Synthesis and characterization of a Eu-containing polymer precursor featuring thenoyltrifluoroacetone and 5-acrylamido-1,10-phenanthroline

Article abstract of DOI:10.1016/j.saa.2011.07.027

A polymerizable ligand, 5-acrylamido-1,10-phenanthroline (L), was synthesized. Its Eu(III) complex with 2-thenoyltrifluoroacetone (HTTA) was prepared and characterized by elemental analysis, IR, MS, and ¹H NMR spectra. The photophysical properties of the complex were studied in detail by using UV, luminescence spectra, luminescence lifetime and quantum yield. The complex shows a remarkable luminescence quantum yield at room temperature (40.1%) upon ligand excitation and a long ⁵D₀ lifetime (590 μs), which makes it not only a promising light-conversion molecular device but also an excellent luminescent polymer precursor.

Full text of DOI:10.1016/j.saa.2011.07.027

Spectrochimica Acta Part A 82 (2011) 159–163
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and characterization of a Eu-containing polymer precursor featuring
thenoyltrifluoroacetone and 5-acrylamido-1,10-phenanthroline
Cun-Jin Xua,b, Bo-Geng Li , Jin-Tao Wan , Zhi-Yang Bu
a,∗
a
a
a
The State Key Laboratory of Chemical Engineering, Department of Chemical and Biochemical Engineering, Zhejiang University, Hangzhou 310027, China
College of Material, Chemistry and Chemical Engineering, Hangzhou Normal University, Hangzhou 310036, China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
A polymerizable ligand, 5-acrylamido-1,10-phenanthroline (L), was synthesized. Its Eu(III) complex with
Received 18 March 2011
Received in revised form 3 July 2011
Accepted 10 July 2011
-thenoyltrifluoroacetone (HTTA) was prepared and characterized by elemental analysis, IR, MS, and 1
2
H
NMR spectra. The photophysical properties of the complex were studied in detail by using UV, lumines-
cence spectra, luminescence lifetime and quantum yield. The complex shows a remarkable luminescence
5
quantum yield at room temperature (40.1%) upon ligand excitation and a long D0 lifetime (590 ␮s),
Keywords:
Europium complex
Photophysical property
which makes it not only a promising light-conversion molecular device but also an excellent luminescent
polymer precursor.
©
2011 Elsevier B.V. All rights reserved.
2
1
-Thenoyltrifluoroacetone
,10-Phenanthroline
Monomer
Synthesis
1
. Introduction
cidation of the luminescence properties difficult [21]. The latter
route, however, offers a well-defined structure around the metal
center, which, in turn, leads to the well-defined photophysical
properties. Recently, most of the approaches to bind a lanthanide
complex to a polymer backbone take advantage of a polymeriz-
able ligand such as acrylic acid (AA) [22–25]. But it should be noted
that the AA ligand makes little contribution to the luminescence
of the complexes, and therefore it is difficult to obtain polymers
with excellent luminescence properties. Hence the design and syn-
thesis of polymerizable ligands as efficient sensitizers and their
metal complexes as highly luminescent precursors have become
an important theme in supramolecular and coordination chem-
istry [26,27]. In this paper, we designed and synthesized a new
ligand, 5-acrylamido-1,10-phenanthroline (L), as well as a highly
luminescent Eu-containing precursor 1 (Scheme 1). We chose
the 1,10-phenanthroline (phen) moiety as a metal binding group
since phen is widely used as assistant antenna groups for pho-
tosensitising lanthanide ion. The acrylamido group appended to
the phen ring represents our rational attempt to provide 1 being
copolymerized with other vinyl monomers for the preparation
of Eu-containing polymer with excellent photophysical proper-
ties. The 2-thenoyltrifluoroacetone (HTTA) ligand was included
because of its high absorption coefficient, and thus high efficiency
of energy transfer (ET) from the ligand to Eu(III) ion [28]. Addition-
ally, we have chosen Eu(III) for our initial studies considering the
ease of characterization the pure red europium emission provides
(∼612 nm) and the rich literature base on this class of emissive
metal complexes.
The last decades have witnessed a growing interest in pho-
toluminescence of lanthanide complexes due to the unique
photophysical features such as long luminescence lifetimes, sharp
emission bands, large Stockes shift, and high quantum yields [1,2].
These highly desirable properties are actively sought for numer-
ous applications, including display devices, chemical and biological
sensors, and optical communications [3–6]. Currently, there are
two approaches to the material development. One is the use of
host–guest system in which the metal complexes are dispersed
in polymeric matrices [7–11]. The other is to covalently embed
the metal-containing coordination chromophores to polymeric
backbones [12]. The latter system has a unique capability in the
prevention of phase separation and leaching of photoactive com-
ponents, which are often associated with the host–guest system.
The system with such advantages can be developed in two
routes. One involves the direct reaction of a polymer ligand with a
metal salt [13–16], while the other directly polymerizes a metal-
containing precursor [17–19]. The polymer luminophores prepared
by the former route usually show serious concentration quench-
ing due to the occurrence of ionic aggregates even at low rare
earth content [20]. Moreover, the microenvironment of each rare
earth ion is very different and complicated, which makes the elu-
∗ Corresponding author. Tel.: +86 571 87952623; fax: +86 571 87951612.
E-mail address: bgli@zju.edu.cn (B.-G. Li).
1
386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2011.07.027

1
60
C.-J. Xu et al. / Spectrochimica Acta Part A 82 (2011) 159–163
NO2
NH
2
HNO3
NH NH H O
2 2 2
H SO
5% Pd/C
2
4
N
N
N
N
N
N
O
F3C
H
N
O
O
N
N
HN
CH2 CHCOCl
EuCl3
Eu
3
O
HTTA, NaOH
S
N
N
L
1
Scheme 1. Synthesis of the Eu-containing precursor 1.
2
. Material and methods
stirring a solution of acryloyl chloride (1.5 mL), triethylamine
2 mL), and acetonitrile (15 mL) at room temperature under an
(
2
.1. Reagents and instruments
argon atmosphere. The reaction was allowed to continue for 24 h.
After concentration under reduced pressure the residue chro-
matographed on a silica column (25 mm × 200 mm) with 9:1
chloroform/ethanol as the eluent. Removal of the solvent from the
desired eluate fraction gave 0.88 g (70%) of yellow crystals. Anal
Lanthanide oxides exceeding 99.99% in purity were purchased
from the Yue-Long Chemical Plant (China). HTTA (99%; Acros
Organics) was used without further purification. The 5% Pd/C cat-
alyst was obtained from Aldrich. Other chemicals were analytical
grade and used as received. Elemental analyses (C, H, N) were per-
for C15H11N O Calcd. (Found): C, 72.28 (72.23); H, 4.45 (4.49); N,
3
−1
1
6.86 (16.89). IR (KBr) ꢀmax: 3360 (NH), 1658 (C O), 1631 cm
C). H NMR (400 MHz, CDCl ): ı (ppm) = 8.98 (d, J = 8.25 Hz,
formed with a Flash-EA1112 elemental analyzer, and lanthanide
1
(C
3
1
ions were analyzed by complexometric titration with EDTA.
H
2
7
2
H), 8.80 (s, 1H), 8.29 (d, J = 8.14 Hz, 1H), 8.03 (d, J = 8.32 Hz, 2H),
and 13C NMR spectra were collected at 400 MHz and 100 MHz,
respectively, with a Bruker-400 spectrometer in the Fourier trans-
form mode, using CDCl3 (for ligand) or DMSO-d6 (for complex)
.52 (dd, J = 7.94, 4.28 Hz, 1H), 7.40 (s, 1H), 6.51 (d, J = 5.25 Hz,
13
H), 5.79 (m, 1H). C NMR (100 MHz, CDCl ): ı (ppm) = 165.41,
3
149.38, 149.24, 145.65, 143.85, 135.68, 130.94, 130.85, 130.71,
as solvent. Mass spectra were measured on an Aligent-5975 spec-
troscopy or a Bruker Esquire 3000
equipped with an electrospray ionization (ESI). Instrument control
and data acquisition were performed using Esquire 5.0 software.
The ion source temperature was 250 C, and needle voltage was
1
28.23, 127.81, 124.49, 123.19, 122.29, and 120.56. EIMS (70 eV)
plus
ion trop mass spectrometer
+
m/z: M 249 (57), 221 (7), 195 (100), 167 (35), 140 (19), 55
(41).
◦
always set at 4.0 kV. Nitrogen was used as the drying and nebu-
2.3. Synthesis of the complexes
−1
lizer gases at a flow rate of 5 L min and a back-pressure of 10 psi.
Infrared spectra of KBr pellets were carried out at room temper-
2.3.1. Synthesis of
−1
ature in the 4000–400 cm region by using a Bruker Tensor-27
FT-IR spectrophotometer. UV spectra were obtained by a Unico UV-
trichlorotri(5-acrylamido-1,10-phenanthroline)gadolinium(III)
dihydrate (GdL Cl ·2H O)
3
3
2
2
102PC spectrophotometer with a resolution of 1 nm between 200
To a stirred solution of GdCl ·6H O (0.74 g, 2 mmol) in 15 mL
3
2
and 400 nm in a 1 cm quartz cuvette. Luminescence spectra at room
temperature were recorded in a Hitachi F-4500 spectrometer with
a 150 W Xenon lamp. For the Eu-containing polymer precursor,
the excitation and emission slits were 5.0 and 1.0 nm, respectively,
of deionized water was added a solution of L (1.49 g, 6.0 mmol) in
◦
30 mL of 95% C H OH. The reaction mixture was stirred at 50 C for
5
2
10 h and then concentrated under reduced pressure to about 10 mL.
After cooling to room temperature the precipitate was filtered off,
washed with water (2 × 10 mL) and ethanol (2 × 10 mL), dried and
−1
with a scan speed of 240 nm min and a PMT voltage of 400 V.
While for ligand L, the excitation and emission slit widths were
37 3 9
5
stored over silica gel. Yield: 1.47 g (70%). Anal for C45H Cl N O Gd
−
1
both set to 2.5 nm, with a scan speed of 240 nm min and a PMT
voltage of 950 V. Phosphorescence spectra at the temperature of
liquid nitrogen were measured by the same spectrometer with a
quartz Dewar and quartz sample tubes in absolute ethanol solu-
Calcd. (Found): C, 51.60 (51.51); H, 3.56 (3.60); N, 12.04 (12.08); and
Gd, 15.01 (15.06).
−
4
−1
tion (5 × 10 mol L ) by using a PMT voltage of 700 V and a scan
2.3.2. Synthesis of the Eu-containing precursor (1)
−1
speed of 60 nm min . Excitation and emission slits were 10.0 and
.0 nm, respectively. Luminescence lifetimes were measured on an
To a stirred solution of HTTA (2.00 g, 9 mmol) and L (0.75 g,
3 mmol) in 40 ml ethanol, 1 N solution of NaOH (0.36 g, 9 mmol)
was added followed by the addition of an aqueous solution of
5
Edinburgh FLS 920 fluorescence spectrograph using a microsecond
flash lamp as the excitation source with the pulse width of 2 ␮s.
Metal luminescence quantum yields were measured relative to qui-
◦
EuCl3·6H2O (1.10 g, 3 mmol). The reaction was heated at 60 C for
8 h. The pink solid precipitate was collected and washed with
ethanol (2.49 g, 78% yield). Anal for C39H23F9N3O7S3Eu Calcd.
(Found): C, 43.99 (43.95); H, 2.18 (2.22); N, 3.95 (4.00); Eu, 14.27
(14.33). IR (KBr) ꢀmax: 3360 (NH), 1601, 1541, 1355, 787, 717,
nine sulfate in 1.0 N H SO4 (˚ = 54.6%) [29] by using 1.0 cm quartz
2
−
1
cuvettes, with a PMT voltage of 400 V, a scan speed of 240 nm min
and both the excitation and emission slit widths of 2.5 nm.
−
. H NMR (400 MHz, DMSO-d ): ı (ppm) = 3.72
6
1 1
5
(
8
81, 484, 457 cm
s, 3H), 5.64–6.92 (m, 9H), 7.22–7.96 (m, 5H), 8.14–8.76 (m, 3H),
.88–9.40 (m, 2H), 10.40 (br, 1H). Negative ESIMS m/z: 1099.7
2.2. Synthesis of 5-acrylamido-1,10-phenanthroline (L)
−
−
−
To
a
suspension of 5-amino-1,10-phenanthroline (0.98 g,
[M+Cl] , 1063.6 [M–H] , 1036.6 [M–C2H4] , 928.8, 877.8, 850.7,
702.8, 464.7.
5
.0 mmol) in 20 mL of acetonitrile was added dropwise with

C.-J. Xu et al. / Spectrochimica Acta Part A 82 (2011) 159–163
161
Fig. 3. Excitation (EX, ꢂem = 612 nm) and emission (EM, ꢂex = 350 nm) spectra of 1,
emission (EM, ꢂex = 350 nm) spectrum of L in solid state at room temperature.
turbation induced by the metal coordination, which confirms that
the UV spectra of the complex reflect essentially absorption of the
ligands, and that both TTA and L have taken part in the formation
of the complex.
Fig. 1. The FT-IR spectra of 1, L and HTTA.
3.3. Luminescence properties
Solution samples were prepared in a four-window quartz 1-cm
fluorescence cell, whereas solid samples for emission lifetime and
spectra measurements were prepared in a 1.75-cm diameter quartz
fluorimetry tube. The 77 K measurements were performed by using
a quartz optical dewar filled with liquid N . Fig. 3 presents the pho-
2
toluminescence spectra of 1 in solid state at room temperature. The
excitation spectrum of the complex was obtained by monitoring the
emission wavelength of the Eu3+ ion at 612 nm. It exhibits a broad
excitation band centered at 350 nm, which indicates an efficient
ligand-to-metal ET, since the most intense feature is a broad band
corresponding to transitions populating ligand-centered excited
states. Further, no 4f–4f excitation lines of the Eu3+ ion have been
observed, thus strongly suggesting an efficient sensitization pro-
cess between the ligands and the Eu3+ ion, with the ligand unit
acting as an antenna.
Fig. 2. UV absorption spectra of HTTA, L and 1 in tetrahydrofuran solution
(
5 × 10− mol L ) at room temperature.
6
−1
3
. Result and discussion
As shown in Fig. 3, the emission spectrum measured with
350 nm as the excitation wavelength exhibits characteristic emis-
sions of Eu(III) ions. The five narrow emission peaks centered at 579,
3
.1. IR spectra
5
7
5
7
The IR spectra provided good evidence that the metal ion is
591, 612, 651 and 698 nm, assigned to the D → F , D → F ,
0
0
0
1
5
7 5 7 5 7
coordinated to the ligands via the C O (TTA), and N atoms (phen)
D → F , D → F , D → F transitions, respectively, are well
0
2
0
3
0
4
5 7
(
Fig. 1). The C O and C C stretching vibrations shift from 1659
resolved. The hypersensitive D → F transition is very intense,
0
2
−
1
−1
and 1632 cm
in the free HTTA to 1601 and 1541 cm in 1,
pointing to a highly polarizable chemical environment around the
respectively. The C N and C–H stretching vibrations shift from
−
1
−1
1
411, 800 and 740 cm in the free L to 1355, 787 and 717 cm
−
1
in 1, respectively. The typical OH absorption at 3200–3500 cm
is undetectable, implying that there are no coordinated H O
2
molecules in the complex, which is in good agreement with the
result of the elemental analysis. It is very important to eliminate
water molecules in complexes to obtain highly efficient lumines-
cence rare earth complexes due to decreasing the deactivation of
O–H oscillators.
3.2. UV spectra
Absorption spectra of the ligands and the complex in tetrahy-
drofuran solution are given in Fig. 2. The absorption bands of free
HTTA at 263, 291 and 334 nm are assigned to the ꢁ–ꢁ* transitions
of ketonic form and enol form, respectively. The absorption peaks
of free L at 240 and 268 nm are attributed to the bands of ꢁ–ꢁ* tran-
sitions of aromatic ring. The spectrum of 1 contains essentially the
combined ligand absorptions, but with slight shifts due to the per-
Fig. 4. Phosphorescence spectra of GdL3Cl3·2H2O and L (ꢂex = 274 nm) in absolute
−
4
−1
ethanol solution (5 × 10 mol L ) at 77 K.

1
62
C.-J. Xu et al. / Spectrochimica Acta Part A 82 (2011) 159–163
Table 1
−1
triplet state energy of phen (22,075 cm [34]) is more suitable for
the sensitization of Eu than that of L.
Experimental photophysical parameters for some selected Eu(III) complexes at room
temperature.
3+
For the complex 1, the luminescence decay curve of the Eu(III)
ꢃa
I ( D0 → 7F2)a
5
ꢄ [␮s]a
˚ [%]b
5
7
Complex
D → F transition was found to be a single exponential (Fig. 5),
0
2
1
19.76
14.78
10.43
20.85
687
252
100
590
224
91
40.1
21.5
12.6
52.0
indicating that all of the Eu(III) ions occupy the same average local
environment [34].
c
Eu(TTA)3(H2O)2
Eu(TTA)2(AA)d
Eu(TTA)3(phen)
c
1008
802
4
. Conclusion
a
The relative intensity of the 5D0 → F2 transition I( D0 → F2), the experimental
7
5
7
intensity parameter (ꢃ) between the D0 → F2 transition and 5D0 → F1 transition,
5
7
7
We have designed and synthesized a polymerizable ligand, 5-
and the lifetime (ꢄ), were obtained in the solid state.
b
The quantum efficiency (˚) measured relative to quinine sulfate
acrylamido-1,10-phenanthroline (L), as an efficient sensitizer of
Eu(III) luminescence. Its Eu(III) complex with thenoyltrifluoroace-
tone was prepared. The photoluminescence of the complex is nearly
monochromatic, characteristic of the europium ion and proceeds
with a high efficiency (40.1%) and a long 5D0 lifetime (590 ␮s),
which makes it not only a promising light-conversion molecular
device but also a potential luminescent polymer precursor. Fur-
ther efforts on the polymerization activity of the complex are in
progress, together with the preparation of Eu-containing polymers.
−
3
−1
−1
(
5 × 10 mol L in 0.5 mol L H2SO4) [29], experimental error 10%. All samples
−6 −1
dissolved in tetrahydrofuran with the concentration of 5 × 10 mol L
.
c
Prepared by Melby’s method [32].
Prepared by Wang’s method [33].
d
Eu3+ ion, and is responsible for the brilliant-red emission color of
the complex. Further, the emission spectrum of the complex shows
only one peak for the 5D → 7F transition, indicating the pres-
0
0
3+
ence of a single chemical environment around the Eu ion and
also showing that the Eu3 ion occupies a low-symmetry site. No
emission band at 427 nm, arising from the free L ligand, has been
observed, suggesting that ET from L to the Eu(III) ion is efficient. The
triplet state energy of L, determined based on the shortest wave-
length phosphorescence band of GdL Cl ·2H O at 77 K (Fig. 4), is
+
Acknowledgments
This work was supported by the National Natural Science Foun-
dation of China (No. 20936006) and the Special Funds for Key
Innovation Team of Zhejing Province (No. 2010R50017).
3
3
2
−1
located at 20000 cm , a suitable energy for the sensitization of
Eu(III) due to a good energy match between the donating level of
Appendix A. Supplementary data
−
1
the ligand and the accepting level of Eu(III) (17200 cm ), suggest-
ing that L ligand not only saturates the coordination sphere but
also acts as photon antenna able to transfer energy to Eu(III) ion
effectively [30].
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.saa.2011.07.027.
The luminescence properties such as the monochromaticity
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5
7
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