Synthesis and combined experimental and computational investigations on spectroscopic and photophysical properties of red emitting 3-styryl coumarins

Article abstract of DOI:10.1016/j.dyepig.2015.03.023

The coumarin derivatives are though highly fluorescent, lack in the absorption and emission in the red region. Modifying them to red emission included the strategy of formylation of 7-(N,N-diethyl amino) coumarin by Vilsmeier-Haak reaction followed by oxidative cyanation. The aldehyde synthesized was reacted with cyanomethyl benzoxazole/benzothiazole to give target compounds. All the compounds were characterised by spectral analysis. The cyanated molecules are found to be red shifted in absorption and emission by 90-100 nm. There was an increase in the quantum yield by about 10 times. The solvent polarity plots revealed the charge transfer process in the synthesized molecules and higher excited state to ground state dipole moment ratio. Density functional theory computations were performed to understand the nature of transitions involved in absorption and emission process.

Full text of DOI:10.1016/j.dyepig.2015.03.023

Accepted Manuscript
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar
PII:
S0143-7208(15)00098-4
10.1016/j.dyepig.2015.03.023
DYPI 4704
DOI:
Reference:
To appear in: Dyes and Pigments
Received Date: 23 January 2015
Revised Date: 20 March 2015
Accepted Date: 23 March 2015
Please cite this article as: Tathe AB, Gupta VD, Sekar N, Synthesis and combined experimental and
computational investigations on spectroscopic and photophysical properties of red emitting 3-styryl
coumarins, Dyes and Pigments (2015), doi: 10.1016/j.dyepig.2015.03.023.
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ACCEPTED MANUSCRIPT
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar *
Graphical abstract

ACCEPTED MANUSCRIPT
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar *
Tinctorial Chemistry Group, Department of Dyestuff Technology,
Institute of Chemical Technology, N. P. Marg, Matunga, Mumbai (MH) India-40001
Email: n.sekar@ictmumbai.edu.in, nethi.sekar@gmail.com
Tel.: +91 22 3361 1111/ 2707; Fax: +91 22 3361 1020
Abstract
The coumarin derivatives are though highly fluorescent, lack in the absorption and emission in
the red region. Modifying them to red emission included the strategy of formylation of 7-(N,N-
diethyl amino) coumarin by Vilsmeier-Haak reaction followed by oxidative cyanation. The
aldehyde synthesized was reacted with cyanomethyl benzoxazole/benzothiazole to give target
compounds. All the compounds were characterised by spectral analysis. The cyanated molecules
are found to be red shifted in absorption and emission by 90 to 100 nm. There was an increase in
the quantum yield by about 10 times. The solvent polarity plots revealed the charge transfer
process in the synthesized molecules and higher excited state to ground state dipole moment ratio.
Density functional theory computations were performed to understand the nature of transitions
involved in absorption and emission process.
Keywords
4-Cyano coumarin, styryl, DFT, TD-DFT, red emitting dyes
Introduction:
The dyes with red emission are employed in the area of OLED [1–4], protein tracking [5],
multicolor imaging [6], far-field optical nanoscopy [7,8]. The red emitting dyes are attractive in
OLEDs to complement their blue [9,10] and green [11,12] dye counterparts in the fabrication of
displays. In biological applications red emitting dyes stand high and apart due to their ability to
produce emission signals discrete from the autofluorescence [13–15] of biomolecules (195-600
nm), low energy excitation, emission in biological window [16,17]. The coumarin molecules with
red emission are rarely synthesized and studied. Considering the structure of the coumarin the
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absorption and emission can be enhanced by placing 1) Electron donor at 7-position [18,19] 2)
electron withdrawing group at 3 and 4 position [20,21] and 3) extension of conjugation [18,22].
This strategy ensures there is enough charge transfer in the coumarin molecule to push the
absorption and emission in the red region. Synthesis of styryl dyes is well documented in the
literature and has an easier protocol [23–26].
In the current study we have synthesized three 4-cyano 3-styryl coumarins (Figure 1) and their
photophysical properties were studied with respect to various solvent polarity parameters. The
photophysical properties were computed with DFT and TD-DFT to have an insight into their
photophysical behaviour.
Methods
All commercial reagents were procured from SD Fine Chemicals (Mumbai) and were used without
further purification. Laboratory reagent grade solvents were purchased from Rankem, Mumbai.
The reactions were monitored by TLC using on 0.25 mm E-Merck silica gel 60 F254 precoated
plates, which were visualized with UV light (254 nm and 344 nm). 1H NMR and 13CNMR spectra
were recorded on Agilent 500MHz NMR. Mass spectra were recorded on FINNIGAN LCQ
ADVANTAGE MAX instrument from Thermo Electron Corporation (USA). The absorption
spectra of the compounds were recorded on a Perkin Elmer Lambda 25 UV-Visible
spectrophotometer; emission spectra were recorded on Varian Inc. Cary Eclipse
spectrofluorometer. The ground state (S0) geometry of the compound 6-9 was optimized in the gas
phase using Density Functional Theory (DFT) [27]. The popular hybrid functional B3LYP was
used, which combines Becke’s three parameter exchange functional (B3)[28] with the nonlocal
correlation functional by Lee, Yang, and Parr (LYP) [29]. All the atoms were treated with 6-31
G(d) basis set, which deems to be sufficient for the molecules involved. The validity of the
structures as local minima on potential energy surface was verified with vibrational analysis and
was confirmed that they are with no imaginary frequencies.TD-DFT (Time Dependent Density
Functional Theory) with same hybrid functional and basis set was used to estimate vertical
excitation and their oscillator strength.The lowest singlet excited state (S1) was relaxed using TD-
DFT to get optimised geometry of the excited state. Emissions were obtained by calculating
vertical excitations of excited state geometry at ground state. Frequency computations were also
carried out on the optimized geometry of the low-lying vibronically relaxed first excited state of
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conformers. Computations in solvents were carried out using the Polarizable Continuum Model
(PCM). Gaussian 09 program [30] was used for all the quantum mechanical computations.
Synthesis
Figure 1 Synthesis of 4-Cyano coumarin 3-styryls (Compound 6-9)
The compound 3 was prepared by cyclisation of 5-(diethylamino)-2-hydroxybenzaldehyde with
diethyl malonate in presence of piperidne and ethanol followed by decarboxylation with conc. HCl
and glacial acetic acid using the reported procedure [31]. Compound 3 was subjected to Vilsmeier-
Haack reaction using DMF/POCl3 to give 7-(diethylamino)-2-oxo-2H-chromene-3-carbaldehyde
(4) according to the procedure has been described by Wu et al. [32]
Synthesis of 7-(diethylamino)-3-formyl-2-oxo-2H-chromene-4-carbonitrile (5)
7-(Diethylamino)-2-oxo-2H-chromene-3-carbaldehyde (4) (1.5 g, 6.9 mmol) was dissolved in
DMF (10 mL) and mixture was cooled to 5°C in ice bath. A solution of sodium cyanide (0.374,
7.6mmol) in water (4 mL) was added drop wise to the cooled mixture. The reaction mixture turns
pale yellow from yellow. The reaction mixture was stirred and allowed to attain room temperature
(~27°C) over a period of 1.5 h. It was cooled to 0°C and bromine liquid (0.548 mL, 10.3mmol)
was added to it dropwise. The solution turns red-brown. The solid separated after 30 min. was then
filtered and dried under vacuum to give brown colored product (0.98 g).
1HNMR (CDCl3, 500MHz, δ ppm): 1.25-1.30 (t, J= 7.2 Hz, 6H), 3.50-3.54 (q, J= 7.2 Hz, 4H),
6.48-6.49 (d, J= 2.5 Hz, 1H), 6.74-6.76 (dd, J= 2.5 & 7.5 Hz, 1H), 7.76-7.78 (d, J= 9.3 Hz, 1H),
10.16 (s, 1H)
13CNMR (CDCl3, 125 MHz, δ ppm): 12.5, 46.5, 97.4, 107.9, 111.6, 112.8, 114.3, 125.3, 130.3,
154.1, 158.0, 160.0, 185.5
HRMS: 271.1087 (M+H+) (Calculated for C15H15N2O3 : 271.1083)
General procedure for synthesis of styryl derivatives of 4 and 5
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2-(Benzo[d]azol-2-yl)acetonitrile (1.2 mmol) was dissolved in ethanol (10 mL) and the reaction
mixture was cooled to 5°C and 7-(diethylamino)-3-formyl-2-oxo-2H-chromene-4-carbonitrile 5 or
7-(diethylamino)-2-oxo-2H-chromene-3-carbaldehyde 4 (1.2 mmol) was added to it in a single
portion, piperidine (0.1 mL) was added to it. The mixture was stirred at 5°C for an hour and
allowed to attain room temperature (~26°C). The reaction was monitored by TLC and was
completed in 12 h. The reaction mass was then poured to ice-water (25 mL) and extracted with
chloroform. The organic layer was washed with water and brine, dried with sodium sulphate and
evaporated under reduced pressure to give the styryl derivative.
2-(Benzo[d]oxazol-2-yl)-3-(7-(diethylamino)-2-oxo-2H- chromen-3-yl)acrylonitrile (6)
1HNMR (CDCl3, 500MHz, δ ppm): 1.19-1.21 (t, J= 7.5 Hz, 6H), 3.39-3.344 (q, J= 7.5 Hz, 4H),
6.42 (s, 1H), 6.59-6.60 (d, J= 5 Hz, 1H), 7.29-7.31 (m, 2H), 7.36-7.38(d, J= 10 Hz, 1H), 7.46-7.49
(t, J= 5 Hz, 1H), 7.70-7.72 (t, J= 5 Hz, 1H), 8.54 (s, 1H), 8.88 (s, 1H).
13CNMR (CDCl3, 125 MHz, δ ppm): 12.4, 45.5, 96.2, 97.5, 109.1, 110.5, 110.6, 112.0, 115.9,
120.5, 125.0, 125.9, 131.8, 141.7, 143.0, 150.7, 153.0, 157.6, 159.5, 161.1.
HRMS: 386.1470 (M+H+) (Calculated for C23H20N3O3: 386.1460)
2-(Benzo[d]thiazol-2-yl)-3-(7-(diethylamino)-2-oxo-2H-chromen-3-yl)acrylonitrile (7)
1HNMR (CDCl3, 500MHz, δ ppm): 1.24-1.28 (t, J= 7.2 Hz 6H), 3.45-3.50 (q, J= 7.2 Hz 4H),
6.49-6.50 (d, J= 5 Hz), 6.64-6.67 (q, J= 5 Hz, 1H), 7.40-7.50 (m, 3H), 7.87-7.88 (d, J= 5 Hz, 1H),
8.07-8.09 (d, J= 10 Hz, 1H), 8.40 (s, 1H), 8.90 (s, 1H)
13CNMR (CDCl3, 125 MHz, δ ppm): 12.5, 45.4, 97.4, 103.5, 109.0, 110.3, 112.3, 116.8, 121.5,
123.7, 125.9, 126.7, 131.6, 134.7, 140.4, 142.7, 152.8, 153.7, 157.4, 161.2, 163.4.
HRMS: 402.1255 (M+H) (Calculated for C23H20N3O2S: 402.1276)
3-(2-(Benzo[d]oxazol-2-yl)-2-cyanovinyl)-7-(diethylamino)-2-oxo-2H-chromene-4-
carbonitrile (8)
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1HNMR (CDCl3, 500MHz, δ ppm): 1.28-130 (t, J= 7.2 Hz, 6H), 3.50-3.54 (q, J= 7.2 Hz, 4H),
6.59-6.60 (d, J= 2.3 Hz, 1H), 6.72-6.74 (dd, J= 2.2 & 5 Hz, 1H), 7.40-7.42 (dd, 2.5 & 3.5 Hz, 2H),
8.33-8.34 (d, J= 9.2 Hz, 1H), 11.79 (s, 1H).
13CNMR (CDCl3, 125 MHz, δ ppm): 12.6, 45.5, 97.6, 104.8, 108.3, 109.6, 111.3, 113.9, 125.53,
126.3, 127.7, 140.6, 148.7, 149.6, 153.8, 154.6, 159.8, 160.4, 165.9
HRMS: 427.1384 (M+OH●) (Calculated for C24H19N4O4: 427.1406)
3-(2-(Benzo[d]thiazol-2-yl)-2-cyanovinyl)-7-(diethylamino)-2-oxo-2H-chromene-4-
carbonitrile (9)
1HNMR (CDCl3, 500MHz, δ ppm): 1.24-1.30 (t, J= 7.3 Hz, 6H), 3.50-3.54 (q, J= 7.3 Hz, 4H),
6.65-6.67 (d, J= 10 Hz, 1H), 6.72-6.74 (d, J= 10 Hz, 1H), 7.45-7.46 (m, 1H), 7.54-7.56 (m, 1H),
7.92-7.94 (d, J=10 Hz, 1H), 8.04-8.05 (d, J= 5 Hz 1H), 8.35-8.37 (m, 1H) 12.26 (s, 1H)
13CNMR (CDCl3, 125 MHz, δ ppm): 12.5, 45.7, 97.6, 104.5, 110.7, 116.5, 121.7, 122.8, 126.6,
127.2, 134.3, 140.3, 153.3, 155.3, 159.5, 164.6, 166.3.
HRMS: 443.1178 (M+H+) (Calculated for C24H19N4O2S: 443.1149)
Results and discussion
Photophysical study
The compounds synthesized were studied for their absorption characteristics in solvents of
different polarity. The compounds without 4-cyano group i.e. compound 6 and 7 absorbed in the
region of 500 nm to 529 nm (Table 1) in various solvents. There is very little effect of presence of
benzoxazole or benzothiazole acceptors on absorption property as the compounds 6 and 7 absorb
at 500 nm and 501 nm in toluene respectively. However the compound 7 was expected to be red
shifted as compared to the compound 6 due to presence of benzothiazole acceptor. Absorption
maxima for the compounds 6 and 7 are sensitive to the solvent polarity and show a clear trend of
positive solvatochromism. The molar extinction coefficient ranges 25795 and 53900 L mol-1 cm-
1. The polar solvents have consistently shown lower molar extinction coefficient value whereas the
chlorinated solvent dichloromethane shows highest value (Table 1)
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The 4-cyanated styryl compounds (8 and 9) absorbed at lower energy by 215 cm-1 to 3279 cm-1
around as compared to their non-cyanated counterparts. The compounds 7 and 8 show single peaks
in the absorption spectrum which mainly consists of the absorption arising from a single
chromophoric unit. It consists of the donor (7-(N,N-diethylamino)-coumarin)-acceptor
(cyanomethyl benzoxazole/benzothiazole unit) system whereas the compounds 8 and 9 show two
peaks in the absorption spectrum originating from the dual chromophoric units, the additional
chromophoric unit consisting of (N,N-diethylamino)-coumarin-acceptor (cyano) system. The
longer and shorter wavelength absorptions are predominant in non-polar and polar solvents
respectively.
Compared to absorption the emission is more sensitive to the solvent polarity and shows a positive
solvatochromism in the compounds 8 and 9. In toluene, compound 8 and 9 emit at 634 nm and 637
nm, whereas in ethanol they emit at 692 nm and 700 nm respectively (Table 1). The 4-cyanated
compounds (8 and 9) are found to be non-fluorescent in polar aprotic solvents, this may be due to
the interaction of more polar cyano coumarin styryl molecules 8 and 9 with polar solvents at the
excited state. In the case of the non-cyanated compounds 6 and 7, they show highest intensity of
fluorescence emission in DMF and DMSO and there is no quenching of fluorescence like cyanated
molecules. However there is a clear red shift is seen in the absorption and emission of the cyanated
molecules (8 and 9), Stokes shifts are lower than those of non-cyanated molecules (6 and 7). The
presence of 4-cyano group is responsible for the decrease in Stokes shift by interacting with the
solvent at excited state.
However the Stokes shifts are lower for compounds 8 and 9 as compared to the compounds 6 and
7 in all the solvents, the quantum yields have improved many folds. This may be attributed to the
restriction of conformations around the styryl double bond. There is about a 10 fold increase in the
quantum yield, when compared to the non-cyanated compounds 6 and 7. Only exception is
compounds 6 and 8 which are benzoxazole derivatives in methanol and ethanol show a reverse
trend. This observation can be attributed to the better hydrogen bonding ability of the benzoxazole
oxygen with the protic solvents. The compounds 6 and 7 tend to show a lower quantum yield in
non-polar solvents and the trend is reversed in their 4-cyano derivatives (compound 8 and 9 )
Table 1 Photophysical Data of compound 6-9
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To understand the nature of the transitions and to have more insights into the photophysical
properties of the dyes studied, quantum chemical computations were performed. The excitation
energies and their oscillator strengths are tabulated in Table 1. The red shift induced by
introducing –CN group at 4-position is also well predicted by TD-DFT computations. The
predicted values for compound 6 and 7 lies between 466 nm to 480 nm in all the solvents. There is
a difference of 18-50 nm in all the computations with experimental measurements. The red shift in
absorption with increase in the polarity is predicted but is not consistent with experiments. There is
a decrease in the oscillator strength value when 4-position is substituted by –CN group.
To understand the red shift induced by the introduction of the –CN group at 4-position, energy of
frontier molecular orbitals were plotted against the solvents (Figure 2).
Figure 2 Lowering of LUMO in compound 8 and 9 as compared to compound 6 and 7
It is clear from the energy profile diagram given in Figure that there is a lowering of both HOMO
and LUMO energies after substitution by –CN group. But the extent of lowering of energy in
LUMO is more as compared to HOMO. This lead to decrease in band gap between HOMO and
LUMO, which is part of important transition due to absorption.
The emission calculated by considering ground state energy at excited state geometry gives
overestimated energies of de-excitations and are given in Table 1. These values also predict a red
shifted emission shown by the compounds 8 and 9 when compared to the compounds 6 and 7
respectively. The paercent deviation of the calculated values of de-excitation energies from the
experimental ones ranges from 2.4 to 11.4%
Solvent polarity function plots
The solvatochromic behaviour of the molecules 6-9 was studied with the help of Lippert [33],
Weller[34] and Rettig’s [34] plots. Lippert’s plot is the plot of stokes shift in cm-1vs orientation
polarizability. The Lippert function is constituted of the polarity function f(ε) and polarizability
function f(η). The Wellers and Rettigs plots were also screened for the linearity, which are the
plots of emission wave numbers of emission versus the respective polarity functions. For
convenience the solvents were choosen which do not have specific interaction with the solute. The
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polar solvents were not used to plot these functions. There is very less correlation was found in the
Lippert plot, however the constituent function f (η) (polarizability function) shows very good
correlation. It is clear from these plots that the solvatochromic behaviour of these molecules is
polarizability dependent and independent of polarity parameter defined by f (ε).
The Weller and Rettig plots show good linear behaviour and is indicative of CT (Charge transfer)
at excited state in these molecules. In the charge transfer process, though absorption spectrum is
not solvent polarity dependent but the emission is highly sensitive to the solvent. As there is
change in the polarity of the solute at excited state the solvent polarity has greater effect on the
emission properties. The solvent polarity function plots are given in supporting information.
The deviations from the above plots observed in the case of alcohols may be attributed to the
specific solvent effects arising from specific solute-solvent interactions (hydrogen bonding, etc.).
The carbonyl Oxygen (>C=O) and the lactone Oxygen (-O-) are the sources of hydrogen bonding
sites in these molecules.
Oscillator strength and transition dipole moment of the dyes
In addition to this the dipole moments between the excited and ground states the charge transfer
character of the fluorophore can be understood from the oscillator strength ( f ) (Table 1) and
transition dipole moment of the dyes (Ma). The effective number of electrons transition from the
ground to excited state is usually described by the oscillator strength, which provides the
absorption area in the electronic spectrum. The oscillator strength ( f ) can be calculated using the
following Equation 1 [35].
ꢀ = 4.32 × 10ꢁꢂ ꢄ(ꢅ
̅
) ꢆꢅ
Where ε is the extinction coefficient (L mol-1 cm -1), and ꢅ
wavenumber (cm-1).
̅
Equation 1
ꢃ
̅
represents the numerical value of
Transition dipole moments for absorption (Ma) which is a measure of the probability of radiative
transitions have been calculated for the dyes different solvent environments using the equation 6
[36].
ꢊ
ꢉ
ꢇꢈ = ꢋ.ꢌꢉ×ꢍꢎ ×ꢑꢒ
Equation 2
ꢏꢐ
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The values of oscillator strength (f) and transition dipole moment (Ma) for compound 6-9 for each
solvent is given in Table 2.
Table 2 Transition dipole moments (Ma) obtained from absorption properties of compound 6-9 in
various solvents.
The transition dipole moments obtained for the 4–CN substituted compounds 8 and 9 shows a
decline in value as compared to the non-cyanated counterpart compound 6 and 7. The molar
extinction co-efficients (ε) and apparently the transition dipole moments (Ma) are lower for cyano
compounds 8 and 9.
Dipole Moment Ratio
The compounds 6-9 responds well to the solvent polarity functions (ε, n), the similar equations are
introduced by Bilot-Kawski [37], Bakhshiev [38] and Liptay [39] for the estimation of ratio of
ꢓ
ꢔ
excited state dipole moment and ground state dipole moment i.e.
.
The dipole moments
ꢓ
ꢕ
calculated with the above equations is given in Table 3.
Table 3 Dipole moment ratio of compound 6-9 by various methods
ꢓ
ꢔ
The compounds 6 and 7 has ꢓ ratio less than unity and implies that the excited state is less polar
ꢕ
ꢓ
ꢔ
for these molecules, on the contrary their 4-cyanated analogues has
ratio more than unity and
ꢓ
ꢕ
suggests the more polar excited state. This leads to a positive solvatochromism. The Bilot-Kawski
ꢓ
equation has consistently estimated lower ꢔ ratio as compared to the Bakhshiev and Liptay
ꢓ
ꢕ
equations.
Excited State Geometry
The styryl molecules 6-8 are observed to have a twist in dihedral angle at ground state which takes
the withdrawing groups out of plane Figure 3. This dihedral angle is important to unsderstand the
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charge transfer from the donor part to acceptor. Lower the twist from planarity more the overlap of
molecular orbitals and in result more the charge transfer.
Figure 3 Twist of dihedral angle and the atoms involved in dihedral angle in compound 6-9
The dihedral angles from the optimized structures at the ground and excited states for all the four
molecules in various solvents are given in Table 4.
Table 4 Dihedral angles calculated with B3LYP/6-31G(d) method and various solvents for
compound 6-9
The dihedral angles optimized at the ground state (GS) and excited state (ES) suggests that there is
an increase in planarity at the excited state. The extent of attaining planarity is solvent dependent
in case of compound 6 and 7, whereas there is very less solvent dependence in compound 8 and 9.
The change in dihedral angle from GS to ES is higher for 4-cyanated compounds (8 and 9) as
compared to compound 6 and 7.
Molecular orbitals
The molecular orbital shapes and density illustrations can throw some light on how the donor-
acceptor relationship is established in a molecule. The MOs involved in excitation and de-
excitation (emission) are HOMO and LUMO for all the molecules. The FMO diagrams show that
the –NEt2 group constitutes the major density in HOMO for molecules 6-9. In the case LUMOs of
the molecules 6 and 7 the electron density is located on the styryl double bond and around,
whereas in LUMOs of the molecules 8 and 9 the electron density is clearly located on 4-cyano
substitution. This suggests the role of –CN group as an efficient acceptor and helps in lowering the
energy of LUMO in molecule 8 and 9.
Conclusion
In conclusion, the styryl compound 8 and 9 from 7-(diethylamino)-3-formyl-2-oxo-2H-chromene-
4-carbonitrile (5) were synthesized and their photophysical properties were compared with the
compound 6 and 7. All the compounds synthesized were confirmed by NMR spectral analysis and
HRMS. The photophysical study revealed that there is not only a red shift imparted by the
introduction of cyano group at the 4-position but there is a many fold increase in the quantum
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yields of these molecules. The study of charge transfer characteristics of the dyes by various
solvent polarity parameter plots shows the evidence of charge transfer at excited state. The DFT
computations of the dyes also supports the red shift induced by –CN group at 4-position. The
geometrical change occurring at the excited state (i.e. the decrease in dihedral angle which brings
the donor and acceptor in a single plane.) also supports the charge transfer at excited state. The
dipole moment ratios calculated with different solvent polarity parameter plots suggests more polar
excited states for the compound 8 and 9. The molecules 8 and 9 can be used as a basic structures to
the dyes or probes requiring emission in red region and moderate quantum yields.
Acknowledgements
Abhinav Tathe is thankful to University Grants Commission, India for award of fellowship as
senior research fellow.
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14

ACCEPTED MANUSCRIPT
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar *
Tables
List of tables
Table 1 Photophysical Data of compound 6-9
Table 2 Transition dipole moments (Ma) obtained from absorption properties of compound 6-9
in various solvents.
Table 3 Dipole moment ratio of compound 6-9 by various methods.
Table 4 Dihedral angles calculated with B3LYP/6-31G(d) method and various solvents for
compound 6-9.

ACCEPTED MANUSCRIPT
Table 1 Photophysical Data of compound 6-9
Experimental
Theoretical*
Stokes
Shift
(cm-1)
2514
2208
2264
2069
2290
2219
2257
2523
2143
2984
2405
2536
2410
2734
2480
2734
2809
2323
1818
1352
2161
--
Vertical
Emission
(nm)
Solvent
λabs
Ε
λem
(nm)
Φ
Excitation
(nm)
471
473
466
475
474
470
472
470
469
476
477
470
480
479
474
477
475
473
546
548
537
551
551
547
547
545
541
549
549
538
554
553
542
549
548
542
f
f
(nm) ( L mol−1 cm−1)
Acetonitrile
Dichloromethane
1,4-dioxane
N,N-dimethylformamide
Dimethylsulphoxide
Ethyl acetate
Ethanol
Methanol
Toluene
Acetonitrile
Dichloromethane
1,4-dioxane
N,N-dimethylformamide
Dimethylsulphoxide
Ethyl acetate
Ethanol
Methanol
Toluene
Acetonitrile
Dichloromethane
1,4-dioxane
N,N-dimethylformamide
Dimethylsulphoxide
Ethyl acetate
Ethanol
Methanol
Toluene
Acetonitrile
Dichloromethane
1,4-dioxane
N,N-dimethylformamide
Dimethylsulphoxide
Ethyl acetate
Ethanol
Methanol
Toluene
510
511
497
529
519
506
516
509
500
506
509
498
528
525
504
511
512
501
602
611
563
594
585
573
607
599
561
597
611
561
525
531
568
602
591
560
37345
53900
30415
40810
36575
33880
32340
25795
34265
27669
42350
38656
40425
35288
31647
30596
40810
31679
12952
17672
15908
10819
9307
19366
12628
10665
13079
28840
28298
23174
27516
22067
21991
30246
27720
28755
0.672 585
0.552 576
0.464 560
0.697 594
0.800 589
0.552 570
0.509 584
0.413 584
0.586 560
0.528 596
0.582 580
0.726 570
0.715 605
0.659 613
0.582 576
0.541 594
0.785 598
0.583 567
0.178 676
0.289 666
0.208 641
0.0071
0.0066
0.0097
0.0307
0.0263
0.0068
0.0158
0.0157
0.0061
0.0027
0.0033
0.0043
0.0122
0.0104
0.0035
0.0048
0.0061
0.0036
0.0658
0.1048
0.0328
--
1.6364
1.6464
1.6177
1.6582
1.6561
1.6122
1.6391
1.6317
1.6360
1.6404
1.6499
1.6247
1.6628
1.6612
1.6617
1.6426
1.6354
1.6426
1.3212
1.3281
1.2923
1.3435
1.3413
1.3142
1.3236
1.3164
1.3111
1.3432
1.3431
1.3067
1.3658
1.3637
1.3502
1.3455
1.3381
1.3253
526
532
534
532
531
530
528
526
537
530
536
535
534
535
533
532
530
539
620
625
617
--
6
7
0.191
0.137
--
--
--
--
--
8
9
0.289 658
0.180 700
0.129 695
0.164 634
0.315 679
0.187 666
0.199 647
2254
2189
2306
2052
2023
1352
2369
--
0.0434
0.0144
0.0121
0.1011
0.0336
0.1034
0.0371
--
620
621
619
622
621
626
616
--
0.168
0.123
--
--
--
--
--
0.187 664
0.340 692
0.353 701
0.263 637
2545
2160
2655
2159
0.0676
0.0213
0.0157
0.0969
620
622
620
622
*TD-B3LYP/6-31G(d)

ACCEPTED MANUSCRIPT
Table 2 Transition dipole moments (Ma) obtained from absorption properties of compound 6-9
in various solvents.
Compound 6
Compound 7
Compound 8
Compound 9
Acetonitrile
Dichloromethane
Dioxane
DMF
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene
8.92
8.09
7.42
9.09
9.74
8.09
7.77
7.00
8.33
7.94
8.35
9.19
9.41
8.95
8.30
8.09
9.67
8.26
5.01
6.43
5.24
5.15
4.33
6.23
5.06
4.25
4.64
6.64
5.17
5.11
4.54
3.91
4.99
6.92
6.99
5.87

ACCEPTED MANUSCRIPT
Table 3 Dipole moment ratio of compound 6-9 by various methods.
6
8
7
9
Bilot-Kawski 0.852 1.036 0.715 1.029
Bakhshiev
Liptay
0.844 1.039 0.699 1.031
0.823 1.027 0.682 1.014

ACCEPTED MANUSCRIPT
Table 4 Dihedral angles calculated with B3LYP/6-31G(d) method and various solvents for
compound 6-9.
6
7
8
9
∆°
∆°
∆°
∆°
GS
ES
GS
ES
GS
ES
GS
ES
21.5 17.8 3.6
22.3 17.6 4.7
24.0 17.6 6.4
21.5 17.9 3.6
21.4 17.9 3.4
21.9 17.8 4.1
21.7 17.8 3.9
21.5 17.9 3.6
23.8 17.6 6.3
21.4 18.9 2.6
22.4 19.0 3.4
23.7 18.7 5.1
21.4 18.9 2.5
21.2 18.9 2.3
22.7 19.0 3.7
21.7 18.9 2.8
21.5 18.9 2.6
23.6 18.7 4.9
26.6 17.5 9.1
27.3 17.7 9.6
29.3 21.0 8.3
26.6 17.5 9.1
26.5 17.5 9.1
27.7 18.9 8.8
26.7 17.5 9.2
26.6 17.5 9.2
29.1 20.9 8.2
25.1 17.9 7.2
27.4 18.2 9.2
29.3 19.5 9.8
25.1 17.9 7.2
25.0 17.8 7.2
27.9 18.4 9.4
25.2 17.9 7.3
25.1 17.9 7.2
29.1 19.4 9.8
Acetonitrile
Dichloromethane
Dioxane
DMF
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene
All the angles expressed in °

ACCEPTED MANUSCRIPT
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar *
Figures
List of Figures
Figure 1 Synthesis of 4-Cyano coumarin 3-styryls (Compound 6-9)
Figure 2 Lowering of LUMO in compound 8 and 9 as compared to compound 6 and 7
Figure 3 Twist of dihedral angle and the atoms involved in dihedral angle in compound 6-9

ACCEPTED MANUSCRIPT
Figure 1 Synthesis of 4-Cyano coumarin 3-styryls (Compound 6-9)

ACCEPTED MANUSCRIPT
Figure 2 Lowering of LUMO in compound 8 and 9 as compared to compound 6 and 7

ACCEPTED MANUSCRIPT
Figure 3 Twist of dihedral angle and the atoms involved in dihedral angle in compound 6-9

ACCEPTED MANUSCRIPT
Highlights of Manuscript
1. Synthesis of novel red emitting coumarins.
2. DFT studies on the 4-cyano 3-styryl coumarins .
3. Photophysical and spectroscopic studies of 4-cyano 3-styryl coumarins.

ACCEPTED MANUSCRIPT
Supporting Information
Synthesis and combined experimental and computational investigations on
spectroscopic and photophysical properties of red emitting 3-styryl coumarins
Abhinav B. Tathe, Vinod D. Gupta, Nagaiyan Sekar *
List of tables
Table 1 Absorption properties of compound 6
Table 2 Absorption properties of compound 7
Table 3 Absorption properties of compound 8
Table 4 Absorption properties of compound 9
Table 5 FMO diagrams for compound 6-9 calculated with B3LYP/6-31G(d) method in acetonitrile
(iso= 0.002)

ACCEPTED MANUSCRIPT
List of figures
Figure 1 Absorption spectrum of the compound 6-9 in various solvents
Figure 2 Emission spectrum of the compound 6-9 in various solvents
Figure 3 Quantum yield of compound 6-9 in various solvents
Figure 4 Solvent polarity function plots of Compound 6
Figure 5 1HNMR spectrum of compound 5
Figure 6 13CNMR spectrum of compound 5
Figure 7 1HNMR spectrum of compound 6
Figure 8 13CNMR spectrum of compound 6
Figure 9 1HNMR spectrum of compound 7
Figure 10 13CNMR spectrum of compound 7
Figure 11 1HNMR spectrum of compound 8
Figure 12 13CNMR spectrum of compound 8
Figure 13 1HNMR spectrum of compound 9
Figure 14 13CNMR spectrum of compound 9
Figure 15 HRMS of compound 5
Figure 16 HRMS of compound 6
Figure 17 HRMS of compound 7
Figure 18 HRMS of compound 8
Figure 19 HRMS of compound 9

ACCEPTED MANUSCRIPT
Table 1 Absorption properties of compound 6
λmax
FWHM εmax
IAC
f
σ
͇
ꢀ
x 108
x 10-19
1.05
Acetonitrile
Dichloromethane
Dioxane
DMF
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene
506
509
498
528
525
504
511
512
501
98
92
85
93
118
90
89
84
89
27669
0.672
0.552
0.464
0.697
0.800
0.552
0.509
0.413
0.586
1.56
8.92
42350
38656
40425
35288
31647
30596
40810
31679
1.62
1.48
1.54
1.35
1.21
1.17
1.56
1.21
1.28
1.07
1.61
1.85
1.28
1.18
0.96
1.36
8.09
7.42
9.09
9.74
8.09
7.77
7.00
8.33
Table 2 Absorption properties of compound 7
λmax
FWHM εmax
IAC
x 108
1.22
f
σ
͇
ꢀ
x 10-19
1.43
Acetonitrile
Dichloromethane
Dioxane
DMF
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene
510
511
497
529
519
506
516
509
500
107
98
37345
0.528
0.582
0.726
0.715
0.659
0.582
0.541
0.785
0.583
7.94
8.35
9.19
9.41
8.95
8.30
8.09
9.67
8.26
53900
30415
40810
36575
33880
32340
25795
34265
2.06
1.16
1.56
1.40
1.29
1.24
0.99
1.31
1.35
1.68
1.65
1.53
1.35
1.25
1.82
1.35
103
96
110
99
99
101
98

ACCEPTED MANUSCRIPT
Table 3 Absorption properties of compound 8
λmax FWHM εmax
IAC
f
σ
͇
ꢀ
x 108
x 10-19
0.49
Acetonitrile
602
110
102
109
249
114
100
113
91
12952
17672
15908
10819
9307
0.178
0.289
0.208
0.191
0.137
0.289
0.180
0.129
0.164
0.41
5.01
Dichloromethane 611
0.68
0.61
0.42
0.36
0.74
0.48
0.41
0.50
0.67
0.48
0.44
0.32
0.67
0.47
0.30
0.38
6.43
5.24
5.15
4.33
6.23
5.06
4.25
4.64
Dioxane
DMF
563
594
585
573
607
599
561
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene
19366
12628
10665
13079
102
Table 4 Absorption properties of compound 9
λmax FWHM εmax
IAC
x 108
f
σ
͇
ꢀ
x 10-19
1.10
Acetonitrile
597 112
28840
0.315
0.187
0.199
0.168
0.123
0.187
0.340
0.353
0.263
0.73
0.43
0.46
0.39
0.28
0.43
0.79
0.82
0.61
6.64
5.17
5.11
4.54
3.91
4.99
6.92
6.99
5.87
Dichloromethane 611 101
28298
23174
27516
22067
21991
30246
27720
28755
1.08
0.89
1.05
0.84
0.84
1.15
1.05
1.09
Dioxane
DMF
561 108
525 126
531 110
568 114
602 116
591 123
560 120
DMSO
Ethyl acetate
Ethanol
Methanol
Toluene