New 1-aryl-spiro[2,5]octan-4-ones as chiral components of induced short-pitch cholesterics

New 1-(4X-phenyl)-spiro-octan-4-ones (X=F, Cl, Br, C6H5, C6H4C6H4OA1k) were synthesized to use for inducement of the helical supra-molecular structure with a short pitch under addition to the nematic liquid crystal (LC) 4-cyano-4'- pentylbiphenyle (5CB). Design of these spiro-compounds was accomplished by the replacement of a double bond in known chiral dopants of a series of isomenthone arylidene derivatives 1 by the cyclopropane ring that made them stable to photochemical E-Z- isomerization typical of initial enones 1. New dopants 2 exhibit the helical twisting power that only slightly reduced as compare to compounds 1. LC mixtures based on the E-63 nematic and containing the most effective 2 possess visible selective light reflection.