Synthesis, crystal growth, thermal, electronic and vibrational spectral studies of 1-(4-Bromophenyl)-3-(3,4-dimethoxy-phenyl)prop-2-en-1-one: A density functional theory study

Article abstract of DOI:10.1016/j.molstruc.2014.08.008

A new chalcone derivative, 1-(4-Bromophenyl)-3-(3,4-dimethoxy-phenyl)prop-2-en-1-one (DMBC) was synthesized and single crystals were grown by slow evaporation technique. The FT-Raman and FT-IR spectra of the sample were recorded in the region 3500-50 cm

Full text of DOI:10.1016/j.molstruc.2014.08.008

Accepted Manuscript
Synthesis, crystal growth, thermal, electronic and vibrational spectral studies of
1-(4-Bromophenyl)-3-(3, 4-dimethoxy-phenyl) prop-2-en-1-one: A density
functional theory study
L. Joseph, B.S. Arunsasi, D. Sajan, V. Shettigar
PII:
S0022-2860(14)00827-8
DOI:
http://dx.doi.org/10.1016/j.molstruc.2014.08.008
MOLSTR 20868
Reference:
Journal of Molecular Structure
To appear in:
Received Date:
Revised Date:
Accepted Date:
6 June 2014
2 August 2014
2 August 2014
Please cite this article as: L. Joseph, B.S. Arunsasi, D. Sajan, V. Shettigar, Synthesis, crystal growth, thermal,
electronic and vibrational spectral studies of 1-(4-Bromophenyl)-3-(3, 4-dimethoxy-phenyl) prop-2-en-1-one: A
density functional theory study, Journal of Molecular Structure (2014), doi: http://dx.doi.org/10.1016/j.molstruc.
2014.08.008
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1ꢀ
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Synthesis, crystal growth, thermal, electronic and vibrational
spectral studies of 1-(4-Bromophenyl)-3-(3, 4-dimethoxy-phenyl)
prop-2-en-1-one: A density functional theory study
L Joseph1,4, B S Arunsasi1,2, D Sajan1* and V Shettigar3
1Department of Physics, Bishop Moore College, Mavelikara, Alappuzha -690110, Kerala, India
2Department of Physics and Research Centre, Scott Christian College (Autonomous), Nagercoil-
629003, Tamil Nadu, India
3Department of Physics, Gokhale Centenary College, N.H.17, Vandige, Ankola-581314, India.
4Department of Physics, C M S College, Kottayam -686001, Kerala, India
E-mail: dsajand@gmail.com , dsajanbmc@gmail.com (D. Sajan)
Abstract. A new chalcone derivative, 1-(4-Bromophenyl)-3-(3,4-dimethoxy-phenyl)prop-2-en-1-
one (DMBC) was synthesized and single crystals were grown by slow evaporation technique. The
FT- Raman and FT-IR spectra of the sample were recorded in the region 3500-50 cm-1 and 4000-
400 cm-1 respectively. The spectra were interpreted with the aid of normal coordinate analysis,
following structure optimizations and force field calculations based on density functional theory
(DFT) at the B3LYP/6-31G(d,p) level of theory. Normal coordinate calculations were performed
using the DFT force field corrected by a recommended set of scaling factors yielding fairly good
agreement between the observed and calculated wavenumbers. DMBC is thermally stable up to
265.0 ºC and optically transparent in the visible region. The total electron density and Molecular
electrostatic potential surfaces of the molecules were constructed by Natural Bond Orbital analysis
using B3LYP/6-311++G(d,p) method to display electrostatic potential (electron + nuclei)
distribution, molecular shape, size, and dipole moments of the molecule. The electronic properties,
HOMO and LUMO energies were measured.
1. Introduction
Organic molecules, especially chalcone derivatives, constitute an important group of natural
products and some of them possess a wide range of biological activities such as antimicrobial, anticancer,
antiviral etc [1-4]. Chalcones have the common skeleton of 1, 3-diaryl-2-propen-1-one and belong to the
flavonoid family. Moreover chalcones belong to nature products and have low toxicity. Some derivatives
ꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀꢀ
* Corresponding author. Tel.:+919495043765; Fax: +914792303230;
E-mail address: dsajand@gmail.com , dsajanbmc@gmail.com (D. Sajan).

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are used as sweeteners, drugs, and sunscreen agents. Chalcone and its derivatives are very versatile as
physiologically active compounds and substrates for the evaluation of various organic syntheses [5-8].
They also serve as a back bone for the synthesis of various heterocyclic compounds. Furthermore, many
chalcone derivatives are a class of organic compounds with excellent NLO properties [9-12], much better
than those observed in inorganic crystals. They have recently received considerable attention owing to
their potential application in photonic device applications such as erasable memory media and optical
switching. Recently, it has been noted that, among many organic compounds reported for their second
harmonic generation, chalcone derivatives are known for their excellent blue light transmittance and good
crystallizability [10-12]. Owing to their good thermal stability, associated with high laser damage
resistance and transparency, this family of compounds has been used in recent years for frequency
doubling of diode lasers down to 470 nm [13]. The addition of various substituents to the chalcone
molecules allows us to control their NLO properties.
The structural studies on the chalcone derivative, 1-(4-Bromophenyl)-3(3, 4-dimethoxy-phenyl)
prop-2-en-1-one (DMBC) have been reported earlier [14]. However, to the best of our knowledge no
detailed studies on DMBC have been made so far. Recently density functional theory (DFT) has emerged
as a powerful tool for analysing vibrational spectra of fairly large molecules. The application of DFT to
chemical systems has received much attention because of faster convergence in time than traditional
quantum mechanical correlation methods [15-23]. In this paper, we report for the first time, the bulk
growth, structural, electronic, thermal and detailed vibrational spectral investigation of DMBC using the
scaled quantum mechanical (SQM) force field technique [24] based on density functional theory (DFT)
calculations.
2. Experimental
2.1 Synthesis of the compound
The chalcone derivative was synthesized by the Claisen–Schmidt condensation reaction [25]. The
title compound was obtained by the condensation of 3, 4 dimethoxy benzaldehyde (0.01 mol) with 4-

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bromoacetophenone (0.01 mol) in ethanol (60mL) in the presence of NaOH (5mL, 20%). After stirring,
the content of the flask was poured into ice-cold water (20mL) and the resulting crude solid was collected
by filtration. The compound was dried and purified by repeated recrystallization from acetone. The
molecular structure of the chalcone derivative under study is shown in figure 1.
O
OCH
Br
3
OCH
3
ꢀ
Figure 1. Molecular structure of the synthesized compound of DMBC
2.2 Crystal growth
Single crystals of DMBC were grown by the slow evaporation solution growth technique from
the acetone solution at room temperature. Pale yellowish, high-quality DMBC single crystals with a
maximum dimension of 12 x 5 x 1.3 mm3 were grown in a period of 10 days. DMBC crystallizes in space
group P21/c with eight molecules (Z=8) in the unit cell with a volume of 2930.17 (10) ǖ3. From the single
crystal XRD data [25] it is observed that the crystal belongs to monoclinic system with the following cell
dimensions: a=31.3937 (5) ǖ, b=4.0139 (1) ǖ, c=25.2400 (4) ǖ, ȕ=112.885º. The grown crystals are
shown in figure 2
ꢀ
Figure 2. Photograph of the crystal DMBC.
ꢀ
2.3 FT-IR, FT- Raman, UV-Vis Spectra and Thermal Studies

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The FT-IR spectrum was recorded by KBr pellet technique using Thermo Nicolet AVATAR 370
DTS FT-IR spectrometer working in the wave number range 4000-400 cm-1.ꢀThe data were collected at 4
cmí1 resolution. The FT-Raman spectrum of the sample was recorded between the 3500-50 cm-1 regions
on a RFS 100/s FT-Raman spectrophotometer. With an Nd:YAG laser at 1064 nm and output of 300 mW
used as the excitation source and with a liquid nitrogen cooled Ge-didode detector,1000 scans
accumulated for over 30 min duration. The resolution after apodization was 2cm-1.ꢀ The UV-Vis
absorption spectrum of the sample was recorded in acetone solution using a Shimadzu UV-Vis
spectrophotometer in the spectral region of 200-400 nm. Thermogravimetric analysisꢀ (TGA) was
carried out to investigate the thermal stability [26] under nitrogen atmosphere at a heating rate of 10/min
using the Perkin Elmer simultaneous TGA/DTA analyzer.
3. Quantum chemical calculation
The quantum chemical calculation has been performed using the B3LYP level of theory
supplemented with the standard 6- 31G (d,p) basis set, using the Gaussian ’09 program [27] to calculate
optimized bond lengths, bond angles, atomic charges, and vibrational wavenumbers with their IR
intensities and Raman scattering activities. After the most stable conformer of the title compound was
determined, geometry optimizations of this conformer have been performed with the 6-31G (d,p) basis set
and the hybrid B3LYP functional approach. The cartesian representation of the theoretical force constants
has been computed at the fully optimized geometry by assuming P21/c point group symmetry. Scaling of
the force fields were performed by the scaled quantum mechanical (SQM) procedure
scaled
B3LYP
ij
F
= CiC j F
ij
(1)
where Ci is the scale factor of coordinate i, FijB3LYP is the B3LYP/6-31G(d,p) force constant in the local
scaled
internal coordinates, and Fij
is the scaled force constant. The multiple scaling of the force constants
was performed by the quantum chemical method with selective scaling in the local symmetry coordinate
representation [28, 29], using transferable scale factors available in the literature [19]. Selective scaling

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was done using a set of 11 transferable scale factors giving an RMS wavenumber 9.46 cm-1. The
transformation of the force field from cartesian to symmetry coordinate, the scaling, the subsequent
normal coordinate analysis and calculations of total energy distribution (TED), IR and Raman intensities,
were done on a PC with the version V7.0-G77 of the MOLVIB programme written by Sundius[30, 31].
The Raman activities (Si) calculated by Gaussian 09 program were converted to relative Raman
intensities (Ii), using the following relationship from the basic theory of Raman scattering [32, 33]
f (νo −νi )4 Si
(2)
Ii =
⎡
−hcν ⎤
⎞
⎛
i
νi 1− exp
⎜
⎝
⎟
⎥
⎢
kT
⎠
⎣
⎦
where o is the exciting frequency (in cm-1 units), i is the vibrational wavenumber of the ith normal mode,
h c and k are universal constants, and is a suitably chosen common scaling factor for all the peak
intensities. Raman and infrared spectra were simulated using a pure Lorentzian band profile
(fwhm=10cm-1).
4. Result and discussion
4.1 NMR spectra
The Nuclear Magnetic Resonance (NMR) spectrum was recorded to confirm the presence of
various types of protons for the formation of the target compound. The recorded NMR spectrum is shown
in figure 3. The aromatic protons of the bromophenyl moiety appear as two doublets at į=8.1 and 7.9
ppm, while the aromatic protons of 3-4 dimethoxyphenyl appeared as two doublets at į=7.0 and 7.3 ppm.
Two closely spaced doublets at į=3.7 and 3.9 ppm correspond to the two –OCH3 groups. These peaks
confirm the formation of the compound.

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O
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
OCH
Br
3
OCH
3
Figure 3. NMR spectrum of DMBC.
4.2 Molecular structure
The optimized structural parameters of DMBC calculated using B3LYP/6-31G(d,p) basis set are
listed in table 1 along with the experimental data [14] , in accordance with the atom numbering scheme in
figure 4. The agreement between the experimental and optimized crystal structure is quite good showing
that the geometry optimization almost exactly reproduces the experimental conformation. The molecule
consists of two phenyl rings (Ph1 and Ph2) which are planar, with dihedral angles C5–C4–C3–C20
=179.94º and C30–C31–C26–C24 =179.63º. The methoxy groups (Me1 and Me2) on the phenyl ring are
coplanar, with dihedral angles C16–O15–C6–C5 =0.03º and C8–O7–C1–C2 =0.0º. With the substitution of
the electron donating methoxy groups on the benzene ring, the symmetry of the ring is distorted, yielding
ring angles smaller than 120.0º at the substitution and slightly larger than 120.0º at the ortho and meta
positions. Geometrical changes are observed in the aryl–O bonds, C1–O7 (for Me1) and C6–O15 (for Me2),
due to ʌ- conjugation. The shortening of angles C1–O7–C8 and C6–O15–C16 is the consequence of the
sharing of lone pair electrons of the methyl group with the p electrons in the ring and the interaction of
these lone pair electrons with the nearby ʌ system.
Table 1. Optimized geometric parameters of DMBC at the B3LYP/6-31G(d,p) level of theory.

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Bond Lengths (A )
6-
Bond Angles ( )
6-
Dihedral Angles ( )
6-
X-
X-
Parameter
Parameter
Parameter
X-Ray [14]
31G(d,p)
Ray[14]
31G(d,p) Ray[14]
31G(d,p)
C1-C2
C2-C3
C3-C4
C4-C5
C5-C6
1.385
1.415
1.399
1.396
1.393
1.360
1.418
1.090
1.097
1.097
1.082
1.085
1.083
1.355
1.420
1.090
1.097
1.097
1.454
1.089
1.351
1.084
1.477
1.231
1.504
1.402
1.394
1.392
1.395
1.390
1.084
1.083
1.083
1.084
1.910
1.377
1.409
1.387
1.402
1.389
1.367
1.427
0.960
0.960
0.960
0.930
0.930
0.930
1.361
C1-C2-C3
C2-C3-C4
C3-C4-C5
121.2
118.2
121.2
120.3
125.2
118.0
105.9
111.6
111.6
119.4
119.4
119.4
125.2
118.1
105.8
111.5
111.5
123.0
115.8
128.4
121.1
120.0
121.6
119.1
123.9
120.9
119.0
121.2
118.9
120.7
120.7
120.1
120.8
119.3
120.7
118.5
121.7
119.1
125.4
116.3
109.4
109.4
109.4
119.6
119.2
120.3
125.0
117.3
109.5
109.4
109.4
122.3
116.6
126.6
119.0
121.9
121.6
118.6
122.9
121.1
119.8
121.7
118.6
119.3
120.5
120.6
C1-C2-C3-C4
C2-C3-C4-C5
C3-C4-C5-C6
C3-C2-C1-O7
C2-C1-O7-C8
-0.08
0.16
-0.11
179.8
-0.4
-179.5
-60.7
61.6
-0.05
-0.4
1.4
178.9
-0.0
176.8
-63.1
56.8
C4-C5- C6
C2-C1- O7
C1- O7-C8
O7-C8- H 9
O7-C8- H 10
O7-C8- H11
C1-C2- H 12
C3-C4- H 13
C4-C5- H 14
C5-C6- O15
C6- O15-C16
C1-O7
O7-C8
C1- O7-C8-H9
C1- O7-C8-H10
C1- O7-C8-H11
O7-C1-C2-H12
C2-C3-C4-H13
C3-C4-C5-H14
C4-C5-C6-O15
C5-C6-O15-C16
C6- O15-C16-H17
C6- O15-C16-H18
C6- O15-C16-H19
C1-C2-C3-C20
C2-C3-C20-H21
C2-C3-C20-C22
C3-C20-C22-H23
C3-C20-C22-C24
C20-C22-C24-O25
C20-C22-C24-C26
C22-C24-C26-C27
C24-C26-C27-C28
C26-C27-C28-C29
C27-C28-C29-C30
C28-C29-C30-C31
C24-C26-C27- H32
C26-C27-C28- H33
C28-C29-C30- H34
C29-C30-C31- H35
C8- H 9
C8- H10
C8- H 11
C2- H 12
C4- H 13
C5- H 14
C6- O 15
O15-C16
C16- H 17
C16- H 18
C16- H 19
C3-C20
C20- H 21
C20-C22
C22- H 23
C22-C24
C24-O25
C24-C26
C26-C27
C27-C28
C28-C29
C29-C30
C30-C31
C27- H32
C28- H33
C30- H34
C31- H35
C29- Br36
0.0
0.9
-179.8
179.9
-179.9
0.03
-179.9
-61.1
61.2
-179.9
178.2
-1.8
0.4
179.1
-4.5
176.2
-13.6
-179.0
-0.3
179.5
178.5
179.0
-4.0
178.5
-58.5
61.4
-178.7
-173.1
6.9
-0.9
179.0
-7.6
171.4
-3.0
-177.5
0.4
-2.0
2.0
2.55
-179.5
-178.0
179.8
176.8
1.436 O15-C16- H 17
0.960 O15-C16- H 18
0.960 O15-C16- H 19
0.960
C2-C3-C20
1.461 C2-C3- H21
0.930 C2-C3-C22
1.339 C20-C22- H 23
0.929
1.476
C20-C22-C24
C22-C24-O25
1.226 C22-C24- C 26
1.503
1.395
1.385
1.379
1.388
1.382 C26-C27- H 32
0.931 C27-C28- H 33
0.929 C29-C30- H 34
0.931 C30-C31- H 35
0.929 C28-C29- Br36
1.908
C24-C26-C27
C26-C27-C28
C27-C28-C29
C28-C29-C30
C29-C30-C31
0.5
-0.09
-0.49
179.4
179.7
179.3
-179.5
119.3 C27-C28-C29- Br36
118.8

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Figure 4. Molecular structure and atomic numbering ofꢀDMBC.
4.3 NBO analysis
NBO analysis provides an efficient method for studying the interactions in both filled and virtual
orbital spaces that could enhance the analysis of intra and inter molecular interactions. The NBO
calculation have been performed using NBO 3.1 program as implemented in the Gaussian ’09 package at
the DFT/B3LYP 6-31 G(d,p) level, and it gives information about intra molecular hydrogen bonding,
delocalisation of electron density and intra molecular charge transfer(ICT) within the molecule. The
second order perturbation theory analysis of Fock matrix in NBO basis shows strong intra molecular
hyper conjugative interactions of ʌ electrons, which are presented in table 2. Larger the E (2) values, the
more intensive the interaction between electron donors and electron acceptors and greater the extent of
conjugation of the whole system [34, 35]. The hyperconjugative interaction energy deduced from the
second order perturbation approach is
2
F 2
ΔE
σ F σ
εσ* − εσ
ij
E(2) = −nσ
= −nσ
(3)
2
where σ F σ or F 2 is the Fock matrix element of the i and j NBO orbitals, εσ and εσ* are the
ij
energies of ı and ı* NBOs and nσ is the population of the donor ı orbital.
The strong intra molecular hyper conjugative interactions of the ı and ʌ electrons of the C-C
bond with the C-C anti bond of both the phenyl rings lead to stabilization of the system. The transfer of
charge taking place within the molecule is more in ʌĺʌ * transition. The intra molecular C-H…O

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hydrogen bond exposed in the NBO analysis is formed by the orbital overlap between LP (O) and ı *(C-
H). The stabilization energy E (2) associated with n2 (O25) ĺı *(C20-H21) interaction is 0.52 kJ molí1,
which indicates the possibility of weak intra molecular hydrogen bonding. Due to rehybridization, the C-
H bond distance is strengthened, shortened and blue shifted in the stretching wave number. The analysis
reveals that charge transfer takes place from lone pairs n (O7) and n (O15) of the methoxy oxygen atom to
the ʌ orbitals of phenyl ring Ph1 with interaction energy 30.60 and 31.54 kJ molí1, respectively.
Table 2. Second order perturbation theory analysis of Fock matrix in NBO basis of DMBC at the
B3LYP/6-31 G(d,p) level of theory.
ED(i)
(e)
E(2) a
(kJ mol-1)
17.59
17.90
18.72
18.52
17.41
17.46
19.59
19.12
19.34
22.93
7.26
E(j)-E(i) b
F(i,j) c
Donor (i)
Acceptor(j) ED(j) (e)
(arbitr.units) (arbitr.units)
ʌC1-C2
1.7241 ʌ*C3-C4
ʌ*C5-C6
0.3756
0.3754
0.3467
0.3754
0.1243
0.3467
0.3756
0.3616
0.3616
0.3795
0.0234
0.0234
0.3754
0.0189
0.0639
0.3756
0.1243
0.0234
0.2856
0.31
0.30
0.28
0.28
0.30
0.30
0.31
0.31
0.29
0.27
1.13
0.34
0.34
0.74
0.70
0.01
0.03
0.02
0.02
0.067
0.067
0.065
0.065
0.068
0.065
0.070
0.069
0.067
0.071
0.081
0.096
0.098
0.018
0.105
0.081
0.072
0.085
0.081
ʌ C3-C4
1.6603 ʌ*C1-C2
ʌ *C5-C6
ʌ *C20-C22
C5-C6
1.6882 ʌ*C1-C2
ʌ*C3-C4
ʌ C28-C29
ʌ C30-C31
1.6745 ʌ*C26-C27
1.6530 ʌ*C26-C27
ʌ*C28-C29
LP(1) O7
LP(2)O7
1.9644 ı*C1-C2
1.8421 ʌ*C1-C2
30.60
31.54
0.52
LP(2) O15 1.8294 ʌ *C5-C6
LP(2)O25
1.8885 ı*C20-H21
ı*C24-C26
19.29
256.67
43.76
196.48
139.99
ʌ*C5-C6
0.3754 ʌ*C3-C4
ʌ*C24- O25 0.2141 ʌ*C20- C22
ʌ*C28- C29 0.3795 ı*C26- C27
ı*C30-C31

10ꢀ
ꢀ
a E(2) is the energy of hyperconjugative interactions.
b Energy difference between donor and acceptor i and j NBO orbitals.
c F(i, j) is the Fock matrix element between i and j NBO orbitals.
4.4 Thermal studies
The result of the TGA/DTA analysis is shown in figure 5. DTA curve shows that the material
undergoes an irreversible endothermic transition where melting begins. The peak of the endothermic at
124.71 ºC where melting terminates, corresponds to its melting point and it is clear that there is no phase
transition before melting. The sharpness of the peak shows good crystallinity and purity of the
sample.TGA curve of the sample indicates that the sample is stable up to 265.0 ºC. The endothermic peak
of DTA at 315.49 ºC corresponds to the first phase of weight loss in the TG curve, indicating
decomposition of the sample. This endothermic peak is followed by an exothermic peak at 380.0 ºC
indicating evaporation of the decomposed compound.
ꢀ
ꢀ
ꢀ
ꢀ
Figure 5 The TGA/DTA curves of the DMBC crystal.
4.5 Absorption spectra
The electronic spectra of DMBC were calculated using the using the Gaussian ’09 program, [27] at
the B3LYP/6-31 G (d,p) level. The observed and simulated UV–Vis spectra are shown in figure 6.ꢀThe
electronic transitions and the corresponding excitation energies are listed in table 3. The computed results
(table 3) show that the HOMO (highest occupied molecular orbital) to LUMO (lowest unoccupied

11ꢀ
ꢀ
molecular orbital) transition corresponds to the Ȝmax absorption band in the UV-vis spectrum. From the
calculations in the gas phase it is seen that the frontier level HOMO has the molecular orbital number 88
with ‘A’ symmetry and the LUMO has the molecular orbital number 89 with the same ‘A’ symmetry.
The strong band observed experimentally at 355 nm was calculated at 367 nm in the gas phase
corresponding to HOMO to LUMO excitation, with the highest oscillator strength. The analyses of the
molecular orbital coefficients based on the optimized geometry indicate that the band is originated by an
nĺʌ* transition. The other transitions are calculated at 378 nm and 312 nm, with lower oscillator
strengths.
Table 3: Experimental and Calculated absorption wavelengths, energies and oscillator strengths of DMBC
using the TD-DFT method at the B3LYP/6-31G(d,p) level.
Excitation
CI expansion
Coefficient
Wavelength (nm)
Calc. Gas phase
Oscillator
Strength (f)
Wavelength
(nm) Expt.
Excited state 1
85ĺ89
Singlet-A
0.46127
0.43686
-0.20944
-0.11385
Singlet-A
0.11061
í0.13061
0.62973
Singlet-A
0.30184
0.59767
-0.11319
378.0
0.002
86ĺ89
87ĺ89
88ĺ89
Excited state 2
86ĺ89
367.0
0.619
355
87ĺ89
88ĺ89
Excited State 3
86ĺ89
312.0
367.0
0.200
0.619
87ĺ89
88ĺ92

12ꢀ
ꢀ
ꢀ
Figure 6. Simulated electronic absorption spectra of DMBC at the B3LYP/6-31G (d, p) level gas phase
(top) UV-VIS spectra of DMBC molecule recorded in gas phase (bottom).
The HOMO and LUMO plot of DMBC, as implemented within the Gauss View Version 5.1
program, is shown in figure 7. The HOMO represents the ability to donate an electron, whereas, LUMO
as an electron acceptor, represents the ability to obtain an electron. Energy difference between the HOMO
and LUMO orbital is called energy gap, which is an important stability reflector for structures. A low
HOMO–LUMO gap implies lower stability of the molecule in the sense of its higher charge transfer in
compounds. The conjugated molecules are characterized by a small HOMO-LUMO separation, which is
the result of a significant degree of ICT from the electron-donor groups to the efficient electron-acceptor
groups through the ʌ conjugated path. The HOMO and LUMO energies are í546.18 kJ/mol and-198.96
kJ/mol at the DFT level. The energy gap 347.22 kJ/mol reflects the lowering of energy gap and hence the

13ꢀ
ꢀ
enhanced biological activity of the molecule. Moreover the lowering of the HOMO and LUMO energy
gap explains the eventual charge transfer interactions taking place within the molecule.
ꢀ
LUMO
ELUMOꢀ=ꢀͲ198.96ꢀkJ/mol
(ExcitedꢀState)
E=ꢀ347.22ꢀkJ/mol
HOMO
(GroundꢀState)
EHOMOꢀ=ꢀо546.18ꢀkJ/mol
Figure 7. HOMO LUMO plot of DMBC by B3LYP/6-31G(d,p) level of theory.
4.6 Vibrational spectral analysis

14ꢀ
ꢀ
The detailed vibrational spectral analysis of DMBC was performed based on the normal
coordinate analysis according to the scaled quantum mechanical (SQM) force field methodology. The
potential energy distribution (PED) reveals that many of the internal modes contribute to a particular
vibrational mode and involve the simultaneous motion of a large number of atoms. The observed and
calculated wavenumbers together with the infrared and Raman intensities and normal modes description
(characterized by PED) of DMBC are reported in table 4.ꢀA comparison of the observed and simulated IR
and FT-Raman spectra of the title compound are presented in figures 8 and 9, which help to understand
the observed spectral features. The calculated spectra were found to be close to the experimental values
with reasonable degree of accuracy. H-atoms involved in intermolecular H-bonds give rise to deviations
of the simulated spectra from the experimental spectra, which is attributed to the fact that the theoretical
spectrum was obtained in gas phase without considering the inter-molecular H-bonding effects.
Figure 8. (a) Experimental FT-IR spectra in the range 4000–400 cmí1 and (b) Simulated IR spectra of
DMBC by B3LYP/6-31G(d,p) level of theory.

15ꢀ
ꢀ
ꢀ
Figure 9. (a) Experimental FT-Raman spectra in the range 3500–50 cmí1 (b) Simulated Raman spectra ofꢀ
DMBC at the B3LYP/6-31G(d,p) level of theory.
4.6.1 Methoxy group vibrations. The methoxy C-H symmetric stretching mode usually appear in the
region 2825-2870 cm-1 where as asymmetric mode lie in the range 2925-2985 cm-1 [36, 37]. The weak
infrared band at 2968 cmí1 and the corresponding weak Raman band at 2971 cmí1 are assigned to CH3
asymmetric stretching (CH3 ops) vibration. The weak infrared band at 2935 cmí1 and the corresponding
weak Raman band at 2938 cmí1 are assigned to CH3 in-plane stretching modes. The symmetric CH3
stretching band is observed at 2839 cm-1 as a weak IR band and at 2841 cm-1 as a weak Raman band,
which is calculated at 2839 cm-1. Though the calculated asymmetric and symmetric stretching
wavenumbers arising from different O-CH3 groups show slight differences in wavenumber, they could
not be separated out in the spectra. The asymmetric and symmetric bending vibrations of methyl group
are expected in the region 1465-1440 cm-1 and 1390-1370 cm-1 respectively [36,37]. The methyl
asymmetric deformation appears as a medium band in IR at 1458 cm-1 and a weak band in Raman at 1453
cm-1. The methyl frequencies are to some extent sensitive to the electro negativity of the attached atom

16ꢀ
ꢀ
and the symmetric deformation is particularly sensitive and it appears at 1400 cm-1 in IR and 1401 cm-1 in
Raman. The rocking vibrations of the CH3 group generally appear as mixed vibrations in the range 1070-
1010 cm-1. The strong band in IR at 1174 cm-1 and the medium band in Raman at 1183 cm-1 are assigned
to CH3 rocking mode.
Table 4. Detailed assignment of fundamental vibrations of DMBC by NCA based on SQM force field
calculations.
Calculated
Observed
wavenumbers
(cm-1)
wavenumbers
IR
Raman
Characterization of normal modes with PEDc
(%)
(cm-1)
Intensitya
Intensityb
Unscaled Scaled
FTIR
Raman
3232
3228
3228
3225
3215
3213
3200
3195
3168
3156
3153
3084
3076
3020
3014
1736
1662
1642
1637
1622
1614
1562
1525
1518
1516
1505
1504
1501
1487
1465
3067
3064
3055
3047
3002
2998
2971
2967
2939
2935
2903
2903
2867
2841
2839
1661
1623
1604
1588
1569
1557
1513
1510
1488
1487
1465
1453
1426
1418
1411
3066vw
3067w
3.51
3.56
0.23
9.51
4.45
17.46
27.07
6.77
8.63
32.02
1.06
39.52
37.29
20.48
88.91
340.69
126.04
269.67
25.03
109.90
550.75
23.75
430.66
41.81
25.11
56.76
13.31
15.39
107.24
19.10
11
Ȟ 20bCHph1(99)
Ȟ 20aCHph1(99)
Ȟ 20bCHph2( 98)
-
-
-
-
-
2.79
3.66
2.49
2.26
7.56
6.89
3.44
1.23
11
2.15
3.84
5.12
7.3
6.93
339
154
248
42.5
144
2.73
69.5
742
14.1
112
214
16
3012 w
Ȟ 20aCHph2( 99)
Ȟ2CHph2( 98)
Ȟ7aCHph2( 57), ȞCH(41)
Ȟ7bCHph2(50) ,ȞCH(48),
Ȟ7bCHph1(98)
-
-
3017 w
-
-
-
-
-
-
-
ȞCH(98)
2968 w 2971 vw
CH3ops2(68), CH3ips2(22)
CH3ops1(67), CH3ips1(23), CH3 ss1(10)
CH3ips2(74) CH3ops2(25)
CH3ips1(74), CH3ops1(25)
CH3 ss2(89)
-
-
2935 w 2938 vw
-
-
-
-
2839 w
1658 vs
1628 vw 1628 vw
1604 vs
1583 w
2841vw
1659 w
CH3 ss1(89)
ȞCO(59), ȞCC(14), įCC(10)
Ȟ8bCCph1(35),ȞCC(26)
Ȟ8aCCph2(32), ȞCCph2(22),ȞCC(11)
Ȟ8bCCph2(46), įCHph2(13)
Ȟ8aCCph1(60)
1607 vs
1584 s
1563 w
-
1560 w
1510 m
-
Ȟ19aCCph2(69), įCHph2(10)
Ȟ19bCCph1(34),įCHph1(31),ȞCO(17)
įCHph2(57), ȞCCph2(39)
CH3as1(61), CH3asyd1(21)
CH3as2(59), CH3asyd2(24)
CH3asyd2(48), CH3as2(20), CH3asyd1(18)
CH3asyd1(50), CH3asyd2(18), CH3as1(18)
CH3syd1(54),ȞCCph1(21)
CH3syd1(54)
1510 w
-
-
-
1488 w
1485 s
-
-
-
1458 m
1453 w
-
1418 w
1510 w
-
6.54
10.5
51.9
1414 m
-
ȞCCph1(37), CH3syd1(28),įCHph1(15)

17ꢀ
ꢀ
1435
1400
1363
1349
1342
1323
1316
1306
1276
1233
1226
1214
1205
1195
1179
1177
1174
1133
1090
1081
1061
1055
1034
1022
1007
994
972
927
885
872
860
855
842
817
789
761
749
716
698
690
643
627
1401
1384
1356
1336
1313
1308
1287
1277
1253
1225
1205
1179
1168
1154
1123
1110
1104
1074
1063
1039
1035
1024
1007
970
962
933
920
891
876
858
833
821
811
789
773
749
743
712
684
674
1400 m
-
1367 w
1331 w
1313 s
1401 w
19.23
22.06
14.06
590.02
15.73
76.98
4.26
75.76
12.82
275.63
17.47
14.10
158.45
11.95
83.46
0.977
16.89
4.61
48.92
167.37
9.42
17.38
142.40
32.11
0.15
0.70
46.25
3.50
115
37.8
129
Ȟ19bCCph2(47),įCHph2(39)
-
-
-
Ȟ19aCCph1(58),įCCH(14)
įCCH(28),ȞCCph1(19),ȞCCph2(18),ȞCC(14)
Ȟ14CCph1(28),įCCH(21),įCHph1(15)
Ȟ14CCph2(89)
43
1318 w
3.19
14.4
8.24
22.2
19.3
78.6
25.7
70.1
26.5
2.19
34.9
2.29
2.14
1.81
28.3
70.1
29.9
5.11
2.97
5.85
1.09
0.867
0368
4.97
4.33
3.82
2.99
0.707
0.261
0.263
27.9
2.41
5.9
1302 vw 1304 w
į3CHph2(61)
-
-
ȞCCph1(28), ȞCOph1(26), įCHph1(13)
įCHph1(54), ȞCCph1(11), įCCH (10)
ȞCOph1(30),Rtrid(13),
Ȟ9aCCph2(42), įCCH (27)
įOM1(27), ȞCCph1(21)
įOM2(44),įOM1(15),CH3ipr(13)
CH3ipr1(71), CH3opr1(23)
CH3ipr2(72), CH3opr2(21)
įCHph2(62), ȞCCph1(16)
Ȟ18bCCph1(19), įOM1(12), įCHph1(11)
įCHph1(50), ȞCCph1(25)
1279 vw 1279 w
1257 vs
1223 vs
-
1225 w
1202 w
1183 m
-
1174 vs
-
-
-
-
-
-
1111 m 1110 vw
-
1074 s
-
1036 m
-
1020 s
1007s
980 s
955 w
-
-
1075 w
įCHph2(59), ȞCCph2(33)
-
ȞCCph2(62), įCHph2(18), ȞCBr(15)
ȞOC1(41), ȞOC2(33), ȞCCph1(14)
ȞOC2(40), Rtrid1(25), ȞOC1(20)
ȞCC(35), ȞCCph2(28)
1038 w
-
1023 w
-
gCHC(56), tCCH(29)
Rtrid2(25), ȞCCph2(12)
Rasyto2(45), Rpuck2(36), Rwag2(18)
ȞCCph1(38),ȞOC1(12),įCCC(11),ȞCOph1(10)
982 w
-
-
-
-
R
puck2(46), Rasyto2(30), Rwag2(24)
Rwag1(86), Rpuck1(7)
wag2(35), g10bCHC(25), gOCC(11)
893 w
876 w
843 m
-
818 vs
-
894 m
876 w
843 vw
4.73
R
18.07
12.23
25.44
10.48
37.63
5.26
4.98
3.94
0.69
11.80
9.26
įCCC(25),, įCCO(16), ȞCCph2(15)
-
-
R
wag2(36),Rwag1(28), gCHC(15)
Rwag1(64), Rwag2(13)
811 w
R
wag2(74)
Rwag1(69)
10a ȞCCph1(28), ȞCOph1(22), Rasyd(11)
puck2(49), Rasyto2(47)
Rpuck2(23), Rasyto2(22) ,Rasyd(11)
puck2(42), Rasyto2(40)
-
-
769 w
-
744 m
710 w
-
673 m
638m
603 vw
596 m
772 w
747 w
R
-
712 w
0.769
21.9
1.19
4.66
12.3
1.09
R
-
-
Rpuck2(44), Rasyto2(41)
4 Rpuck2(49), Rasyto2(46)
637
610
597
631vw
1.75
11.76
7.76
RasydO(84)
-
-
ȞCOph1(35),įCOC(25),įCCC(11)
6a Rwag1(32), Rpuck2(17), Rasyto2(15), Rasyt1(14)
614

18ꢀ
ꢀ
564
530
493
482
473
467
422
409
385
367
297
289
272
265
258
224
219
194
174
155
141
115
100
91
552
516
490
476
459
440
417
401
389
356
297
279
272
265
258
217
214
188
168
151
138
107
96
534 m
533 vw
19.90
5.82
4.87
10.33
4.47
0.01
0.20
2.30
5.37
25.49
0.23
0.13
0.07
2.04
0.84
0.62
0.41
5.82
0.04
1.02
0.42
0.28
0.33
12.41
0.37
0.29
0.01
0.01
0.21
12.2
37.6
5.61
1.06
2.25
2.53
0.986
1.8
36.4
49.9
9.44
1.51
2.04
0.682
22
ȞCBr(16), 6b ȞCCph2(15), Rwag2(12), Rasyt 2(12)
Rasydo1(20),Rasyd1(20),įCOC(17),ȞCCph1(15)
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
-
R
wag2(23), Rasyt 2(22), Rasyd1(17), įCCC(37)
Rwag2(28), Rasyt 2(27)
įCCC(37)
Rwag1(48), Rasyto2(29), Rasyt1(12)
Rasyto2(82),Rwag2(15)
-
419 w
-
-
-
Rwag1(40), Rpuck1(13), Rasyt1(12), Rasyto2(10)
įCOC(38),įCOC(23),ȞCOph1(11),įCCC(10)
ȞCCph2(18),įCOC(14),ȞCCph1(11)
įCBr(22), Rasyto2(10), Rpuck2(13), įCC(12)
tCOCH(48), Rwag1(16), Rasyt1(10)
ȞCBr(23), Rasyd(13)
316 w
-
276 w
-
-
-
-
Rpuck2(40), Rasyto2(36), Rwag2(17)
tCOCH(48),Rasyto1(36)
tCOCH(24), Rasyto1(21), Rwag1(13)
įCBr(23), įCCC(9),įCO(16)
įCO(45), įCBr(12)
6.8
7.15
12.4
3.55
13.4
36.2
16.2
82.1
5.06
21.1
78.7
456
188 vw
-
-
Rasyt2(25), Rpuck1(21), Rasyto1(10)
įCCC(15),ȞCCph2(14),ȞCCph1(12),Rasyd2(11)
tHCCO(14), tCCCH(11)
136 m
-
-
-
-
-
-
-
-
tCCOC(34), tCOCH(12)
tCCOC(15), tHCCH(10)
tCCOC(53), tCOCH(19)
89
77
52
33
25
12
77
54
33
23
Rwag2(22),tOCCC(15), Rasyt2(13)
R
wag1(15),tCCOC(15),Rasyto1(13)
įCCC(43), tOCCC(48)
tOCCC(48),įCCC(18)
981
2830
13
tCCCH(40), tHCCO(32)
vs: very strong; ms: medium strong; s: strong; w: weak; vw: very weak
Ȟ: stretching; ph1: phenyl ring1; ph2: phenyl ring2; t: torsion; g: gauche; wag: wagging; ss: symmetric stretching; as:
asymmetric stretching; sd: symmetric deformation; ips: in plane stretching; ops: out of plane stretching; ipb: in plane
bending; opb: out of plane bending; sb: symmetric bending; rck: rocking; ipr: in plane rocking; opr: out of plane
rocking; ; R: ring; trid: trigonal deformation; asyd: asymmetric deformation; asydo: out of plane asymmetric
deformation; puck: puckering; asyt: asymmetric torsion; asyto: out of plane asymmetric torsion; sc: scissoring;
a Relative absorption intensities normalized wiIJh highest peak absorption equal to 1.
b Relative Raman intensities calculated by Eq. (1) and normalized to 100.
c Only potential energy distribuIJion greater than 10%.
4.6.2 Phenyl ring vibrations. Aromatic structures show characteristic C-H stretching vibrations occuring
in the region 3100-3000cm-1 [36-39]. Wilsons numbering convention is used in the vibrational assignment

19ꢀ
ꢀ
of the phenyl rings [40]. The C–H stretching vibrations in benzene derivatives arise from two non
degenerate modes a1g (3072 cm-1), b1u (3060 cm-1) and two degenerate modes e2g (3047 cm-1), e1u (3099
cm-1), i.e. vibrations 2, 13, 7 and 20, respectively. The DMBC molecule comprises of one tri-substituted
phenyl ring (Ph1) and para-disubstituted phenyl ring (Ph2). In para-disubstituted phenyl rings, 2, 7a, 20a
and 20b are active where as in tri-substituted benzenes, of the four allowed C-H stretching modes 2, 20b,
20a and 7b, except 20a, all allowed ring modes are found to be active. Most of the C-H stretching
vibrations are found to be weak which is due to the charge transfer from the hydrogen atom to the carbon
atom. The mode 20b is active in IR with a weak band at 3066 cm-1 and its counterpart weak Raman band
at 3067cm-1. The normal mode 2 appears as a weak band in Raman at 3017cm-1 and as a weak band in IR
at 3012 cm-1. Normal vibrations 3, 9a, 15, 18a and 18b are the C-H in plane bending vibrations of the
substituted phenyl rings and can be expected in the region 1300-1000 cm-1. The in plane deformation
mode 3 is observed in IR at 1302 cm-1 and 1304 cm-1 in Raman. The strong IR and weak Raman bands at
1223 cm-1 and 1225 cm-1 respectively, correspond to the vibrational mode 9a. The weak band at 1111
cmí1 in IR is assigned to the 18b mode of ring Ph1. The absorption bands arising from C–H out-of-plane
bending vibrations are usually observed in the region 1000-675 cm-1. The out-of-plane vibrations in
benzene arise from b2g (995 cm-1), e2u (975 cm-1), e1g (849 cm-1) and a2u (671 cm-1) modes of benzene. The
10a mode appears in IR as a weak band at 769 cm-1 and as a weak band at 772 cm-1 in Raman,
corresponding to Ph1. The phenyl ring modes 4, 6a, and 6b can be observed in IR spectrum at 673 cm-1,
596 cm-1 and 534 cm-1 respectively.
The ring stretching vibrations are prominent in the vibrational spectra of benzene and its
derivatives, as the double bond is in conjugation with the ring. The phenyl ring gives rise to six ring
stretching modes (8a, 8b, 19a, 19b, 14 and 1), which are more sensitive to substituents [40]. With heavy
substituents, the bands tend to shift to somewhat lower wavenumbers and the greater the number of
substituents on the ring, the broader the absorption regions [40]. The mode with the highest magnitude

20ꢀ
ꢀ
corresponds to the doubly degenerate mode e2g (mode 8) of benzene (1599 cmí1) which splits into two
components (8a, 8b) for substituted benzenes. DFT computation gives vibrational modes at 1569 cm-1 and
1623 cm-1 corresponding to 8a mode and 8b mode of Ph1 respectively and at 1604 cm-1 and 1588 cm-1
respectively corresponding to ring Ph2. The ring mode 8b of Ph1 manifests as a medium shoulder band
around 1628 cm-1 in IR and as an intense Raman band near 1628 cm-1. Its relatively strong companion 8a
appears at 1563 cm-1 in IR. The phenyl ring mode 8b is observed as a weak band in the IR spectra at 1583
cmí1 and an intense band near 1584 cm-1 in Raman is assigned to the para-disubstituted phenyl ring (Ph2).
Similarly, the ranges for the degenerate modes e1u (19a and 19b) are 1520 cmí1 – 1460 cmí1 and 1420
cmí1 – 1370 cmí1 respectively [41]. The observed IR band at 1560 cm-1 is assigned to 19a mode of ring
Ph2, while the corresponding 19b mode appears as a medium band at 1400 cm-1 in IR and as a medium
band at 1401 cm-1 in Raman. The observed weak band in IR at 1331 cm-1 is assigned to the mode 14 of
Ph2. In Ph1 the ring mode 14 is observed as a medium band in IR at 1313 cm-1 and as a weak band in
Raman at 1318 cm-1.
4.6.3 Carbonyl and ethylenic bridge vibrations. The spectral signature of the C=O group is its stretching
vibration which appears as an intense band between 1760–1730 cm-1 [37, 41]. The position of the C=O
stretching vibration is very sensitive to various factors such as the physical state, electronic effects by
substituents, ring strains, etc. The C=O stretching vibrations give rise to characteristic intense bands in IR
and Raman, and the intensity of these bands can increase owing to conjugation or formation of hydrogen
bonds[42]. The C24= O25 stretching is observed in IR as a strong band at 1658 cm-1 and a weak band in
Raman at 1659 cm-1, which are confirmed by their PED values. DFT calculations observed at 1661 cm-1
gives the wavenumber of this mode. The deviation from the calculated wave number for this mode can be
attributed to the under estimation of ʌ-electron delocalisation due to conjugation and hydrogen bonding
network inside the crystal. In DMBC the C=C stretching vibrations of ethylenic bridge overlaps with
vibrations of C24=O25 stretching mode and C-H bending vibrations. The intense band at 1257 cm-1 in IR

21ꢀ
ꢀ
spectrum have been assigned to C–O stretching mode which is coupled with C-C stretch and ring trigonal
deformation.
4.6.4 C-Br Vibrations. Generally, characteristic C-Br stretching vibration is observed in the region 650-
485 cm-1. In the title compound DMBC, a medium band is observed at 534 cm-1 in IR. This mode is a
pure stretching mode, but it is often influenced by neighboring atom or groups [42-43]. The vibrations
belonging to the bond between the ring and the bromine atom are important, as mixing of vibrations are
possible due to the presence of the heavy atom. The in plane and out of plane vibrations of C-Br vibration
is also coupled with other modes, as evident from the PED values.
4.7 Molecular electrostatic potential
The ESP, V(r), at a point r due to a molecular system with nuclear charges {ZA} located at {RA}
and electron density ρ(r) is given by
3
N
′
′
ZA
r − RA
ρ(r )d r
V (r) =
−
∑
∫
′
r − r
(4)
A−1
The graphical representation of the molecular electrostatic potential surface (MEP or ESP), as
described by Kollman and Singh [44] is a series of values representing the evaluation of the interaction
energy between a positively charged (proton) probe and points on a solvent accessible surface as defined
by Connolly [45]. As implemented within the Gauss View version 5.1 program, areas of high electron
density, representing a strong attraction between the proton and the points on the molecular surface, have
the brightest red colour and areas of the lowest electron density have deep blue to indigo colour indicating
the regions of maximum repulsion. The molecular electrostatic potential (ESP) at a point in the space
around a molecule gives an indication of the net electrostatic effect produced at that point by the total
charge distribution (electron + nuclei) of the molecule and correlates with dipole moments,
electronegativity, partial charges and chemical reactivity of the molecule. It provides a visual method to
understand the relative polarity of the molecule. An electron density isosurface mapped with electrostatic
potential surface depicts the size, shape, charge density and site of chemical reactivity of the molecules.

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The different values of the electrostatic potential at the surface are represented by different colours; red
represents regions of most negative electrostatic potential, blue represents regions of most positive
electrostatic potential and green represents regions of zero potential. The potential increases in the order
red < orange < yellow < green < blue. Molecular electrostatic potential mapped on the ȡ(r) = 0.0004 a.u.
isodensity surface for DMBC calculated at the B3LYP/6-311++G(d,p) level of theory is shown in figure
10(a). This figure provides a visual representation of the chemically active sites and comparative
reactivity of atoms.

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Figure 10(a).Molecular electrostatic potential mapped on the ȡ(r) = 0.0004 a.u. isodensity surface for
DMBC in the range from í2.261E-2 (red) to +2.261E-2 (blue) (b) Contour diagram for DMBC calculated
at the B3LYP/6-311++G(d,p) level of theory.
It may be seen that a region of zero potential envelopes the ʌ-system of the benzene rings, leaving
a more electrophilic region in the plane of the hydrogen atoms. The shape of the electrostatic potential
surfaces at sites close to the polar carbonyl group in the molecule and the methoxy group is influenced by
the stereo structure and the charge density distribution. These sites show regions of the most negative
electrostatic potential and high activity of the carbonyl group. In contrast, regions close to the other two
polar atoms – bromine, and oxygen of the methoxy groups – show regions of mildly negative potential.
Figure 10 (b) shows the two-dimensional projection of the map into the molecular plane.
5. Conclusions
A chalcone derivative, 1-(4-Bromophenyl)-3-(3, 4-dimethoxy-phenyl) prop-2-en-1-one has been
synthesized and small crystals are grown by slow evaporation technique. Density functional theory
calculations at the B3LYP/6-31G (d, p) level were used to determine the ground state molecular geometry
(bond lengths and bond angles), harmonic vibrational wavenumbers, infrared intensities and Raman
activities of this compound. Potential energy distributions (PEDs) and normal modes for the spectral data
computed at the B3LYP/6-31G (d, p) level, have also been obtained from force-field calculations. The
wavenumbers found after scaling of the force field showed very good agreement with the experimentally
determined values. A comparison of the theoretical spectra and experimental FT-IR and FT-Raman
spectra of the title molecule has been made and complete vibrational assignments of the observed spectra
have been proposed. DMBC is thermally stable up to 265.0 ºC and optically transparent in the visible
region. The NBO analysis, analysis of electrostatic potential map and the HOMO and LUMO analyses,

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reveals the significant degree of charge transfer interactions taking place in the molecule which is
responsible for the enhanced chemical as well as biological activity of the molecule.
Acknowledgments
The author, Lynnette Joseph thanks the University Grants Commission (UGC), New Delhi, India, for the
financial support, Project No. MRP(S)-899/10-11/KLKE002/UGC-SWRO. The authors are highly
grateful to Prof. T. Sundius for the Molvib program.
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Graphical abstract
Molecular Electrostatic Potential map of the molecule reflects the regions of the most negative
electrostatic potential and high activity of the carbonyl group.ꢀ

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Highlights
A chalcone derivative, DMBC has been synthesized and crystals were grown.
DFT calculations were used to determine the molecular geometries and vibrational
wavenumbers.
Information about the size, shape, charge density distribution and site of chemical
reactivity of the molecules has been obtained by mapping the electron density isosurface
with electrostatic potential surfaces (ESP)