Synthesis, nucleation, growth, structural, spectral, thermal, linear and nonlinear optical studies of novel organic NLO crystal: 4-fluoro 4-nitrostilbene (FONS)

Article abstract of DOI:10.1016/j.saa.2012.12.050

A novel organic nonlinear optical material 4-fluoro 4-nitrostilbene (FONS), with molecular formula (C₁₄H₁₀FNO₂) has been synthesized. Using ethyl methyl ketone as solvent, the synthesized material has been repeatedly recrystallized to minimize the impurities and good optical quality single crystals were harvested by slow evaporation method. Single crystal X-ray diffraction analysis reveals that the grown FONS crystal belongs to monoclinic system with noncentrosymmetric space group P2 ₁ . The powder X-ray diffraction pattern of FONS has been recorded. Functional groups of the title compound were confirmed by FTIR and the molecular structure was confirmed by ¹H NMR. The UV-vis-NIR absorption study reveals no absorption in the visible region and the cut-off wavelength was found to be at 408 nm. Optical band gap (E_g) of the grown crystal was found to be 3.27 eV and also the optical constants were determined. Thermal behaviour of the FONS has been studied by TGA/DTA analyses. From the mass spectrum, the ratio of compound formation of FONS was analyzed. The NLO property has been confirmed by Kurtz and Perry powder SHG technique and the SHG efficiency of FONS (262 mV) crystal was found to be 12 times greater than that of KDP (21.7 mV).

Full text of DOI:10.1016/j.saa.2012.12.050

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, nucleation, growth, structural, spectral, thermal, linear and nonlinear
optical studies of novel organic NLO crystal: 4-fluoro 4-nitrostilbene (FONS)
⇑
Paul M. Dinakaran, S. Kalainathan
Crystal Research Centre, School of Advanced Sciences, VIT University, Vellore 632 014, Tamil Nadu, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
"
A novel organic nonlinear optical
material FONS has been synthesized.
The good optical quality single
crystals were grown by slow
evaporation method.
"
"
The FONS crystal has a wide
transparency in the range of 408–
1100 nm.
"
"
g
Optical band gap (E ) of the grown
crystal is 3.27 eV.
The PL measurements show that the
material is suitable for green light
emission.
a r t i c l e i n f o
a b s t r a c t
Article history:
A novel organic nonlinear optical material 4-fluoro 4-nitrostilbene (FONS), with molecular formula
Received 12 September 2012
Received in revised form 12 December 2012
Accepted 14 December 2012
Available online 2 January 2013
14 2
(C H10FNO ) has been synthesized. Using ethyl methyl ketone as solvent, the synthesized material
has been repeatedly recrystallized to minimize the impurities and good optical quality single crystals
were harvested by slow evaporation method. Single crystal X-ray diffraction analysis reveals that the
1
grown FONS crystal belongs to monoclinic system with noncentrosymmetric space group ‘‘P2 ’’. The
powder X-ray diffraction pattern of FONS has been recorded. Functional groups of the title compound
Keywords:
were confirmed by FTIR and the molecular structure was confirmed by 1H NMR. The UV–vis–NIR absorp-
Organic compound
Chemical synthesis
Nuclear magnetic resonance (NMR)
Optical properties
tion study reveals no absorption in the visible region and the cut-off wavelength was found to be at
g
408 nm. Optical band gap (E ) of the grown crystal was found to be 3.27 eV and also the optical constants
were determined. Thermal behaviour of the FONS has been studied by TGA/DTA analyses. From the mass
spectrum, the ratio of compound formation of FONS was analyzed. The NLO property has been confirmed
by Kurtz and Perry powder SHG technique and the SHG efficiency of FONS (262 mV) crystal was found to
be 12 times greater than that of KDP (21.7 mV).
Photoluminescence
Ó 2013 Elsevier B.V. All rights reserved.
Introduction
hyperpolarizabilities v
(2). In this view, many researchers have
spent their greater effort to develop the higher order nonlinear
organic materials, leading to the discovery of DAST, DSNS and
MMONS [2–4]. Among these materials, 3-methyl 4-methoxy
4-nitrostilbene (MMONS) crystal has large electro optic
Recently significant research interest has been devoted on non-
linear optical (NLO) materials due to their remarkable contribution
in the field of photonics and optoelectronics [1]. Among various
NLO materials, organic materials have much more attention for
their large electro optic coefficient and higher second order
coefficients with r33 = 39.9 pm/V (0.6328
optical coefficients with 33 = 184 pm/V and
1.064 m) [5]. Optimizing the MMONS crystal is a good attempt
l
m) and large nonlinear
d
d24 = 71 pm/V
(
l
to discover new derivative organic nonlinear optical crystals with
high NLO efficiency. We have extended our optimization in
⇑
Corresponding author. Tel.: +91 416 2202350; fax: +91 416 2243092.
E-mail address: kalainathan@yahoo.com (S. Kalainathan).
1
386-1425/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.12.050

5
10
P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
synthesizing 4-fluoro 4-nitrostilbene (FONS) which is a new deriv-
ative of Stilbene family with good NLO efficiency. In FONS molecule
a strong electron donor (fluoro group) was present on one end and
45
Solubility Curve
Nucleation Curve
an acceptor (nitro group) on the other end of the
p
conjugated
40
structure which enhance the optical nonlinearity of the crystal.
To our best knowledge, no work has been reported on FONS crystal
in the literature till date. In this present communication, we report
a novel organic nonlinear optical single crystal of FONS for the first
time. The grown crystals were subjected to various characteriza-
tion studies and the results are discussed in detail in the following
sections.
3
3
2
2
5
0
5
0
Experimental
Material synthesis
15
The FONS (C14
of high purity diethyl p-nitrobenzyl phosphonate (C11
2 5
-fluoro benzaldehyde (C FO) and sodium ethoxide (C H
in equimolar ratio. The mixture was dissolved in 35 ml of ethanol
and kept inside the ultra cryostat water bath and stirred for 12 h
at 0 °C [6]. The ethanol was removed by filtration and the resulting
green coloured FONS were dried and the powdered material was
collected after one day. The FONS material was 10 times recrystal-
lized for purification. The reaction mechanism is as follows
H
10FNO
2
) material was prepared by the addition
P),
ONa)
15
20
25
30
35
40
o
H
16NO
4
Temperatures ( C)
4
7
H
5
Fig. 1. Metastable zone width for FONS.
(Scheme 1).
Solubility and metastable zone width measurements
The solubility and metastable zone width studies were carried
out using a constant temperature water bath of cryostat facility
with accuracy ±0.01 °C. The solubility of FONS was determined in
EMK at six different temperatures, i.e., 20 °C, 25 °C, 30 °C, 35 °C,
4
0 °C and 45 °C. The solubility was measured by adding the excess
amount of solute in EMK at constant temperature with continuous
stirring to attain homogeneous concentration. The saturated solu-
tion was analyzed gravimetrically. Using conventional polythermal
method, the metastable zone width was determined by preparing
the saturated solution according to the solubility data for the same
temperature. The metastable zone width was determined for dif-
ferent temperatures (20–45 °C) with interval of 5 °C. The solubility
and metastable zone width are shown in Fig. 1. The saturated solu-
tion (50 ml) of recrystallized material of FONS was prepared at
Fig. 2. Grown FONS crystals.
diffractometer and BRUKER X-ray diffractometer with Cu K
k = 1.5406 Å) respectively. The FTIR spectrum of FONS sample
a
(
was recorded in the KBr pellet phase using SHIMADZU IRAFFINITY
2
5 °C and taken in a completely closed beaker in order to control
the solvent evaporation rate and kept for crystallization. After
days good optical quality crystals have been harvested and
ꢀ1
spectrometer in the region of 4000–400 cm . Proton NMR spec-
trum was recorded using a BRUKER Spect instrument operating
at 400 MHz with CDCl as solvent to confirm the molecular struc-
3
5
shown in Fig. 2.
ture of the grown FONS crystal. Optical behaviour of FONS was
measured by ELICO SL 218 double beam spectrophotometer in
the range of 190–1100 nm. Thermal behaviour of FONS was ob-
served by TG–DTA curve using thermally analyzed TA Instruments
SBT Q600 apparatus in a nitrogen atmosphere. Mass spectral anal-
ysis was carried out using JEOL GCMATE II GC–MS high resolution
Instruments for characterization
The grown FONS crystal was subjected to single crystal XRD and
powder X-ray diffraction analyses using a NONIUS CAD4/MACH3
NO2
O
O
P
O
H
+
1
2 hrs
ONa
+
O N
2
o
F
Stirring, 0 C
4
-Fluoro-benzaldehyde
Ethyl-(4-nitro-benzyl)-
phosphinic acid ethyl ester
Sodium ethoxide
F
4-Fluoro 4-Nitrostilbene
Scheme 1. Synthesis of FONS material.

P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
511
3
volume = 1793(1) Å . The FONS crystal system satisfies one of the
very essential and basic requirements for the SHG activity.
1
1
1
1
1
800
600
400
200
000
Powder X-ray diffraction analysis
Finely powdered sample of FONS was subjected to powder X-
ray diffraction analysis. The powder XRD spectrum was recorded
at room temperature in step size 0.02° for the angular range 10–
3
5° of 2h using Cu Ka radiation (1.5406 Å). The reflections reveal
8
6
4
2
00
00
00
00
the good crystallinity of the grown FONS crystal. Using TEROR pro-
gram the lattice parameters were calculated and show good agree-
ment with single crystal XRD results. The prominent peaks were
indexed by using APPLEMAN program. The indexed powder XRD
pattern is shown in Fig. 3.
Fourier transform infrared spectroscopy (FTIR)analysis
15
20
25
30
35
2
theta
The Fourier transform infrared (FTIR) spectrum of the synthe-
sized FONS material was recorded at room temperature in the
Fig. 3. Powder X-ray diffraction pattern of FONS.
ꢀ1
range of 4000–400 cm and it is shown in Fig. 4. The peak ob-
ꢀ1
served at 1631.78 cm is due to the C@C stretching vibrations in
2
the aromatic ring. A nitro symmetric stretching vibration (CANO )
double focusing instrument. The photoluminescence spectrum of
FONS crystal was recorded using a Jobin Yvon-Spex spectrofluo-
rometer and 450 W high pressure xenon lamps was used as an
excitation source. The NLO property of the grown crystal was con-
firmed by Kurtz-Perry powder technique. The green light (532 nm)
emission was collected by a photomultiplier tube (PMT Philips
Photonics) after being monochromated (Coherent Molectron, USA
ꢀ1
can be attributed to the peak at 1502.55 cm . The peak at
ꢀ1
748.38 cm is assigned for CAF stretching vibrations. The aro-
matic CAH stretching vibration is confirmed by the presence of
ꢀ1
peaks at 3076.49 and 3107.32 cm [7].
SEM and EDAX analyses
2
000). The cathode ray oscilloscope (CRO) converts the incident
optical signal to output voltage. The input laser energy of 2.4 mJ/
pulse was incident on the powdered sample. SEM and EDAX anal-
yses were carried out using Quanta 200 FEG scanning electron
microscope.
The grown FONS crystal was subjected to scanning electron
microscope and energy dispersive X-ray analyses to determine
the surface morphology and elemental composition of the sample
respectively. From the SEM analysis, it is observed that the micro-
crystals appeared on the grown surface and it is shown in Fig 5a.
EDAX study confirms the elemental compounds of FONS such as
carbon, oxygen, nitrogen and fluorine and it is shown in Fig. 5b.
Results and discussion
Single crystal X-ray diffraction
Proton NMR analysis
The single crystal X-ray diffraction reveals that the crystal
belongs to monoclinic crystal system with noncentrosymmetric
Proton NMR spectrum was recorded for the FONS sample by
dissolving it in CDCl . The signals at 8.230 ppm and 8.224 ppm
3
space group P2
b = 9.864(2) Å, c = 19.501(7) Å,
1
, the unit cell parameters are a = 9.494(4) Å,
= 90.00(0)°, b = 100.96(2)°,
(2H, doublet) are due to the vinylic protons in the structure. The
aromatic protons produce signals around 7.058–7.656 ppm (8H,
a = c
Fig. 4. FTIR spectrum of FONS.

5
12
P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
Fig. 5. (a) Scanning electron microscope (SEM) image (b) EDAX analysis.
1
Fig. 6. H NMR spectrum of FONS.
doublet). Thus the structure of the title compound was confirmed
by the proton NMR spectral analysis. The H NMR spectrum of
FONS is shown in Fig. 6.
and the UV cut off wavelength was found to be at 408 nm [8].
The grown crystals band gap and large transmittance in the visible
and NIR regions are shown in Fig. 7a. Thus it was confirmed that
the material is good NLO candidate for optoelectronic applications.
1
UV–vis NIR absorbance spectral analysis
Determination of optical constants
The optical behaviour of FONS crystal (1.5 mm thickness) was
estimated by recording the UV–vis absorption spectrum (Fig. 7)
From the optical transmittance (Fig. 7b) of grown FONS crystal
it is very clear that the grown crystal has higher transparency

P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
513
4
3
3
2
2
1
1
0
0
.0
.5
.0
.5
.0
.5
.0
.5
.0
(
a)
0
0
0
.0020
.0015
.0010
(
b)
1
00
8
0
0
0
0
6
408 nm
4
2
0.0005
0.0000
0
3
00 400 500 600 700 800 900 1000 1100 1200
Wavelength (nm)
300
400
500
600
700
800
900 1000 1100 1200
Wavelength (nm)
400
500
600
700
800
900
1000
1100
Wavelength (nm)
Fig. 9. Plot of wavelength vs extinction coefficient.
Fig. 7. (a) Absorption spectrum. (b) Transmittance spectrum.
500
100
4
3
2
1
00
00
00
00
0
8
6
4
2
0
0
0
0
0
(
E = 3.27 eV)
g
1.0
1.5
2.0
2.5
3.0
3.5
300
400
500
600
700
800
900
1000 1100 1200
Photon energy (hv) (eV)
)2 vs h
m (eV).
Wavelength (nm)
Fig. 8. Plot of band gap (
ah
m
Fig. 10. Plot of wavelength vs reflectance.
(
(
about 95%) in the entire visible region. The absorption coefficient
) was calculated from the transmittance data (T) using the
a
relation.
ꢀ
ꢁ
1
2
:3026 log T
30
a
¼
ð1Þ
t
10
8
2
2
1
1
5
0
5
0
5
0
5
TGA
DTA
o
510.46
C
where T is the transmittance and t is the thickness of the sample.
The optical band gap of FONS crystal was evaluated from the trans-
o
239.73
C
o
3
67.81
C
mittance data (T) and absorption coefficient (
edge is given by [9]:
a
) near the absorption
6
o
1
=2
334.47
C
ah
m
¼ AðE
g
ꢀ hm
Þ
ð2Þ
4
where A is a constant, h is Planck’s constant, E
g
is the optical band
gap and the frequency of the incident photons. The band gap of
FONS crystal was estimated by plotting ( m and extrapolat-
v
2
-
2
ahm
) vs h
2
-10
-15
ing the linear portion of (
a
hm
) near onset of the absorption edge to
o
140.33
C
o
0
360.64
C
the photon energy axis. Fig. 8. From the plot, it is found that the en-
ergy band gap of the grown FONS crystal is 3.27 eV. Extinction coef-
ficient (K) of the FONS was calculated using the formula [10].
-
20
-2
0
100
200
300
400
500
600
700
800
900
o
k
a
p
Temperature ( C)
K ¼
ð3Þ
4
Fig. 11. Thermal analysis of FONS.

5
14
P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
Fig. 12. Mass spectrum of FONS.
From the spectrum it is evident that the there is no loss near the
wavelength of 430 nm. The transmittance (T) is given by:
4
4
3
3
2
2
1
1
500000
000000
500000
000000
500000
000000
500000
000000
527.05 nm
2
ð1 ꢀ RÞ expðꢀ
a
tÞ
T ¼
ð4Þ
2
1
ꢀ R expðꢀ2
a
tÞ
Reflectance (R) in terms of absorption coefficient can be obtained
from the above equation.
Hence,
pffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
R ¼ 1
ꢁ
ð1 ꢀ expðꢀ
a
tÞ þ expð tÞ
a
ð5Þ
1 þ expðꢀ tÞ
a
The wavelength dependent reflectance of FONS is shown in
Fig. 10 in the range of 380–1100 nm. The reflectance of FONS de-
creases with increase of wavelength then becomes constant. The
low reflectance shows the higher transmittance of the grown FONS
crystal.
5
00000
440
460
480
500
520
540
560
580
600
620
Wavelength (nm)
Thermal analysis
Fig. 13. Emission spectrum of FONS.
Thermal behaviour of the grown FONS crystal was obtained
from the Thermograviometric (TG) and differential thermal (DTA)
analyses and the resultant spectrum is shown in Fig. 11. From
DTA curve, the first sharp endothermic peak at 140.33 °C indicates
the melting point of the grown FONS crystal. The broad second
peak at 334.47 °C was observed due to decomposition of the mate-
rial. No exothermic and endothermic peaks were observed before
the melting point, which shows that there is no decomposition
and phase transition occurred up to the melting point [11].
Sharpness of the endothermic peaks indicates the good crystalline
The spectrum of extinction coefficient as function of wavelength is
shown in Fig. 9.
The K value is strongly dependent on the wavelength in the vis-
ible region. The extinction coefficient gives the fraction of the light
lost due to the scattering and absorption per unit thickness in a
sample medium. The variation K with wavelength values due to
the interaction occurred between incident light and electrons.

P.M. Dinakaran, S. Kalainathan / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 105 (2013) 509–515
515
nature of the sample. The two exothermic peaks were observed at
67.81 °C and 510.46 °C. From TA curve, the fluorine atom elimi-
Conclusion
3
nates at 220 °C and small weight loss (6.7%) occurred. From the
analysis, it is clear that the material is stable up to 239.73 °C, after
which major weight loss occurred and remained as a residue at
An organic nonlinear optical material FONS was synthesized
and good optical quality single crystals were grown from EMK by
slow evaporation method. The crystalline nature and structure
was confirmed by X-ray diffraction analysis. Functional groups
and molecular structure of the FONS crystal have been confirmed
3
60.64 °C.
1
by FTIR and H NMR spectral analyses respectively. The FONS crys-
Mass spectral analysis
tal is highly transparent in the visible and IR regions with low cut
off wavelength at 408 nm. The optical constants of the FONS crys-
tals were determined. From the thermal analysis it was found that
the material is stable up to 239.73 °C and the melting point is
Mass spectroscopy analysis was carried out for FONS crystal to
confirm the exact molecular mass. The peak at 243.0696 (m/z) indi-
cates the presence of the 4-fluoro 4-nitrostilbene. The peak at
1
40.33 °C. The obtained photoluminescence spectrum indicates
9
2
4.9584 (m/z) is due to the fragmentation of NO group with
that the material has green light emission at 527 nm. The SHG effi-
ciency of FONS is 12 times greater than that of KDP and it shows
that the crystal is very promising NLO material for frequency dou-
bling and other optoelectronic applications.
aromatic ring. The loss of fluorine ion from the aromatic ring in
the parent compound is assigned at 123.9439 (m/z) [12]. The
recorded spectrum is shown in Fig. 12.
Acknowledgements
Photoluminescence studies
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
encouragement.
The photoluminescence emission spectrum was acquired at
room temperature for the excitation wavelength of 350 nm in solid
phase and a spectral resolution of 0.2 nm. The recorded emission
spectrum is shown in Fig. 13. The high luminescence intensity
(
4113326.05 a.u) peak is observed at 527.05 nm. Using the conver-
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g
energy was calculated, where k is the wavelength of fluorescence.
The energy band gap of the FONS was calculated to be 2.354 eV.
From the wavelength (527.05 nm) it is concluded that the FONS
emits green fluorescence [13], which suggest that it is an excellent
candidate for nonlinear optical applications and also it can be used
as a good scintillator.
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[
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switched Nd:YAG laser emitting
a fundamental wavelength
[
(
1064 nm) [14]. The powdered sample of standard KDP was taken
as a reference material. The output of FONS is 262 mV for the input
energy 2.4 mJ/pulse while KDP gives 21.7 mV for the same input
energy and hence the measured SHG efficiency of FONS crystal is
ꢂ12 times greater than that of KDP.
[12] D. Jaikumar, S. Kalainathan, G. Bhagavannarayana, Physica B 405 (2010) 2394–
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