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

Abstract

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 B₇ 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 B₇ phase of Vb there was an electro-optical switching in the range 112–114.5 °C with a switching time of about 150 µs at 20 V µm⁻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.