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Luminescent organo-polysiloxanes containing complexed lanthanide ions.

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Full Paper
Received: 1 March 2009
Revised: 29 June 2009
Accepted: 29 June 2009
Published online in Wiley Interscience 18 August 2009
(www.interscience.com) DOI 10.1002/aoc.1536
Luminescent organo-polysiloxanes containing
complexed lanthanide ions
Lei Liu, Haifeng Lu, Hua Wang, Yiling Bei and Shengyu Feng∗
In this study, a type of polysiloxane with the ester as the functional side group was prepared via a hydrosilylation reaction.
The functionalized polysiloxane was then allowed to complex with Tb3+ and Eu3+ ions. Fourier transform infrared, ultraviolet
absorption spectra and 1 H-NMR, 13 C-NMR and 29 Si-NMR spectra were used to confirm the modification. Differential scanning
calorimetry and thermal gravity analysis were used to study the polysiloxane’s thermal properties. The complexes’ luminescence
c 2009 John Wiley & Sons, Ltd.
spectra were recorded, and narrow-width green and red emissions were achieved. Copyright Keywords: hydrosilylation reaction; photoluminescence; polysiloxane; lanthanide ions
Introduction
Appl. Organometal. Chem. 2009 , 23, 429–433
Experimental Section
Chemicals and Procedures
Starting materials and solvents were purchased from China National Medicines Group and were distilled before utilization according to published procedures.[42] Europium and terbium nitrates
were obtained from the corresponding oxides in dilute nitric acid.
The typical procedure for the preparation of ester functionalized linear polysiloxanes is described in Scheme 1 according to the literature.[43,44] Methylmethacrylate (50 mmol) and
poly(methylhydrosiloxane) (PMHS) (1 mmol) were placed in a
flask with dry toluene (60 ml) and heated to 70 ◦ C under N2 , then
four drops of the catalyst platinum–divinyltetramethyldisiloxane
∗
Correspondence to: Shengyu Feng, School of Chemistry and Chemical
Engineering, Shandong University, Jinan 250100, People’s Republic of China.
E-mail: fsy@sdu.edu.cn
School of Chemistry and Chemical Engineering, Shandong University, Jinan
250100, People’s Republic of China
c 2009 John Wiley & Sons, Ltd.
Copyright 429
Luminescent materials have applications in many important devices such as tunable lasers, displays, and amplifiers for optical
communication.[1 – 3] Many studies have focused on the lanthanide
complexes because of their long-lived excited-state characteristic and their especially efficient strong narrow-width emission
band in the visible region.[4] However, the poor thermal stability and mechanical properties of lanthanide complexes limit
their uses as luminophors. The common solution is to trap lanthanide complexes in various hosts which increase the stability
of the complex.[4 – 6] Generally speaking, these host materials
are divided into three categories: inorganic,[7 – 9] organic[10 – 14]
and hybrid.[15 – 24] The preparation of organic/inorganic hybrid
composites is particularly preferred because of the possibility of
tailoring compounds by mixing organic and inorganic components into a single material at around room temperature. Most
of the luminescent hybrid materials’ hosts are composed of Si–O
bonds[15 – 24] Howerver, to the best of our knowledge, there are
only a few excellent works about metallasiloxanes of lanthanide
metals[25 – 29] and no reports of luminescent functionalized polyorganosiloxane coordinated with lanthanide ions.
Functionalized polysiloxane is a versatile material used in a
wide range of applications such as coatings, adhesives, impactresistance plastics, etc.[30 – 33] Polysiloxane has many specific
properties due to its hydrophobicity, lubricity, high flexibility
of main chains, high gas permeability, low variation of viscosity
with temperature, low glass transition temperature, physiological
inertness and excellent thermal stability.[34,35] Recent studies have
focused on investigating the system of siloxane and acrylic
monomers.[36,37] For example, silicone–acrylic graft copolymers
containing cationic groups can enhance the wash fastness of dyed
fabric without affecting the handling properties of the fabric.[37 – 39]
Combining functionalized polysiloxane and lanthanide ions
via coordination can therefore utilize the outstanding properties
of both agents. The main chain of polysiloxane offers excellent
chemical and physical performance. The organic side chain of
functionalized polysiloxane reinforces the energy absorbability
with the chromophoric group, enhancing the efficiency of energy
transfer to the lanthanide ions.[40] This mechanism is called the
antenna effect.[41]
In this paper, we describe the preparation and
characterization of ether functionalized linear polysiloxanes of the type Me3 SiO(MeRSiO)x (Me2 SiO)y SiMe3 selecting poly(methylhydridosiloxane), Me3 SiO(MeSi{H}O)x (Me2SiO)y
SiMe3 , to synthesize this type of functionalized polyorganosiloxane. Poly(methylhydridosiloxane) exhibits unique reactivity
among the commercially available siloxanes and can undergo
hydrosilylation reactions with unsaturated organic linkages, particularly 1-alkenes, to produce new Si-C linkages.[32] Methylmethacrylate may be incorporated as side-arm substituents on the polymer
backbone using this methodology. In this study, derived multifunctionalized organosilane was allowed to complex with lanthanide
ions to obtain luminescent materials.
Our interest in organofunctional polysiloxanes is centered on
their uses as luminescent materials. Consequently, our goal was to
develop a general procedure that could be used to synthesize
luminescent polysiloxane materials with different loadings of
various functional groups.
L. Liu et al.
in 10 ml THF with stirring, and a stoichiometric proportion
RE(NO3 )3 · 6H2 O [Eu(NO3 )3 · 6H2 O or Tb(NO3 )3 · 6H2 O] was added
to the solution. The mixture was agitated magnetically for 4 h to
achieve a single phase.
After the mixture was poured into 50 ml of methanol,
the precipitates were collected by filtration. The solids were
successively washed with methanol, water and acetone. The solids
were then dissolved in THF and precipitated in methanol. The
resulting complex was filtered, washed with acetone in a Soxhlet
extractor for 2 days and dried under vacuum at room temperature.
Measurements
Fourier transform infrared (FTIR) spectra were measured within
the 4000–400 cm−1 region on a Bruker TENSOR27 infrared
spectrophotometer with the KBr pellet technique. 1 H NMR,
13 C-NMR and 29 Si-NMR spectra were recorded in CDCl on a
3
Bruker Avance-300 spectrometer without interference. Ultraviolet
absorption (UV) spectra of these samples (in hexane solution) were
recorded using a Hitachi U-4100. Thermal gravimetric analysis
(TGA) and differential scanning calorimetry (DSC) were performed
with a simultaneous DSC-TGA Q600 under N2 . Luminescence
(excitation and emission) spectra of these solid complexes were
determined with a Perkin-Elmer LS-55 spectrophotometer whose
excitation and emission slits were 10 and 5 nm, respectively.
Results
Scheme 1. (i) Methylmethacrylate, toluene, N2, reflux, catalyst, 4 days,
70 ◦ C; (ii) RE(NO3 )3 · 6H2 O, THF, 4 h.
430
complex were added. The process of the reaction was monitored
by the detection of the frequency of Si–H (2100 cm−1 ) by FTIR. The
frequency of Si–H disappeared after 4 days, suggesting the completion of the reaction. Removal of the solvent in vacuo and subsequent reflux in MeOH yielded the siloxane product. Polymethylmethacrylate (PMMA) residue was removed by dissolving the
product in hexane, followed by filtration or centrifugation of the solution. PMMA is not soluble in hexane. After isolation, a transparent
oil was obtained and identified as functionalized polyorganosiloxane. 1 H-NMR, 13 C-NMR and 29 Si-NMR spectroscopic analyses were
performed to characterize the product, resulting in the following
profile: 1 H-NMR(CDCl3 ): δ3.65(3H,s,a), 2.60(1H,m,b), 1.20(3H,d,c),
0.74(2H,d,d), 0.05(81H,s,e). 13 C-NMR(CDCl3 ): δ178.0(C1 ), 50.4(C2 ),
34.7(C3 ), 22.9(C4 ), 19.6(C5 ), 0.6–1.3(C6 -C8 ). 29 Si-NMR(CDCl3 ):
δ6.4(Sic ), −22.0(Sia ), −37.5(Sib ) (see Scheme 1 and Fig. 1).
The luminescent functionalized polysiloxane was prepared as
follows: the functionalized polyorganosiloxane was dissolved
www.interscience.wiley.com/journal/aoc
The FTIR spectra for methylmethacrylate (a), poly(methylhydrosiloxane) (b), the functionalized polysiloxanes (c) and complexes of europium ions (d) are shown in Fig. 2. Compared with
the curve of poly(methylhydrosiloxane) (b), the ν(C O) vibration
mode was observed at 1743 cm−1 in the curve of the functionalized polysiloxane (c), which indicated the occurrence of the
hydrosilylation reaction. In the curve of methylmethacrylate (a), the
ν(C C) vibration was observed at 1635 cm−1 and the ν(C C–H)
vibration clearly appeared at 2990 cm−1 . They all disappeared
in the curve of functionalized polysiloxanes (c), which indicated
that the hydrosilylation reaction was complete and no residual
methylmethacrylate existed in the functionalized polysiloxanes.
From the curve of poly(methylhydrosiloxane) (b), the ν(Si–H)
vibration was observed at 2160 cm−1 .[45] The ν(Si–H) vibration
vanished in the curve of the functionalized polysiloxanes (c), indicating that all Si–H groups were engaged in the hydrosilylation
reaction.
The ν(C O) vibration mode was observed at 1771 cm−1 in
the curve of complexes of europium ions (d), but was observed
at 1743 cm−1 in the curve of functionalized polysiloxanes (c),
which clearly indicated the coordination between C O group
and lanthanide ions.[15] This coordination is known to cause an
energy transfer between the ligands and the lanthanide ions.[46]
Figure 3 shows the UV absorption spectra of methylmethacrylate (a), poly(methylhydrosiloxane) (b), the functionalized polysiloxanes (c) and complexes of europium ions (d).
Three bands were found, located at 206, 213 and 221 nm, from
the spectra of methymethacrylate (a), These corresponded to
the C C–C O group’s absorption. However, in the spectra of
poly(methylhydrosiloxane) (b), there was no absorption of the
Si–O–Si chain. Apparently, the blue-shift (a → c) of the major
π → π ∗ electronic transition was due to the hydrosilylation reaction, since the modification changed the C C–C O conjugation
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 429–433
Luminescent organo-polysiloxanes
Figure 1. 13 C-NMR and 29 Si-NMR spectra of the functionalized polysiloxanes.
Figure 3. Ultraviolet absorption spectra of methylmethacrylate (a),
poly(methylhydrosiloxane) (b), the functionalized polysiloxanes (c) and
complexes of europium ions (d).
Figure 2. Infrared
spectra
of
methylmethacrylate
(a),
poly
(methylhydrosiloxane) (b), the functionalized polysiloxanes (c) and
complexes of europium ions (d).
to C O conjugation.[45] There is no significant difference between
the spectra of the functionalized polysiloxanes (c) and complexes
of europium ions (d), indicating that the addition of lanthanide
ions did not affect conjugation in the polysiloxanes.
Discussion
Appl. Organometal. Chem. 2009, 23, 429–433
c 2009 John Wiley & Sons, Ltd.
Copyright www.interscience.wiley.com/journal/aoc
431
The thermal properties of the functionalized polysiloxanes are
shown in Fig. 4. Since functionalized polysiloxanes thermogravimetry carried out in an inert atmosphere show a single
weight loss step, we can assume that functionalized polysiloxanes
undergo a thermal degradation reaction which is described by a
one-step Arrhenius reaction term.[47] TGA results show that functionalized polysiloxane is thermally stable up to 200 ◦ C. When the
temperature is raised to 700 ◦ C, this material is totally decomposed
and no residual is observed. Polysiloxane is therefore expected to
improve the thermal stability properties of a luminescent material.
The excitation spectra of the complexes of terbium ions are
shown in Fig. 5 and the emission spectra of the luminescent
functionalized polysiloxane complexes are shown in Figs 6
(terbium ions) and 7 (europium ions).
The excitation spectrum (Fig. 5) was obtained by monitoring the
emission of Tb3+ ion at 545 nm and is dominated by a broad band
centered at 317 nm. This absorption band is a charge-transfer
transition in the Tb3+ –O2− bond: an electron jumps from oxygen
to terbium. The width of the absorption band is evidence of the
coordination of terbium. As a result, a strong green luminescence
was observed in their emission spectra (Fig. 6) when the materials
were excited at 317 nm. The emission bands of the materials
were related to the transition from the triplet state energy level
of Tb3+ to the different single state levels and were assigned to
L. Liu et al.
0
100
endo
Weight (%)
80
60
40
-2
20
0
0
100
200
300 400 500
temperature (°C)
600
700
432
Figure 4. Thermal gravimetric analysis (TGA) and differential scanning
calorimetry (DSC) of the functionalized polysiloxanes.
Figure 6. The emission spectra of the complexes of terbium ions.
Figure 5. The excitation spectra of the complexes of terbium ions.
Figure 7. The emission spectra of the complexes of europium ions.
the 5 D4 → 7 F6 (487 nm), 5 D4 → 7 F5 (545 nm) and 5 D4 → 7 F4
(581 nm) transitions, respectively.
A strong red luminescence was observed in the spectra of the
europium complex (Fig. 7). The emission bands of the materials
were related to the transition from the triplet state energy level of
Eu3+ to the different single state levels and were assigned to the
5 D → 7 F (590 nm), 5 D → 7 F (614 nm), 5 D → 7 F (652 nm)
0
1
0
2
0
3
and 5 D0 → 7 F4 (689 nm) transitions. The transitions of 5 D0 → 7 F0
could not be observed at 580 nm, indicating no inverse center
for Eu(III) ions in the complex. The asymmetry factor, which is the
ratio of the integrated intensity of the 5 D0 → 7 F2 transition to
the 5 D0 → 7 F1 transition, has been widely used as an indicator
of Eu(III) site symmetry.[48] The asymmetry factor of this complex
is 3.5, indicating that the Eu(III) ion in these complexes has lower
symmetric coordination environment.
In comparing the spectrum in Fig. 7 with the spectrum in
Fig. 6, the residual emissions of the polysiloxane in complexes
of europium ions (the broad band located at 400–480 nm) were
not monitored in the spectrum of complexes of terbium ions,
indicating that most of the energy absorbed by polysiloxane
was transferred to the terbium ion. This proves that the ligand
reinforced the energy absorbability and transfer red the energy to
the lanthanide ion with high efficiency. Both the luminescence
of the complex of terbium ions and that of europium ions
show narrow-width emissions, which suggests that this kind of
luminescent material could be utilized comprehensively in optical
applications.
www.interscience.wiley.com/journal/aoc
Conclusions
In summary, a type of functionalized polysiloxane with the ester
as the functional side chain was prepared via a hydrosilylation
reaction in this study. Green and red luminescence were observed
when the functionalized polysiloxane was allowed to complex with
Tb3+ and Eu3+ ions. It is anticipated that this type of functionalized
polysiloxane material with lanthanide ions as the luminous
center will attract interest for its potential utilization in optical
applications. As a result of this study, methodology was developed
that could be utilized to generate a general procedure for the
synthesis of luminescent polysiloxane materials with different
loadings of various functional groups. This type of molecular-based
c 2009 John Wiley & Sons, Ltd.
Copyright Appl. Organometal. Chem. 2009, 23, 429–433
Luminescent organo-polysiloxanes
functionalized polysiloxane material is a promising candidate for
tailoring desired properties to the host in many applications.
Acknowledgments
This work was supported by the National Natural Science
Foundation of China (nos 20574 043 and 20874 057) and the
Key Natural Science Foundation of Shandong Province of China
(no. Z2007B02).
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