Experimental and theoretical insights into the photophysical and electrochemical properties of flavone-based hydrazones

Article abstract of DOI:10.1016/j.molstruc.2021.130965

A small library of flavone-based hydrazones has been designed, synthesized and characterized. In this context, thirteen flavone hydrazones (3a-3 m) were synthesized by the acid-catalyzed condensation of flavone with 2,4-dinitrophenylhydrazine (2,4-DNPH) and characterized by different spectral techniques (IR, UV–Vis, NMR and mass spectrometry). The electrochemical, photophysical and theoretical investigations of such type of compounds are hitherto unknown. The electrochemical behavior of these hydrazones at a platinum electrode has been analyzed by cyclic voltammetry (CV) and was investigated at 200, 100 and 40 mVs^?1 in acetonitrile (CH₃CN). These hydrazones showed a quasi-reversible redox reaction. The oxidation–reduction reactive sites of these derivatives were located via geometry optimization using density functional theory (DFT) at the B3LYP/3–21 g in the Guassian-09 level of theory. Moreover, the target compounds exhibited interesting fluorescent properties. Owing to their excellent photophysical and redox results, a detailed structure-property relationship was established to assess the substituents impact and their position on the physicochemical and electronic properties. All the experimental results were in accordance with the computational studies.

Full text of DOI:10.1016/j.molstruc.2021.130965

Journal of Molecular Structure 1244 (2021) 130965
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Experimental and theoretical insights into the photophysical and
electrochemical properties of flavone-based hydrazones
Meshari A. Alsharifa, Nafeesa Naeemb, Ehsan Ullah Mughalb,∗, Amina Sadiqc,
Rabab.S. Jassasd, Samia Kausara, Ataf Ali Altafe, Muhammad Naveed Zafarf,
Amara Mumtazg, Rami J. Obaida, Reem I. Alsantalih, Safeer Ahmedf, Ishtiaq Ahmedi,
Hatem M. Altassa, Saleh A. Ahmeda,j,k,∗
a Department of Chemistry, Faculty of Applied Science, Umm Al-Qura University, 21955 Makkah, Saudi Arabia
b Department of Chemistry, University of Gujrat, Gujrat 50700, Pakistan
c Department of Chemistry, Govt. College Women University, Sialkot 51300, Pakistan
d Department of Chemistry, Jamoum University College, Umm Al-Qura University, 21955 Makkah, Saudi Arabia
e Department of Chemistry, University of Okara, Okara 56300, Pakistan
f Department of Chemistry, Quaid-i-Azam University, Islamabad 45320, Pakistan
g Department of Chemistry, COMSATS University Islamabad, Abbottabad, Pakistan
h Department of Pharmaceutical Chemistry, Pharmacy College, Taif University, 888 Taif, Saudi Arabia
i Department of Engineering & Biotechnology, University of Cambridge, Cambridge, United Kingdom
j Research Laboratories Unit, Faculty of Applied Science, Umm Al-Qura University, 21955 Makkah, Saudi Arabia
k Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
A small library of flavone-based hydrazones has been designed, synthesized and characterized. In this
context, thirteen flavone hydrazones (3a-3 m) were synthesized by the acid-catalyzed condensation of
flavone with 2,4-dinitrophenylhydrazine (2,4-DNPH) and characterized by different spectral techniques
(IR, UV–Vis, NMR and mass spectrometry). The electrochemical, photophysical and theoretical investiga-
tions of such type of compounds are hitherto unknown. The electrochemical behavior of these hydrazones
at a platinum electrode has been analyzed by cyclic voltammetry (CV) and was investigated at 200, 100
and 40 mVs−1 in acetonitrile (CH3CN). These hydrazones showed a quasi-reversible redox reaction. The
oxidation–reduction reactive sites of these derivatives were located via geometry optimization using den-
sity functional theory (DFT) at the B3LYP/3–21 g in the Guassian-09 level of theory. Moreover, the target
compounds exhibited interesting fluorescent properties. Owing to their excellent photophysical and re-
dox results, a detailed structure-property relationship was established to assess the substituents impact
and their position on the physicochemical and electronic properties. All the experimental results were in
accordance with the computational studies.
Received 26 April 2021
Revised 19 June 2021
Accepted 21 June 2021
Available online 24 June 2021
Keywords:
Flavone hydrazones
UV–vis spectroscopy
Fluorescence spectroscopy
Cyclic voltammetry
Structure-property relationship
Density functional theory
© 2021 Elsevier B.V. All rights reserved.
–
1. Introduction
molecular systems, the hydrazone (-C=N NH-) linkage in com-
pounds has significant nonlinear optical sensitivity due to their ar-
The innovations in the research area have revealed many se-
cret zones that can resolve many known challenges of the ad-
vanced world. Synthetic substances along with naturally originated
substances that show elevated anti-oxidative activity are attracting
high consideration. Many accomplishments have been achieved in
electrochemistry such as obtaining qualitative and quantitative in-
formation about electrochemical reactions.’ ‘Among several organic
chitectural flexibility. Hydrazones are versatile molecules and have
received considerable interest in research both fundamental and
application.
Flavone (Fig. 1) is one of the subclasses of the flavonoid fam-
ily that is present in dietary components found in herbs, cereals,
vegetables and fruits [1–7]. To discover the varied functions of 2-
phenylchromone (flavone), exploring different synthetic methods
and structural variation has now become an essential goal of some
research groups [8,9]. Thus, synthetically acquired flavone scaffold
having a range of bioactivities can be taken as lead [21] com-
pounds for the hydrazones syntheses with various distinct func-
∗
Correspondinag authors.
E-mail addresses: ehsan.ullah@uog.edu.pk (E.U. Mughal), saahmed@uqu.edu.sa
(S.A. Ahmed).
https://doi.org/10.1016/j.molstruc.2021.130965
0022-2860/© 2021 Elsevier B.V. All rights reserved.

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
The modern research developments, particularly in synthetic
chemistry, have coincided with computations to explore numerous
structural features of synthesized analogs [34]. DFT is now becom-
ing a prominent method for its beneficial intuitions to distinguish
key evidence around the mechanism and stability of novel targeted
derivatives. These computational calculations are very important in
recognizing the possible reactive sites of synthesized molecules,
which are susceptible to nucleophilic or electrophilic attacks, as
these sites enhance the physiochemical and electrochemical prop-
erties of potent compounds [35, 36].
There is sufficient literature available on the UV, emission and
redox behavior of different heterocycles [37–40], however, to the
best of our knowledge, there is no literature available on the pho-
tophysical and electrochemical properties of flavone-based hydra-
zones.
Fig. 1. Representative structures of (a) = Flavone, (b) = Flavone hydrazone.
ꢀ
Considering the above-mentioned reports and our continued
interest in the development of novel flavone hydrazone analogs,
herein, we report the design, synthesis and evaluation of flavone-
based hydrazones for their photophysical and electrochemical
properties studies. The experimental results were validated by
a computational approach. In addition, we tried to explain the
structure-property relationship in detail.
tional groups at the 4 -position of flavone skeleton [9a–9c]. The
search for novel therapeutic and electrochemical agents directed
scientists’ attention to Schiff base (azomethines) hydrazones for-
mation.
Schiff bases are recognized as a versatile class of compounds
that have significant properties and an extensive range of applica-
tions in catalysts, dyes, pigments, chemosensors and intermediates
in organic synthesis [10].
2. Material and methods
Flavone hydrazones (Fig. 1) are a chemical family of one of the
Schiff bases, nitrogen compounds, whose existence in nature has
been reported [11, 12]. Azomethines are the most prevalent and
frequently used organic compounds in many domains and play an
essential role in pharmacology and materials chemistry [13–16].
Because of the existence of fundamental sites such as heteroatoms
like ‘O’ and ‘N’, these ligands could form complexes by donating
their non-bonding electron pairs, thus leading to the high stability
of compounds [17, 18].
Most of the starting materials, solvents and chemicals were
bought from Sigma-Aldrich and were utilized as received. Elec-
trothermal digital instrument was used to access the melting
points and are uncorrected. A Bio-Rad spectrophotometer has been
used to record the IR spectra. NMR spectra were obtained us-
ing a Bruker spectrometer (1H, 600 MHz, 13C, 151 MHz). NMR
chemical shift values were defined in δ (ppm) units. The reaction
completion was observed by TLC and spots were visualized under
a UV lamp (254 nm). The QUARTZ cell was used to record the
absorption spectra in CH3CN on the Jasco UV–VIS V-660 instru-
ment. Steady-state fluorescence measurements were carried out on
a Shimadzu RF-6000 Spectro fluorophotometer. Cyclic voltamme-
try (CV) was performed with a typical three-electrode arrangement
consisting of a reference electrode (Ag/AgCl), auxiliary electrode
(platinum wire), and the working electrode (glassy carbon). The
cyclic voltammograms have been recorded in acetonitrile (CH3CN)
in 0.1 M TBAB as the supporting electrolyte with a scan rate rang-
ing from −2.0 to 1.0 Vs−1, using a CHI620 C model electrochemical
potentiostat instrument at ambient temperature.
Fluorescent studies reveal the worth of the pi-electrons rich or-
ganic materials as excellent molecules for use in analytical sen-
sors, electrochromic devices and light-emitting diodes [19, 20][21].
=
In this context, the azomethine (−HC N−) functionality has re-
ceived significant concern because of its distinctive properties such
as auto-fluorescent property attributing to n→π∗ transition of the
C=N bond, and the extensive π-conjugation system [21a]. Organic
fluorescent molecules are believed to be superior as compared to
inorganic ones due to their wide range of λemission and high lu-
minous productivity. The designing of new organic luminogens is
developing as a dynamic study that suggests an economical color
purity, ease of synthesis, purification, liquid state emission and
electrochemical stability in organic light-emitting diodes (OLEDs)
[21b]. Schiff bases give several benefits, e.g., prolonged incandes-
cent excited states and photochemical strengths [22]. Moreover,
the core-functionalization of hydrazone analogs with EDGs and
EWGs has not been used as considerably as potential fluorescent
probes. The reports showed that electron-donating and -accepting
groups can be employed to alter the physicochemical and redox
properties of hydrazones.
2.1. Procedure for the synthesis of chalcones (1a-1 m) [9d], flavones
(2a-2 m) [9d] and flavone hydrazones (3a-3 m) [9a]
A solution of 2ʹ-hydroxyacetophenone (0.12 mL, 1.0 mmol), aq.
sodium hydroxide solution (10 mL) (30%) was dissolved in MeOH
(25.0 mL) and stirred for 30 min at room temperature with the
subsequent addition of various aryl aldehyde (1.0 mmol) dropwise
at the same temperature, the reaction mixture was stirred for fur-
ther 4 h. ‘The reaction mixture progress was observed by TLC us-
ing a mixture of ethyl acetate: n-hexane (1:3) as a mobile phase.
After the completion of the reaction, the reaction mixture was
acidified with dilute HCl (10%). The precipitated solid was filtered,
washed with distilled H2O and ultimately recrystallized from EtOH
to get the purified product. Subsequently, the substituted chalcone
(1.0 mmol), was dissolved in DMSO (10 mL) and oxidatively cy-
clized in the presence of a small amount of iodine I2 (254 mg,
1.0 mmol). The reaction mixture was refluxed at 130–140 °C on
an oil bath for 4–5 hours. Afterwards, the reaction mixture was
poured onto the crushed ice, the resulting solid was treated with a
solution of 10% Na2S2O3 to get rid of unreacted I2, finally with dis-
tilled H2O and recrystallized from EtOH to get a purified product.
Furthermore, the electrochemical studies offer an immense
quantity of indication concerning the mechanism of bio-electron
charge transfer and are used to determine the analog’s impact
on redox behavior [23, 24]. Cyclic voltammetry (CV) is an exten-
sively used voltammetric technique that allows determining the
oxidation–reduction behavior of compounds in the solution form
[25–28]. The electrochemical oxidation and reduction processes of
flavonolic compounds have been investigated using this technique.
The purpose of the current study was to use CV to assess the elec-
trochemical behavior of various flavone hydrazones [29–33]. Thus,
to acquire more information of the structure-property correlations
(emission, absorption and redox properties), a number of differ-
ꢀ
ent donor- and acceptor- functional groups were introduced at 4 -
position of the flavone hydrazone skeleton.
2

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
The obtained substituted flavone and 2,4-dinitrophenylhydrazine
(DNPH) were dissolved in EtOH (15 mL). To this mixture, 3–4 drops
of concentrated sulfuric acid (H2SO4) were added and allowed the
mixture to reflux for 4 h. Upon cooling and diluting with ice-cold
water, an intense colored solid mass separated out, which was fur-
ther recrystallized from ethanol to give the desired product.
similar pattern to that predicted from the DFT work [43]. DFT com-
putations were carried out by using DFT-B3LYP/3–21 g in Guassian-
09 [44]. The ground states geometries of representative analogs
(3a-3j) were optimized using hybrid functional B3LYP and basis set
3–21 g. B3LYP functional combined to 3–21 g basis set includes
exact exchange and GGA corrections along with LDA electron-
electron and electron-nuclei energy. So, this hybrid exchange func-
tional is the simplest parameter to reproduce the geometry of a
test suite of organic molecules as per literature reports [41, 43,
50]. TD-DFT calculations were performed at B3LYP/321 g level to
calculate the UV-Visible spectra whereas vibrational analysis was
carried out by using Freq-DFT/B3LYP/321 g and these theoretical
results were compared with experimental results. The VEDA 4 pro-
gram has been used to perform different vibrational parameters
and PED calculations [51].
2.2. UV–Vis measurement
The UV–Visible absorption spectra have been obtained using a
Jasco UV–Vis V-660 spectrophotometer in 200 to 800 nm wave-
length range. The samples were prepared at a concentration of
0.1 mmol/L using acetonitrile (CH3CN) as a solvent [41]. The faster
the electrons are stimulated, the longer they can absorb the wave-
length of light. The instrument works by passing a beam of light
through a sample and measuring the wavelength of light to the
detector. Synthesized hydrazone derivatives can exhibit a variety of
transitions; π-π∗, n-π∗, σ-σ∗, n-σ∗, due to the presence of σ and
π bond and lone pair of electrons on ‘N’ atoms of flavone moiety.
Characteristically, the most favored transition is from the HOMO
to the LUMO. The UV light absorbed by a molecule can create a
distinct spectrum that helps to identify the product.
3. Results and discussion
3.1. Chemistry
The synthetic method applied for the synthesis of hy-
ꢀ
drazones (3a-3 m) is depicted in Scheme 1. Initially, 2 -
2.3. Fluorescence measurement
hydroxyacetophenone undergoes Claisen-Schmidt condensation
with variously substituted aryl aldehydes using aqueous NaOH in
methanol to form the substituted intermediate chalcones (1a-1 m).
These chalcones were then oxidatively cyclized to yield flavones
(2a-2 m) using a well-known I2-DMSO mixture as the oxidizing
agent. These flavone derivatives were purified via recrystallization
by EtOH and analyzed by IR, NMR and UV–Vis spectroscopy only.
The targeted hydrazones (3a-3 m) were synthesized through con-
densation of flavones with 2,4-dinitrophenylhydrazine (2,4-DNPH)
in the presence of conc. H2SO4 and absolute EtOH under reflux
conditions. The expected final products (Scheme 1) were isolated
as solid materials in moderate to excellent yields. The synthesized
target molecules (3a-3 m) were further purified through recrys-
tallization in EtOH and found quite stable at ambient conditions.
These desired analogs are dissolve in common organic solvents
such as DMSO, CH3CN and DMF, etc. The chemical structures of
all the newly synthesized flavone hydrazones were corroborated
by IR, UV–Vis and NMR spectroscopic techniques. For instance, the
disappearance of an absorption band around 1655 cm−1 and the
appearance of a new peak around 1615 cm−1 in IR spectra clearly
indicates the conversion of the carbonyl group (C = O) into azome-
The fluorescence spectra of hydrazones were examined us-
ing Shimadzu RF-6000 Spectro fluorophotometer equipped with a
450 W Xe laser lamp as the excitation source. Concentration of
1 × 10−3 M of the compound, soluble in CH3CN, has been used to
measure the fluorescence spectra of hydrazones at ambient tem-
perature with 320 nm excitation wavelength [41].
2.4. FTIR measurements
Nicolet FT-IR Impact 400D infrared spectrometer was used for
recording IR spectra of the solid samples by the matrix of KBr
in the range of 500–4000 cm−1 [41]. Each sample was ground
with spectroscopic grade potassium bromide (KBr) powder and
then pressed into 1 mm pellets (2 mg of sample per 200 mg
dry KBr). A blank KBr disk was used as background. FT-IR spectra
were smoothed, and the baseline was corrected automatically us-
ing the spectrophotometer’s built-in software (Spectra ManagerTM
II, JASCO Corporation).
–
2.5. Cyclic voltammetry
thine linkage (C = N) along with other characteristics N H str. vi-
bration band around 3350 cm−1. Their UV–Vis measurements were
taken in CH3CN solution. The absorption bands in the range of
300–350 nm are expectedly due to π → π∗ and n → π∗ tran-
sitions in imine (C = N) group, whereas the bands in 200–400 nm
range can be related to π → π∗ transitions of the aromatics. Like-
wise, 1H NMR spectra indicate a highly downfield singlet around
δ 11.55 ppm and doublet (J = 6.0 Hz) in the range of δ 8.81–
Electrochemical measurements have been performed out on a
Model CHI620 C electrochemical analyzer, in a conventional 3-
electrode electrochemical cell with Pt wire as counter-electrode,
glassy carbon as a working electrode and Ag/AgCl (3 M KCl) as
the reference electrode in acetonitrile (CH3CN). The electrode re-
actions that characterize the electrochemical oxidation of flavone
hydrazones at the glassy carbon electrode (GCE) were studied us-
ing the CV method. TBAB was used as a supporting electrolyte. The
concentration of the sample run was 0.1 mM in CH3CN. The cyclic
voltammograms were recorded at a scan rate of 200, 100 and 40
mVs−1 in the potential range from −2.0 to +1.0 V. The curves were
scanned from the most negative potential about −2.0 V towards a
more positive direction up to about 1.0 V. All the experiments were
carried out at ambient temperature [13, 42].
–
8.86 ppm for N H and the most deshielded aromatic proton re-
spectively. Additionally, proton NMR spectra also show a character-
istic singlet for the proton at position-3 (flavone skeleton) in the
range of δ 7.00–7.10 ppm. The rest of the signals in the range of
7.00–8.00 ppm are related to the aromatic protons of rings A & B
of the flavone structure. Similarly, there is the appearance of a new
signal around δ 160.0 ppm for C = N bond in the 13C NMR spectra.
The NMR peaks around 155, 147 and 145 ppm, etc. are assigned to
the 2,4-DNPH part of the hydrazones. Whereas, the chemical shift
values present in the range of 135–120 ppm are related to aromatic
carbons. Furthermore, the molecular masses of all the newly syn-
thesized hydrazones were verified by EI-MS, and thus all the spec-
troscopic data are good in agreement with the proposed structures
of the desired flavone hydrazones.
2.6. Computational (DFT) calculations
DFT calculations were performed for synthesized electroactive
analogs to accompany the experimental findings of CV. The redox
potentials of the desired derivatives measured from CV showed a
3

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Compound No.
3a.
Structural formula
Compound No.
3h.
Structural formula
Scheme 1. Synthesis of flavone hydrazones (3a-3 m).
ꢀ
The spectroscopic data of already reported 2 -hydroxychalcones
(1a-1 m) and 1a, 1b, 1f, 1 h [9d]; 1c [9e]; 1d, 1k and 1l [9f]; 1e [9
g]; 1 g [9h]; 1i [9i]; 1 m [9j] and substituted flavones (2a-2 m) 2a,
2b, 2f and 2 h [9d]; 2c, 2 g [9k]; 2d [9l]; 2e [9m]; 2i, 2k [9n]; 2l
[9o]; 2 m [9p]; have been given in literature as cited above. Also,
the spectral data of reported hydrazone compounds 3b, 3c, 3f, 3 h
and 3k have been mentioned in the literature [9a].
138.1, 136.0, 132.2, 131.0, 130.4, 128.5, 125.1, 124.0, 123.1, 120.6,
120.0, 118.8, 118.1, 116.2, 115.4, 114.2, 110.7, 21.5; accurate mass (EI-
MS) of [M]+•: Calcd. for C24H19 NO4S 417.10348; found 417.10333.
3.1.2. 2-(1-Tosyl-1H-indol-3-yl)−4H-chromen-4-one (2j)
Light-yellow solid; Yield: 77%; M.P. 135–137 °C; Rf = 0.6; UV–
Vis λmax (CH3CN) = 332 nm; λem (CH3CN) = 680 nm; FTIR (cm−1):
–
3.1.1. 1-(2-Hydroxyphenyl)−3-(1-tosyl-1H-indol-2-yl)prop–2-en-1-one
(1j)
3089 (aromatic C H str.), 1672 (s, C = O str.), 1450 (m, aromatic
C = C str.), 1255 (C O str.), 679 (p-monosubstituted); 1H NMR
–
Light-orange solid; Yield: 84%; M.P. 137–139 °C; Rf = 0.5; UV–
Vis λmax (CH3CN) = 376 nm; λem (CH3CN) = 580 nm; FTIR (cm−1):
3083 (aromatic C–H str.), 1655 (s, C = O str., α,β unsaturated,
aliphatic), 1576 (m, aliphatic C = C str.), 1540 (aromatic), 1280
(600 MHz, DMSO–d6): δ 8.40 (s, 1H, Ar-H), 8.35 (d, J = 6.0 Hz, 1H,
Ar-H), 8.10 (d, J = 6.0 Hz, 1H, Ar-H), 7.99–7.95 (m, 2H, Ar-H), 7.75
(d, J = 12.0 Hz, 1H, Ar-H), 7.50 (d, J = 12.0 Hz, 2H, Ar-H), 7.32–7.20
–
(m, 1H, Ar-H), 7.19 (d, J = 12.0 Hz, 2H, Ar-H), 7.18 (s, 1H, -C = C H),
(C O str.), 659 (C-indole); 1H NMR (600 MHz, DMSO–d6): δ 13.80
7.00–6.90 (m, 1H, Ar-H), 6.90 (d, J = 12.0 Hz, 1H, Ar-H), 2.27 (s, 3H,
CH3); 13C NMR (151 MHz, DMSO–d6): δ 171.1, 161.2, 154.7, 147.6,
144.7, 142.0, 137.8, 135.4, 132.0, 131.2, 130.0, 128.7, 125.0, 124.3,
123.4, 120.3, 120.1, 119.1, 118.0, 116.0, 115.5, 114.3, 110.8, 21.4; ac-
curate mass (EI-MS) of [M]+•: Calcd. for C24H17 NO4S 415.07218;
found 415.07207.
–
(bs, 1H, OH), 8.46 (s, 1H, Ar-H), 8.40–8.30 (m, 2H, Ar-H), 8.15–
=
7.99 (m, 3H, Ar-H), 7.85 (s, 2H, -CH CH-), 7.68 (d, J = 12.0 Hz,
2H, Ar-H), 7.43–7.25 (m, 1H, Ar-H), 7.22 (d, J = 12.0 Hz, 2H, Ar-
H), 7.00–6.90–6.70 (m, 2H, Ar-H), 2.30 (s, 3H, CH3); 13C NMR
(151 MHz, DMSO–d6): δ 191.4, 162.2, 154.7, 147.8, 145.0, 142.2,
4

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
3b.
3i.
3c.
3j.
3d.
3k.
3e.
3l.
3f
3m.
3g.
Scheme 1. Continued
–
–
–
3.1.3.
asym.), 1375 (C NO2 sym.), 1330 (C N str.), 1251 (C O str.), 763
1-(2-(4-Chlorophenyl)−4H-chromen-4-ylidene)−2-(2,4-dinitrophenyl)
hydrazine (3a)
(C Cl str.), 752 (p-monosubstituted); 1H NMR (600 MHz, DMSO–
–
–
d6): δ 11.56 (s, 1H, -N = N H), 8.86 (d, J = 6.0 Hz, 1H, Ar-H), 8.44
Maroon-colored powder; Yield: 85%; M.P. 199–201 °C; Rf = 0.8;
(dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 8.05 (d, J = 12.0 Hz, 1H, Ar-H),
7.95 (d, J = 12.0 Hz, 2H, Ar-H), 7.65 (d, J = 12.0 Hz, 2H, Ar-H),
UV–Vis λmax (CH3CN)
=
290, 358 nm; λem (CH3CN)
=
378,
717 nm; FTIR (cm−1): 3362 (N H str.), 3102 (aromatic C H str.),
7.40–7.31 (m, 2H, Ar-H), 7.09 (s, 1H, -C = C H), 7.04–7.00 (m, 2H,
–
–
–
–
1613 (s, C = N str.), 1573 (m, aromatic C = C str.), 1511 (C NO2
Ar-H); 13C NMR (151 MHz, DMSO–d6): δ 160.5, 159.8, 154.1, 146.1,
5

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
–
142.4, 137.4, 136.0, 131.5, 130.6, 130.0, 129.8, 129.3, 129.0, 128.5,
127.8, 124.0, 123.6, 116.8, 116.0, 115.6, 114.8; accurate mass (EI-MS)
of [M]+•: Calcd. for C21H1335ClN4O5 436.05740; found 436.05723.
(aromatic C H str.), 1613 (s, C = N str.), 1587 (m, aromatic C = C
–
–
–
str.), 1537 (C NO2 asym.), 1355 (C NO2 sym.), 1330 (C N str.),
–
1278 (C O str.), 1214 (C–Thiophene str.), 765 (p-monosubstituted);
1
–
H NMR (600 MHz, DMSO–d6): δ 11.50 (s, 1H, -N = N H), 8.83
3.1.4. N-(4-(4-(2-(2,4-Dinitrophenyl)hydrazono)−4H-chromen-2-
(d, J = 6.0 Hz, 1H, Ar-H), 8.40 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H),
8.03 (d, J = 12.0 Hz, 1H, Ar-H), 7.99–7.98 (m, 2H, Ar-H), 7.90 (dd,
J = 12.0, 6.0 Hz, 1H, Ar-H), 7.60–7.50 (m, 2H, Ar-H),7.35–7.20 (m,
yl)phenyl)acetamide
(3d)
2H, Ar-H), 7.05 (s, 1H, -C = C H); 13C NMR (151 MHz, DMSO–d6):
–
Dark-maroon crystalline solid; Yield: 70%; M.P. 233–235
°C; Rf
=
0.5; UV–Vis λmax (CH3CN)
=
231, 369 nm; λem
–
δ 161.1, 159.2, 158.6, 153.0, 152.1, 143.2, 139.0, 136.1, 134.3, 130.4,
129.6, 128.8, 128.7, 127.3, 126.7,123.5, 118.0, 114.5, 106.0; accurate
mass (EI-MS) of [M]+•: Calcd. for C19 H12N4O5S 408.05284; found
408.05260.
(CH3CN) = 412, 731 nm; FTIR (cm−1): 3303 (N H str.), 3112 (aro-
–
matic C H str.), 1614 (s, C = N str.), 1592 (m, aromatic C = C
–
–
–
str.), 1546 (C NO2 asym.), 1378 (C NO2 sym.), 1330 (C N str.), 1273
(C O str.), 1135 (C–NH str.), 762 (p-monosubstituted); 1H NMR
–
–
(600 MHz, DMSO–d6): δ 11.54 (s, 1H, -N = N H), 10.50 (bs, 1H,
3.1.8. 3-(4-(2-(2,4-Dinitrophenyl)hydrazono)−4H-chromen-2-yl)−1-
NHCOCH3), 8.84 (d, J = 6.0 Hz, 1H, Ar-H), 8.43 (dd, J = 12.0, 6.0 Hz,
1H, Ar-H), 8.02 (d, J = 12.0 Hz, 1H, Ar-H), 7.80 (d, J = 12.0 Hz, 2H,
Ar-H), 7.35 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 7.35–7.10 (m, 3H, Ar-
tosyl-1H-indole
(3j)
Dark maroon powder; Yield: 71%; M.P. 166–168 °C; Rf = 0.6;
UV–Vis λmax (CH3CN) = 215, 264, 365 nm; λem (CH3CN) = 415,
–
H), 7.07 (s, 1H, -C = C H), 6.90 (d, J = 12.0 Hz, 2H, Ar-H), 2.15 (s,
3H, COCH3); 13C NMR (151 MHz, DMSO–d6): δ 170.2, 160.7, 159.6,
154.0, 145.1.0, 141.1, 137.6, 136.0, 130.1, 129.8, 129.2, 129.0, 128.7,
128.0, 124.0, 123.1, 116.4, 115.0, 114.7, 25.2; accurate mass (EI-MS)
of [M]+•: Calcd. for C23H17 N5O6 459.11788; found 459.11768.
749 nm; FTIR (cm−1): 3362 (N H str.), 3102 (aromatic C H str.),
–
–
–
1614 (s, C = N str.), 1583 (m, aromatic C = C str.), 1513 (C NO2
–
–
–
asym.), 1375 (C NO2 sym.), 1329 (C N str.), 1250 (C O str.), 1215
(C–Sulfonamide str.), 762 (p-monosubstituted); 1H NMR (600 MHz,
–
DMSO–d6): δ 11.58 (s, 1H, -N = N H), 8.87 (d, J = 6.0 Hz, 1H, Ar-
3.1.5. 1-(2-(2,4-Dimethylphenyl)−4H-chromen-4-ylidene)−2-(2,4-
H), 8.43 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 8.04 (d, J = 12.0 Hz, 1H,
Ar-H), 8.00–7.94 (m, 2H, Ar-H), 7.85–7.60 (m, 3H, Ar- H), 7.507.28
(m, 2H, Ar-H), 7.22 (d, J = 12.0 Hz, 2H, Ar-H), 7.10 (s, 1H, –C = C–
H), 7.08–7.02 (m, 1H, Ar-H), 6.98 (d, J = 12.0 Hz, 2H, Ar-H), 6.40
(m, 1H, Ar-H), 2.30 (s, 3H, CH3); 13C NMR (151 MHz, DMSO-d6):
δ 162.0, 159.8, 153.8, 148.2, 147.0, 141.7, 139.0, 138.8, 135.8, 133.5,
131.7, 130.2, 129.8, 129.5, 129.0, 128.7, 128.2, 127.3, 126.0, 124.8,
124.0, 120.7, 120.1, 119.8, 118.5, 116.4, 115.9, 114.5, 111.5, 21.5; ac-
curate mass (EI-MS) of [M]+•: Calcd. for C30H21N5O7S 595.11617;
found 595.11602.
dinitrophenyl)hydrazine
(3e)
Dark-orange powder; Yield: 75%; M.P. 177–179 °C; Rf = 0.7;
UV–Vis λmax (CH3CN)
=
213, 362 nm; λem (CH3CN)
=
420,
739 nm; FTIR (cm−1): 3309 (N H str.), 3087 (aromatic C H str.),
–
–
–
1614 (s, C = N str.), 1585 (m, aromatic C = C str.), 1535 (C NO2
–
–
–
asym.), 1336 (C NO2 sym.), 1308 (C N str.), 1279 (C O str.), 1215
(C–Me str.), 762 (o, p-disubstituted); 1H NMR (600 MHz, DMSO–
–
d6): δ 11.53 (s, 1H, -N = N H), 8.83 (d, J = 6.0 Hz, 1H, Ar-H), 8.41
(dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 8.02 (d, J = 12.0 Hz, 1H, Ar-H), 7.70
(dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 7.64 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H),
7.53 (d, J = 12.0 Hz, 1H, Ar-H), 7.24 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H),
3.1.9. 4-(4-(2-(2,4-Dinitrophenyl)hydrazono)−4H-chromen-2-yl)-N,N-
dimethylaniline
–
7.10 (d, J = 6.0 Hz, 1H, Ar-H), 7.02 (s, 1H, -C = C H), 2.38 (s, 6H,
(3l)
Me); 13C NMR (151 MHz, DMSO–d6): δ 160.1, 159.0, 154.0, 143.8,
140.1, 137.0, 135.6, 131.0, 130.0, 129.3, 129.0, 128.4, 128.0, 123.5,
123.0, 116.5, 115.1, 114.7, 64.0, 21.6, 21.1; accurate mass (EI-MS) of
[M]+•: Calcd. for C23H18 N4O5 430.12772; found 430.12750.
Dark maroon crystalline solid; Yield: 73%; M.P. 181–183
°C; Rf
=
0.6; UV–Vis λmax (CH3CN)
=
214, 379 nm; λem
–
(CH3CN) = 427, 750 nm; FTIR (cm−1): 3032 (N H str.), 3010 (aro-
–
matic C H str.), 1614 (s, C = N str.), 1584 (m, aromatic C = C
–
–
–
str.), 1508 (C NO2 asym.), 1390 (C NO2 sym.), 1361 (C N str.), 1241
–
3.1.6. 4-(4-(4-(2-(2,4-Dinitrophenyl)hydrazono)4H-chromen-2-
(C O str.), 1232 (C–dimethylaniline str.), 759 (p-monosubstituted);
1
–
yl)phenyl)morpholine
H NMR (600 MHz, DMSO–d6): δ 11.51 (s, 1H, -N = N H), 8.81
(3 g)
(d, J = 6.0 Hz, 1H, Ar-H), 8.40 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H),
8.01 (d, J = 12.0 Hz, 1H, Ar-H), 7.96 (d, J = 12.0 Hz, 2H, Ar-H),
Dark-red crystalline solid; Yield: 80%; M.P. 139–141 °C; Rf = 0.8;
–
UV–Vis λmax (CH3CN)
=
267, 374 nm; λem (CH3CN)
=
409,
7.88 (d, J = 12.0 Hz, 2H, Ar-H), 7.01 (s, 1H, -C = C H), 3.06 (s, 6H,
724 nm; FTIR (cm−1): 3312 (N H str.), 3084 (aromatic C H str.),
–N (CH3)2);13C NMR (151 MHz, DMSO–d6): δ 160.2, 159.1, 158.0,
153.1, 145.1, 141.0, 138.0, 135.5, 130.0, 129.0, 128.5, 128.5, 128.2,
128.0, 123.1, 122.3, 116.0, 115.1, 114.4, 30.1; accurate mass (EI-MS)
of [M]+•: Calcd. for C23H19 N5O5 445.13862; found 445.13850.
–
–
–
1610 (s, C = N str.), 1591 (m, aromatic C = C str.), 1508 (C NO2
–
–
–
asym.), 1420 (C NO2 sym.), 1306 (C N str.), 1279 (C O str.), 1224
(aromatic C–N str.), 763 (p-monosubstituted); 1H NMR (600 MHz,
–
DMSO–d6): δ 11.52 (s, 1H, -N = N H), 8.86 (d, J = 6.0 Hz, 1H, Ar-
H), 8.44 (dd, J = 12.0, 6.0 Hz, 1H, Ar-H), 8.04 (d, J = 12.0 Hz, 1H,
Ar-H), 7.98 (d, J = 12.0 Hz, 2H, Ar-H), 7.91 (d, J = 12.0 Hz, 2H,
3.1.10. 1-(2,4-Dinitrophenyl)−2-(2-(4-ethoxyphenyl)−4H-chromen-4-
ylidene)hydrazine
–
Ar-H), 7.04 (s, 1H, -C = C H), 3.57 (m, 4H, –N (CH2)2), 3.05 (m,
(3 m)
4H, -N(CH2)2);13C NMR (151 MHz, DMSO–d6): δ 161.0, 159.6, 157.5,
154.1, 145.7, 140.0, 139.1, 137.0, 131.3, 129.8, 128.9, 128.4, 128.2,
127.7, 123.5, 122.8, 116.7, 115.5, 114.5, 55.6, 30.7; accurate mass (EI-
MS) of [M]+•: Calcd. for C25H21N5O6 487.14918; found 487.14901.
Dark-red powder; Yield: 89%; M.P. 170–172 °C; Rf = 0.9; UV–
Vis λmax (CH3CN) = 273, 414 nm; λem (CH3CN) = 429, 730 nm;
FTIR (cm−1): 3302 (N H str.), 3112 (aromatic C H str.), 1614 (s,
–
–
–
C = N str.), 1598 (m, aromatic C = C str.), 1515 (C NO2 asym.), 1329
–
–
–
(C NO2 sym.), 1306 (C N str.), 1272 (C O str.), 1219 (C–OCH2CH3
3.1.7. 1-(2,4-Dinitrophenyl)−2-(2-(thiophen-3-yl)−4H-chromen-4-
str.), 761 (p-monosubstituted); 1H NMR (600 MHz, DMSO–d6): δ
–
ylidene)hydrazine
11.55 (s, 1H, -N = N H), 8.85 (d, J = 6.0 Hz, 1H, Ar-H), 8.42 (dd,
(3i)
J = 12.0, 6.0 Hz, 1H, Ar-H), 8.02 (d, J = 12.0 Hz, 1H, Ar-H), 7.68 (d,
J = 12.0 Hz, 1H, Ar-H), 7.62 (d, J = 12.0 Hz, 1H, Ar-H), 7.30–7.21
Dark orange-maroon powder; Yield: 69%; M.P. 124–126
–
°C; Rf
=
0.7; UV–Vis λmax (CH3CN)
=
217, 374 nm; λem
(m, 2H, Ar-H), 7.06 (s, 1H, -C = C H), 7.03–7.01 (m, 2H, Ar-H), 6.95
(CH3CN) = 390, 700 nm; FTIR (cm−1): 3310 (N H str.), 3094
(d, J = 12.0 Hz, 2H, Ar-H), 4.11–4.04 (m, 2H, -OCH2CH3), 1.37–1.33
–
6

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Fig. 3. A comparative fluorescence spectra of synthesized hydrazones (3a-3 m).
Fig. 2. A comparative absorption spectra of synthesized hydrazones (3a-3 m).
zones (3a-3 m) were measured in CH3CN solution at room temper-
ature with an excitation wavelength of 315 nm for the synthesized
derivatives. Substituted flavone analogs have a lot of potential as
fluorescence probes for bio-labeling in an aqueous medium [16].
The synthesized compounds, when irradiated with UV radiation,
were observed to have fluorescence properties in the blue portion
of the visible region. However, emission intensities showed that
the alkyl groups have a startling effect on the emission strength
of flavone hydrazone derivatives. The alkyl substituents at the ring
B could likely have some effect on the physicochemical properties
due to its electron-donating nature and if we substitute the 2-aryl
group of hydrazones with any heterocyclic moiety having extended
conjugation, the product exhibited better fluorescence properties.
From the fluorescence spectra (Fig. 3)of the envision compounds,
it can be assumed that the insertion of EDG at ring B consider-
ably influences the emission intensity without affecting any blue or
redshift in the emission wavelength, and EWG offers a reverse ef-
fect. ‘In the 4th position of the aryl compounds, various functional-
ities with various electron-releasing and -accepting properties have
been added to further investigate, explore and alter the lumines-
cent features of flavone hydrazones. The various substituents on
flavone hydrazone scaffold generate a wider range of 394–769 nm
for their emission spectra (Table 1).
(m, 2H, -OCH2CH3); 13C NMR (151 MHz, DMSO–d6): δ 160.2, 159.7,
153.9, 144.0, 140.0, 137.5, 136.5, 130.5, 130.0, 129.5, 129.4, 128.9,
128.2, 123.7, 123.4, 116.7, 115.2, 115.1, 114.8, 64.0, 15.0 (two aro-
•
matic carbons are isochronous); accurate mass (EI-MS) of [M]+
:
Calcd. for C23H18 N4O6 446.12263; found 446.12244.
3.2. Electronic absorption study
The UV–Vis absorption of hydrazones is recorded in the CH3CN
solution. It has been generally assumed that the peaks in 300–
390 nm range are involved π→π∗ transitions associated with
azomethine (C = N) groups and phenyl rings whereas the peaks
in 211–410 nm range might be allotted to π→π∗ and n→π∗ tran-
sitions of the aryl rings and C = N bond etc. Moreover, in these
hydrazones, a peak observed at 432 nm was perturbed in their
2,4-DNPH derivatives, which supports the condensation of the 2,4-
DNPH with substituted flavones. The maximum absorption bands
stretching from 340 to 400 nm are assigned to the intramolecu-
lar charge transfer band of the azomethine C = N group. More-
over, λmax of Schiff bases in UV absorption studies is influenced by
the inductive and resonance effect of substituents. The introduc-
tion of an electron-withdrawing or electron-donating substituent
leads to a general trend of λmax hypsochromic shift. The absorp-
tion maxima (λmax) for the compounds (3a-3 m) showed some dif-
ference in absorption wavelength due to the presence of various
substituents at the p-position of the hydrazone derivatives. Sur-
prisingly, the EDG groups such as p–OCH3 and p-CH3, etc. at the
Fig. 3.
3.4. FTIR study
The structures of the synthesized hydrazones (3a-3 m) were
confirmed by the absorption peaks found at their corresponding
ꢀ
4 -position of the ring B of chromone derivatives shifts λmax to-
–
frequencies. Peaks indicating absorption for v(N H), v(C=C) and
v(C O) in ranges 3390–3300 cm−1, 1560–1670 cm−1 and 1120–
wards longer wavelengths, resulting in a bathochromic (red) shift,
whereas the EWG groups such as p-Cl and p-F, etc. results in the
hypsochromic (blue) shift. The absorption peaks are affected sub-
stantially by the aromatic moieties on the terminal phenyl moiety
(Fig. 2).
–
1280 cm−1 individually established the presence of imino linkage
in the hydrazones. Another peak in the region 1601–1680 cm−1
showed the presence of v(C=N) linkage in the hydrazones. The
aim of the vibrational analysis is to decide which of the vibra-
tional modes in the molecule gives rise to each of the observed
bands at specific wavenumbers in the FTIR spectra. The functional
groups present in the molecule were identified and a satisfactory
vibrational band assignment has been made for the fundamental
modes of vibration by observing the position, shape and intensity
of the bands. The spectra of the synthesized compounds (3a-3 m)
3.3. Electronic emission study
ꢀ
Attaching several functional moieties to hydrazones at 4 -
position may not only open numerous routes for the advancement
in enhanced supramolecular structures, but also they may affect
the emission properties of the parent analogs. Owing to their po-
tent functions in electroluminescent displays, fluorescent materi-
als and chemical sensors, have become a significant concern. Ac-
cording to the structural evaluation, the compound has a larger
p-conjugated phenyl system capable of acquiring potent lumines-
cence and effective energy transfer. The emission spectra of hydra-
–
also show several weak bands for the aliphatic and aromatic C H
–
and C O stretching vibration frequencies at the region of 2840–
3070 cm−1 and 1378–1450 cm−1, respectively. The existence of a
strong band at 1340–1530 cm−1 is consolidating the presence of
the NO2 functional group in the flavone hydrazones scaffold (Fig-
ure S5 in SI). The NH stretching vibration gives rise to a weak
7

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Table 1
Emission and absorption data of all the targeted flavones hydrazones (3a-3 m).
Compound No.
Solvent
λexcitation (nm)
λemission (nm)
λabsorption (nm)
Transitions
Stoke Shift λ (nm)
3a.
3b.
3c.
3d
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
Acetonitrile
368
378
375
379
372
385
384
375
384
375
383
389
407
378, 717
421, 744
417, 734
412, 731
420, 739
428, 752
409, 724
415, 738
390, 700
415, 749
410, 740
427, 750
429, 730
290, 358
212, 368
214, 365
231, 369
213, 362
229, 375
267, 374
231, 365
217, 374
215, 264, 365
275, 373
214, 379
273, 396
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
π → π∗ (C = N), π → π∗ & n → π∗ (aromatic rings)
359
376
369
362
377
377
350
373
326
384
367
371
316
3e.
3f.
3 g.
3 h.
3i.
3j.
3k.
3l
3 m.
Fig. 5. The relation between Ipa for 200, 100 and 40 mVs−1 of Compound 3a with
(a) scan rate (υ); (b) square root of υ(υ1/2); (c) lnυ. In these figures, blue color
indicates 200 mVs−1, brown color indicates 100 mVs−1 and gray color indicates 40
mVs−1
.
Fig. 4.
A comparative cyclic voltammograms of synthesized hydrazones at
200 mV/s scan rate (3a-3 m).
Fig. 4 indicates three quasi-reversible oxidation peaks for the
flavone hydrazones, and the presence of one or two cathodic peaks
indicated the number of electrons transferred is more than two
electrons. Ever since, the peak has been followed by two more
physically adsorbed, compressed films, each of which corresponds
to a physically adsorbed process at extremely negative potential.
Moreover, peak potentials (Epc, Epa) and their consequent peak
currents (Ipc, Ipa) values were estimated from Fig. 5 by certain
band at 3500–3300 cm−1. A stronger band at 750–700 cm−1 in
secondary aliphatic amines is due to NH stretching. Secondary aro-
matic amines have a CNH bending absorption near 1510 cm−1 near
the 1500 cm−1 aromatic band.
3.5. 1H and 13 C NMR spectroscopy
factors, for example, peak potential difference (ꢀE = Epa − Epc
)
and the anodic-cathodic currents ratio (Ipa: Ipc) were determined
and mentioned in Table 2. The various factors in Table 2 proved
that the redox outcomes of the hydrazones correspond to quasi-
reversible procedures where the difference in potential values are
greater than 0.3 V and the Ipa: Ipc in the majority cases is lesser
than 1. Likewise, the E1/2 for quasi-reversible and reversible reac-
tions determined by applying subsequent expression and given in
Table 2:
NMR calculations are now attainable and accurate enough to
be useful in exploring the relationship between chemical shift and
molecular structure. The experimental 1H NMR spectrum of the
product (3 m) in DMSO–d6 is given in SI Figure S6. The 1H NMR
chemical shifts (δ/ppm) of all the targeted compounds (3a-3 m)
are assigned in the Result and discussion section.
3.6. Cyclic voltammetric analysis
E1/2 = Epa − DE/2
The oxidation peaks potential and the half peak potential move
towards more positive potentials upon linkage, representing su-
perficial hydrazones oxidation due to the presence of electron-
donating moiety with an electron-withdrawing moiety which de-
creases the electron density on the ring making -NH moiety less
disposed to oxidation.
The electrochemical properties of flavone hydrazones (3a-3 m)
were investigated employing the CV method. The analysis was
recorded in the potential range of −2.0 to +1.0 V at 25 °C with
the scan rate of 200, 100 and 40 mV/s. The CV was initially run for
CH3CN as a blank solution within the desired potential range of –
2.0 to +1.0 V. CV response for blank has ensured the media purity
as no peak was detected in both reverse and forward scan.
The analysis of hydrazone compounds’ redox properties sup-
ported in assessing their electron-transfer potential. The electro-
chemical properties of the flavone hydrazones were examined by
CV on a 0.1 mM solution of the hydrazone at a Pt electrode
in CH3CN having 0.1 M TBAB as supporting electrolyte at a 200
mVs−1 scan rate.
3.7. Effect of scan rate
Scan rate is a factor that influences the electrooxidation of sev-
eral molecules. Using cyclic voltammetry, the impact of scan rate
on electrooxidation of hydrazone was studied from −2.0 to +1.0
Vs−1 (Figure S4 in SI). The peak potential and current for flavone
8

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Table 2
Peak currents, Peak potentials, and potential peak difference of the flavone hydrazones in CH3CN of
0.1 mM concentration at scan rate 200 mV/s.
e
Compound No.
E
pasa (V)
Epcsb (V)
Ec (V)
0.3
Ipad: Ipc (μA)
E (V)
½
3a.
−0.50, 0.25, 0.75
−0.25, 0.50, 0.75
−0.25, 0.50, 0.75
−0.20, –, 0.60
−0.25, –, 0.60
−0.4, −0.1, 0.6
−0.4, 0.3, 0.75
−0.5, −0.2, 0.6
−0.5, −0.2, 0.7
−0.5, –, 0.75
−0.80
20, 25, 70
130
−0.65
−0.55
−0.55
−0.50
−0.50
−0.57
−0.57
−0.67
−0.67
−0.67
−0.65
−0.65
−0.57
3b.
3c.
3d
−0.85
0.6
33, 30, 35
130
−0.85, −1.5
−0.80, −1.5
−0.85, −1.5
−0.75, −1.3
−0.75, −1.5
−0.85, −1.6
−0.80, −1.5
−0.85
0.6
33, 30, 35
130
0.6
25,–, 100
125, 240
40, –,30
130
3e.
3f.
0.6
0.35
0.35
0.35
0.35
0.35
0.3
30, 35, 80
210, 120
20, 10, 50
150, 210
30, 20, 10
150, 200
20, 30, 90
100, 180
40, 50
3 g.
3 h.
3i.
3j.
150
3k.
3l
−0.5, 0.5, 0.7
−0.80, −1.5
−0.80, −1.4
−0.75, −1.5
30, 50, 20
150
−0.5, 0.25, 0.5
−0.4, 0.25, 0.75
0.3
25, 20, 10
90, 70
3 m.
0.35
30, 15, 10
90, 110
a
Epa = Anodic Peak Potential;.
Epc = Cathodic Peak Potential;.
E = Difference of Epa & Epc;.
Ipa = Anodic Peak Current;.
Ipc = Cathodic Peak Current.
b
c
d
e
hydrazone electrooxidation were determined using cyclic voltam-
mograms. The analysis of the reliance of Ip on v1/2 and the analy-
sis of the reliance of lnIp on lnv are two conventional methods for
determining the reversibility of reactions and determining whether
they are diffusion-controlled or adsorption-controlled. The impact
of the scan level on the electrooxidation of 0.1 mM solution of hy-
drazones was studied in the range 200, 100 and 40 mVs−1 as dis-
played in Figure S4 in SI.
given equations:
1
For 1st oxidationpeak : Ipa = {3.18 υ(Vs− )}μA − 2.85 μA; R2 = 0.9989
1
For 2nd oxidationpeak : Ipa = {2.735 υ(Vs− )}μA − 2.65 μA; R2 = 0.9976
1
For 3rd oxidationpeak : Ipa = {2.262 υ(Vs− )}μA − 2.29 μA; R2 = 0.9956
Fig. 6a illustrates that as the rate of scan is increased, the an-
odic peak current of the three anodic peaks increases, implying
that the reactions are regulated by diffusion. Using following equa-
tion, the no. of transferred electrons throughout the compound’s
oxidation reaction was estimated from the linear relationship slope
between v and Ip:
It can be noticed from Fig. 5 that, the oxidation peaks’ potential
moved more toward positive values as the level of scan increased,
while the reduction peaks potential moved more toward nega-
tive numbers, and all peaks’ currents shifted toward higher num-
bers. The quasi-reversible state is ensured by the shift in the redox
peaks as the scan rate is changed. The compounds with electron-
withdrawing substituents made the electrooxidation difficult while
the compound with electron-donating substituents made the elec-
trooxidation easy. This is very much in agreement with the re-
ported work on similar compounds.
nFQv
Ip =
4RT
where,
Q = The quantity of charge obtained by integrating of the
area of cyclic voltammetric peak; F = Faraday’s constant (96,487
Cmol−1);
R
=
The universal gas constant (8.3143 Jmol−1K−1);
T = Kelvin temperature (298 K).
The consecutive oxidation signals are ascribed to the ‘chromen-
4-ylidene’ unit and the substituent attached. The reduction signals
are due to dinitrophenyl hydrazine linkage. More specifically due to
the dinitrophenyl unit. The dinitrobenzene typically gives its quasi-
reversible signatures in the range of −0.5 to −1.5 V. Quite obvi-
ously, the environment affects the peak potential positions. The
signal appearing around +0.5 V appears to be due to the hydra-
zone unit. The results also demonstrate that electrochemically the
hydrazone derivatives are a multi-electron transfer process. This
indicates their rich electroactivity with more than one electroac-
tive center and thus makes them very interesting compounds to
be investigated further for their electrochemical character.
As shown in Figure (5a), the three current oxidation peak and a
scan rate of compound 3a is linearly related and explained by the
The total no. of transferred electrons (n) was 3.3 (≈3).
According to the HOMO, LUMO and the strength of the density
of electronic charge on the hydrazone moiety, the nitrogen atoms
that have a greater electron density than C and O atoms corre-
spond to the oxidizable moiety.
In the scan rate range from −2.0 to 0.1 Vs−1, peak current
(Ip) of hydrazone electrooxidation depends linearly on the υ1/2
(Fig. 5b) and is demonstrated by the equations:
1/2
)
1
For 1st oxidationpeak : Ipa = {3.210 υ1/2(Vs−
For 2nd oxidationpeak : Ipa = {2.715 υ1/2(Vs−
} μA − −2.85 μA; R2 = 0.9999
1/2
1
)
1/2
)
} μA − −2.55 μA; R2 = 0.9992
1
For 3rd oxidationpeak : Ipa = {2.272 υ1/2(Vs−
} μA − −2.295 μA; R2 = 0.9946
The existence of a coefficient value of the linear relation of Ip of
the compound 3a oxidation peaks with υ1/2 shows that a chemical
reaction has occurred on the electrode surface.
9

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Fig. 6. Structure-property relationship of synthesized flavone hydrazones (3a-3 m).
Moreover, the graph of lnIp with lnυ Figure (5c) is linear with
curves that are far from the value of 0.5 (for pure diffusion) but
near to 1, indicating that electrode reaction is regulated by adsorp-
tion as well as diffusion. This relationship can be explained using
the following equations:
(3a-3 m) also exhibit blue fluorescence. Blue fluorescence of cer-
tain molecules is thought to be due to the flavone motif and dif-
ferent substitution pattern. Aromatic moieties that present at the
ꢀ
4 -position of flavone structure form the conjugated π−backbone
and are mostly accountable for photon absorption. Consequently,
the substitution of aryl and alkyl substituents at p-position can be
presumed to have some influence on physicochemical properties.
These findings demonstrate that changing the alkyl group has a
significant impact on emission strength without causing a drastic
change in blue- or red-shift in λem, and the substitution of EDGs
for the conjugated backbone of these molecules can be used to
shift emission intensity. As a result, it is expected that the emis-
sion intensity can be modified by changing the flavone hydrazone
ring substituents, which will be extremely valuable for regulating
the fluorescence and optoelectronic features of OLEDs based on re-
lated luminescence molecules.
1
For 1st oxidationpeak : ln Ipa = {2.57 ln υ(Vs− )} A − −1.35 A; R2 = 0.9993
1
For 2nd oxidationpeak : ln Ipa = {2.525 ln υ(Vs− )} A − −2.25 A; R2 = 0.9997
1
For 3rd oxidationpeak : ln Ipa = {2.233 ln υ(Vs− )} A − −2.115 A; R2 = 0.9992
3.8. Structure-property relationship
The aryl substituents on the terminal benzene moiety had a
major impact on absorption behavior. Compared with the aryl-
substituted compounds, EWGs such as the –Cl, –NO2, –F create
a noticeable hypsochromic and EDGs like (–N(CH3)2, –OCH3, –
NHCOCH3, (–OCH3)2) affect bathochromic (red) shifts of the π–π∗
band, respectively. This study can explain by the expanded systems
of conjugated π-electrons of hydrazones via the non-bonding elec-
tron pairs of the ‘N’ atoms. A broad absorption peak for hydra-
zone derivatives (3a-3 m) is attributable to the π–π∗ transitions
of a conjugate backbone with absorption λmax in the range of 290–
414 nm. Furthermore, owing to the existence of a related flavone
hydrazone nucleus for all the derivatives, the spectral curves are
identical in the electronic ultraviolet absorption spectra. It is re-
markable, that the variation in wavelength and absorption strength
is ascribe merely to the impact of the p-alkyl phenyl moieties at
the p-position of the 2-phenylchromone nucleus.
The electrochemical properties of the hydrazones (3a-3 m) so-
lutions in acetonitrile have been studied by CV. These derivatives
are known to be quasi-reversible and are electrochemically sta-
ble. The same values of cathodic and anodic peaks were detected
for every molecule for three times repeated cycles at various scan
rates 200, 100 and 40 mVs−1. It was recognized that the posi-
tion of different functional groups on the hydrazone scaffold can
affect the redox behavior and current. In the presence of various
substituents on flavone scaffold, 3a-3 m at different scan rates
show no noticeable difference in the cathodic/anodic peak posi-
tion; however, raising the scan rate resulted in an increase in the
current magnitude, suggesting that the electrochemical redox pro-
cess is reversible. The oxidation peak potential of all the synthe-
sized compounds moves to a more positive value. The presence
of EDGs (-CH3, -N(CH3)2, –OCH3, -NHCOCH3, etc.) at p-position
of ring B of flavone hydrazone scaffold increases the redox be-
havior of the structural motif whereas the electron-withdrawing
groups (-NO2, -Cl, -F, etc.) at p-position of ring B decreases the re-
dox behavior of the compounds. Furthermore, the replacement of
aryl ring B with other heterocyclic rings such as thiophene, mor-
pholine, sulfonamide-like moiety also displayed exceptional redox
behavior. Apart from that, all other synthetic flavone hydrazones
demonstrated moderate to excellent oxidation–reduction behavior.
Changes in the values of E1/2 are ascribed to the position of the -
NO2 group of 2,4-DNPH. Overall, the results presented herein show
that nature and substitution patterns at rings B and C increase
the redox potential of these molecules, and thus are accountable
to control it. Since all the proposed structures have a common
substituted flavone hydrazone skeleton in their scaffolds. Further-
more, these findings explain that the position, nature and no. of
substituents on aryl ring significantly affect the physicochemical
The fluorescence properties of compounds (3a-3 m) in CH3CN
solution have been examined and figure S2 in SI presents the emis-
sion spectral data. Similarly, Table 1 shows the emission levels.
Various analogs bearing substituents with variable electronegativ-
ity demonstrate variable fluorescence properties at ambient tem-
perature in the solution state. However, when the substituents are
altered, the typical emission bands of these synthesized deriva-
tives may be expected from 378 to 752 nm. The two bands are
noticed in the emission spectra of all the synthesized compounds
(3a-3 m). For flavone hydrazones, their fluorescence spectra ex-
hibit two bands, a lower intensity band in the range of 378 nm
and another with high intensity in the range of 752 nm, when
being excited at around 315 nm. Because of the various function-
alities at the flavone scaffold, their emission bands display mod-
ifications. Most of them not only display fluorescence characteris-
tics with maximum emission but also alter the maximum emission
bands from 378 to 752 nm due to the different substituents. The
emission spectra of the hydrazones 3a-3 m were then analyzed at
their corresponding excitation wavelengths. Based on the nature
of their λem in the visible spectrum blue region, these derivatives
10

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
and electrochemical properties of these analogs (3a-3 m). Detailed
structure-property relationship is depicted in Fig. 6.
3.9. Density functional theory (DFT) study
Frontier Molecular Orbitals Analysis: The HOMO orbital de-
notes the ability to donate an electron whereas LUMO designates
the capability to accept the electron. Various functional groups of
hydrazone derivatives (3a-3j) have the ability to change the posi-
tions of HOMO-LUMO energy gap, which markedly influences the
oxidation and reduction patterns [45]. The highest reduction po-
tential and most negative ELUMO values designate the ease of re-
duction for a compound [46]. A more negative ELUMO value indi-
cates the favorability for the addition of electrons due to the low-
ering of energies of the orbitals. The compounds 3a and 3 h have
shown the highest reduction potential and most negative ELUMO
values in comparison to others, which correspond to the easiest
reduction (Table 3). A similar trend was observed from the exper-
imental reduction potentials of compounds (3a-3j). In the same
way, less values of EHOMO designates the ease of oxidation for a
compound. The oxidation potentials measured from electrochemi-
cal studies were compared to the EHOMO values obtained from DFT
analysis [47]. Compound 3 g has shown the least negative EHOMO
value among others corresponding to ease of oxidation whereas
the oxidation potential of compound 3 g from experimental studies
has depicted the same (shown in Table 3).
The graphical representation of FMOs of representative com-
pounds (3a-3j) in SI (Figure S7). The HOMO orbitals tend to be lo-
calized on the hydrazone core structure whereas the LUMO orbitals
are spread over the di-nitrobenzene moiety (having EW atoms N
and O). The ELUMO-EHOMO gaps for compounds (3a-3j) were in ac-
cordance with the band gaps analyzed from electrochemical stud-
ies i.e., Ep = Epa-Epc [48] of the compounds shown in Table 3.
Chemical Reactivity Parameters: The chemical reactivity of a
compound lays down its ability to be stabilized by attracting the
charge from the environment [49]. The stability, electrical and
chemical reactivity parameters of the analogs can be calculated us-
ing the energy gap between HOMO-LUMO orbitals [50]. By variat-
ing the energy band gap by substituting different functional groups
within the hydrazone structures can be utilized in the modifica-
tion of chemical reactivity patterns of the compounds. Chemical
reactivity parameters i.e., electronegativity (x) chemical hardness
(ƞ) and chemical potential (μ) and electrophilicity index (ω) were
calculated following the literature [50]. Whereas, IP (-EHOMO) cor-
responds to ionization potential and EA (-ELUMO) is the electron
affinity. These reactivity parameters were calculated for the com-
pounds (3a-3j) and summarized in Table 4.
The chemical potential values of synthesized analogs indicated
the energy absorbed or released due to oxidation and reduction
processes for the compounds (3a-3j). High negative potential val-
ues correspond to high reduction potential as compound 3a has
shown the high negative value and vice versa. But electrode po-
tential is the sum of chemical potential and nonelectrical potential
hence little fluctuation was observed which may be due to differ-
ent functional groups variating the redox properties [52] (Table 3).
A small energy gap indicates a soft and reactive compound, and
on the other hand, a wide energy gap suggests a strong and slow-
reacting molecule [53]. Compound 3 g has the highest softness
characteristics tends to be the most reactive one may be ascribed
to the heterocyclic ring in the structure. Compounds 3a, 3c, 3 h,
and 3i have shown a high value of global hardness tend to be sta-
ble and less reactive as given in Table 4. Moreover, analogs were
found to have more charge transferability and most of the analogs
are more reactive. The chemical reactivity characteristics deter-
mined that these molecules ascribed to have good redox proper-
ties.
11

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Fig. 7. Experimental and DFT-B3LYP/321 g calculated UV-Visible spectra of repre-
sentative compounds (3a and 3j).
Mullikens Atomic Charges Analysis: Mullikens atomic charges
of represented compounds (3a-3j) calculated using DFT-B3LYP/3–
21 G. Figure S8 in SI depicts Mulliken charge distribution on op-
timized compounds (3a-3j), denoted by a color transition on the
atoms with a color scheme and scale (green for positive charge and
red for negative charge). These charges have a very important role
in the quantum chemical approach and affect the electronic struc-
ture and in turn influence redox patterns and also the reactivity
for biological targets [54]. The existence of strongly electronegative
atoms such as O, Cl, F, and N was revealed by the calculated values
of atomic charges, indicating that positive charge is distributed on
carbon atoms and on all forms of hydrogen atoms.
UV-Visible Analysis: UV-Visible spectra of representative com-
pounds 3a and 3j were calculated by TD-DFT-B3LYP/321 g that ex-
plained the electronic absorption patterns in the compounds. Spec-
tra of compounds 3a and 3j are given in Fig. 7 in comparison to
their experimental UV–Vis spectra. Experimental and DFT calcu-
lated spectra for representative compounds were in good agree-
ment to each other as depicted in Fig. 7.
Both these compounds have shown an intense absorption peak
in the region 300–450 nm. involve π→π∗ and n→π∗ transitions
of the aryl rings and C = N bond etc. Moreover, broadening above
400 nm in spectra of these compounds is indicative of conden-
sation of the 2,4-DNPH with substituted flavones as discussed in
the experimental absorption analysis discussion. Slight peak shift-
ing in absorption spectra is ascribed to substitutions on the ter-
minal phenyl moiety. The compound 3j having a p-CH3 group at
ꢀ
the 4 -position of the ring B of chromone derivatives shows a
bathochromic (red) shift, whereas compound 3a having group p-
Cl results in the hypsochromic (blue) shift in accordance with the
experimental results.
Vibrational Analysis: The vibrational frequencies, the nature of
vibrational modes, and the potential energy distributions (PED) of
the representative compounds 3a and 3j of flavone hydrazones are
presented in Table 5 in comparison with the experimental results.
Then, a detailed vibrational study based on PED [55] was per-
formed employing the VEDA 4 program [51] based on the results
of the B3LYP level [55a, b]. This reveals a good correspondence
between theory and experiment in main spectral features. For a
visual comparison, the recorded and calculated FT-IR spectra for
compounds 3a and 3j are presented in Figs. 8a and 8b. The com-
pound 3a with 44 atoms denotes (3N-6) i.e., 126 vibrational modes
in the range 20–4000 cm−1 among which 43 stretching modes,
42 bending modes and 36 are torsional modes. Whereas for com-
pound 3j with 64 atoms ascribes (3N-6) i.e., 186 vibrational modes
among which 63 stretching, 62 bending, 61 torsional and 60 are
–
C H modes. Comparison of theoretical results with experimental
data reveals a good correlation (R2 > 0.9) in obtained vibrational
frequencies as depicted in Fig. 9.
12

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
Table 5
Experimental and calculated values of wavenumber for the selected vibrations of flavone hydrazones (Compound 3a and 3j).
Compound 3a
Compound 3j
Main Assignments (%PED)
Vibrational Frequencies (cm−1
)
Main Assignments (%PED)
Vibrational Frequencies (cm−1
)
Experimental
Theoretical
Experimental
Theoretical
–
–
vN H (76)
3362
3102
1613
1251
1375
1060
763
3213
3208
1577
1252
1341
1051
734
vN H (89)
3362
3102
1614
1250
1375
1061
1215, 967
1644
1375
1533
967
3218
3207
1572
1250
1340
1024
1108, 926
1621
1373
1556
963
–
–
vC H (95)
vC H (94)
=
=
vC N (50)
vC N (45)
=
=
vC O (35)
vC O (28)
–
–
vN O (70)
vN O (60)
–
–
vN N (51)
vN N (36)
–
vC Cl (15)
vS-C (63), vS-O (78)
βHNN (22)
βHNN (41)
βHCC (72)
βCNO (39)
τHCCC (86)
τHCCN (86)
HNNC (32)
1645
1330
654
1626
1378
639
βHCC (83)
βHCH (74)
830
857
τHCCC (84)
τHCCN (60)
CCSN (56)
1105
845
1088
812
923
935
762
616
ν: stretching, β: in-plane bending, τ: torsional.
Fig. 9. Correlation diagram between the calculated and experimental wavenumbers
of flavone hydrazone (3a and 3j).
3.10. N–H vibrations
Fig. 8a. Experimental and DFT-B3LYP/321 g calculated IR spectra of representative
compound (3a).
Generally, the N–H stretching vibrations are facilely determined
by the apparition of a sharp peak at the highest wavenumbers. For
the investigated flavone hydrazone molecules 3a and 3j, the sym-
metric stretching vibrations of N–H are located at 3362 cm−1 of
both analogs. The calculated N–H stretching vibrations for hydra-
zone compounds 3a and 3j are both at 3213 and 3218 cm−1 using
B3LYP methods with a 6–31G(d,p) basis set. The theoretically cal-
culated N–H vibrations of hydrazone are the purest mode as evi-
denced from 76% and 89% of PED in compounds 3a and 3j, respec-
tively.
3.11. C–H vibrations
The molecular structure of flavone-based hydrazones indicates
the presence of the aromatic C–H stretching vibrations. The het-
eroaromatic structure shows the presence of C–H stretching vi-
brations in the region 3100–3000 cm−1 which is the characteris-
tic region for the ready identification of C–H stretching vibrations
[56, 57]. The B3LYP/6–31G(d,p) calculations give bands at 3208
cm−1 and 3207 cm−1 for 3a and 3j compounds, respectively, as CH
modes. As indicated by PED, these modes involve an exact con-
tribution of 95% and 94% suggesting that they are pure stretching
modes. In this region, the bands are not affected remarkably by the
nature of the substituent.
Fig. 8b. Experimental and DFT-B3LYP/321 g calculated IR spectra of representative
compound (3j).
13

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
3.12. C = N and C-O vibrations
molecular structures of these analogs were characterized by dif-
ferent spectroscopic techniques. To illustrate structure-property re-
lationships and the effect of different functionalities on the flavone
scaffold, we have studied their emission and absorption properties
in dilute solutions. A fluorescence study of these hydrazones in di-
lute CH3CN solution showed a change from hypsochromic (blue)
to bathochromic (red) shift. All the analogs showed amazing fluo-
rescence properties and different maximal emission bands due to
the unique nature of the substituents. This work also describes the
electrochemical behavior of the hydrazones where quasi-reversible
redox reactions have been demonstrated, and the electrode reac-
tion has been regulated by the diffusion and adsorption meth-
ods. It has also been found that the presence of an EWG reduced
the activity while an EDG enhanced the activity of the hydrazone
derivatives. From these outcomes, it can be concluded that the po-
sition and nature of the substituents are two essential parameters
influencing the electrochemical and photophysical properties. The
CV results were further endorsed by the DFT study. The in-silico
outcomes were in a great deal with the experimental findings. We
are optimistic that the presented compounds may find promising
applications as organic materials in electronics, and this will be the
focus of our future research.
The bands in the region of 1640–1610 cm−1 are due to C = N
stretching vibrations, which shift the wavenumber and intensity in
a coordination compound fashion depending on the neighboring
group, conjugation effects, H-bonding and molecular tautomerism
[56, 57]. The C–O vibrations were found at 1230–1250 cm–1, which
is normally the result of the combination of vibrational bands of
other functional groups. The bands appearing in the IR spectrum at
1614, 1251 and 1250 cm−1 correspond to the stretching vibrations
–
of the C = N and C O groups. The calculated bands are 1577 (50%)
and 1252 (35%) cm−1 for compound 3a and 1572 (45%) and 1215
(28%) cm−1 for compound 3j at the B3LYP/6- 31G(d,p) level for the
–
C = N and C O vibrational modes.
3.13. N–O and N-N vibrations
–
Generally, the N–O and N N stretching modes of aromatic rings
appeared between 1400 and 1000 cm−1. Consequently, for the
studied compounds 3a and 3j, the N–O stretching vibrations are
observed at 1375 cm−1 for both analogs in the experimental IR
spectrum and the N–N stretching vibrations are observed at 1060
and 1061 cm−1 for both analogs, respectively. Also, the aromatic
C = C stretching vibrations have appeared between 1625 and 1430
cm−1. In flavone-based hydrazones, compounds 3a and 3j, the cal-
culated band was found at 1341 (70%) and 1340 (60%) cm–1 for
N–O and at 1051 (51%) and 1024 (36%) cm–1 for N–N band which
nicely correlated with experimental values, respectively. As indi-
cated by PED, these modes involve an exact contribution of > 80%
suggesting that they are pure stretching modes.
Credit author’s statement
Meshari A. Alsharif: Data analysis and collection, soft-
ware; Nafeesa Naeem: Experimental work performance, first-draft
preparation; Ehsan Ullah Mughal: Main idea, supervision, final
writing the manuscript; Amina Sadiq: Co-supervision, manuscript
writing; Rabab. S. Jassas: Fluorescence analysis and interpretation;
Samia Kausar: Performed DFT studies; Ataf Ali Altaf: Performed
DFT studies; Muhammad Naveed Zafar: Mass spectrometry anal-
ysis and interpretation; Amara Mumtaz: Data analysis and collec-
tion, software; Rami J. Obaid: Data analysis and collection; Reem
I. Alsantali: UV analysis and interpretation; Safeer Ahmed: Cyclic
voltammetric analysis and interpretation; Ishtiaq Ahmed: NMR
characterization; Hatem M. Altass: Data analysis and collection;
Saleh A. Ahmed: Co-supervision and manuscript writing.
3.14. NNH and HCCN vibrations
Mostly, the NNH and HCCN bending and torsional modes of
aromatic rings appeared between 1700 and 1120 cm−1. Conse-
quently, for the studied compounds 3a and 3j, the NNH bending
vibrations are observed at 1645 and 1644 cm−1 respectively in the
experimental IR spectrum and the HCCN torsional vibrations are
observed at 1105 and 923 cm−1 for both analogs, respectively. Also,
the aromatic C = C stretching vibrations have appeared between
1625 and 1430 cm−1. In flavone-based hydrazones, compounds 3a
and 3j, the calculated band was found at 1626 (41%) and 1621
(22%) cm–1 for NNH and at 1088 (86%) and 935 (60%) cm–1 for
the HCCN band which nicely correlated with experimental values,
respectively.
Declaration of Competing Interest
Declare that we have NO conflict of interest.
Acknowledgments
The authors would like to thank the Deanship of Scientific Re-
search at Umm Al-Qura University for supporting this work under
project no. 18-SCI-1-02-0006. The financial support by the Higher
Education Commission of Pakistan (HEC) under Project No. (NRPU-
6484) is gratefully acknowledged.
3.15. C–X, C-S and S-O vibrations
The chlorine compound absorbs strongly in the region 770–670
cm−1 due to the C Cl stretching vibrations and the sulfur com-
–
pound absorbs in the region of 1225–920 cm−1 due to C–S and S–
O. In the spectrum of compound 3a, the (C–Cl) stretching vibration
contributes to the bands computed at 763 cm−1 and in compound
3j spectrum, the (S-C and S-O) stretching vibrations contribute to
the bands calculated at 1108, 926 cm−1, respectively. These results
show excellent agreement with the assignment reported earlier.
According to the calculated PED, the stretching (C–Cl) vibration in
compound 3a contributes 15% and compound 3j contributes upto
78%.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130965.
References
[1] J. Ashraf, E.U. Mughal, A. Sadiq, N. Naeem, S.A. Muhammad, T. Qousain,
M.N. Zafar, B.A. Khan, M. Anees, Design and synthesis of new flavonols as dual
ɑ-amylase and ɑ-glucosidase inhibitors: structure-activity relationship, drug–
likeness, in vitro and in silico studies, J. Mol. Struct. (2020) 128458.
4. Conclusions
[2] E.U. Mughal, A. Sadiq, M. Ayub, N. Naeem, A. Javid, S.H. Sumrra, M.N. Zafar,
B.A. Khan, F.P. Malik, I. Ahmed, Exploring 3-Benzyloxyflavones as new lead
cholinesterase inhibitors: synthesis, structure–activity relationship and molec-
ular modelling simulations, J. Biomol. Struct. Dyn. (2020) 1–14.
[3] M. Singh, M. Kaur, O. Silakari, Flavones: an important scaffold for medicinal
chemistry, Eur. J. Med. Chem. 84 (2014) 206–239.
In summary, we have designed, synthesized and characterized
an interesting series of flavone-based hydrazones carrying distinct
substitution patterns by utilizing the precedent procedure. The
14

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
[4] H. Adibi, J.S. Mojarrad, H. Asgharloo, G. Zarrini, Synthesis, in vitro antimicrobial
and antioxidant activities of chalcone and flavone derivatives holding allylic
substitutions, Med. Chem. Res. 20 (8) (2011) 1318–1324.
[5] W.F. Hodnick, E.B. Mllosavljevic, J.H. Nelson, R.S. Pardini, Electrochemistry of
flavonoids: relationships between redox potentials, inhibition of mitochondrial
respiration, and production of oxygen radicals by flavonoids, Biochem. Phar-
macol. 37 (13) (1988) 2607–2611.
[6] R. de Queiroz Ferreira, S.J. Greco, M. Delarmelina, K.C. Weber, Electrochemical
quantification of the structure/antioxidant activity relationship of flavonoids,
Electrochim. Acta 163 (2015) 161–166.
[7] I.B. Masesane, A comprehensive review of the oxidative cyclisation of 2’-hy-
droxychalcones to aurones and flavones, Int. J. Chem. Stud. 3 (3) (2015) 53–59.
[8] R.K.Y. Shaikh, G. Nazeruddin, Synthesis of flavone skeleton by different meth-
ods, Orient. J. Chem. 29 (4) (2014) 1475–1487.
cence behaviour, structure-activity relationship and molecular modelling stud-
ies, J. Biomol. Struct. Dyn. (2020) 1–16.
[17] A. Sykula, A. Kowalska-Baron, A. Dzeikala, A. Bodzioch, E. Lodyga-Chruscinska,
An experimental and DFT study on free radical scavenging activity of hes-
peretin Schiff bases, Chem. Phys. 517 (2019) 91–103.
[18] N. Uddin, F. Rashid, S. Ali, S.A. Tirmizi, I. Ahmad, S. Zaib, M. Zubair, P.L. Dia-
conescu, M.N. Tahir, J. Iqbal, Synthesis, characterization, and anticancer activity
of Schiff bases, J. Biomol. Struct. Dyn. 38 (11) (2020) 3246–3259.
[19] N. Beyazit, D. Çakmak, C. Demetgül, Chromone-based Schiff base metal com-
plexes as catalysts for catechol oxidation: synthesis, kinetics and electrochem-
ical studies, Tetrahedron 73 (19) (2017) 2774–2779.
[20] H.R. Zare, N. Nasirizadeh, A study of the electrochemical behavior of hema-
toxylin as an important bioactive flavonoid, Electrochim. Acta 56 (11) (2011)
3920–3925.
[9] (a) E.U. Mughal, M. Ayaz, Z. Hussain, A. Hasan, A. Sadiq, M. Riaz, A. Ma-
lik, S. Hussain, M.I. Choudhary, Synthesis and antibacterial activity of sub-
stituted flavones, 4-thioflavones and 4-iminoflavones, Bioorg. Med. Chem.
14 (14) (2006) 4704–4711; (b) S. Imran, M. Taha, N.H. Ismail, S.M. Kashif,
F. Rahim, W. Jamil, M. Hariono, M. Yusuf, H. Wahab, Synthesis of novel
flavone hydrazones: in-vitro evaluation of α-glucosidase inhibition, QSAR
analysis and docking studies, Eur. J. Med. Chem. 105 (2015) 156–170; (c)
A.K. Verma, R. Pratap, Chemistry of biologically important flavones, Tetrahe-
dron 68 (41) (2012) 8523–8538; (d) S. Patel, U. Shah, Synthesis of flavones
from 2-hydroxyacetophenone and aromatic aldehyde derivatives by conven-
tional methods and green chemistry approach, Asian J. Pharmaceut. Clin. Res.
10 (2) (2017) 570–589; (e) D.C.S. Lima, C.R. Vale, J.H. Véras, A. Bernardes,
C.N. Pérez, L. Chen-Chen, Absence of genotoxic effects of the chalcone
(E)-1-(2-hydroxyphenyl)-3-(4-methylphenyl)-prop-2-en-1-one) and its poten-
tial chemoprevention against DNA damage using in vitro and in vivo as-
says, PLoS One 12 (2) (2017) 0171224; (f) M. Cabrera, M. Simoens, G. Falchi,
M.L. Lavaggi, O.E. Piro, E.E. Castellano, A. Vidal, A. Azqueta, A. Monge, A.L. de
Cerain, Synthetic chalcones, flavanones, and flavones as antitumoral agents: bi-
ological evaluation and structure–activity relationships, Bioorg. Med. Chem. 15
(10) (2007) 3356–3367; (g) J. Chen, C.-.F. Liu, G.-.W. Rao, Progress in the syn-
thesis, angiogenesis activity and mechanism of chalcone derivatives, Mini Rev.
Org. Chem. 17 (7) (2020) 814–827; (h) R.S. Joshi, P.G. Mandhane, S.D. Diwakar,
S.K. Dabhade, C.H. Gill, Synthesis, analgesic and anti-inflammatory activities
of some novel pyrazolines derivatives, Bioorg. Med. Chem. Lett. 20 (12) (2010)
3721–3725; (i) M. Cabrera, M.L. Lavaggi, F. Croce, L. Celano, L. Thomson, M. Fer-
nández, C. Pintos, S. Raymondo, M. Bollati, A. Monge, Identification of chal-
cones as in vivo liver monofunctional phase II enzymes inducers, Bioorg. Med.
Chem. 18 (14) (2010) 5391–5399; (j) J. Horkaew, S. Chantrapromma, N. Sae-
wan, H.-.K. Fun, (E)-3-(4-Ethoxyphenyl)-1-(2-hydroxyphenyl) prop-2-en-1-one,
[21] (a) X. Zhang, Y.-.H. Jin, H.-.X. Diao, F.-.S. Du, Z.-.C. Li, F.-.M. Li, Synthesis of
bismaleimides bearing electron-donating chromophores and their fluorescence
behavior during copolymerization, Macromolecules 36 (9) (2003) 3115–3127;
(b) S. Tang, W. Li, F. Shen, D. Liu, B. Yang, Y. Ma, Highly efficient deep-blue
electroluminescence based on the triphenylamine-cored and peripheral blue
emitters with segregative HOMO–LUMO characteristics, J. Mater. Chem. 22 (10)
(2012) 4401–4408.
[22] R. Pohl, V.A. Montes, J. Shinar, P. Anzenbacher, Red− green− blue emission
from Tris (5-aryl-8-quinolinolate) Al (III) complexes, J. Org. Chem. 69 (5)
(2004) 1723–1725.
[23] J.M. Bobbitt, J.P. Willis, Electrochemistry of natural products. Oxidative decar-
boxylation of some tetrahydro-. beta.-carbolinecarboxylic acids, J. Org. Chem.
45 (10) (1980) 1978–1984.
[24] D. Tarinc, B. Dogan-Topal, M. Dolaz, A. Golcu, S.A. Ozkan, Synthesis, charac-
terization, biological activity and voltammetric behavior and determination of
cefaclor metal complexes, Curr. Anal. Chem. 6 (4) (2010) 316–328.
[25] R.F. De Souza, W.F. De Giovani, Synthesis, spectral and electrochemical proper-
ties of Al (III) and Zn (II) complexes with flavonoids, Spectrochim. Acta Part A
61 (9) (2005) 1985–1990.
[26] R.F. De Souza, E.M. Sussuchi, W.F. De Giovani, Synthesis, electrochemical, spec-
tral, and antioxidant properties of complexes of flavonoids with metal ions,
Synth. React. Inorg. Met. Org. Chem. 33 (7) (2003) 1125–1144.
[27] S. Güney, G. Yildiz, A. Capan, T. Ozturk, Evaluation of the electrochemical prop-
erties of 3-hydroxyflavone using voltammetric methods, Electrochim. Acta 55
(9) (2010) 3295–3300.
[28] K. Harisha, B.K. Swamy, E.E. Ebenso, Poly (glycine) modified carbon paste elec-
trode for simultaneous determination of catechol and hydroquinone: a voltam-
metric study, J. Electroanal. Chem. 823 (2018) 730–736.
[29] K. Harisha, B.K. Swamy, P. Ganesh, H. Jayadevappa, Electrochemical oxidation
of haematoxylin at poly (alanine) modified carbon paste electrode: a cyclic
voltammetric study, J. Electroanal. Chem. 832 (2019) 486–492.
[30] K.V. Harisha, B.E.K. Swamy, P.S. Ganesh, H. Jayadevappa, An electrochemical
sensor for the determination of 5-amino salicylic acid at poly (alanine) mod-
ified carbon paste electrode: a cyclic voltammetric study, Anal. Bioanal. Elec-
trochem. 10 (10) (2018) 1273–1287.
Acta Crystallographica Section
C. Baby, M. Moni, K. Subramanian, Synthesis, characterization and dynamic
NMR studies of novel chalcone based N-substituted morpholine deriva-
E 66 (9) (2010) 2346–2347; (k) R. Baskar,
a
tive, J. Mol. Struct. 1040 (2013) 90–97; (l) D. Coutinho, P. Fernandes, Synthe-
sis and biological activity of some 2-Aryl-4H-L-benzopyran-4-ones, J. Indian
Chem. Soc. 69 (5) (1992) 265–267; (m) Y. Hoshino, N. Takeno, Ortho sub-
stituent effect of the side-chain phenyl group on the dehydrogenation of fla-
vanones with 2, 3-dichloro-5, 6-dicyano-p-benzoquinone, Bull. Chem. Soc. Jpn.
60 (12) (1987) 4468–4470; (n) V.N. Badavath, S. Ciftci-Yabanoglu, S. Bhakat,
A.K. Timiri, B.N. Sinha, G. Ucar, M.E. Soliman, V. Jayaprakash, Monoamine oxi-
dase inhibitory activity of 2-aryl-4H-chromen-4-ones, Bioorg. Chem. 58 (2015)
72–80; (o) M. Gharpure, R. Choudhary, V. Ingle, H. Juneja, Synthesis of new
series of 3-hydroxy/acetoxy-2-phenyl-4H-chromen-4-ones and their biologi-
cal importance, J. Chem. Sci. 125 (3) (2013) 575–582; (p) A.M. Sobottka,
W. Werner, G. Blaschke, W. Kiefer, U. Nowe, G. Dannhardt, E.E. Schapoval,
E.P. Schenkel, G.K. Scriba, Effect of flavonol derivatives on the carrageenin-in-
duced paw edema in the rat and inhibition of cyclooxygenase-1 and 5-lipoxy-
genase in vitro, Arch. Pharm. (Weinheim) 333 (7) (2000) 205–210.
[10] A. Gul, Z. Akhter, F. Perveen, S. Kalsoom, F.L. Ansari, M. Siddiq, Molecular dock-
ing and quantitative structure activity relationship (QSAR) studies of some
newly synthesized poly (azomethine) esters, Int. J. Polym. Sci. 8 (2) (2019)
346–350.
[11] S. Patil, P. Utale, S. Gholse, S. Thakur, S. Pande, Synthesis, characterization
and antimicrobial activity of 6-bromo-4-methoxy-4-(substituted phenyl) imi-
noflavone, J. Chem. Pharm. Res. 4 (1) (2012) 501–507.
[12] A. Gomes, E. Fernandes, M.B.Q. Garcia, A.M. Silva, D.C. Pinto, C.M. Santos,
J.A. Cavaleiro, J.L. Lima, Cyclic voltammetric analysis of 2-styrylchromones: re-
lationship with the antioxidant activity, Bioorg. Med. Chem. 16 (17) (2008)
7939–7943.
[13] A. Abdelmadjid, D. Haffar, F. Benghanem, S. Ghedjati, L. Toukal, V. Dorcet,
R. Bourzami, Synthesis, crystal structure, electrochemical, theoretical studies
and antioxidant activities of new Schiff base, J. Mol. Struct. (2020) 129368.
[14] A.M. Fathi, H.S. Mandour, E. HassaneAnouar, Characteristics of multiden-
tate schiff base ligand and its complexes using cyclic voltammetry, fluores-
cence, antimicrobial behavior and DFT-calculations, J. Mol. Struct. 1224 (2020)
129263.
[15] F. Hueso-Urena, N.A. Illán-Cabeza, M.N. Moreno-Carretero, A. Penas-Chamorro,
Ni (II), Cu (II), Zn (II) and Cd (II) complexes with dinegative N, N, O-tridentate
uracil-derived hydrazones, Acta Chim. Slov. 47 (4) (2000) 481–488.
[16] J. Ashraf, E.U. Mughal, A. Sadiq, M. Bibi, N. Naeem, A. Ali, A. Massadaq, N. Fa-
tima, A. Javid, M.N. Zafar, Exploring 3-hydroxyflavone scaffolds as mushroom
tyrosinase inhibitors: synthesis, X-ray crystallography, antimicrobial, fluores-
[31] E.I. Korotkova, O.A. Voronova, E.V. Dorozhko, Study of antioxidant proper-
ties of flavonoids by voltammetry, J. Solid State Electrochem. 16 (7) (2012)
2435–2440.
[32] A. Masek, E. Chrzescijanska, M. Zaborski, Characteristics of curcumin using
cyclic voltammetry, UV–vis, fluorescence and thermogravimetric analysis, Elec-
trochim. Acta 107 (2013) 441–447.
[33] A. Masek, E. Chrzescijanska, M. Zaborski, Electrooxidation of morin hydrate at
a Pt electrode studied by cyclic voltammetry, Food Chem. 148 (2014) 18–23.
˙
[34] F. Kolcu, D. Erdener, I. Kaya, A Schiff base based on triphenylamine and thio-
phene moieties as a fluorescent sensor for Cr (III) ions: synthesis, characteri-
zation and fluorescent applications, Inorganica Chim Acta 509 (2020) 119676.
˙
[35] H. Vural, Ö. Idil, Synthesis, spectroscopic investigation and biological activities
of copper (II) complex of 2-(2, 4-difluorophenyl) pyridine: a combined theo-
retical and experimental study, J. Mol. Struct. 1177 (2019) 242–248.
[36] A. Mishra, E. Mena-Osteritz, P. Bäuerle, Synthesis, photophysical and elec-
trochemical characterization of terpyridine-functionalized dendritic oligothio-
phenes and their Ru (II) complexes, Beilstein J. Org. Chem. 9 (1) (2013) 866.
[37] (a) A.S. Girgis, A.H. Basta, H. El-Saied, M.A. Mohamed, A.H. Bedair, A.S. Salim,
Synthesis, quantitative structure–property relationship study of novel fluo-
rescence active 2-pyrazolines and application, R. Soc. Open Sci. 5 (3) (2018)
171964; (b) M. Soltani, R. Minakar, H.R. Memarian, H. Sabzyan, Cyclic voltam-
metric study of 3, 5-diaryl-1-phenyl-2-pyrazolines, J. Phys. Chem. A 123 (13)
(2019) 2820–2830; (c) V. Ramkumar, P. Kannan, Highly fluorescent semicon-
ducting pyrazoline materials for optoelectronics, Opt. Mater. (Amst) 46 (2015)
605–613.
[38] (a) A.M. Polgar, J. Poisson, N.R. Paisley, C.J. Christopherson, A.C. Reyes,
Z.M. Hudson, Blue to yellow thermally activated delayed fluorescence with
quantum yields near unity in acrylic polymers based on D− π–A pyrimidines,
Macromolecules 53 (6) (2020) 2039–2050; (b) P. Ganesan, R. Ranganathan,
Y. Chi, X.K. Liu, C.S. Lee, S.H. Liu, G.H. Lee, T.C. Lin, Y.T. Chen, P.T. Chou, Func-
tional pyrimidine-based thermally activated delay fluorescence emitters: pho-
tophysics, mechanochromism, and fabrication of organic light-emitting diodes,
Chemistry–A Eur. J. 23 (12) (2017) 2858–2866.
[39] (a) D.-.D. Li, J.-.L. Tian, W. Gu, X. Liu, S.-.P. Yan, A novel 1, 2, 4-triazole-based
copper (II) complex: synthesis, characterization, magnetic property and nu-
clease activity, J. Inorg. Biochem. 104 (2) (2010) 171–179; (b) Z.-.H. Xing,
J.-.Y. Zhuang, X.-.P. Xu, S.-.J. Ji, W.-.M. Su, Z. Cui, Novel oxazole-based emit-
15

M.A. Alsharif, N. Naeem, E.U. Mughal et al.
Journal of Molecular Structure 1244 (2021) 130965
ters for high efficiency fluorescent OLEDs: synthesis, characterization, and op-
toelectronic properties, Tetrahedron 73 (15) (2017) 2036–2042.
[50] S.H. Sumrra, S. Kausar, M.A. Raza, M. Zubair, M.N. Zafar, M.A. Nadeem,
E.U. Mughal, Z.H. Chohan, F. Mushtaq, U. Rashid, Metal based triazole com-
pounds: their synthesis, computational, antioxidant, enzyme inhibition and an-
timicrobial properties, J. Mol. Struct. 1168 (2018) 202–211.
˙
[40] I. Kaya, M. Yıldırım, A. Avcı, Synthesis and characterization of fluorescent
polyphenol species derived from methyl substituted aminopyridine based
Schiff bases: the effect of substituent position on optical, electrical, electro-
chemical, and fluorescence properties, Synth. Met. 160 (9–10) (2010) 911–920.
[41] E.U. Mughal, M. Mirzaei, A. Sadiq, S. Fatima, A. Naseem, N. Naeem, N. Fatima,
S. Kausar, A.A. Altaf, M.N. Zafar, Terpyridine-metal complexes: effects of differ-
ent substituents on their physico-chemical properties and density functional
theory studies, R. Soc. Open Sci. 7 (11) (2020) 201208.
[42] A. Masek, M. Zaborski, E. Chrzescijanska, Electrooxidation of flavonoids at plat-
inum electrode studied by cyclic voltammetry, Food Chem. 127 (2) (2011)
699–704.
[51] K. Benbouguerra, N. Chafai, S. Chafaa, Y.I. Touahria, H. Tlidjane, New
α-Hydrazinophosphonic acid: synthesis, characterization, DFT study and in sil-
ico prediction of its potential inhibition of SARS-CoV-2 main protease, J. Mol.
Struct. 1239 (2021) 130480.
[52] J. Haruyama, T. Ikeshoji, M. Otani, Electrode potential from density functional
theory calculations combined with implicit solvation theory, Phys. Rev. Mater.
2 (9) (2018) 095801.
[53] D. Suresh, M. Amalanathan, S. Sebastian, D. Sajan, I.H. Joe, V.B. Jothy, I. Nemec,
Vibrational spectral investigation and natural bond orbital analysis of pharma-
ceutical compound 7-Amino-2, 4-dimethylquinolinium formate–DFT approach,
Spectrochim. Acta Part A 115 (2013) 595–602.
[43] A.A. Altaf, S. Kausar, A. Badshah, Spectral calculations with DFT, density func-
tional calculations–recent progresses of theory and application (2018) 13.
[44] A. Frisch, Gaussian 09w reference, Wallingford, USA, 25p (2009).
[45] B. Lal, A. Kanwal, A.A. Altaf, A. Badshah, F. Asghar, S. Akhter, S. Ullah, S.I. Khan,
M.N. Tahir, Synthesis, crystal structure, spectral and electrochemical character-
ization, DNA binding and free radical scavenging studies of ferrocene-based
thioureas, J. Coord. Chem. 72 (14) (2019) 2376–2392.
[54] R. Carbó-Dorca, P. Bultinck, Quantum mechanical basis for Mulliken population
analysis, J. Math. Chem. 36 (3) (2004) 231–239.
[55] (a) F.C. Chahar, P.E. Alvarez, C. Zampini, M.I. Isla, S.A. Brandán, Experimental
ꢀ
ꢀ
and DFT studies on 2 ,4 -dihydroxychalcone, a product isolated from Zuccagnia
punctata Cav.(Fabaceae) medicinal plant, J. Mol. Struct. 1201 (2020) 127221;
(b) K. Karrouchi, S.A. Brandán, Y. Sert, M. El Karbane, S. Radi, M. Ferbinteanu,
Y. Garcia, Synthesis, structural, molecular docking and spectroscopic stud-
ies of (E)-N’-(4-methoxybenzylidene)-5-methyl-1H-pyrazole-3-carbohydrazide,
J. Mol. Struct. 1225 (2021) 129072.
[46] M. Marinov, S. Minchev, N. Stoyanov, G. Ivanova, M. Spassova, V. Enchev, Syn-
thesis, spectroscopic characterization and ab initio investigation of thioana-
logues of spirohydantoins, Croat. Chem. Acta 78 (1) (2005) 9–16.
[47] A.A. Altaf, A. Shahzad, Z. Gul, S.A. Khan, A. Badshah, M.N. Tahir, Z.I. Zafar,
E. Khan, Synthesis, crystal structure, and DFT calculations of 1, 3-diisobutyl
thiourea, J. Chem. (2015) 2015.
[56] A. Esme, S. Sagdinc, Theoretical Studies of Molecular Structures, In-
frared Spectra, NBO and NLO Properties of Some Novel 5-aryla-
[48] F. Asghar, S. Fatima, S. Rana, A. Badshah, I.S. Butler, M.N. Tahir, Synthesis, spec-
zo-6-hydroxy-4-phenyl-3-cyano-2-pyridone Dyes, Acta Physica Polonica,
130 (6) (2016).
A
ꢀ
troscopic investigation, and DFT study of N, N -disubstituted ferrocene-based
thiourea complexes as potent anticancer agents, Dalton Trans. 47 (6) (2018)
1868–1878.
[57] H. Sahebalzamani, F. Salimi, E. Dornapour, Theoretical studies of structure,
spectroscopy, and properties of a new hydrazine derivative, J. . 13 (3) (2013).
[49] J. Aihara, Reduced HOMO− LUMO gap as an index of kinetic stability for poly-
cyclic aromatic hydrocarbons, J. Phys. Chem. A 103 (37) (1999) 7487–7495.
16