3,4-Difluoropyrrole-, 3,3,4,4-tetrafluoropyrrolidine- and pyrrolidine-based liquid crystals

A new class of liquid crystals was formed with N-heterocycles as the terminal group, such groups as a 3,4-difluoropyrrole, 3,3,4,4-tetrafluoropyrrolidine, or pyrrolidine. Their properties were modified by varying the terminal heterocycles and/or the length of the alkyl chains on the cyclohexane liquid crystal building block. A comparison of the non-fluorinated and fluorinated pyrrolidine and fluorinated pyrrole as terminal group in the cyclohexane liquid crystals was studied. The mesophase behaviour was affected by altering the polarity of the terminal N-heterocycle. Compounds n/m-4H having the terminal pyrrolidine show a nematic phase. Comparatively, compounds 3/2-4F and 5/2-4F, having a fluorinated pyrrolidine, exhibit SmG phase. With 3,4-difluoropyrrole as terminal group, n/m-2F exhibit the broadest nematic phase range and good thermal stability, thus meeting the criterion for high performance liquid crystals materials. (C) 2013 Elsevier B.V. All rights reserved.