Synthesis, growth and third-order nonlinear optical properties of quinolinium single crystal-PCLQI

Article abstract of DOI:10.1039/c6ra05055g

N-Ethyl quinolinium chromophore crystal 2-[2-(4-chloro-phenyl)-vinyl]-1-ethyl-quinolinium iodide (PCLQI) has been successfully grown by the slow evaporation technique. Single crystal X-ray diffraction studies revealed that the title compound crystallizes in the monoclinic crystal system with the centrosymmetric space group C2/c. The molecular formation of the grown crystal was initially identified using ¹H NMR and FTIR analysis. The linear optical studies of the title crystal were done by UV-vis-NIR studies and the thermal studies revealed the stability of the title material till its melting point at 239.7 °C. The grown crystal exhibited high third order optical nonlinearity which was determined by the Z-scan technique.

Full text of DOI:10.1039/c6ra05055g

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Synthesis, growth and third-order nonlinear optical properties of
quinolinium single crystal-PCLQI
*
1
2
3
S. Karthigha, S. Kalainathan , Fumio Hamada , Manabu Yamada , Yoshihiko Kondo .
Centre for Crystal Growth, School of Advanced Sciences, VIT University, Vellore- 632014, Tamil Nadu
Department of Applied Chemistry for Environments, Graduate School of Engineering and Resource Science,
Akita University, 1-1 Tegatagakuen-machi, Akita, 010-8502, Japan.
1
2
Research Center for Engineering Science, Graduate School of Engineering and Resource Science, Akita
University, 1-1 Tegatagakuen-machi, Akita, 010-8502, Japan.
3
Department of Life Science, Graduate School of Engineering and Resource Science, Akita University, 1-1
Tegatagakuen-machi, Akita, 010-8502, Japan.
Abstract
N-ethyl quinolinium chromophore crystal 2-[2-(4-Chloro-phenyl)-vinyl]-1-ethyl-quinolinium
iodide (PCLQI) has been successfully grown by slow evaporation technique. Single crystal
X-ray diffraction studies revealed that the title compound crystallizes in monoclinic crystal
system with centrosymmetric space group C2/c. The molecular formation of the grown
1
crystal was initially identified using H NMR and FTIR analysis. The linear optical studies of
the title crystal were done by UV-vis-NIR studies and the thermal studies revealed the
O
stability of the title material till its melting point 239.7 C. The grown crystal exhibited high
third order optical nonlinearity which was determined by Z-Scan technique.
1. Introduction
Organic nonlinear optical materials with high second order optical nonlinearities have
attracted much attention for potential applications in various fields such as THz generation,
opto electronics, optical frequency conversion, photonics and integrated optics applications [1
-
3]. The ionic organic NLO crystals are attractive materials for second order nonlinear

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applications [4, 5] due to the presence of delocalized π electrons and coulombic interactions
6-8]. The ionic stilbazolium derivatives, have led to many breakthrough in macroscopic
[
nonlinearities as well as crystal characteristics. Organic ionic crystals are interesting because
they exhibits large NLO properties, posses an easy tunability by changing the counter ion to
crystallize into non centrosymmetric structure [9] and the best combination of donor and
acceptor groups provides a better enhancement. Non centrosymmetric hetero aromatic
pyridinium cations exhibit excellent nonlinear optical properties due to their large first order
hyperpolarizability. Therefore, the electron withdrawing strength of electron acceptor group
is most important to obtain desired optical properties for many applications [10]. One strategy
to enhance the electron withdrawing strength and hyperpolarizability of the cation is by
elongation of its π- conjugated system. Vladimir et al. have depicted the crystal structure for a
new family of quinolinium derived acentric materials, which exhibits high hyperpolarizability
combined with a noncentrosymmetric structure [11]. Recently, a quinolinium acceptor group
with strong π-conjugated system has been introduced, which exhibits a large molecular
hyperpolarizability and large macroscopic nonlinear optical response [12, 13]. For example,
HMQ-T and HMQ-MBS exhibit high order parameter and large optical nonlinearity in the
range of benchmark stilbazolium DAST crystal [14]. Recently, many quinolinium
chromophores have been synthesized and widely investigated by many research groups by
changing the anionic group (aryl sulfonate) to create new molecules with a large NLO
response. However, higher molecular polarizability leads to intensive dipole-dipole
interactions that tends the chromophores to compensate the total dipole moment by packing
in more centrosymmetric structures in organic molecules, which significantly enhances the
third-order nonlinear optical property of the materials [11]. Various ionic organic crystals
chromophore arranged in centrosymmetric manner posses third harmonic generation [15]
which are being perform effectively in information processing devices. The prerequisite for a

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third order chromophore is to have high thermal stability, good transparency, high non-
linearity and process ability. These motivated us to synthesis and investigate the third order
optical nonlinearity of quinolinium derived single crystals and to find application in the fields
of optical switching and optical limiting devices [16].
Here in we report a new organic material 2-[2-(4-Chloro-phenyl)-vinyl]-1-ethyl-quinolinium
iodide, which is a series of π-conjugated styryl quinolinium chromophore from the stilbene
family. Third order optical property were analysed by using Z- scan technique, which reveal
that the PCLQI crystal shows high nonlinear absorption coefficient, making them potential
candidate for optoelectronic and optical switching applications. Further, grown crystal was
investigated by various instrumentation techniques to analyse their structural and optical
properties and to check their suitability for device fabrication.
2
. Experimental procedure
.1 Material synthesis
2
All high purity chemical reagents and solvents were purchased from Alfa Aesar and Sigma
Aldrich and used for synthesis without further purification. The overall synthesis process of
starting material involving two- step synthesis route were shown in scheme 1.
1-Ethyl-2-methyl-quinolinium iodide (1) : 1-Ethyl-2-methyl-quinolinium iodide was
synthesized by taking a solution of 2-methyl quinoline (1mmol) and ethyl iodide (3mmol) in
acetonitrile (25ml). The mixture were heated under reflux for 24h and cooled to ambient
temperature. After cooling diethyl ether was added, the desired quaternary ammonium salt
was collected by filtration. The ether from the combined filtrate was removed by evaporation
and the remaining residue, consisting mainly of the unreacted starting material, was heated
under reflux for another 24h and the steps are repeated as mentioned above. The obtained

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pale yellow salt was dried in an oven. The process was repeated several times to achieve a
suitable yield.
2
-[2-(4-Chloro-phenyl)-vinyl]-1-ethyl-quinolinium iodide (2): The title material PCLQI (2)
was prepared by taking stoichiometric ratio of 1-Ethyl-2-methyl-quinolinium iodide (1)
0.89g, 3mmol) and p-chloro benzaldehyde (0.42g, 3mmol) in methanol (30mL) and
(
piperidine added as a catalyst (few drops). The above mixtures were taken in a 250mL round
bottom flask and the mixture solution was refluxed for 2h. The resulted brown solid was
filtered off and washed 3-5 times with Diethyl ether to remove unreacted starting materials.
The purity of the title compound (2) was increased by repeated recrystallization from
methanol.

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CH CN
3
Acetonitrile(25mL)
+
CH CH I
3 2
Reflux 24h
N
N
CH
3
CH3
I
2
-methyl quinoline
Ethyl iodide
CH3
1-Ethyl-2-methyl-quinolinium iodide
Cl
CHO
N
H
Piperidine
Methanol(30ml)
Reflux 2h
4
-Chloro-benzaldehyde
N
CH3
Cl
I
.0.5 H O
2
2
-[2-(4-Chloro-phenyl)-vinyl]-1-ethyl-quinolinium iodide hemi hydrate
Scheme 1: Synthesis of PCLQI

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2.2 Solubility, crystal growth and morphology
The solubility test plays an important role in deciding the best solvent and temperature to
grow good quality crystals. The solubility measurement provides information about the
nucleation and quantity of the solute material required for the crystal growth. In the present
investigation, the solubility of PCLQI was checked by different combination of organic
solvents namely, methanol, ethanol, methanol-chloroform, methanol-acetonitrile, methanol-
dichloromethane mixed solvents. From this we optimized that the material has high solubility
in methanol-acetonitrile mixed solvent system in the ratio of 3:1. The solubility of purified
0
PCLQI salt was determined for different temperatures from 20 to 40 C. The saturated
0
solution for 20 C was prepared by continuous stirring to ensure homogeneous temperature
and concentration throughout the volume of the solution by using constant temperature water
0
bath with an accuracy of 0.01± C. After attaining saturation, the equilibrium concentration of
the solute has been estimated gravimetrically. The same procedure was repeated for other
0
0
0
temperatures from 25 C to 40 C with 5 C intervals to determine the equilibrium
concentration of the solute. The solubility measurement of PCLQI at different temperatures is
shown in Fig. 1. In the graph, it is seen that the solubility of PCLQI linearly increases with
increasing temperature. Based on the solubility data, the saturated solution of purified PCLQI
0
was prepared by dissolving it in methanol-acetonitrile (3:1) mixed solvent system at 40 C.
The resultant solution was filtered in a 150ml beaker and it was covered with aluminium foil.
After 10 days good quality seed crystals were obtained and from this one of the seed crystal
has been tied up with nylon thread and it was hanged inside the saturated solution. The
0
solution was allowed to slowly evaporate at 40 C in a constant temperature water bath. After
the evaporation period of 20 days, high quality PCLQI single crystal with dimension of 13 x
3
4
x 2mm were harvested. The photographs of as grown crystals were shown in Fig.2 (a& b).

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The morphology of the grown crystal has been simulated using WinXMorph software
program [17]. The CIF data obtained from single crystal XRD data was used as input to
predict the morphology of PCLQI single crystal. It is observed that the growth rate of PCLQI
elongated along crystallographic b-axis compared to other growth directions. The indexed
morphology of grown crystal is shown in Fig. 2c.
3. Results and discussion
3.1 Single crystal x-ray diffraction analysis
In order to analyse the crystal structure, the grown PCLQI crystal of dimension (0.2 X 0.2 X
3
0
.15 mm ) was subjected to single crystal structure analysis using Rigaku R-AXIS RAPID
diffractometer. The Mo-Kα radiation (λ= 0.71075Å) was used to record the reflections in ω
scan mode. The crystal structure was solved by the direct methods using SHELX-97[18] and
refinement was done by Full matrix least squares technique using the SHELX-97 software
program. The crystallographic data and structure refinement details of grown crystal are
presented in Table 1. All atoms except hydrogen atoms were refined anisotropically and
hydrogen atoms were refined according to the Riding model [19]. From the analysis, PCLQI
crystals exhibits monoclinic space group symmetry C2/c with cell parameters a =
o
2
6.0008(11) Å, b = 9.3211(4) Å, c = 15.3597(8) Å, β = 113.3849(14) . The volume of PCLQI
3
crystal system is 3416.8(3) Å . The grown crystal crystallizes in centrosymmetric space
group, which does not exhibit any second-order NLO properties [20]. Selected bond lengths
and bond angles are given in Table 2 and 3, respectively. Fig. 3 exhibits the ORTEP view of
PCLQI showing 50% probability displacement ellipsoids.
The asymmetric unit of the title material consists of 2-[2-(4-chloro phenyl)-vinyl]-1-ethyl
+
-
quinolinium cation (C19
H17ClN ), iodide anion (I ) and 0.5 water molecule. The cation exits
in the trans (E) configuration with respect to the C7 = C8 double bond [1.340(3) Å] which

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o
can be confirmed by the torsion angle C4-C7-C8-C9 = 178.6 (2) . In crystal packing diagram,
the molecules form network chain associated with water molecules and the asymmetric
residue viewed down the ‘b’ axis is shown in Fig. 4. Here the cations are interconnected by
water molecules and iodide ions through weak C—H···O and C—H···I interactions to form a
three dimensional molecular network. Further, the crystal system is also stabilized by π-π
interactions between quinolinium and phenyl rings.
The crystallographic information file for PCLQI has been deposited in the Cambridge
Crystallographic Data Centre (CCDC# 1446060).
3.2 Powder X-ray diffraction analysis
Powder X-ray diffraction analysis were carried out by using Rigaku X-ray diffractometer
with Cu-Kα radiation (λ = 1.540598Å) to demonstrate the crystallinity of the grown crystal.
0
0
-1
The sample was recorded over a range of 10-70 at a scanning rate of 0.02 s . The various
planes of reflections at 2θ angles were indexed by using POWDER X software program [21].
The well defined indexed Bragg’s peak at specific 2θ angles in the powder XRD is shown in
Fig. 5. The refined lattice parameters were a = 25.97514 Å, b = 9.31059 Å, c = 15.3297 Å, β
0
=
113.402 crystallizing in monoclinic structure. The appearance of sharp and well- defined
peaks proved the good crystalline property of grown crystal PCLQI.
3.3 FTIR spectral analysis
In order to confirm the various vibrational modes of functional groups in the grown crystal,
-1
FTIR spectrum were recorded in the range of 4000-400cm using a SHIMADZU
IRAFFINITY spectrometer. The measurements were done by using KBr pellet technique and
-1
the spectrum is shown in Fig. 6. In FTIR spectrum the peak observed at 3032 and 3074cm
_
-1
are due to aromatic C H stretching vibrations and the absorption band at 2949cm is

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assigned to alkyl C- H stretching vibrations. The aromatic C= C stretching vibration of π-
conjugated stilbazolium chromophore (C- C= C- C) was confirmed by the peak observed at
-1
-1
1
604cm . The sharp peak observed at 1006cm confirms the formation of the title compound
-1
by olefinic =C- H bond. The peak at 1583cm is attributed to bending vibration of O- H in
water molecule, which may be due to moisture absorbed from atmosphere. The sharp peaks
-1
observed at 1570 and 1523cm corresponds to the olefinic C- C stretching vibrations. The
-1
2
absorption band around 1438cm corresponds to CH bending vibrations. The peaks that are
-1
observed at 1377 and 1340cm are attributed to the ring C- C stretching and ring C- H in-
plane bending vibrations. The characteristics vibrational frequencies exhibit between 480-
-1
8
00cm are due to the presence of C- X (X- Br, Cl and F) stretching vibrations [22]. The
-1
vibrational frequencies observed in the region 550-850cm can be attributed to the C- Cl
-1
stretching vibrations. The peaks observed in the region 1150-800cm can be assigned to the
skeletal vibrations of C- C and C- N bonds.
3.4 NMR spectral analysis
Nuclear Magnetic Resonance spectroscopy provides the detailed information about molecular
1
structure of synthesized materials and chemical environment of the molecules [23]. The H
NMR for PCLQI was recorded by dissolving the sample in deuterated solvent DMSO-d
6
1
using BRUKER instrument operating with a 400MHz spectrometer. Fig. 7 shows the H
NMR spectra, with the quintet chemical shift at 2.499ppm assigned to DMSO-d6 and water
molecule present in DMSO-d6 shows chemical shift at 3.592ppm. Ethyl group attached to the
_
_
quinolinium ring (N CH
two doublets observed at 7.565ppm and 7.808ppm are due to the two olefinic hydrogens
CH=CH). The two doublets at 9.055 and 8.363ppm are corresponds to the hydrogen atom
present in the fourth and third position of the C H N ring. The triplet signals found at 8.164
2 3
CH ) gives a quartet and triplet at 5.110ppm and 1.556ppm. The
(
2
5
and 8.204ppm was caused by hydrogen atoms present in sixth and seventh position of

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quinolinium ring. The two doublets observed at 8.542 and 8.565ppm are assigned to protons
in the quinolinium ring. Also a chemical shift at7.991 and 7.940 are attributed to the
hydrogen atoms present in the p-substituted benzene ring. In present spectrum the assigned
splitting factors for protons present in PCLQI are (400MHz, DMSO-d6): 5.11 (q, 2H, J=
7
.04Hz, NC H ), 1.556 (t, 3H, J=7.2Hz, NC H ), 7.565 (d, 1H, J=8.8Hz, CH), 7.808 (d, 1H,
2 5 2 5
J=16Hz, CH), 9.055 (d, 1H, J=9.2Hz, C
J=6Hz, C ), 8.542 (d, 1H, J=6.4Hz, C
J=6Hz, C ), 7.991 (d, 2H, J=8.4Hz, C
5
H
2
N), 8.363 (d, 1H, J=7.2Hz, C N), 8.565 (d, 1H,
), 8.164 (t, 1H, J=5.6Hz, C ) 8.204 (t, 1H,
6 4
) and 7.940 (d, 2H, J=7.6Hz, C H ).
5
H
2
6
H
4
6
H
4
6 4
H
6
H
4
6
H
4
13
The C NMR spectrum of PCLQI is shown in Fig. 8. The peak appearing at 43.89 and 19.40
are due to the presence of ethyl carbon attached to the C N ring. The signals observed at
24.39 and 133.57ppm are due to the presence of vinyl carbon. The peaks observed at 44.10,
2
H
5
1
4
4.31, 44.52, 44.72, 124.18, 126.71, 142.23, 149.86, 150.07ppm are attributed to the
1
quinolinium moiety. Thus the formation of the title compound was confirmed by H NMR
13
and C NMR spectral analysis.
3.5 Thermal analysis
The thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of PCLQI
0
were recorded over a range of 30-500 C under nitrogen atmosphere at a heating rate of
-1
1
0Kmin . An initial mass of 7.56mg of title material was used to record the TG-DTA which
is shown in Fig.9. In TGA curve the initial weight loss of 1.74% illustrates the loss of water
molecule and volatile substances in the title material. This is followed by two weight losses,
0
0
the first step with the weight loss of 41.11% in the temperature range of 230.7 C- 254.2 C
0
and another weight loss associated with major weight loss 57.15% occurred up to 314.4 C.
These weight losses attributed to the complete decomposition of PCLQI crystal. In DTA
0
trace, it was observed that the sharp endothermic peak at 239.7 C corresponds to the melting

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0
point of PCLQI crystal and this is followed by rapid decomposition at 309.8 C. This may due
to bulk decomposition of PCLQI crystal and this endotherm coincides with the maximum
weight loss of TGA curve. Hence we conclude that the TG-DTA analysis confirms the
stability of the material and it can be exploited for any suitable optical applications until its
melting point.
3.6 Chemical etching studies
Etching of crystal surface provides more information about the surface features, micro
structural information, spirals, hillocks, and slip patterns on the growing crystal surface. Etch
patterns observed on crystal surface provides detailed information of the growth process and
growth mechanism of the crystal [24]. In present investigation, Etching studies were carried
out for PCLQI crystal using methanol-acetonitrile (3:1) as etchant for a time period of 15s
and 30s. The crystal surface was examined using a Carl ziess optical microscope in reflection
mode. The surface micrograph of as grown crystal is shown in Fig.10 (a-c). Fig. 10a shows
the before etch pattern of the as grown PCLQI crystal. Fig. 10b shows well defined
rectangular etch pits for 15s. When increasing the etch time 15s to 30s, the size of the etch
pits also elongated as shown in Fig. 10c. The observed etch patterns due to the layer growth,
confirmed the two-dimensional mechanism with fewer dislocations [25].
3.7 Optical absorption spectral analysis
The optical absorption spectrum of PCLQI was recorded in the range of 200-1100nm using a
Perkin Elmer UV spectrophotometer. The UV-vis-NIR spectra of PCLQI crystal exhibit
maximum cut-off wavelength at 485nm, which is attributed to π-π* transition due to the
presence of conjugated system in the PCLQI molecule. Optical switching application has
required finding a high third order nonlinear optical material, as well as large transmittance or
low absorption in near IR region. Fig. 11 shows the UV absorption spectrum of PCLQI single

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crystal of 1mm thickness. No absorption band observed in the region between 485-1100nm
and it has very good optical transparency in near infrared region. The measured absorption
values of PCLQI crystal was used to calculate the absorption coefficient (α) by using the
equation [26],
ꢀ
.ꢁꢂꢁꢃꢄꢅꢆ
ꢇ
α =
(1)
Where A is the absorption and t is the thickness of the sample. The optical absorption
coefficient has been used to calculate the energy band gap of the material. The optical band
gap was calculated by using the relation,
2
αhυ = A (Eg ˗ hυ)
(2)
2
The graph is plot between photon energy (hυ) versus (αhυ) and the energy band gap is
figured out by extrapolating the linear part from the maximum absorption end to the photon
energy axis as shown in Fig. 12. The Tauc’s method has been used to measure the optical
band gap of PCLQI crystal and it is found to be 2.15eV. Thus the large transmittance near IR
region and low energy gap of this crystal proves that it is a potential candidate for used in
optical devices such as optical switching and various nonlinear optical applications.
3.8 Z-scan studies
The Third order optical property of PCLQI crystal has been investigated using Z-Scan
technique and it is a accurate method to determine the sign and magnitude of nonlinear
refractive index and nonlinear absorption coefficient developed by Sheik Bahae et al [27].
Here the open aperture and closed aperture Z scan is used for nonlinear absorption coefficient
and nonlinear refractive index measurements and this method has been widely accepted by
nonlinear optics community due to its simplicity and high sensitivity. In this experiment, He-
Ne laser (632.8 nm) with the input intensity of 5mW used for sample excitation, and its

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propagation direction is taken as Z-axis. The Gaussian beam was focused using a convex lens
30mm), and the focal point is taken as Z = 0. The thickness of the sample is very important
(
to minimize the phase transition, for this a sample thickness 0.7mm was used. Thus the
essential criteria of Rayleigh length (Zo < L) were found to be satisfied and it can be
2
o
calculated by using the formula ꢈꢉ = ꢊω /2, where K is 2ꢋ⁄ꢌ and ω is the radius of the
o
focal length. The maximum energy density of the beam is at the focus, which is being
symmetrically reduced both sides for the positive and negative values of z, this leads to the
difference in laser intensity at different z positions. The transmittance intensity variations
corresponding to the z values, the open aperture and closed aperture z-scan curve can be
drawn. The recorded normalized transmittance for PCLQI crystal is shown in Fig. 13 and Fig.
14. The sample can act as a thin lens of variable focal length, as the sample brought closer to
the focus, the irradiance of Gaussian beam increases or decreases depending upon the
material absorption and refractive index. From open aperture method, the nonlinear
absorption coefficient can be easily calculated from maximum or minimum transmittance
curves. It was observed that, the sample transmittance increases while increasing the input
intensity of laser beam, which demonstrates the absence of reverse saturation absorption
(RSA) with enhanced strong saturation absorption (SA) in PCLQI crystal. From the closed
aperture curve, the prefocal valley to post focal peak configuration clearly suggests that the
title crystal has a positive sign of third order nonlinear refractive index and this behaviour
attributed to self focusing effect. This may caused by reduced transmittance and large beam
divergence through the far field aperture, which is an essential property for optical switching
applications [28]. The magnitude of third order nonlinear optical susceptibility ꢍꢎ(ꢁ)ꢏ has
been calculated by using the formula,
(3)
(3)
2
(3) 2 1/2
|
χ | = [(Re(χ )) +(Im(χ )) ]
(3)

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The real and imaginary part of third order susceptibility can be defined as [29],
ꢔꢂꢕꢖꢍɛ ꢘ ꢚ ꢚ ꢏ
ꢙ
ꢙ
ꢐꢑꢍꢎ(ꢁ)ꢏ(ꢑꢒꢓ) =
ꢡꢞꢍꢎ(ꢁ)ꢏ(ꢑꢒꢓ) =
ꢗ
ꢛ
ꢙ
(ꢝꢞ ꢟ )
ꢀ
ꢠꢔ
(4)
(5)
ꢜ
ꢔꢂꢕꢙꢍɛ ꢘ ꢚ ꢢꢣꢏ
ꢙ
ꢙ
ꢗ
ꢛ
(ꢝꢞꢟꢠꢔ)
ꢤꢜꢙ
In closed aperture method, on axis phase shift (ꢀ
Փ
) is calculated from the difference between
) is in
| [30],
the transmittance change of peak and valley and the equation of on axis phase shift (ꢀ
Փ
0
.25
terms of normalised transmittance can be defined as ꢀTP-V = 0.406(1-S)
| ꢀՓ
where S is the aperture linear transmittance (S=2) and it can be calculated by using the
2
relation, S =1-exp [-2r /ω ]. Where r is the radius of aperture and ω , is the beam radius at
a
a
a
a
the aperture. The third order nonlinear refractive index of the crystal can be studied in terms
of on-axis phase shift [31],
n
2
= ꢀՓ
/ K I
o
L
eff
(6)
Here Leff ia an effective thickness of the crystal was calculated using the following relation,
Leff = 1- exp (-αL)/ α. In open aperture method, the nonlinear absorption coefficient (β) has
been estimated from the relation [32],
β =2√2 ꢀT/ I
o
L
eff
(7)
The negative nonlinear absorption has been observed in PCLQI single crystal due to strong
saturation absorption in the material. The obtained values of third order nonlinear refractive
-11
2
-1
-4
-1
index and nonlinear absorption coefficient are 1.56 x 10 m W and 1 x 10 mW
-6
respectively. The third order nonlinear susceptibility of grown crystal is 4.5226 x 10 esu and
it can be related with the second order molecular hyperpolarizability. The molecular second
order hyperpolarizability of PCLQI crystal estimated by using the following equation,
Re (γ) = Re(χ3)⁄ꢥꢦ4
(8)

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Here N is number of molecules per unit volume and f is the local field correction factor
according to Lorentz equation,
2
f = (n
o
+2) ꢁ 3
(9)
Generally third order optical property of materials is related with all optical switching
applications. To know the suitability of grown crystal for all optical switching applications,
two figures of merit, W and T have been calculated from obtained third order optical
parameters. For all optical switching application, a values W >> 1 and T<<1 should be
needed [33]. For PCLQI crystal the values have been calculated to be 17 >> 1 and 0.405 <<
1, which satisfies the requirement of all switching applications. The Z-scan experiment
indicates that the PCLQI single crystal exhibit high nonlinearity for optical application and
the calculated parameters of the title crystal are tabulated in Table. 4. The third order optical
property of PCLQI crystal is compared with some other organic crystals tabulated in Table. 5.
The large value of χ3 can be attributed to high density π- electron cloud within the
quinolinium molecular system [34]. Therefore, the polarization of the π-conjugated electrons
in the quinolinium molecular system will be high and it will contribute to the large value of
χ3 and γ. Thus, the obtained results show that PCLQI crystal has an excellent potential
material for all optical switching and third order optical applications.
4. Conclusion
A quinolinium derived single crystal PCLQI were synthesized and grown by slow
3
evaporation technique. Single crystals of size with 13 x 4 x 2mm were grown and
morphology of the grown crystal was determined by using WinXmorph program. The

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structure of the grown crystal were determined and refined single crystal XRD using
SHELX-97 software program and the obtained lattice parameters were a = 26.0008 (11) Å, b
0
=
9.3211 (4) Å, c = 15.3597 (8) Å and β = 113.3849 (14) . The crystalline perfection was
studied by powder XRD and it confirms the crystalline nature of the PCLQI crystal is fairly
good. The presence of functional groups and structure of title material was confirmed by
FTIR and NMR spectral analysis. Thermal behaviour of PCLQI was studied by TG/DTA
analysis and thermally stable up to its melting point. The UV-vis-NIR spectrum shows that
the cut- off wavelength if found to be 485nm and the lower value of optical band gap
(2.15eV) was obtained by plotting of Tauc’s plot. The third order optical property of grown
-4
-1
crystal reveals that it posses large nonlinear absorption coefficient (β =1 x 10 mW ) and
third order optical susceptibility, which enhances the suitability of grown title crystal for all
optical switching applications. Thus from the above studies suggests that the grown PCLQI
crystal is a new candidate for Third order optical applications.
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LIST OF FIGURES:
Fig.1 solubility curve of PCLQI in Methanol-Acetonitrile solvent system
Fig.2 Photograph of as grown PCLQI crystals

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Fig.3 ORTEP view of PCLQI

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Fig.4 Crystal packing diagram of PCLQI

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Fig.5 Powder XRD pattern of PCLQI
Fig.6 FTIR spectrum of PCLQI

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1
Fig.7 H NMR spectrum of PCLQI
1
Fig.8 C NMR spectrum of PCLQI
3

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Fig.9 TG&DTA curves of PCLQI

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Fig.10 Etch pit patterns of PCLQI crystal with Methanol – Acetonitrile as etchant
a)Before etching (b) 10s (c) 20s
(

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Fig.11 Absorption spectrum of PCLQI crystal
Fig.12 Tauc’s plot for 4CLNS crystals

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Fig.13 Open aperture spectrum of PCLQI crystal
Fig.14 Closed aperture spectrum of PCLQI crystal

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TABLE CAPTION:
TABLE 1
Crystal data and structure refinement for PCLQI
Empirical formula
Formula weight
Temperature
38 2 2 2
C H34Cl N I O
859.41
100K
Wavelength
0.71075Å
Crystal system
Space group
Monoclinic
C /C
2
o
Unit cell dimensions
a = 26.0008(11) Å
b = 9.3211(4) Å
c = 15.3597(8) Å
α
β
γ
= 90
o
= 113.3849(14)
o
= 90
3
Volume
3416.8(3) Å
Z
4
3
Density
1.671 g/cm
-1
Absorption coefficient
F(000)
2.033 mm
1690
3
Crystal size
0.2 x 0.2 x 0.1 mm
o
o
Theta range for data collection
Reflections collected
Unique reflections
0.0 to 25.33
13310
3119 [R(int) = 0.0223]
99.7%
o
Completeness to theta= 25.33
Max. and min. transmission
Refinement method
0.737 and 0.595
2
Full matrix least square on F
3119/ 0 /212
Data/ restraints/ parameters
R indices (all data)
R
1
= 0.0165, Wr
1.082
0.65 and -0.31 e. Å
2
= 0.0414
2
Goodness-of -fit on F
-3
Largest diff. Peak and hole