Novel supramolecular liquid crystals: Cyclodextrin-triphenylene column liquid crystals based on click chemistry

Article abstract of DOI:10.1039/c3nj00474k

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

Full text of DOI:10.1039/c3nj00474k

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Novel supramolecular liquid crystals:
cyclodextrin-triphenylene column liquid
crystals based on click chemistry†
Cite this: DOI: 10.1039/c3nj00474k
Received (in Montpellier, France)
6
th May 2013,
ab
a
a
Fafu Yang,* Yingmei Zhang and Hongyu Guo
Accepted 3rd June 2013
DOI: 10.1039/c3nj00474k
www.rsc.org/njc
Three new cyclodextrin-triphenylene derivatives 6, 7a and 7b were All these literature studies suggested that the supramolecular
designed and synthesized by introducing a triphenylene unit into macrocycle-triphenylene derivatives possessed the guest-recog-
cyclodextrin based on click chemistry and further acylation of nition abilities based on macrocyclic units and the liquid
hydroxyl groups of the cyclodextrin unit. The column liquid crystal crystal behaviors based on triphenylene units. Moreover, the
behaviour of cyclodextrin-triphenylene 7a was observed for the mesomorphic properties were induced or changed by the guest-
first time.
recognition of macrocyclic units, which led to potential appli-
cations such as ion-sensors, ion-selective supramolecular liquid
The self-assembly of relatively simple building blocks into crystals, ion-switch of liquid crystals, etc. However, besides
complex ordered structures is a subject of increasing research these few examples of supramolecular crown ether-triphenylene
interest for the fundamental understanding of soft-matter self- and calixarene-triphenylene derivatives, no other macrocycle-
1
–3
organization.
mesophase between a crystalline solid and an isotropic liquid liquid crystals, are known.
Liquid crystals are typical soft matter with a triphenylene derivatives, such as cyclodextrin-triphenylene
state of matter. Triphenylene is one of the most widely studied
Cyclodextrins (CDs) are cyclic oligosaccharide molecules
discotic liquid crystals with various possible applications in comprising six, seven or eight glucose units which are bonded
organic light-emitting diodes, organic photovoltaic cells, through the a-(1,4)-linkages, assigned as a-, b-, g-CD, respec-
2
3
organic field-effect transistors, gas sensors, photocopying tively. They were used as excellent platforms to construct the
4
–9
machines, etc.
All kinds of triphenylene derivatives with supramolecular cyclodextrin derivatives with potential applica-
unique structures and interesting mesomorphic properties, tions in molecular recognition, molecular self-assembly, bioenzyme
such as hydrogen-bond stabilized triphenylene columns, poly- mimics, etc. However, due to their big irregular shapes and strong
mers or oligomers of triphenylene, dendrimers of triphenylene, hydrogen bonds, it was difficult to construct the cyclodextrin
7
–13
nanoparticles of triphenylene, have been investigated.
Recently, much attention was focused on the supramolecular biphenyl thermotropic liquid crystals and amphiphilic thio-
liquid crystals. Until now, only two examples of cyclodextrin-
2
4,25
macrocycle-triphenylene derivatives. Cammidge et al. first b-cyclodextrin liquid crystals have been reported.
On the
reported the triphenylene dimers linked by a shape-persistent other hand, the click reaction was used as a good method to
conjugated macrocycle and a crown ether macrocycle with prepare liquid crystals recently, such as liquid-crystalline gold
1
4,15
26,27
interesting mesomorphic properties in 2010.
Also, the nanoparticles and liquid-crystalline pillar(arenes).
In this
paper, we wish to describe the design and syntheses of the first
examples of cyclodextrin-triphenylene derivatives based on click
chemistry. Moreover, after the acetylation of hydroxyl groups of
the cyclodextrin unit, the cyclodextrin column liquid crystals
were observed for the first time.
syntheses and mesomorphic properties of a series of crown ether-
based triphenylene dimers were described by Laschat and Peng
1
6–19
at the same time, respectively.
Recently, we reported a series
2
0–22
of calixarene-triphenylene liquid crystals for the first time.
Scheme 1 shows the synthetic routes towards cyclodextrin-
triphenylene derivatives 6, 7a and 7b. The mono-6-azido-b-CD 3
a
College of Chemistry and Chemical Engineering, Fujian Normal University,
Fuzhou 350007, P.R. China. E-mail: yangfafu@fjnu.edu.cn; Tel: +86-591-83465225
Fujian Key Laboratory of Polymer Materials, Fuzhou 350007, P.R. China
Electronic supplementary information (ESI) available: Detailed experimental
2
8–30
b
was obtained from the readily available mono-6-tosyl-b-CD.
On the other hand, triphenylene derivative 5 with the alkynyl
†
3
1
procedures. See DOI: 10.1039/c3nj00474k
group was prepared in high yield according to the literature.
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Fig. 1 The texture of 7a under a POM upon cooling at 120 1C (Â400).
that it underwent no obvious phase transition upon heating and
cooling. The melting point determination also showed that it had
no clear melting point below 200 1C and decomposed gradually
above 200 1C. These results might suggest that compound 6 is an
amorphous solid. Compound 7b showed one peak upon second
heating and cooling, which implied that it underwent one phase
transition upon melting. However, compound 7a exhibited two
phase transitions upon second heating and cooling as shown in
Fig. 2 and Table 1. Combining the experimental results of
polarized optical microscopy and differential scanning calori-
metry, it could be deduced that compound 7a exhibited the liquid
crystal behaviour of solid state–mesophase and mesophase–
isotropic phase upon melting, but compounds 6 and 7b possessed
no mesophase upon melting.
Scheme 1 The synthetic routes towards cyclodextrin-triphenylene 6, 7a and 7b.
Subsequently, the coupling of triphenylene derivative 3 and
b-CD derivative 5 was accomplished via click reaction using
Cu(I) as a catalyst, and the first triphenylene-cyclodextrin
derivative 6 was obtained in a high yield of 80%. After acylation
of compound 6 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,
7
a and 7b were characterized by elemental analysis, FT-IR, ESI-
1
MS and H NMR spectra. Their ESI-MS spectra showed the
corresponding molecular ion peaks. In their H NMR spectra,
1
the signals of protons were assigned well for the structures of
compounds 6, 7a and 7b as shown in Scheme 1.
The phase transition behaviours of compounds 6, 7a and 7b
were first observed using polarized optical microscopy upon
heating and cooling. Results showed that compounds 6 and 7b
undergo the transition from the solid state to the isotropic phase
directly upon melting, and no mesophase could be observed. Table 1 Transition temperatures (1C) and enthalpy changes (kJ mol ) of 6, 7a
However, compound 7a showed two phase transitions of solid and 7b
Fig. 2 The DSC traces of compounds 6, 7a and 7b upon second heating and
À1
cooling (scan rate 10 1C min ).
À1
state–mesophase and mesophase–isotropic phase upon heating
Heating scan
T(DH)
Cooling scan
T(DH)
a
and cooling. The clear columnar fan-shaped texture was formed
as shown in Fig. 1. This texture was similar to the known textures
Compound
Phase transition
6
None
None
None
3
2–37
for columnar phases of triphenylene derivatives.
7a
Cr-Col
Col-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)
Further, the thermal behaviours of compounds 6, 7a and 7b
were studied by differential scanning calorimetry (DSC) as shown
in Fig. 2. Compound 6 exhibited no clear peak, which indicated
7b
a
Cr = crystalline, Col = column liquid crystal, Iso = isotropic.
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acylation of hydroxyl groups, compound 7a with acetyl groups
exhibited the mesophase but compound 7b with butyryl groups
possessed no mesophase. These results suggested that the
structures of alkyl chains of acyl groups also played important
roles in mesomorphic properties. The long alkyl chain might be
not favorable for the liquid crystals. In other words, the
mesomorphic properties of cyclodextrin-triphenylene deriva-
tives were decided by both the hydroxyl groups and the struc-
tures 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 groups
showed no mesophase. Compound 7a with acetyl groups
exhibited the column liquid crystals, which was confirmed by
differential scanning calorimetry (DSC), polarizing optical
microscopy (POM) and X-ray diffraction (XRD). These results
suggested that the mesomorphic properties of cyclodextrin-
Fig. 3 XRD traces of compounds 7a and 7b at 120 1C.
In order to investigate the mesomorphic stacking behaviour triphenylene derivatives were dependent on both the hydroxyl
deeply, compounds 7a and 7b were studied by X-ray powder groups and the structures of acyl groups of cyclodextrin units.
diffraction as shown in Fig. 3. A survey of the literatures The studies on inclusion properties for guests based on cyclo-
indicated that triphenylene liquid crystals with a hexagonal dextrin units and their influences on mesomorphic properties
columnar phase exhibited a low angle peak (2y = 51 approxi- will be further investigated in the following work.
mately) for the diameter of the triphenylene groups and a broad
region feature at a high angle (2y = 18–221) for the average
Experimental
General
distance of the molten alkyl chains and high angle (2y = 251
3
2–37
approximately) for the intracolumnar order.
As shown in
Fig. 3, compound 7b only exhibited the strong reflection of the All chemical reagents were obtained from commercial suppliers
average distance of the molten alkyl chains (2y = 18–241) and no and used without further purification. The other organic solvents
obvious reflection for the triphenylene column. This result and inorganic reagents were purified according to standard
suggested that the triphenylene units of compound 7b could anhydrous methods before use. TLC analysis was performed
not stack orderly in the column phase upon melting. However, using pre-coated glass plates. Column chromatography was
it could be seen that compound 7a exhibited the reflections at performed using silica gel (200–300 mesh). NMR spectra were
2
y = 5.251, 18–241 and 25.11, respectively, which were the typical recorded in CDCl on a Bruker-ARX 400 instrument at 30 1C.
3
peaks of the hexagonal columnar phase of triphenylene liquid Chemical shifts are reported in ppm, using tetramethylsilane
crystals and agreed with the diameter of the triphenylene (TMS) as internal standard. ESI-MS spectra were obtained using
groups (16.8 Å), the average distance of the molten alkyl chains a DECAX-30000 LCQ Deca XP mass spectrometer. Elemental
3
2–37
(4.9–3.7 Å) and the intracolumnar order (3.6 Å), respectively.
analyses were performed using a Vario EL III Elemental Analyzer.
On the other hand, no obvious reflection for the cyclodextrin A polarized optical microscope (Leica DMRX) was used along
2
4,25
unit was observed.
From these XRD results, it could be with a hot stage (Linkam THMSE 600) to examine phase transi-
deduced that compound 7b possessed no triphenylene column tions. Thermal analysis of the materials was carried out using a
but compound 7a had a triphenylene column as a core with differential scanning calorimeter (DSC) (Thermal Analysis Q100)
À1
cyclodextrin units on ancillary lateral sides, which exhibited the at a scan rate of 10 1C min under a N atmosphere. X-ray
2
XRD peaks for the triphenylene column unit but no XRD peak diffraction (XRD) experiments were performed on a SEIFERT-
for the cyclodextrin unit due to the disordered tropism of FPM (XRD7), using Cu Ka 1.5406 Å as the radiation source with
cyclodextrin units on ancillary lateral sides. Comparing the 40 kV, 30 mA power.
structures of compounds 7a and 7b, it could be deduced that
the long butyryl chains of cyclodextrin units in compound 7b
Synthetic procedure of b-cyclodextrin-triphenylene 6
were not favourable for the mesophase. A possible reason was Reaction of compound 3 (0.31 g, 0.43 mmol) with compound 5
that the strong disordered intermolecular forces of twenty long (0.5 g, 0.43 mmol) was carried out in DMF (20 mL) in the
butyryl chains on lateral cyclodextrin units damaged the ordered presence of Cu(I) generated by the reduction of copper sulfate
p–p stacking of the triphenylene column.
(0.011 g, 0.043 mmol) with sodium ascorbate (0.043 g,
Based on the analysis of structures and liquid crystal proper- 0.22 mmol). The mixture was stirred at 60 1C for 8 h and then
ties of compounds 6, 7a and 7b, it could be concluded that the cooled to room temperature. TLC detection indicated the
hydroxyl groups in cyclodextrin units were the obstacle for the disappearance of materials. Then 20 mL of distilled water
liquid crystal behaviors. Moreover, although the influences of and 30 mL of CHCl
3
were added into the solution with vigorous
hydroxyl groups of the cyclodextrin unit were eliminated by stirring at room temperature. Then the solutions were formed
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with three layers: upper layer (DMF and water), middle layer Notes and references
(
3
solid), and lower layer (CHCl ). The middle layer was separated
1
D. N. Reindhout, Supramolecular Materials and Technologies,
Wiley, New York, 1999.
F. J. M. Hoeben, P. Jonkheijm, E. W. Meijer and A. P. H.
Schenning, Chem. Rev., 2005, 105, 1491.
K. Kinbara and T. Aida, Chem. Rev., 2005, 105, 1377.
S. Sergeyev, W. Pisula and Y. H. Geerts, Chem. Soc. Rev.,
out and was further purified by flash column chromatography
on silica gel using a mixture of n-butanol : ethanol : water =
5
in a yield of 80%. Compound 6: H NMR (400 MHz, DMSO)
d (ppm): 0.93 (t, 15H, J = 6.6 Hz, CH
3
4
and CH); IR/cm : 3395, 2930, 2869, 1690, 1616, 1508, 1432,
1
Anal. calcd for C H N O : C, 56.43; H, 7.16; N, 2.24%;
found: C, 56.39; H, 7.21; N, 2.22%.
2
: 4 : 3 as an eluent. Compound 6 was obtained as a gray solid
1
3
4
3
), 1.41–1.85 (m, 30H, CH
2
2
),
),
.44–3.65 (m, 40H, H2–H6), 4.24 (bs, 12H, TpOCH and NCH
2
2007, 36, 1902.
.50–5.88 (m, 29H, CH
2
, CH and OH), 7.90–8.29 (m, 7H, TpH
À1
5 S. Laschat, A. Baro, N. Steinke, F. Giesselmann, C. Hagele,
G. Scalia, R. Judele, E. Kapatsina, S. Sauer, A. Schreivogel
and M. Tosoni, Angew. Chem., Int. Ed., 2007, 46, 4832.
+
366, 1261, 1156, 1035, 583; MS m/z (%): 1896.0 (MNa , 100).
8
8
133 3 40
6
T. Kato, N. Mizoshita and K. Kishimoto, Angew. Chem., Int.
Ed., 2006, 45, 38.
7
8
S. Kumar, Chem. Soc. Rev., 2006, 35, 83.
S. Kumar, Liq. Cryst., 2004, 31, 1037.
Synthetic procedure of b-cyclodextrin-triphenylene 7a
Compound 6 (0.3 g, 0.16 mmol) and I (0.05 g, 0.2 mmol) were
2
9 A. N. Cammidge and H. Gopee, Liq. Cryst., 2009, 36, 809.
0 J. Miao and L. Zhu, Chem. Mater., 2010, 22, 197.
1 A. Zelcer, B. Donnio, C. Bourgogne, F. D. Cukiernik and
D. Guillon, Chem. Mater., 2007, 19, 1992.
2
stirred in acetic anhydride (6 mL) overnight under a N atmo-
1
1
sphere. Then the mixture was stirred at 40 1C and cooled to
room temperature. TLC detection indicated the disappearance
of materials. Then 20 mL of distilled water and sodium
thiosulphate (0.05 g, 0.2 mmol) were added into the solution
with vigorous stirring, and the pH was adjusted to 7 with
1
1
1
1
1
1
1
2 H. K. Bisoyi and S. J. Kumar, Mater. Chem., 2008,
18, 3032.
3 F. F. Yang, J. W. Xie, H. Y. Guo, B. T. Xu and C. C. Li,
Liq. Cryst., 2012, 39, 1368.
4 J. Li, Z. He, H. Gopee and A. N. Cammidge, Org. Lett., 2010,
NaHCO . The organic layer was separated with 30 mL of
3
CH Cl , dried over anhydrous MgSO , and then filtered, con-
2
2
4
centrated and recrystallized in MeOH–CH
2 2
Cl . Compound 7a
12, 472.
was obtained as a beige solid in a yield of 72%. Compound 7a:
5 L. Zhang, H. Gopee, D. Hughes and A. N. Cammidge,
Chem. Commun., 2010, 46, 4255.
6 D. Wang, J. F. Hsu, M. Bagui, V. Dusevich, Y. Wang, Y. Liu,
A. Holder and Z. Peng, Tetrahedron Lett., 2009, 50, 2147.
7 M. Kaller, C. Deck, A. Meister, G. Hause, A. Baro and
S. Laschat, Chem.–Eur. J., 2010, 16, 6326.
1
H NMR (400 MHz, CDCl
.96 (m, 30H, CH ), 2.10 (s, 60H, COCH
and OCH ), 7.84 (s, 6H, TpH), 8.11 (s, 1H, H7);
3
) d (ppm): 0.97 (bs, 15H, CH
3
), 1.47–
1
2
3
), 3.53–5.52 (m, 61H,
CH1-5, NCH
2
2
À1
IR/cm : 2929, 2867, 1747, 1616, 1509, 1433, 1372, 1238, 1166,
1
+
042, 699, 603; MS m/z (%): 2735.4 (MNa , 100). Anal. calcd for
C128H173N O : C, 56.65; H, 6.43; N, 1.55%; found: C, 56.61;
3
60
8 M. Kaller, S. Tussetschl ¨a ger, P. Fischer, C. Deck, A. Baro,
F. Giesselmann and S. Laschat, Chem.–Eur. J., 2009,
H, 6.491; N, 1.49%.
1
5, 9530.
Synthetic procedure of b-cyclodextrin-triphenylene 7b
1
9 M. Kaller, P. Staffeld, R. Haug, W. Frey, F. Giesselmann and
Compound 6 (0.3 g, 0.16 mmol) and I (0.05 g, 0.2 mmol) were
S. Laschat, Liq. Cryst., 2011, 38, 531.
2
stirred in n-butyric anhydride (6 mL) overnight under a N
atmosphere. Then the mixture was stirred at 40 1C and cooled
2
20 F. F. Yang, H. Y. Guo, J. W. Xie and J. R. Lin, Eur. J. Org.
Chem., 2011, 5141.
to room temperature. TLC detection indicated the disappear- 21 F. F. Yang, B. T. Xu, H. Y. Guo and J. W. Xie, Tetrahedron
ance of materials. Then 20 mL of distilled water and sodium
Lett., 2012, 53, 1598.
thiosulphate (0.05 g, 0.2 mmol) were added into the solution 22 F. F. Yang, X. Y. Bai, C. C. Li and H. Y. Guo, Tetrahedron
with vigorous stirring, and the pH was adjusted to 7 with
Lett., 2013, 54, 409.
NaHCO . The organic layer was separated with 30 mL of 23 J. Szejtli, Chem. Rev., 1998, 98, 1743.
3
CH Cl , dried over anhydrous MgSO , and then filtered and 24 L. Chen, T. H. Hu, H. L. Xie and H. L. Zhang, J. Polym. Sci.,
2
2
4
concentrated. Purification was performed by column chroma-
tography on silica gel (100–200 mesh), and the column was 25 C. C. Ling, R. Darcy and W. J. Risse, J. Chem. Soc., Chem.
eluted initially with petroleum ether and then with methanol as
Commun., 1993, 438.
an eluent. Compound 7b was obtained in the yield of 65%. 26 S. Mischler, S. Guerra and R. Deschenaux, Chem. Commun.,
Part A: Polym. Chem., 2010, 48, 2838.
1
Compound 7b: H NMR (400 MHz, CDCl
3
) d (ppm): 0.89–0.99
2012, 48, 2183.
(
t, 75H, CH ), 1.43–2.27 (m, 110H, CH and CH CO), 3.62–5.47 27 I. Nierengarten, S. Guerra, M. Holler, J. F. Nierengarten and
3 2 2
(
7
1
m, 61H, CH2-5, NCH and TpOCH ), 7.52–7.84 (m, 6H, TpH),
R. Deschenaux, Chem. Commun., 2012, 48, 8072.
.89 (s, 1H, H7); IR/cm : 2962, 2874, 1744, 1614, 1510, 1433, 28 L. Jicsinszky and R. Iv ´a nyi, Carbohydr. Polym., 2001,
2
2
À1
+
262, 1170, 1043, 959, 749; MS m/z (%): 3295.5 (MNa , 100).
45, 139.
Anal. calcd for C168H N O
60: C, 61.61; H, 7.79; N, 1.28%; 29 R. C. Petter, J. S. Salek, C. T. Sikorski, G. Kumaravel and
253 3
found: C, 61.66; H, 7.89; N, 1.26%.
F. T. Lin, J. Am. Chem. Soc., 1990, 112, 3860.
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30 M. McNaughton, L. Engman, A. Irmingham, G. Powis and 34 W. Wan, H. Monobe, Y. Tanaka and Y. Shimizu, Liq. Cryst.,
I. A. Cotgreave, J. Med. Chem., 2004, 47, 233. 2003, 30, 571.
31 K. Q. Zhao, H. Zhou, W. H. Yu, P. Hu, B. Q. Wang, 35 C. Ba, Z. Shen, H. Gu, G. Guo, P. Xie and R. Zhang,
H. Monobe and Y. Shimizu, Sci. Sin.: Chim., 2011, 41, 1565. Liq. Cryst., 2003, 30, 391.
3
2 S. K. Prasad, A. S. Rao, S. Chandrasekhar and S. Kumar, 36 J. Paraschiv, A. Tomkinson, M. Giesbers, E. Sudh o¨ lter,
Mol. Cryst. Liq. Cryst., 2003, 396, 121. H. Zuilhof and A. Marcelis, Liq. Cryst., 2007, 34, 1029.
33 W. Wan, P. Y. Wang, H. Z. Jiang and J. Hao, Mol. Cryst. Liq. 37 B. Zhao, B. Liu, R. Q. Png, K. Zhang, K. A. Lim, J. Luo,
Cryst., 2008, 482, 42. J. Shao, P. Ho, C. Chi and J. Wu, Chem. Mater., 2010, 22, 435.
This journal is c The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2013
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