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 f rom 4,4'dihydroxy-2,2',6,6'-tetramethylbiphenyl with different symmetry-bre aking 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 S mC* liquid crystal phases in four SmC hosts with different core structures. Polarization powers delta (p) were measured as a function of the SmC host and compared to delta (p) values previously obtained for an analogous atrop isomeric dopant with X = NO2. Theoretical conformational analyses for rotat ion of the atropisomeric cores about the C-O bonds of the ester groups link ing the core to the side chains were performed at the B3LYP/6-31G(d) level and used in calculating Boltzmann-weighed statistical average transverse di pole moments < mu (perpendicular to)> for the core-diester units. The < mu (perpendicular to)> values were used to normalize delta (p) to study the in fluence of the symmetry-breaking groups X on the polar ordering of the dopa nts. Variations in delta (p(norm)) are rationalized by considering models d escribing either achiral or chiral distortions of the zigzag binding site m odel of the SmC host. Results show that the symmetry-breaking groups X exer t a unique influence on polar ordering of the dopants in the phenylpyrimidi ne host PhP1 that is consistent with a model in which chirality transfer vi a core-core interactions between dopant and host molecules causes a chiral distortion of the zigzag binding site.