H-1, H-2, AND C-13-ENDOR STUDIES OF PHENALENYL RADICALS IN NEMATIC AND SMECTIC MESOPHASES OF LIQUID-CRYSTALS

ESR, 1H, 2H, and 13C ENDOR and TRIPLE experiments have been performed onlabeled chloro-and methvlphen-alenyls (–perinaphthenyls–) in isotropic, nematic. and smectic phases of liquid crystals. Hyperfine coupling constant shiftswere measured and the assignment to molecular positions is discussed. The results suggest that the substituents cause additional alignment effects of the radicals. Smectic A phases have proved to be advantageous as compared to nematic phases in thesestudies. The first successful detection of 13C ENDOR lines in a nematic mesophase is reported. Quadrupole splittings were observed for all of the 2H ENDOR lines, and the complete quadrupole coupling tensor of the ring deuterons (e2qQ/h = (174 ±10) kHz., η = 0.08 ± 0.04) and the quadrupole coupling of the methyl deuterons (e2qQ/h ~ 130 kHz) could be determined. © 1979, American Chemical Society. All rights reserved.