A display device using a liquid crystal compound is widely utilized for a display of a watch, a calculator, a word processor and so forth. The display devices utilize refractive index anisotropy, dielectric anisotropy or the like of the liquid crystal compound.
A liquid crystal phase includes a nematic liquid crystal phase, a smectic liquid crystal phase and a cholesteric liquid crystal phase, but a device utilizing the nematic liquid crystal phase is most widely used. Moreover, examples of display modes include a dynamic scattering (DS) mode, a deformation of aligned phases (DAP) mode, a guest/host (GH) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a thin film transistor (TFT) mode, a vertical alignment (VA) mode, an in-plane switching (IPS) mode and a polymer sustained alignment (PSA) mode.
The liquid crystal compound used in the display modes should show the liquid crystal phase in a wide temperature range centering on room temperature, be sufficiently stable under an environment in which the display device is used, and have sufficient characteristics for driving the display device, but any single liquid crystal compound satisfying the conditions is not currently found.
Consequently, a liquid crystal composition having required characteristics is prepared by mixing several kinds to tens of kinds of liquid crystal compounds under an actual situation. The liquid crystal compositions are required to be stable to moisture, light, heat or air ordinarily present under conditions in which the display device is used, and also stable to an electric field or electromagnetic radiation, and also chemically stable to a compound to be mixed. Moreover, the liquid crystal composition is required to have suitable values of various physical properties such as refractive index anisotropy (Δn) and dielectric anisotropy (Δ∈) depending on the display mode or a shape of the display device. Furthermore, each component in the liquid crystal composition should have a good solubility with each other as an important requirement.
As a mode for overcoming narrowness of viewing angle being a biggest problem of a liquid crystal display device, among the display modes, a mode such as the IPS mode, the VA mode, the OCB mode and the PSA mode has attracted attention in recent years. Among the liquid crystal display devices having the modes, in particular, a device having the VA mode or the IPS mode has been actively developed because such a device has a wide viewing angle and also an excellent responsiveness, and further achieves a high contrast display. Features of the liquid crystal composition used for the liquid crystal display devices having the display modes are in a negative dielectric anisotropy (Δ∈). Then, a liquid crystal composition having a large negative dielectric anisotropy (Δ∈) is known to allow a decrease in a driving voltage of a liquid crystal display device including the liquid crystal composition (Non-patent literature No. 1). Therefore, the liquid crystal compound being a constituent of the liquid crystal composition is also required to have a larger negative dielectric anisotropy (Δ∈).
As a component of the liquid crystal composition having a negative dielectric anisotropy (Δ∈), a liquid crystal compound having a fluorine-substituted phenanthrene ring or a fluorine-substituted dihydrophenanthrene ring has been examined so far (Patent literature No. 1, 2, 3, 4 or 5).
In JP H8-53672 A (Patent literature No. 1), a compound as described below is proposed, but dielectric anisotropy (Δ∈) is not large.

In JP 2005-325113 A (Patent literature No. 2), a compound as described below is proposed, but is unsuitable as a liquid crystal compound because a shape of a molecule is nonlinear.

In U.S. Pat. No. 6,929,834 B (Patent literature No. 3), a liquid crystal composition using a compound represented by formula (a) is proposed.

In the formula, L1 and L2 are independently hydrogen or fluorine. The compound represented by formula (a) has a large negative dielectric anisotropy (Δ∈), but is not sufficient in order to decrease a driving voltage of a liquid crystal display device having the VA mode, the IPS mode or the like. Moreover, the compound generally has a significantly low solubility, and is unstable to light.
In JP 2006-520327 A (Patent literature No. 4), benzochromene derivative (b) is proposed.

In the formula, Y is —CO—, —CS—, —CH2—, —CF2— or —CHF—, and L1 and L2 are independently hydrogen, fluorine, chlorine or —CN. When Y is —CF2—, and L1 and L2 are fluorine, the derivative has a large negative dielectric anisotropy (Δ∈), but a basic skeleton is different from the art of the invention.
In JP H11-508890 A (Patent literature No. 5), a fluorine-substituted dihydrophenanthrene derivative represented by formula (C) is proposed.

In the formula, E1, E2, E3, E4, E5 and E6 are independently —CF— or —CH—, and G is —CF2CF2— or —CF═CF—.
In Examples in the identical Patent literature, compounds as described below are disclosed. However, no Examples of a compound having fluorine on 1-position and 8-position of a 9,10-dihydrophenanthrene ring are found, and physical properties thereof are not explained, either.

In order to decrease the driving voltage of a liquid crystal display device having the VA mode, the IPS mode or the like, a liquid crystal compound having a larger negative dielectric anisotropy (Δ∈), a liquid crystal composition and a liquid crystal display device are desired.
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