Molecular assembly and photophysical properties of quaternary molecular hybrid materials with chemical bond

Article abstract of DOI:10.1111/j.1751-1097.2007.00190.x

In this paper, two long chain aliphatic carboxylic acids (oleic acid [OLA] and stearic acid [STA]) are modified with cross-linking molecules (N-2-aminoethyl-3-aminopropyl-methyl-dimethoxylsiliane, (AEAPMMS, H ₂N(CH₂)₂HN(CH₂)₃SiCH ₃(OCH₃)₂ and 3-aminopropyl-methyl- diethoxylsiliane (APMES, H₂N(CH₂)₃SiCH ₃(OC₂H₅)₂) resulting in four new kinds of structural molecular bridge OLA (STA)-AEAPMMS (APMES). Subsequently, ternary molecular complex systems with four molecular bridges OLA (STA)-AEAPMMS (APMES) and 2,2-bipyridyl (bipy) of lanthanides (terbium and europium) or zinc ions were assembled, which resulted in four novel kinds of quaternary molecular hybrid materials (named as bipy-Ln (Zn)-OLA (STA)-AEAPMMS (APMES) with strong chemical bonds (N-Ln(Zn)-O coordination bonds and Si-O covalent bonds) after a sol-gel (cohydrolysis and copolycondensation) process of the modified molecular bridges (as structural ligand) with inorganic precursor (tetraethoxysilane, TEOS). And especially bipy behaves as functional ligand to sensitize the luminescence of terbium or europium ions through the effective intramolecular energy transfer process, which gives rise to the characteristic emission of metal ions. The design and assembly from structural and functional ligands can help achieve a candidate technology for molecular hybrids.

Full text of DOI:10.1111/j.1751-1097.2007.00190.x

Photochemistry and Photobiology, 2007, 83: 1481–1490
Molecular Assembly and Photophysical Properties of Quaternary Molecular
Hybrid Materials with Chemical Bond
1
Bing Yan* , Kai Qian and H.F. Lu
,2
1
1
1
Department of Chemistry, Tongji University, Shanghai, China
State Key Lab of Rare Earth Materials Chemistry and Applications, Peking University, Bejing, China
2
Received 21 December 2006; accepted 17 May 2007; DOI: 10.1111/j.1751-1097.2007.00190.x
but also on the degree of mixing between them. Sanchez and
ABSTRACT
Ribot discussed the tailoring of diverse multifunctional
advanced materials induced by the mixture at the covalent
bond level to solve the problem of concentration on the
organic–inorganic hybrids (6). One is the mechanical mixture
and it seems impossible to solve the problem of clustering of
emitting centers because only weak interactions (such as
hydrogen bonding, van der Waals force or weak static effect)
exist between organic and inorganic components. In addition,
inhomogeneous dispersion of two phases and leaching of the
photoactive molecules frequently occur in this kind of hybrid
system for which the concentration of complexes is also limited.
The other contains the structural properties of true connec-
tions due to covalent bonding between the organic and
inorganic moieties in a single material. The synergy of the
combination and the special role of the inner interfaces open
up exciting novel areas in materials science. Lately, research
about the covalently bonded hybrids has emerged and the as-
derived molecular-based materials exhibit monophasic appear-
ance even at a high concentration of rare earth complexes (7–
In this paper, two long chain aliphatic carboxylic acids
(
oleic acid [OLA] and stearic acid [STA]) are modified with
cross-linking molecules (N-2-aminoethyl-3-aminopropyl-methyl-
dimethoxylsiliane, (AEAPMMS, N(CH HN(CH
and 3-aminopropyl-methyl-diethoxylsiliane
N(CH SiCH (OC ) resulting in four new
H
2
2
)
2
2 3
)
SiCH (OCH )
3
3 2
(
APMES, H
2
2
)
3
3
2 5 2
H )
kinds of structural molecular bridge OLA (STA)-AEAPMMS
APMES). Subsequently, ternary molecular complex systems
(
with four molecular bridges OLA (STA)-AEAPMMS (AP-
MES) and 2,2-bipyridyl (bipy) of lanthanides (terbium and
europium) or zinc ions were assembled, which resulted in four
novel kinds of quaternary molecular hybrid materials (named as
bipy-Ln (Zn)-OLA (STA)-AEAPMMS (APMES) with strong
chemical bonds (N-Ln(Zn)-O coordination bonds and Si-O
covalent bonds) after a sol-gel (cohydrolysis and copolyconden-
sation) process of the modified molecular bridges (as structural
ligand) with inorganic precursor (tetraethoxysilane, TEOS).
And especially bipy behaves as functional ligand to sensitize the
luminescence of terbium or europium ions through the effective
intramolecular energy transfer process, which gives rise to the
characteristic emission of metal ions. The design and assembly
from structural and functional ligands can help achieve a
candidate technology for molecular hybrids.
2
8). Hence, the critical step to prepare these hybrids is to
synthesize a novel monomer as a covalent bridge that cannot
only develop chelating effects that can bind to lanthanide ions
but also act as precursors of inorganic network. Franville et al.
have concentrated on the modification of pyridine-dicarbox-
3
+
ylic acid or their derivatives and resulted in strong Eu ions
emissions due to efficient ligand-to-metal energy transfer (11).
Zhang and coworkers focused on modification of heterocyclic
ligands including 1,10-phenanthroline and di-pyridine to
construct molecular-based hybrids (7,8,18–20). This study
concerns the preparation of –NHC(=O)NH–urea bridges
connecting both siliceous backbone and aromatic carboxylic
acids (9,16,17,21–26). We propose that the precursor contain-
ing nonhydrolyzable silicon–carbon bond, coordinative activ-
ity and hydrolyzable alkoxy-silicon parts will play an
important role to form covalent linkage between the two
phases.
We put forward the design and assembly of rare earth
molecular hybrid materials in accordance with the coordina-
tion chemistry principle of ternary or quaternary complexes.
Aliphatic carboxylic acids (oleic acid [OLA] and stearic acid
[STA]) without photoactivity were used as structural ligands
to be modified as the molecular bridge through the amidation
reaction with cross-linking reagents (N-2-aminoethyl-3-amino-
INTRODUCTION
With the goal of combining various features together, a wide
range of hybrid organic–inorganic materials have attracted
great scientific interest (1,2). Recently, the hybrid system of
lanthanide organic complexes introduced in silica gel have
already been found to display characteristic emission intensi-
ties compared with simple metal ions in inorganic hosts. The
focus on the photophysical properties of lanthanide coordina-
tion compounds with organic ligands has grown considerably
as such complexes could be seen as light conversion supramo-
lecular devices (3). In particular, anchored lanthanide com-
plexes by aromatic carboxylic acids, b-diketones or
heterocyclic ligands in a sol–gel-derived matrix have been
discussed (4,5). However, the properties of these hybrid
materials depend not only on those of the individual moieties
*
ꢀ
Corresponding author email: byan@tongji.edu.cn (Bing Yan)
2007 The Authors. JournalCompilation. The AmericanSocietyofPhotobiology 0031-8655/07
2 2 2
propyl-methyl-dimethoxylsiliane (AEAPMMS, H N(CH )
1
481

1
482 Bing Yan et al.
1
HN(CH
oxylsiliane (APMES, H
idyl was used as the terminal functional ligand to sensitize the
luminescence of lanthanide ions for the triplet state energy of
2
)
3
SiCH
3
(OCH
3
)
2
and 3-aminopropyl-methyl-dieth-
N(CH SiCH (OC ). 2,2¢-bipyr-
(STA-AEAPMMS: C26
.36 (1H,m) 2.10 (1H,t) 1.85 (3H,s) 1.60 (3H,s) 1.25 (32H,m) 0.85
4H,m) 0.55 (6H,m) 0.15 (3H,s).
56 3 2 3
H O N Si: HNMR(CDCl ):3.30 (3H,t)
2
(
2
2
)
3
3
2 5 2
H )
1
STA-APMES: C26
55 3 3
H O NSi: HNMR(CDCl ): 5.50(3H,s) 4.12(1H,s)
3.75(3H,s) 3.50(2H,m) 3.15(2H,t) 2.30(3H,t) 1.90(4H,m) 1.64(4H,m)
1.25(26H,m) 0.90(2H,m) 0.55(2H,q) 0.15(3H,t)
3
+
bipy is suitable for the resonant emissive energy level of Ln
.
Synthesis of ternary lanthanide (Eu, Tb) and zinc complex systems
with molecular bridge and bipy.The alcohol solution of europium and
The reaction model for the hybridization formula of quater-
nary hybrid materials can be divided into two steps: The
individual hydrolysis of bipy-Ln (Zn)-OLA (STA)-AE-
APMMS (APMES) and TEOS is predominant in the first
step while the second step involves the polycondensation
reactions between hydroxyl groups of both bipy-Ln (Zn)-OLA
terbium nitrate was added with the molar ratio of 3:1 to RE(NO
6H
2
3 3
) Æ
O (RE = Eu, Tb), the resulting solution was stirred for 1 h and
ethanol solution of 2,2-bipyridyl was put into the mixture gradually
(bipy:RE = 1:1). After stirring for 2 h, a stoichiometric amount of
tetraethoxysilane (OLA(STA)-AEAPMMS (APMES):TEOS = 1:1)
and minimum water were added to the solution simultaneously.
(
STA)-AEAPMMS (APMES) and TEOS. After these treat-
Element analysis data: Anal. Calcd. for EuC88
H, 9.19; N, 5.87; Eu, 7.96%. Found: C, 56.13; H, 8.81; N, 5.55; Eu,
8.04%. Anal. Calcd. for TbC88 Si 11: C, 55.18; H, 9.16; N,
.85; Tb, 8.30%. Found: C, 55.26; H, 8.74; N, 6.01; Tb, 8.47%. Anal.
Calcd. for ZnC62 Si : C, 64.02; H, 10.05; N, 7.22; Zn, 5.54%.
Found: C, 64.26; H, 9.64; N, 7.01; Zn, 5.37%. EuC79 Si 11: C,
9.18; H, 10.75; N, 4.37; Eu, 9.48%. Found: C, 59.43; H,10.26; N,
.25; Eu, 9.26%. Anal. Calcd. for TbC79 Si 11: C, 58.92; H,
174 8 3
H N Si O11: C, 55.38;
ments, the molecular-based hybrids bearing the M–O coordi-
nation bond and Si–O covalent bond can exhibit the
characteristic luminescence of metal ions.
H N
174 8
3
O
5
H
116
N
6
2 6
O
171
H N
5
3
O
5
4
EXPERIMENTAL SECTION
H N
171 5
3
O
Modification of aliphatic carboxylic acids (OLA and STA) to molecular
bridge. OLA (STA) was first converted to acyl chloride by refluxing
10.70; N, 4.42; Tb, 9.87%. Found: C, 59.26; H, 10.34; N, 4.22; Tb,
9.67%. Anal. Calcd. for ZnC56H114N Si O : C, 63.39; H, 10.83; N,
4
2
6
in excess SOCl
2
under argon at 70ꢁC in a water bath for 4 h.
5.28; Zn, 6.07%. Found: C, 63.16; H, 10.56; N, 5.06; Zn, 6.23%.
EuC88H180N Si O11: C, 59.96; H, 10.29; N, 6.36; Eu, 8.62%.
Found: C, 60.17; H, 9.90; N, 6.25; Eu, 8.34%. Anal. Calcd. for
After isolation, the acyl chlorides were directly reacted with AE-
APMMS, APMES in ethyl ether in the presence of pyridine. A typical
procedure for the preparation of the reaction scheme is presented in
8
3
TbC88H180N Si O11: C, 59.73; H, 10.25; N, 6.33; Tb, 8.98%. Found:
8
3
Figs. 1 and 2.
C, 59.52; H, 9.88; N, 6.11; Tb, 8.71%. Anal. Calcd. for
ZnC62H120N Si O : C, 63.85; H, 10.37; N, 7.21; Zn, 5.52%. Found:
1
Si: HNMR(CDCl
OLA-AEAPMMS: C26
H O
54 3
N
2
3
): 5.36(3H,s)
6
2
6
3
0
.70(3H,s) 3.45(3H,t) 2.30(2H,m) 2.00(6H,m) 1.65(3H,s) 1.35(28H,m)
.85(4H,m) 0.15(2H,t)
5 3
C, 63.60; H, 10.04; N, 7.03; Zn, 5.33%. EuC79H177N Si O11: C, 58.95;
H, 11.84; N, 4.35; Eu, 9.44%. Found: C, 59.18; H, 11.59; N, 4.14; Eu,
9.16%. Anal. Calcd. for TbC79H177N Si O11: C, 58.70; H, 11.04; N,
1
NSi: HNMR(CDCl
OLA-APMES: C26H O
53 3
3
):8.20(3H,s) 4.10(2H,m)
5
3
3
1
.75(3H,t) 3.50(4H,m) 3.10(2H,s) 1.95(4H,m) 1.70(1H,t) 1.40(14H,m)
.25(14H,m) 0.60(3H,t) 0.20(3H,t)
4.33; Tb, 9.83%. Found: C, 58.58; H, 10.76; N, 4.11; Tb, 9.60%. Anal.
Calcd. for ZnC56H118N Si O : C, 63.15; H, 11.66; N, 5.26; Zn, 6.05%.
4
2
6
Found: C, 63.44; H, 11.36; N, 5.09; Zn, 6.22%. It should be pointed
out that the precursor complex is so easy to hydrolyze that the store of
samples has to be done as carefully as possible (Fig. 1).
Assembly of quaternary molecular hybrid materials. A sol–gel-
derived quaternary hybrid material was prepared as follows: OLA(S-
TA)-AEAPMMS (APMES) was dissolved in pyridine, and TEOS
(
tetraethoxysilane) and H
of diluted hydrochloric acid was added to promote hydrolysis. A
stoichiometric amount of Ln(NO Æ6H O (Ln = Eu, Tb) (or Zn(Ac)
Ac = acetate) was added to the final stirring mixture. The mole ratio
of Ln(NO Æ6H O ⁄ OLA (STA)-AEAPMMS (APMES) ⁄ TEOS ⁄ H
was 1:3:6:24 (Zn(Ac) ⁄ OLA (STA)-AEAPMMS (APMES) ⁄
TEOS ⁄ H O was 1:2:4:16). After hydrolysis, 2 ml of DMF (dimethyl-
2
O were added while stirring; then one drop
3
)
3
2
2
,
3
)
3
2
2
O
2
2
formamide) and an appropriate amount of hexamethylene-tetramine
was added to adjust the pH value to about 6.5. The mixture was stirred
to achieve a single phase and thermal treatment was performed at 60ꢁC
in a covered Teflon beaker until the sample solidified (Fig. 1).
Physical measurements. All measurements were completed under
room temperature. Elemental analyses (C, H, N) were carried out by
the Elementar Cario EL elemental analyzer. FT-IR spectra were
)
1
measured within the 4000–400 cm region on an infrared spectro-
photometer with the KBr pellet technique. Ultraviolet absorption
)
4
)1
spectra of these powder samples (5 · 10 mol L
chloroform
CHCl ) solution) were recorded with an Agilent 8453 spectropho-
tometer. Phosphorescence spectra (5 · 10 mol L CHCl solution)
3
and fluorescence excitation and emission spectrums were obtained on a
Perkin-Elmer LS-55 spectrophotometer.
(
3
)
4
)1
RESULTS AND DISCUSSION
Modification of bridge molecules OLA(STA)-AEAPMMS
(
APMES)
Figure 2 shows the IR spectra of OLA (a), OLA-AE-
APMMS (b) and OLA-APMES (c), repsectively. Compared
with the IR spectrum of OLA, OLA-AEAPMMS presents a
stretching vibration peak of N-H at 3413.29 cm) , stretching
1
Figure 1. Scheme of hydrolysis and polycondensation processes
between quaternary molecular hybrids.

Photochemistry and Photobiology, 2007, 83 1483
(
(
(
a)
b)
c)
Figure 2. FT-IR spectra of (a) OLA, (b) OLA-AEAPMMS and (c) OLA-APMES.
)
1
vibration peak1 of C=O at 1717.84 cm and a bending
1
group of APMES. Figure 3 presents the IR spectra for STA
(a), STA-AEAPMMS (b) and STA-APMES (c), which is
similar to that of Fig. 2. Different from the IR spectrum of
STA, three apparent peaks appear in the IR spectra of STA-
AEAPMMS (3440.37 cm) (N-H stretching vibration),
)
vibration peak of N-H at 1608.02 cm , which suggests that
the carboxylate group of OLA is modified successfully.
Besides, the 1012.29 cm of Si-O further verifies that the
AEAPMMS molecular fragment has been grafted to OLA.
Similarly, there appear four apparent new absorption peaks
in the IR spectrum of OLA-APMES: 3467.65 cm of N-H
stretching vibration, 1708.82 cm of C=O stretching vibra-
of N-H bending vibration and
095.03 cm) of Si-O, respectively, indicating that –COCl
of OLA acyl chloride derivative has reacted with the NH2
)1
1
1699.80 cm) (C=O stretching vibration) and 1635.11 cm
1
)1
)
1
)1
(N-H bending vibration) and STA-APMES (3394.48 cm
)1
)1
for N-H stretching vibration, 1719.80 cm for C=O stret-
)1
)
1
tion, 1645.63 cm
1
ching vibration and 1630.58 cm for N-H bending vibra-
tion), which indicate that the CO=NH group forms and the
amidation reaction takes place. Futhermore, the Si-O peaks
1

1
484 Bing Yan et al.
a)
(
(
b)
(
c)
Figure 3. FT-IR spectra of (a) STA, (b) STA-AEAPMMS and (c) STA- APMES.
at 1113.08 cm) for STA-AEAPMMS and 1095.27 cm)1 for
STA-APMES prove that STA has been grafted with the two
cross-linking molecules (AEAPMMS and APMES) (29–32).
Figure 4a exhibits ultraviolet absorption spectra of OLA,
OLA-AEAPMMS and OLA-APMES, whose prodominant
absorption bands are situated with a maximum wavelength of
1
distribution and gives rise to the larger blueshifts of absorp-
tion, suggesting the achivement of modification. Figure 4b
shows similar features; the main aborption ultraviolet-visible
absorption bands present the maximum absorption peaks at
288, 242 and 244 nm, respectively. The large blueshifts
between STA-AEAPMMS (STA-APMES) and STA indicate
that the two cross-linking molecular fragments have been
grafted onto the STA successfully. The blue-shifts for Fig. 4a
310, 286 and 300 nm, respectively. The graft of AEAPMMS
and OLA-APMES molecular fragments changes the electronic

Photochemistry and Photobiology, 2007, 83 1485
)
1
(
a)
6170, 6400, 6120 and 5740 cm
2
(2970, 3200, 1920 and
540 cm) ), respectively. According to the intramolecular
1
energy mechanism (33–36), the intramolecular energy transfer
efficiency depends chiefly on two energy transfer processes: the
first energy transfer process comes from the triplet level of
3+
ligands to the emissive energy level of the RE
ion by
Dexter’s resonant exchange interaction; the second is just an
inverse energy transfer by a thermal deactivation mechanism.
Both energy transfer rate constants depend on the energy
differences between the triplet level of the ligands and the
3
+
resonant emissive energy of RE . Intramolecular energy
transfer efficiency in rare earth complexes follows Dexter’s
exchange energy transfer theory (37): with the decrease in
energy difference between the triplet state energy of ligands
3
+
and the resonance emission energy of Tb , the overlap
between the luminescence spectrum of energy donor (ligand)
3
+
and the absorption spectrum of energy acceptor (Tb
)
increases. Subsequently, the intramolecular energy transfer
efficiency increases as it is directly proportional to the overlap
integral of them. Thus, ligands with a large energy difference
cannot sensitize rare earth ions effectively because the overlap
integral is too small to produce effective intramolecular energy
transfer. On the other hand, there exists an inverse energy
transfer process that affects luminescence intensity by temper-
ature (38): The activation energy is approximately equal to
energy difference in the inverse energy transfer process and
then a decreasing energy difference increases the energy
transfer ratio to decrease the luminescence intensity. Based
on this evidence, the conclusion can be drawn that the energy
difference is of opposite influence on the two energy transfer
processes and an optimal value can be assumed to exist. Based
on this discussion, it can be primarily predicted that the energy
(
b)
3
+
transfer between PHE-Si and EPHBA and Tb is appropriate
and the corresponding hybrid materials can be expected to
have strong luminescence. The triplet state energies are
Figure 4. The ultraviolet absorption spectra of (a) OLA, OLA-
AEAPMMS and OLA-APMES, and (b) STA, STA-AEAPMMS and
STA-APMES.
3+
suitable for the sensitization of luminescence of Eu
and
3
+
Tb , but the lack of conjugated structure also restricts their
energy absorption ability hindering any effective energy
transfer between them and lanthanide ions. All the triplet
state energies of the four bridge ligands are higher than that of
bipy (about 22900 cm) ). This suggests that there may exist the
intramolecular energy transfer between ligands (OLA(STA)-
AEAPMMS (APMES) and bipy, and bipy may become the
main energy donor in the ternary molecular systems because
bipy possesses the sufficient delocalized conjugate systems to
produce effective energy absorption and energy transfer
(39,40).
are less than those for Fig. 4b, and can be due to the different
structures of OLA and STA: OLA itself possesses an unsat-
urated double bond, while STA does not.
Further, we measured the phosphorescence spectra at 77 K
for these four molecular bridge ligands STA-AEAPMMS
(STA-APMES), whose maximum wavelengths of phosphores-
cence bands were situated at 426 nm (OLA-AEAPMMS),
4
4
1
22 nm (OLA-APMES), 427 nm (STA-AEAPMMS) and
34 nm (STA-APMES), respectively. These differ from those
of the unmodified long chain aliphatic carboxylic acids
430 nm for OLA and 425 nm for STA). Molecular phospho-
(
Assembly of luminescent quaternary molecular hybrids
rescence belongs to the excited state characteristic of organic
molecules, and different phosphorescent emission bands cor-
respond to the different organic ligands. Therefore, the
different phosphorescent bands indicate that the modification
reaction takes place. The corresponding triplet state energies
The reaction model for the hybridization formula of TEOS
and OLA(STA)-AEAPMMS (APMES) may be described as
follows: The hybridization of TEOS and OLA(STA)-
AEAPMMS (APMES), accordingly, proceeds through a
polycondensation reaction between the terminal silanol groups
of OLA (STA)-AEAPMMS (APMES) and the OH groups of
hydrolyzed TEOS. At the beginning of the reaction, the
individual hydrolysis of OLA (STA)-AEAPMMS (APMES)
and TEOS is predominant. By these methods, the molecular-
)
1
for them were determined to be 23470 cm
1
(OLA-
)1
)
AEAPMMS), 23700 cm
(
(OLA-APMES), 23420 cm
)1
STA-AEAPMMS) and 23040 cm (STA-APMES), respec-
tively. The energy differences between the triplet state energies
of OLA-AEAPMMS, OLA-APMES, STA-AEAPMMS and
3
+
STA-APMES and the resonant emissive energy level of Eu
1
based hybrids bearing the Ln–O coordination bond and Si–O
3+
covalent bond exhibit the strong green luminescence of Ln
(
17300 cm) ) (and Tb
3+
(20500 cm )) are calculated to be
)1
.

1
486 Bing Yan et al.
Here we named the cooperation of both OLA (STA)-
AEAPMMS (APMES) and TEOS during the in situ sol-gel
process as cohydrolysis and copolycondensation (similar to
copolymerization of the organic monomer).
The IR spectra of ternary europium (or terbium and zinc)
complex precursor show a feature similar to that of the
corresponding bridge ligand OLA-AEAPMMS except that
)1
the vibration frequency of 1652 cm belonging to the phenyl
ring of 2,2¢-bipyridine becomes weaker than that of free bipy
and the out-of plane bending vibrations of the hydrogen
)
1
atom on the phenyl ring of bipy shift from 867, 744 cm of
)1
free ligand to lower frequency of 855, 737 cm . This verified
that bipy coordinates with europium or terbium ions. Like-
3
+
3+
wise, Eu
or Tb
exhibit a similar coordination behavior
with OLA-AEAPMMS and bipy. Furthermore, the stretching
)1
vibration (mSi-C) located at 1210 cm still exists in the IR
spectra of hybrid materials, which is in agreement with the
fact that no (Si–C) bond split happens during the course of
hydrolysis ⁄ polycondensation reactions. Compared to free
STASi bridge molecule, ternary europium (or terbium)
complex precursors with STASi and bipy show that the
vibration frequency of 1653 cm belonging to the phenyl
ring of 2,2¢-bipyridine becomes weaker than that of free bipy
and the out-of-plane bending vibrations of the hydrogen
Figure 5. The phosphorescence spectra of (A) Gd- STA-AEAPMMS
complex, (B) Gd-bipy complex and (C) bipy-Gd-STA-AEAPMMS
)5
)1
ternary complex (5 · 10 mol L acetone solution) under excitation
wavelength of 278 nm.
)
1
(
a)
)
1
atom on the phenyl ring of bipy shift from 867, 744 cm of
free ligand to lower frequency of 844, 735 cm) , which
verifies the coordination of terminal bipy ligand. For the
1
final quaternary hybrids, the stretching vibration (mSi-C
)
)1
located at 1198 cm still exists in the IR spectra of hybrid
materials, corresponding to the fact that no (Si–C) bond split
happens during the course of hydrolysis ⁄ polycondensation
reactions. Moreover, the broad absorption band at
1
1
085 cm) (mSi-O-Si) originates from the formation of siloxane
bonds (29–32).
The ternary bipy-Tb-OLA-AEAPMMS molecular complex
system present the obvious band at 264 nm shows character-
istic absorption of 2, 2¢-bipyridyl, which can be ascribed as the
absorption of bipy for free bipy appears one absorption peak
at 265 nm. The small redshift of 1 nm is due to the more
extensive conjugated system of electronic distribution form
because the coordination between lanthanide ions and bipy.
Other ultraviolet absorption spectra of ternary molecular
systems all show similar features. Therefore, in the ternary
complex bipy-Ln(Zn)-OLA(STA)-AEAPMMS (APMES),
(
b)
2, 2¢-bipyridyl plays a major energy donor role and will
transfer it to metal ions.
Figure 5 provides the phosphorescence spectra of
(
A) Gd-STA-AEAPMMS complex, (B) Gd-bipy complex
and (C) bipy-Gd-STA-AEAPMMS ternary complex. We can
observe that (B) and (C) are rather similar in terms of the same
organic ligand 2, 2¢-bipyridyl responsible for the emissions.
The peak at 421 nm of (A) shows that the triplet state energy
)
1
level of STA-APMMES is approximately 23753 cm , which is
)1
higher than that of bipy (437 nm, 22880 cm ), therefore,
we suppose that energy transfer process will occur from
STA-APMMES to 2,2¢-bipyridyl, substantiating that the
heterocyclic ligand will become the main energy donor and
3
+
have the possibility of sensitizing Ln ions (39,40).
Figures 6 and 7 show the excitation and emission spectra of
quaternary terbium molecular hybrids with OLA(STA)-
AEAPMMS (APMES)-Si and 2, 2¢-bipyridyl. For the inner
Figure 6. Luminescent spectra of quaternary molecular hybrids bipy-
Tb-OLA-AEAPMMS (APMES) (a) and biby-Tb-OLA-APMES-Si(b).

Photochemistry and Photobiology, 2007, 83 1487
(
a)
(a)
(
b)
(
b)
Figure 7. Luminescent spectra of quaternary molecular hybrids
bipy-Tb-STA-AEAPMMS-Si(a) and bipy-Tb-STA-APMES-Si (b).
(
c)
3
+
plot of these spectra by monitoring the emission of Tb ion at
45 nm, there exist effective broad excitation bands in the
5
range of 200–350 nm with different dominant excitation peaks,
which are the characteristic absorptions of the lanthanide
complexes arising from the efficient transition based on
the conjugated structure. As a result, the emission lines of
the hybrid material were assigned to the transitions from the
5
7
D fi F (J = 6, 5, 4, 3) transitions at around 490, 541, 582
4
J
and 620 nm for terbium ions (as shown in the outer plot of
Figs. 6 and 7). Among these emission peaks, the most striking
5
7
green luminescence ( D fi F ) and blue luminescence
4
5
5
7
(
4 6
D fi F ) were observed in their emission spectra, which
indicated that the effective energy transfer took place between
the bipy and the chelated Tb ions. Comparing Fig. 6, with
Fig. 7, there exists a little distinction for the luminescent
5
7
Figure 8. Luminescent spectra of quaternary molecular hybrids
bipy-Eu-OLA-AEAPMMS-Si(a), bipy-Eu-STA-AEAPMMS-Si(b) and
bipy-Eu-OLA- APMES-Si(c).
intensities of green luminescence ( D
7
4
fi
F
5
) and blue
5
luminescence ( D fi F ). In Fig. 6, the green emission was
4
6
stronger than that of the blue one, while in Fig. 7, it was
5
7
contrary. The reason may be that the emission to D
is an electronic dipole transition, which is greatly influenced by
4
fi
F
6
a magnetic dipole transition, which is less influenced by the
ligand field. The detailed luminescent data are presented in
Table 1.
5
7
the ligand field, different from that to D fi F belonging to
4
5

1
488 Bing Yan et al.
Table 1. Luminescent properties of quaternary metal molecular hybrids bipy-Ln (Zn)-OLA (STA)-AEAPMMS (APMES).
Quaternary molecular hybrids
Emission bands (nm)*
Relative intensities (a.u.)
Lifetimes (ls)†
1048
bipy-Eu-OLA-AEAPMMS
bipy-Eu-OLA- APMES
bipy-Eu-STA-AEAPMMS
bipy-Eu-STA-APMES
bipy-Tb-OLA-AEAPMMS
bipy-Tb-OLA- APMES
bipy-Tb-STA-AEAPMMS
bipy-Tb-STA-APMES
bipy-Zn-OLA-AEAPMMS
bipy-Zn-OLA- APMES
bipy-Zn-STA-AEAPMMS
bipy-Zn-STA-APMES
591, 615, 648, 701
590, 614, 649, 700
591, 616, 650, 701
593, 616, 648, 700
490, 543, 582, 621
489, 543, 584, 622
488, 544, 586, 619
489, 543, 583, 620
391
44.14
95.48
129.28
148.49
126.12
284.15
430.72
585.15
176.98
286.73
740.49
930.83
1105
1340
1420
398
410
420
3
+
5
For Eu : D
7
- F
3+ 5
(J = 1, 2, 3, 4); For Tb : D
7
- F
3+ 5
(J = 6, 5, 4, 3). †For Eu : D
7
- F
3+ 5
transition; For Tb : D
7
- F
*
0
J
4
J
0
2
4
5
transition.
Figure 8 presents the selected luminescent spectra of qua-
ternary europium molecular hybrids bipy-Eu-OLA(STA)-
AEAPMMS (APMES)-Si. All three emission spectra exhibit
(
a)
5
7
5
7
0
1 0 2
that the emission consisting of the D fi F , D fi F ,
5
D
7
5
and D
7
0
fi
00 nm, respectively, of Eu
F
3
0
fi
F
4
transitions at 591, 616, 648 and
+
were obviously obtained and
3
7
5
7
0
2
strong red emission ( D fi F ) was the strongest. Besides,
there exists apparent emission in the short wavelength region
of 450–550 nm, which may be ascribed to the emission of the
Si–O network. These bands 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. Figure 9 shows the luminescent spectra of
quaternary bipy-Zn- OLA(STA)-AEAPMMS (APMES)-Si.
Different from the luminescence principle of lanthanide
molecular hybrids based on the intramolecular energy transfer
3
+
between ligand systems to Ln , the luminescence zinc
molecular hybrid systems derived from the ligands are influ-
2
+
enced by the disturbance of Zn . All four zinc molecular
hybrids show violet emission at 391 nm (bipy-Zn-OLA-AE-
APMMS-Si), 398 nm (bipy-Zn-OLA-APMES-Si), 420 nm
(
b)
(
bipy-Zn-OLA-AEAPMMS-Si) and 410 nm (bipy-Zn-OLA-
APMES-Si), respectively. The lower energy band may be
ascribed to the smaller electronic delocalization (the electro-
2
+
2)
static force between Zn and O ), which cause an increased
conjugation of OLA(STA)-AEAPMMS (APMES) ligands,
and the observed luminescence of the complex is attributed to
the coordinated OLA(STA)-AEAPMMS (APMES) ligand.
The detailed luminescent data are given in Table 1. Besides, we
measured the luminescent lifetimes of four quaternary molec-
ular hybrids selectively, whose data are shown in Table 1. The
luminescent lifetimes are longer than general lanthanide
complexes, whose lifetimes are mostly shorter than 1000 ls,
suggesting that molecular hybrids with strong chemical bonds
enhance the luminescent stability. Accordingly, we may expect
that through this efficient method, leaching of the photoactive
centers can be avoided; higher concentration of metal ions is
reached and clustering of the emitting centers may be
prevented.
Figure 9. Luminescent spectra of quaternary molecular hybrids
bipy-Zn-OLA(STA)-AEAPMMS-Si(a) and bipy-Zn-OLA(STA)-AP-
MES-Si(b).
Figure 10 illustrates the selected scanning electron micro-
graphs for these quaternary molecular hybrids—(a) bipy-Tb-
STA-AEAPMMS-Si, (b) bipy-Tb-STA-APMES-Si and
was obtained because of strong covalent bonds bridging
between the inorganic and organic phase, which belongs to a
complicated huge molecule in nature. They are composed quite
uniformly so that the two phases exhibit distinct properties
(c) bipy-Tb-OLA-APMES-Si, respectively. These pictures
demonstrate that a homogeneous, molecular-based material

Photochemistry and Photobiology, 2007, 83 1489
of AEAPMMS and its molecular fragment possesses two
amino groups and a longer chain, which provide orientation
and induction ability, resulting in the template to control the
microstructure of hybrids.
(
a)
CONCLUSIONS
In summary, by means of the molecular modification of long-
chain aliphatic carboxylic acids (OLA and STA) with cross-
linking molecules (AEAPMMS and APMES) through the
amidation reaction, four kinds of structural molecular bridges
OLA (STA)-AEAPMMS (APMES) were designed to obtain
double reactivity. Further, ternary molecular complex systems
with four molecular bridges and 2,2-bipyridine of lanthanides
(
terbium and europium) and zinc ions were successfully
assembled. The modified molecular bridges behave as struc-
tural ligand to form the covalent bond Si–O network with
matrix precursor (tetraethoxysilane, TEOS) through a sol–gel
process (cohydrolysis and copolycondensation process) and
bipy acts as the energy donor to sensitize the luminescence of
metal ions. A series of quaternary molecular hybrid materials
(
b)
(
bipy-Ln (Zn)-OLA (STA)-AEAPMMS (APMES) with strong
chemical bonds were constructed, which show the character-
istic luminescence and uniform microstructure.
Acknowledgement—This work was supported by the National Natural
Science Foundation of China (20671072).
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