Chemistry Reference
In-Depth Information
N
N
reversible
+
electron transfer
N
N
Fig. 28 Intermolecular complexation and electron transfer behavior between La
2
@C
80
and the
organic donor molecules TMPD
Another useful [2+1] cycloaddition process is the addition of diazocompounds,
generated in situ from tosylhydrazones in basic media, to fullerenes. This reaction has
been used for the preparation of relevant endohedral metallofullerene adducts in the
context of organic photovoltaics, such as endohedral metallofullerene (Sc
3
N@C
80
,
Lu
3
N@C
80
,orCe
2
@C
80
) PCBM-based derivatives [
221
] or the first D-A dyad where
an endohedral metallofullerene, Lu
3
N@C
80
, acts as an electron donor upon photoexci-
tation. In particular, when connected to perylenebisimide units [
222
].
Electrosynthetic routes have also been recently explored for the preparation of
endohedral metallofullerene adducts that might not be accessible by conventional
synthetic routes. In this sense, the different nucleophilicity observed by TNT
dianions [
223
] and trianions [
224
] seems to be particularly relevant for the prepa-
ration of Sc
3
@C
80
derivatives.
Surprisingly, the non-covalent functionalization of endohedral fullerenes has
been scarcely investigated, only a few examples about the complexation with
calixarenes and crown or thiacrown ethers are known, and size matching was
found to be critical to the stability of the resulting complexes [
176
]. The most
promising example is the formation of stable radical ion pairs of
N
-substituted
p
-phenylenediamine with La@C
82
and La
2
@C
80
[
188
,
225
]. Such spin-site
exchange processes are reversible in solution and are readily controllable by
changing the temperature and the solvent (Fig.
28
).
6 Fullerenes for Organic Electronics
As mentioned above, a huge number of fullerene derivatives have been prepared,
many of which have been tested in so-called organic molecular electronics. Their
remarkable electron-accepting ability and low reorganization energy combined
with solubility in organic solvents and outstanding photophysical properties have
made fullerenes a most appealing system to be used in the preparation of electronic
devices such as organic photovoltaics and the study of molecular wires, which are
discussed in detail in the following sections.
