A new way to construct luminescent functionalized silicon hybrid material derived from methyldichlorosilane

Article abstract of DOI:10.1016/j.jphotochem.2009.12.006

The functional precursor (PySi) was derived from the hydrosilylation reaction of methyldichlorosilane and 4-vinylpyridine, and then two series of novel luminescent hybrid materials (RE-PySi, where RE = Tb, Dy) with organic fragments covalently linked to inorganic parts were assembled by a sol-gel process, and characterized by the X-ray diffraction, scanning electron microscopy, and spectroscopy. It is found that the sol-gel treatment has an influence on the organization and microstructure of the hybrid materials, indicating that the hybrid material systems derived from different solvents exhibit different textures. The photoluminescent behavior of these chemically bonded hybrids was studied in detail. The observed green luminescence suggested that the intra-molecular energy-transfer process between the lanthanide ion and the pyridyl group takes place among these molecular-based hybrids.

Full text of DOI:10.1016/j.jphotochem.2009.12.006

Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
Contents lists available at ScienceDirect
Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
A new way to construct luminescent functionalized silicon hybrid material
derived from methyldichlorosilane
Haifeng Lu, Hua Wang, Shengyu Feng∗
School of Chemistry and Chemical Engineering, Shandong University, Jinan 250100, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
The functional precursor (PySi) was derived from the hydrosilylation reaction of methyldichlorosilane
and 4-vinylpyridine, and then two series of novel luminescent hybrid materials (RE-PySi, where RE = Tb,
Dy) with organic fragments covalently linked to inorganic parts were assembled by a sol–gel process, and
characterized by the X-ray diffraction, scanning electron microscopy, and spectroscopy. It is found that
the sol–gel treatment has an influence on the organization and microstructure of the hybrid materials,
indicating that the hybrid material systems derived from different solvents exhibit different textures.
The photoluminescent behavior of these chemically bonded hybrids was studied in detail. The observed
green luminescence suggested that the intra-molecular energy-transfer process between the lanthanide
ion and the pyridyl group takes place among these molecular-based hybrids.
Received 17 September 2009
Received in revised form
16 November 2009
Accepted 11 December 2009
Available online 23 December 2009
Keywords:
Methyldichlorosilane
Hydrosilylation reaction
Hybrid material
© 2009 Elsevier B.V. All rights reserved.
Lanthanide ion
Photoluminescence
1. Introduction
able physical properties [27,28]. Therefore, development of novel
and versatile synthetic methodologies to prepare functionalized
Luminescent materials have numerous applications, including
displays, tunable lasers, amplifiers for communication, and so on
[1]. Because of their colorimetric purity, lanthanide ions have been
used as basic constituents of luminescent materials, such as illu-
mination lamps, cathode ray tube displays, and optical imaging
of cells [2–10]. However, in the past, materials for practical uses
were limited to inorganic solids, whereas lanthanide complexes
were always excluded just because of their limited thermal sta-
bility. Nevertheless, new applications that have been investigated
in recent years make such metal complexes an attractive research
subject again. The common solution is to link lanthanide complexes
to inorganic parts via covalent bonds to generate hybrid materials
[11–20].
Because of their excellent stability and mechanical property,
silicone- and siloxane-based materials can be employed as ver-
satile hosts, including those based on organic functional groups
and transition metals [21,22]. By controlling the conditions of
synthesis, the type of templates and the sol–gel treatment, silicone-
based particles can be tailored with different shapes, such as
nanospheres [22,23], nanorods [24], core–shell particles [25],
hollow nanocapsules [26]. Silicone nanomaterials are attracting
increasing attention, due to their inherent robustness and tun-
silicone nanomaterials that have well-defined shapes and size dis-
tributions is highly desirable.
Among all those synthetic routes, there is an one-spot sol–gel
methodology in which the tetraalkoxy silane Si(OR)4 and the
silane coupling agents (RO)3Si(CH2)3X (where R = Me or Et,
X = complexing groups) were mix together to generate multi-
functional hybrid materials via simultaneous hydrolysis and
condensation reaction in an alcoholic solution in the presence of
an acid or a base catalyst [29]. The sol–gel process has been suc-
cessfully used in the past few years for the production of advanced
multi-functional materials such as monoliths, thin films, fibers, and
powders [30]. This method is particularly useful in the preparation
of nanosized organic/inorganic hybrid composites simply by mix-
ing organic and inorganic components in one pot at around room
temperature. However, the synergy of the combination is critical
in order to obtain composites exhibiting unusual electrochemical,
biological, mechanical, electrical, and optical properties [31,32].
Due to the limitation of the available siloxane coupling
agents, modifications of pre-prepared siloxane precursors with
the appropriate organic compounds to generate new functional
hybrid materials were reported mainly on five paths, that is,
amino-modification [13,14,16], carboxylic-modification [15,17],
sulfonic-modification [18], sulfide-modification [19] and hydroxyl-
modification [20]. Therefore, the design and synthesis of new
siloxane precursors will help synthesize versatile expand the mul-
tiplicity of the functional hybrid materials.
∗
Corresponding author. Tel.: +86 531 88364866.
E-mail address: fsy@sdu.edu.cn (S. Feng).
1010-6030/$ – see front matter © 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2009.12.006

H. Lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
49
of ethanol with stirring. Then 1 mL of CHCl3 was added into the
solution. The mixture was agitated magnetically in a covered ves-
sel for 1 h to achieve a single phase, followed by the addition of
5 mL of water under gentle stirring for 4 h to form an initial multi-
interphase emulsion, which was then dried over a vacuum line at
60 ◦C immediately. The aging of the mixture lead to the formation of
gels (pyridine-functionalized silicone hybrid materials) that were
collected for the physical properties studies. All of these hybrids
are opaque solid powders and named as PySi-CHCl3. When CHCl3
in the reaction above was substituted by DMF, the hybrid material
obtained was named as PySi-DMF.
Scheme 1. The preparation method of pyridine-functionalized siloxane precursor.
(i) CuCl2, N,N,Nꢀ,Nꢀ-tetramethylethylenediamine, reflux, 16 h. (ii) ethylorthofor-
mate, reflux.
In this paper, we will describe the preparation of luminescent
silicon hybrid materials based on tailoring the ternary lanthanide
complexes of pyridyl groups. Methyldichlorosilane was chosen as
the starting reagent to react first with 4-vinylpyridine by hydrosily-
lation [33–36], followed by the reaction with the ethylorthoformate
to prepare the pyridine-functionalized siloxane precursor. The so-
prepared precursor was then utilized to complex with Dy3+/Tb3+
ions via a sol-gel process to obtain the anticipant hybrid mate-
rials. They are generally performed at room temperature where
gel particles have to be stabilized by chemical cross-linking. As
an alternative, we developed a multi-interphase emulsion pro-
cess involving the drying gelatine on a vacuum line, followed by
the rapid condensation of silicates, leading to stable hybrid micro-
particles. The structure of the deposited silica particles appears to
depend on the process of sol–gel treatment.
2.4. Preparation of lanthanide ion centered luminescent
functionalized silicone hybrid materials
According to the above preparation of pyridine-functionalized
silicone hybrid materials, by using 0.2 mmol of RE(NO3)3·6H2O
(RE = Dy3+ and Tb3+
,
respectively), 0.6 mmol of pyridine-
functionalized siloxane precursor (PySi) and 1.2 mmol of
tetraethoxysilane (TEOS) as starting agent, the lanthanide ion cen-
tered luminescent functionalized silicone hybrid materials were
prepared. Hybrid material obtained in CHCl3 was named as RE-
PySi-CHCl3 while hybrid material obtained in DMF was named as
RE-PySi-DMF. Anal. Found for RE-PySi-CHCl3: [C24H33O24N6Si9Tb]
C, 25.0%; H, 4.1%; N, 7.6%; Calcd. for RE-PySi-CHCl3: C, 24.0%; H,
2.8%; N, 7.0%. Anal. Found for RE-PySi-DMF: [C24H33O24N6Si9Tb] C,
25.0%; H, 4.0%; N, 7.5%; Calcd. for RE-PySi-DMF: C, 24.0%; H, 2.8%;
N, 7.0%.
2. Experimental
2.5. Measurements
2.1. Starting materials
Fourier transform infrared (FTIR) spectra were measured within
the 4000–400 cm−1 region on a Bruker TENSOR27 infrared spec-
trophotometer with the KBr pellet technique. 1H NMR spectra and
13C NMR spectra were recorded in CDCl3 on a BRUKER AVANCE-400
spectrometer without internal reference. Luminescence (excitation
and emission) spectra of solid complexes were determined with a
PerkinElmer LS-55 spectrophotometer whose excitation and emis-
sion slits were 10 and 5 nm, respectively. The X-ray diffraction
(XRD) measurements were carried out on powdered samples via a
“BRUKER D8” diffractometer (40 mA 40 kV) using monochromated
Cu K␣1 radiation (ꢀ = 1.54 Å) over the 2ꢁ range of 1–10◦ and range of
10–70◦, respectively. Scanning electronic microscope (SEM) images
were obtained with JEOL JSM-7600F.
Starting materials and solvents were purchased from China
National Medicines Group and were distilled before utilization.
Europium and terbium nitrates were obtained from their corre-
sponding oxides in dilute nitric acid.
2.2. Synthesis of pyridine-functionalized siloxane precursor
The typical procedure for the preparation of pyridine-
functionalized siloxane precursor (PySi) was described in
Scheme
1 according to the published methods [34,35]. A
reaction vessel was charged with 0.2 mole of 4-vinylpyridine,
0.22 mole of methyldichlorosilane, 0.007 mole of N,N,Nꢀ,Nꢀ-
tetramethylethylenediamine and 0.02 mole of cuprous chloride.
The resulting mixture was refluxed temperature for 16 h during
which the temperature rose from 50 ◦C to 210 ◦C. Then 0.32 mole
of ethylorthoformate was added to the reaction mixture to
replace the silicon-bonded chlorine atoms with ethoxy groups.
The resulting mixture was then fractionally distilled to yield
pyridine-functionalized siloxane precursor (PySi), which was
confirmed by infrared analysis, 1H NMR, 13C NMR and mass
spectrum. The boiling point was measured to be 116–124 ◦C at
1 mm. The yield was approximately 20%. Mass spectra: 240 m/e.
1H NMR (CDCl3): ı 0.10(3H, s, –SiCH3), 0.93(2H, m, –SiCH2CH2–),
1.19(6H, t, –OCH2CH3, 3J = 7 Hz), 2.65(2H, m, –SiCH2CH2–), 3.74(4H,
q, –OCH2CH3, 3J = 7 Hz), 7.1(2H, d, pyridyl, 3J = 5.8 Hz), 8.44(2H,
q, pyridyl, 3J = 5.8 Hz). 13C NMR (CDCl3): ı −4.9 (–SiCH3), 14.6
(–SiCH2CH2–), 18(–OCH2CH3), 28(–SiCH2CH2–), 58(–OCH2CH3),
122(pyridyl), 153.5(pyridyl), 149(pyridyl).
3. Results and discussion
3.1. The characterization of the precursor and hybrids
The Fourier Transform Infrared (FTIR) spectra for 4-vinyl pyri-
dine (a), the precursor PySi (b), the Tb-PySi-CHCl3 hybrids (c) and
Tb-PySi-DMF hybrids (d) are shown in Fig. 1. In the spectrum (a),
the ␯(C C) vibration was observed at 1630 cm−1 and the ␯(C C–H)
vibration clearly appeared at 2990 cm−1 [37]. However, these peaks
all disappeared in the curve of the precursor PySi as shown in
spectrum (b), indicating that the hydrosilylation reaction has pro-
ceeded finished completely and no residual C C group existed in
the precursor PySi. 1H NMR, 13C NMR and mass spectra relative to
the precursors are in full agreement with the proposed structure
(The data were mentioned above and they could also be found in
supplementary material of this paper).
2.3. Preparation of pyridine-functionalized silicone hybrid
materials
Two adjacent sharp peaks at 2934 and 2886 cm−1 in spectrum
(b) are ␯as(CH2) and ␯s(CH2) of the long carbon chain in precur-
sors and they could also be observed in the curve of (c) and (d),
which proves their existence in the hybrids. The band centered
0.6 mmol of pyridine-functionalized siloxane precursor (PySi)
and 1.2 mmol of tetraethoxysilane (TEOS) were dissolved in 5 mL

50
H. Lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
in this paper, the frequency of nitrate group is one relatively strong
and sharp at 1658 cm−1, so the nitrate group was ionic in the mate-
rials.
3.2. The photoluminescence of hybrid materials
Fig. 2 is the excitation and emission spectra of the PySi-CHCl3.
An excitation band could be found at 320 nm which was attributed
to the pyridyl group in the hybrid materials, and a broad emission
band centered at 440 nm manifested that the pyridyl group could
convert UV light’s energy from 320 to 440 nm.
The emission spectra of Tb-PySi-CHCl3 (a), Dy-PySi-CHCl3 (b),
Tb-PySi-DMF (c) and Dy-PySi-DMF (d) are shown in Fig. 3. They
were obtained by excitating of 320 nm UV light. The emission bands
of the terbium materials (curves (a) and (c)) were responded to the
transition from the excited state energy level of Tb3+ to the different
single state levels and were assigned to the 5D4 → F6 (487 nm) and
7
5D4 → F5 (545 nm) transitions. The emission bands of the dyspro-
7
sium materials (curves (b) and (d)) were attributed to the transition
from the excited state energy level of Dy3+ to the different single
Fig. 1. Infrared spectra of 4-vinyl pyridine (a), the precursor PySi (b), the Tb-PySi-
CHCl3 hybrids (c) and Tb-PySi-DMF hybrids (d).
4
6
state levels and were assigned to the F9/2 → H15/2 (484 nm) and
6
4F9/2 → H13/2 (578 nm) transitions.
at 2982 cm−1 in curve of the precursors (b) is the ␯s(CH3) in Si-
O-CH2CH3 and Si-CH3 side chains. The ␯(Si-O-C) vibration peaks
emerged at 1100 and 1076 cm−1 in the curve of the precursor PySi
(b) turned into a board band at 1031–1110 cm−1 of the ␯(Si-O-Si)
vibration mode in the curve (c) and (d), indicating the completion
of hydrolysis and condensation reaction. The ␯(O-H) came from the
absorbed water in the hybrid material powders.
Narrow-width green luminescence was observed in the spectra
of terbium-containing samples. It should be noted that the green
luminescence is not due to the f–f emission of the lanthanide ions
alone, but a combination of the blue residual emission of the host
matrix in combination with the emission of the lanthanide ions. It is
well known that the human eye is sensitive to the monochromatic
spectral lights of wavelengths 700 nm (Red), 546.1 nm (Green) and
435.8 nm (Blue) according to the CIE 1931 RGB colorimetric sys-
tem. These terbium-containing samples (545 nm) have an intrinsic
green emission other than the blue background emission of the host
matrix. For dysprosium-containing samples, it is a combination of
the blue residual emission (440 nm) of host matrix with the yellow
emission (484 and 578 nm) of the Dy3+ ions.
In the previous research, the comparison between the infrared
spectrum of a coordinated pyridine and that of the free base has
been used to investigate the coordination process [38–41]. Two
changes observed by these investigators are: (1) an upward shift of
the four principal bands of pyridine between 1430 and 1600 cm−1
(which are due to aromatic C-C and C-N stretching vibrations)
and (2) a shift of the ring breathing frequencies and C-H in-plane
deformations, which appeared at the 985–1250 cm−1 region. The
frequencies of the four principal bands of the pyridyl group in
the reference [41], the precursor PySi, the Tb-PySi-CHCl3 hybrids
and the Tb-PySi-DMF hybrids in the region of 1400–1615 cm−1
are listed in Table 1. Because of the dominating (Si-O-Si) absorp-
tion bands at 1120–1000 cm−1, the two lower frequency bands for
these compounds between 985 and 1250 cm−1 were too weak to
be clearly distinguished; therefore, they are not listed in Table 1.
Comparison of the band shift of these four bands assignment
ring C-C and C-N stretching vibrations between the precursor and
hybrid materials indicate that the pyridyl group is coordinated to
the metal ions. It is well-known that the coordination of pyridyl
ring at endocyclic nitrogen lone pairs will increase the wavenumber
regarding to the coordination strength [38–40]. Thus it is concluded
that ring nitrogen atom is involved in the coordination in the com-
plexes studied.
Comparing the emission spectra in Fig. 2 with Fig. 3, a con-
clusion could be drawn that the pyridyl groups could absorb the
ultraviolet light around 320 nm, lead to emission at 440 nm and
transfer the energy to the lanthanide ions via the coordination, and
then, lanthanide ions produce luminescence. The antenna effect
took place in these systems [44]. However, there are residual emis-
sions of pyridyl groups in the four spectra in Fig. 3, especially in
curve (d), which means that the energy transmissions were not
completely proceeded. Compared (a) with (b), it is concluded that
the energy transmission between pyridyl group and terbium ion is
better than that between pyridyl group and dysprosium ion. Com-
pared (a) with (c), it can be concluded that the different synthesis
technology of hybrid material could result in the different lumines-
cent performance of the hybrid materials. The differences between
two synthetic technologies, one in CHCl3 and the other in DMF,
generated the different coordination environment and then influ-
ence the luminescent performance. It can be observed from this
study that the ethanol–CHCl3–water methodology is better than
ethanol–DMF–water one.
An ionic nitrate group gives rise to one relatively strong and very
sharp combination frequency, while coordinated nitrate groups
give two frequencies [42,43]. In these hybrid materials prepared
3.3. The micro-texture and reaction mechanism of hybrid
materials
Table 1
The frequencies of the four principal bands respond to the pyridyl group in Ref. [41],
the precursor PySi, the Tb-PySi-CHCl3 hybrids and the Tb-PySi-DMF hybrids in the
region from 1400 to 1615 cm−1
.
The scanning electron micrographs (SEM) of these hybrid
materials can give some characteristics of the texture. Fig. 4 demon-
strates that micro-particle materials were obtained. Graphs (a) and
(b) respond to Tb-PySi-CHCl3 hybrid materials, and graphs (c) and
(d) were obtained from Tb-PySi-DMF hybrid materials. As can be
seen in the Graph (a), the Tb-PySi-CHCl3 materials were assem-
bled into irregular nano-particals whose dimensions are about
50–100 nm similar to those of Tb-PySi-DMF materials as shown in
Assignment
Ref. [41]
4Apy
This study
Precursor
M-Ni-4Apy
ꢂ
CHCl3
DMF
ꢂ
ꢃring
ꢃring
ꢃring
ꢃring
1602
1556
1506
1440
1621
1562
1524
1466
19
6
18
26
1600
1560
1494
1414
1611
1559
1506
1421
1612 11
1559
1506 12
1422
1
7

H. Lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
51
Fig. 2. The excitation spectra and emission spectra of PySi-CHCl3.
Graph (c). However, the assembled textures revealed some differ-
ence between two kinds of materials. The Tb-PySi-CHCl3 materials
have some irregular micro-cavity but the Tb-PySi-DMF materials
are massive micro-particles with some edges and planes showing
the tendency of crystallization.
To analysis the assembled textures of these two materials,
the X-ray diffraction graphs were recorded at 1◦ ≤ n ≤ 10◦ and
10◦ ≤ n ≤ 70◦ intervals, as shown in Fig. 5. Curve (a) and (5b)
responded to Tb-PySi-CHCl3 and Tb-PySi-DMF, respectively. The
similarity in XRD graphs proves the similar atom distribution.
The diffractogram of hybrid materials with no sharp peak in
10◦ ≤ n ≤ 70◦ interval reveals that all these materials are mostly
amorphous. They are dominated by a broad peak centered at 23◦.
It is consistent with the SEM graph of hybrid materials (Fig. 4(a)
and (c)). The diffractogram of hybrid materials with no peak at
1◦ ≤ n ≤ 10◦ interval reveals that Tb-PySi-CHCl3 (a) and Tb-PySi-
DMF (b) have no microporous or mesoporous. However, there are
actually some micro-scaled cavities (Fig. 4(b)) and edges (Fig. 4(d))
in the SEM graph. It seems to be conflicted with the SEM graph of
hybrid materials. These are mostly due to the sol–gel treatment.
The formation of silica hybrid, in general, involves two major
steps: the formation of a wet gel, and drying of the wet gel to
Fig. 3. The emission spectra of Tb-PySi-CHCl3 (a), Dy-PySi-CHCl3 (b), Tb-PySi-DMF (c) and Dy-PySi-DMF (d).

52
H. Lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
Fig. 4. (a)–(d) The scanning electron micrographs (SEM) of hybrid materials.
produce many forms of materials [29–32]. Stable colloidal particles
are formed by condensation. The formed structure is controlled by
many parameters, such as temperature, the pH of the medium, the
nature of the solvent, the water content, the concentration and the
drying conditions, etc. [45]. In the sol process, the macro-emulsion
is decisive and responsible for the materials’ final texture. So the
particles of the hybrid materials are about 50–100 nm (Fig. 4(a)
and (c)). When the wet gel is dried on a vacuum line at 60 ◦C, the
solvent is evaporated and the gel gets cracked. Because the CDCl3,
water and ethanol are very volatile on a vacuum line at 60 ◦C, the
shrinkages of the gel lead to the formation of large pores, supply-
ing the pathways for gas escaping (Fig. 4(b)). As the boiling point
of DMF is higher than CDCl3, it leads to a different result. When the
gels shrinked step-by-step, the hybrid materials exhibited some
edges and planes (Fig. 4(d)) and are denser in structure than those
mentioned above.
4. Conclusions
In conclusion, we have successfully synthesized two series
of novel luminescent hybrid material systems (RE-PySi, where
RE = Tb, Dy) by a simple process where the functional precursor
was derived from hydrosilylation reaction of methyldichlorosilane
with 4-vinylpyridine. The material emits green luminescence by
near UV excitation, suggesting that the intra-molecular energy-
transfer process between the rare-earth ion and the pyridyl
group takes place within these molecular-based hybrids. Because
methyldichlorosilane is a convenient starting material for synthesis
of various siloxane precursors, the methodology used in this paper
could be a promising for tailoring silicone hybrids with desired
groups and properties in material in many fields of applications.
More specifically, we report a simple approach to achieving spa-
tially defined organization of colloidal as the main structural motif.
They are generally performed at room temperature where gelatine
particles have to be stabilized by drying on a vacuum line, leading
to stable hybrid micro-texture. The structure of the deposited sil-
ica particles appears to depend on the sol–gel treatment; therefore
the solvent involved in the system should play an important role in
defining the hybrid structures.
Fig. 5. The X-ray diffraction graphs of hybrid materials at 1◦ ≤ n ≤ 10◦ and
10◦ ≤ n ≤ 70◦ intervals. (a) Tb-PySi-CHCl3 and (b) Tb-PySi-DMF.

H. Lu et al. / Journal of Photochemistry and Photobiology A: Chemistry 210 (2010) 48–53
53
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