Crystal structure, photoluminescent and theoretical studies of 3-acetyl-8-methoxy-coumarin derivatives

Article abstract of DOI:10.14233/ajchem.2014.17865

3-Acetyl-8-methoxy-coumarin and its derivative 3-(2,2′-dibromoacetyl)-8-methoxy-coumarin were synthesized and characterized. The structure of 3-(2,2′-dibromoacetyl)-8-methoxy-coumarin was verified by single-crystal X-ray crystallography. The UV-visible absorption and fluorescence of 3-acetyl-8-methoxy-coumarin and 3-(2,2′-dibromoacetyl)-8-methoxy-coumarin were also studied. Both compounds exhibit strong blue emission under ultraviolet light excitation. The molecular structure of 3-(2,2′-dibromoacetyl)-8-methoxy-coumarin was optimized using density functional theory at the B3LYP/6-31G(d) level, showing that the optimized geometer parameters are in good agreement with the experimental data. In addition, the HOMO and LUMO levels of 3-acetyl-8-methoxy-coumarin and 3-(2,2′-dibromoacetyl)-8-methoxy-coumarin were deduced.

Full text of DOI:10.14233/ajchem.2014.17865

Asian Journal of Chemistry; Vol. 26, No. 24 (2014), 8427-8430
ASIAN JOURNAL OF CHEMISTRY
http://dx.doi.org/10.14233/ajchem.2014.17865
Crystal Structure, Photoluminescent and Theoretical
Studies of 3-Acetyl-8-methoxy-coumarin Derivatives
1
2
1,*
XIN SHU , JING LI and MING-KAI LI
1
2
Department of Pharmacology, School of Pharmacy, The Fourth Military Medical University, Xi'an, P.R. China
School of Chemistry and Chemical Engineering, Xi'an University, Xi'an, P.R. China
*Corresponding author: E-mail: mingkai@fmmu.edu.cn
Received: 21 April 2014; Accepted: 7 July 2014;
Published online: 1 December 2014;
AJC-16375
3-Acetyl-8-methoxy-coumarin and its derivative 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin were synthesized and characterized. The
structure of 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin was verified by single-crystal X-ray crystallography. The UV-visible absorption
and fluorescence of 3-acetyl-8-methoxy-coumarin and 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin were also studied. Both compounds
exhibit strong blue emission under ultraviolet light excitation. The molecular structure of 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
was optimized using density functional theory at the B3LYP/6-31G(d) level, showing that the optimized geometer parameters are in good
agreement with the experimental data. In addition, the HOMO and LUMO levels of 3-acetyl-8-methoxy-coumarin and 3-(2,2'-
dibromoacetyl)-8-methoxy-coumarin were deduced.
Keywords: Coumarin, Crystal structure, UV-visible, Fluorescence, Density functional theory.
O
O
O
O
INTRODUCTION
Br
Br
In recent years, coumarin and its derivatives have been
representing an important class of organic heterocycles. They
have received considerable attention because of their wide-
spread usage in several fields.
They possess a wide range of biological activities , inclu-
ding antiinflammatory, anticancer, antifungal, antimicrobial,
antiviral, anticoagulant, antituberculosis, anti-HIV and anti-
carcinogenic activities. Moreover, this group of compounds
O
O
O
O
1,2
DMC
AMC
Fig. 1. Chemical structure of 3-acetyl-8-methoxy-coumarin (AMC) and
3
-(2,2'-dibromoacetyl)-8-methoxy-coumarin (DMC)
3,4
possess unique photochemical and photophysical properties ,
including sufficient fluorescence in the visible light range, high
quantum yields, large Stokes shift, superior photostability and
good solubility in common solvents. Consequently, they are
EXPERIMENTAL
-1
IR spectra (4000-400 cm ) were obtained using a Brucker
Equinox-55 spectrophotometer. H NMR spectra were obtained
1
5,6
very useful in a variety of applications , such as in optical
brighteners, laser dyes, non-linear optical chromophores, solar
energy collectors, fluorescent labels and probes in biology and
medicine, as well as in two-photon absorption materials. For
example, 3-acetylcoumarin displays polymorphism, while
many of its derivatives like the title compound 3-acetyl-8-
methoxy-coumarin (ACM, Fig. 1) are effective anticancer
agents or have been proposed as sensitizers for light-sensitive
using a Varian Inova-400 spectrometer (at 400 MHz). Mass
spectra were obtained using a micrOTOF-Q II mass spectro-
meter. The melting points were taken on a XT-4 micro melting
apparatus and the thermometer was uncorrected. UV-visible
absorption and emission spectra were recorded using a thermo
evolution 300 spectrometer and a cary eclipse spectrometer,
respectively. All the chemicals were commercially available
and used without further purification. All the solvents were
dried using standard methods before use.
7
materials . In this study, we synthesized a new compound 3-
(
2,2'-dibromoacetyl)-8-methoxy-coumarin (DMC, Fig. 1)
Synthesis: 3-Methoxysalicylaldehyde (15.2 g, 0.1 mol),
ethylacetoacetate (12.6 mL, 0.1 mol), piperidine (2 mL) and
ethanol (200 mL) were mixed in a 500 mL round-bottomed
from the compound 3-acetyl-8-methoxy-coumarin and then
studied their photophysical properties.

8
428 Shu et al.
Asian J. Chem.
flask, refluxed under magnetic stirring for 4 h and cooled to
room temperature. The yellowish solid was filtered off and
then recrystallized from ethanol to give 3-acetyl-8-methoxy-
theory (DFT) using a B3LYP/6-31G(d) basis set. The structure
optimization and energy calculations were performed with the
GAUSSIAN 09 program.
8
coumarin .
RESULTS AND DISCUSSION
3
-Acetyl-8-methoxy-coumarin (AMC): m.p. 173-174 °C.
H NMR (CDCl , δ, ppm): 2.732 (s, 3H), 3.988 (s, 3H), 7.177-
.284 (m, 3H), 8.480 (s, 1H). ESI-MS: m/z 219 [M + 1] .
-(2,2'-Dibromoacetyl)-8-methoxy-coumarin (DMC) was
1
3
Crystal structure description: The crystal structure of
+
7
3
-(2,2'-dibromoacetyl)-8-methoxy-coumarin is given in
3
Fig. 2. The selected bond lengths and bond angles of 3-(2,2'-
dibromoacetyl)-8-methoxy-coumarin are listed in Table-2.
obtained by the reaction of 3-acetyl-coumarin with bromine
9
as described in literature and recrystallized from chloroform/
ethanol solution at room temperature to give the desired crystals
suitable for single crystal X-ray diffraction.
3
-(2,2'-Dibromoacetyl)-8-methoxy-coumarin (DMC):
1
m.p. 165-166 °C. H NMR (CDCl
3
, δ, ppm): 2.622 (s, 3H),
4
.158 (s, 1H), 6.247-6.884 (m, 3H), 8.720 (s, 1H). ESI-MS:
+
m/z 376 [M + 1] .
Determination of crystal structure: The X-ray diffraction
data of compound 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
were collected on a Bruker SMART APEX II CCD diffracto-
meter equipped with a graphite monochromated MoK
α
radiation (λ = 0.71073 Å) by using the ω-2θ scan technique at
room temperature. The structure was solved by direct methods
using SHELXS-97 and refined using the full-matrix least
2
squares method on F with anisotropic thermal parameters for
10
Fig. 2. Crystal structure of 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin (DMC)
all non-hydrogen atoms by using SHELXL-97 . Hydrogen
atoms were generated geometrically. The crystal data and
details concerning data collection and structure refinement are
given in Table-1. Molecular illustrations were prepared using
the XP package. Parameters in CIF format are available as
Electronic Supplementary Publication from Cambridge
Crystallographic Data Centre.
TABLE-2
EXPERIMENTAL AND CALCULATED PARAMETERS OF
THE SELECTED BOND LENGTHS AND BOND ANGLES OF 3-
(2,2'-DIBROMOACETYL)-8-METHOXY-COUMARIN
Parameter
DMC
Bond length (Å)
X-ray
Calculation
O(1)–C(1)
O(1)–C(9)
O(2)–C(9)
O(3)–C(10)
O(4)–C(2)
O(4)–C(12)
C(8)–C(10)
1.368
1.392
1.211
1.213
1.357
1.443
1.514
1.359
1.390
1.210
1.215
1.354
1.422
1.502
TABLE-1
CRYSTAL DATA, DATA COLLECTION AND
STRUCTURE REFINEMENT OF COMPOUND
-(2,2'-DIBROMOACETYL)-8-METHOXY-COUMARIN
3
Formula
Mr
Temperature (K)
C H O Br
373.88
273
12
8
4
2
Angle (°)
X-ray
Calculation
Crystal system
Space group
Monoclinic
C(1)–O(1)–C(9)
C(2)–O(4)–C(12)
O(1)–C(1)–C(2)
O(4)–C(2)–C(3)
C(9)–C(8)–C(10)
O(2)–C(9)–O(1)
O(1)–C(9)–C(8)
O(3)–C(10)–C(8)
C(11)–C(10)–C(8)
122.5
116.2
117.2
125.8
121.9
115.6
116.3
119.8
118.7
123.5
118.2
117.3
125.9
122.9
116.7
116.0
120.4
118.1
P2 /n
1
a/Å
b/Å
c/Å
α/°
β/°
6.970 (2)
24.954 (8)
7.016 (2)
90
103.802 (4)
90
1184.9 (7)
4
2.108
6.844
1.6 to 28.2
9821
2094[0.0517]
1679
0.0241
0.0531
989310
γ/° 3
V/Å
Z
–03
Dcalc/g cm
µ(MoK )/mm
θ range/°
Fig. 2 shows that the 3-(2,2'-dibromoacetyl)-8-methoxy-
coumarin molecule is essentially planar because its lactone
and benzene rings are inclined only 0.171(88)° to one another.
The maximum deviation of the atoms in the skeleton (the
lactone and benzene rings) from the molecular plane (C(1)-
C(9)/O(1)) is only 0.0175 Å. The O(2)/C(9)/O(1) and C(2)/
O(4)/C(12) planes are inclined 1.057(284) and 6.261(228)°,
respectively to the molecular plane. However, the O(3)/C(10)/
C(11) plane makes a 3.128(271)° angle with the molecular
plane and atoms O(3) and C(11) deviate from that plane by
0.0105 and 0.1154 Å, respectively. In addition, the C(2)-O(4)
bond (1.3568(36) Å) is significantly shorter than C(12)-O(4)
–
1
α
Reflections collected
No. unique data[R(int)]
No. data with I ≥ 2σ(I)
R1
ωR (all data)
2
CCDC
Quantum chemical calculation: The structures of 3-
acetyl-8-methoxy-coumarin and 3-(2,2'-dibromoacetyl)-
-methoxy-coumarin were optimized by density functional
8

Vol. 26, No. 24 (2014)
Crystal Structure, Photoluminescent and Theoretical Studies of 3-Acetyl-8-methoxy-coumarin Derivatives 8429
(
1.4426(31) Å), indicating a donation of the electrons from
1
.0
.8
1.0
0.8
0.6
0.4
0.2
0.0
the O atom to the aromatic ring.
Strong intermolecular hydrogen bonds are also observed
in the structure. These hydrogen bonds link the molecules
together to form planar structures, which are further held
together via π-π stacking interactions to form a three-dimen-
sional supramolecular architecture. Finally, the molecules are
assembled to form a layer structure (Fig. 3).
AMC
DMC
0
0.6
0.4
0.2
0.0
3
00
400
Wavelength (nm)
Fig. 4. Normalized UV-visible absorption and emission spectra of 3-acetyl-
-methoxy-coumarin and 3-(2,2'-dibromoacetyl)-8-methoxy-
500
600
700
8
coumarin in diluted dichloromethane solutions
data, as listed in Table-1. The average discrepancy of the selected
bond lengths between theoretical and experimental data is less
than ± 0.02 Å and the average discrepancy of the selected bond
angles is less than ± 2°. Therefore, the results using density
functional theory (DFT) at the B3LYP/6-31G(d) level are
creditable.
Fig. 3. Packing diagram in a unit cell
UV-visible absorption and photoluminescence of 3-
acetyl-8-methoxy-coumarin and 3-(2,2'-dibromoacetyl)-8-
methoxy-coumarin: The UV-visible absorption and photo-
luminescence spectra of 3-acetyl-8-methoxy-coumarin and
The HOMO and LUMO levels of 3-acetyl-8-methoxy-
coumarin and 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
were deduced using density functional theory method (Fig. 5),
which is essential for deducing their S and S states. This
3
-(2,2'-dibromo-acetyl)-8-methoxy-coumarin in diluted
dichloromethane solutions are shown in Fig. 4. The absorption
spectrum of coumarin has a sharp absorption peak at 281 nm,
0
1
knowledge is important for better understanding of their
fluorescence and nonlinear optical properties.
11
with a shoulder at 320 nm . 3-Acetyl-8-methoxy-coumarin
only has intense absorption at 316 nm, which is red-shifted
with respect to the sharp absorption peak of coumarin. The
difference in the absorption features of 3-acetyl-8-methoxy-
coumarin and coumarin may be attributed to the introduction
of an electron-attracting acetyl group to the 3-position of
coumarin ring and an electron-repelling methoxyl group to
the 8-position, thereby resulting in a stronger intramolecular
charge transfer.
In addition, the absorption peak at 330 nm of compound
3
-(2,2'-dibromoacetyl)-8-methoxy-coumarin is red-shifted
AMC [HOMO (-6.350 eV)]
AMC [LUMO (-2.394 eV)]
compared with that of compound 3-acetyl-8-methoxy-coumarin
as a result of two electron-attracting chlorine atoms in the acetyl
group, which increase the effect of intramolecular charge
transfer.
Fig. 4 also shows the photoluminescence spectra of 3-
acetyl-8-methoxy-coumarin and 3-(2,2'-dibromoacetyl)-8-
methoxy-coumarin in diluted dichloromethane solutions. The
compound 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
exhibits a bright blue emission, with a maximum emission
peak at 484 nm, which is red-shifted by about 26 nm with
respect to that of compound 3-acetyl-8-methoxy-coumarin at
DMC [HOMO (-6.210 eV)]
DMC [LUMO (-2.514 eV)]
Fig. 5. HOMO and LUMO electron distributions of 3-acetyl-8-methoxy-
coumarin (AMC) and 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
(DMC)
4
58 nm because of the greater strength of the intra-molecular
charge transfer upon the introduction of two chlorine atoms
to the 3-acetyl group.
Quantum chemical calculations: B3LYP/6-31G(d) opti-
mized structure of 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
is close to its X-ray crystal structure. B3LYP/6-31G(d) opti-
mized geometrical data of 3-(2,2'-dibromoacetyl)-8-methoxy-
coumarin is in good agreement with the X-ray crystallographic
The HOMO and LUMO diagrams of 3-acetyl-8-methoxy-
coumarin and 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin
show that the two compounds are likely to exhibit an efficient
electron transfer from the benzene ring of HOMO to the whole
molecular skeleton of LUMO if electronic transitions occur.

8
430 Shu et al.
Asian J. Chem.
The HOMO for the two compounds is localized at the benzene
ring, whereas the LUMO at the whole coumarin moiety. There-
fore, when electrons transfer from HOMO to LUMO, the electron
density significantly decreases in the electron-donating benzene
ring system, accompanied by an increase in the electron density
of the electron accepting lactone ring system. This indicates
that the electrons transfer from the benzene ring to the lactone
ring.
Based on the optimized structure, the HOMO and LUMO
levels of 3-acetyl-8-methoxy-coumarin are -6.350 and -2.394
eV, respectively and the energy gap between HOMO and
LUMO is approximately 3.956 eV. The corresponding levels
for 3-(2,2'-dibromoacetyl)-8-methoxy-coumarin are -6.210
and -2.514 eV and the relative energy gap is 3.696 eV. The
value of the energy gap of 3-(2,2'-dibromoacetyl)-8-methoxy-
coumarin to be lower than that of 3-acetyl-8-methoxy-coumarin,
which leads to the absorption peak of 3-(2,2'-dibromo-acetyl)-
REFERENCES
1
2
.
.
K.C. Fylaktakidou, D.J. Hadjipavlou-Litina, K.E. Litinas and D.N.
Nicolaides, Curr. Pharm. Des., 10, 3813 (2004).
L.K.A.M. Leal,A.A.G. Ferreira, G.A. Bezerra, F.J.A. Matos and G.S.B.
Viana, J. Ethnopharmacol., 70, 151 (2000).
3. H. Zhang, T.Z. Yu, Y.L. Zhao, D.W. Fan, L. Qian, C.H. Yang and K.
Zhang, Spectrochim. Acta A, 68, 725 (2007).
4
5
6
7
.
.
.
.
H. Zhang, T.Z. Yu, Y.L. Zhao, D.W. Fan, L.L. Chen, Y.Q. Qiu, L. Qian,
K. Zhang and C.H. Yang, Spectrochim. Acta A, 69, 1136 (2008).
H. Turki, S. Abid, S. Fery-Forgues and R. El Gharbi, Dyes Pigments,
73, 311 (2007).
C. Féau, E. Klein, P. Kerth and L. Lebeau, Bioorg. Med. Chem. Lett.,
1
7, 1499 (2007).
H.M. Han, C.R. Lu, Y. Zhang, D.C. Zhang, Acta. Cryst., E61, o1864
2005).
(
8. J. Li, Y. He, X. Ren, X. Shi, S. Yang, X. Gao and G. Huang, Chinese J.
Struct. Chem., 31, 1003 (2013).
H.A. Sparkes and J.A.K. Howard, Acta Crystallogr., 63E, o3895 (2007).
0. G.M. Sheldrick, SHELXS 97, Program for the Solution of Crystal Struc-
ture, University of Göttingen, Germany (1997).
9
1
.
8-methoxy-coumarin to be bathochromically shifted compared
11. T.Z. Yu, Y.L. Zhao and D.W. Fan, J. Mol. Struct., 791, 18 (2006).
with that of 3-acetyl-8-methoxy-coumarin.
ACKNOWLEDGEMENTS
This research was supported by grants from the Inno-
vation plan of science and technology of Shaanxi Province
(
2014KTCL03-03).