Chemistry Reference
In-Depth Information
Fig. 32 Chemical structures of some ZnP/C
60
conjugates
with increasing distance between the donor and acceptor moieties is observed,
which implies a through-bond mechanism where the bridge plays an important
role. A damping factor of 0.11
0.05
˚
1
has been determined for these
ʲ
compounds [
247
]. This value is lower than the
value reported for similar systems
bearing exTTF as donor moiety (exTTF-oPPE-C
60
), for which an attenuation factor
of 0.21
˚
1
was determined. This difference has been accounted for by a much
more uniform distribution of the local electron affinity in ZnP-oPPE-C
60
62 due to
higher electron density of ZnP in comparison to exTTF. These results underline the
dependence of the
value and hence the wire-like behavior on the whole DBA
system and not only on the linker.
An extraordinarily small attenuation factor of 0.01
ʲ
0.005
˚
1
was determined
for compounds in which the donor exTTF and the acceptor C
60
are connected
through a
p
-phenylenevinylene oligomer 63 (exTTF-oPPV-C
60
)[
248
,
249
]. This
low
value has been explained attending to the
para
-conjugation of the bridge with
the donor exTTF and the homogeneous distribution of the local electron affinity
throughout the whole bridge. A remarkable value of ~5.5 cm
1
for the coupling
constant (
V
) was determined for these systems, unusually strong over a distance of
40
˚
from the electron donor to the electron acceptor. Analogous systems in which
the donor moiety has been substituted by a porphyrin 66 (ZnP-oPPV-C
60
) give rise
to a slightly higher
ʲ
0.005
˚
1
) due probably to a loss of conjuga-
tion between the donor ZnP and the linker [
250
] (Fig.
33
).
The systematic study of the wire-like behavior in systems in which ZnP/C
60
conjugates are connected through a
para
-cyclophane-oPPV (pCp-oPPV) bridge
has shown a
ʲ
value (0.03
0.001
˚
1
. The inhomogeneous and weaker
ʲ
value of 0.039
