Spectroscopic analysis of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H- pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile

Article abstract of DOI:10.1016/j.saa.2011.03.044

The optimized geometry and vibrational frequencies of 2-(2,3-dihydro-1,5- dimethyl-3-oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile (DOPNA) were obtained by ab initio DFT/B3LYP level with complete relaxation in the potential energy sur

Full text of DOI:10.1016/j.saa.2011.03.044

Spectrochimica Acta Part A 79 (2011) 618–624
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Spectroscopic analysis of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-1H-
pyrazol-4-ylimino)-2-(4-nitro-phenyl)
acetonitrile
M.M. El-Nahassa,∗, M.A. Kamela, E.M. El-Menyawyb
a Physics Department, Faculty of Education, Ain Shams University, Roxy, 11757 Cairo, Egypt
b Solid State Physics Department, Solid State Electronics Lab, National Research Center, Dokki, Cairo 12622, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 14 March 2011
Accepted 16 March 2011
The optimized geometry and vibrational frequencies of 2-(2,3-dihydro-1,5-dimethyl-3-oxo-2-phenyl-
1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetonitrile (DOPNA) were obtained by ab initio DFT/B3LYP
level with complete relaxation in the potential energy surface using 6-31G and 6-311G basis sets. The
Fourier-transform infrared (FT-IR) spectrum of DOPNA has been recorded in the region 4000–400 cm−1
.
Keywords:
FT-IR spectrum
DFT
The harmonic vibrational frequencies were calculated and the scaled values have been compared with
experimental FT-IR spectrum. The calculated frequencies are in comparable agreement with the experi-
mental frequencies. The calculated energy span between the HOMO and the LUMO of DOPNA is 2.94 and
2.87 eV by B3LYP/6-31G and B3LYP/6-311G, respectively.
DOPNA
Molecular structure
Vibrational analysis
Frontier molecular orbitals
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
trile (DOPNA), which is one of the Schiff base families derived from
antipyrine.
Intramolecular donor–acceptor systems typically consist of
electron donating groups (electron rich segments) and electron
acceptors (electron deficient segments) [1–4]. A charge separation
may result from the transfer of an electron upon excitation from
a donor (D) to an acceptor (A) site within a suitable molecule.
This new charge distribution generally leads to an increase of
the molecular dipole moment as well as to structural and elec-
tronic rearrangements within the molecule. These compounds
often undergo relaxation toward a highly polar state and exhibit
anomalous emission properties like dual fluorescence [5].
A considerable number of articles have been published on the
spectral behavior of Schiff bases [6–9]. This originated from the fact
that the Schiff bases and their metal complexes exhibit wide appli-
cations in biological systems [10,11] and industrial uses, especially
in catalysis [12,13] and dying [14–16]. Although Schiff bases con-
taining a heterocyclic nucleus have efficient biological activities,
yet spectral studies of these compounds are comparatively minor
[17–19].
Literature survey reveals that to the best of our knowledge
no ab initio density functional theory (DFT) frequency calcula-
tions of DOPNA have been reported so far. Therefore, the present
investigation was undertaken to study the molecular structure,
vibrational spectra, and frontier molecular orbitals, for the first
time, of the DOPNA molecule completely and to identify the var-
ious normal modes with greater wavenumber accuracy. Ab initio
DFT calculations have been performed to support our wavenum-
ber assignments. In spite of recent study on vibrational spectra
of DOPNA, we represent a combined theoretical and experimental
study for FT-IR spectroscopy using ab initio DFT level.
2. Material synthesis and experimental procedures
2.1. Synthesis of the organic dye
All the chemicals used in this study were obtained from
Aldrich company and used as it is, without any further purifi-
cation. A mixture of 4-nitrobenzylcyanide (1.62, 10 mmol) and
1,2-dihydro-2,3-dimethyl-4-nitroso-1-phenylpyrazol-5-one (2.17,
10 mmol) in ethanol (50 ml) containing a catalytic amount of piperi-
dine (0.2 ml) was added. The reaction mixture was refluxed for 2 h
and solid deposited was collected by filtration and re-crystallized
from ethanol/benzene to give 2-(2,3-dihydro-1,5-dimethyl-3-oxo-
2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitrophenyl) acetonitrile as
In this work, we introduce a novel material, newly synthesized
organic dye, of chemical formula 2-(2,3-dihydro-1,5-dimethyl-3-
oxo-2-phenyl-1H-pyrazol-4-ylimino)-2-(4-nitro-phenyl) acetoni-
∗
Corresponding author. Tel.: +20 125430253.
E-mail address: prof nahhas@yahoo.com (M.M. El-Nahass).
1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.03.044

M.M. El-Nahass et al. / Spectrochimica Acta Part A 79 (2011) 618–624
619
brown crystals; in yield 90%, melting point 208–210 ◦C. IR
(ꢀmax/cm−1
1508.0 (conjugated nitro group); 1592.9 (C N);
Table 1
´
˚
◦
Optimized geometrical parameters, bond length (A) and angle ( ), for DOPNA
molecule.
:
1663.3(C O); 2196.6(C N); 2853.0 (N-methyl group); 2924.7
(methyl group); 1HNMR(DMSO-d6) (ı, ppm): 3.34 (s,3H, CH3); 3.38
(s,3H, N–CH3); 7.52 (m, 5H aromatic H); 8.25 (d.d, 4H aromatic H).
Anal. Calcd for C19H15N5O3: C, 63.15%; H, 4.18%; N, 19.38%. Found:
C, 63.20%; H, 4.12%; N, 19.40%.
Parameters
6-31G
6-311G
´
˚
Bond length (A)
C1–C2
C1–C6
C1–H7
C2–C3
C2–H8
C3–C4
C3–H9
C4–C5
1.3979
1.3959
1.4043
1.0846
1.3997
1.0851
1.4001
1.0848
1.3974
1.0848
1.4028
1.0820
1.4253
1.4679
1.4213
1.2456
1.3904
1.3756
1.4895
1.3699
1.4222
1.4707
1.0893
1.0968
1.0904
1.0980
1.0924
1.0951
1.3065
1.4424
1.4827
1.1745
1.4115
1.4100
1.3895
1.0820
1.3934
1.0838
1.3999
1.0818
1.3964
1.0818
1.4618
1.2656
1.2662
1.4015
1.0810
1.3975
1.0816
1.3977
1.0813
1.3954
1.0813
1.3999
1.0785
1.4269
1.4655
1.4188
1.2447
1.3858
1.3776
1.4883
1.3735
1.4237
1.4706
1.0851
1.0926
1.0862
1.0938
1.0881
1.0909
1.3048
1.4418
1.4817
1.1675
1.4094
1.4081
1.3876
1.0785
1.3916
1.0803
1.3976
1.0783
1.3939
1.0782
1.4623
1.2677
1.2683
2.2. Experimental details
FTIR of as-synthesized DOPNA in powder form is performed
using ATI Mattson (Infinity series FT-IR) infrared spectrophotome-
ter in the spectral range 4000–400 cm−1. A disk shaped from the
as-synthesized DOPNA powder was mixed with vacuum dried
grade KBr.
Cyclic voltammetry measurements for the reaction in dimethyl
formamide (DMF) were performed using oxford potentiostat/wave
generator by using a three-electrode configuration including plat-
inum working electrode, a platinum coil auxiliary electrode and a
silver wire as a reference electrode. DMF was used as a solvent.
C4–H10
C5–C6
C5–H11
C6–N15
C12–C14
C12–N15
C12–O21
C13–C14
C13–N16
C13–C22
C14–N26
N15–N16
N16–C17
C17–H18
C17–H19
C17–H20
C22–H23
C22–H24
C22–H25
N26–C27
C27–C28
C27–C30
C28–N29
C30–C31
C30–C32
C31–C33
C31–H34
C32–C35
C32–H36
C33–C37
C33–H38
C35–C37
C35–H39
C37–N40
N40–O41
N40–O42
3. Computational details
The entire calculations were performed at DFT/B3LYP level on
a Pentium IV/2.8 GHz personal computer using Gaussian 03W [20]
program package, invoking gradient geometry optimization [21].
The geometry of the DOPNA molecule in the ground state is fully
optimized .The input geometry of DOPNA molecule has been first
optimized without any constraint in the potential energy surfaces
at DFT/B3LYP level adopting the 6-31G and 6-311G basis sets. The
resultant-optimized geometry has been used as input for vibra-
tional frequency calculations at the same method and basis sets to
characterize all stationary points as minima.
DFT method, including local or non-local functionals, yields
molecular force fields and vibrational wavenumbers in excellent
agreement with experiment. Among the numerous available DFT
methods, we have selected the B3-LYP [22–24] method, which
combines the Becke’s three-parameter exchange functional (B3)
[23] with the Lee, Young and Parr correlation functional (LYP) [23].
The theoretical results have enabled us to make detailed assign-
ments of the experimental IR spectrum of DOPNA molecule. All
the calculations are performed by using GaussView4.1 molecular
visualization program [25].
Bond angle (◦)
C2–C1–C6
C2–C1–H7
C6–C1–H7
C1–C2–C3
C1–C2–H8
C3–C2–H8
C2–C3–C4
C2–C3–H9
119.5739
120.5743
119.8367
120.3076
119.4993
120.1837
119.7172
120.1229
120.1584
120.5866
120.0962
119.3159
119.3488
121.0081
119.6309
120.4428
120.9021
118.6348
104.517
130.8001
124.4734
109.8593
127.3093
122.7479
108.2919
129.0443
122.3484
125.3023
119.5951
120.5707
119.8199
120.2900
119.5273
120.1735
119.7169
120.1203
120.1612
120.5643
120.0944
119.3405
119.3783
120.9859
119.6210
120.4337
120.8458
118.6987
104.5883
130.5244
124.6574
109.8661
127.5200
122.5500
108.4227
128.3657
122.8050
125.2869
After optimization, we investigated the localization of the fron-
tier molecular orbitals using a single point energy calculation.
The spatial distribution of the frontier molecular orbital (highest
occupied molecular orbital, HOMO and lowest unoccupied molec-
ular orbital, LUMO) provides a strategy for which the photovoltaic
and electrochemical properties (such as charge separation) of the
DOPNA molecule could be understood.
C4–C3–H9
C3–C4–C5
C3–C4–H10
C5–C4–H10
C4–C5–C6
C4–C5–H11
C6–C5–H11
C1–C6–C5
C1–C6–N15
C5–C6–N15
C14–C12–N15
C14–C12–O21
N15–C12–O21
C14–C13–N16
C14–C13–C22
N16–C13–C22
C12–C14–C13
C12–C14–N26
C13–C14–N26
C6–N15–C12
4. Results and discussion
4.1. Molecular geometry
The first task for the computational work is to determine the
optimized geometries of the studied molecule. The atomic num-
bering for the DOPNA molecule is shown in Fig. 1. Our optimized
geometrical parameters (bond length and angles) calculated by ab
initio DFT/B3LYP methods with the 6-31G and 6-311G basis sets
are listed in Table 1. Since the exact crystal structure of the DOPNA
compound is not available till now, our optimized structure can
be only compared with other similar systems for which the crystal
structures have been solved. Therefore, our optimized geometrical
parameters of the molecular structure of Schiff bases Ib obtained

620
M.M. El-Nahass et al. / Spectrochimica Acta Part A 79 (2011) 618–624
Table 1 (Continued)
assignments have been reported to fit with the experimental results
which showed a comparable agreement between our computa-
tional and experimental work. We select only 19 modes of our
calculated modes of vibrational for DOPNA molecule, 10 Aꢀ + 9 Aꢀꢀ,
which fit with our experimental assignments. The Aꢀ modes are in
plane and stretching vibrations while Aꢀꢀ modes correspond to the
out-of-plane vibrations.
Parameters
6-31G
6-311G
C6–N15–N16
C6–N15–C17
C12–N15–N16
C13–N16–N15
C13–N16–C17
N16–C17–H18
N16–C17–H19
N16–C17–H20
H18–C17–H19
H18–C17–H20
H19–C17–H20
C13–C22–H23
C13–C22–H24
C13–C22–H25
H23–C22–H24
H23–C22–H25
H24–C22–H25
C14–N26–C27
N26–C27–C28
N26–C27–C30
C28–C27–C30
C27–C30–C31
C27–C30–C32
C31–C30–C32
C30–C31–C33
C30–C31–H34
C33–C31–H34
C30–C32–C35
C30–C32–H36
C35–C32–H36
C31–C33–C37
C31–C33–H38
C37–C33–H38
C32–C35–C37
C32–C35–H39
C37–C35–H39
C33–C37–C35
C33–C37–N40
C35–C37–N40
C37–N40–O41
C37–N40–O42
O41–N40–O42
120.9001
99.84990
109.3919
107.8710
123.8142
109.5908
111.0091
108.3266
109.2590
108.8464
109.7740
112.1695
108.2551
111.6727
107.5935
107.9672
109.0676
127.9862
124.6598
118.6106
116.5236
119.7903
121.1716
119.0369
120.7201
118.6457
120.6338
120.6962
119.9727
119.3310
118.9290
121.6303
119.4400
118.8830
121.4934
119.6236
121.7324
119.0963
119.1713
118.1807
118.0806
123.7386
120.8300
100.1265
109.3441
107.6977
123.5986
109.7360
110.8950
108.4305
109.2544
108.7041
109.7856
112.2134
108.4613
111.6334
107.5288
107.9781
108.9007
127.2345
124.2279
118.7691
116.7896
119.8122
121.2135
118.9731
120.7253
118.6529
120.6211
120.7232
120.0424
119.2343
118.9919
121.6035
119.4039
118.9223
121.4777
119.5999
121.6614
119.1394
119.1991
118.2772
118.1891
123.5337
Vibrational spectral assignments have been performed on the
recorded FT-IR (powder) spectrum based on the theoretically pre-
dicted wavenumbers by ab initio B3LYP. All of the calculated modes
are numbered from the smallest to the largest frequency within
each fundamental wavenumber. The calculated and scaled vibra-
tional wavenumbers are collected in Table 2 with the scaling factor
0.96 [27] for B3LYP level. All 19 fundamental vibrations are active.
Fig. 2a shows the observed spectrum of DOPNA compound (in
a powder form) while Fig. 2(b and c) shows the stick spectra
of DOPNA molecule at DFT/B3LYP level using 6-31G and 6-311G
basis sets. The broad band at about 3424 cm−1 for powder DOPNA
observed in Fig. 2a corresponds to O–H stretching vibration [28].
The presence of the hydroxyl group O–H in the powder despite
the molecular structure of DOPNA (see Fig. 1) does not contain this
group which indicates that the material absorb water from its sur-
rounding atmosphere. The theoretical calculations confirmed this
interpretation; due to the absence of the vibrational mode corre-
sponding to O–H bond.
Comparison of the frequencies calculated at 6-31G and 6-311G
basis sets with experimental values (see Table 2) reveals that the
6-311G basis set gives reasonable deviations from the experimen-
tal values. Any discrepancy noted between the calculated and the
experimental frequencies may be due to the fact that the calcu-
lations have been actually performed on a single molecule in the
gaseous state contrary to the experimental values recorded in the
presence of intermolecular interactions.
4.3. C–H vibrations
The assignment of carbon–hydrogen stretching mode is straight
forward on the basis of our calculated ab initio predicted fre-
quencies as well known “group frequencies”. Aromatic compounds
have one or more sharp peaks of weak or medium intensity
between 3100 and 3000 cm−1 [29]. In this region; the bands are not
affected appreciably by the nature of the substituent. In our present
work, the computed vibration (mode no. 19) by B3LYP method is
assigned to the aromatic C–H stretching vibration and show a com-
parable agreement with our experimental work; the absorption
from quantum chemical calculations using ASED-MO theory are
compared to those of DOPNA compound [26].
4.2. Vibrational assignments
The molecule DOPNA has 42 atoms has 120 vibrational modes
distributed as 65 Aꢀ + 55 Aꢀꢀ which possesses C1 symmetry. DOPNA
Fig. 1. The molecular structure of DOPNA molecule in its ground state.

M.M. El-Nahass et al. / Spectrochimica Acta Part A 79 (2011) 618–624
621
Table 2
Vibrational wavenumbers obtained for DOBNA molecule at B3LYP level using 6-31G and 6-311G basis sets [harmonic frequency (cm−1) and IR intensities (km mol−1).
No.
Spices
Experimental
6-31G
6-311G
Assignment
Wavenumber
Unscaled
IR intensity
Wavenumber
Unscaled
IR intensity
Scaled
Rel.
Abs.
Scaled
Rel.
Abs.
1
2
3
4
5
5
6
7
8
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀꢀ
Aꢀ
433
495
588
635
687
748
784
851
1006
1052
1109
1176
1339
1413
1508
1593
1663
2197
2930
3105
456
520
613
660
707
778
801
882
1050
1097
1158
1233
1398
1483
1592
1644
1704
2281
3046
3231
438
499
589
634
679
748
769
847
1008
1053
1112
1184
1342
1424
1528
1578
1636
2190
2924
3102
2
5
37
2
30
51
25
2
2
5
8
8
1
1
10
1
8
14
7
1
1
1
2
455
520
610
659
701
776
799
883
1048
1096
1152
1222
1393
1474
1570
1626
1738
2285
3049
3233
437
499
586
633
673
745
767
848
1006
1052
1106
1173
1337
1415
1507
1561
1669
2194
2927
3104
1
5
44
3
26
48
28
3
1
3
9
6
1
3
22
2
13
24
14
2
1
2
5
3
ꢁ(t) CCN + ꢁ(ω) CCC
ꢁ(ω) CCC
ꢁ(t) HCH in CH3
ꢁ(ω) CCN
ꢁ(ω) CCC
ꢁ(ω) CH in aromatic
ꢁ(ω) CCC
ꢁ(ω) CH in aromatic
ꢁ(t) CH in aromatic
ꢁ(t) HCH in CH3
ˇ(ı) CH in aromatic
ˇ(ı) CH in aromatic
9
10
11
12
13
14
15
16
17
18
19
Aꢀ
2
Aꢀ
42
118
11
32
100
1
50
6
11
140
6
ꢀas C–N + ꢀas C C + ˇ(ꢂ) CH in aromatic
CH3 deformation (Umbrella)
ꢀas N–O + ˇ(ı) HCH in CH3
ꢀ C N + ꢀas C C
Aꢀ
70
92
3
100
12
7
Aꢀ
369
5
184
23
16
21
185
6
201
24
13
25
Aꢀ
Aꢀ
ꢀ C
ꢀ C
O
N
Aꢀ
Aꢀ
4
6
ꢀs CH in CH3
ꢀs CH in aromatic
Aꢀ
12
ꢀ: stretching; ꢀs: symmetric stretching; ꢀas: asymmetric stretching; ˇ: in-plane-bending; ꢁ: out-of-plane bending; ı: scissoring; ω: wagging; ꢂ: rocking; t: twisting; ꢃ:
torsion.
band observed at 3105 cm−1 [30], and those reported in literature
[31].
In our present work, the calculated vibration (mode no. 15) by
B3LYP level is assigned to C N stretching which shows a compa-
rable agreement with our experimental work; the absorption band
observed in FT-IR spectrum at 1593 cm−1 [30] and that reported in
literature [35].
Unsaturated or aromatic nitriles, in which the double bond or
ring is adjacent to the C N group, absorbs more strongly in the
infrared than saturated compounds and the band occurs at some-
what lower frequency near 2230 cm−1 [29]. In our present work,
theoretically computed value (mode no. 17) is assigned to stretch-
ing vibration of C N group and it is in a comparable agreement
with our experimental work; the observed band in FT-IR spectrum
at 2197 cm−1 [30].
The aromatic C–H in-plane bending vibrations of benzene and
its derivatives are observed in the region 1300–1000 cm−1 [32]. The
bands are sharp but weak to medium intensity. In our present work,
the calculated vibrations (mode nos. 12, 11 and 10) by B3LYP level
are assigned to C–H in-plane bending vibrations of aromatic ring.
The absorption bands arising from C–H out-of-plane bending
vibrations are usually observed at 1000–675 cm−1 region [33]. In
our present work, the calculated vibrations (mode nos. 8, 7 and 5)
by B3LYP level are assigned to C–H out of plane bending vibrations
of aromatic ring.
4.4. Methyl group vibrations
4.6. C O Vibrations
The methyl groups absorb infrared radiation near 2960 and
2870 cm−1. In many cases, only one band in 2870–2850 cm−1 can
be resolved when both CH3 and CH2 groups are present in the
molecule [29]. The C–H stretching in CH3 occurs at lower fre-
quencies than those of the aromatic ring (3100–3000 cm−1). In
our present work, the calculated vibration mode no 18 by B3LYP
method is assigned to the C–H stretching vibration in methyl group
which is in a comparable agreement with our experimental work;
the absorption band observed at 2930 cm−1 in FT-IR spectrum [30].
In our present work, the calculated vibrations (mode nos. 14, 15,
9 and 3) by B3LYP level are assigned to methyl group deformation.
Most organic compounds containing the C O group shows very
strong infrared absorption in the range 1870–1650 cm−1 [29]. In
our present work, theoretically computed value (mode no. 16) is
assigned to stretching vibration of C O group and it is in a compa-
rable agreement with our experimental work; the observed band
in FT-IR spectrum at 1663 cm−1 [30].
4.7. N–O2 vibrations
Nitro compounds have two very strong absorption bands due to
symmetric and antisymmetric N–O2 stretching. In aromatic com-
pounds, the bands are observed near 1520 and 1350 cm−1 [29]. In
our present work, the calculated vibrations (mode nos. 14) by B3LYP
level are assigned to N–O asymmetric stretching.
4.5. C–N, C N and C N Vibrations
The C–N stretching vibration is likely to be coupled with C–C
stretching and C–C–H bending modes in most molecules. One
expects to find infrared absorption and Raman scattering as a
result of these vibrations in the region 1350–1050 cm−1 [29]. Sil-
verstein et al. [32] assigned C–N stretching absorption in the
region 1386–1266 cm−1 for aromatic amines. The C–N stretching is
observed at 1293 cm−1 [34]. In our present study, the theoretically
computed vibration by B3LYP method (mode no. 12) is assigned
to C–N stretching. This assignment shows a comparable agreement
with our experimental work; the absorption band observed in FT-IR
spectrum at 1339 cm−1 [30].
4.8. Ring vibrations
The benzene ring possesses six stretching vibrations of which
the four with the highest wavenumbers occurring near 1600, 1580,
1490 and 1440 cm−1 are good group vibrations [36]. With heavy
substituents, the bands tend to shift to somewhat lower wavenum-
bers and greater the number of substituents on the ring, broader
the absorption regions [36]. In our present work, the theoretically
computed vibration (mode no. 15) is assigned to C C stretching.

622
M.M. El-Nahass et al. / Spectrochimica Acta Part A 79 (2011) 618–624
Fig. 2. The experimental FT-IR spectrum of DOPNA molecule in powder form (a);
and the theoretical FT-IR spectra of DOPNA molecule by B3LYP level at 6-31G and
6-311G basis sets (b and c).
Sundaraganesan et al. [31] assigned the vibrational mode calculated
at 1602 cm−1 to C C semicircle stretching.
Fig. 3. The frontier molecular orbitals for the ground state of DOPNA molecule.
The fifth ring stretching vibration is active near 1315 65 cm−1
,
frontier orbital gap helps characterize the chemical reactivity and
kinetic stability of the molecule. A molecule with a small frontier
orbital gap is more polarizable and is generally associated with a
high chemical reactivity, low kinetic stability and is also termed
as soft molecule [39]. Fig. 3 shows the wave functions of HOMOs
and LUMOs of DOPNA molecule. It is clear that the HOMOs of
DOPNA molecule are ␲ orbitals while the LUMOs are ␲* orbitals.
It is calculated that the energy span between the HOMO and the
LUMO of DOPNA is 2.94 and 2.87 eV by B3LYP/6-31G and B3LYP/6-
311G, respectively. Fig. 4 shows the cyclic voltammetry of DOPNA
compound. The HOMO and LUMO energy levels were calculated
according to the following equations [40,41]:
a region that overlaps strongly with that of the C–H in-plane defor-
mation [36]. In our present work, the theoretically computed C
stretching vibration (mode no. 12) by B3LYP level are assigned to
C stretching coupled with C–H in-plane bending vibrations of
C
C
aromatic ring.
In our present work, the theoretically computed C–C–C defor-
mation vibrations by B3LYP method (mode nos. 6, 5 and 2) show a
comparable agreement with those in literature [31,37,38].
In our present work, the theoretically computed vibrations
(mode nos. 4 and 1) by B3LYP level are assigned to CCN bending
vibrations.
4.9. Frontier molecular orbitals
EHOMO = −(Eox + 4.71) eV,
ELOMO = −(Ered + 4.71) eV,
Eg = (EHOMO − ELUMO) eV,
(1)
(2)
(3)
The most important orbitals in a molecule are the frontier
molecular orbitals, called HOMO and LUMO. These orbitals deter-
mine the way the molecule interacts with other species. The

M.M. El-Nahass et al. / Spectrochimica Acta Part A 79 (2011) 618–624
623
Table 4
Estimated values of highest occupied molecular orbital and lowest unoccupied
molecular orbital energy levels and band gap of DOPNA from cyclic voltammetry
data.
Ox
red
Material
DOPNA
E
, eV
E
, eV
EHOMO, eV
ELOMO, eV
Eg, eV
onset
onset
1.43
−0.82
6.14
3.89
2.25
its reactivity [43–45]. Accordingly DOPNA molecule is chemically
active as it possesses a high dipole moment value (around 12
Debye) which increases its ability to interact with the surround-
ing matrix. Therefore, DOPNA compound is a promising material
for many applications such as solar cells. Zeyada et al. [46] showed
that the power conversion efficiency of Au/p-DOPNA/p-Si/Al het-
erojunction was estimated to be 5.74%.
5. Conclusion
Fig. 4. Cyclic voltammogram recorded in DMF containing 0.2 M of DOPNA com-
pound.
In this wok, attempts have been made for the proper frequency
assignments for the DOPNA compound from the FT-IR spectrum.
The equilibrium geometries and harmonic frequencies of DOPNA
were determined and analyzed at DFT/B3LYP level of theories uti-
lizing 6-31G and 6-311G basis sets, giving allowance for the lone
pairs functions. The difference between the calculated and exper-
imental wavenumber values of most of the fundamentals is very
small. Any discrepancy noted between the calculated and exper-
imental frequencies may be due to the fact that our calculations
have been actually performed on a single molecule in the gaseous
state contrary to the experimental values recorded in the presence
of intermolecular interactions. Therefore, the assignments made
at higher level of theory (i.e. B3LYP/6-311G) which gives reason-
able deviations from the experimental values) seem to be correct.
DOPNA compound is a promising material for many applications
such as solar cells due to the high calculated value of dipole moment
(around 12 Debye).
where Eox and Ered are the onset oxidation and reduction potential
vs. Ag/AgCl, respectively, observed in cyclic voltammogram, while
Eg is the band gap. The potentials were internally calibrated using
Ag/AgCl redox couple, which is estimated to have an oxidation
potential of −4.71 eV vs. vacuum. The values of HOMO and LUMO
energy levels and the band gap of the above materials, estimated
from the cyclic voltammetry (CV) data are listed in Table 4.
This means that DOPNA compound is a promising material for
solar cell applications since it absorbs energy in the visible region
of the spectrum.
4.10. Other calculated molecular properties
Some of the thermodynamic parameters are calculated by the
two levels and given in Table 3. Scale factors have been rec-
ommended [42] for an accurate prediction in determining the
zero-point vibration energies (ZPVE), and the entropy, Svib(T). The
variations in the ZPVEs seem to be insignificant. The changes in the
total entropy of DOPNA at room temperature are only marginal. It
is stated that, higher dipole moment of a given compound reflects
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LUMO+4
LUMO+3
LUMO+2
LUMO+1
LUMO
HOMO
HOMO−1
HOMO−2
HOMO−3
HOMO−4
Total energy
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Rotational constants
−0.44
−0.81
−0.72
−1.14
−1.00
−1.37
−2.15
−2.35
−3.09
−3.34
−6.03
−6.21
−6.68
−6.92
−6.99
−7.22
−7.34
−7.65
−7.65
−7.89
−1231.97119936
199.21538
0.51599
0.07076
0.06604
−1232.26579346
197.67577
0.51103
0.07093
0.06650
Entropy
Total
Translational
Rotational
Vibrational
Dipole moments
167.917
43.546
36.143
88.229
12.1019
168.812
43.546
36.143
89.123
11.8623

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