ALPHA-FLUORO ESTERS INCORPORATING A CYCLOHEXANE RING - SOME NEW CHIRAL DOPANTS FOR FERROELECTRIC MIXTURES

Several new homologous series of optically active alpha-fluoro esters incorporating a cyclohexane ring and a number of different cores have been synthesized. Several of these chiral dopants possess an enantiotr opic chiral smectic C (S(c)) phase at elevated temperatures. They are characterised by a relatively high spontaneous polarisation, long pit ch and low rotational viscosity. In addition they exhibit exceptional chemical, thermal and photo- and electro-chemical stability. It is sho wn that an ester group in a terminal position of the molecular core of these new chiral dopants leads to an increase in the spontaneous pola risation (compared with the values for the analogous ethers) with only a small increase in the rotational viscosity, as determined in a stan dard S(c) base mixture. An ester group in a central position of the mo lecular core has the opposite effect on these parameters. It is shown that at least two aromatic rings are normally necessary for S(c) forma tion. An optically active alpha-chloro ester incorporating a cyclohexa ne ring was also prepared and compared with the analogous alpha-fluoro ester. A higher spontaneous viscosity were determined for the alpha-f luoro ester. These new alpha-fluoro esters are excellent chiral dopant s for chiral smectic C mixtures for use in the surface-stabilised ferr oelectric liquid-crystal display.