trends have been previously studied23 and will
only be briefly summarized here. As the pH of the PAA
solution, which has a weak carboxylic acid functional
ing by Fe(CN)
6
(b), AQS (O), and NDS(1).
+
group, is increased for a given PPT-NEt3 pH, the PAA
polymer chains attain a higher degree of ionization and
acquire a more extended conformation and thinner
bilayers result. For the various pH conditions studied
film growth was linear in the thickness ranges inves-
tigated, which were as high as 3000 Å with bilayer
thicknesses ranging from 18 to 100 Å at various pH
+
conditions. PPT-NEt3 -based films were of remarkably
high quality with no observable pinholes or uniformity
defects.
+
Figure 6. Bilayer composition of PPT-NEt
3
/PAA films as a
Polymer light-emitting diodes (PLEDs) were created
+
+
function of PAA pH at a fixed PPT-NEt
3
solution pH of 5.0.
by first assembling the green-emitting PPT-NEt3 /PSS
+
or PPT-NEt3 /PAA multilayers on ITO-patterned glass
remains nearly linear. The upward curvature observed
in the SV plots indicates that an additional quenching
pathway becomes active. On the basis of previously
reported investigations of other conjugated polyelectro-
lyte/quencher systems,22 we suspect that the additional
mechanism involves quencher-induced aggregation of
and the subsequent evaporation of 2000 Å thick Ag
electrodes on top of the structure. Prior to evaporation
of the metal electrode the films were dried under
vacuum for 2 h at 90 °C. PLEDs were stored and tested
+
in a drybox under a nitrogen atmosphere. PPT-NEt3 /
+
PSS and PPT-NEt3 /PAA devices in the range of 800-
+
the PPT-NEt3 chains. Quenching is more efficient in
1100 Å thick were made at various pH conditions. PPT-
+
the aggregates because intrachain exciton migration
becomes important, allowing more efficient trapping of
the excitation by the quencher sites.
NEt3 /PSS devices showed superior performance to
+
those made from PPT-NEt3 /PAA. The best device
+
performances were observed for the PPT-NEt3 /PSS
Layer-by-Layer Films and PLED’s. Luminescent
system at pH conditions of 5.0 and 3.5 for the PPT-
+
+
layer-by-layer-assembled PPT-NEt3 -based multilayer
NEt3 and PSS, respectively. This corresponds to a
films were created via incorporation of the polyanion
poly(styrene sulfonic acid) (PSS) and poly(acrylic acid)
bilayer thickness of ∼15 Å ((2 Å) and approximately
+
45% PPT-NEt3 in the structure. Light emission in the
+
(
PAA). Aqueous solutions were prepared in deionized
PPT-NEt3 /PSS PLEDs was observed only under for-
Milli-Q water and filtered through 0.45 µm cellulose
ward bias, i.e., the ITO electrode biased positive with
respect to the metal electrode and devices had external
quantum efficiencies as high as 0.017%.
acetate filters. In the case of the polyanion solutions and
+
-2
PPT-NEt3 , the concentrations were ∼1 × 10 M and
-
3
+
∼
5 × 10 M, respectively (based on the repeat unit
Onset of light output for PPT-NEt3 /PSS PLEDs
molecular weight). Solution pH was adjusted to the
desired value with dilute HCl or NaOH. Polymer light-
emitting diodes (PLEDS) were prepared using cleaned
occurred at ∼11 V with a maximum light output of 110
2
nW (current ) 30 mA/cm ) at a peak voltage of 15 V.
Figure 7 shows a typical normalized absorbance spec-
trum of the multilayer film and electroluminescence
spectrum of the PLEDs. The λmax of absorption and
emission is centered around 450 and 558 nm, respec-
tively, and are red shifted as expected from the values
obtained from solution photoluminescence measure-
15g
ITO-patterned glass obtained from DCI incorporated.
+
The PPT-NEt3 -based multilayers were assembled on
cleaned glass and silicon substrates, while film growth
was monitored by profilometry, ellipsometry, and UV-
vis spectroscopy.
abs
em
ments (λmax 411 nm; λmax 494 nm). The emitted light
The film growth characteristics were investigated for
+
was observed to be of a yellow/orange coloration.
the PPT-NEt3 aqueous solution at pH 4.0 and 5.0, PAA
pH varying between 3.0 and 4.5, and PSS at pH 3.5.
Linear, highly uniform, reproducible growth was achieved
over the pH range studied. There was virtually no
multilayer buildup when the PAA solution pH was set
above 5.0 and below 2.5. Figure 6 illustrates the bilayer
Conclusions
A new water-soluble, substituted cationic poly(p-
phenylene-co-thiophene), PPT-NEt3 , was prepared via
postpolymerization quaternization of alkylamine sites
along the polymer backbone. The mild conditions used
+
+
composition of PPT-NEt3 /PAA films as a function of

Macromolecules, Vol. 38, No. 2, 2005
Poly(p-phenylene-co-thiophene) Polyelectrolyte 241
(300 MHz, CDCl
) 7.20 (s, 2 H), 3.83 (s, 6 H) ppm. 13C NMR
for quaternization prevent polymer chain breakage and
thus allow for molecular weight characterizations of the
neutral polymers to be extended to the water-soluble
species with the realization that additional molecular
weight is added to the polymer after quaternization.
This methodology offers the ability to avoid the direct
molecular weight characterization of a polyelectrolyte.
3
(
75.5 MHz, CDCl ) 153.29, 121.57, 85.44, 57.17 ppm. Anal.
Calcd for C : C, 24.62; H, 2.05. Found: C, 24.31; H,
.89. EI-LRMS calcd for C : 389.9, found 390.
,5-Diiodohydroquinone (3). 2,5-Dimethoxy-1,4-diiodo-
3
8 8 2 2
H O I
1
8 8 2 2
H O I
18
2
benzene (10.00 g, 25.60 mmol) was dissolved in 50 mL of
dichloromethane and cooled in a dry ice/acetone bath. Boron
tribromide (26.50 g, 105.80 mmol) in 15 mL of dichloromethane
was added dropwise via an addition funnel to the solution with
stirring. The reaction mixture was held at -78 °C for 30 min
and then allowed to warm to room temperature overnight. The
reaction was added slowly to 300 mL of ice water. A white
+
The conjugated, water-soluble PPT-NEt3 ’s absorption,
emission, binding, and thin-layer-forming properties
were exploited in order to create new electrostatically
deposited polymer light-emitting diodes and to demon-
+
precipitate was collected and recrystallized from THF/H O
strate the ability of PPT-NEt3 to function as an
2
1
(
7.05 g, 76% yield). mp 192-193 °C. H NMR (300 MHz,
13
extremely sensitive sensor for known anionic quenchers.
These initial discoveries provide insight into the chemi-
cal behavior of the conjugated polyelectrolye, PPT-
acetone-d
6
) 8.75 (s, 2 H), 7.30 (s, 2 H) ppm. C NMR (75 MHz,
) 151.58, 124.93, 84.25 ppm. Anal. Calcd for
: C, 19.90; H, 1.11. Found: C, 19.73; H, 1.08. EI-
LRMS calcd for C : 361.8, found 362.
acetone-d
C H O I
6 4 2 2
6
+
NEt3 , and will stimulate continued research into the
6
4 2 2
H O I
development of water-soluble polymers for a variety of
optical and sensing technologies.
2
,5-Bis(3-[N,N-diethylamino]-1-oxapropyl)-1,4-diiodo-
benzene (DINEt ). A 250 mL three-neck round-bottom flask
2
was equipped with a reflux condenser and Ar gas inlet. 2,5-
Diiodohydroquinone (6.45 g, 17.82 mmol), 2-chlorotriethyl-
Experimental Section
amine hydrochloride (6.75 g, 39.21 mmol), K
4.85 mmol), and 150 mL of acetone (dried over MgSO
added to the reaction flask and heated to reflux. After 3 days
a yellow slurry was poured into 300 mL of H O and a solid
precipitate collected. The precipitate was dissolved in Et O,
and the filtrate was extracted with Et
O (300 mL × 1, 150
mL × 1, 50 mL × 1). The Et O solutions were combined and
washed with 1 M NaOH (300 mL × 1, 150 mL × 1, 50 mL ×
), H O layer
O (300 mL × 1), and brine (300 mL × 1). The Et
was dried over MgSO , and the solvent was removed under
reduced pressure, leaving a yellowish-white solid. The solid
was recrystallized twice from MeOH/H O (7.49 g, 75% yield).
mp 79-80 °C. H NMR (300 MHz, CDCl ) 7.21 (s, 2 H), 4.00
t, J ) 6.0 Hz, 4 H), 2.91 (t, J ) 6.0 Hz, 4 H), 2.66 (q, J ) 7.2
2
CO
3
(10.33 g,
Materials. THF and TMEDA were purified by distillation
over sodium and benzophenone. Thiophene was distilled under
argon from KOH pellets. Anhydrous DMF was used as
supplied by Aldrich Chemical Co. Palladium catalysts were
used as received from Strem Chemical Co. All other chemicals
were purchased from Aldrich Chemical Co. and used as
received, unless otherwise noted. 2,5-Bis(3-[N,N-diethylamino]-
7
4
) were
2
2
2
2
1
2
-oxapropyl)-1,4-dibromobenzene (DBrNEt ) was synthesized
1
2
2
9
as previously reported. Bisneopentylglycol-1,4-phenylene di-
boronate (4) was prepared by the literature procedure24 for the
synthesis of phenylene diboronic acid, followed by esterification
with neopentyl glycol in refluxing toluene.
4
2
1
3
General Methods. NMR spectra were obtained with a
Varian VXR-300 or a Varian Gemini-300. Elemental analyses
were performed by Robertson Microlit, Inc. or in house by
combustion with a Fisons/Carlo-Erba 1106 and 1108. Ultra-
violet-visible (UV-vis) spectra were recorded using a Varian
Cary 5E UV-Vis-NIR spectrophotometer. Fluorescence re-
sults were obtained with a Spex F-112 photon-counting fluo-
rimeter at room temperature. TGA was performed under N
with a Perkin-Elmer TGA 7 Thermogravimetric Analyzer. The
temperature was ramped from 50 to 800 °C at 10 °C/min under
(
13
Hz, 8 H), 1.08 (t, J ) 7.2 Hz, 12 H) ppm. C NMR (75 MHz,
CDCl ) 152.84, 122.82, 86.02, 69.20, 51.49, 47.92, 12.09 ppm.
Anal. Calcd for C18 : C, 38.59; H, 5.40; N, 5.00; I,
5.30. Found: C, 38.81; H, 5.53; N, 4.90; I, 45.10. FAB-HRMS
3
31 2 2 2
H N O I
4
+
(
M + H) calcd for C18
31 2 2 2
H N O I : 561.0475, found 561.0492.
,5-Bis(trimethylstannyl)thiophene (5). The general
19
2
2
preparation of this compound followed literature procedures,
followed by a more rigorous purification needed for polymer-
ization-quality monomer. The crude recovered product was
N
2
atmosphere. GPC results were obtained with a system
-3
distilled under vacuum (90 °C at 5 × 10 mmHg) and then
consisting of a Waters model 590 pump and two 300 × 7.5
mm Polymer Laboratories Linear Mixed Bed (Plgel 5µm
mixed-C) columns in series using a Spectraflow 757 Tunable
UV-Vis Detector. Polymer light-emitting diodes (PLEDS)
were prepared using cleaned ITO-patterned glass obtained
from DCI incorporated. The luminescent multilayer systems
were assembled with a programmable Zeiss glass stainer via
the alternate dipping of the substrate into the polycation and
polyanion for 15 min each followed by three rinsing steps in
deionized Milli-Q water for a total of 6 min. The cleaning
process involved a 1 min etch in 1 M HCl, a 10 min sonification
in a detergent solution, a 15 min sonification in deionized
water, and a 2 min plasma etch. Voltage, current, and light
output of LED devices were measured using an HP3245A
universal source, an HP34401A multimeter, and a Newport
recrystallized twice from pentane to yield a white crystalline
solid. Yields for the reaction were slightly less than those
reported in the literature due to the multiple purification steps
19
employed (4.48 g, 69% yield). mp 100-102 °C (lit. mp 100-
1
1
01.6 °C). H NMR (300 MHz, CDCl
3
) 7.40 (s, 2 H), 0.38 (s, 18
) 143.00, 135.80, -8.15 ppm.
2
Anal. Calcd for C10H20SSn : C, 29.32; H, 4.92. Found: C, 29.65;
13
H) ppm. C NMR (75 MHz, CDCl
3
+
2
H, 4.60. FAB-HRMS (M + H) calcd for C10H21SSn : 411.9330,
found 411.9494.
Poly({2,5-bis[2-(N,N-diethylamino)-1-oxapropyl]-1,4-
phenylene}-alt-1,4-phenylene). General Procedure. A 20 mL
Schlenk flask with stir bar was charged with DINEt
pentylglycol-1,4-phenylene diboronate (4), and NaHCO
flask was evacuated and backfilled with Ar three times. A
solvent system consisting of 25 mL of DMF and 5 mL of H
2
, bisneo-
3
. The
2
O
1
830-C optical power meter controlled by LabView (National
Instruments).
,5-Dimethoxy-1,4-diiodobenzene (2). Following an
sparged with Ar for 30 min was transferred to the reaction
flask via syringe, and the mixture was heated to 50 °C to
2
5
2
2
dissolve all monomers. Pd(OAc) was added, and the temper-
17
iodination procedure outlined by West et al., a 250 mL three-
neck round-bottom flask was charged with 1,4-dimethoxyben-
zene (1) (10.48 g, 75.85 mmol) and 100 mL of 90:7:3 HOAc/
ature was raised to 70 °C for a variable number of hours. The
reaction mixture was precipitated into 200 mL of MeOH and
recovered as a tan solid. The polymer sample was redissolved
H
2
O/H
stirred under Ar until the 1,4-dimethoxybenzene dissolved
completely. I (23.66 g, 91.02 mmol) and KIO (20.93 g, 91.02
2
SO
4
by volume solution. The reaction mixture was
in a minimal amount of hot CHCl
3
and precipitated into 200
mL of MeOH. The tan material was dried in vacuo at 60 °C
1
2
4
overnight. H NMR (300 MHz, CDCl
3
) 7.71 (bm, 4 H), 7.13
mmol) were added, and the reaction was heated to 70 °C
overnight. The reaction was cooled and poured into 500 mL of
H
(bm, 2 H), 4.11 (bm, 4 H), 2.87 (bm, 4 H), 2.62 (bm, 8 H), 1.05
1
3
(bm, 12 H) ppm. C NMR (75 MHz, CDCl
130.53, 129.10, 116.32, 68.32, 51.98, 47.82, 12.03 ppm.
PPP-NEt (I-3). Reagents: DINEt (1.0189 g, 1.819 mmol),
bisneopentylglycol-1,4-phenylene diboronate (4) (0.5492 g,
3
) 150.41, 136.98,
2
O, and a crude orange solid was collected. The crude solid
was recrystallized from THF/H O, yielding a light yellow solid
24.03 g, 81% yield). mp 168-170 °C (lit. mp 169 °C). H NMR
2
2
2
26
1
(

242 Ramey et al.
Macromolecules, Vol. 38, No. 2, 2005
1
.819 mmol), NaHCO
mg, 0.03 mmol). A 0.50 g amount of polymer was recovered
72% yield). Anal. Calcd for C24 0.045: C, 74.24; H, 8.42;
N, 7.22; I, 1.47. Found: C, 67.32; H, 8.42; N, 6.01; I, 1.48. GPC
3
(1.53 g, 18.21 mmol), and Pd(OAc)
2
(6.73
collected by extraction with chloroform (via Soxhlet extraction).
The chloroform-soluble fraction was collected by evaporation
of the solvent and dried in vacuo at 50 °C overnight. A 0.59 g
(
34 2 2
H N O I
1
amount of polymer was recovered (84% yield). H NMR (300
-
1
-1
(
CHCl
Mh ) 16 600 g mol , Mh
PPP-NEt (I-24). Reagents: DINEt
bisneopentylglycol-1,4-phenylene diboronate (4) (0.5169 g,
.712 mmol), NaHCO (1.44 g, 17.12 mmol). and Pd(OAc) (6.73
mg, 0.03 mmol). A 0.52 g amount of polymer was recovered
80% yield). Anal. Calcd for C24 0.023: C, 74.82; H, 8.83;
N, 7.27; I, 0.76. Found: C, 71.85; H, 8.45; N, 6.78; I, 0.77. GPC
3
vs PS) Mh
n
) 10 900 g mol , MP ) 13 300 g mol
,
3
MHz, CDCl ) 7.63 (bm, 2 H), 7.34 (bm, 2 H), 4.24 (bm, 4 H),
-
1
13
w
w
/Mh
n
) 1.52.
3.04 (bm, 4 H), 2.69 (bm, 8 H), 1.11 (bm, 12 H) ppm. C NMR
(75 MHz, CDCl ) 149.53, 139.09, 126.49, 123.26, 113.26, 68.36,
52.09, 42.88, 12.01 ppm. Anal. Calcd for C22
67.38; H, 8.17; N, 7.15; I, 0.97. Found: C, 63.99; H, 8.02; N,
2
2
(0.9589 g, 1.712 mmol),
3
32 2 2
H N O SI0.030: C,
1
3
2
-1
6.51; I, 0.98. GPC (THF vs PS) Mh
n
) 5300 g mol , MP ) 6900
n
-
1
-1
(
34 2 2
H N O I
g mol , Mh
w
) 9000 g mol , Mh
w
/ Mh ) 1.70.
General Quaternization Procedure. Neutral alkoxy-
amine-containing polymers were stirred at room temperature
with an excess of bromoethane in a minimal amount of THF
under Ar with stirring. The partially quaternized amine
polymers began to precipitate out of solution between 3 and 5
days at room temperature. The quaternized polymer solution
was precipitated into acetone, collected on a glass frit, washed
thoroughly with acetone, and dried in vacuo at 50 °C overnight.
Poly{2,5-bis[2-(N,N,N-triethylammonium)-1-oxapropyl]-
-
1
-1
(
CHCl
Mh ) 27 500 g mol , Mh
Poly({2,5-bis[2-(N,N-diethylamino)-1-oxapropyl]-1,4-
phenylene}-alt-2,5-thienylene) (PPT-NEt ). Procedure for
Synthesis (all reactants added at beginning of reaction). A 20
mL Schlenk flask with a stir bar was charged with DINEt
3 n
vs PS) Mh ) 15 300 g mol , MP ) 19 500 g mol ,
-
1
w
w n
/ Mh ) 1.80.
2
2
and 2,5-bis(trimethylstannyl)thiophene (5). The flask was
evacuated and backfilled with Ar three times. A 20 mL amount
of anhydrous DMF, previously sparged with Ar for 30 min,
was added to the reaction flask via syringe. The reaction
mixture was stirred and heated to 50 °C, allowing all mono-
+
1,4-phenylene-alt-2,5-thienylene} Dibromide (PPT-NEt3 ).
1
H NMR (300 MHz, D O) 7.22 (bm, 2 H), 6.90 (bm, 2 H), 3.96
2
(bm, 4 H), 3.12 (bm, 4 H), 2.70 (bm, 8 H), 0.55 (bm, 16.2 H)
ppm. UV-vis (H O) λ
with 411 nm excitation) λ
mers to dissolve. PdCl
2
(PPh
)
3 2
was added in one portion, and
) 411 nm, log ꢀ
max
max 2
) 4.20. PL (H O
2
max
the reaction was heated at 70 °C for a variable number of
hours. The DMF solution was concentrated to ∼5 mL and
precipitated into 150 mL of MeOH. A dark red solid was
collected on a medium porosity glass frit, subsequently ex-
tracted with MeOH for 24 h and acetone for 24 h, and then
collected by extraction with chloroform (via Soxhlet extraction).
The chloroform-soluble fraction was collected by evaporation
) 494 nm.
+
PPT-NEt
3
32 2 2 2 5
(96). Anal. Calcd for C22H N O SI0.037‚2.0 C H -
Br: C, 51.09; H, 6.88; N, 4.58; Br, 26.20. Found: C, 49.87; H,
6
.48; N, 3.18; Br, 24.18.
+
2
2
PPT-NEt
3
(
9
6
-
d
r
o
p
)
.
A
n
a
l
.
C
a
l
c
d
f
o
r
C
H N O SI0.030‚2.0
32 2 2
C
2 5
H Br: C, 51.16; H, 6.89; N, 4.59; Br, 26.24. Found: C, 49.73;
H, 6.52; N, 3.29; Br, 23.62.
1
of the solvent and dried in vacuo at 50 °C overnight. H NMR
(
3
300 MHz, CDCl ) 7.63 (bm, 2 H), 7.34 (bm, 2 H), 4.24 (bm, 4
Acknowledgment. Partial funding for work per-
formed at the University of Florida was provided by the
U.S. Department of Energy, Basic Energy Sciences
1
3
H), 3.04 (bm, 4 H), 2.69 (bm, 8 H), 1.11 (bm, 12 H) ppm.
NMR (75 MHz, CDCl ) 149.53, 139.09, 126.49, 123.26, 113.26,
8.36, 52.09, 42.88, 12.01 ppm. UV-vis (THF) λmax ) 460 nm,
C
3
6
(Grant No. DE-FG-02-96ER14617).
log ꢀmax ) 4.26. PL (THF with 460 nm excitation) λmax
)
5
19 nm.
PPT-NEt
(48). Reaction time of 48 h. Reagents: DINEt
2
Supporting Information Available: Elemental analysis
results for the diamino PPP and PPT monomer and polymers
(Table S1), Optical properties of PPP and PPT polymers in
2
(
1.0895 g, 1.945 mmol), 2,5-bis(trimethylstannyl)thiophene (5)
(
2 3 2
0.7967 g, 1.945 mmol), and 32 mg of PdCl (PPh ) (0.03 mmol).
A 0.45 g amount of polymer was recovered (60% yield). Anal.
Calcd for C22 SI0.079: C, 66.33; H, 8.04; N, 7.03; I, 2.52.
Found: C, 65.23; H, 7.84; N, 6.65; I, 2.50. GPC (THF vs PS)
Mh
Mh
solution (Table S2), TGA thermogram of PPT-NEt
2
and PPT-
+
H
32
N
O
2 2
NEt
and Scatchard Analysis: Binding of Fe(CN)
3
2
under N at a heating rate of 10 °C/min (Figure S1),
4
-
+
6
to PPT-NEt
3
-
1
-1
-1
(Figure S2). This material is available free of charge via the
Internet at http://pubs.acs.org.
n
) 3200 g mol , MP ) 4300 g mol , Mh
/ Mh ) 1.70.
(96). Reaction time of 96 h. Reagents: DINEt
w
) 5200 g mol
,
w
n
PPT-NEt
2
2
(
1.2568 g, 2.243 mmol), 2,5-bis(trimethylstannyl)thiophene (5)
0.9191 g, 2.243 mmol), and 37 mg of PdCl (PPh (0.04 mmol).
References and Notes
(
2
3 2
)
(
1) (a) For reviews in this field, see: Handbook of Conducting
Polymers, 2nd ed.; Skotheim, T. A., Elsenbaumer, R. L.,
Reynolds, J. R., Eds.; Marcel Dekker: New York, 1998. (b)
Chen, L.; Xu, S.; McBranch, D.; Whitten, D. G. J. Am. Chem.
Soc., 2000, 122, 9302. (c) Lukkari, J.; Vinikanoja, A.; Salo-
maki, M.; Aaritalo, T.; Kankare, J. Synth. Met. 2001, 121,
1403. (d) Kim, M.; Sandman, D. J. J. Macromol. Sci. Pure
Appl. Chem. 2001, A38, 1291. (e) Pinto, M. R.; Schanze, K.
S. Synthesis 2002, 9, 1293. (f) Huang, F.; Wu, H.; Wang, D.;
Yang, W.; Cao, Y. Chem. Mater. 2004, 16, 708.
A 0.79 g amount of polymer was recovered (80% yield). Anal.
Calcd for C22 SI0.037: C, 67.13; H, 8.14; N, 7.12; I, 1.19.
Found: C, 63.64; H, 8.03; N, 6.46; I, 1.20. GPC (THF vs PS)
Mh
Mh
32 2 2
H N O
-
1
-1
-1
n
) 4100 g mol , MP ) 5800 g mol , Mh
/ Mh ) 1.68.
(240). Reaction time of 240 h. Reagents: DINEt
w
) 6900 g mol
,
w
n
PPT-NEt
2
2
(
1.4298 g, 2.552 mmol), 2,5-bis(trimethylstannyl)thiophene (5)
1.0456 g, 2.552 mmol), and 35 mg of PdCl (PPh (0.05 mmol).
(
2
3 2
)
A 0.81 g amount of polymer was recovered (82% yield). Anal.
Calcd for C22 SI0.037: C, 67.13; H, 8.14; N, 7.12; I, 1.19.
Found: C, 63.99; H, 7.99; N, 6.51; I, 1.22. GPC (THF vs PS)
Mh
Mh
(
(
2) Yotaro, M. Adv. Polym Sci. 1992, 104, 51-96.
32 2 2
H N O
3) (a) Morawetz, H. Acc. Chem. Res. 1970, 3, 354. (b) Okubo,
T.; Ise, N. Proc. R. Soc. London Ser. A 1972, 327, 413. (c)
Okubo, T.; Ise, N. Bull. Chem. Soc. Jpn. 1973, 46, 2493. (d)
Mita, K.; Kunugi, S.; Okubo, T.; Ise, N. J. Chem Soc., Faraday
Trans. 1 1975, 71, 936. (e) Okubo, T.; Ishiwatari, T.; Mita,
K.; Ise, N. J. Phys. Chem. 1975, 79, 2108. (f) Ise, N.; Okubo,
T. Macromolecules 1978, 11, 439.
-
1
-1
-1
n
) 4200 g mol , MP ) 5400 g mol , Mh
/ Mh ) 1.71.
w
) 7200 g mol
,
w
n
Procedure for Dropwise Synthesis. PPT-NEt
2
(96-
drop). A 20 mL Schlenk flask with stir bar was charged with
DINEt (1.01 g, 1.80 mmol), 25 mg of PdCl (PPh (0.04 mmol),
2
2
3 2
)
and 20 mL of anhydrous DMF, previously sparged with Ar
for 30 min. The solution was warmed to 70 °C. 2,5-Bis(tri-
methylstannyl)thiophene (5) (0.74 g, 1.80 mmol) was dissolved
in 15 mL of DMF and added to a 20 mL addition funnel
attached to the Schlenk flask. Compound 5 was added drop-
wise over the course of 24 h. The reaction mixture was held
at 70 °C for 96 h. The DMF solution was concentrated to ∼5
mL and precipitated into 150 mL of MeOH. A dark red solid
was collected on a medium porosity glass frit, subsequently
extracted with MeOH for 24 h and acetone for 24 h, and then
(4) (a) Meisel, D.; Matheson, M. S. J. Am. Chem. Soc. 1977, 99,
6577. (b) Meisel, D.; Rabani, J.; Meyerstein, D.; Matheson,
M. S. J. Phys. Chem. 1978, 82, 985. (c) Meyerstein, D.;
Rabani, J.; Matheson, M. S. J. Phys. Chem. 1978, 82, 1879.
(
d) Jonah, C. D.; Matheson, M. S.; Meisel, D. J. Phys. Chem.
1
979, 83, 257.
(
5) (a) Chen, L.; Xu, S.; McBranch, D. W.; Wang, H. L.; Helgeson,
R.; Wudl, F.; Whitten, D. G. J. Proc. Natl. Acad. Sci. U.S.A.
1999, 96, 12287. (b) McQuade, D. T.; Pullen, A. E.; Swager,
T. M. Chem. Rev. 2000, 100, 2537. (c) Raz. J. Drug Dev. Res.
2000, 50, 497. (d) Leclerc, M. Can. Chem. News 2000, 52, 22.

Macromolecules, Vol. 38, No. 2, 2005
Poly(p-phenylene-co-thiophene) Polyelectrolyte 243
(
e) Cornil, J.; Beljonne, D.; Calbert, J.-P.; Bredas, J.-L. Adv.
12426. (c) Saadeh, H.; Goodson, T.; Yu, L. Macromolecules
1997, 30, 4608. (d) Wang, F.; Wilson, M. S.; Rauh, R. D.;
Schottland, P.; Thompson, B. C.; Reynolds, J. R. Macromol-
ecules 2000, 33, 2083.
Mater. 2001, 13, 1053. (f) Pron, A.; Rannou, P. Prog. Polym.
Sci. 2001, 27, 135. (g) Leclerc, M. Sens. Update 2001, 8, 21.
(
h) Wang, D.; Gong, X.; Heeger, P. S.; Rininsland, F.; Bazan,
G. C.; Heeger, A. J. Proc. Natl. Acad. Sci. U.S.A. 2002, 99,
(13) Stille, J. K. Angew. Chem., Int. Ed. Engl. 1986, 25, 508.
14) (a) Decher, G.; Hong, J. D.; Schmitt, J. Thin Solid Films 1992,
4
2
9. (i) Tan, C.; Pinto, M. R.; Schanze, K. S. Chem. Commun.
002, 5, 446. (j) DiCesare, N.; Pinto, M. R.; Schanze, K. S.;
(
(
(
2
10/211, 831. (b) Lvov, Y.; Decher, G.; Mohwald, H. Lang-
Lakowicz, J. R. Langmuir 2002, 18, 7785. (k) Dai, L.;
Soundarrajan, P.; Kim, T. Pure Appl. Chem. 2002, 74, 1753.
muir 1993, 9, 520. (c) Hammond, P. Curr. Opin. Colloid
Interface Sci. 2000, 4, 430. (d) Handbook of Polyelectrolytes
and Their Applications; Tripathy, S. K., Kumar, J., Nalwa,
H. S., Eds.; American Scientific Publishers: Stevenson
Ranch, CA, 2002. (e) Multilayer Thin Films; Decher, G.,
Schlenoff, J. B., Eds.; Wiley-VCH: Weinheim, Germany,
(
l) Song, H.; Wang, H.; Shi, J.; Park, J.-W.; Swanson, B. I.
Chem. Mater. 2002, 14, 2342. (m) Lavastre, O.; Illitchev, I.;
Jegou, G.; Dixneuf, P. H. J. Am. Chem. Soc. 2002, 124, 5278.
(
n) Pinto, M. R.; Kristal, B. M.; Schanze, K. S. Langmuir
2
003, 19, 6523. (o) Zherdev, A. V.; Byzova, N. A.; Izumrudov,
2
003.
V. A.; Dzantiev, B. B. Analyst 2003, 128, 1275. (p) Kuroda,
K.; Swager, T. M. Macromol. Symp. 2003, 201, 127.
6) (a) Rau, I. U.; Rehahn, M. Polym. Commun. 1993, 34, 2889.
15) (a) Ferreira, M.; Cheung, J. H.; Rubner, M. F. Thin Solid
Films 1994, 244, 806. (b) Cheung, J. H.; Fou, A. F.; Rubner,
M. F. Thin Solid Films 1994, 244, 985. (c) Cheung, J. H.;
Rubner, M. F. Thin Solid Films 1994, 244, 990. (d) Ferreira,
M.; Rubner, M. F. Macromolecules 1995, 28, 7107. (e) Fou,
A. C.; Rubner, M. F. Macromolecules 1995, 28, 7115. (f) Fou,
A. F.; Onitsuka, O.; Ferreira, M.; Rubner, M. F.; Hsieh, B.
R. J. Appl. Phys. 1996, 79, 7501. (g) Cheung, J. H.; Stockton,
W. B.; Rubner, M. F. Macromolecules 1997, 30, 2712.
16) (a) Ho, P. K. H.; Granstr o¨ m, M.; Friend, R. H.; Greenham,
N. C. Adv. Mater. 1998, 10, 769. (b) Ho, P. K. H.; Kim, J.-S.;
Burroughes, J. H.; Becker, H.; Li, S. F. Y.; Brown, T. M.;
Cacialli, F.; Friend, R. H. Nature 2000, 404, 481.
(
(b) Rau, I. U.; Rehahn, M. Acta Polym. 1994, 45, 3. (c)
Rulkens, R.; Schulze, M.; Wegner, G. Macromol. Rapid
Commun. 1994, 15, 669. (d) Brodowski, G.; Horvath, A.;
Ballauff, M.; Rehahn, M. Macromolecules 1996, 29, 6962. (e)
Cimrova, V.; Schmidt, W.; Rulkens, R.; Schulze, M.; Meyer,
W.; Neher, D. Adv. Mater. 1996, 8, 585. (f) Kowitz, C.;
Wegner, G. Tetrahedron 1997, 53, 15553. (g) Rulkens, R.;
Wegner, G.; Chu, B. Macromolecules 1998, 31, 6119. (h)
Petrekidis, G.; Vlassopoulos, D.; Fytas, G.; Rulkens, R.;
Wegner, G. Macromolecules 1998, 31, 6129. (i) Traser, S.;
Wittmeyer, P.; Rehahn, M. e-Polymers 2002, 32; http://
www.e-polymers.org/papers/rehahn_070702.pdf.
(17) Hong, L.; Powell, D. R.; Hayashi, R. K.; West, R. Macromol-
(
7) (a) Wallow, T. I.; Novak, B. M. Polym. Prepr. (Am. Chem.
Soc., Div. Polym. Chem.) 1991, 32 (3), 191. (b) Wallow, T. I.;
Novak, B. M. J. Am. Chem. Soc. 1991, 113, 7411. (c) Wallow,
T. I.; Novak, B. M. Polym. Prepr. (Am. Chem. Soc., Div.
Polym. Chem.) 1992, 33 (1), 908.
ecules 1998, 31, 52.
(18) Peng, Z.; Gharavi, A. R.; Yu, L. J. Am. Chem. Soc. 1997, 119,
4622.
(
(
(
(
19) Seitz, D. E.; Lee, S.-H.; Hanson, R. N.; Bottaro, J. C. Synth.
Commun. 1983, 13, 121.
(
(
8) (a) Child, A. D.; Reynolds, J. R. Macromolecules 1994, 27,
20) Sandstedt, C. A.; Rieke, R. D.; Eckhardt, C. J. Chem. Mater.
1
975. (b) Kim, S.; Jackiw, J.; Robinson, E.; Schanze, K. S.;
1995, 7, 1057.
Reynolds, J. R.; Baur, J.; Rubner, M. F.; Boils, D. Macromol-
ecules 1998, 31, 964.
21) Kim, W. H.; Kodai, N. B.; Kumar, J.; Tripathy, S. K.
Macromolecules 1994, 27, 1819.
9) Balanda, P. B.; Ramey, M. B.; Reynolds, J. R. Macromolecules
22) Tan, C.; Atas, E.; M u¨ ller, J. G.; Pinto, M. R.; Kleiman, V. D.;
1
999, 32, 3970.
Shanze, K. S. J. Am. Chem. Soc. 2004, 126, 13685.
(
(
10) Kim, S.; Jackiw, J.; Robinson, E.; Schanze, K. S.; Reynolds,
J. R.; Baur, J.; Rubner, M. F.; Boils, D. Macromolecules 1998,
(23) Shiratori, S. S.; Rubner, M. F. Macromolecules 2000, 33, 4213.
3
1, 964.
(24) Coutts, I. G. C.; Goldschmid, H. R.; Musgrave, O. C. J. Chem.
11) (a) Chang, S. C.; Bharathan, J.; Helgeson, R.; Wudl, F.; Yang,
Soc. (C) 1970, 488.
Y.; Ramey, M. B.; Reynolds, J. R. Appl. Phys. Lett. 1998, 73,
(
25) Hunig, S.; Bau, R.; Kemmer, M.; Mixner, H.; Metzenthin, T.;
2
561. (b) Harrison, B. S.; Ramey, M. B.; Reynolds, J. R.;
Peters, K.; Sinzger, K.; Gulbis, J. Eur. J. Org. Chem. 1937,
Schanze, K. S. J. Am. Chem. Soc. 2000, 122, 8561.
12) (a) Bao, Z.; Waikin, C.; Yu, L. Chem. Mater. 1993, 5, 2. (b)
Bao, Z.; Waikin, C.; Yu, L. J. Am. Chem. Soc. 1995, 117,
2, 335.
(
MA048360K