Fluorescent probe 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one: Experimental and DFT based approach to photophysical properties

Article abstract of DOI:10.1016/j.saa.2015.03.113

Abstract Compound 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one was synthesized by Pechmann condensation reaction and characterized by various spectroscopic techniques. The structure of title compound was confirmed by single crystal X-ray diffraction. The compound crystallized in the orthorhombic system with P 21 21 21 space group and the corresponding lattice parameters were found to be a = 4.0138 (11) ?, α = 90°; b = 23.536 (6) ?, β = 90°; c = 10.93 (2) ?, γ = 90°. The crystal packing of molecule showed that intermolecular hydrogen bonds C3-H3?O3 [D = 3.53 ?, C-13-H13?O2 [D = 3.67 a and intermolecular short interaction between C1-H1?C1-H1 [2.68 ? forms a dimeric unit which finally stabilizes the crystal packing in three dimensional network in the molecule. Absorption and emission spectra shows that compound is fluorescent with good Stoke shift values ranging between 57 and 62 nm. Thermal analysis further supports by TGA, DTA. The photophysical results show that the compound exhibits change in fluorescence quantum yield with change in solvent polarity. The structural parameters and the vibrational wave numbers obtained from the optimized geometry of the compound from DFT-B3LYP calculations employing 6-311G (d,p) basis set are in good agreement with the experimental data. UV-Vis spectrum calculated by employing time dependent density functional theory (TD-DFT) is also in very good agreement with the experiment for all solvents.

Full text of DOI:10.1016/j.saa.2015.03.113

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 311–317
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Fluorescent probe 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one:
Experimental and DFT based approach to photophysical properties
Neesha Yadav a, Shailja Singh a, Shrawan Kumar Mangawa a, Sandeep K. Dixit a, Ujval Gupta b,
Yugal Khajuria b, Satish Kumar Awasthi a,
⇑
a Chemical Biology Laboratory, Department of Chemistry, University of Delhi, 110007, India
b School of Physics, Shri Mata Vaishno Devi University, Katra, Jammu & Kashmir 182320, India
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
Coumarin has high fluorescence
quantum yield, large Stokes shift and
excellent light stability.
Interaction with non-polar solvents
depends on the dipole-induced-
dipole forces.
In aprotic solvents the solute–solvent
interaction depends on the strong
dipole–dipole forces.
UV–Vis spectrum calculated by
employing time dependent density
functional theory.
a r t i c l e i n f o
a b s t r a c t
Article history:
Compound 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one was synthesized by Pechmann condensation reac-
tion and characterized by various spectroscopic techniques. The structure of title compound was con-
firmed by single crystal X-ray diffraction. The compound crystallized in the orthorhombic system with
P 21 21 21 space group and the corresponding lattice parameters were found to be a = 4.0138 (11) Å,
Received 27 September 2014
Received in revised form 12 March 2015
Accepted 27 March 2015
Available online 2 April 2015
a
= 90°; b = 23.536 (6) Å, b = 90°; c = 10.93 (2) Å, c = 90°. The crystal packing of molecule showed that
intermolecular hydrogen bonds C3–H3ꢁ ꢁ ꢁO3 [D = 3.53 Å], C-13–H13ꢁ ꢁ ꢁO2 [D = 3.67 Å] and intermolecular
short interaction between C1–H1ꢁ ꢁ ꢁC1–H1 [2.68 Å] forms a dimeric unit which finally stabilizes the crys-
tal packing in three dimensional network in the molecule. Absorption and emission spectra shows that
compound is fluorescent with good Stoke shift values ranging between 57 and 62 nm. Thermal analysis
further supports by TGA, DTA. The photophysical results show that the compound exhibits change in
fluorescence quantum yield with change in solvent polarity. The structural parameters and the vibra-
tional wave numbers obtained from the optimized geometry of the compound from DFT-B3LYP cal-
culations employing 6-311G (d,p) basis set are in good agreement with the experimental data. UV–Vis
spectrum calculated by employing time dependent density functional theory (TD-DFT) is also in very
good agreement with the experiment for all solvents.
Keywords:
Pechmann condensation
Absorption and emission spectra
Quantum yield
TD-DFT
Ó 2015 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +91 11 27666646x121, 134, +91 9582087608.
E-mail addresses: awasthisatish@yahoo.com, skawasthi@chemistry.du.ac.in (S.K. Awasthi).
http://dx.doi.org/10.1016/j.saa.2015.03.113
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

312
N. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 311–317
characterized a series of coumarin analogs and evaluated them
Introduction
for their antiplasmodial activity. Here, we report the synthesis,
crystallographic, UV, fluorescence, DFT calculations and thermal
studies of 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one.
Coumarin is a naturally occurring secondary metabolite widely
found in several plant families, essential oils, microorganisms and
a few animal species. These derivatives possess a remarkably broad
spectrum of biological activities including antibacterial [1,2],
antifungal [3–5], anticoagulant [6], anti-inflammatory [7], antitu-
mor [8,9] and anti-HIV [10]. The commercial application of cou-
marin includes use as additives in food, cosmetics dispersed
fluorescent brightening agents and as dyes for tuning lasers
[11,12]. The structure of benzopyrone has many advantages
including high fluorescence quantum yield, large Stokes shifts,
excellent light stability and low toxicity [13]. Coumarin derivatives
have been used as fluorescent probes [14], for detection of nitric
oxide [15], nitroxide [16], and hydrogen peroxide [17]. Moreover,
coumarin derivatives have also showed good chemosensors of
anions including cyanide, fluoride, pyrophosphate acetate, ben-
zoate and dihydrogenphosphate [18].
Naturally occurring coumarin shows fluorescence properties
which could be further enhanced by attaching of more appropriate
chromospheres at suitable positions especially at position-3 and -7
in coumarin [19,20]. It is well documented that electron donor
groups such as amino, hydroxyl and methoxy at the position-7 and
heterocyclic electron acceptors such as benzothiazole, benzoxazole
and benzimidazole at the position-3 induced bathochromicity and
shows strong fluorescence [21,22]. Coumarin dyes undergo very
little nuclear reorganization, yet are solvatochromic owing to the
change in electronic distribution resulting in an increase in dipole
moments from ground state to excited state [23]. The strong
emissions of coumarins results from the polar character of low-
lying excited states. It is known that the electronic spectra of these
molecules are influenced by their immediate environment. Among
the major environmental factors influencing the electronic spectra,
solvents effects are of particular importance.
Experimental procedure
Material synthesis
Preparation of 4-methyl-7-hydroxycoumarin (1)
Synthesis of title compound 4-methyl-7-hydroxycoumarin was
achieved by reported procedure [30]. Briefly, the concentrated
H2SO4 (20 ml) was taken into a 250 ml round bottom flask and
cooled to 0 °C. A solution of resorcinol (2.0 g, 18.16 mmol) in ethy-
lacetoacetate (2.4 ml, 19.00 mmol) was added dropwise to the
flask with constant stirring, while maintaining the temperature
below 10 °C. The mixture was further stirred overnight at room
temperature. The reaction mixture was poured into crushed ice
with vigorous stirring. A light yellow solid product was formed
which was filtered and washed with cold water. The crude product
was re-crystallized from ethanol to obtain pure 4-methyl-7-hy-
droxycoumarin in 60% yield (1.8 g) as white crystal.
Thus, the study of new coumarins can shed an idea for further
designing of bioactive molecules. In the context of the ongoing
research work in our laboratory aimed at design and synthesis of
anti-microbial compounds [24–27] and X-ray analysis of small
molecules [28,29], we recently designed, synthesized and
Fig. 2. ORTEP diagram of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one.
Fig. 1. Synthesis of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one.

N. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 311–317
313
Synthesis of 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one (2)
solvents were recorded on Carry eclipse fluorimeter. The thermo
gravimetric analysis (TGA) of 7-(prop-2-yn-1-yloxy)-2H-chro-
men-2-one was carried out in the temperature range of 25–
600 °C under nitrogen atmosphere at a heating rate of 10.00 °C/
min.
The compound 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one was
synthesized by reported procedure [31]. Briefly, to a stirred solu-
tion of 4-methyl-7-hydroxycoumarin (1.76 g, 1.0 M equiv) in dry
acetone (25 ml), anhydrous potassium carbonate (1.38 g, 1.0 M
equiv) and propargyl bromide (1.19 g, 1.0 M equiv) were added
and the resultant mixture was stirred at 50 °C for 18 h. The reac-
tion mixture was cooled and the solvent was completely removed
under reduced pressure and the residue was dissolved in 15 ml of
water and extracted with ethylacetate (3 ꢂ 50 ml). The combined
organic phase was washed with water, dried over anhydrous
sodium sulfate and solvent evaporated in vacuo. The crude product
was purified by performing column chromatography using silica-
gel (60–100 mash size) using ethylacetate–hexane mixture as elu-
ent to yield light yellow solid in 90% yield (1.6 g). The overall syn-
thetic scheme is shown in Fig. 1.
Computational details
The title compound was subjected to DFT calculations to obtain
the optimized geometrical parameters, thermodynamics proper-
ties, vibrational frequencies, HOMO–LUMO gap and UV–Vis spec-
trum. The calculations have been performed with Gaussian 09
program [32] package. The gradient correlated density functional
theory (DFT) [33] with three-parameter hybrid functional B3
[34,35] for the exchange part and the Lee–Yang–Parr (LYP) correla-
tion function [36] with standard 6-311G (d,p) basis set has been
used for the computation of molecular structure, vibrational fre-
quencies, thermodynamics properties and UV–Vis spectrum. The
optimized parameters were used for harmonic vibrational frequen-
cies calculations resulting in IR frequencies. B3LYP/6-311G (d,p)
basis set produced satisfactory results for frequency calculations
but with systematic errors due to neglect of electron correlations
resulting in an overestimation of about 10–12%. The computed
wave numbers are scaled by an empirical scaling factor of 0.96 to
fit the experimental wave numbers. The assignments of the calcu-
lated normal modes have been made by the corresponding poten-
tial energy distributions (PEDs). The PEDs are computed from
calculated vibrational frequencies using VEDA [37]. GAUSSVIEW
5.0.9 program [32] has been used to get the visual animation and
for the verification of the normal modes assignments.
Crystal growth
About 10 mg of 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one was
dissolved in 1:1 mixture of CHCl3 and hexane 5 ml and carefully fil-
tered at room temperature using fine pore Whatman filter paper
42. The filtered solution was kept in a small glass tube at room
temperature for few days. By employing the solvent slow evap-
oration method, a good transparent single crystal suitable for X-
ray analysis was harvested from the mother solution.
Characterization
X-ray diffraction data were collected on an Oxford Diffraction
Xcalibur CCD diffractometer with graphite monochromatic Mo
Ka radiation (k = 0.71073 Å) at 298 (2) K. A total number of 7476
reflections were measured, out of which 2020 reflections were
unique. The structure was solved by direct method using
SHELXL-97 and refined by full matrix least-squares method on F2
(SHELXL-97). All calculations were carried out using the WinGX
package of the crystallographic program and PLATON. Program
ORTEP-3 and Mercury were used to generate molecular graphics.
The FT-IR analysis of 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one
was carried out to characterize the presence of functional groups
and their vibrational modes. The spectrum was recorded in KBr
pellet in the range of 400–4000 cmꢃ1 at room temperature using
Perkin-Elmer Fourier Transform Infrared Spectrometer. 1H NMR
and 13C NMR spectrum of compound 7-(prop-2-yn-1-yloxy)-2H-
chromen-2-one was recorded in CDCl3 using JEOL GS-400 model
FT-NMR spectrometer. The UV–visible spectra of the compound
was recorded using Specord250-222 P145 UV–visible spectropho-
tometer equipped with 1.0 cm quartz cell in the range of 195–
1000 nm. The fluorescence spectra of title compound in various
Fig. 4. UV–Visible spectrum of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one.
Fig. 3. Packing diagram of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one.

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Table 1
Absorption and emission spectra data, Stoke shift and quantum yield.
Solvent
Absorption (kmax(ab))
(kmax(ab)) 6-311G (d,p)
Oscillator strength
Emission (kmax(Emisson)
)
Stoke shift (
D
k)
Uf
Acetonitrile
Chloroform
DMF
Ethylacetate
Methanol
316.94
319.42
317.88
316.33
320.03
304.6
305.5
304.20
303.7
304.33
0.421
0.437
0.433
0.420
0.417
0.421
0.437
0.433
0.420
0.417
58.75
58.13
61.09
61.69
57.99
0.62
0.22
0.41
–
0.08
Table 2
Electronic transition from HOMO to LUMO with major contribution.
Solvent
Excitation energies eV (TD-DFT)
Major contributions
Acetonitrile
Chloroform
DMF
Ethylacetate
Methanol
4.0710
4.0586
4.0757
4.0817
4.0740
HOMO ? LUMO (+83%)
HOMO ? LUMO (+83%)
HOMO ? LUMO (+96%)
HOMO ? LUMO (+95%)
HOMO ? LUMO (+82%)
Results and discussion
Single crystal X-ray analysis
The crystal structure of 7-(prop-2-yn-1-yloxy)-2H-chromen-2-
one is shown in Fig. 2. The unit cell parameters showed following
values; a = 4.0138 (11) Å,
a = 90°; b = 23.536 (6) Å, b = 90°;
c = 10.93 (2) Å, = 90° and volume = 1038.5 (4) Å [3]. These values
c
suggested orthorhombic cell setting with the space group of P 21
21 21. The final residual index were found as R = 0.0833,
Rw = 0.1430 for the observed and R = 0.1743, Rw = 0.1776 for all
the reflections using 145 parameters. The complete crys-
tallographic data collection, crystal data and the refinement details
are summarized in Table S1. The calculated and experimental bond
distance and bond angles are given in supporting material Table S2.
The results show that the average discrepancies of the selected
bond lengths and bond angles between theoretical and experimen-
tal data are very small.
Anisotropic displacement parameters (Å2 ꢂ 103) for compound
7-(prop-2-yn-1-yloxy)-2H-chromen-2-one is represented in sup-
porting material Table S3. The anisotropic displacement factor
exponent takes the form: ꢃ2p2[h2a⁄2U11 + . . . + 2 h k a⁄ b⁄ U12].
Table 3
Calculated thermodynamic parameters of the compound with B3LYP method using 6-
311G (d,p) and HF/6-311G (d,p).
Fig. 5. Graphical representation of the frontier orbitals by B3LYP/6 -311G(d,p).
Thermodynamic parameters (298 K)
B3LYP/6-311G
(d,p)
HF/6-311G (d,p)
Crystal packing
SCF energy (Hatrees)
ꢃ727.188468934 ꢃ722.799847356
Total energy (Thermal), Etotal
131.661
140.506
(kcal molꢃ1
)
The compound 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one was
crystallized in orthorhombic cell with space group P 21 21 21 with
four molecules per unit cell. The alternate single and double bond
values in benzopyran ring show slight variation due to the steric
factors. The bond length between C11–C12 was found to be
1.35 Å which is slightly greater than the standard value of 1.34 Å
while the exocyclic angle between C6–C7–C12 was found 124.7°
which is also greater than standard value of 120°. This increase
of 4.7° may be attributed to non-bonded repulsive interaction
between H6 and C12 substitution. On the other hand, exocyclic
angle between O2–C8–C9 was found 114.9° as there are no repul-
sive interactions, since no periplanar angle is found to O2. The
dihedral angle between the fused rings 1 and 2 is 1.21° suggest pla-
nar nature of two rings. The propynyl substitution at 7-position of
benzopyran ring is projected little above the plane thus making an
angle of 5.92°. Further, the O3–C10–C11 angle (127°) is slightly
greater than the O2–C10–O3 (116.4°) because of the steric effect
of substituent at C11. The methyl group angles are tetrahedral
Vibrational energy, Evib(kcal molꢃ1
Zero point vibrational energy, E0
)
129.884
122.871
138.729
132.352
(kcal molꢃ1
)
Heat capacity, Cv (Cal/Mol-Kelvin)
Entropy, S (Cal/Mol-Kelvin)
ELUMO+1 (eV)
ELUMO (eV)
EHOMO (eV)
EHOMOꢃ1 (eV)
ELUMO ꢃ EHOMO (eV)
Rotational constants (GHz)
53.625
118.480
ꢃ0.694
ꢃ1.828
ꢃ6.308
ꢃ7.165
4.480
49.385
114.387
ꢃ3.206
ꢃ2.109
ꢃ8.490
ꢃ9.645
6.382
A
B
C
1.211
0.262
0.216
1.24015
0.26514
0.01051
Dipole moment (Debye)
lx
ly
lz
ltotal
ꢃ2.0347
3.699
ꢃ1.8090
4.1860
0
0.3325
4.2968
4.5602

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315
methyl group at 4-position of coumarin while signal at 56.0 ppm
is due to methylene carbon.
UV–visible analysis
It is well established that coumarin absorbs light in the UV
region and transmits in the remaining region as shown in Fig. 4.
The crystal was transparent in the entire visible and IR region.
The absorption spectrum of compound was recorded in different
solvents of various polarities such as acetonitrile, chloroform,
DMF, ethylacetate and methanol in order to see solvatochromic
effects. The Kamlet–Taft parameters (
study the polarity and hydrogen bonding properties of the solvents
used in the present experiment [38]. Here is a scale of solvent
a
, b, and p⁄) were used to
a
hydrogen bond donor (HBD) acidities, b is a scale of solvent hydro-
gen bond acceptor (HBA) basicities and p⁄ denotes scale of solvent
dipolarity/polarizability which refers the ability of solvent to
stabilize a charge or a dipole.
The p⁄ value is correlated with the solvatochromic behavior
values. The solvatochromic effect of a compound is due to the
interaction between the solute and solvent molecules and showed
Fig. 6. Emission spectrum of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one.
shift of the
p–
p⁄ band [39]. The absorption spectra of the com-
pound was recorded in various solvents and showed absorption
maxima in the UV region at 316.94 nm in acetonitrile, 319.42 nm
in chloroform, 317.88 nm in DMF, 316.33 nm in ethylacetate and
320.03 nm in methanol. All these values are tabulated in Table 1.
The absorption peak at wavelength specifically in between 315
and 320 nm can be assigned as n–p⁄ transition and may be attrib-
uted to the excitation in C@O group of pyrone ring. It is clear from
analysis of the spectral results that there is practically no solvato-
chromism as there is no significant change in absorption as seen
from the Table 1.
within experimental error and the H13A atom lies in the plane of
pyrone ring while the H13B and H13C atoms are displaced equidis-
tantly above and below the ring, respectively. The molecule shows
intermolecular hydrogen bonding between carbon and oxygen C–
Hꢁ ꢁ ꢁO as seen earlier [32]. The intermolecular hydrogen bond
between atom C3–H3ꢁ ꢁ ꢁO3 have bond length of 2.267 Å with
1.5 ꢃ x, ꢃy, ½ + z symmetry code while C13–H13Bꢁ ꢁ ꢁO2 shows
2.689 Å, little longer bond length than standard value having
1.5 ꢃ x, ꢃy, ½ + z symmetry code. Overall, these intermolecular
hydrogen bonds help in crystal packing and stabilize the structure
of molecule in three dimensional. The short interactions between
atoms C1–H1ꢁ ꢁ ꢁC1–H1 (bond length 2.689 Å & symmetry code
½ + x, ½ ꢃ y, 2 ꢃ z) form a dimeric unit at 7-substituted position
and thus plays critical role in crystal packing. The crystal packing
diagram is shown in Fig. 3.
The energy gap between HOMO and LUMO is a critical parame-
ter in determining molecular electronic transport properties. The
maximum absorption wavelength (kmax) corresponds to the elec-
tronic transition from the HOMO to LUMO with major contribution
[40]. The energies of the four important molecular orbital of the
title compound; the second highest and highest occupied
molecular orbitals (HOMO and HOMOꢃ1), the lowest and the sec-
ond lowest unoccupied molecular orbitals (LUMO and LUMO+1)
were calculated and are presented in Table 2 along with other
thermodynamical parameters in Table 3. The lowest singlet to
singlet spin allowed excited states were taken into account for
the TD-DFT calculations in order to investigate the properties
of the electronic absorption. The calculations were performed
with acetonitrile, chloroform, DMF, ethylacetate, and methanol
solvents. The calculated absorption wave lengths, excitation ener-
gies, major contribution for the transition and corresponding oscil-
lator strengths are given in Table 1 along with experimental
wavelengths. The observed wavelengths show a very good agree-
ment with the calculated wavelengths using TD-DFT with 6-
311G (d,p) for all the solvents. The calculations with higher basis
sets were also performed and marginal increases in the wave-
lengths have been observed. From Table 1 it is clear that the calcu-
lated peaks for all the solvents lies between 303 and 306 nm and
FT-IR spectral analysis
Peak at 3303 cmꢃ1 is due to stretching in terminal alkyne C–H
while peak at 2369 cmꢃ1 is due to [HC„C] stretching. The experi-
mental IR values are in well agreement with the calculated fre-
quencies given in supporting material Table S3. The characteristic
absorption bands are also found consistent with the functional
groups presented in the molecule as shown in Table S4.
Experimental and calculated IR spectra are shown in supporting
information Figs. S1 and S2.
NMR analysis
1H NMR spectra shows characteristic peaks, singlet at position
2.4 ppm due to methyl proton attached 4-position of coumarin
and a singlet at 2.57 ppm due to alkyne proton. Further, down field
singlet at 4.76 ppm corresponded to two methylene protons (–O–
CH2–). The down field signal is due to the presence of electron
withdrawing group adjacent methylene group. In aromatic region,
singlet at position 6.16 ppm corresponded to H3 proton of cou-
marin pyran ring while multiplet at 6.93 ppm and 7.50 ppm corre-
sponded to H5, H6 and H8 proton of aromatic ring respectively. The
13C NMR spectrum of compound is depicted in supporting informa-
tion. Carbonyl carbon shows at 160.24 ppm and aromatic carbons
present at 102.04–152.35 ppm. Signal at 18.56 ppm is due to
can be assigned as p–
p⁄ transition. There are no significant changes
in wavelength with different solvents which indicates that solvato-
chromism is not possible so there is not any significant change in
absorption. The 3D plots of important molecular orbitals are shown
in Fig. 5. The energy gap of HOMO–LUMO explains the eventual
charge transfer interaction within the molecule and the frontier
molecular orbital gap in this case is 4.480 obtained from B3LYP/
6-311G (d,p) and 6.382 obtained from HF/6-311G(D.P) as shown
in Table 3. The molecular orbitals show that the electron density
mostly centered on the substituent’s and pyrone ring, clearly

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N. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 311–317
Fig. 7. TG-DTA curve of 7-(Prop-2-yn-1-yloxy)-2H-chromen-2-one
indicating a charge transfer of the type n–p⁄ transition in C@O
group of pyrone ring.
Although the quantum yield is strongly influenced by the
environment and decrease with increasing the polarity of the med-
ium shown in Table 1. The fluorescence quantum yields are low in
polar protic solvents but not in aprotic ones. It is suggested that
proton interaction with electron rich donors reduces the electron
donating capacity of the group, thus changing the efficiency of
ICT and consequently modulates photophysical properties of cou-
marin derivatives proton interaction with the electron acceptor
enhances the electron withdrawing character of this group and
hence changes in fluorescence quantum yield and spectral shifts
are expected.
Fluorescence
Fluorescence spectra were recorded in different polar solvent
viz. acetonitrile, chloroform, DMF, ethylacetate and methanol,
showed emission peak at position 375.69 nm, 377.55 nm,
378.97 nm, 378.02 nm and 378.02 nm respectively as shown in
Fig. 6. The Stoke shift values for different solvents were calculated
and are tabulated in Table 1. It is quite evident from the emission
maxima and Stokes shift values that the compound reported in this
study exhibits strong fluorescence. Further, the fluorescence spec-
trum may be strongly depends on solvent. This characteristic is
most often observed with fluorophores that have highly exited
state dipole moments resulting in fluorescence spectral shifts to
longer wavelength in polar solvents. Coumarin is a polar solute,
its interaction with non-polar solvents depends on the dipole-in-
duced-dipole forces, while with aprotic (polar but non-hydrogen
bonding) solvents, the solute–solvent interaction depends on the
strong dipole–dipole forces. In protic solvents (alcohol), in addition
to dipole–dipole interaction, specific interaction such as H-bonding
may be effective as the intermolecular charge transfer character is
favorable for H-bonding with hydroxyl group in methanol [41].
Thermal analysis
Thermal behavior was studied by Differential Thermal Analysis
(DTA) and Thermogravimetric analysis (TGA). DTA curve showed
an endothermic peak at 133.36 °C which is due to melting point
of sample. The sharpness of this peak at the melting point showed
a good degree of crystalline of the grown crystal. In TGA curve,
there is a gradual weight loss from 50 to 233 °C due to evaporation
of weakly adsorbed and lattice water of the crystal. Further, the
second weight loss occurs in the range of 250–409 °C due to
decomposition of crystal. Overall these results are given in spectra
as shown in Fig. 7.
Fluorescence quantum yield of the compound
Conclusion
The fluorescence quantum yield of coumarin derivative was
measured in different solvents using coumarin 314 (Uf = 0.78) in
ethanol as the reference compound. Fluorescence quantum yields
of coumarin derivative (Uf) were determined according to Eq. (1).
Good quality single crystals of 7-(prop-2-yn-1-yloxy)-2H-chro-
men-2-one were successfully grown by the slow evaporation solu-
tion growth method and X-ray diffraction studies was carried to
elucidate its structure for the first time. The molecule 7-(prop-2-
yn-1-yloxy)-2H-chromen-2-one crystallizes into orthorombic sys-
tem with the space group P 21 21 21. The presence of functional
groups in compound 7-(prop-2-yn-1-yloxy)-2H-chromen-2-one
was further confirmed by FT-IR analysis. DTA and TGA were carried
out on the grown crystal which indicated that the material does
not sublime before it melts at 133.36 °C. The compound did not
show any appreciable solvatochromism. The coumarin molecule
½Asꢄ ½Rsꢄ ½Dxꢄ
Ux
¼
Us
ð1Þ
½Axꢄ ½Rxꢄ ½Dsꢄ
U = fluorescence quantum yield.
Subscripts x and s denotes test and standard, respectively.
R = refractive index of the solvent.
D = area under the corrected, extrapolated emission spectra.
A = excitation wavelength.

N. Yadav et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 148 (2015) 311–317
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S.K.A. is thankful to University of Delhi, Delhi for financial sup-
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(USIC), University of Delhi, Delhi-110007, Delhi India for analytical
data. Y.K. is thankful to DST, India for the financial support to pur-
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Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.03.113.
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