Notizen: Bestimmung des Helixdrehsinnes cholesterischer Phasen mit der Grandjean-Cano-Methode / Determination of the Helical Sense of Cholesteric Liquid Crystals Using the Grandjean-Cano Method

Abstract

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.

The interplay of configuration and conformation in helical perylenequinones: Insights from chirality induction in liquid crystals and calculations

“…Cholesteric pitch and handedness were obtained at T = 298 K by using the lens version of the Grandjean–Cano method [ 38 – 39 ]. The commercially available (Merck) nematic solvent E7 (nematic–isotropic transition temperature T NI ~ 330 K) is composed of a eutectic mixture of cyanobiphenyl and terphenyl compounds [ 30 ].…”

Chiral amplification in a cyanobiphenyl nematic liquid crystal doped with helicene-like derivatives

“…Pitches and handedness of the cholesteric solutions in E7 have been obtained at room temperature using the lens version of the Grandjean-Cano method [ 60 ]. E7 from BDH is a commercial mixture of 4′-pentyl-, 4′-heptyl-, 4′-octyloxy-, and 4′-(4-pentylphenyl)-4-biphenylcarbonitrile in a 51:25:16:8 wt ratio ( T i 60 °C).…”

Esters of (S)-1,2-propanediol and (R,R)-2,3-butanediol — Chiral Compounds Inducing Cholesteric Phases with a Helix Inversion ·

“…The twisting power of the synthesized esters was investigated using the nematic wide range mixtures RO The pitch p and the helical screw sense of the induced cholesteric phases were determined by the modified Grandjean-Cano-method [10][11][12][13],…”

“…Earlier investigations have shown that the sign of the pitch induced by mesogenic chiral compounds depends not only on the absolute configuration but also on the orientation of the chiral centre with respect to the molecular long axis [16]. This is not only demonstrated by the odd-even-rule [12,17] but also by the helix inversion occurring at the change from eis to trans isomers of ortho substituted optically active dialkylazobenzenes [18,19]. Consequently, in order to explain the helix inversion of the compounds investigated here, the assumption of a conformation change should be taken into account.…”