A new series of liquid crystals having a terminal carbonyl group

Article abstract of DOI:10.1246/cl.2000.1040

Some homologs of 5-(4-alkoxyphenyl)-1,3-dioxan-2-one exhibit a monotropic smectic A phase commencing from the pentyloxy homolog.

Full text of DOI:10.1246/cl.2000.1040

1040
Chemistry Letters 2000
A New Series of Liquid Crystals Having a Terminal Carbonyl Group
Hiroaki Okamoto,* Tsuyoshi Okamoto, and Shunsuke Takenaka
Department of Materials Science and Engineering, Faculty of Engineering, Yamaguchi University,
Tokiwadai 2557, Ube, Yamaguchi 755-8611
(Recieved March 13, 2000; CL-000243)
Some homologs of 5-(4-alkoxyphenyl)-1,3-dioxan-2-one
exhibit a monotropic smectic A phase commencing from the
pentyloxy homolog.
Dielectric anisotropy is one of the important physical
parameters of liquid crystal materials for display device.
Positive dielectric anisotropy is an inevitable requisite for the
materials for the TN mode. The dielectric properties are arised
from the dipole moment of polar functional groups within the
molecules. Therefore, a lot of liquid crystals having a terminal
polar group such as a cyano group or a nitro one have been
extensively developed.1
It has been well known that a carbonate group also has a
large dipole moment compared with the cyano and nitro ones.
Thus, we examined the effectiveness of a 1,3-dioxan-2-one core
as a composite of liquid crystal molecule. This paper describes
the synthesis and thermal properties of 5-(4-alkoxyphenyl)-1,3-
dioxan-2-one, shown below.
The smectic phase was further characterized by phase dia-
grams for the mixture of 1c and polar and nonpolar liquid crys-
tals. In Figure 1a, the smectic phase of 1c is miscible with the
smectic Ad phase of 2, and the smectic–nematic(isotropic) tran-
sition temperature shows a linear correlation with the concen-
tration of each component. In the mixtures of nonpolar liquid
crystals, 3 and 4 (Figures 1b and 1c), the smectic–nematic
(isotropic) transition temperatures show a typical phase behav-
ior frequently observed in polar-nonpolar liquid crystal mix-
tures.4 The characteristic behavior suggests that the smectic
phase of 1c is the A modification(Sm A) with a polar nature
similar to that of 2. The Sm A-I transition temperature for the
binary mixture of 1d and 2 shows a similar behavior.
Compounds 1 were prepared according to Scheme, and the
purity was checked by an elementary analysis. The chemical
structures were confirmed by 1H NMR and IR spectroscopies.2
The transition temperatures and the latent heats were deter-
mined using a Seiko SSC-5200 differential scanning calorime-
ter (DSC), where the apparatus was operated at a heating or a
cooling rate of 5 °C/min. The results are summarized in Table
1, where the the isotropic(I)–mesophase(M) transition was
determined from the cooling process. The mesophase with a
focal conic fan texture commences from the pentyloxy
homolog, and the transition temperature increases on ascending
the homolog. The mesophase was characterized from the con-
sideration of binary phase diagrams, shown in Figure 1.
It has been known that 1,3-dioxane5 and 1,3-dithiane6 cores
are important constituents for liquid crystal materials.
However, the core would be poor in polarity. On the other
Copyright © 2000 The Chemical Society of Japan

Chemistry Letters 2000
1041
hand, the 1,3-dioxan-2-one is expected to have a large dipole
moment, due to the –O–CO–O– group. In fact, the dipole
moment calculated by a semi-empirical molecular orbital calcu-
lation (CS MOPAC ver. 6.0) is 7.21 D for 1c, where the most
stable conformation at 25 °C for single molecule was calculated
by an AM1 method.
A similar calculation for 2 gives the dipole moment of 4.67
D. Therefore, we can expect that compounds 1 have a large
dielectric anisotropy similar to 2. The dielectric anisotropy for
1c determined in commercial liquid crystal mixture (3.0 w/w%
in ZLI-4792 (∆ε = 1.2(our observation), Merck) was 2.8 at 25
°C.
(2H, qui, J = 6.9 Hz), 3.44 (1H, tt, J = 10.2, 5.3 Hz), 3.94
(2H, t, J = 6.6 Hz), 4.47 (2H, t, J = 10.2 Hz, 4.53 (2H, dd, J
= 10.2, 5.3 Hz), 6.90 (2H, d, J = 8.9 Hz), 7.13(2H, d, J =
8.9 Hz) ppm. IR (KBr disc): ν = 1729 cm–1 (νCO). The
large coupling constant of the methine proton at 3.44 ppm
indicates that the methine proton is substituted at the axial
position of 1,3-dioxan-2-one. Therefore, it is assumed that
the 1,3-dioxan-2-one core has a half-chaiar form. In this
connection, it has been reported that in 4-substituted cyclo-
hexanone systems, the axial conformation with a chair
form is predominant. (R. D. Stolow, T. Groom, and P. D.
McMaster, Tetrahedron Lett., 1968, 5781.)
Further examination is now underway.
3
4
D. Demus, H. Demus, and H. Zaschke, “Flüssige Kristalle
in Tabellen,” VEB Deutscher Verlag für Grundstoff
Industrie, Leipzig (1976).
P. E. Cladis, “Physical Properties of Liquid Crystals,” ed.
by D. Demus, J. Goodby, G. W. Gray, H. -W. Spiess, and
V. Vill, Wiley–VCH, Weinheim (1999) p. 289.
References
1
L. Pohl and U. Finkenzeller, “Liquid Crystals, Application
and Uses,” ed. by B. Bahadur, World Scientific, Singapore
(1990) p. 140.
2
1c: Anal. Found: C, 68.00 %; H, 7.55%. Calcd for
C15H20O4: C, 68.16 %; H, 7.63%. 1H NMR (CDCl3, 270
MHz) δ 0.93 (3H, t, J = 7.1 Hz), 1.31–1.49 (4H, m), 1.78
5
6
H. Sorkin, Mol. Cryst. Liq. Cryst. Lett., 56, 279 (1980).
H. M. Vorbrodt, J. Vogel, H. Zascheke, G. Pelzl, and D.
Demus, Mol. Cryst. Liq. Cryst., 123, 137(1985).