AbstractFor selected compounds with perfluorinated chains the structure of smectic phases was investigated by X‐ray diffraction measurements. For rod‐like compounds with only one terminal perfluorinated chain the incompatibility of the hydrocarbon and the fluorocarbon moieties leads to a segregation of both parts which can be considered as microphase separation.For swallow‐tailed compounds the structure of smectic phases depends on the position and the length of the perfluorinated chains. If the steric interaction dominates an antiparallel packing of the molecules within the smectic layers is favoured. If the incompatibility of the hydrocarbon and fluorocarbon moieties is of importance the smectic layers are distorted and at lower temperatures the layer structure is transformed into a columnar stru