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Alexander M. Parshin^1,3*, Tatyana A. Zotina^2,3

Author affiliations
¹Kirensky Institute of Physics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russia
²Institute of Biophysics, Federal Research Center KSC SB RAS, Krasnoyarsk, Russia
³Siberian Federal University, Krasnoyarsk, Russia
*Corresponding author: parshin@iph.krasn.ru

Abstract
The orientation effects of pure and chlorophyll b (Chl. b)-doped nematic 5CB using the Faraday method and the Fredericksz transition have been investigated. To analyze these effects, the volume diamagnetic anisotropy ΔΧ, which was considered as an orientation parameter, was determined. This parameter is absent in the symmetric state of the system above the temperature TNI (transition of nematic phase into isotropic liquid) and it appears during spontaneous symmetry breaking, when the system passes to an asymmetric nematic state. A discrepancy between ΔΧ(H) dependences with increasing of magnetic field H was found. The discrepancy is caused by an increase in ΔΧ_LC of the liquid crystal due to the contribution ΔΧ_Chl of Chl. b due to the additional current induced in the porphyrin ring by the magnetic field. A decrease in the threshold field for the chlorophyll-doped nematic 5CB H_th = 3.18 kOe as compared with the value H_th = 3.55 kOe of pure 5CB was obtained. It is associated with an increase in ΔΧ_Chl due to the introduction of a chlorophyll porphyrin ring into the liquid crystal. Orientational transitions during minimization of free energy in a layer of pure and chlorophyll-doped nematic 5CB are considered.

Keywords: nematic liquid crystal, magnetic polarization, orientation parameter