Lanthanide (Eu3+, Tb3+) centered mesoporous hybrids with 1,3-diphenyl-1,3-propanepione covalently linking SBA-15 (SBA-16) and poly(methylacrylic acid)

Article abstract of DOI:10.1002/asia.201000032

1,3-Diphenyl-1,3-propanepione (DBM)-functionalized SBA-15 and SBA-16 mesoporous hybrid materials (DBM-SBA-15 and DBM-SBA-16) are synthesized by co-condensation of modified 1,3-diphenyl-1,3-propanepione (DBM-Si) and tetraethoxysilane (TEOS) in the presence

Full text of DOI:10.1002/asia.201000032

FULL PAPERS
DOI: 10.1002/asia.201000032
Lanthanide (Eu3+, Tb3+) Centered Mesoporous Hybrids with 1,3-Diphenyl-
1,3-Propanepione Covalently Linking SBA-15 (SBA-16) and
Poly(methylacrylic acid)
Ya-Juan Li, Bing Yan,* and Ying Li[a]
Abstract:
1,3-Diphenyl-1,3-propane-
neously, and the final mesoporous
polymeric hybrid materials Ln(DBM-
SBA-15)3PMAA and Ln(DBM-SBA-
16)3PMAA (Ln=Eu, Tb) are obtained
by a sol-gel process. For comparison,
binary lanthanide SBA-15 and SBA-16
mesoporous hybrid materials (denoted
as Ln(DBM-SBA-15)3 and Ln(DBM-
SBA-16)3) are also synthesized. The lu-
minescence properties of these result-
ing materials are characterized in
detail, and the results reveal that terna-
ry lanthanide mesoporous polymeric
hybrid materials present stronger lumi-
nescence intensities, longer lifetimes,
and higher luminescence quantum effi-
ciencies than the binary lanthanide
mesoporous hybrid materials. This indi-
cates that the introduction of the or-
ganic polymer chain is a benefit for the
luminescence properties of the overall
hybrid system. In addition, the SBA-15
mesoporous hybrids show an overall in-
crease in luminescence lifetime and
quantum efficiency compared with
SBA-16 mesoporous hybrids, indicating
that SBA-15 is a better host material
for the lanthanide complex than meso-
porous silica SBA-16.
pione (DBM)-functionalized SBA-15
and SBA-16 mesoporous hybrid mate-
rials (DBM-SBA-15 and DBM-SBA-
16) are synthesized by co-condensation
of modified 1,3-diphenyl-1,3-propane-
pione (DBM-Si) and tetraethoxysilane
(TEOS) in the presence of Pluronic
P123 and Pluronic F127 as a template,
respectively. The as-synthesized meso-
porous hybrid material DBM-SBA-15
and DBM-SBA-16 are used as the first
precursor, and the second precursor
poly(methylacrylic acid) (PMAA) is
synthesized through the addition poly-
merization reaction of the monomer
methacrylic acid. These precursors then
coordinate to lanthanide ions simulta-
Keywords: lanthanides
cence mesoporous materials
polymers · silicates
· lumines-
·
·
Introduction
heterocyclic derivatives, which show strong absorption of ul-
traviolet light and then facilitate an effective intramolecular
energy-transfer process to the central lanthanide ions (an-
tenna effect).[2] As the absorption coefficients of organic li-
gands are many times larger than the molar absorption coef-
ficients of trivalent lanthanide ions, the lanthanide com-
plexes, especially those containing b-diketone ligands, exhib-
it the bright and narrow emission characteristic of metal
ions, and offer several advantages and potential applications
for the design of efficient light-conversion molecular devi-
ces.[3] However, they have so far been excluded from practi-
cal applications as tunable solid-state laser or phosphor de-
vices largely owing to their poor stabilities under high tem-
perature or moisture conditions and low mechanical
strength. Recently, the luminescence properties of Re com-
plexes supported on a solid matrix were studied extensively
since their photophysical properties could be modified by in-
teraction with the host structure.[4,5] Lanthanide complexes
incorporated into inorganic or organic/inorganic matrix by a
low-temperature soft-chemistry process, including the sol-gel
Lanthanide complexes have long been the subject of exten-
sive research owing to their excellent photophysical proper-
ties, which have a variety of potential technological applica-
tions, such as in fluoro-immunoassays, spectroscopic struc-
tural probes in biologically important systems, lasers, optical
amplification, light-conversion molecular devices (LCMDs),
and organic-light emitting diodes (OLEDs).[1] Considerable
studies have been focused on the design and assembly of
lanthanide complexes with organic ligands such as aromatic
carboxylic acids, b-diketones, cryptands, calixarenes, and
[a] Dr. Y.-J. Li, Prof. B. Yan, Dr. Y. Li
Department of Chemistry
Tong Ji University
Shanghai 200092 (China)
Fax : (+86)21-65982287
E-mail: byan@tongji.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.201000032.
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Chem. Asian J. 2010, 5, 1642 – 1651

method and hydrothermal-synthesis process, can effectively
overcome the disadvantages discussed above. The hybrid
materials enable both inorganic and organic dopants to be
incorporated with relatively high thermal stability.[6] Howev-
er, the conventional doping method in a sol-gel procedure
seems unable to solve the problems of clustering of emitting
centers, inhomogeneous dispersion of the two phases, and
leaching of the photoactive molecules, because only weak
interactions (such as hydrogen bonding, van der Waals
forces, and weak static effects) exist between the organic
and inorganic components.[7] As a consequence, another ap-
pealing method has emerged that concerns the covalently
bonded hybrids.The as-derived molecular-based materials
exhibit improved chemical stability and have a monophasic
appearance that is similar in nature to that of the complicat-
ed molecular polymeric Si–O network.[8] Our research group
is concentrating on the design of the rare-earth hybrid mate-
rials with inorganic networks.[9] Compared with chemically
bonded rare-earth hybrids with Si–O polymeric networks,
fewer reports on molecular hybrid materials fabricated with
rare-earth/organic polymers have been published,[10] which is
possibly because suitable polymers or monomers are hard to
select. Recently, more professional investigations have been
altered to focus on the lanthanide hybrid materials concern-
ing inorganic and organic polymerization reactions or imbe-
dding certain polymers that contain long-carbon chains by
covalent bonds. It has been proved that the hybrid materials
with the inorganic networks and organic polymers with high
molecular weight have many excellent properties such as
strong luminescence and high stability.
lanthanide complexes, which may be on account of the diffi-
culties of the availability of zeolite crystals with a narrow
particle-size distribution and well-defined morphology.
Among mesoporous materials, SBA-15 has certainly become
one of the most attractive hosts owing to its high hydrother-
mal stability and the presence of hexagonally ordered large
mesopores (p6mm symmetry group) interconnected by com-
plementary micropores. Recently, our group has reported
the synthesis and luminescence properties of SBA-15 meso-
porous materials covalently bonded with lanthanide com-
plexes by the modified b-diketonates.[13] The results revealed
that the obtained materials possessed good luminescence
properties and photo- or thermal stabilities. Further to SBA-
15, which is a channel-like ordered mesoporous material,
mesoporous silica SBA-16 has also been considered as a
good support on account of its 3D structure consisting of or-
dered interconnected spherical mesopores, which has a
cubic cage-like structure with multidirectional and large-
pore systems that allow good accessibility for both function-
alization and adsorption.[14] However, to the best of our
knowledge, the luminescence of a lanthanide complex sup-
ported on the functionalized SBA-16 has been rarely report-
ed to date.[15] This is probably on account of the difficulties
encountered in the synthesis and especially in the character-
ization of this material.
With the above considerations, we herein present the sys-
tematic and comparative study of the mesoporous materials
covalently bonded with lanthanide complexes containing or-
ganic polymeric chains designated as Ln(DBM-SBA-
15)3PMAA and Ln(DBM-SBA-16)3PMAA (Ln=Eu, Tb;
DBM=1,3-diphenyl-1,3-propanepione; DBM-SBA-15 and
DBM-SBA-16 denote DBM-functionalized SBA-15 mesopo-
rous material and DBM-functionalized SBA-16 material, re-
spectively). For further comparison, SBA-15 and SBA-16 co-
valently bonded with the binary Ln3+ complex with DBM
ligand were also synthesized and denoted as Ln(DBM-SBA-
15)3 and Ln(DBM-SBA-16)3 (Ln=Eu, Tb), respectively.
Full characterization and detailed studies of the lumines-
cence properties of all synthesized materials were investigat-
ed and compared.
Zeolites and mesoporous silica materials are attractive
hosts for the preparation and investigation of inorganic–or-
ganic hybrid materials, presenting a successive ordering
from the molecular up to the macroscopic scale.[11] Recently,
Li and co-workers reported organolanthanide complexes as-
sembled into zeolite L crystals, and the resulting materials
exhibited excellent photoluminescence properties and good
thermal stability.[11,12] Zeolite L can be synthesized in a size
range starting from about 30 nm up to several thousand nm,
whereas the other host mesoporous materials possess an ad-
justable pore size from 2 to 50 nm: currently, most work
mainly concentrates on mesoporous materials as host for
Results and Discussion
DBM-Functionalized Parent Materials (DBM-SBA-15 and
DBM-SBA-16)
Abstract in Chinese:
The presence of the organic ligand DBM covalently bonded
to the mesoporous SBA-15 and SBA-16 were characterized
by FTIR and UV absorption spectroscopy. Figure 1 depicts
the FTIR spectra of DBM (A), DBM-Si (B), DBM-func-
tionalized mesoporous material DBM-SBA-15 (C), and
DBM-SBA-16 (D). Comparing the spectra of DBM (A) and
ꢀ1
ꢀ
ꢀ
DBM-Si (B), the vibration of CH2 at 3059 cm (A) was
replaced by a strong broad band located at 2963 cmꢀ1 (B),
which originated from the three methylene groups of 3-(trie-
thoxysilyl)-propyl isocyanate (TEPIC). Furthermore, the
ꢀ1
ꢀ
spectra of DBM-Si is dominated by n (C Si, 1164 cm ) and
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B Yan et al.
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Figure 1. IR spectra of the free ligand DBM (A), the precursor DBM-Si
(B), DBM-functionalized mesoporous material DBM-SBA-15 (C), and
DBM-SBA-16 (D).
Figure 2. UV absorption spectra of A) DBM, B) DBM-Si, C) DBM-SBA-
15, and D) DBM-SBA-16.
ꢀ1
ꢀ
n (Si O, 1083 cm ) absorption bands, which is characteristic
tems were formed owing to the grafting reaction and the
DBM groups were located on the surface of the mesoporous
material SBA-15 and SBA-16.[13a]
of trialkoxylsilyl functions. This evidence supports the emer-
gence of DBM-Si. The band centered at 3335 cmꢀ1 corre-
ꢀ
ꢀ
sponds to the stretching vibration of grafted NH groups.
Alternatively, the bending vibration (dNH, 1530 cmꢀ1) is fur-
ther evidence of the formation of amide groups. New peaks
at 1700 and 1630 cmꢀ1 in (B) were attributed to the absorp-
tions of the C=O of TEPIC, confirming that 3-(triethoxysil-
yl)-propyl isocyanate was successfully grafted onto the
ligand DBM. In parts (C) and (D) of Figure 1, the formation
Lanthanide (Eu3+, Tb3+) Complexes Covalently Bonded to
DBM-Functionalized Mesoporous Silica and Polymers
Scheme 1 presents the scheme of the synthesis process and
the predicted structure of the mesoporous hybrid materials
Ln(DBM-SBA-16)3PMAA. The modified ligands were cova-
ꢀ ꢀ
ꢀ
of Si O Si is evidenced by the characteristic bands located
lently bonded to the SBA-16 host like an arm through Si
at 1079, 1080 cmꢀ1 (asymmetric vibrations nas, Si O), 798,
O Si by the hydrolysis–condensation reaction of the organic
ꢀ
ꢀ
800 cmꢀ1 (stretching vibrations ns, Si O), and 465, 469 cm
(in-plane bending vibrations d, Si O Si). Bands at 1648,
functionality of DBM-Si. It is very difficult to prove the
exact structure of this kind of non-crystalline hybrid materi-
als and it is hardly possible to solve the coordination behav-
ior of lanthanide ions. However, the main composition and
co-ordination effect according to the lanthanide coordina-
tion chemistry principle and the configuration of the organic
functional groups can be predicted. The rare earth positive
ions are Lewis hard acids so it is easy to coordinate with the
hard base containing the oxygen and nitrogen atoms. Addi-
tionally, most of the lanthanide complexes hold the polar co-
valent bonds as the lanthanide ions always bond through the
6s, 6p, and 5d electronic orbits, whose electron count is nine.
Therefore, it is most stable for the lanthanide complex to
exist with the coordination number of eight or nine. Further-
more, in our experiment we synthesize the material by
adding the appropriate and accurate proportion of reagent
into the system [Ln3+:DBM-SBA-15 (DBM-SBA-
16):PMAA=1:3:2] to obtain the fixed model of lanthanide
complex. Furthermore, in view of the spatial steric hin-
drance effect, we predicted the optimum coordination struc-
ture for the hybrid materials.
ꢀ1
ꢀ
ꢀ ꢀ
ꢀ1
ꢀ
ꢀ
1652, and 1565 cm , originating from the CONH group
of DBM-Si, can be observed in both DBM-functionalized
mesoporous materials DBM-SBA-15 (C) and DBM-SBA-16
(D). This indicates that DBM-Si was successfully incorporat-
ed into both materials and preserved well after both hydrol-
ysis/condensation reaction and surfactant extraction proce-
dure, which is consistent with the fact that the DBM group
in the framework remains intact after both hydrolysis–con-
densation reaction and the surfactant extraction procedure.
Figure 2 shows the ultraviolet absorption spectra of DBM
(A), DBM-Si (B), DBM-SBA-15 (C), and DBM-SBA-16
(D). Comparing the absorption spectrum of DBM-Si (B)
with that of DBM (A), we can see that an obvious blue shift
of the major p–p* electronic transitions A!B (from 254 to
251 nm, from 342 to 334 nm) occurred, which indicates that
the electron distribution of the modified DBM-Si has
changed compared with the free ligand DBM owing to the
introduction of carbonyl group and that the 3-(triethoxysil-
yl)-propyl isocyanate group has been successfully grafted to
the ligand DBM. Compared with DBM-Si (B), the peak
shape of DBM-SBA-15 (C) and DBM-SBA-16 (D) has basi-
cally not changed, but obvious red shifts (251!261, 334!
338 nm for C, and 251!268, 334!339 nm for D) are ob-
served, suggesting that more extensive p–p* conjugating sys-
The FTIR spectra of all obtained mesoporous polymeric
hybrids were measured and are shown in Figure S1 in the
ꢀ
ꢀ
Supporting Information. The appearance of the CONH
group at about 1557 and 1646 cmꢀ1 for all samples demon-
strates that the functionalized organic group DBM-Si re-
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Mesoporous Hybrids of Lanthanide
Figure 3. SAXRD patterns of DBM-SBA-15, Eu(DBM-SBA-15)3PMAA,
and Tb(DBM-SBA-15)3PMAA.
Scheme 1. A) Scheme showing the synthesis of the polymer precursor
PMAA. B) The synthesis process of the mesoporous polymeric hybrids
Ln(DBM-SBA-16)3PMAA. BPO=benzoyl peroxide; TEOS=tetraethox-
ysilane.
Figure 4. SAXRD patterns of DBM-SBA-16, Eu(DBM-SBA-16)3PMAA,
and Tb(DBM-SBA-16)3PMAA.
mains intact after the hydrolysis/condensation reaction and
complex-grafting process.[1c]
The powder XRD patterns of DBM-SBA-15 and DBM-
SBA-16 before and after the introduction of Ln3+ complex
(Ln=Eu, Tb) are shown in Figures 3 and 4, respectively. It
can be observed that Ln(DBM-SBA-15)3PMAA clearly
show the order of the hexagonal array of the SBA-15 struc-
ture and exhibit a strong (100) reflection at a low angle and
two small peaks (110, 200) at a higher angle. Although
Ln(DBM-SBA-16)3PMAA exhibits an intense (110) reflec-
tion and two small peaks owing to the (200) and (211) re-
flections, it can be indexed to the Im3m space group with
cubic symmetry, which is typical of three-dimensional cubic
(Im3m) SBA-16. Compared with those of DBM-SBA-15
and DBM-SBA-16 materials (see Table 1), the d100 spacing
values of Ln(DBM-SBA-15)3PMAA and Ln(DBM-SBA-
16)3PMAA are nearly unchanged, respectively, indicating
that their framework ordering has been preserved well after
the introduction of the lanthanide complex. It is also worth
noting that the Ln(DBM-SBA-15)3PMAA and Ln(DBM-
Table 1. Structural parameters.
[b]
[c]
[c]
Sample
d[a]
a0
SBET
[m2 gꢀ1
V[c]
[cm3 gꢀ1
DBJH
[nm]
t[d]
[nm]
[nm] [nm]
G
]
R
]
DBM-SBA-15
Eu(DBM-SBA-
15)3PMAA
9.81 11.33 613
9.63 11.12 569
0.98
0.59
6.41
4.16
4.92
6.96
Tb(DBM-SBA-
15)3PMAA
9.63 11.12 565
0.59
4.17
6.95
DBM-SBA-16
Eu(DBM-SBA-
16)3PMAA
10.14 14.34 534
10.38 14.68 433
0.44
0.29
3.27
2.63
9.15
10.08
Tb(DBM-SBA-
16)3PMAA
10.38 14.68 469
0.32
2.67
10.04
[a] The interplanar spacing for the most intense reflection peaks, (100)
for the samples with P6mm symmetry group and (110) for the samples
with Im3m symmetry group; [b] The unit cell parameter of SBA-15 was
calculated by the formula a0 =2 d100
[c] SBET =the BET surface area, V=the total pore volume, DBJH =the
p p
/ 3, and for SBA-16 by 2 d110;
average pore diameter; [d] The wall thickness, calculated by a0ꢀDBJH for
p
SBA-15 materials, and for SBA-16 materials by 3a0/2ꢀDBJH
.
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SBA-16)3PMAA materials exhibit decreased diffraction in-
tensity as compared to the parent DBM-SBA-15 and DBM-
SBA-16 materials, respectively. This is probably owing to
the presence of guest moieties on the mesoporous frame-
work of SBA-15 and SBA-16, respectively, resulting in a de-
crease in the ordering degree but not the collapse of the
pore structure of mesoporous materials.
The characterization of N2 adsorption–desorption for
Ln(DBM-SBA-15)3PMAA and Ln(DBM-SBA-16)3PMAA
materials further provides proof of the preservation of the
mesoporous structure after the introduction of the Ln3+ ion.
As shown in Figure 5, Ln(DBM-SBA-15)3PMAA exhibits
typical type IV isotherms with distinct H1-type hysteresis
Figure 6. N2 adsorption–desorption isotherms of DBM-SBA-16,
Eu(DBM-SBA-16)3PMAA, and Tb(DBM-SBA-16)3PMAA.
16)3PMAA are further confirmed by TEM micrographs (see
Figure 7). They present the regular hexagonal array of uni-
form channels and the well-ordered spherical cage structure,
respectively, indicating that the mesostructure of the result-
ing materials can substantially be conserved after the com-
plexation process, which concurs with the obtained XRD
patterns. The distances between the centers of the meso-
pores for Eu(DBM-SBA-15)3PMAA and Eu(DBM-SBA-
16)3PMAA are similar and estimated to be about 10 nm,
which are in good agreement with the values determined
from the corresponding XRD analysis (see Table 1).
Figure 5. N2 adsorption–desorption isotherms of DBM-SBA-15,
Eu(DBM-SBA-15)3PMAA, and Tb(DBM-SBA-15)3PMAA.
loops at high relative pressures according to the IUPAC
classification,[16] characteristic of mesoporous materials with
highly uniform size distributions. Ln(DBM-SBA-16)3PMAA
shows the adsorption isotherms of the SBA-16 silica materi-
als, which are of the type IV adsorption isotherm according
to the IUPAC classification with H2-type hysteresis loops,
which are typical for materials with ink-bottle pores with in-
terconnectivity in a 3D pore system as a result of cavita-
tion[17] (see Figure 6). The pore diameters (d), specific sur-
face areas (SBET), and pore volume (V) of these samples
were calculated by the BJH method, and the results are
summarized in Table 1. From d, SBET, and V of DBM-SBA-
15 and DBM-SBA-16, it can be seen that the data for both
materials are less than those typically reported for pure
SBA-15 and SBA-16 mesoporous silica materials, respective-
ly.47,48 This is probably as a result of the presence of organic
ligand DBM on the pore surface and the co-surfactant effect
of DBM-Si, which interacts with surfactant and reduces the
diameter of the micelles. Furthermore, it can be observed
that the values of SBET, D, and V of the materials decreases
after introducing the Ln3+ ion and organic ligand PMAA,
which further confirmed incorporation of the Ln3+ com-
plexes in the channels of SBA-15 and cavities of SBA-16.
The hexagonal mesostructures of Eu(DBM-SBA-
15)3PMAA and 3D mesostructured Eu(DBM-SBA-
Figure 7. HRTEM images of Eu(DBM-SBA-15)3PMAA (A) and
Eu(DBM-SBA-16)3PMAA (B).
Scanning Electron Micrographs
The scanning electron micrographs for the mesoporous poly-
meric hybrids demonstrate that homogeneous, molecular-
based materials were obtained because of strong covalent
bonds between the organic b-diketone ligand and the inor-
ganic matrices, and the coordinate bonds between organic
ligand b-diketone or polymer ligand and lanthanide ions,
which belong to a complicated huge molecular system in
nature. Compared with the hybrid materials with doped lan-
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Mesoporous Hybrids of Lanthanide
thanide complexes, which generally experience the phase-
separation phenomena, herein we show that the inorganic
and organic phases can exhibit their distinct properties to-
gether in the hybrid materials we obtained that contain co-
valent bonds.[18] Figure 8A and C show the regular gibbous
Figure 9. TGA (c) and DrTGA (b) curves of Tb(DBM-SBA-
16)3PMAA.
nide complex was enhanced as it was covalently introduced
into the mesoporous matrix.
Photoluminescence Properties
Figure 8. SEM images of the mesoporous polymeric hybrid materials
The fluorescence excitation and emission spectra of the re-
sulting europium and terbium mesoporous hybrids are
shown in Figures 10 and 11, respectively. The excitation
spectra were obtained by monitoring the emission of Eu3+
(Figure 10) or Tb3+ (Figure 11) ions at 613 or 545 nm and
Eu(DBM-SBA-15)3PMAA
Eu(DBM-SBA-16)3PMAA (C), and Tb(DBM-SBA-16)3PMAA (D).
(A),
Tb(DBM-SBA-15)3PMAA
(B),
particles on the surface, although the size of the particles is
different, the former with the size of 3 mm and 10 mm for the
latter. It is presumed that the time for sol-gel procedure of
Eu(DBM-SBA-15)3PMAA is longer than that of Eu(DBM-
SBA-16)3PMAA so that the longer process time avails the
particle to grow in the three-dimensional directions. The mi-
crostructures of the material containing the Tb3+ ion display
uniform stripes on the surface as can be seen in Figure 8B
ꢀ
and D owing to the main influence derived from the Si O
networks as there is a trend to form the network-like micro-
structure in the sol-gel process.
Thermogravimetric Analysis
The thermal stability of all obtained mesoporous hybrids
was demonstrated by TGA measurement. Figure 9 shows
the thermogravimetric weight-loss curve (TGA) and deriva-
tive weight-loss (DrTGA) curve of mesoporous polymeric
hybrid Eu(DBM-SBA-16)3PMAA as an example. From the
DrTGA curve, we can see that there are three main weight-
loss peaks in the hybrid Eu(DBM-SBA-16)3PMAA. The
first weight-loss peak (approximately 5%) at around 1008C
is owing to physically absorbed water. This is followed by a
weight-loss peak (approximately 12%) at 3008C, which may
be ascribed to the decomposition of incompletely removed
surfactant.[19] The third weight-loss peak (approximately
14%) at 5578C can be attributed to the decomposition of
the organic lanthanide complex. In addition, the weight-loss
peak of the lanthanide hybrid material containing b-dike-
tone and organic ligand PMAA was reported to be at about
4068C,[3c] suggesting that the thermal stability of the lantha-
Figure 10. Luminescence excitation and emission spectra of the mesopo-
rous hybrid materials: A) Eu(DBM-SBA-15)3, B) Eu(DBM-SBA-
15)3PMAA , C) Eu(DBM-SBA-16)3, and D) Eu(DBM-SBA-16)3PMAA.
are dominated by a series of broad bands centered at about
331–356 or 328–332 nm near the ultraviolet region, respec-
tively, which are attributed to the characteristic absorption
of the lanthanide complexes arising from the efficient transi-
tion based on the conjugated C=O double bonds of 1,3-di-
phenyl-1,3-propanepione (DBM). As a result, Figure 10 pro-
vides the typical luminescence lines of the Eu3+ ion at about
5
7
577, 589, and 613 nm, corresponding to D0! FJ transitions
(J=0, 1, and 2, respectively), and Figure 11 provides the
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B Yan et al.
FULL PAPERS
are much higher than that of binary complex Eu(DBM-
SBA-15)3 and Eu(DBM-SBA-16)3, respectively. There are
two reasonable explanations that may contribute to the im-
proved luminescence: one is that the oxygen atoms in car-
boxyl groups located in the polymer chains of PMAA coor-
dinate to Ln3+ ions, which replace the coordinated water
molecules that exist in complexes of aromatic carboxylic
acid ligands, and the energy loss and clustering of the emit-
ting centers caused by the vibration of the hydroxyl groups
of coordinated water molecules is avoided. The other reason
is that the more effective energy transfer took place from
PMAA to the chelated Eu3+ ions and through this efficient
method, leaching of the photoactive molecules can be avoid-
ed. Furthermore, a higher concentration of metal ions can
be obtained and clustering of the emitting centers can be
prevented because the hybrids belong to the molecular
level. At the same time, it is also worth noting that com-
pared with the SBA-16 mesoporous hybrids Eu(DBM-SBA-
Figure 11. Luminescence excitation and emission spectra of the mesopo-
rous hybrid materials: A) Tb(DBM-SBA-15)3, B) Tb(DBM-SBA-
15)3PMAA C) Tb(DBM-SBA-16)3, and D) Tb(DBM-SBA-16)3PMAA.
typical luminescence lines of a
Table 2. Photoluminescence data of europium hybrid mesoporous materials Eu(DBM-SBA-15)3, Eu(DBM-
SBA-15)3PMAA, Eu(DBM-SBA-16)3, and Eu(DBM-SBA-16)3PMAA.
Tb3+ ion at around 487, 542,
581, and 617 nm, which are as-
Hybrids
Eu(DBM-SBA-
15)3
Eu(DBM-SBA-
15)3PMAA
Eu(DBM-SBA-
16)3
Eu(DBM-SBA-
15)3PMAA
5
7
signed to the D4! FJ (J=6, 5,
4, and 3, respectively). Among
these emission peaks, the prom-
inent red luminescence (5D4!
7F5) and green emissions (5D0!
7F2) were observed in their
emission spectra which indicat-
ed that the effective energy
transfer took place between the
modified organic ligand (DBM-
Si) and the chelated lanthanide
ions. The mesoporous hybrid
materials show relatively strong
emission owing to the chemical-
ly covalently bonded molecular
ꢀ
n00[a] [cmꢀ1
n01[a] [cmꢀ1
n02[a] [cmꢀ1
]
]
]
17391
17123
16420
89.5
17331
16978
16287
172
17361
17036
16313
72.8
17301
16949
16287
165
[b]
I01
[b]
I02
218
459
142
384
I02/I01
t
2.09
2.67
1.95
2.33
0.369
2710
208
2502
8.3
[c] [ms]
0.265
3774
210
3564
5.9
0.448
2232
234
1998
10.5
0.206
4854
202
4652
4.2
texpꢀ1 [sꢀ1
]
Ar [sꢀ1
]
Anr [sꢀ1
h [%]
]
7
7
[a] The energies of the 5D0! FJ transitions (u0J); [b] The integrated intensity of the 5D0! FJ emission curves.
5
7
[c] The luminescence decay times for D0! F2 transitions.
Si O network structure between the complex and the meso-
porous silica. As seen from Figure 10, among the transitions
16)3 and Eu(DBM-SBA-16)3PMAA, the relative emission
intensities and luminescence lifetimes of SBA-15 mesopo-
rous hybrids Eu(DBM-SBA-15)3 and Eu(DBM-SBA-
15)3PMAA exhibit obvious enhancements, which may be at-
tributed to the fact that nonradiative (knr) transition proba-
bilities are higher in SBA-16 mesoporous hybrids Eu(DBM-
SBA-16)3 and Eu(DBM-SBA-16)3PMAA, despite the simi-
lar first coordination shells of the lanthanide ion to those of
SBA-15 mesoporous hybrids Eu(DBM-SBA-15)3 and
Eu(DBM-SBA-15)3PMAA, respectively. The fluorescence
intensity and lifetimes of Tb3+ complexes shows the same
rule. The detailed fluorescence data of Tb3+ complexes have
been listed in Table 3.
of the materials containing Eu3+, the 5D0! F2 at about
7
613 nm show the strongest emission. It is well-known that
5
7
the D0! F2 transition is a typical electric dipole transition
and strongly varies with the local symmetry of Eu3+, where-
7
as the 5D0! F1 transition corresponds to a parity-allowed
magnetic dipole transition, which is independent of the host
material. Therefore, the emission spectra indicate that the
Eu3+ site is situated in an environment without inversion
symmetry.[20]
5
7
In addition, the D0! F1 transition can be used as a refer-
ence to compare luminescence intensities of different Eu3+
-
based materials owing to its magnetic dipole nature. The rel-
To further investigate the luminescence efficiency of these
covalent hybrids, we measured the decay curves of the re-
sulting europium and terbium mesoporous hybrid materials.
The luminescence decay profiles relative to the eight materi-
als could be fitted with single exponentials from which the
room temperature fluorescence lifetimes were calculated to
7
ative luminescence intensities of the5D0! F1 transition (I01)
5
7
7
and the D0! F2/5D0! F1 intensity ratios (red/orange ratio)
for all materials are listed in Table 2. By comparison, it can
be observed that the I01 value of the ternary complexes
Eu(DBM-SBA-15)3PMAA and Eu(DBM-SBA-16)3PMAA
1648
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1642 – 1651

Mesoporous Hybrids of Lanthanide
Table 3. Photoluminescence data of terbium hybrid mesoporous materials Tb(DBM-SBA-15)3, Tb(DBM-
SBA-15)3PMAA, Tb(DBM-SBA-16)3, and Tb(DBM-SBA-16)3PMAA.
The branching ratio for the
7
5D0! F5,6 transitions can be ne-
Hybrids
Emission bands [nm]
Relative intensities[a]
Lifetime [ms][b]
glected as they are not detected
experimentally and the influ-
ence of which can be ignored in
Tb(DBM-SBA-15)3
Tb(DBM-SBA-15)3PMAA
Tb(DBM-SBA-16)3
488, 542, 581, 617
487, 542, 581, 617
487, 543, 580, 617
488, 542, 581, 617
180, 400, 56.6, 24.6
332, 748, 86.6, 36.6
115, 300, 48.2, 21.8
237, 612, 75.5, 32.5
0.425
0.553
0.398
0.479
5
the depopulation of the D0 ex-
Tb(DBM-SBA-16)3PMAA
5
7
cited state. As D0! F1 belongs
[a] Relative intensities (arbitrary units) were obtained by the calculation of the integral area of the same emis-
to the isolated magnetic dipole
7
sion bands; [b] For the5D4! F5 transition of Tb3+
.
transition, it is practically inde-
pendent of the chemical envi-
ronments around the Eu3+ ion,
confirm that all the Ln3+ ions occupy the same average co-
ordination environment. The resulting lifetimes of the Eu3+
and Tb3+ hybrids are given in Tables 2 and 3, respectively.
It was found that the rare-earth/inorganic/organic ternary
polymeric hybrids Ln(DBM-SBA-15)3PMAA and Ln(DBM-
SBA-16)3PMAA present longer luminescence lifetimes than
the corresponding rare-earth/inorganic binary hybrids
Ln(DBM-SBA-15)3 and Ln(DBM-SBA-16)3, which suggest-
ed that the introduction of organic polymeric chains can en-
hance the luminescence stability of the overall hybrid
system. In addition, the DBM-SBA-15 mesoporous hybrids
exhibit a longer lifetime than that of DBM-SBA-16 mesopo-
rous hybrids, indicating that the nonradiative transition
probability in DBM-SBA-16 mesoporous hybrids is higher
than that in DBM-SBA-15 mesoporous hybrids. Further-
more, we selectively determined the emission quantum effi-
and thus can be considered as an internal reference for the
whole spectrum. The experimental coefficients of spontane-
ous emission, A0J can be calculated according to Equa-
tion (5).[23]
A0J ¼ A01ðI0J=I01Þðn01=n0JÞ
ð5Þ
In Equation (5), A0J is the experimental coefficients of
spontaneous emission and A01 is the Einstein coefficient of
5
7
spontaneous emission between the D0 and F1 energy levels.
In vacuum, A01 has a value of 14.65 sꢀ1, when an average
index of refraction n equal to 1.506 was considered, the
value of A01 can be determined to be approximately 50 sꢀ1
(A01 =n3 A01(vac)). I01 and I0J are the integrated intensities of
5
7
5
7
the D0! F1 and D0! FJ transitions (J=0–4) with n01 and
n0J (n0J =1/lJ) energy centers, respectively. n0J refers to the
energy barrier and can be determined from the emission
5
ciencies (h) of the D0 europium ion excited state for Eu3+
bands of Eu3+ꢁs D0! FJ emission transitions. The emission
5
7
hybrids on the basis of the emission spectra and lifetimes of
5
7
5
intensity, I, taken as integrated intensity S of the D0! F0ꢀ4
the D0 emitting level. Assuming that only non-radiative and
emission curves, can be defined as shown in Equation (6).
radiative processes are essentially involved in the depopula-
tion of the 5D0 state, radiative and nonradiative processes in-
fluence the experimental luminescence lifetime as can be
seen in Equation (1).
Iiꢀj ¼ ꢀhwiꢀjAiꢀjNi ꢁ Siꢀj
ð6Þ
In Equation (6), i and j are the initial (5D0) and final
levels (7F0ꢀ4), respectively, wiꢀj is the transition energy, Aiꢀj
is the Einstein coefficient of spontaneous emission, and Ni is
texp ¼ ðArþAnrÞꢀ1
ð1Þ
5
In Equation (1), Ar and Anr are radiative and nonradiative
transition rates, respectively. The quantum efficiency of the
luminescence step, h, can be defined as how well the radia-
tive processes compete with nonradiative processes as seen
in Equation (2).[21]
the population of the D0 emitting level.
On the basis of the above discussion, it can be seen the
value h mainly depends on the values of two quanta: one is
lifetime and the other is I02/I01. As can be clearly seen from
Table 2, the quantum efficiency of the ternary mesoporous
polymeric hybrid kinds Eu(DBM-SBA-15)3PMAA (h=
10.5%) and Eu(DBM-SBA-16)3PMAA (h=8.31%) are
much higher than the binary mesoporous hybrid Eu(DBM-
SBA-15)3 (h=5.9%) and Eu(DBM-SBA-16)3 (h=4.2%),
which can be explained as follows: each dispersed molecule
is a luminescent unit so that the transparency, the dimension
and concentration of dispersed lanthanide composite mole-
cules and the interfacial interaction between the rare-earth
organic complex and the polymer matrix are primary factors
that influence the final luminescence properties of the mate-
rials. Compared with rare-earth hybrid materials synthesized
through simple inorganic polymeric procedures, the larger
interfacial region and the stronger interaction between the
rare-earth complex and the polymer matrix in the obtained
rare-earth/inorganic/organic polymeric hybrids might accel-
h ¼ Ar=ðArþAnrÞ
ð2Þ
So, quantum efficiency can be calculated from the radia-
tive transition rate constant and experimental luminescence
lifetime from Equation (3).[22]
h ¼ Artexp
ð3Þ
Ar can also be obtained by summing over the radiative
5
7
rates A0J for each D0! FJ (J=0–4) transitions of Eu3+, as
in Equation (4).
Ar ¼ SA0J ¼ A00þA01þA02þA03þA04
ð4Þ
Chem. Asian J. 2010, 5, 1642 – 1651
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
1649

B Yan et al.
FULL PAPERS
ated from the desorption branches of the nitrogen isotherms by using the
Barrett-Joyner-Halenda (BJH) model. The fluorescence excitation and
emission spectra were obtained on a Perkin–Elmer LS-55 spectropho-
tometer. Luminescence lifetime measurements were carried out on an
Edinburgh FLS920 phosphorimeter by using a 450 W xenon lamp as exci-
tation source. Scanning electron microscopy (SEM) was performed using
the Philips XL30. Transmission electron microscopy (TEM) experiments
were conducted on a JEOL2011 microscope operated at 200 kV or on a
JEM-4000EX microscope operated at 400 kV. Thermogravimetric analy-
sis (TGA) was performed on a Netzsch STA 409 at a heating rate of
158Cminꢀ1 under nitrogen atmosphere.
erate energy transfer between them and enhance the lumi-
nescence efficiency of the hybrids. In addition, compared
with the SBA-16 mesoporous hybrids Eu(DBM-SBA-16)3
and Eu(DBM-SBA-16)3PMAA, the quantum efficiencies of
SBA-15 mesoporous hybrids Eu(DBM-SBA-15)3 and
Eu(DBM-SBA-15)3PMAA are higher, which may be as-
cribed to the following two aspects. One is that higher Anrad
parameter values occurred in SBA-16 mesoporous hybrids
than in SBA-15 mesoporous hybrids; the other aspect is that
the small pore diameters of SBA-16 mesoporous hybrids
Eu(DBM-SBA-16)3 and Eu(DBM-SBA-16)3PMAA have an
important effect on the results of the reflection and refrac-
tion of the Eu3+ ion luminescent center in the channel,
which leads to the less-efficient intramolecular energy-trans-
fer process (from ligand to Eu3+ ion).
Syntheses
Polymer precursor (PMAA): Methacrylic acid (1 mmol, 0.087 g) was dis-
solved in a small quantity of the solution THF (6 mL) with the initiator
benzoyl peroxide (BPO; 0.01 g) to initiate the addition polymerization
under argon atmosphere purging. The reaction temperature was main-
tained at 508C for about 4 h. The coating liquid was concentrated at
room temperature to remove the solvent THF by using a rotary vacuum
evaporator, and the viscous liquid was obtained and identified as
[C4H6O2]n (see Figure 1A). It was dissolved in DMF for the reaction with
lanthanide ions.
Conclusions
In summary, we conducted a systematic and comparative
study of the luminescent mesoporous polymeric hybrid ma-
terials Ln(DBM-SBA-15)3PMAA and Ln(DBM-SBA-
16)3PMAA (Ln=Eu, Tb). They were prepared by linking
ternary lanthanide (Eu3+, Tb3+) complexes to ordered mes-
oporous SBA-15 and SBA-16 through the functionalized
DBM-Si ligand. Additionally, we prepared binary lanthanide
complexes Ln(DBM-SBA-15)3 and Ln(DBM-SBA-16)3 for
comparison. The structure and properties of all hybrid mate-
rials were characterized in detail. The results demonstrate
that ternary rare-earth mesoporous polymeric hybrid mate-
rials present stronger luminescence intensities, longer life-
times, and higher luminescence quantum efficiencies than
the binary rare-earth mesoporous hybrid materials, which
are attributed to the introduction of organic ligand PMAA.
Furthermore, the SBA-15 mesoporous hybrids materials
show an overall increase in luminescence intensity and life-
time compared with SBA-16 mesoporous hybrids, suggesting
that the mesoporous material SBA-15 is a better candidate
host for supporting the lanthanide complex than the meso-
porous material SBA-16. However, the effect of the micro-
environment between the organic complex and two kinds of
silica matrix on the luminescence properties still needs fur-
ther fundamental investigations.
DBM-functionalized SBA-15 mesoporous material (DBM-SBA-15): The
modified precursor DBM-Si was synthesized according to the procedure
reported in the literature: 1,3-diphenyl-1,3-propanepione (DBM; 1 mmol,
0.2243 g) was dissolved in 20 mL of dehydrated THF and then NaH
(2 mmol, 0.048 g) was added into the solution with stirring. Two hours
later, 3-(triethoxysilyl)-propyl-isocyanate (TEPIC; 2.2 mmol, 0.5442 g)
was added dropwise into the refluxing solution. Then the mixture was
heated at 658C in a covered flask for approximately 12 h under a nitro-
gen atmosphere. A yellow oil (the precursor DBM-Si) was furnished after
isolation and purification. The mesoporous material DBM-SBA-15 was
synthesized from acidic mixture with the following molar composition:
0.0172 P123:0.96 TEOS:0.04 DBM-Si:6 HCl:208.33 H2O. P123 (1.0 g;
TEOS=tetraethoxysilane) was firstly dissolved in the deionized water
(7.5 g) and 2m HCl solution (30 g) at 358C under vigorous stirring. A
mixture of TEOS and DBM-Si (DBM=1,3-diphenyl-1,3-propanepione)
was added into the above solution, which was further stirred at 358C for
24 h and transferred into a Teflon bottle sealed in an autoclave. The auto-
clave was then heated at 1008C for 24 h. The solid product was recovered
by filtration, washed thoroughly with deionized water, and air dried at
room temperature. Removal of copolymer surfactant P123 was conducted
by Soxhlet extraction with ethanol for 48 h. The material was dried in a
vacuum and showed a light-yellow color.
DBM-functionalized SBA-16 mesoporous material (DBM-SBA-16): The
synthesis procedure of DBM-SBA-16 was similar to that of DBM-SBA-
15 except that the copolymer surfactant P123 was replaced by F127, and
the molar composition was 0.0040 F127:0.96 TEOS:0.04 DBM-Si:4
HCl:130 H2O.
SBA-15 mesoporous material and polymer covalently bonded with terna-
ry Ln3+ complexes (denoted as Ln(DBM-SBA-15)3PMAA. Ln=Eu, Tb):
The precursors DBM-SBA-15 and PMAA were dissolved in N,N-dimeth-
yl formamide (DMF) solvent, and an appropriate amount of LnACHTUNGTRENNUNG(NO3)3
ethanol solution was added into the solution while stirring (the molar
ratio of Ln3+/DBM-SBA-15/PMAA=1:3:1). The mixture was stirred at
room temperature for 12 h, followed by filtration and extensive washing
with EtOH. The resulting material Ln(DBM-SBA-15)3PMAA was dried
at 608C under vacuum overnight.
Experimental Section
General
LnACHTUNGTRENNUNG(NO3)3 (Ln=Eu, Tb) were obtained by dissolving their respective
oxides (Eu2O3 and Tb4O7) in concentrated nitric acid (HNO3). Other
chemicals were purchased and used as received. FTIR spectra were mea-
sured within the 4000–400 cmꢀ1 region on an infrared spectrophotometer
with the KBr pellet technique. The ultraviolet absorption spectra were
taken with an Agilent 8453 spectrophotometer. X-ray powder diffraction
patterns were recorded on a Rigaku D/max-rB diffractometer equipped
with a Cu anode in a 2q range from 0.68 to 68. Nitrogen adsorption/de-
sorption isotherms were measured at liquid-nitrogen temperature by
using a Nova 1000 analyzer. Surface areas were calculated by the Bruna-
uer-Emmett-Teller (BET) method and pore-size distributions were evalu-
SBA-16 mesoporous material and polymer covalently bonded with terna-
ry Ln3+ complexes (denoted as Ln(DBM-SBA-16)3PMAA. Ln=Eu, Tb):
The synthesis procedure of Ln(DBM-SBA-16)3PMAA was similar to that
of Ln(DBM-SBA-15)3PMAA except that DBM-SBA-15 was replaced by
DBM-SBA-16. The predicted structure of Ln(DBM-SBA-16)3PMAA is
shown in Scheme 1B.
SBA-15 mesoporous material covalently bonded with the binary Ln3+
complexes (denoted as Ln(DBM-SBA-15)3, Ln=Eu, Tb): The synthesis
procedure for Ln(DBM-SBA-15)3 was similar to that of Ln(DBM-SBA-
1650
www.chemasianj.org
ꢀ 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2010, 5, 1642 – 1651

Mesoporous Hybrids of Lanthanide
15)3PMAA except that the mixed DMF solution of DBM-SBA-15 and
PMAA was replaced by DBM-SBA-15.
Q. M. Wang, D. J. Ma, Inorg. Chem. 2009, 48, 36–44; e) J. L. Liu, B.
Yan, J. Phys. Chem. C 2008, 112, 14168–14178.
SBA-16 mesoporous material covalently bonded with the binary Ln3+
complexes (denoted as Ln(DBM-SBA-16)3, Ln=Eu, Tb): The synthesis
procedure for Ln(DBM-SBA-16)3 was similar to that of Ln(DBM-SBA-
16)3PMAA except that the mixed DMF solution of DBM-SBA-16 and
PMAA was replaced by DBM-SBA-16.
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Received: January 13, 2010
Published online: May 12, 2010
Chem. Asian J. 2010, 5, 1642 – 1651
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