Chemistry Reference
In-Depth Information
Fig. 33 Oligophenylenevinylene, oligofluorene, oligofluorenevinylene, and polythiophene donor/
acceptor conjugates
ˀ
-conjugation of pCp-oPPV related to oPPV accounts for the approximately four
times greater damping factor [
251
].
The comparison of the charge transfer characteristics of oligofluorenes (oFl) 64
vs oligofluorenevinylenes (oFV) 65 shows that it is possible to tune the electronic
properties by slight structural alterations of the compounds. Specifically,
values
of 0.075
˚
1
are obtained for the oFV wires, lower than the value determined for
oFl (0.09
˚
1
)[
252
]. The vinylene groups improve the
ʲ
-conjugation of the wire in
such a way that charge injection into the bridge is favored, facilitating CS and CR
processes [
253
].
When oligothiophenes (nT) are employed as bridges, distances up to 55.7
˚
have
been reached between D and A. For these H
2
P-nT-C
60
systems, a dependency of
the
ˀ
value on solvent polarity was observed (0.11
˚
1
in
o
-dichlorobenzene and
0.03
˚
1
in benzonitrile) [
254
,
255
]. Due to the electron-donating ability of the
polythiophene oligomers, these bridges participate more actively in the CS/CR
processes, which take place almost via the electron-hopping mechanism.
Recently, supramolecular ZnP/C
60
hybrids connected by a Hamilton receptor
and employing different spacers as oPPE, oPPV,
p
-ethynylene, or fluorene have
been systematically studied [
256
]. These studies demonstrate that the electronic
communication between the donor and acceptor moieties is governed by the charge
transfer properties of the conjugated spacers. Thus, spacers with low
ʲ
ʲ
values
facilitate the charge transfer along the supramolecular bridge. The study of the
dependence of the rate constants of CS and CR on the D-A distances allowed the
calculation of the attenuation factor for the first time in a hydrogen-bonding-
mediated electron transfer, rendering a value of 0.11
˚
1
, which is similar to that
obtained for other covalent systems (Fig.
34
).
