Novel liquid crystalline four ring chain difluoromethyleneoxy compounds for quicker response LC mixtures

Article abstract of DOI:10.1080/15421400903065200

A series of chemically stable novel liquid crystalline four ring chain compounds (1a-1c) having a difluoromethyleneoxy (CF₂O) linkage moiety have been designed and prepared, and their properties have been thoroughly investigated. The novel compounds intrinsically possess much higher positive Δε (>32) and Dn (>0.190), relatively low viscosity, wider nematic phase temperature ranges and significantly higher clearing temperatures in comparison to the analogous three ring chain CF₂O compound (2) that is currently applied in almost all the latest TN-TFT monitors, notebook PCs and IPS-TVs. Copyright Taylor & Francis Group, LLC.

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Novel Liquid Crystalline
Four Ring Chain
Difluoromethyleneoxy
Compounds for Quicker
Response LC Mixtures
Takashi Hiraoka a , Atsuko Fujita a , Yasuhiro Kubo a ,
Shuichi Matsui a & Kazutoshi Miyazawa a
a Chisso Petrochemical Corporation , Goi Research
Center , Ichihara, Japan
Published online: 05 Oct 2009.
To cite this article: Takashi Hiraoka , Atsuko Fujita , Yasuhiro Kubo , Shuichi
Matsui & Kazutoshi Miyazawa (2009) Novel Liquid Crystalline Four Ring
Chain Difluoromethyleneoxy Compounds for Quicker Response LC Mixtures,
Molecular Crystals and Liquid Crystals, 509:1, 89/[831]-95/[837], DOI:
10.1080/15421400903065200
To link to this article: http://dx.doi.org/10.1080/15421400903065200
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Mol. Cryst. Liq. Cryst., Vol. 509, pp. 89=[831]–95=[837], 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903065200
Novel Liquid Crystalline Four Ring Chain
Difluoromethyleneoxy Compounds for
Quicker Response LC Mixtures
Takashi Hiraoka, Atsuko Fujita, Yasuhiro Kubo,
Shuichi Matsui, and Kazutoshi Miyazawa
Chisso Petrochemical Corporation, Goi Research Center,
Ichihara, Japan
A series of chemically stable novel liquid crystalline four ring chain compounds
(1aꢀ1c) having a difluoromethyleneoxy (CF2O) linkage moiety have been designed
and prepared, and their properties have been thoroughly investigated. The novel
compounds intrinsically possess much higher positive De (>32) and Dn (>0.190),
relatively low viscosity, wider nematic phase temperature ranges and significantly
higher clearing temperatures in comparison to the analogous three ring chain
CF2O compound (2) that is currently applied in almost all the latest TN-TFT
monitors, notebook PCs and IPS-TVs.
Keywords: difluoromethyleneoxy; four ring chain; nematic mixtures
INTRODUCTON
The vastly expanding market and the leap of the LC display (LCD)
performance, continuously and endlessly require property improve-
ment of liquid crystalline materials. In particular, liquid crystalline
materials exhibiting much quicker response characteristics and better
performances in stability and reliability, that are directly proportional
to the LCD quality, have strongly been demanded. In order to fulfill
the requirements, the practically applied optimized nematic liquid
crystal mixtures are designed as a combination of polar compounds
The authors are indebted to Dr. M. Kondo for the XRD measurements.
Address correspondence to Takashi Hiraoka, Chisso Petrochemical Corporation, Goi
Research Center, 5-1 Goikaigan, Ichihara, Chiba 290-0058, Japan. E-mail: t.hiraoka@
chisso.co.jp
89=[831]

90=[832]
T. Hiraoka et al.
FIGURE 1 Chemical structures of compounds 1aꢀ1c and 2.
and lower viscous non-polar compounds. In particular, the character-
istics of the polar compounds relate to the response time and the driv-
ing voltage of the LCDs, therefore, it is important to develop novel
polar liquid crystal materials with better properties. We have designed
and prepared the three ring chain compound (2) with a CF2O linkage
moiety as a high performance polar liquid crystal compound [1]. The
compound shows high De and low rotational viscosity (c1) and there-
fore it can contribute to low voltage driving and quick response. How-
ever, the compound 2 has no nematic phase and exhibits the low
melting temperature (49.1ꢁC), which results the significant decrease
of the clearing point (TNI) when doped in the lower viscous non-polar
compounds. To overcome these difficulties, we have designed and
synthesized the novel CF2O compounds containing the four ring chain
structure (1aꢀ1c) [Fig. 1].
EXPERIMENTAL SECTION
Materials
The compounds 1aꢀ1c, were synthesized according to the synthetic
scheme shown in Scheme 1. The compounds (3) (R ¼ nC3H7, nC4H9,
SCHEME 1 Synthetic scheme of compounds 1aꢀ1c.

Four Ring Chain Difluoromethyleneoxy Compounds
91/[833]
nC5H11) were prepared by Suzuki cross-coupling reaction of 3,5-
difluorophenylboronic acid and the corresponding 4-(4-alklylphenyl)-
2-fluorophenyl iodides according to the literature [2]. The compounds
n
3 were treated with BuLi in tetrahydrofurane at ꢀ70ꢁC, followed
with CBr2F2 to give the difluoromethylbromides (4). The etherification
of the compounds 4 with 3,4,5-trifluorophenol in a basic condition
(K2CO3 in H2O at 100ꢁC) resulted in the desired compounds 1aꢀ1c.
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 DSC 7 differential scanning
calorimetry and Nikon Optiphot polarizing microscopy with a Mettler
Toledo FP82HT hot stage. X-ray diffraction (XRD): Bruker D8 Dis-
˚
cover diffractometer with a CuKa source (Cu-Ka, k ¼ 1.54 A). Quantum
chemical calculation was carried out by MOPAC AM-1 method [3].
Dielectric anisotropy (De) at 25ꢁC: Hewlett Packard 4284A LCR meter.
Optical anisotropy (Dn) at 25ꢁC: Atago 4 T and 2 T Abbe refract-
ometers. Rotational viscosity (c1) at 25ꢁC: TOYO Corporation
TCM-1. Response time (RT) at 25ꢁC: Otsuka Electronics LCD-
5100WT. Voltage holding ratio and specific resistivity were measured
according to the literature [4].
Mesomorphism
The phase transition temperatures of the synthesized compounds
1aꢀ1c obtained by the DSC measurements with 3ꢁC=min of the heat
rate are summarized in Table 1 with those of the compound 2
as references. Surprisingly, inserting one benzene ring into the
TABLE 1 Phase Sequences and Transition Temperatures
Compound
Transition temperature [ꢁC]
1a
1b
1ca
2
Cr 86.8 N 128.7 Iso
Cr 78.1 (SmA 59.3) N 118.4 Iso
Cr 64.1 (SmA 65.1) N 122.9 Iso
Cr 49.1 Iso
aFound to have at least two crystal structures. The melting point
in the second heating was 10ꢁC lower than that in the first heating.

92/[834]
T. Hiraoka et al.
molecular structure of the compound 2 induces the significant increase
of the liquid crystalline potential. The compounds 1aꢀ1c exhibit the
wide nematic temperature ranges with the high nematic-isotorpic
liquid transition temperatures of greater than 118.4ꢁC, most probably
due to their larger molecular length and width ratio (L=D ratio). The
L=D ratios of the compounds 1aꢀ1c and 2 have been estimated with
the semi-empirical molecular orbital calculation applying MOPAC
AM-1 method and are listed in Table 2. All the four compounds 1aꢀ
1c and 2 possess their widths of the molecular rods in the range of
˚
8.67ꢀ9.76 A, while the molecular lengths are widely distributed as
˚
˚
25.9ꢀ28.2 A for the compounds 1aꢀ1c and 21.6 A for the compound
2, resulting in the significant difference in the L=D ratios of the four-
and the three-ring chain compounds.
As shown in Table 1, the compounds 1b and 1c possessing the
longer alkyl chains i.e., butyl and pentyl have the higher ordered
mesophase smectic A incorporating nematic phase. XRD study of the
compound 1c has been performed and the results are displayed in
Figure 2A. The X-ray diffractogram of the compound 1c at 62ꢁC exhi-
biting SmA shows the sharp reflection in the small angle region that
˚
corresponds to the layer space of d (spacing)-value 26.6 A. There is a
˚
reasonable fit of the layer space value (26.6 A) obtained with the
˚
XRD measurement and 28.2 A that has been estimated by the MOPAC
calculation as the molecular length of the compound 1c. The weak and
broad hollow peak, which is typically observed in XRD of nematic
phase [5], was found in the X-ray diffractogram of compound 1c
measured at 70ꢁC.
The compound 1c was found to have at least two different crystal
structures. The melting point during the 2nd heating process was
lower than that in the 1st heating process for 10ꢁC. As shown in
Figure 2B, two diffraction patterns of the virgin crystal and the crystal
obtained through the crystallization after the melt are quite different
in the small angle and the 15ꢀ20 degree regions. More detailed discus-
sions will be reported separately in elsewhere.
TABLE 2 Results of Molecular Orbital Calculations
˚
˚
Length (L) [A]
Width (D) [A]
L=D
1a
1b
1c
2
25.9
27.2
28.2
21.6
8.67
8.80
9.76
9.70
2.98
3.09
2.89
2.23

Four Ring Chain Difluoromethyleneoxy Compounds
93/[835]
FIGURE 2 X-ray diffractograms of compound 1c obtained in A. (a) SmA
(62ꢁC) and (b) nematic phase (70ꢁC); B. (a) before melting, and (b) crystallized
after melting.
Physical Properties
Physical properties of the compounds 1aꢀ1c, namely TNI, De, Dn, and
c1, that have been estimated as extrapolated values from mixtures of
the compounds 1aꢀ1c (15%) and 85% of a polar base nematic mixture
(TNI: 72.4ꢁC, De: 11.0, Dn: 0.137, c1: 166.0 mPa ꢂ S) comprising of liquid
crystalline benzonitrile derivatives, are summarized in Table 3 with
those of the compound 2 as references. As clearly displayed in
Table 3, the compounds 1aꢀ1c exhibit the significantly high TNI that
are approximately 90ꢁCꢀ100ꢁC higher in comparison to that of the
compound 2. As well as the TNI, the extrapolated De and Dn of the com-
pounds 1aꢀ1c are significantly larger than those of the reference, due
to the extended p-electron conjugation incorporating the additional
fluorine substituents on the benzene rings. The highly conjugated
molecular structures of the compounds 1aꢀ1c induce the 20ꢀ25%
greater De and the Dn of two fold magnitude. The reasonable increase
in the c1 has been observed in the compounds 1aꢀ1c.
It has also been found that the compounds 1aꢀ1c are reasonably
highly stable against UV irradiation and high temperature. As shown
TABLE 3 Extrapolated Physical Properties
Compound
TNI [ꢁC]
De
Dn
c1 [mPa ꢂ S]
1a
1b
1c
2
96.4
89.7
96.4
ꢀ3.6
34.0
32.7
32.1
27.7
0.210
0.190
0.197
0.110
378.1
374.2
411.6
95.6

94/[836]
T. Hiraoka et al.
in Figure 3, the voltage holding ratio (V.H.R.) and the specific
resistivity (q) of the compounds 1aꢀ1c after 2 hours storage at
120ꢁC and UV irradiation (3,000 mJ=cm2) have been estimated and
found to be in the same level as or even better than those of the
compound 2 that is already and widely applied for AM-LCDs.
Representative Nematic Mixtures for Application
Quicker response liquid crystal mixtures that are in demand for
AM-LCDs, can essentially be achieved by lowering c1 of the mixtures.
In the mixture design principle, lowering c1 is the most effective
approach for increasing the contents of the lower viscous non-polar
compounds in the liquid crystal mixtures. Accordingly, the replace-
ment of the compound 2 by the compounds 1aꢀ1c allows increase of
the non-polar compounds contents in the mixtures, which enables c1
of the mixtures reduced without depressing other properties, namely
decreasing the TNI or increasing the crystallizing temperature. Two
representative mixtures Composition 1 and Composition 2 containing
the compounds 1b and 2, respectively, are listed in Table 4. Substituting
the polar component in the mixture from compound 2 (Composition 2) to
compound 1b (Composition 1), that allows the increase of the non-polar
low viscous compounds, resulted in the significant reduction in the
response time of 15% with sustaining other properties, namely TNI
,
De, and Dn. The nematic phase of both mixtures prepared are stable
even at a low temperature (ꢀ20ꢁC) and can be sustained for a long per-
iod (>10 days) without spontaneous crystallization.
FIGURE 3 V.H.R. and specific resistivity of compounds 1aꢀ1c and 2; (a)
V.H.R. (30 Hz, 25ꢁC) of compounds 1aꢀ1c, and 2; (b) Specific resistivity
(25ꢁC) of compounds 1aꢀ1c, and 2.

Four Ring Chain Difluoromethyleneoxy Compounds
95/[837]
TABLE 4 Properties of Representative Liquid Crystal Mixtures
Mixture
TNI [ꢁC]
De
Dn
RT [m sec]
COMPOSITION 1
COMPOSITION 2
74.4
74.4
8.9
8.9
0.100
0.100
8.42
9.92
CONCLUSIONS
A series of chemically stable novel liquid crystalline four ring chain
compounds having a CF2O moiety have been synthesized. The novel
compounds possess much higher De and Dn, and additionally the wider
nematic phase temperature ranges in comparison to the three ring
chain CF2O compound. The addition of the novel compounds in the
liquid crystal mixtures allows the increase in the content of the lower
viscous non-polar compounds. As the result of this approach, the
significant response time reduction of the liquid crystal mixtures
has been realized.
REFERENCES
[1] (a) Matsui, S., Kondo, T., & Sago, K. (2004). Mol. Cryst. Liq. Cryst., 411, 1169;
(b) Pauluth, D. & Tarumi, K. (2004). J. Mater. Chem., 4, 1219.
[2] Kondo, T., Kobayashi, K., Matsui, S., & Takeuchi, H. US patent 6231785.
[3] (a) Fujitsu Limited, MOPAC Ver.6=PM3, QCPE#455; (b) Dewar, M. J. S., Zoebisch,
E. G., Healy, E. F., & Stewart, J. J. P. (1985). J. Am. Chem. Soc., 107, 3902.
[4] Okamoto, M. & Ichinose, H. (2002). EKISHO, 6, 390.
[5] Takanishi, Y. (2002). EKISHO, 6, 51.