Universität Würzburg, Institut für Organische Chemie and Röntgen Research Center for Complex Material Systems, Am Hubland, 97074 Würzburg, Germany.
J Am Chem Soc. 2011 Jun 22;133(24):9580-91. doi: 10.1021/ja202696d. Epub 2011 May 26.
In this work, we have explored for the first time the influence of conformational flexibility of π-core on chiral self-sorting properties of perylene bisimides (PBIs) that are currently one of the most prominent classes of functional dyes. For this purpose, two series of chiral macrocyclic PBIs 3a-c and 4a-c comprising oligoethylene glycol bridges of different lengths at the 1,7 bay positions were synthesized and their atropo-enantiomers (P and M enantiomers) were resolved. Single crystal analysis of atropo-enantiomerically pure (P)-3a not only confirmed the structural integrity of the ethylene glycol bridged macrocycle but also illustrated the formation of π-stacked dimers with left-handed supramolecular helicity. Our detailed studies with the series of highly soluble chiral PBIs 4a-c by 1- and 2-D (1)H NMR techniques, and temperature- and concentration-dependent UV/vis absorption and circular dichroism (CD) spectroscopy revealed that in π-π-stacking dimerization of these PBIs chiral self-recognition (i.e., PP and MM homodimer formation) prevails over self-discrimination (i.e., PM heterodimer formation). Our studies clearly showed that with increasing conformational flexibility of PBI cores imparted by longer bridging units, the binding strength for the dimerization process increases, however, the efficiency for chiral self-recognition decreases. These results are rationalized in terms of an induced-fit mechanism facilitating more planarized π-scaffolds of PBIs containing longer bridging units upon π-π-stacking.
在这项工作中，我们首次探索了π-核心构象柔性对目前最突出的一类功能染料——苝二酰亚胺（PBI）手性自组装性质的影响。为此，我们合成了两个系列的手性大环 PBIs（3a-c 和 4a-c），它们在 1,7-位的 bay 位具有不同长度的聚乙二醇桥。对非对映异构体纯（P）-3a 的单晶分析不仅证实了乙二醇桥接大环的结构完整性，还说明了具有左手超分子螺旋的π-堆积二聚体的形成。我们通过 1-和 2-D（1）H NMR 技术以及温度和浓度依赖性紫外/可见吸收和圆二色性（CD）光谱对高度可溶的手性 PBIs 4a-c 进行了详细研究，结果表明，在这些 PBIs 的π-π 堆积二聚化过程中，手性自识别（即 PP 和 MM 同二聚体形成）优先于自区分（即 PM 异二聚体形成）。我们的研究清楚地表明，随着 PBI 核心构象柔性的增加（由更长的桥接单元赋予），二聚化过程的结合强度增加，但手性自识别的效率降低。这些结果可以用诱导契合机制来解释，该机制有利于在π-π 堆积时使具有更长桥接单元的 PBIs 更平面化的π 支架。
