Quantum chemical modeling, synthesis, spectroscopic (FT-IR, excited States, UV–Vis) studies, FMO, QTAIM, NBO and NLO analyses of two new azo derivatives

Article abstract of DOI:10.1016/j.molstruc.2021.130810

In this research, we report the results of experimental and density functional theory (DFT)/time-dependent DFT analyses of two new azo derivatives that absorb light in the visible range: (E)-2-((4-(diethylamino)phenyl)diazenyl)-6-methoxy-3-methylbenzo[d]thiazol-3-ium (I) and N,N-diethyl-4-((6-methoxybenzo[d]thiazol-2-yl)diazenyl)aniline (II) in the presence of water (I) and chloroform (II). The molecular geometry and excited states of the compounds were investigated, and their natural bond orbital, frontier molecular orbital, quantum theory of atoms in molecules, and nonlinear optical (NLO) parameters were calculated. In addition, Fourier-transform infrared, nuclear magnetic resonance, and ultraviolet/visible spectral parameters were generated from the derived structures and compared to experimental spectral parameters. The practical applicability of the azo derivatives was investigated by determining their electronic and NLO properties, which demonstrated that both molecules have potential for optoelectronic and photonic applications. A high degree of approximation between the calculated and experimental results was demonstrated.

Full text of DOI:10.1016/j.molstruc.2021.130810

Journal Pre-proof
Quantum Chemical Modeling, Synthesis, Spectroscopic (FT-IR,
Excited States, UV/Vis) Studies, FMO, QTAIM, NBO and NLO
Analyses of Two New Azo Derivatives
Erfu Huo , Siyamak Shahab , Sultan Al Saud , Weiqin Cheng ,
Peng Lu , Masoome Sheikhi , Radwan Alnajjar , Sadegh Kaviani
PII:
S0022-2860(21)00943-1
DOI:
Reference:
https://doi.org/10.1016/j.molstruc.2021.130810
MOLSTR 130810
To appear in:
Journal of Molecular Structure
Received date:
Revised date:
Accepted date:
3 March 2021
24 May 2021
27 May 2021
Please cite this article as: Erfu Huo , Siyamak Shahab , Sultan Al Saud , Weiqin Cheng ,
Peng Lu , Masoome Sheikhi , Radwan Alnajjar , Sadegh Kaviani , Quantum Chemical Model-
ing, Synthesis, Spectroscopic (FT-IR, Excited States, UV/Vis) Studies, FMO, QTAIM, NBO
and NLO Analyses of Two New Azo Derivatives, Journal of Molecular Structure (2021), doi:
https://doi.org/10.1016/j.molstruc.2021.130810
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1
Highlights

Two new azo derivatives were synthesized and FT-IR, UV-Vis and NMR spectra were
measured


Detailed structural, physical and chemical properties were studied
Hyperpolarizability calculations reveal suitability for optoelectronic and photonic
applications

2
Quantum Chemical Modeling, Synthesis, Spectroscopic (FT-IR, Excited
States, UV/Vis) Studies, FMO, QTAIM, NBO and NLO Analyses of Two
New Azo Derivatives
Erfu Huo1,2, Siyamak Shahab3,4,5, Sultan Al Saud3,5,*, Weiqin Cheng1, Peng Lu1,2, Masoome
Sheikhi6, Radwan Alnajjar7,8, Sadegh Kaviani9
1Henan Chemical Industry Institute Co. Ltd, Zhengzhou, The People's Republic of China;
2Quality Inspection and Analytical Test Research Center, Henan Academy of Sciences, Zhengzhou, The
People's Republic of China.
3Belarusian State University, ISEI BSU, Minsk, Republic of Belarus
4Institute of Physical Organic Chemistry, National Academy of Sciences of Belarus, 13 Surganov Str.,
Minsk 220072
5Institute of Chemistry of New Materials, National Academy of Sciences of Belarus, 36 Skarina Str.,
Minsk 220141
6Young Researchers and Elite Club, Gorgan Branch, Islamic Azad University, Gorgan, Iran
7Department of Chemistry, Faculty of Science, University of Benghazi, Benghazi, Libya.
8Department of Chemistry, University of Cape Town, Rondebosch 7701, South Africa
9 Mashhad, Iran, Ferdowsi University of Mashhad
*Corresponding author email: sultan@compchemresearch.com

3
ABSTRACT
In this research, we report the results of experimental and density functional theory
(DFT)/time-dependent DFT analyses of two new azo derivatives that absorb light in the
visible range: (E)-2-((4-(diethylamino)phenyl)diazenyl)-6-methoxy-3-
methylbenzo[d]thiazol-3-ium (I) and N,N-diethyl-4-((6-methoxybenzo[d]thiazol-2-
yl)diazenyl)aniline (II) in the presence of water (I) and chloroform (II). The molecular
geometry and excited states of the compounds were investigated, and their natural bond
orbital, frontier molecular orbital, quantum theory of atoms in molecules, and nonlinear
optical (NLO) parameters were calculated. In addition, Fourier-transform infrared,
nuclear magnetic resonance, and ultraviolet/visible spectral parameters were generated
from the derived structures and compared to experimental spectral parameters. The
practical applicability of the azo derivatives was investigated by determining their
electronic and NLO properties, which demonstrated that both molecules have potential
for optoelectronic and photonic applications. A high degree of approximation between
the calculated and experimental results was demonstrated.
Keywords: Optoelectronics; NLO; UV/Vis spectroscopy; NBO
1. INTRODUCTION
Hydrazones are a class of organic compounds with the structure R1R2C=NNH2. The chemistry of
the carbon–nitrogen double bond of hydrazones provides the backbone for condensation reactions in
benzo-fused N–heterocycles [1]. Hydrazones containing azomethine groups are an important class of
compounds for new drug development [2,3]. Many researchers synthesized these compounds and
evaluated their various biological activities. Hydrazides/hydrazones act as antibacterial, antiviral,
analgesic and anti-inflammatory, anti-platelet, vasodilator, anticonvulsant, antioxidant, diuretic, anti-
malarial, anti-arthritis, and anti-trypanosomal agents, as well as hormone antagonists and receptor

4
agonists [3,4]. They can also be integrated in liquid crystal displays, solar cells, and optoelectronics
devices due to their conjugated donor–acceptor network and excellent nonlinear optical (NLO) properties
[5-7]. Thus, we synthesized two azo derivatives and compared the results of quantum chemical
calculations with experimental data to investigate their potential for optoelectronic and photonic
applications.
2. METHODS
2.1 Experimental methods
All materials and reagents were commercially available and used without further purification to
synthesize the azo derivatives (E)-2-((4-(diethylamino)phenyl)diazenyl)-6-methoxy-3-
methylbenzo[d]thiazol-3-ium (I) and N,N-diethyl-4-((6-methoxybenzo[d]thiazol-2-yl)diazenyl)aniline
(II), abbreviated hereafter as GSL and GSL-1, respectively (Scheme 1).
Scheme 1. Synthesis of GSL and GSL-1
To synthesize GSL-1, a solution of 2-amino-6-methoxybenzothiazole (0.2 mol) in sulfuric acid
(50 %, 400.0 mL) was heated to 95 °C until completely dissolved and then cooled to -2 ℃. The solution
was added by dropping sodium nitrite (0.2 mol, 100.0 ml) aqueous solution with a temperature of -5–0
℃. The resulting mixture was stirred at -5–0 ℃ for 1 h. A sulfuric acid (40%, 94.0 mL) solution of N, N-
diethylaniline (0.207 mol) was added to the reaction mixture. The reaction proceeded at 30 ℃ for 2 h, and
the products were then filtered and dried to obtain the solid GSL-1. Yield: 80.79 %; melting point: 145–

5
147 ℃.
To synthesize GSL, GSL-1 (1.0 mol), zinc oxide (1.0 mol), and water (250.0 mL) were added to a
2.0 L round bottom flask. After stirring for 30 min, dimethyl sulfate (3.0 mol) was added dropwise to the
reaction mixture. The reaction proceeded at 30 ℃ for 6 h, and then the mixture was filtered under suction
to remove the solvent from the filtrate. The solid was dissolved in chloroform, and the undissolved matter
was removed by filtering. Zinc chloride (1.2 mol), concentrated hydrochloric acid 32% (180.0 g), and
water (600.0 mL) were added into the reaction mixture. The reaction proceeded at 60 ℃ for 6 h, and then
sodium chloride (600.0 g) was added, followed by cooling to 45 ℃, filtering, and drying to obtain the
dark solid GSL. Yield: 99.8 %; melting point: 195–197 ℃.
GSL and GSL-1 were analyzed using various spectroscopic methods. Nuclear magnetic
resonance (NMR) spectra were measured using a Bruker Avance AV ΙΙ-400 MHz instrument. Fourier-
transform infrared (FT-IR) spectra were recorded using an IR Affinity-1 infrared spectrometer with the
KBr pellet method. Ultraviolet-visible (UV-Vis) absorption spectra were measured using a Cary 60 UV-
Vis scanning spectrophotometer in H2O and CHCl3, for GSL and GSL-1, respectively. These solvents
were used in all analyses, unless stated otherwise.
2.2 Computational methods
Quantum chemical calculations of the GSL and GSL-1 structures were performed using the
density functional theory (DFT) method with the Amsterdam density functional (ADF) modeling suite
[8,9]. Conformational analysis was used to locate the conformation with the lowest energy followed by
geometry optimization, and calculations of the IR spectra [10], molecular electrostatic potential (MEP),
and frontier molecular orbital (FMO) of GSL and GSL-1 in H2O and CHCl3, respectively, using the
GGA:OPBE XC functional with a TZP Slater basis-set [11]. In addition, a TZ2P Slater basis-set was used
for the quantum theory of atoms in molecules (QTAIM) calculations. The COSMO solvent model [12],
using Klamt radii with no geometric constraints, was used for all calculations. Scalar relativistic effects

6
were incorporated via the ZORA formalism [13–15], except for the QTAIM calculations, due to
incompatibility issues in ADF. Furthermore, time-dependent DFT (TD-DFT) excited-state calculations
[16] were conducted with a TZ2P basis-set, while NMR calculations [17] were conducted with a TZ2P-J
basis-set for GSL and GSL-1 in H2O and CHCl3, respectively. These solvents were used in all analyses,
unless stated otherwise. The first 20 excited states were determined via the Davidson method for spin–
orbit (perturbative) singlet and triplet states [18]. The 1H and 13C NMR chemical shift values were
determined considering perturbative spin–spin coupling [19]; however, only chemical shifts without
coupling assuming chemically non-equivalent regions are reported. Natural bond orbital (NBO) [20] and
NLO analyses were conducted using the Gaussian 09W program [21] and the Cam-B3LYP/6-31(d,p)
level of theory for GSL and GSL-1 using the C-PCM solvent model coupled to universal-force-field radii.
3. RESULTS AND DISCUSSION
3.1 Optimized structures of GSL and GSL-1
The computational studies gave optimized molecular structures of GSL and GSL-1, as illustrated
in Fig. 1. with DFT-calculated bond lengths and angles of selected atoms listed in Table 1.
Fig. 1. Optimized molecular structures of GSL and GSL-1

7
Table 1. Selected optimized geometric parameters of GSL and GSL-1
GSL
GSL-1
Bond
Parameter length (Å)
Bond angle
(°)
Bond
Parameter length (Å)
Bond
angle (°)
Parameter
Parameter
O1–C2
1.352
O1–C2–C7
124.2
O1–C2
1.359
O1–C2–C7
C4–C5–
N20
124.2
O1–C19
1.428
C4–C5–N21
127.8
O1–C19
1.423
125.7
C5–N20–
C8
C5–N21
C6-S25
C8–N21
1.399
1.734
1.346
C5–N21–C8
C6-S25–C8
C7–C6-S25
113.4
90
C5–N20
C6-S24
C8–N20
1.407
1.728
1.309
110.1
88
C6-S24–C8
126.5
C7–C6-S24
C8–N21–
N22
C11–C12–
N23
127.6
C8–N22
C8-S25
C9–N22
1.343
1.738
1.35
C8–N22–N23
C11–C12–
N24
C13–C12–
N24
109.8
121.5
121.4
C8–N21
C8-S24
C9–N21
1.371
1.779
1.376
111.6
121.8
121.7
C13–C12–
N23
C15–N24–
C16
C15–N23–
C16
C12–N24
C15–N24
1.348
1.464
115.1
118.2
C12–N23
C15–N23
1.369
1.46
116.9
118.1
C19-O1–C2
C19-O1–C2
N21–N22–
C9
C16–N24
N22–N23
1.464
N22–N23–C9
117.7
C16–N23
N22–N23
1.46
117.1
122.9
N20–C8–
1.306
1.456
N21–C8–N22
C8–N21–C20
123.4
123.5
1.283
N21
C20–N21
3.2 Vibrational analysis
The IR vibrational spectra of GSL and GSL-1 were calculated using OPBE/TZP level of theory.
GSL consists of 48 atoms which show 138 normal modes of IR active vibrations. In the spectra, main
peaks were observed at 1000–1650 cm−1 with higher intensity than those of GSL-1 in the C–N stretching
region (1100–1660 cm−1) due to the additional C–N bond. Minor peaks were observed at 2900–3200 cm−1
corresponding to CH3 stretching, and a 600–900 cm−1 fingerprint region. The peaks extracted from the
theoretical IR spectrum were in good agreement with those from the experimental FT-IR spectrum (Table
2). GSL-1 consists of 44 atoms which undergo 126 normal modes of IR active vibrations, with main
peaks at 1100–1660 cm−1 with approximately equal intensity for GSL and GSL-1, minor peaks at 2900–

8
3200 cm−1 corresponding to CH3 stretching, and a 600–900 cm−1 fingerprint region. As for GSL, the
peaks from the theoretical IR spectrum were in good agreement with those from the experimental FT-IR
spectrum (Table 2).
Table 2. Experimental and theoretical vibrational frequencies of GSL and GSL-1 and their peak
assignments
GSL
GSL-1
vexp (cm-
)
vexp (cm- vcal
)
vcal (cm-1) IIR
Assignment
(cm-1) IIR
Assignment
τC–H(arom)
vC-S–C sym,
τC–H(arom),
βC=C(arom)
vC-S–C
asym, τC–
H(arom),
βC=C(arom)
1
1
617.22w 615
732.95w 735
13.1
τC–H(arom)
623.01w 652
14.48
53.62
119.42 vC-S–C sym, 740.67w 738
τC–H(arom),
βC=C(arom)
vC-S–C
asym, τC–
H(arom),
βC=C(arom)
827.46w 836
862.18w 872
257.7
825.53w 834
65
157.55 βC=C(arom) 1053.13m 1058
155.86 vC-O, ωC–
H(arom),
ωC–H(CH3)
1004.91w 1008
1072.42m 1063
208.09 βC=C(arom), 1076.28m 1068
vC–N
94.48
βC–H(arom),
ωC–H(CH3)
212.7
vC-O, ωC–
H(arom),
1134.14s 1127
665.47 βC–H(arom),
vC–N, ωC–
ωC–H(CH3)
H(CH3)
1126.43m 1129
1153.43s 1146
262.74 βC–H(arom), 1228.66m 1222
503.27 βC–H(arom),
vC–N, vC-O
509.45 βC–H(arom),
vN=N,
vC–N
468.11 βC–H(arom), 1255.66m 1260
vC–N
vC=C, vC-O,
ωC–H(CH3),
vC–N
1172.72s 1162
1205.51m 1215
1240.23m 1258
716.67 βC–H(arom), 1307.74m 1313
157.73 βC–H(arom),
vC–N,
vC=C, ωC–
H(CH3)
111.46 βC–H(arom),
vC–N,
vC=C, ωC–
H(CH3)
936.57 vN=N,
vC=C, vC=N
vC–N, ωC–
H(CH3)
180.53 βC–H(arom), 1332.81m 1352
vC–N, vC-O
72.74
vN=N, βC–
1344.38m 1389
H(arom)

9
thiazol, βC–
H(arom),
βC–
H(CH3),vC–
N
1263.37s 1270
1288.45m 1279
2059.83 βC–H(arom), 1406.11w 1415
111.7
vC=C, vC=N
thiazol, βC–
H(CH3),vC–
N
vC–N, vC=C,
vC-O
125.12 βC–H(arom), 1490.97m 1507
805.02 vC=C asym,
vC=N
vC=C, vC-
O,vC–N,
ωC–H(CH3),
N=N
thiazol, βC–
H(CH3),vC–
N
1327.03m 1306
3524.26 βC–H(arom), 1593.2s
vC–N, vC=C,
1616
1517.97 vC=N
thiazol,
ωC–H(CH3),
vC=C asym
vN=N
1344.38m 1337
1365.6m 1354
506.77 βC–H(arom), 2370.51w -
-
vCO2(air)
vC–N, vC=C,
ωC–H(CH3)
1082.42 βC–H(arom), 2931.8w 2985
103.22 vC–
H(CH3)sym
vC–N, vC=C,
ωC–H(CH3),
vN=N
1402.25w 1395
104.3
vN=N,
2974.23w 3012
187.52 vC–
H(CH3)sym
vC=C, vC=N
thiazol, βC–
H(arom),
ωC–
H(CH3),vC–
N
1427.32m 1420
1458.18w 1435
1481.33w 1487
383.17 vC=C, vC=N
thiazol, βC–
H(CH3),vC–
N
175.45 vC=C, vC=N
thiazol, βC–
H(CH3),vC–
N
158.04 vC=C asym,
vC=N
thiazol, βC–
H(CH3),vC–
N
1543.05m 1530
103.85 vC=C asym,

10
vC=N
thiazol, βC–
H(CH3),vC–
N
1558.48m 1553
256.7
58.6
vC=C asym,
vC=N
thiazol, βC–
H(CH3),vC–
N
1595.13m 1591
1608.63s 1615
vC=C asym,
vC=N thiazol
1655.12 vC=N
thiazol, vC=C
asym
2370.51w -
-
vCO2(air)
2978.09w 2996
82.26
vC–
H(CH3)sym
IIR, IR intensity; v, stretching; β, in plane bending; ω, out of plane bending (wagging); τ, torsion; asym, asymmetric;
sym, symmetric; arom, aromatic; w, weak; m, medium; s, strong
3.3. Molecular electrostatic potential maps
MEP maps were calculated using OPBE/TZP level of theory. The total electron density mapped
with an electrostatic surface is illustrated in Fig. 2, while the contour map of the electrostatic potential is
illustrated in Fig. 3. In MEP maps, the negative sites with high electron density (which are prone to
electrophilic attack) are shown in red, orange, and yellow, whereas the positive sites (which are prone to
nucleophilic attack) are shown in blue [22]. According to the MEP maps, the regions prone to
electrophilic attack in both GSL and GSL-1 are the azo region and the oxygen atoms (including N20 in
GSL-1 and excluding methylated N21 in GSL). The regions prone to nucleophilic attack are the hydrogen
atoms on methyl carbon atoms including N24 in GSL and N23 in GSL-1.

11
Fig. 2. Total electron density mapped with electrostatic surface GSL, GSL-1
Fig. 3. Contour map of electrostatic potential GSL, GSL-1
3.4. Electronic structure and excited states
Twenty excited states of GSL and GSL-1 were calculated using OPBE/TZ2P level of theory,
where the nearly forbidden excitations f ≈ 0 were ignored [23].
GSL. According to our calculations, the optimal transitions are at λ = 662.99 nm (f = 1.4520)
S0→S1 with single orbital contributions (94 → 95) 92.6% and (92 → 95) 6.5%. In addition, a transition
was observed at λ = 498.16 nm (f = 0.1771) S0→S3 with single orbital contributions (92 → 95) 74.1%,
(91 → 95) 19.3%, and (94 → 95) 4.2%. Moreover, a transition is apparent at λ = 433.18 nm (f = 0.1675)
S0→S4 with single orbital contributions (91 → 95) 77.6%, (92 → 95) 14.9%, (94 → 95) 2.1%, and (94 →
98) 1.8%, in addition to a lower probability transition at λ = 328.98 nm (f = 0.0524) S0→S6 with single
orbital contributions (94 → 96) 89.2%, (92 → 96) 3.5%, (89 → 95), 1.5%, (94 → 97) 1.2%, and (94 →
98) 1.1%. Excitation of an electron from (94 → 95) molecular orbital gives the main contribution to the
absorption band at 662.99 nm in the visible region of the spectrum (Table S1). The theoretical excitation

12
spectrum is in good agreement with the experimental UV-Vis absorption spectra of GSL in water (1×10-6
mol·L-1). (Fig. 4.)
Fig. 4. Experimental UV-Vis absorption spectra of GSL (a) and GSL-1 (b).
GSL-1. According to our calculations, the optimal transitions are at λ = 585.81 nm (f = 1.5491)
S0→S1 with single orbital contributions (90 → 91) 96.1% and (88 → 91) 2.4%. In addition, a lower
probability transition is observed at λ = 332.76 nm (f = 0.0955) S0→S7 with single orbital contributions
(90 → 92) 46.5%, (90 → 93) 42.7%, (86 → 91) 4.3%, and (88 → 93) 3.3%. Moreover, an additional
lower probability transition is apparent at λ = 306.97 nm (f = 0.0946) S0→S9 with single orbital
contributions (84 → 91) 88.2%, (83 → 91) 2.9%, (90 → 96) 2.5% and (88 → 94) 1.2%, in addition to a
transition at λ = 429.81 nm (f = 0.0561) S0→S4 with single orbital contributions (87 → 91) 51.6%, (88 →
91) 40.4%, (90 → 94) 4.2%, and (90 → 91) 1.7%. Excitation of an electron from (90 → 91) molecular
orbital gives the main contribution to the absorption band at 585.81 nm in the visible region of the
spectrum (Table S2). The theoretical excitation spectrum is in good agreement with the experimental UV-
Vis absorption spectra of GSL-1 in CHCl3 (1×10-6 mol·L-1) (Fig. 4.)
3.5. FMO analysis and electronic properties
The electronic properties of GSL and GSL-1 were deduced from FMO analysis using OPBE/TZP
level of theory. The results are shown in Table 3 and Fig. 5. The figures show that the highest occupied

13
molecular orbital (HOMO) orbitals of GSL and GSL-1, respectively, are relatively localized throughout
the molecule with the exception of some single bond (–C–C-), and sulfur in the case of GSL-1. However,
the lowest unoccupied molecular orbital (LUMO) orbitals are mainly concentrated around double bonds
(–C=N-, –N=N-), the double bond (–C=C-) of one of the phenyl rings, the single bond (–C–N-), and
sulfur atoms.
Fig. 5. (a) HOMO and (b) LUMO of GSL. (c) HOMO and (d) LUMO of GSL-1
The HOMO and LUMO energy levels (EHOMO and ELUMO, respectively) are related to the
ionization potential (I = - EHOMO)and the electron affinity (A = -ELUMO). The global hardness (η) is defined
as the resistance of an atom or a group of atoms to charge transfer. The electronegativity (χ) is a measure
of the power of an atom or a group of atoms to attract electrons. The electronic potential (μ) is a measure
of the tendency of electrons in an atom or a group of atoms to escape its ground state. The chemical
softness (S) measures the capacity of an atom or group of atoms to receive electrons. Here, η, χ, μ, ω, and
S were calculated using the following equations [24]. GSL had a smaller energy gap (Eg) and η than GSL-
1. Therefore, GSL is a softer molecule with higher reactivity and lower kinetic stability than GSL-1. In
addition, GSL is more electronegative and electrophilic than GSL-1, with a higher tendency of accepting
electrons.

14
η = I-A/2
χ = I + A/2
μ = −(I + A)/2
ω = μ2/2η
S = 1/2η
Table 3. Calculated electrical parameters of GSL and GSL-1
Property
Bond energy
(eV)
GSL
GSL-1
-293.009
-5.352
-3.922
1.43
-276.902
-4.826
EHOMO (eV)
ELUMO (eV)
Eg (eV)
I (eV)
-3.3235
1.5025
5.352
4.826
A (eV)
3.922
3.3235
χ (eV)
4.637
4.07475
0.75125
-4.07475
11.05064
0.665557
η (eV)
0.715
μ (eV)
-4.637
15.0362
0.699301
ω (eV)
S (eV)
3.6 QTAIM analysis
QTAIM analysis was conducted using OPBE/TZ2P level of theory to determine the nature of
chemical bonding in GSL and GSL-1. The following results were calculated at the bond critical points
(BCPs) of selected bonds, as listed in Table 4, where the electron density p(r) describes the strength of a
chemical bond, the Laplacian electron density ∇2p(r) determines where the electronic charge is locally
concentrated or depleted, and the ellipticity of the electron density ε provides a quantitative assessment of
the anisotropy of the electron density [25]. The molecular graphs containing BCPs are illustrated in Fig.
6. The results revealed two hydrogen-hydrogen bonds in GSL and GSL-1 with low p(r) and positive
∇2p(r) values, which is an indication of noncovalent interactions. In addition, the hydrogen-hydrogen

15
bonds exhibit an ε value that suggests a higher density delocalization of their interaction. Moreover, the
O1–C19 bond has the lowest ε amongst the selected bonds in GSL and GSL-1. The strongest bond
according to QTAIM analysis is azo N22–N23 and N21–N22 in GSL and GSL-1, respectively, with a
negative ∇2p(r) indicating covalent interactions. The azo bond in GSL-1 is stronger than that in GSL,
which is consistent with the shorter N=N bond in GSL-1. The additional methyl group C20–N21 in GSL
reduces the strength of C8–N21 and C5–N21 relative to C8–N20 and C5–N20 in GSL-1, and also
increases ε relative to C8–N20 and C5–N20 in GSL-1.
Table 4. Calculated topological parameters at the BCPs of selected bonds of GSL and GSL-1
GSL
∇2p(r)
(a.u.)
-0.46896
GSL-1
∇2p(r)
(a.u.)
0.0017 O1–C19 0.250959 -0.49525
p(r)
(a.u.)
p(r)
(a.u.)
Bond
ε (a.u.)
Bond
ε (a.u.)
0.0052
O1–C19
O1–C2
C6-S25
C8-S25
C5–N21
C8–N21
0.24648
0.298893
0.206177
0.206204
0.299356
0.332773
0.35103
-0.59687
-0.35642
-0.35567
-0.82441
-0.99996
-1.08907
0.0586
0.1760
0.0276
O1–C2 0.293305
C6-S24 0.208023
C8-S24 0.190324
-0.58175
-0.36399
-0.27486
-0.93565
-1.15578
-0.98772
0.0565
0.1830
0.2380
0.1080
0.2250
0.1460
0.1520 C5–N20 0.320493
0.2610 C8–N20 0.366412
C8–N22
N22–
0.1670 C8–N21 0.329434
N21–
N23
0.407259
0.334148
-0.87041
-1.01096
0.0949
N22 0.431255
-0.98886
-0.93703
0.1170
0.1350
C9–N23
C12–
N24
H30–
H36
H31–
H34
C20–
N21
0.1670 C9–N22
C12–
0.31861
0.327912
0.015483
0.015348
0.251629
-0.95872
0.060196
0.059449
-0.59473
0.1820
0.9320
0.8930
0.0246
N23 0.313662
H29–
H35 0.018115
H30–
-0.90906
0.064499
0.063507
0.1720
0.6080
0.5970
H33 0.017843

16
Fig. 6. QTAIM topological map with BCPs and contour electron density of (a) GSL and (b) GSL-1
3.7 NMR analysis
The 1H and 13C NMR chemical shifts of GSL and GSL-1 were calculated using OPBE/TZ2P-J
level of theory. The experimental 1H chemical shifts of GSL and 1H and 13C NMR chemical shifts of
GSL-1 are compared.
GSL. The predicted 1H chemical shifts for all hydrogen atoms on both phenyl rings, namely H26,
H27, H28, H29, H30, H31, and H32 are 7.9302, 8.4008, 8.1333, 8.4549, 7.9022, 7.9317, and 8.6351 ppm,
respectively. The chemical shifts of hydrogen atoms H33, H34, H35, H36, H46, H47, and H48 on C20,
C15, and C16 that are bound to N21 and N24 are 3.8758, 4.3262, 3.8770, 4.3256, 5.5738, 3.9280, and
3.9775 ppm respectively. The high chemical shift of H46 in equivalent region of H46, H47, and H48 is
due to hydrogen bonding with H32. The chemical shift for hydrogen atoms H37, H38, H39, H40, H41,
and H42 on C17 and C18 are 1.5893, 1.6732, 1.4672, 1.6422, 1.6505, and 1.4632 ppm, respectively. The
chemical shifts of H43, H44, and H45 on C19 bonded to O1 are 4.6665, 4.1424, and 4.1421 ppm
respectively. Although the theoretical chemical shifts showed a downward shift compared to experimental
values, they were in relatively good agreement with experimental 1H NMR (400 MHz, D2O) δ(ppm): 7.21

17
(b, 1H), 6.99-7.01 (d, J=8.4 Hz, 1H), 6.89 (b, 1H), 6.78 (b, 1H), 6.47 (b, 4H), 3.75 (s, 6H), 3.70 (s, 4H),
1.24 (b, 6H).
Furthermore, the predicted 13C chemical shifts for all carbon atoms on both phenyl rings, namely
C2, C3, C4, C5, C6, C7, C9, C10, C11, C12, C13, and C14 are 161.2172, 120.2606, 116.0847, 135.3127,
131.6228, 104.5784, 147.1176, 141.5555, 117.2259, 153.7163, 119.3396, and 121.1767 ppm,
respectively. The higher chemical shifts on C2, C9, and C12 are due to de-shielding by neighboring
oxygen and nitrogen atoms. The chemical shift of C8 in thiazole is 174.5153 ppm, which is the most-de-
shielded carbon in GSL. The chemical shifts of shielded carbon atoms C15, C16, and C20 bound to N21
and N24 are 48.2822, 48.3885, and 34.8636 ppm, respectively. In addition, the chemical shifts of C17 and
C18 bound to C15 and C16 are 11.5378 and 11.1531 ppm, respectively, which are the most-shielded
carbon atoms in GSL. The chemical shift of C19 bound to O1 is 58.5009 ppm.
GSL-1. The predicted 1H chemical shifts for all hydrogen atoms on both phenyl rings, namely,
H25, H26, H27, H28, H29, H30, and H31 are 7.6118, 8.4343, 8.0648, 8.3844, 7.7076, 7.7204, and 8.5002
ppm, respectively. The chemical shifts of hydrogen atoms H32, H33, H34, and H35 on C15 and C16 that
are bound to N23 are 3.7322, 4.4645, 3.7208, and 4.4747 ppm, respectively. The chemical shift for
hydrogen atoms H36, H37, H38, H39, H40, and H41 on C17 and C18 are 1.4565, 1.1798, 1.8907, 1.4687,
1.1891, and 1.8963 ppm, respectively. The chemical shifts of H42, H43, and H44 on C19 bonded to O1
are 4.5361, 4.0608, and 4.0499 ppm respectively. The theoretical chemical shifts, although exhibiting a
downward shift relative to the experimental values, are in relatively good agreement with experimental 1H
NMR (400 MHz, CDCl3) δ(ppm):7.93-7.96 (m, 3H), 7.28-7.29 (d, 1H, J=2.4 Hz), 7.04-7.07 (m, 1H),
6.71-6.74 (d, 2H, J=9.6 Hz), 3.89 (s, 3H), 3.46-3.52 (q, J=7.2 Hz, 4H), 1.24-1.28 (t, 6H, J=7.8 Hz).
Furthermore, the predicted 13C chemical shifts for both phenyl ring carbon atoms C2, C3, C4, C5,
C6, C7, C9, C10, C11, C12, C13, and C14 are 159.9456, 117.3063, 125.3089, 149.0541, 138.7721,
102.0303, 143.8061, 138.1642, 114.8590, 152.3618, 116.9037, and 117.6215 ppm, respectively. The
higher chemical shifts on C2, C5, C6, C9, and C12 is due to de-shielding by neighboring oxygen,

18
nitrogen, and sulfur atoms. The chemical shift of C8 in thiazole is 180.2112 ppm, which is the most de-
shielded carbon in GSL-1. The chemical shifts of shielded carbon atoms C15 and C16 bound to N23 are
42.5751 and 42.5145 ppm, respectively. In addition, the chemical shifts of C17 and C18 bound to C15
and C16 are 11.1985 and 11.1423 ppm, respectively, which are the most-shielded carbon atoms in GSL-1.
The chemical shift of C19 bound to O1 is 57.4765 ppm. The theoretical chemical shifts are in good
agreement with experimental 13C NMR (400 MHz, CDCl3) δ(ppm): 175.32, 158.45, 151.89, 147.34,
142.45, 135.59, 127.71, 127.40, 124.53, 115.34, 111.22, 104.53, 55.71, 44.91, 12.61.
3.8 Natural Charge analysis
As the atomic charges determine many properties of molecular systems, the natural charges were
computed by NBO analysis and the results are shown in Table 5-6 (atom numbering according to Fig. 1).
Here, N21–24 and S25 in GSL are equivalent to N20–23 and S24 in GSL-1.
GSL. The carbon atoms on both phenyl rings are negative, except C2, C5, C9, and C12 that are
bonded to electron-withdrawing nitrogen and oxygen atoms, with C2 bonded to O1 and C12 bonded to
N24 being the most-positively charged carbon atoms in the molecule, whereas C3, C7, and C11, C13 are
the most-negatively charged carbon atoms on the phenyl rings due to their proximity to positive C2 and
C12, respectively. The rest of the carbon atoms are negative with the exception of thiazole C8, which is
bonded to two electron-withdrawing nitrogen atoms and one electron-donating sulfur atom. The most-
negative carbon atom in GSL is C20, which is attached to the methyl group via N21, followed by methyl
C17 and C18. All oxygen and nitrogen atoms have a negative charge, with N24 being the most negative
and azo N23 being the least negative nitrogen atoms in the molecule, which suggests that azo N23 is more
susceptible to nucleophilic attack than azo N22. In contrast, thiazole S25 has a positive charge as it
donates electrons to C6 and C8. All hydrogen atoms are positive and similarly charged with methyl H46
on C20 bonded to N21 being the most positive, whereas H44 and H45 of C19 bonded to O1 being the
least positive hydrogen atoms in the molecule.

19
Table 5. NBO charges of GSL
Atom Charge Atom Charge
Atom Charge Atom Charge Atom Charge
O1
C2
C3
C4
C5
C6
C7
C8
C9
C10
-0.53035 C11
0.34617 C12
-0.2687 C13
-0.23821 C14
0.12628 C15
-0.21266 C16
-0.32642 C17
0.29653 C18
0.06829 C19
-0.14801 C20
-0.31731 N21
0.28779 N22
-0.2939 N23
-0.1734 N24
-0.282 S25
-0.34343 H31
-0.34896 H32
-0.16943 H33
-0.37602 H34
0.50632 H35
0.27346 H36
0.27717 H37
0.27798 H38
0.27388 H39
0.26791 H40
0.26796 H41
0.27773 H42
0.26274 H43
0.25816 H44
0.26265 H45
0.2583 H46
0.24594 H47
0.24741 H48
0.25754
0.24741
0.25751
0.24799
0.22422
0.22424
0.28051
0.2674
-0.28216 H26
-0.71781 H27
-0.71787 H28
-0.35013 H29
-0.50595 H30
0.26719
0.24604
GSL-1. Similar to GSL, carbon atoms on both phenyl rings are negative, except for C2, C5, C9,
and C12, which are bonded to electron-withdrawing nitrogen and oxygen atoms with C2 bonded to O1,
and C12 bonded to N23, being the most-positively charged carbon atoms in the molecule, whereas, C3,
C7 and C11, C13 are the most negative carbon atoms on the phenyl rings due to their proximity to
positively charged C2 and C12, respectively. The rest of the carbon atoms are negative, with the
exception of thiazole C8, which is bonded to two electron-withdrawing nitrogen atoms and one electron-
donating sulfur atom. The most-negative carbon atoms in GSL-1 are methyl C17 and C18. All oxygen
and nitrogen atoms have a negative charge, with N20 being the most negative and azo N22 being the least
negative in the molecule. Of the nitrogen atoms in the molecule, azo N22 has a higher susceptibility to
nucleophilic attack than azo N21. Non-methylated N20 has a higher negative charge (susceptibility to
electrophilic attack) in GSL-1 than in GSL. Thiazole S24 has a positive charge as it donates electrons to
C6 and C8. Similar to GSL, all hydrogen atoms in GSL-1 are positive and similarly charged, with phenyl
H31 being the most positive, whereas H43 and H44 of C19 bonded to O1 are the least-positive hydrogen
atoms in the molecule.

20
Table 6. NBO charges of GSL-1
Atom Charge Atom Charge Atom Charge Atom Charge Atom Charge
O1
C2
C3
C4
C5
C6
C7
C8
C9
C10
-0.53497 C11
0.33928 C12
-0.29473 C13
-0.21685 C14
0.09058 C15
-0.22012 C16
-0.34398 C17
0.21511 C18
0.04101 C19
-0.17641 N20
-0.31974 N21
0.24159 N22
-0.30352 N23
-0.1934 S24
-0.27197 H25
-0.27222 H26
-0.718 H27
-0.26144 H31
-0.1887 H32
-0.43938 H33
0.37881 H34
0.26263 H35
0.26351 H36
0.26488 H37
0.26192 H38
0.2544 H39
0.25446 H40
0.26837 H41
0.23983 H42
0.25229 H43
0.23925 H44
0.25243
0.23929
0.24311
0.2191
0.21914
0.25321
0.24517
-0.71778 H28
-0.34663 H29
-0.45726 H30
0.23924
0.25323
0.24525
3.9. NBO analysis
NBO analysis was used to study the interactions between orbitals and thereby demonstrate
intramolecular charge transfer, delocalization, and conjugation of the electron density. The results of the
NBO analysis, such as the occupation numbers, polarization coefficient values, intramolecular donor–
acceptor interactions, and stabilization energies of selected bonding atoms in GSL and GSL-1 were
calculated and the results are shown in Table S3-S6. The atoms are numbered according to Fig. 1, where
N21–24 and S25 in GSL are equivalent to N20–23 and S24 in GSL-1, respectively. One of the phenyl
rings of GSL displays a preferred quinonoid structure leaving C9 with a lone pair, and forming C12=N24
instead of C12–N24. The most stabilizing interactions in both molecules are high occupancy π→π*
transitions that move back and forth around azo N22–N23 in GSL and N21–N22 in GSL-1. High
occupancy n→π* and lower occupancy n→σ* transitions occur from nitrogen, sulfur, and oxygen lone
pairs, as well as C9 in the GSL quinonoid structure. Finally, for the low occupancy σ→σ* transitions,
sulfur-bonded atoms contribute greatly to the conjugation. In addition, the size of the polarization
coefficients of the two hybrid orbitals from atom A and B demonstrates their importance in forming

21
bonds, where higher values indicate higher importance. The fraction of the hybrid orbital character
between hybrids A and B, as well as the fraction of p–character, give information about the overall bond
character and strength, as well as intramolecular charge transfer [26]. The oxygen atoms in both GSL and
GSL-1 have the highest individual hybrid character and polarization coefficients in their C–O bonds,
followed by nitrogen in C–N bonds, and carbon in C–S bonds. Both structures showed low energy
hyperconjugative interactions between σ→ π*.
3.10 NLO properties
NLO analysis was used to study the influence of the molecular structure on the polarizabilities
and hyperpolarizabilities of the studied compounds to evaluate their suitability for optoelectronics and
photonics applications. The total static dipole moment (μ), mean polarizability (α), anisotropy of
polarizability (∆α), and the mean first-order hyperpolarizability (β) of GSL and GSL-1 were estimated.
The x,y,z components of μ, α, and β were used to extract the values of interest using the following
equations [27].
√
√
(
)
(
)
(
)
(
)
√
√
The NLO results are shown in Table 7 and compared with urea as a reference standard. The
calculated values were converted to electrostatic units (esu) from atomic units (a.u.) using a conversion

22
factor of 0.1482×10-24 for α and 8.6393×10-30 for β. GSL and GSL-1 showed high β values, which were
61 and 343 times higher than urea, respectively (μ=1.3732 Debye, β=0.3728×10-30 esu) [27]. Moreover,
the μ and α values of both molecules showed that GSL is preferable for linear optics applications, whereas
the β values of GSL-1 show that it is favorable for applications in non-linear optics.
Table 7. NLO parameters of GSL and GSL-1
Parameter
GSL GSL-1
Dipole moment (μ) Debye
μx
μy
μz
μ
-12.0278
0.3310
-6.3476
0.0279
5.4400
8.3598
39.5364
41.3268
Polarizability (α) ×10-24 esu
αxx
αxy
αyy
αxz
αyz
αzz
α
78.9424 59.4735
-0.7080 0.3220
22.9476 20.7202
-53.2239 -34.4952
1.5576
0.3379
144.5349 113.4435
82.1416 64.5457
140.0635 100.3818
∆α
Hyperpolarizability (β) ×10-30
esu
βxxx
βxxy
βxyy
βyyy
βxxz
βxyz
βyyz
βxzz
βyzz
βzzz
βx
14.6161
-1.1254
0.3219
-0.0179
3.0623 27.6162
0.3886
-0.0998
-22.9894 -54.3163
1.4952 0.2476
18.4321 83.8290
-8.0514 -63.3696
-9.8200
0.0642
0.7667
-0.0057
-0.1545
-0.2888
βy
0.3519
0.3061
βz
β
21.3946 111.1564
22.8621 127.9514

23
CONCLUSION
The calculated parameters of GSL and GSL-1 revealed differences in their electronic properties,
MEP maps, NBO parameters and NLO properties. The preferred quinonoid structure of one of the phenyl
rings of GSL explains the red-shift observed in the UV-Vis spectrum. Both molecules display charge
transfer capabilities through light absorption in the visible range. However, the additional methyl group in
GSL generates a charged molecule that prevents use of a protic solvent, which limits the extent of a
realistic comparison of the two structures. The electronic properties, including the HOMO–LUMO gap,
are affected by the choice of solvent, as well as the NBOs, and MEP maps. The NLO values were
enhanced in the presence of water, especially the hyperpolarizability values; however, benchmarking gas-
phase calculations suggest similar favorable trends compared to the values in solvent with respect to the
NLO activity of GSL and GSL-1. Overall, the results presented here provide a foundation for further
studies using GSL and GSl-1 for optoelectronic and photonic applications.
Acknowledgments: Funding: This work was supported by the Henan Academy of Sciences, Republic of
China (Nos. 200408004, 190608026 and 200908002).
Conflict of Interest: The authors declare that there are no conflicts of interest
Ethics declarations: The ethical standards have been met.
Consent to publish: All authors consent to the publication of the manuscript
Consent to participate: Not Applicable
Availability of data and materials: Not Applicable

24
References
[1] J.P. Soni, K.S. Chemitikanti, S.V. Joshi, N. Shankaraiah, The microwave-assisted
syntheses and applications of non-fused single-nitrogen-containing heterocycles, Org.
Biomol. Chem. 18(48) (2020) 9737–9761. doi: 10.1039/d0ob01779e.
[2] G. Verma, A. Marella, M. Shaquiquzzaman, M. Akhtar, M.R. Ali, M.M. Alam, A review
exploring biological activities of hydrazones, J. Pharm. Bioallied Sci. 6(2) (2014) 69–80.
doi: 10.4103/0975-7406.129170.
[3] P. Mondal, R. Kumar, R. Gogoi, Azomethine based nano–Chemicals: Development, in
vitro and in vivo fungicidal evaluation against Sclerotium rolfsii, Rhizoctonia bataticola
and Rhizoctonia solani, Bioorg. Chem. 70 (2017) 153–162. doi:
10.1016/j.bioorg.2016.12.006.
[4] M. Yadav, S. Sharma, J. Devi, Designing, spectroscopic characterization, biological
screening and antioxidant activity of mononuclear transition metal complexes of
bidentate Schiff base hydrazones, J. Chem. Sci. 133(1) (2021). doi: 10.1007/s12039-020-
01854-6.
[5] V. Manzoni, L. Modesto-Costa, J. Del Nero, T. Andrade-Filho, R. Gester. Strong
enhancement of NLO response of methyl orange dyes through solvent effects: A
sequential Monte Carlo/DFT investigation. Opt. Mater. 94 (2019), 152-159. doi:
10.1016/j.optmat.2019.05.018
[6] A. Bogdanov, A. Vorobiev. Photo-orientation of azobenzene-containing liquid-crystalline
materials by means of domain structure rearrangement. J. Phys. Chem. B, 117(44) (2013)
13936-13945. doi: 10.1021/jp4080509

25
[7] H. Etesami, M. Mansouri, A. Habibi, F. Jahantigh. Synthesis and investigation of double
alternating azo group in novel para-azo dyes containing nitro anchoring group for solar
cell application. J. Mol. Struct. 1203 (2020) 127432. doi:
10.1016/j.molstruc.2019.127432
[8] ADF, SCM, 2020, http://www.scm.com. Theoretical Chemistry, Vrije Universiteit
Amsterdam, The Netherlands.
[9] G. te Velde, F.M. Bickelhaupt, E.J. Baerends, C. Fonseca Guerra, S.J.A. van Gisbergen,
J.G. Snijders, T. Ziegler, Chemistry with ADF, J. Comp. Chem. 22(9) (2001) 931–967.
https://doi.org/10.1002/jcc.1056.
[10]
L. Fan, T. Ziegler, Application of density functional theory to infrared absorption
intensity calculations on main group molecules, J. Chem. Phys. 96(12) (1992) 9005–
9012. https://doi.org/10.1063/1.462258.
[11]
E. van Lenthe, E.J. Baerends, Optimized Slater-type basis sets for the elements
1–118, J. Comp. Chem. 24(9) (2003) 1142–1156. https://doi.org/10.1002/jcc.10255.
[12]
C.C. Pye, T. Ziegler, An implementation of the conductor-like screening model
of solvation within the Amsterdam density functional package, Theor. Chem. Acc. Theor.
Comput. Model. (Theor. Chim. Acta) 101(6) (1999) 396–408.
https://doi.org/10.1007/s002140050457.
[13]
E. van Lenthe, E.J. Baerends, J.G. Snijders, Relativistic regular two‐component
Hamiltonians, J. Chem. Phys. 99(6) (1993) 4597–4610. https://doi.org/10.1063/1.466059.
[14]
E. van Lenthe, E.J. Baerends, J.G. Snijders, Relativistic total energy using regular
approximations, J. Chem. Phys. 101(11) (1994) 9783–9792.
https://doi.org/10.1063/1.467943.

26
[15] E. van Lenthe, A. Ehlers, E. Baerends, Geometry optimizations in the zero order regular
approximation for relativistic effects, J. Chem. Phys. 110(18) (1999) 8943–8953.
https://doi.org/10.1063/1.478813.
[16]
S.J.A. van Gisbergen, J.G. Snijders, E.J. Baerends, Implementation of time-
dependent density functional response equations, Comput. Phys. Commun. 118(2–3)
(1999) 119–138. https://doi.org/10.1016/S0010-4655(99)00187-3.
[17]
J. Autschbach, T. Ziegler, Nuclear spin–spin coupling constants from regular
approximate relativistic density functional calculations. I. Formalism and scalar
relativistic results for heavy metal compounds, J. Chem. Phys. 113(3) (2000) 936–947.
https://doi.org/10.1063/1.481874.
[18]
F. Wang, T. Ziegler, A simplified relativistic time-dependent density-functional
theory formalism for the calculations of excitation energies including spin-orbit coupling
effect, J. Chem. Phys. 123(15) (2005) 154102. https://doi.org/10.1063/1.2061187.
[19]
G. Schreckenbach, T. Ziegler, Calculation of NMR shielding tensors using gauge-
including atomic orbitals and modern density functional theory, J. Phys. Chem. 99(2)
(1995) 606–611. https://doi.org/10.1021/j100002a024.
[20] NBO, 7.0. E.D. Glendening, J, K. Badenhoop, A. E. Reed, J. Eng. Carpenter, J. A.
Bohmann, C. M. P. Karafiloglou, Morales, C. R. Landis, and F. Weinhold, Theoretical
Chemistry Institute, University of Wisconsin, Madison (2018).
[21]
M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R.
Cheeseman, G. Scalmani, V. Barone, G.A. Petersson, H. Nakatsuji, X. Li, M. Caricato,
A. Marenich, J. Bloino, B.G. Janesko, R. Gomperts, B. Mennucci, H.P. Hratchian, J.V.
Ortiz, A.F. Izmaylov, J.L. Sonnenberg, D. Williams-Young, F. Ding, F. Lipparini, F.

27
Egidi, J. Goings, B. Peng, A. Petrone, T. Henderson, D. Ranasinghe, V.G. Zakrzewski, J.
Gao, N. Rega, G. Zheng, W. Liang, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J.
Hasegawa, M. Ishida, T. Nakajima, Y. Honda, O. Kitao, H. Nakai, T. Vreven, K.
Throssell, J.A. Montgomery, Jr., J.E. Peralta, F. Ogliaro, M. Bearpark, J.J. Heyd, E.
Brothers, K.N. Kudin, V.N. Staroverov, T. Keith, R. Kobayashi, J. Normand, K.
Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M. Cossi, J.M. Millam,
M. Klene, C. Adamo, R. Cammi, J.W. Ochterski, R.L. Martin, K. Morokuma, O. Farkas,
J.B. Foresman, D.J. Fox, Gaussian, Inc., Wallingford CT, Gaussian 09, Revision D.01
(2016).
[22]
M. Sheikhi, S. Shahab, R. Alnajjar, M. Ahmadianarog, Adsorption properties of
the new anti-cancer drug alectinib on CNT(6,6-6) Nanotube: Geometry Optimization,
Molecular Structure, Spectroscopic (NMR, UV/Vis, Excited State), FMO, MEP and
HOMO–LUMO Investigations, J. Clust. Sci. 30(1) (2019).
https://doi.org/10.1007/s10876-018-1460-9.
[23]
S. Shahab, M. Sheikhi, L. Filippovich, Z. Ihnatovich, E. Koroleva, M.
Drachilovskaya et al., Spectroscopic (FT-IR, excited states, UV/vis, polarization)
properties, synthesis and quantum chemical studies of new azomethine derivatives, Dyes
Pigments 170 (2019). https://doi.org/10.1016/j.dyepig.2019.107647, 107647.
[24]
S. Shahab, H.A. Almodarresiyeh, L. Filippovich, F.H. Hajikolaee, R. Kumar, M.
Darroudi, M. Mashayekhi, Geometry optimization and excited state properties of the new
symmetric (E)-stilbene derivative for application in thermostable polarizing PVA-films:
A combined experimental and DFT approach, J. Mol. Struct. 1119 (2016) 423–430.
https://doi.org/10.1016/j.molstruc.2016.04.092.

28
[25] S. Siyamak Shahab, M. Sheikhi, L. Filippovich, E. Dikusar, M. Darroudi, S. Kaviani et
al., Optimization, spectroscopic (excited states, UV/vis, polarization) studies, FMO, ELF,
LOL, QTAIM, NBO analysis and electronic properties of two new azomethine
derivatives: A theoretical and experimental investigations, Russ. J. Phys. Chem. A 94(9)
(2020) 1848–1865. https://doi.org/10.1134/S0036024420090241.
[26]
S. Shahab, M. Sheikhi, E. Kvasyuk, A.G. Sysa, R. Alnajjar, A. Strogova et al.,
Geometry optimization, UV/vis, NBO, HOMO and LUMO, excited state and antioxidant
evaluation of pyrimidine derivatives, Lett. Org. Chem. 17 (2020).
https://doi.org/10.2174/1570178617999200812133402.
[27]
J. Prashanth, G. Ramesh, J.L. Naik, J.K. Ojha, B.V. Reddy, G.R. Rao, Molecular
Structure, vibrational analysis and first order hyperpolarizability of 4-Methyl-3–
Nitrobenzoic acid using density functional theory, Opt. Photonics J. 05(3) (2015) 91–107.
doi: 10.4236/opj.2015.53008.

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Graphical Abstract