New chiral tolane series with antiferroelectric properties

A new series of chiral tolane with aliphatic end chains ranging from heptyloxy to dodecyloxy has been synthesized and characterized. The mesomorphic properties have been analyzed by optical microscopy on pure compounds and mixtures, D.S.C, electro-optical and pitch measurements. This series displays a very rich polymesomorphism including S-A, S-C*(alpha),S-C*, S-C*(FI), S-C*(A), S-I*(A) and S-J* phases with reference to the compound MHPOBC through miscibility test. One of the characteristic of this serie is the two S-C*(FI) phases (S-C*(FI1) and S-C*(FI2)) between S-C* and S-C*(A) phases. The electro-optical measurements were carried out with the classical SSFLC geometry. The threshold field is measured in each tilted mesophase; this one is peculiarly high in S-J*, S-I*(A) and S-C*(A) phase (respectively more than 6; 4 and 1V/mu m). In the S-C*(FI) phase one can note a first plateau between 0.3V/mu m an 0.7V/mu m, and the saturation is reached at 1V/mu m. Helical pitch measurement shows a strong variation of the pitch at the S-C*(A)-S-C*(FI) and S-C*(FI)-S-C* transitions.