INDUCTION OF A FERROELECTRIC S-C-ASTERISK 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 S-c phase in two S-c liqui d crystal hosts using a novel chiral dopant (-)-1 that incorporates an atropisomeric core derived from 4,4'-dihydroxy-2,2'-dimethyl-6,6'-din itrobiphenyl. The racemic dopant was synthesized in 11 steps with an o verall yield of 9% and resolved by chiral stationary phase HPLC in opt ically pure form. The magnitude and sign of the spontaneous polarizati on (P-s) induced by (-)-1 were found to depend strongly on the nature of the S-c host. In a cyclohexanecarbonitrile host, (-)-1 induces a po sitive polarization that is measurable over the dopant mole fraction r ange 0.02 < x(d) < 0.044; in a phenyl benzoate host, (-)-1 induces a n egative polarization that falls below detection limit at x(d) less tha n or equal to 0.05. The polarization power (delta(p)) of (-)-1 in the cyclohexanecarbonitrile host is +170 nC/cm(2), which is more than eigh t times that estimated as upper limit in the phenyl benzoate host. The se results are rationalized on the basis of the Boulder model for the molecular origins of P-s by modeling the conformational behavior of th e biphenyl core in the achiral lattice of the S-c host using semiempir ical AM1 calculations. The dependence of delta(p) on the nature of the S-c host is correlated to the large difference in negative dielectric anisotropy (epsilon parallel to - epsilon perpendicular to) of the tw o hosts.