作者:D. Ster、U. Baumeister、J. Lorenzo Chao、C. Tschierske、G. Israel
DOI:10.1039/b705519f
日期:——
N-Alkyl-pyridinium derivatives 1–3 and N-alkyl-stilbazolium halides 4–6 with hydroxy, methoxy and hydrogen 4′-substituents and long non-branched alkyl chains (n = 14, 16, 18, 20, 22) were synthesized and characterized by polarizing microscopy, differential scanning calorimetry and X-ray measurements. The compounds exhibit liquid crystalline SmA phases when heated above their melting point. Phenyl substitution in the 3- and 4-position of the pyridinium ring causes a large tendency to decrease the clearing temperature in comparison to the 4-methyl substituted N-alkyl-pyridinium salts. By elongation of the pyridinium ring to the 4′-substituted stilbazolium unit the clearing points of the new compounds 4–6 increase drastically up to temperatures ≥200 °C in which partial decomposition of the compounds sets in. The length of the alkyl chains and the type of counter ions have large influences on the stability of the mesophase. Elongation of the alkyl chain length n increases the temperature range of the liquid crystalline phase. The counter ions increase the stability of the SmA phase in order Cl− > Br− > I− > BPh4−. When CH3–C6H5SO3− is introduced as an anion no liquid crystalline phase can be observed. UV/Vis measurements indicate the presence of a charge-transfer complex between the pyridinium cation and the iodide anion. Differences in the liquid crystalline behaviour of N-alkyl-4′-substituted stilbazolium halides 4–6 compared with N-alkyl-3- and -4-substituted-pyridinium derivatives 1–3 may be explained by additional intramolecular charge-transfer and resulting strong dipole–dipole interactions between stilbazolium compounds.
合成并表征了具有羟基、甲氧基和氢的4′-取代基以及长的非分支烷基链(n = 14、16、18、20、22)的N-烷基吡啶鎓衍生物1–3和N-烷基斯替巴唑鎓卤化物4–6,采用了偏振显微镜、差示扫描量热法和X射线测量。化合物在加热至其熔点以上时表现出液晶SmA相。吡啶环3位和4位的苯基取代导致其清晰温度相较于4-甲基取代的N-烷基吡啶盐大幅降低。通过将吡啶环延伸至4′-取代的斯替巴唑鎓单元,新化合物4–6的清晰点大幅增加,达到≥200 °C的温度,在此温度下化合物开始部分分解。烷基链的长度和对离子的类型对中间相的稳定性有较大影响。烷基链长度n的延长增加了液晶相的温度范围。对离子按照Cl− > Br− > I− > BPh4−的顺序增加了SmA相的稳定性。当引入CH3–C6H5SO3−作为阴离子时,无法观察到液晶相。UV/Vis测量表明吡啶鎓阳离子和碘离子之间存在电荷转移复合物。与N-烷基-3和-4取代的吡啶衍生物1–3相比,N-烷基-4′-取代的斯替巴唑鎓卤化物4–6在液晶行为上的差异可以通过额外的分子内电荷转移和斯替巴唑化合物之间强的偶极-偶极相互作用来解释。