Synthesis and mesomorphic properties of some chiral liquid crystals with semifluorinated chains

Article abstract of DOI:10.1080/15421400701432149

Three series of chiral compounds with semifluorinated chains have been synthesized. These compounds were characterized by IR, 1H NMR, 19F NMR, MS-mass spectrum, and elemental analysis. Their phase-transition behavior was investigated by DSC-differential s

Full text of DOI:10.1080/15421400701432149

This article was downloaded by: [Selcuk Universitesi]
On: 21 December 2014, At: 02:46
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 Some Chiral
Liquid Crystals with
Semifluorinated Chains
Yonggang Yang a , Haitao Li a & Jianxun Wen a
a School of Chemistry and Chemical Engineering,
Suzhou University , Suzhou, China
Published online: 22 Sep 2010.
To cite this article: Yonggang Yang , Haitao Li & Jianxun Wen (2007)
Synthesis and Mesomorphic Properties of Some Chiral Liquid Crystals with
Semifluorinated Chains, Molecular Crystals and Liquid Crystals, 469:1, 51-58, DOI:
10.1080/15421400701432149
To link to this article: http://dx.doi.org/10.1080/15421400701432149
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. 469, pp. 51–58, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701432149
Synthesis and Mesomorphic Properties of Some Chiral
Liquid Crystals with Semifluorinated Chains
Yonggang Yang
Haitao Li
Jianxun Wen
School of Chemistry and Chemical Engineering, Suzhou University,
Suzhou, China
Three series of chiral compounds with semifluorinated chains have been synthe-
sized. These compounds were characterized by IR, 1H NMR, 19F NMR, MS-mass
spectrum, and elemental analysis. Their phase-transition behavior was investi-
gated by DSC-differential scanning calorimetry and polarizing optical microscopy.
Both the introduction of a triple bond and lateral difluorosubstitution in the core
decrease the clearing points and suppress the formation of the SmCꢀ phase.
Keywords: Ferroelectric; fluorocarbon; liquid crystal; mesomorphic
INTRODUCTION
Chiral smectic liquid crystals are some of the most interesting systems
for future display devices, especially the liquid crystals that show the
smectic Cꢀ or the smectic CAꢀ phases. Recently, a variety of liquid crys-
tals with a SmCꢀ phase have been synthesized [1–3]. Earlier work by
different groups on liquid crystals showed that the formation of smec-
tic mesophases and their liquid-crystalline thermal stabilities were
enhanced with the introduction of perfluoroalkyl or semifluoroalkoxy
chains [4–19]. In particular, molecules with semifluorinated chains
exhibit tilted smectic phases, and some are inherently ferroelectric
[4–6]. With the introduction of a chiral center, a smectic Cꢀ phase will
be formed, which may be suitable for application in ferroelectric liquid
crystal display (FLCD) mixtures [20,21]. Therefore, the synthesis and
study of liquid crystals with semifluorinated chains and chiral centers
became more attractive.
Address correspondence to Yonggang Yang, School of Chemistry and Chemical
Engineering, Suzhou University, Suzhou 215123, China. E-mail: ygyang@suda.edu.cn.
51

52
Y. Yang et al.
Several years ago, we obtained a liquid crystal with a broad (54ꢁC)
SmCꢀ phase by the introduction of a semifluorinated chain and a
chiral center [19]. Here we developed three new series of liquid crys-
tals, some of which also show a broad SmCꢀ phase range.
RESULTS AND DISCUSSION
The phase-transition temperatures of all the compounds were determ-
ined by differential scanning calorimetry (DSC) with a heating rate of
5ꢁC minꢂ1. The mesomorphic textures were observed on polarizing
optical textures for determining the types of mesophases. The tran-
sition temperatures shown in all the tables are the maxima of the
transition peaks on each DSC trace.
The compounds were obtained by routes depicted in Scheme 1. The
intermediates and final compounds were synthesized according to
literature methods [18,22–24]. The phase behavior of the final com-
pounds is summarized in Tables 1 and 2 and was determined with
DSC and polarizing optical microscopy.
The phase-transition temperatures of compounds nT8F are summar-
ized in Table 1. Figure 1 plots the transition temperature of compounds
nT8F as a function of the number of methylenic units (n) in the nonfluori-
nated chain. All of these compounds exhibit only smectic mesophases.
When the alkoxy chains are short, only enantiotropic SmA and mono-
tropic SmB phases are found. An enantiotropic SmCꢀ phase appears only
when the carbon numbers of the alkoxy chaꢁins are longer than 7. Gene-
rally, the SmCꢀ phase ranges are around 20 C. By increasing the alkoxy
chain length, the clearing points decrease gradually with a slight
odd–even effect; however, the melting points are similar.
Compounds nBP8F are similar to compounds nT8F but without
triple bonds in the cores. The phase-transition temperatures of
compounds nBP8F are summarized in Table 2. All of these compounds
also exhibit smectic mesophases. When the alkoxy chain is short, a
SmB phase is exhibiteꢁd. When the carbon numbers are 8 and 9, broad
ranges (more than 40 C) of the SmCꢀ phase are seen, which may be
suitable for FLCD mixtures. With the difluorosubstitution of com-
pounds nT8F, we obtained compounds n2FT8F. The phase-transition
temperatures of compounds n2FT8F are also summarized in Table 2.
Only an enantiotropic SmA phase is identified; the SmCꢀ phase is
strongly suppressed by lateral difluorosubstitution [23–25].
For a clear understanding of the effects of the introduction of the
triple bond and lateral difluorosubstitution, the phase-transition
properties of three compounds, 7BP8F, 7T8F, and 72FT8F, are
summarized in Figure 2. From the phase-transition properties of

Chiral Liquid Crystals with Semifluorinated Chains
53
SCHEME 1 Synthetic route.
7BP8F and 7T8F, the introduction of a triple bond into the core, the
clearing points, melting points, and the thermostability of SmCꢀ
phase are decreased. Possibly the triple bond interfered with the con-
jugation of the molecule; the lateral–lateral interactions were then
weakened. Although the clearing points of 7T8F and 72FT8F are
nearly the same, the clearing point of 7T8F decreases by 24.5ꢁC with
lateral difluorosubstitution. The lateral difluorosubstitution strongly
decreases the lateral interactions between the aromatic cores.
In summary, three series of chiral compounds with semifluorinated
chains have been synthesized. Two of them show broad ranges (more
than 40ꢁC) of the SmCꢀ phase. Both the introduction of a triple bond
and lateral difluorosubstitution in the core decrease the clearing
points and suppress the formation of the SmCꢀ phase.

54
Y. Yang et al.
TABLE 1 Transition Temperature of Compounds
Compound
n
Transition temperature (ꢁC)
4T8F
5T8F
6T8F
7T8F
8T8F
4
Cr, 115.4; SmA, 215.0; I, 213.0, SmA, 106.9; SmB; 99.1 Recr
Cr, 123.0, SmA, 207.0; I, 204.6, SmA, 112.8 Recr
Cr, 120.4; SmA, 202.0; I, 199.4; SmA, 110.2 Recr
Cr, 121.6; SmA, 197.2; I, 195.3; SmA, 120.2; SmCꢀ, 114.3 Recr
Cr, 118.8; SmCꢀ, 135.2; SmA, 191.6; I, 189.5; SmA, 134.5;
SmCꢀ, 112.1 Recr
5
6
7
8
9T8F
9
10
12
Cr, 119.7; SmCꢀ, 142.5; SmA, 187.1; I, 185.2; SmA, 142.1;
SmCꢀ, 112.9 Recr
Cr, 120.4; SmCꢀ, 146.5; SmA, 183.1; I, 180.9; SmA, 146.1;
SmCꢀ, 113.6 Recr
Cr, 122.0; SmCꢀ, 142.0; SmA, 172.0; I, 169.1; SmA, 141.4;
SmCꢀ, 116.2 Rec
10T8F
12T8F
Note. Cr ¼ crystal; SmA ¼ smectic A; SmCꢀ ¼ chiral smectic C; SmB ¼ smectic B;
I ¼ isotropic liquid; Recr ¼ recrystal.
EXPERIMENTAL
Characterization
The structures of the final products and intermediates were determ-
ined by a variety of spectral methods. IR spectra were taken on a
PE-983G spectrophotometer, using KBr pellets of the solids or films
TABLE 2 Transition Temperatures of Compounds
Compound
5BP8F
n
Transition temperature (ꢁC)
5
Cr, 96.4; CrE, 104.1; SmB, 115.7; SmA, 217.7; I, 214.8;
SmA, 114.7; SmB, 98.5; Cr, E75.4 Recr
7BP8F
7
8
Cr, 108.0; SmCꢀ, 138.1; SmA, 204.0; I, 202.4; SmA, 137.3;
SmCꢀ, 107.6; SmB, 100.3 Recr
Cr, 109.9; SmCꢀ, 152.7; SmA, 197.3; I, 194.1; SmA, 152.1;
SmCꢀ, 103.9 Recr
8BP8F
9BP8F
9
Cr, 113.4, SmCꢀ, 155.0; SmA, 190.8; I, 188.8; SmA, 154.3;
SmCꢀ, 108.6 Recr
10BP8F
10
Cr, 121.7; SmCꢀ, 126.0; SmA, 176.4; I, 173.5; SmA, 125.4;
SmCꢀ, 114.0 Recr
32FT8F
42FT8F
72FT8F
102FT8F
3
4
7
Cr, 118.8; SmA, 188.2; I, 185.8; SmA, 101.1 Recr
Cr, 119.7; SmA, 188.3; I, 185.8; SmA, 101.5 Recr
Cr, 121.4; SmA, 172.7; I, 170.2; SmA, 109.2 Recr
Cr, 123.7; SmA, 161.0; I, 157.4; SmA, 115.7 Recr
10
Note. Cr ¼ crystal; SmA ¼ smectic A; SmCꢀ ¼ chiral smectic C; SmB ¼ smectic B;
CrE ¼ crystal E; I ¼ isotropic liquid; Recr ¼ recrystal.

Chiral Liquid Crystals with Semifluorinated Chains
55
FIGURE 1 Transition behavior of the compounds nT8F: dependence of
the transition temperatures on the number (n) of methylene units of the
nonfluorinated chain.
FIGURE 2 Comparison of mesomorphic properties of compounds 7BP8F,
7T8F, and 72FT8F.

56
Y. Yang et al.
of liquids. 1H NMR spectra, with TMS as internal NMR standard,
were recorded on a Varian EM 360L spectrometer (60 MHz) or a
Fx-90Q (90 MHz) instrument; 19F NMR spectra, with trifluoroacetic
acid (TFA) as external standard, were recorded on a Varian EM
360L spectrometer (60 MHz). For spectra spectrum 19F NMR, the high
field was positive. MS spectra were measured with a Finnigan-4021
spectroscope.
The phase-transition temperatures of the target compounds
were measured by optical microscopy using a polarizing microscope
(Olympus PM-6) fitted with a heating stage (Mettler FP-80) and con-
trol unit (FP-82) and by DSC (Shimidazu DSC-50 calorimeter) with
a data system and heating and cooling rates of 5ꢀC minꢁ1). The tran-
sition temperatures reported in this article were the peak values of the
transition on DSC traces. Phase identification was made by comparing
the observed textures with those reported in the literature.
Synthesis
All of the obtained liquid crystals were purified by column chromato-
graphy on silica gel using petroleum ether (bp 60–90ꢀC)=ethyl acetate
(20:1) as eluent and then recrystallized from petroleum ether
(bp 60–90ꢀC) and acetone=methanol.
Synthesis of Compound 7BP8F
A typical synthetic procedure is as follows. 4-n-Heptyloxybiphenyl-
40-carboxylic acid (0.60 mmol), compound 3 (0.60 mmol), N,N0-dicyclo-
hexylcarbodiimide (0.7 mmol), catalytic 4-(dimethylamino)pyridine
(DMAP), and dry THF (10 ml) were stirred under N2 at room temperature
for 48 h. The mixture was filtered, and the residue was washed with THF.
The collected filtrates were evaporated on a rotary evaporator. The residue
was purified by flash chromatography and recrystallized from acetone=
methanol to give a white solid. [a]2D0 ¼ ꢁ12.3 (c 1.0, CHCl3). Mp 108.0ꢀC.
IR (KBr) tmax: 2933, 1748, 1729, 1603, 1505, 1202, 832 cmꢁ1 1H
.
NMR dH (300 MHz; CDCl3; TMS): 0.92 (t, J ¼ 6.6 Hz, 3H, CH3), 1.34–
1.87 (m, 13H, aliphatic hydrogens), 2.49 (tt, J1 ¼ 18.2, J2 ¼ 6.4 Hz,
2H, RfCH2), 4.02 (t, J ¼ 6.6 Hz, 2H, RCH2O), 4.49 (t, J ¼ 6.3 Hz, 2H,
RCH2O), 4.79 (q, J ¼ 6.8 Hz, H, R1R2CHO), 6.94 (d, J ¼ 9.1 Hz, 2H,
ArH), 7.01 (d, J ¼ 8.7 Hz, 2H, ArH), 7.15 (d, J ¼ 9.1 Hz, 2H, ArH),
7.60 (d, J ¼ 8.7 Hz, 2H, ArH), 7.69 (d, J ¼ 8.4 Hz, 2H, ArH), 8.22 (d,
J ¼ 8.3 Hz, 2H, ArH) ppm. 19F NMR dF (56.4 MHz, CDCl3, TFA): 3.60
(s, 3 F), 36.10 (m, 2 F), 44.70–46.30 (m, 10 F), 49.00 (s, 2F) ppm. MS
m=z (rel. int.): 923 (Mþ þ 1, 0.51), 295 (C7H15OC6H4C6H4COþ,
100.00), 197 (HOC6H4C6H4COþ, 9.66). Elemental analysis: calculated

Chiral Liquid Crystals with Semifluorinated Chains
57
(for C39H35F17O6) C, 50.77; H, 3.82; F, 35.00%; found C, 50.90; H, 3.90;
F, 34.77%.
Synthesis of Compound 7 T8F
A typical synthetic procedure is as follows. To a mixture of 4-heptyl-
oxyphenylacetylene (0.44 mmol), compound 4 (0.4 mmol), bis(triphe-
nylphosphine)palladium dichloride (20 mg), and CuI (60 mg) under
dry N2, 20 mL of anhydrous triethylamine were added. The obtained
mixture was heated under reflux with stirring for 2 h. Analysis by
thin-layer chromatography (TLC) revealed completion of the reaction.
The precipitate formed was then filtered off and washed with ether.
The solvent was removed in vacuo, and the residue was purified by
column chromatography on silica gel using petroleum ether=
dichloromethane as elucent. The obtained compound was recrystal-
lized from petroleum ether (bp 60–90ꢁC) and subsequently acetone=
methanol. [a]D20 ¼ ꢂ13.4 (c 1.0, CHCl3). Mp 121.6ꢁC. IR (KBr) tmax
:
2929, 2857, 2214, 1748, 1726, 1599, 1506, 1250, 1201, 834 cmꢂ1. H
NMR dH (300 MHz; CDCl3; TMS): 0.91 (t, J ¼ 6.7 Hz, 3H, CH3), 1.45–
1.84 (m, 13H, aliphatic hydrogens), 2.49 (tt, J1 ¼ 18.2, J2 ¼ 6.4 Hz,
2H, RfCH2), 4.00 (t, J ¼ 6.6 Hz, 2H, RCH2O), 4.49 (t, J ¼ 6.3 Hz, 2H,
RCH2O), 4.79 (q, J ¼ 6.8 Hz, H, R1R2CHO), 6.87–6.94 (m, 4H, ArH),
7.13 (d, J ¼ 6.7 Hz, 2H, ArH), 7.50 (d, J ¼ 8.7Hz, 2H, ArH), 7.62 (d,
J ¼ 8.5 Hz, 2H, ArH), 8.16 (d, J ¼ 8.4 Hz, 2H, ArH) ppm. 19F NMR dF
(56.4 MHz, CDCl3, TFA): 3.50 (s, 3 F), 36.00 (m, 2F), 44.50–46.00 (m,
10F), 48.70 (s, 2F) ppm. MS m=z (rel. int.): 947 (Mþ þ 1, 2.04), 318
(C7H15OC6H4ꢂꢃꢂC6H4COþꢂ1, 100.00), 221 (HOC6H4ꢂꢃꢂC6H4COþ,
7.13). Elemental analysis: calculated (for C41H35F17O6) C, 52.02; H,
3.73; F, 34.12%; found C, 51.92; H, 3.43; F, 33.83%.
1
Synthesis of Compound 72FT8F
[a]D20 ¼ ꢂ11.3 (c, 1.0, CHCl3). Mp 121.4ꢁC. tmax(KBr): 2925, 2213,
1
1750, 1728, 1602, 1505, 1252, 1198, 827 cmꢂ1. H NMR dH (300 MHz,
CDCl3, TMS): 0.90 (t, J ¼ 6.7 Hz, 3H, CH3), 1.45–1.84 (m, 13H, aliphatic
hydrogens), 2.49 (tt, J1 ¼ 18.2, J2 ¼ 6.4 Hz, 2H, RfCH2), 4.00 (t, J ¼
6.6 Hz, 2H, RCH2O), 4.49 (t, J ¼ 6.3 Hz, 2H, RCH2O), 4.79 (q,
J ¼ 6.8 Hz, H, R1R2CHO), 6.69–7.25 (d, J ¼ 8.5 Hz, 6H, ArH), 7.64
(d, J ¼ 8.5 Hz, 2H, ArH), 8.16 (d, J ¼ 8.4 Hz, 2H, ArH) ppm, 19F
NMR dF (56.4 MHz, CDCl3, TFA): 3.60 (s, 3F), 36.33 (m, 2F), 44.90–
46.50 (m, 10F), 49.20 (s, 2F), 56.30 (d, J ¼ 18.8 Hz, F), 81.30 (d, J ¼
18.8 Hz, F) ppm. MS m=z (rel. int.): 983 (Mþ þ 1, 1.19), 354
(C7H15OC6H2F2ꢂꢃꢂC6H4COþꢂ1, 100.00), 257 (HOC6H2F2ꢂꢃꢂC6H4COþ,
14.51). Elemental analysis: calculated (for C41H33F19O6) C, 50.11; H,
3.38; F, 36.73%; found C, 50.20; H, 3.25; F, 36.60%.

58
Y. Yang et al.
ACKNOWLEDGMENT
This work was partially supported by the Jiangsu Provincial Key
Laboratory of Organic Chemistry Foundation and Suzhou University
Starting Foundation.
REFERENCES
[1] Largerwall, J. P. F. & Giesselmann, F. (2006). Chem. Phys. Chem., 7, 20.
[2] Ikuma, N., Tamura, R., Shimono, S., Uchida, Y., Masaki, K., Yamauchi, J., Aoki, Y.,
& Nohira, H. (2006). Adv. Mater., 18, 477.
[3] Lagerwall, J. P. F., Giesselmann, F., Saipa, A., & Dabrowski, R. (2004). Liq. Cryst.,
31, 1175.
[4] Tournilhac, F. G., Blinov, L. M., Simon, J., & Yablonsky, S. V. (1992). Nature, 359,
621.
[5] Tournilhac, F. G., Bosio, L., Simon, L., Blinov, L. M., & Yablonsky, S. V. (1993). Liq.
Cryst., 14, 405.
[6] Lobko, T. A., Ostrovskii, B. J., Pavluchenko, A. I., & Sulianov, S. N. (1993). Liq.
Cryst., 15, 361.
[7] Kromm, P., Cotrait, M., Roullon, J. C., Barois, P., & Nguyen, H. T. (1996). Liq.
Cryst., 21, 121.
[8] Kromm, P., Cotrait, M., & Nguyen, H. T. (1996). Liq. Cryst, 21, 95.
[9] Nguyen, H. T., Sigaud, G., Archard, M. F., Hardouin, F., Twing, R. J., & Betterton,
K. (1991). Liq. Cryst., 10, 389.
[10] Chen, B., Yang, Y., & Wen, J. (1998). Liq. Cryst., 24, 539.
[11] Liu, H. & Nohira, H. (1997). Liq. Cryst., 22, 217.
[12] Johansson, G., Percec, V., Ungar, G., & Smith, K. (1997). Chem. Mater., 9, 164.
[13] Takenaka, S. (1992). J. Chem. Soc. Chem. Commun., 1748.
[14] Okamoto, H., Murai, H., & Takenaka, S. (1997). Bull. chem. Soc. Jpn., 3163.
[15] Arehart, S. V. & Pugh, C. (1997). J. Am. Chem. Soc., 119, 3027.
[16] Yang, Y., Tang, G., & Wen, J. (2002). Mol. Cryst. Liq. Cryst., 373, 25.
[17] Yang, Y. & Wen, J. (2001). Liq. Cryst., 28, 1735.
[18] Yang, Y. & Wen, J. (2002). Liq. Cryst., 29, 161.
[19] Yang, Y. & Wen, J. (2002). Liq. Cryst., 29, 159.
[20] Cowling, S. J., Hall, A. W., & Goodby, J. W. (2005). Liq. Cryst., 32, 1483.
[21] Krueger, M. & Giesselmann, F. (2005). Phys. Rev. E, 71, 041704.
[22] Li, H., Yang, Y., & Wen, J. (2000). Chin. J. Chem., 18, 900.
[23] Yang, Y., Wang, K., & Wen, J. (2001). Liq. Cryst., 28, 1553.
[24] Yang, Y., Li, H., Wang, K., & Wen, J. (2001). Liq. Cryst., 28, 375.
[25] Gray, G. W., Hird, M., Lacey, D., & Toyne, K. J. (1989). J. Chem. Soc. Perkin
Trans., 2, 2041.