Ultrafast dynamics in nonaromatic cation based ionic liquids: A femtosecond raman-induced kerr effect spectroscopic study

Article abstract of DOI:10.1246/BCSJ.20200198

Herein, the data of the intermolecular vibrations of forty nonaromatic cation based ionic liquids (ILs) at 293 K measured by femtosecond Raman-induced Kerr effect spectroscopy are reported. The low-frequency spectra in the frequency range of 0.3700 cm¹¹ were obtained by Fourier transform deconvolution analysis. The line shapes of the low-frequency spectra below ³200 cm¹¹ were discussed on the basis of the ion species. The spectral intensity in nonaromatic cation based ILs was much lower than that in aromatic cation based ILs owing to the absence of the aromatic ring, i.e., the libration of the aromatic species had a strong spectral intensity in the low-frequency region. However, nonaromatic cation based ILs with a flat anion, such as dicyanamide and tricyanomethanide, showed stronger spectral intensity because of the libration of the anion. Other unique spectral features were also discussed in the context of the structure of the ion species. Liquid properties, such as density, viscosity, electrical conductivity, and surface tension, were also estimated. On comparing the low-frequency spectra with the bulk liquid properties of the nonaromatic cation based ILs, a mild linear relationship between the first moment of the low-frequency spectrum and a bulk parameter comprised of surface tension and density was observed.

Full text of DOI:10.1246/BCSJ.20200198

Advance Publication Cover Page
Ultrafast Dynamics in Nonaromatic Cation Based Ionic Liquids:
A Femtosecond Raman-Induced Kerr Effect Spectroscopic Study
Hideaki Shirota,* Masatoshi Ando, Shohei Kakinuma, and Kotaro Takahashi
Advance Publication on the web July 28, 2020
doi:10.1246/bcsj.20200198
©
2020 The Chemical Society of Japan
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Publication manuscripts.

Ultrafast Dynamics in Nonaromatic Cation Based Ionic Liquids:
A Femtosecond Raman-Induced Kerr Effect Spectroscopic Study
Hideaki Shirota,* Masatoshi Ando, Shohei Kakinuma, and Kotaro Takahashi
Department of Chemistry, Chiba University, 1-33 Yayoi, Inage-ku, Chiba 263-8522
E-mail: shirota@faculty.chiba-u.jp
Abstract
Herein, the data of the intermolecular vibrations of forty
frequency domain spectroscopies, such as steady-state Raman
and far-infrared (far-IR) spectroscopies. In particular, fs-RIKES
can even be used to observe orientational dynamics in liquids
and solutions. By virtue of these advantageous attributes,
fs-RIKES has often been used to study the intermolecular
vibrational and orientational dynamics in liquids and
nonaromatic cation based ionic liquids (ILs) at 293 K measured
by femtosecond Raman-induced Kerr effect spectroscopy are
reported. The low-frequency spectra in the frequency range of
-1
0
.3–700 cm
were obtained by Fourier transform
7
-13
14-16
deconvolution analysis. The line shape of the low-frequency
solutions, as well as complex systems.
Ionic liquids (ILs), the target material in this study, are
-1
spectra below ~200 cm were discussed on the basis of the ion
species. The spectral intensity in nonaromatic cation based ILs
was much lower than that in aromatic cation based ILs owing
to the absence of the aromatic ring, i.e., the libration of the
aromatic species had a strong spectral intensity in the
low-frequency region. However, nonaromatic cation based ILs
with a flat anion, such as dicyanamide and tricyanomethide,
showed stronger spectral intensity because of the libration of
the anion. Other unique spectral features were also discussed in
the context of the structure of the ion species. Liquid properties,
such as density, viscosity, electrical conductivity, and surface
tension, were also estimated. On comparing the low-frequency
spectra with the bulk liquid properties of the nonaromatic
cation based ILs, a mild linear relationship between the first
moment of the low-frequency spectra and a bulk parameter
comprised of surface tension and density was observed.
1
7,18
molten salts at room temperature.
They exhibit unique
properties, such as a low melting point (for salts), non-volatility
at ambient temperature and pressure conditions (for liquids),
high electrical conductivity, viscous behavior, glass-forming
1
9,20
nature, inhomogeneous structure, and so on.
The molecular
and reaction dynamics and photochemistry in ILs often shows
characteristic behavior in comparison with common (neutral)
2
1-25
solvents.
The unique features in ILs are mainly attributed to
the amphiphilic nature of the cation in most cases, which forms
complicated microscopic structures and engages in
2
6-29
intermolecular interactions.
Accordingly, it is important to
study the intermolecular vibrations in ILs to understand the
molecular-level aspects of ILs, because the intermolecular
vibration directly reflects on the microscopic structure and
intermolecular interactions. To date, the intermolecular
vibrations in ILs have been studied by time- and
3
0-36
Keywords: Nonaromatic Cation Based Ionic Liquids,
Low-Frequency Spectrum, femtosecond Raman
Induced Kerr Effect Spectroscopy
frequency-domain Raman and IR spectroscopies.
In
particular, fs-RIKES has been extensively used to study
3
7-45
46-55
ILs,
solvents, because the detection frequency range of fs-RIKES
approximately 0.3–700 cm-1 in our setup) is sufficiently wide
in the frequency range for studying the intermolecular
IL mixtures,
and IL-related deep eutectic
5
6
(
1
. Introduction
5
7,58
Intermolecular vibrational dynamics in liquids and
solutions is a central theme in chemistry, physics, and biology,
because it significantly influences the elementary processes of
chemical reactions such as electron transfer, proton transfer,
and isomerization in solutions, the dynamics of structural
changes in biological systems, phase transition dynamics, and
vibrations of liquids, except for water.
However, as
previous studies focus on specific and topical themes, a
systematic overview of the intermolecular vibrations of ILs
based on a large number of samples is still needed.
In 2016, we have reported the spectral data of the
intermolecular vibrational dynamics of forty aromatic cation
based ILs, such as imidazolium- and pyridinium-based ILs,
1
,2
so on. Fortunately, the development of femtosecond laser
technology has made it possible to detect the time-domain data
of intermolecular vibrations in liquids and solutions directly.
Intermolecular vibrations, such as libration, collision- and
interaction-induced motions, in liquids and solutions occur on
the time scale ranging from subpicoseconds to picoseconds,
which corresponds to the terahertz region in the frequency
domain. Femtosecond Raman-induced Kerr effect spectroscopy
5
9
gathered using fs-RIKES. The unique features of the
low-frequency Kerr spectra of aromatic cation based ILs were
discussed based on the constituent ion species. Furthermore, a
linear relation between the first moment (M
1
) of the
low-frequency spectrum and the bulk parameter (square root of
1
/2
surface tension divided by density, (/) ) was discovered.
5
9
This study is a continuation of our previous work. The
intermolecular vibrational dynamics of forty nonaromatic
cation based ILs was investigated by fs-RIKES. The majority
of published reports on the intermolecular vibrations of ILs
study aromatic cation based ILs, and the number of the reports
(
(
(
fs-RIKES) and time-domain terahertz spectroscopy
THz-TDS) are especially suited for obtaining low-frequency
3
-6
or terahertz) spectra. The former technique captures the
polarizability response and the latter one observes the dipole
response. Further, these time-domain spectroscopic techniques
provide low-frequency spectra with a high signal to noise ratio
and in lower-frequency range in comparison with conventional
4
1,44,45,60-66
on nonaromatic cation based ILs is rather limited.
Therefore, the main objectives in this study are: (i) collecting
the intermolecular vibrational spectrum data of a substantial
1

number of nonaromatic cation based ILs, (ii) overviewing and
elucidating the unique spectral features of such ILs, and (iii)
examining the relationship between the intermolecular
vibrations and bulk properties. The data relating to the liquid
properties of the forty nonaromatic cation based ILs, such as
density , viscosity , electrical conductivity , and surface
tension , are also reported in this study.
resolution of 3072 points at 0.5 m/step that corresponds to
3.34 fs/step) were made for a short time window (~10.2 ps).
Measurements of longer time window transients (~334 ps) of
2000 points at 25.0 m/step that corresponds to 167 fs/step
were also made. A pure heterodyne signal was obtained by
recording the scans for both plus and minus ~1.5° rotations of
the input probe beam using a quarter wave plate; these signals
were then combined to eliminate the residual homodyne signal.
The rotations of the probe beam polarization using the quarter
wave plate were performed while monitoring the intensity of
the local oscillator. The numbers of scans for the short and long
time window transients were 3 and 5 in each polarization,
respectively. The ILs were injected into a 3 mm optical path
length quartz cell (Tosoh Quartz) through either a 0.2 m or
0.02 m pore size Anotop filter (Whatman). During the
fs-RIKES experiments, the samples were kept at a temperature
of 293.0 ± 0.2 K by a Peltier-based temperature controller
(Quantum Northwest, Luma 40).
2
. Experiments and Quantum Chemistry Calculations
While most ILs used in this study were obtained from
6
0,61,63,67
chemical companies, several ILs were synthesized
6
1,68-70
according to the protocols established in our laboratory.
The sample ILs studied here and their abbreviations, as well as
their sources, are listed in Table 1. Since the cation in
[
N
112Bz][NTf
2
] has an aromatic ring, the IL might not be very
suitable to treat as a “nonaromatic” cation based IL. But, we
tentatively categorize [N112Bz][NTf ] into nonaromatic cation
2
based IL in this study. This is because; the cation is an
ammonium cation whose charged moiety is not aromatic, and
Density functional theory (DFT) quantum chemistry
calculations based on the B3LYP/6-311+G(d,p) level of
1
/2
the plot of M vs. (/) for 1-benzyl-1-methylpyrrolidinium
1
7
3,74
bis(trifluoromethylsulfonyl)amide showed the relation for
theory
were performed for geometry optimizations of some
7
5
nonaromatic cation based ILs, not for aromatic cation based
cations and anions using the Gaussian 16 program. Normal
mode Raman spectra of some cations and anions were
calculated on the basis of their optimized structures. Using the
4
4
ILs. [Pyrr13][DCA] obtained from Iolitec was slightly yellow
in color, and was therefore purified by activated charcoal
treatment using acetonitrile as a solvent to be colorless. The
polarizability tensor elements ij of optimized ions, the mean
1
76
synthesized ILs were characterized by H NMR and elementary
polarizability 
0
was calculated using eq. (1)
analysis (SI2-1 of the Electronic Supporting Information). In
elementary analysis, the obtained values of carbon, hydrogen,
and nitrogen for the ILs agreed with their calculated values
within 0.4%. The details of the preparation methods and
analytical data of the synthesized ILs are summarized in the
Electronic Supporting Information (SI2-1). The sample ILs
were dried in a vacuum oven at 313 K for more than 36 h
before experiments.
The densities () of the ILs were measured at 293.0 ± 0.2
K with a densitometer (Anton Paar, DMA 4100 M). The
viscosities (η) of the ILs were determined using a reciprocating
electromagnetic piston viscometer (Cambridge Viscosity,
ViscoLab 4100) equipped with a circulating water bath
훼푥푥 + 훼푦푦 + 훼푧푧
훼0 =
(1)
3
and the polarizability anisotropy anis was calculated by,76
훼푎푛푖푠 = [{(훼푥푥 − 훼푦푦)2 + (훼 − 훼 ) + (훼 − 훼푥푥)2 +
2
푦푦
푧푧
푧푧
ꢀ훼푥푦2 + 훼푦푧2 + 훼푧푥2ꢁ}/ꢂ]1/2
6
(2)
The atom coordinates of the optimized geometries of cations
and anions are summarized in Tables S2-3 and S2-4 of the
Electronic Supporting Information.
(Yamato, BB300) at 293.0 ± 0.2 K. The electrical
conductivities () of the samples were measured by an
electrical conductivity meter (Mettler Toledo, S470
SevenExcellence) kept at 293.0 ± 0.2 K using a laboratory
assembled Peltier module temperature controller (VICS,
VPE35-5-20TS). The surface tensions () of the samples were
obtained using a contact angle meter (Kyowa Interface Science,
DMs-401) maintained at 293.0 ± 0.2 K by a circulating water
bath (EYELA, NBC-1210). When the measured values of the
liquid properties of the ILs differed significantly from the
reported values, the measurements were repeated to confirm the
obtained data. The water contents of the sample ILs were
estimated by Karl Fischer titrations using a coulometer
3
. Data Analysis
The time-domain data (Kerr transients) of the ILs
measured with fs-RIKES were analyzed on the basis of the
standard Fourier transform deconvolution analysis method
developed by McMorrow and Lotshaw
low-frequency spectra. The details of the Fourier transform
deconvolution analysis procedure followed in our laboratory
has already been reported elsewhere.
analytical method was exactly the same as in our previous
77,78
to obtain the
13,34
In this study, the
59
report on forty aromatic cation based ILs, for the sake of
consistency of the spectral data between the aromatic and
nonaromatic cation based ILs. For this reason, the analytical
procedure in this study has been described briefly.
Figure 1a shows the Kerr transient of [Pyrr13][DCA] from
.5 fs to 300 ps with the logarithmic scales. Figure 1b
illustrates the linear scale in the early time stage, with
magnification of the Kerr transient in the time range of –0.5–3
ps. The intensity of the Kerr transient was normalized for the
intensity at t = 0, which is because of the electronic response.
The Kerr transient from 3 to 300 ps was analyzed by a
triexponential function, ꢃ + ∑ ꢃ exp (−푡/휏 ), where a
(Hiranuma, AQ-300). The water content values of the ILs are
summarized in Table 2 (vide infra).
The details of the femtosecond optical heterodyne
detected (OHD) RIKES apparatus built in our laboratory have
3
1
3,71
been reported previously.
setup, the light source was a titanium sapphire laser (KMLabs,
Griffin) pumped by the second harmonic light of a Nd:YVO
In the current fs-OHD-RIKES
4
7
2
diode laser (Spectra Physics, Millennia Pro 5sJ). The output
power of the titanium sapphire laser was approximately 420
mW. The temporal response of the fs-RIKES setup was
measured using a 200 m thick KDP crystal (type I) as the
cross-correlation between the pump and probe pulses, and it
was typically approximately 38 fs (full-width at half-maximum,
FWHM). In the fs-RIKES experiments, scans with a high time
ꢄ
0
푖ꢅ1
푖
푖
0
is
i
are the amplitude and time
the offset parameter, and a
i
and 
constant of the i-th exponential component, respectively. The fit
is also given in Figure 1a. The triexponential fit parameters for
the present forty nonaromatic cation based ILs are summarized
2

Table 1. Abbreviations and Supplier Sources of ILs Used in This Study.
No.
1
2
3
4
5
6
7
8
Abbreviation
Name
Source
TCI
This work
TCI
TCI
Ref. 61
TCI
Kanto
Kanto
This work
TCI
Iolitec
Ref. 60
Ref. 63
TCI
Ref. 63
Ref. 63
Ref. 63
Ref. 63
Merck
This work
This work
This work
TCI
Kanto
Kanto
Ref. 63
Ref. 63
Wako
[N1113][NTf
2
]
Trimethylpropylammonium bis(trifluoromethylsulfonyl)amide
Butyldiethylmethylammonium bis(trifluoromethylsulfonyl)amide
Tributylmethylammonium bis(trifluoromethylsulfonyl)amide
Tributylmethylammonium dicyanamide
Triethyloctylammonium bis(trifluoromethylsulfonyl)amide
Benzylethyldimethylammonium bis(trifluoromethylsulfonyl)amide
Diethylmethyl(2-methoxyethyl)ammonium bis(trifluoromethylsulfonyl)amide
Diethylmethyl(2-methoxyethyl)ammonium tetrafluoroborate
1-Methyl-1-propylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-Methyl-1-propylpyrrolidinium bis(fluorosulfonyl)amide
1-Methyl-1-propylpyrrolidinium dicyanamide
1-Butyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-Butyl-1-methylpyrrolidinium bis(fluorosulfonyl)amide
1-Butyl-1-methylpyrrolidinium dicyanamide
1-Butyl-1-methylpyrrolidinium bis(pentafluoroethylsulfonyl)amide
1-Butyl-1-methylpyrrolidinium cyclohexafluoropropane-1,3-bis(sulfonyl)amide
1-Butyl-1-methylpyrrolidinium trifluoromethanesulfonate
1-Butyl-1-methylpyrrolidinium tricyanomethanide
1-Butyl-1-methylpyrrolidinium tris(perfluoroethyl)trifluorophosphate
1-Hexyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-Methyl-1-octylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-Decyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-Allyl-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-(2-Methoxyethyl)-1-methylpyrrolidinium bis(trifluoromethylsulfonyl)amide
1-(2-Methoxyethyl)-1-methylpyrrolidinium tetrafluoroborate
1-(2-Methoxyethyl)-1-methylpyrrolidinium bis(fluorosulfonyl)amide
1-(2-Methoxyethyl)-1-methylpyrrolidinium hexafluorophosphate
[N1224][NTf
[N1444][NTf
2
]
]
2
[N1444][DCA]
[N2228][NTf
[N112Bz][NTf
[N122(1O2)][NTf
[N122(1O2)][BF
2
]
2
]
2
]
4
]
9
[Pyrr13][NTf
[Pyrr13][NF
[Pyrr13][DCA]
[Pyrr14][NTf
[Pyrr14][NF
[Pyrr14][DCA]
[Pyrr14][NPf
2
]
1
1
0
1
2
]
1
1
1
1
1
1
1
1
2
2
2
2
2
2
2
2
2
2
3
3
3
3
3
3
3
3
3
3
4
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
1
2
3
4
5
6
7
8
9
0
2
]
2
]
2
]
[Pyrr14][NCyF]
[Pyrr14][OTf]
[Pyrr14][TCM]
[Pyrr14][FAP]
[Pyrr16][NTf
[Pyrr18][NTf
2
]
]
2
[Pyrr1,10][NTf
[PyrrA1][NTf
[Pyrr1(1O2)][NTf
[Pyrr1(1O2)][BF
[Pyrr1(1O2)][NF
[Pyrr1(1O2)][PF
2
]
]
2
2
]
4
]
2
]
6
]
[Pyrr1(1O2)][NCyF] 1-(2-Methoxyethyl)-1-methylpyrrolidinium cyclohexafluoropropane-1,3-bis(sulfonyl)amide
[Pip13][NTf
[Pip14][NTf
2
]
]
1-Methyl-1-propylpiperidinium bis(trifluoromethylsulfonyl)amide
1-Butyl-1-metylpiperidinium bis(trifluoromethylsulfonyl)amide
4-(2-Ethoxyethyl)-4-methylmorpholinium bis(trifluoromethylsulfonyl)amide
Tributylmethylphosphonium bis(trifluoromethylsulfonyl)amide
Triethyloctylphosphonium bis(trifluoromethylsulfonyl)amide
Tributyldecylphosphonium bis(trifluoromethylsulfonyl)amide
Tributyldecylphosphonium bis(fluorosulfonyl)amide
Tributyldecylphosphonium bis(pentafluoroethylsulfonyl)amide
Tributyldecylphosphonium trifluoromethanesulfonate
Triethyl(methylthio)methylphosphonium bis(fluorosulfonyl)amide
Tributyl[2-(ethylthio)ethyl]phosphonium tetrafluoroborate
Triethylsulfonium bis(trifluoromethylsulfonyl)amide
Wako
This work
Wako
2
2
[Mor1(2O2)][NTf ]
[P1444][NTf
[P2228][NTf
2
]
]
TCI
2
Ref. 61
This work
This work
This work
This work
Ref. 67
Ref. 67
Aldrich
[P444,10][NTf
2
]
[P444,10][NF
[P444,10][NPf
2
]
2
]
[P444,10][OTf]
[P222(1S1)][NF
[P444(2S2)][BF
[S222][NTf
2
]
]
4
2
]
3

in the Electronic Supporting Information (Table S2-1 of the
Electronic Supporting Information). Figure 1c shows the
Fourier transform Kerr spectra of [Pyrr13][DCA]. The entire
spectrum was decomposed into two parts, namely, the
overdamped relaxation component (triexponential fit excluded
because heavy atoms (> 4th period) are not included in the
target ILs in this study.
The line shape of broadened spectral band of each IL,
which is mainly due to intermolecular vibrations, was also
analyzed. The model function to fit the line shape of the
low-frequency spectrum used in this study was a sum of the
the fast component, a
0
+ a
2
exp(–t/
2
) + a
3
3
exp(–t/ )) and the
7
9
spectrum produced by the subtraction of the overdamped
Ohmic functions (IO,i()),
relaxation component. Because the relaxation time constants of
퐼O,푖(ω) = ∑푛 ꢃO,푖휔exp (−휔/휔O,푖
푖ꢅ1
)
(3)
the first exponential components (a
1
1
exp(–t/ )) in the ILs were
a few picoseconds, i.e., a similar time scale in the dephasing of
typical intramolecular vibrations and the collision- or
interaction-induced intermolecular motions, this component
was included in the low-frequency spectra in this study (Figure
S1 of the Electronic Supporting Information). The broadened
band below ~150 cm in the spectrum without the slow
relaxation component was mainly attributed to intermolecular
vibrations such as librations (orientational vibrations) and
collision- and interaction-induced motions (translational
dynamics). It is also noted that the Kerr response was
normalized at the intensity at t = 0 in the time domain data,
which is the electronic response. Thus the intensities of the
spectra are not exactly comparable, but it can be a rough guide
where aO,i and O,i are the amplitude and characteristic
frequency, respectively, of the i-th Ohmic component, and a
sum of anti-symmetrized Gaussian functions (IG,i()),
8
0
-1
푛
2
−
ꢂꢀ휔 − 휔G,푖ꢁ
퐼G,푖(휔) = ꢆ ꢃG,푖 ꢇexp ꢈ
ꢉ
2
Δ휔
푖ꢅ1
G,푖
2
−
ꢂꢀ휔 + 휔G,푖ꢁ
−exp ꢈ
ꢉꢊ
(4)
2
G,푖
Δ휔
where aG,i, G,i, and G,i are the amplitude, characteristic
frequency, and width parameter, respectively, of the i-th
Figure 2. Line shape analysis results for the
low-frequency Kerr spectra of (a) [N112Bz][NTf
2
], (b)
Figure 1. (a) Logarithmic plot of the normalized Kerr
transient (red line) together with its triexponential fit
function (blue line) and (b) short time window transient
from –0.5 to 3.0 ps for [Pyrr13][DCA]. (c) Fourier
transform Kerr spectra: entire spectrum (black line),
picosecond overdamped relaxation component (blue line),
and entire spectrum minus picosecond overdamped
relaxation component (red line).
[
Pyrr13][DCA], and (c) [P222(1S1)][NF ]. Black dots denote
2
the experimentally obtained spectra, red lines represent the
entire spectral fits, blue areas denote the Ohmic functions,
green areas correspond to the anti-symmetrized Gaussian
functions, brown areas represent the Lorentz functions
(intramolecular vibrational bands), and red areas denote
the sums of the Ohmic and anti-symmetrized Gaussian
functions.
4

anti-symmetrized Gaussian function component. When a clear
intramolecular vibrational band was observed in the
and [Pyrr1,10][NTf
value of [Pyrr1n][NTf
2
]). It is evident from the figure that the 
] series decreased with the increasing
2
low-frequency spectrum, the band was fitted by a Lorentzian
function,
length of the alkyl group. This is a rather general feature of
liquid density in not only pyrrolidinium-based ILs, but also
ꢃL
other ILs such as imidazolium-based and pyridinium-based
퐼L(휔) =
(5)
ILs.

19,59,116
Previously, we showed the linear relations between
for 1-alkyl-3-methylimidazolium
MIm][NTf ] (n = 2–10),
bis(trifluoromethylsulfonyl)amides,
] (n = 4–12), and 1-alkyl-3-methylimidazolium
2
2
L
(
휔 − 휔 ) + Δ휔
L
and
N
RC
where a
L
, 
L
, and 
L
are the amplitude, characteristic
frequency, and width parameter, respectively. Figure 2 displays
the line shape fits to the low-frequency spectra of
bis(trifluoromethylsulfonyl)amides, [C
N-alkylpyridinium
Py][NTf
tetrafluoroborates, [C
dependence of  in [Pyrr1n][NTf
n
2
[
C
n
2
[
N112Bz][NTf
2
], [Pyrr13][DCA], and [P222(1S1)][NF
2
], as
59
n
MIm][BF
4
] (n = 2–10). The alkyl group
] is, however, represented by
examples. All low-frequency Kerr spectra of the forty
nonaromatic cation based ILs were fitted with a similar fit
quality. All the low-frequency Kerr spectra of the ILs and the
line shape analysis results are summarized in the Electronic
Supporting Information (Figure S1). The forty values of the
2
an exponential function, as shown in Figure 3:
-1

(g mL ) = 1.086 + 0.4700 exp(–0.1027NRC) (7)
first moment (M
1
) of each low-frequency spectrum (sum of
where NRC is the number of carbons of the alkyl group in the
cation. As the nonlinearity of  in relation to NRC for
[Pyrr1n][NTf ] was not significant, it is possible that we missed
2
Ohmic and anti-symmetrized Gaussian components), were
8
1
defined as,
the nonlinear behavior of  with respect to NRC for the aromatic
cation based ILs in that study.
푀 = ∫ 휔퐼(휔)푑휔/ ∫ 퐼(휔)푑휔
(6)
59
1
where I() is the frequency-dependent intensity of a spectrum
that does not include the contributions of the picosecond
overdamped relaxations and clear intramolecular vibrational
modes. For the present ILs, these intensities were estimated in
-1
the frequency region of 0–1000 cm and are listed in Table 2.
In the line shape analysis (Figure 2), each function is not
infallible to assign a band to its origin vibrational mode, unlike
common intramolecular vibrational modes. This is because the
intermolecular vibrations overlap in the frequency region (as
well as the time region), and the vibrational bands in the liquid
phase are broad in comparison with the intermolecular
vibrational band in the gas phase. In addition, the
intermolecular vibrational modes in liquids and solutions are
often coupled with each other. Molecular dynamics (MD)
simulations indicate that the cross-term (or coupling term) of
different kinds of intermolecular vibrations in both molecular
Figure 3. Plots of liquid density, , vs. number of carbons
+
of the alkyl group in [Pyrr1n] , NRC, for [Pyrr13][NTf
2
],
[Pyrr ][NTf ], [Pyrr ][NTf ], [Pyrr ][NTf ], and
1
4
2
16
2
18
2
2
[Pyrr1,10][NTf ]. Fit curve by an exponential function is
also indicated by a solid curve.
8
2,83
liquids
and ILs provides either a positive or negative
8
4-86
intensity depending on the target system.
Although there
have been attempts to obtain a more realistic feature from the
line shape analysis of the low-frequency spectrum in molecular
Figure 4 shows the plot of  vs. the total number of
carbons of the alkyl and aromatic groups of [N1113][NTf
2
],
1
3,87,88
liquids,
study are removing the contributions of clear intramolecular
vibrational modes from a broad spectrum, estimating M of the
the purposes of the line shape analysis in this
[
N
1224][NTf
2
], [N1444][NTf ], [N2228][NTf ], and [N112Bz][NTf
2
2
2
].
Note that Figure 4 shows the plot for the total number of
carbons of cations, but Figure 3 is for the number of carbons of
only the alkyl groups in the cations. It is clear from Figure 4
that the  values of the ammonium-based ILs depended on the
1
spectrum, and representing the low-frequency spectrum
quantitatively for overview of the intermolecular vibrational
bands of the forty nonaromatic cation based ILs.
2
total number of carbons of the cation, except for [N112Bz][NTf ].
This was attributed to the nature of the compact (or dense)
structure of the phenyl ring. The dependence of  on the total
4
4
. Results and Discussion
.1 Bulk Liquid Properties
.1.1 Density   The  values for the forty nonaromatic
number of carbons of the cations in the ammonium-based ILs
4
–
with [NTf
2
] , except for [N112Bz][NTf
2
], is given as follows:
cation based ILs at 293 K estimated in this study are
summarized in Table 2. The  values of the ILs at 293 K and/or
-1

(g mL ) = 0.8794 + 0.7568 exp(–0.05176N
C
)
(8)
4
1,61,67,89-115
near temperatures from previous reports
are also
given in Table 2. The  values measured in this study were
quite similar to the reported values, i.e., within experimental
errors if we consider the effect of temperature on the liquid
density. The  data of some ILs (e.g., [Pyrr1(1O2)][NCyF],
Comparing the  values of [N1224][NTf
2 2
], [Pyrr14][NTf ],
and [Pip13][NTf ] provides an insight into the effect of the
2
structures of cation skeletons on the density, because the
number of carbons of the cations is the same. The trend of
decreasing influence on density is as follows: [Pip13
+
[
P
444,10][NF
2
], and so on) have not been reported to date, to the
best of our knowledge.
Figure 3 shows the plot of  versus the number of
]
>
+
+
[Pyrr14
ammonium-based ILs, [N1444][NTf
their respective phosphonium-based ILs, [P1444][NTf
[P2228][NTf ], revealed that the densities of the
ammonium-based ILs, [N1444][NTf ] and [N2228][NTf ], and
their respective phosphonium-based ILs, [P1444][NTf ] and
]
> [N1224] . A comparison of the  values of the
] and [N2228][NTf ], and
] and
2
2
carbons
of
the
alkyl
group,
N
RC
,
of
2
+
1
-alkyl-1-methylpyrrolidinium cations ([Pyrr1n] , n = NRC) for
2
–
the
bis(trifluoromethylsulfonyl)amide
], [Pyrr14][NTf ], [Pyrr16][NTf
([NTf
2
2
] )
salts
2
2
([Pyrr13][NTf
2
2
], [Pyrr18][NTf
2
],
2
5

Table 2. Physical Properties of Nonaromatic ILs at 293 K.
No.
1
Ionic Liquid
FW
g/mol)

(g/mL)
1.433
V
m

(cP)
95.3

(mS/cm)
1.89


M
(cm )
44.0
1
-1
2
H O Cont.
(ppm)
42
2
(
(mL/mol)
267
(Scm /mol)
(mN/m)
[N1113][NTf
2
]
382.34
424.42
480.53
266.43
494.55
0.504
0.381
0.176
0.220
0.235
34.4
(35.1118)
33.6
(
1.430e89, 1.43d90
1.358
)
(78.1e89, 95a117
157
)
(3.03e89, 3.24d90
1.22
)
2
[N1224][NTf
[N1444][NTf
2
]
]
313
380
281
395
49.7
52.9
65.4
49.4
50
91
35
41
(
1.34a91, 1.38 d92
1.265
)
(161a91, 120 d92
784
)
(1.0a91, 1.6 d92
0.464
)
3
2
30.8
(30.6i93)
44.1
94
(2.10j119)
0.783
(
1.270a93, 1.26794)
0.948
(819.2 )
4
[N1444][DCA]
[N2228][NTf
407
(410d95)
211
(
0.98d95)
1.253
(0.57d95)
0.595
5
2
]
32.0
(32.8b61, 33.1c96
37.7
(
1.249b61, 1.251c96
1.429
)
(227.0b61, 221.4c96
)
(0.33d120)
0.441
)
6
7
[N112Bz][NTf
2
]
2
444.41
426.39
311
302
650
88.8
0.137
0.622
47.2
49.6
56
82
[N122(1O2)][NTf
]
1.413
2.06
35.0
(33.6d97)
50.6
(
1.42d92, 1.407d97
1.182
)
(69d92, 70.96d97
544
)
(2.6d92)
1.26
8
9
[N122(1O2)][BF
4
]
233.06
408.37
308.36
194.28
422.40
322.39
208.31
522.42
434.41
291.33
232.32
587.28
450.46
197
285
230
189
302
246
205
353
300
232
230
370
336
0.248
0.816
1.13
72.0
45.2
44.7
63.9
46.8
47.0
64.0
44.9
49.0
65.9
54.9
41.3
47.2
61
63
22
78
29
47
68
41
20
47
68
44
69
(
1.20d92)
1.432
(426d92)
69.5
(1.3d92)
2.86
[Pyrr13][NTf
[Pyrr13][NF
[Pyrr13][DCA]
[Pyrr14][NTf
[Pyrr14][NF
[Pyrr14][DCA]
[Pyrr14][NPf
2
]
35.3
(34.4d108)
47.9
(
1.434c98, 1.432a99
1.343
)
(63c121, 72a99
47.1
)
(3.6c121, 2.20a99
4.91
)
1
0
1
2
]
(
1.339c98)
1.029
1.038a100)
1.399
(40c122, 39a123
28.7
)
(6.4c122, 9.14a123
8.18
)
1
1.55
57.3
(
(33.2a100, 27.1a124
96.4
)
(15.7a124)
1.96
1
1
1
1
1
1
1
1
2
2
3
4
5
6
7
8
9
0
2
]
0.592
1.41
33.6
(33.0d108)
44.6
63
(2.84f125, 1.77a99
5.72
(
1.396e89, 1.399a99
1.311
1.311a101, 1.306d102
1.015
)
(97.1 , 95a99)
)
2
]
62.1
63
(5.25a101)
6.63
(10.1a124)
0.671
(35.04d102)
53.0
(
)
)
(61.4 , 64.13a101)
36.8
1.36
(
1.013d103)
1.480
1.481a99)
1.449
(36.5d103, 38.863)
324
(56.2k126)
30.1
2
]
0.237
0.225
0.387
1.28
63
(0.774f125, 0.42a99
0.716
(
(341.0 , 350a99)
)
[Pyrr14][NCyF]
[Pyrr14][OTf]
[Pyrr14][TCM]
[Pyrr14][FAP]
459
486 )
34.1
36.4
6
3
(0.35a127)
1.67
(
1.256
222
63
(1.3a105)
5.55
(
1.256a104, 1.256a105
1.008
(227 , 221.7a39)
30.4
51.1
(48.04l106)
33.7
63
(8.7d107)
1.10
(
1.001l106, 1.01d107
1.588
)
(33.0 , 29.0d42)
260
0.407
0.380
(
1.580d103, 1.589a43
1.340
)
(221.0d103, 28863)
137
(1.053d128)
1.13
(35.0a129)
32.0
2
[Pyrr16][NTf ]
(
1.32d108)
(133.2a130)
(1.0a131, 1.2a130
)
(31.7d108)
6

2
2
2
2
2
2
2
2
2
3
3
3
3
3
1
2
3
4
5
6
7
8
9
0
1
2
3
4
[Pyrr18][NTf
[Pyrr1,10][NTf
[PyrrA1][NTf
[Pyrr1(1O2)][NTf
2
]
478.51
506.56
406.36
424.37
231.04
324.36
289.20
436.38
422.40
436.43
454.40
497.49
511.52
623.74
1.294
1.289d109)
1.255
370
404
279
291
187
235
207
289
299
315
310
395
410
544
178
(138.17d109)
239
0.787
(0.54a131)
0.585
0.291
0.236
0.696
0.949
0.485
1.09
31.6
46.9
49.2
42.4
49.2
68.9
51.1
70.2
56.5
46.3
46.9
47.2
52.7
53.5
54.0
76
37
35
70
74
71
36
42
36
44
34
33
76
90
(
2
]
31.8
(31.4d108)
36.1
(
1.25d108)
1.454
(150d108)
70.9
(0.37a131)
2.49
2
]
(
1.447m110)
(52c121, 39.5m110
64.4
)
(3.7c121, 4.2m110
3.26
(3.88d132, 3.45d27
2.59
)
2
]
1.458
35.9
(35.26d132)
52.6
63
(
1.46g41, 1.459a99
1.234
)
(64.0 , 62a99)
)
[Pyrr1(1O2)][BF
[Pyrr1(1O2)][NF
4
]
217
1.235d111)
1.379
(232 , 213d111)
63
(2.9d111)
4.65
(7.66n133)
0.587
(
2
]
47.0
47.9
50.7
35.4
6
3
(
47.9 , 43.6n133)
[Pyrr1(1O2)][PF
6
]
1.397
1.510
1.414
768
0.122
0.199
0.361
0.325
0.200
0.228
0.326
0.226
6
3
(
753 )
289
[Pyrr1(1O2)][NCyF]
0.688
6
3
(
308 )
184
[Pip13][NTf
[Pip14][NTf
2
2
]
]
1.21
(1.58e89)
1.03
35.8
(34.4j118, 35.6o94
34.2
(
1.414e89, 1.416a94
1.384
1.38d93, 1.38d112,)
1.464
)
(145.8e89, 198.1a94
253
)
)
(
(183d112, 247.7a94
341
)
(1.11d90, 1.2d112
)
(34.5p94)
35.1
[Mor1(2O2)][NTf
2
]
0.643
1.46d112)
1.259
(298d112)
352
(1.1
d112
)
(
[P1444][NTf
[P2228][NTf
2
2
]
]
0.576
30.7
(
1.28d113)
1.249
(207d113)
151
(0.42d113)
0.797
31.6
(32.7b61)
30.2
(
1.244b61, 1.244d114
1.146
)
(123.3b61, 119.42d114
)
(0.891d114)
0.415
[P444,10][NTf
2
]
324
(301.06d114)
438
(
1.142d114)
1.077
(0.226d114)
0.408
3
3
3
3
5
6
7
8
[P444,10][NF
[P444,10][NPf
2
]
523.72
723.75
492.66
359.40
486
598
473
267
0.198
0.207
0.155
0.698
34.4
28.0
30.5
47.8
52.7
53.5
62.8
56.1
77
56
50
72
2
]
1.211
1.041
647
900
0.347
0.327
[P444,10][OTf]
[P222(1S1)][NF
2
]
1.344
58.4
2.61
6
7
67
67
67
(
1.344 )
1.075
(58.2 )
(2.925 )
(47.2 )
3
4
9
0
[P444(2S2)][BF
4
]
378.30
352
273
1825
0.337
0.119
35.4
60.6
56.0
89
46
6
7
67
67
67
(
1.076 )
(1847 )
(0.332 )
(36.6 )
[S222][NTf
2
]
399.38
1.465
37.9
4.88
1.33
35.4
(35.5p94)
a115
(41.1 , 30d134
a94
(7.1d134)
(
1.46 , 1.46794)
)
a
j
b
c
d
e
f
g
h
i
Data at 293.15 K. Data at 297 K. Data at 298 K. Data at 298.15 K. Data at 298.2 K. Data at 305 K. Data at 295K. Data at 296K. Data at 294.399 K.
Data at 303 K. Data at 293.05 K. Data at 308.15 K. Data at 303.15 K. Data at 296.15 K. Data at 293.4 K. p Data at 293 K.
k
l
m
n
o
7

Figure 4. Plot of liquid density  vs. total number of
carbons of the cations N for [N1113][NTf ], [N1224][NTf ],
], [N2228][NTf ] (circles), and [N112Bz][NTf
triangle). Fit curve by an exponential function for
Figure 5. Semi-logarithmic plots of viscosity, , vs.
+
c
2
2
number of carbons of alkyl group in [Pyrr1n] , NRC, for
[
(
[
[
N1444][NTf
2
2
2
]
[Pyrr13][NTf
[Pyrr18][NTf
2
],
[Pyrr14][NTf
2
],
2
[Pyrr16][NTf ],
2
], and [Pyrr1,10][NTf
2
]. The fit curve is
N1113][NTf
2228][NTf
2
],
[N1224][NTf
2
],
[N1444][NTf
2
],
and
indicated by a black line.
N
2
] is also given.
Substitution of an alkyl group of the cation with the respective
alkoxyalkyl group reduced the IL viscosity, as shown in Table
[
P
2228][NTf
2
], revealed that the densities of the
2
. Comparison of the IL viscosities of the ammonium and
phosphonium-based ILs were slightly higher than those of the
respective ammonium-based ILs. Tsunashima and Sugiya, as
well as our group, have previously reported similar density
behavior of phosphonium-based ILs as compared to
ammonium-based ILs. It is also noteworthy that the substitution
of an alkyl group in the cations with its respective ether group
+
+
+
phosphonium cations ([N1444
]
vs. [P1444
]
and [N2228] vs.
1
35
+
6
1
[P2228] ) revealed a substantial reduction in the viscosity for the
phosphonium-based ILs. Further, it was evident from the data
in Table 2 that the pyrrolidinium-based ILs had a lower
viscosity than their corresponding piperidinium-based ILs (e.g.,
[
Pyrr14][NTf
It is also known that the viscosity of an IL depends
strongly on the anion species. The trend of decreasing  in the
2 2 2
] vs. [Pip13][NTf ] or [Pip14][NTf ]).
+
+
(e.g., [Pyrr1(1O2)] vs. [Pyrr14] ) gives a higher density in ILs.
This is a rather general feature of the ether group substitution
effect of cations on the density of ILs, as well as (neutral)
molecular liquids.
+
[Pyrr14] -based ILs with eight different anions in this study
1
9,136
–
–
–
–
–
–
2 2 2
was: [NCyF] > [NPf ] > [FAP] > [OTf] > [NTf ] > [NF ]
> [DCA] > [TCM] .
.1.3 Electrical Conductivity   The  data of the
Regarding anion species, we compared the  values of
–
–
+
the 1-butyl-1-methylpyrrolidinium ([Pyrr14] )-based ILs with
eight anions in this study, as shown in Table 2. The decreasing
trend of densities of the anion species was: [FAP] > [NPf ] >
2
4
forty nonaromatic cation based ILs are summarized in Table 2.
The  values of the ILs reported previously are also given in
–
–
–
–
–
–
–
–
[NCyF] > [NTf
2
] > [NF
2
] > [OTf] > [DCA] ~ [TCM] . In
data of the
Table
references.
2
as
The
addition, it was evident from the
1
was likely in between [NTf
between [OTf] and [DCA] or [TCM] .

6
7,89-92,95,99,101,105,107,110-114,119-125,127,128,130-134,137
–
-methxoyethyl-1-methylpyrrolidinium-based ILs that [PF
6
]
–
–
–
molar electrical conductivities , defined as V
m
, are also
2
] and [NF
2
] , and [BF
4
] was in
-1
given in Table 2. Figure 6 shows (a) plots of  vs.  and (b)
–
–
–
-1
logarithmic plots of  vs.  for the forty nonaromatic cation
4
.1.2 Viscosity   The viscosity data at 293 K for the
based ILs in this study. In addition, the data for the forty
present ILs are given in Table 2. The  values of the ILs
reported in preceding works are also listed in Table
2

estimated in this study (within the range of experimental error),
taking the effect of temperature into consideration overall.
It is known that the viscosity in ILs depends strongly on
1
3
aromatic cation-ILs in our previous work are also plotted in
Figure 6. It is clear from Figure 6a that the plots for the ILs
6
1,63,67,89,91,92,94-97,99-101,103,108-114,117,121-124,130,133,134
.
The reported
values of the ILs were in a good agreement with those
-1
show almost linear relationships between  and  . The
-1
relations between the electrical conductivity  and  for
different types of ILs are:
-1
-1

(mS/cm) = 205 (cP ) + 0.118
nonaromatic cation based ILs)
1
9
the length of the alkyl group of cations.
The
] studied here also showed
this viscosity behavior. Figure 5 shows the semi-logarithmic
(
(10)
(11)
–
pyrrolidinium-based ILs with [NTf
2
-1
-1

(mS/cm) = 292 (cP ) – 0.068
aromatic cation based ILs)
plots of  vs. NRC for [Pyrr1n][NTf
and NRC is:
2
]. The relation between 
(
For both types ILs,
log( (cP)) = 1.664 + 0.07323NRC
(9)
-1
-1

(mS/cm) = 256 (cP ) + 0.001
both ILs)
(
(12)
The slope for [Pyrr1n][NTf
MIm][NTf ] (log( (cP)) = 1.457 + 0.07404NRC), but the
viscosity at the intercept for [Pyrr1n][NTf ] was similar to that
of [C Py][NTf ] (log( (cP)) = 1.628 + 0.06392NRC).
In terms of the effect of the total number of carbons of the
2
] was found to be close to that for
[
C
n
2
The relations between the molar electrical conductivity  and
2
-1
138

are analyzed by the fractional Walden rule:
n
2
2
-1
-1 0.753
 (Scm /mol) = 19.5[ (cP )]
(nonaromatic cation based ILs)
+
ammonium cations, except for [N112Bz] , on the viscosity, there
was no simple N dependence of  evident for [N1113][NTf ],
], [N1444][NTf ], and [N2228][NTf ] in Table 2. It
seems that the van der Waals interactions originating from the
bulky cation strongly affected the viscosity in [N1444][NTf ].
(13)
(14)
c
2
2
-1
-1 0.911

(Scm /mol) = 46.6[ (cP )]
(aromatic cation based ILs)
[
N
1224][NTf
2
2
2
2
8

2
-1
-1 0.872

(Scm /mol) = 36.2[ (cP )]
both ILs)
than aromatic cation based ILs.
In addition to the overall picture of the electrical
conductivities of nonaromatic cation based ILs, the NRC
(
(15)
dependence of
bis(trifluoromethylsulfonyl)amide, [Pyrr1n][NTf

for the 1-alkyl-1-methylpyrrolidnium
], series is
2
shown in Figure 7. Note that Figure 7 shows semi-logarithmic
plots. It is clear from the figure that  decreases with the
increasing length of the alkyl group for the [Pyrr1n][NTf ]
2
series. As seen in Figure 7, the  and  values do not simply
express an exponential feature. Previously, a variant of the
1
40-143
Vogel-Tammann-Fulcher (VTF) equation
express the dependence of
-alkyl-1-methylimidazolium-based
was used to
N
RC

and
ILs

for
1
with
bis(trifluoromethylsulfonyl)amide and tetrafluoroborate anions
5
9
n 2 2
and [C Py][NTf ]. The results for [Pyrr1n][NTf ] also showed
the VTF-type behavior in electrical conductivity and molar
electrical conductivity:
휎 = 휎 exp[퐵/ꢀ푁 − 푁푅퐶,0ꢁ]
(16)
(17)
0
푅퐶
훬 = 훬 exp[퐵′/ꢀ푁 − 푁′푅퐶,0ꢁ]
0
푅퐶
where 
that is related to a parameter of the carbon number sensitivity to
 and NRC,0 is a constant that could be the critical carbon
number of the alkyl group where the electrical conductivity
diverges,  is the limiting molar electrical conductivity, Bʹ is a
0
is the limiting electrical conductivity, B is a constant

0
constant related to a parameter of the carbon number sensitivity
to  and NʹRC,0 is a constant that could be the critical carbon
number of the alkyl group where the molar electrical
conductivity diverges. The fit parameters obtained for
-
1
Figure 6. (a) Plots of  vs.  and (b) logarithmic plots of

-1
vs.  for forty nonaromatic cation based ILs studied
here (blue symbols). Data for forty aromatic cation based
ILs reported in Ref. 59 are also given (red symbols). Fit
curves for nonaromatic and aromatic cation based ILs are
shown by red and blue lines, respectively. Fits for all data
of nonaromatic and aromatic cation based ILs are given by
black lines. Black dashed line denotes the ideal Walden
line with the unity slope.
[Pyrr1n][NTf
−5.09,  = 0.0781 (Scm /mol), Bʹ = 6.40, and NʹRC,0 = −3.28.
From the comparison with the parameters of [C MIm][NTf ]s
and [C Py][NTf ], B and Bʹ for [Pyrr1n][NTf ] are slightly low,
as well as NRC,0 and NʹRC,0. This indicates that the (molar)
electrical conductivity for the [Pyrr1n][NTf ] series was less
2
0
] were:  = 0.0949 (mS/cm), B = 12.0, and NRC,0
2
=
0
n
2
n
2
2
2
sensitive to the alkyl group and possess the larger critical
carbon number of the alkyl group.
It is evident from Figure 6 that the slopes in the plots for
the aromatic cation based ILs are slightly steeper than those for
the nonaromatic cation based ILs, i.e., the electrical
conductivity was more sensitive to the viscosity of the aromatic
cation based ILs than that of the nonaromatic cation based ILs.
This implied that the nonaromatic cation based ILs required
lower viscosity to achieve the same molar electrical
conductivity as the aromatic cation based ILs. Watanabe and
coworkers have reported a larger value of the ratio of the molar
conductivities estimated by electrical conductivity and NMR
measurements
for
nonaromatic
cation
based
ILs
(butyltrimethylammonium bis(trifluoromethylsulfonyl)amide
2
and [Pyrr14][NTf ]) than that for aromatic cation based ILs
(
1-butyl-3-methylimidazolium
bis(trifluoromethylsulfonyl)amide and
N-butylpyridinium
1
39
bis(trifluoromethylsulfonyl)amide). Because the value of the
ratio of the molar conductivities estimated by electrical
conductivity and NMR measurements is essentially related to
the percentage of ions (charged species) contributing to the
ionic conduction in the diffusing species, nonaromatic cation
based ILs are more ionic in nature than aromatic cation based
ILs. Therefore, the results in Figure 6 indicate that a higher
ionicity increases the viscosity of ILs. It looks that this
tendency is clearer in the higher viscosity region, as shown in
Figure 6b. The analysis results based on the fractional Walden
Figure 7. Plots of (a) log() vs. NRC and (b) log() vs. NRC
for [Pyrr1n][NTf ]. The VTF fit curves are also shown by
2
solid lines.
1
38
rule also show that the exponent value is farer from unity for
nonaromatic cation based ILs than aromatic cation based ILs.
This implies that nonaromaic cation based ILs tend to be more
decoupled between the electrical conductivity and viscosity
9

The decreasing trend of  with respect to the eight anions
in the [Pyrr14] -based ILs in this study was found to be: [DCA]
value. For example, the  values of [Pyrr14][NTf
2
] and
+
–
[Pyrr1(1O2)][NTf
2
] were 33.6 and 35.9 mN/m, respectively
–
–
–
–
–
–
>
[
2 2
[NF ] > [TCM] > [NTf ] > [OTf] > [FAP] > [NCyF] >
(Table 2).
–
+
NPf
similar to that for 1-butyl-3-methylimidazolium-based ILs and
-ethyl-3-methylimidazolium-based ILs.
.1.4 Surface Tension  : The values of  of the target
2
] . Overall, this trend of  for the [Pyrr14] -based ILs is
From Table 2, the decreasing order of  with respect to
+
the different anions for the [Pyrr14] -based ILs was found to be:
–
–
–
–
–
–
1
2
[DCA] > [TCM] > [NF ] > [OTf] > [NCyF] > [FAP] ~
–
–
4
[NTf
2
] > [NPf
2
] .
nonaromatic cation based ILs are listed in Table 2. As far as we
Maroncelli and coworkers have reported a correlation
1
08
know, the  data of only about a half of the present ILs are
between  and V
a similar correlation between  and V
m
in molten salts including ILs. Subsequently,
was identified in
aromatic cation based ILs. In the latter study, a dramatic
change in V was observed in the low-V region. Figure 9
displays the plots of  vs. V for the present forty nonaromatic
6
1,67,93,94,96,97,102,106,108,118,126,129,132
reported.
The  values of the
m
5
9
remaining ILs are reported here, for the first time.
Figure 8 shows the  value as a function of the number of
m
m
carbons of the alkyl group in the cations of the [Pyrr1n][NTf
series. For comparison, the data of the [C MIm][NTf ] series
] series fitted an
2
]
m
n
2
cation based ILs. The data for previously reported forty
aromatic cation based ILs are also shown in the plots. The
5
9
are also given. The data of the [Pyrr1n][NTf
2
exponential function:
m
correlation between  and V in the nonaromatic cation based
ILs was slightly different from that in the case of aromatic
cation based ILs. Similar to the reported data on the aromatic
cation based ILs, the correlation for the nonaromatic cation
based ILs was expressed by a single exponential function:

(mN/m) = 28.3 exp(–NRC / 1.48) + 31.6
(18)
In the case of the [Pyrr1n][NTf
by  (mN/m) = 27.5 exp(–NRC/1.38) + 30.6, as shown in Figure
. It is clear from Figure 8 that the change in  to NRC for the
2
] series, the relationship is given
8

(mN/m) = 265.1 exp(–0.0123V
m
) + 29.4
(19)
pyrrolidinium-based ILs is quite similar to that for the
imidazolium-based ILs. However, the saturated  value to NRC
in the pyrrolidinium-based ILs (31.6 mN/m) is slightly higher
than that in the imidazolium-based ILs (30.6 mN/m). This
implies that the surface of the IL is more structured (covered
with alkyl groups) in the imidazolium-based ILs than in the
pyrrolidinium-based ILs. The X-ray scattering study by Russina
et al. showed that the nonaromatic piperidinium-based ILs are
Compared to the correlation for the aromatic cation based ILs
( (mN/m) = 178.5 exp(–0.0124V ) + 28.7), the parameters of
m
the amplitudes of the exponential terms of the two types of ILs
were different. This indicated that the intrinsic surface tension,
which is defined as the value at zero molar volume, of the
nonaromatic cation based ILs was higher than that of the
aromatic cation based ILs.
5
9
2
8
less segregated than their comparable imidazolium-based ILs.
Using sum frequency generation spectroscopy that is a
surface-selective vibrational spectroscopy, looser or more
defective structure of alkyl groups of cations in ammonium-
1
44
and pyrrolidinium-based ILs than imidazolium-based ILs
was also observed.
1
45
The higher surface tension in the
pyrrolidinium-based ILs than the respective imidazolium-based
ILs is likely related to a similarly weak segregation or defective
structure in the former ILs compared to the latter ILs.
Figure 9. Plots of  vs. V
m
for the present forty
nonaromatic cation based ILs (red circles) and forty
5
9
aromatic cation based ILs (blue triangles). Exponential
fits are shown by corresponding colored lines.
4
.2 Ultrafast Dynamics: Low-Frequency Spectra
4
.2.1 General Features of Nonaromatic Cation Based
ILs: The intensity of the low-frequency spectrum in liquids and
solutions obtained by fs-RIKES with the polarization
configuration for the depolarized signal (like this study)
depends on the magnitude of the collective polarizability
Figure 8. Plots of  vs. NRC for [Pyrr1n][NTf
2
] (red circles)
5
9
and [C MIm][NTf ] (blue squares). Exponential fit
n 2
functions are also shown by the respective colored lines.
7
,146
anisotropy of the sample.
The molecular polarizability
anisotropy of an aromatic molecule is usually larger than that of
1
47,148
On comparing the  values of the pyrrolidinium- and
piperidinium-based ILs, it was evident that the surface tension
of the former ILs was slightly lower than that of the respective
the corresponding nonaromatic molecule.
for ILs.
This is also true
3
4,44,60
Therefore, the line shape in the low-frequency
spectra of aromatic cation based ILs, such as imidazolium- and
pyridinium-based ILs, is governed by the aromatic group. In
fact, this makes difficult to understand the effect of the anion,
whose magnitude of polarizability anisotropy is small, and thus
its effect on the line shape of the spectrum, is relatively small
as compared to that of typical aromatic cations.
piperidinium-based ILs: 35.3 mN/m for [Pyrr13][NTf
mN/m for [Pip13][NTf ], and 33.6 mN/m for [Pyrr14][NTf
4.2 mN/m for [Pip14][NTf ]. The  values of the ammonium-
and phosphonium-based ILs ([N1444][NTf ] vs. [P1444][NTf
and [N2228][NTf vs. [P2228][NTf ]) were similar. The
substitution of an alkyl group with its respective alkoxyalkyl
group (C – → CH OCH CH –) gave a slightly higher 
2
] vs. 35.8
2
2
] vs.
3
2
2
2
]
2
]
2
Figure 10 compares the low-frequency Kerr spectra of the
4
H
9
3
2
2
bis(fluorosulfonyl)amide
salts
of
10

1
1
-butyl-1-methylpyrrolidinium
-butyl-3-methylimidazolium ([C
([Pyrr14][NF
2
])
and
in this section. As discussed in section 4.2.1, the contribution of
the nonaromatic cation to the spectral density in the
low-frequency broadened spectrum of the IL is small as
compared to that of the aromatic cation. Therefore, the
contribution of the anion species to the spectral line shape is
often buried under the spectrum arising from the cation species.
Consequently, it is useful to measure the low-frequency spectra
of nonaromatic cation based ILs with a wide variety of anion
species to understand their effects on the spectral line shape of
the low-frequency Kerr spectrum of ILs.
4
MIm][NF ]) cations, as an
2
example. The spectral intensity relative to the electronic
response of [Pyrr14][NF ] is smaller than that of [C MIm][NF ].
According to the quantum chemistry calculations based on the
B3LYP/6-311+G(3df) level of theory, the polarizability
anisotropy anis of [Pyrr14]+ was about half of that of [C
In this study, we also confirm that the results of the quantum
chemistry calculations based on the B3LYP/6-311+G(d,p) level
of theory show similar difference in anis of the two cations
2
4
2
6
0
+
4
MIm] .
+
3
+
3
(

anis([Pyrr14] ) = 3.515 Å and anis([C
4
MIm] ) = 7.317 Å
Figure 11 compares the low-frequency spectra of ILs with
–
–
(Table S2-4 of the Electronic Supporting Information). This is
spherical top anions, [PF
6 4
] and [BF ] . The spectral density
consistent with the results in this study shown in Figure 10.
This feature in the spectral density is rather general for the
low-frequency spectra of other aromatic and nonaromatic
mainly arises from the cations because of zero polarizability
anisotropy of these anions ([PF ] : O and [BF ] : T ). Thus, the
6 h 4 d
spectral line shapes of the ILs with the spherical top anions are
largely attributable to the cations. It is evident from Figure 11
–
–
3
4,60
cation based ILs, as well.
that the line shapes of the low-frequency spectra of the three
–
[
BF
4
] salts ([P444(2S2)][BF
4
] in particular) are different.
Figure 10. Comparison of the low-frequency Kerr spectra
of (a) [Pyrr14][NF ] and (b) [C MIm][NF ]. The spectrum
of [C MIm][NF ] was previously reported in Ref. 59.
2
4
2
4
2
There is a clear difference in the spectral line shapes
between [Pyrr14][NF ] and [C MIm][NF ], as shown in Figure
0. The line shape of the low-frequency Kerr spectrum of
Pyrr14][NF ] is triangular, while that of [C MIm][NF ] is
bimodal. The stronger spectral density in the high-frequency
2
4
2
1
[
2
4
2
-1
region above ~50 cm in aromatic cation based ILs, such as
3
4,44
imidazolium- and pyridinium-based ILs,
compared to the
nonaromatic cation based ILs with the same anions, is
attributed to the libration of an aromatic ring. In fact, a
substantial contribution of the aromatic ring libration to the
low-frequency Kerr spectrum is observed not only for aromatic
cation based ILs but also in aromatic molecular liquids. On
comparing the low-frequency spectra of [Pyrr14][NF
MIm][NF ], as shown in Figure 10, it was evident that the
spectral line shape having the low-frequency peak at ~20 cm
2
] and
[
C
4
2
-1
–
2
was mainly due to the anion [NF ] . Accordingly, the line shape
of the low-frequency spectrum of nonaromatic cation based ILs
is useful to clarify the effects of the anion species on the
spectrum line shape. In the following discussion, examples of
low-frequency Kerr spectra are given for the forty nonaromatic
cation based ILs with different cations and anions.
Figure 11. Low-frequency Kerr spectra of ILs with
spherical top anions. (a) [Pyrr1(1O2)][PF ], (b)
and (d)
6
[
Pyrr1(1O2)][BF
4
444(2S2)][BF ].
4
],
(c)
4
[N122(1O2)][BF ],
[
P
4
.2.2 Effect of Anion Species: The effect of the anion
species on the low-frequency Kerr spectrum of ILs is focused
11

The line shapes of the low-frequency spectra of
] and [Pyrr1(1O2)][BF ] are similar. However, the
spectral intensity in the high-frequency region above ~70 cm
is slightly higher than that for
[Pyrr1(1O2)][PF
6
4
-1
4
for [Pyrr1(1O2)][BF ]
-1
[
Pyrr1(1O2)][PF
Pyrr1(1O2)][BF
50 cm-1 and that for [Pyrr1(1O2)][PF
6
]
(the spectral intensity at 100 cm for
] was ~0.6 relative to the maximum intensity at
] was ~0.5). The
[
4
~
6
difference in the low-frequency spectra of [Pyrr1(1O2)][PF
Pyrr1(1O2)][BF was similarly observed in
-butyl-3-methylimidazolium-based ILs with [PF
6
] and
the
[
1
4
]
]– and
6
–
59
[
BF
4
] . Therefore, the origin of this type of difference in the
–
–
spectra of the salts of [PF
6
] and [BF
4
] is the nature of the
–
6
anions. As the molar volume and mean polarizability of [PF ]
–
are larger than those of [BF
4
] , the collision-induced (or
interaction-induced) intermolecular vibrational motion of
–
[PF
6
] likely contributed more strongly to the spectral density
–
than [BF
4
] , as observed by the higher spectral intensity in
] than [Pyrr1(1O2)][BF ] (Figure 11).
[Pyrr1(1O2)][PF
6
4
Figure 12 shows the low-frequency spectra of
+
]–, [NTf
–
–
–
[
[
Pyrr14] -based ILs with [NF
2
2
] , [NPF
2
] , [NCyF] , and
–
OTf] . When we compare the spectra of the ILs with the
–
anions of bis(perfluoroalkylsulfonyl)amide derivatives, [NF
2
] ,
] , triangular spectral line shapes are
observed. The peak shifts to lower frequencies in the order of
–
–
[
2 2
NTf ] , and [NPF
-1
-1
[
[
Pyrr14][NF
Pyrr14][NPf
2
] (~21 cm ) > [Pyrr14][NTf
] (~18 cm ). This order is also valid for the
2
] (~20 cm ) >
-1
2
-1
spectral peak in the low-frequency region below 30 cm in the
tributyldecylphosphonium-based ILs, although the peak is a
little ambiguous for the spectral density of the cation (Figure
S1 of the Electronic Supporting Information). Previously, we
assigned the peak for imidazolium-based ILs with these anions
to the anion species, and the trend for the ILs was the same as
+
149
the results of [Pyrr14] -based ILs.
This order is trivial,
because the order of the peak frequencies of the three ILs is the
inverse of the trend of the volumes and masses of the anion
species. In addition to the order of the peak frequencies, the
spectral intensity in the higher frequency region above ~50
-1
2 2
cm increased in the order of [Pyrr14][NF ] < [Pyrr14][NTf ] <
[
Pyrr14][NPf
The line shape of the low-frequency spectrum of
Pyrr14][OTf] is quite different from those of [Pyrr14][NF ],
Pyrr14][NTf ], and [Pyrr14][NPf ]; rather, it is closer to that of
Pyrr1(1O2)][PF ], [Pyrr1(1O2)][BF ] (Figure
2
].
[
[
[
2
2
2
6
4 4
], and [N122(1O2)][BF
–
1
1). In fact, the polarizability anisotropy of [OTf] is almost
–
3
null (anis([OTf] ) = 0.327 Å , Table S2-4 of the Electronic
Supporting Information). On the other hand, the other anions
possess the substantial magnitudes of the polarizability
anisotropy (anis([NF
and (anis([NPf
–
3
–
3
2
] ) = 3.396 Å , anis([NTf
2
] ) = 3.942 Å ,
–
3
2
] ) = 6.052 Å , Table S2-4 of the Electronic
Supporting Information). Thus, the distinct line shape of the
low-frequency spectrum of [Pyrr14][OTf] compared to
[
Pyrr14][NF
2 2 2
], [Pyrr14][NTf ], and [Pyrr14][NPf ] is attributed to
Figure 12. Low-frequency Kerr spectra of (a)
the polarizability anisotropy of the anion.
[Pyrr14][NF
2 2 2
], (b) [Pyrr14][NTf ], (c) [Pyrr14][NPf ], (d)
The line shape of the low-frequency Kerr spectrum of
Pyrr14][NCyF] is triangular and similar to those of
Pyrr14][NF
[Pyrr14][NCyF], and (e) [Pyrr14][OTf].
[
[
2
], [Pyrr14][NTf
2
], and [Pyrr14][NPf
2
], as shown in
–
12 are assigned to the modes of the anion species. The quantum
chemistry calculations also show no strong Raman-active
Figure 12. [NCyF] possesses
polarizability anisotropy value (anis([NCyF] ) = 2.694 Å ,
Table S2-4 of the Electronic Supporting Information) as [NF
a
similar structure and
–
3
-1
–
modes in the low-frequency region below 70 cm . Thus, the
differences in the low-frequency broadened spectra of
2
] ,
–
–
[NTf
2
] , and [NPf
2
] .
–
2 2 2
[Pyrr14][NF ], [Pyrr14][NTf ], [Pyrr14][NPf ], [Pyrr14][NCyF],
Figure 13 shows the calculated Raman spectra of [NF
2
] ,
–
–
–
–
and [Pyrr14][OTf] shown in Figure 12 arise primarily from the
difference in the intermolecular vibrations of the anion species.
The line shape of the low-frequency spectrum of
[NTf
2
2
] , [NPf ] , [NCyF] , and [OTf] . The strong Raman
-1
–
-1
–
bands at 104 cm for [NTf
coupled bending modes (symmetric N–S–C bending motions).
The strong bands at 120 cm observed in the Kerr spectrum of
2 2
] and at 95 cm for [NPf ] are the
-1
[Pyrr14][NCyF] is similar to that of [Pyrr14][NTf
2
] and
-1
[Pyrr14][NPf ]. On the other hand, the spectral shape for
2
2 2
[Pyrr14][NTf ] and 106 cm for [Pyrr14][NPf ] shown in Figure
12

–
3
–
anisotropies (anis([DCA] ) = 8.035 Å and anis([TCM] ) =
6
3
.883 Å , Table S2-4 of the Electronic Supporting Information)
and the strong librational motions of the anions. Previously, we
observed that the temperature-dependent spectral features of
+
the low-frequency spectra of [Pyrr14] -based ILs, as well as
1
-butyl-3-methylimidazolium-based ILs, with flat- and
–
–
– 63,150
rod-shaped anions, such as [DCA] , [TCM] , and [SCN] ,
were different from those of the ILs with common anions, e.g.,
–
–
–
2 4
[NTf ] , [BF ] , [OTf] . The difference spectra between the
low-frequency spectra at 293 K and higher temperatures of
these ILs showed a negative difference spectral area in the
-1
frequency region of ~50–100 cm . This feature is attributed to
the red shift of the librational motion of the flat- and
rod-shaped anions, because it is also commonly observed in the
aromatic cation based ILs owing to the librational motions of
Figure 13. Calculated Raman spectra of [NF
2
]– (black
–
–
–
2 2
line), [NTf ] (blue line), [NPf ] (red line), [NCyF]
–
34
(
green line), and [OTf] (purple line) optimized at the
the aromatic cations.
B3LYP/6-311+G(d,p) level of theory.
The line shapes of the low-frequency spectra of
[
Pyrr14][DCA] and [Pyrr14][TCM] are similar. However, the
-1
peak frequency of the spectrum of [Pyrr14][DCA] (35 cm ) is
higher than that of [Pyrr14][TCM] (32 cm ). This indicates that
the bulk and higher molecular weight of [TCM] as compared
to that of [DCA] slows the librational motion of the former
[
Pyrr14][OTf], whose anion is a simple mono functional-type, is
-1
+
monomodal and totally different from that of [Pyrr14] -based
ILs with the bis(sulfonyl)amide-type anions whose spectral
–
–
shape
is
triangular.
Therefore,
the
anion.
bis(perfluoroalkylsulfonyl)amide-type anions give a unique
Figure 15 shows the low-frequency spectrum of
-1
triangular line shape having a peak at ~20 cm in the
low-frequency spectrum, regardless of whether there could be
different conformers or not (rigid cyclic shape).
[Pyrr14][FAP]. The line shape of the low-frequency spectrum of
-
1
[
Pyrr14][FAP] is a triangle having a peak at 19 cm and similar
], [Pyrr14][NPf ], and [Pyrr14][NCyF]
Figure 12). It appears that the ILs with non-spherical top
anions having relatively large molecular weights (M > ~200
g/mol) show a triangular low-frequency spectrum peaked at
to that of [Pyrr14][NTf
(
2
2
The low-frequency spectra of [Pyrr14][DCA] and
[Pyrr14][TCM] are shown in Figure 14, which compares the
w
different numbers of cyano groups in the anion. On the basis of
the quantum chemistry calculations, the strong band at 180
-1
~
20 cm . Such a triangular line shape of the low-frequency
-1
cm for [Pyrr14][DCA] is assigned to the bending mode
spectrum of ILs with non-spherical top anions having relatively
large molecular weight, such as [FAP] , [NF
–
-1
(NC–N–CN) of [DCA] , and that at 157 cm
for
–
–
–
2
] , [NTf
2
] ,
[Pyrr14][TCM] is assigned to the degeneracy bending modes
–
–
[
NPf ] , and [NCyF] , might arise from the librational motion
2
–
(NC–C–CN) of [TCM] . Regarding the frequency region below
of the anions. In comparison to the calculated Raman spectrum,
-1
~
100 cm , the intensities of the low-frequency spectra of
[Pyrr14][DCA] and [Pyrr14][TCM] shown in Figure 14 are very
high as compared with the low-frequency spectra of
+
[
Pyrr14] -based ILs (see Figure 12). The strong spectrum
intensities in these ILs are attributed to the larger polarizability
Figure 15. (a) Low-frequency Kerr spectrum of
[
Pyrr14][FAP] and (b) calculated Raman spectrum of
–
[FAP] optimized on the basis of the B3LYP/6-311+G(d,p)
Figure 14. Comparison of low-frequency Kerr spectra of
level of theory.
(a) [Pyrr14][DCA] and (b) [Pyrr14][TCM].
13

many bands above 100 cm-1 in the Kerr spectrum are
essentially attributable to the intramolecular vibrational bands
of [FAP] .
Figure 16 shows the low-frequency Kerr spectra of the
[Pyrr1n][NTf ] series. Though there are small differences in the
spectral shapes in the frequency range from 150 to 250 cm of
the [Pyrr1n][NTf ] series probably owing to the intramolecular
2
–
-1
4
.2.3 Effects of Cation Species: We examine the effect
2
of the cation species on the low-frequency Kerr spectrum in
this section. Compared to the anion species, the contribution
of the cation species to the low-frequency Kerr spectrum in ILs
is not large. However, it is also important to understand the
effect of the cations on the low-frequency Kerr spectrum in
detail.
vibrational modes of the alkyl groups, the line shapes of the
low-frequency broadened bands in the frequency below 100
-1
cm are quite similar. This spectral feature in the [Pyrr1n][NTf
series is in contrast to the [C MIm][NTf ] series. The difference
in the line shapes of the low-frequency spectra of the
[C MIm][NTf ] series was attributed to the bending mode
between the imidazolium ring and alkyl group, which shifts to
2
]
n
2
n
2
5
9
lower frequencies for ILs with longer (heavier) alkyl groups.
+
Calculated Raman spectra of the [Pyrr1n] based on the ab
initio quantum chemistry calculations are shown in Figure 17.
A significant alkyl group substitution effect is confirmed in the
bend and torsion coupled with the pyrrolidinium ring torsion:
35 cm for [Pyrr13] , 300 cm for [Pyrr14] , 240 cm for
Pyrr16] , 178 cm for [Pyrr18] , and 155 cm for [Pyrr1,10] .
-
1
+
-1
+
-1
3
+
-1
+
-1
+
[
On the other hand, the Raman intensities of the low-frequency
-1
+
modes below 100 cm of [Pyrr1n] are very weak. Therefore, it
is as concluded that the intramolecular band does not influence
the line shape of the low-frequency spectrum. Consequently,
the line shapes of the low-frequency Kerr spectra of the five
2
[Pyrr1n][NTf ] are quite similar (Figure 16).
Figure 17. Calculated Raman spectra of [Pyrr13]+ (black
+
+
+
line), [Pyrr14
(
]
(red line), [Pyrr16
]
(blue line), [Pyrr18
]
+
green line), and [Pyrr1,10] (purple line) optimized at the
B3LYP/6-311+G(d,p) level of theory.
Figure 18 compares the low-frequency Kerr spectra of the
ammonium- and phosphonium-based ILs, [N1444][NTf
2
] and
-1
[P1444][NTf ]. The spectral intensity at ~50 cm relative to that
2
-1
at ~20 cm is slightly higher in [P1444][NTf
2
] as compared to
[
[
N
N
1444][NTf
2228][NTf
2
]. Such a spectral feature was also observed in
6
1
2
] and [P2228][NTf
2
]
(also see the Electronic
Supporting Information). Because the phosphonium cations
show stronger intramolecular vibrational bands in the
-1
frequency range above 150 cm than the ammonium cations,
the spectral wing at the low-frequency side of the
intramolecular vibrational bands likely contribute to the higher
-1
relative intensity at ~50 cm in the phosphonium-based ILs as
compared to the ammonium-based ILs. Compared to the
+
+
calculated Raman spectra of [N1444
quantum chemistry calculations
]
and [P1444
based
]
by the
the
on
B3LYP/6-311+G(d,p) level of theory shown in Figure 19, one
can think that the stronger spectral intensity in the frequency
-1
region 50 – 100 cm of the low-frequency Kerr spectrum of
] than that of [N1444][NTf ] might be attributed to
the lower frequencies of the torsional motions of the butyl
[
P
1444][NTf
2
2
Figure 16. Low-frequency Kerr spectra of the
[
[
(
Pyrr1n][NTf
Pyrr14][NTf
e) [Pyrr1,10][NTf
2
]
series.
], (c) [Pyrr16][NTf
].
(a)
[Pyrr13][NTf
], (d) [Pyrr18][NTf
2
],
(b)
], and
+
+
groups in [P1444
frequency of 170 – 300 cm in Figure 19 are only the most
]
than [N1444
]
(note that bands in the
2
2
2
-1
2
stable conformation in each cation).
14

Figure 20. Low-frequency Kerr spectra of [Pyrr14][NF
blue) and [Pyrr1(1O2)][NF ] (red).
2
]
(
2
intramolecular Raman-active band is also observed for the
+
-1
optimized [Pyrr1(1O2)
]
at ~250 cm (see Figure 21). The
-1
+
vibrational band at ~240 cm of [Pyrr1(1O2)] is hard to confirm
in the ILs with more complicated anions, but the ILs with
–
–
4 6
simpler anions ([BF ] and [PF ] ) also show this band (Figure
S1 of the Electronic Supporting Information).
Figure 18. Comparison of low-frequency Kerr spectra of
ammonium-
and
phosphonium-based
].
ILs.
(a)
[
N1444][NTf
2
] and (b) [P1444][NTf
2
The low-frequency Kerr spectra of [Pyrr14][NF
2
] and
2
[Pyrr1(1O2)][NF ] are shown in Figure 20 and illustrate the effect
of substituting an alkyl group with its respective alkoxyalkyl
group. The spectral line shapes of the two ILs are quite similar,
as shown in Figure 20. A small difference in the low-frequency
spectra between the two ILs is confirmed in the frequency
-
1
range of ~80–150 cm . [Pyrr1(1O2)][NF
higher spectral intensity in this frequency region than
Pyrr14][NF ]. Other ILs with butyl and methoxyethyl groups in
this study also show similar spectral line shapes. This spectral
feature was also confirmed in [Pyrr14][NTf and
]. As seen in the spectra of the Raman-active
2
] shows a slightly
Figure 21. Calculated Raman spectra of [Pyrr14]+ (blue
[
2
+
line) and [Pyrr1(1O2)
]
(red line) optimized at the
B3LYP/6-311+G(d,p) level of theory.
2
]
[
Pyrr1(1O2)][NTf
normal modes of [Pyrr14
B3LYP/6-311+G(d,p) level of theory of Figure 21, [Pyrr1(1O2)
has a weak intramolecular mode at ~140 cm that is the
torsional mode of the pyrrolidinium ring coupled with the
bending motion of the methoxyethyl group and pyrrolidinium
ring. This vibrational band can influence the slight difference in
the frequency region of ~80–150 cm . In addition, we found a
weak intramolecular vibrational band at ~240 cm of
Pyrr1(1O2)] , which is not observed in [Pyrr14] . A weak
2
+
+
4.3 Relationship between Low-Frequency Spectrum and
Bulk Parameter
]
and [Pyrr1(1O2)
]
based on the
+
]
-1
Previously, we have reported that there is a linear
1
/2
relationship between M and (/) for forty aprotic molecular
1
1
3
liquids. The idea of this type of plots is based on a simple
consideration that the intermolecular vibrational band regards
as the harmonic oscillator. The vibrational frequency of the
harmonic oscillator 휈̃ is given as
-1
-1
+
+
[
ꢋ
푘
휇
휈̃ =
√
(20)
ꢂ휋푐
where c is the velocity of light, k is the force constant, and  is
the reduced mass. For the intermolecular vibrational band, Eq.
(20) can be rewritten as
훾
휌
푀 ∝ √
(21)
1
The constants k and  in the harmonic oscillator correspond to
and  in the intermolecular vibration, respectively. It should
be noted that k and  are the parameters of the oscillator itself
intramolecular parameters), but  and  are the bulk

(
Figure 19. Calculated Raman spectra of [N1444]+ (red line)
parameters. In a sense, Eq. (21) implies a sort of scaling
relation between the microscopic (intermolecular vibration) and
macroscopic (bulk liquid properties) quantities. A linear
+
and
[P1444
]
(blue
line)
optimized
at
the
B3LYP/6-311+G(d,p) level of theory.
1
/2
relation between M
1
and (/) was also observed in aromatic
cation based ILs, although it is different from that for aprotic
15

molecular liquids.59
Figure 22 plots the M
the ILs show different relations for nonaromatic and aromatic
ILs. In addition, the relation for nonaromatic ILs is close to that
values to the (/)1/2 for the
1
1
/2
nonaromatic cation based ILs. As shown in the figure, there is a
mild linear correlation between the two quantities, though the
data are scattered compared to aprotic MLs. The figure also
shows that the relation for the nonaromatic cation based ILs is
close to that for aprotic molecular liquids, but clearly different
from that for aromatic cation based ILs. The relations estimated
by the linear fits together with their correlation parameters, r,
are followings:
for aprotic MLs. This relation between M
1
and (/) in
liquids seems to be universal, except for aromatic cation based
1
/2
1
ILs. However, slightly weaker (/) dependence of M is
observed for the nonaromatic cation based ILs than aprotic
MLs. This might also be originated from the micro segregation
structure in nonaromatic cation based ILs, though it is not
significant when compared to that in aromatic cation based ILs.
1
/2
We therefore believe that the relation between M and (/) in
1
liquids is rather universal, although the segregation structure
also influences the relation. Accordingly, liquids with no
segregation structure likely obey this relationship between the
microscopic and macroscopic quantities.
푀 (cmꢌ1) = 7.ꢋꢋ(±ꢋ.ꢂ8)ꢍ훾(mN/m)⁄휌(g/mꢎ) +
1
ꢋ4.5(±7.ꢏ)
(푟 = ꢏ.67)
(
nonaromatic cation based ILs)
(22)
푀 (cmꢌ1) = 3.5ꢋ(±ꢏ.95)ꢍ훾(mN/m)⁄휌(g/mꢎ) +
1
5
. Conclusions
4
8.6(±5.ꢂ)
(
(푟 = ꢏ.5ꢋ)
In this study, we reported the low-frequency spectral data
of as many as forty nonaromatic cation based ILs via fs-RIKES,
as well as the data of liquid properties, , , , and . On the
basis of the data of liquid properties of [Pyrr14] -based ILs, the
following trends were identified:
density (), [FAP] > [NPf
OTf] > [DCA] ~ [TCM] ;
viscosity (), [NCyF] > [NPf
NF ] > [DCA] > [TCM] ;
2
aromatic cation based ILs)59
(23)
(24)
푀 (cmꢌ1) = ꢋꢋ.ꢂ(±ꢏ.9)ꢍ훾(mN/m)⁄휌(g/mꢎ) −
1
+
9
.ꢋꢂ(±5.ꢋ)
(푟 = ꢏ.86)
(
aprotic MLs)13,72,151
–
–
–
]– > [NF
2
]– >
]– >
2
–
] > [NCyF] > [NTf
2
–
–
[
It should be reminded that the relation for aprotic molecular
liquids includes the data for both aromatic and nonaromatic
MLs.
–
–
–
–
2
] > [FAP] > [OTf] > [NTf
2
–
–
–
[
–
]– > [TCM]–
electrical conductivity (), [DCA] > [NF
] > [OTf] > [FAP] > [NCyF] > [NPf ] ;
2 2
surface tension (), [DCA] > [TCM] > [NF
2
–
>
–
–
–
–
[NTf
–
–
–
–
2
] > [OTf] >
–
–
–
–
[
NCyF] > [FAP] ~ [NTf
2 2
] > [NPf ] .
On the basis of the results of the [Pyrr1n][NTf
2
] series, the
relationships between the liquid properties and the number of
carbons of the alkyl groups for 1-alkyl-1-methylpyrrolidinium
-1
cations were also estimated. The plots of  or  vs.  for the
nonaromatic cation based ILs showed a linear relationship,
which was somewhat different from that of aromatic cation
based ILs. In addition, the relationship between  and V
m
for
nonaromatic cation based ILs, especially in the lower V region
m
below ~300 mL/mol, was different from that in the case of
aromatic cation based ILs.
Further, the broad low-frequency Kerr spectra in the
-1
frequency below ~200 cm were discussed on the basis of the
ion species. Compared to common aromatic cation based ILs,
the intensity of the low-frequency spectrum of nonaromatic
cation based ILs was quite low because of the absence of an
aromatic ring, whose libration has a strong spectral intensity.
However, ILs with a flat anion, such as dicyanamide and
tricyanomethide, showed a relatively strong spectral density
owing to the libration of the anions. From the comparison of
Figure 22. Plots of M
cation based ILs (red circles). Linear fit for the data is
shown by a red solid line. Relationships between M and
1
versus (/)1/2 for nonaromatic
1
1
/2
(
/) for aprotic MLs (nonaromatic MLs: black circles;
13,72,151
aromatic MLs: black triangles)
based ILs (blue triangles).
and aromatic cation
5
9
–
–
–
+
2 2 2
the anions [NF ] , [NTf ] , and [NPf ] for [Pyrr14] -based ILs
In previous preliminary results, a less sensitive M
/)1/2 relation is found for the aromatic cation based ILs than
aprotic MLs and nonaromatic cation based ILs (only ten
1
to
and 1-(methoxy)ethyl-1-methylpyrroldnium-based ILs, the
(
-1
peak at ~20 cm shifted to lower frequency with the increasing
–
–
–
size of the anions: [NF
the low-frequency spectrum of [Pyrr1n][NTf
to the alkyl group, unlike the [C MIm][NTf
2
] > [NTf
2
] > [NPf
2
] . The line shape of
] was not sensitive
] and [C Py][NTf
3
4
nonaromatic cation based ILs in that study). The weak bulk
parameter dependence of M in aromatic cation based ILs as
2
1
n
2
n
2
]
compared to that in aprotic MLs (and some nonaromatic cation
based ILs) was mainly attributed to the spectral density and the
series. From the results of the normal mode quantum chemistry
calculations of 1-alkyl-1-methylpyrrolidinium cations, it was
found that there was no intense Raman-active intramolecular
3
4
more segregated structure in ILs.
MIm][NTf ] (aromatic cation based ILs) showed clearer
low-Q (low scattering vector) peaks at ~4 nm owing to micro
segregation than 1-alkyl-1-methylpiperidinium
bis(trifluoromethylsulfonyl)amides (nonaromatic cation based
This is because
[
C
n
2
-1
vibrational band in the low-frequency region below ~100 cm ,
-1
where the intermolecular vibrational band typically appears.
The line shapes of the low-frequency Kerr spectra of
ammonium-based ILs and the respective phosphonium-based
ILs were significantly different. The difference could be largely
attributed to the lower-frequency intramolecular vibrational
bands of the phosphonium cation compared to the respective
1
52
ILs). On the basis of the data of these forty nonaromatic
cation based ILs, it is clear that the relationships for the
nonaromatic and aromatic cation based ILs are different in this
study. It should be emphasized that aprotic MLs show a single
linear correlation for both aromatic and nonaromatic MLs, but
ammonium cation. The substitution of the butyl group of
+
[
Pyrr14] by a methoxyethyl group did not influence the line
16

shape of the low-frequency spectrum of the ILs.
19 P. Wasserscheid, T. Welton, Ionic Liquids in Synthesis. 2
ed., P. Wasserscheid, T. Welton, Wiley-VCH, Weinheim, 2008.
20 H. Ohno, Electrochemical Aspects of Ionic Liquids. H.
Ohno, Wiley-Interscience, Hoboken, 2005.
21 J. A. Ingram, R. S. Moog, N. Ito, R. Biswas, M.
Maroncelli, J. Phys. Chem. B 2003, 107, 5926-5932.
22 A. Samanta, J. Phys. Chem. Lett. 2010, 1, 1557-1562.
23 Y. Nagasawa, J. Photochem. Photobiol. C: Photochem.
Rev. 2011, 12, 31-45.
In addition, a linear relationship between the first moment
M
(
1
of the low-frequency spectrum and the bulk parameter,
/)1/2, was observed. Compared to our previous studies of
1
3
59
aprotic MLs and aromatic ILs, this relationship for the
nonaromatic cation based ILs was quite similar to that for
aprotic MLs, including nonaromatic and aromatic analogs.
However, it was different from that for aromatic cation based
1
/2
ILs. The distinct feature in the relation between M and (/)
1
for aromatic cation based ILs could be attributed to the
significant segregation liquid structure in these ILs as
compared to the nonaromatic cation based ILs, as well as
aprotic MLs.
24 Y. Murakami, H. Kikuchi, A. Kawai, J. Phys. Chem. B
2013, 117, 5180-5187.
25 K. Fujii, M. Aramaki, Y. Kimura, J. Phys. Chem. B 2018,
122, 12363-12374.
2
6
C. Hardacre, J. D. Holbrey, M. Nieuwenhuyzen, T. G. A.
Acknowledgements
Youngs, Acc. Chem. Res. 2007, 40, 1146-1150.
27 E. W. Castner, Jr., C. J. Margulis, M. Maroncelli, J. F.
Wishart, Annu. Rev. Phys. Chem. 2011, 62, 85-105.
28 O. Russina, A. Triolo, L. Gontrani, R. Caminiti, J. Phys.
Chem. Lett. 2012, 3, 27-33.
This work was partially supported by JSPS KAKENHI
(15K05377 and 19K05382), the Takahashi Industrial and
Economic Research Foundation, and Chiba University (Global
Prominent Research Program: Soft Molecular Activation). S.K.
was supported by JSPS Research Fellowship for Young
Scientists (18J12979).
29 J. C. Araque, J. J. Hettige, C. J. Margulis, J. Phys. Chem.
B 2015, 119, 12727-12740.
3
0
E. W. Castner, Jr., J. F. Wishart, H. Shirota, Acc. Chem.
Electronic Supporting Information
Res. 2007, 40, 1217-1227.
Synthethesis procedures of ILs, quantum chemistry
calculation results, data of the Kerr transients and Fourier
transform Kerr spectra, and lists of the fitting parameters for
the Kerr transients and spectra of the nonaromatic cation based
ILs are given in the Electronic Supporting Information.
31 K. Iwata, H. Okajima, S. Saha, H.-O. Hamaguchi, Acc.
Chem. Res. 2007, 40, 1174-1181.
32 K. Fumino, S. Reimann, R. Ludwig, Phys. Chem. Chem.
Phys. 2014, 16, 21903-21929.
33 V. H. Paschoal, L. F. O. Faria, M. C. C. Ribeiro, Chem.
Rev. 2017, 117, 7053-7112.
References
34 H. Shirota, ChemPhysChem 2012, 13, 1638-1648.
35 H. Shirota, H. Fukazawa, in Ionic Liquids: Theory,
Properties, New Approaches, ed. by A. Kokorin, InTech, Rijeka,
Croatia, 2011, Chap. 9, pp. 201-224.
1
A. Nitzan, Chemical Dynamics in Condensed Phases.
Relaxation, Transfer and Reactions in Condensed Molecular
Systems., Editor, Oxford University Press, Oxford, 2006.
2
A. M. Kelley, Condensed-Phase Molecular Spectroscopy
36 T. Sonnleitner, D. A. Turton, S. Waselikowski, J. Hunger,
A. Stoppa, M. Walther, K. Wynne, R. Buchner, J. Mol. Liq.
2014, 192, 19-25.
and Photophysics. Editor, John Wiley & Sons, Inc., Hoboken,
2
013.
3
D. McMorrow, W. T. Lotshaw, G. A. Kenney-Wallace,
37 B. R. Hyun, S. V. Dzyuba, R. A. Bartsch, E. L. Quitevis, J.
Phys. Chem. A 2002, 106, 7579-7585.
IEEE J. Quantum. Electron. 1988, QE-24, 443-454.
4
5
6
4
7
R. Righini, Science 1993, 262, 1386-1390.
C. A. Schmuttenmaer, Chem. Rev. 2004, 104, 1759-1779.
J. B. Baxter, G. W. Guglietta, Anal. Chem. 2011, 83,
38 J. R. Rajian, S. F. Li, R. A. Bartsch, E. L. Quitevis, Chem.
Phys. Lett. 2004, 393, 372-377.
39 D. Xiao, J. R. Rajian, A. Cady, S. Li, R. A. Bartsch, E. L.
Quitevis, J. Phys. Chem. B 2007, 111, 4669-4677.
40 D. Xiao, L. G. Hines, Jr., S. Li, R. A. Bartsch, E. L.
Quitevis, O. Russina, A. Triolo, J. Phys. Chem. B 2009, 113,
6426-6433.
41 H. Shirota, A. M. Funston, J. F. Wishart, E. W. Castner, Jr.,
J. Chem. Phys. 2005, 122, 184512/1-12.
42 H. Shirota, K. Nishikawa, T. Ishida, J. Phys. Chem. B
2009, 113, 9831-9839.
342-4368.
W. T. Lotshaw, D. McMorrow, N. Thantu, J. S. Melinger,
R. Kitchenham, J. Raman Spectrosc. 1995, 26, 571-583.
S. Kinoshita, Y. Kai, T. Ariyoshi, Y. Shimada, Inter. J.
Mod. Phys. B 1996, 10, 1229-1272.
8
9
1
1
E. W. Castner, Jr., M. Maroncelli, J. Mol. Liq. 1998, 77,
-36.
0
J. T. Fourkas, in Ultrafast Infrared and Raman
Spectroscopy, ed. by M. D. Fayer, Marcel Dekker, Inc. , New
York, 2001, Chap. 11, pp. 473-512.
43 H. Shirota, T. Ishida, J. Phys. Chem. B 2011, 115,
10860-10870.
1
1
N. A. Smith, S. R. Meech, Int. Rev. Phys. Chem. 2002, 21,
5-100.
Q. Zhong, J. T. Fourkas, J. Phys. Chem. B 2008, 112,
5529-15539.
H. Shirota, T. Fujisawa, H. Fukazawa, K. Nishikawa, Bull.
44 H. Shirota, H. Matsuzaki, S. Ramati, J. F. Wishart, J.
Phys. Chem. B 2015, 119, 9173-9187.
45 S. Kakinuma, S. Ramati, J. F. Wishart, H. Shirota, J.
Chem. Phys. 2018, 148, 193805/1-10.
46 D. Xiao, J. R. Rajian, S. F. Li, R. A. Bartsch, E. L.
Quitevis, J. Phys. Chem. B 2006, 110, 16174-16178.
47 D. Xiao, J. R. Rajian, L. G. Hines, Jr., S. Li, R. A. Bartsch,
E. L. Quitevis, J. Phys. Chem. B 2008, 112, 13316-13325.
48 F. Bardak, D. Xiao, L. G. H. Jr., P. Son, R. A. Bartsch, E.
L. Quitevis, P. Yang, G. A. Voth, ChemPhysChem 2012, 13,
1687-1700.
7
1
1
1
2
3
Chem. Soc. Jpn. 2009, 82, 1347-1366.
B. J. Loughnane, R. A. Farrer, A. Scodinu, T. Reilly, J. T.
Fourkas, J. Phys. Chem. B 2000, 104, 5421-5429.
1
4
1
6
1
5
R. A. Farrer, J. T. Fourkas, Acc. Chem. Res. 2003, 36,
05-612.
N. T. Hunt, A. A. Jaye, S. R. Meech, Phys. Chem. Chem.
6
Phys. 2007, 9, 2167-2180.
J. S. Wilkes, M. J. Zaworotko, J. Chem. Soc., Chem.
Commun. 1992, 965-967.
J. S. Wilkes, Green Chem. 2002, 4, 73-80.
49 L. Xue, G. Tamas, R. P. Matthews, A. J. Stone, P. A. Hunt,
E. L. Quitevis, R. M. Lynden-Bell, Phys. Chem. Chem. Phys.
2015, 17, 9973-9983.
1
7
1
8
50 E. Gurung, D. Meng, L. Xue, G. Tamas, R. M.
17

Lynden-Bell, E. L. Quitevis, Phys. Chem. Chem. Phys. 2018,
Farkas, J. B. Foresman, D. J. Fox, Gaussian 16. Editor,
Gaussian, Inc., Wallingford, CT, 2016.
76 D. A. Long, The Raman Effect. Editor, John Wiley &
Sons, West Sussex, 2002.
77 D. McMorrow, W. T. Lotshaw, Chem. Phys. Lett. 1990,
174, 85-94.
2
5
0, 26558-26569.
G. Giraud, C. M. Gordon, I. R. Dunkin, K. Wynne, J.
1
Chem. Phys. 2003, 119, 464-477.
D. A. Turton, J. Hunger, A. Stoppa, G. Hefter, A. Thoman,
M. Walther, R. Buchner, K. Wynne, J. Am. Chem. Soc. 2009,
5
2
1
5
1
5
5
31, 11140-11146.
78 D. McMorrow, W. T. Lotshaw, J. Phys. Chem. 1991, 95,
10395-10406.
79 J. A. Bucaro, T. A. Litovitz, J. Chem. Phys. 1971, 54,
3846-3853.
80 Y. J. Chang, E. W. Castner, Jr., J. Chem. Phys. 1993, 99,
7289-7299.
3
H. Shirota, R. Biswas, J. Phys. Chem. B 2012, 116,
3765-13773.
4
5
H. Shirota, J. Phys. Chem. B 2013, 117, 7985-7995.
H. Shirota, S. Kakinuma, Y. Itoyama, T. Umecky, T.
Takamuku, J. Phys. Chem. B 2016, 120, 513-526.
5
1
5
6
R. Biswas, A. Das, H. Shirota, J. Chem. Phys. 2014, 141,
34506/1-11.
E. W. Castner, Jr., Y. J. Chang, Y. C. Chu, G. E. Walrafen,
81 J. L. McHale, Molecular Spectroscopy. 2nd ed., Editor,
CRC Press, Boca Raton, 2017.
82 S. Ryu, R. M. Stratt, J. Phys. Chem. B 2004, 108,
6782-6795.
7
J. Chem. Phys. 1995, 102, 653-659.
5
2
5
8
C. J. Fecko, J. D. Eaves, A. Tokmakoff, J. Chem. Phys.
002, 117, 1139-1154.
H. Shirota, S. Kakinuma, K. Takahashi, A. Tago, H.
83 M. D. Elola, B. M. Ladanyi, J. Chem. Phys. 2005, 122,
224506-1-15.
84 Z. Hu, X. Huang, H. V. R. Annapureddy, C. J. Margulis, J.
Phys. Chem. B 2008, 112, 7837-7849.
9
Jeong, T. Fujisawa, Bull. Chem. Soc. Jpn. 2016, 89, 1106-1128.
6
2
6
0
T. Fujisawa, K. Nishikawa, H. Shirota, J. Chem. Phys.
009, 131, 244519-1-14.
H. Shirota, H. Fukazawa, T. Fujisawa, J. F. Wishart, J.
85 T. Ishida, K. Nishikawa, H. Shirota, J. Phys. Chem. B
2009, 113, 9840-9851.
86 T. Ishida, H. Shirota, J. Phys. Chem. B 2013, 117,
1136-1150.
1
Phys. Chem. B 2010, 114, 9400-9412.
6
6
6
1
6
2
S. Kakinuma, H. Shirota, J. Phys. Chem. B 2018, 122,
87 J. S. Bender, S. R. Cohen, X. He, J. T. Fourkas, B.
Coasne, J. Phys. Chem. B 2016, 120, 9103-9114.
88 J. S. Bender, J. T. Fourkas, B. Coasne, J. Phys. Chem. B
2016, 121, 11376-11382.
89 S. Katsuta, Y. Shiozawa, K. Imai, Y. Kudo, Y. Takeda, J.
Chem. Eng. Data 2010, 55, 1588-1593.
033-6047.
3
307-1323.
4
S. Kakinuma, H. Shirota, J. Phys. Chem. B 2019, 123,
D. A. Turton, T. Sonnleitner, A. Ortner, M. Walther, G.
Hefter, K. R. Seddon, S. Stana, N. V. Plechkova, R. Buchner, K.
Wynne, Faraday Discuss. 2012, 154, 145-153.
90 T. Abdallah, D. Lemordant, B. Claude-Montigny, J.
Power Sources 2012, 201, 353-359.
6
5
T. Sonnleitner, D. A. Turton, G. Hefter, A. Ortner, S.
Waselikowski, M. Walther, K. Wynne, R. Buchner, J. Phys.
Chem. B 2015, 119, 8826-8841.
91 M. L. P. Le, F. Alloin, P. Strobel, J.-C. Lepretre, C. P. d.
Valle, P. Judeinstein, J. Phys. Chem. B 2010, 114, 894-903.
92 Z.-B. Zhou, H. Matsumoto, K. Tatsumi, Chem.-Eur. J.
2005, 11, 752-766.
93 D. Blanco, J. L.Viesca, M. T. Mallada, B. Ramajo, R.
Gonzalez, A. H. Battez, Surf. Coat. Technol. 2016, 302, 13-21.
94 A. Bhattacharjeea, A. Luis, J. H. Santos, J. A.
Lopes-da-Silva, M. G. Freirea, P. J. Carvalhoa, J. A. P.
Coutinho, Fluid Phase Equilib. 2014, 381, 36-45.
95 K. Tsunashima, S. Kodama, M. Sugiya, Y. Kunugi,
Electrochim. Acta 2010, 56, 762-766.
6
6
J. Reichenbach, S. A. Ruddell, M. Gonzalez-Jimenez, J.
Lemes, D. A. Turton, D. J. France, K. Wynne, J. Am. Chem.
Soc. 2017, 139, 7160-7163.
6
7
H. Shirota, K. Takahashi, M. Ando, S. Kakinuma, J.
Chem. Eng. Data 2019, 64, 4701-4707.
6
2
6
2
7
8
H. Shirota, E. W. Castner, Jr., J. Phys. Chem. B 2005, 109,
1576-21585.
9
010, 114, 6323-6331.
0
T. Masaki, K. Nishikawa, H. Shirota, J. Phys. Chem. B
H. Shirota, T. Mandai, H. Fukazawa, T. Kato, J. Chem.
96 M. H. Ghatee, M. Bahrami, N. Khanjari, J. Chem.
Thermodyn. 2013, 65, 42-52.
Eng. Data 2011, 56, 2453-2459.
7
7
7
7
7
7
1
2
3
4
H. Shirota, J. Chem. Phys. 2005, 122, 044514/1-12.
H. Shirota, J. Phys. Chem. A 2011, 115, 14262-14275.
A. D. Becke, J. Chem. Phys. 1993, 98, 5648-5652.
C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37,
97 M. Krolikowski, M. Krolikowska, C. Wisniewski, J.
Chem. Thermodyn. 2016, 103, 115-124.
98 O. Borodin, W. Gorecki, G. D. Smith, M. Armand, J.
Phys. Chem. B 2010, 114, 6786-6798.
99 G. B. Appetecchi, M. Montanino, M. Carewska, M.
Moreno, F. Alessandrini, S. Passerini, Electrochim. Acta 2011,
56, 1300-1307.
100 G. Annat, M. Forsyth, D. R. MacFarlane, J. Phys. Chem.
B 2012, 116, 8251-8258.
101 T. Makino, M. Kanakubo, T. Umecky, A. Suzuki, T.
Nishida, J. Takano, J. Chem. Eng. Data 2012, 57, 751-755.
102 U. Domanska, P. Okuniewska, K. Paduszynski, M.
Krolikowska, M. Zawadzki, M. Wieckowski, J. Phys. Chem. B
2017, 121, 7689-7698.
103 G. McHale, C. Hardacre, R. Ge, N. Doy, R. W. K. Allen,
J. M. MacInnes, M. R. Bown, M. I. Newton, Anal. Chem. 2008,
80, 5806-5811.
104 F. M. Gacino, T. Regueira, L. Lugo, M. J. P. Comunas, J.
Ferandez, J. Chem. Eng. Data 2011, 56, 4984-4999.
105 M. Moreno, M. Montanino, M. Carewska, G. B.
Appetecchi, S. Jeremias, S. Passerini, Electrochim. Acta 2013,
85-589.
M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E. Scuseria,
5
M. A. Robb, J. R. Cheeseman, G. Scalmani, V. Barone, G. A.
Petersson, H. Nakatsuji, X. Li, M. Caricato, A. V. Marenich, J.
Bloino, B. G. Janesko, R. Gomperts, B. Mennucci, H. P.
Hratchian, J. V. Ortiz, A. F. Izmaylov, J. L. Sonnenberg, D.
Williams-Young, F. Ding, F. Lipparini, F. Egidi, J. Goings, B.
Peng, A. Petrone, T. Henderson, D. Ranasinghe, V. G.
Zakrzewski, J. Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M.
Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T.
Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K.
Throssell, J. J. A. Montgomery, J. E. Peralta, F. Ogliaro, M. J.
Bearpark, J. J. Heyd, E. N. Brothers, K. N. Kudin, V. N.
Staroverov, T. A. Keith, R. Kobayashi, J. Normand, K.
Raghavachari, A. P. Rendell, J. C. Burant, S. S. Iyengar, J.
Tomasi, M. Cossi, J. M. Millam, M. Klene, C. Adamo, R.
Cammi, J. W. Ochterski, R. L. Martin, K. Morokuma, O.
18

9
1
2
1
9, 108-116.
9, 2353-2358.
06 U. Domanska, M. Krolikowska, K. Walczak, J. Sol. Chem.
014, 43, 1929-1946.
07 V. L. Martins, A. J. R. Rennie, R. M. Torresi, P. J. Hall,
136 D. R. Lide, CRC Handbook of Chemistry and Physics. 89
ed., D. R. Lide, CRC Press, Boca Raton, 2008.
137 M. H. Ibrahim, M. Hayyan, M. A. Hashim, A. Hayyan, M.
K. Hadj-Kali, Fluid Phase Equilib. 2016, 427, 18-26.
138 W. Xu, E. I. Cooper, C. A. Angell, J. Phys. Chem. B 2003,
107, 6170-6178.
139 H. Tokuda, K. Ishii, M. A. B. H. Susan, S. Tsuzuki, K.
Hayamizu, M. Watanabe, J. Phys. Chem. B 2006, 110,
2833-2839.
140 H. Vogel, Physik. Z. 1921, 22, 645-646.
141 G. Tammann, W. Hesse, Z. Anorg. Allg. Chem. 1926, 156,
245-257.
142 G. S. Fulcher, J. Am. Ceram. Soc. 1925, 8, 789-794.
143 G. W. Scherer, J. Am. Ceram. Soc. 1992, 75, 1060-1062.
144 T. Iimori, T. Iwahashi, K. Kanai, K. Seki, J. Sung, D. Kim,
H.-o. Hamaguchi, Y. Ouchi, J. Phys. Chem. B 2007, 111,
4860-4866.
145 C. Aliaga, G. A. Baker, S. Baldelli, J. Phys. Chem. B
2008, 112, 1676-1684.
146 L. C. Geiger, B. M. Ladanyi, Chem. Phys. Lett. 1989, 159,
413-420.
147 S. Kakinuma, H. Shirota, J. Phys. Chem. B 2015, 119,
4713-4727.
148 Y. J. Chang, E. W. Castner, Jr., J. Phys. Chem. 1996, 100,
3330-3343.
Phys. Chem. Chem. Phys. 2017, 19, 16867-16874.
08 H. Jin, B. O’Hare, J. Dong, S. Arzhantsev, G. A. Baker, J.
F. Wishart, A. J. Benesi, M. Maroncelli, J. Phys. Chem. B 2008,
12, 81-92.
09 J.-M. Andanson, N. Papaiconomou, P.-A. Cable, M.
Traıkia, I. Billard, P. Husson, Phys. Chem. Chem. Phys. 2017,
9, 28834-28840.
10 T.-Y. Wu, S.-G. Su, H. P. Wang, Y.-C. Lin, S.-T. Gung,
M.-W. Lin, I.-W. Sun, Electrochim. Acta 2011, 56, 3209-3218.
11 Z.-B. Zhou, H. Matsumoto, K. Tatsumi, Chem.-Eur. J.
006, 12, 2196-2212.
12 M. J. Monteiro, F. F. Camilo, M. C. C. Ribeiro, R. M.
Torresi, J. Phys. Chem. B 2010, 114, 12488-12494.
13 K. Tsunashima, M. Sugiya, Electrochem. 2007, 75,
34-736.
14 F. Philippi, D. Rauber, J. Zapp, R. Hempelmann, Phys.
Chem. Chem. Phys. 2017, 19, 23015-23023.
15 M. Hayyan, F. S. Mjalli, M. A. Hashim, I. M. A. Nashef,
T. X. Mei, J. Ind. Eng. Chem. 2013, 19, 106-112.
16 K. R. Seddon, A. Stark, M. J. Torres, ACS Symp. Ser.
002, 819, 34-49.
17 Y. Kimura, M. Fukuda, K. Suda, M. Terazima, J. Phys.
Chem. B 2010, 114, 11847-11858.
18 R. Osada, T. Hoshino, K. Okada, Y. Ohmasa, M. Yao, J.
Chem. Phys. 2009, 130, 184705/1-8.
19 P.-Y. Chen, C. L. Hussey, Electrochim. Acta 2004, 49,
1
1
1
1
1
1
2
1
1
7
1
1
1
2
1
149 H. Fukazawa, T. Ishida, H. Shirota, J. Phys. Chem. B
2011, 115, 4621-4631.
150 S. Kakinuma, T. Ishida, H. Shirota, J. Phys. Chem. B
2017, 121, 250-264.
1
1
5
1
1
1
2
1
125-5138.
151 H. Shirota, T. Kato, J. Phys. Chem. A 2011, 115,
8797-8807.
152 A. Triolo, O. Russina, B. Fazio, G. B. Appetecchi, M.
Carewska, S. Passerini, J. Chem. Phys. 2009, 130, 164521/1-6.
20 J. Sun, M. Forsyth, D. R. MacFarlane, J. Phys. Chem. B
998, 102, 8858-8864.
21 A. Orita, K. Kamijima, M. Yoshida, J. Power Sources
010, 195, 7471-7479.
22 H. Matsumoto, H. Sakaebe, K. Tatsumi, M. Kikuta, E.
Ishiko, M. Kono, J. Power Sources 2006, 160, 1308-1313.
23 Y. Wang, K. Zaghib, A. Guerfib, F. F. C. Bazito, R. M.
Torresi, J. R. Dahn, Electrochim. Acta 2007, 52, 6346-6352.
24 C. Wolff, S. Jeong, E. Paillard, A. Balducci, S. Passerini,
J. Power Sources 2015, 293, 65-70.
25 F. Castiglione, M. Moreno, G. Raos, A. Famulari, A.
Mele, G. B. Appetecchi, S. Passerini, J. Phys. Chem. B 2009,
13, 10750-10759.
26 L. G. Sanchez, J. R. Espel, F. Onink, G. W. Meindersma,
A. B. d. Haan, J. Chem. Eng. Data 2009, 54, 2803-2812.
27 S. Jeremias, M. Carewska, L. Conte, S. Passerini, G. B.
Appetecchi, RSC. Adv. 2013, 3, 17755-17761.
28 A. E. Somers, B. Khemchandani, P. C. Howlett, J. Sun, D.
R. MacFarlane, M. Forsyth, ACS Appl. Mater. Interface 2013, 5,
1544-11553.
1
1
1
1
1
1
1
1
1
8
1
29 C. Yao, W. R. Pitner, J. L. Anderson, Anal. Chem. 2009,
1, 5054-5063.
30 U. L. Bernard, E. I. Izgorodina, D. R. MacFarlane, J.
Phys. Chem. C 2010, 114, 20472-20478.
31 G. B. Appetecchi, M. Montanino, D. Zane, M. Carewska,
F. Alessandrini, S. Passerini, Electrochim. Acta 2009, 54,
1
1
1
325-1332.
32 Z. Chen, Y. Huo, J. Cao, L. Xu, S. Zhang, Ind. Eng. Chem.
Res. 2016, 55, 11589-11596.
33 P. J. Fischer, M. P. Do, R. M. Reich, A. Nagasubramanian,
M. Srinivasan, F. E. Kuhn, Phys. Chem. Chem. Phys. 2018, 20,
1
2
1
2
1
9412-29422.
34 H. Matsumoto, T. Matsuda, Y. Miyazaki, Chem. Lett.
000, 29, 1430-1431.
35 K. Tsunashima, M. Sugiya, Electrochem. Commun. 2007,
19