Nematic liquid crystal compounds with five-ring framework

Article abstract of DOI:10.1080/15421400903065440

A series of novel liquid crystal compounds with five-ring framework having a-CF₂O-linkage group (1a-1e) has been synthesized and their physical properties were measured. These compounds are characterized to have higher nematicisotropic liquid t

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Nematic Liquid Crystal
Compounds with Five-Ring
Framework
Hiroyuki Tanaka a & Atsuko Fujita a
a Chisso Petrochemical Corporation, Goi Research
Center , Chiba, Japan
Published online: 05 Oct 2009.
To cite this article: Hiroyuki Tanaka & Atsuko Fujita (2009) Nematic Liquid Crystal
Compounds with Five-Ring Framework, Molecular Crystals and Liquid Crystals, 509:1,
118/[860]-133/[875], DOI: 10.1080/15421400903065440
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Mol. Cryst. Liq. Cryst., Vol. 509, pp. 118=[860]–133=[875], 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903065440
Nematic Liquid Crystal Compounds with
Five-Ring Framework
Hiroyuki Tanaka and Atsuko Fujita
Chisso Petrochemical Corporation, Goi Research Center,
Chiba, Japan
A series of novel liquid crystal compounds with five-ring framework having a
ꢀCF2O- linkage group (1a–1e) has been synthesized and their physical properties
were measured. These compounds are characterized to have higher nematic-
isotropic liquid transition temperatures and broader mesophase temperature range.
As for the anisotropic properties, this series is categorized as compounds having
large De and Dn. Although these compounds possess five rings in their structures,
they exhibit high miscibility caused by the rotately non-symmetric structures
including the lateral fluorine substituted phenylene rings. One of the novel com-
pounds exhibits SmF phase and shows the second-order phase transition of SmA
to SmC. The compounds are effective to improve the response property of the mix-
tures due to their high elastic constants. These five-ring compounds possess diversi-
fied properties and of high potential materials for improving the LCD performances.
Keywords: difluoromethyleneoxy; five-ring framework; nematic liquid crystal
compound; nematic mixtures
INTRODUCTION
Nowadays, the active matrix liquid crystal displays (AM-LCDs) are
used to the various kinds of applications, such as PC monitors, TVs,
and cellular phones. With the recent progress of the technology, the
requirements for characteristics of AM-LCDs are increasing and diver-
sifying, for example, the quicker response, the lower driving voltage
and the higher contrast ratio. In order to adapt to these diversified
The authors are acknowledge Dr. K. Miyazawa and indebted to Dr. M. Kondo for the
XRD measurements.
Address correspondence to Hiroyuki Tanaka, Chisso Petrochemical Corporation,
Goi Research Center, 5-1 Goikaigan, Ichihara, Chiba 290-0058, Japan. E-mail:
tanaka-hiroyuki@chisso.co.jp
118=[860]

Nematic Liquid Crystal Compounds with Five-Ring Framework 119/[861]
FIGURE 1 Chemical structures of compounds 1a–1e, 2, and 3.
requirements, liquid crystal compounds that fulfill the physical
properties i.e., higher nematic-isotropic liquid transition temperature,
higher dielectric anisotropy (De), higher optical anisotropy (Dn), simul-
taneously are essentially demanded. As well as the physical properties,
miscibility is also considerable issue in the practical application.
In order to fulfill the requirements, the practically optimized
nematic liquid crystal mixtures are designed as the combination of
the polar compounds and the lower viscous non-polar compounds. In
particular, the characteristics of the polar compounds relate to the
response time and the driving voltage of LCDs, therefore, it is impor-
tant to develop novel polar liquid crystal compounds with improved
properties. To find out the high potential liquid crystal compounds,
we have designed the compounds 1a–1e possessing the five-ring
framework, and their properties were verified and compared with
those of the analogous three- and four-ring compounds 2 [1] and 3 [2]
(Fig. 1).
FIGURE 2 Synthetic route of compound 1a.

120/[862]
H. Tanaka and A. Fujita
FIGURE 3 Synthetic route of compounds 1b and 1c.
EXPERIMENTAL SECTION
Synthesis
The five-ring compound 1a was synthesized according to the
scheme shown in Figure 2. The compound 4 was prepared by Suzuki
cross-coupling reaction [3] of 3,5-difluorophenylboronic acid and the
corresponding halide. The compound 4 was converted to the bromodi-
fluoromethyl derivative 5 with n-BuLi followed by CBr2F2. The ether-
ification of the compound 5 with the phenol derivative 6 resulted in
the desired compound 1a.
The compounds 1b and 1c were synthesized as shown in Figure 3.
The compounds 7 were converted to the four-ring compounds 8
through the iodination and Suzuki cross-coupling reaction. The
desired compounds 1b and 1c were obtained with the same manner
as described in Figure 2.
The synthetic route of the compound 1d is shown in Figure 4. The
compound 10 was prepared from 4-bromobenzoic acid according to
the literature [4]. The desired compound 1d was obtained by Suzuki
cross-coupling reaction of the bromide 10 and the corresponding
boronic acid 11 [5].
FIGURE 4 Synthetic route of compound 1d.

Nematic Liquid Crystal Compounds with Five-Ring Framework 121/[863]
FIGURE 5 Synthetic route of compound 1e.
The compound 1e was synthesized according to the synthetic route
shown in Figure 5. First, the compound 12 was converted to the cyclo-
hexanone 13 through the nucleophilic addition, the dehydration, the
hydrogenation and the deprotection. The compound 13 was converted
to the difluorinated methylenecyclohexane 14 with a Wittig type reac-
tion [6]. The compound 14 was converted to the desired compound 1e
through the bromination, the etherification and the hydrogenation [1a].
RESULTS AND DISCUSSIONS
Measurement Conditions and Instruments
1H-NMR: Bruker DRX 500 (500 MHz); d (ppm) ¼ 7.26 for chloroform.
19F-NMR: Bruker DRX 500 (470 MHz); CFCl3 as internal reference.
Transition temperature: Perkin Elmer Diamond DSC differential
scanning calorimetry and Nikon Optiphot polarizing microscopy with
a Mettler Toledo FP82HT hot stage. X-ray diffraction (XRD): Bruker
˚
D8 Discover diffractometer with a CuKa source (Cu-Ka, k ¼ 1.54 A).
Quantum chemical calculation was carried out by MOPAC AM-1
method [7]. Dielectric anisotropy (De) and Elastic constants at 25ꢁC:
Hewlett Packard 4284A LCR meter. Optical anisotropy (Dn) at 25ꢁC:
Atago 4 T and 2 T Abbe refractometer. Rotational viscosity (c1) at
25ꢁC: TOYO Corporation TCM-1. Response time at 25ꢁC: Otsuka
Electronics LCD-5100WT.
Phase Sequences
Transition temperatures of the five-ring compounds 1a–1e are shown
in Table 1 together with those of the reference compounds 2 and 3.

122/[864]
H. Tanaka and A. Fujita
TABLE 1 Transition Temperatures of Compounds 1a–1e, 2, and 3
Compound
Transition Temperature (ꢁC)a
C 79.4 SmA 138 N 223 Iso
C 87.1 SmA 181 N 255 Iso
C 87.5 N 271 Iso
C 76.9 SmF 114 SmC 143 SmA 215 N 305 Iso
C 70.1 SmA 194 N 330 Iso
C 46.1 Iso
1a
1b
1c
1d
1e
2
3
C 86.8 N 129 Iso
aThe temperatures were detected by DSC analyses, and the mesophase
types were determined by microscopic texture observations.
As shown in Table 1, the compounds 1a–1e have the higher
nematic-isotropic liquid transition temperatures and the wider range
of the mesophases in compared to the three- and the four-ring
compounds 2 and 3. The wide mesophases temperature ranges of
the compounds 1a–1e are resulted by the high N-I temperatures
(>223ꢁC) accompanied with the moderate melting temperatures
(70.1–87.5ꢁC) that are comparable to that of the compound 3
(86.8ꢁC). It should be noteworthy that such large molecules containing
five rings exhibit their melting temperatures at such lower tempera-
ture region (<90ꢁC).
XRD study, namely the measurements of the temperature depen-
dences of the layer space (d-value) and the molecular tilt angle in
the smectic phase of the compound 1d has been carried out to inves-
tigate the polymorphism more in detail. Figure 6a shows the dif-
fractogram measured at 25ꢁC of a super-cooled smectic phase of
the compound 1d. The diffractogram shows the first-order reflection
peak in the small angle region that corresponds to the d-value
˚
28.5 A, and shows the strong hollow peak that is typically observed
in highly ordered smectic phases. The molecular length of the com-
˚
pound 1d was estimated to be 31.9 A by a molecular orbital calcula-
tion (MOPAC AM-1 method). From this result, the molecules in the
smectic phase can be assumed to be tilted to the layer normal for
27.0 degrees.
The temperature dependences of the d-value and the molecular
tilt angle of the compound 1dꢁare shown in Figure 6b. The d-value
˚
(32.1 A) measured at 160–200 C fits with the calculated molecular
˚
length (31.9 A), which represents that the smectic phase over this
temperature range is a non-tilted phase. The continuous decrease
ꢁ
˚
˚
of the d-value at 110–160 C (32.1 A ! 29.3 A) could indicate that

Nematic Liquid Crystal Compounds with Five-Ring Framework 123/[865]
FIGURE 6 (a) XRD pattern of the compound 1d measured at 25ꢁC;
(b) Temperature dependence of d-value and molecular tilt angle.
these is a second-order transition of smectic A to smectic C. This
result might also be reasonably understood from the DSC analysis
(Figure 7), that no exothermic peak is found over 110–160ꢁC.

124/[866]
H. Tanaka and A. Fujita
FIGURE 7 DSC chart of the compound 1d.
Physical Properties
The physical properties of the five-ring compounds 1a–1e are shown
in Table 2. The value for TN-I, De, and Dn were extrapolated from mix-
tures that respectively consist of 15 wt% of the five-ring compounds
and 85% of a high polar base mixture Mix-01 (TN-I: 72.4ꢁC, De: 11.0,
Dn: 0.137) containing the four benzonitrile derivatives. The value for
rotational viscosity (c1) was extrapolated from mixtures that respec-
tively consist of 20 wt% of the five-ring compounds and 80% of a base
mixture Mix-02 (c1: 166 mPa ꢂ S) containing the nine fluorinated com-
pounds. The compositions of the base mixtures Mix-01 and Mix-02 are
shown in Figure 8.
TABLE 2 Physical Properties of Compounds 1a–1e, 2, and 3
Compound
TN-I (ꢁC)
De
Dn
c1 (mPa ꢂ S)
1a
1b
1c
1d
1e
2
146
169
189
218
216
ꢀ3.60
96.4
39.0
36.7
22.9
11.7
6.77
27.7
34.0
0.237
0.257
0.210
0.224
0.130
0.110
0.210
730
699a
706
530
548
95.6
378
3
aExtrapolated from 10 wt% of the compound in the base mixture Mix-02.

Nematic Liquid Crystal Compounds with Five-Ring Framework 125/[867]
FIGURE 8 Compositions of Mix-01 and Mix-02.
As clearly figured in Table 2, the compounds 1a–1e have higher
TN-I (146–218ꢁC) in comparison to those of the compounds 2(ꢀ3.6ꢁC)
and 3 (96.4ꢁC). The extrapolated De and Dn of the compounds 1a–1e
spread widely, depending on the position and the number of the fluor-
ine substituents and the ring structures. The compounds 1a–1c with
the higher p-conjugated and fluorinated structures exhibit higher De
and Dn simultaneously. The replacement of the benzene ring into
the cyclohexane ring, and the decrease of the number of the fluorine
substituents induce the decrease in the De value and the depress of
the Dn magnitude, respectively, as displayed in the properties of the
compounds 1d and 1e. As for the viscosity, the compounds 1d and
1e have relatively lower c1 compared to the other five-ring compounds
1a–1c. It suggests that the viscosity is specifically influenced by the
existence of the two fluorine substituents on the benzene ring of the
a,a-difluorobezyloxy moiety (ꢀAr-CF2Oꢀ).
These five-ring compounds possess diversified TN-I, De, Dn, and c1
according to the position of the ꢀCF2O- moiety, the number of the
fluorine atoms, and the ring structures. Therefore, it will be possible
to provide the mixtures having diverse characteristics that are suita-
ble to fulfilling the requirements by the appropriate selections of the
structures of the five-ring compounds.
Miscibility
The miscibility of the compounds 1b, 1f, and 1g into the base
mixture Mix-01 are displayed in Table 3 with that of the compound
15 as the reference. The compounds 1f and 1g were prepared accord-
ing to the scheme in Figure 3, and the compound 15 was synthesized
by the procedures reported in the literature [8]. The miscibility

126/[868]
H. Tanaka and A. Fujita
TABLE 3 Difference in Miscibility of Compounds 1b, 1f, 1g, and 15
Transition
Miscibility
temperature DHC-SmA
in mix-01
Compound
(ꢁC)
(kJ=mol)
(%)
1b
1f
C 87.1 SmA
181 N 255 I
22.4
15
C124 SmA
206 N 270 I
24.4
34.0
33.5
5
1g
15
C125 SmA
167 N 240 I
5
C106 SmA
169 N 200 I
5
has been estimated as followings. We prepared three samples with
concentrations of 5%, 10%, and 15% of compounds, respectively. These
samples were preserved at 20ꢁC for 30 days. After that, we visually
determined whether solid or smectic phase separation appeared in
the samples. If no solid or smectic phase separation was observed in
the 15% sample, its miscibility was regarded to be over 15%, and if
solid or smectic phase separation was observed in the 15% sample,
the miscibility was regarded to be lower than 10%. In the same way,
each miscibility was estimated.
The transition temperatures and the melting enthalpies of the com-
pounds 1b, 1f, 1g, and 15 are also summarized in Table 3, because the
miscibility of liquid crystal compounds is intimately related to melting
points and melting enthalpy [9].
As shown in Table 3, the miscibility of the compound 1b is signifi-
cantly high among the tested five-ring compounds and the reference
four-ring compound 15. Even though the melting enthalpies of the
compounds 1b (22.4 kJ=mol) and 1f (24.4 kJ=mol) are similar,

Nematic Liquid Crystal Compounds with Five-Ring Framework 127/[869]
the miscibilities of the compounds 1b (15%) and 1f (5%) are notably
different. It suggests that the differences of the miscibilities of the
compounds are strongly influenced by the melting temperatures of
the compounds, as observed in 1b (87.1ꢁC) and 1f (124ꢁC).
Molecular Conformations
For further investigation about the significant differences in miscibil-
ities and the melting temperatures of the compounds 1b, 1f, and 1g,
the distribution of the conformations of 1b was calculated and the
results are displayed in Figure 9a, as the relationship of the heat of
formations to the torsion angle a-b-c-d (h1) and the angle a-b-e-f (h2),
where the heat of formation of the most stable conformation is indi-
cated as 0 kcal=mol. The calculations were carried out by the MOPAC
AM-1 method. As shown in Figure 9a, the compound 1b has a number
of stable conformations, in which the connecting benzene rings have
the torsion angles of 45 degrees one to another. This result means that
the compound 1b is able to exist stable in many conformational states
in liquid crystal mixtures.
The distributions of the conformations of the compounds 1f and 1g
are shown in Figures 9b and c, respectively. While the distributions
of the stable conformations of the compounds 1f and 1g are similar to
that of 1b, their conformations in 180–360 degrees of h1 exhibit as
the same conformations in 0–180 degrees of h1, so that the number of
the stable conformations of the compounds 1f and 1g is limited by half.
The results suggest that the better miscibility of the compound 1b
(15%) is induced by the less-symmetric structure of the compound
1b introduced by the existence of the two mono-fluorinated phenylene
rings in compared to the compounds 1f (5%) and 1g (5%), and by the
existence of the –CF2O- moiety in compared to the four-ring compound
15. From the results of the miscibility investigations and the molecu-
lar orbital calculations, it might be assumed that the non-symmetric
structures inducing the diversified distribution of the molecular con-
formers as the compound 1b have a tendency to be prevented in
forming ordered structures, which may help to decrease a growth of
the crystalline structures and, as a result of this, to sustain the high
miscibility.
Response Property
With the recent progress of LCD technology, the most important
requirement in terms of characteristics of the liquid crystal mixtures
is quick response. The response property of the TN mode LCDs is

128/[870]
H. Tanaka and A. Fujita
FIGURE 9 (a) Conformational distribution of 1b; (b) Conformational distribu-
tion of 1f; (c) Conformational distribution of 1g.

Nematic Liquid Crystal Compounds with Five-Ring Framework 129/[871]
described as the following two formulas (1) and (2) [10].
Trise ¼ c1d2=p2KðV2=Vc2 ꢀ 1Þ ¼ c1d2=e0DeðV2 ꢀ V2c Þ
Tdecay ¼ c1d2=p2K
ð1Þ
ð2Þ
(Trise: Rise time, Tdecay: Decay time, d: Cell thickness, K: Elastic con-
stant, V: Applied voltage, Vc: Threshold voltage, e0: Dielectric constant
of a vacuum).
As shown in the formulas (1) and (2), the total response time
(Trise þ Tdecay) is proportional to c1 and K, so that enlargement of K
without increasing c1 is essentially important for the improvement
of the response property. The elastic constant is represented as
K ¼ K11 þ ðK33 ꢀ 2K22Þ=4
ð3Þ
where K11, K22, and K33 are the splay, twist and bend elastic constants,
respectively. As for the relationship between the elastic constants and
the molecular structure, K33 is known to be proportional to the mole-
cular length (L) [11], and the elastic constant ratio (K33=K11) is
roughly correlated to the molecular length and width ratio (L=D) [12].
The L=D ratio of the compound 1a (3.39) has been estimated with
the molecular orbital calculation applying MOPAC AM-1 method
and is listed in Table 4 together with those of the reference compounds
2 (2.23) and 3 (2.98). As clearly seen in Table 4, the compound 1a has
the longest molecular length among the compounds estimated, which
may suggests that the five-ring compounds are expected to have larger
K33 and K33=K11 ratios, which would work in the right direction into
reducing the response time.
For further investigation of the elastic constants of the five-ring
compounds, the following three mixtures (Mixture A–Mixture C) were
prepared. The properties of the mixtures containing 10% each of
the compound 1a, the three-ring compound 2 and the four-ring
compound 3, respectively, as their high polar components, are shown
in Table 5. The other components in the three mixtures were adjusted
to settle their TN-I, De, Dn and c1 in the same ranges.
TABLE 4 Results of Molecular Orbital Calculations
˚
˚
L (A)
D (A)
L=D
1a
2
3
32.4
21.6
25.9
9.57
9.70
8.67
3.39
2.23
2.98

130/[872]
H. Tanaka and A. Fujita
TABLE 5 Properties of Mixture A–Mixture C
Mixture A
Mixture B
Mixture C
Property
TN-I (ꢁC)
De
106
5.8
106
5.6
107
5.5
Dn
0.101
109
0.100
106
0.101
108
c1 (mPa ꢂ S)
Composition (wt%)
1a
2
3
10
–
–
–
10
–
–
–
10
The elastic constants and the elastic constant ratio (K33=K11) of
Mixture A–Mixture C are measured and shown in Table 6. As expected
from the calculated large value of L and L=D ratio of the compound 1a,
the Mixture A shows the significantly large K33 and K33=K11 ratio that
are greater than those of the other two mixtures.
The temperature dependence of the response time and c1 of
Mixture A–Mixture C were measured, and the influence of the elastic
constants onto the response property has been studied (Figures 10
and 11).
The total response time (Tall) of Mixture A is the shortest among
those of the investigated three mixtures and the difference is wider
at the lower temperature region (Figure 10a). This difference in the
Tall is derived mainly from the Tdecay characteristics (Figure 10b,
Figure 10c). In contrast to the response time, the viscosity of
Mixture A was found to be larger than those of the other two mixtures,
in which the gap becomes larger according to the decrease of the
temperature.
The shorter response time of Mixture A at low temperature, even
though the viscosity is larger than the other mixtures, indicates that
the temperature dependence of the elastic constant of Mixture A is
smaller than that of the other mixture. From the effect notably
observed, the five-ring compounds will be effective for improvement
TABLE 6 Elastic Constants of Mixture A–Mixture C
K11 (pN)
K22 (pN)
K33 (pN)
K
33=K11
Mixture A
Mixture B
Mixture C
12.8
12.6
13.0
12.4
11.0
11.6
28.1
25.7
23.5
2.20
2.04
1.81

Nematic Liquid Crystal Compounds with Five-Ring Framework 131/[873]
FIGURE 10 (a) Temperature dependence of Tall; (b) Temperature dependence
of Trise; (c) Temperature dependence of Tdecay
.
of the response property of the current liquid crystal mixture,
especially at low temperature, and the result suggests that the use
of the five-ring compounds reported in this paper will provide a favor-
able improvement in elastic constants of liquid crystal mixtures.

132/[874]
H. Tanaka and A. Fujita
FIGURE 11 Temperature dependence of c1.
CONCLUSIONS
A series of novel liquid crystal compounds with five-ring framework
having a ꢀCF2O- linkage group has been synthesized and their physi-
cal properties were measured. These compounds are characterized to
have higher nematic-isotropic liquid transition temperatures, broader
mesophase, large De and large Dn. Although the novel compounds pos-
sess five rings in their structures, they exhibit remarkably high misci-
bility caused by the rotately non-symmetric structures and the lateral
fluorine substituted phenylene rings. The high elastic constants of the
compounds allow the mixtures containing them to provide the reduc-
tion of the response time especially at the low temperature region.
These five-ring compounds possess diversified properties and they
are potential materials for the improvement of the LCD performances.
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