Ferroelectric liquid crystals induced by atropisomeric biphenyl dopants: influence of the SmC host mixture composition

Abstract

We have investigated the induction of ferroelectric SmC* liquid crystals using an atropisomeric biphenyl dopant (R)-1 in binary SmC host mixtures consisting of a 2-phenylpyrimidine host, either 2-PhP1 or 2-PhP2, and one of three structurally similar smectic components (co-hosts). The co-hosts include two 5-phenylpyrimidine derivatives (5-PhP1 and 5-PhP2) and one 6-phenylpyridazine derivative (6-PhPz), all of which feature a non-planar central core with chiral topography in the ground state. In the three binary host mixtures 2-PhP1–5-PhP1, 2-PhP1–6-PhPz and 2-PhP2–5-PhP2, the absolute value of the reduced polarization P_o increases with increasing proportions of the co-host, which is consistent with the assumption that chiral perturbations exerted by (R)-1 should propagate more effectively by causing a shift in the conformational equilibrium of the 5-phenylpyrimidine and 6-phenylpyridazine cores towards one enantiomeric conformation rather than causing a chiral distortion of the planar 2-phenylpyrimidine core. This trend is also observed in the electroclinic coefficient of the binary host mixture 2-PhP1–5-PhP1 doped with (R)-1. We also observed a surprisingly good alignment of SmC* phases with the 2-PhP1–5-PhP1 binary host mixture. This alignment was achieved in the absence of a N* phase above the SmA* and SmC* phases without applying an electric field.