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Discrete Stacking of Aromatic Oligoamide Macrocycles

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posted on 13.05.2015, 00:00 by Xiangxiang Wu, Rui Liu, Bharathwaj Sathyamoorthy, Kazuhiro Yamato, Guoxing Liang, Lin Shen, Sufang Ma, Dinesh K. Sukumaran, Thomas Szyperski, Weihai Fang, Lan He, Xuebo Chen, Bing Gong
Unlike the precise structural control typical of closed assemblies, curbing the stacking of disc- and ring-shaped molecules is quite challenging. Here we report the discrete stacking of rigid aromatic oligoamide macrocycles 1. With increasing concentration, the aggregation of 1 quickly plateaus, forming a discrete oligomer, as suggested by 1D 1H, 2D nuclear Overhauser effect, and diffusion-ordered NMR spectroscopy. Quantum-chemical calculations indicate that the tetramer of 1 is the most stable among oligomeric stacks. X-ray crystallography revealed a tetrameric stack containing identical molecules adopting two different conformations. With a defined length and an inner pore capable of accommodating distinctly different guests, the tetramers of 1 densely pack into 2D layers. Besides being a rare system of conformation-regulated supramolecular oligomerization, the discrete stacks of 1, along with their higher-order assemblies, may offer new nanotechnological applications.