Poly symmetry breaking

Supramolecular chemistry can be used to create the bent cores that give rise to the symmetry breaking in this family of liquid crystals [139]. The formation of a complex between a calamitic benzoic acid derivative and a bent core terminated with a pyridyl group—neither of which display mesomorphic behaviour—gave rise to a material which displayed SmCP mesophases. The achiral bent cores can also give rise to symmetry breaking when they are attached to flexible polymeric chains, such as poly(siloxane) [140]. 

M. Baitoul, J. W6ry, S. Lefrant, E. Faulques, J.-P. Buisson, and O. Chau-vet. Evidence of electron-hole symmetry breaking in poly(p-phenylene vinylene). Phys. Rev. B Condens. Matter, 68(19) 195203, Nov 2003. 

Chirality and optical activity in the main chain need stronger short range asymmetry at the level of the repetitive unit. The enchainment of some cyclic or diunsaturated monomers, a few copolymers and mainly the inclusion of symmetry breaking heteroatoms in the main chain led to such results. This situation makes poly condensations easier to handle. 

The symmetry breaking of the bond lengths also applies to more complex molecules such as poly-paraphenylene vinylene (PPV). The three possible double bond configurations of this molecule are shown schematically in Figure 9.4.a-c. 

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