Synthesis and Phase-transition of 4-alkoxycarbonylphenyl 4′-n-alkoxy-2,3,5, 6-tetrafluorobiphenyl-4-carboxylates

Abstract

Two new homologous series of compounds containing symmetrically tetrafluorinated phenyl units, 4-[(s)-2-methylbutoxycarbonyl]phenyl and 4-n-pentyloxyphenyl 4′-n-alkoxy-2,3,5,6-tetrafluorobiphenyl-4-carboxylates (n = 5-10) have been synthesized from 1-pentafluorophenyl-2-trimethylsilylacetylene as a starting material, and studied by thermal polarizing microscopy. The members of the chiral series display enantiotropic cholesteric and monotropic smectic C (S*_c) phases for n = 5-9, and the homolog of n = 10 shows enantiotropic smectic C(S*_c): smectic A and cholesteric phases. However, the homologs of the achiral series exhibit enantiotropic nematic and smectic A phases for n = 5,7,8 and 9, and the member of n = 6 displays only a nematic phase, whereas the homolog of n = 10 shows enantiotropic smectic A and monotropic smectic C phases. 4-[(s)-2-methylbutoxycarbonyl]phenyl 4′-n-octyloxy-2′, 3′, 5′, 6′-tetrafluorobiphenyl-4-carboxylate has also been prepared and found not to be thermotropic mesogen. It is showed by comparison that the symmetrical tetrafluorination of biphenyl has a destabilizing effect on the mesophase, and the effect differs at the different substituted positions.

Key Words:

• Tetrafluorobiphenyl
• chiral smeetic phase
• thermal polarizing microscopy
• fluorinated liquid crystals