Chemistry Reference
In-Depth Information
Fig. 10 a
Chemical structures of benzene-1,3,5-tricarboxamide derivatives (
12
-
14
)which
form columnar phases through the assembly of
b
hydrogen-bonded stacks and
c
examples
of larger benzene-1,3,5-tricarboxamide derivatives, a bulky derivative (
15
)andalarge
intra-hydrogen-bond stabilized disc
16
, both of which are known form stable columnar
phases
than simply being used to hold pre-made discs together as is discussed
above. For example, Meijer et al. have reported the self-assembly of disc-
like structures driven by self-complementary four hydrogen bonded array
motifs. Figure 11a shows examples of two four hydrogen-bond motifs, ure-
idiotriazene (
17
) and ureidopyrimidinone (
18
) derivatives [82] which upon
dimerization form columnar mesophases (K 25 M 131 I and 25 M 180 I, respec-
tively for R = C
12
H
25
; M is an undefined mesophase). The same group has also
shown that tethering two of these supramolecular motifs with an appropriate
spacer results in ditopic materials (
19
and
20
) that also yield stable columnar
mesophases (Fig. 11b) [83]. These systems are akin to the main-chain polymers
discussed in the previous section but on account of a combination of the nature
of the spacer,
π
π
stacking and phase segregation, they form polymeric stacks
that organize into columnar mesophases. In the case of the ureidopyrimidinone
derivatives (
19
) the nature of the alkyl length, which was varied from 5 to 8, re-
sulted in dramatic changes in the stability of the mesophase. For example, for
-
Search WWH ::
Custom Search