Synthesis, growth, spectral, thermal, mechanical and optical properties of 4-chloro-4′dimethylamino-benzylidene aniline crystal: A third order nonlinear optical material

Article abstract of DOI:10.1016/j.saa.2009.05.028

An organic nonlinear optical material, 4-chloro-4′dimethylamino-benzylidene aniline (CDMABA), was synthesized by the condensation of the p-chloroaniline and p-dimethylaminobenzaldehyde. Solubility of CDMABA was determined in acetone at different temperatu

Full text of DOI:10.1016/j.saa.2009.05.028

Spectrochimica Acta Part A 74 (2009) 78–83
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, growth, spectral, thermal, mechanical and optical properties
of 4-chloro-4ꢀdimethylamino-benzylidene aniline crystal:
A third order nonlinear optical material
S. Leelaa, K. Ramamurthia,∗, G. Bhagavannarayanab
a Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu, India
b Materials Characterization Division, National Physical Laboratory, Dr. K.S. Krishnan Marg, New Delhi 110012, India
a r t i c l e i n f o
a b s t r a c t
An organic nonlinear optical material, 4-chloro-4ꢀdimethylamino-benzylidene aniline (CDMABA), was
synthesized by the condensation of the p-chloroaniline and p-dimethylaminobenzaldehyde. Solubility of
CDMABA was determined in acetone at different temperatures. Single crystals were grown by the solvent
evaporation method from acetone solution at room temperature. Grown crystal was subjected to FTIR, FT-
Raman and 1H NMR spectral analyses to confirm the synthesized compound. The range and percentage
of optical transmission was ascertained by recording UV–vis–NIR spectrum. Thermal properties were
investigatedbyThermoGravimetric, DifferentialThermalandDifferentialScanningCalorimetricanalyses.
High Resolution X-ray Diffractometry (HRXRD) was employed to evaluate the perfection of the grown
crystal. The third order nonlinear optical parameters (nonlinear refractive index and nonlinear absorption
coefficient) were derived by the Z-scan technique.
Article history:
Received 29 November 2008
Received in revised form 24 April 2009
Accepted 13 May 2009
PACS:
81.10.Dn
61.66.H
65.60
Keywords:
Solution growth
Organic compounds
Powder diffraction
Nuclear magnetic resonance
Nonlinear optical materials
© 2009 Elsevier B.V. All rights reserved.
1. Introduction
gated ␲-electron systems and exhibit extremely large second order
optical nonlinearities, such as 4-nitro-4ꢀmethyl benzylidene aniline
Search for new materials with high optical nonlinearities has
been the important task because of their practical application in
harmonic generation, amplitude and phase modulation, switch-
ing and other signal processing devices [1–3]. An ultimate goal
for designing the molecules with large third order nonlinearities
is to incorporate them into devices used in all optical signals pro-
cessing [4,5]. Nonlinear optical absorption (NOA) has shown its
potential application in optical information storage, all optical logic
gates, laser radiation protection, and locked laser mode. Interest
in searching for NOA materials has been gradually increased [6].
Organic molecules have been the subjects of great attention due
to their potential applications in nonlinear optics (NLO), optical
switching, and light emitting diodes. Indeed, the potential use of
organic device materials in optoelectronics is now a very serious
matter [7]. Organic compounds formed by the condensation of
primary amines with aldehydes or ketones yield Schiff bases con-
taining imine (C N) functional group [8]. Some of these compounds
are donor–acceptor benzene derivatives, which conform the conju-
(NMBA) [9] and 4-nitro-4ꢀmethoxy benzylidene aniline (NMOBA)
[10]. Benzylidene anilines constitute an important class of Schiff
bases that have been widely used in coordinate, medical and
biological chemistry. They possess significant anticancer and anti-
inflammatory activities and may also serve as reagents for stereo
selective organic synthesis [11]. Recently, the thermochromism,
photochromism and nonlinear optical properties of the Schiff base
compounds find applications in modern technologies. The structure
of the CDMABA compound was studied by You et al. and the space
group of the compound is P21/c [12]. However, to our knowledge no
systematic studies on the growth and characterization of 4-chloro-
4ꢀdimethylamino-benzylidene aniline (CDMABA) have been made.
Hence in the present work systematic studies on the growth and
structural, optical, thermal, mechanical and third order nonlinear
optical properties of 4-chloro-4ꢀdimethylamino-benzylidene ani-
line are reported.
2. Experiment
2.1. Material synthesis and purification
∗
CDMABA was synthesized by the condensation reaction
between 4-dimethylaminobenzaldehyde (p-DMAB) and 4-chloro-
Corresponding author. Tel.: +91 431 2407057; fax: +91 431 2407045.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
1386-1425/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2009.05.028

S. Leela et al. / Spectrochimica Acta Part A 74 (2009) 78–83
79
Scheme 1.
Fig. 1. Harvested CDMABA crystal.
aniline (p-ca) taken in equimolar ratio [12]. The reaction mixture
was refluxed in ethanol about 8 h and the solution was filtered
using Whatman filter paper and the resulting product of 4-chloro-
4ꢀdimethylamino-benzylidene aniline was obtained. The reaction
mechanism is depicted in Scheme 1. Activated charcoal was added
in solution at the hot condition for removing colored impurities.
The purified product was shinny and yellow in color. The Thin Layer
Chromatography (TLC) confirmed the yield of single compound of
the synthesized material. Important factor that influences the habit
of growing crystals is the polarity of the solvents [13]. Hence, in
this study a few organic solvents were employed to identify the
reasonable solvent. Table 1 presents the electric dipole moment
of these solvents [14] and their influence on the growth habits of
CDMABA crystal. The solubility of CDMABA in acetone was assessed
as a function of temperature in the range of 20–40 ◦C. Single crys-
tals of CDMABA were grown from saturated acetone solution of
the synthesized salt by the slow evaporation technique at room
temperature. During the slow evaporation, transparent crystal of
dimension 8 mm × 5 mm × 4 mm was grown in a period of 16 days
and is shown in Fig. 1.
Fig. 2. FTIR spectrum of CDMABA.
of characteristic aldehyde band at 2720 cm−1 indicates that there
is no aldehyde group in the final product. The FT-Raman spectrum
was recorded at 300 K using a Thermo Electron Corporation, USA
spectrometer in the range of 100–3600 cm−1. The FT-Raman spec-
trum also shows the presence of the functional groups in the crystal
and shown in Fig. 3. The observed experimental values of FTIR and
FT-Raman spectra were tabulated in Table 2.
3. Characterization
3.1. FTIR and FT-Raman spectral analyses
FTIR and FT-Raman spectral analyses were carried out to char-
acterize the functional groups of the CDMABA crystal molecules
[15]. FTIR spectrum was recorded for the purified sample using
PerkinElmer- Paragon-500 by KBr pellet technique between
400 cm−1 and 4000 cm−1 and shown in Fig. 2. Benzylidene anilines
display their C N stretching as a band at 1600 cm−1 [16]. The band
obtained at 1599 cm−1 is due to the formation of imine group (C N)
as a result of the condensation reaction between aldehyde and
amine. C–H stretching absorption, a weak absorption, is observed at
3055 cm−1. C C stretching absorption is confirmed from the band
at 1525 cm−1. As para-di-substituted benzenes show C–H defor-
mation vibrations in the region 840–800 cm−1 [16], the presence of
C–Hdeformationisevidentfromthevibrationat827 cm−1. Absence
3.2. NMR spectral analysis
In the present study, the proton NMR spectral analysis was
made on the CDMABA crystal sample in deutrated CdCl3 using in
Bruker AC200–NMR Spectrometer. The Proton NMR spectrum of
CDMABA (Fig. 4) shows six important absorption peaks namely,
Table 2
Important spectral band assignment of FTIR and FT-Raman lines of CDMABA.
Experimental wave number (cm−1
)
Modes of vibration
Table 1
FTIR
FT-Raman
Effect of solvents on the growth habits of CDMABA crystal.
1599(s)
2853(m)
1552(s)
1162(m)
827(s)
1596(s)
2988(s)
1551.2(m)
1162.5(m)
–
␯ (C N)
␯ (N–CH3) or (C–H)
␯ (C C)
␯ (C–H)
␦ (C–H)
Solvents
Electric dipole moment (Debye)
Morphology
Visual quality
Benzene
Acetone
Ethylacetate
Chloroform
0
Platelet
Prismatic
Platelet
Good
Good
Good
Poor
2.88
1.78
1.04
Prismatic
(s) strong; (m) medium; (␯) stretching; (␦) bending or deformation.

80
S. Leela et al. / Spectrochimica Acta Part A 74 (2009) 78–83
Fig. 3. FT-Raman spectrum of CDMABA.
A, B, C, D, E and F. They represent the hydrogen atoms present
in five different chemical environments in the CDMABA molecule
[17]. Different types of protons in different groups corresponding
to peaks A, B, C, D, E and F are identified by the chemical shift
(ı) values: one proton singlet (CH N) = 8.2ı [A], two proton dou-
ꢀ
ꢀ
blet (Ha − Ha ) = 6.7ı [B], two proton doublet (Hb − Hb ) = 7.7ı [C],
ꢀ
the other two proton doublet (Hc − Hc ) = 7.1ı [D], two proton dou-
ꢀ
blet (Hd − Hd ) = 7.3ı [E], and six singlet proton [(CH3)2] = 3.0ı [F].
The absorption peak A in the spectrum is a singlet, which corre-
sponds to the C–H proton. This is because the number of proton
present in the neighboring carbon is zero. Therefore, the splitting
pattern is singlet at 8.2ı. In the NMR spectrum of CDMABA, the ratio
of steps obtained are, A:B:C:D:E:F = 1:2:2:2:2:6. Thus, the numbers
of protons associated with the signals are: A, 1H; B, 2H; C, 2H; D,
2H; E, 2H; F, 6H, respectively; thus confirming the formation of
CDMABA.
Fig. 5. Morphology of the CDMABA crystal.
3.3. Single crystal and powder XRD
3.4. High resolution X-ray diffraction analysis
The powder X-ray diffraction pattern was recorded using pow-
der X-ray diffractometer with CuK␣1 radiation (ꢀ = 1.54060 Å).
Finely crushed powder of CDMABA crystal was scanned in the 2ꢁ
values ranging from 10 to 70◦. The obtained peaks were indexed and
are shown in Fig. 5. Single crystal XRD studies show that the crystal
belongs to monoclinic system with cell parameters of a = 9.599 Å,
b = 16.417 Å, c = 9.764 Å and ˇ = 119.17◦. The morphology and the
crystallographic planes of the CDMABA crystal are indexed from
single crystal XRD and are shown in Fig. 6.
The study on the grown crystal to ascertain its quality has signif-
icant importance for device fabrication. The defects created during
growth have severe consequences on the physical properties of the
crystal. Hence studies to reveal the quality of the grown crystals
are important. In this work the degree of crystalline perfection of
CDMABA was obtained by recording high resolution X-ray diffrac-
tion (HRXRD) curves. A multicrystal X-ray diffractometry (MCD)
[18] developed at National Physical Laboratory (NPL), New Delhi,
was used to study the quality of the solution grown CDMABA sin-
Fig. 4. 1H-NMR spectrum of CDMABA.
Fig. 6. Powder XRD pattern of CDMABA.

S. Leela et al. / Spectrochimica Acta Part A 74 (2009) 78–83
81
Fig. 7. HRXRD spectrum of CDMABA.
gle crystal. Before recording the diffraction curve, to remove the
non-crystallized solute atoms remained on the surface of the crys-
tal and also to ensure the surface planarity, the specimen was
first lapped and chemically etched in a non-preferential etchant
of water and acetone mixture in 1:2 volume ratios. This process
also ensures to get rid from surface layers, which may some times
form a complexating epilayer on the surface of the crystal due to
organic additives [19]. Fig. 7 shows the high-resolution diffraction
curve (DC) recorded for a typical CDMABA specimen using MoK␣1
radiation (0.70926 Å) in symmetrical Bragg geometry of the mul-
ticrystalX-raydiffractometer. Thediffractingplanechosentorecord
Fig. 8. UV–vis–NIR spectrum of CDMABA.
has the sensitivity compared to interferameteric methods. Using a
single Gaussian laser beam in tight focus geometry, as depicted in
Fig. 9, the transmittance of a nonlinear medium through a finite
aperture in the far field as a function of the sample position Z can
be measured with respect to the focal plane. The nonlinear absorp-
tion and refractive index of CDMABA crystals (thickness ≈3 mm)
were estimated using the single beam Z-scan method with CW
laser beam intensity of 15 mW and the wavelength of 632.8 nm.
The study of nonlinear refraction by the Z-scan method depends
on the position (Z) of the thin samples under the investigation
along a focused Gaussian laser beam. The sample causes an addi-
tional focusing or defocusing, depending on whether nonlinear
refraction is positive or negative. In the most reported experiments,
0.1 < S (transmittance) <0.5 has been used for determining nonlin-
ear refraction. Obviously, the S = 1 corresponds to the collection of
all transmitted light and therefore is insensitive to any nonlinear
beam distortion due to nonlinear refraction [22]. Such a scheme,
referred to as an “Open aperture” Z-scan, is suited for measuring
nonlinear absorption in the sample. Results obtained from a typical
closed aperture Z-scan study for the grown CDMABA are presented
in Fig. 10. The nonlinear refractive index (n2) of the crystal was
calculated using the standard relations given below [20–22]:
¯
the DC was (2 2 1). As seen in Fig. 7, the curve does not contain a
single diffraction peak. The solid line, which follows well with the
experimental points (filled circles), is the convoluted curve of two
peaks using the Lorentzian fit. The additional peak depicts an inter-
nal structural low angle (tilt angle ˛ > 1 arc min but less than a
deg.) grain boundary [19] whose tilt angle (misorientation angle
between the two crystalline regions on both sides of the structural
grainboundary)is182 arc sfromitsadjoiningregion. TheFullWidth
Half Maximum (FWHM) of the main peak and the very low angle
boundary are respectively 210 and 90 arc s. Though the crystal con-
tains a low angle boundary, the relatively low angular spread of
around 500 arc s of the DC shows that the crystalline perfection is
fairly good [18,19].
3.5. Linear and nonlinear optical properties
In order to estimate the optical transparency in the
200–1200 nm region of the electromagnetic spectrum, the
optical transmittance study was carried out on the CDMABA
crystal of thickness ∼0.2 mm employing Shimadzu 1601 model
spectrophotometer. In this study the transmittance of the sample,
which is the descriptive of the result of absorption processes, was
recorded at room temperature. ␲–␲* transition occurs at 280 nm
due to the C N (imine group) bond. The lower cutoff wavelength
of the CDMABA is at about 367 nm (Fig. 8) and the crystal is
transparent in the entire visible and near infrared region.
0.406(1 − S)0.25∗
ꢂTP−V
=
(1)
ꢂꢃ0
where ꢂTP−V is the difference between the normalized peak and
valley transmittance, ꢂTP−V/ꢂꢃ0 is the on-axis phase shift at the
focus, S is the linear transmittance of the aperture. The nonlinear
refractive index (n2) and nonlinear absorption coefficient (ˇ) are
given by,
ꢂꢃ0
n2
≈
(2)
3.6. Z-scan technique
kI0Leff
In present case, we choose to work at 632.8 nm in order to eval-
uate materials at visible wavelengths in which there exist interest
for switchable holographic filters and refractive optical limiters [5].
Hence the Z-scan method has gained rapid acceptance by the non-
linear optics community as a standard technique for separately
determining the nonlinear changes in refractive index and change
in optical absorption. Sheik-Bahae et al. [20] and Vanstryland and
Sheik-Bahea [21] have reported a single beam method for measur-
ing the sign and magnitude of nonlinear refractive index (n2) that
Fig. 9. Experimental setup for the Z-scan measurements.

82
S. Leela et al. / Spectrochimica Acta Part A 74 (2009) 78–83
Fig. 10. Z-scan (close) spectrum of CDMABA.
Fig. 11. Z-scan (open) spectrum of CDMABA.
and
√
2
2ꢂT
I0Leff
ˇ =
(3)
where k is the wave number (k = 2ꢄ/ꢀ), and Leff = [1 − exp(−˛L)]/˛
with I0 = P/(ꢄω02) defined as the peak intensity within the sam-
ple, where L is the thickness of the sample, and ˛ is the linear
absorption coefficient. The ratio of the signals with and without
the aperture accounts for the nonlinear absorption and gives the
information about purely nonlinear refraction. The enhanced trans-
mission near the focus is indicative of the saturation of absorption
at high intensity. Absorption saturation in the sample enhances
the peak and decreases the valley in the closed aperture Z-scan.
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,
consequently, a spatial variation of the refractive index that acts
as a thermal lens resulting in phase distortion of the propagating
beam (Fig. 10). The nonlinear absorption property of the D–␲- A
type ␲-electron system can be related closely to the ␲-electron
conjugate degree and delocalization capacity of the molecule. The
three dimensional X-ray crystal structure solution of this crys-
tal showed that the torsion angles C8–N1–C7–C1 = 179.93(13)◦,
C15–N2–C4–C5 = 179.36(18)◦ and C15–N2–C4–C3 = 0.1(3)◦, in these
conjugated chains, are coplanar [12]. These are all favourable
to nonlinear optical absorption, especially to saturated absorp-
tion. Nonlinear refractive index (n2) of the CDMABA calculated is
5.8107 × 10−7 cm2/W the value of nonlinear absorption coefficient
(ˇ) (Fig. 11) estimated from the open Z-scan curve is 0.1854 cm/W.
Fig. 12. TGA/DTA spectrum of CDMABA.
transition at 799 ◦C. The melting point of the substance measured
using ‘GUNA make’ melting point apparatus was 150–153 ◦C. TGA
curve shows that there is a sharp weight loss at 361 ◦C and sam-
ple undergoes gradual weight loss till 800 ◦C. Differential scanning
calorimetry (DSC) study performed for the grown CDMABA using
NETZSCH-Geratebau GmbH Thermal analysis (STA 409PC) in the
temperature range 27–250 ◦C at a heating rate of 10 K/min in the
Nitrogen atmosphere is shown in Fig. 13. 10.500 mg of sample was
placed in the Alumina crucible. The crystal of CDMABA is stable up
to its melting point (152 ◦C). The sharpness of the peak confirms the
good crystallinity of the synthesized compound [23].
3.7. Thermal analysis
Thermogram and differential thermogram analyses on CDMABA
were carried out using STA 409PC. Thermogravimetric (TG) and dif-
ferential thermal analysis (DTA) of CDMABA recorded at a heating
rate of 10 K/min under nitrogen atmosphere is shown in Fig. 12.
Thermal Gravimetric Analysis (TGA) curve shows that there is no
weight loss between 100 ◦C and 200 ◦C. This indicates that there is
no inclusion of water in the crystal lattice. As there is no weight
loss before melting point, the material is moisture-free and stable
upto 152 ◦C. The final residue weight is 1.26%. From the DTA curve
it is observed that the material is stable up to 152.9 ◦C, the melting
point of the substance and it undergoes irreversible endothermic
Fig. 13. DSC spectrum of CDMABA.

S. Leela et al. / Spectrochimica Acta Part A 74 (2009) 78–83
83
Resolution X-ray Diffraction study shows that the perfection of the
crystal is fair even though it contains a low angle boundary. The
relative third order nonlinear optical absorption and the nonlinear
optical refractive index were calculated by the Z-scan technique.
Acknowledgment
One of the authors (SL) thanks to Dr. A. Ilangovan, School of
Chemistry, Bharathidasan University, Tiruchirappalli for fruitful
discussion and Dr. Sastikumar, Professor and Head, NIT, Tiruchi-
rappalli for his permission to utilize the facilities available at the
Optics Laboratory. Further the authors thank University Grant Com-
mission, Government of India for financial assistance [File No.
3237/2007 (SR)].
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4. Conclusion
Optical quality single crystals of CDMABA were grown at room
temperature using the solution growth technique. The morphology
unveils the growth habits of the material. The UV–vis–NIR spec-
trum elucidates that the crystal is transparent between 360 nm
and 1200 nm. From the FTIR, FT-Raman and NMR spectrum, the
formation of the imine group of the material was confirmed. Ther-
mal analyses indicate that the crystal has good thermal stability. A
sharp peak observed at 150 ◦C in the DSC curve corresponds to the
melting point of the material. The microhardness study revealed
that the crystal develops cracks for load more than 50 g. High