Unusual properties of electropolymerized 2,7- and 3,6- carbazole derivatives

Article abstract of DOI:10.1016/j.electacta.2013.12.108

Differently linked carbazole derivatives possessing pyrene and selenophene moieties were electrochemically investigated. Cyclic voltammetric as well as differential pulse voltammetric studies demonstrated that they display comparatively low oxidation potentials. One-step cyclic voltammetric process was used for the preparation of their highly dimensional, stable and electroactive polymers. The electrodeposited polymers displayed unusual properties upon electrochemical doping that may help tailoring the dimensional features of these polymers. The electrodeposited polymers were investigated by electrochemical and optical tools and correlation between different parameters such as oxidation characteristics or absorption behavior and the effective conjugation length was established. Spectroelectrochemical investigations showed the polaronic and bipoloronic features of the electropolymers. Multielectrochromic properties of electrodeposited polymers on successive doping suggested their application as electroactive layers in electrochromic devices.

Full text of DOI:10.1016/j.electacta.2013.12.108

Electrochimica Acta 128 (2014) 430–438
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Unusual properties of electropolymerized 2,7- and 3,6- carbazole
derivatives
P. Dataa,b,∗,1, P. Pandera, M. Lapkowskia,b, A. Swistc, J. Soloduchoc,
R.R. Reghud, J.V. Grazuleviciusd
a Faculty of Chemistry, Silesian University of Technology, M. Strzody 9, 44-100 Gliwice, Poland
b Center of Polymer and Carbon Materials, Polish Academy of Science, M. Curie-Sklodowskiej 34, 41-819 Zabrze, Poland
c Wroclaw University of Technology, Faculty of Chemistry, Wybrzeze Wyspianskiego 27, 50-370 Wroclaw, Poland
d Department of Organic Technology, Kaunas University of Technology, Radvilenu pl. 19, LT-50254, Kaunas, Lithuania
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 July 2013
Received in revised form
28 November 2013
Accepted 17 December 2013
Available online 3 January 2014
Differently linked carbazole derivatives possessing pyrene and selenophene moieties were electrochem-
ically investigated. Cyclic voltammetric as well as differential pulse voltammetric studies demonstrated
that they display comparatively low oxidation potentials. One-step cyclic voltammetric process was used
for the preparation of their highly dimensional, stable and electroactive polymers. The electrodeposited
polymers displayed unusual properties upon electrochemical doping that may help tailoring the dimen-
sional features of these polymers. The electrodeposited polymers were investigated by electrochemical
and optical tools and correlation between different parameters such as oxidation characteristics or
absorption behavior and the effective conjugation length was established. Spectroelectrochemical inves-
tigations showed the polaronic and bipoloronic features of the electropolymers. Multielectrochromic
properties of electrodeposited polymers on successive doping suggested their application as electroactive
layers in electrochromic devices.
Keywords:
Carbazole
UV-Vis spectroelectrochemistry
Selenophene
Pyrene
Band-gap
© 2013 Elsevier Ltd. All rights reserved.
1. Introduction
and combination of the conducting polymers with other materials
are widely used [8,9].
The era of flexible and highly stable electronic devices demands
␲-conjugated organic polymers with the certain sets of properties
including mechanical strength and with the possibilities of tailoring
of the properties by structural modification. Thus, it is necessary to
develop novel materials with the required sets of properties for
specific applications. A large number of applications of conjugated
polymers depend mainly on their electrochromic properties, which
rely on the reproducible switching of characteristics of conjugated
polymers [1–6]. The properties of conducting polymers strongly
depend on their structural characteristics, which imply the modi-
fication of their monomer structures to tune the properties of the
polymers (electronic, optical, charge-transporting etc.) according
to the intended applications. The physical and chemical properties
of the conjugated polymers can be controlled efficiently by some
basic factors such as bond length alternation, variation of aromatic-
ity and substitution [7]. For this purpose, functionalization of the
electroactive monomer structures prior to electropolymerization
Conjugated polymeric systems based on selenophene or
carbazole are among the most promising materials for the devel-
opment of new generation, highly efficient OLED devices [10–12].
Carbazole and selenophene-based monomer units, especially in
combination with electron-poor aromatic units, lead to novel
polymeric electron donor structures [13–17] that possess a num-
ber of properties useful for the improvement of the photovoltaic
characteristics [11], such as energy level alignment with that of
electron acceptors [18], low energy gap which favors light har-
vesting and increase the short-circuit current of the device [13],
high charge mobility [19] and good solubility in organic solvents
and good film-forming properties [20]. Polycarbazoles are known
not only as efficient short wavelength emitters but also as strong
electro-donating (p-type) chromophores [21–26]. The advantage of
carbazole moiety is that it can be easily functionalized at its C-2, C-3,
C-6, C-7 or N-positions [27–29]. Furthermore, poly (3,6-carbazole)s
demonstrate interesting electrochromic properties because of the
conjugation breaks that are present due to the possession of 3,6-
linkages. The ability of poly (3,6-carbazole) derivatives to form
multi-oxidation states results in the exhibition of many colors on
the ITO/glass surface upon applied positive potentials [30,31]. Since
2,7-substituted carbazoles have been theoretically found to have
∗
Corresponding author.
E-mail address: Przemyslaw.Data@polsl.pl (P. Data).
1
ISE member.
0013-4686/$ – see front matter © 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.electacta.2013.12.108

P. Data et al. / Electrochimica Acta 128 (2014) 430–438
431
Fig. 1. Structures of investigated compounds.
smaller band gaps than the 3,6-substituted carbazoles, the small
energy gaps of these monomers are expected to contribute to a
lowering of the band gaps in the resulting polymers [22–25]. Due
to the simplicity of the synthesis, there are many reports regarding
poly (3,6-carbazole)s [32]. Oligo- and poly(2,7-carbazole) deriva-
tives have been successfully used in polymer light emitting diodes
(PLEDs) and organic field-effect transistors (OFETs) [31]. Carbazole
moiety is fully aromatic and possess good chemical and envi-
ronmental stability. Taking all these considerations into account
we expect, that development of new carbazole-based low-band
gap copolymers will lead to interesting properties useful for pho-
tovoltaic applications. However, one possible problem that still
concerns 2,7-carbazole-based copolymers is their electrochemi-
cal instability due to the build-up of charge at the free para-(3-
and 6-) positions [33]. Big progress has been made recently in the
field of electrochemically deposited polyselenophene derivatives
for electrochromic devices [34,35], and chemically synthesized
regioregular poly(3-hexylselenophene) for solar cells [36–38]. In
addition, there are also some applications of the copolymers in
organic light emitting diodes [39], OFETs [40] and near IR emit-
ter [39,41] applications. The new aspect of the investigation into
selenophene derivatives is use of selenophene moieties as a donor
groups in donor-acceptor copolymers. Lee and co-workers [42] pre-
sented the synthesis, optical and photovoltaic characteristics of
alkylselenophene-substituted quinoxaline based donor-acceptor
low band-gap polymers. It was observed that the length of the C-
C bond between selenophene rings is shorter than that between
thiophene rings (ref). Therefore oligoselenophenes with enhanced
conjugation in the polymer backbone show red shift in the absorp-
tion spectra as compared to oligothiophenes [42–46]. In the present
study, a comparison of differently linked carbazole derivatives is
presented. In selenophene derivatives 2,7- and 3,6-substituted car-
bazole moieties are inside the molecules while in pyrene-based
derivatives they serve as the side arms.
Fig. 1.
2. Experimental
2.1. Materials
All solvents for the synthesis were dried and then distilled
before use. Other commercially available substances and reagents
were used as received. The solutions of 1.0 mM concentration of all
monomers were used for all cyclic voltammetry measurements.
Electrochemical studies were conducted in 0.1 M solutions of
Bu4NBF4, 99% (Sigma Aldrich) in dichloromethane (DCM) solvent,
(CHROMASOLV®, 99.9% from Sigma Aldrich) at room temperature.
UV-Vis spectroelectrochemical measurements were performed on
Indium Tin Oxide (ITO) quartz glass working electrode coated with
polymers. Polymeric layers were synthesized on an ITO electrode
under conditions similar to those of cyclic voltammetry measure-
ments.

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P. Data et al. / Electrochimica Acta 128 (2014) 430–438
Scheme 1. Synthesis of selenophene derivatives. Conditions of reactions: (i) n-BuLi, Sn(Bu)3Cl, THFanh, -10 ◦C–rt, N2, 5 h; (ii) n-BuLi, 2-isopropoxy-4,4,5,5-tetramethyl-1,3,2-
dioxoboralane, THFanh, -78 ◦C–rt, N2, 18 h; (iii) Pd(PPh3)4, toluene, N2, 110 ◦C, 24 h; (iv) Pd(PPh3)4, 2 M K2CO3aq, toluene, N2, 90 ◦C, 72 h.
Fig. 2. Cyclic voltammograms of investigated monomers. Measurement conditions: scan rate 50 mV/s, calibrated against ferrocene/ferrocenium redox couple.

P. Data et al. / Electrochimica Acta 128 (2014) 430–438
433
2.1.1. General synthesis of bis(selen-2-yl)-N-nonylcarbazole
The synthesis of compounds 1 and 2 was based on our pre-
vious work [47]. It was established that the Stille and Suzuki
procedures allowed the preparation of these carbazole derivatives.
However, it was found that using Suzuki reaction, resulted in signif-
icantly higher yields (by ca. three times) (Scheme 1). The synthesis
of selenophene-based monomers of 2,7- and 3,6-bis(selenophen-
2-yl)-N-nonylcarbazole was performed starting from carbazole.
N-nonylcarbazole [48] was successfully brominated in position
3 and 6 (8) using a modified procedure [49], requiring the
usage of N-bromosuccinimide (NBS) and equal volume mixture of
glacial acetic acid and dichloromethane. Whereas, 2,7-dibromo-N-
nonylcarbazole (9) was synthesized by alkylation of commercially
available 2,7-dibromocarbazole with 1-bromononane in toluene
and sodium hydroxide solution in the presence of benzyltriethy-
lammonium chloride as a catalyst. Boron- (7) and tin-derivatives
(6) of selenophene were prepared as described in the literature
[50–52].
Fig. 3. DPV of investigated monomers. Measurement conditions: scan rate 50 mV/s,
Ag/AgCl - quasireference electrode, calibrated against a ferrocene/ferrocenium
redox couple.
2.1.2. 2,7-dibromo-N-nonylcarbazole (9)
To a stirred solution of 2,7-dibromocarbazole (2 g, 6.15 mmol),
50 ml toluene, 20 ml 50% NaOHaq 1-bromononane (1.27 g,
Fig. 4. Cyclic voltammograms of the electrochemical doping-dedoping process of polymers. Measurement conditions: scan rate 50 mV/s, calibrated against fer-
rocene/ferrocenium redox couple.

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P. Data et al. / Electrochimica Acta 128 (2014) 430–438
Pd(PPh3)4 (0.08 g, 0.07 mmol) was then added under a nitro-
gen atmosphere and the mixture was heated at 90 ◦C for 72 h
under nitrogen. The separated aqueous layer was extracted with
dichloromethane (3 × 15 ml). The organic phase was washed thrice
with water (15 ml). Combined organic layers were dried over anhy-
drous magnesium sulfate, and the solvent was removed by rotary
evaporation. The crude product was purified by silica gel column
chromatography with hexane:ethyl acetate (10:1, V/V) as eluent.
Product 2 was obtained as a yellow-green solid with yield 66%
(0.81 g, 1.46 mmol), tm = 53-54 ◦C. 1H NMR (300 MHz, CDCl3): 8.30
(d, J = 1.8 Hz, 2H), 7.94-7.92 (dd, J = 1.1 Hz, J = 5.6 Hz, 2H), 7.72-7.69
(dd, J = 1.8 Hz, J = 8.5 Hz, 2H), 7.52-7.51 (dd, J = 1.1 Hz, J = 3.8 Hz, 2H),
7.38-7.35 (m, 4H), 4.28 (t, J = 7.2 Hz, 2H), 1.91-1.83 (m, 2H), 1.41-
1.25 (m, 12H), 0.88 (t, J = 6.7 Hz, 3H). 13C NMR (300 MHz, CDCl3):
152.2, 140.6, 130.8, 128.8, 128.0, 125.0, 124.2, 123.3, 118.4, 109.3,
43.3, 32.0, 29.6, 29.5, 29.4, 29.1, 27.4, 22.8, 14.3.
2.1.4. 2,7-bis(selenophen-2-yl)-N-nonylcarbazole (1)
Fig. 5. Cyclic voltammograms of the doping-dedoping process of electropolymer-
ization products in a monomer free medium. Measurement conditions: scan rate
-300 mV/s, calibrated against ferrocene/ferrocenium redox couple.
The synthesis of compound 1, performed similar to that of
compound 2, which allowed to obtain 0.85 g (1.54 mmol, 70%) of
product in form of yellow-green solid with 70% yield, tm = 56-57 ◦C.
1H NMR(300 mHz, CDCl3): 8.03 (d, J = 8.2 Hz, 2H), 7.99-7.97 (dd,
J = 1.1 Hz, J = 5.6 Hz, 2H), 7.58-7.56 (dd, J = 1.1 Hz, J = 3.8 Hz, 2H), 7.54
(d, J = 1.1 Hz, 2H), 7.48-7.45 (dd, J = 1.5 Hz, J = 8.1 Hz, 2H), 7.39-7.36
(dd, J = 3.8 Hz, J = 5.6 Hz, 2H), 4.35 (t, J = 7.2 Hz, 2H), 1.95-1.90 (m,
2H), 1.48-1.25 (m, 12H), 0.86 (t, J = 6.7 Hz, 3H). 13C NMR (300 mHz,
CDCl3): 152.1, 141.5, 134.3, 130.7, 129.9, 125.2, 122.3, 120.7, 118.5,
106.4, 43.1, 32.0, 29.7, 29.5, 29.4, 29.2, 27.3, 22.8, 14.2.
6.13 mmol) and benzyltriethylammonium chloride (0.55 g,
2.41 mmol) were added. Reaction mixture was stirred for 20 h at
40 ◦C, then toluene phase was washed with water and ammonium
chloride, while water phase was extracted with dichloromethane.
The residue was purified by silica gel column chromatography
(eluent–hexane) followed by evaporation to afford a cream-
colored crystals with 98% yield (2.78 g, 6.15 mmol), tm = 72 ◦C. 1H
NMR (300 MHz, CDCl3): 7.89 (d, J = 8.3 Hz, 2H), 7.53 (d, J = 1.6 Hz,
2H), 7.36-7.32 (dd, J = 1.6 Hz, J = 8.3 Hz, 2H), 4.19 (t, J = 7.3 Hz, 2H),
1.88-1.79 (m, 2H), 1.36-1.26 (m, 12H), 0.88 (t, J = 6.7 Hz, 3H).
1,3,6,8-Tetra(9-ethyl-9H-carbazol-2-yl) Pyrene (3) and 1,3,6,8-
Tetra(9-ethyl-9H-carbazol-3-yl) Pyrene (4) monomers were syn-
thesized according to our previously published procedures[53].
2.1.3. 3,6-bis(selenophen-2-yl)-N-nonylcarbazole (2)
2.2. Measurements
Suzuki’s procedure was used for the preparation of the com-
pounds 1 and 2. To a three-necked flask the following chemicals
were added: 3,6-dibromo-N-nonylcarbazole (8) (1.0 g, 2.22 mmol),
4,4,5,5-tetramethyl-2-(selenophen-2-yl)-1,3,2-dioxoboralane (7)
(1.38 g, 5.35 mmol), and a mixture of anhydrous toluene (35 ml)
and 2 M aqueous potassium carbonate solution (15 ml). The flask
equipped with a condenser was then evacuated and filled with
nitrogen several times to remove traces of the air. The catalyst
Melting points were determined on automatic melting point
SMP40 (Stuart) apparatus. NMR spectra were obtained in CDCl3 by
Avance 400 (Bruker) at 300 MHz for 1H and at 75.5 MHz for 13C. The
electrochemical investigation was carried out using potentiostats
Autolab PGSTAT20 and PGSTAT100 (Metrohm Autolab). The elec-
trochemical cell comprised of platinum disk with 1-mm diameter
of working area as working electrode (CV, DPV) and ITO glass
Fig. 6. Cyclic voltammograms of the doping-dedoping process of the electrodeposited polymers at low oxidation limit p(3)l, p(4)l and high oxidation limit p(3)h, p(4)h in a
monomer free media. Measurement conditions: scan rate – 300 mV/s, calibrated against ferrocene/ferrocenium redox couple.

P. Data et al. / Electrochimica Acta 128 (2014) 430–438
435
Fig. 7. Energy diagrams of HOMO-LUMO levels and band-gaps of monomers and polymers.
(spectroelectrochemistry) as a working electrode, Ag/AgCl elec-
trode as reference electrode and platinum coil as auxiliary
electrode. Cyclic voltamperometric measurements were conducted
at room temperature under argon atmosphere and at scan rate
of 50 mV/s and were calibrated against ferrocene/ferrocenium
redox couple. UV-Vis-NIR spectroscopy and spectroelectrochem-
istry analyses were recorded by QE6500 and NIRQuest detectors
(Ocean Optics).
1 and 2, selenophene group was accountable for the first oxidation
process (ref).
When it is assumed that the oxidation peak is related with
the HOMO band and the reduction peak with the LUMO band,
the electrochemical band-gap value for monomers will be the in
the range between these two peaks. In the investigated series
of carbazolyl derivatives, monomer 4 with a 3-linkage to pyrene
core possessed the lowest band gap. For selenophenyl derivatives,
where the carbazole group is inside the two selenophene units, the
lowest band-gap was observed for monomer 1.
Cyclic voltammetric experiments were carried out in elec-
tropolymerization conditions to investigate the synthesized
polymers. Polymers were immersed into a monomer-free Bu4NBF4
DCM electrolyte and it was noted that the electrochemical stability
of polymers during doping-dedoping process under polymer-
ization conditions was moderate (Fig. 4). Comparatively good
stability was observed for polymer p(2) obtained from monomer
2. Similar behavior was observed for the previously reported
thiophene analogue of this polymer [54]. Polymer p(1) with 2,7-
bis(selenophen-2-yl) group possessed the lowest potential value
of oxidation peak, while polymer p(4) with carbazolyl substituted
pyrene core via C-3 position of carbazole moiety displayed the high-
est oxidation peak potential.
3. Results and Discussion
It is known that introduction of substituents at C-2, C-3, C-6,
C-7 positions carbazole moiety affects the optical and electronic
properties of carbazole derivatives [22–33]. In this study, cyclic
voltammetry (CV) measurements were performed to understand
the effect of 2,7- and 3,6- substitution on the electronic structures of
two different types of carbazole derivatives. Electrochemical inves-
tigation of the solutions of the compounds in dichloromethane
demonstrated that all molecules underwent multi-electron oxida-
tion processes (Fig. 2). The lowest oxidation potential was observed
for monomer 4 where carbazole units are linked to pyrene core
via C-3 position. During successive CV scan of 1 mM solution of
monomers 1 and 2, potentiodynamic growth of the conductive
layer was observed (Fig. 2a,b) above the first oxidation peak. During
the first scan, because of absence of the redox couple, irreversible
peaks were observed at 0.71 V (for 1) and 0.59 V (for 2), respectively.
For monomers 3 and 4 (Fig. 2c,d), redox couples were observed at
first oxidation stage at 0.64 V (for 3) and 0.52 V (for 4). At higher
oxidation potentials but below the second irreversible oxidation
peak the current growth in successive scan was observed.
During successive voltammetric scans, the formation and
growth of new wide bands at lower potential compared to those of
monomers were observed. New peaks were not observed and only
the growing peaks of monomers were observed. These observations
suggested the formation of electroactive moieties on the electrode.
The potential shift between the monomer peak and two peaks of
electrodeposited layer suggests that the layer is formed by a species
more conjugated than the monomer; i.e, in this case it was the con-
jugated polymer. The peakless behavior of electrodeposited layers
suggested the formation of polymers with wide molecular weight
distribution. The comparison the CV peaks with absolute peaks of
oxidation and reduction processes in Differential Pulse Voltam-
metry (DPV) measurements (Fig. 3) revealed the lowest oxidation
potential peaks for monomer 3. The first oxidation of monomers 3
and 4 is related to the oxidation of pyrene core [53]. For monomers
HOMO and LUMO energy levels as well as electrochemical band-
gap values were estimated by electrochemical analysis of doping-
dedoping processes. Fig. 5 represents the cyclic voltammograms
of polymers upon p- and n-doping at a scan rate of 300 mVs−1
.
For all the investigated compounds, both p- and n- redox processes
were observed. However, it was noted that the n- redox cycles were
irreversible. Unusual results were observed during the analysis of
CV curves of polymers p(3) and p(4) CV curves. In contrastr to the
previous investigation [53], the peak at ca. 1.5 V was not observed
and the band-gap values were by almost 1 eV lower.
To explain the aforementioned unusual behavior, both experi-
ments are compared in Fig. 6. The main differences between both
the experiments were in the thickness of the electrodeposited poly-
mer layers and in the voltage range of electropolymerizations. In
the present study, polymers p(3)l and p(4)l were formed at lower
oxidation potentials of 0.85 V and 0.95 V as compared to 1.15 V and
1.10 V observed in the previous study [53]. Moreover, the poly-
mers were electrodeposited during 10 scans rather than 3 scans
as it was in the previous case [53]. It is interesting to note that
the current density observed in both the cases was different. This
observation can be due to the different thickness of polymer layers
since the active area in CV curves was found to be the same in both
the measurements. It is also assumed that the more linear forms

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P. Data et al. / Electrochimica Acta 128 (2014) 430–438
Fig. 8. UV-Vis spectra recorded during electrochemical oxidation of polymers p(1), p(2), p(3), p(4).
(2-arm connection) of p(3)l and p(4)l were deposited on the elec-
trode at lower oxidation potentials. This assumption is supported
by the absence of new peaks in higher oxidation range. It should
be noted that it is almost impossible to oxidize all four carbazolyl
arms of the monomers at mild electrochemical conditions to form
fully branched polymers. Hence, to conclude, the oxidative peak at
ca. 1.5 V might be originated from the pyrene core that apparently
stronger for the linear polymers compared to the branched ones
The HOMO–LUMO energy levels and the electrochemical band-
gap values of the electrochemically generated polymers are

P. Data et al. / Electrochimica Acta 128 (2014) 430–438
437
Fig. 9. Proposed structure of the electrodeposited polymers.
provided in Fig. 7 and tabulated in Table 1. These values were
calculated from the first oxidation and reduction potential onsets.
The difference in onset potentials obtained from the p- and n-
doping sides can be taken as a measure of the band gap (EG) values
of the polymers (Fig. 5, 6).
The optical band-gap values were slightly different from those
of the electrochemical ones, which suggests that the absorption
onsets might be not always related to ␲-␲ band transitions. The
lowest optical and electrochemical band-gap values were observed
for polymer p(4)l whereas the highest HOMO energy level was
observed for p(3)h.
polymers were investigated by UV-Vis-NIR spectrometry. Fig. 8
demonstrates the results of spectroelectrochemical investigation of
polycarbazoles at potentiostatic conditions. No significant changes
during doping process was observed for p(1) during several exper-
iments (Fig. 8a). However, neutral p(2) was characterized by the
two overlapping absorption peaks located at ꢀmax1 = 280 nm and
ꢀmax2 = 418 nm. During the oxidation processes of the film of p(2),
the absorption band of neutral polymer at 200-550 nm dimin-
ished and the new broad band of polarons developed between
550 and 900 nm (Fig. 8b) with an isosbestic point at 482 nm. For
p(2), absorption bands developed beyond 900 nm with maxima at
ꢀmax = 986 nm which is attributed to the formation of bipolarons.
The neutral p(3)l showed a maximum absorbance at ꢀmax = 300 nm
and ꢀmax = 404 nm; which can be attributed to the interband ␲→␲*
transitions. The UV-Vis spectra recorded during the oxidation of
p(3)h, showed the absorption band (200–480 nm) from neutral
polymer (Fig. 8c) which was found to be gradually losing its inten-
sity as the applied potential was increased. Meanwhile, new wide
absorption bands (480– > 1700 nm) with maxima at ꢀmax = 672 nm
and ꢀmax = 960 nm and an isosbestic point at 430 nm could be
accounted for polarons and bipolarons in the conducting polymer
layer.
For the investigated polymers, increase in the intensity of pola-
ronic band was observed beyond the applied potential of 0.7 V.
Increase of poloronic intensity unlike the expected increase of bipo-
laronic band at higher doping levels suggested the oxidation of
on the working electrode of polymer with low extent of conjuga-
tion [57]. It should be noted that the effective conjugation length
would be different for differently linked polymers, e.g., for poly-
mers coupled via 2-arms, 3-arms or 4-arms (Fig. 9). It is assumed
that electrodeposited polymers possessing low conjugation levels,
e.g., polymers coupled via 2-arms or 3-arms, might undergo further
oxidation at higher applied potentials which lead to the effective
increase of polaronic bands. This observation can provide a new
approach for tailoring the dimensional features of electrodeposited
polymers.
Thin polymeric films were electrodeposited on ITO-coated
quartz glass substrates using cyclic voltammetry under the con-
ditions similar to those shown in Fig. 2. Electrochemically formed
Table 1
Electrochemical and optical band-gap.
el
op
EOx
[V]a
ERed
[V]b
EHOMO
[eV]c
ELUMO
[eV]d
EG
EG
[eV]e
[eV]f
1
2
3
4
0.64
−2.67
−3
−5.74
−5.61
−5.59
−5.61
−5.23
−5.07
−5.44
−5.21
−5.51
−5.31
−2.43
−2.1
3.31
3.51
2.86
2.81
2.38
2.32
1.59
1.37
2.57
2.36
3.06
3.16
2.85
2.82
2.39
2.34
1.54
1.33
2.53
2.44
0.51
0.49
0.51
0.13
−0.03
0.34
0.11
0.41
0.21
−2.37
−2.3
−2.73
−2.8
p(1)
p(2)
p(3)l
p(4)l
p(3)h
p(4)h
−2.25
−2.35
−1.25
−1.26
−2.16
−2.15
−2.85
−2.75
−3.85
−3.84
−2.94
−2.95
a
first oxidation potentials of monomers from DPV and polymers from CV mea-
surements;
b
first reduction potentials of monomers from DPV and polymers from CV mea-
surements;
c
Energy of Highest Occupied Molecular Orbital calculated from EHOMO = -
(Ep + 5.1), where Ep is DPV oxidation peak potential for monomers and onset of CV
oxidation potential versus Fc/Fc+[54–56];
d
Energy of Lowest Unoccupied Molecular Orbital calculated from ELUMO = -
(En + 5.1), where En is DPV reduction peak potential for monomers and onset of
CV reduction potential versus Fc/Fc+[54–56];
During doping processes, the color of the electrodeposited
polymer layers was found to change to almost black (Fig. 8c,d),
which suggested that they possess multielectrochromic proper-
ties. Thus it is possible to prepare electroactive layers with black
electrochromic properties by electropolymerizatio.
e
Energy of band-gap calculated from the difference between Energy of HOMO
and LUMO band;
Energy of band-gap calculated from UV-Vis spectroscopy EGop = hc/␭onset, where
f
h is Planck’s constant, c is speed of light in a vacuum, ꢀonset is polymer onset of
absorption [54–56].

438
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