Bent-core compounds with two branched chains: evidence of a new dark conglomerate mesophase

Biphenyl-3,4'-diol derived bent-core compounds with branched side chains have been synthesized and characterized to study the influence of terminal branched groups on mesophase properties and transition temperatures of bent-core mesogens. The liquid crystalline properties of the compounds were investigated by differential scanning calorimetry, optical polarizing microscopy and X-ray scattering. Depending on the length of the chain, the size of molecular branches and the position of branched chains, either enantiotropic or monotropic rectangular columnar phases were observed. For one of the compounds combining two different branched side chains, a new type of optically isotropic dark conglomerate phase (M-Iso[*]) was found. It is proposed to be a distorted version of a non-tilted or only slightly tilted B-6-like intercalated smectic phase with additional in plane order.