Effect of additives on the large-size growth of 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) single crystal: An efficient stilbazolium derivative NLO crystal with potential terahertz wave properties

Article abstract of DOI:10.1039/c4ce01350f

We explored the growth of the highly nonlinear optical stilbazolium salt 4-N,N-dimethylamino-4-N-methyl stilbazolium naphthalene-2-sulfonate (DSNS) by a slow evaporation method. The grown crystals are large size and exhibit the good optical quality. The h

Full text of DOI:10.1039/c4ce01350f

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Effect of additives on the large size growth of 4-N, N-dimethylamino-4-N-
methyl stilbazolium naphthalene-2-sulfonate (DSNS) single crystal:
An efficient stilbazolium derivative NLO crystal
with potential Terahertz Wave properties
a
a
a
K.Senthil , S.Kalainathan *, A.Rubankumar ,
a, a*
Centre for Crystal Growth, School of Advanced sciences, VIT University,
Vellore ꢀ 632 014, Tamilnadu, India.
a
*
Corresponding author
Prof.S.Kalainathan
VIT University, Vellore ꢀ 632014, Tamilnadu, India.
Phone: +91ꢀ416ꢀ2202350, Fax: 0416ꢀ2243092
Eꢀmail Address: kalainathan@yahoo.com
Abstract
We explored the growth of the highly nonlinear optical stilbazolium salt 4ꢀN, Nꢀdimethylaminoꢀ4ꢀ
Nꢀmethylstilbazolium naphthaleneꢀ2ꢀsulfonate (DSNS) by slow evaporation method. The grown
crystals are record size of crystals and exhibit the good optical quality. The harvested crystals have
2
2
the suitable dimensions ~5 x 3mm and the thickness in the range of 0.2ꢀ0.5mm is reported for the
first time by introducing the anionic additives STPB (Sodium tetraphenylborate) and DTPA
(Diethylenetrimine pentaacetic acid anion) in the pure DSNS solutions. The grown crystals are
highly suitable for fabrication of photonic devices and waveguiding applications. Through
recrystallization of DSNS using various mixed solvents and conditions, we have obtained different
crystalline phases. The grown crystals have been subjected to single crystal xꢀray diffraction
analysis to confirm the cell parameters. The crystallinity of the grown crystals was examined by
using powder xꢀray diffraction analysis. The various modes of functional groups present in the
synthesized compound were confirmed using FTꢀIR and NMR spectral analysis. The transparency
1

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range was analyzed using the UVꢀVisꢀNIR spectral studies. The TGA/DTA analysis reveals the
crystal is stable up to 300.2 °C.
1
. Introduction
In recent years, the design of organic polar crystals with πꢀconjugated chromophores has attracted
intensive attention because of large nonlinear optical susceptibilities compared with pure inorganic
1
ꢀ3
materials. The large second harmonic generation (SHG) efficiency of organic salts are most
often based on strong Coulomb interactions between appropriate electron donor and acceptor
4
,5
groups at the end of the πꢀconjugated structure. However, the molecular nonlinearity is
associated with orientation of πꢀchromophores in the crystal lattice. In addition, they have many
advantages such as bulk nonꢀlinearity, longꢀterm stability and a higher tendency to override the
6
,7
dipoleꢀdipole interactions in the chromophores and thus form nonꢀcentrosymmetric structure.
Hence, intense efforts have been made worldwide to synthesis of extended πꢀconjugated system
with donor and acceptor substituent because of their applications in the field of optical computing,
telecommunication, high speed optical information processing, laser remote sensing, and laser
8
ꢀ10
frequency shifting applications.
crystals) have been examined during the recent decade, it has been proved that the ionic organic
crystals are of high concern because of their advantages in mechanical, chemical, superior longꢀ
A variety of organic nonlinear optical chromophores material
(
1
1ꢀ12
term thermal, photochemical stability and orientation of ionic chromophore.
Among these
compounds, DAST (4ꢀdimethylaminoꢀNꢀmethylꢀ4ꢀstilbazolium tosylate) is the most important one
due to its large secondꢀorder nonlinear optical susceptibility (1000 times than that of the urea
ꢀ1
13ꢀ16
standard at 1907 nm) and electroꢀoptic coefficient r11 of 77 pm V at 800nm.
In the past few
years, various crystal engineering techniques have been employed to control the morphology and
1
7ꢀ19
improve the optical quality of DAST crystal.
For example, for integrated optic applications
such as optoelectronics, photonics and THz wave’s generation and detection, thin films with
2

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2
0ꢀ25
crystals having a thickness in the range of 0.1 mm to few mm scale are needed.
However, its
bulk growth with sufficient optical quality crystal or thickness of DAST crystals remains a
2
6, 27
significant challenge.
aligned chromophore is DSNS have been reported the powder SHG efficiency showed around
0% higher than DAST crystal at 1907 nm. They also demonstrated the growth of single crystal of
One of the promising stilbazolium DAST derivative with perfectly
5
DSNS approximately 2mm in length with a diameter less than 100 ꢁm grown between two glass
plates by slow evaporation method and the grown crystals observed between the crossed polarizers
in a microscope was only reported to date. However, the growth of DSNS crystals is still a very
challenging and is being investigated by many research groups worldwide the growth of thin films
2
8ꢀ30
or bulk of DSNS.
In this paper, large size single crystals of DSNS were successfully obtained by introducing
additives such as STPB and DTPA adding in pure DSNS solutions. We have found that the rate of
nucleation is reduced in the presence of additive in the solutions and also suppressing the clusters
formation in the case of pure DSNS solution. The unit cell dimensions of the grown crystals were
measured by a single crystal xꢀray diffraction technique. The grown crystals of DSNS have been
characterized by different instrumentation techniques such as powder Xꢀray diffraction (PXRD)
analysis, spectroscopic analysis, optical absorbance, and thermal studies. Up to date, to the best of
our knowledge, there is no report in the literature about DSNS to improve their growth by adding
the effect of the organic additives and their characterizations. So far, we discuss these for the first
time was described in detail.
2
. Experimental methods
2
.1 Material Synthesis. General considerations, all the necessary reagents, were purchased as
high purity from SigmaꢀAldrich, Alfa aesar and Merck Company. They were used without further
purification. The overall synthesis process and reaction are illustrated in Scheme 1.
3

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1
, 4 Dimethylpyridinium Iodide 1. 1, 4 Dimethylpyridinium Iodide 1 was synthesized by
equimolar ratio of 4ꢀPicoline (2ml, 20mmol) and iodomethane (1.3ml, 20mmol) in acetone (30ml).
The mixture solution was refluxed for 2 hours and cooled to ambient temperature. After removing
the solvent and the salt dried at oven. The title salt 1 was obtained in quantitative yield.
4
-[2-(4-Dimethylamino-phenyl)-vinyl]-1-methyl-pyridinium iodide 2. To the result of 1 (2.35g
1
0mmol) in hot methanol (30ml), 4ꢀdimethylamino benzaldehyde (1.49g 10mmol), and piperidine
(0.98ml, 10mmol) were added. The total above mixture was taken in the 250ml round bottom
flask. Then the mixture solution was refluxed for 12 hrs under a dry nitrogen atmosphere.
The resulting purple solid was filtered using a whatmann filter paper and three times washed with
Diethyl ether for removal of unreacted starting materials. The title compound 2 was formed as a
purple needleꢀshaped single crystals obtained by successive recrystallization from methanol by
slow evaporation at ambient temperature. It had a melting point of 266 to 268°C.
DSNS. The mixture 2 (3.7g 10mmol) was dissolved in Millipore water (100ml) by heating.
The hot aqueous solution of naphthaleneꢀ2ꢀ sulfonate (2.3g 10mmol) was added to the above
solution. The above mixed solution was heated for 2 hours at 80°C and was cooled to ambient
temperature. The red precipitate was filtered off and dried at 140°C for 1 hour by keeping the
precipitate in hot air oven. The purity of DSNS was improved by repeated recrystallization by
using methanol. The recrystallized high purity salt was used for the solubility studies and crystal
growth.
2
.2 Solubility Studies.
The solubility test plays a significant part in choosing the best solvent and temperature in the field
of crystal growth. DSNS, whose chromophores are aligned perfectly parallel such a configuration,
are of most interest for crystal growth experiments because it showed 50% larger SHG activity
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than DAST. However, its high potential for various applications, the growth of bulk size DSNS
crystals has not yet been investigated in detail because it has not well soluble in mostꢀpolar
solvents. In the present investigation, we have studied the solubility of DSNS using purified salt at
different temperatures ranging from 30 to 45°C in five different combinations of solvents, namely
methanolꢀchloroform (1:2), methanolꢀwater (9:1), methanolꢀDMF (9:1), methanolꢀacetonitrile
(1:1), and methanolꢀDMSO (9:1). The solubility study was carried out by dissolving the solute in
1
00ml of above said mixed solvent system in 150ml airtight containers. After that, the mixture was
kept in an ultraꢀcryostat (UC) water bath maintained at 30°C, and the mixture was continuously
stirred by using motorized magnetic stirrer to get the saturation. The UC stability is within
±
0.01°C. After attaining the equilibrium concentration of the solute solubility was determined by
gravimetrically according to the following formula.
Weight of the solute
Weight of the (solute +solvent)
Solubility (Wt%) =
x100
The same procedure was repeated to determine the equilibrium concentration of the solute with
temperatures from 35°C to 45°C with 5°C interval. The solubility curves of pure DSNS with
separate mixed solvent system at different temperatures are shown in Figure 1. From the graph, it
can be observed that the solubility DSNS increase linearly with an increase of temperature.
3
3
. Results and discussion
.1 Crystal growth by different mixed solvent system.
Here, the crystallization experiments have been achieved in on a hot plate of heating energy
controlled by energy regulator. To grow the single crystals of pure DSNS 500ml saturated solution
was prepared according to its solubility diagram of DSNS at 45°C. Then the solution was
continuously stirred with the help of magnetic stirrer to get the homogeneous and transparent
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solution. The prepared solutions were filtered by using a Whatman filter paper. After that, the
filtered solution was evenly divided into five identical good quality borosil glass beakers (150 ml)
with the help of a measuring jar. Again the beakers were covered tightly with aluminum foil with
few holes and then placed on a hot plate, and the solutions were maintained at 50°C up to
complete evaporation of the solvent by slow evaporation method. From this solvent system, many
plateꢀlike spontaneously has grown crystals were harvested from methanolꢀDMF (9:1) and
methanolꢀDMSO (9:1) mixed solvent system. The low and high solubility of DSNS in methanolꢀ
water and methanolꢀchloroform mixed solvent system the crystallizations were absent due to low
solubility of DSNS and fast evaporation of the solvent that in turn yielded only precipitation.
3
.2 Effect of STPB and DTPA on crystal growth.
Plateꢀlike single crystals of pure DSNS were grown in a mixed solvent system and obtained in the
range of crystals approximately 0.5ꢀ 1.0mm thickness with different crystallographic faces from
the slow evaporation method. However, in crystal engineering the morphology control is important
for organic electroꢀoptic crystals, which are very promising applications in imaging and terahertz
(THz) wave generation and detection in terahertz timeꢀdomain spectroscopy (THzꢀTDS)
3
1ꢀ33
applications.
In this investigation, nonpolar hydrophobic Teflon containers were used to avoid
interface induced nucleation. In a glass container having hydrophilic surface, the nucleation first
appears near the interface between air and evaporationꢀinduced local supersaturation solution on
3
4
the hydrophilic glass wall with surface interactions effect. Considering the above problems
during the DSNS crystal growth; we used Teflon containers to prevent the influence of effect.
Therefore, the slow evaporation and slow cooling methods are suitable for the growth of DSNS
crystal.
In this present research work, we examined the significance of beneficial effects of adding an
additive on the growth rate of DSNS by the known concentrations of pure DSNS dissolved in
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methanol: acetonitrile (1:1) mixed solvent system. To grow bulk size crystals of DSNS, a known
quantity of DSNS salt was dissolved in 100ml of methanol: acetonitrile (1:1) mixed solvent at
3
5°C with 20, 30 and 50ppm concentrations of STPB and DTPA added separately in the pure
DSNS solutions. The resulting solution was continuously stirred for 2hrs in order to get the
homogeneous saturation. Then the solution was filtered it using Whatman filter paper to remove
extraneous solid. The additive added crystals were obtained by transferring filtered solution in
Teflon beaker, which was tightly covered with aluminum foil with few holes. Optically transparent
good quality single crystals of DSNS obtained by slow evaporation method for a period of 50ꢀ60
days from 50ppm of STPB and DTPA added pure DSNS solutions and for 20 and 40ppm yielded
smaller crystals. Figure 2 shows the asꢀgrown crystal of DSNS and different concentrations of
STPB and DTPA added DSNS crystals. This small crystal size is a very attractive limit for the
3
5
generation of highꢀpower broadband THz waves. The molecular structure of additives STPB and
DTPA is given in Chart 1.
It has found that the additive added DSNS crystal is in higher growth rate, higher quality and with
higher transparency. The addition of STPB and DTPA additives to the pure DSNS solutions are
found to controlling the nucleation rate and suppress the crystal quality, inclusions by capturing
metallic ions present in the solution with significantly compared to the pure one. The possibility of
+
2
+2
+2
+2
the commercially available chemicals has impurities of heavy metals like Ca , Mg , Pb ,Cu ,
etc. These impurities may induce the secondary nucleation and such impurities, having a long
residence time in the adsorbed layer, become stoppers for the elementary steps and at higher
supersaturations enhance the rate of heterogeneous nucleation on the surface. The distribution of
metals becomes more difficult by the addition of additives has a high affinity to complex with
metal cations, and the resulting complex does not enter and also prevents the entry of impurities
36
into the crystal. Thereby good quality crystals are expected to grow for device applications.
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The additive incorporation also alters the nucleation time of the polymorphs in the solution. Due to
the controlled evaporation of the solvent and the solution attains supersaturation and is responsible
for nucleation as well as the growth promoting effect was also noticed in the presence of additives
added DSNS solutions. Similar influence has also observed in the growth of DAST crystal.
3
.3 Instruments for characterization
The single crystal lattice parameters of grown pure DSNS and STPB, DTPA added DSNS were
obtained using a Bruker Kappa APEX II diffractometer with MoKα radiation (λ=0.71073Å) at
room temperature. The grown single crystal was subjected to powder Xꢀray diffraction using a
BRUKER XꢀRay diffractometer with the CuKa radiation (λ=1.5406 Å), scanning angle ranges
◦
from 10 to 80° were used at a scan rate of 0.02 /s. The FTꢀIR spectra of the grown crystal have
recorded in the range of 4000ꢀ400cmꢀ1 by using SHIMADZU IRAFFINITY spectrometer by the
KBr pellet method to verify the functional groups in the material. The optical transparency of the
crystals was studied using an ELICO SL 218 double beam UVꢀVisꢀNIR spectrophotometer in the
region of 190ꢀ1100nm. In the present study, the formation of functional groups was identified
from BRUKERꢀ400MHz FTꢀNMR spectrometer using Dimethylsulfoxide (DMSOꢀd6) as solvent.
The photoluminescence spectra of the sample were recorded by using Fꢀ7000 FL
Spectrophotometer. The TGA/DTA study was carried out using NETZSCH STAꢀ449F3 analyzer
in the temperature range 25ꢀ500°C with a heating and cooling scan rate of 10°C/min in a nitrogen
atmosphere.
3
.4 X-ray diffraction analysis
Single crystal xꢀray diffraction study has been carried out for the grown crystals to determine the
lattice parameters, and to determine the crystal system. Table 1 represents the comparison of
lattice parameters value of pure DSNS grown by using mixed solvent system and additive added
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DSNS solutions, and these are in good agreement with the reported work by Blanca Ruiz et.al
2
8
(
CCDCꢀ 292764). The powder xꢀray diffraction analysis has been also carried out for the grown
crystals to analyze whether the title material is crystalline or amorphous. The xꢀray diffraction
pattern of pure DSNS and STPB, DTPA added crystals depicted in the Figure 3. No additional
peaks were observed in the diffraction pattern of additive added DSNS crystal. Thus, it confirms
that the added additives did not affect any change in the triclinic crystal structure of the DSNS
crystal and did not induce a polymorphism, but significantly influenced the crystal morphology as
shown in Figure 2. Thus, the observed prominent peaks confirm the good crystalline property of
the grown DSNS crystals.
3
.5 Density Measurement
The density measurement is one of the mostꢀsensitive methods to evaluate the purity of crystals.
3
7, 38
The density of the crystals were measured by floatation method
at room temperature (also
called the swim or sink technique), and the obtained density values are presented in the Table 2.
In this analysis, CCl4 and was used as denser liquid and toluene was used as lower density liquid.
For comparison, the density was also calculated using the crystallographic data
ρ= (MZ)/ (NV),
where M is the molecular weight DSNS crystal (M=446.55 g/mol), Z is the number of molecules
3
per unit cell (Z=1), V is the volume of the unit cell (V= 564.1 cm /unit cell), and N is the
Avogadro number. Thus, the experimentally measured density is wellꢀmatched with the
theoretically calculated values.
3
.6 FT-IR Spectroscopic analysis
The recorded FTIR spectra for pure DSNS and the effect additive STPB and DTPA added DSNS
ꢀ1
crystals are depicted in Figure 4 (aꢀc). The band observed at 3392.79, and 3412cm is typical for
the OH stretching vibration in H O and which is due the moisture absorption from the air.
2
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ꢀ
1
ꢀ1
The peak at 3061.03 cm is due to the aromatic CꢀH stretch. The band at 2914.43cm is attributed
ꢀ1
to the alkyl CꢀH stretching mode. The peaks seen at 1629.85cm are expected to C=C stretching
ꢀ1
mode of vibrations. The absorption peaks at 1591.27, 1558.48 and 1593.20, 1525.69cm are
assigned to the aromatic ring vibrations. The observed frequencies between 1438.90 and
1
1
332.81cmꢀ1 are due to the CH bending absorption mode and C–N stretching mode. The band at
3
ꢀ1
39
193.94 and 1155.36 cm is assigned to the symmetrically stretching vibration of SO group.
3
ꢀ1
The sharp peak at 962.48 and 999.13cm is attributed to the vinyl =C–H stretching vibrations.
ꢀ1
Absorption wave numbers from 500 to 1000cm are due to the substituent group of the aromatic
ring vibrations. By comparing the graphs, (a) for the FTIR of pure DSNS crystal, (b) for STPBꢀ
added (c) for DTPA added DSNS crystal, there are no major shifts or additional peaks
corresponding to STPB and DTPA added crystals compared to the pure crystal.
3
.7 UV-Vis-NIR spectral analysis.
The optical absorption spectra of pure DSNS and STPB, DTPA added crystals were subjected to
UVꢀVisꢀNIR analysis by recording it in liquid form (dissolved in methanol) are depicted in
Figure 5 (aꢀc). It was observed that the both pure DSNS and STPB, DTPA added DSNS crystals
gives two peaks along with a large transmission in the VisꢀNIR region, which is one the
mostꢀdesired properties for applications in the red and near IR wavelength range and better
4
0
photostability applications. From the obtained spectrum, the minor peak at near 271 nm is
corresponding to nꢀ π* transition and another one is found around at 476nm represents the πꢀπ*
transition. The observed major absorption peak 476nm is due to the stilbazolium chromophore.
The λmax values in the UVꢀVisꢀNIR spectra of above results indicate that there is no addition peak
found in the case of adding an additive in pure DSNS electronic structure. Thus, the absorption
behavior of additive added DSNS solutions shows the cutoff wavelength in the visible range is in
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0

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good agreement with pure DSNS in the solutions phase. The λmax value of DSNS is compared with
a few other stilbazolium derivatives are listed in Table 3.
1
13
3
.8 H NMR and C NMR Spectral studies.
1
13
The H NMR and C NMR spectral analysis were made on the powder form of pure DSNS crystal
1
was recorded by dissolving it in DMSOꢀd6 as solvent. Figure 6 shows the H NMR spectrum of
pure DSNS crystal. The singlet at 3.019ppm and 8.14ppm is assigned to six Nꢀ(CH ) hydrogens
3
2
and one of C H SO hydrogen’s. The singlet lies at 4.169ppm is expected to the three protons in
1
0
7
3
the NꢀCH . The observed singlet at 3.367ppm and quintet signal at 2.514ppm are assigned due to
3
the water molecule in DMSOꢀd6 and DMSOꢀd6 solvent. The doublet at 7.180ppm is expected to
the two olefinic hydrogen’s (CH=CH). The doublet at 6.794ppm and 7.701ppm is assigned due to
the four hydrogen’s of the Nꢀ(CH ) ꢀC H in the aromatic ring. The multiple at 7.524 ppm is
3
2
6
4
2
8
corresponding to the two hydrogens of the naphthalene ring (2HꢀC H SO ). The doublet at
1
0
7
3
8
.041, 8.68ppm, and 7.726ppm are assigned due to the four hydrogens of the NꢀC H pyridinium
6 4
ring and one hydrogen of a naphthalene ring. The multiple peaks observed at 7.985ppm, and
.849ppm is attributed the four hydrogens in the naphthalene ring (4Hꢀ C H +CH).
7
1
0
7
1
3
C NMR spectrum of pure DSNS crystal is shown in Figure 7. The signal at 18.53, 46.32 and
6.01 ppm indicate that the presence methyl group carbon in pure DSNS. There are nine peaks
32.12, 130.11, 117.10, 144.31, 111.92, 145.64, 132.68, 123.98 and 153.33ppm, which are due to
5
1
the stilbazolium moiety. The naphthaleneꢀ2ꢀ sulfonate ring carbons were identified at 126.36,
27.42, 141.86, 126.26 and 122.43ppm. Thus, the NMR spectral analysis confirmed the formation
the title compound.
.9 Photoluminescence studies.
1
3
1
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Photoluminescence (PL) spectral analysis is a one of the nondestructive method to provide the
electronic structure of materials and also widely used to identify the impurities and finds
applications in lighting technologies. Luminescence properties may expect in compound
containing aromatic structure with extended conjugated double bonds with a high degree of the
4
2, 43
resonance stability exhibits luminescence.
Luminescence materials find extensive applications
in branches of biological and biomedical science, and chemical research fields, for analyzing
4
4
organic compounds. The emission spectra of pure DSNS were carried out at room temperature
using an Fꢀ7000 FL Spectrophotometer, in the scanned wavelength range between 530 ꢀ 820nm.
For this emission spectrum, the excitation wavelength was used for this sample is 476nm from the
UV spectral studies. The recorded PL spectrum of pure DSNS is given in Figure 8. The recorded
spectrum consist two peaks in the visible region, and one is highꢀintensity emission peak at 2.03
eV (608nm) and followed another one is medium intense peak wavelength at 1.84 eV (665nm).
It may do due the anionic and cationic group present in DSNS crystal matrix. From this
wavelength, it covers the red emission in the visible region concluded that DSNS has a red
luminescence emission. Thus, it may suggest that DSNS is most useful for nearꢀinfrared optical
switching applications.
3
.10 TGA/DTA Analysis.
Figure 9 shows the thermo gravimetric analysis (TGA) and differential thermal analysis (DTA)
response curves of pure DSNS powder sample. The initial mass of the powdered crystal subjected
to the analyses was 1.20 mg. The TGA curve shows that loss of weight of about 2.90% between 30
and 246 °C. This indicated that removal of water and evaporation of volatile substances during this
temperature range. The DTA trace gives one sharp endothermic at 300.2°C, which is
corresponding to the melting point of DSNS crystal. The sharpness of this endothermic peak
illustrates the good degree of crystallinity and purity of the crystal. After melting, there are two
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endothermic peaks are observed around at 353.93 °C and 413.81°C. This indicates that complete
decomposition of the stilbazolium ion from DSNS. In the TGA spectrum, there is a significant
weight loss of about 33.34% starting at 307.22 °C and it continuous up to 364.10 °C. There is
another 31.23% weight loss up to 549.50 °C. These weight losses are due to complete
decomposition of the DSNS and release of SO . The final residue weight left over after a major
3
weight loss was about 32.52% remains as carbon residue, which is present in the DSNS material at
5
50 °C. Based on this study, it is concluded that the crystal is thermally stable up to 300.2 °C and
greater than DAST and its derivatives. The melting point of DSNS is comparison with some
stilbazolium derivatives crystals with promising NLO materials was listed in Table 4.
4
. Conclusions
We have investigated the growth of DSNS crystal by mixed solvent system and adding of
additives STPB and DTPA in pure DSNS solutions. It has been noticed that enhanced the growth
rate of the crystals as well as effectively change the crystal morphology while increasing the
concentration of additives compared to the pure DSNS. It may be due to suppressing the activities
of the metal ions present in the solution. The refined single crystal XRD results confirm that there
is no incorporation of additives in the grown crystal structure. The solubility of DSNS in several
mixed solvents system was estimated by the gravimetric method. From the solubility
measurements, it is found that methanol: acetonitrile (1:1) mixed solvent was suitable for the
growth process. The FTIR spectral analysis confirm that the presence of functional groups in the
grown crystals. The UV–VisꢀNIR spectral studies reveal that the low cutoff wavelength and there
is no absorption in the entire visible region (476 ꢀ1100nm), and also no extra phase in absorption
window for additive added crystals as compared to that of pure crystal. The good transparency of
the pure and additive added DSNS crystal in the entire VisꢀNIR region ensures its suitability for
NLO device fabrication. Luminescence studies exhibit that the DSNS crystal has red luminescence
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emission property. The melting and decomposition temperature range of the grown single crystal
has been studied from TGA/DTA analysis, and it reveals the purity and the crystals show an
improved thermal stability up to 300.2 °C, compared to DAST and its derivatives crystals. Based
on the obtained results, we conclude that the additives played a drastic role in the changes of the
growth process and the morphology (shape) of the DSNS crystals and also noticed that there is no
incorporation of STPB or DTPA in the DSNS molecular structure. Future investigations to this
extent for various applications are in progress and will be our future publication. Thus, the
obtained results which will in turn the scientific community and introduce the efficient method of
growing highꢀquality DSNS crystal and its derivative crystals in the development of optoꢀ
electronic industry.
Acknowledgment.
We gratefully acknowledge financial support of this research by Defense Research and
Development Organization (DRDO), Government of India for financial assistance. The authors are
grateful for the management of VIT University, Vellore for their excellent research
facilities and constant support and encouragements.
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Caption of the Tables
Table 1. Comparison of lattice parameters value of pure and additive added DSNS.
Present work
2
8
Lattice
Pure DSNS
STPB added
DSNS
DTPA added Reported work
DSNS
parameters
Crystal system
Triclinic
P1
Triclinic
Triclinic
P1
Triclinic
P1
Space group
a (Å)
P1
7.887±0.0012
8.145±0.001
9.910±0.0008
7.846±0.009
8.120±0.014
9.911±0.015
7.849±0.001
8.144±0.010
9.900±0.010
7.864
8.054
9.893
70.04
73.31
83.69
564.1
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
69.355±0.005 69.124±0.012 69.182±0.015
73.234±0.011 72.922±0.008 72.923±0.0013
84.212±0.014 84.023±0.003 84.091±0.002
3
Volume (Å )
571.4±0.1
564.3±0.4
567.3±0.2
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Table 2 Comparison of density of pure and additive added DSNS with theoretical density.
S.No
Density of grown crystal by
floatation method (g/cc)
Theoretical density of DSNS (g/cc)
from crystallography data)
(
1
2
3
Pure DSNS crystal :1.307
STPB (50 ppm) added DSNS crystal:1.310
DTPA (50 ppm) added DSNS crystal:1.300
1.314
Table 3. Comparison of λmax Values of stilbazolium derivatives.
3
9
Crystal
λmax [a]
DSHS
474± 1
DSMAS
DAST
474± 1
475± 1
DSMOS
DSAS
476± 1
476± 1
DSNS
Present work
[a] In methanol in room temperature
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Table 4. Comparative of melting point of stilbazolium derivatives
Crystal
DAST
Melting point (°C)
256± 1
References
(29)
DSMAS
DSTMS
DSANS
DSMOS
DSDMS
DSAS
256± 1
(41)
258± 1
(29)
263± 1
(29)
264± 1
(41)
267± 1
(29)
272± 1
(41)
DSSS
277± 1
(46)
DASC
281± 1
(45)
DSNS
300± 1
Present work
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Scheme 1. Synthesis of DSNS
4

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Chart 1. Molecular structure of the STPB and DTPA.
O
O
O
O
N
O
N
B
O
N
Na
O
O
O
O
(
b)
(
a)
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Caption of the Figures
.
Figure 1. Solubility of DSNS: AꢀMethanolꢀChloroform (1:2), BꢀMethanolꢀWater (9:1),
CꢀMethanolꢀDMF (9:1), DꢀMethanolꢀAcetonitrile (1:1), EꢀMethanolꢀDMSO (9:1).
6

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Figure 2.(a) and (b) DSNS crystals grown by slow evaporation method from the pure DSNS
solution prepared at 45°C by using mixed solvent system (methanol:DMSO (9:1))
and (b) methanol:DMF (9:1). STPB and DTPA concentrations. (c) STPBꢀ20 ppm, (d) STPBꢀ30
ppm, (e) STPBꢀ50 ppm, (f) DTPAꢀ20 ppm, (g) DTPAꢀ30 ppm, (h) DTPAꢀ50 ppm.
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Figure 3. Powder XꢀRay Diffraction pattern observed for (a) Pure DSNS and (b) 50ppm
STPB added DSNS and (c) 50ppm DTPA added DSNS.
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Figure 4. FTꢀIR Spectrum of (a) pure DSNS and (b) 50 ppm STPB added DSNS and
c) 50ppm DTPA added DSNS crystal.
(
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Figure 5. UVꢀVisꢀNIR Spectrum of (a) pure DSNS, 50 ppm STPB added DSNS and 50ppm
DTPA added DSNS crystal.
1
0

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.
1
Figure 6. HNMR Spectrum of Pure DSNS.
1
1