Ferroelectric Liquid Crystals Induced by Atropisomeric Biphenyl Dopants: Dependence of the Polarization Power on the Nature of the Symmetry-Breaking Groups

Abstract

Four new chiral dopants containing an atropisomeric biphenyl core derived from 4,4'-dihydroxy-2,2',6,6'-tetramethylbiphenyl with different symmetry-breaking groups at the 3,3'-positions (X = F, Cl, Br, and Me) were synthesized in optically active form. These dopants were used to induce ferroelectric SmC * liquid crystal phases in four SmC hosts with different core structures. Polarization powers δ p were measured as a function of the SmC host and compared to δ p values previously obtained for an analogous atropisomeric dopant with X = NO 2 . Theoretical conformational analyses for rotation of the atropisomeric cores about the C-O bonds of the ester groups linking the core to the side chains were performed at the B3LYP/6-31G(d) level and used in calculating Boltzmann-weighed statistical average transverse dipole moments for the core-diester units. The values were used to normalize 6p to study the influence of the symmetry-breaking groups X on the polar ordering of the dopants. Variations in δ p(norm) are rationalized by considering models describing either achiral or chiral distortions of the zigzag binding site model of the SmC host. Results show that the symmetry-breaking groups X exert a unique influence on polar ordering of the dopants in the phenylpyrimidine host PhPl that is consistent with a model in which chirality transfer via core-core interactions between dopant and host molecules causes a chiral distortion of the zigzag binding site.