Institute for Complex Molecular Systems, Laboratory of Macromolecular and Organic Chemistry, Eindhoven University of Technology, PO Box 513, 5600 MB Eindhoven, The Netherlands.
Chemistry. 2012 Sep 10;18(37):11761-70. doi: 10.1002/chem.201200883. Epub 2012 Aug 2.
The design of supramolecular motifs with tuneable stability and adjustable supramolecular polymerisation mechanisms is of crucial importance to precisely control the properties of supramolecular assemblies. This report focuses on constructing π-conjugated oligo(phenylene ethynylene) (OPE)-based one-dimensional helical supramolecular polymers that show a cooperative growth mechanism. Thus, a novel set of discotic molecules comprising a rigid OPE core, three amide groups, and peripheral solubilising wedge groups featuring C(3) and C(2) core symmetry was designed and synthesised. All of the discotic molecules are crystalline compounds and lack a columnar mesophase in the solid state. In dilute methylcyclohexane solution, one-dimensional supramolecular polymers are formed stabilised by threefold intermolecular hydrogen bonding and π-π interactions, as evidenced by (1)H NMR measurements. Small-angle X-ray and light scattering measurements reveal significant size differences between the columnar aggregates of C(3)- and C(2)-symmetrical discotics, that is, the core symmetry strongly influences the nature of the supramolecular polymerisation process. Temperature-dependent CD measurements show a highly cooperative polymerisation process for the C(3)-symmetrical discotics. In contrast, the self-assembly of C(2)-symmetrical discotics shows a smaller enthalpy release upon aggregation and decreased cooperativity. In all cases, the peripheral stereogenic centres induce a preferred handedness in the columnar helical aggregates. Moreover, one stereogenic centre suffices to fully bias the helicity in the C(2)-symmetrical discotics. Finally, chiral amplification studies with the C(3)-symmetrical discotics were performed by mixing chiral and achiral discotics (sergeants-and-soldiers experiment) and discotics of opposite chirality (majority-rules experiment). The results demonstrate a very strong sergeants-and-soldiers effect and a rather weak majority-rules effect.
具有可调稳定性和可调超分子聚合机制的超分子结构设计对于精确控制超分子组装体的性质至关重要。本报告重点构建基于π-共轭寡聚（苯乙炔）（OPE）的一维螺旋超分子聚合物，其表现出协同生长机制。因此，设计并合成了一组新的盘状分子，其包含刚性 OPE 核、三个酰胺基团和具有 C(3)和 C(2)核对称性的外围溶胀楔形基团。所有盘状分子都是结晶化合物，在固态中缺乏柱状中间相。在稀甲基环己烷溶液中，一维超分子聚合物通过三倍的分子间氢键和π-π相互作用稳定形成，这可通过（1）H NMR 测量证明。小角 X 射线和光散射测量揭示了 C(3)-和 C(2)-对称盘状分子的柱状聚集体之间存在显著的尺寸差异，即核对称性强烈影响超分子聚合过程的性质。温度依赖性 CD 测量显示 C(3)-对称盘状分子的聚合过程具有高度协同性。相比之下，C(2)-对称盘状分子的自组装在聚集时释放出较小的焓值并且协同性降低。在所有情况下，外围立体中心在柱状螺旋聚集体中诱导出手性。此外，一个立体中心足以完全偏向 C(2)-对称盘状分子的手性。最后，通过混合手性和非手性盘状分子（中士与士兵实验）和具有相反手性的盘状分子（多数规则实验）进行 C(3)-对称盘状分子的手性放大研究。结果表明存在非常强的中士与士兵效应和较弱的多数规则效应。
