Ferroelectric liquid crystals induced by dopants with axially chiral 2,2 '-spirobiindan-1,1 '-dione cores: diether vs. diester side-chains

摘要

A series of axially chiral 5,5'-and 6,6'-dialkanoyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-2 and (R)-4a-4c were synthesized in optically pure form and their ferroelectric polarization powers, delta(p), measured in four liquid crystal hosts with isotropic (I)-nematic (N)-smectic A (SmA)-smectic C (SmC) phase sequences. The results show that the sign of polarization P-S induced by (R)-2 and (R)-4a-4c follows the same trend as that previously reported for the 5,5'-and 6,6'-diheptyloxy-2,2'-spirobiindan-1,1'-dione dopants, (R)-1 and (R)-3. The polarization induced by (R)-2 in the host DFT is below detection limits, and the sign of PS was found to invert as a function of temperature at mole fractions as low as 0.01. On the other hand, the polarization power of the 6,6'-diheptanoyloxy dopant (R)-4b in the host NCB76 is 21449 nC cm(-2), the fourth highest value reported so far, and more than three times the delta(p) value of the 5,5'-diheptanoyloxy analogue (R)-2 in that host (+474nC cm(-2)). Results of H-2 NMR experiments suggest that (R)-4b exerts stronger local perturbations in NCB76 than (R)-2, and that these perturbations may be chiral in nature.