Design, synthesis, growth and characterization of 4-methoxy-4′- dimethylamino-benzylidene aniline (MDMABA): A novel third order nonlinear optical material

Article abstract of DOI:10.1016/j.saa.2010.08.012

Synthesis, growth, X-ray crystal structure and characterization of a novel third order nonlinear optical material, 4-methoxy-4′-dimethylamino- benzylidene aniline (MDMABA), are reported for the first time. The asymmetric unit of MDMABA compound contains two crystallographically independent molecules (A and B), and they exist in the E-configuration. The structural perfection of the grown crystal is analyzed by high-resolution X-ray diffraction rocking curve analysis. The functional groups present in MDMABA are investigated by FTIR and FT-Raman spectral analyses. The placement of the protons is determined using HNMR spectrum. The range and percentage of optical transmission were ascertained by recording UV-vis-NIR spectrum. Thermal and mechanical properties are reported. Dielectric study shows that the dielectric constant of the crystal varies with frequency and temperature. The third order nonlinear optical absorption coefficient of the MDMABA crystal is determined by the Z-scan technique.

Full text of DOI:10.1016/j.saa.2010.08.012

Spectrochimica Acta Part A 77 (2010) 927–932
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Design, synthesis, growth and characterization of
ꢀ
4
-methoxy-4 -dimethylamino-benzylidene aniline (MDMABA): A novel third
order nonlinear optical material
S. Leela , R. Hema , Helen Stoeckli-Evans , K. Ramamurthi , G. Bhagavannarayanad
a
b
c
a,∗
a
Crystal Growth and Thin Film Laboratory, School of Physics, Bharathidasan University, Tiruchirappalli 620024, Tamil Nadu, India
Department of Physics, Seethalakshmi Ramaswamy College (Autonomous), Tiruchirappalli 620002, India
Institute of Physics, University of Neuchatel, Rue Emile-Argand 11, CH-2009 Neuchatel, Switzerland
Materials Characterization Division, National Physical Laboratory, Dr. K. S. Krishnan Marg, New Delhi 110012, India
b
c
d
a r t i c l e i n f o
a b s t r a c t
Article history:
Synthesis, growth, X-ray crystal structure and characterization of a novel third order nonlinear optical
material, 4-methoxy-4 -dimethylamino-benzylidene aniline (MDMABA), are reported for the first time.
The asymmetric unit of MDMABA compound contains two crystallographically independent molecules
Received 22 January 2010
Received in revised form 21 July 2010
Accepted 4 August 2010
ꢀ
(A and B), and they exist in the E-configuration. The structural perfection of the grown crystal is analyzed
by high-resolution X-ray diffraction rocking curve analysis. The functional groups present in MDMABA
are investigated by FTIR and FT-Raman spectral analyses. The placement of the protons is determined
using HNMR spectrum. The range and percentage of optical transmission were ascertained by recording
UV–vis–NIR spectrum. Thermal and mechanical properties are reported. Dielectric study shows that the
dielectric constant of the crystal varies with frequency and temperature. The third order nonlinear optical
absorption coefficient of the MDMABA crystal is determined by the Z-scan technique.
Keywords:
Growth from solution
Crystal structure
Spectral studies
Dielectric studies
©
2010 Elsevier B.V. All rights reserved.
1
. Introduction
increased [9]. Indeed, the potential use of organic device materials
in optoelectronics is now a very serious matter [10].
To design and prepare molecular crystals having desired and
Schiff base (azo methine) formed by the condensation of
primary amines with aldehydes or ketones yield Schiff bases
containing the imine (C N) functional group [11]. Benzyli-
dene anilines constitute an important class of Schiff bases
that have been widely used in coordinate, medical and bio-
logical chemistry. They possess significant anticancer and
anti-inflammatory activities and may also serve as reagents
for stereo selective organic synthesis. Recently, the ther-
mochromism, photochromism and nonlinear optical properties
of these compounds find applications in modern technolo-
predictable structures it requires an understanding of the inter-
molecular interactions that link molecules together in the solid
state. Combinatorial chemistry is a new field of synthetic chemistry
which leads to fast synthesis of a wide variety of products for par-
ticular applications. The recent success of combinatorial methods
in the field of drug discovery has triggered exploration in the field
of materials such as inorganic luminescent materials and catalysts
[
1,2]. Search for new materials with high optical nonlinearities has
been the important task because of their practical application in
harmonics generation, amplitude and phase modulation, switch-
ing and other signal processing devices [3–6]. An ultimate goal for
designing the molecules with large third order nonlinearities is to
incorporate them into devices used in the optical signals processing
ꢀ
gies [12]. Benzylidene aniline derivatives, of 4-nitro-4 -methyl
ꢀ
benzylidene aniline (NMBA) [13] and 4-nitro-4 -methoxy ben-
zylidene aniline (NMOBA) [14] crystallize in noncentrosymmetric
structure and exhibit second order nonlinear optical properties.
ꢀ
[
7,8]. As nonlinear optical absorption (NOA) has shown its poten-
Another derivative of benzylidene aniline, 4 -nitrobenzylidene-
tial application in optical information storage, optical logic gates,
laser radiation protection, and locked laser mode, due to the large
applications interest in searching for NOA materials has gradually
3-aceatamino-4-methoxyaniline (MNBA) on nitrobenzylidene-3-
ethylcarbonyl-amino-4-methoxyaniline (MNBA-Et) material, finds
application as a nonlinear optical waveguide [15]. The low dielectric
constants make them suitable for high frequency or low switching
energy devices. In the present investigation systematic studies on
the synthesis, growth, structural, spectral, optical, thermal, dielec-
tric studies and third order nonlinear optical properties of one of
∗ Corresponding author. Tel.: +91 4312407057; fax: +91 4312407045.
E-mail address: krmurthin@yahoo.co.in (K. Ramamurthi).
ꢀ
the derivatives of benzylidene aniline, named as 4-methoxy-4 -
1
386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.08.012

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S. Leela et al. / Spectrochimica Acta Part A 77 (2010) 927–932
3. Results and discussion
3.1. X-ray crystal structure determination
Three dimensional crystal structure of MDMABA was deter-
mined by single crystal X-ray diffraction analysis. Suitable crystals
of MDMABA were obtained as yellow blocks by slow evaporation
technique. The data set was obtained using a Stoe Image Plate
Diffraction System [16] using MoK␣ graphite monochromated radi-
ation at 173 K. The structure was solved by Direct methods using
the programme SHELXS-97 and refined by full-matrix least squares
method on F2 using SHELXL-97 [17]. The H-atoms could all be
located in difference electron-density maps. The water H-atoms
were freely refined, while the remainder of the H-atoms were
included in calculated positions and treated as riding atoms using
SHELXL default parameters. The crystal structure is monoclinic and
the system is P21/n.
Scheme 1.
dimethylamino-benzylidene aniline (MDMABA), are reported for
the first time.
The molecular structure and atomic connectivity of the title
compound are illustrated in the PLATON [18] drawing, Fig. 1. The
asymmetric unit of the MDMABA compound contains two crystal-
lographically independent molecules, A and B. Both molecules exist
in the E-configuration. All the C–C and C–N bond lengths in the six-
member ring are comparable to related values in the literature.
The crystal structure is stabilized by a number of weak C–H· · ·␲
interactions and the other details are presented in the paper [19].
2
. Experimental procedure
2.1. Material preparation
The condensation reaction between the primary amine and
aldehyde yields the Schiff base compounds containing imine group.
The commercially available organic compound p-dimethyl aminio
benzaldehyde as take as aldehyde (LOBA Chemie, 99%) and p-
methoxyaniline as take as primary amine (SRL, 99%) were refluxed
3.2. Powder and high-resolution XRD
in ethanol for 6 h to form the Schiff base compound, 4-methoxy-
Powder X-ray diffraction patterns were recorded using powder
ꢀ
4
-dimethylamino-benzylidene aniline (MDMABA). The reaction
˚
X-ray diffractometer with CuK␣1 radiation (ꢀ = 1.54060 A). Finely
crushed powder of a MDMABA crystal was scanned in the 2ꢁ val-
mechanism is shown in Scheme 1. On cooling, the synthesized
compound (MDMABA) deposits at room temperature as a deep yel-
low microcrystalline powder. The material was purified again from
acetone solution by the recrystallization process and the purity of
the sample was confirmed by Thin Layer Chromatography (TLC)
test.
◦
ues ranging from 10 to 70 and the corresponding peaks were
indexed. The study of the defect distribution in the grown crys-
tal is of significant importance because the defects created during
growth have severe consequences on the physical properties of
the crystal. The degree of crystalline perfection can be obtained by
recording high-resolution X-ray diffraction rocking curves. A mul-
ticrystal X-ray diffractometer (MCD) developed at NPL was utilized
to record high-resolution diffraction curves (DCs) [20]. In this sys-
2.2. Single crystal growth
2
tem a fine focus (0.4 × 8 mm ; 2 kW Mo) X-ray source energized by
The solubility of the MDMABA in acetone was determined in the
a well-stabilized Philips X-ray generator (PW 1743) was employed.
The diffracting plane chosen to record the DC was (020). As seen in
Fig. 3 the curve does not contain a single diffraction peak. The solid
line, which follows well with the experimental points (filled cir-
cles), is the convoluted curve of two peaks using the Lorentzian fit.
◦
range of 25–50 C and its variation with temperature. The MDMABA
compound exhibits a high solubility and positive solubility tem-
perature coefficient in acetone. The solubility is one of the most
important parameter to grow a crystal. MDMABA single crystals
3
of size 5 × 2 × 2 mm were grown from saturated acetone solu-
The additional peak depicts an internal structural very low angle
tion of the synthesized compound by slow evaporation method at
room temperature. Further, the saturated solution under the good
controlled evaporation with the paraffin film yielded good quality
ꢀ
(
tilt angle ˛ ≤ 1 ) grain boundary whose tilt angle (misorientation
angle between the two crystalline regions on both sides of the
ꢀꢀ
structural grain boundary) is only 26 from its adjoining region.
3
single crystal of dimension 14 × 3 × 3 mm in a growth period of 30
The Full Width Half Maximum (FWHM) of the main peak and the
days and is shown in Fig. S1.
ꢀꢀ
ꢀꢀ
very low angle boundary are 11 and 35 , respectively. The rela-
Fig. 1. View along the a axis of the crystal packing in MDMABA.

S. Leela et al. / Spectrochimica Acta Part A 77 (2010) 927–932
929
Fig. 2. HRXRD curve of the MDMABA.
tively very low FWHM values of the main peak and the boundary,
which are close to that of the expected theoretical value from the
dynamical theory of plane wave X-ray diffraction [21], show that
the crystalline perfection is good, as is shown in Fig. 2. It may be
mentioned that such a very low angle boundaries could be detected
with resolved peak in the diffraction curve only because of the
high-resolution of the multicrystal X-ray diffractometer used in the
present study. The influence of such minute defects on the physical
properties is very insignificant. However, a quantitative analysis of
such unavoidable defects is of great importance, particularly in case
of orientation dependent device applications like phase matching
applications.
Fig. 3. FTIR and FT-Raman spectrum of MDMABA.
Table 1
Comparison of FTIR and FT-Raman of MDMABA.
Band assignment
C–H stretching
FTIR
FT-Raman
−
−
−1
−
1
1
−1
2923 cm
1609 cm
1580 cm
1163 cm
2987 cm
–
1586 cm
1166 cm
–
C
C
C–O
N
−1
−1
C aromatic stretching
1
−
−
1
C–H deformation band
C–Cl
823 cm
533 cm
1
−1
502 cm
–
3.3. Fourier transform infrared (FTIR) and FT-Raman analyses
−1
3421 cm
Aromatic N–H
Vibrational spectroscopy gives information on molecular vibra-
tions and this information is of immense help to organic chemists
because it can be directly related to molecular structure [22]. To
analyze the presence of functional groups in MDMABA qualita-
tively, Fourier transform infrared (FTIR) and FT-Raman spectra
were recorded. The sample was in pellet form in the KBr phase. FTIR
spectrum shown in Fig. 3 presents the functional groups of the com-
pound. Benzylidene aniline displays the C N stretching as a band
pare well with the corresponding vibrations of FTIR and shown in
Table 1.
3.4. Nuclear magnetic resonance (NMR) analysis
The 1H NMR spectrum of the MDMABA was recorded employ-
1
ing a Brucker AC 200 MHz NMR spectrometer in CDCl . The
H
3
−1
−1
at 1600 cm . The band obtained at 1609 cm is a proof for the
formation imine group. Para-di-substituted benzenes show C–H
NMR spectrum shows, the singlet at 8.33 ppm which confirms
the formation of Schiff base compounds containing imine (C N)
group. The adjacent four doublet protons are aromatic ring proton.
The singlet at 3.81 ppm shows the methoxy group of the aniline
phenyl ring proton and the singlet peak at 3.03 ppm is due to the
−
1
deformation vibration in the region 840–800 cm and in this work
−
1
the C–H deformation vibration appears at 823.82 cm . FTIR spec-
trum does not show any signal corresponds to aldehyde and aniline
group present in the reactant. FT-Raman spectrum also shows the
functional groups of the compound. The FT-Raman results com-
[–N–(CH3) ] amino methyl group protons as shown in Fig. 4. In
2
the NMR spectrum of MDMABA, the ratio of steps obtained is,
Fig. 4. NMR spectrum of MDMABA.

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S. Leela et al. / Spectrochimica Acta Part A 77 (2010) 927–932
Fig. 5. (a) Plot of frequency vs. dielectric constant. (b) Plot of frequency vs. dielectric loss.
A:B:C:D:E:F:G = 1:2:2:2:2:3:6. Thus, the number of protons asso-
ciated with the signals are A, 1H; B, C, D and E, 2H; F, 3H and G, 6H,
respectively
is transparent in the region 360–1200 nm one can use MDMABA as
the third harmonic generator.
3.7. Z-scan studies
3.5. Dielectric studies
Sheik-Bahae et al. [26] and Vanstryland and Sheik-Bahea [27]
have reported a single beam method for measuring the sign and
Dielectric properties are correlated with the electro-optical
property of the crystals. Carefully discerned sample of MDMABA
was cut and polished and coated by the ohmic contact to make the
sample as parallel plate capacitor. Agilent Model LCR meter was
used to measure the capacitance, and dielectric loss (tan ı) of the
sample as a function of frequency (100 Hz to 1 MHz) and tempera-
magnitude of nonlinear refractive index (n ) and nonlinear absorp-
2
tion coefficient that is more sensitive compared to interferometer
methods. Using a single Gaussian laser beam in tight focus geom-
etry, 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 absorption
of MDMABA crystals (thickness ≈ 3 mm) was studied using the sin-
gle beam Z-scan method with Nd:YAG laser at 532 nm. The study
of nonlinear optical parameters by the Z-scan method depends on
the position (Z) of the thin samples under the investigation along a
focused Gaussian laser beam. The linear transmittance of the aper-
ture (S), S = 1 corresponds to the collection of all transmitted light
and therefore is insensitive to any nonlinear beam distortion due
◦
ture (45–120 C). The dielectric constant was calculated using the
relation
[
Ccrys − Cair(1 − Acry/Aair)]
Aair
εr =
×
(1)
C
Acry
air
In Eq. (1), Ccrys and Cair are the capacitance of the crystal and air
respectively, and Acry and Aair are the area of the crystal and air
respectively. The maximum dielectric constant obtained for the
◦
MDMABA crystal at 110 C is 120 (100 Hz) and this value decreases
to 40 at 1 MHz which is shown in Fig. S2. It is observed that the
dielectric constant of the crystal at higher frequencies is almost
constant. At lower frequencies, the dielectric constant was found
to be considerably higher than that at higher frequencies. This type
of dielectric response is of great interest in applications in which
materials with high dielectric constant values are good candidates
for heating devices [23]. The magnitude of the dielectric constant
(
εr) depends on the degree of polarization. The dielectric constant
◦
of MDMABA crystal vs. frequency at 100 C is 120 [100 Hz] and this
value decreases to 39 at 1 MHz, as shown in Fig. 5. These curves
suggest that the dielectric constant and dielectric loss strongly
depends on the frequency of the applied field, similar to what com-
monly happens with the dielectric constant in the ionic system
[
24,25].
3.6. UV–vis–NIR transmission
The UV–vis–NIR spectrum of the as grown MDMABA crystal was
recorded using Schimadzu 1601 UV–vis–NIR spectrometer in the
wavelength range 200–1200 nm and is shown in Fig. S3. The spec-
trum shows that UV lower cutoff occurs at about 367 nm, and there
is no remarkable absorption in the entire region of the spectrum.
The transmittance of MDMABA is 81% at 367 nm. Since the crystal
Fig. 6. Z-scan (open) curvature of the MDMABA.

S. Leela et al. / Spectrochimica Acta Part A 77 (2010) 927–932
931
Fig. 7. TGA/DTA spectrum of the MDMABA.
to nonlinear refraction [27]. 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 open aperture Z-scan
study for the grown MDMABA crystal are presented in Fig. 6. The
nonlinear absorption coefficient (ˇ) of the crystal was calculated
using the standard relations given below [26–28]
ues with the applied load is shown in Fig. S4. The hardness value
increases with increasing load. The plane considered for study
exhibits the reverse indentation size effect. The specimen thus leads
to a larger indentation size which gives rise to a lower hardness at
low loads [29]. For loads above 100 g, cracks started developing
around the indentation mark. It is concluded that the hardness of
the MDMABA crystal is moderately good.
√
ˇ = 2
2 ꢂT
(2)
I0Leff
4. Conclusion
where Leff = [1 − exp(−˛L)]/˛ with I = P/(ꢃω02) defined as the peak
0
intensity within the sample, where L is the thickness of the sample,
and ˛ is the linear absorption coefficient. The enhanced transmis-
sion near the focus is indicative of the saturation of absorption
at high intensity. The focusing effect is attributed to a thermal
nonlinearity resulting from absorption of radiation at 532 nm.
Localized absorption of a tightly focused beam propagating through
an absorbing medium produces a spatial distribution of tempera-
ture in the crystal and, the value of nonlinear absorption coefficient
Our results show the potential use of combinatorial synthe-
sis for obtaining targeted libraries in materials chemistry. The
title compound might be utilized as an active dopant in polymer
based second harmonic generating, electro optic or photorefractive
materials. The UV–vis–NIR spectrum elucidates that the crystal is
transparent between 370 and 1200 nm. From the FTIR, FT-Raman
and NMR spectra, the formation of the imine group of the mate-
rial was confirmed. Thermal analyses indicated that the crystal has
good thermal stability. The hardness of the crystal was recorded.
High-resolution X-ray diffraction study shows that the perfection
of the crystal is fair even though it contains a low angle boundary.
The Z-scan technique carried out showed that the relative third
order nonlinear optical absorption coefficient is 0.18539 cm/W.
(
ˇ) estimated is 0.18539 cm/W.
3.8. Thermal analysis
The thermogravimetric analysis (TGA) of MDMABA was carried
◦
◦
out between room temperature (30 C) and 1200 C at a heating
rate of 10 K/min. The experiment was performed in a nitrogen
Acknowledgements
◦
atmosphere. The material is stable up to 250 C after which decom-
position starts and it shows that there are no water molecules in the
One of the authors (SL) thanks Dr. A. Ilangovan, School of
Chemistry, Bharathidasan University, Tiruchirappalli for fruitful
discussions. SL also thanks Dr. Reji Philip, Associate Professor,
Raman Research Institute, Bangalore, India for Z-scan studies. One
of the authors (SL) thanks to Dr. C.K. Magadevan for Dielectric stud-
ies and the fertile discussion. The authors thank the University
Grants Commission, Government of India [File No. 32-37/2007 (SR)]
for financial assistance.
◦
compound. A major weight loss (88%), which starts at 250 C and
◦
ends at 420 C, is attributed to the loss of carbonyl compounds. The
second weight loss is due to the loss of nitrogen molecules between
◦ ◦
30 C and 820 C. The material is fully decomposed at the tempera-
ture of 1100 C. A sharp endothermic peak at 145.6 C corresponds
to the melting point. The sharpness of the peak reveals the good
crystallinity of the synthesized compound, and is shown in Fig. 7.
4
◦
◦
3.9. Mechanical property
Appendix A. Supplementary data
The structure and composition of the crystalline solids are
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2010.08.012.
related to the mechanical hardness. Microhardness testing is one of
the best methods to understanding mechanical properties of mate-
rials such as fracture behavior, yield strength, brittleness index, and
temperature of cracking. The measurements were done at room
temperature for different forces. The measurements were made on
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