Large electroclinic effect in SmA* liquid crystals induced by an atropisomeric biphenyl dopant

Abstract

Electroclinic coefficients (e_c) and reduced polarizations (P_o) were measured in the SmA* and SmC* liquid crystal phases formed by 4 mol% mixtures of the chiral dopant (–)-2,2′,6,6′-tetramethyl-3,3′-dinitro-4,4′-bis[(4-nonyloxybenzoyl)oxy]biphenyl [(–)-1] in the binary host mixture of 5-(4-butyloxyphenyl)-2-octyloxypyrimidine (5-PhP1) and 2-(4-butyloxyphenyl)-5-octyloxypyrimidine (2-PhP1) over the mole fraction range 0 ≤ x_5-PhP1 ≤ 0.24. Both e_c and P_o increase with x_5-PhP1, which is consistent with the assumption that 5-PhP1 should be more effective in propagating chiral perturbations exerted by (–)-1. At x_5-PhP1 = 0.24 and T − T_C = +5 K, the electroclinic coefficient is 0.34° µm V⁻¹, which is one order of magnitude greater than the highest e_c value previously reported for a chiral dopant at the same mole fraction and reduced temperature.