Design and investigation of de Vries liquid crystals based on 5-phenyl-pyrimidine and (R,R)-2,3-epoxyhexoxy backbone

Calamitic liquid crystals based on 5-phenyl-pyrimidine derivatives have been designed, synthesized, and characterized. The 5-phenyl pyrimidine core was functionalized with a chiral (R,R)-2,3-epoxyhexoxy chain on one side and either siloxane or perfluoro terminated chains on the opposite side. The one involving a perfluorinated chain shows SmA* phase over a wide temperature range of 82 degrees C, whereas the siloxane analog exhibits both SmA* and SmC* phases over a broad range of temperatures, and a weak first-order SmA*-SmC* transition is observed. For the siloxane analog, the reduction factor for the layer shrinkage R (relative to its thickness at the SmA*-SmC* transition temperature, T-AC) is similar to 0.373, and layer shrinkage is 1.7\% at a temperature of 13 degrees C below the T-AC. This compound is considered to have ``de Vries smectic'' characteristics with the de Vries coefficient C-deVries of similar to 0.86 on the scale of zero (maximum-layer shrinkage) to 1 (zero-layer shrinkage). A three-parameter mean-field model is introduced for the orientational distribution function (ODF) to reproduce the electro-optic properties. This model explains the experimental results and leads to the ODF, which exhibits a crossover from the sugar-loaf to diffuse-cone ODF some 3 degrees C above T-AC.