Thermotropic Liquid-Crystalline and Light-Emitting Properties of Bis(4-aalkoxyphenyl) Viologen Bis(triflimide) Salts

Article abstract of DOI:10.3390/molecules25102435

A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized by ¹H and ¹³C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both crystal-to-smectic A (SmA) transitions, T_ms, and SmA-to-isotropic transitions, T_is. Those with longer length of alkoxy chains had relatively low T_ms at which they formed the SmA phases that persisted up to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in the temperature range of 330-370 ^?C. Their light-emitting properties in methanol were also included.

Full text of DOI:10.3390/molecules25102435

molecules
Article
Thermotropic Liquid-Crystalline and Light-Emitting
Properties of Bis(4-aalkoxyphenyl) Viologen
Bis(triflimide) Salts
Pradip K. Bhowmik 1,
*
, Muhammed Kareem M. Al-Karawi 1, Shane T. Killarney 1,
Erenz J. Dizon 1, Anthony Chang 1 , Jongin Kim 1, Si L. Chen 1, Ronald Carlo G. Principe 1,
Andy Ho 1, Haesook Han 1, Hari D. Mandal 2, Raymond G. Cortez 2, Bryan Gutierrez 2,
Klarissa Mendez 2, Lewis Sharpnack 3, Deña M. Agra-Kooijman 4, Michael R. Fisch 5 and
Satyendra Kumar 6
1
Department of Chemistry and Biochemistry, University of Nevada Las Vegas, 4505 S. Maryland Parkway
Box 454003, Las Vegas, NV 89154-4003, USA; malkarawi@outlook.com (M.K.M.A.-K.);
shanekillarney126@gmail.com (S.T.K.); dizone2@gmail.com (E.J.D.); Changa14@unlv.nevada.edu (A.C.);
kimj80@unlv.nevada.edu (J.K.); chens19@unlv.nevada.edu (S.L.C.); princr1@unlv.nevada.edu (R.C.G.P.);
hoa3@unlv.nevada.edu (A.H.); hanh3@unlv.nevada.edu (H.H.)
2
Department of Biology and Chemistry, Texas A & M International University, 5201 University Blvd., Laredo,
TX 78041, USA; hmandal@tamiu.edu (H.D.M.); Raymond_cortez@dusty.tamiu.edu (R.G.C.);
bryangtz11@hotmail.com (B.G.); klarissa11@live.com (K.M.)
Department of Earth Science, 1006 Webb Hall, University of California, Santa Barbara, CA 93106, USA;
3
lsharpnack@geol.ucsb.edu
Advanced Materials and Liquid Crystal Institute, Kent State University, Kent, OH 44242, USA;
4
dagrako@kent.edu
5
College of Aeronautics and Engineering, Kent State University, Kent, OH 44242, USA; mfisch@kent.edu
Division of Research, University at Albany, Albany, NY 12222, USA; satyenkumar@albany.edu
6
*
Correspondence: pradip.bhowmik@unlv.edu; Tel.: +1-(702)-895-0885; +1-(702)-895-4072
ꢀꢁꢂꢀꢃꢄꢅꢆꢇ
Academic Editor: Roberta Cassano
Received: 28 April 2020; Accepted: 21 May 2020; Published: 23 May 2020
ꢀꢁꢂꢃꢄꢅꢆ
Abstract: A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different
lengths were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen
dichloride salts, which were in turn prepared from the reaction of Zincke salt with the corresponding
4-n-alkoxyanilines, with lithium triflimide in methanol. Their chemical structures were characterized
1
by H and 13C nuclear magnetic resonance spectra and elemental analysis. Their thermotropic
liquid-crystalline (LC) properties were examined by differential scanning calorimetry, polarizing
optical microscopy, and variable temperature X-ray diffraction. Salts with short length alkoxy
chains had crystal-to-liquid transitions. Salts of intermediate length alkoxy chains showed both
crystal-to-smectic A (SmA) transitions, Tms, and SmA-to-isotropic transitions, Tis. Those with longer
length of alkoxy chains had relatively low Tms at which they formed the SmA phases that persisted up
to the decomposition at high temperatures. As expected, all of them had excellent thermal stabilities in
the temperature range of 330–370 ◦C. Their light-emitting properties in methanol were also included.
Keywords: extended viologens; Zincke salt; metathesis reaction; ionic liquid crystals; thermotropic;
smectic phase A; differential scanning calorimetry; polarizing optical microscopy; X-ray diffraction;
thermogravimetric analysis
1. Introduction
Thermotropic ionic liquid crystals (ILCs) are an important class of materials that combine the
properties of both ionic liquids and liquid crystals. The liquid-crystalline (LC) phases offer many
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www.mdpi.com/journal/molecules

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advantages over the liquid phases. For example, ion conduction is significantly enhanced in smectic
A (SmA) and columnar phases as compared with the isotropic liquid phases. The unique properties
of ILCs make them suitable for many technological applications including display technology, solar
cells, ion conductors in batteries, and templates for the synthesis of nanomaterials [1–14]. They are
even considered as organized reaction media in which many organic reactions including Diels–Alder
reactions; intramolecular Diels–Alder reactions can be performed with highly regio- and chemoselective
reactions, with the additional advantage of being recycled [15–17]. They are usually composed of
varied suitably modified organic cations and organic and inorganic anions. Among the common cations
are quaternary ammonium, quaternary phosphonium, pyrrolidinium, piperidinium, guanidinium,
imidazolium, pyridinium pyrazolium, triazolium, among other cations and the common anions are
Br−, NO3−, BF4−, CF3SO3−,PF6−, ClO4−, N(SO2CF3)2−, OTs−, ReO4−, among other anions. These are
examples of monocations and monoanions employed for the synthesis of ILCs [
they can be versatile in their chemical architectures. They can be dicationic, tricationic, and multicationic
in their makeups [18 30]. For example, viologens are examples of dicationic salts that are symmetric
(alkyl groups similar) and exhibit LC phases (n = 6, 7, 8, 14–20) even at room temperature [31 33].
1–14]. Additionally,
–
–
Asymmetric (alkyl groups dissimilar) types with triflimides a◦s counterions exhibit smectic LC phases
◦
with a wide range of stability that range from as low as 0 C to as high as 146 C. Consequently,
they have increased range
salts [34]. In the further development of ILCs, there are several reports in the literature on extended
viologen salts I–VI), in which viologen moiety is elongated with the phenyl residue as shown in
Figure 1, and also display smectic LC phases [35–37].
s of stability of LC phases as compared with those for symmetric viologen
(
,
As a continuation of our research efforts on ILCs, herein, we describe the synthesis of a series of
extended viologen salts with bis(triflimide) (n = 1, 6, 8, 10, 12, 14, 16, 18, and 20), where n denotes
the carbon atoms in the alkoxy chain. We determine their chemical structures by 1H and 13C NMR
spectra, as well as elemental analysis, and the characterization of their thermotropic LC properties
by several experimental techniques including differential scanning calorimetry (DSC), polarizing
optical microscopy (POM), and variable temperature X-ray diffraction (VT-XRD) studies. Their
thermal stabilities by thermogravimetric analysis (TGA) are also included. The general structures
and designations for these synthesized extended viologen salts, and their synthetic routes are shown
in Scheme 1. The LC properties of these salts with these triflimide anions enable one to establish
the structure–property relationship of this important class of ILCs. Additionally, in contrast to other
anions, the reports of ILCs on triflimide anions are relatively less studied [24
the impetus for this study.
,31–34,38–40] which give

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Figure 1. Chemical structures of extended viologen salts that exhibit smectic A (SmA) phases.

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Scheme 1. Synthetic routes for the preparation of extended viologen bis(triflimide) salts (EVn).
Note that the compounds n = 10, 12, and 14 corresponding to structure IV were reported in [36].
2. Results and Discussion
In this study, a series of extended viologen bis(triflimide) salts (EVn) with variable alkoxy chains
were synthesized, characterized for their chemical structures, and further characterized for their
thermotropic LC properties using DSC, POM, and VT-XRD techniques. The thermal stabilities of the
salts were determined using TGA technique. Their light-emitting properties including their chloride
precursors in methanol were studied using UV-Vis and photoluminescence spectrometer.
2.1. Synthesis of Bis(4-n-alkoxyphenyl)-4,40-bipyridinium Bis(triflimide) Salts (EV1, EV6, EV8, EV10, EV12,
EV14, EV16, EV18, and EV20)
The 4-n-alkoxyanilines were prepared in accordance with the modified literature procedure [41].
The bis(4-alkoxyphenyl)-4,40-bipyridinium dichloride (EV1Cl, EV6Cl, EV8Cl, EV10Cl, EV12Cl, EV14Cl,
EV16Cl, EV18Cl, and EV20Cl) with alkyl chains of different lengths were synthesized as shown in
Scheme 1 [42–44]. The synthetic route was based on a two-step procedure involving the aromatic
nucleophilic substitution between the 1-chloro-2,4-dinitrobenzene and 4,40-bipyridine to give the
Zincke salt and its subsequent ANRORC (anionic ring opening and ring closing) reaction with the
corresponding 4-n-alkoxyanilines. For the preparation of Zincke salt, the usual solvent acetonitrile was
used. For the ANRORC reaction, the usual solvent ethanol was used except for EV18Cl and EV20Cl. In
these cases, DMAc was used for the better solubility of these long carbon chains 4-n-alkoxyanilines [36].
The structures of chlorides salts of shorter carbon chains, up to n = 12, were established from their 1H
and 13C NMR spectra obtained in CD3OD (Figures S1–S5). For the longer carbon chains, n = 14–20,
we were able to verify their chemical structures from 1H NMR spectra in CD3OD only (Figures S6–S9).
Then. these chlorides salts were converted to bis(triflimides) salts by the metathesis reaction with
lithium triflimides in a common solvent methanol [31–33]. For EV1, the metathesis reaction was carried
out in water. Then, the bis(triflimide) salts with shorter carbon chains, up to n = 12, were characterized
analyzing the 1H and 13C-NMR spectra obtained in CD3OD (Figures S10–S14), while those with longer
carbon chains, n = 14, 16, 18, 20, were characterized analyzing the 1H and 13C NMR spectra obtained
in d6-DMSO (Figures S15–S18). Their purity was also determined from their elemental analysis.

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2.2. Thermotropic LC Properties of EVn by DSC, POM, and VT-XRD
Figure 2 displays the DSC thermograms of EV1 in the heating and cooling cycles. It clearly shows
two endotherms in each of the two heating cycles. The peak maxima of the endotherms, as well
as heat of enthalpies in the second heating cycle, were slightly lower than those in the first heating
cycle [45–49].
Figure 2. Differential scanning calorimetry (DSC) thermograms of EV1 obtained at heating and cooling
rates of 10 ◦C /min.
In the first cooling cycle, there were cooling exotherms with large supercooling and decreased
heat of enthalpies. In the second cooling cycle, there were no exotherms which suggested that no
crystallization occurred under the experimental conditions used. Figure 3 shows diffraction patterns
of EV1 that indicated that it has crystalline phase at room temperature, an isotropic phase of diffuse
scattering rings at 200 ◦C, and incipient crystalline phase at 160 ◦C on slow cooling from the isotropic
phase. These results suggested that the high-temperature endotherm corresponded to crystal-to-liquid
transition, Tm, at 164 ◦C. The low-temperature endotherm corresponded to crystal-to-crystal transition.
The POM studies also corroborated these statements. Thus, EV1 did not form any LC phase.
Figure S19 shows the DSC thermograms of EV6 in its heating and cooling cycles. In the first heating
cycle, it showed three endotherms located at 81, 93, and 114 ◦C. In the second heating cycle, the absence
of low-temperature endotherms and only the presence of a large endotherm at 105 ◦C with the increased
heat of enthalpy suggested that low-temperature endotherms were related to crystal-to-crystal transition
and high-temperature was related to crystal-to-liquid transition. The presence of cooling exotherm in
each of the cooling cycles suggested that the crystallization from the isotropic liquid occurred under the
experimental conditions used. The first cooling and second cooling exotherms underwent a relatively
low degree of supercooling of 14 and 6 ◦C, respectively.

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(a)
(b)
(c)
Figure 3. The X-ray diffraction patterns of EV1. (
a) Crystalline phase at room temperature; (b) Isotropic
phase taken at 200 ◦C; ( ) Incipient crystalline phase at 160 ◦C; on cooling from isotropic phase. It can
c
be seen that this compound scatters X-ray poorly.
The POM studies also corroborated by the fact that it formed the typical crystal texture. Thus,
similar to EV1, EV6 did not form any LC phase.
Figure 4 shows the DSC thermograms of EV8 in its heating and cooling cycles. In the first heating
cycle it showed three endotherms located at 108, 122, and 190 ◦C. In the second heating cycle, there
were four endotherms located at 104, 112, 122, and 190 ◦C. In each of the cooling cycles, there were
three exotherms. In conjunction with VT-XRD studies, it was found that the endotherm at 190 ◦C
corresponded to SmA-to-isotropic transition, Ti, and that at 122 ◦C it corresponded to crystal-to-SmA
transition, Tm, since it showed diffraction patterns of diffuse rings at 200 ◦C, inner arcs of SmA at
190 ◦C, and sharp inner ring and outer diffuse ring at 180 ◦C (Figure 5). The endotherm(s) prior to
the Tm corresponded to crystal-to-crystal transition(s). The exotherm prior to the recrystallization
exotherm in each of the cooling cycles presumably corresponded to the transition from the SmA to
another (monotropic) mesophase. Interestingly, both Tm and Ti underwent very little supercooling in
the cooling cycles which was in stark contrast to many ILCs [50–54]. Additionally, the POM studies also
indicated that EV8 formed an SmA phase, since its optical texture exhibited the so-called focal-conic
◦
texture taken at 160 C on cooling from the isotropic phase (Figure 6) [45
–
49]. Thus, these results
suggested that EV8, unlike EV1 and EV6, showed an SmA phase after Tm and a Ti leading to the LC
phase range of 68 ◦C. The analogous salt containing n-octyl group has a Tm at 103 ◦C and Ti at 180 ◦C
resulting in the LC phase range of 77 ◦C [37].
107 °C
188 °C
118 °C
107 °C
2C
188 °C
190 °C
119 °C
1C
2H
104 °C
112 °C
122 °C
122 °C
1H
108 °C
190 °C
50
100
150
200
250
Temperature (°C)
Figure 4. DSC thermograms of EV8 obtained at heating and cooling rates of 10 ◦C /min.

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(a)
(b)
(c)
Figure 5. The X-ray diffraction patterns of EV8. (
of SmA taken at 190 ◦C; (c) SmA of inner ring sharp and outer ring diffuse at 180 ◦C.
a b) Sharp inner arcs
) Isotropic phase taken at 200 ◦C; (
Figure 6. The focal-conic texture of EV8 obtained at 160 ◦C on cooling from the isotropic phase
(magnification 200×).
Figure 7 shows the DSC thermograms of EV10 in its heating and cooling cycles. In the first heating
cycle, it showed three endotherms located at 106, 127, and 253 ◦C. In the second heating cycle, there
were also three endotherms located at 104, 123, and 251 ◦C. In each of the cooling cycles, there were
four exotherms. In the POM studies, we determined that its Tm at 104 ◦C and Ti at 251 ◦C resulted in
an LC phase range of 147 ◦C and confirmed the results, as reported in the literature [36]. The exotherm,
prior to the recrystallization exotherm in each of the cooling cycles, presumably corresponded to the
transition from the SmA to another (monotropic) mesophase. The corresponding salt having n-decyl
group has a Tm at 75 ◦C and Ti at 175 ◦C resulting in the LC phase range of 100 ◦C [37]. However,
we were at variance with the fact that there was an additional endotherm in between Tm and Ti in each
of the heating cycles, although the nature of this endotherm remains unknown. This endotherm was
probably related to the LC-to-LC transition. Similar to EV8, both Tm and Ti exhibited little supercooling
in contrast to many ILCs that undergo large supercooling, also known as hysteresis [50–57].

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Figure 7. DSC thermograms of EV10 obtained at heating and cooling rates of 10 ◦C /min.
Figure 8 shows the DSC thermograms of EV12 in its heating and cooling cycles. In the first
heating cycle, it showed a large endotherm located at 105 ◦C and a small endotherm at 131 ◦C. In the
second heating cycle, there was also a large endotherm located at 104 ◦C and a small endotherm at
130 ◦C. In each of the cooling cycles, there were three exotherms. In the POM studies, we determined
that its large endotherm corresponded to Tm at 104 ◦C which was in excellent agreement as reported
in the literature [36]. The exotherm prior to the recrystallization exotherm in each of the cooling
cycles presumably corresponded to the transition from the SmA to another (monotropic) mesophase.
We tried to confirm its reported Ti at 305 ◦C and found that this transition appeared in the first heating
cycle followed by decomposition (Figure S20), since the Tm endotherm in the first heating cycle
was not reproducible in the second heating cycle. However, we were at variance with the fact that
there was an additional endotherm after Tm in each of the heating cycles, although the nature of this
endotherm remains unknown. Presumably, they were related to the LC-to-LC transition. Unlike EV8
and EV10, EV12 showed Tm after which it formed an SmA phase that persisted up to the decomposition
temperature at high temperature (vide infra) [45–49].
95 °C
127 °C
97 °C
2C
95 °C
128 °C
98 °C
1C
2H
104 °C
105 °C
130 °C
1H
131 °C
150
50
100
200
250
Temperature (°C)
Figure 8. DSC thermograms of EV12 obtained at heating and cooling rates of 10 ◦C /min.
Figure 9 shows the DSC thermograms of EV14 in its heating and c◦ooling cycles. In the first
heating cycle, it showed four endotherms located at 11, 44, 76, and 106 C. In the second heating
cycle, there were three endotherms located at 12, 44, and 104 ◦C. The POM studies suggested that
the highest-temperature endotherm at 104 ◦C is its Tm after which it transformed into SmA which
persisted up to the decomposition at high temperature. This Tm was in excellent agreement with that

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in the literature [36]. However, it did not show Ti. In contrast, the corresponding salt with n-tetradecyl
◦
◦
◦
group has a Tm at 80 C and Ti at 320 C resulting in the LC phase range of 240 C [37]. Again,
we were at variance with the Ti at 328 ◦C which was also determined by POM and not detected by
DSC [36]. Additionally, the additional endotherms prior to the Tm corresponded to crystal-to-crystal
transition which is known as polymorphism [58–62]. It was verified by observations of a highly
birefringence texture. There were sharp textural defects and absence of homogeneity in the domains
suggesting its crystal phases. The features for the DSC thermograms of EV16, EV18, and EV20 in
their heating and cooling cycles were essentially identical (Figures S21–S23) with a minor exception.
They showed essentially similar Tms (101, 106, and 107 ◦C, respectively,) similar to EV14 (104 ◦C), after
which they transformed into SmA phases (Figure 10) which persisted up to their decomposition at
high temperatures. They also showed the polymorphism phenomenon since there were additional
endotherms prior to the Tms. In the cases of EV16 and EV20, each of them exhibited an exotherm at ca.
260 ◦C in the first heating cycle in the SmA phase. The reason for this exotherm remains to be explored,
although there exists a precedence in the literature [22], such as exotherms in the smectic phases of
other ILCs without any definitive answers. However, we speculate the reason for the exotherm was
related to conversion of metastable state of smectic phase to stable state of smectic phase, since it
appeared only in the first heating cycle.
90 °C
2C
23 °C
22 °C
90 °C
1C
2H
12 °C
40 °C
44 °C
50
104 °C
1H
11 °C
76 °C
106 °C
0
100
150
200
250
Temperature (°C)
Figure 9. DSC thermograms of EV14 obtained at heating and cooling rates of 10 ◦C /min.
The thermodynamic properties of phase transition temperatures of EVn determined from DSC
measurements and decomposition temperatures from TGA measurements are compiled in Table 1.
It shows that EV1 had the highest melting point of 164 ◦C in the series but no LC property. EV6 had
the lower melting point of 105 ◦C as compared with EV1 and had no LC property, similar to EV1
.
Interestingly, all other members in the series formed SmA phases at their respective Tms. EV8 had
the highest Tm and the rest of the members had essentially similar low Tms. EV8 and EV10 also
exhibited Tis, thus resulting in the LC phase ranges of 68 and 147 ◦C, respectively. EV12–EV20 formed
SmA phases at low Tms that persisted up to decomposition temperature at high temperatures. On the
one hand, these results can be rationalized by the fact that the short alkyl (alkoxy) chain does not
permit the nanosegregation between the ionic groups and hydrophobic groups, and thus prevents the
formation layer structures. On the other hand, the long alkyl (alkoxy) chain permits the nanosegregation
between the ionic moieties and hydrophobic moieties leading to layered smectic phases, in which
ionic layers are alternated with hydrophobic alkoxy/alkyl layers, which is the essential criterion for the
formation of ILCs [63–65]. The results also suggested that the length of the alkoxy had little effect on
Tms but a significant effect on the Tis, which was in stark contrast to molecular LCs [66]. The longer
the alkoxy chain, the higher the temperature at which an LC phase transformed into an isotropic phase

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and the larger the LC temperature range [67]. These results are in excellent agreement with those
of other ILCs including the Cnmim family (1-alkyl-3-methylimidazolium salts) [54 68 69]. Although
,
,
triflimide counterion is a large size ion with diffuse electron cloud, it can provide low electrostatic
attraction interactions with many cations, thus, leading to many ionic liquids, but it is also capable
of forming ILCs with suitably designed cations such as extended viologen cation moieties which are
similar to the viologen moieties reported earlier in the literature [31–34]. Specifically, the thermotropic
liquid-crystallinity of the short alkoxy chain, as low as octyloxy in the extended viologen moiety,
with this triflimide ion is quite an interesting result in the field of ILCs.
Figure 10. Optical textures of EV16, EV18, and EV20 taken at (
displaying SmA phases (magnification 400×).
a) 240, (b) 150, and (c
) 290 ◦C, respectively,
Table 1. Thermodynamic properties of phase transition temperatures of extended viologen bis(triflimide)
salts (EVn) obtained from DSC measurements and decomposition temperatures obtained from
thermogravimetric analysis (TGA) measurements.
Tm b ◦C
Ti d ◦C
Td f ◦C
Sample
Tm a ◦C
TLC-LC c ◦C
∆T e ◦
C
EV1
EV6
EV8
EV10
EV12
EV14
EV16
EV18
EV20
104 g (17.4), 164 (25.8)
-
-
-
-
-
-
-
-
-
370
328
330
332
331
337
337
331
330
75 g (0.84), 105 (38.2)
-
-
-
-
-
-
-
104 g (4.6), 112 g (0.36), 122 (43.5)
104 (46.1)
190 (1.8)
68
147
123 (0.6)
130 (0.3)
251 (2.3)
305 h (3.4)
104 (56.8)
-
-
-
-
-
12 g (2.1), 40 g (5.5), 104 (55.9)
54 g (1.0), 82 g (3.3), 101 (49.2)
63 g (2.4), 70 g (6.2), 106 (69.6)
71 g (2.9), 83 g (4.5), 107 (71.8)
-
-
-
-
328 h
-
-
-
a Tm = crystal-to-isotropic phase transition. Datum was taken from the second heating cycle of the DSC thermogram
b
at a heating rate of 10 ◦C/min. The value in the parentheses was the enthalpy in kJ/mol for this transition. Tm
= crystal-to-LC phase transition. Datum was taken from the second heating cycle of the DSC thermogram at a
c
heating rate of 10 ◦C/min. The value in the parentheses was the enthalpy in kJ/mol for this transition. TLC-LC
=
d
LC-to-LC phase transition. Ti = LC-to isotropic transition. Datum was taken from the second heating cycle of the
DSC thermogram at a heating rate of 10 ◦C/min. The value in the parentheses was the enthalpy in kJ/mol for this
e
f
transition.
∆
T = (Ti-Tm), that is, the LC phase range. Td = the temperature at which a 5% weight loss of the
salt occurred at a heating rate of 10 ◦C/min in nitrogen. Crystal-to-crystal transition. Datum was taken from the
g
second heating cycle of the DSC thermogram at a heating rate of 10 ◦C/min. The value in the parentheses was the
h
enthalpy in kJ/mol for this transition. from reference [36].

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2.3. Thermal Stabilities of Extended Viologen Bis(triflimide) Salts (EVn)
The stabilities for all extended viologen salts were studied by TGA analyses. They are defined as the
temperature (◦C) at which a 5% weight loss for each of the salts occurred at a heating rate of 10 ◦C/min
in nitrogen. Despite the presence of flexible alkyl chains, the representative TGA thermograms of five
salts were plotted, as shown in Figure 11, and display relatively high thermal stabilities that are in
the temperature range of 330–370 ◦C (Table 1, Figure S24). There were no apparent specific trends
along the series. However, EV1 had the highest thermal stability and EV20 had the lowest thermal
stability. Triflimide is one of best counterion that imparts the high thermal stability of any ionic liquids,
ILCs, and ionic polymers reported in the literature [70–72], because it has non-nucleophilic character
being the conjugate base of a super acid. Therefore, it causes decomposition of the associated cationic
moieties nucleophilically at relatively high temperatures.
EV1
EV6
100
EV8
EV10
EV12
80
60
40
20
0
50 100 150 200 250 300 350 400 450 500 550
Temperature (°C)
Figure 11. TGA thermograms of EV1–EV12 obtained a heating rate of 10 ◦C/min in nitrogen.
2.4. Light Emission Properties of EVCl6 and EV6
All the extended viologens with dichloride and bis(triflimide) showed essentially identical,
absorption, excitation, and emission spectra in methanol as measured by UV-Vis and luminescence
spectrometer. Figure 12 shows the emission spectra of EV6Cl and EV6 in methanol that are representative
of the light emission properties of this class of salts (Figures S25–S27). Each of them showed a major
peak at 572 nm when excited at various excitation wavelengths of 205–260 nm. This major emission
peak was independent of the counterions (chloride and triflimide) and the length of alkoxy groups
attached to the extended viologen moiety.

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(a)
1000
900
800
700
600
500
400
300
200
100
0
205 nm
240 nm
252 nm
260 nm
Monitored at 572 nm
572 nm
205 nm
532 nm
512 nm
280 nm
252 nm
424 nm
391 nm
200
300
400
500
600
700
800
Wavelength (nm)
(b)
1000
900
800
700
600
500
400
300
200
100
0
206 nm
252 nm
260 nm
280 nm
572 nm
205 nm
Monitored at 572 nm
532 nm
512 nm
280 nm
252 nm
430 nm
200
300
400
500
600
700
800
Wavelength (nm)
Figure 12. Emission spectra of (a) EV6Cl and (b) EV6 in methanol at various excitation wavelengths.
3. Materials and Methods
3.1. Instrumentation
1
The H and 13C nuclear magnetic resonance (NMR) spectra of all the extended viologen
bis(triflimide) salts in CD3OD or d6-DMSO were recorded by using VNMR 400 spectrometer operating
(Varian Inc., Palo Alto, CA, USA.) at 400 and 100 MHz, at room temperature. Elemental analysis was
performed by Atlanta Microlab Inc., (Norcross, GA, USA). Differential scanning calorimetry (DSC)
measurements of all the salts were conducted on a TA module DSC Q200 series (TA Instruments,
New Castle, DE, USA) in nitrogen at heating and cooling rates of 10 ◦C/min. The temperature axis
of the DSC thermograms was calibrated before use with reference standards of high purity indium
and tin. Their thermogravimetric analyses (TGA) were performed using a TGA Q50 instrument
(
TA Instruments, New Castle, DE, USA) at a heating rate of 10 ◦C/min, in nitrogen. Optical studies
were performed on these viologen salts sandwiched between a standard microscope glass slide
and coverslip. The samples were heated and cooled on a Mettler hot-stage (FP82HT) and (FP90)

Molecules 2020, 25, 2435
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controller (Mettler Toledo, Columbus, OH, USA) and observations of the phases made between crossed
polarizers of an Olympus BX51 microscope (Olympus America Inc., New York, NY, USA). In short,
salts were heated above their clearing transitions, whenever possible, and cooled at 5 ◦C/min to room
temperature, with brief pauses to collect images and observe specific transitions. In some cases, the
salts were heated well above the Tms to make thin films, and photomicrographs were taken at specific
temperatures. X-ray diffraction studies of salts contained in flame sealed 1 mm quartz capillaries were
performed using a Rigaku Screen Machine (Rigacu, Inc., The Woodlands, TX, USA). The salt under
study was placed inside the Linkam HFS350X-Cap capillary (Linkam Scientific Instruments, Tadworth,
UK) hot-stage 78 mm away from the two-dimensional (2D) detector, with temperature controlled
to the accuracy of
±
0.1 ◦C. A magnetic field of ~2.5 kG was applied to the samples using a pair of
samarium cobalt permanent magnets with B nearly parallel to the beam stop. Scattering patterns were
collected using a Mercury 3 CCD detector (Rigacu, Inc., The Woodlands, TX, USA) with resolution
1024 × 1024 pixels (size, 73.2 µm × 73.2 µm) and copper Kα radiation generated by a microfocus sealed
X-ray tube with copper anode (λ = 1.542 Å). The UV-Vis absorption spectra in methanol were recorded
with a Varian Cary 3 Bio UV-Vis spectrophotometer (Agilent Technologies, Santa Clara, CA, USA)
at rt. Photoluminescence spectra in methanol solutions were recorded with a Perkin–Elmer LS 55
luminescence spectrometer (Perkin Elmer, Akron, OH, USA) with a xenon lamp light source.
3.2. Materials
4-Hydoxyacetanilide, n-hexyl bromide, n -octyl bromide, n -decyl bromide, n -dodecyl bromide,
n -tetradecyl bromide, n -hexadecyl bromide, n -octadecyl bromide, eicosyl bromide, 4,40-bipyridine,
1-chloro-2,4-dintrobenzene, 4-methoxyaniline, potassium carbonate, sodium hydroxide, and lithium
triflimide were purchased from TCI America (Portland, OR, USA) and used as received. For synthesis
and purification purposes, reagent grade solvents including acetonitrile, ethanol, methanol, ethyl
acetate, N,N-dimethylacetamide (DMAc), spectral grade methanol were used as obtained from
Sigma-Aldrich (Milwaukee, WI, USA).
3.3. Synthesis of 4-n-Alkoxyanilines (n = 6, 8, 10, 12, 14, 16, 18, 20)
All the 4-n-alkoxyanilines were prepared according to the slightly modified literature
procedure [41]. The modification was the use of acetone instead of N,N-dimethylformamide in
the alkylation of 4-hydroxyacetanilide with the respective n-alkyl bromide followed by hydrolysis of
4-n-alkoxyacetanilide. The overall yields for the synthesis of 4-n-alkoxyamines in two-step reaction
were 74%, 60%, 67%, 62%, 845, 805, 85%, and 86%.
3.4. Synthesis of Zincke Salt
Zincke salt was prepared from the reaction of 1-chloro-2,4-dinitrobenzene (2.5 equiv) with
4,40-bipyridine (1 equiv) on heating in acetonitrile according to the procedure described in the
literature [42,43].
3.5. General Procedure for the Synthesis of Bis(4-alkoxyphenyl)-4,40-Bipyridinium Dichloride (EV1Cl, EV6Cl,
EV8Cl, EV10Cl, EV12Cl, EV14Cl, EV16Cl, EV18Cl, and EV20Cl)
The procedure that was adopted for the synthesis of EV1Cl from the reaction of
Zincke salt with 4-methoxyaniline [44], as an example, is as follows: Ethanol was added
to 1,10-bis(2,4-dinitrophenyl)-(4,40-bipyridine)-1,10-diium chloride (2.00 g, 3.56 mmol) and
4-methoxyaniline (1.10 g, 8.90 mmol) to form a yellow solution. The reaction mixture was heated
on stirring to reflux under nitrogen, for 24 h. At the end of the reaction, it was brought to room
temperature. Ethanol was removed from the reaction mixture using a rotary evaporator to yield the
reaction products that were, then, dried overnight in vacuum to remove any residual solvent. Then,
the desired crude product was obtained by removing 2,4-dintroaniline with plenty of hot acetone
and collected by vacuum filtration. Finally, it was purified from recrystallization from methanol

Molecules 2020, 25, 2435
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yielding (1.44 g, 3.26 mmol) a yellow to dark yellow powder. Similarly, EV6Cl, EV8Cl, EV10Cl, EV12Cl,
EV14Cl, and EV16Cl were prepared from the corresponding 4-n-alkoxyanilines and recrystallized
from an appropriate solvent or solvent mixtures (vide infra). In the cases of EV18Cl and EV20Cl,
the solvent DMAc was used because of better solubility of these amines instead of ethanol according
to the procedure reported in the literature [36].
Data for EV1Cl: Yield 92%. δH (CD3OD, 400 MHz, ppm): 9.50 (4H, d, J = 7.2 Hz), 8.90 (4H, d,
J = 7.2 Hz), 7.90 (4H, br), 7.32 (4H, br), 3.96 (6H, s). δC (CD3OD, 400 MHz, ppm): 162.48, 149.69, 145.35,
135.47, 126.87, 125.49, 115.41, 55.17.
Data for EV6Cl: Recrystallized from methanol/ethyl acetate, yield 81%. δH (CD3OD, 400 MHz,
ppm): 9.49 (4H, d, J = 7.2 Hz), 8.79 (4H, d, J = 7.2 Hz), 7.89 (4H, br), 7.30 (4H, br), 4.15 (4H, t, J = 6.4 Hz),
1.81–1.87 (4H, m), 1.38–1.55 (12H, m), 0.96 (6H, t, J = 6.8 Hz). δC (CD3OD, 400 MHz, ppm): 161.94,
149.64, 145.30, 135.32, 126.88, 125.47, 115.85, 68.54, 31.30, 28.74, 25.36, 22.26, 12.98.
Data for EV8Cl: Recrystallized from methanol/ethyl acetate, yield 78%. δH (CD3OD, 400 MHz,
ppm): 9.50 (4H, d, J = 7.2 Hz), 8.90 (4H, d, J = 7.2 Hz), 7.90 (4H, br), 7.31 (4H, br), 4.16 (4H, t, J = 6.4 Hz),
1.82–1.88 (4H, m), 1.33–1.53 (20H, m), 0.92 (6H, t, J = 6.8 Hz). δC (CD3OD, 400 MHz, ppm): 161.93,
149.64, 145.30, 135.32, 126.89, 125.48, 115.85, 68.54, 31.58, 29.04, 28.98, 28.78, 25.69, 22.31, 13.05.
Data for EV10Cl: Recrystallized from ethanol/ethyl acetate, yield 80%. δH (CD3OD, 400 MHz,
ppm): 9.49 (4H, d, J = 7.2 Hz), 8.90 (4H, d, J = 7.2 Hz), 7.89 (4H, br), 7.30 (4H, br), 4.16 (4H, t, J = 6.4 Hz),
1.83–1.87 (4H, m), 1.32–1.53 (28H, m), 0.92 (6H, t, J = 6.8 Hz). δC (CD3OD, 400 MHz, ppm): 161.94, 149.64,
145.30, 135.31, 126.87, 125.46, 115.85, 68.54, 31.65, 29.31, 29.28, 29.07, 29.04, 28.78, 25.69, 22.32, 13.05.
Data for EV12Cl: Recrystallized from ethanol, yield 60%. δH (CD3OD, 400 MHz, ppm): 9.49 (4H,
d, J = 7.2 Hz), 8.90 (4H, d, J = 7.2 Hz), 7.89 (4H, br), 7.30 (4H, br), 4.16 (4H, t, J = 6.4 Hz), 1.83–1.87 (4H,
m), 1.32–1.53 (36H, m), 0.92 (6H, t, J = 6.8 Hz). δC (CD3OD, 400 MHz, ppm): 161.94, 149.64, 145.30,
135.31, 126.87, 125.46, 115.85, 68.54, 31.65, 29.31, 29.28, 29.07, 29.04, 28.78, 25.69, 22.32, 13.05.
Data for EV14Cl: Recrystallized from ethanol, yield 80%. δH (CD3OD, 400 MHz, ppm): 9.49 (4H,
d, J = 5.6 Hz), 8.88 (4H, d, J = 6.0 Hz), 7.87 (4H, br), 7.30 (4H, br), 4.16 (4H, t, J = 6.4 Hz), 1.82–1.87 (4H,
m), 1.30–1.54 (44H, m), 0.92 (6H, t, J = 6.8 Hz).
Data for EV16Cl: Recrystallized from ethanol, yield 82%. δH (CD3OD, 400 MHz, ppm): 9.50 (4H,
d, J = 6.8 Hz), 8.88 (4H, d, J = 7.2 Hz), 7.87 (4H, br), 7.30 (4H, br), 4.14 (4H, t, J = 6.4 Hz), 1.87–1.78 (4H,
m), 1.22–1.42 (52H, m), 0.91 (6H, t, J = 6.8 Hz).
Data for EV18Cl: Recrystallized from ethanol, yield 45%. δH (CD3OD, 400 MHz, ppm): 9.49 (4H,
d, J = 7.2 Hz), 8.80 (4H, d, J = 7.2 Hz), 7.87 (4H, br), 7.30 (4H, br), 4.16 (4H, t, J = 6.4 Hz), 1.83–1.87 (4H,
m), 1.29–1.54 (60H, m), 0.91 (6H, t, J = 6.8 Hz).
Data for EV20Cl: Recrystallized from ethanol, yield 45%. δH (CD3OD, 400 MHz, ppm): 9.50 (4H,
d, J = 6.8 Hz), 8.87 (4H, d, J = 7.2 Hz), 7.87 (4H, br), 7.30 (4H, br), 4.16 (4H, t, J = 6.4 Hz), 1.82–1.87 (4H,
m), 1.29–1.54 (68H, m), 0.91 (6H, t, J = 6.8 Hz).
3.6. Synthesis of bis(4-Methoxyphenyl)-4,40-Bipyridinium Bis(triflimide) Salt (EV1)
A clear solution of 0.95 g (3.31 mmol) lithium triflimide in 5 mL water was added dropwise to
the clear solution of 0.66 g (1.50 mmol) of EV1Cl in 25 mL water on stirring at room temperature.
The precipitation occurred immediately in the reaction mixture and it was stirred overnight to complete
the reaction. Then, the product was filtered, washed with plenty of water, and dried in a vacuum
to yield 1.19 g (1.28 mmol) of the pure product EV1. Yield 85%. δH (CD3OD, 400 MHz, ppm): 9.44
(4H, d, J = 6.8 Hz), 8.80 (4H, d, J = 6.8 Hz), 7.84 (4H, br), 7.30 (4H, br), 3.95 (6H, s). δC (CD3OD,
400 MHz, ppm): 162.49, 149.87, 145.34, 135.26, 126.83, 125.44, 121.28, 118.09, 115.38, 55.13. Anal. calcd

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for C28H22N4O8F12S4 (930.74): C, 36.13; H, 2.38; N, 6.02; S, 13.78%. Found C, 36.42; H, 2.26; N, 6.09;
S, 13.66%.
3.7. General Procedure for the Synthesis of Bis(4-n-alkoxyphenyl)-4,40-bipyridinium Bis(triflimide) Salts (EV6,
EV8, EV10, EV12, EV14, EV16, EV18, EV20) by Metathesis Reaction
The following procedure [31–33], as an example, was adopted for the synthesis of EV20 from the
metathesis reaction of EV20Cl with lithium triflimide. An amount of 0.33 g (0.34 mmol) EV20Cl was
dissolved in methanol on boiling to get a clear solution to which clear methanol solution of lithium
triflimide 0.22 g (0.75 mmol) dissolved in 5 mL was added on stirring. The reaction mixture was heated
to reflux on stirring overnight for the completion of the metathesis reaction. The product precipitated
out on cooling the reaction mixture to the ambient temperature. It was collected by filtration, washed
with plenty of water, and recrystallized from methanol yielding 0.24 g (0.16 mmol). In the cases of EV6
EV8, EV10, and EV12, after the completion of the metathesis reaction, methanol was removed by
rotatory evaporator to give the crude product that was repeatedly washed with water to give the
pure product.
,
Data for EV6: Yield 67%. δH (CD3OD, 400 MHz, ppm): 9.43 (4H, d, J = 6.8 Hz), 8.79 (4H, d,
J = 6.8 Hz), 7.83 (4H, br), 7.29 (4H, br), 4.15 (4H, t, J = 6.4 Hz), 1.81–1.87 (4H, m), 1.36–1.55 (12H, m), 0.96
(6H, t, J = 7.2 Hz). δC (CD3OD, 400 MHz, ppm): 161.97, 149.82, 145.29, 135.26, 126.82, 125.41, 121.28,
118.09, 115.82, 68.53, 31.28, 28.71, 25.33, 22.23, 12.93. Anal. calcd for C38H42N4O10F12S4 (1071.00): C,
42.61; H, 3.95; N, 5.23; S, 11.98%. Found C, 42.38; H, 3.38; N, 5.20; S, 12.27%.
Data for EV8: Yield 79%. δH (CD3OD, 400 MHz, ppm): 9.43 (4H, d, J = 7.2 Hz), 8.79 (4H, d,
J = 7.2 Hz), 7.84 (4H, br), 7.29 (4H, br), 4.15 (4H, t, J = 6.4 Hz), 1.81–1.87 (4H, m), 1.33–1.54 (20H, m), 0.93
(6H, t, J = 7.2 Hz). δC (CD3OD, 400 MHz, ppm): 161.96, 149.82, 145.29, 135.26, 126.83, 125.41, 121.28,
118.09, 115.83, 68.52, 31.55, 29.01, 28.96, 28.75, 25.66, 22.28, 13.00. Anal. calcd for C42H50N4O10F12S4
(1127.11): C, 44.76; H, 4.47; N, 4.97; S, 11.38%. Found C, 44.54; H, 4.48; N, 4.92; S, 11.40%.
Data for EV10: Yield 80%. δH (CD3OD, 400 MHz, ppm): 9.43 (4H, d, J = 6.8 Hz), 8.79 (4H, d,
J = 6.8 Hz), 7.82 (4H, br), 7.28 (4H, br), 4.15 (4H, t, J = 6.4 Hz), 1.81–1.88 (4H, m), 1.32–1.54 (28H, m),
0.92 (6H, t, J = 7.2 Hz). δC (CD3OD, 400 MHz, ppm): 161.96, 149.82, 145.28, 135.25, 126.83, 125.41,
121.28, 118.09, 115.83, 68.52, 31.64, 29.35, 29.26, 29.05, 29.02, 28.75, 25.66, 22.30, 13.02. Anal. calcd for
C46H58N4O10F12S4 (1183.21): C, 46.69; H, 4.94; N, 4.71; S, 10.84%. Found C, 46.44; H, 4.84; N, 4.73;
S, 10.73%.
Data for EV12: Yield 79%. δH (CD3OD, 400 MHz, ppm): 9.44 (4H, br), 8.79 (4H, br), 7.83 (4H, d,
J = 8.8 Hz), 7.28 (4H, d, J = 8.8 Hz), 4.15 (4H, t, J = 6.4 Hz), 1.83–1.87 (4H, m), 1.31–1.54 (36H, m), 0.92 (6H, t,
J = 7.2 Hz). δC (CD3OD, 400 MHz, ppm): 161.98, 149.82, 145.29, 135.25, 126.81, 125.40, 121.29, 118.09, 115.83,
115.75, 68.53, 31.64, 29.35, 29.32, 29.29, 29.04, 28.76, 25.66, 22.30, 13.01. Anal. calcd for C50H66N4O10F12S4
(1239.32): C, 48.46; H, 5.37; N, 4.52; S, 10.35%. Found C, 48.48; H, 5.32; N, 4.51; S, 10.20%.
Data for EV14: Recrystallized from ethanol, yield 72%. δH (d6-DMSO, 400 MHz, ppm): 9.60 (4H,
d, J = 6.8 Hz), 8.98 (4H, d, J = 6.8 Hz), 7.88 (4H, br), 7.30 (4H, br), 4.11 (4H, t, J = 6.8 Hz), 1.73–1.76 (4H,
m), 1.22–1.44 (44H, m), 0.85 (6H, t, J = 6.8 Hz). δC (d6-DMSO, 400 MHz, ppm): 161.39, 148.75, 146.04,
145.99, 135.52, 126.90, 126.59, 124.70, 121.50, 118.30, 116.11, 68.79, 31.73, 29.49, 29.48, 29.45, 29.20, 29.15,
28.93, 25.87, 22.53, 14.36. Anal. calcd for C54H74N4O10F12S4 (1295.43): C, 50.07; H, 5.76; N, 4.32; S,
9.90%. Found C, 50.61; H, 5.77; N, 4.31; S, 9.79%.
Data for EV16: Recrystallized from ethanol, yield 74%. δH (d6-DMSO, 400 MHz, ppm): 9.60 (4H,
br), 8.98 (4H, br), 7.87 (4H, br), 7.29 (4H, br), 4.11 (4H, t, J = 5.6 Hz), 1.71–1.78 (4H, m), 1.22–1.42 (52H,
m), 0.84 (6H, t, J = 6.4 Hz). δC (d6-DMSO, 400 MHz, ppm): 161.39, 148.75, 146.08, 146.03, 145.99, 135.52,
126.90, 126.59, 124.70, 121.50, 118.30, 116.11, 68.80, 31.73, 29.49, 29.48, 29.45, 29.20, 29.15, 28.93, 25.88,
22.52, 14.37. Anal. calcd for C58H82N4O10F12S4 (1351.53): C, 51.54; H, 6.12; N, 4.15; S, 9.49%. Found C,
51.63; H, 6.11; N, 4.06; S, 9.31%.

Molecules 2020, 25, 2435
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Data for EV18: Recrystallized from ethanol, yield 61%. δH (d6-DMSO, 400 MHz, ppm): 9.59 (4H,
br), 8.98 (4H, br), 7.87 (4H, br) 7.29 (4H, br) 4.11 (4H, t, J = 6.4 Hz), 1.71–1.78 (4H, m), 1.22–1.42 (60H,
m), 0.84 (6H, J = 6.4 Hz). δC (d6-DMSO, 400 MHz, ppm): 161.39, 148.76, 146.04, 145.99, 135.52, 126.90,
126.59, 124.70, 121.50, 118.30, 116.11, 68.79, 31.74, 29.48, 29.45, 29.40, 29.39, 29.38, 29.23, 29.15, 28.95,
25.89, 22.53, 14.34. Anal. calcd for C62H90N4O10F12S4 (1407.64): C, 52.90; H, 6.44; N, 3.98; S, 9.11%.
Found C, 53.10; H, 6.53; N, 4.01; S, 8.99%.
Data for EV20: Recrystallized from methanol, yield 47%. δH (d6-DMSO, 400 MHz, ppm): 9.63 (4H,
d, J = 6.4 Hz), 9.02 (4H, d, J = 6.4 Hz), 7.90 (4H, br) 7.33 (4H, br) 4. 14 (4H, t, J = 6.4 Hz), 1.75–1.79 (4H,
m), 1.24–1.46 (68H, m), 0.87 (6H, J = 6.8 Hz). δC (d6-DMSO, 400 MHz, ppm): 161.38, 148.69, 146.01,
135.52, 126.87, 126.61, 124.70, 121.50, 118.30, 116.12, 68.80, 31.72, 29.47, 29.46, 29.44, 29.21, 29.13, 28.94,
25.88, 22.52, 14.38. Anal. calcd for C66H98N4O10F12S4 (1463.75): C, 54.16; H, 6.75; N, 3.83; S, 8.76%.
Found C, 54.27; H, 6.60; N, 3.86; S, 8.87%.
4. Conclusions
A series of bis(4-alkoxyphenyl) viologen bis(triflimide) salts with alkoxy chains of different lengths
were synthesized by the metathesis reaction of respective bis(4-alkoxyphenyl) viologen dichloride
salts, which in turn prepared the reaction of Zincke salt with the corresponding 4-n-alkoxyanilines,
with lithium triflimide in methanol. Their chemical structures were established using spectroscopic
techniques and elemental analysis. Their thermotropic LC properties as determined by DSC, POM,
and VT-XRD suggested that the salts with short alkoxy chains (n = 1 and 6 carbon atoms) did not form
LC phase on melting, but the salts with long alkoxy chains (n = 8 and 10 carbon atoms) exhibited
crystal–LC transitions, Tms, and LC–isotropic transitions, Tis, and showed Schlieren or focal conic
textures indicative of their SmA phases. Those of higher alkoxy chains (n = 12, 14, 16, 18, and 20)
exhibited SmA phases at relatively low Tms and their SmA phase persisted up to their decomposition
at high temperatures. The majority of them also exhibited crystal-to-crystal transitions prior to the Tms.
They had good thermal stability in the temperature range of 330–370 ◦C. These results suggest that they
exhibited LC phases at relatively low Tms which have practical implications. Importantly, triflimide
counterion is not only interesting for the preparation of ILs but also interesting for the preparation
of ILCs, an important class of LC.
Supplementary Materials: The following are available online at http://www.mdpi.com/1420-3049/25/10/2435/s1,
1
1
Figures S1–S5: H and 13C spectra of EV1Cl, EV6Cl, EV8Cl, EV10Cl, and EV12Cl, Figures S6–S9: H spectra of
EV14Cl, EV16Cl, EV18Cl and EV20Cl, Figures S10–S18: 1H and 13C NMR spectra of EV1, EV6, EV8, EV10, EV12,
EV14, EV16, EV18, and EV20, Figures S19–S23: DSC thermograms of EV6, EV12, EV16, EV18, and EV20, Figure
S24: TGA thermograms of EV14, EV16, EV18, and EV20, Figures S25–S27: Emission spectra of EV1Cl and EV1,
EV8Cl and EV8, and EV10Cl and EV10.
Author Contributions: Conceptualization, P.K.B., H.H., and H.D.M.; methodology, M.K.M.A.-K, S.T.K., E.J.D., J.K.,
S.L.C., A.H., R.G.C., B.G., and K.M.; software, E.J.D., A.C., R.C.G.P, D.M.A.-K., and L.S.; validation, P.K.B., H.H.,
and R.G.C.P.; formal analysis, R.C.G.P. and H.H.; investigation, P.K.B., H.H., and M.R.F.; resources, P.K.B.; data
curation, H.H., E.J.D., and R.C.G.P.; writing—original draft preparation, P.K.B., E.J.D., and S.L.C.; writing—review
and editing, P.K.B., H.H., and S.L.C.; visualization, P.K.B., R.C.G.P., and M.R.F.; supervision, P.K.B. and H.H.;
project administration, P.K.B. and S.K.; funding acquisition, P.K.B., S.K., and H.D.M. All authors have read and
agreed to the published version of the manuscript.
Funding: This work is in part supported by the NSF under grant no. 0447416 (NSF EPSCoR RING-TRUE III),
grant no. DMR-1410649 (US Ireland Partnership), NSF-Small Business Innovation Research (SBIR) Award (grant
OII-0610753), NSF-STTR Phase I IIP-0740289, NASA GRC contract no. NNX10CD25P, and Welch Foundation
grant no. BS0040.
Acknowledgments: We at the University of Nevada Las Vegas thank Jung Jae Koh for his help in the measurement
of light-emitting properties of extended viologen bis(triflimide) salts. We (H.D.M., R.G.C., B.G., and K.M.) at Texas
A & M International University, thank the Department of Biology and Chemistry for financial support of this
research project.
Conflicts of Interest: The authors declare no conflict of interest.

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Sample Availability: Samples of the compounds are not available from the authors.
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