Synthesis of europium(III) phenanthroline-β-diketonate silicon-containing complex. Photoluminescence in solution and in sol-gel film

Article abstract of DOI:10.1134/S1070363210090069

A phenanthroline benzoyltrifluoroacetonate europium complex showing a bright red photoluminescence at a wavelength 616 nm was synthesized by reacting 3-isocyanatopropyltriethoxysilane with anhydrous europium(III) tris(benzoyltrifluoroacetonate) and then with phenanthroline.

Full text of DOI:10.1134/S1070363210090069

ISSN 1070-3632, Russian Journal of General Chemistry, 2010, Vol. 80, No. 9, pp. 1758–1761. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © V.V. Semenov, N.V. Zolotarev, M.A. Lopatin, G.A. Domrachev, 2010, published in Zhurnal Obshchei Khimii, 2010, Vol. 80, No. 9,
pp. 1439–1442.
Synthesis of Europium(III) Phenanthroline-β-diketonate
Silicon-containing Complex. Photoluminescence
in Solution and in Sol–Gel Film
V. V. Semenov, N. V. Zolotarev, M. A. Lopatin, and G. A. Domrachev
Razuvaev Institute of Organometallic Chemistry, ul. Tropinina 49, Nizhny Novgorod, 603950 Russia
e-mail: vvsemenov@iomc.ras.ru
Received November 13, 2009
Abstract―A phenanthroline benzoyltrifluoroacetonate europium complex showing a bright red photo-
luminescence at a wavelength 616 nm was synthesized by reacting 3-isocyanatopropyltriethoxysilane with
anhydrous europium(III) tris(benzoyltrifluoroacetonate) and then with phenanthroline.
DOI: 10.1134/S1070363210090069
Europium(III) β-diketonate complexes with red
luminescence are used in immunofluorescent analysis
[1, 2]. They are also of interest to photonics, laser
optics, and technology of electroluminescent devices
[3, 4]. For successful application in practice a material
with a bright luminescence is required, which is
provided in the case of a high quantum yields. We
have shown previously [5] a possibility of obtaining a
silicon-containing europium complex capable of
forming transparent luminescent sol–gel films. The
new ligand was synthesized from 3-isocyanatopropyl-
triethoxysilane and acetylacetone. The europium com-
plex was obtained in two ways: (1) by interaction of
the ligand with europium isopropoxide and (2) by
interaction of tris(acetylacetonato)europium with 3-
isocyanatopropyltriethoxysilane.
The benzoyltrifluoroacetonate ligand provides a more
intense europium photoluminescence in comparison
with acetylacetonate. To increase the luminosity of the
complexes, neutral ligands are commonly used,
phenanthroline in particular.
Our attempts to synthesize 3-benzoyltrifluoro-
acetonate derivatives of aminopropyltriethoxysilane
and 3-isocyanatopropyltriethoxysilane and to obtain
pure samples of the ligands failed. The interaction of
benzoyltrifluoroacetone with aminopropyltriethoxy-
silane and 3-isocyanatopropyltriethoxysilane was ac-
companied by the formation of impurities, and the
target compound could not be purified by vacuum
distillation. At the same time, the reaction of an-
hydrous europium tris(benzoyltrifluoroacetonate) with
3-isocyanatopropyltriethoxysilane led to the expected
complex I, which reacted with phenanthroline
affording compound II. The reaction with 3-iso-
cyanatopropyltriethoxysilane can be easily monitored
by infrared spectroscopy, by observing decrease in the
intensity of the very strong characteristic absorption
band of NCO at 2274 cm–1. After 7-h heating of
europium tris(benzoyltrifluoroacetonate) with 3-iso-
cyanatopropyltriethoxysilane almost all isocyanate was
consumed. The addition of the phenanthroline solution
caused precipitation of complex II.
The product of these reactions readily forms
transparent films, but the cationic luminescence is low
[5]. The absorbed light energy is emitted rather as a
broad band centered at 450 nm of silicon oxide matrix.
Now we report on the preparation of benzoyl-
trifluoroacetonate and phenanthrolinbenzoyltrifluoro-
acetonate silicon-containing europium complexes with
bright red cationic photoluminescence both in film and
in solution.
The cationic luminescence intensity depends on the
structure of organic ligand, from which the absorbed
energy is transferred to the resonant level of lanthanide
and then emitted as a narrow band of f–f-transition.
IR spectra of compounds I and II are of complex
structure due to diversity of their fragments. The most
intense are the bands of β-dicarbonyl group bound
with the europium cation (1692, 1624 cm–1), and
1758

SYNTHESIS OF EUROPIUM(III) PHENANTHROLINE-β-DIKETONATE
1759
F3C
F3C
O
O
O
O
+
(EtO)3Si
C
(EtO) Si
N
H
NCO
Eu
Eu
3
3
O
Ph
Ph
3
3
I
F3C
N
N
O
Phen
(EtO)3Si
C
O
N
H
Eu
O
Ph
3
II
triethoxysilyl group (1140 , 1076, 944, 792 cm–1). The
stretching NH vibrations in the amide group appear as
a broad band of moderate intensity at 3340 cm–1. Two
peaks, at 1716 and 1540 cm–1 (amide I, amide II)
should be assigned to the amide group. In the low-
frequency region between 850 and 650 cm–1 two
narrow lines (764, 704 cm–1) are observed related to
the out-of-plane C–H bending vibrations of aryl group.
The bands of the in-plane vibrations at 1100, 1188, and
1292 cm–1 are overlapped by the absorption of tri-
ethoxysilyl and trifluoromethyl fragments. Stretching
vibrations of C–H bonds in the groups C2H5O and
(CH2)3 appear as strong bands at 2975, 2927, and
2890 cm–1, and those in the aromatic fragments, as less
intense absorption at 3150–3000 cm–1.
1H NMR spectrum of compound I is poorly
resolved because of the presence of the paramagnetic
europium cation, but virtually all fragments can be
identified. Two of the most intense multiplets at 1.23
and 3.85 ppm belong to the protons of CH3CH2O
fragment, three multiplets at 0.8, 1.7, and 3.1 ppm
belong to the trimethylene bridge SiCH2CH2CH2N,
and a multiplet at 7.1 ppm, to the phenyl group
protons. In the electronic spectrum of complex II there
are three absorption bands, at 222, 268, and 322 nm,
with high extinction coefficients (104 to 105 l mol–1 cm–1).
Figure 1 shows the excitation and emission spectra
of the complex I taken as a film on a quartz substrate.
The excitation spectrum of photoluminescence regis,-
tered at a wavelength 615 nm has four bands with
poorly resolved maxima at 305, 340, 370, and 470 nm.
Structure of the emission spectra somewhat changed
depending on the wavelength of the exciting light, due
to the complexity of the composite film. At λexc
=
340 nm the spectrum contains five narrow bands, of
which four (582, 594, 616, 654, 704 nm) belong to the
transitions from the excited level 5D0 of Eu3+ cation on
7
the levels of the ground-state multiplet Fi (i = 0–4)
5
7
and one (540 nm) band corresponds to D1 → F1
transition. Initiation with the light of longer wavelength
(λexc = 370 nm) causes appearance of an additional
short-wave maximum with λ = 500 nm, due to the
7
5D2 → F3 transition. In both cases the most intense
transition is 5D0 → 7F2 with λ = 616 nm. The fluorescence
of the silicon oxide matrix is expressed as a low-
intensity broad band in the range from 390 to 550 nm.
Figure 2 shows the photoluminescence and the
photoluminescence excitation spectra of a solution of
the complex II in acetonitrile. A large dilution (to C =
2×10–6 M) was necessary to obtain a spectrum that fits
to the scale of the registrar with a minimum of the
monochromator slit (2.5 nm) that showed a high
luminosity of the complex. The relative quantum yield
of luminescence calculated by comparison with a
standard dye rhodamine 6G is 66%. Measurements
with dilute solutions indicate the absence of lumine-
scence of silicon component of the complex and the
correspondence between the electron absorption
spectrum and the excitation spectrum.
Compound I, which is a viscous liquid, readily
forms a transparent thick (100–200 μm) sol–gel film at
the deposition onto a substrate by pouring. The
dilution with ethanol makes it possible to adjust the
thickness of the coating. The curing time is 5 to 20 h
depending on the thickness of the layer. Thick films
suffer cracking at storage, while thin films (5–20 μm)
are stable.
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010

1760
SEMENOV et al.
I
1000
800
600
400
200
I
250
200
5D0→7F2
1
5D0→7F2
2
1
3
2
150
100
50
0
0
300
400
500
600
700
300
400
500
λ, nm
600
700
λ, nm
Fig. 1. Excitation (1, lreg = 615 nm) and emission (2, lexc
340 nm; 3, lexc = 370 nm) spectra of the complex I film.
=
Fig. 2. Excitation (1, lreg = 615 nm) and emission (2, lexc
=
340 nm) spectra of complex II in acetonitrile, C = 2×10–6 M,
The film thickness was 134 microns, slit 5 nm.
slit 2.5 nm.
EXPERIMENTAL
Europium(III) tris[2-(3'-triethoxysilylpropylamino-
carbonyl)-1,1,1-trifluoro-4-phenylbut-2-en-2-ol-4-
onate](1,10-phenanthroline) (II). To a solution of
1.21 g (0.006 mol) of benzoyltrifluoroacetone in 5 ml
of THF was added in a vacuum 0.61 g (0.002 mol) of
europium isopropoxide. The reaction mixture was heated
for 4 h at 80°C in a sealed evacuated ampule, and then
the volatile products were removed. 1.11 g (70%) of
europium tris(benzoyltrifluoroacetonate) was obtained
as a white powder. To a dispersion of 1.00 g
(0.001 mol) of europium tris(benzoyltrifluoro-
acetonate) in 5 ml of toluene was added 0.74 g
(0.003 mol) of 3-isocyanatopropyltriethoxysilane. The
mixture was heated at 110°C for 8 h in an evacuated
ampule. A small amount of precipitate was separated
in a centrifuge, the liquid was decanted, the volatile
substances were removed in a vacuum. 1.08 g (70%)
of compound I was obtained as a yellow-orange oily
liquid. IR spectrum (ν, cm–1): 3340 m (NH), 3063 v.w
(HC=C), 2975 v.s (CH), 2927 s (CH), 2890 s (CH),
2734 v.w (CH2N), 1716 s (C=O, amide I), 1692 m
(Eu–O–C=C–C=O), 1624 v.s (Eu–O–C=C–C=O),
1540 s (NH, amide II), 1445 m (CH), 1387 m (CH),
1292 v.s (CH, CF), 1188 s (CH-aryl, CF), 1140 v.s
(SiOEt), 1100 s (CH-aryl, CF ), 1076 v.s (SiOEt), 944
s (SiOEt), 792 s (SiOEt), 764 (CH-aryl), 704 s (CH-
aryl).
The IR spectra were taken from the compounds as
liquid film between KBr or CaF2 plates, or as
suspensions in mineral oil, and recorded on an FSM
1201 IR-Fourier spectrometer. Electron absorption
spectra were measured on a Perkin-Elmer Lambda 25
spectrophotometer, fluorescence and fluorescence
excitation spectra, on a Perkin-Elmer LS-55 spectro-
fluorimeter. The spectral width of the slit of excitation
and recording monochromators was 2.5 to 5.0 nm. The
film was set at an angle to the exciting light, and
fluorescence emission was collected from its surface.
In addition, before the monochromator of registering
unit a correcting built-in filter was placed blocking the
scattered and reflected exciting radiation. The spectra
obtained were corrected for spectral sensitivity of the
photomultiplier and the spectral transmittance curve of
1
the filter. The H NMR spectra of solutions in CDCl3
were recorded on a Bruker Avance DPX-200 instru-
ment (200 MHz) at 25ºC, internal reference Me4Si.
3-Isotcyanatopropyltriethoxysilane (Aldrich) was
distilled in a vacuum before use, rhodamine 6G (LC
5900) (Lambda Physik) was used without further
purification. Europium isopropylate was synthesized
from anhydrous europium chloride and sodium
isopropylate by the procedure in [6]. Quartz substrate
(3×12×40) for the formation of films was processed
for 10 h with a saturated solution of NaOH in
isopropyl alcohol, then 10 h with a mixture of
potassium bichromate with sulfuric acid, and then was
washed with water and dried at 150–170°C.
To a solution of 0.90 g (0.0006 mol) of compound I
in ethanol was added 0.16 g (0.0009 mol) of 1,10-
phenanthroline. A few minutes later a dense finely
dispersed precipitate separated, which was filtered off,
washed with ethanol, and dried in a vacuum. 0.90 g
RUSSIAN JOURNAL OF GENERAL CHEMISTRY Vol. 80 No. 9 2010

SYNTHESIS OF EUROPIUM(III) PHENANTHROLINE-β-DIKETONATE
(87%) of compound II was obtained as a white-pink
ACKNOWLEDGMENTS
1761
powder. IR spectrum (ν, cm–1): 3345 m (NH), 3060
v.w (HC=C), 2724 v.w (CH2N), 1722 m (C=O, amide
I), 1611 m ( Eu–O–C=C–C= O), 1577 v.s (Eu–O–
C=C–C=O), 1529 s (NH, amide II), 1320 m (CH),
1289 v.s (CH, CF), 1245 m (CH), 1184 s (CH-aryl,
CF), 1140 v.s (SiOEt), 1103 v.s (CH-aryl, CF), 1079 m
(SiOEt), 940 m (SiOEt), 798 s (SiOEt ), 768 s (CH-
aryl), 700 m (CH-aryl). Electron spectrum (λ, nm; ε,
l mol–1 cm–1): 222, 6.5×104, 268, 1.3×105, 322,
1.1×105; Found, %: C 50.83, H 5.11. C72H89Eu·
F9N5O18Si3. Calculated, %: C 50.20, H 5.22.
This work was supported by Russian Foundation
for Basic Research (projects nos. 08-03-00771 and 08-
03-90024 Bel), the Presidential Council for support of
scientific schools (project NSH 1396.2008.3), and the
Bureau of State Contract 02.513.11.0002 of Russia
Academy Sciences (Program “Fundamental problems
of physics and chemistry of nanostructures and
nanomaterials,” “Directional synthesis of substances
with desired properties and creation of functional
materials based on them”).
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