Novel cyclotriveratrylene columnar liquid crystal with three alkyl chains: The balance between the number and length of alkyl chains for liquid crystalline behavior

Article abstract of DOI:10.1080/15421406.2017.1414256

Series of cyclotriveratrylene (CTV) derivatives with triazole ring and three alkyl groups were prepared by one-pot click condensation in yield of 80–88%. The structures and crown conformations were confirmed by NMR and MS. Their liquid crystalline properties were investigated by DSC, POM and XRD analysis. The studies on mesomorphic properties suggested that the CTV derivatives with pentyl, hexyl or dodecyl groups show no mesophase but the one with octadecyl groups possesses ordered hexagonal columnar mesophase. In comparison with the reported columnar CTV liquid crystals with six alkyl chains at least, the CTV columnar CTV liquid crystal with three alkyl chains was reported for the first time. These results suggested a subtle balance between the number and length of alkyl chains for columnar CTV liquid crystalline behavior.

Full text of DOI:10.1080/15421406.2017.1414256

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: http://www.tandfonline.com/loi/gmcl20
Novel cyclotriveratrylene columnar liquid crystal
with three alkyl chains: The balance between
the number and length of alkyl chains for liquid
crystalline behavior
Anna Ruan, Hongyu Guo, Chuang Yang & Fafu Yang
To cite this article: Anna Ruan, Hongyu Guo, Chuang Yang & Fafu Yang (2017) Novel
cyclotriveratrylene columnar liquid crystal with three alkyl chains: The balance between the number
and length of alkyl chains for liquid crystalline behavior, Molecular Crystals and Liquid Crystals,
658:1, 59-68, DOI: 10.1080/15421406.2017.1414256
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
, VOL. , –
https://doi.org/./..
Novel cyclotriveratrylene columnar liquid crystal with three
alkyl chains: The balance between the number and length of
alkyl chains for liquid crystalline behavior
Anna Ruana, Hongyu Guoa,b, Chuang Yanga, and Fafu Yanga,c
aCollege of Chemistry and Material Sciences, Fujian Normal University, Fuzhou, P. R. China; bFujian Key
Laboratory of Polymer Materials, Fuzhou, P. R. China; cFujian provincial Key Laboratory of Advanced Materials
Oriented Chemical Engineering, Fuzhou, P. R. China
ABSTRACT
KEYWORDS
Alkyl; cyclotriveratrylene;
mesophase; synthesis
Series of cyclotriveratrylene (CTV) derivatives with triazole ring and
three alkyl groups were prepared by one-pot click condensation in
yield of 80–88%. The structures and crown conformations were con-
firmed by NMR and MS. Their liquid crystalline properties were inves-
tigated by DSC, POM and XRD analysis. The studies on mesomorphic
properties suggested that the CTV derivatives with pentyl, hexyl or
dodecyl groups show no mesophase but the one with octadecyl groups
possesses ordered hexagonal columnar mesophase. In comparison with
the reported columnar CTV liquid crystals with six alkyl chains at least,
the CTV columnar CTV liquid crystal with three alkyl chains was reported
for the first time. These results suggested a subtle balance between the
number and length of alkyl chains for columnar CTV liquid crystalline
behavior.
Introduction
Liquid crystalline materials have been paid much attention and exhibited extensive applica-
tions [1–5]. In the past decades, columnar liquid crystals, as one of the important part of liquid
crystals, attracted considerable research interests based on their unique properties [6, 7]. This
kind of subclass of mesophase shows the strong π-π stacking action in column, which is favor-
able for 1D conduction of charge and/or energy, resulting in potential application in organic
light-emitting diodes, organic field-effect transistors and organic photovoltaic cells [8–11].
Usually, columnar liquid crystals were obtained by modifying rigid aromatic cores with 4∼12
alkyl chains in high symmetric structures. For instances, the columnar liquid crystals con-
taining the rigid core of triphenylene or hexabenzocoronene derivatives with few alkyl chains
were investigated up to now [12–19]. Lately, Percec reported series of perylene columnar liq-
uid crystals with the crown conformations [20–23].
Recently, the calixarene skeleton, in which several aromatic groups were bridged by methy-
lene spacers in cyclic structure, was developed to construct columnar liquid crystal success-
fully. Some columnar calixarene-based liquid crystals were presented by grafting mesogenic
CONTACT Hongyu Guo
guohongyuyang@.com; Fafu Yang
Material Sciences, Fujian Normal University, Fuzhou , P. R. China.
yangfafu@fnu.edu.cn;
College of Chemistry and
Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/gmcl.
Supplemental data for this article can be accessed on the publisher’s website
©  Taylor & Francis Group, LLC

60
A. RUAN ET AL.
Figure . Three types of the reported CTV liquid crystals.
units on calixarene sketelon [24–32]. Cyclotriveratrylene (CTV), usually adopting crown
conformation with bowl-shape structure, also has been used to prepare the liquid crystalline
molecules. The survey of literatures suggested that the reported CTV liquid crystals could
be divided into three types as shown in Figure 1. For the type (I), three normal alkyl chains
were introduced onto CTV and only the nematic liquid crystal were obtained [33–36]. For
the types (II) and (III), 6, 9, 12 or 18 alkyl chains were grafted onto CTV, resulting in nematic
or columnar mesophase [37–41]. These literatures suggested that the three aromatic rings
were not enough to form the strong π-π stacking action for columnar CTV liquid crystals. If
the other aromatic groups with multiple alkyl chains were introduced onto CTV, the colum-
nar CTV liquid crystals could be prepared based on the strong π-π stacking action of the
more aromatic groups in most cases. Moreover, the reported columnar CTV liquid crystals
possessed six alkyl chains at least in these literatures. But the columnar CTV liquid crystals
with 6–18 alkyl chains were usually prepared by stepwise method with complicated separa-
tion. Thus, a arisen question is whether the columnar CTV liquid crystal can be obtained with
less alkyl chains such as three alkyl chains, because this kind of CTV derivative could be eas-
ily prepared by simple one-pot synthesis. In this article, series of CTV derivatives with three
alkyl chains (pentyl, hexyl, dodecyl and octadecyl) based on click chemistry were designed
and synthesized in high yields with simple procedure. Moreover, their mesomorphic proper-
ties implied that only the CTV derivative with three octadecyl exhibited ordered hexagonal
columnar mesophase. These results indicated that a balance between the number and length
of alkyl chains for columnar CTV liquid crystalline behavior. The length of alkyl chains could
make up for the shortage of numbers of alkyl chains in a certain degree. This study reported
firstly the columnar CTV liquid crystal with three alkyl chains, supplying a new strategy to
design and synthesis of columnar CTV liquid crystals with less alkyl chains and simple syn-
thetic procedure.
Results and discussion
Synthesis and characterization
The synthetic routes for novel columnar CTV liquid crystals were exhibited in Scheme 1. As
analyzed above, it is difficult to form columnar CTV liquid crystal for normal CTV deriva-
tives due to the weak π-π stacking action of the three aromatic rings in CTV skeleton. In
Scheme 1, the click chemistry was applied for the synthesis of target compounds, because
of not only the high efficient and concise synthetic procedure of click reaction but also the
enhancing π-π stacking action based on the three new aromatic triazole ring. In the step of

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
61
Scheme . The synthetic routes for CTV derivatives 3, 4, 5 and 6.
preparing CTV skeleton, the simple one-pot method was used to synthesize compound 2 with
simple separation in high yield. Also, in order to investigate the influence of alkyl length on
mesomorphic property, the pentyl, hexyl, dodecyl and octadecyl groups were introduced onto
CTV skeleton. As shown in Scheme 1, compound 1 was prepared conveniently by reacting o-
methoxyphenol with propargyl bromide in yield of 88%. By further treating compound 1 with
paraformaldehyde using BF3-Et2O as catalyst, compound 2 was obtained in 85% yield after a
rapid column chromatography. Then, the target compounds 3–6 was synthesized efficiently
by the click reaction of compound 2 with the corresponding alkyl azides. The yields were as
high as 80–88%. All new compounds showed only one spot on TLC plate under all kinds of
solvents, suggesting they were pure compounds.
The structures of these novel CTV derivatives 3–6 were confirmed by MS and NMR spec-
tra. The strong peaks in their HR-MS spectra at 862.4971, 904.5444, 1156.8223 and 1409.1060
were exactly in accordance with the molecular weight of compounds 3–6. In their 1H NMR
spectra, the proton signals were well assigned for their structures (see SI). Specially, a pair
of doublets for the methylene of CTV skeleton certainly supported the crown conformations
for these derivatives, which were favorable for the bowl-shape structures. The slight splits of
methyl might be attributed the flexibility of the crown conformation based on the non-rigid
methylene bridges. The 13C NMR spectra also agreed with their structures.
Mesomorphic studies
The mesomorphic behaviors of compounds 3, 4 and 5 were firstly studied by differential
scanning calorimetry (DSC). The results of DSC detection were shown in Figure 2 and the
corresponding thermodynamic parameters were summarized in Table 1. One can see that
compounds 3, 4, and 5 exhibited one endothermic peak on second heating at 41.5°C, 43.3°C
Table . Transition temperatures (°C) and enthalpies (kJ·mol−) of compounds 3, 4, 5 and 6.
Comp.
Phase transition[a]
T(ꢀH) Heating scan
T(ꢀH) Cooling scan
3
4
5
6
Cr-Iso(Iso-Cr)
Cr-Iso(Iso-Cr)
Cr-Iso(Iso-Cr)
Cr-Col(Col-Cr)
Col-Iso(Iso-Col)
.(.)
.(.)
.(.)
.(.)
.(..)
.(.)
.(.)
.(.)
.(.)
.(.)
[a]Cr = crystalline, Col = columnar phase, Iso = isotropic

62
A. RUAN ET AL.
Figure . The DSC traces of compounds 3, 4, 5 and 6 on second heating and cooling (scan rate °C min−).
and 48.4°C, respectively. Upon cooling, they also only showed one exothermic peaks at
40.9°C, 41.2°C and 46.3°C, respectively. These results might suggest the solid state-isotropic
phase transition and no mesophase for compounds 3, 4 and 5. However, compound 6 with
octadecyl groups displayed the utterly different changes on DSC trace in comparison with
compounds 3, 4 and 5. On the second heating, two endothermic peaks were obviously
observed at 22.6°C and 63.9°C. Upon cooling, two exothermic peaks appeared at 18.9°C and
54.6°C for compound 6. The broad thermic peaks could be attributed to such long wobbly
chains and high viscous morphology for melting. These data implied the phase transition of
solid state-mesophase-isotropic phase for compound 6, which were further supported by the
investigation of POM (polarizing optical microscopy) and XRD (X-ray diffraction) analysis.
The melting points of compounds 3, 4, 5 and 6 increased orderly with the increase of length
of alkyl chains. These DSC traces might be explained by the structures of compounds 3, 4, 5
and 6. Due to six aromatic rings in these novel CTV derivatives, the three alkyl chains (pentyl,
hexyl and dodecyl) of compounds 3, 4 and 5 were too short to produce the liquid crystalline
property. But the octadecyl groups in compound 6 are long enough to induce the appearance
of mesophase. The slight hysteresis for exothermic peak of compound 6 was common
super-cooling phenomenon for such highly viscous material. The molecular stacking mode
of compound 6 in mesophase was further investigated by POM and XRD as follows.
Furthermore, the phase transition behaviors of compounds 3, 4, 5 and 6 were investigated
by POM. For compounds 3, 4 and 5, the white powder melted gradually at 40–50 °C and the
whole view became black slowly. On cooling, the clear liquid transferred to the white solid
slowly at the corresponding temperatures of the thermic peaks in DSC curves. No obvious
mesophase texture was observed for compounds 3, 4 and 5. These phenomena indicated the
phase transition of solid state-isotropic phase only for compounds 3, 4 and 5. However, for
compound 6, the two kinds of phase transitions on heating and cooling were observed clearly.
Upon heating, the solid of compound 6 melted and a cloudy liquid appeared slowly. This
kind of cloudy liquid became clear gradually over 60 °C. When cooling from the isotropic
phase, the cloudy liquid appeared again for compound 6 and turned more and more bright
and colorful with specific texture, which became the solid finally with the decrease of temper-
ature. Figure 3 illustrated the texture of compound 6 at crystalline state and mesophase. One
can see that compound 6 was small particle with irregular shape in solid state but exhibited

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
63
Figure . The photos of compound 6 under POM at crystalline state and mesophase on cooling at  °C
(Zoom in  times for big box and  times for small box).
uniform and regular texture in mesophase. The dark part in mesophase might indicate the
coexistence of isotropic and liquid crystalline state, which could be ascribed to the highly
viscous morphology at 40 °C. This observed texture possessed the focal-conic pattern, which
was the typical characteristic for columnar liquid crystal. All these POM results were in
accordance with the DSC data, suggesting that compounds 3, 4 and 5 have no mesophase
and compound 6 with three octadecyl groups exhibited columnar mesomorphic property.
The XRD analysis was employed to investigate the possible molecular packing patterns for
the mesophase of compound 6. The XRD trace at 40 °C for the mesophase was illustrated in
Figure 4. It can be seen that, although the curve was rough in a certain due to the coexistence
of isotropic and liquid crystalline state as described in POM analysis, three reflections at 2.18°,
3.78° and 4.36° were observed obviously for compound 6 in the small-angle region. After cal-
culating by the Bragg’s formula d = λ/(2Sinθ), the corresponding d-spacings were 40.50, 23.38
˚
and 20.25 A, which agreed with 1: 1/ꢀ3:1/ꢀ4 for the [100], [110] and [200] planes of hexago-
nal columnar mesophase. At the wide-angle regions, the broad halos at 2θ = 15∼25° implied
˚
the mean distance of 4.5 A and the short correlation length of alkyl chains. In addition, a small
˚
reflection peak at 20.70° was distinguished, suggesting the distance of 4.28 A. This value was
coincident with the typical intracolumnar distance for π-π interaction of ordered hexagonal
Figure . XRD trace of compound 6 measured at  °C.

64
A. RUAN ET AL.
Figure . The proposed schematic representation of the hexagonal columnar mesophase of compound 6.
columnar liquid crystal. All these XRD data supported the hexagonal columnar liquid crystals
for compound 6. On the other hand, as estimated by CPK molecular model, the diameter of
˚
compound 6 was 71 A when assuming the straight linear structure for alkyl chains and bowl-
shape structure for CTV core. After calculation based on the XRD data, the lattice parame-
˚
ter (ɑ) for mesophase of compound 6 was 46.8 A, which near 35% less than the diameter of
compound 6. These results might suggest that the curly structure for alkyl chains or the pos-
sible alkyl interdigitation in the neighboring columns. Thus, the possible molecular stacking
model for the hexagonal mesophase of compound 6 was proposed in Figure 5. Combing all
the analysis of DSC, POM and XRD analyses, it could be summarized that compounds 3, 4
and 5 with pentyl, hexyl or dodecyl groups exhibited no mesophase, but CTV derivative 6
with three octadecyl groups showed good liquid crystalline behavior with ordered hexagonal
mesophase. There results indicated a subtle balance between the number and length of alkyl
chains for columnar CTV liquid crystalline behavior. The length of alkyl chains could make
up for the numbers of alkyl chains and resulted in the columnar mesophase.
Conclusion
In conclusion, CTV derivatives with three alkylnyl groups were prepared by one-pot method
in 85% yield. Further treating it with alkyl azides, the target CTV derivatives with triazole

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
65
rings and three alkyl groups was obtained efficiently by the click reaction in yield of 80–88%.
The structures and crown conformations were confirmed by NMR and MS. Their liquid
crystalline properties were investigated by DSC, POM and XRD. The results implied that the
CTV derivatives with pentyl, hexyl or dodecyl groups possess no mesophase but the one with
octadecyl groups exhibited ordered hexagonal columnar mesophase. Unlike the reported
columnar CTV liquid crystals with six alkyl chains at least, this article reported the CTV
columnar liquid crystal with three alkyl chains for the first time. These results indicated that
a subtle balance between the number and length of alkyl chains for columnar CTV liquid
crystalline behavior. This study supplied a new idea to design and synthesis of columnar
CTV liquid crystals with less alkyl chains and the simple synthetic procedure.
Experimental
General methods
The inorganic and organic reagents chemical reagents were purchased from Aladdin LLC and
used directly for reaction. The organic solvents of reaction were purified by standard anhy-
drous methods before application. TLC analysis was done by pre-coated glass plates. Rapid
column chromatography was performed by using silica gel (200–300 mesh) as adsorbent.
NMR spectra were obtained on a Bruker-ARX 400 instrument at 26 °C by using tetramethylsi-
lane as internal standard. The MS spectra were performed on Bruker mass spectrometer. The
phase transitions were examined by POM (Leica DMRX) with a hot stage (Linkam THMSE
600). Thermal analysis was done on DSC (Thermal Analysis Q100) with a scanning rate of
10°C/min under N2 atmosphere. The XRD curves were measured on SEIFERT-FPM (XRD7),
˚
using Cu Kα 1.5406A as the radiation source with 40 kV, 30 mA power.
Synthesis of compound 1
The mixture of o-methoxyphenol (2.0 g, 16 mmol), propargyl bromide (1.5 mL), and K2CO3
(2.7 g, 20 mmol) was stirred and refluxed in 40 mL of dry MeCN for 10 h. The reaction was
monitored by TLC technique. As the starting materials were disappeared, the reaction was
cooled to room temperature and then treated with 50 mL of CH2Cl2. The obtained mixture
was filtered and the filtrate was washed by distilled water for three times. The organic layer was
concentrated under reduced pressure to afford compound 1 as canary yellow liquid in yield
of 88%. 1HNMR (400 MHz, CDCl3) δ (ppm): 6.82–7.08 (m, 4H, ArH), 4.74 (s, 2H, OCH2C),
3.82 (s, 3H, OCH3), 2.48 (s, 1H, CࣕCH).
Synthesis of compound 2
Under N2 atmosphere, compound 1 (16 mmol) and paraformaldehyde (0.5 g, 16 mmol) was
added in 40 mL of CH2Cl2. After stirring for 5 min under ice bath, 5 mL of BF3-Et2O was
dropped in the reaction system. The obtained mixture was stirred at room temperature for
48 h. Then the solution was washed by distilled water for two times. The organic layer was
separated, concentrated and purified by rapid column chromatography (eluent: CH2Cl2: ethyl
acetate = 30: 1). Compound 2 was obtained as white solid in yield of 85%. 1HNMR (400 MHz,
CDCl3) δ (ppm): 7.03 (s, 3H, ArH), 6.86 (s, 3H, ArH), 4.72 (bs, 9H, ArCH2Ar and OCH2C),
3.83–3.85 (m, 9H, OCH3), 3.57 (d, 3H, J = 12.0 Hz, ArCH2Ar), 2.49 (s, 3H, CࣕCH). HR-ESI-
MS: m/z calculated for C33H30O6: 545.1934 [MNa]+, found 545.1947.

66
A. RUAN ET AL.
Synthesis of compounds 3, 4, 5 and 6
The corresponding alkyl bromide (5 mmol) and NaN3 was stirred in 15 mL of DMF at
50 °C for 10 h. After cooling, the solution was filtered. Then compound 2 (0.52 g, 1 mmol),
CuSO4·H2O (0.39 g, 1.6 mmol) and sodium ascorbate (0.7 g, 3.6 mmol) were added in the
filtrate. The obtained mixture was stirred at 60 °C for 24 h. After reaction, the solution was
partitioned by 50 mL of distilled water and 50 mL of CH2Cl2. Then the organic layer was
separated and concentrated. The residue was purified by column chromatography (eluent:
CH2Cl2: ethyl acetate = 25: 1). Compound 3, 4, 5 and 6 was collected as white powder in
yields of 80%, 84%, 86% and 88%, respectively.
1
Compound 3: HNMR (400 MHz, CDCl3) δ (ppm): 7.57 (s, 3H, C = CH), 7.06 (s,
3H, ArH), 6.83 (s, 3H, ArH), 5.28 (m, 6H, OCH2), 4.73 (d, 3H, J = 12.0 Hz, ArCH2Ar),
4.29 (m, 6H, NCH2), 3.82–3.86 (m, 9H, Me), 3.52 (d, 3H, J = 12.0 Hz, ArCH2Ar), 1.80∼1.87
(m, 6H, CH2), 1.28∼1.32 (m, 12H, CH2), 0.86 (t, 9H, J = 8.0 Hz, CH3); 13C NMR(100 MHz,
CDCl3) δ (ppm): 148.15, 146.21, 132.04, 131.62, 125.55, 122.93, 115.82, 113.50, 63.17, 56.16,
50.23, 36.15, 29.62, 28.32, 21.96, 13.58. HR-ESI-MS: m/z calculated for C48H63N9O6: 862.4974
[M+H]+, found 862.4971.
Compound 4: 1HNMR (400 MHz, CDCl3) δ (ppm): 7.57 (m, 3H, C = CH), 7.06 (s, 3H,
ArH), 6.83 (s, 3H, ArH), 5.28 (s, 6H, OCH2), 4.73 (d, 3H, J = 12.0 Hz, ArCH2Ar), 4.34∼4.25
(m, 6H, NCH2), 3.83–3.86 (m, 9H, OCH3), 3.54 (d, 3H, J = 12.0 Hz„ ArCH2Ar), 1.80∼1.87
(m, 6H, CH2), 1.28∼1.32 (bs, 18H, CH2), 0.89 (bs, 9H, CH3); 13C NMR(400 MHz, CDCl3)
δ (ppm): 148.19, 146.34, 132.72, 131.93, 122.73, 116.13, 115.67, 113.41, 63.43,56.07, 50.41,
36.34, 31.13, 30.15, 25.79, 22.48, 13.78. HR-ESI-MS: m/z calculated for C51H69N9O6: 904.5444
[M+H]+, found 904.5444.
1
Compound 5: HNMR (400 MHz, CDCl3) δ (ppm): 7.57 (s, 3H, C = CH), 7.06 (s, 6H,
ArH), 6.84 (s, 6H, ArH), 5.28 (s, 6H, OCH2), 4.72 (d, 3H, J = 12.0 Hz, ArCH2Ar), 4.31∼4.25
(m, 6H, NCH2), 3.85–3.89 (m, 9H, OCH3), 3.53 (d, 3H, J = 12.0 Hz, ArCH2Ar), 1.90∼1.25
(m, 60H, CH2), 0.91∼0.87 (t, J = 6.0 Hz, 9H, CH3).13C NMR(400 MHz, CDCl3) δ (ppm):
148.05, 146.33, 1132.77, 131.91, 125.06, 122.78, 115.70, 113.22, 63.30, 56.21, 51.45, 50.36,
36.39, 31.91, 30.19, 29.61, 29.34, 29.16, 28.98, 28.83, 26.71, 26.47, 22.69, 14.13. HR-ESI-MS:
m/z calculated for C69H105N9O6: 1156.8260 [M+H]+, found 1156.8223.
1
Compound 6: HNMR (400 MHz, CDCl3) δ (ppm): 7.57 (s, 3H, C = CH), 7.06 (s, 6H,
ArH), 6.82 (s, 3H, ArH), 5.28 (s, 6H, OCH2), 4.72 (d, 3H, J = 8.0 Hz, ArCH2Ar), 4.30∼4.25
(m, 6H, NCH2), 3.85–3.90 (s, 9H,OCH3), 3.53 (d, 3H, J = 8.0 Hz, ArCH2Ar), 1.18∼1.93
(m, 96H, CH2), 0.91∼0.88(t, J = 8.0 Hz, 9H, CH3). 13C NMR(400 MHz, CDCl3) δ
(ppm):148.20, 146.40, 132.48, 131.53, 122.95, 122.68, 115.73, 113.40, 63.46, 56.28, 50.37,
36.49, 31.85, 30.22, 29.72, 29.58, 29.38, 29.00, 26.51, 22.71, 14.14. HR-ESI-MS: m/z calculated
for C87H141N9O6: 1409.1077 [M+H]+, found 1409.1060.
Funding
Financial support from the National Natural Science Foundation of China (No: 21406036) and Fujian
Natural Science Foundation of China (No. 2017J01571) are greatly acknowledged.
Supporting information
The experimental procedure and the spectral characterization are given in Supporting Information.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
67
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