Conformationally switchable TTFV-phenylacetylene polymers: Synthesis, properties, and supramolecular interactions with single-walled carbon nanotubes

Article abstract of DOI:10.1039/c3tc30317a

A series of π-conjugated polymers made up of tetrathiafulvalene vinylogue (TTFV) and phenylacetylene repeat units was synthesized and investigated as supramolecular hosts for non-covalent functionalization of single-walled carbon nanotubes (SWNTs). Adopting a folding conformation in the neutral state, these polymers can effectively interact with individual SWNTs forming supramolecular complexes with good solubility in organic solvents. Responding to certain external chemical stimuli (e.g., oxidation or protonation), however, the polymers change their molecular shapes into a linear structure driven by the formation of TTFV cations and hence result in reversible dissociation of the polymers from SWNTs. Such a process allows the efficient releasing of pristine SWNTs from polymer dispersants. The detailed polymer-SWNT interactions and relevant selectivity for certain types of SWNTs were examined by various spectroscopic analyses. Intriguing bulk materials, such as bucky gels and conductive bucky films , were obtained from the polymer-SWNT composites and their structural and physical properties were characterized as well. The Royal Society of Chemistry 2013.

Full text of DOI:10.1039/c3tc30317a

Journal of
Materials Chemistry C
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PAPER
Conformationally switchable TTFV–phenylacetylene
polymers: synthesis, properties, and supramolecular
interactions with single-walled carbon nanotubes†
Cite this: J. Mater. Chem. C, 2013, 1,
5477
*
Shuai Liang, Guang Chen and Yuming Zhao
A series of p-conjugated polymers made up of tetrathiafulvalene vinylogue (TTFV) and phenylacetylene
repeat units was synthesized and investigated as supramolecular hosts for non-covalent
functionalization of single-walled carbon nanotubes (SWNTs). Adopting a folding conformation in the
neutral state, these polymers can effectively interact with individual SWNTs forming supramolecular
complexes with good solubility in organic solvents. Responding to certain external chemical stimuli (e.g.,
oxidation or protonation), however, the polymers change their molecular shapes into a linear structure
driven by the formation of TTFV cations and hence result in reversible dissociation of the polymers from
SWNTs. Such a process allows the efficient releasing of pristine SWNTs from polymer dispersants. The
detailed polymer–SWNT interactions and relevant selectivity for certain types of SWNTs were examined
by various spectroscopic analyses. Intriguing bulk materials, such as “bucky gels” and conductive “bucky
films”, were obtained from the polymer–SWNT composites and their structural and physical properties
were characterized as well.
Received 18th February 2013
Accepted 24th June 2013
DOI: 10.1039/c3tc30317a
www.rsc.org/MaterialsC
far, the methods that fall within the category of so-called “non-
covalent functionalization” have received considerable atten-
Introduction
tion.10 Apart from the advantages of being non-destructive and
highly effective, the non-covalent approach can exibly use a
large variety of molecules and macromolecules as dispersants to
produce suspensions of debundled SWNTs in different types of
solvents with satisfactory solubility and stability. Moreover, by
means of rational molecular design and tailoring, selective non-
covalent interactions between dispersants and a collection of
specic types of SWNTs have been made possible, which in turn
provides solution to the well-recognized “structural heteroge-
neity” problem encountered in the production of SWNTs. Over
the past decade, a great number of highly selective non-covalent
methods have been established for this purpose, where crude
SWNT samples were enriched or puried in varied degrees to
afford better-quality nanotubes featuring improved homogeneity
in terms of diameters, electronic types, or even chiral indices.11–24
While sufficient non-covalent interactions (e.g., p-stacking
or van der Waals) with the backbone of SWNTs are a requisite
for effective dispersion of SWNTs, the design of dispersants that
strongly bind to SWNTs may not be an always favoured goal
from a practical point of view. Especially in the cases where the
performance of SWNT-based electronic and optoelectronic
devices is highly susceptible to the level of contaminants or
impurities, removal of SWNT dispersants in a clean and
complete manner aer solution processing has become highly
desirable. This hence requires the binding between SWNTs
and dispersants to be reversible and controllable. As many
Single-walled carbon nanotubes (SWNTs), ever since their rst
discovery in the early 1990s,1 have attracted enormous research
interest owing to their superior mechanical properties and
unique structure-dependent electronic and photonic behaviour.2
Indeed the wide-ranging applications of SWNTs have made
profound impacts in numerous elds of modern science and
technology, among which nanoscale electronics,3 photovoltaics,4
chemo-/biosensors,5 bioimaging,6 drug delivery,7 and advanced
composite materials8 are topics of growing interest. Nevertheless,
the direct use of as-produced SWNTs in device fabrication is still
problematic due to the purity and compatibility issues. The
hydrophobicity and strong inter-tube p-stacking of SWNTs lead
to a substantial degree of aggregation and bundling that makes
pristine SWNTs virtually insoluble in most solvents. This setback
hence signicantly hinders the progress in both fundamental
studies and technological application of SWNTs. To overcome
this obstacle, various chemical functionalization methods have
been devised to manipulate and modify the processability and
properties of pristine SWNTs.9 Of various methods developed so
Department of Chemistry, Memorial University, St. John's, NL, A1B 3X7, Canada.
E-mail: yuming@mun.ca; Fax: +1-709-864-3702; Tel: +1-709-864-8747
† Electronic supplementary information (ESI) available: NMR spectra of new
compounds, detailed procedures for multi-cycle dispersion and release of
SWNTs with polymer 4a, detailed cross-section analysis of AFM imaging of 4a
and SWNTs, and DFT calculation results for protonated TTFV model
compounds. See DOI: 10.1039/c3tc30317a
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aromatic-rich polymers and macromolecules interact with supramolecular interactions with SWNTs, and some intriguing
SWNTs so strongly and even irreversibly, they are not ideal bulk materials (bucky gels and thin lms) derived henceforth.
dispersants to satisfy the device applications just aforemen-
tioned. Circumvention of this problem thus requires the inte-
gration of some new mechanisms in the molecular design of
dispersants, which allows the control over reversibly and cleanly
Results and discussion
Synthesis
breaking down supramolecular SWNT–dispersant complexes.
In recent years, a number of novel strategies have been devel-
oped to achieve this goal, among which the incorporation of
stimuli-responsive building blocks into molecular constructs
appears to be a very promising approach. As early as 2001,
Smalley and co-workers discovered that a water-soluble poly-
mer, polystyrene sulfonate (PSS), could disperse SWNTs in
aqueous solution through non-covalent wrapping to eliminate
the hydrophobic interface between SWNTs and the aqueous
medium.25 The resulting polymer–SWNT complexes could be
reversibly dissociated by simply changing the solvent system to
reduce the hydrophobic effect. Taking a similar strategy, Moore
and Zang recently reported the use of oligo(m-phenylene ethy-
nylene)s (m-OPEs) to reversibly wrap and unwrap around
SWNTs under the control of solvent polarity.26 Chen and
Wang used temperature and pH-sensitive polymers, such as
poly(N-isopropylacrylamide) (PNIPAAm) and poly-L-lysine (PLL),
to attain reversible dispersion and release of SWNTs in water.27
Zhang and co-workers recently developed a poly(ethylene
glycol)-terminated malachite green derivative (PEG-MG)
which could non-covalently interact with SWNTs to form
soluble complexes in water.28 Upon UV-vis irradiation for 1 h,
the malachite green group underwent a photoinduced C–C
bond breaking process to form a cationic trityl product that
led to decomplexation of the SWNT–PEG assemblies. Adronov
and co-workers recently prepared a photo-responsive azo-
benzene-containing conjugated polymer to achieve selective
interactions with SWNTs under photochemical control.29 A CO2-
responsive polymer carrying pyrene and amidinium moieties
was synthesized by the Zhang group, showing controllable
dispersion and aggregation of SWNTs.30 Very recently, a
number of pH-responsive dispersants (e.g., water-soluble pillar-
[6]arenes) have been reported to reversibly solubilize and
precipitate SWNTs and even multi-walled carbon nanotubes
(MWNTs).31
The synthetic route to TTFV–phenylacetylene co-polymers 4a–c
is outlined in Scheme 1. First, acetylenic TTFV precursor 1
underwent a protodesilylation reaction to give the free terminal
alkyne product, which was immediately subjected to a double
Sonogashira cross-coupling reaction with 2 equiv. of n-decyl
substituted aryliodide 2a under the catalysis of Pd(PPh3)4 and
CuI with Et3N as base to afford TTFV–phenylacetylene 3a.
Desilylation of 3a with K2CO3, followed by a Pd/Cu-catalyzed
ꢀ
alkyne homocoupling polymerization at 70 C under open air
for 36 h, gave n-decyl pendent TTFV co-polymer 4a in 90% yield.
In this polymerization, 10% molar equiv. of aryliodide 2a was
added to act as endcapping reagent for a two-fold purpose: (i) to
control the degree of polymerization, and (ii) to improve the
chemical stability of the resulting polymers. Following the same
strategy, n-heptyl and n-pentyl appended TTFV–phenyacetylene
co-polymers 4b and 4c were prepared in yields of 70% and 90%
respectively. Polymers 4a–c are yellow coloured solids and show
reasonable solubility in non-polar organic solvents, such as
toluene, CH2Cl2, and chloroform. Their molecular structures
were characterized by 1H NMR and FT-IR spectroscopic analyses
(see the ESI†). Gel permeation chromatographic (GPC) analysis
of 4a reveals that the number average molecular weight (Mn) is
13 400 g molꢁ1, the weight average molecular weight (Mw) is
51 900, and the polydispersity index (PDI) is 3.9. The GPC data
concurs with the 1H NMR data that the resulting polymer 4a has
an average chain length at the stage of hexamer. GPC analysis of
Of various stimuli-responsive polymer dispersants devel-
oped so far in the literature, the polymers featuring redox-
responsiveness, to our surprise, have been scarcely surveyed.
Compared with other types of external stimuli (e.g., solvent,
temperature, photoradiation), the redox stimulus is advanta-
geous in terms of controllability, recyclability, environmental
friendliness, scalability, and cost-effectiveness. Upon this
consideration, we recently reported in a communication article
that a tetrathiafulvalene vinylogue (TTFV)-containing p-conju-
gated phenylacetylene polymer was capable of reversibly inter-
acting and releasing SWNTs in non-polar organic solvents.32
Our design principle is based on the reversible electrochemical
redox property of TTFV and the intriguing conformational
switching behaviour associated with it.33 In this report, we
present a full account on the design and synthesis of a series of
TTFV–phenylacetylene co-polymers (4a–c, Scheme 1), detailed Scheme 1 Synthesis of TTFV–phenylacetylene co-polymers 4a–c.
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polymers 4b and 4c was obscured by their limited solubility and
signicant aggregation as a result of their relatively shorter side
alkyl chains. Nevertheless, 1H NMR analysis on the integration
ratios of endcapping TMS protons versus the alkyl and aromatic
protons in the repeat unit suggests that the degrees of poly-
merization for 4b and 4c are similar to that of 4a.
Fig. 2 Space filling model of a TTFV–phenylacetylene tetramer wrapping around
a (10,0) SWNT optimized using the SYBYL force field. (A) Side view. (B) Front view.
Molecular modeling study
The molecular structural properties of n-decyl substituted
polymer 4a were investigated by molecular mechanics calcula-
tions using the SYBYL force eld implemented in the Spartan'10
soware package.34 Fig. 1 shows the optimized molecular
structure of 4a at the hexamer stage without endcapping
groups. From the structure, it is clear that even at the hexamer
stage the backbone of polymer 4a already adopts a shape of two-
turn helix, while the conformations of the TTFV moieties show
only a small degree of structural deviation from that of the
crystal structure of TTFV monomer 1.33b Of interest is that all the
n-decyl pendent groups are oriented outside the folding poly-
mer framework with favoured alkyl–alkyl stacking, leaving such
a sizeable central cavity (ca. 2–3 nm in dimension) that in theory
should well accommodate a single strand of typically sized
SWNTs.
Fig. 3B shows the UV-vis spectra of n-heptyl and n-pentyl
substituted polymers 4b and 4c and related TTFV precursors 3b
and 3c. Comparison of these data with those of n-decyl
substituted 4a and 3a reveals that the TTFV–phenylacetylene
polymers have similar degrees of effective p-conjugation length
(ECL), and the chain length of the pendent alkyl group has no
effect on the UV-vis absorption properties. This is in line with
the modeling results (see Fig. 1) which suggest that all the alkyl
pendent groups prefer to orient outwardly with respect to the
folding conjugated backbone of the polymer and hence do not
cause any signicant interference to the helical geometry.
The ability of TTFV–phenylacetylene foldamers to wrap
around SWNTs was simulated by molecular mechanics calcu-
lation as well. Fig. 2 illustrates the supramolecular complexa-
tion of a TTFV–phenylacetylene tetramer with a (10,0) SWNT. To
save computational expense, the pendent alkyl chains were
omitted. The optimized structure shows that the tetramer can
tightly wrap around the surface of SWNT via p–p interactions.
Electrochemical redox properties of polymers 4a–c and related
TTFV precursors
The electrochemical properties of polymers 4a–c and related
TTFV precursors were studied by cyclic voltammetric (CV)
analysis in CH2Cl2 at room temperature. The cyclic voltammo-
grams measured are shown in Fig. 4, and detailed redox data are
summarized in Table 1.
Electronic absorption properties of polymers 4a–c and related
TTFV precursors
The electronic absorption properties of polymers 4a–c and
related TTFV precursors were investigated by UV-vis spectro-
scopic analysis. Fig. 3A compares the UV-vis spectra of n-decyl
substituted polymer 4a and precursors 3a and 1. The spectrum
of 4a shows a low-energy absorption peak at 438 nm and a
relatively weak high-energy band at 319 nm. The maximum
UV-vis absorption peaks for 3a and 1 are relatively blueshied to
398 and 380 nm respectively, as
a result of reduced
p-conjugation.
Fig. 1 Space filling model of the hexamer of 4a optimized using the SYBYL force
field. (A) Top view. (B) Side view.
Fig. 3 UV-vis absorption spectra for (A) 1, 3a, and 4a; (B) 3b, 3c, 4b, and 4c.
Spectra were measured in CH2Cl2 at room temperature.
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Fig. 4 (A) Comparison of cyclic voltammograms for 1, 3a, and 4a. (B) Compar-
ison of cyclic voltammograms for 4a, 4b, and 4c. Experimental conditions: analyte
(ca. 10ꢁ3 M); supporting electrolyte: Bu4NBF4 (0.1 M); solvent: CH2Cl2; working:
glassy carbon; counter: Pt wire; reference: Ag/AgCl; scan rate: 0.2 V sꢁ1
.
The CV prole of short TTFV precursor 1 shows a reversible
redox wave pair assigned to the characteristic simultaneous
two-electron transfer process occurring on the diphenyl-TTFV
unit that assumes a pseudo-cis conformation in the neutral
state (Scheme 2A).33,35,36 For the long TTFV precursor 3a, further
extension of p-conjugation along the phenylacetylene direction
only results in a small change in the Epc value by less than 0.1 V.
The voltammograms of polymers 4a–c exhibit very similar
features of a reversible redox wave pair with insignicant vari-
ations of redox potentials. The CV data manifest that the
multiple TTFV units in the polymers do not have effective
electronic communication between one another via the phe-
nylacetylene linkages and therefore they undergo independent
redox processes in a simultaneous manner. Furthermore, the
slight shi in the redox potentials of polymers 4a–c in
comparison with those of TTFV precursor 1 suggests that the
TTFV moieties embedded in the polymer backbones are of
similar pseudo-cis conformation, as the redox properties of
TTFV are known to be structure-dependent.33,35–37
Scheme 2 Redox properties of diphenyl-TTFV and TTFV-phenylacetylene poly-
mers as well as associated conformational changes.
results; that is, the electrochemical oxidation of TTFV 3a
undergoes a bielectronic transfer step to form corresponding
TTFV dication [3a]2+. No intermediary radical cation is observed
as a consequence of “potential inversion”.38 The spectroelec-
trochemical analysis of polymer 4a shows a similar result of
TTFV dication band growing at 647 nm, but with only one iso-
sbestic point at 487 nm discernible during the entire oxidation
process. Overall, the CV and spectroelectrochemistry behav-
iours of the TTFV–phenylacetylene polymers are consistent with
those of the TTFV derivatives known to undergo redox-
controlled cis to trans conformational changes,33,35 which bodes
well for their redox-controllable conformational switchability as
illustrated in Scheme 2B.
Besides the CV analysis, redox properties of the TTFV poly-
mers and related precursors were also probed by UV-vis spec-
troelectrochemistry. Fig.
5 illustrates the UV-vis spectral
changes of TTFV 3a and polymer 4a under varied applied
potentials. From Fig. 5A, it can be seen that with increasing
degree of oxidation the absorption peak at 390 nm diminishes
and a relatively broad band at 647 nm evolves progressively. Two
isosbestic points are clearly observed at 377 and 470 nm. The
trend of UV-vis spectral change here is consistent with the CV
Table 1 Redox potential data for polymers 4a–c and TTFV precursors 1 and 3a
Responsiveness of TTFV polymers to pH stimulus
Entry
Epa (V)
Epc (V)
E1/2 (V)
As early as 1993, Giffard and co-workers investigated the reac-
tivity of simple TTF molecules toward protonation and dis-
closed that the neutral dithiole group of TTF could be converted
into an aromatic dithiolium ion upon treatment with a strong
Brønsted acid.39 Similar properties for diphenyl-substituted
TTFV derivatives have been observed in our recent
1
+0.70
+0.70
+0.65
+0.69
+0.67
+0.43
+0.52
+0.53
+0.53
+0.49
+0.57
+0.61
+0.59
+0.61
+0.58
3a
4a
4b
4c
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Fig. 5 UV-vis spectral changes for (A) TTFV 3a (400 to 1300 mV, step: 100 mV),
and (B) polymer 4a (500 to 1300 mV, step: 200 mV) with increasing applied
potential. Experimental conditions: supporting electrolyte: Bu4NBF4 (0.1 M);
solvent: CH2Cl2; working: Pt mesh; counter: Pt wire; reference: Ag/AgCl. Insets:
expansion of the spectra for clearer views of the isosbestic points.
Scheme 3 (A) Protonation of TTFV 1 in a two-step equilibrium. (B) Optimized
geometry of mono-protonated diphenyl-TTFV. (C) Optimized geometry of di-
protonated diphenyl-TTFV. Calculations done at the B3LYP/6-311G* level of theory.
of polymer 4a upon addition of TFA, which are similar to those
of TTFV 1. Moreover, protonated polymer 4a could be readily
neutralized by aqueous K2CO3, and the recovered polymer 4a
investigations, wherein relatively stable mono-protonated and
di-protonated TTFV cations were formed in two-step equilibria
(i.e., the two-step protonation reactions of TTFV 1 shown in
Scheme 3).
UV-vis analysis offers an ideal tool to monitor the two-step
protonation process, since the resulting TTFV mono- and dica-
tions bore very different electronic absorption features. Fig. 6A
depicts two distinct stages of UV-vis spectral changes of TTFV 1 in
response to the addition of a strong organic acid, triuoroacetic
acid (TFA). In the rst stage, the intensity of the absorption band
at 380 nm, which is due to the p / p* transition of neutral
TTFV, continuously decreases with increasing acidity. In the
meantime, two new long-wavelength absorption bands at 640
and 950 nm emerge and grow steadily. These two bands appear
to be in line with the known UV-vis absorption features of TTF
radical cations, and hence are assigned to the mono-protonated
[1$H]+.40 In addition, a shoulder band at 710 nm is observable in
this process, the origin of which is attributed to the partial
formation of dication [1$2H]2+. Evidence for this assignment can
be found from the spectroelectrochemical data shown in Fig. 5.
As the acidication continues, the spectral changes enter into a
second stage, where the two bands at 640 nm and 950 nm (due to
[1$H]+) diminish and the band at 710 nm (due to [1$2H]2+) grows
signicantly (Fig. 6A).
UV-vis titrations of TTFV 3a and polymer 4a with TFA gave
very similar outcomes, indicating that the protonation of TTFV
is facile and barely inuenced by the substituents attached to it.
Fig. 6 UV-vis absorption spectra of (A) TTFV 1 protonated with various amounts of
TFA, (B) TTFV polymer 4a protonated with various amounts of TFA and after
For instance, Fig. 6B shows two-stage UV-vis spectral responses neutralization with K2CO3. Experiments were done in CH2Cl2 at room temperature.
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gave the same UV-vis absorption prole as that before proton-
ation. This observation indicates that protonation/deprotona-
tion of the TTFV units in polymer 4a is chemically reversible and
readily controllable.
Density functional theory (DFT) calculations disclose that
the protonation steps are associated with dramatic structural
changes; in particular, the di-protonated TTFV unit prefers to
take a trans conformation to minimize disfavoured charge
repulsions (see Scheme 3B and C). Such a property equipped us
with another useful chemical stimulus, in addition to the redox
means, to exert control over the conformation of TTFV polymers
(vide infra).
Fig. 8 SEM image of the thin film of 4a after protonation by TFA. Inset:
photographic image of protonated thin film of 4a.
Morphological properties of TTFV–phenylacetylene
polymer 4a
All the obtained TTFV–phenylacetylene polymers 4a–c can
readily form yellow-coloured transparent lms upon drying
their solutions in organic solvents such as CH2Cl2 or toluene. To
investigate the microscopic structural properties of these poly-
mers, a thin lm of 4a was subjected to scanning electron
microscopic (SEM) analysis.
lm. Soaking the protonated thin lm of 4a in a diluted aq.
solution of NaHCO3 for a while restored the colour of the thin
lm to light yellow, which indicates that the acidication–
basication processes can be reversibly executed on the TTFV
polymer lm.
The surface morphology of polymer 4a as revealed by SEM
shows some interesting patterns where ordered disc-like
aggregates can be seen to scatter across the smooth surface of
the thin lm (Fig. 7). These nanodiscs possess relatively
uniform sizes with an average diameter of ca. 460 nm. It is also
observed that in some regions of the lm the nanodiscs are
gradually fused together, which is evidence that the nanodiscs
actually constitute the basic structural unit of the polymer thin
lm as a result of organized packing.
Interfacial self-assemblies of polymer 4a were prepared by
spin-casting its diluted toluene solution on a freshly cleaved
mica surface, and the resulting surface aggregates were inves-
tigated by atomic force microscopy (AFM). According to the AFM
study, neutral polymer 4a tends to form column-shaped aggre-
gates on the surface with an average height of ca. 4.4 nm
(Fig. 9A). To examine the responsiveness of the polymer aggre-
gates to acidity, an excess amount of TFA was added to the
When the thin lm of 4a was dipped into a diluted solution
of TFA in acetonitrile, protonation took place swily as evi-
denced by the observation of an immediate colour change from
yellow to dark green (see the inset of Fig. 8). The acidied thin
lm of 4a was examined by SEM, and the results show some
crystalline-like micro-akes with a wide range of size distribu-
tion (from ca. 10ꢁ1 to 10 mm) on the thin lm surface (Fig. 8).
Obviously, protonation of the TTFV moieties in polymer 4a has
resulted in dramatically changed microscopic structures in the
Fig. 9 AFM imaging of (A) polymer 4a, and (B) polymer 4a after acidification
with TFA. Samples were prepared by spin-casting on freshly cleaved mica surfaces
and examined in the non-contact mode.
Fig. 7 SEM image of the thin film of 4a. Inset: photographic image of the thin
film of 4a laid on a piece of white paper printed with letters.
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polymer solution and then the acidied solution was spin-cast are clearly seen in the range of 500–1500 nm. In the spectrum of
on a mica surface. The AFM imaging shows that aer acidi- CoMoCAT SWNT solution, a prominent absorption peak at
cation the polymer aggregates retain similar columnar shapes 999 nm is observed, which is assigned to SWNTs with a chiral
in morphology, but the heights of the aggregates exhibit a index of (6,5).41 In addition, assignments to (7,5), (7,6), (8,6),
notable increase with an average height of 8.45 nm (Fig. 9B). In and (8,7) species are made to other noticeable absorption bands
combination with previous UV-vis studies, the morphological according to literature results.26,42,43 These assignments are in
variations here can be reasonably attributed to the conforma- agreement with photoluminescence (PL) mapping studies
tional changes of the TTFV polymer with increasing acidity.
(Fig. 11), which show that the major species of the CoMoCAT
SWNTs dispersed by polymer 4a are (6,5), (7,5), and (8,6) tubes.42
In the UV-vis-NIR spectrum of HiPCO SWNT–polymer 4a
suspension, the peaks appearing in the range of 930–1500 nm
are attributed to inter-band transitions of semiconducting
SWNTs (S11), while the peaks from 500–930 are due to metallic
(M11) and semiconducting (S22) bands.17,44,45 The UV-vis-NIR
absorption data convincingly show that polymer 4a is capable of
forming soluble supramolecular complexes with various
SWNTs. Apart from polymer 4a, the UV-vis-NIR spectra of
SWNTs dispersed with polymer 4b and 4c were also measured
(see Fig. 10). Comparison of the normalized spectra of SWNTs
dispersed by the three polymers 4a–c manifests noticeable
differences which are suggestive that the alkyl chains may have
some effects to induce selectively dispersion of different types of
nanotubes (vide infra).
The supramolecular interactions between SWNTs and poly-
mer 4a were further investigated by AFM. In this study,
SWNT–4a suspensions were spin-cast on mica surfaces to form
interfacial assemblies, which were rinsed with chloroform to
remove excess polymers before being examined by AFM. Fig. 12
depicts the AFM image of the supramolecular assemblies of
CoMoCAT SWNTs and polymer 4a. The AFM image clearly
reveals the presence of a debundled single strand of SWNT,
which is consistent with the UV-vis-NIR analysis. Most inter-
estingly, features corresponding to a bare nanotube (site a,
Fig. 12), polymer wrapping of SWNT (site b, Fig. 12), and poly-
mer aggregates (site c, Fig. 12) are observed (for detailed cross-
section analysis see Fig. S11–S13 in the ESI†). The AFM char-
acterization agrees well with the molecular modeling results
(vide supra), manifesting that wrapping is an important inter-
action mode for helical TTFV polymers to associate with SWNTs
of suitable diameters.
Dispersion of SWNTs with TTFV–phenylacetylene polymers
To understand the properties of the synthesized TTFV–phenyl-
acetylene polymers in terms of forming supramolecular
complexes with SWNTs, the most soluble n-decyl-substituted
polymer 4a was rst investigated. Two types of commercially
available as-produced SWNTs, namely HiPCO and CoMoCAT
nanotubes, were chosen for this study. Suitable amounts of
these nanotubes were rst subjected to ultrasonication for 30
min in the toluene solution of 4a. The mixtures were observed to
form stable black suspensions, which were subsequently
ltered through a tightly packed cotton plug to remove any
insoluble components. The resulting black solution was ana-
lysed by UV-vis-NIR spectroscopy in order to check whether
SWNTs were dispersed in the polymer solution or not. Fig. 10
shows the UV-vis-NIR absorption spectra of HiPCO and CoMo-
CAT SWNTs dispersed in the toluene solution of 4a (baseline
corrected). For both types of SWNTs, distinctive absorption
bands characteristic of the electronic transitions between Van
Hove singularities in the electronic density of states of SWNTs
AFM imaging of the suspensions of HiPCO SWNTs in
toluene using polymer 4a did not give any observation of
Fig. 10 UV-vis-NIR spectra of SWNTs dispersed in the toluene solutions of
polymers 4a–c. For easy comparison, the spectra were baseline-corrected using
the Fityk software.48
Fig. 11 PL mapping of CoMoCAT SWNTs dispersed in toluene with polymer 4a.
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and AFM studies have demonstrated that the inner cavity of the
folding TTFV polymer can adequately accommodate relatively
small SWNTs in a wrapping interaction mode, which in turn
leads to the formation of debundled individual tubes aer
dispersion. The dispersed HiPCO SWNTs by polymer 4a, on the
other hand, contain both small and large-diameter components
as disclosed by the Raman analysis (Fig. 13). Whereas the
smaller tubes can be readily wrapped by the folding polymer,
the large-diameter tubes likely favour interaction with the
polymer via a non-wrapping mode. Given the abundant pres-
ence of long alkyl side chains in polymer 4a, signicant alkyl–p
interactions are envisioned to serve as a key non-covalent
binding force.47 As such, two interaction modes are in principle
at work in the dispersion of HiPCO SWNTs with polymer 4a: (i)
wrapping smaller-size HiPCO tubes, and (ii) alkyl–p stacking for
larger-size HiPCO tubes. Hence, it is reasonable to assume that
a synergistic effect of these two binding modes organizes the
HiPCO–polymer 4a assemblies in an interwoven network-like
microstructure (Scheme 4) rather than individualized tubes as
observed for CoMoCAT tubes.
The role of alkyl–p stacking in the supramolecular interac-
tions between TTFV polymers and various SWNTs was further
investigated by a comparative Raman analysis on CoMoCAT and
HiPCO nanotubes dispersed with TTFV polymers 4a–c. This
study was aimed at gaining an insight into the alkyl chain effect
on polymer–SWNT interactions. Fig. 14A shows the RBM region
of normalized Raman spectra of CoMoCAT nanotubes dispersed
by the three TTFV polymers. From the spectra, it is clearly seen
that the low-frequency bands corresponding to large-diameter
nanotubes steadily decrease with decreasing alkyl chain length,
while a similar trend can be observed in the Raman spectra for
polymer dispersed HiPCO SWNTs (Fig. 14B). Since reduction of
alkyl chain length should lead to decreasing alkyl–p stacking, the
observed alkyl chain effect unambiguously conrms that alkyl–p
stacking is the dominating binding mode for the interactions of
TTFV polymers with large-size tubes. As for the interactions of
TTFV polymer with relatively smaller SWNTs, the wrapping mode
operates as the primary mechanism.
Fig. 12 AFM image (non-contact mode) of a CoMoCAT nanotube coated with
polymer 4a. Cross-section analysis shows that the heights at sites a–c are 0.8 nm,
1.7 nm, and 9.4 nm, respectively.
discrete features of nanotubes despite numerous trials under
various conditions. The different microscopic morphologies
suggest the interaction modes between polymer 4a and various
SWNTs are complicated and somewhat tube structure-depen-
dent. Raman spectroscopic analysis has cast some light on this
issue. Fig. 13 shows the Raman spectra of CoMoCAT and HiPCO
tubes dispersed by 4a in the radial breathing mode (RBM)
region, where the vibrational frequencies are inversely propor-
tional to the diameters of SWNTs (dt) as described by the
equation, uRBM ¼ 223.5/dt + 12.5.26 According to this equation,
the peaks in the region of 240–270 cmꢁ1 can be ascribed to
SWNTs with diameters in the range of ca. 0.8–0.9 nm, while the
peaks at 190–210 cmꢁ1 are assigned to tubes with relatively
larger diameters (dt ꢂ 1.2 nm). From Fig. 13, it can be clearly
seen that the CoMoCAT SWNTs dispersed by polymer 4a are
primarily composed of small-diameter tubes (<1.0 nm). This is
also evidenced by the UV-vis-NIR and PL mapping results that
the CoMoCAT tubes dispersed are mainly (6,5), (7,5), and (8,6)
species. Theoretically calculated diameters of these tubes are
0.75 nm, 0.82 nm, and 0.96 nm respectively.2,46 Both modeling
Reversible dispersion and release of SWNTs with TTFV–
phenylacetylene polymers
To demonstrate the performance of TTFV polymers in terms of
reversibly interacting with SWNTs, two methods for
Fig. 13 The RBM region of the Raman spectra (lex ¼ 534 nm) for SWNTs
dispersed by polymer 4a in comparison with raw SWNTs.
Scheme 4 Schematic of network-like microstructure composed of polymer 4a
and HiPCO SWNTs.
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ultrasonication. The resulting suspension was then ltered and
acidied by addition of excess TFA. A dark greenish solution
immediately formed aer TFA addition, accompanied by the
precipitation of pristine SWNTs as black solids. Filtration was
then performed to separate the released SWNTs, while the
protonated polymer solution was neutralized with aq. NaHCO3
solution to give polymer 4a in a high recovery yield. The
recovered polymer 4a was examined by 1H NMR and UV-vis
analysis, conrming no changes in the molecular structure aer
the acid/base treatment. The collected SWNTs from the rst
cycle were then subjected to the same sequences of dispersion
and releasing using polymer 4a.
In each cycle of dispersion, the resulting SWNT suspension
was subjected to UV-vis-NIR analysis to monitor the composi-
tional changes in the dispersed SWNTs, and the detailed
spectral results are summarized in Fig. 15. From the UV-vis-
NIR analysis it can be seen that aer three cycles of dispersion/
releasing, CoMoCAT SWNTs attained noticeable enrichment of
tubes with certain chiral indices, such as (6,5), (7,6), and (8,6),
whereas HiPCO SWNTs did not show any signicant compo-
sitional variations. The results can be explained by TTFV
polymers preferring to wrap around small-diameter SWNTs
which are the major components of the CoMoCAT sample,
and the wrapping mode is believed to give rise to chirality
selectivity to some extent. HiPCO SWNTs in contrast contain
species with a much wider range of tube diameters. The
interactions of TTFV polymers with HiPCO tubes occur
through two binding modes, wrapping and alkyl–p stacking.
Fig. 14 The RBM region of Raman spectra (lex ¼ 534 nm) for (A) CoMoCAT
SWNTs and (B) HiPCO SWNTs dispersed by polymers 4a–c.
dissociation of TTFV polymer–SWNT complexes were surveyed. As such, the selectivity of polymer 4a for particular types of
Sequential chemical oxidation and reduction reactions were SWNTs is poor.
rst executed on the suspension of SWNTs and polymer 4a. In
this study, we chose iodine as the oxidant, since it is known to
readily oxidize the TTFV unit into [TTFV]2+. Indeed, addition of
iodine to the suspension of SWNTs and polymer 4a immediately
resulted in the precipitation of SWNTs, which could be sepa-
rated by ltration. The resulting solution of oxidized polymer 4a
could be recovered by treatment with excess aq. Na2S2O3 to
afford neutral polymer 4a, the structure of which was
further conrmed by 1H NMR and UV-vis analyses. Although the
result has validated the feasibility of reversible dispersion and
release of SWNTs using the redox-controlled approach, the
method of iodine-promoted oxidation is not ideal for practical
operation, since signicant decomposition of polymer 4a was
found to be associated with the oxidation processes resulting in
low yielding polymer recovery. In addition, the excess iodine
showed a strong affinity for the precipitated SWNTs, making
purication of the released SWNTs somehow troubling and
tedious.
To avert the problem arising from iodine oxidation, an
alternative pH stimulus was subsequently explored to manipu-
late the interaction and release of SWNT with TTFV polymers,
since it has been established that the TTFV unit could be
reversibly protonated to form TTFV cation and dication with a
dramatic conformational change similar to the redox process.
Multi-cycle dispersion and releasing experiments were under-
Fig. 15 UV-vis-NIR absorption spectra monitoring multi-cycle dispersion and
taken. In the experiments, a suitable amount of SWNTs was rst
release of SWNTs with polymer 4a. (A) CoMoCAT SWNTs, (B) HiPCO SWNTs. For
dispersed in the toluene solution of polymer 4a by means of easy comparison, the spectra were baseline-corrected using the Fityk software.48
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Table 2 Outcomes of ultrasonicating HiPCO SWNTs with TTFV polymer 4a in 1
Properties of bucky gels and bucky lms resulting from the
complexes of HiPCO SWNTs and TTFV polymers
mL of toluene for 30 min
In preparing the dispersion of HiPCO SWNTs with TTFV poly-
mers, to our surprise, stable sol–gels rather than suspensions
were frequently formed (see Fig. 16A and B). In particular, when
the amounts of polymers and nanotubes surpass a certain
threshold, gelation could be induced with very good reproduc-
ibility. Also of note is that the gelation phenomenon was only
observed for HiPCO SWNTs, whereas CoMoCAT tubes invari-
ably formed stable suspensions in organic solvents under the
same conditions. These results are interesting, since neither the
TTFV polymers nor the SWNTs are gelators. There have been
reports in the literature that SWNT-containing gels were
prepared by mixing small quantities of SWNTs with some
organic gelators.49 The preparation of SWNT gels without the
use of gelators, however, has been rarely known. A prominent
example of this is the discovery of “bucky gels” resulting from
grinding carbon nanotubes with ionic liquids reported by Aida
and co-workers.50 To further investigate the unique gelation
property of TTFV polymers and SWNTs, a systematic survey on
the conditions that lead to gelation was undertaken. For
discussion purpose, we herein adopt the term of “bulky gel” to
refer to the gelatinous materials composed of SWNTs and TTFV
polymers.
Amount of 4a (mg)
Amount of HiPCO SWNTs (mg)
Observationa
1
2
3
4
5
5
5
5
5
5
5
5
5
1
2
3
4
5
Suspension
Suspension
Semi-gel
Semi-gel
Suspension
Suspension
Semi-gel
Semi-gel
Bucky gel
a
A diagnostic test to differentiate bucky gel and semi-gel is to turn a
test-tube containing the gelatinous sample upside-down and then to
note whether the sample ows under its own weight.
Similar gelation properties were observed when TTFV-poly-
mers 4b and 4c were mixed with HiPCO SWNTs in toluene. To
better understand the microscopic properties of the bucky gels,
SEM imaging was conducted. As can be seen from Fig. 16D, the
bucky gel prepared from mixing 4a and HiPCO SWNTs is made
up of coarse interwoven micro-bres. Dilution of the bucky gel
with toluene allowed individual strands of the micro-bres to be
exfoliated for clear imaging (Fig. 16E). The SEM results show
that the widths the micro-bres that constitute the bucky gel are
on the scale of tens of microns. Combining the SEM results and
the Raman data aforementioned, the formation of bucky gel is
believed to originate from the network-like microstructures
engendered by the synergistic effect of wrapping and alkyl–p
stacking interactions taking place between HiPCO SWNTs and
TTFV polymers (as illustrated in Scheme 4).
Table 2 lists the various conditions tested for dispersing
HiPCO SWNTs with polymer 4a in toluene. In the experiments,
the ultrasonication periods were all kept at 30 min in order to
make an easy and reliable comparison. The results indicate that
gelation can be effected on condition that the quantities of
HiPCO SWNTs and polymer 4a are no less than 5 mg mLꢁ1 for
each.
The bucky gels of HiPCO SWNTs and TTFV polymers could
be easily applied to smooth substrates to form uniform “bucky
coatings”. Upon drying of the coatings under air, robust solid
thin lms could be obtained (henceforth referred to as bucky
lms, see Fig. 16C). The redox properties of a bucky lm made
up of polymer 4a and HiPCO SWNTs were investigated by CV
analysis, and the detailed results are shown in Fig. 17. Unlike
the CV proles of TTFV polymers, there are no reversible redox
features characteristic of the TTFV unit observable for the bucky
lm, likely due to the strong noncovalent interactions between
the polymers and SWNTs in the solid state. Nonetheless, the
lm still exhibits certain redox features, such as a notable
cathodic peak at ca. ꢁ0.04 V, in its cyclic voltammogram.
The thermal stability of the bucky lm was studied by ther-
mogravimetric analysis (TGA). Fig. 18 shows the TGA thermo-
gram of the bucky lm in comparison with that of polymer 4a.
The bucky lm starts a signicant weight loss at an onset
ꢀ
temperature of 338 C, which is similar to the onset tempera-
ꢀ
ture of polymer 4a at 330 C. This process is attributed to the
Fig. 16 (A) Photographic image of polymer 4a (5 mg) and HiPCO SWNTs (5 mg)
mixed in toluene before ultrasonication. (B) Photographic image of polymer 4a (5
mg) and HiPCO SWNTs (5 mg) mixed in toluene after ultrasonication for 30 min.
(C) Photographic image of a thin film resulting from drying the HiPCO SWNT–
polymer 4a gel. (D) SEM image of HiPCO SWNT–polymer 4a bucky gel. (E) SEM
image of HiPCO SWNT–polymer 4a bucky gel after dilution with toluene.
thermal decomposition of the alkyl chains of the TTFV polymer.
As temperature continues to increase, polymer 4a is seen to
show a second stage of weight loss at the onset temperature of
ꢀ
511 C, which is likely due to the decomposition of the conju-
gated TTFV and phenylacetylene units. Such a thermal process
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for processing as-produced SWNTs with custom-made polymer
dispersants in a recyclable manner. It is envisioned that this
approach would lead to selective and cost-effective methods for
sorting out or enrichment of specic types of SWNTs.
Mechanistically, two types of non-covalent forces are iden-
tied to play signicant roles in the SWNT–polymer interac-
tions. For small-diameter SWNTs, p–p interactions arising
from wrapping the conjugated polymer backbones around
individual SWNTs are the dominant binding force, which gives
rise to highly effective dispersion of SWNTs and formation of
well solubilized SWNT–polymer solutions. For large-diameter
SWNTs, however, alkyl–p stacking becomes the major binding
mode besides wrapping. As a consequence, when samples of
SWNTs containing a wide distribution of diameters (e.g., as-
produced HiPCO SWNTs) are treated with the TTFV polymers,
both wrapping and alkyl–p stacking come into play, resulting in
the formation of network-like supramolecular assemblies.
Based upon such binding properties, some interesting SWNT-
based bulk materials, such as bucky gels and bucky lms, have
been produced and characterized.
Fig. 17 Cyclic voltammogram of the bucky film prepared from polymer 4a and
HiPCO SWNTs. Experimental conditions: supporting electrolyte: Bu4NBF4 (0.1 M);
solvent: acetonitrile; working: bucky film; counter: Pt wire; reference: Ag/AgCl;
scan rate: 10 mV sꢁ1
.
Experimental
Synthesis
Chemicals and reagents were purchased from commercial
suppliers and used without further purication. HiPCO SWNTs
were purchased from Carbon Nanotechnologies Inc. CoMoCAT
SWNTs were purchased from Southwest NanoTechnologies Inc.
Et3N and toluene were distilled from CaH2. All reactions were
performed in standard dry glassware. Compounds 1 and 2a–c
were synthesized according to the literature procedures with
suitable modications.33,51
Compound 3a. To a solution of TTFV 1 (83 mg, 0.11 mmol) in
THF–MeOH (10 mL, 1 : 1) was added K2CO3 (91 mg, 0.66 mmol).
The mixture was stirred for 0.5 h at room temperature, and then
diluted with CH2Cl2, washed with water, dried over MgSO4, and
concentrated in vacuo. To the residue was added Et3N (30 mL)
and iodoarene 2a (269 mg, 0.440 mmol). The mixture was
deoxygenated by vigorous N2 bubbling. To the mixture was then
added CuI (12 mg, 0.011 mmol) and Pd(PPh3)4 (6.0 mg, 0.030
Fig. 18 TGA thermograms of bucky film and polymer 4a measured under air
with a scan rate of 5 ꢀC minꢁ1
.
is not observable in the TGA trace of the bucky lm. The thermal
decomposition completes at ca. 550 ꢀC; for polymer 4a, only
13% of weight remains while for the bucky lm 37% weight is
le. The TGA results conrm that the bucky lm possesses
better thermal stability than that of pure polymer 4a.
ꢀ
mmol), and the mixture was heated at 60 C and kept stirring
overnight. The resulting reaction mixture was diluted with
CH2Cl2, washed sequentially with aq. NH4Cl and water, dried
over MgSO4, and concentrated in vacuo. The residue was puri-
Conclusions
In conclusion, a series of alkyl-pendent TTFV–phenylacetylene ed by silica column chromatography (CH2Cl2–hexanes 5 : 95)
co-polymers 4a–c has been synthesized via Pd/Cu-catalysed to yield TTFV monomer 3a (116 mg, 0.0732 mmol, 67%) as a
oxidative homocoupling reactions and their electronic, redox, yellow oil. 1H NMR (500 MHz, CDCl3) d 7.45 (d, 4H, J ¼ 8.5 Hz),
and morphological properties have been characterized. The 7.37 (d, 4H, J ¼ 8.4 Hz), 6.93 (s, 2H), 6.92 (s, 2H), 4.00–3.93 (m,
polymers show sensitive responsiveness to redox and pH 8H), 2.43 (s, 6H), 2.38 (s, 6H), 1.84–1.75 (m, 8H), 1.53–1.46 (m,
stimuli and the processes are accompanied by dramatic 8H), 1.39–1.19 (m, 48H), 0.86 (m, 12H), 0.25 (s, 18H); 13C NMR
conformational changes. Most importantly, the TTFV polymers (75 MHz, CDCl3) d 154.4, 153.7, 138.2, 136.9, 132.1, 129.0, 126.6,
can effectively interact with SWNTs to cause debundling and 125.4, 123.9, 121.8, 117.5, 117.1, 114.6, 113.9, 101.5, 100.3, 95.4,
dispersion in organic solvents, while under the control of 87.0, 69.81, 69.76, 32.17, 29.92, 29.88, 29.8, 29.7, 29.64, 29.61,
external stimuli such as redox potential or pH the SWNT– 29.56, 26.31, 26.25, 22.96, 19.2, 19.1, 14.43, 14.40; FTIR (neat)
polymer complexes can be reversibly dissociated. Such proper- 2922, 2854, 2152, 1503, 1465, 1378, 1277, 1213, 1019 cmꢁ1
;
ties have in turn allowed multi-cycles of dispersion and HRMS (MALDI-TOF, +eV) m/z calcd for C90H126O4S8Si2
releasing sequences to be executed, which opens a new avenue 1582.6960, found 1582.7006 [M+].
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Compound 3b. To a solution of TTFV 1 (255 mg, 0.34 mmol) Then iodoarene 2a (11 mg, 0.036 mmol) was added and the
in THF–MeOH (16 mL, 1 : 1) was added K2CO3 (260 mg, 2.04 mixture was stirred for 36 h. Aerwards, methanol was added
mmol). The mixture was stirred for 0.5 h at room temperature, and the resulting precipitates were collected by ltration to
and it was then diluted with CH2Cl2, washed with water, dried afford TTFV polymer 4a (526 mg, 90%) 1H NMR (500 MHz,
over MgSO4, and concentrated in vacuo. To the residue were CDCl3) d 7.46 (d, 20H, J ¼ 7.8 Hz), 7.38 (d, 20H, J ¼ 7.9 Hz), 6.97
added Et3N (50 mL) and iodoarene 2b (900 mg, 1.7 mmol). The (m, 20H), 4.05–3.90 (m, 50H), 2.43 (s, 30H), 2.38 (s, 30H),
mixture was deoxygenated by vigorous N2 bubbling. To the 1.81 (m, 49H), 1.51–1.43 (m, 55H), 1.39–1.19 (m, 445H), 0.90–
mixture were then added CuI (19 mg, 0.102 mmol) and 0.79 (m, 128H), 0.06 (s, 18H); 13C NMR (75 MHz, CDCl3) d 155.0,
Pd(PPh3)4 (39 mg, 0.034 mmol). The mixture was heated at 60 ꢀC 153.5, 138.1, 137.9, 136.8, 131.9, 129.1, 128.8, 128.2, 126.3,
and kept stirring overnight. The resulting reaction mixture was 125.3, 125.1, 123.6, 121.4, 117.7, 116.9, 115.2, 112.5, 95.7, 86.7,
diluted with CH2Cl2, washed sequentially with aq. NH4Cl and 79.6, 79.4, 69.8, 69.6, 31.9, 29.7, 29.64, 29.61, 29.57, 29.5, 29.4,
water, dried over MgSO4, and concentrated in vacuo. The 29.3, 29.2, 26.1, 26.01, 25.96, 22.7, 21.5, 19.0, 18.9, 14.2, 14.1.
residue was puried by silica column chromatography (CH2Cl2– FTIR (neat) 2915, 2849, 2202, 1509, 1467, 1417, 1376, 1272,
hexanes 5 : 95) to yield TTFV monomer 3b (297 mg, 210 mmol, 1211, 1017 cmꢁ1. GPC: Mn ¼ 13 400 g molꢁ1, Mw ¼ 51 900 g
62%) as a yellow oil. 1H NMR (500 MHz, CDCl3) d 7.46 (d, 4H, J ¼ molꢁ1, PDI ¼ 3.9.
8.6 Hz), 7.38 (d, 4H, J ¼ 8.6 Hz), 6.92 (d, 4H, J ¼ 2.63 Hz), 4.00–
Polymer 4b. To a solution of TTFV monomer 3b (123 mg,
3.93 (m, 8H), 2.43 (s, 6H), 2.38 (s, 6H), 1.84–1.74 (m, 8H), 1.54– 0.087 mmol) in THF–MeOH (20 mL, 1 : 1) was added K2CO3 (72
1.46 (m, 8H), 1.37–1.24 (m, 26H), 0.90 (m, 12H), 0.25 (s, 18H); mg, 0.524 mmol). The mixture was stirred at room temperature
13C NMR (75 MHz, CDCl3) d 154.3, 153.6, 138.1, 136.8, 132.0, for 0.5 h, diluted with CH2Cl2, washed with water, dried over
128.9, 126.4, 125.3, 123.8, 121.7, 117.4, 117.0, 114.5, 113.8, MgSO4, and concentrated in vacuo. To the residue were added
101.4, 100.2, 95.2, 86.9, 69.8, 69.7, 32.0, 29.6, 29.5, 29.3, 29.2, toluene (6 mL), CuI (5 mg, 0.026 mmol), PdCl2(PPh3)2 (6 mg,
26.2, 22.82, 22.81, 19.1, 19.0, 14.4, 14.3, 0.16; FTIR (neat) 2920, 0.009 mmol) and DBU (1.0 mL, 0.009 mmol). The mixture was
2851, 2150, 1500, 1463, 1378, 1275, 1212, 1020 cmꢁ1; HRMS heated at 70 ꢀC under stirring for 1 h. Then iodoarene 2b (2 mg,
(MALDI-TOF, +eV) m/z calcd for C78H102O4S8Si2 1414.5082, 0.004 mmol) was added and the mixture was stirred for 36 h.
found 1414.5084 [M+].
Aerwards, methanol was added and the resulting precipitates
Compound 3c. To a solution of TTFV 1 (276 mg, 0.36 mmol) in were collected by ltration to afford TTFV polymer 4b (105 mg,
THF–MeOH (12 mL, 1 : 1) was added K2CO3 (320 mg, 2.19 92%) 1H NMR (500 MHz, CDCl3) d 7.46 (d, 50H, J ¼ 7.5 Hz), 7.38
mmol). The mixture was stirred for 0.5 h at room temperature, (d, 50H, J ¼ 7.5 Hz), 6.98–6.94 (m, 50H), 4.02–3.96 (m, 120H),
diluted with CH2Cl2, washed with water, dried over MgSO4, and 2.44 (s, 75H), 2.40 (s, 75H), 1.82–1.81 (m, 120H), 1.51–1.26 (m,
concentrated in vacuo. To the residue was added Et3N (60 mL) 600H), 0.87–0.81 (m, 180H), 0.26 (s, 18H); FTIR (neat) 2921,
and iodoarene 2c (1.05 mg, 1.8 mmol). The mixture was deox- 2857, 2206, 1600, 1463, 1420, 1378, 1269, 1211, 1018 cmꢁ1
ygenated by vigorous N2 bubbling. To the mixture were then Polymer 4c. To a solution of TTFV monomer 3c (318 mg, 0.24
.
added CuI (25 mg, 0.108 mmol) and Pd(PPh3)4 (51 mg, 0.036 mmol) in THF–MeOH (20 mL, 1 : 1) was added K2CO3 (202 mg,
mmol). The mixture was heated at 60 ꢀC and kept stirring 1.46 mmol). The mixture was stirred at room temperature for 0.5
overnight. The resulting reaction mixture was diluted with h, and then it was diluted with CH2Cl2, washed with water, dried
CH2Cl2, washed sequentially with aq. NH4Cl and water, dried over MgSO4, and concentrated in vacuo. To the residue were
over MgSO4, and concentrated in vacuo. The residue was puri- added toluene (10 mL), CuI (13 mg, 0.072 mmol), PdCl2(PPh3)2
ed by silica column chromatography (CH2Cl2–hexanes 5 : 95) (16 mg, 0.024 mmol) and DBU (4.0 mL, 0.024 mmol). The mixture
to yield TTFV monomer 3c (309 mg, 237 mmol, 65%) as a yellow was heated at 70 ꢀC under stirring for 1 h. Then iodoarene 2c (5
oil. 1H NMR (500 MHz, CDCl3) d 7.45 (d, 4H, J ¼ 8.9 Hz), 7.37 (d, mg, 0.012 mmol) was added and the mixture was stirred for 36 h.
4H, J ¼ 8.9 Hz), 6.93 (d, 4H, J ¼ 2.3 Hz), 4.00–3.95 (m, 8H), 2.43 Aerwards, methanol was added and the resulting precipitates
(s, 6H), 2.38 (s, 6H), 1.87–1.76 (m, 8H), 1.55–1.33 (m, 18H), 0.96– were collected by ltration to afford TTFV polymer 4c (260 mg,
0.85 (m, 14H), 0.86 (m, 12H), 0.26 (s, 18H); 13C NMR (75 MHz, 90%) 1H NMR (500 MHz, CDCl3) d 7.48 (d, 76H, J ¼ 8.1 Hz), 7.40
CDCl3) d 154.3, 153.6, 138.1, 136.8, 132.0, 128.8, 126.5, 125.2, (d, 76H, J ¼ 8.0 Hz), 6.97 (s, 76H), 4.03–3.96 (m, 160H), 2.44–2.36
123.8, 121.7, 117.5, 117.0, 114.5, 113.8, 101.4, 100.2, 95.2, 86.9, (m, 255H), 1.88–1.79 (m, 168H), 1.53–1.37 (m, 361H), 0.97–0.90
69.7, 69.6, 29.20, 29.17, 28.40, 28.37, 22.7, 22.6, 19.1, 19.0, 14.28, (m, 260H), 0.07 (s, 18H); FTIR (neat) 2920, 2855, 2205, 1600, 1463,
14.26, 0.15; FTIR (neat) 2926, 2863, 2149, 1500, 1415, 1378, 1419, 1378, 1269, 1211, 1017 cmꢁ1
.
1261, 1211, 1012 cmꢁ1; HRMS (MALDI-TOF, +eV) m/z calcd for
C
70H86O4S8Si2 1302.3830, found 1302.3806 [M+].
Theoretical modeling
Polymer 4a. To a solution of TTFV monomer 3a (574 mg,
0.364 mmol) in THF–MeOH (10 mL, 1 : 1) was added K2CO3 (302 Molecular mechanics calculations were conducted the SYBYL
mg, 2.18 mmol). The mixture was stirred at room temperature force eld, coordinates of SWNTs were initially generated by
for 0.5 h, and then it was diluted with CH2Cl2, washed with TubeGen 3.4 soware46 and then imported into Spartan'10
water, dried over MgSO4, and concentrated in vacuo. To the soware34 for further calculations. Density functional theory
residue were added toluene (30 mL), CuI (20 mg, 0.11 mmol), (DFT) calculations were performed at the B3LYP/6-311G* level
PdCl2(PPh3)2 (25 mg, 0.036 mmol) and DBU (5.4 mL, 0.036 of theory implemented in Spartan'10 running on a Mac Pro
mmol). The mixture was heated at 70 ꢀC under stirring for 1 h. workstation.
5488 | J. Mater. Chem. C, 2013, 1, 5477–5490
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Journal of Materials Chemistry C
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Characterization
1H and 13C NMR spectra were measured on a Bruker Avance 500
MHz spectrometer or a Tecmag APOLLO 300 MHz spectrom-
eter. Chemical shis are reported in ppm downeld from the
signal of the internal reference SiMe4. Coupling constants (J) are
given in Hz. UV-vis-NR absorption spectra were recorded on a
Cary 6000i spectrophotometer. Infrared spectra (IR) were
recorded on a Bruker Tensor 27 spectrometer equipped with a
ZnSe ATR module. MALDI-TOF MS were measured on an
Applied Biosystems Voyager instrument using dithranol as the
matrix. Gel permeation chromatography (GPC) measurements
were performed on a Waters 515 system equipped with a UV
detector using polystyrene standards and THF as eluent. UV-vis
absorption spectra were obtained on a Varian diode-array
spectrophotometer (model Cary 500) using 1 cm path length
quartz cells. Atomic force microscopy (AFM) images were taken
with a Quesant Q-Scope 250 microscope operated in the tapping
mode. Scanning electron microscopy (SEM) images were taken
on a Hitachi S570 microscope operated at 15 kV. Raman spectra
were measured on a Horiba Jobin Yvon confocal Raman spec-
trometer operated at a laser wavelength of 534 nm. Cyclic vol-
tammetric (CV) experiments were carried out in a standard
three-electrode setup controlled by a BASi Epsilon workstation.
Thermogravimetric analysis (TGA) was conducted on a TA
instrument Q500 thermogravimetric analyzer. Photo-
luminescence (PL) mapping was performed using a Jobin-Yvon
SPEX Fluorolog 3.22 equipped with a 450 W Xe lamp, and tted
with a liquid-nitrogen cooled InGaAs photodiode detector. Slit
widths were set to 7 nm band-pass on both excitation and
emission, and samples were illuminated in a quartz cell using 5
nm wavelength steps.
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Acknowledgements
This work was supported by Natural Sciences and Engineering
Research Council of Canada (NSERC), Canada Foundation for
Innovation (CFI), and Memorial University. Prof. Jean-François
Morin of Laval University is acknowledged for assistance in GPC
analysis, and Prof. Alex Adronov of McMaster University is
acknowledged for assistance in PL mapping study.
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