不对称苯并菲盘状液晶的合成及取代基对介晶性的影响

Synthesis of Unsymmetrical Triphenylene Discotic Liquid Crystals and the Influence of Substituent on Mesomorphism

合成了一系列新型含间位二硝基苯甲酸酯不对称苯并菲盘状液晶化合物2-(3,5-二硝基苯甲酰氧基)-3,6,7,10,11-五烷氧基苯并菲(3a～3f).通过偏光显微镜(POM)和差示扫描量热计(DSC)对其介晶性进行了研究.结果显示:此类化合物有高的清亮点,稳定的六方柱状相以及较宽的介晶相范围,且随着软链碳原子数的增加,化合物的熔点和清亮点均出现下降趋势,但六方柱状相的有序性却没有发生很明显的变化.同时通过与其它三类苯并菲盘状液晶2-苯甲酰氧基-3,6,7,10,11-五烷氧基苯并菲(4a～4f),2-二茂铁甲酰氧基-3,6,7,10,11-五烷氧基苯并菲(5a～5f),2,3,6,7,10,11-六烷氧基苯并菲(6a～6f)的对比研究,探讨了酯基,强吸电子基团,以及取代官能团体积对介晶性的影响.证实了苯并菲化合物中分子结构小的变化将引起介晶性大的改变.

A series of new unsymmetrical triphenylene discotic liquid crystals containing m-dinitrobenzoate moiety, 2-（3,5-dinitrobenzoyloxy）-3,6,7,10,11-pentaalkoxy triphenylene derivatives （3a～3f） were prepared. Their mesomorphic properties were studied with polarizing optical microscopy and differential scanning calorimetry. The results showed that these compounds exhibit high clearing points, stable columnar mesophases and wide mesophase ranges. It was discovered that, as the length of soft chains increase, the melting points and clearing points of these compounds decreased, but the order of hexagonal columnar mesophases had no obvious change. The mesomorphism of compounds 3a～3f was compared and con- trasted with other three series of compounds, 2-benzoyloxy-3,6,7,10,11-pentaalkoxytriphenylene （4a～4f）, 2-ferrocenylcarbonyloxy-3,6,7,10,11-pentaalkoxytriphenylene （Sa ～ 5f）, and 2,3,6,7,10,11-hexaalkoxy- triphenylene （6a～6f）. The influences of ester substituent, electron deficient group, and the size of substituent on the mesomorphism were discussed. The results confirmed the notion that small change in chemical structures of discotic liquid crystals could cause a big difference in their mesomorphism.