Chemistry Reference
In-Depth Information
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(a)
(c)
(b)
(d)
Figure 7.14
Molecular structure of the 1,10-phenanthroline-based gelator.
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(a)
Micrograph of the gel under visible light, and (b), (c), (d) under UV-
light irradiation. (c) Shows the fluorescence of the gel after addition of
TFA, and (d) after a heating process was applied to the gel shown in (c).
photochromic materials and multiswitchable organogelators.
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For example,
Tian and coworkers have designed a fluorescent photochromic gelator based on
a bisthienylethene core bridging two naphthalimide-cholesteryl boundary
groups
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(Figure 7.15). Excellent reversible photochromic properties were
characterised for this low molecular weight gelator in its gel and liquid phases,
thus facilitating the description of a multistimuli-responsive system. Sur-
prisingly, when a yellow gel of the bisthienylethene derivative was irradiated
with UV light at 365 nm, a photoinduced ring closing was prompted, and a new
absorption band at round 537 nm appeared, turning the colour of the gel from
yellow to red (Figures 7.15a and b). This change in the absorption spectra was
attributed to the extended p-electron delocalisation favoured in its cyclic form,
and it was switchable by subsequent visible-light irradiation. Importantly, a
difference in the luminescence spectra between the two gel states was estab-
lished, while a strong fluorescence emission was observed in the cyclic form (460
nm), a weak fluorescence emission was characterised for the acyclic phase.
The use of metal ions in molecular gelators can give rise to materials with
very interesting optical properties, a subject that has received attention in
