Blue fluorescence from pyridinyl coumarincarboxymides structure having high quantum yield in solution

Article abstract of DOI:10.1016/j.molstruc.2021.131229

Small molecules having fluorescence quantum yields are required to promote biological and organic material applications. In this work, we introduced a series of pyridinyl coumarincarboxymides derivatives, namely 4-XP. These compounds exhibited intense blue fluorescence with high fluorescence quantum yield. By spectral measurement and analysis, it is identified that these pyridine-coumarin conjugates displayed high fluorescence quantum yields (Φ_F = 0.77–0.82) blue fluorescence at about 455 nm in nonpolar solvents. Additionally, the solvent effect and fluorescence properties were verified and explained by DFT and TD-DFT calculations.

Full text of DOI:10.1016/j.molstruc.2021.131229

Journal of Molecular Structure 1247 (2022) 131229
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstr
Blue fluorescence from pyridinyl coumarincarboxymides structure
having high quantum yield in solution
∗
Zichun Zhou, Xue Tang, Yanhong Cui, Shuai Xue, Zihua Yu, Yujin Li
College of Chemical Engineering, Zhejiang University of Technology, Hangzhou 310014, People’s Republic of China
a r t i c l e i n f o
a b s t r a c t
Article history:
Small molecules having fluorescence quantum yields are required to promote biological and organic ma-
terial applications. In this work, we introduced a series of pyridinyl coumarincarboxymides derivatives,
namely 4-XP. These compounds exhibited intense blue fluorescence with high fluorescence quantum
yield. By spectral measurement and analysis, it is identified that these pyridine-coumarin conjugates dis-
played high fluorescence quantum yields (ꢀF = 0.77–0.82) blue fluorescence at about 455 nm in nonpolar
solvents. Additionally, the solvent effect and fluorescence properties were verified and explained by DFT
and TD-DFT calculations.
Received 31 March 2021
Revised 15 July 2021
Accepted 30 July 2021
Available online 2 August 2021
Keywords:
Pyridinecarboxamide
Coumarin
© 2021 Published by Elsevier B.V.
Blue fluorescence
High quantum yield
TD-DFT calculations
1. Introduction
lamine based coumarin-rhodamine hybrids dyes with large Stokes
shift and viscosity sensing [15]. Kaya reported a new coumarin-
The fluorescent small molecule dyes that have been reported
to be used have relatively low fluorescence quantum yield, which
limits their application. Therefore, there is an urgent need to de-
velop new small molecule organic fluorescent dyes with high flu-
orescence quantum yield. Coumarin is an important small fluo-
rophore because of their excellent photophysical properties such
as large Stokes shift, high molar absorption coefficient and high
quantum yield etc [1,2]. Accordingly, coumarin derivatives are
widely used in science and technology, such as perfume, cos-
metic, as a disperse dye [3], biocompatible fluorescence dyes
triazole-based dye with a mirror image and significantly highly of
the quantum yields(up to 0.68) [16]. Recently, we developed a flu-
orescent dyes based on 3-imidazolyl coumarin with unusual solu-
tion and solid dual efficient luminescence in high quantum yield
(ꢀF = 0.90–0.94 in CHCl ) [17]. Nonetheless, most coumarin fluo-
3
rescent dyes show green fluorescence, and there are relatively few
reports on blue fluorescence of coumarin dyes. Four blue emit-
ting coumarin amide derivatives have been synthesized by Wu
and recognized cyanide anion [18]. 7-Diethylaminocoumarin amide
compounds exhibited intense blue fluorescence and high fluores-
cence quantum yields in THF (0.43) [19]. Recently, pyridine moi-
ety is considered as the orientation of heteroaromatic ring align-
ing toward the donor component can serve as structural tuning
factors to modulate the degree of intramolecular charge transfer
(ICT) [20,21]. A few literatures have been reported wherein fluo-
rescent dyes of 7-diethylaminocoumarin amide compounds with
pyridinyl terminal group. Previous reports suggested that the in-
troduction of pyridine substitutent on the fluorescent molecules
could serve as an interesting strategy for tuning the photophys-
ical properties [22,23]. The development of blue fluorescent dyes,
especially with high fluorescence quantum yield, is the focus of re-
search [24,25]. Herein, a series of pyridinyl coumarincarboxymides
based on coumarin derivatives were synthesized and the optical
properties were investigated. The coumarin derivatives emitted in-
tense blue fluorescence in different solvents with high quantum
yields.
[
4], charge-transfer agent, solar energy collectors, organic light-
emitting diodes (OLEDs) [5], anti-counterfeiting applications [6] etc
7–9]. Therefore, the development of easily synthesizable coumarin
fluorescent dyes are highly desirable for practical purposes
10–12].
Coumarin fluorophore can be able to enhance the fluorescence
performance based on the intramolecular charge transfer process
ICT) due to the substitution in 7-position and 3-position [13]. For
[
[
(
example, Hu’s group reported that they prepared coumarin con-
jugate to employ the intramolecular charge transfer (ICT) to pro-
duce quantum yield (ꢀF = 0.68) in toluene and the coumarin con-
jugate was used as an effective fluorescence water probe in or-
ganic solvents [14]. Sekar reported a deep red emitting tripheny-
∗
Corresponding author.
E-mail address: lyjzjut@zjut.edu.cn (Y. Li).
https://doi.org/10.1016/j.molstruc.2021.131229
0
022-2860/© 2021 Published by Elsevier B.V.

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
Scheme 1. Synthesis of coumarin derivatives 4.
Table 1
Optical data of 4-XP1 determined in different solvents at room temperature.
a
max (M−1·cm−1
b
c
d
SSe (nm)
Dye
-XP1
Solvent
λ
abs (nm)
ε
)
λ
em (nm)
ФF
4
Toluene
DCM
424
432
431
423
423
428
433
435
429
432
42,900
47,300
51,000
46,400
44,700
47,500
48,100
44,500
50,500
47,500
446
463
454
459
461
473
478
483
474
476
0.79
0.80
0.82
0.77
0.77
0.19
0.16
0.17
0.21
0.11
22
31
26
36
38
45
45
48
45
44
CHCl3
EA
THF
MeCN
DMF
DMSO
EtOH
MeOH
Note: aAll of the values correspond to the strongest absorption peaks.
b
Molar absorption coefficient.
c
Emission wavelength.
d
Fluorescence quantum yields (ФF) are measured using an integrating sphere method and
standard errors are less than 5%.
e
The Stokes shift of the experimental results.
4
−1
−1
2
. Results and discussion
absorption coefficient (4.5 × 10
M
·cm ), and the color of 4-
XP1 in different solution appeared as pale yellow under visible
light (Fig. 2). Different from the absorption spectrum of 4-XP1, it
was obvious that the intensity of the fluorescence emission peaks
2
.1. Synthesis
Preparation route of target molecules coumarin derivatives 4
and the fluorescence quantum yields (ꢀ ) were also greatly af-
F
were shown in Scheme 1. Precursors 3-carboxycoumarin 2 were
prepared by the reaction of salicylaldehyde derivatives with mel-
drum’s acid in refluxing ethanol solution, which resulted in 85%
fected by the solvents. 4-XP1 showed a strong fluorescence with
the similar emission wavelengths ranged from 446 to 476 nm in
organic solvents (Table 1), which exhibited the blue fluorescence
with high fluorescence quantum yield. As shown in Fig. 1(b), the
intensity of the fluorescence emission peaks in non-polar solvents
were about 10 times in polar solvents. The emission wavelength
of compound 4-XP1 in non-polar solvents were about 460 nm
and the corresponding ꢀF were higher than 0.77, such as DCM
(0.80), toluene (0.79), THF (0.77), and EA (0.77). Relatively, the ꢀF
were sharply reduced in the polar solvents such as MeCN (0.19),
DMF (0.16), DMSO (0.17), ethanol (0.21) and methanol (0.11), with
a slight red shift of the emission wavelengths around 10–20 nm.
This can be explained by the fact that the molecule of 4-XP1 was
more stable in the excited state in the polar solvents, which in-
duced non-radiative energy increased and then lead to a red shift
of the emission wavelengths [26]. It is noteworthy that the emis-
sion wavelength underwent the slight red shift with the increase
of solvent polarity and 4-XP1 produced a bright blue fluorescence
at 446 nm with ꢀF = 0.77 in toluene. Additionally, in CHCl3, the
(
R1 = H) and 76% (R1 = NEt ) yields. Then, with the acyl chlo-
2
ride reaction of thionyl chloride, the 3-carboxycoumarin 2 con-
verted to 3-acyl chloride coumarin in 83% (R1 H) and
3
=
8
7% (R1 = NEt ) yields. The target amide coumarin derivatives
2
were produced by using the amide reaction of 3-acyl chloride
coumarin 3 and 2-aminopyridine derivatives under Et N condition,
3
which were yielded in 17% to 47%, respectively. The structures of
coumarin derivatives 4 were characterized by 1H NMR, 13C NMR
and HR-MS analysis.
2
2
.2. UV–vis absorption and fluorescence emission spectra
.2.1. The solvent selection of 4-XP1
4-XP1 showed strong fluorescence intensity and obvious sol-
vent effect, so 4-XP1 was chosen for solvent analysis. The absorp-
tion and emission spectra of compound 4-XP1 in different solvents
were detected and the results were shown in Table 1 and Fig. 1.
Compound 4-XP1 exhibited the sharp absorption peak in various
organic solvents. Moreover, the solvent had slightly effect on the
maximum absorption wavelength (about 430 nm) and the molar
ꢀ
F of 4-XP1 was the highest (0.82) and the emission peak of 4-
XP1 was found at 454 nm. Furthermore, although the ꢀF of 4-XP1
was lower in the polar solvents, but it had larger Stokes shift (44–
48 nm) than that in the non-polar solvents (22–38 nm).
2

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
Fig. 1. (a) UV–Vis absorption spectra and (b) fluorescence spectra of 4-XP1 in different solvents (For interpretation of the references to color in this figure, the reader is
referred to the web version of this article.).
at around 375 nm with a weak fluorescence intensity (ФF = 0.03).
It is obvious that the solution color of 4-HX displayed colorless
with fluorescence quenching (Fig. 4). It can be seen from the re-
sults that 4-XP1, 4-XP2 and 4-XP3 had similar absorption peaks
at about 431 nm and the blue fluorescence emission wavelength
at about 460 nm. It is worth mentioning that 4-XP3 showed an-
other absorption peak at 315 nm due to the π-π transition. On
moving from 4-XP1 to 4-XP2 and 4-XP3, the fluorescence emis-
sion peak was slightly redshifted from 455 to 467 nm. Mean-
while, 4-XP1 and 4-XP2 exhibited intense blue fluorescence and
high fluorescence quantum yields (4-XP1: 0.82, 4-XP2: 0.85) in
CHCl . It is worth noting that the absorption and fluorescence
3
emission peaks of compounds 4-XP (diethylamino substituted in
7
-position) were redshifted obviously and intensity increased dra-
matically compared with 4-XH (H in 7-position), which indicated
that the introduction of the diethylamine group in coumarin 7-
position was benefit to the absorption and fluorescence proper-
ties of the compounds. In comparison, due to the introduction of
the nitro group in pyridine 5-position, 4-XP3 exhibited the high-
Fig. 2. The color of 4-XP1 (left to right: toluene, CHCl3, EA, THF, DCM, MeCN, DMF,
DMSO, EtOH, MeOH) under the visible light (upper row) and the UV lamp (365 nm,
lower row) (For interpretation of the references to color in this figure, the reader is
referred to the web version of this article.).
4
−1
−1
est molar absorption coefficient (ε = 5.5 × 10
M
·cm ) and the
lowest fluorescence quantum yield (ФF = 0.12) relative to that of
4
-XP1 and 4-XP2 in CHCl . Although the molar absorption coef-
3
Table 2
ficient and ꢀF of 4-XP1, 4-XP2 and 4-XP3 were higher than 4-
Optical data of compound 4 in CHCl3.
XH in CHCl , the introduction of diethylamino group reduced the
3
a
maxb (M−1·cm−1
c
d
SSe (nm)
corresponded Stokes shift (68 nm) to the ranged of 23–26 nm. As
clearly seen from Fig. 4., 4-XP1 and 4-XP2 appeared as pale-yellow
color under visible light and intense blue fluorescence under UV
radiation in CHCl3, yet 4-XP3 displayed dark yellow color and were
shown as weak blue fluorescence.
Dye
λ
abs (nm)
ε
)
λ
em (nm)
ФF
4
4
4
4
-XH
307
431
431
444
13,900
51,000
34,800
54,500
375
454
457
467
0.03
0.82
0.85
0.12
68
26
23
23
-XP1
-XP2
-XP3
Note: aAll of the values correspond to the strongest absorption peaks.
b
Molar absorption coefficient.
2.3. Theoretical calculation
c
Emission wavelength.
d
Fluorescence quantum yields (ФF) are measured using an integrating sphere
To better understand the optical properties of the fluorescent
molecule 4, DFT and TD-DFT calculations were applied to our re-
search [27–32]. The geometrical configuration of the compound
method and standard errors are less than 5%.
e
The Stokes shift of the experimental results.
4-XP1 was optimized by applying the DFT to obtain the optimal
2
.2.2. Optical properties of compound 4 in CHCl3
structure at the B3LYP/6–311 G level of theory, as implemented in
the Gaussian 09 program package (Fig. 5) [33]. Further, we had cal-
culated the absorption and emission spectra by using polarizable
continuum model (PCM) in different solvents at the B3LYP/6–311 G
level. By using the DFT calculations, the orbital energies of LUMO
and HOMO were calculated, and then the absorption and emission
spectra were computed by using TD-DFT (Table 3).
According to the spectral performance of compound 4-XP1 in
different solvents, the UV–Vis absorption and fluorescence emis-
sion spectrum of compound 4 (4-XH, 4-XP2 and 4-XP3) were mea-
sured in CHCl3 and the results were shown in Table 2 and Fig. 3.
Compound 4-XH showed an absorption peak at 307 and 347 nm
4
−1
−1
and its molar absorption coefficient (ε) was 1.4 × 10
M
·cm . In
the structure of 4-XH, the charge was concentrated in the pyridine
ring, and a strong intramolecular charge transfer (ICT) occurred
during the excitation process, so an ICT peak (347 nm) was gen-
erated. The corresponded fluorescence emission peak of 4-XH was
In order to determine the stable structure of 4-XP1, the ground
state energies of enol and keto configuration of amide structure
were calculated in different solvents and the energy of keto form
was lower than enol form. Therefore, the stable structure of 4-XP1
3

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
Fig. 3. (a) UV–Vis absorption spectra and (b) fluorescence spectra of compounds 4 in CHCl3.
sults. As shown in Fig. 7, the LUMO energy levels were -2.63 and
2.64 eV in the nonpolar solvents chloroform and THF, while in the
-
polar solvent DMSO, the LUMO energy levels dropped to -2.67 eV.
The energy gap also decreased with the increase of solvent polar-
ity, from 3.50 eV (toluene) to 3.21 eV (DMSO), and the emission
wavelength was red shifted.
We also calculated the optical properties of compound 4 based
on the structure optimization. In order to further verify the exper-
imental results, the geometry of compound 4 was optimized by
DFT calculation at the B3LYP / 6–311+G (d) level through the polar-
ization continuum model (PCM) in CHCl3. Based on the optimized
structure, the frontier orbital energy of compound 4 was calculated
by time-dependent density functional theory (TD-DFT), and then
the absorption and emission spectra were calculated (Table 4 and
Fig. 8).
Fig. 4. The color of compound 4 in CHCl3 under the visible light and the UV lamp
(365 nm) (For interpretation of the references to color in this figure, the reader is
referred to the web version of this article.).
was stable in keto form and the stable geometry in CHCl3 was
shown in Fig. 5. In the molecular structure of 4-XP1, coumarin and
amide are in plane structure through hydrogen bond between car-
bonyl group on coumarin ring and hydrogen of amide, while pyri-
dine ring has a certain dihedral angle with coumarin plane through
C-N bond rotation.
From the frontier molecular orbitals and transition energies of
compound 4 (Fig. 8 and Table 4), it can be seen that the tran-
sition mode of 4-XP was from HOMO to LUMO, while that of
4
-XH was from HOMO-3 to LUMO. The electron cloud of 4-XH
was mainly concentrated on the pyridine ring in the ground state
HOMO), while in excited state was mainly concentrated on the
(
The optimized ground state and excited state configurations in
different solvents were shown in Fig. 6 and it can be seen that the
pyridine ring of 4-XP1 (the single bond between C19 and N18) ro-
tates in the excited state. In non-polar solvent, the rotation angles
coumarin ring (LUMO). During the excitation process, intramolecu-
lar charge transfer (ICT) led to the increase of non-radiative en-
ergy, resulting in lower fluorescence intensity and larger Stokes
shift [34,35]. Pyridine as a key contributing part of the designed
dyes. The introduction of pyridine ring increased the conjugation
system of 4-XP1 and 4-XP2 and the electron delocalization, which
resulted the electron cloud of HOMO and LUMO orbitals evenly
distributed in the whole molecule. This may be one of the fac-
tors affecting the higher fluorescence intensity. At the same time,
we also noticed that the HOMO electron cloud of 4-XP3 is con-
centrated on the coumarin ring, while the LUMO electron cloud
is concentrated on the pyridine ring, similar to 4-XH, resulting in
the decrease of fluorescence intensity, which was consistent with
the experimental results. It can be seen from Fig. 8 that the pos-
sible reason is that the introduction of the electron withdrawing
group (nitro group) and the electron donor group (diethylamino
were 23.70° (toluene) and 23.95° (CHCl ), respectively, but it in-
3
creased to 37.59° in DMSO and 37.31° in methanol. The increase of
rotation angle leaded to the increase of nonradiative energy, which
may be the cause of the decrease of fluorescence intensity, the red
shift of absorption and emission wavelength and the increase of
Stokes shift of 4-XP1 in polar solvents. There were in good agree-
ment with the experimental results.
Based on the optimized structure, the absorption and emission
spectra of 4-XP1 in five different solvents (toluene, CHCl , tetrahy-
3
drofuran, dimethyl sulfoxide and methanol) were calculated by TD-
DFT (Table 3 and Fig. 7). As shown in Table 3, the absorption and
emission wavelengths of 4-XP1 were increased with the increase
of solvent polarity, which was consistent with the experimental re-
Fig. 5. Optimized geometry of 4-XP1 at B3LYP/6–311 G level.
4

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
Table 3
Calculation data of compounds 4-XP1 in differrent solvents at B3LYP/6–311 G level.
a
cal (nm) / f e
b
c
cal (nm) / f e
d
Solvent
λ
λ
abs (nm)
λ
λ
em (nm)
Energy gap (eV)
Toluene
CHCl3
THF
390 / 1.0192
403 / 1.1023
409 / 1.1370
419 / 1.1927
419 / 1.1880
424
431
423
435
432
412 / 0.9638
426 / 1.0827
432 / 1.1122
443 / 1.1696
442 / 1.1651
446
454
461
483
476
3.50
3.27
3.25
3.21
3.22
DMSO
MeOH
Note: aThe calculated maximum absorption wavelength.
b
The experimental maximum absorption wavelength.
c
The calculated maximum emission wavelength.
d
The experimental maximum emission wavelength.
e
Oscillator strength coefficients.
Fig. 6. Ground state and excited state configuration of compound 4-XP1 in CHCl3 and DMSO.
Fig. 7. Frontier molecular orbitals of 4-XP1 in CHCl3, THF and DMSO.
Table 4
Calculation data of compounds 4 in differrent solvents at B3LYP/6–311+G(d) level.
a
cal (nm) / f e
b
c
cal (nm) / f e
d
Dye
λ
λ
abs (nm)
λ
λ
em (nm)
Energy gap (eV)
4
4
4
4
-XH
303 / 0.3337
401 / 1.1336
401/ 1.1403
476 / 0.4665
307
431
431
444
386 / 0.2672
425 / 1.1481
426 / 1.1690
632 / 0.1872
375
454
457
467
4.13
3.32
3.31
2.25
-XP1
-XP2
-XP3
Note: aThe calculated maximum absorption wavelength.
b
The experimental maximum absorption wavelength.
c
The calculated maximum emission wavelength.
d
The experimental maximum emission wavelength.
e
Oscillator strength coefficients.
group) at the 7 position of the coumarin in the 4-XP3 molecule
formed a push-pull effect, which significantly changed the elec-
tron cloud distribution of 4-XP1 resulting a very small energy gap
to the introduction of diethylamino group. The emission wave-
lengths of 4-XP1 and 4-XP2 were red shifted from 386 nm (4-XH)
to about 425 nm. The theoretical calculated data have the same
trend with the experimental values. The energy gap of 4-XH was
4.13 eV, while the other three compounds were relatively small
(2.25–3.32 eV), so it was easier to transition than 4-XH. The calcu-
lation results of TD-DFT verified the reason that the fluorescence
of 4-XP was stronger in the experimental results.
(
2.25 eV), which caused a red shift of the absorption and emission
wavelengths.
From the specific spectral data in Table 4, the maximum ab-
sorption wavelength of 4-XH was at 303 nm and the maximum
absorption wavelengths of 4-XP were red shifted 98–173 nm due
5

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
Fig. 8. Frontier molecular orbitals of compounds 4 in CHCl3 at B3LYP/6–311+G(d) level.
3
. Conclusion
in solution were measured using an integrating sphere method and
dilute solutions of the compounds in organic solvent were used
(1 × 10− mol/L). The fluorescence spectra were recorded 3 times.
5
In conclusion,
a series of pyridinecarboxamides based on
coumarin derivatives were designed and synthesized. These dyes
exhibited the blue fluorescence with high quantum yields in
nonpolar solvents. Moreover, the emission wavelength underwent
a red shift and the fluorescence quantum yields were signifi-
cantly reduced in polar solvent. Such solvent-sensitive fluores-
cent dyes provide experimental reference data for the research
of microenvironment-sensitive fluorescent probes. We also found
that compound 4-XP3 with nitro substituted on the pyridyl ring
reduced fluorescence intensity and underwent a red shift of ab-
sorption/emission wavelength. The electron donating group linked
on the pyridine ring has little effect on the fluorescence perfor-
mance, but the linking electron withdrawing group significantly
changes the fluorescence performance. This type of dyes can be
used for different applications by modifying the substituents. Be-
sides, the absorption and emission spectra of compounds 4 in dif-
ferent solvents were calculated by DFT calculations agreed with the
experimental spectra. The results showed that pyridinecarboxam-
ides based on coumarin derivatives displayed attractive and tun-
able luminescent properties which can be applied in blue fluores-
cent dyes, fluorescent sensor and biological imaging.
4.3. General procedure for the synthesis of compounds
4.3.1. General preparation of compounds 3-carboxycoumarin
derivatives 2
A mixture of salicylaldehyde 1a (10.0 mmol, 1.210 g), meldrum’s
acid (10.0 mmol, 1.441 g) in ethanol (10 mL) was stirred to reflux
for 12 h. The reaction was complete detected by TLC and cooled
to room temperature, and then the reaction precipitate was fil-
tered to give crude product. The crude product was purified by re-
crystallized from anhydrous ethanol solvent (5 mL) to afford target
compound 2a (1.616 g, 85%) as white solid without further purifi-
cation. The synthesis process of 2b was similar to 2a.
4.3.2. General preparation of compounds 3-acyl chloride coumarin
derivatives 3
A mixture of 3-carboxycoumarin 2a (10.0 mmol, 1.901 g), an-
hydrous thionyl chloride (4 mL) and anhydrous DMF (0.1 mL) was
stirred at room temperature for 1 h. The reaction was complete
detected by TLC and the solvent was removed under reduced pres-
sure to afford target compound 3a (1.447 g, 83%) as white solid.
The synthesis process of 3b was similar to 3a.
4. Experimental
4
.1. Materials and equipment
4.3.3. General preparation of compounds 3-carboxamide coumarin
derivatives 4
All of the chemicals used in the current study were purchased
3-Acyl chloride coumarin 3a (0.416 g, 2.0 mmol), Et N (2.021 g,
3
from commercial vendors and used as received without further pu-
rification, unless otherwise noted. All solvents were purified and
dried using standard methods prior to use. Nuclear magnetic reso-
nance ( H, 13C) spectra were recorded on a Bruker AM 500 spec-
trometer with chemical shifts reported as ppm at 500, 125 MHz,
respectively, (in DMSO, CDCl3 and TMS as the internal standard).
The high-resolution mass spectra were recorded on a Thermo
Scientific LTQ Orbitrap XL (ESI) and melting points (Mp.) were
recorded on a X-4 electro-thermal digital melting point apparatus.
20.0 mmol), 2-aminopyridine (0.188 g, 2.0 mmol) and DCM (10 mL)
were added in turn to a 50 mL round-bottomed flask. The reaction
was stirred for 12 h at room temperature and completed the reac-
tion was detected by TLC analysis. The mixture was washed with
water (20 mL) and extracted with dichloromethane (3 × 30 mL).
The organic layer was combinated and dried with Na SO , and
1
2
4
then removed the solvent under reduced pressure. The residue was
purified by silica gel chromatography eluting (silica gel, petroleum
ether/ethyl acetate = 2:1) to afford complex 4-XH (0.177 g, 33%) as
a white solid. The synthesis process of 4-XP1∼4-XP3 was similar
to 4-XH.
4
.2. Absorbance, fluorescence and quantum yield
The solvents used in the photochemical measurements were
4.3.4. 2-oxo-N-(pyridin-2-yl)-2H-chromene-3-carboxamide
(compound 4-XH)
spectroscopic grade. All the experiments were performed repeat-
edly, and reproducible results were obtained. UV–Vis absorption
spectra were measured on a UV-2550. Fluorescence spectra were
White solid. Yield 33%. Mp. 252–254 °C. 1H NMR (500 MHz,
DMSO-d ) δ (ppm): 11.17 (s, 1H), 9.07 (s, 1H), 8.39 (d, J = 3.9 Hz,
6
obtained with an Edinburgh FS5 spectrofluorometer. The ꢀ values
1H), 8.28 (d, J = 8.3 Hz, 1H), 8.07 (d, J = 6.9 Hz, 1H), 7.90
F
6

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
(
t, J = 7.0 Hz, 1H), 7.82 (t, J = 7.8 Hz, 1H), 7.57 (d, J = 8.4 Hz,
Acknowledgement
13
1
H), 7.50 (t, J = 7.4 Hz, 1H), 7.27–7.16 (m, 1H). C NMR (125 MHz,
DMSO-d ) δ (ppm): 161.45 (1C), 160.35 (1C), 154.55 (1C), 151.38
We gratefully acknowledge the financial supported by the
Natural Science Foundation of China (21606201) and the National
Natural Science Foundation of Zhejiang (LY13B020016) and the Un-
dergraduate Science and Technological Innovation Program in Zhe-
jiang Province (Zhejiang Xinmiao Talents Program) (2017R403066).
6
(
1C), 149.11 (1C), 148.98 (1C), 139.18 (1C), 135.19 (1C), 131.08 (1C),
25.87 (1C), 120.87 (1C), 119.15 (1C), 119.03 (1C), 116.77 (1C),
14.22 (1C).
1
1
4
.3.5. 7-(diethylamino)-2-oxo-N-(pyridin-2-yl)-2H-chromene-3-
Supplementary materials
carboxamide (compound 4-XP1)
Yellow solid. Yield 42%. Mp. 255–256 °C. 1H NMR (500 MHz,
Supplementary material associated with this article can be
found, in the online version, at doi:10.1016/j.molstruc.2021.131229.
CDCl ) δ (ppm): 11.32 (s, 1H), 8.76 (s, 1H), 8.36 (d, J = 8.2 Hz,
3
2
1
H), 7.72 (t, J = 8.7 Hz, 1H), 7.45 (d, J = 9.0 Hz, 1H), 7.09–7.00 (m,
H), 6.66 (d, J = 9.0 Hz, 1H), 6.52 (s, 1H), 3.46 (q, J = 7.1 Hz, 4H),
References
1
3
1
.24 (t, J = 7.1 Hz, 6H). C NMR (125 MHz, CDCl ) δ (ppm): 162.52
3
[
1] S.H. Zhou, J.H. Jia, J.R. Gao, L. Han, Y.J. Li, W.J. Sheng, The one-pot synthesis and
fluorimetric study of 3-(2 -benzothiazolyl)coumarins, Dyes Pigments 86 (2010)
(
1C), 158.02 (1C), 153.00 (1C), 148.69 (2C), 148.29 (1C), 138.04 (1C),
ꢀ
131.42 (2C), 119.64 (1C), 114.68 (1C), 110.14 (2C), 108.58 (1C), 96.75
123–128.
+
[2] T.Z. Yu, S.D. Yang, Y.L. Zhao, H. Zhang, X.Q. Han, D.W. Fan, Y.Q. Qiu,
L.L. Chen, Synthesis, crystal structures and fluorescence properties of
(
(
1C), 45.20 (2C), 12.44 (2C). HRMS (ESI) m/z calcd for C19 H20N O
M+H) + 338.14992, found 338.14975.
3
3
3-(2-pyridyl)coumarin derivatives, J. Photoch. Photobio. A 214 (2010) 92–99.
[
3] K.V. Basavarajappa, Y.A. Nayaka, R.O. Yathisha, P. Manjunatha, Synthesis, Char-
acterization, Optical, Electrochemical and Current-Voltage Characteristics of
Coumarin Dyes, J. Fluoresc. 29 (2019) 1201–1211.
4
.3.6. 7-(diethylamino)-N-(4-methylpyridin-2-yl)-2-oxo-2H-
[4] L. Sun, J. Liu, S. Xu, B. Dong, J. Lv, S. Hu, B. Zhou, B. Shen, Y. Wang, L. Xu,
chromene-3-carboxamide (compound 4-XP2)
W. Xu, X. Bai, H. Song, High fluorescence LaOBr/coumarin organic–inorganic
composite nanomaterials for ultra-sensitive Fe3+ sensing, fluorescence imag-
Yellow solid. Yield 47%. Mp. 267–268 °C. 1H NMR (500 MHz,
CDCl ) δ (ppm): 11.26 (s, 1H), 8.76 (s, 1H), 8.34–8.02 (m, 2H), 7.46
ing and water-based ink anti-counterfeiting applications, J. Mater. Chem. C 8
3
(
2020) 13733–13742.
(
d, J = 9.0 Hz, 1H), 6.87 (d, J = 4.9 Hz, 1H), 6.66 (d, J = 11.3 Hz,
[
[
[
5] A. Alizadeh, B. Farajpour, S.S. Mohammadi, M. Sedghi, H. Naderi-Manesh, C. Ja-
niak, T.O. Knedel, Design and Synthesis of Coumarin-Based Pyrazolopyridines
as Biocompatible Fluorescence Dyes for Live-Cell Imaging, ChemistrySelect 5
1
H), 6.53 (s, 1H), 3.46 (q, J = 7.1 Hz, 4H), 2.39 (s, 3H), 1.25 (t,
13
J = 7.1 Hz, 6H).
C NMR (125 MHz, CDCl ) δ (ppm): 162.49
3
(
2020) 9362–9369.
(
1C), 161.51 (1C), 157.98 (1C), 152.96 (1C), 151.83 (1C), 149.40 (1C),
6] S.A.R. Nurhayatun, J. Joazaizulfazli, C. Subhash, W. Roswanira Abdul,
P.B. Deepak, K.S. Terry, S. Murugesan, Coumarin-Oxadiazole Derivatives: Syn-
thesis and Pharmacological Properties, Mini Rev. Org. Chem. 17 (2020)
780–794.
7] F.J. Chen, G.Z. Liu, Y.J. Shi, P.X. Xi, J. Cheng, J.P. Hong, R. Shen, X.J. Yao, D.C. Bai,
Z.Z Zeng, A coumarin-derived fluorescent chemosensor for selectively detect-
ing Cu2+: Synthesis, DFT calculations and cell imaging applications, Talanta 124
148.59 (1C), 147.89 (1C), 131.40 (1C), 120.86 (1C), 115.20 (1C),
1
10.05 (1C), 109.98 (1C), 108.57 (1C), 96.74 (1C), 45.19 (2C), 21.42
+
1C), 12.44 (2C). HRMS (ESI) m/z calcd for C20H22N O
3 3
(M+H) +
(
352.16557, found 352.16574.
(2014) 139–145.
4
3
.3.7. 7-(diethylamino)-N-(5-nitropyridin-2-yl)-2-oxo-2H-chromene-
-carboxamide (compound 4-XP3)
Orange solid. Yield 17%. Mp. 277–278 °C. 1H NMR (500 MHz,
[8] C.J. Hua, K. Zhang, M. Xin, T. Ying, J.R. Gao, J.H. Jia, Y.J. Li, High quantum yield
and pH sensitive fluorescence dyes based on coumarin derivatives: fluores-
cence characteristics and theoretical study, RSC Adv. 6 (2016) 49221–49227.
[
9] P. Li, M. Zhang, X. Sun, S. Guan, G. Zhang, M. Baumgarten, K. Mullen, A den-
drimer-based highly sensitive and selective fluorescence-quenching sensor for
Fe3+ both in solution and as film, Biosens. Bioelectron. 85 (2016) 785–791.
CDCl ) δ (ppm): 11.36 (s, 1H), 8.75 (s, 1H), 8.39 (d, J = 2.2 Hz,
3
1
H), 8.31 (d, J = 8.8 Hz, 1H), 7.80 (dd, J = 8.8, 2.4 Hz, 1H),
[
10] N. Ahmed, B.V. Babu, S. Singh, P.M. Mitrasinovic, An Efficient One-Pot
Three-Component Synthesis of Highly Functionalized Coumarin Fused Inden-
odihydropyridine and Chromeno[4,3-b]quinoline Derivatives, Heterocycles 85
7
.45 (d, J = 9.0 Hz, 1H), 6.66 (dd, J = 9.0, 2.4 Hz, 1H), 6.52 (d,
13
J = 2.3 Hz, 1H), 3.47 (q, J = 7.1 Hz, 4H), 1.25 (t, J = 7.1 Hz, 6H).
C
(2012) 1629–1653.
NMR (125 MHz, CDCl ) δ (ppm): 162.54 (1C), 161.62 (1C), 158.04
3
[
11] A. Thakur, R. Singla, V. Jaitak, An Efficient One-Pot Three-Component Syn-
thesis of Highly Functionalized Coumarin Fused Indenodihydropyridine and
Chromeno[4,3-b]quinoline Derivatives, Eur. J. Med. Chem. 101 (2015) 476–495.
(
(
1C), 153.12 (1C), 150.53 (1C), 149.07 (1C), 148.80 (1C), 140.41
1C), 131.50 (1C), 115.82 (1C), 114.47 (1C), 110.24 (1C), 109.43 (1C),
1
08.55 (1C), 96.72 (1C), 45.22 (2C), 12.44 (2C). HRMS (ESI) m/z
[12] C. Fan, X. Huang, L. Han, Z. Lu, Z. Wang, Y. Yi, Novel colorimetric and fluores-
cent off–on enantiomers with high selectivity for Fe3+ imaging in living cells,
Sens. Actuators B Chem. 224 (2016) 592–599.
calcd for C19 H19 N O5+ (M+H) + 383.13500, found 383.13559.
4
[13] G. Mata, N.W. Luedtke, Synthesis and Solvatochromic Fluorescence of Biaryl
Pyrimidine Nucleosides, Org. Lett. 15 (2013) 2462–2465.
Declaration of Competing Interest
[14] K.P. Wang, Y. Lei, J.P. Chen, Z.H. Ge, W. Liu, Q. Zhang, S.J. Chen, Z.Q Hu, The
coumarin conjugate: synthesis, photophysical properties and the ratiometric
fluorescence response to water content of organic solvent, Dyes Pigments 151
We declare that we have no financial and personal relationships
with other people or organizations that can inappropriately influ-
ence our work, there is no professional or other personal interest
of any nature or kind in any product, service and/or company that
could be construed as influencing the position presented in, or the
review of, the manuscript entitled.
(
2018) 233–237.
[15] K. Shantaram, G.J. Amol, S. Nagaiyan, Deep red emitting triphenylamine based
coumarin-rhodamine hybrids with large Stokes shift and viscosity sensing:
Synthesis, photophysical properties and DFT studies of their spirocyclic and
open forms, Dyes Pigments 137 (2017) 329–341.
[
16] M. Kaya, E. Mente s¸ e, Synthesis and solvent-dependent photophysics of
novel fluorescent triazole-coumarin-based dye, J. Heterocycl. Chem. 57 (2020)
714–1719.
a
1
[
17] Z.C. Zhou, A.N. Zheng, Y.H. Cui, Z.Q. Lin, W.J. Niu, Y.J. Zhang, J.R. Gao, Y.J. Li,
Rational design and synthesis of 3-heteroaromatics coumarin molecules with
unusual solution and solid dual efficient luminescence, Tetrahedron 75 (2019)
CRediT authorship contribution statement
2958–2964.
Zichun Zhou: Visualization, Formal analysis, Writing – review &
editing. Xue Tang: Methodology, Formal analysis, Writing – review
[18] Q.Q. Wu, Z.Q. Liu, D.X. Cao, R.F. Guan, K.G. Wang, Y.Y. Shan, Y.G. Xu, L. Ma,
Coumarin amide derivatives as fluorescence chemosensors for cyanide anions,
Mater. Chem. Phys. 161 (2015) 43–48.
&
editing. Yanhong Cui: Methodology, Formal analysis, Writing –
review & editing. Shuai Xue: Formal analysis, Writing – review
editing. Zihua Yu: Formal analysis, Writing – review & editing.
Yujin Li: Project administration, Formal analysis, Writing – review
editing.
[
19] Y.T. Sun, Y.H. Sun, S.F. Zhao, D.X. Cao, R.F. Guan, Z.Q. Liu, X.Y. Yu, X. Zhao,
Efficient Solution- and Solid-State Fluorescence for Series of 7-Diethy-
laminocoumarin Amide Compounds, Asian J. Org. Chem. 7 (2018) 197–202.
a
&
[
20] C. Zhang, M. Li, W. Liang, G. Zhang, L. Fan, Q. Yao, S. Shuang, C. Dong, Sub-
stituent Effect on the Properties of pH Fluorescence Probes Containing Pyridine
Group, ChemistrySelect 4 (2019) 5735–5739.
&
7

Z. Zhou, X. Tang, Y. Cui et al.
Journal of Molecular Structure 1247 (2022) 131229
[
21] K.C. Pan, S.W. Li, Y.Y. Ho, Y.J. Shiu, W.L. Tsai, M. Jiao, W.K. Lee, C.C. Wu,
C.L. Chung, T. Chatterjee, Y.S. Li, K.T. Wong, H.C. Hu, C.C. Chen, M.T. Lee, Ef-
ficient and Tunable Thermally Activated Delayed Fluorescence Emitters Having
Orientation-Adjustable CN-Substituted Pyridine and Pyrimidine Acceptor Units,
Adv. Funct. Mater. 26 (2016) 7560–7571.
[29] S. Khemakhem, S. Elleuch, N.B. Azaza, H. Ammar, Y. Abid, Hydrolysis and sub-
stitution effects on the optical properties of coumarin derivatives studied by
vibrational spectroscopy and DFT calculation, J. Mol. Struct. 1168 (2018) 65–72.
[30] E. Borkowski, F.M. Cecati, F.D. Suvire, D.M. Ruiz, C.E. Ardanaz, G.P. Romanelli,
R.D. Enriz, Mass spectrometry and theoretical calculations about the loss of
methyl radical from methoxilated coumarins, J. Mol. Struct. 1093 (2015) 49–58.
[31] A. Dhar, N.S. Kumar, P.K. Paul, S. Roy, R.L. Vekariya, Influence of tagging thio-
phene bridge unit on optical and electrochemical properties of coumarin based
dyes for DSSCs with theoretical insight, Org. Electron. 53 (2018) 280–286.
[32] J. Zheng, Y.J. Li, Y.H. Cui, J.H. Jia, Q. Ye, L. Han, J.R. Gao, Isatin-phenylhydrazone
dyes and boron complexes with large Stokes shifts: synthesis and solid-state
fluorescence characteristics, Tetrahedron 71 (2015) 3802–3809.
[
22] G. Gogoi, D. kashyap, R.J. Sarma, Mechano-Luminescent Behavior of a Pyridine–
Containing Anthracene Derivative: Role of Aromatic Stacking Interactions,
Cryst. Growth Des. 18 (2018) 4963–4970.
[23] K.N. Indravath, B. Ramakrishna, S. raditya, M. Navendu, K.D. Samar, Func-
tional Molecular System of Bis(pyrazolyl)pyridine Derivatives: Photophysics,
Spectroscopy, Computation, and Ion Sensing, ACS Omega
035.
3 (2018) 3022–
3
[
24] C.J. Hua, H. Zheng, K. Zhang, M. Xin, J.R. Gao, Y.J. Li, A novel turn off fluo-
rescent sensor for Fe(III) and pH environment based on coumarin derivatives:
the fluorescence characteristics and theoretical study, Tetrahedron 72 (2016)
[33] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheese-
man, V.G. Zakrzewski, J.A. Montgomery, R.E. Stratmann, J.C. Burant, S. Dap-
prich, J.M. Millam, A.D. Daniels, K.N. Kudin, M.C. Strain, O. Farkas, J. Tomasi,
V. Barone, M. Cossi, R. Cammi, B. Mennucci, C. Pomelli, C. Adamo, S. Clif-
ford, J. Ochterski, G.A. Petersson, P.Y. Ayala, Q. Cui, K. Morokuma, D.K. Malick,
A.D. Rabuck, K. Raghavachari, J.B. Foresman, J. Cioslowski, J.V. Ortiz, B.B. Ste-
fanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaromi, R. Gomperts, R.L. Mar-
tin, D.J. Fox, T. Keith, M.A. Al-Laham, C.Y. Peng, A. Nanayakkara, C. Gonzalez,
M. Challacombe, P.M.W. Gill, B.G. Johnson, W. Chen, M.W. Wong, J.L. Andres,
M. Head-Gordon, E.S. Replogle, J.A. Pople, Gaussian 09, Gaussian:, Wallingford,
CT, 2009.
8365–8372.
[
25] Z.C. Zhou, W.J. Niu, Z.Q. Lin, Y.H. Cui, X. Tang, Y.J. Li, A novel “turn-off” fluores-
cent sensor for Al3+ detection based on quinolinecarboxamide-coumarin, Inorg.
Chem. Commun. 121 (2020) 108168.
[
26] K. Zhang, H. Zheng, C.J. Hua, M. Xin, J.R. Gao, Y.J. Li, Novel fluorescent
N,O-chelated fluorine-boron benzamide complexes containing thiadiazoles:
Synthesis and fluorescence characteristics, Tetrahedron 74 (2018) 4161–4167.
[
27] S. Sasaki, G.P.C. Drummen, G. Konishi, Recent advances in twisted intramolec-
ular charge transfer (TICT) fluorescence and related phenomena in materials
chemistry, J. Mater. Chem. C 4 (2016) 2731–2743.
[34] L. Vachova, V. Novakova, K. Kopecky, M. Miletina, P. Zimcik, Effect of in-
tramolecular charge transfer on fluorescence and singlet oxygen production of
phthalocyanine analogues, Dalton Trans. 41 (2012) 11651.
[35] J.Y. Lia, C.Y. Zhang, S. Wu, X. Wen, Z. Xi, L. Yi, Facile synthesis of green-light
and large Stokes-shift emitting coumarins for bioconjugation, Dyes Pigments
151 (2018) 303–309.
[
28] E.J. Gabriel, A.S. Claudia, S.G. Natalia, J.T. Juan, A.G. Carlos, M.P. Carlos, B.P. Adri-
ana, A.V. Mariano, A.C. Carlos, A.M. Hernan, An experimental and TD-DFT the-
oretical study on the photophysical properties of Methylene Violet Bernthsen,
Dyes Pigments 112 (2015) 341–351.
8