Twisting power of a novel binaphthyl derivative possessing laterally attached mesogenic units

Article abstract of DOI:10.1080/15421400903065663

We prepared a novel binaphthyl derivative possessing laterally attached mesogenic units, (R)-2, 2′-bis{6-[2-(4-octyloxyphenyloxycarbonyloxy)-5- octyloxyphenyloxycarbonyl]hexyloxy}-1,1′-binaphthyl [(R)-1], and that possessing terminally attached mesogenic

Full text of DOI:10.1080/15421400903065663

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Twisting Power of a Novel
Binaphthyl Derivative
Possessing Laterally Attached
Mesogenic Units
Keiko Kobayashi a & Atsushi Yoshizawa a
a Department of Frontier Materials Chemistry ,
Graduate School of Science and Technology, Hirosaki
University , Hirosaki, Japan
Published online: 05 Oct 2009.
To cite this article: Keiko Kobayashi & Atsushi Yoshizawa (2009) Twisting Power
of a Novel Binaphthyl Derivative Possessing Laterally Attached Mesogenic
Units, Molecular Crystals and Liquid Crystals, 509:1, 213/[955]-222/[964], DOI:
10.1080/15421400903065663
To link to this article: http://dx.doi.org/10.1080/15421400903065663
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Mol. Cryst. Liq. Cryst., Vol. 509, pp. 213=[955]–222=[964], 2009
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400903065663
Twisting Power of a Novel Binaphthyl Derivative
Possessing Laterally Attached Mesogenic Units
Keiko Kobayashi and Atsushi Yoshizawa
Department of Frontier Materials Chemistry, Graduate
School of Science and Technology, Hirosaki University,
Hirosaki, Japan
We prepared a novel binaphthyl derivative possessing laterally attached mesogenic
units, (R)-2, 20-bis{6-[2-(4-octyloxyphenyloxycarbonyloxy)-5-octyloxyphenyloxycar-
bonyl]hexyloxy}-1,10-binaphthyl [(R)-1], and that possessing terminally attached
mesogenic units, (R)-2, 20-bis{6-[4-(4-octyloxyphenyloxycarbonyl)phenyloxycarbo-
nyl]hexyloxy}-1, 10-binaphthyl [(R)-2]. We investigated their induced helical senses
and pitches in the chiral nematic (Nꢀ) and chiral smectic C (SmCꢀ) phases in the
mixture with a host liquid crystal. (R)-1 induced a left-handed (LH) helix in the Nꢀ
phase, whereas (R)-2 induced a right-handed (RH) helix. We discuss chirality
transfer from each binaphthyl derivative to a host liquid crystal.
Keywords: binaphthyl; chirality; liquid crystal
1. INTRODUCTION
Investigation of chirality in liquid crystals is an exciting area of liquid
crystal science [1]. Chirality-dependent frustrated phases have been
investigated: twist grain boundary phases (TGB) and blue phases
(BP) [2]. The appearance of these phases is created through competi-
tion between chiral twisting force and the molecules’ packing such
that they fill the space uniformly. The question of how molecular
chirality is translated into bulk chirality of the liquid crystalline phase
is a fundamental issue of liquid crystal science. Chirality transfer pro-
cesses in liquid-crystalline phases have therefore been investigated
This work was partially supported by a Grant-in-Aid for Scientific Research from the
Japan Society for the Promotion of the Science (No. 19550175).
Address correspondence to Atsushi Yoshizawa, Department of Frontier Materials
Chemistry, Graduate School of Science and Technology, Hirosaki University,
3 Bunkyo-cho, Hirosaki 036-8561, Japan. E-mail: ayoshiza@cc.hirosaki-u.ac.jp
213=[955]

214=[956]
K. Kobayashi and A. Yoshizawa
extensively [3–9]. Binaphthyl derivatives possessing axial chirality are
known to induce chirality-dependent properties not only for organic
synthesis, but also for liquid crystal science. Akagi et al. reported an
asymmetric synthesis of helical polyacetylene with a chiral nematic
reaction field, which was prepared by adding a binaphthyl derivative
to a host liquid crystal [10]. Kirste and Scherowsky investigated
temperature-dependent helix inversion in induced chiral nematic
phases of a binaphthyl ester and a nematic mixture [11]. They specu-
lated that temperature-dependent conformational changes between
cisoid and transoid of the 1,1-binapthyl derivative are responsible
for that behaviour. We have investigated chirality transfer from a
binaphthyl derivative to a host nematic liquid crystal. We found that:
1) host-guest molecular recognition affects on the chirality transfer
[12] and 2) two mesogenic parts connected via a binaphthyl group
can induce a helical structure [13].
For the present study, we prepared a novel binaphthyl derivative
possessing laterally attached mesogenic units [(R)-1] and that posses-
sing terminally attached mesogenic units [(R)-2], and investigated
FIGURE 1 Molecular structures of (R)-1 possessing laterally attached meso-
genic units and (R)-2 possessing terminally attached mesogenic units.

Binaphthyl with Laterally Attached Mesogens
215/[957]
there induced helical senses and pitches in the chiral nematic (Nꢀ)
and chiral smectic C (SmCꢀ) phases in the mixture with a host liquid
crystal. Figure 1 shows the molecular structures.
2. EXPERIMENTAL
2.1. Spectroscopic Analysis
The purities of all final compounds were checked using HPLC
(JAIGEL-1H column, LC9101; Japan Analytical Industry Co., Ltd.).
Chloroform was used as eluent. Detection of products was achieved
using UV irradiation (k ¼ 254 nm).
Infrared (IR) spectroscopy (FTS-30; Bio-Rad Laboratories, Inc.) and
proton nuclear magnetic resonance (1H NMR) spectroscopy (JNM-
A400 or JNM-ECA500; JEOL) elucidated the structures of the final
products.
2.2. Preparation of Materials
Compound (R)-1 was prepared by the synthesis outlined in Scheme 1.
Preparation of (R)-2, 20-bis[6-(ethyloxycarbonyl)hexyloxy]-1,10-bina-
phthyl [(R)-Et-6] and (R)-2, 20-bis(6-carboxyhexyloxy)-1, 10-binaphthyl
was already reported [13].
2.2.1. (R)-2, 20-Bis{6-[2-(4-octyloxyphenyloxycarbonyloxy)-5-
octyloxyphenyloxycarbonyl]hexyloxy}-1,10-binaphthyl [(R)-1]
To a solution of 2, 4-dihydroxybenzoic acid (7.7 g, 50 mmol) and
1-bromooctane (10.4 g, 53 mmol) in ethanol (70 ml) was added a solu-
tion of KOH (10.3 g, 184 mmol) in water (40 ml). The mixture was stir-
red at 95ꢁC for 10 h. After the solvent was removed, the residue was
acidified with aq. HCl. The solution was extracted with diethylether
(3 ꢂ 50 ml). The organic layers were combined, dried over anhydrous
magnesium sulfate, filtered and evaporated to give 2-hydroxy-4-
octyloxybenzoic acid; yield 1.23 g (9%).
To a solution of 2-hydroxy-4-octyloxybenzoic acid (1.0 g, 3.8 mmol)
and 4-octyloxyphenol (0.84 g, 3.8 mmol) in dichloromethane (30 ml),
N, N0-dicyclohexylcarbodiimide (0.8 g, 4 mmol), and 4-(N,N-dimethyla-
mino)pyridine (0.05 g, 0.4 mmol) were added. The resulting solution
was stirred at room temperature for 3 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 hexane and ethyl acetate (15=1) mixture as the eluent. Recrystalliza-
tion gave 4-octyloxyphenyl 2-hydroxy-4-octyloxyphenylcarboxylate;
yield 0.71 g (40%).

216/[958]
K. Kobayashi and A. Yoshizawa
SCHEME 1 Synthesis of (R)-1.
To a solution of (R)-2, 20-bis(6-carboxyhexyloxy)-1,10-binaphthyl
(0.16 g, 0.3 mmol) and 4-octyloxyphenyl 2-hydroxy-4-octyloxyphenyl-
carboxylate (0.29 g, 0.6 mmol) in dichloromethane (15 ml), N,N0-
dicyclohexylcarbodiimide (0.17 g, 0.8 mmol), and 4-(N,N-dimethyl-
amino)pyridine (0.01 g, 0.06 mmol) were added. The resulting solution
was stirred at room temperature for 7 h. Precipitated materials were

Binaphthyl with Laterally Attached Mesogens
217/[959]
removed by filtration. After removal of the solvent by evaporation, the
residue was purified by column chromatography on silica gel with a
toluene and ethyl acetate (15=1) mixture as the eluent to give the
desired product: yield 0.24 g (55%). 1H NMR (400 MHz, solvent CDCl3,
standard TMS) dH=ppm: 8.17 (d, 2H, Ar-H, J ¼ 8.8 Hz), 7.94 (d, 2H, Ar-
H, J ¼ 8.8 Hz), 7.84 (d, 1H, Ar-H, J ¼ 8.3 Hz), 7.39 (d, 2H, Ar-H,
J ¼ 8.8 Hz), 7.32–7.16 (m, 6H, Ar-H), 7.05 (d, 4H, Ar-H, J ¼ 9.3 Hz),
6.92–6.86 (m, 6H, Ar-H), 6.64 (d, 2H, Ar-H, J ¼ 2.4 Hz), 4.04 (t, 4H,
-O-CH2, J ¼ 6.3 Hz), 3.98–3.82 (m, 8H, -OCH2-), 2.38 (t, 4H,
-OCOCH2-, J ¼ 7.8 Hz), 1.86–1.74 (m, 8H, -OCH2CH2-), 1.46–1.31 (m,
48H aliphatic-H), 1.01–0.81 (m, 20H aliphatic-H); IR (neat)
n
max=cmꢃ1: 2929, 1767, 1736, 1245, 1132; HPLC: 100%.
2.2.2. (R)-2, 20-Bis{6-[4-(4-octyloxyphenyloxycarbonyl)phenyl-
oxycarbonyl]hexyloxy}-1,10-binaphthyl [(R)-2]
To a solution of 4-methoxycarbonyloxybiphenyl-40-carboxylic acid
(1.2 g, 6.1 mmol) and diethylazodicarboxylate (1.0 g, 6.0 mmol) in tetra-
hydrofuran (THF, 80 ml) was added triphenylphosphine (1.9 g,
7.1 mmol) in THF (28 ml). The reaction mixture was stirred at room
temperature for 24 h. After the filtration of participate, the solvent
was removed by evaporation. The residue was purified by column
chromatography on silica gel with a toluene and ethyl acetate (15=1)
mixture to give 4-octyloxyphenyl 4-methoxycarbonyloxybenzoate;
yield 0.48 g (20%).
To a solution of 4-octyloxyphenyl 4-methoxycarbonyloxybenzoate
(0.28 g, 0.7 mmol) in ethanol (30 ml) was added an aqueous ammonia
solution (28ꢄ30%, 1.6 ml). The reaction mixture was stirred at room
temperature for 3 h. The solvent was removed by evaporation. To
the residue was added water and the solution was extracted with
diethylether (60 ml). The combined organic layers were dried over
anhydrous magnesium sulfate. After the drying agent and the solvent
were removed, 4-octyloxyphenyl 4-hydroxybenzoate was obtained
without further purification; yield 0.24 g (99%).
To a solution of (R)-2, 20-bis(6-carboxyhexyloxy)-1,10-binaphthyl
(0.11 g, 0.2 mmol) and 4-octyloxyphenyl 4-hydroxybenzoate (0.14 g,
0.4 mmol) in dichloromethane (30 ml), N,N0-dicyclohexylcarbodiimide
(0.12 g, 0.6 mmol), and 4-(N,N-dimethylamino)pyridine (0.01 g,
0.06 mmol) were added. The resulting solution was stirred at room
temperature for 24 h. Precipitated materials were removed by filtra-
tion. After removal of the solvent by evaporation, the residue was pur-
ified by column chromatography on silica gel with a toluene and ethyl
acetate (15=1) mixture, and then washed with etanol to give the
desired product: yield 0.10 g (41%). 1H NMR (500 MHz, solvent CDCl3,

218/[960]
K. Kobayashi and A. Yoshizawa
standard TMS) dH=ppm: 8.22 (d, 2H, Ar-H, J ¼ 9.2 Hz), 7.94 (d, 2H,
Ar-H, J ¼ 9.2 Hz), 7.86 (d, 1H, Ar-H, J ¼ 8.0 Hz), 7.42 (d, 2H, Ar-H,
J ¼ 8.0 Hz), 7.33–7.16 (m, 10H, Ar-H), 7.10 (d, 4H, Ar-H, J ¼ 9.2 Hz),
6.93 (d, 4H, Ar-H, J ¼ 8.6 Hz), 4.03–3.99 (m, 2H, -OCH2-), 3.96 (t,
4H, -O-CH2, J ¼ 6.6 Hz), 3.93–3.88 (m, 2H, -OCH2-), 2.35 (t, 4H,
-OCOCH2-, J ¼ 7.5 Hz), 1.86–1.76 (m, 4H, -OCH2CH2-), 1.47–1.23 (m,
28H aliphatic-H), 1.09–0.88 (m, 14H aliphatic-H); IR (neat)
n
max=cmꢃ1: 2928, 1761, 1736, 1270, 1247; HPLC: 100%.
2.3. Physical Properties
The initial phase assignments and corresponding transition tempera-
tures for the products were determined by thermal optical microscopy
using a polarizing microscope (POL, Optiphoto; Nikon Corp.) equipped
with a microfinance (FP82; Mettler Inst. Corp.) and control unit
(FP80). The heating and cooling rates were 5ꢁC minꢃ1. Temperatures
and enthalpies of transition were investigated using differential
scanning calorimetry (DSC, DSC 6200 calorimeter; Sꢃe1iko Corp.). The
materials were studied at a scanning rate of 5ꢁC min for both heat-
ing and cooling cycles after being encapsulated in aluminum pans. The
helical pitch in the Nꢀ phase was measured using the Cano wedge
technique for a chiral nematic mixture consisting of a host nematic
liquid-crystalline material, 4-pentyloxyphenyl 4-octyloxybenzoate
(5P-8-PA) and 2 wt% of each chiral additive. Molecular structure and
phase transition temperatures of 5P-8-PA are shown in Figure 2. The
mixtures were studied using the contact method; their chiral nematic
helical twist senses were established. The standard materials used in
the contact study were (R)-3-methyladipic acid bis[4-(5-octyl-2-
pyrimidinyl)phenyl]ester [14] and (S)-2-methylbutyl 4-(4-decyloxyben-
zylideneamino)cinnamate (DOBAMBC [15]). The helical pitch in the
SmCꢀ phase was obtained directly by measuring the distance between
the lines corresponding to the full pitch under polarized light micro-
scopy for a homogeneously aligned sample in a cell with 300 mm spa-
cing. The helical twist senses in the SmCꢀ phase were measured by
FIGURE 2 Molecular structure and phase transition temperatures of the
host liquid crystal.

Binaphthyl with Laterally Attached Mesogens
219/[961]
using the contact method. The helical twist definition used in this
report is identical to that used by Goodby [16].
3. RESULTS AND DISCUSSION
On cooling, (R)-1 exhibited a glass transition at ꢃ15ꢁC, whereas
(R)-2 showed the following phase sequence: isotropic liquid 28ꢁC
(2.3 kJmolꢃ1) unidentified mesophase I 24ꢁC (8.7 kJmolꢃ1) unidenti-
fied mesophase II; the melting temperature was 42ꢁC.
We investigated the chirality transfer from each binaphthyl
derivative to the host liquid crystal. A macroscopic measure of this
chirality transfer is the helical pitch or helical twisting power
(HTP). We observed the helical sense and pitch induced by each
chiral dopant in the host 5P-8-PA. Figure 3 shows the temperature
dependence of chiral nematic (Nꢀ) helical pitch values induced by
2 wt% of (R)-1 in 5P-8-PA. (R)-1 was found to induce left-handed
(LH) helical structures. The helical pitch value at 72.2ꢁC was
24.6 mm. The helical pitch is independent of the temperature. On
the other hand, a dechiralization line in the chiral smectic C
(SmCꢀ) was not observed, indicating that helical structure in the
SmCꢀ phase is incomplete.
Figure 4 shows the temperature dependence of Nꢀ and SmCꢀ
helical pitch values induced by 2 wt% of (R)-2 in 5P-8-PA. (R)-2 was
found to induce right-handed (RH) helical structures in the Nꢀ and
FIGURE 3 Temperature dependence of Nꢀ helical pitch values induced by
2 wt% of (R)-1 in 5P-8-PA.

220/[962]
K. Kobayashi and A. Yoshizawa
FIGURE 4 Temperature dependence of Nꢀ and SmCꢀ helical pitch values
induced by 2 wt% of (R)-2 in 5P-8-PA.
SmCꢀ phases. Both Nꢀ and SmCꢀ pitches shorten with decreasing
the temperature.
To clarify the effects of the binaphthyl group on twisting power, we
investigated a helical structure induced by a binaphthyl derivative
without an attached mesognic group, (R)-Et. Figure 5 shows the tem-
perature dependence of Nꢀ helical pitch values induced by 2 wt% of
(R)-Et in 5P-8-PA. (R)-Et was found to induce a LH helical structure.
The helical pitch is independent of the temperature. In the SmCꢀ
phase, a dechiralization line was not observed, indicating that helical
structure in the SmCꢀ phase is incomplete.
The present results are explainable in terms of two origins for twist-
ing power of a binaphthyl derivative [13]. The binaphthyl derivative
possessing terminally attached biphenyl moieties has two origins for
the twisting power: an asymmetric axis of the binaphthyl unit and a
twist conformation of the two biphenyl moieties. Both (R)-1 and
(R)-Et induce a LH helical structure in the Nꢀ phase, and the helical
pitches are independent of the temperature. Then, the twisting power
of each chiral compound is too weak to form a helix in the SmCꢀ phase.
Therefore, the twisting power of (R)-1 in the Nꢀ and SmCꢀ phases can
result from an asymmetric axis of the binaphthyl unit. The two phe-
nylbenzoate moieties are thought to be far from each other, thus, they
cannot form a twist conformation. On the other hand, (R)-2 induces a
RH helical structure in the Nꢀ and SmCꢀ phases, and the helical pitch
shortens as decreasing the temperature. Twisting power of (R)-2 is

Binaphthyl with Laterally Attached Mesogens
221/[963]
FIGURE 5 Temperature dependence of Nꢀ helical pitch values induced by
2 wt% of (R)-Et in 5P-8-PA.
thought to attributed to a twist conformation of the terminally
attached phenyl benzoate moieties.
4. CONCLUSION
We prepared two binaphthyl derivatives, i.e., (R)-1 possessing
laterally attached phenyl benzoate moieties and (R)-2 possessing
terminally attached phenyl benzoate moieties. They were found to
induce different helical structures, i.e., opposite twist senses and dis-
tinct temperature dependence of helical pitch in the Nꢀ phase in the
mixture with a host liquid crystal, 5P-8-PA. These results are consis-
tent with our reported chirality transfer mechanism of a binaphthyl
derivative possessing laterally attached mesogenic moieties [13].
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