Novel T-shaped chiral oligomers with a wide temperature range of a blue phase

Article abstract of DOI:10.1080/15421400701679939

The crystal structure of (S)-1-methylheptyl-4'-{4-octyloxy-2-{11-[4-(5- hexylpyrimidin-2-yl)phenoxy]undecanoyloxy}benzoyloxy}biphenyl-4-carboxylate, which has a relatively wide temperature range of blue phase III on cooling, has been determined. The molec

Full text of DOI:10.1080/15421400701679939

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Novel T-shaped Chiral
Oligomers with a Wide
Temperature Range of a Blue
Phase
Masatada Sato a , Atsushi Yoshizawa a & Fumitaka
Ogasawara b
a Department of Frontier Materials Chemistry,
Faculty of Science and Technology , Hirosaki
University , Hirosaki, Japan
b Tohoku Chemical Corporation , Hirosaki, Japan
Published online: 22 Sep 2010.
To cite this article: Masatada Sato , Atsushi Yoshizawa & Fumitaka Ogasawara
(2007) Novel T-shaped Chiral Oligomers with a Wide Temperature Range of
a Blue Phase, Molecular Crystals and Liquid Crystals, 475:1, 99-112, DOI:
10.1080/15421400701679939
To link to this article: http://dx.doi.org/10.1080/15421400701679939
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Mol. Cryst. Liq. Cryst., Vol. 475, pp. 99–112, 2007
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400701679939
Novel T-shaped Chiral Oligomers with a Wide
Temperature Range of a Blue Phase
Masatada Sato
Atsushi Yoshizawa
Department of Frontier Materials Chemistry, Faculty of Science and
Technology, Hirosaki University, Hirosaki, Japan
Fumitaka Ogasawara
Tohoku Chemical Corporation, Hirosaki, Japan
The crystal structure of (S)-1-methylheptyl-40-{4-octyloxy-2-{11-[4-(5-hexylpyri-
midin-2-yl)phenoxy]undecanoyloxy}benzoyloxy}biphenyl-4-carboxylate, which has a
relatively wide temperature range of blue phase III on cooling, has been determ-
ined. The molecule was found to form a k-shaped structure. We have prepared a
homologous series of the chiral oligomers and investigated effects of structure on
appearance of the blue phase. All compounds were found to show a phase sequence
of Iso-BP-Nꢀ-glass on cooling. The structure-property correlations reveal that
(1) chirality does not affect on the Iso-BP transition temperature, (2) increasing
chirality destabilizes the Nꢀ phase, and (3) the longer spacer lowers the BP-Nꢀ
transition temperature.
Keywords: blue phase; chirality; liquid crystal; molecular biaxiality
1. INTRODUCTION
Investigation of chirality in liquid crystals is one of the most exciting
areas of liquid crystal science. Frustrated phases induced by chirality
are the most interesting phenomena above all. Blue phase (BP), twist
grain boundary (TGB) phase and smectic Q (SmQ) phase have been
observed and structure-property correlations investigated [1]. Blue
This work was partially supported by Aomori Prefecture Collaboration of Regional
Entities for the Advancement of Technological Excellence, JST and a Grant for priority
Research Designated by the President of Hirosaki University.
Address correspondence to Atsushi Yoshizawa, Department of Frontier Materials
Chemistry, Faculty of Science and Technology, Hirosaki University, 3, Bunkyo-Cho,
Hirosaki 036-8561, Japan. E-mail: ayoshiza@cc.hirosaki-u.ac.jp
99

100
M. Sato et al.
phases are of particular interest because they have a fluid lattice
whose structure is stabilized by lattice defects. Appearance of
blue phases results from the competition between the chiral twisting
force and the desire for molecules to pack in ways such that they fill
space uniformly. Blue phases are believed to consist of double twist
cylinder, so are classified into 3 categories depending on packing struc-
ture of double twist cylinder, i.e., blue phase I (BPI), blue phase II
(BPII) and blue phase III (BPIII). The packing structure of BPI is
bodyꢁcentered cubic structure, and BPII is simple cubic structure.
On the other hand, theoretical insights have revealed that BPIII and
the isotropic phase have the same symmetry. It can be expected that
BPIII consists of double twist cylinders with arbitrary orientation [2].
Usually, blue phases are found in a very narrow temperature
range (ꢂ1K) between the isotropic liquid and the chiral nematic (Nꢀ)
phase of sufficiently short pitch, except in a few cases where a SmA
to BPI transition has been observed [3–5]. Recently, smectic blue
phases (SmBPs) have been observed between the isotropic and smectic
phases [6,7]. Yamamoto et al. reported novel smectic blue phase
‘SmBPIso’ in the binary mixture system [8]. Blue phases have the
potential of applications as fast light modulators or tunable photonic
crystals, but their narrow temperature range is a critical problem.
Kikuchi et al. reported polymer-stabilized blue phases in which the
temperature range is extended to more than 60 K and they demon-
strated fast electro-optical switching for the stabilized blue phase [9].
Coles et al. reported that eutectic mixtures of three homologues of
symmetric dimer doped with a small percentage of a highly twisting
chiral additive shows the BPI of a very wide temperature range, and
the BPI shows wide color range of reflected color in applied electric
fields [10]. On the other hand, many kinds of liquid – crystalline mate-
rials possessing a center of chirality have been investigated. A single
chiral compound with a wide temperature range of a blue phase has
never been obtained. Theoretical work suggests that biaxiality plays
an important role in the blue phases [11]. However, the biaxiality in
most chiral nematic liquid crystals is slight, thus the double twist
structure can not exist in a wide temperature range. We reported a
U-shaped molecule that induces a smectic-like layer ordering in the
nematic phase and noted possibility that the nematic (N) phase has
biaxiality [12]. We designed coupling between axial chirality and the
U-shaped system [13–15]. The designed binaphthyl derivatives were
found to show an unusual phase sequence of Iso-BP-SmA (Fig. 1(a)).
Recently we reported a novel T-shaped chiral oligomer possessing mol-
ecular biaxiality exhibiting a blue phase with a wide temperature
range on cooling (Fig. 1(b)) [16]. We have prepared a homologous series

Novel T-shaped Chiral Oligomers with a Blue Phase
101
FIGURE 1 Molecular structures of (a) binaphthyl derivatives (R)-n and
(b) T-shaped chiral oligomer T-1.
of the T-shaped chiral oligomers and investigated the structure-
property relations. In the present study, we report a crystal structure
of the T-shaped compound and effects of molecular structure on
appearance of a blue phase of the T-shaped compounds.
2. EXPERIMENTAL
Characterization of Materials
The purification of final products was carried out using column
chromatography over silica gel (63–210 mm) (KANTO CHEMICAL
Co., INC.) using a toluene-ethyl acetate mixture as the eluent, followed
by the recrystallization from ethanol. The purity was checked by thin
layer chromatography (TLC, aluminum sheets, silica gel 60 F254 from
Merck) using a toluene-ethyl acetate mixture as the eluent. Detection
of products was achieved by UV irradiation (k ¼ 254 and 365 nm).
The structures of the products were elucidated by infrared (IR)
spectroscopy (BIO RAD FTS-30) and proton nuclear magnetic reson-
ance (1H-NMR) spectroscopy (JEOL JNM-A400). The analyses of the
structures of the products by spectroscopic methods were found to be
consistent with the predicted structures.
Preparation of Materials
The T-shaped chiral oligomers (T-1(m, n), T-2(10, 6)) were prepared
by the synthesis outlined in Scheme 1. (R)-2-Octanol was obtained

102
M. Sato et al.
SCHEME 1 The preparative route for the homologous series of the T-shaped
chiral oligomers T-1(m, n) [(m, n) ¼ (9, 8), (5, 8), (10, 6)], T-2(10, 6): (i) NaOH,
H2O, then HCl, (ii) DEAD, (C6H5)3P, THF, (iii) NH3(aq), ethanol, (iv) KOH,
EtOH-H2O, and (v) DCC, DMAP, CH2Cl2, and (vi) DCC, DMAP, CH2Cl2.
from Tokyo Kasei Kogyo Co., Ltd, and (S)-2-octanol was obtained from
Aldrich. 5-Octyl-2-(4-hydroxyphenyl)pyrimidine was obtained from
Midori Kagaku Co., Ltd.
(S)-1-Methylheptyl-40-{4-octyloxy-2-{10-[4-(5-octylpyrimidin-
2-yl)phenoxy]decanoyloxy}benzoyloxy}biphenyl-4-
carboxylate, T-1(9, 8)
To a solution of sodium hydroxide (2.8 g, 70 mmol) in water (100 ml),
which had been cooled to 0ꢀC, 4-hydroxybiphenyl-40-carboxylic
acid (5.0 g, 23 mmol) was added. The reaction mixture was stirred

Novel T-shaped Chiral Oligomers with a Blue Phase
103
vigorously and methyl chloroformate (3.9 g, 45 mmol) was added
slowly to the resulting suspension. The reaction mixture was stirred
at 0ꢃC for 5h and then brought to pH 2 by the addition of aq. HCl.
The voluminous white precipitate produced was filtered off and recrys-
tallized from acetic acid (400 ml). 4-Methoxycarbonyloxybiphenyl-40-
carboxylic acid was obtained. Yield: 5.8g (92%).
To a solution of 4-methoxycarbonyloxybiphenyl-40-carboxylic acid
(2.5 g, 9.2mmol) and diethylazodicarboxylate (1.6 g, 9.2mmol) in tetra-
hydrofuran (THF, 120 ml) was added triphenylphosphine (2.6 g,
10 mmol) in THF (40 ml). The reaction mixture was stirred at room
temperature for 24h. After the filtration of participate, the solvent
was removed by evaporation. The residue was purified by column
chromatography on silica gel with dichloromethane. (S)-1-methyl-
heptyl-4-methoxycarbonyloxybiphenyl-40-carboxylate was obtained.
Yield: 2.3g (65%).
To a solution of (S)-1-methylheptyl 4-methoxycarbonyloxybiphenyl-
40-carboxylate (2.2 g, 5.8 mmol) in ethanol (95ml) was added an
aqueous ammonia solution (28ꢂ30%, 14 ml). The reaction mixture
was stirred at room temperature for 24 h. The solvent was removed
by evaporation. To the residue was added water and the solution
was extracted with diethylether (100 ml). The combined organic layers
were dried over anhydrous sodium sulfate. After the drying agent and
the solvent were removed, (S)-1-Methylheptyl-4-hydroxybiphenyl-40-
carboxylatewas obtained without further purification. Yield: 1.6g
(85%).
To a solution of 2,4-dihydroxybenzoic acid (7.7 g, 50 mmol) and
1-bromooctane (9.0 g, 47 mmol) in ethanol (70 ml) was added a solution
of KOH (10.3 g, 1.85 mol) in water (40ml). The mixture was stirred
under reflux for 10 h. After the solvent was removed, the residue was
acidified with aq. HCl. The solution was extracted with diethylether
(3 ꢄ 50ml). The organic layers were combined, dried over anhydrous
magnesium sulfate, filtered and evaporated. The intermediate product,
2-hydroxy-4-octyloxybenzoic acid, was obtained. Yield: 1.3 g (10%).
To a solution of 2-hydroxy-4-octyloxybenzoic acid (1.0 g, 3.8mmol)
in dichloromethane (30ml), (S)-1-methylheptyl-4-hydroxybiphenyl-
40-carboxylate (1.0 g, 3.1mmol), dicyclohexylcarbodiimide (0.78 g,
3.8 mmol), and 4-(N, N-dimethylamino)pyridine (0.047 g, 0.38mmol)
were added. The resulting solution was stirred at room temperature
for 30h. Precipitated materials were removed by filtration. After removal
of the solvent by evaporation, the residue was purified by column chroma-
tography on silica gel with toluene as the eluent. (S)-1-Methylheptyl-40-
(2-hydroxy-4-octyloxybenzoyloxy)biphenyl-4-carboxylate was obtained.
Yield: 1.02g (47 %).

104
M. Sato et al.
5-Octyl-2-(4-hydroxyphenyl)pyrimidine (0.57 g, 2.0mmol) was
added in a mixture of ethanol (20ml) and sodium hydroxide (0.26 g,
6.6mmol) in water (20ml). The mixture was heated and stirred while
10-bromodecanoic acid (0.50 g, 2.0 mmol) was added slowly. The reac-
tion mixture was heated under reflux for 7h. The solvent was removed
by evaporation and then the solution was acidified with aq. HCl. The
solution was extracted with dichloromethane (3 ꢄ 50 ml). The organic
layers were combined, dried over anhydrous magnesium sulfate. After
the drying agent and the solvent were removed, the desired product
was recrystallized from acetic acid (10ml). 10-[4-(5-Octylpyrimidin-
2-yl)phenoxy]decanoic acid was obtained. Yield: 0.23 g (25%).
To a solution of 10-[4-(5-octylpyrimidin-2-yl)phenoxy]decanoic acid
(0.18 g, 0.4mmol) in dichloromethane (10 ml), (S)-1-methylheptyl-40-
(2-hydroxy-4-octyloxybenzoyloxy)biphenyl-4-carboxylate (0.18g, 0.4mmol),
dicyclohexylcarbodiimide (0.083 g, 0.4 mmol), and 4-(N,N-dimethyl-
amino)pyridine (0.005 g, 0.04 mmol) were added. The resulting
solution was stirred at room temperature for 17 h. Precipitated
materials were removed by filtration. After removal of the solvent by
evaporation, the residue was purified by column chromatography on
silica gel with a toluene-ethylacetate (15:1) mixture as the eluent.
Recrystallization from ethanol gave the desired product. Yield: 0.17g
(56%).
1H NMR (400 MHz, solvent CDCl3, standard TMS) dH=ppm: 8.59(s,
2H, ArꢁH), 8.36(d, 2H, ArꢁH, J ¼ 9.3Hz), 8.21(d, 1H, ArꢁH, J ¼
8.8Hz), 8.13(d, 2H, ArꢁH, J ¼ 8.3 Hz), 7.67(d, 2H, ArꢁH, J ¼ 8.8Hz),
7.66(d, 2H, ArꢁH, J ¼ 8.3Hz), 7.27(d, 2H, ArꢁH, J ¼ 8.6Hz), 6.99(d,
2H, ArꢁH, J ¼ 8.8Hz), 6.89(dd, 1H, ArꢁH, J ¼ 8.8Hz, 2.4Hz),
6.67(d, 1H, ArꢁH, J ¼ 2.4Hz), 5.23–5.16(m, 1H, ꢁCꢀH(CH3)),
4.05(t, 2H, ꢁOCH2, J ¼ 7.1Hz), 4.02(t, 2H, ꢁOCH2, J ¼ 6.6Hz),
2.64-2.60(m, 2H, ArꢁCH2ꢁ, 2H, ꢁOCOCH2ꢁ), 1.87–1.31(m, 51H,
aliphaticꢁH), 0.93–0.88(m, 9H, ꢁCH3); IR (KBr) nmax=cmꢁ1: 2927,
2856, 1728, 1613, 1428, 1257, 1135.
The other compounds presented in this paper were obtained by a
similar method to that for T-1(9, 8). Analytical data for the other
compounds are given.
(S)-1-Methylheptyl-40-{4-octyloxy-2-{6-[4-(5-octylpyrimidin-
2-yl)phenoxy]hexanoyloxy}benzoyloxy}biphenyl-4-carboxylate,
T-1(5, 8)
1H NMR (400 MHz, solvent CDCl3, standard TMS) dH=ppm: 8.59(s,
2H, ArꢁH), 8.35(d, 2H, ArꢁH, J ¼ 9.3Hz), 8.21(d, 1H, ArꢁH,
J ¼ 8.8 Hz), 8.12(d, 2H, ArꢁH, J ¼ 8.3Hz), 7.66(d, 2H, ArꢁH,

Novel T-shaped Chiral Oligomers with a Blue Phase
105
J ¼ 8.3Hz), 7.65(d, 2H, ArꢁH, J ¼ 8.3 Hz), 7.27(d, 2H, ArꢁH,
J ¼ 8.6Hz), 6.97(d, 2H, ArꢁH, J ¼ 8.8Hz), 6.90(dd, 1H, ArꢁH,
J ¼ 8.0Hz, 2.7 Hz), 6.68(d, 1H, ArꢁH, J ¼ 2.4Hz), 5.24–5.16(m, 1H,
ꢁCꢀH(CH3)), 4.05( m, 2H, ꢁOCH2, J ¼ 5.9Hz), 4.02( m, 2H, ꢁOCH2,
J ¼ 6.6Hz), 2.64–2.60(m, 2H, ArꢁCH2ꢁ, 2H, ꢁOCOCH2ꢁ), 1.87–
1.31(m, 43H, aliphaticꢁH), 0.94–0.89(m, 9H, ꢁCH3); IR (KBr)
n max=cmꢁ1: 2928, 2857, 1716, 1611, 1430, 1273, 1126.
(S)-1-Methylheptyl-40-{4-octyloxy-2-{11-[4-(5-hexylpyrimidin-
2-yl)phenoxy]undecanoyloxy}benzoyloxy}biphenyl-4-
carboxylate, T-1(10, 6)
1H NMR (400MHz, solvent CDCl3, standard TMS) dH=ppm: 8.59(s,
2H, ArꢁH), 8.36(d, 2H, ArꢁH, J ¼ 9.3Hz), 8.21(d, 1H, ArꢁH,
J ¼ 9.3Hz), 8.13(d, 2H, ArꢁH, J ¼ 8.3Hz), 7.67(d, 2H, ArꢁH,
J ¼ 8.8Hz), 7.66(d, 2H, ArꢁH, J ¼ 8.8 Hz), 7.28(d, 2H, ArꢁH,
J ¼ 8.6Hz), 6.99(d, 2H, ArꢁH, J ¼ 8.8Hz), 6.89(dd, 1H, ArꢁH,
J ¼ 8.8Hz, 2.5 Hz), 6.67(d, 1H, ArꢁH, J ¼ 2.4Hz), 5.23–5.16(m, 1H,
ꢁCꢀH(CH3)), 4.05(t, 2H, ꢁOCH2, J ¼ 5.9Hz), 4.02(t, 2H, ꢁOCH2,
J ¼ 6.4Hz), 2.62 (t, 2H, ArꢁCH2ꢁ, 2H, ꢁOCOCH2ꢁ, J ¼ 7.6 Hz),
1.87–1.31(m, 49H, aliphaticꢁH), 0.94–0.88(m, 9H, ꢁCH3); IR (KBr)
n max=cmꢁ1: 2926, 2854, 1734, 1613, 1428, 1260, 1131.
(S)-1-Methylheptyl-40-{4-octyloxy-2-{11-[4-(2-(2-fluoro-
4-hexyloxyphenyl)pyrimidin-5-yl)phenoxy]undecanoyloxy}-
benzoyloxy}biphenyl-4-carboxylate, T-2(10, 6)
1H NMR (400MHz, solvent CDCl3, standard TMS) dH=ppm: 9.01(s,
2H, ArꢁH), 8.21(d, 1H, ArꢁH, J ¼ 8.8 Hz), 8.15–8.10(m, 3H, ArꢁH),
7.67(d, 2H, ArꢁH, J ¼ 8.8 Hz), 7.66(d, 2H, ArꢁH, J ¼ 7.8Hz), 7.27(d,
2H, ArꢁH, J ¼ 8.6Hz), 7.05(d, 2H, ArꢁH, J ¼ 8.8Hz), 6.90(dd, 1H,
ArꢁH, J ¼ 8.8Hz, 2.4Hz), 6.84(dd, 1H, ArꢁH, J ¼ 8.8 Hz, 2.4 Hz),
6.76(dd, 1H, ArꢁH, J ¼ 12.8Hz, 2.2 Hz), 6.67(d, 1H, ArꢁH,
J ¼ 2.4Hz), 5.23–5.16(m, 1H, ꢁCꢀH(CH3)), 4.07–4.00(m, 6H, ꢁOCH2),
(t, 2H, ꢁOCOCH2ꢁ, J ¼ 7.6Hz), 1.87–1.27(m, 47H, aliphaticꢁH),
0.96–0.88(m, 9H, ꢁCH3); IR (KBr) n max=cmꢁ1: 2924, 2854, 1737,
1613, 1438, 1246, 1134.
Liquid-Crystalline and Physical Properties
The initial assignments and corresponding transition temperatures
for the final products were determined by thermal optical microscopy
using a Nikon Optiphoto POL polarizing microscope equipped with a

106
M. Sato et al.
Mettler FP82 microfurnace and FP80 control unit. The heating
and cooling rates were 5ꢃC minꢁ1. Temperatures and enthalpies of
transition were investigated by differential scanning calorimetry
(DSC) using a Seiko DSC 6200 calorimeter. The material was studied
at a scanning rate of 5ꢃC minꢁ1, for both heating and cooling cycles,
after being encapsulated in aluminum pans. The helical pitch in the
Nꢀ phase was measured by the Cano wedge method for a chiral
nematic mixture consisting of nematic liquid-crystalline material,
4-hexyl-40-cyanobiphenyl (6CB) (purchased from BDH) and each
chiral additive. The helical pitch in the SmCꢀ phase was measured
by observing a length between the dechirallization lines corresponding
to a full pitch band for a mixture consisting of 5-octyloxy-2-(4-hexylox-
yphenyl)pyrimidine (8-PYP-6O) and each chiral additive. The helical
pitches were measured at room temperature. The mixtures were
studied using the contact method and their chiral helical twist senses
were established. The definition of the helical twist senses used in this
article is the same as that of Goodby [17].
Crystal Structure
A single crystal of T-1(10, 6) was obtained by slow evaporation
methods of an ethanol=n-hexane (1:1) solution. This crystal was
mounted on a glass fiber. All measurements were made on a Rigaku
RAXIS RAPID imaging plate area detector with graphite mono-
chromated Mo-Ka radiation at room temperature. The structure was
solved by applying programs SAPI90 [18] and refined using DIRDIF99
[19].
Crystal data for T-1(10, 6): C63H84O8N2, M ¼ 997.37 g molꢁ1, color-
less platelet, 0.50 ꢄ 0.45 ꢄ 0.07mm, triclinic, space group Pꢀ, a ¼
i
˚
˚
˚
10.699(7)A, b ¼ 15.597(8)A, c ¼ 18.28(1)A, a ¼ 86.42(4); b ¼ 84.22(5);
c ¼ 81.78(5); V ¼ 3000.4(3)A, Z ¼ 2, Dcalc ¼ 1.104 g cmꢁ3, F000 ¼
˚
1080.00, l(MoKa ) ¼ 0.72cmꢁ1, 2hmax ¼ 46.5; 19370 reflections
measured, 8549 unique (Rint ¼ 0.038), GoF ¼ 3.64, R[I > 3.00r
(I)] ¼ 0.182, Rw[I > 3.00r (I)] ¼ 0.173.
3. RESULTS AND DISCUSSION
3.1. Crystal Structure
Figure 2 shows molecular structure of T-1(10, 6) exhibiting blue phase
and Nꢀ phase (see Table 1). The final R-value is relatively high (0.182)
due to disorder. The terminal alkyl chains were not determined. The
compound was found to have a k-shaped structure instead of T-shaped.

Novel T-shaped Chiral Oligomers with a Blue Phase
107
FIGURE 2Molecular structure of T-1(10, 6v)iewed along the a axis.
Gauche configurations exist in the central spacer. Owing to MM2
calculations, the k-shaped structure is more stable than the T-shaped
and the energy difference between them is estimated to be
31 kJ molꢁ1. Figure 3 shows crystal structure of T-1(10, 6). The
molecules are almost antiparallel to each other, giving a smectic-like
layer structure in which the molecules are tilted to the layer normal.
3.2. Liquid-Crystalline Properties and Pitch Measurements
Molecular structures of T-shaped chiral oligomer T-1(m, n) and
T-2(10, 6) are shown in Figure 4. Temperatures and enthalpies of
the transition for the homologous series of T-shaped chiral oligomers
T-1(m, n) and T-2(10, 6) determined by optical microscopy and
differential scanning calorimetry (DSC) are listed in Table 1.
FIGURE 3Crystal structure of T-1(10, 6)viewed along the a axis.

108
M. Sato et al.
FIGURE 4 Molecular structures of T-shaped chiral oligomers T-1(m, n) and
T-2(10, 6).
All T-shaped chiral oligomers were found to show a phase sequence
of Iso-BP-Nꢀ-glass on cooling. All the liquid crystal phases of these
mesogens are monotropic. The texture of the blue phase is blue fog
texture without any platelet texture, indicating that the blue phase
is BPIII. The spacer length (m) and terminal chain length (n) slightly
affected on stability of the blue phase. As the spacer length (m) was
shorter, the temperature range of the blue phase was narrower. Inter-
esting odd-even effect was observed for appearance of a blue phase of
some chiral dimeric liquid crystals [20]. However, the present chiral
TABLE 1 Transition Temperatures (ꢃC) on Cooling and Enthalpies (kJmolꢁ1
of Transition (in Brackets) for T-1(m, n) and T-2(10, 6)
)
b
glassa
Nꢀ
BP
I
mpa
T-1(10, 8)
T-1(9, 8)
T-1(5, 8)
T-1(10, 6)
T-2(10, 6)
. ꢁ 25
. ꢁ 23
. ꢁ 19
. ꢁ 22
. ꢁ 16
.15
.19
.28
.14
.72
.28 (1.4)
.28 (1.2)
.32 (0.6)
.25 (1.4)
.77 (0.7)
.
.
.
.
.
63 (66)
45 (48)
68 (53)
40 (47)
80 (45)
aThe melting points and glass transition temperatures were measured by DSC.
bEnthalpies of the BP to Nꢀ transition were too small to be detected.

Novel T-shaped Chiral Oligomers with a Blue Phase
109
TABLE 2 Helical Pitch (mm) in the Nꢀ and SmCꢀ Phases for a Mixture
Consisting of 2 wt% of each Chiral Compound and the Helical Twist Senses
(in Brackets), i.e., Right-hand (RH) or Left-hand (LH)a
Compound
SmCꢀ
Nꢀ
T-1(10, 8)
T-1(9, 8)
T-1(5, 8)
T-1(10, 6)
T-2(10, 6)
20 (RH)
18 (RH)
54 (RH)
22 (RH)
23 (RH)
7.0 (RH)
8.5 (RH)
7.0 (RH)
7.0 (RH)
10 (RH)
aHelical pitch (mm) in the Nꢀ phase for a chiral nematic mixture of 6CB and 2 wt% of
each chiral compound and that in the SmCꢀ phase for a chiral mixture of 8-PYP-6O and
2 wt% of each chiral compound were observed at room temperature.
oligomers did not show the odd-even effect. From the crystal study,
gauche and trans configurations coexist in the central spacer of
T-1(10, 6). Thus parity of the spacer does not play an important
role in the molecular structure. T-2(10, 6) possessing a [2-(2-fluoro-
4-hexyloxyphenyl)pyrimidine-5-yl]phenyl unit was found to show the
markedly higher Iso-BP transition temperature than T-1(10, 6). The
higher Iso-BP transition temperature can be attributed to the increase
of liquid crystallinity of T-2(10, 6) having the three ring unit.
Table 2 shows the helical pitch values and helical twist sense in the
Nꢀ and SmCꢀ phases of each chiral compound.
Pitch measurements reveal that there is no significant difference in
the twisting power in the Nꢀ phase among the present compounds. The
crystal structure suggests that the T-1(10, 6) exists as a k-shaped
structure rather than a T-shaped structure. Thus T-1(10, 6) is thought
to have two possible molecular long axes, i.e. an axis through the
biphenylbenzoate unit and the other through the phenylpyrimidine
unit. We can say that T-1 has molecular biaxiality. T-1(5, 8)
with the shorter central spacer showed the higher BP-Nꢀ transition.
Flexibility of T-1(5, 8) is thought to be less than that of T-1(10, 6).
Decreasing the flexibility can decrease the molecular biaxiality.
3.3. Miscibility Studies
We investigated chiral effect on the transition behavior of T-1(10, 8).
Figure 5 shows a binary phase diagram on cooling of (S)T-1(10, 8)
and its isomer (R)T-1(10, 8). The transition temperatures were
determined by optical microscopy.

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M. Sato et al.
FIGURE 5 Binary phase diagram on cooling for mixtures of (R)T-1(10, 8) and
(S)T-1(10, 8.)
On decreasing the optical purity, the Iso-BP transition temperature
did not change, however, the BP-Nꢀ transition temperature increased
markedly. The blue phase was found to disappear as the percentage of
the isomer rose above 25 wt%.
In order to stabilize the blue phase, we investigated transition beha-
vior of binary mixtures between T-1(10, 8) and T-2(10, 6). The phase
diagram on cooling is shown in Figure 6(a). The blue phase of both
materials proved to be miscible across the full composition range,
FIGURE 6 (a) Binary phase diagram on cooling for mixtures of T-1(10, 8) and
T-1(10, 6), and (b) binary phase diagram on cooling for mixtures of T-1(10, 8)
and 1.

Novel T-shaped Chiral Oligomers with a Blue Phase
111
FIGURE 7 Structure-property correlations for the T-shaped chiral liquid-
crystalline oligomers on appearance of the blue phase.
however, the temperature range of the blue phase was not extended.
Figure 6(b) shows a phase diagram between T-1(10, 8) and achiral
compound 1.
The blue phase was observed for a mixture containing 75 wt% of
T-1(10, 8). The Iso-BP transition temperature of the mixture is higher
than that of T-1(10, 8), however, the marked increase of the BP-Nꢀ
transition temperature of the mixture decreases a temperature range
of the blue phase. The change of the BP-Nꢀ transition temperature
across the diagram is explainable by two reasons, i.e. (1) BP-Nꢀ tran-
sition temperature of T-1(10, 8) is not the same as Iso-N transition
temperature of compound 1, and (2) the chirality is changing across
the diagram.
The miscibility studies reveal that (1) a high degree of chirality
destabilizes the Nꢀ phase and (2) the blue phase can be stabilized by
doping achiral nematic material which has higher Iso-N transition
temperature than T-shaped chiral oligomer.

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M. Sato et al.
4. CONCLUSIONS
We have prepared the homologous series of the T-shaped chiral liquid
crystalline oligomers and investigated effects of molecular structure
on appearance of the blue phase. The crystal structure study suggest
that (1) the oligomer forms a k-shaped structure, (2) gauche and trans
configurations coexist in the central spacer, and (3) the molecules are
almost antiparallel to each other. The structure-property correlations
are summarized in Figure 7. Coupling of chirality and molecular
biaxiality of the k-shaped chiral oligomer can induce the double twist
structure of the blue phase by destabilizing the uniaxial helix of the
Nꢀ phase.
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