Chemistry Reference
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Fig. 14 The employed materials by Ogi and collaborators together with the structures of the
fabricated hetero-LB films (from [
41
])
shed light on the peculiarities of each process [
41
]. A polyimide derivative was used
as one of the materials constituting the LB films in consideration of enhanced
chemical, mechanical, and thermal characteristics of polymeric substances. The
typical thickness of a polyimide layer is about 0.40 nm. The ample availability of
polyimide derivatives permits to modulate the electronic characteristics of the
immobilized structures; in fact, the employed diimide moieties evidence substantial
electron affinity and hence their resulting LB films electron-accepting characteris-
tics. At the same time, porphyrins have been largely used as photo-absorbing
and electron-donating substances. In the light of these considerations, Ogi and
coworkers fabricated hetero-multilayers containing poly[isobutylmethacrylate-
-
5-(4-acryloyloxyphenyl)-10,15,20-triphenyl-porphyrin], indicated as poly(iBMA-
co
co
-AOTPP), and polyimide. Therefore, in the immobilized films, the transfer
process takes place from photoactivated porphyrins to the pyromellitic diimide
moieties in polyimide derivatives. This phenomenon was studied through the
quenching of the porphyrin fluorescence. The structure of the deposited hetero-
LB films is reported in the next figure, where PI is the polyimide and TPP the
tetraphenylporphyrin (Fig.
14
).
The Perrin model [
42
] was applied to this case; the fluorescence intensity
significantly diminishes as the number of polyimide layers increases. Then the
