When dithiafulvenyl functionalized π-conjugated oligomers meet fullerenes and single-walled carbon nanotubes

Article abstract of DOI:10.1039/c3tc30626g

A series of π-conjugated oligomers taking linear and Z-shaped molecular structures were synthesized with electron-donating dithiafulvenyl (DTF) groups functionalized at the terminal positions. Besides significantly enriched electronic and redox properties as disclosed by UV-Vis absorption and voltammetric analyses, these DTF-endcapped oligomers also exhibited a facile reactivity of oxidative CC bond cleavage sensitized by fullerenes under air, converting the non-fluorescent DTF-oligomers to highly fluorescent aldehyde-endcapped oligomer products. This reaction provides an appealing approach for efficient fluorescence turn-on sensing of fullerenes. Furthermore, the DTF-attached oligomers showed strong noncovalent interactions with single-walled carbon nanotubes (SWNTs) to form soluble supramolecular assemblies in certain chlorinated organic solvents such as methylene chloride and chloroform. The dispersion of SWNTs effected by the DTF-oligomers was found to be highly efficient (up to 0.29 mg of SWNTs per mL) and shows selectivity for small-diameter nanotubes. The resulting SWNT suspensions could be easily dissociated upon addition of hydrocarbon solvents such as hexanes, releasing pristine SWNTs which were free of oligomer dispersants after filtration and solvent rinsing.

Full text of DOI:10.1039/c3tc30626g

Journal of
Materials Chemistry C
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PAPER
When dithiafulvenyl functionalized p-conjugated
oligomers meet fullerenes and single-walled carbon
Cite this: J. Mater. Chem. C, 2013, 1,
5116
nanotubes†
*
Karimulla Mulla and Yuming Zhao
A series of p-conjugated oligomers taking linear and Z-shaped molecular structures were synthesized with
electron-donating dithiafulvenyl (DTF) groups functionalized at the terminal positions. Besides significantly
enriched electronic and redox properties as disclosed by UV-Vis absorption and voltammetric analyses,
these DTF-endcapped oligomers also exhibited a facile reactivity of oxidative C]C bond cleavage
sensitized by fullerenes under air, converting the non-fluorescent DTF–oligomers to highly fluorescent
aldehyde-endcapped oligomer products. This reaction provides an appealing approach for efficient
fluorescence turn-on sensing of fullerenes. Furthermore, the DTF-attached oligomers showed strong
noncovalent interactions with single-walled carbon nanotubes (SWNTs) to form soluble supramolecular
assemblies in certain chlorinated organic solvents such as methylene chloride and chloroform. The
dispersion of SWNTs effected by the DTF–oligomers was found to be highly efficient (up to 0.29 mg of
SWNTs per mL) and shows selectivity for small-diameter nanotubes. The resulting SWNT suspensions
could be easily dissociated upon addition of hydrocarbon solvents such as hexanes, releasing pristine
SWNTs which were free of oligomer dispersants after filtration and solvent rinsing.
Received 4th April 2013
Accepted 14th June 2013
DOI: 10.1039/c3tc30626g
www.rsc.org/MaterialsC
active TTFV derivatives and related macromolecular systems.2
The role of DTF in electronic substitution for structurally
Introduction
Dithiafulvene (DTF) acts as a good electron-donating group,
since its dithiole ring, aer releasing one electron, is converted
into an aromaticity-stabilized dithiolium ion. Therefore,
oxidation of an aryl-substituted DTF usually leads to a radical
cation intermediate which swily undergoes a dimerization
process, forming a new C–C bond and giving a tetrathiafulve-
lene vinylogue (TTFV) product (Scheme 1).1
dened conjugated p-oligomer systems is still far from being
thoroughly examined; nonetheless, there have been some
studies in the recent literature which have addressed this topic.
For instance, Roncali and co-workers made a class of star-sha-
ped conjugated systems with a triphenylamine (TPA) core, and
applied these molecular materials in polymer-based solar cells
and electrochromism.3 Garın and co-workers synthesized a
´
Because of its unique electrochemical reactivity, the DTF
group has been used to functionalize various molecular struc-
tures, acting as a synthetic handle that enables further elec-
trochemical coupling and/or polymerization to generate redox
series of donor–acceptor (D–A) functionalized oligoenes, where
DTF was used as the electron donor to bring about enhanced
second-order nonlinear optical (NLO) properties.4 Very recently,
Yang and co-workers reported that D–A endcapping of a
diphenylthiophene p-framework using DTF as the electron
donor could lead to remarkably increased device efficiency for
dye-sensitized solar cells.5 Our group has previously investi-
gated a series of DTF-endcapped oligoynes and disclosed their
electronic properties as well as applicability in preparing elec-
trochromic polymer lms on conducting substrates via
electropolymerization.6
In this contribution, we investigated the substitution effects of
DTF on structurally dened p-conjugated oligomers. A group of
oligo(phenylene ethynylene) (OPE) and oligo(phenylene vinylene)
(OPV) based conjugated co-oligomers7 were designed and
synthesized in both the linear and Z-shaped structures for the
study of structure–property relationships. Through a phosphite-
promoted olenation reaction,8 DTF endgroups were efficiently
attached to the terminal positions of these oligomers, and the
Scheme 1 Oxidative dimerization of DTF.
Department of Chemistry, Memorial University, St. John's, NL, Canada A1B 3X7.
E-mail: yuming@mun.ca; Fax: +1 709 863 3702; Tel: +1 709 864 8747
† Electronic supplementary information (ESI) available: Detailed spectroscopic,
microscopic, and electrochemical characterization of new compounds and
related SWNT dispersions. See DOI: 10.1039/c3tc30626g
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resulting DTF–oligomer hybrids served as reasonable models to p-ethynylbenzaldehyde (1) with p-diiodobenzene (2) afforded
allow the interplay between DTF endgroups with the p-frame- oligomer 3 in a crude yield of 78%. Compound 3 showed very
works of conjugated oligomers to be compared and assessed. Our poor solubility in common organic solvents due to the lack of
studies in this work have disclosed some unprecedented molec- solubilizing groups, and was therefore obtained merely in a
ular and supramolecular behaviours arising from DTF function- crude form. Despite the difficulty in attaining satisfactory
alization. In particular, investigations on the photophysical purity, 3 was subjected to a P(OMe)3-mediated olenation
properties of the DTF–oligomers have revealed an interesting reaction8 with thione 4,10 giving DTF-endcapped phenyl-
C]C bond cleavage reaction promoted by singlet oxygen in the acetylene trimer 5 that showed much better solubility and was
presence of fullerenes. This reaction converts non-uorescent readily puried by column chromatography. Through an
DTF-functionalized oligomers into highly uorescent aldehyde- approach similar to the synthesis of 5, a longer OPE framework
pendent oligomers, providing a new way for uorescence turn-on 7 was prepared from Sonogashira coupling of compound 6 with
sensing of fullerenes. On the other hand, the excellent electron p-diiodobenzene (2). The aldehyde groups of 7 were then sub-
donating property of DTF was also predicted to result in strong jected to an olenation reaction, furnishing DTF-endcapped
affinity for carbon-based nanomaterials. For example, Bao and phenylacetylene pentamer 8 in a good yield of 76%.
co-workers recently reported the use of DTF/thiophene copoly-
The construction of Z-shaped OPE/OPV co-oligomers is out-
mers to disperse single-walled carbon nanotubes (SWNTs) for lined in Scheme 3. First, a Wittig–Horner reaction7b,c was pre-
making thin lm transistors.9 In our work, supramolecular formed between o-iodobenzaldehyde (9) and bisphosphonate
interactions between the DTF–oligomers and SWNTs have been 10 in the presence of NaH to give diiodo-OPV 11 in 46% yield.
examined. Although relatively small p-oligomers are not gener- Compound 11 underwent a double Sonogashira coupling with
ally reckoned to induce sufficient dispersion of SWNTs in solu- compound 1 to yield Z-shaped oligomer 12, which was then
tion, to our great surprise, the DTF-functionalized oligomers not converted into DTF–OPE/OPV 13 through the P(OMe)3-
only gave rise to highly effective SWNT dispersion in certain promoted olenation.8 By a similar sequence of Sonogashira
organic solvents, but also enabled reversible control over the coupling and olenation, a longer Z-shaped DTF–OPE/OPV 15
dispersion/releasing of SWNTs by a simple solvent effect. The was produced in a very good yield.
following content describes the detailed synthesis of these DTF–
oligomers and studies of their interesting molecular and supra-
molecular properties.
Electronic absorption and emission properties
Fig. 1 shows the UV-Vis absorption spectra of DTF–oligomers in
comparison with their aldehyde–oligomer precursors except
compound 3 due to its limited solubility. The detailed absorp-
tion spectroscopic data are summarized in Table 1.
Results and discussion
Synthesis
It can be seen from Fig. 1A that the maximum absorption
Scheme 2 describes the synthetic routes to linear-shaped DTF- wavelength of long linear DTF–OPE 8 (at 423 nm) is redshied
endcapped phenylacetylene oligomers. Sonogashira coupling of by only 12 nm relative to short DTF–OPE 5 (at 412 nm), as a
Scheme 2 Synthesis of linear OPEs with DTF endgroups.
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Scheme 3 Synthesis of Z-shaped OPE/OPV co-oligomers with DTF endgroups.
Table 1 Summary of photophysical data for DTF–oligomers and their aldehyde–
oligomer precursors
Absorption l/nm
Emissiona
l/nm
Quantum
yield (F)
Entry
(3/104 cmꢀ1 Mꢀ1
)
5
7
412 (6.72), 319 (2.56)
407 (7.92), 331 (4.45),
299 (3.42),
488, 466
485, 454
0.012
0.591
8
12
423 (11.2), 326 (3.82)
387 (2.51), 361 (3.65),
318 (5.38)
487, 468
487, 462
0.0134
0.406
296 (3.98), 246 (1.78)
402(s) (4.90), 368 (6.49),
301 (4.14)
401(s) (6.21), 366 (7.65),
327 (5.98), 308 (6.41)
432 (8.47), 406 (10.5),
384 (9.33), 357 (7.52),
314 (6.19), 245 (5.04)
13
14
15
444
0.0109
0.676
487, 474
488, 466
0.0131
a
For 13 and 14, excitation wavelength (lex) ¼ 350 nm; for 5, 7, 8, 12 and
15, lex ¼ 370 nm.
oligomer unit. The spectrum of short Z-shaped DTF–OPE/OPV
13 shows a low-energy absorption band at 368 nm along with a
shoulder at 402 nm. Its aldehyde precursor 12 exhibits a similar
low-energy spectral prole, but the absorption band and
shoulder are slightly blueshied to 361 nm and 387 nm
respectively. The spectrum of long Z-shaped DTF–OPE/OPV 15
shows a maximum absorption band at 408 nm, which is similar
to that of its aldehyde precursor 14 (lmax ¼ 407 nm). The
spectrum of 15 shows a distinctive absorption band at 388 nm
and a shoulder at 432 nm in the low-energy region.
Fig. 1 Normalized UV-Vis absorption spectra of oligomers 5, 7, 8, and 12–15
measured in CHCl3 at room temperature.
consequence of an increased p-conjugation degree of the olig-
omer framework. Comparison of the absorption spectra of
DTF–OPE 8 and aldehyde–OPE 7 (lmax ¼ 408 nm) reveals a
redshi of lmax by 15 nm, which is ascribed to the substitution
effect of DTF endgroups on the electronic properties of the
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The electronic emission properties of DTF-functionalized
Journal of Materials Chemistry C
OPEs and related aldehyde–oligomer precursors were investi-
gated by uorescence spectroscopic analysis. The aldehyde-
endcapped oligomers are highly uorescent (Fig. 2A) with
quantum yields in the range of ca. 40–70% (see Table 1). For the
DTF-endcapped oligomers, however, the emission is substan-
tially attenuated with quantum yields around ca. 1% (see Table
1). The reduced emission can be explained by a non-radiative
decay mechanism in which photoinduced electron transfer
(PeT) from a DTF donor to the oligomer uorophores competes
effectively with uorescent emission.
Electrochemical properties
The electrochemical redox properties of DTF-functionalized
oligomers were investigated by cyclic voltammetry (CV). Fig. 3
shows the cyclic voltammograms that were measured in the
multi-cycle scan mode.
In the rst cycle of CV scans, the voltammogram of DTF–OPE
5 clearly shows an anodic peak at +0.82 V and a cathodic peak at
+0.54 V, which are assigned to the oxidation of DTF into [DTF]+
and reverse reduction.1,6 Starting from the second cycle of CV
scans, a new anodic peak at ca. +0.6 V emerges and its intensity
grows steadily with the increasing cathodic peak at +0.54 V. The
rise of this new peak is due to the continuous formation of
[TTFV]2+ as a result of oxidative dimerization of DTF (see
Scheme 1) on the surface of the working electrode.1,6 The vol-
tammogram of longer DTF–OPE 8 shows a similar growth of the
[TTFV]2+ peak upon multi-cycle scans; however, the [DTF]+ peak
at ca. +0.82 V appears to reduce more dramatically in intensity
in comparison with 5. Rationalization for the different CV
Fig. 3 Cyclic voltammograms of DTF–oligomers measured in the multi-cycle scan
mode. Experimental conditions: Bu4NBF4 (0.1 M) as the supporting electrolyte,
CH2Cl2 as the solvent, glassy carbon as the working electrode, Pt wire as the counter
electrode, Ag/AgCl as the reference electrode, and scan rate ¼ 100 mV sꢀ1
.
patterns can be made as follows: when one of the DTF groups in
5 undergoes oxidative dimerization, the resulting [TTFV]2+
dication imposes a signicant electron-withdrawing effect on
the other DTF group via the relatively short OPE p-spacer, which
in turn lowers its reactivity toward further oxidative dimeriza-
tion. The electrochemical reactions on the working electrode
therefore are mainly dimerization or low-degree oligomeriza-
tion of 5, aer which a signicant amount of DTF endgroups
still remain intact. For DTF–OPE 8, however, the relatively
longer OPE bridge attenuates electronic communications
between the two DTF endgroups. As a result, each of them
undergoes oxidative dimerization independently, resulting in a
quicker consumption of DTF units and relatively higher degree
of polymerization upon multiple CV scans. The voltammogram
of long Z-shaped DTF–OPE/OPV 15 shows similar electro-
chemical behavior to that of long linear DTF–OPE 8. Of partic-
ular note are the CV features of short Z-shaped DTF–oligomer
13. In the rst cycle of scans, two anodic peaks at +0.82 V and
+1.09 V and two cathodic peaks at +0.56 V and +0.94 V can be
seen. This result suggests that the two DTF groups in 13 have a
signicant degree of electronic communications such that they
are oxidized in a stepwise rather than a simultaneous manner.
As the cycles of CV scans increase, the [TTFV]2+ peak at ca. +0.61
V becomes observable but with a very weak current intensity.
The voltammogram of 13 clearly shows that its DTF endgroups
are relatively unreactive towards oxidative dimerization. Such
different electrochemical behaviour is attributable to the strong
Fig. 2 Fluorescence spectra of oligomers 5, 7, 8, and 12–15 measured in CHCl3
at room temperature.
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electronic communications between the two DTF groups via the
short Z-shaped OPE/OPV p-bridge of 13. Overall, our compar-
ative CV analyses conrm that the p-spacers have a key effect on
the electrochemical reactivities of DTF-endcapped oligomers.
Fullerene-sensitized photo-oxygenation of DTF–oligomers
and consequential uorescence sensing for fullerenes
Scheme
4
Proposed mechanism for singlet oxygen-induced C]C bond
When a small amount of fullerene (C60 or C70) was added into
the diluted solutions of DTF–oligomers, steadily increased
uorescence was observed. This property at the rst look was a
bit puzzling, given the known uorescence quenching effects
arising from both DTF endgroups and fullerenes on oligomer
uorophores. To shed light on this issue, 1H NMR analysis was
performed on a mixture of oligomer 15 and C60 fullerene in
deuterated benzene (C6D6) at various time intervals, with the
solution not being deliberately degassed. The NMR spectra
shown in Fig. 4 unambiguously delineate a process in which the
DTF units of oligomer 15 are gradually converted into aldehyde
groups, leading to compound 14 and thione as the products. In
addition to the NMR test, the reaction has also been attempted
on a larger scale, where 15 (ca. 10 mg) was converted into 14 in a
high yield of 89% (isolated) in the presence of C60 (3 molar
equiv.) at room temperature within 20 hours. Fullerene C60 has
a wide spectral absorption range and a low-lying triplet state.11 It
is therefore reasonable to assume that upon exposure to
ambient light, a fullerene-sensitized reaction pathway leads to
singlet oxygen (1O2) formation.12 Singlet oxygen is known
to react with electron-rich alkene to form 1,2-dioxetane, which
subsequently undergo O–O bond breaking to yield C]O prod-
ucts.13 Scheme 4 shows a proposed mechanism accounting for
the transformation of DTF to aldehyde induced by singlet
oxygen. Non-uorescent DTF–oligomers undergoing this singlet
oxygen involved C]C cleavage reaction hence afford highly
cleavage of DTF.
uorescence aldehyde–oligomers, giving rise to the observed
uorescence enhancement. The involvement of singlet oxygen
as an oxidant in the fullerene-sensitized C]C bond cleavage is
evidenced by the following experimental observations: (i) the
reaction rate was considerably slowed down when the reaction
was carried out under argon. (ii) The use of a classical singlet
oxygen sensitizer, methylene blue, in place of C60, also led to the
same C]C bond cleavage reaction. (iii) Upon UV light irradia-
tion under air, a condition known to generate singlet oxygen,
compound 15 underwent the same C]C bond cleavage reaction
as well without the presence of C60 (see ESI for detailed exper-
imental results†).
To further probe the kinetic properties of the fullerene-
sensitized C]C bond photo-oxygenation and subsequent
cleavage reactions, diluted solutions of 15 mixed with either
C60 or C70 fullerene were examined by uorescence spectro-
scopic analysis at varied times (Fig. 5). From Fig. 5A, the
uorescence enhancement (F ꢀ F0) is observed to show a linear
relationship with reaction time (s) in the rst 16 hours.
Assuming that (F ꢀ F0) is proportional to the concentration of
uorescent product 14, the correlation is in line with zero-
order kinetics. When C70 was used in lieu of C60 as the
Fig. 4 1H NMR spectra in the aromatic and aliphatic regions showing the gradual conversion of DTF–oligomer 15 to aldehyde–oligomer 14 in the presence of C60
fullerene at 298 K. Initial concentration of 15: 8.9 ꢁ 10ꢀ4 M, concentration of C60: 26.7 ꢁ 10ꢀ4 M, and solvent: C6D6.
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properties is currently underway and the results will be dis-
closed in due course. It is worth noting that the fullerene-
sensitized photo-oxygenation reaction of 15 at the DTF moiety
gives a substantial increase in the uorescence efficiency of the
DTF–oligomer solution. For instance, the solution of 15 in
benzene was found to show
a substantial uorescence
enhancement of 149-fold aer mixing with C60 fullerene for 24
hours, and 162-fold with C70 for 6 hours. The dramatic uo-
rescence response to fullerenes can be useful for further
developing highly efficient detection methods and quantica-
tion protocols for different types of fullerenes.
Supramolecular interactions of DTF–oligomers with SWNTs
Noncovalent functionalization of SWNTs has received consid-
erable attention in the eld of nanotube-based science and
technologies, not only because it provides a direct solution to
the problems of insolubility and poor processability of as-
produced SWNTs, but also because it enables easy ways for
sorting specic types of SWNTs out of as-produced SWNT
mixtures.14 Usually, macromolecule-based dispersants such as
surfactants, polymers, and DNA are preferred for debundling
and dispersion of SWNTs in various solvents, as they tend to
form stable complexes with SWNTs with sufficient dispersant–
SWNT interactions via van der Waals forces or p-stacking. The
use of relatively small p-conjugated oligomers to disperse
SWNTs, however, has not been extensively studied yet. In recent
years, various DTF- and TTF-containing compounds have been
found to show signicant supramolecular interactions with
SWNTs.9,15 These results thus inspired us to investigate the
supramolecular interactions between the DTF–oligomers and
the SWNTs. In this work, two commercially available SWNT
products, namely HiPCO and CoMoCAT nanotubes, were
chosen for study. The dispersion experiments were conducted
in a straightforward manner: a suitable amount of SWNT
sample was added to the solution of a DTF–oligomer (ca. 10ꢀ3
Mꢀ1) in a selected solvent. The mixture was ultrasonicated for 1
hour at room temperature and then subjected to a sequence of
ltration, centrifugation, and ltration treatments. The ltrate
solution was let stand still for a few hours and then checked
both visually and by UV-Vis-NIR analysis. The photographic
images in Fig. 6 depict the outcomes of HiPCO SWNTs
dispersed with DTF–oligomers, from which it is clearly seen that
HiPCO SWNTs form stable black suspensions in the chloroform
solutions of all four DTF–oligomers, where long oligomers 8
and 15 give much better dispersion results than short oligomers
5 and 13. In methylene chloride, long oligomers 8 and 15 can
also induce efficient dispersion of HiPCO SWNTs, but short
oligomers 5 and 13 cannot. For other common organic solvents,
including chlorobenzene, toluene, and hexanes, no effective
dispersion of HiPCO SWNTs can be obtained using DTF–olig-
omers as dispersants. Although both short and long Z-shaped
oligomers 13 and 15 were able to effect dispersion of SWNTs in
chlorobenzene immediately aer sonication and ltration
through a cotton plug, the suspensions were not stable enough
and SWNTs precipitated out of the solution within a short
period of time.
Fig. 5 (A) Fluorescence spectra of 15 (1.8 ꢁ 10ꢀ6 M) with C60 in benzene at
varied times. (B) Fluorescence spectra of 15 with C70 in benzene at varied times.
Inset plots: fluorescence enhancement (F ꢀ F0) as a function of time (s). F0 and F
denote fluorescence intensities measured at initial and later stages at 440 nm.
Inset image: a photograph of 15 mixed with C60 in benzene taken at 0 h (left) and
24 h (right) under UV light irradiation.
sensitizer, the correlation of (F ꢀ F0) with s appears to be in a
good agreement with a rst-order kinetics. A tentative ration-
alization on these different kinetic properties can be made
based on the kinetic analysis described in Scheme 5. In the
case where singlet oxygen generation is the rate determining
step and the concentration of dissolved oxygen in solution is
deemed as constant, a steady-state approximation can be made
to give zero-order behaviour for the observed reaction rate. In
contrast, if the C]C bond cleavage is the rate determining
step, a rapid equilibrium approximation is valid, which leads
to a rst-order kinetics for the overall reaction. The results of
kinetics analysis suggest that C70 produces singlet oxygen at a
much faster rate than C60. A systematic survey on the kinetic
Scheme 5 Kinetics of singlet oxygen induced C]C bond cleavage of aryl-DTF.
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solutions of long oligomers 8 and 15 is much greater than in
short oligomers 5 and 13, likely due to their longer p-conju-
gated lengths and more solubilizing decyl side chains.
The HiPCO SWNTs released from the suspension in the
solution of 15 were examined by Raman spectroscopy. As shown
in Fig. 8, the spectrum of the released SWNTs shows only one
signicant peak at 272 cmꢀ1 in the region of radial breathing
mode (RBM). The spectral feature is quite similar to that of the
HiPCO SWNTs dispersed in the chloroform solution of 15. For
pristine SWNTs, the Raman spectrum shows two signicant
peaks at 267 and 225 nm respectively. Given the fact that the
Raman frequency in this region is inversely proportional to the
diameter of the nanotubes,16 it is concluded that oligomer 15
can selectively disperse the nanotubes of relatively smaller
diameters in pristine HiPCO SWNTs. The dispersion and
releasing behaviours combined together offer a simple and
effective method for sorting the small-diameter species out of
the as-produced HiPCO SWNTs. Reversible dispersion and
release of SWNTs using stimuli-responsive dispersants have
received growing attention in recent years.17 It is important to
note that the released SWNTs are cleanly separated from olig-
omer dispersants, which is evidenced by Raman spectroscopic
analysis. As shown in Fig. 9, the spectrum of the released
SWNTs does not show signicant signals at ca. 2200 cmꢀ1
,
Fig. 6 Photographic images of filtrates of DTF–oligomer solutions mixed with
HiPCO SWNTs after sonication for 1 h. Rows: (A) oligomer 5, (B) oligomer 8, (C)
oligomer 13, and (D) oligomer 15. Solvents tested (from left to right): chloroform,
chlorobenzene, toluene, methylene chloride, and hexanes.
which is due to the C^C stretching mode of oligomer 15. In the
fabrication of SWNT-based semiconducting electronic devices,
suitable noncovalent pre-treatment of SWNTs such as selective
dispersion is usually conducted. However, it is known that
Table 2 Solubility of HiPCO SWNTS in DTF–oligomer chloroform solutions
The solvent effect on dispersion turns out to be valuable for
processing SWNTs, since it allows reversible releasing of SWNTs
to be readily accomplished by a simple solvent mixing control.
For instance, when an equal amount of hexanes was added to
the stable suspension of HiPCO SWNTs and oligomer 15 in
chloroform, SWNTs immediately precipitated out of the solu-
tion (see Fig. 7), and they were readily separated by vacuum
ltration. The ltrate solution was then checked by UV-Vis-NIR
analysis, showing that only a trace amount of SWNTs remained
in the solution phase aer this treatment. By this way, pristine
SWNTs were conveniently recovered from the dispersion. The
actual solubility of SWNTs in DTF–oligomer solutions was then
determined. As listed in Table 2, the solubility of SWNTs in the
Concentration
of oligomer (mM)
Solubility of
Entry
SWNTS (mg mLꢀ1
)
5
8
13
15
2.34
1.58
2.00
1.39
0.01
0.20
0.05
0.29
Fig. 8 Normalized Raman spectra showing the RBM region of (a) HiPCO SWNTs
released from the dispersion, (b) HiPCO SWNTs dispersed with 15, and (c) pristine
HiPCO SWNTs.
Fig. 7 Photographic images of (A) HiPCO SWNT suspension with 15 in chloro-
form and (B) after addition of an equal amount of hexanes.
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Fig. 9 Normalized Raman spectra of the released SWNTs, pristine SWNTs, and
pure oligomer 15 in the region of 1500 to 2500 cmꢀ1
.
organic dispersants introduced in the dispersion process tend
to cause negative effects on the semiconducting properties of
SWNTs, which in turn signicantly reduce the device perfor-
mance. To avoid this trouble, the interactions between disper-
sants and SWNTs are desired to be reversible. The solvent-
controlled reversibility observed in the interactions between the
DTF–oligomers and the HiPCO SWNTs thus contribute a useful
method for this application.
The HiPCO SWNTs dispersed by DTF–oligomers 5, 8, 13, and
15 in chloroform were further investigated by UV-Vis-NIR and
Raman spectroscopic analysis. As can be seen from Fig. 10, the
Vis-NIR absorption and Raman spectral proles of the SWNTs
dispersed by the four oligomers are very similar to one another.
Since these analytical data are directly correlated with the
structures and electronic types of SWNTs, the outcome indi-
cates that the four DTF–oligomers show a similar selectivity for
the types of nanotubes to be dispersed.
Fig. 10 (A) Normalized UV-Vis-NIR spectra of HiPCO SWNTs dispersed by DTF–
oligomers in chloroform. (B) Raman spectra of HiPCO SWNTs dispersed by DTF
oligomers in the RBM region (lex ¼ 534 nm).
The microscopic properties of HiPCO SWNTs dispersed with
DTF–oligomers were examined by atomic force microscopic
(AFM) analysis. The AFM studies have revealed signicant
interactions between individual strands of SWNTs and the
DTF–oligomers. For example, Fig. 11 shows the morphology of
HiPCO SWNTs dispersed with long linear-shaped DTF–olig-
omer 8, wherein oligomer agglomerates are clearly observed to
stack around the sidewalls of debundled SWNTs. Such inter-
actions are believed to be the major driving force for effective
dispersion of SWNTs in the solution phase.
At this juncture, there are several points worth remarking: (1)
the dispersion of HiPCO SWNTs with DTF–oligomers appears to
be particularly effective in chloroform. The exact reason is
unclear and awaits further investigation. Nevertheless, 1H NMR
Fig. 11 AFM image of supramolecular assemblies of HiPCO SWNTs and oligomer
8 spin-cast on a mica surface (tapping mode).
analysis on DTF–oligomer 15 discloses a dramatic degree of assemblies of DTF–oligomers and HiPCO SWNTs more effec-
changes in the resonance frequencies of aromatic protons in tively than other organic solvents. (2) The pristine SWNTs can
different solvents (see Fig. S20, ESI†). Of particular note is that be easily released from the oligomer–SWNT assemblies
one of the vinyl protons was found greatly downeld shied dispersed in chloroform by addition of another organic solvent
from 7.84 ppm (in CDCl3) to 8.29 ppm (in C6D6). This behaviour such as hexanes to it. (3) The dispersion of CoMoCAT SWNTs by
is indicative of substantial changes in conformation and the DTF–oligomers appears to be less effective than HiPCO
aggregation states in different solvent systems,18 which is SWNTs. In fact, only the long linear oligomer 8 was found to
believed to cause the different dispersion outcomes in various induce a modest degree of dispersion in chloroform as evi-
solvents. Nonpolar chlorinated solvents such as chloroform and denced by UV-Vis-NIR analysis (see Fig. S28, ESI†). This obser-
methylene chloride happen to solubilize the supramolecular vation suggests that the interactions between DTF–oligomers
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and SWNTs are dependent on the types of nanotubes. (4) The 1,4-diiodobenzene (2) (0.409 g, 1.23 mmol), PdCl2(PPh3)2
DTF group is a crucial and indispensable factor to SWNT (21.2 mg, 0.0299 mmol), CuI (11.5 mg, 0.0603 mmol), and Et3N
dispersion. This point has been conrmed by a comparative (40 mL). The solution was degassed by N2 bubbling at room
study in which the aldehyde–oligomer precursors (3, 7, 12, and temperature for 5 min, and then the resultant solution was
14) were tested for SWNT dispersion under the same conditions heated to 45 ꢂC under stirring and N2 protection overnight.
used by the DTF–oligomers. The results clearly showed that, Solids precipitated out of the reaction mixture were collected by
without DTF groups, the p-oligomers could not induce any vacuum ltration, washed with CH2Cl2 and air dried to give
effective dispersion on SWNTs in common organic solvents.
compound 3 (0.365 g, 1.09 mmol, 78% crude) as an off-white
solid. M.p. 191–194 ꢂC; IR (neat): 1696, 1595, 1417, and
1204 cmꢀ1; meaningful 1H NMR and 13C spectra of 3 could not
be obtained due to poor solubility. HRMS (MALDI-TOF, +eV) m/z
calcd for C24H14O: 334.0994; found: 334.1039 [M]+.
Conclusions
In summary, we have synthesized a series of DTF-endcapped
OPE/OPV hybrid conjugated oligomers in a linear and Z-shaped
molecular structure. The electronic and electrochemical proper-
ties of the DTF groups have been found to vary with the proper-
ties of the p-oligomer. As a strong electron donor, the DTF group
exerted a substantial quenching effect on the uorescence
emission of the p-oligomers. When the DTF-endcapped oligo-
mers were mixed with fullerenes (C60 and C70), the C]C bond of
DTF would undergo a facile oxidative cleavage reaction under air
and ambient light to form highly uorescent aldehyde-endcap-
ped oligomers as the product. A fullerene-sensitized photo-
oxygenation mechanism has been proposed to rationalize this
reaction, while C70 fullerene appeared to be a more efficient
sensitizer than C60 in promoting this unique reaction. The
consequence of this reaction is a substantial uorescence turn-on
response to fullerenes by these DTF–oligomers, suggesting
potential use in fullerene sensing and recognition. The DTF
endgroups have imparted the p-oligomers with remarkable
effectiveness at dispersing SWNTs in chloroform or methylene
chloride. The dispersion outcomes are highly solvent-dependent
and very easy to control. Based on this property, reversible
dispersion and release of SWNTs in the solution phase were
achieved, which are expected to nd usefulness in making
SWNT-based semiconducting electronic devices. In conclusion,
our current work has demonstrated that DTF is a fascinating
substituent group which not only introduce rich redox and
electronic properties, but also can bring about novel chemical
reactivities, photophysical and supramolecular properties to
organic functional materials. Continued exploration of DTF as a
versatile building block in various molecular and supramolecular
systems is anticipated to produce fruitful results.
DTF–OPE 5. A solution of thione 4 (0.109 g, 0.396 mmol) and
compound 3 (0.342 g, 0.172 mmol) in trimethylphosphite
(20 mL) was stirred and heated to 130 ꢂC for about 6 h under a
N2 atmosphere, then the excess trimethylphosphite was
removed by vacuum distillation, and the resulting crude
product was puried by silica ash column chromatography
(EtOAc–hexanes, 1 : 99) followed by recrystallization from
acetone to yield pure compound 5 (0.0500 g, 0.0418 mmol, 13%)
ꢂ
as a yellow solid. M.p. 103–104 C; IR (neat): 2916, 2846, 1571,
1414, 933 cmꢀ1; 1H NMR (500 MHz, CD2Cl2) d ¼ 7.52 (t, J ¼ 5.2
Hz, 8H), 7.22 (d, J ¼ 8.4 Hz, 4H), 6.49 (s, 2H), 2.85 (td, J ¼ 7.3, 2.6
Hz, 8H), 1.69–1.62 (m, 8H), 1.45–1.39 (m, 8H), 1.32–1.27 (m,
48H), 0.89–0.86 ppm (m, 12H); 13C NMR (75 MHz, CD2Cl2) d ¼
136.9, 134.9, 132.1, 131.9, 128.3, 126.9, 125.4, 123.5, 120.1,
113.6, 91.9, 89.9, 36.6, 36.5, 32.3, 30.3, 30.2, 29.97, 29.93, 29.7,
29.5, 28.92, 28.90, 23.0, 14.3 ppm; HRMS (MALDI-TOF, +eV) m/z
calcd for C70H98S8: 1194.5434; found: 1194.5444 [M]+.
Aldehyde–OPE 7. To an oven-dried round-bottom ask pro-
tected under N2 were charged compound 6 (0.102 g, 0.309
mmol), 1,4-diiodobenzene (2) (0.369 g, 0.679 mmol),
PdCl2(PPh3)2 (5.30 mg, 0.0075 mmol), CuI (2.80 mg, 0.014
mmol), and Et3N (50 mL). The solution was degassed by N2
bubbling at room temperature for 5 min, and then the resultant
ꢂ
solution was heated to 45 C under stirring and N2 protection
overnight. Aer the reaction was complete as checked by TLC
analysis, the solvent was removed by rotary evaporation. The
residue was diluted with CH2Cl2 and the diluted residue was
ltered through a MgSO4 pad. The solvent was removed by
vacuum evaporation and the residue was washed with hexanes
to give pure compound 7 (0.275 g, 0.237 mmol, 78%) as a yellow
solid. M.p. 123–124 ꢂC; IR (neat): 2919, 2850, 1698, 1596, 1459,
1
1212, 943 cmꢀ1; H NMR (300 MHz, CDCl3) d ¼ 10.02 (s, 2H),
Experimental
Materials
7.87 (d, J ¼ 8.4 Hz, 4H), 7.68 (d, J ¼ 8.2 Hz, 4H), 7.51 (s, 4H), 7.03
(d, J ¼ 0.9 Hz, 4H), 4.05 (t, J ¼ 6.4 Hz, 8H), 1.91–1.82 (m, 8H),
1.60–1.50 (m, 8H), 1.41–1.25 (m, 48H), 0.89–0.85 ppm (m, 12H);
13C NMR (75 MHz, CDCl3) d ¼ 191.3, 153.9, 153.7, 135.4, 132.0,
131.5, 129.8, 129.6, 123.3, 116.9, 116.8, 114.7, 113.3, 95.0, 94.0,
90.2, 87.9, 69.7, 69.6, 31.91, 31.90, 29.7, 29.6, 29.43, 29.36, 29.33,
26.1, 22.70, 22.68, 14.14, 14.12 ppm; HRMS (MALDI-TOF, +eV)
m/z calcd for C80H102O6: 1158.7676; found: 1158.7665 [M]+.
DTF-oligomer 8. A solution of thione 4 (0.190 g, 0.396 mmol)
and compound 7 (0.200 g, 0.172 mmol) in trimethylphosphite
Chemicals were purchased from commercial suppliers and
used directly without purication. HiPCO SWNTs were
purchased from Carbon Nanotechnologies Inc. CoMoCAT
SWNTs were purchased from Southwest NanoTechnologies Inc.
Thione 4,19 compounds 6 (ref. 7c and 20) and 10 (ref. 7c and 20)
were prepared according to the literature procedures.
Synthesis
4,40-(1,4-Phenylenebis(ethyne-2,1-diyl))dibenzaldehyde (3). (15 mL) was stirred and heated to 130 ꢂC for about 3 h under an
To an oven-dried round-bottom ask protected under N2 were N2 atmosphere. On completion, the excess trimethylphosphite
charged p-ethynylbenzaldehyde (1) (0.354 g, 2.72 mmol), was removed by vacuum distillation. The obtained crude
5124 | J. Mater. Chem. C, 2013, 1, 5116–5127
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Journal of Materials Chemistry C
product was puried by silica ash column chromatography (MALDI-TOF, +eV) m/z calcd for C40H26O2: 538.1933; found:
(EtOAc–hexanes, 1 : 99) followed by recrystallization from 538.1939 [M]+.
acetone to yield pure compound 8 (0.264 g, 0.131 mmol, 76%) as
DTF–oligomer 13. A solution of thione 4 (0.408 mg, 0.888
a yellow solid. M.p. 81–82 ꢂC; IR (neat): 2918, 2850, 1568, 1460, mmol) and compound 12 (0.208 g, 0.386 mmol) in trimethyl-
1212, 1059 cmꢀ1; 1H NMR (500 MHz, CD2Cl2) d ¼ 7.52–7.50 (m, phosphite (15 mL) was stirred and heated to 130 ꢂC for about 3 h
8H), 7.22 (d, J ¼ 8.6 Hz, 4H), 7.03 (s, 4H), 6.49 (s, 2H), 4.04 (td, J under a N2 atmosphere, and then the excess trimethylphosphite
¼ 6.4, 1.9 Hz, 8H) 2.84 (td, J ¼ 7.4, 1.8 Hz, 8H), 1.88–1.83 (m, was removed by vacuum distillation. The obtained crude
8H), 1.69–1.52 (m, 8H), 1.59–1.54 (m, 8H), 1.56–1.50 (m, 4 H), product was puried by silica ash column chromatography
1.45–1.37 (m, 16 H), 1.34–1.27 (m, 88H), 0.89–0.86 ppm (m, (EtOAc–hexanes, 1 : 99) to yield pure compound 13 (0.362 g,
24H); 13C NMR (75 MHz, CDCl3) d ¼ 154.1, 154.0, 136.7, 134.7, 0.258 mmol, 67%) as thick syrup. IR (neat): 2919, 2849, 1671,
132.0, 131.8, 128.4, 126.9, 125.4, 123.7, 120.5, 117.2, 117.1, 1599, 1458, 1259, 957 cmꢀ1; 1H NMR (500 MHz, CDCl3) d ¼ 7.77
114.7, 113.9, 113.7, 95.6, 94.8, 88.5, 87.0, 70.0, 32.3, 36.6, 36.5, (d, J ¼ 16.4 Hz, 2H), 7.73 (d, J ¼ 7.7 Hz, 2H), 7.60 (s, 4H), 7.56 (d,
32.3, 30.3, 30.2, 30.1, 30.0, 29.97, 29.94, 29.84, 29.77, 29.73, J ¼ 7.7 Hz, 4H), 7.34 (t, J ¼ 7.5 Hz, 2H), 7.25–7.20 (m, 6H), 6.45
29.55, 29.53, 28.93, 28.91, 26.5, 23.11, 23.09, 14.31, 14.28 ppm; (s, 2H), 2.84–2.79 (m, 8H), 1.69–1.60 (m, 8H), 1.42–1.37 (m, 8H),
HRMS (MALDI-TOF, +eV) m/z calcd for
C
126H186O4S8: 1.29–1.24 (m, 48H), 0.89–80 ppm (m, 12H); 13C NMR (75 MHz,
CDCl3) d ¼ 138.9, 137.5, 136.9, 134.9, 132.9, 132.0, 130.1, 128.9,
2019.2117; found: 2019.2097 [M]+.
1,4-Bis((E)-2-iodostyryl)benzene (11). To an oven-dried ask 128.3, 127.8, 127.5, 127.0, 125.4, 125.1, 122.7, 120.4, 113.6, 95.3,
protected under N2 were charged bisphosphonate 10 (1.03 g, 88.9, 36.6, 36.5, 32.3, 30.3, 30.1, 29.9, 29.7, 29.6, 28.96, 28.91,
2.64 mmol), NaH (0.320 g, 60%, 7.92 mmol), and dry THF (50 23.1, 18.9, 14.3 ppm; HRMS (MALDI-TOF, +eV) m/z calcd for
mL). The solution was observed to gradually turn into a dark
yellow colour at 50 ꢂC. A solution of o-iodobenzaldehyde (9)
C
86H110S8: 1398.6373; found 1398.6267 [M]+.
Aldehyde–oligomer 14. To an oven-dried round-bottom ask
(1.21 g, 5.21 mmol) in THF (20 mL) was added in small portions protected under N2 were charged compound 11 (0.260 g, 0.490
over a period of 10 min via a syringe. The reaction was kept mmol), compound 6 (0.661 g, 1.07 mmol), PdCl2(PPh3)2
under stirring at the same temperature for another 30 min (6.80 mg, 0.0970 mmol), CuI (3.60 mg, 0.0194 mmol), and Et3N
before workup. Aer the reaction was complete as checked by (100 mL). The solution was degassed by N2 bubbling at room
TLC analysis, the reaction mixture was poured into ice, and the temperature for 5 min, and then the resultant solution was
resulting solid was extracted with CH2Cl2 and the organic layer heated to 45 ꢂC under stirring and N2 protection overnight. Aer
was washed with water several times and then dried over the reaction was complete as checked by TLC analysis, the
MgSO4, concentrated under vacuum to afford compound 11 solvent was removed by rotary evaporation. The residue was
which was nally washed with methanol to give to the pure form diluted with CH2Cl2 and the diluted residue was ltered
(0.690 g, 1.29 mmol, 49%) as a yellow solid. M.p. 159–161 ꢂC; IR through a MgSO4 pad. The solution obtained was washed with
(neat): 1460, 1424, 1007, 957, 814 cmꢀ1 1H NMR (500 MHz, water, dried over MgSO4, and concentrated under vacuum to
;
CDCl3) d ¼ 7.89 (dd, J ¼ 7.9, 1.1 Hz, 2H), d 7.65 (dd, J ¼ 7.8, 1.5 give crude product 14, which was further puried by silica ash
Hz, 2H) 7.57 (s, 4H), 7.37–7.34 (m, 4H), 7.00–6.95 ppm (m, 4H); column chromatography (hexanes–EtOAc, 9 : 1) to yield pure
13C NMR (75 MHz, CDCl3) d ¼ 140.2, 139.7, 136.7, 132.6, 131.1, compound 14 (0.480 g, 0.352 mmol, 72%) as a yellow solid. M.p.
129.0, 128.4, 127.2, 126.2, 100.6 ppm; HRMS (EI-TOF, +eV) m/z 153–155 ꢂC; IR (neat): 2919, 2851, 2204, 1704, 1598, 1420, 1340,
calcd for C22H16I2: 533.9341; found 533.9336 [M]+.
1213 cmꢀ1; 1H NMR (500 MHz, CDCl3) d ¼ 10.00 (s, 2H), 7.84–
Aldehyde–OPV 12. To an oven-dried round-bottom ask 7.81 (m, 8H), 7.74 (d, J ¼ 7.9 Hz, 2H), 7.65 (d, J ¼ 8.2 Hz, 4H),
protected under N2 were charged compound 11 (0.301 g, 0.561 7.58–7.56 (m, 4H), 7.35 (t, J ¼ 7.7 Hz, 2H) 7.25–7.22 (m, 4H), 7.06
mmol), compound 1 (0.183 g, 1.40 mmol), PdCl2(PPh3)2 (9.80 (s, 4H), 4.03 (t, J ¼ 6.3 Hz, 8H), 1.87–1.81 (m, 4H), 1.76–1.71 (m,
mg, 0.0139 mmol), CuI (5.30 mg, 0.027 mmol), and Et3N (50 4H), 1.56–1.46 (m, 8H), 1.41–1.31 (m, 12H), 1.27–1.16 (m, 36H),
mL). The solution was degassed by N2 bubbling at room 0.86–0.82 ppm (m, 12H); 13C NMR (75 MHz, CDCl3) d ¼ 191.3,
temperature for 5 min, and then the resultant solution was 153.9, 153.6, 138.8, 137.1, 135.3, 132.7, 132.0, 129.8, 129.5,
heated to 45 ꢂC under stirring and N2 protection overnight. Aer 128.6, 127.3, 127.2, 126.9, 124.7, 122.4, 117.2, 116.8, 115.2,
the reaction was complete as checked by TLC analysis, the 113.1, 93.98, 93.95, 91.1, 90.3, 77.2, 69.9, 69.6, 45.8, 31.89, 31.87,
solvent was removed by rotary evaporation. The residue was 29.7, 29.61, 29.59, 29.56, 29.5, 29.4, 29.2, 26.1, 25.9, 22.7, 14.1
diluted with CH2Cl2 and the diluted residue was ltered ppm; HRMS (MALDI-TOF, +eV) m/z calcd for C96H114O6:
through a MgSO4 pad. The solution obtained was washed with 1362.8615; found: 1362.8542 [M]+.
water, dried over MgSO4, and concentrated under vacuum to
DTF–oligomer 15. A solution of thione 4 (0.169 g, 0.354
give crude product 12, which was further puried by silica ash mmol) and compound 14 (0.210 g, 0.153 mmol) in trimethyl-
column chromatography (hexanes–EtOAc, 95 : 15) to yield pure phosphite (15 mL) was stirred and heated to 130 ꢂC for about 3 h
compound 12 (0.197 g, 0.366 mmol, 65%) as a yellow solid. M.p. under a N2 atmosphere, and then the excess trimethylphosphite
175–178 ꢂC; IR (neat): 1695, 1598, 1389, 1293, 1206, 1158, 1013 was removed by vacuum distillation. The obtained crude
1
cmꢀ1; H NMR (500 MHz, CDCl3) d ¼ 10.04 (s, 2H), 7.91–7.87 product was puried by silica ash column chromatography
(m, 4H), 7.76–7.70 (m, 8H), 7.59–7.58 (m, 4H), 7.40 (t, J ¼ 7.4 Hz, (EtOAc–hexanes, 1 : 99) followed by recrystallization from
2H), 7.30–7.23 ppm (m, 2H); a meaningful 13C NMR spectrum of acetone to yield pure compound 15 (0.240 g, 0.107 mmol, 71%)
12 could not be obtained due to its limited solubility. HRMS as a yellow solid. M.p. 92–93 ꢂC; IR (neat): 2918, 2948,
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Journal of Materials Chemistry C
Paper
1601,1565, 1419, 1383, 1213, 1027 cmꢀ1 1H NMR (500 MHz,
;
Acknowledgements
CD2Cl2) d ¼ 7.85 (d, J ¼ 16.4 Hz, 2H), 7.77 (d, J ¼ 7.9 Hz, 2H),
7.61 (s, 4H), 7.57 (dd, J ¼ 7.7, 1.0 Hz, 2H), 7.49 (d, J ¼ 8.4 Hz,
4H), 7.37 (td, J ¼ 7.5, 1.0 Hz, 2H), 7.29–7.25 (m, 4H), 7.18 (d, J ¼
8.4, 4H), 7.07 (d, J ¼ 0.8 Hz, 4H), 6.46 (s, 2H), 4.04 (td, J ¼ 6.7, 3.1
Hz, 8H), 2.84 (td, J ¼ 6.6, 0.9 Hz, 8H), 1.86–1.81 (m, 4H), 1.77–
1.71 (m, 4H), 1.69–1.62 (m, 8H), 1.56–1.50 (m, 4H), 1.45–1.35
(m, 16H), 1.34–1.17 (m, 92H), 0.90–0.82 ppm (m, 24H); 13C NMR
(75 MHz, CD2Cl2) d ¼ 154.0, 139.1, 137.5, 136.7, 134.6, 132.9,
132.0, 130.2, 129.0, 128.4, 127.7, 127.6, 127.2, 126.9, 125.3,
125.1, 122.8, 120.6, 117.2, 114.6, 114.3, 113.7, 95.6, 93.7, 91.8,
87.1, 70.2, 70.1, 36.6, 36.5, 32.32, 32.29, 30.3, 30.2, 30.1, 30.0,
29.98, 29.94, 29.89, 29.82, 29.79, 29.76, 29.74, 29.6, 29.56, 29.54,
28.94, 28.92, 26.6, 26.4, 23.12, 23.09, 14.32, 14.29 ppm; HRMS
(MALDI-TOF, +eV) m/z calcd for C142H198O4S8: 2223.3056; found
2223.3082 [M]+.
The authors thank Natural Sciences and Engineering Research
Council of Canada (NSERC) and Canada Foundation for Inno-
vation (CFI) for funding support.
Notes and references
1 (a) D. Lorcy, R. Carlier, A. Robert, A. Tallec, P. Le Magueres
and L. Ouahab, J. Org. Chem., 1995, 60, 2443–2447; (b)
J. Roncali, J. Mater. Chem., 1997, 7, 2307–2321; (c)
N. Bellec, K. Boubekeur, R. Carlier, P. Hapiot, D. Lorcy and
A. Tallec, J. Phys. Chem. A, 2000, 104, 9750–9759; (d)
R. Carlier, P. Hapiot, D. Lorcy, A. Robert and A. Tallec,
Electrochim. Acta, 2001, 46, 3269–3277; (e) J. Massue,
N. Bellec, M. Guerro, J.-F. Bergamini, P. Hapiot and
D. Lorcy, J. Org. Chem., 2007, 72, 4655–4662; (f) Y. Zhao,
G. Chen, K. Mulla, I. Mahmud, S. Liang, P. Dongare,
D. W. Thompson, L. N. Dawe and S. Bouzan, Pure Appl.
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4600–4608; (c) K. Naka, S. Inagi, Y. Murachi and Y. Chujo,
J. Polym. Sci., Part A: Polym. Chem., 2006, 44, 2027–2033; (d)
Synthesis of 14 by fullerene-sensitized oxidation of 15. To a
solution of compound 15 (10.3 mg, 0.00462 mmol) in benzene
(1 mL) was added C60 fullerene (10.1 mg, 0.0140 mmol). The
reaction mixture was stirred at room temperature for 20 h in the
presence of air. The reaction mixture was then diluted and
extracted with ethylacetate. The organic layer was washed with
water, dried over MgSO4, and concentrated under vacuum to
give crude 14. Pure compound 14 (5.60 mg, 0.00410 mmol, 89%)
was obtained aer silica column chromatographic separation
(hexanes–EtOAc, 9 : 1) and its molecular structure was
`
P. Frere and P. J. Skabara, Chem. Soc. Rev., 2005, 34, 69–98;
1
conrmed by H, 13C NMR, and MALDI-TOF MS analyses.
(e) T. Uemura, K. Naka and Y. Chujo, in New Synthetic
Methods, Springer, Berlin, 2004, vol. 167, pp. 81–106.
3 (a) N. Cocherel, P. Leriche, E. Ripaud, N. Gallego-Planas,
P. Frere and J. Roncali, New J. Chem., 2009, 33, 801–806; (b)
E. Ripaud, P. Leriche, N. Cocherel, T. Cauchy, P. Frere and
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Apparatus
All reactions were conducted in standard, dry glassware and
under an inert atmosphere of nitrogen unless otherwise noted.
Evaporation and concentration were carried out with a water-
aspirator. Flash column chromatography was performed using
240–400 mesh silica gel, and thin-layer chromatography (TLC)
was carried out with silica gel F254 covered on plastic sheets
and visualized by UV light. Melting points (m.p.) were measured
with the SRS OptiMelt melting point apparatus and are uncor-
rected. 1H and 13C NMR spectra were recorded on a Bruker
Avance 500 MHz spectrometer and a Bruker Avance III 300 MHz
multinuclear spectrometer. Chemical shis (d) are reported in
ppm downeld from the signal of the internal reference SiMe4
for 1H and 13C NMR spectra. Coupling constants ( J) are given in
Hz. Infrared spectra (IR) were recorded on a Bruker tensor
27 spectrometer. UV-Vis-NIR absorption spectra were recorded
on a Cary 6000i spectrophotometer. Emission spectra were
recorded on a Photon Technology International (PTI) Quanta-
master 6000 spectrouorometer equipped with a continuous
xenon arc lamp as the excitation source. Atomic force micros-
copy (AFM) images were taken with a Q-Scope AFM operated in
the tapping mode. Raman spectra were recorded on a Horiba
Jobin Yvon confocal Raman spectrometer operated at a laser
´
´
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