Blue phases induced by doping chiral nematic liquid crystals with nonchiral molecules.

The emergence of the blue phases I and II that are thought to exist in highly chiral systems has been found in chiral nematic liquid crystals (N* LCs) when they are doped with achiral bent-core liquid crystals (banana mesogens). The same effect was also observed by adding racemic 4-(1-methylheptyl oxycarbonyl)phenyl 4'-octyloxybiphenyl-4-carboxylate (MHPOBC), while achiral terephthal-bis(p-butylaniline) (TBBA) was not effective. The difference was attributed to the different conformations, i.e., MHPOBC is known to have a bent shape, but not TBBA. The doping effect is more remarkable in N* LCs with higher chiral content for both banana mesogens and MHPOBC. This unusual doping effect was attributed to selective chiral interaction between the chiral conformers of guest molecules and chiral host molecules and/or the decrease of the surface elastic constant on adding bent-shaped guest molecules.