Synthesis and fluorescent properties of coumarin–chalcone hybrids

Article abstract of DOI:10.3184/174751917X15035711817504

Four coumarin–chalcone hybrids were synthesised utilising condensation of acetylcoumarin with three benzaldehydes and cinnamaldehyde, respectively. Moreover, the absorption and fluorescence spectra of these synthesised compounds in dichloromethane were me

Full text of DOI:10.3184/174751917X15035711817504

534 RESEARCH PAPER
VOL. 41 SEPTEMBER, 534–536
JOURNAL OF CHEMICAL RESEARCH 2017
Synthesis and fluorescent properties of coumarin–chalcone hybrids
Fang Yang, Hongli Fan, Ziyan Xue and Xiaolong Wang*
The School of Chemical and Biological Engineering, Lanzhou Jiaotong University, Lanzhou 730070, P.R. China
Four coumarin–chalcone hybrids were synthesised utilising condensation of acetylcoumarin with three benzaldehydes and
cinnamaldehyde, respectively. Moreover, the absorption and fluorescence spectra of these synthesised compounds in dichloromethane
were measured.
Keywords: coumarin, chalcone, hybrid, absorption spectra, fluorescence spectra
Coumarin and its derivatives have attracted much attention due
to their various pharmacological activities, such as antiviral,
anti-inflammatory and antitumour activity.1 Furthermore,
coumarins are widely used as laser dyes, nonlinear optical
chromophores, fluorescent probes, fluorescent whiteners
and solar energy collectors due to their outstanding optical
properties, including superior photostability, large Stokes shifts
and high quantum yields.2,3
be used as chemosensors for cyanide anions, copper ions and
biothiols.8,9 Recently, our research group has been interested
in preparing a diverse class of coumarin derivatives as well as
investigating their fluorescent properties.10–12 On the basis of
the abovementioned observations, and as an extension of our
study on fluorescent coumarins, we present herein the concise
synthesis and fluorescent properties of several coumarin–
chalcone hybrids.
Chalcones are one of the major classes of organic compounds
and have been extensively investigated due to their variety of
applications. They are reported to have antioxidant, antitumour
and anti-inflammatory activities. Furthermore, chalcones
exhibit excellent nonlinear optical properties and they can be
used in organic light-emitting diodes.4
Therefore, incorporation of a coumarin nucleus with a
chalcone moiety should likely to lead to a hybrid compound
with significant properties. Indeed, coumarin–chalcone hybrids
have been reported to have anti-inflammatory, antioxidant and
antiviral activities.5,6 They also show good thermal stability and
fluorescent properties.7 Moreover, these hybrid molecules can
As electron-withdrawing groups at the 3-position and
electron-donating groups at the 7-position in the coumarin
system have been shown to enhance the fluorescence of
the molecules,13 we employed the commercially available
4-(diethylamino)salicylaldehyde as the starting material for
the synthesis of the title compounds. The synthetic strategy
to achieve the target molecules is outlined in Scheme 1.
Initially, 4-(diethylamino)salicylaldehyde (1) reacted with
ethyl acetoacetate under solvent-free conditions in the presence
of piperidine to afford 3-acetyl-7-(diethylamino)coumarin
(2) in high yield. Next, the intermediate 2 was subjected to
Claisen–Schmidt condensation with benzaldehyde catalysed
O
CHO
a
N
OH
N
O
O
1
2
O
N
O
O
3
O
b
O
O
N
O
O
O
O
c
d
e
4
O
N
O
2
N
O
O
F
5
O
N
O
O
6
Scheme 1 Synthesis of compounds 3–6. Regents and conditions: (a) ethyl acetoacetate, piperidine, solvent-free, r.t. 0.5 h, 91%; (b) benzaldehyde,
piperidine, ethanol, reflux, 8 h, 56%; (c) piperonal, piperidine, ethanol, reflux, 10 h, 49%; (d) 4-fluorobenzaldehyde, piperidine, ethanol, reflux, 6 h, 66%;
(e) cinnamaldehyde, piperidine, ethanol, reflux, 10 h, 51%.
* Correspondent. E-mail: wangxl@mail.lzjtu.cn

JOURNAL OF CHEMICAL RESEARCH 2017 535
by piperidine in ethanol under reflux conditions to furnish
the corresponding coumarin–chalcone hybrid 3 in moderate
yield. The same condensation was also attempted in ethanol
promoted by NaOH, but the expected product was obtained in
very low yield along with appreciable quantities of byproducts.
Compound 2 also underwent condensation with piperonal
and 4-fluorobenzaldehyde in ethanol catalysed by piperidine
to give the coumarin–chalcone hybrids 4 and 5, respectively.
Moreover, we also examined the condensation of intermediate
2 with cinnamaldehyde. Fortunately, the reaction proceeded
well and the desired product 6 was obtained in moderate
yield. As far as we know, the synthesis and photoluminescence
properties of these four compounds 3–6 have not been reported
in the literature. Then, the UV-Vis absorption and fluorescence
spectra of the intermediate 2 and the four synthesised
coumarin–chalcone hybrids 3–6 were measured in diluted
dichloromethane solutions.
The UV-Vis absorption spectra are presented in Fig. 1. It
can be seen that the linear absorption peak of intermediate 2
exists at 433 nm, which is very close to the reported value in
chloroform solution.14 The coumarin–chalcone hybrids 3–6
derived from 2 display obvious red-shift absorption maxima at
455, 458, 455 and 460 nm, respectively, due to their extended
conjugation. In the cases of compounds 3–5, although the
molecular structures are modified in the terminal phenyl ring
where different substituents are attached, they exhibit almost
identical absorption spectra. Compared with 3, compound 6
shows a slight bathochromic shift in the absorption maximum
owing to its larger conjugation.
The fluorescence spectra of compounds 2–6 in
dichloromethane are shown in Fig. 2. It is observed that
intermediate 2 exhibits an emission peak at 465 nm, which
is also similar to the reported value in chloroform solution.14
Compounds 3–6 show emission maxima at 508, 506, 507 and
517 nm, respectively, which show a remarkable bathochromic
shift compared with that of compound 2. It also can be seen
that the emission maxima of compounds 3–5 with different
terminal phenyl moieties are very close to each other. However,
compound 6 displays the highest emission peak among these
compounds, obviously resulting from it having the largest
conjugated system.
been described. The study also reveals that the absorption
and emission maxima of these hybrids show a remarkable
bathochromic shift compared with the acetylcoumarin
precursor. In particular, the hybrid with the longest conjugation
length exhibits the highest emission peak. The applicability of
these coumarin–chalcone hybrids is yet to be established.
Experimental
Reagents and solvents were all from commercial sources and used
without further purification. IR spectra were performed on a Digilab
1
FTS-3000 FT-IR spectrophotometer. H NMR and 13C NMR spectra
were recorded on a Mercury Plus 400 MHz spectrometer. Melting
points were measured on a Kofler apparatus and uncorrected. Column
chromatography purifications were performed on 200–300 mesh silica
gel. Analytical thin-layer chromatography (TLC) was performed on
silica gel GF254 plates. High-resolution mass spectra (HRMS) were
determined on a Bruker Daltonics APEX II 47e spectrometer. UV-
Vis absorption and fluorescence spectra were recorded on a Hitachi
U-3900H spectrometer and on a Hitachi F7000 FL spectrophotometer,
respectively.
3-Acetyl-7-(diethylamino)coumarin (2)
4-(Diethylamino)salicylaldehyde (1.16 g, 6.0 mmol), ethyl
acetoacetate (0.78 g, 6.0 mmol) and piperidine (0.5 mL) were added
to a mortar successively. The mixture was ground well with a pestle
at room temperature for 30 min. Then the mixture was dissolved in
ethyl acetate (100 mL), neutralised with 3N HCl and extracted with
brine (3 × 50 mL). The organic layer was dried over Na2SO4, filtered
and concentrated under reduced pressure. The resulting residue was
recrystallised in ethanol to afford 2 as: Yellow solid; yield 91%; m.p.
155–156 °C (lit.15 151–153 °C).
Synthesis of coumarin–chalcone hybrids (3–6); general procedure
3-Acetyl-7-(diethylamino)coumarin (1.0 mmol) and the corresponding
aldehyde (1.0 mmol) were dissolved in ethanol (30 mL) and piperidine
(0.5 mL) was added. The mixture was stirred under reflux conditions
and monitored by TLC. When the reaction was judged to be complete,
the organic solvent was evaporated under reduced pressure. Then
the mixture was dissolved in ethyl acetate (50 mL), neutralised
with diluted aqueous hydrochloric acid and extracted with brine
(3 × 50 mL). The organic layer was dried over Na2SO4, filtered and
concentrated under reduced pressure. The resulting residue was
purified by column chromatography using petroleum ether/ethyl
acetate (v/v = 5:1) as eluent to afford the product.
In conclusion, the facile synthesis of four coumarin–chalcone
hybrids by Claisen–Schmidt condensation of 3-acetyl-7-
(diethylamino)coumarin respectively with benzaldehyde,
piperonal, 4-fluorobenzaldehyde and cinnamaldehyde has
7-(Diethylamino)-3-(3-phenylacryloyl)coumarin (3): Yellow solid;
yield 56%; m.p. 161–163 °C; IR (KBr) (cm–1): 2972, 1707, 1618, 1504,
1
1350, 1178, 1059, 780, 700; H NMR (400 MHz, CDCl3): δ 8.53 (s,
1.0
1.0
2
3
4
5
2
3
4
5
6
0.8
0.6
0.4
0.2
0.0
0.8
6
0.6
0.4
0.2
0.0
300
350
400
450
500
550
400
450
500
550
600
650
Wavelength / nm
Wavelength / nm
Fig.
1
Normalised absorption spectra of compounds 2–6 in
Fig.
2
Normalised emission spectra of compounds 2–6 in
dichloromethane (1 × 10–5 mol L–1).
dichloromethane (1 × 10–5 mol L–1).

536 JOURNAL OF CHEMICAL RESEARCH 2017
1H), 8.16 (d, J = 15.6 Hz, 1H), 7.82 (d, J = 15.6 Hz, 1H), 7.69–7.67 (m,
2H), 7.42–7.38 (m, 4H), 6.61 (d, J = 8.8 Hz, 1H), 6.48 (s, 1H), 3.44 (q, J
= 6.8 Hz, 4H), 1.24 (t, J = 6.8 Hz, 6H); 13C NMR (100 MHz, CDCl3): δ
186.4, 160.8, 158.7, 152.9, 148.7, 143.2, 135.4, 131.8, 130.1, 128.7, 128.6,
124.9, 116.6, 109.8, 108.6, 96.6, 45.1, 12.4. HRMS calcd for C22H22NO3
[M + H]+: 348.1594; found: 348.1603.
7-(Diethylamino)-3-[3-(3,4-methylenedioxyphenyl)acryloyl]
coumarin (4): Yellow solid; yield 49%; m.p. 222–224 °C; IR (KBr)
(cm–1): 2973, 1716, 1584, 1502, 1348, 1172, 1132, 814, 772, 679;
1H NMR (400 MHz, CDCl3): δ 8.53 (s, 1H), 8.00 (d, J = 15.6 Hz, 1H),
7.75 (d, J = 15.6 Hz, 1H), 7.41 (d, J = 9.2 Hz, 1H), 7.22 (d, J = 1.2 Hz,
1H), 7.14 (dd, J = 8.0, 1.2 Hz, 1H), 6.81 (d, J = 8.0 Hz, 1H), 6.61 (dd, J
= 8.8, 2.4 Hz, 1H), 6.48 (d, J = 2.0 Hz, 1H), 6.01 (s, 2H), 3.45 (q, J = 7.2
Hz, 4H), 1.24 (t, J = 7.2 Hz, 6H); 13C NMR (100 MHz, CDCl3): δ 186.2,
160.8, 158.6, 152.9, 149.6, 148.5, 148.2, 143.1, 131.7, 129.9, 125.2, 123.0,
116.7, 109.8, 108.6, 108.4, 107.1, 101.5, 96.6, 45.1, 12.4. HRMS calcd
for C23H22NO5 [M + H]+: 392.1492; found: 392.1486.
Electronic Supplementary Information
The ESI is available through: http://ingentaconnect.com/
content/stl/jcr/2017/00000041/00000009
Received 26 July 2017; accepted 21 August 2017
Paper 1704901
https://doi.org/10.3184/174751917X15035711817504
Published online: 30 August 2017
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Acknowledgement
This work was supported by the Natural Science Foundation of
Gansu Province (1508RJZA091).