Liquid crystalline conjugated oligomers: synthesis and mesomorphic properties of laterally and terminally alkyl-substituted oligo(1,4-phenyleneethynylene)s
作者:Tetsuo Yatabe、Yasuzo Suzuki、Yuji Kawanishi
DOI:10.1039/b808036d
日期:——
A new series of liquid crystalline conjugated oligomers, namely laterally and terminally alkyl-substituted derivatives of oligo(1,4-phenyleneethynylene)s, were synthesized, and the relationships between the molecular structures and the mesomorphic properties were investigated. The mesomorphic properties of the oligomer derivatives were examined by differential scanning calorimetry and polarizing microscopy. In the alkyl-substituted oligomers with varying core lengths, C8H17C6H4CC[C6H2(C2H5)2CC]nC6H4C8H17 where n = 2–5, the trimer (n = 2) exhibited a monotropic nematic phase, and the others showed enantiotropic nematic phases. In the alkyl-substituted tetramers, R1C6H4CC[C6H2(R2)2CC][C6H2(R3)2CC][C6H2(R2)2CC]C6H4R1 where R1, R2, and R3 = alkyl chains of varying lengths and H, most of the tetramer derivatives exhibited nematic phases, whereas the others did not show any mesophases. It was found that the formation of the mesophase and the crystalline–nematic and nematic–isotropic transition temperatures are strongly affected by the structural features of the oligomer molecules: (i) the length of the oligomer core, (ii) the length, number, and position of the lateral chains, and (iii) the length of the terminal chains.
合成了一系列新的液晶共轭低聚物,即低聚(1,4-亚苯基乙炔基)的侧面和末端烷基取代衍生物,并研究了分子结构和介晶性质之间的关系。通过差示扫描量热法和偏光显微镜检查了低聚物衍生物的介晶性质。在具有不同核心长度的烷基取代低聚物中,C8H17C6H4CC[C6H2(C2H5)2CC]nC6H4C8H17,其中n = 2–5,三聚体(n = 2)表现出单向向列相,其他表现出对映向列相。在烷基取代的四聚体中,R1C6H4CC[C6H2(R2)2CC][C6H2(R3)2CC][C6H2(R2)2CC]C6H4R1,其中R1、R2和R3=不同长度的烷基链,并且H是四聚体的大部分衍生物表现出向列相,而其他衍生物则不表现出任何中间相。研究发现,中间相的形成以及结晶-向列和向列-各向同性转变温度受到低聚物分子结构特征的强烈影响:(i) 低聚物核的长度,(ii) 长度、数量、侧链的位置和位置,以及 (iii) 末端链的长度。