The synthesis and luminescence of europium (III) complex based on deprotonated 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobutane-1,3- dionate and 1,10-phenanthroline

Article abstract of DOI:10.1016/j.saa.2012.11.029

A new β-diketone ligand, 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4- trifluoro-butane-1,3-dione(HL) was synthesized by four steps reaction (Suzuki-Miyaura cross-coupling, Cadogan cyclization, N-ethylation and Claisen condensation reaction) from 1-(4-bromo-3-nitrophenyl)ethanone and thiophen-2-ylboronic acid. Deprotonated ligand (L^-1) and 1,10-phenanthroline (phen) coordinated to Eu³⁺ to obtain a new europium (III) complex, EuL₃(phen). The complex was characterized by elementary analysis, IR, ¹H NMR, UV-Visible absorption spectroscopy, thermogravimetric analysis (TGA) and photoluminescence (PL) measurements in detail. TGA shows that the decomposition temperature of the complex is up to 320 °C. PL measurement results indicate that the Eu(III) complex exhibit intense red-emission with the characteristic of europium ion. Red LED device was successfully fabricated by employing the complex onto 380 nm-emitting InGaN chip, which shows that the complex can act as red phosphor in combination with 380 nm-emitting chips.

Full text of DOI:10.1016/j.saa.2012.11.029

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 417–422
Contents lists available at SciVerse ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
The synthesis and luminescence of europium (III) complex based on
deprotonated 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobutane-1,3-
dionate and 1,10-phenanthroline
⇑
Sheng-Gui Liu , Wen-Yi Su, Rong-Kai Pan, Xiao-Ping Zhou, Xin-Lan Wen, Yi-Zhao Chen, Sheng Wang,
Xiao-Bo Shi
School of Chemistry Science and Technology, Zhanjiang Normal University, Zhanjiang 524048, PR China
g r a p h i c a l a b s t r a c t
h i g h l i g h t s
A new europium (III) complex was synthesized from deprotonated 1-(4-ethyl-4H-thieno[3,2-b]indol-6-
yl)-4,4,4-trifluoro-butane-1,3-dione(HL) and 1,10-phenanthroline (phen). The Eu(III) complex exhibit
intense red-emission with the characteristic of europium ion. Red LED device was successfully fabricated
by precoating complex onto 380 nm-emitting InGaN chip, which shows that the complex can act as red
phosphor in combination with 380 nm-emitting chips.
"
A new b-diketonato europium (III)
complex was synthesized.
The europium (III) complex exhibits
red intense emission of europium
ion.
"
"
LEDs device was fabricated by
precoating the complex onto 380 nm
emission InGaN chip.
S
N
N
O
Eu
N
O
3
F3C
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 7 August 2012
Received in revised form 4 November 2012
Accepted 6 November 2012
Available online 28 November 2012
A new b-diketone ligand, 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluoro-butane-1,3-dione(HL)
was synthesized by four steps reaction (Suzuki–Miyaura cross-coupling, Cadogan cyclization, N-ethyla-
tion and Claisen condensation reaction) from 1-(4-bromo-3-nitrophenyl)ethanone and thiophen-2-ylbo-
ronic acid. Deprotonated ligand (LÀ1) and 1,10-phenanthroline (phen) coordinated to Eu3+ to obtain a new
europium (III) complex, EuL3(phen). The complex was characterized by elementary analysis, IR, 1H NMR,
UV–Visible absorption spectroscopy, thermogravimetric analysis (TGA) and photoluminescence (PL)
measurements in detail. TGA shows that the decomposition temperature of the complex is up to
320 °C. PL measurement results indicate that the Eu(III) complex exhibit intense red-emission with the
characteristic of europium ion. Red LED device was successfully fabricated by employing the complex
onto 380 nm-emitting InGaN chip, which shows that the complex can act as red phosphor in combination
with 380 nm-emitting chips.
Keywords:
Lanthanide complex
b-Diketone
Chemical synthesis
Luminescence
Ó 2012 Elsevier B.V. All rights reserved.
⇑
Corresponding author. Tel.: +86 759 3183176; fax: +86 759 3183510.
E-mail address: lsgui@sohu.com (S.-G. Liu).
1386-1425/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.saa.2012.11.029

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S.-G. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 417–422
Shenzhen Meryer Chemistry Technology Company. Solvents were
Introduction
freshly distilled and dried by standard methods. Elemental analysis
for the synthesized ligand and the Eu(III) complexes were carried
out with an Elementar vario EL elemental analyzer. Electrospray
ionisation mass spectra (ESI-MS) were acquired on a Thermo Finn-
igan LCQ DECA XP ion trap mass spectrometer, equipped with an
Lanthanide complexes have long been known to give bright
emission under UV irradiation because of the effective energy
transfer from ligands to central ion called antenna effect and have
found many applications such as chiral sensing, antibody labels in
DELFIA immunoassays, and new materials based on sol–gel
glasses, liquid crystals, near-IR LEDs or polymers [1–6].
Diketonato complexes have attracted considerable attention be-
cause of their high fluorescence emission efficiency caused by the
high absorption coefficient of b-diketonato molecule [7–9]. The
intensity of 4f–4f photoluminescence is the result of a balance
among absorption by the ligands, rates of ligand-rare earth ion en-
ergy transfer, nonradiative decays and radiative emission rates. In
this way, the emitting 4f level is, in general, populated much more
efficiently than by direct excitation of the rare earth ion levels [10–
12].. Whether high efficiency of energy transfer can be achieved
was depended on the selection of appropriate organic ligand.
When b-diketonato was employed to sensitize europium ion to
emit red emission, b-diketonato ligand should have appropriate
ESI source. 1H NMR spectra were recorded on
a
Bru-
ker AVANCE 400. Photoluminescence excitation (PLE) and emission
(PL) spectra were measured with an EDINBURGH FLS 920 Com-
bined Fluorescence Lifetime and Steady State Spectrophotometer.
UV–Visible absorption spectra were recorded on a UV-2501PC
UV–Visible Spectrophotometer. IR spectra were recorded on a
Nicolet Avatrar 330 FT-IR spectrometer. Thermogravimetric analy-
sis (TGA) was carried out up to 600 °C with a heating speed of
10.0 K/min in atmosphere on an NETZSCH TG-209 Thermogravi-
metric Analyzer. The quantum yield of the complex was measured
with an EVERFINE PMS-80 PLUS UV–VIS-near IR. The emission
spectra of the fabricated LEDs and the overall quantum yield of
the europium (III) complex was measured with an EVERFINE
PMS-50 PLUS UV–VIS-near IR Spectrophotocolorimeter. All mea-
surements were carried out at room temperature.
p-conjugated system. If p-conjugated system is too small, it will
not effectively absorb light energy, if is too big, it will not sensitize
the europium ion to emit red emission [13,14]. A well known
example of a highly efficient b-diketonato sensitizer is 2-thenoyl-
trifluoroacetonate, which could coordinate to europium (III) ion
to yield excellent red emission complex [Eu(tta)3(phen)] [14].
Carbazole is an attractive molecule unit of organic dyes with
interesting photoconducting, charge-transporting properties and
thermal stability, which was widely introduced to polymers and
applied to luminescent device, and dye-sensitized solar cells [15–
18].
In comparison with carbazole, thieno[3,2-b]indole structure is
also based on the indole structure but in which a thiophene ring,
instead of a second benzene ring, is fused onto the five-membered
ring at the 2–3 position of the indole (Fig. 1). Organic compounds
containing thieno[3,2-]indole moiety are of little information to
us [19–24]. Motivated by our research interest in europium com-
plex based on carbazole b-diketonate ligand [25–28], we expect
to know whether thieno[3,2-b]indole b-diketonate have appropri-
Synthesis of 1-(3-nitro-4-(thiophen-2-yl)phenyl)ethanone
1-(3-Nitro-4-(thiophen-2-yl)phenyl)ethanone was synthesized
by Suzuki–Miyaura cross-coupling reaction [29]. 1-(4-bromo-3-
nitrophenyl)ethanone (4.88 g, 0.02 mol), thiophen-2-ylboronic
acid (2.56 g, 0.02 mol), K2CO3 (2.76 g, 0.02 mol) and Pd(PPh3)4
(0.22 g, 0.02 mmol) were dissolved in 150 ml toluene and 30 ml
water then heated at 110 °C for 24 h. The crude product was ex-
tracted with CH2Cl2. After removal of organic solvent, the solid
crude 1-(3-nitro-4-(thiophen-2-yl)-phenyl)ethanone was obtained
but not further purified just ESI-MS was executed to determine
that product had been formed: m/z, 248 (M + H+).
Synthesis of 1-(4H-thieno[3,2-b]indol-6-yl)ethanone
The synthesis of 1-(4H-thieno[3,2-b]indol-6-yl)ethanone is
realized by Cadogan cyclization reaction [30,31]. All the previous
step crude product 1-(3-nitro-4-(thiophen-2-yl)phenyl)-ethanone
and PPh3 (11.8 g, 0.045 mol) were added into o-dichlorobenzene
(o-DCB) and refluxed for 8 h. The most byproducts and impurities
have been removed by precipitation from hexane. No further puri-
fication was executed, since the major impurity, PhPh3 and PPh3O,
will not take part in the next step reaction, but ESI-MS was used to
determine that product had been formed. ESI-MS: m/z, 216
(M À H+).
ate
p-conjugated system to sensitize europium ion to emit red
light.
In this paper, we synthesize a new europium (III) complex
based on a new thieno[3,2-b]indole b-diketonato ligand, 1-(4-
ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobutane-1,3-dionate
(LÀ1). We investigated the thermal stability, luminescence property
of the europium complex. This complex can be excited by GaInN
380 nm emitting chips light. We fabricated a red emission LED
device by employing this europium complex as red emitting
material. To the best of our knowledge, it is the first report that
thieno[3,2,-b]indole-based b-diketonato ligand sensitize europium
ion to emit red light.
Synthesis of 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)ethanone
Crude 1-(4H-thieno[3,2-b]indol-6-yl)ethanone and 4.0 ml
C2H5Br were added into the mixture of KOH (0.8 g, 0.02 mol) and
200 ml acetone. The reaction solution was reduced after being stir-
red for 2 days at room temperature. Then the solution was poured
into water. The precipitate was then filtered, washed with water,
and recrystallized from alcohol to give crude 1-(4-ethyl-4H-thie-
no[3,2-b]indol-6-yl)ethanone. No further purification was exe-
cuted. ESI-MS was employed to determine that product had been
formed. ESI-MS: m/z, 244 (M À H+).
Experimental
Materials and methods
1-(4-Bromo-3-nitrophenyl)ethanone,
thiophen-2-ylboronic
acid, ethyl trifluoroacetate and Pd(PPh3)4 were purchased from
H
H
N
Synthesis of 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobu-
tane-1,3-dione
N
1-(4-Ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobutane-
1,3-dione was synthesized by Claisen condensation reaction from
acetylthieno[3,2-b]indole and ethyl trifluoroactate. The mixture
S
Fig. 1. The structures of carbazole and thieno[3,2-b]indole.

S.-G. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 417–422
419
of 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)ethanone, CF3COOC2H5
(2.1 g, 0.015 mol) and C4H9OK (0.73 g, 0.006 mol) was refluxed
for 6 h in toluene. Then the mixture was treated with diluted
hydrochloric acid and extracted with toluene. The solvent was
evaporated in vacuum to give crude solid product. The crude prod-
uct was recrystallized from ethanol. Then further separated by col-
umn chromatography (dichloromethane-petroleum ether) (0.33 g).
The elemental analysis data for C16H12F3NO2S were found (calcu-
lated)%: C, 56.71(56.63), H, 3.64(3.56), N, 4.22 (4.13). 1H NMR
(300 MHz, CDCl3): d 1.53 (t, 3H,), d 4.43 (q, 2H), d 6.72 (s, 1H), d
7.14–7.16(d, 1H) d 7.58–7.60 (d, 1H), 7.73–7.84 (q, 2H), d 8.13 (s,
were mixed with a molar ratio of 3:1:1 in 40 ml alcohol. The PH va-
lue of mixture were adjusted to 8–9 by NaOH solution and heated
at 60 °C for 6 h under stirring. The precipitate was filtered and
washed with alcohol, dried at 50 °C, yellow precipitate was ob-
tained (0.09 g, yield: 66%). The elemental analysis data for EuL3(-
phen) (C60H47EuF9N5O6S3) were found (calculated) %: C, 53.38
(53.26); H, 3.59 (3.50) N, 5.16 (5.18), 1H NMR (300 MHz, CDCl3):
d 1.72–1.83 (m, 9H, CH3A), d 3.46 (s, 3H, enol-c-CHA) d 4.63 (q,
6H, CH2A), d 6.04 (d, 3H, ArAH) d 7.21 (d, 9H, ArAH), 7.39 (d, 3H,
ArAH), d 8.18 (s, 2H, ArAH), d 8.51 (d, 2H, ArAH) d 10.21 (s, 2H,
ArAH), d 10.68 (d, 2H, ArAH). FT-IR (KBr):
1625, 1566, 1474, 1336, 1303, 1275, 1239, 1129, 854, 822, 784,
602 cmÀ1
t = 3427, 2920, 1667,
1H). ESI-MS: m/z, 340 (M À H+). FT-IR (KBr):
t = 3442, 2980,
1585, 1508, 1466, 1337, 1274, 1216, 1147, 879, 793, 576 cmÀ1
.
.
Synthesis of EuL3(phen)
Fabrication of LED
1-(4-Ethyl-4H-thieno[3,2-b]indol-6-yl)-4,4,4-trifluorobutane-
1,3-dione (0.1020 g, 0.0003 mol), (0.0366 g,
0.0001 mol) 1, 10-phenanthroline (phen) (0.0198 g, 0.0001 mol)
Red light-emitting diode device was fabricated by combination
of a 380 nm-emitting InGaN chip with the Eu(III) complex as phos-
phor. The phosphor was blended with commercially-available sil-
EuCl3Á6H2O
O
Br
O2N
S
B(OH)2
+
[Pd(PPh3)]4
toluene
O2N
S
O
O
O
H
N
PPh3
N
CH3CH2Br
acetone, NaOH
reflux
o-DCB
S
S
O
O
N
CF3COOCH2CH3
tert-BuOK, toluene
CF3
S
O
O
N
CF3
CH3CH2OH
NaOH
3
+
EuCl3
+
S
N
N
S
N
N
N
O
Eu
O
3
F3C
Fig. 2. The synthesis route of ligand and europium complex.

420
S.-G. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 417–422
ica gels (6175A and 6175B, purchased from Sil–More Industrial
Ltd., China) in order to be precoated onto the LED chip. The thick-
ness of the admixture precoated onto the chip was the same due to
the fixed size of the reflector cup. The admixture was cured in an
oven at 150 °C for 1 h. Then, another silicone layer was coated onto
the phosphor and was cured for another 1 h in order to prevent the
phosphor from dispersing into the epoxy resins. Eventually, the
LEDs lamp device was obtained by curing transparent epoxy resin
at 180 °C for 1 h.
100
90
80
70
60
50
40
30
Results and discussions
Synthesis, 1H NMR, IR and thermal stability
The key steps in the ligand synthesis routine (see Fig. 2) are the
synthesis of 1-(3-nitro-4-(thiophen-2-yl)phenyl)ethanone by Su-
zuki–Miyaura cross-coupling reaction, and 1-(4H-thieno[3,2-b]in-
dol-6-yl)ethanone by Cadogan cyclization. In this way, the
difficulty of formation 2-acetyl thieno[3,2-b]indole ring was over-
come. The substitution of the NH hydrogen atom of 1-(4H-thie-
no[3,2-b]indol-6-yl)ethanone by ethyl enable to carry out the
Claisen condensation reaction smoothly and avoid the decreasing
of intensity of europium ion emission. The formation of b-diketone
group was adopted by common Claisen condensation reaction
from ketone and ester. The europium complex is obtained from
b-diketone, 1,10-phenanthroline and europium ion in the base
alcohol solution.
0
100
200
300
Centigrade
400
500
600
Fig. 3. The thermogravimetric analyze of complex.
in this range. The absorption band of the complex from 300 to
420 nm is mostly attributed to the
ligand.
p–
pà transition absorption of
The excitation and emission spectra of ligand, complex powder
samples are shown in Fig. 5. The free ligand emits green–yellow
light with the maximal peak at 550 nm under 300–500 nm wave-
length light, which red-shift by about 70 nm in comparison with
carbazole–diketone free ligand [25,26]. The complex emit red light
upon excitation with 380 nm. The complex appears emission band
at 594, 613, 653 nm with the characteristic properties of europium
ion, which are ascribed to 5D0 ? 7F1, 5D0 ? 7F2, 5D0 ? 7F3 transi-
tion. The strongest peak located at 613 nm. Monitored at 613 nm,
the excitation band fall within 300–420 nm with the maximal peak
at about 350 nm, which exhibit blue shifted wavelength by 70 nm
in comparison with carbazole–diketonato complex [13]. In the
complex, no green–yellow light remain, which shows that the li-
gand could absorb energy and transfer completely to the europium
ion.
The 1H NMR spectra of 1-(4-ethyl-4H-thieno[3,2-b]indol-6-yl)-
4,4,4-trifluorobutane-1,3-dione (see Supplemental Material,
Fig. S1) confirms the structure of ligand. Only one ACHA hydrogen
atom in b-diketone group is detected, which suggests that b-dike-
tone adopt enol configuration form in CDCl3 solution.
The 1H NMR spectra of complex (see Supplemental Material,
Fig. S2), In comparison with the free ligand, all the aromatic hydro-
gen atoms chemical shift values shifted to high magnetic field but
N-ethyl hydrogen atoms to low magnetic field. The enol-c-CHA in
b-diketone group are shifted from 6.72 to 3.46 ppm, which are sim-
ilar to the behavior of europium complex based on b-diketone li-
gand containing carbazole moiety [13]. The signal at d = 6.04,
7.21 and 7.39 ppm come from the hydrogen atoms of thieno[3,2-
b]indole moiety. The signals at d = 8.18, 8.51, 10.21 and
10.68 ppm attribute to 1, 10-phenanthroline hydrogen atoms.
Comparison with the IR absorption spectra of ligand and com-
plex shows that the peaks in ligand are all red shifted in the com-
plexes. 1585 cmÀ1 of C@O was shifted to 1667 cmÀ1, 1496 cmÀ1 of
C@C of ligand appeared on 1566 cmÀ1 in complexes. This is the
characteristic of b-diketonate coordinated with rare earth ions
since C@O bond was converted into vibrating structure of CAOAEu
bond and C@OAEu bond. The element analyzes for ligand and the
europium complex are well agreement with theory calculation
data.
The luminescence decay time of the 5D0 state in complex is
283 ls. The curve fits with a single exponential function, indicating
that the Eu3+ in complex molecule is only located in the same par-
ity sites. The decay curve of Eu3+ 5D0 excited state of complex is
1.5
357 nm
1.2
complex
0.9
High thermal stability is an essential requirement for fabrica-
tion of LED device. TGA curve of the complex EuL3(phen) is shown
in Fig. 3. TGA shows that the decomposition temperature of the
complex is up to 320 °C. The complex meets with the thermal sta-
bility requirement of fabrication of LED luminescence application.
0.6
0.3
0.0
347 nm
ligand
375
UV–visible absorption and photoluminescence
The UV–visible absorption spectra of the ligand and the com-
plex EuL3(phen) in alcohol solution (1 Â 10À5 mol/L) are shown
in Fig. 4. The maximal absorption peak of the complex is red-
shifted by 10 nm than the free ligand. In the complex, the ligand
contributes to the key absorption for the complex, since the aque-
ous Eu3+ ion and 1, 10-phenanthroline show very weak absorption
300
325
350
400
425
450
Wavelength (nm)
Fig. 4. The UV–Visible absorption spectra of the ligand and the complex EuL3(phen)
in alcohol solution (1 Â 10À5 mol/L).

S.-G. Liu et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 103 (2013) 417–422
421
6x105
5x105
4x105
3x105
2x105
InGaN chip emission
1.0
device emission
0.8
0.6
c
0.4
0.2
0.0
d
1x105
0
a
b
300
350
400
450
500
550
600
650
700
750
300
350
400
450
500
550
600
650
Wavelength (nm)
wavelength (nm)
Fig. 7. The emission spectra of the original InGaN LED without phosphor (dash line)
and the LED with the complex (solid line) under 20 mA forward bias.
Fig. 5. The excitation and emission spectra of ligand and complex powder samples
(a: emission spectra of ligand, kex = 460 nm, b: emission spectra of complex,
kex = 380 nm, c: excitation spectra of ligand, kem = 550 nm, d: excitation spectra of
ligand, kem = 614 nm).
mained exciting light from 380 nm chip could be used to excite
blue and green phosphors to obtain white-emitting LED. This result
indicates that complex can be used as a red component in the fab-
rication of white LED.
shown in Fig. 6. The europium complex has been of importance for
fluorometric applications in biochemistry and molecular biology
owing to its longer luminescence lifetime [32]. The overall quan-
tum yield of the complex was measured in solid state using an
integrating sphere according to the method described by Lin
[33]. The overall quantum yields are 18% for EuL3(phen).
Conclusions
In summary, a new ligand 1-(4-ethyl-4H-thieno[3,2-b]indol-6-
yl)-4,4,4-trifluorobutane-1,3-dione(HL) was synthesized by four
reaction steps (Suzuki–Miyaura cross-coupling, Cadogan cycliza-
tion, N-ethylation and Claisen condensation reaction). Deproto-
nated ligand (LÀ1) further coordinated to europium ion to obtain
a new complex, EuL3(phen). The complex show high thermal sta-
bility (320 °C). Deprotonated thieno[3,2-b]indole b-diketonate
can well sensitize europium ion to emit red light. Red LED device
was successfully fabricated by employing the complex onto
380 nm-emitting InGaN chip. The complex can act as red phosphor
in combination with 380 nm-emitting chips.
Emission spectra of the fabricated LED
Complex EuL3(phen) was employed as a phosphor to fabricate
LED in a mass ratio of 1:20 of phosphor to silicone gel with
380 nm-emitting InGaN chips. The emission spectra of the original
380 nm LED without phosphor and the LED fabricated with the
complex and a 380 nm chip under 20 mA forward bias are shown
in Fig. 7. The peaks at 594, 613, 653, and 700 nm for the com-
plex-LED are due to the Eu3+ emission from the complex in the
LED chip. Based on the emission spectrum, the CIE chromaticity
coordinates of the LED device are calculated as x = 0.6227 and
y = 0.3211, confirming that the complex can be excited by InGaN
chip 380 nm emission light from the LED. The efficiency of the fab-
ricated LED device with the complex achieves 2.38 lm/W. The re-
Acknowledgments
This work was financially supported by the Natural Science
Foundation of Guangdong Province (No. 10152404801000017)
and Zhanjiang Normal University Research funds.
Appendix A. Supplementary material
50000
40000
30000
20000
10000
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2012.11.029.
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