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

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 δp were measured as a function of the SmC host and compared to δp values previously obtained for an analogous atropisomeric dopant with X = NO2. 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 〈μ⊥〉 for the core−diester units. The 〈μ⊥〉 values were used to normalize δp to study the influence of the symmetry-breaking groups X on the polar ordering of the dopants. Variations in δp(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 PhP1 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.