Chemistry Reference
In-Depth Information
Figure 3.12. Molecular structure of the amphiphilic polythiophene derivative dis-
cussed in the text.
crystal engineering concepts that are also relevant to the fabrication of conducting
molecule-based films. A series of amphiphilic regioregular polythiophene deriva-
tives have been prepared with alternating hydrophobic and hydrophilic side chains
as illustrated in Fig. 3.12 (Bjørnholm
et al.
, 1999). At the air/water interface,
the hydrophilic groups are directed to allow interaction with the water surface
while the hydrophobic tails can then orient away from the water surface as in a
traditional amphiphile. Langmuir films readily form under isothermic compres-
sion leading to densely packed MLs in which the polythiophene backbones are
π
-stacked parallel to the water surface. The stacking of the polymers is highly
ordered. When compressed beyond the collapse point on the trough the MLs spon-
taneously fold intomicrometre-long wire-like structures. Undoped bundles of wires
exhibit
10
−
5
−
1
cm
−
1
but when the bundles are exposed to iodine or AuCl
3
σ
RT
∼
−
1
cm
−
1
.
vapours,
σ
RT
increases up to 40
Self-assembled monolayers
SAMs are ordered molecular assemblies formed by the adsorption of an active
surfactant on a solid inorganic surface. As for the LB films case the molecules
exhibit two well-differentiated end groups: head and tail. The adsorbate interacts
with the surface through its head group, forming
strong covalent bonds
(sulfur-
gold, carbon-silicon), thus defining robust ML/solid interfaces. The tail chemi-
cal function can be selected (methyl, carboxylic acid, amides, etc.) and thus the
ML/environment interfaces can be chemically controlled. In SAMs the packing
and ordering are essentially determined by the contribution of the chemisorptive
