Supramolecular functionalization of single-walled carbon nanotubes (SWNTs) with dithieno[3,2- b:2′,3′-d ]pyrrole (DTP) containing conjugated polymers

Article abstract of DOI:10.1021/ma201610y

Fluorene and dithieno[3,2-b:2′,3′-d]pyrrole (DTP) containing conjugated polymers, {2,7-[9,9-didodecylfluorene]-alt-2,6-[N-dodecyldithieno(3, 2-b:2′,3′-d)pyrrole]} (PF-DTP1) and {2,7-[9,9-didodecylfluorene]- alt-2,6-[N-3,4,5(n-dodecyloxy)phenyldithieno(3,2-b:2′,3′-d)pyrrole]} (PF-DTP2), have been successfully synthesized using Suzuki polycondensation. These polymers possess excellent thermal stability with decomposition temperatures over 365 °C under Ar. The introduction of soluble side chains on the DTP units and incorporation with soluble dialkyl-substituted fluorene resulted in highly soluble polymers with novel optoelectronic properties. The supramolecular complex formation of these DTP containing polymers with single-walled carbon nanotubes (SWNTs) has been studied, and it was found that these polymers can form strong supramolecular polymer-nanotube assemblies and produce stable complexes in solution. UV-vis-NIR absorption, photoluminescence excitation (PLE), and Raman spectroscopy were used for the characterization and identification of the nanotube species that are present in THF solution. The strong nanotube emission was observed from individual SWNTs even after removal of excess free polymer by filtration and washing. On the basis of these two polymers, it was found that the interactions with the SWNT surface are more strongly dictated by the polymer backbone than the side chain, though further studies may be warranted.

Full text of DOI:10.1021/ma201610y

ARTICLE
pubs.acs.org/Macromolecules
Supramolecular Functionalization of Single-Walled Carbon
Nanotubes (SWNTs) with Dithieno[3,2-b:20,30-d]pyrrole (DTP)
Containing Conjugated Polymers
Patigul Imin, Mokhtar Imit, and Alex Adronov*
Department of Chemistry and Chemical Biology, the Brockhouse Institute for Materials Research, McMaster University, Hamilton,
Ontario, Canada
S Supporting Information
b
ABSTRACT: Fluorene and dithieno[3,2-b:20,30-d]pyrrole (DTP)
containing conjugated polymers, {2,7-[9,9-didodecylfluorene]-alt-
2,6-[N-dodecyldithieno(3,2-b:20,30-d)pyrrole]} (PF-DTP1) and
{2,7-[9,9-didodecylfluorene]-alt-2,6-[N-3,4,5(n-dodecyloxy)phenyl-
dithieno(3,2-b:20,30-d)pyrrole]} (PF-DTP2), have been successfully
synthesized using Suzuki polycondensation. These polymers possess
excellent thermal stability with decomposition temperatures over
365 °C under Ar. The introduction of soluble side chains on the DTP
units and incorporation with soluble dialkyl-substituted fluorene
resulted in highly soluble polymers with novel optoelectronic proper-
ties. The supramolecular complex formation of these DTP containing polymers with single-walled carbon nanotubes (SWNTs) has
been studied, and it was found that these polymers can form strong supramolecular polymerꢀnanotube assemblies and produce
stable complexes in solution. UVꢀvisꢀNIR absorption, photoluminescence excitation (PLE), and Raman spectroscopy were used
for the characterization and identification of the nanotube species that are present in THF solution. The strong nanotube emission
was observed from individual SWNTs even after removal of excess free polymer by filtration and washing. On the basis of these two
polymers, it was found that the interactions with the SWNT surface are more strongly dictated by the polymer backbone than the
side chain, though further studies may be warranted.
’ INTRODUCTION
processability, and unique optoelectronic properties.14,26,29ꢀ36
Recently, it has been found that fluorene- and thiophene-
containing conjugated polymers can form stable complexes with
SWNTs and exhibit excellent solubility and solution stability
properties even after removal of excess free polymer.27,29 Interest
in this class of conjugated polymers has gained much recent
popularity as reports of selective solubilization of certain SWNT
species have begun to be published.20,30,31,37,38 It is therefore
desirable to develop a detailed understanding of how variations in
the backbone or the side chain of a conjugated polymer can affect
the interactions between the polymer and the SWNT surface. In
particular, structural components that increase the strength of
polymer binding to the nanotube surface are of significant
interest. Although the fused-ring precursors of poly(thiophene)s
should result in stronger nanotube binding behavior when com-
pared to the previously reported alkylthiophene-containing
analogues due to the planarity of the fused thiophene rings,
the noncovalent functionalization of carbon nanotubes with
dithieno[3,2-b:20,30-d]pyrrole (DTP)-containing conjugated
polymers has not been reported.
Single-walled carbon nanotubes (SWNTs) are of special
interest in current research due to their extraordinary mechan-
ical, electronic, and optical properties.1ꢀ5 Their unique structure,
remarkable thermal and electrical conductivity, and high me-
chanical strength make SWNTs viable candidates for a wide
range of device applications, including chemical sensors,6ꢀ8 field-
effect transistors,9 nanoscale integrated radio receivers,10,11
photovoltaics,12ꢀ14 and field-emission displays.3,15 However,
the inherent insolubility of carbon nanotubes in most organic
and aqueous solvents has hindered the widespread application of
these novel nanostructures. Therefore, a great deal of research
has been focused on functionalization of SWNTs, mainly to
enhance their solubility and solution phase processability.5,16,17
The supramolecular functionalization methodology has received
much recent attention because this approach does not introduce any
defects in the nanotube side wall, thus preserving the electrical and
mechanical properties of the resulting materials.18ꢀ20
Recently, it has been shown that various conjugated polymers
form strong supramolecular complexes with SWNTs, enabling
their dissolution in organic solvents, as well as water, depending
on the nature of the side chain.19,21ꢀ28 Among all conjugated
polymers, fluorene- and thiophene-containing conjugated poly-
mers are of particular interest due to their good solubility,
Received: July 14, 2011
Revised:
October 17, 2011
Published: November 02, 2011
r
2011 American Chemical Society
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Conjugated polymers containing dithieno[3,2-b:20,30-d]pyrrole
(DTP) units exhibit lower band gaps when compared to the
alkylthiophene-containing analogues due to better π-conjugation
across the fused thiophene rings.39ꢀ46 In addition, the conjugated
polymers having DTP units in their backbone exhibit interesting
optoelectronic properties, making them potentially useful in a
variety of device applications including field effect transistors,39,47
photovoltaic cells,41,44 and other optoelectronic devices.45,46,48
Furthermore, it has been shown that the optoelectronic proper-
ties of the DTP containing polymers can be easily tailored by
altering the composition of the polymer backbone and side
chains.39,46,49 In an attempt to produce a new type of functional
nanostructure, we have focused our attention on supramolecular
functionalization of carbon nanotubes with DTP and fluorene-
containing conjugated polymers. In order to improve the solu-
bility of the resulting polymers and their supramolecular com-
plexes with SWNTs, the polymer backbone was composed of
DTP and fluorene units having long alkyl side chains, and two
copolymers were prepared that have an identical aromatic back-
bone but differ in the solubilizing substituents. Here we report
the full details of the monomer and polymer preparation, studies of
the supramolecular complex formation properties of these polymers
with SWNTs, and complete optoelectronic and photophysical
characterization of the resulting materials. The effect of changing
side chains of the polymer on the interaction between polymer and
nanotubes was also investigated.
’ RESULTS AND DISCUSSION
Schemes 1 and 2 show the synthetic route to the target
monomers. 3,30-Dibromo-2,20-bithiophene (2) was synthesized
according to literature procedures starting from bithiophene in
two steps.50,51 3,4,5-Tri(n-dodecyloxy)aniline (7) was prepared
according to a slightly modified literature procedure starting
from 1,2,3-trihydroxybenzene.19,52ꢀ54 The N-substituted dithieno-
[3,2-b:20,30-d]pyrrole precursors (compounds 3 and 8) were
prepared from primary amines and 3,30-dibromo-2,20-bithio-
phene using the BuchwaldꢀHartwig reaction.41,47,55 In both
cases the reactions were carried out in toluene under reflux over-
night, with 2,20-bis(diphenylphosphino)-1,10-binaphthyl (BINAP)
as the ligand and tris(dibenzylideneacetone)dipalladium(0)
Scheme 1. Synthetic Routes to Monomer 4
Table 1. Molecular Weight and Polydispersity Index Values
for the Synthesized Polymers
polymer
Mn (kg/mol)a
PDI
Mn (kg/mol)b
PF-DTP1
PF-DTP2
10.8
18.5
6.1c
6.2c
11.0
14.5
a Measured by GPC. b Estimated by NMR. c GPC chromatogram of the
polymers showed a broad bimodal distribution.
Scheme 2. Synthetic Routes to Monomer 9
Scheme 3. Synthetic Route to the Polymers
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Figure 1. 1H NMR spectra of the polymers in CDCl3. Insets show magnified view of the aromatic (6.5ꢀ7.9 ppm) regions.
Figure 2. Thermograms of PF-DTP1 (A) and PF-DTP2 (B) measured under an Ar atmosphere.
(Pd2(dba)3) as the Pd source. The reaction products were
isolated by simple column chromatography with high yields.
By using a slight excess of dodecylamine, we were able to obtain
N-dodecyldithieno[3,2-b:20,30-d]pyrrole (DTP) (compound 3)
in over 95% yield. When N-dodecyldithieno[3,2-b:20,30-d]-
pyrrole was treated with N-bromosuccinimide (NBS) in
CHCl3/DMF at 0 °C, the target compound 2,6-dibromo-
N-dodecyldithieno[3,2-b:20,30-d] pyrrole (compound 4) was
successfully synthesized in 71% yield.56 However, when a similar
reaction procedure was followed for compound 8, the bromina-
tion occurred not only at the 2- and 6-positions of the DTP ring
but also on the phenyl ring due to the presence of the three
activating alkoxy groups. We therefore investigated iodination as
an alternative, more regioselective route to the desired monomer.
The diiodo-substituted N-3,4,5(n-dodecyloxy)phenyldithieno-
[3,2-b:20,30-d]pyrrole was successfully synthesized using N-iodo-
succinimide (NIS) in CHCl3 at 0 °C.52
(3:1 v/v) as the solvent and tetrakis(triphenylphosphine) palla-
dium (Pd(PPh3)4) as the polymerization catalyst. In both cases
polymers were obtained as orange solids in yields of over 80%.
The crude polymers were purified by precipitation twice in
methanol. Both polymers exhibited excellent solubility in com-
mon organic solvents such as THF, chloroform, and dichlor-
obenzene at room temperature, which can be attributed to the bulky
side chains. Molecular weights of the polymers were determined by
gel permeation chromatography (GPC) with polystyrene standards
and a mixture of THF and 1% of acetonitrile as the mobile phase.
The molecular weight (Mn) and polydispersity index (PDI) values
of the polymers are listed in Table 1.
The chemical structures of polymers (PF-DTP1 and PF-
1
DTP2) were confirmed by H NMR spectroscopy (Figure 1).
The single peak at 7.32 ppm (Figure 1A) corresponds to the
aromatic protons from DTP, and the peaks at 7.60ꢀ7.66 ppm
correspond to the aromatic protons of fluorene. On the basis of
the relative areas of these peaks, the molar ratio of fluorene and
DTP was determined to be 1:1 in both polymers, which is
consistent with the alternating copolymer structure expected
from the Suzuki polycondensation of the monomers. Phenyl
groups were also successfully introduced at both ends of the
polymer as end-caps, and the two sets of doublets at 7.01, 7.15
The polymers PF-DTP1 and PF-DTP2 were prepared using a
Suzuki polycondensation from 9,9-didodecylfluorene-2,7-bis-
(trimethyleneboronate) and the corresponding N-substituted
dithieno[3,2-b:20,30-d]pyrrole monomers (compounds 4 and 9,
respectively), as depicted in Scheme 3.27,29 Preparation of these
polymers was performed in a mixture of DMF and toluene
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Figure 3. UVꢀvis absorption data from polymer, SDBSꢀSWNT, and polymerꢀSWNT complexes for PF-DTP1 (A) and PF-DTP2 (B).
Figure 4. Emission spectra of free polymer and polymerꢀSWNT complexes using PF-DTP1 (A) and PF-DTP2 (B) polymers, with the excitation
wavelength set to the absorption maximum of each sample (485 nm for PF-DTP1 and PF-DTP1 + SWNT; 480 nm for PF-DTP2 and PF-DTP2 +
SWNT).
Figure 5. TEM images of PF-DTP1 + SWNT at different magnifications. The high-magnification image clearly shows the presence of individual
polymer-wrapped SWNTs. Scale bars are 500 nm (A), 100 nm (B), and 10 nm (C).
ppm for PF-DTP1 and 7.15, 7.20 ppm for PF-DTP2 (Figure 1)
were assigned as the end-group phenyl protons.57 This end-
group assignment was also confirmed by the 2-dimensional
(DP) and Mn were be estimated. The DP and Mn values were
calculated to be 13 and 11.0 kg/mol for PF-DTP1 and 11 and
14.5 kg/mol for PF-DTP2, respectively. It should be noted that,
although the two polymers have identical backbone structures,
the different side chains impart significant differences to their
solubility. Not surprisingly, the larger and branched side chain of
PF-DTP2 results in a more easily soluble material. Although both
polymers were fully soluble in THF, chloroform, and dichloro-
methane, dissolution of PF-DTP2 occurred much faster relative
to PF-DTP1.
1
protonꢀproton correlation spectrum (1Hꢀ H COSY), hetero-
nuclear single quantum correlation spectrum (1Hꢀ C HSQC),
13
13
and heteronuclear multiple bond correlation spectrum (1Hꢀ C
HMBC) of the PF-DTP1 (see the Supporting Information,
Figures S4ꢀS6). On the basis of the integral ratio of the fluorene
proton (or DTP proton) signals in the polymer repeat unit to the
end-group proton signal, the average degree of polymerization
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The thermal stability of PF-DTP1 and PF-DTP2 was char-
acterized by thermogravimetric analysis (TGA), carried out
under an Ar atmosphere (Figure 2). These data indicate that it
is not possible to completely decompose the two polymers by
heating to 800 °C under Ar. The major mass loss occurs at
375 °C for PF-DTP1, amounting to 48%, and 365 °C for PF-
DTP2, amounting to 59%. These mass losses correspond well
with the loss of side chains within these polymers. Interestingly,
PF-DTP2 exhibits a second decomposition, amounting to ∼8%
at 491 °C, which corresponds to the loss of the benzene ring from
each repeat unit.
The supramolecular interaction of PF-DTP1 and PF-DTP2
with SWNTs was studied using our previously reported methods.29
In a typical experiment, a SWNT sample (5 mg) was added to a
solution of polymer in THF (15 mg/20 mL), and the mixture
was ultrasonicated in a bath sonicator for 1 h. The resulting
solution was centrifuged for 45 min at 8300 g and allowed to
stand overnight. The supernatant was carefully transferred by
pipet to another vial, producing dark colored and stable
polymerꢀnanotube complex solutions. The isolated superna-
tant was further diluted with 50 mL of THF, sonicated for 5 min,
filtered through a 200 nm pore diameter Teflon membrane, and
repeatedly washed with THF until the filtrate was colorless,
ensuring removal of all excess free polymer. 20 mL of THF was
added to the recovered SWNT residue, and the vial was further
sonicated for 5 min. The resulting dark suspension was centri-
fuged at 8300 g for 30 min and allowed to stand overnight
undisturbed. It was found that the resulting polymerꢀSWNT
complexes exhibited very good solubility, and the solutions
remained stable for periods of at least 3 months with no
observable precipitation.
The UVꢀvis absorption properties of polymers and their
corresponding SWNT complexes were measured at room tem-
perature in THF (Figure 3). Because of the high solubility of the
polymerꢀSWNT complexes, all solutions prepared in THF were
diluted more than 20-fold in order to make them suitable for
absorption and photoluminescence (PL) studies. For reference,
the absorption spectra of just the nanotubes, measured from
aqueous suspensions with sodium dodecylbenzenesulfonate
(SDBS) surfactant, are also shown in Figure 3. PF-DTP1 and PF-
DTP2 exhibited an absorption maximum (λmax) of 485 nm (with
a low-energy shoulder at 516 nm) and 480 nm (with a low-energy
shoulder at 509 nm) in THF, respectively. The overall absorption
profiles of the PF-DTP1 and PF-DTP2 were very similar.48,49
From comparison of the polymerꢀSWNT absorption spec-
trum and that of the free polymer, it is clear that the absorption
characteristics of both polymer and SWNTs are evident in the
polymerꢀSWNT absorption spectra. To emphasize the absorp-
tion properties of the nanotube-adsorbed polymer, the nanotube
component of the polymerꢀSWNT complex spectra was sub-
tracted to give the subtraction curves shown in Figure 3 for each
of the two polymers (curve labeled “Subtraction”). From these
subtraction spectra, it appears that the shoulder peaks at lower
energy became much more dominant in polymerꢀSWNT com-
plexes, relative to the free polymer, most likely because of
increased electron delocalization.48 These results indicate that
the polymer backbone becomes more planar on the nanotube
surface, leading to an enhanced effective conjugation length
within the polymer.27,29
Figure 6. PL contour maps of HiPco SWNTs dispersed with SDBS in
D2O (A), with PF-DTP1 in THF (B), and with PF-DTP2 in THF (C).
(Figure 4). From the normalized emission spectra it is clear that
highly efficient quenching of fluorescence occurs when the
polymers are adsorbed on the nanotube surface. The fluores-
cence quenching is likely the result of photoinduced energy or
electron transfer between the excited-state conjugated polymer
and the SWNT, as previously reported for other systems.18,31,58
TEM analysis of the polymerꢀSWNT complexes revealed the
presence of numerous structures resembling individual polymer-
coated nanotubes. The high solubility of these complexes in THF
allowed deposition and observation of large numbers of SWNT
on the TEM grid. However, practically all sample preparation
methods resulted in nanotubes localizing on the carbon film of
the holey carbon coated TEM grids, diminishing the contrast
between the nanotube features and the carbon background. Only
a few regions were found with nanotubes spanning holes, where
the contrast was great enough for high-resolution imaging. Such
images from the PF-DTP1 + SWNT sample are given in Figure 5.
In particular, Figure 5C shows the presence of individual,
exfoliated SWNTs that are wrapped with polymer chains. From
The fluorescence spectra of the free polymers and poly-
merꢀSWNT complexes were also measured in THF. Both PF-
DTP1 and PF-DTP2 exhibited strong emission in solution
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Figure 7. (A) NIRabsorptionspectraof SDBS/SWNT(a), PF-DTP1+SWNT(b), andPF-DTP2+SWNT(c). (B) Raman data(withexcitationat 785 nm)
for SDBS/SWNT (a), PF-DTP1 + SWNT (b), PF-DTP2 + SWNT (c), and pristine SWNT (d), showing only the radial breathing modes of the
nanotube samples.
this image, it is clear that nanotubes are separated from bundles
by the interaction with the conjugated polymer, consistent with
the absorption and emission properties of the polymerꢀSWNT
complexes presented below. For the PF-DTP2 + SWNT sample,
the same general features were observed (see Supporting In-
formation, Figure S8), but regions where the sample cleanly
spanned a hole could not be found. It should be noted that a large
number of iron nanoparticles were also observed within the sample,
which are introduced during the synthesis of the raw HiPco SWNTs
that were used in this study without any purification.
was used (see Table S2, where the most intense signal of each
dispersion was set to a value of 1, and the normalized PLE signal
intensities were calculated accordingly). The dominant species
within these solutions were found to be (7, 5) and (7, 6) for both
polymerꢀSWNT complexes. Interestingly, signals for both of
these nanotube types were not very intense in the PLE maps of
the SDBSꢀSWNT sample in aqueous solution. These results
indicate that both polymers may preferentially select nanotubes
with a certain diameter range (0.76ꢀ1.03 nm).
UVꢀvis-NIR absorption studies were performed on poly-
merꢀSWNT complex solutions in THF as well as the aqueous
solution of SWNTs dispersed using SDBS. The UVꢀvisꢀNIR
absorption spectra are depicted in Figure 7A. The absorption
spectrum exhibited features that correspond to the first (E11) and
second (E22) interband transitions for semiconducting tubes,
which are found from 900 to 1600 nm and 600 to 900 nm,
respectively.61,49 The absorption peaks of the polymerꢀSWNT
complexes become better resolved (Figure 7A, curves b and c)
and showed relatively stronger semiconducting transitions when
compared to the absorption spectrum of SWNTs dispersed in
D2O using SDBS (Figure 7A,a). All of the transitions of poly-
merꢀSWNT complexes were found to be red-shifted more than
20 nm relative to the aqueous solution, which is consistent to
what was observed in the photoluminescence maps and has been
reported previously with comparable polymers.20,30,37 The over-
all absorption profiles of the polymerꢀSWNT complexes for
both polymers (PF-DTP1 and PF-DTP2) are nearly identical.
Raman spectroscopy was used to further characterize the
polymerꢀSWNT samples. Sample preparation involved drop-
casting dilute polymerꢀSWNT solutions in THF onto a glass
microscope slide and air-drying prior to measurement. Raman
measurements were performed in air, using an excitation wave-
length of 785 nm (Supporting Information Figure S7). It has
been reported that the radial breathing mode (RBM) profiles at
this excitation wavelength can be used as a valuable tool for
evaluating the extent of aggregation occurring in a sample.62,63
RBM profiles of the as-received HiPco sample, SDBSꢀSWNT,
as well as the soluble polymerꢀSWNT complexes are shown in
Figure 7B. The pristine Hipco SWNTs have five major RBM
bands at Raman frequencies of ∼281, 250, 243, 233, and
229 cmꢀ1 (Figure 7B,d), which is consistent with what has been
observed previously with Hipco nanotubes.62ꢀ65 Small shifts and
Photoluminescence excitation maps (PLE) of the samples
were measured over a large range of excitation (300ꢀ900 nm)
and emission (900ꢀ1450 nm) wavelengths. As the absorption
(E22) and emission (E11) properties strongly depend on the type
of the carbon nanotubes, the semiconducting species that are
present in solution can be easily identified.59,60 Figure 6 depicts
the photoluminescence excitation (PLE) maps of SWNTs dis-
persed in THF using the DTP containing polymers (PF-DTP1
and PF-DTP2, respectively), which can be compared to the PLE
maps of an aqueous dispersion using SDBS. High intensities are
displayed in red and low intensities are displayed in blue. The
chiral indices (n, m) for the identified species are labeled on the
maps, where the assignment was based on the previously
reported results from Weisman and co-workers.59,60 Figure 6A
shows the PLE map of the pristine SWNT sample dispersed in
D2O using SDBS, where 17 different semiconducting nanotubes
were detected.20,60 When the same material was mixed with
polymers PF-DTP1 and PF-DTP2 in THF, entirely different
results were obtained. Figures 6B and 6C depict the PLE maps of
the SWNT complexes with PF-DTP1 and PF-DTP2, respec-
tively. The observed strong nanotube emission indicates that
individual SWNTs are solubilized and isolated by the polymer
and that removal of free polymer by filtration does not result in
any rebundling. It was found that both excitation and emission
wavelengths of the polymerꢀSWNT complexes were red-shifted
relative to the aqueous solution by 10ꢀ30 nm (Table S1), which
is consistent with other previously reported comparable
systems.14,20,30,37 It is obvious from the PLE map that both
polymers enable solubilization and isolation of eight major
species including (7, 5), (7, 6), (8, 6), (8, 7), (9, 4), (9, 5), (6, 5),
and (8, 4) in THF, and the relative emission intensity of each
solubilized species is slightly different when a different polymer
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significant changes in intensity of various bands can be observed
when comparing the RBM signals of the solubilized samples to
the as received SWNTs. All of the peaks of the polymerꢀSWNT
complexes and SWNTꢀSDBS show a characteristic red shift of
3ꢀ6 cmꢀ1 (284, 254, 247, 239, 230 cmꢀ1) relative to the equi-
valent peaks in the spectrum of the starting material. The signal at
284 cmꢀ1 is much more dominant in spectra of pristine bundled
SWNTs, and this feature nearly disappeared in the polymer
functionalized samples as well as the SDBS dispersed sample.
This result indicates that the nanotubes are individually dispersed
by polymers in solution, and there is no evidence of aggregation
when they are drop-cast onto the glass substrate. Interestingly,
both polymerꢀSWNT complexes exhibit a strong signal at 247 cmꢀ1
(corresponding to diameters of ∼0.96 nm), indicating that both
polymers selectively bring a specific nanotube species into reso-
nance when excited at 785 nm.
(CCEM). P.I. gratefully acknowledges the Ontario Ministry of
Training for an Ontario Graduate Scholarship (OGS).
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’ CONCLUSION
We have successfully synthesized a new class of highly soluble
alternating copolymers of fluorene and dithieno[3,2-b:20,30-
d]pyrrole (DTP). Thermogravimetric analysis indicated that
both polymers exhibit excellent thermal stability under Ar. The
resulting polymers were subsequently utilized for the preparation
of supramolecular polymerꢀSWNT composite materials, and
excellent nanotube solubility and solution stability was achieved.
UVꢀvis absorption measurements revealed a bathochromic shift
in the polymer absorption spectrum as a result of complex
formation with nanotubes. Flourescence measurements showed
that polymer emission is highly quenched in the corresponding
SWNT complexes. Both TEM and photoluminescence experi-
ments showed that efficient and selective dispersal of SWNT is
possible by using the DTP and fluorene containing copolymers.
UVꢀvisꢀNIR, photoluminescence, and Raman measurements
indicated that the SWNTs were successfully debundled and
isolated by polymer in solution, and removal of the free polymer
by filtration did not cause further bundling.
’ ASSOCIATED CONTENT
S
Supporting Information. Full experimental details,
b
1H NMR spectra of the monomers 4, 8, and 9, 2D COSY, HSQC,
HMBC spectra of PF-DTP1, and Raman spectra; tables of the
relative content of the identified nanotube species from the PLE
maps. This material is available free of charge via the Internet at
http://pubs.acs.org.
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Chem. Commun. 2006, 4937–4939.
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’ AUTHOR INFORMATION
Corresponding Author
*Tel: (905) 525-9140 x23514. Fax: (905) 521-2773. E-mail:
adronov@mcmaster.ca.
’ ACKNOWLEDGMENT
Financial support for this work was provided by the Natural
Science and Engineering Research Council of Canada (NSERC),
the NSERC Photovoltaic Innovation Network, the Canada
Foundation for Innovation (CFI), and the Ontario Innovation
Trust (OIT). The authors thank Ms. Julia Huang and Dr.
Andreas Korinek for their help with electron microscopy, which
was performed in the Canadian Centre for Electron Microscopy
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