High contrast distorted helix effect electro-optic devices and tight ferroelectric pitch ferroelectric pitch ferroelectric liquid crystal compositions useful therein

A ferroelectric liquid crystal composition comprising a chiral dopant and a host mixture which exhibits a ferroelectric phase and a chiral nematic phase at temperatures above said ferroelectric phase, wherein the natural helix pitch in said nematic phase at temperatures at least about 1.degree.--2.degree. C. above the N* transition point is at least about 4 times longer than the natural helix pitch in said ferroelectric phase at about room temperature, wherein said chiral dopant is a chiral nonracemic compound of the formula:

• R--A--Z.sub.1 --B--O--M
• wherein A and B are, independently of one another, selected from 1,4-phenylene, 1,4-phenylene in which one or two of the ring carbon atoms are replaced with nitrogen atoms, or 1,4-cyclohexylene, Z.sub.1 is a single bond, a --CO--O-- group, a --O--CO--group, or an O atom if one of A or B is a 1,4-cyclohexylene, R is a group having from one to twenty carbon atoms in which one or more non-neighboring carbon atoms can be replaced with a double bond, an O atom, a S atom or a Si(CH.sub.3).sub.2 group, and O-M is a 2,3-dihaloalkoxy moiety of the formula:
• ##STR15## where * represents an asymmetric carbon, X and Y, independently of one another, are halogens, R' is a group having from one to about twenty carbon atoms in which one or more non-neighboring carbon atoms can be replaced with a double bond, an O atom, a S atom or a Si(CH.sub.3).sub.2 group, or is an acyl group --OCO--R" where R" is a group having from one to twenty carbon atoms and wherein one or more non-neighboring carbon atoms can be replaced with a double bond, an O atom, a S atom or a Si(CH.sub.3).sub.2 group.