新颖的含乙炔桥键液晶分子设计与合成

为降低液晶分子的双折射率并获得宽液晶相区, 用环己基替代传统二苯乙炔液晶分子中的一个苯环, 得到一类结构新颖的含乙炔桥键的负介电各向异性液晶分子4a, 4b. 目标化合物采用1-trans-4-(trans-4-正戊基环己基)环己基乙炔与4-碘-2,3-二氟苯基醚进行Sonogashira偶联反应制备, 反应总产率27%～28%. 产物结构经MS, IR, NMR鉴定确认. 采用DSC结合偏光显微镜对液晶相变温度进行了测试, 结果表明新化合物4a, 4b清亮点分别为212, 216 ℃, 向列相温区均达到140 ℃, 与传统二苯乙炔类液晶的相变温区基本相当. 物理性能测试表明, 分子骨架共轭程度的削弱不仅使双折射率大幅降低, 而且介电各向异性绝对值还有所增大, 为分子设计提供了新的思路. 新化合物综合性能得到显著改善, 在大尺寸液晶电视领域具有非常好的应用前景.

Molecular Design and Synthesis of New Ethynyl-bridged Bond Liquid Crystal Compounds

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.