Cyanoalkyl difluoro-terphenyl-carboxylate chiral dopants

Article abstract of DOI:10.1016/j.molliq.2012.03.018

A liquid crystal like difluoroterphenyl chiral dopant was synthesized to match the dimensions of a host chiral dopant mixture. The melting point of the chiral dopants was decreased by increasing the length of the alkyl chain. The melting point of the chiral dopants also decreased when fluorine was on the same ring as the ester i.e. at 2″, 3″ position. These dopants were formulated with terphenyl host mixture and liquid crystal properties were assessed. New dopants, when added to the host mixture, maintain SmA¹ but the SmC² phase was reduced markedly. There was a decrease in spontaneous polarisation when fluorine was on the same ring as the ester i.e. at 2″, 3″ position. As the molecular weight of the chiral dopant increased (pentyl ↑ heptyl ↑ nonyl), spontaneous polarisation decreased.

Full text of DOI:10.1016/j.molliq.2012.03.018

Journal of Molecular Liquids 170 (2012) 11–19
Contents lists available at SciVerse ScienceDirect
Journal of Molecular Liquids
journal homepage: www.elsevier.com/locate/molliq
Cyanoalkyl difluoro-terphenyl-carboxylate chiral dopants
b
c
Zohra N. Kayani a, , Robert A. Lewis , Shahzad Naseem
⁎
a
Lahore College for Women University, Lahore, Pakistan
b
Department of Chemistry, University of Hull, Hull, HU6 7RX, UK
Centre for Solid State Physics, University of the Punjab, Lahore-54590, Pakistan
c
a r t i c l e i n f o
a b s t r a c t
Article history:
A liquid crystal like difluoroterphenyl chiral dopant was synthesized to match the dimensions of a host chiral
dopant mixture. The melting point of the chiral dopants was decreased by increasing the length of the alkyl
chain. The melting point of the chiral dopants also decreased when fluorine was on the same ring as the ester
i.e. at 2″, 3″ position. These dopants were formulated with terphenyl host mixture and liquid crystal proper-
ties were assessed. New dopants, when added to the host mixture, maintain SmA1 but the SmC2 phase was
reduced markedly. There was a decrease in spontaneous polarisation when fluorine was on the same ring as
the ester i.e. at 2″, 3″ position. As the molecular weight of the chiral dopant increased (pentyl→heptyl→nonyl),
spontaneous polarisation decreased.
Received 4 October 2011
Received in revised form 21 February 2012
Accepted 19 March 2012
Available online 5 April 2012
Keywords:
Chiral dopant
Host mixture
© 2012 Elsevier B.V. All rights reserved.
Spontaneous polarisation
Ferroelectric liquid crystal
1. Introduction
involving physicists, electrical engineers, computer engineers, and
chemists. As in nematic technology, the FLC material is not a single
A chiral dopant (BE80F2N3) that has proved to be successful is the
octyloxyfluorobiphenyl ester which has a chiral cyanohydrin as the
branched asymmetric group.
component, but a mixture of many compounds. It is best to employ
an achiral room temperature ‘host’ SmC with a broad LC phase tem-
perature range, low viscosity, good stability etc. and to dope this
with a chiral material. One example of a chiral dopant is (BE80F2N)
which has proven increase in the Ps and decrease in the pitch length.
The latter effects result from the restricted rotation caused by length-
ening the chain. Syntheses of the longer chain cyanohydrin esters in-
volve a different route, starting from amino acids. The synthetic
targets chosen, will examine the effect of the position of the ortho-
difluoro substituent and the chain length. The synthetic routes in-
volve directed lithiation and Suzuki palladium catalysed cross cou-
pling of boronic acids with arylhalides as a key component [3].
Target chiral dopants are given below.
F
O
CN
C8H17
O
(S)
O
This molecule, when added to an achiral FLC4 host mixture (5–12%
w/w) provides an FLC mixture with a reasonable compromise of liq-
uid crystalline and electro-optic properties. Enhancement of the dop-
ants' mesogenic properties can be obtained from using a terphenyl
[1,2] structure and further improvement may be obtained from in-
creasing the length of the chain attached to the cyanohydrin. The in-
creased chain length may, however also increase polarisation and
decrease the pitch length of the material. The study of ferroelectric
liquid crystals (FLCs) has fast developed into multidisciplinary field
⁎
Corresponding author at: Centre for Solid State Physics, University of the Punjab,
Lahore-54590, Pakistan. Tel.: +92 3224042222; fax: +92 42 99203077.
E-mail address: zohrakayani@yahoo.com (Z.N. Kayani).
Smectic A.
Smectic C.
Octyloxyfluorobiphenyl ester.
1
2
3
4
Ferroelectric liquid crystal.
0167-7322/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.molliq.2012.03.018

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Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
prepared, five of which possess fluorine on the alkyl side and the
other three on the chiral side. In six dopants a chiral centre was intro-
duced using commercially available (S)-lactamide. L-leucine and L-
norvaline were also used to induce a chiral centre in the ortho
difluoro-substituted materials to produce two dopants.
2.1. Synthesis schemes
Here are six schemes to elaborate the synthesis of all intermedi-
ate compounds as well as dopants. In Fig. 1 synthesis of bromo-
biphenyl cynohydrin ester is given which is an intermediate
compound for the synthesis of 4-heptyl-2,3-difluoro terphenyl ni-
trile and 4-nonyl-2,3-difluoroterphenyl nitrile [4]. In Fig. 2, syn-
thesis of 4-heptyl-2,3-difluoro terphenyl nitrile (D7), 4-nonyl-2,3-
difluoro terphenyl nitrile (D9), 4-pentyl-2″,3″-difluoro terphenyl
nitrile (D5R) and 4-heptyl-2″,3″-difluoro terphenyl nitrile (D7R)
are presented while Fig. 3 gives the synthesis route for 4-pentyl-
2,3-difluoro terphenyl nitrile (D5)[4] and Fig. 4 for 4-nonyl-2″,3″-
difluoro terphenyl nitrile (D5R). Figs. 5 [5] and 6 provide the
synthesis route for dopants (S)-(−)-1-cyno-pentyl-4-pentyl
difluoroterphenyl-4′-carboxylate (D52) and (S)-(−)-1-cyno-2-
(S)-(−)-1-cyno-2-methylbutyl-4-pentyl-difluoroterphenyl-
4′-carboxylate
methylbutyl-4-pentyl difluoroterphenyl-4′-carboxylate
(D53)
respectively [6].
2.1.1. 4-pentyl-2,3-difluoro terphenyl carbonyl nitrile (D5)
2.1.1.1. Quantities. 4-pentyl-2,3-difluoro terphenyl carbonyl amide
(1 g, 12.16 mmol, 473 g/mol), POCl3 (1.33 ml,14.5 mmol,153 g/mol)
and dry DMF (27.5 ml).
(S)-(−)-1-cyno-2-methylbutyl-4-pentyl difluoroterphenyl-
4′-carboxylate
2.1.1.2. Procedure. Dry DMF was cooled to 0 °C. POCl3 was added slow-
ly by syringe under nitrogen keeping the temperature below 5 °C. It
was stirred for 20 min and turned coloured. Pentyl-2,3-difluoro ter-
phenyl carbonyl amide was added in portion and stirred for 20 h at
room temperature. The solution was poured in ice and water mixture,
swirled around and was placed to settle down. A precipitate was
2. Synthesis details of ferroelectric liquid crystals
The initial aim of this work was to synthesize ortho difluoro
substituted materials that possess a central terphenyl core and to in-
corporate a chiral centre in the terminal chain. Eight materials were
Fig. 1. Synthesis steps of biphenyl cyanohydrin ester.

Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
13
Fig. 2. Synthesis steps of 4-akyl-2″,3″ difluoro terphenyl nitrile using coupling reactions [1].
CDCl3) 13.99, 19.01, 22.45, 28.77, 29.71, 31.44, 57.77 (CHMe),
117.59 (CN), 124.11 (dd, JC,F3.1, 2.3), 124.88 (dd, JC,F4.6, 4.5), 127.1,
127.2, 127.4, 127.6, 129.4, 129.5, 130.6, 131.3, 131.5, 135.2 (d, JC,F
2.3), 139, 146.09, 164.57 (CO).
obtained. It was then filtered by micro-filtration by dissolving in THF.
The solvent was removed in vacuo to get the dry product. Then it was
re-crystallised twice through acenitrile. It was put in desiccators
overnight.
Yield (0.17 g, 18.18%); M.P. 131.8 °C (from acenitrile); elemental
analysis: calc. for (found: C, 74.67; H, 6.04; N, 3.10. C29H29F2NO2 re-
quires C, 74.81; H, 5.81; N, 3.23%); m/z 433 (M+, 100%), 376, 363,
323, 306, 277, 153; transitions/°C K 106.1 (48.2 J/g) SmA* 132.1
(83.21 J/g) I; IR(KBr)υmax/cm−1 2928(CH), 1728 s(CO), 1458, 1263,
1095, 810, 771; δH(400 MHz; CDCl3) 0.92 (3H, t, J7, CH3CH2), 1.35–
1.39 (4H, m), 1.66(2H, quint, J7.5, ArCH2CH2), 1.81(3H, d, J7, Me),
2.71 (2H, t, J 7.4, ArCH2), 5.69 (1H, q, J7, CHMe), 7.02 (1H, ddd, J6.8,
6.6, 1.5, 20H), 7.16 (1H, ddd, J6.8, 6.4, 1.6, 19H), 7.66 (2H, dd, J 8.4,
1.3, 6- and 18-H), 7.72 (2H, d, J 8.4, 1- and 17-H), 7.75 (2H, d, J 8.6,
10- and 14-H), 8.15 (2H, d, J8.6, 11 and 13H); δF(376;CDCl3) 143.30
(1F, dd, JF,F20.81, JF,H6.9), 143.88 (1F, dd, JF,F18.5, JF,H6.9); δC(100.5;
2.1.2. 4-heptyl-2,3-difluoro terphenyl carbonyl nitrile (D7)
2.1.2.1. Quantities and procedure. (S)-1-cynoethyl-4-bromo diphenyl-
4′-carboxylate (1 g, 3.03 mmol, 330 g/mol), 2,3-diflouro-4-nanoyl
phenyl boronic acid (2.56 g, 10 mmol, 256 g/mol), potassium
phosphate (1.93 g, 9.09 mmol, 212.28 g/mol) and dioxan (40 ml)
were added under dry nitrogen at room temperature. The flask was
flushed by nitrogen three times and then tetrakis (triphenyl
phosphine) palladium (0) (0.162 g, 0.1401 mmol, 1156 g/mol) was
added. The stirred mixture was heated under reflux (ca. 140 °C) for
23 h (i.e., until g.l.c/t.l.c. analysis revealed a complete reaction). The

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Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
Fig. 3. Synthesis steps of 4-pentyl-2,3 difluoro terphenyl nitrile using coupling reactions [1].
mixture was filtered by hypo flow and the solvent was evaporated to
get the dry product. The dry product was purified by addition to a
packed chromatography column of silica gel [silica gel, DCM:
hexane: 20:80] to yield a white product. Product was re-crystallised
twice through acenitrile. It was cooled quickly in liquid nitrogen to
avoid it becoming gel. It was filtered by pressure. It was again filtered
by micro-filtration by dissolving in THF to remove the dust particles
and was evaporated to get the dry product. It was put in the desicca-
tors overnight.
Yield (0.42 g, 30.88%); M.P.122 °C (from acenitrile) elemental anal-
ysis: calc. for (found: C, 75.22; H, 6.54; N, 2.93. C29H29F2NO2 requires C,
75.47; H, 6.33; N, 3.03%); m/z 461 (M+, 100%), 408, 391, 376, 363, 323,
277, 153; transitions/°C K 121 I (47.51 J/g); IR (KBr) υmax/cm−1 2924
(CH), 1724 vs, (CO), 1606, 1487, 1464, 1398, 1317, 1274, 1206, 1181,
1110, 1039, 1004, 895, 846, 810, 767; δH(400 MHz; CDCl3), 0.89 (3H,
t, CH3CH2), 1.28–1.43 (8H, m), 1.66 (2H, quint, J7.79, ArCH2CH2), 1.81
(3H, d, J 6.78, Me), 2.71 (2H, t, J 7.51, ArCH2), 5.69 (1H, q, J 6.96,
CHMe), 7.03 (1H, ddd, J 6.78, 6.6, 1.5, 20H), 7.15 (1H, ddd, J 6.78, 6.6,
1.5, 19H), 7.67 (2H, dd, J 6.78, 1.47, 6- and 18-H), 7.72 (2H, d, J 8.3,
1- and 17-H), 7.75 (2H, d, J 8.3,10- and 14-H), 8.15 (2H, d, J 8.3,11-
and 13-H); δF(376; CDCl3) −143.29 (1F, dd, JF,F20.81, JF,H6.9)–143.88
(1F, dd, JF,F20.81, JF,H6.9), δC(100.5; CDCl3), 14.1, 19.01, 22.65, 28.81,
29.08, 29.25, 30.04, 31.77, 57.76 (CHMe), 117.6(CN), 124.1 (dd,
J
C,F3.8, 2.3), 124.88 (dd, JC,F4.6, 3.8), 127.06, 127.21, 127.44, 127.58,
129.43, 129.46, 130.59, 131.32, 131.46, 135.2, 139.0, 146.09, 164.57
(CO).
2.1.3. 4-nanoyl-2,3-difluoro terphenyl carbonyl nitrile (D9)
2.1.3.1. Quantities. (S)-1-cynoethyl-4-bromo diphenyl-4′-carboxylate
(0.1.39 g, 4.21 mmol, 330 g/mol), 2,3-diflouro-4-nanoyl phenyl boronic
acid (2.92 g, 10.28 mmol, 284 g/mol), potassium phosphate (2.68 g,
12.63 mmol, 212.28 g/mol) tetrakis (triphenyl phosphine) palladium
(0) (0.093 g, 0.0804 mmol, 1156 g/mol)and dioxan (60 ml).
2.1.3.2. Procedure. The experimental procedure was as described for
the compound D7 except that when dry product was re-crystallised
through acenitrile, it turned into gel. So it was purified by addition
to a packed chromatography column of silica gel [silica gel, DCM:hex-
ane: 75:25] to yield a white product. It was then filtered by micro-
filtration by dissolving in THF and was evaporated to get the dry
product. It was put in the desiccators overnight.

Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
15
Fig. 4. Synthesis steps of 4-nonyl-2″,3″ difluoro terphenyl nitrile using coupling reactions.
Fig. 5. Synthesis route for (S)-(−)-1-cyno-2-methylbutyl-4-pentyl-difluoroterphenyl-4′-carboxylate [2].

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Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
Fig. 6. Synthesis route for (S)-(−)-1-cyno-pentyl-4-pentyl-difluoroterphenyl-4′-carboxylate.
Yield (1.05 g, 50.97%); M.P. 119 °C; elemental analysis: calc. for
Yield (0.6 g, 55.05%); M.P.103.2 °C (from isopropanol); elemental
analysis: calc. for (found: C, 75.01; H, 5.86; N, 3.09. C27H25F2NO2 re-
quires C, 74.81; H, 5.81; N, 3.23%); m/z 433 (M+, 100%), 390, 376,
363, 335, 323, 278, 165, 153; transitions/°C SmC* 102.8 (15.85 J/g)
SmA* 164.9 (16.45 J/g)I.
(found: C, 76.19; H, 7.12; N, 2.73. C31H33F2NO2 requires C, 76.05; H,
6.79; N, 2.86%); m/z 489 (M+ 100%), 376, 323, 277, 153;
transitions/°C K 118 I (37.83 J/g).
IR(KBr)υmax/cm1 2923(CH), 1724vs (CO), 1607, 1487, 1464,
1397, 1317, 1274, 1206, 1181, 1110, 1039, 1004, 895, 846, 810,
767; δH(400 MHz; CDCl3) 0.89 (3H, t, J6.96, CH3CH2), 1.24–1.39
(8H, m), 1.65 (2H, quint, J7.3, ArCH2CH2), 1.81 (3H, d, J6.8, Me),
2.71 (2H, t, J7.7, ArCH2), 5.69 (1H, q, J7, CHMe), 7.02 (1H, ddd, J
6.6, 6.4, 1.5, 20H), 7.16 (1H, ddd, J 7, 6.6, 1.7, 19H), 7.66 (2H, dd, J
8.4, 1.5, 6- and 18-H), 7.72 (2H, d, J 8.6, 1- and 17-H), 7.75 (2H, d,
J 8.6, 10- and 14-H), 8.15 (2H, d, J 8.6, 11- and 13-H); δF(376;
CDCl3) −143.29 (1F, dd, JF,F20.81, JF,H6.9), −143.88(1F, dd, JF,F
20.81, JF,H6.9); δC(100.5; CDCl3) 14.11, 19.01, 22.67, 28.81, 29.28,
29.31, 29.41, 29.51, 30.04, 31.87, 57.76 (CHMe), 117.59(CN), 124.10
(dd, JC,F3.8, 2.3), 124.88 (dd, JC,F4.6), 127.06, 127.20, 127.44, 127.57,
129.43, 129.46, 130.59, 131.33, 131.46, 135.2, 139.01, 146.09, 164.57
(CO).
IR(KBr)υmax/cm−1 2925 (CH), 1723vs (CO), 1623, 1506, 1459,
1399, 1313, 1295, 1212, 1141, 1096, 1038, 808, 775; δH(400 MHz;
CDCl3) 0.91 (3H, t, J7.2, CH3CH2), 1.34–1.38 (4H, m), 1.66 (2H,
quint, J7.5, ArCH2CH2), 1.82 (3H, d, J7, Me), 2.66 (2H, t, J7.7, ArCH2),
5.67 (1H, q, J 7, CHMe), 7.29 (2H, d, J 8.4), 7.36 (1H, ddd, J 8.5, 8.4,
1.6), 7.57 (2H, d, J 8.2), 7.65 (2H, dd, J 8.4, 1.6), 7.72 (2H, d, J 8.6),
7.80 (1H, ddd, J 8.5, 6.2, 1.6); δF(376 MHz; CDCl3), −132.39 (1F, dd,
JF,F 25.4, JF,H 6.9), −141.00 (1F, dd, JF,F 25.4, JF,H 6.9); δC(100.5;
CDCl3) 14.04, 18.9, 22.57, 31.17, 31.56, 35.61, 58.16 (CHMe), 116.86
(d, JC,F6.1), 117.19 (CN), 124.52 (dd, JC,F3.8, 2.3), 126.38 (d, JC,F4.6),
126.97, 127.32, 129.01, 129.29 (d, JC,F3.84), 131.93 (d, JC,F3.84),
136.15, 136.25, 137.41, 142.11, 142.85, 161.68 (dd, JC,F 3.8, 3.1, CO).
2.1.5. 4-heptyl-2″,3″-difluoro terphenyl carbonyl nitrile (D7R)
2.1.4. 4-pentyl-2″,3″-difluoro terphenyl carbonyl nitrile (D5R)
2.1.5.1. Quantities. 4-heptyl-2″,3″-difluoro terphenyl carbonyl amide
(0.8 g, 1.69 mmol, 473 g/mol), POCl3 (1.06 ml, 11.40 mmol, 153 g/
mol) and dry DMF (22 ml).
2.1.4.1. Quantities. 4-pentyl-2″,3″-difluoro terphenyl carbonyl amide
(1.2 g, 2.59 mmol, 463 g/mol), POCl3 (1.59 ml, 17.095 mmol, 153 g/
mol) and dry DMF (33 ml).
2.1.5.2. Procedure. The experimental procedure was as described for
the preparation of 4-pentyl-2″,3″-difluoro terphenyl carbonyl nitrile.
Yield (0.57 g, 75%); M.P. 95.8 °C (fromisopropanol); elemental
analysis: (found: C, 74.49; H, 6.41; N, 2.72. Calc. for C29H29F2NO2: C,
75.47; H, 6.33; N, 3.03%); m/z 461 (M+, 100%), 391, 376, 363, 323,
2.1.4.2. Procedure. The experimental procedure was as described for
the preparation of 4-pentyl-2,3-difluoro terphenyl carbonyl nitrile
except that it was filtered and washed with water. The dry product
was recrystallised through isopropanol.

Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
17
2.1.6.2. Procedure. The experimental procedure is as described by 4-
pentyl-2″,3″-difluoro terphenyl carbonyl nitrile.
Table 1
Transition temperatures (°C) and enthalpy change taken by optical polarising micro-
scope and differential scanning calorimeter for the 4-alkyl-2, 3-difluoro terphenyl ni-
trile, (S)-(−)-1-cyno-2-methylbutyl-4-pentyl -difluoroterphenyl-4′-carboxylate and
(S)-(−)-1-cyno-2-methylbutyl-4-pentyl difluoroterphenyl-4′-carboxylate.
Yield (1.12 g, 38.62%); M.P 85.43 °C (13.93 J/g) (from isopropa-
nol); transition temperature/°
C K 79.46 (13.65 J/g) SmX 94.9
(0.30 J/g) SmA 131.6 (11.42 J/g) I; Elemental analysis: calc. for
(found: C, H, N. C31H33F2NO2 requires C, 76.05; H, 6.79; N,2.86%);
δH(400 MHz; CDCl3) 0.88 (3H, t, J7.0, CH3CH2), 1.24–1.41 (13H,
m), 1.66 (2H, quint, J7.7, ArCH2CH2), 1.80–1.88 (3H, m), 2.66 (2H, t, J
7.9, ArCH2), 5.67 (1H, q, J 7), 7.29 (2H, d, J 8.4), 7.36 (1H, ddd, J 8.4,
6.4, 1.6), 7.56 (2H, d, J8.2), 7.64 (2H, dd, J8.6, 1.6), 7.71 (2H, d, J8.6),
7.80 (1H, ddd, J8.4, 6.4, 1.8); δF(376; CDCl3) 132.40 (1F, dd, JF,F20.81,
JF,H6.9), 141.00 (1F, dd, JF,F20.81, JF,H6.9); δC(100.5; CDCl3) 14.09,
18.87, 22.66, 29.33 (d, J3.8), 29.53 (d, J3.1), 31.15, 31.88, 35.63, 58.15,
116.85 (d, J6.9), 117.17, 124.50 (dd, JC,F4.6, 2.3), 126.36 (dd, JC,F4.6,
Structure
Mesomorphic behaviour
F
F
O
Melting point: 131.6 °C
Transitions/°C K 106.1(48.2 J/g)
SmA* 132.1 (83.21 J/g) I
CN
C5H11
O
F
F
O
Melting point:121 ° C
Transitions/°C K 121 (47.51 J/g) I
CN
C7H15
O
F
F
O
Melting point:118.9 °C
Transitions/°C K 118 (37.83 J/g) I
CN
3.1), 126.94, 127.30, 128.98, 129.27 (d,
JC,F3.1), 131.92, 136.13,
C9H19
136.24, 137.38, 142.09, 142.85, 152.78, 161.67.
O
H
H3C
COCN
CH3
Melting point:72.54 °C (14.39 J/g)
Transitions/°C K 102.8 °C (55.82 J/g) I
F
F
2.1.7.
carboxylate (D53)
(S)-(−)-1-cyno-2-methylbutyl-4-pentyldifluoroterphenyl-4′-
H
O
O
C5H11
2.1.7.1. Quantities. (S)-1-carbamoyl-2-methylbutyl-4-pentyl
difluoroterphenyl-4′-carboxylate (1 g, 2.02 mmol, 494 g/mol),
POCl3 (1.27 ml,1 3.65 mmol, 153 g/mol) and dry DMF (30 ml).
O
CN
Melting point: °C
Transitions/°C K–I
F
F
O
O
C5H11
2.1.7.2. Procedure. The experimental procedure is the same as de-
scribed for 4-pentyl-2″,3″-difluoro terphenyl carbonyl nitrile.
Yield (0.71 g, 73.96%), M.P 102.8 °C (from ethanol);transition/°C
melting point 72.54 °C (from ethanol) (14.39 J/g) K 103.2 (55.82 J/g) I;
278, 165, 153; transitions/°C SmC* 95.2 (14.61 J/g) SmA* 145.5
(14.85 J/g)I.
IR(KBr)υmax/cm−1 2923 (CH), 1733s (CO), 1653, 1635, 1623, 1559,
1507, 1458, 1399, 1313, 1212, 1142, 1037, 808, 775; δH(400 MHz;
CDCl3) 0.89 (3H, t, J7.1, CH3CH2), 1.24–1.42 (8H, m), 1.66 (2H, quint,
J 7.7, ArCH2CH2), 1.81(3H, d, J 7, Me), 2.66 (2H, t, J7.5, ArCH2), 5.67
(1H, q, J 7, CHMe), 7.29 (2H, d, J 8.4) 7.36 (1H, ddd, 6.8, J 6.6, 1.6),
7.56 (2H, d, J 8.2), 7.65 (2H, dd, J 7, 1.6), 7.72 (2H, d, J 8.6), 7.8 (1H,
ddd, J 6.4, 2.0); δF(376;CDCl3) −132.4 (1F, dd, JF,F18.5, JF,H6.9), 141.01
(1F, dd, JF,F20.8, JF,H6.9); δC(100.5; CDCl3) 14.10, 18.89, 22.67, 29.18,
29.33, 31.48, 31.81, 35.64, 58.15 (CHMe), 116.85 (dJC,F6.9), 117.18,
124.51 (dd, JC,F3.8, 3.1), 126.35 (dd, JC,F3.8, 3.1), 126.95, 127.31,
129.00, 129.27 (dJC,F3.1), 131.93, 136.15, 136.25, 137.39, 142.10,
142.86, 161.67 (dd, JC,F6.1, 3.8).
2.1.6. 4-nonyl-2″-3″-difluoroterphenyl carbonyl nitrile (D9R)
2.1.6.1. Quantities. 4-nonyl-2″-3″-difluoroterphenyl carbonyl amide
(3 g, 5.9 mmol, 508 g/mol), POCl3 (3.7 ml, 39.8 mmol, 153 g/mol)
and dry DMF (85 ml).
Table 2
Transition temperatures (°C) and enthalpy change taken by optical polarising micro-
scope and differential scanning calorimeter for the 4-alkyl-2″,3″-difluoro terphenyl
nitrile.
Structure
Mesomorphic behaviour
F
F
Melting point: 103.2 °C
Transitions/°C SmC* 102.8
(15.85 J/g) SmA* 164.9 (16.45 J/g)
I
O
CN
C5H11
O
Melting point: 95.78 °C
Transitions/°C SmC* 95.2 (14.61 J/
g) SmA* 145.5 (14.85 J/g) I I
F
F
O
CN
C7H15
O
Melting point:85.43 °C (13.93 J/g)
Transitions/°C K 82.9 (13.93 2 J/g)
SmY 94.9 (0.40 J/g) SmX 100.99
(0.44 J/g) SmA 131.6 (11.42 J/g) I
F
F
Fig. 7. (a) Mixture of 7% D7R in HM1; focal conic texture of the SmA* phase which
arises because of an energetically favoured packing of the lamellar structure to give a
system of curved, equidistant layers and (b) mixture of 7% D7R in HM1; the scheliring
texture of SmC* phase.
O
CN
C9H19
O

18
Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
elemental analysis: (found: C, 75.77; H, 6.57; N, 2.95. calc. for
30H31F2NO2: C, H, N, %); δH(400 MHz; CDCl3) 0.92 (3H, t, J 7.1), 1.04
(3H, t, J 7.5), 1.23 (3H, d, J 6.8), 1.33–1.52 (5H, m), 1.63–1.74 (3H, m),
2.05–2.17 (1H, m), 2.70 (2H, t, J 7.9), 5.58 (1H, d, J 5.5), 7.02 (1H, ddd,
chain to the nitriles increases, the melting point decreases which is
evident by comparing the three compounds although materials are
purely smectogenic materials, exhibiting a SmC* phase and having a
SmA* phase at high temperatures.
C
J
C,F8.1, 6.6, 1.6), 7.15 (1H, ddd, JC,F8.4, 6.4, 1.8), 7.66 (2H, dd, JC,F8.6,
Liquid crystal phases were viewed through optical polarising mi-
croscope and the results are given in Fig. 7(a, b).
1.5), 7.72 (2H, d, JC,F8.4), 7.75 (2H, d, JC,F8.6), 8.14 (2H, d, JC,F8.6);
δF(376; CDCl3) −143.29 (1F, dd, JF,F20.81, JF,H4.6), 143.87 (1F, dd,
J
F,F20.8, JF,H6.9); δC(100.5; CDCl3) 11.21, 14.01, 14.69, 22.46, 25.16,
3.3. Mixture comparison with respect to ferroelectric properties
28.79, 29.73, 31.45, 37.60, 66.00, 116.04, 124.13 (dd, JC,F3.8, 2.3), 124.9
(dd, JC,F4.6, 3.8), 127.11–127.69 (m), 129.47 (d, JC,F 3.1), 130.57,
131.34, 131.47, 135.20, 139.07, 146.09, 164.66, 170.99 (CO).
The automatic liquid crystal tester was used to measure the ferro-
electric liquid crystal properties of various mixtures prepared during
this study. Fig. 8 shows various ferroelectric mixtures that contain 3%
or 7% chiral dopants in achiral host mixture HM1.
3. Results and discussions
The spontaneous polarisation increases as the alkyl chain length
attached to the chiral dopant increases. When the di fluorine is at-
tached to the 2″–3″-position i.e. towards the chiral centre then the
polarisation has small values as compared to the fluorine attached
to the alkyl side i.e. at the 2–3 position. At the same time the sponta-
neous polarisation increases with the increase of the percentage of
the chiral dopant while the viscosity increases with the increase of
alkyl length. Viscosity for the dopants having fluorine on the chiral
side has lesser value than the dopants having fluorine on the alkyl
side. Viscosity decreases with increase of % of dopant.
3.1. 4-alkyl-2,3-difluoro terphenyl nitrile
Table 1 shows the transition temperatures and handedness of any
helical phases formed from a series of three 4-alkyl-2,3-difluoro terphe-
nyl nitrile which differ only due to the length of alkyl chain attached to it.
4-heptyl-2,3-difluoro terphenyl nitrile and 4-nanoyl-2,3-difluoro
terphenyl nitrile did not pose a problem since a chiral dopant need
not necessarily be mesogenic as the chiral structure can still induce
chirality into phases of an achiral host mixture. 4-heptyl-2, 3-difluoro
terphenyl nitrile and 4-nanoyl-2, 3-difluoro terphenyl nitrile did not
exhibited any mesomorphic behaviour due to their comparative
long terminal chain length than 4-pentyl-2, 3-difluoro terphenyl ni-
trile. The lack of any liquid crystal phase, however does not pose any
problem in the potential behaviour of compounds as chiral dopant in
ferroelectric mixtures, various weight percentage composition mix-
tures were prepared and analysed by optical microscope in the HM1.
4. Conclusions
Eight chiral dopants were successfully synthesized. The melting
point of the dopants decreased as the length of alkyl chain to dopant
increased. When difluorine was on the same ring as the ester i.e. at 2″,
3″ position then melting point is lower as compared to dopants when
difluorine was on the 2″, 3″ position. Spontaneous polarisation in-
creases while viscosity decreases with increase of % of dopant. The
spontaneous polarisation and viscosity increase as the alkyl chain
length attached to the chiral dopant increases [6].
3.2. 4-alkyl-2″,3″-difluoro terphenyl nitrile
Table 2 shows the transition temperatures and handedness of any
helical phases formed from a series comprising three 4-alkyl-2″,3″-
difluoro terphenyl nitriles which differ only due to the length of the
alkyl chain attached to it.
From the results obtained it is apparent that the length of the alkyl
chain has a considerable effect on the melting point, transition tem-
peratures and mesophase morphology. As the length of the alkyl
Abbreviations
D5
D7
D9
D5R
4-pentyl-2,3 difluoro terphenyl nitrile
4-heptyl-2,3 difluoro terphenyl nitrile
4-nonyl-2,3 difluoro terphenyl nitrile
4-pentyl-2″,3″ difluoro terphenyl nitrile
Fig. 8. Shows variation of polarisation with Tc–T °C of mixture of 4-(pentyl, heptyl, nonyl)-2,3 difluoro terphenyl nitrile and 4-(pentyl, heptyl, nonyl)-2″,3″ difluoro terphenyl nitrile
in HM1.

Z.N. Kayani et al. / Journal of Molecular Liquids 170 (2012) 11–19
19
D7R
D9R
D52
4-heptyl-2″,3″ difluoro terphenyl nitrile
4-nonyl-2″,3″ difluoro terphenyl nitrile
(S)-(−)-1-cyno-2-methylbutyl-4-pentyl-difluoroterphenyl-
4′-carboxylate
for providing laboratory facilities, Higher Education Commission Paki-
stan for funding and Kingston Chemicals Limited UK for providing the
materials.
D53
(S)-(−)-1-cyno-2-methylbutyl-4-pentyl difluoroterphenyl-
4′-carboxylate
References
DMF
THF
Diethylformamide
tetrahydrofuran
[1] G.W. Gray, M. Hird, D. Lacey, K.J. Toyne, J. Chem. Soc.,Perkin Trans. 2 (1989)
2041–2053.
[2] M. Hird, K.J. Toyne, A.J. Slaney, J.W. Goodby, J. Mater.Chem. 5 (1995) 423–430.
[3] N. Miyama, T. Yanagi, A. Suzuki, Synth. Commun. 11 (1981) 513–519.
[4] Z. Kayani, R.A. Lewis, Poster Presentation at Conference of British Liquid Crystal
Society, Bristol 2009, UK, 2009.
[5] R.A. Lewis, Z. Kayani, Presented at International Conference on Ferroelectric Liquid
Crystal, Zaragoza 2009, Spain, 2009.
[6] Z. N. Kayani, PhD Thesis, University of the Punjab, Lahore, Pakistan, 2009.
Acknowledgement
The paper is extracted from the PhD thesis of Dr. Zohra Nazir Kayani.
The author wishes to thank The University of the Hull, United Kingdom