Thermal and nonlinear optical studies of newly synthesized EDOT based bent-core and hockey-stick like liquid crystals

Article abstract of DOI:10.1039/c7nj04807f

Novel EDOT based bent-core and hockey-stick shaped mesogens bearing terminal alkyl chains and alkoxy terminal chains, respectively, have been designed and synthesized via the Sonogashira coupling reaction. Molecular structures of these new compounds were

Full text of DOI:10.1039/c7nj04807f

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Jason B. Benedict et al.
The role of atropisomers on the photo-reactivity and fatigue of
diarylethene-based metal–organic frameworks
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DOI: 10.1039/C7NJ04807F
Thermal and nonlinear optical studies of newly synthesized EDOT based bentꢀcore and
hockeyꢀstick like liquid crystals
Ashwathanarayana Gowda, Litwin Jacob, Nithin Joy, Reji Philip, Pratibha R & Sandeep Kumar*
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore ꢀ 560 080, India
Phone: +91 80 23610122, Fax: +91 80 23610492, Eꢀmail: skumar@rri.res.in
Keywords: EDOT, bent core, hockeyꢀstick liquid crystal, Sonogashira coupling reaction
Abstract
Novel EDOT based bent core and hockeyꢀstick shaped mesogens bearing terminal alkyl chains
and alkoxy terminal chains, respectively have been designed and synthesized via Sonogashira
coupling reaction. Molecular structures of these new compounds were determined by using
spectral and elemental analysis. The mesomorphic behaviour of all the novel compounds was
primarily investigated by a combination of polarising optical microscopy (POM), differential
scanning calorimetry (DSC) and Xꢀray diffraction studies (XRD). All the compounds exhibit
enantiotropic nematic phase in lower homolog. However, a smectic A phase at lower
temperature along with the high temperature nematic phase was observed in higher homologue
of BC and hockeyꢀstick LCs. The density functional theory study has been carried out to
investigate the stable configuration. The bent angle of these molecules was intermediate between
calamitic LCs and banana LCs. The photophysical properties of all the compounds were studied
in anhydrous chloroform solvent and shows absorption patterns around 370–395 nm and
emission between 418–465 nm. We have also reported large effective twoꢀphoton absorption in
these novel compounds when measured under excitation by nanosecond laser pulses at 532 nm.
All the mesogenic compounds are nonlinear materials, which make them suitable candidates for
optical limiting applications.
1

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1. Introduction
Liquid crystalline state is the unique state of soft matter with the combination of order and
mobility, i.e. anisotropic properties from crystals and mobility from the isotropic liquid. Thereby
liquid crystals (LCs) adapt various degrees of orientational order, positional long range order and
molecular mobility.1 Among the many practical applications, this combination is essential key
factor for biological selfꢀassembly. LCs with bent molecular shape are called bent core liquid
crystal or bananaꢀshaped liquid crystals (BC LCs). In 1929, several bentꢀshaped molecules were
synthesised and their mesogenic properties were reported by Vorländer2 but that time they were
just considered as “bad calamitic” LCs. After 60 years, the rebirth of BC liquid crystal research
by Matsunaga and coworkers3–6 rehabilitated the synthesis of achiral compound consists of
Schiff base bentꢀcore molecules with five benzene rings in 1991 and further, the detail
mesomorphic characterisation of one of the molecules, 1,3ꢀphenylene bis[4ꢀ(4ꢀ nꢀ
octyloxyphenyliminomethyl) benzoate] was reinvestigated by Niori et al. in 1996.7 It opened a
new era of liquid crystal research all over the world. Eventually, studies reveal unique features of
ferroelectric switching in these achiral molecules. Subsequent studies have also shown that
subtle variation in the structure of BC LCs compounds results in the significant changes in the
type of mesophases.8–16 A majority of BC LCs described up to now contains five, six and seven
phenyl rings.9,10,17–19 Very recently bent core mesogens exhibiting nematic phase at room
temperature have been reported by Pal et al.20 Several hundred BC LCs derived from different
central cores such as benzene, resorcinol, naphthalene, oxazole, oxadiazole, triazole, thiazole,
thiadiazole, thiophene, ethylenedioxythiophene, benzothiophene, benzodithiophene, pyridineꢀ
2,6ꢀdicarbaldehyde, pyrazabole, fluorenone etc. have been realized.21–22
Shorting of one ‘arm’ in bentꢀcore mesogens leads to hockeyꢀstick shape compounds. The
asymmetric shape anisotropy of the molecules often exhibit unusual mesomorphic properties
resulting between bent core and calamitic mesogens.23,24 BC and hockeyꢀstick LCs containing
heterocyclic rings are of great importance as a core unit in thermotropic liquid crystals because
the presence of hetero atoms (N, O and S) can strongly influence lateral or longitudinal dipole,
mesomorphism, polarisability, polarity, dielectric, luminescence, phase transition and molecular
geometry.5,25–34 Incorporation of five membered heterocyclic rings as a central core widens the
bend angle and shows extensive mesomorphic behaviour.21ꢀ35 LC mesogens derived from
2

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thiophene central core have significantly helped to contribute to physical parameters such as
increased lateral dipole moments, optical anisotropy, elevation of negative dielectric anisotropy,
reduction in the melting point, fast switching response,36,37 and stability of mesophase, which
promote advance technological promising materials.38–44
Among all thiophene derivatives, 3,4ꢀethylenedioxythiophene (EDOT) represents electron rich
unique building block for designing various molecular π– conjugated polymeric materials. They
have been widely studied over the past decade because the presence of EDOT moiety, which
results in a smaller intrinsic band gap in polymers, enhances electron donor ability, gives high
thermal stability and improved electro optical properties.45–48 EDOT undergoes rapid
polymerization at room temperature, which finds significant potential applications in the
fabrication of various electronic and optoelectronic devices such as, field effect transistors, solar
cells, nonꢀlinear optical materials, light emitting diodes, and molecular switches.49–53 Several
LCs derived from thiophene central core are known in the literature.36–44 Recently we have
reported the synthesis and mesomorphic characterisation of BC LCs derived from novel EDOT
central core.54,55 Herein, we report the synthesis and mesomorphic characterization of some new
BC and hockeyꢀstick LCs derived from EDOT central unit.
2. Results and Discussions
2.1. Density functional theory studies
Density functional theory (DFT) based quantum chemical calculation has been performed in
gaseous phase to calculated the related molecular parameters such as, bend angle, molecular
length, dihedral angle etc., using Gaussian 16 computational package at the level of 6ꢀ311 G(d)
basis set, Becke’s threeꢀparameter functional and LeeꢀYangꢀParr correlation functional
(B3LYP). The internal coordinates of the molecular system, which is used as input for Gaussian
16 computational program was generated by the Gauss View 06 program.56 The absence of any
imaginary frequency in the calculated vibrational frequencies ensure that the optimized geometry
corresponds to a true energy minimum. DFT computational calculations reveal the energy and
the length of fully extended bentꢀcore mesogen 9b to be ꢀ6,113,866.99 kJ molꢀ1 and 40.64 Å
respectively (Fig.1a). The dihedral angle between first phenyl ring and second phenyl ring with
3

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acetylene ring, the central EDOT core and first phenyl ring is ~180º and~170º, respectively.
Similarly, the energy and length of fully extended hockeyꢀstick shaped mesogen 10d were found
to be ꢀ12,260,268.33 kJ molꢀ1 and 35.45 Å respectively, (Fig. 1b). The dihedral angle between
first pꢀbromoꢀphenyl ring and central EDOT core, the second phenyl ring and central EDOT
core, second phenyl ring and third phenyl ring with acetylene linkage is ~170 º, 170º and 179.2º,
respectively (Fig.S1). The bending angle or bent angle (θ) is calculated by (θ) = (θ1 + θ2)/2 as
shown in Fig.1. The DFT computational analysis (Table 1) indicates that, the bend angle is
151.5º in bentꢀcore mesogens 9b and 152.2º in hockeyꢀstick like mesogens 10d respectively.57
Fig. 1 DFT optimized molecular structures: (a) bentꢀcore mesogen 9b and (b) hockeyꢀstick like
mesogen 10d. The bent angles are 151.5º and 152.2º respectively.
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Table 1. The DFT quantum chemical calculations data of representative bentꢀcore and hockeyꢀ
stick like mesogens (9b and 10d).
Compounds Selected bond length (Å) Selected dihedral angle (º) Selected bond angle (º) Bent angle (º)
1.47 (O6ꢀC7; O9ꢀC8)
1.40 (O9ꢀC3; O6ꢀC2)
1.83 (C4ꢀS5; C1ꢀS5)
1.22(C22≡C24;
Ring 1ꢀRing 2 = 180.0
Ring 2ꢀRing 3 = 170.6
Ring 3ꢀRing 4 = 170.6
Ring 4ꢀRing 5 = 179.8
C1ꢀS5ꢀC4 = 91.7
C2ꢀO6ꢀC7 = 114.2
C3ꢀO9ꢀC8 = 114.2
151.5º
152.2º
9b
C23≡C25)
1.95 (C19ꢀBr23)
Ring 1ꢀRing 2 = 169.7
Ring 2ꢀRing 3 = 170.0
Ring 3ꢀRing 4 = 179.2
C1ꢀS5ꢀC4 = 91.6
C2ꢀO6ꢀC7 = 114.2
C3ꢀO9ꢀC8 = 114.2
1.47 (O6ꢀC7; O9ꢀC8)
1.40 (O9ꢀC3; O6ꢀC2)
1.83 (C4ꢀS5; C1ꢀS5)
1.22 (C22≡C24)
10d
1.39 (C28ꢀO31)
2.2. Synthesis
The synthesis of these BC and hockeyꢀstick LCs is shown in Scheme 1. Compounds 8a and 8b
were purchased from a commercial source. Oꢀalkylation of 4ꢀiodophenol 1 with an alkyl halide
in the presence of dry potassium carbonate and dry DMF solvent under reflux condition gives 1ꢀ
alkoxyꢀ4ꢀiodobenzene 2. Sonogashira coupling reaction between compound 2 with 2ꢀmethylꢀ3ꢀ
butynꢀ2ꢀol in the presence of palladium and copper catalyst gives compound 3. The intermediate
compound 4 was obtained by refluxing compound 3 in sodium hydroxide and toluene solvent.
The palladiumꢀcatalyzed C‒H bond arylations58 of EDOT 5 with bromobenzene gives diarlylated
EDOT 6 in good yield which on bromination gives the key intermediate compound 7. The final
compounds were obtained by the Sonogashira coupling reaction between key intermediated
compounds 7 with 4ꢀalkyl (8 and 4) or 4ꢀalkoxy phenyl acetylene (9 & 10) in good yield.
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Scheme 1. Synthesis of novel bentꢀcore and hockeyꢀstick compounds: (i) alkyl halide, anhydrous
K2CO3, dry DMF, reflux, 24 h; (ii) 2ꢀmethylꢀ3ꢀbutynꢀ2ꢀol, bis(triphenylphosphine)palladium (II)
dichloride (PdCl2(PPh3)2), copper (I) iodide (CuI), triethylamine (TEA), reflux, 24 h; (iii) NaOH,
toluene, reflux, 3 h; (iv) bromobenzene, palladium acetate (Pd(OAc)2), triphenylphosphine
(PPh3), cesium carbonate (Cs2CO3), toluene, 110 ºC, 24 h; (v) Br2, dry. DCM, 6 h, r.t; (vi) 1ꢀ
ethynylꢀ4ꢀalkylbenzene, PdCl2(PPh3)2, CuI, TEA, reflux, 24 h; (vii) 1ꢀethynylꢀ4ꢀalkoxybenzene,
PdCl2(PPh3)2, CuI, TEA, reflux, 24 h.
3. Mesomorphic properties:
The thermotropic behaviour of all the synthesised compounds was first investigated by polarising
optical microscopy. The exact phase transition temperature and associated enthalpy values were
determined by differential scanning calorimetry on heating and cooling scans and the thermal
behaviour is summarized in the Table 2. The onset temperatures are given in ºC and the numbers
in parentheses indicate the transition enthalpy (ꢁH) in kJ mol−1. The five membered bent core
compounds 9a–9b exhibit wide range enantiotropic nematic phase along with SmA for 9b
compound at lower temperature. Similarly, homologous series of compounds with hockeyꢀstick
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like molecules 10a–10e exhibit exclusively wide range enantiotropic nematic phase along with
SmA phase for longer alkyl chain compounds, respectively.
Table 2. Phase transition temperature (peak in DSC, ºC, on heating scan) and enthalpy of phase
transition (ꢀH, kJ mol–1, in parentheses) of bentꢀcore and hockeyꢀstick like molecules (9a–9b &
10a–10e).
Phase transition
Peak temperature (ºC); (ꢀH, kJ mol–1) Peak temperature (ºC); (ꢀH, kJ mol–1)
Compounds
on second heating scan
on second cooling scan
9a
9b
Cr 181.3 (68.2) N 249.5 (1.7) I
I 233 (ꢀ1.4) N 170 (ꢀ24.1) Cr
Cr1 135 (4.4) Cr2 143.4 (22.0) SmA I 256.4 (ꢀ0.6) N 188.9 (ꢀ0.3) SmA
191.3 (0.1) N 257.9 (0.6) I
122.5 (ꢀ24.3) Cr2 78.6 (ꢀ2.7) Cr1
I 189.8 (ꢀ0.3) N 129.9 (ꢀ31.2) Cr
I 179.7 (ꢀ0.3) N 131.4 (ꢀ38.2) Cr
10a
10b
10c
Cr 159.2 (34.9) N 190.8 (0.3) I
Cr 146.1 (40.4) N 180.3 (0.3) I
Cr1 137.4 (6.6) Cr2 144.9 (37.4) N I 171.3 (ꢀ0.4) N 121.2 (ꢀ41.6) Cr
171.8 (0.4) I
10d
10e
Cr1 81.6 (8.5) Cr2 133.8 (39.8) SmA I 163.2 (ꢀ0.4) N 152.2 (ꢀ0.3) SmA
153 (0.3) N 163.9 (0.4) I
104.7 (ꢀ35.0) Cr
Cr 129 (52.0) SmA 154.5 (1.8) I
I 153.6 (ꢀ1.5) SmA 112.6 (ꢀ53.3) Cr
The mesophase textures of all the liquid crystalline compounds were viewed under optical
microscopy with crossed polarisers which display characteristic defect textures. The microscopic
textures were recorded by placing small amount of compounds on a normal glass slide and
covered with a cover slip. Five membered bent core compound 9a exhibits exclusively
enantiotropic nematic phase with wide temperature range. The early growing nematic droplets
and four brush nematic textures of compounds 9a are shown in Fig. 2a and 2b respectively.
Compound 9b shows SmA phase along with a nematic phase at lower temperature. To
investigate the nature of smectic phase, we used polyimideꢀ coated cells with approximately 9
ꢂm thickness for planer alignment in the mesophase. The compound 9b was filled uniformly in
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the LC cell at isotropic temperature. Upon slow cooling from the nematic phase, focal conic
texture of smectic A phase appears as shown in Fig. 2c. The series of compounds in hockeyꢀstick
like molecules 10a–10e display enantiotropic nematic phase with broad temperature ranges
followed by the appearance of SmA phase at a lower temperature for compounds 10d as shown
in Fig. 2d. Compound 10e exhibits an enantiotropic SmA phase only. Compound 9a melts at
182 ºC and become isotropic liquid at 250 ºC; the nematic texture observed on slow cooling from
the isotropic liquid (Fig. 2a and 2b). Compound 9b melts at 143 ºC to a SmA phase but prior to
that it exhibits a crystalꢀcrystal transition at 135 °C. On further heating it shows a nematic phase
at about 192 ºC that goes to the isotropic phase at 258 ºC. The nematic droplets were observed on
slow cooling from the isotropic liquid and SmA phase observed at 172 ºC (Fig. 2c) which
crystallizes at 122 ºC. The hockeyꢀstick like compound 10a melts at 159 ºC and become isotropic
liquid at 191 ºC. The nematic phase observed on slow cooling from isotropic liquid. The next
homologue of the series, 10b, becomes isotropic liquid at 180 ºC and the nematic textures were
observed on cooling from isotropic liquid. Upon heating, compound 10c endures with the
crystalꢀcrystal transition at 137 ºC and melts at 145 ºC to a nematic phase that becomes clear
liquid at 172 ºC. Nematic droplets were observed on slow cooling from the isotropic melt.
Compounds 10d and 10e show significant changes in texture from schlieren texture to the fanꢀ
like texture of smectic phase at low temperature. Compound 10d goes through crystalꢀ crystal
transition at 82 ºC and melts at 134 ºC and becomes isotropic liquid at 164 ºC. On slow cooling,
the nematic phase appears at about 163 ºC that changes to a SmA phase at 152 ºC (Fig. 2d).
Compound 10e melts at about 129 ºC and transforms to the isotropic liquid at 155 ºC. On
cooling, SmA phase appears at about 153 ºC that crystallises at 112 ºC.
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Fig. 2 Polarising optical microscopy textures, for compounds 9a: (a) early growing nematic
droplets after cooling from the isotropic liquid at 233 ºC, (b) growing of nematic schlieren
texture on further cooling to 198 ºC, for compounds 9b: (c) SmA focal conic texture observed at
172 ºC, for compounds 10d: (d) SmA texture observed at 152 ºC. All the POM textures were
viewed at 200X magnification.
The thermal behaviour of all the mesogenic compounds were also further investigated with DSC
measurements on both heating and cooling scan rate of 10 ºC min−1 and recorded under a
nitrogen atmosphere. The phase transition temperatures obtained in DSC agree very well with
POM observations. The bent core compound 9a exhibits enantiotropic nematic phase over broad
temperature range with two types of endothermic phase transition. The peak temperature at 181.3
ºC, with phase transition enthalpy (ꢀH) 68.2 kJ mol–1 is attributed to crystalline phase to N phase
while the peak at 249.5 ºC with a lower enthalpy (ꢀH = 1.7 kJ mol–1) corresponds N phase to
isotropic phase transition. On the other hand, compound 9b exhibited Cr to SmA phase at lower
temperature 143.4 ºC (ꢀH = 22.0 kJ mol–1); a weak phase transition from SmA to N phase at
191.3 ºC (ꢀH = 0.1 kJ mol–1) and N phase to isotropic phase transition at 257.9 ºC (ꢀH = 0.6 kJ
mol–1). Similarly, hockeyꢀstick compounds 10a–10c shows two types of endothermic phase
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transition from crystal to nematic phase at a lower temperature and nematic phase to isotropic
phase at higher temperature. The compound 10a shows Cr to N phase at 159.2 ºC (ꢀH = 34.9 kJ
mol–1) and N phase to isotropic phase at 190.8 ºC (ꢀH = 0.3 kJ mol–1). Compound 10b and 10c
exhibited N phase at 146.1 ºC (ꢀH = 40.4 kJ mol–1) and 144.9 ºC (ꢀH = 37.4 kJ mol–1)
respectively and transition from N phase to isotropic phase at 180.3 ºC (ꢀH = 0.3 kJ mol–1),
171.8 ºC (ꢀH = 0.4 kJ mol–1) respectively. However, on heating and cooling scans, compounds
10d exhibit additional enantiotropic SmA phase transition in between crystalline phase and
nematic phase. It displayed Cr to SmA phase at 133.8 ºC (ꢀH = 39.8 kJ mol–1); SmA to N phase
and N phase to isotropic phase at 153 ºC (ꢀH = 0.3 kJ mol–1) and 163.9 ºC (ꢀH = 0.4 kJ mol–1)
respectively. Compound 10e exhibit only a smectic phase. The crystalline compound melts to
SmA phase at 129 ºC, with transition enthalpy 52.0 kJ mol–1 which goes to the isotropic phase at
154.5 ºC (ꢀH = 1.8 kJ mol–1). As representative example, the DSC of compound 10d is shown in
Fig. 3
Fig. 3 DSC thermograms obtained for the hockeyꢀstick mesogen 10d showing phase transitions
on heating and cooling cycles at a scan rate of 10 °C min−1. Vertical arrow indicates phase
transition point.
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3.1.
Xꢀray scattering measurements
The liquid crystalline behaviour of both the novel BC LCs (9a and 9b) and hockeyꢀstick liquid
crystals (10a–10e) was further examined by Xꢀray scattering studies of unoriented samples filled
in Lindemann capillaries. A representative and typical diffraction pattern obtained for BC
compound 9b at 210 ºC in the nematic phase and at 160 ºC for the SmA phase are shown in Fig.
4 (a) and (b), respectively. The XRD pattern for nematic phase at 210 ºC shows diffuse peak at
small angle region and a diffuse wide angle maxima at d = 4.48 Å, which corresponds to typical
nematic phase as shown in Fig. 4 (a). However, the XRD pattern at 160 ºC shows a sharp
reflection in the small angle regime with dꢀ spacings 37.37 Å as shown in the Fig. 4 (b). Based
on POM observation and calculated molecular length (35.45 Å), this phase was deduced as a
SmA phase. The diffuse peak at wide angle maxima at 4.46 Å responsible for fluid like
correlation of the molecules in the layers.
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(a) 210 °C
105
104
103
d = 4.48
Å
0
5
10
15
20
25
30
2θ (degrees)
(b) 160
°
C
105
104
103
d = 37.37
Å
d = 4.46
Å
0
5
10
15
20
25
30
2θ (degrees)
Fig. 4 XRDpatterns recorded for BC LCs compound 9b on cooling from isotropic temperature:
(a) nematic phase at 210 °C; (b) smectic A phase at 160 °C respectively.
3.2. Thermogravimetric analysis
The thermal stability of all the liquid crystalline compounds was investigated by
thermogravimetric analysis (TGA). All the samples (9a–9b and 10a–10e) are subjected to heat
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scan of 10 ºC min−1 under a nitrogen atmosphere. All the mesogenic compounds show no weight
loss till about 350 ºC as shown in Fig. 5. The five membered bent core compounds 9a–9b initiate
weight loss at about 380 ºC–400 ºC and decompose at 520 ºC. Similarly, hockeyꢀstick like
compounds 10a–10e initiates weight loss at about 350 ºC and the whole process was completed
at about 500 ºC. The decomposition temperature of hockeyꢀstick like compounds decreases with
increasing terminal alkyl chain length. The thermal stability of five membered bent core
compounds was higher than hockeyꢀstick like compounds. The decomposition temperatures for
all the compounds were much higher than isotropic temperature. It concludes that all the
mesogenic compounds possess good thermal stability.
120
9a
9b
10a
10b
100
10c
10d
10e
80
60
40
20
0
200
400
Temperature
600
800
(°C)
Fig. 5. The thermogravimetric analysis of compounds 9a–9b and 10a–10e.
3.3. Raman spectroscopy
The molecular structures of novel liquid crystalline compounds were further investigated by
Raman spectroscopy. Raman spectra were recorded using Horiba Jobin Yvon T6400 Micro
Raman using He–Ne laser operating at λ = 632.8 nm. The laser power at 1.8 mW was kept
constant throughout measurement. The Raman spectral data obtained at an optical resolution of
50 × objective lenses and accumulated at 10 s to obtained data with sufficiently high signalꢀtoꢀ
noise ratio at room temperature as shown in Fig. 6. All the solid samples were placed in a normal
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glass slide and covered with a cover slip. Theoretical Raman values were compared with
experimentally obtained values are represented in Table 3. The peaks at lower regions at 919–
1193 cm–1, correspond to aliphatic chains vibrations. The intense peak at 1142 cm–1 is for the
central heteroaromatic EDOT ring ν (CꢀS). The vibrational peaks at 1437–1597 cm–1 are
obtained for aromatic and hetero aromatic rings. The intense prominent vibrational peak at 2213
cm–1 is responsible for alkyne linking group in all the mesogenic derivatives. All experimentally
1
̶
obtained Raman shift (wavenumbers, cm ) values were matching with the respective functional
groups as shown in Table 3.
70000
1597
2213
1142
1476
1437
60000
50000
40000
30000
20000
10000
0
1193
919
10e
10d
10c
10b
10a
9b
9a
-10000
1000
1500
Raman shift
2000
cmꢀ1
2500
(
)
Fig. 6 Raman data of all the mesogenic compounds (9a–9b) and (10a–10e).
Table. 3. Comparison of experimental Raman shift values of all the mesogens (9a‒9b and 10a‒
10e) with theoretical Raman shift values.
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Compounds Theoretical
Experimental
Functional
1
1
̶
̶
group/vibration
Raman shift (cm ) Raman shift (cm )
800‒950
919
υ (CꢀOꢀC)
1080‒1100
1060‒1150
1450‒1505
1550‒1610
2100‒2250
1142
υ (CꢀS) aromatic
υ (CꢀOꢀC) asym
υ (CꢀC) aromatic
υ (CꢀC) hetero ring
υ (C≡ C)
9a‒9b
&
1193
10a‒10e
1437, 1476
1597
2213
3.4. Photophysical properties:
The photophysical properties of novel compounds were investigated by PerkinꢀElmer UVꢀvis
lambda 35 doubleꢀbeam spectrometer absorption spectra. The UV absorption properties of all
the compounds (9a–9b & 10a–10e) were studied in anhydrous chloroform solvent (10ꢀ5 M)
recorded at room temperature to know absorption maxima as presented in Fig. 7 (a) and the
values were summarized in Table 4. The bentꢀcore compounds (9a–9b) exhibit maximum
absorption band at λmax = 392 nm. Similarly, hockeyꢀstick compounds (10a–10e) exhibit
maximum absorption at λmax = 375‒378 nm. The highly delocalized electronic systems and
π–π* transitions in the heteroaromatic portion (central EDOT), phenyl rings and acetylene
linking group, and high molar absorption coefficient (ε
= 6.5‒11.2 × 106 Lmol‒1cm‒1)
attributed to the maximum absorption in these compounds. Generally, the extent of light
absorption and intensity of peak in the absorption spectrum largely depends on the number of
molecules that absorb light of a given wavelength. It is also known that extended conjugation
in bentꢀcore mesogens (9a–9b) causes bathochromic shift (longer wavelength) with respect to
hockeyꢀstick like liquid crystalline compounds (10a–10e). Photoluminescence spectra of all
the mesogens (9a–9b & 10a–10e) were recorded using a spectrofluorometer (Flurologꢀ3,
Horiba Jobin Yvon), the emission spectra were recorded with a slit size of 2 nm in dilute
anhydrous chloroform solution at room temperature and all the compounds are excited at λex
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= 390 nm. The bentꢀcore mesogens (9a–9b) exhibit strong dual emission bands at 442 nm
and 464 nm along with negligible shoulder peak at 490 nm as shown in Fig. 7 (b). Similarly,
emission spectra of hockeyꢀstick compounds (10a–10e) exhibits strong dual emission bands
at 418‒423 nm and 440 nm along with shoulder peak at 468 nm. The photoluminescence
mechanism of bentꢀcore mesogens (9a‒9b) and hockeyꢀstick compounds (10a–10e) involves
two strong stable emission bands and one shoulder emission peak which attributed to the
electronic transition from lowest unoccupied molecular orbital (LUMO) to the highest
occupied molecular orbital (HOMO) and occupied molecular orbitals below HOMO (Hꢀ1, Hꢀ
2) respectively. No appreciable changes were observed on increasing number of methylene
group in the terminal chains.
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Fig. 7 (a) UVꢀVisible absorption spectrum, (b) fluorescence emission spectrum of all the
novel mesogens.
Table. 4. Photophysical properties of the bentꢀcore and hockeyꢀstick like mesogens recorded
in the anhydrous chloroform (10ꢀ5 M) solution.
Compounds Absorption λabs/nm Emission λem/nm
(ε
/106 Lmol‒1cm‒1)
9a
392 (11.2)
392 (9.1)
377 (6.5)
375 (8.2)
378 (6.6)
377 (11.1)
376 (7.1)
442, 463
443, 464
423, 441
419, 441
418, 440
421, 441
419, 441
9b
10a
10b
10c
10d
10e
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3.5. Nonlinear optical transmission measurements
Liquid crystals are known to exhibit large optical nonlinearities which have been the subject
of considerable research interest in recent years, from both experimental and theoretical point
of view. Since LC molecules typically have extended delocalized πꢀelectrons and geometrical
configuration, they are believed to be potential source of fast and large nonlinearities. In this
open aperture Zꢀscan technique (Fig. S2), the transmission of all the samples is measured as a
function of the input laser fluence. For varying the laser fluence the beam was focused using
a planoꢀconvex lens of 9.5 cm focal length, and the transmission was measured at different
positions (zꢀaxis) with respect to the beam focus. All the compounds were dissolved in
anhydrous chloroform solvent and taken in a 1 mm path length cuvette to have linear
transmission of 89% at 532 nm excitation wavelength. The samples experiences different
fluences at different z, with a maximum at the focal point (z = 0). The laser pulse energy was
100 µJ and the transmitted energy was measured using a pyro electric energy detector (Laser
probe, RJPꢀ735). A curve can be obtained by plotting the normalized transmittance,
ꢀꢁꢂꢃꢄ (where the linear transmission is taken as unity) with z position, which is called the Z
scan curve as shown in Fig. 8
Fig. 8 (a) Zꢀscan measurement of novel mesogenic compounds (9a–9b) and (10a–10e)
respectively. The experimental measurements were carried out at room temperature with very
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high dilute anhydrous chloroform solvent. (b) Normalized transmission as a function of input
laser fluence, calculated from open aperture Zꢀscan measurements recorded at laser pulse energy
of 100 micro Joules respectively.
For a spatially filtered Gaussian beam, the fluence (Fin (z)) at any position z can be obtained
from the relation,
ꢌ
ꢍ
ꢐ
ꢍ
ꢍ
ꢈ ꢊ
ꢅꢆꢇ ꢉ = 4ꢈꢋꢇ2ꢊ ꢎꢆꢇ/ꢏ ꢑꢈꢉꢊ
Where the beam radius ꢑ ꢈꢉꢊ is given by
ꢍ
ꢗ
ꢘ
ꢔ
ꢈ ꢊ
ω z = ωꢒꢈ1 + ꢓꢔ ꢖ ꢊ
ꢕ
ꢍ
⁄
ꢑꢒ is the focal spot size and ꢉꢒ is the Rayleigh length given by ꢉꢒ = ꢏꢑꢒ ꢙ. We find that the
nonlinear transmission has contributions from both reverse saturable absorption (RSA,
sometimes referred to as effective twoꢀphoton absorption (2PA) in literature)59,60 and saturable
absorption (SA).61 The nonlinear absorption coefficient is given by,
ꢚꢒ
ꢈ ꢊ
ꢚ ꢛ =
+ ꢝꢛ
ꢛ
ꢛꢜ
1 +
ꢍ
⁄
Where ꢛꢜ is the saturation intensity (in ꢞ ꢟ ) and β is the reverse saturable absorption
⁄
coefficient (in ꢟ ꢞ). Is and β can be obtained by numerically fitting the pulse propagation
equation to the measured transmission data. The obtained values are tabulated in Table 5. The
presence high electron conjugation imparts nonlinear optical properties to these molecules. This
can be attributed due to strong dipole moment and polarization of the molecules.
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ꢠꢛ
ꢚꢒ
= − ꢢ
+ ꢝꢛꢣ ꢛ
I
ꢛꢜ
ꢠꢡ
1 +
Table 5. RSA coefficient (ꢝ) and saturation intensity (ꢛꢜ) calculated for the samples from the
data given in Fig. 8
Compounds Liner
Transmission
Beta (β)
(X ꢤꢥꢦꢤꢤ
m/W)
Omega zero Energy
ꢧꢨ
(X ꢤꢥꢤꢤ
W/ꢩꢪ)
(uJ)
ꢫꢥ
(X ꢤꢥꢦꢬ m)
(%)
9a
9b
89
89
89
89
89
89
89
5.6
3.3
1.9
1.3
2.3
1.5
1.5
9.8
58
45
50
50
25
9
22
20
19
22
18
20
22
100
100
100
100
100
100
100
10a
10b
10c
10d
10e
We believe that the 2PA observed in the present samples originates from excited state
absorption. In bentꢀcore mesogens (9a‒9b), the acetylene (‒C≡C‒) linking group acts as the
conjugating spacer between central heteroaromatic EDOT ring and phenyl group with flexible
alkoxy chain entities. These compounds is expected to be higher extended delocalized πꢀ
electronic conjugation and geometrical shape of the molecules, which further enhance the high
nonlinearities. Similarly, unsymmetrical molecular structure and electron acceptor bromo group
at one end of the molecule and electron donor ability of phenyl acetylene group through central
heteroaromatic EDOT in hockeyꢀstick like liquid crystals (10a‒10e) enhance the nonlinear
optical properties.
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4. Experimental section
4.1. General procedure for the synthesis of intermediate and final compounds.
The compounds 1ꢀalkoxyꢀ4ꢀiodobenzene, 4ꢀ(4ꢀalkoxyphenyl)ꢀ2ꢀmethylbutꢀ3ꢀynꢀ2ꢀol and 1ꢀ
ethynylꢀ4ꢀalkoxybenzene were synthesised as reported62 and confirmed by spectral and
elemental analysis.
4.1.1. Synthesis of 5,7-Diphenyl-2,3-dihydrothieno[3,4-b][1,4]dioxine (6)
In a two neckꢀflak containing palladium (II) acetate (Pd(OAc)2) (5 mol %), PPh3 (10 mol %)
ligand, Cs2CO3 (2.4 mmol) in toluene solvent (50 mL) was added EDOT (1.0 mmol) and
bromobenzene (2.2 mmol) under argon atmosphere. The reaction mixture was heated at 110 ºC
for 24 h under argon. After completion of the reaction, the reaction mixture was cooled to room
temperature, an excess of water was added. The aqueous layer was extracted with ethyl acetate
(3× 100 mL) and the combined organic layers were dried over Na2SO4 and concentrated under
vacuum. The crude compound was further purified by column chromatography using silica gel.
gel (nꢀhexane/ ethyl acetate 9:1) gives desired pure product. Recrystallization of the pure
compound with a mixture of DCM: hexane (1:9) gives light green solid 6. Yield: 75 %. IR (film)
1
ν
max: 2912, 2872, 2852, 1597, 1518, 1454, 1359 cm–1; H NMR (500 MHz, CDCl3): δ = 7.76–
13
7.73 (m, 4 H), 7.38–7.34 (m, 4 H), 7.24–7.19 (m, 2 H), 4.34 ppm (s, 4 H); C NMR (125 MHz,
CDCl3): δ = 138.61, 132.96, 128.65, 126.62, 126.11.15.39, 64.59 ppm; elemental analysis:
C18H14O2S; calculated (%): C 73.44, H 4.78, S 10.87; found: C 73.51, H 4.84, S 10.91.
4.1.2. Synthesis of 5,7-bis(4-bromophenyl)-2,3-dihydrothieno[3,4-b][1,4]dioxine (7)
A solution of bromine (5.43 g, 33.97 mmol) in dry chloroform (20 mL) was added drop wise to a
stirring solution of compound 6 (5g, 16.98 mmol) in dry chloroform (75 mL) at 0 ºC, and slowly
allowed to room temperature. The resulting reaction mixture was stirred for 6 h at room
temperature. After completion of the reaction, the reaction mixture was successfully washed with
3% aqueous NaOH, saturated NaHSO3 and excess of water. The aqueous layer was extracted
with chloroform (3 × 75 mL) and the combined organic layers were dried over Na2SO4 and
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concentrated under vacuum. The crude compound was purified from column chromatography
using silica gel (nꢀhexane/ ethyl acetate 8:2) gives desired pure compound 7. Recrystallization of
pure compound from hexane afford offꢀwhite solid. Yield: 90%. IR (film) νmax: 2922, 2911,
2854, 1591, 1454, 1373, 1085 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.60 (d, J = 8.8 Hz, 4 H),
13
7.48 (d, J = 8.8 Hz, 4 H), 4.36 ppm (s, 4 H); C NMR (125 MHz, CDCl3): δ = 138.97, 131.72,
127.49, 120.35, 114.50, 64.58 ppm; elemental analysis: C18H14O2S; calculated (%): C 47.81, H
2.67, S 7.07; found: C 47.86, H 2.71, S 7.11.
4.1.3. Synthesis of final bent core and hockey-stick mesogenic compounds.
All the mesogenic derivatives were prepared by Sonogashira C–C coupling reaction between
5,7ꢀbis(4ꢀbromophenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀb][1,4]dioxine 7 with 1ꢀethynylꢀ4ꢀalkylbenzene
or 1ꢀethynylꢀ4ꢀalkoxybenzene in the presence of PdCl2(PPh3)2 and CuI in anhydrous
triethylamine solvent. The general method is described as follows.
In a threeꢀneck flask, deoxygenated solution of compound 7 (1 eq), PdCl2(PPh3)2 (0.04 eq) and
CuI (0.05 eq) in 75 mL anhydrous triethylamine solvent was allowed to stir at room temperature
under argon atmosphere for 10 minutes. To this, added 1ꢀethynylꢀ4ꢀalkylbenzene (2.5 eq) or 1ꢀ
ethynylꢀ4ꢀalkoxybenzene (2.5 eq) in triethylamine (50 mL) solvent. The resulted reaction
mixture was heated 72 ºC for 24 h. After cooled to room temperature, the reaction mixture was
diluted with diethyl ether and filtered through celite bed. The filtrate was then extracted with
diethyl ether (3 × 100 mL). The combined organic layers were dried over Na2SO4 and
concentrated under vacuum. The crude compound was purified through silica gel (nꢀhexane/
ethyl acetate 7:3) gives desired pure compound. Recrystallization of pure compound with cold
ethanol gives pale green colour compound. Yield: 55–60 %.
5,7ꢀbis(4ꢀ((4ꢀbutylphenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀb][1,4]dioxine (9a):
IR (film) νmax: 2953, 2926, 2852, 2210, 1606, 1541, 1454, 1354, 1120, 1082 cm–1; 1H NMR (500
MHz, CDCl3): δ = 7.73 ( d, J = 8 Hz, 4 H), 7.51 (d, J = 8 Hz, 4 H), 7.44 (d, J = 8 Hz, 4 H), 7.16
(d, J = 8 Hz, 4 H), 4.36 (s, 4 H), 2.62 (t, J = 7.5 Hz, 4 H), 1.63–1.58 (m, 4 H), 1.39–1.32 (m, 4
H), 0.93 ppm (t, J = 7 Hz, 6 H); 13C NMR (125 MHz, CDCl3): δ = 143.38, 139.23, 132.57,
131.77, 131.50, 128.48, 125.72, 121.49, 120.46, 115.56, 90.39, 89, 64.60, 35.61, 33.38, 22.31,
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13.91 ppm; elemental analysis: C42H38O2S; calculated (%): C 83.13, H 6.30, S 5.27; found: C
13
83.20, H 6.38, S 5.31. 1H NMR and C NMR spectrum showed in supplementary information
Fig. S3
5,7ꢀbis(4ꢀ((4ꢀhexylphenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀb][1,4]dioxine (9b):
IR (film) νmax: 2955, 2924, 2852, 2220, 1604, 1577, 1454, 1361, 1222, 1082 cm–1; 1H NMR (500
MHz, CDCl3): δ = 7.73 (d, J = 8.5 Hz, 4 H), 7.51 (d, J = 8 Hz, 4 H), 7.45 (d, J = 8 Hz, 4 H), 7.16
(d, J = 8 Hz, 4 H), 4.39 (s, 4 H), 2.61 (t, J = 7.5 Hz, 4 H), 1.64–1.58 (m, 4 H), 1.36–1.25 (m, 12
H), 0.88 ppm (t, J = 6 Hz, 6 H); 13C NMR (125 MHz, CDCl3): δ = 143.43, 139.22, 132.57,
131.77, 131.49, 128.47, 125.72, 121.49, 120.44, 115.56, 90.39, 88.99, 64.60, 35.92, 31.69, 31.19,
28.91, 22.58, 14.06 ppm; elemental analysis: C46H46O2S; calculated (%): C 83.34, H 6.98, S
4.82; found: C 83.39, H 7.03, S 4.89. 1H NMR and 13C NMR spectrum showed in supplementary
information Fig. S4
5ꢀ(4ꢀbromophenyl)ꢀ7ꢀ(4ꢀ((4ꢀ(hexyloxy)phenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀ
b][1,4]dioxine (10a):
IR (film) νmax: 2955, 2924, 2854, 2206, 1604, 1519, 1454, 1377,
1249, 1085 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.71 (d, J = 8 Hz, 2 H, 7.61 (d, J = 8.5 Hz, 2
H), 7.50–7.45 (m, 6 H), 6.86 (d, J = 8.5 Hz, 2 H), 4.37 (s, 4 H), 3.97 (t, J = 6.5 Hz, 2 H), 1.81–
1.75 (m, 2 H), 1.49–1.43 (m, 6 H), 0.91 ppm (t, J = 6.5 Hz, 3 H); 13C NMR (125 MHz, CDCl3): δ
= 159.26, 139.11, 139.03, 133.01, 132.31, 131.81, 131.70, 131.66, 127.50, 125.71, 121.71,
120.30, 115.37, 115.16, 114.67, 114.57, 90.31, 88.21, 68.11, 64.59, 31.57, 29.17, 25.69, 22.58,
14.01 ppm; elemental analysis: C32H29BrO3S; calculated (%): C 67.01, H 5.09, S 5.57; found: C
13
67.09, H 5.14, S 5.61. 1H NMR and C NMR spectrum showed in supplementary information
Fig. S5
5ꢀ(4ꢀbromophenyl)ꢀ7ꢀ(4ꢀ((4ꢀ(octyloxy)phenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀ
b][1,4]dioxine (10b):
IR (film) νmax: 2953, 2922, 2852, 2210, 1608, 1521, 1454, 1359,
1255, 1085 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.71 (d, J = 8.5 Hz, 2 H), 7.62 (d, J = 8.5 Hz,
2 H), 7.50–7.45 (m, 6 H), 6.86 (d, J = 9 Hz, 2 H), 4.38 (s, 4 H), 3.97 (t, J = 6.5 Hz, 2 H), 1.81–
1.76 (m, 2 H), 1.47–1.42 (m, 2 H), 1.34–1.25 (m, 8 H), 0.89 ppm (t, J = 6.5 Hz, 3 H); 13C NMR
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(125 MHz, CDCl3): δ = 159.26, 139.03, 139, 133.01, 132.31, 131.70, 131.66, 127.50, 125.71,
121.68, 120.30, 115.40, 115.15, 114.68, 114.57, 90.30, 88.21, 68.12, 64.59, 31.80, 29.20, 26.02,
22.64, 14.07 ppm; elemental analysis: C34H33BrO3S; calculated (%): C 67.88, H 5.52, S 5.31;
1
found: C 67.92, H 5.59, S 5.35. H NMR and 13C NMR spectrum showed in supplementary
information Fig. S6
5ꢀ(4ꢀbromophenyl)ꢀ7ꢀ(4ꢀ((4ꢀ(decyloxy)phenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀ
b][1,4]dioxine (10c):
IR (film) νmax: 2953, 2924, 2852, 2212, 1606, 1541, 1454, 1377,
1253, 1084 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.71 (d, J = 8.5 Hz, 2 H), 7.61 (d, J = 8.5 Hz,
2 H), 7.49–7.44 (m, 6 H), 6.86 (d, J = 8.5 Hz, 2 H), 4.36 (s, 4 H), 3.96 (t, J = 6.5 Hz, 2 H), 1.81–
1.75 (m, 2 H), 1.48–1.42 (m, 2 H), 1.34–1.27 (m, 12 H), 0.88 ppm (t, J = 7 Hz, 3 H); 13C NMR
(125 MHz, CDCl3): δ = 159.26, 139.11, 139.03, 133.01, 132.31, 131.81, 131.70, 131.66, 127.50,
125.70, 121.71, 120.30, 115.37, 114.67, 114.57, 90.32, 88.22, 68.12, 64.58, 31.90, 29.57, 29.55,
29.31, 29.21, 26.02, 22.68, 14.10 ppm; elemental analysis: C36H37BrO3S; calculated (%): C
68.67, H 5.91, S 5.08; found: C 68.72, H 5.96, S 5.13. 1H NMR and 13C NMR spectrum showed
in supplementary information Fig. S7
5ꢀ(4ꢀbromophenyl)ꢀ7ꢀ(4ꢀ((4ꢀ(dodecyloxy)phenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀ
b][1,4]dioxine (10d):
IR (film) νmax: 2953, 2922, 2852, 2210, 1608, 1519, 1438, 1377,
1247, 1085 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.71 (d, J = 8 Hz, 2 H), 7.61 (d, J = 8.5 Hz, 2
H), 7.50–7.44 (m, 6 H), 6.86 (d, J = 8.5 Hz, 2 H), 4.37 (s, 4 H), 3.96 (t, J = 6.5Hz, 2 H), 1.81–
1.75 (m, 2 H), 1.48–1.42 (m, 2 H), 1.35–1.26 (m, 18 H), 0.88 ppm (t, J = 7 Hz, 3 H); 13C NMR
(125 MHz, CDCl3): δ =159.26, 139.10, 139.03, 133.01, 132.30, 131.81, 131.70, 131.65, 127.50,
125.70, 121.71, 120.30, 115.15, 114.67, 114.57, 90.31, 88.21, 68.12, 64.58, 31.91, 30.89, 29.65,
29.63, 29.56, 29.38, 29.34, 29.20, 26.01, 22.68. 14.09 ppm; elemental analysis: C38H41BrO3S;
calculated (%): C 69.39, H 6.27, S 4.86; found: C 69.45, H 6.32, S 4.92. 1H NMR and 13C NMR
spectrum showed in supplementary information Fig. S8
5ꢀ(4ꢀbromophenyl)ꢀ7ꢀ(4ꢀ((4ꢀ(tetradecyloxy)phenyl)ethynyl)phenyl)ꢀ2,3ꢀdihydrothieno[3,4ꢀ
b][1,4]dioxine (10e):
IR (film) νmax: 2955, 2920, 2852, 2214, 1606, 1508, 1454, 1377,
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1242, 1082 cm–1; 1H NMR (500 MHz, CDCl3): δ = 7.64 (d, J = 8 Hz, 2 H), 7.54 (d, J = 8.5 Hz, 2
H), 7.42–7.37 (m, 6 H), 6.79 (d, J = 8.5 Hz, 2 H), 4.29 (s, 4 H), 3.89 (t, J = 6.5 Hz, 2 H), 1.73–
1.68 (m, 2 H), 1.48 (br, 2 H), 1.39–1.35 (m, 2 H), 1.27–1.19 (m, 22 H), 0.81 (t, J = 6.5 Hz, 3 H);
13C NMR (125 MHz, CDCl3): δ = 158.25, 138.10, 138.02, 132, 131.29, 130.80, 130.69, 130.64,
126.48, 126.69, 120.70, 119.28, 114.36, 114.14, 113.66, 113.56, 89.31, 87.20, 67.10, 63.57,
30.91, 28.67, 28.66, 28.64, 28.58, 28.55, 28.37, 28.34, 28.20, 25.01, 21.67, 13.09 ppm; elemental
analysis: C40H45BrO3S; calculated (%): C 70.06, H 6.60, S 4.66; found: C 70.11, H 6.64, S 4.72.
1H NMR and 13C NMR spectrum showed in supplementary information Fig. S9
5. Conclusions
Two new series of BC and hockeyꢀstick like liquid crystals from central EDOT core were
synthesized and characterized. The BC LCs exhibits wide range of enantiotropic nematic phase
for lower homologues and SmA phase for higher homologues at lower temperature. Similarly,
hockeyꢀstick compounds exhibit wide range enantiotropic nematic phase for lower homologues,
while SmA phase obtained from higher homologues at lower temperature respectively. DFT
calculations revealed that the bent angle of these compounds is around 151º‒153º. All the
compounds exhibits strong photoluminescence in chloroform solvent under excitation
wavelength of 390 nm. The presence of extended delocalized πꢀelectron conjugations in these
novel mesogens exhibit large optical nonlinear properties which make them potential candidates
for technological applications.
Supplementary Information
13
The general methods, DFT calculations, NLO experimental set up and NMR spectra (1H and
NMR) of all the mesogens are provided.
Acknowledgements
The author thanks Dr. Vijayaragavan for recording NMR spectra. Dr. Srinivas HT, Ms. Vasuda
for their technical support. Mr. Yathendran for Raman studies.
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DOI: 10.1039/C7NJ04807F
Graphical abstract
Thermal and nonlinear optical studies of newly synthesized EDOT based bent-core and
hockey-stick like liquid crystals
Ashwathanarayana Gowda, Litwin Jacob, Nithin Joy, Reji Philip, Pratibha R & Sandeep Kumar*
Raman Research Institute, C.V. Raman Avenue, Sadashivanagar, Bangalore - 560 080, India
Phone: +91 80 23610122, Fax: +91 80 23610492, E-mail: skumar@rri.res.in
The synthesis and characterisation of some novel bent-core and hockey-stick like liquid crystals
from EDOT are reported. All the compounds exhibit enantiotropic mesophase with wide
temperature range. These mesogens shows good photophysical and nonlinear optical properties.