Synthesis, spectroscopic properties, and DFT correlative studies of 3,3′- carbonyl biscoumarin derivatives

Article abstract of DOI:10.1016/j.molstruc.2021.130781

A facile and simple method for the synthesis of a library of 3,3′- Carbonyl biscoumarin derivatives via a one-pot chemical reaction is reported. The synthesized fluorescent dyes were purified and characterized by analytical methods. The IR, ¹H-NMR, and MS results confirmed the corresponding structure of the fluorescent dyes. The absorption and fluorescence spectra of fluorescent dyes were recorded in different solvents of varying polarity to understand the solvatochromic behaviour and dipole moments. Stoke's shift exhibits a redshift with an increase in solvent polarity for all molecules indicating a π→π^? transition. The ground state dipole moments of all fluorescent dyes are estimated theoretically from ab initio computations (integral equation formalism of polarizable continuum model) and experimentally from the solvatochromic method and the results are compared. Further, using solvatochromic correlations like Lippert's, Bakhshiev's, Kawski-Chamma-Viallet's, and solvent polarity parameter the excited state dipole moments are determined. Results show that the excited state dipole moments are higher than the ground state dipole moments which suggests that, all fluorescent dyes are more polar in the excited state. The HOMO-LUMO energy gaps computed from density functional theory and absorption threshold wavelengths are found to be in good agreement and also support intramolecular charge transfer (ICT). Using HOMO-LUMO energies, the chemical hardness (η) of the molecules is determined and the chemical stability is discussed. Further, using DFT molecular electrostatic potential (MESP) plots, the electrophilic site and nucleophilic site which are useful in photochemical reactions were identified. The preliminary observations and results suggest that the fluorescent dyes can be considered as potential candidates for fluorescent probes and construction of dye-sensitized solar cell in future

Full text of DOI:10.1016/j.molstruc.2021.130781

Journal of Molecular Structure 1243 (2021) 130781
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Synthesis, spectroscopic properties, and DFT correlative studies of
ꢀ
3,3 - carbonyl biscoumarin derivatives
Shashikant Walki a, G.H. Malimathb, K.M. Mahadevana,∗, Soniya Naikc, Suraj M. Sutard,
Hemantkumar Savanure, Lohit Naikb,∗
a Department of Chemistry, Kuvempu University, P. G. Centre Kadur, Shivamoga, Karnataka, India
b UG & PG Department of Physics, Karnatak Science College, Dharwad, Karnataka, India
c Department of Chemistry, IIT Bombay, Powai, Mumbai 400076, India
d Department of Chemistry, Karnatak Science College, Dharwad, Karnataka, India
e Department of Studies and Research in Chemistry, P. C. Jabin Science College, Hubli, Karnatak 580021, India
a r t i c l e i n f o
a b s t r a c t
ꢀ
Article history:
A facile and simple method for the synthesis of a library of 3,3 - Carbonyl biscoumarin derivatives via a
one-pot chemical reaction is reported. The synthesized fluorescent dyes were purified and characterized
by analytical methods. The IR, 1H-NMR, and MS results confirmed the corresponding structure of the flu-
orescent dyes. The absorption and fluorescence spectra of fluorescent dyes were recorded in different sol-
vents of varying polarity to understand the solvatochromic behaviour and dipole moments. Stoke’s shift
exhibits a redshift with an increase in solvent polarity for all molecules indicating a π→π∗ transition.
The ground state dipole moments of all fluorescent dyes are estimated theoretically from ab initio compu-
tations (integral equation formalism of polarizable continuum model) and experimentally from the solva-
tochromic method and the results are compared. Further, using solvatochromic correlations like Lippert’s,
Bakhshiev’s, Kawski-Chamma-Viallet’s, and solvent polarity parameter the excited state dipole moments
are determined. Results show that the excited state dipole moments are higher than the ground state
dipole moments which suggests that, all fluorescent dyes are more polar in the excited state. The HOMO-
LUMO energy gaps computed from density functional theory and absorption threshold wavelengths are
found to be in good agreement and also support intramolecular charge transfer (ICT). Using HOMO-LUMO
energies, the chemical hardness (η) of the molecules is determined and the chemical stability is dis-
cussed. Further, using DFT molecular electrostatic potential (MESP) plots, the electrophilic site and nu-
cleophilic site which are useful in photochemical reactions were identified. The preliminary observations
and results suggest that the fluorescent dyes can be considered as potential candidates for fluorescent
probes and construction of dye-sensitized solar cell in future
Received 26 February 2021
Revised 18 May 2021
Accepted 26 May 2021
Available online 30 May 2021
Keywords:
Carbonyl biscoumarin
Dipole moments
HOMO-LUMO
Solvatochromism
Chemical hardness
© 2021 Elsevier B.V. All rights reserved.
1. Introduction
9], their inclusion in zeolites could lead to artificial antenna sys-
tems [10], active material for organic light-emitting devices [11],
The well-known family of coumarin derivatives, called bis-
coumarin (dimeric coumarins) occupies an interesting position due
to its interesting application in the optoelectronic and pharma-
cological industry [1–4]. These compounds occur naturally in a
large number of plants and micro-organisms and it shows anti-
fungal, anti-anthelmintic, anti-coagulants, analgesic, anti-tumor,
anti-HIV, anti-apoptotic, and antioxidant activities [5–7]. Along
with these properties biscoumarin derivatives are also the most
widely used class of fluorescent dyes, highly efficient laser dyes [8–
dying stuff [12] and signaling units in fluorescent ion sensors [13].
These properties of biscoumarin dyes are influenced by the na-
ture and position of substituents. Additionally, the way the two
coumarin moieties are linked to each other, as well as the chem-
ical nature of the bridge, play a determining role in the optical
properties.
In recent decades, many researchers focused on the develop-
ment of suitable synthetic methodologies for biscoumarin due
to their different optoelectronic and biological applications. The
novel method for the synthesis of biscoumarin derivatives is
the Knoevenagel-Michael reaction. Because of the importance of
biscoumarin essentially bis(4-hydroxycoumarin) in the mentioned
fields, many catalysts in various conditions [14] have been intro-
∗
Corresponding author.
E-mail address: lohitresearch@gmail.com (L. Naik).
https://doi.org/10.1016/j.molstruc.2021.130781
0022-2860/© 2021 Elsevier B.V. All rights reserved.

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
ꢀ
Scheme 1. Synthesis of 3, 3 - Carbonylbiscoumarin.
good agreement with the proposed structures. The FT-IR, 1H-NMR,
and MS spectra are given in supplementary files. The schematic
duced for the preparation of them such as o-benzenedisulfonimide,
phospho sulfonic acid, [bmim]BF4, cellulose sulfonic, SDS, [PSebim]
[OTf], propane-1,2,3-triyl tris (hydrogen sulfate),boron-sulfuric acid
Nanoparticles, [pyridine–SO3H]Cl, W-doped ZnO nanocomposite, Bi
(NO3)3ꢀ5H2O, choline hydroxide, P4VPy–CuO-NPs sulfonated rice
husk ash, silica-Bonded Npropylpiperazine sodium n-propionate,
ꢀ
synthesis of 3,3 -Carbonylbiscomarins are shown in Scheme 1 and
its derivatives are listed in Table 1.
3.1.1. 3-(2-oxo-2H-chromene-3-carbonyl)-2H-chromen-2-one (3a)
[33,48]
White solid, mp: 247-249 °C (Lit. 251-252°C); IR (KBr, cm−1):
1731, 1658, 1272,1095. 1H NMR (400MHz, DMSO-d6, δ ppm): 8.68
P4VPy-BuSO3H
[15–32].
X(AlCl3),
and
4-(dimethylamino)
pyridine
Although these methods suffer from harsh reaction conditions,
some of them have relatively long reaction times, low yields, use of
metals and toxic solvents. In view of the above, in these findings,
we have synthesized a library of carbonyl biscoumarin derivatives
using piperidine as the catalyst and studied the solvatochromic
behavior and dipole moment using theoretical and experimental
techniques.
ꢀ
ꢀ
(s, 1H and 1 H), 7.97 (d, J= 7.60 Hz, 1H and 1 H), 7.76-7.80 (m,
ꢀ
ꢀ
1H and 1 H), 7.45-7.47 (m, 2H and 2 H). LC-MS: 319.0(M+1).
3.1.2. 7-(diethylamino)-3-(7-(diethylamino)-2-oxo-2H-chromene-3-
carbonyl)-2H-chromen-2-one (3b)
[12,33,34,48]
Yellow solid, mp: 208-209 °C (Lit. 214-217°C); IR (KBr, cm−1
)
1705, 1638, 1076, 1349. 1H NMR (400MHz, DMSO-d6, δ ppm): 8.28
2. Experimental
ꢀ
ꢀ
(s, 1H and 1 H), 7.60-7.64 (m, 1H and 1 H), 6.77- 6.80 (m, 1H and
ꢀ
ꢀ
2.1. Material and methods
1
H), 6.58 (s, 1H and 1 H), 3.48 (q, J= 6.80 Hz, 13.6Hz, 4H and
ꢀ
ꢀ
4 H), 1.14 (s, J= 14Hz, 6H and 6 H). LC-MS: 461.0 (M+1)
Chemicals and reagents used for the synthesis and analy-
sis were procured from a commercial supplier, Sigma Aldrich,
India. Analytical grade solvents were purchased from Loba
chemie. Pvt Ltd., Mangalore. The Melting points of the synthe-
sized compounds were determined by electrothermal apparatus
3.1.3. 6,8-dichloro-3-(6,8-dichloro-2-oxo-2H-chromene-3-carbonyl)-
2H-chromen-2-one (3c)
[33]
Red solid, mp: 245-246 °C (Lit. 246-248°C); IR (KBr, cm−1) 1716,
1665, 1086, 1060. 1H NMR (400MHz, DMSO-d6, δ ppm): 8.63 (s, 1H
in open capillaries in
a Boetius-Mikroheiztisch. TLC was per-
and 1’H), 8.24 (d, J= 3.2Hz, 1H and 1 H), 7.92-7.93 (m, 1H and 1
ꢀ
ꢀ
formed by using an aluminum foil fluorescent indicator from
Merck KGaA (silica gel 60 F254, layer thickness 0.2 mm). 1H-
ꢀ
H), 7.51 (d, J= 12Hz, 1H and 1 H).LC-MS: 478.2 (M+2).
NMR spectrum was recorded using
a Jeol with 100MHz op-
erating frequency deuterated chloroform (CDCl3) solvents. IR
spectra were of the dyes recorded using Nicolet 5700 FT-IR
instrument.
3.1.4. 8-ethoxy-3-(8-ethoxy-2-oxo-2H-chromene-3-carbonyl)-2H-
chromen-2-one (3d)
[33]
The absorption, fluorescence, and fluorescence lifetime mea-
surements were measured using Carry-100, Hitachi F-7000, and ISS
ChronoBH time-correlated single-photon counting spectrometer.
Light yellow solid, mp: 263-265 °C (Lit. 264-266°C); IR (KBr,
cm−1) 1731, 1658, 1272, 1095. 1H NMR (400MHz, DMSO-d6, δ
ꢀ
ꢀ
ppm): 8.64 (s, 1H and 1 H), 7.49(d, J= 6.80Hz, 1H and 1 H),
ꢀ
ꢀ
7.45(d, J= 8.40 Hz, 1H and 1 H), 7.37 (d, J= 16Hz, 1H and 1 H),
ꢀ
ꢀ
4.20 (q, J= 13.6Hz, 2H and 2 H), 1.41 (t, J= 13.6Hz, 3H and 3 H).
LC-MS: 407.4(M+1).
3. Result and discussions
3.1. Synthesis and characterization
3.1.5. 6-bromo-3-(6-bromo-2-oxo-2H-chromene-3-carbonyl)-2H-
chromen-2-one (3e)
In the present work, we described the expedite, cheaper and
ꢀ
[33]
benign synthesis of some important fluorescent organic 3,3 - Car-
White solid, mp: 316-318°C (Lit. 316-318); IR (KBr, cm−1) 1740,
bonylbiscoumarin derivatives which seem to be very important
and useful for dye-sensitized solar cells (DSSC) applications. To a
mixture of dimethyl-1,3 acetone dicarboxylate (0.5g, 0.0287mol),
the appropriate salicylaldehyde (0.54g, 0.00442, mole ratio 1:2),
absolute ethanol (10-20 ml) and a catalytic amount of piperidine
was added. The obtained clear solution was stirred at room tem-
perature (25°C) for 12 hrs. After completion of the reaction (mon-
itored by TLC) the solvent was evaporated under a vacuum. The
crude product was washed with the diethyl ether and residue mass
obtained was further recrystallized from acetic acid to get ana-
1679, 1088, 1028. 1H NMR (400MHz, DMSO-d6, δ ppm): 3.38 (s, 1H
ꢀ
ꢀ
ꢀ
and 1 H), 8.60 (s, 1H and 1 H), 8.05-8.16 (m, 1H and 1 H). LC-MS:
458.8 (M+2)
3.1.6. 7-hydroxy-3-(7-hydroxy-2-oxo-2H-chromene-3-carbonyl)-2H-
chromen-2-one (3f)
[33]
White solid, mp: 215-217°C (Lit. 216-218°C); IR (KBr, cm−1
3124, 1720, 1651, 1245. 1H NMR (400MHz, DMSO-d6, δ ppm): 11.10
)
ꢀ
ꢀ
ꢀ
lytically pure yellow coloured 3,3 -Carbonylbiscomarins (3a-h) in
(s, 1H and 1 H), 8.50 (s, 1H and 1 H), 7.78 (d, J=11.6Hz, 1H and
ꢀ
ꢀ
ꢀ
moderate to good yields. Their structural identities and purities
were confirmed by 1H-NMR, IR, and MS and were found to be in
1 H) 6.86-6.89 (m, 1H and 1 H), 6.80 (d, J= 2.80Hz, 1H and 1 H).
LC-MS: 351.4(M+1).
2

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Table 1
ꢀ
list of derivatives of 3, 3 - Carbonylbiscoumarin.
Time
% of
Yield
Entry
Sub-2
Products
(in hrs)
O
O
O
O
H
O
O
3a
4
70
75
OH
O
O
O
O
O
O
H
3b
5
Et2N
OH
Et2N
NEt2
3

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Table 1a
3.1.7. 8-methoxy-3-(8-methoxy-2-oxo-2H-chromene-3-carbonyl)-2H-
chromen-2-one (3g)
Some physical constants along with the calculated values of various polarity
functions.
[33]
N
Solvent
Ɛ
n
ET
F(ε,n)
F1(ε,n)
F2(ε,n)
Light Yellow solid, mp: 260-262°C (Lit. 264-266°C); IR (KBr,
cm−1) 1776, 1665, 1275, 1086. 1H NMR (400MHz, DMSO-d6, δ
Toluene
2.40
1.49
1.37
1.40
1.42
1.39
1.37
1.34
1.43
1.47
0.09
0.22
0.20
0.30
0.58
0.61
0.46
0.38
0.44
0.01
0.20
0.21
0.21
0.26
0.27
0.30
0.27
0.26
0.03
0.49
0.55
0.58
0.74
0.78
0.86
0.83
0.84
0.35
0.49
0.55
0.58
0.64
0.64
0.66
0.71
0.74
ꢀ
ꢀ
Ethyl Acetate
Tetrahydrofuran
Dichloromethane
Butanol
6.08
ppm): 8.64 (s, 1H and 1 H), 7.46-7.52 (m, 2H and 2 H), 7.37-7.41
ꢀ
ꢀ
7.58
(m, 1H and 1 H), 3.93 (s, 3H and 3 H). LC-MS: 379.2 (M+1).
8.90
17.40
20.18
36.64
38.25
46.70
Prpoane-2-ol
Acetonitrile
DMF
3.1.8. 2-(3-oxo-3H-benzo [f]chromene-2-carbonyl)-3H-benzo
[f]chromen-3-one (3h) [12]
White solid, mp: >350 °C (Lit. >350 °C); IR (KBr, cm−1) 1716,
1665, 1086. 1H NMR (400MHz, DMSO-d6, δ ppm): 9.4 (s, 1H and
DMSO
tN
ε, n, ET values are taken from the literature [39–41].
ꢀ
ꢀ
ꢀ
1 H), 8.75 (d, J= 7.6Hz, 1H and 1 H), 8.38 (d, J= 9.2Hz, 1H and 1
ꢀ
ꢀ
H), 8.13 (d, J= 8Hz, 1H and 1 H), 7.81 (d, J= 6.80Hz, 1H and 1 H),
ꢀ
7.69-7.71 (m, 2H and 2 H). LC-MS: 419.2 (M+1)
Where F(ε, n) is Lippert’s polarity function and is given by,
ꢀ
ꢁ
ε − 1
n2 − 1
F ε, n
(
=
−
(2)
)
2ε + 1 2n2 + 1
3.2. Estimation of ground and excited-state dipole moments
The expression for Stoke’s shift according to Bakhshiev [36] is
The absorption and fluorescence spectra of fluorescent dyes (3a-
3h) in toluene, ethyl acetate, tetrahydrofuran, dichloromethane, bu-
tanol, propane-2-ol, acetonitrile, dimethylformamide (DMF), and
dimethyl sulfoxide (DMSO) were recorded multiple numbers times
to check the reproducibility of readings, to avoid any procedural
mistakes and the verified spectra are shown in Figs. 1 and 2. The
absorption maxima, emission maxima, Stoke’s shift, and arithmetic
mean of Stoke’s shift values in different solvents for all molecules
are tabulated in Tables-S1–S8. The value of Stokes shift undergoes
redshift with an increase in solvent polarity for all the molecules,
which indicates π→π∗ transition and also suggests that the dipole
moments for all the molecules in the excited state may be higher
than the ground state.
given by,
υa − υ = S F ε, n + const
(3)
(
)
1
1
f
Where F1(ε, n) is Bakhshiev’s polarity function and is given by,
ꢀ
ꢁ
2n2 + 1 ε − 1 n2 − 1
−
F ε, n
=
(4)
(
)
1
n2 + 2 ε + 2 n2 + 2
According to Kawski-Chamma-Viallet’s [37] equation,
ꢂ
ꢃ
1
2
υa + υ = S F ε, n + const
(5)
(
)
2
2
f
Where F2(ε, n) is Kawski-Chamma-Viallet’s polarity function
and is given by
When a molecule is excited, the solvent dipoles can reorient
or relax around the excited probe molecule and lowers the energy
of the excited state. Further, as the solvent polarity increases, this
effect becomes larger, which in turn, may result in the emission
at lower energies or longer wavelengths. When the molecule is
in the excited state, there will be a redistribution of the charges,
which may lead to the change in the dipole moment. In the ex-
cited state, no more the fluorophore remains in equilibrium with
its environment. As the molecule relaxes and attains equilibrium
with the surrounding environment, some amount of energy is dis-
sipated in the form of non-radiative energy and as a result, the
fluorescence emission wavelength gets shifted. In addition to this,
there may be specific interactions between the probe molecule and
solvent like hydrogen bonding, formation of charge-transfer states,
complex formation, etc., which may lead to large spectral shifts.
Therefore, a systematic analysis of the solvent effect is useful to
understand the effect of the environment and the various mecha-
nisms of deexcitation and relaxation of an excited molecule in so-
lution.
ꢄ
ꢅ
ꢀ
ꢁ
2n2 + 1 ε − 1 n2 − 1
3
2
n4 − 1
ꢂ
ꢃ
F ε, n
=
−
+
(6)
(
)
2
ꢂ
ꢃ
ε + 2 n2 + 2
2
2 n2 + 2
n2 + 2
Here ῡa and ῡf are absorption and fluorescence maxima in wave
numbers respectively and other terms have their usual meaning.
The dielectric constants, refractive indices, solvent polarity pa-
rameter, and the calculated values of various polarity functions like
F(ε, n), F1(ε, n), and F2(ε, n) are given in Table 1a.
From Eqs. (1), (3) and (5), it follows that (ῡa - ῡf) versus F(ɛ, n),
(ῡa - ῡf) versus F1(ɛ, n) and 1/2(ῡa + ῡf) versus F2(ɛ, n) plots should
be linear with slopes S, S1 and S2 respectively and are given as,
2(μe − μg)2
S =
(7)
(8)
hca30
2
2 μ − μ
(
)
g
e
S1
=
hca30
In this regard, the theories developed by various researchers
in the field of estimation of ground and excited-state dipole mo-
ments through solvatochromic methods are used in the present
study. Lippert [35] derived equations based on Onsager’s reaction
field theory for the determination of dipole moments considering
fluorophore as a point dipole in a continuous medium of uniform
dielectric constant. The excited-state dipole moments can also be
estimated using Bakhshiev’s [36] equations. Kawski [37] have de-
veloped a simple quantum mechanical second-order perturbation
theory to explain absorption and fluorescence band shifts in dif-
ferent solvents of refractive index (n) and varying permittivity (ε0)
corresponding to the band position of a solute molecule
and
2(μ2e − μ2g )
S2
=
(9)
hca30
Where μe and μg are excited and ground-state dipole moments
respectively. Here the term ‘h’ is Planck’s constant, ‘c’ is the veloc-
ity of light in vacuum and ‘a0’ is the Onsager cavity radius of the
probe molecule and is calculated using Edward’s [38] atomic incre-
ment method (Table 5).
The Stoke’s shift vs. F(ε, n), Stoke’s shift vs. F1(ε, n), and arith-
metic mean of Stoke’s shift vs. F2(ε, n) plots for fluorescent dyes
are shown in Fig. 3. The statistical data like slopes, intercepts, and
correlation coefficients for all molecules are reported in Tables 2–
4. It is observed that the correlation coefficient values are greater
According to Lippert [35], the expression for Stoke’s shift is
υa − υ = SF ε, n + const
(1)
(
)
f
4

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 1. Absorption spectra of 3a-3h in different solvents.
5

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 2. Fluorescence spectra of 3a-3h in different solvents.
than 0.8, which indicates good linearity for the slopes S, S1, and
S2.
for ground-state dipole moment (μg), excited state dipole moment
(μe), and the ratio of μe and μg are given by,
Assuming that the symmetry of the probe molecule remains
unchanged upon electronic transition and considering the ground
and excited-state dipole moments to be parallel, the expression
ꢀ
ꢁ
1/2
hca30
S2 − S1
μg =
(10)
2
2S1
6

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 3. Plot of Lippert’s (Stoke’s shift vs. F(ε,n)), Bakhshiev’s (Stoke’s shift vs. F1(ε,n)), Kawski-Chamma-Viallet’s, (arithmetic mean of Stoke’s shift vs F2(ε,n)), and Stoke’s shift
vs. (ETtN ) of synthesized fluorescent dyes.
7

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Table 2
Slope, intercepts, and correlation coefficient of Lippert’s plot of 3a–3h molecules.
Molecule
Slope (cm−1
)
Intercepts (cm−1
)
Correlation coefficient
No. of data
3a
3b
3c
3d
3e
3f
3086
769
10351
5972
9585
6106
8460
9183
11037
5239
0.880
0.828
0.896
0.819
0.867
0.840
0.899
0.844
5
5
5
8
5
6
6
7
1186
2870
7214
3035
2331
1761
3g
3h
Table 3
Slope, intercepts and correlation coefficient of Bakhshiev’s correlation of 3a–3h molecules.
Molecule
Slope (cm−1
)
Intercepts (cm−1
)
Correlation coefficient
No. of data
3a
3b
3c
3d
3e
3f
1040
254
10384
5988
9588
6107
8908
9176
11053
5276
0.878
0.842
0.869
0.906
0.994
0.913
0.872
0.871
5
5
5
8
5
6
6
7
417
998
1901
1051
770
3g
3h
555
Table 4
Slope, Intercepts, and Correlation coefficient of Kawski-Chamma-Viallet’s correlation plot of 3(a–h)
molecules.
Molecule
Slope (cm−1
)
Intercepts (cm−1
)
Correlation coefficient
No. of data
3a
3b
3c
3d
3e
3f
3583
4721
1733
4205
2605
4961
4056
2498
29001
27272
27586
26715
54312
29089
29656
24815
0.920
0.894
0.870
0.874
0.889
0.864
0.855
0.903
7
8
8
8
8
9
9
8
3g
3h
Table 5
Ground and Excited-state dipole moment values of 3(a–h).
Theoretical Ground
Excited State Dipole moment μe (D) according to
State Dipole Moment
˚
sample Radius (A)
Ground State Dipole
Kawski-Chamma- Solvatochromic
μg (in D)
Moment μg (in D)
Lippert
Bakhshiev
Viallet
method
Solvent Polarity Parameter
3a
3b
3c
3d
3e
3f
4.67
4.69
4.27
4.39
4.19
4.10
4.24
4.40
5.95
8.69
4.70
5.73
4.55
7.74
6.60
5.64
3.97
14.16
2.84
4.65
1.69
4.99
5.15
3.79
9.55
16.97
5.88
9.39
7.93
9.58
9.35
7.65
7.21
15.78
4.64
7.55
4.42
7.67
7.56
5.96
7.21
15.78
4.64
7.55
4.42
7.67
7.56
5.96
7.21
15.78
4.64
7.55
4.42
7.66
7.56
5.96
7.14
18.16
4.29
6.58
6.89
7.29
7.37
5.53
3g
3h
is determined from the following equation.
ꢀ
ꢁ
1/2
ꢆ
hca30
ꢂ
ꢃ
ꢂ
ꢃ
1
S2
S3
S1 + S2
cosθ =
μ2g + μ2e
−
μ2e − μ2g
(13)
μe =
(11)
(12)
2μgμe
2
2S1
The angle between ground and excited state dipole moments is
calculated according to Eq. (13) and the results are presented in
Table 6.
μe
=
S1 + S2
S2 − S1
; S > S1
(
)
2
μg
The parameters S, S1andS2 occurring in (1) (3) and (f) for
the difference υa − υf and the sum υa + υf of the wavenumbers,
which are linear functions of the solvent polarity parameters F(ε,
n), F1(ε, n)and F2(ε, n), can be determined from the slopes of the
straight lines. With this method we use the extrapolation tech-
nique of the linear fit to the experimental data corresponding to
the gaseous phase. In this way we obtain dipole moments of an
isolated molecule, free from solvents. The problem of determina-
tion of authentic dipole moments from solvatochromic shifts based
on the theories of different authors [35–37] has been discussed
Using the slopes S1 and S2, the values of μg, μe, and their ra-
tio μe/μg were calculated according to Eqs. (10)–(12) and the re-
sults are given in Tables 5 and 6. Further, by substituting the value
of μg calculated from Eq. (10), the excited state dipole moment
(μe) is calculated according to Lippert’s, Bakhshiev’s, and Kawski-
Chamma-Viallet’s method i.e. from Eqs. (7), (8) & (9) respectively,
and the results are presented in Table 5.
If the angle between ground and excited state dipole moments
are not parallel, then the angle θ between the two dipole moments
8

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Table 6
Change in dipole moment, ratio, and angle between μe & μg.
The ratio of Excited & Ground
Change in Dipole moment (ꢀμ) (D) from
state dipole moment
Angle between μg & μe
θ in Degree
Molecule
Solvatochromic Method
Solvent Polarity Parameter
μe/μg
3a
3b
3c
3d
3e
3f
3.24
1.62
1.80
2.90
2.73
2.68
2.42
2.17
3.17
4.45
1.45
1.93
2.18
2.31
2.22
1.74
1.82
1.11
1.69
1.62
2.61
1.54
1.47
1.57
0
0
0
0
0
0
0
0
3g
3h
in detail in [39]. It should be stressed that the short-range spe-
cific interactions between the solute and the solvent molecules,
as hydrogen bonding, the tendency of polar solvent molecules to
form aggregate of two or more molecules (alcohols) are not taken
into account in the mentioned theories. Having this in mind one
has to select appropriate solvents which should possess moderate
electric permittivity ε. Moreover, anisotropic solvent media such
as nematic liquid crystals [39] cannot be used to determine the
real dipole moment both in the ground and excited state based
on the mentioned theories. However, the change in ε and n in
an aprotic solvent can be obtained by increasing temperature T
in a high-pressure cell (thermochromic method) provided that the
solute does not undergo any kind of a chemical change. In this
way, the values of ε and n can be changed continually, which sup-
ports the analysis of the absorption and fluorescence shift observed
[40,41].
change in dipole moment (ꢀμ) for both the molecules were calcu-
lated using Eq. (16) and the results are presented in Tables 5 and
6.
The ground state dipole moment of 3b is higher as compared
to other molecules (Table 5) and it may be due to the substitu-
tion tertiary amine at the 7 position of 3,3’- Carbonylbiscoumarin
electronegativity difference between oxygen and carbon atoms. The
introduction of an electronegative atom decreases the bond length
and increases polarizability, which may lead to the increase in the
dipole moment of the 3b molecule [43,44]. It is also observed from
Table 5 that, the excited state dipole moment (μe) for molecule
3c is less than the other molecule. The decrease of excited-state
dipole moment (μe) for molecule 3c may suggest different geom-
etry for the singlet excited state than the remaining molecules, in-
dicating a significant difference in the charge distribution.
As it is evident from Table 5, the excited state dipole moment
(μe) determined by using Bakhshiev’s, KawskiChamma-Viallet’s,
and solvatochromic equations were found to be in good agree-
ment with each other. The higher values of excited-state dipole
moment (μe) observed in the case of Lippert’s method compared
to other methods may be due to the non-accountability of polar-
izability. However, μe calculated by using solvent polarity parame-
ter ETN (Eq. (16)) is found to be smaller than μe determined from
Bakhshiev’s, Kawski-Chamma-Viallet’s, and solvatochromic meth-
ods. This may be due to the reason that these methods do not
take into account specific solute-solvent interactions like hydrogen
bonding, complex formation, and molecular aspects of solvation,
whereas they are incorporated in the solvent polarity parameter
[44].
3.3. Change in dipole moment (ꢀμ) and excited state dipole moment
N
(μe) by solvent polarity parameter (ET
)
This method is based on solvent polarity parameter (ETN ) to es-
timate the change in dipole moment (ꢀμ) proposed by Reichardt
[45] and developed by Ravi et al. [46]. In this method, the problem
associated with the estimation of Onsager cavity radius has been
minimized.
The expression for Stoke’s shift according to Reichardt and Ravi
et al. is,
ꢄ
ꢅ
ꢇ
ꢈ
2
ꢉ
ꢊ
3
ꢀμ
ꢀμB
aB
a
υa − υ f = 11307.6
ETN + const
(14)
The μe values are found to be higher than μg values for all
the molecules (Table 5). The higher values of μe indicate that
the probe molecules are more polar in the excited state than
the ground state. The angle between the ground and excited-state
dipole moment for both the molecules are found to be zero de-
grees (Table 6) which suggests that, μg and μe are parallel to each
other and the molecular symmetry remains the same upon elec-
tronic transition [42]. Further, it is observed that the change in
dipole moment (ꢀμ) value is found to be higher. The higher val-
ues of ꢀμ may indicate the existence of a more relaxed excited
state and which may be due to ICT. The possible intramolecular
charge transfer may be attributed to the resonance structures of
3a molecules as shown in Fig. 4 and the remaining molecule reso-
nance structures are shown in Figs.S23-S30.
˚
where ꢀμB (= 9D) and aB (= 6.2 A) is the change in dipole mo-
ment on excitation and Onsager cavity radius of reference betaine
dye molecule and ꢀμ and ‘a’ are the change in dipole moment
and molecular radius of the molecule under investigation.
The change in dipole moment (ꢀμ) is determined from the fol-
lowing equation.
ꢋ
m × 81
ꢀμ = μe − μg =
(15)
ꢂ
ꢃ
311307.6
6.2
ao
Where m is the slope obtained from the linear plot of Stoke’s
shift versus (ETN ).
Then by using Eq. (15) and knowing the value of μg (From Eq.
(10)), the excited state dipole moment is determined from the fol-
lowing equation.
3.4. Computational analysis
μe = ꢀμ + μg
(16)
The absorption and emission spectra of all molecules in differ-
ent solvents were computed by using Gaussian 09W to compare
with the experimental results. For this purpose, the molecule is
optimized for the ground and excited state using DFT and TD-DFT
with the basis sets B3LYP/3-211G combined with integral equa-
The relevant plots of Stoke’s shift vs. (ETN ) required for the de-
termination of change in dipole moment (ꢀμ) for all the probe
molecules are shown in Fig. 3. Using the slopes calculated from
Stoke’s shift versus ETN, the excited state dipole moment (μe) and
9

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
O
Fig. 4. Possible resonance structures of 3a.
Table 7
Theoretical ground state dipole moment (μg) of 3(a-h) in different solvents.
Solvent
3a
3b
3c
3d
3e
3f
3g
3h
in D
in D
in D
in D
in D
in D
in D
in D
Toluene
7.18
8.25
8.40
8.50
8.77
8.82
8.93
8.95
8.97
10.44
12.07
13.48
12.51
12.96
13.01
13.23
13.24
14.53
5.61
6.31
6.43
6.51
6.74
6.76
6.87
6.88
6.91
6.57
7.12
7.20
7.27
7.44
7.46
7.57
7.58
7.62
5.50
6.30
6.40
6.48
6.70
6.72
6.83
6.84
6.87
9.32
8.00
8.98
9.14
9.26
9.59
9.69
9.82
9.86
9.87
6.48
6.66
6.78
6.97
7.12
7.23
7.32
739
Ethyl Acetate
Tetrahydrofuran
Dichloromethane
Butanol
10.97
12.36
11.12
12.34
13.45
11.71
13.69
11.76
Prpoane-2-ol
Acetonitrile
DMF
DMSO
7.44
tion formalism variant-Polarizable Continuum Model (IEFPCM) sol-
vation model.
more polar in the excited state than the ground state. It is interest-
ing to note that the computational studies also reproduce a similar
trend as observed experimentally. However, the theoretically com-
puted ground- and excited-state dipole moments were found to be
higher than the experimental dipole moments [47].
The ground-state dipole moment of the probe molecule in the
gaseous state is also estimated theoretically by using DFT with ba-
sis sets B3LYP/3-11G and the result is presented in Table 5. The
optimized molecular geometry of all molecules along with the di-
rection of dipole moment is shown in Fig. 5.
The 3D plots of HOMO and LUMO of synthesized fluorescent
dye are shown in Fig. 6. The HOMO, LUMO energies, and HOMO-
LUMO energy bandgap (ꢀE) values for the probe molecule are
It is observed from Tables 5 and 6 that the theoretically com-
puted μg value is higher than the experimental μg value. It is
to be noted that the experimental methods take solvent and en-
vironmental effects like solute-solvent interactions into account,
whereas the ab initio computations are based on the gaseous
phase [37–38]. Further, to analyze the solute-solvent interactions,
the ground dipole moments are estimated theoretically for all the
studied solvents by using the IEF-PCM solvation model and the re-
sults are given in Table 7. and it is noticed that the ground-state
dipole moment values for each of the solvents are found to be
higher than the ground-state dipole moment value of the probe
molecule in the gaseous phase. The increase in the dipole mo-
ment value is due to the consideration of environmental effects
like solute-solvent interactions in the IEF-PCM solvation model.
Further, the excited-state dipole moment values were found to be
higher than the corresponding ground-state dipole moment values
for all the solvents and this suggests that the probe molecule is
presented in Tables S9–S16. The optical band gap Eopt is deter-
g
mined from the absorption threshold wavelength for all molecules
in different solvents and the result is tabulated in Tables S9–S16.
It is observed that the HOMO-LUMO energy bandgap is in order
with the experimental optical energy bandgap. The lower values of
the energy gap for the probe molecule also support the observed
higher values of excited-state dipole moments. The determination
of HOMO-LUMO energies also helps in understanding the chemical
stability of a molecule in terms of a parameter known as chem-
ical hardness (η). The molecules possessing a large HOMO-LUMO
energy gap are considered as hard, whereas molecules possess-
ing small HOMO-LUMO energy gaps are considered soft molecules
[38,42]. The chemical hardness (η) of a molecule [44] is deter-
mined from Eq. (17).
EL − EH
η =
(17)
2
10

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 5. Ground-state optimized molecular geometries of fluorescent dyes. The arrow mark indicates the direction of dipole moment.
11

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 6. 3D plots of HOMO-LUMO with energy levels.
12

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
Fig. 7. Molecular electrostatic potential (MESP) plots. (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this
article.)
13

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
where EH and EL are the HOMO and LUMO energies
Lohit Naik reports financial support, administrative support, and
statistical analysis were provided by Hirasugar Institute of tech-
nology, Belgaum,. Shashashikant Walki reports a relationship with
Hirasugar Institute of technology, Belgaum that includes: employ-
ment. Shashikant Walki has patent NIl pending to nil.
The chemical hardness (η) is estimated for all fluorescent dyes
and is given in Tables S9–S16. The small values of chemical hard-
ness (η) and HOMO-LUMO energy gaps suggest that the molecule
may be considered as a soft molecule [44]. These results also sup-
port the observed higher values of μe.
CRediT authorship contribution statement
The molecular electrostatic potential (MESP) plots provide the
information for determining a suitable position for nucleophilic
and electrophilic attacks along with the hydrogen bonding interac-
tions of solvent. The MESP 3D plot of the fluorescent dyes is shown
in Fig. 7. In this plot, different colors correspond to different values
of the electrostatic potential at the surface. The red color repre-
sents the negative phase, which can be related to the electrophilic
site, and the blue color represents the positive phase, which cor-
responds to the nucleophilic site. From Fig. 7, it is observed that
the MESP plot of all molecules shows negative phases around 2-
oxo-2H-pyran-3-carbaldehyde whereas positive phases around all
hydrogen atoms.
Shashikant Walki: Conceptualization, Data curation, Formal
analysis, Investigation, Methodology, Resources, Software. G.H.
Malimath: Conceptualization. K.M. Mahadevan: Conceptualization,
Data curation, Formal analysis, Investigation, Methodology, Re-
sources, Software, Supervision, Validation, Visualization, Writing –
original draft, Writing – review & editing. Soniya Naik: Data cu-
ration, Methodology. Suraj M. Sutar: Conceptualization, Data cura-
tion, Formal analysis. Hemantkumar Savanur: Writing – review &
editing. Lohit Naik: Conceptualization, Data curation, Formal anal-
ysis, Investigation, Methodology, Resources, Software, Supervision,
Validation, Visualization, Writing – original draft, Writing – review
& editing.
4. Conclusions
Acknowledgment
ꢀ
In the present studies, we have synthesized a library of 3,3 -
Carbonylbiscoumarin derivatives via a one-pot chemical reaction.
To investigate the solvatochromic behavior and dipole moments,
the absorption and fluorescence spectra of the fluorescent dyes
were recorded in different solvents. The ground state dipole mo-
ments for fluorescent dyes are estimated theoretical and exper-
imental methods. The result shows that the theoretical ground
state dipole moments (μg) values are higher than the experi-
mental ground state dipole moments values. Further, the ground
state dipole moments of the probe molecules in different sol-
vents are also estimated theoretically by using the IEF-PCM sol-
vation model. By using Lippert’s, Bakhshiev’s, Kawski-Chamma-
Viallet’s, and solvent polarity parameter equation, the excited state
dipole moments are determined. It is observed that the excited
state dipole moments (μe) determined from Bakhshiev’s, Kawski-
Chamma-Viallet’s, solvatochromic equations are found to be in
good agreement with each other. Further, the excited state dipole
moments determined from all the methods are found to be higher
than the ground state dipole moments for all molecules under in-
vestigation and this suggests that the fluorescent dyes are more
polar in the excited state than in the ground state. It is observed
that the angle between μg and μe all molecules are found to be
zero degrees, which suggests that, μg and μe is parallel to each
other and there is no change in the symmetry upon electronic
transition. The changes in dipole moment (ꢀμ) values are found
to be higher for all the molecules, which may indicate the exis-
tence of a more relaxed excited state. The HOMO-LUMO energy
band gaps determined from DFT computations and also from opti-
cal energy band gaps using absorption threshold wavelengths are
found to be in good agreement. Using HOMO-LUMO energies, the
chemical hardness of the molecules is studied and the results sug-
gest that all the molecules exhibit a soft nature. The computational
studies performed using DFT calculations imply that the fluores-
cent dyes exhibit both nucleophilic and electrophilic sites. These
preliminary observations and results suggest that the fluorescent
dyes may be considered as potential and interesting candidates for
luminescence materials, fluorescent probes, and dye-sensitized so-
lar cell materials in the future.
Dr. K. M. Mahadevan thankful to the department of science and
technology, ministry of science and Technology, India for provid-
ing finical supports. The authors are thankful to the authorities of
USIC, Karnatak University, Dharwad, for providing the instrumental
facility for our research work. One of the author Shashikant walki
is thankful to the principal, Hirasugar Institute of technology, Bel-
gaum, for their continuous support and encouragement.
Supplementary materials
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.130781.
References
[1] S. Stanchev, G. Momekov, F. Jensen, I. Manolov, Synthesis computational study
and cytotoxic activity of new 4-hydroxycoumarin derivatives, Eur. J. Med.
Chem. 20 (2007) 1–13.
[2] I. Kostava, I. Manolov, I. Nicolova, S. Konstantonov, M. Karaivanova, New lan-
thanide complexes of 4-methyl-7-hydroxycoumarin and their pharmacological
activity, Eur. J. Med. Chem. 36 (2001) 339–347.
[3] Z.H. Chohan, A.U. Shaikh, A. Rauf, C. Supuran, Antibacterial, antifungal and
cytotoxic properties of novel N-substituted sulfonamides from 4-hydroxy-
coumarin, J. Enzym. Inhib. Med. Chem. 21 (2006) 741–748.
[4] J.W. Hinman, H. Hoeksema, E.L. Caron, W.G. Jackson, The partial structure of
novobiocin (streptonivicin), J. Am. Chem. Soc. 78 (1956) 1072–1074.
[5] J.H. Lee, H.B. Bang, S.Y. Han, J.G. Jun, An efficient synthesis of (+)-decursinol
from umbelliferone, Tetrahedron Lett. 48 (16) (2007) 2889–2892.
[6] H. Zhao, N. Neamati, H. Hang, A. Mazumder, S. wang, S. Sunder, G.W. Milne,
Y. Pommier, Coumarin-based inhibitors of HIV integrate, J. Med. Chem. 40 (2)
(1997) 242–249.
[7] R.S. Manian, J. Jayashankaran, R. Raghunathan, A rapid access o indolo [2,1-a]
ꢀ
ꢀ
pyrrolo [4 ,3 : 4,5] pyrano [5,6-c] coumarin / [6,5-c] chromone derivatives by
domino knoe- venagal intramolecular hetero Diels-Alder reactions, Tetrahe-
dron Lett. 48 (8) (2007) 1385–1389.
[8] M.M. Asimov, V.M. Nikitchenko, A.I. Novikov, A.N. Rubinov, New high-effi-
ciency biscoumarin laser dyes, Chem. Phys. Lett. 149 (1988) 140–144.
[9] M.R. Padhye, S. Varadarajan, A.V. Deshpande, Biscoumarins -new laser dyes in
coumarin series, Spectrosc. Lett. 17 (1984) 369–376.
[10] A. Khatyr, H. Maas, G. Calzaferri, Synthesis of new molecules containing head,
spacer, and label moieties, J. Org. Chem. 67 (19) (2002) 6705–6710.
[11] J.P. Chen, P.S. Horns, B.R. Hsieh, Fluorescent bis-coumarins for organic light-
emitting devices, Patent no. US 2003164499; 2003.
[12] A. Chandrasekhar, S Padmanabhan, S Seshadri, Synthesis of biscoumarins and
biscoumarinyl ketones, Dyes Pigments 7 (1986) 13–21.
[13] H. Tuncer, C. Erk, The synthesis of chromophore ended glycoles, part IV.
bis-coumarin derivatives ended polyglycols, J. Heterocycl. Chem. 43 (2006)
1135–1139.
Declaration of Competing Interest
[14] N.O. Mahmoodi, F. Ghanbari-Pirbasti, Z. Jalalifard, Recent advances in the syn-
thesis of biscoumarin derivatives, J. Chin. Chem. Soc. 65 (2018) 383–394.
[15] J. Khurana, S. Kumar, Ionic liquid: an efficient and recyclable medium for the
synthesis of octahydroquinazolinone and biscoumarin derivatives, Monatshefte
für Chem. Chem. Mon. 141 (2010) 561–564.
The authors declare the following financial interests/personal
relationships which may be considered as potential competing in-
terests:
14

S. Walki, G.H. Malimath, K.M. Mahadevan et al.
Journal of Molecular Structure 1243 (2021) 130781
[16] H. Mehrabi, H. Abusaidi, Synthesis of biscoumarin and 3,4-dihydropyrano
[c]chromene derivatives catalysed by sodium dodecyl sulfate (SDS) in neat wa-
ter, J. Iran. Chem. Soc. 7 (2010) 890–894.
[32] J. Li, C.W. Lv, X.J. Li, D. Qu, Z. Hou, M. Jia, X.X. Luo, X. Li, M.K. Li, Synthesis of
biscoumarin and dihydropyran derivatives and evaluation of their antibacterial
activity, Molecules 20 (2015) 17469–17482.
[17] W. Li, Y. Wang, Z. Wang, L. Dai, Y. Wang, Novel SO3H-functionalized ionic liq-
uids based on benzimidazolium cation: efficient and recyclable catalysts for
one-pot synthesis of biscoumarin derivatives, Catal. Lett. 141 (2011) 1651–1658.
[18] R. Rezaei, M. Fatemeh, M.M. Doroodmand, Propane-1,2,3-triyl ris(hydrogen sul-
fate): a mild and efficient recyclable catalyst for the synthesis of biscoumarin
derivatives in water and solvent-free conditions, Chin. Chem. Lett. 25 (2014)
183–186.
[19] M.A. Zolfigol, A.R. Moosavi-Zare, M. Zarei, Friedel-crafts alkylation of 4-hydrox-
ycoumarin catalyzed by sulfonic-acid-functionalized pyridinium chloride as a
new ionic liquid, C. R. Chim. 17 (2014) 1264–1267.
[33] M.V.R. Reddy, E.P. Reddy, 3-Acyl coumarins, thiochromones and quinolones and
therapeutic uses, here of field of invention, PCT Patent no:WO 2006132947
[34] D. Huang, J. Sun, L. Ma, C. Zhang, J. Zhao, Preparation of ketocoumarins as
heavy atom-free triplet photosensitizers for triplet-triplet annihilation upcon-
version, RSC Photochem. Photobiol. Sci. 12 (2013) 872–882.
[35] E. Lippert, Speksre &opiSohe b&hnmmg dee Dipolmomentes ammatiseber
Verbindqen im ersten amregten SingdeMzmstand, Z. für Elektrochem. 61
(1957) 962–975.
[36] N.G. Bakhshiev, Universal intermolecular interactions and their effect on the
position of the electronic spectra of molecules in 2-component solutions, Opt.
Spectrosc. 16 (1964) 821–832.
[20] A.R. Kiasat, L. Hemat-Alian, Phospho sulfonic acid:
a versatile and effi-
cient solid acid catalyst for facile synthesis of bis-(4- hydroxycoumarin-3-yl)
methanes under solvent-free conditions, Res. Chem. Intermed. 41 (2015)
873–880.
[37] A. Kawski, On the estimation of excited state dipole moments from solva-
tochromic shifts of absorption and fluorescence spectra, Z. Naturforsch. 57A
(2002) 255–262.
[21] M. Sedighi, N. Montazeri, Synthesis of biscoumarin derivatives as biological
compounds using cellulose sulfonic acid, Adv. Stud. Biol. 7 (2015) 89–95.
[22] F. Shirini, M. Abedini, S. Zamani, H.F. Moafi, Introduction of W-doped ZnO
nanocomposite as a new and efficient nanocatalyst for the synthesis of bis-
coumarins in water, J. Nanostruct. Chem. 5 (2015) 123–130.
[38] J.T. Edward, Molecular volumes and the Stokes-Einstein equation, J. Chem.
Educ. 47 (1970) 261–270.
[39] M.S. Zakerhamidi, M. Ghanadzadeh, A.M. Tajalli, Anisotropic and isotropic sol-
vent effects on the dipole moment and photophysical properties of rhodamine
dyes, Spectrochim. Acta Part A 77 (2010) 767–777.
•
[23] S. Zahiri, M. Mokhtary, Bi(NO3)3 5H2O: an efficient catalyst for one-pot syn-
[40] I. Gryczynski, A.Z. Kawski, Temperatura bhängigkeit der statischen Dielek-
trizitätskonstante und des optischen Brechungsindexes von Flüssigkeiten, Z.
Naturforsch. A 30a (1975) 287.
thesis of 3-((aryl)(diethylamino)methyl)-4-hydroxy-2H-chromen-2-ones and
biscoumarin derivatives, J. Aibah Univ. Sci. 9 (2015) 89–94.
[24] A. Zhu, S. Bai, L. Li, M. Wang, J. Wang, Choline hydroxide: an efficient and bio-
compatible basic catalyst for the synthesis of biscoumarins under mild condi-
tions, Catal. Lett. 145 (2015) 1089–1093.
[41] A. Kawski, B. Kuklinski, P. Bojarski, Thermochromic shifts of absorption and
fluorescence spectra and excited state dipole moment of PRODAN, Z. Natur-
forsch. 55a (2000) 550.
[25] B. Maleki, Green synthesis of bis-Coumarin and Dihydropyrano
[3,2-c]chromene Derivatives Catalyzed by o- Benzenedisulfonimide, Org.
Prep. Proced. Int. 48 (2016) 303–318.
[42] L. Naik, C.V. Maridevarmath, I.A.M. Khazi, G.H. Malimath, Photophysical
and computational studies on optoelectronically active thiophene substituted
1,3,4-oxadiazole derivatives, J. Photochem. Photobiol.
200–209.
A Chem. 368 (2019)
[26] F. Shirini, A. Fallah-Shojaei, L. Samavi, M. Abedini,
A clean synthesis of
bis(indolyl)methane and biscoumarin derivatives using P4VPy–CuO nanoparti-
cles as a new efficient and heterogeneous polymeric catalyst, RSC Adv. 6 (2016)
48469–48478.
[43] C.V. Maridevarmath, L. Naik, G.H. Malimath, Synthesis, photophysical, DFT
and solvent effect studies on biologically active benzofuran derivative:
(5-methyl-benzofuran-3-yl)-acetic acid hydrazide, Chem. Data Collect. 21
(2019) 100221.
[27] M. Seddighi, F. Shirini, M. Mamaghani, Sulfonated rice husk ash (RHA-SO3H)
as a highly efficient and reusable catalyst for the synthesis of some bis-hete-
rocyclic compounds, RSC Adv. 3 (2013) 24046–24053.
[28] K. Niknam, A. Jamali, Silica-bonded N-propylpiperazine sodium n-Propionate
as recyclable basic catalyst for synthesis of 3,4-Dihydropyrano [c]chromene
derivatives and biscoumarins, Chin. J. Catal. 33 (2012) 1840–1849.
[29] H.O. Foroughi, A. Khalafi-Nezhad, Synthesis of Bis-4-hydroxycoumarins via a
multi component reaction using silica boron- sulfuric acid nanoparticles (SB-
[44] C.V. Maridevarmath, L. Naik, G.H. Malimath, Synthesis characterization and
photophysical studies on novel benzofuran-3-acetic acid hydrazide derivatives
by solvatochromic and computational methods, J. Mol. Struct. 1188 (15) (2019)
142–152.
[45] C. Reichardt, Solvatochromic dyes as solvent polarity indicators, Chem. Rev. 94
(8) (1994) 2319–2358.
[46] M. Ravi, T. Soujanya, A. Samanta, T.P. Radhakrishnan, Excited state dipole mo-
ments of some coumarin dyes from a solvatochromic method using the solvent
polarity parameter, J. Chem. Soc. Faraday Trans. 91 (1995) 2739–2742.
[47] M.B. Smith, J. March, March’s Advanced Organic Chemistry: Reactions, Mecha-
nisms and Structure, 6th Ed., Wiley, New York, 2012.
SANs) as an efficient heterogeneous solid acid catalyst, Org. Chem. Res.
(2016) 148–161.
2
[30] K.P. Boroujeni, P. Ghasemi, Synthesis and application of a novel strong and sta-
ble supported ionic liquid catalyst with both Lewis and Bronsted acid sites,
Catal. Commun. 37 (2013) 50–54.
[48] D.P. Specht, P.A. Martic, S. Farid, A new class of triplet sensitizers, Tetrahedron
38 (9) (1982) 1203–1211.
[31] A. Tzani, A. Douka, A. Papadopoulos, E.A. Pavlatou, E. Voutsas, A. Detsi, Syn-
thesis of biscoumarins using recyclable and biodegradable task-specific ionic
liquids, ACS Sustain. Chem. Eng. 1 (2013) 1180–1185.
15