Synthesis, growth, structural, optical, spectral, thermal and mechanical studies of 4-methoxy 4-nitrostilbene (MONS): A new organic nonlinear optical single crystal

Article abstract of DOI:10.1016/j.saa.2012.07.128

4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based on the solubility data good quality single crystal with dimensions up to 38 × 11 × 3 mm³ has been grown by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the crystalline property and also the diffraction planes have been indexed. The lattice parameters for the grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been analysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infrared (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown crystal. The UV-vis absorption spectrum has been recorded in the range of 190-1100 nm and the cut off wavelength 499 nm has been determined. The optical constants of MONS have been determined through UV-vis-NIR spectroscopy. The MONS crystals were further subjected to other characterizations. i.e., ¹H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55× greater than that of KDP crystal.

Full text of DOI:10.1016/j.saa.2012.07.128

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, growth, structural, optical, spectral, thermal and mechanical studies
of 4-methoxy 4-nitrostilbene (MONS): A new organic nonlinear optical single crystal
Paul M. Dinakaran a, G. Bhagavannarayana b, S. Kalainathan a,
⇑
a School of Advanced Sciences, VIT University, Vellore 632 014, India
b National Physical Laboratory, New Delhi 110 012, India
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
"
"
"
4-Methoxy 4-nitrostilbene (MONS)
crystal was grown by slow
evaporation method.
Lattice parameters of the crystal
were determined by single crystal
XRD.
Crystalline perfection was studied
using high resolution X-ray
diffraction.
"
"
1H NMR confirms the structure of
the MONS crystal.
SHG efficiency of the MONS was
found to be 1.55 times greater than
that of KDP.
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 22 May 2012
Received in revised form 25 July 2012
Accepted 27 July 2012
Available online 8 August 2012
4-Methoxy 4-nitrostilbene (MONS), a new organic nonlinear optical material has been synthesized. Based
on the solubility data good quality single crystal with dimensions up to 38 ꢀ 11 ꢀ 3 mm3 has been grown
by slow evaporation method using ethyl methyl ketone (MEK) as a solvent. Powder XRD confirms the
crystalline property and also the diffraction planes have been indexed. The lattice parameters for the
grown MONS crystals were determined by using single crystal X-ray diffraction analysis and it reveals
that the crystal lattice system is triclinic. The crystalline perfection of the grown crystals has been ana-
lysed by high resolution X-ray diffraction (HRXRD) rocking curve measurements. Fourier transform infra-
red (FTIR) spectrum for powdered MONS sample confirms the functional groups present in the grown
crystal. The UV–vis absorption spectrum has been recorded in the range of 190–1100 nm and the cut
off wavelength 499 nm has been determined. The optical constants of MONS have been determined
through UV–vis–NIR spectroscopy. The MONS crystals were further subjected to other characterizations.
i.e., 1H NMR, TG/DTA, photoluminescence and microhardness test. The Kurtz and Perry powder technique
confirms the NLO property of the grown crystal and the SHG efficiency of MONS was found to be 1.55ꢀ
greater than that of KDP crystal.
Keywords:
Growth from solution
Organic compound
X-ray diffraction
Nonlinear optical crystal
IR spectrum
Ó 2012 Elsevier B.V. All rights reserved.
Introduction
[1]. 3-Methyl 4-methoxy 4-nitrostilbene (MMONS) was found to
be significantly more efficient (1250ꢀ greater than Urea) for sec-
In the past decades significant research attention has been paid
to organic NLO materials due to their large advanced applications
in fast developing fields such as photonics and optoelectronics
ond harmonic generation. Optimization of MMONS can be done
in order to get new derivatives that possess higher order optical
nonlinearities and better characteristics with high optical quality
single crystals for various optoelectronic applications using differ-
ent crystal growth techniques [2] Shoukui et al. [3] reported that
3-methoxy 4-methoxy 4-nitrostilbene (MOMONS) crystal has been
⇑
Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092.
E-mail address: kalainathan@yahoo.com (S. Kalainathan).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.07.128

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P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
grown by melt growth technique with SHG efficiency 0.2–3ꢀ
material in ethyl methyl ketone solvent in an airtight container
for each temperature. The solution was stirred for 2 h for homoge-
nization. The solubility of MONS is shown in Fig. 1. Good quality
crystal of size 10 ꢀ 6 ꢀ 3 mm3 (Fig. 2) were obtained after three
days by slow evaporation method at room temperature (see Fig. 3).
greater than that of KDP, which was measured by the powder tech-
nique. The MONS crystals composed of aromatic molecules with
p
electron donor and acceptor substitutions normally exhibits inter-
molecular charge transfer that leads to the non centrosymmetric
property which makes them as a good frequency conversion mate-
rial [4]. The identification, design, synthesis of new molecules and
tailoring of molecular structure has been utilized to promote crys-
tallization of potentially useful molecules in non centrosymmetric
crystal structures [5]. Interestingly, only powder SHG studies were
carried out on this material using different solvents [6]. To the best
of our knowledge, no other report is available on MONS crystal till
date. In this communication, we report the novel MONS crystal,
which is a derivative of Stilbene family with NLO property and it
was grown by the slow evaporation method. The grown crystals
were subjected to the characterizations like X-ray diffraction anal-
yses, high resolution XRD, FTIR, 1HNMR, TG/DTA, UV–vis absorp-
tion spectrum, photoluminescence and SHG test.
Results and discussion
Single crystal X-ray diffraction
The single crystal X-ray diffraction analysis was carried out
using a Nonius CAD-4/MACH3 diffractometer to determine unit
cell parameters and space group of the grown MONS crystal. We
found that the crystal system is triclinic with cell parameters
a = 11.716 (4) (Å); b = 12.002 (4) (Å); c = 14.949 (5) (Å),
a
= 110.33(3) Å, b = 103.59 (4) Å,
c = 91.21(3) Å, and vol-
ume = 1904(1) Å3 and the space group is ‘P1’.
Powder X-ray diffraction
Experimental procedure
A powder X-ray diffraction study was carried out using BRUKER
X-ray diffractometer with the CuKa radiation (k = 1.5406 Å) in the
Material synthesis
range of 10°–35°, in steps of 0.02°. Powder XRD pattern is shown in
Fig. 4. It reflects good crystallinity of the grown crystals. The lattice
parameters were calculated using the TREOR programs which coin-
cide with the single crystal XRD results and the peaks were in-
dexed using APPLEMAN program from the observed 2h values.
The title compound was synthesized by the addition of diethyl
p-nitrobenzyl phosphonate (C11H16NO5P) and p-anisaldehyde
(C8H8O2) in the presence of sodium ethoxide as catalyst. The mix-
ture was taken in ethanol 35 ml. The mixture was stirred well for
about 12 h at 0 °C and refluxed for 2 h and then the yellowish pre-
cipitate MONS (C15H13NO3) product was filtered. The synthesized
and dried MONS was collected [7]. The MONS material was puri-
fied by repeated recrystallization using ethyl methyl ketone
(EMK) as solvent. The chemical reaction as follows:
HR X-ray diffractometry
High resolution X-ray diffraction analysis was carried out to
evaluate the crystalline perfection of the grown MONS crystal.
The obtained beam with well collimated and monochromated
C2H5ONa
MoKa1 from three monochromator Si crystals set in dispersive
C11H16NO4P þ C8H8O2
!
C15H13NO3
Strring
0
ꢁC
(+,ꢂ,ꢂ) configuration has been used in exploring the X-ray beam.
The specimen crystal with good optical quality is rotated about a
vertical axis, which is perpendicular to the plane of diffraction with
0.4 arc s angular intervals [8]. In identical experimental conditions,
rocking curves (RC) were recorded for the MONS specimen crystal
using (111) diffracting planes in symmetrical Bragg geometry.
Using Lorentzian fit, the solid line follows the experimental points
which represent the convoluted curve of two peaks. The additional
peak has the tilt angle of 212 arc s from its adjoining region and
shows an internal structural low angle boundary [9]. The low angle
boundary and the FWHM (full width at half maximum) of the main
peak are 72 and 110 arc s respectively. The crystal contains a low
Solubility and crystal growth
The solubility of MONS was determined for five different tem-
peratures such as 25, 30, 35, 40 and 45 °C by using a constant tem-
perature ultracryostat water bath with magnetic stirrer rotation
facility. The measurements were performed dissolving the MONS
40
Solubility Curve - MONS
35
30
25
20
25
30
35
40
45
Temperature (oC)
Fig. 1. Solubility.
Fig. 2. Grown crystals of MONS.

P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
997
212"
MNS
1500
1000
500
0
MoKα
1
(+,−,−,+)
110"
72"
-400
-200
0
200
400
Glancing angle [arc sec]
Fig. 5. Rocking curve recorded for
a typical MONS single crystal for (111)
diffracting planes by employing the multicrystal X-ray diffractometer with MoKa1
radiation.
1H NMR spectrum
The proton NMR spectrum (1H NMR) of MONS crystal was re-
corded using BRUKER Spect instrument operating at 400 MHz with
CDCl3 solvent as shown in Fig. 7. The singlet peak lies at 3.833 ppm
(3H, S, OCH3) is due to three protons in the methoxy group. The
aromatic protons produce signals around 6.896 and 8.160 ppm
(8H, multiplet). The doublet peak lies at 8.165 and 8.178 ppm to
confirm the vinylic protons in the structure. Thus the structure of
the title compound is confirmed by the proton NMR [11].
Fig. 3. Morphology of the grown crystal.
1000
800
600
400
200
Optical studies
The optical absorption spectrum of MONS crystal was recorded
at room temperature using Elico SL218 Double beam UV–vis spec-
trophotometer in the wavelength range 190–1100 nm, which cov-
ers the entire near-UV, visible and NIR regions. The recorded
spectrum is shown in Fig. 8. The thickness of the sample used for
measurement was 1.5 mm. The absorbance was reduced drasti-
cally between the wavelength of 438 and 1100 nm due to its good
optical behaviour [12]. The crystal has sufficient transmission in
the UV region and enables good optical transmission of the second
harmonic frequencies of Nd:YAG laser.
10
15
20
25
30
35
2 Theta
Determination of optical band gap and optical constants
Fig. 4. Powder X-ray diffraction pattern.
The absorption coefficient (a) was calculated from the transmit-
tance data (T) using the relation [13]
2:303 logð1=TÞ
angle boundary with a low angular spread of 500 arc s of the Rock-
ing Curve (RC) which indicates that the quality of the crystal is
fairly good. The recorded rocking curve (RC) is shown in Fig. 5.
a
¼
ð1Þ
t
where T is the transmittance and t is the thickness of the sample.
The optical band gap (Eg) has been estimated from the transmission
spectra and the optical absorption coefficient (
tion edge is given by
a) near the absorp-
Fourier transform infrared spectroscopic studies
1=2
The Fourier transform infrared spectrum was recorded using
SHIMADZU IRAFFINITY instrument for the powder sample of the
crystals using the KBr pellet technique in the range of 4000–
400 cmꢂ1. The FTIR spectrum of MONS is shown in Fig. 6. The peaks
around 686.66–970.19 cmꢂ1 corresponds to aromatic C–H bending
vibrations. The peak at 3021 cmꢂ1 corresponds to C–H stretching
alkenes. The peaks at 1510.26 and 1336.67 cmꢂ1 corresponds to
NO2 asymmetric and symmetric stretching vibrations respectively.
The peak at 3072.60 cmꢂ1 corresponds to aromatic C–H stretching
vibration. The peaks observed at 2962.66 and 1587.42 cmꢂ1 corre-
sponds to @C–H stretching and C–C stretching of the olefinic dou-
ble bond [10].
a
h
m
¼ Aðh
m
ꢂ EgÞ
ð2Þ
where A is a constant, Eg is the optical band gap, h is the plank’s con-
stant and is the frequency of incident photons. The optical band
gap was evaluated by plotting (
hv)2 vs. hv as shown in Fig. 9 and
extrapolating the linear portion of (
hv)2 in the photon energy axis
gives the optical band gap of the crystal. The optical band gap of the
MONS is 3.28 eV.The Extinction coefficient (k) can be obtained from
the following equation
m
a
a
k
a
K ¼
ð3Þ
4p

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P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
100
75
50
%T
25
0
4000
3500
3000
2500
2000
1/cm
MONS
1500
1000
500
Fig. 6. FTIR spectrum of MONS.
Fig. 7. 1H NMR spectrum of MONS.
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ꢂðR þ 1Þ ꢃ ðꢂ3R2 þ 10R ꢂ 3
The extinction coefficient is the fraction of electromagnetic en-
ergy lost due to absorption and scattering per unit distance in a
sample medium. The extinction coefficient (k) vs. wavelength (k)
is shown in Fig. 10. The extinction coefficient decreases with in-
crease of wavelength and it shows the light loss steeply decreases
from 438 to 515 nm and nullified for higher wavelengths.
The reflectance (R) in terms of the absorption coefficient can be
obtained from the equation [14]
n ¼
ð5Þ
2ðR ꢂ 1Þ
The optical conductivity (
rop) of MONS crystal was calculated using
the following relations [16]
anc
r
¼
ð6Þ
4p
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1 ꢃ ð1 ꢂ expðꢂ
a
tÞ þ expð tÞ
a
R ¼
ð4Þ
where c is the velocity of light. The optical conductivity against
absorption coefficient was plotted and shown in Fig. 12. From the
spectrum it is evident that the optical conductance increases with
increase of photon energy. The optical conductivity of the material
ð1 þ expðꢂ Þ
a
The wavelength dependent reflectance of MONS shown is in Fig. 11
in the range of 375–1100 nm. The reflectance decreases with in-
crease of wavelength, then becomes constant. The low reflectance
value shows higher transmittance of the grown MONS crystal.The
refractive index (n) can be calculated from reflectance data using
the following equation [15]
depends on the absorption coefficient (a) and refractive index (n)
and also it is clearly observed from the graph. The optical conduc-
tivity increases from the photon energy 1.97–2.20 eV and small
variations obtained for higher photon energies.

P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
999
5
4
3
2
1
0
100
80
60
40
20
0
438 nm
300
400
500
600
700
800
900
1000
400
500
600
700
800
900
1000 1100 1200
Wavelength (nm)
Wavelength (nm)
Fig. 11. Plot of wavelength (k) vs. Reflectance (R).
Fig. 8. Solid UV absorption spectrum.
60000000
50000000
40000000
30000000
20000000
10000000
0
400
300
200
100
0
-10000000
1.0
1.2
1.4
1.6
1.8
2.0
2.2
2.4
2.6
Eg=3.28 eV
Photon energy (hv)
1.0
1.5
2.0
2.5
3.0
3.5
Photon energy (hv)
Fig. 12. Optical conductivity against absorption coefficient of MONS crystal.
Fig. 9. Plot of (a
hv)2 vs. Photon energy (hv).
Thermal analysis
Thermal stability of the newly grown organic nonlinear optical
MONS crystal was identified by thermograviometric (TG) and dif-
ferential thermal analysis (DTA). The analyses were carried out
using a TA Instruments SBT Q600 apparatus thermally analyzed
in a nitrogen atmosphere. The different stages of mass losses are
shown in Fig. 13. In DTA curve, only one sharp endothermic peak
was observed at 135.97 °C which corresponds to the melting point
of the material. The sharpness shows the good crystalline nature
and purity of the grown crystal. Two sharp and broadened exother-
mic peaks were observed at 376 and 645.24 °C. TGA curve shows
that the material is stable upto 201.65 °C and there is no phase
transition occurred before the melting point. After the occurrence
of steep weight loss at 387.95 °C, the weight loss gradually de-
creased and remained as residue at 716.04 °C [17].
0.0010
0.0008
0.0006
0.0004
0.0002
0.0000
Photoluminescence study
The photoluminescence (PL) measurement of MONS was car-
ried out at room temperature using the Jobin Yvon-Spex spectro-
fluorometer (Fluorolog version-3; Model FL3-11), 450 W high
pressure xenon lamp was used as an excitation source. The spec-
400
500
600
700
800
900
1000
Wavelength (nm)
Fig. 10. Plot of wavelength (k) vs. Extinction coefficient (k).

1000
P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
trum was recorded (Fig. 14) for a spectral resolution of 0.2 nm and
25
20
15
10
5
645.240C
excitation wavelength of 350 nm. A broad band observed in the
range of 540–650 nm and also the maximum intensity was found
at 564 nm. The result indicates that the MONS crystals have a
bright emission in the visible region [18].
80
60
40
20
0
TGA
3760C
201.650C
Microhardness studies
402.750C
DTA
The microhardness study was carried out using Mututoyo
MH112, Japan hardness tester with Vickers indenter. Microhard-
ness testing is the versatile method to understand the mechanical
properties of the crystal [19]. The crystal plane (111) was gently
indented by diagonal pyramid shaped Vickers indenter for differ-
ent loads (10, 25, 50 and 100 g) with dwell time of 10 s. The Vickers
hardness number was calculated using the expression
387.950C
-20
-40
-60
135.970C
0
716.040C
0
100 200 300 400 500 600 700 800 900
TemperatureoC
HV ¼ 1:8544ðP=d2Þkg=mm2
Fig. 13. TG/DTA spectra of MONS.
where HV is the hardness number in kg/mm2, P is the applied load in
g. 1.8544 is a constant geometric factor for diagonal pyramid and d
is the diagonal length of the indentation. The variation of HV as a
function of applied load ranging from 10 to 100g for the MONS crys-
tal is shown in Fig. 15. The graph shows that the hardness value
(HV) increases with the increase of load. This is known as load
dependent hardness.
20000000
18000000
16000000
14000000
12000000
10000000
8000000
564 nm
SHG studies
SHG conversion efficiency of the powdered sample of MONS
was measured by the Kurtz and Perry technique with 1064 nm la-
ser radiations. A Quanta Ray Spectra Physics Nd:YAG laser produc-
ing pulses with a width of 8 ns and a repetition rate of 10 Hz was
used. The SHG efficiency is confirmed by bright green light emis-
sion which is collected by a photomultiplier tube (PMT) (Philips
photonics 8563) after being monochromated (Coherent Molectron
USA 2000). The incident optical signal in PMT was converted into
voltage output at the CRO (Tektronix TDS 3052B) [20]. The second
harmonic signal of 33.7 mV was obtained for an input energy of
2.4 mJ/pulse, while the reference material Potassium dihydrogen
orthophosphate (KDP) sample gives a SHG signal of 21.7 mV for
the same input energy. The SHG relative efficiency of MONS with
that of KDP has been calculated. It is found that the efficiency of
the title crystal is 1.55ꢀ greater than that of KDP [3].
540
560
580
600
620
640
660
Wavelength (nm)
Fig. 14. Emission spectrum of MONS.
92
90
88
86
84
82
80
78
76
0
Conclusion
Organic material MONS has been synthesized and the good
optical quality single crystals have been grown from ethyl methyl
ketone (EMK) by slow evaporation technique. The structure of the
grown MONS crystal was confirmed by single crystal XRD. From
the Fourier transform infrared spectrum, functional groups have
been confirmed. Proton NMR spectroscopic analysis confirms the
molecular structure of the grown crystal. The optical absorption
study reveals the transparency of the crystal with a UV cut-off at
499 nm. The optical band gaps (Eg), extinction coefficient (k),
reflectance (R) have been calculated as a function of wavelength.
The optical conductivity of the grown crystal was determined.
The thermal analysis reveals that the grown MONS crystal is stable
up to 201.65 °C. The photoluminescence measurement shows that
the MONS material can be a good scintillator. Microhardness test-
ing shows the load dependent hardness of the crystal. The SHG test
confirms that the NLO efficiency of the grown crystal is 1.55ꢀ
greater than that of KDP.
20
40
60
80
100
Load (g)
Fig. 15. Vickers hardness analysis.

P.M. Dinakaran et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 97 (2012) 995–1001
1001
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Acknowledgements
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[8] K. Jagannathan, S. Kalainathan, T. Gnansekaran, N. Vijayan, G.
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[11] K. Jagannathan, S. Kalainathan, G. Bhagavannarayana, Spectrochim. Acta A:
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Authors would like to express their gratitude to Department of
Science and Technology (DST), India for providing a financial sup-
port and VIT University management for their constant encourage-
ment. The authors thank Dr. Madhusoodhanan, IGCAR,
Kalppakkam for support in photoluminescence studies.
[12] T. Sudhan, N.P. Rajesh, P.V. Dhanaraj, C.K. Mahadevan, Spectrochim. Acta A:
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