Synthesis and properties of novel liquid crystalline compounds having a difluoromethyleneoxy moiety as a linkage group

Article abstract of DOI:10.1080/15421400490434919

Novel liquid crystal compounds having a difluoromethyleneoxy group as a linkage group have been prepared by the new synthetic method using dibromo-difluoromethane in good yield, from the results of physical property measurements; i.e., transition temperature, dielectric anisotropy (Δε), birefringence (Δn) and viscosity, it becomes obvious that the derivatives having 3,5-Difluorophenyl group at the carbon side of difluoromethyleneoxy group (1) have high dielectric anisotropy and low viscosity, and the derivatives having 1,4-cyclohexylene group at the carbon side of difluoromethyleneoxy group (2) have good balance of their physical properties. Moreover, 1 and 2 indicate high voltage holding ratio. Therefore, a novel series of the compounds having a difluoromethyleneoxy linkage group is an eminently suitable material that can lower driving voltage and achieve quicker response time of the AM-LCDs.

Full text of DOI:10.1080/15421400490434919

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Synthesis and Properties
of Novel Liquid Crystalline
Compounds having a
Difluoromethyleneoxy Moiety
as a Linkage Group
Shuichi Matsui a , Tomoyuki Kondo a & Kouki Sago a
a Specialty Chemicals Research Center , Chisso
petrochemical Corporation , Ichihara, Chiba, Japan
Published online: 18 Oct 2010.
To cite this article: Shuichi Matsui , Tomoyuki Kondo & Kouki Sago (2004) Synthesis
and Properties of Novel Liquid Crystalline Compounds having a Difluoromethyleneoxy
Moiety as a Linkage Group, Molecular Crystals and Liquid Crystals, 411:1, 127-137,
DOI: 10.1080/15421400490434919
To link to this article: http://dx.doi.org/10.1080/15421400490434919
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Mol. Cryst. Liq. Cryst., Vol. 411, pp. 127=[1169]–137=[1179], 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080=15421400490434919
SYNTHESIS AND PROPERTIES OF NOVEL
LIQUID CRYSTALLINE COMPOUNDS HAVING
A DIFLUOROMETHYLENEOXY MOIETY AS
A LINKAGE GROUP
Shuichi Matsui, Tomoyuki Kondo, and Kouki Sago
Chisso petrochemical Corporation, Specialty Chemicals Research
Center, 5-1 Goikaigan, Ichihara, Chiba, 290-8551, Japan
Novel liquid crystal compounds having a difluoromethyleneoxy group as a
linkage group have been prepared by the new synthetic method using dibromo-
difluoromethane in good yield. From the results of physical property measure-
ments; i.e., transition temperature, dielectric anisotropy (De), birefringence
(Dn) and viscosity, it becomes obvious that the derivatives having 3,5-
Difluorophenyl group at the carbon side of difluoromethyleneoxy group (1)
have high dielectric anisotropy and low viscosity, and the derivatives having
1,4-cyclohexylene group at the carbon side of difluoromethyleneoxy group (2)
have good balance of their physical properties. Moreover, 1 and 2 indicate high
voltage holding ratio. Therefore, a novel series of the compounds having a
difluoromethyleneoxy linkage group is an eminently suitable material that
can lower driving voltage and achieve quicker response time of the AM-LCDs.
Keywords: active matrix LCD; dibromodifluoromethane; difluoromethyleneoxy; high dielec-
tric anisotropy; low viscosity
INTRODUCTION
According to expansion in application of the AM-LCDs, e.g., PC-monitor,
note PC, cellar phone or TV, required characteristics for liquid crystalline
materials became very diverse. In particular, reduction of driving voltage
and response time is the most important aim for any kind of driving mode,
e.g., TN, IPS, VA or OCB. One of the common solutions to reduce driving
voltage is to develop the compound with high dielectric anisotropy; thus,
many liquid crystalline compounds have been investigated to meet this
Address correspondence to Shuichi Matsui, Chisso Petrochemical Corporation, Speciality
Chemicals Research Center, 5-1 Goikaigan, Ichihara, Chiba 290-8551, Japan. E-mail:
s.matsui@chisso.co.jp
127=[1169]

128=[1170]
S. Matsui et al.
aim. To design a compound having high dielectric anisotropy, introduction
of one or more fluorine atom at a ring structure or a side chain moiety
according to a molecular long axis is well known method [1]. Nevertheless,
this method normally causes nematic temperature range reduction and
viscosity increase in proportion to rise of De.
Although, as formerly described, there were many reports about intro-
duction of the fluorine atom to a ring structure or a side chain moiety,
research works of a compound having a fluorinated linkage group were
quite limited [2]. Therefore, we focused on compounds having a fluorinate
linkage group to increase De without rise of viscosity, especially compounds
with a difluoromethyleneoxy group (ꢀCF2Oꢀ) [3]. Here we now report
new synthetic methods and physical properties of compounds 1 and 2
which are relatively different from ordinal liquid crystalline compounds.
RESULT AND DISCUSSION
Synthesis
Preparation of Compound 1 (Scheme 1)
Previously, as preparation of a compound having phenyl group at a
carbon side of a difluoromethyleneoxy linkage, A. Haas has been reported
SCHEME 1

Synthesis and Properties of Novel Liquid Crystalline
129=[1171]
a three steps route including photobromination of the difluoromethyl-
benzen that was derived from benzaldehyde and SF4, following etheri-
fication [4]. However, this method is not applicable to practical scale
production. We developed a new synthetic route to compound (1) involving
direct difluorobromomethylation of 3,5-Difluorobenzen derivatives (A)[5a].
Compound A was treated by n-BuLi in THF below ꢀ70ꢁC, and then gener-
ated phenyl lithium reacted with CF2Br2 to give an intermediate bromodi-
fluoromethylbenzene (CF2Br-form) derivative. The intermediate was
converted into a desired material (1) by the Williamson etherification in
DMF under K2CO3 basic condition with a halogenated phenol. The isolation
yield of 1a (X ¼ L1 ¼ F) is 32% based on 40-propyl-3,5-difluorobiphenyl.
This synthetic process provides a convenient alternative to formerly known
methods from both handling and yield.
This reaction also produced brominated derivatives (Br-form). The ratio
of CF2Br-form to Br-form is affected by a chemical structure of the sub-
strate A. The correlation between selectivity of Br-form and the structure
of A was shown in Table 1.
TABLE 1 Selectivity of Bromodifluoromethylation
GC ratio(%)
R–
CF2Br-form
Br-form
C3H7-
74
70
26
30
80
84
20
16
Not detected
15

130=[1172]
S. Matsui et al.
From Table 1, when the substrate having an electron withdrawing group,
such as 5-alkyl-1,3-dioxane-2-yl or alkylated phenyl, bromodifluoromethy-
lation selectivity is higher than the case of a substrate containing an elec-
tron donating group, such as alkyl or alkylated cyclohexyl. However, when
3-fluorophenyl or non fluorinated phenyl derivatives was used as a sub-
strate, a bromodifluoromethylated product was not obtained.
Wakselman et al. reported two considerable mechanisms of the reaction
between perhaloalkanes (CF2X2, X ¼ Cl or Br) and a phenoxide or a thio-
phenoxide as a nucleophile: 1) an ionic chain reaction mechanism which
involves the difluorocarbene (:CF2), 2) a radical mechanism [6]. In our
case, since no difluoromethane product was observed, we assume that
the newly developed method carried out in a different pathway from two
mechanisms proposed by Wakselman et al.
NMR and GC-MS data of Compound 1a(X ¼ L1 ¼ F in general foumula 1)
1H-NMR: d(ppm) 0.956–0.985(t,3H), 1.658–1.702(m,2H), 2.630–
2.661(m,2H), 6.956–7.013(m,2H), 7.191–7.212(d,2H), 7.306–7.322(d,2H),
7.481–7.498(d,2H)
19F-NMR: d(ppm) -62.00- -62.16(t,2F), -111.09- -111.22(m,2F), -133.97-
-133.07(m,2F), -163.68- -163.79(m,1F)
EIMS(m=e): 27(1.2%), 41(1.1), 51(1.0), 69(1.4), 75(1.0), 81(1.5),
119(2.9), 126(6.1), 131(1.2), 147(1.4), 163(1.3), 170(1.2), 183(5.0),
187(1.3), 201(7.0), 232(1.9), 237(2.2), 252(36.4), 259(2.7), 265(1.8),
281(100), 428(1.4, Mþ)
Synthesis of Compound 2 (Scheme 2)
As synthetic method of difluoromethyleneoxy derivatives having an
aliphatic group at the carbon side, it is generally known that fluorination
SCHEME 2

Synthesis and Properties of Novel Liquid Crystalline
131=[1173]
ꢀ
of the thioester by means of DAST [7] or n-Bu4þ H2F3 with an oxidative
condition using NBS and the like [8]. However, if an aromatic ester substi-
tuted by fluorine atoms, yield of thioester was very low (around 10%). It is
difficult to apply these methods to our target compounds in practical
production. Therefore, we have developed a novel synthetic method of
compound 2 (Scheme 2) applicable to bulk scale [5b].
Referred to report of D. G. Naae et al. or N. Ishikawa et al. [9], we pre-
pared a difluorovinyliden derivative B by means of dibromodifluoro-
methane and trisdiethyl aminophosphine. Addition of bromine to B gave
an intermediate C which could be converted into an intermediate D by
treatment with a phenol and K2CO3 owing to proceed both etherification
and dehydrobromination at the same time. The intermediate D was hydro-
genated under Pd=C cat. to give 2 in 22% isolated yield based on 4-(trans-
4-propylcyclohexyl)cyclohexanone.
This novel synthetic method is a useful and convenient introduction way
of a difluoromethylene moiety not only for commercial production of 2 but
also for a general synthetic technique.
NMR and GC-MS data of Compound 2b(n ¼ 1, X ¼ L1 ¼ F in general
formula 2)
1H-NMR: d(ppm) 0.858–0.887(m,5H), 0.991–1.054(m,7H), 1.131–
1.154(t,3H), 1.297–1.340(m,4H), 1.700–1.745(m,3H), 1.770–1.780(d,2H),
1.996–2.019(m,3H), 6.820–6.847(m,2H),
19F-NMR: d(ppm) -79.33- -79.34(d,2F), -133.76- -133.83(m,2F), -165.21-
-165.31(m,1F)
EIMS(m=e): 29(5.9%), 41(34.1), 55(60.7), 69(93.3), 83(100), 97(41.5),
111(68.7), 123(22.2), 131(14.1), 148(17.8), 213(5.9), 256(45.9),
404(14.8, Mþ)
PROPERTIES
The chemical structures and physical properties of 1a ꢂ 1c are listed in
Table 2. Further, 2D plot of De and rotational viscosity (c1) is shown in
Figure 1. For comparison, physical properties measured in same condition
of three compounds 3 ꢂ 5 [1b, 10] which have analogous structures to 1
are also shown. Where, physical properties of 5 is measured as a 20 wt%
mixture of three alkyl analogs of R in the formula (C2H5 : C3H7 : C5H11
¼
6 : 8 : 6) in FB-01 [1b]. From Figure 1, 1a ꢂ 1c are higher De and lower
viscosity compared with analogous compounds 3 and 4. In comparison
with the ester 5, 1a is almost the same De, on the contrary, extremely
low viscosity. It became obvious that 1a shows better balance of De–c1
than 3 ꢂ 5.

132=[1174]
S. Matsui et al.
TABLE 2 Structure and Physical Properties of Compounds 1a-1c
No.
Chemical structures
Transition Temp. (ꢁC) TNI(ꢁC) De
Dn c1(mPaꢃs)
1a
C 47.01
ꢀ16.4 22.3 0.125
63.3
1b
1c
C 40.91
C 38.71
1.1 16.8 0.135
77.8
14.6 19.3 0.135
108.8
FB-01 [1b]
112.6
4.8 0.080
171.3
Clearing points (TNI), dielectric anisotropy (De), birefringence (Dn), and rotational
viscosity (c1) are extrapolated data at 20ꢁC, 20 wt% of each compound in the liquid crystal
mixture FB-01 (Chisso Corp.).
FIGURE 1 Relation of rotational viscosity (c1) to dielectric anisotropy (De).

Synthesis and Properties of Novel Liquid Crystalline
133=[1175]
Moreover, in comparison with 4 having no fluorine atom at the linkage
group, significant difference was observed on balance of De–c1. It is usually
understood that the introduction of an oxygen atom or substitution of a flu-
orine atom at a side chain or a ring structure constructing molecular frame-
work causes increase of viscosity. However, viscosity of 1 indicates unusual
tendency to generally known liquid crystalline compounds. The study for
these unusual tendencies of some physical properties possessed by this ser-
ies are still under working, it would contribute to design and develop of
new liquid crystalline materials.
The quantum chemical calculation (MOPAC Ver.6 AM1) results of the
compound 1a, 1d and 2b are shown in Figure 2. For the reason of predomi-
nantly high De of 1a, the calculation resulted that 1a has large dipole mo-
ment (l) and comparatively small angle (b) between the l and a
molecular long axis (principal moment of inertia).
Structures and physical properties of 2a ꢂ 2d are listed in Table 3.
These compounds have high extrapolated De for Dn. Additionally, 2b and
2c have very wide nematic temperature range. To compare to 6 ꢂ 9[1b, 10],
their 2D plot of De–c1 and TNI–De are also shown in Figure 3. The De–c1 plot
shows that 2b has higher De than the other compound except the ester (8).
Concerning viscosity, 2b has almost the same as directly connected 6 and
lower than compounds with the other linkage groups. In the plot of TNI–
De, 2b shows good balance of properties compare to the other compounds
6 ꢂ 9.
Therefore, we conclude compound 2 is a practical material with good
balance of physical properties required to AM-LCDs, excel especially in
De–c1 balance. Here, to consider the fluorine introduction effect on the
linkage group, we paid notice to difference of physical properties between
FIGURE 2 Dipole moment l=DEBYE and angle between molecule long axis and
dipole moment b=DEG by MOPAC Ver.6 AM-1.

134=[1176]
S. Matsui et al.
TABLE 3 Structure and Physical Properties of Compounds 2a-2c
No.
Chemical structures
Transition temp. (ꢁC) TNI(ꢁC) De
Dn
c1(mPaꢃs)
ꢀ94.2
2a
C ꢀ 0.6 I
ꢀ63.9 7.8 0.035
2b
C 42.9 N 105.5 I
99.6 9.8 0.070
184.8
2c
2d
C 35.6 N 129.0 I
C 32.0 N 136.5 I
125.6 6.3 0.070
125.1 8.3 0.080
212.3
242.8
Clearing points (TNI), dielectric anisotropy (De), birefringence (Dn), and rotational
viscosity (c1) are extrapolated data at 20ꢁC, 20 wt% each compound in the liquid crystal
mixture FB-01 (Chisso Corp.).
FIGURE 3 Physical properties of compound 2b and relative compounds 6-9.

Synthesis and Properties of Novel Liquid Crystalline
135=[1177]
the compound with a methyleneoxy linkage group (7) and 2b. Figure 3 indi-
cates that introduction of two fluorine atoms into the methyleneoxy group
induced a rise of TNI, increase of De and decrease of viscosity.
One of the most important factor for the AM-LCDs materials is reli-
ability, i.e. voltage holding ratio (VHR) and specific resistance. Figure 4
shows VHR dependence on temperature of the mixtures comprising each
20wt% of 1a and 2b, and 80wt% of FB-01. The existing AM-LCDs materi-
als, 3, 6 and 8, are also shown for reference in the same figure.
The mixtures including 1a and 2b indicated the same level of VHR as
common AM-LCDs materials not only at ambient temperature but also at
high temperature. It is proven that a series of compound having difluoro-
methyleneoxy as a linkage group has very high reliability.
To develop low driving voltage LC mixture, we prepared some new LC
mixtures including compound 1 and 2. The threshold voltage-viscosity
correlation of prepared mixtures and common low driving voltage mixtures
are shown in Figure 5. The new LC mixture was able to reduce 20% of
viscosity from the referred common LC-mixture when both were compared
at same threshold voltage.
In order to lower viscosity, LC mixture is usually controlled their
viscosity by mixing a high De material which usually has relatively high
viscosity and low viscosity material without effective dipole moment
(neutral material)[11]. Since the compound 1 and 2 had both high De and
low viscosity, it became clear that these compounds are eminently suitable
for the component of mixture aiming quick response.
FIGURE 4 Voltage holding ratio(%) of compounds 1a, 2b and relative compounds
3, 6, and 8.

136=[1178]
S. Matsui et al.
FIGURE 5 Characteristic the new LC mixture comprise compound 1a and 2b
CONCLUSIONS
Novel liquid crystal compound 1 and 2 having a difluoromethyleneoxy
group as a linkage group have been prepared in good yield by the new syn-
thetic methods with reactions using dibromodifluoromethane as a key step.
From the result of physical properties measurement of 1 and 2, it becomes
obvious that 1 has high dielectric anisotropy and low viscosity, and 2 has
good balance of their physical properties in comparison with the com-
pounds having non or the other known linkage groups. Moreover, 1 and 2
indicate high voltage holding ratio owing to their high stability. Therefore,
this series is eminently suitable materials, which can achieve lower driving
voltage and quicker response time of AM-LCDs.
To consider the Fluorine introduction effect on linkage group, we
compared physical properties of the compound with a methyleneoxy and
a difluoromethyleneoxy linkage group. As a result, introduction of two
Fluorine atoms into the methyleneoxy group induces a rise of TNI, increase
of De and decrease of viscosity.
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