E.S.R. investigation of helix inversion in induced cholesteric phases

The phenomenon of a reversible helix inversion in induced cholesteric mesophases caused by variation of the temperature has been investigated by E.S.R. spectroscopy using the nitroxide radical tempone as spin probe. Chiral esters of optically active (R)-(+)-2,2′-dihydroxy-1,1′-binaphthyl were added as dopants to the nematic mixture RO-TN 404. The inversion temperatures and the handedness of the helices were determined. In addition to the distortion parameter which is a measure of the helix pitch, order parameters and rotational correlation times of the spin probe were obtained from line-shape analyses.