Influence of polar substituent on central bending unit of bent core mesogens: Synthesis, photophysical, mesomorphism and DFT studies

Article abstract of DOI:10.1016/j.molstruc.2016.04.060

New five ring bent core mesogens derived from substituted 1,3-phenylenediamine (4-nitro-1,3-phenylenediamine, 4-chloro-1,3-phenylenediamine) were synthesized. Their molecular structures, photophysical properties and mesogenic behaviors were investigated.

Full text of DOI:10.1016/j.molstruc.2016.04.060

Journal of Molecular Structure 1119 (2016) 177e187
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Influence of polar substituent on central bending unit of bent core
mesogens: Synthesis, photophysical, mesomorphism and DFT studies
a
,
*
a
b
b
Manoj Kumar Paul , Gayatri Kalita , Barnali Bhattacharya , Utpal Sarkar
a
Department of Chemistry, Assam University, Silchar 788011, India
Department of Physics, Assam University, Silchar 788011, India
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 10 February 2016
Received in revised form
New five ring bent core mesogens derived from substituted 1,3-phenylenediamine (4-nitro-1,3-
phenylenediamine, 4-chloro-1,3-phenylenediamine) were synthesized. Their molecular structures,
photophysical properties and mesogenic behaviors were investigated. The molecular structures and the
purity of the bent core molecule have been characterized by spectroscopic studies and elemental analysis
respectively. Photophysical properties of bent core compounds were investigated in chloroform by using
UVevisible and fluorescence spectroscopic studies. The phase transition temperatures were detected by
differential scanning calorimetry analysis and the phases are confirmed by polarizing optical microscopy.
The polar substituents on bent core unit of bent shaped molecule influence the mesomorphic behaviors
of the bent core mesogens. The polar nitro group at 4-position of the bent core unit displays tilted
smectic C phase and unknown smectic X phase whereas chloro group at 4-position exhibits orthogonal
smectic A phase. The bent core mesogens are fluorescent in nature. The density functional theory
calculation was carried out to obtain the stable molecular conformation and chemical reactivity of the
bent core molecules. Orbitals involved in the electronic transitions and their corresponding energies
together with oscillator strengths have been reported.
19 April 2016
Accepted 20 April 2016
Available online 23 April 2016
Keywords:
Bent core molecule
Photophysical
Mesomorphism
Computational studies
©
2016 Elsevier B.V. All rights reserved.
1
. Introduction
mesophase behavior and their transition temperatures. Generally,
the substitutions viz., fluoro, chloro, bromo, nitro, cyano, methyl
etc. attached to the central bending unit change the bending angle
of the molecule which in turn leads to the formation of different
types of mesophase [3]. The structure-property relationship of the
bent core molecules are well documented in excellent reviews
[4e7]. The most of the rigid bent core unit used in mesogenic bent
core molecule consists of resorcinol molecule whereas mesogenic
bent core molecules obtained from 1,3-phenylene diamine rigid
bent core are rare and limited [8e10]. Further, lateral substituents
on the central resorcinol bending unit or the outer phenyl ring
significantly influence the mesogenic behavior [11e21]. Moreover,
it is established that mesophase behavior of the BCMs are much
more strongly influenced by the substituent at the central bent core
unit than by these at the outer phenyl ring [22e25]. The dipolar
effects are more significant than the steric effects due to the pres-
ence of the polar substituent on the central or outer phenyl ring of
the molecule. The first symmetrical achiral bent core molecule
Since more than last two decades, achiral bent core mesogens
BCMs) paid a special attention in the area of soft materials due to
(
their interesting functional properties such as macroscopic polar
order due to restricted rotation along molecular long axis (viz.,
ferro- and anti-ferroelectricity) [1], macroscopic chiral structure
due to spontaneous achiral symmetry breaking [2] and exhibited
fascinating optical textures. The manifestation of such interesting
properties and exotic optical textures in BCMs depend on the mo-
lecular structural arrangement and their intermolecular in-
teractions. The molecular structure and the intermolecular
interactions are further governed by the factors such as bent core
unit, number of the phenyl rings, length of the terminal chain, di-
rection and the conjugation of the linking group between the two
phenyl rings units and nature of substituents on the bending unit or
outer phenyl ring of the bent core molecule. Moreover, in general,
small changes in these factors led to drastic change in the
0
0
derived from 1,3-phenylene diamine viz., N, N -bis[4-(4 -n-alkox-
ybenzoyloxy)benzylidene]-phenylene 1,3-diamine exhibited
and or B phase depending on the 4-n-alkoxy chain length [26]. To
B
6
*
Corresponding author.
1
E-mail address: paulmanojaus@gmail.com (M.K. Paul).
http://dx.doi.org/10.1016/j.molstruc.2016.04.060
022-2860/© 2016 Elsevier B.V. All rights reserved.
0

178
M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
the best of our knowledge, influence of substitutions on bent core
2.4. Synthesis of 4-n-tetradecyloxybenzoyloxybenzaldehyde (2)
0
0
unit of a bent molecule N, N -bis[4-(4 -n-tetradecyloxybenzoyloxy)
benzylidene]-phenylene 1,3-diamine have not been studied. This
may be due to the complexity in the synthesis and purification of
the compounds. Moreover, in recent years, light emitting mesogens
drags attention as new functional materials due to their potential
application in organic light emitting diodes. The photophysical
studies of the bent core mesogenic functional materials are less
studied [27e30].
In this article, we report the influence of the strong (nitro) and
weak (chloro) electron withdrawing lateral substituents on the
bending unit of the bent core molecule. The dipolar properties of
the nitro group are significantly differs from the chloro group.
Therefore, the nature of the mesophase is greatly influenced by the
substitution of nitro and chloro group at the bending unit of the
bent core molecule. As mentioned, the two new bent core com-
The synthesis of 4-n-tetradecyloxybenzoyloxybenzaldehyde
was prepared by following earlier reported procedure [38].
2.5. General procedure for synthesis of bent core compounds (3-X)
4-n-tetradecyloxybenzoyloxybenzaldehyde
(219
mg,
5 ꢂ 10ꢁ mol) was dissolved in absolute ethanol with few drops of
glacial acetic acid and reflux for 30 min. To this refluxing solution,
an absolute ethanolic solution of substituted 1,3-phenylenediamine
4
ꢁ
4
[viz., 4-nitro-1,3-phenylenediamine (39 mg, 2.5 ꢂ 10 mol), 4-
ꢁ
4
chloro-1,3-phenylenediamine (36 mg, 2.5 ꢂ 10
mol)] was
added drop by drop with constant stirring. The reaction mixture
was refluxed for 4 h with constant stirring. The excess of ethanol
was evaporated to obtain the yellow solid which was washed
several times with ice cold dry hexane to get the compound.
2
pounds 3-NO and 3-Cl have been synthesized and study their
photophysical properties, mesophase behavior and to explore the
structural and electronic properties of the BCMs by computational
studies.
0
0
2.5.1. N, N -bis[4-(4 -n-tetradecyloxybenzoyloxy)benzylidene]-4-
nitrophenylene-1,3-diamine (3-NO
Yield: 119 mg (46%); IR (
max in cmꢁ1): 1687 (
imine), 1564 ( C) aromatic), 1487, 1447, 1387 (
(CDCl , 300 MHz):
¼ 8.60 (s, 1H, CH]N), 8.20 (s, 1H, CH]N),
.06e6.94 (19H, AreH), 4.04 (t, 4H, J ¼ 6.4 Hz, eOCH e), 1.83e1.28
(m, 48H,e(CH ). Elemental
12e), 0.90 (t, 6H, J ¼ 6.8 Hz, eCH
analysis calculated for C62 : C, 74.89; H, 8.11; N, 4.63;
Found: C, 75.01; H, 8.24; N, 4.51%.
2
)
y
C O C N
n ] ), 1606 (n ]
nNO nitro). HNMR
1
n
(C
]
2
. Experimental
3
d
8
2
2.1. Chemical and instruments
2
)
3
79 3 8
H N O
The chemicals used for the synthesis of BCMs were procured
from M/s Alfa Aesar, Sigma Aldrich and Tokyo Kasei Kogyo Co. Ltd.
The solvents and reagents are of AR grade and were distilled and
dried before use. Micro analysis of C, H and N elements were
0
0
2.5.2. N, N -bis[4-(4 -n-tetradecyloxybenzoyloxy)benzylidene]-4-
chlorophenylene-1,3-diamine(3-Cl)
determined on Perkin Elmer 2400elemental analyzer. IR spectra
Yield: 90 mg (37%); IR (
), 1606 ( imine), 1564 (
HNMR (CDCl , 300 MHz):
¼ 8.45 (s, 1H, CH]N), 8.19 (s, 1H, CH]
N), 8.08e6.98 (19H, AreH), 4.03 (t, 4H, J ¼ 6.8 Hz, eOCH e),
1.86e1.26 (m, 48H,e(CH ).
12e), 0.89 (t, 6H, J ¼ 6.6 Hz, eCH
Elemental analysis calculated for C62 Cl: C, 75.92; H, 8.04;
y
max in cmꢁ1):2981, 2850 (
n
CH), 1731
1
were recorded on a Shimadzu IR Prestige-21 on KBr disk. The
H
(
n ]
C O
n
C
]
N
(C
n ]C) aromatic), 1487, 1447.
1
nuclear magnetic resonance spectra were recorded either on JEOL
AL300 FTNMR multinuclear spectrometer in CDCl (chemical shift
in parts per million) solution with TMS as internal standard.
3
d
3
2
d
2
)
3
UVevisible absorption spectra of the compounds in chloroform
were recorded on a Perkin Elmer lambda 35 UVevisible spectro-
79 2 6
H N O
N, 2.93; Found: C, 75.70; H, 8.09; N, 2.85%.
photometer (lmax in nm). Fluorescence emission spectra of the
compounds in chloroform were recorded with a Perkin Elmer LS45
spectro-fluorophotometer. The phase transition temperatures,
associated enthalpies and entropies were recorded at a heating/
3. Results and discussion
3.1. Synthesis and molecular characterization
ꢀ
ꢁ1
cooling rate of 5 C min on differential scanning calorimetry
DSC) (PerkineElmer Pyris-1 system). The DSC was calibrated with
(
Achiral five ring bent core molecules derived from 4-substituted
1,3-phenylenediamine possessing ester and imine linkage had been
designed with 4-n-tetradecyloxy chain at both ends. The ester and
imine linking groups are more commonly used linking group in
liquid crystalline molecule due to fact that these linking moieties
enhances conjugation of the molecule and in turn more conductive
to liquid crystal formation. The detail synthesis of the compounds
as shown in Scheme 1 was carried out by the following procedure
described in experimental section. The alkylation of 4-
hydroxyethylbenzoate with 4-n-tetradecylbromide followed by
acid hydrolysis to gives 4-n-tetradecyloxybenzoic acid (1). The 4-n-
tetradecyloxybenzoic acid was further esterified with 4-
hydroxybenzaldehyde by phase transfer method using tetrabuty-
lammonium bromide (TBAB) as catalyst to gives4-n-tetradecylox-
ybenzoyloxybenzaldehyde (2). The condensation of 4-n-
tetradecyloxybenzoyloxybenzaldehyde (2) with substituted 1,3-
phenylene diamine (4-nitro-1,3-phenylediamine and 4-chloro-
ꢀ
ꢁ1
ꢀ
ꢁ1
indium (156.6 C, 28.4 Jg ) and tin (232.1 C, 60.5 Jg ). The liquid
crystalline properties of the compounds were characterized by
using polarized optical microscope (Nikon optiphot-2-pol attached
with hot and cold stage HCS402, with STC200 temperature
controller configured for HCS402 from INSTEC Inc. USA).
2.2. Computational details
The density functional theory (DFT) has been used to explore the
structural and electronic properties of the BCMs. We have used
Becke's three-parameterized exchange functional and Lee-Yang-
Parr correlation functional (B3LYP) [31,32] and 6-31G (d) basis set
[33e35]. All DFT calculations are performed with Gaussian 09
program package [36]. To see the effects of solvent, calculations are
also presented in the presence of chloroform as solvents.
1
,3-phenylenediamine) in absolute ethanol with a few drops of
glacial acetic acid to yield final target achiral five ring bent core
and Cl). The introduction nitro and
2.3. Synthesis of 4-n-tetradecyloxybenzoic acid (1)
compounds (3-X, X ¼ NO
2
chloro substituents on the bending unit of bent core molecule is
due to their strong and weak electron withdrawing nature which in
turn influences the dipolar nature of the bent core molecule. The
4
-n-tetradecyloxybenzoic acid was prepared following the
earlier reported procedures [37].

M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
179
absorption peak at 260 nm (εmax ¼ 21970 Lmolꢁ cm ). These
1
ꢁ1
absorption band with large molar extinction coefficient reflects the
p-
p* transition of polar C]O and C]N groups of the molecule. The
absorption band ranging from 300 to 437 with small molar
ꢁ
1
ꢁ1
extinction coefficient (εmax ¼ 2310 Lmol cm ) indicates n-
p*
transition of the molecule as presented in Fig. 1. The chloro
substituted bent core compound (3-Cl) exhibited absorption peaks
ꢁ
1
ꢁ1
at 290 nm (εmax ¼ 53600 Lmol cm ) and broad band ranging
ꢁ1
ꢁ1
from 309 to 409 nm (εmax ¼ 1920 Lmol cm ) indicated n-
transition as presented in Fig. 2. The fluorescence emission spectra
of the bent core compounds (3-X, X ¼ NO and Cl) were examined
in chloroform solution (1 ꢂ 10 M), and it was found that com-
pound (3-NO ) exhibited strong fluorescence in ultraviolet region
em ¼ 305 nm) on excitation at 260 nm (see Fig. 3) whereas 3-Cl
emitted in the visible region (
em ¼ 420 nm) with a shoulder at
09 nm on excitation at 310 nm which is tailing over 600 nm as
presented in Fig. 4. The photophysical properties of the ligands (3-
X, X ¼ NO and Cl) in chloroform are presented in Table 1. The
emission peak for compound (3-NO ) observed at 305 nm with a
ss) of 222222 cm and 3-Cl observed at 420 nm and
p*
2
ꢁ
5
2
(l
l
5
2
2
ꢁ
1
stoke shift (
n
Scheme 1. Synthetic route for the preparation of the bent core compounds. Reagents
and conditions: (i) Absolute EtOH, KOH, KI (catalytic amount), reflux 40 h; (ii) HCl, H O,
reflux, 6 h; (iii) SOCl , reflux, 3 h; (iv) Dry DCM, K CO , TBAB, Stir 24 h at room tem-
perature; (v) Absolute EtOH, glacial AcOH, 4-nitro-1,3-phenylenediamine or 4-chloro-
,3-phenylenediamine.
ꢁ1
2
509 nm with a stoke shift of 90909 and 50251 cm respectively.
2
2
3
The stoke shift value of the 3-Cl is larger as compared to the
compound 3-NO . The larger stoke shift value for the chloro
2
substituted compound can be due to the significant structural
changes that occur between the ground and excited state. Despite
similar skeletal structure of the molecule, a large red-shift in
1
compounds (3-X, X ¼ NO
2
andCl) were purified by washing pre-
2
fluorescence ~115 nm for 3-Cl in contrast to 3-NO is intriguing.
cipitate several times with cold dry hexane till the appearance of
single spot in neutral alumina thin layer chromatographic plate.
The molecular structure and the chemical purity of the newly
This may be due to the replacement of nitro group by the chloro
group, which further led to change in the electronic structure of the
molecule. Interestingly, 3-Cl showed characteristic dual emission
peaks. The emission peak at the lower wavelength ~420 nm cor-
responds to the radiative transition from local excited state or Frank
Condon state while the second emission peak observed at the
longer wavelength ~509 nm due to intramolecular charge transfer
transition state [39].
synthesized bent core compounds (3-X, X ¼ NO
2
and Cl) were
confirmed by spectral and elemental analysis. The formation of the
compounds were confirmed by Fourier transform infrared (FTIR)
with the appearance of characteristic imine (C]N) stretching peak
ꢁ1
in the range of 1606e1600 cm , ester (C]O) stretching in the
range of 1687e1649 cm 1and ether CeO stretching at
ꢁ
ꢁ
1
1
1
(
8
257 cm respectively. H NMR spectra of the bent core molecule
3-X, X ¼ NO and Cl) show two signal appeared in the range of
.20e8.60 ppm due to imine proton and confirmed the formation
of the Schiff base. All the aromatic protons appeared in the range of
2
8
.23e6.42 ppm.
2.5
2.0
1.5
1.0
0.5
0.0
3.2. Photophysical studies
3-NO
The emission properties of organic bent core mesogens are
currently an active area of research due to their potential applica-
tions in opto-electronics. Emissive mesogens are fascinating sys-
tems for soft materials research because they couple molecular self-
assembly with intrinsic light generation capability. The substituent
on the central core plays an important role in the modification of
the electronic characteristics of the molecules. Hence, the absorp-
tion and emission properties of the compounds were studied, and
the results are presented. The UVevisible absorption spectra of the
bent core compounds (3-X, X ¼ NO
2
and Cl) in chloroform were
studied at concentration of 1 ꢂ 10 M as presented in Table 1. The
-nitro substituted bent core compound (3-NO exhibited
250
300
350
400
450
500
ꢁ
4
Wavelength (nm)
4
2
)
in chloroform (c ¼ 1 ꢂ 10ꢁ M).
4
Fig. 1. UVevisible absorption spectra of 3-NO
2
Table 1
A summary of the photophysical properties of the compounds in chloroform.
ss (cm 1
ꢁ
)
Compounds
Abs,
l
max (nm)
Molar extinction coefficient, ε
Excited wavelength
l
ex (nm)
Fl.
lem (nm)
Stoke shift,
222222
n
ꢁ
1
ꢁ1
(Lmol cm )
3
-NO
-Cl
2
260
21970
2310
53600
1920
260
310
305
3
00e437
290
09e409
3
420
508
90909
50251
3

180
M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
0.6
crystalline phases. The transition temperatures, enthalpies and
entropies associated with the phase transitions of the BCMs (3-NO
and 3-Cl) which were obtained from DSC at a scan rate of
2
ꢀ
ꢁ1
5
C min in the first heating and cooling scans are presented in
3-Cl
Table 2. The DSC thermogram of compound 3-NO is presented in
2
0.4
Fig. 5. The phase transition temperature of compound 3-Cl could
not be recorded in DSC due to either viscous nature of the sample
that leads to slow crystallization or vitrification of the mesophase.
The compound 3-NO
whereas 3-Cl exhibited only SmA phase as observed by POM. On
slow cooling the compound 3-NO from isotropic liquid, branched
2
exhibited SmC and unidentified SmX phase
0.2
2
like texture grow from black field (isotropic liquid) of the crossed
ꢀ
polarizers at 127.1 C as presented in Fig. 6a. The branched texture
0.0
transform to two and four brushes defects schlieren texture at
300
350
400
ꢀ
126.5 C as presented in Fig. 6b, a typical texture of smectic C phase.
Wavelength (nm)
On further cooling, the smectic C phase undergoes a transition to an
unidentified SmX phase at 123 C as presented in Fig. 6c. The
ꢀ
Fig. 2. UVevisible absorption spectra of 3-Cl in chloroform (c ¼ 1 ꢂ 10ꢁ4 M).
birefringent unidentified SmX phase completely grows as pre-
ꢀ
sented in Fig. 6d. Finally, crystallization occurs at 86 C. The phase
transition temperatures obtained from the DSC thermogram of the
100
2
compound (3-NO ) are matches with the transition temperature
obtained from polarized optical microscopy. The DSC could not
detect the SmC-SmX transition. This indicates that enthalpy change
3-NO
2
80
60
40
20
ꢁ
1
during SmCeSmX phase transition is very small (<0.01 kJ mol
)
and is second order transition. The large enthalpy change
ꢁ1
(
~6 kJ mol ) during isotropic to SmC transition indicate strong first
order character of transition [40]. On slow cooling the sample (3-Cl)
from isotropic liquid, batonnets texture appears which further co-
alesces to form typical focal conic texture with a dark (homeo-
ꢀ
tropic) region at 116.8 C indicates SmA phase as presented in
Fig. 7a. The homeotropic region increases either by application of
the mechanical stress or by shearing the glass slides, confirmed
SmA phase. On further cooling, the homeotropic regions lowly
disappeared to a focal conic texture. The focal conic SmA texture
persist to room temperature as presented in Fig. 7b.
0
2
80
300
320
340
360
380
400
Wavelength (nm)
) recorded in chloroform (1 ꢂ 10ꢁ M)
5
Fig. 3. Emission spectrum of compound (3-NO
at excited 260 nm.
2
3.4. DFT studies
Geometry optimization was performed without imposing mo-
lecular symmetry constraints to determine the stable configuration.
The optimized structures have no imaginary frequency which
confirms that they correspond to minimum in the potential energy
surface. Our calculation [see in supporting information Table S1
40
30
20
10
3-Cl
(aeb)] shows that some dihedral angles get changed in solvent
phase compare to gas phase. The dihedral angles changed signifi-
cantly near the rigid aromatic core region than the flexible long
aliphatic region of the 3-X (X ¼ Cl, NO
2
) molecule. Since nitro group
is a strong electron withdrawing group than chloro group, the
change in dihedral angles is more intensive near the nitro group
2
than chloro group. It is observed that, in case of 3-NO substituted
system, there is large change in bending angle when the system
undergoes transition from gas phase to solvent phase and this
change is much greater than 3-Cl substituted system [see Fig. 8].
Therefore, a noticeable change in dihedral angle in solvent phase
0
3
50
400
450
500
550
600
Wavelength (nm)
2
has been found near the core region for 3-NO substituted system.
Fig. 4. Emission spectrum of compound (3-Cl) recorded in chloroform (1 ꢂ 10ꢁ M) at
5
The bending angle of core compounds (3-X, X ¼ NO
2
and Cl),
excited 310 nm.
reduced in solvent phase compare to gas phase.
The UVevisible absorption spectra of the compounds have been
studied using time dependent density functional theory (TD-DFT).
The calculated electronic excitations of maximum intensity as well
3
.3. Mesomorphic behavior: polarized optical microscopy and
differential scanning calorimetric studies
as highest oscillator strength are listed in Table 3. For 3-NO
2
substituted system, the UVevisible spectra in both gas phase and
solvent phase shows that the maximum peak corresponds to
highest oscillator strength. But for 3-Cl substituted system, in both
gas phase and solvent phase the UVevisible spectra shows that the
To confirm the observed phase transition temperatures ob-
tained by differential scanning calorimetry (DSC), the polarized
optical microscopy (POM) were performed and examined liquid

M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
181
Table 2
ꢀ
Phase transition temperatures ( C) of the bent core compounds recorded for first heating (first row) and first cooling
ꢀ
ꢁ1
(
second row) cycles at 5 C min from DSC and confirmed by polarized optical microscopy. The enthalpies (DH in
ꢁ
1
ꢁ1 ꢁ1
S in Jmol K ) respectively are presented in parentheses.
kJ mol ) and entropies (
D
ꢀ
Compounds
Phase transition temperature in C (enthalpy, entropy)
3
-NO
-Cla
2
Cr 85.4 (11.53, 32.17) SmX 88.8 (6.88, 19.01) SmC 128.5 (6.60, 16.43) Iso
Cr 78.1 (13.16, 37.27) SmX 86.0 (18.36, 51.14) SmC 127.3 (6.39, 15.96) Iso
Cr 106.0 SmA 169.6 Iso
3
Iso 167.0 SmA 87.0 Cr
a
Indicates the polarizing optical microscopic temperature.
ꢀ
Fig. 5. DSC thermogram of compound 3-NO
2
in the heating and cooling cycle at 5 C/min.
ꢀ
Fig. 6. Polarizing optical photograph of 3-NO
2
during cooling: (a) branched like schlieren growth from isotropic liquid at 127.1 C; (b) Typical two and four brushes schlieren texture
ꢀ
ꢀ
ꢀ
of the smectic C phase at 126.5 C; (c) transition of smectic C phase to SmX phase at 123 C. (d) unidentified SmX phase at 122.5 C.

182
M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
ꢀ
ꢀ
Fig. 7. Polarizing optical photograph of 3-Cl during cooling: (a) focal conic texture of smectic A at 116.8 C; (b) focal conic texture of SmA phase at 30 C.
2 2 2
Fig. 8. Optimized geometries of 3-Cl and 3-NO with bending angle in both gas and solvent phase (a) 3-Cl in gas phase; (b) 3-Cl in chloroform; (c) 3-NO in gas phase; (d) 3-NO in
chloroform.
Table 3
2
Calculated electronic transitions for maximum peak in UVeVisible absorption spectra of bent core compounds (3-NO and 3-Cl) in gas medium and chloroform.
Compounds
Medium
Gas
Abs,
l
max (nm)
Oscillator strength, f
Excitation transitions
3-Cl
289.755
0.422
HOMO-3 / LUMO (15%)
HOMO-2 / LUMO (16%)
HOMO / LUMOþ2 (19%)
HOMO / LUMOþ3 (33%)
HOMO / LUMO (29%)
HOMO / LUMOþ1 (59%)
(maximum peak)
3
59.299
highest Osc. strength)
294.981
maximum peak)
56.039 (highest Osc. strength)
0.5004
0.5218
0.626
0.754
0.364
(
Chloroform
Gas
HOMO-2 / LUMOþ1 (39%)
HOMO-1 / LUMOþ1 (30%)
HOMO / LUMO (51%)
HOMO / LUMOþ1 (37%)
HOMO-1 / LUMO (34%)
HOMO / LUMO (41%)
HOMO-2 / LUMOþ1 (20%)
HOMO-1 / LUMOþ1 (24%)
HOMO-1 / LUMOþ2 (10%)
HOMO / LUMOþ2 (19%)
HOMO-3 / LUMO (42%)
HOMO-1 / LUMO (40%)
HOMO-1 / LUMOþ1 (64%)
(
3
3-NO
2
354.542 (maximum peak)
290.053
(2nd highest peaks)
Chloroform
362.906 (maximum peak)
0.543
0.408
296.519
(2nd highest peaks)

M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
183
peak that corresponds to highest oscillator strength is not the
maximum one. The second highest peak corresponds to highest
oscillator strength. The calculated UVevisible absorption spectra of
phase calculation underestimate
one, but the another peak (at
experimental value (260 nm). Surprisingly, the solvent phase
calculated max (highest peak) leads to further underestimation.
l
max compares to experimental
l
¼ 290.053 nm) is relatively closer to
the two compounds 3-NO
2
and 3-Cl in different medium are shown
l
in Figs. 9 and 10 respectively. For 3-Cl substituted system, the
UVevisible spectra show two strong peaks. Interestingly, the in-
clusion of solvent lowers the intensity of maximum peak and in-
crease the intensity of second highest peak compared to gas phase.
Thus the difference in intensity between two strong peaks is less in
solvent phase compare to gas phase. The compound 3-Cl in gas
phase exhibit highest peak at 289.755 nm corresponds to oscillator
strength f ¼ 0.422which agrees well with the experimental peak at
The broad absorption band extending up to 437 nm as seen in
experiment is also found in the calculation. On comparing the ab-
sorption spectra in gas and solvent phases, it is seen from Table 3
that the maximum absorption peak of both compounds 3-Cl and
2
3-NO are red shifted in the solvent phase. Actually in solvent
phase, the solvents interact with solute molecules and may lower
the energy of the excited state or increase the ground state energy.
Therefore, decreases the energy of transition and absorption
maximum appears red shifted in going from gaseous medium to
solvent medium. This red shift is comparatively smaller for 3-Cl
substituted system which indicates that, the interaction of solute
molecule with solvent is less for 3-Cl substituted system compare
2
90 nm. This peak originates from the excitation transitions
HOMOꢁ3) / LUMO, (HOMOꢁ2) / LUMO, HOMO / (LUMOþ2)
and HOMO / (LUMOþ3). The orbital analysis shows that the
transition is n- *. p orbital of Cl; p , p and p orbital of C; p and p
orbital of N and p , p and s orbital of O is basically responsible for
(
p
z
z
y
x
y
x
z
x
to 3-NO
solvent phase calculated
equal to experimental value. Additionally, the comparison of
UVevisible spectra of 3-Cl and 3-NO substituted system shows
2
substituted system. That is why both the gas phase and
this transition. Moreover, the UVevisible absorption spectrum of
the compound (3-Cl) in gas phase shows some possible transition
at 359.299, 346.119, 318.134, 296.667, 292.241and 286.077 nm
respectively. The second highest peak at 359.299 nm corresponds
to highest oscillator strength f ¼ 0.50. The compound 3-Cl in sol-
vent phase has highest peak at 294.981 nm with oscillator strength,
l
max of 3-Cl substituted system is nearly
2
that, the substitution of the chloro group by the nitro group leads to
a red shift of maximum peak towards lower energy both in gas
phase and solvent phase.
f
(
¼
0.522. This peak is mainly characterized by
HOMOꢁ2) / (LUMOþ1) and (HOMOꢁ1) / (LUMOþ1) transi-
* transition. This transition in originating
orbital of Cl; p , p and p orbital of C; p and of N and
orbital of O. Excluding maximum peak, there are some other
transitions found at 355.131, 350.512, 319.725, 281.275, 266.315,
and 263.895 nm respectively. The gas-phase calculated
maximum peak) value for compound 3-Cl is blue shifted compared
to the experimental data but red shifted for solvent phase calcu-
lated value. Additionally, the gas-phase calculated max (maximum
3
.5. Chemical reactivity
tions and indicate n-
mainly from p
p
z
z
y
x
y
Frontier molecular orbitals i.e., the highest occupied molecular
p
y
orbital (HOMO) and lowest unoccupied molecular orbital (LUMO)
are important quantum chemical parameters which determine the
reactivity and light absorption ability of molecules. HOMO plays the
role of electron donor and LUMO plays the role of electron acceptor.
In accordance with the frontier molecular orbital theory, the tran-
sition state is arises due to an interaction between the frontier or-
bitals (HOMO and LUMO) of reactants. Calculated values of HOMO
and LUMO energies along with HOMO-LUMO energy gap are listed
in Table 4. The HOMO and LUMO energies of the compound 3-Cl are
l
max
(
l
peak) value for compound 3-Cl is closer with experimental data. A
broad absorption band observed in the experiment from 309 to
4
09 nm and is also observed in our calculation. Similar to 3-Cl
substituted system, the UVevisible spectra of 3-NO substituted
2
2
lower than that of 3-NO . Also, the HOMO and LUMO energies in
system also shows two peaks, but now the increase in intensity of
second highest peak is comparatively less than that observed in 3-
solvent phase are higher than that of gas phase. HOMO-LUMO
energy gap can reflect the chemical stability and can be used as
stability index of the molecules. The HOMO-LOMO energy gaps for
the compounds3-Cl and 3-NO are 4.035 and 3.911 eV respectively
2
in gas phase. The corresponding HOMO-LUMO gaps in solvent
phase are 4.099 and 3.805 eV respectively. The calculated gap in-
dicates that 3-Cl is more stable than 3-NO
gap increases in the presence of chloroform solvent for 3-Cl com-
pounds but decreases for 3-NO compounds. Fig. 11 depicts the
Cl substituted system. The calculated absorption spectrum of 3-NO
in gas phase shows that the maximum peak is located at
2
3
54.542 nm with highest oscillator strength f ¼ 0.754 and second
highest peak at 290.036 nm with f ¼ 0.364. In solvent phase, the
maximum peak is observed at 362.906 nm with highest oscillator
strength f ¼ 0.543. In solvent phase another strong peak has been
found at 296.519 nm with oscillator strength f ¼ 0.408. The gas
2
. Moreover, the energy
2
2
Fig. 9. UVeVisible absorption spectra of 3-NO (a) in gas and (b) solvent phases.

184
M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
Fig. 10. UVevisible absorption spectra for 3-Cl. (a) in gas and (b) solvent phases.
Table 4
Calculated HOMO, LUMO, HOMO-LUMO gap, IP EA, dipole moment and polarizability of bent core compounds (3-NO
2
and 3-Cl) in gas medium and chloroform.
Compounds
Medium
Energy (eV)
HOMO
Energy gap (eV)
IP (eV)
EA (eV)
Dipole moment (Debye)
Polarizability (Bohr3)
LUMO
3
-NO
-Cl
2
Gas
Chloroform
Gas
ꢁ6.106
ꢁ6.267
ꢁ5.656
ꢁ5.904
ꢁ2.195
ꢁ2.462
ꢁ1.620
ꢁ1.805
3.911
3.805
4.035
4.099
7.022
6.373
6.762
6.083
1.031
2.232
0.654
1.655
10.366
13.661
7.391
833.40
952.20
820.60
930.69
3
Chloroform
8.986
frontier HOMO-LUMO orbital pictures. The ionization potential can
be correlated with the energy of the HOMO and the energy of the
LUMO is directly associated with the electron affinity. Thus, the
HOMO value indicates a tendency of the molecule to donate elec-
trons to appropriate acceptor while the values of LUMO energy
indicate the possibility to accept electrons. From Fig. 11, it is clearly
observed that the charge density is different from one part of the
polarizability in the solvent phase compare to gas phase for this
core compounds (3-X, X ¼ NO and Cl), indicating a substantial
redistribution of -electron densities in solvent phase. In addition,
the ground state dipole moment and polarizability is higher for 3-
NO substituted system than 3-Cl substituted system [see Table 4].
The presence of the lateral polar NO group with large dipole
moment at an angle to the long axis of the bent core molecule fa-
vors tilted and biaxial smectic C phase whereas lateral Cl group
favors orthogonal smectic A phase as observed in the optical
texture studies. Therefore, the suitable interplay of the molecular
structural anisotropy and the shape factor with the required
polarizability anisotropy can be important factor which lead to the
biaxial smectic phase. Ionization potential (IP) has been calculated
as the energy difference between neutral system and the positive
ion i.e., IP ¼ E(Nꢁ1)ꢁE(N). The electron affinity (EA) has been
calculated as the energy difference between neutral system and the
negative i.e., EA ¼ E(N)ꢁE(N þ 1). The calculated values of IP and EA
are given in Table 4. In both gas and solvent phases, 3-Cl has lower
2
p
2
2
2
molecule to the other. Both for 3-Cl and 3-NO , the HOMO-LUMO
plot in gas phase and solvent phase indicates that the charge is
mainly accumulated in the central core and substituted functional
group not in the outer phenyl rings. In case of 3-Cl substituted
system, HOMO is mainly located on chloro group and LUMO has
very small contribution on it, both in gas and solvent phase.
Another observation is that, in HOMO, more charge is accumulated
near chloro group in gas phase compare to solvent phase. In case of
3
-NO
mulated from the nitro group. Moreover, from the HOMO-LUMO
orbital picture, it is found that the filled -orbital (HOMO) is
2
substituted system, in LUMO, the charge is mainly accu-
p
more extended in solvent phase than gas phase. In addition, the
change in LUMO and HOMO picture due to inclusion of solvent
2
IP as well as EA values than 3-NO . In the solvent phase, both the
compounds have lower values of IP than in the gas phase. On the
other hand, the compounds have higher values of EA in the solvent
phase than in the gas phase. Thus, it can be inferred that it is easier
to remove or add electrons when the compounds are in solvent
phase.
indicates a substantial redistribution of
solvent phase and the redistribution of -electron densities is more
intensive in 3-NO substituted system than 3-Cl substituted sys-
p-electron densities in
p
2
tem. The dipole moment and polarizability provide information
about the charge distribution in the molecule. Using the x,y,z car-
tesian component, the magnitude of total dipole moment and
polarizability, can be written as,
Global reactivity parameters help to study the reaction pathway
[41]. Chemical reactivity descriptors such as chemical potential (
chemical hardness ( ) and electrophilicity index ( ) can be suc-
cessfully used to predict reactivity trends in different systems
m),
h
u
ꢀ
ꢁ
1
2
[42,43]. These quantities are calculated as
2
2
2
m
¼
m
þ
m
þ
m
(1)
tot
x
y
z
1
3
À
Á
IP þ EA
a
tot
¼
a
xx
þ
a
yy
þ
a
zz
(2)
m
¼ ꢁ
(3)
2
There is a considerable increase in dipole moment and

M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
185
Fig. 11. HOMO, LUMO plot of 3-NO
2
2 2
and 3-Cl in both gas and solvent phase (a) 3-Cl in gas phase; (b) 3-Cl in chloroform; (c) 3-NO in gas phase; (d) 3-NO in chloroform.
Chemical potential measures the electron escaping tendency from
the system. Electrons tend to flow from systems with higher
chemical potential to systems with lower chemical potential. Thus,
systems having lower chemical potential values have higher elec-
h
¼ IP ꢁ EA
(4)
(5)
2
m
u
¼ 2
tron attracting power. 3-NO has lower
m
values than 3-Cl i.e., the
) makes the compound 3-NO more
electrons attracting in nature compared to 3-Cl compound. More-
over, value in solvent phase is lower than in the gas phase.
2
h
presence of nitro group (NO
2
2
These reactivity parameters not only describe the ground state
behavior of the system but also explain the excited state phe-
m
nomena [44e48]. Reactivity parameters are also helpful to analyze
toxicity [49,50]. Table 5 presents the calculated values of m, h and u.
Chemical hardness indicates resistance to charge transfer and can
give a measure of the chemical stability of the system. It is obvious
from Table 5 that among the two compounds, 3-Cl has higher
2
hardness value than 3-NO which indicates that the compound 3-Cl
Table 5
is chemically more inert. The chemical hardness value decreases in
the solvent phase suggests that the compounds become more
reactive in the solvent phase. Electrophilicity index is an important
reactivity descriptor which gives a measure of the stabilization in
energy when the system acquires electrons from surrounding [51].
Electrophilicity index is a quantity which contains kinetic and
thermodynamic information of the system [52e55]. Among the
Calculated values of chemical potential (
m
), chemical hardness (
h) and electrophi-
licity index (
chloroform.
u
) of bent core compounds (3-NO and 3-Cl) in gas medium and
2
Compounds
Medium
m
(eV)
h
(eV)
U (eV)
3
-NO
-Cl
2
Gas
Chloroform
Gas
ꢁ4.027
ꢁ4.141
ꢁ3.708
ꢁ3.869
5.991
4.303
6.108
4.428
1.353
1.993
1.126
1.690
3
Chloroform
2
two compounds, 3-NO has higher u i.e., the nitro substituted

186
M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
compound 3-NO
chloro substituted compound 3-Cl. Also the tendency of the com-
pounds to acquire electrons also increases in solvent phase.
2
has higher tendency to accept electrons than
[11] W. Weissflog, H.N.S. Murthy, S. Diele, G. Pelzl, Philos. Trans. R. Soc. A 364
2006) 2657, http://dx.doi.org/10.1098/rsta.2006.1845.
(
[12] G. Pelzl, S. Diele, S. Grande, A. Jakli, C. Lischka, H. Kresse, H. Schmalfuss,
I. Wirth, W. Weissflog, Liq. Cryst. 26 (1999) 401, http://dx.doi.org/10.1080/
026782999205182.
[
13] I. Wirth, S. Diele, A. Eremin, G. Pelzl, S. Grande, L. Kovalenko, N. Pancenko,
W. Weissflog, J. Mater. Chem. 11 (2001) 1642, http://dx.doi.org/10.1039/
B100924I.
4
. Conclusion
New five ring bent core molecule derived from 4-substituted
,3-phenylenediamine with ester imine linkage have been syn-
[14] S. Shubashree, B.K. Sadashiva, S. Dhara, Liq. Cryst. 29 (2002) 789, http://
dx.doi.org/10.1080/02678290210138830.
1
[15] U. Dunemann, M.W. Schroder, R.A. Reddy, G. Pelzl, S. Diele, W. Weissflog,
thesized and characterized. The influence of polar substitution at
the central bent core was investigated with respect to its effects
upon the structures of the mesophases. The nitro group substitu-
tion at the 4-position of the bent core unit of the bent core molecule
exhibited tilted SmC and unidentified SmX phase. The replacement
of the nitro group by the chloro group leads to a drastic change in
the mesophase behaviors and displayed orthogonal SmA phase.
Both the bent core mesogens are fluorescent in nature with large
stoke shift. The bent core mesogens possess nitro and chloro sub-
stitution at the central bent core unit display interesting intrinsic
light generating ability. The nitro substituted bent core mesogen
emits in the region Ultra-Violet (280e400 nm) region whereas
chloro substitution at the central bent core emits in the
J. Mater. Chem. 15 (2005) 4051, http://dx.doi.org/10.1039/B507458D.
[16] G. Dantlgraber, D. Shen, S. Diele, C. Tschierske, Chem. Mater. 14 (2002) 1149,
http://dx.doi.org/10.1021/cm010634k.
[
17] D. Shen, A. Pegenau, S. Diele, I. Wirth, C. Tschierske, J. Am. Chem. Soc. 122
(2000) 1593, http://dx.doi.org/10.1021/ja993572w.
[18] D. Shen, S. Diele, G. Pelz, I. Wirth, C. Tschierske, J. Mater. Chem. 9 (1999) 661,
http://dx.doi.org/10.1039/A808275H.
19] D. Shen, S. Diele, I. Wirth, C. Tschierske, Chem. Commun. (1998) 2573, http://
dx.doi.org/10.1039/A807547F.
[20] W. Weissflog, L. Kovalenko, I. Wirth, S. Diele, G. Pelzl, H. Schmalfuss, H. Kresse,
[
Liq. Cryst. 27 (2000) 677, http://dx.doi.org/10.1080/026782900202543.
[
21] H.T. Nguyen, J.C. Rouillon, J.P. Marcerou, J.P. Bedel, P. Barois, S. Sarmento, Mol.
Cryst. Liq. Cryst. 328 (1999) 177, http://dx.doi.org/10.1080/
10587259908026057.
[22] H. Nadasi, W. Weissflog, A. Eremin, G. Pelzl, S. Diele, B. Das, S. Grande, J. Mater.
Chem. 12 (2002) 1316, http://dx.doi.org/10.1039/B111421B.
23] R.A. Reddy, B.K. Sadashiva, J. Mater. Chem. 14 (2004) 1936, http://dx.doi.org/
[
3
50e600 nm region. Theoretical calculation predicts the greater
10.1039/B313295A.
stability and less reactivity of 3-Cl compound over 3-NO com-
2
[24] H.N.S. Murthy, B.K. Sadashiva, J. Mater. Chem. 14 (2004) 2813, http://
dx.doi.org/10.1039/B406548B.
pound and shed insights on the higher dipole moment, polariz-
ability and electron attracting power of 3-NO2 compound than 3-Cl
compound. Moreover the inclusion of solvent makes these systems
more reactive and increases the dipole moment and polarizability.
Based on the results obtained from TD-DFT calculation, it is clear
that, accurate prediction of the excitation energy does not require
the inclusion of solvent. The solvent phase calculation underesti-
[25] C.V. Yelamaggad, I.S. Shashikala, U.S. Hiremath, G. Liao, A. Jakli, D.S.S. Rao,
S.K. Prasad, Q. Li, Soft Matter
B608278E.
2 (2006) 785, http://dx.doi.org/10.1039/
[
[
[
[
[
26] W. Weissflog, I. Wirth, S. Diele, G. Pelzl, H. Schmalfuss, Liq. Cryst. 28 (2001)
1603, http://dx.doi.org/10.1080/02678290110075075.
27] M.K. Paul, Y.D. Singh, N.B. Singh, U. Sarkar, J. Mol. Struct. 1081 (2015) 316,
http://dx.doi.org/10.1016/j.molstruc.2014.10.031.
28] M.K. Paul, P. Paul, S.K. Saha, S. Choudhury, J. Mol. Liq. 197 (2014) 226, http://
dx.doi.org/10.1016/j.molliq.2014.05.007.
29] M.K. Paul, S.K. Saha, Y.D. Singh, P. Mondal, Liq. Cryst. 41 (2014) 1367, http://
dx.doi.org/10.1080/02678292.2014.920931.
30] R. Deb, R.K. Nath, M.K. Paul, N.V.S. Rao, F. Tuluri, Y. Shen, R. Shao, Dong Chen,
C. Zhu, I.I. Smalyukh, Noel A. Clark, J. Mater. Chem. 20 (2010) 7332, http://
dx.doi.org/10.1039/c0jm01539c.
mate the value of
lmax compare to experiment, but gas phase
calculated value is near the experimentally observed one. Our
calculated UVevisible spectra of compound 3-Cl in gas phase has
highest peak at 289.755 nm which matches well with experimental
value.
[31] A.D. Becke, J. Chem. Phys. 98 (1993) 5648, http://dx.doi.org/10.1063/1.464913.
[
[
[
[
[
32] C. Lee, W. Yang, R.G. Parr, Phys. Rev. B 37 (1988) 785, http://dx.doi.org/
0.1103/Phys.Rev.B.37.785.
33] W.J. Hehre, L. Radom, P.R. Schleyer, J.A. Pople, Ab Initio Molecular Orbital
Theory, Wiley, New York, 1986.
34] R. Ditchfield, W.J. Hehre, J.A. Pople, J. Chem. Phys. 54 (1971) 724, http://
dx.doi.org/10.1063/1.1674902.
35] V.A. Rassolov, M.A. Ratner, J.A. Pople, P.C. Redfern, L.A. Curtiss, J. Comp. Chem.
1
Acknowledgment
Authors acknowledge Department of Science and Technology,
New Delhi (Number: SR/S2/CMP-70/2007) for financial assistance.
22 (2001) 976, http://dx.doi.org/10.1002/jcc.1058.
36] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb,
J.R. Cheeseman, G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson,
H. Nakatsuji, M. Caricato, X. Li, H.P. Hratchian, A.F. Izmaylov, J. Bloino,
G. Zheng, J.L. Sonnenberg, M. Hada, M. Ehara, K. Toyota, R. Fukuda,
J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven,
J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E. Brothers,
K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand,
K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi,
N. Rega, J.M. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo,
J. Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi,
C. Pomelli, J.W. Ochters, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, O. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, Revision B.01, Gaussian Inc.,
Wallingford CT, 2010.
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.molstruc.2016.04.060.
References
[
1] T. Niori, T. Sekine, J. Watanabe, T. Furukawa, H. Takezoe, J. Mater. Chem. 6
1996) 1231, http://dx.doi.org/10.1039/JM9960601231.
(
[
2] D.R. Link, G. Natale, R. Shao, J.E. Maclennan, N.A. Clark, E. K o€ rblova,
D.M. Walba, Science 278 (1997) 1924, http://dx.doi.org/10.1126/
science.278.5345.1924.
[
[
[
[
[
[
3] W. Weissflog, H. Nadasi, U. Dunemann, G. Pelzl, S. Dele, A. Eremin, H. Kresse,
J. Mater. Chem. 11 (2001) 2748, http://dx.doi.org/10.1039/B104098G.
4] G. Pelzl, S. Diele, W. Weissflog, Adv. Mater. 11 (1999) 707, http://dx.doi.org/
[37] M.M. Naoum, H. Seliger, E. Happ, Liq. Cryst. 23 (1997) 247, http://dx.doi.org/
10.1080/026782997208514.
[38] R.A. Reddy, M.W. Schroder, M. Bodyagin, H. Kresse, S. Diele, G. Pelzl,
W. Weissflog, Angew. Chem. Int. Ed. 44 (2005) 774, http://dx.doi.org/10.1002/
anie.200461490.
[39] M.G. Reddy, N.P. Lobo, E. Varathan, S. Easwaramoorthi, T. Narasimhaswamy,
RSC Adv. 5 (2015) 105066, http://dx.doi.org/10.1039/C5RA22261C.
[40] P.K. Muherjee, H. Pleiner, H.R. Brand, J. Chem. Phys. 117 (2002) 7788, http://
dx.doi.org/10.1063/1.1509055.
1
0.1002/(SICI)1521-4095(199906)11:9<707::AIDDMA707>3.0.CO;2-D.
5] R.A. Reddy, C. Tschierske, J. Mater. Chem. 16 (2006) 907, http://dx.doi.org/
0.1039/B504400F.
6] M.B. Ros, J.L. Serrano, M.R. de la Fuente, C.L. Folcia, J. Mater. Chem. 15 (2005)
093, http://dx.doi.org/10.1039/B504384K.
7] H. Takezoe, Y. Takanishi, Jpn. J. Appl. Phys. 45 (2006) 597, http://dx.doi.org/
0.1143/JJAP.45.597.
1
5
1
[41] M. Elango, R. Parthasarathi, V. Subramanian, U. Sarkar, P.K. Chattaraj, J. Mol.
8] W. Weissflog, I. Wirth, S. Diele, G. Pelzl, H. Schmalfuss, T. Schoss,
A. Wurflinger, Liq. Cryst. 28 (2001) 1603, http://dx.doi.org/10.1080/
Struct.
(Theochem)
723
(2005)
43,
http://dx.doi.org/10.1016/
j.theochem.2004.11.057.
02678290110075075.
[42] K. Srinivasu, S.K. Ghosh, R. Das, S. Giri, P.K. Chattaraj, RSC Adv. 2 (2012) 2914,
http://dx.doi.org/10.1039/C2RA00643J.
[43] P.K. Chattaraj, B. Maiti, U. Sarkar, J. Phys. Chem. A 107 (2003) 4973, http://
dx.doi.org/10.1021/jp034707u.
[9] N.V.S. Rao, M.K. Paul, I. Miyake, Y. Takanishi, K. Ishikawa, H. Takezoe, J. Mater.
Chem. 13 (2003) 2880, http://dx.doi.org/10.1039/b304964g.
[10] N.V.S. Rao, R. Deb, M.K. Paul, T. Francis, Liq. Cryst. 36 (2009) 977, http://
dx.doi.org/10.1080/02678290903165979.
[44] M. Khatua, U. Sarkar, P.K. Chattaraj, Eur. Phys. J. D. 68 (2014) 22, http://

M.K. Paul et al. / Journal of Molecular Structure 1119 (2016) 177e187
187
dx.doi.org/10.1140/epjd/e2013-40472-y.
45] P.K. Chattaraj, U. Sarkar, Theor. Comput. Chem. 19 (2007) 269, http://
[50] U. Sarkar, D.R. Roy, P.K. Chattaraj, R. Parthasarathi, J. Padmanabhan, J. Chem.
Sci. 117 (2005) 599, http://dx.doi.org/10.1007/BF02708367.
[
[
[
[
[
dx.doi.org/10.1016/S1380-7323(07)80014-8.
46] P.K. Chattaraj, U. Sarkar, Int. J. Quantum Chem. 91 (2003) 633, http://
dx.doi.org/10.1002/qua.10486.
47] P.K. Chattaraj, B. Maiti, U. Sarkar, J. Chem. Sci. 115 (2003) 195, http://
dx.doi.org/10.1007/BF02704259.
48] U. Sarkar, M. Khatua, P.K. Chattaraj, Phys. Chem. Chem. Phys. 14 (2012) 1716,
http://dx.doi.org/10.1039/C1CP22862E.
[51] P.K. Chattaraj, U. Sarkar, D.R. Roy, Chem. Rev. 106 (2006) 2065, http://
dx.doi.org/10.1021/cr040109f.
[52] P.K. Chattaraj, U. Sarkar, M. Elango, R. Parthasarathi, V. Subramanian, arXiv
preprint physics/0509089. http://arxiv.org/abs/physics/0509089, 2005.
[53] P.K. Chattaraj, U. Sarkar, D.R. Roy, M. Elango, R. Parthasarathi, V. Subramanian,
Ind. J. Chem. A 45A (2006) 1099.
[54] R. Parthasarathi, M. Elango, J. Padmanabhan, V. Subramanian, D.R. Roy,
U. Sarkar, P.K. Chattaraj, Ind. J. Chem. A 45 (2006) 111.
49] U. Sarkar, J. Padmanabhan, R. Parthasarathi, V. Subramanian, J. Mol. Struct.
(
Theochem)
758
(2006)
119,
http://dx.doi.org/10.1016/
[55] P.K. Chattaraj, U. Sarkar, R. Parthasarathi, V. Subramanian, Int. J. Quantum
Chem. 101 (2005) 690, http://dx.doi.org/10.1002/qua.20334.
j.theochem.2005.10.021.