1. Vibrational spectra, molecular structure, NBO, UV, NMR, first order
hyperpolarizability, analysis of 4-Methoxy-40
-Nitrobiphenyl by density
functional theory
K. Govindarasu, E. Kavitha ⇑
Department of Physics (Engg.), Annamalai University, Annamalainagar 608 002, India
h i g h l i g h t s
The FTIR and FT-Raman spectra of
4M40
NBPL were reported.
The first order hyperpolarizability
was calculated.
UV–Vis spectra were recorded and
compared with calculated values.
NMR and MEP studies were analyzed.
g r a p h i c a l a b s t r a c t
a r t i c l e i n f o
Article history:
Received 24 September 2013
Received in revised form 16 October 2013
Accepted 31 October 2013
Available online 9 November 2013
Keywords:
4-Methoxy-40
-Nitrobiphenyl
TD-DFT
NBO
UV–Vis
NMR
Hyperpolarizability
a b s t r a c t
In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic
resonance studies of 4-Methoxy-40
-Nitrobiphenyl (abbreviated as 4M40
NBPL) were investigated by utiliz-
ing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The equilibrium geometry, vibrational wavenumbers
and the first order hyperpolarizability of the 4M40
NBPL have been calculated with the help of density
functional theory computations. The FT-IR and FT-Raman spectra were recorded in the region 4000–
400 cmÀ1
and 3500–50 cmÀ1
respectively. Natural Bond Orbital (NBO) analysis is also used to explain
the molecular stability. The UV–Vis absorption spectra of the title compound dissolved in chloroform
were recorded in the range of 200–800 cmÀ1
. The HOMO–LUMO energy gap explains the charge interac-
tion taking place within the molecule. Good correlation between the experimental 1
H and 13
C NMR chem-
ical shifts in chloroform solution and calculated GIAO shielding tensors were found. The dipole moment,
linear polarizability and first order hyperpolarizability values were also computed. The linear polarizabil-
ity and first order hyperpolarizability of the studied molecule indicate that the compound is a good can-
didate of nonlinear optical materials. The chemical reactivity and thermodynamic properties of
4M40
NBPL at different temperature are calculated. In addition, molecular electrostatic potential (MEP),
frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.
Published by Elsevier B.V.
Introduction
The nonlinear optical responses induced in various materials
are of great interest in recent years because of the applications in
photonic technologies such as optical communications, data
storage and image processing [1]. In recent years, the synthetic
approaches to various biphenyl derivatives and their biological
activity were studied. Analysis of the scientific and patent litera-
ture indicates that the biphenyl group is used to create a wide
range of the drugs and products for agriculture [2,3]. Some biphe-
nyl derivatives are patented and widely used in medicine as the
1386-1425/$ - see front matter Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2013.10.122
⇑ Corresponding author. Tel.: +91 9442477462.
E-mail address: eswarankavitha@gmail.com (E. Kavitha).
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
2. anti androgenic and hypotensive drugs [4,5]. Antimicrobial prepa-
rations based on biphenyl derivatives are of great interest and are
used in medicine and in agriculture [6–8]. 4-Methoxy-3-Nitrobi-
phenyl is a biphenyl derivative which displays a twisted conforma-
tion with the two benzene rings making a dihedral angle of 36.69°
[9]. Our molecule 4M40
NBPL has the following properties: Pale
yellow solid: m.p.: 107–108 °C [10]
Stille et al. [11] reported organic synthesis of 4M40
NBPL. Anne
Colonna et al. [12] investigate the chirped molecular vibration in
a stilbene derivative (4-Methoxy-40
-nitrostilbene) in solution.
Hulliger et al. [13] reported on intrinsic and extrinsic defect-
forming mechanisms determining the disordered structure of
4-iodo-40
-Nitrobiphenyl crystals. To best of our knowledge, there
is not any review summarizing the literature on the TD-DFT fre-
quency calculations of 4M40
NBPL have been reported so far. The
FTIR and FT Raman spectroscopy combined with Quantum chemi-
cal computations have been recently used as an effectively tool in
vibrational assignments of nonlinear optical molecule.
The present work mainly deals with detailed structural confor-
mation, experimental FT-IR and FT-Raman spectra, vibrational
assignments using total energy distribution (TED) and NLO activity
as well as HF and DFT/B3LYP calculations for 4M40
NBPL. The elec-
tron density (ED) in various bonding and anti bonding orbital and
E2 energies have been calculated by Natural Bond Orbital (NBO)
analysis using DFT method. The UV spectroscopic studies along
with HOMO–LUMO analysis have been used to explain the charge
transfer within the molecule.
Experimental details
The compound 4-Methoxy-40
-Nitrobiphenyl in the solid form
was purchased from TCI INDIA chemical company at Chennai with
a stated purity greater than 98% and it was used as such without fur-
ther purification. The FT-IR spectrum of this compound was re-
corded in the range of 4000–400 cmÀ1
on a Perkin Elmer FT-IR
spectrometer using KBr pellet technique. The spectrum was re-
corded in the room temperature, with scanning speed of 10 cmÀ1
.
FT-Raman spectrum of the title compound was recorded using
1064 nm line of Nd:YAG laser as excitation wavelength in the region
3500–50 cmÀ1
on a BRUKER RFS 27 FT-Raman Spectrometer
equipped with FT-Raman molecule accessory. The spectral resolu-
tion was set to 2 cmÀ1
in back scattering mode. The laser output
was kept at 100 mW for the solid sample. The ultraviolet absorption
spectra of 4M40
NBPL were examined in the range 200–800 nm using
Cary 5EUV–VIS–NIR spectrometer. The UV pattern is taken from a
10–5 M solution of 4M40
NBPL, dissolved in chloroform. The theoret-
ically predicted IR and Raman spectra at B3LYP/6-31G(d,p) level cal-
culation along with experimental FT-IR and FT-Raman spectra are
shown in Figs. 1 and 2. The spectral measurements were carried
out at Indian Institute of Technology (IIT), Chennai.
Computational details
In the present study, the HF and density functional theory
(DFT/B3LYP) at the 6-31G(d,p) basis set level was adopted to cal-
culate the optimized parameters and vibrational wavenumbers of
the normal modes of the 4M40
NBPL molecule. All the theoretical
calculations were performed using the Gaussian 03 W program
package [14] with the default convergence criteria, without any
constraint on the geometry [15]. The equilibrium geometry
corresponding with the true minimum on the potential energy
surface (PES) was effectively obtained by solving self-consistent
field equation. The vibrational spectra of the 4M40
NBPL were
obtained by taking the second derivative the energy, computed
4000 3500 3000 2500 2000 1500 1000 500
3003
2659
1636
1378
1197
900
563
3062
2930
2836
2445
1935
1509
1482
1342
1186
1016
839
696
814
1090
1164
1251
1338
1459
1587
2899
3067
1123
1224
1406
1520
B3LYP/6-31 G(d,P)
Experimental
Wavenumber (cm-1)
Transmittance(%)IRintensity(arb.units)
Fig. 1. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-IR spectra for 4-Methoxy-40
Nitrobiphenyl.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 131
3. analytically. The optimized structural parameters were used in
the vibrational frequency calculations at DFT levels to character-
ize all stationary points as minima using the GAUSSVIEW
animation program [16]. By the use of total energy distribution
(TED) using VEDA 4 program [17] along with available related
molecules, the vibrational frequency assignments were made
with a high degree of accuracy. The Natural Bond Orbital (NBO)
calculations were performed using NBO 3.1 program [18] as
implemented in the Gaussian 03W [16] package at the
DFT/B3LYP level. 1
H and 13
C NMR chemical shifts were calculated
with GIAO approach [19,20] by applying B3LYP method. The the-
oretical 1
H and 13
C NMR chemical shift values were obtained by
subtracting the GIAO calculation [21,22]. We have utilized HF
and DFT/B3LYP approach with 6-31G(d,p) as basis set for compu-
tation of molecular structure, vibrational frequencies and energies
of optimized structures, in the present work.
Prediction of Raman intensities
The Raman activities (SRa) calculated with Gaussian 03 program
[14] converted to relative Raman intensities (IRa) using the follow-
ing relationship derived from the intensity theory of Raman scat-
tering [23,24]
Ii ¼
fðmo À miÞ4
Si
mi½1 À expðhcmi=ktÞŠ
where mo is the laser exciting wavenumber in cmÀ1
(in this work, we
have used the excitation wavenumber mo = 9398.5 cmÀ1
, which
corresponds to the wavelength of 1064 nm of a Nd-YAG laser), mi
the vibrational wavenumber of the ith
normal mode (cmÀ1
) while
Si is the Raman scattering activity of the normal mode mi. f (is a con-
stant equal to 10À12
) is a suitably chosen common normalization
factor for all peak intensities. h, k, c and T are Planck and Boltzmann
constants, speed of light and temperature in Kelvin, respectively.
For the simulation of calculated FT-Raman spectra have been plot-
ted using pure Lorentizian band shape with a bandwidth of Full
Width at Half Maximum (FWHM) of 10 cmÀ1
.
Results and discussion
Conformational stability
In order to describe conformational flexibility of the title mole-
cule, the energy profile as a function of C17AO16AC4AC3 torsion an-
gle was achieved with B3LYP/6-31G(d,p) method (supplementary
material S1). The conformational energy profile shows two maxima
near 150° and 210° for (C17AO16AC4AC3) torsion angle. The maxi-
mum energies are obtained À782.5191 and À782.5194 Hartree for
150° and 210° respectively. It is clear from supplementary material
S1, there are two local minima (stable conformers) observed at 0°
or 360° having the energy of À782.5289 Hartree and 180° having
the energy of À782.5207 Hartree for T (C17AO16AC4AC3). There-
fore, the most stable conformer is for 0° torsion angle for
C17AO16AC4AC3 rotation. Further results are based on the most
stable conformer of 4M40
NBPL molecule to clarify molecular struc-
ture and assignments of vibrational spectra.
74
222
410
518
619
794
989
1090
1170
1264
1338
1587
2899
3067
3500 3000 2500 2000 1500 1000 500
3081
1596
1337
1108
1013
801
421
76
1474
1158
897
298
Ramanintensity(arb.units)
B3LYP/6-31G(d,p)
Experimental
Wavenumber (cm-1
)
Fig. 2. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-Raman spectra for 4-Methoxy-40
Nitrobiphenyl.
132 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
4. Molecular geometry
The optimized geometric parameters such as bond lengths,
bond angles and dihedral angles of the title molecule were given
in Table 1 using HF and Density functional theoretical calculation
with 6-31G(d,p) as a basis set. The atom numbering scheme
adopted in this study is given in Fig. 3. Owing the absence of exper-
imental data of the molecule 4M40
NBPL is compared with XRD data
of closely related molecule 4-Methoxy-3-Nitrobiphenyl [9]. Our
title molecule contains two phenyl rings and Methoxy group is
substituted to 4th position (atom C4) of the phenyl ring A and Nitro
group is substituted to 40
th position (atom C10) of the phenyl ring
B. In the benzene ring, CAC bond length is about 1.396 Å [25]. From
the Table 1 the optimized bond lengths of CAC in phenyl ring
fall in the range from 1.386 to 1.480 Å at B3LYP method and
1.375 to 1.487 Å at HF method. From the theoretical values, it is
found that most of the optimized bond lengths are slightly larger
than the experimental values due to fact that the theoretical
Table 1
Calculated optimized parameter values of the 4-Methoxy-40
-Nitrobiphenyl [Bond length in (Å), angles in (°)].
Bond length B3LYP HF a
Exp Bond angle B3LYP HF a
Exp Dihedral angle B3LYP HF a
Exp
C1AC2 1.402 1.386 1.384 C2AC1AC6 117.5 117.7 C6AC1AC2AC3 0.12 0.10
C1AC6 1.409 1.398 1.387 C2AC1AC7 121.3 121.2 C6AC1AC2AH18 178.21 178.69
C1AC7 1.480 1.487 1.473 C6AC1AC7 121.2 121.1 C7AC1AC2AC3 À179.76 À179.80
C2AC3 1.395 1.388 1.370 C1AC2AC3 121.8 121.8 C7AC1AC2AH18 À1.68 À1.21
C2AH18 1.086 1.076 0.930 C1AC2AH18 119.6 119.7 C2AC1AC6AC5 0.14 0.13
C3AC4 1.400 1.386 1.385 C3AC2AH18 118.6 118.5 C2AC1AC6AH21 178.26 178.74
C3AH19 1.083 1.073 0.930 C2AC3AC4 119.6 119.6 C7AC1AC6AC5 À179.98 À179.97
C4AC5 1.404 1.394 1.398 C2AC3AH19 119.3 119.1 C7AC1AC6AH21 À1.86 À1.36
C4AO16 1.361 1.345 1.336 C4AC3AH19 121.1 121.3 C2AC1AC7AC8 144.30 137.00
C5AC6 1.386 1.375 1.370 C3AC4AC5 119.4 119.4 116.2 C2AC1AC7AC12 À35.66 À42.97 À36.6
C5AH20 1.085 1.074 – C3AC4AO16 124.8 124.7 C6AC1AC7AC8 À35.58 À42.90 À36.2
C6AH21 1.086 1.076 0.930 C5AC4AO16 115.8 115.9 C6AC1AC7AC12 144.47 137.13
C7AC8 1.409 1.395 1.383 C4AC5AC6 120.2 120.3 C1AC2AC3AC4 À0.24 À0.21
C7AC12 1.409 1.395 1.381 C4AC5AH20 118.5 118.6 C1AC2AC3AH19 179.11 179.34
C8AC9 1.389 1.381 1.377 C6AC5AH20 121.3 121.2 H18AC2AC3AC4 À178.35 À178.82
C8AH22 1.085 1.074 0.930 C1AC6AC5 121.4 121.3 H18AC2AC3AH19 1.01 0.73
C9AC10 1.394 1.383 1.363 C1AC6AH21 119.6 119.7 C2AC3AC4AC5 0.11 0.09
C9AH23 1.083 1.072 C5AC6AH21 119.0 119.0 C2AC3AC4AO16 À179.90 À179.92
C10AC11 1.394 1.383 1.358 C1AC7AC8 121.0 120.7 H19AC3AC4AC5 À179.23 À179.45
C10AN13 1.467 1.455 C1AC7AC12 121.0 120.8 H19AC3AC4AO16 0.75 0.54
C11AC12 1.389 1.381 1.376 C8AC7AC12 118.1 118.5 C3AC4AC5AC6 0.14 0.14
C11AH24 1.083 1.072 0.930 C7AC8AC9 121.3 121.1 C3AC4AC5AH20 À179.29 À179.43
C12AH25 1.085 1.074 0.930 C7AC8AH22 119.5 119.7 O16AC4AC5AC6 À179.85 À179.86
N13AO14 1.232 1.195 – C9AC8AH22 119.1 119.1 O16AC4AC5AH20 0.73 0.57
N13AO15 1.232 1.194 A C8AC9AC10 118.9 118.8 C3AC4AO16AC17 0.28 0.47
O16AC17 1.421 1.401 1.420 C8AC9AH23 121.7 121.2 C5AC4AO16AC17 À179.73 À179.54
C17AH26 1.091 1.080 0.960 C10AC9A H23 119.4 120.0 C4AC5AC6AC1 À0.27 À0.25
C17AH27 1.097 1.086 0.960 C9AC10AC11 121.6 121.7 C4AC5AC6AH21 À178.40 À178.87
C17AH28 1.097 1.086 0.960 C9AC10AN13 119.2 119.2 H20AC5AC6AC1 179.15 179.31
C11AC10AN13 119.2 119.2 H20AC5AC6AH21 1.01 0.69
C10AC11AC12 118.8 118.8 C1AC7AC8AC9 À179.98 179.98
C10AC11AH24 119.4 120.0 C1AC7AC8AH22 À1.69 À1.41
C12AC11AH24 121.8 121.2 C12AC7AC8AC9 À0.02 À0.04
C 7AC12AC11 121.3 121.1 C12AC7AC8AH22 178.27 178.57
C7AC12AH25 119.5 119.7 C1AC7AC12AC11 179.74 179.77
C11AC12AH25 119.1 119.2 C1AC7AC12AH25 À1.97 À1.64
C10AN13AO14 117.8 117.7 C8AC7AC12AC11 À0.22 À0.21
C10AN13AO15 117.8 117.7 C8AC7AC12AH25 178.07 178.38
O14AN13AO15 124.5 124.5 C7AC8AC9AC10 0.21 0.22
C4AO16AC17 118.4 119.9 C7AC8AC9AH23 179.45 179.58
O16AC17AH26 106.0 106.2 109.5 H22AC8AC9AC10 À178.09 À178.40
O16AC17AH27 111.6 111.4 109.5 H22AC8AC9AH23 1.15 0.96
O16AC17AH28 111.6 111.4 109.5 C8AC9AC10AC11 À0.15 À0.15
H26AC17AH27 109.2 109.2 C8AC9AC10AN13 179.88 179.88
H26AC17AH28 109.2 109.1 H23AC9AC10AC11 À179.41 À179.52
H27AC17AH28 109.2 109.4 H23AC9AC10AN13 0.62 0.50
C9AC10AC11AC12 À0.09 À0.10
C9AC10AC11AH24 À179.31 À179.44
N13AC10AC11AC12 179.88 179.88
N13AC10AC11AH24 0.67 0.54
C9AC10AN13AO14 180.00 À179.65
C9AC10AN13AO15 À0.03 0.34
C11AC10AN13AO14 0.03 0.38
C11AC10AN13AO15 À180.00 À179.64
C10AC11AC12AC7 0.28 0.28
C10AC11AC12AH25 À178.03 À178.32
H24AC11AC12AC7 179.48 179.61
H24AC11AC12AH25 1.18 1.01
C4AO16AC17AH26 179.67 179.61
C4AO16AC17AH27 60.88 60.84
C4AO16AC17AH28 À61.57 À61.63
a
Taken from Ref. [9].
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 133
5. calculations belong to isolated molecules in gaseous phase and the
experimental results belong to molecules in solid state [26]. Many
authors [27–29] have been explained the changes in frequency or
bond length of the CAH bond on substitution due to change in
the charge distribution on the carbon atom of the benzene ring.
The optimized molecular structure of title molecule reveals that
the substituted nitro group is in planar with the benzene ring
(C11AC10AN13AO14 = 0.03°). Inclusion of the NO2 group known
for its strong electron-withdrawing nature, in the 4’th (atom
C10) position is expected to increase a contribution of the reso-
nance structure, in which the electronic charge is concentrated at
this site. This is the reason for the shortening of bond lengths
N13AO14 = 1.195 Å and N13AO15 = 1.194 Å obtained by HF meth-
od. The same bond lengths calculated by DFT method is found to be
1.232 and 1.232 Å. The benzene ring appears to be a little distorted
because of the NO2 group substitution as seen from the bond an-
gles C9AC10AC11, which are calculated as (121.7°) and (121.6°)
respectively, by HF and B3LYP methods and are larger than typical
hexagonal angle of (120°). With the electron donating (methoxy)
substituents on the benzene ring, the symmetry of the ring is dis-
torted, yielding ring angles smaller than (120°) at the point of sub-
stitution [30]. Due to the electron donating effect of methoxy
group, it is observed that the bond angle at the point of substitu-
tion C3AC4AC5 (119.4°) for both DFT and HF method. All the
CAH bond lengths are presented as nearly equal values at
1.086 Å and 1.076 Å for the C6AH21 and C2AH18 bonds, for both
DFT and HF methods respectively, in benzene ring. On the other-
hand, a small increment occurs in the methyl group C17AH27
and C17AH28 bonds which are almost 1.097 Å at DFT and
1.085 Å at HF method. In the methoxy group of H27 and H28 atoms
are alone lying out-of-plane of the molecule. Owing to this reason,
the bond angles and dihedral angles are varied in the above case.
The bond angle O16AC17AH26 and O16AC17AH27 and
O16AC17AH28 are calculated at (106.0°) and (111.6°) and
(111.6°) at DFT method and (106.2°) and (111.4°) and (111.4°) at
HF method. The dihedral angles are calculated according to follow-
ing atoms C4AO16AC17AH27 is (60.88°) at DFT method and
(60.84°) at HF method and C4AO16AC17AH28 is (À61.57°) at
DFT method and (À61.63°) at HF method. The dihedral angle
C6AC1AC7AC8 between two phenyl rings is (À35.58°) at DFT
method which is good agreement with experimental value
(À36.2°).
Vibrational assignments
Vibrational spectroscopy has been shown to be effective in the
identification of functional groups of organic compounds as well as
in studies on molecular conformations and reaction kinetics [31].
The title molecule consists of 28 atoms, which undergo 78 normal
modes of vibrations. It agrees with C1 point group symmetry, all
vibrations are active both in Raman and infrared absorption. The
detailed vibrational assignment of fundamental modes of
4M40
NBPL along with the calculated IR and Raman frequencies
and normal mode descriptions using TED are reported in Table 2.
The calculated frequencies are usually higher than the correspond-
ing experimental quantities, due to the combination of electron
correlation effects and basis set deficiencies. After applying the
scaling factors, the theoretical calculations reproduce the experi-
mental data well in agreement. In our study we have followed
scaling factor of 0.9026 for HF/6-31G(d,p) and 0.9608 for
B3LYP/6-31G(d,p) respectively.
CAH vibrations
The aromatic structure shows the presence of CAH stretching
vibration in the region 3100–3000 cmÀ1
, which is the characteris-
tic region for the prepared recognition of CAH stretching vibration
[32,33]. In this region, the bands are not affected appreciably by
the nature of the substituent. In our present work the CAH stretch-
ing band observed at 3101, 3061, 3017, 2968, and 2930 cmÀ1
in FT-
IR spectrum and 3080 cmÀ1
in FT-Raman spectrum. The calculated
wavenumbers at 3062, 3044, 3028, 2985, 2933 and 2873 cmÀ1
in
HF method and 3101, 3081, 3068, 3031, 2963, and 2901 cmÀ1
in
B3LYP method are assigned to CAH stretching vibration. As evident
from the TED column, they are pure vibrations almost contributing
to 93%. The CACAH in-plane bending vibrations are normally oc-
curred as a number of strong to weak intensity bands in the region
1300–1000 cmÀ1
[34]. In our case CACAH in-plane bending vibra-
tions observed at 1600, 1574, 1508, 1486, 1400, 1301, 1273, 1185
and 1118 cmÀ1
in FT-IR spectrum and 1508, 1395, 1291, and
1108 cmÀ1
in FT-Raman spectrum. The computed wavenumbers
at 1680, 1626 1535, 1460, 1430, 1305, 1200, 1179,1120 and
1083 cmÀ1
in HF method and 1604, 1584,1504, 1412, 1386, 1299,
1262, 1168, 1100 and 1088 cmÀ1
in B3LYP method are assigned
to CACAH in-plane bending vibrations. The CAH out-of-plane
bending vibrations are well identified in the recorded spectra with-
in their characteristic region 1000–750 cmÀ1
[35]. In our case the
CAH out-of-plane bending vibrations are observed at 1483, 1476,
1171 and 1145 cmÀ1
in HF method and 1457, 1446, 1164 and
1131 cmÀ1
in B3LYP method. No bands observed for CAH out-of-
plane bending vibrations both FT-IR and FT-Raman spectra.
CAC and CACAC vibrations
The ring carbon–carbon stretching vibrations occur in the re-
gion 1625–1430 cmÀ1
[33]. Varsanyi [36] observed these bands
are of variable intensity at 1625–1280 cmÀ1
. In the present study
CAC stretching vibration observed at 1400, 1301, 1273, 1250,
1185 and 1015 cmÀ1
in FT-IR spectrum and 1595, 1395, 1291,
1192, 1012 and 420 cmÀ1
in FT-Raman spectrum. The computed
wavenumbers at 1640, 1430, 1305, 1183, 1179, 1016, and
428 cmÀ1
in HF method and 1597, 1386, 1299, 1250, 1168, 1006,
and 422 cmÀ1
in B3LYP method are assigned to CAC stretching
vibration. The theoretically calculated CAC stretching vibrations
show good agreement with recorded spectral data. The in-plane
deformation vibration is at higher frequencies than the out-of-
plane vibrations. Shimanouchi et al. [37] gave the frequency data
for these vibrations for different benzene derivatives as a result
of normal coordinate analysis. In our case the CACAC in-plane
bending vibrations observed at 1574, 1486, 999, 722 and
625 cmÀ1
in FT-IR spectrum and 627, 420 and 115 cmÀ1
in FT-Ra-
man spectrum. The computed wavenumbers at 1626, 1505, 1011,
731,633, 428, 276 and 142 cmÀ1
in HF method and 1584, 1471,
991, 710, 629, 422, 271 and 139 cmÀ1
in B3LYP method are as-
signed to CACAC in plane bending vibration. The CACAC out of
Fig. 3. Optimized Molecular structure and atomic numbering of 4-Methoxy-40
-
Nitrobiphenyl.
134 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
7. plane bending vibration observed at 550 and 492 cmÀ1
in FT-IR
spectrum and 358 and 115 cmÀ1
in FT-Raman spectrum. The theo-
retically predicted wavenumbers at 555, 508, 355 and 142 cmÀ1
in
HF method and 539, 498, 349 and 139 cmÀ1
in B3LYP method are
assigned to CACAC out of plane bending vibration. The computed
wavenumbers at 721, 708, 416, 192, 69, and 58 cmÀ1
in HF method
and 703, 681, 406, 192, 77 and 64 cmÀ1
in B3LYP method are as-
signed to CACACAC inplane bending vibration. This vibration
experimentally observed at 173 and 76 cmÀ1
in FT-Raman spec-
trum. The theoretically computed wavenumbers at B3LYP method
gives good agreement with experimental data, when compare to
HF method.
CAO vibrations
The CAO stretching band of the aromatic ether in IR spectrum is
characterized by the frequencies around 1270–1230 cmÀ1
, while
the band in Raman spectrum usually presents a weak activity in
the region of 1310–1210 cmÀ1
. In our case CAO stretching vibra-
tion observed at 1033 cmÀ1
in FT-Raman spectrum. The computed
wavenumbers at 1067 cmÀ1
in HF method and 1034 cmÀ1
in B3LYP
method are assigned to CAO stretching vibration. The TED corre-
sponding to this vibration suggests that it is a strong mode and ex-
actly contributing to 66%. The theoretically predicted wavenumber
at 257 cmÀ1
in HF method and 253 cmÀ1
in B3LYP method are as-
signed to CACAO in-plane mode.
OACH3 vibrations
Electronic effects such as back-donation and induction, mainly
caused by the presence of atom adjacent to CH3 group, can shift
the position of CH stretching and bending modes [38–41]. The
asymmetric stretching vibrations of CH3 are expected in the region
3000–2925 cmÀ1
and the symmetric CH3 stretching vibrations in
the range 2940–2905 cmÀ1
[42,43]. In the present study the asym-
metric stretching vibrations of CH3 are observed at 3017 and
2968 cmÀ1
in FT-IR spectrum. The theoretically predicted wave-
numbers at 2933 and 2085 cmÀ1
in HF method and 3031 and
2963 cmÀ1
in B3LYP method assigned to CAH asymmetric stretch-
ing vibration of the CH3 group. As evident from the TED column,
they are pure stretching vibrations almost contributing to 99%.
The symmetric stretching vibrations of CH3 are observed at
2930 cmÀ1
in FT-IR spectrum. The theoretically predicted wave-
numbers at 2873 cmÀ1
in HF method and 2901 cmÀ1
in B3LYP
method assigned to CAH symmetric stretching vibration of the
CH3 group. The TED corresponding to this vibration suggests that
it is a pure mode and exactly contributing to 91%. The computed
wavenumbers at 1483 and 1476 cmÀ1
in HF method and 1457
and 1446 cmÀ1
in B3LYP method are assigned to scissoring of the
CH3 unit. The calculated TED corresponding to this mode is also
as a mixed mode with 82% of scissoring mode. The computed
wavenumbers at 1171 and 1145 cmÀ1
in HF method and 1164
and 1131 cmÀ1
in B3LYP method are assigned to rocking mode of
the CH3 unit. The calculated TED corresponding to this mode is also
as a mixed mode with 14% of rocking mode.
NO2 vibrations
Aromatic nitro compounds have strong absorptions due to
asymmetric and symmetric stretching vibrations of the NO2 group
at 1570–1485 and 1370–1320 cmÀ1
, respectively, Hydrogen bond-
ing has a little effect on the NO2 asymmetric stretching vibrations
[44,45]. In our present work OAN stretching vibrations observed at
1342 and 839 cmÀ1
in FT-IR spectrum and 1338 cmÀ1
in FT-Raman
spectrum. The computed wavenumbers at 1395 and 871 cmÀ1
in
HF method 1338 and 834 cmÀ1
in B3LYP method are assigned to
NAO stretching vibration of NO2 group. The deformation vibrations
of NO2 group are in the low frequency region [46]. In our molecule
the in-plane bending vibrations of the NO2 group are observed at
1342, 839 and 722 cmÀ1
in FT-IR spectrum and 1338 cmÀ1
in FT-
Raman spectrum. The theoretically predicted wavenumbers at
1395, 871 and 731 cmÀ1
in HF method and 1338, 834 and
710 cmÀ1
in B3LYP method are assigned to in-plane bending vibra-
tions of the NO2 group. The calculated wavenumbers are good
agreement with experimental findings.
NBO analysis
The natural bond orbitals (NBO) calculations were performed
using NBO 3.1 program [47] as implemented in the Gaussian 03
package at the DFT/B3LYP level in order to understand various sec-
ond-order interactions between the filled orbitals of one subsys-
tem and vacant orbitals of another subsystem, which is a
measure of the intermolecular delocalization or hyper conjuga-
tion.NBO analysis provides the most accurate possible ‘natural Le-
wis structure’ picture of ‘j’ because all orbital details are
mathematically chosen to include the highest possible percentage
of the electron density. A useful aspect of the NBO method is that it
gives information about interactions of both filled and virtual orbi-
tal spaces that could enhance the analysis of intra and inter molec-
ular interactions. The second-order Fock-matrix was carried out to
evaluate the donor–acceptor interactions in the NBO basis. The
output obtained by the 2nd-order perturbation theory analysis is
normally the first to be examined by the experienced NBO user
in searching for significant delocalization effects. However, the
strengths of these delocalization interactions, E(2), are estimated
by second order perturbation theory as estimated by the following
equation.
E2 ¼ DEij ¼ qi
Fði; jÞ
2
ej À ei
qi is the donor orbital occupancy; Ei, Ej is the diagonal elements and
Fij is the off diagonal NBO Fock matrix element.
Table 2 (continued)
Mode Nos. Experimental
wavenumbers/cmÀ1
Theoretical wavenumbers/cmÀ1
Vibrational assignments with TED (P10%)
HF/6-31G(d,p) B3LYP/6-31G(d,p)
FT-IR FT-Raman Unscaled Scaled a
IIR
b
IRa Unscaled Scaled a
IIR
b
IRa
72 173 213 192 2.24 5.14 200 192 1.72 3.66 dCNO(15) + sCCCC(24)
73 115 157 142 0.75 2.38 144 139 0.38 1.14 dCCC(13) + cCCCC(22) + sCCOC(16)
74 96 87 5.70 30.2 102 98 4.18 18.13 dCCC(15) + sCCCC(12) + sCCOC(51)
75 76 77 69 1.02 6.87 81 77 1.18 6.57 sCCCC(78)
76 65 58 1.87 15.05 66 64 1.09 7.35 dCCC(34) + cCCCC(10) + sCCOC(11) + sCCCC(10)
77 49 44 0.67 7.15 51 49 0.81 7.18 cCCCC(49)
78 42 38 0.15 1.86 39 38 0.18 2.07 cCCCC(50)
m – stretching; d – in-plane-bending; c – out-of-plane bending; s – torsion; w – weak; s – strong; vs – very strong; vw – very weak; m – medium.
a
IIR-IR Intensity (K mmolÀ1
).
b
IRa-Raman intensity (Arb units) (intensity normalized to 100%).
136 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
8. The larger E(2), value the more intensive is the interaction be-
tween electron donors and acceptor, i.e. the more donation ten-
dency from electron donors to electron acceptors and the greater
the extent of conjugation of the whole system [48]. In this present
work the p electron delocalization is maximum around C1AC2,
C3AC4, C5AC6 distributed to p*
antibonding of C5AC6, C1AC2
and C3AC4 with a stabilization energy of about 20.68, 16.93 and
21.34 kJ/mol as shown in Table 3. The other interaction energy in
this molecule is p electron donating from p(C7AC12)?p*
(C10AO11), p(C8AC9)?p*
(C7AC12), p(C10AC11)?p*
(N13AO14)
resulting a stabilization energy of about 25.39, 21.26 and
26.02 kJ/mol. The most important interaction is LP(1)O16 ? r*
(C3AC4), r*
(C7AH26), r*
(C7AH27), r*
(C7AH28) and with a
stabilization energy of about 7.60, 1.83, 1.26 and 1.22 kJ/mol.
The another most important interaction energy is LP(2)O14 ? r*
(C10AN13), r*
(N13AO15) and LP(2)O15 ? p*
(N13AO14) and
LP(2)O16 ? p*
(C3AC4) of about 12.32, 19.24 and 162.56 and
31.87 kJ/mol shows higher values than those of the other delocal-
ization around the ring. The p*
(C3AC4) of the NBO conjugated with
p*
(C1AC2), p*
(C5AC6) resulting to stabilization of 308.53 and
263.61 kJ/mol respectively shown in Table 3.
13
C and 1
H NMR spectral analysis
The molecular structure of 4M40
NBPL compound was optimized
by using B3LYP method in conjunction with 6-31G(d,p) as basis
set. Then, gauge-including atomic orbital (GIAO) 13
C and 1
H chem-
ical shift calculations of the compound were made. The GIAO
[49,50] method is one of the most common approaches for calcu-
lating nuclear magnetic shielding tensors. For the same basis set
size GIAO method is often more accurate than those calculated
with other approaches [51]. NMR spectra are recorded on
MERCURY (400 MHz for 1
H NMR, 100 MHz for 13
C NMR) spectrom-
eters; chemical shifts are expressed in ppm (dunits) relative to TMS
signal as internal reference in CHCl3 [52]. The NMR spectra calcu-
lations were performed for CHCl3 solvent. The chemical shifts with
respect to tetramethylsilane (TMS). The recorded 1
H, 13
C and NMR
spectra of 4M40
NBPL in chloroform solution are shown in supple-
mentary material S2 and S3. Theoretical and experimental chemi-
cal shifts of title molecule in 13
C and 1
H NMR spectra are gathered
in supplementary material S4 [52]. Taking into account that the
range of 13
C NMR chemical shifts for a typical organic molecule
usually is 100 ppm [53,54], the accuracy ensures reliable inter-
pretation of spectroscopic parameters. In the present work, 13
C
NMR chemical shifts in the ring for the title compound are
100 ppm, as they would be expected. The oxygen and nitrogen
atoms polarize the electron distribution in its bond to carbon and
decrease the electron density at the ring carbon. Therefore, the cal-
culated 13
C chemical shifts values of (C4) and (C10) bonded to the
oxygen and nitrogen atoms that are too high in the rings. The
chemical shift values of C4 and C10 which are in the ring has been
observed at 158.6 and 133.4 ppm (CAO and CAN) and calculated
149.3 and 137.2 ppm respectively. Similarly, other three carbon
peaks in the rings are observed at 55.3, 114.1 and 127.7 ppm and
are calculated at 47.2, 115.1 and 122.8 ppm in chloroform. In the
1
H NMR spectrum just one type of protons appears at 3.85 ppm
as a singlet (OACH3), where as the chemical shift value of
3.82 ppm in chloroform have been determined, the values are
listed in supplementary material S3. In that, we calculated chemi-
cal shifts for H20 and H21 and H22 are 6.97 and 7.49 and 7.54 ppm
also give a good correlation with the experimental observations of
6.97 and 7.48 and 7.93 ppm, respectively. This shows that the cor-
relations between theory and experiment chemical shifts for the ti-
tle compound are good.
Nonlinear optical (NLO) effects
The polarizability (a) and the hyper polarizability (b) and the
electric dipole moment (l) of the 4-Methoxy-40
-Nitrobiphenyl
are calculated by finite field method using HF/6-31G(d,p) basis
set. To calculate all the electric dipole moments and the first hyper
polarizabilities for the isolated molecule, the origin of the Cartesian
Table 3
Second order Perturbation theory analysis of Fock Matrix in NBO basis for 4-Methoxy-40
-Nitrobiphenyl.
Donor (i) ED (i)(e) Acceptor (j) ED (j)(e) E(2)a
(kJ molÀ1
) E(j)ÀE(i)b
a.u F(i,j)c
a.u
p(C1AC2) 1.656 p*
(C3AC4) 0.393 17.74 0.27 0.063
p*
(C5AC6) 0.305 20.68 0.28 0.069
p(C3AC4) 1.646 p*
(C1AC2) 0.374 22.66 0.29 0.073
p*
(C5AC6) 0.305 16.25 0.29 0.062
p(C5AC6) 1.711 p*
(C1AC2) 0.374 16.93 0.29 0.064
p*
(C3AC4) 0.393 21.34 0.28 0.071
p(C7AC12) 1.605 p*
(C8AC9) 0.290 17.10 0.28 0.063
p*
(C10AO11) 0.392 25.39 0.27 0.074
p(C8AC9) 1.666 p*
(C7AC12) 0.355 21.26 0.29 0.070
p*
(C10AC11) 0.392 18.89 0.28 0.066
p(C10AC11) 1.640 p*
(C7AC12) 0.356 17.19 0.29 0.063
p*
(C8AC9) 0.290 20.91 0.29 0.071
p*
(N13AO14) 0.633 26.02 0.15 0.059
LP(2)O14 1.899 r*
(C10AN13) 0.102 12.32 0.58 0.075
r*
(N13AO15) 0.057 19.24 0.70 0.105
LP(2)O15 1.450 p*
(N13AO14) 0.633 162.56 0.14 0.138
LP(2)O16 1.833 p*
(C3AC4) 0.393 31.87 0.34 0.098
p*
(C3AC4) 0.393 p*
(C1AC2) 0.374 308.53 0.01 0.080
p*
(C5AC6) 0.305 263.61 0.01 0.082
p*
(C5AC6) 0.305 RY*
(3)C5 0.001 2.11 0.62 0.082
RY*
(4)C6 0.000 2.02 0.78 0.091
LP(1)O16 1.964 r*
(C3AC4) 0.029 7.60 1.10 0.082
r*
(C7AH26) 0.007 1.83 1.00 0.039
r*
(C7AH27) 0.019 1.26 0.98 0.031
r*
(C7AH28) 0.019 1.22 0.98 0.031
ED Means electron density.
a
E(2) Means energy of hyper conjugative 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.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 137
9. coordinate system (x, y, z) = (0,0,0) was chosen at own center of
mass of 4M40
NBPL.
The NLO activity provide the key functions for frequency shift-
ing, optical modulation, optical switching and optical logic for the
developing technologies in areas such as communication, signal
processing and optical interconnections [55,56]. The first static
hyperpolarizability (bo) and its related properties (b, ao and Da)
have been calculated using HF/6-31G(d,p) level based on finite
field approach. In the presence of an applied electric field, the en-
ergy of a system is a function of the electric field and the first
hyperpolarizability is a third rank tensor that can be described
by a 3 Â 3 Â 3 matrix. The 27 components of the 3D matrix can
be reduced to 10 components because of the Kleinman symmetry
[57]. The matrix can be given in the lower tetrahedral format. It
is obvious that the lower part of the 3 Â 3 Â 3 matrices is a tetra-
hedral. The components of b are defined as the coefficients in the
Taylor series expansion of the energy in the external electric field.
When the external electric field is weak and homogeneous, this
expansion is given below:
E ¼ Eo
À laFa À 1=2aabFaFb À 1=6babcFaFbFcþ......
where Eo
is the energy of the unperturbed molecules, Fa is the field
at the origin, la,aab and babc are the components of dipole moment,
polarizability and first hyperpolarizability, respectively.
The total static dipole moment l, the mean polarizability ao, the
anisotropy of the polarizability Da and the mean first hyperpolar-
izability bo, using the x, y and z components are defined as:
Dipole moment is
l ¼ ðl2
x þ l2
y þ l2
z Þ
1=2
Static polarizability is
a0 ¼ ðaxx þ ayy þ azzÞ=3
Total polarizability is
Da ¼ 2À1=2
½ðaxx À ayyÞ2
þ ðayy À azzÞ2
þ ðazz À axxÞ2
þ 6a2
xzŠ
1=2
First order hyperpolarizability is
b ¼ ðb2
x þ b2
y þ b2
z Þ
1=2
where
bx ¼ ðbxxx þ bxyy þ bxzzÞ
by ¼ ðbyyy þ byzz þ byxxÞ
bz ¼ ðbzzz þ bzxx þ bzyyÞ
b ¼ ½ðbxxx þbxyy þbxzzÞ2
þðbyyy þbyzz þbyxxÞ2
þðbzzz þbzxx þbzyyÞ2
Š
1=2
Since the values of the polarizabilities (a) and hyperpolarizability
(b) of the Gaussian 03 output are reported in atomic units (a.u.),
the calculated values have been converted into electrostatic units
(esu) (For a: 1a.u. = 0.1482 Â 10À24
esu; For b: 1a.u. = 8.639 Â
10À33
esu). The mean polarizability ao and total polarizability Da
of our title molecule are 22.735 Â 10À24
esu and 22.932 Â 10À24
esu
respectively. The total molecular dipole moment and first order
hyperpolarizability are 2.775 Debye and 15.589 Â 10À30
esu,
respectively and are depicted in Table 4. Total dipole moment of
4M40
NBPL molecule is approximately two times greater than that
of urea and first order hyperpolarizability is 41 times greater
than that of urea (l and b of urea are 1.3732 Debye and
0.3728 Â 10À30
esu obtained by HF/6-311G(d,p) method). This re-
sult indicates the good nonlinearity of the title molecule.
Electronic properties
UV–Vis spectral analysis
The time dependent density functional method (TD-DFT) is able
to detect accurate absorption wavelengths at a relatively small
computing time which correspond to vertical electronic transitions
computed on the ground state geometry, especially in the study of
solvent effect [58–60]; thus TD-DFT method is used with B3LYP
function and 6-31G(d,p) basis set for vertical excitation energy of
electronic spectra. Calculations are performed for gas phase, and
CHCl3 environment. The calculated visible absorption maxima of
k which are a function of the electron availability have been re-
ported in Table 5. The excitation energies, absorbance and oscilla-
tor strengths for the title molecule at the optimized geometry in
the ground state were obtained in the frame work of TD-DFT calcu-
lations with the B3LYP/6-31G(d,p) method. TD-DFT methods are
computationally more expensive than semi-empirical methods
but allow easily studies of medium size molecules [61,62]. Exper-
imentally, electronic absorption spectra of title molecule in chloro-
form solvent showed two bands at 240 and 340 nm (Fig. 4) .The
computed UV spectra predicts one intense electronic transition at
303.15 nm with an oscillator strength f = 0.0049 a.u in chloroform
solvent and electronic transition at 291.16 nm with an oscillator
strength f = 0.0003 a.u in gas phase that shows good agreement
with measured experimental data k (exp) = 340 nm. Calculations
of molecular orbital geometry show that the visible absorption
maxima of title molecule correspond to the electron transition be-
tween frontier orbitals such as transition from HOMO to LUMO. As
can be seen from the UV–Vis spectra absorption maxima values
have been found to be 240 and 340 nm. The kmax is a function of
substitution, the stronger the donor character of the substitution,
the more electrons pushed into the molecule, the larger kmax. These
values may be slightly shifted by solvent effects. The role of sub-
stituents and of the solvent influence on the UV-spectrum. This
band may be due to electronic transition of the ring B to ring A
Table 4
The electric dipole moment, polarizability and first order hyperpolarizability of 4-Methoxy-40
-Nitrobiphenyl by HF/6-31G(d,p) method.
Dipole moment, l (Debye) Polarizability a First order hyperpolarizability b
Parameter Value (DB) Parameter a.u. esu (Â10À24
) Parameter a.u. esu (Â10À33
)
lx 2.039 axx 214.091 31.728 bxxx À1103.338 À9531.734
ly À0.011 axy 12.356 1.831 bxxy 50.933 440.010
lz 1.887 ayy 76.061 11.272 bxyy 32.745 282.883
l 2.775 axz 54.860 8.130 byyy À0.267 À2.3100
ayz À21.533 À3.191 bxxz À870.261 À7518.188
azz 170.077 25.205 bxyz À19.476 À168.256
ao 153.409 22.735 byyz 50.306 434.591
Da 154.735 22.932 bxzz À472.376 À4080.859
byzz À44.441 À383.926
bzzz À115.892 À1001.192
btot 1804.606 15589.992
b = (15.589 Â 10À30
esu)
138 K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
10. through bridge (transition of p–p*
). Both the (HOMO) and (LUMO)
are the main orbitals that take part in chemical stability [63].
Frontier molecular orbitals
The HOMO represents the ability to donate an electron, LUMO
as an electron acceptor represents the ability to obtain an electron
[64]. The frontier molecular orbitals play an important role in the
electric and optical properties, as well as in UV–Vis spectra and
chemical reactions [65,66]. The atomic orbital compositions and
energy levels of the HOMO and LUMO orbitals computed at the
B3LYP/6-31G(d,p) level for the title compound is shown in supple-
mentary material S5. Molecular orbital and their properties like en-
ergy are very useful to the physicists and chemists and their
frontier electron density used for predicting the most reactive po-
sition in p-electron system and also explained several types of
reaction in conjugated systems [67]. Owing to the interaction be-
tween HOMO and LUMO orbital of a structure, transition state
transition of p–p*
type is observed with regard to the molecular
orbital theory [68]. Therefore, while the energy of the HOMO is di-
rectly related to the ionization potential, LUMO energy is directly
related to the electron affinity. Energy difference between HOMO
and LUMO orbital is called as energy gap that is an important sta-
bility for structures [69]. The energy gap between HOMO and
LUMO is a critical parameter in determining molecular electrical
transport properties [70]. In addition, according to B3LYP/6-
31G(d,p) calculation, the energy band gap of the 4M40
NBPL mole-
cule is 3.760 eV. The HOMO are localized mainly on the both the
ring. On the other hand, the LUMO are localized mainly on biphe-
nyl ring and exception of methyl group.
HOMO energy ¼ À6:093eV
LUMO energy ¼ À2:333eV
HOMO À LUMO energy gap ¼ 3:760eV
Atomic charges
The mulliken atomic charges are calculated at B3LYP/6-
31G(d,p) level by determining the electron population of each
atom as defined by the basis function. It may be the reason of
the substitution of methoxy group, the carbon atoms C4 (0.357e)
have the highest positive charge when compared with all other
carbon atoms as shown in the histogram supplementary material
S6. Mulliken atomic charges show that the H23 and H24 atoms
have maximum and equal positive atomic charges [(0.136e for
both H23, H24)] than the other hydrogen atoms. The methoxy
group oxygen atoms have the maximum negative charge value
O16 (À0.514e) compare to other oxygen atom of the nitro group,
O14 (À0.402e) and O15 (À0.402e) atoms respectively at B3LYP
method. Nitrogen atom has large positive charge value N13
(0.382e). This is due to the presence of electronegative atom in
the nitro group.
Molecular electrostatic potential (MEP)
The molecular electrostatic potential, V(r) is related to the elec-
tronic density and is a very useful descriptor for determining sites
for electrophilic attack and nucleophilic reactions as well as hydro-
gen bonding interaction [71,72]. MEP values were calculated using
the equation [73]:
VðrÞ ¼
X
ZA=jRA À rj À
Z
qðr0
Þ=jr0
À rjd3r0
where ZA is the charge of nucleus A located at RA, q(r0
) is the elec-
tronic density function of the molecule, and r’ is the dummy inte-
gration variable. To predict reactive sites for electrophilic and
nucleophilic attack for the title molecule, MEP was calculated at
the B3LYP/6-31G(d,p) optimized geometry. In the majority of the
MEPs, while the maximum negative region which preferred site
for electrophilic attack indications as red color, the maximum posi-
tive region which preferred site for nucleophilic attack symptoms as
white color and blue represents the region of zero potential. The
importance of MEP lies in the fact that it simultaneously displays
molecular size, shape as well as positive, negative and neutral elec-
trostatic potential regions in terms of color grading and is very use-
ful in research of molecular structure with its physicochemical
property relationship [74,75]. In the present study, a 3D plot of
MEP of title molecule is illustrated in supplementary material S7.
The color code of these maps is in the range between À0.0409
a.u. (deepest red) and +0.0500 a.u. (white) in our molecule. As can
be seen from the MEP map of the 4M40
NBPL molecule, while regions
having the negative potential are over the electronegative atom
(oxygen atom), the regions having the positive potential are over
the hydrogen atoms. The negative potential value is À0.0409 a.u.
for oxygen atom. A maximum positive region localized on the H
atoms bond has value of +0.0500 a.u. The negative (red color) re-
gions of MEP were related to electrophilic reactivity and the posi-
tive (white color) ones to nucleophilic reactivity.
Global reactivity descriptors
By using HOMO and LUMO energy values for a molecule, the
global chemical reactivity descriptors of molecules such as hard-
ness (g), chemical potential (l), softness (S), electronegativity (v)
and electrophilicity index (x) have been defined [76,77]. On the
basis of EHOMO and ELUMO, these are calculated using the below
equations.
Using Koopman’s theorem for closed-shell molecules,
The hardness of the molecule is
g ¼ ð1 À AÞ=2
Table 5
The experimental and computed absorption wavelength k (nm), excitation energies E
(eV), absorbance and oscillator strengths (f) of 4-Methoxy-40
-Nitrobiphenyl in
Chloroform solution and gas phase.
Experimental TD-DFT/B3LYP/6-31G(d,p)
Chloroform Chloroform Gas
k(nm) Abs. k(nm) E(eV) F(a.u) k(nm) E(eV) f(a.u)
– – 396.81 3.1245 0.4435 361.06 3.4339 0.3787
240 2.0479 320.35 3.8703 0.0018 330.37 3.7529 0.0050
340 2.5209 303.15 4.0898 0.0049 291.16 4.2582 0.0003
200 300 400 500 600 700 800
0.0
0.5
1.0
1.5
2.0
2.5
Wavelength (nm)
Abs
340
240
Fig. 4. The UV–Vis spectrum (CHCl3) of 4-Methoxy-40
-Nitrobiphenyl.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 139
11. The chemical potential of the molecule is
l ¼ Àð1 þ AÞ=2
The softness of the molecule is
S ¼ 1=2g
The electronegativity of the molecule is
v ¼ ð1 þ AÞ=2
The electrophilicity index of the molecule is
x ¼ l2
=2g
where A is the ionization potetional and I is the electron affinity of
the molecule. I and A can be expressed through HOMO and LUMO
orbital energies as I = ÀEHOMO and A = ÀELUMO. The Ionization pote-
tional A and an electron affinity I of our molecule 4M40
NBPL calcu-
lated by B3LYP/6-31G (d,p) method is 2.333 eV and 6.093 eV
respectively. The calculated values of the Hardness, Softness, Chem-
ical potential, electronegativity and electrophilicity index of our
molecule is 1.880, 0.266, À4.213, 4.213 and 4.721 respectively as
shown in supplementary material S8. Considering the chemical
hardness, large HOMO–LUMO gap represent a hard molecule and
small HOMO–LUMO gap represent a soft molecule.
Thermodynamic properties
Based on the vibrational analysis of our title molecule at B3LYP
6-31G(d,p) basis set, the thermodynamic parameters such as Heat
capacity C0
p;m, entropy (S0
m) and enthalpy (H0
m) were calculated
using perl script THERMO.PL [78] and are listed in Supplementary
material S9. From the Supplementary material S8 it can be seen
that, when the temperature increases from 100 to 1000 K the ther-
modynamic functions (C0
p;m, S0
m, H0
m) are also increases, because
molecular vibrational intensities increase with temperature [79].
Fitting factor (R2
) of the thermodynamic functions such as heat
capacity, entropy and enthalpy changes are 0.995, 0.965 and
0.974 respectively. The correlation graphics of temperature depen-
dence of thermodynamic functions for 4M40
NBPL molecule are
shown in Supplementary material S10. Vibrational zero-point en-
ergy of the 4M40
NBPL is 569.60 kJ/mol.
Conclusion
The optimized geometry and FT-IR and FT-Raman vibrational
analysis of the molecule 4-Methoxy-40
-Nitrobiphenyl have been
carried out with the help of HF and DFT method using
6-31G(d,p) as basis set. The calculated vibrational modes are com-
pared with experimental values. It has been observed that all
scaled frequencies are in good agreement with experimental val-
ues. The difference between the observed and scaled wavenumber
values of most of the fundamentals is very small. The UV spectrum
was measured in chloroform solution and results are compared
with theoretical results. The NBO analysis revealed that the
p*
(C3AC4) ? p*
(C1AC2) interaction gives the strongest stabiliza-
tion to the system around at 308.53 kJ/mol. The 1
H and 13
C NMR
magnetic isotropic chemical shifts were calculated by B3LYP/6-
31G(d,p) basis set and compared with experimental findings. Total
dipole moment of 4M40
NBPL molecule is approximately two times
greater than that of urea and first order hyperpolarizability is 41
times greater than that of urea. The calculated first order hyperpo-
larizability for 4M40
NBPL (15.589 Â 10À30
esu) gives information
about it’s for NLO applications. The difference in HOMO and LUMO
energy supports the interaction of charge transfer within the mol-
ecule. The MEP map shows that the negative potential sites are
around oxygen atoms as well as the positive potential sites are
around the hydrogen atoms. The chemical hardness, chemical soft-
ness and electrophilicity index of the 4M40
NBPL molecule are cal-
culated. The thermodynamic properties (heatcapacity, entropy
and enthalphy) in the temperature range from 100 to 1000 K also
calculated.
Acknowledgement
The authors are thankful to Dr. N. Sundaraganesan, Professor of
physics, Annamalai University, Tamilnadu, India for providing
Gaussian 03 W facility.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2013.10.122.
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K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 141
![Vibrational spectra, molecular structure, NBO, UV, NMR, first order
hyperpolarizability, analysis of 4-Methoxy-40
-Nitrobiphenyl by density
functional theory
K. Govindarasu, E. Kavitha ⇑
Department of Physics (Engg.), Annamalai University, Annamalainagar 608 002, India
h i g h l i g h t s
The FTIR and FT-Raman spectra of
4M40
NBPL were reported.
The first order hyperpolarizability
was calculated.
UV–Vis spectra were recorded and
compared with calculated values.
NMR and MEP studies were analyzed.
g r a p h i c a l a b s t r a c t
a r t i c l e i n f o
Article history:
Received 24 September 2013
Received in revised form 16 October 2013
Accepted 31 October 2013
Available online 9 November 2013
Keywords:
4-Methoxy-40
-Nitrobiphenyl
TD-DFT
NBO
UV–Vis
NMR
Hyperpolarizability
a b s t r a c t
In this study, geometrical optimization, spectroscopic analysis, electronic structure and nuclear magnetic
resonance studies of 4-Methoxy-40
-Nitrobiphenyl (abbreviated as 4M40
NBPL) were investigated by utiliz-
ing HF and DFT/B3LYP with 6-31G(d,p) as basis set. The equilibrium geometry, vibrational wavenumbers
and the first order hyperpolarizability of the 4M40
NBPL have been calculated with the help of density
functional theory computations. The FT-IR and FT-Raman spectra were recorded in the region 4000–
400 cmÀ1
and 3500–50 cmÀ1
respectively. Natural Bond Orbital (NBO) analysis is also used to explain
the molecular stability. The UV–Vis absorption spectra of the title compound dissolved in chloroform
were recorded in the range of 200–800 cmÀ1
. The HOMO–LUMO energy gap explains the charge interac-
tion taking place within the molecule. Good correlation between the experimental 1
H and 13
C NMR chem-
ical shifts in chloroform solution and calculated GIAO shielding tensors were found. The dipole moment,
linear polarizability and first order hyperpolarizability values were also computed. The linear polarizabil-
ity and first order hyperpolarizability of the studied molecule indicate that the compound is a good can-
didate of nonlinear optical materials. The chemical reactivity and thermodynamic properties of
4M40
NBPL at different temperature are calculated. In addition, molecular electrostatic potential (MEP),
frontier molecular orbitals (FMO) analysis were investigated using theoretical calculations.
Published by Elsevier B.V.
Introduction
The nonlinear optical responses induced in various materials
are of great interest in recent years because of the applications in
photonic technologies such as optical communications, data
storage and image processing [1]. In recent years, the synthetic
approaches to various biphenyl derivatives and their biological
activity were studied. Analysis of the scientific and patent litera-
ture indicates that the biphenyl group is used to create a wide
range of the drugs and products for agriculture [2,3]. Some biphe-
nyl derivatives are patented and widely used in medicine as the
1386-1425/$ - see front matter Published by Elsevier B.V.
http://dx.doi.org/10.1016/j.saa.2013.10.122
⇑ Corresponding author. Tel.: +91 9442477462.
E-mail address: eswarankavitha@gmail.com (E. Kavitha).
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa](https://image.slidesharecdn.com/e6b8733f-51ee-4050-8954-57161c880a3a-160601043249/85/1-s2-0-S1386142513013000-main-1-320.jpg)
![anti androgenic and hypotensive drugs [4,5]. Antimicrobial prepa-
rations based on biphenyl derivatives are of great interest and are
used in medicine and in agriculture [6–8]. 4-Methoxy-3-Nitrobi-
phenyl is a biphenyl derivative which displays a twisted conforma-
tion with the two benzene rings making a dihedral angle of 36.69°
[9]. Our molecule 4M40
NBPL has the following properties: Pale
yellow solid: m.p.: 107–108 °C [10]
Stille et al. [11] reported organic synthesis of 4M40
NBPL. Anne
Colonna et al. [12] investigate the chirped molecular vibration in
a stilbene derivative (4-Methoxy-40
-nitrostilbene) in solution.
Hulliger et al. [13] reported on intrinsic and extrinsic defect-
forming mechanisms determining the disordered structure of
4-iodo-40
-Nitrobiphenyl crystals. To best of our knowledge, there
is not any review summarizing the literature on the TD-DFT fre-
quency calculations of 4M40
NBPL have been reported so far. The
FTIR and FT Raman spectroscopy combined with Quantum chemi-
cal computations have been recently used as an effectively tool in
vibrational assignments of nonlinear optical molecule.
The present work mainly deals with detailed structural confor-
mation, experimental FT-IR and FT-Raman spectra, vibrational
assignments using total energy distribution (TED) and NLO activity
as well as HF and DFT/B3LYP calculations for 4M40
NBPL. The elec-
tron density (ED) in various bonding and anti bonding orbital and
E2 energies have been calculated by Natural Bond Orbital (NBO)
analysis using DFT method. The UV spectroscopic studies along
with HOMO–LUMO analysis have been used to explain the charge
transfer within the molecule.
Experimental details
The compound 4-Methoxy-40
-Nitrobiphenyl in the solid form
was purchased from TCI INDIA chemical company at Chennai with
a stated purity greater than 98% and it was used as such without fur-
ther purification. The FT-IR spectrum of this compound was re-
corded in the range of 4000–400 cmÀ1
on a Perkin Elmer FT-IR
spectrometer using KBr pellet technique. The spectrum was re-
corded in the room temperature, with scanning speed of 10 cmÀ1
.
FT-Raman spectrum of the title compound was recorded using
1064 nm line of Nd:YAG laser as excitation wavelength in the region
3500–50 cmÀ1
on a BRUKER RFS 27 FT-Raman Spectrometer
equipped with FT-Raman molecule accessory. The spectral resolu-
tion was set to 2 cmÀ1
in back scattering mode. The laser output
was kept at 100 mW for the solid sample. The ultraviolet absorption
spectra of 4M40
NBPL were examined in the range 200–800 nm using
Cary 5EUV–VIS–NIR spectrometer. The UV pattern is taken from a
10–5 M solution of 4M40
NBPL, dissolved in chloroform. The theoret-
ically predicted IR and Raman spectra at B3LYP/6-31G(d,p) level cal-
culation along with experimental FT-IR and FT-Raman spectra are
shown in Figs. 1 and 2. The spectral measurements were carried
out at Indian Institute of Technology (IIT), Chennai.
Computational details
In the present study, the HF and density functional theory
(DFT/B3LYP) at the 6-31G(d,p) basis set level was adopted to cal-
culate the optimized parameters and vibrational wavenumbers of
the normal modes of the 4M40
NBPL molecule. All the theoretical
calculations were performed using the Gaussian 03 W program
package [14] with the default convergence criteria, without any
constraint on the geometry [15]. The equilibrium geometry
corresponding with the true minimum on the potential energy
surface (PES) was effectively obtained by solving self-consistent
field equation. The vibrational spectra of the 4M40
NBPL were
obtained by taking the second derivative the energy, computed
4000 3500 3000 2500 2000 1500 1000 500
3003
2659
1636
1378
1197
900
563
3062
2930
2836
2445
1935
1509
1482
1342
1186
1016
839
696
814
1090
1164
1251
1338
1459
1587
2899
3067
1123
1224
1406
1520
B3LYP/6-31 G(d,P)
Experimental
Wavenumber (cm-1)
Transmittance(%)IRintensity(arb.units)
Fig. 1. Comparison of experimental and theoretical B3LYP/6-31G(d,p) FT-IR spectra for 4-Methoxy-40
Nitrobiphenyl.
K. Govindarasu, E. Kavitha / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 122 (2014) 130–141 131](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)