Search for the B phase in an achiral non-symmetric banana-shaped materials

Article abstract of DOI:10.1080/15421400490435279

We synthesised a series of banana-shaped materials to search for the B phase in an achiral non-nymmetric system. Almost compounds were found to exhibit the B phase, B1 and B2. Interestingly some compounds formed the classical mesophases which were observe

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Search for the B Phase in an
Achiral Non-symmetric Banana-
Shaped Materials
T. Niori a , J. Yamamoto a & H. Yokoyama a
a Yokoyama Nano-structured Liquid Crystal Project ,
Japan Science and Technology Corporation , Ibaraki,
Tsukuba, Japan
Published online: 18 Oct 2010.
To cite this article: T. Niori , J. Yamamoto & H. Yokoyama (2004) Search for the B
Phase in an Achiral Non-symmetric Banana-Shaped Materials, Molecular Crystals and
Liquid Crystals, 411:1, 283-291, DOI: 10.1080/15421400490435279
To link to this article: http://dx.doi.org/10.1080/15421400490435279
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Mol. Cryst. Liq. Cryst., Vol. 411, pp. 283=[1325]–291=[1333], 2004
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080=15421400490435279
SEARCH FOR THE B PHASE IN AN ACHIRAL
NON-SYMMETRIC BANANA-SHAPED MATERIALS
T. Niori, J. Yamamoto, and H. Yokoyama
Japan Science and Technology Corporation, Yokoyama
Nano-structured Liquid Crystal Project, 5-9-9 Tokodai,
Tsukuba, Ibaraki 300-2635, JAPAN
We synthesised a series of banana-shaped materials to search for the B phase in
an achiral non-symmetric system. Almost compounds were found to exhibit the
B phase, B1 and B2. Interestingly some compounds formed the classical meso-
phases which were observed in usual rod-like molecular system. In this paper
we will report the synthesis and the mesophase properties of these materials.
Keywords: B phase; nematic phase; non-symmetric banana-shaped material
INTRODUCTION
Since the discovery of the novel electro-optical properties in an achiral sys-
tem composed of the banana-shaped material [1], many research groups
have been drawn much interests by this field from both the physical and
chemical points of view. As consequence of the vigorous works, a large
number of compounds have been reported in this last five years [2] and
the seven, or maybe more, types of B phase has been discovered. In these
B phases, B2 phase is the most interesting and the most investigated one
due to not only its electro-optical behaviour but also its variety of the
ground state [3]. In the banana-shaped molecular system, the mesophase
properties are very much sensitive to the chemical structure. For example,
the original banana-shaped compound with terminal octyloxy chain forms
B2 phase [4,5], whereas the chloro substitution at the terminal benzene
ring [6] or the nitro substitution at the central core [7] with the same ter-
minal chain makes the phase behaviour completely different. These materi-
als show B7 phase. In Addition, it is amazing that the banana-shaped
compound can form the conventional mesophases such as smectic A, C
Address correspondence to T. Niori, Japan Science and Technology Corporation, Yokoyama
Nano-structured Liquid Crystal Project, 5-9-9 Tokodai, Tsukuba, Ibaraki 300-2635, Japan.
283=[1325]

284=[1326]
T. Niori et al.
and nematic phases [8,9] as well as B phases. We have already reported the
mesophase properties of some achiral non-symmetric banana-shaped com-
pounds [8]. This time we synthesised new series of banana-shaped materi-
als for the purpose of searching for the B phase in the non-symmetric
system and investigated their mesophase properties by means of the classi-
cal method; DSC, POM, XRD and electro-optical measurement. Almost
materials were found to form the B phase (B1 or B2) but some of them
exhibited conventional smectic phases. Moreover a nematic phase was
observed for some compounds.
MATERIALS
All materials synthesised are listed in Figure 1 and their transition tempera-
tures are summarised in Table 1. The synthetic route of compound 9 is
shown in Scheme 1 and each step is described below.
.
3-Chloro-4-n-octyloxybenzoic Acid (I)
Ethyl 3-chloro-4-hydroxybenzoate (0.1 mol) and Potassium carbonate
(0.1 mol) was dissolved in 200 ml of Ethanol and the solution was heated.
Then 1-Bromooctane (0.15 mol) in 10 ml of Ethanol was gradually added
to this solution with vigorously stirring. The final mixture was kept with
reflux for 20 hrs. The reaction mixture was cooled down and the precipi-
tated KBr was filtered off. The solvent was reheated and Sodium hydroxide
(0.12 mol) in 100 ml of water was added. The mixture was refluxed for
further 4 hrs and then cooled down. Then the solution was acidified by
HCl and the precipitates were collected. The crude product was recrystal-
lised twice from n-Hexane.
.
4-Nitrophenyl 3’-chloro-4’-n-octyloxybenzoate (II)
4-Nitrophenol (0.05 mol) and 3-Chloro-4-n-octyloxybenzoic acid (0.05 mol)
was dissolved in 100 ml of Chloroform and to this solution DCC (0.06 mol)
and catalytic amount of DMAP was added. The mixture was kept with stir-
ring for 24 hrs at room temperature. The precipitated urea was filtered off
and the solvent was removed under reduced pressure. The residue was
recrystallised twice from Ethanol/n-Hexane mixture. The final product
was purified by column chromatography (Silica gel, Chloroform as eluent).
.
4-Aminophenyl 3’-chloro-4’-n-octyloxybenzoate (III)
4-Nitrophenyl 30-chloro-40-n-octyloxybenzoate (0.03 mol) was dissolved in
Ethyl acetate and Ethanol mixture. The solvent was kept with stirring for
24 hrs at room temperature in the presence of Palladium on carbon under

Non-symmetric Banana-Shaped Materials
285=[1327]
FIGURE 1 Chemical structures of non-symmetric banana-shaped materials.
Hydrogen atmosphere. Then the catalyst was filtered off and the solvent
was removed under reduced pressure. The crude product was recrystal-
lised twice from Ethanol=n-Hexane mixture. The final product was purified
by column chromatography (Alumina activated, Chloroform as eluent).

286=[1328]
T. Niori et al.
TABLE 1 Phase Transition Temperatures of Series 1,2,3, 4 and 5
Series 1
Series 2
Series 3
1
2
Iso. – 180ꢀC – B2 – 166ꢀC – K
Iso. – 160ꢀC – BXI – 110ꢀC – BX2 – 85ꢀC – K
Iso. – 144ꢀC – B1 – 110ꢀC – K
3
4
Iso. – 143ꢀC – B1- 82ꢀC – K
5
Iso. – 137ꢀC – B2 – 93ꢀC – K
6
Iso. – 246ꢀC – B2 – 241ꢀC – K
7
Iso. – 201ꢀC – B1 – 126ꢀC – K
8
Iso. – 163ꢀC – B1 – 86ꢀC – K
9
Iso. – 147ꢀC – B2 – 60ꢀC – G
10
11
12
13
14
15
16
17
18
Iso. – 108ꢀC – B1 – 40ꢀC – G
Iso. – 223ꢀC – SmA – 199ꢀC – K
Iso. – 205ꢀC – SmA – 114ꢀC – K
Iso. – 143ꢀC – unique phase – 71ꢀC – K
Iso. – 116ꢀC – N – 79ꢀC – K
Series 4
Series 5
Iso: ꢁ ꢁ100ꢀC ꢁ ꢁN ꢁ ꢁ83ꢀC ꢁ ꢁSmA ꢁ ꢁ41ꢀC ꢁ ꢁK
Iso. – 284ꢀC – N – 250ꢀC – SmC – 108ꢀC – K
Iso. – 95ꢀC – N – 79ꢀC – B4
Iso. – 201ꢀC – N – 162ꢀC – B1 – 56ꢀC – K
G : Glass state.
.
2-Methoxy-5-formylphenyl 4’-formylbenzoate (IV)
Terephthalaldehydic acid (0.1 mol) and Isovanillin (0.1 mol) was added to
the solution of DCC (0.12 mol) in 200 ml of Chloroform. DMAP was added
as catalyst and the mixture was kept with stirring for 24 hrs at room
SCHEME 1

Non-symmetric Banana-Shaped Materials
287=[1329]
temperature. The precipitates were filtered off and the solvent was re-
moved under reduced pressure. The crude product was recrystallised twice
from Ethanol and the final product was purified by column chromatography
(Silica gel, Chloroform as eluent).
.
Compound 9
3 mmol of (III) and 1.3 mmol of (IV) was dissolved in the mixture of Chlor-
oform=Ethanol (1:4). The solution was refluxed for 5 hrs and the reaction
mixture was cooled down. The precipitates were filtered off and the resi-
due was recrystallised from Chloroform=Ethanol mixture. The final product
was purified by column chromatography (Alumina activated, Chloroform as
eluent).
RESULTS
As can be seen in Table 1, all compounds prepared formed mesophase.
They are categorised into five series for convenience. Series 1 and 2 are
the materials showing B phases and the former series are composed of 5
benzene rings, whereas the later are of 6 benzene rings. Two compounds
in series 3 form SmA phase. Series 4 exhibits unique phase behaviour
[10] and series 5 is all nematogenic compounds. We will report here the
mesophase properties of series 1,2,3 and compound 15, 18. The rest will
be introduced in another report [10]. Almost B phases can be easily ident-
ified by the polarised microscopy and confirmed by X-ray diffraction
measurement. Up to date, however, two phases observed for compound 2
could not be assigned so that they are temporarily designated as BXI and
BX2, respectively. The typical textures of B1, B2 and SmA phases are
shown in Figures 2. In general, the texture of B1 phase appears as platelet
and coalesces to the mosaic-like texture shown in Figure 2(a). Whereas the
grainy texture is usually observed for B2 phase as can be seen in Figure
ˆ
2(b). In SmA phase, the batonnets are initially appeared from the isotropic
melt and coalesce to the focal conic fan-shaped domain (see Fig. 2(c)).
Shearing the glass plates in the SmA state, homeotropic alignment can
be easily achieved and no birefringence is observed under the polarised op-
tical microscope. We have carried out the X-ray investigations for all mate-
rials and the results of the layer spacing are listed in Table 2. The layer
spacings of B and SmA phases were found to be independent of the tem-
perature. The typical X-ray patterns are shown in Figures 3. It is difficult
to orient the molecules in a glass capillary but the unit cell of the B1 phase
can be easily estimated by the assumption that the inner and outer sharp
reflections are associated with (110) and (200), respectively. The

288=[1330]
T. Niori et al.
FIGURE 2 Typical textures of (a) B1, (b) B2, and (c) SmA phases.
calculated unit cell parameters a and c, are listed in Table 3 together with
the number of the molecule (n) in the unit cell. We are strongly interested
in how the molecular shape is in the uniaxial SmA state. However all
attempts to obtain the oriented sample were unsuccessful so that the direct
evidence of molecular shape is still unclear. Therefore we tried to make a
TABLE 2 List of the Layer Spacing of B Phases and SmA Phase
˚
41A
˚
30.1A, 20.8A
˚ ˚
42.3A (BX1), 43.7A (BX2)
1
2
4
˚
˚
˚
35.6A, 23.8A
3
˚
5
41.6A
6
——a)
˚
˚
33.7A, 24.0A
˚ ˚
42.8A, 24.0A
7
8
˚
˚
˚
33.7A, 24.4A
9
42.8A
10
12
18
˚
˚
31.5A
˚ ˚
11
15
45.0A
˚
41.0A
32.9A, 26.2A
a) X-ray measurement could not be carried out due to the narrow temperature range.

Non-symmetric Banana-Shaped Materials
289=[1331]
FIGURE 3 Typical X-ray patterns of (a) B1 phase for compound 3 at 135ꢀC, (b) B2
phase for compound 5 at 120ꢀC and (c) SmA phase for compound 11 at 215ꢀC.
comparison between the X-ray results and the molecular length calculated
from the all-trans conformation. In Table 4, the experimental results (d)
and the calculated molecular length (L) are summarised. As consequence,
the layer spacings of the compound 11 and 15 are comparable to the all-
trans molecular length. It indicates that the molecular shape in the SmA
TABLE 3 List of the Unit Cell Parameter of B1 Phase
˚
a(A)
˚
c(A)
Compound
n
3
4
41.6
47.6
48
24.4
28.5
47.3
94.5
27.7
42.3
5.4
6.3
10.5
21
7
8
48
10
18
48.7
52.4
6.2
9.4

290=[1332]
T. Niori et al.
TABLE 4 List of the layer spacing of SmA and
the molecular length
˚
d (A)
˚
L (A)
Compound
11
12
15
45.0
31.5
41.0
46.9
43.2
47.7
state of these materials may be possibly bent, although the intercalated
structure of the linear molecules is also still possible. If the molecule is bent
shape in the SmA state, the electrooptical response could be expected even
in an achiral system, since the spontaneous polarisation within the layer is
probably rotated from one layer to the next just like a SmCꢂ phase (no bi-
refringence in homeotropic). On the other hand, we are not able to explain
the observed layer spacing which is much smaller than the molecular length
for compound 12. It should be noted here that the introduction of the sub-
stitution into the central core sometimes leads the conformational change
of the whole molecule [9]. Keeping this in mind, let us look around the
chemical structures again. For all compounds exhibited the SmA phase
the substitution is introduced into the central core. Therefore the confor-
mational change is also the possibility for SmA phase appearance, although
the temperature dependence of the layer spacing could not be detected. In
this case, the intercalated smectic phase is the most plausible model.
SUMMARY
We synthesised the new series of achiral non-symmetric bananashaped
materials and investigated the mesophase properties. Almost compounds
were found to form the B phases but some of them exhibited the conven-
tional mesophase as usually observed in the rodlike molecular system. Es-
pecially we are strongly interested in the molecular shape in the classical
smectic phase. If the bent shape molecules constitute the SmA phase,
the electro-optical response would be expected even in an achiral system.
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[10] see proceedings of ILCC2002, ‘‘Dynamics of the nematic phase formed by an achiral
banana-shaped materials’’, Niori, T. et al.