Chemistry Reference
In-Depth Information
Fig. 63
Conceptual design of Janus liquid-crystalline supermolecular systems, where the
Janusheadiscomposedofanematicliquidcrystal(
right
) and a smectic liquid crystal
left
Both Janus compounds,
52
and
53
, were isolated as single compounds in
a glassy state at room temperature. The predicted and experimental isotopic
distribution for the mass ion overlay each other identically confirming the
purity of the material and demonstrating the utility of Maldi-
tof
in the deter-
mination of structure in supermolecular systems.
On heating
52
, a broad melting endotherm with onset at 33.8
◦
C(
H
=
6.26 kJ mol
-1
) was followed by a transition from the liquid crystal state to the
liquid at 60.8
◦
C(
∆
H
= 2.73 kJ mol
-1
). The cooling cycle from the isotropic
liquid showed a broad, weak exotherm, onset at 60.3
◦
C, marking the tran-
sition to the chiral nematic phase. A second exotherm occurred on cooling,
onset 36.1
◦
C, marking a second-order transition to a chiral smectic C
∗
phase.
Further cooling induced a glass transition at approximately -2.8
◦
C. This se-
quence of events was reproducible in subsequent heating and cooling cycles.
It is noteworthy that the transitions have extremely low
∆
H
values, suggest-
ing that the system is relatively disordered and highly flexible. In addition, it
is important to note that the formation of chiral mesophases by compound
52
means that the nematic phase is thermochromic and the smectic C
∗
phase is
ferroelectric and pyroelectric and will exhibit electrostrictive properties.
In contrast, compound
53
exhibits only one enantiotropic transition by
DSC, which occurs between a chiral nematic phase and the isotropic liquid, in
∆
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