Journal of Crystallization Process and Technology, 2013, 3, 148-155
http://dx.doi.org/10.4236/jcpt.2013.34023 Published Online October 2013 (http://www.scirp.org/journal/jcpt)
Effect of Substituent Position on the Properties of
Chalcone Isomer Single Crystals
R. Gandhimathi1, G. Vinitha2, R. Dhanasekaran1*
1Crystal Growth Centre, Anna University, Chennai, India; 2Division of Physics, Vellore Institute of Technology, Chennai, India.
Received June 24th, 2013; revised July 24th, 2013; accepted July 31st, 2013
Copyright © 2013 R. Gandhimathi et al. This is an open access article distributed under the Creative Commons Attribution License,
which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
This paper summarizes the synthesis, growth and the effect of the position of the substituent in the thienyl ring and also
the properties of the grown chalcone crystals, 2-CTP and 3-CTP. The formation of compound is confirmed by the re-
corded H1NMR spectra. A FT-IR spectrum confirms the presence of all functional groups in both of the crystals. Single
crystal XRD reports that even though these two compounds crystallize in monoclinic crystal system, 2-CTP has centro-
symmetric P21/c space group and 3-CTP has non-centrosymmetric space group P21. Thermal properties of grown crys-
tals analyzed by TG/DTA study explain that the 3-CTP compound is slightly more stable than 2-CTP. The transparency
of these isomers in the vis-IR region has been studied. Second and third order nonlinear optical properties of 3-CTP and
2-CTP crystals have been investigated by powder SHG and Z-scan technique respectively.
Keywords: Solution Growth; Characterization; Chalcones; Nonlinear Optical Materials
1. Introduction
Chalcones are  , β unsaturated ketones. Chalcone mole-
cules with a π-conjugated system provide a large charge
transfer axis. The theory of charge transfer in molecules
reveals the relationship between structure and NLO
properties of organic compounds [1,2]. A series of chal-
cone materials have been reported for their very high
second harmonic efficiency and third order nonlinear
optical effects. Accordingly, we have chosen two chal-
cone materials for our investigation such as 3-(4-chloro-
phenyl)-1-(2-thienyl)-prop-2-en-1-one (2-CTP) and 3-(4-
chlorophenyl)-1-(3-thienyl)-prop-2-en-1-one (3-CTP). The
interesting fact is that 2-CTP and 3-CTP compounds are
positional isomers i.e. molecules with the same molecu-
lar formula have bonded together in different orders. On
close observation it has been found that 2-CTP and 3-
CTP hold opposing views such as different molecular
packing and optical properties. The arrangement of mo-
lecules in a crystal determines its physical and chemical
properties. The 2-CTP and 3-CTP compounds have iden-
tical chemical compositions, but crystallize in different
space groups where 2-CTP crystallizes in centro sym-
metric space group monoclinic P21/c [3] and 3-CTP has
noncentrosymmetric space group P21. Many publica-
tions on chalcones are mostly focused on biological ac-
tivities and second harmonic generation studies. Very
recently chalcones have been studied for their third order
nonlinear optical properties. Third order nonlinear re-
fractive index (n2), its sign, nonlinear absorption coeffi-
cient (
 ) and third order nonlinear susceptibility ( 
3) of a
thin nonlinear medium can be obtained from a linear re-
lationship between the observed transmittance changes
and the induced phase distortion by using Z-scan tech-
nique [4]. A strong delocalization of π-electrons in the
prop2-en-1-one system of chalcone determines a very
high molecular polarizability and hence the remarkable
third order nonlinearities [5]. Taking this into cognizance,
efforts have been taken to measure third order nonlinear
refractive index, nonlinear absorption coefficient and
nonlinear susceptibility of 2-CTP crystals by Z-scan tech-
nique. To show second order nonlinear optical effects, it
is essential that the molecules are packed in such a way
as to produce a non-vanishing electrical dipole moment.
Substitution of prop2-en-1-one chain on 3-postion of
thiophene ring influences noncentrosymmetric crystal
packing in 3-CTP and the molecules exhibit non-zero

values. Hence it is suitable for second harmonic genera-
tion. The main focus of this paper is to analyze the rela-
tionships between structure and nonlinear optical (NLO)
properties of compounds in terms of influence of mo-
*Corresponding author.

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
149
lecular configuration on linear and NLO properties.
2. Experiment
2.1. Synthesis
Chalcones consist of two aromatic rings in trans-confi-
gurations separated by three carbons of which two are
connected by double bond while the third is a carbonyl
group. The general structure of chalcone [6] is
αβ
XCC C Y
O
 
‖
The chalcone isomers 2-CTP and 3-CTP have been
synthesized by Claisen Schmit condensation method [7-
9]. However the precursors taken for these two com-
pounds are different. These chalcones consist of a thio-
phene ring, prop2-en-1-one and a benzene ring. The po-
sitional isomerism arises due to the attachment of side
chain (prop2-en-1-one functional group along with the
benzene ring) at 2, 3 positions of thiophene ring. The
molecular formula for these isomers is C13H9ClSO.
2.2. Determination of Solubility
The solubility of 2-CTP and 3-CTP in acetone has been
determined by the gravimetric method. A small amount
of 2-CTP compound was dissolved in 20ml of acetone
and it was allowed to stir for 2 hrs at 30˚C. The stirring
was then stopped to allow the undissolved material to
settle down. From the clear solution, 10ml of sample was
carefully taken and placed into a pre-weighed container.
The solvent was allowed to evaporate at room tempera-
ture to determine the mass of the remaining material.
Thus the solubility of 2-CTP in acetone at 30˚C was de-
termined. This process was repeated for various tem-
peratures namely, 35˚, 40˚, 45˚and 50˚C and the solubil-
ity process has been carried out for 3-CTP compound
also. Solubility curves of 2-CTP and 3-CTP in acetone
are shown in Figure 1. Both the compounds dissolve
in acetone, however their solubility differs from each
other. 2-CTP dissolves more than 3-CTP single crys-
tals.
2.3. Growth of 2-CTP and 3-CTP Single Crystals
Chalcone family crystals were grown by low temperature
solution growth method because these compounds dis-
solve well in organic solvents and easily grow from solu-
tion. 200 ml of saturated solutions of 2-CTP and 3-CTP
in acetone were prepared at 35˚C and 40˚C respectively
and kept inside a constant temperature bath. The growth
was initiated by slow evaporation of acetone, which leads
to the formation of crystals within a period of seven days.
The grown 2-CTP crystals by solvent evaporation tech-
nique are shown in Figure 2(a) and 3-CTP crystals ob-
tained by solvent evaporation method are shown in Fig-
ures 2(b) and (c). The colours of isomers are pale yel-
low.
3. Results and Discussion
3.1. NMR Spectra
H1-NMR spectra of 2-CTP and 3-CTP crystals show
signals for nine protons and it indicates five different
kinds of hydrogen environment present in the 3-CTP
molecule. The recorded NMR spectra are shown in Fig-
urs 3 and 4 respectively. The NMR spectrum of 2-CTP
shows a multiplet at 7.18 - 7.20 ppm, which corresponds
to a proton at 3-position of the thiophene ring. A multi-
Figure 1. Solubility curves of 2-CTP and 3-CTP compounds
in acetone.
Figure 2. 2-CTP and 3-CTP single crystals grown by solvent
evaporation and slow cooling techniques.

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
150
Figure 3. H1 NMR spectrum of 2-CTP.
Figure 4. H1 NMR spectrum of 3-CTP.
plet which appears at 7.35 - 7.41 ppm corresponds to two
chalcone protons. The aromatic protons appear as a mul-
tiplet at 7.68 - 7.88 ppm. A doublet at 7.57 ppm corre-
sponds to 4 th and 5th position protons of thiophene ring.
The H1NMR spectrum of 3-CTP shows a multiplet at
8.19 - 8.18 ppm, which corresponds to a proton at 2-po-
sition of thiophene ring. A multiplet, which appears at
7.77 - 7.66 ppm corresponds to two chalcone protons.
The aromatic protons appear as a multiplet at 7.40 - 7.35
ppm. A doublet at 7.55 ppm corresponds to 4 and 5th po-
sition protons of thiophene ring. These peaks confirm the
formation of the compounds [10,11]. The compound
formation was confirmed by the recorded H1NMR spec-
tra and they reveal the substitution to 2-position of
thienyl ring in 2-CTP causing a downfield shift of ap-
proximately 0.9 - 1 ppm from the substitution to 3-posi-
tion of thienyl ring in 3-CTP. H1NMR peak assignments
are tabulated in Table 1.
3.2. FT-IR Studies
The FT-IR absorption spectra of grown crystals recorded
in mid-IR range 400 cm−1 - 4000 cm−1 is shown in Fig-
ure 5. The difference in strength of the absorbance of
peaks shows the existence of bonds with different dipole
moment in the 2-CTP and 3-CTP molecules. The shift in
frequency shows the different energy requirement for the
molecule for absorbing infrared radiation. The peak as-
signments of functional groups are tabulated in Table 2.
It has been noted that these two compounds differ sig-
nificantly in the finger print region. C-C stretching of
thiophene to prop2-en-1-one side chain has been ob-
served at around 1195 cm−1. It is a doublet in the 3-CTP
material, where as in the 2-CTP spectrum it appears as a
single peak.
Table 1. H1NMR chemical shift assignments.
2-CTP 3-CTP
Chemical shift
assignments
7.18 - 7.20 (m,1H)
7.35 - 7.41 (m,2H)
7.57 (d,2H)
7.68 - 7.88 (m,4H)
8.19-8.18 (m, 1H)
7.77-7.66 (m, 2H)
7.55 (d, 2H )
7.40-7.35 (m, 4H)
3,2-H of thienyl
prope2-en-1-one
4,5-H of thienyl
aromatic
Table 2. Peak assignments.
Wave number (cm−1)
2-CTP 3-CTP Peak assignments
3155 3160 Aromatic weak C-H stretching
3076 3083 C-H stretch C is part of aliphatic
1641 1652 C=O stretching
1584 1565 C=C stretching of aliphatic chain
1195 1190 C-C stretching
1067 1068 C-H out-of-plane bend
859 860 Aryl halides C-Cl stretching
813 806 1,4,disubstituted benzene
769 758 C-H deformation
733 720 C-S stretching, weak
Figure 5. FT-IR spectra of 2-CTP and 3-CTP single crystals.

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
151
3.3. Powder XRD Spectra of Chalcone Isomers
X-ray powder diffraction analysis was carried out using a
SEIFERT JSO-DEBYE FLEX 2002 Powder X-ray dif-
fractometer with CuK  radiation of wavelength (1.541Å)
in the scanning range from 10˚ to 50˚. The obtained XRD
peaks were indexed by using Winpltor software package.
The XRD patterns of powdered 2-CTP and 3-CTP crys-
tals are shown in Figure 6. From the recorded X-ray dif-
fraction pattern, it was found that the peak corresponding
to (105) has a maximum count of 400 and it is the more
intense diffraction peak in the case of 3-CTP crystals
whereas in 2-CTP, (114) peak is the strongest. Due to the
changes in symmetry of 2-CTP and 3-CTP molecules,
these isomers show different XRD patterns.
3.4. Single Crystal X-Ray Diffraction
Single crystal XRD analysis has been performed using
Enraf Nonius CAD4-MV31 single crystal X-ray diffrac-
tometer. From the results it is known that the grown
crystals belong to monoclinic crystal system. However,
2-CTP crystals crystallize with centrosymmetric space
group P21/c and the incorporation of characteristic chal-
cone chain at 3-position of thiophene in 3-CTP makes the
material to crystallize with noncentrosymmetric space
group P21. The evaluated lattice parameter values are ta-
bulated in Table 3.
3.5. Thermal Analysis
To study the thermal stability of grown 2-CTP and 3-
CTP crystals, the DTA/TGA analyses were carried out in
the temperature range of 0˚C and 600˚C in the nitrogen
atmosphere with a heating rate of 10˚C/min using
Netzsch STA 409 CD thermal analyzer. The DTA/TGA
curves of 2-CTP and 3-CTP were shown in Figure 7. In
the thermogram, DTA curves of the samples show two
endothermic peaks. The first endothermic peaks corre-
spond to the melting points of 2-CTP and 3-CTP crystals
which were found at 130˚C and 125˚C respectively. The
second endothermic peak in the DTA trace of 2-CTP
indicates the boiling point as 306˚C whereas in the DTA
of 3-CTP, the boiling point is observed at 340˚C. TGA
curves of both the samples show decomposition in a sin-
gle stage and before the melting point no weight loss is
observed. It has been found that 3-CTP crystal is slightly
stable than 2-CTP crystal. However TGA curves of iso-
mers show the full degradation after 350˚C.
3.6. Vis-IR Spectra
The optical absorption spectra of both the samples of
2-CTP and 3-CTP were recorded using CARY 5E UV-
VIS-NIR spectrophotometer. The visible-IR spectra of
the samples were shown in Figure 8. The Vis-IR spec-
tra of the 2-CTP and 3-CTP crystals show the transpar-
ency around 50% and 40% in the visible IR region re-
spectively. Their cutoff values are almost the same and
the maximum absorbance is assigned to n-* transition.
Only n-*electronic transition is possible since the C=O
group of chalcones absorb UV light and promote exci-
tation of electrons from one of the unshared pair n (from
non bonding orbital) to anti bonding * orbital in the
molecules [12].
3.7. Nonlinear Optical Studies
The relative third order nonlinear effects were studied
Figure 6. Powder XRD patterns of 3-CTP and 2-CTP crystals.

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
152
Figure 7. TG/DTA analyses of 2-CTP and 3-CTP single crystals.
Table 3. Lattice parameter values of 2-CTP and 3-CTP
single crystals.
Lattice parameters 2-CTP 3-CTP
a (Å) 5.99 5.95
b (Å) 10.10 4.86
c (Å) 18.97 20.09
 93.98 95.99
Figure 8. Vis-IR spectra of 2-CTP and 3-CTP single crys-
tals.
using Z-Scan technique. Experiments were performed
using a 532-nm diode-pumped Nd:YAG laser beam,
which was focused by a 3.5 cm focal length lens. The
laser beam waist

0 at the focus is measured to be 15.84
µm and the Rayleigh length is 1.48 mm. The optical non-
linearity of the 2-CTP solution with 60% transmission
has been carried out by using z scan technique. The sign
and magnitude of third-order refractive nonlinearities
were calculated from closed aperture data. The closed
aperture Z-scan trace of the 2-CTP exhibited a negative
(defocusing) nonlinearity and large nonlinear refractive
index of the order of 10−8 cm2/W. The nonlinearity is of
thermal origin. In chalcones, third order nonlinearity
varies according to the distribution of -electron density
in the molecules [3]. The hetero cyclic 2-thienyl group
and α, β unsaturated prop2-en-1-one at the centre of
2-CTP molecule have an effect of high electron donating
and electron withdrawing property respectively. The
chloro group attached at the other end of the 2-CTP mo-
lecules act as an electron acceptor. Hence the 2-CTP
molecules possess donor-acceptor-acceptor type struc-
ture.
The open aperture curve of 2-CTP was shown in Fig-
ure 9(a). From the open-aperture Z-scan data, the mag-
nitude of intensity-dependent nonlinear absorption was
derived, which exhibited a maximum transmittance at the
focus (z = 0) that results off an induced negative nonlin-
ear absorption effect due to the passage of laser light
through prepared 2-CTP solution. Two-photon absorp-
tion coefficient of 2-CTP was calculated from the open
aperture data. Pure nonlinear refractive index is obtained
by dividing the closed aperture transmittance values by
the corresponding open aperture scans [13]. The ratio of
open aperture and closed aperture transmittance is shown
in Figure 9(b), which gives pure nonlinear refractive

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
153
index n2 of 2-CTP. The third-order nonlinear optical sus-
ceptibility χ(3) was calculated using the real and imagi-
nary parts of third order nonlinear optical susceptibility

(3) according to the following relations


22 2
34002
Re10 cnn cm esu W





(1)


22
32002
2
Im10 4π
cnn cm
esu W





(2)
 
22
333
Re Im   (3)
(3) for 2-CTP was found to be 4.86 × 10−6 e.s.u. The
measured susceptibility

(3) is relatively large when
compared to other chalcone’s values reported which is in
the order of 10−13 e.s.u [14].
3.8. Birefringence Measurement on 3-CTP
The interference of emergent ordinary and extraordinary
waves from a briefringent crystal, after passing through
an analyzer oriented at 45˚ generates intensity distribu-
tion patterns. The observed fringes and their spacing de-
pend on the orientation of the crystallographic axes (x, y,
z) and the different parameters characterizing the bire-
fringence [15]. Initially a beam of light from the He-Ne
laser source was passed through a well-polished 3-CTP
single crystal of 0.5 mm thickness (not along the optic
axis). Upon entering 3-CTP crystal it splits into two
plane polarized light components (ordinary and extraor-
dinary rays) which travel with different velocities and
maintain a constant phase difference with respect to each
other. The vibration plane of the polarized lights should
be at 45˚ to the plane containing optic axis of the crystal.
This is achieved by rotating the crystal until the intensi-
ties of the ordinary and the extraordinary rays are same.
Hence the emergent rays from a coherent source polar-
ized at right angles to each other. After travelling through
the crystal, the light was allowed to enter the analyzer.
When these two rays pass through the analyzer, they su-
perimpose to produce constructive or destructive inter-
ference patterns depending upon the path difference ex-
isting between them. The interference pattern (bright and
dark fringes) was captured on the screen which was
placed behind the analyzer. The interference patterns
obtained are shown in Figures 10(a) and (b) exhibiting
uniform spacing between the fringes, which is an indica-
tion of no defects and refractive index being identical
throughout the orientation. Figures 10(c) and (d) show
distortions in the fringe pattern which is attributed to the
patterns formed by the defective portion of the crystals.
A power meter was used to detect the light transmitted
through the analyzer. The birefringence (n) can be cal-
culated using the relation [16].
1
sin
πo
I
ndI


 (4)
where I and Io are the intensities of light reaching the
detector with and without sample, respectively and d is
the thickness of the sample. The birefringent value is
calculated for 3-CTP single crystals is 0.024 at a particu-
lar wavelength of 632.8 nm.
3.9. SHG Study on 3-CTP
To find the SHG conversion efficiency of the NLO crys-
tals, the powder technique developed by Kurtz and Perry
[17] were used. However, the powder SHG observed for
any given sample may vary with a number of parameters,
including laser wavelength, particle size, temperature,
crystallization solvent and sample preparation. In our
present investigation, the powdered sample of 3-CTP
Figure 9. (a) and (b) open aperture and ratio of closed and open aperture curves.

Effect of Substituent Position on the Properties of Chalcone Isomer Single Crystals
154
(a) (b)
(c) (d)
Figure 10. Interference fringe pattern of 3-CTP single crys-
tals.
was packed in a triangular cuvette and it was subjected to
the irradiation of laser from Nd:YAG with wavelength of
1064 nm. A laser beam with the 8 nanosecond pulses and
the energy of 300 mJ (each laser pulse) has been allowed
to transmit through the cuvette. A Hamamatsu R-928
photomultiplier tube was used for the detection of emer-
gent signal. SHG-measurement directly displayed on the
oscilloscope screen was recorded (peak to peak volts).
The same experimental procedure was repeated five
times and an average of these five voltages gives the
signal height. For the KDP crystal powdered with identi-
cal size of sample was subjected to same experimental
procedure and the SHG efficiency of the 3-CTP has been
found to be 2.7 times than that of reference material KDP.
The comparison of SHG efficiency of 3-CTP material
with KDP is shown in Figure 11. Nonlinear optical prop-
erties of chalcone isomers were tabulated in Table 4.
4. Conclusion
Chalcone isomers 2-CTP and 3-CTP were synthesized
and grown as single crystals by solution growth tech-
nique. H1NMR and FT-IR studies confirm the formation
and presence of all functional groups in the compounds.
The single crystal XRD studies confirm the monoclinic
crystal system of the synthesized materials and the re-
sults indicate that the position of the chalcone chain has
remarkable impacts on molecular packing of crystalliza-
tion. The Vis-IR studies prove the good transparency of
the material in visible absorption and indicate the possi-
bility for utilization in nonlinear optical devices. Thus the
difference in molecular structure alters the electronic
properties of the molecules and leads to different order in
nonlinear optical effects in organic compounds. En-
hanced -electron density through the prop2-en-1-one
Figure 11. Comparison of SHG efficiency of 3-CTP with
KDP.
Table 4. Nonlinear optical properties of chalcones.
Materials
Properties 2-CTP 3-CTP
1. Linear refractive index by
Brewster angle method 1.572 1.60
2. Second harmonic generation - 2.7 times better
than KDP
3. Third order nonlinear
optical effects
a) nonlinear refractive
index n2 (cm2/W)
b) nonlinear absorption
coefficient β (cm/W)
c) nonlinear
Susceptibility 
(3) (esu)
1.13 × 10−8
2.46 × 10−3
4.86 × 10−6
--
conjugated bridge increases the third order nonlinear
response of the 2-CTP compound. Noncentrosymmetric
space group, good transparency in visible region, moder-
ate birefringent value compared to other organic materi-
als and high SHG efficiency of 3-CTP crystals are factors
that confirm that this material is a prospective material
for frequency conversion applications.
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