Typical liquid crystal display cells include TN-LCD (twisted nematic liquid crystal display devices) which are utilized in the fields of clocks, watches, electronic calculators, electronic notebooks, pocket computers, word processors and personal computers. The information density on one display has been increased with an increase in information to be processed by OA apparatuses in recent years. Conventional TN-LCD can no longer meet requirements of high multiplex drive systems, particularly word processors and personal computers with respect to the quality level of visual field angle and contrast.
Under such circumstances, STN (super twisted nematic) -LCD have been developed by Scheffer et al (SID'85 Digest, p. 120 (1985)) and Kinukawa et al (SID'86 Digest, p. 122 (1986)) and are beginning to widely spread for use in display of high information processing in word processors and personal computers.
As one of a useful liquid crystal compound in a STN-LCD, there is a compound represented by ##STR2## (wherein R represents a straight-chain alkyl group) (hereinafter referred to as PCH).
PCH is a useful P-type liquid crystal compound having positive dielectric anisotropy. But the dielectric anisotropy value (.DELTA..epsilon.) of PCH is not so large, as much as about +12 to 13. Thus there is disadvantageous in that when PCH is mixed with widely employed nematic liquid crystal materials, decrease in the threshold voltage of the liquid crystal material is small.