Spectral and physicochemical characterization of dysprosium-based multifunctional ionic liquid crystals

Article abstract of DOI:10.1021/acs.jpca.5b01180

We report on the synthesis and characterization of multifunctional ionic liquid crystals (melting points below 100 °C) which possess chirality and fluorescent behavior as well as mesomorphic and magnetic properties. In this regard, (1R,2S)-(-)-N-methylephedrine ((-)MeEph), containing a chiral center, is linked with variable alkyl chain lengths (e.g., 14, 16, and 18 carbons) to yield liquid crystalline properties in the cations of these compounds. A complex counteranion consisting of trivalent dysprosium (Dy³⁺) and thiocyanate ligand (SCN^-) is employed, where Dy³⁺ provides fluorescent and magnetic properties. Examination of differential scanning calorimetry (DSC) and hot-stage polarizing optical microscopy (POM) data confirmed liquid crystalline characteristics in these materials. We further report on phase transitions from solid to liquid crystal states, followed by isotropic liquid states with increasing temperature. These compounds exhibited two characteristic emission peaks in acetonitrile solution and the solid state when excited at _ex = 366 nm, which are attributed to transitions from ⁴F_9/2 to ⁶H_15/2 and ⁴F_9/2 to ⁶H_13/2. The emission intensities of these compounds were found to be very sensitive to the phase.

Full text of DOI:10.1021/acs.jpca.5b01180

Article
pubs.acs.org/JPCA
Spectral and Physicochemical Characterization of Dysprosium-Based
Multifunctional Ionic Liquid Crystals
Chengfei Lu, Susmita Das, Noureen Siraj, Paul K. S. Magut, Min Li, and Isiah M. Warner*
Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803, United States
S
* Supporting Information
ABSTRACT: We report on the synthesis and characterization of
multifunctional ionic liquid crystals (melting points below 100
°C) which possess chirality and fluorescent behavior as well as
mesomorphic and magnetic properties. In this regard, (1R,2S)-
(−)-N-methylephedrine ((−)MeEph), containing a chiral center,
is linked with variable alkyl chain lengths (e.g., 14, 16, and 18
carbons) to yield liquid crystalline properties in the cations of
these compounds. A complex counteranion consisting of trivalent
dysprosium (Dy3+) and thiocyanate ligand (SCN−) is employed,
where Dy3+ provides fluorescent and magnetic properties.
Examination of differential scanning calorimetry (DSC) and
hot-stage polarizing optical microscopy (POM) data confirmed
liquid crystalline characteristics in these materials. We further
report on phase transitions from solid to liquid crystal states,
followed by isotropic liquid states with increasing temperature. These compounds exhibited two characteristic emission peaks in
acetonitrile solution and the solid state when excited at λex = 366 nm, which are attributed to transitions from 4F9/2 to 6H15/2 and
6
4F9/2 to H13/2. The emission intensities of these compounds were found to be very sensitive to the phase.
thermotropic mesophases, they have the potential to offer
increased selectivity for asymmetric synthesis and stereo-
selective polymerization due to their abilities to order
reactants.18−21
INTRODUCTION
■
Ionic liquid crystals (ILCs) are a class of liquid-crystalline
compounds that contain ions (anions and cations) and possess
the collective characteristics of ionic liquids (ILs) as well as
liquid crystals.1 Thus, these compounds have the properties of
ionic liquids, such as low volatility, nonflammability, high ionic
conductivity, and large electrochemical windows, which differ-
entiates them from conventional organic liquid crystals.
Similarly, the basic properties of liquid crystals, e.g. as ordered
molecular arrangement, make these ILCs highly structured
solvents and birefringence. Because of their unique properties,
ILCs have been investigated for multiple applications, including
as electrolytes for solar cells,2 anisotropic ion conductors,3−5
templating agents for the synthesis of inorganic nanostruc-
tures,6 and as organized reaction media.7−10
Over the past few decades, intense research has been
conducted to incorporate functional groups either into the
anion or the cation of ILs in order to develop multifunctional
materials.11−16 Multifunctional ILCs which integrate chiral,
magnetic, and luminescence functionalities as well as inherent
properties of ILCs into single ion pairs provide advantages that
reach beyond the sum of the individual properties. Chirality is
an important feature for functionalization of ILCs.17 Much
effort has been concentrated into developing asymmetric
synthesis and catalysis using chiral ionic liquids as solvents,
and preliminary results suggest that chiral ionic liquids are
promising reaction media for chiral discrimination.7−10 In
addition, if chiral ionic liquids, which are used as solvents, show
Several advantages of metal-containing ILCs have been
widely explored as multifunctional materials due to a
combination of the mesomorphic behavior and unique
properties of metal ions redox activity, magnetism, and
luminescence.22−26 Functional materials with optoelectronic
characteristics can be developed by introducing lanthanide ions
into ILCs.13,27 These metal containing ILCs provide distinct
advantages of simple design and synthesis for π-conjugated
molecular crystals. One application of these lanthanide ion
containing ILCs is that polarized light can be produced to
merge the luminescence characteristic of metal ions and the
anisotropic feature of these compounds. By exploiting the high
magnetic anisotropy of the lanthanide ion in ILCs, alignment of
the mesophase in an external magnetic field can be achieved.
Such compounds provide potential applications as electric and
magnetic switchable device.13
To the best of our knowledge, multifunctional ILCs that
possess chirality, luminescence, paramagnetism, and meso-
phases in a single compound have not yet to be reported in the
literature. The compound (1R,2S)-(−)-N-methylephedrine
Received: February 4, 2015
Revised: April 20, 2015
Published: April 22, 2015
© 2015 American Chemical Society
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Scheme 1. Synthesis of Multifunctional Ionic Liquid Crystals
((−)MeEph) is a natural chiral resource which is used as the
starting material for syntheses of the multifunctional metal
containing ILCs described herein. In this study, (−)MeEph-
dysprosium-based multifunctional ionic liquid crystals
(MFILCs) consisting of chiral cations and metal-containing
anions were synthesized and characterized. The thermal and
photophysical properties of these compounds were also
investigated in detail. Evaluation of the properties measured
in this study suggests potential applications of these materials as
organized reaction media and temperature sensors.
mL of cold dichloromethane (DCM), and the solution was
kept in a refrigerator for 24 h in order to precipitate the excess
KSCN. After filtration of the excess KSCN, the solvent was
evaporated and the product, [(−)MeEphCnH2n+1] [SCN] (n =
14, 16, 18), was dried under vacuum for 48 h. In the third step,
Dy(ClO4)3·6H2O was prepared by dissolving Dy2O3 in a 70%
HClO4 aqueous solution, with subsequent removal of water by
use of lyophilization. A mixture of [(−)MeEphCnH2n+1] [SCN]
(n = 14, 16, 18) (5 equiv), KSCN (3 equiv), and Dy(ClO4)3·
6H2O (1 equiv) was stirred in anhydrous ethanol at room
temperature for 24 h. The byproduct (KClO4) was removed by
filtration, and the final products, [(−)MeEphCnH2n+1]5[Dy-
(SCN)8] (n = 14, 16, 18), were purified and collected
employing the method described above.
EXPERIMENTAL SECTION
■
Materials. The compounds (1R,2S)-(−)-N-methylephe-
drine, (1S,2R)-(+)-N-methylephedrine, 1-bromotetradecane,
1-bromohexadecane, 1-bromooctadecane, potassium thiocya-
nate, dysprosium(III) oxide, and perchloric acid (70%) were
obtained from Sigma-Aldrich (Milwaukee, WI) and used
without further purification. Ethanol, methanol, acetonitrile,
chloroform, and dichloromethane were of anhydrous grade
(Sigma-Aldrich, Milwaukee, WI), and all other solvents such as
acetone, hexane, and water were of HPLC grade (J.T. Baker,
Phillipsburg, NJ).
1
Instruments and Methods. The H NMR (400 MHz)
spectra were acquired by use of a Bruker Avance 400 NMR
1
spectrometer. The H chemical shifts are given in parts per
million (δ) with TMS as an internal standard. Mass spectra
were collected using an Agilent 6210 electrospray time-of-flight
mass spectrometer using both positive and negative ion mode.
FT-IR spectra were obtained by use of a Bruker Alpha FT-IR
spectrometer. Samples were analyzed in pure form using a
Platinum ATR apparatus. Elemental analyses were contracted
to Atlantic Microlab (Atlanta, GA). Luminescence spectra were
recorded at temperatures ranging from 25 to 100 °C using a
Spex Fluorolog-3 spectrofluorometer (model FL3-22TAU3;
Jobin Yvon, Edison, NJ) equipped with a 450 W xenon lamp
and R928P photomultiplier tube (PMT) emission detector. All
CD measurements were obtained by analyzing 1 mM
methanolic solutions at room temperature in 4 mm quartz
cuvettes on a Jasco-815 CD spectrometer. Magnetic properties
were measured using approximately 80−100 mg of sample in a
Quantum Design Superconducting Quantum Interference
Device (SQUID) magnetometer (San Diego, CA) at temper-
atures between 2 and 300 K and magnetic fields between
−70 000 and 70 000 Oe.Thermal properties of MFILCs were
investigated using a DSC Q 100 differential calorimeter (TA
Instruments, USA) by cooling 5−10 mg of MFILCs to −20 °C
and subsequently heating at a rate of 5 °C/min to 150 °C.
Polarized optical microscopy (POM) was performed using an
Olympus BH polarizing optical microscope with a hot stage
and MD 1900 camera. Samples for POM were prepared by
redissolving the MFILCs in DCM and ethanol and coating the
solution on the surface of glass slides using spin-coating. Images
were acquired at temperatures ranging from 25 to 100 °C. The
samples were incubated for 30 min to allow the mesophase to
equilibrate before acquiring images.
Material Synthesis. A facile three-step synthesis procedure
was used to prepare (1R,2S)-(−)-N-methylephedrine-dyspro-
sium-based MFILCs. In the first step, (1R,2S)-(−)-N-
methylephedrine ((−)MeEph) (1500 mg, 8.37 mmol) was
dissolved in dry ethanol. A 1.1 mol equiv of 1-bromote-
tradecane or 1-bromohexadecane or 1-bromooctadecane as
needed was dissolved separately in dry ethanol. The two
solutions were mixed and the reaction mixture was refluxed for
2 days at 90 °C under an argon atmosphere. After cooling to
room temperature, the majority of the solvent was removed by
use of a rotary evaporator. Upon addition of the concentrated
ethanol solution to cold diethyl ether, the product [(−)-
MeEphCnH2n+1][Br] (n = 14, 16, 18) precipitated as a white
powder. The product was then filtered, washed two times using
diethyl ether, and then dried under vacuum. In the second step,
three methylephedrin-dysprosium compounds were synthe-
sized according to a previously described procedure. The
compounds [(−)MeEphCnH2n+1][Br] (n = 14, 16, 18) and 2
mol equiv of potassium thiocyanate (KSCN) were dissolved
separately in dry acetonitrile. The two solutions were then
mixed, and the reaction mixture was stirred for 2 days. The
compound KBr, the reaction byproduct, formed as a white
precipitate and was removed by filtration. Acetonitrile was
removed by use of a rotary evaporator. To further purify the
compounds produced, the resulting solid was redissolved in 30
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CD spectra of [(−)MeEph C16H33]5 [Dy(SCN)8], and
[(+)MeEph C16H33]5 [Dy(SCN)8] are presented in Figure 1.
Three bands were observed at 255, 261, and 267 nm for both
compounds, while positive and negative signals were
represented by [(−)MeEph C16H33]5 [Dy(SCN)8] and
[(+)MeEph C16H33]5 [Dy(SCN)8], respectively. Evaluation of
these results demonstrates that the MFILCs isomers retain
chiroptical properties and exhibit an extremely precise mirror
image relationship after structural modification.
RESULTS AND DISCUSSION
■
Synthesis of Multifunctional Ionic Liquid Crystals.
(1R,2S)-(−)-Methylephedrine ((−)MeEph) were alkylated
Luminescence Spectroscopy of Multifunctional Ionic
Liquid Crystals. The emission spectra of these MFILCs were
recorded at an excitation wavelength of 366 nm both in the
solid state and in acetonitrile solution. Solid samples were
prepared by spin-coating (3000 rmp) an ethanolic solution of
MFILCs onto glass slides and then allowed to dry under
vacuum overnight. Trivalent dysprosium, Dy3+, with a 4f9
electron configuration, has been found to be fluorescent in
the blue and yellow-orange regions of the electromagnetic
Figure 1. Circular dichroism spectra of [(−)MeEph C16H33]5
[Dy(SCN)8] (black) and [(+)MeEph C16H33]5 [Dy(SCN)8] (red)
in ethanol.
4
6
4
6
spectrum due to respective F9/2 to H15/2 and F9/2 to H13/2
transitions.13 As depicted in Figure 2, two characteristic
emission peaks were observed in both solution and solid states
for all three MFILCs of variable alkyl chain length. The
intensity and relative intensities of these two emission peaks,
however, are quite different in solution and in solid states. This
suggests that transitions are hypersensitive to the environment.
The relative orders of emission intensity for these MFILCs in
acetonitrile solution were [(−)MeEph C14H29]5 [Dy(SCN)8] >
[(−)MeEph C16H33]5 [Dy(SCN)8] > [(−)MeEph C18H37]5
[Dy(SCN)8]. In contrast, the emission intensity of the MFILCs
using n-alkyl bromides containing 14, 16, and 18 carbons to
obtain cations with chiral centers. The metal containing
MFILCs were obtained via an anion exchange reaction,
followed by an addition reaction with the above (−)MeEph-
based salts. In the first anion exchange, the reaction was
performed to replace the Br− ion with the SCN− ion. A second
step involved addition of the metal and formation of a SCN−
anion complex, resulting in a dysprosium−thiocyanate complex
anion. Synthesis of the MFILCs is outlined in Scheme 1.
Chiroptical Activity of Multifucntional Ionic Liquid
Crystals. Ephedrine possesses two chiral centers which give
rise to four stereoisomers.9,28 The enantiomers with opposite
stereochemistry around the chiral centers (1R,2S-(−) and
1S,2R-(+)) are named ephedrine, while the enantiomers with
the same stereochemistry around the chiral carbons (1R,2R and
1S,2S) are designated pseudoephedrine. In this study, only
(1R,2S)-(−)-methylephedrine was used for structural mod-
ification and production of MFILCs used in this study. To
investigate the chiral properties of MFILCs, the enantiomer of
[(−)MeEph C16H33]5 [Dy(SCN)8] and [(+)MeEph C16H33]5
[Dy(SCN)8] were synthesized to perform circular dichroism
studies using (1R,2S)-(−)-methylephedrine and (1S,2R)-(+)-
methylephedrine as starting materials. The same protocol as
described earlier for [(−)MeEph C16H33]5 [Dy(SCN)8] was
used for synthesis of [(+)MeEph C16H33]5 [Dy(SCN)8]. The
4
6
films showed a reverse order. The transition F9/2 to H13/2 at
573 nm is the most intense peak for all compounds in
acetonitrile, which is in agreement with previous studies.15 It is
well established that the 4f−4f transitions are parity forbidden.
The excitation of Dy (III) at 366 nm is due to the existence of
(−)MeEph-based cation which serves as an antenna for energy
transfer to Dy3+.15 The forbidden 4f−4f transitions also result
in long-lived excited states and consequently a reduction in
photobleaching.
Magnetic Properties of Multifunctional Ionic Liquid
Crystals. In addition to luminescence arising from the 4f9
electron configuration, the Dy3+ ion is also magnetically active.
As a result, the MFILCs exhibited paramagnetic behavior at
room temperature. These magnetic susceptibilities were
measured by use of a superconducting quantum interference
device (SQUID) magnetometer. The magnetic property of
Figure 2. Emission spectra with transition assignments of [(−)MeEph C14H29]5 [Dy(SCN)8] (red), [(−)MeEphC16H33]5 [Dy(SCN)8](blue), and
[(−)MeEph C18H37]5 [Dy(SCN)8](black) in acetonitrile solution (a) and at solid state (b) under excitation at λex = 366 nm.
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Figure 3. Magnetic property of [(−)MeEphC16H33]5[Dy(SCN)8]. Temperature dependence of the static molar susceptibility (a) and reciprocal
molar susceptibility (b) at a field of 10 000 Oe. Temperature dependence of the product of the temperature and the static molar susceptibility (c)
and the effective magnetic moment (d) at a field of 10 000 Oe.
Figure 5. DSC traces observed on heating of [(−)MeEph C18H37]5
[Dy(SCN)8] prepared with DCM (in blue) and ethanol (in black)
(closed aluminum pan, heating rate 5 °C/min; S−LC: solid to liquid
crystalline transition; LC−I: liquid crystalline to isotropic liquid
transition).
Figure 4. DSC traces observed on heating of [(−)MeEph C16H33]5
[Dy(SCN)8] prepared with DCM (in blue) and ethanol (in black)
(closed aluminum pan, heating rate 5 °C/min; S−LC: solid to liquid
crystalline transition; LC−I: liquid crystalline to isotropic liquid
transition).
were 10.5 and 10.3 μB, which are very close to the calculated
value.29 Because of the large anisotropic magnetic moment of
Dy3+ in ionic liquid crystals, these MFILCs can be manipulated
in an external magnetic field. Therefore, these MFILCs are
expected to align in the direction of an applied external
magnetic field. Paramagnetic properties of [(−)MeEph
C18H37]5 [Dy(SCN)8] are listed in the Supporting Information.
Thermal Properties of Multifunctional Ionic Liquid
Crystals. Thermal properties of all compounds were examined
using differential scanning calorimetry (DSC) and polarizing
optical microscopy (POM). Two different solvents, i.e.
dichloromethane (DCM) and ethanol, were independently
used to recrystallize MFILCs. The MFILCs were dissolved in a
solvent, followed by drying in a vacuum desiccator prior to
[(−)MeEph C16H33]5 [Dy(SCN)8] is summarized in Figure 3.
Examination of Figure 3 clearly shows a decrease in static molar
magnetic susceptibility with increasing temperature in a plot of
χmol against temperature (K). This observation suggests that
[(−)MeEphC16H33]5 [Dy(SCN)8] is paramagnetic (Figure 3a).
The respective molar magnetic susceptibilities of [(−)MeEph
C16H33]5 [Dy(SCN)8] and [(−)MeEph C18H37]5 [Dy(SCN)8]
at 300 K were obtained as χmol = 0.046 and 0.044 emu mol−1,
all of which fit well with the expected value for Dy3+.29 The
effective magnetic moment (μeff) for Dy3+ has been calculated
as 10.48 μB. The measured respective μeff values of [(−)MeEph
C16H33]5 [Dy(SCN)8] and [(−)MeEph C18H37]5 [Dy(SCN)8]
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Figure 6. Micrographs of the textures observed by POM (200× magnification). Textures of [(−)MeEphC16H33]5 [Dy(SCN)8] ethanol sample at 70
°C (a) and DCM sample at 60 °C (b), second heating at 75 °C (c); [(−)MeEphC18H37]5 [Dy(SCN)8] ethanol sample at 95 °C (d) and DCM
sample at 85 °C (e), second heating at 70 °C (f), and second heating at 90 °C (g).
analyses (for convenience, we called these samples DCM
sample or ethanol sample). Interestingly, we observed that the
thermal properties of these compounds are impacted by the
solvent used for recrystallization. The thermal properties of
[(−)MeEphC14H29]5 [Dy(SCN)8] will not be discussed since it
did not exhibit a mesophase upon heating, likely due its short
alkyl chain. The DSC thermograms of [(−)-
MeEphC18H37]5[Dy(SCN)8] and [(−)MeEphC16H33]5[Dy-
(SCN)8] are respectively shown in Figures 4 and 5. Only the
first DSC heating traces are displayed since the phase transition
could not be detected by use of DSC in the cooling trace and
second scan. In the DCM samples for both [(−)MeEph
C18H37]5 [Dy(SCN)8] and [(−)MeEph C16H33]5 [Dy(SCN)8],
an additional peak was observed prior to the solid-to-
mesophase transition peak. This additional peak is likely due
to desolvation of trace DCM that remains in the compounds.
The [(−)MeEph C16H33]5 [Dy(SCN)8] DCM sample
displayed a mesophase range from 41.9 to 66.9 °C, while the
ethanol sample displayed a mesophase range from 44.1 to 74.9
°C. The [(−)MeEph C18H37]5 [Dy(SCN)8] DCM sample
showed a much lower crystalline solid to liquid crystalline
transition temperature than that of the ethanol sample. The
transition of liquid crystalline to isotropic liquid for the DCM
sample was observed at 85.6 °C. However, the phase transition
of the ethanol sample could not be detected by use of DSC.
A POM investigation was performed in order to examine
alterations of anisotropic behavior upon heating of [(−)MeEph
C18H37]5 [Dy(SCN)8] and [(−)MeEph C16H33]5 [Dy(SCN)8].
Microscopy images of the textures of these compounds are
shown in Figure 6. For both compounds, the ethanol samples
exhibited a nematic phase, while the DCM samples displayed a
typical fan-shaped texture of an SmA phase. Examination of
POM data for [(−)MeEph C16H33]5 [Dy(SCN)8] confirmed
that the optical data agreed well with DSC data. In addition to
confirming the DSC studies, POM examination also provided
further information which could not be detected by use of
DSC. A POM investigation of [(−)MeEph C18H37]5 [Dy-
(SCN)8] indicated that the liquid crystalline to isotropic liquid
transition occurs at 98 °C, regardless of the recrystalline
method. Furthermore, although no thermal events were
observed during the cooling and second heating process by
use of DSC, the POM investigations revealed mesophases
during the second heating for these MFILCs (Figure 6).
Phase-Dependent Luminescence Intensity of Multi-
functional Ionic Liquid Crystals. In order to investigate the
influence of phase transitions on luminescence, two emission
transitions (4F9/2 to H15/2 and from F9/2 to H13/2) were
recorded over a wide range of temperatures (20−100 °C).
Figure 7 shows changes in 4F9/2 to 6H15/2 emission intensities of
[(−)MeEphC16H33]5 [Dy(SCN)8] and [(−)MeEph-
C18H37]5[Dy(SCN)8] as a function of temperature. Based on
DSC studies and optical data, the temperature-dependent
luminescence intensity changes were divided into three regions:
(i) solid crystalline state, (ii) liquid crystalline state, and (iii)
isotropic liquid state. All samples exhibited enhanced
luminescence intensity upon second heating in the liquid
crystalline state except [(−)MeEphC16H33]5[Dy(SCN)8]. It
was observed that [(−)MeEphC16H33]5[Dy(SCN)8] and
[(−)MeEphC18H37]5[Dy(SCN)8] DCM samples showed a
sharp decrease in luminescence intensity in the solid state
with increasing temperature due to the presence of trace DCM
remaining in samples, as previously noted. In the liquid
crystalline state, the luminescence intensity displayed a linear
increase with increasing temperature until a full liquid crystal
state was achieved. Interestingly, [(−)MeEphC18H37]5[Dy-
(SCN)8] exhibited two luminescence intensity increases in
the liquid crystalline state during the second heating. This was
because the sample first formed fan-shaped SmA phase and
then formed a nematic phase with increasing temperature. As
the temperature increased, a dramatic decrease in luminescence
intensity was observed at the liquid crystalline to isotropic
liquid transition. Typically, these MFILCs in isotropic liquid
state are nonfluorescent; this may be due to a hindrance of
energy transfer as a result of increased distance between the
cations and the anions in the liquid state. Because of a specific
linear response range with temperature and dramatically
enhanced luminescence intensity in the liquid crystalline
state, we believe that these MFILCs are potential candidates
6
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4
6
Figure 7. Temperature-dependent luminescence intensity from F9/2 to H15/2 transition (blue light emission, excitation at 366 nm) of
[(−)EphC16H33]5 [Dy(SCN)8] ethanol sample (a); DCM sample (b); second heating (c); as well as of [(−)EphC18H37]5[Dy(SCN)8] ethanol
sample (d); DCM sample (e) and second heating (f).
for use in construction of sensitive chemosensors or
optoelectronic devices.
liquid crystalline state and dramatically decreased luminescence
in the isotropic liquid state. Based on these unique properties,
these compounds or similar compounds can be potentially
useful for preparation of optical devices.
CONCLUSIONS
■
We have synthesized and characterized a group of novel
MFILCs which incorporate luminescence, chirality, para-
magnetism, and mesophase into a single ion pair. These
MFILCs retain the chirality of the starting material and may be
used as reaction media for synthesis of chiroptically active
compounds in combination with liquid crystalline and magnetic
properties. These compounds show structure and solvent
dependent liquid crystalline mesophases below 100 °C and in
turn show phase-dependent luminescence intensities. Append-
ing longer alkyl chains lead to easier formation of mesophase
textures but reduce the mesophase window. Use of DCM for
recrystallization of these compounds results in SmA mesophase,
while the use of ethanol induces nematic mesophases. Both
compounds exhibit enhanced luminescence intensity in the
ASSOCIATED CONTENT
■
S
* Supporting Information
Characterization results; more optical and magnetic properties
of multifunctional ionic liquid crystals. The Supporting
Information is available free of charge on the ACS Publications
website at DOI: 10.1021/acs.jpca.5b01180.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail iwarner@lsu.edu; Ph 1-225-578-2829 (I.M.W.).
Notes
The authors declare no competing financial interest.
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(20) Van Buu, O. N.; Aupoix, A.; Vo-Thanh, G. Synthesis of Novel
Chiral Imidazolium-Based Ionic Liquids Derived from Isosorbide and
Their Applications in Asymmetric Aza Diels−Alder Reaction.
Tetrahedron 2009, 65, 2260−2265.
ACKNOWLEDGMENTS
■
This material is based upon work supported by the National
Science Foundation under Grant CHE-1307611.
(21) Wang, Z.; Wang, Q.; Zhang, Y.; Bao, W. Synthesis of New
Chiral Ionic Liquids from Natural Acids and Their Applications in
Enantioselective Michael Addition. Tetrahedron Lett. 2005, 46, 4657−
4660.
REFERENCES
■
(1) Binnemans, K. Ionic Liquid Crystals. Chem. Rev. 2005, 105,
4148−204.
(22) Prodius, D.; Macaev, F.; Lan, Y.; Novitchi, G.; Pogrebnoi, S.;
Stingaci, E.; Mereacre, V.; Anson, C. E.; Powell, A. K. Evidence of Slow
Relaxation of Magnetization in Dysprosium-Based Ionic Liquids.
Chem. Commun. 2013, 49, 9215−9217.
(2) Chi, W. S.; Jeon, H.; Kim, S. J.; Kim, D. J.; Kim, J. H. Ionic Liquid
Crystals: Synthesis, Structure and Applications to I2-Free Solid-State
Dye-Sensitized Solar Cells. Macromol. Res. 2013, 21, 315−320.
(3) Abate, A.; Petrozza, A.; Cavallo, G.; Lanzani, G.; Matteucci, F.;
Bruce, D. W.; Houbenov, N.; Metrangolo, P.; Resnati, G. Anisotropic
Ionic Conductivity in Fluorinated Ionic Liquid Crystals Suitable for
Optoelectronic Applications. J. Mater. Chem. A 2013, 1, 6572−6578.
(4) Kato, T. Self-Assembly of Phase-Segregated Liquid Crystal
Structures. Science 2002, 295, 2414−2418.
(23) Lee, C. K.; Peng, H. H.; Lin, I. J. Liquid Crystals of N,N′-
Dialkylimidazolium Salts Comprising Palladium(II) and Copper(II)
Ions. Chem. Mater. 2004, 16, 530−536.
(24) Lin, I. J.; Vasam, C. S. Metal-Containing Ionic Liquids and Ionic
Liquid Crystals Based on Imidazolium Moiety. J. Organomet. Chem.
2005, 690, 3498−3512.
(5) Sasi, R.; Rao, T. P.; Devaki, S. J. Bio-Based Ionic Liquid
Crystalline Quaternary Ammonium Salts: Properties and Applications.
ACS Appl. Mater. Interfaces 2014, 6, 4126−4133.
(25) Neve, F. Transition Metal Based Ionic Mesogens. Adv. Mater.
1996, 8, 277−289.
(26) Nockemann, P.; Thijs, B.; Postelmans, N.; Van Hecke, K.; Van
Meervelt, L.; Binnemans, K. Anionic Rare-Earth Thiocyanate
Complexes as Building Blocks for Low-Melting Metal-Containing
Ionic Liquids. J. Am. Chem. Soc. 2006, 128, 13658−13659.
(27) Tang, S.; Babai, A.; Mudring, A.-V. Europium-Based Ionic
Liquids as Luminescent Soft Materials. Angew. Chem., Int. Ed. 2008, 47,
7631−7634.
(6) Taubert, A. CuCl Nanoplatelets from an Ionic Liquid-Crystal
Precursor. Angew. Chem. 2004, 116, 5494−5496.
́
(7) Pastre, J. C.; Genisson, Y.; Saffon, N.; Dandurand, J.; Correia, C.
R. Synthesis of Novel Room Temperature Chiral Ionic Liquids:
Application as Reaction Media for the Heck Arylation of Aza-
Endocyclic Acrylates. J. Braz. Chem. Soc. 2010, 21, 821−836.
(8) Prechtl, M. H.; Scholten, J. D.; Neto, B. A.; Dupont, J.
Application of Chiral Ionic Liquids for Asymmetric Induction in
Catalysis. Curr. Org. Chem. 2009, 13, 1259−1277.
(28) Thanh, G. V.; Pegot, B.; Loupy, A. Solvent-Free Microwave-
Assisted Preparation of Chiral Ionic Liquids from (−)-N-Methylephe-
drine. Eur. J. Org. Chem. 2004, 2004, 1112−1116.
(29) Mallick, B.; Balke, B.; Felser, C.; Mudring, A. V. Dysprosium
Room-Temperature Ionic Liquids with Strong Luminescence and
Response to Magnetic Fields. Angew. Chem., Int. Ed. 2008, 47, 7635−
7638.
(9) Truong, T.-K.-T.; Nguyen Van Buu, O.; Aupoix, A.; Pegot, B.;
Vo-Thanh, G. Chiral Ionic Liquids Derived from (−)-Ephedrine and
Carbohydrates: Synthesis, Properties and Applications to Asymmetric
Synthesis and Catalysis. Curr. Org. Synth. 2012, 9, 53−64.
(10) Wang, W.-H.; Wang, X.-B.; Kodama, K.; Hirose, T.; Zhang, G.-
Y. Novel Chiral Ammonium Ionic Liquids as Efficient Organocatalysts
for Asymmetric Michael Addition of Aldehydes to Nitroolefins.
Tetrahedron 2010, 66, 4970−4976.
(11) Zhao, Y.; He, L.; Tang, N.; Qin, S.; Tao, G. H.; Liang, F. X.,
Structures and Properties of Luminescent Pentanitratoeuropate (Iii)
Ionic Liquids. Eur. J. Inorg. Chem. 2014.
́
(12) Baudequin, C.; Bregeon, D.; Levillain, J.; Guillen, F.;
Plaquevent, J.-C.; Gaumont, A.-C. Chiral Ionic Liquids, a Renewal
for the Chemistry of Chiral Solvents? Design, Synthesis and
Applications for Chiral Recognition and Asymmetric Synthesis.
Tetrahedron: Asymmetry 2005, 16, 3921−3945.
(13) Getsis, A.; Balke, B.; Felser, C.; Mudring, A.-V. Dysprosium-
Based Ionic Liquid Crystals: Thermal, Structural, Photo-and Magneto-
physical Properties. Cryst. Growth Des. 2009, 9, 4429−4437.
(14) Li, M.; De Rooy, S. L.; Bwambok, D. K.; El-Zahab, B.; DiTusa, J.
F.; Warner, I. M. Magnetic Chiral Ionic Liquids Derived from Amino
Acids. Chem. Commun. 2009, 6922−6924.
(15) Li, M.; Ganea, G. M.; Lu, C.; De Rooy, S. L.; El-Zahab, B.;
Fernand, V. E.; Jin, R.; Aggarwal, S.; Warner, I. M. Lipophilic
Phosphonium−Lanthanide Compounds with Magnetic, Luminescent,
and Tumor Targeting Properties. J. Inorg. Biochem. 2012, 107, 40−46.
(16) Uchida, Y.; Oki, S.; Tamura, R.; Sakaguchi, T.; Suzuki, K.;
Ishibashi, K.; Yamauchi, J. Electric, Electrochemical and Magnetic
Properties of Novel Ionic Liquid Nitroxides, and Their Use as an EPR
Spin Probe. J. Mater. Chem. 2009, 19, 6877−6881.
(17) Payagala, T.; Armstrong, D. W. Chiral Ionic Liquids: A
Compendium of Syntheses and Applications (2005−2012). Chirality
2012, 24, 17−53.
́
(18) Pegot, B.; Vo-Thanh, G.; Gori, D.; Loupy, A. First Application
of Chiral Ionic Liquids in Asymmetric Baylis−Hillman Reaction.
Tetrahedron Lett. 2004, 45, 6425−6428.
(19) Van Buu, O. N.; Aupoix, A.; Hong, N. D. T.; Vo-Thanh, G.
Chiral Ionic Liquids Derived from Isosorbide: Synthesis, Properties
and Applications in Asymmetric Synthesis. New J. Chem. 2009, 33,
2060−2072.
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DOI: 10.1021/acs.jpca.5b01180
J. Phys. Chem. A 2015, 119, 4780−4786