Bulk size crystal growth, spectroscopic, dielectric and surface studies of 4-N,N-dimethylamino-4-N′-methylstilbazolium m-nitrobenzenesulfonate (DSMNS): A potential THz crystal of stilbazolium family

Article abstract of DOI:10.1016/j.saa.2015.05.022

The synthesis and growth of a potentially useful and efficient nonlinear optical organic single crystal of 4-N,N-dimethylamino-4-N′-methylstilbazolium m-nitrobenzenesulfonate (DSMNS) is reported. The growth experiment involved the slope nucleation method

Full text of DOI:10.1016/j.saa.2015.05.022

Accepted Manuscript
Bulk size crystal growth, spectroscopic, dielectric and surface studies of 4-N,
N-dimethylamino-4-N’-methylstilbazolium m-nitrobenzenesulfonate
(DSMNS): A potential THz crystal of stilbazolium family
A. Antony Raj, S. John Sundaram, R. Gunaseelan, P. Sagayaraj
PII:
S1386-1425(15)00610-1
http://dx.doi.org/10.1016/j.saa.2015.05.022
SAA 13689
DOI:
Reference:
To appear in:
Spectrochimica Acta Part A: Molecular and Biomo-
lecular Spectroscopy
Received Date:
Revised Date:
Accepted Date:
6 December 2014
23 March 2015
5 May 2015
Please cite this article as: A. Antony Raj, S. John Sundaram, R. Gunaseelan, P. Sagayaraj, Bulk size crystal growth,
spectroscopic, dielectric and surface studies of 4-N, N-dimethylamino-4-N’-methylstilbazolium m-
nitrobenzenesulfonate (DSMNS): A potential THz crystal of stilbazolium family, Spectrochimica Acta Part A:
Molecular and Biomolecular Spectroscopy (2015), doi: http://dx.doi.org/10.1016/j.saa.2015.05.022
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Bulk size crystal growth, spectroscopic, dielectric and surface studies of 4-N, N-
dimethylamino-4-N'-methylstilbazolium m-nitrobenzenesulfonate (DSMNS): A
potential THz crystal of stilbazolium family
a
A. Antony Raj , S. John Sundaram , R. Gunaseelan and P. Sagayaraj
a
b
a*
a
Department of Physics, Loyola College (Autonomous), Chennai-600 034, India
b
Department of Physics, Adhi College of Engineering and Technology, Kanchipuram-631 605,
India
Abstract
The synthesis and growth of a potentially useful and efficient nonlinear optical
organic single crystal of 4-N, N-dimethylamino-4-N'-methylstilbazolium m-
nitrobenzenesulfonate (DSMNS) is reported. The growth experiment involved the slope
nucleation method coupled with slow cooling as well as slow solvent evaporation techniques.
Single crystal X-ray diffraction (XRD), Fourier transform infrared (FT-IR), FT-Raman and
nuclear magnetic resonance (NMR) techniques have been employed to ascertain the structure
and composition of the crystal. Second harmonic generation (SHG) efficiency of the sample
has been examined by Kurtz and Perry powder test. Thermogravimetry (TG), differential
thermal analysis (DTA) and differential scanning calorimetry (DSC) techniques are employed
to investigate the thermal behavior of the grown crystal. The frequency/temperature
dependent dielectric properties of the organic crystal of DSMNS are studied. The surface
features of the grown crystal are investigated by chemical etching study and atomic force
microscopy (AFM).
Keywords: Stilbazolium derivatives; Nonlinear optical material; Growth from solutions;
Spectral analysis; Thermal analysis
*
Corresponding author
Dr. P. Sagayaraj, Associate Professor of Physics, Loyola College (Autonomous), Chennai-
00034, India
Email: psagayaraj@hotmail.com, Tel: +9144 28178200; Fax: +9144 28175566.
6

1
. Introduction
The design and synthesis of organic materials for high second order nonlinear optical
NLO) effect has become a hot area of research due to their widespread applications in the
(
fields of optical signal processing, integrated photonics, optical switching, optical data
storage, electro-optic modulation, spectroscopy and, terahertz (THz) wave generation and
detection [1-4]. THz wave, being a non-ionizing source, its generation and detection assumes
significance in the field of nonlinear spectroscopy and biomedical imaging [5, 6]. Organic
materials exhibiting large macroscopic nonlinearity can be potentially used for the generation
of high power THz wave [7]. Hence, researchers are aiming at the development of organic
materials particularly; ionic organic crystals with high chromophore density are of special
interest for large NLO effect. The stable packing of chromophores in this class of crystals
results in high thermal, mechanical and photochemical stability [8]. Among the various ionic
organic crystals, 4-N, N-dimethylamino-4-N'-methylstilbazolium tosylate (DAST) is one of
the widely reported crystals [9]. The generation of THz wave employing DAST crystal has
been investigated recently using optical rectification (OR) and difference frequency
generation (DFG) methods [10, 11]. DAST crystal consists of a stilbazolium cation and
tosylate anion with strong columbic interaction, overwhelming the dipole-dipole interaction
and thereby facilitating the formation of polar sheets of cation [4]. It is evident from the
literature that the stilbazolium cations are the most attractive species and their molecular
nonlinearity can be easily preserved by the introduction of novel counter-ions. The counter
anion approach has boosted the research to explore diverse design possibilities by effectively
varying the structure with a suitable anion to achieve the desired physical and chemical
properties [12]. Every minor change in the structure of counter anion is found to have an
important effect in the crystal stacking. Moreover, well designed counter anions have resulted
in noncentrosymmetric structure with higher second order NLO activity close to or better
than DAST [1, 13-15]. In the recent past, our research group has been involved in the growth
of a few stilbazolium derivatives such as 4-N, N-dimethylamino-4-N’-methylstilbazolium 4-
styrenesulphonate
(DSSS),
4-N,
N-dimethylamino-4-N’-methylstilbazolium
p-
methoxybenzenesulfonate (DSMOS) and 4-N, N-dimethylamino-N′-methylstilbazolium p-
chlorobenzenesulfonate (DASC) [16-18]. In our continued efforts to develop ionic organic
crystal with potential THz properties, in this article we are reporting on 4-N, N-
dimethylamino-4-N’-methylstilbazolium m-nitrobenzenesulfonate (DSMNS), yet another
stilbazolium derivative with promising physicochemical properties. The title compound
(
DSMNS) was synthesized by changing the tosylate anion of DAST with m-

nitrobenzenesulfonate, without altering the stilbazolium cation. In an early attempt, Okawa et
al. have synthesized DSMNS along with various other derivatives. The crystal of DSMNS in
its powder form had shown second harmonic generation (SHG) activity [19]. However, the
grown samples of DSMNS were thin needle crystal of mm size only. In the present work, our
effort has been directed to explore the possibilities to grow good quality macro size crystals
of DSMNS in order to realize its practical applications for THz generation and electro-optic
(
EO) modulation. We have made an attempt to grow the DSMNS crystal via slope nucleation
method coupled with slow cooling (SNM-SC), an efficient technique employed by our
research group and also a few other researchers for developing DAST and its derivatives [16,
2
0]. The crystal was also grown by the slope nucleation method coupled slow solvent
evaporation (SNM-SE) technique and the results are compared. Further, attention has been
paid to investigate the structural, spectral and physicochemical properties of the grown
crystals. Detailed investigations including Fourier transform infrared (FT-IR), FT-Raman,
nuclear magnetic resonance (NMR) spectroscopic studies, dielectric measurement and
surface properties of the crystal are reported for the first time.
2
. Experimental Procedure
2
.1. Material synthesis
The chemicals employed in this work were of analytical grade (Sigma Aldrich) with
high purity. DSMNS was synthesized by metathesization of 4-N, N-dimethylamino-4-N'-
methylstilbazolium iodide (DMSI) with silver m-nitrobenzenesulfonate. In the first stage,
DMSI was synthesized by Knoevenagel condensation [21], where carbon-carbon π-bond
between dimethylamino benzaldehyde and active hydrogen compound of 1, 4 dimethyl
pyridinium iodide is formed by eliminating the water molecule from it in the presence of
piperidine. In our experiment, 1, 4-dimethyl pyridinium iodide (2.35 g, 10 mmol) and 4-N, N-
dimethylaminobenzaldehyde (1.79 g, 10 mmol) were dissolved in 30 ml of methanol in the
presence of piperidine and condensed to form DMSI under mild conditions. The above
mixture was refluxed for several hours at 70 ºC using the Dean-Stark apparatus. The product
was then cooled to room temperature and the red colored crystalline salt was obtained. The
product was initially recrystallized in methanol and then in ethanol for at least 3-4 times to
eliminate the unreacted materials. During the second stage, silver m-nitrobenzenesulfonate
was synthesized by separately dissolving equimolar ratio of sodium m-nitrobenzenesulfonate
and silver nitrate in minimum quantity of water. The prepared solutions were thoroughly
mixed and stirred for several minutes to obtain a turbid white precipitate and the product was

dissolved by gentle heating. The resultant solution was filtered and the filtrate was heated to
achieve the required supersaturation and then cooled naturally. Thus obtained precipitate of
silver m-nitrobenzenesulfonate was collected by filtration.
The title compound (DSMNS) was synthesized by metathesization reaction, adopting
the procedure previously reported [19]. The reaction scheme is illustrated in Fig.1. Initially,
DMSI cation (0.732 g, 2 mmol) was dissolved in 50 ml of methanol under mild heat.
Simultaneously, in another beaker, silver m-nitrobenzenesulfonate (0.62 g, 2 mmol) was
dissolved in 30 ml of methanol under moderate hot conditions. Thereafter the two hot
solutions were thoroughly mixed through magnetic agitation which forms a precipitate
immediately. The content was stirred for about 30 minutes and then the silver iodide
byproduct was removed by filtration. The filtrate was then concentrated to supersaturation
upon heating and then cooled to ambient temperature. The resulting DSMNS precipitate was
collected by suction filtration. The purity of the synthesized DSMNS powder was further
improved by recrystallization in methanol for at least 5-6 times.
2
.2. Solubility
The solubility of the as-synthesized DSMNS salt in methanol solvent was estimated at
different temperatures (35, 45, 55 and 65 ºC). It is evident from the solubility diagram (Fig.2)
that DSMNS has a positive solubility coefficient in methanol, thus encouraging its growth by
low temperature solution growth methods. Interestingly, quite a few stilbazolium crystals
were reported to grow favorably in methanol solvent while grown by slow solvent
evaporation or slow cooling techniques [13, 17].
2
.3. Crystal growth
Crystal growth of DSMNS was achieved by employing slope nucleation method
coupled with slow cooling (SNM-SC) technique and also via slope nucleation method
coupled with slow evaporation (SNM-SE) technique. For achieving growth by SNM-SC, the
saturated solution was prepared by dissolving 2.0 g of DSMNS in 100 ml of methanol at 55
°C. The saturated solution was filtered and then shifted to a Teflon beaker. To promote slope
nucleation, a Teflon plate with parallel grooves was kept inside the beaker. The beaker was
then sealed with a cap and kept in a constant temperature bath at 50 °C and then slow cooled
3
at a rate of 0.5-1 °C/day. After 20-25 days, crystals with size up to 14 × 1 × 1 mm were
harvested. The crystals appeared reddish (Fig. 3a) with predominantly needle shape,
possessing a fairly flat surface. In order to grow the crystal by SNM-SE technique, the
saturated solution was prepared by dissolving the synthesized powder in 200 ml of methanol

at 35 °C. The prepared solution was kept in a Teflon beaker and then sealed with a perforated
lid and housed in a constant temperature bath to encourage the slow solvent evaporation.
After 3-4 weeks, bulk size crystals of size up to 2.5 cm in length, 3 mm in breadth and 2 mm
in thickness were harvested. The bulk size crystals grown from SNM-SE technique are shown
in Fig. 3b. It is evident that the DSMNS crystals grown by slow evaporation technique tend to
grow much thicker and broader than those grown by SNM-SC, but their surface is rather
rough and the edges are not sharp. The crystals grown in the present work are at least 7 fold
bigger than the previously reported size [19]. The improvement in size is attributed to the
slope nucleation method which enables efficient control of nucleation and growth habit.
2
.4. Characterization
Single crystal X-ray diffraction data were collected by using a Bruker X8 KAPPA
APEX II single crystal X-ray diffractometer with MoK (λ = 0.71073 Å) radiation. The FT-
α
-1
IR spectrum of DSMNS was recorded in the region 400-4000 cm with a Perkin-Elmer FT-
IR spectrometer using KBr pellet technique. The NIR FT-Raman spectrum of DSMNS was
recorded with a Bruker RFS 27: stand alone FT-Raman spectrometer using a Nd:YAG laser
at 1064 nm with a 470 mW output as the excitation source. The proton NMR spectrum was
recorded employing a Bruker ADVANCE III 500 MHz FT-NMR spectrometer by dissolving
the sample in deuterated methanol. The NLO test was done on the sample using a Q-switched
mode locked Nd:YAG laser (1064 nm, Quanta ray series, Spectra Physics) with a beam of
energy 10 ns pulse width and 0.68 J power. The TG/DTA thermal analyses for DSMNS
powder sample were carried out between 25 and 500 ºC using a Perkin Elmer TGA-7 thermal
analyzer at a heating rate of 10 ºC per minute. The DSC thermogram of DSMNS was
obtained using a Perkin Elmer DSC-7 differential scanning calorimeter. For dielectric
measurements HIOKI 3532-50 LCR Hitester was employed. A sample of known dimension
was silver coated and then placed inside a dielectric cell. The capacitance was measured at
different temperatures (308, 328, 348 and 368 K) and frequencies (50 Hz to 5 MHz). The
chemical etching analysis was carried out using a Nikon Eclipse LV100 POL microscope.
The surface features of the DSMNS crystals were analyzed by atomic force microscopy
(
AFM) employing the Park systems XE-70 (South Korea). All measurements were
performed at room temperature, and images were collected in non-contact mode at a scan rate
of 0.5 Hz. In this mode, the tip hovers around 50-150 Å above the sample surface. Attractive
van der Waals forces acting between the tip and the sample are detected, and topography
images are constructed by scanning the tip above the surface.

3
. Results and Discussion
3
.1. Single crystal XRD analysis
Single crystal XRD data of the DSMNS crystal is presented in Table. 1. It is observed
that the grown crystal belongs to monoclinic system with space group P2 . The results
1
obtained in the present work are in concurrence with the literature and thus confirms the
identity of DSMNS [19].
3
.2. FT-IR and FT-Raman spectral analyses
The infrared and Raman spectroscopy are essential tools to identify various kinds of
vibrational modes present in the molecules [22]. Vibrational frequencies depend on the
bonds, crystal structure and field force experienced by the atoms and hence vital information
on intermolecular interactions of the molecules can be obtained [23]. The vibrational spectral
analysis of DSMNS sample was performed on the basis of the characteristic vibrations of the
stilbazolium cation and nitrobenzenesulfonate anion. The overall stilbazolium cation
vibrations comprise of the vinyl group, phenyl and pyridine rings, methyl and skeletal mode.
The anion (m-nitrobenzenesulfonate) consists of aromatic nitro and sulfonate group
vibrations. The FT-IR and FT-Raman spectra recorded for the DSMNS crystal are depicted in
Fig. 4 and 5, respectively.
3
.2.1. Vinyl group vibrations
The vibrations of ethylenic bridge are very sensitive to the degree of charge transfer
between the donor and the acceptor groups, hence such stretching modes draw the special
attention of the spectroscopists. The alkene bond stretching vibrations in conjugated systems
without a center of symmetry are likely to produce two C=C stretching bands, one near at
-
1
-1
-1
1
650 cm and the other one at 1600 cm [23]. The bands observed at 1647 and 1589 cm in
-
1
the IR and those at 1618 and 1586 cm in the Raman spectra can be attributed to the C=C
stretching vibrations of ethylenic bridge. [24]. The aliphatic C–H stretching bands for
-
1
stilbazolium derivatives are expected in the region between 3050 and 3000 cm [23, 25]. In
-
1
DSMNS crystal, the weak band observed at 3074 cm (IR spectrum) can be attributed to the
aliphatic C–H stretching.
3
.2.2. Phenyl and pyridine ring vibrations
The aromatic ring vibrational modes of DSMNS have been analyzed on the basis of
stilbazolium ring vibrations that are composed of para disubstituted phenyl and pyridine rings
connected by ethylenic bridge. The C–H in-plane and out-plane bending vibrations are
-1
-1
observed in the regions 1300-1000 cm and 1000-675 cm , respectively [23]. The C–H in-

plane bending vibrations are marked as characteristic bands at 1215, 1180, 1164 and,
-1
-1
1
033 cm in the IR spectrum and at 1206, 1183 and 1617 cm in the Raman spectrum. The
C–H out-of-plane bending vibrations are observed in the IR spectrum at 970, 945, 875 and
-
1
-1
7
56 cm , where as it is observed in the Raman spectrum at around 776 cm . The 1, 4
-
1
distributed aromatic ring C–H vibration is expected in the region of 800-875 cm [26]. The
-1
peak at 825 cm in the IR spectrum is attributed to the 1, 4 distributed aromatic ring C–H.
-1
The phenyl ring mode deformation vibrations are observed at 663, 613 and 532 cm in the IR
-
1
spectrum, and at 722, 666, 615 and 532 cm in the Raman spectrum [23].
3
.2.3. Methyl group vibrations
Methyl groups are normally referred to as an electron donating substituents in the
aromatic ring system [23]. For methyl (CH
manifest as characteristic bands at 2916 and 2956 cm in the IR and Raman spectra,
respectively. The asymmetrical and symmetrical bending vibrations of CH group are
expected in the regions of 1465-1440 and 1390-1370 cm , respectively [27]. The band
3
) group, the asymmetric stretching vibrations
-1
3
-
1
-
1
-1
positioned at 1473 cm in the IR and the other band at 1474 cm in Raman spectra have been
assigned to the asymmetrical bending vibrations of methyl group. The intense IR band
-1
observed at 1369 cm can be attributed to the symmetrical bending vibrations. For CH
3
-1
group, the rocking mode usually appears in the region 1070-1010 cm [23]. This mode
-1
-1
appears as the weak band at 1072 cm and 1047 cm in the IR and Raman spectra,
respectively.
3
.2.4 Sulfonate group vibrations
The SO group gives rise to asymmetric and symmetric stretching vibrations in the
range 1420-1000 cm with high intensity peaks. At the same time, the wave numbers of the
SO compounds may overlap with those of other functional groups [28]. In DSMNS crystal,
the strong bands at 1180 and 1164 cm in the IR, and those at 1183 and 1167 cm in the
2
-1
2
-1
-1
Raman spectra are characteristic of SO
2
asymmetric stretching vibrations. Thus the bands
-1
-1
observed at 1072 cm in the IR spectrum and at 1047 cm in the Raman spectrum can be
-
1
assigned to the SO symmetric stretching vibrations. The band seen at 494 cm in the IR
2
-1
spectrum and the band at 500 cm in the Raman spectrum can be attributed to SO
3
deformation [23].
3
.2.5. Nitro group vibrations
For an aromatic nitro compound, the strong absorption bands due to the asymmetric
-
1
and symmetric vibrations of the NO
2
group are expected in the region 1560-1500 cm and
-1
-1
1
360-1300 cm , respectively [28]. The very strong IR band viewed at 1523 cm and the

-
1
Raman band at 1514 cm can be attributed to the NO
2
asymmetric stretching vibrations. The
-1
-1
strong bands seen at 1346 cm in the IR and at 1338 cm in the Raman spectra are assigned
to the NO
2
symmetric stretching vibrations.
3
.2.6. Skeletal mode vibrations
The absorption bands for C–N and C–C stretching vibrations are generally identified
-1
-1
-1
in the region 1150-850 cm [23]. The bands positioned at 876 cm and at 875 cm in the IR
and Raman spectra are assigned to C–N stretching mode.
3
.2.7. Other vibrations
-1
The band noticed at wavenumber 3448 cm corresponds to the O–H stretching, which
-1
might be due to the air moisture. The Raman band observed at 85 cm is possibly attributed
-
1
to the CH
assignments for DSMNS crystal are presented in Table 2.
.3. NMR analysis
The proton NMR spectrum (Fig. 6) of DSMNS was recorded by dissolving the sample
in deuterated methanol. The singlets at 3.08 and 4.23 ppm are assigned to the six hydrogens
of N–(CH and three hydrogens of N–CH , respectively. The intensity of the peak at 3.08
ppm substantiates the number of contributing nuclei. The doublets positioned at 6.79 and 7.62
3
torsional vibration [23]. The FT-IR and FT-Raman wavenumbers (cm ) and their
3
3
)
2
3
ppm are due to the four hydrogens of (CH
3
)
2
5
–N–C
6
H aromatic ring. The doublets at 7.79 and
4
8
7
8
.52 ppm represent the four hydrogens of C
H
4
N aromatic ring. The doublets seen at 7.11 and
.85 ppm are due to the two oliphinic hydrogen atoms (HC=CH). The doublets observed at
.20 and 8.63 ppm are corresponding to the two aromatic hydrogens that are present in the
positions ortho to –SO
ortho to nitro group alone. The triplet observed at 7.72 ppm is due to the aromatic hydrogen
which present in the meta position to both NO and SO groups.
3
. The doublet seen at 8.32 ppm is assigned to the aromatic hydrogen
2
3
3
.4. CHN analysis
The calculated CHN values of C22
.52% and the corresponding experimentally found values are; C = 59.81%, H = 5.24% and
23 3 5
H N O S are; C = 59.85%, H = 5.25% and N =
9
N = 9.39%. Both the theoretical and experimental values resemble each other.
.5. SHG efficiency test
The second harmonic generation (SHG) efficiency of DSMNS was performed by
3
Kurtz and Perry technique [29]. The sample was made into a very fine powder and tightly
packed in a microcapillary tube. It was then mounted on the path of a Q-switched Nd:YAG
laser (1064 nm, Quanta ray series) of pulse width of 10 ns with 0.68 J power. The SHG signal

generated at 532 nm is split from the fundamental frequency using an IR separator.
Microcrystalline powder sample of urea was employed as the reference material to compare
the efficiency of the DSMNS. When a laser beam of 0.68 J was passed through the sample,
an output pulse of 382 mV was recorded for DSMNS. The SHG study confirmed that
DSMNS crystal exhibits an efficiency which is nearly 27 times higher than that of the urea
crystal.
3
.6. Thermal analysis
From the TG curve (Fig. 7a), one can ascertain that the sample is thermally stable up
to 237 ºC and it decomposes immediately after melting. The material undergoes a weight loss
of 53.56% from 237 ºC up to 486.5 ºC and the remaining 46.4% of the sample is left out as
residue at 500 ºC. The endothermic peak at 235.1 ºC in the DTA curve (Fig. 7a) could be
attributed to the melting of the material. Another exothermic peak positioned at 323.2 ºC,
could be assigned to the complete breakage of stilbazolium ion. The DSC thermogram (Fig.
7
b) shows an endothermic peak at 235.4 ºC with a thermal heat capacity of 96 J/g,
representing the melting point of the material. The observed melting point of DSMNS is
slightly lower than the DAST (259 ºC) [20]. However, organic materials with thermal
stability above 200 ºC could be considered as thermally stable materials for realizing practical
applications.
3
.7. Dielectric studies
Fig. 8a illustrates the variation of dielectric constant (ε
r
) of DSMNS crystal as a
function of log frequency at different temperatures. It is noticed that at a constant
temperature, the dielectric constant decreases with frequency. The high dielectric constant at
low frequency is due to the existence of electronic, ionic, dipole orientation and space charge
polarizations [30]. At low frequencies, all the four contributions may be active. Particularly,
the higher value of dielectric constant at low frequency is due to the space charge
polarizations that depend on the purity and perfection of crystals [31, 32]. When the
frequency increases, the net polarizations of the material drops to zero since, the entire
polarizations end to contribute and it appears in the graph as an exponential reduction in the
dielectric constant value. The variation of dielectric loss (tan δ) with frequency (Fig. 8b) is
also measured. Fig. 8b shows that the dielectric loss decreases with frequency. This is a
r
normal dielectric behavior that both ε and tan δ decrease with increasing frequency [33]. At
low frequencies, the dielectric loss is high and it can be related to the space charge
polarizations owing to the charged lattice defect [34]. The low dielectric constant of the
materials at high frequency is an added advantage for photonics and electro-optic device

fabrications [35]. It has been already reported that DAST, a prominent crystal of stilbazolium
family has low dielectric permittivity with much higher electro optic (EO) coefficient [3].
Based on the dielectric study, it can be concluded that DSMNS, a derivative of stilbazolium
possesses low dielectric constant at high frequencies and hence the material is potentially
suitable for EO applications.
3
.8. Etching studies
Chemical etching study is very simple and suitable technique to reveal the crystal
defects and growth mechanism by knowing the microstructural imperfection or dislocation of
the grown crystal [36]. Etching study was made on the DSMNS crystal grown by both SNM-
SC and SNM-SE techniques. Methanol was utilized as an etchant and the experiment was
performed at room temperature. The crystals were immersed in the etchant for an etching
time of 10 and 15 s and then gently wiped with tissue paper. The etched patterns were then
examined under an optical microscope. Fig. 9 (a) and (b) displays the etch patterns recorded
on the surface of DSMNS crystal grown by SNM-SC. It is observed from Fig. 9a that
striation like etch pit patterns are formed with an etching time of 10 s, while increasing the
etching time to 15 s, a clearly visible and deep etch pit pattern is spotted at the dislocation site
(
Fig. 9b). Moreover, the further increase in etch time has not produced any change in the
morphology of etch pit and the observed pattern was stable over a longer period. Fig. 10a and
b demonstrates the etch patterns of DSMNS crystal grown by SNM-SE technique. This etch
pit pattern is more or less similar to those crystals grown by SNM-SC, but the density of
striation-like pattern is found to be more and also irregular in shape. Compared to SNM-SE
grown crystal, the number of etch pits is relatively less in SNM-SC grown crystal and this
could be attributed to the difference in growth condition which influences the crystalline
perfection.
3
.9. Atomic force microscopy
AFM provides a three dimensional (3D) profile of the surface on a nanoscale, it
measures the forces between a sharp probe (<10 nm) and the surface at very short distance
0.2-10 nm probe-sample separation). To better comprehend the morphology of a surface, a
(
quantitative description of the surface topography must be carried out. The topography matrix
data should be treated in each profile line (2D) or over all profiles extending the analysis to
surface (3D). Figs. 11&12 demonstrate the 2D and 3D image morphologies of the DSMNS
crystals grown by SNM-SC and SNM-SE techniques, respectively. It is evident from the
morphology (Fig. 11b) that the surface of the crystal grown by SNM-SC contains very few

major hillocks. Whereas, the crystal grown by SNM-SE (Fig. 12b) is free from major
hillocks, but contains a deep cavity. It is well known that a large number of peaks and valleys
in an image may significantly affect the average roughness (S
values [37]. The estimated roughness values for crystal grown by SNM-SC are found to be S
15.775 nm and S = 18.930 nm. While, the values are quite higher (S = 23.337 nm and S
0.038 nm) for the crystal grown by SNM-SE.
The ten point height (S ) which is regarded as the difference in height between the
average of the five highest peaks and the five lowest valleys along the assessment length of
the profile. S is found to be 101.745 and 220.435 nm for DSMNS crystal grown by SNM-SC
a
) and root mean square (S
q
)
a
=
q
a
q
=
3
z
z
and SNM-SE, respectively. The Surface skewness (Ssk) and kurtosis (Sku) moments are the
parameters used to measure the asymmetry and flatness, respectively. It has been reported
that if the height distribution is asymmetrical and the surface has more peaks than valleys,
then the skewness moment is positive. If the surface is more planar and the valleys are
predominant, the skewness is negative [37]. The Ssk values for the crystals grown by SNM-
SC (0.409) and SNM-SE (0.558) are positive. Similarly, another important surface parameter,
namely, Surface kurtosis (Sku) is the measure of surface sharpness. If the value of Sku is lesser
than 3, the surface is regarded as a perfectly flat one and if Sku is greater than 3, the surface is
set to have more peaks than valleys [38]. The Sku values are found to be 2.564 and 4.038 for
the samples grown by SNM-SC and SNM-SE, respectively. The Sku values indicate that the
DSMNS crystal grown by SNM-SC has moderately flat surface and free from cavities than
the crystal surface of SNM-SE. The various roughness parameters of the as-grown crystal
surfaces of DSMNS are listed in Table 3.
4
. Conclusion
The bulk size crystals of DSMNS were successfully grown via SNM-SC and also
from SNM-SE method using methanol solvent. Crystals grown by SNM-SC were found to
have smooth surface with needle morphology. Though the SNM-SE method offers promise
for achieving bulk size crystal growth, the harvested crystals require further improvement in
terms of their surface features and morphology. Single crystal X-ray diffraction revealed the
monoclinic crystal structure with space group P21. The crystal structure, molecular weight
and the presence all the functional groups were confirmed by FT-IR, FT-Raman, CHN and
NMR studies. The SHG efficiency of DSMNS was found to 27 times higher than the urea
crystal. The TG/DTA and DSC thermograms confirmed that the DSMNS is thermally stable
up to 235 ºC. The material showed low dielectric constant at high frequency. The chemical
etching and atomic force microscopic studies confirmed the moderately good surfaces of the

grown crystals. Thus the ability to grow as bulk size crystal of good crystalline quality
coupled with high SHG activity and low dielectric constant of DSMNS crystal make it a
potential candidate material for nonlinear optics, photonics and THz applications.
Acknowledgement
The authors acknowledge the DST-SERB, India for funding this research work
(
SR/S2/LOP-29/2013).
References
[
1] Z. Sun, X. Liu, X. Wang, L. Li, X. Shi, S. Li, C. Ji, J. Luo, M. Hong, Cryst. Growth
Des. 12 (2012) 6181-6187.
[
[
2] Y. Dai, J. Tan, N. Ye, Z. Yang, CrystEngComm 16 (2014) 636-641.
3] F. Pan, G. Knopfle, Ch. Bosshard, S. Follonier, R. Spreiter, M.S. Wong, P. Gunter,
Appl. Phys. Lett. 69 (1996) 13-15.
[
[
4] D. Guo, Y. Ren, J. Liu, X. Tao, Dyes Pigm. 98 (2013) 384-392.
5] Andrei G. Stepanov, C. Ruchert, J. Levallois, C. Erny, C.P. Hauri, Opt. Mater.
Express 4 (2014) 870-875.
[
[
6] E. Pickwell, V.P. Wallace, J. Phys. D: Appl. Phys. 39 (2006) R301-R310.
7] J.H. Jeong, B.J. Kang, J.S. Kim, M. Jazbinsek, S.H. Lee, S.C. Lee, I. Baek, H. Yun, J.
Kim, Y.S. Lee, J.H. Lee, J.H. Kim, F. Rotermund, O. Kwon, Sci. Rep. 3 (2013) 3200.
8] J. Yin, L. Li , Z. Yang, M. Jazbinsek, X. Tao, P. Gunter, H. Yang, Dyes Pigm. 94
[
[
(
2012) 120-126.
9] S.R. Marder, J.W. Perry, W.P. Schaefer, Science 245 (1989) 626-628.
[
[
[
[
[
10] K. Kawase, M. Mizuno, S. Sohma, H. Takahashi, T. Taniuchi, Y. Urata, S. Wada, H.
Tashiro, H. Ito, Opt. Lett. 24 (1999) 1065-1067.
11] A. Schneider, M. Neis, M. Stillhart, B. Ruiz, R.U.A. Khan, P. Gunter, J. Opt. Soc.
Am. B: Opt. Phys. 23 (2006) 1822-1835.
12] Z. Yang, M. Jazbinsek, B. Ruiz, S. Aravazhi, V. Gramlich, P. Gunter, Chem. Mater.
1
9 (2007) 3512-3518.
13] Z. Yang, L. Mutter, M. Stillhart, B. Ruiz, S. Aravazhi, M. Jazbinsek, A. Schneider, V.
Gramlich, P. Gunter, Adv. Funct. Mater. 17 (2007) 2018-2023.
14] Z. Yang, S. Aravazhi, A. Schneider, P. Seiler, M. Jazbinsek, P. Gunter, Adv. Funct.
Mater. 15 (2005) 1072-1076.

[
[
15] B. Ruiz, Z. Yang, V. Gramlich, M. Jazbinsek, P. Gunter, J. Mater. Chem. 16 (2006)
839-2842.
2
16] R. Jerald Vijay, N. Melikechi, Tina Thomas, R. Gunaseelan, M. Antony Arockiaraj,
P. Sagayaraj, J. Cryst. Growth 338 (2012) 170-176.
[
[
[
17] R. Gunaseelan, P. Sagayaraj, Mater. Chem. Phys. 136 (2012) 379-385.
18] R. Gunaseelan, A. Antony Raj, P. Sagayaraj, Optik 125 (2014) 3791-3797.
19] J. Ogawa, S. Okada, Z. Glavcheva, H. Nakanishi, J. Cryst. Growth 310 (2008) 836-
8
42.
[
[
20] R. Jerald Vijay, N. Melikechi, Tina Thomas, R. Gunaseelan, M. Antony Arockiaraj,
P. Sagayaraj, Mater. Chem. Phys. 132 (2012) 610-617.
21] E.Y. Choi, M. Jazbinsek, J.H. Jeong, O.P. Kwon, CrystEngComm 14 (2012) 1045-
1
048.
[
[
22] Ch. Bosshard, R. Spreiter, L. Degiorgi, P. Gunter, Phys. Rev. B 66 (2002) 205107.
23] T. Vijayakumar, I. Hubert Joe, C.P. Reghunadhan Nair, M. Jazbinsek, V.S.
Jayakumar, J. Raman Spectrosc. 40 (2009) 52-63.
[
[
[
24] D. Sajan, J. Binoy, I. Hubert Joe, V.S. Jayakumar, J. Zaleski, J. Raman Spectrosc. 36
(
2005) 221-236.
25] J.P. Abraham, D. Sajan, V. Shettigar, S.M. Dharmaprakash, I. Hubert Joe, V.S.
Jayakumar, J. Mol. Struct. 917 (2009) 27-36.
26] John Coates, in: R.A. Meyers (Eds.), Interpretation of Infrared Spectra, A Practical
Approach, John Wiley & Sons Ltd, Chichester, 2000, pp. 10815-10837.
27] C. Ravikumar, I. Hubert Joe, D. Sajan, Chem. Phys. 369 (2010) 1-7.
28] M. Reichenbacher, J. Popp, Challenges in Molecular Structure Determination,
Springer, Verlag Berlin Heidelberg, 2012.
[
[
[
[
29] S.K. Kurtz, T.T. Perry, J. Appl. Phys. 39 (1968) 3798-3813.
30] M. Hasmuddin, P. Singh, M. Shkir, M.M. Abdullah, N. Vijayan, G.
Bhagavannarayana, M.A. Wahab, Spectrochim. Acta, Part A 123 (2014) 376-384.
31] R. Hanumantharao, S. Kalainathan, G. Bhagavannarayana, U. Madhusoodanan,
Spectrochim. Acta, Part A 103 (2013) 388-399.
[
[
[
[
[
32] S. Das, A.J. Bhattacharyya, J. Phys. Chem. B 115 (2011) 2148-2154.
33] J.C. Anderson, Dielectrics, Chapman and Hall, London, 1967.
34] N. Goel, N. Sinha, B. Kumar, Opt. Mater. 35 (2013) 479-486.
35] B.R. Bijini, S. Prasanna, M. Deepa, C.M.K. Nair, K. Rajendra Babu, Spectrochim.
Acta, Part A 97 (2012) 1002-1006.

[
[
36] A. Senthil and P. Ramasamy, J. Cryst. Growth 401 (2014) 200-204.
37] M. Raposo, Q. Ferreia, P.A. Ribeiro, in: A. Mendz-Vilas, J. Diaz (Eds.), Modern
Research and Educational Topics in Microscopy, Formatex, 2007, pp. 758-769.
38] T. Rajesh Kumar, R. Jeyasekaran, S.M. Ravi Kumar, M. Vimalan, P. Sagayaraj, Appl.
Surf. Sci. 257 (2010) 1684-1691.
[

Figure Caption
Fig.1. Synthesis scheme for DSMNS
Fig. 2. Solubility curve for DSMNS in methanol
Fig. 3. Photographs of DSMNS crystals grown by (a) SNM-SC and (b) SNM-SE techniques
Fig. 4. FT-IR spectrum of DSMNS crystal
Fig. 5. FT-Raman spectrum of DSMNS crystal
Fig. 6. NMR spectrum of DSMNS crystal
Fig. 7. (a) TG/DTA and (b) DSC thermograms for DSMNS crystal
Fig.8. Frequency dependence of a) dielectric constant and b) dielectric loss of DSMNS
Fig.9. Etch pattern observed for DSMNS crystal grown by SNM-SC for (a) 10 s and
(
b) 15 s
Fig.10. Etch pattern observed for DSMNS crystal grown by SNM-SE for (a) 10 s and
b) 15 s
(
Fig. 11. a) 2D and b) 3D AFM images of DSMNS crystal grown by SNM-SC
Fig. 12. a) 2D and b) 3D AFM images of DSMNS crystal grown by SNM-SE
Table Caption
Table 1 Single crystal XRD data of DSMNS crystal
Table 2 FT-IR and FT-Raman wavenumbers and their assignments of DSMNS
Table 3 Roughness parameters of as-grown crystals surface of DSMNS

Fig.1. Synthesis scheme for DSMNS

Fig.2. Solubility curve for DSMNS in methanol

(
a)
(
b)
Fig.3. Photographs of DSMNS crystals grown by (a) SNM-SC and (b) SNM-SE techniques

Fig.4. FT-IR spectrum of DSMNS crystal
Fig.5. FT-Raman spectrum of DSMNS crystal

Fig.6. NMR spectrum of DSMNS crystal

Fig.7. (a) TG/DTA and (b) DSC thermograms for DSMNS crystal

Fig.8. Frequency dependence of (a) dielectric constant and
b) dielectric loss of DSMNS
(

Fig.9. Etch pattern observed for DSMNS crystal grown by SNM-SC for (a) 10s and
b) 15s
(
Fig.10. Etch pattern observed for DSMNS crystal grown by SNM-SE for (a) 10s and
b) 15s
(

Fig.11. a) 2D and b) 3D AFM images of DSMNS crystal grown by SNM-SC
Fig.12. a) 2D and b) 3D AFM images of DSMNS crystal grown by SNM-SE

Table 1 Single crystal XRD data of DSMNS crystal.
Formula
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
α (deg)
β (deg)
22 23 3 5
C H N O S
441.50
Monoclinic
P2
1
9.356 (6)
6.462 (5)
17.957 (10)
90
101.38
90
1064.32 (10)
γ (deg)
V (Å )
3
Table 2 FT-IR and FT-Raman wavenumbers and their assignments of DSMNS
-
1
-1
ν
IR (cm )
ν
Raman (cm )
Assignments

3
3
2
1
1
-
448 w
074 w
916 w
647 m
589 vs
-
O–H stretching
-
Vinyl C–H stretching
2956 vw
1618s
1586vs
1550 s
1514 s
1474 vw
1435 w
-
3
CH asymmetric stretching
ν (C= C)/vinyl C–H rock
Ring ν (C=C)
Ring ν (C=C)
1
1
1
1
1
1
1
1
1
1
9
9
8
8
7
-
523 vs
473 m
442 m
369 s
N–O asymmetric stretch
CH
Ring ν (C=C)
CH symmetric deformation
3
asymmetric deformation
3
346 s
1338s
1317 s
1206 s
1167, 1183 s
1047 w
-
N–O Symmetric stretch
Ring ν (C=C)
315 s
215 vs
164, 1180 vs
072 m
033 s
Ring δ (C–H)
Ring δ (C–H /ν
a
(SO
2
)
CH rocking/ν
3
s
(SO
2
)
Ring δ (C–H)
Ring δ (C–H)
Ring δ (C–H)
70 m
-
45 m
-
76 s
875 vw
-
Ring δ (C–H)/C-N stretching
1,4-Distribution of aromatic ring C–H
Ring δ(C–H)
25 s
56 s
776 w
722
Ring δ(CCC)
6
6
5
4
-
63 s
13 s
32 s
94 w
666 vw
615 vw
532 vw
500 vw
85 w
Ring δ(CCC)
Ring δ(CCC)
Ring δ(CCC)
–
SO
3
deform
CH
3
torsion
a ; s
Abbreviations: ν-stretching; δ-deformation vibration, ν -asymmetric stretching ν -symmetric
stretching; vs-very strong; s-strong; m- medium; w-weak; vw-very weak
Crystal grown by Crystal grown by
SNM-SC SNM-SE
Roughness parameters

2
3.337 nm
Roughness average (S
Root mean square (S
Surface skewness (Ssk
Surface kurtosis (Sku
Peak-peak roughness (S
Ten point height (S
a
)
15.775 nm
18.930 nm
0.5583
q
)
30.038 nm
0.409
)
)
2.564
4.038
y
)
101.745 nm
101.745 nm
220.435 nm
220.435 nm
z
)
Table 3 Roughness parameters of as grown crystal surface of DSMNS

Graphical abstract

Highlights
ꢀ
ꢀ
ꢀ
ꢀ
A potentially useful ionic organic NLO crystal of DSMNS is grown in bulk size.
The growth is achieved by modified slope nucleation approach.
A detailed FTIR and FT Raman spectral analyses is carried out.
The NLO, thermal, dielectric and surface properties are reported.