Synthesis and mesomorphic properties of two series of laterally fluorinated symmetric ester liquid crystals

Article abstract of DOI:10.1080/15421400802198359

Two series of symmetric ester liquid crystals (nAFBHQ and nADFBHQ) with lateral fluorine atoms have been synthesized. Their chemical structures were measured by FTIR, 1H NMR, and elemental analysis (EA). Their mesomorphic properties were investigated by d

Full text of DOI:10.1080/15421400802198359

This article was downloaded by: [Northeastern University]
On: 11 October 2014, At: 22:28
Publisher: Taylor & Francis
Informa Ltd Registered in England and Wales Registered Number: 1072954
Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH,
UK
Molecular Crystals and Liquid
Crystals
Publication details, including instructions for
authors and subscription information:
http://www.tandfonline.com/loi/gmcl20
Synthesis and Mesomorphic
Properties of Two Series
of Laterally Fluorinated
Symmetric Ester Liquid Crystals
Qiang Wei a , Xiaotao Yuan a , Lipei Zhang a , Liping
Wang a , Huai Yang a & Yangbin Wang a
a School of Materials Science and Engineering.
University of Science and Technology Beijing ,
Beijing , China
Published online: 31 Aug 2012.
To cite this article: Qiang Wei , Xiaotao Yuan , Lipei Zhang , Liping Wang , Huai
Yang & Yangbin Wang (2008) Synthesis and Mesomorphic Properties of Two Series of
Laterally Fluorinated Symmetric Ester Liquid Crystals, Molecular Crystals and Liquid
Crystals, 487:1, 52-60, DOI: 10.1080/15421400802198359
To link to this article: http://dx.doi.org/10.1080/15421400802198359
PLEASE SCROLL DOWN FOR ARTICLE
Taylor & Francis makes every effort to ensure the accuracy of all the
information (the “Content”) contained in the publications on our platform.
However, Taylor & Francis, our agents, and our licensors make no
representations or warranties whatsoever as to the accuracy, completeness,
or suitability for any purpose of the Content. Any opinions and views
expressed in this publication are the opinions and views of the authors, and
are not the views of or endorsed by Taylor & Francis. The accuracy of the
Content should not be relied upon and should be independently verified with
primary sources of information. Taylor and Francis shall not be liable for any
losses, actions, claims, proceedings, demands, costs, expenses, damages,

and other liabilities whatsoever or howsoever caused arising directly or
indirectly in connection with, in relation to or arising out of the use of the
Content.
This article may be used for research, teaching, and private study purposes.
Any substantial or systematic reproduction, redistribution, reselling, loan,
sub-licensing, systematic supply, or distribution in any form to anyone is
expressly forbidden. Terms & Conditions of access and use can be found at
http://www.tandfonline.com/page/terms-and-conditions

Mol. Cryst. Liq. Cryst., Vol. 487, pp. 52–60, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802198359
Synthesis and Mesomorphic Properties of Two Series
of Laterally Fluorinated Symmetric Ester Liquid Crystals
Qiang Wei, Xiaotao Yuan, Lipei Zhang, Liping Wang,
Huai Yang, and Yangbin Wang
School of Materials Science and Engineering. University of Science
and Technology Beijing, Beijing, China
Two series of symmetric ester liquid crystals (nAFBHQ and nADFBHQ) with
lateral fluorine atoms have been synthesized. Their chemical structures were mea-
sured by FTIR, 1H NMR, and elemental analysis (EA). Their mesomorphic proper-
ties were investigated by differential scanning calorimetry (DSC) and polarizing
optical microscopy (POM). It was found that both series showed nematic phase
only. And their melting point and clearing point decreased with the number of car-
bon atoms in alkoxy group. It can also be found that nAFBHQ have approximately
the same temperatures of melting point but much higher temperatures of clearing
point than their corresponding compound in nADFBHQ series.
Keywords: ester; fluorinated liquid crystal; mesomorphic property; synthesis
INTRODUCTION
Ester liquid crystals are considered as one of the important
components of high-grade liquid crystal mixtures for their favorable
advantages such as high clearing point and large birefringence [1].
Thereinto ester liquid crystals with hydroquinone moieties attracted
more attention for their scientific and practical applications. Many
works [2–8] have been done on the synthesis and mesomorphic proper-
ties of these ester compounds with different substituent groups.
Recently fluorinated liquid crystals become a hot field because the
replacement of one or several hydrogen atoms by fluorine atoms
confers to the resulting materials unusual and peculiar properties
[9]. Particularly, liquid crystals with lateral fluoro-substituents are
Address correspondence to Huai Yang, School of Materials Science and Engineering,
University of Science and Technology Beijing, Beijing 100083, China. E-mail: yanghuai@
mater.ustb.edu.cn
52

Laterally Fluorinated Symmetric Ester
53
FIGURE 1 Aim structure of the laterally fluorinated ester compounds.
of more importance and attracted much more attention [10–14]. The
advantage of these laterally fluorinated materials is that they may
exhibit many attractive properties such as negative dielectric
anisotropy, low viscosities, optical and chemical stability, low melting
point, and low conductivity.
In order to obtain liquid crystal materials with broad nematic
temperature ranges and low viscosity, and to establish the relation-
ships between structures and properties of laterally fluorinated mate-
rials, we synthesized and characterized two kinds of novel laterally
fluorinated ester liquid crystals with hydroquinone moiety. The gen-
eral structures of these compounds are indicated in Fig. 1 (series
nAFBHQ and nADFBHQ).
EXPERIMENT
Characterization
1
IR spectra were recorded on a Nicolet 510P instrument and H NMR
spectra on Bruker DMX-400 instrument in CDCl3. EA measurements
were carried out on a Thermo Finnigan Flash EA1112 elemental
analyzer. The mesomorphic properties of the compounds were studied
by an Olympus BX-51 polarizing microscope equipped with hot stage.
For differential scanning calorimeter (DSC), a Perkin-Elmer DSC-6
instrument was used, the scanning rate was 10ꢀC=min, the samples
were sealed in aluminum capsules, and the holder atmosphere was
dry nitrogen.

54
Q. Wei et al.
FIGURE 2 Synthesis routes of the aim structures.
Synthesis
The synthetic routes to these compounds were shown in Fig. 2, proce-
dures were summarized below. Both series dealt with in this study
were prepared similarly and the whole process for the preparation of
6AFBHQ and 6ADFBHQ was described as examples.
Synthesis of 2-Fluoro-4-hexyloxybenzoic Acid (6AFBA)
The mixture of 13.7 g (0.1 mol) 2-fluoro-4-hydroxybenzonitrile, 4.4 g
(0.11 mol) NaOH, 4 g anhydrous KI, 0.11 mol hexyl bromide and
100 mL butanone were heated to 60ꢀC for 10 hr. After cooling, the inso-
lubles were removed and the filtrate was washed with 10% NaOH
water solution for 2 times. The butanone was then removed through
evaporation and the residues were mixed with 80 mL 10% NaOH
water solution, refluxing for 24 hr. After cooling, the mixture was
acidified with hydrochloric acid, and the precipitate was collect by
suction filtration, recrystallized from 95% ethanol. The yield was
72%. FTIR, n=cmꢁ1: 2552–3170 (acidic ꢁOH stretching), 1684 (C O
=
=
stretching), 1575, 1508 (aromatic C C stretching), 1242 (C-O stretch-
ing). 1H NMR: d 0.92–1.86 (m, 11H, alkyl protons), d4.01–4.04 (m, 2H,
J ¼ 6.48 Hz, ꢁCH2-O), d6.65–6.68 (d, H, JHF ¼ 12.90 Hz, Ar-H), 6.74–
6.76 (d, H, J ¼ 8.94 Hz, Ar-H), d7.96–8.01 (m, 1H, J ¼ 8.70 Hz,
2JHF ¼ ꢁ8.74 Hz, Ar-H). Anal. Calcd. For C13H17FO3: C, 64.98; H,
7.13. Found C, 64.72; H, 7.1.5.

Laterally Fluorinated Symmetric Ester
55
Synthesis of 2,6-Difluoro-4-hexyloxybenzoic Acid (6ADFBA)
2,6-difluoro-4-hydroxybenzonitrile 15.5 g (0.1 mol) was added to
100 mL of 10% NaOH water solution, refluxing for 24 hr, and then
acidified by hydrochloric acid, the precipitate collected and recrystal-
lized from alcohol. A 92% yield of 2,6-difluoro-4-hydroxybenzoic acid
was obtained.
KOH 2.8 g (50 mmol) in 50 mL of distilled water was added to a
slurry of 2, 6-difluoro-4-hydroxybenzoic acid (25 mmol) in ethanol
(200 mL), and the mixture heated under reflux for 1 hr, hexyl
bromide (75 mmol) was added and the mixture was heated a further
12 hr. KOH water solution (100 mL, 10%) was added and reflux
continued for 2 hr. After cooling, the mixture was acidified by
hydrochloric acid and filtered. The crude product was recrystallized
from ethanol giving a 70% yield of 6DFABA. IR, n=cmꢁ1: 2530–
=
=
3118 (acidic -OH), 1692 (C O), 1575, 1450 (aromatic C C), 1277
(C-O-Ar). 1H NMR: d0.90–1.81 (m, 11H, alkyl protons), d3.96–3.99
(m, 2H, J ¼ 6.45 Hz, -CH2-O), d6.48–6.50 (d, 2H, JHF ¼ 11.47 Hz,
Ar-H). Anal. Calcd. For C13H16F2O3: C, 60.46; H, 6.24. Found C,
60.29; H, 6.25.
Synthesis of Aim Compounds nAFBHQ and nADFBHQ
Dicyclohexylcarbodiimide 10.3 g (50 mmol) and N,N-dimethylami-
nopyridine 20 mg were added to a solution of 50 mmol substituted
alkoxybenzoic acid (nAFBA or nADFBA) and hydroquinone 2.75 g
(25 mmol) in 120 mL of dichloromethane (DCM). The mixture was
stirred for 12 h. The dicyclohexylurea was filtered off and the
solvent from the filtrate was removed under reduced pressure.
The crude product was purified by column chromatography (silica
gel, DCM) giving a 69% yield of 6AFBHQ and a 83% yield of
6ADFBHQ. 6AFBHQ: IR, n=cmꢁ1: 2967, 2920, 2876, 2854 (aliphatic
=
=
C-H), 1718 (C O), 1618, 1575, 1510 (aromatic C C), 1264 (C-O-Ar).
1H NMR: d0.94–1.87 (m, 11H, alkyl protons), d4.04–4.07 (m, 2H,
1
J ¼ 6.52 Hz, -CH2-O), d6.71–6.74 (d, H, JHF ¼ 12.72 Hz, Ar-H),
d6.80–6.82 (d, H, J ¼ 8.88 Hz, Ar-H), d7.28–7.30 (d, 2H, Ar-H), d8.06–
2
8.10 (m, 1H, J ¼ 8.68 Hz, JHF ¼ ꢁ8.60 Hz, Ar-H). Anal. Calcd. For
C32H36F2O6: C, 69.30; H, 6.54. Found C, 69.12; H, 6.55. 6ADFBHQ:
IR, n=cmꢁ1: 2963, 2932, 2870 (aliphatic C-H), 1744 (C O), 1575,
=
1502, 1450 (aromatic C C), 1256 (C-O-Ar). 1H NMR; d0.94–1.87
=
(m, 11H, alkyl protons), d4.01–4.04 (m. 2H, J ¼ 6.51 Hz, -CH2-O),
1
d6.55–6.58 (d, 2H. JHF ¼ 10.55 Hz, Ar-H), d7.29–7.33 (d, 2H,
Ar-H). Anal. Calcd. For C32H34F4O6: C, 65.08; H, 5.80. Found C,
64.82; H, 5.81.

56
Q. Wei et al.
RESULTS AND DISCUSSION
By using POM and DSC, the liquid crystalline properties of the two
series of compounds were measured carefully. It was found that all
aim compounds showed similar mesomorphic properties. The DSC
spectra scanned in heating and cooling cycles of the typical aim com-
pounds 6AFBHQ and 6ADFBHQ were shown in Fig. 3. In the heating
scan, the POM observation indicated that 6AFBHQ and 6ADFBHQ
only showed nematic properties. On cooling, the formation of the
nematic phase beginning as small droplets, followed on further cooling
by the formation of a schlieren texture (Fig. 4a, b), was observed in the
melts of 6AFBHQ and 6ADFBHQ, respectively. The detailed data of
phase variant, transition temperature, and associated enthalpy
changes of all the members of the two series were summarized in
Table 1.
The results in Table 1 revealed that the number of fluorine atoms
introduced into the aim compounds and the number of carbon atoms
in alkoxy chains had significant effect on the thermal stability of the
FIGURE 3 DSC spectra of 6AFBHQ and 6ADFBHQ.

Laterally Fluorinated Symmetric Ester
57
FIGURE 4 Textures of the aim structures on cooling cycle.
aim compounds’ mesophase. The melting point and clearing point
temperatures of the two series show no clear even-odd effects and they
all decreased with the number of carbon atoms in their alkoxy chains,
which is similar to their non-fluorinated analogs (here we designated
them as nABHQ) as described in Ref. [8]. Furthermore, because the
introduction of lateral fluorine atoms debased the symmetry and low-
ered the slenderness ratio of the molecules, so the melting point and
clearing point temperatures of nAFBHQ and nADFBHQ was always
lower than their corresponding analogs in non-fluorinated series
nABHQ.

58
Q. Wei et al.
TABLE 1 Phase Transition Temperature and Associated Enthalpy Changes
of nAFBHQ and nADFBHQ
Phase transition temperature (ꢀC) and enthalphy
Compound
6AFBHQ
changes (kJ=mol, in parantheses)ꢂ
94:0ð29:1Þ
184:6ð1:9Þ
*
)
*
I
)
Cr
Cr
N
58:5
183:1
116:8ð34:8Þ
193:3ð1:4Þ
*
)
*
I
)
5AFBHQ
N
82:5
190:5
121:7ð26:1Þ
217:8ð1:8Þ
106:1ð1:7Þ
*
)
*
I
)
4AFBHQ
Cr1 ꢁꢁꢁꢁꢁ* Cr2
N
100
213
105:3ð7:1Þ
)
150:8ð32:4Þ
229:1ð2:2Þ
)
*
130:2
*
)
*
I
3AFBHQ
Cr1
Cr2
N
138:1
227:0
166:2ð39:1Þ
269:9ð2:7Þ
)
*
)
*
267:7
2AFBHQ
Cr
Cr
Cr
Cr
Cr
Cr
N
I
I
156:4
93:6ð45:4Þ
)
146:0ð2:0Þ
*
68:5
*
)
6ADFBHQ
N
I
143:1
116:7ð58:8Þ
153:4ð1:8Þ
*
)
*
)
5ADFBHQ
N
N
N
N
101:7
151:5
138:1ð54:8Þ
176:2ð2:44Þ
*
)
*
)
4ADFBHQ
I
98:3
174:1
151:3ð31:2Þ
183:01:74Þ
)
*
)
*
I
3ADFBHQ
117:0
181:1
160:1ð45:4Þ
221:9ð2:6Þ
*
)
*
)
2ADFBHQ
I
120:9
220:0
ꢂCr: crystal; N: nematic; I: isotropic.
FIGURE 5 Effect of lateral fluorine atoms on the phase transition properties.

Laterally Fluorinated Symmetric Ester
59
To make the effect of the introduced fluorines at the lateral
positions clearer, the transition temperatures for the two series
together with their non-fluorinated analogs nABHQ were plotted
against the carbon number in their alkoxy chains and shown in Fig. 5.
It could be seen from Fig. 5 that nAFBHQ had much lower melting
point temperatures and slightly lower clearing point temperatures
than nABHQ and so the thermal range of mesophase of nAFBHQ
was broader than their corresponding analogs in nABHQ. But as to
the series with two lateral fluorine atoms (nADFBHQ), their melting
and clearing point temperatures were both greatly lowered and exhib-
ited narrower thermal range of mesophase than nABHQ. When
compared nAFBHQ with nADFBHQ, it could be found that nAFBHQ
had approximately the same temperatures of melting point but much
higher temperatures of clearing point than their corresponding
compound in nADFBHQ series. From these results it can be concluded
that one lateral fluorine atom was propitious to the preparation of
promising liquid crystals.
CONCLUSIONS
We have successfully synthesized and characterized two series of
laterally fluorinated symmetric liquid crystal compounds. It was found
that both series showed nematic phase only. And their melting point
and clearing point all decreased with the number of carbon atoms in
their alkoxy chains. It also can be found when compared nAFBHQ
with nADFBHQ that the former had approximately the same
temperatures of melting point but much higher temperatures of clear-
ing point than their corresponding compound in nADFBHQ series.
ACKNOWLEDGMENT
This research was supported by the Scientific Program of Beijing
under Grant No. Y4050004040121 and the Major Project of Ministry
of Education of the People’s Republic of China under Grant No.
104187.
REFERENCES
[1] Shen, N. & Gao, A. A. (2002). Chinese J. Synth. Chem., 10, 228.
[2] Schoreder, J. P. (1980). Mol. Cryst. Liq. Cryst., 61, 229.
[3] Kossmehl, G., Gerecke, B., Harmsen, N., Schrocder, F., & Vieth, H. M. (1995). Mol.
Cryst. Liq. Cryst. Sci. Techn. Sect A: Mol Cryst. Liq. Cryst., 269, 39.
[4] Kossmehl, G., Gerecke, B., Harmsen, N., Vieth, H. M., & Wolff, D. (1998). Mol.
Cryst. Liq. Cryst. Sci. Techn. Sect. A: Mol. Cryst Liq. Cryst., 317, 1.

60
Q. Wei et al.
[5] Mundhe, P. G. (1999). Asian J. Chem., 11, 130.
[6] Small, A. C. & Pugh, C. (2002). Macromolecules, 35, 2105.
[7] Hu, J. S., Zhang, B. Y., Sun, K., & Li, Q. Y. (2003). Liq. Cryst., 30, 1267.
[8] Michael, J. S. D. & Ronald, S. G. (1970). J. Am. Chem. Soc., 92, 1582.
[9] Guittard, F., Taffin de Givenchy, E., Geribaldi, S., & Cambon, A. (1999). J. Fluorine
Chem., 100, 85.
[10] Lee, C. K., Kim, J. H., Choi, E. J., Zin, W. C., & Chien, L. C. (2001). Liq. Cryst., 28,
1749.
[11] Lee, C. K., Kwon, S. S., Zin, W. C., Kim, D. C., Slim, S. T., Song, J. H., Choi, E. J., &
Chien, L. C. Liq. Cryst., 30, 415.
[12] Murthy, S. H. N. & Sadashiva, B. K. (2004). Liq. Cryst., 31, 1337.
[13] Sun, G. X., Chen, B., Tang, H., & Xu, S. Y. (2003). J. Mater. Chem., 13, 742.
[14] Sun, G., Chen, B., Tang, H., Shi, G., & Xu, S. (2004). Liq. Cryst., 31, 1151.