The synthesis, characterization and thermotropic properties of novel asymmetrically substituted discotic molecules, perylene diester benzimidazoles (PDBIs), are presented. PDBIs were designed with an imidazole unit at 3,4 positions and a bisester moiety at 9,10 positions of the perylene tetracarboxylic acid core. By attaching linear or branched aliphatic substituents at the ester moiety and two alkyl or alkoxy substituents at the benzimidazole unit, sufficient solubility and the flexibility to obtain mesophases was guaranteed. Thermotropic behaviour, which is strongly influenced by the nature of the respective substituents at the diester and benzimidazole moiety, was investigated using differential scanning calorimetry (DSC), polarization optical microscopy (POM) and X-ray diffraction measurements (XRD). All PDBIs under investigation self-organize into liquid crystalline columnar hexagonal phases (Colh), among them PDBI-3 even at room temperature. Also the formation of a room temperature columnar plastic phase (Colhp) and the formation of a lamellar phase was observed. Due to extension of the π-conjugation system, the absorption of these well soluble discogens is significantly extended to longer wavelengths in the visible regime up to 680 nm.
本文介绍了新型不对称取代盘状分子--过烯二酯
苯并咪唑(PDBIs)的合成、表征和趋热特性。PDBIs 的设计在过烯四
羧酸核心的 3、4 位上有一个
咪唑单元,在 9、10 位上有一个双酯分子。通过在酯基上添加直链或支链脂肪族取代基,在
苯并咪唑单元上添加两个烷基或烷氧基取代基,保证了足够的溶解度和获得介相的灵活性。研究人员使用差示扫描量热法(
DSC)、偏振光学显微镜(POM)和 X 射线衍射测量法(XRD)对热各向同性行为进行了研究,这种行为受到二酯和
苯并咪唑各自取代基性质的强烈影响。所研究的所有 PDBI 都能自组织成液晶柱状六方相(Colh),其中 PDBI-3 甚至能在室温下自组织成液晶柱状六方相。此外,还观察到室温下柱状塑性相(Colhp)的形成和片状相的形成。由于π-共轭体系的扩展,这些溶解性很好的 Discogens 的吸收明显扩展到可见光范围内更长的波长,最高可达 680 纳米。