Synthesis and characterization of 9,10-[di-p-(7-diethylamino- coumarin-3-yl) thiopheneyl]anthracene as fluorescent material

Article abstract of DOI:10.1080/17415993.2017.1391813

A novel N-coumarin derivative, namely 9,10-[di-p-(7-diethylamino-coumarin-3-yl) thiopheneyl]anthracene ((CTh)₂A), containing anthracene as the core and 3-thiophene N-coumarin as the substituent was synthesized, and its structure was confirmed by ¹H NMR and IR spectroscopies. The optical, electrochemical and thermal properties were investigated. Thermogravimetric analysis and PL spectra reveal the high thermal and good photoluminescence characteristics. The coumarin derivative exhibits blue photoluminescence with high fluorescence quantum yield in solution (up to 40%). The results show that the derivative would serve as promising organic light-emitting diode luminescent material.

Full text of DOI:10.1080/17415993.2017.1391813

Journal of Sulfur Chemistry
ISSN: 1741-5993 (Print) 1741-6000 (Online) Journal homepage: http://www.tandfonline.com/loi/gsrp20
Synthesis and characterization of 9,10-
[di-p-(7-diethylamino- coumarin-3-yl)
thiopheneyl]anthracene as fluorescent material
Qinglong Luo, Hui Zhang, Yuling Zhao, Jun Wang & Tianzhi Yu
To cite this article: Qinglong Luo, Hui Zhang, Yuling Zhao, Jun Wang & Tianzhi Yu (2017):
Synthesis and characterization of 9,10-[di-p-(7-diethylamino- coumarin-3-yl) thiopheneyl]anthracene
as fluorescent material, Journal of Sulfur Chemistry, DOI: 10.1080/17415993.2017.1391813
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Date: 28 October 2017, At: 04:42

JOURNAL OF SULFUR CHEMISTRY, 2017
https://doi.org/10.1080/17415993.2017.1391813
Synthesis and characterization of 9,10-[di-p-(7-diethylamino-
coumarin-3-yl) thiopheneyl]anthracene as fluorescent
material
a
a
b
a
a
Qinglong Luo , Hui Zhang , Yuling Zhao , Jun Wang and Tianzhi Yu
a
Key Laboratory of Opto-Electronic Technology and Intelligent Control (Ministry of Education), Lanzhou
b
Jiaotong University, Lanzhou, People’s Republic of China; School of Chemical and Biological Engineering,
Lanzhou Jiaotong University, Lanzhou, People’s Republic of China
ABSTRACT
ARTICLE HISTORY
A novel N-coumarin derivative, namely 9,10-[di-p-(7-diethylamino-
coumarin-3-yl) thiopheneyl]anthracene ((CTh)2A), containing
anthracene as the core and 3-thiophene N-coumarin as the sub-
stituent was synthesized, and its structure was confirmed by
Received 11 July 2017
Accepted 10 October 2017
KEYWORDS
N-coumarin; thiophene;
anthracene;
1
H NMR and IR spectroscopies. The optical, electrochemical and ther-
mal properties were investigated. Thermogravimetric analysis and
PL spectra reveal the high thermal and good photoluminescence
characteristics. The coumarin derivative exhibits blue photolumi-
nescence with high fluorescence quantum yield in solution (up to
photoluminescence;
fluorescence
4
0%). The results show that the derivative would serve as promising
organic light-emitting diode luminescent material.
CONTACT Tianzhi Yu
yutianzhi@hotmail.com; Hui Zhang
zhanghui5@mail.lzjtu.cn
Key Laboratory of
Opto-Electronic Technology and Intelligent Control (Ministry of Education), Lanzhou Jiaotong University, Lanzhou 730070,
People’s Republic of China
©
2017 Informa UK Limited, trading as Taylor & Francis Group

2
Q. LUO ET AL.
1. Introduction
A variety of fluorescent compounds have been developed based on the 1-benzopyran-
-one (coumarin) platform [1,2]. The photophysical and spectroscopic properties can
be readily modified by the introduction of substituents (–CO H, –CO R, –CN, –COR,
2
2
2
+
–
N R , –OH, –OR, amine, etc.) in the coumarin at three or four or seven positions giving
3
themselves more flexibility to fit well in various applications. Coumarin and its derivatives
are well known as highly efficient luminescent materials, because of sufficient fluorescence
in the visible light range, large Stokes shifts, high fluorescence quantum yields, excel-
lent light stability, visible excitation, good thermal stability, good emission wavelengths
and nontoxicity [3,4]. They are used extensively as laser dyes, fluorescent probes, optical
brighteners, light absorbers for solar cells [5]. Electroluminescence was initially studied for
fundamental interest [6–8]. The coumarin derivatives are also used extensively as emissive
dopants in organic light-emitting diodes (OLEDs) application [9,10]. Many fluorescent
blue emitters have been reported, such as anthracene derivatives [11], pyrene deriva-
tives [12], fluorene derivatives [13], phosphorescent iridium complexes [14] and so on.
Anthracene derivatives produce high thermal and good photoluminescence characteris-
tics, and new classes of anthracene-based blue-light emitters with improvements in terms
of efficiency and color purity remain to be explored.
This paper report the synthesis and characterization of 9,10-[di-p-(7-diethylamino-
coumarin-3-yl) thiopheneyl]anthracene ((CTh) A). The use of anthracene as the core can
2
suppress emission quenching of the highly fluorescent coumarin caused by aggregation,
as well as increasing the hole-transporting capability, thermal stability of the molecule.
The introduction of 7-(diethylamino)-3-(thiophen-2-yl)coumarin moiety would increase
the long π-conjugation system and luminous intensity, aiming at obtaining new mate-
rial with higher fluorescent property. Meanwhile, integration of the coumarin deriva-
tive based on D-π-D [15] construction could suppress aggregation of the planar ring,
as well as improve photoluminescence characteristics ability and thermal stability. The
photophysical, electrochemical properties and thermal stabilities of the derivative were
investigated.
2. Results and discussion
2
.1. FT-IR spectrum of (CTh) A
2
The FT-IR spectrum of (CTh) A is shown in Figure 1. The strong absorption peak around
2
−
1
about 1710 cm for (CTh) A represents the vibrations of the (ν
) groups, that is a
2
C=O
general feature of coumarin derivatives. There are other strong absorption peak around
584 (ν ), 1512 (ν ), 1133 (νC–O–C), 825 (νArC–H). The characteristic stretching
1
C=C
ArC=C
−
1
vibration bands of –CH and –CH are clearly observed at 2900–3000 cm .
3
2
2.2. Photochemical properties
The UV–VIS absorption and fluorescence spectrum of (CTh) A in dilute CH Cl solutions
2
2
2
are presented in Figure 2. Table 1 lists the UV–VIS absorption maxima (λa,max), emis-
sion maxima (λe,max), Stokes shift (ꢀλ), fluorescent quantum yield (ꢁ), molar extinction
coefficient (ε) and fluorescent lifetime (τ) of the tested (CTh) A.
2

JOURNAL OF SULFUR CHEMISTRY
3
Figure 1. The FT-IR spectrum of (CTh)2A.
Table 1. Photophysical, thermal and electrochemical properties of the (CTh)2A.
Eg,optical
(eV)d
UV–VIS
(nm)
PL
ꢀλ
ꢁ
τ
ε
λonset
(nm)
EOX
(V)
HOMO LUMO
(eV)
−
1
−1
a
b
(eV)c
Comp
(nm) (nm)
(%) (ns) (L mol cm
)
5
(
CTh)2A 340.415
502 87
40
8.0
4.14 × 10
507
0.76
−5.02
−2.57
2.45
a
+
The value is referred to Ag/AgCl and calibrated by Fc/Fc .
Eg,optical = 1241/λonset.
b
c
EHOMO = −e(EOX − 0.54 + 4.8) (eV), the energy level of ferrocene/ferrocenium as −4.80 eV [17].
d
ELUMO = Eg,optical = EHOMO.
The UV–VIS absorption spectrum of (CTh) A feature two major regions at 270–370 nm
2
and 370–530 nm. The former correspond to the π-π* local electron transition of the indi-
vidual aromatic units [18], while the peak at longer wavelength is assigned to the π-π*
Figure 2. UV–VIS absorption and photoluminescence spectrum of (CTh)2A in dilute CH2Cl2 solution.

4
Q. LUO ET AL.
electron transition in the thiophene-substituted N-coumarin conjugated backbones [19],
and probably originated from the delocalized π-π* transition of phenyl- or thiophene-
bridged coumarin moiety, which were bathochromically shifted compared to that of
coumarin [20]. The photoluminescence spectrum has emission peak at 502 nm. The
(
CTh) A shows 87 nm Stokes shift indicating less energy loss during the relaxation process
2
and efficient fluorescence. The fluorescence quantum yields (ꢁ) of (CTh) A measured at
2
room temperature in dilute CH Cl solution is 0.40 (Table 1).
2
2
2.3. Photostability
To investigate the photo-stability of the (CTh) A, we inspected the photo-stabilities of
2
our synthesized (CTh) A by exposing each dichloromethane solution state of (CTh) A
2
2
under the 365 nm UV light irradiation in air. As shown in Figure 3, the photolumines-
cence emission peak of the (CTh) A with the maximal peak at approximately 502 nm was
2
decreased as the exposure time of (CTh) A solution to the UV light was increased. After
2
5
.5 h of irradiation by UV light, the (CTh) A maintained 95% of its initial light emission
2
at the maximal photoluminescence emission peaks. Therefore, the above results demon-
strated that (CTh) A shows good photostability. As many literature reported in this field,
2
derivatives of coumarin generally show good photostability which is rather unusual among
fluorescent dyes [21].
2.4. Thermal properties
TGA measurement was performed in flowing drying nitrogen atmosphere at the heat-
−1
ing rate of 10°C min . The results of TGA measurement of tested (CTh) A are shown
2
in Figure 4. (CTh) A displays good thermal stability up to 305°C (<2% weight loss). At
2
3
37°C, there is a sharp weight loss in its TGA curve, indicating that (CTh) A begins to
2
Figure 3. Photoluminescence spectra intensity of compound (CTh)2A in dichloromethane solutions
−
5
(
C = 1.0 × 10 mol/L) under the 365 nm UV light illumination in air.

JOURNAL OF SULFUR CHEMISTRY
5
decompose at this temperature. The result indicates that (CTh) A meet with the thermal
2
stability requirement of fabrication of OLED luminescence application.
2
.5. Electrochemical properties
The cyclic voltammograms of the (CTh) A are shown in Figure 5. The (CTh) A exhibit
2
2
two quasi-reversible oxidation processes. The first oxidation wave corresponded to the
removal of electrons from the thiophene ring or anthracene group to form a radical cation.
The ionization potential may be regarded as HOMO energy level, and the electron affinity
may be regarded as LUMO energy level [22,23]. The E represent the band gap between
g
HOMO and LUMO, and the value can be calculated from optical absorption edge. From
the UV–VIS absorption spectra, the optical band gap of (CTh) A was estimated to be 507,
2
which corresponds to 2.45 eV. The HOMO and LUMO energy levels can be calculated
according to the relations reported [24]. The overall EHOMO, ELUMO and E data of the
g
(
CTh) A were listed in Table 1.
2
2.6. Transient PL decay characteristics
Figure 6 shows the transient PL decay of (CTh) A in dichloromethane at room temper-
2
ature. The fluorescence lifetime is defined as the time at which the fluorescence analysis
resides in the excited state before returning to the ground state. The photoluminescence
rapidly decreased on the order of sub-microseconds at the end of the excitation pulse
owing to the short fluorescence lifetime of the emitting molecules, which indicates S –S
0
1
fluorescence lifetime is 8 ns and the (CTh) A is fluorescent material.
2
Through the above discussion and analysis, we compared the compound of
ꢀ
(
CTh) A with a similar structure compound of 3,3 -((9-(P-tolyl)-9H-carbazole-3,6-
2
diyl)bis(thiophene-5,2-diyl))bis(7-(diethylamino))coumarin (Cz-2(Th-C)) [25] in the
article we have just published. The absorption spectra of the Cz-2(Th-C) in dichloro-
methane show maximum peak at 445 nm and the emission spectra of the Cz-2(Th-C) in
Figure 4. Thermogravimetric analyses (TGA) of (CTh)2A.

6
Q. LUO ET AL.
Figure 5. Cyclic voltammograms of ferrocene and (CTh)2A.
Figure 6. Transient PL decay characteristics of (CTh)2A in dichloromethane at room temperature.
dichloromethane show maximum peak at 524 nm. It was found that the UV absorption and
fluorescence of (CTh) A were blue shift and the fluorescence quantum yield was lower than
2
Cz-2(Th-C)(ꢁ = 50.1), because the core of compound (CTh) A is anthracene, and the
2
core of compound Cz-2(Th-C) is carbazole. Anthracene is relatively low in hole transport
performance compared with carbazole, and thiophene-substituted N-coumarin is more
suitable for the transport of holes.
3
. Conclusion
It can be concluded that blue-fluorescent material based on anthracene, having
-(diethylamino)-3-(thiophen-2-yl)coumarin as substituents, has been designed and
7

JOURNAL OF SULFUR CHEMISTRY
7
synthesized by a convergent approach using stepwise palladium-catalyzed Suzuki cross-
coupling reactions. The compound exhibits high fluorescence quantum yield (40%) and
strong blue emission (502 nm). These results indicate that the high π-conjugated molecule
structure enhances the light absorption and the fluorescence emission ability of (CTh) A
2
due to the contribution of anthracene and 7-(diethylamino)-3-(thiophen-2-yl)coumarin
groups. The (CTh) A has good thermal stability, suggesting this material have sufficient
2
potential for use in fluorescence OLED application.
4. Experimental
4.1. Materials and instruments
All materials and reagents were of AR grade and directly used. All of the organic solvents
used in this study were dried over appropriate drying agents and distilled prior to use. 1
IR spectrum was taken with a Shimadzu IR Prestige-21 FT-IR spectrophotometer. H
NMR spectra were obtained on Varian Mercury Plus 400 MHz and Agilent Technologies
DDZ 600 MHz Spectrometer with tetramethylsilane as the internal standard. Mass spectra
were recorded using a Thermo Scientific Orbitrap Elite mass spectrometer. The absorption
spectrum was recorded by a Shimadzu UV-2550 spectrometer. The photoluminescence
spectrum was obtained using a PerkinElmer LS-55 spectrometer. Thermogravimetric
analysis (TGA) was performed on a PerkinElmer Pyris system. The photoluminescence
quantum yield was measured by an absolute method using the Edinburgh Instruments
FLS920. Cyclic voltammetry was carried out on a CH Instruments 760 B with a three
electrode system (a Pt working electrode, a Pt-wire counter electrode and an Ag/AgCl
−1
reference electrode) in the presence of n-Bu NPF (0.1 mol L ) as a supporting electrolyte
4
6
in CH Cl . The synthetic routes of the (CTh) A is outlined in Scheme 1.
2
2
2
Scheme 1. Synthesis of (CTh)2A.

8
Q. LUO ET AL.
4
.2. Synthesis and characterization
4.2.1. Preparation of 9,10-dibromoanthracene (1)
The compound anthracene (1 g, 5.62 mmol) was placed in 30 ml chloroform, NBS (3 g,
1
6.86 mmol) was dissolved in the mixture of acetic acid (30 ml) and chloroform (30 ml)
and stirred for 20 min at room temperature, then added dropwise to the anthracene solu-
tion and the mixture was stirred at 40°C for 2 h. Afterwards, the mixture was neutralized
with KOH solution, and the product was extracted with chloroform (4 × 100 mL), then
the combined organic layer was dried by anhydrous Na SO and concentrated under
2
4
reduced pressure. The residue was purified by column chromatography on silica gel using
petroleum ether as eluent to afford compound 1 in 75% yield as yellow solid. m.p.:
1
2
3
22–224°C. H NMR (400 MHz, CDCl ) δ 8.57 (dd, J = 6.7, 3.1 Hz, 4H), 7.62 (dd, J = 6.8,
3
.1 Hz, 4H).
4
.2.2. Preparation of 7-(diethylamino)-3-(thiophen-2-yl)coumarin (2)
1
Compound 2 was prepared similar to the procedure previously described [16], H NMR
(
600 MHz, CDCl ) δ 7.88 (s, 1H), 7.66 (dd, J = 3.6, 0.9 Hz, 1H), 7.36–7.27 (m, 2H), 7.08
3
(
dd, J = 5.0, 3.8 Hz, 1H), 6.61 (dd, J = 8.8, 2.4 Hz, 1H), 6.53 (d, J = 2.2 Hz, 1H), 3.43 (q,
J = 7.0 Hz, 4H), 1.22 (t, J = 7.2 Hz, 6H).
ꢀ
.2.3. Preparation of 3-(4-bromothiopheneyl)-7-(N,N -diethylamino)coumarin (3)
Compound 3 was obtained by the reaction of compound 2 with NBS. H NMR (400 MHz,
4
1
CDCl ) δ 8.24 (s, 1H), 7.32 (dd, J = 6.5, 3.8 Hz, 2H), 7.05–6.98 (m, 1H), 6.62 (dt, J = 8.9,
3
2
1
.1 Hz, 1H), 6.52 (d, J = 2.4 Hz, 1H), 3.43 (dq, J = 7.1, 3.5 Hz, 4H), 1.23 (td, J = 7.1,
.4 Hz, 6H).
4
.2.4. Preparation of 3-(4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl) thiopheneyl)-
ꢀ
7-(N,N - diethylamino)coumarin (4)
ꢀ
The suspension of 3-(4-Bromothiopheneyl)-7-(N,N - diethylamino) coumarin (3) (4.5 g,
1
5
1.9 mmol), bis(pinacolato) diboron (4.85 g, 19.1 mmol), potassium acetate (5.62 g,
7.3 mmol) and Pd(dppf)Cl (0.7 g, 0.96 mmol) in absolute 1,4-dioxane (80 mL) was
2
placed in a three-necked flask. The mixture was heated up to 95°C and stirred for 36 h
under N . After the solvent was evaporated under vacuum, the mixture was dissolved in
2
dichloromethane, washed with water (3 × 50 mL). The organic layer was dried over MgSO4
and concentrated in vacuum. The crude was purified by chromatography on silica gel using
1
CH Cl /petroleum ether (1:20–1:5) to form orange solid (yield 68%). m.p.: 81–83°C. H
2
2
NMR (400 MHz, CDCl ) δ 7.93 (s, 1H), 7.76 (d, J = 3.7 Hz, 1H), 7.59 (d, J = 3.7 Hz, 1H),
3
7
.30 (t, J = 6.8 Hz, 1H), 6.61 (dd, J = 8.9, 2.5 Hz, 1H), 6.52 (d, J = 2.4 Hz, 1H), 3.43 (q,
J = 7.1 Hz, 4H), 1.35 (s, 12H), 1.22 (t, J = 7.1 Hz, 6H).
4.2.5. Preparation of 9, 10-[di-p-(7-diethylamino-coumarin-3-yl)thiopheneyl]
anthracene ((CTh) A)
2
To a toluene solution (20 mL) of compound 9,10-dibromoanthracene (1) (0.6 g,
1
.79 mmol) was added the stirred mixture of compound 4 (3.04 g, 7.16 mmol), Pd(pph3)4
(0.31 g, 0.27 mmol), TBAB (0.07 g, 0.27 mmol), 2M Na CO (85 mmol, aq) and freshed
2
3
toluene (100 ml) under N atmosphere, then the mixture was refluxed at 120°C for
2

JOURNAL OF SULFUR CHEMISTRY
9
2
4 h. Bright yellow precipitate appear in the solution. After cooled, filtered and rinsed
with ethanol four times, the brown solid powder was collected and extracted with
dichloromethane (3 × 100 mL), then the combined organic layer was dried by anhydrous
Na SO and concentrated under reduced pressure. The residue was purified by col-
2
4
umn chromatography on silica gel using dichloromethane/ethyl acetate/petroleum ether
(
4/0.5/10, v/v/v) as eluent to yield the orange solid powder (CTh) A. m.p.: >250°C. IR
2
−
1
(
KBr pellet, cm ): 1710 (C=O), 1584(C=C),1260 (C–O–C), 1400–1530 (anthracene
1
skeleton). H NMR (400 MHz, CDCl ) δ 8.02 (dd, J = 6.8, 3.3 Hz, 4H), 7.98 (s, 2H),
3
7
.93 (d, J = 3.7 Hz, 2H), 7.42 (dd, J = 6.9, 3.2 Hz, 4H), 7.36 (d, J = 8.8 Hz, 2H), 7.20
(
d, J = 3.6 Hz, 2H), 6.64 (dd, J = 8.8, 2.3 Hz, 2H), 6.58 (d, J = 2.2 Hz, 2H), 3.46 (q,
1
3
J = 7.1 Hz, 8H), 1.24 (t, J = 4.8 Hz, 12H). C NMR (151 MHz, CDCl , δ, ppm):160.46,
3
1
1
55.61, 150.55, 139.10, 136.82, 131.36, 130.18, 128.91, 126.77, 126.21, 125.68, 125.40,
09.29, 108.80, 97.17, 44.87, 44.73, 29.67, 29.34, 24.50, 22.67, 22.17, 14.0, 12.60. MS (ESI)
+
m/z 773.25 [M+H] , calculated for C H N O S , 772.98.
4
8
40
2
4 2
Disclosure statement
No potential conflict of interest was reported by the authors.
Funding
This work was financially supported by the Gansu Universities Research Fund [grant number 2015A-
0
66], Gansu Natural Science Foundation [grant number 1606RJZA018], and National Natural
Science Foundation of China [grant number 51563014].
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