Synthesis, crystal growth, studies on vibrational spectroscopy and nonlinear optical properties of 4-methoxy-4′-chlorochalcone

Article abstract of DOI:10.1016/j.materresbull.2013.11.003

Good quality organic non linear optical (NLO) crystals of 4-methoxy-4′-chlorochalcone (4MCC) have been grown by slow evaporation solution growth method. The grown crystals were investigated with various spectroscopy techniques such as the structural confi

Full text of DOI:10.1016/j.materresbull.2013.11.003

Materials Research Bulletin 50 (2014) 446–453
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Materials Research Bulletin
journal homepage: www.elsevier.com/locate/matresbu
Synthesis, crystal growth, studies on vibrational spectroscopy and
nonlinear optical properties of 4-methoxy-40-chlorochalcone
S. Prabu a, R. Nagalakshmi b, J. Balaji a, P. Srinivasan a,
*
a University College of Engineering Panruti (A Constituent College of Anna University Chennai, India), Panruti 607 106, India
b Department of Physics, National Institute of Technology, Tiruchirappalli, India
A R T I C L E I N F O
A B S T R A C T
Good quality organic non linear optical (NLO) crystals of 4-methoxy-40-chlorochalcone (4MCC) have
been grown by slow evaporation solution growth method. The grown crystals were investigated with
various spectroscopy techniques such as the structural confirmation by powder XRD. The various
vibration frequency of the crystal are investigated by factor group analysis, FTIR and FT-Raman
spectrum. The crystal has wide range of transparency in visible region investigated by UV–vis spectrum.
Using SHG powder method, the SHG efficiency of the title crystal was greater than that of urea. The
mechanical properties of grown crystal was studied by Vickers microhardness tester and the load
Article history:
Received 10 January 2013
Received in revised form 2 September 2013
Accepted 4 November 2013
Available online 11 November 2013
Keywords:
A. Optical materials
A. Organic compounds
B. Crystal growth
dependence hardness was observed. The first order hyperpolarizability (
the title compound was theoretically investigated by GAUSSIAN 03 package.
ß 2013 Elsevier Ltd. All rights reserved.
b) and HOMO–LUMO analysis of
D. Mechanical properties
D. Optical properties
1. Introduction
or acceptor groups like OCH3, SCH3, Cl, Br, etc. to enhance the
asymmetric electronic distribution in either or both ground and
excited states, leading to an increased optical nonlinearity [6]
Several donor substituted co-crystals of chalcones have been
prepared and the crystal structures have been reported [7–10].
In continuation of our work on chalcone family crystals [10], in
this investigation we report the synthesis, crystal growth and
characterization of a good NLO response chalcone crystal 4-
methoxy-40-chlorochalcone (4MCC). The title crystal has been
already reported elsewhere [11,12]. In the present article, a
thorough and systematic investigation has been performed over
the title crystal.
In modern society the organic nonlinear optical materials are
playing vital role due to their potential application in optical
switches, modulators, optical limiters, and optical data storage
[1,2] and also they have greater optical susceptibilities, and higher
optical thresholds for laser power compared to inorganic materials,
as well as inherent ultrafast response times [3]. The NLO effect in
the organic molecules originates from a strong donor acceptor
intermolecular interaction, a delocalized
p-electron system, and is
also due to the ability to crystallize in non-centrosymmetric
manner. In organic crystal research, chalcones have attracted great
attention due to their nonlinear optical responsibility and also
biological activities. The chalcone derivatives chemically consists
of open-chain flavonoids in which the two aromatic rings are
2. Experimental
connected by a three-carbon
The NLO response is greatly increased upon lengthening of the
chain of the conjugated -bridge and chalcone derivatives have
such a configuration, with two planar rings connected by a
conjugated double bond and hence, show significant nonlinearity
[5]. The chalcone derivatives also provide a well disposed synthetic
route to design a NLO active material. In these systems two
benzene rings have to be substituted with suitable electron donor
a,b-unsaturated carbonyl system [4].
2.1. Synthesis and crystal growth
p
The commercially available AR grades of chemicals were used
without further purification. A mixture of equimolar quantities of
4-methoxybenzaldehyde and 4-chloroacetophenone were taken
and stirred in ethanol (60 ml) and aqueous solution of NaOH (3%)
was added drop by drop into mixture solution. After a particular
drop, the whole solution turned out to be a precipitate. The
obtained precipitate was filtered, dried and grained. The schematic
diagram of the synthesis of the title compound is shown in Scheme
1 and molecular structure of 4MCC shown in Fig. 1. The
synthesized material was purified over and again from ethanol
solution by recrystallization process. Selection of suitable solvents
*
Corresponding author at: Department of Physics, University College of
Engineering Panruti, Panruti 607 106, India. Tel.: +91 9488046400.
E-mail address: sril35@gmail.com (P. Srinivasan).
0025-5408/$ – see front matter ß 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.materresbull.2013.11.003

S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
447
O
compound were performed at both HF (Hartree-fock) and hybrid
Density Functional B3LYP (Becke-Lee-Young-Parr) with 6-31G (d)
level used to analyze the vibrational frequency and conformational
dependent NLO activity. All calculations were performed using
Gaussian ‘03 W program package. The present work deals with the
density functional theory computations and vibrational spectral
analysis to derive information about the spectral features, nature
of hydrogen bonding, electronic effects and other molecular
interactions within the crystal.
Cl
p-chloroacetophenone
Ethanol
O
O
4-methoxy benzaldehyde
NaOH
Before calculating the hyperpolarizability for the investigat-
ed compound, the geometry taken from the starting structures
based on its crystallogrphic data was optimized in the UHF
(unrestricted open-shell Hartree-Fock) level. Molecular geome-
tries were fully optimized by Berny’s optimization algorithm
using redundant internal coordinates. All optimized structures
were confirmed to be minimum energy conformations. An
optimization is complete when it has converged – i.e. when it has
reached a minimum on the potential energy surface, thereby
predicting the equilibrium structures of the molecules. This
criterion is very important in geometry optimization. The
inclusion of d polarization and double zeta function in the split
valence basis set is expected to produce a marked improvement
in the calculated geometry [14]. At the optimized structure no
imaginary frequency modes were obtained proving that a true
minimum on the potential energy surface was found. The electric
dipole moment and dispersion free first order hyperpolariz-
ibility were calculated using finite field method. The finite field
method offers a straight forward approach to the calculation of
hyperpolarizabilities [15]. All the calculations were carried out
by using GAUSSIAN 03 package.
Cl
O
O
4-methoxy 4'-chlorochalcone
Scheme 1. The synthesis of 4MCC.
The nonlinear response of an isolated molecule in an electric
Fig. 1. The molecular structure of 4MCC.
field Ei(
v) can be represented as a Taylor expansion of the total
dipole moment mt induced by the field.
is very authoritative for the growth of good quality single crystals
[13]. After trying with various solvents, we found that N,N
Dimethylformamide (DMF) showed good solubility gradient.
Hence DMF has been used a solvent for the growth of 4MCC
crystal by slow cooling solution growth method at room
temperature. The solution of recrystallized 4MCC was prepared
at 35 8C using DMF as the solvent. The solution was housed in a
constant temperature bath (ꢀ0.1 8C) and continuously stirred using
teflon coated magnetic stirrer. When the solution was subjected to
slow cooling (0.5 8C/day), the temperature was achieved (32 8C) to
initiate nucleation and the temperature has been thereafter reduced
at a rate of 0.15 8C/day. Needle shaped crystals were harvested after
one week. The obtained crystals of 4MCC are shown in Fig. 2.
mt
¼
m0
þ
ai j ꢁ Ei þ bi jk ꢁ EiEjþ
(1)
where
a
is linear polarizability,
m
0 the permanent dipole moment
and bijk are the first order hyperpolarizability tensor components
The components of first order hyperpolarizability can be
determined using the relation
X
1
bi
¼
biii
þ
ðbi j j
þ
bji j
þ
bj ji
Þ
(2)
3 i ¼ j
Using the x, y and z components the magnitude of the total static
dipole moment ), isotropic polarizability 0), first order
(
m
(a
hyperpolarizability
following equations.
(
btotal
)
tensor, can be calculated by the
2.2. Computation details
The computational works of the equilibrium geometry, wave
number calculation and first order hyperpolarizability of 4MCC
1=2
m01 ¼ ðm2x
btot ¼ ðb2x
þ
my2
by2
þ
mz2
Þ
(3)
(4)
þ
þ
b2z Þ1=2
The complete equation for calculating the first order hyperpo-
larizability from GAUSSIAN 03 output is given as follows [16].
2
2
Þ
btot ¼ ½ðbxxx
þðbzzz
þ
bxyy
þ
bxzzÞ þ ðbyyy
þ
byzz
þ
byxx
1=2
2
þ
bzxx
þ
bzyyÞ ꢂ
(5)
The
b components of GAUSSIAN 03 output are reported in atomic
units, the calculated values have to be converted into electrostatic
Fig. 2. The single crystal of 4MCC.
units (1 a.u. = 8.3693 ꢃ 10ꢄ33 e.s.u.).

448
S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
the region of 10–808 for 2u. The powder X-ray diffraction spectrum
of 4MCC is shown in Fig. 3. All reflections could be indexed to the
orthorhombic crystal structure system and Pna21 space group. The
diffraction data were used to calculate the cell parameter value by
XRDA software and the value were obtained a = 12.7980 A8,
b = 26.2867 A8, c = 3.8899 A8 and V = 1308.644 A83. These values
are in good agreement with the literature [11].
3.2. Analysis of vibrational spectra
The room temperature mid Fourier Transform Infrared (FTIR)
spectrum of 4MCC was recorded in the region 400–4000 cmꢄ1 at a
resolution of ꢀ 4 cmꢄ1 by using Perkin Elmer Fourier transform
infrared spectrophotometer (model SPECTRUM RX1), equipped with
a LiTaO3 detector, a KBr beam splitter, He–Ne Laser source and boxcar
apodization used for 250 averaged interferogrammes collected for
both the sample and the background. KBr pellets containing a fine
4MCC powder obtained from the grown single crystals were prepared
and used as sample. The FT-Raman spectrum of 4MCC was recorded
on a BRUKER RFS 27 model interferometer. The spectrum was
recorded in the 5000–100 cmꢄ1 stokes region using the 1064 nm line
of an Nd:YAG laser for excitation operating at 100 mW (srl = 320)
power. The calculated vibrational frequency and spectrum of title
compound were performed by DFT analysis of B3LYP method with 6-
31G (d) level basic set using GAUSSIAN 03 package. The FTIR
experimental and computed spectrum of 4MCC is shown in Fig. 4, and
FT-Raman experimental and computed spectrum of 4MCC is given in
Fig. 5.
Fig. 3. The powder X-ray pattern of 4MCC.
3. Results and discussion
3.1. X-ray diffraction studies
The X-ray diffraction (XRD) structural analysis of the 4MCC
were performed on a Bruker, Germany (D8 Advance) POWDER X-
ray diffractometer with Lynx Eye detector, 2.2KW Cu anode,
ceramic X-ray tube at room temperature. The scanning was done in
Fig. 4. The FT-IR spectrum of 4MCC (a) experimental observation and (b) computed result.

S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
449
Fig. 5. The FT-Raman spectrum of 4MCC (a) experimental observation AND (b) computed result.
3.2.1. Factor group analysis
3.2.2. Hydrogen bonding
The 4MCC crystallizes in the orthorhombic system, with
Pna21(C2V) space group. As there are 32 atoms in the unit cell
(Z = 4), there are 384 branches to phonon dispersion curves. The
representation of Gtotal of all vibrations can be decomposed
according to the irreducible representation of the point group as
The hydrogen bonding plays a pivotal role in NLO activity of a
compound. The hydrogen bond bridges two atoms that have high
electro negativity (such as O, OCH3) than hydrogen. The hydrogen
bonds most often found in non-linear optical crystals of organics
involve an interaction between a hydrogen bond to sp3 methoxy or
oxygen and an oxygen atom with more s-bond character although
more symmetrical interactions also occur. The profound influences
of hydrogen bonding will be different depending on whether the
hydrogen bond is intramolecular or intermolecular and in the
latter case on the specific extent and mode of interaction. Using the
computation method calculated frequencies at 3233, 3230, 3220,
3219, 3218, 3206, 3199, 3189, 3171 and 3164 cmꢄ1 and
experimental observation of the FTIR broad band at about 3471,
G
total = 95A1 + 96A2 + 95B1 + 95B2 apart from three acoustic modes
(
Gacou = A1 + B1 + B2) are included that correspond to the block
transitions of the crystal. The formal classification of fundamental
mode predicts 360 internal vibrations which can be distributed as
(90A1 + 90A2 + 90B1 + 90B2) and 24 external modes such as
(3A1 + 3A2 + 3B1 +3B2) translational, (3A1 + 3A2 + 3B1 + 3B2) vibra-
tional modes. The results of factor group analysis are presented in
Table 1.
Table 1
Factor group analysis of 4MCC.
Factor group species C2
4-methoxy
cone C1 site
40-chlorochal-
Total modes
Optical modes
Acoustic modes
Activity
IR
v
Internal modes
External modes
C
H
Cl
O
Raman
A1
90
90
90
90
3T, 3R
3T, 3R
3T, 3R
3T, 3R
48
48
48
48
39
3
6
96
96
96
96
95
96
95
95
01
00
01
01
Tz
azxx
azxy
azxz
azyz
; ;
azyy azzz
A2
B1
B2
39
39
39
3
3
3
6
6
6
Rz
Tx; Ry
Ty; Rx
360
12T, 12R
192
156
12
24
384
381
03

450
S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
3415and 3145 cmꢄ1 are assigned due to Hydrogen bonding
between phenyl functional group.
3.2.3. C–H vibrations
The experimental result the C–H stretching vibrational bands
occurs at 3074 and 3005 cmꢄ1 in the Raman and the FTIR
counterpart is occurs at 3145 and 2972 cmꢄ1 which is good
agreement with calculated value at 3094 and 3032 cmꢄ1. The C–H
bending vibration occurs in experimental Raman and FTIR band at
1320 and 1298 cmꢄ1 respectively and calculated counterpart
frequencies appear at 1344, 1334, 1328 and 1310 cmꢄ1. In the
substituted aromatic, the C–H band out-of-plane bending vibra-
tions observation of the calculated frequency values occurs at
1038, 1028, 1024, 994, 961, 956 and 949 cmꢄ1 and the
experimental observation of the FTIR Vibrational band at 1029,
1010 and 991 cmꢄ1 and Raman counterparts appeared at 1030,
1010 cmꢄ1. The FTIR vibration band appearing at 2839 cmꢄ1 is
assigned to CH3 stretching vibration. The calculated frequency
values at 1619, 1615, 1565, 1534, 1532 and 1521 cmꢄ1 and the
experimental result, the FTIR vibrational band at 1595, 1573 and
1512 cmꢄ1 and the Raman counterparts strong band occurring at
1587 and 1565 cmꢄ1 are assigned to C55C stretching vibration.
Fig. 6. The UV–vis spectrum of 4MCC.
that the absorption cut off wavelength of this crystal is 423 nm can
3.2.4. C–O vibration
be assigned to n !
p* and may be attributed to the excitation in
the aromatic ring and C55O group [18]. For optical device
The experimental FTIR vibrational band at 1656 cmꢄ1 and
calculated frequency at 1739, 1674, 1650 and 1644 cmꢄ1 are
applications, the transparency in the near IR region is significant
assigned to C55O stretch due
a
,
b
-unsaturated carbonyl group. The
rather than the visible region because, 1.3 and 1.5 mm wavelengths
region below 1500 cmꢄ1 is the called fingerprint region. A large
number of single band vibration occur here like C–O, C–C, C–N and
which act as an identifying fingerprint of each organic molecule.
The characteristic band of C–O stretching vibrations appear in the
region 1000–1300 cmꢄ1. The experimental FTIR Vibrational band
at 1259, 1213, 1184, 1170 and 1089 cmꢄ1 and in Raman band at
1262, 1209, 1177 and 1090 cmꢄ1 are assigned to Ar–O–C stretch,
which is in good agreement with calculated frequencies at 1246,
are used in optical telecommunication systems [19]. The 4MCC
crystal has transparency in visible spectral region and this
compound may be used for NLO application in room temperature.
3.4. Powder SHG test
Quantitative measurement of relative second harmonic gener-
ation (SHG) efficiency of 4MCC with respect to well known SHG
materials KDP and Urea was made by Kurtz and Perry powder
technique [20]. The schematic representation of the used
experimental setup is shown in Fig. 7. The experimental details
of the same has been already reported elsewhere [10]. The KDP,
Urea and 4MCC were powdered and differentiated to various
1238, 1218, 1213, 1207, 1184, 1148, 1139, 1109, 1074, 1056 cmꢄ1
.
3.2.5. CH3–O vibration
The experimental, the vibrational band at 1398 cmꢄ1 in the FTIR
and the Raman counterpart vibrational band occurs at 1488, 14226
and 1398 cmꢄ1 and also calculated frequencies at 1499, 1474,
1443, 1388, 1368 and 1353 cmꢄ1 were assigned to CH3–O
stretching vibration.
particle sizes using standard sieves of 90 and 150
mm.
The beam energy of Nd:YAG laser operating at 1064 nm is set to
680 mJ/pulse. The SHG efficiency of 4MCC is found to be greater
than Urea and KDP. The SHG signal energy output values for
3.2.6. Halide vibration
particle size < 90
for 4MCC, Urea and KDP respectively and also SHG signal energy
output values for the particle size range of 90–150 m was found
to be 12.4 mJ, 8.4 mJ and 3.3 mJ for 4MCC, Urea and KDP
respectively. From the SHG output energy of 4MCC we could see
that as the particle size increases the SHG output energy also
increases. Such type of behaviour is observed only for the materials
that are phase matchable [21]. Likewise, The existence of a phase
matching direction facilitates high SHG efficiency at the phase
mm were found to be 10.13 mJ, 8.2 mJ and 2.5 mJ
The formation of 4MCC is evidenced by the presence of halide
group. The halides of C–Cl stretching modes appears in the region
of 850–500 cmꢄ1. The experimental vibration band at 812, 740,
561 and 516 cmꢄ1 in the FTIR and the Raman counterpart band
appeared at 638 and 561 cmꢄ1 and also calculated frequencies are
observed in this region. The C–Cl in plane mode vibration
frequency appear at 287, 270, 256, 237 and 198 cmꢄ1 in the
calculated value and experimental Raman band occurs at
291 cmꢄ1. The C–Cl out of plane mode vibration band appear at
168 cmꢄ1 in the experimental Raman and calculated frequencies at
m
179 and 154 cmꢄ1
.
3.3. UV-spectral analysis
The absorption spectrum for the 4MCC crystal was recorded
using Labindia UV1300 UV–vis spectrophotometer in the wave-
length range from 200 nm to 900 nm. A good optical transmittance
is very desirable in an NLO crystal since the absorptions, if any, in
an NLO material near the fundamental or the second harmonic will
lead to the loss of conversion efficiency in those wavelengths [17].
The UV–vis spectrum of 4MCC is shown in Fig. 6. From this we infer
Fig. 7. The schematic of the experimental SHG efficiency set-up.

S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
451
Table 2
matching angle. In the title compound the existence of phase
The first order hyperpolarizibility (
b
) of 4MCC derived from DFT/B3LYP calculation.
Values (a.u.)
matchable direction is confirmed by fact that the SHG energy
output varies with respect to the particle size [20,21]. The high NLO
efficiency of the sample is dependent on the molecular structure. In
4MCC molecule, the electron donating group of methoxy group is
placed in para position of the benzene ring and the acceptor groups
of Cl is placed in para position of benzene ring and the carbonyl
group (C55O) placed the middle of the molecule. The charge
b
component
bxxx
bxxy
bxyy
byyy
bxxz
bxyz
byyz
bxzz
byzz
bzzz
ꢄ1512.911571
971.2991391
50.3277972
ꢄ52.0934282
36.781817
14.4435784
transfer from methoxy donor group through
p bridge to acceptor
ꢄ2.7587053
23.710649
group thus create D- -A type molecule which plays in major role
p
12.293483
in the NLO efficiency of the title compound. Also hydrogen bonded
interaction enhances the SHG efficiency. Based on above facts we
could strongly suggest that the title compound of 4MCC can be well
used for NLO applications.
8.4607879
bTotal
bTotal
1439.448328 a.u
1.2436 ꢃ 10ꢄ29 e.s.u.
3.5. Microhardness studies
properties of many of these compounds have been investigated
by both experimental and theoretical methods [23] and also
Microhardness studies of the system have a direct correlation
with crystal structure and is very sensitive to the presence of any
other phase or phase transition and lattice perfections. Hardness of
the material depends on different crystallographic parameters
such as lattice energy, Debye temperature, heat of formation and
inter atomic spacing. Thus microhardness plays the principle role
in electron–phonon an-harmonicities due to the crucial role of
inter-molecular interactions [22].
Micro hardness studies of the 4MCC crystals were performed by
Matsuzawa (mmT-X) Vickers micro hardness tester by varying the
applied load from 1 gm to 50 gm. The indentation time was
maintained constant at 5 s. Vickers micro hardness number was
calculated by using the relation.
organic molecules, containing conjugated
p electrons are
characterized by large values of molecular first order hyperpolar-
izabilities, were analyzed by means of vibrational spectroscopy
[24,25].
The first order hyperpolarizibility (bijk) of the molecular system
of the title compound is calculated using HF/6-31G (d) basis set
based on finite field approach. Hyperpolarizibility is a third rank
tensor that can be described by a 3 ꢃ 3 ꢃ 3 matrix. It strongly
depends on the method and basis set used. The 27 components of
3D matrix can be reduced to 10 components due to Kleinman
symmetry [26]. The title compound of 4MCC was investigated for
its structural and bonding features contributing to the hyperpo-
larizability enhancement. In that direction, The calculated first
order hyperpolarizability of 4MCC is 1.2436 ꢃ 10ꢄ29 e.s.u., which is
nearly 33 times that of Urea and the dipole moment is 1.93 Debye.
Hv ¼ 1:8544 P=d2 kg mmꢄ2
The calculated first order hyperpolarizability (
moment ( ) were collected in Tables 2 and 3. The theoretical
calculation seems to be more helpful in determination of particular
components of tensor than in establishing the real values of
Domination of particular components indicates the substantial
delocalization of charges in those directions. The maximum was
due to the behaviour of non-zero value. In the case of molecules
b) and dipole
where P is the applied load in kg and d is the mean diagonal length
of the indenter impression in millimetre. Load dependence of
microhardness was carried out. The Fig. 8 shows the variation of
Hv with applied load. It was observed from the study that Vickers
hardness value decreases with increase in load which satisfies the
normal indentation size effect.
m
b
b.
b
m
with lower symmetry, it is interesting to note that an alternated
stack would necessarily result in a non-centrosymmetric chain. In
the title 4MCC molecule the non-centrosymmetric structure may
arise due to the influence of C–Hꢁ ꢁ ꢁO interaction [11]. Although
dipole–dipole interactions lead to a quasi cancellation of the
nonlinearity in the solid state, the structure proves that the
methoxy substituent can be used for promoting acentric align-
ments of chromophores through hydrogen-bonded networks. The
repeating units along the entire extent of the chain ensure nonzero
SHG efficiency. Planar molecular structure and better conditions
for electron conjugation and charge transfer also result in larger
3.6. First order hyperpolarizability
The potentiality of the compound for nonlinear optical
applications were studied from the molecular structure assemblies
and also by structure sensitive methods. Since the potential of
organic materials for NLO devices have been proven, NLO
values of
b.
3.7. HOMO–LUMO analysis
In the title molecule the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) are very
Table 3
The dipole moment (m) of 4MCC derived from DFT/B3LYP calculation.
Dipole (
m) component
Values
mx
my
mz
mTotal
1.8614063
ꢄ0.5144187
0.0411639
1.93 Debye
Fig. 8. The variation of Hv with applied load of 4MCC.

452
S. Prabu et al. / Materials Research Bulletin 50 (2014) 446–453
important parameters for quantum chemistry. The excitation
energies of molecule to calculate the simplest one involves the
difference between the highest occupied molecular orbital
(HOMO) and lowest unoccupied molecular orbital (LUMO) of a
neutral system. HOMO, which can be thought the outermost
orbital containing electrons, tends to give these electrons such as
an electron donor. On the other hand; LUMO can be thought of the
innermost orbital containing free places to accept electrons [27].
This form corresponds to the frozen orbital approximation, as the
ground state properties are used to calculate the excitation values.
The density functional methods (which are based on Hohemberg
and Kohn theorem) [28] are designed to yield total energies.
However, the orbitals in this case (Kohn–Sham orbitals) are not
electronic orbitals but mathematical arrangements and their eigen
values are not directly related to the electronic excitation energies
[29]. Nevertheless, it is often a good approximation to neglect these
formal inconsistencies and consider them as electronic orbitals and
orbital energies, as they are in the HF framework [30]. Owing to the
analogy between the highest occupied and the lowest unoccupied
Kohn–Sham orbitals and the frontier molecular orbitals, HOMO
and LUMO respectively [31–33]. To understand this phenomenon
in the context of molecular orbital picture, the molecular HOMOs
and molecular LUMOs are generated via Gaussian 03. The
conjugated molecules are characterized by a small HOMO–LUMO
energy separation which is the electronic absorption correspond-
ing to the intramolecular charge transition from the ground to the
first excited state and is mainly described by one electron
excitation from the end capping electron donor groups (HOMO)
over the electron donor group of OCH3 atom on the phenylene
group consequently the HOMO ! LUMO transition implies an
electron density transfer to Cl substituted benzene ring from OCH3
atoms.
Energy difference between HOMO and LUMO orbital is called as
energy gap that is an important stability for structures [35]. The
HOMO–LUMO energy gap of 4MCC was calculated using the HF/6-
31G (d,p) and B3LYP/6-31 (d,p) level and it reveals that the energy
gap reflects the chemical activity of the molecule as shown in
Table 4. In addition, a lower HOMO–LUMO energy gap explains the
fact that eventual charge transfer interaction is taking place within
the molecule. The HOMO–LUMO plots are given in Fig. 9.
4. Conclusion
The chalcone derivative NLO crystals of the 4MCC has been
grown successfully by slow evaporation solution growth method
at room temperature using DMF as
a solvent. The lattice
parameters obtained from powder XRD are in good agreement
with the literature. The presence of various functional groups and
intermolecular hydrogen bonding is identified and confirmed from
the factor group analysis, FT-IR and FT-Raman spectrum. The
crystal has good optical transparency in visible spectral region. The
cut off wavelength of the crystal is 423 nm. The SHG efficiency in
the Kurtz powder test increases with increasing particle size
indicating that it should be possible to phase match single 4MCC
crystals. The first order hyperpolarisability of 4MCC was found to
be 1.2436 ꢃ 10ꢄ29 e.s.u. The results of theoretical calculations are
substantiated with powder SHG measurement. HOMO and LUMO
calculations were performed for the title crystal. Based on the
above facts, it could be proposed that this material can be better
placed for optical applications.
to the efficient acceptor groups (LUMO) through
path. The charge transfer interaction between HOMO and LUMO
orbital of a structure, transition state transition of * type is
p conjugated
p–p
observed with regard to the molecular orbital theory [34]. In 4MCC,
LUMO the substitution electron acceptor group of Cl atom is placed
on the benzoyl moiety which is
p nature and the HOMO is located
Acknowledgement
Table 4
The authors acknowledge Department of Physics, B.S. Abdur
Rahman University, Chennai for their help rendered in second
harmonic generation studies.
HOMO–LUMO energy values of 4MCC calculated by HF and B3LYP methods.
Parameters
Method/basis set
HF/6-31G (d)
B3LYP/6-31G (d)
Appendix A. Supplementary data
HOMO energy (a.u.)
ꢄ0.296
0.052
-0.217
-0.076
-0.141
LUMO energy (a.u.)
Supplementary material related to this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.materresbull.
2013.11.003.
HOMO–LUMO energy gap (a.u.)
ꢄ0.244
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