Ghosh Suhrit, Li Xue-Qing, Stepanenko Vladimir, Würthner Frank
Universität Würzburg, Institut für Organische Chemie and Röntgen Research Center for Complex Material Systems, Am Hubland, 97074 Würzburg, Germany.
Chemistry. 2008;14(36):11343-57. doi: 10.1002/chem.200801454.
The synthesis, self-assembly, and gelation ability of a series of organogelators based on perylene bisimide (PBI) dyes containing amide groups at imide positions are reported. The synergetic effect of intermolecular hydrogen bonding among the amide functionalities and pi-pi stacking between the PBI units directs the formation of the self-assembled structure in solution, which beyond a certain concentration results in gelation. Effects of different peripheral alkyl substituents on the self-assembly were studied by solvent- and temperature-dependent UV-visible and circular dichroism (CD) spectroscopy. PBI derivatives containing linear alkyl side chains in the periphery formed H-type pi stacks and red gels, whereas by introducing branched alkyl chains the formation of J-type pi stacks and green gels could be achieved. Sterically demanding substituents, in particular, the 2-ethylhexyl group completely suppressed the pi stacking. Coaggregation studies with H- and J-aggregating chromophores revealed the formation of solely H-type pi stacks containing both precursor molecules at a lower mole fraction of J-aggregating chromophore. Beyond a critical composition of the two chromophores, mixed H-aggregate and J-aggregate were formed simultaneously, which points to a self-sorting process. The versatility of the gelators is strongly dependent on the length and nature of the peripheral alkyl substituents. CD spectroscopic studies revealed a preferential helicity of the aggregates of PBI building blocks bearing chiral side chains. Even for achiral PBI derivatives, the utilization of chiral solvents such as (R)- or (S)-limonene was effective in preferential population of one-handed helical fibers. AFM studies revealed the formation of helical fibers from all the present PBI gelators, irrespective of the presence of chiral or achiral side chains. Furthermore, vortex flow was found to be effective in macroscopic orientation of the aggregates as evidenced from the origin of CD signals from aggregates of achiral PBI molecules.
报道了一系列基于苝二酰亚胺（PBI）染料的有机凝胶因子的合成、自组装和凝胶化能力，这些染料在亚胺位置含有酰胺基团。酰胺官能团之间的分子间氢键和PBI单元之间的π-π堆积的协同作用引导溶液中自组装结构的形成，超过一定浓度会导致凝胶化。通过溶剂和温度依赖性紫外可见光谱和圆二色光谱（CD）研究了不同外围烷基取代基对自组装的影响。外围含有线性烷基侧链的PBI衍生物形成H型π堆积和红色凝胶，而通过引入支链烷基链可以实现J型π堆积和绿色凝胶的形成。空间位阻较大的取代基，特别是2-乙基己基基团完全抑制了π堆积。与H-和J-聚集发色团的共聚集研究表明，在较低摩尔分数的J-聚集发色团下，仅形成同时包含两种前体分子的H型π堆积。超过两种发色团的临界组成，会同时形成混合的H-聚集体和J-聚集体，这表明存在自分类过程。凝胶因子的多功能性强烈依赖于外围烷基取代基的长度和性质。CD光谱研究揭示了带有手性侧链的PBI结构单元聚集体的优先螺旋性。即使对于非手性PBI衍生物，使用手性溶剂如（R）-或（S）-柠檬烯也能有效地优先形成单手螺旋纤维。原子力显微镜（AFM）研究表明，所有现有的PBI凝胶因子都会形成螺旋纤维，无论是否存在手性或非手性侧链。此外，如非手性PBI分子聚集体的CD信号来源所示，发现涡旋流对聚集体的宏观取向有效。
