Influence of terminal groups on the mesogenic properties of self-assembly systems

Article abstract of DOI:10.1080/15421406.2011.591682

Two novel hydrogen-bonded liquid crystal homologous series are synthesized and characterized. A hydrogen bond is formed between various p-n alkyloxy benzoic acids and chloro/hydroxy benzaldehyde. The formation of hydrogen bonds is evinced through Fourier Infra Red Spectroscopy studies. The terminal group of the aldehyde group has been varied and the thermal, optical, and electrical results are compared and analyzed. Both series exhibit rich liquid crystalline-phase polymorphism. Phase diagrams are constructed from the Differential Scanning Calorimetry and optical polarizing microscopic data. The phase sequence is same for both the series, with nematic, smectic C, and smectic G phases. A noteworthy point is the observation of optical shuttering action in the homologous series with the chloro terminal group of the aldehyde group and absence of the same in the other homologous series. The influence of terminal group of the aldehyde group with respect to occurrence of phase variance, tilt angle, optical shuttering action, and odd-even effect is discussed. Copyright Taylor &Francis Group, LLC.

Full text of DOI:10.1080/15421406.2011.591682

This article was downloaded by: [Laurentian University]
On: 16 April 2013, At: 09:26
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered
office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK
Molecular Crystals and Liquid Crystals
Publication details, including instructions for authors and
subscription information:
http://www.tandfonline.com/loi/gmcl20
Influence of Terminal Groups on the
Mesogenic Properties of Self-Assembly
Systems
N. Pongali Sathya Prabu a , V. N. Vijayakumar a & M. L. N. Madhu
Mohan a
a Liquid Crystal Research Laboratory (LCRL), Bannari Amman
Institute of Technology, Sathyamangalam, India
Version of record first published: 07 Oct 2011.
To cite this article: N. Pongali Sathya Prabu , V. N. Vijayakumar & M. L. N. Madhu Mohan (2011):
Influence of Terminal Groups on the Mesogenic Properties of Self-Assembly Systems, Molecular
Crystals and Liquid Crystals, 548:1, 142-154
To link to this article: http://dx.doi.org/10.1080/15421406.2011.591682
PLEASE SCROLL DOWN FOR ARTICLE
Full terms and conditions of use: http://www.tandfonline.com/page/terms-and-conditions
This article may be used for research, teaching, and private study purposes. Any
substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing,
systematic supply, or distribution in any form to anyone is expressly forbidden.
The publisher does not give any warranty express or implied or make any representation
that the contents will be complete or accurate or up to date. The accuracy of any
instructions, formulae, and drug doses should be independently verified with primary
sources. The publisher shall not be liable for any loss, actions, claims, proceedings,
demand, or costs or damages whatsoever or howsoever caused arising directly or
indirectly in connection with or arising out of the use of this material.

Mol. Cryst. Liq. Cryst., Vol. 548: pp. 142–154, 2011
Copyright © Taylor & Francis Group, LLC
ISSN: 1542-1406 print/1563-5287 online
DOI: 10.1080/15421406.2011.591682
Influence of Terminal Groups on the Mesogenic
Properties of Self-Assembly Systems
N. PONGALI SATHYA PRABU, V. N. VIJAYAKUMAR,
AND M. L. N. MADHU MOHAN∗
Liquid Crystal Research Laboratory (LCRL), Bannari Amman Institute of
Technology, Sathyamangalam, India
Two novel hydrogen-bonded liquid crystal homologous series are synthesized and char-
acterized. A hydrogen bond is formed between various p-n alkyloxy benzoic acids and
chloro/hydroxy benzaldehyde. The formation of hydrogen bonds is evinced through
Fourier Infra Red Spectroscopy studies. The terminal group of the aldehyde group has
been varied and the thermal, optical, and electrical results are compared and analyzed.
Both series exhibit rich liquid crystalline-phase polymorphism. Phase diagrams are
constructed from the Differential Scanning Calorimetry and optical polarizing micro-
scopic data. The phase sequence is same for both the series, with nematic, smectic C,
and smectic G phases. A noteworthy point is the observation of optical shuttering action
in the homologous series with the chloro terminal group of the aldehyde group and
absence of the same in the other homologous series. The influence of terminal group
of the aldehyde group with respect to occurrence of phase variance, tilt angle, optical
shuttering action, and odd–even effect is discussed.
Keywords Hydrogen-bonded liquid crystal; odd–even effect; optical shuttering action;
phase variance
1. Introduction
Liquid crystals are the intermediate state of matter between molecularly oriented solid
and free flow liquids. They are mostly formed by the intermolecular hydrogen bonding
between the complexes which prompted scientists to turn their interest toward hydrogen
bonding. Katoandhiscoworkers [1–8] investigatedmanysuchsystemswithcomplementary
components. It is noteworthy that it is not necessary that both of the complexes exhibit
mesogenic properties. To induce mesomorphic state, various molecular interactions, such as
charge transfer and ionic–dipolar interactions between the different molecular species, have
been used. Normally, to obtain the enormous use of hydrogen-bonded liquid crystals, the
mesogens containing only two aromatic rings have been used to stimulate room temperature
mesogens. Hydrogen bonding is one of the prime interactions for chemical and biological
processes in nature due to its directionality and dynamics. Hydrogen bonding plays a vital
role in the association of molecules for molecular aggregation.
∗Address correspondence to M. L. N. Madhu Mohan, Liquid Crystal Research Laboratory
(LCRL), Bannari Amman Institute of Technology, Sathyamangalam 638 401, India. Tel.: +91-4295-
223-480; Fax: +91-4295-223-775. E-mail: mln.madhu@gmail.com
142

Influence of Terminal Groups
143
The chemical molecular design of liquid crystal mesogen plays a vital role in under-
standing the various mesogenic and other physical properties exhibited by it. From the
literature, it can be inferred that various moieties of the chemical structure contribute to
various properties exhibited by the mesogen. The transverse and longitudinal dipoles have
greater impact on the conjugation and the electrical properties. Thus, the engineering of the
molecular structure for the desired properties is an interesting aspect from the applicational
point of view.
We have already reported [9–17] single, double, and multiple hydrogen bond formation
between the mesogenic and nonmesogenic complexes. The self-assembly systems formed
by alkyloxy carboxylic acids exhibit rich phase polymorphism. It has previously been
reported by us that these self-organized systems induce variety of new phenomena like
reentrant phase occurrence [9,10], light modulation [11], optical shuttering action [12–15],
and field-induced transitions [11,16,17]. A successful attempt has been made to understand
the influence of the terminal groups (OH and Cl) on the self-assembly system comprising
of aldehyde and alkyloxy benzoic acids.
2. Experimental
Optical textural observations are made with a Nikon polarizing microscope equipped with
Nikon (Japan) digital CCD camera system with 5 megapixels and 2560 × 1920 pixel
resolutions. The temperature control is equipped with Instec HCS402-STC 200 (USA)
temperature controller to a resolution of 0.1◦C. The liquid crystal sample is filled by
capillary action in its isotropic state into a commercially available (Instec, USA) polyamide
buffed cell with 5 micron spacer. An optical extinction technique [18] is used for the
determination of tilt angle. Transition temperatures and corresponding enthalpy values are
obtained by Differential Scanning Calorimetry (DSC) (Shimadzu DSC-60, Japan) while
Fourier Infra Red Spectroscopy (FTIR) spectra is recorded (ABB FTIR MB3000, Canada)
and analyzed using the MB3000 software. The p-n-alkyloxy benzoic acids (nBA) and
hydroxy and chloro benzaldehyde are supplied by Sigma Aldrich (Germany) and all the
solvents used are HPLC grade.
2.1 Synthesis of Liquid Crystalline Compounds
Intermolecular hydrogen-bonded mesogens are synthesized by the addition of one mole of
p-n-alkyloxy benzoic acids with one mole of chlorobenzaldehyde/hydroxybenzaldehyde in
N, N-dimethyl formamide (DMF). Further, they are subject to constant stirring for 12 h
at ambient temperature (30◦C) till a white precipitate in a dense solution is formed. The
white crystalline crude complexes are obtained by removing excess DMF recrystallized with
dimethyl sulfoxide(DMSO) andtheyieldvariedfrom75%to99%. Themolecularstructures
of the present homologous series of p-n-alkyloxy benzoic acids with chlorobenzaldehyde
(CBA+nBAO)/hydroxybenzaldehyde (HBA+nBAO) are depicted in Figs. 1(a) and (b),
respectively, where n represents the alkyloxy carbon number. Thus, the above two series of
hydrogen-bonded complexes are labeled as CBA+nBAO and HBA+nBAO, respectively.
3. Results and Discussion
The synthesized hydrogen-bonded liquid crystals are highly stable at ambient temperature
(30◦C). They show high thermal and chemical stability when subjected to repeated thermal
scans performed during polarizing optical microscopic (POM) and DSC studies.

144
N. Pongali Sathya Prabu et al.
Figure 1. Molecular structure of (a) CBA+nBAO series and (b) HBA+nBAO series.
3.1 Phase Identification
The observed phase variants, transition temperatures, and corresponding enthalpy values
of CBA+nBAO and HBA+nBAO obtained by DSC in cooling and heating cycles for the
complexes are presented in Tables 1(a) and (b), respectively.
3.2 Polarizing Optical Microscopic Studies (POM)
The above hydrogen-bonded complexes are found to exhibit characteristic textures [19],
viz., nematic (threaded texture), smectic C (broken focal conic texture), and smectic G
(mosaic texture), respectively. The general phase sequence of the present hydrogen-bonded
complexes in the cooling run is observed as:
Isotropic → Nematic → SmC → SmG → Crystal CBA + nBAO (n = 7 − 12)
Isotropic → Nematic → SmG → Crystal CBA + 6BAO
Isotropic → Nematic → Crystal CBA + 5BAO
Isotropic → Nematic → SmG → Crystal HBA + nBAO (n = 5, 6)
Isotropic → Nematic → SmC → SmG → Crystal HBA + nBAO (n = 7 − 12).
3.3 Infrared Spectroscopy (FTIR)
Figure 2 illustrates the solid state spectra, i.e., FTIR spectra of the hydrogen-bonded
CBA+12BAO complex in solid state, at room temperature (30◦C) as a representative case.
The solid state spectra of p-n alkyloxy benzoic acid is reported [11,20] to have two sharp
bands at 1685 cm−1 and 1695 cm−1 due to the frequency ν(C O) mode. The doubling
feature of this stretching mode confirms the dimeric nature of alkyloxy benzoic acid at room
temperature [20]. Further, in the present CBA+12BAO hydrogen-bonded complex, a band
appearing at 2924 cm−1 is assigned to ν(O-H) mode of the carboxylic acid group while
bands appearing at 1605 cm−1 and 1680 cm−1 are assigned to ν(C O) mode. Various bands
of ν(O-H) and ν(C O) modes corresponding to individual complexes of CBA+nBAO and
HBA+nBAO are tabulated in Table 2.

Influence of Terminal Groups
145
Table 1. Transition temperatures and enthalpy values of CBA+nBAO series obtained by
various techniques
Phase
variance Study
Crystal
to melt
Complex
N
C
G
Crystal
CBA +5BAO
N
DSC (H)
DSC (C)
POM (C)
114.2
(116.55) (9.28)
145.8
143.4
107.0
(105.24)
107.8
(8.71)
146.3
CBA +6BAO
CBA +7BAO
NG DSC (H)
94.9
(40.11) (4.61)
146.7
151.2
DSC (C)
87.3 (Merged 85.4
with crystal) (36.35)
(9.00)
147.2
144.6
POM (C)
NG DSC (H)
87.9
#
86.6
89.8
(142.22) (7.16)
141.5
DSC (C)
POM (C)
81.5
(1.62)
82.1
71.1
(105.7)
71.8
(5.95)
142.4
CBA +8BAO NCG DSC (H)
77.4
(54.49) (7.9)
143.3
146.95
98.3
(2.39)
97.9
90.9
(17.98)
87.9
DSC (C)
56.7
(38.43)
57.6
(7.35) (2.81)
(20.49)
88.3
#
POM (C)
CBA +9BAO NCG DSC (H)
144.7
140.6
(121.8) (8.98)
136.1
98.5
114.7
(3.4)
109.4
93.4
DSC (C)
81.8
(16.04)
82.2
#
67.8
(70.36)
68.6
(8.56) (3.55)
136.8 110.3
140.6 116.09
(143.08) (13.18) (3.49)
POM (C)
CBA +10BAO NCG DSC (H)
87.3
DSC (C)
137.5
(9.6)
138.2
139.9
112.4
(3.22)
113.1
127.3
82.8
(26.3)
83.4
#
67.1
(28.47)
67.9
POM (C)
CBA +11BAO NCG DSC (H)
96.9
(135.84) (6.83) (5.47)
136.9 124.2
(7.85) (3.47)
137.7
137.1
(127.25) (3.43)
132.3
DSC (C)
80.0
(25.23)
80.8
100.2
(5.15)
80.1
(23.22)
80.9
70.3
(27.39)
71.1
POM (C)
CBA +12BAO NCG DSC (H)
124.9
#
94.53
DSC (C)
POM (C)
126.3
68.6
(81.6)
69.7
(6.69) (2.88)
132.9 127.5
# Phase not resolved; (H) heating run, (C) cooling run.

146
N. Pongali Sathya Prabu et al.
Table 2. Transition temperatures and enthalpy values of HBA+nBAO series obtained by
various techniques
Phase
variance Study
Crystal
to melt
Complex
N
#
C
#
G
#
Crystal
HBA+12BAO NCG DSC (h)
107.7
(44.30)
DSC (c)
109.4
87.3
84.2
81.1
(7.77) (merged
with G)
(19.76)
(39.60)
POM (c)
HBA +11BAO NCG DSC (h)
110.8
#
88.1
#
84.9
#
81.8
107.0
(23.09)
DSC (c)
118.6
(0.06) (0.23)
119.5
114.5
114.2
108.0
(4.85)
108.7
95.8
91.4
(112.69)
91.8
POM (c)
HBA +10BAO NCG DSC (h)
115.1
#
85.6
(41.17) (1.26)
111.1
(20.78)
DSC (c)
108.2 92.6 (merged 82.5
with crystal) (22.41)
(0.13) (6.14)
POM (c)
HBA +9BAO NCG DSC (h)
112.9
#
109.3
#
93.5
#
82.9
93.6
(62.85)
DSC (c)
106.5
(3.83) (17.35)
107.8
#
90.3
74.3
(33.14)
74.9
#
62.0
(43.27)
62.4
POM (c)
HBA +8BAO NCG DSC (h)
91.7
#
100.0
(36.23)
DSC (c)
116.3
101.4
94.8
75.1
(merged (1.44)
with C)
(25.64)
(27.96)
POM (c)
HBA +7BAO NCG DSC (h)
117.6
#
102.9
#
95.3
#
75.5
92.4
(79.88)
DSC (c)
106.1
(0.03) (0.97)
107.5
#
99.7
88.2
(24.27)
89.1
#
83.3
(93.05)
83.8
POM (c)
100.9
HBA +6BAO
HBA +5BAO
NG DSC (h)
DSC (c)
101.2
(36.56)
107.7
(1.04)
108.8
#
93.2
(30.47)
94.3
114.7
(21.31)
110.2
(50.61)
83.5
(38.60)
84.0
POM (c)
NG DSC (h)
104.3
(73.07)
DSC (c)
POM (c)
122.1
(merged
with G)
123.2
88.0
(56.77)
111.4
88.7
# Phase not resolved; (H) heating run, (C) cooling run.

Influence of Terminal Groups
147
60
40
20
CBA+12BAO
4000
3000
2000
-1
1000
Wave number cm
Figure 2. FTIR spectra of the CBA+12BAO complex.
3.4 DSC Studies
DSC thermograms for all the complexes have been recorded at a scan rate of 10◦C min−1
for the heating and cooling runs, and analyzed. The transition temperatures and enthalpy
values for all the homologues of CBA+nBAO and HBA+nBAO are tabulated in Tables 1(a)
and (b), respectively.
As a representative case, Fig. 3 illustrates the thermogram of CBA+9BAO hydrogen-
bonded complex recorded at a scan rate of 10◦C min−1 in the heating and cooling runs. In
the cooling run of DSC thermogram, the above compound possesses four distinct transitions
namely isotropic to nematic, nematic to Sm C, Sm C to Sm G, and Sm G to crystal with
transition temperatures 136.1◦C, 109.4◦C, 81.8◦C, and 67.8◦C, and corresponding enthalpy
values 8.56 J g−1, 3.55 J g−1, 16.04 J g−1, and 70.36 J g−1, respectively. While in the heating
cycle, three distant transitions namely crystal to melt, melt to Sm G, and Sm G to Sm C
Table 2. FTIR data representing the various modes for CBA+nBAO and HBA+nBAO
homologous series, respectively
υ(OH)
υ (CO)
υ(OH)
υ (CO)
Compound
CBA+nBAO
HBA+nBAO
5BAO
6BAO
7BAO
8BAO
9BAO
10BAO
11BAO
12BAO
2933
2933
2932
2927
2924
2924
2924
2924
1605
1605
1605
1605
1605
1605
1608
1605
1690
1690
1674
1692
1682
1680
1680
1680
2955
2939
2932
2932
2924
2924
2924
2924
1597
1597
1605
1605
1605
1605
1605
1605
1682
1682
1674
1674
1674
1674
1674
1674

148
N. Pongali Sathya Prabu et al.
25
20
15
10
5
Crystal
G
Iso.
C
N
Cooling
0
-5
Heating
CBA+9BAO
-10
-15
40
60
80
100
120
140
Temperature/oC
Figure 3. DSC thermogram of the CBA+9BAO complex.
are obtained at 93.4◦C, 140.6◦C, and 114.7◦C with corresponding enthalpy values of 121.8
J g−1, 8.98 J g−1J/g, and 3.4 J/g, respectively.
The transition temperatures and enthalpy values for other hydrogen-bonded complexes
are analyzed and represented in Table 1. All of these transition temperatures of the present
homologous series concur with POM studies.
3.5 Phase Diagrams
3.5.1 Pure p-n-Alkyloxy Benzoic Acids. The phase diagram of pure p-n-alkyloxy benzoic
acid is reported [9,14] to be composed of two phases, namely nematic and smectic C.
3.5.2 CBA+nBAO Series. The phase diagram of CBA+nBAO series is depicted in Fig. 4
which reveals the following points:
a) The phase diagram is composed of orthogonal and tilted phases, viz., nematic and
Sm. C and Sm. G.
b) Nematic phase is observed in all the members of the present homologous series.
c) Odd–even effect is observed in transition temperatures of isotropic to nematic
transition.
d) A noteworthy point is that at even carbon numbers, tilted phases are induced, viz.,
at the hexyloxy carbon number, Sm. G is induced while at octyloxy carbon number,
smectic C phase is induced.
e) The thermal span of the nematic is found to be greatly reduced with the induction
of the higher order smectic C phase.
f) The lower homologous have the larger thermal span of the nematic phase compared
to their higher counterparts.

Influence of Terminal Groups
149
160
140
120
100
80
CBA+nBAO
Isotropic
Nematic
Sm C
Sm G
60
Crystal
6
8
10
12
Alkyloxy carbon number
Figure 4. Phase diagram of the CBA+nBAO series.
g) The total mesogenic range in the present homologous series started to increase up
to octyloxy carbon number and then it saturated with the further increment of the
carbon number.
3.5.3 HBA+nBAO Series. The phase diagram of HBA+nBAO series is depicted in Fig. 5,
which reveals the following points:
a) The HBA+nBAO hydrogen-bonded complex exhibits nematic as orthogonal phase
and smectic C and smectic G as tilted phases.
b) The thermal range of the mesogenic phases increased with increase in the alkyloxy
carbon number up to nonyloxy carbon and then starts to decrease till dodecyloxy
benzoic acid.
HBA+nBAO
Isotropic
120
100
80
N
C
G
60
Crystal
8
5
6
7
9
10
11
12
Alkyloxy carbon number
Figure 5. Phase diagram of the HBA+nBAO series.

150
N. Pongali Sathya Prabu et al.
c) Smectic G phase is observed in all the complexes of the present homologous series
while ordered smectic C phase is induced in the higher homologous alkyloxy carbon
numbers.
d) The liquid crystalline thermal range is largest for nonyloxy carbon and starts to
reduce up to undecyloxy carbon.
e) A systematic decrease in the crystallization temperatures is observed up to nony-
loxy benzoic carbon number. From then on, the crystallization temperatures start
to increase proportionally along with its corresponding carbon number, with an
exception of the dodecyloxy carbon number.
4. Odd–Even Effect in the Present Homologous Series
In the present homologous series, odd–even effect is noticed. Figure 6 depicts the variation
of isotropic to nematic transition temperatures in HBA+nBAO and CBA+nBAO series. In
the literature, such behavior has been reported [21] and is referred to as the odd–even effect.
It may be noted that the present complex of liquid crystalline molecules is composed of rigid
and flexible parts. The rigid core length varies with increment in the benzoic acid carbon
number. The rich liquid crystalline phase polymorphism and the associated enthalpy values
with increment of alkyloxy carbon number are thus attributed to this part of the chemical
structure. Hence, the rigid core plays a vital role in establishing the pronounced odd–even
effect as evinced in the present homologous series. A perfect zig-zag pattern is observed
for the series with the choloro terminal group attached to the aldehyde group while for the
other series, the odd–even effect is not so pronounced.
4.1 Optical Tilt Angle Studies in Smectic C
Optical tilt angle has been experimentally measured (Fig. 7) by the optical extinction
method [18] in the smectic C phase of CBA+nBAO, (n = 9–12) and HBA+nBAO, (n =
7–11) series, as shown in Figs. 7 and 8, respectively. From Figs 7 and 8, it is generally
observed that the magnitude of the tilt angle increases with decreasing temperature and
160
Iso - N Transition temperatures
150
CBA+nBAO
HBA+nBAO
140
130
120
110
6
8
10
12
Alkyloxy carbon number
Figure 6. Odd – even effect at Iso-N transition temperature of CBA+nBAO and HBA+nBAO series.

Influence of Terminal Groups
151
20
15
10
5
Smectic C
CBA+9BAO
CBA+10BAO
CBA+11BAO
CBA+12BAO
0
0
5
10
15
(T-TC) / OC
Figure 7. Tilt angle in smectic phase of CBA+nBAO series (n = 9–12).
attains a saturation value. The large magnitudes of the tilt angle are attributed [22] to the
direction of the soft covalent hydrogen bond interaction which spreads along the molecular
long axis with finite inclination. Tilt angle is a primary order parameter [21,23] and the
temperature variation is estimated by fitting the observed data of θ (T) to the relation
θ (T ) α (T − TC)β.
(1)
The critical exponent β value estimated by fitting the data of θ (T) to the above
equation (1) is found to be 0.50 which agrees with the mean field theory [23] prediction.
The solid lines in Figs 7 and 8 depict the fitted data. Furthermore, the agreement of β with
16
Smectic C
12
8
HBA+7BAO
HBA+8BAO
HBA+9BAO
4
HBA+10BAO
HBA+11BAO
0
0
1
2
3
4
5
(T-Tc) / OC
Figure 8. Tilt angle in smectic phase of HBA+nBAO series (n = 7–11).

152
N. Pongali Sathya Prabu et al.
Figure 9. Light intensity versus applied field demonstration of optical shuttering in nematic of
CBA+10BAO complex.
mean field theory value infers the long-range interaction of transverse dipole moment for
the stabilization of tilted smectic phase.
4.2 Optical Shutter Action in CBA+10BAO
It is reported [24–33] that when a mesogen is subjected to an applied external field in
cholesteric, nematic, or smectic C∗ phase, there can be a phase transition. When the
CBA+10BAO compound is in its nematic phase, i.e., when an applied dc bias voltage
exceeds a particular threshold value, the phase of the compound is observed to prefer
homeotropic-like alignment with light being optically extinct which is referred to as optical
shutter. Figures 10(a)–(d) depict two regions of the nematic texture, one under the influence
of various applied fields and the other with the nonconducting surface. It is interesting to
note that immediately after withdrawing the bias voltage from the induced transition, the
original texture of the nematic phase is retained. Thus, this process is reversible with bias
voltage. In the entire thermal span of nematic phase, a ∼137◦C to ∼112◦C transition is
observed. While in the other phases, i.e., the preceding and succeeding nematic phases, no
such transition is found. Thus, the field-induced transitions can be represented as:
E0 → Optical shutter (E1).
A quantitative approach has been made to study the effect of applied electric field
on hydrogen-bonded CBA+10BAO with optical textural and light intensity studies (Fig.
9). The nematic phase with a bias voltage (both polarities) less than or equal to 4.20 V
micron−1 is referred to as E0, where there is no change in the texture of the smectic phase,
as depicted in Fig. 10(a). As the voltage is increased in small steps, the intensity of the light
from the texture drops, as can be seen from Figs. 10(b)–(d).

Influence of Terminal Groups
153
Figure 10. Nematic texture in conducting and nonconducting regions of CBA+10BAO (a) at a field
of 0 V µ−1, (b) at a field of 2.5 V µ−1, (c) at a field of 4 V µ−1, (d) at a field of 4.5 V µ−1
.
An important observation is that when a dc-bias voltage of 4.60 V micron−1 is applied,
optical extinction is observed with the optical texture of the compound suddenly disappear-
ing; this new phase is designated as optical shutter (E1) which is depicted as Fig. 10(d).
One of the possible reasons for this interesting phenomenon may be the realignment of the
molecules to form a homeotropic-like alignment.
5. Effect of Terminal Groups
The following conclusions are drawn from the above results:
a) Terminal group chlorine favored phase variants of nematic, smectic C, and smectic
G while the OH favored nematic, smectic C, and smectic F.
b) In both the series, higher order phases are induced in the higher homologues only.
c) Both the series exhibit odd–even effect in the isotropic to nematic transition tem-
perature. However, it is more pronounced in the CBA+nBAO series.
d) By increasing alkyloxy carbon number, the mesogenic thermal range is increased
in the CBA+nBAO, but the trend is reversed in the HBA+nBAO series.
e) The isotropic temperatures are more in the CBA+nBAO series when compared to
HBA+nBAO series.
f) The CBA+nBAO series homologues exhibit larger magnitude of the tilt angle
(∼20◦) compared to the HBA+nBAO series (∼16◦). The steric hindrances, which
govern the molecular rotation, are more in the HBA+nBAO series.
g) The terminal group chlorine to the aldehyde favored optical shuttering action. This
may be due to the high magnitude of electron negativity of the chlorine atom.

154
N. Pongali Sathya Prabu et al.
Acknowledgments
The authors acknowledge the financial support rendered by the Department of Science and
Technology, Govt. of India. Infrastructural support provided by Bannari Amman Institute
of Technology is gratefully acknowledged.
References
[1] Kato, T., & Frechet, J. M. J. (1995). Macromol. Symp., 98, 311.
[2] Kato, T., & Frechet, J. M. J. (1989). J. Am. Chem. Soc., 111, 8533.
[3] Kato, T., & Frechet, J. M. J. (1989). Macromolecules, 22, 3818.
[4] Kato, T., Nakano, M., Moteki, T., Uryu, T., & Ujiie, S. (1995). Macromolecules, 28, 8875.
[5] Kato, T., Frechet, J. M. J., Wilson, P. G., Saito, T., Uryu, T., Fujishima, A., Jin, C., & Kaneuchi,
F. (1993). Chem. Mater., 5, 1094.
[6] Kato, T., Wilson, P. G., Fujishima, A., & Frechet, J. M. J. (1990). Chem. Lett., 19(11), 2003.
[7] Kato, T., Fukumasa, M., & Frechet, J. M. J. (1995). Chem. Mater., 19(11), 7, 368.
[8] Fukumasa, T., Kato, T., Uryu, T., & Frechet, J. M. J. (1993). Chem. Lett., 22(1), 65.
[9] Vijayakumar, V. N., Mugugadass, K., & Madhu Mohan, M. L. N. (2010). Mol. Cryst. Liq.
Cryst., 43, 517.
[10] Chitravel, T., & Madhu Mohan, M. L. N. (2010). Mol. Cryst. Liq. Cryst., 524, 131.
[11] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2009). Ferroelectrics., 392, 81.
[12] Vijayakumar,V. N., & Madhu Mohan, M. L. N. (2010). Mol. Cryst. Liq. Cryst., 517, 113; (2010).
Mol. Cryst. Liq. Cryst., 524, 54.
[13] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2009). J. Optoelectron. Adv. Mater., 11, 1139.
[14] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2009). Braz. J. Phys., 39, 677.
[15] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2010). Mol. Cryst. Liq. Cryst., 528, 163.
[16] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2009). Solid State Sci., 12, 482.
[17] Vijayakumar, V. N., & Madhu Mohan, M. L. N. (2009). Solid State Commun., 149, 2090.
[18] Noot, C., Perkins, S. P., & Coles, H. J. (2000). Ferroelectrics, 244, 331.
[19] Gray, G. W., & Goodby, J. W. G. (1984). Smetic Liquid Crystals – Textures and Structures,
Leonard Hill: London.
[20] Swathi, P., Sreehari Sastry, S., Kumar, P. A., & Pisipati, V. G. K. M. (2001). Mol. Cryst. Liq.
Cryst., 365, 523.
[21] Chandrasekhar, S. (1977). Liquid Crystals, Cambridge University Press: New York.
[22] Barmatov, E. B., Bobrovsky, A., Barmatova, M. V., & Shibaev, V. P. (1999). Liq. Cryst., 26,
581.
[23] Stanley, H. E. (1971). Introduction to Phase Transition and Critical Phenomena, Clarendon
Press: New York.
[24] Madhu Mohan, M. L. N., Kumar, P. A., & Pisipati, V. G. K. M. (1999). Ferroelectrics, 227, 105.
[25] Kobayashi, S., & Ishibashi, S. (1994). Mol. Cryst. Liq. Cryst., 257, 181.
[26] Jong-Guang, W., & Shu-Hsia, C. (1994). Jpn. J. Appl. Phys., 33, 6249.
[27] Qian, T., & Taylor, P. L. (1999). Phys. Rev. E, 60, 2978.
[28] Napoli, G. (2006). J. Appl. Math., 71, 34.
[29] Schlangen, L. J. M., Alexandre, P., & Cornelissen, H. J. (2000). J. Appl. Phys., 87, 3723.
[30] Hurd, A. J., Fraden, S., Lonberg, F., & Meyer, R. B. (1985). J. Physique., 46, 905.
[31] Zhang, S., Wen, B., Keast, S. S., Neubert, M. E., Taylor, P. L., & Rosenblatt, C. (2000). Phys.
Rev. Lett., 84, 4140.
[32] Rotinyan, T. A., Ryumtsev, E. I., & Yazikov, S. B. (1987). JETP Lett., 46, 417.
[33] Cladiss, P. E., Garel, T., & Pieranski, P. (1986). Phys. Rev. Lett., 57, 2841.