Electronic Structure, Optical Properties and Quantum Chemical Investigation on Synthesized Coumarin Derivative in Liquid Media for Optoelectronic Devices

Article abstract of DOI:10.1007/s10895-019-02409-w

The newly synthesized 3,3′-((3-bromo-4-methoxyphenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (3-BMH) derivative have been investigated in a selected number of organic solvents having different polarity and refractive index at room temperature. From the

Full text of DOI:10.1007/s10895-019-02409-w

Journal of Fluorescence
https://doi.org/10.1007/s10895-019-02409-w
ORIGINAL ARTICLE
Electronic Structure, Optical Properties and Quantum Chemical
Investigation on Synthesized Coumarin Derivative in Liquid Media
for Optoelectronic Devices
A. G. Pramod1 & C. G. Renuka1 & Y. F. Nadaf2
Received: 21 April 2019 /Accepted: 2 July 2019
#
Springer Science+Business Media, LLC, part of Springer Nature 2019
Abstract
The newly synthesized 3,3′-((3-bromo-4-methoxyphenyl)methylene)bis(4-hydroxy-2H-chromen-2-one) (3-BMH) de-
rivative have been investigated in a selected number of organic solvents having different polarity and refractive
index at room temperature. From the absorption and emission spectra of the synthesized derivative in studied
solvents showed bathochromic shift in both the cases (Uv-vis and emission spectra), the ground state dipole
moment (μg) and excited state dipole moment (μe) were obtained by implementing [Chamma-Kwaski-Villate,
Bakhshiev, Lippert-Mataga, McRay and Suppan] solvatochromic shift techniques depending on solvent polarity
parameters. The larger dipole moment value is observed in the excited state as compared to the ground state
dipole moment and this discrepancy in the dipole moment value is due to polar nature of the molecule. From the
results of both experimental and theoretical energy gap is found to 3.14 eV in average, from this, it can be
concluded that the 3-BMH molecule showed a good agreement with the semiconducting material bandgap so that
the 3-BMH molecule can be used as a potential material for the optoelectronic application. Also, from results of
quantum chemical studies, the electrostatic potential maps studies reveal the molecule is how much stable it
describes the defining reactivity of the molecule towards positively and negatively charged reactants, size, shape,
the location of nucleophilic and electrophilic sites. Further, the optoelectronic properties were investigated the
CIE, CRI, color purity and CCT results of the 3-BMH in all studied solvents revels that this compound exhibits
blue emission (National television standard committee system (NTSC) for the ideal blue chromacity coordinate
0.14, 0.08) and from the CIE results show the color emission of the molecule in order to design the desired
OLED device application.
.
.
.
.
Keywords Hypsochromic Dipole moment Energy gap Potential maps Opto-electronic
Introduction
In view of this, coumarin dyes have received special
substantial attention of the research community because
of their potential role in anticoagulants, HIV inhibitors,
pharmaceutical agents like anti-inflammatory and antiox-
idant agents, also due to long spectral range, enhanced
fluorescence quantum yields, photostability, and good
solubility in the safest solvents [1, 2]. Nevertheless,
for physiological and enzymatic measurements, these
dyes were used as fluorescent labels, pigments and as
fluorescent probes [2]. Further, among coumarin deriva-
tives, dimeric coumarins biscoumarins are the ones
which occupy a fascinating position and these exist nat-
urally in numerous micro-organisms and in plants ex-
tracts [2]. Nonetheless, biscoumarins have drawn good
In the recent past, there is an endless demand for novel
organic molecules, for the high-technology industry,
nonlinear devices and in the field of biological sciences.
* C. G. Renuka
renubub@gmail.com
1
Department of Physics, Jnanabharathi Campus, Bangalore
University, Bengaluru, India
2
Department of Physics and Material Research Centre, Maharani
Science College for Women Bengaluru, Bengaluru, India

J Fluoresc
potential interest in recent years due to their versatile
medical and biological application viz., anticancer, anti-
bacterial, anti-inflammatory and antioxidant agents and
many more [3–5]. In addition, these dyes can strongly
exhibit tubulin aggregation also played an important
role against cancer [6, 7]. Also, it has been reported
that [8], the biscoumarin dyes showed excellent optical
properties [9].
Different methods namely stark splitting, electric-di-
chroism, electronic polarization of fluorescence and
microwave conductivity are available in the literature
for the determination of dipole moments in the excit-
ed-state, but the use of those methods are limited
since those methods are equipment sensitive and also
related to a very simple molecule. Nevertheless, the
solvatochromic method is simpler and accurate com-
pared above mention methods and also it gives a
straight measure of the distribution of electrons in
the molecule, photons causing excitation of electrons
in a molecule resulting the charge distribution takes
place which leads to a conformational change in the
excited state [22–24]. Many of the researchers have
intensively reported for the determination of ground
and excited state dipole moments experimentally and
theoretically, in different types of organic fluorescent
compounds like indoles, purines, thiadiazole Nile red
dyes, phloroglucinol, quinolones, coumarins, excite
dyes, laurdan, badan, benzimidazolone, chalcones
[25–28] etc.
Further, the organic semiconducting materials
(OSCs) have received the potential application in de-
signing of hybrid and organic electronic devices such
as organic field effect transistors (OFETs), organic
light emitting devices (OLEDs), and organic photovol-
taic cells (OPVs) [29, 30]. Therefore, the semiconduct-
ing properties of OSCs and the relationship in-between
molecular and supramolecular structures have become
one of the important findings [31] over the past years
moreover, most of them are concerning the evaluation
of band gap of OSCs. In view of this, the energy gap
(Eg) defines the separation (energy) between the lowest
unoccupied molecular orbital (LUMO) to highest occu-
pied molecular orbital (HOMO) for OSCs which is
analogs to valance band and conduction band in inor-
ganic semiconductors respectively [32, 33]. This
knowledge of the Eg is one of the important parame-
ters in designing organic electronic materials. The di-
pole moment of the molecule will also play a major
role in determining the band gap of the molecule be-
cause of the polarity effect. Since the Eg of the organ-
ic molecule is determined by both theoretically and
experimentally [34, 35]. The quantum chemical inves-
tigation was also performed in order to determine the
chemical reactivity of the molecule in a vacuum and in
acetone solvent.
The effect of solvents should be understood in
depth intending to understand and to determine the
performance of electronic devices in different media.
Their molar absorption coefficient was much larger
than that of monocoumarins, and also their linear ab-
sorption and emission spectra were red-shifted, whilst
their fluorescence quantum yield was high [10, 11].
Therefore, biscoumarin compounds are of great inter-
est in the field of fluorescent dyes. In view of this,
organic compounds consisting of (D-π-A) donor π
acceptor functionality are of great interest for en-
hanced NLO property, high emission yield and of
course several properties of the dye in solution main-
ly depend on the nature of their corresponding sol-
vents environment. The increase of optical response
in organic molecules is not only due to a high level
of π conjugated charge transfer but it is also the in-
crease in the conjugation length which plays an es-
sential determining role in the delocalization of π
electrons under light excitation [11–13].
The specific solute-solvent interactions viz., hydro-
gen bonding, donor-acceptor interactions and/or non-
specific interactions such as polar and Vander Walls
interactions are generally responsible for the solvent-
dependent spectral shifts, knowledge of the impact of
both types of solute-solvent interactions plays a very
substantial role in analyzing the solvent effects [10,
14, 15]. The solute-solvent polarity, as well as the
polarizability, performs a vital role in solute spectral
properties. Effect of the solvent is related closely to
the degree and nature of intermolecular solute-
solvents interactions. Optical absorption and emission
studies reveal that solute-solvent interactions can be
best described from the intensity of the spectrum,
shape, and wavelength. In recent days, the effect of
solvents on excitation and emission characteristics has
become a subject of extensive research [16–18].
Furthermore, the knowledge of excited state dipole
moment of molecule is very much useful in providing
the valuable information in designing nonlinear opti-
cal materials and geometrical and electronic structure
of the molecule in the short-lived excited state, for a
chromophore as a function of polarity of the medium,
the tunability range of emission energy can also be
evaluated using excited-state dipole moment [19–21].
Hence, in the present work involves the systematic
investigation of optical (absorption and emission), di-
pole moment (using solvatochromic method) of synthe-
sized 3-BMH compound dissolved in a suitable sol-
vent. The optical property (band gap) experimentally
and using Gaussian 09 W software theoretically of

J Fluoresc
the molecule, MEP, SAS and TED calculation were
also discussed in this article from the result we can
observe that the obtained band gap is in good agree-
ment with inorganic semiconducting material which
can be used for designing optoelectronic devices. In
this regard we made an attempt in order to develop
an OLED exhibiting property for our molecule for this,
the CIE color coordinates, color purity, CRI, and other
parameters were estimated by using the software.
operating in the range of 200–1100 nm equipped with
a deuterium and halogen lamps with a resolution of
1 nm at room temperature. The fluorescence spectra
were collected at room temperature with the help of
Hitachi F-2000 fluorescence spectrophotometer operat-
ing in the range of 220–800 nm with a resolution of
1 nm having a light source of 150 W Xenon lamp.
The absorption and fluorescence measurements were
repeated for several times and the spectra were consis-
tent at all the times and also the instruments were well
calibrated before the scan. The fluorescence lifetime
was recorded using (TCSPC) Time-Correlated Single
Photon Counting technique (Edinburgh Instruments,
Model: FSP920) along with a Hamamatsu PMT
detector.
Synthesis and Experimental Techniques
Synthetic Route for 3-BMH
The 3-BMH molecule was synthesized by using a mix-
ture of 4-hydroxycoumarin (2 equivalent) and 1-
Bromo-2-methoxybenzene (1 equivalent) taken in a
100 ml round bottom flask to this 10 ml of acetic acid
is added, this mixture was refluxed for 3 h. The prog-
ress of the reaction was monitored by TLC (Eluent:
EtOAc and n-hexane). The evaporation of the solvent
in vacuum afforded the crude product which was re-
crystallized from acetic acid to get 3-BMH in 94%
yield, the reaction scheme of 3-BMH is presented in
Fig. 1.
Computational Method
Density Functional Theory (DFT) measurements were
performed keeping Becke’s 3 Lee-Yang-Parr/6–311(d)
(DFT-B3LYP/6–311(d)) basic set using Gaussian 09 W
program package software [36] the 3-BMH is optimized
(ground state) in vacuum phase. Highest Occupied
Molecular Orbital (HOMO), Lowest Unoccupied
Molecular Orbital (LUMO) plots, energy levels and
HOMO LUMO energy band gaps (Eg), and the electro-
static energy potential maps were also constructed in
studied solvents using DFT-B3LYP/6–311(d) basic set.
The basis set 6-31G(d,p) augmented by‘d’ polarization
function on heavy atom and ‘p’ polarization func-tion
on hydrogen atoms were used for better description of
polarbonds of molecules. It should be emphasized that
‘p’ polar-ization functions on hydrogen atoms useful not
only for reproduc-ing the out-of-plane vibrations involv-
ing hydrogen atoms are butalso for a better description
of the molecular geometry and othernormal vibration
modes.
Solvents
The spectroscopic grade solvents viz., methanol, ace-
tone, cyclohexane, 1,4-dioxane, hexadecane, propanol,
dimethyl sulfoxide, ethyl acetate, and ethanol were pro-
cured from SD Fine chemicals and used without further
purification (the purity of all solvents is of 99.9%). The
samples were prepared using these solvents and the con-
centration of the solution was maintained for about 10−5
to 10−6 mM because of self-aggregation and inner filter
effects.
Characterization of Synthesized 3-BMH Compound
Theoretical Background and Calculations
The linear absorption spectra were recorded using
Perkin Elmer Lambda–35 UV–Vis spectrometer
Despite different assumptions and theories (resulting
in the same expression for Stokes shift) available in
Fig. 1 Reaction scheme for
synthesis of 3-BMH

J Fluoresc
~νaþ~ν f
the literature, we adopted the solvatochromic method
to estimate the ground state (μg) and excited singlet
state (μe) dipole moments because of its simplicity in
arriving the results. And in this method, the
solvatochromic relations have been estimated by
implementing the simplest quantum-mechanical sec-
ond-order perturbation theory and by considering the
Onsager reaction field for a polarizable dipole into
account [37].
equations i.e.,
v/s F1(D, n), ~νa –~νf v/s F2(D, n),
2
~νa –~νf v/s F3(D, n), ~νa v/s F4(D) and ~ν av/s F5(D)
should results in linear graphs with slopes q1, q2, q3,
q4, and q5 respectively are listed below.
ꢄ
ꢅ
ꢅ
ꢅ
2 μ2e−μ2g
q1 ¼
q2 ¼
ð11Þ
ð12Þ
hca3
ꢄ
2
2 μe−μg
Chamma-Kwaski-Villate equation [38–40].
hca3
ꢄ
2
~νa þ ~νf
2 μe−μg
¼ −q1 F1 ðD; nÞ þ constant
ð1Þ
2
q3 ¼
q4 ¼
q5 ¼
ð13Þ
ð14Þ
ð15Þ
hca3
ꢄ
ꢅ
ꢅ
Bakhshiev’s equation [41].
μg μe−μg
hca3
~νa–~νf ¼ q2 F2ðD; nÞ þ constant
Lippert’s equation [42]
ð2Þ
ð3Þ
ð4Þ
ð5Þ
ꢄ
μg μe−μg
hca3
~νa−~νf ¼ q3 F3ðD; nÞ þ constant
McRae’s equation [43]
Where, μgand μe are ground state and excited state
dipole moment of solute molecules, ‘h’and ‘c’ are
Planck’s constant and velocity of light in vacuum re-
spectively. ‘a’ is Onsager cavity radius of a solute mol-
ecule obtained by according to Edward atomic incre-
ment method [45]. By assuming the fact that the ground
state and excited state dipole moments are almost par-
allel to one another, the following relations are used to
determine the dipole moments
~νa ¼ −q4 F4ðDÞ þ Constant
Suppan’s equation [44]
~νa ¼ −q5 F5ðDÞ þ Constant
The relations F1 (D, n) (Viallet’s-Chamma-Kawski
polarity relation), F2 (D, n) (Bakhshiev’s polarity rela-
tion), F3 (D, n) (Lippert’s polarity relation), F4 (D)
(McRae’s polarity relation) and F5(D) (Suppan’s polarity
relation) are listed below.
1
2
ꢂ
ꢃ
q1−q2 hca3
μg ¼
ð16Þ
2
2q2
1
2
ꢂ
ꢃ
q1 þ q2 hca3
"
#
ꢀ
ꢁ
ꢃ
2n2 þ 1
D−1
n2−1
3ðn4−1Þ
μg ¼
μe ¼
ð17Þ
ð18Þ
2
2q2
F1ðD; nÞ ¼
−
þ
ð6Þ
ð7Þ
2
2ðn2 þ 2Þ D þ 2 n2 þ 2
2ðn2 þ 2Þ
ꢂ
ꢃ
q2 þ q3
μg; q2 > q3
ꢂ
2n2 þ 1 D−1
n2−1
q3−q2
F2ðD; nÞ ¼
F3ðD; nÞ ¼
−
n2 þ 2 D þ 2 n2 þ 2
To derive for optoelectronic applications, the evalua-
tion of mass extinction coefficient (αmass Lg−1 cm−1) at
a given wavelength the light absorbed per unit mass
density of the compound are important parameters and
which are given by the equations [46].
ꢂ
ꢃ
D−1
n2−1
−
ð8Þ
ð9Þ
2D þ 1 2n2 þ 1
ꢂ
ꢃ
2ðD−1Þ
F4ðDÞ ¼
αmass ¼ ε=
ð19Þ
ð20Þ
D þ 2
Mw
A
b*c
ꢂ
ꢃ
ε ¼
2ðD−1Þ
2D þ 2
F5ðDÞ ¼
ð10Þ
Here, ‘ε’ (Lmol−1 cm−1) is the molar extinction co-
efficient, ‘A’ is the absorption of light by the compound
for a particular temperature, ‘b’ is the distance of light
which travelled through the sample, ‘c’ is the concen-
tration and ‘Mw’ molecular weight of the compound.
Here, ~νa and ~νf are excitation and emission maxima
are in wavenumbers (cm−1). ‘n’ and ‘D’ are refractive
index and dielectric constants of the solvents respec-
tively. Now, plotting the graphs for the above

J Fluoresc
The optical band gap energy or the forbidden bandwidth
of optical transition Eg depends on ‘α’ (cm−1) absorp-
tion coefficient and ‘hν’ (eV) photon energy is given by
equation [37].
transitions [49], and this range also attributed to the π
to π* transition which is occurred from So → S1 or
So → Sn transitions depending polarity of the solvent
used in the study. In Fig. 2., a small change in absorp-
tion maximum on varying the solvent polarity has been
observed and is ascribed to some polar character in
ground state [50]. However, it is also evident that in
studied solvents the excitation spectra showed a blue
shift due to the large degree of stabilizati0n of the
ground state in polar environments [51]. Also due to
the formation of hydrogen-bonded solvated clusters in-
between protic solvents and probe molecule and the
blue-shifted spectra is often reported in charge transfer
systems [20].
The synthesized 3-BMH compound exhibited a
broad emission band under 350 nm excitation wave-
length as shown in Fig. 3. The fluorescence emission
spectra of a synthesized compound which is solvent
dependent and exhibited a broad peak. The emission
band is located in the wavelength range ranging in
between 380 and 500 nm and it has been assigned to
π → π* electronic transitions which are due to delocal-
ization in aromatic rings and -OH group with the sol-
vent, conjugation between the bridge, -OH···Br interac-
tions were also participating in these transitions [49].
Hence it is worthwhile to assign the observed peaks to
the π → π* electronic transitions due to delocalization
in the aromatic ring and conjugation bridge in the mol-
ecule also due to the solvent interaction and lone pair
of electrons [50, 51].
From the fluorescence spectra (Fig. 3) of studied
compound it clear that the fluorescence spectra suffer
a bathochromic shift with an increase in the solvent
polarity. The same kind of bathochromic shift of fluo-
rescence spectra was observed for ip2 by sidir et al.
[49] and for 6-MQ in their corresponding fluorescence
spectra with an increase in solvent polarity [19]. The
bathochromic shift of fluorescence spectra with solvent
polarity indicating that basicity is increased in the com-
pound and which further indicates the greater stabiliza-
tion of excited state in polar solvents [52]. Further, from
the absorbance spectra (Fig. 2) of examined 3-BMH
molecule, it is very much clear that the absorption
bands are showing the bathochromic shift with an in-
crease in solvent polarity. This bathochromic (spectral)
shift in both the cases (absorption and emission) is oc-
curred by the stabilization of the molecule also due to
the increase in the polarity of the solvents used through
hydrogen bonding [53]. Further, the charge distribution
is varied or disturbed in between the ground and excited
state of the molecule because of strong intermolecular
interactions with polar solvents in the excited state,
which is one of the major aspect leading to the
À
Á
1=2
αðhνÞ ¼ P* hν−Eg
ð21Þ
Here, P* is constant, and the allowed direct transition band
gap is mentioned in Eq. 21.
The quantum yield (Φ) provides significant informa-
tion about the excited state, radiationless transitions,
and coupling of electronic to vibrational states
[38–40]. However, it is also used to determine the
appropriateness of laser media, sample purity, and
chemical structure, the relative ‘Φ’ can be calculated
by using Eq. 22.
Φs FuðODsÞn2u
Φ ¼
ð22Þ
FsðODuÞn2s
Where Φs is the quantum yield of the standard ref-
erence, Fu and Fs are the integrated areas under the
curve of emission spectra of the unknown and standard
sample, ODu and ODs are optical densities of the un-
known and standard sample, and nu and ns are the re-
fractive index of both unknown and standard sample.
The decay rate constants such as radiative (kr) and
non-radiative (knr) constants were determined by using
the equations, where τ0 is the lifetime in (ns) [47, 48].
Φ
kr ¼
ð23Þ
ð24Þ
τ0
1
knr
¼
−kr
τ0
Results and Discussions
Influence of Solvents on Absorption and Fluorescence
Properties of 3-BMH
The electronic absorption and emission spectra of the
molecule in selected polar and nonpolar solvents at am-
bient temperature were recorded and given predictable
evidence about solvation effect on the ground state
(μg) and excited state (μe), all the spectroscopic solvent
parameters and solvent polarity functions are summa-
rized in Table 1 Fig. 2 shows the broad absorption
spectra of the studied 3-BMH derivative in selected sol-
vents having two bands, from which it is evident that
the molecule excite between the range 331–341 nm and
346–355 nm (both are in UV region), these two bands
are obtained due to intermolecular charge transfer (ICT)

J Fluoresc
Table 1 Solvent polarity
parameters of 3-BMH in all
studied solvents
Solvents
(D)
(n)
F1(D, n)
F2(D, n)
F3(D, n)
F4(D, n)
F5(D, n)
Cyclohexane
Hexadecane
1,4-Dioxane
Ethyl acetate
Propanol
2.01
2.04
2.21
6.02
20.1
20.6
22.4
32.6
46.6
1.424
1.427
1.420
1.370
1.383
1.357
1.359
1.326
1.476
4.385
−0.004
0.001
0.043
0.490
0.778
0.790
0.802
0.855
0.841
−0.002
0.010
0.021
0.201
0.274
0.285
0.287
0.309
0.264
0.504
0.515
0.575
1.252
1.729
1.735
1.754
1.827
1.877
0.336
0.342
0.377
0.715
0.905
0.907
0.915
0.940
0.958
4.402
4.799
8.605
10.744
10.896
10.973
11.495
11.390
Acetone
Ethanol
Methanol
Dimethyl sulfoxide
bathochromic shift with an increase in the polarity of
the solvents. Nevertheless, the significant change in
the emission band compared to absorption band sig-
nifies the molecule in the ground state is less polarized
by the polar solvents. Hence, the solvents affectability
can be implicit in terms of π → π* transition with ICT
intermolecular charge transfer, signifying that the non-
bonding electrons are not involved in n → π* transition
[47, 54]. From Table 6, it can be seen that the μe
values are varied significantly, which clearly suggest
that the emission spectra are c0mparatively much sensi-
tive to solvent-induced solute-solvent interactions and
conformational difference related to that of excitation
spectra, which confirms significant changes in the ge-
ometry of excited state (μe) compared to ground state
(μg).
(23 and 24), the emissive rate constants for 3-BMH in
all studied solvents having different polarities clearly
suggests more effective transient displacement of
charges between the ground and excited state.
Obtained results are strongly suggesting as the solvent
polarity varies, the relative quantum yield also varies
from 40 to 70%. The molar extinction and mass ex-
tinction coefficient considerably enhanced in all stud-
ied solvents for 3-BMH compound Table 2 This result
confirms that the fluorescence emission of 3-BMH in
excited energy states are strongly dependent on the
solvent environment.
Estimation of Dipole Moments
To estimation the dipole moment in ground state (μg) and
excited state (μe) of the synthesized derivative 3-BMH the
solvent polarity functions F1(CKV) (D, n), F2 (BKS) (D, n), F3
(L-M) (D, n), F4 (McRay) (D) and F5 (Suppan) (D) was used based
on solvatochromic shift methods, the slopes (q), correlation
The 3-BMH in all solvents energy yield of fluores-
cence is less than unity because of Stoke’s losses. This
is further supported by more knr and fewer kr values.
The decay rate constants radiative (kr) and non-
radiative (knr) (Table 2) were calculated by using Eq.
1250
Dimethyl sulphoxide
Acetone
Hexadecane
Ethyl acetate
1,4-Dioxane
Cyclohexane
Ethanol
Methanol
Propanol
Acetone
0.5
Cyclohexane
1000
Dimethyl sulphoxide
Ethanol
Ethyl acetate
Hexadecane
Methanol
Propanol
1,4-dioxane
0.4
750
500
250
0.3
0.2
0.1
0.0
350 375 400 425 450 475 500 525 550 575 600
Wavelength (nm)
320
340
360
380
400
420
440
Wavelengthn (nm)
Fig. 3 Photoluminescence emission spectra of 3-BMH in all studied
Fig. 2 UV-Vis absorption spectra of 3-BMH in all studied solvents
solvents

J Fluoresc
Table 2 Mass extinction coefficient (αmass), molar extinction coefficient (εx104), fluorescence quantum yield (ΦF), fluorescence decay times (τ0),
radiative rate constant (kr) and non-radiative rate constant (knr) in solvents with different refractive index ‘n’ and dielectric constant ‘D’
Solvents
λabs
(nm)
λemi
(nm)
Stokes shift (Δλ)
αmass
ε × 104
Quantum yield
(ΦF)
τ0
(ns)
kr
knr
(M−1 cm−1
)
(L mole−1 cm−1
)
(107 s−1
)
(107 s−1
)
Cyclohexane
Hexadecane
1,4-Dioxane
Ethyl acetate
Propanol
347
355
347
356
357
348
356
355
356
428
425
432
430
431
429
431
425
430
81
70
85
74
74
81
75
70
74
3.85
1.81
3.69
2.91
3.23
2.75
2.82
3.46
3.38
2.01
0.94
1.92
1.51
1.68
1.43
1.47
1.80
1.76
0.40( 0.001)
0.68( 0.001)
0.48( 0.001)
0.51( 0.001)
0.52( 0.001)
0.69( 0.001)
0.45( 0.001)
0.47( 0.001)
0.70( 0.001)
1.2
1.4
1.8
1.7
2.0
1.9
1.5
1.4
1.9
33.4
48.7
21.5
29.3
26.1
36.6
30.4
33.6
36.8
49
22
33
29
23
15
36
37
15
Acetone
Ethanol
Methanol
Dimethyl sulfoxide
~νaþ~ν f
in the value of excited state dipole moment may be in part, due
to assumptions and simplifications done in the solvatochromic
method. As in Table 3 from which it is found that Stokes shift
increased with increasing solvent polarity. The magnitude of
Stokes shift represent that the excited state geometry could be
significantly different from that of the ground state and thus
large values of excited state dipole moments are expected. The
obtained values of dipole moments are summarized in Table 5,
and from which it is evident that, the value of μe is found to be
more than μg. The differences in the ground and excited state
dipole moment clearly reveal that, the investigated
biscoumarin derivative is more polar in its excited state than
in its ground state and which further concludes that solvent-
solute interactions are significantly stronger in the excited
state than in the ground state, explaining an essential redistri-
bution of charge densities between both electronic states, the
change in dipole moment on excitation reveals that because of
hydrogen bonding effect and strong solvent polarity due to the
possibility of the excited state is twisted intermolecular charge
coefficients and intercepts are derived by plotting
vs.
2
F1(VCK) (D, n) i.e., Chamma-Kwaski-Villate polarity, Stoke
shift vs. F2 (BKS) (D, n), Stoke shift vs. F3 (L-M) (D, n),ν~ avs.
4 (McRay) (D) and ~νa v/s. F5 (Suppan) (D) (Figs. 4, 5, 6, 7, and 8
F
respectively, absorption and emission wavenumber data were
presented in Table 3) and the slopes q1, q2, q3, q4 and q5 (Eqns.
11–15) which are taken from these graphs respectively. The
values such as correlation coefficient (R2), slope (m), and
intercept (z) were evaluated through linear fitting using origin
software and all the values are summarized in Table 4, from
which it is evident that the correlation coefficients found to be
greater than 0.96 which indicates a good linearity of Stokes
shift points. However, a small amount of deviation from line-
arity have been noticed in some solvents, it is due to specific
solvent-solute interactions, and also probably due to hydrogen
bonding nature of the molecule at the same instant time charge
transfer in the excited state [55]. The μg and μe values esti-
mated in the present investigation are in fair agreement with
those estimated by different methods [56–58]. This difference
26000
25900
25800
25700
5500
5250
5000
0.00
0.25
0.50
0.75
1.00
4
5
6
7
8
9
10
11
F
(
D, n
)
F (D, n)
2
1
Fig. 4 A plot of ~ν þ~ν function versus F1 (D, n) of 3-BMH
Fig. 5 A plot of ~νa –~νf function versus F2 (D, n) of 3-BMH
a
f
2

J Fluoresc
5600
5400
5200
5000
28875
28700
28525
28350
28175
0.0
0.1
0.2
0.3
0.3
0.4
0.5
0.6
F
0.7
0.8
0.9
1.0
F (D, n)
3
5
Fig. 6 A plot of ~νa –~νf function versus F3 (D, n) of 3-BMH
Fig. 8 A plot of ~νa function versus F5 (D) of 3-BMH
transfer in nature (TICT). Hence, due to large TICT molecule
become polar as compared to ground state and change in di-
pole moment is observed.
outcome. Since, it is well understood that the DFT methods
are not able to take care of week non-bonding interactions
present in a particular system this moderates electron distribu-
tion of the model system and hence, electron density becomes
significantly irregular [20, 60]. This features a virtual increase
in polarity of the system, which is a path not quite the same as
the original system. It is expected that a mixture of the method
with a larger amount of electron correlation with higher order
basic set, there is possible to improve in the figured dipole
moment values. Whereas in case of considerably large mole-
cules like 3-BMH the application of greater order method and
considerably different size basic sets increases the computa-
tional cost effectively. Overwhelm, it is also found that the
dipole moment of the molecule is affected by the solvent po-
larity used in this article.
The dipole moment was also calculated theoretically by
using Gaussian 09 W program package software, in order to
calculate the ground state dipole moment, the DFT-B3LYP/6–
311(d) basic set is used whereas to calculate the excited state
dipole moment, the TD-DFT-B3LYP/6–311(d) basic set is
used. The synthesized derivative was optimized for both the
basic set. From the observed results the obtained dipole mo-
ment (theoretical) is higher than the experimentally deter-
mined [59]. This discrepancy in dipole moment is because
of organic molecules depends on the charge transfer process
within the molecule, we found that the 3-BMH molecule is
more polar in the excited state than the ground state.
Therefore, the molecule is more sensitive to the solvent effect,
this is perhaps due to some inherent circumstance of DFT
formalism are responsible for this kind of inappropriate
Theoretical and Experimental Linear Optical Bandgap
Estimation of band gap from absorption measurements the
result signifies a major role in the optoelectronic application.
Higher the bandgap more tightly the valance electrons are
bound to the nucleus. In this regard, the dependency of photon
energy with an optical absorption coefficient is used to study
the band structure and the type of transition involved. The
optical band gap is determined by making use of the Tauc
and Davis & Mott model [61] in the maximum absorption
region. The general method for determining the bandgap to
draw a plot of (αhν)2 (cm−1 eV)2versus ‘hν’ (eV) in solution
phase are presented in Fig. 9. The linearity observed in the
curves is shown by the arrows which confirm that the elec-
tronic transitions are direct allowed transitions. The Eg optical
energy bandgap is estimated by means of extrapolating the
linear region (Fig. 9). Hence, the calculated and measured
bandgap Eg values are dissipated in Table 6. As we can con-
clude by observing Table 6 the experimental bandgap values
of the studied molecule is found in the range between 3.37 to
28800
28600
28400
28200
0.5
1.0
1.5
2.0
F (D)
4
Fig. 7 A plot of ~νa function versus F4 (D) of 3-BMH

J Fluoresc
Table 3 The absorption and emission wavenumber data in different solvent medium of 3-BMH molecule
Solvents
~νa
~νf
~νa –~ν
~νa + ~ν
~νa + ~νf /2
(cm−1
f
f
(cm−1
)
(cm−1
)
(cm−1
)
(cm−1
)
)
Cyclohexane
Hexadecane
1,4-Dioxane
Ethyl acetate
Propanol
28818
28169
28818
28089
28011
28735
28089
28169
28089
23364
23529
23148
23255
23201
23310
23201
23529
23255
5454.0
4639.6
5670.3
4834.1
4809.3
5425.6
4888.0
4639.6
4834.1
52182.9
51698.4
51966.6
51345.7
51213.1
52045.7
51291.7
51698.4
51345.7
26091
25849
25983
25672
25606
26022
25645
25849
25672
Acetone
Ethanol
Methanol
Dimethyl sulfoxide
3.44 eV [62]. Thus, the redshift in bandgap energy was ob-
served by rising different solvents polarity. The degree of
structural disorder and order was led to changes in Eg values
and also which will change the distribution of energy levels
within the energy gap [63]. Here, Eg values (Table 6) were
shifted and it is found that the values are increasing or de-
crease (depend on dielectric constant, refractive index and
viscosity) when the sample was exposed in the different sol-
vent environment.
The theoretical band gap energy is calculated by using
Gaussian 09 W software by implementing DFT-B3LYP/6-
31G (d) basic set in ground state the calculated HOMO,
LUMO energies and theoretical band gap energy were also
dissipated in Table 6. The molecular orbitals of 3-BMH in one
of studied acetone solvent are presented in Fig. 10 and the left
of solvents such as cyclohexane, hexadecane, 1,4-dioxane,
ethyl acetate, propanol, ethanol, methanol, and dimethyl
sulphoxide HOMO, LUMO, and oscillator strength values
are dissipated in Table 6 The orbital diagrams are plotted with
the counter value of 0.02 a.u. peru color (Fig. 10) indicates
positive and royal blue color indicates a negative value of the
density distribution plots of HOMO and LUMO. This density
distribution shows the typical π molecular orbital characteris-
tics, from this analysis we infer that the lowest lying singlet to
singlet absorption and electronic transition of π → π* type.
The HOMO and LUMO energies for acetone solvent are
found to be −5.5167 eV and − 1.6186 eV respectively.
Hence, the HOMO-LUMO band gap is 3.898 eV. As we can
see from the HOMO LUMO figures of acetone (Fig. 10), the
HOMO is dominantly localized on 1-bromo-2-
methoxybenzene group of the molecule along with some of
the carbon and hydrogen atoms linked to this group because of
–Br:-OCH3 group present in the molecule. The LUMO is
localized on almost all part of the molecule except the substit-
uent group and the last benzene ring present in the parent
group of the molecule. Hence, the molecular orbital densities
HOMO and LUMO showed similar observations for all other
studied solvents. Therefore, we can infer that the double bond
has a maximum electron density distribution in the LUMO as
compared to the HOMO [63]. The overall energy gap Eg was
found in the range between 3.71 to 3.89 eV. Nevertheless, it is
very much significant to point out that the obtained discrep-
ancies in between theoretically and experimental obtained re-
sults can be ascribed due to the fact that the experimental
results belonged to solution phase in which there are several
inter- and intra-molecular interactions within the solvent and
solution can be seen. Whereas, in case of theoretical calcula-
tions (using the software) it may belong to the solvent phase of
an isolated single molecule. Thus, this bandgap (wide) and the
optical transparency of the compound with the lower Eg can
be especially preferred in the field of optoelectronics as a
source of light emitting diodes and laser diodes.
Table 4 Statistical treatment of
correlation of solvents spectral
shifts of 3-BMH
Compound
3-BMH
Method
Slope
(m)
Intercept
(z)
Correlation coefficient (R2)
Viallet’s-Chamma-Kawski
Bakhshiev’s
Lippert’s
−31.2434
768.222
2063.56
460.328
1007.78
26092
4958
0.9858
0.9542
0.9681
0.9824
0.9832
4945
McRae
27946
27832
Suppan

J Fluoresc
Table 5 Ground and excited state
dipole moment of 3-BMH
Compound
(3-BMH)
Dipole moment (Debye)
μga
μgb
μec
μed
μee
μef
μeg
μeh
0.238
0.127
6.661
1.254
3.142
4.897
2.123
3.015
Debye (D) =3.33564 × 10–30 cm = 10-18 esu cm
a The ground states dipole moments calculated using Gaussian software
b The ground states dipole moments calculated using Eq. (16)
c The excited states dipole moments calculated using Gaussian software
d The experimental excited states dipole moments calculated from Chamma-Kwaski-Villate equation
e The experimental excited states dipole moments calculated from Bakshiev’s equation
f The experimental excited states dipole moments calculated from Lippert’s equation
g The experimental excited states dipole moments calculated from McRay equation
h The experimental excited states dipole moments calculated from Suppan equation
Electrostatic Potential Maps
density plots studies were estimated in a vacuum and in all
solvents used in this article, the obtained result showed the
The Electrostatic potential maps are an important tool in
defining reactivity of the molecule towards positively or
negatively charged reactants, also it provides knowledge
about size, shape, the location of electrophilic, nucleophil-
ic sites, polarity and charge density of molecule. The 3-
Dimensional molecular, electrostatic and total density
maps were constructed with DFT theory with DFT-
B3LYP/6–311(d) basic set are shown in Fig. 11. Electron
uniform distribution and here only the acetone solvent
density plot is dissipated [52]. The total electron density
plots are showed uniform distribution. An MEP is a very
influential tool describes, the molecular sites of hydrogen
bonding interaction, nucleophilic reactions, and electro-
philic attack. By using 6-311G level theory we calculated
the ρ(r) - the molecular electrostatic potential surface is
−5
found that 5 × 10
electrons/bohr3 contour of the total
Fig. 9 Tau plot of 3-BMH in liq-
uid media for all studied solvents

J Fluoresc
Table 6 Experimental and theoretical energy gap of 3-BMH in all studied solvents
Solvents
HOMO (eV)
LUMO
(eV)
Band gap (eV)
Eg(Theo)
Oscillator strength
Eg(Exp)
Cyclohexane
Hexadecane
1,4-Dioxane
Ethyl acetate
Propanol
−5.5988
−5.5912
−5.5757
−5.6355
−5.6782
−5.5167
−5.6268
−5.5469
−5.6026
−1.8988
−1.7092
−1.7690
−1.7636
−1.7818
−1.6186
−1.8735
−1.7943
−1.7965
3.711
3.881
3.806
3.871
3.896
3.898
3.753
3.752
3.806
3.422
3.443
3.441
3.431
3.448
3.394
3.392
3.382
3.371
0.797
0.811
0.807
0.790
0.787
0.789
0.765
0.798
0.789
Acetone
Ethanol
Methanol
Dimethyl sulfoxide
self-consistent field (SCF) electron density for 3-BMH
dye. In Fig. 11 the localized electron regions with electro-
static potential are red in color as negative, and green in
color as positive distribution maps [18]. The negative
MEP (red colour) region of high electron density which
are mapped on 3C (E = −1.13 eV), 5C (E = −1.34 eV), 8C
(E = −1.25 eV), 26O (E = −0.83 eV), and 29H (E =
−1.08 eV) for in vacuum and at 2C (E = −0.93 eV), 4C
(E = 1.46 eV), 14C (E = 1.16 eV), 15C (E = −1.48 eV),
39C (E = −0.81 eV), 41C (E = −1.03 eV), 42C (E =
−0.69 eV), 49H (E = −1.01 eV), 52H (E = −1.48 eV),
23O (E = −0.48 eV), and 24O (E = −0.31 eV) in acetone
solvent respectively. The positive MEP (green colour) re-
gions of highly depleted electron density, which are
mapped on these bounded atoms 11C-12C (E = 0.42 and
0.21 eV), 13C - 9C (E = 0.04 and − 0.11 eV), 10C - 7C
(E = 0.26 and − 0.39 eV), 21C - 10C (E = −0.10 and −
0.08 eV), 35C - 19C (E = 0.21 and − 0.25 eV), 16C -
21C (E = −0.47 and − 0.11 eV), 38H - 45Br (E = −0.61
and − 0.66 eV), 44C - 46H (E = −0.62 and − 0.45 eV),
44C - 48H (E = −0.62 and − 0.02 eV), 44C - 47H (E =
−0.48 and − 0.42 eV), in vacuum and in acetone solvent.
E
g = -5.51
CIE Color Space Chromaticity, Coordinate, and Color
Purity
HOMO
LUMO
The organic semiconductors are receiving great demand for
designing organic light emitting diodes (OLED), polymer
light-emitting diodes (PLEDs) and display device application,
the advancement will create a fundamental cutting edge for the
development showcases and the lighting in future. Therefore, it
is important to estimate the characteristics of color emission. In
order to determine the CIE color coordinate and color purity of
the 3-BMH molecule, The Commission Internationale de
I’Eclairage (CIE) color coordinate values have been determined
by using Osram Sylvania CIE co-ordinates software [Ref
OSARM]. This system consists of three primary color stimuli
symbolized by X, Y and Z tristimulus integrals
E
g = -1.61
X
x ¼
y ¼
ð25Þ
ð26Þ
X þ Y þ Z
Y
X þ Y þ Z
Fig. 10 HOMO LUMO plots of 3-BMH in acetone solvent

J Fluoresc
Maps
MEP
Vacuum
Acetone
Fig. 11 MEP, TED, and ESP
maps of 3-BMH in
acetone solvent
TED
ESP
strength of 1-bromo-2-methoxybenzene emission tuning
is more highlighted. x and y chromacity values of
3-BMH in all solvents are nearly well matched to
National television standard committee system (NTSC)
for the ideal blue chromacity coordinate (0.14, 0.08)
[33]. Color correlated temperature (CCT), U′ V′ and
DUV these are an important aspect of color appearance
how cool (bluish) or how warm (yellowish) light ap-
pearance. DUV with a positive sign for above and neg-
ative sign for below the Planckian locus is defined as
the distance from the test light source to the nearest
point on the Planckian locus of the CIE coordinates.
The CCT was determined by transforming the x, y co-
ordinates of a light source to U’V’, of the Planckian
locus by using the following equations.
Where,
750
X ¼ ∑ SPDðλÞxðλÞdλ
190
750
Y ¼ ∑ SPDðλÞyðλÞdλ
190
750
Z ¼ ∑ SPDðλÞzðλÞdλ
190
Hence, it is clear from Fig. 12 the CIE color coordi-
nates will lie in the deep blue region for all the solvents
studied in this article, the corresponding X and Y coor-
dinates values are tabulated in Table 7. It is found that
3-BMH showed color coordinate x = 0.14 → 0.16 and
y = 0.08 → 0.31. Because of an electron withdrawing

J Fluoresc
Fig. 12 CIE color coordinate spectra of 3-BMH in all studied solvents
1
8
4x
U0 ¼
V0 ¼
ð27Þ
ð28Þ
8
CRI ¼
∑
i¼1Ri
ð29Þ
−2x þ 12y þ 3
9y
−2x þ 12y þ 3
The detailed calculation of Ri (special color rendering index)
was given by Aritra Ghosh et al. [64]. The performance of
3-BMH in all solvents of different polarities have high CRI
values which are in greater average or equal to 87% (Table 7).
This result can be concluded that higher achievable CRI values
also offers higher CCT values for interior light applications
[65–68]. Also, the color purity is one of the major parameters
in order to estimate the percentage of color purity of the studied
molecule in this work for OLED’s and display application. The
color purity is calculated by the equation used below
The CCT values of 3-BMH in all solvents are found to be
4267 to 5587 K (Table 7) and shown in Fig. 13. Therefore, the
3-BMH was highly useful for the production of artificial blue
light to be similar to those natural blue light simulates the
natural color of daylight applications. The Du’v’ output indi-
cates error between the test lamp CCT and 3-BMH CCT as
computed by software [52], so our results are considered as
acceptable Du’v’ errors. Color rendering index (CRI) is the
quantitative measurement of the capability of a light source to
reproduce the colors of different objects truly in comparison
with natural light or an ideal source. The general color render-
ing index (CRI) is given by
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
2
2
ðx−x1Þ þ ðy−y1Þ
qffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
Color purity ¼
 100%
ð30Þ
2
2
ðx2−x1Þ þ ðy2−y1Þ
Table 7 Photometric parameters
of 3-BMH in all studied solvents
Solvents
CIE Coordinate
U′
V′
CCT
(K)
DU’V′
CRI
Color Purity
in %
X
Y
Cyclohexane
Hexadecane
1,4-Dioxane
Ethyl acetate
Propanol
0.15423
0.15785
0.16521
0.15487
0.14456
0.15231
0.14872
0.16952
0.14321
0.05214
0.04213
0.05879
0.07546
0.08752
0.07895
0.08213
0.04215
0.05678
0.1860
0.1979
0.1958
0.1723
0.1537
0.1672
0.1613
0.2141
0.1687
0.1915
0.1889
0.2208
0.1889
0.2094
0.1951
0.2004
0.2198
0.1905
4787
4267
4703
5587
5558
5238
4054
4993
4554
−0.2542
−0.2773
−0.2394
−0.2069
−0.1881
−0.2010
−0.1961
−0.2779
−0.2454
92
88
78
84
90
87
84
92
88
93.4
94.6
89.8
89.0
89.8
89.1
89.5
92.4
95.1
Acetone
Ethanol
Methanol
Dimethyl sulfoxide

J Fluoresc
temperature and color rendering Index of 3-BMH compound
dissolved in different solvents to understand the photometric
properties. To this end, the 3-BMH in all studied solvents
exhibited deep blue color (x = 0.14, y = 0.08) and is a prom-
ising material for optoelectronic applications.
0.22
0.18
0.16
0.14
0.10
~ 4860 K
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Where, (x, y) are CIE chromaticity coordinate values of the
studied compound, (x1, y1) is the color coordinate of white
illumination and (x2, y2) is the CIE coordinate of the dominant
emission wavelength. In this report the (x1, y1) = (0.310,
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