Effect of organic solvents on solvatochromic, fluorescence, and electrochemical properties of synthesized thiazolylcoumarin derivatives

Article abstract of DOI:10.1002/bio.4044

In this present investigation, thiazolylcoumarin derivatives (5a–5k) were synthesized from thiosemicarbazide, ethyl acetoacetate, and naphthaldehyde through a multistep route. The formation of thiazolylcoumarin derivatives with bioactive scaffolds was con

Full text of DOI:10.1002/bio.4044

Received: 5 June 2020
DOI: 10.1002/bio.4044
Revised: 5 February 2021
Accepted: 16 March 2021
R E S E A R C H A R T I C L E
Effect of organic solvents on solvatochromic, fluorescence, and
electrochemical properties of synthesized thiazolylcoumarin
derivatives
1
2
3
4
Ali Bahadur | Shahid Iqbal
| Rabail Ujan | Pervaiz Ali Channar
|
5
4
6
Murefah Mana AL-Anazy | Aamer Saeed | Qaiser Mahmood
|
4
7
4
4
Muhammad Shoaib | Mazloom Shah | Ifzan Arshad | Ghulam Shabir
|
4
2
8
Muhammad Saifullah | Guocong Liu | Muhammad Abdul Qayyum
1
Department of Transdisciplinary Studies, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, South Korea
School of Chemistry and Materials Engineering, Huizhou University, Huizhou, Guangdong, China
Dr. M. A. Kazi Institute of Chemistry, University of Sindh, Jamshoro, Pakistan
2
3
4
5
6
7
8
Department of Chemistry, Quaid-i-Azam University, Islamabad, Pakistan
Department of Chemistry, College of Science, Princess Nourah bint Abdulrahman University, Riyadh, Saudi Arabia
Institute of Chemistry, Chinese Academy of Sciences, Beijing, China
Department of chemistry, Abbottabad University of Science and Technology, Abbottabad, Pakistan
Department of Chemistry Division of Science and Technology University of Education Lahore, Pakistan
Correspondence
Abstract
Shahid Iqbal and Guocong Liu, School of
Chemistry and Materials Engineering, Huizhou
University, Huizhou 516007, Guangdong
China.
In this present investigation, thiazolylcoumarin derivatives (5a–5k) were synthesized
from thiosemicarbazide, ethyl acetoacetate, and naphthaldehyde through a multistep
route. The formation of thiazolylcoumarin derivatives with bioactive scaffolds was
confirmed through nuclear magnetic resonance spectroscopy. A solvatochromic study
of synthesized thiazolylcoumarin derivatives was carried out using ultraviolet–visible
methods for dimethylformamide (DMF), ethyl acetate, and ethanol solvents. The
redox behaviour of as-synthesized thiazolylcoumarin derivatives (5a–5k) was
examined in dimethyl sulphoxide by conducting an electrochemical study. Fluores-
cence properties of thiazolylcoumarin derivatives were studied in DMF, ethanol, and
ethyl acetate to visualize the solvent effect on the emitting ability of
thiazolylcoumarin derivatives.
Email: shahidiqbal@hzu.edu.cn;
gcl_109@163.com
Aamer Saeed, Department of Chemistry,
Quaid-i-Azam University, 45320 Islamabad,
Pakistan.
Email: aamersaeedqau@gmail.com
Murefah Mana AL-Anazy, Department of
Chemistry, College of Science, Princess
Nourah bint Abdulrahman University, 11671,
Riyadh, Saudi Arabia.
Email: mmalanazy@pnu.edu.sa
K E Y W O R D S
fluorescence, solvatochromic study, solvent effect, thiazolylcoumarin derivatives,
thiosemicarbazide
*Ali Bahadur and Shahid Iqbal contributed equally to this study.
Luminescence. 2021;1–9.
wileyonlinelibrary.com/journal/bio
© 2021 John Wiley & Sons Ltd.
1

2
BAHADUR ET AL.
1
|
INTRODUCTION
2.2
|
Preparation of starting compounds
| Preparation of 2-acetyl-3H-benzo[f]
Biologically active heterocyclic compounds, especially coumarin deriv-
2.2.1
chromen-3-one (1)
[1–5]
atives, have potential application in the medical field.
Coumarins
are naturally occurring heterocycles as well as secondary metabo-
[
3,6–8]
lites.
Many other publications are available describing coumarin
Briefly, for the synthesis of 2-acetyl-3H-benzo[f]chromen-3-one
(1), ethylacetoacetate (100 mmol, 12.64 ml) and 2-hydroxy-1-1
naphthaldehyde (100 mmol) were mixed in piperidine (1 g, 1.12 ml) at
and its derivatives that show that these compounds are highly
[
9–13]
bioactive in nature.
Thiazoles are widely used in diverse
ꢀ
chemical reactions as parent nuclei and as intermediates, as well as
0 C and stirred for 0.5 h. The resulting 2-acetyl-3H-benzo[f]chromen-
substituents. Thiazoles heterocycles are also used to synthesize
3-one (1) product was washed several times with ethanol and crystal-
[14–18]
various thiazolyl coumarin derivatives.
2
lized in H O to obtain the pure product (1) (Figure 1).
Regarding thiazole-based coumarinyl scaffold bioactivity (after
surveying other publications), coumarin derivatives such as thiazole and
azetidine exhibit antibacterial, insecticidal, antifungal, antiproliferative,
antioxidant, antitubercular, anti-inflammatory, and anticancer proper-
2.2.2
|
Preparation of 2-(2-bromoacetyl)-3H-benzo
[f]chromen-3-one (2)
[19–24]
ties.
Therefore, these derivatives are very important in the fields
of agriculture, organic chemistry, and medicine for the synthesis of
3 2
Product (1) of the previous step was dissolved in CHCl and Br
[25–27]
fungicides, dyes, and drugs, repectively.
Coumarins have a double
solution (1.72 g, 0.01 mol) was added dropwise. The resulting solution
ꢀ
bond in trans conformation that features in the high fluorescence
was refluxed for 3 h and cooled to 25 C. The final product was
quantum yield, strong fluorescence, and photostability in most of the
3
crystallization in CHCl :ethanol (1:2) to get pure 2-(2-bromoacetyl)-
[
28–33]
coumarin derivatives.
Coumarin derivatives have very good
3H-benzo[f]chromen-3-one (2) (Figure 1).
fluorescence properties and have potential application on a commercial
[34–36]
scale as photoluminescent materials.
Enhanced coumarin derivatives screening biological activity have
made it necessary to study these chemical classes, as these scaffolds
2.2.3
(4a–4k)
|
Synthesis of thiosemicarbazide derivatives
[35,37–39]
have substantial therapeutic capabilities.
From a recent review
of other publications, triazoles and chromenes, heterocyclic derivatives
have been often applied in biotechnology, medicine, and industry. There-
Thiosemicarbazide (0.138 g, 1.0 mM) was dissolved in 25 ml absolute
ethanol and substituted aldehydes (3a–3k) (1.0 mM) along with 1–2
drops of acetic acid were added to the thiosemicarbazide solution.
The mixture was refluxed until the solid crystals of the product were
formed. Solid products were recrystallized in ethanol to produce
thiosemicarbazide derivatives (4a–4k) (Figure 1).
[40–42]
fore, in this study, novel coumarin derivatives were synthesized.
In this present investigation, thiazolylcoumarin derivatives were
synthesized through a multistep route. The effect of different organic
solvents [ethyl acetate, ethanol, and dimethylformamide (DMF)] on
the solvatochromic, electrochemical, and fluorescence properties of
synthesized thiazolylcoumarin derivatives was studied. All synthesized
thiazolylcoumarin derivatives were used effectively as a tool to
visualize electrochemical behaviour and fluorescence phenomena.
The solvatochromic, electrochemical, and fluorescence results of
synthesized thiazolylcoumarin derivatives were highly encouraging.
2.2.4
|
General procedure of thiazolylcoumarin
derivatives (5a–5k) synthesis
Thiazolylcoumarin derivatives (5a–5k) were synthesized by heating a
mixture of 2-(2-bromoacetyl)-3H-benzo[f]chromen-3-one (2) (5 mol),
and 4(a–k) (6.2 mol) in 25 ml of sodium acetate/ethanol. After 5 h, the
solution was cooled to get solid products (Figure 2). As-synthesized
thiazolylcoumarin derivatives (5a–5k) were filtered and crystallized in
ethanol (Table 1). Supplementary data contains complete characteriza-
2
2
|
EXPERIMENTAL
| Materials
.1
[
43]
tion data.
Thiosemicarbazide (CH
3, 99%, Sigma , naphthaldehyde (C10
substituted aromatic aldehydes (3a–3k), sodium acetate (C
8%, Sigma), bromine (Br , 98.5%, Sigma), piperidine (C 11N, 99%,
Sigma), chloroform (CHCl , 99%, Sigma), ethanol (C OH, 99.8%,
Sigma), DMF (C N, 99.8%, Sigma), ethyl acetate (C
9.8%, Sigma), dimethyl sulfoxide (DMSO, 98%, Sigma), and
5
N
3
S, 99%, Sigma), ethyl acetoacetate
CHO, 98%, Sigma),
NaO
(
C
6
10
H O
)
H
7
H
2 3
2
,
2.3
|
Characterizations
9
2
5
H
3
2
H
5
Structures of the thiazolylcoumarin derivatives were determined using
1
H
3 7
4
8
H O
2,
a Bruker DPX 300 NMR spectrometer (300 MHz) with H-NMR and
13
9
C-NMR spectra (Figures S1 and S2). Ultraviolet (UV) light studies
acetic acid (CH
3
COOH, 98%, Sigma) were used to synthesize
were performed using the UV-Genesys spectrophotometer. FTIR
spectra were obtained using a Nicolet IR 100 FTIR spectrometer
thiazolylcoumarin derivatives and used without further purification.

BAHADUR ET AL.
3
FIGURE 1 Synthesis of
thiosemicarbazide derivatives (4a–4k)
FIGURE 2 Synthesis of thiazolylcoumarin derivatives
(
5a–5k)
(
Figure S3). An IME6X electrochemical workstation voltage −1.5 V to
in all the synthesized derivatives. The λmax for 5c and 5h was
392 nm, and might be due to the π–π* transition of bromobenzene
and pyridine rings; this value was the largest for all the prepared
derivatives. Many electrons are need to generate a bathochromic
shift. Sulfur atoms present in the nucleus have less electronegativity
relative to oxygen and, consequently, have a greater ability to pro-
vide electrons, resulting in a larger λmax value. The smallest λmax
value for 5h (340 nm) was due to the existence of the methylene
groups between the aryl group and coumarin motif that produced a
hypsochromic shift. The higher λmax (362–386 nm) for 5e, 5c-g, and
5i,j was due to π–π* transitions of π electrons, and the n–π*
transition of lone pairs of electrons. There was no large difference
in the λmax value for any given compound with change in polarity
1
.5 V was used for cyclic voltammetry. A Fluoromax-4 spectrofluo-
rometer (Horiba Scientific Japan) was used for emission spectra. An
FL-980 Steady-Transient state fluorescence spectrometer (Edinburgh
Instruments, UK) for time-resolved photoluminescence (TRPL)
spectroscopy.
3
3
|
RESULTS AND DISCUSSION
.1
|
Preparation of thiazolylcoumarins derivatives
(
5a–5k)
Thiazolylcoumarins derivatives (5a–5k) were prepared by heating a
mixture of 4(a–k) (6.2 mmol) and 2-(2-bromoacetyl)-3H-benzo[f]
chromen-3-one (2) (5 mmol) in 25 ml of ethanol/sodium acetate. After
heating for 5 h, the solution was cooled to obtain the final products,
thiazolylcoumarin derivatives (5a–5k), which were then cleaned by fil-
of the solvent because the λmax values for thiazolylcoumarin
derivatives do not depend on the nature of the solvents. Our results
suggested that the π–π* transitions were due to B-type bands and
independent of solvent, and therefore no solvatochromism phenom-
enon was detected.
[
43]
tering and crystallization in ethanol.
Absorption bands due to C=N of the imine, and C=O, Ar–H, and
N–H of lactone were observed from FTIR spectra of the
thiazolylcoumarin derivatives (5a–5k). Absorption band values at
3360–3390, 2980–3170, 1730–1755, 1630–1660, 1520–1540,
1415–1450, 1280–1295, 1115–1160, 845–870, and 780–830 cm−
were due to the vibration frequencies of C=C, C=S, and C–O, C=C,
C=S, and C–O. For thiazolylcoumarin 5a, the band values at
3
.2
|
Structural confirmation of thiazolylcoumarin
1
derivatives (5a–5k)
UV spectroscopy, FTIR spectroscopy, and NMR spectroscopy were
used to confirm the structure of the thiazolylcoumarin derivatives
3375 cm− and 3170 cm−1 were due to N–H and =C–H (str.).
1
[44]
A
peak at 1729 cm− revealed the presence of an ester linkage in the
carbonyl of the cyclic esters. Conversely, all thiazolylcoumarin deriva-
tives had similar stretching vibrations peaks for N–H, C=C–H, and
C=O groups. Peaks at 1155 cm−1, 1535, and 860 cm−1 were the
result of C–O stretching, C=C stretching, and C=C stretching vibra-
tions, respectively. These peaks were mainly due to the presence of
1
(
5a–5k). Figure
3
illustrates the UV–vis absorption spectra of
coumarinyl derivatives (5a–5k); the corresponding spectral data are
shown in Table 2. UV–vis spectra of thiazolylcoumarin derivatives
(
5a–5k) showed the highest absorption in the 340–392 nm range
Figure 3a–c). This absorption range may be due to the π–π*
(
transition of electrons in the naphthalene and benzene rings present

4
BAHADUR ET AL.
TABLE 1 As-synthesized thiazolylcoumarin derivatives (5a–5k)
Thiazolylcoumarin derivatives
-R
Yield (%)
5a
5b
5c
85%
83%
78%
5
5
5
d
e
f
78%
75%
73%
5
5
g
h
77%
76%

BAHADUR ET AL.
5
TABLE 1 (Continued)
Thiazolylcoumarin derivatives
-R
Yield (%)
5
i
86%
5
5
j
66%
68%
k
FIGURE 3 UV/vis spectra of
thiazolylcoumarin (5a–5k) derivatives in
(
(
a) ethanol, (b) DMF, and (c) ethyl acetate.
1
d) H-NMR of thiazolylcoumarin
derivative 5a
aromatic rings in 5a–5k, whereas other peaks were the result of other
functional groups and agreed with the reported values for the
structures.
A singlet at 2.3 ppm for 3H on the methyl group substituted in
1
the benzene ring was found using H-NMR spectroscopy for
thiazolylcoumarin 5a. In addition, the N–H substituted heterocyclic

6
BAHADUR ET AL.
TABLE 2
λ
max (nm) of thiazolylcoumarin derivatives (5a–5k)
conjugated. Fluorescence spectra for the thiazolylcoumarin deriva-
tives (5a–5k) were generated in chronological order from a 385 nm
source, as shown in Figure 4(a–c), at different excitation wavelengths.
The fluorescence spectra demonstrated the effect of intensity at spe-
cific wavelengths when varying the excitation wavelengths. All fluo-
rescent dyes exhibited a single emission peak only, but with different
Sr. no.
Ethanol (λmax
)
DMF (λmax
)
Ethyl acetate (λmax)
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
336
353
332
363
392
388
375
379
370
392
389
375
378
351
366
365
381
381
344
emission intensities. The 5h dye displayed the maximum fluorescence
intensity on excitation of the solution at 10−7 to 10−8 M concentra-
381
371
372
360
tions (Figure 4) at 505 nm wavelength. In addition, ethanolic solutions
showed the highest fluorescence intensity, whereas DMF and ethyl
acetate exhibited smaller fluorescence intensities that might be due to
the presence of thiazoles in these solvents that produced a decrease
in fluorescence intensity. This higher fluorescence intensity make
these compounds extremely suitable for bio-labelling and bio-imaging.
g
h
i
369
375
372
376
366
375
j
373
380
k
375
378
and phenyl rings in coumarin displayed a singlet at 12.25 ppm. A
multiplet between 7.80–8.34 ppm was observed due to six aromatic
protons. All thiazolylcoumarin derivatives were distinguished by the
existence of coumarin H-4 at 9.251 ppm. p-Disubstituted benzene
was suggested by a doublet at 7.562 and 7.663 ppm (Figure 3d). Aro-
matic carbons in 5a were confirmed by peaks at 112.1, 114.1, 115.6,
3.4
|
Time-resolved study of thiazolylcoumarins
derivatives (5a–5k)
A radiation emission study was carried out using TRPL spectroscopy.
Absolute ethanol was used as a solvent to prepare thiazolylcoumarin
derivatives (5a–5k) sample solutions for TRPL. This study used the
time-correlated single-photon counting technique (TCSPT). TRPL
measurements were performed at room temperature using a laser
beam (305 nm) as an excitation source with 25 ps of time resolution.
Thiazolylcoumarin derivative decay times have been used as a factor
in TRPL measurements and photoluminescence (PL) decay kinetics is
biexponential. The relative decay time of thiazolylcoumarin deriva-
tives is shown in Figure 4(d). The thiazolylcoumarin derivatives were
1
1
16.9, 120.1, 121.9, 126.5, 128.9, 129.1, 129.5, 129.7, 130.5, 133.2,
13
34.1, 135.8, 136.4, 137.2, 144.8, and 152.7 ppm in C-NMR spec-
tra. Conversely, carbonyl carbon was confirmed at 169.3 ppm, methyl
carbon in the benzene ring at 21.06 ppm, and imine carbon at
1
59.1 ppm. Similarly, other thiazolylcoumarin derivatives 5a–5k were
1
confirmed from their corresponding H-NMR spectra (Figure 3d).
ꢀ
excited with 305 nm laser radiation at 25 C. Zero time values were
3
.3
|
Fluorescence studies
measured after the laser pulse; PL from several decay time gates was
recorded instantly after excitation by the laser pulse. After excitation
of the thiazolylcoumarin derivatives with radiation, the time taken for
the electron–hole pair to recombine was termed the radiative period.
A biexponential decay function was used to fit the experimental data
from the decay profile. These results showed that the excitation
All the thiazolylcoumarin derivatives (5a–5k) demonstrated moderate
fluorescence data, as shown in Table 3. All the prepared derivatives
met the requirements for fluorescence, as the thiazolylcoumarin deriv-
atives had no rotational or vibrational signals and were markedly
TABLE 3 Fluorescence data of
thiazolylcoumarin derivatives (5a–5k) in
λ
Emission (nm)
Stokes’ shift
λ
Exitation
Dye
(nm)
445
445
450
450
450
436
440
460
440
440
443
Ethanol
452
460
464
461
466
455
456
507
459
453
459
DMF
450
490
461
520
510
456
4950
500
495
495
530
Ethyl acetate
451
Ethanol
16
DMF
17
45
25
60
62
19
58
47
60
50
76
Ethyl acetate
ethanol, ethyl acetate, and DMF
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
11
75
18
94
45
22
47
28
64
60
70
530
18
460
15
560
10
490
11
450
14
g
h
i
485
16
496
45
4900
500
15
j
16
k
526
14

BAHADUR ET AL.
7
FIGURE 4 Fluorescence spectra of
thiazolylcoumarin derivatives (5a–5k) in
(
(
a) ethanol, (b) ethyl acetate, and (c) DMF.
d) Combined fitted decays in TRPL plot
of thiazolylcoumarin derivatives (5a–5k)
lifetime decreased to a very limited extent and appeared almost the
same, except for thiazolylcoumarin derivative (5i), which had a rela-
tively long lifetime compared with the other thiazolylcoumarin deriva-
tives. Longer lifetime and a less nonexponential decay for the exciton
PL was due to a reduction in the energy transference rate. Exciton
lifetime was decreased for other thiazolylcoumarin derivatives and the
decay curve was increasingly nonexponential as the detection was
moved to higher energies, possibly due to the creation of additional
discrete energy levels for the depopulation of the excited state.
3
.5
|
Electrochemical study of thiazolylcoumarin
derivatives (5a–5k)
Electrochemical characteristics of thiazolylcoumarin derivatives
(
5a–5k) were investigated using cyclic voltammograms (CV) and a
FIGURE 5 Cyclic voltammogram of thiazolylcoumarin derivatives
5a–5k) in ethanol
(
glassy carbon electrode, and 0.1 M TBAPF in DMF as the electrolyte.
6
The CV (Figure 5) were used to estimate lowest unoccupied molecular
orbital (LUMO) and highest occupied molecular orbital (HOMO)
energy value redox potentials (Table 4).
performance of halogens (as electron donor and acceptor). Con-
versely, the lowest redox potential value was seen for 5i and was due
to sulfur atoms in the thiophene ring that had electron-donating
effects and mutable oxidation states.
3
.5.1
|
Redox potentials (E1/2) of thiazolylcoumarin
derivatives
3
.5.2
|
Bandgap energy (E ) of thiazolylcoumarin
g
Thiazolylcoumarin derivatives 5c and 5d have Br and a chlorophenyl
ring attached to thiazole and had the highest redox potential; 5i has a
thiophene ring on the chromophore and produced the lowest value
derivatives (5a–5k)
To calculate the optical bandgap values, a standard previously reported
procedure was used. Every solid has an energy-band value that is
(
Table 4). The higher redox potential value might be due to the dual

8
BAHADUR ET AL.
TABLE 4 Bandgap energy and LUMO/HOMO energy levels of
thiazolylcoumarin derivatives (5a–5k)
thiazolylcoumarins derivatives (5a–5k) produced strong absorption
in the 370–400 nm range. UV–vis light absorption of these novel
thiazolylcoumarins derivatives (5a–5k) was determined in ethanol,
ethyl acetate, and DMF solvents; the highest value was obtained
for DMF as the polar solvent shifted the π–π* transition wavelength
to a higher value. Thiazolylcoumarins showed a solvatochromic
effect in absorbance and fluorescence. This effect was observed in
different solvents, but with increase in the polarity of the solvents,
a bathochromic shift was observed. The maximum emission and a
higher Stokes’ shift were observed for 5h. Thiazolylcoumarins
LUMO energy levels
1/2 (V)
HOMO energy levels
(V)
Sr. no.
E
LUMO (eV)
−4.07
−3.97
−3.98
−3.99
−3.94
−4.39
−4.20
−3.99
−3.99
−4.86
−5.16
E
g
HOMO (eV)
−7.58
−7.35
−7.23
−7.59
−7.65
−7.83
−7.49
−7.67
−7.29
−8.14
−8.54
5
5
5
5
5
5
5
5
5
5
5
a
b
c
d
e
f
−0.7232
−0.83
3.51
3.38
3.25
3.60
3.71
3.44
3.29
3.68
3.30
3.28
3.35
−0.817
−0.806
−0.465
−0.01
3
derivatives containing CH O– groups had high HOMO energy levels
g
h
i
−0.601
−0.488
−0.807
−0.469
0.361
and the lowest bandgap. The as-synthesized thiazolylcoumarin
derivatives showed a sharp emission in the 430–510 nm range in
fluorescence spectra and UV absorption in the 330–400 nm range.
These high fluorescence properties make the as-synthesized
thiazolylcoumarin derivatives useful for bio-imaging and bio-labelling
applications.
j
k
responsible for its electronic characteristics. The bandgap energy values
for the coumarinyl derivatives are given in Table 4 and ranged from
ACKNOWLEDGEMENTS
Murefah Mana AL-Anazy extends her sincere appreciation to the
Deanship of Scientific Research at Princess Nourah bint
Abdulrahman University through the Fast-track Research Funding
Programme.
3.25 to 3.71 eV. The bandgap energy value was maximum for 5d, 5e,
5h, and lowest for 5c, 5g, and 5j, and was dependent on the precursor
2
used and as well as on the substituents. Br and NO groups involved in
5c and 5f are at m to each other and act as donor and acceptor groups.
When increasing the electron density, energy levels become closer and,
therefore, the bandgap energy value is reduced.
CONFLICT OF INTEREST
There is no conflict of interest.
ORCID
3
.5.3
|
LUMO and HOMO energy levels of
Shahid Iqbal
https://orcid.org/0000-0003-3866-3216
thiazolylcoumarin derivatives (5a–5k)
REFERENCES
To evaluate the LUMO energy related to the vacuum level, redox data
were standardized by a ferricenium/ferrocene pair taking an absolute
energy value of −4.8 eV. Electron-donating groups (EDG) on the
coumarinyl side lowered the LUMO energy, and vice versa; LUMO
energies shown in Table 4 are in the range −4.94 eV to −5.16 eV.
LUMO energy varies through increases in delocalization of electrons
and energy modifications decrease by increasing conjugation, and vice
versa. The lowest LUMO energy was found for 5i, based on chlor-
othiophene, in which sulfur provided electrons and decreased the
LUMO energy. Table 4 illustrates the HOMO energy level values in
the range −7.23 to −8.54 eV for 5a–5k. The pyridine and thiophene
rings attached to chromophores lowered the HOMO energy levels for
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SUPPORTING INFORMATION
Additional supporting information may be found online in the
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How to cite this article: Bahadur A, Iqbal S, Ujan R, et al.
Effect of organic solvents on solvatochromic, fluorescence,
and electrochemical properties of synthesized
thiazolylcoumarin derivatives. Luminescence. 2021;1–9.
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