3,4-Difluoropyrrole-, 3,3,4,4-tetrafluoropyrrolidine-based tolan liquid crystals

A series of new 3,4-difluoropyrrole-, 3,3,4,4-tetrafluoropyrrolidine-based tolan liquid crystals resulted from palladium-free Sonogashira coupling reactions of 1-(4-iodophenyl)-3,4-difluoropyrrole, 1-(4-iodophenyl)-3,3,4,4-tetrafluoropyrrolidine with terminal phenyl acetylenes. These new compounds exhibit typical nematic and smectic phases, good thermal stabilities, and high clearing points in comparison to the liquid crystal phase of 3,4-difluorobenzene-based tolan. These encouraging results lead us to believe this class of compounds could be used as new liquid crystalline materials. It is possible that the fluorinated N-heterocycles, 3,4-difluoropyrrole and 3,3,4,4-tetrafluoropyrrolidine, could replace the expensive 2,3-difluorobenzene, 3,4-difluorobenzene, and 3,4,5-trifluorobenzene components in the tolan core structure to form promising liquid crystalline materials.