Synthesis, spectral, thermal, optical and theoretical studies of (2E,6E)-2-benzylidene-6-(4-methoxybenzylidene)cyclohexanone

Article abstract of DOI:10.1016/j.saa.2013.10.003

Single crystals of (2E,6E)-2-benzylidine-6-(4-methoxybenzylidine) cyclohexanone are grown by slow evaporation of ethanolic solution at room temperature. The characteristic functional groups present in the molecule are confirmed by Fourier transform infrared and Fourier transform Raman analyses. The scanning electron microscopy study reveals the surface morphology of the material. Thermogravimetric/differential thermal analysis study reveals the purity of the material and the crystal is transparent in the visible region having a lower optical cut-off at ～487 nm. The second harmonic generation efficiency of as-grown material is estimated by Kurtz and Perry technique. Optimized geometry has been derived using Hartree-Fock calculations performed at the level 6-31G (d,p) and the first-order molecular hyperpolarizability (β) is estimated. The specimen is further characterized by nuclear magnetic resonance spectroscopy.

Full text of DOI:10.1016/j.saa.2013.10.003

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 72–76
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis, spectral, thermal, optical and theoretical studies of
(2E,6E)-2-benzylidene-6-(4-methoxybenzylidene)cyclohexanone
⇑
V. Meenatchi, K. Muthu, M. Rajasekar, SP. Meenakshisundaram
Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamilnadu, 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
ꢀ
ꢀ
ꢀ
Synthesis and characterization of
novel chalcone derivative is reported.
Product formation was confirmed by
FT-IR and NMR spectral studies.
First-order molecular
hyperpolarizability is estimated.
a r t i c l e i n f o
a b s t r a c t
Article history:
Single crystals of (2E,6E)-2-benzylidine-6-(4-methoxybenzylidine)cyclohexanone are grown by slow
evaporation of ethanolic solution at room temperature. The characteristic functional groups present in
the molecule are confirmed by Fourier transform infrared and Fourier transform Raman analyses. The
scanning electron microscopy study reveals the surface morphology of the material. Thermogravimet-
ric/differential thermal analysis study reveals the purity of the material and the crystal is transparent
in the visible region having a lower optical cut-off at ꢁ487 nm. The second harmonic generation effi-
ciency of as-grown material is estimated by Kurtz and Perry technique. Optimized geometry has been
derived using Hartree–Fock calculations performed at the level 6-31G (d,p) and the first-order molecular
hyperpolarizability (b) is estimated. The specimen is further characterized by nuclear magnetic resonance
spectroscopy.
Received 7 June 2013
Received in revised form 28 September
2013
Accepted 2 October 2013
Available online 11 October 2013
Keywords:
Chalcone
Nuclear magnetic resonance spectroscopy
FT-IR
Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved.
First-order molecular hyperpolarizability
Theoretical studies
Introduction
2,6-bis(benylidene)cyclohexanone was discovered as perspective
nonlinear optically (NLO) active chromophore in the crystal state
The cytotoxic, anticancer, chemopreventative and mutagenic
properties of a number of chalcones have been received [1].
and it is used in second harmonic generation (SHG) applications
[2]. Recently, we have investigated the synthesis, structure,
growth and characterization of 1,5-diphenylpenta-1,4-dien-3-
one [3] and 1,5-diphenylpenta-2,4-dien-1-one [4]. Molecular
structure investigations of 1,5-diphenylpenta-1,4-dien-3-one
have been reported [5]. As a part of our investigations on the
growth and characterization of chalcones, the title study was
2,6-Bis(arylidene)cyclohexanone is
a useful precursor for the
construction of biologically important heterocycles. In addition,
undertaken.
(2E,6E)-2-benzylidine-6-(4-methoxybenzylidine)-
⇑
Corresponding author. Tel.: +91 4144 221670.
E-mail addresses: meenas1957@gmail.com, aumats2009@gmail.com (SP. Mee-
cyclohexanone (BMBC) was synthesized, crystals grown and
characterized.
nakshisundaram).
1386-1425/$ - see front matter Crown Copyright Ó 2013 Published by Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2013.10.003

V. Meenatchi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 72–76
73
ꢁ1654 (FT-IR) and 1661 cmÀ1 (FT-Raman) are assigned to C@O
Experimental
stretching vibrations [7]. The a,b-unsaturated carbonyl and aromatic
C@C bending modes are observed at ꢁ1508 and ꢁ1442 cmÀ1 respec-
tively [8]. The aliphatic CAH stretching frequencies are observed at
ꢁ2843 and 2931 cmÀ1. The observed FT-IR and FT-Raman (Fig. 2b)
vibrational bands of BMBC are listed in Table 1.
Synthesis and crystal growth
BMBC is synthesized by mixing stoichiometric amounts of
cyclohexanone, benzaldehyde and p-methoxy benzaldehyde in
the molar ratio of 1:1:1. The reactants were dissolved in ethanol,
thoroughly mixed using a magnetic stirrer (10 min) and 20% NaOH
solution was added drop by drop at 25 °C for 30 min [6]. After stir-
ring for 3 h the contents of the flask were poured into ice-cold
water. The resulting crude solid was collected by filtration, dried
and purified by recrystallization process using ethanol as a solvent.
Purity of the compound was checked by thin layer chromatography
and melting point techniques.
NMR
1H NMR and 13C NMR spectra were recorded on BRUCKER AVIII
400 MHz NMR spectrometer operating at 400.13 MHz for 1H and
100.61 MHz for 13C using standard parameters. BMBC is dissolved
in 0.5 ml of CDCl3 solvent and TMS (tetramethylsilane) was used as
an internal standard.
CHO
CHO
O
O
Ethanol
H
HC
CH
OCH3
+
+
NaOH
OCH3
(2E,6E)-2-benzylidene-6-
(4-methoxybenzylidene)cyclohexanone
Fig. 3 shows the 1H NMR spectrum of BMBC. A sharp singlet at
3.84 ppm corresponds to methoxy proton of the phenyl group and
the doublet at 2.93 ppm, corresponding to four protons, are due to
methylene (H-3, H-5) protons of the cyclohexyl ring. Sharp singlet
at 1.80 ppm, corresponding to two protons, is due to para methy-
Single crystals were grown from an ethanolic solution by slow
evaporation solution growth technique at room temperature. A
saturated solution of BMBC in ethanol was prepared and the solu-
tion stirred for 3 h at room temperature to obtain a homogenous
solution. The solution was tightly covered with a perforated poly-
thene sheet and kept at a constant temperature in dust free envi-
ronment. Numerous tiny crystals were formed at the bottom of
the beaker due to spontaneous nucleation. Yellow colored crystals
of chalcones are harvested in a period of 7–9 days. Photograph of
as - grown BMBC crystal is shown in Fig. 1.
lene (H-4) protons of the cyclohexyl ring. a,b-Unsaturated protons
appeared as a triplet at 7.40 ppm. The multiplets in the range of
6.93–7.80 ppm are due to nine aromatic protons of the phenyl ring.
Fig. 4 shows the 13C NMR spectrum of BMBC. Weak signals at
190 and 160 ppm are due to carbonyl carbon and ipso carbon of
the methoxy substituted phenyl ring respectively. The signals at
28.5 and 23.1 ppm are due to methylene carbon of the cyclohexyl
Results and discussion
ring.
a,b-Unsaturated carbons appeared at 137.0 ppm. The aro-
FT-IR and FT-Raman
matic carbons appeared in the range of 113.9–136.6 ppm. The sig-
nal at 55.4 ppm represents the methoxy carbon of the phenyl ring.
FT-IR and FT-Raman spectra of BMBC recorded using
AVATAR 330 FT-IR by KBr pellet technique and BRUKER RFS 100/
S Instrument are shown in Fig. 2. The absorption bands at
ꢁ1601 cmÀ1 in FT-IR and 1596 cmÀ1 in FT-Raman are aromatic
C@C stretching frequencies of BMBC. The absorption bands
UV–visible study
UV–vis spectrum of BMBC was recorded using CARY 5E UV–vis
spectrophotometer. The purpose of this investigation is to find out
the transmission region and the lower optical cut-off wavelength.
The optical absorption spectrum (Fig. 5) shows good transmission
in the visible region and the lower cut-off wavelength is ꢁ487 nm
[9].
Thermal analysis
TG/DTA analysis of BMBC was carried out using NETZSCH STA
449F3 thermal analyzer in nitrogen atmosphere. TG/DTA curve of
BMBC is shown in Fig. 6. There is no physically adsorbed water
in the molecular structure of the crystal. In DTA, a sharp endother-
mic peak at ꢁ95 °C is due to the melting point of the material and
it was confirmed by using Sigma instrument melting point appara-
tus (ꢁ94–95 °C). The sharpness of the peak shows good degree of
crystallinity and purity of material. TG curve shows a single stage
weight loss at ꢁ350–475 °C and it is due to decomposition of BMBC
into fragments and its subsequent volatilization. In DTA curve the
exo and endothermic peaks observed at ꢁ375 and ꢁ425 °C could
be due to decomposition of the material.
Fig. 1. Photograph of as-grown BMBC crystal.

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V. Meenatchi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 72–76
(a)
(b)
Wavenumbers (cm-1
)
Fig. 2. (a) FT-IR and (b) FT-Raman spectra of BMBC.
Table 1
SEM
Observed vibrational bands of BMBC (cmÀ1).
FT-IR
FT-Raman
Assignments of vibration
The surface morphology of the as - grown crystals was observed
using a JEOL JSM 5610 LV scanning electron microscope with a res-
olution of 3.0 nm and accelerating voltage 20 kV. The SEM micro-
graphs at different magnifications of the as-grown BMBC (Fig. 7)
reveal structure defect centers with crystal voids.
1654
1601
1442
2843, 2931
1661
1596
1445
2836, 2947
C@O stretching
conjugatedAC@C-stretching
C@C bending modes of
CAH stretching
a,b-unsaturated carbon
Fig. 3. 1H NMR spectrum of BMBC.

V. Meenatchi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 72–76
75
Fig. 4. 13C NMR spectrum of BMBC.
Fig. 5. UV–vis spectrum of BMBC.
Temperature/° C
Fig. 7. SEM images of BMBC.
Fig. 6. TG/DTA curve of BMBC.
was used as the optical source and directed on the samples
through a filter. The grown crystals were ground to a uniform par-
Second harmonic generation efficiency
ticle size of 125–150
uniform bore and exposed to laser radiation at 8.8 mJ/pulse.
lm and then packed in a micro capillary of
SHG test was performed by Kurtz and Perry powder method
[10]. An Nd:YAG laser with a modulated radiation of 1064 nm

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V. Meenatchi et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 120 (2014) 72–76
34.164 Â 10À24 esu, 3.414 Â 10À30 esu (>12 times of urea), 3.033
D respectively (Table 2). The high value of b, a required property
for an NLO material, associated with charge transfer is due to the
Table 2
The calculated
esu), dipole moment (in D) and SHG efficiency
(output I2 in mV).
b components, btot value (in
x
behavior of nonzero
l values. The behavior of high b with a mod-
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
À427.655
50.860
25.147
À124.956
À9.922
0.191
erate SHG-activity could be associated with orientation factor. The
optimized molecular structure of BMBC is shown in Fig. 8.
Conclusions
byyz
bxzz
byxx
bzzz
44.445
19.591
10.894
40.293
3.414
3.033
5.1
10
(2E,6E)-2-benzylidine-6-(4-methoxybenzylidine)cyclohexa-
none was synthesized and grown from ethanolic solution by
slow evaporation. The product formation was qualitatively con-
firmed by FT-IR, FT-Raman and NMR techniques. Optimized
geometry by theoretical calculations is in tune with the exper-
imental observations. Defect centered morphology is observed
in SEM micrographs. Title chalcone looks like a promising
NLO material and the factors in favor of it are, a good first-order
molecular hyperpolarizability with moderate SHG-activity and
minimum absorbance in the visible region. By proper substitu-
tion, the NLO character can be engineered further.
btot (Â10À30
)
l
SHG efficiency I2
I2 (KDP)
x
x
Acknowledgments
The authors thank the Council of Scientific and Industrial Re-
search (CSIR), New Delhi, for financial support through research
Grant No. 03(1233)/12/EMR-II and V.M. is grateful to CSIR for the
award of a Senior Research Fellowship (SRF). One of the authors,
K.M. is thankful to CSIR, New Delhi, for the award of SRF.
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Fig. 8. Optimized molecular structure of BMBC.
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The calculated polarizability (
a), first-order molecular hyperpo-
larizability (b) and dipole moment (
l
) of the specimen are