Supramolecular functionalization of Single-Walled Carbon Nanotubes (SWNTs) with a photoisomerizable conjugated polymer

Article abstract of DOI:10.1021/ma300403q

A fluorene- and azobenzene-containing conjugated polymer, poly[2,7-(9,9-didodecylfluorene)-alt-4,4′-azobenzene] (F12AZO) has been successfully synthesized using Suzuki polycondensation. The introduction of two dodecyl chains on the flourene unit resulted

Full text of DOI:10.1021/ma300403q

Article
pubs.acs.org/Macromolecules
Supramolecular Functionalization of Single-Walled Carbon
Nanotubes (SWNTs) with a Photoisomerizable Conjugated Polymer
Patigul Imin, Mokhtar Imit, and Alex Adronov*
Department of Chemistry and Chemical Biology, The Brockhouse Institute for Materials Research, McMaster University, 1280 Main
Street West, Hamilton, Ontario, L8S 4M1, Canada
S
* Supporting Information
ABSTRACT: A fluorene- and azobenzene-containing conju-
gated polymer, poly[2,7-(9,9-didodecylfluorene)-alt-4,4′-azoben-
zene] (F12AZO) has been successfully synthesized using Suzuki
polycondensation. The introduction of two dodecyl chains on
the flourene unit resulted in a highly soluble polymer. F12AZO
possesses excellent thermal stability, with a decomposition
temperature over 400 °C under Ar. The reversible photo-
isomerization of the azobenzene units was achieved upon
alternating photoirradiation with light of wavelength less than
450 nm (cis-form), and light in the range of 450−600 nm (trans-form). The supramolecular complex formation of trans-
F12AZO, and cis-F12AZO with single-walled carbon nanotubes (SWNTs) has been studied, and it was found that this polymer
can form very strong supramolecular polymer-nanotube assemblies. Furthermore, the trans and cis isomers of F12AZO enable the
selective dispersal of individual SWNTs in toluene or THF, and the selectivity of the SWNTs is strongly dependent on the
solvent, as well as the type of isomer used. UV−vis−NIR, and photoluminescence−excitation spectroscopy (PLE) were used for
the characterization and identification of the nanotube species that are solubilized and exfoliated by this polymer.
noncovalent functionalization of SWNTs with stimuli-respon-
sive polymers that are modulated by light, pH, and temperature
enables reversible modification of electronic properties within
the resulting CNT-based nanostructures.39−41 In particular,
structural components that can control the strength of polymer
binding to the nanotube surface in response to external stimuli
are of significant interest.
INTRODUCTION
■
Since their discovery,1 single-walled carbon nanotubes
(SWNTs) have attracted significant attention due to their
remarkable mechanical, thermal, optical, and electronic proper-
ties.2−9 Various potential applications of SWNTs, including
their incorporation within chemical sensors,10−12 field-effect
transistors,13−16 nanoscale integrated radio receivers,17,18
photovoltaics,19−21 field-emission displays,22,23 and many
other devices24,25 have been extensively explored over the
past 2 decades. However, the inherent insolubility of carbon
nanotubes in most organic and aqueous solvents and
coexistence of various tube types in as-produced SWNT
samples have severely limited the widespread application of
these novel nanostructures. To improve their solubility and
processability, various carbon nanotube surface modification
techniques have been developed, including covalent and
noncovalent functionalization.26−28 Noncovalent functionaliza-
tion of SWNTs with aromatic macromolecules or conjugated
polymers is of particular interest because this approach does
not introduce any defects in the nanotube sidewall, thus leaving
the extended nanotube π-network, along with all of its
consequent properties, unperturbed.29−32
Azobenzene (AZO) is a well-known photoisomerizable
molecule exhibiting a reversible trans to cis isomerization that
can easily be achieved upon photoirradiation, even when
incorporated within polymeric structures.39,42,43 The conforma-
tional change of the AZO unit upon photoirradiation can
significantly affect the molecular shape of AZO-containing
polymers, resulting in reversible coiling/uncoiling pro-
cesses.44,45 Recently, several conjugated polymers incorporating
the AZO unit have been reported, and have even been shown
to undergo supramolecular functionalization of SWNTs.39,40,43
For example, Imahori and co-workers found that alternating
copolymers of AZO with phenylene or vinylene units enable
the dissolution of SWNTs, where the degree of dissolution
depended on the cis/trans ratio of the AZO units in the starting
polymer.43 Interestingly, it was not possible to isomerize the
AZO units after nanotube complexation in solution because of
the strong supramolecular interaction between the AZO units
in the polymer backbone and the nanotube sidewall, a result
Recently, supramolecular functionalization of SWNTs with
fluorene-containing conjugated polymers has generated sig-
nificant interest due to the excellent solubility and solution
stability of the resulting polymer-SWNT nanocomposites.31−35
Interest in this class of conjugated polymers has increased as
reports of selective solubilization of certain SWNT species have
begun to be published.33,36−38 It has also been shown that
Received: February 26, 2012
Revised: May 25, 2012
© XXXX American Chemical Society
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Scheme 1. Synthetic Route to the F12AZO Polymer
that has also been found in other studies.39,40,43 Furthermore,
the polymers reported in these studies were not found to be
selective toward specific nanotube types within a mixture.
These observations inspired us to investigate the incorpo-
ration of the AZO unit within conjugated polymer backbones
that have been previously found to be selective for specific
nanotube chiralities, such as poly(9,9-di-n-alkylfluorene)-based
polymers,46,47 and to determine if AZO photoisomerization can
influence this selectivity. Here, we report the supramolecular
functionalization of SWNTs using a photoresponsive con-
jugated polymer, poly[2,7-(9,9-didodecylfluorene)-alt-4,4′-azo-
benzene] (F12AZO), and describe the detailed optoelectronic
and photo physical characterization of the resulting F12AZO-
SWNT complexes. The effect of changing solvent, and
changing the polymer conformation upon photoirradiation on
the interaction between the polymer and nanotubes is also
described.
1
Figure 1. H NMR spectrum of the polymer in CDCl3.
copolymer structure expected from the Suzuki polycondensa-
tion. Phenyl groups were also successfully introduced at both
ends of the polymer as end-caps, and the two sets of small
multiplets centered at 7.57 and 7.51 ppm, and the doublet at
7.97 ppm (Figure 1) were assigned as the end group phenyl
protons.49 On the basis of the integration ratio of the fluorene
proton signals in the polymer repeat units to the end-group
proton signals, the average degree of polymerization (DP) and
Mn were estimated to be approximately 9 and 6.3 kg/mol,
respectively. The estimated Mn value by NMR is in surprisingly
good agreement with the molecular weight measurements from
GPC.
The thermal stability of F12AZO was characterized by
thermogravimetric analysis (TGA), carried out under an Ar
atmosphere (Figure S1, Supporting Information). This data
indicates that the major mass loss occurs at 400 °C for
F12AZO, amounting to 50%. This mass loss corresponds well
with the loss of side chains within this polymer. Above this
temperature, the mass decreases slowly, and levels off at ca. 45%
when heated to 800 °C, at which point it is likely converted to
char.
RESULTS AND DISCUSSION
■
4,4′-Diiodoazobenzene (1) was synthesized according to
literature procedures starting from 4-iodoaniline.48 Poly[2,7-
(9,9-didodecylfluorene)-alt-4,4′-azobenzene] (F12AZO) was
prepared using a Suzuki polycondensation from 9,9-didodecyl-
fluorene-2,7-bis(trimethyleneboronate) and 4,4′-diiodoazoben-
zene as depicted in Scheme 1. F12AZO was obtained as an
orange solid in 76% yield, and the resulting polymer exhibited
excellent solubility in common organic solvents, including
THF, toluene, and chloroform. The molecular weight of the
polymer was determined by gel permeation chromatography
(GPC) relative to polystyrene standards, and indicated a
number-average molecular weight (Mn) of 6.6 kg/mol with a
polydispersity index (PDI) of 2.0.
1
The chemical structure of F12AZO was confirmed by H
NMR spectroscopy (Figure 1). The multiplet centered at 7.85
ppm corresponds to the aromatic protons from flourene, and
the peaks centered at 8.06 and 7.71 ppm correspond to the
aromatic protons of AZO. On the basis of the relative areas of
these peaks, the molar ratio of fluorene and azobenzene was
determined to be 1:1, which is consistent with the alternating
Optical properties of the F12AZO were characterized by
UV−vis absorption spectroscopy. F12AZO exhibits an
absorption maximum (λmax) at 417 nm in THF (Figure S2,
Supporting Information), which is in good agreement with
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previously reported values for similar polymers of nearly equal
molecular weight.42 It has been reported that all azobenzene
units in the polymer backbone are most stable in the trans form
when the polymer is kept in solution.42−45 To achieve trans-to-
cis isomerization, a THF solution of F12AZO (0.017 g/L) in a
quartz cuvette was irradiated with light of wavelength <450 nm
for 20 min. This resulted in a decrease in the absorption band
centered at 417 nm (Figure S2, Supporting Information, A).
The reverse isomerization (cis-to-trans) was achieved by
irradiating with light in the range of 450−600 nm. In both
cases the absorption spectra recorded at different irradiation
times indicated that the full extent of isomerization was
complete within 15 min of irradiation (Figure S2, Supporting
Information). The changes of the polymer absorption in THF
upon alternating photoirradiation in the two wavelength ranges
(<450 nm, and 450−600 nm) at room temperature for 15 min
were also measured to confirm that F12AZO can undergo
reversible trans−cis photoisomerization (Figure S3, Supporting
Information).
The supramolecular interaction of F12AZO with SWNTs
was studied using our previously reported methods.32 In a
typical experiment, a SWNT sample (2.5 mg) was added to a
solution of polymer in THF or toluene (7.5 mg/10 mL), and
the mixture was ultrasonicated in a bath sonicator for 1 h. The
resulting solution was centrifuged for 45 min at 8,300 g,
allowed to stand overnight, and then the supernatant was
carefully transferred by pipet to another vial. A dark colored,
relatively concentrated polymer−nanotube complex solution
was obtained in THF, while significant nanotube precipitation
was observed in toluene, leaving a clear, orange solution
(Figure S4, Supporting Information).
complex when excited at the absorption maximum of the
polymer (λex = 417 nm), in both THF and toluene. This
resulted in no observable sensitized nanotube emission (Figure
S6, Supporting Information), indicating that energy transfer
from the excited-state polymer to the nanotube does not occur.
This result is in agreement with previous studies, which found
that it was not possible to photoisomerize the AZO units once
they are bound to the nanotube surface.39,40,43
In order to confirm how the interactions between the
F12AZO and the SWNTs can be affected by the conforma-
tional changes (trans vs cis) of the F12AZO, the supramolecular
complexes of F12AZO-SWNT were prepared using the above
protocol with both trans and cis isomers of F12AZO (see
Supporting Information), and THF or toluene as the dispersing
solvents. The UV−vis-NIR absorption spectra of both trans-
F12AZO-SWNT and cis-F12AZO complexes in THF and
toluene are depicted in Figure 2. For reference, the absorption
spectrum of just the nanotubes dispersed in D2O using sodium
dodecylbenzenesulfonate (SDBS) surfactant is also shown in
Figure 2 (curve a).
The supramolecular complexes of trans-F12AZO with
SWNTs in THF were further investigated to determine if
polymer can be released from the carbon nanotube surface
upon photoirradiation. In a typical experiment, the isolated
supernatant in THF 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 excess free polymer.
A 10 mL aliquot of THF was added to the recovered SWNT
residue and the vial was further sonicated for 5 min. The
resulting dark suspension was centrifuged at 8300g for 45 min
and allowed to stand overnight undisturbed. The UV−vis
absorption properties of trans-F12AZO and their correspond-
ing SWNT complexes in THF were measured (Figure S5,
Supporting Information). It was found that the absorption
maximum of the polymer exhibited a characteristic bath-
ochromic shift and slight broadening once bound to the
nanotube surface (Figure S5A, Supporting Information).
A diluted THF solution of trans-F12AZO-SWNT (after
removal of excess polymer) in a glass cuvette was irradiated to
cause trans-to-cis isomerization, and the changes in the
absorption spectra were recorded. Although the polymer
absorption band intensity slightly decreased when irradiated
below 450 nm, the change in SWNT absorption was negligible.
There was no noticeable SWNT aggregation or precipitation
observed after irradiation for 4 h (Figure S5B, Supporting
Information). It is possible that either the polymer con-
formation is “locked” by its interaction with the nanotube
surface, or there is a rapid energy transfer that occurs from the
excited state of the polymer to the SWNT, both of which would
inhibit the photoisomerization. To rule out the latter possibility,
we measured the emission spectrum of the F12AZO-SWNT
Figure 2. NIR absorption spectra of SDBS/SWNT (a), trans-F12AZO
+ SWNT in THF (b), cis-F12AZO + SWNT in THF (c), trans-
F12AZO + SWNT in toluene (d), and cis-F12AZO + SWNT in
toluene (e). Dotted lines are meant to guide the eye in comparing
absorption bands from identical nanotubes.
The spectra show that the dispersing ability is affected by
both the conformational state of the F12AZO polymer (trans vs
cis isomers) and the solvent. In comparison to aqueous
dispersions of SWNTs using the surfactant SDBS (Figure 2,
curve a), the absorption peaks of the F12AZO-SWNT
complexes in both toluene and THF (Figure 2, curves b, c, d,
and e) are more intense, indicating efficient exfoliation into
individual tubes, and exhibit relatively strong absorptions at
wavelengths corresponding to semiconducting SWNTs (600−
800 and 900−1500 nm). All of the transitions of F12AZO-
SWNT complexes were found to be red-shifted 8−25 nm
relative to the aqueous solution, which is consistent with what
has been reported previously with comparable systems.33,37,38
Upon closer examination of the each individual absorption
spectrum, small shifts and changes in intensity of several signals
can be observed, indicating that the trans- and cis-F12AZO
show a slightly different preference for certain SWNT tube
types in both THF and toluene solution. The total absorbance
of several species is reduced in toluene solution when
compared to THF, due to the substantial reduction in the
number of different nanotube species present in F12AZO/
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Figure 3. PL contour maps of HiPco SWNTs dispersed with trans-F12AZO in THF (A), trans-F12AZO in toluene (B), cis-F12AZO in THF (C),
cis-F12AZO in toluene (D), and SDBS in D2O (E).
Figure 4. Normalized PLE signal intensities of the major SWNT species observed in solution, in order of increasing diameter (left to right): (a)
trans-F12AZO+SWNT in THF, (b) cis-F12AZO+SWNT in THF, (c) trans-F12AZO+SWNT in toluene, and (d) cis-F12AZO+SWNT in toluene.
toluene solutions. Several major absorption peak positions in
the 900−1500 nm region were correlated to the corresponding
chiral indices (n, m), where the assignments are based on
previously reported results.50,51 It has been shown that the
absorbance intensity of SWNTs is proportional to the amount
of solubilized SWNTs present, independent of whether the
tubes are isolated or bundled.51,52 Therefore, it is difficult to
attribute the changes in absorption peak intensities to
individual, exfoliated tube types.
photoluminescence excitation (PLE) maps of the trans- and cis-
F12AZO-SWNT in toluene and THF were measured over a
large range of excitation (500−900 nm) and emission (900−
1450 nm) wavelengths. Figure 3 depicts the PLE maps of
SWNTs dispersed in toluene and THF using both trans-
F12AZO (maps A and B) and cis-F12AZO (maps C and D),
which can be compared to the PLE map of a dispersion in D2O
using the nonselective SDBS surfactant (map E). In these maps,
areas of high intensity are depicted in red and areas of low
intensity are depicted in blue. The chiral indices (n, m) for the
identified species are labeled on the maps, where the
assignments are based on previously reported results.51,53 The
Photoluminescence spectroscopy has been used as a
powerful tool to identify the solubilized species due to its
sensitivity to the degree of SWNT exfoliation.37,51 Thus,
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PLE map of the pristine SWNT sample dispersed in D2O using
SDBS shows the presence of 17 different semiconducting
nanotubes, a distribution that is similar to what has previously
been reported.33,53 When the same material was mixed with
trans-F12AZO and cis-F12AZO in toluene or THF, entirely
different results were obtained. Parts A and B of Figure 3 depict
the PLE maps of the SWNT complexes with trans-F12AZO in
THF and toluene, and parts C and D of Figure 3 show the PLE
maps of cis-F12AZO complexes in THF and toluene,
respectively. The observed strong nanotube emission indicates
that individual SWNTs are solubilized and isolated by the
polymer. It was found that both excitation and emission
wavelengths of the trans-F12AZO + SWNT complex was red-
shifted relative to the aqueous solution by 10−30 nm, which is
consistent with previously reported comparable systems (Table
S1, Supporting Information).21,33,37,38 It is obvious from the
PLE maps (Figure 3, A and B) that the distribution of SWNT
species depends on the solvent used, and the relative emission
intensity of each solubilized species is considerably different
with each solvent. When trans-F12AZO was used, eight major
carbon nanotube species were identified in THF, including (6,
5), (8, 4), (7, 5), (7, 6), (9, 4), (9, 5), (8, 6), and (8, 7), and the
dominant species were found to be (6, 5) and (7, 5) (Figure
3A). Figure 4 depicts the normalized PLE signal intensities of 8
major SWNT species, where the most intense signal from each
solution was set to a value of 1 (for numerical data, see Table
S2, Supporting Information). The nanotube species depicted in
Figure 4 are organized by diameter, which ranges from 0.757
nm for the (6, 5) tube to 1.032 nm for the (8, 7) tube (for a
complete list of diameters, see Table S2, Supporting
Information). It is interesting to note that the nanotube
diameter seems to dictate both the relative solubility in the two
solvents and the selectivity of cis- or trans-F12AZO polymers
for specific nanotube types. The polymer−nanotube complexes
with SWNTs having diameters below 0.90 nm (consisting of
the (6, 5), (7, 5), (8, 4), and (7, 6) species) all exhibit higher
emission intensities in THF relative to toluene, while those
with diameters above 0.92 nm (the (8, 6), (9, 5), and (8, 7)
species) exhibit higher intensities in toluene than in THF.
Furthermore, as can be seen from Figure 4, the largest
differences in emission intensities as a function of cis/trans
polymer conformation were observed for the low diameter
tubes (most notably for (6, 5), (7, 5), and (7, 6) species),
whereas cis/trans selectivity was weakest for the highest
diameter tubes (specifically the (8, 6), (9, 5), and (8, 7)
species, especially in toluene). It is not clear why the cis-
F12AZO polymer seems to show greater preference for
solubilizing the (7, 6) tube, while trans-F12AZO shows greater
preference for the (6, 5) and (7, 5) species in THF. All of these
results warrant further investigation. It should be noted that the
above discussion implies a correlation between nanotube
emission intensity and solution concentration, which assumes
that SWNT fluorescence quantum yield is not affected by the
polymer conformation or the surrounding solvent. This
assumption will need to be tested in future studies.
excellent thermal stability under Ar. The changes to the
polymer absorption in THF upon alternating photoirradiation
below 450 nm and between 450 and 600 nm, respectively, at
room temperature confirmed that F12AZO can undergo
reversible trans−cis photoisomerization. The trans-F12AZO
and cis-F12AZO were utilized for the preparation of supra-
molecular polymer−SWNT composites, and excellent nano-
tube solubility and solution stability was achieved in THF. UV−
vis absorption measurements revealed a bathochromic shift and
broadening in the polymer absorption spectrum as a result of
complex formation with nanotubes. Photoirradiation of trans-
F12AZO-SWNT complexes below 450 nm does not cause
polymer isomerization on the nanotube surface, and no
noticeable SWNT aggregation or precipitation was observed.
Photoluminescence excitation maps showed that efficient and
selective dispersal of SWNTs is possible by using trans-
F12AZO or cis-F12AZO and that both solvent and polymer
conformation played a role in the selectivity. It was found that
low diameter nanotubes are more strongly differentiated by the
cis- and trans-F12AZO polymer conformers, and nanotube
diameter also determines whether the polymer−nanotube
complexes will be more soluble in THF or toluene.
ASSOCIATED CONTENT
* Supporting Information
■
S
Full experimental procedures as well as TGA, UV−vis, and
fluorescence data and a photograph of F12AZO in THF, the
F12AZO + SWNT complex in THF, and the F12AZO +
SWNT complex in toluene. This material is available free of
charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
■
*Telephone: (905) 525-9140 x 23514. Fax: (905) 521-2773. E-
mail: adronov@mcmaster.ca.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
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 Dr. Kalaichelvi
Saravanamuttu, Alex Hudson, and Matthew Ponte for their help
with photoisomerization experiments. P.I. gratefully acknowl-
edges NSERC for a Canada Graduate Scholarship (CGS-D).
REFERENCES
■
(1) Iijima, S.; Ichihashi, T. Nature 1993, 363, 603−605.
(2) Kataura, H.; Kumazawa, Y.; Maniwa, Y.; Umezu, I.; Suzuki, S.;
Ohtsuka, Y.; Achiba, Y. Synth. Met. 1999, 103, 2555−2558.
(3) Ajayan, P. M. Chem. Rev. 1999, 99, 1787−1799.
(4) Kaiser, A. B. Rep. Prog. Phys. 2001, 64, 1−49.
(5) Hennrich, F.; Lebedkin, S.; Malik, S.; Tracy, J.; Barczewski, M.;
Rosner, H.; Kappes, M. Phys. Chem. Chem. Phys. 2002, 4, 2273−2277.
(6) Dai, H. J. Surf. Sci. 2002, 500, 218−241.
CONCLUSIONS
■
The photoresponsive azobenezene containing polymer, poly-
[2,7-(9,9-didodecylfluorene)-alt-4,4′-azobenzene] (F12AZO)
has been synthesized using Suzuki polycondensation, and the
resulting polymer exhibited good solubility in a number of
organic solvents, including THF, toluene, and chloroform.
Thermogravimetric analysis indicated that F12AZO exhibits
(7) Dai, H. J. Acc. Chem. Res. 2002, 35, 1035−1044.
(8) Bradley, K.; Gabriel, J. C. P.; Gruner, G. Nano Lett. 2003, 3,
1353−1355.
(9) Kaiser, A. B.; Skakalova, V. Chem. Soc. Rev. 2011, 40, 3786−3801.
́ ́
(10) Wang, F.; Gu, H. W.; Swager, T. M. J. Am. Chem. Soc. 2008, 130,
5392−5393.
E
dx.doi.org/10.1021/ma300403q | Macromolecules XXXX, XXX, XXX−XXX

Macromolecules
Article
(11) Rahman, M. M.; Umar, A.; Sawada, K. Sensor Actuators, B:
Chem. 2009, 137, 327−333.
(46) Nish, A.; Hwang, J.; Doig, J.; Nicholas, R. Nat. Nanotechnol.
2007, 2, 640−646.
(47) Hwang, J.-Y.; Nish, A.; Doig, J.; Douven, S.; Chen, C.-W.; Chen,
L.-C.; Nicholas, R. J. J. Am. Chem. Soc. 2008, 130, 3543−3553.
(48) Zeitouny, J.; Aurisicchio, C.; Bonifazi, D.; De Zorzi, R.;
Geremia, S.; Bonini, M.; Palma, C.-A.; Samori, P.; Listorti, A.;
Belbakra, A.; Armaroli, N. J. Mater. Chem. 2009, 19, 4715−4724.
(49) Yokoyama, A.; Suzuki, H.; Kubota, Y.; Ohuchi, K.; Higashimura,
H.; Yokozawa, T. J. Am. Chem. Soc. 2007, 129, 7236−7237.
(50) Tu, X.; Manohar, S.; Jagota, A.; Zheng, M. Nature 2009, 460,
250−253.
(12) Pang, X.; Imin, P.; Zhitomirsky, I.; Adronov, A. Macromolecules
2010, 43, 10376−10386.
(13) Martel, R.; Schmidt, T.; Shea, H.; Hertel, T.; Avouris, P. Appl.
Phys. Lett. 1998, 73, 2447.
(14) Artukovic, E.; Kaempgen, M.; Hecht, D. S.; Roth, S.; GrUner, G.
Nano Lett. 2005, 5, 757−760.
(15) Engel, M.; Small, J. P.; Steiner, M.; Freitag, M.; Green, A. A.;
Hersam, M. C.; Avouris, P. ACS Nano 2008, 2, 2445−2452.
(16) Avouris, P.; Chen, Z.; Perebeinos, V. Nat. Nanotechnol. 2007, 2,
605−615.
(51) Bachilo, S. M.; Strano, M. S.; Kittrell, C.; Hauge, R. H.; Smalley,
R. E.; Weisman, R. B. Science 2002, 298, 2361−2366.
(52) O’Connell, M. J.; Bachilo, S. M.; Huffman, C. B.; Moore, V. C.;
Strano, M. S.; Haroz, E. H.; Rialon, K. L.; Boul, P. J.; Noon, W. H.;
Kittrell, C.; Ma, J. P.; Hauge, R. H.; Weisman, R. B.; Smalley, R. E.
Science 2002, 297, 593−596.
(17) Jensen, K.; Weldon, J.; Garcia, H.; Zettl, A. Nano Lett. 2007, 7,
3508−3511.
(18) Rutherglen, C.; Burke, P. Nano Lett. 2007, 7, 3296−3299.
(19) Rowell, M. W.; Topinka, M. A.; McGehee, M. D.; Prall, H. J.;
Dennler, G.; Sariciftci, N. S.; Hu, L. B.; Gruner, G. Appl. Phys. Lett.
2006, 88 (233506), 233501−233503.
(20) Kymakis, E.; Amaratunga, G. A. J. Rev. Adv. Mater. Sci. 2005, 10,
300−305.
(21) Schuettfort, T.; Nish, A.; Nicholas, R. J. Nano Lett. 2009, 9,
3871−3876.
(53) Weisman, R. B.; Bachilo, S. M. Nano Lett. 2003, 3, 1235−1238.
(22) Saito, Y.; Nishiyama, T.; Kato, T.; Kondo, S.; Tanaka, T.;
Yotani, J.; Uemura, S. Mol. Cryst. Liq. Cryst. 2002, 387, 303−310.
(23) Zhang, D. H.; Ryu, K.; Liu, X. L.; Polikarpov, E.; Ly, J.;
Tompson, M. E.; Zhou, C. W. Nano Lett. 2006, 6, 1880−1886.
(24) Endo, M.; Strano, M. S.; Ajayan, P. M. Top. Appl. Phys. 2008,
111, 13−62.
(25) Schnorr, J. M.; Swager, T. M. Chem. Mater. 2011, 23, 646−657.
(26) Hirsch, A. Angew. Chem., Int. Ed. 2002, 41, 1853−1859.
(27) Britz, D. A.; Khlobystov, A. N. Chem. Soc. Rev. 2006, 35, 637−
659.
(28) Campidelli, S.; Klumpp, C.; Bianco, A.; Guldi, D. M.; Prato, M.
J. Phys. Org. Chem. 2006, 19, 531−539.
(29) Chen, J.; Liu, H. Y.; Weimer, W. A.; Halls, M. D.; Waldeck, D.
H.; Walker, G. C. J. Am. Chem. Soc. 2002, 124, 9034−9035.
(30) Cheng, F. Y.; Adronov, A. Chem.Eur. J. 2006, 12, 5053−5059.
(31) Cheng, F. Y.; Imin, P.; Maunders, C.; Botton, G.; Adronov, A.
Macromolecules 2008, 41, 2304−2308.
(32) Imin, P.; Imit, M.; Adronov, A. Macromolecules 2011, 44, 9138−
9145.
(33) Hwang, J. Y.; Nish, A.; Doig, J.; Douven, S.; Chen, C. W.; Chen,
L. C.; Nicholas, R. J. J. Am. Chem. Soc. 2008, 130, 3543−3553.
(34) Imin, P.; Cheng, F. Y.; Adronov, A. Polym. Chem 2011, 411−
416.
(35) Imin, P.; Cheng, F. Y.; Adronov, A. Polym. Chem 2011, 1404−
1408.
(36) Nish, A.; Hwang, J. Y.; Doig, J.; Nicholas, R. J. Nanotechnology
2008, 19 (095603), 095601−095606.
(37) Nish, A.; Hwang, J. Y.; Doig, J.; Nicholas, R. J. Nat. Nanotechnol
2007, 2, 640−646.
(38) Chen, F. M.; Wang, B.; Chen, Y.; Li, L. J. Nano Lett. 2007, 7,
3013−3017.
(39) Bluemmel, P.; Setaro, A.; Popeney, C. S.; Haag, R.; Reich, S.
Phys. Status. Solidi B 2010, 247, 2891−2894.
(40) Vijayakumar, C.; Balan, B.; Kim, M.-J.; Takeuchi, M. J. Phys.
Chem. C 2011, 115, 4533−4539.
(41) Lemasson, F.; Tittmann, J.; Hennrich, F.; Stuerzl, N.; Malik, S.;
Kappes, M. M.; Mayor, M. Chem. Commun. 2011, 47, 7428−7430.
(42) Zhang, W.; Yoshida, K.; Fujiki, M.; Zhu, X. Macromolecules
2011, 44, 5105−5111.
(43) Umeyama, T.; Kawabata, K.; Tezuka, N.; Matano, Y.; Miyato,
Y.; Matsushige, K.; Tsujimoto, M.; Isoda, S.; Takano, M.; Imahori, H.
Chem. Commun. 2010, 46, 5969−5971.
(44) Izumi, A.; Teraguchi, M.; Nomura, R.; Masuda, T. Macro-
molecules 2000, 33, 5347−5352.
(45) Izumi, A.; Nomura, R.; Masuda, T. Macromolecules 2001, 34,
4342−4347.
F
dx.doi.org/10.1021/ma300403q | Macromolecules XXXX, XXX, XXX−XXX