Noncovalent functionalization and solubilization of carbon nanotubes by using a conjugated Zn-porphyrin polymer

Article abstract of DOI:10.1002/chem.200600302

A highly soluble, conjugated Zn-porphyrin polymer was synthesized and found to strongly interact with the surface of single-walled carbon nanotubes, producing a soluble polymernanotube complex. Successful complexation required the addition of trifluoroace

Full text of DOI:10.1002/chem.200600302

FULL PAPER
DOI: 10.1002/chem.200600302
Noncovalent Functionalization and Solubilization of Carbon Nanotubes by
Using a Conjugated Zn–Porphyrin Polymer
Fuyong Cheng and Alex Adronov*[a]
Abstract: A highly soluble,conjugated
Zn–porphyrin polymer was synthesized
and found to strongly interact with the
surface of single-walled carbon nano-
tubes,producing a soluble polymer–
nanotube complex. Successful complex-
ation required the addition of trifluoro-
acetic acid to the solvent (THF). It was
found that the complex remained solu-
ble after excess free polymer was re-
moved from solution,and could be
centrifuged at high speed with no ob-
servable sedimentation. Furthermore,
the polymer–nanotube assembly result-
ed in enhanced planarization and con-
jugation within the porphyrin polymer,
which was manifested in a 127 nm
bathochromic shift of the Q-band ab-
sorption. Control experiments with the
Zn–porphyrin monomer indicated that
homogeneous solutions could be pre-
pared by means of sonication,but the
monomer–nanotube interactions were
significantly weaker,leading to nano-
tube precipitation within minutes.
Atomic force microscopy (AFM) stud-
ies indicated that the polymer enables
exfoliation of nanotube bundles and is
able to “stitch” multiple nanotubes to-
gether into a series of long,intercon-
nected strands.
Keywords: absorption
spectros-
A
nanotubes
·
noncovalent inter-
A
Introduction
method involves physical adsorption of molecules capable
of p-stacking or van der Waals interactions with the conju-
gated aromatic nanotube sidewall. This strategy preserves
the electronic and structural integrity of SWNTs,permitting
the use of both their conductivity and strength properties in
eventual applications. For this reason,noncovalent attach-
ment of numerous aromatic species to the nanotube surface
has been investigated.[13–28] Most notably,conjugated poly-
mers such as poly(phenylenevinylene)[17–19] and poly(aryl-
The functionalization and subsequent dissolution of single-
walled carbon nanotubes (SWNTs) has received significant
attention over the past several years and has resulted in the
development of a number of functionalization methods.
These methods can be divided into two broad categories,
namely,covalent and noncovalent (supramolecular) ap-
proaches.[1–5] Covalent functionalization has been widely in-
vestigated,and has produced an array of modified nanotube
structures bearing both small molecules and polymers.[6–10]
However,this strategy significantly perturbs the conjugated
p system of a carbon nanotube and can result in dramatic
changes in its electronic and structural properties.[11,12]
Therefore,covalently modified SWNTs may not be suitable
in applications that rely on the high conductivity or mechan-
ical strength of SWNTs. Conversely,the supramolecular
A
as pyrene,[13–16,20] anthracene,[22] and phthalocyanine[23] deriv-
atives that bind to SWNTs through p-stacking interactions
have been used to decorate the nanotube surface and
modify solubility and electronic properties. More recently,
supramolecular functionalization of nanotubes with porphy-
A
flat,planar aromatic structures are ideal for p-stacking inter-
actions with the aromatic sidewalls of SWNTs and they ex-
hibit unique photophysical and electrochemical proper-
ties.[30] Nakashima and co-workers were first to show that
Zn–protoporphyrins (ZnPP) can bind to the SWNT surface,
resulting in stable nanotube–ZnPP solutions in DMF as long
as excess porphyrin is present in solution.[24] However,upon
removal of excess ZnPP,it was found that the nanotube–
ZnPP complex precipitates within a few days. Sun and co-
[a] Dr. F. Cheng,Prof. Dr. A. Adronov
Department of Chemistry
McMaster University
Hamilton,Ontario L8S 4M1 (Canada)
Fax : (+1)905-521-2773
E-mail: adronov@mcmaster.ca
Supporting information for this article is available on the WWW
under http://www.chemeurj.org/ or from the author.
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5053

workers have reported selective interactions of porphyrins
with SWNTs,allowing the separation of semiconducting
nanotubes from metallic nanotubes.[25] Again,removal of
excess porphyrin from solution resulted in the recovery of
insoluble SWNTs,indicating that the SWNT–porphyrin
complex could easily be dissociated. Also in their work,it
was found that free-base porphyrins interacted with SWNTs
in THF,but Zn–porphyrins exhibited no solubilizing interac-
tions (a result somewhat contradictory to that of Nakashi-
ma). Additionally,Kamat and co-workers reported the use
of protonated porphyrins to assemble SWNTs into supramo-
lecular porphyrin–nanotube aggregates.[27] These macroscop-
ic nanotube bundles could be suspended in THF by means
of sonication,but were easily sedimented by centrifugation,
indicating a lack of molecular-level solubility.
rather than free-base porphyrins,it nevertheless exhibited
strong interactions with the nanotube surface in THF upon
addition of small quantities of trifluoracetic acid (TFA).
This interaction resulted in porphyrin coplanarization and a
consequent increase in the effective conjugation within the
polymer (Figure 1). The increased conjugation leads to a
greater degree of electron delocalization and a smaller
HOMO–LUMO gap,which results in a large bathochromic
shift of the Q band in the polymer absorption spectrum.
Results and Discussion
Synthesis and characterization: Synthesis of the target por-
phyrin polymer 2 was accomplished through minor modifi-
cation of previously published procedures (Scheme 1).[33]
Briefly, treatment of commercially available methyl 3,4,5-tri-
hydroxybenzoate with three equivalents of 1-bromohexade-
cane resulted in methyl 3,4,5-tris(hexadecyloxy)benzoate
Building on these results,we were interested in examining
macromolecular structures bearing multiple porphyrin units
in an attempt to increase the interaction strength through
multivalent binding. Conjugated porphyrin polymers con-
taining butadiyne bridges linked directly to the porphyrin
(3),which was reduced with LiAlH and subsequently oxi-
4
[31]
meso-carbon atoms,first reported by Anderson et al.,
ex-
dized with MnO2 to give aldehyde 5 in a 74% yield (over
three steps). Subsequent treatment of 5 with pyrrole,fol-
lowed by condensation with trimethylsilylpropynal and met-
alation with ZnII acetate afforded the trimethylsilyl (TMS)-
hibit unique spectroscopic and redox properties that make
them promising candidates for applications in nonlinear
optics and molecular electronics.[32,33] The fully conjugated,
rigid structure of these polymers,coupled with their strong
electron-donating properties,make them highly complemen-
tary to the conjugated,rigid,but electron-accepting
SWNTs.[34] It was therefore reasonable to expect that the in-
teraction between SWNTs and conjugated porphyrin poly-
mers would be much stronger than the analogous interaction
with monomeric porphyrins. To date,only three examples of
soluble,conjugated porphyrin-containing polymers have
been reported,each of which was rendered soluble by ali-
phatic side chains linked via ester[31] or amide[32] bonds.
Here we report the synthesis of a highly stable and soluble
Zn–porphyrin polymer that has three hexadecyl branches
linked via robust ether bonds to the aryl substituents on
both of the porphyrin meso positions. It was found that,al-
though this target polymer was composed of Zn–porphyrins
protected monomer,which was deprotected with tetra
N
N
AHCTREUNG
1 (24% yield over four steps). Metalation of the monomer
with Zn is important as it improves the stability of the por-
phyrin,allows polymerization to occur cleanly without cata-
lyst coordination/deactivation (known to occur with free-
base porphyrins),and improves the solubility of the product
in coordinating solvents such as THF. The Glaser–Hay cou-
pling of monomer 1 using CuCl and N,N,N’,N’-tetramethyl-
A
in rapid polymerization at room temperature,allowing the
isolation of polymer 2 in a 90% yield.
1
The H NMR spectrum of polymer 2 in CDCl3 exhibited
all the expected signals for the polymer repeat units and
confirmed the disappearance of terminal alkyne protons at
Figure 1. Supramolecular assembly of the conjugated Zn–porphyrin polymer with SWNTs,forming a soluble polymer–nanotube complex.
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Carbon Nanotubes
FULL PAPER
shifts from 625 nm in monomer
1
to 793 nm in polymer 2,
caused by the extended conju-
gation and significant electronic
communication between the
porphyrin repeat units. Addi-
tionally,the polymer exhibits a
broad fluorescence emission
band at 816 nm,whereas the
monomer emits at 638 and
691 nm. This further confirms
that the polymer has a much
smaller HOMO–LUMO gap
than that of the monomer.
Supramolecular
interactions
with SWNTs: The observed
electronic and structural prop-
erties of the polymer encour-
aged us to study its supramolec-
ular interactions with SWNTs.
In all of the studies,the
SWNTs,prepared by the high-
Scheme 1. Synthesis of 2. Conditions: i) RBr,K 2CO3,KI,DMF,85%; ii) LiAlH
4,THF,88%; iii) MnO
,
2
pressure
(HiPco)
carbon
disproportionation
monoxide
CH2Cl2,99%; iv) pyrrole,CH 2Cl2,95%; v) 3-trimethylsilylpropynal,BF 3·OEt2,DDQ,CH 2Cl2,28%; vi) Zn-
(OAc)2,CHCl 3/MeOH,95%; vii) TBAF,CH 2Cl2,96%; viii) CuCl,TMEDA,CH 2Cl2/pyridine,90%.
ACHTREUNG
process,were used as purchased
without further treatment. As
d=4.16 ppm (see the Supporting Information). Gel permea-
tion chromatography (GPC),relative to polystyrene stand-
ards,resulted in a polymer number-average molecular
weight (Mn) of 45700 gmolꢀ1,with a polydispersity of 1.93,
in accordance with previous examples of similar polymeriza-
tion reactions.[32,33] Because it is well known that GPC analy-
sis of rigid-rod polymers using polystyrene standards can
overestimate the molecular weight,[35] we compared our re-
sults with those obtained from GPC analyses of monomer 1.
The monomer gave an Mn value of 3250 gmolꢀ1,which is
higher than the theoretical molar mass of 2016.51 gmolꢀ1
for this compound. We therefore estimate that the degree of
polymerization for 2 was approximately 14 repeat porphyrin
units. Unfortunately,all our attempts to perform matrix-as-
sisted laser desorption/ionization time-of-flight (MALDI-
TOF) mass spectrometry (MS) on polymer 2 resulted in no
observable signal,presumably due to the difficulty of trans-
ferring the polymer structures into the gas phase. Based on
the GPC data and previous molecular modeling and crystal-
lography studies,[36] the average length of the polymer was
estimated to be approximately 18 nm. Polymer 2 was found
to be highly soluble in CH2Cl2 and CHCl3 in the presence of
small quantities of pyridine (1% v/v). However,this poly-
mer was most soluble in THF,in which coordination of the
furan oxygen to the polymer Zn atoms greatly diminishes
polymer aggregation and facilitates dissolution.[33]
polymer 2 was found to be most soluble in THF,this was
chosen as the optimal solvent for investigating the supramo-
lecular interactions with the SWNTs. Unfortunately,mixing
and sonication of 2 and the SWNTs in THF resulted in no
observable nanotube solubility,consistent with previous ob-
servations of Sun and co-workers.[25] It was postulated that
coordination of THF to the Zn–porphyrin repeat units pro-
hibits the polymer from closely interacting with the carbon-
nanotube surface. However,when the same experiment was
conducted in acidified THF,containing 5% trifluoroacetic
acid (TFA) (v/v),we were surprised to observe a high
ꢀ1
degree of nanotube solubility,reaching close to 1 mgmL
In a typical experiment,a sample of SWNTs (10 mg) was
.
added to a solution of 1 or 2 (30 mg) in acidified THF
(10 mL). The resulting suspension was sonicated for one
hour at room temperature and then diluted with a further
50 mL of the acidified THF. This produced a homogeneous
solution that was then filtered through a 450 nm-pore Teflon
membrane and was repeatedly washed with acidified THF
until the filtrate was colorless; this indicated the removal of
all excess porphyrin monomer 1 or polymer 2. The residue
G
was then collected and the solid was resuspended in acidi-
fied THF (10 mL) with sonication for five minutes. When
this procedure was carried out with monomer 1,a homoge-
neous solution initially formed,but this solution was not
stable and the SWNTs precipitated after standing for a few
minutes (Figure 2B). In contrast,when polymer 2 was used,
a very dark and stable solution was obtained after sonication
for 5 min (Figure 2D),leaving practically no observable in-
soluble nanotube residue. This solution remained stable
The UV spectrum of polymer 2 closely resembles that of
previously reported polymers of this type (see Figure S3 in
the Supporting Information).[32,33] It reveals a broadened
Soret band at 468 nm and a long-wavelength Q band,which
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5055

F. Cheng and A. Adronov
Notably,the absorption of 2 in acidified THF was almost
identical to that in neat THF,which suggests that TFA nei-
ther changes the electronic structure of the polymer,nor af-
fects the Zn ions coordinated to the porphyrin repeat
units.[38] The exact role of TFA in promoting supramolecular
interactions between SWNTs and the zinc–porphyrin poly-
mer is not fully understood and is currently under investiga-
tion. Nevertheless,the interaction between polymer 2 and
the SWNTs is evident from changes in the Soret and Q
Figure 2. Photograph of four samples in acidified THF (containing 5%
TFA): A) pristine full-length SWNTs; B) monomer 1/SWNT mixture;
C) polymer 2; D) polymer 2/SWNT mixture,which forms a dark,homo-
geneous solution.
bands of the polymer in the polymer–SWNT complex. Fig-
N
ure 3d displays an increase in the intensity of the longer
wavelength shoulder of the Soret band,shifting the lmax
from 467 to 498 nm. Additionally,the Q band shifted from
796 to 923 nm in the complex. However,the absorption
spectrum of the polymer–nanotube complex also exhibits
absorption bands at 467 and 796 nm,corresponding to free
polymer in solution. Clearly,the inherent solubility of the
polymer results in some polymer chains desorbing from the
nanotube surface,thus creating an equilibrium between free
and bound polymer in solution.
upon standing for several weeks,with no sedimentation
even after centrifugation for 20 min at 5000 rpm. This result
indicates that the multivalent polymer–nanotube interaction
is very strong,and allows the retention of significant
amounts of polymer bound to the nanotube surface even
after excess unbound polymer has been removed.[37] Clearly,
the flat,planar aromatic porphy
rins are responsible for the
The origin of the absorption red-shifts in the UV-visible
spectrum of the polymer–SWNT complex is likely a copla-
narization of the porphyrins in the polymer. It is known that
there is no steric barrier to rotation about the butadiyne
links in the porphyrin polymer structure,which allows the
free polymer to adopt conformations that are not entirely
coplanar.[32,33] Anderson and co-workers applied bidentate
binding strength,while the six long aliphatic chains append-
ed to each porphyrin repeat unit impart a high degree of
solubility. The fact that porphyrin polymer 2 can be used to
form a very stable and highly soluble polymer–SWNT com-
posite,whereas the mono meric porphyrin results in an un-
A
stable suspension,implies that multivalent binding and the
enhanced p conjugation of polymer 2 are responsible for
strengthening the supramolecular nanotube interactions. As
an additional control experiment,when only the SWNTs
were suspended in acidified THF under the conditions out-
lined above,nanotube solubility was not observed to any
extent.
Formation of the polymer–SWNT complex is also evident
from changes in the UV-visible spectrum of the polymer.
Figure 3 shows the absorption spectra of polymer 2 in THF,
polymer 2 in acidified THF,unfunctionalized SWNTs in
DMF,and the polymer 2–SWNT complex in acidified THF.
ligands,such as 44,
’-bipyridine or 1,4-diazabicyclo-
AHCTREUNG
complex with porphyrin polymers.[33] It was found that this
self-assembly process restricts the porphyrin rotation about
the butadiyne links,which increases the coplanarity between
neighboring porphyrins along the polymer chain. This in-
creased coplanarity extends the p-conjugation length,result-
ing in a redshift of the electronic absorption spectrum by
75 nm. In our supramolecular nanotube assembly,a similar
coplanarity induction is likely achieved due to the rigid
nanotube sidewall structure. Here,the nanotube acts as a
template that restricts torsional disorder within the polymer
backbone and induces a coplanar arrangement of porphyrin
repeat units (for a schematic illustration,see Figure 1). The
consequent extension of p conjugation is manifested in the
observed large absorption redshift of 127 nm.
The soluble polymer–SWNT complex was also investigat-
ed by using atomic force microscopy (AFM). Several drops
of the polymer–nanotube solution in acidified THF were
spin coated onto freshly cleaved mica. Figure 4A depicts an
amplitude image of this sample obtained by tapping mode
AFM. It is clear that numerous features resembling nano-
tube-containing structures are observable on the substrate.
Based on height profile analysis,it seems that these struc-
tures are mostly individual nanotubes coated with the por-
phyrin polymer. This can be more clearly seen in the higher-
magnification height image (Figure 4B),in which a range of
heights was observed for different strands corresponding to
a progression from a few single,uncoated SWNT segments
(i) exhibiting heights of approximately 1 nm,to polymer-
Figure 3. UV/Vis absorption spectra of a) 2 in THF,b) 2 in acidified
THF,c) SWNTs in DMF,and d) the mixture of polymer 2 and SWNTs in
acidified THF. a.u.=arbitrary units.
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Carbon Nanotubes
FULL PAPER
development of light-harvesting photovoltaic systems and
other optoelectronic devices.
Experimental Section
General: Single-walled carbon nanotubes (SWNTs) were purchased from
Carbon Nanotechnologies,Inc. (Houston,TX). All reagents and solvents
were purchased from commercial suppliers and used as received. Atomic
force microscopy was carried out by using a Digital Instruments Nano-
Scope IIIa Multimode AFM,with samples prepared by spin coating
(2500 rpm) onto freshly cleaved mica substrates. The images were record-
ed with standard tips in the tapping mode at a scan rate of 1.0 Hz. FTIR
analyses were performed on a BIO-RAD FTS-40 instrument. NMR spec-
troscopy was performed on a Bruker 200,500,or 600 MHz instrument.
UV-visible spectra were measured by using a Cary 50 UV-visible spectro-
photometer. Ultrasonication was carried out in a Banson Ultrasonics
B1510 bath sonicator. High-resolution (HR) electrospray ionization
(ESI) MS measurements were carried out on the Micromass Ultima
Global instrument (quadrupole time-of-flight) and high-resolution
MALDI-MS analyses were performed on the Waters/Micromass MALDI
Micro instrument (a-cyano-4-hydroxycinnamic acid as the matrix). Filtra-
tion was performed through a 450 nm-pore Teflon membrane (Millipore).
Polymer molecular weight and polydispersity index (PDI) were estimated
from gel permeation chromatography (GPC) analyses by using a Waters
2695 Separations Module equipped with a Waters 2996 photodiode array
detector,a Waters 2414 refractive-index detector,a Waters 2475 Multi-
lfluorescence detector,and four Polymer Labs PLgel individual pore-size
columns. Polystyrene standards were used for calibration,and THF was
Figure 4. AFM images (scale barsffi1 mm) of polymer–SWNT complexes
spin cast from acidified THF. A) AFM amplitude image of the SWNT–
polymer complex on freshly cleaved mica (white box indicates region
magnified in B). B) Higher magnification AFM height image showing
the polymer coating on nanotube strands (white); arrows indicate loca-
tions where cross-sectional analysis was performed to determine feature
heights,shown at right.
coated SWNTs (ii,iii) that make up the majority of the ob-
served features with heights of approximately 5 to 6 nm.
These values are consistent with estimated dimensions of a
single SWNT coated with polymer 2 (see Figure S5 in the
Supporting Information). Interestingly,the height analysis of
some thicker regions (such as iv) indicates heights in the
range of 10 to 12 nm,which match well with the expected
height of two overlapping polymer-coated nanotubes. In
some regions,heights corresponding to three or more over-
lapping nanotubes were also found. These observations indi-
cate that sonication in the presence of polymer 2 allows de-
bundling of SWNTs to some extent,and the stabilization of
individual nanotubes in solution. In addition,the AFM
image indicates that polymer-coated nanotubes form long,
interconnected strands. Considering that the nanotubes,on
average,range in length from 0.5 to 3 mm,it seems that the
porphyrin polymers are capable of “stitching” individual
nanotubes together into a series of long,interconnected
nanofibers that span distances of more than 5 mm (Fig-
ure 4A).
used as the eluent at a flow rate of 1.0 mLminꢀ1
.
Synthesis
Methyl 3,4,5-tris(hexadecyloxy)benzoate (3): A mixture of trihydroxyl-
benzoate methylester (10.0 g,54 mmol),1-bromohexadecane (100.0 g,
328 mmol,6 equiv),K 2CO3 (89.0 g,648 mmol,12 equiv),and KI (27.0 g,
162 mmol,3 equiv) in DMF (1 L) was heated at reflux for 24 h under an
argon atmosphere. The DMF was evaporated under vacuum and the
crude product was dissolved in CH2Cl2 (1 L),and washed with water. The
solvent was evaporated under vacuum and the residue was dissolved in a
minimum of CH2Cl2 and precipitated into MeOH. Upon filtration,wash-
ing with MeOH,and drying,a white powder was obtained (40.0 g,85%).
1H NMR (CDCl3,200 MHz): d=0.87 (t, J=6.71 Hz,9H),1.25–1.30 (m,
39H),1.40–1.55 (m,6H),1.65–1.85 (m,6H),3.88 (s,3H),4.00 (t,
6.36 Hz,6H),7.24 ppm (s,2H);
J=
13C NMR (CDCl3,50 MHz): d=14.1,
22.7,26.1,29.3,29.7,30.3,31.9,52.1,69.1,73.5,107.9,124.6,142.3,152.8,
ꢀ1
166.4 ppm; IR (KBr): n˜ =2920,2853 (CH ),1719 (C =O),1220,1118 cm
2
(C O); HRMS (ESI): m/z calcd for C56H104O5 [M]+: 856.7884; found:
ꢀ
856.7865.
Conclusion
3,4,5-Tris(hexadecyloxy)benzyl alcohol (4): Compound
3
(33.0 g,
38.5 mmol) in anhydrous THF (200 mL) was added dropwise to a suspen-
sion of LiALH4 (3.66 g,96.2 mmol) in anhydrous THF (100 mL) at 0 8C.
Then the resulting mixture was warmed to room temperature,stirred for
2 h,and re-cooled to 0 8C before water was added to quench the excess
of LiALH4. The mixture was extracted with CH2Cl2 (100 mL) followed
by additional CH2Cl2 (2”50 mL). The combined extracts were washed
with H2O (3”100 mL) dried over Na2SO4,and filtered. The filtrate was
evaporated to dryness and 4 was obtained as a white solid (28.0 g,88%).
1H NMR (CDCl3,200 MHz): d=0.87 (t, J=6.71 Hz,9H),1.25–1.30 (m,
39H),1.46–1.50 (m,6H),1.67–1.82 (m,6H),3.89–3.99 (m,6H),4.58 (d,
J=5.51 Hz,2H),6.55 ppm (s,2H); 13C NMR (CDCl3,50 MHz): d=14.1,
22.7,26.1,29.4,29.7,30.3,31.9,65.7,69.1,73.4,105.3,136.0,138.1,
Highly soluble,conjugated porphyrin polymers are capable
of strong supramolecular interactions with SWNTs and
result in the formation of very stable and highly soluble
polymer–SWNT nanocomposites. It was found that addition
A
of TFA to the polymer–nanotube solution greatly enhanced
the supramolecular interaction. The polymer–nanotube as-
sembly process induces a coplanarization in the polymer
repeat units,causing enhanced conjugation and a 127 nm
bathochromic shift of the Q-band absorption. In addition,
AFM studies indicate that the polymer can exfoliate nano-
tube bundles and “stitch” multiple nanotubes together into
long strands. The broad absorption spectrum of the poly-
mer–nanotube complex,ranging from the UV to the near-
IR,coupled with the high nanotube solubility,opens this
novel supramolecular system to potential applications in the
ꢀ1
ꢀ
153.3 ppm; IR (KBr): n˜ =3416 (O H),2920,2852 cm
(CH2); HRMS
(ESI): m/z calcd for C55H105O4 [M+1]+: 829.8013; found: 829.8050.
3,4,5-Tris(hexadecyloxy)benzaldehyde (5): Activated MnO2 (40 g,0.46
mol) was added to a solution of 4 (20.0 g,24.1 mmol) in anhydrous
CH2Cl2 (300 mL) at room temperature,and the resulting suspension was
stirred for 6 h. The reaction mixture was filtered through Celite with
CH2Cl2 (5”50 mL) as the eluent. The solvent was removed under
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5057

F. Cheng and A. Adronov
vacuum to give compound 5 as a white powder (20.0 g,99%). 1H NMR
(CDCl3,200 MHz): d=0.87 (t, J=6.71 Hz,9H),1.25–1.30 (m,39H),
1.46–1.50 (m,6H),1.62–1.86 (m,6H),4.08–3.99 (m,6H),7.08 (s,2H),
9.83 ppm (s,1H); 13C NMR (CDCl3,50 MHz): d=14.1,22.7,26.1,29.4,
13C NMR (CDCl3,50 MHz): d=14.1,22.7,26.1,26.3,29.4,29.7,30.5,
31.9,69.2,73.6,83.9,85.9,100.0,114.2,122.7,131.1,133.0,136.9,137.7,
ꢁ ꢀ
150.4,150.9,152.3 ppm; IR (KBr): n˜ =2921,2852 (CH 2),3311 (C C H),
2095 cmꢀ1 (C C); UV/Vis (THF): lmax (loge”103)=433 (5.50),444
ꢁ
(5.54),577 (4.40),625 nm (4.55 mol ꢀ1 dm3 cmꢀ1); HR-MALDI-MS: m/z
calcd for C132H212N4O6Zn [M]+: 2013.5698; found: 2013.5618.
29.7,30.4,31.9,69.2,73.6,107.8,131.4,143.8,153.5,191.3 ppm; IR (KBr):
ꢀ1
n˜ =2917,2849 (CH 2),1693 cm
(C=O); HRMS (ESI): m/z calcd for
C55H102O4 [M]+: 826.7778; found: 826.7795.
Polymer2
:
CuCl (1.02 g,10.27 mmol) and TMEDA (1.55 mL,
10.27 mmol) were added to a vigorously stirred solution of 1 (0.25 g,
0.12 mmol) in CH2Cl2 (200 mL) and pyridine (1.9 mL) with dry air bub-
bled through it. After 30 min,the reaction mixture was washed repeated-
ly with water and the solvents were evaporated. The residue was dis-
solved in a minimum of chloroform/1% pyridine and precipitated into
methanol. The precipitate was washed twice with methanol (2”50 mL)
and vacuum dried to yield polymer 2 (0.23 g,90%). 1H NMR (CDCl3/
1% [D5]pyridine,500 MHz): d=0.86–0.81 (m,18H),2.00–1.19 (m,56H),
4.19 (brs,8H),4.35 (brs,4H),7.42 (s,4H),9.08 (brs,4H),9.90 ppm
(brs,4H); 13C NMR (CDCl3/1% [D5]pyridine,125 MHz): d=14.0,22.60,
22.64,26.2,26.4,29.28,29.34,29.5,29.7,29.79,29.84,30.7,31.8,31.9,69.6,
73.5,100.2,114.8,123.7,130.8,133.1,138.2,150.3,151.3,153.1 ppm; IR
2,2’-{[3,4,5-Tris(hexadecyloxy)phenyl]methylene}bis(1H-pyrrole) (6):
solution of 5 (20.0 g,8.62 mmol) in pyrrole (200 mL) was degassed by
bubbling with Ar for 30 min,and then TFA (0.6 mL) was added. The so-
A
ACHTREUNG
m
100 mL),dried over Na 2SO4,and filtered. After removal of the low-boil-
ing solvent,the excess pyrrole was recovered by distillation under
vacuum,and the residue was dissolved in CH 2Cl2 (100 mL) and precipi-
tated by addition of MeOH. The resulting suspension was filtered and
dried under vacuum,resulting in a white powder (21.5 g,95%). 1H NMR
(CDCl3,200 MHz): d=0.86 (t, J=6.71 Hz,9H),1.24–1.32 (m,39H),
1.46–1.50 (m,6H),1.68–1.86 (m,6H),3.81–3.90 (m,6H),5.41 (s,1H),
5.90 (m,2H),6.16 (m,2H),6.71 (m,2H),6.80 (s,2H),8.15 ppm (brs,
2H); 13C NMR spectra of 6 could not be adequately measured because 6
was found to be unstable in solution over the duration of the measure-
ꢀ1
ꢁ
(KBr): n˜ =2924,2853 (CH 2),2123 cm
(C C); UV/Vis (THF): lmax
=
468,793 nm; GPC (THF): Mn ꢂ45700 gmolꢀ1; Mw ꢂ88300 gmolꢀ1
.
ꢀ1
ꢀ
ment; IR (KBr): n˜ =2919,2851 (CH 2),1116 cm
(C O); HRMS (ESI):
m/z calcd for C63H111N2O3 [M+1]+: 943.8595; found: 943.8608.
5,15-Bis[3,4,5-tris(hexadecyloxy)phenyl]-10,20-bis[2-(trimethylsilyl)eth-
Acknowledgements
A
gassed solution of dipyrromethane 6 (17.0 g,18 mmol) and trimethylsilyl-
propynal (4.0 mL,3.84 mmol) in CH 2Cl2 (1.8 L) at 08C. After stirring at
08C for 1 h, 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ; 7.0 g,
31 mmol) was added and the stirring was continued for 30 min at room
temperature. The reaction mixture was concentrated and the product was
purified by using flash chromatography on silica gel with CH2Cl2/hexane
(1:1) as the eluent. This yielded the pure product as a purple solid (5.2 g,
28%). 1H NMR (CDCl3,200 MHz): d=ꢀ2.20 (s,2H),0.60 (s,18H),
0.85–0.88 (m,18H),1.88–1.21 (m,56H),4.11 (m,8H),4.30 (m,4H),7.38
(s,4H),8.92 (d, J=4.4 Hz,4H),9.58 ppm (d, J=4.4 Hz,4H); 13C NMR
(CDCl3,50 MHz): d=0.3,14.1,22.7,26.2,29.7,32.0,69.4,71.0,73.8,
We would like to thank Andy Duft for help with the AFM measure-
ments. Financial support for this work was provided by the Natural Sci-
ence and Engineering Research Council of Canada (NSERC) Strategic
Grants program,the Canada Foundation for Innovation (CFI),the On-
tario Innovation Trust (OIT),and the Materials and Manufacturing On-
tario Emerging Materials Knowledge Fund (EMK).
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ꢀ1
ꢀ
ꢁ
(KBr): n˜ =2920,2852 (CH 2),3316 (N H),2140 cm
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2924,2854 (CH 2),2135 cm
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ꢀ1
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www.chemeurj.org
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Received: March 3,2006
Published online: May 2,2006
Chem. Eur. J. 2006, 12,5053 – 5059
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA,Weinheim
www.chemeurj.org
5059