Branched-arm macromolecule liquid crystals-containing fluorine and isosorbide-structure and properties

Article abstract of DOI:10.1016/j.molstruc.2015.02.050

A new series of cholesteric fluorated branched-arm liquid crystals (CHFBALCs) compound (MFA₁-MFA₄), with isosorbide as chiral core, was synthesized. Four precursors of branched-arm FA₁-FA₄ were obtained firstly

Full text of DOI:10.1016/j.molstruc.2015.02.050

Journal of Molecular Structure 1092 (2015) 96–103
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Branched-arm macromolecule liquid crystals-containing fluorine and
isosorbide-structure and properties
⇑
Xiao-Zhi He , Fang-di Zhang, Ying Jia, Fan-Bao Meng, Ying-gang Jia
Centre for Molecular Science and Engineering, Northeastern University, Shen-yang 110004, People’s Republic of China
h i g h l i g h t s
ꢀ
ꢀ
ꢀ
Four precursor of nematic liquid crystalline branched-arm and four chiral liquid crystalline branched-arm LC were synthesized.
The structures of the prepared compounds have been investigated by different spectroscopic techniques.
The thermal behavior, optical texture property and optical activity have been evaluated.
a r t i c l e i n f o
a b s t r a c t
Article history:
A new series of cholesteric fluorated branched-arm liquid crystals (CHFBALCs) compound (MFA1–MFA4),
with isosorbide as chiral core, was synthesized. Four precursors of branched-arm FA1–FA4 were obtained
firstly and then were esterized separately with isosorbide to get four chiral branched-arm liquid crys-
talline (MFA1–MFA4). The structures and properties were characterized by conventional spectrum meth-
ods, thermal analysis and texture analysis. The results showed that FA1–FA4 all were nematic phase with
schlieren, threaded-like or droplet texture. When the isosorbide was successfully inducted, the phase of
FA1–FA4 turned into cholesteric phase with oily streak texture, finger print texture or cholesteric dro-
plets. The values of melting point and clearing point for FA1–FA4 and MFA1–MFA4 all changed irregularly,
which may be due to the effect of different branched arm, warping of chiral agent and fluorine atom.
MFA1–MFA4 had the same handedness as isosorbide core and did not show selective reflection. MFA3
and MFA4 were hopeful to realize the combination of the processability of polymers and the mobility
of small molecules.
Received 14 December 2014
Received in revised form 13 February 2015
Accepted 13 February 2015
Available online 21 February 2015
Keywords:
Branched-arm
Liquid crystal
Chiral
Texture
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
units were decorated with different functional group, a new style
LC materials may be obtained.
Liquid crystals (LC) as soft functional materials are of increasing
interest in materials science within the last few years [1–5]. While
non-conventional LC, such as disco-, banana- and dentritic, which
broke down the traditional LC theory, is also an interesting class
of liquid crystals and has been paid much attention in recent years.
The main attention is focused on photoactive, chiral and
supramolecular dendrimers with regard to future developments
[6–20]. Dentritic LC is under the spotlight, including multiarm-
mesogens (branched-arm LC), dendrons, dendrimers and
supramolecular mesogens, which are hopeful to overcome the
drawbacks of linear polymers. These compounds can be used as
soft functional materials, such as an isotropic electron/hole-, ion-,
proton-conducting and opto-electronic materials.
Fluorinated traditional liquid crystals with terminal or lateral
fluorine substituents are well suited for achieving a strongly
dielectric anisotropy owing to the strong dipole moment of the
CAF bond, and with many interesting properties due to fluorine’s
small size, large electronegativity, low polarizability, and large
fluorine repulsion [21–24].
Derivatives of benzene [25–32], condensed aromatic rings [33],
cyclotriphosphazene [33,34], tetrachlorosilane [35] and pentaery-
thritol [36] are often taken as cores of the multi-arm compounds.
To obtain cholesteric branched-arm LCs (CHBALCs), chiral cores
or chiral arms would be constructed into the molecular structures.
When chiral and fluorine atom are inducted into the branched-
arm system, the material will possess the over-all properties of chi-
ral, fluorinated material and branched LC and have wide prospect
of application. The reason we chose isosorbide is that it possesses
a high twisting power and obviously a high molar fraction of
isosorbide generated helixes with a pitch which is too small (or
Branched-arm LCs (BALCs) usually consist of a core and a few
mesogenic units as the side arm. When the core and the mesogenic
⇑
Corresponding author.
http://dx.doi.org/10.1016/j.molstruc.2015.02.050
0022-2860/Ó 2015 Elsevier B.V. All rights reserved.

X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
97
large) for an interaction with visible light [37]. Otherwise isosor-
bide derivatives are usually synthesized as doping agent to make
cholesteric color filter. So the research on CHBALCs with isosorbide
as chiral core is of great significance.
pyridine, chloroform, dichloromethane and tetrahydrofuran were
bought from Shenyang Chemical Industry Company (China).
Isosorbide was got from Yangzhou Shen Zhou new material Co.
Ltd (China). All solvents were purified by standard methods.
The researches on the field of CHBALCs have been done by our
team. Cholesteric mesogenic units were introduced into phloroglu-
cinol, glucose or nematic mesogenic units were introduced into
glucose or maltose or isosorbide, which all can obtain in synthesiz-
ing CHBALCs [38–40]. In present study, the core still is isosorbide,
but the arm of liquid crystals changed into fluorated substance. It is
very necessary to study the inner relationship between structure
and function. And at the same time, a new synthetic way is used
insteading of DCC–DMAP esterification ways whose afterprocess-
ing is complicated. Four intermediate of nematic branched-arm
LC had been synthesized first and then isosorbide were introduced
into the chloride of the four precursor by esterification under the
reaction system of dichloromethane and pyridine with small
amount of aminopyridine as catalysis agent, which can improve
the product yield and simplify afterprocessing as well. The influ-
ence of the chiral core, fluorine atom and different mesogenic
branched arms on the mesomorphic properties of CHFBALCs were
studied and discussed here.
Measurement
IR spectra were measured by Perkin Elmer spectrum FT-IR spec-
trometer (Perkin Elmer Instruments, USA). H NMR, 13C NMR spec-
1
tra (400 MHz) were recorded on a Bruker AV 400 spectrometer in
5 mm o.d. sample tubes. The elemental analyses were carried out
with Elementar Vario EL III (Elementar, Hanau, Germany).
Specific rotation was performed with Perkin Elmer 341 polarime-
ter. All optical activity measurements of CHBALCs were carried
out in tetrahydrofuran (THF) with 2 mL cuvette of 100 mm length
using light of a Na-lamp at k = 589 nm. Ultraviolet–visible spec-
trophotometry was measured by PerkinElmer Lambda 950
instrument.
Phase transition temperatures and thermodynamic parameters
were determined by using a Netzsch DSC 204 (Netzsch, Germany)
with a liquid nitrogen cooling system. The heating and cooling
rates were 10 °C/min. A Leica DMRX (Leica, Germany) polarizing
optical microscope (POM) equipped with a Linkam THMSE-600
(Linkam, England) hot stage was used to observe phase transition
temperatures and analyzed LC properties for the monomers and
polymers through optical textures observation. XRD measure-
Experimental procedures
Materials
ments were performed with
a
nickel-filtered Cu
Ka
Parafluorobenzoic acid was obtained from Su Zhou Chemical
Regent Company (China). 4,4-Dihydroxybiphenyl, adipic acid,
(k = 0.1542 nm) radiation with a DMAX-3A Rigaku (Rigaku, Japan)
powder diffractometer.
Scheme 1. The synthetic routes of the precursor of branched-arm LCs.

98
X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
Scheme 2. The synthetic routes and the molecular model of CHFBALCs.
Synthesis
IR (KBr, cmꢁ1): 3250–2500(ACOOH), 1750, 1732(ACOOA),
FA1:
The synthetic routes of mesogenic arms (FA1–FA4) and chiral
branched-arm LCs (MFA1–MFA4) were shown in Schemes 1 and 2.
1706(ACOOH), 1602–1508 (ArA), 1215 (CAF).
1H NMR(CDCl3): d1.78–2.63(m, 8H, ACH2A), 7.14–8.25
(m, 12H, ArAH)Yield: 46.0%. mp:160.3 °C.
IR (KBr, cmꢁ1): 3500–2500(ACOOH), 1750, 1732(ACOOA),
1690(ACOOH), 1604–1450 (ArA), 1215 (CAF).
1H NMR(CDCl3): d1.79–2.68(m, 8H, ACH2A), 7.16–
FA2:
FA3:
FA4:
Syntheses of 6-(40-(4-fluorobenzoyloxy)biphenyl-4-yloxy)-6-
oxohexanoic acid (FA1)
12 g (0.047 mol) of adipic dichloride (synthesized in laboratory)
was dissolved in the mixture of chloroform (100.0 mL) and dichlor-
omethane (100 mL). The solvent was slowly dropped into the
round-bottom flask (500 mL) containing 5 g (0.15 mol) of
40-hydroxybiphenyl-4-yl 4-fluorobenzoate (synthesized in lab-
oratory) with tetrahydro-furan (100 mL), stirring 0.5 h at room
temperature, and then refluxed 18 h. The cold reaction mixture
were precipitated into water. The crude products were washed
with hot water and were crystallized from alcohol.
8.26(m, 16H, ArAH).
Yield: 90.2%. mp:183.9 °C.
IR (KBr, cmꢁ1): 3500–2500(ACOOH), 1751, 1730(ACOOA),
1702(ACOOH), 1602–1508 (ArA), 1215 (CAF).
1H NMR(CDCl3): d1.45–2.75(m, 16H, ACH2A), 6.90–
8.24(m, 27H,ArAH).
Yield: 88.9%. mp:154.9 °C.
IR (KBr, cmꢁ1): 3500–2500(ACOOH), 1750,
1732(ACOOA), 1708(ACOOH), 1602–1508 (ArA), 1215
(CAF).
Syntheses of 4-(6-(40-(4-fluorobenzoyloxy)biphenyl-4-yloxy)-6-
oxohexanoyloxy) benzoic acid (FA2),3,5-bis(6-(40-(4-
fluorobenzoyloxy)biphenyl-4-yloxy)-6-oxohexan oyloxy) benzoic acid
(FA3), 3,4,5-tris(6-(40-(4-fluorobenzoyloxy)biphenyl-4-yloxy)-6-
oxohexanoyloxy)benzoic acid (FA4)
1H NMR(CDCl3): d1.33–2.76(m, 24H, ACH2A), 7.20–
8.31(m, 38H, ArAH).
Yield: 87.6%. mp:151.6 °C.
FA2, FA3, FA4 can be obtained from the esterification of FA1 with
4-hydroxybenzoic acid, 3,5-dihydroxybenzoic acid and 3,4,5-
trihydroxybenzoic acid. All the synthetic routes are similar, so
FA4 was described as following.
2.075 g of FA1 of acyl chloride was dissolved in the blending of
dichloromethane (30 mL). The component solvent was slowly
added into round-bottom flask (150 mL) containing 0.236 g of gal-
lic acid with dichloromethane (50 mL) and pyridine (20 mL), stir-
ring 1 h at room temperature, and then refluxing 24 h. The cold
reaction mixture was precipitated into dilute acidic solution over
night and filtrate. After washing to neutral. The crude product
was crystallized from alcohol.
Syntheses of isosorbide 2,5-di-6-(40-(4-fluorobenzoyloxy)biphenyl-4-
yloxy)-6-oxohexanoic ester (MFA1), isosorbide 4-(6-(40-(4-fluoro-
benzoyloxy)biphenyl-4-ylox y)-6-oxohexanoyloxy)benzoate](MFA2),
isosorbide 2,5-di(3,5-bis(6-(40-(4-fluoro-benzoyloxy)biphenyl-4-
yloxy)-6-oxohexanoyloxy)) benzoic acid (MFA3), isosorbide 2,5-di-
(3,4,5-tris(6-(40-(4-fluorobenzoyloxy)biphenyl-4-yloxy)-6-oxohexa-
noyloxy)) benzoate) (MFA4)
The synthesis routes of MFA1, MFA2, MFA3 and MFA4 are simi-
lar, so MFA4 was described as following.
10 g of 3,4,5-tris(6-(40-(4-fluorobenzoyloxy)biphenyl-4-yloxy)-
6-oxohexanoylo-xy) benzoic acid in fleshly distilled thionyl chloride

X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
99
(40 ml) was refluxed for 5 h and then the excess thionyl chloride was
164.9(PhACOOA), 167.4(PhAF), 171.8(PhAOOCA).
Elemental analysis calculated for C170H132O42F6: C,
68.96%; H, 4.46%. Found: C, 68.74%; H, 4.58%. Yield:
77.2%. mp:131.6 °C.
removed under reduced pressure and brown viscous solid was
obtained. Dry benzene was put into it and then the benzene with
remained thionyl chloride was removed under reduced pressure
for three times in order to extirpate the remained thionyl chloride.
5.992 g of 3,4,5-tris(6-(40-(4-fluorobenzoyloxy)biphenyl-4-
yloxy)-6-oxohexano-yloxy) benzoyl chloride with 20 mL of dry
dichloromethane was added dropwise into a mixture of 0.2843 g
of isosorbide with 30 mL dichloromethane and 10 mL pyridine
with 0.03 g DMAP as catalytic agent, stirring 0.5 h under room
temperature. And then the reacting mixture refluxed for 20 h until
the IR peak OH of isosorbide disappeared. And then was poured
into water and boiled for 1 h to make the surplus acyl chloride
hydrolyze thoroughly. The obtained precipitate was filtered. The
crude product was purified by acetone and alcohol.
MFA1: IR (KBr, cmꢁ1): 2950–2820(ACH2A), 1757, 1732,
1720 (C@O), 1602–1508 (ArA), 1257–1150 (CAOAC).
1H NMR(CDCl3): d1.79–2.62(m, 16H, ACH2A), 3.58–
5.23 (m, 8H, isosorbide-H), 7.15–8.26 (m, 24H, ArAH).
13C NMR(CDCl3): 24.3, 24.8(methylene-C), 33.8, 34.2
(COACH2), 62.0, 73.8, 77.3, 81.9(isosorbide-C), 115.6,
115.8, 121.8, 125.5, 128.0(aromatic tertiary C), 132.7,
132.8, 138.2, 150.2(aromatic quaternary-C),
Fig. 1. 1H NMR spectrum of MFA1.
164.8(PhACOOA), 167.3(PhAF), 172.2(PhAOOCA).
Elemental analysis calculated for C56H48O14F: C,
69.78%; H, 4.98%. Found: C, 69.47; H, 5.01%. Yield:
75.1%. mp: 124.9 °C.
Table 1
Phase transition temperatures and specific rotations of precursor and CHFBA LCs.
MFA2: IR (KBr, cmꢁ1): 2950–2820(, ACH2A), 1757, 1732,
1715 (C@O), 1610–1508 (ArA), 1257–1150 (CAOAC).
a
20
Sample Transition temperature (°C) (corresponding
D
T1
a
589
enthalpy changes, J gꢁ1) Heating
1H NMR(CDCl3): d1.79–2.68(m, 16H, ACH2A), 3.51–
FA1
FA2
FA3
FA4
Crb160.3(54.18)Nb246.1(1.10)I
Cr183.9(34.56)N279.3(0.22)I
Cr 154.9(6.67)N218.7(1.01)I
Cr 151.6(14.2)N259.3(0.40)I
85.8
95.4
63.8
–
–
–
5.48 (m, 8H, isosorbide-H), 7.16–8.26(m, 32H, ArAH).
13C NMR(CDCl3): 24.3, 24.6(methylene-C), 33.9, 34.4
107.7
(COACH2), 68.5, 72.3, 77.3, 80.6(isosorbide-C), 115.7,
115.9, 121.8, 125.7, 128.2(aromatic tertiary C), 131.3,
132.8, 138.3, 150.1(aromatic quaternary-C),
Chc
Cr64.8(84.5)I
–
+55.21
30.9 +23.50
77.6 +9.45
66.1 +42.48
104.2 +8.16
MFA1
MFA2
MFA3
MFA4
Cr124.9(23.12)Chb155.8(0.46)I
Cr180.1(35.65)Ch258.7 (0.98)I
Cr145.3(9.90)Ch211.4(1.00)I
Cr131.6(12.49)Ch235.8(1.09)I
164.9(PhACOOA), 167.5(PhAF), 171.7(PhAOOCA).
Elemental analysis calculated for C68H56O18F2: C,
73.18%; H, 5.02%. Found: C, 72.96; H, 5.12%. Yield:
77.2%. mp:180.1 °C.
a
b
c
Mesophase temperature ranges on heating cycle.
Cr: crystal; N: nematic; Ch: cholesteric.
Ch: isosorbide.
MFA3: IR (KBr, cmꢁ1): 2987–2800(ACH2A), 1757, 1732,
1717 (C@O), 1610–1508 (ArA), 1257–1150 (CAOAC).
1
1H NMR(CDCl3): H NMR(CDCl3): d1.45–2.75(m, 32H,
ACH2A,), 3.56–5.23 (m, 8H, isosorbide-H), 6.90–
8.24(m, 54H, ArAH).
13C NMR(CDCl3): 24.1, 24.3(methylene-C), 33.8, 34.3
(COACH2), 63.6, 76.7, 78.4, 80.2(isosorbide-C), 115.7,
115.9, 121.5, 125.7, 128.2(aromatic tertiary C), 131.3,
132.8, 138.0, 150.2(aromatic quaternary-C),
164.9(PhACOOA), 167.4(PhAF), 171.8(PhAOOCA).
Elemental analysis calculated for C120H94O30F4: C,
68.9%; H, 4.49%. Found: C, 68.98; H, 4.34%.brown solid
powders. Yield: 79.2 %. mp:145.3 °C.
MFA4: IR (KBr, cmꢁ1): 2987–2868(ACH2A), 1732, 1719
(C@O), 1610–1508(ArA), 1257–1150 (CAOAC).
1H NMR(CDCl3): d1.33–2.76(m, 48H, ACH2A), 3.61–
5.28 (m, 8H, isosorbide-H), 7.20–8.31(m, 76H, ArAH).
13C NMR(CDCl3): 24.3, 24.6(methylene-C), 32.6, 33.9
(COACH2), 63.5, 70.3, 77.3, 80.7(isosorbide-C), 115.6,
115.8, 121.9, 125.6, 128.1(aromatic tertiary C), 131.3,
132.8, 138.3, 150.3(aromatic quaternary-C),
Fig. 2. DSC thermographs of FA1 and MFA1.

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X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
acylchloride of FA1–FA4 with isosorbide separately. The remains
From the above structure analysis, it can be concluded that the
of thionyl chloride exhausted through benzene and the obtained
products purified by repeating recrystallization with the mixed
solution of acetone–alcohol. And the IR spectra of MFA1–MFA4
did not show carboxylic acid and acetone–alcohol OH stretching
obtained substance are consistent with our molecule design. The
representative of H NMR spectrum was shown on Fig. 1.
1
Results and discussion
bands, the peak of the carboxylic acid C@O stretching vibration
1
disappeared as well. The H NMR spectra of MFA1–MFA4 showed
Synthesis
multiplet at 6.95–8.24 ppm, 3.59–5.23 ppm, 1.79–2.68 ppm
corresponding respectively to the chemical shift of aromatic,
isosorbide-H, methyleneoxy and methylene, respectively. The
results of FT-IR, Element analysis and 1H NMR, 13C NMR spec-
troscopy confirmed the expected structure and the high chemical
purity for those compounds.
The mesogenic branched-arm units (FA2, FA3, FA4) were synthe-
sized by reacting acylchloride of FA1 with p-hydroxybenzoic acid,
3,5-dihydroxybenzoic acid, 3,4,5-tri hydroxybenzoic acid in com-
ponent solvent of dichloromethane and pyridine. IR spectra of
FA1–FA4 showed characteristic bands at 3300–2500, 1750–1732,
1706–1698, 1600–1460, 1250–1100 attributed to carboxylic
acid(AOH), ester(C@O), carboxylic acid(C@O), phenyl(C@C) and
CAF stretching bands. MFA1–MFA4 were obtained by reacting
Thermal analysis
The phase behavior of LC molecule may be readily evaluated by
DSC which provides an effective measurement of the energy
required to raise the temperature as a function of temperature.
Phase-transition temperatures and corresponding enthalpy
changes of FA1–FA4 and MFA1–MFA4, obtained on the second heat-
ing and cooling cycle, were summarized in Table 1, and the repre-
sentative DSC curves were presented in Fig. 2. The trends of Tg, Ti
and the range temperature of LC phase are shown on Fig. 3.
The melting process of materials is the molecular structure
from three-dimensional space to
a disordered arrangement.
There are many factors effect the melting point, such as quality
of materials, molecular mass, the degree of branching, the crystal-
lization environment and space rotating steric and so on. From
Table 1 and Fig. 2, the melting point of FA2 increased first and then
decreased. The melting points of FA2 is higher 23.6 °C than FA1,
because of FA2 having a more benzene ring. The benzene ring
offered not only more molecular mass but also rigidity of molecule,
which all increased the melting point. While, the melting points of
FA3 decreased quickly, due to the branched structure of FA3, which
decreased the melting point by effecting the molecular stacking.
And for FA4, the structural symmetry increased, so its melting
point decreased very slowly.
Fig. 3. The change trend of melting point, clearing point and range of LC phase.
Fig. 4. The photographs of FA series. (a) FA1 heating to 224.9 °C. (b) FA2 heating to 277.9 °C. (c) FA3 heating to 204.2 °C. (d) FA4 cooling to 250.3 °C.

X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
101
Seen from Fig 3, the melting points of MF series increased first
and then decreased. And the melting points of MFA2 is the highest.
When the structure is line shape, the introduction of benzene ring
have great effect on the Tm values, but when the structure is
branched-arm shape, the effect of benzene is weaker than the dis-
symmetrical structure, which tends to decrease the melting point.
It can be seen that the influence of molecular mass cannot bal-
anced the effect of the dissymmetrical structure. Upward factors
not only affected the melting point but also the isotropization tem-
peratures (Ti), so the Ti values irregularly changed which thanks to
the counterbalance the molecule weight and symmetry. The Ti
values of FA3 and MFA3 are all the lowest than the other three,
which due to their unsymmetrical structure. It also can conclude
that the distortion of isosorbide affected the thermal properties.
Optical rotation and reflection spectra analysis
Isosorbide has optically active in water solution in the light of a
Na-lamp at k = 589 nm. The specific rotation (SROT) of isosorbide
was +56.41° (c = 0.4 g/L). MFA1–MFA4 (in THF, c = 0.4 g/L) exhibited
optical active, too. Generally, solvent, temperature, chain length
and substituent play an important effect on handedness of the
Fig. 5. The photographs of MFA series. (a) MFA1 heating to 128.7 °C. (b) MFA2 cooling to 220.5 °C. (c) MFA2 cooling to 183.4 °C. (d) MFA3 heating to 160.0 °C. (e) MFA3 cooling
to 198.6 °C. (f) MFA4 cooling to 187.1 °C. (g) MFA1 cooling to room temperature.

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X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
cholesteric liquid crystals. In present study, MFA1–MFA4 showed
the same handedness as chiral cores. The SROTs of MFA1–MFA4
were 23.5, 9.45, 42.48 and 8.16, respectively. When the arms were
introduced into isosorbide, multi-arm should have effects on the
SROT values and their rotate direction, which is due to the
multivariate distortion of branched-arm.
texture of nematic phase, while MFA3 started to appear cholesteric
droplets texture, so FA3 is nematic phase, MFA3 is cholesteric
phase.
For FA4 and MFA4:
When heating, they are all first viscous, which is due to the high
molecular weight and branched structure. As the temperature is
increasing, FA4 began to turn to threaded-like texture of nematic
phase, and MFA4 has not typical texture first and gradually turn
to coalescence of texture of the cholesteric phase. When cooling,
FA4 turned out droplets and schlieren texture, while MFA4 started
to appear cholesteric droplets texture, and then finger texture. It
can be concluded that FA4 is nematic phase, MFA4 is cholesteric
phase. Comparing to ethyl substituents of cholesteric branched-
arm LCs [40], the finger print texture and cholesteric droplets
turned out easily due to the small steric hindrance of fluorine
atom.
The characterization photography of above all are shown on
Fig. 4(a–d) and 5(a–f). From the above analysis, it can be seen that
MFA3 and MFA4 own viscous phenomenon of polymer and still
appeared characterization texture of LC phase owing to their good
fluidity. So such LC material is hopeful to realize the combination
of the processability of polymers and the mobility of small mole-
cules. At the same time, it can be seen that the increasing arm
did not change the nematic properties from FA1 to FA4. However,
when the chiral agent is introduced into the system, the cholesteric
The wavelength of reflected light from a cholesteric sample (k)
is calculated as follows:
ꢂ
ꢀ
ꢁ
ꢀ
ꢁꢃ
1
2
sin h1
n
sin h2
n
kmax ¼ nP cos arcsin
þ arcsin
where n is the average refractive index of the LC phase, p is the pitch
height of the helicoidal arrangement, and h is the incident angle of
beam.
The cholesteric phase, due to its helical arrangement of mole-
cules, exhibits some unique optical properties. The most striking
is the so-called selective reflection. When the pitch of the choles-
teric structure is in the range of visible spectrum, the phenomenon
can readily be observed by the naked eye as an iridescent color
play. The helical pitch is an important parameter in connection
with optical properties of the cholesteric phase. The helical pitch
and optical properties of cholesteric LC mainly depend on the con-
dition of branched-arm, the rigidity of mesogenic units, the length
of the flexible spacer, and the outer conditions (e.g., temperature,
force field, electric field, magnetic). In general, the structure of
MFA1 and MFA2 is easy to turn out the selective reflection, but in
this system, the effect of the rigid core and fluorine atom make
the P value out of the range of visible spectrum, so the selective
reflection of MFA1–MFA4 all cannot be observed.
Texture analysis
The optical textures were characterized by POM with hot stage
under nitrogen atmosphere.
The characterization of POM can tell us not only the melting
point, clearing point and changes of different LC phase but also
the morphologic question of texture and orientate defect, which
can tell which type of LC phase it belongs to.
For FA1 and MFA1:
The sample of FA1 began to melt and gradually changed into
threaded-like texture when it was heated to 169.4 °C. And when
it was cooled to 244.5 °C, the nematic droplets can be seen. The
wonderful color flashed away again and again when pressing the
glass. It can tell us that the FA1 is nematic phase.
While the sample of MFA1 started to melt and oily-streak tex-
ture and finger-texture gradually turned out at the temperature
of 125.6 °C. The background color turned from yellow to blue.
The similar change process can be observed when it was cooled.
So MFA1 is cholesteric phase.
For FA2 and MFA2:
The FA2 began to melt and turned to schlieren texture at the
temperature of 125.6 °C and the similar schlieren texture can also
be seen when cooling. So FA2 is nematic phase.
When MFA2 was observed on heating cycle, the oily-streak
texture can be seen. The background color changed from green-
pink-yellow to blue. When it was cooled, the cholesteric droplets
and oily-streaked texture appeared first, and gradually the focal-
conic texture can be seen, pressing it, the oily-streaked texture
turned out again. It can be concluded that MFA2 is cholesteric
phase.
For FA3 and MFA3:
When heating, they are all first viscous, which is due to the high
molecular weights. As the temperature is increasing, FA3 began to
turn to threaded-like texture of nematic phase and MFA3 turn to
small focal conic texture. When cooling, FA3 turned out droplets
Fig. 6. (a) X-ray curves of MFA series. (b) X-ray curves of MFA1 at room
temperature.

X.-Z. He et al. / Journal of Molecular Structure 1092 (2015) 96–103
103
phase can be obtained for MFA1–MFA4. At the same time, they all
turned out crystallization process on cooling cycle. The representa-
tion picture of MFA1 at room temperature is shown on Fig. 5(g).
combination of the processability of polymers and the mobility
of small molecules.
Acknowledgments
X-ray diffraction analysis
Fundamental Research Funds for the Central Universities
(N110705001). National Natural Science Foundation (51273035).
Scientific and Technical Bureau Foundation of Shen Yang City.
XRD analysis allowed for a complementary assessment of the
nature of the phases observed by DSC and POM, giving additional
information about their structural parameters. In general, a smec-
tic, nematic and cholesteric structure have a broad peak associated
with lateral packing at 2h ꢂ 16–21° in wide-angle X-ray diffraction
(WAXD) curve. A sharp and strong peak at low angle (1° < 2h < 6°)
in small-angle X-ray scattering (SAXS) curve can be observed for
smectic structure, but it cannot be seen for nematic and cholesteric
structure. XRD curves were measured by the method of powder
XRD. WAXD patterns of MFA1–MFA4 are shown in Fig. 6(a).
During heating and cooling cycle, the positions of absorbance peak
did not change.
For MFA1–MFA4, the reflection peak in small angel didn’t
appear, and appeared broad peaks at 2h of 19.6(d1 = 4.52 Å),
19.7(d2 = 4.50 Å), 19.2(d3 = 4.62 Å), 19.3(d4 = 4.59 Å). The distance
of MFA3, MFA4 between the mesogenic side groups increased due
to their stronger twist structure. Connecting with POM and DSC,
they are further proved that MFA1–MFA4 are cholesteric phase.
At the same time, their powder XRD at room temperature were
measured. They all turned out the similar absorption peak at
2h = 2.76°, 5.52°, 19.76°, etc., which is characteristic peak of crystal.
The representative curve of MFA1 is shown on Fig. 6(b). The XRD
data were consistent with their optical textures and DSC curves.
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In the present study, four nematic branched-arm precursor and
four cholesteric branched-arm LC had been synthesized. The
chemical structure of compounds were confirmed by FTIR, 1H
NMR spectroscopy and elemental analysis. The results showed that
the materials all consisted with our molecule design. The proper-
ties of liquid crystalline were characterized by DSC and POM. The
results showed that FA1–FA4 turned out nematic phase and
MFA1–MFA4 appeared cholesteric phase. The changes of melting
and clearing point were irregular which were owe to different
branched-arm, molecular asymmetry and molecular weight. The
warping of isosorbide had effect on the thermal behavior and
phase behavior. The liquid crystalline phases were affirmed in-
depth by X-ray. MFA1–MFA4 has not absorbent peak at small angle
and only have absorbent peak at wide-angle X-ray diffraction
when they are at LC phase. MFA1–MFA4 had the same rotation as
chiral core. Chiral core induced nematic two, four and six arms
compounds into cholesteric phase. And MFA1–MFA4 cannot be
seen selective reflection in the visible range of the spectrum. This
sort of LC material as MFA3, MFA4 is hopeful to realize the
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