The first examples of discotic liquid crystalline gemini surfactants

Article abstract of DOI:10.1016/j.tetlet.2010.08.022

Six novel gemini imidazolium salts tethered with hexaalkoxytriphenylene moieties were prepared by quaternization of imidazole nitrogen with ω-bromo-substituted triphenylene derivatives. Their chemical structures were examined by ¹H NMR, IR, UV, MS, and elemental analyses. The mesomorphic properties of these discotic dimeric salts were investigated by polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction studies. These triphenylene-imidazole-based gemini dimers with bromide as counter ion were found to exhibit liquid crystalline behavior over a wide temperature range and display ionic conductivity in the range of 10 ^-6 to 10^-5 S/m. These materials tend to form monolayer at the air-water interface.

Full text of DOI:10.1016/j.tetlet.2010.08.022

Tetrahedron Letters 51 (2010) 5459–5462
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
The first examples of discotic liquid crystalline gemini surfactants
*
Sandeep Kumar , Satyam Kumar Gupta
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore 560 080, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Six novel gemini imidazolium salts tethered with hexaalkoxytriphenylene moieties were prepared by
Received 14 June 2010
Revised 4 August 2010
Accepted 8 August 2010
Available online 12 August 2010
quaternization of imidazole nitrogen with
x-bromo-substituted triphenylene derivatives. Their chemical
1
structures were examined by H NMR, IR, UV, MS, and elemental analyses. The mesomorphic properties
of these discotic dimeric salts were investigated by polarizing optical microscopy, differential scanning
calorimetry, and X-ray diffraction studies. These triphenylene-imidazole-based gemini dimers with bro-
mide as counter ion were found to exhibit liquid crystalline behavior over a wide temperature range and
display ionic conductivity in the range of 10 to 10 S/m. These materials tend to form monolayer at the
air–water interface.
Keywords:
ꢀ6
ꢀ5
Gemini surfactant
Ionic liquid crystal
Discotic
Ó 2010 Elsevier Ltd. All rights reserved.
Triphenylene
Imidazole
Columnar mesophase
Recently there has been considerable interest in the field of non-
conventional low molar mass liquid crystals (LCs), especially in
liquid crystal dimers because of their interesting mesomorphic
lar assemblies containing ionic liquids may find relevance as heat
carriers in solar thermal energy generators and as electrolytes for
batteries and capacitors. Imidazolium-based ionic salts, which
6
1
properties due to restricted molecular motions. Non-conventional
have been well-investigated as ionic liquids can be easily trans-
formed into ionic liquid crystals by modifying periphery.7 Forma-
tion of lamellar phases has been noticed in a number of calamitic
liquid crystals are those materials whose structure and property
deviate from ordinary or conventional LCs. One can realize materials
of interesting properties by combining contrasting functionalities
within a molecule. A variety of combinations are possible, for exam-
ple, thermotropic/lyotropic, hydrophilic/hydrophobic, non-polar/
polar, hydrocarbon/fluorocarbon, rigid/flexible, disk/rod, electron
donor/electron acceptor, etc.2 A liquid crystal dimer is composed
of molecules containing two mesogenic groups (either identical or
different) linked via a flexible or rigid spacer. Physical properties of
liquid crystalline dimers are significantly different than that of con-
ventional low molar mass liquid crystals. Dimers represent ideal
model compounds for polymers or networks, due to their ease of
purification and characterization, and the possibility of freezing, in
their mesophase, to a glassy state. They have considerable applica-
tion potential in many technological fields.1
8
mesomorphic imidazolium salts which have been well-studied
for unidirectional ionic conductivity in addition to their mesomor-
9
,10
phic properties.
We have previously incorporated discotic units
in ionic liquids to generate monomeric, dimeric, and polymeric
11
discotic liquid crystals (DLCs) exhibiting columnar mesophases.
Their interactions with biomolecules have also been studied in
1
2
our laboratory. Discotic ionic molecules containing 2,4,6-triaryl-
1
3,14
14
15
pyrylium,
2,4,6-triarylpyridinium, crown ethers, 3,5-dia-
1
6
17
18
ryl-1,2-dithiolium, phthalocyanine, and tricycloquinazoline
moieties are also reported to display mesomorphism.
A molecule composed of two hydrophilic head groups and two
hydrophobic terminal chains linked with a spacer is commonly
,3
19
known as a gemini surfactant. These dimeric surfactants possess
Considerable research effort is currently focused on the inter-
play between ionic conduction property of ionic liquids and meso-
morphic behavior of liquid crystals. Ionic molecules are known to
superior properties compared to those of conventional surfactants,
such as lower critical micelle concentrations (CMC), lower limiting
surface tensions, low Krafft temperature, better solubilizing, wet-
4
20
form amphitropic liquid crystals. The first report on the existence
ting and foaming ability, higher adsorption efficiency, etc. Liu
of mesophase in ionic salts was reported by Skoulios and co-work-
er in alkalies metal soaps. This was followed by the identification
of liquid crystalline behavior in alkylammonium, pyridinium, vina-
midinium, phosphonium salts, etc. The formation of supramolecu-
et al. reported effective dispersion of multi-walled carbon nano-
tubes (MWCNT) in imidazole-based gemini surfactant. Stability
of these MWCNT suspensions in double chain gemini surfactant
was higher as compared to their dispersion in single chain imidaz-
5
2
1
ole-based surfactant. A few calamitic liquid crystalline gemini
surfactants have been realized and known to display lyotropic as
*
Corresponding author. Tel.: +91 80 23610122; fax: +91 80 23610492.
2
2
E-mail address: skumar@rri.res.in (S. Kumar).
well as thermotropic mesophases. A very interesting gemini-like
0
040-4039/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2010.08.022

5
460
S. Kumar, S. K. Gupta / Tetrahedron Letters 51 (2010) 5459–5462
macrodiscogen was reported by Jiang et al.23 This copper-bis(b-
diketonate)-based molecule displays rectangular columnar meso-
phases. However, to the best of our knowledge, any liquid crystal-
line gemini surfactant incorporating discotic liquid crystalline
units has not yet been investigated. Here we present the synthesis
and physical properties of novel triphenylene-imidazole-imidaz-
ole-triphenylene diads consisting of two imidazolium moieties as
ionic part, linked with two mesogenic triphenylenes via alkyl
spacer. Six discotic gemini ionic dimers have been designed and
synthesized using microwave dielectric heating. All the newly syn-
thesized compounds were characterized using spectral techniques
and elemental analysis. The mesophase behavior of all the com-
pounds was investigated by polarizing optical microscopy and dif-
ferential scanning calorimetry. The mesophase structure of these
compounds was established with the help of X-ray diffractometry.
Table 1
Phase transition temperatures (peak, °C) and associated enthalpy changes
kcal mol 1, in parentheses) of novel symmetrical ionic dimers (see Scheme 1 for
ꢀ
(
chemical structures)
Compound First heating scan
First cooling scan
180.1 (0.48) I I 173.9 (0.29) Col
120.6 (0.37) I 93.8 (1.3) Col
4IM6TP
Cr 48.3 (7.9) Col
Cr 59.7 (14.5) Col
I
h
h
5IM12TP
h
h
8IM8TP
Cr 58.7 (15.2) Col
h
h
87.3 (0.71) I I 84.2 (0.41) Col
h
18.9 (1.77)
13.5 (5.6) x
x
8IM9TP
Cr 58.8 (16.2) Col
Cr 57.9 (15.8) I
Cr 57.7 (12.5) I
86.3 (0.26) I I 60.8 (0.31) Col
h
8
8
IM10TP
IM12TP
No phase transition
No phase transition
Cr: crystal; Col
crystalline.
h
: hexagonal columnar phase; I: isotropic phase; x: partially
x
-Brominated triphenylene 6TPO-m-Br was prepared in four
24
steps starting from catechol as reported previously. The synthesis
of imidazole dimer involves sodium hydride-mediated nucleo-
philic substitution of bromide with imidazole nitrogen as shown
in Scheme 1. Ionic dimers nIMmTP were prepared by irradiating
a mixture of 6TPO-m-Br (2.5 equiv) and IM-n-IM (1 equiv) under
2
5
2
6
microwaves. Under classical heating reactions (refluxing in tolu-
ene for 24–48 h), the product does form but in much lower yield.
The thermal behavior of all the compounds was investigated by
polarizing optical microscopy (POM) and differential scanning cal-
orimetry (DSC). The transition temperature and associated enthal-
py data obtained from the heating and cooling cycles of DSC or
POM are collected in Table 1. In the case of materials which were
mesomorphic, classical textures of discotic columnar mesophases
appeared upon cooling from the isotropic liquid as shown in Fig-
ure 1. The textures obtained from polarizing optical microscopy
were similar for all compounds, and were typical of well known
h
textures for Col phases. All the ionic dimers contain two identical
triphenylenes substituted with five hexyloxy peripheral chains
linked to two imidazoles through methylene spacer. The two cen-
tral imidazole rings are also connected to each other via methylene
spacer. The length of methylene spacers connecting two imida-
zoles as well as imidazole to triphenylene core has been varied.
The dimers 8IM10TP and 8IM12TP having the longest spacer link-
ing triphenylene with imidazole (10 and 12 carbon atom) as well
as two imidazole rings (eight carbon atom) failed to display liquid
crystalline phase. These ionic dimers melt from crystalline solid
Figure 1. Optical micrograph of 4IM6TP at 170 °C on cooling from the isotropic
liquid (crossed polarizer, magnification 200ꢁ).
state to isotropic liquid at 57.9 and 57.7 °C, respectively, on heating
and on cooling these materials did not show any sign of crystalli-
zation or mesophase formation. All other members display enan-
tiotropic mesophase behavior. For liquid crystalline derivatives
6 13
OC H
O
(CH2)m
Br
6 13
C H O
(i)
N
H
N
(CH2)n
N
N
N
N
C H13O
6
IM-n-IM
OC H
6
13
OC H
(ii)
6
13
6
TPO-m-Br
OC H
OC H
6 13
6
13
O
(CH2)m
N
N
(CH )
N
N
(CH )
O
2 n
2 m
C H13O
Br
Br
OC H
6
6
1
3
nIMmTP
C H13O
n = 4, 5, 8
OC H
6
6
m = 6, 8, 9, 10, 12
13
OC H
C H13O
6
6
13
OC H
OC H
6
6
13
13
Scheme 1. Synthesis of triphenylene-imidazole-based ionic dimmers. Reagents: (i) Br(CH
2 n
) Br, NaH, DMF; (ii) N-methylpyrrolidone, microwaves.

S. Kumar, S. K. Gupta / Tetrahedron Letters 51 (2010) 5459–5462
5461
an increase in total number of carbon atoms in both the spacers
tends to a decrease in columnar to isotropic transition tempera-
ture. Increasing spacer length reduced the mesophase range of
the gemini ionic dimers. In their DSC thermograms, the liquid crys-
talline dimers display a solid to mesophase transition followed by
mesophase to isotropic transition on heating. Upon cooling they
show isotropic to mesophase transition and the mesophase re-
mains stable down to room temperature or transition to another
phase was observed at lower temperature which was not detect-
able in microscopic experiments. A typical example, the DSC ther-
mogram of compound 8IM8TP is shown in Figure 2. The low
h
enthalpy values of Col -I phase transition in these materials indi-
cate a highly disordered nature of the mesophase.
In order to reveal the mesophase structure and hence the supra-
molecular organization of these compounds, X-ray diffraction
experiments were carried out using unoriented samples. X-ray
diffraction patterns for ionic dimers were recorded in the columnar
phase 10 °C below the clearing temperature while cooling from the
isotropic phase. The X-ray diffraction patterns of the mesophase
exhibited by samples are supportive of a discotic hexagonal-
columnar arrangement. As a typical example, the X-ray diffraction
pattern of compound 8IM8TP and its one-dimensional intensity
versus theta (h) graph derived from the pattern are shown in Figure
8IM8TP
3. Qualitatively all the compounds show similar X-ray diffraction
patterns. As can be seen from the figure, in the small angle region
1000
seven reflexions are seen whose d-spacings are in the ratio of 1:1/
p
p p p p p
3
:1/ 4:1/ 7:1/ 9:1/ 11:1/ 12, consistent with a two-dimen-
sional hexagonal lattice. In the wide angle region a diffuse reflec-
tion appears at 4.35 Å. This corresponds to the liquid-like order
of the aliphatic chains.
In conclusion, we have synthesized a number of novel symmet-
rical gemini dimers based on imidazole and triphenylene moieties
using microwave irradiation. They exhibit columnar mesophase
over a wide range of temperature. Hexagonal columnar structure
of the mesophase of these triphenylene-imidazole-based gemini
ionic dimers was established by X-ray diffraction studies. Shorter
spacer length is in favor of liquid crystalline property in these sym-
metrical gemini dimers. Preliminary experiments have been made
to study the ionic conductivity of these materials using a lock-in
amplifier (Stanford Research Systems model SR830) at 1 kHz fre-
quency on cooling from the isotropic phase. These materials dis-
1
00
4
8
θ
Figure 3. X-ray diffraction pattern and intensity versus h profile of 8IM8TP at 75 °C.
ꢀ6
ꢀ5
play ionic conductivity in the range of 10
to 10 S/m. The
Acknowledgments
synthesized gemini dimers tend to form monolayer at the air–
water interface. These results will be published in due course.
We would like to thank Professor V.A. Raghunathan for helpful
discussions. We also thank K.N. Vasudha and A.V. Radhakrishnan
for their help in x-ray experiments. The IISc is gratefully acknowl-
edged for providing MS and NMR spectra.
8
IM8TP
2
2
2
7
4
1
References and notes
1.
Imrie, C. T.; Henderson, P. A. Chem. Soc. Rev. 2007, 36, 2096.
2. Tschierske, C. J. Mater. Chem. 1998, 8, 1485.
3.
Imrie, C. T.; Luckhurst, G. R.. In Handbook of Liquid Crystal; Demus, D., Goodby, J.
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2B, p 801.
4.
5.
6.
Tschierske, C. Curr. Opin. Colloid Interface Sci. 2002, 7, 355.
Skoulios, A.; Luzzati, V. Acta Crystallogr. 1961, 14, 278.
A large number of papers have appeared on thermotropic ionic liquid crystals.
It is difficult to cover all these and, therefore, only a few selected references are
given here. (a) Bruce, D. W.; Dunmur, D. A.; Lalinde, E.; Maitlis, P. M.; Styring, P.
Nature 1986, 323, 791; (b) Marcos, M.; Ros, M. B.; Serrano, J. L.; Esteruelas, M.
A.; Sola, E.; Oro, L. A.; Barbera, J. Chem. Mater. 1990, 2, 748; (c) Bravo-Grim-aldo,
E.; Navarro-Rodriguez, D.; Skoulios, A.; Guillon, D. Liq. Cryst. 1996, 20, 393; (d)
Bernhardt, H.; Weissflog, W.; Kresse, H. Liq. Cryst. 1998, 24, 895; (e) Cui, L.;
Sapagovas, V.; Lattermann, G. Liq. Cryst. 2002, 29, 1121; (f) De Roche, J.; Gordon,
C. M.; Imrie, C. T.; Ingram, M. D.; Kennedy, A. R.; Celso, F. L.; Triolo, A. Chem.
Mater. 2003, 15, 3089; (g) Bhowmik, P. K.; Han, H.; Nedeltchev, I. K.; Cebe, J. J.
Mol. Cryst. Liq. Cryst. 2004, 419, 27; (h) Haristoy, D.; Tsiourvas, D. Liq. Cryst.
2004, 31, 697.
0
40
80
Temperature/°C
Figure 2. DSC thermogram of the gemini ionic dimer 8IM8TP on heating and
ꢀ
1
cooling cycles (scan rate 10 °C min ).
7. Lin, I. J. B.; Vasam, C. S. J. Organomet. Chem. 2005, 690, 3498.

5
462
S. Kumar, S. K. Gupta / Tetrahedron Letters 51 (2010) 5459–5462
8
.
(a) Lee, K. M.; Lee, C. K.; Lin, I. J. B. Chem. Commun. 1997, 899; (b) Gordon, C. M.;
dibromoalkane was added and the resulting mixture was heated at 70 °C for
4 h with vigorous stirring. After the reaction was over, the mixture was poured
into a mixture of ethyl acetate and water (100 ml). The organic phase was
separated; the aqueous phase was extracted with ethyl acetate three times.
The combined organic extracts were washed with water and saturated NaCl
solution, respectively. The resulting organic phase was dried over anhydrous
sodium sulfate and concentrated under reduced pressure. The residue was
purified through column chromatography over silica gel (eluent: 4–10%
methanol in ethyl acetate) to give pure product IM-4-IM as highly viscous
Holbrey, J. D.; Kennedy, A. R.; Seddon, K. R. J. Mater. Chem. 1998, 8, 2627; (c)
Holbrey, J. D.; Seddon, K. R. J. Chem. Soc., Dalton Trans. 1999, 2133; (d) Lee, K.
M.; Lee, Y. T.; Lin, I. J. B. J. Mater. Chem. 2003, 13, 1079; (e) Li, X.; Bruce, D. W.;
Shreeve, J. M. J. Mater. Chem. 2009, 19, 8232; (f) Kouwer, P. H. J.; Swager, T. M. J.
Am. Chem. Soc. 2007, 129, 14042.
9
.
Yoshio, M.; Kato, T.; Mukai, T.; Yoshizawa, M.; Ohno, H. Mol. Cryst. Liq. Cryst.
2
004, 413, 99.
1
0. (a) Yoshio, M.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem. Soc. 2004, 126, 994; (b)
Yoshio, M.; Kagata, T.; Hoshino, K.; Mukai, T.; Ohno, H.; Kato, T. J. Am. Chem.
Soc. 2006, 128, 5570; (c) Shimura, H.; Yoshio, M.; Hoshino, K.; Mukai, T.; Ohno,
H.; Kato, T. J. Am. Chem. Soc. 2008, 130, 1759.
liquid. Selected data for compound IM-4-IM: 1H NMR (400 MHz, CDCl1
): d 7.44
3
3
(s, 2H), 7.07 (s, 2H), 6.86 (br s, 2H), 3.93 (m, 4H), 1.76 (m, 4H). C NMR
(100 MHz, CDCl
compound IM-5-IM: H NMR (400 MHz, CDCl
6.88 (br s, 2H), 3.92 (m, 4H), 1.79 (m, 4H), 1.2–1.4 (m, 2H). C NMR (100 MHz,
CDCl ): 136.98, 129.63, 118.65, 46.72, 30.64, 23.68. Selected data for
compound IM-8-IM: H NMR (400 MHz, CDCl
6.90 (br s, 2H), 3.91 (m, 4H), 1.75 (m, 4H), 1.1–1.5 (m, 8H).
A mixture of 6TPO-6-Br (2.5 equiv) and IM-4-IM (1 equiv) in NMP was
3
): d 136.98, 129.87, 118.54, 46.33, 28.11. Selected data for
1
1
1. (a) Kumar, S.; Pal, S. K. Tetrahedron Lett. 2005, 46, 2607; (b) Kumar, S.; Pal, S. K.
Tetrahedron Lett. 2005, 46, 4127; (c) Pal, S. K.; Kumar, S. Tetrahedron Lett. 2006,
3
): d 7.47 (s, 2H), 7.07 (s, 2H),
13
47, 8993; (d) Pal, S. K.; Kumar, S. Liq. Cryst. 2008, 35, 381.
3
d
1
1
1
2. Suresh, K. A.; Nayak, A. Mol. Cryst. Liq. Cryst. 2009, 512, 57 [1903].
3. Veber, M.; Sotta, P.; Davidson, P.; Levelut, A. M.; Jallabert, C.; Strzelecka, H. J.
Phys. France 1990, 51, 1283.
3
): d 7.46 (s, 2H), 7.04 (s, 2H),
26.
1
1
4. Veber, M.; Berruyer, G. Liq. Cryst. 2000, 27, 671.
5. (a) Percec, V.; Johansson, G.; Heck, J.; Ungar, G.; Batty, S. V. J. Chem. Soc., Perkin
Trans. 1 1993, 1411; (b) Beginn, U.; Zipp, G.; Moller, M. Adv. Mater. 2000, 12,
irradiated in a microwave oven for 30 s. The vial was removed from the oven
and left to stand for about 45 s and again irradiated for 30 s. This process was
repeated 12 times until the reaction was complete (TLC monitoring). The
cooled reaction mixture was then extracted with a mixture of chloroform and
distilled water (5:3 volume ratio). The organic extract was dried over
anhydrous sodium sulfate concentrated and the product was purified by
fourfold recrystallization from a mixture of diethyl ether/hexane (7:3). Spectral
data and elemental analysis of all the compounds were in good agreement with
their structures. Selected data for compound 4IM6TP: Yield: 15%; 1H NMR
5
10.
16. Artzner, F.; Veber, M.; Clerc, M.; Levelut, A. M. Liq. Cryst. 1997, 23, 27.
17. Van Nostrum, C. F.; Nolte, R. J. M. Chem. Commun. 1996, 2385.
18. Kadam, J.; Faul, C. F. J.; Scherf, U. Chem. Mater. 2004, 16, 3867.
19. Menger, F. M.; Littau, C. A. J. Am. Chem. Soc. 1991, 113, 1451.
20. Menger, F. M.; Keiper, J. S. Angew chem., Int. Ed. 2000, 39, 1906.
21. Liu, Y.; Yu, L.; Zhang, S.; Yuan, J.; Shi, L.; Zheng, L. Colloids Surf., A 2010, 359, 1–3.
(400 MHz, CDCl
only the number of alkyl chain CH
7.68 (br s, 2H), 7.06 (br s, 2H), 4.39 (m, 4H), 4.23 (m, 28H), 2.09 (m, 4H), 1.93
(m, 28H), 0.8–1.7 (m, 98H); Elemental Anal. Calcd for C118 O:
12ꢂ4H
C, 68.78; H, 9.10; N, 2.70. Found: C, 69.27; H, 9.54; N, 2.29. ESI-MS (methanol,
3
, all the other ionic dimers give similar spectra differing in
6
6.
2
protons): d 10.31 (br s, 2H), 7.83 (s, 12H),
2
2. (a) Fuller, S.; Hopwood, J.; Rahman, A.; Shinde, N.; Tiddy, G. J.; Attard, G. S.;
Howell, O.; Sproston, S. Liq. Cryst. 1992, 12, 521; (b) Pindzola, B. A.; Jin, J.; Gin,
D. L. J. Am. Chem. Soc. 2003, 125, 2940; (c) Dreja, M.; Gramberg, S.; Tieke, B.
Chem. Commun. 1998, 1371; (d) Fuller, S.; Shinde, N. N.; Tiddy, G. J. T.; Attard, G.
S.; Howell, O. Langmuir 1996, 12, 1117; (e) Sikiric, M.; Smit, I.; Bozic, L. T.;
Tomasic, V.; Pucic, I.; Primozic, I.; Vincekovic, N. F. Langmuir 2003, 19, 10044;
H
180Br
2
4
N O
2
ꢀ
+
ꢀ +
m/z): 922.8 (Mꢀ2Br /2) , 1025.1 (MꢀBr ) . UV-vis(CHCl
362 nm. Selected data for compound 5IM12TP: Elemental Anal. Calcd for
12ꢂ4H O: C, 69.59; H, 9.54; N, 2.48. Found: C, 69.74; H, 9.38; N,
2.46. ESI-MS (methanol, m/z): 1014.5 (Mꢀ2Br /2) , 2108.7 (MꢀBr ) . Selected
data for compound 8IM8TP: Elemental Anal. Calcd for C126 O:
12ꢂ4H
C, 69.08; H, 9.39; N, 2.56. Found: C, 69.41; H, 9.25; N, 2.91. ESI-MS (methanol,
3
) kmax 314, 346,
C
131
H206Br
2
N
4
O
2
ꢀ
+
ꢀ +
(
f) Sharma, V.; Borse, M.; Devi, S.; Dave, K.; Pohnerkar, J.; Prajapati, A. J.
Dispersion Sci. Technol. 2005, 26, 421; (g) Ryhänen, S. J.; Pakkanen, A. L.; Säily,
M. J.; Bello, C.; Mancini, G.; Kinnunen, P. K. J. J. Phys. Chem. B 2002, 106, 11694.
3. Jiang, J.; Shen, Z.; Lu, J.; Fu, P.; Lin, Y.; Tang, H.; Gu, H.; Sun, J.; Xie, P.; Zhang, R.
Adv. Mater. 2004, 16, 1534.
4. (a) Gupta, S. K.; Raghunathan, V. A.; Kumar, S. New J. Chem. 2009, 33, 112; (b)
Gupta, S. K.; Raghunathan, V. A.; Lakshminarayanan, V.; Kumar, S. J. Phys. Chem.
B 2009, 113, 12887.
5. A typical procedure for the synthesis of IM-4-IM is as follows; a DMF solution
of imidazole (1 g, 14.7 mmol) in a round-bottomed flask (100 ml) equipped
with a stirring bar was deaerated under reduced pressure, and the flask was
filled with argon. The deaeration was repeated three times to remove oxygen
in the flask thoroughly. The flask was kept in an ice-bath to maintain the
temperature of about 0 °C inside. After that 384 mg of NaH (16 mmol) was
added slowly into the reaction mixture. Then 1.44 g (6.67 mmol) of
H
196Br
2
4
N O
2
ꢀ
+
2
2
m/z): 979.3 (Mꢀ2Br /2) , 1102.0. MALDI-MS (methanol, m/z): 1102.3, 1957.3,
2039.2. IR: (Nuzol) max 1616, 1518, 1443, 1377, 1263, 1173, 1070, 1026,
837 cm . Selected data for compound 8IM9TP: Elemental Anal. Calcd for
O: C, 69.29; H, 9.45; N, 2.53. Found: C, 69.79; H, 9.76; N,
m
ꢀ
1
C
128
H200Br
2
N
4
O
12ꢂ4H
2
ꢀ
+
2.19. ESI-MS (methanol, m/z): 993.5 (Mꢀ2Br /2) , 1116.2. MALDI-MS
2
(methanol, m/z): 1985.4, 2065.4. Selected data for compound 8IM10TP:
Elemental Anal. Calcd for C130
H
204Br
2
N
4
O
12ꢂ4H
2
O: C, 69.49; H, 9.51; N, 2.49.
ꢀ
+
Found: C, 69.77; H, 9.63; N, 2.44. ESI-MS (methanol, m/z): 1007.4 (Mꢀ2Br /2) ,
1129.9. Selected data for compound 8IM12TP: Elemental Anal. Calcd for
C
2.26.
134
H
212Br
N
2 4
O
12ꢂ4H
2
O: C, 69.88; H, 9.63; N, 2.43. Found: C, 70.29; H, 9.65; N,