Vinyl-substituted liquid crystal dimers

Article abstract of DOI:10.1080/15421400802122698

A series of vinyl-substituted liquid crystal dimers, -(4-cyanobiphenyl-4'- yloxy)alkyl 4'-(4-pentenyloxy)-4-biphenylcarboxylates, was prepared. The compounds exhibited nematic and smectic liquid crystalline behavior depending on the chain length of the flexible spacer. The nematic-isotropic and smectic-isotropic transition temperatures and the entropy changes associated with the transitions showed odd-even effects as the number of atoms in the flexible spacer was varied, in which the even members exhibited higher values. The liquid crystalline properties of the compounds were compared with those of related known liquid crystal dimers and trimers.

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Vinyl-Substituted Liquid Crystal
Dimers
Toshio Itahara a & Jun-ichi Inadome a
a Faculty of Engineering, Kagoshima University ,
Korimoto , Kagoshima , Japan
Published online: 31 Aug 2012.
To cite this article: Toshio Itahara & Jun-ichi Inadome (2008) Vinyl-Substituted
Liquid Crystal Dimers, Molecular Crystals and Liquid Crystals, 487:1, 3-12, DOI:
10.1080/15421400802122698
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Mol. Cryst. Liq. Cryst., Vol. 487, pp. 3–12, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802122698
Vinyl-Substituted Liquid Crystal Dimers
Toshio Itahara and Jun-ichi Inadome
Faculty of Engineering, Kagoshima University, Korimoto,
Kagoshima, Japan
A
series of vinyl-substituted liquid crystal dimers, x-(4-cyanobiphenyl-40-
yloxy)alkyl 40-(4-pentenyloxy)-4-biphenylcarboxylates, was prepared. The com-
pounds exhibited nematic and smectic liquid crystalline behavior depending on
the chain length of the flexible spacer. The nematic-isotropic and smectic-isotropic
transition temperatures and the entropy changes associated with the transitions
showed odd–even effects as the number of atoms in the flexible spacer was varied,
in which the even members exhibited higher values. The liquid crystalline proper-
ties of the compounds were compared with those of related known liquid crystal
dimers and trimers.
Keywords: liquid crystal dimer; nematic; odd–even effect; smectic; vinyl
INTRODUCTION
Liquid crystalline compounds with attached alkenyl groups (mesogenic
olefins) are of importance as monomers for side chain liquid crystal
polymers. On the other hand, liquid crystal dimers, which are defined
as molecules containing two mesogenic units joined by one flexible
spacer, have been extensively studied as model compounds for main
chain liquid crystal polymers [1–4]. The liquid crystal dimers, such as
BCBOn [5], exhibit an interesting odd–even effect of liquid crystalline
properties, depending on the number of atoms in the flexible spacer
[1–5]. The odd–even effect has been explained on the basis of the mol-
ecular shapes of all-trans-conformation of the compounds containing
odd and even membered flexible spacers [1–4]. We are very interested
in side chain liquid crystal polymers containing liquid crystal dimers,
in connection with potential functional materials, such as liquid crystal
elastomers [6]. We also previously reported on the synthesis of liquid
Address correspondence to Toshio Itahara, Faculty of Engineering, Kagoshima
University, Korimoto, Kagoshima 890-0065, Japan. E-mail: itahara@be.kagoshima-u.ac.jp
3

4
T. Itahara and J. Inadome
FIGURE 1 Structures of compound (1), BCBOn, and trimer (2).
crystal trimers (2) from a-bromo-x-(4-cyanobiphenyl-40-yloxy)alkanes
(3) and x-(4-cyanobiphenyl-40-yloxy)alkyl 40-hydroxy-4-biophenylcar-
boxylates (4) [7]. The present article reports on the synthesis of a
new series of vinyl-substituted liquid crystal dimers (1) from 4 and
5-bromo-1-pentene (Fig. 1). The liquid crystalline properties of 1 were
compared with those of BCBOn and 2.
EXPERIMENTAL
Elemental analyses were performed at the Analytical Center of Kyoto
1
University. H-NMR spectra (400 M Hz) were obtained with a JEOL
GSX 400 spectrometer. The chemical shifts (d-values) were measured
in parts per million (ppm) down-field from tetramethylsilane as an
internal reference. Infrared (IR) spectra were recorded with a JASCO
FT=IR-420 spectrometer. Measurements in CDCl3 were made with a
0.1 mm KBr cell. Differential scanning calorimetry (DSC) measure-
ments were carried out with a Shimadzu DSC-60. Polarizing
microscopy observations were performed under a Nikon Eclipse
E600 POL equipped with a hot stage (Linkam LK-600PH).
x-(4-Cyanobiphenyl-40-yloxy)alkyl 40-(4-pentenyloxy)-4-
biphenylcarboxylate (1)
A mixture of x-(4-cyanobiphenyl-40-yloxy)alkyl 40-hydroxy-4-biophe-
nylcarboxylate (4) [7] (1.0 mmol) and 5-bromo-1-pentene (1.2 mmol)
in N,N-dimethylformamide (40 ml) in the presence of K2CO3
(1.0 mmol) was stirred for 24 h at room temperature. The reaction

Vinyl-Substituted Liquid Crystal Dimers
5
TABLE 1 Elemental Analyses and Yields of Compounds (1)
n
Yielda
Calculated (%)
Found (%)
3
4
5
6
7
8
9
10
11
12
71
70
73
75
70
74
71
76
72
73
C34H31NO4: C:78.89, H, 6.04; N, 2.71
C, 79.08; H, 6.11; N, 2.65
C, 79.19; H, 6.31; N, 2.55.
C, 79.33; H, 6.47; N, 2.55.
C, 79.31; H, 6.56; N, 2.56.
C, 79.56; H, 7.01; N, 2.43.
C, 79.85; H, 7.15; N, 2.38.
C, 80.04; H, 7.19; N, 2.35.
C, 80.00; H, 7.43; N, 2.29.
C, 80.03; H, 7.61; N, 2.22.
C, 80.16; H, 7.70; N, 2.17.
C
C
35H33NO4: C:79.07, H, 6.26; N, 2.63
36H35NO4: C:79.24, H, 6.46; N, 2.57
C37H37NO4: C:79.40, H, 6.66; N, 2.50
C38H39NO4: C:79.55, H, 6.85; N, 2.44
C39H41NO4: C, 79.70; H, 7.03; N, 2.38
C40H43NO4: C:79.84, H, 7.20; N, 2.33
C41H45NO4: C, 79.97; H, 7.37; N, 2.27
C42H47NO4: C, 80.08; H, 7.52; N, 2.22
C
43H49NO4: C, 80.21; H, 7.67; N, 2.18
aYield based on the amount of 4 used.
mixture was evaporated to give a residue, which was chromato-
graphed over silica gel. Elution of a mixture of chloroform and hexane
(2:1) gave 1. The yields of 1 (n ¼ 3–12) are shown in Table 1.
RESULTS AND DISCUSSION
Compounds (1) were synthesized according to the procedure shown in
Figure 2. Previously, we reported on the synthesis of liquid crystal tri-
mers (2) from 3 and 4 [7]. The reaction of 4 with 5-bromo-1-pentene in
N,N-dimethylformamide in the presence of K2CO3 gave 1 in 70–76%
yields. The elemental analyses of 1 (n ¼ 3–12) are shown in Table 1.
The IR spectral data of 1 (Table 2) showed the presence of a cyano
group at 2227 cmꢀ1, an ester group at ca. 1711 cmꢀ1, and a vinyl group
at ca. 1653 cmꢀ1 (weak bands). The 1H-NMR spectral data of 1 are
FIGURE 2 Synthesis of compounds (1).

6
T. Itahara and J. Inadome
TABLE 2 IR Spectral Data of Compounds (1)
n
cmꢀ1=CDCl3
3
4
5
6
7
8
9
10
11
12
2949, 2879, 2227, 1714, 1653, 1606, 1525, 1496, 1400, 1279, 1248, 1182, 1115
2952, 2875, 2227, 1712, 1653, 1606, 1525, 1497, 1389, 1277, 1248, 1182, 1115
2948, 2873, 2227, 1712, 1653, 1606, 1524, 1495, 1394, 1279, 1248, 1182, 1115
2939, 2860, 2227, 1711, 1853, 1606, 1523, 1495, 1390, 1279, 1248, 1182, 1115
2939, 2858, 2227, 1711, 1653, 1606, 1523, 1496, 1396, 1279, 1247, 1182, 1115
2937, 2858, 2227, 1714, 1653, 1606, 1523, 1496, 1389, 1279, 1248, 1182, 1115
2937, 2858, 2227, 1711, 1655, 1606, 1525, 1495, 1390, 1279, 1248, 1182, 1115
2931, 2858, 2227, 1711, 1653, 1606, 1523, 1495, 1390, 1279, 1248, 1182, 1115
2931, 2856, 2227, 1709, 1653, 1606, 1523, 1495, 1389, 1279, 1248, 1182, 1115
2929, 2856, 2227, 1711, 1651, 1606, 1525, 1495, 1390, 1279, 1248, 1182, 1115
summarized in Table 3. The absorptions of 1 at d 5.88, 5.08, and 5.02
were assigned to the vinyl group.
The thermal mesomorphic phases of 1 (n ¼ 3–12) were analyzed by
means of DSC and polarizing microscopy. The transition properties
are summarized in Table 4. Compounds (1) (except for n ¼ 4) exhibited
enantiotropic liquid crystalline behavior, although 1 (n ¼ 4) exhibited
the nematic phase only upon cooling. Compounds (1) (n ¼ 3–6) dis-
played only nematic liquid crystalline behavior, while 1 (n ¼ 7, 8, 10,
and 12) manifested both the nematic and smectic phases and 1 (n ¼ 9
and 11) showed only the smectic phase. Figure 3 shows the representa-
tive polarizing microscopic images of 1. The nematic phase of 1 (n ¼ 3)
had a Schlieren optical texture (Fig. 3A). The smectic phase of 1 (n ¼ 9)
(Fig. 3B) had a focal-conic fan texture, which was characteristic of smec-
tic A. It is known that BCBOn [5] and 2 [7] exhibit only nematic liquid
crystalline behavior. Therefore, the formation of the smectic phase of
1 may result from the existence of the vinyl group.
The polarizing microscopy observations substantiated the formation
of the nematic and smectic A phases of 1 (n ¼ 7). Figures 3c and d
shows the optical textures of the smectic A phase at 136ꢁC and the
nematic phase at 155ꢁC upon heating, respectively. However, it was
not easy to find the SmA-N transition peak in the DSC thermogram
because the peak was very small. Figure 4 shows the enlarged DSC
thermogram of 1 (n ¼ 7). In contrast to the very small peak of the
SmA-N transition of 1 (n ¼ 7), the DSC thermograms of 1 (n ¼ 8, 10,
and 12) showed distinct peaks of the SmA-N transition, although the
smectic phase of 1 (n ¼ 8) was found only upon cooling. Figures 3e, f
shows the optical textures of the smectic A phase at 105ꢁC and the
nematic phase at 111ꢁC for 1 (n ¼ 10) upon heating, respectively.
The difference in the SmA-N transitions between 1 (n ¼ 7) and

Vinyl-Substituted Liquid Crystal Dimers
7
TABLE 3 1H-NMR Spectral Data of Compounds (1)
n
3
d=CDCl3
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 7.00(d, 2H, J ¼ 8 Hz),
6.98(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.56(t,2H, J ¼ 6.5 Hz), 4.21(t, 2H, J ¼ 6.5 Hz), 4.03(t,
2H, J ¼ 6.5 Hz), 2.31(quintet, 2H, J ¼ 6.5 Hz), 2.27(q, 2H, J ¼ 6.5 Hz), 1.92(quin-
tet, 2H, J ¼ 6.5 Hz).
4
8.06(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.99(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.35(broad t, 2H), 4.11(broad t, 2H), 4.03(t, 2H,
J ¼ 6.5 Hz), 2.27(q, 2H, J ¼ 6.5 Hz), 2.01(broad m, 4H), 1.92(quintet, 2H,
J ¼ 6.5 Hz).
5
6
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.38(t, 2H, J ¼ 6.5 Hz), 4.05(t, 2H, J ¼ 6.5 Hz), 4.03(t,
2H, J ¼ 6.5 Hz), 2.27(q, 2H, J ¼ 6.5 Hz), 1.96-1.85(m, 6H), 1.68(quintet, 2H).
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.62(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.36(t, 2H, J ¼ 6.5 Hz), 4.03(t, 2H, J ¼ 6.5 Hz), 4.02(t,
2H, J ¼ 6.5 Hz), 2.27(q, 2H, J ¼ 6.5 Hz), 1.92(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.5(m, 4H).
7
8
9
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.62(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.35(t, 2H, J ¼ 6.5 Hz), 4.02(t, 2H, J ¼ 6.5 Hz), 4.01(t,
2H, J ¼ 6.5 Hz), 2.27(q, 2H, J ¼ 6.5 Hz), 1.92(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.4(m, 6H).
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.62(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.34(t, 2H, J ¼ 6.5 Hz), 4.02(t, 2H, J ¼ 6.5 Hz), 4.01(t,
2H, J ¼ 6.5 Hz), 2.26(q, 2H, J ¼ 6.5 Hz), 1.92(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.4(m, 8H).
8.07(d, 2H, J ¼ 8 Hz), 7.68(d, 2H, J ¼ 8 Hz), 7.62(d, 2H, J ¼ 8 Hz), 7.60(d, 2H,
J ¼ 8 Hz), 7.54(d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.36(t, 2H, J ¼ 6.5 Hz), 4.03(t, 2H, J ¼ 6.5 Hz), 4.02(t,
2H, J ¼ 6.5 Hz), 2.26(q, 2H, J ¼ 6.5 Hz), 1.92(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.3(m, 10H).
(Continued)

8
T. Itahara and J. Inadome
TABLE 3 Continued
n
d=CDCl3
10 8.07(d, 2H, J ¼ 8 Hz), 7.69(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.61(d, 2H,
J ¼ 8 Hz), 7.55(d, 2H, J ¼ 8 Hz), 7.52(d, 2H, J ¼ 8 Hz), 6.98(d, 2H, J ¼ 8 Hz),
6.97(d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.33(t, 2H, J ¼ 6.5 Hz), 4.02(t, 2H, J ¼ 6.5 Hz), 4.00(t,
2H, J ¼ 6.5 Hz), 2.26(q, 2H, J ¼ 6.5 Hz), 1.91(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.3(m, 12H).
11 8.07(d, 2H, J ¼ 8 Hz), 7.69(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.61(d, 2H,
J ¼ 8 Hz), 7.55 (d, 2H, J ¼ 8 Hz), 7.51(d, 2H, J ¼ 8 Hz), 6.99(d, 2H, J ¼ 8 Hz),
6.98 (d, 2H, J ¼ 8 Hz), 5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd,
1H, J ¼ 12 Hz, J ¼ 2 Hz), 4.33(t, 2H, J ¼ 6.5 Hz), 4.02 (t, 2H, J ¼ 6.5 Hz), 4.00(t,
2H, J ¼ 6.5 Hz), 2.26(q, 2H, J ¼ 6.5 Hz), 1.92(quintet, 2H, J ¼ 6.5 Hz), 1.84-
1.74(m, 4H), 1.6-1.3(m, 14H).
12 8.07(d, 2H, J ¼ 8 Hz), 7.69(d, 2H, J ¼ 8 Hz), 7.63(d, 2H, J ¼ 8 Hz), 7.61(d, 2H,
J ¼ 8 Hz), 7.55 (d, 2H, J ¼ 8 Hz), 7.52(d, 2H, J ¼ 8 Hz), 6.98(d, 4H, J ¼ 8 Hz),
5.88(m, 1H), 5.08(dd, 1H, J ¼ 16 Hz, J ¼ 2 Hz), 5.02(dd, 1H, J ¼ 12 Hz, J ¼ 2 Hz),
4.33(t, 2H, J ¼ 6.5 Hz), 4.02 (t, 2H, J ¼ 6.5 Hz), 4.00(t, 2H, J ¼ 6.5 Hz), 2.26(q,
2H, J ¼ 6.5 Hz), 1.91(quintet, 2H, J ¼ 6.5 Hz), 1.84-1.74(m, 4H), 1.6-1.3(m, 16H).
1 (n ¼ 8, 10, and 12) may be related to an odd–even effect, depending
on the number (n) of methylene units of the polymethylene group of 1.
Figure 5 shows the dependence of the liquid crystal phases on the
number (n) of methylene units of the polymethylene group of 1. The
nematic-isotropic and smectic-isotropic transition temperatures
TABLE 4 Transitional Properties of Compounds (1)
n
k
T
M=ꢁC
T
SN=ꢁC
T
SI=ꢁC
T
NI=ꢁC DSM=R DSSN=R DSSI=R DSNI=R
3
6
7
8
157
131
125
105
134
108
118
103
101
97
203
10.58
12.92
11.06
9.56
8.48
8.22
10.06
8.94
9.72
1.36
(0.18)
1.51
0.20
1.72
0.22
4
5
6
7
8
9
(115)
182
118
164
119
9
10
11
12
137
(100)
0.06
(0.46)
155
149
3.19
3.27
10 13
11 14
12 15
110
122
122
0.98
0.55
0.60
0.62
112
9.35
n: the number of methylene units of the polymethylene chain of 1. k ¼ n þ 3: the num-
ber of atoms in the flexible spacer of 1. M: melting point. SN: smectic-nematic transition.
SI: smectic-isotropic transition. NI: nematic-isotropic transition. Parentheses indicate
monotropic transitions.

Vinyl-Substituted Liquid Crystal Dimers
9
FIGURE 3 Representative polarizing microscopic images of compounds (1).
A: Compound (1) (n ¼ 3) at 199ꢁC upon cooling. B: Compound (1) (n ¼ 9)
at 151ꢁC upon cooling. C: Compound (1) (n ¼ 7) at 136ꢁC upon heating. D:
Compound (1) (n ¼ 7) at 155ꢁC upon heating. E: Compound (1) (n ¼ 10) at
105ꢁC upon heating. F: Compound (1) (n ¼ 10) at 111ꢁC upon heating.
exhibited an odd–even effect as the number (n) of methylene units was
varied, in which the odd numbers exhibited higher values. However,
the number (k) of atoms in the flexible spacer of 1 is n þ 3. Therefore,
the results indicate that even numbers of atoms in the flexible spacer
exhibit higher values, and are consistent with the known odd–even
effect of liquid crystal dimers [1–5].
The thermodynamic data of 1 were compared with those of BCBOn
[5] and the liquid crystal trimers (2) [7]. Figure 6 shows the depen-
dence of the entropy changes associated with the nematic-isotropic
and smectic-isotropic transitions (DSNI=R and DSSI=R) on the number
(k) of atoms in the flexible spacers for 1, BCBOn, and 2. In Fig. 6, the
abscissa indicates the number (k) of atoms in the flexible spacers of 1,
BCBOn, and 2. That is to say, k is n þ 3 for 1, k is n þ 2 for BCBOn,

10
T. Itahara and J. Inadome
FIGURE 4 DSC thermogram of compound (1) (n ¼ 7), obtained upon second
heating and cooling at a rate of 5ꢁC=min.
FIGURE 5 Dependence of liquid crystal phases on number (n) of methylene
units of polymethylene chain for compounds (1) upon heating. C: crystal.
N: nematic. SA: smectic A. I: isotropic liquid. Compound (1) (n ¼ 4) showed
the nematic phase upon cooling at 115ꢁC. Compound (1) (n ¼ 8) showed the
smectic A phase upon cooling at 100ꢁC.

Vinyl-Substituted Liquid Crystal Dimers
11
FIGURE 6 Dependence of entropy change associated with nematic-isotropic
and smectic-isotropic transitions on number (k) of atoms in flexible spacers
for compounds (1), BCBOn, and trimers (2). k ¼ n þ 3 for 1, k ¼ n þ 2 for
BCBOn, and k ¼ n þ 2 for 2. &: Nematic-isotropic transition (except for
k ¼ 12 and 14) and smectic-isotropic transition (k ¼ 12 and 14) of 1. .:
Nematic-isotropic transition of BCBOn. ~: Nematic-isotropic transition of 2.
and k is n þ 2 for 2. Figure 6 unquestionably shows an odd–even effect
of DSNI=R and DSSI=R for 1 as the number of atoms in the flexible
spacers is varied, in which the even members exhibit higher values.
The odd–even effect of 1 resembles those of BCBOn and 2 very much.
However, it can be seen from Fig. 6 that the values of DSNI=R of 1 are
clearly lower than those of BCBOn and 2. The differences between 1
and BCBOn may result from the polarizability and shape of liquid
crystal dimers. Furthermore, the values of DSNI=R of 1 are about half
those of 2, although Imrie et al. have already reported similar thermo-
dynamic behavior of liquid crystal dimers and trimers [8–10].
CONCLUSION
A series of vinyl-substituted liquid crystal dimers (1) were prepared.
The compounds (1) (n ¼ 3–6) exhibited only nematic liquid crystalline
behavior, while 1 (n ¼ 7, 8, 10, and 12) showed both the nematic and

12
T. Itahara and J. Inadome
smectic phases and 1 (n ¼ 9 and 11) showed only the smectic phase.
The entropy change associated with the smectic-nematic transition
of 1 (n ¼ 7) was very small, compared with those of 1 (n ¼ 8, 10, and
12). The liquid crystalline properties of 1 were compared with those
of BCBOn and the trimers (2). Since BCBOn and 2 show the nematic
phase but no smectic phase, the formation of the smectic phase of 1
may result from the existence of the vinyl group. The entropy changes
associated with the nematic-isotropic and smectic-isotropic transitions
of 1 definitely exhibited an odd–even effect as the number (k) of atoms
in the flexible spacers was varied, in which the even numbers exhib-
ited higher values. The odd–even effects of 1 resembled those of
BCBOn and 2, but the entropy changes associated with the nematic-
isotropic transition of 1 exhibited lower values in comparison with
those of BCBOn and 2. The values of 1 were about half those of 2.
These results are consistent with the odd–even effects seen in the
transitional behavior of the known liquid crystal dimers and trimers
[1, 8–10].
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