Novel nematic liquid crystalline compounds having a tetrahydropyrane ring

Article abstract of DOI:10.1080/15421400802430042

A series of novel liquid crystalline compounds with a tetrahydropyrane ring were synthesized, and the physical properties have been measured. The compounds showed peculiar dependency of the dielectric anisotropy value on the connecting position of the tet

Full text of DOI:10.1080/15421400802430042

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Novel Nematic Liquid
Crystalline Compounds Having
A Tetrahydropyrane Ring
Mayumi Goto a , Tokifumi Masukawa a , Tomoyuki
Kondo a & Atsuko Fujita a
a Chisso Petrochemical Corporation, Goi Research
Center , Chiba, Japan
Published online: 05 Apr 2011.
To cite this article: Mayumi Goto , Tokifumi Masukawa , Tomoyuki Kondo &
Atsuko Fujita (2008) Novel Nematic Liquid Crystalline Compounds Having A
Tetrahydropyrane Ring, Molecular Crystals and Liquid Crystals, 494:1, 58-67, DOI:
10.1080/15421400802430042
To link to this article: http://dx.doi.org/10.1080/15421400802430042
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Mol. Cryst. Liq. Cryst., Vol. 494, pp. 58–67, 2008
Copyright # Taylor & Francis Group, LLC
ISSN: 1542-1406 print=1563-5287 online
DOI: 10.1080/15421400802430042
Novel Nematic Liquid Crystalline Compounds Having
A Tetrahydropyrane Ring
Mayumi Goto, Tokifumi Masukawa, Tomoyuki Kondo,
and Atsuko Fujita
Chisso Petrochemical Corporation, Goi Research Center,
Chiba, Japan
A series of novel liquid crystalline compounds with a tetrahydropyrane ring were
synthesized, and the physical properties have been measured. The compounds
showed peculiar dependency of the dielectric anisotropy value on the connecting
position of the tetrahydropyrane ring. This positional dependency is discussed
with the measurement of the temperature dependency of the dielectric constants,
and the semi empirical quantum calculation. In accordance with the experimental
result, it was found that the difference of the dielectric anisotropy value is influ-
enced by the difference of the dipole moment value and the direction of the dipole
at the most stable conformation.
Keywords: negative dielectric anisotropy; structural dependency; tetrahydropyrane
derivatives; VA-LCDS
INTRODUCTION
Active matrix liquid crystal displays (AM-LCDs) have been applied to
various kinds of display, such as PC monitors, TVs, and cellular
phones. The required characteristics for liquid crystalline materials
are low driving voltage and quick response, and wide viewing angle.
The viewing-angle dependency has been significantly improved
through new display technologies, namely the vertical alignment
(VA) modes [1–3], applying liquid crystalline materials with large
negative dielectric anisotropy (De).
Usually, the nematic liquid crystal compounds are made up of a
benzene ring, a cyclohexane ring, a dioxane ring, and a pyrimidine
Address correspondence to Mayumi Goto, Chisso Petrochemical Corporation, Goi
Research Center I, 5-1 Goikaigan Ichihara, Chiba 290-8551, Japan. E-mail: m.furuya@
chisso.co.jp
58

LC Compounds Having a Tetrahydropyrane Ring
59
ring, etc. However, since dioxane and pyrimidine rings have the
polarity along the molecule long axis, these heterocyclic rings are
not suitable as a structural fragment for the negative De materials.
To expand the possibility of the combination of the kind of the ring
systems, a heterocyclic ring which can be applied for negative com-
pounds has been demanded. Here, we took notice of a tetrahydropyr-
ane ring, which has a polarity along the vertical direction to the
molecule long axis.
Liquid crystalline compounds with a tetrahydropyrane ring and
their preparation have been reported recently [4–8]. However, nega-
tive De-type tetrahydropyrane compounds have not been reported up
to now. Here we report the first synthesis of negative De-type com-
pounds having a tetrahydropyrane ring system (compounds 1–4),
and their physical properties. These compounds show peculiar depen-
dency of De values on the substitution position of the tetrahydropyrane
ring. In addition, we have investigated temperature dependency of
the dielectric constants, and calculated rotational barrier, dipole
moment and the angle of dipole moment by utilizing the semi-empirical
quantum calculation method.
SYNTHESIS
Compounds 1 and 3 have been prepared as shown in Figure 1. Alde-
hyde A was converted into Lactone B through the protection with
the amine, Michael addition, deprotection, reduction of the formyl moi-
ety, and cyclization. Compounds 1 and 3 were finally obtained through
coupling reaction with the lithium reagent and reduction, with a
10 ꢀ 15% yield (6 steps).
The synthetic method of compound 2 is shown in Figure 2. Lactone
C was prepared in the same manner as described in Figure 1.
Compound 2 was obtained through coupling reaction with pentynyl
lithium, dehydration, and hydrogenation, with a 48% yield (3 steps).
Compound 4 was synthesized as shown in Figure 3. Oxetane D
was converted into Lactone E through the coupling reaction, and
hydrolysis, then cyclization. After this, compound 4 was obtained
through two fold reductions, with a 10% yield (4 steps).
The NMR spectra is identical to the compounds 1–4.
1: 1H-NMR: d(ppm, CDCl3) 0.89 (t, J ¼ 7.2 Hz, 3H), 1.09–1.68 (m, 12H),
1.83–1.87 (m, 2H), 1.95–1.99 (m, 2H), 3.22 (t, J ¼ 11.1 Hz, 1H), 4.04–
4.07 (m, 1H), 4.11 (q, J ¼ 7.0 Hz, 2H), 4.51 (d, J ¼ 9.8 Hz,
4
1H), 6.72 (td, J ¼ 9.0 Hz, JHF ¼ 1.8 Hz, 1H), 7.10 (td, J ¼ 9.0 Hz,
4JHF ¼ 2.2 Hz, 1H).

60
M. Goto et al.
FIGURE 1 Synthetic route of compounds 1 and 3.
19F-NMR:
d(ppm, CFCl3)–144.05
(dd,
4JHF ¼ 7.6 Hz,
3JFF ¼ 19.4 Hz, 1 F), ꢁ160.50 (dd, 4JHF ¼ 7.6 Hz, 3JFF ¼ 19.8 Hz, 1 F).
MS (EI): 151 (100%), 171 (30%), 186 (60%), 312 (70%) [Mþ].
2: 1H-NMR: d(ppm, CDCl3) 0.89 (t, J ¼ 7.0 Hz, 3H), 0.90–1.53 (m, 9H),
1.71–1.79 (m, 4H), 1.94–2.00 (m, 2H), 3.03–3.11 (m, 1H), 3.28–3.36
(m, 1H), 3.39 (t, J ¼ 11.1 Hz, 1H), 3.98–4.01 (m, 1H), 4.07–4.11 (q,
4
J ¼ 7.0 Hz, 2H), 6.67 (td, J ¼ 9.0 Hz, JHF ¼ 1.8 Hz, 1H), 6.81 (td,
4
J ¼ 9.0 Hz, JHF ¼ 1.8 Hz, 1H).
19F-NMR:
d(ppm,
CFCl3)–142.36
(dd,
4JHF ¼ 7.4 Hz,
3JFF ¼ 19.8 Hz, 1 F), ꢁ159.56 (dd, 4JHF ¼ 7.6 Hz, 3JFF ¼ 19.9 Hz, 1 F).
MS (EI): 156 (100%), 184 (50%), 197 (40%), 241 (25%), 312
(20%) [Mþ].
3: 1H-NMR: d(ppm, CDCl3) 0.87 (t, J ¼ 7.3 Hz, 3H), 0.95–1.58 (m,
16H), 1.71–1.79 (m, 4H), 1.86–1.99 (m, 2H), 3.34 (t, J ¼ 11.1 Hz,
1H), 4.10 (q, J ¼ 7.0 Hz, 2H), 4.13–4.17 (m, 1H), 4.48 (d,
4
J ¼ 11.2 Hz, 1H), 6.71 (td, J ¼ 8.9 Hz, JHF ¼ 1.5 Hz, 1H), 7.10 (td,
4
J ¼ 9.4 Hz, JHF ¼ 2.1 Hz, 1H).
19F-NMR:
d(ppm,
CFCl3)–144.11
(dd,
4JHF ¼ 7.5 Hz,
3JFF ¼ 19.8 Hz, 1 F), ꢁ160.55 (dd, 4JHF ¼ 8.0 Hz, 3JFF ¼ 20.2 Hz, 1 F).
MS (EI): 156 (30%), 184 (15%), 366 (100%) [Mþ].
FIGURE 2 Synthetic route of compound 2.

LC Compounds Having a Tetrahydropyrane Ring
61
FIGURE 3 Synthetic route of compound 4.
4: 1H-NMR: d(ppm, CDCl3) 0.88 (t, J ¼ 7.2 Hz, 3H), 0.90–1.53 (m,
16H), 1.71–1.79 (m, 4H), 1.94–2.00 (m, 2H), 3.05–3.09 (m, 1H),
3.37 (t, J ¼ 11.0 Hz, 1H), 3.98–4.02 (m, 1H), 4.08 (q, J ¼ 7.0 Hz,
4
2H), 6.67 (td, J ¼ 8.9 Hz, JHF ¼ 1.8 Hz, 1H), 6.81 (td, J ¼ 9.3 Hz,
4JHF ¼ 2.2 Hz, 1H).
19F-NMR:
d(ppm,
CFCl3)–142.35
(dd,
4JHF ¼ 7.3 Hz,
3JFF ¼ 19.9 Hz, 1 F), ꢁ159.55 (dd, 4JHF ¼ 7.6 Hz, 3JFF ¼ 19.9 Hz, 1 F).
MS (EI): 184 (30%), 197 (100%), 241 (80%), 366 (20%) [Mþ].
RESULTS AND DISCUSSION
Physical Properties
Transition temperatures of compounds 1–4 are shown in Table 1
together with those of reference compounds ref. 1 and ref. 2. As
shown in Table 1, compounds 3 and 4 have a nematic phase, moreover,
compound 3 also has a monotropic smectic phase. On the other hand,
compounds 1 and 2 don’t have any mesophase.
Table 2 shows the nematic-isotropic transition temperature (TNI),
De, and optical anisotropy (Dn) of the synthesized compounds along
with the reference compounds ref. 1 and ref. 2, which were estimated
by the linear extrapolation method using a nematic mixture (Host
Mixture), consisting of phenyl cyclohexylcarboxylates. (Most com-
pounds don’t exhibit nematic phase at room temperature, so the linear
extrapolation method is available for comparison [9].)
The TNI values of compounds 1 and 2 are lower than that of compound
ref. 1. Interestingly, compound 1 showed a lower magnitude of De and
compound 2 showed a higher magnitude of De, than that of compound
ref. 1. A similar tendency was observed in the comparison of the three
ring compounds 3, 4, and ref. 2. The synthesized compounds exhibit

62
M. Goto et al.
TABLE 1 Transition Temperatures of the compounds 1–4, ref. 1, and ref. 2
Transition temperature (ꢂC)
1
Cr ꢃ 56.4 ꢃ Iso
2
Cr ꢃ 50.6 ꢃ Iso
3
Cr ꢃ 107.7 (ꢃ SmB ꢃ 94.6) ꢃ N ꢃ 164.0 ꢃ Iso
Cr ꢃ 65.5 ꢃ N ꢃ 139.7 ꢃ Iso
Cr ꢃ 51.6 ꢃ Iso
4
ref. 1
ref. 2
Cr ꢃ 66.9 ꢃ SmB ꢃ 79.9 ꢃ N ꢃ 185.1 ꢃ Iso
slightly lower Dn values than those of the cyclohexane derivatives ref. 1,
ref. 2, which would indicate that the tetrahydropyrane ring works in the
direction to decrease the optical anisotropy of the molecules.
Temperature Dependency of the Dielectric Constants
e
and e//
?
For meaningful comparison of the De values of compounds 1, 2, and
ref. 1, as well as compounds 3, 4, and ref. 2 possessing the different
nematic-isotropic transition temperatures, we examined the tempera-
ture dependency of the dielectric constants.
The temperature dependency of the dielectric constants e and e
?
k
were examined with the following methods (e and e are the respec-
k
?
tive dielectric constants parallel and perpendicular to the nematic
direction). The dielectric constants e and e of the samples each
?
k
containing 15 wt% of compounds 1–4, ref. 1, ref. 2, and 85 wt%
of the Host Mixture, were measured at various temperatures. The
graphs of the temperature dependence of e and e were made by
?
k
utilizing the extrapolated data based on the measured data and
the constant reduced temperature T=Tc (Tc: nematic-isotropic

LC Compounds Having a Tetrahydropyrane Ring
63
TABLE 2 Physical properties of the compounds 1–4, ref. 1, and ref. 2
TNI (ꢂC)
De
Dn
1
4.6
ꢁ 3.3
0.067
2
ꢁ14.7
138.6
121.3
17.3
ꢁ8.3
ꢁ3.8
ꢁ7.3
ꢁ6.3
ꢁ5.4
ꢁ1.3
0.063
0.112
0.107
0.074
0.114
0.087
3
4
ref. 1
ref. 2
158.7
74.6
Host Mixture
i) Extrapolated data from mixtures containing 15 wt% of the synthesized compounds
in Host Mixture 85 wt%.
ii) Measurement temperature of De and Dn; 25ꢂC.
transition temperature) [10]. Two graphs for the compounds 1, 2, and
ref. 1, and the compounds 3, 4, and ref. 2 are shown as 4-1 and 4-2
in Figure 4.
As shown in Figure 4, the e values for all of the samples are
k
temperature independent, while the e values are greater in the lower
?

64
M. Goto et al.
FIGURE 4 Temperature dependence of the dielectric constants e and e==.
?
temperature region, and decrease gradually with increasing tempera-
ture. This means that the De values greatly depend on the e values.
?
By comparison of the e curves of compounds 1, 2, and ref. 1, com-
?
pound 2 exhibited higher e values over the entire temperature region.
?
The same tendency was found in the case of compounds 3, 4, and ref. 2.
The Calculation of the Comformations
The interesting observed relationship between the De values and the
structure of the synthesized compounds was studied applying a
computer-aided calculation. It was presumed that the position of
the oxygen atom in the tetrahydropyrane ring greatly influences the
stable conformation of each compound. To examine the conformations
of compounds 1–4, the rotational barrier has been calculated by
utilizing the semi-empirical quantum calculation method MOPAC=
AM1 [11]. The calculated heat of formation at each 30 degree of
0 ꢀ 360 degree dihedral angle (a, b, c, d) is shown in Figure 5.
As shown in Figure 5, the DH depends on the dihedral angle, and
the conformations of compounds 1-4 were most stabilized at around
0ꢀ60 degrees. In Figure 5-2 and 5-4, the conformations of compounds
2, 4 were also stabilized at 180 degree. On the other hand, in
Figures 5-1 and 5-3, compounds 1, 3 exhibited unstable conformations

LC Compounds Having a Tetrahydropyrane Ring
65
FIGURE 5 Rotational barrier in different conformations.
at 180 degrees. It is expected that the electric repulsion between
the oxygen atom and the fluorine atom influences the stability of the
corresponding conformations of compounds 1 and 3 at 180 degrees.
The Calculation of the Dipole Moment and the Angle
of the Dipole Moment
The values of the dipole moment m and the angle of the dipole moment
b at the most stable formations have been calculated. The results are
shown in Table 3.
Maximum b (90 degrees) indicates that the dipole moment is exactly
parallel to the molecular short axis. Compounds having b close to 90
degrees and larger dipole moment m exhibit greater negative De [12].

66
M. Goto et al.
TABLE 3 The calculated data of DH, m, b at the most stable formation
Dihedral angle
(degree)
DH (kcal=mol) m (Debye) b (degree)
1
30
ꢁ 196.38
ꢁ197.19
3.50
61.3
2
3
0
4.50
3.50
89.0
63.0
0 ꢀ 60
ꢁ210.88
(averageꢄ)
(averageꢄ) (averageꢄ)
4
0
ꢁ212.62
4.49
89.4
ꢄThese are mean values of three points at 0, 30, and 60 degree.
As shown in Table 3, the significant differences between compounds 1,
3 and 2, 4 were observed. Since the m and b values of compounds 1 and
3 were smaller, they should exhibit lower negative De. On the other
hand, compounds 2 and 4 showed larger values of m and b, that can
induce greater negative De.
The 3D models of compounds 3 and 4 at their most stable confor-
mation are shown in Figure 6. As shown in Table 3 and Figure 6, there
is a close relation between the m and b values, and the molecular struc-
ture. In compounds 1 and 3, since the lone-pair electron of the oxygen
atom faces to the different direction of the fluorine atoms, it causes the
decrease of the total dipole and the total angle of the dipole moment.
On the other hand, as to compounds 2 and 4, the direction of the
lone-pair electron of the oxygen atom is on the same side as the
FIGURE 6 The 3D models of the compounds 3 and 4 at the most stable
conformation.

LC Compounds Having a Tetrahydropyrane Ring
67
fluorine atoms, inducing the greater m and b values. We considered
that this is caused by the difference of the position of the oxygen atom
in the tetrahydropyrane ring.
CONCLUSIONS
A series of novel liquid crystalline compounds with a tetrahy-
dropyrane ring has been synthesized. These compounds showed the
peculiar dependency of the dielectric anisotropy (De) values on the sub-
stitution position of the tetrahydropyrane ring. The same result was
found when measuring the temperature dependency of the dielectric
anisotropy constants e and e , and the reason of the peculiar depen-
?
k
dency of the De values has been considered based on the result of
the semi-empirical quantum calculations. Compounds 2 and 4, exhi-
biting larger negative De, are suitable for the vertical alignment
(VA) mode LCDs.
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