Chemistry Reference
In-Depth Information
device irrespective of the high generation. This has been explained by negative steric
effects in the higher generation, which partially inhibits the
interactions with C
60
.
Aida and coworkers [21] have reported the preparation of fullerene-rich dendritic
structures resulting from the apical coordination of C
60
derivatives bearing pyridyl
moieties to dendritic molecules appended with multiple Zn(II) porphyrin units. For
example, compound
p
-
p
17
bound
18
strongly to form stable [(
17
)
(
18
)
12
] (Figure 6.8).
in CHCl
3
at 25
C,
Upon titration with
displayed a large spectral change in the
Soret and Q-bands, characteristic of the axial coordination of zinc porphyrins, with a
clear saturation profile at a molar ratio
18
17
exceeding 12. The average binding
affinity (K), as estimated by simply assuming a one-to-one coordination between the
individual zinc porphyrin and pyridine units, is 1.2
18
/
17
10
6
M
1
. This value is more
than 2 orders of magnitude greater than association constants reported for mono-
dentate coordination between zinc porphyrins and pyridine derivatives [22]. The
sizeable increase of stability can be ascribed to the simultaneous coordination of two
Zn centers of
17
by the two pyridine moieties of
18
. Similar increases in the
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2
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18
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18
[(
17
)
.
(
18
)
12
]
17
FIGURE 6.8
Compounds
17
and
18
and schematic representation of the self-assembly
process leading to the fullerene-rich dendrimer [(
17
)
(
18
)
12
].
