Journal of The Electrochemical Society, 162 (9) G75-G81 (2015)
G75
0
013-4651/2015/162(9)/G75/7/$33.00 © The Electrochemical Society
Synthesis and Characterization of Thiophene and
Thieno[3,2-b]thiophene Containing Conjugated Polymers
a
b
c,d
a,z
Elvin Rustamlı, Seza Goker, Simge Tarkuc, Yasemin Arslan Udum,
b,e,f,g
and Levent Toppare
a
Department of Advanced Technologies, Gazi University, 06500 Ankara, Turkey
Department of Chemistry, Middle East Technical University, 06800 Ankara, Turkey
Department of Chemical Engineering, Delft University of Technology, 2628 BL Delft, The Netherlands
Arcelik A. S. Central R&D Department, 34950 Tuzla/Istanbul, Turkey
Department of Biotechnology, Middle East Technical University, 06800 Ankara, Turkey
b
c
d
e
f
Department of Polymer Science and Technology, Middle East Technical University, 06800 Ankara, Turkey
g
¨
The Center for Solar Energy Research and Application (GUNAM), Middle East Technical University, 06800 Ankara,
Turkey
Herein, we report the synthesis of two donor-acceptor-donor polymers (P1 and P2) based on thiophene (M1) and thieno
[
3,2-b]thiophene (M2) as the donor and 2,5-bis(dodecyloxy)benzene as the acceptor unit. The effects of different donor units
on the polymers’ electrochemical and optical properties were examined by cyclic voltammetry and spectroelectrochemical analysis.
Introducing thieno[3,2-b]thiophene unit as the donor unit enhances π-stacking and consequently lowering the bandgap of the result-
∗
ing polymer. The electronic band gaps, defined as the onset of the π- π transition, were found to be 2.0 eV for P1 and 1.7 eV for P2.
Both P1 and P2 films revealed multi-colored electrochromism. A dual-type complementary colored electrochromic device (ECD)
using P2/PEDOT in sandwich configuration was constructed. Spectroelectrochemistry, switching ability and open circuit memory
of the ECD were investigated.
©
Manuscript submitted April 14, 2015; revised manuscript received June 16, 2015. Published June 30, 2015.
During the past decade, the field of organic electronics has
progressed enormously as a result of growing interest in materials
chemistry. The first generation of conducting organic materials
were composed of predominantly carbon-based molecular structures
such as linear acenes, poly acetylene, and poly(p-phenylene viny-
fact that they are more processable than inorganic electrochromic ma-
terials and offer the advantage of a high degree of color tailorability.
Electrochromism is defined as the reversible change in transmittance
and/ or reflectance of the material upon applied voltage. The color
changes between a transparent state and a colored state or between
the two colored states are associated with electrochemically induced
oxidation-reduction reactions.
In this paper, we report two new donor-acceptor-donor conjugated
polymers which were synthesized by combining electron-accepting
2,5-bis(dodecyloxy)benzene with electron-donating thiophene and
thieno[3,2-b]thiophene. The influence of the structural differences of
the electron-donating units on the electrochemical and optical prop-
erties of the resulting polymers was investigated.
1
–3
lene) derivatives (PPV).
The following generation involved the
widespread incorporation of heterocycles into the conjugated back-
4
–6
bone such as thiophene, pyrrole and their derivatives. Currently,
conjugated polymers and small organic molecules have been designed
7
–10
using “donor-acceptor” strategy.
This method involves synthesiz-
ing monomers and polymers with a delocalized π-electron system that
consists of alternating electron-rich (donor) and electron-deficient
(
(
acceptor) units. The combination of high-lying HOMO levels
residing on the donor units) and low-lying LUMO levels (residing on
the acceptor units) results in a local electron density gradient along the
11,12
Experimental
backbone, creating a lower energy charge-transfer transition.
The
presence of this lower energy transition leads to smaller optical band
gaps. A low bandgap leads to absorption in the visible region. Low
bandgap, stability, solubility (which is crucial for their processability),
planarity (which is important for obtaining good π-orbital overlap
and effective electron delocalization) are the main requirements for
organic electronic materials. In an attempt to manipulate relevant
parameters to fulfill these requirements through synthetic expertise,
numerous organic heterocyclic and pendant groups have been incorpo-
rated into the backbones of donor-acceptor conjugated polymers and
small molecules. Thiophene based materials have demonstrated great
potential as donor units due to their desirable properties such as sta-
bility, ease of synthesis, and modification. In recent years, thiophene
General.— All reagents and chemicals were obtained from
commercial sources and used without further purification unless
44
otherwise mentioned. 1,4-Bis(dodecyloxy)benzene, 1,4-dibromo-
44
45
2
,5-bis(dodecyloxy)benzene,
tributyl(thiophen-2-yl)stannane,
46
tributyl(thieno[3,2-b]thiophen-2-yl)stannane
were synthesized
according to previously published procedures. Tetrahydrofuran
THF) was dried over sodium and benzophenone. Bruker Spectrospin
(
1
Avance DPX-400 Spectrometer was used to record H NMR and
13
3
C NMR spectra of synthesized materials in CDCl . Chemical
shifts were recorded in ppm downfield from tetramethylsilane. Elec-
tropolymerization of monomers were achieved in a three-electrode
electrochemical cell. Indium Tin Oxide doped glass slide (ITO) as
the working electrode, platinum wire as the counter electrode, and
Ag wire as the pseudo reference electrode were used under ambient
conditions using a Gamry potentiostat. Spectroelectrochemical stud-
ies of polymers were performed on a Varian Cary 5000 UV–Vis–NIR
spectrophotometer. Minolta CS-100 colorimeter was used to perform
colorimetry studies.
13
14,15
19
moiety was coupled with benzoselenadiazole, benzotriazole,
1
6
17,18
carbazole,
benzothiadiazole,
ethylenedioxythiophene,
20
21
22
diketopyrrolopyrrole,
benzimidazole.
3-alkylthiophene,
quinoxaline,
and
2
3
The study of the opto-electronic properties of conjugated polymers
and small organic molecules designed based on D-A approach pro-
vides valuable information for understanding the structure-property
relationship. And also it allows designing materials with an en-
hanced opto-electronic property. These materials have been used in
Synthesis.– 1,4-bis(dodecyloxy)benzene (2).— To a solution of hy-
droquinone (4.00 g, 36.3 mmol) in dry DMF (50.0 ml), K
3.6 mmol) was added and the solution was stirred under inert atmo-
2 3
CO (20.8 g,
2
4–27
28–31
organic light-emitting diodes,
organic solar cells,
field effect
8
32–34
35–37
38–43
transistors,
sensors,
and electrochromic devices (ECDs).
◦
sphere at 100 C for 1 hour. Then 1-bromododecane (15.1 g, 109 mmol)
was added to the mixture. After 42 hours, the mixture was cooled
to room temperature and poured onto distilled water. The product
Conjugated polymers have gained great attention for ECDs due to the
2 2 4
was extracted with CH Cl , and dried over anhydrous MgSO . After