Synthesis and characterization of novel cholesterol based mesogenic compounds using 'click' chemistry

Article abstract of DOI:10.1039/b9nj00744j

An efficient route for the synthesis of hitherto unreported non-symmetric dimesogens consisting of a cholesteryl moiety and an aromatic mesogenic unit interconnected through a pentamethylene or decamethylene spacer by Cu(i)-catalyzed azide-alkyne cycloadd

Full text of DOI:10.1039/b9nj00744j

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www.rsc.org/njc | New Journal of Chemistry
Synthesis and characterization of novel cholesterol based mesogenic
compounds using ‘click’ chemistry
K. C. Majumdar,* Shovan Mondal and Randhir K. Sinha
Received (in Victoria, Australia) 10th December 2009, Accepted 2nd March 2010
First published as an Advance Article on the web 26th March 2010
DOI: 10.1039/b9nj00744j
An efficient route for the synthesis of hitherto unreported non-symmetric dimesogens consisting of
a cholesteryl moiety and an aromatic mesogenic unit interconnected through a pentamethylene or
decamethylene spacer by Cu(I)-catalyzed azide–alkyne cycloaddition ‘click’ chemistry has been
developed. The aromatic units consist of two phenyl rings linked to a triazole moiety. A new
trimesogen consisting two cholesteryl esters and an aromatic segment joined by pentamethylene
spacer has also been synthesized. The newly synthesized mesogens show N*, TGB and partially
bilayered SmC* (SmCd*) phases. The liquid crystalline phases were investigated with the help of
polarizing optical microscopy (POM), differential scanning calorimetry (DSC) and powder X-ray
diffraction studies. DFT study was also used to locate the orientation of the dipole at the centre
position i.e. at ester linkage. All the compounds were characterized from their elemental analyses
and spectral data.
Dimesogenic compounds (twins) consisting of two different
mesogenic units interlinked through a central spacer are a
relatively new class of liquid crystalline (LC) compounds that
still require more intensive research in order to establish the
relationship between their structure and LC properties.1–9
Among different LC phases, the SmC phase can be obtained
only by cooling three types of liquid crystalline phases—the
nematic, SmA and SmD phases. Therefore, it can only inherit
different textures from the aforesaid phases and should exhibit
the schlieren texture. The texture obtained from the SmA
phase is either schlieren or focal conic fan. Recently we have
reported some unique LC properties of several different types
of dimesogenic compounds and some of them showing different
smectic phases.10 Nonsymmetric dimers derived from naturally
occurring cholesterol represent an exemplary and emerging
class of chiral liquid crystals. These contain a cholesteryl
moiety and another aromatic mesogen such as Schiff’s base,9a
azobenzene,9b stilbene,11 aromatic ester,12 or tolane unit.9c
Here we report a unique class of cholesterol dimers where
the aromatic mesogens are derived from Cu(I)-catalyzed
azide–alkyne cycloaddition ‘click’ chemistry.
90–95% yields by stirring azides 6a,b and alkynes 7a–c in the
presence of a catalytic amount of CuI in DMSO at 60 1C
for 2 h (Scheme 1). The trimesogen 11 was obtained by the
condensation of the amine 9 with aldehyde 10. The amine 9
was in turn obtained by the reduction of dimesogen 8d with
SnCl2ꢁ2H2O in refluxing EtOAc for 2 h (Scheme 2).
The transition temperatures and the associated enthalpy
values obtained from DSC for compounds 8a–d and 11 are
summarized in Table 1. The TGB transitions were not detected
in DSC thermogram as their enthalpy change is very low.
Textural analysis was performed with the help of a polarizing
optical microscope (POM). The dimesogens 8a–d show the
phase sequence Cr–SmC*–TGB–N*–I. On cooling the isotropic
phase of the compound 8a, a cholesteric phase with the
characteristic fingerprint texture and oily streak texture was
observed after shearing the sample on a glass plate. On further
cooling, a TGB phase appeared over a very short temperature
interval of about B0.5 1C before transforming into SmC*
phase. The SmC* phase appears as a typical fan-shaped
texture14,15 when placed in a thin cell with a cell gap of
d = 5 ꢂ 0.2 mm under homogeneous planar boundary
conditions. On cooling the isotropic liquid, the SmC* phase
forms a fan-shaped texture which is more reminiscent of a
SmC* phase than of a SmA* phase (Fig. 1a). Fig. 1b illustrates
the transition from TGB to SmC* phase as the temperature is
lowered from cholesteric phase. The other dimesogenic
compounds 8b–d show the same phase sequence.
The new dimesogens 8a–d and trimesogen 11 were
synthesized starting from azides 6a,b. These key intermediates
were obtained by diazotization of the amines 5a,b in tetra-
fluoroboric acid (40% solution in water) with dropwise addi-
tion of sodium nitrite (solution in water) at 0 to ꢀ5 1C and
stirring for 1 h. Sodium azide was added to the methanolic
solution of the diazotized salt and stirred for 1 h at rt to give
azido derivatives 6a,b in 70–75% yields. The compounds 5a,b
were prepared by the reduction of nitro derivatives 4a,b using
SnCl2ꢁ2H2O and refluxing in EtOAc for 5–6 h. The nitro
derivatives 4a,b were in turn prepared using earlier published
standard protocol.13 The dimesogens 8a–d were obtained in
The trimesogen 11, with two cholesteryl ester units was
designed and synthesized to study the stability of the SmC*
phase. Optical observation of the trimesogen 11 shows a
cholesteric phase in association with a TGB phase.16 This
observation is in complete agreement with the available data in
the literature17 which indicates that the TGB phase is stabilized in
compounds which are highly chiral. The specific rotation
measurements of the di- and trimesogens were carried out to
exhibit the following results: [a]D = ꢀ20.578 (c 0.90 in CHCl3)
Department of Chemistry, Kalyani University, Kalyani-741235,
West Bengal, India. E-mail: kcm_ku@yahoo.co.in
ꢃc
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Scheme 2 Synthesis of trimesogen 11. Reagents and conditions:
(i) SnCl2ꢁ2H2O, EtOAc, reflux, 2 h; (ii) AcOH, EtOH, reflux, 12 h.
From the powder X-ray diffraction pattern it is difficult to
distinguish the SmC phase, where the director is tilted with
respect to layer normal from that of the SmA phase. The only
difference is that the layer spacing would be reduced due to the
tilt in the SmC phase. From the molecular modelling of the
compound 8a, the molecular length (L) was calculated as
33.05 A. The approximate d/L ratio is 1.4 and hence the
smectic C phase appeared as partially bilayer in nature and
designated as SmCd. The schematic representation is shown in
Fig. 4. The non-cooperative tilt angle yt can be deduced from
molecular length L and d-spacing as the molecules are
arranged in a partially bilayered fashion within d-spacing and
found to be B451 (yt = 44.11). We know that if SmC undergoes
a transition directly to the nematic phase, yt is generally found
to be temperature independent and usually about 451.18
The position of the permanent dipole is important in
determining the contribution of the anisotropic part of the
induction forces. van der Meer and Vertogen19 concluded that
an acentral dipole, particularly an acentral transverse dipole is
very important in the thermal stability of the SmC* phase. It is
suggested that there is an optimal location for this dipole in the
molecule, i.e., the alignment of the induced and permanent
dipoles creates the force for tilting the resistance to tilt. This is
being contributed to by a combination of van der Waal’s forces
and hard core repulsions. To show the stability of SmC* phase
several models were considered where the electrostatic or steric
interactions were taken into account.20,21 Besides these models
Goossens22 and other authors23,24 developed theoretical models
as molecular tilt is an intrinsic property of any layered
quadrupolar structure. Strong quadrupolar moments due
to acentral transverse dipoles (‘outboard’ dipoles) play an
important role in the stabilization of the SmC* phase.
Scheme 1 Synthesis of dimesogens 8a–d. Reagents and conditions:
(i) THF, pyridine, rt, 12 h; (ii) p-nitrophenol, acetone, reflux, 12 h;
(iii) SnCl2ꢁ2H2O, EtOAc, reflux, 5–6 h; (iv) HBF4, NaNO2, NaN3, 1 h;
(v) CuI, DMSO, 60 1C, 2 h.
for 8a, ꢀ20.92 (c 1.00 in CHCl3) for 8b, ꢀ15.0 (c 0.40 in
CHCl3) for 8c, ꢀ16.44 (c 1.08 in CHCl3) for 8d and ꢀ21.959
(c 0.98 in CHCl3) for trimesogen 11. The appearance of
SmC* phase in trimesogen 11 is somehow different from the
dimesogens and equidistant stripes were observed in the focal
conic fans. The appearance of equidistance stripes in the focal
conic fans is one of the important signatures of SmC* phase.
Fig. 2 illustrates the polarizing optical micrograph (POM) of
dimesogens 8b–d and trimesogen 11.
The X-ray diffraction pattern of the compound 8a shows
two sharp peaks at y = 0.95861 (d0 = 46.07 A) and another
reflection at y = 2.4961 (d = 17.7 A). The second peak
corresponding to d spacing of 17.7 A may be due to the
second order transition from nematic to SmC as the intensity
is very weak compared to the first peak at low angle region.
The fairly sharp diffuse scattering at wide angle lamellar
distance of 4.5 A corresponds to an in-layer short-range
liquid-like order (Fig. 3).
ꢃc
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Table 1 Phase transition temperature/1C (DH/kJ mol–1 a
)
Compound
Heating
Cooling
8a
8b
8c
8d
11
Cr 178.2(45.2) SmC* 182.3(30.1) N* 208.9(3.7) I
Cr 130.5(53.4) SmC* 135.8(0.5) N* 153.1(1.4) I
Cr 90.5(15.6) SmC* 134.7(5.2) N* 156.1(0.3) I
Cr 115.1(2.1) SmC* 124.5(32.3) N* 134.9(1.4) I
Cr 162.7(37.2) SmC* 180.3(26.2) N* 238.1(3.3) I
I 205.5(3.5) N* 175.3(19.1) SmC* 169.3(21.5) Cr
I 152.4(1.3) N* 134.9(0.7) SmC* 115.9(50.9) Cr
I 146.5(2.3) N* 129.5(5.9) SmC* 126.4(9.4) 88.2(19.1) Cr
I 134.4(1.5) LC phase
I 228.9(4.9) N* 173.7 (13.1) SmC* 159.9(20.7) Cr
a
TGB transition temperatures were not detected in DSC thermogram as their enthalpy change is very low.
Fig. 1 POM micrograph of 8a.
Fig. 3 X-Ray diffraction pattern of compound 8a at 175 1C.
Fig. 4 Schematic representation of partially bilayer SmC phase
Fig. 2 Polarizing micrograph of SmC* phases of compounds 8b–d
and 11 at different temperatures.
deduced from powder X-ray pattern.
The direction of the dipole of the compound 8a was calculated
by Density Functional Theory (DFT), which may determine
the presence of dipolar interaction within the molecules. All
calculations have been performed by the Chem3D (version
10)25 with GAUSSIAN 03 Interface.26 We have computed the
DFT (B3LYP) level of theory using the basis set 6-31G to obtain
the dipole moment and dipolar orientation of molecules. The
dipole moment of 8a has been calculated as 8.9106 D
(X = ꢀ7.4802, Y = ꢀ4.2888, Z = 2.2478). Geometry
optimization of the compound 8a was performed by addition
of atoms step by step. The optimized structure suggests that the
molecule is completely rod in shape (Fig. 5).
X-axis, and if we suppose Z-axis as a molecular axis then the
direction of maxima of the dipole is along the negative of X-axis
which is centrally transverse and this is a favorable condition for
the appearance of SmC phase, in which a permanent dipole in
one molecule induces a dipole in a neighboring molecule. The
alignment of the induced and the permanent dipoles that creates
the force to tilt and the associated tilting is being contributed by a
combination of van der Waal’s forces and hard core repulsions,
where the molecules are allowed to rotate freely and flexible
enough to make allowances for changes in molecular structure.
Fig. 6 illustrates the optimized structure of the compound 8a
and the geometry optimization was done at the central part (at
oxygen atom of ester linkage) of the molecule. To find out the
dipole moment and the direction of dipole at central part we
carried out a DFT calculation and found it to be 8.0968 D
(X = ꢀ6.8656, Y = ꢀ3.9197, Z = 1.7487). Here again we
First optimization was conducted by MM2 method followed
by AM1 method and finally DFT was performed as stated
earlier. From the calculated value of the dipole moment it is
found that the maxima of the dipole is in the direction of negative
ꢃc
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containing cholesteryl moiety by Cu(I)-catalyzed azide–alkyne
cycloaddition ‘click’ chemistry. To the best of our knowledge
so far, there is only one report of cholesterol based liquid
crystal using ‘click’ chemistry.28 The newly synthesized
mesogenic compounds show SmC* phase along with TGB
and cholesteric phase. The mesophases were characterized
with the help of polarizing optical microscopy, DSC, powder
X-ray diffraction pattern and some computational study.
From DFT study of the central part of molecule (at oxygen
atom), it has been shown that the outboard transverse dipole
has a crucial role in stabilizing the SmC* phase. The branched
chain of the rigid cholesteryl part also plays an important role
in stabilizing the SmC* phase.
Experimental
General
All the chemicals were procured from either Sigma Aldrich
Chemicals Pvt. Ltd. or Spectrochem, India. Silica gel
(60–120 mesh) was used for chromatographic separation.
Silica gel G [E-Merck (India)] was used for TLC. Petroleum
ether refers to the fraction boiling between 60 1C and 80 1C. IR
spectra were recorded on a Perkin-Elmer L 120-000A spectro-
meter (nmax in cmꢀ1) on KBr disks. 1H NMR (400 MHz)
spectra were recorded on a Bruker DPX-500 spectrometer in
CDCl3 (chemical shift in d) with TMS as internal standard.
13C-NMR spectra were determined for solutions in CDCl3 on
a Bruker DPX-75. CHN was recorded on a Perkin Elmer
2400 series II CHN analyzer. The liquid crystalline properties
were established by thermal microscopy (Nikon polarizing
microscope LV100POL attached with Instec hot and cold
stage HCS302, with STC200 temperature controller configured
for HCS302) and the phase transitions were confirmed by
differential scanning calorimetry (Perkin-Elmer DSC Pyris1
system). X-Ray diffraction was carried out on a Philips
powder diffractometer (PAN analytical model no. PW 3015)
operating on X’pert pro software, equipped with a temperature
controller permitting low as well as high temperature operation
as needed (with CuKa radiation of l = 1.5418 A).
Fig. 5 Optimized geometry of 8a from DFT study. Direction of
central dipole is clearly visible along negative of the X-axis.
Fig. 6 Central part optimized geometry of compound 8a and direction
of dipole is outboard transverse (negative direction of X-axis).
General procedure for the synthesis of azido derivatives 6a,b
To a magnetically well-stirred mixture of the amine 5a
(500 mg, 0.845 mmol) in tetrafluoroboric acid (40% solution
in water, 5 mL), a solution of NaNO2 (116.68 mg, 1.69 mmol)
in water (2 mL) was added drop wise at 0 to ꢀ5 1C and stirring
was continued for 1 h. The solid diazonium salt was filtered
and dried. The solid salt was then taken in dry MeOH (10 mL)
and sodium azide (109.9 mg, 1.69 mmol) was added all at once
at ice cool condition. After stirring for 1 h at rt, the solvent was
removed in vacuo and the residue was extracted with Et2O
(3 ꢄ 30 mL) and the ether extract was washed with water (20 mL),
dried (Na2SO4) and concentrated to afford the azido derivative 6a
as white solid. The other amine compound 5b (500 mg,
0.755 mmol) was similarly treated to afford product 6b.
observed that the direction of the dipole moment is outboard
transverse i.e. along the negative direction of the X-axis with
slight decrease in total dipole moment of the whole molecule.
Central location of dipole may be responsible for determining
the direction of dipole of the molecule itself.
It is a well known fact that the terminal branched chain can
often stabilize the existence of SmC phase. However, in our
case there is no terminal branched chain at one end but if we
consider the terminal branched chain of the cholesteryl moiety
(2,6-dimethylheptane) there is a chance of exhibiting SmC*
phase. As discussed above we have not observed schlieren
texture of SmC* phase on the cooling cycle, only the broken
focal conic fans were observed27 and that is quite possible
where only broken focal conic fans appear.
Compound 6a. Yield (391 mg) 75%; mp 88–90 1C. IR (KBr):
2948, 2109, 1726, 1505, 1246 cmꢀ1 1H NMR (400 MHz,
;
In conclusion, we have developed a new and efficient route
for the synthesis of new di- and trimesogenic compounds
CDCl3): dH = 0.66–2.32 (m, 51H), 3.92 (t, J = 6.1 Hz,
2H), 4.59–4.62 (m, 1H), 5.36 (d, J = 4.0 Hz, 1H), 6.85
ꢃc
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(d, J = 8.5 Hz, 2H), 6.92 (d, J = 8.5 Hz, 2H). 13C NMR
(100 MHz, CDCl3): dC = 21.2, 22.7, 23.0, 24.0, 24.4, 24.9,
25.7, 28.0, 28.1, 28.4, 29.1, 32.0, 32.1, 34.7, 35.9, 36.3, 36.7,
37.1, 38.3, 39.7, 39.9, 42.4, 50.2, 56.3, 56.8, 68.2, 74.0, 115.9,
120.1, 122.8, 132.3, 139.8, 156.6, 173.1. Anal. calcd. for
C39H59N3O3: C, 75.81; H, 9.62; N, 6.80%. Found: C, 75.94;
H, 9.69; N, 6.72%.
[a]D ꢀ20.92 (c 1.00 in CHCl3). Anal. calcd. for C52H75N3O3:
C, 79.04; H, 9.57; N, 5.32%. Found: C, 79.24; H, 9.65;
N, 5.38%.
Compound 8c. Yield (230 mg) 90%; IR (KBr): 2933, 1734,
1517, 1250 cmꢀ1 1H NMR (400 MHz, CDCl3): dH
; =
0.66–2.28 (m, 61H), 4.00 (t, J = 6.1 Hz, 2H), 4.59–4.62
(m, 1H), 5.06 (s, 2H), 5.36 (d, J = 4.0 Hz, 1H), 7.02 (d,
J = 7.2 Hz, 2H), 7.09 (d, J = 7.0 Hz, 4H), 7.39–7.42 (m, 6H),
7.92 (d, J = 8.7 Hz, 1H). 13C NMR (100 MHz, CDCl3):
dC = 12.3, 19.1, 19.7, 23.0, 23.2, 24.2, 25.5, 26.4, 28.4, 28.6,
29.5, 29.7, 29.9, 32.3, 32.4, 35.1, 36.2, 37.4, 38.6, 39.9, 40.1,
42.7, 50.4, 56.6, 57.1, 68.9, 70.5, 74.1, 115.3, 115.4, 115.7,
123.0, 127.9, 128.2, 128.5, 129.0, 129.4, 140.1, 173.7. [a]D
ꢀ15.0 (c 0.40 in CHCl3). Anal. calcd. for C59H81N3O4: C,
79.06; H, 9.11; N, 4.69%. Found: C, 79.18; H, 9.18; N, 4.57%.
Compound 6b. Yield (364 mg) 70%; mp 70–72 1C. IR (KBr):
2919, 2113, 1736, 1504, 1237 cmꢀ1 1H NMR (400 MHz,
;
CDCl3): dH = 0.66–2.30 (m, 61H), 3.91 (t, J = 6.6 Hz, 2H),
4.59–4.62 (m, 1H), 5.36 (d, J = 3.6 Hz, 1H), 6.86 (d, J = 9.0 Hz,
2H), 6.92 (d, J = 8.9 Hz, 2H). 13C NMR (100 MHz,
CDCl3): dC = 25.2, 26.0, 26.1, 28.0, 28.1, 28.4, 29.1, 29.2,
29.3, 29.4, 29.5, 29.5, 29.6, 29.6, 32.0, 32.1, 34.8, 35.9, 36.3,
36.7, 37.2, 38.3, 39.7, 39.9, 42.5, 50.2, 56.3, 56.8, 68.6, 69.2,
73.9, 110.9, 115.9, 120.1, 121.7, 122.0, 122.7, 132.3, 139.9,
156.7, 173.4. Anal. calcd. for C44H69N3O3: C, 76.81; H, 10.11;
N, 6.11%. Found: C, 76.68; H, 10.21; N, 6.17%.
Compound 8d. Yield (203 mg) 93%; IR (KBr): 2945, 1712,
1517 cmꢀ1 1H NMR (400 MHz, CDCl3): dH = 0.66–2.95
;
(m, 51H), 4.00 (t, J = 6.1 Hz, 2H), 4.59–4.62 (m, 1H), 5.36
(d, J = 4.0 Hz, 1H), 7.02 (d, J = 8.4 Hz, 2H), 7.64 (d, J = 6.9 Hz,
2H), 7.79 (t, J = 6.9 Hz, 2H), 7.97 (d, J = 8.4 Hz, 2H), 8.21 (s,
1H). 13C NMR (100 MHz, CDCl3): dC = 21.2, 22.7, 22.9,
24.0, 24.4, 24.8, 25.7, 28.0, 28.1, 28.3, 29.0, 32.0, 32.0, 33.0,
33.2, 34.7, 35.9, 36.3, 36.7, 37.1, 38.3, 39.6, 39.8, 42.4, 50.2,
56.3, 56.8, 68.3, 115.5, 119.2, 122.4, 122.8, 123.9, 125.8, 129.0,
130.1, 135.0, 139.2, 139.8, 146.3, 148.7, 159.8, 173.1. [a]D
ꢀ16.44 (c 1.08 in CHCl3). Anal. calcd. for C47H64N4O5: C,
73.79; H, 8.43; N, 7.32%. Found: C, 73.98; H, 8.48; N, 7.27%.
General procedure for the synthesis of dimesogenic compounds
8a–d by ‘click’ chemistry
To a well-stirred solution of the azides 6a,b (0.285 mmol) and
alkynes 7a–c (0.428 mmol) in DMSO (10 mL), catalytic
amount (10 mol%) of CuI (I) was added and stirred for 2 h
at 60 1C. After cooling the reaction mixture was poured into
water (100 mL) and extracted with CHCl3 (3 ꢄ 30 mL). The
organic layer was washed with water (20 mL) and brine
(10 mL), dried (Na2SO4) and concentrated under vacuum.
The crude product was purified by column chromatography
over silica gel using (1 : 1) ethyl acetate : petroleum ether as
eluent, which afforded the dimesogenic compounds 8a–d in
90–95% yields.
Synthesis of amine derivative 9
To a solution of the dimesogenic compound 8d (250 mg,
0.327 mmol) in EtOAc (10 mL), SnCl2ꢁ2H2O (369 mg,
1.634 mmol) was added and refluxed for 2 h. The reaction
mixture was cooled and portion wise poured into saturated
bicarbonate solution. The mixture was then filtered through
Celite bed and repeatedly washed with ethyl acetate. The
organic layer was dried (Na2SO4) and evaporated. The crude
product was purified by column chromatography over silica
gel using 1 : 1 ethyl acetate : petroleum ether as eluent.
Compound 8a. Yield (195 mg) 95%; IR (KBr): 2939, 1731,
1524, 1260 cmꢀ1 1H NMR (400 MHz, CDCl3): dH
; =
0.66–2.32 (m, 51H), 4.00 (t, J = 6.1 Hz, 2H), 4.59–4.62
(m, 1H), 5.36 (d, J = 4.0 Hz, 1H), 7.00 (d, J = 8.4 Hz,
2H), 7.35 (d, J = 6.9 Hz, 1H), 7.44 (t, J = 6.9 Hz, 2H), 7.65
(d, J = 8.4 Hz, 2H), 7.89 (d, J = 7.2 Hz, 2H), 8.09 (s, 1H). 13
C
NMR (100 MHz, CDCl3): dC = 18.7, 19.3, 21.0, 22.5, 22.8,
23.8, 24.2, 24.7, 25.5, 27.8, 28.0, 28.2, 28.8, 31.8, 31.9, 34.5,
35.7, 36.1, 36.5, 36.9, 38.1, 39.5, 39.7, 42.2, 49.9, 56.1, 56.6,
68.0, 73.8, 115.2, 117.8, 122.1, 122.6, 125.8, 128.3, 128.9, 130.3,
139.6, 148.1, 159.3, 173. [a]D ꢀ20.578 (c 0.90 in CHCl3).
HRMS: calculated for C47H65N3O3: 720.5099 [M + H].
Found: 720.5078 [M + H]. Anal. calcd. for C47H65N3O3: C,
78.40; H, 9.10; N, 5.84%. Found: C, 78.54; H, 8.99; N, 5.95%.
Compound 9. Yield (231 mg) 96%; IR (KBr): 3441, 3362,
1
2952, 1717, 1520, 1261 cmꢀ1; H NMR (400 MHz, CDCl3):
d
H = 0.66–2.60 (m, 51H), 3.74 (s, 2H), 4.00 (t, J = 6.1 Hz, 2H),
4.59–4.62 (m, 1H), 5.36 (d, J = 4.0 Hz, 1H), 6.73 (d, J = 7.9 Hz,
2H), 6.99 (d, J = 8.3 Hz, 2H), 7.51 (d, J = 7.5 Hz, 2H),
7.63 (t, J = 7.6 Hz, 2H), 7.96 (s, 1H). 13C NMR (125 MHz,
CDCl3): dC = 12.3, 14.4, 19.1, 19.7, 23.0, 23.2, 24.2, 25.2, 26.0,
28.2, 28.4, 28.6, 29.3, 31.4, 31.5, 32.3, 32.4, 35.0, 36.2, 37.4,
38.6, 39.9, 42.7, 50.4, 56.5, 57.1, 68.5, 74.3, 115.7, 115.8, 116.6,
117.0, 121.9, 122.5, 123.1, 125.0, 127.6, 128.1, 131.0, 140.1,
144.0, 149.1, 159.6, 173.4. Anal. calcd. for C47H66N4O3: C,
76.80; H, 9.05; N, 7.62%. Found: C, 76.71; H, 9.15; N, 7.67%.
Compound 8b. Yield (212 mg) 94%; IR (KBr): 2934, 1733,
1521, 1171 cmꢀ1 1H NMR (400 MHz, CDCl3): dH
; =
0.66–2.31 (m, 61H), 4.00 (t, J = 6.1 Hz, 2H), 4.59–4.62
(m, 1H), 5.36 (d, J = 4.0 Hz, 1H), 7.01 (d, J = 8.6 Hz, 2H),
7.35 (t, J = 7.0 Hz, 1H), 7.44 (t, J = 7.4 Hz, 2H), 7.65 (d,
J = 8.6 Hz, 2H), 7.89 (d, J = 7.5 Hz, 2H), 8.09 (s, 1H). 13C NMR
(100 MHz, CDCl3): dC = 18.7, 19.3, 21.0, 22.5, 22.8, 23.8,
24.2, 25.0, 26.0, 27.8, 28.0, 28.2, 29.0, 29.1, 29.2, 29.3, 29.3,
29.4, 31.8, 31.9, 34.7, 35.8, 36.1, 36.6, 37.0, 38.1, 39.5, 39.7,
42.3, 50.0, 56.1, 56.6, 68.4, 73.7, 115.3, 117.8, 122.1, 122.6,
125.8, 128.3, 128.8, 130.3, 130.4, 139.7, 148.1, 159.4, 173.3.
Synthesis of trimesogenic compound 11
A mixture of the compound 9 (138 mg, 0.187 mmol) and
cholesteryl benzoate 10 (114 mg, 0.187 mmol) was refluxed in
absolute ethanol (15 mL) in the presence of a catalytic amount
of glacial acetic acid for 12 h. The trimesogen 11 was obtained
ꢃc
This journal is The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2010 New J. Chem., 2010, 34, 1255–1260 | 1259

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as a precipitate from the hot reaction mixture. It was repeatedly
washed with hot ethanol and dried under vacuum.
Liq. Cryst., 2002, 29, 755–763; (d) J.-W. Lee, Y. Park, J.-I. Jin,
M. F. Achard and F. Hardouin, J. Mater. Chem., 2003, 13,
1367–1372; (e) K.-N. Kim, E.-D. Do, Y.-W. Kwon and J.-I. Jin,
Liq. Cryst., 2005, 32, 229–237.
Compound 11. Yield (243 mg) 98%; IR (KBr): 2946, 2867,
1732, 1517, 1251 cmꢀ1; H NMR (400 MHz, CDCl3): dH
10 (a) K. C. Majumdar, S. Mondal, N. Pal and R. K. Sinha, Tetra-
hedron Lett., 2009, 50, 1992–1995; (b) K. C. Majumdar,
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1
=
0.66–2.81 (m, 102 H), 4.00 (t, J = 6.1 Hz, 4H), 4.59–4.62
(m, 2H), 5.36 (d, J = 4.0 Hz, 2H), 7.00 (d, J = 7.8 Hz, 6H),
7.66 (d, J = 7.5 Hz, 2H), 7.71 (d, J = 7.5 Hz, 2H), 7.84 (d,
J = 7.2 Hz, 2H), 8.08 (s, 1H), 8.34 (s, 1H). 13C NMR (100 MHz,
CDCl3): dC = 22.3, 22.5, 23.5, 24.0, 24.4, 25.3, 25.3, 27.5, 27.7,
27.9, 28.5, 31.1, 31.5, 31.6, 32.5, 34.2, 35.5, 35.9, 36.3, 36.7,
37.9, 39.2, 39.4, 42.0, 49.7, 55.8, 56.4, 67.5, 67.8, 73.5, 114.4,
115.0, 117.1, 118.0, 121.8, 122.3, 123.9, 126.6, 127.1, 129.2,
130.1, 130.2, 137.2, 139.3, 139.4, 148.0, 150.7, 158.2, 159.0,
161.4, 172.6, 172.7. [a]D ꢀ21.959 (c 0.98 in CHCl3). Anal.
calcd. for C87H124N4O6: C, 79.05; H, 9.45; N, 4.24%. Found:
C, 79.24; H, 9.33; N, 4.31%.
11 F. Hardouin, M. F. Achard, J.-I. Jin, Y.-K. Yun and S. J. Chung,
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The financial support from Department of Science and
Technology through SERC project no. SR/S1/OC-44/2005 is
gratefully acknowledged. Two of us (S. M. and R. K. S.) are
thankful to CSIR (New Delhi) for their fellowships. We also
thank Dr Raghunathan of the Raman Research Institute
(Bangalore) for providing HRXRD data of compound 8a.
We also thank Prof. S. Ghosh of the IACS, Kolkata for
specific rotation measurements.
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