Chiral discotic materials

More recently, chiral discotic materials that exhibit tilted columnar mesophases have attracted attention because of their potential for ferroelectric switching. A spontaneous polarisation is generated because of the restriction in rotation of the peripheral chiral chains. 

The authors like to express their warm thanks to the many co-workers from our laboratories and our collaborators who participated in the work reported here for their enthusiasm to be actively involved in the field of chiral discotic liquid crystalline materials. Also the continuing discussions to unravel the many features of these systems are highly acknowledged. Their names appear in the list of references. 

Serrano and co-workers have investigated similar diketonato metal complexes bearing ten chiral aliphatic chains for potential uses as new types of ferroelectric discotic materials. The materials were obtained by replacement of the alkoxy chains of (55) by chiral chains derived from L-(—)-lactic acid (—20CC H(Me)OC H2 +i). Six, new, ten-chain metal complexes were prepared ((55) M = Cu, Pd, VO R = H, n = 6 and 7) and characterized fully. The NMR spectra... 

As mentioned in chapter 3, the synthesis of discotic materials in which the peripheral units are different is quite difficult and general synthetic routes to such systems are only just becoming available. Accordingly, early chiral discotic liquid crystals have a structure where all of the peripheral units are chiral e.g compound 18). 

Compound 20 is an example of a phenanthrene discotic material that incorporates peripheral chiral units based on lactic acid. Compound 20 only exhibits ferroelectric behaviour when mixed with other chiral phenanthrene compounds. 

As an aside, it may be of interest to the reader that although selective reflection is usually a phenonemon associated with cal-amitic liquid crystalline systems, various multiyne materials have recently been demonstrated to show selective reflection as well as a helix inversion in chiral discotic nematic phases [15, 16]. 

When the disks have no long-range translational order, an analog of the nematic phase, identified as N, is formed. Very few compounds exhibit an Ng phase. It is not entirely miscible with the nematic phase formed by calamitic systems. If a chiral center is incorporated into a nematic discogen, the material usually exhibits a chiral nematic discotic phase. Figure 2.12 shows disk-shaped molecules exhibiting discotic liquid crystal phases between the solid and isotropic liquid phases. 

---