Ferroelectric liquid crystals induced by atropisomeric dopants: Dependenceof the polarization power on the core structure of the smectic C host

A series of 11 chiral dopants with an atropisomeric core derived from 4,4'- dihydroxy-2,2',6:6'-tetramethyl-3,3'-dinitrobiphenyl were synthesized in op tically pure form. These compounds were doped into five different smectic C (S-C) liquid crystal hosts to induce a ferroelectric S-C* liquid crystal p hase, and the reduced polarization P-o was measured as a function of the do pant mole fraction xd over the range 0.005 < x(d) less than or equal to 0.0 5. The polarization power 6, was found to strongly depend on the core struc ture of the Sc host. For example. the dopant (+)-2,2',6,6'-tetramethyl-3,3' -dinitro-4,4'-bis[(4-octyloxybenzoyl)oxy]biphenyl gave delta(p) values of < 30 nC/cm(2) in a phenyl benzoate S-C host and 1738 nC/cm(2) in a phenylpyri midine S-C host; the latter is one of the highest polarization power values reported thus far in the literature. In the phenylpyrimidine S-C host, the polarization power was found to depend on the length of the dopant side ch ains and on the position of the atropisomeric core with respect to those of the surrounding S-C host molecules, on the time average. The polarization power followed a trend opposite to that followed by the S-C* helical pitch. Analysis of these results suggests that chirality transfer from the atropi someric core of the dopant to those of the S-C host molecules plays a key r ole in amplifying the polarization induced in the phenylpyrimidine host. It is likely that such intercore chirality transfer results in an asymmetric distortion of the S-C* lattice, which in turn, further increases the confor mational asymmetry of the chiral dopant by virtue of increased diastereomer ic bias between the S-C* lattice and the chiral conformations of the dopant .