Multichromic benzimidazole-containing polymers: Comparison of donor and acceptor unit effects

Article abstract of DOI:10.1002/pola.26144

This study reports a comparative study on electrochromic properties of two donor-acceptor-donor (DAD)-type polymers namely poly(2-heptyl-4,7-di(thiophen-2- yl)-1H-benzo [d]imidazole) (BImTh) and poly(4,7-bis(2,3-dihydrothieno[3,4-b] [1,4]dioxin-5-yl)-2-he

Full text of DOI:10.1002/pola.26144

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Multichromic Benzimidazole-Containing Polymers: Comparison of Donor
and Acceptor Unit Effects
Ayda Goycek Nurioglu,1 Hava Akpinar,2 Merve Sendur,1 Levent Toppare1,2,3,4
1Department of Chemistry, Middle East Technical University, 06800 Ankara, Turkey
2Department of Polymer Science and Technology, Middle East Technical University, 06800 Ankara, Turkey
3
¨
The Center for Solar Energy Research and Application (GUNAM), Middle East Technical University, 06800 Ankara, Turkey
4Department of Biotechnology, Middle East Technical University, 06800 Ankara, Turkey
Correspondence to: L. Toppare (E-mail: toppare@metu.edu.tr)
Received 6 March 2012; accepted 24 April 2012; published online
DOI: 10.1002/pola.26144
ABSTRACT: This study reports a comparative study on electro-
chromic properties of two donor–acceptor–donor (DAD)-type
polymers namely poly(2-heptyl-4,7-di(thiophen-2-yl)-1H-benzo
[d]imidazole) (BImTh) and poly(4,7-bis(2,3-dihydrothieno[3,4-b]
[1,4]dioxin-5-yl)-2-heptyl-1H-benzo[d]imidazole) (BImEd). DAD-
type monomers were polymerized electrochemically on indium
tin oxide-coated glass slides to determine the optical properties
of the polymers. Electrochemical p-doping experiments were
performed to determine the band gap and absorption band val-
ues of the polymer films at different redox states. Polymerization
of BImTh and BImEd yields multichromic polymers. Donor and
acceptor effects are studied by comparing the PBImEd and
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PBImTh with corresponding benzotriazole derivatives.
2012
Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 000: 000–
000, 2012
KEYWORDS: benzimidazole; conjugated polymers; donor-
acceptor theory; electrochemistry; electrochromism; functional-
ization of polymers; thin films
INTRODUCTION Most of the conducting polymers exhibit an
absorption band in the UV/vis region. Their energy gap lies
between the valence band and the conduction band in their
neutral states. As the polymer is doped with counter anions
(p-doped) or cation insertion (n-doped), this absorption band
becomes less intense and another band at lower energy
occurs. Generation of new absorption bands and hence differ-
ent colors upon doping (switching of redox states) is called
electrochromism. Polymeric electrochromics have proven to
be highly advantageous over their inorganic counterparts in
various manners such as a variety of colors and contrast
values, low cost, and easier processability.1 Besides these
benefits, having easy methods of preparation made them a
fundamental subject over the past couple of decades.2(a–h)
band gap and hence the electronic and optical properties by
small structural modifications. The investigation on electro-
chromic properties of poly(3,4-ethylenedioxythiophene)
(PEDOT)4 was an important step to modify the structures of
electrochromic-conjugated polymers. As it has powerful
properties, many 3,4-ethylenedioxythiophene (EDOT)-con-
taining polymers were synthesized and their electrochromic
behaviors were widely studied.5(a,b) Recently poly-4,7-bis
(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-dodecyl-2H-benzo
[1,2,3] triazole (PBEBT) (Fig. 1) was synthesized to discuss
the donor–acceptor–donor (DAD) approach. DAD polymers
are similar to DA alternative copolymers in terms of donor
acceptor push–pull character.6 Containing benzotriazole
(BTz) as the acceptor and EDOT as the donor unit resulted
more paramount properties than that of PEDOT itself.7 Elec-
trochromic properties of polythiophene and its derivatives
were also investigated profoundly.8(a,b) In 2009, a monomer
designed to have thiophene and BTz units was synthesized
and polymerized both chemically and electrochemically
(PTBT) (Fig. 1). PTBT switches not only between all RGB
(red–green–blue) colors but also has transmissive and black
states.2(h)
An electrochromic material changes its color consistently
and also reversibly upon applied potential. Polymeric elec-
trochromics show different redox states that derive distinct
absorption bands at different wavelengths. When more than
two redox states are achievable in visible region, the mate-
rial is said to be multichromic. There are several examples
investigated as multichromic conjugated polymers up to
now.3(a–c)
Improving the optical, mechanical, and electronic properties
of conducting polymers, obtaining polymers with different
Many different derivatives of conducting polymers have been
synthesized and characterized as it is possible to change the
C
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led us to figure out the importance of the acidic proton in
the imidazole ring. The presence of a free acidic proton in
the polymer backbone results in drastic changes in the elec-
trochemical properties of the monomers. Herein, we high-
lighted the electrochemical synthesis, optical, and electro-
chemical properties of two DAD-type polymers containing
EDOT and thiophene as the donor unit and 2-heptylbenzimi-
dazole as the acceptor unit. Besides clarifying the donor unit
effect on resulting polymers, electrochromic properties of
BTz-containing polymers were compared to have a better
understanding of the acceptor unit effect on electrochromic
properties of PBImTh, PBImEd, PBEBT, and PTBT (Fig. 1).
RESULTS AND DISCUSSION
Monomer Synthesis
FIGURE 1 Molecular structures of PBImTh (a), PTBT (b),
Monomers were prepared via Pd(PPh3)2Cl2-catalyzed Stille
coupling utilizing brominated benzimidazole unit and stanny-
lated EDOT (BImEd) and thiophene (BImTh) units as shown
in Scheme 1. Brominated benzimidazole unit was prepared
starting with the bromination of benzothiadiazole. It was per-
formed in the presence of Br2/HBr in a convincing yield.14
Subsequent reduction of (2) was achieved using NaBH4 in
ethanol to obtain (3).15 4,7-Dibromo-2-heptyl-1H-benzo[d]
imidazole (4) was synthesized as the acceptor unit by conden-
sation of octanal with (3) from an adapted procedure
described for the synthesis of 2-arylbenzimidazoles.16 Substi-
tuting alkyl chain to the monomer structure increases the
solubility of the polymer which is a vital property for applica-
tions like constructing photovoltaic devices. As intended,
resulting polymers were soluble in aprotic solvents such as
dimethylformamide and dimethyl sulfoxide. Hence, condensa-
tion with longer-chain aldehydes results in more soluble poly-
mers.17 The molecular structures of BImEd and BImTh were
proven by 1H and 13C NMR and also with mass analysis.
PBImEd (c), and PBEBT (d).
colors and lower band gap can be achieved using many
methods such as bond-length alternation, creating highly pla-
nar systems, inducing order by interchain effects, resonance
effects along the polymer backbone, and the DAD approach
which is mainly focused in recent research. DAD approach is
a method that increases double-bond character between the
aromatic rings and causes smaller band gaps than either of
the polymers of both units owing to resonance.9 This
method leads to control the band gap value via choosing dif-
ferent donor and acceptor units. In the literature, several
examples of polymers were synthesized containing different
donor groups to understand the effect of the donor unit on
optical and electronic properties of polymers. To discover
the donor effect on resulting polymers, benzazole derivatives
such as benzothiadiazole, BTz, and benzoselenodiazole as the
acceptor unit are widely studied.10(a–e)
BIm-containing polymers and copolymers were widely syn-
thesized and characterized by several groups.11(a–e) Electro-
chromic investigation of electrochemically polymerized BIm-
containing DA-type polymers was first accomplished by our
Electrochemistry
To directly synthesize and investigate potential electrochro-
mic characteristics of the polymer films, electrochemical
group.12
A
new benzimidazole unit; 40-(tert-butyl)spiro
[benzo[d]imidazole-2,10-cyclohexane] was synthesized and
coupled with different donor units namely 3-hexylthiophene
and EDOT via Stille coupling.13
There is still a lack of research on investigating the effect of
donor unit on resulting polymers such as the investigation of
electrochromic behaviors when the electron-deficient BIm
unit was incorporated into the polymer chain as the acceptor
unit. In our previous study,12 we obtained three different
DAD-type monomers keeping the donor unit (EDOT) con-
stant. Benzimidazole unit was functionalized with three dif-
ferent substituents on 2-C position of the imidazole ring to
investigate the acceptor unit effect. Electrochemical results
proved that modification of the benzimidazole unit with ben-
zene, EDOT, and ferrocene molecules significantly affected
the electrochromic properties of the resulting polymers.
However, in the present study, we kept the acceptor unit
constant and altered the donor units to investigate the donor
unit effect on the corresponding polymers. This study also
SCHEME 1 Synthetic route for monomers.
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FIGURE 2 Electrochemical polymerizations of monomers (left) and scan rate dependence of corresponding polymers (right);
BImTh and PBImTh (a), BImEd (inset: in the presence of base) and PBImEd (b).
polymerizations were carried out. BImTh and BImEd were
polymerized potentiodynamically on indium tin oxide (ITO)-
coated glass slides using equimolar 0.1 M sodium perchlo-
rate (NaClO4) and lithium perchlorate (LiClO4) as the sup-
porting electrolyte in a mixture of dichloromethane (DCM)
and acetonitrile (ACN) (5/95, v/v) with repeated scan inter-
vals between 0 and 1300 mV versus Ag wire pseudo-refer-
ence electrode (Fig. 2). As the monomers bear an alkyl chain
in their structure, oligomers were soluble in pure DCM. For
this reason, a mixture of DCM and ACN was used as the sol-
vent system. Monomer oxidation peaks at 1.01 V (BImTh)
and 1.30 V (BImEd) appeared in the first cycle of the vol-
tammograms and reversible redox peak couples of polymers
were centered at 0.68 and 0.52 V (PBImTh), 0.76 and 0.68 V
(PBImEd) versus Ag wire pseudo-reference electrode.
not the case for the thiophene-containing monomer. In prov-
ing this, we run CV of BImEd in the presence of a small
amount of base (0.01 M NaOH) [Fig. 2(b)]. As shown in Fig-
ure 2(b), the oxidation potential of the monomer decreased
by more than 0.1 V even with the addition of 50 lL of base.
In the second run, we observed nearly ꢀ 0.25 V smaller
redox couple than that of the polymer obtained in neutral
medium. These results prove the fact that decreased planar-
ity caused by H-bonding resulted in a higher oxidation
potentials.18 Still the oxidation potential of PBImTh in neu-
tral solution is lower than the one for PBImEd in an alkaline
solution. This may be owing to the fact that the presence of
a small amount of base hinders the formation of a polymer
film on the electrode surface. In the CV, further cycles do not
bring the current increase, revealing that the polymerization
does not take place owing to the quenching effect of the
base. Hence, its negative effect on the polymerization nega-
tive effect on the polymerization dominates hindering to
make a healthy comparison between the two polymers.
19
We observed nearly a 0.30 V larger oxidation potential for
BImEd than BImTh. As EDOT is more electron rich than thio-
phene, incorporation of EDOT unit to the monomer structure
was expected to reduce the oxidation potential of the mono-
mer. This unexpected result is most probably caused by the
NAH group on the BIm unit. NAH interacts with the EDOT
oxygen, resulting in a deviation from the planarity which is
€
Furthermore, Salzner and Kose proved that the DA match
has a significant effect in this regard. This match is caused
by the remarkable interaction between the different donor
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TABLE 1 Optoelectronic Properties of Polymers Bearing EDOT and Thiophene as the Donor and Benzimidazole and Benzotriazole
as the Acceptor Units
Ep,a (V)
Polymers
PBImEd
Em,a (V)
Ep,c (V)
Eg (eV)a
lmax (nm)b
Optical Contrasts (%)
Switching Times (s)
1.30
0.76
0.68
0.23
ꢁ0.04
0.68
0.52
1.00
0.60
1.74
533
1,120
618
40.3 (533 nm)
52.5 (1,120 nm)
53 (618 nm)
0.25 (533 nm)
0.28 (1,120 nm)
1.1 (618 nm)
PBEBT
PBImTh
PTBT
a
0.97
1.01
1.20
1.60
1.93
1.65
1,600
440
71 (1,600 nm)
25.7 (440 nm)
33.0 (1,114 nm)
35.0 (503 nm)
74.0 (1,271 nm)
2.9 (440 nm)
2.3 (1,114 nm)
2.0 (503 nm)
0.6 (1,271 nm)
1,114
503
1,271
Calculated from the onset of p–p* transitions in UV.
Calculated from the absorption spectra of polymer films in visible and NIR region.
b
and the acceptor moieties owing to the low-energy difference
in HOMO–LUMO energy levels of these moieties as much as
the intramolecular interactions.20
increasing scan rates. A direct relationship between the cur-
rent response and the scan rate was perceived for both
PBImTh and PBImEd (Fig. 2), which proved that the electro-
chemical processes are not diffusion-limited and quasi-re-
versible even at high scan rates.24
Theoretically speaking, the electron-rich or deficient groups
on the polymer backbone ease the p-electron delocalization
and hence lower the band gap. However, electronic effect is
not the only parameter to determine the band gap but pa-
rameters like coplanarity and contribution of the bulky alkyl
chains to the structure also take role.21 All those parameters
together determine the donor-to-acceptor charge transfer
character which specifies the oxidation and reduction poten-
tials, and band gap of the polymers.22 These properties
remain constant or differ slightly when the donor moiety on
the polymer backbone is changed while varying the acceptor
unit results in significant changes.22 Thus, the electronic and
optical changes can be compared by differing the acceptor
unit.
Spectroelectrochemistry
Observing the changes in electronic absorption spectra upon
doping process offers a direct means of evaluating the opti-
cal and structural responses of the polymer films. UV–Vis–
NIR spectra of PBImTh and PBImEd films electrodeposited
on ITO glass slides via multiple scan voltammetry were
recorded in a monomer-free, 0.1 M NaClO4–LiClO4/ACN solu-
tion, after compensating the polymers via electrochemical
reduction.
The donor–acceptor nature of polymers yields two transi-
tions; the low-energy transition affected the color of neutral
film of BImTh dominantly, as the high-energy transition was
not in the visible region. The high-energy transition is attrib-
uted to the transition from the thiophene-based valence
band to its antibonding counterpart and the low-energy tran-
sition is attributed to the transition to the substituent-local-
ized conduction band. The energy and intensity of these
transitions are determined by the DA interactions and the
match between donor and acceptor units. This phenomenon
is in agreement with the blue shift with decreasing donor
strength.12
The acceptor units of benzazoles can be diversified by plac-
ing different atoms like C or N to the 2-position. This var-
iance not only causes different bond properties between
NACAN and NANAN but also changes the polarizability and
hence yields different acceptor strengths.15,23 As indicated in
our previous study,12 BIm-containing monomer is expected
to have a lower monomer oxidation than a BTz derivative.
However, as stated before, the change in electronic proper-
ties of polymers cannot be explained by focusing only on the
individual properties of the constituents. The match of the
donor and acceptor moieties and planarity play an important
role in determining the electrochemical properties of the
polymer. As summarized in Table 1, monomer oxidation
potentials increase in the order of BEBT < BImTh < TBT <
BImEd. Although both acceptor units are quite similar except
for 2-position of the heterocyclic rings, this disparity results
from the presence of the NAH…O interaction which directly
affects the planarity of the molecule.
The evolution of the electronic band structure during elec-
trochemical p-doping of the polymers was recorded as a
function of applied potential and shown in Figures 3 and 4.
The undoped PBImTh and PBImEd films display absorption
maxima in the visible region at 440 and 533 nm, respec-
tively, corresponding to optical band gaps of 1.93 and 1.74
eV as calculated from the onset of the p–p* transitions. Both
polymers show absorptions at around 1000 nm in their neu-
tral state which may indicate that the films cannot be fully
reduced. During spectroelectrochemistry, as potential is grad-
ually increased, the peak intensity at 440 nm (PBImTh) and
533 nm (PBImEd) decreased and new bands at lower energy
Scan-Rate Dependence
The polymer films were coated potentiodynamically on ITO-
coated glass slides as described previously and cycled at
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FIGURE 3 Electronic absorption spectra of PBImTh film in 0.1 M NaClO4–LiClO4/ACN solution for neutral film (0.0 V) and between
0.6 and 1.2 V with 0.1 V potential intervals.
at 671–1114 nm (PBImTh) and 720–1120 nm (PBImEd)
evolved owing to the formation of charge carriers such as
polarons and bipolarons.
by colorimetry to define colors precisely. The PBImTh is or-
ange (L: 61.806, a: ꢁ5.956, b: 34.539) in the neutral state,
whereas the oxidized states are green (L: 51.387, a:
ꢁ12.622, b: 23.598) at 1.1V and blue (L: 45.266, a: ꢁ5.483,
b: 4.128) at its fully oxidized state. PBImEd film changed
from a purple (L: 45.387, a: 7.713, b: ꢁ4.849) neutral state
to a blue (L: 66.106, a: ꢁ8.479, b: 1.583) oxidized state with
gray (L: 49.200, a: ꢁ5.739, b: 4.366) color at 1.1V.
As shown in Figure 3, for PBImTh, two well-separated
absorption maxima centered at 440 and 671 nm, which is a
necessity to maintain green color, occurred by applying
1.10 V. PBImEd reveals gray color at this applied potential
(Fig. 4) which makes it multichromic.
In DAD-type monomers, the HOMO energy is close to the
HOMO of the donor, and the LUMO is close to that of the
acceptor unit. As EDOT has higher HOMO level than thio-
phene, one obtains a smaller band gap when EDOT is
coupled with the same acceptor unit. As summarized in
Table 1, both PBImEd and PBImTh possess maximum
absorptions at shorter wavelength than PBEBT and PTBT,
respectively. These results indicate that when BIm and BTz
are coupled with the same donor units (compare to BIm and
BTz as the acceptor units), the resultant BIm-containing
polymers have higher LUMO levels and hence higher band
gaps than the ones containing BTz. Band gap values
Upon doping, change in spectra was observed only above
0.40 V which is in accordance with cyclic voltammogram as
no current increase was seen up to 0.40 V. The stepwise
increase between 0.40 V and the oxidation potential of the
polymers in the polaronic region can be attributed to the ox-
idation of the polymer film and the sudden rise in absorb-
ance of polaronic states corresponds to the oxidation of the
film.
Spectroelectrochemical studies of the polymer film demon-
strate that the film’s color changed during the p-doping (oxi-
dation) process. The color changes were further investigated
FIGURE 4 Electronic absorption spectra of PBImEd film in 0.1 M NaClO4–LiClO4/ACN solution for neutral film (0.3 V) and between
0.5 and 1.3 V with 0.1 V potential intervals.
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spectra of the synthesized molecules were recorded in CDCl3
on Bruker Spectrospin Avance DPX-400 Spectrometer. Chemi-
cal shifts were given in ppm downfield from tetramethylsi-
lane. Mass analysis was carried out on a Bruker time-of-
flight mass spectrometer with an electron impact ionization
source. Electropolymerization was performed with a Voltalab
50 potentiostat in a three-electrode cell consisting of ITO-
coated glass slide as the working electrode, platinum wire as
the counter electrode, and an Ag wire as the pseudo-refer-
ence electrode. The reference electrode was calibrated with
respect to Fc/Fcþ (0.3 V). To perform the spectroelectro-
chemical studies of the polymer films, Varian Cary 5000 UV–
Vis spectrophotometer was used. Colorimetry measurements
were performed via Minolta CS-100 spectrophotometer.
Synthesis of 4,7-Dibromo-2-heptyl-1H-benzo[d]
imidazole (4)
FIGURE 5 Square wave potential step chronoamperometry
studies of PBITh at 440 and 1114 nm between 0.3 and 1.2 V (ver-
sus Ag wire reference electrode) with 5-s switching intervals.
4,7-Dibromo-2-heptyl-1H-benzo[d]imidazole (4) was synthe-
sized using a modified version of a previously described pro-
cedure.16 3,6-Dibromobenzene-1,2-diamine (3) (500 mg, 1.88
mmol) and octanal (429 mg, 3.76 mmol) were dissolved in 8
mL ACN. After addition of H2O2 (0.8 mL, 8 mmol), the mix-
ture was stirred for 10 min. Ammonium cerium (IV) nitrate
(110 mg, 0.4 mmol) was added to the mixture and refluxed
for 24 h. The mixture was cooled to room temperature and
20 mL distilled water was added into solution. The mixture
was extracted with 3 ꢂ 50 mL ethyl acetate. Combined or-
ganic phases were dried over MgSO4 and evaporated under
vacuum. The crude product was purified by silica gel. Fur-
ther purification through recrystallization in chloroform gave
the white solid (429 mg, 374 mmol, 67%). 1H (400 MHz,
DMSO-d6, d): 12.9 (s, 1H), 7.32 (s, 2H), 2.91 (m, 2H), 1.60–
1.18 (m, 10H), 0.88 (t, 3H). 13C NMR (100 MHz, CDCl3, d):
156.6, 142.2, 131.1, 126.6, 124.6, 111.3, 100.7, 30.7, 28.6,
28.1, 26.9, 25.5, 21.6, 13.0.
increases in the order of PBEBT < PTBT < PBImEd <
PBImTh. These results predicate that BTz molecule has a
stronger accepting ability than BIm molecule and also n-
dopable property as it has higher number of imine bonds
than that of BIm unit. Furthermore, when acceptor unit is
held constant by altering the donor unit, it is seen that the
thiophene moiety causes red-shift as consistent with the red-
shift in BTz-containing polymers.
Kinetic Studies
Kinetic studies were performed to determine the optical con-
trast between neutral and oxidized states of the polymers as
a function of time at their maximum absorption wavelengths.
Besides the changes in transmittance, the switching times of
the polymers were calculated using the chronoamperometry
studies. The polymers were electrochemically deposited on
the ITO-coated glass surface and the kinetic studies were
performed in a monomer-free, 0.1 M NaClO4–LiClO4/ACN so-
lution with 5-s stepping intervals with UV–Vis–NIR spectro-
photometer. PBImTh revealed 25.7% contrast at 440 nm and
33.0% contrast at 1114 nm with 2.98- and 2.33-s switching
times, respectively (Fig. 5). Replacing the thiophene unit
with a better donor unit EDOT enhanced the kinetic proper-
ties, revealing 40.3% contrast at 533 nm with 0.25-s switch-
ing times and 52.5% contrast at 1120 nm with 0.28-s
switching times (Fig. 6).
EXPERIMENTAL
General
All chemicals were used as purchased from commercial sour-
ces; Aldrich and Across. Tetrahydrofuran was dried over ben-
zophenone and Na metal for Stille coupling reactions. Stille
coupling reactions for monomer synthesis were performed
under argon flow. 4,7-Dibromobenzothiadiazole (2),14 3,6-
dibromobenzene-1,2-diamine (3),15 tributyl(thiophen-2-yl)
FIGURE 6 Square wave potential step chronoamperometry
studies of PBImEd at 533 and 1120 nm between 0.3 and 1.3 V
(versus Ag wire reference electrode) with 5-s switching
intervals.
stannane
(5),
and
tributyl(2,3-dihydrothieno[3,4-b]
[1,4]dioxin-5-yl)stannane (6)25 were synthesized according
to the previously described procedures. 1H and 13C NMR
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Wudl, F. Chem. Mater. 2004, 16, 574–580; (c) Reeves, B. D.;
Thompson, B. C.; Abboud, K. A.; Smart, B. E.; Reynolds, J.
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J.; Choi, S. J.; Kim P.; Park, S. A.; Kim, J.; Son, S. J.; Xiao
R.; Kim, S. H.; Lee, S. B. Adv. Mater. 2005, 17, 171–175; (e)
Wu, C. G.; Lu, M. I.; Chang, S. J.; Wei, C. S. Adv. Funct.
Mater. 2007, 17, 1063–1070; (f) Druy, M. A.; Seymour, R. J.
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neri, N.; Boysel, M.; Wudl, F.; Heeger, A. J. J. Chem. Phys.
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Synthesis of 2-Heptyl-4,7-di(thiophen-2-yl)-1H-benzo[d]
imidazole (7, BImTh)
2-Heptyl-4,7-di(thiophen-2-yl)-1H-benzo[d]imidazole (7) was
synthesized according to a previously described procedure.25
(4) (200 mg, 0.54 mmol) and (5) (798 mg, 2.14 mmol) were
dissolved in 30 mL dry THF under argon atmosphere. After
30-min stirring, dichlorobis(triphenylphosphine)palladium(II)
(60 mg, 0.054 mmol) was added into solution and the mix-
ture was left to reflux for 20 h. After removing the solvent
under reduced pressure, the crude product was purified
over silica gel to obtain a light yellow solid (7) with a yield
of 52% (108 mg, 0.28 mmol). 1H (400 MHz, CDCl3, d): 7.69
(s, 2H), 7.44 (s, 2H), 7.33 (d, 1H), 7.32 (d, 1H), 7.12 (m, 2H),
2.87 (t, 2H), 1.84–1.76 (m, 2H), 1.40–1.21 (m, 8H), 0.86 (t,
3H). 13C NMR (100 MHz, CDCl3, d): 155.4, 140.7, 127.9,
125.5, 125.4, 125.1, 121.0, 31.7, 29.5, 29.4, 29.0, 28.3, 22.6,
14.1. HRMS-ESIþ (m/z): Calcd for C22H24N2S2 380.5701,
found 380.5703.
3 (a) Tarkuc, S.; Unver, E. K.; Udum, Y. A.; Toppare, L. Eur.
Polym. J. 2010, 46, 2199–2205; (b) Chen, W. H.; Wang, K. L.;
Hung, W. Y.; Jiang, J. C.; Liaw, D. J.; Lee, K. R.; Lai, J. Y.;
Chen, C. L. J. Polym. Sci. Polym. Chem. 2010, 48, 4654–4667;
(c) Cheng, S. H.; Hsiao, S. H.; Su, T. H.; Liou, G. S. Macromole-
cules 2005, 38, 307–316.
4 Jones, F.; Heywang, G.; Schmidtberg, W. (Bayer AG). Eur.
Pat. DE38 589 A1, 1988.
5 (a) Dubois, C. J.; Reynolds, J. R. Adv. Mater. 2002, 14,
1844–1846; (b) Sonmez, G.; Meng, H.; Wudl, F. Chem. Mater.
2003, 15, 4923–4929.
Synthesis of 4,7-Bis(2,3-dihydrothieno[3,4-b][1,4]
dioxin-5-yl)-2-heptyl-1H-benzo[d]imidazole (8, BImEd)
This monomer was prepared with the same procedure
described for (7) using (4) (200 mg, 0.54 mmol), (6) (914
mg, 2.14 mmol) and dichlorobis(triphenylphosphine)palla-
dium(II) (60 mg, 0.054 mmol). The crude product was puri-
fied over silica gel to obtain a yellow solid (8) with a yield
of 38% (106 mg, 0.21 mmol). 1H (400 MHz, CDCl3, d): 7.85
(s, 2H), 6.36 (s, 2H), 4.28 (s, broad, 4H), 4.22 (s, broad, 4H),
2.90 (t, 2H), 1.79 (p, 2H), 1.42–1.18 (m, 8H), 0.82–0.78
(m,3H). 13C NMR (100 MHz, CDCl3, d): 151.8, 139.6, 132.9,
125.1, 125.0, 118.4, 110.4, 97.3, 62.9, 62.2, 29.6, 27.5, 27.3,
27.2, 26.9, 25.9, 20.5, 11.9 HRMS-ESIþ (m/z): Calcd for
6 Balan, A.; Baran D.; Toppare, L. J. Mater. Chem. 2010, 20,
9861–9866.
7 Balan, A.; Gunbas, G.; Durmus, A.; Toppare, L. Chem. Mater.
2008, 20, 7510–7513.
8 (a) Udum, Y. A.; Yildiz, E.; Gunbas, G.; Toppare, L. J.
Polym. Sci. Polym. Chem. 2008, 46, 3723–3731; (b) Atwani, O.;
Baristiran, C.; Erden, A.; Sonmez, G. Synth. Met. 2008, 158,
83–89.
9 Mullekom, H. A. M.; Vekemans, J. A. J. M.; Havinga, E. E.;
Meijer, E. W. Mater. Sci. Eng. 2001, R32, 1–40.
10 (a) Unver, E. K.; Tarkuc, S.; Udum, Y. A.; Tanyeli, C.; Top-
pare, L. J. Polym. Sci. Polym. Chem. 2010, 48, 1714–1720; (b)
Unver, E. K.; Tarkuc, S.; Udum, Y. A.; Tanyeli, C.; Toppare, L.
Org. Electron. 2011, 12 1625–1631; (c) Akbasoglu, N.; Balan, A.;
Baran, D.; Cirpan, A.; Toppare, L. J. Polym. Sci. Polym. Chem.
2010, 48, 5603–5610; (d) Sendur, M.; Balan, A.; Baran, D.; Kara-
bay, B.; Toppare, L. Org. Electron. 2010, 11, 1877–1885; (e) Icli,
M.; Pamuk, M.; Algi, F.; Onal, A. M.; Cihaner, A. Chem. Mater.
2010, 22, 4034–4044.
C26H28N2O4S2 496.6412, found 496.6413.
CONCLUSIONS
Two DAD-type monomers were synthesized and their elec-
trochemical polymerizations were achieved on ITO-coated
glass slides to determine the optoelectronic properties of the
polymers. Both polymers showed multichromic properties.
Hence, to determine the donor unit effect, both thiophene
and EDOT were coupled with the same acceptor unit via
Stille coupling reaction to obtain the monomers. Our results
indicate that the replacing of the EDOT with thiophene
caused a bathochromic shift in the absorption spectra of the
corresponding polymers. Energy levels of subsequent aro-
matic units play a more important role than the electronic
nature of the units as proven by spectroelectroanalytical
studies of the resulting polymers.
11 (a) Tanimoto, A.; Shiraishi, K.; Yamamoto, T. Bull. Chem.
Soc. Jpn. 2004, 77, 597–598; (b) Nurulla, I.; Tanimoto, A.;
Shraishi, K.; Sasaki, S.; Yamamoto, T.; Polymer 2002, 43,
1287–1293; (c) Hedberg, F. L.; Marvel, C. S.; J. Polym. Sci.
Polym. Chem. 1974, 12, 1823–1828; (d) Kokelenberg, H.; Marvel,
C. S. J. Polym. Sci. Polym. Chem. 1970, 8, 3199–3209; (e) Hig-
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12 Akpinar H.; Balan, A.; Baran, D.; Unver, E. K.; Toppare, L.
Polymer 2010, 51, 6123–6131.
ACKNOWLEDGMENT
13 Ozelcaglayan, A. C.; Sendur, M.; Akbasoglu, N.; Apaydin,
D. H.; Cirpan, A.; Toppare, L. Electrochim. Acta 2012, 67,
224–229.
The authors thank TUBA for financial support.
14 Neto, B. A. D.; Lopes, A. S.; Ebeling, G.; Goncalves, R. S.;
Costa, V. E. U.; Quina, F. H.; Dupont, J. Tetrahedron 2005, 61,
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