Microstructures
of the Porphyrin/Viologen Monolayer
on the Clay Surface: Segregation or Integration?
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Abstract
Microstructures
of the porphyrin/viologen monolayer on an anionic
clay surface (synthetic saponite) were investigated by the observation
of photochemical behavior of porphyrin. Fluorescence behaviors of
porphyrin–viologen–clay complexes were observed by steady
state and time-resolved fluorescence spectroscopy. Although fluorescence
of porphyrin was effectively quenched by coadsorbed viologen on the
clay surface, a part of the fluorescence of porphyrin was not quenched
and remained even at high loading level of viologen. According to
time-resolved fluorescence measurement, the decay profile of excited
singlet porphyrin can be analyzed by two- or three-component fitting
for porphyrin–viologen–clay complexes. These results
indicate that porphyrin and viologen adsorb with island (segregation)
structure on the clay surface. The size of the island formed by porphyrin
was quantitatively estimated for two kinds of porphyrins. It turned
out that the porphyrin molecular structure affects the size of the
island. It has been believed that electron transfer on a clay surface
is inefficient due to segregation of dyes between clay sheets (A.
J. Bard et al., <i>J. Phys. Chem.</i> <b>1984</b>, <i>88</i>, 5519). Our results indicate that segregation behavior
sensitively depends on the structure of the dye, and it is possible
to construct an efficient electron transfer system on the clay surface
