A display device containing a liquid crystal compound has been widely used for a display for a watch, a calculator, a word processor and so forth. The display devices utilize an optical anisotropy, a dielectric anisotropy and so forth of the liquid crystal compound.
A liquid crystal phase includes a nematic liquid crystal phase, a smectic liquid crystal phase or a cholesteric liquid crystal phase, and the liquid crystal phase utilizing the nematic liquid crystal phase has been most widely used. Moreover, a display mode includes a mode such as dynamic scattering (DS), deformed aligned phase (DAP), guest/host (GH), twisted nematic (TN), super twisted nematic (STN), thin film transistor (TFT), vertical alignment (VA), in-plane switching (IPS) and polymer sustained alignment (PSA).
The liquid crystal compound used according to the display modes should show a liquid crystal phase in a wide temperature range centering on room temperature, be sufficiently stable under conditions where the display device is used, and have sufficient characteristics for driving the display device. However, a single liquid crystal compound satisfying the conditions has not been found at present.
Therefore, a liquid crystal composition with required characteristics is actually prepared by mixing several kinds or several tens of kinds of liquid crystal compounds. The liquid crystal compositions are required to be stable to moisture, light, heat and air ordinarily present under conditions where the display device is used, and stable also to an electric field or electromagnetic radiation and chemically stable to a compound to be mixed. Moreover, the liquid crystal composition is needed to have a suitable value in characteristics such as an optical anisotropy (Δn) and a dielectric anisotropy (As) depending on the display mode or a shape of the display device. Furthermore, having a good solubility with each other is important in each component in the liquid crystal composition.
In order to perform a good liquid crystal display, cell thickness of the liquid crystal display device constituting the display, and a value of the optical anisotropy of the liquid crystal composition to be used are preferably constant (E. Jakeman et al., Phys. Lett., 39A. 69 (1972)). Moreover, a response speed of the liquid crystal display device is inversely proportional to a square of thickness of a cell used. Therefore, the device should have a liquid crystal composition having a large value of the optical anisotropy in order to manufacture a liquid crystal display device applicable also to moving images and so forth and allowing a high speed response. A variety of compounds have been developed as a liquid crystal compound having a large value of the optical anisotropy. However, generally, such a compound having a large optical anisotropy is difficult to use as a constituent of a liquid crystal composition having good electric characteristics because the compound has a highly conjugated molecular structure and tends to have a poor compatibility with other liquid crystal compounds. Furthermore, a high stability is required for a liquid crystal compound used as a constituent of a liquid crystal composition in which a high insulation (specific resistance) is required for a liquid crystal display device according to a thin film transistor mode and so forth.
Moreover, among the operating modes as described above, an IPS mode, a VA mode, a PSA mode and so forth is an operating mode utilizing homeotropic alignment of liquid crystal molecules, and is known to allow improvement of a limited viewing angle being a defect of an existing display mode such as a TN mode and an STN mode.
Then, a large number of liquid crystal compounds in which hydrogen on a benzene ring is replaced by fluorine have been examined as a component of a liquid crystal composition that can be conventionally used for a liquid crystal display device according to the operating modes and has a negative dielectric anisotropy (see Patent literature No. 1 to No. 8).
For example, compound (s-1) in which hydrogen on a benzene ring is replaced by fluorine and that has alkyl in a side chain has been examined in Patent literature No. 1, and compound (s-2) in which hydrogen on a benzene ring is replaced by fluorine and that has alkenyl in a side chain has been examined in Patent literature No. 2.

However, compound (s-1) has a small dielectric anisotropy and even compound (s-2) has no sufficient magnitude of the dielectric anisotropy. Moreover, as a compound having alkyl in a side chain and having a polar group such as halogen in a lateral group, compound (s-3) is disclosed in Patent literature No. 3, and compound (s-4) and compound (s-5) are disclosed in Patent literatures No. 4 to No. 7.
In addition, compound (s-6) having alkoxy in both side chains and having a polar group such as halogen in a lateral group is disclosed in Patent literature No. 8. However, as in the invention, a two-ring compound having alkoxy or alkenyloxy in both side chains or a three-ring compound having 2,3-dihalogeno-1,4-phenylene in a center ring and having alkoxy or alkenyloxy in both side chains is not disclosed.

Furthermore, because compound (s-3) has a very small dielectric anisotropy, a liquid crystal display device cannot be driven by a liquid crystal composition containing compound (s-3). Moreover, compound (s-4) and compound (s-5) have no sufficiently large dielectric anisotropy and a low compatibility with other liquid crystal compounds, and therefore only a small amount of compound (s-4) and compound (s-5) can be contained in the liquid crystal composition. Furthermore, compound (s-6) has a small optical anisotropy and a high viscosity, and therefore, a liquid crystal composition containing compound (s-6) has points requiring a further improvement, such as incapability of decreasing a driving voltage thereof.