Mesogenic Chiral Dopants With Unusual High Helical Twisting PowerMesogenic chiral esters of 1-phenyl-1,2-ethandiol, l-cyclohexyl-l,2-ethanediol, 1,2-diphenyl-1,2-ethanediol, l,l'-bi-2-naphthol, 1-phenylethanol, 1-phenyl-2,2,2-trifluorethanol and l-(9-anthryl)-2,2,2-trifluorethanol were synthesized. The temperature dependence of the molecular twisting power was determined in the nematic wide range mixture RO-TN 404. All compounds show good solubility and unusual high values of the Einleitung
A simple way of determining the helix screw sense of a cholesteric phase using the Grandjean-Cano method is described. The helix pitch as well as its sense is investigated for ten cholesteric phases, induced by mesogenic chiral compounds in the nematic isomere mixture of 4-methoxy-4′-n-butylazoxybenzene (Nematic Phase 4, Merck). For the chiral compounds with nematic-like molecular structure it is found that the screw sense alternates with the number of bonds between the chiral centre and the ring system.
Mesogenic chiral esters of optically active (S)-l,2-propanediol and (R,R)-2,3-butanediol were synthesized. The compounds, added to a nematic phase induce cholesteric phases exhibiting a helix inversion with temperature variation. This effect is independent of the molecular structure of the nematic solvent. The inversion temperature varies only slightly with concentration but can be influenced by the mesogenic substituent.
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