An experimental and theoretical study on a novel donor-π-acceptor bridge type 2, 4, 5-trimethoxy-4′-chlorochalcone for optoelectronic applications: A dual approach

Article abstract of DOI:10.1016/j.saa.2016.09.022

In this article the authors aim is to investigate and analyze the various key parameters of an organic D-π-A type novel nonlinear optical material 2, 4, 5-trimethoxy-4′-chlorochalcone (2,4,5TMCC) through experimental and quantum chemical studies. The Clai

Full text of DOI:10.1016/j.saa.2016.09.022

An experimental and theoretical study on a novel donor-π-acceptor bridge
ꢀ
type 2, 4, 5-trimethoxy-4 -chlorochalcone for optoelectronic applications: A
dual approach
Mohd. Shkir, P.S. Patil, M. Arora, S. AlFaify, H. Algarni
PII:
DOI:
Reference:
S1386-1425(16)30539-X
doi: 10.1016/j.saa.2016.09.022
SAA 14668
To appear in:
Received date:
Revised date:
Accepted date:
10 May 2016
1 September 2016
17 September 2016
Please cite this article as: Mohd. Shkir, P.S. Patil, M. Arora, S. AlFaify, H. Algarni,
An experimental and theoretical study on a novel donor-π-acceptor bridge type 2, 4, 5-
ꢀ
trimethoxy-4 -chlorochalcone for optoelectronic applications: A dual approach, (2016),
doi: 10.1016/j.saa.2016.09.022
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ACCEPTED MANUSCRIPT
An experimental and theoretical study on a novel donor-π-acceptor bridge type 2, 4, 5-
Trimethoxy-4′-chlorochalcone for optoelectronic applications: A dual approach
a*
b
c
a
a
Mohd. Shkir , P.S. Patil , M. Arora , S. AlFaify , H. Algarni
a
Advanced Functional Materials & Optoelectronic Laboratory (AFMOL), Department of
Physics, Faculty of Science, King Khalid University, P.O. Box. 9004 Abha 61413, Saudi Arabia
b
Department of Physics, K. L. E. Institute of Technology, Opposite Airport, Gokul,
Hubbali 580 030, India
c
CSIR-National Physical Laboratory, Dr K. S. Krishnan Road, New Delhi 110012, India
Abstract
In this article the authors aim is to investigate and analyze the various key parameters of a
organic D-π-A type novel nonlinear optical material 2, 4, 5-Trimethoxy-4′-chlorochalcone
(2,4,5TMCC) through experimental and quantum chemical studies. The Claisen–Schmidt
condensation reaction mechanism was applied to synthesize the 2,4,5-TMCC compound and its
single crystal was grown by a slow evaporation solution growth (low cost) technique. The crystal
structural was confirmed by powder X-ray diffraction analysis. The robust vibrational study has
been done using FT-IR and FT-Raman spectra and its NLO activity has been discussed. The
factor group analysis was also performed. The optical absorption spectrum was recorded and the
band gap was calculated to be 2.8 eV. In Photoluminescence spectrum, an intense emission band
at ~540 nm has been observed which shows that the grown crystals can be used in green organic
light emitting diodes and laser applications. To achieve the stable ground state molecular
geometry of 2,4,5TMCC, the computational techniques were applied at different levels of theory
using 6-31G* basis set. The calculated geometrical parameters and vibrational spectra are found
to be in good agreement with the experimental results. To probe the optical properties of the title
compound the time dependent density functional theory has been applied. The excitation
wavelength was observed at ~398.63 nm calculated at B3LYP/6-31G* level of theory and found
1

ACCEPTED MANUSCRIPT
close to experimental value (i.e. 396 nm). The static first hyperpolarizability value is found to be
1
36 times higher than prototype urea molecule. Additionally, the molecular level approach was
attained as HOMO–LUMO gap and electrostatic potential maps. The DSC study reveals that the
titled material is stable up to 149 ºC. The photophysical and nonlinear optical properties suggest
that the titled material could be a better choice for the fabrication of optoelectronic devices.
Keywords: Chalcones, vibrational spectroscopy, optical properties, nonlinear optical material,
Density functional theory.
*
Corresponding author:
Dr. Mohd Shkir
E-mail: shkirphysics@gmail.com, shkirphysics@kku.edu.sa
Fax: +966 7 241 8319; Tel: +966 530683673
1
. Introduction
Nonlinear optical (NLO) materials in the form of single crystal or fiber are having enormous
applications in photonic devices which are used for carrying the information, data storage,
telecommunications, lasers, optical computers, optical sensing, lighting, energy and display,
national security and devices and manufacturing the optical systems and components etc. [1-5].
Among the large number of nonlinear optical materials, the single crystals of chalcone (1, 3-
diaryl-2-propen-1-ones) derivatives show brilliant stability, relatively short cutoff wavelengths of
transmittance, outstanding blue light transmittance [6-11], remarkable NLO or second harmonic
generation (SHG) efficiency response due to flexible intermolecular interactions [12-18], and
extraordinary optical properties along with high extinction coefficients for ultra-violet absorption
[
19-22]. These are open chain flavonoids that are broadly biosynthesized in plants and having a
variety of applications in medical and biomedical science as anti-cancer, anti-ulcer, anti-mitotic,
anti-inflammatory, anti-malarial, anti-fungal, anti - HIV and antioxidants etc. [23-30].
Furthermore, the chalcone molecules with a π-conjugated arrangement provide a large charge
2

ACCEPTED MANUSCRIPT
transfer axis in which on two aromatic rings the opposite groups of molecules act as donors and
acceptors and use to transfer the charge [31, 32]. Due to such significant importance of
chalcones, in recent past the NLO properties of a series of chalcone derivatives have been
studied experimentally and shown inspiring result to be applied in the future device like
nonlinear frequency conversion and optical limiters [12, 17, 33-36]. Therefore, it is necessary to
grow the good quality single crystals of such kind of materials and also to build up such devices
for future applications, it is essential to figure out the principal chattels concerning their
structural and electronic origin of the optoelectronic properties. The density functional theory
(DFT) has been found to be extremely effective and computationally unpretentious for
elucidation the above key properties in an enormous class of materials such as from atoms and
molecules to crystals and complex lengthened structures including liquids and glasses. Because
of such effectiveness of DFT method it has established as common machination in first-
principles computation aimed at to visualize and illustrate the key functions of molecular and
solid state design. The density functional theory offers unique spectra for every definite
compound to identify the constituents and given the information about the molecular structure,
conformation, functional groups and inter and intra-molecular exchanges. In recent the Hartree-
Fock (HF) and density functional theory (DFT) studies has been performed on a variety of
organic, semiorganic, inorganic, chalcones, and their complexes and interconnected well with
experimental reports [15, 37-56]. Recently, we have studied the experimental and theoretical
properties on 1-(4-bromophenyl)-3-(2,4,5-trimethoxyphenyl) prop-2-en-1-one (2,4,5 TMBC)
chalcone derivative[15]. Here we have chosen a another relatively new chalcone derivative 2, 4,
5
-Trimethoxy-4′-chlorochalcone (2,4,5TMCC) [see chemical structure in Figure 1] of D-π-A
type structure reported by Patil et al., and shows its importance in optoelectronic devices [57,
3

ACCEPTED MANUSCRIPT
5
8]. In their report they have found that the 2,4,5TMCC molecule possess high second harmonic
generation as it is 4.3 times higher than standard urea molecule as well as that many other
previously reported chalcone derivatives [15, 59, 60]. Due to such exceptional properties of
2
,4,5TMCC molecule it seems to be necessary and justified for further studies from various
applications point of view and also to have deep understanding of it.
Figure 1: Chemical structure of 2, 4,5TMCC molecule.
Consequently, as per the current available literature there is no report on its relationship between
experimental and theoretical investigations. In the current work, we have performed both
experimental and theoretical studies on 2,4,5TMCC in details as these are essential components
to have bottomless understanding of it for various photonic device applications. In experimental
part, the single crystal were grown by a simplest route and subjected to FT-IR, FT-Raman, ultra
violet-visible-near infrared (UV-VIS-NIR), Photoluminescence (PL) and thermal etc. studies.
Furthermore, the unique and cost effective computational methods has been applied to evaluate
the molecular structure, photophysical and nonlinear optical properties and compared with the
experimental findings.
2
. Experimental details
4

ACCEPTED MANUSCRIPT
The synthesis and single crystal growth of 2,4,5-TMCC was attain by taking and mixing the
calculated amount of 2,4,5-trimethxybenzaldehyde (0.01 mol) with 4-chloroacetophenone (0.01
mol) each in 50 ml ethanol in the presence of catalytic NaOH solution (5 mL, 20%)as per the
previously reported procedure [57, 58].
Further, the grown crystals were subjected to FT-IR spectroscopy measurement in the
-1
wavenumber range of 4000–400 cm using a NICOLET 6700 FT-IR spectrometer with the
-1
resolution of 4 cm at room temperature. The FT-Raman spectroscopy measurement was carried
out on grown crystal at THERMO SCIENTIFIC, DXR FT-RAMAN spectrometer in the
-1
wavenumber range of 3500–9 cm using a green laser of wavelength and power of 532 nm and 2
-1
mW, at estimated resolution 5.1 to 8.3 cm and size of the aperture pinhole was kept 50 μm.
The optical absorbance of the grown crystals was recorded using a JASCO V-570 UV-VIS-NIR
spectrophotometer in the wavelength range of 190-1300 nm at room temperature and optical
parameters such as optical transparency and optical band gap was calculated.
The photoluminescence (PL) spectrum of titled material was documented using a Lumina
fluorescence spectrophotometer (Thermo Fisher Scientific) having PMT of voltage 700V, in the
wavelength range of 400 – 750 nm at room temperature. The spectral bandwidth was kept 1 nm
for emission monochromator.
Thermal analysis was carried out on the titled compound using DSC (SETARAM)measurement
in the range of 34 to 300 ºC at the heating rate of 10 °C/m.
3
. Computational details
GAUSSIAN 09 program [61] was used for all the theoretical calculations of the titled molecule
by taking the initial geometrical data from its crystal structure report (CCDC-624172) [58]. The
stable molecular geometry 2,4,5TMCC molecule has been obtained using B3LYP (Becke’s three
5

ACCEPTED MANUSCRIPT
parameter exchange functional B3 combined with Lee-Yang-Parr correlation functional LYP)
[
62, 63] with 6-31G* basis set. The stability of the optimized geometry was further confirmed by
evaluating their analytical frequencies using B3LYP as well as Hartree-Fock (HF) at same basis
sets. The foremost advantages these methods are to establish and imitate the sensible and precise
molecular geometries, vibrational frequencies. For calculating the electronic properties of the
titled compound we have applied five different methods such as hybrid functionals B3LYP,
PBE0 [64] and MO6 [65], long range corrected functionals CAM-B3LYP [66] and wb97xd [67].
These methods are proficient in computing the electronic properties which are greatly better than
the conventional methods [41, 43, 44, 47, 48, 68-72]. Gauss view 5 visualization program [73]
was used to visualize all the obtained results. It is well known that the range separated
functionals are greatly reliant on the range separation parameters. Therefore there is a way to
eliminate these uncertainties is to tune the range separation parameter particularly for donor-
acceptor complexes [74, 75]. In addition, these techniques may well correlate the theoretical
calculations with experiment. The obtained results by all the applied methods were compared
and discussed.
The values of total static first hyperpolarizability ( tot ) and its components were calculated using
finite field (FF) approach at different levels of theory. This approach has been extensively
applied to compute the value of first hyperpolarizability of organic, inorganic as well as
semiorganic molecules and offers stable results. In FF approach, usually a static electric field (F)
is applied and the energy (E) of the subjected molecule has been stated as per the following
equation:
ꢈ
ꢈ
ꢈ
ꢁꢂꢃ
ꢀ
ꢄꢅ ꢇ ꢄ ꢊ ꢇꢇ ꢄ ꢎ ꢇꢇꢇ ꢄ
ꢑ ꢇꢇꢇ ꢇ ꢄꢓꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢈꢃ
ꢋꢌꢏꢒ ꢋ ꢌ ꢏ ꢒ
ꢆ ꢆ
ꢋꢌ ꢋ ꢌ
ꢋꢌꢏ ꢋ ꢌ
ꢏ
ꢉ
ꢍ
ꢉꢐ
6

ACCEPTED MANUSCRIPT
Here the total energy of molecule in the absence of an electronic field, vector component of the
(0)
dipole moment, linear polarizability, second and third order polarizability are represented by E ,
and respectively, while x, y and z label the i, j and k components, respectively.

,

,


For obtaining the values of μ, α, β, and γ it can be seen from Eq.1 that differentiating E with
respect to F. In the current work we have determined the values of electronic dipole moment (ꢅ),
molecular polarizability (ꢊ) and first hyperpolarizability (ꢎ).
The dipole moment (μ) is defined as follows:
ꢚ
ꢛ
ꢖ
ꢖ
ꢖ
ꢅꢀꢁꢅ ꢗꢅ ꢗꢅ ꢃ ꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢉꢃ
ꢕ
ꢘ
ꢙ
The average polarizability (ꢊ ) can be evaluated by:
ꢂ
ꢈ
ꢊ ꢀ ꢁꢊ ꢗꢊꢘꢘ ꢗꢊ ꢃꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢜꢃ
ꢂ
ꢕꢕ
ꢙꢙ
ꢜ
The anisotropy of polarizability (ꢝꢊ) can be calculated by:
ꢈ
ꢖ
ꢖ
ꢖ
ꢖ
ꢝꢊꢀ
ꢟꢠꢡꢊ ꢄꢊ ꢢ ꢗꢔꢡꢊ ꢄꢊ ꢢ ꢗꢁꢊ ꢄꢊ ꢃ ꢗꢍꢊ ꢣꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢐꢃ
ꢕꢕ ꢘꢘ ꢘꢘ ꢙꢙ ꢙꢙ ꢕꢕ ꢕꢙ
ꢞꢉ
The resultant of total static first hyperpolarizability (β ) value can be calculated by:
tot
ꢖ
ꢖ
ꢖ
ꢎꢤꢥꢤ ꢀꢟꢡꢎ ꢗꢎ ꢗꢎ ꢢꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢦꢃ
ꢕ
ꢘ
ꢙ
Where β , β and β are:
x
y
z
βx = (βxxx + βxxy + βxyy)
β = (β + β + β )
y
yyy
xxz
yyz
β = (β + β +β )
z
xzz
yzz
zzz
Hence,
ꢎꢤꢥꢤ ꢀꢔꢟꢠꢡꢎꢕꢕꢕ ꢗꢔꢎꢕꢕꢘ ꢗꢎꢕꢘꢘꢢ ꢗꢔꢡꢎ
ꢖ
ꢖ
ꢖ
ꢗꢔꢎꢕꢕꢙꢗꢔꢎꢘꢘꢙꢢ ꢗꢔꢡꢎꢕꢙꢙꢗꢔꢎꢘꢙꢙ ꢗꢎꢙꢙꢙꢢ ꢣꢔꢔꢔꢁꢍꢃ
ꢘꢘꢘ
7

ACCEPTED MANUSCRIPT
The static first hyperpolarizability or second-order polarizability (β) is a third rank tensor which
can be illustrates by a 3 × 3 × 3 matrix. As per rule of Kleinman symmetry (β = β = β ,
xyy
yxy
yyx
β = β = β ,… likewise other permutations also take similar value), the 27 components of the
yyz
yzy
zyy
3
D matrix can be reduced to 10 components (the details are presented in Table 4) [76]. In the
same way, the time dependent density functional theory (TD-DFT) has been applied to evaluate
the values of transition energies of titled molecule using all above explained methods.
4
. Results and discussion
4
.1. X-ray diffraction analysis
Powder X-ray diffraction pattern of grown crystals was recorded using a Shimadzu X-600 Japan
powder X-ray diffractometer (PXRD) at the scan rate of 0.02º/m over the angular range of 5° ≥
2
ꢧ≥ 70° at 300K as shown in Figure 2 with hkl indexing. The highly crystalline nature of the
grown crystals has been confirmed by sharpness of the peaks and their intensity. The recorded
data was further used to calculate the lattice parameters and confirm the crystal system. The
crystal system is found to be orthorhombic with space group P2 2 2 and lattice parameters are
1
1 1
found to be a= 7.02950 Å, b= 10.51419 Å and c= 22.24292 Å and unit cell volume 1643.96357
3
Å which are in great agreement with the reported values [58]. The density of the grown crystals
-3
was also calculated and found to be 1.344 mg m .
8

ACCEPTED MANUSCRIPT
1
1
1
1
500
350
200
050
9
7
6
4
3
1
00
50
00
50
00
50
0
5
10 15 20 25 30 35 40 45 50 55 60 65 70
o
Angle 2
Figure 2: Powder X-ray diffraction pattern of 2,4,5TMCC crystals
.2. Molecular Geometry analysis
4
The optimized geometry of 2,4,5TMCC molecule has been shown in Figure 3 (a) obtained at
B3LYP/6-31G* level of theory. Additionally the geometry optimization was also performed at
other levels of theory [see supplementary information Figure 1S (a-e)]. The achieved
theoretically optimized molecular geometry is found to be in good agreement with the
experimentally obtained geometry [Figure 3(b)]. The calculated values of bond lengths and
angles of the titled molecule are found to be in very good agreement to the experimentally
reported values of current as well as other similar kind of molecules [15, 58, 77].
9

ACCEPTED MANUSCRIPT
Figure 3: Molecular geometry of 2,4,5TMCC molecule (a) Optimized at B3LYP/6-31G* level
of theory and (b) experimentally observed (ORTEP diagram)
The 2,4,5TMCC molecule possess two intra-molecular hydrogen bonding between O(2) and
H(19) with bond length 2.332 Å and O(1) and H(19) with bond length 2.433 Å calculated by
B3LYP, while these values by HF are 2.364 Å and 2.448 Å, by CAM-B3LYP are 2.314 Å and
2
2
.378 Å, LC-BLYP are 2.314 Å and 2.378 Å, by wb97xd are 2.346 Å and 2.436 Å, by MP2 are
.332 Å and 2.433 Å, by PBE0 and MO6 are 2.332 Å and 2.433 Å,, respectively. All these
values are in fine relation with the experimental values. As shown in figure 3(a) that in
,4,5TMCC molecule two methoxy group are attached at C(24) and C(25) are almost coplanar
2
with attached aryl group of benzene ring C(32)-O(3)-C(24)-C(22) and C(36)-O(4)-C(25)-C(26).
The third methoxy group attached at C(21) is twisted away from atom C(20) and C(21) of aryl
group of benzene ring. As per the experimental findings reported by Patil et al., [58] the crystal
10

ACCEPTED MANUSCRIPT
structure of the titled molecule has been stabilized by C—Hꢓπ intermolecular interactions
involving the C(12) and C(14) benzene ring centroid Cg1 and Vander wall forces.
4
.3. Vibrational (Experimental and theoretical) study
To recognize the existence of various kinds of functional groups, bonding as well as to
understand different molecular conformations and reaction mechanism the Infrared (IR) and
Raman spectroscopy methods are very helpful through tentatively assigning their critical
vibrational modes [78-85]. The variation in the position of vibrational bands is particularly
explained in terms of the alteration in crystalline field effect rouse electronic effects, bonding of
hydrogen and Fermi resonance Electronic effects occurs due to back donation and induction of
bonded groups exists in any molecule. It is well known that when H atom and N, O or F atoms
are present within the molecule or between two molecules, the intermolecular and intramolecular
hydrogen bonding appears. The modes of vibration in two phenyl rings will vary in wave number
and the magnitude of splitting will be dependent on the strength of interaction between different
parts of the two rings. This splitting is too small for some that they may be considered as quasi-
degenerate and a significant splitting is found for the other vibration modes.A comprehensive
experimental and theoretical vibrational analysis has been performed on 1-(4-Chlorophenyl)-3-
(2,4,5-trimethoxyphenyl)prop-2-en-1-one or 2, 4, 5-Trimethoxy-4′-chlorochalcone (2,4,5 TMCC,
molecular formula: C H ClO , acquire orthorhombic structure with lattice Parameters: a =
1
8
17
4
7
.0295 (4) Å, b = 10.5127 (6) Å, c = 22.2438 (13) Å, Space group: P2 2 2 , Z= 4 number of
1 1 1
molecules per unit cell) molecule.
It is well known that for the analysis of spectra of solids the site group and the factor group are
key factors in group theoretical methods. Moreover, the factor group analysis method offers a
foundation for the prophecy of theoretical lattice vibrations and can be acquired by IR and
11

ACCEPTED MANUSCRIPT
Raman spectral analyses. The titled molecule belongs to orthorhombic crystal system with space
2
group P2 2 2 (D ) with four numbers of molecules per unit cell present at C site symmetry and
1
1 1
4
1
C2v factor group symmetry. Rousseau et al. [86]factor group analysis method is used for this
crystal IR and Raman vibrations analysis. TMCC single molecule consists of 40 atoms and its
unit cell contains (40×4) 160 atoms. According to Group theory, it has total 480 vibrational
optical modes which can be given: 480 = 120A + 119B + 119B + 119B apart from three
1
2
3
acoustic modes B +B +B . The symmetry of the factor group analysis of TMCC is given in
1
2
3
Table 1.
Table 1 Factor group analysis of 2,4,5 TMCC crystal
Factor
Site Symmetry
External Internal
114
C
H
O
4
Cl Optical Acoustic
Modes Modes
Activity
Total
120
Group
4
18
17
IR Raman
(
D )
2
A
54
51
12
3
120
0
 ,
xx
yy, zz
B1
B2
B3
3T 4R
3T 4R
114
114
114
54
54
54
51
51
51
12
12
12
3
3
3
120
120
120
480
1
1
1
3
Z
Y
X
xy
xz
yz
119
119
119
477
3T
4R
Total
9T 12R
456
216 204 48 12
The basic modes of vibrations of 1-(4-Chlorophenyl)-3-(2,4,5-trimethoxyphenyl)prop-2-en-1-
one achieved theoretically reveals 456 internal vibrations and 24 external modes. The external
modes are categorized into 9 translational and 12 rotational modes apart from 3 acoustic modes.
-1
The bands between the wavenumber range of 4000 - 400 cm region arise from the internal
vibrations of the different groups present in TMCC. A( ,  ,  ), B ( ), B ( ) and B ( )
xx
yy
zz
1
xy
2
xz
3
yz
symmetry components are Raman active and B (zz), B (yy) and B (xx) are IR active [87], their
1
2
3
correlation is shown as follows:
12

ACCEPTED MANUSCRIPT
Further the optimized values of lattice parameters were used in the evaluation of vibrational
frequencies. No imaginary frequency has been found in the calculated vibrational frequencies,
which shows that the optimized molecular geometry of titled molecule is located at the local
minimum point of the potential energy surface. The scaling factor was applied for the calculated
spectra [for B3LYP it was 0.9613 and for HF it was 0.8929][15] to compare with experimental
results. The theoretically calculated (at B3LYP/6-31G* level of theory) and experimentally
recorded FT- IR and FT- Raman spectra are shown in Figure 4 (a1,b1) and (a2,b2) respectively.
Here B3LYP and HF both the methods have been applied using same basis set to obtain the
infrared (IR) and Raman spectra.The experimental and theoretical IR and Raman spectra
examination of 2,4,5-TMCC crystal has done on the basis of the typical vibrations of the various
functional groups available in the molecule such as: methoxy, carbonyl, methyl, phenyl ring with
ortho- and para-substitution, chloro-phenyl group and prop-2-en-1-one bridge. The entire
investigation of obtained vibration peaks pertaining to different functional groups are discussed
in the following sections:
4
.2.1. Phenyl ring vibrations
13

ACCEPTED MANUSCRIPT
2
,4,5 TMCC molecule contains two phenyl rings bonded at 1 and 3 position of prop-2-en-1-one
as 4-Chlorophenyl (ring1) and 2,4,5-trimethoxyphenyl (ring2) groups. It is well known that
benzene ring has D symmetry and acquire C site symmetry in crystal lattice which permits
6
h
2v
activation of its all twenty vibrations in IR and Raman vibrational spectra. The logical
Herzberg’s numbering scheme has been employed for tentative assignment of phenyl ring modes
[
84, 85]. The C-H stretching vibrations in 2,4,5 TMCC phenyl ring are observed in 3100-2990
-1
cm region. The non-degenerate 1(a ) and 5(b ) vibrations of benzene C-H stretching modes
1
g
1u
-1
are obtained at [3085 (exp.), 3075 (HF), 3108 (B3LYP) cm ], [2999 (exp.), 3046 (HF), 3047
-1
-1
(
B3LYP) cm ] in IR spectra and at [3085 (exp.), 3075 (HF), 3108 (B3LYP) cm ], [3034 (exp.),
-1
3
053 (HF), 3047 (B3LYP) cm ] in Raman spectra respectively as very weak bands. The low
intensity of these peaks is attributed to stearic hindrance caused by conjugated structure and
charge carrier localization in twisted phenyl rings. The C-C asymmetric stretching vibration of
-1
e (16) mode of two phenyl rings are observed at [1681, 1654 (ring1), 1512 (ring2) cm ] (exp.),
2
g
-1
-1
1
532 (ring2) cm (HF), [1687 (ring1), 1514 (ring2) cm ] (B3LYP) in IR transmission spectra
-1
and at [1683, 1650 (ring1), 1510 (ring2) cm ] (exp.), 1532 (ring2) (HF) in Raman spectra. The
minor variation in C-H stretching modes peak position for these two rings mode are not
substituent dependent as they have different bonding groups and at nearly same frequencies. IR
-1
transmission spectra shows C-H ring stretching mode at [1610, 1590, 1577 cm ] (exp.), 1617
-1
-1
cm (HF), 1576 cm (B3LYP),while in Raman spectra C-H ring stretching mode is obtained at
-1
1
577 (exp.), 1617 (HF), 1576 (B3LYP) cm . The interaction between C-C stretching and C-H
in-plane bending vibrations results in appearance of number of peaks in both IR and Raman
-1
experimental and theoretical spectra in the region 1500-1100 cm . C-C symmetric stretching e
1
u
-1
-1
(
13) vibration mode expected at ~ 1450 cm and b (9) vibration mode at ~ 1300 cm for these
2u
14

ACCEPTED MANUSCRIPT
-1
two phenyl rings are observed at [1410, 1398 (ring1), 1326 (ring2) cm ] (exp.), [1403 (ring1),
-
1
-1
1
1
317 (ring2) cm ] (HF), [1398 (ring1) cm (B3LYP) in IR transmission spectra and at [1408,
-1
-1
395 (ring1), 1321 (ring2) cm ](exp.), [1403 (ring1), 1317 (sh) (ring2) cm ] (HF) and 1398
-1
(
ring1) cm (B3LYP) in Raman experimental and theoretical spectra. The intensity variation
between the two phenyl rings C-C stretching vibrational modes is explained on the electron
withdrawing or donating effects arising from three methoxy and one chloro groups bonded to the
two phenyl rings present in this crystal structure. The b2u (9) mode vibration is observed as
-1
-1
strong band at 1363 cm and 1360 cm in IR and Raman (exp.) spectra respectively. The
simultaneous activation of the phenyl ring e (16), e (13) and b (9) IR and Raman vibrational
2
g
1u
2u
modes confirms the charge transfer from electron donating methoxy group to phenyl ring -
system to facilitate easy transfer of electron within crystalline network. In tetra-substituted
benzene, the C-C-H in-plane bending modes of a2g (3), e2g (17)a, e1u (14)a and e1u (14)b
-1
vibrations are observed in 1300–1000 cm [83] region where a and b are assigned for higher and
lower wavenumbers respectively doubly degenerate e vibrations. The strong band in IR at 1189
-1
cm corresponds to ring vibration of e (14)b mode. While e (17)a vibration mode is observed
1
u
2g
-1
as a very weak band in Raman (exp.) spectrum at 1187 cm . The higher intensity in (exp.)
spectra as compared to theoretical spectra has been attributed to the presence of strong electron
donor substituent (OCH groups) [78, 79, 83] which strongly interact with the phenyl ring. The
3
-1
out-of-plane C-C-H bending vibrational modes are obtained in 1000–675 cm [79, 83, 88]
-
region. The C-C-H out-of-plane e (19) bending vibration is obtained as a weak band at 856 cm
2
u
1
-1
and 855 cm in IR and Raman (exp.) spectra respectively. The e1g (11)a vibration modes
-1
-1
corresponding to are observed as medium intensity and weak band at 744 cm and 745 cm in
IR transmittance (Exp.) and Raman spectrum respectively. These results are in agreement with
15

ACCEPTED MANUSCRIPT
the theoretical results. As evident from PED, the symmetric and asymmetric, puckering and
trigonal deformation modes of phenyl ring 1 and ring 2 are highly coupled modes.
4
.2.2. Chloro-phenyl vibrations
-1
The stretching mode of chloro phenyl (Cl-C H ) group is expected at ~ 1100 cm , in these
6
4
-1
-1
spectra as strong peak at 1091 cm IR (exp.) and as weak peak at 1102 cm in Raman (exp.)
-1
spectra. The asymmetric stretching vibrations C-Cl occur in 900 - 700 cm region. In IR (exp.)
spectrum, the asymmetric stretching peaks on interaction with phenyl ring pertaining to HC=C-
-1
Cl, C-Cl and HC-C-C-Cl bonding groups are found at 830 and 813 cm respectively. The
-1
theoretical HF and B3LYP calculated IR peak position for this mode are at [839, 817 cm ] and
-1
[
821, 805 cm ] respectively. Similarly in Raman (exp.), (HF) and (B3LYP), the symmetric
-1
-1
stretching modes of C-Cl bonded groups appear at [832, 817 cm ], [846, 817 cm ] and [851,
-1
-1
8
28 cm ] respectively. C-Cl vibrational mode at 832 cm has dominating contribution. Besides
-1
C-Cl symmetric stretching modes is observed at 660, 651, 628 cm in (exp.) IR transmission
spectrum. The removal of degeneracy among these components arises from the phenyl ring
contribution and low site symmetry in crystal lattice. The C-Cl in-plane and out of plane bending
-1
vibrations are predicted in the region 550-250 cm in both calculated FTIR and FT-Raman
spectra. The C-Cl out-of-plane bending vibrations are assigned in FT-Raman spectra as a strong
-1
band at 269 and 375 cm .
4
.2.3. Hydroxyl group vibrations
The hydroxyl (OH) or hydrogen bonded group vibrations are very sensitive to the environment,
which effects its peak position, intensity and shape. The free hydroxyl group absorbs strongly in
-1
the region 3600–3300 cm , while hydrogen bonded O-H stretching vibrations appears in 3500–
-1
3
100 cm region as a broad absorption/transmission band pertaining to intermolecular or intra-
16

ACCEPTED MANUSCRIPT
molecular hydrogen bonding in molecule. The asymmetric stretching vibration of O-H group is
-1
-1
obtained as broad transmission band in 3600 – 3300 cm region with maximum at 3455 cm .
The presence of this peak confirms the atmospheric moisture. While, hydrogen bonded of ketone
-1
and methoxy oxygen group shows peaks at 3297 cm in IR(exp) transmission spectrum. In
-1
Raman (exp.) spectrum this mode appeared at 3157 and 3139 cm . The O-H bending vibration
interacts with phenyl ring C-C stretching and C-H bending vibrations which may result in the
shift in peak position. The O-H out-of-plane bending vibrations are obtained in IR spectra at
-
1
-1
-1
-1
[
[
717, 690 cm ] (exp.), 735 cm (B3LYP) and at [724, 713 cm ] (exp.), [732, 703 cm ] (HF),
-
1
735, 704 cm ] (B3LYP) in Raman spectra. The calculated values for these vibrations are in
good agreement with the experimental ones. The C=O..H stretching mode is appeared at [1295,
-1
-1
1
278 cm ] and [1287, 1274 cm ] in (exp.) IR transmission and FT Raman spectra respectively.
The existence of C=O stretching mode in these spectra confirms of the hydrogen bonded enol
form in this crystal.
4
.2.4. Methoxy group vibrations
In 2,4,5 TMCC molecule, three methoxy groups are bonded at 2, 4 and 5 positions in phenyl
ring, the electronic charge is back donated from the oxygen lone pair to the of C-H bonds which
weaken C-H bonds due to increase in C-H bond length and the decrease in force constant. The
CH asymmetric and symmetric stretching vibrations are observed as strong peak at [2999],
3
-1
-1
[
2952, 2929] cm and [3034], [2934] cm in IR transmission and Raman (exp.) spectra
respectively. In theoretically calculated spectra, these stretching vibrational peaks appeared at
-
1
-1
-1
[
(
3046], [2925] cm (HF), [3047], [2916] cm (B3LPY) IR transmission and [3053], [2925] cm
-1
HF), [3047], [2916] cm (B3LYP) Raman spectra. Methyl group bending modes calculated
-1
-1
-1
values 1482 cm (HF), 1475 cm (B3LYP) for IR transmission spectra and at 1460 cm (HF),
-1
1
475 cm (B3LYP) respectively in Raman spectra. C=O..H bending vibration appears as a
17

ACCEPTED MANUSCRIPT
-1
-1
medium intensity at 1745 cm and 1744 cm in (exp.) IR transmission and Raman spectra of
-1
this sample. The very strong broad transmittance peaks in 1225 – 1150 cm region with
-1
components at 1216, 1205, 1172 cm are tentatively assigned to C-H
and CH3rock modes as
bend.
-1
observed (exp.) IR transmission spectrum. The peak components at 1216 and 1205 cm are
-1
attributed to C-Hbend.modes. While the peak component at 1172 cm is tentatively assigned to
CH rocking mode. When the CH group is directly attached to an oxygen atom, the C-H
3
3
stretching and bending bands peak position shifts due to change in crystalline field effect
depending upon the nature of bonded substituting groups present in molecule. This may result in
the wide spread of O-CH stretching bands over a larger region than that of C-CH group. In the
3
3
-1
present case, this spreading is observed between 1100 and 950 cm . The vibrational peak
pertaining to C-O and O-C stretching modes are obtained in (exp.) IR transmission spectrum
str.
str.
-1
as medium intensity peaks at [1041, 1029] and [1010, 991] cm respectively. The C-O-CH in
3
-1
plane bending vibration is observed as a greatly mixed mode in the region 600–200 cm . The O-
-1
CH torsion mode has been calculated at 296, 237 cm and found to be in good match with the
3
-1
peaks observed at 318, 241 cm in FT-Raman spectra. The current mode is attached with phenyl
ring torsion modes and the torsion about C-C bonds bridging the two phenyl rings.
4
.2.5. Methylene group vibrations
C-H stretching vibration of the methylene group is at low frequencies than those of the
aromatic C-H ring stretchings. The asymmetric CH stretching vibrations are generally observed
2
-1
in the region of 3000 of 2900 cm ,while the CH symmetric stretching found in the region of
2
-1
3
000-2900 cm . In the current study the CH asymmetric and symmetric stretching vibrations
2
-1
-1
are observed at [2975], [2867] cm and strong peaks observed at [2975], [2867] cm in FT-
IR/FT-Raman spectra by both the computational method. The four bending vibrations of the
18

ACCEPTED MANUSCRIPT
methylene group are referred as scissoring, twisting, wagging and rocking. The scissoring mode
-1
is distinguished by the strong IR band at 1475 cm and the FT-Raman band at the same value
-1
which is computed at 1436 cm . The vibrational modes subsequent to the twisting, wagging and
-1
rocking of the methylene group emerge in the region 1200–900 cm . C-H in-plane bending
-1
vibrations are identified at 1151 and 1128 cm and three C-H out-of-plane bending vibrations are
-1
found at 950 and 904 cm . As per the available literature, the in-plane and out-of-plane bending
vibrational frequencies are established to be well within their attributed regions.
4
.2.6. Understanding NLO activity through Vibrational Spectroscopy
The vibrational spectroscopy has been successfully used to reveal Non-Linear Optical
(NLO) activity possessing -conjugated systems present in a single crystal molecule. Such
molecules have large second order molecular polarizabilities which activate of some modes in IR
as well as Raman spectrum. In 2,4,5 TMCC crystal, 16, 13 and 9 phenyl ring modes are observed
in both IR and Raman spectra. They play vital role in NLO activity of the crystal. The C-C
asymmetric stretching e2g (16) mode of two phenyl rings are observed at [1681, 1654 (ring1),
-1
-1
1
512 (ring2) cm ] and [1683, 1650 (ring1), 1510 (ring2) cm ] (exp.)in IR and Raman (exp.)
spectra respectively. While C-C symmetric stretching e (13) and b (9) vibration modes phenyl
1
u
2u
-1
-1
ring are expected at ~ 1450 cm and ~ 1300 cm for these two phenyl rings are observed at
-1
[
1410, 1398 (ring1), 1326 (ring2) cm ] in IR (exp.) spectrum and at 1408, 1395 (ring1), 1321
-1
(
ring2) cm ]in Raman(exp.) spectrum. The b (9) mode vibration is observed as strong band at
2u
-1
-1
1
363 cm and 1360 cm in IR and Raman (exp.) spectra respectively. The simultaneous
activation of the phenyl ring e2g (16), e (13) and b (9) IR and Raman vibrational modes
1u
2u
confirms the charge transfer from electron donating methoxy group to phenyl ring -system to
facilitate easy transfer of electron within crystalline network.
19

ACCEPTED MANUSCRIPT
1
20000
00000
Theor_Raman
Exp_Raman
(a2)
40000
38000
2
1
1
00
50
00
(b2)
1
3
6000
80000
60000
40000
20000
34000
32000
30000
28000
26000
3
500
3400
3300
3200
3100
3000
2900
2800
5
0
0
1
800 1600 1400 1200 1000 800
600
400
200
0
3000
2500
2000
1500
1000
1)
500
0
-1
-
Raman shift (cm )
Raman shift (cm
3000
2500
2000
1500
1000
500
0
100
Exp_IR
0
90
500
80
7
6
5
4
3
2
0
0
0
0
0
0
1
1
2
2
3
3
4
000
500
000
500
000
500 (a1)
10
0
(b1)
Theor_IR
000
3
500
3000
2500
2000
1500
-1
1000
500
3000
2500
2000
1500
1000
500
0
-
1)
Wavenumber (cm
Wavenumber (cm
)
Figure 4: Estimated and experimental FT-IR (a1 & b1) and Raman (a2 & b2) spectra of 2, 4, 5-
Trimethoxy-4′-chlorochalcone
4
.3.Opto-electronic properties
4
.3.1. UV-vis.-NIR spectroscopic study
To know the appropriateness of any materials to be used in optoelectronic device it is essential to
examine the optical absorption or transmission phenomenon of light in it. Hence, the UV-vis.-
NIR spectrum of 2,4,5TMCC crystals was recorded from which we can get the vital evidence
about its structure, as it is know that the absorption of UV-VIS light engaged with the promotion
of electrons in σ and π orbitals from the ground to higher energy states. To fabricate the
optoelectronic device from any nonlinear optical material it must have wide range of optical
20

ACCEPTED MANUSCRIPT
transparency window, thus it seems to be compulsory to study the UV-vis.-NIR spectrum. The
recorded UV-vis.-NIR absorbance spectrum of 2,4,5TMCC crystals has been shown in Figure
5
1
(a). From figure it is confirmed that the grown crystal is having very low absorbance in 500-
300 wavelength range. This indicates that the grown crystal is highly transparent which makes
it suitable to be used in optical window for SHG laser radiation applications [49, 89, 90]. Three
absorption bands are observed in 2,4,5TMCC at 397 nm, 280 nm and 220 nm.
4
3
3
2
2
1
1
00
0.35
0.30
0.25
0.20
0.15
0.10
0.05
0.00
50 (b)
(a)
00
50
00
50
00
E =2.8 eV
g
5
0
0
2
00 300 400 500 600 700 800 900 1000 1100 1200 1300
2
.0 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 2.9 3.0 3.1 3.2
E (eV)
Wavelength (nm)
Figure 5: (a) Recorded UV-vis.-NIR optical absorbance spectrum and (b) Plots of
ꢖ
ꢁ
ꢊꢨꢩꢃ ꢔꢪꢫꢔꢨꢩꢔfor 2,4,5 TMCC crystals.
4
.3.2. Optical band gap analysis
The recorded absorbance data was used to calculate the optical energy band gap of 2,4,5TMCC
to have bottomless understanding about its enactment and function in photonic devices.
opt
Therefore, the optical energy band gap (Eg ) was evaluated according to following steps:
The absorption coefficient (α) was calculated using the following relation:
ꢮꢯꢰꢥꢱꢯꢲꢳꢴꢵ
ꢊꢀꢉꢬꢜꢭꢜ
ꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢈꢃ
ꢶ
Where, d (= 0.12cm) is the thickness of the crystal.
opt
The Eg was calculated using the following equation [91-93]:
21

ACCEPTED MANUSCRIPT
ꢚ
ꢸ
ꢁ
ꢊꢨꢷꢃ
ꢀꢹꢡꢨꢩꢄ ꢺꢢꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢔꢁꢉꢃ
Where, the constants such as A, h, ν are having their standard meanings, r is defined as an index
value that differentiate the optical absorption process and the value of it for direct allowed
transitions, 1/2, for direct forbidden transitions, 3/2, for indirect allowed transitions, 2 and for
opt
indirect forbidden transitions, 3 [94-97]. Eg of 2,4,5TMCCcrystals was calculated for all the
transition values of r. The best fitting curve was noticed for n=1/2 which indicates to direct
ꢖ
allowed transition in the titled molecule. The ꢁꢨꢷꢃ ꢔꢪꢫꢔꢨν, plot has been shown in Figure 5(b)
and the value of optical energy band gap was obtained from the point of interception on ꢻꢁꢨνꢃ
ꢖ
axis ꢁꢨꢷꢃ ꢀꢭand found to be 2.8 eV.
4
.3.3. Photoluminescence (PL) study
The PL is a light emission from any kind of material after the absorption of photons or
electromagnetic radiation. The recorded PL excitation and emission spectra of 2,4,5TMCC
crystals at room temperature are shown in Figure 6 (a) and (b) respectively. For measuring the
emission spectrum the grown crystals were crushed into fine powder and dissolved in DMF
solution. In the excitation spectrum, the strong and high intensity absorption at ~415 nm of violet
light has been observed. Further to record the emission spectra it was excited at 415 nm and a
strong and intense emission band at ~522 nm has been observed which is assigned to green
emission of light and shows that the titled compound possess green fluorescence and may used in
the fabrication of green light emitting diodes (LEDs).
22

ACCEPTED MANUSCRIPT
50000
40000
30000
20000
10000
0
50000

= 520 nm

= 415 nm
exc
em
(a)
(b)
40000
30000
20000
10000
0
200
250
300
350
400
450
500
450
500
550
600
650
700
750
800

(nm)
(nm)
Figure 6: Photoluminescence (a) excitation and (b) emission spectra of 2,4,5TMCC crystals
4
.3.4. TD-DFT study
TD-DFT is established as an excellent tool to calculate the electronic structure in both quantum
chemistry and solid state physics. The modern density functional approach shows a gratifying
balance between precision and computational cost in comparison to traditional ab initio and
semi-empirical approaches.
To explore the nature of electronic transition in 2,4,5-TMCC molecule, the TD-DFT approach
has been applied five different levels of theory such as B3LYP, CAM-B3LYP, wb97xd, M06,
PBE0 at 6-31G* basis set in gas phase. It is well know that an accurate absorption wavelength
can be easily perceive by such study at reasonably small computing time on the basis of
optimized ground state geometry [98-100]. The experimental UV-vis.-NIR spectrum of 2,4,5-
TMCC has been shown in Figure 5. The calculated excitation wavelength, energies, oscillator
strengths and major contributions and given in Table 2. Figure 7 shows the theoretically obtained
UV-vis. spectrum of 2,4,5-TMCC at different levels of theory. It is clear from figure that there is
a great variation in the value of absorption wavelengths evaluated at CAM-B3LYP and wb97xd
levels of theory while calculated at other methods are moderately varied. The comparison has
been made between theoretically calculated and experimentally recorded absorption spectrum.
23

ACCEPTED MANUSCRIPT
The calculated value of absorption wavelengths at TD-B3LYP/6-31G* level of theory was found
at ~398 nm, 296 nm and 240 nm which are in close agreement with the experimental values
observed at 397nm, 280 nm and 220 nm (see figure 4). The value of maximum absorption
wavelength (398nm) obtained from theoretical (at TD-B3LYP/6-31G* level of theory) and
experimental (397nm) results are in good agreement when compared with all other applied
methods (Table 2).The optimized molecular geometry indicates that the visible absorption
maximum is corresponds to the electron transition from HOMO to LUMO.TD-DFT calculation
shows that the absorption bands at 398 nm and 296 nm initiates mainly due to ꢼꢽꢾand
ꢼ
ꢽꢾꢗꢈexcitations respectively.
Table 2 Excitation wavelength (λ ), energies E(eV), oscillator strengths (ꢿ), and major
exc
0
contributions for transitions in 2,4,5TMCC calculated at different levels of theory.
Method
B3LYP
λexc
E(eV)
3.110
3.704
3.756
3.223
3.235
ꢿ0
0.506
Major contributions
H→L (69.4%)
H→L (62%)
398.63
334.704
330.12
384.71
383.28
CAM-B3LYP
Wb97xd
PBE1
0.655
0.663
0.554
0.592
H→L (61%)
H→L (70%)
MO6
H→L (70%)
24

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25000
20000
15000
10000
B3LYP
CAM_B3LYP
wb97xd
PBE1
MO6
5000
0
50
100 150 200 250 300 350 400 450 500 550

(nm)
Figure 7: UV-vis. spectrum of the 2,4,5TMCC molecule calculated at different levels of theory
using 6-31G* basis set.
4
.3.5. Frontier molecular orbitals (FMOs) and GCRD parameters analysis
The FMOs play a vital role in understanding the phenomenon of reactivity in any molecule and
for the development of any chemical reaction which involves in the formation of complex, the
communication of HOMO and LUMO between reacting species is very important amongst other
FMOs. These orbitals also play the same role as donor and acceptor respectively and used for
predicting the reactive position in π-electron system. The energy values HOMO and LUMO were
*
obtained at five different levels of theory, the values calculated at B3LYP/6-31G are given in
Table 3. The value of energy gap between HOMO and LUMO is found to be 3.402eV with its
chemical hardness value of 1.701 eV, these values indicates that the titled molecule possess
better kinetic stability. The electronic transition in 2,4,5TMCC molecule has been observed at
3
.110 eV predicted by TD-DFT calculations which is corresponding to the transition from
25

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ground state to first excited state and also show charge transfer from HOMO to LUMO. The
value of excitation energy obtained at same level of theory from TDDFT is in good relationship
with HOMO-LUMO energy gap. Figure 8 shows the 3-D plots of HOMO and LUMO orbitals
and the values of their respective energy (in a.u. as well in eV) are presented in Table 3. HOMO
shows that the charge density is localized mainly on carbonyl, methylsulfanyl, ethylenic bridge
and ring 2 while LUMO is delocalized over the Cl group, ring1, carbonyl and ethylenic bridge.
The small value of the energy separation between the HOMO and LUMO and their atomic
orbital compositions imply a charge transfer interaction within the molecule, which influence the
NLO activity of the molecule. The lowering of the HOMO-LUMO band gap is essentially a
consequence of the large stabilization of the LUMO due to the strong electron-acceptor ability of
the electron-accepter group. Experimental result shows that the titled compound has an
advantage of low value of absorbance and significant optical transparency. Further this was also
demonstrated by the theoretically obtained transition energy value which is comparatively higher
and belongs to violet region of the spectrum.
Figure 8: The 3-D plot of the frontier molecular orbital’s of 2, 4, 5-Trimethoxy-4′-
chlorochalcone molecule with counter values of ±0.02 a.u.
26

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Table 3 Calculated energy values and their differences of frontier molecular orbitals (FMOs)
Orbital energy a.u.
eV.
EHOMO
EHOMO-1
ELUMO
-0.195 -5.306
-0.234 -6.368
-0.070 -1.905
-0.022 -0.599
ELUMO+1
∆
EHOMO– LUMO
0.125
0.212
0.063
3.402
5.769
1.701
∆EHOMO– 1– LUMO+1
Hardness (η)
Potential (µ)
-0.133 -3.606
Softness (S)
Electronegativity (χ)
Electrophilic index (ω)
0.011
0.133
0.141
0.294
3.606
3.822
To understand the correlation between structure, stability and global chemical reactivity of
molecules the study of GCRD parameters are very important. These are useful in the
development of quantitative structure activity, property, and toxicity relationships. DFT gives the
explanation of foremost universal insight on stability of the structure of molecule and reactivity
[
101] and the strength of any material is connected to the aromaticity [102]. Here we have
calculated the various global chemical reactivity descriptor such as η, μ, χ and ω by taking orbital
energies of HOMO and LUMO as ionization energy (I) and electron affinity (A) respectively.
The absolute global hardnessꢁꣀꢃ, electronic chemical potentialꢁꢅꢃ, softnessꢁꣁꢃ,
ꢆ
electronegativityꢁꣀꢃand electrophilicityꢁꣂꢃparameters were evaluated by usingꢔꣀꢀ ꢁꣃ꣄ꣅ꣆꣇ꢄ
ꢖ
꣊
꣋ꢮ
꣊
꣊꣋ꢮ
꣐ꢛ
ꣃ꣈꣇꣆꣇
ꢃ, μ ꢀꢄ꣉ ꢖ ꣌꣍ ꣎ꢀ ꢔ꣍ χ ꢀ꣉ ꢖ ꣌and ꣂꢀ , respectively and presented in Table 3.
ꢖ꣏ ꢖ꣏
The obtained GCRD result reveals that the titled molecule possesses good chemical strength and
chemical stability.
4
.3.6. Second order polarizability analysis
27

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Hyperpolarizability plays a significant role to understand the nonlinear optical process in any
molecule to be used for the fabricate the technologically important nonlinear optical devices and
justify the increasing applications of it to calculate accurately[103, 104]. It is clear from the
currently available literature [105-107] that in addition to a suitable action of electron correlation
and a careful selection of the functional and basis set, the insertion of the contributions occurring
from the nuclear activity is of basic significance for the estimation of electrical properties such as
polarizability and hyperpolarizability at molecular level. Hence, we have calculated such
parameters using various schemes like B3LYP, CAM-B3LYP,LC-BLYP, wb97xd and MP2 at 6-
3
1G* basis set. The values of electronic total dipole moment (μ ), molecular total and
tot
anisotropy of polarizability (α and Δα), static and total first hyperpolarizability (β , β ) along
0
0
tot
with their components determined at B3LYP/6-31G* level of theory are given in Table 4.
Further the calculated values of all above parameters estimated at HF, CAM-B3LYP, LC-BLYP,
wb97xd and MP2 are also provides in Table 1S (1-5) (see supplementary information). The
obtained result shows that the values of polarizability and hyperpolarizability are leaded by their
diagonal components (i.e. the components along dipole moment axis) of α and β . Figure 2S
xx
xxx
(supplementary information) shows the variation of total hyperpolarizability values determined
at all currently applied levels of theory and concludes that its value is higher at B3LYP levels of
theory in comparison to other applied techniques. The value of total dipole moment (μ ) is
tot
found to be 6.043D and the highest value of component of μ is μ (=-5.905D) which is a major
tot
x
contributor to it. Also, the value of average polarizability (α ), anisotropy of polarizability (Δα)
0
−
24
−24
−30
and total first hyperpolarizability (β ) are 38×10 , 45×10 and 30×10 esu. respectively.
tot
The value of β for titled molecule at molecular level is found to be 136 times larger than that of
tot
prototype urea molecule as well as comparable to other molecules calculated at same level of
28

ACCEPTED MANUSCRIPT
theory recently [15, 108]. The measured experimental second harmonic generation value of the
titled molecule at bulk level is observed to be 4.3 times higher than urea [57]. Therefore, the
values of calculated hyperpolarizability (β ) and measured second harmonic generation are
tot
numerous times superior than the other reported organic as well as other materials [52-54, 109-
1
16]. The high value of β and SHG makes the titled molecule a unique candidate for nonlinear
tot
optical applications.
Table 4 Calculated values of polarizability, hyperpolarizability and dipole moment along their
individual tensor components of titled molecule at B3LYP/6-31G* level of theory.
Polarizability and dipole moment
Hyperpolarizability
−24
−30
Components
a. u.
443
esu (×10
)
Components
a. u.
esu (×10
)
αxx
65.653
0.593
35.123
0.889
-1.186
13.931
38
βxxx
4781
41.256
-16.74
0.371
-0.155
0.811
-0.138
0.009
-0.397
-0.112
-0.043
18
αxy
αyy
4
237
βxxy
βxyy
-1940
43
αxz
6
βyyy
-18
94
αyz
-8
βxxz
αzz
94
βxyz
-16
1
α0
258
βyyz
Δα
304
45
βxzz
-46
-13
-5
μx
-2.323
0.505
-0.076
2.378
1.66
-5.905D
1.283D
-0.194D
6.043D
4.24D
βyzz
μy
βzzz
μz
β0
2078
3463
μtot
μtot(urea)
βtot
30
βtot (urea)
26
0.22[108]
−
24
−30
For α, 1 a. u. = 0.1482×10 esu, for β, 1 a. u. = 0.008629×10 esu, μUrea= 1.3732 D and βUrea
=
−
30
0
.3728×10 esu[109]
29