Lanthanide/zinc centered photoactive hybrids with functional sulfonamide linkage: Coordination bonding assembly, characterization and photophysical properties

Article abstract of DOI:10.1016/j.poly.2009.07.037

In this paper, two novel kinds of organic-inorganic monomer, SUA-APEMS and SUA-APS, have been achieved by modifying 5-sulfosalicylic acid (SUA) with 3-aminopropyl-methyl-diethoxylsilane (APEMS) and 3-aminopropyl trimethoxysilane (APS). These two organic-i

Full text of DOI:10.1016/j.poly.2009.07.037

Polyhedron 29 (2010) 226–231
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Lanthanide/zinc centered photoactive hybrids with functional sulfonamide linkage:
Coordination bonding assembly, characterization and photophysical properties
Kai Qian, Bing Yan *
Department of Chemistry, Tongji University, Shanghai 200092, China
a r t i c l e i n f o
a b s t r a c t
Article history:
Available online 24 July 2009
In this paper, two novel kinds of organic–inorganic monomer, SUA-APEMS and SUA-APS, have been
achieved by modifying 5-sulfosalicylic acid (SUA) with 3-aminopropyl-methyl-diethoxylsilane (APEMS)
and 3-aminopropyl trimethoxysilane (APS). These two organic–inorganic monomers were used as
multi-functional bridged components, which can coordinate to metal ions (Tb3 /Eu /Zn ) with carbonyl
groups, strongly absorb ultraviolet and effectively transfer energy to metal ions through their triplet
excited state, as well as involve in the sol–gel process with inorganic host precursor tetraethoxysilane
+
3+
2+
Keywords:
Organic/inorganic hybrid material
Coordination bonding assembly
Sulfonamide linkage
(TEOS), resulting two series of molecular hybrid materials (named as SUA-APEMS/APS-RE) with double
Photophysical property
chemical bond (RE(Zn)–O coordination bond and Si–O covalent bond). The effective intra-molecular
energy transfer process gives rise to the characteristic emission of metal ions and the chemical bond
make the hybrid materials owning better properties.
Ó 2009 Elsevier Ltd. All rights reserved.
1
. Introduction
very low, and the photoactive molecules can be easily leached, so
it is hard to obtain transparent and uniform material. Poor
Luminescent materials can be applied in many fields such as
tunable laser, display and amplifier for optical communication
1]. Much research work has been focused on the lanthanide com-
plexes for their unique luminescence properties such as broad
spectral range (from ultraviolet to infrared region), particular
strong narrow-width emission in the visible region and wide range
of lifetimes [2,3]. The design of efficient rare-earth complexes de-
pends on the selection of diverse classes of ligands: b-diketones
mechanical property of them also restricts their practical applica-
tion. So the present work is focused on the class II hybrid system
of lanthanide complex luminescent centers bonded with a siloxane
matrix through Si–O linkages. Franville et al. have concentrated on
the modification of pyridine-dicarboxylic acid or their derivatives,
[
3
+
which results in strong Eu ions emissions due to efficient ligand-
to-metal energy transfer [20]. Zhang and coworkers are focused on
modification of heterocyclic ligands (1,10-phenanthroline and di-
pyridine) to construct molecular-based hybrids [21,22]. Our re-
search team has also carried out extensive work concerning the
covalently bonded hybrid materials. In previous research, three
methods have been used to synthesis lanthanide based optical ac-
tive covalent hybrid materials: amino-modification [23,24], car-
boxyl-modification [25,26], and hydroxyl-modification [27,28]. As
for the preparation of such hybrid materials, the sol–gel technique
has proven to be a convenient synthetic method because of its un-
ique characteristics, namely low temperature and versatility
[29,30].
From these researches, it can be concluded that the critical step
to prepare these hybrids is to synthesize a novel monomer as a
covalent bridge between the organic and inorganic part. So the
development of novel linkages for tethering organic compounds
to inorganic solid supports is an area of active investigation. In this
paper, a novel sulfonamide linkage is selected to link these two
parts, which is based on the modification of 5-sulfosalicylic acid
with APEMS and APS for sulfosalicylic acid possesses the reactive
functionalized sulfo group and excellent photoactive unit. A new
[4–6], heterocyclic ligands [7,8], cryptands [9], calixarenes
[10,11], macrocyclic ligands [12], terphenyl ligands [13], proteins
[14], etc. But the poor thermal stability and mechanical property
of lanthanide complexes limit their usage. Recently, in order to
overcome the above-mentioned shortcomings, entrapping of
rare-earth complexes with b-diketones, aromatic carboxylic acids,
and heterocyclic ligands in inorganic host has been studied exten-
sively because these organic–inorganic hybrid materials combine
the advantages of both organic and inorganic parts. According to
the interaction among the different phases in hybrid systems,
these hybrid materials can be mainly divided into two major clas-
ses: class I is physically mixed with weak interactions (hydrogen
bond, Van der Waals force or weak static effect); class II belongs
to chemically bonded hybrids with strong covalent bonds [15–
1
9]. However, these hybrid materials of class I have many disad-
vantages: the dopant concentration of lanthanide complexes is
*
Corresponding author. Tel.: +86 21 65984663; fax: +86 21 65982287.
E-mail address: byan@tongji.edu.cn (B. Yan).
0
277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.07.037

K. Qian, B. Yan / Polyhedron 29 (2010) 226–231
227
series of luminescent hybrid molecular-based materials is achieved
2.4. Physical measurement
via a special sol–gel process. Compared with other existing materi-
als, these kinds of hybrid materials not only provide a new modi-
fication and assembly path, but also develop a new type of rare-
earth organic/inorganic hybrids.
All measurements were completed under room temperature.
Fourier transform infrared (FTIR) spectra were measured within
the 4000–400 cm region on an (Nicolet Nexus 912 AO446) infra-
red spectrophotometer with the KBr pellet technique. Ultraviolet
ꢁ1
absorption spectra were recorded with an Agilent 8453 spectro-
1
photometer. H NMR spectra were recorded in CDCl
3
on a BRUKER
2
. Experimental
AVANCE-500 spectrometer with tetramethylsilane (TMS) as inter
reference. Scanning electronic microscope (SEM) images were ob-
tained with a Philips XL-30. Luminescence (excitation and emis-
sion) spectra of these solid complexes were determined with a
RF-5301 spectrophotometer. Luminescence lifetime measure-
ments were carried out on an Edinburgh FLS920 phosphorimeter
2.1. Starting materials
All the chemicals were purchased from Aldrich and used as re-
ceived. All normal organic solvents were distilled before utilization
according to the literature procedures. Europium and terbium ni-
trates were obtained from the corresponding oxides in concen-
trated nitric acid.
29
using a 450 w xenon lamp as excitation source. Solid-state Si ma-
gic-angle spinning (MAS) NMR spectrum was recorded at
7
9.46 MHz using a Bruker Avance 400 spectrometer. The chemical
shifts were quoted in ppm from tetramethylsilane.
2.2. Modification of 5-sulfosalicylic acid to molecular bridge
3
. Result and discussion
About 1.016 g (4 mmol) 5-sulfosalicylic acid was dissolved in
The FTIR spectra for SUCl (a), SUA-APS (b), and Tb-SUA-APS (c)
are shown in Fig. 2, respectively. From the curve of the sulfonic
2
0 mL chloroform and then 0.476 g (4 mmol) SOCl
the solution drop by drop. The mixed solution was refluxing at
20 °C for 4 h. After isolation, the residue was recrystallized by tol-
2
was added to
chloride, the
m
as(O@S@O) and
m
s
(O@S@O) absorption bands located
m(C@O) vibration was observed at
1
ꢁ1
at 1387 and 1251 cm . The
uene. Then a yellow solid powder was obtained, named as 5-sulfo-
salicylic sulfonic chloride (5-SUCl). The sulfonic chloride can
directly reacted with APS, APEMS in pyridine. The sulfonamide
linkage was formed as follows: 4 mmol sulfonic chloride was dis-
solved in pyridine by stirring and 4 mmol APS or APEMS was then
added to the solution by drops. The whole mixture was refluxing at
ꢁ1
1
667 cm due to the existence of –COOH. In the curve of the sul-
fonamide precursor (b), the grafting reaction is evidenced by the
ꢁ1
sharp band located at 1243 cm corresponding to
m
(S–N) [31]. Be-
(Si–O–C)
ꢁ1
sides the
m
(–CH
2
–) located at 2932, 2860 cm and the
located at 1099 cm further proved the occurrence of reaction.
m
ꢁ1
8
0 °C for 4 h. After isolation, a red oil sulfonamide precursor was
obtained.
4
C
3
2.3. Assembly of molecular hybrid materials
The sol–gel derived hybrid material was prepared as follows
(
Fig. 1): sulfonamide precursor (1 mmol) was dissolved in the mix-
ture of 5 mL DMF and 2 mL ethanol by stirring. Then 0.3 mmol RE
NO O (RE = Eu, Tb) and 2.0 mmol tetraethoxysilane (TEOS)
B
2
(
3
3
) ꢀ6H
2
was added into the solution. One drop of diluted hydrochloric acid
was put into it to promote hydrolysis. The mixture was stirred
magnetically in a covered Teflon beaker for an hour. After that it
was aged at 60 °C for the gelation in 3 days. The gels were collected
and ground as powder materials for the optic studies. The hybrid
material containing Zn2 was also prepared in the same way, but
1
A
+
0
the mole ratio of Zn(Ac)
2
ꢀ2H
2
O: sulfonamide precursor was 1:2.
5
00
1000
1500
2000
2500
3000
-1
3500
4000
Comparing with the materials containing different metal ions
those hybrid materials without metal ions were also synthesized
for the photophysical studies.
Wavenumbers / cm
Fig. 2. The selected FTIR spectra for SUCl (A), SUA-APS (B), and Tb-SUA-APS (C).
Fig. 1. Scheme of the syntheses process of SUA-APS and SUA-APEMS.

2
28
K. Qian, B. Yan / Polyhedron 29 (2010) 226–231
3
Q
2
2
1
1
0
0
.5
.0
.5
.0
.5
.0
SUA-APEMS
SUA-APS
4
Q
SUA
3
2
T
T
250
300
350
400
0
-50
-100
Chemical shifts / ppm
-150
-200
Wavelength / nm
Fig. 4. The selected 29Si MAS NMR spectroscopy of Tb-SUA-APEMS.
Fig. 3. The ultraviolet absorption spectra of SUA, SUA-APS, SUA-APEMS.
0.8
ꢁ1
The
m(O@S@O) was still obviously observed at 1377 cm in the
curve of the final material (c), while most other vibrations are
ꢁ1
weak. The wide absorption band at around 1100 cm indicated
the dominating of (O–Si–O). There exists wide band absorption
m
0.6
ꢁ
1
at about 3400 cm in all these three curves. And the absorption
band in curve c is more obvious because there were more crystal
water in the final material due to the sol–gel process (the
Tb-SUA-APS
0.4
Tb-SUA-APEMS
ꢁ
1
m
the
(H–O–H): 3600–3000 cm ). In spectra of precursor (SUA-APS),
ꢁ1
m
(C@O) vibration is located at 1683 cm . But in the spectra
(C@O) vibration is
6
20 nm
of the hybrid material (SUA-APS-Tb), the
m
ꢁ1
489 nm
5
shifted to the 1629 cm . The shift is a proof of the coordination
0.2
of the carboxylic group to the metallic ion with the oxygen atoms
5
83 nm
[
32,33].
Fig. 3 shows the ultraviolet absorption spectra of SUA, SUA-APS
46 nm
0
.0
2
and SUA-APEMS. The ultraviolet absorption spectra of SUA-APS,
00
400
600
800
SUA-APEMS are similar compared with the SUA. The absorption
*
Wavelength / nm
bands corresponding to the
p
?
p
electronic transition are located
at 249, 256, 257 nm, respectively. It is observed that a red shift of
Fig. 5. The selected UV–Vis DRS of Tb-SUA-APEMS and Tb-SUA-APS.
*
the major
p ? p electronic transitions occurs and it is estimated
that during the modification of 5-sulfosalicylic acid, the different
ligand may hinder the conjugating effect of double bonds (S@O)
and decrease the energy difference levels among electron transi-
tions. Besides the absorption peaks of the SUA-APS and SUA-
important role in the energy absorption process. The rare-earth
ions can be excited by intra-molecular energy transfer after the en-
ergy absorption process. So the broad absorption band in the short
wavelength region leads to the good luminescence properties of
these hybrid materials which can be proved by the emission spec-
trum of the materials. The negative absorption peaks correspond-
ing to the characteristic emission peak at 489, 546, 583, 620 nm
of the active terbium ions can be observed in the spectrum. These
APEMS are wider than that of SUA. It is also obvious that there exist
*
absorption peaks corresponding to the
p
?
p
electronic transition
in the spectra of SUA-APS and SUA-APEMS, located at around
3
10 nm while this peak can not be seen in the spectrum of SUA.
All these differences in the ultraviolet absorption spectra between
SUA and the modified 5-sulfosalicylic acid indicate the success of
the modification [31,33].
5
7
4 J
negative absorption peaks are due to the D – F transitions of the
3
+
Tb ion excited by the UV component in the incident ray during
the measurement. Compared with the spectrum of SUA-APEMS-
Tb, SUA-APS-Tb has the same peaks but with weaker intensities,
Besides, selected 29Si MAS NMR spectroscopy of Tb-SUA-APEMS
is shown in Fig. 4. Distinct resonances can be observed for the
n
3+
siloxane [Q = Si–(OSi)
n
(OH)4ꢁn
,
n = 2–4] and organosiloxane
because other emission peak of Tb are obscure except for the
m
[
T
= R–Si–(OSi)
m
(OH)3ꢁm, m = 1–3] species. The relative inte-
characteristic peak at 546 nm [33].
1
2
3
grated intensities of the organosiloxane T , T , and T NMR signals
can be employed to estimate the degree of hydrolysis–condensa-
Figs. 6 and 7 show the excitation and emission spectra of the
chemically bonded hybrids without metal ions (SUA-APEMS,
SUA-APS) and zinc hybrid materials (Zn-SUA-APEMS, Zn-SUA-
APS). For Fig. 6, both excitation and emission spectra of the two hy-
brids without metal ions show the broad bands, 130 nm range
(from 220 to 350 nm) excitation band and 200 nm range (from
350 to 550 nm) emission band, respectively. The excitation spectra
of SUA-APEMS and SUA-APS are similar except for the distinction
of intensity, suggesting the same typical characteristic of organic
molecule units of SUA. But the emission spectra of them are differ-
ent in spite of the 200 nm range. SUA-APEMS hybrid material
1
2
tion of organic functional groups. Compared with T and T organ-
osiloxane centers, the predominance of T3 [the T :(T + T + T )
ratio is 0.74] suggests that the hydrolysis and condensation of
the organo functionality (BSPA-Si) in the order structure is nearly
complete, indicating a strong linkage (three Si–O–Si covalent
bonds) between the organic ligand and the silica matrix.
3
3
2
1
Fig. 5 shows the UV–Vis DRS of Tb-SUA-APEMS, Tb-SUA-APS.
Both have broad absorption band ranging from 200 to 480 nm.
The broad absorption suggests that the organic part played an

K. Qian, B. Yan / Polyhedron 29 (2010) 226–231
229
f
f
Em (λ = 325 nm)
ex
SUA-APEMS
Ex
λem= 615 nm)
Em
Ex (λ = 400 nm, 450 nm)
(λ = 300 nm)
em
(
ex
Eu-SUA-APS
Host absorption
of Si-O network
SUA-APS
Eu-SUA-APEMS
5D0
7
F1, 2
250
300
350
400
450
500
550
300
400
500
600
700
Wavelength / nm
Wavelength / nm
Fig. 6. The emission spectra of the non-metallic hybrid materials.
Fig. 8. The emission spectra of the europium hybrid materials.
the energy transfer is not effective between the organically modi-
Ex (λ = 450 nm)
Em (λex = 310 nm)
3+
em
fied (SUA unit) Si–O host and Eu . Generally, 5-sulfosalicylic acid
3
+
Zn-SUA-APEMS
is not suitable for the luminescence of Eu for the higher energy
difference [34]. All these emission spectra exhibit that the emission
5
7
5
7
consisting of the
D
0
? F
1
,
D
0
? F
2
, transitions at 588, 614 nm,
3
+
respectively, of Eu can be obviously obtained and the red emis-
5
7
sion ( D
0 2
? F ) possesses the strongest intensity. But a prominent
phenomenon that should be noticed in these spectra is the inten-
5
7
5
7
0 2 0 1
sity ratios I02( D ? F )/I01( D ? F ). In these europium hybrid
materials, from SUA-APEMS-Eu to SUA-APS-Eu, the intensity ratios
5
7
5
7
I
02( D
D
0
7
? F
2
)/I01( D
0 1
? F ) are 1.322 and 2.133, respectively.
5
Zn-SUA-APS
0
? F
1
transition is magnetic-dipolar transitions and insensitive
5
7
to their local structure environment while
0 2
D ? F transition is
electric-dipolar transitions and sensitive to the coordination envi-
3
+
5
7
ronment of the Eu ion. Usually the intensity ratio of D
0
? F
2
to
5
7
D ? F is regarded as a probe to detect the inversion environ-
0 1
250
300
350
400
450
500
550
600
3
+
3+
mental symmetry around Eu . If the RE ions occupy the host
sites with inversion symmetry, optical transitions inside the 4fn
configuration are strictly forbidden as electric dipole transition.
So it can be concluded that the Eu ion is not located at the site
with inversion symmetry. Besides, there exists apparent emission
in the short wavelength region of 450–550 nm, which may be as-
cribed to the emission of the Si–O network. The occurrence of host’
Wavelength / nm
Fig. 7. The emission spectra of the zinc hybrid materials.
3
+
presents the violet luminescence with maximum wavelength of
around 405 nm, while SUA-APS hybrid material shows the blue
emission with maximum wavelength at 460 nm. This suggests that
the different Si–O unit of APEMS and APS has influence on the
luminescence position of the hybrid materials. For Fig. 7, both of
the two zinc hybrids show the similar luminescent feature to the
hybrids without metal ions. The luminescence principle of zinc
hybrids is different from that of lanthanide molecular hybrids.
Lanthanide molecular hybrids based on the intra-molecular energy
5D
7
F
Ex
4
5
(
λem= 540 nm)
Em
(λ = 320 nm)
transfer between ligand systems to Ln3 , but the luminescence zinc
molecular hybrid systems derived from the ligands are influenced
by the disturbance of Zn2 . Different from the emission spectra of
SUA-APEMS and SUA-APS, the two zinc hybrids shows the similar
blue luminescence with maximum wavelength of around 450 nm,
suggesting that the disturbance of Zn2+ has great influence on the
emission of SUA-APEMS. The zinc hybrid materials also show the
stronger emission intensity, which also suggests the disturbance
+
ex
Host absorption
of Si-O network
+
Tb-SUA-APEMS
5D4
7F6
Tb-SUA-APS
5
7
of Zn2+
.
D
F
4, 3
4
Fig. 8 illustrates the typical photoluminescence spectra of the
europium hybrid materials. The excitation spectra of Eu-SUA-
APEMS and Eu-SUA-APS show the two main excitation bands,
one is ascribed to the CTS and SUA modified Si–O host, the other
corresponds to the f–f transition of Eu3 . It is found that the two
excitation bands show the similar weak intensities, suggesting
2
50
300
350
400
450
500
550
600
Wavelength / nm
+
Fig. 9. The emission spectra of the terbium hybrid materials.

2
30
K. Qian, B. Yan / Polyhedron 29 (2010) 226–231
luminescence also verifies that the energy transfer from Si–O net-
work host to Eu is not effective [35,36].
So quantum efficiency can be calculated from radiative transi-
tion rate constant and experimental luminescence lifetime from
the following equation:
3
+
The excitation and emission spectra of the resulting terbium hy-
brid materials are shown in Fig. 9. Different from the excitation
spectra of Eu hybrids, two strong broad excitation bands can be ob-
served, corresponding to the host absorption of Si–O network,
while the f–f excitation bands are too weak to be checked. This
indicates that the energy transfer from the host absorption of
g
¼ A
r
s
exp
ð3Þ
where A
for each
r
can be obtained by summing over the radiative rates A0J
D ? F transitions of Eu .
0 J
5
7
3+
3
+
Si–O network and Tb is effective. Subsequently, the strong green
luminescence can be observed in their emission spectra excited by
X
A
r
¼
A
0J ¼ A00 þ A01 þ A02 þ A03 þ A04
ð4Þ
3
20 nm. The emission lines of the hybrid materials were assigned
The branching ratio for the 5D
? 7F5,6 transitions can be ne-
5
7
0
to the transitions from the
4 J
D ? F (J = 6, 5, 4, 3) transitions at
glected as they both are not detected experimentally, whose influ-
around 485, 540(548), 580 and 618 nm for terbium ions. Among
5
5
7
ence can be ignored in the depopulation of the
Since D ? F
0 1
D
0
excited state.
belongs to the isolated magnetic dipole transition,
it is practically independent of the chemical environments around
4 5
these emission peaks, the green luminescence ( D ? F ) was
5
7
most striking, which indicated that the effective energy transfer
took place between the SUA-APEMS (APS) and the chelated Tb ions.
It is obviously different between the intensities of the green and
the blue emission since the green emission was stronger than that
3
+
the Eu ion, 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 the equation.
5
7
of the blue one. The reason may be that the emission to D
4 6
? F
is an electronic dipole transition, which is greatly influenced by the
ligand field, while the emission to D ? F belongs to a magnetic
4 5
A0J ¼ A01ðI0J=I01Þð
t
01
=
t
0J
Þ
ð5Þ
5
7
dipole transition, which is less influenced by the ligand field.
Besides, these bands in the short wavelength region cannot be
clearly found in the spectra of terbium hybrids, suggesting that
there exist more effective energy transfer process in the terbium
hybrids than europium ones.
Here A0J is the experimental coefficients of spontaneous emis-
sions, among A01 is the Einstein’s coefficient of spontaneous emis-
5
7
sion between the D0 and F1 energy levels. In vacuum, A01 as a
ꢁ
1
value of 14.65 s , when an average index of refraction n equal
to 1.506 was considered, the value of A can be determined to
0
1
The typical decay curve of these two Eu3 hybrid materials were
+
ꢁ1
3
be 50 s
approximately (A01 = n A01(vacuum)). I is the emission
measured and they can be described as a single exponential
intensity and can be taken as the integrated intensity of the
), indicating that all Eu3 ions occupy the
+
5
7
(
Ln(S(t)/S
0
) = ꢁk
1
t = ꢁt/
s
0 J
D ? F emission bands. t0J refers to the energy barycenter and
3
+
5
7
same average coordination environment. The resulting lifetime
data of Eu hybrid materials were given in Table 1. Furtherly,
we selectively determined the emission quantum efficiencies of
0 J
can be determined from the emission bands of Eu ’s D ? F
3
+
emission transitions. Here the emission intensity, I, taken as inte-
5
7
grated intensity S of the D ? F
0
0–4
emission curves, can be de-
5
3+
the D
0
excited state of europium ion for Eu hybrids on the basis
fined as below:
5
of the emission spectra and lifetimes of the D
0
emitting level, the
detailed luminescent data were shown in Table 1. The quantum
efficiency of the luminescence step, expresses how well the radi-
ative processes (characterized by rate constant A ) compete with
non-radiative processes (overall rate constant Anr) [37–41].
I
iꢁj ¼ ꢀh
x
iꢁj
A
iꢁj
N
i
ꢂ Siꢁj
ð6Þ
g
5
) and final levels (7F0–4), respec-
0
r
where i and j are the initial ( D
tively, iꢁj is the transition energy, Aiꢁj is the Einstein’s coefficient
of spontaneous emission, and N emit-
is the population of the 5
ting level. On the basis of the above discussion, the quantum effi-
ciencies of these two kinds of europium hybrid materials can be
calculated and the related data and the result were also given in Ta-
x
i
D
0
g
¼ A
r
=ðA
r
þ Anr
Þ
ð1Þ
Non-radiative processes influence the experimental lumines-
cence lifetime by the equation:
ble 1. From the equation of g, it can be seen the value g mainly de-
þ AnrÞꢁ1
pends on the values of two quantum parameters: lifetimes and red/
orange ratio (I02/I01). If the lifetimes and red/orange ratio are large,
the quantum efficiency must be high. So the different composition
of the hybrid materials may have influence on the luminescent life-
times and quantum efficiencies.
s
exp ¼ ðA
r
ð2Þ
Table 1
The luminescence efficiencies and lifetimes of the europium covalent hybrids.
The scanning electron micrographs of Eu-SUA-APEMS, Tb-SUA-
APEMS are shown in Fig. 10. These images for the hybrid materials
demonstrate that homogeneous, molecular-based materials were
obtained where no phase separation was observed because of
strong covalent bonds bridging between the inorganic and organic
phases which belong to a complicated huge molecule in nature,
and that they are composed quite uniformly so that the two phases
can exhibit their distinct properties together. On the surface of
these hybrid materials, uniform cuboid particles can be observed.
These phenomena are mostly attributed to the sol–gel treatment.
In the sol process, the o/w macro-emulsion is decisive and respon-
sibility for the materials’ final texture. The isolated cube is easy to
understand because the weak interactions between the organic
Systems
Eu–M
1
Eu–M
2
s
t
t
t
t
(ms)
01 (cm
0.24
0.31
ꢁ
ꢁ
1
a
a
)
16 965
16 284
15 383
14 278
129.6
257.4
13.215
13.1
50
103.5
5.6
6.02
213.9
4.0
16 996
16 284
15 314
14 342
306.7
02 (cm 1)
-
1 a
03 (cm
)
04 (cm )a
ꢁ1
b
b
I
I
I
I
01
02
410.548
48.9
40.216
50
b
b
03
04
ꢁ
ꢁ
ꢁ
ꢁ
1
1
1
1
A
A
A
A
A
g
01 (s
02 (s
03 (s
04 (s
)
)
)
)
69.8
8.8
7.8
136.4
4.3
moieties such as van der Waals, London, or p–p staking were able
ꢁ
1
rad (s
(%)
)
to induce an organization [42–44]. Ultimately, compared with the
two SEM pictures, the uniform cuboid particles on the surface of
Tb-SUA-APEMS system are closer to the rectangular cube, which
may be due to the difference of the precursor molecules.
a
The energies of the 5
The integrated intensity of the
? 7
D
0
J
F transitions (t0J).
b
5
7
D
0
?
F
J
emission curves.

K. Qian, B. Yan / Polyhedron 29 (2010) 226–231
231
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Acknowledgements
This work was supported by the National Natural Science Foun-
dation of China (20671072) and Program for New Century Excel-
lent Talents in University (NCET-08-0398).