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Abstract
Chiral dopants were obtained by acylation of enantiomerically pure ephedrine and pseudoephedrine with promesogenic carbonyl reagents. The products have been investigated with respect to their chiral transfer ability on nematic host matrices characterized by extreme differences of the dielectric anisotropy. It has been found that the medium dependence of the helicity induction nearly disappears at reduced temperatures. Based on variable temperature 1H NMR studies on monoacylated homologues, the estimated coalescence temperatures and free activation enthalpies for the hindered rotation around C‒N bonds could be correlated with the helical twisting power. Measurements by dielectric spectroscopy reveal the correlation between the molar mass of substituents linked to the chiral building block and the dynamic glass transition of corresponding chiral dopants. Furthermore, the effect of intramolecular and intermolecular hydrogen bonds has been studied by ATR-FTIR spectroscopy.
Funding
Financial support by the German Federal Ministry of Economics and Technology within the aeronautical research project “INGA - Innovative Galley” (20K1103D) is highly acknowledged.