Spectral Properties of Highly Emissive Derivative of Coumarin with N,N-Diethylamino, Nitrile and Tiophenecarbonyl Moieties in Water-Methanol Mixture

Article abstract of DOI:10.1007/s10895-019-02446-5

The new derivative of coumarin (E)-3-[7-(diethyloamino)-2-oxo-chromen-3yl]-2-(tiophene-2-carbonyl)prop-2-enenitrile (NOSQ) was easy synthesized with commercial substrates as a result of the search of new Michael type addition sensors based on coumarins. Spectral properties of highly emissive NOSQ were investigated by steady state analysis (absorption and fluorescence measurements) and time-resolved analysis (fluorescence lifetime measurements). The effect of water-methanol mixture on the photophysical properties of the NOSQ molecule was analyzed. With increasing of volumetric fraction of water the intensity of absorbance and fluorescence was strongly reduced. The NOSQ quantum yield in methanol was quite high and the first portions of water caused a significant increase in this value. Water, which is usually a quencher, in this case caused the increase in the quantum yield. The fluorescence lifetimes had second-order decay and the values of fluorescence lifetime increased with increasing alcohol content. Density functional theory (DFT) calculations and experimental data remained in agreement and showed that the interaction between the NOSQ molecule and the solvent affects the appearance of the new conformer.

Full text of DOI:10.1007/s10895-019-02446-5

Journal of Fluorescence
https://doi.org/10.1007/s10895-019-02446-5
ORIGINAL ARTICLE
Spectral Properties of Highly Emissive Derivative of Coumarin
with N,N-Diethylamino, Nitrile and Tiophenecarbonyl Moieties
in Water-Methanol Mixture
1
2
1
2
3
Anna Kolbus
& Andrzej Danel & Danuta Grabka & Mateusz Kucharek & Karol Szary
Received: 25 March 2019 /Accepted: 1 October 2019
The Author(s) 2019
#
Abstract
The new derivative of coumarin (E)-3-[7-(diethyloamino)-2-oxo-chromen-3yl]-2-(tiophene-2-carbonyl)prop-2-enenitrile
NOSQ) was easy synthesized with commercial substrates as a result of the search of new Michael type addition sensors based
(
on coumarins. Spectral properties of highly emissive NOSQ were investigated by steady state analysis (absorption and fluores-
cence measurements) and time-resolved analysis (fluorescence lifetime measurements). The effect of water-methanol mixture on
the photophysical properties of the NOSQ molecule was analyzed. With increasing of volumetric fraction of water the intensity of
absorbance and fluorescence was strongly reduced. The NOSQ quantum yield in methanol was quite high and the first portions of
water caused a significant increase in this value. Water, which is usually a quencher, in this case caused the increase in the
quantum yield. The fluorescence lifetimes had second-order decay and the values of fluorescence lifetime increased with
increasing alcohol content. Density functional theory (DFT) calculations and experimental data remained in agreement and
showed that the interaction between the NOSQ molecule and the solvent affects the appearance of the new conformer.
.
.
.
Keywords Derivative of coumarin Binary solvent mixture Quantum yield Fluorescence study
Introduction
action is warfarin – initially a rat poison and at present an
important medication [5]. Due to specific scent coumarin
is used in tobacco and perfumery industry. Many couma-
rin derivatives exhibit strong emission with high fluores-
cence quantum yield and a superior photostability. Their
photophysical properties can be easily modified by intro-
duction of electro donating/accepting groups like NR2,
OH, CN or by fusion with other aromatic groups leading
to so-called π-expanded coumarins [6]. These compounds
are widely used as laser dyes, optical brighteners or bio-
logical markers [7–9]. Coumarins were applied as emis-
sive materials in organic light emitting diodes OLED too.
For example Kodak patented coumarin based laser dye C-
2
H-Chromen-2-one commonly known as coumarin is an
important natural oxygen heterocycle which was isolated
for the first time from tonka seeds in 1820 [1, 2]. Forty
eight years later an English chemist William Henry Perkin
synthesized coumarin from salicylic aldehyde and acetic
anhydride [3]. Without doubt neither the discoverers nor
Perkin didn’t predicted that today derivatives of coumarin
will find such numerous applications. Some of them are
biologically active substances like naturally occurring an-
ticoagulant substance- dicumarol [4]. Similar in mode of
5
45 TB and used it as a dopant in a device ITO/NPB/
AlQ :1%C-545 TB/AlQ /Mg:Ag. The device showed a
*
Anna Kolbus
3
3
anna.kolbus@ujk.edu.pl
saturated green emission with a luminescent efficiency
2
of 12.9 Cd/m , EQE of 3.68% and an impressive bright-
2
1
2
3
ness of 64,991 cd/m [10]. Just recently Zheng et al. used
Institute of Chemistry, The Jan Kochanowski University,
Swietokrzyska 15G, 25-406 Kielce, Poland
two coumarin derivatives as thermally activated delayed
fluorescence (TADF) emitters achieving the highest exter-
nal quantum efficiency as far as coumarins is concerned
so far. The values are 17.8% and 19.6% respectively with
Institute of Chemistry, Faculty of Food Technology, University of
Agriculture, Balicka St. 122, 31-149 Kraków, Poland
Institute of Physics, The Jan Kochanowski University,
Swietokrzyska 15G, 25-406 Kielce, Poland
2
luminance reaching 10,000 cd/m [11]. Regardless of

J Fluoresc
laser dyes or OLED luminophores in the recent years a
significant growth in application of 2H-chromen-2-one
derivatives as fluorescent chemosensors can be observed.
Thus Yang and co-workers synthesized malononitrile cou-
Optical Properties Measurements
Measurements of absorption spectra were taken on the UV-
3600 Shimadzu Spectrophotometr. Fluorescence spectra
were recorded on the Hitachi F-7000 Spectrofluorymetr
and calibrated on photomultiplayer sensivity using N,N-
−
marin derivative for HSO detection. In the presence of
3
this ion a hypsochromic shift both in absorbance and
emission is observed [12]. Biologically important thiols
derivatives like cysteine, homocysteine and glutathione
are important targets for fluorescent sensors. Quite a lot
of them were prepared from 7-N,N-dialkyl-3-
formylcoumarine via Knoevenagel condensation with ac-
tivated methylene group ex. diethylmalonate or
methylaryl ketones. The resulted α,β-unsaturated com-
pounds exhibit usually weak fluorescence or doesn’t emit
the light at all. After Michael addition of thiol type com-
pound the fluorescence is recovered [13–15]. New analyt-
ical techniques of cations detecting are of great interest to
scientists engaged in clinical biochemistry or natural en-
vironment protection. Derivatives of comarine can be
dimethylamino-m-nitrobenzene (C H N O ), dissolved
8 10 2 2
in mixture of n-hexane and benzene (proportions by vol-
ume respectively 70% n-hexane and 30% benzene). All
spectra were carried out at room temperature. The excita-
tion wavelength of the fluorescence was fixed as 510 nm.
The fluorescence quantum yield, ϕ , was calculated using
f
4-dimethyloamino-4-nitrostilbene in o-dichlorobenzene as
the standard. The quantum yield of standard was taken
equal 0.7 [18]. The refractive index, n, and the dielectric
permittivity, ε, was calculated with respect to water and
methanol participation:
n ¼ %VMeOH *nMeOH þ %VH O*nH O
ð1Þ
ð2Þ
2
2
2
+
used as the sensors of cations, e.g. Hg where as a mer-
cury receptor 1,4,7,10-tetraoxa-13-azacyclopentadecane
ε ¼ %VMeOH *εMeOH þ %VH O*εH O
2
2
+
The solvent polarity was calculated according to the equa-
tion [19]:
w a s a p p l i e d [ 1 6 ] o r K f o r w h i c h 6 , 7 - ( 4 -
methyl)coumaro[2,2,2]cryptand was designed for measur-
ing potassium ions [17]. We synthesized the new deriva-
tive of coumarin: (E)-3-[7-(diethyloamino)-2-oxo-chro-
men-3yl]-2-(tiophene-2-carbonyl)prop-2-enenitrile
2
ε−1 1 n −1
ε þ 2 2 n þ 2
f ðε; nÞ ¼
−
ð3Þ
2
(
NOSQ) – promising candidate for Michael type addition
The fluorescence lifetime was measured using the Pico Quant
compact FLIM and FCS module based on Nikon A1R confocal
microscope. The solution was transferred to microscope slide
and illuminated using picosecond laser head. Repetition rate of
485 nm pulse laser was set to 10 Mhz. The fluorescence signal
was recorded using single photon detector - PMA Hybrid 40.
The photon distribution histogram created by TCSPC electronics
based on PicoHarp 300 was then analyzed in Symphotime64
software. Instrument Response Function (IRF) was recorded
with fluorescein quenched by saturated potassium iodide.
sensor. In this paper we present the photophysical proper-
ties of NOSQ in methanol and in binary methanol – water
mixture in consideration the possibility of later applica-
tion in biological systems.
Experimental
Chemicals
Table 1 Content of water and methanol in binary solvent mixtures
(
E)-3-[7-(diethyloamino)-2-oxo-chromen-3yl]-2-(tiophene-2-
l.p.
Volume of water
Volume of methanol
[cm ]
Water content
[% of volume]
carbonyl)prop-2-enenitrile (denoted as NOSQ) was synthe-
sized in the Institute of Chemistry at the Agricultural
University in Krakow. Products used in the synthesis were
received from POCH S.A.. Methanol had the spectroscopic
purity and it was used as received from POCH S.A.
For spectroscopic measurements, solutions of NOSQ in
organic solvent (methanol) and in binary mixture (water-
methanol) were prepared. The concentration of NOSQ in
pure methanol and all binary solvents was equal 1.06 ×
3
3
[cm ]
1.
2.
3.
4.
5.
0
2.5
2.4
2.3
2.2
2.1
2.0
1.9
1.8
1.7
1.6
1.5
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
4
8
12
16
20
24
28
32
36
40
6
7
8
9
1
.
.
−
5
1
0
M. The participation of volume of water and metha-
.
nol in binary mixtures shows Table 1. It was considered
mixtures containing no more than 40% of the volume of
water in binary mixtures. Higher content of water caused
precipitation of black sediment.
.
0.
11.

J Fluoresc
Computational Methodology
acetylthiophene and acetonitrile in the presence of sodium
hydride. At last 7-(N,N-diethylamino)-3-formylcoumarin
3 and thiophene derivative 6 were reacted together in
the presence of catalytic amount of piperidine in boiling
ethanol yielding derivative 7.
The theoretical calculations were done using the commer-
cial SCIGRESS program (version FJ 2.7). In the first step
the valence, configuration and shape of rings was checked
and corrected if necessary. Then the molecule was opti-
mized by performing DFT calculation with the B88-LYP
GGA functional and the DZVP basis set. In the same way,
the water and the methanol molecules were performed.
For the optimized structures several systems were created
in which the hydrogen bond between the NOSQ molecule
and water molecule or the NOSQ molecule and methanol
molecule was marked. For each system, DFT calculations
were performed with the same initial conditions as
previously.
A round-bottomed flask (25 mL) equipped with reflux
condenser was charged with aldehyde 1 (245 mg, 1 mmol),
3-oxo-3-(2-thienyl)propanenitrile (200 mg, 1.3 mmol), 3
drops of piperidine and ethanol (15 mL). The contents
was refluxed for 3 h. After cooling the resulted red precip-
itate was filtered off and crystallized from toluene. To pre-
pare an analytical sample the resulted compounds was pu-
rified on column packed with silica gel Merck 60 (70–230
mesh) using toluene and subsequently toluene/ethyl acetate
(3:1) mixture as eluent. Dark crystals with green metallic
1
3
luster, 273 mg, 72%, mp. 210–11 °C. C NMR(150 MHz,
CDCl ): 179.01; 161.11; 158.06; 153.68; 148.61; 144.39;
42.07; 135.04; 133.95; 132.28; 128.45; 118.32; 111.19;
Synthesis
3
1
1
The synthesis of coumarin derivative 7 is summarized in
Scheme 1. Compound 3 was synthesized starting from
c o m m e r c i a l l y a v a i l a b l e 4 - N , N -
diethylaminosalicylaldehyde 1 and diethyl malonate. The
resulted 7-(N,N-diethylamino)coumarin 2 was formylated
110.45; 108.84; 105.26; 97.20; 45.45; 12.54.
H
NMR(300 MHz, CDCl ): 8.96(s, 1H); 8.58(1H, s);
3
7.73(dd, J = 4.96 Hz, J = 1.01 Hz); 7.44(d, J = 9.08 Hz);
7.19–7.18(m, 1H); 6.65(dd, J = 9.03 Hz, J = 2.48 Hz,
1H); 6.47(d, J = 2.19 Hz, 1H); 3.49(q, 4H); 1.26(t, 6H).
with DMF/POCl yielding 3 [20]. The second reagent 3-
Anal. calcd for C21H N O S: C 66.67%; H 4.79%; N
18 2 3
3
oxo-3-(2-thienyl)propanenitrile 6 was prepared from 2-
7.40%; Found C 66.53%; H 4.71%; N 7.28%.
a
b
1
2
3
c
4
5
6
d
3
+
6
7
3
Scheme 1 a diethyl malonate/piperidine and next HCl; b DMF/POCl ; c toluene/NaH/100 °C/24 h; d ethanol/piperidine (cat) /boiling/2 h.

J Fluoresc
Fig. 1 Optimized chemical structure of NOSQ obtained by DFT
calculation in Scigress program (a). Particular atoms have been marked
with colors: carbon – dark grey, hydrogen – white, nitrogen – light grey,
oxygen – red and sulfur – yellow. On the right (b), the electron density is
shown. Red indicates the highest electronegativity and blue indicates
positive values of potential
Results and Discussion
dihedral angles occurring in NOSQ molecule where no weak
bonds were considered. The calculated values of dihedral an-
gles for NOSQ molecule without any weak bond and with
weak bonds formed with the solvent molecule are collected
in Table 2. In most cases the weak bonds do not change the
geometry of NOSQ. But there are significant changes in
values of dihedral angles when the weak bond is formed be-
tween the oxygen atom with double bond attached to the main
skeleton of NOSQ molecule and methanol. It shows that there
is a possibility of existence of two NOSQ different conformers
in water-methanol mixture.
Calculations
Optimized chemical structure of NOSQ is shown in Fig. 1a.
The molecule is polar: the dipole moment in ground state
equals 13.4 D. NOSQ molecule has several electronegative
atoms with free electron pairs (areas marked in red in Fig.
1
b), which can potentially form weak bonds with water or
methanol. Taking this into account, pairs of molecules
NOSQ molecule – solvent molecule) were constructed in
(
which a hydrogen bond was formed between the NOSQ mol-
ecule and the water molecule or between the NOSQ molecule
and the methanol molecule. The further calculations were per-
formed. For obtained NOSQ structures which formed hydro-
gen bonds with the solvent molecule, the values of dihedral
angles in NOSQ molecule were measured and compared with
Spectral Analysis of NOSQ in Binary Mixture
The electronic absorption spectra of NOSQ in pure methanol
and water-methanol mixtures are shown in Fig. 2. The most
intensive absorption band is observed in the range 16,000–
Table 2 Calculated values of dihedral angles for NOSQ molecule. In the first column, it is pointed out the NOSQ atom that forms a weak bond with the
particular solvent.
The values of dihedral angles for NOSQ
molecule
C17 – C18 –
C20 – C27 [ ]
C13 – C17 –
C18 – C19 [ ]
C19 – C18 –
C20 – C27 [ ]
without weak bonds
-77,9
-76,7
-95,7
-76,9
176,7
174,1
-177,2
176,8
103,0
106,5
81,9
–
–
–
O22 – H O
2
O22 – CH OH
3
O15 – H O
103,8
2

J Fluoresc
Fig. 2 Absorption spectra of
NOSQ in binary mixture for
different content of water and
methanol. For solid lines, the
arrow shows the water volume
percentage increase in the system
80000
0% H O
2
70000
60000
50000
40000
30000
20000
10000
0
4
% H O
2
12% H O
2
2
2
3
4
0% H O
2
8% H O
2
6% H O
2
0% H O
2
15000
20000
25000
30000
35000
40000
-1
[
cm ]
−
1
2
3,000 cm . The first portion of added water (4% V/V)
solvent decreases the energy gap between the more polar ex-
cited state and the less polar ground one of the molecule.
The fluorescence spectra are shown in Fig. 3. The dual
causes slight increase of absorbance value. Next portions of
water decrease the absorption intensity. With the increasing of
water volumetric fraction from 0% to 40%, the value of ab-
sorbance maximum is reduced 2.5 times while the concentra-
tion of NOSQ is constant. The red shift with increasing of the
percentage of water in the sample is noticed. The dielectric
permittivity and refractive index is much bigger for water than
for methanol. Therefore the system becomes more polar with
increasing water content. From the batochromic shift we con-
clude that interaction between the molecule and the polar
−1
−1
fluorescence with maxima at 16200 cm and 14,500 cm
is observed. These maxima do not shift with addition of water.
The same effect like in absorption is noticed in fluorescence –
the band intensity increases after adding the first portion of
water and afterwards decreases. The Stokes shift and fluores-
cence quantum yield are smaller and smaller when the water
volumetric percentage increases from 4% to 40% V/V. The
spectroscopic data for NOSQ in binary mixture, like
Fig. 3 Fluorescence spectra of
NOSQ in binary mixture for
different content of water and
methanol. For solid lines, the
arrow shows the water volume
percentage increase in the system
0
% H O
2
4% H O
2
1
2
2
3
4
2% H O
2
0% H O
2
8% H O
2
6% H O
2
0% H O
2
14000
15000
16000
17000
18000
19000
-1
[
cm ]

J Fluoresc
0
1
0
Table 3 Photophysical properties of NOSQ in the water-methanol mix-
fluorescence quantum yield, τ , τ [ns] – fluorescence lifetime, τ , τ
natural fluorescence lifetime, f(ε,n) – polarity function)
–
2
1
2
−1
3
−1
−1
ture (eνa, [cm ] – absorption maximum, ɛmax,abs [dm ·mol ·cm ] – the
−
1
value of the molar absorption coefficient in maximum, Δeν [cm ] –
Stokes shifts relative to the short-wavelength fluorescence band, ϕ
f
–
0
1
0
%
of H
2
O
f(ε,n)
eν
a
ɛ
max, abs
Δ eν
ϕ
f
τ
1
τ
2
τ
τ
2
0
4
8
13,290
13,292
13,293
13,295
13,296
13,298
13,300
13,301
13,303
13,304
13,306
19,300
19,200
19,200
19,100
19,000
19,000
18,900
18,900
18,900
18,800
18,800
18,800
19,200
17,200
16,000
15,900
13,400
12,400
13,000
13,000
12,000
10,600
2600
2500
2500
2400
2300
2300
2200
2200
2200
2100
2100
0,59
0,87
0,80
0,82
0,74
0,76
0,57
0,52
0,49
0,46
0,48
3,51
3,80
3,65
3,70
3,29
4,10
3,43
2,95
3,46
4,24
3,56
0,207
0,196
0,186
0,171
0,166
0,166
0,161
0,142
0,142
0,14
5,01
4,37
4,56
4,51
4,45
5,39
6,02
5,67
7,06
9,22
7,42
0,298
0,226
0,232
0,208
0,224
0,218
0,282
0,273
0,290
0,304
0,271
1
1
2
2
2
3
3
4
2
6
0
4
8
2
6
0
0,13
absorption maximum, the value of the molar absorption coef-
ficient in maximum, Stokes shifts relative to the
shortwavelength fluorescence band, fluorescence quantum
yield, fluorescence lifetimes and natural fluorescence lifetimes
are collected in Table 3. The decay of NOSQ fluorescence in
pure methanol and in binary mixture is bi-exponential. This
phenomenon and the dual fluorescence suggest the existence
of two conformers of NOSQ [21–23]. The experimental re-
sults are in good agreement with the theoretical one.
The dependence of solvent polarity (calculated from eq. 3)
on Stokes shifts, quantum yield and fluorescence lifetimes are
shown on Fig. 4. The quite good linear relation between sol-
vent polarity function and Stokes shifts, quantum yield and
shorter fluorescence lifetime, τ is observed. The correlation
2
coefficient is equal 0.97, 0.83 and 0.99 for the f(ε, n) depen-
dence from Δeν, ϕ and τ , respectively. The weakest correla-
f
2
tion occurs between polarity function and quantum yield, but
at consideration only data of binary mixtures the correlation
coefficient increases to 0.95. The first portion of water causes
that the quantum yield of NOSQ fluorescence in mixture is
higher than in pure methanol. Then this quantum yield de-
creases, but its values in the water-methanol mixtures are
higher than in the pure methanol solution unless the percent-
age of water is about 25%. Although the fluorescence inten-
sity decreases the quantum yield is high. It can be explained
by the smaller and smaller absorbance value at the excitation
Fig. 4 The solvent polarity
dependence on Stokes shifts,
quantum yield and fluorescence
lifetimes
2800
0
0
,9
,8
0
4
1
2
8
2
2
2
2
600
400
200
000
20
f
16
4
8
1
2
0,7
0
16
2
0
0
0
,6
,5
2
4
24
3
2
28
2
8
3
6
32
4
0
4
0
36
0,4
,22
4
4
4
3
3
3
3
3
2
,4
,2
,0
,8
,6
,4
,2
,0
0
3
6
0
2
0
0,20
0,18
0,16
4
1
4
2
8
1
2
8
4
0
12
0
16 20
3
2
2
4
24
1
6
2
8 32
36
0
,14
2
8
40
,8
0,12
0,81
0
,81
0,82
0,83
0,84
0,82
0,83
0,84
f
(
)
f
(
)

J Fluoresc
7
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1
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(
NOSQ) in methanol and in water-methanol binary mixtures.
The steady state and time-resolved fluorescence indicate the
presence of two conformers of NOSQ molecule, which is in
agreement with theoretical calculations. The interaction be-
tween NOSQ and solvent does not significantly affect mole-
cule geometry, except one case when dihedral angles change.
Adding small portions of water (up to about 25% of sample
volume) to the methanol solutions is beneficial for the emis-
sive properties of the system. Water is often the quencher, but
in this case it increases the quantum yield. This phenomenon
can be promising for possibility of application of NOSQ in
spectral studies of biological systems, for e.g. as the sensor of
ions dissolved in water what is planned in our next studies.
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Katerinopoulos HE (2010) A “turn-on” Coumarin-Based
Fluorescent Sensor with High Selectivity for Mercury Ions in
Aqueous Media Chem. Commun. 46:3292–3294
1
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ME, Kurtz I (1990) Synthesis and Characterization of a New
Fluorescent Probe for Measuring Potassium. Am J Phys 258:
F438–F443
Acknowledgments A.K. would like to thank mgr Monika Tutalak for
helping with absorption and fluorescence measurements. The synthetic
part of this work was financed by the basic funding of the Agricultural
University (DS 3711/ICh/2018).
1
1
2
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