A mesoporous silica functionalized by a covalently bound calixarene-based fluoroionophore for selective optical sensing of mercury(II) in water

Article abstract of DOI:10.1039/b501897h

With the aim of optical sensing of Hg²⁺ in water, a calixarene bearing two dansyl fluorophores was grafted on a large pore mesoporous silica material (SBA-15) via two long alkyl chains containing triethoxysilane groups. The characterization of

Full text of DOI:10.1039/b501897h

View Article Online / Journal Homepage / Table of Contents for this issue
PAPER
www.rsc.org/materials | Journal of Materials Chemistry
A mesoporous silica functionalized by a covalently bound calixarene-based
fluoroionophore for selective optical sensing of mercury(II) in water
ab
R e´ mi M e´ tivier, Isabelle Leray,* B e´ n e´ dicte Lebeau* and Bernard Valeur
ab
c
ab
Received 7th February 2005, Accepted 14th March 2005
First published as an Advance Article on the web 24th March 2005
DOI: 10.1039/b501897h
2
+
With the aim of optical sensing of Hg in water, a calixarene bearing two dansyl fluorophores
was grafted on a large pore mesoporous silica material (SBA-15) via two long alkyl chains
containing triethoxysilane groups. The characterization of the obtained material 2-SBA-15 shows
that the organized structure is preserved after the post-grafting procedure. A detailed study of the
complexing and fluorescence properties of 2-SBA-15 is reported. The functionalized material is
2+
able to reversibly detect Hg with a response time of a few seconds and a detection limit of 3.3 6
2
7
21
mol L in water. Furthermore, this system offers a high selectivity over several interfering
1
0
+
+
2+
2+
2+
2+
cations (Na , K , Ca , Cu , Cd , Pb ).
2
+
6
Pb with outstanding sensitivity and selectivity. Further-
Introduction
more, we found that a calixarene functionalized by two dansyl
2+
Sensing detrimental and harmful compounds is a critical topic
for environmental monitoring. Among hazardous species,
mercury is a well-known and highly toxic heavy metal. This
common pollutant poses severe risks for human health and
natural ecosystems. Initial inorganic mercury contamination
usually occurs through continuous natural (volcanic emission)
or anthropogenic sources (mines, waste incineration, and
large-scale combustion of coal). Adverse long-term deleterious
health effects of mercury exposure, such as neurological
diseases, are mainly due to methyl mercury compounds, which
are produced from inorganic mercury in a second step, owing
to microorganisms’ conversion activity. As a consequence, the
level of any mercury compounds in the environment is the
object of official norms in the ppb range. Accurate quantifica-
tion of trace concentrations of mercury in wastewater currently
requires a weighty analysis by means of standard techniques,
groups (compound 1, Scheme 1) allows Hg detection in the
27
21
mol L concentration range with a very high selectivity
1
0
2+
+
towards Hg over other potential interfering cations (Na ,
+
2+
2+
2+
2+
2+ 7
K , Ca , Cu , Zn , Cd and Pb ).
In order to make an optical sensor device, the immobiliza-
tion of the fluoroionophore is of major importance. The
fluoroionophore can be grafted on the surface or embedded
8
into the matrix. However, such systems have strong limita-
tions concerning relatively slow diffusion of the analyte in the
matrix due to the poorly ordered microporosity. Nevertheless,
several examples have been described in the literature, where
the promising use of grafted fluoroionophores on solid
9
supports is highlighted.
1
such as cold vapours atomic absorption spectrometry or
2
inductively coupled plasma-mass spectrometry. The develop-
ment of optical sensors would offer a wide variety of
advantages, including real-time and remote measurements,
sensitivity and selectivity against competing analytes, compact,
reliable and low cost detection. A well suited approach is to
design a fluorescent molecular sensor, called a fluoroiono-
phore, that consists of a recognition moiety (ionophore) linked
3
to a fluorescent moiety (fluorophore). Several examples of
fluoroionophores for mercury(II) have been described in the
literature. Most of them display strong drawbacks in terms of
4
sensitivity, selectivity, or solubility for potential applications.
Nevertheless some new systems recently described permit
2
+
27
detection of Hg down to the 10 mol L concentration
21
5
range. In order to obtain selective fluoroionophores towards
heavy metal ions through a versatile synthesis path, we focused
our attention on calixarene-based systems. In particular, a
calixarene bearing four dansyl groups was shown to detect
Scheme 1 Calixarene-based fluoroionophores 1 and 2 bearing two
*icmleray@ppsm.ens-cachan.fr (Isabelle Leray)
Benedicte.Lebeau@uha.fr (B e´ n e´ dicte Lebeau)
dansyl fluorophores.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2965–2973 | 2965

View Article Online
Ordered periodic micro-, meso- and macroporous materials
allow the construction of composites with many guest types,
e.g. organic molecules, inorganic ions, semiconductor clusters
for 24 hours and then at 85 uC for 48 hours. The white
precipitate was recovered by B u¨ chner filtration and dried at
60 uC. The templating agent P123 was removed by calcination
under air at 500 uC for 6 hours.
1
0
or polymers. These host–guest materials combine high
stability of the inorganic host system, new structure forming
mechanisms due to the confinement of guests in well-defined
pores, and a modular composition. In previous studies, several
proposals were already made to use such mesoporous systems
1-Tosyloxyundec-10-ene 3. 1-Hydroxyundec-10-ene (7 g,
41 mmol) and toluenesulfonyl chloride (22 g, 115 mmol) in
triethylamine (35 mL) and dichloromethane (380 mL) were
stirred for 4 hours under an argon atmosphere. The reaction
mixture was evaporated in vacuo, then washed with a solution
of 1 M HCl and distilled water. The organic layer was
separated, dried over MgSO4 and evaporated to afford the
crude product, which was purified by column chromatography
(SiO , CH Cl –cyclohexane) to provide a 75% yield of
1
1
as optical materials and as highly specific chemical sensors.
Particular interest was focused on the use of ordered
mesoporous silica (OMS) materials for trapping and detection
1
of heavy metal ions. In several studies, the detection of heavy
2
1
3
metal ions was carried out by electrochemistry. Only a few
reports on the elaboration of optical sensors from OMS
2
2
2
1
4
materials functionalized with chromophores
or fluoro-
colorless oil 3. dH (300 MHz, CDCl ) 1.23 (br s, 10 H), 1.36
3
1
phores have been published.
5
(m, 2 H), 1.63 (m, 2 H), 2.03 (m, 2 H), 4.02 (t, J 6.4, 2 H), 4.50–
2
+
Regarding the high selectivity of 1 towards Hg , we
planned to design an analogue 2 of this compound (see
Scheme 1), which possesses an additional grafting ability on
the silica surface. Long aliphatic chains were chosen in order to
keep the same complexing behaviour as 1, and then control
independently the cation-binding and surface-grafting proper-
ties of the multifunctional molecule. In this paper, we describe
the successive steps leading to the multiscale architectured
material for optical sensing of mercury(II): (i) the synthesis of
the inorganic mesostructured matrix, (ii) the grafting of the
fluorescent calixarene-based ligand on the surface, (iii) a
thorough study of the complexing and photophysical proper-
ties, and (iv) the analytical behaviour of the grafted material.
To the best of our knowledge, the present paper is the first
report on the elaboration of organically-modified ordered
mesoporous silica for selective optical sensing of mercury(II) in
water.
5.01 (m, 2 H), 5.38–5.51 (m, 1 H), 7.34 (d, J 7.8, 2 H), 7.79 (d, J
1
8.0, 2 H). C NMR (CDCl , 100 MHz): 21.5 (CH Ph), 25.2
3
3
3
(CH ), 28.7 (CH ), 28.8 (CH ), 28.9 (CH ), 29.1 (CH ), 33.6
2
2
2
2
2
(CH ), 70.5 (CH ), 114.0 (CH ), 127.8 (2 CHAr), 129.6
2
2
2
(2CHAr), 133.3 (CqAr), 139.0 (CHalkene), 144.5 (CqAr).
5,11,17,23-Tetra-tert-butyl-25,27-bis(undec-109-enyl)oxy-
calix[4]arene 4. Potassium carbonate (6.4 g, 46.0 mmol)
was added to a solution of p-tert-butylcalix[4]arene (3.0 g,
4.6 mmol) in acetonitrile (60 mL). Compound 3 (3.0 g,
9.2 mmol) was added to the stirred mixture after 1 h, then
heated to reflux for 20 h and concentrated at reduced pressure
to give a crude product which was dissolved in dichloro-
methane. The solution was washed with 1 M HCl and distilled
water, dried over MgSO and evaporated in vacuo. The residue
4
was purified by column chromatography (SiO , CH Cl –
2
2
2
cyclohexane 1 : 4) to afford a 90% yield of white solid 4. dH
300 MHz, CDCl ) 1.01 (s, 18 H), 1.28 (s, 18 H), 1.30–1.50 (br
(
3
m, 24 H), 1.65 (m, 4 H), 2.04 (m, 4 H), 3.30 (d, J 12.9, 4 H),
Experimental
3
.96 (t, J 6.6, 4 H), 4.29 (d, J 12.9, 4 H), 4.91–5.02 (m, 4 H),
1
3
General procedures
5
.80–5.95 (m, 2 H), 6.84 (s, 4 H), 7.03 (s, 4 H). C NMR
, 100 MHz): 25.8 (CH ), 26.8 (CH ), 28.8 (CH ), 28.9
), 29.9 (CH ), 30.1 (CH ), 31.0 (CH , tBu), 31.6 (CH
tBu), 31.7 (CH ), 33.7 (CH ), 33.8 (Cq), 76.3 (CH O), 114.2
1
(CDCl
CH
3
2
2
2
H NMR spectra were recorded at room temperature on a
(
2
2
2
3
3
,
Bruker AC300 spectrometer using tetramethylsilane as refer-
ence; chemical shifts are reported in ppm. Elemental analyses
were performed at the Institut de Chimie des Substances
Naturelles (France). All chemicals were of reagent grade and
were used without further purification unless otherwise noted.
Toluene, tetrahydrofuran (THF), dimethylformamide (DMF),
dichloromethane and acetonitrile, received from Aldrich or
SDS, were distilled prior to use following standard methods.
2
2
2
(
(
(
CH ), 124.9 (2 CHAr), 125.3 (2 CHAr), 127.8 (CqAr), 132.7
2,
CqAr), 138.9 (CHalkene), 141.1 (CqAr), 146.5 (CqAr), 150.0
CqAr), 150.7 (CqAr), Anal. Calc. for C66 (953.47): C,
3.06; H, 10.02. Found: C, 82.92; H, 9.92%.
96 4
H O
8
5
,11,17,23-Tetra-tert-butyl-25,27-diethoxycarbonylmethyl-
eneoxy-26,28-bis(undec-109-enyl)oxy-calix[4]arene 5.
Compound 4 (2 g, 2.1 mmol) was dissolved under an argon
atmosphere in a solution of sodium hydride (0.4 g, 10.0 mmol)
in dry DMF (15 mL) and dry THF (50 mL). After stirring for
1 h and addition of ethyl bromoacetate (1.9 mL, 17.0 mmol),
the mixture was heated to reflux for 24 h. Most of the solvents
were evaporated under reduced pressure, dichloromethane
was added, and the solution was washed with 10% HCl and
distilled water. The organic layer was separated, dried over
Synthesis
Inorganic synthesis of the SBA-15 mesoporous silica. The
pure siliceous SBA-15-type matrix was synthesis from the
1
6
procedure reported by Zhao et al. 8 g of block copolymer
Pluronic P123 ((CH –CH –O–)20–(CH –CH(CH )–O)70
CH –CH –O)20, a gift from BASF) was first dissolved in
50 ml of 1.9 M HCl at 40 uC. 15.95 g of tetraethoxysilane
TEOS, purchased from Fluka) were added under stirring to
the previous solution kept at 40 uC. The initial molar ratio was
.0 TEOS : 0.018 P123 : 6.2 HCl : 181 H O. The final solution
was transferred to a closed polyethylene flask and aged at 40 uC
2
2
2
3
–
(
2
2
2
(
MgSO
product, which was purified by column chromatography
(SiO , CH Cl –methanol 9 : 1) to provide a 80% yield of
orange oil 5. d (300 MHz, CDCl ) 0.97 (s, 18 H), 1.17 (s,
4
and concentrated in vacuo to furnish the crude
1
2
2
2
2
H
3
2
966 | J. Mater. Chem., 2005, 15, 2965–2973
This journal is ß The Royal Society of Chemistry 2005

View Article Online
1
3
8 H), 1.25–1.40 (br m, 30 H), 1.92 (m, 4 H), 2.07 (m, 4 H),
5,11,17,23-Tetra-tert-butyl-25,27-[(59-N,N-dimethyl-
aminonaphthalene-19-sulfonyl)carbamoylmethoxy]-26,28-
bis(undec-119-tri e´ thoxysilyl)oxy-calix[4]arene 2.
Divinyltetramethylsiloxane platinum catalyst (100 mL, 0.1 M
xylene solution, 0.01 mmol) was introduced under argon
atmosphere in a carefully degassed solution of compound 7
(0.26 g, 0.17 mmol) and triethoxysilane (0.23 mL, 1.2 mmol) in
dry toluene (3 mL). The mixture was heated to reflux for 12 h,
and evaporated in vacuo. The residue was purified by flash
column chromatography (SiO , CH Cl –acetone 7 : 3) to
.16 (d, J 12.5, 4 H), 3.82 (t, J 7.4, 4 H), 4.20 (m, 4 H), 4.63 (d,
J 12.9, 4 H), 4.82 (s, 4 H), 4.91–5.03 (m, 2 H), 5.75–5.88 (m,
2
H), 6.63 (s, 4 H), 6.90 (s, 4 H).
5
,11,17,23-Tetra-tert-butyl-25,27-dicarboxymethyleneoxy-
5
2
6,28-bis(undec-109-enyl)oxy-calix[4]arene 6. Compound
(
1.8 g, 1.6 mmol) was dissolved in a solution of sodium
hydroxide (15%) in ethanol. The mixture was refluxed for 5 h,
then concentrated under reduced pressure. Dichloromethane
was added, the solution was washed with 10% HCl, dried over
MgSO4 and concentrated in vacuo. After purification by
2
2
2
provide a 67% yield of dark oil 2. dH (300 MHz, CDCl ) 0.08
3
(m, 4 H), 1.07 (s, 18 H), 1.15 (s, 18 H), 1.20–1.30 (br m, 42 H),
column chromatography (SiO
2
, CH
2
Cl
2
–methanol 95 : 5), a
3
(300 MHz, CDCl )
1.94 (br m, 8 H), 2.86 (s, 12 H), 3.30 (d, J 11.8, 4 H), 3.85 (q, J
7.0, 12 H), 3.99 (m, 4 H), 4.28 (d, J 12.1, 4 H), 4.42 (s, 4 H),
7.00 (s, 4 H), 7.09 (s, 4 H), 7.14 (d, J 7.5, 2 H), 7.50 (m, 4 H),
6
1
4
4
7
2
2
1% yield of white solid 6 was obtained. d
H
.09(br s, 18 H), 1.17 (br s, 18 H), 1.25 (br s, 24 H), 1.80 (br s,
H), 2.01 (m, 4 H), 3.30 (d, J 12.5, 4 H), 4.15 (m, 4 H), 4.3–
.40 (br m, 8 H), 4.89–4.99 (m, 4 H), 5.72–5.87 (m, 2 H), 7.00–
1
3
8.34 (d, J 7.5, 2 H), 8.48 (d, J 8.1, 2 H), 8.63 (d, J 8.2, 2 H).
C
NMR (CDCl , 100 MHz): 10.3 (CH –Si), 14.0 (CH ), 18.2
3
2
2
1
3
.20 (br s, 8 H). C NMR (CDCl
3
, 100 MHz): 25.6 (CH
), 29.4 (CH
2
),
),
(
CH
CH
3
), 22.6 (CH
2
), 25.7 (CH
2
), 29.3 (CH
2
), 29.6 (CH
2
), 30.0
), 33.8
6.8 (CH ), 28.8 (CH ), 28.9 (CH ), 29.1 (CH
2
2
2
2
2
(
2
), 31.1 (CH
3
, tBu), 31.2 (CH
3
, tBu), 31.8 (CH
2
9.5 (CH ), 29.6 (CH ), 30.2 (CH ), 31.1 (CH , tBu), 31.3
3
2
2
2
3 2 2
(Cq), 34.0 (Cq), 45.3 (CH ), 58.1 (CH ), 76.9 (CH O), 78.0
(
CH , tBu), 33.7 (CH ), 33.7 (CH ), 33.9 (Cq), 75.5 (CH O),
3
2
2
2
2 , , ,
(CH O), 114.5 (CHAr ), 121.1 (CHAr ), 123.1 (CHAr ), 125.5
7
1
1
2
7.2 (CH O), 114.1 (CH2,), 125.4 (2 CHAr), 126.4 (CqAr),
(
(
(
(
CHAr ), 126.4 (CHAr ), 127.0 (CHAr ), 128.8 (CHAr ), 129.9
, , , ,
33.1 (CqAr), 134.6 (CHAr), 139.1 (CHalkene), 146.5 (CqAr),
47.3 (CqAr), 148.9 (CqAr), 149.4 (CqAr).
CqAr), 130.0 (CqAr), 134.4 (CqAr), 134.5 (CqAr), 139.0
CqAr), 146.8 (CqAr), 147.7 (CqAr), 148.4 (CqAr), 149.6
CqAr), 151.2 (CqAr), 174.8 (CqAr), Anal. Calc. for
5,11,17,23-Tetra-tert-butyl-25,27-[(59-N,N-dimethylamino-
naphthalene-19-sulfonyl)carbamoylmethoxy]-26,28-bis(undec-
C
106 156 4 16 2 2
H N O S Si (1862.69): C, 68.35; H, 8.44; N, 3.01.
Found: C, 69.70; H, 8.9; N, 2.6%.
1
2
0
09-enyl)oxy-calix[4]arene 7. Oxalyl chloride (0.25 mL,
.7 mmol) was added to a solution of compound 6 (0.32 g,
.3 mmol) in anhydrous benzene (12 mL) under an argon
Grafting of compound 3 on mesoporous silica particles. SBA-
1
5 mesoporous silica particles (0.5 g) were dried under vacuum
for 4 days at 150 uC and then introduced into dry toluene
10 mL) under an argon atmosphere. After stirring for 30 min,
atmosphere. The mixture was heated to reflux for 5 h and the
solvent was quickly removed in vacuo. Without further
purification, the intermediate product was immediately intro-
duced under argon in a solution of dansylamide (0.6 g,
(
compound 3 (65 mg, 35 mmol) in dry toluene was added
dropwise through a pressure-equalizing dropping funnel to the
suspension. The reaction mixture was stirred at room
temperature for 2 h and heated to reflux for 20 h. Grafted
2
.4 mmol) and potassium hydride (0.45 g, 3.9 mmol) in dry
THF (15 mL). The mixture was stirred for 10 h at room
temperature. After destroying the excess of KH and evapora-
tion of the solvent, dichloromethane was added and the
mixture was carefully washed with a solution of saturated
sodium chloride, 1 M HCl and Millipore filtered water. The
organic layer was evaporated under reduced pressure, and the
mesoporous silica particles were intensively centrifuged (2 6
3
0 rpm) with chloroform (90 mL) and methanol (200 mL) and
1
desiccated for one week. Elemental analyses (%) for grafted
SBA-15: C, 4.48; N, 0.14%.
crude product was purified by column chromatography (SiO
CH Cl –methanol 98 : 2) to afford a 48% yield of dark oil 7.
dH (300 MHz, CDCl ) 1.08 (s, 18 H), 1.15 (s, 18 H), 1.20–1.40
2
,
SBA-15 characterisation. SBA-15 silica materials were
characterized before and after functionalization with com-
pound 2 by X-ray diffraction (Phillips 1130, CrKa radiation
2
2
3
(
(
br m, 24 H), 1.92 (br s, 4 H), 2.01 (m, 4 H), 2.86 (s, 12 H), 3.30
˚
(l 5 2.29 A)), N adsorption–desorption (Micromeritics
2
d, J 12.2, 4 H), 3.99 (m, 4 H), 4.29 (d, J 12.4, 4 H), 4.43 (s, 4 H),
ASAP 2010) for surface area and porous size distribution
29
4
7
8
.90–5.04 (m, 2 H), 5.75–5.86 (m, 2 H), 7.01 (s, 4 H), 7.09 (s, 4 H),
evaluation,
Si MAS (Magic Angle Spinning) and CP
.13 (d, J 7.7, 2 H), 7.48 (m, 4 H), 8.34 (d, J 7.4, 2 H), 8.46 (d, J
13
(
Cross Polarization)-MAS NMR and C CP-MAS NMR
Bruker MSL300, nSi 5 59.6 MHz, n 5 75.5 MHz, t(p/6) 5
.5 ms/recycle delay 5 60 s for MAS experiments, t(p/2) 5
13
.5, 2 H), 8.63 (d, J 8.4, 2 H). C NMR (CDCl , 100 MHz): 25.6
3
(
C
(
(
(
CH
2
2
), 28.9 (CH
), 30.0 (CH
2
), 29.1 (CH
), 31.1 (CH
), 76.9 (CH
2
), 29.3 (CH
, tBu), 31.2 (CH
O), 78.0 (CH
2
), 29.4 (CH
2
), 29.8
1
4
CH
2
3
3
, tBu), 33.8
29
.5 ms/recycle delay 5 10 s/contact times 5 5 ms ( Si) or 2 ms
Cq), 34.0 (Cq), 45.3 (CH
3
2
2
O),
13
(
C) for CP-MAS experiments).
1
1
1
1
1
13.9 (CHAr ), 114.5 (CH ), 121.1 (CHAr ), 123.1 (CHAr ),
,
2,
,
,
25.5 (CHAr
,
), 126.4 (CHAr
,
), 127.0 (CHAr
,
), 128.8 (CHAr
,
),
Fluorescence measurements
29.9 (CqAr), 130.0 (CqAr), 134.3 (CqAr), 134.5 (CqAr),
39.0 (CqAr), 139.2 (CHalkene), 146.8 (CqAr), 147.7 (CqAr),
48.4 (CqAr), 149.6 (CqAr), 151.2 (CqAr), 174.8 (CqAr). Anal.
2
8
21
21
cm
Millipore filtered water (conductivity , 6 6 10
V
at 20 uC) and acetonitrile from Aldrich (spectrometric
grade) were employed as solvents for fluorescence measure-
ments. Sodium thiocyanate, potassium thiocyanate, calcium
Calc. for C H N O S + CH Cl (1616.83): C, 70.47; H,
9
4
124
4
10
2
2
2
7
.84; N, 3.46. Found: C, 70.55; H, 7.77; N, 3.49%.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2965–2973 | 2967

View Article Online
perchlorate, copper(II) perchlorate, zinc perchlorate, cadmium
perchlorate, mercury(II) perchlorate, mercury(II) nitrate and
lead(II) thiocyanate, from Aldrich or Alfa Aesar, were of the
highest quality available and vacuum dried over P O prior to
IV which is characteristic of a mesoporous material. The sharp
condensation capillary step observed at about P/P 5 0.74
indicates a narrow pore size distribution. An average pore size
0
1
8
˚
of 66 A was calculated by the Barret–Joyner–Halenda (BJH)
method from the adsorption branch. The surface area
2
5
use. Solutions at pH 4.0 were prepared with perchloric acid
1
calculated by the Brunauer–Emmet–Teller (BET) method is
9
(
99.99%) in water.
2 21 20,21
710 m g .
Corrected emission spectra were obtained on a Jobin-Yvon
Spex Fluorolog 1681 spectrofluorometer. Fluorescence mea-
surements were done in a 1 cm quartz cuvette containing a
magnetic-stirred suspension of grafted mesoporous silica
Synthesis and grafting of the fluoroionophore 2 on SBA-15
mesoporous silica
(
0.10–0.25 mg) in 2.5 mL of water at pH 4.0. The emission
The synthesis of the fluoroionophore 2 was performed
according to Scheme 2. 1-Hydroxyundec-10-ene was tosylated
with toluene-p-sulfonyl chloride in the presence of triethyl-
spectra were obtained after an equilibration time of 2 h. The
thermodynamical constants and photophysical parameters
were determined by using the Specfit Global Analysis System
V3.0 for 32-bit Windows system, which provided the
complexation constants with good accuracy. This software
uses singular value decomposition and non-linear regression
2 2
amine in CH Cl to afford 3 in 75% yield. The reaction of two
equivalents of 3 with 4-tert-butylcalix[4]arene and 10 equiv. of
K CO in acetonitrile gave the dialkylate compound 4 in 90%
2
3
yield. The reaction of the two remaining hydroxyl groups of 4
with ethyl bromoacetate with NaH in dry DMF led to 5 in 80%
yield, and the following saponification of the obtained ester
afforded the acid 6 in 61% yield. Compound 7 was obtained in
1
7
modeling by the Levenberg–Marquardt method. For this
analysis, the ligand concentration was evaluated from ele-
0
mental analysis of carbon and nitrogen to be C 5 3.5 6
1
2
2
L
2
6
21
mol L for a suspension of 0.25 mg of 2-SBA-15 in
0
4
8% yield by reaction of the corresponding diacyl chloride,
2+
2
.5 ml of H O. Unfortunately, concentrations of Cu above
obtained from the treatment of compound 6 with oxalyl
2
3
21
mol L
6 10
could not be investigated because of
chloride, with dansylamide (5-(dimethylamino)-naphthalene-1-
22
sulfonamide) and KH in dry THF. The hydrosilylation of
interfering precipitation of the cations.
compound 7 was finally performed by using a catalyst
Results and discussion
(
divinyltetramethylsiloxaneplatinum) according to the proce-
2
dure described by Audebert et al. The compound was isolated
3
Characterisation of the SBA-15 mesoporous silica
1 13
in 67% yield. H and C and elemental analysis confirmed the
The X-ray diffraction (XRD) pattern of the calcined SBA-15
structure of the compound. Furthermore, all the calixarene-
1
based systems showed H NMR spectra characteristic of a
mesoporous silica showed four peaks in the range of 2H 5
2
cone conformation. For such compounds, a cone conforma-
4
1
–4u that can be indexed in a two-dimensional (2-D) hexagonal
˚
structure (p6mm) and correspond to the d100 (92.7 A), d
110
tion of the final ligand is actually desired for optimizing the
2+
˚
54.0 A), d2 (46.9 A) and d
˚
˚
(35.7 A) d-spacings. The
(
selectivity towards Hg , as already described in our previous
7
work. Grafting of 2 on SBA-15 was achieved by refluxing a
00
210
˚
unit cell parameter ahex was calculated to be 107.0 A (a
5
hex
2d100/!3). The presence of these distinct reflections is indicative
suspension of silica in a toluene solution of 2, considering that
of long-range order. The N -sorption isotherm obtained is type
2
the ethoxysilane groups of the fluoroionophore react with the
Scheme 2 Synthesis of the fluoroionophore 2.
2
968 | J. Mater. Chem., 2005, 15, 2965–2973
This journal is ß The Royal Society of Chemistry 2005

View Article Online
n
shifts and relative amounts of the Q units are similar for both
unfunctionalized and functionalized SBA-15 silica materials.
Consequently, the post-synthesis procedure of the grafting of
fluoroionophore 2 did not change much the structure of the
parent material. No T units corresponding to any condensed
species from the silylated fluoroionophore 2 could be clearly
2
9
observed by Si MAS and CP-MAS on the functionalized
SBA-15 sample. These results suggest that the amount of
grafted fluoroionophores 2 is probably too low to be
2
9
detectable by the
Si NMR technique under classical
3
1
acquisition conditions. However, a
C CP-MAS NMR
spectrum recorded on the functionalized SBA-15 sample
exhibited broad resonances at 17 (–CH –Si and –CH –CH –
2
2
2
Si), 30–34 (–OCH
tert-butyl, CH
8–63 (CH –CH
21–Si–), 121–154 (aromatic carbons) and 179 ppm (–CO–)
2
–(CH
2
)
9
–CH
2
Si– from R
2
, C and CH
3
from
2
from calixarene macrocycle), 45 (N–CH
3
),
5
3
2
–O–Si), 69–85 (–O–CH –CO– and –O–CH –
2
2
10
C H
that are characteristic of the fluoroionophore 2. This result is
consistent with the introduction of fluoroionophore 2 as an
intact organic moiety. Two weight losses of 0.5 and 2% were
observed by TGA–DTA analysis in the temperature ranges
Scheme 3 Grafting of compound 2 on mesoporous silica particles.
5
0–100 uC and 310–410 uC, respectively. The first weight loss
2
5
silanol groups of silica (Scheme 3). Too high loadings of
fluorophores could result in aggregate formation that causes
self-quenching of the fluorescence.
associated with an endothermic peak with a maximum at 80 uC
is due to the removal of physisorbed water molecules. The
second weight loss associated with an exothermic peak with a
maximum at 375 uC is mainly due to the decomposition of the
organic moiety. From this second weight loss, the amount of
organic moieties was calculated to be about 0.07 mol%
Characterisation of the functionalized SBA-15
The XRD pattern recorded on the functionalized SBA-15
mesoporous silica displayed three distinct peaks corresponding
(
relative to the silicon content) while about 0.43% was initially
introduced. This value may be compared to that estimated
from the elemental analysis of nitrogen: 0.15%. The relative
discrepancy between those two measurements is explained by
the very low grafting rate. Assuming a statistical monolayer
dispersion of the grafted species, the surface concentration is
˚
˚
˚
to the d100 (89.7A), d110 (63.0 A) and d200 (46.2 A) d-spacings
of a 2-D hexagonal structure. The cell parameter ahex was
˚
calculated to be 103.6 A. A type IV isotherm was obtained by
N -sorption analysis showing that the material is mesoporous
2
with a narrow pore size distribution. An average BJH pore size
˚
of 64.2 A was measured from the adsorption branch. A BET
2
2
22
y1.5 6 10
molecules nm , and the average distance
between the fluoroionophores is then estimated to be y80 A˚ .
Even if the distribution of surface hydroxyl groups was
partially heterogeneous, leading to a non-statistical coverage
2
21
surface area of 520 m g was calculated. A lower value of the
BET surface area is usually observed after post-synthesis
grafting of organic moieties on the pore surface of ordered
2
9
of grafted fluoroionophores as described by both Lochm u¨ ller
2
6
mesoporous silicas.
The CBET parameter that is a measure of the adsorption
3
0
and our previous works, the density of molecules is therefore
low enough to allow the fluoroionophores to be considered as
single molecules, without any interaction.
2
7
force of the first adsorbed layer and is directly related to
the N2 affinity for the surface of the material decreased to
1
00 (CBET 5 140 for unfunctionalized SBA-15 sample) for the
Fluorescence and complexing properties of the functionalized
mesoporous silica 2-SBA-15
functionalized SBA-15 sample. This result is consistent with
2
the presence of organic moieties on the pore surface.
8
Both XRD and N -sorption analyses showed that the
2
(1) Photophysical properties of the functionalized mesoporous
silica. The emission spectrum of a 2-SBA-15 suspension in
water at pH 4.0 showed a noticeable blue shift of y30 nm
as compared to that of 1 in a mixture of CH CN–H O
hexagonal arrangement of the mesopores was not affected
during the functionalization process. The slight decrease of the
cell parameter ahex observed for the functionalized SBA-15
sample may be due to a small contraction of the network that
occurred during the functionalization process.
3
2
(60 : 40 v/v) at the same pH (Fig. 1). Such a shift can be
explained by the difference in solvent nature and by the
possible interaction of the fluorophores with the matrix.
Moreover, according to our previous study on the photo-
physical properties of calixarenes bearing two and four dansyl
2
9
Si MAS and CP-MAS NMR spectra recorded on the
functionalized sample showed three resonances at 291.8,
2
101.0 and 2109.8 ppm that are characteristic of the Q , Q
3
2
4
and Q units (Q 5 Si(OSi) (OH) , n 5 2–4), respectively,
n
31
n
42n
fluorophores in homogeneous solutions, it is likely that
2
forming the silica framework. Relative amounts of Q , Q and
3
the proportion of the basic dansyl group is larger in the case of
2-SBA-15. Interactions of 2 with the matrix could in fact lead
to some deprotonation of the fluorophore through acid–base
4
Q units of 4, 26 and 70%, respectively were measured from the
2
deconvolution of the Si MAS NMR spectrum. The chemical
9
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2965–2973 | 2969

View Article Online
Fig. 2 Emission spectra of 2-SBA-15 (0.25 mg) in the presence of
Fig. 1 Emission spectra of 2-SBA-15 in water (0.25 mg in 2.5 mL) at
two different pH values (pH 4.0 and 6.3, full lines). For comparison,
the dotted line represents the emission spectrum of 1 in a mixture of
2
increasing concentration of Hg in water (2.5 mL) at pH 4.0. lexc
+
5
3
50 nm. Inset: Evolution of the normalized fluorescence I/I
0
of 2-SBA-
3 2
5 (lem 5 540 nm) and 1 (C 5 1.6 6 10 M, CH CN–H O 6 : 4 v/v,
2
2
5
1
3 2
CH CN–H O 6 : 4 v/v (pH 4.0). lexc 5 350 nm.
+
pH 4.0, lem 5 575 nm) as a function of Hg
.
reaction with the silica surface. In other respects, no broad-
ening of the emission spectrum is noticed after grafting.
case of 1 (see inset of Fig. 2). Since no mercury is expected to
3
be adsorbed on the unfunctionalized mesostructured silica,
2
2
2) Hg -induced photophysical changes and complexing
+
the fluorescence titration data were analyzed by considering
only the complexation between the grafted calixarene-based
(
properties of 2-SBA-15. Before reporting the complexation
effect of mercury on the photophysical properties of 2-SBA-15,
it is worth examining the complexing and photophysical
properties of compound 1. In an acetonitrile–water mixture
2+
fluorescent ligand and Hg . Analysis of the whole emission
spectra upon mercury binding by means of the Specfit software
(global analysis) showed that the titration curve is consistent
with the formation of a single complex with 1 : 1 stoichiometry
2+
(
60 : 40 v/v) at pH 4, the complexation by Hg induces a
5
strong quenching of the fluorescence and a slight blue shift of
the emission band (20 nm). A very efficient and thermo-
dynamically allowed electron transfer from the dansyl
fluorophore to the metal center (DGET y 2.7 eV) is responsible
and a stability constant of 5 6 10 . The value obtained
with compound 1 in a mixture of CH CN–H O (60 : 40 v/v) is
3 2
7
1.5 6 10 , i.e. 53 times larger. Such a difference is likely to be
due to the different solvent and/or to the lower flexibility of the
grafted calixarene.
7
for such a drastic fluorescence quenching. The emission blue
2+
shift is due to a deprotonation of the sulfocarboxamide group
1
of the dansyl fluorophore upon complexation. H NMR
Regarding the photophysical effects induced by Hg
binding, the fluorescence quenching is less efficient for the
2-SBA-15 than in the case of 1 in a mixture of CH CN–H O,
which can be tentatively explained by i) a small fraction of
experiments in CD CN/D O (60 : 40 v/v) revealed that the free
3
3
2
2
ligand exists simultaneously in the cone, partial cone and 1,3-
alternate conformations proving a very fast interconversion
2+
fluoroionophores that might be unreachable by Hg ions and
ii) a reduced efficiency of electron transfer due to reduced
flexibility of the grafted fluoroionophore. Some additional
steric effect or unfavourable conformations could then lead to
a reduction of the electron transfer rate. We can expect for
instance that the distance between the bound cation and the
sulfocarboxamide group of the dansyl is a bit higher than in
complexes of 1 in solution. Such an explanation is consistent
with the lower electron transfer efficiency that is observed in
the case of the calixarene bearing four dansyl groups compared
2+
of the calixarenes. Upon complexation with Hg , only the
cone conformation of the calixarene was observed, which
2+
shows that the Hg cation fixes the calixarene into the cone
7
conformation.
The complexing studies of the fluoroionophore grafted on
SBA-15 were carried out on a 2-SBA-15 suspension in water at
controlled pH (pH 4.0). The measurements were done at pH 4
in order to observe the strongest photophysical effects upon
cation binding. In fact, since the complexation of a cation
induces a deprotonation of the dansyl fluorophore, larger
photophysical effects are expected when a high proportion of
the fluorophores in the calixarene unit are in the neutral
7
to compound 2.
The sensing ability of the functionalized material 2-SBA-15
is then mainly governed by the high affinity of the grafted
ligand for mercury(II). No specific effect of the surface was
observed. The mesoporous silica can thus be considered as
an inert matrix with respect to the complexation process, as
3
1
2+
form. Upon gradual addition of small amounts of Hg , a
strong quenching and a slight blue shift (12 nm) of the
emission spectra of 2-SBA-15 were observed (Fig. 2). But
the extent of the fluorescence quenching is not as large as in the
3
3
already mentioned in recent works, which allows one to
2
970 | J. Mater. Chem., 2005, 15, 2965–2973
This journal is ß The Royal Society of Chemistry 2005

View Article Online
Fig. 3 a) Emission spectra (lexc 5 350 nm) of 2-SBA-15 and its complexes in water at pH 4.0. b) Normalized fluorescence response I/I
2+
0
of 2-SBA-
2+
+
1
5 (0.25 mg in 2.5 mL of water at pH 4.0) as functions of cation concentration: Hg , Cu , and Na (lexc 5 350 nm, lem 5 540 nm). The curves
fitting the experimental points were calculated using the SPECFIT software.
2+
control independently the different properties of the organic–
inorganic hybrid system.
than with 1 in solution. The selectivity for Hg is higher than
y40 with respect of the other cations.
As seen in Fig. 3b, the concentration ranges where the com-
plexation induces changes in fluorescence are very different
according to the cation. These changes appear at much
(
3) Interference with other cations. Let us examine now
+
+
the effects of possible interfering cations such as Na , K ,
2
+
2+
2+
2+
2+
2+
Ca , Cu , Zn , Cd and Pb . Upon addition of these
cations to a solution of compound 1 in a mixture of CH CN–
O (60 : 40 v/v) or to 2-SBA-15 in water, changes in the
lower concentration with Hg than with all other cations, in
accordance with the relative stability constants of the
complexes.
3
H
2
+
2+
fluorescence spectrum were observed only with Na , Pb and
2
+
Cu . It should be noticed again that these changes are less
pronounced for 2-SBA-15 than for 1 in solution. A steric
hindrance of the grafted fluoroionophore may explain this
difference. Fig. 3a displays the fluorescence spectra of 2-SBA-
(4) Analytical performance of the functionalized SiO
2
for
mercury detection in water. A response time of only a few
2
+
seconds was observed upon addition of Hg
(Fig. 4).
Furthermore, the reversibility of the process was clearly
demonstrated by adding a large excess of EDTA in the
mercury-complexed 2-SBA-15, which induces an instanta-
neous increase of the fluorescence signal. The fluorescence is
1
5 and its complexes determined from the titration data
analysis. For both 1 and 2-SBA-15, a blue shift of the emission
+
2+
spectrum was observed upon Na and Pb binding which
indicates that cation binding induces a deprotonation of
the sulfocarboxamide group of the dansyl fluorophore.
In the case of copper(II) binding, both energy transfer
and electron transfer from the fluorophore to the complexed
cation may be invoked to explain the observed fluorescence
quenching.
Regarding the stability constants of the complexes of
+
2+
2+
compound 1 with Na , Pb and Cu (see Table 1), they
were found to be much lower than that observed for the
2+
mercury complex. The selectivity for Hg , expressed as the
ratio of the stability constants, is higher than y500 with
respect to the other possible interfering cations. Such an
2+
outstanding selectivity of compound 1 towards Hg should be
emphasized. The stability constants obtained for the com-
plexes with 2-SBA-15 (see Table 1) were found to be smaller
Table 1 Stability constants (expressed as logK) of compound 1 and
compound 2-SBA-15 determined by fluorescence spectroscopy
2+
+
2+
2+a
Hg
Na
Pb
Cu
Fig. 4 Time-dependent fluorescence response of 2-SBA-15 (0.25 mg
2
a
1
2
a
7.20 ¡ 0.28 4.49 ¡ 0.05 4.00 ¡ 0.10 4.64 ¡ 0.05
5.47 ¡ 0.02 3.90 ¡ 0.15 3.10 ¡ 0.10 3.16 ¡ 0.05
+
b
in 2.5 mL of water at pH 4.0) upon addition of 30 mm of Hg followed
by an addition of 100 mM of EDTA (sodium salt). lexc 5 350 nm;
-SBA-15
b
CH
3
CN–H O (60 : 40 v/v) at pH 4.
2
2
H O pH 4.
lem 5 540 nm.
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2965–2973 | 2971

View Article Online
2
7
21
mol L , (iii) this material shows a very high
3
.3 6 10
selectivity towards Hg
2+
over interfering cations at low
concentration. This work showed the possibility to combine
the complexing and photophysical properties of a well-tried
fluoroionophore with a well-defined mesoporous silica, to
obtain a fully optimized system for mercury sensing. The use
of a mesoporous silica as a support for grafting fluoroiono-
phores opens new opportunities to achieve an efficient optical
sensor for heavy metals in water.
ab
ab
c
R e´ mi M e´ tivier, Isabelle Leray,* B e´ n e´ dicte Lebeau* and
ab
Bernard Valeur
CNRS UMR 8531: Laboratoire de Photophysique et Photochimie
a
Supramol e´ culaires et Macromol e´ culaires, D e´ partement de Chimie,
ENS-Cachan, 61 Avenue du Pr e´ sident Wilson, F-94235 Cachan Cedex,
France. E-mail: icmleray@ppsm.ens-cachan.fr; Fax: 331 4740 2454;
Tel: 331 4740 2704
b
Laboratoire de Chimie G e´ n e´ rale, Conservatoire National des Arts et
M e´ tiers, 292 rue Saint-Martin, F-75141 Paris Cedex, France
CNRS UMR 7016: Laboratoire de Mat e´ riaux a` Porosit e´ Contr oˆ l e´ e,
Fig. 5 Normalized fluorescence response I/I
0
of 2-SBA-15 (0.15 mg in
2.5 mL of water at pH 4.0) in the presence of various metal ions (3 mm).
c
The dark bars represent the response of 2-SBA-15 in the presence of
Ecole Nationale Sup e´ rieure de Chimie de Mulhouse, 3 rue Alfred
Werner, F-68093 Mulhouse Cedex, France.
E-mail: Benedicte.Lebeau@uha.fr; Fax: 333 8933 6885;
Tel: 333 8933 6882
the cation of interest. The light bars represent the response upon
2
+
addition of 3 mm of Hg to a solution of 2-SBA-15 and the cation of
interest. I corresponds to the emission of 2-SBA-15 without cation.
exc 5 350 nm and lem 5 540 nm.
0
l
References
almost fully restored under these conditions. These important
features can be accounted for by the very fast diffusion times in
1
J. Sanz, J. C. Raposo, J. Larreta, I. Martinez-Arkarazo, A. de
Diego and J. M. Madariaga, J. Sep. Sci., 2004, 27, 1202.
˚
2 E. Lambertsson and E. Bj o¨ rn, Anal. Bioanal. Chem., 2004, 380,
71–875.
mesoporous materials (pore size of y65 A). The variation of
8
the emission intensity at 540 nm as a function of the mercury
concentration can be used as a calibration curve for mercury
detection (see inset of Fig. 2). The detection limit calculated as
three times the standard deviation of the background noise
3
(a) A. P. de Silva, H. Q. N. Gunaratne, T. Gunnlaugsson,
A. J. M. Huxley, C. P. McCoy, J. T. Rademacher and T. E. Rice,
Chem. Rev., 1997, 97, 1515; (b) B. Valeur and I. Leray, Coord.
Chem. Rev., 2000, 205, 3.
2
1
27
21
4 (a) L. Prodi, C. Bargossi, M. Montalti, N. Zaccheroni, N. Su,
J. S. Bradshaw, R. M. Izatt and P. B. Savage, J. Am. Chem. Soc.,
was found to be 66 mg L (3.3 6 10 mol L ) and linear
measurement is possible until 800 mg L (4 6 10 mol L
2
1
26
21
)
2
000, 122, 6769; (b) K. Rurack, M. Kollmannsberger, U. Resch-
with good accuracy. These parameters and the range of
concentration accessible are very similar to the analytical
properties of compound 1 in solution, which means that the
analytical characteristics are entirely preserved after grafting
the fluoroionophore on mesoporous silica. The selectivity is a
conjunction of two factors: stability constants and cation-
induced photophysical changes. The interfering cations such as
Genger and J. Daub, J. Am. Chem. Soc., 2000, 122, 968; (c)
J. D. Winkler, C. M. Bowen and V. Michelet, J. Am. Chem. Soc.,
1
998, 120, 3237; (d) H. Sakamoto, J. Ishikawa, S. Nakao and
H. Wada, Chem. Commun., 2000, 2395; (e) M. E. Padilla-Tosta,
J. M. Lloris, R. Martinez-Manez, M. D. Marcos, M. A. Miranda,
T. Pardo, F. Sancenon and J. Soto, Eur. J. Inorg. Chem., 2001,
1
475.
5
(a) A. B. Descalzo, R. Martinez-Manez, R. Radeglia, K. Rurack
and J. Soto, J. Am. Chem. Soc., 2003, 125, 3418; (b) E. M. Nolan
and S. J. Lippard, J. Am. Chem. Soc., 2003, 125, 14270; (c) X. Guo,
X. Qian and L. Jia, J. Am. Chem. Soc., 2004, 126, 2272; (d) A. Ono
and H. Togashi, Angew. Chem., Int. Ed., 2004, 43, 4300.
R. M e´ tivier, I. Leray and B. Valeur, Chem. Commun., 2003, 996.
R. M e´ tivier, I. Leray and B. Valeur, Chem. Eur. J., 2004, 10, 4480.
8 (a) Fiber Optic and Chemical Sensors and Biosensors, ed.
O. S. Wolfbeis, vol. 1 & 2, CRC Press, Boca Raton, Florida,
+
2+
2+
Na , Pb , Cu induce smaller photophysical effects than
2+
Hg (Fig. 3b), and the effects are even negligible if we consider
the fluorescence intensity at lem 5 540 nm. Finally, the
selectivity diagram (displayed in Fig. 5) clearly shows an
extremely good selectivity for mercury at low concentration
against all the other cations tested.
6
7
1991; (b) H. Hisamoto and K. Suzuki, Trends Anal. Chem., 1999,
18, 513; (c) E. Bakker, P. B u¨ hlmann and E. Pretsch, Chem. Rev.,
1997, 97, 3083.
Conclusion
9
(a) M. Ayadim, J. L. Habib-Jiwan, A. P. De Silva and
J. Ph. Soumillion, Tetrahedron Lett., 1996, 39, 7039; (b) N. J. van
der Veen, S. Flink, M. A. Deij, R. J. M. Egberink, F. C. J. M. van
Veggel and D. N. Reinhoudt, J. Am. Chem. Soc., 2000, 122, 6112;
(c) E. Brasola, F. Mancin, E. Rampazzo, P. Tecilla and
U. Tonellato, Chem. Commun., 2003, 3026–3027.
A calixarene-based fluoroionophore was synthesized and
grafted on SBA-15 mesostructured silica. The characterization
of this organic–inorganic hybrid material by XRD, NMR
spectroscopy and TGA–DTA analysis shows that the meso-
scopic arrangement of the host solid and the structure of the
grafted fluoroionophore are not affected during the function-
alization process. The ability of this new sensing material
1
1
0 K. Moller and T. Bein, Chem. Mater., 2003, 10, 2950.
1 (a) A. Stein, B. J. Melde and R. C. Schroden, Adv. Mater., 2000,
1
2, 1403–1419; (b) B. J. Scott, G. Wirnsberger and G. D. Stucky,
Chem. Mater., 2001, 13, 3140–3150; (c) C. Sanchez, B. Lebeau,
F. Chaput and J.-P. Boilot, Adv. Mater., 2003, 15, 1969.
2 (a) X. Feng, G. E. Fryxell, L. Wang, A. Y. Kim, J. Liu and
K. M. Kemner, Science, 1997, 276, 923; (b) R. I. Nooney,
M. Lakyanaraman, G. Kennedy and E. J. Maginn, Langmuir,
2001, 17, 528; (c) A. Walcarius, M. Etienne and J. Bessiere, Chem.
2+
to detect Hg in water was clearly demonstrated: (i) a
rapid response of only few seconds is observed, (ii)
mercury(II) complexation induces a strong quenching of the
fluorescence that allowed us to determine a detection limit of
1
2
972 | J. Mater. Chem., 2005, 15, 2965–2973
This journal is ß The Royal Society of Chemistry 2005

View Article Online
Mater., 2002, 14, 2757; (d) A. Walcarius, M. Etienne and
B. Lebeau, Chem. Mater., 2003, 15, 2161.
20 D. Zhao, Q. Huo, J. Feng, B. F. Chmelka and G. D. Stucky, J. Am.
Chem. Soc., 1998, 120, 6024.
1
3 A. Walcarius, N. L u¨ thi, J.-L. Blin, B.-L. Su and L. Lamberts,
Electrochim. Acta, 1999, 44, 4601; S. Sayen, M. Etienne, J. Bessi e` re
and A. Walcarius, Electroanalysis, 2002, 14, 1521; A. Walcarius,
M. Etienne, S. Sayen and B. Lebeau, Electroanalysis, 2003, 15, 414;
W. Yantasee, Y. Lin, T. S. Zemanian and G. E. Fryxell, Analyst,
21 M. Imp e´ ror-Clerc, P. Davidson and A. Davidson, J. Am. Chem.
Soc., 2000, 122, 11925.
22 G. G. Talanova, N. S. A. Elkarim, V. S. Talanov and R. A. Bartsch,
Anal. Chem., 1999, 71, 3106.
23 P. Audebert, S. Sallard and S. Sadki, J. Phys. Chem. B, 2003, 107,
1321.
24 Calixarenes 2001, ed. Z. Asfari, V. B o¨ hmer, J. Harrowfield and
J. Vicens, Kluwer Academic, Dordrecht, 2001.
25 I. Leray, M. Ayadim, C. Ottermans, J. L. Habib Jiwan and
J. P. Soumillion, J. Photochem. Photobiol. A, 2000, 132, 43.
26 D. Brunel, A. Cauvel, F. Fajula and F. DiRenzo, Stud. Surf. Sci.
Catal., 1995, 97, 173.
27 L. Jelinek and E. sz. Kov a´ ts, Langmuir, 1994, 10, 4225.
28 D. Brunel, A. Cauvel, F. Fajula and F. DiRenzo, Stud. Surf. Sci.
Catal., 1995, 97, 173.
2003, 128, 467; W. Yantasee, Y. Lin, G. E. Fryxell and B. J. Busche,
Anal. Chim. Acta, 2004, 502, 207.
1
1
4 L. Nicole, C. Boissi e` re, D. Grosso, P. Hesemann, J. Moreau and
C. Sanchez, Chem. Commun., 2004, 2312; E. Palomares, R. Vilar
and J. R. Durrant, Chem. Commun., 2004, 362.
5 (a) A. B. Descalzo, D. Jimenez, M. D. Marcos, R. Martinez-
Manez, J. Soto, J. El Haskouri, C. Guillem, D. Beltran, P. Amoros
and M. V. Borrachero, Adv. Mater., 2002, 14, 966; (b) V. S.-Y. Lin,
C.-Y. Lai, J. Huang, S.-A. Song and S. Xu, J. Am. Chem. Soc.,
2001, 123, 11510; (c) G. Wirnsberger, B. J. Scott and G. D. Stucky,
Chem. Commun., 2001, 119; (d) A. B. Descalzo, K. Rurack,
H. Weisshoff, R. Martinez-Manez, M. Dolores Marcos,
P. Amoros, K. Hoffmann and J. Soto, J. Am. Chem. Soc., 2005,
29 C. H. Lochm u¨ ller and M. T. Kersey, Langmuir, 1988, 4, 572.
30 R. Metivier, I. Leray, M. Roy-Auberger, N. Zanier-Szydlowski
and B. Valeur, New J. Chem., 2002, 26, 411; R. M e´ tivier, I. Leray,
J.-P. Lef e` vre, M. Roy-Auberger, N. Zanier-Szydlowski and
B. Valeur, Phys. Chem. Chem. Phys., 2003, 5, 758.
31 R. M e´ tivier, I. Leray and B. Valeur, Photochem. Photobiol. Sci.,
2004, 3, 374.
127, 184.
1
1
1
1
6 D. Zhao, J. Feng, Q. Huo, N. Melosh, G. H. Fredrickson,
B. F. Chmelka and G. D. Stucky, Science, 1998, 279, 548.
7 H. Gampp, M. Maeder, C. J. Meyer and A. D. Zuberb u¨ hler,
Talanta, 1985, 32, 95.
32 L. Mercier and T. Pinnavaia, Environ. Sci. Technol., 1998, 32,
2749–2754.
8 P. Barrett, L. G. Joyner and P. Halenda, J. Am. Chem. Soc., 1951,
7
3, 373.
9 S. Brunauer, P. H. Emmett and E. Teller, J. Am. Chem. Soc., 1938,
0, 309.
33 R. Casasus, M. D. Marcos, R. Martinez-Manez, J. V. Ros-Lis,
J. Soto, L. A. Villaescusa, P. Amoros, D. Beltran, C. Guillem and
J. Latorre, J. Am. Chem. Soc., 2004, 126, 8612.
6
This journal is ß The Royal Society of Chemistry 2005
J. Mater. Chem., 2005, 15, 2965–2973 | 2973