Sulfur makes the difference: Synthesis and mesomorphic properties of novel thioether-functionalized imidazolium ionic liquid crystals

Article abstract of DOI:10.1016/j.tet.2014.03.050

Novel thioether-linked imidazolium ionic liquid crystals were synthesized starting from methyl 2-mercaptoacetate. The mesomorphic properties were determined by differential scanning calorimetry (DSC), polarizing optical microscopy (POM), and X-ray diffraction. All mesogens displayed smectic A mesophase geometries with strongly interdigitated bilayer structures. Comparison of the thioether-linked imidazolium salts with the corresponding amine- and amide-linked imidazolium salts as well as simple N-alkyl-imidazolium salts showed that both mesophase width and stability increased with increasing softness of the linking unit, thus indicating the beneficial effect of sulfur. Additionally, an increase of the length of the linking unit decreased the interdigitation of the alkyl chains.

Full text of DOI:10.1016/j.tet.2014.03.050

Tetrahedron xxx (2014) 1e7
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Sulfur makes the difference: synthesis and mesomorphic properties
of novel thioether-functionalized imidazolium ionic liquid crystals
*
Markus Mansueto, Katharina Christina Kreß, Sabine Laschat
€
€
Institut fur Organische Chemie, Universitat Stuttgart, Pfaffenwaldring 55, D-70569 Stuttgart, Germany
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel thioether-linked imidazolium ionic liquid crystals were synthesized starting from methyl 2-
mercaptoacetate. The mesomorphic properties were determined by differential scanning calorimetry
(DSC), polarizing optical microscopy (POM), and X-ray diffraction. All mesogens displayed smectic A
mesophase geometries with strongly interdigitated bilayer structures. Comparison of the thioether-
linked imidazolium salts with the corresponding amine- and amide-linked imidazolium salts as well
as simple N-alkyl-imidazolium salts showed that both mesophase width and stability increased with
increasing softness of the linking unit, thus indicating the beneficial effect of sulfur. Additionally, an
increase of the length of the linking unit decreased the interdigitation of the alkyl chains.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 27 January 2014
Received in revised form 3 March 2014
Accepted 14 March 2014
Available online xxx
Keywords:
Ionic liquid crystals
Sulfur compounds
1. Introduction
2. Results and discussion
The introduction of sulfur atoms into organic structures gener-
ates a plethora of opportunities regarding molecular electronics
applications. Archetypal examples for such sulfur compounds are
thiophenes1 and tetrathiafulvalenes.2 The incorporation of such
moieties in thermotropic liquid crystals is also well known.3,4 For
example, because of the soft character of the sulfur atom due to the
more delocalized d-orbitals, discotic hexathioalkyltriphenylenes
show a decreased electronic band-gap and charge carrier mobilities,
which are up to three orders of magnitude larger than those for the
corresponding hexaalkoxytriphenylenes.5,6 The combination of
properties of liquid crystals with those of ionic liquids creates the
special features of ionic liquid crystals as anisotropically-ordered
liquid electrolytes.7 Very recently, this novel class of materials has
been successfully applied as anisotropic lithium ion conductors,8 as
electrolytes in solid-state dye-sensitized solar cells (DSSCs)9 and in
particular, iodine-free DSSCs.10 Among the various cationic head-
groups employed for ionic liquid crystals, imidazolium salts are the
most widely used class of compounds.7d,11 Although some
thiophene-based ILCs are known in the literature,12 the issue of
sulfur-containing ILCs is much less explored as compared to classical
thermotropic liquid crystals. Based on our recent work on glycine-
derived imidazolium ILCs,13 we noticed that the incorporation of
an amine or amide moiety in the side chain influenced mesophase
widths significantly as compared to the corresponding N-methyl-N-
alkylimidazolium salts. Thus, we wondered how the replacement of
a hard amine by a soft sulfur would affect the mesomorphic prop-
erties of ILCs. The results are discussed below.
The synthesis of thioether-containing ILCs 6(Cn)X commenced
with the S-alkylation of methyl 2-mercaptoacetate 1 in the pres-
ence of K2CO3 according to the procedure by Townsend (Scheme
1).14 Subsequent saponification of the methylester 2 with LiOH in
EtOH provided the free carboxylic acid 3, which was reduced with
borane dimethylsulfide to the corresponding alcohol 4. Compound
4 was submitted to Appel reaction following the procedure by
Kukovinets15 and the resulting bromide 5 was subsequently reac-
ted with N-methylimidazole under microwave conditions to give
the desired imidazolium bromide 6(Cn)Br. A final salt metathesis
step yielded the ILCs 6(Cn)X with different anions.
Mesomorphic properties of thioether-imidazolium ILCs 6(Cn)X
were initially studied by differential scanning calorimetry (DSC).
The results in Table 1 and Fig.1 clearly reveal the strong dependence
of the mesophase stability on the chain lengths and on the hard/soft
character of the counterions. While imidazolium bromide 6(C8)Br
showed no crystallisation point or glass transition in the cooling
cycles, a liquid crystalline phase was observed between 22 ꢀC and
51 ꢀC during the heating cycles (Fig. 1a). The corresponding ho-
mologous imidazolium bromide 6(C10)Br displayed enantiotropic
mesomorphism between 35 ꢀC and 148 ꢀC in the heating cycle and
a significant hysteresis possibly due to supercooling (Fig. 1b).
However, for compounds 6(Cn)Br with n¼12, 14, 16 and 18 the
clearing points were shifted to around 200 ꢀC and isotropizationwas
accompanied by decomposition (Table 1 entries 3e6) (Fig. 1c).
Further evidence for the thermal instability of the bromides was
verified using thermogravimetric analysis (TGA) (see Supplemen-
tary. data, Fig. S1). In prior work we were able to improve the
thermal stability by replacing bromide by triflate counterions.13,16
* Corresponding author. E-mail address: sabine.laschat@oc.uni-stuttgart.de (S.
Laschat).
0040-4020/$ e see front matter Ó 2014 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tet.2014.03.050
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

2
M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
point, which is hardly visible in the DSC curve, was significantly
shifted below the decomposition temperature. Replacement of the
triflate counterion by tetrafluoroborate for the C18 derivative 6(C18
)
BF4 showed again a pronounced tendency for decomposition dur-
ing the clearing process (entry 13).
Investigations by polarizing optical microscopy (POM) yielded
homeotropic textures typical for SmA phases. Characteristic ex-
amples of the obtained POM textures are shown in Fig. 2.
Upon comparison with the simple N-alkyl-N-methyl-imidazo-
lium salts 7(Cn)X17 and previously-prepared amine and amide de-
rivatives 8(Cn)X and 9(Cnꢁ1)X, respectively (Scheme 2, Fig. 3), it is
clearly visible that sulfur does indeed have a beneficial effect on
both the mesophase width and stability as long as triflates are
concerned. Thus clearing points are increased while melting points
are in the range from ambient temperature up to 55 ꢀC. Further-
more, the clearing points of the triflates are still far below their
decomposition temperatures (see Supplementary data, Fig. S1).
Small- and wide-angle X-ray diffraction measurements (SAXS
and WAXS, respectively) confirmed the proposed SmA phase ge-
ometry. A representative WAXS pattern of 6(C18)OTf is shown in
Fig. 4 with a strong fundamental diffraction peak (001) in the small-
angle region and a diffuse halo in the wide-angle region from the
molten alkyl chains.
Layer spacings d001 were obtained at different temperatures
using a Gaussian distribution on the corresponding diffraction
signal (001). All thioether-linked triflates 6(Cn)OTf showed, as seen
with the previous published amines and amides,13
a linear
temperature-dependency of the layer spacing (Fig. 5), whereby the
layer spacing decreased with increasing temperature. These values
indicate a bilayer structure of the molecules with strongly in-
terdigitated alkyl chains and d001 values of Lcalcd<d001<2Lcalcd
,
where Lcalcd is the length of the fully extended molecule with an all-
trans configuration of the alkyl moiety. Layer spacings dred at a re-
duced temperature (d001 at 0.95 Tiso)
19 were determined for better
comparison of the imidazolium salts bearing different groups
(Table 2). For example, the calculated molecular length of 6(C16)OTf
is 2770 pm,18 whereas dred is 3498 pm. This concludes that the
mesogens are organized in a bilayer structure (Fig. 6). The calcu-
lated layer spacing dcalcd is 3480 pm18 (fully interdigitated alkyl
chains of the cations 2060 pm plus two times the methyl-
imidazolium core with 710 pm each), which is close to the dred
value of 3480 pm (Table 2). Overall, the layer spacings d001 increase
with increasing alkyl chain length.
A comparison of the smectic layer distances dred of thioethers
6(Cn)OTf with the distances for amines 8(Cn)OTf and amides
9(Cnꢁ1)OTf, respectively, showed that the interdigitation of thio-
ethers 6(Cn)X lies in between smaller dred values for amines 8(Cn)X
and larger dred values for amides 9(Cnꢁ1)X (Fig. 5).
Scheme 1. Synthesis of thioether-imidazolium ILCs 6(Cn)X.
Table 1
Phase transition temperatures [ꢀC] and enthalpies [kJ molꢁ1
] of thioether-
imidazolium ILCs 6(Cn)X (X¼Br, OTf, BF4)a,b
Entry
n
X
Heating cycle
(1)
(2)
(3)
(4)
(5)
(6)
(7)
(8)
8
Br
Cr
Cr
Cr
Cr
Cr
Cr
22 (24.0) SmA 51 (0.2)
35 (30.2) SmA 148 (0.7)
I
I
Second heat
Second heat
10 Br
12 Br
14 Br
16 Br
18 Br
46
55
62
41
SmA w200
SmA w200
SmA w200
SmA w200
I (dec) Second heatc
I (dec) Second heatc
I (dec) Second heatc
I (dec) Second heatc
Second heat
8
OTf Liquid
10 OTf Cr
12 OTf Cr
14 OTf Cr
16 OTf Cr
18 OTf Cr
18 BF4 Cr
4 (17.3)
6 (11.4)
28 (16.6) SmA 71 (0.8)
43 (22.4) SmA 124 (0.7)
54 (24.9) SmA 149 (0.7)
64 (27.9) SmA w200
I
Second heat
(9)
SmA 36 (0.3)
I
I
I
I
Second heat
Second heat
Second heat
Second heat
(10)
(11)
(12)
(13)
3. Conclusion
I (dec) Second heatc
We have presented the synthesis of novel imidazolium ionic
liquid crystals bearing a thioether unit. Simple reaction conditions
were used with good to quantitative yields throughout. The sulfur-
linked bromides displayed decreased mesophase ranges compared
to the corresponding alkylated species. After an anion exchange
from Br to OTf the thioether compounds showed the widest mes-
ophases compared to previously described amines and amides. The
following trend was observed: The softer the anion, the wider was
the mesophase range. All mesogens displayed smectic A meso-
phase geometries and with increasing alkyl chain lengths an in-
crease of the mesophase width was observed.
a
Phase transitions were determined by DSC upon second heating. Heating/
cooling rate 10 K minꢁ1
.
b
he following phases were observed: crystalline (Cr), smectic A (SmA), isotropic
(I).
c
In case of entries (3)e(6), (13) exothermal decomposition was observed during
isotropization. Therefore, melting points were determined by polarizing optical
microscopy (POM).
As shown in Table 1, this strategy was successful for the derivatives
with the chain lengths C12eC18. Whereas imidazolium triflates
6(C8)OTf and 6(C10)OTf displayed only isotropic melting (entries 7,
8), all other derivatives 6(Cn)OTf where n¼12e18 showed enan-
tiotropic mesomorphism with almost no hysteresis (entries 9e12)
(Fig. 1d). The TGA experiments further revealed that the clearing
XRD experiments showed an almost linear dependency of the
layer spacings d001 with increasing temperature and a bilayer
alignment of the mesogens. A maximum degree of interdigitation
up to the heteroatom group is assumed for the analyzed thioethers.
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
3
Fig. 1. DSC traces of (a) 6(C8)Br, (b) 6(C10)Br, (c) 6(C12)Br and (d) 6(C18)OTf (heating/cooling rate 10 K minꢁ1). A: second heating, B: first heating, C: first cooling, D: second cooling.
Fig. 2. Typical POM textures of thioether-linked ILCs. (a) 6(C12)OTf at 10 ꢀC (first heating), (b) 6(C12)OTf at 22 ꢀC (first heating), (c) and (d) 6(C18)OTf at 126 ꢀC (first cooling). Focal
conic and Maltese cross textures indicative for a SmA mesophase. (magnification: 200ꢂ, heating/cooling rate 10 K minꢁ1).
Therefore the interdigitation of the alkyl chains decreased while
increasing the linking unit.
The current work provides further insight in the structure-
property relationship of imidazolium salts. The observation that
mesomorphic properties of imidazolium ILCs were improved by the
sulfur linker might be taken as indication that the performance of
DSSCs can be further improved by such thioether ILCs as compared
to N-methyl-N-alkyl-imidazolium ILCs. Those turned already out to
be auspicious due to their high ionic conductivity and good pore
filling property.9,20
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

4
M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
Fig. 3. Mesophase stabilities of the imidazolium derivatives with (a) bromide and (b) triflate anion. * Monotropic phase behaviour was observed. The values for amines 8(Cn)OTf and
amides 9(Cnꢁ1)OTf are from Ref. 13, for 7(Cn)OTf from Ref. 17.
Fig. 4. Diffraction pattern of 6(C18)OTf at 79 ꢀC with the corresponding WAXS image
(inset).
Fig. 5. Temperature dependency of the d001 layer spacings obtained from SAXS in-
vestigations. Key: ◄ 6(C14)OTf, 6(C16)OTf, : 6(C18)OTf, C 8(C14)OTf, A 8(C16)OTf,
;
- 8(C18)OTf, ꢂ 9(C16)OTf, þ 9(C18)OTf. The values for amines 8(Cn)OTf and amides
9(Cnꢁ1)OTf were taken from Ref. 13.
4. Experimental section
4.1. General methods
(40e70 mm). For thin layer chromatography silica gel sheets TLC
silica gel 60 F254 from Merck were used. 1H and 13C NMR were
recorded with Bruker Avance 300 and Avance 500 spectrometers at
296 K. FTIR spectra were recorded with a Bruker Vektor22 spec-
trometer with an MKII Golden Gate Single Reflection Diamant ATR
Commercially obtained chemicals were used as received. For
a better clarity and simplicity a non-IUPAC nomenclature was used.
Column chromatography was carried out on silica 60Dm
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
5
Table 2
under reduced pressure. Solid products were poured on ice water,
filtered, solubilized in CH2Cl2 and dried over anhydrous MgSO4.
Liquid products were washed with water and CH2Cl2 were added to
the organic phase, which was dried over anhydrous MgSO4. The
solvent was removed in vacuum to yield the thioethers 2aef.14
Comparison of the calculated18 and experimental layer spacings dred of the imida-
zolium compounds 9(AA,Cn) and 10(Gly,Cm)OTf
Compound
Tred/ꢀC
dred/pm
dcalcd/pm
6(C14)OTf
6(C16)OTf
6(C18)OTf
8(C14)OTf
8(C16)OTf
8(C18)OTf
9(C16)OTf
9(C18)OTf
68
118
142
72
109
110
83
3267
3498
3683
3205
3468
3582
3616
3783
3220
3480
3730
3000
3250
3510
3600
3860
4.2.1. Methyl 2-(octadecylthio)acetate 2f. Colourless solid (3.40 g,
9.49 mmol, quant.). 1H NMR (300 MHz, CDCl3, TMS):
d
¼0.88 (t,
J¼6.8 Hz, 3H, CH3), 1.21e1.42 (m, 30H, CH2), 1.53e1.66 (m, 2H,
SCH2CH2), 2.59e2.67 (m, 2H, SCH2), 3.23 (s, 2H, COCH2S), 3.74 (s,
3H, CO2CH3) ppm; 13C NMR (75 MHz, CDCl3, TMS):
28.76, 28.98, 29.19, 29.37, 29.51, 29.59, 29.70, 31.9 (CH2), 32.8, 33.5
d
¼14.1 (CH3),
107
(CH2), 52.4 (CO2CH3),171.1 (CO) ppm; FTIR (ATR):
n
e¼2916 (vs), 2849
(s), 1737 (m), 1467 (w), 1436 (w), 1280 (m), 1135 (w), 1010 (w), 721
(w) cmꢁ1; MS (ESI): m/z: 381 [MNaþ], 300 [MNaþꢁC2H2O2]; HRMS
(ESI): m/z calculated for C21H42NaO2Sþ: 381.2798 [MNaþ]; found:
381.2817; mp: 34 ꢀC.
4.3. General procedure for the deprotection to the acids 3aef
The corresponding thioether 2aef (7.82 mmol) was dissolved in
ethanol (300 mL) and LiOH (0.79 g, 33.0 mmol) was added and
stirred for 48 h at room temperature. The reaction mixture was
acidified with 1 N HCl until reaching pH¼3. For solid products the
mixture was poured on ice water, the solid was filtered, in CH2Cl2
solubilized and dried over anhydrous MgSO4. For liquid products
the solvent was removed in vacuo and H2O was added. The phases
were separated and the organic was dried over anhydrous MgSO4.
After removal of the solvent under reduced pressure 3aef was
obtained.
4.3.1. 2-(Octadecylthio)acetic acid 3f. Colourless solid (2.69 g,
7.82 mmol, 95%). 1H NMR (300 MHz, CDCl3, TMS):
d
¼0.88 (t,
J¼6.8 Hz, 3H, CH3), 1.20e1.44 (m, 30H, CH2), 1.55e1.67 (m, 2H,
SCH2CH2), 2.61e2.70 (m, 2H, SCH2), 3.26 (s, 2H, COCH2S) ppm; 13
NMR (75 MHz, CDCl3, TMS):
¼14.1 (CH3), 22.7, 28.74, 28.90, 29.19,
29.37, 29.50, 29.60, 29.67, 29.71, 31.9 (CH2), 32.8, 33.5 (CH2), 175.7
C
d
(CO) ppm; FTIR (ATR):
n
e¼2955 (w), 2916 (vs), 2874 (s), 1722 (w),
Fig. 6. Proposed packing model of the smectic phase (left) and example of the cal-
culated layer spacing dcalcd of 6(C18)OTf (right).
1694 (m), 1470 (w), 1460 (w), 1425 (w), 1397 (w), 1316 (w), 1267
(w), 1208 (w), 1145 (w), 1080 (w), 1031 (w), 906 (vs), 733 (vs), 650
(w) cmꢁ1; MS (ESI): m/z: 367 [MNaþ], 301 [MHþꢁCO2]; HRMS
(ESI): m/z calculated for C20H40NaO2Sþ: 367.2641 [MNaþ]; found:
367.2616; mp: 84 ꢀC.
system. Mass spectrometry was performed on a Varian MAT 711
mass spectrometer with EI ionization (70 eV) and a Bruker
micrOTOF_Q with electrospray ionization. Elementary analysis
were performed on a Carlo Erba Strumentazione Elemental Ana-
lyzer Model 1106. Differential scanning calorimetry was performed
using a Mettler Toledo DSC822 with a heating/cooling rate of
10 K minꢁ1 (ꢃ1 K), melting points (uncorrected) and mesophase
textures were obtained by polarizing optical microscopy using an
Olympus BX 50 polarizing microscope combined with a Linkam LTS
4.4. General procedure for the preparation of alcohols 4aef
The corresponding acid 3aef (0.29 mmol) was dissolved in abs.
THF (10 mL), cooled to 0 ꢀC and a borane dimethylsulfide complex
solution (0.07 g, 0.09 mL, 0.87 mmol; 94% in dimethylsulfide) was
added dropwise. The reaction mixture was stirred for 2 h at 0 ꢀC
and a borane dimethylsulfide complex solution (0.07 g, 0.09 mL,
0.87 mmol; 94%) was added again and the solution was allowed to
reach room temperature overnight. H2O was added slowly until the
development of gas ceased. The organic solvent was removed un-
der reduced pressure and CHCl3 (10 mL) was added. The organic
phase was dried over anhydrous MgSO4 and the solvent was re-
moved in vacuum yielding 4aef.
350 hot stage. X-ray powder experiments were performed using
ꢀ
a Bruker Nanostar with monochromatic Cu Ka1 beam (
l
¼1.5405 A)
was obtained using a ceramic tube generator (1500 W) with cross-
€
coupled Gobel mirrors as the monochromator. Calibration of the
patterns was carried out with the powder pattern of Ag-Behenate.
Samples were prepared using glass tubes (0.7 mm outside di-
ameter) from Fa. Hilgenberg GmbH and tempered on a tempera-
ture-controlled hot stage (ꢃ1 K).
4.4.1. 2-(Octadecylthio)ethanol 4f. Colourless solid (0.10 g,
4.2. General procedure for the synthesis of thioethers 2aef
0.30 mmol, quant.). 1H NMR (300 MHz, CDCl3, TMS):
d
¼0.88 (t,
J¼6.7 Hz, 3H, CH3), 1.20e1.42 (m, 30H, CH2), 1.52e1.64 (m, 2H,
SCH2CH2), 2.11e2.23 (br, 1H, OH), 2.48e2.56 (m, 2H, SCH2),
To a suspension of K2CO3 (2.80 g, 28.3 mmol) in acetone (30 mL)
and DMSO (10 mL) was added successively the corresponding
bromoalkane (9.42 mmol) and 2-methylmercaptoacetate 1 (1 g,
9.42 mmol). The reaction mixture was stirred for 48 h at room
temperature, filtered through a Celite and the solvent was removed
2.70e2.77 (m, 2H, SCH2CH2O), 3.68e3.76 (m, 2H, CH2OH) ppm; 13
C
NMR (75 MHz, CDCl3, TMS):
29.52, 29.60, 29.67, 29.68, 29.70, 31.59, 31.93, 33.4 (CH2), 60.1
(CH2OH) ppm; FTIR (ATR):
d
¼14.1 (CH3), 22.7, 28.87, 29.23, 29.37,
n
e¼2924 (m), 2853 (m), 2361 (w), 2252
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

6
M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
(w), 1712 (w), 1466 (w), 1366 (w), 1171 (w), 1058 (w), 905 (s), 728
(vs), 649 (m) cmꢁ1; MS(EI): m/z (%): 330 (21) [Mþ], 299 (12)
[MþꢁCH3O], 285 (100) [MþꢁC2H5O], 97 (6), 83 (7), 57 (8), 43 (5);
HRMS (ESI): m/z calculated for C20H42OSþ: 330.2956 [Mþ]; found:
330.2958.
30H, CH2), 1.51e1.62 (m, 2H, SCH2CH2), 2.52e2.60 (m, 2H, SCH2),
2.94e3.03 (m, 2H, SCH2CH2Im), 4.01 (s, 3H, ImCH3), 4.41e4.49 (m,
2H, CH2Im), 7.23e7.25 (m,1H, Im), 7.37e7.39 (m,1H, Im), 9.42e9.44
(m,1H, NCHN) ppm; 13C NMR (125 MHz, CDCl3, TMS):
d
¼14.1 (CH3),
22.7, 28.7, 29.22, 29.37, 29.43, 29.53, 29.62, 29.67, 29.71, 31.9 (CH2),
32.15, 32.19 (CH2), 36.6 (ImCH3), 49.4 (ImCH2), 122.49, 122.80 (Im),
4.5. General procedure for the synthesis of bromides 5aef
137.9 (NCHN) ppm; FTIR (ATR):
n
e¼3152 (w), 3115 (w), 2957 (w),
2918 (vs), 2850 (s), 2361 (w), 2253 (w), 1667 (w), 1576 (W), 1468
(w), 1379 (w), 1337 (w), 1256 (vs), 1225 (m), 1162 (s), 1031 (s), 908
(m), 735 (s), 639 (s), 621 (w), 574 (w) cmꢁ1; MS (ESI): m/z: 395
[Mþ], 335, 313 [MþꢁC4H6N2]; 149 [Mꢁ]; HRMS (ESI): m/z calculated
for C24H47N2Sþ: 395.3454 [Mþ]; found: 395.3434; calculated for
CF3O3Sꢁ: 148.9515 [Mꢁ]; found: 148.9534; DSC: Cr 54 ꢀC
[24.9 kJ molꢁ1] SmA 149 ꢀC [0.7 kJ molꢁ1] I.
The corresponding alcohol 4aef (0.91 mmol) and PPh3 (0.32 g,
1.23 mmol) were dissolved in abs. CH2Cl2 (10 mL) and CBr4 (0.41 g,
1.23 mmol) was added. The reaction mixture was stirred overnight
at room temperature. The solvent was removed under reduced
pressure and the crude product was purified through column
chromatography (hexanes/EtOAc 40:1; Rf¼0.7) to yield 5aef.15
4.5.1. (2-Bromoethyl)(octadecyl)sulfane 5f. Colourless solid (0.25 g,
4.7.2. 1-Methyl-3-(2-(octadecylthio)ethyl)-1H-imidazol-3-ium tetra-
0.65 mmol, 71%). 1H NMR (300 MHz, CDCl3, TMS):
d¼0.88 (t,
fluoroborate 6(C18)BF4. Colourless solid (13 mg, 0.02 mmol, 87%).
J¼6.8 Hz, 3H, CH3), 1.20e1.42 (m, 30H, CH2), 1.52e1.65 (m, 2H,
SCH2CH2), 2.51e2.59 (m, 2H, SCH2), 2.89e2.99 (m, 2H, SCH2CH2Br),
3.44e3.52 (m, 2H, CH2Br) ppm; 13C NMR (75 MHz, CDCl3, TMS):
1H NMR (500 MHz, CDCl3, TMS):
d
¼0.88 (t, J¼6.9 Hz, 3H, CH3),
1.18e1.41 (m, 30H, CH2),1.52e1.62 (m, 2H, SCH2CH2), 2.53e2.62 (m,
2H, SCH2), 2.95e3.05 (m, 2H, SCH2CH2Im), 4.02 (s, 3H, ImCH3),
4.45e4.53 (m, 2H, CH2Im), 7.22e7.25 (m, 1H, Im), 7.38e7.41 (m, 1H,
Im), 9.64e9.69 (m, 1H, NCHN) ppm; 13C NMR (125 MHz, CDCl3,
d
¼14.1 (CH3), 22.7, 28.8, 29.20, 29.37, 29.51, 29.59, 29.65, 29.67,
29.71, 29.79, 30.6, 31.9 (CH2), 32.4 (CH2), 34.2 (CH2Br) ppm; FTIR
(ATR):
n
e¼2921 (vs), 2951 (s), 2360 (w), 1739 (w),1466 (w),1189 (w),
TMS):
d
¼14.1 (CH3), 22.7, 28.8, 29.24, 29.37, 29.45, 29.54, 29.63,
721 (w), 613 (w) cmꢁ1; MS(EI): m/z (%): 392 (7) [Mþ], 313 (26), 286
(18), 285 (100), 97 (5), 69 (7), 57 (9), 43 (9); HRMS (EI): m/z cal-
culated for C20H41BrSþ: 392.2112 [Mþ]; found: 392.2112.
29.67, 29.68, 29.71, 31.9 (CH2), 32.23, 32.26 (CH2), 36.7 (ImCH3),
49.5 (ImCH2), 122.47, 122.74 (Im), 137.8 (NCHN) ppm; FTIR (ATR):
n
e¼3161 (w), 2958 (w), 2923 (m), 2852 (m), 2364 (w),1575 (w),1467
(w), 1379 (w), 1261 (w), 1171 (w), 1057 (m), 907 (s), 731 (vs), 646
4.6. General procedure for preparation of imidazolium bro-
mides 6(Cn)Br
(w), 622 (w) cmꢁ1 MS (ESI): m/z: 395 [Mþ], 335, 313
;
[MþꢁC4H6N2]; 87 [Mꢁ]; HRMS (ESI): m/z calculated for
C
24H47N2Sþ: 395.3454 [Mþ]; found: 395.3434; calculated for BF-4:
The corresponding bromide 5aef (0.15 mmol) and 1-
87.0024 [Mꢁ]; found: 87.0027; DSC: Cr 64 ꢀC [27.9 kJ molꢁ1]; de-
composition upon reaching the clearing temperature.
methylimidazole (0.12 mL, 12 mg, 0.15 mmol) were given in a mi-
crowave vial and irradiated in a microwave for 8 h at 140 ꢀC. The
crude product was recrystallized from EtOAc to afford the imida-
zolium bromides 6(Cn)Br.
Acknowledgements
€
Generous financial support by the Ministerium fur Wissen-
€
4.6.1. 1-Methyl-3-(2-(octadecylthio)ethyl)-1H-imidazol-3-ium bro-
schaft, Forschung und Kunst des Landes Baden-Wurttemberg, the
mide 6(C18)Br. Colourless solid (64 mg, 0.13 mmol, 91%). 1H NMR
Bundesministerium fur Bildung und Forschung (shared in-
€
(300 MHz, CDCl3, TMS):
d
¼0.88 (t, J¼6.7 Hz, 3H, CH3), 1.21e1.41 (m,
strumentation grant #01 RI 05177) and the Fonds der Chemischen
Industrie is gratefully acknowledged. We would like to thank
Christoph Schneck for the TGA experiments.
30H, CH2), 1.51e1.63 (m, 2H, SCH2CH2), 2.55e2.64 (m, 2H, SCH2),
3.01e3.09 (m, 2H, SCH2CH2Im), 4.09 (s, 3H, ImCH3), 4.59e4.66 (m,
2H, CH2Im), 7.22e7.24 (m, 1H, Im), 7.41e7.43 (m, 1H, Im), 10.74 (s,
1H, NCHN) ppm; 13C NMR (75 MHz, CDCl3, TMS):
d¼14.1 (CH3),
Supplementary data
22.7, 28.7, 29.24, 29.37, 29.46, 29.53, 29.62, 29.67, 31.9 (CH2), 32.39,
32.45 (CH2), 36.6 (ImCH3), 49.5 (ImCH2), 122.43 (Im), 138.6 (NCHN)
Further experimental results and supplementary figures. Sup-
plementary data related to this article can be found at http://
dx.doi.org/10.1016/j.tet.2014.03.050.
ppm; FTIR (ATR):
n
e¼3038 (w), 2953 (w), 2918 (vs), 2847 (s), 2360
(w), 1557 (w), 1466 (m), 1310 (w), 1217 (w), 1171 (m), 908 (w), 760
(w), 736 (m), 722 (m), 641 (w), 621 (w) cmꢁ1; MS (ESI): m/z: 395
[Mþ], 313 [MþꢁC4H6N2]; HRMS (ESI): m/z calculated for
References and notes
C
24H47N2Sþ: 395.2454 [Mþ]; found: 395.3469; mp: 41 ꢀC; de-
1. Reviews: (a) Colella, N. S.; Zhang, L.; Briseno, A. L. Mater. Matters 2012, 7, 18e20;
(b) Bunz, U. H. Angew. Chem., Int. Ed. 2010, 49, 5037e5040; (c) Handbook of
Thiophene-Based Materials; Perepichka, I. F., Perepichka, D. F., Eds.; 2009; vol. 2,
composition upon reaching the clearing temperature.
€
4.7. General procedure for the anion exchange
pp 595e646; (d) Mishra, A.; Ma, C.-Q.; Bauerle, P. Chem. Rev. 2009, 109,
1141e1276; (e) Torroba, T.; García-Valverde, M. Angew. Chem., Int. Ed. 2006, 45,
8092e8096.
The respective imidazolium bromide 6(Cn)Br (0.13) was dis-
solved in MeCN (10 mL), the corresponding potassium salt
(0.14 mmol) was added and stirred under reflux for 1 h. After
cooling to room temperature the solvent was removed under re-
duced pressure, the residue dissolved in CH2Cl2 (10 mL) and fil-
tered. The solvent was removed under reduced pressure to obtain
the corresponding imidazolium triflates 6(Cn)OTf or tetra-
fluoroborate 6(C18)BF4.
2. Reviews: (a) Martín, N. Chem. Commun. 2013, 7025e7027; (b) Zhao, Y.; Chen,
G.; Mulla, K.; Mahmud, I.; Liang, S.; Dongare, P.; Thompson, D. W.; Dawe, L. N.;
Bouzan, S. Pure Appl. Chem. 2012, 84, 1005e1025; (c) Salle, M.; Canevet, D.;
Balandier, J.-Y.; Lyskawa, J.; Trippe, G.; Goeb, S.; Le Derf, F. Phosphorus, Sulfur
Silicon Relat. Elem. 2011, 186, 1153e1168; (d) Nielsen, M. B. Phosphorus, Sulfur
ꢁ
Silicon Relat. Elem. 2011, 186, 1055e1073; (e) Canevet, D.; Salle, M.; Zhang, G.;
ꢁ
Zhang, D.; Zhu, D. Chem. Commun. 2009, 2245e2269; (f) Herranz, M. A.;
ꢁ
Sanchez, L.; Martín, N. Phosphorus, Sulfur Silicon Relat. Elem. 2005, 180,
1133e1148.
3. Reviews: (a) Seed, A. Chem. Soc. Rev. 2007, 36, 2046e2069; (b) Bryce, M. R. J.
Mater. Chem. 2000, 10, 589e598.
4. Recent examples: (a) Folcia, C. L.; Ortega, J.; Etxebarria, J.; Rodríguez-Conde, S.;
Sanz-Enguita, G.; Geese, K.; Tschierske, C.; Ponsinet, V.; Barois, P.; Pindak, R.;
Pan, L.; Liu, Z. Q.; McCoy, B. K.; Huang, C. C. Soft Matter 2013, 10, 196e205; (b)
Cheng, W.-C.; Yang, C.-Y.; Kang, B.-Y.; Kuo, M.-Y.; Ruan, J. Soft Matter 2013, 9,
4.7.1. 1-Methyl-3-(2-(octadecylthio)ethyl)-1H-imidazol-3-ium
flate 6(C18)OTf. Colourless solid (13 mg, 0.02 mmol, 87%). 1H NMR
(500 MHz, CDCl3, TMS):
¼0.88 (t, J¼6.9 Hz, 3H, CH3), 1.21e1.41 (m,
tri-
d
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050

M. Mansueto et al. / Tetrahedron xxx (2014) 1e7
7
10822e10831; (c) Reddy, M. K.; Reddy, K. S.; Prakash, M.; Narasimhaswamy, T.
Mol. Cryst. Liq. Cryst. 2013, 582, 1e14; (d) Dong, J.; Kawabata, K.; Seino, T.; Yang,
F.; Goto, H. Liq. Cryst. 2013, 40, 1455e1465; (e) Chen, X.; Chen, L.; Yao, K.; Chen,
Y. ACS Appl. Mater. Interfaces 2013, 5, 8321e8328; (f) Cheng, X.; Gao, H.; Tan, X.;
Yang, X.; Prehm, M.; Ebert, H.; Tschierske, C. Chem. Sci. 2013, 4, 3317e3331; (g)
Hegde, G.; Alla, R. A.; Matharu, A.; Komitov, L. J. Mater. Chem. C 2013, 1,
3600e3605; (h) Bu, W.; Gao, H.; Tan, X.; Dong, X.; Cheng, X.; Prehm, M.;
Tschierske, C. Chem. Commun. 2013, 1756e1758; (i) Yin, B.; Zhong, K.; Jiang, S.;
Wang, H.; Hou, R. Heterocycles 2012, 85, 3021e3028; (j) Garcia, G.; Moral, M.;
Bruce, D. W.; Houbenov, N.; Metrangolo, P.; Resnati, G. J. Mater. Chem. A 2013, 1,
6572e6578; (c) Rohini, R.; Lee, C.-K.; Lu, J.-T.; Lin, I. J. B. J. Chin. Chem. Soc. 2013,
60, 745e754; (d) Westphal, E.; da Silva, D. H.; Molin, F.; Gallardo, H. RSC Adv.
2013, 3, 6442e6454; (e) Yang, M.; Mallick, B.; Mudring, A.-V. Cryst. Growth Des.
2013, 13, 3068e3077; (f) Schenkel, M. R.; Shao, R.; Robertson, L. A.; Wiesenauer,
B. R.; Clark, N. A.; Gin, D. L. Liq. Cryst. 2013, 40, 1067e1081; (g) Ji, Y.; Shi, R.;
Wang, Y.; Saielli, G. J. Phys. Chem. B 2013, 117, 1104e1109; (h) Gao, Y.; Slattery, J.
M.; Bruce, D. W. New J. Chem. 2011, 35, 2910e2918; (i) Ichikawa, T.; Yoshio, M.;
Taguchi, S.; Kagimoto, J.; Ohno, H.; Kato, T. Chem. Sci. 2012, 3, 2001e2008; (j)
Getsis, A.; Mudring, A.-V. Eur. J. Inorg. Chem. 2011, 2011, 3207e3213; (k) Star-
kulla, G.; Kaller, M.; Frey, W.; Axenov, K. V.; Laschat, S. Liq. Cryst. 2011, 38,
1515e1529; (l) Getsis, A.; Mudring, A.-V. Z. Anorg. Allg. Chem. 2010, 636,
1726e1734.
ꢁ
ꢁ
ꢁ
Granedino-Roldan, J. M.; Garzon, A.; Navarro, A.; Fernandez-Gomez, M. J. Phys.
Chem. C 2013, 117, 15e22.
5. Sergeyev, S.; Pisula, W.; Geerts, Y. H. Chem. Soc. Rev. 2007, 36, 1902e1929.
6. (a) Savage, R. C.; Mativetsky, J. M.; Orgiu, E.; Palma, M.; Gbabode, G.; Geerts, Y.
H.; Samorí, P. J. Mater. Chem. 2010, 21, 206e213; (b) Lemaur, V.; da Silva Filho,
D. A.; Coropceau, V.; Lehmann, M.; Geerts, Y.; Piris, J.; Debije, M. G.; van de
12. (a) Causin, V.; Saielli, G. J. Mater. Chem. 2009, 19, 9153e9162; (b) Yazaki, S.;
Funahashi, M.; Kagimoto, J.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2010, 132,
7702e7708; (c) Yazaki, S.; Funahashi, M.; Kato, T. J. Am. Chem. Soc. 2008, 130,
13206e13207; (d) Bhowmik, P. K.; Han, H.; Cebe, J. J.; Burchett, R. A.; Acharya,
B.; Kumar, S. Liq. Cryst. 2003, 30, 1433e1440; (e) Kijima, M.; Setoh, K.; Shir-
akawa, H. Chem. Lett. 2000, 29, 936e937; (f) Haramoto, Y.; Yin, M.; Matukawa,
Y.; Ujiie, S.; Nanasawa, M. Liq. Cryst. 1995, 19, 319e320.
ꢁ
Craats, A. M.; Senthilkumar, K.; Siebbeles, L. D. A.; Warman, J. M.; Bredas, J.-L.;
Cornil, J. J. Am. Chem. Soc. 2004, 126, 3271e3279; (c) Cornil, J.; Lemaur, V.;
ꢁ
Calbert, J.-P.; Bredas, J.-L. Adv. Mater. 2002, 14, 726e729; (d) Adam, D.;
€
Schuhmacher, P.; Simmerer, J.; Haussling, L.; Siemensmeyer, K.; Etzbachi, K. H.;
Ringsdorf, H.; Haarer, D. Nature 1994, 371, 141e143.
7. Reviews: (a) Ringstrand, B.; Kaszynski, P. Acc. Chem. Res. 2013, 46, 214e215; (b)
Chen, S.; Eichhorn, S. H. Isr. J. Chem. 2012, 52, 830e843; (c) Axenov, K. V.; La-
schat, S. Materials 2011, 4, 206e259; (d) Douce, L.; Suisse, J.-M.; Guillon, D.;
Taubert, A. Liq. Cryst. 2011, 38, 1653e1661; (e) Kato, T.; Mizoshita, N.; Kishimoto,
K. Angew. Chem., Int. Ed. 2006, 45, 38e68; (f) Binnemans, K. Chem. Rev. 2005,
105, 4148e4204.
13. Mansueto, M.; Frey, W.; Laschat, S. Chem.dEur. J. 2013, 19, 16058e16065.
14. Jones, P. B.; Prrish, N. M.; Houston, T. A.; Stapon, A.; Bansal, N. P.; Dick, J. D.;
Townsend, C. A. J. Med. Chem. 2000, 43, 3304e3314.
15. Kukovinets, O. S.; Kukovinets, A. G.; Kasradze, V. G.; Salimova, E. V.; Abdullin,
M. I. Russ. J. Org. Chem. 2010, 46, 798e806.
€
16. Butschies, M.; Haenle, J. C.; Tussetschlager, S.; Laschat, S. Liq. Cryst. 2013, 40,
8. Rondla, R.; Lin, J. C. Y.; Yang, C. T.; Lin, I. J. B. Langmuir 2013, 29, 11779e11785.
9. Costa, R. D.; Werner, F.; Wang, X.; Groenninger, P.; Feihl, S.; Kohler, F. T. U.;
Wasserscheid, P.; Hibler, S.; Beranek, R.; Meyer, K.; Guld, D. M. Adv. Energy
Mater. 2013, 3, 657e665.
52e71.
17. Bradley, A. E.; Hardacre, C.; Holbrey, J. D.; Johnston, S.; McMath, S. E. J.; Nieu-
wenhuyzen, M. Chem. Mater. 2002, 14, 629e635.
18. Cambridgsoft, Chem3D Pro 12, 2013.
10. Chi, W. S.; Jeon, H.; Kim, S. J.; Kim, D. J.; Kim, J. H. Macromol. Res. 2013, 21,
315e320.
11. Recent examples: (a) Ji, S.-P.; Tang, M.; He, L.; Tao, G.-H. Chem.dEur. J. 2013, 19,
4452e4461; (b) Abate, A.; Petrozza, A.; Cavallo, G.; Lanzani, G.; Matteucci, F.;
19. Kouwer, P. H. J.; Swager, T. M. J. Am. Chem. Soc. 2007, 129, 14042e14052.
20. Wang, H.; Zhang, X.; Gong, F.; Zhou, G.; Wang, Z.-S. Adv. Mater. 2012, 24,
121e124.
Please cite this article in press as: Mansueto, M.; et al., Tetrahedron (2014), http://dx.doi.org/10.1016/j.tet.2014.03.050