RETRACTED ARTICLE: Novel supramolecular liquid crystal: Synthesis of cyclodextrin-triphenylene column liquid crystal based on click chemistry

Article abstract of DOI:10.1016/j.tetlet.2013.07.018

Three new cyclodextrin-triphenylene derivatives 6, 7a and 7b were designed and synthesized by introducing triphenylene unit on cyclodextrin based on click chemistry and further acylation of hydroxyl groups of cyclodextrin unit. The column liquid crystal b

Full text of DOI:10.1016/j.tetlet.2013.07.018

Tetrahedron Letters 54 (2013) 4953–4956
Contents lists available at SciVerse ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Novel supramolecular liquid crystal: synthesis of cyclodextrin–
triphenylene column liquid crystal based on click chemistry
a,b,
⇑
a
a
a
Fafu Yang
, Yingmei Zhang , Hongyu Guo , Jianrong Lin
a
College of Chemistry and Chemical Engineering, Fujian Normal University, Fuzhou 350007, PR China
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, PR China
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Three new cyclodextrin–triphenylene derivatives 6, 7a and 7b were designed and synthesized by intro-
ducing triphenylene unit on cyclodextrin based on click chemistry and further acylation of hydroxyl
groups of cyclodextrin unit. The column liquid crystal behaviour of cyclodextrin–triphenylene 7a was
observed for the first time by differential scanning calorimeter (DSC), polarizing optical microscopy
Received 2 April 2013
Revised 13 May 2013
Accepted 3 July 2013
Available online 10 July 2013
(POM) and X-ray diffraction (XRD).
Ó 2013 Elsevier Ltd. All rights reserved.
Keywords:
Cyclodextrin
Triphenylene
Synthesis
Mesophase
The self-assembly of relatively simple building blocks into com-
plex ordered structures is a subject of increasing research interest
for the fundamental understanding of soft-matter self-organiza-
changed by the guest-recognition of macrocyclic units, which
exhibited application prospects on ion-sensors, ion-selective
supramolecular liquid crystals, ion-switch of liquid crystal, etc.
However, besides these few examples of supramolecular crown
ether-triphenylene and calixarene–triphenylene derivatives, the
other macrocycle-triphenylene derivative, such as cyclodextrin–
triphenylene liquid crystal, was completely unknown up to now.
Cyclodextrins (CDs) are cyclic oligosaccharide molecules com-
prising six, seven or eight glucose units which are bonded through
1
–3
tion.
Liquid crystals were typical soft-matter with mesophase
between a crystalline solid and an isotropic liquid state of matter.
Triphenylene is one of the most widely studied discotic liquid crys-
tals with possible various applications in organic light-emitting
diodes, organic photovoltaic cells, organic field-effect transistors,
gas sensors, photocopying machines, etc.4 All kinds of triphenyl-
ene derivatives with unique structures and interesting mesomor-
phic properties, such as hydrogen-bond stabilized triphenylene
columns, polymers or oligomers of triphenylene, dendrimers of tri-
phenylene and nanoparticles of triphenylene, were investigated up
–9
the
a-(1,4)-linkages, assigned as a-, b- and c
-CD, respectively.23
They were used as excellent platforms to construct the supramo-
lecular cyclodextrin derivatives with the application prospects in
molecular recognition, molecular self-assembly, bioenzyme mim-
ics, etc. However, due to their big irregular shapes and strong
hydrogen bonds, it was difficult to construct the cyclodextrin
liquid crystal. Until now, only two examples of cyclodextrin-biphe-
7
–13
to now.
Recently, much attention was focused on the supramo-
lecular macrocycle-triphenylene derivatives. Cammidge first re-
ported the triphenylene dimers linked by shape-persistent
conjugated macrocycle and crown ether macrocycle with interest-
nyl thermotropic liquid crystal and amphiphilic thio-b-cyclodex-
14,15
24,25
ing mesomorphic properties in 2010.
Also, the syntheses and
trin liquid crystal were reported.
In this Letter, we wish to
mesomorphic properties of series crown ether-based triphenylene
dimers were described by Laschat and Peng at the same time,
describe the design and syntheses of the first examples of cyclo-
dextrin–triphenylene derivatives based on click chemistry. More-
over, after the acetylation of hydroxyl groups of cyclodextrin
unit, the cyclodextrin column liquid crystal was observed for the
first time.
1
6–19
respectively.
of calixarene–triphenylene liquid crystals.
Lately, we reported the first examples of series
20–22
All these literatures
suggested that the supramolecular macrocycle-triphenylene deriv-
atives possessed the guest-recognition abilities based on macrocy-
clic units and the liquid crystal behaviours based on triphenylene
units. Moreover, the mesomorphic properties were induced or
Scheme 1 shows the synthetic routes of cyclodextrin–triphenyl-
ene derivatives 6, 7a and 7b. The mono-6-azido-b-CD 3 was ob-
tained from the readily available mono-6-tosyl-b-CD.2
6–28
On the
other hand, triphenylene derivative 5 with alkynyl group was pre-
2
9
pared in high yield according to the literature. Subsequently, the
coupling of triphenylene derivative 3 and b-CD derivative 5 was
⇑
Corresponding author. Tel./fax: +86 591 83465225.
E-mail address: yangfafu@fjnu.edu.cn (F. Yang).
0
040-4039/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.tetlet.2013.07.018

4
954
F. Yang et al. / Tetrahedron Letters 54 (2013) 4953–4956
OH
TsO
TsCl
NaOH/H
OH
N
3
OH
cooling
7
6
6
4
2
0
2
4
6
NaN
3
2
O
DMF/H
O
2
o
Cr
LC
Iso
0
-5 C
o
8
0 C
7a
OH
14
OH
OH
Cr
Cr
Iso
1
4
14
7b
1
3
2
Iso
Iso
7b
-
-
5
OC H
11-n
OC
5
H11-n
5 11
n-C H O
5 11
n-C H O
Cr
LC
5
OC H11-n
Br
OC
5
H
11-n
7a
6
OH
K
2
CO
3
, MeCN, refluxing
5 11
n-C H O
O
n-C
5
H
11
O
-6
-8
OC
5
H11-n
OC
5
H11-n
Second heating
100
5
4
OC
5
H11-n
0
50
150
200
n-C
5
H
11
O
Temperature oC
5
OC H11-n
CuSO4
OH
3
+
5
6
sodium ascorbate
O
o
N
Figure 2. The DSC traces of compounds 6, 7a and 7b on second heating and cooling
DMF, 60 C
N
À1
(
scan rate 10 °C min ).
n-C
5
H
11
O
N
6
OC
5
H11-n
OH
14
Table 1
2
(RCO) O
Transition temperatures (°C) and enthalpy changes (kJ/mol) of 6, 7a and 7b
OC
5
H
11-n
11-n
Phase transitiona
Compound
Heating scan T (
D
H) Cooling scan T (DH)
5 11
n-C H O
O
R
OC
5
H
11-n
6
7a
None
None
None
O
Cr–LC
LC–Iso
Cr–Iso
115.2 (8.68)
160.4 (10.46)
158.2 (7.72)
100.1 (8.14)
135.3 (10.86)
147.2 (3.21)
6
O
N
N
7b
5 11
n-C H O
N
OC
5
H
a
Cr = crystalline, LC = liquid crystal, Iso = isotropic.
O
1
4
7
a (R=CH -)
3
O
R
7
b (R=CH CH CH -)
The phase transition behaviours of compounds 6, 7a and 7b
3
2
2
were first observed under polarized optical microscopy upon heat-
ing and cooling. Results showed that compounds 6 and 7b possess
the transition from solid state to isotropic phase directly on melt-
ing process, and no mesophase could be observed. However, com-
pound 7a showed two phase transitions of solid state-mesophase
and mesophase-isotropic phase on heating and cooling. The clear
columnar fan-shaped textures were formed as shown in Figure 1.
This texture was similar to the known textures for columnar
Scheme 1. The synthetic routes of cyclodextrin–triphenylene derivatives 6, 7a and
b.
7
accomplished via click reaction and the first triphenylene–cyclo-
dextrin derivative 6 was obtained in high yield of 80%. After acyl-
ation with acetic anhydride or butyric anhydride, the
triphenylene–cyclodextrin derivatives 7a and 7b were prepared
in yields of 72% and 65%, respectively. The novel compounds 6,
3
0–35
phases of triphenylene derivatives.
Further, the mesomorphic behaviours of compounds 6, 7a and
7b were studied by differential scanning calorimeter (DSC) as
shown in Figure 2. Compound 6 exhibited no clear peak, which
indicated it possessed no obvious phase transition on heating
and cooling below 200 °C. The melting point determination also
7
a and 7b were characterized by elemental analysis, FT-IR, ESI-
1
MS and H NMR spectra. Their ESI-MS spectra showed the corre-
sponding molecular ion peaks. In their H NMR spectra, the signals
of protons were assigned well for the structures of compounds 6,
7
1
a and 7b as shown in Scheme 1.
2
000
000
0
5
.25
7b
1
25.1
7a
20
40
Scattering angle 2θ (degree)
Figure 1. The texture of 7a under POM on cooling at 120 °C (Â400).
Figure 3. XRD traces of compounds 7a and 7b at 120 °C.

F. Yang et al. / Tetrahedron Letters 54 (2013) 4953–4956
4955
OC5H11-n
n-C5H11O
n-C5H11O
O
CH3
OC H11-n
5
O
6
O
N
N
N
OC H11-n
5
O
1
4
O
H3C
Figure 4. The schematic representation of columnar mesomorphic stacking behaviour for compound 7a.
showed it was a solid and had no clear melting point below 200 °C
but decomposed gradually over 200 °C. Compound 7b showed one
peak on second heating and cooling, which implied that compound
behaviours. Moreover, although the influences of hydroxyl groups
of cyclodextrin unit were eliminated by acylation of hydroxyl
groups, compound 7a with acetyl groups exhibited mesophase
but compound 7b with butyryl groups possessed no mesophase.
These results suggested the structures of alkyl chains on acyl
groups also played important roles on mesomorphic properties.
The long alkyl chain might be not favourable for the liquid crystal.
In a word, the mesomorphic properties of cyclodextrin–triphenyl-
ene derivatives were decided by both the hydroxyl groups and the
structures of acyl groups of cyclodextrin units.
In conclusion, the design and synthesis of the first examples of
cyclodextrin–triphenylenes 6, 7a and 7b were accomplished in
high yields. Compounds 6 and 7b with butyryl group showed no
mesophase. Compound 7a with acetyl groups showed the column
liquid crystal, which was confirmed by differential scanning calo-
rimeter (DSC), polarizing optical microscopy (POM) and X-ray dif-
fraction (XRD). These results suggested that the mesomorphic
properties of cyclodextrin–triphenylene derivatives were depen-
dent on both the hydroxyl groups and the structures of acyl groups
of cyclodextrin units. The studies on inclusion property for guests
based on cyclodextrin units and its influences on mesomorphic
property will be further investigated in the following work.
7
b possess one phase transition on melting process. However,
compound 7a exhibited two phase transitions upon second heating
and cooling as shown in Figure 2 and Table 1. Combining the
experiment results of polarized optical microscopy and differential
scanning calorimeter, it could be deduced that compound 7a
exhibited the liquid crystal behaviour of solid state-mesophase
and mesophase-isotropic phase on melting process, but com-
pounds 6 and 7b possessed no mesophase on melting process.
In order to investigate the mesomorphic stacking behaviour
deeply, compounds 7a and 7b were studied by X-ray powder dif-
fraction as shown in Figure 3. A survey of the literatures indicated
that triphenylene liquid crystal with the columnar phase exhibited
a low angle peak (2h = 5 approximately) for the diameter of the
triphenylene groups, broad region feature at
2h = 18–22) for the average distance of the molten alkyl chains
and high angle (2h = 25 approximately) for the intracolumnar
a high angle
(
3
0–35
order.
reflection of average distance of the molten alkyl chains
2h = 18–24) and no obvious peak for the diameter of the triphen-
In Figure 3, compound 7b only exhibited the strong
(
ylene groups and the intracolumnar order of triphenylene column.
This result suggested the triphenylene units of compound 7b could
not stack in column orderly on melting. However, it could be seen
that compound 7a exhibited the reflections at 2h = 5.25, 18–24 and
Acknowledgments
Financial support from the NSFC (No: 20402002), FNSFC (No.
2011J01031), Project of Fujian provincial department of education
(JA11044), Program for Innovative Research Team in Science and
Technology in Fujian Province University (IRTSTFJ) and Program
for Excellent young researchers in University of Fujian Province
(JA10056) was greatly acknowledged.
2
5.1, respectively, which were the typical peaks of the columnar
phase of triphenylene liquid crystal and agreed with the diameter
of the triphenylene groups (16.8 Å), the average distance of the
molten alkyl chains (4.9–3.7 Å) and the intracolumnar order(3.6 Å),
respectively. On the other hand, no obvious reflection for cyclodex-
trin unit was observed.2
4,25
From these XRD results, it could be de-
duced that compound 7b possessed no triphenylene column but
compound 7a had triphenylene column as core with cyclodextrin
units on ancillary lateral sides, which exhibited the XRD peaks
for triphenylene column unit but no XRD peak for cyclodextrin unit
due to the disorderly tropism of cyclodextrin units on ancillary lat-
eral sides. The possible mesomorphic molecular stacking behav-
iour of compound 7a was deduced as in Figure 4. Comparing
with the structures of compounds 7a and 7b, it could be deduced
that the short methyl chain in compound 7a eliminated the influ-
ences of hydroxyl groups, and resulted in mesomorphic property.
But the long butyryl chains of cyclodextrin units in compound 7b
was no favourable for mesophase, which might be attributed to
the strong intermolecular dispersion forces of twenty long butyryl
chains on cyclodextrin units that enhanced viscosity greatly and
damaged the orderly stacking of triphenylene column.
Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.tetlet.2013.07.
0
18.
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