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of columnar mesophases. The addition of alkyl chains encourages more over-
lap of the aromatic cores on account of alkyl-alkyl interactions and phase
segregation. Electron-rich/electron-poor aromatic pairs structurally achieve
a similar result by maximizing
-system overlap.
Bushby et al. were able to access similar AB stacks with derivatives of
25
using aromatic units, which are not electron-poor [86-88]. They showed that
hexakis(4-nonylphenyl)triphenylene (
28
,
n
= 8) forms alternating stacks with
25
(Fig. 13). Unlike the electron-deficient derivatives mentioned previously,
which exhibit single liquid crystal phases over a wide composition range of
the two components, phase separation between the
25
:
28
and the
25
or
28
mesogenic phases occurs [89]. The driving force for the AB stack formation
is a combination of a number of different non-covalent interactions which the
authors termed “complimentary polytopic interactions” (CPIs).
π
Fig. 13
Self-assembly of alternating stacks can be achieved with an electron-rich
25
and
electron-poor
26
or mellitic triimde
27
. Alternatively, complimentary polytopic interac-
tions (CPI) can be used to organize
25
and
28
as shown, yielding the desired assemblies
Electron donor-acceptor (EDA) stacks have been accessed by Percec
et al. [90] using partially fluorinated dendrons (Fig. 14) to form LC columnar
phases. The self-assembly of the dendrons is primarily driven by phase segre-
gation of the fluorinated chains and the aromatic units. Functionalization of
the dendrons at their apex with either an aromatic electroactive donor (
29a
)
or an acceptor (
29b
) group yields LC columnar structures, further aided by
the additional interaction between the aromatic units, which have optoelec-
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