A liquid crystal display device is widely utilized for a display of a personal computer, a television and so forth. The device utilizes optical anisotropy, dielectric anisotropy or the like of a liquid crystal compound. As an operating mode of the liquid crystal display device, various modes are known, such as a phase change (PC) mode, a twisted nematic (TN) mode, a super twisted nematic (STN) mode, a bistable twisted nematic (BTN) mode, an electrically controlled birefringence (ECB) mode, an optically compensated bend (OCB) mode, an in-plane switching (IPS) mode, a vertical alignment (VA) mode, a fringe field switching (FFS) mode and a polymer sustained alignment (PSA) mode.
Among the modes, the IPS mode, the FFS mode and the VA mode are known to improve narrowness of a viewing angle being a disadvantage of the operating mode such as the TN mode and the STN mode. In the liquid crystal display device having the mode of the kind, a liquid crystal composition having a negative dielectric anisotropy is mainly used. In order to further improve characteristics of the liquid crystal display device, the liquid crystal compound contained in the composition preferably has physical properties described in (1) to (8) below:    (1) high stability to heat, light and so forth;    (2) high clearing point;    (3) low minimum temperature of a liquid crystal phase;    (4) small viscosity (η);    (5) suitable optical anisotropy (Δn);    (6) large negative dielectric anisotropy (Δ∈);    (7) suitable elastic constant (K33: bend elastic constant); and    (8) excellent compatibility with other liquid crystal compounds.
An effect of the physical properties of the liquid crystal compound on the characteristics of the device is as described below. A compound having a high stability to heat, light and so forth as described in (1) increases a voltage holding ratio of the device. Thus, a service life of the device becomes long. A compound having a high clearing point as described in (2) extends a temperature range in which the device can be used. A compound having a low minimum temperature of the liquid crystal phase such as a nematic phase and a smectic phase, as described in (3), particularly, a compound having a low minimum temperature of the nematic phase also extends a temperature range in which the device can be used. A compound having a small viscosity as described in (4) shortens a response time of the device.
A compound having a suitable optical anisotropy as described in (5) improves a contrast of the device. According to a design of the device, a compound having a large optical anisotropy or a small optical anisotropy, mare specifically, a compound having a suitable optical anisotropy is required. When the response time is shortened by decreasing a cell gap of the device, a compound having a large optical anisotropy is suitable. A compound having a large negative dielectric anisotropy as described in (6) decreases a threshold voltage of the device. Thus, an electric power consumption of the device becomes small.
With regard to (7), a compound having a large elastic constant shortens the response time of the device. A compound having a small elastic constant decreases the threshold voltage of the device. Accordingly, a suitable elastic constant is required according to characteristics to be desirably improved. A compound having an excellent compatibility with other liquid crystal compounds as described in (8) is preferred. The reason is that physical properties of the composition are adjusted by mixing liquid crystal compounds having different physical properties.
Various kinds of liquid crystal compounds having a negative dielectric anisotropy have been synthesized so far (Patent literature Nos. 1 to 2, for example). Patent literature No. 1 discloses compound (A) and compound (B). Patent literature No. 2 discloses compound (C). Patent literature No. 3 discloses compound (D). However, the compounds are far from being fully suitable for a mode of a liquid crystal display device in recent years.

A new compound can be expected to have excellent physical properties that are not found in a conventional compound. The new compound is expected to have a suitable balance regarding two of physical properties required upon preparing the liquid crystal composition. In view of such a situation, development has been desired for a compound having excellent physical properties and a suitable balance regarding the physical properties with regard to (1) to (8) as described above.