Electrochemical and spectral properties of meta-linked 1,3,5-tris(aryl) benzenes and 2,4,6-tris(aryl)-1-phenoles, and their polymers

Article abstract of DOI:10.1016/j.electacta.2010.07.005

We present electrochemical and spectral properties of symmetric monomers 1,3,5-tris(aryl)benzenes and 2,4,6-tris(aryl)-1-phenols and their polymers. These compounds contain thienyl, furyl or EDOT moieties attached to central benzene or phenol ring at the

Full text of DOI:10.1016/j.electacta.2010.07.005

Electrochimica Acta 55 (2010) 7419–7426
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Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Electrochemical and spectral properties of meta-linked 1,3,5-tris(aryl)benzenes
and 2,4,6-tris(aryl)-1-phenoles, and their polymers
Krzysztof R. Idzika,b,∗, Przemyslaw Ledwonc, Rainer Beckerta,∗∗, Sylwia Golbac,
Jaroslaw Frydele, Mieczyslaw Lapkowskic,d
a Institute of Organic and Macromolecular Chemistry, Friedrich Schiller Universität Jena, Humboldstraße 10, D-07743 Jena, Germany
b Department of Chemistry, Faculty of Medicinal Chemistry and Microbiology, Wroclaw University of Technology, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
c Silesian University of Technology, Faculty of Chemistry, Strzody 9, 44-100 Gliwice, Poland
d Centre of Polymer and Carbon Materials, Polish Academy of Sciences, ul. Sowinskiego 5, 44-121 Gliwice, Poland
e Technische Universität Darmstadt, Eduard-Zintl-Institut für Anorganische und Physikalische Chemie, Petersenstr. 20, 64287 Darmstadt, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
We present electrochemical and spectral properties of symmetric monomers 1,3,5-tris(aryl)benzenes and
2,4,6-tris(aryl)-1-phenols and their polymers. These compounds contain thienyl, furyl or EDOT moieties
attached to central benzene or phenol ring at the meta-position, synthesized by a Stille cross-coupling
procedure. All monomers are electroactive and undergo electropolymerization creating thin films on
an electrode surface. Polymers with meta-linkages were obtained by electrochemical oxidation. Detailed
cyclic voltammetry and in situ UV–vis spectroelectrochemistry show that polymers with hydroxy groups
exhibit higher conductivity and better stability than with benzene core. Interesting and different behavior
occurs for 2,4,6-tris(2-thienyl)-1-phenol, for which the characteristic, sharp, redox peak is observed.
© 2010 Elsevier Ltd. All rights reserved.
Received 14 January 2010
Received in revised form 2 July 2010
Accepted 3 July 2010
Available online 30 July 2010
Keywords:
Stille coupling procedure
Meta-linkage
Branched polymers
Electrochemical polymerization
Hydroxyl substituent
1. Introduction
their conductivity [11]. Moreover dendrite structures exhibit inter-
esting properties like energy transfer and photochemical antenna
Blue light-emitting materials have been the subject of extensive
studies in recent years. The band gap of the materials can be tuned
by attaching substituents to a polymer backbone or introducing
the design of ␲-conjugated linkages which include nonconju-
gated carbon bridges. For example the presence of meta-linkage
units along polymer chain effectively interrupts ␲-conjugation [1].
M-phenylenes units reveal great linearity of optical properties,
inversion of conjugation length, and enhancement of photolu-
minescence efficiency [2]. Blue light-emitting materials can be
synthesised on the base of this polymers.
It has previously been reported in the literature, that branched
oligothiophenes and oligothienylbenzenes act as monomers in
cross-linked semiconducting polymers [3–5], and as components of
conjugated dendrimers [6–10]. This type of polymers can be char-
acterized by a three-dimensional structure, which is on the sake of
function [12].
Herein, we describe a convenient and simple method for
creating conjugated polymers, namely poly(arylbenzene)s, based
on thiophene, furan and EDOT linkages. Aside from a typical
application of polymers for high surface area materials, such
as gas storage or catalyst support, the conjugated polymers
may find new applications in the field of organic electronics or
optoelectronic compounds. The conjugated polymers in general,
and polythiophenes in particular, have found widespread use in
organic–electronic devices, such as organic light-emitting diodes
(OLEDs) [13], organic field-effect transistors (OFETs) [14], organic
solar cells, and photovoltaic cells [15,16].
Symmetrical molecules can be used as central cores for vari-
ous oligomers and to decrease the length of the step synthesis.
C3-symmetric compounds based on a di- and tri-thienylbenzene
core and symmetrical conjugated oligo(phenylene ethynylene)s
are useful in the design of organic electroluminescent devices.
Suzuki, Stille, Kumada, and Negishi coupling reactions are well
established [17,18]. In this paper, we present a series of various
C3-symmetric compounds which were synthesized by Stille cross-
coupling procedure. The obtained compounds are characterized by
a high yield (84–92%).
∗
Corresponding author at: Institute of Organic and Macromolecular Chemistry,
Friedrich Schiller Universität Jena, Humboldstraße 10, D-07743 Jena, Germany.
Tel.: +49 15779202076; fax: +49 3641948212.
∗∗
Corresponding author. Tel.: +49 3641948230; fax: +49 3641948212.
E-mail addresses: krzysztof.idzik@pwr.wroc.pl (K.R. Idzik),
rainer.beckert@uni-jena.de (R. Beckert).
0013-4686/$ – see front matter © 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.electacta.2010.07.005

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We performed electrochemical and spectroscopic studies.
0.4 mmol). The resulting mixture was stirred for 48 h in 110 ◦C.
After this time the mixture was cooled down to the room temper-
ature. Water was added and the resulting solution was extracted
with 3 × 50 mL portions of CHCl3. The combined organic layers
were washed with 50 mL of brine, dried over MgSO4 and evapo-
rated to until a dark brown oil appeared. The crude product was
purified by a column chromatography (silica gel, hexane/AcOEt,
10:1). The palladium-catalyzed Stille cross-coupling reaction of
compound 1 or 2 with 2-(tributylstannyl)arylenes gave the desired
products: 1,3,5-tris(2-thienyl)-benzen (TPh), 1,3,5-tris(2-furyl)-
benzene (FPh), 1,3,5-tris[2-(3,4-ethylenedioxythienyl)]-benzene
(EPh), 2,4,6-tris(2-thienyl)-1-phenol (TOPh), 2,4,6-tris(2-furyl)-
1-phenol (FOPh) (Scheme 1) with an yield of 84–92%. All the
monomers were obtained as white, green, yellow, and brown
crystals and characterized by spectroscopic methods. All spectral
data confirm their molecular structures.
We focused on oxidative polymerization of the monomers and
thoroughly elucidated optical and electrochemical properties of
polymers in dependence of thiophene, EDOT, and furan moieties.
It is also worthy to mention, that oligomers containing hydroxyl
groups provide both a good stability and a high conductivity to the
film.
2. Experimental
2.1. Synthesis of monomers
All chemicals, reagents and solvents are commercially available
and were used without further purification, except toluene, which
was distilled over sodium/benzophenone. 2-(Tributylstannyl)-3,4-
ethylenedioxythiophene was synthesized according to a previously
reported method [19]. The structures have been characterized by
1H NMR and 13C NMR in one of our previous papers [20].
2.3. Electrochemistry
2.2. General procedure for the preparation of
1,3,5-tris(aryl)benzene (TPh, FPh, EPh) and
2,4,6-tris(aryl)-1-phenol (TOPh, FOPh)
Electrosynthesis and studies on polymer films were per-
formed on Ecochemie AUTOLAB potentiostat–galvanostat model
PGSTAT20. The results were analyzed using GPES software (Gen-
eral Purpose Electrochemical System). Cyclic voltammetry (CV) was
used for electrochemical measurements. In order to perform all
experiments three-electrode arrangement was employed. Polymer
films were synthesized on the platinum wire at a scan rate 50 mV/s.
An Ag pseudo-reference electrode was used and its exact potential
To 1,3,5-tribrombenzene (1) (2.0 mmol) or 2,4,6-tribrom-
1-phenol (2) (2.0 mmol) in a 250 mL round two-bottom flask
under nitrogen into an anhydrous toluene (150 mL) was added
2-(tributylstannyl)arene (6.6 mmol) and Pd(PPh3)4 (0.460 g,
Scheme 1. Synthesis of monomers: (a) 1,3,5-tris(2-thienyl)-benzene (TPh), (b) 1,3,5-tris(2-furyl)-benzene (FPh), (c) 1,3,5-tris[2-(3,4-ethylenedioxythienyl)]-benzene (EPh),
(d) 2,4,6-tris(2-thienyl)-1-phenol (TOPh), (e) 2,4,6-tris(2-furyl)-1-phenol (FOPh).

K.R. Idzik et al. / Electrochimica Acta 55 (2010) 7419–7426
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was measured versus ferrocene. Platinum wire served as a counter
electrode.
Cyclic voltammetry curves of 1,3,5-tris(2-furyl)-benzene (FPh) are
considerably different from 2,4,6-tris(2-furyl)-1-phenol (FOPh).
ox
Spectroelectrochemical measurements were carried out using
a UV–vis spectrophotometer Hewlett Packard 8452A. The target
polymer was synthesized on the indium–tin-oxide (ITO) coated
quartz electrode, acting as a ‘working electrode’. UV–vis spectra
of polymer films were recorded during p-doping. ITO potential was
scaled versus ferrocenu before film polymerization.
Hydroxyl group decreases the first oxidation potential Em
at
about 0.56 V, nevertheless we observed at least one more oxidation
peak. The same effect occurs during oxidation of 1,3,5-tris(2-
thienyl)-benzene (TPh) and 2,4,6-tris(2-thienyl)-1-phenol (TOPh),
a similar shift in oxidation potentials is visible, as in the case of
furyl derivatives. Among monomers with benzene core 1,3,5-tris[2-
All experiments were performed in acetonitrile (POCH 99.8%) or
dichloromethane (POCH 99.8%), in presence of 0.1 M tetrabutylam-
monium tetrafluoroborate (Aldrich) as an inert electrolyte.
(3,4-ethylenedioxythienyl)]-benzene, the (EPh) monomer exhibits
ox
the lowest Em
of approximately 0.81 V, while for monomer
with thienyl Emox = 1.02 V, and with furyl groups the highest
Emox = 1.13 V is observed. Similar situation occurs for monomers
with phenol core. The values of Emox for TOPh and FOPh amount to
Emox = 0.55 V, and Emox = 0.57 V, respectively.
3. Results and discussion
All monomers were irreversibly oxidized already in the first oxi-
dation step. In the case of FPh cyclic voltammetry (Fig. 2a) yellow
film was formed on the electrode surface at the beginning of first
oxidation peak at 0.91 V, with the highest oxidation peak in the
first scan. The peak decreases during all next scans. However, the
reduction peak is not observed. It indicates the formation of a poor
conductive polymer on the electrode surface. In the case of FOPh
(Fig. 2b) a different behavior is observed. Namely, the first 10 scans
reveal an increase of the peak of interest in every subsequent scan,
3.1. Cyclic voltammetry
All monomers under potentiodynamic conditions were elec-
trochemically active. Fig. 1 shows oxidation of monomers in
CH3CN. Different processes during oxidation were recorded in
their dependence on both the terminal arm moieties and pres-
ence of hydroxyl group attached to benzene ring. Monomers
undergo irreversible oxidation at least in two step reaction.
Fig. 1. Cyclic voltammograms obtained in wide range of potentials on Pt electrode; potential sweep rate v= 50 mV/s; 1 mM monomer solutions in 0.1 M Bu4NBF4 in CH3CN:
(a) FPh, (b) FOPh, (c) TPh, (d) TOPh, (e) EPh.

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Fig. 2. Cyclic voltammograms obtained during polymerization on Pt electrode; potential sweep rate v= 50 mV/s; 1 mM monomer solutions in 0.1 M Bu4NBF4 in CH2Cl2: (a)
FPh, (b) FOPh, (c) TPh, (d) TOPh, (e) EPh.
while the oxidation onset appears at the value of the oxidation
potential of −0.15 V. Hydroxyl substituent considerably changes
the monomer behavior during electropolymerization.
scan a peak with maximum at approximately 0.34 V and in the third
scan an additional peak at 0.07 V appear. In every subsequent scan
the peak undergoes a shift towards the higher potential. During
the reverse cycles we observe a peak at 0.35 V due to dedoping of
polymers. The peak at −0.76 V originates from deprotonation of ␴-
dimers. However, one could observe peaks also for FPh at −0.32 V
and TPh at −0.34 V. It was impossible to obtain stable polymers at
the second peak, owing to their degradation during polymerization
in this potential range. According to the well known electropoly-
merization mechanism, the coupling between thiophene, furan or
EDOT moieties in 5-position was expected [21].
The oxidation of TPh (Fig. 2c) results in covering of the working
electrode with a light yellow film. After the second scan a new peak
appears at 0.49 V, which reveals a subsequent shift towards a higher
potential according to the number of scans, achieving at the stage of
the 10th scan the value of 0.76 V. During the whole experiment the
value of the current has to be stabilized due to a poor conductivity
of a polymer film. The formation of a black film is observed during
polymerization of TOPh (Fig. 2d). A new oxidation peak appears
during subsequent scans at values of the potential being in the
range of 0.36–0.42 V. Oxidation onset and reduction peak appear at
the oxidation potential values of −0.07 V and 0.18 V, respectively.
An increased value of the current even after 100 scans indicates
much better conductivity of a film being formed, than it takes place
for TPh. In case of TPh the largest increase of the current occurs after
the first scan, while afterwards this effect is strongly hampered.
Replacement of central benzene ring by phenol results not only in
decreasing the oxidation potential but also considerable strength-
ens the film conductivity of copolymers with furan or thiophene
moieties. The result of CV performed on EPh is slightly different
from the previously described monomers (Fig. 2e). In the second
There are some differences in the increase of both polymer films
and oxidation potentials, depending on the used solvent (Fig. 3).
Oxidation potentials of monomers in CH3CN are lower than in
CH2Cl2 (Table 1). Only in the case of FPh (Fig. 3a) the situation is
ox
different, CH2Cl2 lowers Em at about 0.08 V. However, the shape
of voltammetric curves and compound behavior during polymer-
ization reveal the similar tendency. The second scan of FOPh in
CH3CN (Fig. 3b) introduce a new peak (the oxidation onset at −0.19
V), which increases with following scans, but the clear maximum is
not observed. Polymerization of TPh in CH3CN (Fig. 3c) reveals both
a less intense increase of the current, and a smaller shift towards
higher potential values according to subsequent scans. The con-

K.R. Idzik et al. / Electrochimica Acta 55 (2010) 7419–7426
7423
Fig. 3. Cyclic voltammograms obtained during polymerization on Pt electrode; potential sweep rate v= 50 mV/s; 1 mM monomer solutions in 0.1 M Bu4NBF4 in CH3CN: (a)
FPh, (b) FOPh, (c) TPh, (d) TOPh, (e) EPh.
cerned range edges of 0.52 V and 0.65 V are related to the second
and the 10th scan, respectively. In the case of poly(TOPh), the influ-
ence of solvent polarity used in electropolymerization is of the main
interest (Fig. 3d). Regarding CH3CN, in the second scan an addi-
tional redox system appears at the oxidation potential of −0.40 V
simultaneously with the corresponding reduction peak at −0.65
V. Moreover, the monomer oxidation potential peak shifts towards
lower values of the potential according to the number of scans start-
ing from the value of 0.55 V and achieving 0.50 V in the 10th scan.
This indicates the formation of a very well conducting layer. This
feature facilitates efficiently the oxidation of monomers. In the case
of EPh we observe very similar behavior in both solvents (Fig. 3e).
Fig. 4 illustrates all cyclic voltammetry curves for obtained poly-
mers. The anodic cycle of poly(FPh) in CH2Cl2 reveals a not clear
oxidation peak (Fig. 4a), positioned close to the monomer oxida-
tion potential. However, this peak disappears after only few scans.
This confirms, that the poly(FPh) film has poor stability and con-
ductivity, and a low molecular mass. The cycling of the poly(FOPh)
film performed in the polymerization potential range in a monomer
free electrolyte solution reveals an oxidation peak located at about
0.35 V (oxidation onset at 0 V) and a reduction peak at 0.22 V
(Fig. 4b). A sharp drop in the current value after changing polar-
ization direction indicates the formation of the conducting layer.
In addition, the obtained polymer is quite stable, as evidenced by
recording repetitive voltammetric waves during multiple doping
and de-doping processes. A similar influence of hydroxyl sub-
stituent occurs in the case of thiophene copolymers. The polymer
of TPh (Fig. 4c) has oxidation potential of 0.87 V, comparing to the
monomer is smaller by 0.23 V, what indicates short conjugation
length. Moreover, poly(TPh) is middle stable. In the first anodic
cycle of poly(TOPh) (Fig. 4d) there is an oxidation peak located at the
Table 1
Oxidation potential values of monomers and corresponding polymers in different
ox
ox
solvents, where: Em is the monomer oxidation potential; Ep is the polymer oxi-
dation potential.
Compound
Solvent
CH3CN
CH2Cl2
Em [V]
CH3CN
Ep [V]
CH2Cl2
Ep [V]
ox
ox
ox
ox
Em [V]
TPh
FPh
EPh
TOPh
FOPh
1.02
1.13
0.81
0.55
0.57
1.10
1.05
0.89
0.66
0.66
0.69
0.87
a
a
0.51
−0.41b
0.25
0.43
−0.41b
0.40
a
Ill-defined peak.
Potential value determined from the second scan.
b

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Fig. 4. Cyclic voltammograms performed on thin polymer films on Pt electrode; potential sweep rate v= 50 mV/s; in 0.1 M Bu4NBF4 in CH2Cl2: (a) poly(FPh), (b) poly(FOPh),
(c) poly(TPh), (d) poly(TOPh), (e) poly(EPh).
potential 0.46 V, while in subsequent scans the additional oxidation
peak appears at the potential of −0.41 V. However, the total charge
consumed during the oxidation process remains almost the same.
The first sharp and reversible spike in the cyclic voltammogram
after which the current decreases, at the polymer poor conductivity
in range −0.3 V to 0.0 V, might indicate a phase transformation [22]
or pure redox reaction between particular hydroquinone–quinoine
like states [23]. A small insertion of strong acid leads to the dis-
appearance of the redox system that may confirm an appearance
of the structure, which is shown in Scheme 2. The second, broad
polymer oxidation peak indicates a variety of chain lengths. Clar-
ification of this process comprises the subject for further studies.
The poly(TOPh) film is much more stable during multiple doping
and de-doping processes, than the poly(TPh) one. This confirms,
Scheme 2. Proposed mechanism of the redox reaction during oxidation of poly(TOPh) in the range from −0.9 V to −0.3 V.

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7425
Fig. 5. UV–vis spectra recorded during oxidation of polymer films on ITO electrode in 0.1 M Bu4NBF4 solution in CH3CN of: a) poly(TOPh), potentials from −0.9 V to 0.7 V in
intervals of 0.2 V; (b) poly(FOPh), potentials from −0.3 V to 0.5 V in intervals of 0.2 V.
that a phenol core improves the electric properties of the poly-
mers and their stability, when comparing to a benzene core. In the
case of poly(EPh) (Fig. 4e) we observe the oxidation onset at 0.14 V,
and the maximum at 0.43 V. After switching of the scanning direc-
tion, a sharp drop in the current and the minimum at 0.34 V are
observed.
ing oxidation reveals a decrease in the absorption ␲–␲* transition
band, and an increase in the oxidation product absorption. More-
over, a stable isosbestic point is observed at 423 nm.
Following empirical studies, the absorption maxima of the
thienyl substituted benzenes change proportionally to the conjuga-
tion length. One can find in the literature [24,25], that the number
of conjugated double bonds (n) of oligothiophenebenzenes is esti-
mated by Eq. (1), where Emax (eV) is the energy at the absorption
maximum.
3.2. UV–vis spectroscopy
7.32
Emax − 2.26
Fig. 5a shows the spectrum of poly(TOPh) recorded at different
values of potential representing various oxidation levels. How-
ever, one can conclude from the spectrum, the total film de-doping
after synthesis is not visible at values of the potential of −0.9 V
and −0.7 V. Poly(TOPh) in the neutral state absorbs the light in
a broad range, and has at least two absorption maxima located at
ꢀmax1 = 401 nm and ꢀmax2 = 484 nm. This may indicate the presence
of at least two polymer fractions with different effective conjuga-
tion lengths. At the higher values of the potential, which correspond
to the characteristic sharp voltammetric peak, both the decrease
in the absorption maximum, and formation of a new band in a
higher wavelength range are observed. This confirms the forma-
tion of oxidation products, probably polarons. A further increase of
the electrode potential up to a value of the second oxidation peak
is accompanied by a change in the shape of the spectrum with the
decay at 400 nm. This originates from the products with the short-
est conjugation length, and an increase in polaron or bipolaron band
intensity.
n =
(1)
Substituting the values of Emax for TPh (Emax = 4.16 eV) and TOPh
(Emax = 4.11 eV) monomers, the calculated values of n are equal
to 3.95 and 3.85, respectively. Eq. (1), when applied to the poly-
mers, gives the values of n = 4.11 and n = 24.24 for poly(TPh) and
poly(TOPh). The analysis of these results leads to the conclusion,
that there is a lack of coupling among the thiophene arms, and
a negligible conjugation between the benzene rings of TPh, TOPh
monomers and poly(TPh). However, the behavior of poly(TOPh) is
quite different. Large number of conjugated bonds indicate, that
hydroxyl groups enable coupling among the thiophene arms at
the meta-position. On the other hand, the quinoine structure of
the connector between two polymer arms, which is shown in
Scheme 3 assures that there is much better conjugation than meta-
substitution in benzene. The analysis of Fig. 6a and b confirms the
theoretical calculations. While the spectra of monomers TPh and
TOPh are similar, the spectrum of poly(TOPh) differs significantly
from that of poly(TPh).
UV–vis spectra of poly(FOPh) are presented in Fig. 5b. The
polymer in its neutral state has two absorption maxima at
ꢀmax1 = 288 nm and ꢀmax2 = 363 nm. The analysis of the spectra dur-
Fig. 7 illustrates, that the poly(EPh) film has two absorption
maxima at 330 nm and 492 nm. The first one is related to the light
Fig. 6. UV-Vis spectra of monomers in CH3CN and polymer films of: a) (—) TOPh (
) poly(TOPh); b) (—) TPh (
) poly(TPh). (For interpretation of the references to
color in this figure legend, the reader is referred to the web version of the article.)

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Generally, the application of the meta-linkages is rarely
reported. However, in some cases meta-substitution is desired,
mainly due to the better control of the energy gap (Eg). We obtained
poly[1,3,5-tris(aryl)benzene]s with relatively large Eg, which is
required for blue light-emitting materials. In addition, following the
data set resulting from optical and electrochemical measurements,
we conclude, that oligomers containing EDOT groups are much
more stable and probably also better conducting, than thienyl, or
furyl analogues. The hydroxyl substituent has a significant influ-
ence on the electrochemical and spectroelectrochemical properties
of oligoarylbenzenes. In the whole class of these compounds the
decrease of oxidation potential and energy gap is observed. On the
other hand, this substituent enables coupling among particular aryl
arms, which are connected at the meta-position. Thus, this leads
to the improvement of the polymer overall stability and signifi-
cant enhancement of polymer conductivity. The overall analysis
from point of view of chemistry, electrochemistry supported by
spectroscopic methods confirms, that the compounds described in
this paper could be considered as a material for the whole class of
organic–electronic devices.
Scheme 3. Proposed conjugation paths in poly(TOPh) in its oxidized state at approx-
imately −0.3 V.
Acknowledgments
This work was supported by grant of Ministry of Science and
Higher Education NN205106935, by the European Community
from the European Social Fund within the RFSD 2 project, and the
European Union Project SNIB, MTKD-CT-2005-029554.
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absorption by a polymer in its neutral state, while the second one
arises from its oxidized form. In fact, the oxidized form appears
because polymer does not undergo entirely the de-doping pro-
cess. In the case of poly(FPh) spectra one maximum at 291 nm is
present, while for poly(FOPh) two maxima at 288 nm and 363 nm
are observed. The energy gap values amount to 3.34 eV, 2.8 eV and
2.74 eV for poly(FPh), poly(TPh) and poly(EPh), respectively. Tak-
ing under consideration the polymers with hydroxyl groups, the
value of Eg is lowered significantly achieving 2.73 eV and 2.00 eV for
poly(FOPh) and poly(TOPh), respectively. This may be attributed to
the strong influence of a hydroxyl substituent on the aryl arms, not
only by decreasing the oxidation potential, but also by increasing
the effective conjugation length between the aryl arms. This cou-
pling is present only in polymers and suggests that the conjugation
itself can expand beyond the hydroxyl groups through thiophene
or furan moieties.
4. Conclusion
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because all of target compounds are electroactive and undergo
electropolymerization creating thin films directly on the surface
of electrodes.
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