Synthesis of symmetric liquid crystal dimers based on 1,2-bis{-[-(4- alkoxybenzoyloxy)benzylidene]amino)phenoxy}ethane and investigation of phase behaviour by varying alkoxy terminal chain length

Article abstract of DOI:10.1080/15421400802331091

With the objective to study the effect of alkoxy terminal chain length on mesomorphic properties of liquid crystals, We have synthesized ester and Schiff base dimers from diamine derivative containing 1,2-dioxyethylene as short spacer with aldehyde deriva

Full text of DOI:10.1080/15421400802331091

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Synthesis of Symmetric
Liquid Crystal Dimers
Based on 1,2-bis{-[-(4-
alkoxybenzoyloxy)benzylidene]am
and Investigation of Phase
Behaviour by Varying Alkoxy
Terminal Chain Length
Chang Sin Lee a , Tae Hyeong Kim a , B. Ramaraj a ,
Seok Gn Ryu b , Hyun Hoon Song b , Soo-Min Lee a &
Kuk Ro Yoon a
a Organic and Polymer Synthesis Laboratory,
Chemistry Department, Hannam University ,
Daejeon , Korea
b Polymer Structural Physics Laboratory, Advanced
Materials Department , Hannam University ,
Daejeon , Korea
Published online: 31 Aug 2012.
To cite this article: Chang Sin Lee , Tae Hyeong Kim , B. Ramaraj ,
Seok Gn Ryu , Hyun Hoon Song , Soo-Min Lee & Kuk Ro Yoon (2008)
Synthesis of Symmetric Liquid Crystal Dimers Based on 1,2-bis{-[-(4-
alkoxybenzoyloxy)benzylidene]amino)phenoxy}ethane and Investigation of Phase
Behaviour by Varying Alkoxy Terminal Chain Length, Molecular Crystals and Liquid
Crystals, 492:1, 117/[481]-129/[493], DOI: 10.1080/15421400802331091
To link to this article: http://dx.doi.org/10.1080/15421400802331091

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Mol. Cryst. Liq. Cryst., Vol. 492, pp. 117=[481]–129=[493], 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802331091
Synthesis of Symmetric Liquid Crystal Dimers Based
on 1,2-bis{-[-(4-alkoxybenzoyloxy)benzylidene]amino)-
phenoxy}ethane and Investigation of Phase Behaviour
by Varying Alkoxy Terminal Chain Length
Chang Sin Lee1, Tae Hyeong Kim1, B. Ramaraj1, Seok Gn
Ryu2, Hyun Hoon Song2, Soo-Min Lee1, and Kuk Ro Yoon1
1Organic and Polymer Synthesis Laboratory, Chemistry Department,
Hannam University, Daejeon, Korea
2Polymer Structural Physics Laboratory, Advanced Materials
Department, Hannam University, Daejeon, Korea
With the objective to study the effect of alkoxy terminal chain length on mesomorphic
properties of liquid crystals, We have synthesized ester and Schiff base dimers from
diamine derivative containing 1,2-dioxyethylene as short spacer with aldehyde deri-
vatives having different lengths of terminal alkoxy chains (n¼ 6–12). The chemical
structure of the final products was investigated by fourier transform infrared (FT-
IR) spectroscopy and proton nuclear magnetic resonance (1H NMR) spectroscopy.
The mesomorphic properties and optical textures of the resultant dimers were charac-
terized by differential scanning calorimetry (DSC) and polarized optical microscopy
(POM). It was found that all the dimers show mesomorphic properties and the
increase in terminal alkoxy chain length has pronounced effect on the mesomorphic
properties. The temperature range of smectic phase window widens and nematic-
isotropic phase window narrows sharply with increasing alkoxy chain length.
Keywords: differential scanning calorimetry; ester and Schiff base; liquid crystal
dimmers; optical microscopy
1. INTRODUCTION
Since the discovery of liquid crystal dimmers [1] and subsequent interest
in these materials [2] many dimeric systems have been reported. Liquid
crystal dimers are of interest because they act as models for main group
This work was supported from Hannam University Research fund.
Address correspondence to Kuk Ro Yoon, Organic and Polymer Synthesis Labora-
tory, Chemistry Department, Hannan University, Daejeon 305-811, Korea. E-mail:
kryoon@hannam.ac.kr
117=[481]

118=[482]
C. S. Lee et al.
liquid crystalline polymers that allow the study of flexibility and
properties of different mesogenic groups. Thus dimeric liquid crystals
retain the crucial structural components of many thermotropic main
group polymers. Furthermore, as a distinct class of compounds with
unusual properties and potential application, dimeric liquid crystals is
of interest in their own right. In typical dimers where two individual
mesogenic entities are attached to each other by flexible polymethylene
spacer units, the mesomorphic behavior of these compounds is basically
dependent on its molecular architecture in which a slight change in the
molecular geometry brings about considerable change in its mesomorphic
properties. Dimmers containing identical mesogenic units are referred as
symmetric dimmers, while the non-symmetric dimmers consist of two
differing mesogenic groups. The structure of the mesophases can be
modified through change in spacer length and terminal chain length.
Many studies of symmetric dimers have been reported [3,4]. For
example, the symmetric Schiff base dimmers prepared by date et al.
[3], namely the a, x-bis(4-alkylanilinebenzylidene-40-oxy) alkanes;
these dimers were found to exhibit a rich smectic polymorphism. In
1969, Kelker and coworkers [5] reported for the first time that the
Schiff base liquid crystal compound 4-methoxybenzylidene-40-butyla-
niline (MBBA) which exhibits a room temperature nematic phase.
Since then, Schiff bases, especially Schiff base esters have attracted
much attention of liquid crystal researches. Over the past few decades,
lot of low molar mass Schiff base esters have been synthesized and
investigated extensively for liquid crystalline applications [6–11].
In our ongoing efforts to investigate the correlation between mol-
ecular structure and mesomorphic properties [12–15] of these novel
materials, here we report the synthesis and the mesomorphic proper-
ties of symmetric ester and Schiff base dimers (2ESn), which have
terminal alkoxy chains (ꢀOCnH2nþ1; n ¼ 6–12) and 1,2-dioxyethylene
(ꢀOCH2CH2Oꢀ) as a short spacer. The acronym used to refer to these
dimmer is 2ESn, where 2 represents the number of mesogenic units,
ES stands for ester-Schiff base and ‘‘n’’ refers the number of carbon
atoms in the terminal alkoxy chain. The molecular structure of the
title compounds were characterized by 1H NMR and FT-IR techniques.
The mesomorphic phase transition behaviour of these compounds was
investigated by DSC and POM.
2. EXPERIMENTAL
2.1. Materials
1-Fluoro-4-nitrobenzene, ethylene glycol, hydrazine monohydrate,
palladium on activated carbon (Pd=C, 10%), 4-hydroxybenzaldehyde,

Synthesis of Symmetric Liquid Crystal Dimers
119=[483]
4-alkoxybenzoic acid (n ¼ 6–12), 1,3-dicyclohexylcarbodiimide (DCC),
tetrahydrofuran (THF), p-toluenesulfonic acid (PTSA), anhydrous
ethanol were purchased from Aldrich Chemical Co. and used as
received. All other solvents and reagents were purchased commer-
cially and used without further purification.
2.2. Synthesis of Ester and Schiff (2ESn) Base Dimmers
The 2ESn dimesogens were prepared as illustrated in Figure 1. The
synthetic route used in the preparation of Ester and Schiff dimesogens
(2ESn) involved four steps: (1) reaction of 1-fluoro-4-nitrobenzene with
ethylene glycol in presence of potassium carbonate to obtain 1,2-bis(4-
nitrophenoxy)ethane (NPE), (2) then the reduction of nitro group with
hydrazine monohydrate in the presence of palladium on activated
carbon to obtain 1,2-bis(4-aminophenoxy)ethane (APE), (3) the 4-(4-
alkoxy benzoyloxy) benzaldehyde was obtained by reacting 4-hydroxy-
benzaldehyde with 4-alkoxybenzoic acid, and (4) the final product
1,2-bis(4-(4-(4-alkoxybenzoyloxy) benzylidene amino)phenoxy)ethane
was prepared by reacting 4-(4-alkoxy benzoyloxy) benzaldehyde
(22mmol) (ABBn) [16,17] in anhydrous ethanol (50 mL) with
FIGURE 1 Synthetic pathyway for ester-Schiff base dimesogens (2ESn).

120=[484]
C. S. Lee et al.
1,2-bis(4-amino phenoxy)-ethane (11 mmol) in presence of catalytic
amount of PTSA and then the reaction mixture was stirred for 16 h
at the room temperature. The resulting precipitate was isolated by fil-
tration and purified by the recrystallization of both chloroform and
ethyl acetate solvents (off-white solid, 54–75%). The syntheses of final
1
products were confirmed by FRT-IR and H NMR.
2ES6: Yield, 75%. IR (KBr pellet, cmꢀ1): 3070 (ArꢀH), 2860, 2930
(aliphatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). 1H NMR (CDCl3,
ppm): d 0.85–0.94 (t, 6H, ꢀCH3), 1.24–1.50 (m, 12H, ꢀ(CH2)3ꢀ),
1.79–1.84 (m, 4H, ꢀCH2CH2Oꢀ), 4.02–4.07(t, 4H, ꢀCH2CH2Oꢀ),
4.37 (s, 4H, ꢀOCH2CH2Oꢀ), 6.96–7.02 (t, 8H, ArꢀH), 7.24–7.33 (d,
8H, ArꢀH), 7.94–7.97 (d, 4H, ArꢀH), 8.13–8.16 (d, 4H, ArꢀH), 8.49
=
=
=
(s, 2H, ꢀCH N).
2ES7: Yield, 56%. IR (KBr pellet, cmꢀ1): 3070 (ArꢀH), 2860, 2930
(aliphatic CꢀH), 1740 (C O), 1604 (ꢀCH Nꢀ). 1H NMR (CDCl3,
ppm): d 0.84–0.91 (t, 6H, ꢀCH3), 1.15–1.51 (m, 16H, ꢀ(CH2)4ꢀ),
1.79–1.88 (m, 4H, ꢀCH2CH2Oꢀ), 4.03–4.08 (t, 4H, ꢀCH2CH2Oꢀ),
4.38 (s, 4H, ꢀOCH2CH2Oꢀ), 6.97–7.03 (t, 8H, ArꢀH), 7.24–7.34 (d,
8H, ArꢀH), 7.95–7.98 (d, 4H, ArꢀH), 8.14–8.17 (d, 4H, ArꢀH), 8.50
=
=
=
(s, 2H, ꢀCH N).
2ES8: Yield, 75%. IR (KBr pellet, cmꢀ1): 3072 (ArꢀH), 2850, 2922
(aliphatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). 1H NMR (CDCl3,
ppm): d 0.86–0.91 (t, 6H, ꢀCH3), 1.24–1.50 (m, 20H, ꢀ(CH2)5ꢀ),
1.77–1.84 (m, 4H, ꢀCH2CH2Oꢀ), 4.02–4.06 (t, 4H, ꢀCH2CH2Oꢀ),
4.37 (s, 4H, ꢀOCH2CH2Oꢀ), 6.96–7.02 (t, 8H, ArꢀH), 7.24–7.33 (d,
8H, ArꢀH), 7.95–7.98 (d, 4H, ArꢀH), 8.13–8.16 (d, 4H, ArꢀH), 8.49
=
=
=
(s, 2H, ꢀCH N).
2ES9: Yield, 58%. IR (KBr pellet, cmꢀ1): 3071 (ArꢀH), 2850, 2922
(aliphatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). 1H NMR (CDCl3,
ppm): d 0.86–0.91 (t, 6H, ꢀCH3), 1.24–1.50 (m, 24H, ꢀ(CH2)6ꢀ),
1.77–1.84 (m, 4H, ꢀCH2CH2Oꢀ), 4.02–4.06 (t, 4H, ꢀCH2CH2Oꢀ),
4.37 (s, 4H, ꢀOCH2CH2Oꢀ), 6.96–7.02 (t, 8H, ArꢀH), 7.24–7.33 (d,
8H, ArꢀH), 7.95–7.98 (d, 4H, ArꢀH), 8.13–8.16 (d, 4H, ArꢀH), 8.49
=
=
=
(s, 2H, ꢀCH N).
2ES10: Yield, 73%. IR (KBr pellet, cmꢀ1): 3072 (ArꢀH), 2850, 2922 (ali-
1
=
=
phatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). H NMR (CDCl3, ppm): d
0.86–0.91 (t, 6H, ꢀCH3), 1.24–1.50 (m, 28H, ꢀ(CH2)7ꢀ), 1.77–1.84 (m,
4H, ꢀCH2CH2Oꢀ), 4.02–4.06 (t, 4H, ꢀCH2CH2Oꢀ), 4.37 (s, 4H,
ꢀOCH2CH2Oꢀ), 6.97–7.03 (t, 8H, ArꢀH), 7.24–7.33 (d, 8H, ArꢀH),
=
7.95–7.98 (d, 4H, ArꢀH), 8.14–8.17 (d, 4H, ArꢀH), 8.49 (s, 2H, ꢀCH N).
2ES11: Yield, 54%. IR (KBr pellet, cmꢀ1): 3070 (ArꢀH), 2850, 2922
1
=
=
(aliphatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). H NMR (CDCl3, ppm):
d 0.86–0.91 (t, 6H, ꢀCH3), 1.24–1.51 (m, 32H, ꢀ(CH2)8ꢀ), 1.77–1.84

Synthesis of Symmetric Liquid Crystal Dimers
121=[485]
(m, 4H, ꢀCH2CH2Oꢀ), 4.02–4.06 (t, 4H, ꢀCH2CH2Oꢀ), 4.37 (s, 4H,
ꢀOCH2CH2Oꢀ), 6.95–7.01 (t, 8H, ArꢀH), 7.24–7.33 (d, 8H, ArꢀH),
7.95–7.98 (d, 4H, ArꢀH), 8.13–8.16 (d, 4H, ArꢀH), 8.49 (s, 2H,
=
ꢀCH N).
2ES12: Yield, 71%. IR (KBr pellet, cmꢀ1): 3070 (ArꢀH), 2850, 2922
1
=
=
(aliphatic CꢀH), 1736 (C O), 1604 (ꢀCH Nꢀ). H NMR (CDCl3, ppm):
d 0.91–0.86 (t, 6H, ꢀCH3), 1.24–1.50 (m, 36H, ꢀ(CH2)9ꢀ), 1.77–1.84
(m, 4H, ꢀCH2CH2Oꢀ), 4.02–4.06 (t, 4H, ꢀCH2CH2Oꢀ), 4.37 (s, 4H,
ꢀOCH2CH2Oꢀ), 6.96–7.02 (t, 8H, ArꢀH), 7.24–7.33 (d, 8H, ArꢀH),
7.95–7.98 (d, 4H, ArꢀH), 8.13–8.16 (d, 4H, ArꢀH), 8.50 (s, 2H,
=
ꢀCH N).
2.3. Measurements
IR spectra were recorded with a Perkin-Elmer 1000 FT-IR spectro-
1
photometer on KBr pellets. H NMR spectra were recorded by using
a Varian Mercury 300 (300 MNz) NMR spectrometer. Differential
scanning calorimetric measurements were performed using a TA
instrument 910 S DSC apparatus under dry nitrogen flow at the scan-
ning rate of 10ꢁC=min. The crude product was repeatedly recrystal-
lized until the transition temperatures were found to be constant
and reproducible. The transition temperatures were taken at the
maximum point of the peaks for each sample. The transition enthal-
pies were evaluated from the integrated area of the endothermic peaks
using a reference indium sample as the standard. Optical microscopy
observation was carried out using a Nikon Labophot-2 polarizing
microscope fitted with a RTC-1 temperature controller (Instec Inc.,
Broom-field, Co.) and a mettler FP-82HT hot stage.
3. RESULTS AND DISCUSSION
3.1. Synthesis and Characterization
The synthetic routes used for the preparation of dimesogenic liquid
=
crystals (2ESn) containing ꢀCOOꢀ and ꢀCH Nꢀ units are outlined
in Figure 1. The structures of final products were confirmed by
1
1H NMR (Fig. 2) and FT-IR (Fig. 3) spectroscopy. In H NMR spectra,
=
the synthesized 2ESn compounds showed CH N peak at 8.49 ppm
and the central spacer (ꢀOCH2CH2Oꢀ) at 4.37 ppm. The IR spectral
frequencies of the synthesized 2ESn compounds were obtained using
KBr pellets. The absorption peak of ester group was observed
at 1736–1740 cmꢀ1 and CH Nꢀ stretching frequencies occurred
=
at 1604 cm along with aliphatic CꢀH stretching frequencies at

122=[486]
C. S. Lee et al.
FIGURE 2 1H NMR spectra of 2ES8 compound.
2850–2860, 2922–2930 cmꢀ1. All seven compounds synthesized in the
2ESn series were found to exhibit mesophases. The mesophase transi-
tions exhibited by these symmetrical dimmers were investigated by
means of DSC and POM.
FIGURE 3 FT-IR spectra of 2ESn series compounds.

Synthesis of Symmetric Liquid Crystal Dimers
123=[487]
3.2. The Dependence of Transitional Properties on the Length
of Alkoxy Terminal Chains
Figure 4 presents the DSC heating traces of dimesogens (2ESn, n ¼ 6–
12) and crystalline, smectic and nematic transitions. Table 1 sum-
marizes the thermal transitions and associated enthalpy changes of
2ESn dimesogens. With increase in alkoxy terminal chain length from
6 to 12, smectic to nematic transitions appears. With increase in chain
length (n ¼ 6–12), the smectic C transition increased from 229.8 to
311.8ꢁC, however, the nematic transition decreased from 351.4 to
306.6ꢁC, and smectic C-nematic transitions become closer. The exist-
ence of smectic C to nematic (SmC-N) transition was confirmed by
the observation of schlieren textures in optical microscopy when com-
pound were heated from smectic C phase. It can be seen from the
Table 1, the crystal to smectic A phase transition at 167.4ꢁC (2ES6)
decreased to 152.6ꢁC (2ES12) with increase in chain length indicating
the reduction in crystallanity and increase in flexibility of the
dimmers.
Figure 5 shows the dependence of the transition temperature on the
terminal chain length (n). This figure clearly shows the increase in
phase window of smectic A and smectic C phases, where as the
nematic phase window narrows sharply with increasing alkyl chain
length. The increasing terminal chain length is anticipated to increase
significantly the length-to-breadth ratio in resulting in liquid crystal
FIGURE 4 Differential scanning calorimetry thermograms for ester-Schiff
base dimesogens (2ESn; n ¼ 6–12) in the heating scans (10ꢁC=min). The arrows
indicate the phase transitions observed in optical microscope.

124=[488]
C. S. Lee et al.
TABLE 1 Thermal Transition Temperatures and Associated Enthalpy
Changes of Ester-Schiff’s Base Dimesogens (2ESn)
Phase transition temperatures (ꢁC) and
associated enthalpy change (DH, kJ=mol)
Number of carbons
in 2ESn series
Crystalline
phase
Smectic
A phase
Smectic
C phase
Nematic
phase
6
7
8
167.4(26.6)
165.3(53.6)
162.2(49.7)
161.0(47.0)
157.4(46.0)
156.2(44.4)
152.6(43.8)
–
–
229.8(0.34)
273.9(0.98)
293.6(1.40)
302.2(1.70)
310.5(1.93)
311.8(1.93)
–
351.4(10.5)
343.9(9.76)
337.1(11.5)
329.7(7.22)
325.8(12.3)
319.4(7.66)
306.6(25.2)
188.5(8.11)
187.8(4.43)
191.4(5.26)
190.3(5.33)
188.6(5.19)
9
10
11
12
phases, and particularly smectic phases, being stabilized at higher
temperatures for higher homologues. These results demonstrate that
the tendency toward smectic mesomorphism and the thermal stability
of smectic phase increases with increasing terminal alkoxy chain
length. The effects of the terminal chain length on the transition
temperatures and phases behavior observed in this series are in
accordance with those observed for conventional low molar mass meso-
gens. However the odd-even effect observed [4] for similar compounds
were not observed for these 2ESn compounds.
FIGURE 5 Dependence of transition temperatures on the increasing number
of carbon atoms (n) in the terminal alkoxy chains for the 2ESn series
compounds.

Synthesis of Symmetric Liquid Crystal Dimers
125=[489]
FIGURE 6 Dependence of enthalpy changes (DH) associated with transition
temperatures on the increasing number of carbon atoms (n) in the terminal
alkoxy chain for the 2ESn series compounds.
Figure 6 shows the dependence of enthalpy changes associated with
crystalline-smectic A (Cr-SmA), smectic A-smetic C (SmA-SmC), smec-
tic C-nematic (SmC-N) and nematic-isotropic (N–I) phase transitions
on carbon number (n) of the terminal chain. It is interesting to observe
that the odd-even effect for mesophase transitions in general and
nematic-isotropic (N–I) transition in particular. The N–I transition
enthalpies for even numbers are in most instances much higher than
those of the odd number terminal chains. However, the enthalpy
changes associated with crystallization decreased from 53.6 to
43.8 kJ=mol indicating effect of chain length on the crystallization
behaviour. Eventhough enthalpy changes does not identify the meso-
phases, it can give an indication about existence different type of
mesophases and further enthalpy changes associated with the crystal-
line phase are generally higher than that observed for mesophase as
observed here.
3.3. Optical Properties
DSC analysis reveals the existence of enantiotropic transitions and
these transitions are more visible and sharp with increase in alkoxy
terminal chain especially for ES (8–11) compounds. The optical tex-
tures of these selective compounds in the observed mesophase window
are shown Figures 7–10 in the order. The properties of liquid
crystalline phases were studied using POM with a hot stage. Optical
micrographs of 2ES8 obtained during the heating cycle at different
temperatures are shown in Figure 7 and optical micrographs of

126=[490]
C. S. Lee et al.
FIGURE 7 Optical textures of (1) SmA of 2ES8 (183ꢁC); (2) SmC of 2ES8
(289ꢁC); (3) SmC-N transition of 2ES8 (293ꢁC); (4) N of 2ES8 (297ꢁC).
2ES10 are shown in Figure 8. The optical textures of these new types of
compounds are tentatively identified based on DSC results and its
resemblance. Schlieren optical texture of 2ES8 (Fig. 4) reveals the
FIGURE 8 Optical textures of (1) Cr of 2ES9 (144ꢁC); (2) SmA of 2ES9 (182ꢁC);
(3) SmC of 2ES9 (245ꢁC); (4) N of 2ES9 (305ꢁC).

Synthesis of Symmetric Liquid Crystal Dimers
127=[491]
FIGURE 9 Optical textures of (1) Cr of 2ES10 (153ꢁC); (2) SmA of 2ES10
(183ꢁC); (3) SmC of 2ES10 (300ꢁC); (4) N of 2ES10 (316ꢁC).
transformation of smectic phase into nematic (N) transitions on
heating. Smectic A phase of 2ES8 at 183ꢁC is shown in Figure 4(1),
smectic C phase of 2ES8 at 289ꢁC is shown in Figure 4(2), smectic
FIGURE 10 Optical textures of (1) Cr of 2ES11 (150ꢁC); (2) SmA of 2ES11
(180ꢁC); (3) SmC of 2ES11 (301ꢁC); (4) N of 2ES11 (312ꢁC).

128=[492]
C. S. Lee et al.
C-nematic (SmC-N) transition of 2ES8 at 293ꢁC at Figure 4(3) and
nematic (N) phase of 2ES8 at 297ꢁC is shown in Figure 4(4) respect-
ively. The different mesomorphic phases of 2ES10 are shown in Figure
5(1)-crystalline phase at 153ꢁC, 5(2)-smectic A phase at 183ꢁC, 5(3)-
smectic C phase at 300ꢁC and 5(4)-nematic(N) phase at 316ꢁC respect-
ively. The different mesomorphic phases observed are consistent with
the DSC analysis results.
4. CONCLUSIONS
We have synthesized a new series of ester and schiff base liquid crys-
talline compounds from diamine derivative containing 1,2-dioxyethy-
lene as short spacer with aldehyde derivatives having terminal
alkoxy chains (n ¼ 6–12). The chemical structures of the final products
were investigated by FT-IR and 1H NMR spectroscopy. The meso-
morphic properties and optical textures of the resultant dimers were
characterized by DSC and POM. The existence of smectic C-nematic
(SmC-N) transitions was confirmed by the observation of schlieren
textures in optical microscopy when compound were heated from
smectic phase. It was found that all the dimers show mesomorphic
properties and the change in terminal alkoxy chain length has pro-
nounced effect on the mesomorphic properties. The temperature range
of smectic phase window widens and nematic phase window narrows
sharply with increasing alkoxy chain length.
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