Physico-chemical properties of new liquid crystals incorporating a lactone ring

Article abstract of DOI:10.1080/15421400590957233

Synthesis and physico-chemical properties of 4-alkoxyphenyl and 4-alkoxybiphenyl-4′-yl 2H-pyran-2-one-5-carboxylates, 2H-chromen-2-one-6- yl 4-alkoxybenzoates and 4-alkoxybiphenyl-4′-carboxylates, and 2H-chromen-2-one-7-yl 4-alkoxybenzoates and 4-alkoxybiphenyl-4′- carboxylates are described. Terminal 2H-pyran-2-one and chronten-2-one cores are effective in enhancing liquid crystalline properties. The layer structure was examined by a small angle X-ray measurement, and the results are discussed in terms of the molecular structure. The polar effect of the terminal lactone group is recognized in the thermal properties and the layer structure of smectic A (SmA) phase.

Full text of DOI:10.1080/15421400590957233

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Physico-Chemical Properties
of New Liquid Crystals
Incorporating a Lactone Ring
a
a
Yuki Morita , Takeyasu Tasaka , Remuto
a
a
Yamaguchi , Hiroaki Okamoto & Shunsuke
a
Takenaka
a
Department of Advanced Materials and Science,
Faculty of Engineering , Yamaguchi University ,
Tokiwadai, Ube, Yamaguchi, Japan
Published online: 31 Aug 2006.
To cite this article: Yuki Morita , Takeyasu Tasaka , Remuto Yamaguchi , Hiroaki
Okamoto & Shunsuke Takenaka (2005) Physico-Chemical Properties of New Liquid
Crystals Incorporating a Lactone Ring, Molecular Crystals and Liquid Crystals, 439:1,
209/[2075]-220/[2086], DOI: 10.1080/15421400590957233
To link to this article: http://dx.doi.org/10.1080/15421400590957233
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Mol. Cryst. Liq. Cryst., Vol. 439, pp. 209=[2075]–220=[2086], 2005
Copyright # Taylor & Francis Inc.
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400590957233
Physico-Chemical Properties of New Liquid Crystals
Incorporating a Lactone Ring
Yuki Morita
Takeyasu Tasaka
Remuto Yamaguchi
Hiroaki Okamoto
Shunsuke Takenaka
Department of Advanced Materials and Science, Faculty of Engineering,
Yamaguchi University, Tokiwadai, Ube, Yamaguchi, Japan
Synthesis and physico-chemical properties of 4-alkoxyphenyl and 4-alkoxybi-
0
phenyl-4 -yl 2H-pyran-2-one-5-carboxylates, 2H-chromen-2-one-6-yl 4-alkoxy-
0
benzoates and 4-alkoxybiphenyl-4 -carboxylates, and 2H-chromen-2-one-7-yl
0
4
2
-alkoxybenzoates and 4-alkoxybiphenyl-4 -carboxylates are described. Terminal
H-pyran-2-one and chromen-2-one cores are effective in enhancing liquid crystal-
line properties. The layer structure was examined by a small angle X-ray measure-
ment, and the results are discussed in terms of the molecular structure. The polar
effect of the terminal lactone group is recognized in the thermal properties and the
layer structure of smectic A (SmA) phase.
Keywords: 2H-chromen-2-one; 2H-pyran-2-one; layer structure; liquid crystal; smectic
A phase
INTRODUCTION
It is well known that terminal polar groups such as a cyano or a nitro
group play important roles in determining thermal properties of liquid
crystal (LC) molecules. Especially, the polar interactions cause a
complex polymesomorphism involving plural smectic A (SmA), C
phases, and also reentrant nematic one [1].
This work was partially supported by The Sumitomo Foundation.
Address correspondence to Yuki Morita, Department of Advanced Materials Science
and Engineering, Faculty of Engineering, Yamaguchi University, Tokiwadai 2557, Ube,
Yamaguchi 755-8611, Japan. E-mail: y-morita@po.cc.yamaguchi-u.ac.jp
209=[2075]

2
10=[2076]
Y. Morita et al.
FIGURE 1 Dipole moments of ester and lactone compounds. Dipole moments
(
(
mcal, D) were estimated by a semi-empirical molecular orbital calculation
MOPAC2000).
Although cyano and nitro groups have been considered to be the
typical example of a polar substituent, in practice, a lactone ring has
larger dipole moment than those, as shown in Figure 1.
An ester group intrinsically should have a large dipole moment due
to electronic distortion on two oxygen atoms. However, the dipole
moment of ethyl acetate, for example, is not so high (1.78 D). Cancel-
lation of the electronic distribution in the conformation should be
responsible for the reduction. A semi-empirical molecular orbital
calculation (MOPAC2000) predicts the reduction of dipole moment
(
1.87 D). In contrast, dipole moments of cyclic esters (lactones) such
as furan-2(5H)-one and 5,6-dihydropyran-2-one are much larger than
those of benzonitrile and nitrobenzene. These facts predict that the
related lactone, 2H-pyran-2-one also has a large dipole moment.
We are interested in the polar effect of 2H-pyran-2-one and the
related lactone, 2H-chromen-2-one on LC properties, since MO calcu-
lation predicts that these have a planer structure being preferable in
displaying LC properties and large dipole moment, 5.44 and 4.82 D,
respectively. In this paper, we describe preparation and LC properties
of new compounds 1ꢀ3. The smectic layer structure will be discussed
in terms of physical properties of the molecules. The chemical
structures are illustrated in Figure 2.
EXPERIMENTAL
Materials
Compounds 1a-n and 1b-n were prepared by a conventional esterifi-
cation (DCC method in THF) with 2H-pyran-2-one-5-carboxylic acid
0
and 4-alkoxyphenols or 4-alkoxybiphenyl-4 -ols. 2a-n and 2b-n were

Physico-Chemical Properties of New LC Materials
211=[2077]
FIGURE 2 Chemical structure of 1ꢀ3.
prepared by a similar esterification of 6-hydroxy-2H-chromen-2-one and
the acids. 6-Hydroxy-2H-chromen-2-one was prepared according to the
synthetic scheme in Figure 3, while another way has been reported [8].
Compounds 3a-n and 3b-n were prepared by a similar esterifica-
tion with 7-hydroxy-2H-chromen-2-one and 4-alkoxybenzoic acids or
0
4
-alkoxybiphenyl-4 -carboxylic acids.
Methods
The transition temperatures and latent heats were determined using a
Seiko SSC-5200 DSC. Mesophases were characterized using a Nikon
POH polarizing microscope fitted with a Mettler thermo-control
system (FP-900).
X-ray diffraction experiments for the smectic phases were per-
formed using a Rigaku-denki RINT 2200 diffractometer, where
˚
CuKa (k ¼ 1.541 A) was used as an X-ray source. Temperature was
controlled using a Rigaku PTC-20A thermo-controller.

2
12=[2078]
Y. Morita et al.
FIGURE 3 Synthetic scheme of 6-hydroxy-2H-chromen-2-one.
RESULTS AND DISCUSSION
Thermal Properties
Transition temperatures of 1a-n and 1b-n are summarized in Table 1.
Considering the fact that 4-alkoxyphenyl 4-cyanobenzoates exhibit
nematic (N) phase and SmA one which commences from the octyloxy
homologue, and the N-isotropic (I) transition temperatures for the
TABLE 1 Transition Temperatures of 1a-n and 1b-n
Compounds
n
C
SmAlow
SmA
N
I
1
a
5
. 68
. 76
. 72
. 80
. 72
. 74
–
–
–
–
–
–
–
–
–
–
–
–
–
–
.
.
.
.
.
.
6
7
8
9
(. 48)
(. 59)
(. 65)
(. 69)
1
0
1
b
4
5
6
7
. 151
. 145
. 148
. 144
(. 142)
(. 130)
(. 129)
(. 120)
–
–
. 203
. 197
. 190
. 189
.
.
.
.
. 172
. 174
C, SmA, N, and I indicate crystal, smectic A, nematic, and isotropic phases, respect-
ively. Parentheses represent a monotropic transition temperature.

Physico-Chemical Properties of New LC Materials
213=[2079]
ꢁ
homologues are ca. 90 C, the terminal lactone core for 1a-n may be less
favorable than benzonitrile one for the appearance of the N phase [9].
Compounds 1b-4ꢀ1b-7 exhibit N and SmA phases, and 1b-6 and
1
b-7 exhibit two kinds of SmA phases, namely SmA
and SmA in
low
Table 1. The latent heats for the SmAlow–SmA transition were so small
that the phase transition temperature was only determined by a
microscopic observation, where a quick and notable change of texture
was observed near the phase transition point.
Transition temperatures of 2a-n and 2b-n are summarized in
Table 2.
Considering the fact that N–I transition temperatures for 2-cyano-
ꢁ
naphthalene-6-yl 4-alkoxybenzoates are up to 150 C, the 2H-chromen-
2
-one core may be less favorable than the 2-cyanonaphthalene one in
displaying LC properties [10].
Similar tendency is observed in 2b-4ꢀ2b-7, where N–I transition
ꢁ
temperatures are 30ꢀ40 C lower than those of 2-cyanonaphthalene-
0
6
-yl 4-alkoxybiphenyl-4 -carboxylates [10].
Transition temperatures of 3a-n and 3b-n are summarized in
Table 3.
Compounds 3b-4 and 3b-5 instantaneously exhibit N phase on the
cooling process. The bent geometry around the terminal position
should be responsible for low N–I transition temperature.
The thermal properties of SmA phases were examined by binary
phase diagrams, and the results are shown in Figures 4.
TABLE 2 Transition Temperatures for 2a-n and 2b-n
Compounds
2a
n
C
SmA
N
I
ꢂ
2
. 160
. 102
. 98
. 88
. 96
. 101
. 105
. 104
. 106
. 108
–
–
–
–
–
–
1
.
.
.
.
.
.
.
.
.
.
3
4
5
6
7
8
9
0
2
(. 75)
(. 78)
(. 78)
(. 80)
(. 84)
ꢂ
ꢂ
ꢂ
2
2
2
–
–
(. 88)
(. 84)
(. 95)
. 108
–
–
–
1
1
2
b
5
6
7
8
. 155
. 149
. 154
. 151
–
–
–
. 249
. 240
. 235
. 232
.
.
.
.
. 208
ꢂ
ꢂ
1
A schlierene texture was observed before recrystallization. 2 Transition tempera-
tures were determined from binary phase diagrams, for example, in Figure 6a.

2
14=[2080]
Y. Morita et al.
TABLE 3 Transition Temperatures for 3a-n and 3b-n
Compounds
n
C
N
I
3a
6
8
2
. 116
. 112
. 112
–
–
–
.
.
.
1
3b
4
5
. 209
. 215
(. 207)
.
.
ꢂ
.
1
ꢂ
1
A schlierene texture was observed before recrystallization.
0
FIGURE 4 Binary phase diagrams for mixtures of: (a) 4-octyloxy-4 -cyano-
biphenyl (8OCB) (on left) and 1a-9 (on right), (b) 4-decyloxyphenyl 4-decyloxy-
benzoate (DODO) and 1a-9, (c) 8OCB and 1b-6, and (d) 4-octyloxybiphenyl-4-yl
4-cyanobenzoate (8OBCB) and 1b-6. Transitions below melting points were
observed on the monotropic process.

Physico-Chemical Properties of New LC Materials
215=[2081]
0
For the mixture of 4-octyloxy-4 -cyanobiphenyl (8OCB) and 1a-9 in
Figure 4a, the SmA phase of 1a-9 is miscible with that of 8OCB, and
the SmA–N (I) transition temperature shows a linear correlation
against mol% of each component. However, the N phase of 8OCB
hides under the SmA phase around 30 mol% of 1a-9, suggesting that
the N–I transition temperature of 1a-9 is low compared with the
SmA–I one.
In the binary phase diagram for the mixture of 4-decyloxyphenyl
4
-decyloxybenzoate (DODO) and 1a-9 (Fig. 4b), the SmA–I transition
temperature shows an upward convexity (ca. 15 K around the center
of the diagram). The peculiar feature is frequently observed in polar
and non-polar LC mixtures, and molecular interactions and the
rearrangement of each component are supposed to be responsible for
the enhancement [11].
Compounds 1b-6 and 1b-7 exhibit two kinds of SmA phases and
experience the SmAlow–SmA transition. The miscible relation between
SmA phases of 1b-6 and 8OCB was examined, and the results are
shown in Figure 4c. Thereby, the SmA phase of 8OCB has been
assigned to the SmAd modification, where the layer spacing is 1.5
times of the fully extended molecular length [12]. Although the
SmA–N transition temperature varies linearly through the mixture,
another SmA–SmA transition should occur in the range between 0
and 20 mol% of 8OCB.
0
4-Octyloxybiphenyl-4 -yl 4-cyanobenzoate (8OBCB) should have a
similar geometrical and electrostatic nature to 1b-n and show a phase
transition sequence of SmC–SmA–SmA–N–I type [13]. For the mix-
ture of 8OBCB and 1b-6 in Figure 4d, both SmA phases at the lower
temperature region are miscible each other, and the SmA–SmA(N)
transition temperature shows a linear correlation to mol% of each
component, indicating that low SmA phases of both components have
similar physical properties and a monolayer arrangement (SmA ). On
1
the other hand, the SmA phases at the higher temperature region are
discontinuous in the diagram, and reentrant N phase is exhibited
around their boundary. Therefore, both SmA phases should be
classified into ‘‘SmA ’’ modification.
d
XRD Measurement
The layer structure of SmA phase was further characterized by a small
angle X-ray diffraction method.
The observed layer spacing (dobs) of 1a-n is plotted against tempera-
ture and the hydrocarbon chain length (n) in Figures 5a and 5b,
respectively.

2
16=[2082]
Y. Morita et al.
FIGURE 5 Plots of: (a) layer spacings (dobs) vs. temperature for 1a-n, and (b)
layer spacings (dobs
,
ꢁ
) and calculated molecular length (lcal
,
ꢃ
) vs. n.
ꢁ
˚
The d
of 1a-9 varies in the range between 33.3 A at 63 C and
obs
ꢁ
˚ ˚
3.8 A at 54 C in Figure 5a, so that 33.7 A was used as the mean value
3
in Figure 5b. The layer spacings for the other homologues in Figure 5a
are almost independent of temperature. The dobs is plotted against n in
Figure 5b, and apparently has a linear correlation with n within the
range of n ¼ 7ꢀ10, and a linear curve fitting method for the plot gives
˚
d
(A) ¼ 1.70n þ 18.5, meaning that the extrapolated layer spacing of
obs
˚
1
1
a-1 is 20.2 A, and the d
for n ¼ 7ꢀ10 homologues increases by
obs
˚
.70 A=n.
In order to correlate these results with molecular parameters, the
molecular shape and length were estimated by a semi-empirical
molecular orbital calculation (MOPAC2000). The MO calculation pre-
dicts that the alkoxy chain extends linearly beside the aromatic ring in
the most stable conformation, so that the calculated molecular length
(
lcal) is proportional to n, as shown in Figure 5b. The linear curve fit-
˚
ting method gives lcal (A) ¼ 1.21n þ 13.2, indicating that the molecular
˚
˚
length is 14.4 A for 1a-1 and increases by 1.21 A=n on ascending the
homologues.
A molecular arrangement model in SmA phase is illustrated in
Figure 6a, where molecules are voluntarily put in an x–y coordinate,
and the x-axis is supposed to be a smectic layer.
In such conditions, the dobs is given by lcorecos hcore þ lchaincos hchain
,
where lcore and lchain are longitudinal lengths of LC core and hydro-
carbon chain, respectively. lcore and lchain can be obtained easily and
exactly by the MO calculation. Of course, the plot of lcal values vs.

Physico-Chemical Properties of New LC Materials
217=[2083]
FIGURE 6 Molecular arrangement models in SmA phase for 1a-10.
a) monolayer, (b) partially bilayer.
(
n gives a straight line, as shown in Figure 5b. A similar treatment of
X-ray data has been tried by several authors [14–16].
For the model in Figure 6a, increment of the layer spacing should
˚
˚
be 1.25 A=n (1.51cos55.5, CꢄC bond length ¼ 1.51 A, CꢄCꢄC bond
ꢁ
angle ¼ 111 ), when h
¼ 0, that is, the hydrocarbon chain arranges
˚
chain
orthogonal to the smectic layer. The large slope (1.70 A=n) for the d
obs
of 1a-n in Figure 5b suggests that an interdigitation of molecules
occurs within the smectic layer. In fact, the dobs is far long from the
longest molecular lengths.
Based on these results, a modified model is postulated and illustrated
in Figure 6b, where molecules interdigitate within the smectic layer.
For the model, the LC core is supposed to arrange orthogonal to the
˚
smectic layer, and the lcore is set to 20.2 A on the analogy of the d of
1
obs
˚
a-1, and corresponds to 1.40 times of calculated core length (14.4 A).
In such conditions, the reflected length of the hydrocarbon chain on
the y-axis is given by 2dchain(i.e., 2lchaincos hchain), and the dobs is given
by 2dchain þ d . From these equations, we can calculate the tilt angle
core
ꢁ
(
hchain) of the hydrocarbon chain to the smectic layer, giving 47 for
1
a-n in Figure 5b.
A similar feature is observed for the plots of 1b-n. The plots of the
dobs vs. T and n are shown in Figures 7a and 7b, respectively.

2
18=[2084]
Y. Morita et al.
FIGURE 7 Plots of: (a) layer spacings (dobs) vs. temperature for 1b-n, (b)
layer spacings (dobs ) and calculated molecular lengths (lcal ) vs. n.
Bold lines indicate the temperature dependency of layer spacings.
,
ꢁ
,
ꢃ
In Figure 7a the dobs values of 1b-4 and 1b-5 are almost inde-
pendent of temperature. In contrast, those of 1b-6 and 1b-7 are
considerably large compared with 1b-4 and 1b-5, and in addition,
the temperature dependency is notable. The notable temperature
dependency may be concerned with the fact that these homologues
have two kinds of SmA phases, and experience the SmAlow–SmA
ꢁ
transition at ca. 130 C. The layer spacing of the SmA
phase,
low
unfortunately, could not be measured due to recrystallization.
˚
˚
In Figure 7b the dobs values of 1b-4 (21.4 A) and 1b-5 (22.5 A) are in
˚
good agreement with the lcals (21.2 and 22.6 A, respectively), indicat-
ing that the SmA phase has a monolayer arrangement. Supposing that
the plots of 1b-6 and 1b-7 show a straight line, the line is presented as
˚
˚
dobs(A) ¼ 1.70n þ 24.8, where the extrapolated d
of 1b-1 is 26.5 A.
obs
˚
On the other hand, the l (A) is given by 1.22n þ 16.3, where the mol-
cal
˚
ecular length for 1b-1 is 17.5 A. Considering the fact that the ratio of
dobs to lcal is 1.51, the interdigitation also occurs in the SmA phase of
1
b-6 and the after homologues. Interestingly, the slope of 1.70 is simi-
lar to that of 1a-n, so that the tilt angle of the alkoxy chain to the
ꢁ
smectic layer may be ca. 45 .
Although both 2a-10 and 2a-12 exhibit a monotropic SmA phase,
the X-ray measurement for the former was unsuccessful because of
˚
recrystallization. The dobs of 2a-12 is 37.9 and 37.8 A at 98 and
ꢁ
˚
04 C, respectively, corresponding to 1.3 times of lcal (29.4 A).
1

Physico-Chemical Properties of New LC Materials
219=[2085]
For 2b-n, SmA phase was observed from the octyloxy homologue.
˚
The dobs of the SmA phase for 2b-8 is 38.1, 37.7, and 37.5 A at 177,
ꢁ
1
65, and 157 C, respectively, indicating that the layer spacing is
almost independent of temperature. The dobs corresponds to 1.25 times
˚
of the molecular length of 2b-8 (28.4 A).
Interestingly, X-ray profiles for the N phase of 2b-7 also show a
ꢁ
wide and intense reflection peak at 2h ¼ 2.46, 2.48, and 2.48 at 183,
ꢁ
1
68, and 153 C, respectively, while the SmA phase could not be
observed by microscopic and DSC measurements. These results sug-
gest that cybotactic domains with the SmA layer structure are present
in the N phase of 2b-7.
Conclusively, polar interactions around the terminal lactone moi-
eties are considered to play important roles in modification of the layer
structure in SmA phase.
Dielectric Properties
The effect of the lactone group on dielectric properties has been
reported in our previous paper, and it was clarified that the lactone
moieties increase the positive dielectric anisotropy (Deꢀ20) [17,18].
CONCLUSIONS
2
H-Pyran-2-one and 2H-chromen-2-one are a useful segment of LC
molecules. The polar interaction around the lactone moieties causes
of complex phase transition behavior in smectic A phases, where the
layer spacing is 1ꢀ1.5 times of the molecular length. These cores
enhance the positive dielectric anisotropy.
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[
[
[
[
[
[
[
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[
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20=[2086]
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0
[
13] 4-Octyloxybiphenyl-4 -yl 4-cyanobenzoate (8OBCB) has
a phase sequence of
ꢁ
.
.
.
.
.
.
.
.
.
.
C 129 SmC 125 SmA 153 SmA 160 N 235 I (T= C). The layer spacing of the SmA
phase at high temperature region is 39.9 and 40.0 A at 160 and 155 C, respectively,
and those at low temperature region are 27.2 A in the range between 151 and 125 C,
and 27.5 A at 120 C. Both reflection peaks co-exist in the temperature range
˚
ꢁ
˚
ꢁ
˚
ꢁ
ꢁ
between 140 and 160 C, and the relative intensity of both peaks notably varies
˚
without changing their positions. The layer spacings of 40.0 and 27.2 A correspond
˚
to 1.48 and 1.0 times of the calculated molecular length (26.9 A).
[
[
14] Blumstein, A. & Patel, L. (1978). Mol. Cryst. Liq. Cryst., 48, 151.
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[
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