Chemistry Reference
In-Depth Information
Fig. 19
Bottom
: RAS spectra measured at LB layers of sapphyrin whose thicknesses nominally
are in the range 0-10 monolayers: (
a
) polycrystalline gold (
filled dots
); (
b
) 2 ML (
empty dots
); (
c
)
4ML(
crosses
); (
d
) 6 ML (
filled triangles
); (
e
) 8 ML (
empty triangles
); and (
f
)10ML(
filled
squares
).
Top
: RAS spectra measured at LB layers of sapphyrin whose thicknesses nominally are
in the range 12-20 monolayers: (
g
)12ML(
filled dots
); (
h
)14ML(
empty dots
);
i
)16ML
(
crosses
); (
l
)18ML(
filled triangles
); and (
m
)20ML(
empty triangles
). The absolute sign of the
RAS spectra is arbitrary. In the
inset
: structure of E
2
M
8
-sapphyrin. The two perpendicular optical
dipoles in the plane of the molecule are indicated by
arrows
(From Di Natale et al. [
32
].
Reproduced with permission. Copyright 2000, AIP Publishing LLC.)
whose parameters were determined on the base of a semiempirical quantum
chemistry approach, its structure being defined by using ab initio geometrical
optimization [
32
]. The following results were obtained from calculations: (i) the
optical anisotropy is not directly related to the sapphyrin ring itself, but it is mainly
due to the peripheral substituents; (ii) the main anisotropy structure measured
below 500 nm is associated to the in-plane optical anisotropy of the sapphyrin
molecule. RAS results thus provide a clear evidence of the ordering of the
sapphyrin molecules in the LB films studied. On the other hand, for coverages
below one monolayer, the possibility of RAS to give significant information about
