Electro-optical properties of a new series of fluorinated antiferroelectric orthoconic liquid crystalline esters

The electro-optical properties of orthoconic antiferroelectric liquid crystals of some analogues of (S)‑MHPOBC ((S)‑4 ‑(1 ‑methylheptyloxy)carbonylphenyl 4'-octyloxy-4-biphenylcarboxylate) have been investigated and discussed in terms of the structure property correlations of liquid crystalline molecules. Polarisation field reversal technique has been used for their characterisation. In this study the occurrence of such a high value of spontaneous polarisation (P-s) for the investigated compound is especially noteworthy as they comprise a bulky chiral unit, zigzag ester linkage and polar fluorinated terminal. Lengthening of oligomethylene spacer in the terminal chain and placement of fluorine atom in the molecular core structure leads to reduction in the value of P-s. The P-s data suggest that the nature of the chiral smectic C (SmC*) to smectic A (SmA) phase transition is of second order and the critical exponent beta is in the range 0.19-0.34. The 'V-shaped' mode or thresholdless switching in such high-polarisation ferroelectric liquid crystals has also been discussed.