Ion complexation-induced mesomorphic conversion between two columnar phases of novel symmetrical triads of triphenylene-calix[4]arene-triphenylenes

Article abstract of DOI:10.1016/j.tetlet.2012.11.029

Two novel symmetrical triads of triphenylene-calix[4]arene-triphenylenes 6a and 6b bridged by hydrazone spacers were synthesized in high yields. They possessed interesting ion complexation-induced mesomorphic conversion between two columnar phases. The neat compounds 6a and 6b showed mesophase with calixarene's bowlic column as cores. The Ag⁺-complexes of 6a and 6b exhibited mesophase with triphenylene column as cores.

Full text of DOI:10.1016/j.tetlet.2012.11.029

Tetrahedron Letters 54 (2013) 409–413
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Ion complexation-induced mesomorphic conversion between two
columnar phases of novel symmetrical triads of triphenylene-calix[4]arene-
triphenylenes
Fafu Yang a,b, , Xiaoyan Bai a, Hongyu Guo a, Congcong Li a
⇑
a College of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, PR China
b Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Two novel symmetrical triads of triphenylene-calix[4]arene-triphenylenes 6a and 6b bridged by hydra-
zone spacers were synthesized in high yields. They possessed interesting ion complexation-induced
mesomorphic conversion between two columnar phases. The neat compounds 6a and 6b showed meso-
phase with calixarene’s bowlic column as cores. The Ag+-complexes of 6a and 6b exhibited mesophase
with triphenylene column as cores.
Received 2 September 2012
Revised 15 October 2012
Accepted 6 November 2012
Available online 14 November 2012
Ó 2012 Elsevier Ltd. All rights reserved.
Keywords:
Triphenylene
Calix[4]arene
Mesophase
Synthesis
Complexation
Triphenylene derivatives with aliphatic chains are the most
widely studied discotic liquid crystals with possible various appli-
cations in organic light-emitting diodes, organic photovoltaic cells,
organic field-effect transistors, gas sensors, photocopying ma-
chines, etc.,1–4 All kinds of triphenylene derivatives were synthe-
sized and exhibited excellent mesomorphic properties in the past
decades.1–8 Recently, much attention was paid to the macrocy-
cle-modified triphenylenes. The mesomorphic properties of this
kind of compounds could be changed by the guest recognition of
macrocycle units. In 2010, Cammidge reported the triphenylene di-
mers linked by shape-persistent conjugated macrocycle and crown
ether macrocycle with interesting mesomorphic properties.9,10
Laschat and Peng also described the syntheses and mesomorphic
properties of a series of crown ether-based triphenylene dimers
at the same time, respectively.11–14 Lately, Wang synthesized tri-
phenylene-fused porphyrins with good UV–vis absorptions.15 All
these literatures indicated that the mesomorphic properties were
induced or influenced by the ion complexation behaviors of crown
ether units. Obviously, the mesomorphic properties tuned by the
complexation capabilities exhibited application prospects such as
ion-sensors, ion-selective supramolecular liquid crystals, and ion-
switch of liquid crystal. However, besides these few examples of
crown ether-modified triphenylenes, the other macrocycle-based
triphenylenes were almost unknown so far.
Calixarenes possess tuneable 3D-shaped cavities and are easily
modified to prepare various calixarene derivatives with unique
complexation properties.16,17 Some of the calixarene-based liquid
crystals were also synthesized by introducing the long alkyl chain
on the upper or lower rim of calixarene skeleton.18–23 Lately, we re-
ported the first examples of calixarene-linked triphenylene di-
mers.24,25 They exhibited interesting mesomorphic stacking
behavior with calixarene’s bowlic column as cores or triphenylene
column as cores. However, the influences of complexation behav-
iors on mesomorphic properties of these novel calixarene-linked
triphenylene were not investigated up to now. In this Letter, we
wish to describe the design and syntheses of two novel symmetri-
cal triads of triphenylene-calix[4]arene-triphenylenes 6a and 6b
bridged by aromatic hydrazone spacers. Moreover, the studies on
relationship between complexation and mesomorphic properties
indicated that they possessed an interesting ion complexation-in-
duced mesomorphic conversion between two columnar phases,
which was observed for the first time.
Scheme 1 showed the synthetic route of novel symmetrical tri-
ads of triphenylene-calix[4]arene-triphenylenes 6a and 6b bridged
by aromatic hydrazone spacers.
x-Bromo-substituted triphenyl-
enes 2a, 2b, and calix[4]arene 1,3-bis-hydrazide derivative 5 were
synthesized by literature methods, respectively.26,27 By reacting
compounds 2a or 2b with 4-hydroxy benzaldehyde, triphenylene
derivatives with aldehyde group 3a and 3b were obtained in yields
of 85% and 86%, respectively. Then by ‘1+2’ Schiff-base condensa-
tion of compounds 3a and 3b with compound 5 under CHCl3/
⇑
Corresponding author. Tel./fax: +86 591 83465225.
E-mail address: yangfafu@fjnu.edu.cn (F. Yang).
0040-4039/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2012.11.029

410
F. Yang et al. / Tetrahedron Letters 54 (2013) 409–413
OR
RO
RO
OR
Br
K2CO3
n Br
RO
OH
OR
RO
O
Br
n
RO
RO
2
OR
1
K2CO3, HO
CHO
RO
OR
RO
OH
O
O
CHO
n
3
RO
OR
NH2
NH
NH2
HN
O
O
O
EtO
O
O
OEt
O
OH
OH
OH
NH2NH2
O
O
But
But
But
But
But
But
But
But
4
5
OR
OR
OR
OR
RO
RO
OR
OR
RO
RO
O
O
O
O
CHCl3 / MeOH
5
3
+
CH
N
HN
CH
N
NH
O
O
R= -C5H11
OH
O
OH
O
6a ( n = 6 )
6b ( n = 10 )
But
But
But
But
Scheme 1. The synthetic route of novel triads of triphenylene-calix[4]arene-triphenylenes 6a and 6b.
MeOH system for 12 h, target triads 6a and 6b was successfully ob-
tained in yields of 88% and 86% with recrystallization, respectively.
Although compounds 6a and 6b were prepared by the stepwise
procedures, the separation of each step was simple with recrystal-
lization and the total yields were as high as 58%.
New compounds were characterized by elemental analyses, FT-
IR, ESI-MS, and NMR spectra. The ESI-MS spectra of them showed
corresponding molecular ion peaks. All the protons were assigned
well in their 1H NMR spectra. Two singlets (1:1) for the tert-butyl
groups and one pair of doublets (1:1) for the methylene bridges
in the calixarene skeleton of compounds 6a and 6b indicated that
the calix[4]arene units adopt a stable cone conformation.
metallic ions (CHCl3/H2O, 1 Â 10À3 M for both guest and host solu-
tions).28 The extraction percentages of 6a for Li+, Na+, K+, Ag+, Hg2+
,
and Cu2+ were 65.6%, 72.4%, 68.8%, 81.5%, 67.7%, and 57.5%, respec-
tively. The extraction percentages of 6b for these cations were 60.4%,
73.6%, 61.3%, 80.8%, 64.2%, and 60.1%, respectively. These results
indicated compounds 6a and 6b were excellent hosts for cations,
especially, for Ag+. In order to investigate deeply the complexation
behaviors, the 1:1 complexes of triads 6a(6b) with AgClO4 were pre-
pared in DMSO solutions. Their 1H NMR spectra were recorded as
shownin Figure 1. The peaks of NH and OH of triads 6a and 6b shifted
from high field to low field obviously. These results suggested the
NH and OH groups were involved in the coordination and the ions
were bound in the cavitiescomposed of N-containing chainsand cal-
ixarene skeletons in complexation systems.
The ion complexation abilities of compounds 6a and 6b were pre-
liminarily studied by liquid–liquid extraction experiments for

F. Yang et al. / Tetrahedron Letters 54 (2013) 409–413
411
cooling
LC
Cr
Cr
6b+Ag+
Iso
Iso
LC
Iso
6b
Cr
Cr
6b
LC
Iso
6b+Ag+
LC
second heating
Figure 1. The 1H NMR spectra of triads 6a, 6b, and their 1:1 complexes with
AgClO4.
50
100
150
Temperature (°C )
1.5
cooling
Figure 3. The DSC traces of 6b and complex 6a+Ag+ on second heating and cooling
(scan rate 10 °C minÀ1).
6a+Ag+
1.0
0.5
Iso
Iso
LC
LC
Cr
6a
Table 1
Cr
Cr
0.0
Phase transfer temperatures (°C) and associated enthalpy changes (kJ/mol in
parentheses) of 6a, 6b, and their complexes
-0.5
-1.0
-1.5
-2.0
-2.5
LC
Triads
Phase transitiona
T(
D
H) Heating scan
T(DH) Cooling scan
Iso
6a
6a
Cr–Col
Col–Iso
Cr–Col
Col–Iso
Cr–Col
Col–Iso
Cr–Col
Col–Iso
42.1(8.68)
32.6(7.88)
93.9(7.53)
Cr
100.3(10.93)
34.6(24.46)
128.1(40.17)
46.0(6.78)
113.7(9.97)
42.1(9.29)
LC
6a+Ag+
Iso
6b
34.1(28.54)
118.7(41.17)
31.1(6.89)
103.3(12.24)
41.0(19.79)
129.5(11.88)
second heating
6a+Ag+
6b+Ag+
50
100
150
142.4(12.66)
Temperature (°C)
a
Cr = crystalline, Col = columnar, Iso = isotropic.
Figure 2. The DSC traces of 6a and complex 6a+Ag+ on second heating and cooling
(scan rate 10 °C minÀ1).
In order to investigate the mesomorphic stacking behavior fur-
ther, triads 6a, 6b, and their complexes were studied by the XRD.
The results were shown in Figures 6 and 7. It was interesting that
neat compounds and complexes exhibited utterly different reflec-
tion peaks, which might suggest the different molecular stacking
behaviors for neat compounds and complexes.
Moreover, the mesomorphic behaviors of 6a, 6b, and their com-
plexes were studied. The complexes 6a and 6b with AgClO4 were
obtained by evaporating the solvent of the corresponding 1:1 com-
plexation DMSO solutions. Their DSC results were exhibited in Fig-
ure 2, Figure 3 and Table 1. All of them exhibited two phase
transitions upon second heating and cooling. For example, com-
pound 6a showed two phase transfer temperatures at 42.1 °C
and 100.3 °C upon second heating process and two reverse pro-
cesses at 32.6 °C and 93.9 °C on cooling. However, the phase trans-
fer temperatures of neat compounds 6a and 6b were different from
those of their complexes. Also, the mesomorphic ranges of com-
plexes became wider from 60 °C to 70 °C for 6a and from 94 °C
to 109 °C for 6b, respectively. These DSC results strongly implied
that mesophases existed on the melting process with state-meso-
phase-isotropic phase for 6a, 6b, and their complexes. The different
phase transfer temperatures indicated the complexation influ-
enced the mesomorphic properties greatly. These results were also
in accordance with the DSC results of complexes of crown ether-
As we reported previously,24,25 there had been two possible
mesomorphic staking behaviors for liquid crystal of calix[4]ar-
ene-linked triphenylene dimers as shown in Figure 8. One way
was calixarene column as cores, that is the calixarene’s bowlic col-
umn with two triphenylene units as ancillary lateral columns,
which should show the XRD peaks for both calixarene columns
and triphenylene columns (Fig. 8 (a)).24 Another way was triphen-
ylene column as cores, that is, triphenylene column with calixa-
rene units on ancillary lateral sides ( Fig. 8 (b)), which should
exhibit XRD peaks for triphenylene and might had some peaks
for calixarene column decided by the tropism of calixarene units.25
A survey of literatures indicated a low angle peak (2h = 2–4 and/or
5–6), a mid angle peak (2h = 8–9), and a broad region feature at
high angle (2h = 18–22) for calixarene liquid crystal with bowlic
columnar phase.35–39 On the other hand, literatures suggested a
low angle peak (2h = 5 approximately), a broad region feature at
high angle (2h = 18–22), and a high angle (2h = 25 approximately)
for triphenylene liquid crystal with columnar phase.29–34 From
the XRD traces of neat 6a and 6b in Figures 6 and 7, the d-spacings
of the reflections observed for 6a and 6b at 2h = 3.4 (25.9 Å), 5.1
(17.3 Å), and 18.6 (4.8 Å) were associated with the first, second,
and third reflections of the calixarene bowlic columnar phase,35–39
and 2h = 6.0 (14.7 Å), 18–22 (4.04–4.92 Å), and 24.1 (3.7 Å) were
agreed with the diameter of the triphenylene groups, the average
distance of the molten alkyl chains and the intracolumnar order
11–14
based triphenylene with ions.
Further, based on the DSC results, the phase textures of meso-
phase of compounds 6a, 6b, and their complexes with AgClO4 were
investigated by polarized optical microscopy. Two phase transi-
tions of solid state-mesophase and mesophase-isotropic phase on
heating and cooling were observed. Their mesophases were shown
in Figures 4 and 5. It could be seen that the clear columnar fan-
shaped textures were formed. These textures were similar to the
known textures for columnar phases of triphenylene deriva-
tives.29–34 These results of POM experiments were in accordance
with the results of DSC experiments.

412
F. Yang et al. / Tetrahedron Letters 54 (2013) 409–413
Figure 4. The textures of 6a and 6b under POM on cooling at 70 °C (Â400).
Figure 5. The textures of complexes 6a and 6b with AgClO4 under POM on cooling at 70 °C (Â400).
6a
6b
6b+Ag+
6a+Ag+
10
20
30
10
20
30
Figure 6. XRD traces of neat triad 6a and its complex at 70 °C.
Figure 7. XRD traces of neat triad 6b and its complex at 70 °C.
of the two ancillary lateral triphenylene columns, respectively.29–34
These XRD results indicated that neat 6a and 6b had mesomorphic
properties of calixarene’s bowlic column with two triphenylene
units as ancillary lateral columns (Figure 8 (a)). On the other hand,
the XRD results of their complexes showed peaks at 2h = 5.0
(17.6 Å), 18–22 (4.04–4.92 Å), and 24.0 (3.7 Å), which were the
typical peaks of the columnar phase of triphenylene liquid crystal
and agreed with the diameter of the triphenylene groups, the
average distance of the molten alkyl chains, and the intracolumnar
order, respectively.29–34 However, no obvious peak of calixarene
liquid crystal was observed for complexes inFigures 6 and 7. These
XRD results of complexes indicated the complexes possessed novel
mesomorphic molecular stacking behaviors of the triphenylene
column with calixarene units on ancillary lateral sides ( Fig. 8
(b)), which were in accordance with previous report.25
These interesting XRD changes of mesomorphic molecular
stacking behaviors before and after complexation could be ex-
plained by that the cavity of calixarene was occupied by ions after
complexation, which was an obstacle for the stacking of calixarene

F. Yang et al. / Tetrahedron Letters 54 (2013) 409–413
413
neat compound
OR
OR
ORRO
OR
OR
RO
RO
(a)calixarenes bowlic column with two triphenylene
units as ancillary lateral columns
ORRO
OH
O
O
O
Ag+
OH
O
Ag+
Ag+
complex with Ag+
But
But
But
But
(b) triphenylene column with calixarene
units on ancillary lateral side
Figure 8. Two kinds of schematic representation of the columnar layered molecular arrangement for triads of triphenylene-calixarene-triphenylenes 6a and 6b before and
after complexation.
6. Kumar, S. Liq. Cryst. 2004, 31, 1037–1059.
7. Gupta, S. K.; Raghunathan, V.; Kumar, S. New. J. Chem. 2008, 33, 112–117.
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bowlic columnar phase. As a result, the complexes adopt novel
molecular stacking behaviors of triphenylene column with calixa-
rene units on ancillary lateral sides to avoid the steric hindrance.
These interesting ion complexation-induced mesomorphic conver-
sions between two columnar phases were observed for the first
time in supramolecular chemistry and might be applied in ion-
selective supramolecular liquid crystals, ion-induced switch of li-
quid crystal, etc.
In conclusion, the design and synthesis of novel symmetrical
triads of triphenylene-calix[4]arene-triphenylenes 6a and 6b
bridged by hydrazone spacers were described in good yields. Their
mesophase behaviors were studied by differential scanning calo-
rimetry, polarizing optical microscopy, and X-ray diffraction. They
exhibited interesting ion complexation-induced mesomorphic
conversion between two columnar phases. The neat compounds
6a and 6b showed mesophase with calixarene’s bowlic column
as cores. But their Ag+-complexes exhibited mesophase with tri-
phenylene column as cores. The influences on mesomorphic prop-
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Acknowledgments
Financial support from the NSFC (No: 20402002), the FNSFC
(No. 2011J01031), the Project of Fujian provincial department of
education(JA11044), and Program for Excellent young researchers
in University of Fujian Province (JA10056) were greatly
acknowledged.
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Supplementary data
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