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Kyosuke Isoda et al.
tive oxidation of 2a and 2b, with PbO in CHCl (see the
Supporting Information).
phase are observed as sharp peaks at 183.5 and 169.98C, re-
spectively.
2
3
Unsubstituted FFV molecules are nearly insoluble in or-
ganic solvents except for DMSO and DMF. However, the
long-chain alkoxy substituents of 2a and 2b conferred high
The X-ray diffraction (XRD) pattern of 1a at 258C re-
veals three reflection peaks at 42.0 ꢂ (100), 24.2 ꢂ (110),
and 21.0 ꢂ (200) in the low-angle 2q region with the recip-
p
solubility in various organic solvents, including CHCl , ace-
rocal d-spacing ratio of 1: 3:2 (Figure 2). These results
3
tone, ethyl acetate, and even n-hexane.
Of the four compounds, the UV/Vis spectrum of 1a dis-
plays the lowest energy absorption maximum at 440 nm in
CH Cl , which is bathochromically shifted as compared to
2
2
that of 2a at 419 nm (Figure S1, Supporting Information).
This indicates that p-conjugation in 1a is expanded by the
oxidation of 2a: the 20p electron system of 2a is converted
[15]
into the 18p one of 1a with Hꢁckel aromaticity, and the
electronic character of the system is changed from the anti-
[15]
aromatic species 2a to the aromatic 1a. The behavior of
1
b and 2b is very similar to that of 1a and 2a.
The LC behavior of 1a and 2a is summarized in Table 1,
together with the phase transition behavior of 1b and 2b.
By differential scanning calorimetry (DSC), as shown in Fig-
Figure 2. X-ray diffraction patterns of two LC states at room tempera-
ture: (a) 1a in the hexagonal columnar structure and (b) 2a in the tetrag-
onal columnar structure.
imply that 1a self-assembles into a hexagonal columnar LC
structure. Meanwhile, 2a exhibits two reflection peaks at
Table 1. Liquid-crystalline behavior of 1 and 2.
[7]
[
a]
Compound
Phase transition
Col 73.6 (8.30) Iso
Cr 183.5 (38.78) Iso
3
2.4 ꢂ (100) and 22.9 ꢂ (110) with the reciprocal d-spacing
p
[
b]
1
1
2
2
a
b
a
b
h
ratio of 1: 2, which indicates self-assembly into a tetragonal
columnar LC structure. Furthermore, the intercolumnar
[7]
[
b]
Col
t
130.6 (3.79) Iso
Cr 169.9 (11.21) Iso
distance of 48.5 ꢂ in the LC phase of 1a at 258C is larger
than that of 32.4 ꢂ in 2a. This result suggests that each adja-
cent TANC moiety of 1a connects in a head-to-head forma-
tion with weak H-bonds of a CH···N type to form a 1D p-
stacking column (Figure S5, Supporting Information). Mean-
while, 2a also forms a 1D p-stacking column in the LC
state, similarly to 1a. However, each adjacent FFV moiety
of 2a is connected with strong H-bonds of the N-H···N type
in the lateral direction, thereby giving an alternative inver-
sion arrangement (Figure S5, Supporting Information). A
similar example, in which LC molecules based on imidazole
frameworks self-assembled into a tetragonal columnar struc-
ture analogous to 2a through strong H-bonds of the Nꢀ
[
a] Phase transition temperatures (8C) and enthalpy changes in parenthe-
ꢀ
1
ses (kJmol ) were determined by DSC measurements at the second
cycle at a scanning velocity of 108Cmin . Col
ꢀ1
h
: hexagonal columnar;
Col : tetragonal columnar; Cr: crystalline; Iso: isotropic. [b] No distinct
t
transition peaks were detected by DSC measurement above ꢀ1008C.
ure S2 in the Supporting Information, 1a and 2a maintain
columnar LC phases at room temperature, and their phase
transitions from isotropic liquids to columnar LC phases on
cooling have broad peak temperatures at 35.78C and
73.48C, respectively. The transition temperature for the for-
[24]
mation of the LC phase of 1a is much lower than that of 2a,
despite having similar mesogenic cores. The IR spectrum of
H···N type has been reported. Moreover, their intercolum-
nar distances of 48.5 ꢂ for 1a and 32.4 ꢂ for 2a in the col-
umnar LC phases, as estimated by XRD measurements, are
shorter than the fully extended molecular length of approxi-
mately 56 ꢂ for 1a and 43 ꢂ for 2a (Figure S5, Supporting
Information). The interdigitation of alkoxy chains between
the neighboring columns would occur in the columnar LC
phases.
2
a in the columnar LC state has an intense broad peak re-
ꢀ
1
lated to the n(NH) stretching vibration around 3200 cm ,
which is characteristic of an intermolecular H-bond of the
NꢀH···N type connecting the FFV frameworks of 2a (Fig-
ure S3, Supporting Information). On heating, when the
phase transition occurs from the columnar LC phase to the
isotropic liquid, the intensity of the n(NH) peak for 2a de-
creases. By contrast, the IR spectrum of 1a shows no
change in the analogous peak in relation to an intermolecu-
lar H-bond before or after the phase transition (Figure S4,
Supporting Information). The intermolecular H-bonds be-
tween the FFV frameworks of 2a would stabilize the forma-
tion of the columnar LC state. In contrast, 1b and 2b, with
linear chain alkoxy groups, exhibit no LC phases, and their
phase transitions from isotropic liquids to the crystalline
Macroscopically, the uniaxial alignments of these two col-
umnar LC structures are achieved by shearing 1a and 2a be-
tween sandwiched glass plates at room temperature. Obser-
vations by polarized light microscopy revealed that 1a and
2a tend to align parallel to the shearing direction. As shown
in Figure 3, the birefringence of the aligned samples of 1a
and 2a alternately changes between light and dark upon
a 458 rotation under the crossed Nicols condition (Figure 3
[25]
and Figure S6, Supporting Information).
&
&
Chem. Asian J. 2013, 00, 0 – 0
2
ꢀ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Isoda, Kyosuke
