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Structure–property correlation of a hockey stick-shaped compound exhibiting
N-SmA-SmCa phase transitions
P. Sathyanarayana,a S. Radhika,b B. K. Sadashivab and Surajit Dhara*a
Received 17th September 2011, Accepted 25th November 2011
DOI: 10.1039/c2sm06767f
We report the measurement of birefringence, dielectric constant, splay, bend elastic constants androtational viscosity in the nematic phase (N) of a hockey stick-shaped compound exhibiting smectic-A(SmA) and anticlinic smectic-C (SmCa) phase transitions at lower temperature. It is found that thephysical properties are significantly different than calamitics and partially similar to the bent-coreliquid crystals. It exhibits the positive dielectric and the negative elastic anisotropy. The optical and thethermal measurements show that all the transitions are first order. The rotational viscosity iscomparatively higher than calamitic liquid crystals and exhibits weak pre-transitional divergence. The
temperature dependent static dielectric measurements indicate antiparallel correlation of both thelongitudinal and the transverse components of dipole moments in both the smectic phases. The parallel
component of the dielectric constant exhibits a single Debye type relaxation in all the phases. The
activation energy in the N, SmA and SmCa phases are comparatively larger than that of the respective
phases of calamitic liquid crystals and can partially be attributed to the higher rotational viscosity of thehockey stick-shaped compound.

I.

Introduction

The structure–property correlation in conventional liquid crystals
made of rod-like molecules has been studied extensively andmostly well established. Efforts have always been made to design
new molecules with improved physical properties that canenhance the display performance. In this context liquid crystals
made of bent-core molecules have created worldwide interest after
the discovery of electrooptical switching in achiral bent-corecompounds.1 Subsequently several groups reported the synthesisof new liquid crystal compounds with various molecular shapes
like T, H and W.2–4 It has been established that molecular shape
has a significant role on their phase structures and physicalproperties.5–7 Commonly bent-core molecules exhibit the so calledbanana mesophases, B1–B8 and occasionally they also exhibit
some phases of calamitic liquid crystals like N, SmA and SmC etc.
To understand the effect of molecular shape nematic has always
been preferred for its simple structure and easy to perform
experiments. It has been reported that bent-core nematic
liquid crystals exhibit sign inversion of elastic anisotropy,8,9unusual electroconvection,10–12 giant flexoelectricity,13,14 large
viscosity,15,16 Kerr coefficient,17 induced18 and spontaneous
biaxiality.19,20 In the case of compounds with T shaped molecules
it was reported that the splay and bend elastic constants are almostaSchool of Physics, University of Hyderabad, Hyderabad, 500046, India.
E-mail: sdsp@uohyd.ernet.inb
Raman Research Institute, C. V. Raman Avenue, Bangalore, 560080,
India

2322 | Soft Matter, 2012, 8, 2322–2327

equal (i.e., K11 x K33) in the entire N phase.21 As mentioned thesecompounds also exhibit occasionally various smectic phases atlower temperature and the structure–property correlation of such
unconventional liquid crystals in these phases are meagre. In thispaper we report measurement of birefringence, static dielectric
constant and dielectric dispersion in the N, SmA and SmCa phases
and in addition splay, bend elastic constants, and rotational
viscosity of a hockey stick-shaped compound as a function oftemperature. The results are compared with conventionalcalamitic liquid crystals and interpreted in terms of the molecular
structure, shape and dipolar correlation in the mesophase.

II. Experimental
Two indium tin oxide (ITO) coated glass plates were thoroughly
cleaned to prepare liquid crystal cells. These plates were spincoated with polyimide (AL-1254) and cured at 180  C for 1 h andrubbed in an antiparallel manner for planar or homogeneousalignment of the sample. ITO plates were spin coated with JALS204 and were cured at 200  C for homeotropic alignment of thesample. The cell thickness was measured by using a fibre optic
spectrometer (Ocean Optics, HR-4000). The typical cell thickness
used in the experiment was 5 mm. The empty cell was heated
and filled with the sample in the isotropic phase. The phasetransition temperatures and enthalpies of the compound were
measured using differential scanning calorimetry (DSC) (PerkinElmer, Pyris ID). The textures were observed using a polarising
optical miscroscope (Nikon, LV100POL). The perpendicularand parallel components of the static dielectric constant wereThis journal is ª The Royal Society of Chemistry 2012

measured in planar and homeotropic cells respectively by using
an impedance analyser (Novocontrol, Alpha-A). In the case of
the planar cell the measuring voltage was below the Freedericksz
threshold voltage.
The temperature dependent optical retardation in the planarcell was measured by using a phase modulation technique22 withthe help of a Helium–Neon laser (HT PS-Ec-1, Thor Labs),
photoelastic modulator (PEM-100, Hinds Instruments) anda lock-in amplifier (Ametek, SR-7265). A sinusoidal voltage of
frequency 4.111 kHz and amplitude 0.5 V was used for thetemperature dependent dielectric measurement. The dielectricdispersion was measured at various temperatures in thefrequency range of 100 Hz to 10 MHz. The splay elastic constant(K11) is obtained from the Freedericksz threshold voltage (Vth)and is given by K11 ¼ 3oD3(Vth/p)2, where D3 ¼ 3k  3t is thedielectric anisotropy. At strong surface anchoring condition, thevoltages above the threshold voltage Vth, the retardation (Df) is
given by the parametric equations:23
qﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃð j¼ p
2
V2¼
1 þ g sin2 ðfm Þ
Vth p
j¼0
sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
1 þ k sin2 ðfm Þsin2 ðjÞ
dj (1)
2ð1 þ g sin ðfm Þsin2 ðjÞÞð1  sin2 ðfm Þsin2 ðjÞÞThe rotational viscosity (g1) was measured in a planar cell byusing a phase-decay time dependant measurement technique. An
arbitrary signal generator (Tektronix, AFG3102) was used toapply sinusoidal voltage at a frequency of 4.111 kHz anda photomultiplier tube (Hamamatsu, H6780-01) was used tomeasure the time dependent transmitted intensity. A small
voltage (Vb) corresponding to the first maxima or minima wasapplied depending on transmission intensity such that the total
phase retardation of sample was np, where n is an integer. At
time t ¼ 0, the bias voltage (Vb) was switched off and therelaxation transmission intensity change of the liquid crystal cell
was measured with an oscilloscope (Tektronix, TDS 2012B).
This procedure was repeated at various temperatures in the entire
nematic phase.
The time dependent transmittance at a particular temperature
in a planar cell is given by28
I(t) ¼ Io sin2 {[Dtot  d (t)]/2}(3)

where Io is the maximum intensity change and Dtot is the total
phase difference. The optical phase difference d (t), for small
director distortion can be approximated as d (t) ¼ do exp(2t/so),
where do is the total phase difference of a liquid crystal under bias
voltage (Vb) that is not far from the Freedericksz threshold01
ﬃ
ð j¼ p sﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
2
2
2
2
2
ð1
þ
g
sin
ðf
Þsin
ðjÞÞð1
þ
k
sin
ðf
Þsin
ðjÞÞ
m
m
B
C
dj
ð1  sin2 ðfm Þsin2 ðjÞÞð1 þ n sin2 ðfm Þsin2 ðjÞÞne d Bno C
B j¼0
Csﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃﬃ
Df ¼ 2p
 C
B
ne C
l B ð j¼ p2 ð1 þ g sin2 ðf Þsin2 ðjÞÞð1 þ ksin2 ðf Þsin2 ðjÞÞ
@
A
m
m
dj
ð1  sin2 ðfm Þsin2 ðjÞÞj¼0

where d is the cell thickness, fm is the tilt angle at the middle ofthe cell and the other terms of the reduced quantities are: g ¼ (3k/3t)  1, k ¼ (K33/K11)  1, n ¼ (ne2/no2)  1. f is the z-dependent
tilt angle and fm is the maximum tilt angle at the middle of thecell (z ¼ d/2) and substituted with sin(f) ¼ sin(fm) sin(j). The
sample retardation at higher voltages were fitted to the above
equations by an iterative procedure to get the bend elastic
constant K33.24,25 To verify the anchoring condition we estimated the pretilt angle (a) in the planar cell by putting thelower limit of the integration j ¼ a instead of zero in eqn (1)and (2) as a fit parameter. It was found that a # 1 at all
temperatures indicating the strong anchoring at the surface,hence a was assumed to be zero in the present analysis. It has
been reported that the pretilt angle of bent-core nematic liquid
crystals (BCN) on a planar alignment layer is very low (#1 )due to the presence of flexible alkyl chains on both sides.26
Recently we have found that a wide temperature BCN provides
a very low pretilt angle on the present alignment layer (AL1254).16 Further it may be mentioned that the flexoelectriceffect in unconventional liquid crystals could be significant andcan affect K33 measurements. From voltage dependent dielectricmeasurements it was shown by Brown et al.27 that it can slightly
underestimate K33 when the flexoelectric effect is neglected. In
our experiment we measured retardation over a small region(<1  106 m2) using a He–Ne laser and expected that such aneffect is minimum and hence not included in the present
analysis.
This journal is ª The Royal Society of Chemistry 2012(2)

voltage (Vth). In case do is close to np, d (t) becomes d (t) ¼ do exp(4t/so). The slope of the variation ln[do/d (t)] with time (t) yields
the relaxation time (so). The rotational viscosity (g1) of the liquid
crystal is given by g1 ¼ soK11p2/d2, where d is the thickness of theliquid crystal sample.

III.
A.

Results and discussion
Optical and static dielectric measurements

The hockey stick-shaped compound we studied is 4-n-butyloxyphenyl[4-(4-n-heptyloxybenzoyloxy4-benzoyloxy)]biphenyl-3carboxylate and exhibits metastable liquid crystalline phasetransitions. The chemical structure and the phase transition
temperatures of the compound is shown in Fig. 1(a). The
synthesis and some preliminary characterisation was reported
recently.29
The molecule is achiral, asymmetric, hockey stick-shaped andhas several strong dipolar groups. The texture obtained in
between two glass plates without any surface treatment is shownin Fig. 1(b). In the nematic phase a typical schlieren texture withfour brush defects is observed (Fig. 1(b) (i)). SmA is spontaneously aligned homeotropically below the N–SmA transition
temperature (Fig. 1(b) (iii)) and again the dark region of the
texture is transformed into schlieren texture as the temperature is
reduced to SmCa phase. SmCa exhibits two and four brush
defects with dynamic fluctuations (Fig. 1(b) (iv)), suggesting it toSoft Matter, 2012, 8, 2322–2327 | 2323

Fig. 1 (a) Chemical structure of the compound and the phase transition
temperatures (heating). (b) Photomicrographs obtained in an untreatedcell under cooling at different temperatures (i) N phase (ii) at N-SmA
transition (iii) SmA (iv) SmCa.

be an anticlinic SmC (SmCa) phase. Recently it has been reported
that the bent-core liquid crystals with D3 > 0 can be aligned
homeotropically on conventional alignment layers whereas
compounds with D3 < 0 in general do not align homeotropically.30 The results were explained due to the stronger dipolarinteraction of resultant dipole moment with the surfaces. The
present compound exhibits D3 > 0 (see later) and provides good
homeotropic alignment both in the N and SmA phases andsupports in favour of the explanation i.e., the strong dipolarinteraction between the substrate surface and the molecule ofmaterials with D3 > 0 stabilise homeotropic alignment. The
textures obtained in planar and homeotropic cells undera polarising optical microscope are shown in Fig. 2. It is noticed
that all the phases can be aligned well in planar cells. In the
homeotropic cell both N and SmA phases are well aligned. Incase of SmCa phase the overall texture is dark in the homeotropic
cell except that some comparatively brighter and smaller regions
are seen due to the tilting of the molecules with respect to thelayer normal.
The temperature dependent variation of Dn and a differential
scanning calorimetric (DSC) thermogram are shown in Fig. 3(a).
The enthalpies of I to N, N to SmA and SmA to SmCa transitions
are 0.38, 0.98 and 0.23 kJ mol1 respectively. Dn jumps to x0.06
from 0 at the nematic–isotropic (NI) transition and gradually
increased as the temperature was lowered. At N–SmA transition
it shows a significant increase (x0.02) and tends to saturate in
the SmA phase. A similar jump (x0.02) in Dn is also seen at
SmA–SmCa transition and it further increases as the temperature
is decreased. Since Dn f S, where S is the orientational orderparameter, it is anticipated that the orientational order parameter increases with decreasing temperature showing finite jumps
across the transitions. Hence, these are first order phase transitions. Further, N–SmA transition (Fig. 3(a)) is comparatively
2324 | Soft Matter, 2012, 8, 2322–2327

Fig. 2 Photomicrographs obtained in planar cell (i, iii, v) and inhomeotropic cell (ii, iv, vi) at various temperatures under a polarising
optical microscope. White arrows indicate the rubbing directions.

less sharp than SmA–SmCa transition due to the presence ofsmectic short-range fluctuations in the N phase. Finite enthalpies
of these transitions also suggest that the transitions are first

Fig. 3 (a) A DSC thermogram in cooling cycle (rate 5 min1) andvariation of birefringence (Dn). (b) Variation of the real part of thedielectric constant (3k, 3t and 3) as a function of temperature. Dottedvertical lines are drawn to indicate the transitions. Dashed line denotes
the extrapolated value of isotropic dielectric constant.

This journal is ª The Royal Society of Chemistry 2012

order. It may be pointed out that usually the measurement of Dn
in lower symmetric smectic phases are difficult and rare due topoor alignment. Moreover SmCa is biaxial because of tilting of
the molecules from the layer normal. The narrow lines along the
rubbing direction in Fig. 2(v) could be due to the local biaxial
order of SmCa phase. Nevertheless in the present system it waspossible to measure Dn because the director in the SmA phase iswell aligned (Fig. 2(iii)) and the effective principal axis in the
SmCa phase still remains parallel to the rubbing direction
because of opposite tilt of the molecules in the successive layers.
Temperature dependent variation of dielectric constants 3k, 3t
and average value, 3 (¼(3k + 23t)/3) are shown in Fig. 3(b). 3 in
the nematic phase is less and further reduces in smectic phasesfrom the extrapolated value of the isotropic dielectric constant.
Usually 3 is expected to increase as the temperature is reduced
due to the increase in density and the contribution fromthe orientational polarisation.31 In the present compound the
opposite behaviour, especially in the smectic phases, is due to thestrong antiparallel correlation of the longitudinal components ofdipole moments. The dielectric anisotropy D3 (¼ 3k  3t) is
positive in all the phases. 3k increases as the temperature islowered in the N phase and starts to decrease sharply at the N–
SmA transition and decreases rather slowly in the SmCa phase.
The decrease in 3k in conventional and in unconventional
compounds with similar molecular structure is also reported andattributed to the increase in antiparallel correlation between thelong axis components of dipoles in the SmA layer.8,21 The slow
decrease of 3k as the temperature is reduced in the SmCa phase isdue to the tilting of the molecules in addition to the antiparallelcorrelation. 3t decreases in the N phase as the temperature isdecreased from the I phase. It is further lower in the SmA phasethan both N and SmCa with slope change at the transitions. The
lower value of 3t in the SmA phase suggests that there is also anantiparallel correlation between the short axis components of thedipoles in the SmA layer. This result is opposite to the behaviour
seen in other unconventional liquid crystals reported recently.8,21
It may be mentioned that since the molecules have anticlinic tilt
in successive layers of the SmCa phase, 3k in this phase refers to
the dielectric constant when the electric field is parallel to thelayer normal rather than the director. Further, both the planarand homeotropic alignment of the SmCa phase are relatively
poorer than the SmA phase due to the reason mentioned above
and the absolute accuracy in the measurements of Dn, 3k and 3tin this phase is expected to be somewhat less than both in N and
SmA phases.
B. Viscoelastic measurements
To measure K11 and K33 we measured the voltage dependent
optical retardation (Df) at various temperatures in the nematic
phase. The temperature variation of K11 and K33 is shown in
Fig. 4(a). A typical variation of Df together with the best fit ofeqn (1) and (2) is also shown in the inset of Fig. 4(a). K11 issignificantly higher than K33 in the entire N phase except very
close to the NI transition, hence elastic anisotropy (DK ¼ K33 K11) is negative. K33 increases much slower than K11 withdecreasing temperature and shows strong pre-transitional
divergence as the SmA phase is approached. In case of calamitic
liquid crystals with rigid rod-like molecules DK is mostly positive
This journal is ª The Royal Society of Chemistry 2012

Fig. 4 (a) Variation of splay (K11) and bend (K33) elastic constants in the
N phase as a function of temperature. (inset) Retardation (Df) as
a function of applied voltage at T  TNI ¼ 4.5  C. Continuous line in
the inset is a theoretical fit to eqn(1) and (2). (b) Variation of rotational
viscosity (g1) as a function of temperature. (inset) Variation of ln[do/d (t)]at two temperatures namely T  TNI ¼ 7.5  C and 2.5  C with best
fits. Continuous red and green lines are drawn as a guide to the eye.

whereas in pure bent-core compounds and in their mixtures it has
been found to be negative.8,32,33 It has been shown that the bentshape of the molecules facilitates bend distortion and as a result
K33 is lower than K11. The hockey stick-shaped molecule also has
an asymmetric bent-shape and the present result is the manifestation of the same effect.
We also measured rotational viscosity (g1) in the N phase as
a function of temperature by using the time dependent phasedecay method. Representative variation of ln[do/d (t)] with time(t) at two different temperatures together with the best fits areshown in the inset of Fig. 4(b). g1 increases as the temperature islowered in the N phase and a change in curvature is observed at T
 TNI x 5  C suggesting a pre-transitional effect of the smectic
short-range order in the N phase. g1 in this compound is slightly
larger than in pure bent-core nematic liquid crystals16 andsignificantly higher than that of many known calamitic nematic
liquid crystals and their mixtures.16,32 The larger rotational
viscosity in this hockey stick-shaped compound partially may
arise due to the effect of molecular weight compared to thecalamitics. However in the case of bent-core compounds it was
attributed to the existence of temporarily fluctuating smectic
clusters of a few molecules in the N phase that are expected tooriginate from the restricted free rotation of the bent-coremolecules along the long axis.9,15 Existence of such temporary
clusters in the nematic phase is also revealed in rheological34 andSoft Matter, 2012, 8, 2322–2327 | 2325

dynamic light scattering35 studies and more recently in small
angle X-ray studies.36–39 The hockey stick-shaped molecule canbe considered as a highly asymmetric bent-core molecule andhence the enhanced rotational viscosity is believed to originate
from the temporarily fluctuating clusters.

compounds.40 Since the relaxation region due to ITO is partiallyoverlapped with dipolar relaxation we fitted complex dielectric
constant (3(u) ¼ 30 (u)  i300 (u)) as a function of frequency to findthe exact dipole relaxation frequency. The complex dielectric
function is given by3ðuÞ* ¼ 32 þ

C. Dielectric relaxation
The hockey stick-shaped molecule has several dipolar groups
which are oriented in different directions. Since D3 > 0, it isanticipated that the molecule has relatively strong longitudinal
dipole moment along the long axis and as a result 3k can relax at
relatively low frequency. In the case of 3t no dipolar relaxation
was found up to 10 MHz. Variation of 3k as a function of
frequency in the three phases at three different temperatures areshown in Fig. 5(a). It is observed that there are two relaxations,
one is temperature dependent (below 1 MHz) and the relaxation frequency decreases with decreasing temperature. The otherone is above 1 MHz frequency and temperature independent.
The high frequency relaxation is temperature independent and is
attributed to the relaxation due to the finite resistance of ITO
which is even present in the empty cell. The low frequency
relaxation is due to the longitudinal component of the molecular
dipole moment of the long axis. Cole–Cole plots of the dielectric
constant are shown in Fig. 5(b). They are semicircular with thecenters on the x-axis suggesting that the relaxation is Debye type.
Similar low frequency relaxations are also seen in other bent-core

3o  311 þ ðius1 Þ

1a1

þ

31  32
1 þ ðius2 Þ1a2(4)

where 3o is the static dielectric permittivity, 3i and si are thefrequency limits and relaxation times of the ith mode. ai is theCole–Cole distribution parameters of the respective modes.
It is found that both a1 and a2 are very small (<0.01) at all
temperatures and the relaxation time s2 is independent of
temperature as expected. The temperature variations of dielectricstrength (30  3N) and relaxation time s1 with temperature areshown in Fig. 6. The dielectric strength increases rapidly in the Nphase due to the increase in the orientational order and decreases
sharply at the N–SmA transition (Fig. 6(a)). The sharp decrease
below N–SmA transition is due to strong antiparallel correlationof the longitudinal components of the dipoles in the smectic
phases as discussed earlier. s1 increases and varies linearly with
the inverse of temperature (Fig. 6(b)) and can be fitted well with
the Arrhenius equation, s1 ¼ s0exp(U/RT). The activation energy
U of the N, SmA and SmCa phases are 158, 117 and 127 kJ mol1,
respectively. These values are comparatively higher than many
calamatics in their respective phases.41,42 Similar behaviour was
also reported very recently in a binary liquid crystal mixture (rodand bent-core) showing N–SmCa phase transition.40 Since theactivation energy represents the energy barrier associated withthe flip-over of the long molecular axis it suggests that the0

Fig. 5 (a) Frequency dispersion of the real (3k) (open symbols) and00
imaginary (3k ) (filled symbols) parts of the dielectric constant at threedifferent temperatures namely 119  C (N), 112  C (SmA) and 104  C(SmCa). Continuous lines are theoretical fit to eqn (4). (b) Cole–Cole plot
for 3k relaxation at the same temperatures. The centers of the semicircles
0
lie on the 3k axis suggesting that the relaxation is Debye type. Dashedlines are theoretical fit to the Cole–Cole equation. The high frequency
portion of the semicircles are due to the ITO cell relaxations.

2326 | Soft Matter, 2012, 8, 2322–2327

Fig. 6 (a) Variation of dielectric strength (30  3N) with temperature. (b)Variation of relaxation time s1 as a function of 1/T. Dashed lines aretheoretical fit to the equation s1 ¼ s0exp(U/RT). Vertical lines indicate thephase transition temperatures.

This journal is ª The Royal Society of Chemistry 2012

flip-over motion is relatively less easy in hockey stick or bent-coresystems than in calamitic liquid crystals. Presumably this could
arise due to the shape and larger rotational viscosity (Fig. 4(b)) of
the hockey stick-shaped and bent-core compounds. However
further investigations are needed to shine more light on this aspect.

IV. Conclusion
In conclusion, we have measured detailed physical properties ofan unconventional liquid crystal with hockey stick-shaped
molecules for the first time. All phase transitions are detected tobe first order from optical and thermal (DSC) measurements.
Dielectric measurements indicate that there exists antiparallel
dipolar correlation of both the longitudinal and transverse
components of dipole in the SmA and SmCa phases. The bendelastic constant is significantly lower than splay elastic constantas seen in other bent-core nematic liquid crystals. Rotational
viscosity is comparatively larger than calamitics and are influenced by pre-transitional smectic fluctuations. Dielectric relaxation of the longitudinal components of dipole moments is Debye
type and the relaxation frequency exhibits Arrhenius behaviour
with comparatively higher activation energy. Finally it may beasserted that some of the physical properties of hockey stickshaped compounds are noticeably different than that of calamitic
liquid crystals and the shape is an important parameter fortuning the physical properties.

Acknowledgements
One of the authors S. D. gratefully acknowledges the financial
support from the UGC-CAS School of Physics and DST, govt. ofIndia (Project no: SR/NM/NS-134/2010). P. Sathyanarayana
acknowledges CSIR-UGC for the fellowship. BKS thanks the
Indian National Science Academy, New Delhi for financial support.

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