Liquid crystals SmCP phases

Schroder, M. W. Diele, S. Pelzl, G. Weissflog, W. Field-induced switching of the layer chirality in SmCP phases of novel achiral bent-core liquid crystals and their unusual large increase in clearing temperature under electric field application. ChemphysChem... 

We see from Figure 8.13 that a number of liquid crystal phases, SmC of chiral rod-shape and the tilted columnar phase of chiral disc shape molecules, as well as the SmCP of achiral bent-core, and the tilted bowl-shape molecules all have C2 symmetry with eight independent piezoelectric coefficients. The direct and converse i- piezoelectric effects have been mostly studied in the fluid SmC liquid crystals. 

MHPOBC was not only the first reported antiferroelectiic liquid crystal, but it was also very useful for the discovery of other liquid crystal phases. It does exhibit not only SmC and SiuCa but also all of the now well-established secondary phases, SmC , SmCpH (AF), and SmCpn (SmCy ). The existence of several phases has been reported prior to the authors by Furukawa et al. [47] and Fukui et al. [55]. We have reported the existence of SmCa, SmCp, and SmCy between the SmA and SmCA phases. It was then claimed that SmCp is the same as SmC. Thereafter, objections were raised by other groups [56-58] and experiments using a compound with high optical purity were used to confirm that SmCp is the same as SmCFj2. ... 

First it was argued to be due to a chiral molecular configuration characteristic of the particular type of bent-shape molecules, such as twisted or propeller shape (conformational chirality). The concept of conformational chirality was supported by simulations by Earl et al. [61], and was demonstrated by the observation that doping calamitic cholesteric liquid crystal by achiral bent-core molecules can lead to a decrease of the helical pitch, indicating an enhanced rotatory power of the mixture [62]. Unfortunately there is no proof that the decrease of the pitch is not due to a decrease of the twist elastic constant caused by the addition of bent-core units. Although the conformational chirality is usually not questioned in the solid B4 phase [20], its role has been questioned by Walba et al. [20] by arguing that these chiral conformations have very short lifetime, therefore they average out in fluid smectic, such as SmCP or SmCo phases. 

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