Ester type banana-shaped liquid crystalline monomers:: synthesis and physical properties

New ester-type banana (bent-shaped) monomers, 1,3-phenylene bis[4'-(alken-1-yloxy)-biphenyl-4-carboxylate] s Ia - Vb, with different substituent(s) on the central phenyl ring (H, CH3, Cl or NO2) and alkenyl tails in the side arms ( decenyl or undecenyl) were prepared. The analogues IIIa - IVb with 4-chloro- or 4,6-dichloro-substituents exhibited a nematic phase, while Va, Vb with 2-nitro-substituent showed a B-7 phase at relatively low temperature. All the compounds were stable, no degradation or polymerization was observed under applied electric fields or heat treatments. Electro-hydrodynamic instabilities were observed in the nematic phase of each sample. In the B-7 phase of Vb there was an electro-optical switching in the range 112 - 114.5 degreesC with a switching time of about 150 mus at 20 V mum(-1) field. At lower temperatures no electro-optical switching occurred, but a ferroelectric-type spontaneous polarization of 22 nC cm(-2) could be detected. The bend angle was calculated by the semiempirical CAChe/MOPAC/PM5 method.