Polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl--cyclodextrin) [P(Py--DMCD)] films prepared by
potential cycling in aqueous acidic solutions on indium tin oxide (ITO)-coated glass and gold electrodes
were studied by in situ UV–vis and Raman spectroscopy. Characteristic UV–vis and Raman bands were
identified and their dependencies on the electrode potential have been discussed. Spectroelectrochemical
results reveal differences both in the position of the spectral bands and their potential dependence for PPy
and P(Py--DMCD) films indicating interactions between polymer chains and CDs during electropolymerization process. The films were also characterized by cyclic voltammetry and FT-IR spectroscopy.
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Spectrochimica Acta Part A 78 (2011) 1–6
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journa l homepage: www.e lsev ier .co
Review article
In situ R
poly(py
Jalal Arjo
a Faculty of Che
b Department o
c National Cent
d Faculty of Che
e Technische Un
a r t i c l
Article history:
Received 8 Jun
Received in re
Accepted 7 De
Keywords:
Spectroelectro
-Dimethyl cy
Polypyrrole
Conducting po
Electropolymerization
Contents
1. Introd
2. Exper
2.1.
2.2.
3. Result
Ackno
Refer
1. Introdu
Polypyrr
materials o
use energy
trochemica
spectroelec
structural e
intrinsically
onance Ram
to study ch
[25–27]. SE
∗ Correspon
E-mail add
1386-1425/$ –
doi:10.1016/j.uction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
imental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Preparation of (pyrrole-cyclodextrin) complex . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Polypyrrole and P(pyrrole-cyclodextrin) film electrosynthesis in aqueous solution . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
s and discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
wledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
ences . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
ction
ole is one of the most extensively studied functional
f the conducting polymers family due to its wide
storage devices, microelectronic devices and elec-
l/chemical sensors [1–5]. In situ optical and Raman
trochemical methods have been very useful for the
lucidation and study of optoelectronic properties of
conducting polymers [6–24]. Surface Enhanced Res-
an Spectroscopy (SERS) has been used extensively
emically and electrochemically polymerized PPy films
RS can be used to identify oxidation (doping) state and
ding author. Tel.: +98 8118270820.
ress: jalal.arjomandi@s2004.tu-chemnitz.de (J. Arjomandi).
the doping level in a conducting polymer film. As an example SERS
can selectively enhance the Raman bands associated with the oxi-
dized species of polythiophene [28].
In recent years, oxidation reactions of host–guest compounds
have attracted enormous research interest by several authors
[29–31]. Cyclodextrins (CDs) are cyclic oligosaccharides composed
of from 1,4-glucopyranose units that exhibit a torus-shaped struc-
ture with a hydrophobic cavity and a hydrophilic exterior. They
can form inclusion complexes only with guest molecules of the
proper sizes [32]. This has led to considerable interest in using CDs
in the synthesis of conducting polymers. It has been found that CDs
bound to the electrode acted as molecular templates to restrict the
growth sites of PPy within the -CDs cavities [33]. Several reports
have focused on the synthesis and preparation of an inclusion
complex of poly(aniline--cyclodextrin) [34], poly(bithiophene-
hydroxypropyl--cyclodextrin) [35], poly(pyrrole-sulfonated -
see front matter © 2009 Elsevier B.V. All rights reserved.
saa.2009.12.026aman and UV–vis spectroscopic studies of polypyrrole and
rrole-2,6-dimethyl--cyclodextrin)
mandia,∗, Anwar-ul-Haq Ali Shahb, Salma Bilal c, Hung Van Hoangd, Rudolf Holzee
mistry, Buali Sina University, Hamedan 6517838683, Iran
f Chemistry, Abdul Wali Khan University Mardan, N.W.F.P., Pakistan
er of Excellence in Physical Chemistry, University of Peshawar, N.W.F.P., Pakistan
mistry, Hanoi National University of Education, 136 Xuan Thuy, Hanoi, Viet Nam
iversität Chemnitz, Institut für Chemie, Straße der Nationen 62, D-09111 Chemnitz, Germany
e i n f o
e 2009
vised form 3 December 2009
cember 2009
chemistry
clodextrin
lymer
a b s t r a c t
Polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl--cyclodextrin) [P(Py--DMCD)] films prepared by
potential cycling in aqueous acidic solutions on indium tin oxide (ITO)-coated glass and gold electrodes
were studied by in situ UV–vis and Raman spectroscopy. Characteristic UV–vis and Raman bands were
identifiedand their dependencies on the electrodepotential havebeendiscussed. Spectroelectrochemical
results reveal differences both in the position of the spectral bands and their potential dependence for PPy
and P(Py--DMCD) films indicating interactions between polymer chains and CDs during electropoly-
merization process. The films were also characterized by cyclic voltammetry and FT-IR spectroscopy.
© 2009 Elsevier B.V. All rights reserved.m/locate /saa
2 J. Arjomandi et al. / Spectrochimica Acta Part A 78 (2011) 1–6
cyclodextrin), [36–38] and polypyrrole/-cyclodextrin [39]. We
have shown the role of -DMCD molecules in the polymeriza-
tion process, optical absorption and the conductivity of PPy and
PNMPy films in two differentmedia [40,41], and P3MPy in acetoni-
trile, previo
(UV–vis an
aqueous sol
The change
modes of PP
2. Experim
Cyclodex
as received
LiClO4 used
uum. Cyclic
potentiosta
card operat
metry (CV)
∼0.4 cm2) e
Chemicals),
as counter
used as ref
a BioRad FT
with a liqui
using the K
the polyme
electrode in
a standard
ment; a cuv
wasplaced
ingly positi
the negativ
(as indicate
an ISA T640
detection sy
ing laser lig
70 Series io
with aCohe
(polycrysta
to confer S
aqueous so
(ORC) treatm
with 25 sca
effect are 5
ber of cycle
found to be
were rinsed
under vacu
ples were p
experiment
purged solu
2.1. Prepara
A (1:1) (
tions were
1.33g (1m
DMCD) com
evaporator.
2.2. Polypy
in aqueous s
0.05M (
solving 1.74
aman
d on d
nt.
LiC
rgin
ning towards positive potentials from 0.00<ESCE < 1.80V at
rate of 50mVs−1. The electrosynthesis was stopped after 35
The PPy film was also prepared in the same way. The elec-
merizationmediumwas 69.1L (1mm) of themonomer in
of 0.1M LiClO4 aqueous solution.
ults and discussion
1 shows the Raman spectra of PPy films deposited on
ubstrates with and without ORC treatment. No meaning-
rmation can be obtained from the Raman spectroscopy if
posits on a gold substrate without ORC pre-treatment. The
spectra of PPy deposited on the roughened Au indicated
marked increase in intensity and a better resolution.
s of PPy and P(Py--DMCD) were deposited by cyclic
metry. Suitable films with good transition of vibration
S measurement can be prepared after 35 cycles from
SCE <1.80V.Althoughat thepotential limit of 1.8V therewas
f overoxidationof pyrrole, itwas a good choice for the sakeof
rison with electropolymerization of (pyrrole-cyclodextrin)
ex as also reported in the literature for the electropolymer-
of PPy, PPy-sulfated--CD [37] and PPy, PPy--CDfilms [39]
at a gold electrode at applied potentials up to ESCE = 1.80V
ypical CVs of PPy and P(Py--DMCD) films in 0.1M LiClO4
n are shown in Fig. 2. Apparently the CVs seem to be of the
ature. Nevertheless, differences can be observed especially
position of the oxidation peaks (around E SCE = 0.14V). In
e of P(Py--DMCD), the oxidation peak is shifted by 0.12V
s higher potential values. This indicates that the presence of
extrin not only increases the oxidation potential of PPy butusly [42]. In the present paper spectroelectrochemical
d Raman) results of PPy and P(Py--DMCD) films in
ution, using Kr+ ion laser (647.1nm) light, are reported.
s in intensity and characteristics of various vibrational
y and (Py--DMCD) films are discussed.
ental
trin (Wacker Chemie, Burghausen, Germany)was used
. Pyrrole (Aldrich, 99%) was distilled under vacuum.
as electrolyte (Heraeus, Germany)wasdriedunder vac-
voltammograms were recorded with a custom-built
t interfaced with a standard PC via an ADDA-converter
ingwith custom-developed software. For cyclic voltam-
, a gold electrode (99.99%, Schiefer, Hamburg-area
mbedded in epoxy ARALDIT D/HY 956 (Ciba Special
was used as working electrode. A gold sheet served
electrode and a saturated calomel electrode SCE was
erence electrode. Infrared spectra were recorded on
S-40 Fourier transform infrared (FT-IR) spectrometer
d-nitrogen-cooledmercury cadmium telluride detector
Br pellet technique. UV–vis spectra were recorded with
r films deposited on an optically transparent ITO-glass
the supporting electrolyte solution (0.1M LiClO4) in
10mm cuvette using a Shimadzu UV 2101-PC instru-
ette with the same solution and an uncoated ITO glass
in the referencebeam. Spectrawere recordedat increas-
ve potentials; in a few cases, spectra were recorded in
e-going potential direction in order to test reversibility
d in selected figures). Raman spectra were recorded on
00 spectrometer connected to a spectraview 2D CCD
stem. SER spectra were recorded using 647.1nm excit-
ht from Kr+ ion lasers, provided by a Coherent Innova
n laser; the laser power wasmeasured at the laser head
rent200powermeter. Rougheningof thegold electrode
lline 99.99%, polished down to 0.3mAl2O3) employed
ERS activity was performed in a separate cell with an
lution of 0.1M KCL by 25 oxidation–reduction cycles
entbetweenESCE =−0.28 toESCE = 1.22Vat500mVs−1
ns. The optimum cathodic and anodic scans for SERS
00 and 1000mVs−1, respectively. The optimum num-
for roughening the Au substrate in ORC treatment was
25 cycles [43]. After the ORC treatment the electrodes
thoroughly with distilled water, and finally dried in a
um dryer for 24h at room temperature. Then the sam-
laced in a desiccator filled with nitrogen before use. All
s were performed at room temperature with nitrogen-
tions.
tion of (pyrrole-cyclodextrin) complex
mole–mole) pyrrole/2,6-dimethyl--cyclodextrin solu-
prepared by mixing 69.1L (1mmole) of pyrrole and
mole) -DMCD in 5mL methanol. The formed (Py--
plexwas isolated by removing themethanol in a rotary
rrole and P(pyrrole-cyclodextrin) film electrosynthesis
olution
Py--DMCD) complex solution was prepared by dis-
g (1.25mmol) solid (Py--DMCD) complex in 25mL
Fig. 1. R
deposite
treatme
of 0.1M
gen pu
by scan
a scan
cycles.
tropoly
25mL
3. Res
Fig.
gold s
ful info
PPy de
Raman
both a
Film
voltam
in SER
0.00<E
a risk o
compa
compl
ization
grown
[36]. T
solutio
same n
in the
the cas
toward
cyclodspectra of PPy films prepared in 0.1M LiClO4 aqueous solution and
ifferent gold substrates (a) with ORC treatment and (b) without ORC
lO4 aqueous solutions. After vigorousmixing and nitro-
g (10min) cyclic voltammetric synthesis was initiated
J. Arjomandi et al. / Spectrochimica Acta Part A 78 (2011) 1–6 3
Fig. 2. Cyclic v
PPy (solid line
solution. Scan
also affects
extent.
In situ SE
tion lineatd
The general
tra previou
632.8nm e
gradually fr
goes positi
this region
The double
the C–H in-
ESCE = 1.00V
then remai
increasing
1094 cm−1
1056 cm−1.
to the ring
band aroun
ESCE = 0.80 u
belonging t
are attribut
band aroun
n situ
e with
solut
SCE =
retch
ring
dical
seem to be valid in the present context as the band at
−1 shows decrease in intensity with the potential increaseoltammograms of a gold substrate (with ORC treatment) coatedwith
) and P(Py--DMCD) films, (dashed line) in 0.1M LiClO4 aqueous
rate =50mVs−1.
the properties of the resulting polymer film to some
RS spectra of PPy film obtained with 647.1nm excita-
ifferentpotentials in theanodic scanare shown inFig. 3.
appearance of the Raman spectra is similar to the spec-
sly reported for PPy films in 0.1M LiClO4 solution with
xcitation line [44]. The C C stretching band is shifted
om 1599 to 1617 cm−1 when the electrode potential
Fig. 3. I
electrod
aqueous
from E
ring st
to the
and ra
ments
998 cmvely from ESCE = 0.00 to 1.80V. The wave number in
is representative of the redox state of PPy [33,37,44].
peaks at about 1056 and 1094 cm−1 are attributed to
plane deformation [27]. With applied potential up to
the intensity of the peak at 1056 cm−1 decreases and
ned nearly constant up to ESCE = 1.80V. However, with
potential from ESCE = 1.00 to ESCE = 1.80V, the peak at
is getting stronger as compared to the band around
The peaks around 1332 and 1396 cm−1 are attributed
-stretching mode of PPy [25,27]. The intensity of the
d 1396 cm−1 increases with the potential increase from
p to ESCE = 1.80V. Both the 1094 and 1396 cm−1 bands,
o the C–H in-plane and the ring stretching, respectively,
ed to the oxidized PPy [25,37]. The intensity of the
d 1431 cm−1 also increases with increasing potential
beyond a ce
940 cm−1 in
at 931 cm−1
dopants [48
Thismight b
at 940 cm−1
Fig. 4 sh
ferent elect
features as
stretching f
sity with t
The ring de
sity with th
about 1431
cies and is o
Table 1
Band assignments for Raman spectra of PPy and P(Py--DMCD) in 0.1M LiClO4 aq
Assignment PPy/cm
C–H out-of-plane deformation 940–946
Ring deformation 996–1001
C–H in-plane deformation 1056–1066
N–H/C–H in-plane deformation 1261–12,767
Ring stretching 1331–1343
1344–1357
C–N stretching 1390–1396
1427–1437
C C backbone stretching 1599–1650Raman spectra at 647.1nm excitation of PPy film on gold substrate
ORC treatment taken at different potentials imposed in 0.1M LiClO4
ion.
0.00 to ESCE = 1.80V. This band is associated with the
ing [45]. The bands about 940 and 998 cm−1, assigned
deformation, are associated with dications (bipolaron)
cations (polaron), respectively [46,47]. These assign-rtain value. However, the intensity of the band around
creases gradually with the potential increase. The peak
attributed to the symmetric stretchingmode of ClO4−1
] does not show a well-defined potential dependency.
e due to overlappingwith the peak of ring deformation
.
ows Raman spectra of a P(Py--DMCD) film at dif-
rode potentials. Generally the spectra show the same
that for PPy film (Fig. 3). The broad peak of C C bond
rom1570 to 1641 cm−1 shows a slight increase in inten-
he potential shifting from ESCE = 0.00 to ESCE = 1.80V.
formation peak at about 940 cm−1 increases in inten-
e potential only after ESCE = 1.00V. The broad peak at
cm−1 for PPy has been shifted towards higher frequen-
bserved at about 1462 cm−1 in the present case. These
ueous solution at =647.1nm excitation.
P(Py--DMCD)/cm
939–939
986–994-weak
1052–1063
1256–1265
1311–1332
1351–1361
1380–1399
1462–1463
1570–1647
4 J. Arjomandi et al. / Spectrochimica Acta Part A 78 (2011) 1–6
Fig. 4. In situ Raman spectra at 647.1nm excitation of P(Py--DMCD) film on gold
substrate electrode with ORC treatment taken at different potentials imposed in
0.1M LiClO4 aqueous solution.
peaks are attributed to the C–N stretching. Surprisingly the inten-
sity of this peak for P(Py--DMCD) film does not change with the
applied potential. Raman peak frequencies of both polymer films
with corresponding assignments are listed in Table 1.
The slight differences in the position of the peaks and their
potential dependence for PPy and P(Py--DMCD) films indi-
cate some interaction between polymer chain and CDs during
electropolymerization process. Thus by careful selection of the
excitation wavelength, SERS technique not only can be used as
a powerful tool for analyzing the changes in redox state of con-
ducting polymers but also gives information about the interactions
between host and guest during polymerization process.
Fig. 5a and b shows the absorption spectra of a PPy film on
ITO-glass electrode recorded after stepwise increases of poten-
tial from ESCE = 0.0 to 1.80V and the potential dependence of the
absorbance at three selected wavelengths, respectively. The spec-
trawere recorded in 0.1M LiClO4 solution. Themain features in the
spectra are essentially the same as reported before [49,50], where
three absorption peaks, which depend in bothmagnitude and posi-
tion on potential, can be distinguished. The highest absorption
around=350nm is causedby the→* electronic transition and
is characteristic of the reduced formof the polymer. The decrease in
intensity of this bandwith increasing potential indicates reduction
in concentration of the reduced sites because of their transforma-
tions to oxidized sites. The absorption in the range of 490–530nm
also shows sensitivity towards the potential shift. This absorption
is assigned to the high-energy polaron transition [40,37,51,52]. The
third absorptionattributed to the fully oxidized form is around860-
880nm. The spectra show that the absorption bands at about 530
and 880nm increases and shifts to 490 and 860nm, respectively,
with the increase in potentials up to ESCE = 1.80V.
Fig. 6a shows the UV–vis spectra of a P(Py--DMCD)-coated
electrode recorded in 0.1M LiClO4 at different applied potentials
successively increasing in the anodic direction. The spectral fea-
tures of the
different fro
Fig. 5. (a) UV–vis spectra of a PPy film-coated ITO-glass electrode, obtained at different electrode potent
plot for three selected wavelengths, derived from spectra displayed above.P(Py--DMCD)-coated electrode reflect characteristics
m those of a simple PPy-coated electrode. Two absorp-
ial values, ranging from ESCE = 0.0 to 1.80. (b) Absorbance vs. potential
J. Arjomandi et al. / Spectrochimica Acta Part A 78 (2011) 1–6 5
Fig. 6. (a) UV– t electrode potential values, ranging from ESCE = 0.0 to 1.80. (b) Absorbance
vs. potential p
tion bands c
than three
about 860–
of a broad
case for P(P
around360
sible ways.
reported in
490–530nm
spectra of
the high-en
polymer ch
entire abso
towards low
at 360nm i
→* tran
Fig. 6a). Sim
due to the
shifted to 3
possibility
decreases c
supported b
400nm wh
the involve
of the polym
the absorba
potential.
Fig. 7 sh
DMCD) and
IR spectra o
ratory cond
to the differ
vibrational
synthesized
our previou
to that of PPy formed in the absence of CD. The data for PPy
ood agreement with values reported elsewhere [54,55–57].
broadpeakoccurringat 3417 cm−1 inPPy is attributed to the
retch
5 cmvis spectra of a P(Py--DMCD) film-coated ITO-glass electrode, obtained at differen
lot for two selected wavelengths, derived from spectra displayed above.
an be observed in the spectra of P(Py--DMCD) rather
absorption bands. The absorption band observed at
880nm for PPy (Fig. 5a) can be observed in the form
absorption band at about 760–820nm in the present
y--DMCD) film. The other absorption band is located
–400nm.Thesedifferences canbeexplained in twopos-
Firstly, like P(Py--DMCD) in nonaqueous solution as
our previous work [40], the absorption band around
similar
are in g
The
N–Hst
at 152in the spectra of PPy disappears completely in the
P(Py--DMCD). The reason might be the absence of
ergy polaron transition because of interaction between
ain andCDsduringelectropolymerizatio