Induction of a Ferroelectric SC Liquid Crystal Phase by an Atropisomeric Dopant Derived from 4,4‘-Dihydroxy-2,2‘-dimethyl-6,6‘-dinitrobiphenyl

We report the induction of a ferroelectric SC* phase in two SC liquid crystal hosts using a novel chiral dopant (−)-1 that incorporates an atropisomeric core derived from 4,4‘-dihydroxy-2,2‘-dimethyl-6,6‘-dinitrobiphenyl. The racemic dopant was synthesized in 11 steps with an overall yield of 9% and resolved by chiral stationary phase HPLC in optically pure form. The magnitude and sign of the spontaneous polarization (P S) induced by (−)-1 were found to depend strongly on the nature of the SC host. In a cyclohexanecarbonitrile host, (−)-1 induces a positive polarization that is measurable over the dopant mole fraction range 0.02 < x d < 0.044; in a phenyl benzoate host, (−)-1 induces a negative polarization that falls below detection limit at x d ≤ 0.05. The polarization power (δp) of (−)-1 in the cyclohexanecarbonitrile host is +170 nC/cm2, which is more than eight times that estimated as upper limit in the phenyl benzoate host. These results are rationalized on the basis of the Boulder model for the molecular origins of P S by modeling the conformational behavior of the biphenyl core in the achiral lattice of the SC host using semiempirical AM1 calculations. The dependence of δp on the nature of the SC host is correlated to the large difference in negative dielectric anisotropy (ε∥ − ε⊥) of the two hosts.