An electroactive polymeric material and its voltammetric response towards alkali metal cations in neat water

Article abstract of DOI:10.1016/j.tetlet.2008.03.139

The syntheses and characterization of a unique system based on thiophene, pyrrole and benzo-15-crown-5 (SNS-Crown) and its corresponding polymer (PSNS-Crown) are reported. Furthermore, selective, clear and reversible voltammetric responses of the conjugated polymer (PSNS-Crown) film towards the alkali series Li⁺, Na⁺ and K⁺ in both neat water and organic media (ethanol) are described.

Full text of DOI:10.1016/j.tetlet.2008.03.139

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Tetrahedron Letters 49 (2008) 3530–3533
An electroactive polymeric material and its voltammetric
response towards alkali metal cations in neat water
a,
b
*
Fatih Algı , Atilla Cihaner
a Laboratory of Organic Materials, Department of Chemistry, C¸ anakkale Onsekiz Mart University, 17100 C¸ anakkale, Turkey
b Chemistry Group, Faculty of Engineering, Atılım University, 06836 Ankara, Turkey
Received 6 December 2007; revised 3 March 2008; accepted 27 March 2008
Available online 29 March 2008
Dedicated to Professor Metin Balci on the occasion of his 60th birthday
Abstract
The syntheses and characterization of a unique system based on thiophene, pyrrole and benzo-15-crown-5 (SNS-Crown) and its
corresponding polymer (PSNS-Crown) are reported. Furthermore, selective, clear and reversible voltammetric responses of the conju-
gated polymer (PSNS-Crown) film towards the alkali series Li+, Na+ and K+ in both neat water and organic media (ethanol) are
described.
Ó 2008 Elsevier Ltd. All rights reserved.
Keywords: Chemosensor; Ion sensing; Crown ethers; Polythiophene; Polypyrrole
Redox-switched binding is well established and enables
the strength of a binding interaction to be controlled by
oxidation or reduction.1–4 In particular, the binding of
guest molecules at conducting polymers bearing suitable
recognizing groups allows modulating and switching the
transport behaviour of the conjugated chains if the recog-
nition process is reversible. This principle may be exploited
in iono-electronics devices in which the complexation/
decomplexation process results in an externally induced
ON/OFF switching. Considerable effort has been devoted
to that end where polythiophenes are substituted with
crown ethers and/or polyether chains to design modified
electrodes for electrochemical and bioelectrochemical sen-
sors.5–10 However, polypyrroles functionalized with crown
ethers for molecular recognition have been much less
exploited due to the difficulties in their synthesis.11,12 Fur-
thermore, most of the polymers with crown ether append-
ages have solubility problems and water incompatibility.
Herein, we report the synthesis of an electroactive poly-
meric material and its voltammetric response towards
alkali metal cations (Li+, Na+ and K+) in both neat (with
no organic solvent and/or additive) water and ethanol. Our
inspiration came not only from previous reports,11,12 but
also from the fact that SNS-based polymers13,14 can be
amplified to create viable materials.
The synthesis of monomer, SNS-Crown, was carried out
via a two-step reaction sequence: acylation of thiophene
with succinyl dichloride to give 1,4-di(thien-2-yl)butane-
1,4-dione15 followed by Paal–Knorr reaction of the dione
with 4-amino-benzo-15-crown-5 (see Supplementary data).
Anodic oxidation of SNS-Crown in 0.1 M tetrabutylam-
monium perchlorate (TBAClO4)/ethanol solution gave a
single irreversible peak at 0.68 V (vs Ag/AgCl). During
the second scan, a reversible redox couple (Epa = 0.56 V,
Epc = 0.39 V) was observed and the current intensity of this
peak increased after each successive cycle (Fig. 1a) which
clearly indicated the formation of an electroactive polymer
(PSNS-Crown) on the working electrode surface (Scheme
1). PSNS-Crown was soluble in acetone, DMSO, DMF,
propylene chloride and N-methyl-2-pyrolidone.
*
Corresponding author. Tel.: +90 2862180018 1860; fax: +90
2862180533.
E-mail address: falgi@comu.edu.tr (F. Algı).
0040-4039/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2008.03.139

F. Algı, A. Cihaner / Tetrahedron Letters 49 (2008) 3530–3533
3531
Fig. 1. (a) Repeated scan electropolymerization of 1.0 Â 10À3 M SNS-Crown and (b) cyclic voltammogram of PSNS-Crown film using an ITO electrode
at 100 mV/s in 0.1 M TBAClO4/ethanol solution.
Electrochemical
S
N
O
S
S
N
O
S
S
N
O
S
= Li+
Na+
K+
Polymerization
n
n
O
O
O
O
O
O
O
O
O
O
O
O
PSNS-Crown-M
PSNS-Crown
SNS-Crown
Scheme 1. Electrochemical polymerization of SNS-Crown and ion recognition by the PSNS-Crown film to give PSNS-Crown-M.
We first examined the redox behaviour of the polymer
film by cyclic voltammetry. The polymer film exhibited a
of PSNS-Crown-M after interaction of the ions with the
macrocyclic appendage of the conjugated polymer. It was
also evident that the observed shifts were in agreement with
the well-established size-fit concept in terms of cavity size
single and well-defined reversible redox couple (Epa
=
0.50 V, Epc = 0.38 V vs Ag/AgCl) when the potential was
scanned between 0.0 V and 0.7 V (Fig. 1b).
˚
of benzo-15-crown-5 (1.7–2.2 A). Since the diffusion and
Next we investigated the changes in the redox behaviour
of the PSNS-Crown film in the presence of alkali cations:
Li+, Na+ and K+ in neat water. The PSNS-Crown film
was cycled in the presence of alkali cations: Li+, Na+ and
K+ as perchlorate salts in neat water. We were delighted
to note that the anodic peak due to polymer oxidation
was shifted negatively, and reversibly in water, and stabi-
lized after two scans (Fig. 2).
Similar results were obtained when ethanol was used as
the solvent instead of water. Table 1 summarizes the shifts
of the anodic peak of PSNS-Crown when replacing TBA+
by Li+, Na+ and K+. The observed negative shifts in the
case of PSNS-Crown can be attributed to the formation
the mobility of K+ into the polymer would be more difficult
when compared to Li+ or Na+ due to ionic radius, a smal-
ler shift in the oxidation potential was observed (Table 1).
However, the presence of Na+ the size of which matched
well with the size of the crown ether caused the largest shift.
On the other hand, the observed shifts might also be attrib-
uted to a conformational change in the polymeric structure
after complexation with the cations to give PSNS-Crown-
M.
The voltammetric responses are quite good when com-
pared to known polypyrroles containing crown ether
appendages11,12 which either showed no recognition or
only minor responses to alkali cations in water. Conse-

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F. Algı, A. Cihaner / Tetrahedron Letters 49 (2008) 3530–3533
Table 1
Alkali cation diameters16 and the shifts of the anodic peaks of PSNS-
Crown film with respect to TBA+ after addition of alkali cations in water
and ethanol
˚
M
Diameter (A)
In water
In ethanol
DEpa (mV) DEpc (mV) DEpa (mV) DEpc (mV)
Li+ 1.36
Na+ 1.94
À252
À279
À186
À3
36
3
À87
À112
>300
À25
18
5
K+
2.66
sity of the polymer film (Fig. 3a). It was evident that the
plot of concentration versus anodic peak current could be
used to determine the ion concentration in solution
(Fig. 3b).
It is noteworthy that the selective voltammetric response
of PSNS-Crown film in neat water towards alkali cations;
Li+, Na+ and K+, reveals the transduction of chemical
information into an electrical response which now paves
the way for voltammetric determination of the above ions
in water. The polymeric sensor keeps working even after
prolonged standing under ambient conditions.
To conclude, the synthesis of an electroactive polymeric
material and its clear and reversible voltammetric response
towards alkali metal cations (Li+, Na+ and K+) in both
neat water and ethanol were described. The present study
circumvents the aforementioned problems through a
rational design of a processable hybrid material where
the stability of polythiophene, conductivity of polypyrrole
and selectivity of benzo-15-crown-5 towards alkali cations
are combined. Work to design and synthesize of other
polymeric sensors is currently underway in our
laboratories.
Fig. 2. Cyclic voltammograms of PSNS-Crown film (13 mC/cm2) using an
ITO electrode in 0.1 M TBAClO4/ethanol and successive voltammograms
of the same film in separate solutions of 0.1 M LiClO4, NaClO4 and
KClO4/water at a scan rate of 100 mV/s for the second run.
quently, it can be stated that PSNS-Crown is an efficient
sensor for these cations since it gives significant reversible
shifts in neat water as well as in organic media.
As an aside, we also examined changes in the oxidation
potential of PSNS-Crown versus ion concentration (Li+
and Na+) by cyclic voltammetry. Addition of ions (as
LiClO4 and NaClO4) to PSNS-Crown film in TBAClO4/
ethanol solution resulted in a decrease in the current inten-
Fig. 3. (a) Cyclic voltammograms of PSNS-Crown on ITO in ethanol solution containing 0.1 M TBAClO4 on the addition of alkali metal salts at a scan
rate of 50 mV/s and (b) anodic peak currents of PSNS-Crown as a function of concentration.

F. Algı, A. Cihaner / Tetrahedron Letters 49 (2008) 3530–3533
3533
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Acknowledgements
We thank the Scientific and Research Council of Turkey
(TUBITAK) and University Funding (COMU) for finan-
cial support of this work.
Supplementary data
Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tetlet.2008.
03.139.
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