Synthesis and characterization of novel chiral dimers exhibiting highly frustrated liquid crystal phases

Article abstract of DOI:10.1016/j.tet.2014.05.072

Two novel series of optically active dimers comprising cholesterol and biphenyl-4-yl 4-(n-alkoxy)benzoate cores interlinked though either an odd-parity/even-parity spacer have been prepared and characterized. They stabilize an extremely complex, frustrated liquid crystalline state viz., the twist grain boundary (TGB) phase with chiral smectic C structure, denoted as TGBC^- phase, over a wide (50-110 °C) temperature range. Notably, the dimers with an odd-parity spacer show an additional frustrated liquid crystal phase namely, the blue phase (BP). The presence of such frustrated phases suggests that the synthesized dimers are characterized by high enantiomeric excess and strong molecular chirality. Thus, 12 new optically active, nonsymmetric dimers reported herein constitute new examples of rarely found strongly chiral, optically pure dimers showing frustrated liquid crystal phase over an adequately wide thermal range.

Full text of DOI:10.1016/j.tet.2014.05.072

Tetrahedron 70 (2014) 4745e4753
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and characterization of novel chiral dimers exhibiting
highly frustrated liquid crystal phases
*
Uma S. Hiremath
Centre for Soft Matter Research, Prof. U. R. Rao Road, PO Box No. 1329, Jalahalli, Bangalore 560013, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel series of optically active dimers comprising cholesterol and biphenyl-4-yl 4-(n-alkoxy)ben-
zoate cores interlinked though either an odd-parity/even-parity spacer have been prepared and char-
acterized. They stabilize an extremely complex, frustrated liquid crystalline state viz., the twist grain
Received 19 March 2014
Received in revised form 16 May 2014
Accepted 17 May 2014
boundary (TGB) phase with chiral smectic C structure, denoted as TGBC
phase, over a wide (50e110 ꢀC)
*
Available online 24 May 2014
temperature range. Notably, the dimers with an odd-parity spacer show an additional frustrated liquid
crystal phase namely, the blue phase (BP). The presence of such frustrated phases suggests that the
synthesized dimers are characterized by high enantiomeric excess and strong molecular chirality. Thus,
12 new optically active, nonsymmetric dimers reported herein constitute new examples of rarely found
strongly chiral, optically pure dimers showing frustrated liquid crystal phase over an adequately wide
thermal range.
Keywords:
Liquid crystals
Dimers
Chirality
Frustrated phases
Ó 2014 Published by Elsevier Ltd.
1. Introduction
Blue phases usually exist over
a narrow thermal range
(w0.5e2 ꢀC) between the N
*
/smectic (Sm) phase and the isotropic
Since the discovery of chiral liquid crystalline state by Reinitzer
in 1888,1,2 mesogens possessing molecular chirality have been in-
tensively investigated.3e9 In particular, a variety of new chiral
mesogenic materials have been realized based on the rational
molecular engineering.4 This has, in fact, resulted in the invention
of a great variety of novel LC superstructures10e20 that are enor-
mously significant in the context of both basic research and various
emerging technologies21,22 as well as bioscience.23 In general,
molecular chirality favours a twist in the orientation of LC mole-
cules. However, interestingly, the invention of new phases appears
to be associated with an increase of complexity of their structures.
Their self-organization into an asymmetric chiral LC structure with
a superimposed macroscopic twist of the constituent mesogens
liquid (I) phase. However, in recent times there have been efforts to
improve vastly the thermal stabilities of these phases24,25 owing to
their potential for photonic application.22,26 Three types of blue
phase viz., BPI, BPII and BPIII are known to exist as a consequence of
the competition among the chiral twisting force and the inclination
of mesogens to pack so as to fill space uniformly. Their structure
comprises double twist cylinders.6,16 In BPI and BPII, the packing of
double twist cylinders give rise to body-centred cubic and simple
cubic structures, respectively. Whereas in the BPIII phase, the ori-
entational order of molecules is not periodic and the symmetry is
the same as that of the isotropic phase. Thus, BPIII consists of
double twist cylinders with arbitrary orientation. Analogous to BPs,
TGB phases occur over a short temperature range at the phase
yields states such as N
*
and chiral smectic C (SmC
*
) phases, which
transition from the isotropic (I) or chiral nematic (N
*
) to smectic A
are characterized by a helicoidal macroscopic structure; in these
structures the helical arrangement is achieved without any defects.
In chiral mesogens with high enantiomeric excess and strong mo-
lecular chirality5 (intrinsic high twisting power), the twisting
structure accompanies defects that adds complexity in the struc-
ture. Frustrated LC phases namely BPs,6,16,22e26 and twist grain
boundary (TGB) phases6,18e20,27,28 are well-known examples where
the defects are not only present but are imperative in the formation
and stabilization of these complex, superstructures.
(SmA) or SmC
*
phases.6,17e20 Although their significance in applied
science is yet to be figured out, they have attracted a considerable
amount of attention in view of the fact that in 1988 Renn and
Lubensky invented them as LC analogues of the Abrikosov phases
exhibited by type-II superconductors in an external magnetic
field.27 They get stabilized when the constituent chiral mesogens
endeavour to form helical (with the N helix axis perpendicular to
*
their long molecular axes) and lamellar (smectic) structures con-
currently. These two structures, being opposite to or in conflict with
each other, cannot coexist. However, the coexistence of layering
and twist is attained by an array of screw dislocation wall twist
grain boundaries in the layering, which basically segregate the
* Tel.: þ91 80 23084232; fax: þ91 80 28382044; e-mail addresses: hiremath@
csmr.res.in. umahiremath66@gmail.com.
0040-4020/$ e see front matter Ó 2014 Published by Elsevier Ltd.
http://dx.doi.org/10.1016/j.tet.2014.05.072

4746
U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
structure into smectic slabs. Thus, different types of TGB phases
varying in the local structure of smectic slabs have been theoreti-
cally predicted and discovered. However, three main types of TGB
phases are the TGBA, TGBC and TGBC
thogonal smectic A (SmA), tilted smectic C (SmC) and helical SmC
characters, respectively. Among these, the TGBC phase is of out-
standing interest as it is highly complex structure where a helix
along the smectic layer normal direction exists (due to bulk SmC
*
where the slabs have or-
*
*
*
phase), besides the TGB helix. Here, the helical axis of the smectic
structure remains perpendicular to that of the TGB helix. Owing to
its complex nature, the search for mesogens capable of exhibiting
the TGBC phase over wide thermal range has been a challenging
*
venture for liquid crystal chemists where the generation of general
strategy in the form of molecular engineering and synthesis of
novel chiral LC materials is crucial.
In this paper, we report 12 novel LC dimers, belonging to two
series, exhibiting the TGBC phase over an exceptionally wide
*
thermal (50e110 ꢀC) range; notably, one of the series of dimers
show BP additionally, albeit over only a short thermal width. The
molecular design incorporates natural cholesterol covalently join-
ing to a long, calamitic (three-ring ester) moiety though a flexible
spacer. This particular design was conceived based on the literature
reports that nonsymmetric dimers consisting of cholesterol as the
chiral entity joined to different aromatic mesogens through
a spacer show frustrated phases and unusual LC phase sequences.28
In particular, in the context of present study, it must be mentioned
Scheme 1.
here that dimers derived from cholesterol stabilize TGBC phase
*
(including other TGB phase/s) over a moderate28e33 to wide ther-
oxy)hexaneate (2-5).36 In the final step the phenols 2-4 and 2-5
were reacted with 4-(n-alkoxy)benzoic acids (3-8, 3-9, 3-10, 3-11,
3-12 and 3-16) in the presence of dicyclohexylcarbodiimide (DCC)
and a catalytic amount of 4-dimethylaminopyridine (DMAP) in
dichloromethane (DCM) for 24 h at refluxing temperature to obtain
the final compounds in good yield. These acids were prepared
starting from of ethyl 4-hydroxybenzoate; it was O-alkylated with
1-bromoalkanes in presence of a mild base to obtain ethyl 4-(n-
alkoxy)benzoates, which upon subjecting to alkaline hydrolysis
furnished 4-n-alkoxybenzoic acids in almost quantitative yields.
The molecular structures of all the dimers and their intermediates
were confirmed by standard spectroscopic methods of analyses and
microanalytical data (see Experimental part for the details).
mal range.34,35 For example, we have recently reported the exis-
tence of the TGBC phase over an unprecedented thermal range in
*
chiral dimers where a three-ring salicylaldimine core with an n-
alkoxy tail is covalently tethered to cholesterol through an even-
parity (u
-oxyalkanoyloxy) spacer.35 This remarkable behaviour is
considered to be originating from the extended molecular length
and thus, rigid rod-like geometry of the dimers. This observation
motivated us to design similar lengthy, cholesterol-based dimers.
Thus, in order to realize such dimers, we intended to interlink
a three-ring anisometric moiety with cholesterol through an
u-
oxyalkanoyloxy spacer. To understand the structureeproperty
correlations, we proposed to vary the lengths of the alkylene
spacers as well as those of the terminal alkoxy chains attached to
three-ring core. Specifically, both odd-parity (5-oxypentanoyloxy)
and even-parity (6-oxyhexanoyloxy) spacers were chosen to link
cholesterol and three-ring entities; n-alkoxy chains such as
n-octyloxy, n-nonyloxy, n-decyloxy, n-undecyloxy, n-dodecyloxy
and n-hexadecyloxy chains were selected as terminal substituents.
Accordingly, two series of compounds namely 40-((5-
cholesteryloxy-5-oxopentyl)oxy)biphenyl-4-yl 4-(n-alkoxy)-ben-
zoates and 40-((6-cholesteryloxy-6-oxohexyl)oxy)-biphenyl-4-yl 4-
(n-alkoxy)benzoates (see Scheme 1) have been synthesized; for the
sake of convenience they are hereafter referred to as BD-4,m and
BD-5,m series where B denotes the presence of biphenyl moiety, D
refers to dimer, 4 and 5 indicate the number of methylene units
present in the spacers and m represents the length of the terminal
tail.
2.2. Mesomorphic behaviour
2.2.1. Optical and calorimetric studies. Having synthesized the di-
meric molecules and confirmed their molecular structures, we
examined these compounds for their thermal behaviour. It was
accomplished with the help of polarizing optical microscope (POM)
and differential scanning calorimeter (DSC). However, X-ray dif-
fraction (XRD) measurement was also carried out for the essential
LC phase of some selected samples of both the series. For pre-
liminary POM observation, especially to verify the liquid crystal
property (fluidity and birefringence) of the dimers, the sample
placed between a clean untreated glass slide and a cover slip was
used. For unequivocal mesophase assignment, two different surface
coated slides, one treated for homogeneous (planar) alignment and
another with homeotropic alignment, were employed. The phase
transition temperatures noted during the POM study were found to
be in good agreement with those of the calorimetric experiments.
The phase sequences, transition temperatures and enthalpies of the
phase transitions of both series of dimers are listed in Table 1.
It is apparent from the results accumulated in Table 1 that all the
compounds exhibit enantiotropic LC behaviour. As can be seen, the
two series of dimers synthesized primarily differ in the parity of
2. Results and discussion
2.1. Synthesis and characterization
All the target compounds were prepared by the synthetic route
depicted in Scheme 1. Mono O-alkylation of 4,4-dihydroxybiphenyl
with cholesteryl 5-bromopentanoate (1-4) and cholesteryl 6-
bromohexanoate (1-5)36 under Williamson ether synthesis pro-
tocol respectively yielded cholesteryl 5-(40-hydroxybiphenyl-4-
oxy)pentanoate (2-4) and cholesteryl 6-(40-hydroxybiphenyl-4-
central flexible (u-oxyalkanoyloxy) spacer and thus, vary notably in
their thermal behaviour. That is, the dimers of BD-4,m series are

U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
4747
Table 1
and b, respectively, shows the space-filled, energy-minimized
molecular structures of an odd-member (BD-4,9) and even-
member (BD-5,11) of the present series where the respective
bent-structure and rod-like shape can be visualized. In essence, the
effective change in molecular shape (geometry) evolving from the
spacer parity affects the liquid crystalline behaviour of the present
dimers. For instance, the dimers with even-parity spacers, regard-
less of variation in their terminal chain lengths, exhibit two enan-
b
Phase transition temperatures (ꢀC)a and enthalpies [J gꢁ1
] of chiral dimers of BD-
4,m and BD-5,m series
Dimers
Heating
Cooling
I 223.3 [1.4]d BP-N
[0.4] TGBC 95.8 [13.4] Cr
I 222.6 [1.5]d BP-N
170.7
[0.5] TGBC 97.1 [11.8] Cr
I 212.5 [1.4]d BP-N
169.8
[0.6] TGBC 83.5 [12.4] Cr
I 204 [1.5]d BP-N
168.8
[0.5] TGBC 68.1 [8.7] Cr
I 209 [1.8]d BP-N
183.1
[0.5] TGBC 71.5 [11.1] Cr
I 196.2 [1.8]d BP-N
185.9
[0.6] TGBC 97.8 [13.6] Cr
I 243.3 [3.7] N
172.8e TGBC
116.6 [12.3] Cr
BD-4,8
Cr 136.9 [25]c TGBC
*
159.1 [0.6]
172.1 [0.6]
*
157.9
N
*
224.3 [1.4] I
Cr 130.6 [5.6]c TGBC
223.9 [1.5] I
Cr 122.7 [50.9] TGBC
216.1 [1.7] I
Cr 106.6 [15.5] TGBC
204.4 [1.6] I
Cr 119.2 [39.9] TGBC
211.5 [1.9] I
Cr 120.9 [27.5] TGBC
201.9 [2] I
Cr 142.4 [42.3] TGBC
245.2 [3.9] I
Cr 141.2 [48.2] TGBC
235.3 [4.7] I
Cr 146.1 [38.2] TGBC
233.7 [4.7] I
Cr 133.4 [41.4] TGBC
242 [4.2] I
Cr 119 [34.1] TGBC
235.3 [4.5] I
Cr 132.7 [38.3]d TGBC
227.9 [5.6] I
*
BD-4,9
*
*
N
*
*
BD-4,10
BD-4,11
BD-4,12
BD-4,16
BD-5,8
*
176.8 [0.7]
170.3 [0.5]
188.2 [0.7]
190 [0.6]
174.1e
*
tiotropic mesophases such as N
*
and TGBC phases whereas those
*
N
*
*
*
*
*
*
*
*
*
*
with odd-numbered spacers additionally exhibit BP phase. The
occurrence of these mesophases was established clearly with the
help several complementary studies, which we describe as follows.
Firstly, we discuss about our studies concerning BD-5,m series
of dimeric molecules where the two mesogenic segments are
separated by an even-parity spacer. As mentioned earlier, all the
N
*
*
*
N
*
*
*
N
*
*
*
*
*
N
*
members of this series show N
samples, held between a cover slip and untreated glass slide, upon
heating, melt into the TGBC phase exhibiting a hazy texture con-
*
and TGBC
*
phases. These crystalline
BD-5,9
186.6e
I 232.5 [4.8] N
109.3 [50.4] Cr
I 230.1 [4.7] N
88 [19.6] Cr
I 240.8 [4.5] N
*
185e TGBC
*
N
*
BD-5,10
BD-5,11
BD-5,12
BD-5,16
198.3e
*
192.4e TGBC
*
N
*
sisting of square grid pattern as well as undulated filaments, which
arise due to planar and homeotropic orientations of mesogens,
204.9 [0.2]
*
203.8 [0.2]
N
*
TGBC 93.3 [26.6] Cr
*
respectively. On heating the samples further, the TGBC
transforms into the N phase exhibiting a planar texture having oily
streaks that remains unaltered till isotropic liquid state. Upon
cooling these samples gradually from the liquid state, the N phase
*
phase
*
200.6e
214.7e
I 235.1 [4.2] N
86.6 [26.6] Cr
I 227.2 [5.7] N
*
199e TGBC
*
*
N
*
*
*
211.7e TGBC
*
N
*
117.7 [29.9] Cr
blocks; SmC : chiral
*
appears at a well defined temperature manifesting optically in the
form of fan-like focal-conic domains. As a representative case, the
microphotographs of such a textural pattern observed for dimer
BD-5,10 are shown in Fig. 2a.
It may be mentioned here that for the sake of completeness, we
show other textural patterns observed on different occasions for
Cr: crystal; TGBC
*
: twist grain boundary phase having SmC
*
*
smectic C phase; N : chiral nematic phase; BP: blue phase; I: isotropic phase.
*
a
Phase transition temperatures were determined by both POM (5 ꢀC minꢁ1) and
DSC studies: peak temperatures in the DSC traces obtained during the first heating
and cooling cycles (at 5 ꢀC minꢁ1) coupled with optically measured temperatures
are given.
b
Transition enthalpies were obtained from the DSC thermograms.
Additional crystal to crystal transitions have been observed for the compounds
c
this dimer only. On further cooling, the TGBC
view with textural pattern shown in Fig. 2b where thick lines
appearing like filaments are seen. However, when the N phase
*
phase comes into
BD-4,8 (129.3 [64.2]), BD-4,9 (126.2 [38.9]) and BD-5,16 (97.5 [11.8]).
d
BP is a transient phase and thus the
transitions.
The phase transition was observed under POM; too weak to be recognized
in DSC.
DH represents the combined enthalpy for
*
IeBPeN
*
e
with focal-conic texture was subjected to the gentle mechanical
shearing, the pattern transformed sharply in to a planar texture
where the director (n) remains parallel to the plane of the glass
plates. This confirms that the helical axis is normal to the sub-
strates, i.e., along the viewing direction. Further lowering of the
odd-members as they possess5-oxypentanoyloxy spacer where
five carbon atoms separate the two segments while BD-5,m series
of materials are even-homologues as they contain 6-
oxyhexanoyloxy spacer. As is well-known, the phase transitional
properties including clearing transition temperature of dimers
critically depend on the parity of the spacer. This behaviour is
generally attributed to molecular shape of dimers in their all-trans
conformation imposed by the number of atoms (generally carbons)
present in the spacer. In dimers with an even-numbered spacer, the
mesogenic units are anti-parallel to give an overall rod-like
(calamitic) shape, while the odd-membered dimers attain bent-
shape as the mesogenic entities are inclined to each other. Fig. 1a
sample temperature, the planar texture of the N phase changes
*
sharply to a square grid pattern. Fig. 2c shows a transition from the
planar texture of the TGB phase to the square grid pattern of the
TGBC
*
phase while Fig. 2d shows the texture for the completely
phase. When glass plates coated with a polyimide
formed TGBC
*
solution and unidirectionally rubbed (to account for planar an-
choring) were used, the aforesaid characteristic textural patterns
were observed for these two mesophases. In order to rule out the
possibility that the presence of the square grid is due to some in-
stability in the helical structure such as SmC
*
phase, the TGBC
*
phase of the samples was examined in slides treated for homeo-
tropic anchoring where a filament texture was observed with an
undulatory structure as shown in Fig. 2e.
Further, when the samples were examined in a wedge-type cell
(where the thickness varies from one end to other end of the cell)
with similar surface treatment to the parallel cell, an array of
Grandjean Cano dislocation lines were observed for the N
whereas, the TGBC phase appeared with a striking square grid
pattern forming over the dislocation lines (Fig. 2f). As mentioned
earlier, in the TGBC structure, besides a helical superstructure due
to the TGB helix, there exists another helical structure due to bulk
SmC phase; the helical axis of the latter is perpendicular to that of
*
phase;
*
*
*
the TGB helix. Such a complex organization of mesogens produces
square grids over planar texture/Grandjean Cano dislocation lines.
In general, the DSC thermograms of these dimers exhibited two
endothermic peaks in the heating cycle due to CreN
transitions; as expected, during cooling scan, the samples showed
two exothermic peaks due to IeN and N eCr phase sequences.
*
and N eI
*
Fig. 1. Space-filling, energy-minimized molecular structures of dimers BD-4,9 (odd-
member) (a) and BD-5,11 (even-member) (b); notice that dimer BD-4,9 attains a bent-
shape while compound BD-5,11 has rod-like conformation.
*
*

4748
U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
Fig. 2. Polarized light micrographs of the textures of the N
*
and TGBC
*
phases observed for dimer BD-5,10: (a) the focal-conic texture of the N
phase (190 ꢀC); (c) the square grid pattern of the TGBC
phase (RHS) (192.2 ꢀC); (d) the square grid pattern of the completely formed TGBC phase (189 ꢀC); (e) the undulated
phase seen when slides treated for homeotropic alignment were used (103 ꢀC); (e) the texture showing Grandjean Cano dislocation lines su-
perposed on the square grid pattern when the TGBC
phase (186 ꢀC) was viewed in a wedge-type cell with the glass plates treated for planar anchoring.
*
phase occurring just below the
isotropic melt (229 ꢀC); (b) texture of the TGBC
*
phase grown on top of focal-conic pattern of the N
(243.6 ꢀC) on top of the Granjean-planar texture of the N
filamentary pattern of the TGBC
*
*
phase (LHS) growing
*
*
*
*
However, as shown in Fig. 3a, the DSC traces of both heating and
it is evident from Table 1 that these mesogens, the BD-5,m series of
cooling cycles of dimer BD-5,11 displayed the peaks due to
dimeric molecules, stabilize TGBC phase in the thermal range of
*
TGBC
*
eN
*
and N
*
eTGBC
*
transitions with the enthalpy value 0.2 J/g
55e110 ꢀC, which is noteworthy given the highly complex and
suggesting the phase transition being first order. Most importantly,
frustrated nature of the phase.
6
2.9
2.8
(a)
(b)
6
5
4
3
2
1
2.55
2.40
5
2.7
2.6
2.5
4
2.4
170
172
174
202
203
204
205
206
207
Cr2
Cr1
Heating
Cooling
3
2
1
TGBC*
N*
I
TGBC*
TGBC*
Cr
Heating
N*
N*
N*
I
TGBC*
Cr
I
Cooling
Cr
I
100
150
200
250
50
100
150
200
Temperature (0C)
Temperature (0C)
Fig. 3. DSC traces of the first heating (black-curve)ecooling (red-curve) cycles obtained for the dimers BD-5,11 (a) and BD-4,9 (b). Notice that in these traces the signatures due to
TGBC eN phase transition can be distinctly seen (see insets).
*
*

U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
4749
We now discuss the thermal behaviour of BD-4,m series of di-
mers possessing an odd-membered (5-oxypentanoyloxy) spacer. It
is apparent from the results summarized in Table 1 that all the
members of the series behave analogously. They stabilize addi-
tionally, unlike their counterparts with even-parity spacer, the BP
range (0.3 ꢀC) is typical of the BPI/BPII phase. On further cooling,
a focal-conic texture (Fig. 4b) appeared, which upon shearing
transformed into oily streak pattern occurring over a planar texture
(Fig. 4c) signifying the presence of the N
planar texture of the N phase, the TGBC phase with characteristic
square grid pattern appears at 170.7 ꢀC that persists till the sample
crystallizes out at 97 ꢀC; thus, the TGBC
phase exists for about
*
phase. On cooling the
*
*
phase. That is, these dimers show BP, N
*
and TGBC phases that
*
were established, as before, with the help of calorimetric and POM
studies. Clear signatures were seen in the DSC trances of the
transitions between these phases. As an example, the DSC ther-
mograms obtained during the first heating-cooling cycles for the
dimer BD-4,9 are shown in Fig. 3b. The heating curve (black-trace)
shows, besides transformation between crystalline forms, shows
*
73 ꢀC. Likewise, other members of the series stabilize the TGBC
*
phase over wide thermal range (60e110 ꢀC). The occurrence of the
other frustrated mesophase viz., BP phase in these dimers is also
noteworthy.
three reversible transitions at 130.6 ꢀC (
D
H¼25 J/g), 172.1 ꢀC (0.6 J/
2.2.2. X-ray diffraction measurements. From the analysis of the
foregoing experimental results it is clear that the chiral dimers
g) and 224.3 ꢀC (1.4 J/g) associated with the CreTGBC
*
, TGBC
*
eN
*
and N
*
eI phase transitions. The corresponding transitions of the
realized in the present study display TGBC phase over an excep-
*
cooling cycle were observed at 222.6 ꢀC (1.5 J/g), 170.7 ꢀC (0.5 J/g)
tionally wide thermal range. The occurrence of such a frustrated
phase was further substantiated by XRD measurements on un-
and 97.1 ꢀC (11.8 J/g); however, the enthalpy of the first transition
(1.5 J/g) represents the combined value for N
*
eBP transition as the
aligned (powder) samples with Cu K
Specifically, the lamellar ordering of the TGBC
a
(
l
¼0.15418 nm) radiation.
BP was clearly observed during the cooling cycle only. Again, unlike
*
phase was ascer-
in the case of the dimers with even-parity spacer (except BD-5,11),
tained using dimers BD-4,9 and BD-5,11 as representative cases.
The chosen samples were inserted into a Lindemann capillary
(1 mm diameter) tube in the isotropic phase and both the ends of
tube were flame sealed carefully. The samples, placed in a temper-
ature-controlled device, were slowly cooled from the isotropic
phase and the diffraction patterns were collected at different
the peak observed due to N
members can be ascribed to the lower order parameter of the N
phase. Further, the N eI transition enthalpy values, ranging from
*
eTGBC
*
transition for all these odd-
*
*
1.4 to 1.8 J/g, found for these odd-members are lower than that
obtained for dimers with even-parity spacers for which the values
lie between 3.9 and 5.6 J/g. Such results certainly originate from the
temperatures while cooling the TGBC phase. Identical diffracto-
*
order parameter of the N
*
phase of a given dimer. Needless to say,
grams were obtained for both the dimers and established the lay-
ered structure of the mesophase. Fig. 5 illustrates the resemblance
among one-dimensional intensity versus 2q profiles obtained for
molecular geometries of the dimers namely the bent-conformation
and rod-like shape of the odd- and even-members, respectively, are
responsible for such differences in order parameters of the N
phase.
*
BD-4,9 and BD-5,11 at 130 ꢀC and 170 ꢀC, respectively. As can be
seen, each diffractogram shows two low-angle reflections, the first
one very intense (d1) and the other very weak (d2), and a diffuse
reflection (d3) at wide angles (see insets of Fig. 5).
As mentioned earlier, POM studies carried out for all the sam-
ples evidenced the presence of BP, N and TGBC phases. For ex-
*
*
ample, on slow cooling (2 ꢀC/min) the isotropic liquid of dimer BD-
4,9 placed between a clean glass slide and a cover slip, a textural
pattern emanating from the black background was observed at
222.6 ꢀC (Fig. 4a). This texture existing for a very short thermal
Fig. 6 illustrates the layer spacings (d1) of the low-angle Bragg
reflections as a function of temperature. Needless to say, the
spacing of the lowest angle intense peak corresponds to the smectic
layer thickness in the TGBC phase. The second peak seen is
*
Fig. 4. Microphotograph of the textures observed for the LC phases of dimer BD-4,9: (a) the platelet texture of the BPI/BPII (at 222.6 ꢀC); (b) the focal-conic texture of the N
(at 220 ꢀC); (c) the characteristic oily streak texture of the N seen at 210 ꢀC when the focal-conic pattern of the same phase was sheared gently; (d) the square grid pattern of the
TGBC
phase (170.7 ꢀC).
*
phase
*
*

4750
U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
a Chem3D molecular model. It is perceptible from the results (Table
2) that the layer spacing d1 is less than the molecular length (l) (also
see Fig. 1) and thus, the d1/l ratio falls below 1. This is predictable
d3
d3
d1
d1
2500
50
10
given the situation that in the SmC
*
layers of the TGBC phase, the
*
constituent mesogens tilt with respect to the layer normal di-
rection. It can also be seen that the d1-value decreases progressively
12
20
(deg)
28
2θ
when the TGBC phase is cooled. This means that the tilt angle of
*
the dimers within the smectic blocks increases on decreasing the
temperature. Thus, the XRD study clearly supports the tilted ori-
entation of dimers within the smectic blocks and thus validates the
60
d2
d2
20
presence of TGBC phase unequivocally.
*
500
d23.8
4.3
2θ (deg)
4.8
d2
2.3. Analysis of the results
2
3
4
5
In essence, it is thus evident from the collected experimental
results that the thermal behaviour of the present dimers shows
critical dependence on the parity of the spacer as well as on the
structure of three-ring calamitic unit namely, biphenyl-4-yl 4-(n-
alkoxy)benzoate attached to cholesterol. In particular, the effect of
the parity of the central spacer on the clearing temperature is no-
2θ (deg)
Fig. 5. The low-angle and wide-angle (inset) regions of the XRD patterns obtained for
the TGBC
phase of dimer BD-4,9 (blue traces) and BD-5,11 (red-traces) at 130 ꢀC and
*
170 ꢀC, respectively.
table. That is, the dimers of BD-4,m series with
a 5-
oxypentanoyloxy (odd-parity; C5) spacer show lower clearing
temperatures when compared to that of even-members (BD-5,m
series of dimers). As discussed earlier, such a behaviour can be in-
terpreted in terms of the overall molecular shape of the dimer
imposed by the geometry and flexibility of the spacer. The enthalpy
values
associated
with
N
*
eI
phase
transitions
also
exhibit oddeeven effect. The reduction in the shape anisotropy, due
to bent-conformation, lowers the clearing temperatures and their
enthalpy values effectively. From the results it can also be seen that
on increasing the length of the terminal tails within the series the
clearing temperature generally shows a decreasing trend that can
be ascribed to the progressive softening of the mesogens. Most
importantly, the thermal range of the TGBC appears to widen with
*
the increase in the length of terminal tail attached to biphenyl-4-yl
4-(n-alkoxy)benzoate core supporting our earlier observation that
moderately lengthy, three-ring dimers derived from cholesterol
stabilize TGBC
phase over a wide thermal range.35 Needless to say,
*
the three-ring biphenyl-4-yl 4-(n-alkoxy)benzoate core present in
the molecular design also favours the stabilization of frustrated
phase; this observation is in agreement with the earlier observa-
tions that cholesterol-based dimers having 4,40-disubstituted
phenylbenzoate core stabilize frustrated phases.28,37
Fig. 6. The layer spacing (d1) as a function of temperature obtained in the TGBC
for the nonsymmetric dimers BD-4,9 (blue-trace) and BD-5,11 (red-trace).
*
phase
a characteristic feature of dimeric molecules and is known to
stemm from the two individual mesogenic entities28 interlinked via
a flexible spacer to form the dimer. The diffuse reflection at wide
angles spacing (d3) corresponds to the inter-molecular separation
within the smectic layer arising due to the liquid-like positional
correlation within the smectic layer.
Table 2 gives the spacings corresponding to the low-angle and
wide-angle reflections as well as the ratio d1/l, where l signifies the
estimated molecular length (in all-trans from) derived from
3. Summary
Twelve new lengthy dimers belonging to two different series
have been synthesized and their phase transitional behaviour has
been evaluated by several complementary studies. They are made
by covalently joining cholesterol and three-ring mesogenic entities
through an
u-oxyalkanoyloxy spacer. They have been especially
designed and realized to explore the possibility of stabilizing
frustrated phase(s). The lengths of the central flexible spacers as
well as those of the n-alkoxy chains attached to terminus of
three-ring core have been varied to understand how chemical
structure influences the occurrence of frustrated phase(s). In par-
ticular, both odd-parity (5-oxypentanoyloxy) and even-parity (6-
oxyhexanoyloxy) spacers have been employed to covalently join
cholesterol and three-ring entities; n-alkoxy tails such as n-octy-
loxy to n-dodecyloxy and n-hexadecyloxy chains were used as
terminal substituents. The dimeric molecules with even-parity
Table 2
ꢀ
The all-trans molecular length (l/A) of dimers, the measured spacings of the low-
angle and wide-angle reflections of TGBC phase of BD-4,9 and BD-5,11 and d1/l ratio
*
Dimer (l/A)
BD-4,9 (42)
Temperature/ꢀC
d1/A
d2/A
d3/A
d1/l
ꢀ
ꢀ
ꢀ
ꢀ
150
130
120
180
170
160
140
120
39.66
39.21
38.72
42.72
41.67
40.96
39.95
39.35
19.88
19.49
19.41
21.43
20.93
20.51
20.05
19.83
5.31
5.31
5.31
4.97
4.97
4.97
4.97
4.97
0.94
0.93
0.92
0.77
0.75
0.74
0.72
0.71
spacer show enantiotropic N
counterparts comprising odd-parity spacer display BP additionally.
As expected, both the series of dimers show thermodynamically
*
and TGBC phases whereas their
*
BD-5,11 (55.4)
stable TGBC
*
phase over an exceedingly wide thermal range. This is
profoundly interesting and noteworthy given the complex and

U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
4751
highly frustrated nature of the TGBC
*
phase. We attribute this be-
equipped with a magnetic stirring bar, reflux condenser and argon
inlet was charged with cholesteryl
-(40-hydroxybiphenyl-4-oxy)
haviour to the combined effect of extended geometry (conforma-
tion), strong chirality and the enantiomeric excess of the molecules.
Although there is a striking similarity between the two series of
u
alkanoate (2-4/2-5) (0.3 mmol, 1 equiv), 4-(n-alkoxy)benzoic acid
(3-8/3-9/3-10/3-11/3-12/3-16) (0.33 mmol, 1.1 equiv), dichloro-
methane (25 ml), DCC (0.74 g, 0.36 mmol, 1.2 equiv) and DMAP
(catalytic amount). The flask was flushed with argon and the re-
action mixture was stirred at 40 ꢀC for 24 h. The resulting reaction
mixture was cooled, diluted with 10 ml of chloroform and stirred at
room temperature for 2 h. The urea separated from the reaction was
removed by filtration through Celite bed and the filtrate was
evaporated to dryness in vacuo. The off-white residue obtained was
purified by column chromatography on silica gel (100e200 mesh).
Elution with a mixture of dichloromethane/hexanes (1:3) afforded
the product. It was further purified by repeated recrystallizations
from a mixture of dichloromethane/hexanes (1:2) to obtain pure
compound in 67e82% yield.
compounds in the context of stabilizing TGBC phase, several sig-
*
nificant differences in their transitional behaviour were also ob-
served. For example, the dimers with odd-parity spacer, unlike
even-members, show another frustrated phase namely, the BP
phase. The clearing transition temperatures and the associated
enthalpies alternate where the odd-members exhibit lower values
when compared to those of even-members. These results clearly
demonstrate that the geometry (rod-like and bent-conformation)
and the thermal behaviour of dimers are greatly influenced by the
spacer parity.
Thus, the dimers reported in this work constitute new examples
of rarely encountered strongly chiral, optically pure dimers show-
ing the TGBC phase over a notable thermal width. We believe that
*
the molecular design approach adopted in this work facilitates the
efforts of realizing chiral mesogens capable of stabilizing frustrated
phase(s) with sufficiently wide thermal range.
4.3.1.1. BD-4,8: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(octyloxy)benzoate. Yield: 81%; a bright yellow solid. Found:
C, 79.5; H, 9.0; C59H82O6 requires C, 79.87; H, 9.32; IR (KBr Pellet):
nmax in cmꢁ1 2933, 2868, 1730, 1605, 1469 and 1379; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.4 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.4 Hz, 2H, Ar), 6.98 (d,
J¼6 Hz, 2H, Ar), 6.96 (d, J¼6 Hz, 2H, Ar), 5.38 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.67 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.03 (t, J¼4.4 Hz, 2H, 1ꢂOCH2), 2.40e1.08 (m, 49H, 6ꢂCH, 20ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.88 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
4. Experimental
4.1. Materials
The essential starting chemicals such as cholesterol, 6-
bromohexanioc acid, 5-bromovaleric acid, 4,4-dihydroxybiphenyl
and 1-bromoalkanes procured from Aldrich were used as re-
ceived. Deuterated chloroform (CDCl3) obtained from same com-
pany was used to record NMR of the samples. The reagent grade
solvents (DMF and dichloromethane) purchased were distilled over
appropriate drying agents. Thin layer chromatography (TLC) was
performed on aluminium sheets pre-coated with silica gel (Merck,
Kieselge 60, F254). The target compounds and some of the in-
termediates were purified by column chromatographic technique
using either silica gel (100e200 mesh) as stationary phase. The
target dimeric molecules were further purified by repeated re-
crystallizations from a mixture of two solvents until the constant
clearing temperatures were obtained.
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.84, 165.03, 163.55,
158.55, 150.04, 139.66, 138.49, 132.98, 132.28, 128.11, 127.67, 122.64,
121.98,121.58,114.81,114.30, 73.91, 68.34, 67.49, 56.69, 56.15, 50.03,
42.32, 39.74, 39.52, 38.16, 37.00, 36.60, 36.19, 35.79, 34.30, 29.32,
29.21, 29.10, 28.68, 28.22, 28.01, 27.82, 25.98, 24.28, 23.83, 22.80,
22.64, 22.55, 21.74, 21.03, 19.31, 18.71, 14.08 and 11.85.
4.3.1.2. BD-4,9: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(nonyloxy)benzoate. Yield: 80%; a bright yellow solid. Found:
C, 80.0; H, 9.2; C60H84O6 requires C, 79.96; H, 9.39; IR (KBr Pellet):
nmax in cmꢁ1 2942, 2868, 1730, 1604, 1501, 1469 and 1380; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.4 Hz, 2H, Ar), 7.58 (d, J¼8 Hz, 2H, Ar),
7.51 (d, J¼8.4 Hz, 2H, Ar), 7.25 (d, J¼8.4 Hz, 2H, Ar), 6.98 (d, J¼6.8 Hz,
2H, Ar), 6.96 (d, J¼6.8 Hz, 2H, Ar), 5.37 (br d, J¼4.4 Hz, 1H,
1ꢂolefinic), 4.64 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.4 Hz, 2H, 1ꢂOCH2),
4.04 (t, J¼6.8 Hz, 2H, 1ꢂOCH2), 2.38e1.08 (m, 51H, 6ꢂCH, 21ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
4.2. Instrumentation
The 1H and 13C (100 MHz) NMR spectra were recorded on
a Bruker AMX-400 (400 MHz) using CDCl3. Chemical shifts are re-
ported in parts per million (ppm) relative to tetramethylsilane
(TMS; SiMe4) as an internal standard. IR spectra were recorded
using Perkin Elmer Spectrum 1000 FT-IR spectrometer. Elemental
analyses were carried out by Eurovector model EA 3000 elemental
analyzer. Phase transition temperatures and textures of the meso-
phases were determined using an Olympus BX50 microscope
equipped with a digital camera and a programmable hot stage
(Mettler FP90). The melting transitions of non-mesogenic com-
pounds were recorded using the same setup. The enthalpies of the
transitions were determined from the thermograms recorded on
a differential scanning calorimeter (Perkin Elmer DSC7) at the op-
erating rate of 5 ꢀC/min. Powder XRD data were collected using the
PANalytical X’Pert PRO MP X-ray diffractometer consisting of a fo-
cussing elliptical mirror and a fast resolution detector (PIXCEL). The
energy-minimized space-filling molecular structures of dimers
were obtained using MM2 computations of the CS ChemDraw3D
(version 5) program.
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.87, 165.06, 163.59,
158.59, 150.08, 139.70, 138.52, 133.02, 132.32, 128.15, 127.71, 122.67,
122.01, 121.62, 114.85, 114.34, 73.95, 68.38, 67.53, 56.73, 56.19,
50.07, 42.36, 39.78, 39.56, 38.20, 37.04, 36.64, 36.23, 35.83, 34.34,
31.94, 31.90, 29.54, 29.44, 29.40, 29.28, 29.14, 28.72, 28.26, 28.04,
27.86, 26.02, 24.32, 23.87, 22.84, 22.70, 22.65, 22.59, 21.78, 21.07,
19.35, 18.75, 14.13 and 11.89.
4.3.1.3. BD-4,10: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(decyloxy)benzoate. Yield: 82%; a bright yellow solid. Found:
C, 79.9; H, 9.5; C61H86O6 requires C, 80.04; H, 9.47; IR (KBr Pellet):
nmax in cmꢁ1 2951, 2857, 1728, 1605, 1496, 1468 and 1381; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼6 Hz, 2H, Ar), 6.96 (d, J¼5.6 Hz, 2H, Ar), 5.37 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.67 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.03 (t, J¼4.4 Hz, 2H, 1ꢂOCH2), 2.40e1.04 (m, 53H, 6ꢂCH, 22ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.88 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
4.3. Synthesis and characterization data
4.3.1. General procedure for the preparation of BD-4,m and BD-5,m
series of dimers. An oven-dried, 100-mL, round-bottomed flask
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.82, 165.02, 163.55,

4752
U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
158.55, 150.04, 139.70, 138.48, 132.98, 132.28, 128.11, 127.67, 122.63,
121.97,121.58,114.81,114.30, 73.90, 68.34, 67.49, 56.69, 56.15, 50.04,
42.32, 39.74, 39.52, 38.16, 37.00, 36.60, 36.19, 35.79, 34.30, 31.88,
29.54, 29.35, 29.30, 29.10, 28.68, 28.22, 28.00, 27.82, 25.98, 24.28,
23.83, 22.80, 22.67, 22.55, 21.74, 21.03, 19.31, 18.71, 14.09 and 11.85.
Ar), 7.50 (d, J¼8.8 Hz, 2H, Ar), 7.24 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼7.6 Hz, 2H, Ar), 6.95 (d, J¼7.6 Hz, 2H, Ar), 5.37 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.62 (m, 1H, 1ꢂCHOCO), 4.05 (t, J¼6.4 Hz, 2H, 1ꢂOCH2),
4.0 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.34e1.04 (m, 51H, 6ꢂCH, 21ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.91 (d, J¼6.4 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼2 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
4.3.1.4. BD-4,11: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(undecyloxy)benzoate. Yield: 78%; a bright yellow solid.
Found: C, 79.8; H, 9.4; C62H88O6 requires C, 80.13; H, 9.54; IR (KBr
Pellet): nmax in cmꢁ1 2961, 2851,1729, 1605, 1496 and 1467; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼5.6 Hz, 2H, Ar), 6.96 (d, J¼5.6 Hz, 2H, Ar), 5.38 (br d, J¼4.4 Hz, 1H,
1ꢂolefinic), 4.67 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.03 (t, J¼4.4 Hz, 2H, 1ꢂOCH2), 2.38e1.08 (m, 55H, 6ꢂCH, 23ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.88 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 173.03, 165.03, 163.55,
158.64, 150.02, 139.68, 138.5, 132.91, 132.27, 128.10, 127.66, 122.61,
121.97, 121.58, 114.8, 114.3, 73.82, 68.34, 67.74, 56.69, 56.15, 50.04,
42.32, 39.74, 39.51, 38.16, 37.0, 36.60, 36.18, 35.78, 34.59, 31.90,
31.87, 31.79, 29.31, 29.20, 29.10, 28.96, 28.22, 28.0, 27.82, 25.98,
25.63, 24.80, 24.28, 23.83, 22.80, 22.64, 22.55, 21.03, 19.31, 18.71,
14.08 and 11.85.
4.3.1.8. BD-5,9: 40-((6-cholesteryloxy-6-oxohexyl)oxy)biphenyl-
4-yl 4-(nonyloxy)benzoate. Yield: 79%; a bright yellow solid. Found:
C, 80.3; H, 9.3; C61H86O6 requires C, 80.04; H, 9.47; IR (KBr Pellet):
nmax in cmꢁ1 2929, 2852, 1728, 1601, 1499 and 1376; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.4 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼7.2 Hz, 2H, Ar), 6.96 (d, J¼7.2 Hz, 2H, Ar), 5.37 (br d, J¼4.8 Hz, 1H,
1ꢂolefinic), 4.66 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.01 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.34e1.08 (m, 53H, 6ꢂCH, 22ꢂCH2,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.90 (d, J¼6 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.67 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.84, 165.02, 163.55,
158.55, 150.04, 139.66, 138.48, 132.98, 132.28, 128.11, 127.67, 122.64,
121.97, 121.58, 114.81, 114.30, 73.91, 68.34, 67.49, 56.69, 56.15, 50.03,
42.32, 39.74, 39.52, 38.16, 37.00, 36.60, 36.19, 35.79, 34.30, 31.90,
29.58, 29.55, 29.35, 29.10, 28.68, 28.22, 28.00, 27.82, 25.98, 24.28,
23.83, 22.80, 22.67, 22.55, 21.74, 21.03, 19.31, 18.71, 14.10 and 11.85.
4.3.1.5. BD-4,12: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(dodecyloxy)benzoate. Yield: 80%; a bright yellow solid.
Found: C, 80.1; H, 9.6; C63H90O6 requires C, 80.21; H, 9.62; IR (KBr
Pellet): nmax in cmꢁ1 2926, 2851, 1728, 1605, 1495 and 1380; 1H
NMR (400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz,
2H, Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼5.6 Hz, 2H, Ar), 6.96 (d, J¼5.6 Hz, 2H, Ar), 5.38 (br d, J¼3.6 Hz, 1H,
1ꢂolefinic), 4.67 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼5.6 Hz, 2H, 1ꢂOCH2),
4.02 (t, J¼4.4 Hz, 2H, 1ꢂOCH2), 2.38e1.06 (m, 57H, 6ꢂCH, 24ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼1.6 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 173.02, 165.03, 163.55,
158.64, 150.03, 139.69, 138.50, 132.91, 132.28, 128.10, 127.67, 122.61,
121.97, 121.59, 114.80,114.30, 73.81, 68.34, 67.74, 56.70, 56.15, 50.04,
42.32, 39.74, 39.52, 38.17, 37.00, 36.60, 36.19, 35.79, 34.59, 31.91,
31.86, 29.50, 29.36, 29.24, 29.10, 28.97, 28.22, 28.00, 27.82, 25.98,
25.63, 24.80, 24.28, 23.83, 22.80, 22.66, 22.55, 21.03, 19.31, 18.71,
14.09 and 11.85.
4.3.1.9. BD-5,10: 40-((6-cholesteryloxy-6-oxohexyl)oxy)biphenyl-
4-yl 4-(decyloxy)benzoate. Yield: 80%; a bright yellow solid. Found:
C, 80.0; H, 9.1; C62H88O6 requires C, 80.13; H, 9.54; IR (KBr Pellet):
nmax in cmꢁ1 2936, 2860, 1730, 1605, 1499 and 1378; 1H NMR
(400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.4 Hz, 2H, Ar), 6.98 (d,
J¼7.6 Hz, 2H, Ar), 6.96 (d, J¼7.2 Hz, 2H, Ar), 5.37 (br d, J¼5.2 Hz, 1H,
1ꢂolefinic), 4.66 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.02 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.34e1.04 (m, 55H, 6ꢂCH, 23ꢂCH2,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.90 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d, J¼2 Hz, 3H, 1ꢂCH3) and 0.67 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.82, 165.02, 163.55,
158.55, 150.04, 139.66, 138.48, 132.98, 132.28, 128.11, 127.67, 122.64,
121.98, 121.58, 114.81, 114.30, 73.90, 68.34, 67.49, 56.70, 56.15,
50.04, 42.32, 39.74, 39.52, 38.17, 37.00, 36.60, 36.19, 35.79, 34.30,
31.91, 29.63, 29.58, 29.55, 29.35, 29.10, 28.68, 28.22, 28.01, 27.83,
25.98, 24.28, 23.83, 22.80, 22.68, 22.55, 21.75, 21.03, 19.31, 18.72,
14.10 and 11.85.
4.3.1.6. BD-4,16: 40-((5-cholesteryloxy-5-oxopentyl)oxy)biphenyl-
4-yl 4-(hexadecyloxy)benzoate. Yield: 71%; a bright yellow solid.
Found: C, 80.6; H, 9.9; C67H98O6 requires C, 80.51; H, 9.88; IR (KBr
Pellet): nmax in cmꢁ1 2924, 2850, 1730, 1604, 1468 and 1379; 1H
NMR (400 MHz, CDCl3): 8.16 (d, J¼9.2 Hz, 2H, Ar), 7.58 (d, J¼8.4 Hz,
2H, Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.99 (d,
J¼5.6 Hz, 2H, Ar), 6.96 (d, J¼5.6 Hz, 2H, Ar), 5.37 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.67 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.03 (t, J¼4.4 Hz, 2H, 1ꢂOCH2), 2.40e1.08 (m, 65H, 6ꢂCH, 28ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.86 (d, J¼2 Hz, 3H, 1ꢂCH3) and 0.68 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 173.04, 165.04, 163.55,
158.65, 150.03, 139.69, 138.51, 132.92, 132.28, 128.11, 127.67, 122.62,
121.97, 121.59, 114.81, 114.31, 73.82, 68.34, 67.74, 56.70, 56.15, 50.04,
42.32, 39.74, 39.52, 38.17, 37.00, 36.60, 36.19, 35.79, 34.60, 33.96,
31.91, 31.88, 29.54, 29.35, 29.30, 29.10, 28.97, 28.22, 28.01, 27.83,
25.98, 25.64, 24.93, 24.80, 24.28, 23.83, 22.80, 22.67, 22.55, 21.03,
19.31, 18.71, 14.09 and 11.85.
4.3.1.10. BD-5,11: 40-((6-cholesteryloxy-6-oxohexyl)oxy)biphenyl-
4-yl 4-(undecyloxy)benzoate. Yield: 82%; a bright yellow solid.
Found: C, 80.4; H, 9.4; C63H90O6 requires C, 80.21; H, 9.62; IR (KBr
Pellet): nmax in cmꢁ1 2937, 2856,1731,1623,1498 and 1377; 1H NMR
(400 MHz, CDCl3): 8.17 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz, 2H,
Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.4 Hz, 2H, Ar), 6.99 (d,
J¼7.6 Hz, 2H, Ar), 6.96 (d, J¼7.6 Hz, 2H, Ar), 5.38 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.64 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.02 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.35e1.04 (m, 57H, 6ꢂCH, 24ꢂCH2,
1ꢂCH3), 1.02 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.89 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.87 (d, J¼2 Hz, 3H, 1ꢂCH3) and 0.67 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 172.83, 165.02, 163.55,
158.55, 150.04, 139.66, 138.48, 132.98, 132.27, 128.11, 127.67, 122.64,
121.97,121.59,114.81,114.30, 73.90, 68.34, 67.48, 56.69, 56.15, 50.03,
39.74, 39.52, 38.17, 37.00, 36.19, 35.79, 34.30, 31.92, 31.87, 29.69,
29.65, 29.58, 29.55, 29.36, 29.10, 28.68, 28.22, 28.00, 27.82, 25.98,
24.28, 23.83, 22.80, 22.55, 21.74, 19.31, 18.71, 14.13 and 11.85.
4.3.1.7. BD-5,8: 40-((6-cholesteryloxy-6-oxohexyl)oxy)biphenyl-
4-yl 4-(octyloxy)benzoate. Yield: 80%; a bright yellow solid. Found:
C, 80.2; H, 9.2; C60H84O6 requires C, 79.96; H, 9.39; IR (KBr Pellet):
nmax in cmꢁ1 2937, 2857, 1729, 1604, 1497 and 1376; 1H NMR
(400 MHz, CDCl3): 8.15 (d, J¼8.8 Hz, 2H, Ar), 7.57 (d, J¼8.8 Hz, 2H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 173.01,165.01,163.54,158.64,
150.02, 139.68, 138.49, 132.90, 132.27, 128.09, 127.66, 122.61, 121.96,
121.58, 114.80, 114.29, 73.80, 68.33, 67.73, 56.69, 56.14, 50.03, 42.31,

U.S. Hiremath / Tetrahedron 70 (2014) 4745e4753
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24.27, 23.83, 22.80, 22.67, 22.55, 21.03, 19.30, 18.71, 14.09 and 11.85.
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4.3.1.11. BD-5,12: 40-((6-cholesteryloxy-6-oxohexyl)oxy)biphenyl-
4-yl 4-(dodecyloxy)benzoate. Yield: 75%; a bright yellow solid.
Found: C, 79.9; H, 9.8; C64H92O6 requires C, 80.29; H, 9.69; IR (KBr
Pellet): nmax in cmꢁ1 2931, 2863, 1730, 1604, 1495 and 1378; 1H
NMR (400 MHz, CDCl3): 8.16 (d, J¼9.2 Hz, 2H, Ar), 7.58 (d, J¼8.8 Hz,
2H, Ar), 7.51 (d, J¼8.4 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼7.2 Hz, 2H, Ar), 6.96 (d, J¼7.2 Hz, 2H, Ar), 5.37 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.66 (m, 1H, 1ꢂCHOCO), 4.06 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.02 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.34e1.08 (m, 59H, 6ꢂCH, 25ꢂCH2,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d, J¼2 Hz, 3H, 1ꢂCH3) and 0.67 (s, 3H,
1ꢂCH3); 13C NMR (100 MHz, CDCl3):
d 173.02, 165.02, 163.54,
158.63, 150.02, 139.67, 138.49, 132.90, 132.27, 128.09, 127.65, 122.60,
121.96,121.57, 114.79,114.29, 73.81, 68.33, 67.73, 56.68, 56.14, 50.03,
42.31, 39.73, 39.51, 38.15, 36.99, 36.59, 36.18, 35.78, 34.58, 31.89,
31.86, 29.57, 29.54, 29.48, 29.33, 29.09, 28.95, 28.21, 27.99, 27.81,
25.97, 25.62, 24.79, 24.27, 23.82, 22.79, 22.67, 22.54, 21.02, 19.30,
18.70, 14.09 and 11.84.
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4.3.1.12. BD-5,16
:
40-((6-cholesteryloxy-6-oxohexyl)oxy)bi-
phenyl-4-yl 4-(hexadecyloxy)benzoate. Yield: 67%; a bright yellow
solid. Found: C, 81.0; H, 9.6; C68H100O6 requires C, 80.58; H, 9.94; IR
(KBr Pellet): nmax in cmꢁ1 2928, 2858, 1731, 1603, 1497 and 1379; 1H
NMR (400 MHz, CDCl3): 8.16 (d, J¼8.8 Hz, 2H, Ar), 7.58 (d, J¼8.4 Hz,
2H, Ar), 7.51 (d, J¼8.8 Hz, 2H, Ar), 7.25 (d, J¼8.8 Hz, 2H, Ar), 6.98 (d,
J¼7.2 Hz, 2H, Ar), 6.96 (d, J¼7.2 Hz, 2H, Ar), 5.37 (br d, J¼4 Hz, 1H,
1ꢂolefinic), 4.66 (m, 1H, 1ꢂCHOCO), 4.05 (t, J¼6.6 Hz, 2H, 1ꢂOCH2),
4.01 (t, J¼6.4 Hz, 2H, 1ꢂOCH2), 2.34e1.04 (m, 67H, 6ꢂCH, 29ꢂCH2,
1ꢂCH3), 1.01 (s, 3H, 1ꢂCH3), 0.92 (d, J¼6.8 Hz, 3H, 1ꢂCH3), 0.87 (d,
J¼1.6 Hz, 3H, 1ꢂCH3), 0.85 (d, J¼1.2 Hz, 3H, 1ꢂCH3) and 0.67 (s, 3H,
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d 173.02, 165.02, 163.55,
158.64, 150.02, 139.68, 138.50, 132.91, 132.27, 128.09, 127.66, 122.61,
121.97,121.58,114.80,114.30, 73.81, 68.33, 67.73, 56.69, 56.15, 50.04,
42.31, 39.74, 39.52, 38.16, 37.00, 36.60, 36.19, 35.79, 34.59, 31.91,
31.87, 29.69, 29.65, 29.58, 29.55, 29.35, 29.10, 28.96, 28.22, 28.00,
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Acknowledgements
The author expresses her sincere appreciation and gratitude to
Department of Science and Technology, Ministry of Science and
Technology, New Delhi, Govt. of India, for financial support through
WOS-A scheme (SR/WOS-A/CS-19/2010). She conveys her sincere
thanks to Dr. D.S. Shankar Rao for providing XRD data and helpful
discussions. She extends her gratefulness to Dr. Geetha G. Nair
(mentor of the project), Dr. S. Krishna Prasad, Prof. K.A. Suresh and
Dr. Praveer Asthana for their constant support and encouragement.
35. Hiremath, U. S.; Sonar, G. M.; Shankar Rao, D. S.; Yelamaggad, C. V. J. Mater.
Chem. 2011, 21, 4064e4067.
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