We designed unique negative dielectric molecules, which were tricyclic compounds with a 5,5,6,6-tetrafluorocyclohexa-1,3-diene moiety in the mesogen, and then for the first time developed an effective synthetic protocol from commercially available 4-bromo-3,3,4,4-tetrafluorobut-1-ene. We also evaluated their physical properties for new mesogenic compounds, such as birefringence, dielectric anisotropy and shear viscosity, which are important characteristics for flat LC display device applications. The molecules clearly showed not only a large negative dielectric anisotropy and birefringence but also high viscosity.

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Herein, we demonstrate an improved short-step protocol for the synthesis of multicyclic molecules having a CF2CF2-containing cyclohexadiene or cyclohexane framework in a mesogenic structure. These molecules are promising candidates for vertical alignment (VA)-mode liquid crystal (LC) display devices owing to their large negative dielectric constant. The tetrafluorinated multicyclic molecules were successfully obtained in only five or six reaction steps without the need for special handling techniques, as is generally required for thermally unstable organometallic species, representing a reduction of three reaction steps. The improved short-step synthetic protocol was also amenable to the multigram preparation of these promising molecules, which may contribute significantly to the development of novel negative-type LC molecules containing CF2CF2 carbocycles.