Synthesis and characterization of new chiral liquid crystal monomers containing steroid unit

Article abstract of DOI:10.1080/15421406.2018.1553744

To reduce the bulky steric hindrance, improve the reactivity of diosgenin and cholesterol, and obtain mesophase of their derivatives, the commercially available cholesterol and diosgenin were allowed to be structurally modified. Four new chiral LC intermediate compounds (c～f) and the corresponding monomers (M₁?M₄) with different longer spacer were synthesized. The chemical structures, optical texture, thermal behavior and mesophase structure of all the mesogenic compounds obtained in this study were characterized by FT-IR, ¹H-NMR, polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction measurements. The experimental results showed that the intermediate compounds containing diosgenyl groups c and d only showed a mesophase and exhibited fan-shaped texture of a smectic A (S_A) phase, while the compounds containing terminal cholesteryl groups e and f showed two mesophases and exhibited fan-shaped texture of a S_A phase, and oily streak texture and focal conic texture of cholesteric phase, respectively. The four chiral monomers M₁?M₄ all revealed cholesteric oily streak texture and focal conic texture. In addition, the melting temperature (T_m) and isotropic temperature (T_i) of the mesogenic compounds decreased with increasing the flexible spacer length. Compared with the intermediate compounds or monomers based on cholesterol, the compounds or monomers based on diosgenin showed higher T_m and T_i.

Full text of DOI:10.1080/15421406.2018.1553744

Molecular Crystals and Liquid Crystals
ISSN: 1542-1406 (Print) 1563-5287 (Online) Journal homepage: https://www.tandfonline.com/loi/gmcl20
Synthesis and characterization of new chiral liquid
crystal monomers containing steroid unit
Qifan Chen, Xiaofeng Liu, Zhihao Guo, Xiaoxu Xu & Yanhua Lu
To cite this article: Qifan Chen, Xiaofeng Liu, Zhihao Guo, Xiaoxu Xu & Yanhua Lu (2018)
Synthesis and characterization of new chiral liquid crystal monomers containing steroid unit,
Molecular Crystals and Liquid Crystals, 669:1, 1-11, DOI: 10.1080/15421406.2018.1553744
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MOLECULAR CRYSTALS AND LIQUID CRYSTALS
018, VOL. 669, NO. 1, 1–11
2
https://doi.org/10.1080/15421406.2018.1553744
Synthesis and characterization of new chiral liquid crystal
monomers containing steroid unit
a
b
b
a
a,c
Qifan Chen , Xiaofeng Liu , Zhihao Guo , Xiaoxu Xu , and Yanhua Lu
a
b
School of Chemical Engineering, Eastern Liaoning University, Dandong, P. R. China; Center for
Molecular Science and Engineering, College of Science, Northeastern University, Shenyang, P. R. China;
c
Key Laboratory of Functional Textile Materials, Liaoning Province, Dandong, P. R. China
ABSTRACT
KEYWORDS
diosgenin; cholesterol;
liquid crystal;
monomer; chiral
To reduce the bulky steric hindrance, improve the reactivity of dios-
genin and cholesterol, and obtain mesophase of their derivatives,
the commercially available cholesterol and diosgenin were allowed
to be structurally modified. Four new chiral LC intermediate com-
pounds (cꢀf) and the corresponding monomers (M ꢁM ) with dif-
1
4
ferent longer spacer were synthesized. The chemical structures,
optical texture, thermal behavior and mesophase structure of all the
mesogenic compounds obtained in this study were characterized by
1
FT-IR, H-NMR, polarizing optical microscopy, differential scanning
calorimetry, and X-ray diffraction measurements. The experimental
results showed that the intermediate compounds containing dio-
sgenyl groups c and d only showed a mesophase and exhibited fan-
shaped texture of a smectic A (S ) phase, while the compounds con-
A
taining terminal cholesteryl groups e and f showed two mesophases
and exhibited fan-shaped texture of a S
ture and focal conic texture of cholesteric phase, respectively. The
four chiral monomers M all revealed cholesteric oily streak tex-
ꢁM
ture and focal conic texture. In addition, the melting temperature
) and isotropic temperature (T ) of the mesogenic compounds
A
phase, and oily streak tex-
1
4
(
T
m
i
decreased with increasing the flexible spacer length. Compared with
the intermediate compounds or monomers based on cholesterol, the
compounds or monomers based on diosgenin showed higher T
and Ti.
m
1. Introduction
Liquid crystal (LC) materials have been widely used for display devices because their
flexible ordered structures can lead to systems displaying switchable optical modulation.
The LC compounds can potentially be used as new functional materials for electron,
ion, molecular transporting, sensory, catalytic, optical and bioactive materials [1, 2]. In
recent year, chiral LC compounds with helical supramolecular structure are always fasci-
nating and have attracted considerable attention and interest because they possess excel-
lent electro-optical properties, including selective reflection of light, thermochromism,
ferroelectricity, and circular dichroism, and important potential applications in various
areas such as non-linear optical devices, flat-panel displays, thermal imaging, rewritable
CONTACT Xiaoxu Xu
3x.931@163.com
ß 2018 Taylor & Francis Group, LLC

2
Q. CHEN ET AL.
full-color image recording, and photostable UV screens [3–17]. Chirality can be intro-
duced into LC molecules at various levels, and be devided into three types, including
point chirality, axial chirality (e.g. BINOL) [18, 19] and planar chirality (e.g. phanes)
[20]. Point chirality is usually introduced as a branching point somewhere in the alkyl-
tail of a liquid crystal, but some are located in the terminal position of the mesogenic
core, such as steroids. The cholesteric phase is formed by rod-like, chiral molecules
responsible for macroscopical alignment of cholesteric domains. Depending to chemical
structures, it may be feasible to achieve a macroscopic alignment of cholesteric domains.
In general, the formation of mesophases may be affected by aspect ratio, flexible spacer
at the center, and polarity of the monomers [21, 22].
As a kind of natural mesogen, diosgenin and cholesterol with many chiral centers
have a strong optical activity or high specific optical rotation [23]. Until now, they have
become an attractive candidate to synthesize new LC materials [24–30]. Therefore, it
would be both necessary and useful to synthesize various kinds of chiral LC materials
to explore their potential applications. In the present work, we aimed to design new
chiral LC materials based on diosgenin and cholesterol. To investigate the effect of spa-
cer length and terminal groups on molecular interaction and physical properties of the
chiral materials, four new chiral LC intermediate compounds and the monomers with
different longer spacer were synthesized. Their structure and phase behavior were char-
1
acterized using FTIR, H NMR, POM, DSC, and XRD.
2. Experimental method
2.1. Materials
All chemicals were obtained from the indicated sources. Tosyl chloride, methacrylic
acid, palladium 10% on carbon and benzyl chloride were purchased from Sinopharm
Chemical Reagent Co., Ltd. (Shenyang, China). 1,6-Hexanediol and 1,8-octanediol were
purchased from Qingdao Lilai Fine Chemical Industry Co., Ltd. (Qingdao, China).
Diosgenin was purchased from Wuhan Chemical Industry Co., Ltd. (Wuhan, China).
Cholesterol was purchased from Xiayi Beier Biological Products Co., Ltd. (Xiayi,
China). All other solvents and reagents used were purified by standard methods.
2.2. Measurements
FTIR spectra were measured on a PerkinElmer spectrum One (B) spectrometer
1
(
PerkinElmer, Foster City, CA). H NMR spectra were obtained using a Bruker ARX
6
00 (Bruker, F €a llanden, Swiss) high resolution NMR spectrometer, and chemical shifts
were reported in ppm with tetramethylsilane (TMS) as an internal standard. The optical
texture was observed with a Leica DMRX POM (Leica, Wetzlar, Germany) equipped
with a Linkam THMSE-600 (Linkam, London, UK) cool and hot stage. The thermal
behavior was determined with a Netzsch DSC 204 (Netzsch, Hanau, Germany) equipped
with a cooling system. XRD measurements were performed with a nickel-filtered Cu-Ka
radiation with a Bruker D8 Advance (Bruker, Germany) powder diffractometer.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
3
2.3. Synthesis of the intermediate compounds
The synthetic route of the intermediate compounds a-f is outlined in Scheme 1.
Diosgenyl-p-toluene sulfonate (a), cholesteryl-p-toluene sulfonate (b), 6-diosgenoxyhex-
ane-1-ol (c) 8-diosgenoxyoctane-1-ol (d), 6-cholesteroxy- hexane-1-ol (e) and 8-choles-
teroxyoctan-1-ol (f) were synthesized as described in the literatures [31–34].
2
.3.1. Synthesis of 6-diosgenoxyhexane-1-ol (c)
ꢂ
ꢁ1
Yield: 73%, mp: 109.8 C. IR (KBr, cm ): 3333 (–OH); 2929, 2850 (CH –, –CH –);
1
3
2
1
241, 1097 (C–O–C). H NMR (d, CDCl , 600 MHz): 5.34 (t, 1H, H-6), 4.41(q, 1H, H-
3
Scheme 1. Synthetic route of the compounds a–f.

4
Q. CHEN ET AL.
1
6), 3.64 (t, 2H, HOCH –), 3.49-3.38 (m, 4H, H-26 and HOCH CH O–), 3.12 (m, 1H,
2
2
2
H-3), 2.37-0.80 [m, 44H, H-diosgenyl and –(CH ) –].
2
4
2
.3.2. Synthesis of 8-diosgenoxyhexane-1-ol (d)
ꢂ
ꢁ1
Yield: 65%, mp: 105.2 C. IR (KBr, cm ): 3372 (–OH); 2930, 2855 (CH –, –CH –);
1
3
2
1
242, 1080 (C–O–C). H NMR (d, CDCl , 600 MHz): 5.34 (t, 1H, H-6), 4.41(q, 1H, H-
3
1
6), 3.64 (t, 2H, HOCH –), 3.48-3.43 (m, 4H, H-26 and HOCH CH O–), 3.12 (m, 1H,
2
2
2
H-3), 2.37-0.80 [m, 48H, H-diosgenyl and –(CH ) –].
2
6
2
.3.3. Synthesis of 6-cholesteroxyhexane-1-ol (e)
ꢂ
1
ꢁ1
Yield: 64%, mp: 66.2 C. IR (KBr, cm ): 3339 (–OH); 2934, 2851 (CH –, –CH –);
3
2
1
241, 1097 (C–O–C). H NMR (d, CDCl , 600 MHz): 5.38 (t, 1H, H-1), 3.65 (t, 2H,
3
HOCH –), 3.42 (m, 2H, HOCH CH O–), 3.10 (m, 1H, H-2), 2.33-0.68 [m, 51H, H-cho-
2
2
2
lesteryl and –(CH ) –].
2
4
2
.3.4. Synthesis of 8-cholesteroxyoctan-1-ol (f)
ꢂ
1
ꢁ1
Yield: 62%, mp: 66.0 C. IR (KBr, cm ): 3394 (–OH); 2933, 2852 (CH –, –CH –);
3
2
1
266, 1057 (C–O–C). H NMR (d, CDCl , 600 MHz): 5.37 (t, 1H, H-1), 3.65 (t, 2H,
3
HOCH –), 3.43 (m, 2H, –CH CH O–), 3.12 (m, 1H, H-2), 2.34-0.68 [m, 55H, H-choles-
2
2
2
teryl and –(CH ) –].
2
6
2
.4. Synthesis of chiral monomers
The synthetic route of the chiral monomers M –M is outlined in Scheme 2. They were
1
4
synthesized using the same method, and the detailed synthetic process of M1 is
described as follows as an example.
2
.4.1. Synthesis of 6-diosgenoxyhexyl acrylate (M1)
The compound c (2.06 g, 3 mmol), dried chloroform (15 mL), pyridine (5 mL) and a
small amount of hydroquinone were placed in a three-neck flask with a magnetic stir
bar and then acryloyl chloride was added dropwise. The system was reacted for 2 h at
ꢂ
room temperature and for 5 h at 45 C. After that, the mixture was cooled to tempera-
ture and poured into methyl alcohol, and there were white precipitates appeared. The
crude product was purified by silica gel column chromatography (ethyl acetate/hexane
ꢁ
1
=
1:1) to result in white solid. Yield: 47%. IR (KBr, cm ): 2932, 2852 (CH –, –CH –);
3 2
1
1
1
4
3
730 (C ¼ O); 1641 (C ¼ C); 1231 (C–O–C). H NMR (d, CDCl , 600 MHz): 6.38 (m,
3
H, CH =, trans-), 6.11 (m, 1H, =CH–), 5.75 (m, 1H, CH =, cis-), 5.34 (t, 1H, H-6),
2
2
.42(q, 1H, H-16), 3.64 (t, 2H, HOCH -), 3.49-3.37 (m, 4H, H-26 and –CH CH O-),
.12 (m, 1H, H-3), 2.37-0.79 [m, 44H, H-diosgenyl and –(CH ) –].
2
2
2
2
4

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
5
Scheme 2. Synthetic route of the monomers M1–M4.
2.4.2. Synthesis of 8-diosgenoxyoctyl acrylate (M2)
In a way similar to the synthesis of M , new diosgenyl derivative M was accordingly
1
2
ꢁ
1
prepared. Yield: 42%. IR (KBr, cm ): 2932, 2855 (CH –, –CH –); 1735 (C ¼ O); 1643
3
2
1
(
C ¼ C); 1238, (C–O–C). H NMR (d, CDCl , 600 MHz): 6.37 (m, 1H, CH =, trans-),
3
2
6
3
3
.10 (m, 1H, =CH–), 5.77 (m, 1H, CH =, cis-), 5.33 (t, 1H, H-6), 4.41(q, 1H, H-16),
2
.64 (t, 2H, HOCH –), 3.48-3.42 (m, 4H, H-26 and HOCH CH O–), 3.13 (m, 1H, H-
), 2.37-0.79 [m, 48H, H-diosgenyl and –(CH ) –].
2
2
2
2
6
2
.4.3. Synthesis of 6-cholesteryloxyhexyl acrylate (M3)
In a way similar to the synthesis of M , new cholesteryl derivative M was accordingly
1
3
ꢁ
1
prepared. Yield: 64%. IR (KBr, cm ): 2935, 2850 (CH –, –CH –); 1730 (C ¼ O); 1642
3
2
1
(
6
C ¼ C); 1240 (C–O–C). H NMR (d, CDCl , 600 MHz): 6.35 (m, 1H, CH =, trans-),
3
2
.12 (m, 1H, =CH–), 5.76 (m, 1H, CH =, cis-), 5.38 (t, 1H, H-1), 3.65 (t, 2H,
2
HOCH –), 3.41 (m, 2H, HOCH CH O–), 3.12 (m, 1H, H-2), 2.33-0.68 [m, 51H, H-cho-
2
2
2
lesteryl and –(CH ) –].
2
4
2
.4.4. Synthesis of 8-cholesteryloxyoctyl acrylate (M4)
In a way similar to the synthesis of M , new cholesteryl derivative M was accordingly
1
4
ꢁ
1
prepared. Yield: 43%. IR (KBr, cm ): 2934, 2851 (CH –, –CH –); 1732 (C ¼ O); 1641
3
2

6
Q. CHEN ET AL.
1
(
6
C ¼ C); 1262 (C–O–C). H NMR (d, CDCl , 600 MHz): 6.36 (m, 1H, CH =, trans-),
3
2
.13(m, 1H, =CH–), 5.76 (m, 1H, CH =, cis-), 5.37 (t, 1H, H-1), 3.64 (t, 2H, HOCH –),
2
2
3
.43 (m, 2H, HOCH CH O–), 3.12 (m, 1H, H-2), 2.33-0.69 [m, 51H, H-cholesteryl
2 2
and –(CH ) –].
2
4
3. Results and discussion
3.1. Optical textures
POM was used to observe the optical textures of liquid crystal (LC) intermediates and
monomers. POM can not only clearly observe the typical textures of the mesophase, but
also record the melting temperature (T ), the LC phase transition temperature, and the
m
isotropic temperature (Ti).
3
.1.1. Optical textures of the intermediates
As the POM results, the intermediate c exhibited the fan-shaped texture of a smectic A
ꢂ
ꢂ
(
1
S ) phase at 118 C, and heated to 135.0 C, the texture disappeared. When cooled to
A
ꢂ
31.0 C, the fan-shaped texture of a S phase started to appear and grew up with the
decrease of temperature. Continued cooling to 40 C, crystallization phenomenon
appeared. The intermediate d started to melt at 101 C, and exhibited the fan-shaped
texture of a S phase at 111 C, and an isotropic phase was observed at 121 C. On the
cooling process, the fan-shaped texture of a S phase appeared at 115 C, and crystal-
lized at 64 C. The intermediate e started to melt at 64 C, and showed the fan-shaped
texture of a S phase at 81 C and oily streak texture of cholesteric phase at 91 C. The
A
ꢂ
ꢂ
ꢂ
ꢂ
A
ꢂ
A
ꢂ
ꢂ
ꢂ
ꢂ
A
ꢂ
ꢂ
texture disappeared 98 C. When cooled to 93 C, the focal conic texture appeared, and
no crystallization phenomenon was observed during the cooling process. The intermedi-
ꢂ
ꢂ
ate f melted at 64 C, and exhibited the fan-shaped texture of a S phase at 70 C and
A
ꢂ
oily streak texture of cholesteric phase at 73 C. Continued heating, the texture disap-
ꢂ
ꢂ
peared at 87 C. When cooled to 80 C, the focal conic texture appeared. As an example,
the optical textures of the compound f at different temperatures are shown in Figure 1.
In general, the mesomorphic properties of LC compounds depend on the terminal
groups, the rigidity of the LC core and the flexible spacer length. For the intermediates
Figure 1. Optical textures of the compound f (200ꢃ) (a) fan-shaped texture of a S phase on heat-
A
ꢂ
ꢂ
ing to 70 C, (b) oily streak texture of cholesteric phase on heating to 73 C.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
7
c-f, the chiral terminal groups exhibited obvious effect on the phase behavior. For
example, the intermediates c and d with diosgenin groups only showed smectic phase,
however, the intermediates e and f with cholesteryl groups showed both smectic phase
and cholesteric phase.
3
.1.2. Optical textures of the monomers
The monomers M -M showed enantiotropic mesophase with the oily streak texture
1
4
and the focal conic texture of cholesteric phase during heating and cooling cycles, which
was also confirmed by XRD analysis. Herein, M was chosen as a representative to dis-
4
cuss the mesophase behavior in detail. On the heating process, M showed oily streak
4
ꢂ
texture of cholesteric phase at 55 C, along with selective reflection phenomenon, and
the reflection shifted to blue wavelength with the increase of the temperature. When
ꢂ
heated to 112 C, the texture disappeared. On the cooling process, the typical focal conic
ꢂ
texture appeared at 108 C and grew up with the decrease of the temperature. If a shear
force was applied to the sample at the moment, the focal conic texture immediately
changed to the oil streak texture, which was the characteristic of cholesteric phase. The
optical textures of the monomer M are shown in Figure 2.
4
3
.2. Thermal behaviors
DSC was used to study the thermal behavior of the LC intermediates and monomers.
The corresponding phase transition temperatures and enthalpy changes were obtained
during first cooling and second heating scans.
3
.2.1. Thermal behavior of the intermediates
The thermal analytical results of the intermediates c-f are summarized in Table 1.
According to DSC curves, the intermediates c and d only showed an endothermic peak
on heating process and an exothermic peak on cooling process, which represented the
melting temperature and crystallization transition temperature. There was no transition
peak between the mesophase and isotropic state. However, the fan-shaped texture of a
Figure 2. Optical textures of the monomer M (200ꢃ) (a) focal conic texture of cholesteric phase on
4
ꢂ
ꢂ
cooling to 108 C, (b) oily streak texture of cholesteric phase on heating to 55 C.

8
Q. CHEN ET AL.
Table 1. Thermal properties of intermediate compounds c ~ f.
o
-1
Phase transition temperature ( C) and enthalpy changes (Jꢄg )
Compound
heating cycle
cooling cycle
a
c
d
e
f
K109.8(30.1) S
K105.2(28.8) S
A
A
135.2 (–)I
121.3 (–)I
90.9(1.3)Ch98.8(1.1)I
75.9(0.5)Ch87.2(1.1)I
I128.2(7.1)S
I107.9(6.0)S
A
–K
–K
a
A
K66.4(24.2)S
K66.2(23.3)S
A
I97.8(1.2)Ch89.6(1.2)S
I86.3(1.3)Ch68.2(0.4)S
A
21.9(46.9)K
13.8(6.8)K
A
A
a
K ¼ crystal; S ¼smectic A phase; Ch ¼ cholesteric phase; I ¼ isotropic. Data obtained with POM
A
smectic phase was observed by the POM. For example, the melting range of the inter-
ꢂ
mediate c was from 119 to 139 C on the DSC results, and according to the POM result,
ꢂ
the intermediate c exhibited isotropic phase transition at 135 C and the isotropic tem-
perature range was quite narrow.
The intermediates e and f showed three endothermic peaks on heating process and
three exothermic peaks on cooling process. On heating curves, the peak at low tempera-
ture represented the melting phase transition, the second peak represented a S phase
A
to cholesteric phase transition, and the peak at high temperature represented cholesteric
phase to isotropic phase transition. Three exothermic peaks on the cooling curves repre-
sented an isotropic to cholesteric phase transition, a cholesteric to S phase transition
A
and crystallization transition, respectively.
The terminal groups, the rigidity of the LC core and the flexible spacer length have
an obvious effect on the thermal behavior of LC compounds. As seen from the data in
Table 1, compared with the intermediates with terminal diosgenyl groups, those with
terminal cholesteryl groups had a lower melting temperature (T ), lower isotropic tem-
m
perature (T ) and wider mesophase temperature range (DT). For example, the T , T
i
i
m
ꢂ
ꢂ
ꢂ
and DT of the intermediate e were 66.4 C, 98.8 C and 32.4 C, while the T of the
compound c was 109.8 C, and the T and DT obtained from POM were 135.2 C and
5.4 C, respectively. Furthermore, a longer spacer could cause the decrease of the T ,
m
ꢂ
ꢂ
i
ꢂ
2
m
Ti, and DT. For example, compared with the intermediate e with six methylene spacer,
the T , T and DT of the intermediate f with eight methylene spacer decreased by
m
i
ꢂ ꢂ ꢂ
0
.2 C, 11.6 C and 12.4 C, respectively.
3
.2.2. Thermal behavior of the monomers
The phase transition temperature of the monomers M -M is summarized in Table 2.
1
4
As the DSC curves, the monomers M and M with diosgenyl groups showed a glass
1
2
transition and a cholesteric to isotropic phase transition, which indicated they were
amorphous LC compounds. However, the monomers M3 and M4 with cholesteryl
groups showed the melting transition and a cholesteric to isotropic phase transition,
which indicated they were crystalline LC compounds. All of these indicated that the ter-
minal groups and the flexible spacer length had a similar effect on the thermal behavior
of monomers similar to intermediates.

MOLECULAR CRYSTALS AND LIQUID CRYSTALS
9
Table 2. Thermal properties of monomers M ~M .
1
4
o
-1
Phase transition temperature ( C) and enthalpy changes (Jꢄg )
Monomer
heating cycle
cooling cycle
M
1
M
2
M
3
M
4
G21.6Ch111.9(1.7)I
G11.6Ch113.0(5.6)I
K98.7(31.8)Ch109.7(0.9)I
K40.5(7.8)Ch57.8(0.8)I
I101.9(1.8)Ch–G
I110.8(4.1)Ch–G
I108.3(1.0)Ch67.3(23.0)K
I55.3(1.2)Ch40.4(–)K
G ¼ glass; K ¼ crystal; Ch ¼ cholesteric phase; I ¼ isotropic.
ꢂ
ꢂ
Figure 3. XRD patterns of (a) the intermediate f at 60 and 72 C, and (b) the monomer M at 50 C.
4
3.3. Mesophase structure
XRD measurement was used to further study the mesophase structure of the LC com-
pounds, especially the determination of the smectic phase and the study of the molecu-
ꢂ
ꢂ
lar orientatio. In general, there is a Bragg scattering (1 <2h < 5 ) for the smectic phase,
and no peak in the small-angle region for the nematic or cholesteric phase.
The XRD measurement of the intermediates and monomers in variable temperature
attached to different mesophase range was carried out. The XRD patterns of the inter-
mediates c and d showed a sharp reflection at small-angle region. For e and f, their
XRD patterns at low temperature revealed a sharp reflection at small-angle region, but
those at high temperature only showed a broad peak at wide-angle region. Combined
with the POM results, the intermediates c and d could be confirmed as a S phase, and
A
e and f showed a S phase at low temperature and a cholesteric phase at high tempera-
A
ture. For example, the compound f at low temperature revealed a strong peak at
ꢂ
2
h ¼ 3.92 , which represented that the molecules arranged in layers with short range,
and the corresponding d-spacing was estimated to be 22.5 Å, however the compound f
ꢂ
at high temperature displayed a broad peak at 2h ¼ 16.9 . Furthermore, the XRD pat-
terns of the monomers M -M only showed a broad peak at wide-angle region, which
1
4
were confirmed to be a cholesteric phase according to the oily streak texture and the
focal conic texture observed with POM. As an example, the XRD curves of the inter-
ꢂ
ꢂ
mediate f at 60 and 72 C, and the monomer M at 50 C are shown in Figure 3.
4

1
0
Q. CHEN ET AL.
4. Conclusions
In this work, we reported four LC intermediates and their corresponding acrylate
monomers with diosgenyl or cholesteryl groups. The intermediates c and d exhibited a
S phase, and e and f showed a S phase and cholesteric phase, while four monomers
A
A
M -M only showed a cholesteric phase. Compared with the compounds with terminal
1
4
diosgenin groups, that with terminal cholesteryl groups had a lower T , lower T and
m
i
broader mesophase temperature range. Furthermore, a longer spacer could cause the
decrease of the T and T and the narrowing of the mesophase temperature range.
m
i
Acknowledgements
This work was supported by the National Natural Science Foundation of China (51873084),
Department of Education of Liaoning Province (ldxy2017002), and Science and Technology
Committee of Liaoning Province (201602342).
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