158548-58-4Relevant articles and documents
Ester type banana-shaped liquid crystalline monomers: Synthesis and physical properties
Fodor-Csorba, Katalin,Vajda, Aniko,Jakli, Antal,Slugov, Christian,Trimmel, Gregor,Demus, Dietrich,Gacs-Baitz, Eszter,Holly, Sandor,Galli, Giancarlo
, p. 2499 - 2506 (2004)
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 NO 2) 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 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.
A new series of liquid crystalline dimers with exceptionally high apparent tilt
Olsson, Nils,Schroeder, Martin,Diele, Siegmar,Andersson, Gunnar,Dahl, Ingolf,Helgee, Bertil,Komitov, Lachezar
, p. 2517 - 2525 (2008/09/20)
A new series of dimeric chiral antiferroelectric materials using a trisiloxane as the central connecting linker and having fluorinated tails has been synthesized together with their corresponding monomers. Spacer lengths of 3-6 and 11 methylene groups were used. As a comparison to see the effect of the siloxane length on the phase behaviour, one dimer with a tetrasiloxane core was also synthesized. Monomers with 3-6 carbons in the spacer showed just orthogonal smectic phases and only the long 11 carbon spacer 7F4PPB11 showed tilted phases in a very similar way to what was found in the unfluorinated monomers previously studied. All trisiloxanes showed a high temperature antiferroelectric phase and those with a spacer length of 4 or more carbons also showed one or two columnar antiferroelectric phases when decreasing the temperature. The spontaneous polarisation Ps was high, especially in the columnar phases where it ranged from 800-1200 nC cm-2 and upward. The apparent tilt angles were exceptionally high, above 45 degrees for all materials studied. In accordance with the trend described previously, the tetrasiloxane containing dimer showed a ferroelectric phase at high temperature. But in this case the columnar phase was found to be antiferroelectric. Hence, the general idea that trisiloxane cores promote antiferroelectricity and tetrasiloxanes promote the ferroelectric phase is still correct also for these materials in the SmC* phase, but not for the columnar phase. It can also be noted that the phase separation between siloxane, fluorinated tail and mesogenic parts of the molecules was so high that the material became columnar on lowering the temperature. The Royal Society of Chemistry 2007.
