Fluoro- and nitro-substitution effect of some chiral compounds

Article abstract of DOI:10.1080/15421400802406463

Four chiral compounds have been synthesized. Their phase transition behavior was investigated by differential scanning calorimetry and polarized optical microscopy. Two of them show monotropic smectic C* phases. Moreover, one of them shows an enantiotropic blue phase. The lateral fluoro-substitution strongly suppressed the formation of SmC* phases and decreased clearing points. Although the introduction of nitro group in the core decreased the length-diameter ratio, the temperature range of monotropic SmC* phase did not change much.

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Fluoro- and Nitro-Substitution
Effect of Some Chiral
Compounds
Yongmin Guo a , Lifeng Bi a , Baozong Li a , Yonggang
Yang b & Jianxun Wen b
a Key Laboratory of Organic Synthesis of Jiangsu
Province, College of Chemistry and Chemical
Engineering, Suzhou (Soochow) University , Suzhou ,
Jiangsu , China
b Shanghai Institute of Organic Chemistry, Chinese
Academy of Sciences , Shanghai , China
Published online: 31 Aug 2012.
To cite this article: Yongmin Guo , Lifeng Bi , Baozong Li , Yonggang Yang
& Jianxun Wen (2008) Fluoro- and Nitro-Substitution Effect of Some Chiral
Compounds, Molecular Crystals and Liquid Crystals, 493:1, 65-70, DOI:
10.1080/15421400802406463
To link to this article: http://dx.doi.org/10.1080/15421400802406463
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Mol. Cryst. Liq. Cryst., Vol. 493, pp. 65–70, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802406463
Fluoro- and Nitro-Substitution Effect of Some Chiral
Compounds
Yongmin Guo1, Lifeng Bi1, Baozong Li1, Yonggang Yang2,
and Jianxun Wen2
1Key Laboratory of Organic Synthesis of Jiangsu Province, College of
Chemistry and Chemical Engineering, Suzhou (Soochow) University,
Suzhou, Jiangsu, China
2Shanghai Institute of Organic Chemistry, Chinese Academy of
Sciences, Shanghai, China
Four chiral compounds have been synthesized. Their phase transition behavior
was investigated by differential scanning calorimetry and polarized optical
microscopy. Two of them show monotropic smectic CÃ phases. Moreover, one of
them shows an enantiotropic blue phase. The lateral fluoro-substitution strongly
suppressed the formation of SmCÃ phases and decreased clearing points. Although
the introduction of nitro group in the core decreased the length-diameter ratio, the
temperature range of monotropic SmCÃ phase did not change much.
Keywords: chiral; fluoro; liquid crystal
INTRODUCTION
Liquid crystals with smectic CÃ (SmCÃ) phases attracted many
researchers, which are suitable to be applied in ferroelectric liquid
crystal displays (FLCD) [1–13]. Because liquid crystals with fluoro-
substituents show low viscosity, low conductivity, and high chemical
and thermostability, many liquid crystals with fluoro-substituents
both in the cores and alkoxy chains were designed and synthesized
[7–15]. Moreover, chiral compounds with donors and acceptors are also
attractive because they can be used as second-order nonlinear optical
materials [16]. For the preparation of multifunctional materials which
can potentially be applied in FLCD, second-order nonlinear optics, and
photorefractive materials, one series of chiral liquid crystals with
Address correspondence to Yonggang Yang, School of Chemistry and Chemical Engin-
eering, Suzhou University, Suzhou, Jiangsu 215123, China. E-mail: ygyang@suda.edu.cn
65

66
Y. Guo et al.
SCHEME 1 Synthesis of compounds A, B, C, and D. a) (S-) CH3 (CH2)5
CꢀH(CH3)OH, DEAD=PPh3, THF; b) HNO3; c) 1) NaOH aq., EtOH 2) HCl
aq.; d) p-I-phenol=DCC=DMAP, THF; e) 4-n-octoxyphenylacetylene,
Pd(PPh3)2Cl2, CuI, PPh3, THF=Et3N; f) 4-n-octoxytetrafluorophenylacetylene,
Pd(PPh3)2Cl2, CuI, PPh3, THF=Et3N.
nitro, fluoro, and (S-) 2-methylbutoxy groups were synthesized [17]
with molecular structures that are similar to those shown in the
Scheme. Generally, they show only the cholesteric (Ch) phase. The
fluoro- and nitro-substitution effect was preliminary studied. Both
fluoro- and nitro-substituents suppress the formation of liquid crystal-
line phases. Herein, the (R-) 1-methylheptoxy group was used as the

Chiral Liquid Crystals
67
TABLE 1 Transition Temperatures of Compounds A, B, C, and D
A
B
C
D
Cr 52.2 Ch 127.5 I 127.5 Ch 48.5 SmCꢀ 34.8 Recr
Cr 25.0 Ch 42.5 I 41.2 Ch 3.0 Recr
Cr 77.6 Ch 88.0 BP 88.5 I 88.5 BP 88.0 Ch 57.6 SmCꢀ 40.7 Recr
liquid at r.t.
Cr ¼ crystal; Ch ¼ cholesteric phase; SmCꢀ ¼ chiral smectic C phase; BP ¼ Blue phase;
I ¼ isotropic liquid; Recr ¼ recrystal.
chiral alkoxy one. Because it is longer than the (S-) 2-methylbutoxy
group, the association of the alkoxy chains may induce the formation
SmCꢀ phase [18].
RESULTS AND DISCUSSION
The intermediates were synthesized according to literature methods
[9,10]. Compounds A, B, C, and D were synthesized according to the
scheme.
The phase transition behavior of the final compounds was summar-
ized in the table and figure, which was determined with polarizing
optical microscopy. Compound A shows an enantiotropic cholesteric
phase and a monotropic SmCꢀ phase. Compared with previous results
[17], the lateral interactions among the hydrocarbon chains should
play an important role on the formation of the SmCꢀ phase. Compound
B, with fluoro-substituents in the core, smectic phases were sup-
pressed. It shows only an enantiotropic cholesteric phase. Moreover,
the clearing point decreases by 85ꢁC. The lateral fluoro-substitution
may not only suppress the lateral–lateral interactions among the
cores, but also decrease the length–diameter ratio of B. However, it
is interesting to find that the melting point is 25ꢁC. It may be suitable
to use in the FLCD mixtures [19,20].
Compound C which is A with a nitro group in the core shows enan-
tiotropic cholesteric and blue phases, as well as a monotropic SmCꢀ
phase. Although the nitro group decreases the length-diameter ratio,
it increases the polarity of C. Therefore, the SmCꢀ phase temperature
range did not change much. Moreover, because the existence of the
chiral unit and the nitro group, compound C may be applied in second
order nonlinear optical materials. During the last several years, more
researchers were focused on studying blue phases. In 2002, H. Kikuchi
et al. reported that the temperature range of polymer-stabilized liquid
crystal blue phases could reach 66ꢁC [21]. Recently, Sumsung intro-
duced blue phase LCD technology at Society for Information Display
2008 symposium. Compound C shows an enantiotropic blue phase

68
Y. Guo et al.
with a temperature range of 0.5ꢁC. After being mixed with polymers or
grafted on polymer main chains, the obtained materials may show
blue phase with broader temperature ranges, which may be useful
as the candidate in blue phase LCD. Compared with A, the introduc-
tion of a nitro group and a fluoro-substituent, compound D is liquid at
room temperature. Unfortunately, it is difficult to purify.
CONCLUSION
In summary, four chiral compounds have been synthesized. The lat-
eral fluoro-substitution strongly suppressed the formation of SmCꢀ
phases and decreased clearing points. Although the introduction of a
nitro group in the core decreased the length-diameter ratio, the mono-
tropic SmCꢀ phase temperature range did not change much. Moreover,
a blue phase was identified.
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
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 spec-
trometer (60 MHz). MS spectra were measured with a Finnigan-4021
spectrometer.
The phase transition temperatures of the target compounds were
measured by optical microscopy using apolarizing microscope (Olympus
PM-6) fitted with a heating stage (Mettler FP-80) and control unit
(FP-82), and by differential scanning calorimetry (DSC, Shimidazu
DSC-50 calorimeter with a data system, heating and cooling rate
5ꢁC minꢂ1). The transition 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 (b.p. 60–90ꢁC)=ethyl acetate
(20=1) as eluent and then recrystallized from acetone=methanol.

Chiral Liquid Crystals
69
Typical synthetic process: to a mixture of compound 4-n-octoxy-
phenylacetylene (0.44 mmol), compound 1 (0.4 mmol), bis(triphenyl-
phosphine)palladium
dichloride
(20 mg),
triphenylphosphine
(60 mg), and CuI (60 mg), under dry N2, was added 20 mL of anhy-
drous triethylamine. The obtained mixture was heated under reflux
under stirring for 2 h. Analysis by 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 eluent. The obtained compound
was recrystallizeꢁd from acetone=mꢁethanol. Compound A:
20
[a]D ¼ ꢂ 1.60 (25 C, CHCl3). Mp 49.5 C. IR (KBr) tmax: 2925,
2854, 2217, 1727, 1604, 1511, 1467, 1210, 1168, 833 cmꢂ1
.
1H
NMR dH (60 MHz; CDCl3; TMS): 0.88–1.90(m, 31H, aliphatic hydro-
gens), 3.96(t, J ¼ 6 Hz, 2 H), 4.30–4.50(m, H), 6.70–7.55(m, 10H,
ArH), 8.05(d, J ¼ 8 Hz, 2 H, ArH) ppm. MS m=z (rel. int.): 554(Mþ,
1.69), 233(C8H17OC6H4COþ, 43.70), 121(HOC6H4COþ, 100.00).
Elemental analysis: calculated (C37H46O4), C, 80.11; H, 8.36%;
found, C, 79.62; H, 8.23%.
Compound B: [a]D20 ¼ ꢂ 6.91 (25ꢁC, CHCl3). Mp 25.0ꢁC. IR (KBr)
1
t
max: 2929, 1734, 1603, 1510, 1492, 1207, 1167, 990 cmꢂ1. H NMR
dH (90 MHz; CDCl3; TMS): 0.88–1.90(m, 31 H, aliphatic hydrogens),
4.20–4.50(m, 3 H), 6.80–8.17(m, 8 H, ArH) ppm. 19F NMR dF
(56.4 MHz, CDCl3, TFA): 61.10(d, J ¼ 18.8 Hz,
2 F), 80.20(d,
J ¼ 18.8 Hz, 2F) ppm. MS m=z (rel. int.): 627(Mþ þ 1, 1.28),
233(C8H17OC6H4COþ, 100.00), 121(HOC6H4COþ, 96.44). Elemental
analysis: calculated (C37H42F4O4), C, 70.91; H, 6.75; F, 12.13%; found,
C, 70.87; H, 6.94; F, 11.95%.
Compound C: [a]D20 ¼ ꢂ2.45 (25ꢁC, CHCl3). Mp 77.1ꢁC. IR (KBr)
t
max: 2928, 2856, 2217, 1729, 1618, 1514, 1467, 1204, 1165, 838 cmꢂ1
.
1H NMR dH (60 MHz; CDCl3; TMS): 0.85–2.00(m, 31H, aliphatic
hydrogens), 4.02(t, J ¼ 6 Hz, 2 H), 4.70(q, J ¼ 6 HZ, H), 6.75–7.60(m,
9 H, ArH), 8.17–8.53(m, 2 H, ArH) ppm. MS m=z (rel. int.):
600(Mþ þ 1, 5.65), 166(HO(NO2)C6H3COþ, 100.00). Elemental analy-
sis: calculated (C37H45NO6), C, 74.10; H, 7.56; N, 2.33%; found, C,
73.54; H, 7.72; N, 1.86%.
Compound D: IR (KBr) tmax: 2929, 2857, 1740, 1612, 1510,
1492, 1204, 1168, 990 cmꢂ1 1H NMR dH (90 MHz; CDCl3; TMS):
.
0.88–1.90(m, 31 H, aliphatic hydrogens), 4.20–4.70(m,
3 H),
7.10–8.60(m, 7 H, ArH) ppm. 19F NMR dF(56.4 MHz, CDCl3,
TFA): 61.10(d, J ¼ 18.8 Hz, 2F), 80.20(d, J ¼ 18.8 Hz, 2 F) ppm.
MS m=z (rel. int.): 672(Mþ þ 1, 1.80), 166(HO(NO2)C6H3COþ,
100.00).

70
Y. Guo et al.
ACKNOWLEDGMENT
This work was partially supported by Jiangsu Provincial Key Labora-
tory of Organic Chemistry Foundation and Natural Science Foundation
of Jiansu Province (No. BK2007047).
REFERENCES
[1] Inukai, T., Saitoh, S., Inoue, H., Miyazawa, K., Terashima, K., & Furukawa, K.
(1986). Mol. Cryst. Liq. Cryst., 141, 251.
[2] Terashima, K., Ichihashi, M., Kikuchi, M., Furukawa, K., & Inukai, T. (1986). Mol.
Cryst. Liq. Cryst., 141, 237.
[3] Scherowsky, G. & Lotz, A. (1993). Liq. Cryst., 14, 733.
[4] Scherowsky, G. & Lotz, A. (1993). Liq. Cryst., 14, 1295.
[5] Ikemoto, T., Kageyama, Y., Onuma, F., Shibuya, Y., Ichimura, K., Sakashita, K., &
Mori, K. (1994). Liq. Cryst., 17, 729.
[6] Cowling, S. J., Hall, A. W., & Goodby, J. W. (2005). Liq. Cryst., 32, 1483.
[7] Guittard, F., de Givenchy, E. T., Geribaldi, S., & Cambon, A. (1999). J. Fluorine
Chem., 100, 85.
[8] Buchecker, R., Kelly, S. M., & Fuenfschilling, J. (1990). Liq. Cryst., 8, 217.
[9] Turmes, W., Wand, M. D., & Vohra, R. T. (1993). Liq. Cryst., 14, 1061.
[10] Hird, M., Goodby, J. W., Hindmarsh, P., Lewis, R. A., & Toyne, K. J. (2002).
Ferroelectrics, 276, 219.
[11] Wen, J., Tian, M., & Chen, Q. (1994). Liq. Cryst., 16, 445.
[12] Xu, Y., Wang, W., Chen, Q., & Wen, J. (1996). Liq. Cryst., 21, 65.
[13] Yin, H. & Wen, J. (1996). Liq. Cryst., 21, 217.
[14] Yang, Y. & Wen, J. (2002). Liq. Cryst., 29, 159.
[15] Yang, Y. & Wen, J. (2002). Liq. Cryst., 29, 161.
[16] Trollsas, M., Orrenius, C., Sahlen, F., Gedde, U. W., Norin, T., Hult, A., Hermann, D.,
Rudquist, P., Komitov, L., Lagerwall, S. T., & Lindstrom, J. (1996). J. Am. Chem. Soc.,
118, 8542.
[17] Yang, Y., Li, H., & Wen, J. (2007). Liq. Cryst., 34, 975.
[18] Lagerwall, J. P. F. & Giesselmann, F. (2006). Chem. Phys. Chem., 7, 20.
[19] Potukuchi, D. M., Goud, B. V. S., & Pisipati, V. G. K. M. (2003). Ferroelectrics,
289, 77.
[20] Naciri, J., Ruth, J., Crawford, G., Shashidhar, R., & Ratna, B. R. (1995). Chem.
Mater., 7, 1397.
[21] Kikuchi, H., Yokota, M., Hisakado, Y., Yang, H., & Kajiyama, T. (2002). Nature
Materials, 1, 64.