New Chromophore Systems from Coumarin-Oxazol-5-one Combination

Article abstract of DOI:10.1007/s10895-017-2078-2

Coumarin-oxazol-5-one (COX), 3a-d, were synthesized with 7-methoxy-2-oxo-2H-chromene-4-carbaldehyde and benzoylglycine derivatives. The characterizations of the COX derivatives by ¹H NMR, FT-IR and elemental analysis were achieved. To obtain the photophysical data of the synthesized COX derivatives were used spectrophotometric and spectrofluorimetric methods. Evaluation of the absorption and emission properties of the structures was carried out in six different solvents. Maximum absorption and emission wavelengths (λ; nm), molar extinction coefficients (ε; cm^?1?M^?1), Stoke’s shifts (Δλ_ST; nm) and quantum yields (?_F), of the COX derivatives were declared.

Full text of DOI:10.1007/s10895-017-2078-2

J Fluoresc
DOI 10.1007/s10895-017-2078-2
ORIGINAL ARTICLE
New Chromophore Systems from Coumarin-Oxazol-5-one
Combination
Derya Topkaya1 & Serap Alp1
Received: 21 November 2016 /Accepted: 4 April 2017
#
Springer Science+Business Media New York 2017
Abstract Coumarin-oxazol-5-one (COX), 3a-d, were synthe-
sized with 7-methoxy-2-oxo-2H-chromene-4-carbaldehyde
and benzoylglycine derivatives. The characterizations of the
COX derivatives by 1H NMR, FT-IR and elemental analysis
were achieved. To obtain the photophysical data of the syn-
thesized COX derivatives were used spectrophotometric and
spectrofluorimetric methods. Evaluation of the absorption and
emission properties of the structures was carried out in six
different solvents. Maximum absorption and emission wave-
lengths (λ; nm), molar extinction coefficients (ε; cm−1 M−1),
Stoke’s shifts (ΔλST; nm) and quantum yields (ϕF), of the
COX derivatives were declared.
changed by the connection of different substituent to the cou-
marin ring and this position giving them more flexibility to fit
well in various applications. For example, coumarins
substituted at position 7 with an electron-donating group are
exhibited strong fluorescence [15]. In the previous studies
have been reported that the photophysical properties like max-
imum wavelength, quantum yield, lifetime, polarization, and
excited-state dipole moment of these compounds not only
depend on the position of substituent group in the molecule
but also vary with surrounding media [16–21].
Coumarin derivatives are well known as having high levels
of biological activity besides the photophysical properties. For
example, polycyclic coumarin derivatives like calanolides
which obtained from Callophyllum plant have anti-HIV
(NNRTI) properties [22]. Coumarins are found at the structure
of some antibiotics such as novobiocin, clorobiocin and
coumermycin A1 and these antibiotics are strong catalytic in-
hibitor of the DNA [23]. In many studies it has been reported
that 7-hydroxycoumarin derivatives show anti-tumor activity
in the human tumor cell [24].
Coumarins can be synthesized by various methods includ-
ing the Perkin [25], Pechmann [26], Knoevenagel [27],
Reformatsky [28] and Wittig [29] reactions. Among these,
the Pechmann reaction has been the most widely used method
since it proceeds from very simple starting materials and gives
good yields of variously substituted coumarins. Substituted
phenols are condensed with β-keto esters in the presence of
an acid to afford coumarins. Various acids have been used to
carry out this reaction [30–32].
.
.
Keywords Coumarin Oxazol-5-one Chromophore
Introduction
Coumarin derivatives have an important position in synthetic
organic chemistry and naturally occurring products, they have
been extensively investigated for different studies [1–5]. Because
of their high thermal stability, superior optical properties and
photostability, they have many optical applications in laser dyes
[6], polymers science [7, 8], optical recording and solar energy
collectors [9–11]. Furthermore, coumarins are used as non- linear
optical chromophores and as a probe to study solvation dynamic
in homogeneous solutions as well as arranged media [12–14].
Another feature of the coumarin derivatives is that
photophysical and spectroscopic properties can be easily
The other part of the synthesized target molecule consists
of oxazol-5-one derivatives. Oxazol-5-ones exhibit a wide
spectrum of pharmacological activities including anticancer,
antimicrobial, antifungal, sedative, etc. [33]. Oxazol-5-ones
that are internal anhydrides of N-acyl amino acids make an
important class of five-membered heterocycles. These are
* Serap Alp
serap.alp@deu.edu.tr
1
Department of Chemistry, Faculty of Sciences, Dokuz Eylul
University, Tinaztepe Campus, 35160, Buca, Izmir, Turkey

J Fluoresc
highly versatile intermediates used for the synthesis of several
organic molecules, including amino acids, peptides, antimi-
crobial or antitumor compounds [34].
Synthesis of of
7-methoxy-2-oxo-2H-chromene-4-carbaldehyde (2)
Recently, oxazol-5-one derivatives containing N-phenyl-
aza-15-crown-5 moiety [35] or carbazole structures [36] have
been synthesized and evaluations of the spectroscopic proper-
ties of these derivatives have been carried out in different
solvents.
In this study, coumarin-oxazol-5-one (COX) derivatives
were synthesized to combine the advantages of coumarin
and oxazol-5-one heterocyclics. For this purpose, four push-
pull substituted COX derivatives were obtained and the basic
photophysical properties were exhibited.
7-methoxycoumarin (1.9 g 0.01 mol) was dissolved in 50 mL
dimethylbenzene during heating. Following this, selenious
acid (1.93 g, 0.015 mol) was added. The reaction solution
was refluxed for 20 h. After the work up and purification
processes, the yellow crystal product was obtained [4].
Yield %78 mp 128–130 °C.
FT-IR (KBr) (cm−1): 3057–2985 (=CH), 2960, 2744
(-CH), 1724, (-O-C = O), 1704(-HC = O) 1613 (-C = C-) cm−1.
1H NMR (CDCl3, 400 MHz) δ(ppm); 3.97 (s, 3H, -OMe);
6.50 (s, 1H, H3); 6.97–7.95 (d,1H, H8); 6.97–7.95 (d,1H, H6);
7.01(s,1H, H8); 7.98(s,1H, H5); 10,61(s,1H, H-C = O). Anal.
calcd. for C11H8O4: C, 64.65; H, 3.91. Found: C, 64.49; H, 3.89.
Experimental
General Synthesis of coumarin-oxazol-5-one (COX)
Derivatives (3a-d)
Reagents and Apparatus
All solvents used in this study were analytical grade and have
been purchased from Merck, Fluka, and Riedel. All melting
points were measured in sealed tubes using an electrothermal
digital melting points apparatus and are uncorrected. Infrared
spectra were recorded on a Perkin ELMER FTIR infrared
spectrometer (spectrum BX-II). 1H-NMR spectra were obtain-
ed on a high resolution fourier transform Bruker WH-400
NMR spectrometer with CDCl3 as an internal standard.
Analytical and preparative thin layer chromatography (TLC)
was carried out using silica gel &0 HF_254 (Merk). Column
chromatography was carried out by using 70–230 mesh silica
gels (0.063–0.2 mm, Merk). UV/visible absorption spectra
were recorded with Schimadzu UV-1601 spectrophotometer.
All fluorescence measurements were undertaken by using
Varian-Carry Eclipse spectrofluorimeter.
A solution of 4-formyl-7-methoxy coumarin 2(1 g; 4.88 mmol),
4-methylbenzoyl glycine (1.16 g; 4.88 mmol), acetic anhydride
(1.84 mL; 9.76 mmol) and sodium acetate (0.66 g; 4.88 mmol)
was heated until the mixture just liquefied, and then heating was
continued for 4 h. After completion of the reaction (determined
by thin layer chromatography), ethanol (20 mL) was added and
the mixture was kept at room temperature for 18 h. The solid
product thus obtained was purified by washing cold ethanol,
hot water and then a small amount of hexane. The solid was
recrystallized from hot ethanol to afford pure crystals of 3c [34].
The other coumarin-oxazol-5-ones were prepared the same pro-
cedure using appropriate glycine derivatives 3a, 3b and 3d.
Structural Analysis
of 4-[(7-methoxy-2-oxo-2H-chromen-4-yl)methylene]
-2-phenyl-1,3-oxazol-5(4H)-one (3a)
Synthesis
Yield: 70%. M.p. 245–248 °C.
The synthetic route of the target compounds is presented in
Fig. 1.
FT-IR (KBr) (cm−1): 3088–3010 (=CH), 2944 (-CH), 1732
(-O-C = O, -coumarin-), 1801 (-O-C = O, -oxazol-5-one-),
1623 (-C = N-),
Synthesis of 7-methoxy-4-methyl-2H-chromen-2-one (1)
1H NMR (CDCl3) (ppm); 3.91 (s, 3H, -OCH3), 6.95–6.89
(m, 2H, H6^, H8^); 7.60–7.55 (m, 3H, H3’, H5’, H3^); 7.68–7.69,
(t,1H, H4’); 7.72–7.70 (d,1H, H5^); 8.23–821 (d, 2H, H2’, H6’).
Anal. calcd. for C20H13NO5: C, 69.10; H, 3.74; N, 4.03
Found: C, 68.86; H, 3.46, N, 3.85.
3-methoxyphenol (12.4 g, 0.1 mol) was dissolved in 15 mL of
75% concentrated H2SO4, then solution was heated to 75 °C
and ethyl acetoacetate (13.4 g, 0.1 mol) was added dropwise.
After 40 min, the reaction solution was poured into 100 g ice.
The precipitate was collected, washed with water and recrys-
tallized with ethanol [18].
Structural Analysis of 4-[(7-methoxy-2-oxo-2H-chromen-
4-yl)methylene]-2-(1-naphthyl)-1,3-oxazol-5(4H)-one(3b)
Yield %85, mp 156–158 °C,
FT-IR (KBr) (cm−1): 3065, 3022 (=CH), 2949 (-CH), 1725
(-O-C = O), 1608(-C = C-),
Yield: 65%. M.p. 224–228 °C.
FT-IR (KBr) (cm−1): 3092–3014 (=CH), 2935 (-CH), 1717
(-O-C = O, -coumarin-), 1797 (-O-C = O, -oxazol-5-one-),
1615 (-C = N-),
1H NMR (CDCl3) (ppm); 2.40 (s, 3H, Me); 3.78 (s,
3H, -OMe); 6.13 (s, 1H, H3); 6.76–7.51 (m, 3H, H5, H6, H8);

J Fluoresc
CH3
Fig. 1 Synthetic route of COX
derivatives. i) Ethyl acetoacetate,
12 M H2SO4, 80 °C, 6 h; ii)
H2SeO3, 1,4-dioxan, 24 h reflux,
iii) NaOAc, Ac2O,
OH
C
H3
i
O
O
O
ArCONHCH2COOH, 80 °C, 3 h
O
1
C
H3
ii
H3C
O
O
H
iii
O
O
O
H3C
O
O
O
N
O
2
Ar
3
3a
Fig. 2 Schematic structures of
COX (3a-d) derivatives. (3a)
(4Z)-4-[(7-methoxy-2-oxo-2H-
chromen-4-yl)methylene]-2-phe-
nyl-1,3-oxazol-5(4H)-one.
(3b) (4Z)-4-[(7-methoxy-2-oxo-
2H-chromen-4-yl)methylene]-2-
(1-naphthyl)-1,3-oxazol-5(4H)-
one. (3c) (4Z)-4-[(7-methoxy-2-
oxo-2H-chromen-4-
yl)methylene]-2-(4-nitrophenyl)-
1,3-oxazol-5(4H)-one. (3d) (4Z)-
4-[(7-methoxy-2-oxo-2H-chro-
men-4-yl)methylene]-2-(4-
methylphenyl)-1,3-oxazol-5(4H)-
one
H C
3
O
H3C
O
6''
6''
7''
7''
8''
8''
5''
5''
3b
4''
f
4''
O
O
f
O
5
O
O
O
4
3''
4
5
3''
N
O
N
O
2
8'
2
1'
1'
2'
7'
6'
5'
2'
3'
6'
3'
4'
4'
5'
H3C
O
7''
8''
H3C
O
6''
6''
7''
5''
4''
8''
3c
5''
3d
f
O
O
4''
O
f
O
O
O
4
5
3''
4
5
3''
N
O
N
O
2
2
1'
6'
5'
1'
2'
6'
5'
2'
3'
4'
3'
4'
N+
O
CH3
-O

J Fluoresc
1H NMR (CDCl3) (ppm); 3.91 (s, 3H, -OCH3), 6. 96–6.89 (m,
2H, H6^, H8^); 7.42 (s, 1H, Hf) 7.56–7.65 (m, 3H, H5’, H6’, H3^);
7.73–7.79, (m,2H, H3’, H5^]); 7.95–7.97 (d,1H, H7’); 8.15–8.17
(d, 1H, H4’); 8.46–8.48, (d, 1 H, H2’), 9.37–9.39 (d, 1H, H8’).
Anal. calcd. for C25H15NO5: C, 75.49; H, 3.77; N, 3.52
Found: C, 75.27; H, 3.56, N, 3.59.
7.72–7.70, (d, 1H, H5^); 8.16–8.18 (d, 2H, H2’, H6’);. 8.29–
8.27 (d, 2H, H3’, H5’).
Anal. calcd. for C20H12N2O7: C, 61.17; H, 3.05; N, 7.13
Found: C, 60.57; H, 3.05; N, 6.92.
Structural Analysis of 4-[(7-methoxy-2-oxo-2H-
chromen-4-yl)methylene]-2-(4-methylphenyl)-1,3-
oxazol-5(4H)-one (3d)
Structural Analysis of 4-[(7-methoxy-2-oxo-2H-
chromen-4-yl)methylene]-2-(4-nitrophenyl)-1,3-oxazol-
5(4H)-one (3c)
Yield: 45%. M.p. 239–242 °C.
FT-IR (KBr) (cm−1): 3080–3010 (=CH), 2981(-CH), 1712
(-O-C = O, -coumarin-), 1800 (-O-C = O, -oxazol-5-one -),
1613 (-C = N-),
Yield: 53%. M.p. 263–264 °C.
FT-IR (KBr) (cm−1): 3092–2969 (=CH), 2841(-CH), 1707
(-O-C = O, −coumarin-), 1799 (-O-C = O, -oxazol-5-one-),
1612 (-C = N-), 1557 (-NO2) cm−1.
1H NMR (CDCl3) (ppm); 3.91 (s, 3H, -OCH3), 6.94–
6.90 (m, 2H, H6^, H8^); 7.36–7.39 (m, 3H, H3’, H3^,
H6’); 7.67 (s, 1H, Hf); 7.72–7.70 (d, 1H, H5^); 8.10–
8.12 (d, 2H, H2’, H6’).
1H NMR (CDCl3) (ppm); 3.87 (s, 3H, -OCH3), 6.68 (s, 1H,
H3^); 6. 90–6.87 (s, H6^); 6.99, (s,1H, H8^), 7.42 (s, 1H, Hf),
Fig. 3 1H NMR spectrum of 3d

J Fluoresc
Table 1 Spectral data obtained
from absorption and emission
spectra for compouns 3a-3d
λab
(nm)
εmax
λemis
(nm)
λexc
max
(nm)
Δλ (nm)
ϕf
max
max
(M−1 cm−1
)
3a
3b
3c
3d
Toluene
365
368
366
365
377
357
402
401
400
393
408
391
358
357
356
371
360
352
358
357
373
371
377
365
10,900
10,400
44,347
27,200
2990
540
537
555
560
530
577
545
545
577
592
570
570
564
565
583
597
566
570
564
565
550
555
541
570
362
361
361
365
377
365
405
410
400
391
415
520
361
361
361
355
300
360
361
361
370
361
377
365
175
179
189
195
153
220
143
144
177
199
162
179
203
204
222
242
206
218
203
204
180
194
164
144
Xylene
Dichloromethane
Tetrahydrofuran
Chloroform
Acetonitrile
Toluene
0,19
0,17
7800
0,13
10,000
34,170
15,384
14,800
17,400
22,000
31,800
12,300
11,671
15,000
14,000
15,000
31,800
12,300
12,044
22,000
20,000
30,000
Xylene
Dichloromethane
Tetrahydrofuran
Chloroform
Acetonitrile
Toluene
0,67
0,39
0,22
Xylene
Dichloromethane
Tetrahydrofuran
Chloroform
Acetonitrile
Toluene
0,06
0,07
0,05
Xylene
Dichloromethane
Tetrahydrofuran
Chloroform
Acetonitrile
0,32
0,20
0,12
Anal. calcd. for C21H15NO5: C, 69.73; H, 4.05; N, 3.875
Found: C, 70.23; H, 3.93; N, 4.03.
Firstly, 3-methoxy phenol was condensed with β-keto ester in
the presence of an acid to prepared 7-methoxy-2-oxo-2H-
chromene-2-one by Pechmann reaction [18]. After that, meth-
yl group at four position of the coumarin ring in this derivative
was oxidized to aldehyde with selenious acide [37].
Oxazolone derivatives were performed by condensation reac-
tion of several benzoylglycine derivatives with this aldehyde
group on the coumarin ring [34]. The structural analysis of the
Results and Discussion
Figure 2 shows schematic structures of the newly synthesized
four COX derivatives according to synthetic route at Fig. 1.
Fig. 4 Absorption spectra of
compounds 3a-d measured in
dichloromethane

J Fluoresc
Fig. 7 The photostability test result of 3a-d in dichloromethane after 1 h
of monitoring
Fig. 5 Emission and excitation spectra of compounds 3a-d measured in
dichloromethane
recorded absorption spectra of the COX derivatives demon-
strated only one absorption band over 300 nm (See Fig. 4).
The molecules excited around maximum absorption wave-
lengths, the recorded fluorescence emission spectra were
again demonstrated only one emission band (See Fig. 5) as
shown in Table 1. This can be attributed that the new chromo-
phore system formed by integration of two different chromo-
phores (coumarin and oxazole-5-one). Other evidence can be
found with evaluation of IR spectra. The infrared spectra of
these derivatives support where the most delocalization part
occurred in new COX compounds. The wavenumber values
synthesized derivatives was done by elemental analysis, FT-
1
1
IR and H-NMR spectroscopic techniques. The H–NMR
spectrum of 3d derivative was given as an example in Fig. 3.
Absorption and emission spectroscopic studies of all COX
derivatives were performed in the solvents of toluene, xylene,
dichloromethane, tetrahydrofuran, chloroform and acetonitrile
(Table 1, Figs. 4 and 5).
Although COX derivatives have two different chromo-
phore parts, which are coumarin and oxazol-5-one ring, the
Fig. 6 The infrared spectra of 3a-3b derivatives and the wavenumber values of carbonyl stretching vibration bands

J Fluoresc
of carbonyl stretching vibration bands given in Fig. 6 are used
for explaining this concept. From the analysis of these bands,
it can be concluded that, while the carbonyl group of oxazol-
5-one is not influenced with the exchange of aryl groups, the
carbonyl group of coumarin is influenced. As a result, the
electronic delocalization of COX derivatives have changed
and a new chromophore system has occurred. The new chro-
mophore systems have shown with bold black parts on mole-
cule structures in Fig. 2.
To determine the photophysical parameters UV-vis absorp-
tion and emission spectra of COX derivatives were measured
and given in Table 1. Evaluation of the absorption and emis-
sion properties of the structures was carried out in six solvents
having different polarity.
Molar extinction coefficients and Stokes’ shift values of
each derivative in all solvents were calculate to be in
the range of 1.0 × 104−4.5 × 104 cm−1 M−1 and 143–242 nm
respectively.
Quantum yield values were also calculate only in three
solvents, acetonitrile, tetrahydrofuran and dichloromethane.
8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt
(HPTS) was used as reference quantum yield standard at
λex = 400 nm and the quantum yields (ΦF) of synthesized
COX derivatives were determined by the formula [38]:
by substituting at the 2- position of the oxazol-5-one ring in
order to form a set of push-pull effect. After the structural
characterization by H NMR, FT-IR, elemental analysis, the
1
photophysical properties of the new compounds were studied
by UV–vis and emission spectroscopy. As it was expected, the
characteristic absorption and emission bands of the two dif-
ferent heterocyclic coumarin and oxazolone chromophore
systems at the new synthesized molecules were not observed.
Surprisingly, a single new absorption and emission bands in
different wavelengths were detected. This can be attributed to
the formation of a new chromophore system with high molar
extinction coefficients the Coumarin-oxazol-5-one deriva-
tives. By evaluation of the carbonyl stretching bands extracted
from the FT-IR Spectra, forming of the new chromophore
were also proved.
Emission quantum yields were obtained for all derivatives
in several solvents. Among them, 3b derivative in dichloro-
methane exhibited the highest quantum yield value of 0.67.
This favourable value can be defined with the effect of naph-
thalene having condensed π electron system.
Consequently, because of the chemical and biological ac-
tivities of the coumarin and oxazol-5-one cores, all COX com-
pounds are promising for future works.
À
Á À
Á
Φ ¼ Φstdx F Astdη2 = FstdAηstd
2
References
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The photostabilities of 3a-3d derivatives were tested in all
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