Carbonyl chiral smectics

Tbe purpose of tbe bydroxyl group is to acbieve some hydrogen bonding with the nearby carbonyl group and therefore hinder the motion of the chiral center. Another way to achieve the chiral smectic Cphase is to add a chiral dopant to a smectic Chquid crystal. In order to achieve a material with fast switching times, a chiral compound with high spontaneous polarization is sometimes added to a mixture of low viscosity achiral smectic C compounds. These dopants sometimes possess Hquid crystal phases in pure form and sometimes do not. 

Along with the prediction and discovery of a macroscopic dipole in the SmC phase and the invention of ferroelectric liquid crystals in the SSFLC system, the discovery of antiferroelectric liquid crystals stands as a key milestone in chiral smectic LC science. Antiferroelectric switching (see below) was first reported for unichiral 4-[(l-methylheptyloxy)carbonyl]phenyl-4/-octyloxy-4-biphenyl carboxylate [MHPOBC, (3)],16 with structure and phase sequence... 

C1/C2 chevrons, ferroelectric devices 644 cadmium selenium TFT address 233 Cano wedge, chiral nematics 347 f, 351 Canon technology, ferroelectric devices 648 capillaiy flow, shear viscosity 143 carbocyclic compounds, charge transfer systems 958 carbocyclic rings, smectogens 412 carbon atoms, intercalated smectics 808 carbon-carbon bonds, dimers 823 carbon-carbon double bonds, chiral smectics 498 carbonaceous phases 693 carbonyl connectors, antiferroelectrics 687 carbonyl groups... 

When the terminal ester functionality in the phenyl propiolates is replaced with a carbonyl group, i.e., a keto function, TGB phases disappear altogether indicating that the increased size of the lateral dipole at terminus to the core has detrimental effects on the stability of TGB phases [35]. These small variations in structure show how delicate the stability of the TGB phase is, nevertheless, most chiral nematic to smectic phase transitions are accompanied by a TGB phase no matter how transient it is. 

Compound 46 shows the effect of the polar carbonyl unit in a terminal chain (in fact the carbonyl group can be, and often is, referred to as a linking group between the chain and the core). As can be seen, in comparison with compound 32 the smectic phase stability is much greater for compound 46 despite the steric effect of the carbonyl units which tends to disrupt lamellar attractions. Similarly, the use of a polar branching substituent e.g., F, Cl or CN) in a terminal chain (usually chiral) tends to give smectic phases and will be discussed in Chapter 6. 

When incorporating a chiral branching in the a position to the ester carbonyl group near the mesogen, the tilted smectic phase was lost [25]. However, the introduction of a chiral branching in the 3 position resulted in polymer 21, which exhibited a Sc phase... 

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