Supramolecular dendrimers: Unusual mesophases of ionic liquid crystals derived from protonation of DAB dendrimers with facial amphiphilic carboxylic acids
作者:Andrew G. Cook、Ute Baumeister、Carsten Tschierske
DOI:10.1039/b415892j
日期:——
Supramolecular liquid crystalline (LC) dendrimers were prepared by self-assembly of first to fifth generation amino terminated DAB dendrimers with facial amphiphilic carboxylic acids. These carboxylic acids are composed of three distinct incompatible segments, a rigid rod-like terphenyl core, two terminal alkyl chains and a polar lateral carboxylate group. The COOH groups were either directly connected to the terphenyl core or via oligo(oxyethylene) chains of different lengths. Depending upon the length of the polyether chain used, the dendrimer generation, the ratio of dendrimer to carboxylic acid or the temperature, a series of six different LC phases were observed. As well as a smectic phase (SmA), two different square columnar phases (Colsqu), a mesophase combining a layer structure with a hexagonal organisation of columns (channelled layer phase, ChLhex) and two additional mesophases (Colhex and M) with unknown structures were found. The square columnar phases are either composed of square cylinders (plane group p4mm) or a regular arrangement of square and triangular cylinders (plane group p4gm). In these dendrimer–carboxylic acid complexes protons are transferred from the COOH groups to the amino groups of the dendrimer, which gives rise to ionic complexes (dendroelectrolyte–amphiphile complexes). This concept allows the tailoring of the mesomorphic properties in a thermodynamically controlled self assembly process. The T-shaped ternary amphiphilic structure of the acid components and the incompatibility of the ionic species formed during the self assembly process are responsible for the formation of unconventional mesophase structures.
通过自组装法,以氨基封端的DAB树状大分子(第1至第5代)与面型两亲性羧酸制备了超分子液晶树状大分子。这些羧酸包含三个不相容的不同部分,刚性的带状三联苯核心、两个末端的烷基链和一个极性侧羧酸盐基团。羧酸基团的羟基要么直接与三联苯核心相连,要么通过不同长度的聚氧乙烯链连接。根据所用的聚醚链的长度、树状大分子的代数、树状大分子与羧酸的比例或温度,观察到六种不同的液晶相。除了一个近晶相(SmA)外,还发现了两个不同的四方柱状相(Colsqu),一个结合了层状结构和柱的六角排列的中介相(沟道层状相,ChLhex),以及两个具有未知结构的中介相(Colhex和M)。四方柱状相既包含有四方柱(平面群p4mm),也包含规则排列的四方柱和三角柱(平面群p4gm)。在这些树状大分子-羧酸复合物中,质子从羧酸基团转移到树状大分子的氨基上,形成离子复合物(树状电解质-两亲复合物)。这个概念使得在中介相的自组装过程中能通过热力学控制来裁剪液晶性质。酸组分的T型三元两亲结构和自组装过程中形成的离子物种的不兼容性是形成非传统中介相结构的原因。