Synthesis and comparative study on phase transition behavior of triazole-cored liquid crystals armed with cholesterol and double or triple aromatic rings systems

Article abstract of DOI:10.1039/c3nj00053b

Two homologous series of optically active bent-shaped mesogens comprising a cholesterol unit as one of the side arms connected to a 1,2,3-triazole ring while the other arm of the triazole ring is connected to two- and three-ring aromatic systems with varying terminal chain lengths have been synthesized. The molecular structure, thermal and optical activities have been studied extensively in which the compounds from both series exhibit polymorphism ranging from chiral nematic (N*), chiral smectic A (SmA*), chiral smectic C (SmC*) and twist grain boundary (TGBC*) phases. A further comparison between the two series of target compounds has drawn a common remark of which the phase behavior is found to be dependent on the length of the terminal tail and number of aromatic rings in the mesogenic units.

Full text of DOI:10.1039/c3nj00053b

NJC
PAPER
Synthesis and comparative study on phase transition
behavior of triazole-cored liquid crystals armed with
cholesterol and double or triple aromatic rings
systems†
Cite this: NewJ.Chem., 2013,
37, 1906
Guan-Yeow Yeap,*a Subramanian Balamurugan,a Murugesan Vijay Srinivasanb and
Palaninathan Kannanb
Two homologous series of optically active bent-shaped mesogens comprising a cholesterol unit as one
of the side arms connected to a 1,2,3-triazole ring while the other arm of the triazole ring is connected
to two- and three-ring aromatic systems with varying terminal chain lengths have been synthesized. The
molecular structure, thermal and optical activities have been studied extensively in which the
compounds from both series exhibit polymorphism ranging from chiral nematic (N*), chiral smectic A
(SmA*), chiral smectic C (SmC*) and twist grain boundary (TGBC*) phases. A further comparison
between the two series of target compounds has drawn a common remark of which the phase
behavior is found to be dependent on the length of the terminal tail and number of aromatic rings in
the mesogenic units.
Received (in Montpellier, France)
13th January 2013,
Accepted 11th March 2013
DOI: 10.1039/c3nj00053b
www.rsc.org/njc
phases has also received great attention. There are three main
types of TGB phases including the TGBA, TGBC and TGBC*
1. Introduction
Since the discovery of chiral anisotropic fluid phases formed by
chiral mesogens or induced by chiral dopants, materials with
optically active properties have continued to attract attention
from researchers.1 The molecular chirality is inclined to self-
organize leading to the formation of helical structures in a
chiral phase.2,3 It has been claimed that the helical structure of
the molecule can produce chiral nematic (N*), chiral smectic C
(SmC*), chiral smectic A (SmA*) and frustrated LC phases such
as blue phase and twist grain boundary (TGB). Each of these
chiral phases possess potential applications. For instance, the
N* phase has been exploited in optical and thermal sensing
device applications.4–7 The SmC* and SmA* phases formed by
chiral mesogens have been well-exploited in electro-optical and
spatial light modulation applications, respectively,8 and the
frustrated blue phase has been studied extensively to determine
their potential for the use as media in advanced technology. In
the midst of searching for new applications, the studies on TGB
wherein the smectic order is of orthogonal SmA, SmC and
helical SmC*, respectively.7
The design of chiral liquid crystalline materials requires the
selection of a core, linking groups and terminal functional-
ities.9 Since the term ‘click’ reaction was reported, it has gained
a great deal of attention owing to its high specificity and
quantitative yields.10 Among the ‘click’ chemistry reactions,
the Huisgen dipolar cycloaddition reaction between an azide
and an alkyne leading to the formation of 1,2,3-triazole was
claimed to be the most convenient method adopted by
researchers.11 The importance of this reaction for researchers
working on liquid crystals can be rationalized by the presence
of the heteroatoms, which are found to be more polarizable
than carbon atoms and can promote the desired physical and
chemical changes.12 Recently, Gimeno and co-workers reported
that the presence of a 1,2,3-triazole ring would promote well-
built intermolecular interactions.13
Although attempts to obtain 1,2,3-triazole-based liquid
crystals have extensively been carried out in recent years,13–15
the formation of 1,2,3-triazole derivatives armed with cholesterol
group has rarely been reported. Hence, we report in this paper a
new class of low molar mass mesogens derived from cholesterol
which represents an exemplary and emerging class of
chiral liquid crystals. The cholesterol unit is linked with the
a Liquid Crystal Research Laboratory, School of Chemical Sciences,
Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia.
E-mail: gyyeap@usm.my; Fax: +60-4-6574854
b Department of Chemistry, Anna University, Chennai 600-025, Tamil Nadu, India
† Electronic supplementary information (ESI) available: Full experimental details,
including the general procedure for the synthesis of intermediate and final
compounds. See DOI: 10.1039/c3nj00053b
c
1906 New J. Chem., 2013, 37, 1906--1911
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

Paper
NJC
mesogenic units through the 1,2,3-triazole ring. Two series of
The phase transition behavior of both series was evaluated
target compounds are designed wherein the 1,2,3-triazole ring using polarizing optical microscopy (POM) and differential
serves as a linking group situated between a cholesterol and a scanning calorimetry (DSC). The sample was sandwiched
mesogenic unit. The first series contains the mesogenic unit between a clean untreated glass slide and a cover slip. The
with two aromatic ring while the latter series consists of three planar and homeotropically aligned cells were employed in
rings in the same unit. For both series, the alkyl group CnH2n+1 order to substantiate the mesophase. The details of these
(where n = 6 to 12) is employed as terminal chain attached to studies will be discussed in the following section.
the mesogenic unit.
3. Results and discussion
2. Experimental
2.1 Synthesis and characterization
3.1 Microscopic and calorimetric studies of intermediates 3
and 4
The target bent shaped compounds of series 1 and 2 are
The new class of 1,2,3-triazole containing compounds (series 1
obtained from the intermediates with NO2 and NH2 functiona-
and 2) were prepared using the method summarized in
lized compounds 3 and 4, respectively. Both of these compounds
Schemes 1 and 2. 4-Azidonitrobenzene (1) was prepared from
4-nitroaniline by a known diazotization method.14 The azide
was reacted with propiolic acid using CuI as a catalyst to obtain
3 and 4 also consist of cholesterol group and hence are chiral.
It is apparent that compound 3 shows the phase sequence
Cr–SmA–I on heating and these transitions are reversible on
1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carboxylic acid (2). The
cooling. However, compound 4 is found to be non-mesogenic
esterification of compound 2 with commercially available
(Table 1). The difference between compound 3 and 4 merely lies
cholesterol in the presence of DCC and DMAP to yield
cholesteryl(1-(4-nitrophenyl)-1H-1,2,3-triazole-4-carboxylate) (3).
The nitro group of compound 3 was reduced by iron powder
and ammonium chloride to obtain cholesteryl(1-(4-amino-
on the terminal substituent of NO2 and NH2 of which the
earlier possesses higher clearing point (327 1C) than the latter
(230 1C).
phenyl)-1H-1,2,3-triazole-4-carboxylate) (4). The acid catalyzed
3.2 Microscopic and calorimetric studies of compounds 6a–6g
condensation of compound 4 with 4-n-alkyloxybenzaldehyde
The compounds 6a–6g possess a 1,2,3-triazole ring as a central
(5a–5g) or 4-(4-n-alkyloxybenzoyloxy)-benzaldehyde (8a–8g) in
core armed with promesogen cholesterol and another arm
ethanol gave the target compounds in reasonably good yields.
made up from two aromatic rings attached by terminal chains
The detailed synthetic procedures and characterization data for
of CnH2n+1 where n ranges from 6 to 12. The phase transition
behaviors for 6a–6g are summarized in Table 2. It is apparent
all the compounds are given in the ESI† under the experimental
section.
from Table 1 that compounds 6a–6g have very high thermal
stabilities as indicated by the high clearing temperatures. For
6a, however, there was partial thermal decomposition at 290 1C
before it turned into an isotropic liquid. As for the compounds
6b–6g, they possess decomposition temperatures close to the
isotropic temperature. These results indicate that the com-
pounds possess high mesophase stability.
In general, the chiral liquid crystal material can induce the
cholesteric phase wherein at zero field it exhibits two optical
contrasting stable states with planar (oily streak and fingerprint)
texture and focal conic texture. As such, most of the mesophase
can be identified according to the typical optical textures. From
the POM observation the compounds 6a–6g exhibit cholesteric
oily streak texture on heating cycle since the compounds are of
high viscous nature. Generally, the calamitic liquid crystals of
lower members are nematic, the medium members show
nematic and smectic and higher members are merely smectic
in nature.16 The generalization is applicable for this series. The
lower homologues 6a and 6b show chiral nematic (N*) phase,
the medium member of 6c exhibits N* and SmC phase and the
higher homologues 6d–6g show SmA and/or SmC phase. For
compound 6a, it exhibits typical cholesteric oily streak texture
on heating but decomposes before isotropization. Whereas
the compound 6b placed between two ordinary glass slides
Scheme 1 Reagents and conditions: (i) HCl, NaNO2, NaN3; (ii) CuI, THF, N2 atm.
upon heating shows oily streak texture (Fig. 1a) characteristics
of cholesteric phase and the N* phase appears with a focal
(iii) DCC, DMAP, CH2Cl2; (iv) Fe powder, NH4Cl, ethanol; (v) DCC, DMAP, CH2Cl2;
(vi) HCl, ethanol.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1906--1911 1907

NJC
Paper
Scheme 2 Synthetic pathway of series 1 and 2.
Table 1 Phase transition temperatures (1C) and associated enthalpies [kJ molÀ1
for intermediates 3 and 4
]
the mechanical stress indicating the long pitch of the N* phase.
On further cooling the N* phase changed to SmA* phase
(Fig. 2b) through the formation of both striking focal-
conic and pseudoisotropic textures. The SmA* phase was con-
firmed by the sample subjected to homeotropically treated
cell which shows a characteristic focal conic texture and a dark
field of view (Fig. 2c). Finally the compound 6c crystallized
at 172 1C.
Phase transitions (1C)
Heating
Cooling
Compound
R
The remaining members of 6d–6f exhibit the phase transi-
tion sequence of I-SmA*–SmC*–Cr. These compounds display
typical cholesteric oily streak texture on heating. In order to
clarify further, the discussion will be based on a representative
compound 6f. The compound 6f exhibits the monotropic SmA*
and SmC* phases. The focal conic texture appears as a
pseudoisotropic pattern typical of the SmA phase when the
3
4
NO2 Cr 296 [55.3] SmA 327a
NH2 Cr 230 [78.7] I
I
I 320a SmA 288 [48.6] Cr
I 209 [67.2] Cr
Phase transition temperatures were determined by DSC thermogram.
Abbreviations: Cr = crystal, SmA* = chiral smectic A phase; I = isotropic
phase. Data obtained by POM.
a
conic texture upon cooling. The focal conic texture transformed sample placed between homogeneously treated thin cell with a
to planar texture having oily streak (Fig. 1b) by shearing the gap of d = 5 Æ 0.2 mm. On further cooling the sample SmC*
mesophase.
phase appears as nucleating batonnets superimposed by the
The compound 6c shows polymorphism on cooling from the equidistant patterns as shown in Fig. 3a. On further cooling the
isotropic liquid and the phase sequence is found as Iso-N*– sample crystallized at 157 1C. The last member of the series 6g
SmA*–Cr. For this compound, on cooling from isotropic phase exhibits usual oily streaks texture on heating cycle and SmC*
exhibits N* phase with planar fingerprint texture (Fig. 2a). The phase (Fig. 3b) was observed on cooling from the isotropic
fingerprint texture was regained when it was applied with liquid.
c
1908 New J. Chem., 2013, 37, 1906--1911
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

Paper
NJC
Table 2 Phase transition temperatures (1C) and associated enthalpies [kJ molÀ1] for compounds 6a–6g
Phase sequence
n
Heating
Cooling
Compound
6a
6b
6c
6d
6e
6f
5
6
7
8
9
10
11
Cr 184 [54.1] N* 290b
I
—
Cr 183 [68.7] Ch 288 [18.6] I
Cr 180 [47.9] Ch 295 [12.0] I
Cr 175 [22.3] Ch 260 [22.3] I
Cr 171 [42.7] Ch 257 [17.4] I
Cr 166 [35.6] Ch 255c I
I 285 [17.8] N* 179a Cr
I 290 [10.6] N* 257c SmA* 172 [24.8] Cr
I 255 [8.5] SmA* 213c SmC*161 [14.6] Cr
I 256 [13.7] SmA* 222 [5.3] SmC* 158 [29.5] Cr
I 250 [9.8] SmA* 249c SmC*157 [24.2] Cr
I 253 [26.4] SmC* 125c Cr
6g
Cr 131 [41.5] Ch 258c I
Phase transition temperatures were determined by DSC thermogram. Abbreviations: Cr = crystal, Ch = cholestric phase; N* = chiral nematic phase;
a
b
SmA* = chiral smectic A phase; TGBC* = twist grain boundary phase with SmC* blocks; I = isotropic phase. Data obtained by POM. A partial
c
decomposition of the material at the isotropic liquid was detected by POM. Phase transition was weak and could only be observed under POM.
Fig. 1 Photomicrographs of the textures of compound 6a: (a) oily streak texture
Fig. 3 Photomicrographs of the textures (a) SmC* phase (243 1C) of compound
of the N* phase at 243 1C, and (b) planar texture of N* transformation for focal
6f seen from the homeotropically treated cell, and (b) planar SmC* phase
conic texture on subjected to mechanical stress at 269 1C.
appearing just below the isotropic phase of the compound 6g.
3.3 Microscopic and calorimetric studies of compounds 9a–9g
sample is subjected to the homeotropic alignment it displays
filamentary pattern of the TGBC* phase (Fig. 4b).
In this series the 1,2,3-triazole ring connected with a choles-
terol unit in one arm and another arm comprises of three
aromatic ring attached by terminal alkyl chain of CnH2n+1 where
n ranges from 6 to 12. The phase transition behaviors of the
compounds 9a–9g are summarized in Table 3. All homologues
in this series display enantiotropic mesomorphism. The first
member 9a displays oily streak texture of chiral nematic phase
while cooling from the isotropic phase. The N* phase with a
focal conic texture is changed to oily streak (Grandjean planar)
texture when it was subjected to mechanical stress. Further
cooling the N* phase has led to TGBC* phase by the planar
pattern in a homogeneous glass slides (Fig. 4a). When the
Similarly the compound 9b exhibits N* phase on cooling
from the isotropic state and further cooling, the TGBC*
phase appeared as a filament texture which is stable over
a temperature range of 13 1C. The presence of TGBC*
phase indicates that the compound is strongly chiral and
thus the pitch of their N* phase is shorter. The other member
of 9c exhibits a chiral oily streak pattern on heating cycle
and upon cooling focal conic texture was observed. The
focal conic texture was destroyed and Grandjean planar texture
formed when a gentle shearing was applied on the glass plate.
The observation is a characteristic of the unique nature of N*
Fig. 2 Photomicrographs of the textures observed for different mesophase of compound 6c: (a) the planar finger print texture of the N* phase at 285 1C, (b) focal
conic texture of the SmA* phase at 185 1C, and (c) focal conic texture of SmA phase in homogeneously aligned cell.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1906--1911 1909

NJC
Paper
Table 3 Phase transition temperatures (1C) and associated enthalpies [kJ molÀ1] for compounds 9a–9g
Phase sequence
n
Heating
Cooling
Compound
9a
9b
9c
9d
9e
9f
5
6
7
8
9
10
11
Cr 148 [33.5] N* 271 [4.7] I
Cr 145 [29.1] N* 269 [8.2] I
Cr 144 [43.6] N* 266 [11.3] I
Cr 140 [20.7] SmA* 261 [6.6] I
Cr 163 [26.1] SmA* 278 [7.2] I
Cr 160 [36.5] SmC* 216a SmA 260 [4.5] I
Cr 158 [18.7] SmC* 232a SmA 258 [9.4] I
I 266 [4.5] N* 150a TGBC* 143 [25.8] Cr
I 265 [7.7] N* 155a TGBC*142 [22.6] Cr
I 259 [11.0] N* 141 [31.5] Cr
I 257 [5.9] SmA* 137 [20.0] Cr
I 266 SmA* 158b Cr
I 252 [4.1] SmA* 210a SmC* 156 [36.2] Cr
I 255 [8.8] SmA* 224a SmC* 153 [18.4] Cr
9g
Phase transition temperatures were determined by DSC thermogram. Abbreviations: Cr = crystal, Ch = cholestric phase; N* = chiral nematic phase;
b
SmA* = chiral smectic A phase; TGB = twist grin boundary phase with SmC* blocks; I = isotropic phase. a Data obtained by POM. Phase transition
was weak and could only be observed under POM.
Fig. 5 Photomicrographs of the texture of compound 9g phase observed from
Fig. 4 Photomicrographs of the texture of compound 9a. (a) Phase transforma-
homeotropically treated cell (a) SmA* phase at 220 1C, and (b) SmC* at 188 1C.
tion from N* to TGBC* (150 1C) and (b) filamentary texture of the homeo-
tropically aligned TGBC* phase (148 1C).
define the textural pattern will be based on compound 9d. On
phase. Finally, the compounds 9b and 9c crystallized at 145 1C heating the sample 9d between the clean glass slides to
and 151 1C, respectively.
isotropic liquid and cooling slowly the formation of focal conic
The compounds 9d and 9e undergo slow cooling from the fans suggests a layered structure. This SmA* phase was
isotropic liquid whereupon the SmA* phase was observed at confirmed by unique focal conic texture observed on slides
257 1C and 266 1C, respectively. The discussion on how to treated for planar orientation and a dark field of view when
Fig. 6 Correlation between transition temperature and methylene chain length for (a) compound 6a–g and (b) compound 9a–g.
c
1910 New J. Chem., 2013, 37, 1906--1911
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013

Paper
NJC
subjected to homogeneously treated cell. Finally the compound References
9d crystallized at 137 1C.
1 (a) F. Renitzer, Monatsh. Chem., 1888, 9, 421–441; (b) C. V.
Yelamaggad, N. L. Bonde, A. S. Achalkumar, D. S. Shankar
Rao, S. Krishna Prasad and A. K. Prajapathi, Chem. Mater.,
2007, 19, 2463–2472.
2 (a) M. Marcos, J. L. Serrano, T. Sierra and M. J. Gimenez,
Angew. Chem., Int. Ed. Engl., 1992, 31, 1471–1472;
(b) M. J. Baena, J. Barbera, P. Espinet, A. Ezcurra, M. B. Ros
and J. L. Serrano, J. Am. Chem. Soc., 1994, 116, 1899–1906.
3 H. Kizerow, in Chirality in Liquid Crystals, ed. H. S. Kitzerow
and C. Bahr, Springer-Verlag, New York, 2001.
4 (a) I. Sage, in Liquid Crystals. Applications and Uses,
ed. B. Bahadur, World scientific, Singapore, 1992, vol. 3,
ch. 20; (b) J. Constant, D. G. McDonnell and E. P. Raynes,
Mol. Cryst. Liq. Cryst., 1987, 144, 161–168.
5 D. M. Walba, F. Stevens, N. A. Clark and D. C. Parks, Acc.
Chem. Res., 1996, 29, 591–597.
6 (a) P. P. Crooker, Liq. Cryst., 1989, 5, 751–775;
(b) P. P. Crooker, Mol. Cryst. Liq. Cryst., 1983, 98, 31–45.
7 (a) P. J. Collings and J. S. Patel, Handbook of Liquid Crystal
Research, Oxford University Press, New York, Oxford, 1997;
(b) G. Shanker and C. V. Yelamaggad, New J. Chem., 2012,
36, 918–926; (c) S. Garoff and R. Meyer, Phys. Rev. Lett., 1977,
38, 848–851.
8 S. T. Lagerwall, M. Matuszcyk, P. Rodhe and L. Odma, in The
Optics of Thermotropic Liquid Crystals, ed. S. J. Elston and
J. R. Sambles, Taylor and Francis, London, 1998.
9 D. Demus, J. Goodby, G. W. Gray, H. W. Spiess and V. Vill,
Handbook of liquid crystals, Wiley-VCH, New York, 1998, vol. 3.
10 (a) H. C. Kolb, M. G. Finn and K. B. Sharpless, Angew. Chem.,
Int. Ed., 2001, 40, 2004–2021; (b) Z. P. Demko and
K. B. Sharpless, Angew. Chem., Int. Ed., 2002, 41,
2110–2113; (c) Z. P. Demko and K. B. Sharpless, Angew.
Chem., Int. Ed., 2002, 41, 2113.
11 (a) R. Huisgen, G. Szeimies and L. Mobius, Chem. Ber., 1967,
100, 2494–2507; (b) K. V. Gothelf and K. A. Jorgensen, Chem.
Rev., 1998, 98, 863–909.
The higher homologues 9f and 9g exhibit dimesomorphic
sequence of I-SmA*–SmC*–Cr under the POM. When the
homogeneously treated cell was filled by these compound 9g
and cooled from the isotropic phase, it exhibits a pseudoisotropic
pattern characteristics of the SmA* phase. On further cooling
to 220 1C the SmA* phase (Fig. 5a) changed to SmC* phase
which appears as nucleating batonnets superimposed by the
equidistant line pattern (Fig. 5b) at 188 1C. It can also be seen in
Fig. 6 which represents the correlation between the transition
temperatures and respective terminal chain lengths. The
lower homologues of both series exhibit nematic phase while
increasing the terminal chain length will lead to the formation
of smectic phase. Interestingly, the highly frustrated TGBC*
phase prevails in lower homologues of three rings system
(series 2). This material could be used as one of the compo-
nents for preparing mixtures capable of stabilizing TGBC*
phase.
Conclusions
Two series of click chemistry assisted cholesterol-based liquid
crystals have been synthesized and characterized. In the first
series, two aromatic rings are connected to triazole ring; while
in second series three aromatic rings are connected to triazole
ring. In both series the length of the terminal tail was varied
from 6 to 12. The structural factors strongly influence the phase
transition behaviour of target compounds. All members of
these series show mesomorphism viz. mono, di and poly-
morphism. These mesophases possess very high thermal
stability and the isotropic temperature is >250 1C. The lower
homologues 6a and 6b of the first series exhibits N* phase, the
medium homologues 6c shows dimesomorphic sequence invol-
ving the transition from SmA*–N* phase, whereas the higher
homologues display the smectic phase SmA* and/or SmC*
phase. Interestingly, the lower homologues 9a and 9b of the
second series exhibited dimesomorphic sequence of N*–TGBC*.
The compound 9c of the medium homologues displayed N*
phase, compounds 9d and 9e showed SmA* phase, and the
higher homologues 9f and 9g displayed nucleating batonnet
SmC* phase. In both series the smectogenic properties of the
compounds increased with increasing terminal chain length.
12 G. Y. Yeap, A. Alshargabi, M. M. Ito, W. A. K. Mahmood and
D. Takeuchi, Mol. Cryst. Liq. Cryst., 2012, 557, 126–133.
13 N. Gimeno, R. Martin-Rapun, S. Rodriguez-Conde,
J. L. Serrano, C. L. Folcia, M. A. Pericas and M. B. Ros,
J. Mater. Chem., 2012, 22, 16791–16800.
14 (a) K. C. Majumdar, S. Mondal and R. K. Sinha, New J. Chem.,
2010, 34, 1255–1260; (b) C. V. Yelamaggad, A. S. Achalkumar,
N. L. Bonde and A. K. Prajapathi, Chem. Mater., 2007, 19,
2463–2472; (c) V. I. Kopp, B. Fan, H. K. M. Vithana and
A. Z. Genack, Opt. Lett., 1998, 23, 1707–1709.
Acknowledgements
The main author (G-Y. Yeap) would like to thank the Malaysian
Ministry of Higher Education or MOHE for the Fundamental 15 Z. Cui, Y. Zhang and S. He, Colloid Polym. Sci., 2008, 286,
Research Grant Scheme (FRGS) no. 203/PKIMIA/6711265. 1553–1559.
Authors are also grateful to Prof. Masato M. Ito from Soka 16 P. J. Collings and M. Hird, Introduction to Liquid Crystals
University for the support of some chemicals from TCI, Japan.
Chemistry and Physics, Taylor and Francis Ltd., London, 1997.
c
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
New J. Chem., 2013, 37, 1906--1911 1911

Copyright of New Journal of Chemistry is the property of Royal Society of Chemistry and its
content may not be copied or emailed to multiple sites or posted to a listserv without the
copyright holder's express written permission. However, users may print, download, or email
articles for individual use.