Monodispersive unsymmetrical tetramers exhibiting a columnar phase

Article abstract of DOI:10.1080/714965611

Oligomeric liquid crystals that are formed by joining two or more mesogenic segments axially through a flexible spacer (or multiple spacers) seem to be interesting materials from the points of view of both basic research and practical applications owing to their multifunctional characteristics and properties similar to those of polymers while retaining fluidity, viscosity etc. associated with those of low molar mass liquid crystals. The synthesis and evaluation of mesomorphic behavior of two novel monodispersive unsymmetrical tetramesogens have been presented here in detail. The molecular design, of these tetramesogens incorporates the cholesteryl ester (as a chiral entity), biphenyl (as a supportive entity for mesomorphism), azobenzene (as a photoactive mesogen), and tolan (as a half-disc) segments interconnected through even-even-odd and odd-even-odd alkylene spacers. The target liquid crystalline tetramers have been realized by employing convenient synthetic strategies, which involves the preparation of two important unsymmetrical dimers and finally their condensation. The molecular structures of all the intermediates and unsymmetrical tetramers have been characterized by spectroscopic analyses. The mesomorphic property of both the unsymmetrical tetramers has been evaluated by optical microscopic, calorimetric and X-ray diffraction studies. Our study reveals that both oligomers show an identical mesophase. While X-ray studies suggest that the structure of the mesophase is similar to that of a rectangular columnar (Col_r) mesophase; a pseudoisotropic texture was seen under the microscope.

Full text of DOI:10.1080/714965611

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Monodispersive Unsymmetrical
Tetramers Exhibiting a
Columnar Phase
C. V. Yelamaggad a , S. Anitha Nagamani a , Uma S.
Hiremath a , D. S. Shankar Rao a & S. Krishna Prasad
a
a Centre for Liquid Crystal Research , P.B.No. 1329,
Jalahalli, Bangalore, 560 013, India
Published online: 18 Oct 2010.
To cite this article: C. V. Yelamaggad , S. Anitha Nagamani , Uma S. Hiremath , D.
S. Shankar Rao & S. Krishna Prasad (2003) Monodispersive Unsymmetrical Tetramers
Exhibiting a Columnar Phase, Molecular Crystals and Liquid Crystals, 397:1, 207-229,
DOI: 10.1080/714965611
To link to this article: http://dx.doi.org/10.1080/714965611
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Mol. Cryst. Liq. Cryst., Vol. 397, pp. 207/[507]–229/[529], 2003
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421400390214112
MONODISPERSIVE UNSYMMETRICAL TETRAMERS
EXHIBITING A COLUMNAR PHASE
C. V. Yelamaggad*, S. Anitha Nagamani, Uma S. Hiremath,
D. S. Shankar Rao, and S. Krishna Prasad
Centre for Liquid Crystal Research, P.B.No. 1329, Jalahalli,
Bangalore-560 013, India
Oligomeric liquid crystals that are formed by joining two or more mesogenic
segments axially through a flexible spacer (or multiple spacers) seem to be
interesting materials from the points of view of both basic research and prac-
tical applications owing to their multifunctional characteristics and properties
similar to those of polymers while retaining fluidity, viscosity etc. associated
with those of low molar mass liquid crystals. The synthesis and evaluation of
mesomorphic behavior of two novel monodispersive unsymmetrical tetrameso-
gens have been presented here in detail. The molecular design of these tetra-
mesogens incorporates the cholesteryl ester (as a chiral entity), biphenyl (as a
supportive entity for mesomorphism), azobenzene (as a photoactive mesogen),
and tolan (as a half-disc) segments interconnected through even-even-odd and
odd-even-odd alkylene spacers. The target liquid crystalline tetramers have
been realized by employing convenient synthetic strategies, which involves the
preparation of two important unsymmetrical dimers and finally their con-
densation. The molecular structures of all the intermediates and unsymme-
trical tetramers have been characterized by spectroscopic analyses. The
mesomorphic property of both the unsymmetrical tetramers has been evaluated
by optical microscopic, calorimetric and X-ray diffraction studies. Our study
reveals that both oligomers show an identical mesophase. While X-ray studies
suggest that the structure of the mesophase is similar to that of a rectangular
columnar (Colr) mesophase; a pseudoisotropic texture was seen under the
microscope.
Keywords: oligomers; tetramers; multifunctions; synthesis; columnar phase
We are grateful to Prof. S. Chandrasekhar for many useful discussions and for inviting us to
present this paper at the International Conference on Discotic Liquid Crystals at Trieste, Italy,
and thankfully acknowledge the help from Dr. Geetha G. Nair in the experiments.
*Corresponding author. E-mail: yelamaggad@yahoo.com
207/[507]

208/[508]
C. V. Yelamaggad et al.
INTRODUCTION
The formation of a thermotropic liquid crystalline phase is predominately
caused by anisometric molecules, which have either a rod-shape [1]
(calamitic) or a disc-shape [2] (discotic). By employing these two aniso-
metric moieties many conventional low molar mass (monomers) as well as
high molar mass (polymers) liquid crystalline systems have been designed
and synthesized. The thermal behaviors of such monomeric and polymeric
liquid crystals are well understood and consequently have been used as
active media in display device technology [3]. They are also considered as
potential candidates in applications involving information storage [4],
nonlinear optics [5] and photoconductivity [6]. It is known that in both
monomeric and polymeric liquid crystals (LCs), the shape of the aniso-
metric entity determines the type of mesophase formed. Thus LCs with
rod-like molecules exhibit nematic (N) and/or smectic (Sm) mesophases
whereas LCs with flat disc-shaped and also cone-shaped [7] molecules
organize to give N and/or columnar (Col) mesophases. Additionally,
tapered or cone-shaped amphiphilic [8] or dendritic [9] systems are shown
to self assemble into Col or micellar cubic (Cub) mesophases.
Recently, the design, synthesis and evaluation of the thermal behavior of
new types of molecular structure which can be thought of as bridging the
gap between calamitic and disc-shaped mesogens, has been the subject of
numerous scientific publications [10–11]. One approach to realize these
‘‘non-conventional’’ LCs has been the synthesis of mesogens that combine
the features of both types molecular geometries in which rod-like and disc-
like (or rather half-disc type) entities are covalently attached to each other
through the functional linkage. The examples of this type of LCs are the
polycatenars [10b], in which the central rod-like rigid core is connected to
the two terminal half disc-shaped moieties through an ester or an imine
linkage. Many polycatenars have been reported and interestingly some of
the tetracatenar, especially the biforked type, mesogens have indeed
exhibited both lamellar and Col phases in addition to the Cub and N
mesophases [10e,h,i].
An alternative approach in this direction has been to link the anisometric
entities through flexible spacers [12–15]. Here again two different routes
have been followed yielding oligomeric liquid crystals (OLCs). One way is
to connect the different mesogenic segments around a certain central unit
[12]. The second route is to join the mesogenic segments in an end-end
(axial) fashion by means of polymethylene or a oligo(oxyethylene) or a
oligosiloxyl group. The latter type of materials which we refer to as linear
OLCs is attracting special attention not only because they are considered as
model compounds for polymeric liquid crystals but also due to their unique

Columnar Phase in Unsymmetrical Tetramers
209/[509]
thermal behavior [13–15]. Most importantly, OLCs can exhibit properties
usually associated with polymers, while still retaining the fluidity and
viscosity of a low molar mass LC. The transitional properties of such OLCs
shows a dramatic dependence on the length and parity of the flexible
spacer. This is most often attributed to the dependence of the molecular
shape on the parity of the spacer considered in the all-trans conformation.
Further, if the OLC is monodisperse it will lead to rather well defined
properties unlike in polymers.
Of all the linear oligomeric molecular architectures known to support
liquid crystalline behavior, the first member, namely the dimer (also
referred to as dimesogen) composed of either identical (symmetrical) or
non-identical (unsymmetrical) mesogenic segments connected by a central
spacer has been extensively studied [13] in their own right because they
exhibit quite different behavior to conventional low molar mass liquid
crystals containing just a single mesogenic unit.
The addition of one to six mesogenic moieties to a dimer via a flexible
spacer results in the next higher oligomers which have been called in
general as a trimer, tetramer, pentamer, hexamer, heptamer and octamers
respectively. Based on the molecular structure of the individual mesogenic
segments, there can be three combinations: (i) symmetrical OLCs where all
the segments are structurally similar (ii) partially identical OLCs in which
some of segments are identical and (iii) unsymmetrical OLCs where no two
segments are identical.
Trimers of types (i) and (ii) were reported for the first time in 1986 and
since then a few other examples have been reported [14a–f]. Recently,
there have been two reports [14g–i], including one from our laboratory [14i]
of the first examples of trimers of type (iii). The unsymmetrical trimer that
we synthesized consists of three different calamitic mesogenic entities
connected by paraffinic spacers. The motivation behind the molecular
design of this molecule was to realize a multifunctional OLC which could
perhaps replace mixtures of mesogenic compounds, which have been used
in different applications, thereby solving phase separation problems asso-
ciated with such mixtures [16]. Interestingly this oligomer stabilizes a
recently discovered highly frustrated phase viz., undulated twist grain
boundary (UTGBC*)phase over a wide temperature range of 90ꢀC.
A type (i) tetramer was first reported by Keller et al. in 1985 but this
material was not mesogenic [15a]. Later in 1989 Griffin’s group reported
a series of tetrameric monodisperse model compounds chemically rela-
ted to known main chain liquid crystalline polymers; interestingly all of
them were found to be mesogenic [15c]. It was only recently that Imrie
et al. extended this approach to furnish the first examples of the type
(ii) tetramers [15d,e]. To the best of our knowledge the unsymmetrical

210/[510]
C. V. Yelamaggad et al.
tetramers consisting of four non-identical mesogenic segments con-
nected linearly [type (iii)] have not been reported till now.
This prompted us to set our goal to design and synthesize OLC that
(i) has chiral, thermochromic and photochromic segments, (ii) can
possibly bridge the gap between rod-like and disc-like LCs and also (iii)
bridge the gap between low molar mass LCs and polymers and thus
furnish the first liquid crystalline unsymmetric tetramer composed of
four structurally different mesogenic entities [21]. To meet the first
criterion, the cholesterol moiety was chosen to be the chiral segment
because it is a naturally occurring commercial product with a rigid
structure possessing multiple chiral centers but on derivatization to its
esters namely cholesteryl esters it exhibits LC phases [1]. Recently it has
been shown that the combination of the cholesteryl ester unit with a
tolan (diarylacetylene) [13e] or biphenyl unit [13f] via polymethylene
spacer furnishes dimers exhibiting a chiral nematic (N*) mesophase
known for thermochromic properties (temperature dependent wave-
length of selective reflection) [17]. The linking of the cholesteryl ester
entity with a biphenyl unit through a paraffinic spacer accounts for two
mesogenic segments of the tetramer and is anticipated to impart the
thermochromic functionality to it.
Azobenzene derivatives with appropriate substitutions exhibit meso-
morphic properties. Upon irradiation with UV light the azo chromophore
undergoes cis and trans isomerism (photochromism) and the resulting
photoinduced phenomenon is promising for many practical applications
[18]. To incorporate a molecular segment with photochromic function-
ality we included an azobenzene moiety which links to other mesogenic
segments through the spacer.
As mentioned earlier, among the polycatenars, the tetracatenar
especially the biforked, type mesogens exhibit a rich mesomorphism
showing lamellar, Col Cub and N phases. To have such an attractive
feature in the proposed tetramer we planned to incorporate a tetra-
catenar type of structure. A linear addition of several mesogenic moi-
eties through spacers leads to a macromolecule that may generally have
a high clearing temperature and suffers from solubility problem in most
common organic solvents. These problems are known to be solved by a
lateral substitution. Therefore the fourth mesogenic entity needs to be
like a semi-biforked entity having a lateral alkoxy substitution giving the
segment the appearance of half-disc like structure. During our careful
design we kept all these points in view, which led us to the synthesis of
a new 2,3,4-trialkoxy substituted diphenylacetylene (tolan) segment that
is used as the fourth mesogenic unit.

Columnar Phase in Unsymmetrical Tetramers
211/[511]
RESULTS AND DISCUSSION
Synthesis and Molecular Structural Characterization
In our present studies the molecular design incorporates the cholesteryl
ester (as a chiral entity), biphenyl (as a supportive entity for thermo-
chromism, azobenzene (as a photoactive mesogen), and tolan (as a
half-disc) segments interconnected through even-even-odd (EEO) and
odd-even-odd (OEO) paraffinic spacers. Such novel systems demand high
yielding and convenient synthetic strategy. Here we present in detail the
synthetic steps involved to realize the target liquid crystalline tetramers 1
and 2. Schemes I, IIa,b,c and III, involve the preparation of two important
unsymmetrical dimers 3a,b and 4 and finally their condensation. Initially,
SCHEME I Synthesis of unsymmetrical dimers 3a and 3b.

212/[512]
C. V. Yelamaggad et al.
SCHEME IIA Synthesis of a half disc-shaped 2,3,4-trialkoxysubstituted diaryl-
acetylene 13.
cholesteryl bromoalkanoates 5a and 5b were obtained by esterification of
commercial optically pure cholesterol with 5-bromopentanoyl and 6-bro-
mohexanoyl chlorides respectively. These bromoesters were heated with
SCHEME IIB Synthesis of 4,40-dihydroxyazobenzene 15.

Columnar Phase in Unsymmetrical Tetramers
213/[513]
SCHEME IIC Synthesis of an unsymmetrical dimer 4.
4,4-dihydroxybiphenyl under mild basic reaction conditions to obtain
unsymmetrical dimeric phenols [19] 6a and 6b, which upon treatment with
1,4-dibromobutane afforded dimers 3a and 3b carrying bromine atom
substitution at terminal alkoxy chain (Scheme I).
A thermally stable half-disc shaped 2,3,4-trialkoxy substituted diaryla-
cetylene (tolan) segment (13), which has not been reported previously, was
prepared starting from 1,2,3-tridodecyloxybenzene (7). Firstly trialkoxy
azobenzene was iodinated to get trialkoxy iodobenzene 8 which upon cou-
pling with 2-methyl-3-butyn-2-ol under Hagihara-Sonogashira [20] reaction
conditions to get protected phenylacetylene 9. The deprotection of acetylene
functionality by refluxing with potassium hydroxide in toluene furnished
phenylacetylene 10 which was then coupled with THP-protected, 4-
iodophenol to obtain diarylacetylene-THP ether 11. Upon deprotection, the
phenolic diarylacetylene 12 obtained was treated with 1,5-dibromopentane
to get the half disc-shaped entity the tetracatenar 13, in almost quantitative
yield (Scheme IIa). 4,4-Dihydroxyazobenzene (15) was synthesized as
shown in Scheme IIb. The coupling of diazonium salt of 4-methoxyaniline
with phenol furnished 4-hydroxy-40-methoxyazobenzene (14) which on
treatment with aluminium trichloride/pyridine mixture in refluxing chloro-
form yielded compound 15. The condensation of half equivalent of diaryla-
cetylene 13 with azobenzene 15 finally gave the key dimeric intermediate 4
bearing terminal phenolic hydroxyl functionality (Scheme IIc). Optimization
of the final coupling involving O-alkylation of dimeric phenol 4 with dimeric
alkylbromide 3a and 3b to realize novel tetramer 1 and 2 finally proved that
the presence of mild base (anhyd. potassium carbonate) in DMF, heating at
85ꢀC for a period of 12 hrs is the superior condition than the others
(Scheme III). Thus the tetramers 1 and 2 were obtained as a yellow powder in

214/[514]

Columnar Phase in Unsymmetrical Tetramers
215/[515]
1
FIGURE 1 (a) and (b) show H and 13C NMR spectrum of the tetramer 1.
49 and 42% yield respectively. The spectral data of all the intermediates and
tetramers were confirmed by spectroscopic analysis. The IR, 1H and 13C NMR
of both the Tetramers are comparable with each other. The IR spectrum

216/[516]
C. V. Yelamaggad et al.
absorption bands in the region of umax/cmꢁ1 2923-2852 (C-H paraffinic),
1
1728–1737 (C¼O stretching), 1581–1603 (C¼C ring stretching). In the H
NMR spectrum 22 aromatic protons appear as eight doublets and one mul-
tiplet at d 7.87, 7.13, 7.01, 6.98, 6.95, 6.936, 6.85, 6.60, and 7.46 respectively,
while the olefinic, methine of (ester) and oxymethylene (of paraffinic chain)
proton resonate at d 5.37, 4.62, and 4.0 as broad d, multiplet(m) and triplet(t)
respectively. In the 13C NMR (SEFT; Spin Echo Fourier Transform) spectra at
higher frequency region (downfield) tetramer 1 shows 24 peaks. As the
expected number of peaks are 31, it indicates the equivalence of 7 sets of
carbons (3 sets of quaternary and 4 sets of tertiary carbons are equivalent).
Tetramer 2 shows 26 peaks, as the expected number of peaks are 31, it
indicates the equivalence of 5 sets of carbons (1 set of quaternary and 4 sets
of tertiary carbons are equivalent) (see experimental section for details and
1
also). As a representative case H and 13C NMR of tetramer 1 have been
presented in Figure 1.
THERMAL BEHAVIOR
Optical microscopic observations indicate that on melting at a tem-
perature of 134.8ꢀC for 1 and at 98.8ꢀC for 2, both the samples showed
a pseudoisotropic texture. Figure 2a shows the pseudoisotropic texture
seen for the tetramer 2 at about 150ꢀC. This was true whether the
substrate was a just a clean glass plate or a glass plate treated with
either a polyimide solution for planar orientation or a silane solution for
homeotropic alignment. On shearing the pseudoisotropic pattern chan-
ged to a birefringent texture, which almost immediately relaxed back
into the pseudoisotropic texture in case of sample 1. The birefringent
pattern was like the sandy texture (Fig. 2b) usually observed in poly-
meric samples. Even at high magnification of microscope we could not
get more details about the texture. This birefringent texture remained
till the samples transformed to the isotropic phase at 191.2ꢀC and
202.5ꢀC for 1 and 2 respectively. On cooling from the isotropic phase, a
slight supercooling was observed and the transition to the mesophase
with the sandy texture was observed at 188.6ꢀC (DH ¼ 13.1 J/g) and
201.2ꢀC (DH ¼ 15.1 J/g) for 1 and 2 respectively. In case of the tetramer
1, no other textural change was seen till crystallization, at 93ꢀC. The
differential scanning calorimetric (DSC) trace shown in Figure 3 (a:
heating and b: cooling) corroborates these observations. These transi-
tions are highly reproducible indicating the stability of this tetramer.
In sample 2, while cooling, neither a textural change nor crystallization
was seen till room temperature. The DSC traces shown in Figure 4 (b and
c) support these optical observations. In addition it appears to show a

Columnar Phase in Unsymmetrical Tetramers
217/[517]
FIGURE 2 (a) Microphotograph of the pseudoisotropic texture seen for the tet-
ramer 1 at 150ꢀC, (b) sandy texture seen when pseudoisotropic texture subjected
to shear. (See Color Plates XX & XXI).
glassy state [see inset (d) and (e) in Fig. 2] at 77.4ꢀC. The glassy state stays
till À65ꢀC, the lowest temperature that could be achieved by the instru-
ment. On subsequent heating from À65ꢀC, the glassy phase transforms to
the mesophase at 97.2ꢀC, which remains unaltered till isotropic phase. It is

218/[518]
C. V. Yelamaggad et al.
FIGURE 3 DSC traces obtained for the tetramer 1 at a rate of 5ꢀC/min; (a) first
heating scan from 50ꢀC and (b) first cooling scan from isotropic phase.
known that upon keeping the sample at room temperature for a certain
period of time, the glassy state slowly transforms into crystalline state. But
this phenomenon does not seem to occur with the sample 2 even after
several months. These transitions are also highly reproducible during
repeated heating and cooling cycles. As a representative case the chemical
stability of the sample 2 was investigated by taking DSC scans after keeping
the sample at 110ꢀC for 15 hours and found that the transition tempera-
tures agree well with the previous runs.
X-RAY STUDIES
The diffraction patterns obtained in the mesophase of both the samples
were quite similar. The pattern along with the derived one-dimensional
intensity vs. 2y profile obtained at 170ꢀC with the tetramer 1 is shown in
Figure 5 (a and b). In the low-angle region four sharp peaks are observed;
one very strong and three weak reflections. Identifying the first peak with
the Miller index (200), the four reflections confirm to the expected values
from a two-dimensional rectangular lattice. In the wide-angle region there
is a diffuse reflection corresponding to spacing of 4.7ꢀA. Based on these
features we propose that the mesophase could be a rectangular columnar
(Colr) mesophase. This proposal is partially supported by the following

Columnar Phase in Unsymmetrical Tetramers
219/[519]
FIGURE 4 Differential scanning calorimeter traces obtained for tetramer 2 at a
rate of 5ꢀC/min.; (a) first heating, (b) subsequent cooling from isotropic liquid state
to till ꢁ65ꢀC and (c) subsequent heating from ꢁ65ꢀC till the isotropic liquid
transition. As can be seen neither crystallization nor melting peaks are observed
instead peaks at 77.4ꢀC and at 97.2ꢀC corresponding to the transition between the
glassy state and the mesophase appear during the cooling and the heating cycles
(inset d and e) respectively.
observations. For some polar calamitic molecules [8c] and pure polycatenar
compounds with non-polar chains no lamellar mesophase has been
observed [10b]. This kind of a behavior especially in polycatenars is
expected because of small differences in space filling between the rigid
cores and the pendant terminal chains can be compensated by tilting of the
aromatic cores with respect to the layer normal. If, however, the difference
is substantial, tilting of molecule alone cannot sufficiently reduce this steric
frustration. In such cases the layers may break up into ribbon-like aggre-
gates which can organize to a columnar phase. Assuming such a structure,
the lattice parameters are calculated to be a ¼ 128ꢀA and b ¼ 37.2ꢀA.
However in the absence of a clear optical texture it is not possible to
uniquely identify the mesophase. The appearance of a pseudoisotropic

220/[520]
C. V. Yelamaggad et al.
FIGURE 5 (a) X-ray diffraction pattern obtained at 170ꢀC for the tetramer 1 (b)
one-dimensional intensity vs. 2y profile derived from the pattern shown in figure.
Closely similar diffraction pattern has been observed for the tetramer 2.
texture suggest that a uniaxial phase and hence the presence of a two-
dimensional lattice seems to be contradictory. Detailed studies on this and
related systems will shed more light on the possible structure.

Columnar Phase in Unsymmetrical Tetramers
221/[521]
SUMMARY
In conclusion we have achieved the synthesis of the first thermotropic
monodispersive liquid crystalline tetramers possessing four non-identical
anisometric entities connected by flexible spacers. Molecular design of
these novel tetramers incorporates the cholesteryl ester (as a chiral
entity), biphenyl (as a supportive entity for thermochromism), azobenzene
(as photoactive mesogen), and tolan (as a half-disc) segments inter-
connected through even-even-odd (EEO) and odd-even-odd (OEO) par-
affinic spacers. These compounds are thus multifunctional and such
systems can possibly bridge the gap between rod-like and disc-like LCs. In
addition, such OLCs can exhibit properties usually associated with poly-
mers, whilst still retaining the fluidity and viscosity of low molar mass LCs
and thereby bridging the gap between low molar mass LCs and high molar
mass polymeric LCs. The concept of such molecular design originates from
the novel approach that, by grafting different anisometric sub-units
(mesogens) associated with a particular function/phenomenon in a single
component system through covalent flexible linkages one can obtain
supramolecular systems not only able to form thermotropic mesophases
due to their anisotropic molecular shape but also capable of structure
formation resulting from non-covalent intermolecular interactions. An
exhaustive investigation focussing on molecular design and synthesis
leading to multifunctional OLCs is very much essential in order to provide
potential materials required for many practical applications.
EXPERIMENTAL
General Information
Chemicals were obtained from Fluka or Aldrich Company or a local source
and used as such without any purification, while solvents were dried fol-
lowing standard procedures. Column chromatographic separation were
performed using either silicagel or neutral aluminium oxide. Thin layer
chromatography (TLC) was performed on aluminium sheets precoated
with silica gel (Merck, Kieselge60.F254). IR spectra were recorded using
1
Perkin Elmer Spectrum 1000 FT-IR spectrometer. H NMR spetra were
recorded using a Bruker DRX-500 (500 MHz) or Bruker AMX-400
(400 MHz) Bruker Aveance series DPX-200 (200 MHz) spectrometers. For
1H NMR, the chemical shifts are reported in parts per million (ppm) rela-
tive to tetramethylsilane (TMS) as an internal standard. Mass spectra were
recorded on Jeol JMS-600H spectrometer. The LC property of the tetra-
mers were investigated using i) optical polarizing microscope (Leitz

222/[522]
C. V. Yelamaggad et al.
DMRXP) in conjunction with a programmable hot stage (Mettler FP90) ii)
differential scanning calorimeter (Perkin Elmer DSC7). Xray diffraction
studies were carried out using an Image Plate Detector (MAC Science,
Japan) equipped with a double mirror focussing optics and the sample
contained in a Lindemann capillary tube.
General Procedure for the Preparation of Cholesteryl o-[40-
(4-bromobutyloxy)biphenyl-4-oxy]alkanoates (3a and 3b):
A flask equipped with magnetic stir bar, reflux condenser and argon inlet
was charged with 6a or 6b (2 g, 2.98 mmoles, 1eq) [19], anhydrous K2CO3
(1.7 g, 11.95 mmoles, 4eq), 1,4-Dibromobutane (4 g, 17.92 mmoles, 6eq)
and dry acetone (15 ml). The reaction mixture was heated to 85ꢀC for 24
hours. Evaporation of solvent afforded a white coloured mass which was
extracted into CH2Cl2 (10 ml62). The organic layer was washed with brine
and dried over Na2SO4. Upon evaporation of solvent a white solid was
obtained which was purified by column chromatography using silica gel
(100–200 mesh). Elution, first with Hexane followed by mixture of 5%
EtOAc-Hexanes afforded the product as a pure white solid.
Cholesteryl 5-[40-(4-bromobutyloxy)biphenyl-4-oxy]
pentanoate (3a)
Yield ¼ 85%(1.9 g); Rf value: 0.39 (10% Ethyl acetate-Hexanes); IR (KBr
1
Pellet) umax in cmꢁ1: 2938, 2869, 1729, 1609, 1502, 1251, 1170; H NMR
(400 MHz, CDCl3): 7.45 (d, J ¼ 8.56 Hz, 4H, Ar), 6.93 (d, J ¼ 8.6 Hz, 4H,
Ar), 5.36 (brd, J ¼ 3.84 Hz, 1H, Olefinic), 4.61 (m, 1H, CHOCO), 3.99 (m,
4H, 26OCH2), 3.5 (t, J ¼ 6.58 Hz, 2H, 16CH2Br), 2.4-2.27 (m, 4H,
26allylic methylene), 2.12-1.05 (m, 34H, 146CH2, 66CH), 1.01 (s, 3H,
16CH3), 0.91(d, J ¼ 6.52 Hz, 3H, 16CH3), 0.87 (d, J ¼ 1.44 Hz, 3H,
16CH3), 0.85 (d, J ¼ 1.4 Hz, 3H, 16CH3), 0.67 (s, 3H, 16CH3); FAB
Mass: [Mþ]: 787.6 Calcd for C48H69O4Br.
Cholesteryl 6-[40-(4-bromobutyloxy)biphenyl-4-oxy]
hexanoate (3b)
Yield ¼ 85% (1.9 g); Rf value: 0.39 (10% Ethyl acetate-Hexanes); IR
1
(KBr Pellet): umax in cmꢁ1: 2939, 2867, 1736, 1607, 1501, 1250, 1170; H
NMR (400 MHz, CDCl3): 7.45 (d, J ¼ 8.76 Hz, 2H, Ar), 7.44 (d, J ¼ 8.76 Hz,
2H, Ar), 6.92 (d, J ¼ 8.56 Hz, 4H, Ar), 5.36 (brd, J ¼ 3.96 Hz, 1H, Olefinic),
4.61(m, 1H, CHOCO), 3.99 (m, 4H, 26OCH2), 3.5 (t, J ¼ 6.58 Hz, 2H,
16CH2Br), 2.36-2.28 (m, 4H, 26allylic methylene), 2.12-1.05 (m, 36H,
156CH2, 66CH), 1.01(s, 3H, 16CH3), 0.91(d, J ¼ 6.52 Hz, 3H, 16CH3),
0.87 (d, J ¼ 1.72 Hz, 3H, 16CH3), 0.85 (d, J ¼ 1.68 Hz, 3H, 16CH3), 0.67
(s, 3H, 16CH3); FAB Mass: [Mþ]: 801.6 Calcd for C49H71O4Br.

Columnar Phase in Unsymmetrical Tetramers
223/[523]
1,2,3-Tridodecyloxybenzene (7)
A mixture of KOH (5.2 g, 92.6 mmoles, 6eq), dry DMSO (10 ml) was
placed in a two necked round bottomed flask under continuous Argon
flow and the reaction mixture was heated to 65ꢀC. After the addition of
Pyrogallol (2 g, 15.85 mmoles, 1eq) a brown colored solution was
obtained. To this 1-Bromo dodecane (12.14 g, 48.72 mmoles, 3.2eq) was
added dropwise and the reaction mixture was allowed to stir at the same
temperature for 24 hours. Water was added to the cooled reaction mix-
ture. The aqueous phase was repeatedly extracted into hexane
(20 ml62). The combined organic layer was washed with brine and dried
over Na2SO4. Evaporation of solvent gave a white solid which was purified
with column chromatography on neutral Al2O3, elution with hexane
afforded the product as a white solid. Yield ¼ 84% (8.4 g); Rf value: 0.45 in
1
Hexanes; IR (KBr Pellet) umax in cmꢁ1: 2915, 2849, 1597, 1502, 1256; H
NMR (400 MHz, CDCl3): 6.90 (m, 1H, Ar), 6.53 (d, J ¼ 8.3 Hz, 2H, Ar),
4.0(m, 6H, 36OCH2), 2.0-1.0 (m, 60H, 306CH2), 0.88 (t, J ¼ 6.4 Hz, 9H,
36CH3); Fab Mass: [Mþ]: 630.5 Calcd for C42H78O3.
2,3,4-Tridodecyloxyiodobenzene (8)
A mixture of compound (7) (2.87 g, 4.56 mmoles, 1eq), I2 (578 mg,
2.27 mmoles, 0.5eq), Acetic acid (12.71 ml) was placed in round bottomed
flask. After the addition of a few drops of con H2SO4 to the stirred
reaction mixture a solution of HIO3 (200 mg, 1.139 mmoles, 0.25eq) in
water was added dropwise over period of 4–5 hours. After stirring the
reaction mixture for 24 hours it was poured into 10% Na2SO3 solution
and extracted with hexane (20 ml63). The combined organic phase was
washed with a saturated solution of Na2CO3 and then washed with brine
and dried over Na2SO4. Evaporation of the solvent yielded a white solid
which was purified by column chromatography using 230–400 mesh silica
gel, upon elution with hexane pure product was obtained as white solid.
Yield: 2.0 g (58%); Rf value: 0.21 in Hexanes; IR (KBr Pellet) umax in
cmꢁ1: 2922, 2853, 1463, 1087; 1H NMR (400 MHz, CDCl3): 7.37 (d,
J ¼ 8.7 Hz, 1H, Ar), 6.5 (d, J ¼ 9 Hz, 1H, Ar), 4.0 (m, 6H, 36OCH2),
1.45-1.1 (m, 60 H, 306CH2), 0.88 (t, J ¼ 6.6 Hz, 9H, 36CH3); Fab Mass:
[Mþ]: 756.0 Calcd for C42H77O3I.
4-[2,3,4-tridodecyloxyphenyl]-2-methyl-3-butyn-2-ol (9)
A mixture of compound (8) (1 g, 1.332 mmoles, 1eq), 2-methyl-3-butyn-
2-ol (0.2 g, 2.2 mmoles, 1.5eq), bis (triphenylphosphine)palladium(II)
chloride (8 mg, 0.01 mmole, 0.5%), triphenylphosphine (14.8 mg,
0.056 mmole, 2.5%) and copper(I)iodide (8.6 mg, 0.045 mmoles, 2%) in dry
triethylamine(5 ml) was stirred at 65ꢀC under Argon atmosphere for 16

224/[524]
C. V. Yelamaggad et al.
hours. The reaction mixture was cooled and filtered through celite bed. The
filtrate was evaporated in vacuo to get a pale yellow oil which was then
purified by column chromatography using silica gel (100–200 mesh). Elu-
tion with mixture of 10% EtOAc-Hexane furnished a pale yellow coloured
viscous mass. Yield: 0.8 g (85%); Rf value: 0.25 in 30% CH2Cl2-Hexanes; IR
1
(KBr Pellet) umax in cmꢁ1: 3368, 2931, 2878, 1203; H NMR (400 MHz,
CDCl3): 7.04 (d, J ¼ 8.7 Hz, 1H, Ar), 6.5 (d, J ¼ 8.4 Hz, 1H, Ar), 4.0 (m, 6H,
36OCH2), 1.45-1.1 (m, 61H, 306CH2, 16OH), 1.61(s, 6H, 16CH3), 0.88
(t, J ¼ 6.75 Hz, 9H, 36CH3); Fab Mass: [Mþ]: 711.7 Calcd for C47H84O4.
2,3,4-Tridodecyloxyphenylacetylene (10)
A mixture of Compound (9) (1 g, 1.404 mmoles, 1eq), KOH (400 mg,
7.02 mmoles, 5eq) and dry toluene (10 ml) was heated to reflux for 2 hours
under Argon atmosphere. The solvent was evaporated to dryness in vacuo
and the brown semisolid obtained was poured into ice-cold water (50 ml).
The aqueous layer was extracted into hexanes (20 ml62). The organic
layer was then washed with brine and dried over Na2SO4. Evaporation of
solvent furnished pale brown oil which was further purified by column
chromatography using alumina (neutral). Hexanes elution furnished a pale
yellow viscous liquid. Yield: 0.65 g (65%); Rf value: 0.53 in 10% EtOAc-
1
Hexanes; IR (KBr Pellet) umax in cmꢁ1: 2924, 2854, 2106, 1592; H NMR
(400 MHz, CDCl3): 7.11 (d, J ¼ 8.6 Hz, 1H, Ar), 6.56 (d, J ¼ 8.6 Hz, 1H, Ar),
4.1 (m, 6H, 36OCH2), 3.13(s, 1H, alkyne H), 1.9-1.1 (m, 60H, 306CH2),
0.88 (t, J ¼ 6.47 Hz, 9H, 36CH3); Mass: [Mþ]: 654.8 Calcd for C44H78O3.
4-[(2,3,4-Tridodecyloxy)phenylethynyl]-O-(tetrahydro
pyran-2-yl)phenol (11)
A mixture of compound (10) (1 g, 1.52 mmoles, 1.1eq), 4-Iodo-O-(tet-
rahydro-pyran-2-yl)phenol (0.424 g, 1.53 mmoles, 1.01eq), bis(triphenyl
phosphine)palladium(II) chloride (8 mg, 0.01 mmole, 0.5%), triphenyl-
phosphine (14.8 mg, 0.056 mmoles, 2.5%) and copper(I)iodide (8.6 mg,
0.045 mmoles, 2%) in dry Triethylamine(5 ml) and dry THF (5 ml) was
stirred at 65ꢀC under Argon atmosphere for 16 hours. The reaction mixture
was cooled and filtered through celite bed. The filtrate was evaporated
in vacuo to get pale yellow oil which was then purified by column chro-
matography using silica gel (100–200 mesh) . Elution with a mixture of
10% EtOAc-Hexane furnished a pale yellow coloured viscous mass. Yield:
0.77 (78%); Rf value: 0.4 in 30% CH2Cl2-Hexanes; IR (KBr Pellet) umax in
cmꢁ1: 2923, 1510, 1239, 1094; 1H NMR (400 MHz, CDCl3) : 7.42 (d,
J ¼ 8.8 Hz, 1H, Ar), 7.12 (d, J ¼ 8.6 Hz, 2H, Ar), 7.0 (d, J ¼ 8.8 Hz, 1H, Ar),
6.59 (d, J ¼ 8.6 Hz, 2H, Ar), 5.42 (t, J ¼ 3.12 Hz, 1H, 16CHOCO), 4.0 (m,
8H, 46OCH2), 2.1-1.18 (m, 66H, 336CH2,), 0.87 (t, J ¼ 6.44 Hz, 9H,
36CH3); Mass: [Mþ]: 745.61 Calcd for C55H90O5.

Columnar Phase in Unsymmetrical Tetramers
225/[525]
4-[(2,3,4-Tridodecyloxy)phenylethynyl]phenol (12)
Compound 11(1 g, 1.2 mmoles) was taken in a mixture of THF and
MeOH and a pinch of PTSA was added and stirred for 30 minutes. Solvent
was removed under vacuo to get a brown coloured mass, which was diluted
with CH2Cl2 and washed with NaHCO3 followed by brine and dried over
Na2SO4. Evaporation of solvent furnished a brown colored mass which was
purified by column chromatography using 60–120 mesh silica gel. Elution
with 20% EtOAc-Hexanes furnished a pale yellow viscous mass. Yield: 0.68
(78%); Rf value: 0.2 in 10% EtOAc-Hexanes; IR (KBr Pellet) umax in cmꢁ1
:
3381, 2923, 2853, 1608, 1270; 1H NMR (400 MHz, CDCl3): 7.39 (d,
J ¼ 8.56 Hz, 2H, Ar), 7.12 (d, J ¼ 8.6 Hz, 1H, Ar), 6.78 (d, J ¼ 8.56 Hz, 2H,
Ar), 6.59 (d, J ¼ 8.6 Hz, 1H, Ar), 5.06 (brs, 1H, 16OH), 4.0 (m, 6H,
36OCH2), 1.9-1.0 (m, 60H, 306CH2), 0.88 (t, J ¼ 6.74 Hz, 9H, 36CH3);
Mass: [Mþ]: 745.9 Calcd for C50H82O4.
4-[(2,3,4-Tridodecyloxy)phenylethynyl]-(5-bromopentyl
oxy)benzene (13)
A 100 ml flask equipped with water condenser and argon inlet, was
charged with acetone (HPLC grade, 50 ml), anhydrous potassium carbo-
nate (1.47 g, 10.68 mmoles, 4eq), compound 12 (2 g, 2.67 mmoles, 1eq),
and 1,5-Dibromopentane (3.68 g, 16.02 mmoles, 6eq), and then flushed
with argon for some time. After closing the neck with a septum, the
reaction mixture was heated to reflux for 24 hours with vigorous stirring
and filtered hot through a celite bed. The filtrate was evaporated and the
crude mass obtained was dissolved in CH2Cl2, washed with brine, dried
over Na2SO4. Evaporation of solvent gave an off white solid which was
purified by column chromatography using silica gel(100–200 mesh). Elu-
tion with a mixture of 5% EtOAc-Hexanes yielded a white solid. Yield: 0.68
(78%); Rf value: 0.4 in 30% CH2Cl2-Hexanes; IR (KBr Pellet) umax in cmꢁ1
:
1
2923, 2853, 1606, 1286; H NMR (400 MHz, CDCl3): 7.42 (d, J ¼ 9 Hz, 2H,
Ar), 7.14 (d, J ¼ 8.5 Hz, 1H, Ar), 6.83 (d, J ¼ 9 Hz, 2H, Ar), 6.59 (d,
J ¼ 8.5 Hz, 1H, Ar), 4.0 (m, 6H, 26OCH2), 3.44 (t,J ¼ 7 Hz, 2H, CH2Br),
1.9-1.0 (m, 66H, 336CH2,), 0.88 (t, J ¼ 6.6 Hz, 9H, 36CH3); Mass: [Mþ]:
894.8 Calcd for C55H91O4Br.
4-Hydroxy-40-methoxyazobenzene (14)
NaNO2 (6.9 g, 100 mmoles, 1eq) was added dropwise to a well stirred
and precooled solution of p-Anisidene (12.3 g, 100 mmoles, 1eq) in mixture
of 40 ml H2O and 30 ml Conc H2SO4. The resulting diazonium solution was
quenched with a solution of Phenol (9.4 g, 100 mmoles, 1eq) in NaOH(4 g)
and Na2CO3 (12 g) in 100 ml of water at 0–5ꢀC. As the reaction mixture
was allowed to warm up to room temperature an orange coloured solid

226/[526]
C. V. Yelamaggad et al.
precipitates out which was filtered on a buchner funnel. The air dried
sample was further purified by repeated recrystallization from aqueous
EtOH. Yield: quantitative; Rf value: 0.4 in 30% EtOAc-Hexanes; IR (KBr
Pellet) umax in cmꢁ1: 3332, 1597, 1239; 1H NMR (200 MHz, CDCl3): 7.85 (m,
4H, Ar), 6.9 (m, 4H, Ar), 3.88 (s, 3H, 16OCH3), 1.6 (brs, 1H, 16OH); FAB
Mass: [Mþ]: 227.92 Calcd for C13H12O2N2.
1-(4-Hydroxyazobenzene-4-oxy)-5-{[(2,3,4-tridodecyloxy)-
phenylethynyl]phenoxy}-pentane (4)
A mixture of 13 (1 g, 1.09 mmoles, 0.5eq), 4,40-dihydroxyazobenzene
(560 mg, 2.61 mmoles, 1.2eq), anhydrous K2CO3 (0.6 g, 4.4 mmoles, 2eq)
in Dry DMF was heated at 70ꢀC for 24 hours under Argon atmosphere.
The cooled reaction mixture was poured into water and the aqueous layer
was extracted into CH2Cl2 (2620 ml). The combined organic layer was
washed with brine dried over Na2SO4. Evaporation of the solvent gave an
orange coloured solid which was purified by column chromatography
using 100–200 mesh silica gel. Upon elution with 10% EtOAc-Hexanes,
orange coloured crystals were obtained. Yield: 0.4 g (40%); Rf value: 0.25
in 30% EtOAc-Hexanes; IR (KBr Pellet) umax in cmꢁ1: 3304, 2919, 2851,
1603, 1510; 1H NMR (400 MHz, CDCl3): 7.85 (d, J ¼ 8.84 Hz, 2H, Ar),
7.82 (d, J ¼ 8.76 Hz, 2H, Ar), 7.42 (d, J ¼ 8.48 Hz, 2H, Ar), 7.12 (d,
J ¼ 8.56 Hz, 1H, Ar), 6.98 (d, J ¼ 8.76 Hz, 2H, Ar), 6.92 (d, J ¼ 8.64 Hz,
2H, Ar), 6.85 (d, J ¼ 8.52 Hz, 2H, Ar), 6.59 (d, J ¼ 8.64 Hz, 1H, Ar), 5.20
(brs, 1H, -OH), 4.12 (m, 10H, 56OCH2), 1.97-1.15 (m, 66H, 336CH2,),
0.87 (t, J ¼ 6.68 Hz, 9H, 36CH3); Mass: [Mþ]: 1028.00 Calcd for
C67H100O8N2.
4,40- Dihydroxyazobenzene (15)
AlCl3 (Excess, 4 g) was added to well stirred solution of Compound (14)
(0.91 g, 4 mmoles, 1eq) in CHCl3 placed in a 2 necked round bottomed flask
equipped with a water condenser and N2 inlet, and was heated to 50ꢀC. Dry
Pyridine (8.4 ml) was added dropwise through the second neck over a
period of 1 hour. The reaction mixture was then refluxed for 30 hours and
then cooled to 0ꢀC and acidified with 10% HCl. The product was extracted
into diethyl ether (20 ml63). The combined ether layer was repeatedly
washed with cold water. Upon evaporation of the solvent an orange
coloured solid was obtained which was purified by column chromatography
on silica gel (100–200 mesh). Upon elution with 20% EtOAc-Hexanes
initially the unreacted starting material elutes and then with 30% EtOAc-
Hexanes the pure product elutes out. Yield: 40% (1.8 g); Rf value: 0.21 in
1
30% EtOAc-Hexanes; IR (KBr Pellet) umax in cmꢁ1: 3326, 1583, 1213; H
NMR (200 MHz, CDCl3): 7.87 (m, 4H, Ar), 6.9 (m, 4H, Ar); FAB Mass: [Mþ]:
214 Calcd for C12H10O2N2.

Columnar Phase in Unsymmetrical Tetramers
227/[527]
Tetramer 1 and 2
A mixture of compound 3a or 3b (0.4 g, 0.5 mmoles, 1eq), compound 4
(0.56 g, 5.54 mmoles, 1.1eq), and anhydrous K2CO3 (1.1 g, 2.5 mmoles,
5eq) was heated at 85ꢀC for 24 hours under Argon atmosphere. The cooled
reaction mixture was poured into water and the aqueous layer was
extracted into CH2Cl2 (2620 ml). The combined organic layer was washed
with brine dried over Na2SO4. Evaporation of the solvent gave an orange
coloured solid which was purified by column chromatography using 100–
200 mesh silica gel. Upon elution with 10% EtOAc-Hexanes, orange
coloured crystals were obtained. 1: Rf ¼ 0.57 (4:1 CH2Cl2-Hexanes). A
yellow solid; m.p. 202ꢀC; Yield: 177 mg (42%); IR (KBr pellet): gmax 2923,
2852, 1730, 1603, 1581 and 1513 cmꢁ1; 1H NMR (400 MHz, CDCl3): 7.87 (d,
J ¼ 8.88 Hz, 4H, Ar), 7.46 (m, 6H, Ar), 7.13 (d, J ¼ 8.6, 1H, Ar), 7.01 (d,
J ¼ 2.76, 2H, Ar), 6.98 (d, J ¼ 2.76, 2H, Ar), 6.95 (d, J ¼ 7.32, 2H, Ar), 6.93
(d, J ¼ 7.36, 2H, Ar), 6.85 (d, J ¼ 8.88, 2H, Ar), 6.60 (d, J ¼ 8.76, 1H, Ar),
5.37 (brd, J ¼ 4.52, 1H, Olefinic), 4.62 (m, 1H, -CH-O-CO-), 4.02 (m, 16H,
86-OCH2-), 2.32 (brt, J ¼ 7.38, 4H, 26allylic methylene), 2.03-0.86 (m,
117H, 56-CH3, 486-CH2-, 66-CH-), 1.01 (s, 3H, -CH3), 0.86 (d, J ¼ 4.8,
3H, -CH3) and 0.68 (s, 3H, -CH3); 13C NMR (100 MHz, CDCl3, Spin Echo
FT): 172.77 (CO), 161.12 (C), 161.01 (C), 158.82 (C), 158.06 (C), 154.36
(C), 153.99 (C), 147.07 (C), 141.98 (C), 139.7 (C), 133.56 (C), 132.78
(CH), 127.67 (CH), 127.47 (CH), 124.33 (CH), 122.53 (CH), 116.05 (C),
114.78 (CH), 114.68 (CH), 114.46 (CH), 111.03 (C), 108.20 (CH), 91.59
(C), 84.7 (C), 74.22 (CH2), 73.82 (CH), 73.76 (CH2), 68.84 (CH2), 68.05
(CH2), 67.77 (CH2), 67.54 (CH2), 56.71 (CH), 56.18 (CH), 50.01 (CH),
42.33 (CH2), 39.76 (CH2), 39.53 (CH2), 38.12 (CH2), 37.01 (CH2), 36.61
(CH2), 36.21 (CH2), 35.79 (CH), 34.59 (CH2), 31.92 (CH2), 30.52 (CH2),
30.34 (CH2), 29.69 (CH2), 29.36 (CH2), 29.00 (CH2), 28.22 (CH2), 28.00
(CH), 27.84 (CH2), 26.25 (CH2), 26.12 (CH2), 26.04 (CH2), 25.64 (CH2),
24.81 (CH2), 24.28 (CH2), 23.85 (CH2), 22.79 (CH3), 22.68 (CH2), 22.55
(CH3), 21.04 (CH2), 19.23 (CH3), 18.72 (CH3), 14.08 (CH3) and 11.86
(CH3); FAB Mass: 1737.0 [MH]þ; Elemental analysis calcd. for
C
116H168N2O10: C 79.5, H 9.78 and N 1.59; found C 79.25, H 9.86 and N 1.21.
Tetramer 2: For molecular structural characterization data refer to our
publication [21].
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