surfactant, and in the thin film FS191 prepared in the presence
of P123.
1 and TEOS gave rise to a material in which the azobenzene
moieties are tightly packed, so that the isomerization process
was strongly hindered.
No isomerization of azobenzene was observed upon UV
irradiation of the thin films F1 and F191. In contrast, Fig. 8
shows the changes in the absorption spectrum of FS191 upon
UV irradiation. After 25 minutes of irradiation, a progressive
trans to cis isomerization was observed as a decrease in the
350 nm absorbance (Fig. 8b). UV irradiation for a longer
period did not cause further spectral change. Exposure to
room light for 20 minutes caused the reverse isomerization
(Fig. 8c), the intensity of the 350 nm absorption band
exceeding slightly that of the as-prepared film after 18 h
(Fig. 8d).
Thus, the present study shows that both methods allowing
the organization of hybrid materials, self-directed assembly
and surfactant-directed self-assembly, are complementary,
giving rise to materials with different properties.
Eric Besson,a Ahmad Mehdi,a Dan A. Lerner,b Catherine Reye´a and
Robert J. P. Corriu*a
aLaboratoire de Chimie Mole´culaire et Organisation du Solide, UMR
5637 CNRS, Universite´ de Montpellier II, Sciences et Techniques du
Languedoc, Place E. Bataillon, F-34095 Montpellier Cedex 5, France.
E-mail: reye@univ-montp2.fr; Fax: 33 467153852; Tel: 33 467143832
bENSCM, UMR 5618 CNRS, 8, rue de l’Ecole Normale, F-34296
Montpellier Cedex 5, France
This drastic difference concerning the photo-responsiveness
of azobenzene moieties located in the thin films FS191 and F191
is supported by their UV/visible spectra: the UV/visible
spectrum of FS191 is similar to that of 1 in solution. That
suggests that the bridged azobenzene moieties are sufficiently
away from each other in FS191 to allow the isomerization
process, as in solution and also at the surface of silica.24 In
contrast, the UV/visible spectrum of F191 was very different
from that of FS191 and close to that of F1 suggesting that in
F191 and F1, the azobenzene moieties are in close proximity.
This arrangement of azobenzene moieties should prevent the
isomerization process from occurring in both materials. This
situation is close of that observed by Brinker et al. in hybrid
silicates prepared by self-assembly from an azobenzene-
bridged silsesquioxane.25 In their case, the azobenzene moieties
should be in close proximity to each other and linked by
hydrogen bonding, which allows the self-assembly of the
material but hinders the isomerization process.
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808 | J. Mater. Chem., 2005, 15, 803–809
This journal is ß The Royal Society of Chemistry 2005