Naphthalenediimide bridged D-A polymers: Design, synthesis and electrochromic properties Dedicated to Professor Eyup Ozdemir.

Article abstract of DOI:10.1016/j.electacta.2014.08.019

We have synthesized two new D-A electrochromic polymers; poly(N,N'-bis(2-hexyl)-2,6-dithiophene-1,4,5,8-naphthalenediimide) (PTNDI) and poly(N,N'-bis(2-hexyl)-2,6-(3,4-ethylenedioxythiophene)-1,4,5, 8-naphthalenedimiide) (PENDI) bearing a naphthalenedimiide chromophore in the backbone. Structural characterization of initial compounds and products were carried out by using FT-IR and ¹H-NMR spectroscopies. The optical and electrochemical properties of these polymers were investigated by UV-Vis absorption spectroscopy and cyclic voltammetry, respectively. The results of spectroelectrochemical studies indicate that both polymers reveal various colors due to ambipolar redox behavior at cathodic and anodic regime. Both polymer films have reasonable redox stability (in the range of 75-80% after 1000 cycles), coloration efficiency (in the range of 80-100 cm² C ^-1), and response time (approx. 1s). Moreover, it is clearly seen that replacing donor unit from thiophene to EDOT results in change only in neutral state color.

Full text of DOI:10.1016/j.electacta.2014.08.019

Electrochimica Acta 143 (2014) 106–113
Contents lists available at ScienceDirect
Electrochimica Acta
journal homepage: www.elsevier.com/locate/electacta
Naphthalenediimide bridged D-A polymers: Design, synthesis and
ଝ
electrochromic properties
Emre Sefera,b, Fatma Baycan Koyuncua,b,∗
a
Department of Chemistry, Faculty of Sciences and Arts, C¸ anakkale Onsekiz Mart University, 17020, C¸ anakkale, Turkey
Polymeric Materials Research Laboratory, C¸ anakkale Onsekiz Mart University, 17020, C¸ anakkale, Turkey
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 24 July 2014
Received in revised form 9 August 2014
Accepted 10 August 2014
Available online 19 August 2014
We have synthesized two new D-A electrochromic polymers; poly(N,N’-bis(2-hexyl)-2,6-dithiophene-
1
1
,4,5,8-naphthalenediimide) (PTNDI) and poly(N,N’-bis(2-hexyl)-2,6-(3,4-ethylenedioxythiophene)-
,4,5,8-naphthalenedimiide) (PENDI) bearing a naphthalenedimiide chromophore in the backbone.
1
Structural characterization of initial compounds and products were carried out by using FT-IR and H-
NMR spectroscopies. The optical and electrochemical properties of these polymers were investigated
by UV-Vis absorption spectroscopy and cyclic voltammetry, respectively. The results of spectroelectro-
chemical studies indicate that both polymers reveal various colors due to ambipolar redox behavior at
cathodic and anodic regime. Both polymer films have reasonable redox stability (in the range of 75-80%
after 1000 cycles), coloration efficiency (in the range of 80-100 cm C ), and response time (approx. 1s).
Moreover, it is clearly seen that replacing donor unit from thiophene to EDOT results in change only in
neutral state color.
Dedicated to Professor Eyup Ozdemir.
Keywords:
Electrochromic polymers
Naphthalenedimiide
2
−1
3
,4-ethylenedioxythiophene
Thiophene
©
2014 Elsevier Ltd. All rights reserved.
1
. Introduction
time, and low operation voltage. On the other hand, five membered
imide substituents have been used to impart n-type characteristics
to small-molecule organic semiconductors because of their strong
electron-withdrawing character. There are tremendous studies
about imide-functionalized small molecules for n-type organic
materials based on the arylene such as naphthalenediimide (NDI)
and perylenediimide (PDI) [17–19]. The arylene imides are attrac-
tive candidates as the electron-accepting co-monomers in low band
gap D–A polymers by virtue of their extremely facile synthesis and
variable substitution at the nitrogen which allows a better manip-
ulation of polymer solubility, packing and morphology. Moreover,
the insertion of strong electron-withdrawing imide groups into
polymer backbones can effectively change energy levels result-
ing in even n-type and p-type behavior [20–24]. Nevertheless,
there are only a few reports about conjugated polymers contain-
ing imide-functionalized p-systems such as thiopheneimides [25],
bithiopheneimide [26], iso-thianaphtheneimide [27], phthalimide
[28] and aryleneimide [17–22].
Herein, we have designed, synthesized and investigated the
electrochromic features of two new D–A type polymers with NDI
as the acceptor unit along the backbone of polymers containing
thiophene (TNDI) and 3,4-ethylenedioxythiophene (EDOT) (ENDI)
as the donor moiety. Besides, effects of the donor moiety on the
electronic and optical properties of monomers and their resulting
polymers were investigated and compared in detail. Upon applied
potentials on the polymer films resulted in numerous colors as
Electrochromism is defined as a reversible and visible color
change in a material upon applied voltage. Initially, inorganic semi-
conductors such as tungsten trioxide (WO ) and iridium oxide
3
(
IrO ) are widely used in the electrochromic technology [1], then
2
organic small molecules such as metallophthalocyanines and vio-
logens [2], and finally conducting polymers have received great
attention for electrochromic applications [3]. Among the elec-
trochromics, the conducting polymers have a great potential due
to their structurally controllable HOMO–LUMO band gap that pro-
vides easy tunability of colors, solution processability, high contrast
ratio, and fast response time [4]. These valuable properties ren-
der conducting polymers promising candidates to be used in smart
windows [5,6], mirrors [7,8], displays [9], electrochromic devices
[
10–12], and camouflage materials [13–15].
Polythiophene derivatives [16] have gained a considerable
interest in electrochromic technology over inorganic materials and
other conductive polymers owing to some useful properties such
as their good film forming characteristics, multicolor changes in
the same structure, high switching stability as well as fast response
ଝ
Deceased March 25, 2014.
Corresponding author. Tel.: +90 286 2180018; fax: +90 286 2180533.
E-mail address: fatmabaycan@hotmail.com (F. Baycan Koyuncu).
∗
http://dx.doi.org/10.1016/j.electacta.2014.08.019
0
013-4686/© 2014 Elsevier Ltd. All rights reserved.

E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
107
a result of multistep redox behavior at both anodic and cathodic
regime.
(t, 8H, EDOT-CH -); 4,12 (t, 4H, N-CH ); 1,76 (m, 4H, -CH -); 1,37
2 2 2
(m, 12H, -CH - CH - CH -); 0,97 (t, 6H, -CH ).
2
2
2
3
2
. Experimental
2.1. Materials
All chemicals were purchased from Aldrich Chemical and used
without further purification.
N,N’-bis(2-hexyl)-2,6-dibromo-1,4,5,8-naphthalenediimide
was prepared using a previously reported method [29].
2.2. Synthesis of
N,N’-bis(2-hexyl)-2,6-dithiophene-1,4,5,8-naphthalene diimide
(
TNDI)
2
.4. Electrochemical polymerization of monomers
N,N’-bis(2-hexyl)-2,6-dibromo-1,4,5,8-naphthalenediimide
0.25 g, 0.42 mmol) and 30 mL THF were stirred in a 100 mL flask
(
Electrochemical polymerization was carried out in CH CN-
3
under Ar atmosphere. Then, 2-thiophene boronic acid (0.14 g,
.1 mmol), 2.5 M Na CO aqueous solution and Pd(PPh ) (5 mol %)
−
3
CH Cl solution (1/5; v/v) of 2.0 × 10 M monomer and 0.1 M
2
2
1
2
3
3 4
LiClO by repetitive cycling at a scan rate of 100 mV/s. The polymer
◦
4
were added to solution mixture. The mixture was refluxed at 80 C
for 24 h under Ar. At the end of the reaction, the reaction mixture
was cooled to room temperature, poured into a large amount of
methanol, and filtered. The precipitate was collected and purified
2
was deposited onto platinum (0.02 cm ) or indium–tin oxide/glass
(
ITO/glass, 8–12 ˝, 0.8 cm × 5 cm). A platinum wire was used as a
counter electrode while Ag wire served as a reference electrode.
The film was rinsed with CH CN to remove electrolyte salt.
3
with column chromatography (CHCl ) to give N,N’-bis(2-hexyl)-
3
(
2,6-dithiophene)-1,4,5,8-naphthalenediimide (TNDI) as a red
2
.5. Instrumentation
solid with a yield of 78%.
UV-Vis (␭max, nm, DCM): 359, 379, 469; FT-IR (cm−1): 3094 (C–H
FT-IR spectra were recorded by a Perkin Elmer FT-IR Spectrum
aromatic); 2957, 2931, 2856 (C-H aliphatic); 1701(C = O); 1578
(
2
2
−
1
1
One by using an ATR system (4000–650 cm ). H-NMR spectra
were recorded on a Bruker Avance DPX-400 at 25 C in deuterated
chloroform solutions with TMS as internal standard.
C = C aromatic); 1441 (C-N); 1H-NMR (CHCl -d, ppm): ␦ 8,55 (s,
3
◦
H, Ar-Haa
H, Ar-Hbb
ꢀ
); 6,94 (d, 2H, Ar-Hcc
); 3,71(t, 4H, N-CH ); 1,56 (m, 4H, -CH -); 1,46 (m, 12H,
); 6,55 (d, 2H, Ar-Hdd ); 6,31 (t,
ꢀ ꢀ
ꢀ
2
2
Electrochemical measurements were carried out using
a
-
CH - CH CH2-); 0,88 (t, 6H, -CH ).
2 2- 3
Biologic SP-50 electrochemical workstation. All measurements
were carried out under argon atmosphere., Oxidation and
reduction potential onsets of TNDI and ENDI monomers and
corresponding polymers were used to calculate the HOMO-LUMO
energy levels. The experiments were calibrated with the stan-
◦
+
dard ferrocene/ferrocenium redox system
30]. UV-Vis absorption spectra were measured using an Analytic
(E (Fc/Fc ) = +0.48 V)
[
Jena Speedcord S-600 diode-array spectrophotometer. The optical
band gaps (Eg) of products were calculated from their absorption
edges [31].
Spectroelectrochemical measurements were carried out using
absorption spectra of the polymer films under applied potential.
The spectroelectrochemical cell includes a quartz cuvette, an Ag
wire (RE), Pt wire counter electrode (CE), and ITO/glass as the trans-
parent working electrode (WE). 0.1 M TBAPF6 in CH CN was used
3
as the supporting electrolyte.
2.3. Synthesis of N,N’-bis(2-hexyl)-2,6-(3,4-
Colorimetric measurements were performed using an Analytic
Jena Specord S600 UV-Vis spectrophotometer which consists of
a chromometer module in reflection mode (standard illuminator
D65, field of with 10 observer) with the viewing geometry as rec-
ommended by CIE. According to the CIE system, the color is made
ethylenedioxythiophene)-1,4,5,8-naphthalenediimide
(
ENDI)
◦
N,N’-bis(2-hexyl)-2,6-dibromo-1,4,5,8-naphthalenediimide
0.25 g, 0.42 mmol) and 30 mL toluene were stirred in a 100 mL
(
up of three attributes; luminance (L), hue (a), and saturation (b)
flask under Ar atmosphere. 2-(tributyl)stannyl-EDOT (0.47 g,
[
32]. Platinum cobalt DIN ISO 621, iodine DIN EN 1557, and Gard-
1
.1 mmol) and Pd(PPh3)4 (5 mol %) were added. The reaction
◦
ner DIN ISO 6430 are the references that are used for colorimetric
measurements. These parameters were applied for the neutral and
oxidized states of the polymers deposited onto ITO/glass surface.
AFM measurements were carried out at room temperature and
ambient conditions using an Ambios QScope 250 instrument. The
non-contact mode (wave mode) was used to take topographic
images. A 20 ␮m scanner equipped with silicon tips having 10 nm
tip-curvature and an ITO/glass substrate were used for measure-
ments. The system is covered with an acoustic chamber to prevent
electromagnetic noises which may affect the measurements.
mixture was refluxed at 110 C under Ar atmosphere for 24 h. At
the end of the reaction, the reaction mixture was cooled to room
temperature, poured into a large amount of ethanol, and filtered.
The product was purified by column chromatography (silica gel,
◦
CHCl ). The purple product was dried at 60 C in vacuum oven. 73%
3
yield
UV-Vis (␭max, nm, DCM): 318, 362, 381,525; FT-IR (cm−1): 3183
(
1
C–H aromatic); 2957, 2921, 2857 (C-H aliphatic); 1707(C = O);
577 (C = C aromatic); 1494 (C-S aromatic); 1433 (C-N); 1H-NMR
(
CHCl -d, ppm): ␦ 8,78 (s, 2H, Ar-H ); 6,97 (s, 2H, Ar-Hbb ); 4,25
ꢀ
ꢀ
3
aa

1
08
E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
Fig. 1. Repeated potential scans of (a) TNDI and (b) ENDI in 0.1 M LiClO4 in CH3CN/CH2Cl2 (1/5; v/v), with a scan rate of 100 mV/s.
3
. Results and discussion
3.1. Synthesis and Characterization
The initial compounds (1 and 2) were synthesized and fully
characterized according to the literature [33]. The monomer, TNDI,
was synthesized from the Suzuki-coupling reaction between 2
and 2-thiopheneboronic acid. The other electroactive monomer,
ENDI, was obtained from the Still-coupling reaction between 2
and 2-(tributyl)stannyl-3,4-ethylenedioxythiophene (Scheme 1).
After completion of the synthetic work, chemical structures of all
1
molecules were characterized by FT-IR and H NMR spectroscopies.
Significant changes were observed in the spectral properties of the
initial compounds and the products.
In the 1H-NMR spectra of TNDI and ENDI, the specific naph-
thalenediimide core proton signals were observed as singlet at a
higher ppm (8.80 ppm) than that of other proton signals due to
electron-accepting ability of imide C = O moiety. Besides, the aro-
matic peaks between 7.59 and 7.20 ppm were attributed to the
thiophene moiety while the aromatic peak at 6.60 ppm and the
peaks between 4.40 and 4.20 ppm were attributed to the EDOT
moiety, showing successful synthesis of monomers. (Fig. S2-S3 in
supporting information).
Fig. 2. UV-Vis absorption spectra of (a) 2; (b) TNDI; (c) ENDI in CH Cl .
2
2
NDI core are blue-shifted with the attachment of donor moieties
like thiophene or EDOT. The typical broad charge transfer band
was observed at about 470 and 540 nm for TNDI and ENDI, respec-
tively due to electronic interaction between donor moiety (EDOT or
thiophene) and NDI acceptor core (Fig. 2b-c). The stronger donor
character of EDOT compared to thiophene results in a more red
shifted charge transfer band. Finally, the absorption onset of TNDI
is at 550 nm corresponding to an energy band gap of 2.25 eV. On the
other hand, ENDI has an onset value of 610 nm (equals to a band
gap of 2.03 eV) which shows a 60 nm red shift with respect to TNDI.
Electrochemical polymerization behaviors of TNDI and ENDI
−3
solutions (2.0 × 10 M) were examined both onto the platinum
disc and/or ITO/glass surface with repetitive scans in 0.1 M
LiClO /CH CN-CH Cl (1/5; v/v) serving as supporting electrolyte.
4
3
2
2
Polymerization of TNDI was carried out using repetitive cycles at
a potential of 0 to 1.5 V. A new redox couple with a half wave
ox
m,1/2
potential (E
) of 0.99 V was observed and the intensity of these
reversible peaks increased after each successive cycle, clearly indi-
cating the formation of polymer on the working electrode surface
3
.3. Electrochemical properties
(Fig. 1a). Due to the stronger electron donor character of EDOT
compared to thiophene, electrochemical polymerization of ENDI
requires lower potentials than that of TNDI. Therefore, electro-
chemical polymerization of ENDI was carried out by repetitive
The electrochemical properties of TNDI and ENDI monomers
and the corresponding polymers were examined by cyclic voltam-
metry (CV). An explicit difference in redox behavior of the TNDI
and ENDI can be observed from the CV depicted in Fig. 3. During CV
scanning in the anodic regime, TNDI exhibited an irreversible oxi-
cycling at a potential between -0.4 and 1.2 V, and a new redox
couple with a half wave potential (E po ,x 1/2) of 0.18 V was observed
(Fig. 1b). Polymer films deposited onto ITO/glass surface were elec-
ox
dation peak at E = 1.48 V, and this oxidation potential is higher
trochemically dedoped in a monomer free-electrolyte solution to
equilibrate the redox behavior and remove unreacted monomers
m,a
ox
than that of ENDI (irreversible; E = 1.05 V.) (Fig. 3). According to
m,a
this result, it can be deduced that EDOT moiety has more electron-
donor nature than D-A system containing thiophene and NDI as an
electron withdrawing moiety in a similar system. Due to extended
and/or oligomeric species by washing with CH CN.
3
3.2. Optical Properties
conjugation after polymerization, reversible oxidation potentials
ox
were observed at lower potentials for PTNDI (reversible; E
=
m,a
The optical properties of TNDI and ENDI were investigated by
1.02 V and E= 0.96 V; E= 0.99 V) and for PENDI (reversible; E= 0.17 V
and E= 0.19 V; E= 0.18 V) when compared to the corresponding
monomers (Fig. 1). On the other hand, in the cathodic regime, cyclic
voltammograms of monomers have characteristic two reversible
redox couples at E= -0.60 V and E= -0.50 V (E= −0.55 V); and
UV-Vis absorption spectroscopy recorded in CH Cl2 (liquid phase).
2
UV–Vis spectrum of the dibromo naphthalenediimide molecule (2)
exhibits three characteristic absorption bands at ␭max = 366, 378,
and 405 nm (Fig. 2a) [34]. The characteristic absorption bands of

E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
109
Scheme 1. Synthetic route to TNDI and ENDI monomers.
Fig. 3. Cyclic voltammogram of (a) TNDI (b) ENDI in 0.1 M LiClO4/CH3CN-CH2Cl2 (1/5; v/v), scan rate 100 mV/s.
−
1
Fig. 4. Scan rate dependence of (a) PTNDI and (b) PENDI films deposited onto ITO/glass electrode in 0.1 M TBAPF6/CH3CN at different scan rates vs. Ag wire: from 25 mV s
−
1
to 800 mV s
.

1
10
E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
Table 1
HOMO and LUMO energy levels, electrochemical (E ) and optical band gap (Eg) values of TNDI, ENDI, PTNDI, and PENDI.
ꢀ
g
Molecules
Reduction
potential
Oxidation
potential
(V)
HOMO
(eV)
LUMO
(eV)
Eg’;
Eg, Optical
band gap
(eV)
Electrochemical
band gap
(
V)
(
eV)
E= -0.60 E=
0.50
E= -1.0
E= 1.48
irreversible
E= 1.22
-5.54
-3.88
1.66
2.25
-
E= -0.92
reversible
E= -0.44
E= -0.48
E= 1.00
-4.88
-3.96
0.92
1.91
E= -0.40
E= 0.90
E= -0.92 E=
semi-reversible
E= 0.56
-
0.82
reversible
E= -0.36
E= -0.68 E=
E= 1.08
-5.24
-3.80
1.44
1.96
-
0.58
E= -1.08 E=
0.96
irreversible
E= 0.92
-
reversible
E= -0.52
E= -0.51 E=
E= 0.20
-4.14
-3.90
0.24
1.71
-
0.47
E= -0.91 E=
0.80
E= 0.18
reversible
E= -0.18
-
reversible
E= -0.42
E= -1.02 V and E= -0.93 V (E= −0.98 V) for TNDI; and E= -0.68 V and
E= -0.58 V (E= −0.63 V); and E= -1.08 V and E= -0.96 V (E= −1.02 V)
for ENDI attributed to two-electron stepwise reduction process of
NDI moiety (Fig. 3). Also, the linear relationship of peak current
intensities as a function of scan rates demonstrates that the poly-
mer films firmly attach onto the ITO/glass electrode and it proves
a non-diffusional redox behavior (Fig. 4). In addition, the HOMO-
LUMO energy levels of all compounds were calculated according
to the onset values of their oxidation and reduction potentials
3.5. Spectroelectrochemical Properties
The spectroelectrochemical properties of PTNDI and PENDI
films were investigated using UV-Vis spectrophotometer with
diode-array detector. Upon applied positive potential to PTNDI
film, the valence band-conduction band (␲→␲* transition) at
about 400-600 nm started to decrease and a new absorption band
appeared in the NIR region. The red color of the polymer film turned
into blue upon applied positive potentials. On the other hand, in the
negative regime, anion radicals formed on the carbonyl groups of
the NDI moiety on the PTNDI structure. During the scan from 0 to
-1.6 V (Fig. 6a), the absorption band at about 500 nm intensified and
new shoulders were observed at around 700 and 780 nm (Fig. 5b).
Therefore, during the reduction process, the polymer film exhibited
a color change from red to reddish purple.
(Table 1). As a result of the data in Table 1, it can be concluded
that the optical and electrochemical properties of the molecules
were greatly influenced by the type of donor moiety attached to
the electron-withdrawing NDI core.
3.4. Surface Morphologies
On the other hand, PENDI has well defined three absorption
maxima at 390, 460, and 575 nm corresponding to purple color
at the neutral state. When a positive potential from -0.4 to 1.6 V
was applied to the PENDI film, the intensity of these broad bands
between 400-700 nm slightly decreased. Besides, the new broad
band at 850 nm started to intensify due to formation of charge car-
riers on the polymer backbone. The purple color of the film at the
neutral state changed to dark grey corresponding to broad absorp-
tion bands from visible to near IR region (Fig. 7a). In the negative
regime, n-doping behavior of the PENDI film was confirmed as
The morphologies of PTNDI and PENDI film surfaces were
studied by AFM. Both of the film thicknesses were arranged as
approximately 550-600 nm by using electrochemical deposition
process on to ITO/glass surface (Fig. 5). As typical for coating by this
method, rough films were obtained. The RMS (root mean surface)
roughnesses were found to be 77.4 and 87.2 nm. The AFM images
of both polymer films exhibit non-uniform structures (Fig. 5). High
RMS values and agglomerated non-uniform structures can be due
to non-controlled electrochemical coating and bulky NDI core.

E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
111
Fig. 5. AFM images of (a) PTNDI and (b) PENDI polymer films prepared via electrochemical process.
in PTNDI. The intensity of ␲-␲ transition bands between 380 and
50 nm as well as the broad band at around 800 nm start to inten-
sify concurrently. Therefore, during the reduction process, purple
color of the film turned into khaki (Fig. 7b).
All electrochromic parameters of PTNDI and PENDI were sum-
marized in Table 2. Kinetic studies of polymer films were monitored
by increments and decrements of transmittance at the point of
absorption maxima with respect to time while switching the poten-
tial step between neutral and oxidized states with a residence time
of 10 s (Fig. 8). The optical contrast change (ꢀT%) of PTNDI between
neutral (at 0 V) and oxidized states (at 1.8 V) was observed as 23% at
770 nm. On the other hand, there is no significant contrast change
in the visible regime of PENDI when applied potential is between
neutral (-0.4 V) and oxidized state (1.6 V). Moreover, PENDI has
an outstanding optical contrast of 26% at 870 nm in the near IR
regime. In addition, the oxidation and reduction response time and
optical activity against switching were compared for the PTNDI
and PENDI films. The oxidation and reduction response times were
measured as 1.4 and 0.7 s for PTNDI, and 1.2 and 1.4 s for PENDI,
respectively. The visible spectral change activities of PTNDI and
PENDI films were retained by 77% and 74% even after 1000 cycles of
operation, respectively. Also, the coloration efficiency (CE) which
5
Fig. 6. Electronic absorption spectra and the color changes of PTNDI at (a) anodic regime and (b) cathodic regime deposited onto ITO/glass surface in 0.1 M TBAPF6/CH3CN.
Fig. 7. Electronic absorption spectra and the color changes of PENDI at (a) anodic regime and (b) cathodic regime onto ITO/glass surface in 0.1 M TBAPF6/CH3CN.

1
12
E. Sefer, F. Baycan Koyuncu / Electrochimica Acta 143 (2014) 106–113
Table 2
Electrochromic parameters for the PTNDI and PENDI.
Molecules
Optical
contrast
change (ꢀT%)
Response time
(s)
Visible spectral
change activity
after 1000
CIE color
Coloration
efficiency,
parameters
Luminance (L)
hue (a)
2
−1
)
(cm
C
cycles
(
%)
saturation (b)
PTNDI
23% (770 nm)
Oxidation
77
Neutral state
L: 34.1; a: 11.9;
b: 6.2
Oxidized state
L: 37.2; a: -4.6;
b: -9.3
82
1
.4
Reduction
.7
0
Reduced state
L: 44.7; a: 7.1;
b: 1.1
PENDI
26% (870 nm)
Oxidation
.2
Reduction
.4
74
Neutral state
L: 36.1; a: 3.6;
b: -7.2
Oxidized state
L: 57.1; a: -5.9;
b: 3.9
94
1
1
Reduced state
L: 47.5; a: -9.3;
b: 8.1
Fig. 8. Electrochromic switching, optical absorbance monitored at 770 nm for PTNDI between 0 and 1.8 V (a) and 870 nm for PENDI between -0.4 and 1.6 V (b).
is one of the most important parameters for the electrochromic
applications was calculated using CE = ꢀOD/Qd and ꢀOD = log
exhibited low band gap (1.91 eV and 1.71 eV), reasonable redox sta-
bility, coloration efficiency, and response time due to non-uniform
structures and high RMS values revealed by AFM
(
Tcolored/Tbleached), where Q is the injected/ejected charge between
d
neutral and oxidized states, Tcolored and Tbleached are the transmit-
tance in the oxidized and neutral states, respectively. Using these
equations, CE of PTNDI and PENDI were calculated as 82 and 94
Acknowledgement
2
−1
cm C , respectively. By considering all data, it can be clearly
seen that the electrochromic performance of the polymer is greatly
affected by the attached donor moiety to the electron-withdrawing
naphthalanediimide unit. Furthermore, PTNDI and PENDI polymer
films exhibited dual dopable property, reasonable response time,
resistance to over oxidation, and narrow driving voltage range.
Finally, PENDI film has not only a broad absorption in the visible
region at the neutral state, but also a broad absorption in the visi-
ble and the NIR region at oxidized state, therefore PENDI could find
various applications as a visible-NIR filter.
We gratefully acknowledge to Scientific and Technical Research
Council of Turkey (TUBITAK, project #: 112T707) for financial sup-
port.
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