Liquid crystal composition with high refractive index and display device thereof

#The present invention relates to a liquid crystal composition, particularly to a liquid crystal composition having a higher retardation amount, a higher transmittance, a larger optical anisotropy, a proper clearing point, a lower rotational viscosity, a good low-temperature storage stability, and a rapid response. The present invention also relates to a liquid crystal display device comprising the same.

#The liquid crystal display device operates by utilizing the optical anisotropy and dielectric anisotropy of the liquid crystal material itself, and has been widely used at present. Based on the different characteristics and working modes of the liquid crystal materials, the device can be designed into various working modes, wherein the conventional display devices generally use a TN mode (i.e., twisted nematic mode—the liquid crystal compound has a nematic structure twisted by about 90 degrees), STN mode (i.e., super-twisted nematic mode), SBE mode (i.e., super-twisted birefringence mode), ECB mode (i.e., electronically controlled birefringence mode), VA mode (i.e., vertical alignment mode), IPS mode (i.e., in-plane switching mode), etc. There are many improved modes based on the above various modes. Devices operating in TN, STN, and SBE modes generally use positive dielectric anisotropic liquid crystals, devices operating in ECB and VA modes use negative dielectric anisotropic liquid crystals, and the IPS mode can use both positive and negative dielectric anisotropic liquid crystals.

#Generally, the passive driving is used in the low information volume. As the information volume increases, the display size and the number of display channels increase, and crosstalk and contrast reduction become severe, an active matrix (AM) driving method is thus generally employed. Currently, thin film transistors (TFTs) are more used for driving. In the AM-TFT element, the TFT switching device is addressed in a two-dimensional grid, and charges the pixel electrode for a limited time during conduction, and then turns off again until it is addressed in the next cycle. Therefore, between two address cycles, the change of voltage at the pixel is undesired; otherwise the transmittance of the pixel will change, resulting in instability of the display. The discharge rate of a pixel depends on the electrode capacity and the resistivity of the dielectric material between the electrodes. Therefore, the liquid crystal material is required to have a higher resistivity, a suitable optical birefringence value Δn (generally, the Δn value is around 0.08-0.10), and a lower threshold voltage to achieve reductions in driving voltage and power consumption. The liquid crystal material is also required to have a lower viscosity to meet the requirement of rapid response. Such liquid crystal compositions have been reported in many literatures, for example, WO9202597, WO9116398, WO9302153, WO9116399, CN1157005A and the like.

#The present invention will be illustrated by combining the detailed embodiments below. It should be noted that, the following examples are exemplary embodiments of the present invention, which are only used to illustrate the present invention, not to limit it. Other combinations and various modifications within the conception of the present invention are possible without departing from the subject matter and scope of the present invention.

#For the convenience of the expression, the group structures of the liquid crystal compositions in the following Examples are represented by the codes listed in Table 1:

#TABLE 1 Codes of the group structures of the liquid crystal compounds Unit structure of group Code Name of the group C 1,4-cyclohexylidene P 1,4-phenylene G 2-fluoro-1,4-phenylene U 2,5-difluoro-1,4-phenylene I indan-2,5-diyl —F F fluorine substituent —CH═CH— V alkenyl —CF2O— Q difluoro ether group —OCF3 OCF3 trifluoromethoxy —CF3 CF3 trifluoromethyl —CH═CF2 V(2F) 1,1-difluorovinyl —C2H4— 2 ethylene —CnH2n+1 or —CmH2m+1 n or m alkyl