A narrow range multielectrochromism from 2,5-di-(2-thienyl)-1H-pyrrole polymer bearing pendant perylenediimide moiety Dedicated to Professor Eyup Ozdemir.

Article abstract of DOI:10.1016/j.dyepig.2014.08.003

A new 2,5-di-(2-thienyl)-1H-pyrrole (SNS) moiety containing perylenediimide (PDI) acceptor as pendant side chain has been synthesized for an electroactive monomer and then directly deposited onto ITO/glass surface via electrochemical polymerization process. The observed electronic interaction only at the excited state due to the presence of phenylene spacer between SNS-donor and PDI-acceptor moiety leads to efficient fluorescence quenching. This charge separation behavior was also proved by theoretical DFT calculations. Thin films of the polymer electropolymerized onto transparent electrode exhibited ambipolar multi-electrochromic behavior including purple, violet-red-khaki-blue colors in both anodic and cathodic regime only between -1.2 and 1.0 V. We further demonstrated that this polymer film has a high contrast ratio (ΔT = 45% at 900 nm), a faster response (0.5 s), high coloration efficiency (254 cm ² C^-1) and retained its performance by 92% even after 5000 cycles.

Full text of DOI:10.1016/j.dyepig.2014.08.003

Dyes and Pigments 113 (2015) 121e128
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
A narrow range multielectrochromism from 2,5-di-(2-thienyl)-1H-
pyrrole polymer bearing pendant perylenediimide moiety
,
*
Emre Sefer a, Hakan Bilgili b, Burak Gultekin b, Murat Tonga c, Sermet Koyuncu d
a Department of Chemistry, Faculty of Sciences and Arts, Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey
b Solar Energy Institute, Ege University, Bornova, 35100, Izmir, Turkey
c Department of Chemistry, University of Massachusetts-Amherst, Amherst, MA, 01003, USA
d Department of Chemical Engineering, Faculty of Engineering, Çanakkale Onsekiz Mart University, 17020, Çanakkale, Turkey
a r t i c l e i n f o
a b s t r a c t
Article history:
A new 2,5-di-(2-thienyl)-1H-pyrrole (SNS) moiety containing perylenediimide (PDI) acceptor as pendant
side chain has been synthesized for an electroactive monomer and then directly deposited onto ITO/glass
surface via electrochemical polymerization process. The observed electronic interaction only at the
excited state due to the presence of phenylene spacer between SNS-donor and PDI-acceptor moiety leads
to efficient fluorescence quenching. This charge separation behavior was also proved by theoretical DFT
calculations. Thin films of the polymer electropolymerized onto transparent electrode exhibited ambi-
polar multi-electrochromic behavior including purple, violet-red-khaki-blue colors in both anodic and
cathodic regime only between ꢀ1.2 and 1.0 V. We further demonstrated that this polymer film has a high
Received 19 June 2014
Received in revised form
21 July 2014
Accepted 4 August 2014
Available online 14 August 2014
Dedicated to Professor Eyup Ozdemir.1
contrast ratio (
D
T ¼ 45% at 900 nm), a faster response (0.5 s), high coloration efficiency (254 cm2 Cꢀ1
)
Keywords:
Conjugated polymers
Donoreacceptor polymers
Electrochromic materials
Photoinduced electron transfer
Perylenediimides
and retained its performance by 92% even after 5000 cycles.
© 2014 Elsevier Ltd. All rights reserved.
2,5-di-(2-thienyl)-1H-pyrrole
1. Introduction
as 0.3e0.5 eV which results from alternating electron donor and
electron-accepter units combined through -conjugation with
p
Since polyacetylene as first conducting polymer was announced
by Shirakawa and co-workers in 1977 [1], these polymers have
received much attention in the field of science and technology [2].
These polymers have various application areas such as light emit-
ting diodes (LEDs) [3e6], organic photovoltaics (OPV) [7e9],
organic transistors (OFETs) [10,11], displays [12], smart windows
[13] and camouflage materials [14]. Construction of conjugated
polymers containing multiple redox-active chromophores is
important for the preparation of new polymeric optoelectronic
materials, which exhibit various low redox states derived from
distinct absorption bands at different wavelengths, depending on
the structure of the material [15,16]. In the literature, lots of
building blocks have been used to obtain conjugated polymers with
different optical, electrochemical and physical properties. It is
essential to achieve electroactive polymers with band gaps as low
intrinsic intramolecular charge transfer (ICT) character. Thus, this
methodology offers an effective way to reduce the band gap of
resultant polymers by the incorporation of building segments with
a higher HOMO and a lower LUMO level [17,18]. Electroactive
polymers are also suitable for use in electrochromic materials
because of not only their structurally controlled energy band gap
but also easy color tunability, processibility, high contrast ability
and a fast response time [19e24]. Furthermore, electrochromic
polymers can exhibit electrochemical stability upon continuous
redox switching between their various colored states without any
noticeable decline in performance, so they have been considered
excellent candidates for the practicality of electrochromic devices
[15e26].
On the other hand, recently reported materials, 2,5-di-(2-
thienyl)-1H-pyrrole (SNS) derivatives [27,28], have outstanding
properties for electrochromic applications such as (i) the oxidation
potential of the SNS derivatives is lower (about þ0.7 V vs. SCE) than
those of many of other electroactive materials, (ii) PaaleKnorr
synthesis offers easy attachment of side chains into the main
monomer, (iii) providing good quality of the films of poly-SNS
* Corresponding author. Tel.: þ90 286 2180541; fax: þ90 286 2180540.
E-mail addresses: skoyuncu@comu.edu.tr, sermetkoyuncu@hotmail.com
(S. Koyuncu).
1
Deceased March 25, 2014.
http://dx.doi.org/10.1016/j.dyepig.2014.08.003
0143-7208/© 2014 Elsevier Ltd. All rights reserved.

122
E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
which can be easily generated onto ITO/glass surface, and thus can
yield a high performance [26]. Moreover, the introduction of an
electroactive or a photoactive moiety into SNS backbone can pro-
vide the band gap tunability and valuable properties. On the other
hand, perylenediimides (PDIs) represent a class of highly stable n-
type semiconductors with relatively high electron affinity and
excellent charge transport property [29]. There has been an
increasing interest in the incorporation of PDIs as energy- or
electron-acceptors. PDIs have been inserted between donor and
acceptor segments in conjugated oligomeric or polymeric building
blocks in order to avoid extensive clustering and macro phase
separation of the donor and acceptor phases, which may occur in
case of blending the two separate components [30,31]. PDI exhibits
an efficient charge separation in the solution and solid state. Due to
the favorable interactions of the donor parts with acceptor parts in
the solid state, these polymers result in the formation of alternating
SNS and PDI assemblies [32,33].
In this paper, we present a new SNS based electroactive
monomer bearing PDI with a branched alkyl chain as acceptor
subunit. Remarkable fluorescence quenching in the PDI core was
observed due to efficient intramolecular electron transfer from
SNS-donor to PDI-acceptor at the excited state. The polymer film
was obtained onto ITO/glass surface by electrochemical process.
Owing to dual redox behavior in low driving potential, the poly-
meric film exhibits a wide range of colors including purple, violet-
red-khaki-blue in both anodic and cathodic regime. Therefore, the
generation of an attractive palette of colors in a narrow range
of ꢀ1.2e1.0 V makes these polymers promising candidate for
electrochromic devices.
2.3. Electrochemical polymerization of SNS-PDI
Electrochemical polymerization processes were carried out in a
dichloromethane solution of 2.0 ꢂ 10ꢀ3 M SNS-PDI monomer and
0.1 M TBAPF6 by repetitive cycling between 0 and 1.0 V at a scan
rate of 100 mV sꢀ1. A platinum wire was used as a counter electrode
and Ag wire as a reference electrode. The polymer was directly
deposited onto platinum disk (0.02 cm2) or ITO/glass surface
(8e12 Ώ, 0.8 ꢂ 5 cm2, active area adjusted to 1 cm2). After depo-
sition of poly-SNS-PDI, the ITO/glass surface was washed with
acetonitrile to remove the impurities and oligomeric by-products in
electrolyte (Scheme 1).
2.4. Instrumentation
FT-IR spectra were recorded by a Perkin Elmer FT-IR Spectrum
One by using ATR system (4000e650 cm-1). 1H NMR (Bruker
Avance DPX-400) data were recorded at 25 ꢁC by using CHCl3-d as
solvent and TMS as internal standard.
Cyclic voltammetry (CV) technique used for electrochemical
measurements were performed by Biologic SP-50 electrochemical
workstation. These measurements were carried out under argon
atmosphere and the electrochemical cell includes an Ag wire as
reference electrode (RE), Pt wire as counter electrode and glassy Pt
disk as working electrode (WE) immersed in supporting electrolyte
solution in consist of 2.0 ꢂ 10ꢀ3 M SNS-PDI monomer and 0.1 M
TBAPF6 in dichloromethane. HOMO and LUMO energy levels of
SNS-PDI and corresponding polymer were calculated according to
the inner reference ferrocene redox couple Eꢁ(Fc/Fcþ)on ¼ þ0.38 V
(vs. Ag wire; see Supplementary data, Fig. S8) by using the equation
EHOMO/LUMO ¼ ee(Eox/red ꢀ EFc) þ (ꢀ4.8 eV) [38]. Onset values of
oxidation/reduction potentials were taken into account while
calculating HOMO/LUMO energy levels. UVeVis absorption spectra
were measured by Analytic Jena Speedcord S-600 diode-array
2. Experimental
2.1. Materials
All materials were supplied from Aldrich, Merck and Fluka, and
were used without further purification. The syntheses and char-
acterizations of 1,4-Bis(2-thienyl)butan-1,4-dione [34], 1-(4-
nitrophenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole
di(thiophen-2-yl)-1H-pyrrol-1-yl)aniline
ethylhexyl)perylene-3,4,9,10-tetracarboxylic acid diimide [37], N-
(2-Ethylhexyl)-3,4,9,10-perylenetetracarboxylic acid 3,4-
anhydride-9,10-imide [37] were previously described in the
literature.
[35],
[36],
4-(2,5-
N,N-di(2-
2.2. Synthesis of SNS-PDI
N-(2-Ethylhexyl)-3,4,9,10-perylenetetracarboxylic acid 3,4-
anhydride-9,10-imide (0.533 g, 1.92 mmol), was added into 40 mL
dry pyridine and refluxed under argon atmosphere for 30 min.
Then,
4-(2,5-di-2-thienyl-1H-pyrrole-1-yl)aniline[4-(2,5-di-2-
thienyl-1H-pyrrole-1-yl)phenyl]amine (0.155 g, 0.481 mmol) was
added in small portions and this mixture was stirred at 120 ꢁC for
8 h. Then, the reaction mixture was cooled to room temperature
and poured into HCl solution (3 M, 500 mL). The resulting precip-
itate (1.11 g) was collected by filtration, washed with NaHCO3 so-
lution (100 mL) and water (50 mL), and then the product was
purified by column chromatography (silica gel, 3/1; CHCl3/hexane).
The pure product dried at 80 ꢁC in vacuum oven. Yield: 89% 0.25 g.
FT-IR (cmꢀ1): 3036, 3012 (CeH, aromatic); 2922, 2851(CeH
aliphatic); 1697, 1656 (C]O imide); 1573, 1563 (C]C aromatic). 1H-
NMR (CHCl3-d):
d ppm, 8.64 (d, 4H, CeH perylene); 8.52 (d, 4H, per-
ylene); 8.10 (d, 2H, Hf), 7,91 (d, 2H, Ha) 7,62 (d, 2H, He); 7.43 (d, 2H,
Hc); 7.32 (m, 2H, Hb); 6.84-(s, 2H, Hd); 4.32 (m, 2H, NeCH2); 1.51e0.83
(m, 15H, CeH aliphatic), MALDI-ToF (m/z): [Mþ] calcd. for
C
50H39N3O4S2, 809.99; found, 809.92.
Scheme 1. Electrochemical polymerization reaction of SNS-PDI.

E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
123
spectrophotometer. The optical band gap (Eg) of products was
calculated from their absorption edges by using this formula
Eg(eV) ¼ 1241/lon [39]. Frontier molecular orbitals have been
studied by DFT calculations with Spartan10 program at the pa-
rameters of B3LYP and 6-31G** basis set.
toluene as solvent. The nitro compound, 2, was reduced to 4-(2,5-
di(thiophen-2-yl)-1H-pyrrol-1-yl)aniline by using Pd on activated
charcoal (Pd/C) and hydrazinium hydroxide (N2H5OH) (3) [36].
Meanwhile, N,N-di(2-ethylhexyl)perylene-3,4,9,10-tetracarboxylic
acid
dimide
[37],
N-(2-Ethylhexyl)-3,4,9,10-
Spectro-electrochemical measurements were carried out to
evaluate absorption spectra of these polymer films under applied
potential [40]. The spectro-electrochemical cell consists of Ag wire
(RE), Pt wire (CE) and ITO/glass as transparent working electrode
(WE) in a quartz cell. All measurements were carried out in the
0.1 M TBAPF6 as supporting electrolyte in acetonitrile. Colorimetry
measurements were performed by using an Analytic Jena Specord
S600 UVeVis spectrophotometer, which contains a chromameter
module (standard illuminator D65, field of with 10ꢁ observer) with
viewing geometry as recommended by “International Commission
on Illumination” (CIE) [41]. According to the CIE system, the color is
consist of three attributes; luminance (L), hue (a), and saturation
(b). Platinum cobalt DIN ISO 621, iodine DIN EN 1557, and Gardner
DIN ISO 6430 are the references of colorimetric measurement.
These parameters were applied for the neutral, oxidized and
reduced states of poly-SNS-PDI deposited onto ITO/glass surface.
perylenetetracarboxylic acid 3,4-anhydride-9,10-imide (5) were
synthesized and fully characterized according to the previously
reported study [37]. The final product, SNS-PDI, was obtained by
the condensation reaction between 3 and 5 with a yield of 81%.
Structures of all compounds were also fully identified by using
FT-IR and 1H NMR spectra. Significant changes were observed be-
tween the spectral properties of the initial compounds and SNS-PDI
product. The characteristic signals arising from the amine group
(eNH2) in 3 and anhydride carbonyl (OeC]O) in 5 disappeared in
FT-IR spectrum of SNS-PDI product. Furthermore, characteristic
strong imide (NeC]O) peaks at 1697e1656 cmꢀ1 appeared by the
formation of SNS-PDI after the completion of final condensation
reaction. In the 1H NMR spectrum of SNS-PDI, doubletedoublet
signals at 8.64e8.52 ppm are arising from the perylenediimide
protons as expected. The singlet signal observed at 6.84 ppm is
attributed to the protons on the pyrole unit of SNS moiety. Besides,
doublet signals at 8.10 and 7.62 ppm belonging to phenylene bridge
between SNS-donor and PDI-acceptor moieties are the strongest
evidence for the formation of the final product (see Supplementary
data Fig. S1e7).
3. Results and discussion
3.1. Synthesis and characterization
Potentiodynamic electrochemical polymerization of SNS-PDI
A novel electroactive SNS monomer containing PDI subunit was
synthesized in six steps (Scheme 2). The SNS containing nitro
subunit, 1-(4-nitrophenyl)-2,5-di(thiophen-2-yl)-1H-pyrrole (2)
[35], was synthesized via PaaleKnorr reaction with 1,4-Bis(2-
thienyl)butan-1,4-dione [34] and 1-amino-4-nitrobenzene in
presence of p-toluenesulfonic acid (PTSA) as catalyst by using
carried out repetitive cycling at a potential between 0 and 1.0 V
ox
exhibited a new redox couple at 0.49e0.59 V ðE
¼ 0:54VÞ. The
p;1=2
increased current density after each successive cycle clearly indi-
cated the formation and deposition of poly-SNS-PDI onto the sur-
face of the WE (Fig. 1). The polymer film onto ITO/glass surface was
dedoped by electrochemically in
a monomer-free electrolyte
Scheme 2. Synthetic route for the synthesis of SNS-PDI.

124
E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
ox
m;1=2
half wave potential ðE
Þ of 0.57 V observed as a result of
attached SNS unit on the PDI-acceptor core (Fig. 2b). This positive
shift of the potential proved that there is a slight interaction be-
tween PDI and SNS at the neutral state, though there is no conju-
gation between them. Upon the electrochemical polymerization,
polymer deposited onto WE was immersed into the monomer-free
electrolyte for CV measurement to determine the oxidation and the
reduction potentials. At the end of the electrochemical polymeri-
zation, the semi-reversible oxidation became reversible, broader
ox
and shifted to lower potential with half wave potential of ðE
Þ
p;1=2
0.45 V (Fig. 2c) due to extended conjugation on the backbone of
SNS-donor. Beside these, the reversible two step reduction became
broader and shifted positively to half wave potential of
red1
E
¼ ꢀ0:75V (Fig. 2c). These results indicated that a donor-
p;1=2
acceptor polymer working as both anodically and cathodically in a
narrow potential range was obtained. Also, by using oxidation and
reduction onsets, the electrochemical band gaps for SNS-PDI
monomer and corresponding polymer were calculated as 1.13 eV
and 0.72 eV, respectively. The dramatic decrease in the band gap of
the corresponding polymer results from enlargement of
conjugation of SNS-donor moiety.
pep
Fig. 1. Repeated potential scanning of SNS-PDI with a scan rate of 100 mV sꢀ1, vs. Ag
wire.
3.3. Optical properties
solution and washed with acetonitrile to remove the oligomeric by-
products and residues.
The optical properties of the SNS-PDI donor-acceptor system
were investigated by UVeVis absorption and fluorescence spec-
troscopy recorded with a concentration of 2 ꢂ 10ꢀ6 M solution in
CH2Cl2 (Fig. 3). In the UVeVis spectra of standard PDI, characteristic
triple bands of PDI at 455, 487 and 522 nm were observed (Fig. 3a)
[29]. After attaching SNS moiety, no change in PDI absorption bands
was observed, however a new band at about 328 nm arising from
SNS unit appeared (Fig. 3b). This result provides an evidence for the
lack of electronic interaction between SNS-donor and PDI-acceptor
in the ground state. In the fluorescence spectrum of PDI standard,
characteristic triple bands of PDI at 541, 580, 616 nm was observed
using excitation at 487 nm (Fig. 3a) [29]. However, when the
fluorescence spectra of SNS-PDI was examined, a remarkable
fluorescence quenching was noted almost in the same spectral
region of the PDI excited at 487 nm where emission of SNS moiety
is at minimum (Fig. 3b). This indicates that there is an intra-
molecular charge transfer from SNS-donor to PDI-acceptor at the
exited state [37,43,44]. Furthermore, the energy transfer process in
the molecule was studied by fluorescence spectroscopy of the SNS-
PDI. We investigated the fluorescence spectrum using excitation at
328 nm, since at this wavelength SNS has a strong absorption
where the emission of PDI is at a minimum. The fluorescence of
both SNS moiety and PDI in the molecule is quenched strongly,
indicating a very efficient deactivation of its excited state. We
believe that simultaneous energy and electron transfer processes
from SNS to PDI results in the fluorescence quenching of not only
the SNS moiety but also PDI in the molecule. Fluorescence
quenching experiments using PDI as fluorophore and SNS as
quencher were conducted. The results showed that as SNS-
standard concentration increases, the emission intensity of PDI
standard decreases (is quenched) when excited at both 328 nm and
487 nm which confirms that the quenching is mainly via electron
transfer mechanism (see Supplementary data Fig. S10e12). Overall,
photophysical studies exhibited that high efficiencies of both
electron and energy transfer from SNS-donor to PDI-acceptor
[44,45].
3.2. Electrochemical properties
The electrochemical properties of SNS-PDI monomers and cor-
responding polymers were investigated by cyclic voltammetry (CV)
(Fig. 2). During the cathodic scan regime, a cyclic voltammogram of
5 which is referred as PDI standard undergoes two reversible redox
red1
couples at ꢀ0.58 to ꢀ0.64 V ðE
¼ ꢀ0:61VÞ and ꢀ0.78 to ꢀ0.84 V
r;1=2
red2
ðE
¼ ꢀ0:81VÞ which are attributed to two-electron stepwise
r;1=2
reduction processes of PDI moiety (Fig. 2a) [42]. In comparison to
PDI standard, SNS-PDI has higher electron density on the PDI part
because of the electron donating effect of the SNS moiety to PDI.
Therefore, the reduction waves of SNS-PDI was observed at more
negative regime than that of PDI standard with half wave potentials
red1
red1
of E
¼ ꢀ0:72V and E
¼ ꢀ0:91V (Fig. 2b). In the anodic
m;1=2
m;1=2
regime, SNS-PDI exhibited a semi-reversible oxidation wave with
Upon comparison of the optical and electrochemical band gaps
(Table 1), these values are not in a good agreement. It shows that
the photoactive centers and electroactive centers behave inde-
pendent from each other.
Fig. 2. Cyclic voltamograms of (a) PDI standard (b) SNS-PDI (c) poly-SNS-PDI in
TBAPF6/CH2Cl2 with a scan rate of 100 mV sꢀ1, vs. Ag wire.

E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
125
Fig. 3. UVeVis absorption and fluorescence spectra of PDI standard (a), SNS-PDI (b), and comparison of fluorescence intensity (c) and fluorescence quenching (d) in dichloro-
methane solution.
In addition, frontier molecular orbitals have been studied by DFT
calculations with Spartan10 program at the parameters of B3LYP
and 6-31G** basis set. The charge distribution in the frontier mo-
lecular orbitals is shown in Fig. 4. These calculations support the
efficient charge separation between SNS-donor and PDI-acceptor
obtained data from electrochemical and optical measurements. As
expected, the HOMO of SNS-PDI is localized completely on the SNS-
donor part, while the LUMO completely exists on the PDI-acceptor
part. The charge separations at HOMO and LUMO energy levels
confirm that there is no interaction between SNS-donor and PDI-
acceptor at the neutral state.
positive potential to poly-SNS-PDI film, the valance-conduction
band between 400 and 600 nm (blue to green regime) show no
remarkable change between 0.0 and 1.0 V (Fig. 5). In the anodic
scan regime of SNS-PDI, the intensified broad band at about 900 nm
indicated the formation of polarons and bipolarons on SNS moiety
of polymer backbone. As a result of applied positive potential of
0e1.0 V to the polymer, the red colored film (L: 34; a: 51; b: 46)
turned into khaki (L: 33; a: ꢀ19; b: ꢀ2) and then dark blue (L: 13; a:
19; b: ꢀ35), respectively.
On the other hand, mono-anion and di-anion radicals formed
on the carbonyl groups of the PDI moiety of the poly-SNS-PDI
structure in the negative regime. Upon applied potential be-
tween 0 and ꢀ0.9 V, new absorption bands attributed to mono-
anion radicalic form of poly-SNS-PDI intensified at 704, 802, and
960 nm (Fig. 6). Besides, the slight decrease in the intensity of
main band of neutral state at about 480 nm leads to color con-
version from red (L: 34; a: 51; b: 46) to violet (L: 24; a: 20; b:
ꢀ31).
3.4. Spectro-electrochemical properties
Optical behavior of poly-SNS-PDI film deposited onto ITO/glass
surface against to p- and n-doping processes were studied inten-
sively. The dominant red color of PDI part is used to determine the
color of neutral state of SNS-PDI and poly-SNS-PDI. Upon applied
Table 1
HOMO and LUMO energy levels, electrochemical ðEg0 Þ and optical band gaps (Eg) of SNS-PDI and poly-SNS-PDI.
Molecule
Reduction peak potentials (V) Oxidation peak potentials (V) HOMO (eV) LUMO (eV) Eg0 , electrochemical band gap (eV) Eg, optical band gap (eV)
PDI (C]O)
SNS (ring)
ox1
red1
SNS-PDI
ꢀ4.95
ꢀ3.82
1.13
2.32
E
E
¼ 0:70
¼ 0:43
E
E
E
E
¼ ꢀ0:76
m;a
m;c
ox1
m;c
red1
m;a
red2
p;c
red2
m;a
¼ ꢀ0:68
¼ ꢀ0:95
¼ ꢀ0:87
semi-reversible
ox
E
¼ 0:53
m;on
reversible
red
E
E
E
¼ ꢀ0:60
¼ ꢀ0:80
¼ ꢀ0:70
m;on
ox1
red
Poly (SNS-PDI)
ꢀ4.63
ꢀ3.91
0.72
2.20
E
E
¼ 0:50
¼ 0:40
p;a
p;c
ox1
p;c
red
p;a
reversible
reversible
ox
red
E
¼ 0:21
E
¼ ꢀ0:51
p;on
p;on

126
E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
Fig. 6. Spectro-electrochemical measurements and color changes of poly-SNS-PDI film
deposited onto ITO/glass surface with applied potential of 0V to ꢀ0.9 V.
Fig. 4. Molecular orbital diagrams of the a) HOMO and b) LUMO levels of the SNS-PDI.
During the second reduction process of poly-SNS-PDI, the bands
attributed to mono-anion form of polymer film disappeared, and
the new band intensified at 490, 520 and 575 nm upon applied
potential of ꢀ0.9 to ꢀ1.2 V (Fig. 7). According to this absorption
spectrum, violet colored film (L: 24; a: 20; b: ꢀ31) turned into
purple (L: 20; a: 30; b: ꢀ18).
Overall, poly-SNS-PDI exhibits both reversible oxidation and
reduction waves with two redox couples attributed to two-electron
stepwise reduction processes of PDI moiety. Considering these
properties, poly-SNS-PDI, as an electrochromic material, has fur-
nished multiple separate colors appeared as dianionic, anionic,
neutral, polaronic and bipolaronic species at range of
only ꢀ1.2e1.0
V
(Fig. 8). Such
a
narrow range multi-
electrochromism offers
applications.
a great advantage in various ECDs
Fig. 7. Spectro-electrochemical measurements and color changes of poly-SNS-PDI film
deposited onto ITO/glass surface with applied potential of ꢀ0.9 V to ꢀ1.2 V.
Fig. 5. Spectro-electrochemical measurements and color changes of poly-SNS-PDI film
deposited onto ITO/glass surface with applied potential of 0 Ve1.0 V.
Fig. 8. Color changes of poly-SNS-PDI film deposited onto ITO/glass surface with
applied potential of ꢀ1.2 V to 1.0 V.

E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
127
Fig. 9. Chronoabsorptometry experiments for poly-SNS-PDI deposited onto ITO with a switched potential of 0 Ve1.0 V.
Fig. 10. Chronoabsorptometry experiments for poly-SNS-PDI deposited onto ITO with a switched potential of 0 V to ꢀ1.2 V.
Additionally, double step chronoamperometry technique was
used to monitor the changes in the electro-optical responses of the
SNS-PDI polymer film during anodically and cathodically switch-
ing. Electrochromic parameters of the polymer film was analyzed
by observing the changes in the transmittance (increments or
decrements of the absorption band with respect to time) during
stepwise switching the potential between neutral, oxidized and
reduced states with a residence time of 5 s. In the anodic regime the
SNS type electrochromic polymers reported in the literature
[26,46e50].
4. Conclusion
Herein, we report the synthesis and characterization of a new
electroactive monomer and corresponding polymer consisting of
SNS-donor and PDI-acceptor moieties. The monomer SNS-PDI was
directly polymerized by electrochemical means onto transparent
ITO/glass surface to give electrochromic polymer film. Because of
the efficient intramolecular electron transfer from SNS-donor to
PDI-acceptor at the excited state, a remarkable fluorescence
quenching of the perylene core was observed. Frontier molecular
orbitals have been studied by DFT calculations and the charge
distributions at HOMO and LUMO confirm the absence of
communication between SNS-donor and PDI-acceptor at the
neutral state. In addition, electrochromic properties of the polymer
films were investigated by the spectro-electrochemical measure-
ments. Poly-SNS-PDI exhibited an ambipolar multi-electrochromic
behavior including purple, violet-red-khaki-blue colors in both
anodic and cathodic regime in a narrow range of ꢀ1.2e1.0 V.
Furthermore, electrochemical and electrochromic results such as
reversible redox behavior both at anodic and cathodic regime, low
response time, high resistance to over oxidation, low driving po-
tential and high coloration efficiency point out that poly-SNS-PDI
would be promising material for the construction and/or the
development of ECDs and optical displays.
change in maximum percentage transmittance (DT%) of poly-SNS-
PDI between the neutral (0 V) and oxidized states (1.0 V) were
found 48% (Fig. 9). Besides, the oxidation and reduction response
times, which is the time required to change a color between a
“bleached” state and a “colored state”, or between two colored
states, were measured as 0.9 and 0.4 s for poly-SNS-PDI. Optical
activities of the poly-SNS-PDI film were retained by 92% even after
5000 cycles of operation (Fig. 9).
However, in the cathodic regime, the change in maximum per-
centage transmittance (DT%) of poly-SNS-PDI between the neutral
(0 V) and reduced states (ꢀ1.2 V) were found 34% (Fig. 10). The
reduction and oxidation response times were measured as 1.65 and
4.10 s for poly-SNS-PDI. Optical activities of the poly-SNS-PDI film
were retained by 46% after 5000 cycles of operation (Fig. 10).
The coloration efficiency (CE) is one of the most important is-
sues for the electrochromic application. CE was calculated by using
CE ¼
D
OD/Qd and
D
OD ¼ log(Tcolored/Tbleached), where Qd is the
injected/ejected charge between neutral and oxidized states, Tcol-
ored and Tbleached are the transmittance in the oxidized-neutral and/
or reduced-neutral states, respectively. In the anodic regime, upon
switching potential (deposited onto ITO glass surface with an active
area of 1 cm2) between 0 V and 1.0 V, CE of poly-SNS-PDI was
measured as 254 cm2 Cꢀ1 by chronoamperometry. On the other
hand, CE was measured as 112 cm2, with a switched potential be-
tween 0 V and ꢀ1.2 V. In consequence, the coloration efficiency of
poly-SNS-PDI in the anodic regime is one of the highest values for
Acknowledgment
We gratefully acknowledge the supports from Çanakkale
Onsekiz Mart University Grants Commission (Project Number:
2010/99).

128
E. Sefer et al. / Dyes and Pigments 113 (2015) 121e128
[26] Koyuncu FB, Sefer E, Koyuncu S, Ozdemir E. The new branched multi-
Appendix A. Supplementary data
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