In order to lower the Δn value and obtain broad mesophase range, new negative dielectrics anisotropy liquid crystal compounds 4a and 4b were designed by replacement a phenyl ring with a cyclohexyl ring in the common tolane liquid crystals. The target molecules were synthesized through a Sonogashira coupling reaction of 1-trans-4-(trans-4-n-pentylcyclohexyl)cyclohexylacetylene and 4-iodo-2,3-difluoro- phenyl ether with total yields of 27%～28%. Structures of the compounds were identified by IR, NMR and MS. Their mesomorphic properties were studied with polarizing optical microscopy and differential scanning calorimetry. The results show that compounds 4a and 4b have clearing points of 212 and 216 ℃ respectively, and a nematic range of about 140 ℃, which is comparable to the similar tolane liquid crystals. Physical property tests reveal that the less conjugated compounds 4a and 4b have not only lower Δn but also larger Δε values than the similar tolane liquid crystals, which gives us a new way to molecular design. The remarkable improvement of integrated properties makes the new compounds very favorable to large size liquid crystal TV.

Key words: liquid crystals, ethynyl-bridged bond, synthesis, mesophase, dielectrics anisotropy, birefringence