Green to highly transmissive switching multicolored electrochromes: Ferrocene pendant group effect on electrochromic properties

Article abstract of DOI:10.1016/j.reactfunctpolym.2010.11.024

Two new quinoxaline and ethylenedioxythiophene (EDOT) based polymers; poly(5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-(phenyll) -3-ferrocenylquinoxaline) (P1) and poly(5,8-bis(2,3-dihydrothieno[3,4-b][1,4] dioxin-5-yl)-2,3-di(naphthalen-2-yl) qui

Full text of DOI:10.1016/j.reactfunctpolym.2010.11.024

Reactive & Functional Polymers 71 (2011) 168–174
Contents lists available at ScienceDirect
Reactive & Functional Polymers
journal homepage: www.elsevier.com/locate/react
Green to highly transmissive switching multicolored electrochromes: Ferrocene
pendant group effect on electrochromic properties
a
a
a
a
a,b,c,
⇑
Sß erife Özdemir , Abidin Balan , Derya Baran , Özdemir Do g˘ an , Levent Toppare
a
Department of Chemistry, Middle East Technical University, 06531 Ankara, Turkey
Department of Biotechnology, Middle East Technical University, 06531 Ankara, Turkey
Department of Polymer Science and Technology, Middle East Technical University, 06531 Ankara, Turkey
b
c
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 August 2010
Received in revised form 8 November 2010
Accepted 20 November 2010
Available online 2 December 2010
Two new quinoxaline and ethylenedioxythiophene (EDOT) based polymers; poly(5,8-bis(2,3-dihydrothi-
eno[3,4-b][1,4]dioxin-5-yl)-2-(phenyll)-3-ferrocenylquinoxaline) (P1) and poly(5,8-bis(2,3-dihydrothie-
no[3,4-b][1,4]dioxin-5-yl)-2,3-di(naphthalen-2-yl) quinoxaline) (P2) were synthesized and
characte- rized in terms of their electrochemical and spectroelectrochemical properties. The polymers
were both p and n-type dopable. The polymers can be switched between green and transparent states
during p-doping/dedoping. They were compared with their previously reported analogues in order to
investigate ferrocene pendant group effect on electrochromic characteristics.
Keywords:
Electrochromism
Ferrocene
Ó 2010 Elsevier Ltd. All rights reserved.
Donor–acceptor
Substitution effect
1
. Introduction
The reversible and visible change in optical properties, i.e.
technologies, investigation and improvement of multicolored elec-
trochromes are crucial.
Metal functionalized conducting polymers attracted attention
of a great deal of scientists in recent years and different metals
such as Pt [12], Rh [13], Au [14] and Ru [15] were used to function-
alize conducting polymers. However, most of the interest focused
on introducing ferrocene units into conducting polymers [16]. Dis-
covery of ferrocene increased the popularity of organometallic
chemistry and even after 60 years it is still receiving a great deal
of interest. Incorporation of ferrocene into conjugated polymers
either on main chain or as pendant group leads different redox
behaviors due to its reversible and narrow electrochemical signal
which is affected by its electronic and steric environment [17].
Electron rich character of ferrocene, stability in both Fe(II) and
Fe(III) oxidation states and easy substitution on aromatics make
ferrocene a great candidate for functionalization of conducting
polymers [17]. In this context, recent studies showed that ferroce-
nyl (Fc) group bearing polymers posses a significant potential for
optoelectronic applications such as electrochromics and memory
devices [18]. Oligothienylferrocene complexes [16] were also re-
ported. Conducting polymers functionalized by ferrocene is
aroused since these type of polymers show the redox properties
of both groups [19]. These are useful in a range of applications
and studies such as sensors [20,21], electro active Langmuir/Blodg-
ett films [22], free-standing redox-active films [23]. Conducting
polymers containing ferrocene on main conjugation path of poly-
mer backbone were also synthesized [16,24].
transmittance or reflectance upon external bias is called as electro-
chromism [1,2]. Conjugated polymers as next generation semicon-
ductors are mostly employed in electrochromic devices because of
their fast switching times [3], high optical contrasts [4], process-
ability [5], and fine tuning in electronic and optical properties via
small structural alternations [6].
There are numerous applications for electrochromic materials
such as optical displays [7] and smart windows [8]. Altering colors
for different redox states determine the potential application areas.
Red, green, blue (RGB) are the three main colors for display tech-
nology since all other subtractive colors can be achieved by mixing
these three [9]. Among RGB colors, neutral state green polymers
with highly transmissive oxidized states were missing until benzo-
thiadiazole and quinoxaline based EDOT bearing polymers were
synthesized and characterized in terms of their electrochromic
properties [10]. This investigation opened the way of commercial-
ization for electrochromic display devices. However; in the context
of low cost and high performance display devices, the main
demand is becoming to achieve multi-colored redox achievable
states from a single polymer [11]. Towards the future display
⇑
Corresponding author at: Department of Chemistry, Middle East Technical
University, 06531 Ankara, Turkey. Tel.: +90 312 2103251; fax: +90 312 2103200.
E-mail address: toppare@metu.edu.tr (L. Toppare).
1
381-5148/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.reactfunctpolym.2010.11.024

Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
169
We report here the synthesis and electrochemical properties of
two newly designed donor–acceptor–donor type green electrochro-
mic polymers 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-
(101 MHz, CDCl3) d 152.8, 147.0, 135.4, 134.5, 133.9, 130.8,
130.3, 129.1, 128.9, 128.4, 126.2, 125.4, 125.0, 124.8.
(
phenyl)-3-ferrocenylquinoxaline (P1) and 5,8-bis(2,3-dihydrothie-
no[3,4-b][1,4]dioxin-5-yl)-2,3-di(naphthalen-2-yl)quinoxaline
P2). Both polymers are green in their neutral states and revealed
2
.4. Synthesis of 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-2-
(
phenyll)-3-ferrocenylquinoxaline (M1)
(
highlytransmissiveoxidizedstates. Effect ofpendant Fc unit onelec-
trochemical and spectral behavior of the resulting polymers by a
comparison between their Fc free counterparts were given in detail.
5
,8-Dibromo-2-phenyl-3-ferrocenylquinoxaline (240 mg, 0.438
mmol) and tributyl (2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-
stannane (1.393 g, 2.19 mmol) were dissolved in dry THF (100 mL).
The solution was purged with argon for 30 min. and PdCl
was added under argon atmosphere. The mixture was stirred at
00 °C under argon atmosphere for 18 h, cooled and concentrated
on the rotary evaporator. The residue was subjected to column
chromatography (silica gel, CHCl :hexane, 2:1) to afford a red solid
in 68.0% yield (198 mg, 0.295 mmol). H NMR (400 MHz, CDCl
.63 (d, 1H), 8.55 (d, 1H), 7.78–7.70 (m, 2H), 7.46 (dd, J = 8.0,
.0 Hz, 3H), 6.65 (s, 1H), 6.49 (s, 1H), 4.79–4.76 (m, 2H), 4.41 (dd,
J = 5.2, 2.4 Hz, 2H), 4.37 (dd, J = 5.2, 2.4 Hz, 2H), 4.34–4.32 (m, 2H),
2 3 2
(PPh )
2
. Experimental
1
2.1. General
3
1
All chemicals and reagents were obtained from commercial
3
) d
sources and used without further purification. THF was dried over
sodium and benzophenone. 2-Hydroxy-2-phenyl-1-ferrocenyleth-
anone (3) [25], 2-hydroxy-1,2-di(naphthalen-2-yl)ethanone
8
3
.31 (dd, J = 3.7 Hz, 2H), 4.27 (dd, J = 4.1 Hz, 2H), 3.95 (s, 5H). 13
) d 151,9, 150,1, 141.4, 141.3, 140.3, 140.2,
C
(9) [25], 1-ferrocenyl-2-phenylethanedione (4) and 1,2-di(naph-
4
thalen-2-yl)ethane-1,2-dione (10) [25], 4,7-Dibromo-2,1,3-
benzothiadiazole [26], 3,6-Dibromo-1,2-phenylenediamine [27],
5
NMR (101 MHz, CDCl
3
1
1
7
37.5, 136.9, 135.9, 133.3, 133.1, 129.6, 128.9, 128.6, 128.0, 127.8,
27.7, 127.6, 127.5, 127.0, 126.6, 126.2, 113.4, 103.1, 102.7, 82.3,
1.8, 70.0, 64.9, 64.3.
,8-dibro-mo-2-phenyl-3-ferrocenylquinoxaline and 5,8-dibro-
mo-2,3-di-(naphthalen-2-yl)quinoxaline [28], tributyl(2,3-dihy-
drothieno-[3,4-b][1,4]dioxin-5-yl)stannane [29] were synthesized
according to previously published procedures. 1H NMR and
13
C
2
2
.5. Synthesis of 5,8-bis(2,3-dihydrothieno[3,4-b][1,4]dioxin-5-yl)-
,3-di(naphthalen-2-yl)quinoxaline (M2)
NMR spectra were recorded on a Bruker Spectrospin Avance
DPX-400 Spectrometer with TMS as the internal standard and
3
CDCl as the solvent. All shifts were given in ppm. Electrochemical
5
,8-Dibromo-2,3-di(naphthalen-2-yl)quinoxaline (400 mg, 0.74
studies were performed in a three-electrode cell consisting of an
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 under ambient conditions using a Voltalab 50
potentiostat. HOMO–LUMO values were calculated taking the va-
lue of NHE as ꢀ4.75 eV vs vacuum. Cary 5000 UV–Vis spectropho-
tometer was used to perform the spectroelectrochemical studies of
polymers.
mmol) and tributyl (2,3-dihydrothieno[3,4-b][1,4]dioxin-5-
yl)stannane (2.35 g, 3,7 mmol) were dissolved in dry THF
130 mL). The solution was purged with argon for 30 min. and
PdCl (PPh was added under argon atmosphere. The mixture
was stirred at 100 °C under argon atmosphere for 18 h, cooled
(
2
3 2
)
and concentrated on the rotary evaporator. The residue was sub-
jected to column chromatography (silica gel, CHCl
to afford a red solid in 65.0% yield (318.48 mg, 0.48 mmol).
NMR (400 MHz, CDCl ) d 9.23–8.44 (m, 6H), 8.38–7.60 (m, 8H),
.59–7.39 (m, 2H), 6.51 (s, 2H), 4.35 (dd, J = 3.55, 4H), 4.25 (dd,
J = 3.78, 4H). C NMR (101 MHz, CDCl
40.6, 139.1, 137.4, 135.4, 134.3, 131.1, 129.01, 128.9, 125.9,
3
:hexane, 2:1)
1
H
3
2.2. Synthesis of 5,8-dibromo-2-phenyl-3-ferrocenylquinoxaline (11)
7
1
3
3
) d 148.9, 146.4, 141.4,
A solution of 3,6-dibromo-1,2-phenylenediamine (166 mg, 0.63
1
1
mmol) and 1-ferrocenyl-2-phenylethanedione (200 mg, 0.63
mmol) in EtOH (50 mL) was refluxed overnight with a catalytic
amount of p-toluene sulfonic acid (PTSA). The mixture was cooled
to 0 °C and concentrated on the rotary evaporator. The residue was
subjected to column chromatography (silica gel, hexane:EtOH,
25.1, 124.9, 124.3, 123.2, 112.1, 103.4, 65.0, 64.3.
3
. Results and discussions
1
(
7
2
1
1
0:1). Compound 11 was obtained as a purple solid in 73.0% yield
249 mg, 0.45 mmol). 1H NMR (400 MHz, CDCl
) d 7.79 (d, 1H),
.76 (d, 1H), 7.59–7.55 (m, 2H), 7.41–7.35 (m, 3H), 4.57–4.53 (m,
H), 4.28–4.25 (m, 2H), 3.91 (s, 5H). 13C NMR (101 MHz, CDCl
) d
56.3, 153.73, 139.7, 138.7, 138.3, 132.7, 131.8, 129.8, 129.3,
28.1, 123.8, 123.1, 96.1, 82.1, 71.6, 70.2, 70.2.
3
.1. Synthesis
3
The synthetic route to the monomers was outlined in Scheme 1.
-Hydroxy-2-phenyl-1-ferrocenylethanone (3) and 2-hydroxy-1,2-
3
2
di(naphthalen-2-yl)ethanone (9) were synthesized by benzoin
condensation of ferrocene carboxaldehyde (1) and b-naphtalde-
hyde (2, 8) [5]. Oxidation of 2-hydroxy-2-phenyl-1-ferrocenyleth-
2
.3. Synthesis of 5,8-dibromo-2,3-di(naphthalen-2-yl)quinoxaline
anone (3) by MnO
a red solid with sufficient yields [25]. Oxidation of 2-hydroxy-
,2-di(naphthalen-2-yl)ethanone (9) took place and 1,2-di(naph-
thalen-2-yl)ethane-1,2-dione (10) was afforded via refluxing in
HNO . Bromination of 1,3-benzothiadiazole yielded dibrominated
compound 6 in high yield [26]. Then the reduction of this com-
pound by NaBH as described in the literature [27] gave desired
dibromodiamine 7. Condensation of 7 with diketones in ethanol
afforded 5,8-dibromo-2-phenyl-3-ferrocenylquinoxaline (11) and
5,8-dibromo-2,3-di(naphthalen-2-yl)quinoxaline (12) [28]. The
Stille coupling of these compounds with tributyl(2,3-dihydrothie-
no[3,4-b][1,4]dioxin-5-yl)stannane [29] gave the desired mono-
mers M1 and M2 (Scheme 1).
2
gave 1-ferrocenyl-2-phenylethanedione (4) as
(12)
1
A
solution of 3,6-dibromo-1,2-phenylenediamine (86 mg,
0
.33 mmol) and 1,2-di(naphthalen-2-yl)ethane-1,2-dione (100
3
mg, 0.322 mmol) in EtOH (25 mL) was refluxed overnight with a
catalytic amount of p-toluene sulfonic acid (PTSA). The mixture
was cooled to 0 °C. The precipitate was isolated by filtration and
washed with EtOH several times then the residue was subjected
4
to column chromatography (silica gel, CHCl
3
:hexane, 1:1) to get
the product as a yellow solid in 67% yield (116 mg, 0.214 mmol).
1
H NMR (400 MHz, CDCl
3
) d 8.96–8.81 (m, 1H), 8.55–7.99 (m,
1
3
7
H), 7.95 (d, 2H), 7.92–7.65 (m, 4H), 7.56–7.46 (m, 2H). C NMR

1
70
Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
Scheme 1. Synthetic routes for M1 and M2.
3.2. Cyclic voltammetry
were used as the working electrode whereto polymer films pro-
duced electrochemically. Fig. 1 represents cyclic voltammetry
(CV) results for both M1 and M2 monomers and formation of cor-
responding polymers P1 and P2. In the first cycle of oxidative
electrochemical polymerization of M1, characteristic ferrocene
The potentiodynamic electropolymerizations for M1 and M2
were performed in 0.1 M tetrabutylammonium hexafluorophos-
phate (TBAPF in acetonitrile (ACN)/dichloromethane (DCM)
95:5, v:v) mixture. Indium tin oxide coated glass slides (ITO)
6
)
+
(
oxidation (Fc/Fc ) peak was recorded at 0.58 V. The monomer

Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
171
6
Fig. 1. Repeated potential scan electropolymerization of: (a) M1 and (b) M2 in 0.1 M TBAPF /ACN/DCM on ITO electrode.
oxidation was achieved at 0.8 V which accompanied with a
reversible redox couple resulting from the presence of oligomers
and polymer chains. During the first scan, reduction of Fc was
blanketed due to the reduction of preliminary chains (Fig. 1a).
Monomer oxidation potential for M2 was observed at 0.85 V
which was the lowest potential for monomer oxidation among
its analogues (Table 1).
doping/dedoping potentials were increased for P1. The trend was
also observed for p-type doping/dedoping potentials of P2 com-
pared to PDEFNQ. This can be attributed to the electroactive behav-
+
+
ior of the Fc unit where oxidation of Fc to Fc results in positively
charged pendant group on polymer backbone which makes elec-
tron extraction from the polymer more difficult compare to Fc free
analogues. Comparison between optical band gaps of all four poly-
mers showed that incorporation of Fc unit as a pendant group in-
creased the band gap of the polymer.
Resulting polymers were subjected to CV in order to examine
the n-type doping property of the polymers (Fig. 2). P1 and P2 re-
vealed both p- and n-doping property which were proved by well
defined reversible redox couples at ꢀ1.95 V/ꢀ1.30 V (Fig. 2a) and
at ꢀ2.05 V/ꢀ1.42 V (Fig. 2b) for P1 and P2, respectively. Although
almost all conjugated polymers have a tendency to be p doped,
only handful of them reveal ambipolar characteristics which have
numerous applications such as; light emitting diodes and ambipo-
lar transistors [30]. It is striking to notice that full cycles (p and n
doping) for P1 and P2 were recorded with consecutive cycles un-
der ambient conditions which indicates the stability of doped
states [31].
The cyclic voltammograms for both polymer films were re-
corded at different scan rates (between 100 and 300 mV/s) in
monomer free medium and the scan rate dependence of the anodic
and cathodic peak currents were observed (Fig. 3). This linear
dependence illustrates that the charge transfer process for well ad-
hered polymer films were non diffusion controlled [32].
Table 1 summarizes electrochemical behaviors of synthesized
polymers and their analogues without Fc. As seen, when Fc was re-
placed by one phenyl unit in PDPEQ (Scheme 2), both p-and n-type
3.3. Spectroelectrochemistry
Spectroelectrochemical properties of the polymers were inves-
tigated between ꢀ0.5 and 1.0 V in 0.1 M TBAPF /ACN electrolyte–
6
solvent couple and UV–Vis–NIR spectra were recorded upon
external bias. Electrochemically produced polymer films on ITO
were reduced to their neutral states at ꢀ0.5 V in order to remove
any trapped charge and dopant ion during electrochemical poly-
merization prior to spectroelectrochemical analysis. The spectral
responses of polymer films to stepwise oxidation were noted as
the potential was gradually increased. As seen in Fig. 4, P1 has
maximum absorption wavelengths in the visible region were cen-
tered at 447 and 703 nm whereas P2 revealed relatively red shifted
absorption maxima at 450 and 760 nm which were attributed to
ꢁ
low and high energy
p
–p
transitions. Optical band gaps (E ) for
g
P1 and P2 were calculated from the onsets of lower energy transi-
tions as 1.43 eV and 1.24 eV, respectively. Calculated E values sug-
g
gest that both polymers can be regarded as low band gap polymers
Table 1
Electrochemical and optical results for P1, P2 and their counterparts.
mon
op
Polymer (V)
P1
E
E
p-doping
E
p-dedoping
E
n-doping
E
n-dedoping
k
max
T%
Switching time (s)
E
(eV)
g
ox
0.58c
.98
1.0
0.35
ꢀ1.95
ꢀ1.30
447
703
700
1.3
1.68
1.43
0
40
22
1
1
1
1
448
35
29
77
1.2
0.7
2
PDPEQa
1.05
0.3
ꢀ0.02
0.42
ꢀ1.55
ꢀ1.70
ꢀ2.05
ꢀ1.10
ꢀ1.35
ꢀ1.42
732
800
1.01
1.3
PDEFNQb
0.72c
450
760
750
0.8
1.6
1.1
0.85
0.60
33
40
450
21
17
57
0.6
0.5
0.9
P2
0.85
0.35
760
800
1.24
a
b
c
Data were taken from Ref. [10b].
Data were taken from Ref. [33].
+
Fc/Fc oxidation potential was observed in the first cycle during CV.

1
72
Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
6
Fig. 2. Single scan voltammograms for P1 and P2 in monomer free, 0.1 M TBAPF /ACN solutions.
Fig. 3. Scan rate dependence of: (a) P1 and (b) P2 films at 100, 150, 200, 250, and 300 mV/s.
Scheme 2. Chemical structures of related polymers.
with strong absorption in the visible region tailing into near IR
NIR).
Upon stepwise oxidation of polymer films, the absorption in
was not the case for P2. This absorption also induced a
(
black colored intermediate state for P1 where almost all
visible light was harvested by the polymer film. Since polaronic
and bipolaronic states absorptions were not in the visible
region, both polymers ended up with highly transmissive oxi-
dized forms.
Spectroelectrochemical and colorimetry studies showed that
incorporation of Fc unit in polymer backbone resulted in multicol-
ored oxidation states whereas quinoxaline based polymers without
ferrocene switched only between green and highly transmissive
states (Fig. 5). Intermediate colored states appeared due to
the visible region diminished as the new bands were intensified
at around 1000 nm and 1700 nm. These lower energy transitions
indicate the formation of charge carriers such as polarons and
bipolarons. Although both polymers switched between green
and transmissive states as their two extreme states, partial
oxidation of P1 film resulted in different intermediate state col-
ors (Fig. 4). Difference between two homologue polymers is a
consequence of bridge-like absorption at 500 nm for P1 which

Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
173
Fig. 4. Spectroelectrochemistry of: (a) P1 and (b) P2 films on an ITO coated glass slide in monomer free, 0.1 M TBAPF
.0 V.
6
/ACN electrolyte–solvent couple between ꢀ0.5 V and
1
Fig. 5. Colors of P1 and P2 at their neutral (0.0 V) and different oxidized states.
Fig. 6. Percent transmittance changes as a function of time for: (a) P1 and (b) P2 at their maximum absorption wavelengths in visible and NIR regions.
contribution of orange and blue colors which are the characteristic
colors of Fc and Fc+ respectively. This was also proven by the
different spectral response of Fc containing polymers upon step-
wise oxidation compared to that of non-containing ones.
3.4. Kinetic studies
Kinetic studies were conducted in order to determine switching
times and percent transmittance changes (DT%) of the polymers

1
74
Sß . Özdemir et al. / Reactive & Functional Polymers 71 (2011) 168–174
between their neutral and oxidized states. The polymer films were
stepped between two states with 5 s time intervals. Due to multi-
(b) U. Bulut, F. Yilmaz, Y. Yagci, L. Toppare, React. Funct. Polym. 61 (2004) 63–
0.
3] (a) A. Kumar, D.M. Welsh, M.C. Morvant, F. Piroux, K.A. Abboud, J.R. Reynolds,
Chem. Mater. 10 (1998) 896–902;
7
[
color formation between its two extreme states,
DT% for P1 in the
visible region was only observable at 703 nm as 40%. However, in
the visible region at the maximum absorption wavelengths
(b) A. Balan, G. Gunbas, A. Durmus, L. Toppare, Chem. Mater. 20 (2008) 7510–
7
513.
4] (a) S. A Sapp, G.A. Sotzing, J.R. Reynolds, Chem. Mater. 10 (1998) 2101–2108;
b) S.J. Yoo, J.H. Cho, J.W. Lim, S.H. Park, J. Jang, Y.E. Sung, Electrochem.
[
[
(
450 nm and 760 nm), P2 film revealed 21% and 17% transmittance
(
changes between the neutral and oxidized states. In this manner
incorporation of Fc unit as pendant group increased the transpar-
ency of the oxidized states as in P1 and PDEFNQ compared to their
Fc free counterparts while resulting in a slower switching time
Commun. 12 (2010) 164–167.
5] (a) G. Sonmez, H.B. Sonmez, C.K.F. Shen, R.W. Jost, Y. Rubin, F. Wudl,
Macromolecules 38 (2005) 669–675;
(
b) D. Baran, A. Balan, S. Celebi, B.M. Esteban, H. Neugebauer, N.S. Sariciftci, L.
Toppare, Chem. Mater. 22 (2010) 2978–2987;
(
(
c) B.C. Kim, G. Spinks, C.O. Too, G.G. Wallace, Y.H. Bae, React. Funct. Polym. 44
2000) 31–40.
(
Table 1). In NIR region, P2 was repetitively switched between its
p-type doped/dedoped states and revealed 57% optical contrast
Fig. 6).
How fast the electrochromic materials change their colors is
[
6] (a) I. Schwendeman, R. Hickman, G. Sonmez, P. Schottland, K. Zong, D. Welsh,
J.R. Reynolds, Chem. Mater. 14 (2002) 3118–3122;
(
(
b) F.C. Krebs, Nat. Mater. 7 (2008) 766–767.
[
[
7] R.J. Mortimer, A.L. Dyer, J.R. Reynolds, Displays 27 (2006) 2–18.
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[9] G. Sonmez, Chem. Commun. (2005) 5251–5259.
also an important parameter as well as percent transmittance
changes at maximum absorption wavelengths for optical applica-
tions. Switching time is defined as the period required for the color
change of a material between its neutral and oxidized/reduced
states. Utilizing the kinetic studies of P1 and P2, switching times
were calculated for visible and NIR regions. P1, at its dominant
wavelength (703 nm), switched its color from green to transmis-
sive within 1.3 s which was outstanding since three colors were
detectable in that period. For P2, switching times were calculated
as 0.6 s, 0.5 s and 0.9 s at 450 nm, 760 nm and 1800 nm, respec-
tively. When pristine phenyl and naphthalene containing polymers
PDPEQ and P2 are compared in terms of their switching abilities, it
was seen that P2 has shorter switching times than that of PDPEQ.
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Structural designs for P1 and P2 were accomplished in order to
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