Supramolecular assemblies of polyaniline through cooperative bundling by a palladium-complex-appended synthetic cross-linker

Article abstract of DOI:10.1002/chem.200902305

A synthetic cross-linker (1) bearing two binding sites for imine moieties in polyaniline has been used to organize polyaniline emeraldine base (EB) or polyaniline emeraldine salt (ES) into aligned assemblies. Complex 1 exhibited highly cooperative binding

Full text of DOI:10.1002/chem.200902305

FULL PAPER
DOI: 10.1002/chem.200902305
Supramolecular Assemblies of Polyaniline through Cooperative Bundling by
a Palladium-Complex-Appended Synthetic Cross-Linker
Takahiro Kaseyama,[a, b, c] Shinji Takebayashi,[b] Rie Wakabayashi,[b] Seiji Shinkai,*[b]
Kenji Kaneko,[d] and Masayuki Takeuchi*[a, c]
Abstract: A synthetic cross-linker (1)
bearing two binding sites for imine
moieties in polyaniline has been used
to organize polyaniline emeraldine
base (EB) or polyaniline emeraldine
salt (ES) into aligned assemblies. Com-
that the diimine moieties in mEB are
recognized cooperatively in anti-con-
formation by 1. The ordered structures
organized from 1 and EB or ES were
efficiently formed through supramolec-
ular bundling. These ordered assem-
blies have a periodicity of 2.5 nm that
was confirmed by means of transmit-
tance electron microscopy (TEM) and
high-resolution TEM (HRTEM). The
cooperative binding would be impor-
tant for the bundling and alignment of
the polymers, as evidenced by the fact
that neither reference compounds 2
nor 3 were capable of producing simi-
lar assemblies. The electric conductivity
of the samples was measured and the
results were discussed.
plex
1 exhibited highly cooperative
binding toward mEB (a repeating unit
analogue of EB), for which the associa-
tion constants K1 and K2 were evaluat-
ed to be 2.2ꢀ104 and 9.4ꢀ105 m-1, re-
spectively. 1H NMR studies revealed
Keywords: allosterism
· conjuga-
tion · palladium · polyaniline · poly-
mers · supramolecular chemistry
Introduction
application to rechargeable batteries, electrochromic devi-
ces, capacitors, field-effect transistors, light-emitting diodes,
solar cells, and so forth.[2–5] In particular, polyaniline (PANI)
is one of the most extensively studied conducting polymers
to date, due to its ease of synthesis by chemical and electro-
chemical polymerization, chemical stability, and inexpen-
siveness.[6,7] Poor processability and low solubility into
common organic solvents, however, would be the bottleneck
for its commercial applications. Many attempts to manipu-
late PANI in organic or aqueous solvents have been carried
out by many research groups and they can be categorized
into three approaches. The first approach is a synthetic one;
for example, the introduction of side chains into the PANI
main chain, such as poly(o-toluidine).[8] The second ap-
proach is the use of ion complexation of surfactant anions
with protonated PANI. Dodecylbenzensulfric acid, camphor
sulfonic acid (CSA), and other sulphonic acids bearing long
alkyl chains are often employed as the surfactant anion;[9]
although they are not perfectly dissolved into solvents, but
are instead dispersed uniformly or organized into fine struc-
tures. The third one is a supramolecular method, in which
PANI is incorporated into cyclodextrin, cucurbituril, and
biomolecules.[10] The resultant composites are homogeneous-
ly soluble in solvents. In these approaches, it is of impor-
tance to segregate polymers into individual chains and to
control the alignment of PANI with defined conformation
Conductive polymers have attracted considerable attention
because of their mechanical flexibility, light weight, and
electronic and photonic properties.[1] They have potential for
[a] T. Kaseyama, Prof. M. Takeuchi
Macromolecules Group
Organic Nanomaterials Center
National Institute for Materials Science
Tsukuba 305-0047 (Japan)
Fax : (+81)29-859-2101
Takeuchi.Masayuki@nims go.jp
[b] T. Kaseyama, Dr. S. Takebayashi, Dr. R. Wakabayashi,
Prof. S. Shinkai
Department of Chemistry and Biochemistry
Graduate School of Engineering
Kyushu University, Fukuoka 819-0395 (Japan)
[c] T. Kaseyama, Prof. M. Takeuchi
Department of Materials Science and Engineering
Graduate School of Pure and Applied Science
Tsukuba University, Tsukuba 305-0047 (Japan)
[d] Prof. K. Kaneko
HVEM Laboratory, Kyushu University
Fukuoka 819-0395 (Japan)
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200902305.
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and arrangement for the production of PANI-based
devices.[11]
Recently we reported a new concept for aligning and as-
Results and Discussion
ACHTUNGTRENNUNG
Molecular design and synthesis: The design of cross-linker
(aligner) molecules is of importance to generate program-
med assemblies of conjugated polymers with defined spac-
ings and arrangements. We have recently utilized the dative
bonds between porphyrinatozinc and diamine moiety in
PPE to cross-link PPEs, which contribute to the high affinity
and distinct bonding geometry. To design an aligner mole-
cule for cross-linking EB and ES, we chose a palladium
complex similar to that developed by Hirao et al.,[15,16] be-
cause we expected high affinity toward the imine moiety in
EB. We thus designed an aligner molecule 1 bearing two
palladium tweezers, each of which consists of two palladium
centers. The palladium-complex-based binding sites in 1 can
freely rotate around the phenylene-1,4-diyne axle, whereas
the rotation is suppressed when the guest(s) binds to the
clefts. In this process, the binding of the first guest molecule
or polymer to an aligner molecule facilitates the second
binding, which should result in the ready formation of
sembling conjugated polymers through the action of supra-
molecular cross-linking molecules (aligner).[12,13] The con-
cept was inspired by the action of bundling proteins in
animal cells, in which one-dimensional (1D) actin filaments
are cross-linked to form aligned bundles and the distinct
properties of bundling proteins determine the types of as-
semblies.[12c] We demonstrated this concept by utilizing the
coordination bonds formed between porphyrinatozinc and
amine-functionalized poly(phenylene ethynylene) (PPE) de-
rivatives, which contribute to the high affinity and distinct
bonding geometry of these species. In addition, we applied a
dynamic molecular recognition concept—positive homotrop-
ic allosterism—to this system. In positive allosteric systems,
the recognition of the first guest molecule facilitates the sub-
sequent binding of the other guests. For the binding of con-
jugated polymers, the first binding event enhances the
second one to form aligned supramolecular assemblies. Such
a process would be indispensable to avoid the formation of
random, disordered assemblies. As a result, these binding
events enable 1D polymers to form supramolecular two-di-
mensional (2D) polymer structures.[14] It occurred to us that
our recent finding regarding aligner molecules could be ap-
plied to the alignment of polyaniline to prepare crystalline
sheet structures. In this paper, as one of the post-alignment
schemes, we report that compound 1 cooperatively cross-
links polyaniline emeraldine base (EB) and polyaniline
emeraldine salt (ES) to form ordered structures with perio-
aligned
assemblies,
as
we
previously
reported
(Scheme 1b).[12,13] As a result, each pair of the palladium
complexes in 1 cross-links diimine moiety of EB and ES in
an allosteric manner to form polymer bundles. In such poly-
mer bundles, the distance between the two binding subunits
was estimated to be about 2.3 nm by computational methods
(Insight II, Discover, see Supporting Information). Thus,
compound 1 was synthesized according to Scheme 2, and
1
identified by H NMR, MALDI TOF MS spectroscopic evi-
dence and elemental analysis. Compounds 2 and 3 were syn-
thesized and used for control experiments (Scheme S1 in the
Supporting Information).
dicity of 2.5 nm through
(Scheme 1).
a supramolecular bundling
Complexation behavior of a re-
peating unit analogue, mEB:
We first used a low-molecular-
weight and a repeating unit an-
alogue of EB (thereafter,
mEB) so as to confirm the
complexation behaviors be-
tween imine moieties and 1
and 3. Upon addition of 3 to a
solution of mEB in THF, ab-
sorption maxima of mEB shift-
ed from 580.0 to 686.0, then to
790.0 nm with two distinct iso-
sbestic points (Figure 1a and
Figure S2 in the Supporting In-
formation). This stepwise com-
plexation of 3 to mEB is ra-
tionalized by the view that two
imine moieties were coordinat-
ed with palladium(II) in a se-
quential manner, as depicted
Scheme 1. a) Chemical structures of aligner, control molecules and conjugated polymers used in this study. b)
Schematic illustration of the alignment of polyaniline (EB) by 1. The first polymer binding event to 1 predis-
poses the second recognition site (denoted by the asterisk) such that it has an even higher affinity toward the
second polymer. EBs are expected to be bundled to each other to form organized assemblies.
in Figure 1b. Observed spectral
changes are coincident with
those observed for the study
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Supramolecular Chemistry
FULL PAPER
on the palladium-complex–
mEB coordination system re-
ported by Hirao et al.[15]
Meanwhile, the 1·mEB com-
plex was formed in a coopera-
tive manner. Formation of the
complex was estimated from
changes in the UV/Vis absorp-
tion spectra of mEB (112 mm)
upon the successive addition of
1 (0–158 mm) to a solution of
mEB in THF (Figure 2a). The
values of lmax of mEB shifted
to longer wavelengths from
581.0 to 790.0 nm with distinct
isosbestic points (470.0 and
629.0 nm), indicating that the
reaction between mEB and 1
consists of only two species
under one equilibrium. From
the plots of absorbance versus
[1]/ACTHNUGRTNEUNG[mEB] (Figure 2a inset),
the stoichiometry between 1
was confirmed to be 1:2 ([1·-
AHCTUNRTGEG(NNNU mEB)2]). It is worth noting
that unlike conventional palla-
dium complex 3, the four palla-
dium centers in 1 coordinate to
imine moieties of two mEB
molecules under equilibrium.
Scheme 2. Synthetic scheme for the preparation of aligner molecule 1.
To obtain quantitative infor-
mation, 1 (5.9 mm) was re-ti-
trated with mEB (0–48 mm) in THF at 258C and followed by
UV/Vis absorption spectroscopy (Figure S3 in the Support-
ing Information). The differential spectral changes enabled
us to evaluate the complex formation of 1·mEB; upon in-
creasing mEB concentration, the absorption band of
367.0 nm of
1 shifted to a longer wavelength region
(390.0 nm) with an isosbestic point (363.5 nm). Importantly,
plots of absorbance at 390.0 nm versus [mEB] showed a sig-
moidal curvature characteristic of positive homotropic allos-
terism. These mEB bindings to 1 were initially analyzed
with the Hill equation:[17] log{y/
(1Ày)}=nH log
ACHTUNGTRENNUNG[guest]+
logK, in which K, y, and nH are the association constant, ex-
tents of saturation, and Hill coefficient, respectively, and y=
K/ACTHNUTRGNEUNG
([guest]Àn +K). From the slope and the intercept of the
linear plots (Hill plot), we obtained log K and nH (Figure S3
in the Supporting Information). The Hill coefficient nH of
2.0 indicates that the mEB binding occurs cooperatively,
since a higher value of nH is related to a higher degree of co-
operativity[18] and the maximum is equal to the number of
available binding subunits; in this case, 1 has two binding
sites for mEB. From analysis of the binding isotherm in Fig-
ure 2c using a standard non-linear curve fitting method, we
calculated the association constants (Kn [mÀ1]) to be K1 =
Figure 1. a) UV/Vis spectral changes of mEB (27 mm) upon addition of 3
(0–108 mm) in THF at 258C. b) Schematic illustration of complexation be-
tween mEB and 3.
2.2ꢀ104 and K2 =9.4ꢀ105 for the formation of 1·
These results clearly show that the positive cooperative
ACHTUNGTRENNUNG(mEB)2.
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M. Takeuchi, S. Shinkai et al.
tweezers in 1 suppresses the motion around the phenylene-
1,4-diyne axis in 1,[21] which facilitates the binding of the
second mEB moiety, as illustrated in Scheme 3.
To obtain further insight into the 1·
ACHTUNGRTEN(NUNG mEB)2 complex,
1H NMR spectra for [1]/
AHCTUNGTRENNUNG
sured in [D1]chloroform/[D3]acetonitrile 1:1 mixed solvent
([1]=0.73 mm, Figure 3). The complexation-induced chemi-
Figure 3. 1H NMR spectra of a) mEB ([mEB]=1.46 mm), b) 1:mEB=1:1
([1]=[mEB]=0.73 mm), c) 1:mEB=1:2 ([1]=0.73 mm, [mEB]=
1.46 mm), and d) 1 ([1]=0.73 mm) in [D1]chloroform/[D3]acetonitrile 1:1
mixed solvent at 298 K.
cal shifts of mEB protons gradually moved to a lower mag-
netic field up to [1]/ACTHNUTRGNE[NUG mEB]=1:2 ratio and were then saturat-
Figure 2. a) UV/Vis spectral changes of mEB (112 mm) upon addition of 1
(0–158 mm) in THF at 258C. Inset: Plots of absorbance at 790.0 nm of
mEB (112 mm) vs. [1]/ACHTUNGTRENNUNG[mEB]. b) Differential spectral changes of 1 ([1]=
5.9 mm) upon addition of mEB ([mEB]=0–48 mm); this spectral changes
were obtained by the subtraction of the absorption spectra of mEB from
Figure S3a in the Supporting Information. c) Plots of the absorbance at
390.0 nm of 1 (5.9 mm) versus [mEB]. The solid line represents the theo-
ed. No peak broadening due to the formation of supra-
molecular polymer between 1 and mEB occurred in this
system. It is known that mEB adopts two different confor-
mations, anti- and syn-conformations in solution, although
one cannot distinguish them by NMR spectroscopy due to
the fast exchange at room temperature. The observed peaks
for mEB complexed with 1 appear as four doublets that are
assignable to anti-conformation. These results are consistent
with those observed for the study on the palladium-com-
plex–mEB coordination system.[15a] We confirmed from
these NMR and UV/Vis spectroscopic studies that the palla-
dium complexes in 1 cooperatively recognize two mEB mol-
ecules in an anti-conformation (Scheme 3 and Figure 3). The
retical curve for the formation of 1:2 [1·ACTHNUTRGNENUG(mEB)2] complex. We used solu-
tion of 1 in chloroform/acetonitrile (1:1) as a stock solution. Without ace-
tonitrile, the palladium complexes of 1 tend to form oligomers via inter-
molecular coordination of carbonyl moieties to palladium complexes (see
reference [16]).
binding takes place between 1 and mEB.[19,20] This is because
the binding of the first mEB moiety to one set of palladium
Scheme 3. Schematic representation for cooperative recognition process between 1 and mEB. The binding of the first mEB moiety to 1 suppresses the ro-
tational motion of the phenylene-1,4-diyne axle in 1, which facilitates the binding of the second mEB moiety. As a result, highly cooperative binding of
mEB to 1 is achieved.
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appearance of this high cooperativity in the binding of mEB
and its complexation in an anti-conformation play a signifi-
cant role for organizing EB into aligned, rather than
random assemblies or ladder-type assemblies.[22] In the poly-
aniline bundling process using 1, the binding of the first EB
moiety to 1 facilitates the binding of the second moiety,
which results in the ready formation of aligned assemblies
(Scheme 1b).
blies are dominant (Figure S6 in the Supporting Informa-
tion). This is because complex 3 cannot cross-link EBs and 2
cannot exhibit cooperativity in the binding of EBs. Only
under the conditions in which the [2]/[EB]unit ratio was over
0.5, were partially crystalline 2·EB assemblies obtained (Fig-
ure S6b in the Supporting Information).
We subjected the sample prepared from EB and 1 to
TEM observation so as to reveal how 1·EB assemblies are
organized. We prepared solution-cast films of the 1·EB as-
semblies formed in various mixing ratios of [1] and [EB]unit
on a TEM grid. Given the association constants we obtained
in this study, complex 1 is supposed to complex completely
with EB under the conditions we used. Among seven sam-
ples with [1]/[EB]unit =0:1–0.5:1 mixing ratio, micron-sized
sheet morphologies with clear electron diffraction patterns
were observed under the conditions of [1]/[EB]unit =0.20:1 to
0.25:1 (Figure S5 and S7 in the Supporting Information).
This higher cross-linking ratio than that found in our previ-
ous supramolecular organization of poly(phenyleneethyny-
lene)s bearing alkyl chains is probably due to the lack of
alkyl chains in EB. To maintain sheet morphologies with the
periodicity of nm scale, we infer that alkyl chains in the po-
lymer and/or aligner are of importance. In the image of a
thick assembly prepared with the mixing ratio of [1]/
[EB]unit =0.20:1, we observed a crossed dark stripe contrast
together with moire fringes (Figure 5a and 5b), indicating
that a few thin sheets with striped structures were over-
lapped and the alignment among sheet assemblies could not
be achieved in this system. Figure 5c displays HRTEM
images of the 1·EB assemblies ([1]/[EB]unit =0.20:1) in which
the periodicity of the multilamellar contrast, over a distance
of a few hundred nanometers, was 2.5 nm, as determined
from the Fourier-filtered image. Judging from data reported
previously,[12,13] we deduce that the darker sections in the
electron micrographs of 1·EB assemblies are domains con-
taining ordered p-stacked layers and Pd (the heaviest atom).
Indeed, the energy dispersive X-ray spectroscopic (EDX)
study on the 1·EB assembly revealed that the sheet structure
contains Pd (Figure S7 in the Supporting Information), al-
though from EDX analysis we could not specify spatial dis-
tribution of Pd. As mentioned above, PdII atoms coordinate
to the imine moieties in EB and, therefore, the EB are prob-
ably ordered along these dark contrast regions. It is worth
noting that the distance of 2.5 nm is almost identical to that
which we calculated when EBs are bundled by 1 in an anti-
conformation.
Supramolecular assemblies of EB with 1–3: From the
above-mentioned findings, one can expect that the diimine
moieties in the repeating unit of EB would be recognized
cooperatively in an anti-conformation by 1 and then become
bundled, because the association constants are high enough.
Indeed, the addition of 1 to a solution of EB (Mn =20000,
[EB]unit =15 mm: [EB]unit denotes the concentration of the re-
peating unit of EB in Scheme 1a) in THF at 258C resulted
in the bathochromic shifts of lmax of EB from 598.0 to
785.0 nm with broadening of the absorption band up to
1200 nm (Figure 4). This spectral change is similar to those
Figure 4. UV/Vis/NIR spectral changes of [EB]unit (15 mm) upon addition
of 1 (0–95 mm) in THF at 258C.
observed for 1·mEB and those observed upon doping EB
with protons (vide infra). These results indicate that diimine
moieties of EB make coordination bonds with the palladium
complexes in 1. When we used longer EB (Mn =300000,
[EB]unit =15 mm), a shift of lmax from 602.0 to 778.0 nm was
observed upon increase of the concentration of 1. The poor
solubility in THF of longer EB as well as its assembly with
1, however, produced a bottleneck that limited the acquisi-
tion of further information.
The electron micrographs and electron diffraction pat-
terns of EB assemblies provide information regarding how
EB are organized into aligner·EB assemblies. Firstly, we pre-
pared solution-cast films of 1, 2, or EB (Mn =20000) and
confirmed using TEM that the aligner or EB alone is not
able to make organized assemblies; only amorphous aggre-
gates with the size of a few hundred by a few hundred nm
were produced on the TEM grid (see Figure S4 and S5a in
the Supporting Information). In cases in which 2 and 3 are
used as the palladium complexes to form EB assemblies, we
confirmed from TEM observation that amorphous assem-
Pre-doping before adding aligner molecule: We tried to pre-
dope EB before complexation with 1, because the acidity of
EB·nH+ (emeraldine salt: ES) is much lower than that of
commonly used dopant acids such as sulfonic acids. The pro-
tons in ES could be displaced by the palladium centers in 1
to produce the 1·ES assembly (Scheme 4). The in situ addi-
tion of camphor sulfonic acid (CSA) to a solution of EB in
THF,[23] which should induce protonation of the imine
groups in EB to produce ES units, was monitored by UV/
Vis/NIR absorption spectral methods. The lmax of ES ap-
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M. Takeuchi, S. Shinkai et al.
Figure 5. Electron micrographs (no staining) of EB aligned by 1. a) TEM image of 1·EB assemblies. ([EB]unit =12 mm and [1]=2.4 mm) Inset: Electron dif-
fraction pattern. b) Enlarged view of a). c) HRTEM images of 1·EB assemblies consisting of alternating dark and light stripes and extracted peropdocal
patterns from Fourier translation image. The periodicity between dark lines is 2.5 nm.
peared at 782.0 nm with broad-
ening of the absorption band
up to 1200 nm; the characteris-
tic polaron absorption[23] ap-
peared at 435.0 nm. Upon ad-
dition of 1 to a solution of ES
in THF, partial displacement
from protons in ES to the pal-
ladium centers of 1 was ob-
Scheme 4. Schematic illustration of the formation of 1·ES assembly.
served. A high substitution ratio of 1 (over [1]/[ES]unit
=
0.250:1), however, resulted in precipitation of 1·ES assembly
(over ten micron-sized sheet assemblies) and entangled 1·ES
assemblies (granular assemblies) were observed in the TEM
images (Figure S8 in the Supporting Information). Under
the conditions of [1]/[ES]unit =0.125:1, the shift of absorption
maxima of ES from 782.0 to 793.0 nm indicates that a dis-
placement reaction occurred (Figure 6). We further con-
firmed the formation of 1·ES assemblies by using atomic
force microscopy (AFM), TEM and HRTEM (Figures 7 and
8).
Figure 7a displays an AFM image of ES (deposited from
a 1.5 mm solution in THF) in which ES assembly is dispersed
in a dot shape[24] on HOPG; by mixing ES ([ES]unit =1.5 mm)
with 1 (0.18 mm) in solution, large sheet morphologies with a
height of 1.0 nm were observed (Figure 7b). Given the
degree of polymerization of ES, 1 must bundle with and
noncovalently splice ES to form such supramolecular 1·ES
assemblies. It is shown from TEM and HRTEM images in
Figure 8 (and Figure S8 in the Supporting Information) that
crystalline sheet morphologies with multilamellar contrast
were dominant. Furthermore, EDX studies clearly showed
that the crystalline sheet morphologies contain Pd together
with sulfur, which comes from dopant CSA. The stripe pe-
riodicity of 2.5 nm over a 200 nm-wide distance in the multi-
lamellar contrast was determined from the Fourier-filtered
image (Figure 8b). The distance of 2.5 nm is identical to
that observed for 1·EB assemblies, indicating that ESs are
bundled by 1 in an anti-conformation to yield the crystalline
assemblies. Most likely the interpolymer spacing of 2.5 nm
Figure 6. UV/Vis/NIR spectral changes of ES ([ES]unit =14 mm) upon ad-
dition of 1 (0–7.0 mm) in THF at 258C. High substitution ratio of 1 (over
[1]/[ES]unit =0.125:1) resulted in the decrease of absorbance of ES due to
the precipitation.
Figure 7. AFM images of a) ES assembly and b) 1·ES assembly ([1]/
[ES]unit =0.125:1, [ES]unit =1.5 mm). Inset: the height profile of the black
line in a).
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is determined by the distance between binding sites in 1.
Compound 1 could act as a carrier trap that hampers the
higher conduction. We deduce, however, that the decrease
in conductivity by the palladium binding is minimal because
the effect of alignment of ES by 1 would have an antagonis-
tic activity towards the decrease in the conductivity. Basical-
ly, this approach would resolve two critical issues associated
with conjugated polymer-based devices; the segregation of
polymers in individual chains and controlled alignment. In-
troducing new interaction sites toward EB and ES, such as
sulfonic acid based binding sites for imines, would result in
the formation of crystalline assemblies expected to have
higher conductivity. Furthermore, by introducing liquid-crys-
talline moieties into aligner molecules, the alignment of
sheet assemblies would be achieved.
Figure 8. Electron micrographs (no staining) of ES aligned by 1. a) TEM
images of 1·ES assemblies ([ES]unit =14 mm, [1]/[ES]unit =0.125:1). Inset:
Electron diffraction pattern of a), indicating that the assemblies show the
crystalline nature. b) HRTEM images of 1·ES assemblies consisting of al-
ternating dark and light stripes and extracted periodical patterns from
Fourier translation image. The periodicity between dark lines is 2.5 nm.
would be large enough to accept dopant CSAs within 1·ES
assemblies.
Experimental Section
The electric conductivity of the samples was measured by
using a four-point probe. We first tried to measure a thin
film prepared by means of spin coating; however, we could
not obtain reliable values. We thus prepared solution-cast
films of ES ([ES]unit =240 mm) and 1·ES assemblies
([ES]unit =240 mm, 1/[ES]unit =0.125:1) formed in THF on a
glass plate. The bulk conductivity was calculated from sur-
face resistivity and film thickness. The conductivity of
0.19 ScmÀ1 for 1·ES assemblies is the same as that of ES
(0.20 ScmÀ1). We infer that the aligner molecule 1 acts as a
charge carrier trap.[25] Moreover, the alignment of sheet as-
semblies could not be achieved in this system, as indicated
by our TEM measurements. These could be the reasons why
the conductivity of 1·ES assemblies is not so high in compar-
ison with that of ES and thereby, the effect of the alignment
of ESs by the aid of 1 would be canceled out.
General: All starting materials and solvents were purchased from Al-
drich, Tokyo Kasei Chemicals or Wako Chemicals and used as received.
The 1H NMR spectra were recorded on a Bruker DRX 600 (600 MHz)
spectrometer. EBs were purchased from Aldrich and used without purifi-
cation. Chemical shifts are reported in ppm downfield from tetramethyl-
silane as the internal standard. Mass spectral data were obtained using a
Perceptive Voyager RP MALDI TOF mass spectrometer, a JEOL JMS
HX110 A high-resolution magnetic sector FAB mass spectrometer,
Bruker micrOTOF focus high-resolution CSI mass spectrometer, and a
JEOL JMS T100CS high-resolution ESI mass spectrometer. UV/Vis and
UV/Vis/NIR spectra were recorded using Shimadzu UV-2500 PC and
UV-3100 spectrophotometer, respectively.
Binding isotherm analysis: The cooperative guest-binding process was an-
alyzed according to the Hill equation: log{y/
G
ACHTUNGTREN[NUNG guest]+logK,
in which K, y, and nH are the association constant, the extent of complex-
ation, and the Hill coefficient, respectively. The slope and the intercept
of the linear (Hill) plots allow K and nH to be estimated; these values are
useful measures of cooperativity. A higher value of nH is related to a
higher degree of cooperation; the maximum value is equal to the number
of binding sites. In the analysis of binding isotherm from the Hill plot, we
evaluated the concentration of unbound guest ([guest]) by assuming that
the 1:2 complex of 1 is formed quantitatively when the absorption
change is saturated.
Conclusions
Transmission electron microscopy (TEM), high-resolution TEM
(HRTEM), and atomic force microscopy (AFM) measurements: TEM
and HRTEM images were acquired using a JEOL TEM-2010 (accelerat-
Since the discovery of conducting polymers, it has been the
goal of many research efforts to control the molecular orien-
tation and alignment of these materials, especially because
the molecular alignment appears to be important in increas-
ing conductivity. The supramolecular bundling approach in-
spired by the mode of action of actin filament bundling pro-
teins is now applicable to polyanilines (EB and ES) to or-
ganize into crystalline assemblies. We designed and synthe-
sized aligner 1, bearing four Pd centers, which exhibited
high cooperativity and high affinity in the binding of two
mEBs. Furthermore, use of 1 enabled us to monitor the
binding process of mEB, EB, and ES by means of UV/Vis,
UV/Vis/NIR, NMR spectroscopy, and electron microscopes
in order to analyze their crystalline assemblies. The results
obtained so far showed that the palladium coordination to
the imine moieties in EB and ES results in the formation of
crystalline assemblies with the periodicity of 2.5 nm, which
ing voltage: 120 kV) and
a TECNAI-20 FEI (accelerating voltage:
200 kV), respectively. A sample solution was placed on a copper TEM
grid upon a holey carbon support film. Energy dispersive spectroscopy
(EDX) spectra and EDX line scan profiles were obtained using
a
TECNAI-20, FEI. The TEM grid was dried under reduced pressure for
6 h prior to TEM observation. AFM images were acquired in air using a
NanoScope IIIa (tapping mode).
Sample preparation for TEM and AFM measurements: A solution of the
sample in THF was cast on a copper TEM grid upon a holey carbon sup-
port film. The sample was prepared by drop casting on HOPG and dried
for 6 h under reduced pressure before TEM and AFM observation.
Conductivity measurements: The conductivity of the samples ([EB]unit
=
240 mm) was measured using a four-point probe (1116SLD, BAS Inc.).
The probe was equipped with four spring-loaded tungsten carbide nee-
dles spaced 1 mm apart. The conductivity of the EB-CSA (ES) and EB-
CSA-1 film coated on the glass plate was calculated from the surface re-
sistivity and the film thickness, which was measured by an a-step surface
procedure.
Chem. Eur. J. 2009, 15, 12627 – 12635
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12633

M. Takeuchi, S. Shinkai et al.
Synthesis: Compounds used in this study were synthesized according to
Scheme 2 and Scheme S1 in the Supporting Information. Compound 4
was purchased and used without further purification. Compounds 6,[26]
9,[27] and 12[12] were synthesized according to the method in the literature.
Compound 11: In a 50 mL two-neck flask, NaOH (10 mg, excess) was
added to a solution of 10 (20 mg, 22 mmol) in anhydrous toluene (6 mL).
The reaction was kept under reflux for 5.5 h. The reaction was monitored
by TLC (silica gel, chloroform/methanol 10:1). After completion, the in-
soluble materials were filtered off. The filtrate was evaporated to pro-
duce 11 as a slightly yellow solid (15 mg, 80%). 1H NMR (600 MHz,
CDCl3, TMS standard, RT): d=0.96–0.99 (m, 12H), 1.43–1.47 (m, 8H),
1.63–1.68 (m, 8H), 3.10 (s, 1H), 3.49–3.53 (m, 8H), 5.28 (s, 4H), 7.45 (d,
J=8.0 Hz, 1H), 7.51 (d, J=8.7 Hz, 2H), 7.52 (d, J=8.8 Hz, 2H), 7.63
(dd, J=1.7, 8.1 Hz, 1H), 7.66 (d, J=8.2 Hz, 2H), 7.68 (d, J=8.2 Hz, 2H),
7.71 (s, 4H), 7.86 (d, J=1.4 Hz, 1H), 7.95 (s, 2H), 7.96 ppm (s, 2H);
MALDI TOF MS: m/z calcd for [M+H]+: 865.46; found: 865.3655; HR
FABMS: m/z calcd for [M+H]+: 865.4574; found 865.4656.
2-(4-Bromomethylphenyl)-4,4,5,5-tetramethyl-1,3,2-dioxaborolane (5): In
a
300 mL round-bottomed flask, benzoyl peroxide (BPO; 0.27 g,
1.1 mmol, 0.05 equiv) was added to a solution of 4 (4.8 g, 22 mmol,
1 equiv) and N-bromoscineimide (NBS; 4.3 g, 24 mmol, 1.1 equiv) in tet-
rachloromethane (150 mL) under an N2 atmosphere. The reaction mix-
ture was kept under reflux for 3 h. The reaction was monitored by TLC
(silica gel, chloroform: n-hexane=1:2 (v/v)). After completion, the in-
soluble materials were filtered off and the filtrate was evaporated. Com-
pound 5 was isolated as a white solid (4.6 g, 71%) by recrystallization
from ethanol. 1H NMR (600 MHz, CDCl3, TMS standard, RT): d=1.34
(s, 12H), 4.49 (s, 2H), 7.39 (d, J=7.9 Hz, 2H), 7.78 ppm (d, J=7.9 Hz,
2H); elemental analysis calcd (%) for C13H18BBrO2: C 52.57, H 6.11;
found: C 52.82, H 5.95.
Compound 13: In a 50 mL two-neck flask, anhydrous diisopropylamine
(6.0 mL, excess) was added to a solution of 11 (190 mg, 0.22 mmol,
2.2 equiv), 12 (70 mg, 0.10 mmol, 1 equiv), [PdACHTNUTRGNE(UNG PPh3)4] (46 mg,
0.04 mmol, 0.4 equiv), and CuI (7.6 mg, 0.04 mmol, 0.4 equiv) in anhy-
drous DMF (14.0 mL). The reaction was stirred at 608C for 4.5 h under
an Ar atmosphere. The solvent was evaporated and then chloroform was
added to the residue. The solution was washed by saturated NH4Cl solu-
tion (30 mLꢀ3) and H2O (30 mL), then dried over anhydrous Na2SO4.
The insoluble materials were filtered off and the filtrate was evaporated.
The residue was purified by column chromatography (silica gel, chloro-
form/acetonitrile 10:1) to produce 13 as a yellow solid (57 mg, 26%).
1H NMR (600 MHz, CDCl3, TMS standard, RT): d=0.82 (t, J=7.2 Hz,
6H), 0.94–1.00 (m, 24H), 1.12–1.15 (m, 28H), 1.35–1.40 (m, 4H), 1.41–
1.48 (m, 20H), 1.63–1.69 (m, 20H), 3.46–3.53 (m, 16H), 3.90 (t, J=
Diethyl 4-{4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzyloxy}pyri-
dine-2,6-dicarboxylate (7): In a 200 mL round-bottomed flask, 5 (2.5 g,
8.4 mmol, 1.1 equiv) was added to a solution of K2CO3 (2.2 g, 16 mmol,
2.0 equiv) and 6 (1.9 g, 8.0 mmol, 1 equiv) in dry acetonitrile (50 mL).
The solution was stirred at 858C for 2.5 h. The reaction was monitored
by TLC (silica gel, dichloromethane). After completion, the insoluble
materials were filtered off and the filtrate was evaporated. Diethyl ether
was added to the residue and the resulting solution was washed with H2O
and dried over anhydrous Na2SO4. The residue was purified by column
chromatography (silica gel, chloroform/methanol 10:1) to produce 7 as a
white solid (2.5 g, 69%). 1H NMR (600 MHz, CDCl3, TMS standard,
RT): d=1.35 (s, 12H, s), 1.41 (t, J=6.9 Hz, 6H), 4.47 (q, J=7.2 Hz, 4H),
5.24 (s, 2H), 7.43 (d, J=7.7 Hz, 2H), 7.85–7.86 ppm (m, 4H); MALDI
TOF MS (dithranol): m/z calcd for [M+H]+ =456.21; found: 455.9853;
elemental analysis calcd (%) for C24H30BNO7: C 63.31, H 6.64, N 3.08;
found: C 63.17, H 6.67, N 3.12.
6.4 Hz, 4H), 5.25 (s, 4H), 5.29 (s, 4H), 6.77ACTHNUTRGNE(NUG s, 2H), 7.49–7.54 (m, 10H),
7.61–7.63 (m, 2H), 7.68–7.72 (m, 8H), 7.79 (d, J=8.0 Hz, 4H), 7.89–7.91
(m, 6H), 7.96 ppm (s, 8H); MALDI TOF MS (dithranol): m/z calcd for
[M+H]+: 2195.30; found: 2195.2979.
Compound 1: Compound 1 was prepared according to the previously re-
ported method.[28] In
a ACHTUNGTERNUN(G OAc)2] (17 mg,
25 mL two-neck flask, [PdII
74 mmol, 4.0 equiv) was added to a solution of 13 (40 mg, 18 mmol,
1 equiv) in acetonitrile (8.0 mL) and chloroform (4.0 mL) under an Ar at-
mosphere. The solution was stirred at room temperature for 1 day. The
reaction was monitored by TLC (silica gel, chloroform/methanol 10:1).
After completion, the insoluble materials were filtered off and the filtrate
was evaporated to produce 1 as a yellow solid (46 mg, 90%). 1H NMR
(600 MHz, [D1]CDCl3/[D3]CD3CN 1:1, TMS standard, RT): d=0.83 (t,
J=7.2 Hz, 6H), 0.95 (q, J=7.2 Hz, 24H), 1.11–1.15 (m, 28H), 1.37–1.41
(m, 24H), 1.51–1.53 (m, 20H), 3.24 (q, J=8.4 Hz, 16H), 3.94 (t, J=
6.2 Hz, 4H), 5.31 (s, 8H), 6.81 (s, 2H), 7.16 (s, 4H), 7.19 (s, 4H), 7.54–
7.57 (m, 10H), 7.70 (dd, J=1.5, 8.2 Hz, 2H), 7.72 (d, J=8.1 Hz, 4H),
7.79 (d, J=7.9 Hz, 4H), 7.89 ppm (d, J=1.3 Hz, 2H); HR CSI TOF MS:
m/z calcd for [(M+2Na)/2]2+: 1399.9698; found: 1399.9645.
4-(4-(4,4,5,5-Tetramethyl-1,3,2-dioxaborolan-2-yl)benzyloxy)-N,N-dibutyl-
pyridine-2,6-dicarboxamide (8): In a 300 mL round-bottomed flask, n-bu-
tylamine (27 mL, excess) was added to a solution of 7 (1.0 g, 2.2 mmol,
1 equiv) and DMAP (530 mg, 4.4 mmol, 2 equiv) in dry THF (40 mL).
The reaction was kept under reflux for 68 h under Ar atmosphere. The
reaction was monitored by TLC (silica gel, chloroform/methanol 10:1).
The solvent was evaporated. Chloroform was added to the residue and
the resulting solution was washed by H2O (50 mLꢀ3) and dried over an-
hydrous Na2SO4. The insoluble materials were filtered off, and the filtrate
was purified by column chromatography (silica gel, chloroform/methanol
10:1) to produce 8 as a white solid (1.0 g, 91%). 1H NMR (600 MHz,
CDCl3, TMS standard, RT): d=0.98 (t, J=7.3 Hz, 6H), 1.34 (s, 12H),
1.41–1.47 (m, 4H), 1.62–1.67 (m, 4H), 3.50 (q, J=6.9 Hz, 4H), 5.25 (s,
2H), 7.42 (d, J=7.9 Hz, 2H), 7.65 (s, 2H), 7.83 (d, J=7.9 Hz, 2H),
7.90 ppm (s, 2H); MALDI TOF MS (dithranol): m/z calcd for [M+H]+:
510.31; found: 509.9092; HR FABMS: m/z calcd for [M+H]+: 510.3061;
found: 510.3112; elemental analysis calcd (%) for C28H40BN3O5: C 66.01,
H 7.91, N 8.25; found: C 65.99, H 7.91, N 8.24.
Acknowledgements
Compound 10: In a 100 mL two-neck flask, an aqueous solution of
Na2CO3 (9 mL; 290 mg, 2.8 mmol, 3 equiv) and [PdACTHUNGRTNEUNG(dppf)Cl2] (150 mg,
M.T. and T.K. thank Dr. K. Sugiyasu of NIMS for valuable comments
and Mr. M. Frank for reading of the manuscript. This study was support-
ed partially by a Grant-in-Aid for Science Research in a Priority Area
“Super-Hierarchical Structures” (19022026 to M.T.) and a Grant-in-Aid
for Scientific Research for Priority Area Coordination Programming
(area 2107) (21108010 to M.T.) from the Ministry of Education, Culture,
Science, Sports, and Technology (Japan). T.K. thanks JSPS for the Re-
search Fellowship for Young Scientists for financial support.
0.18 mmol, 0.2 equiv) were added to a solution 9 (290 mg, 0.92 mmol,
1 equiv) and 8 (1.4 g, 2.8 mmol, 3.0 equiv) in 1,4-dioxane (50 mL). The re-
action was kept under reflux for 1.5 h under an Ar atmosphere. The reac-
tion was monitored by TLC (silica gel, chloroform/methanol 30:1). After
completion, the insoluble materials were filtered off and the filtrate was
evaporated. The residue was washed with methanol and was then puri-
fied by column chromatography (silica gel, chloroform/acetonitrile 30:1)
1
to produce 10 as a gray solid (580 mg, 69%). H NMR (600 MHz, CDCl3,
TMS standard, RT): d=0.97–1.00 (m, 12H), 1.43–1.47 (m, 8H), 1.50 (s,
6H), 1.63–1.68 (m, 8H), 2.30 (s, 1H), 3.49–3.53 (q, J=6.9 Hz, 8H), 5.29–
5.33 (m, 4H), 7.46 (d, J=8.1 Hz, 1H), 7.49 (d, J=8.0 Hz, 2H), 7.52 (d,
J=8.0 Hz, 2H), 7.60 (dd, J=1.4, 8.9 Hz, 1H), 7.65–7.69 (m, 8H), 7.77 (d,
J=1.8 Hz, 1H), 7.93 (s, 2H), 7.95 ppm (s, 2H); MALDI TOF MS (di-
thranol): m/z calcd for [M+Na]+: 945.50; found: 945.5026; HR ESI TOF
MS: m/z calcd for [M+H]+: 923.5071; found 923.5047.
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Received: August 20, 2009
Published online: November 2, 2009
Chem. Eur. J. 2009, 15, 12627 – 12635
ꢁ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
12635