Synthesis, growth, optical, mechanical, dielectric and thermal properties of 4-chloro-4′-chlorobenzylidene aniline single crystal

Article abstract of DOI:10.1016/j.saa.2011.07.004

The organic material 4-chloro-4′-chlorobenzylidene aniline (CCBA) was synthesized and confirmed by NMR and FTIR spectral analyses. CCBA crystal was grown from chloroform by slow evaporation at room temperature and the single crystal cell parameters were d

Full text of DOI:10.1016/j.saa.2011.07.004

Spectrochimica Acta Part A 82 (2011) 91–96
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, growth, optical, mechanical, dielectric and thermal properties of
4-chloro-4ꢀ-chlorobenzylidene aniline single crystal
A. Subashinia, G. Bhagavannarayanab, K. Ramamurthia,∗
a Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620 024, India
b Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110 012, India
a r t i c l e i n f o
a b s t r a c t
The organic material 4-chloro-4ꢀ-chlorobenzylidene aniline (CCBA) was synthesized and confirmed by
NMR and FTIR spectral analyses. CCBA crystal was grown from chloroform by slow evaporation at room
temperature and the single crystal cell parameters were determined by single crystal X-ray diffraction
method. The perfection of the grown crystal was analyzed by high resolution X-ray diffraction rock-
ing curve analysis. Fluorescence spectrum indicated violet emission at 428 nm. The range of optical
absorbance was ascertained by recording UV–vis–NIR spectrum. Load dependant microhardness mea-
surements on this crystal revealed the mechanical behavior of the material. Stiffness constant, Meyer
index and yield strength of CCBA crystal were calculated. Dielectric studies were carried out to estimate
the dielectric parameters of the grown crystal in the frequency range from 100 Hz to 100 kHz. The thermal
behavior of CCBA was investigated using differential scanning calorimetry (DSC) and no phase transition
was identified in the temperature region 30–100 ◦C. Further, the CCBA crystal was subjected to open
aperture Z-scan studies in order to investigate the third order nonlinear optical (NLO) properties of CCBA
crystal.
Article history:
Received 3 December 2010
Received in revised form 30 June 2011
Accepted 3 July 2011
PACS:
61.66.Hq
42.70.Mp
78.20.Ci
Keywords:
Organic crystals
Benzylideneaniline derivative
NMR analysis
Fluorescence
© 2011 Elsevier B.V. All rights reserved.
Differential scanning calorimetry
Nonlinear optical studies
1. Introduction
the nonplanar conformation of the molecule in the solid [11], in
the gas phase [12], and in solution [13]. The insertion of donar
Nonlinear optical (NLO) properties of various materials have
been subjected to intensive studies. For example, materials hav-
ing reverse saturable absorption (RSA) (the transmittance reduces
with the increase of optical intensity) was used in two-photon
microscopy and optical limiters [1–3]. It is well known that the
open-aperture (OA) Z-scan technique, which was discussed by
Sheik-Bahae et al. [4], has been extensively used as an effective and
convenient tool for exploring the nonlinear absorption properties
of various materials [4–8]. The Z-scan technique is based on the
principle of spatial beam distortion and offers simplicity as well
as very high sensitivity for distinguishing the contribution of the
real part (nonlinear refraction) and the imaginary part (nonlinear
absorption) of third-order nonlinear susceptibility ꢀ(3) [9]. Benzyli-
deneanilines belong to an important class of Schiff bases which
have been widely used in coordinate, medical and biological chem-
istry. They possess significant anticancer and anti-inflammatory
activities and may also serve as reagents for stereo selective organic
synthesis [10]. Structural studies of benzylideneaniline confirm
or acceptor group at para-position of benzylideneaniline would be
expected to have a significant effect on molecular properties such
as the ground and excited state dipole moments, electron den-
sity, highly occupied molecular orbital (HOMO) energy level and
molecular planarity [14]. The NLO properties exhibited by benzyli-
deneaniline derivatives of 4-chloro-4ꢀdimethylamino-benzylidene
aniline (CDMABA) and 4-methoxy-4ꢀdimethylamino-benzylidene
aniline (MDMABA) were investigated by Leela et al. [15,16]. In
the present study, we report on the synthesis, growth, structural,
spectral, optical, mechanical, dielectric and thermal properties of
4-chloro-4ꢀ-chlorobenzylidene aniline (CCBA) single crystal, one of
the benzylideneaniline derivatives and its third-order NLO absorp-
tion by Z-scan technique.
2. Experimental
2.1. Synthesis and growth of CCBA
CCBA was synthesized by condensation method from p-
chlorobenzaldehyde (p-CB) and p-chloroaniline (p-CA) taken in
equimolar ratio. The reaction mixture was taken in a round bot-
tomed flask which was immersed in a preheated oil bath at 100 ◦C.
∗
Corresponding author. Tel.: +91 431 2407057; fax: +91 431 2407045.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.07.004

92
A. Subashini et al. / Spectrochimica Acta Part A 82 (2011) 91–96
OHC
Cl
NH2
Cl
+
+
Cl
H2 O
Cl
N
C
H
Scheme 1.
The reaction mixture was refluxed in ethanol about 8 h and then
cooled to room temperature, which yielded solid product of 4-
chloro-4ꢀ-chlorobenzylidene aniline. The reaction mechanism is
depicted in Scheme 1. The synthesized salt was purified by repeated
recrystallization process using ethanol. The crystal grown in chlo-
roform was transparent and platelet but the crystal grown from
ethanol was needle shaped and less transparent. The solubility of
CCBA in ethanol (1.323 g in 100 mL) at room temperature is less
than that of in chloroform (15.488 g in 100 mL). Hence, the single
crystals of CCBA were grown from chloroform. Beaker contain-
ing chloroform solution of CCBA was covered by parafilm and the
slow evaporation of chloroform produced transparent rectangular
platelet-like crystal of about 14 mm × 4 mm × 1 mm size (Fig. 1) in
about twenty days.
Fig. 2. FTIR spectrum of CCBA crystal.
groups present in the grown crystals. The recorded spectrum is
shown in Fig. 2. The band at 710.42 cm−1 is due to mono chlo-
rinated aromatic C–Cl stretching vibration. Benzylidene anilines
display their C N stretching vibrational frequency at 1600 cm−1
[19]. The band obtained at 1591.37 cm−1 is due to the formation of
imine group (C N) as a result of the condensation reaction between
aldehyde and amine. Para-disubstituted benzenes show C–H defor-
mation vibration in the region of 800–840 cm−1 and hence the
frequency observed at 828.75 cm−1 is due to C–H deformation
vibrations. The band at 1484.35 cm−1 is due to C C stretching
vibration. Two sharp bands of medium intensity observed at
1081.83 cm−1 and 1007.45 cm−1 [20] are due to the in-plane defor-
mation modes of the aromatic C–H. Thus the FTIR spectral analysis
confirms the formation of the CCBA.
3. Results and discussion
3.1. NMR spectral analysis
1H NMR spectral analysis was made on the CCBA crystal sample
in deutrated organic solvent of chloroform (CDCl3) using Bruker AC
200-NMR spectrometer. 1H NMR spectrum of CCBA, presented in
Fig. S1 shows five different peaks as expected, at different chemi-
cal shift positions from the reference standard [17]. NMR spectrum
shows singlet at 8.64 ı ppm, due to single proton of CH N. This sin-
glet signal corresponds to the proton of imine group [18] confirms
the formation of Schiff base compound. Four doublets at 7.94 ı ppm,
7.59 ı ppm, 7.46 ı ppm and 7.30 ı ppm are due to aromatic protons.
In the NMR spectrum of CCBA, the ratio of the relative intensities
obtained are A:B:C:D:E = 1:2:2:2:2 which reveals that the number
of protons associated with the signals is A, 1H; B, C, D and E, 2H,
respectively. Thus the molecular structure of CCBA is confirmed by
1H NMR studies.
3.3. Single crystal and powder X-ray analyses
The single crystal XRD data of the CCBA crystal were obtained
using a single crystal Diffractometer CAD4/MACH 3. The unit cell
parameters determined from XRD revealed that the grown crystal
belongs to the orthorhombic system with the lattice parameters
˚
˚
˚
˚
a = 24.568 (9) A (24.503 (5) A), b = 6.356 (2) A (6.334 (1) A), c = 7.342
3
˚
˚
˚
(2) A (7.326 (1) A) and V = 1146.4 (7) A . These values compare
well with the reported values [21] given in parenthesis. Finely
crushed powder of CCBA crystal was scanned in the 2ꢁ values rang-
ing from 10 to 60◦ and powder X-ray diffraction patterns were
recorded using powder X-ray diffractometer with CuK␣1 radiation
3.2. Fourier transform infrared (FTIR) spectral analysis
The FTIR spectrum of CCBA crystal was recorded in the range of
400–4000 cm−1 employing a Perkin Elmer-paragon-500 FTIR spec-
trometer by KBr pellet technique in order to study the functional
˚
(ꢂ = 1.54060 A). The powder XRD peaks for the grown crystal were
indexed using WinPLOTR software and presented in Fig. 3.
3.4. HRXRD analysis
The crystalline perfection of the grown single crystals was stud-
ied by HRXRD by employing a multicrystal X-ray diffractometer
developed at NPL [22]. The well-collimated and monochromated
MoK␣1 beam obtained from the three monochromator Si crystals
set in dispersive (+,−,−) configuration has been used as the explor-
ing X-ray beam. The specimen crystal is aligned in the (+,−,−,+)
configuration. Due to dispersive configuration, though the lattice
constant of the monochromator crystal(s) and the specimen are dif-
ferent, the unwanted dispersion broadening in the diffraction curve
of the specimen crystal is insignificant. More details of the diffrac-
tometer and the measurement procedure including the sample
Fig. 1. Photograph of the CCBA crystal.

A. Subashini et al. / Spectrochimica Acta Part A 82 (2011) 91–96
93
Fig. 3. Powder XRD pattern of CCBA crystal.
preparation are given by Bhagavannarayana and Kushwaha [23].
Fig. 4 shows the high resolution diffraction curve (DC) recorded for
a typical CCBA crystal using (4 0 0) diffracting planes in symmetrical
Bragg geometry by employing the multicrystal X-ray diffractome-
ter described above with MoK␣1 radiation. As seen in the figure the
DC is sharp without any satellite peaks which may otherwise be
observed either due to internal structural grain boundaries [24] or
due to epitaxial layer which may sometimes form in crystals grown
from solution [25]. The full width at half maximum (FWHM) of the
diffraction curves is 36 arc sec (Fig. 4), which is very close to that
expected from the plane wave theory of dynamical X-ray diffraction
[26]. The single sharp diffraction curve with low FWHM indicates
that the crystalline perfection is reasonably good without having
any internal structural grain boundaries.
3.5. Fluorescence and UV–vis–NIR spectral analyses
Fig. 5. (a) Fluorescence spectrum of CCBA crystal and (b) Optical absorbance spec-
trum of the grown CCBA crystal.
Fluorescence finds wide applications in biochemical, medical
and chemical research fields for analyzing organic compounds [20].
Fluorescence generally occurs in compounds containing aromatic
*
functional groups with low-energy ␲ → ␲ transition levels [27].
FP6500 spectrofluorometer was used to record the fluorescence
spectrum of the CCBA crystal in the range of 300–500 nm and the
spectrum is given in Fig. 5a. The spectrum indicates the violet emis-
sion at 428 nm. The optical absorption spectrum of CCBA single
crystal was recorded in the range of 200–1100 nm using Varian Cary
5E UV-vis-NIR spectrophotometer. Fig. 5b shows the UV–vis–NIR
spectrum recorded with transparent single crystal of CCBA of thick-
ness 1 mm. It is observed that the lower cut off of CCBA crystal is at
∼450 nm and the crystal is found to be transparent in the region of
450–1100 nm.
3.6. Z-scan studies
As shown in Fig. 5b, the absorption spectrum of CCBA crystal
showed relatively low linear absorption in the visible wavelength
range, which promises low intensity loss and little temperature
change by photon absorption during the NLO measurements. The
nonlinear absorption performance of CCBA crystals (thickness
≈1 mm) was studied by the single beam Z-scan technique with
He–Ne laser at 632.8 nm under an open-aperture configuration.
The sample was moved along the travelling Z-direction of the
laser beam across the focal point, and a transmittance change was
recorded as a function of sample position Z. Fig. 6 shows that as the
sample was moved close to the focus, the transmittance decreased
as the laser irradiance increased. At the focus (Z = 0) where the laser
irradiance approached a maximum which displayed an obvious
reverse saturated absorption (RSA). The nonlinear absorption coef-
Fig. 4. HRXRD spectrum recorded for (4 0 0) diffracting planes for a typical CCBA
crystal by employing a multicrystal X-ray diffractometer.

94
A. Subashini et al. / Spectrochimica Acta Part A 82 (2011) 91–96
Fig. 6. Open aperture Z-scan transmittance of CCBA crystal.
Fig. 7. Load P versus hardness H .
v
ficient (ˇ) of the crystal was calculated using the standard relations
given below [28,29]
The calculated stiffness constant for different loads is shown in
Table 1. Work hardening coefficient (n), a measure of the strength
of the crystal, is computed from log P versus log d plot. The plot
of log P versus log d yields a straight line and its slope gives the
work hardening coefficient. The value of n is ∼9.2. According to the
√
2
2ꢃT
ˇ =
(1)
I0Leff
where Leff = [1 − exp (−˛L)]/˛ with I0 = P/(ꢄω2) defined as the peak
intensity within the sample, where L is the t0hickness of the sam-
ple, and ˛ is the linear absorption coefficient at 632.8 nm. The
focusing effect is attributed to a thermal nonlinearity resulting
from absorption of radiation at 632.8 nm. Localized absorption of
a tightly focused beam propagating through an absorbing medium
produces a spatial distribution of temperature in the crystal and
the value of nonlinear absorption coefficient (ˇ) estimated is
−2.1684 × 10−3 m/W.
Onistch concept, if n is less than 2, H decreases with increasing
v
load, whereas for n is greater than 2, H increases with increasing
v
load [33]. In our case, n is greater than 2 which shows the CCBA
crystal belongs to soft material. According to Meyer’s law,
P = k1dn
(4)
where k1 is the standard hardness which is found out from P versus
n graph. It is known that the materials take some time to revert to
d
elastic mode after the applied loading is removed, so a correction
x is applied to the observed d value. Kick’s law may be satisfied as
given below
3.7. Mechanical properties
Microhardness is not only a mechanical characteristic routinely
measured, but also it has been developed as a microstructural
investigation method, due to the fact that microhardness is
sensitive to structural parameters as well as the mechanical charac-
terization parameters [30,31]. Transparent CCBA crystal free from
visible inclusions or cracks was selected and the Vickers microhard-
ness values were recorded on the prominent face of CCBA crystal
at room temperature using Leitz - Wetzler Vicker’s hardness tester
fitted with a diamond pyramidal indenter. The load P was varied
between 1 and 50 g for making indentations. The Vickers hardness
value (Hv) was calculated from the following relation
P = k2(d + x)2
(5)
where k2 is constant. The constant k2 depends on the applied load P
while k1 is the geometrical conversion factor whose value depends
on the indenter geometry.
Simplifying Eqs. (4) and (5) yields
ꢀ
ꢁ
ꢀ
ꢁ
1/2
1/2
k2
k1
k2
k1
dn/2
=
d +
x
(6)
The slope of dn/2 versus d yields (k2/k1)1/2 and the intercept is a
measure of x. Yield strength ꢅy of a material is its ability to resist
permanent deformation under the action of applied load and is a
measure of the elastic limit of a material. For a particular value of
the applied load the material ceases to resist deformation and at
this point large deformation takes place without any increase in
load. The value of hardness corresponding to this point is called
yield strength. The yield strength is calculated using the value of
P
d2
H
v
= 1.8544 (kg/mm2)
(2)
where P is the applied load (kg) and d is the average diagonal length
of the indentation impression (mm) and 1.8544 is a constant, a geo-
metrical factor for the diamond pyramid indenter. The variation of
microhardness values with applied load for CCBA crystal is illus-
trated in Fig. 7 which shows increase in microhardness values with
load up to 50 g and for load above 50 g significant cracks occurred.
At lower loads there is an increase in the hardness with load, which
can be attributed to the work hardening of the surface layer and
the occurrence of significant cracking beyond 50 g of load may be
due to the release of internal stresses generated locally by inden-
tation. The elastic stiffness constant (c11) was obtained following
Wooster’s empirical relation [32]
Table 1
Stiffness constant of CCBA crystal calculated from H .
v
H
(kg/mm2)
c11
6.06075
17.9063
31.6469
84.2652
179.3303
v
2.8
5.2
7.2
12.6
19.4
c11 = H7/4
(3)

A. Subashini et al. / Spectrochimica Acta Part A 82 (2011) 91–96
95
Fig. 8. Variation of the dielectric constant and dielectric loss as a function of the
frequency.
Fig. 9. DSC of CCBA crystal.
microhardness (H ) and Meyer’s index (n) [34]. For n is greater than
2, the yield strength may be calculated using the expression [35]
v
V24.2 Build 107 differential scanning calorimeter. The DSC spec-
trum was recorded in the temperature range of 30–150 ◦C. 5.3 mg
of CCBA was taken and heated at a rate of 10 ◦C/min in inert nitrogen
atmosphere. Alumina (Al2O3) was used as the reference material for
the measurement and the resultant DSC curve is shown in Fig. 9.
An irreversible endothermic peak was obtained at ∼112 ◦C which
corresponds to the melting point of the grown crystal. The material
shows good thermal stability between 30 and 100 ◦C and no phase
transition was observed in this region. The absence of any phase
transition promises that this material can be used in the above
temperature region for optical applications.
ꢂ
ꢃ
n−2
(3 − n) 12.5(n − 2)
ꢅy
=
H
v
(7)
2.9
3 − n
The load-dependant hardness parameters n, k1, k2, x and ꢅy
are calculated from the hardness studies for CCBA crystal are
9.2, 1.81 × 1012 g/m, 6.95 × 104 g/m, 0.054 ␮m and 9.3 Gpa, respec-
tively.
3.8. Dielectric properties
A study of dielectric response in crystals reveals information
about the electric field distribution and charge transport mecha-
nism. The dielectric studies of the CCBA crystal was carried out
using a HIOKI 3532 LCR HITESTER instrument in the frequency
region of 100 Hz–100 kHz at room temperature. To guarantee the
precision of data, the sample of thickness about 1 mm was polished
smoothly, covered by silver paste, and then mounted between two
electrodes. The capacitance of the parallel plate capacitor with the
sample as the dielectric medium was measured at room tempera-
ture. The dielectric constant (εr) was calculated using the relation
4. Conclusion
Optical quality single crystals of CCBA were grown from chlo-
roform by slow evaporation technique at room temperature. The
FTIR spectral analysis confirms the formation of imine group and
the NMR studies reveal the molecular structure of CCBA. Further,
the single crystal XRD confirmed that the CCBA crystallizes in
orthorhombic crystal structure. High resolution X-ray diffraction
study showed that the crystalline perfection of the CCBA crystal
is reasonably good without having any internal structural grain
boundaries. The CCBA crystal exhibits violet fluorescence emission.
The Z-scan technique of CCBA showed that the relative third order
nonlinear optical absorption coefficient is −2.1684 × 10−3 m/W.
From the mechanical hardness measurements, it was observed that
the hardness increases with increasing load. The work hardening
coefficient is greater than 2, which shows CCBA crystal belongs
to the soft materials category. The frequency dependant dielectric
constant decreases with increasing frequency. Differential scan-
ning calorimetric study showed the melting point is at ∼112 ◦C and
no phase transition in the temperature region 30–100 ◦C and hence
its stability in this temperature range.
Cd
εr =
(8)
ε0A
where C is the capacitance, d is the thickness of the crystal, ε0 is
the permittivity of free space, and A is the area of the crystal. The
dielectric loss was calculated using the relation εꢀꢀ = εrD, where D
is the dissipation factor. Fig. 8 shows the variation of the dielectric
constant and dielectric loss, respectively at different frequencies
measured at room temperature. From the curve, it is observed that
the dielectric constant and dielectric loss decrease with increasing
frequency and attain saturation at higher frequencies. The very high
value of dielectric constant at low frequencies is due to the presence
of all four polarizations, namely ionic, electronic, orientation and
space charge polarization. The low dielectric constant value of the
crystal at high frequency is attributed to space charge polarization
[36]. The low values of dielectric constant at higher frequencies are
important for these materials in the construction of photonic and
NLO devices.
Acknowledgements
The authors thank Dr. S. Natarajan, Chairperson, School of
Physics, Madurai Kamaraj University, Madurai-21, Dr. D. Sastiku-
mar, Professor, National Institute of Technology, Tiruchirappalli-15
and Dr. K. Sivaji, Assistant Professor, Department of Nuclear Physics,
University of Madras, Chennai-25 for extending their facility to
record single crystal X-ray diffraction data, Z-scan measurement
and microhardness values respectively. The authors thank the
University Grant Commission, Government of India [File No. 32-
37/2007 (SR)] for financial assistance. One of the authors (AS) thank
3.9. Thermal studies
Differential scanning calorimetry (DSC) analysis of the grown
crystalline powder was measured using TA instrument, Model Q20

96
A. Subashini et al. / Spectrochimica Acta Part A 82 (2011) 91–96
University Grant Commission, New Delhi for providing UGC: Mer-
itorious Fellowship [File No. 4- 1/2008 (BSR)].
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Spectrochim. Acta 77A (2010) 927–932.
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Appendix A. Supplementary data
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Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.07.004.
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