Systematic extension of the length of the organic conjugated π-system of mesoporous silica-based organic-inorganic hybrid materials

Article abstract of DOI:10.1039/b801034j

The first systematic investigations on the optical properties of mesoporous silica-based organic-inorganic hybrid materials is reported. It could be shown that the optical absorption properties of the incorporated organic functionalities are tuneable by adjusting the length of the conjugation of the π-electron systems or by integration of heteroatoms therein. For this purpose, two new bis-silylated compounds with 18 π-electron systems, namely 4,4′-bis((E)-2-(triethoxysilyl)vinyl)stilbene and 1,2-bis(4-((E)-2- (triethoxysilyl)vinyl)phenyl)diazene and their related mesoporous hybrid materials, were synthesised. On the basis of solid state UV-vis absorption spectra it is demonstrated that for highly conjugated and elongated organic bridges the absorption maximum reaches the visible region resulting in a yellow powder for a pure hydrocarbon backbone and a deep red powder for an azobenzene containing material.

Full text of DOI:10.1039/b801034j

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PAPER
www.rsc.org/materials | Journal of Materials Chemistry
Systematic extension of the length of the organic conjugated p-system
of mesoporous silica-based organic–inorganic hybrid materials†
a
Maximilian Cornelius, Frank Hoffmann, Boris Ufer, Peter Behrens and Michael Froba
b
c
c
b
*
¨
Received 21st January 2008, Accepted 27th March 2008
First published as an Advance Article on the web 18th April 2008
DOI: 10.1039/b801034j
The first systematic investigations on the optical properties of mesoporous silica-based organic–
inorganic hybrid materials is reported. It could be shown that the optical absorption properties of the
incorporated organic functionalities are tuneable by adjusting the length of the conjugation of the
p-electron systems or by integration of heteroatoms therein. For this purpose, two new bis-silylated
compounds with 18 p-electron systems, namely 4,40-bis((E)-2-(triethoxysilyl)vinyl)stilbene and
1,2-bis(4-((E)-2-(triethoxysilyl)vinyl)phenyl)diazene and their related mesoporous hybrid materials,
were synthesised. On the basis of solid state UV-vis absorption spectra it is demonstrated that for highly
conjugated and elongated organic bridges the absorption maximum reaches the visible region resulting
in a yellow powder for a pure hydrocarbon backbone and a deep red powder for an azobenzene
containing material.
heteroaromatic or saturated dendrimer-like moieties.6 Depend-
ing on the employed SDA and the reaction parameters like
temperature or pH value the mesopores can be adjusted within
a certain range. Furthermore these settings determine the pore
structure of the material, like hexagonal, cubic or lamellar. One
special and unique feature of these PMOs, which can not be
found in pure silica materials, is a crystal-like pore wall struc-
ture.7–12 The origin of these crystal-like arrangement of the
organic bridges is not yet fully understood but due to the fact that
this behaviour is only observed for rigid unsaturated or aromatic
compounds, i.e. molecules with p-electron systems, it is most
likely that this assembly is the result of a p-stacking effect.
Recently, Sayari and Wang13 and Cornelius et al.14 prepared
a novel PMO material with a fully conjugated 10 p-electron
system as an organic bridge which exceeds the benzene ring. This
was accomplished by synthesising the corresponding precursor
via a Pd-catalysed double Heck coupling of 1,4-dibromobenzene
with vinyltriethoxysilane. As was pointed out in our previous
paper14 this was only regarded as a starting point for new PMOs
with extended p-systems. Consequently, following this
approach, we present here not only two new organic–inorganic
hybrid materials with organic units comprising 18 fully conju-
gated p-electrons, thereby reaching the optical absorption region
of mesoporous hybrid materials as will be shown below, but we
also report for the first time on the systematic investigation of the
optical properties of such silica-based mesoporous hybrid
materials with p-systems in general. In particular the field of
organic–inorganic hybrid materials with special or unique optical
properties, for instance luminescence features,15,16 is a new and
interesting topic.
Introduction
Since the discovery of mesoporous materials in the early 1990s by
researchers of the Mobil Oil Company the scientific results within
this field of porous materials have expanded rapidly.1,2 With the
utilisation of supramolecular structure directing agents (SDAs)
formed by amphiphilic molecules, inorganic mesoporous mate-
rials became widely available. At first, these preparation routes
were applied in the synthesis of mesoporous pure silica materials.
As a logical consequence of these promising results different
research groups tried to transfer this procedure to silsesquiox-
anes, i.e. molecular precursors which were already well known
from sol–gel chemistry. The resulting organic–inorganic hybrid
materials should combine the major advantages of pure inor-
ganic materials like for instance thermal stability with the variety
of potential organic functionalisations within one homogeneous
material by offering a high specific surface area at the same time.
In 1999 a major breakthrough was achieved independently by
three working groups who succeeded in preparing a silica-based
ordered mesoporous organic–inorganic hybrid material, i.e.
periodic mesoporous organosilica (PMO).3–5 Up to now a variety
of functional organic groups, which are genuine integral part of
the pore walls, i.e. are covalently bonded on both ends to the
silica matrix, could be successfully incorporated within these
materials, among them, for instance, aliphatic, aromatic,
aInstitute of Inorganic and Analytical Chemistry, Justus Liebig University
Giessen, Heinrich-Buff-Ring 58, D-35392 Giessen, Germany
bInstitute of Inorganic and Applied Chemistry, University of Hamburg,
Martin-Luther-King-Platz 6, D-20146 Hamburg, Germany. E-mail:
michael.froeba@chemie.uni-hamburg.de; Fax: +49 40 428 38 6348; Tel:
+49 40 428 38 3137
cInstitute of Inorganic Chemistry, Leibniz University Hannover, Callinstr.
9, D-30167 Hannover, Germany
† Electronic
In order to gain deeper insights into the way in which the
optical properties depend on the length of the (conjugated)
p-system we investigated the following five mesoporous organic–
inorganic hybrid materials with increasing numbers of p-elec-
trons (the first three materials are already known from the
established stock of PMOs): ethene-bridged (1, 2 p-electrons),
supplementary
information
(ESI)
available:
Characterisation of the new organosilane precursors as well as ethene-,
benzene- and 1,4-divinylbenzene-bridged PMOs. See DOI:
10.1039/b801034j
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The synthesis of the new precursor with the diazene group (5)
was carried out in two steps with (E)-4,40-dibromoazobenzene as
the intermediate,20 followed by
a Heck coupling with
vinyltriethoxysilane. In a typical synthesis 10.0 g (0.029 mol)
(E)-4,40-dibromoazobenzene were mixed in approx. 120 ml
dimethylformamide in a 250 ml three-necked flask. To this
mixture 20 ml (0.096 mol) of vinyltriethoxysilane and 20 ml
(0.144 mol) triethylamine as well as 100 mg (8.6 ꢀ 10ꢁ4 mol)
tetrakis(triphenylphosphine)palladium(0) were added. After-
wards, this deep red-brown mixture was heated to 115 ꢂC
whereas the educt was dissolved completely. After stirring the
reaction mixtureꢂfor 4 d at this temperature the resulting solution
was cooled to 0 C to complete the precipitation of the formed
salt (HNEt3Br). After removal of the salt by filtration the solvent
and surplus liquid educts were removed under reduced pressure.
The residue was taken up in toluene and the insoluble solid was
removed by filtration. The filtrate was concentrated under
reduced pressure. The residue was extracted by Soxhlet extrac-
tion with n-hexane. After removal of the solvent a red oil was
obtained: 10.2 g (0.018 mol, yield: 62%). The product was
Fig. 1 Structural formulae and abbreviations of the organic bridges of
the mesoporous organic–inorganic hybrid materials, from which the
optical properties were investigated in this publication (Si ¼ Si(OEt)3).
benzene-bridged (2, 6 p-electrons), 1,4-divinylbenzene-bridged
(3, 10 p-electrons), 4,40-divinylstilbene-bridged (4, 18 p-elec-
trons), and 4,40-divinylazobenzene-bridged (5, 18 p-electrons)
hybrid material samples (for structural formulae see Fig. 1)
Since PMOs are regarded as promising materials for various
applications in the fields of chromatography, separation, fabri-
cation of low-k devices, immobilisation of bio-molecules and
catalysis, this work can also be regarded as a first step in order to
open up a new field of potential applications due to their tuneable
optical properties.
characterised by H and 13C NMR measurements and IR spec-
1
troscopy (for details see ESI,† Fig. S4–S6).
Syntheses of the hybrid materials. In a typical synthesis for the
4,40-divinylstilbene-bridged hybrid material 0.69 g (1.9 ꢀ 10ꢁ3
mol) of octadecyltrimethylammonium chloride (OTAC) was
dissolved under vigorous stirring in a solution of 0.08 g (2.0 ꢀ
10ꢁ3 mol) NaOH in 20 ml distilled water. Afterwards, a solution
of 0.75 g (1.3 ꢀ 10ꢁ3 mol) BTEVS in 2 ml THF was added in
order to adjust the molar ratio of the reaction mixture to BTEVS
1 : OTAC 1.47 : NaOH 1.48 : H2O 824. The suspension was
stirred at room temperature for 24 h followed by a hydrothermal
treatment in a closed PE autoclave at 95 ꢂC for 24 h. After
filtration the as-synthesised composite material was obtained as
a yellow powder which was washed three times with 200 ml of
distilled water. The surfactant was removed by Soxhlet extrac-
tion with ethanol/HCl (conc.) (100 : 3, v/v) for 8 h.
In a typical synthesis for the 4,40-divinylazobenzene-bridged
hybrid material 0.366 g (1.05 ꢀ 10ꢁ3 mol) of OTAC was dissolved
under vigorous stirring in a solution of 0.253 g (6.3 ꢀ 10ꢁ3 mol)
NaOH in 20 ml distilled water. Afterwards this solution was
added to 0.4 g (7.15 ꢀ 10ꢁ4 mol) BTEVAB in order to adjust the
molar ratio of the reaction mixture to BTEVAB 1 : OTAC 1.47 :
NaOH 8.84 : H2O 1552. The suspension was stirred at room
temperature for 24 h followed by a hydrothermal treatment in
a closed PE autoclave at 95 ꢂC for 24 h. After filtration the
as-synthesised composite material was obtained as a red powder
which was washed three times with 200 ml of distilled water. The
surfactant was removed by Soxhlet extraction with ethanol–HCl
(conc.) (100 : 3, v/v) for 8 h.
Experimental
Syntheses
All syntheses were carried out in vacuum-dried glass vessels with
purified and dry solvents under argon atmosphere using Schlenk
techniques. The chemicals were purchased from Sigma-Aldrich,
Fluka and ABCR and were used without further purification.
Precursor syntheses. The precursors 1–3 were synthesised
according to standard literature procedures.14,17,18
The synthesis of the new (pure hydrocarbon) organosilane
precursor (4) was accomplished via a two-step synthesis with
(E)-4,40-dibromostilbene as an intermediate.19 In the second step
a
palladium-catalysed double Heck coupling of (E)-4,40-
dibromostilbene with vinyltriethoxysilane was carried out. In
a typical synthesis 15.02 g (0.044 mol) of (E)-4,40-dibromo-
stilbene was added to 250 ml dimethylformamide in a 500 ml
three-necked flask. To this mixture 15 ml (0.11 mol) triethyl-
amine, 25 ml (0.12 mol) vinyltriethoxysilane and 0.148 g (1.28 ꢀ
10ꢁ4 mol) of tetrakis(triphenylphosphine)palladium(0) were
added. The educt dissolved completely during heating to 120 ꢂC.
After stirring the reaction mixture for 4 d at this temperature the
ꢂ
resulting solution was cooled to 0 C to complete the precipita-
tion of the formed salt (HNEt3Br). After removal of the salt by
filtration the solvent was removed under reduced pressure. The
residue was taken up in 150 ml CCl4 and the mixture was filtered
again. The solvent was again removed and the resulting brown
oil was taken up in 100 ml Et2O. After filtration the brownish
solution was concentrated. The obtained raw product (light
brown oil) was purified by a twofold kugelrohr distillation under
high vacuum. 15.3 g (0.027 mol, yield: 61%) of the organosilane
precursor were obtained as a light yellow solid (solidification
occurred after cooling to room temperature). The product was
characterised by 1H and 13C NMR measurements and IR
spectroscopy (for details see ESI,† Fig. S1–S3).
Characterisation
Powder X-Ray diffractograms were recorded at room tempera-
ture on a PANalytical X0Pert PRO instrument by applying
filtered Cu-Ka radiation. The data in the SAXS region 2q < 10ꢂ
were recorded with the following setup: 25 s stepꢁ1; 0.0167ꢂ step
size; 0.518ꢂ active length of the detector; divergence slit 1/32ꢂ.
The data in the WAXS region 2q > 10ꢂ were recorded with the
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following setup: 20 s stepꢁ1; 0.0167ꢂ step size; 2.122ꢂ active 2q
range of the detector; fixed radiated length of 10 mm.
Transmission electron micrographs were obtained with
a Philips C 30 microscope operating at 300 kV.
of these signals an accurate calculation of the corresponding d-
values is not possible. The shapes as well as the low intensities of
these signals suggest that these reflections are not caused by
a strict crystal-like arrangement of the organic bridges but are
rather results of (i) diffuse scattering processes meaning that
intensity contributions will occur even if the Bragg condition is
not fulfilled—this might be provoked by lattice planes that are
not strictly parallel but show some modulations concerning their
relative preferential orientation, and (ii) the circumstance that
very short periodic assemblies of the organic spacers are present,
which extend only over a few lattice planes so that even
‘‘non-crystalline regions’’ do not exclusively lead to destructive
interference. In other words, even if the structure factor (|F|2) is
well defined, the convolution with the poor-defined lattice
function (5|G|2) can be responsible for the reflection shifts
compared to the expectation value, which would correspond
exactly to the length of the organic spacer.
Nitrogen physisorption data were recorded on a Quanta-
chrome Autosorb 6 instrument at 77 K. The BET surface areas
were calculated from the adsorption branch in the range of p/pꢂ
¼ 0.03–0.3 while the BJH pore diameter distribution was
determined from the desorption branch.
29Si MAS NMR spectra were recorded with a 7 mm MAS
system at a resonance frequency of 79.4 MHz using a Bruker
MSL-400 spectrometer. The samples were spun at 3.5 kHz.
Further experimental parameters were a p/2 pulse width of 6 ms,
a recycle delay of 300 s and 1500 scans.
The UV-vis spectra of the precursors in n-hexane solution were
recorded on an Agilent/HP-8453 spectrometer in the range from
200 to 800 nm. The solutions were diluted so that the absorbance
was below 1. The UV-vis measurements of the hybrid materials
were conducted in diffuse reflectance mode (Harrick or so-called
Praying Mantis setup on a Varian Cary 5E spectrometer); BaSO4
was used as white standard and dilutor. The obtained spectra
were re-calculated to remission function F(R) by applying the
Kubelka–Munk theory in order to ensure that pure diffusive
reflectivity values are obtained.21
The occurrence of only one very broad shoulder in the small-
angle region of the P-XRD diffractogram is supported by the
transmission electron micrographs (see ESI,† Fig. S13), in which
only a wormhole-like mesopore structure is observable but no
mesoscale ordering. Nevertheless, it is clearly visible that the
porosity extends over the whole hybrid material particles.
It is always useful to declare exactly the reasons which are
responsible if the ordering process in the presence of the SDA
failed, but a plausible explanation in this case could be the fact
that 4 is solid and therefore has to be dissolved in an organic
solvent prior to the hydrolysis and condensation step. This
organic solvent is able to disturb the formation of a liquid crystal
phase and therefore leads to non-periodic mesoporous hybrid
materials.
Results and discussion
As ethene-, benzene-, and 1,4-divinylbenzene-bridged hybrid
materials are already known in the literature and were
synthesised according to the procedures described therein the
characterisation (X-ray diffraction, N2 physisorption) of these
materials is only summarised in the ESI† (Fig. S7–S12).
The nitrogen physisorption measurement (Fig. 3) reveals an
isotherm typical of mesoporous materials with a capillary
condensation step at p/pꢂ ¼ 0.7. The mean pore diameter and the
pore volume, as determined from the desorption branch by the
BJH method, are 5.4 nm and 0.76 ꢀ 10ꢁ6 m3 gꢁ1, respectively. The
specific BET surface area amounts to 620 m2 gꢁ1. A possible
explanation for this high pore diameter value could be due the
fact that the hydrophobicity of the precursor increases with the
4,40-Divinylstilbene-bridged hybrid material
In Fig. 2 the powder X-ray diffractogram of the 4,40-divinyl-
stilbene-bridged hybrid material is shown.
This material reveals only one broad shoulder in the small
angle region at ca. 1.5ꢂ 2q, indicating that almost no periodicity
on the mesoscale is present. In addition four broad reflections,
approximately at 2q ¼ 4.8ꢂ (d ¼ 1.8 nm), 9.6ꢂ (0.9 nm), 14.5ꢂ
(0.6 nm) and 28.4ꢂ (0.3 nm), are observed. Note, due to the width
Fig. 3 Nitrogen adsorption–desorption isotherms of the mesoporous
4,40-divinylstilbene-bridged hybrid material and BJH pore size
distribution (inset) measured at 77 K.
Fig. 2 P-XRD pattern of the mesoporous 4,40-divinylstilbene-bridged
hybrid material. Small angle region (large), wide angle region (inset).
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Fig. 5 P-XRD pattern of the mesoporous 4,40-divinylazobenzene-
bridged hybrid material. Small angle region (large), wide angle region
(inset).
Fig. 4 Comparison of the IR spectra of 4 (black, top) and the
corresponding 4,40-divinylstilbene-bridged hybrid material (red, bottom).
length of the organic bridge. At the same time the polarity of the
precursor and of the structure directing agent are converging
which causes a diffusion of the precursor into the inner part of
the micelles as a result of ‘‘polarity matching’’. This process could
then lead to a swollen micellar shape which yields an increased
pore diameter within the hybrid material. Up to now this model
is still hypothetical; further investigations covering the double
role of the precursor as a swelling agent and as the framework
material are currently taking place.
in the wide angle region are probably caused by very few ordered
domains within almost X-ray amorphous particles.
In the TEM image of this sample only a wormhole-like
mesophase with no preferential direction of the channels is
observable (see ESI,† Fig. S14).
The nitrogen physisorption measurement shows a type IV
isotherm with a capillary condensation step at p/pꢂ ¼ 0.8 (Fig. 6).
The mean pore diameter and the pore volume, as determined
from the desorption branch by the BJH method, are 8.1 nm and
0.44 ꢀ 10ꢁ6 m3 gꢁ1, respectively. The specific BET surface area is
240 m2 gꢁ1. This unexpectedly high value for the pore diameter
could be explained by the same processes taking place as in the
case of the BTEVS related material (as mentioned above).
The IR spectra of 5 and the corresponding hybrid material are
shown in Fig. 7. Due to the similarity of this organic moiety to
the stilbene derivative almost the same vibrational modes are
detectable and can be assigned as follows: 803 cmꢁ1 (breathing
mode of the benzene ring); 1513 cmꢁ1 (d(C–H)i.p.arom.; 1600 cmꢁ1
(n(C]C)arom.); 1629 cmꢁ1 (n(C]C)vinyl.); 3422 cmꢁ1 (n(O–H)).
Again, for the same reasons as mentioned above, it can be
To investigate the status of the organic functionality within the
hybrid material two complementary methods were applied: (i) IR
spectroscopy and (ii) 29Si MAS NMR measurement. Based on
the results of the IR spectroscopic data (Fig. 4) it is possible to
check the integrity of the organic moieties as such, however, it is
not possible to inspect the status of the silicon–carbon bonds
with the help of vibrational spectroscopy, as was demonstrated
recently by Hoffmann et al.22 In order to determine the covalent
attachment of the organic spacers to the silica matrix solid state
29Si MAS NMR measurements were carried out (see ESI,†
Fig. S12). Therein only T2 and T3 (corresponding to C–Si
(OSi)2(OH) and C–Si(OSi)3 respectively) signals but no Qn
signals (attributed to silicon atoms tetrahedral surrounded by
oxygens) in the range <ꢁ90 ppm are visible, meaning that
virtually no Si–C bond cleavage occurred during the synthesis
procedure.
From the IR spectra of the hybrid material the following
vibrational modes can be assigned: 798 cmꢁ1 (breathing mode of
the benzene ring); 1512 cmꢁ1 (d(C–H)i.p.arom.); 1604 cmꢁ1
(n(C]C)arom.); 1626 cmꢁ1 (n(C]C)vinyl.); 3418 cmꢁ1 (n(O–H)).
With the logical exception of the O–H band (caused by
the silanol groups, which are formed during the hydrolysis
process) all other bands are also detected in the non-hydrolysed
precursor, clearly indicating the integrity of the organic moiety.
4,40-Divinylazobenzene-bridged hybrid material
Fig. 5 shows the X-ray diffraction pattern of the 4,40-divinyl-
azobenzene-bridged hybrid material.
Fig. 6 Nitrogen adsorption–desorption isotherms of the mesoporous
4,40-divinylazobenzene-bridged hybrid material and BJH pore size
distribution (inset) measured at 77 K.
It shows neither a periodic arrangement of the mesopores nor
a lamellar crystal-like pore wall structure. The broad reflections
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Fig. 7 Comparison of the IR spectra of 5 (black, top) and the
corresponding 4,40-divinylazobenzene-bridged hybrid material (red,
bottom).
Fig. 9 Comparison of the UV-vis spectra of the organic–inorganic
hybrid materials with various conjugated p-electron systems measured in
reflectance mode, plotted as remission function F(R).
concluded that the organic group is preserved after the synthesis
procedure.
experimental setup. Furthermore, due to the increasing
possibilities of electronic transitions in more extended p-systems
the absorption bands become broader. The obtained spectra are
in good agreement with the expected corresponding ones of the
pure, un-silylated hydrocarbon compounds, which are well
documented in the literature. A substitution of a hydrogen atom
with a silicon containing moiety should result in a bathochromic
shift of about +5 to +10 nm, due to the +I effect of silicon.
Note that in comparison to the precursor spectra the hybrid
materials (Fig. 9) show a slight bathochromic shift of the
absorption bands.
UV-vis measurements
In order to investigate the optical properties UV-vis spectra of
the precursors and of the corresponding mesoporous materials
were recorded. The position of the centre of gravity of the band
with the highest wavelengths corresponds to the energy of the
HOMO–LUMO transition. However, in order to describe the
optical signatures completely the indication of these positions is
not sufficient. In this case, the highest wavelength where
absorption occurs at all has also to be considered as this
contributes to the overall colour impression of the sample.
Therefore, we determined also the points where the absorption
curve begins to rise (from the low-energy side).
This shift is more pronounced for the 18 p-electron system
(approx. +32 nm) and less for the shorter organic bridges
(+8 nm). This effect may be attributed to p–p interactions
between adjacent unsaturated organic bridges, which should be
more intense for extended p-systems. For the 4,40-divinyl-
stilbene-bridged hybrid material the absorption reaches the
visible region, which results in a pale yellow colour of the sample.
In the case of the azobenzene derivative the absorption occurs
even within the green part of the visible spectrum due to a lower
excitation energy for the n–p* transition, resulting in a deep-red
colour of the material (see Fig. 10).
The UV-vis spectra of the precursors (Fig. 8) reveal a clear and
expected bathochromic shift with increasing length of the
(conjugated) p-system. The p–p* transition of the ethene-
bridged precursor should be located in the vacuum UV region,
i.e. below 185 nm, but is not detectable with the applied
All hybrid materials show relatively broad absorption bands in
their spectra. This broadening in comparison to the respective
precursor spectra is more pronounced for the longer organic
bridges and might be due to more extended vibronic couplings.
All structures of the precursors and the determined charac-
teristic absorption wavelengths as well as those of the hybrid
materials are summarised in Table 1.
Fig. 10 Photographs of the mesoporous hybrid materials with various
conjugated p-electron systems: a) ethene-, b) benzene-, c) 1,4-divinyl-
benzene-, d) 4,40-divinylstilbene-, e) 4,40-divinylazobenzene-bridged.
Fig. 8 Comparison of the UV-vis spectra of the organosilane precursors
with various conjugated p-electron systems in n-hexane solution.
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Table 1 Formulae and abbreviations of the precursors, the characteristic absorption wavelengths of the precursors and of the related hybrid materials
Precursora/hybrid materialb
Name
BTEE
Precursor/nm
—
Hybrid material/nm
—
BTEB
280
325
380
410
288
340
412
530
BTEVB
BTEVS
BTEVAB
a
Si ¼ Si(OEt)3. b Si ¼ SiO1.5
.
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By synthesising two completely new organosilane precursors,
each consisting of a fully conjugated 18 p-electron system, an
approach of extending the length of the organic bridge of
organic–inorganic hybrid materials was successfully developed.
Even though it was not possible to obtain real PMO materials
from these extended precursors we were able to show for the first
time that it is possible to obtain coloured mesoporous hybrid
materials from one single bis-silylated silica source, which may
open up new fields of applications, for instance those related to
chemical sensing. In this sense the portfolio of such organic–
inorganic hybrid materials was augmented considerably with the
work at hand, showing that is possible to tune the optical
properties, i.e. UV-vis absorption characteristics, by varying the
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Acknowledgements
´
´
´
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The authors thank Prof. M. Hunger (University of Stuttgart) for
the 29Si MAS NMR spectrum, G. Koch (Justus Liebig University
Giessen) for recording the TEM images and Dr P. Reisenauer
(Justus Liebig University Giessen) for helpful discussions
concerning the UV-vis spectra. Financial support by the Fonds
der Chemischen Industrie (FCI) is gratefully acknowledged.
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This journal is ª The Royal Society of Chemistry 2008