Chemistry Reference
In-Depth Information
O
O
O
O
O
O
N
N
O
O
N
NN
Cu
N
O
O
N
N
O
O
O
O
O
O
Figure 3.11. Scheme of the CuPc(OC
2
OBz)
8
molecule.
exchange within the layers is antiferromagnetic and a magnetic ordering transition
is observed at 13.5 K.
The LB technique provides some degree of control over intermolecular mag-
netic interactions. This has been proven for the radical C
n
PNN. Magnetic stud-
ies performed on a LB ML were compared to the same molecule in a cast film.
Superconducting quantum interference device (SQUID) magnetometry revealed
weak antiferromagnetic interactions in the cast film, with
9 K. In con-
trast, a ML deposited onto silica displays ferromagnetic interactions with
θ
W
−
0
.
θ
W
2
.
5
K (Gallani
et al.
, 2001).
From themechanical point of viewunusually robust fibre bundles can be achieved
by compression of large planar molecules. This is the case for Pcs modified at eight
positions with benzyloxyethoxy groups, CuPc(OC
2
OBz)
8
and H
2
Pc(OC
2
OBz)
8
,
which formclosed packed arrays (see Fig. 3.11).When these self-organizingmolec-
ular systems are compressed on the surface of a LB trough, the Pc columns align
parallel to the compression barriers and form rigid bilayer films that can be me-
chanically removed from the trough, preserving their integrity. This behaviour arises
from the multiple
interactions between adjacent Pcs, resulting in strong non-
covalent interactions (Smolenyak
et al.
, 1999).
Finally, although this topic has been intentionally not focused on polymers, there
is an example worth being discussed, since it illustrates the importance of some
π
−
π
