Novel viologen derivatives for electrochromic ion gels showing a green-colored state with improved stability

Article abstract of DOI:10.1016/j.orgel.2017.10.001

We successfully synthesized a novel viologen derivative (1,1′-bis(3-fluoro-4-(trifluoromethyl)phenyl)-4,4′-bipyridinium bis(trifluoromethylsulfonyl)imide, TFMFPhV(TFSI)₂) exhibiting a green-colored state. We selected cyanophenyl viologen (CNPhV²⁺), a conventional electrochromic (EC) chromophore with a green color indication, to compare EC performance. Ion gels consisting of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-co-HFP) and 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) were employed as a solid-state electrolyte for EC devices (ECDs). In comparison to CNPhV²⁺-containing devices, the ECDs with TFMFPhV²⁺ showed higher transmittance contrast, larger coloration efficiency, faster coloration and bleaching responses, and better coloration/bleaching operational stability. Cyclic voltammetry revealed that the more stable redox behavior of TFMFPhV²⁺ is the origin of the outstanding ECD performance.

Full text of DOI:10.1016/j.orgel.2017.10.001

Accepted Manuscript
Novel viologen derivatives for electrochromic ion gels showing a green-colored state
with improved stability
Hwan Oh, Dong Gyu Seo, Tae Yong Yun, Seong Been Lee, Hong Chul Moon
PII:
S1566-1199(17)30491-3
10.1016/j.orgel.2017.10.001
ORGELE 4334
DOI:
Reference:
To appear in: Organic Electronics
Received Date: 5 September 2017
Revised Date: 27 September 2017
Accepted Date: 2 October 2017
Please cite this article as: H. Oh, D.G. Seo, T.Y. Yun, S.B. Lee, H.C. Moon, Novel viologen derivatives
for electrochromic ion gels showing a green-colored state with improved stability, Organic Electronics
(2017), doi: 10.1016/j.orgel.2017.10.001.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to
our customers we are providing this early version of the manuscript. The manuscript will undergo
copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please
note that during the production process errors may be discovered which could affect the content, and all
legal disclaimers that apply to the journal pertain.

ACCEPTED MANUSCRIPT
“Graphical Abstract”

ACCEPTED MANUSCRIPT
Novel Viologen Derivatives for Electrochromic Ion Gels Showing a
Green-Colored State with Improved Stability
Hwan Oh, Dong Gyu Seo, Tae Yong Yun, Seong Been Lee, Hong Chul Moon*
Department of Chemical Engineering, University of Seoul, Seoul 02504, Republic of Korea
* Corresponding authors. E-mail: hcmoon@uos.ac.kr (H.C.M)
1

ACCEPTED MANUSCRIPT
Abstract
We successfully synthesized
(trifluoromethyl)phenyl)-4,4’-bipyridinium
a
novel viologen derivative (1,1’-bis(3-fluoro-4-
bis(trifluoromethylsulfonyl)imide,
(TFMFPhV)(TFSI)2 exhibiting a green-colored state. We selected cyanophenyl viologen
(CNPhV2+), a conventional electrochromic (EC) chromophore with a green color indication,
to compare EC performance. Ion gels consisting of poly(vinylidene fluoride-co-
hexafluoropropylene)
(PVDF-co-HFP)
and
1-ethyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) were employed as a solid-state electrolyte
for EC devices (ECDs). In comparison to CNPhV2+-containing devices, the ECDs with
TFMFPhV2+ showed higher transmittance contrast, larger coloration efficiency, faster
coloration and bleaching responses, and better coloration/bleaching operational stability.
Cyclic voltammetry revealed that the more stable redox behavior of TFMFPhV2+ is the origin
of the outstanding ECD performance.
Keywords
Electrochromism; Ion Gel; Viologen; Zincke Reaction; Electrochemical Display
2

ACCEPTED MANUSCRIPT
1. Introduction
Electrochromism (EC) corresponds to reversible changes in transmittance and color by
redox reactions when appropriate electrical stimuli are applied across electrochemical cells
[1–9]. In addition to the modulation of optical properties, EC devices (ECDs) exhibit
characteristic low voltage operation and low power consumption. Thus, ECDs have been
employed in diverse applications such as smart windows for cars or buildings, anti-glare car
rear-view mirrors, protective eyewear, and information displays [10,11]. There are a number
of chemical EC-active chromophores [6–9]. In general, ECDs based on conducting polymers
or metal oxides are composed of multiple layers, including ion conductive electrolytes and
ion storage layers, in addition to the EC layer. In contrast, small organic materials can provide
a much simpler device configuration (namely, an EC layer between two electrodes) because
both colored and bleached species are dissolved in the electrolyte layer.
One representative organic EC material is 1,1’-disubstituted-4,4’-bipyridinium salt
(viologen), in which EC properties can be tuned by selecting various substituents. For
example, when the substituents are alkyl groups, bluish colored states are induced [8,12].
More abundant colors can be obtained with functionalized phenyl substituents, although the
synthetic processes, including the Zincke reaction, are relatively more complex. For example,
the radical cation of the 1,1’-bis(4-cyanophenyl)-4,4’-bipyridinium (CN-PhV2+) is a typical
EC chromophore with a green colored state [13–15]. However, CN-PhV2+ could form a dimer
in hydrophilic electrolytes due to strong π-π stacking or spin pairing [16]. The dimer
exhibited a quasi-reversible characteristic, which leads to an aging process [17-20]. This
process impacts device operational stability. Recently, Kao et al. demonstrated greenish
ECDs with improved device coloration/bleaching stability based on phenyl viologen (PV)
and vinyl benzyl viologen (VBV), in which the VBV moieties were thermally cured with
MMA to prevent dimerization [21]. However, purity of the greenish colored state was not
high according to the CIELAB color coordinate of L*= 40.9, a* = –9.7, b* = –19.0. Therefore,
the development of a new EC chromophore is essential to realizing pure and stable greenish
ECD pixels for display applications.
3

ACCEPTED MANUSCRIPT
In this work, a novel viologen derivative, 1,1’-bis(3-fluoro-4-(trifluoromethyl)phenyl)-
4,4’-bipyridinium(TFMFPhV2+), with a greenish colored state was successfully synthesized
via the Zincke reaction, and was employed in ECDs based on ion gels consisting of
copolymers (poly(vinylidene fluoride-co-hexafluoropropylene), PVDF-co-HFP) and ionic
liquids (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMI][TFSI]). To
verify device performance, a TFMFPhV2+-containing ECD was compared with one including
CN-PhV2+. For both devices, the change in color to green commenced at similar applied
voltages: –0.13 V (CNPhV2+) and –0.20 V (TFMFPhV2+). However, when we evaluated color
purity based on the CIELAB coordinates, a more negative a* value (namely, closer to the
green component) was obtained from the ECD including TFMFPhV2+ (L*= 51.5, a*= –34.1,
b*= 29.8) in comparison to the CNPhV2+-containing device (L*= 54.7, a*= –22.8, b*= 18.8).
With respect to device dynamics, much faster coloration and bleaching responses were
observed in TFMFPhV2+-containing ECDs: tc ~22 s for coloration at –0.35 V, tb ~32 s and
~10 s for bleaching under open-circuit and short-circuit conditions, respectively. In addition
to slower responses, the incomplete recovery from the colored state to the original bleached
state was detected from the ECD with CNPhV2+ due to poor redox reversibility of the EC
chromophore. This feature significantly affects coloration/bleaching cycling behaviors. The
CNPhV2+-based device rapidly deteriorated. For example, ~72% of the initial ∆T was lost
after 1 h working. Although a continuous 24 h operation cut transmittance contrast (∆T) in
half, colored and bleached states were clearly distinguishable for TFMFPhV2+-containing
ECDs. Overall, TFMFPhV2+ has high potential as a stable green EC component for display
applications.
4

ACCEPTED MANUSCRIPT
2. Experimental
2.1 Materials
Scheme 1. Synthetic routes of CNPhV(TFSI)2 and TFMFPhV(TFSI)2.
All materials were purchased from Sigma-Aldrich and used as received without further
purification unless otherwise noted. The synthetic route and molecular structure of EC
materials (CNPhV(TFSI)2 and TFMFPhV(TFSI)2) are given in Scheme 1. In brief, a mixture
of 4,4’-bipyridine (32 mmol, 1 eq) and 2,4-dinitrochlorobenzene (128 mmol, 4 eq) dissolved
in dry acetonitrile (80 mL) was refluxed for 72 h, and the resulting yellowish solution was
cooled to room temperature and filtered. Bright yellow precipitates were obtained, and
washed with anhydrous acetonitrile. The crude products were recrystallized from DI-
water/acetone and dried in vacuum for 24 h, producing yellow-green products (1,1’-bis(2,4-
dinitrophenyl)-4,4’-bipyridinium dichloride, DNPhVCl2). The DNPhVCl2 (1.78 mmol, 1eq)
was dissolved in 50% aqueous ethanol (40 mL) and an ethanol solution (10 mL) of 4-
aminobenzonitrile (10.68 mmol, 6eq) was added dropwise. After refluxing for 72 h, the
solution was cooled to room temperature. The reddish solution was evaporated by a rotary
5

ACCEPTED MANUSCRIPT
evaporator to remove the excess ethanol. The additional DI water (200 mL) was introduced
and stirred for 1 h at room temperature. The solution was filtered and the filtrate was
evaporated, producing 1,1’-bis(2,4-cyanophenyl)-4,4’-bipyridinium dichloride, CNPhVCl2.
For an anion exchange, a solution of excess lithium bis(trifluoromethanesulfonyl)imide
[Li][TFSI] in DI water reacted with the aqueous CNPhVCl2 solution for 20 min at room
temperature. The precipitated CNPhV(TFSI)2 was collected and dried in vacuum for 24 h. An
ionic liquid (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMI][TFSI])
was synthesized by an anion exchange reaction between 1-ethyl-3-methylimidazolium
chloride [EMI][Cl] and an excess amount of [Li][TFSI] in DI water [22].
2.2 Preparation of EC gels and ECDs
The EC ion gels and ECDs were prepared in ambient air. First, all components of the gel,
including redox active materials [CNPhV(TFSI)2 or TFMFPhV(TFSI)2 (cathodic species) +
dmFc
(anodic
species)],
copolymers
(poly(vinylidenefluoride-co-
hexafluoropropylene), PVDF-co-HFP), and room temperature ionic liquids (1-ethyl-3-
methylimidazolium bis(trifluoromethylsulfonyl)imide, [EMI][TFSI]) at a pre-determined
o
weight ratio of 2 or 3:4:36 were fully dissolved in acetone at 50 C. The equimolar cathodic
and anodic species were mixed. The prepared homogeneous solution was cast onto a slide
glass and dried in ambient air. The residual acetone was then fully removed in vacuum. The
EC gel was placed on ITO-coated glass (sheet resistance: 10 Ω/sq, Asahi Glass Co.) via a
“cut-and-stick” method [23,24]. The fabrication of ECDs was completed by placing another
ITO-coated glass on the gel, which was firmly fixed using 88-µm-thick, double-sided tape.
Fig. S1 in the Supporting Information showed the whole fabrication process by the “cut-and-
stick” strategy.
2.3 Device characterization
The cyclic voltammograms were recorded on a potentiostat (Wave Driver 10, Pine
6

ACCEPTED MANUSCRIPT
Instrument) at a sweep rate of 50 mV/s, where a platinum disk, Ag wire, and ITO-coated
glass were employed as the working, reference, and counter electrode, respectively. The
redox potentials of CNPhV2+ and TFMFPhV2+ were calculated according to the redox
potential of an internal standard, dmFc+/dmFc. The variation of the UV-vis absorption spectra
of the ECDs were measured by a UV-vis spectrometer (V-730, Jasco) from 400 to 850 nm at
a scan speed of 400 nm/min. The applied DC voltage was supplied by a Sourcemeter
(Keithley 2400, Tektronix). Transient current and transmittance profiles were recorded by a
combination of the UV-vis spectrometer and potentiostat. CIELAB color coordinates of
ECDs in colored and bleached states were estimated using Spectra Magic NX software (CM-
S100w, Konica Minolta). The L* represents the lightness of the color, and a* and b*
correspond to the positions of the color; green (–) to red (+) and blue (–) to yellow (+),
respectively.
3. Results and discussion
Fig.1a depicts a schematic diagram of ECDs and chemical structures of components in EC
gels. Because both EC chromophores (cathodic species) and dimethyl ferrocene (anodic
species) were dissolved in the gel (electrolyte), the ECD can be simply fabricated by inserting
an EC gel between two ITO-coated glasses. The prepared ion gels were based on P(VDF-co-
HFP) and [EMI][TFSI] at a weight ratio of 1:9 because the resulting gel electrolyte exhibited
high ionic conductivity (~6.7 mS/cm) and good mechanical moduli (>104 pa) at room
temperature [25]. Fig. 1b displays the change in UV-vis spectra of the ECDs including
CNPhV2+ and two representative photographs of the device in bleached and colored states.
No absorption peaks were observed under –0.13 V except a peak at ~450 nm arising from the
dmFc in the gel. Before coloration occurred, the device was slightly yellowish in the bleached
state due to the dmFc. The dmFc served as an anodic species, such as ferrocene [26],
hydroquinone [27,28], and potassium ferrocyanide [29], which is essentially required for low-
voltage electrochemical devices. As the applied voltage increased, the device absorbed a
7

ACCEPTED MANUSCRIPT
broad range of wavelengths and showed characteristic peaks at ~596 and 655 nm. The
corresponding device indicated a green colored state (see Fig. 1b). For example, the CIELAB
coordinates (L*, a*, b*) at –0.23 V were (54.7, –22.8, 18.8). While the yellowish bleached
state was the same for the TFMFPhV2+-containing ECD (Fig. 1c), the coloration to green
commenced at a slightly higher voltage of –0.20 V than the ECD CNPhV2+. However, when
we estimated the color coordinates of the induced green, the a* remarkably shifted to a
negative value [i.e. (L*, a*, b*) ~ (51.5, –34.1, 29.8)]. This implies that a purer green color
was realized using the synthesized TFMFPhV2+. To determine the operation type of the
device, we disassembled the ECD including TFMFPhV2+ after coloration. As a result, we
could observe green-colored gel without any residual solids on the electrodes (see Fig. S2 in
the Supporting Information). Based on the bleached (TFMFPhV2+) and colored species
(TFMFPhV+●) dissolved in the gel, we conclude that the ECDs including TFMFPhV2+
correspond to the Type I ECD.
Fig. 1. (a) ECD configuration (left) and molecular structures of components in the EC gels
(right). Dependence of UV/vis spectra on the applied voltages and two representative
photographs of the bleached and colored states for ECDs based on (b) CNPhV2+ and (c)
TFMFPhV2+.
8

ACCEPTED MANUSCRIPT
Fig. 2. Transient transmittance profiles of ECDs containing (a) CNPhV2+ at 596 nm and –
0.23 V and (b) TFMFPhV2+ at 596 nm and –0.35 V, respectively.
To understand device dynamics, we recorded transient transmittance profiles at 596 nm
that corresponds to the wavelength for one of characteristic peaks (Fig. 2a and 2b). When –
0.23 V was applied, the transmittance of the ECD containing CNPhV2+ decreased gradually.
The coloration time, defined as the time interval to reach 90% (∆t90%) of the total
transmittance change, was ~74 s. On the other hand, the bleaching times were measured as
~398 s and ~122 s at open- and short-circuit conditions, respectively. The three-times faster
transmittance recovery under shorting was quite predictable. Under the open-circuit condition,
a pathway toward the non-colored state (namely, CNPhV2+), i.e., chemical bleaching by a
9

ACCEPTED MANUSCRIPT
reaction between CNPhV+● and dmFc+ in bulk, is the only one available. When the circuit is
shorted, a relatively rapid direct re-oxidation of CNPhV+● (or dmFc+) simultaneously occurs
near the electrode. As a result, faster bleaching behavior was achieved under the short-circuit
condition, which is in agreement with the behaviors of previously reported gel-based Type I
ECDs [25,26]. In contrast, the ECD including TFMFPhV2+ showed faster response times: ∆tc
~22 s at –0.35 V for coloration and ∆tb ~10 s (short-circuit condition) and ~32 s (open-circuit
condition) for bleaching. In addition, good reversibility of coloration/bleaching cycles (see
Fig. 2b) was also observed. Specifically, the transmittance level of the bleached state was
nearly recovered by either open- or short-circuit conditions. These high transmittance
changes (∆T ~73%) can be favorably compared to other green-colored ECDs based on
viologens. Recently, Chang et al. reported that the solid-state ECDs composed of heptyl-
viologen, phenyl-viologen, and UV-cured electrolyte did not exhibit remarkable performance
degradation after 3000 switchings, but the initial ∆T values at 610 nm and 438 nm were
smaller than reported here: ~55.8% and ~48.9%, respectively [30]. Li et al. fabricated ECDs
based on 1-(9-hexyl-9H-carbazole)-1’-(propylphosphonic acid)-4,4’-bipyridinium dichloride
and 4-(diphenylamino)phenyl)methylphosphonic acid) exhibiting high stability, but those
also gave relatively lower ∆T (~63% at 670 nm) [31].
The coloration efficiency (η), which is defined by the change in optical density (∆OD) per
injected charge density (Q), can also be extracted from Fig. 3. Although the coloration
voltage was slightly higher, TFMFPhV2+ demanded a smaller amount of charge for coloration
of the specific area. By the linear fit on Fig. 3a and 3b, the η values for CNPhV2+ and
TFMFPhV2+ were determined as ~73.92 cm2/C at –0.23 V and ~79.39 cm2/C at –0.35 V,
respectively, which lie on the η range of analog viologen systems reported by other groups.
For example, Kavanagh et al. reported a relatively lower η (~10.7 cm2/C at 610 nm) of solid-
state ECDs based on photo-polymerized gel networks containing viologen-based ionic liquids
[32]. The UV-cured EC gel including ferrocene/nonyl viologen (Fc/NV(BF4)2) also provided
a lower η of ~36.2 cm2/C at 605 nm [33]. The ECDs composed of the methyl viologen (MV2+)
and graphene quantum dot (GQD) in a poly(vinyl alcohol) (PVA) matrix showed an η of 65
10

ACCEPTED MANUSCRIPT
cm2/C [34]. In contrast, two asymmetric viologens (Ethyl/CNPh- and benzyl/CNPh-viologen)
exhibited higher η values: 118 cm2/C and 180 cm2/C under application of –0.80 V,
respectively, although overall coloration potentials were larger than ours [35].
Fig. 3. Charge density dependence of the change in optical density for ECDs containing (a)
CNPhV2+ and (b) TFMFPhV2+, where the coloration efficiency (η) was extracted from the
slope of the linear zone.
11

ACCEPTED MANUSCRIPT
Fig. 4. The normalized transmittance variation of ECDs containing CNPhV2+ (black) and
TFMFPhV2+ (red) as a function of time.
One of the required features for ECDs is to minimize drops in device performance even
after continuous coloration and bleaching cycles. We plotted the variation of normalized
transmittance (∆T) over time (Fig. 4). For the device with CNPhV2+, a dramatic reduction
(~72%) from the initial value (∆To) was observed at an early stage (~1 hour), followed by
further degradation up to ∆T of 0.06. Alternatively, only a ~14% decrease of ∆To occurred
from the TFMFPhV2+-containing ECD. Although the ∆To level was halved, the distinct EC
transition between colored and bleached states was shown even after 24 h operation.
To reveal the origin of the difference in device stability, cyclic voltammograms (CVs) of
ECDs containing either CNPhV2+ or TFMFPhV2+ were obtained (Fig. 5a and b). Herein, the
dmFc functioned as the internal standard material as well as the anodic species. Thus, the
redox potentials of the EC materials were calculated on the basis of that of the dmFc+/dmFc.
The redox peaks at –0.23
V
for the CNPhV2+/CNPhV+● –0.35
V
for
TFMFPhV2+/TFMFPhV+● were determined by taking the midpoint potentials, which are
consistent with the coloration voltage. However, the CNPhV2+ did not clearly show the
anodic peak, by which the corresponding cathodic peak abruptly decreased as the voltage
sweep proceeded (Fig. 5a). This supports the irreversible bleaching behavior (see Fig. 2a) and
poor operational stability (Fig. 4) of the resulting device. On the other hand, quite symmetric
12

ACCEPTED MANUSCRIPT
anodic/cathodic peaks were detected with TFMFPhV2+. As a result, a smaller decrease in both
peaks was induced, although the cathodic peak was relatively more depressed. This result
indicates that the electrochemical stability of EC chromophores is intimately related to ECD
performance.
Fig. 5. Cyclic voltammograms (CVs) of EC gels containing (a) CNPhV2+ and (b)
TFMFPhV2+ during 100 continuous voltage sweeps at a rate of 50 mV/s, in which a platinum
disk, Ag wire, and ITO-coated glass were utilized as the working, reference, and counter
electrodes, respectively.
13

ACCEPTED MANUSCRIPT
4. Conclusion
We successfully developed a new EC material (TFMFPhV2+) showing green-colored states.
For comparative purposes, a typical EC chromophore exhibiting green color, CNPhV2+, was
chosen. Both devices based on the CNPhV2+ and TFMFPhV2+ exhibited a low-voltage
operation characteristic; coloration occurred at –0.13 V and –0.20 V, respectively. Compared
to the ECDs containing CNPhV2+, the ECDs with TFMFPhV2+ showed higher color purity,
faster response times, higher coloration efficiency, and improved operational stability. All
these features were attributed to the better electrochemical stability of the TFMFPhV2+.
Overall, the results indicate the TFMFPhV2+ can be a promising EC candidate for ion gel-
based electrochemical displays.
Acknowledgements
This work was supported by the National Research Foundation of Korea (NRF) grant funded
by the Korea government (MSIT) (NRF-2016R1C1B2006296). This research was supported
by X-mind Corps program of National Research Foundation of Korea (NRF) funded by the
Ministry of Science, ICT (NRF-2017H1D8A1030582).
References
[1] J.R. Platt, Electrochromism, a Possible Change of Color Producible in Dyes by an Electric
Field, J. Chem. Phys. 34 (1961) 862
[2] P.M.S Monk, The Viologens: Physicochmical Properties, Synthesis, and Applications of
the Salts of 4,4’-Bipyridine, J. Wiley & Sons, Chichester, U. K. 1998.
[3] P.M.S. Monk, R.J. Mortimer, D.R. Rosseinsky, Electrochromism: Fundamentals and
Applications, VCH, Weinhim, 1995.
[4] N.M. Rowley, R.J. Mortimer, New electrochromic materials. Science progress. 85 (2002)
243-262.
14

ACCEPTED MANUSCRIPT
[5] H.N. Ashtiani, A. Bahari, S. Ghasemi, A dual electrochromic film based on
nanocomposite of aniline and o-toluidine copolymer with oxide nanoparticles. Org. Electron.
37 (2016) 213-221.
[6] P.M.S. Monk, R.J. Mortimer, D.R. Rosseinsky, Electrochromism and Electrochromic
Devices. Cambridge University Press: Cambridge, U. K. 2007.
[7] R.J. Mortimer, Electrochromic materials, Chem. Soc. Rev. 26 (1997) 147-156.
[8] R.J. Mortimer, Organic electrochromic materials, Electrochim. Acta 44 (1999) 2971-2981.
[9] R.J. Mortimer, A.L. Dyer, J.R. Reynolds, Electrochromic organic and polymeric materials
for display applications, Display 27 (2006) 2-18.
[10] D.R. Rosseinsky, R.J. Mortimer, Electrochromic systems and the prospects for devices,
Adv. Mater. 13 (2001) 783-793.
[11] C.G. Granqvist, Chrommogenic materials for transmittance control of large-area
windows, Crit. Rev. Solid State Mater. Sci. 16 (1990) 291-308.
[12] A. Yasuda, H. Mori, J. Mizuguchi, Blue Electrochromism in Viologen-
Cyclodextrin/Ferrocyanide System, Jpn. J. Appl. Phys. 26 (1987) 1352-1355.
[13] D.R. Rosseinsky, P.M.S. Monk, Electrochromic cyanophenylparaquat (CPQ: 1,1’-bis-
cyanophenyl-4,4’-bipyridinium) studied voltammetrically, spectroelectrochemically and by
ESR, Sol. Energy mater. Sol. Cells 25 (1992) 201-210.
[14] R.G. Compton, A.M. Waller, P.M.S. Monk, D.R. Rosseinsky, Electron paramagnetic
resonance spectroscopy of electrodeposited species from solutions of 1,1’-bis-(p-
cyanophenyl)-4,4’-bipyridilium (cyanophenyl prarauat, CPQ), J. Chem. Soc. Faraday Trans.
86 (1990) 2583-2586.
[15] P.Y. Chen, C.S. Chen, T.H. Yeh, Organic Multiviologen Electrochromic Cells for a Color
Electronic Display Application, J. Appl. Polym. Sci. 131 (2014) 40485
[16] P.M.S. Monk, N.M. Hodgkinson, S.A. Ramzan, Spin pairing (‘dimerisation’) of the
15

ACCEPTED MANUSCRIPT
viologen radical cation: kinetics and equilibria, Dyes Pigm 43 (1999) 207-217.
[17] P.M.S. Monk, The effect of ferrocyanide on the performance of heptyl viologen-based
electrochromic display devices. J. Electroanal. Chem. 432 (1997) 175-179.
[18] S.Y. Kao, Y. Kawahara, S. Nakatsuji, K.C. Ho, Achieving a large contrast, low driving
voltage, and high stability electrochromic device with a vilogen chromophore. J. Mater.
Chem. C 3 (2015) 3266-3272
[19] R. Sydam, M. Deepa, A.G. Joshi, A novel 1,1’-bis[4-(5.6-dimethyl-1H-benzimidazole-1-
yl)butyl]-4,4’-bipyridinium dibromide (viologen) for a high contrast electrochromic device,
Org. Electron. 14 (2013) 1027-1036.
[20] K. Kanazawa, Y. Komiya, K. Nakamura, N. Kobayashi, Red luminescence control of
Eu(Ⅲ) complexes by utilizing the multi-colored electrochromism of viologen derivatives,
Phys. Chem. Chem. Phys. 19 (2017) 16979-16988.
[21] S.Y. Kao, H.C. Lu, C.W. Kung, H.W. Chen, T.H. Chang, K.C. Ho, Thermally Cured
Dual Functional Viologen-Based All-in-One Electrochromic Devices with Panchromatic
Modulation, ACS Appl. Mater. Interfaces 8 (2016) 4175-4184.
[22] H.C. Moon, T.P. Lodge, C.D. Frisbie, Electrochemiluminescent displays based on ion
gels: correlation between device performance and choice of electrolyte, J. Mater. Chem. C 4
(2016) 8448-8453.
[23] K.H. Lee, M.S. Kang, S. Zhang, Y. Gu, T.P. Lodge, C.D. Frisbie, “Cut and Stick”
Rubbery Ion Gels as High Capacitance Gate Dielecrics, Adv. Mater. 24 (2012) 4457-4462.
[24] H.C. Moon, C.H. Kim, T.P. Lodge, C.D. Frisbie, Multicolored, Low-Power, Flexible
Electrochromic Devices Based on Ion Gels, ACS Appl. Mater. Interfaces 8 (2016) 6252-6260.
[25] H. Oh, D.G. Seo, T.Y. Yun, C.Y. Kim, H.C. Moon, Voltage-Tunable Multicolor, Sub- 1.5
V , Flexible Electrochormic Devices Based on Ion Gels. ACs Appl. Mater. Interfaces 9 (2017)
7658-7665.
[26] H.C. Moon, T.P. Lodge, C.D. Frisbie, Solution Processable, Electrochromic Ion Gels for
16

ACCEPTED MANUSCRIPT
Sub-1 V, Flexible Displays on Plastic, Chem. Mater. 27 (2015) 1420-1425.
[27] G. Chidichimo, M.D. Benedittis, J. Lanzo, B.C.D. Simone, D. Imbardelli, B. Gabriele, L.
Veltri, G. Salerno, Solid Thermoplastic Laminable Electrochormic Film, Chem. Mater. 19
(2007) 353-358.
[28] M. Rafiee, D. Nematollahi, Voltammetry of Electroinacitve Species Using
Quinone/Hydroquinone Redox: A Known Redox System Viewed in a New Perspective,
Electroanalysis, 19 (2007) 1382-1386.
[29] Y. Alesanco, A. Vinuales, J. Palenzuela, I. Odriozola, G. Cabanero, J. Rodriguez, R.T.
Zaera, Multicolor Electrochromics: Rainbow-Like Devices, ACS Appl. Mater. Interfaces 8
(2016) 14795-14801.
[30] T.H. Chang, H.C. Lu, M.H. Lee, S.Y. Kao, K.C. Ho, Multi-color electrochromic devices
based on phenyl and heptyl viologens immobilized with UV-cured polymer electrolyte, Sol.
Energy mater. Sol. Cells (2017) DOI: 10.1016/j.solmat.2017.05.004.
[31] M. Li, Y. Wei, J. Zheng, D. Zhu, C. Xu, Highly contrasted and stable electrochromic
device based on well-matched viologen and triphenylamine, Org. Electron. 15 (2014) 428-
434.
[32] A. Kavanagh, K.J. Fraser, R. Byrne, D. Diamond, An Electrochromic Ionic Liquid:
Design, Characterization, and Performance in a Solid-State Platform, ACS Appl. Mater.
Interfaces 5 (2013) 55-62.
[33] H.C. Lu, S.Y. Kao, H.F. Yu, T.H. Chang, C.W. Kung, K.C. Ho, Achieving Low-Energy
Driven Viologens-Based Electrochromic Devices Utilizing Polymeric Ionic Liquids, ACS
Appl. Mater. Interfaces 8 (2016) 30351-30361.
[34] E.H. Hwang, S.H. Seo, S.R. Bak, H.L. Lee, M.S. Min, H.Y. Lee, An Electrolyte-Free
Flexible Electrochromic Device Using Electrostatically Strong Graphene Quantum Dot-
Viologen Nanocomposites, Adv. Mater. 26 (2014) 5129-5136.
[35] Y. Alesanco, A. Vinuales, G. Cabanero, J. Rodriguez, R.T. Zaera, Colorless to Neutral
17

ACCEPTED MANUSCRIPT
Color Electrochromic Devices Based on Asymmetric Viologens, ACS Appl. Mater. Interfaces
8 (2016) 29619-29627.
18

ACCEPTED MANUSCRIPT
Highlights
· A novel electrochromic material is designed and synthesized via the Zincke reaction.
· The ion gel-based ECDs with very simple configuration are successfully demonstrated.
· The performance of ECD containing TFMFPhV2+ is compared to that with CNPhV2+.
· The TFMFPhV2+ shows better cyclic stability and higher color purity.