Vortex fibril structure and chiroptical electrochromic effect of optically active poly(3,4-ethylenedioxythiophene) (PEDOT*) prepared by chiral transcription electrochemical polymerisation in cholesteric liquid crystal

Article abstract of DOI:10.1039/b818993e

Chiroptical electroactive poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically synthesised in a cholesteric liquid crystal (CLC) electrolyte solution from the terEDOT monomer. PEDOT synthesised from terEDOT was found to enable the formation of a

Full text of DOI:10.1039/b818993e

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Vortex fibril structure and chiroptical electrochromic effect of optically active
poly(3,4-ethylenedioxythiophene) (PEDOT*) prepared by chiral transcription
electrochemical polymerisation in cholesteric liquid crystal†
*
Hiromasa Goto
Received 27th October 2008, Accepted 6th May 2009
First published as an Advance Article on the web 8th June 2009
DOI: 10.1039/b818993e
Chiroptical electroactive poly(3,4-ethylenedioxythiophene) (PEDOT) was electrochemically
synthesised in a cholesteric liquid crystal (CLC) electrolyte solution from the terEDOT monomer.
PEDOT synthesised from terEDOT was found to enable the formation of a fibril structure. In contrast,
the EDOT monomer produced PEDOT without fibrils. Electrochemical polymerisation using this
method provides a polymer with a distinct fibril structure and vortex texture. This indicates that the
individual main chains are arranged by the topological transcription of structural chirality in the
epitaxial electrochemical polymerisation in CLC as a one-handed helically twisted matrix. The polymer
was confirmed to exhibit chiroptical electrochromism, diffraction, and the generation of a charge
carrier in a chiral environment. This suggests formation of helical polarons of PEDOT.
monomer has no rigid rod-like molecular shape and was not
Introduction
organized before polymerisation in the CLCs. Herein, polymer-
isation of biEDOT may improve these drawbacks due to the
linearity of biEDOT. Employment of terEDOT for polymerisa-
tion in CLCs may further improved these points, and it is
expected to produce polymers with high conversion because the
number of arylene units in the monomer increases, thus reducing
the oxidation potential.
Cholesteric liquid crystals (CLC) have phase chirality,1,2 and thus
exhibit strong optical rotary power. The helical arrangement of
a CLC on a macromolecular scale greatly enhances the physical
manifestation of chiroptical properties to such an extent that the
optical rotation of a chiral molecule can be enhanced in the CLC
phase. Therefore, chiral conjugated polymers with CLC-like
macromolecular formations are expected to exhibit considerable
optical activity.
In the present study, electrochemical polymerisation in a CLC
electrolyte solution15 is performed using terEDOT, a triaryl
system, to afford a high-performance optically electroactive p-
conjugatedpolymer. AmethodforproducingterEDOTwithhigh-
resolution electronic spectra has been previously reported.16,17
Here, a novel synthetic route for preparing the terEDOT mono-
mer is reported. The rigid rod-like shape of terEDOT provides
good affinity for LCs in blends. The terEDOT as a monomer itself
can be pre-organized into a chiral sense prior to polymerisation in
the CLC medium. The terEDOT is expected to have a high poly-
merisation activity due to its low oxidation potential.
Liquid crystals (LC) are a useful reaction medium, having both
liquid-like fluidity and structures that can be imprinted on the
forming molecules. A LC can thus function as both a reaction
field and a chiral molecular template. Chemical reactions in
CLCs may be particularly effective for producing chiral
compounds from achiral materials, since the phase chirality of
the CLC provides a three-dimensional (3D) sequential chiral field
for the chemical reaction.
LC solvents have been employed for many decades for
preparing polyacetylenes with high electrical conductivities using
the Ziegler–Natta catalytic system.3–5 The polyacetylene films
that are produced display a high degree of fibril orientation.
CLCs have been employed to prepare helical polyacetylene.6 LC
materials are widely used in chemistry and physics as molecular
templates for synthesising aromatic p-conjugated polymers with
supramolecular order.7–13
The fibril-forming result of PEDOT from terEDOT prepared
in a CLC electrolyte solution by the transcription electro-
chemical polymerisation enables the visualization of CLC due to
the polymer orientation. The resultant polymer exhibits a coiled
fibril structure and the entire surface has a vortex pattern
showing chiroptical electrochromism. Furthermore, the diffrac-
tion properties and the chiral-spin magnetic structure for the
polymer have been evaluated. Polymerisation in a nematic LC
(NLC) was also conducted and the birefringence was quantified.
This also can provide quantitative information as to how the
properties of the polymer reflect those of the liquid crystal host.
The CLC structure occurs in many instances in nature. For
example, the cuticle of crusted insects such as Cetonia (beetle)
exhibits a CLC structure, resulting in the wavelength-selective
reflection of circularly polarized light.18,19 Polymerisation of the
organic constituent in the secretion of these insects proceeds in
such a manner as to produce CLC order, and the material
In a previous study, polyEDOT prepared in CLCs showed no
fibril structure.14 However, it was successfully polymerised in
CLCs; the polyEDOT appearing as a partially spiral structure
over the entire film surface.14 This may be because the EDOT
Graduate School of Pure and Applied Sciences, Institute of Materials
Science, University of Tsukuba, Tsukuba, Ibaraki 305-8573, Japan.
E-mail: gotoh@ims.tsukuba.ac.jp; Fax: +81-298-53-4490; Tel: +81-298-
53-5128
† Electronic supplementary information (ESI) available: UV-vis, CD and
ORD spectra. See DOI: 10.1039/b818993e
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produced is both insoluble and infusible. Similarly, the bio-
mineralization of vaterite in egg yolk proceeds via a LC template
to produce multilayered shells.20 Biological LCs thus function
both as a reaction field and as a template to guide the formation
of the organic structure. The CLC-based polymerisation mech-
anism considered in the present study attempts to achieve
structural chirality by imprinting in a manner comparable to
these biological processes as a form of biomimetic technology.
Results and discussion
Polymer synthesis
Scheme 1 shows the synthetic route for monomer 2,3,20,30,200,300-
hexahydro-[5,50:70,500]ter(thieno[3,4-b][1,4]dioxine) (terEDOT).
The precursor 5,7-dibromo-2,3-dihydro-thieno[3,4-b][1,4]dioxine
Fig. 1 POM image of cholesteric liquid crystal (CLC) containing the
monomer (terEDOT), supporting salt (tetrabutylammonium perchlorate,
TBAP), and CLC inducer (cholesteryl pelargonate) at 25 ꢀC.
(1) was first synthesised by bromination using N-bromosuccini-
mide (NBS) in a mixed solvent consisting of chloroform–glacial
acetic acid at room temperature according to a method reported in
the literature.21–23 EDOT was then coupled with 1 via the Grignard
reaction with the aid of a Ni(II) catalyst to yield terEDOT. The
cholesteric electrolyte solution used as the reaction field was
prepared by adding a CLC inducer (cholesteryl pelargonate) to 4-
cyano-40-hexyl biphenyl (6CB). Tetrabutylammonium perchlo-
rate (TBAP) was then added as a supporting salt. Electrochemical
polymerisation of the monomer was carried out in the CLC
electrolyte solution between two indium-tin-oxide (ITO) glass
electrodes. Molecular structures constituting CLC electrolyte
containing EDOT monomer are shown in Scheme 1 (lower). The
CLC electrolyte solution displays a typical fingerprint texture
under polarizing optical microscopy (POM) observation at 25 ꢀC
(Fig. 1). Prior to electrochemical polymerisation, the electrolyte
solution was heated in a vial to 40 ꢀC under an argon atmosphere
in order to completely dissolve the supporting salt, monomer, and
chiral inducer in the 6CB (LC solvent). Electrochemical poly-
merisation was then performed by injecting the mixture between
two sandwiched ITO-coated glass electrodes with a Teflon sheet
(thickness, ca. 0.2 mm) as a spacer. The reaction cell was initially
heated to 40 ꢀC, and then gradually cooled to room temperature
ꢀ
(25 C) to afford the CLCs with a good fingerprint texture. A
voltage of 4.0 V was then applied across the cell. The optical
texture of the cholesteric mixture remained unchanged upon the
application of a voltage. After 30 min, an insoluble and infusible
polymer thin film was obtained. It coated the anode side of the
ITO electrode. The film on the ITO was then washed with meth-
anol, water, acetonitrile, methanol, water, and acetone in that
order, and dried under reduced pressure to afford the chiroptical
terEDOT polymer film (PEDOT*).
Polarizing optical microscopic image
POM observations of PEDOT* prepared in the CLC electrolyte
solution revealed that the polymer exhibits a fingerprint texture
resembling (but not identical to) that of the original CLC system
(Fig. 2). In CLCs, the optical texture is closely related to the
individual molecular ordering forming the matrix, and the
present PEDOT* film exhibits birefringence along with an
Scheme 1 Synthetic route for PEDOT* and constituents of the chole-
steric liquid crystal (CLC) electrolyte solution. (1) N-Bromosuccinimide,
chloroform–glacial acetic acid, chloroform. (2) n-BuLi, THF, then
MgBr2, Et2O. (3) Ni(dppp)Cl2, THF.
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Fig. 3 (A) Laser diffraction patterns of PEDOT*. (B) PEDOT* film
under fluorescent light. (C) PEDOT* film showing interference colour
with an oblique angle of incidence from a white light emitting diode
beam.
constant, and q is the incident angle (glancing angle). In the case
of this system, P/2 (distance between the stripes) is the lattice
constant.
Fig. 2 Polarizing optical microscopic (POM) image of PEDOT*
prepared in unoriented cholesteric electrolyte solution at different
magnifications.
Uniaxial PEDOT* prepared in oriented electrolyte solution by
shear stress exhibits an oriented optical texture (top) and an
oriented laser diffraction pattern (bottom), as shown in Fig. 4.24
excellent colour distribution due to optical retardation under
POM, similar to that of the CLC. In other words, the molecular
arrangement of the individual main chains was oriented in
a helical manner, similar to that of the CLC. However, the
polymer is not a CLC.
Diffraction
The CLC-like periodic structure of the PEDOT* film produces
two optical effects: the diffraction of light and the iridescent
reflection of light. Diffraction can be observed by irradiating the
PEDOT* film on the ITO electrode with a laser set perpendicular
to the film surface and visualizing the transmitted pattern on
a screen. A circular diffraction pattern (a Fourier-transformed
image) is produced due to the random diffraction function of the
present polymer, as shown in Fig. 3(A). Three wavelengths of
laser light were tested (red, green, blue), and each produced
a diffraction circle of characteristic radius. The circle diameter
increases with an increase in the laser wavelength (blue < green <
red). The grating period corresponds to the distance between
adjacent stripe features of the polymer film. Although the
inherent colour of the polymer is dark blue [Fig. 3(B)],
a rainbow-coloured iridescent reflection occurs under irradiation
with white light, and the reflected wavelengths vary with the
angle of incidence and the wavelength composition of the inci-
dent light beam [Fig. 3(C)].13 This iridescent reflection originates
from the periodic stripe structure of the polymer surface. Thus,
the diffraction by the polymer satisfies Bragg’s law, nl ¼ 2dsinq,
where n is the integral number, l is the wavelength, d is the lattice
Fig. 4 (Top) POM image of PEDOT* prepared in oriented cholesteric
electrolyte solution. (Bottom) Laser diffraction pattern (arrow indicates
orientation).
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The orientation of PEDOT* is normal to the shear direction of
the CLC electrolyte solution (slightly tilted), suggesting that the
shear stress aligns the fingerprint pattern of the CLC electrolyte
solution, whereas individual CLC molecules are aligned normal
to the shear direction. In the polymerisation of terEDOT, the
polymer molecules are aligned according to the CLC electrolyte
solution, and are thus aligned normal to the shear direction of the
CLC electrolyte solution. These results indicate that the laser
diffraction effectively expresses the molecular orientation of the
polymer.
preparation from the EDOT monomer in CLCs,14 and helical
polyacetylenes prepared by acetylene gas–CLC interfacial poly-
merisation.27 This difference can be attributed to the difference in
molecular shape and crystallinity of PEDOT* prepared by the
present route. The SEM observations confirm that the wedge
pattern identified by POM corresponds to the assembly of fibrils.
Vortices consisting of coil-like fibrils are apparent between the
helical bundles. Furthermore, the fibrils between fingerprint
features form thin helical bundle structures that are twisted
clockwise (Fig. 6(H)).
The characteristic structure may originate from that of indi-
vidual molecules of the polymer growth along the gradually
twisted order of the CLC from the anode (ITO) with the elec-
trochemical epitaxial growth process. The helical formation from
the director of the CLC provides a different degree of growth for
the polymer on the electrode. It is important to note that the
SEM
Scanning electron microscopy (SEM) images of the present
polymer taken at 25ꢀ to the surface are shown in Fig. 5 (the four
images are from the same sample at different regions). The high
conversion and rigidity of the monomer combined with the p-
stacking of the polymer, result in a mode of polymer aggregation
that produces a fibril structure during electrochemical growth.
This structure differs from that of chiral polybithiophene,25 chiral
polypyrrole,26 PEDOT synthesised by electrochemical
Fig. 6 Plausible polymerisation mechanism of terEDOT in a CLC
electrolyte solution. (A) Helical ordering of the CLC. (B) Twisted
directors continuum of the CLC (red arrows) and epitaxial growth
directions of the polymer from the anode side (sky blue arrows). (C)
Helical twist formation of PEDOT*. (D) Formation of individual
PEDOT* main chains and (E) aggregation. (F) PEDOT* deposited on
ITO. (G) 3D possible structure of the polymer surface. (H) SEM image of
PEDOT* showing a helical bundle (polymer grew at the region where
directors of the CLC are oriented in parallel to the electrode surface) and
lamellar type structure (polymer grew at the region between directors of
the CLC oriented in parallel to the electrode surface).
Fig. 5 Scanning electron microscopy (SEM) images of PEDOT*
prepared in cholesteric liquid crystal electrolyte solution. SEM images of
PEDOT* taken from a direction oriented 25ꢀ from the surface [(A)
3500ꢁ, (B) 4000ꢁ]. (C) SEM image of the polymer surface in the normal
direction (5000ꢁ). (D) Magnification of surface image (10000ꢁ) in the
normal direction.
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fibrils grow well in the region in which the CLC directors are
oriented normal to the electrode surface. The fibrils with helical
bundle are observed in the region where the director of the CLC
is parallel to the electrode. The fingerprint pattern with the fibril
structure observed is similar to the molecular model of the dome-
type polygonal texture of CLC materials,28 and the photo-
polymerised polymer obtained in a CLC.29,30
The CLC of the biomolecules is solidified during the process of
skeletal formation.31 The characteristic structure is utilized for
structural colour in insects such as butterflies. The morphology
and polymerisation process of the PEDOT* in the present study
may be similar to those for other biological systems. Moreover,
the morphology is very similar to the microstructure of the
tangential section of tubercles of Carcinus maenas (littoral crab)18
[Fig. 5(C)]. A distinct surface image taken at high magnification
is shown in Fig 5(D). In the SEM image, an S-shaped structure is
observed between three lines of bundles.
Plausible polymerisation mechanism
A plausible polymerisation mechanism of terEDOT in the CLC
electrolyte solution is shown in Fig. 6. The CLC electrolyte
solution has one-handed helical ordering [Fig. 6(A)]. Polymeri-
sation is performed in the sequential helical director field [red
arrows in Fig. 6(B)] of the CLC electrolyte solution with an
electrochemical epitaxial growth mechanism, and the chiral field
provides a one-handed twist of the main chain [Fig. 6(C)]. The
lamella-like structure can be considered an advanced form of the
helical arranged structure. The CLC thus provides a chiral
reaction field and functions as a chiral molecular vessel.
Individual twisted PEDOT* main chains [Fig. 6(D)] aggregate
to form lamella-like semicircles [Fig. 6(E), 6(F), 6(G)]. The top-
view SEM image of the polymer shows a lamellar structure with
the ‘‘S-shaped’’ form [Fig. 6(H)]. The right-handed helical
bundles of the polymer are located in the region where the
directors of CLC are oriented parallel to the electrode surface.
This may be due to the fact that the helical torque of the CLC
affects the polymer during the growth process in this region. The
polymer may thus form a characteristic structure in the CLC
electrolyte solution.
Fig. 7 (A) POM image of nematic electrolyte solution containing ter-
EDOT as a monomer. (B) PEDOT prepared in nematic electrolyte
solution (N-PEDOT) in the schlieren texture region. (C) PEDOT
prepared in nematic electrolyte solution (N-PEDOT) at a thread-like
texture region. (D, E) SEM images of N-PEDOT.
the rotation of the POM analyser, as generally observed for
NLC, indicating that the present polymer has schlieren-like
molecular ordering. These results further suggest that the
thread-like pattern of the NLC is imprinted on the polymer
during polymerisation, as shown in Fig. 7(C). The fibrils of N-
PEDOT are aligned in a thread-like pattern, indicating that the
NLC directs the growth of the polymer. The insolubility of the
polymer in the NLC electrolyte then facilitates phase separa-
tion.32
Electrochemical polymerisation in a nematic liquid crystal
Electrochemical polymerisation of the monomer was also carried
out in the same manner using a nematic LC (NLC) to afford N-
PEDOT (PEDOT prepared in a NLC). The electrolyte solution
for this polymerisation consisted of 0.29 g 6CB, 0.6 mg TBAP,
and 8 mg terEDOT. A POM image of the NLC electrolyte
containing the monomer is shown in Fig. 7(A).
The distribution of the director around the structural defect in
NLC has been predicted theoretically,28a and the SEM image of
N-PEDOT visually confirms the presence of the NLC topology,
including the fibril orientation reflecting the vector field around
the wedge-type loops near the centre of the defect. The N-
PEDOT topology has disclination parameters of s ¼ ꢂ1 and s ¼
ꢂ1/2 [Fig. 7(D, E)], where 2ps is the angle at which the director
turns on a closed curve around the centre. The alignment of
fibrils in N-PEDOT thus allows the LC directors to be visual-
ized as vectors, and confirms that N-PEDOT growth occurs to
form a texture similar to that of NLC in the same manner as
observed for the polymerisation in the CLC. That is, tran-
scription of the NLC order occurred at the molecular level in the
polymerisation of PEDOT by this method. N-PEDOT is not
The primary feature of molecular organisation in a NLC is the
orientational order of the molecular axis, where the average
direction of the long axes defines the director (n), which may be
treated as a vector. The LC displays a schlieren texture,
appearing as a brush-like pattern or thread-like texture, reflect-
ing the disclinations and directors of individual LC molecules in
the system.
N-PEDOT film exhibits birefringence and a schlieren texture
with two-fold brushes under POM, as shown in Fig. 7(B). The
brushes of the schlieren texture on the film visually rotate with
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chiral and exhibits no Cotton effect in circular dichroism (CD)
spectroscopy.
polymerisation because the weak Cotton effect is only observed
at wavelengths in the range 240–340 nm. PEDOT* did not
produce any signals related to the CLC inducer in infrared (IR)
absorption spectroscopy measurements. The reversible inversion
of the sign of the Cotton effect at 450 nm in the doping–dedoping
(oxidation–reduction) process via a change in the electronic state
of the polymer indicates that the polymers have an inherently
chiral structure.
The ORD spectra of PEDOT* at various potentials vs. Fc/Fc+
in 0.1 M TBAP–acetonitrile solution is shown are Fig. 8 (bottom)
and Fig. S2 (lower) (ESI†). Upon oxidation, an optical rotation
trough at 430 nm and a peak at 560 nm appear in the spectrum,
with an isosbestic point at 772 nm, which could be attributed to
the electrochemical doping–dedoping of perchlorate ions in the
redox process. This result confirms that the polymer is electro-
chiroptically active and that the optical rotation can be
controlled via the electrochemical process. This property of the
polymer can be regarded as an ‘‘electrochemically driven chi-
roptical effect.’’
Optical activity
In situ optical absorption, CD, and optical rotatory dispersion
(ORD) spectra for the polymer films were obtained under
various electrochemical conditions in monomer-free 0.1 M
TBAP–acetonitrile solution. The measurement cell included
a platinum wire as the counter electrode, an Ag/Ag+ reference
electrode (calibrated against Fc/Fc+), and the polymer deposited
on ITO. The optical absorption spectrum of oxidized (electro-
chemically doped) PEDOT* exhibits a peak at 538 nm accom-
panied by a weakening of the p–p* transition of the main-chain
and a strengthening of the peaks at 756 nm and 1298 nm due to
the generation of radical cations and dications on the main chain
(Fig. S1, ESI†). The radical cations and dications on the main
chain can be referred to as polarons and bipolarons, respec-
tively.33–35 The colour of the polymer changed reversibly from
dark blue to sky blue upon oxidation, which proceeds by the
electrochemical doping of perchlorate ions. This doping–
dedoping behaviour is typical for electroactive polymers.36–38
As shown in Fig. 8 (top, oxidation process), PEDOT* exhibits
a Cotton effect associated with the p–p* transition of the poly-
mer main chain, which is related to the polaron region in elec-
trochemical doping and dedoping. CD spectra of the
electrochemical reduction process of the polymer are shown in
Fig. S2 (top) (ESI†). These results indicate that the redox process
for the CD of the polymer is reversible. The CD signals cannot be
due to the CLC inducer, cholesteryl pelargonate, employed in the
The PEDOT* displayed a bisignate (split type) CD in the
reduced state. CD spectra induced by poor solvents or the casting
of polythiophene film with an optically active substituent have
been ascribed to exciton coupling.39 Exciton coupling requires
the presence of an unconjugated chromophore in the chiral
arrangement, which can occur through interchain interactions in
the aggregate state. The bisignate band in the reduced state of the
PEDOT* suggests the presence of an intermolecular process
upon aggregate formation. The aggregate induced band is
a charge transfer-type p–p* stacking of the main chain, arising
due to electronic communication. Furthermore, oxidation
process physically increases the distance between main chains in
chiral aggregation due to the intercalation of the perchlorate ion
between the main chains. Therefore, it is possible that the
intrusion of the ions does not completely break the chiral
aggregation. In the helical aggregation state of the polymer,
several hierarchical levels of chiral structure are plausible,
including a helical main chain structure produced by transcrip-
tion from the CLC.
Electrochemical potential change to electroactive p-conju-
gated polymers reflects the exact doping level, and this process
gives changes in the electronic state, resulting in a colour change
for polymers. Achiral p-conjugated polymers prepared in
isotropic electrolyte solutions show no optical activity, although
the polymers display a colour change with the redox process. On
the other hand, the PEDOT* thus synthesised in the CLC shows
not only a colour change but also tunable chiroptical properties
with the redox process.40,41
ESR
Fig. 9 (top) shows the electron spin resonance (ESR) spectra of
PEDOT* at three potentials. The intensity of the ESR signals
changes according to the applied potential, which reflects the
state of the electrochemical doping. This result suggests that the
spins on the polymer are derived from the induced charge (S ¼ 1/
2) in the p-electron system. The g value of 2.0027 for the present
polymer indicates the formation of charge carriers in the poly-
mer, such as polarons.35 The ESR result at ꢂ0.7 V indicates that
electrochemical dedoping is not complete, with ESR signals
Fig. 8 (Top) CD spectra and (bottom) ORD spectra of monomer-free
PEDOT* at various potentials vs. Fc/Fc+ during electrochemical oxida-
tion in monomer-free 0.1 M TBAP–acetonitrile solution.
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polymer surface may be referred to as a ‘‘chiral carpet with
vortex’’ structure. The polymer exhibits chiroptical electro-
chromism, diffraction properties, and charge carrier generation.
The CD and the ESR results suggest the formation of polarons in
one-handed helical structures for the polymer. Synthesis of the
polymer by the present method is applicable to the fabrication of
new optoelectronic devices such as chiral electrochromic displays
and optical rotation modulators, and provides valuable insight
into the behaviour and structure of liquid crystals.
Experimental
Synthesis of 5,7-dibromo-2,3-dihydro-thieno[3,4-b][1,4]dioxine
(dibromo-EDOT) (1)
This synthesis was carried out according to a previously reported
method.423 Quantities used: CHCl3 (50 mL), glacial acetic acid
(50 mL), 3,4-ethylenedioxythiophene (EDOT) (3 g, 21.1 mmol),
N-bromosuccinimide (NBS) (8 g). Yield ¼ 73% (4.63 g, white
crystals).
Synthesis of 2,3,20,30,200,300-hexahydro-[5,50:70,500]ter(thieno[3,4-b]-
[1,4]dioxine) (terEDOT) (3)
Into a solution of EDOT (1.9 g, 13.4 mmol) in tetrahydrofuran
(THF) a quantity of 5 mL of n-butyl lithium–hexane solution
was added (2.71 mol Lꢂ1 in hexane, 13.4 mmol) under argon flow
at ꢂ79 ꢀC. The reaction mixture was stirred for 60 min. Then, the
temperature of the reaction mixture was maintained at 0 ꢀC, and
3.46 g (13.4 mmol) of MgBr2 in Et2O was added to the mixture
and stirred. After 30 min, dibromo-EDOT (1) (2 g, 6.7 mmol)
was added. Subsequently, [Ni(dppp)Cl2] (0.14 g, 2.68 ꢁ 10ꢂ4
mol) was slowly added to the reaction mixture. After 12 h, the
solution was evaporated, washed thoroughly with water, and
extracted with dichloromethane. After evaporation, the crude
product was purified by column chromatography (silica gel,
dichloromethane). The silica gel was pretreated by passing
through approximately 50 mL triethyl amine to avoid polymer-
isation of the product during the purification procedure. Yield ¼
63% (3.6 g, dark yellow powder). The chemical structure of the
desired material was confirmed by 1H NMR in CDCl3 (one drop
of triethyl amine was added to the NMR tube to avoid poly-
Fig. 9 (Top) ESR spectra of PEDOT* at ꢂ0.7 V, ꢂ0.5 V, and ꢂ0.3 V vs.
Fc/Fc+. (Bottom) Possible structure of polarons in the main chain and
chiral aggregation structure.
indicating the existence of radicals derived from residual
polarons. The intensity of the ESR signal at ꢂ0.5 V increases
with an increase in radical cation concentration, and decreases
with the generation of dications (reduction in radical concen-
tration on the main chain). This ESR result is consistent with the
absorption spectrum, which reveals the emergence of an
absorption band at 756 nm (polaron) with increasing voltage.
The CD results for the polymer are also consistent with the ESR
spectra. With increasing voltage, the CD signal at 450 nm
weakens and the peak at 619 nm strengthens. Furthermore, the
CD signals at 850 nm are negative at ꢂ0.7 V and positive at ꢂ0.5
V. Plausible structures of chiral aggregation forms produced in
the CLC electrolyte solution and polaron as a charge carrier in
the main chain are shown in Fig. 9 (bottom). Polarons locate
individual main chains, and gradually twist in a helical manner to
form chiral aggregation polarons. Moreover, the results suggest
the formation of inter-chain helical polarons of the conducting
polymer.
1
merisation). H NMR (d from TMS, signals of terEDOT): 4.21
(m, 6H), 4.33 (m, 6H), 7.1 (m, 2H).
Preparation of cholesteric liquid crystal electrolyte solution
The cholesteric electrolyte solution used as the reaction field was
prepared by adding a CLC inducer (cholesteryl pelargonate, 0.02
g, 0.038 mmol) to 4-cyano-40-hexyl biphenyl (6CB, 0.459 g),
a well-known nematic LC. Tetrabutylammonium perchlorate
(TBAP, 1 mg, 0.3 ꢁ 10ꢂ5 mmol) was then added as a supporting
salt. Liquid crystallinity was confirmed to be maintained after
addition of the monomer (terEDOT, 20 mg, 0.047 mmol). A
scheme of the constituents of the CLC electrolyte solution system
employed in this study is provided in Scheme 1. The cholesteric
electrolyte solution system exhibits a fingerprint texture typical
of the cholesteric phase when observed by polarizing optical
microscopy (POM) at room temperature, where the distance
between stripes in the optical texture of the cholesteric electrolyte
Conclusions
PEDOT having chiroptical properties was electrochemically
synthesised in CLC electrolyte solution from the terEDOT
monomer. Electrochemical polymerisation by this method
afforded a polymer with a distinct fibril structure and vortex
texture imprinted CLC structure indicating that the individual
main chains were arranged by the topological transcription of
structural chirality in the epitaxial electrochemical polymerisa-
tion in CLC as a one-handed helically twisted matrix. The fibril-
forming property enables the polymer to direct the LC. The
4920 | J. Mater. Chem., 2009, 19, 4914–4921
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11 L. Huang, Z. Wang, H. Wang, X. Cheng, A. Mitra and Y. Yan, J.
Mater. Chem., 2002, 12, 388–391.
12 D. Kim, J. Choi, K. J.-Y. Kim, Y. K Han and D. Sohn,
Macromolecules, 2002, 35, 5314–5316.
13 H. Goto, F. Togashi, A. Tsujimoto, R. Ohta and K. Kawabata, Liq.
Cryst., 2008, 35, 847–856.
solution corresponds to the helical half-pitch of the CLC. The
mixture of LC, monomer, CLC inducer, and supporting salt is
employed as an electrolyte solution for electrochemical poly-
merisation in place of conventional systems containing a sup-
porting salt in isotropic solution.
14 H. Goto and K. Akagi, Macromol. Rapid Commun., 2004, 25, 1482–
1486.
Techniques
15 H. Goto, Phys. Rev. Lett., 2007, 98, 253901.
16 D. Wasserberg, S. C. J. Meskers, R. A. J. Janssen, E. Mena-Osteritz
€
Absorption spectra were obtained using a Hitachi U-2000 spec-
trophotometer, and circular dichroism and optical rotation
measurements were performed using a Jasco J-720 spectrometer
with an ORDE-307W ORD unit. Electrochemical measurements
of polymers were conducted using an electrochemical analyser
(PGSTAT 12, Autolab, Netherlands), and optical textures were
observed using a Nikon ECLIPS LV 100 high-resolution polar-
izing microscope with Nikon LU Plan Fluor and Nikon CFIUW
lenses at 1000ꢁ and 500ꢁ magnifications without immersion oil.
and P. Bauerle, J. Am. Chem. Soc., 2006, 128, 17007–17017.
17 G. A. Sotzing, J. R. Reynolds and P. J. Steel, Adv. Mater., 1997, 9,
795–798.
18 Y. Bouligand, Tissue Cell, 1972, 4, 189–190, 192–217.
19 Y. Bouligand, J. P. Denefle, J. P. Lechaire and M. Maillard, Biol.
Cell., 1985, 54, 143–162.
20 H. Tong, P. Wan, W. Ma, G. Zhong, L. Cao and J. Hu, J. Struct.
Biol., 2008, 163, 1–9.
21 Y. Zhu, I. Heim and B. Tieke, Macromol. Chem. Phys., 2006, 207,
2206–2214.
22 H. Meng, D. F. Perepichka and F. Wudl, Angew. Chem., Int. Ed,
2003, 42, 658–661; H. Meng, D. F. Perepichka and F. Wudl,
Angew. Chem., 2003, 115, 682–685.
23 G. A. Sotzing and J. R. Reynolds, Chem. Mater., 1996, 8, 882–889.
24 The polymerisation cell was set perpendicular to the ground, and the
CLC electrolyte solution was injected into the cell. The electrolyte
solution flowed to the bottom of the cell, producing shear stress. An
appropriate voltage was then applied to induce electrochemical
polymerisation in the oriented CLC field. This simple procedure
affords uniaxial CLC-like polymer films.
25 H. Goto and K. Akagi, Macromolecules, 2005, 38, 1091–1098.
26 H. Goto, J. Polym. Sci., Part A: Polym. Chem, 2007, 45, 1377–1387.
27 G. Piao, S. Kaneko, I. Higuchi, K. Akagi, H. Shirakawa and
M. Kyotani, Synth. Met., 1999, 101, 94.
Materials
TBAP and cholesteryl pelargonate were obtained from Tokyo
Kasei (TCI) Japan. 6CB was purchased from Merck. EDOT was
obtained from Aldrich. The ITO glass (Furuuchi Chemical
Corporation) consists of a 0.2–0.3 mm-thick ITO layer on glass (9
U cmꢂ2).
Acknowledgements
28 (a) D. Demus, L. Richter, Texture of Liquid Crystals, Verlag Chemie,
Weinheim, New York, 1978; (b) Y. Bouligand, J. Phys. France, 1972,
33, 715–736.
The author thanks the Chemical Analysis Center at the
University of Tsukuba, for NMR spectra and elemental analysis
data, and the Engineering Workshop of University of Tsukuba,
for glasswork.
29 (a) Kihara, T. Miura and R. Kishi, Macromol. Rapid Commun., 2004,
25, 445–449; (b) G. A. Held, L. L. Kosbar, I. Dierking, A. C. Lowe,
G. Grinstein, V. Lee and R. D. Miller, Phys. Rev. Lett., 1997, 79,
3443–3446; (c) I. Dierking, L. L. Kosbar, A. Afzali-Ardakani,
A. C. Lowe and G. A. Held, J. Appl. Phys., 1997, 81, 3007–3014.
30 M. Mitov and N. Dessaud, Nat. Mater., 2006, 5, 361–364.
31 J. Watanabe, H. Takezoe, Structural colour in biological systems–
principal and applications, ed. S. Kinoshita and S. Yoshioka, Osaka
University Press, Osaka, 2005, pp. 329–337.
32 (a) H. Kihara and T. Miura, Polymer, 2005, 46, 10378; (b) H. Kihara,
T. Miura, R. Kishi, T. Yoshidsa, M. Shibata and R. Yosomiya, Liq.
Cryst., 2003, 30, 799; (c) H. Kihara, T. Miura and R. Kishi,
Macromol. Rapid Commun., 2004, 53, 445.
References
1 S. Courty, A. R. Tajbakhsh and E. M. Terentjev, Phys. Rev. Lett.,
2003, 91, 085503.
2 S. Courty, A. R. Tajbakhsh and E. M. Terentjev, Phys. Rev. E: Stat.,
Nonlinear, Soft Matter Phys., 2006, 73, 011803.
3 K. Araya, A. Mukoh, T. Narahara and H. Shirakawa, Chem. Lett,
1984, 1141–1142.
4 K. Araya, A. Mukoh, T. Narahara and H. Shirakawa, Synth. Met.,
1986, 14, 199–206.
5 H. Shirakawa, K. Akagi, S. Katayama, K. Araya, A. Mukouh and
T. Narahara, J. Macromol. Sci. Chem., 1988, A25, 643–654.
6 M. Goh, T. Matsushita, M. Kyotani and K. Akagi, Macromolecules,
2007, 40, 4762–4779.
33 K. Marumoto, Y. Muramatsu, S. Ukai and S. Kuroda, Synth. Met.,
2005, 154, 45–48.
34 Y. Furukawa, J. Phys. Chem., 1996, 100, 15644–15653.
35 A. J. Heeger, S. Kivelson, J. R. Schrieffer and W.-P. Su, Rev. Mod.
Phys., 1988, 60, 781–850.
36 T. Ohsawa, K. Kaneto and K. Yoshino, Jpn. J. Appl. Phys., 1984, 23,
L663–L665.
37 C. L. Gaupp, K. Zong, P. Schottland, B. C. Thompson, C. A. Thomas
and J. R. Reynolds, Macromolecules, 2000, 33, 1132–1133.
38 T. Ohsawa, T. Kabata, O. Kimura, M. Onoda and K. Yoshino, Jpn.
J. Appl. Phys., 1989, 28, 996–999.
39 (a) R. Fiesel, C. E. Halkyard, M. E. Rampey, L. Kloppenburg,
S. L. Studer-Martinez, U. Scherf and U. H. F. Bunz, Macromol.
Rapid Commun., 1999, 20, 107–111; (b) F. J. M. Hoeben,
P. Jonkheijm, E. W. Meijer and A. P. H. J. Schenning, Chem. Rev.,
2005, 105, 1491–1546.
40 (a) H. Goto, Adv. Funct. Mater., 2009, 19, 1335–1342; (b)
H. Yoneyama, K. Kawabata, A. Tsujimoto and H. Goto,
Electrochem. Commun., 2008, 10, 965–969.
41 A phenomenon of chirality of electroactive conjugated polymers
changes based on electrochemical redox process.
42 G. A. Sotzing and J. R. Reynolds, Chem. Mater., 1996, 8, 882–889.
7 (a) H. Goto, K. Akagi, Book of Abstracts of the International
Conference of Science and Technology of Synthetic Metals, Research
Center for Theoretical Physics, Fudan University, Shanghai, China,
2002, p 17; (b) H. Goto, N. Nomura and K. Akagi, J. Polym. Sci.,
Part A: Polym. Chem., 2005, 43, 4298–4302; (c) H. Goto and K.
Akagi, Jpn. Pat. No. 362979, 2002.
8 P. C. Ewbank, G. Nuding, H. Suenaga, R. D. McCullough and
S. Shinkai, Tetrahedron Lett., 2001, 42, 155–157.
9 C. Li, M. Numata, T. Hasegawa, T. Fujisawa, S. Haraguchi,
K. Sakurai and S. Shinkai, Chem. Lett, 2005, 34, 1532–1533.
10 T. Hatano, A.-H. Bae, M. Takeuchi, N. Fujita, K. Kaneko, H. Ihara,
M. Takafuji and S. Shinkai, Angew. Chem., Int. Ed., 2004, 43, 465–
469; T. Hatano, A.-H. Bae, M. Takeuchi, N. Fujita, K. Kaneko,
H. Ihara, M. Takafuji and S. Shinkai, Angew. Chem., 2004, 116,
471–475.
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