van der Weegen Rob, Teunissen Abraham J P, Meijer E W
Laboratory of Macromolecular and Organic Chemistry, Institute for Complex Molecular Systems, Eindhoven University of Technology, P.O. Box 513, 5600 MB, Eindhoven, The Netherlands.
Chemistry. 2017 Mar 13;23(15):3773-3783. doi: 10.1002/chem.201605872. Epub 2017 Feb 16.
The self-assembly behaviour of a library of tetra-amidated porphyrin molecules decorated with a variety of solubilizing wedges is investigated as dilute solutions in methylcyclohexane. Small changes in the solubilising wedge of the porphyrins resulted in different aggregated states, as evidenced by CD and UV/Vis absorption spectroscopy. The porphyrins form co-facially stacked H-aggregates, slip-stacked J-aggregates or a mixture of both. Detailed thermodynamic and kinetic analysis showed that in all cases the formation of J-aggregates proceeds via an isodesmic mechanism whereas H-aggregates are formed via a cooperative mechanism. It is shown that these aggregates assemble in a parallel pathway, in which both compete for the monomer, compared to a sequential pathway, in which one of the aggregates interconverts into the other. Interestingly, kinetic analysis of porphyrins that only form H-aggregates in thermodynamic equilibrium revealed that the competing pathway towards J-aggregates is operational in these systems as well. Our findings show that the balance between H- and J-aggregates depends on remarkably small changes in the architecture of the solubilising wedges.
研究了一系列带有各种增溶楔的四酰胺基卟啉分子在甲基环己烷稀溶液中的自组装行为。卟啉增溶楔的微小变化导致了不同的聚集状态，圆二色光谱（CD）和紫外可见吸收光谱证明了这一点。卟啉形成面对面堆叠的H-聚集体、滑移堆叠的J-聚集体或两者的混合物。详细的热力学和动力学分析表明，在所有情况下，J-聚集体的形成通过等键机制进行，而H-聚集体通过协同机制形成。结果表明，与一种聚集体相互转化为另一种聚集体的顺序途径相比，这些聚集体以平行途径组装，两者都与单体竞争。有趣的是，对在热力学平衡中仅形成H-聚集体的卟啉的动力学分析表明，在这些系统中，通向J-聚集体的竞争途径也是起作用的。我们的研究结果表明，H-聚集体和J-聚集体之间的平衡取决于增溶楔结构非常微小的变化。
